Palynology Acritarchs from the Ordovician-Silurian ...

This article was downloaded by: [Vecoli, Marco] On: 25 May 2011 Access details: Access Details: [subscription number 923869798] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 3741 Mortimer Street, London W1T 3JH, UK

Palynology

Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t913285617

Acritarchs from the Ordovician-Silurian boundary beds of the Valga-10 drill core, southern Estonia (Baltica) and their stratigraphical and palaeobiogeographical implications Aurélien Delabroyeab; Marco Vecolib; Olle Hintsc; Thomas Servaisb a Université Paul Sabatier, Toulouse, France b Université Lille 1 Laboratoire Geosystemes, Cité Scientifique, Villeneuve d'Ascq, France c Institute of Geology at Tallinn University of Technology, Ehitajate tee, Tallinn, Estonia Online publication date: 23 May 2011 To cite this Article Delabroye, Aurélien , Vecoli, Marco , Hints, Olle and Servais, Thomas(2011) 'Acritarchs from the

Ordovician-Silurian boundary beds of the Valga-10 drill core, southern Estonia (Baltica) and their stratigraphical and palaeobiogeographical implications', Palynology, 35: 1, 4 — 45 To link to this Article: DOI: 10.1080/01916122.2010.491639 URL: http://dx.doi.org/10.1080/01916122.2010.491639

PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

Palynology Vol. 35, No. 1, June 2011, 4–45

Acritarchs from the Ordovician–Silurian boundary beds of the Valga-10 drill core, southern Estonia (Baltica) and their stratigraphical and palaeobiogeographical implications Aure´lien Delabroyea,b*, Marco Vecolib, Olle Hintsc and Thomas Servaisb a

Universite´ Paul Sabatier, LMTG, UMR 5563 du CNRS, 31400 Toulouse, France; bUniversite´ Lille 1 Laboratoire Geosystemes, FRE 3298 du CNRS, SN5, Cite´ Scientifique 59655 Villeneuve d’Ascq, France; cInstitute of Geology at Tallinn University of Technology, Ehitajate tee 5 19086 Tallinn, Estonia

Downloaded By: [Vecoli, Marco] At: 06:51 25 May 2011

Fourteen samples of the Valga-10 drill core, south Estonia, from the lower Jelgava Formation (middle Pirgu Regional ~ Stage, Upper Katian) to the lowermost Ohne Formation (lowermost Juuru Regional Stage, Lower Rhuddanian) were investigated for acritarchs. The section is biostratigraphically and chemostratigraphically well constrained; it comprises the rugata, taugourdeaui and scabra chitinozoan zones, the ordovicicus and giradeauensis conodont zones and the Hirnantian Isotopic Carbon Excursion (HICE). The good preservation allowed the identification of three prasinophyte phycomata and 52 acritarch species including the four new species Evittia porkuniensis, Helosphaeridium tongiorgii, Nexosarium leherissei and ?Veryhachium bulliferum. One new combination is proposed: Poikilofusa obliquipunctata (Uutela & Tynni 1991) comb. nov. Comparison with contemporaneaous palynofloras shows that eastern Laurentia and Baltica share a high number of species during the latest Katian–Hirnantian. Some of these species show a potential for future improvement of biostratigraphical correlation between the uppermost Katian– Hirnantian strata of low to mid-latitude carbonate platforms in eastern Laurentia and Baltica. Conversely, significant taxonomic differences exist between the assemblage studied and typical Gondwanan palynofloras. These results suggest that the Laurentian/Baltic and Gonwanan phytoplanktonic palaeoprovinces existed during latest Ordovician times. Published data reveal similar distribution pattern for chitinozoans and graptolites during the Hirnantian. A bathymetric ridge rise associated with the opening of the Rheic Ocean, coupled with the Hirnantian glacially-driven sea-level fall might have prevented water mass exchange and mixing/migration of phytoplankton between Gondwana and Laurentia/Baltica, thus being at the origin of the observed acritarch bioprovincialism. Additionally, distribution and diversity patterns of acritarchs are compared to those of other microfossils in the Valga-10 section. Near the base of the Hirnantian (Porkuni Regional Stage), benthic organisms (ostracods and scolecodonts) and phytoplankton (acritarchs) show increasing diversity with appearances of new taxa and new morphologies. Planktonic (chitinozoans) and nektonic (conodonts) organisms show a different pattern, with a decline in diversity during the earliest Hirnantian and a marked increase in the later part of the stage. Two alternative hyptotheses are proposed to explain these differences in diversification patterns: (1) the development of a shallower, proximal environment in the locality studied during the Hirnantian glaciation may have been more favourable to the diversification of benthonic organisms; (2) the planktonic and nektonic organisms suffered the effects of glaciation more than benthonic ones. Keywords: acritarchs; Ordovician–Silurian boundary; biostratigraphy; palaeobiogeography; Baltica; Laurentia; Gondwana

1.

Introduction

The Late Ordovician–Early Silurian was a period of drastic palaeoenvironmental changes and biospheric perturbations. Precise dating and correlation of the different physical and biological events recorded in the sediments are needed in order to establish a global relative chronology and to explore cause–effect relationships among the different events. For this important internal, global correlation among different palaeocontinents is usually based on graptolites, which are planktonic organisms essentially found in shaly sediments. Consequently, application of graptolite biozonations for correlation between shallow water

sediments is problematical. In eastern Laurentia and Baltica, shallow water carbonate platforms developed during the Late Ordovician. Despite the lack of diagnostic graptolites, relative age determinations and correlations are possible by means of accurate chitinozoan based zonations in each area. Recently, new material from eastern Laurentia (Anticosti, Canada) and Baltica (Valga, Estonia) provided an opportunity to study and compare the phytoplankton assemblages (acritarchs) of the two areas at the Ordovician–Silurian boundary. Due to a higher morphological disparity and diversity than other microfossils, establishment of acritarch biozonations

*Corresponding author. Email: [email protected] ISSN 0191-6122 print/ISSN 1558-9188 online Ó 2011 AASP – The Palynological Society DOI: 10.1080/01916122.2010.491639 http://www.informaworld.com

5


Palynology is still difficult. More comparison of assemblages and populations is still needed to accurately determine inter- and intraspecific morphological variability and to discriminate between phenotypic and genotypic controls. Acritarchs, like dinoflagellates, were extremely dependent on several environmental factors, e.g. salinity, oxygenation, luminosity and water agitation (Kokinos and Anderson 1995; Dale 1996; Ellegaard 2000; Pross 2001; Servais et al. 2004; Mertens et al. 2009; Rochon et al. 2009). Notwithstanding, they hold considerable potential for detailed biostratigraphy when analysed in detail, for instance, the messaoudensis–trifidum acritarch assemblage and its correlation with the base of the Floian (Molyneux et al. 2007). The present study, based on detailed analysis and comparison of latest Katian–Hirnantian acritarchs from Baltica, reveals interesting insights into the palaeobiogeography, and potential for future improvement of biostratigraphical correlations of low to middle palaeolatitude localities at this time. In addition to biostratigraphical and biogeographical results, acritarchs and other local microfossils (conodonts, scolecodonts, ostracods, chitinozoans) reveal different diversity trends during the Late Ordovician glaciation, which need to be compared in order to better understand relationships in space and time of organisms occupying different biotopes. 2. Geological setting During the Palaeozoic, Estonia was located in the south-western part of Baltica (Cocks and Torsvik 2004). At the end of the Ordovician, when the Tornquist Sea closed by the convergence of Avalonia and Baltica (Torsvik and Rhenstro¨m 2003), it was situated at about 308S latitude (Cocks and Torsvik 2004), and corresponded to an epicontinental marine basin (Po˜ldvere 2001). In this region, shallow water

sediments are represented by the carbonate Estonian and Lithuanian shelves (North Estonian and Lithuanian Confacies Belts of Jaanusson, 1995), respectively, in northern Estonia and Lithuania (Harris et al. 2004) (Figure 1a). Deeper water sediments of the Scandinavian Basin (graptolitic shale and grey shale) are found westward in Sweden (Central Baltoscandian Confacies Belt of Jaanusson, 1995) (Figure 1A). Transitional environments of the Livonian Basin (marls and argillaceous limestones) are found in southern Estonia and Latvia (Figure 1; Harris et al. 2004). The entire Baltoscandian region was surrounded in the north by the Fennoscandian Shield, in the south by the Belarussian Shield and in the east by the Moscow Basin (Figure 1). The palynological material studied is from Upper Ordovician strata of the Valga-10 drill core, located in southern Estonia close to the border with Latvia (578 48.240 N; 268 4.650 E; Figure 1B). In this area, the sediments are representative of the transitional deposit environments close to the border between the Estonian Shelf and the Livonian Basin (Figure 1A). 3.

Material and stratigraphy

For acritarch analyses, 14 samples were collected from the Valga-10 core, from the Jelgava Formation (middle ~ Pirgu Regional Stage) to the lowermost Ohne Formation (lowermost Juuru Regional Stage; lower Rhuddanian; Figure 2). The Jelgava Formation (five samples) consists of 18.5 m of greenish light grey calcitic marls, with some dolomitised beds and red spots in the lower part. Argillaceous, finely crystalline limestone interlayers also occur (Po˜ldvere 2001). Two bentonite layers are present in the Jelgava Formation at 339.8 and 335.9 m (Kiipli et al. 2004). The succeeding Paroveja Formation consists of 1.4 m of grey to dark grey, slightly argillaceous microcrystalline dolostones

Figure 1. (A) Late Ordovician facies belts and palaeogeographical features of the Baltic region (Harris et al. 2004). The star indicates the position of the Valga-10 drill core; (B) present geographical location of the Valga-10 drill core. Reprinted from Palaeogeography, Palaeoclimatology, Palaeoecology, 210, Harris et al., pp. 135–148, copyright (2004), with permission from Elsevier.

Figure 2. The stratigraphical section of the Valga-10 drill core showing lithofacies, positions of the samples, and range, age assignment and relative abundances of the three prasinophyte phycomata and 52 acritarch species recovered from the Pirgu, Porkuni and Juuru regional stages. Lithostratigraphical column modified from Po˜ldvere (2001). Chitinozoan biozones from No˜lvak (2001). Conodont biozones from Ma¨nnik (2001). Carbon isotopic curve after Kaljo et al. (2007). Acritarch assemblages (AS1 to AS4) are discussed in the text. The question mark refers to the problematic stratigraphical position of the base of the Hirnantian Stage in the core section as discussed in the text. Note also that the abundance, and consequently the scarcity of some species, is dependent on the preparation method used for palynological slides. Slides of the 15–180 mm fraction allow good estimation of absolute frequencies but necessarily dilute palynomorphs compared to slides of the 15–50 mm and 450 mm fractions.


6 A. Delabroye et al.


Palynology (Po˜ldvere 2001). The uppermost unit of the Pirgu Regional Stage in the Valga-10 core is the Kuili Formation (one sample), which consists of 6.6 m of greenish grey to reddish brown dolomitic marls intercalated with argillaceous crystalline dolostone (Po˜ldvere 2001). No˜lvak (2001) identified the Conochitina rugata Chitinozoan Zone from the middle Jelgava Formation (341.00 m) to the upper Kuili Formation (327.3 m). The Porkuni Regional Stage is represented in the Valga-10 section by the Kuldiga (10.3 m) and Saldus (2.2 m) formations (Figure 3). The Kuldiga Formation is further subdivided into the Bernati (1.3 m) and Edole (9.0 m) members. The Bernati Member consists of greenish light grey to grey dolomitic marls (Po˜ldvere 2001; one sample). The Edole Member is represented by light grey to grey, finely crystalline dolomitic marls interbedded with thin intervals of argillaceous crystalline dolostones (Po˜ldvere 2001; three samples). No˜lvak (2001) identified the Spinachitina taugourdeaui Chitinozoan Biozone in the Bernati Member and the Conochitina scabra Chitinozoan Biozone at the base of the Edole Member. The Saldus Formation is also subdivided into two members: the Piltene (0.6 m) and Broceni (1.6 m) (Figure 2). The former consists of light grey to brownish, finely crystalline dolostones (one sample), and the latter of grey, finely crystalline dolostones and dolomitic marls, with silt and sand at the base (Po˜ldvere 2001) (one sample). No˜lvak (2001) recognised a chitinozoan assemblage composed of six morphotypes in the upper Edole Member and the overlying Saldus Formation, which are yet to be identified at the species level and possibly represent a redeposited assemblage. The two remaining samples are from the base of the ~ Ohne Formation, represented by the Puikule and Ruja members (Juuru Regional Stage; basal Rhuddanian, lowermost Silurian; Figure 2). The former consists of greenish to dark grey dolomitic marls with argillaceous, crystalline dolostones in its upper part, whilst the

7

latter is represented by light grey microcrystalline dolostones (Po˜ldvere 2001). Distribution patterns of chitinozoans (No˜lvak 2001), conodonts (Ma¨nnik 2001), scolecodonts (Hints 2001) and ostracods (Meidla 2001) in the Ordovician and Silurian sediments of the Valga-10 drill core have been studied. Chitinozoans provide good biostratigraphical control leading to the recognition of the rugata, taugourdeaui and scabra chitinozoan biozones (Figure 2). Early Silurian chitinozoan biozones have not been identified. Moreover, the gamachiana Biozone, known from other Baltic sections between the rugata and taugourdeaui zones, is missing or has not been identified because of insufficient sampling resolution in the Valga10 section (J. No˜lvak, personal communication, 2007). Ma¨nnik (2001) identified the Amorphognathus ordovicicus Conodont Biozone from the base of the Saunja Formation (middle Katian) to the lowermost Kuldiga Formation (base of the Porkuni Regional Stage; lowermost Hirnantian). The Noixodontus girardeauensis fauna occurs in the overlying strata (uppermost Bernati Member and Edole Member). This species occurs in graptolite-bearing strata of the Hirnantian age in Yukon, Canada (Barrick 1986). The lowermost Silurian sediments yield eight conodont species, probably indicating the kentuckyensis biozone (Ma¨nnik 2007). Kaljo et al. (2007) recognised the HICE (Hirnantian Isotopic Carbon Excursion; Bergstro¨m et al. 2006) in the Kuldiga and Saldus formations of the Porkuni stage (Figure 2). The start of the ascending leg of the local HICE begins at the base of the Kuldiga Formation in the Bernati Member, correlating with the taugourdeaui chitinozoan zone. The HICE reached its highest value in the middle of the succeeding Edole Member at the top of the local scabra Zone and, next, begins to progressively decrease until it again reaches pre-excursion values at the base of the Silurian strata ~ of the Ohne Formation. The base of the Hirnantian Stage was correlated with the base of the Porkuni Stage and the base of the

Figure 3. Upper Ordovician stratigraphy in the East Baltic (modified from Harris et al. 2004 (Palaeogeography, Palaeoclimatology, Palaeoecology, 210, Harris et al., pp. 135–148, copyright (2004), with permission from Elsevier) according to Hints et al. 2005 and No˜lvak et al. 2006). Time Slices according to Webby et al. (2004). The question mark refers to the problematic stratigraphical position of the base of the Hirnantian in Baltica as discussed in the text.

8

A. Delabroye et al.


taugourdeaui Chitinozoan Biozone by Baltic stratigraphers (Kaljo et al. 2008; Hints et al. 2010). At Anticosti, Canada, however, the base of the Hirnantian is correlated with the base of the gamachiana biozone (Achab et al. 2011; Desrochers et al. 2010). For Baltic sections, this would mean that the base of the Hirnantian lies within the upper part of the Pirgu Regional Stage. Both these views have supporting biostratigraphical and geochemical evidence and therefore no definite conclusion can be drawn (Delabroye and Vecoli 2010). 4. Palynological preparations The acritarchs were extracted using acid treatment. After spiking with Lycopodium marker spores to facilitate the calculation of absolute palynomorph abundances (Stockmarr 1971; Stricanne et al. 2004, 2006), 50 g of each sample were treated successively with cold 34% HCl, cold 48% HF and hot HCl for the respective removal of carbonates, silicates and fluorosilicates. Samples were neutralised with distilled water between acid treatments. The resultant residues were filtered through 180 and 15 mm nylon screens, thus yielding 4180 mm, 15– 180 mm, and 515 mm fractions from each sample. Density separation treatment by ZnBr (sg 2.00) was used for final mineral cleaning of the 15–180 mm fraction to facilitate the absolute counting after slide mounting. One slide of the 4180 mm fraction and two slides of the 15–180 mm fraction were prepared using ‘Eukitt’ as the mounting medium for each sample. The 515 mm fractions were not studied because they were almost devoid of palynomorphs. SEM stubs were also prepared for the productive samples. All the slides were completely examined for palynomorph identification using transmitted and reflected light on Zeiss Axioskop 2 and Zeiss Axioplan 2 microscopes. Photomicrographs were taken on a Zeiss Axioplan 2 microscope equipped with a Plan-Apochromat 63U/ 1.40 oil objective and Fluar 100/1.30 oil objective and on SEM. Image acquisition with scale were made in optical microscopy, using a Zeiss Axiovision 2.0 programme installed on a PC using a standard video camera, and on SEM. Measurements of the numerous photographed specimens were made using TpsDIG 2.12. A minimum of 250 palynomorphs were counted for each sample. Absolute and relative countings of major palynomorphs groups (different groups of acritarchs, chitinozoans, scolecodonts, cryptospores and melanoslerites) have been used to characterise their distribution patterns. The slides and SEM stubs are named according to the locality (VA ), core number (Po˜ldvere et al. 2001, appendix 1) and depth (e.g. VA 44 (338.8 m);

see Figure 2). The core is housed at the Sa¨ghaua field station of the Institute of Geology at Tallinn University of Technology (Estonia). The material studied is housed in the collections of the Laboratoire Geósyste`mes of Lille 1 University (Villeneuve d’Ascq, France). 5.

Acritarch floras

Five samples proved barren of palynomorphs (Figure 2). In the productive samples, the material is generally rich. The acritarchs are moderately diverse, moderately to well-preserved (often in 3D), light yellow in colour, and translucent. Three prasinophyte phycomata and 52 acritarch species were recovered (Appendix 1). Their relative abundance in each of the productive samples is presented in Figure 2. All major morphotypes were figured in Plates 1–16. The small specimens are attributed to Micrhystridium; these are difficult to distinguish using light microscopy. Some netromorph and acanthomorph acritarchs displaying similar morphologies under the light microscope revealed minor differences in wall microsculpture in SEM. A full description and systematic treatment is discussed for some species which are new or considered to have good potential for latest Katian and Hirnantian biostratigraphy at low latitudes, and for palaeobiogeography. Well-preserved cryptospores have also been observed. Figure 2 shows the stratigraphical ranges of the species identified. Four assemblages (AS1 to AS4) have been identified within the limit of the sampling resolution (Figure 2). AS1 is represented by the lowermost sample VA 46 (345.6 m) and is characterised by the common large and well-preserved specimens of Baltisphaeridium perclarum (Tappan & Loeblich 1971) (Plate 2, figures 9–11), which does not stratigraphically extend into the overlying samples. Other species uniquely characteristic of this assemblage and occurring in rare abundances are ?Carminella sp. (Plate 10, figures 8–9), Aremoricanium squarrosum Loeblich & MacAdam 1971 (Plate 1, figures 1–2), Comasphaeridium sp. A (Plate 6, figure 1), and Multiplicisphaeridium sp. A (Plate 9, figures 7–9). AS2 is an interval assemblage between AS1 and AS3, and represented by the five productive samples, VA 45 (340.6 m), VA 44 (338.8 m), VA 44 (335.5 m), VA 42 (328.9 m) and VA 40 (322.7 m). It is not defined by any particular species. Species commonly found are Baltisphaeridium adialstaltum (Plate 2, figures 5–6), B. aliquigranulum (Plate 2, figures 7–8), B. curtatum (Plate 1, figures 6, 9–10), Buedingiisphaeridium balticum (Plate 16, figures 1–3), Evittia denticulate denticulata (Plate 4, figures 4–5), Nexosarium leherissei

9


Palynology

Plate 1. All scale bars represent 20 mm when not specified. The photomicrographs were all taken using plain transmitted light. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2. Aremoricanium squarrosum Loeblich & MacAdam 1971. VA 46 (345.6 m)/2, G31/1; high and low focus, respectively. Figures 3, 4. Baltisphaeridium sp. A. VA 38 (313.2 m)/1, E41/4; high and low focus, respectively. Figure 5. Baltisphaeridium sp. A., outer layer of the vesicle, VA 38 (313.2 m)/1, S27/2. Figure 6. Baltisphaeridium curtatum Playford & Wicander 2006. VA 42 (328.9 m)/1, F25/ 3. Figures 7, 8. Baltisphaeridium sp. A. VA 38 (313.2 m)/2, P35/1; low and high focus, respectively. Figure 9. Baltisphaeridium curtatum Playford & Wicander 2006. VA 46 (345.6 m)/1, J23/2. Figure 10. Baltisphaeridium curtatum Playford & Wicander 2006. VA 42 (328.9 m)/2, B17.

A. Delabroye et al.


10

Plate 2. All scale bars represent 20 mm when not specified. Figures 1–9 were taken using plain transmitted light; Figures 10– 11 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. ?Baltisphaeridium sp. VA 40 (320.0 m)/2, K39/3. Figures 2, 3. ?Baltisphaeridium sp. VA 40 (320.0 m)/2, Q28; high and low focus, respectively. Figure 4. ?Baltisphaeridium sp. VA 40 (320.0 m)/2, R27. Figures 5, 6. Baltisphaeridium adialstaltum Wicander, Playford & Robertson 1999. VA 44 (338.8 m)/2, E38/4. Figures 7, 8. Baltisphaeridium aliquigranulum Tappan & Loeblich 1971. VA 38 (313.2 m)/1, M26; low and high focus, respectively. Figure 9. Baltisphaeridium perclarum Tappan & Loeblich 1971. VA 46 (345.7 m)/1, L21/3. Figures 10, 11. Baltisphaeridium perclarum Tappan & Loeblich 1971. VA 46 (345.7 m)/SEM stub.

11


Palynology

Plate 3. All scale bars represent 20 mm when not specified. Figures 1–3, 7–8 and 10–12 were taken using plain transmitted light; figures 4–6, 9 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2, 3. Baltisphaeridium sp. aff. B. aspersilumiferum Tappan & Loeblich 1971. VA 46 (345.7 m)/1, N32; high, median and low focus, respectively. Figures 4, 5. Baltisphaeridium sp. aff. B. aspersilumiferum Tappan & Loeblich 1971. VA 46 (345.7 m)/SEM stub. Figure 6. Baltisphaeridium sp. aff. B. aspersilumiferum Tappan & Loeblich 1971. VA 46 (345.7 m)/SEM stub. Figures 7, 8. Cheleutochroa sp. aff. C. venosa Uutela & Tynni 1991. VA 38 (313.2 m)/1, E37/2; high and low focus, respectively. Figure 9. Cheleutochroa sp. aff. C. venosa Uutela & Tynni 1991. VA 38 (313.2 m)/SEM stub. Figure 10. Dilatisphaera wimanii (Eisenack 1968) Le He´risse´ 1989. VA 46 (345.6 m)/2, F33. Figure 11. Dorsennidium hamii (Loeblich 1970) Sarjeant & Stancliffe 1994. VA 44 (335.5 m)/ 1, K46/2. Figure 12. Cheleutochroa gymnobrachiata Loeblich & Tappan 1978. VA 46 (345.7 m)/1, Q17/1.

A. Delabroye et al.


12

Plate 4. All scale bars represent 20 mm when not specified. Figures 1, 4, 7–12 were taken using plain transmitted light; figures 2– 3 and 5–6 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. Comasphaeridium lanugiferum Jacobson & Achab 1985. VA 38 (313.2 m)/1, N24/1. Figure 2. Comasphaeridium lanugiferum Jacobson & Achab 1985. VA 38 (313.2 m)/SEM stub. Figure 3. Ammonidium sp. VA 40 (320.0 m)/SEM stub. Figure 4. Evittia denticulata denticulata (Cramer 1970) Le He´risse´ 1989. VA 38 (313.2 m)/1, J47/4. Figure 5. Evittia denticulata denticulata (Cramer 1970) Le He´risse´ 1989. VA 44 (338.8 m)/SEM stub. Figure 6. Micrhystridium taeniosum Uutela & Tynni 1991. VA 46 (345.6 m)/SEM stub. Figures 7, 8, 9. Micrhystridium taeniosum Uutela & Tynni 1991. VA 40 (320.2m)/2, S28/2; low, median and high focus, respectively. Figure 10. Leiosphaeridia sp. VA 40 (320.2 m)/2, O47. Figure 11. Leiosphaeridia sp. VA 44 (338.8 m)/2, F46. Figure 12. Tasmanites sp. VA 38 (313.2 m)/2, C21.

13


Palynology

Plate 5. All scale bars represent 20 mm when not specified. Figures 1–2, 5–8 and 10–11 were taken using plain transmitted light; figures 3–4, 7 and 9 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2. Goniosphaeridium sp. A. VA 40 (320.0 m)/1, J18/3; low and high focus, respectively. Figures 3, 4. Goniosphaeridium sp. A. VA 44 (335.5 m)/SEM stub. Figures 5, 6. Stellechinatum helosum Turner 1984. VA 38 (313.2 m)/1, D31; low and high focus, respectively. Figures 7, 9. Stellechinatum helosum Turner 1984. VA 38 (313.2 m)/SEM stub. Figure 8. Comasphaeridium williereae (Deflandre & Deflandre-Rigaud 1965 ex Lister 1970) Sarjeant & Stancliffe 1994. VA 46 (345.6 m)/1, R23/3. Figure 10. Dorsennidium sp. cf. D. europaeum (Stockmans & Willie`re 1960) Sarjeant & Stancliffe 1994. VA 46 (345.6 m)/1, R22/2. Figure 11. Veryhachium oklahomense Loeblich 1970. VA 46 (345.6 m)/1, E25/3.

A. Delabroye et al.


14

Plate 6. All scale bars represent 20 mm when not specified. Figures 1–2, 5–8 and 10–11 were taken using plain transmitted light; figures 3–4, 7 and 9 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. Comasphaeridium sp. A; VA 46 (345.6 m)/1, G32/3. Figure 2. Multiplicisphaeridium ramispinosum Staplin 1961. VA 46 (345.6 m)/1, L32/1. Figure 3. Multiplicisphaeridium ramispinosum Staplin 1961. VA 38 (313.2 m)/SEM stub. Figures 4, 5. Hoegklintia visbyensis (Eisenack 1959) Dorning 1981. VA 38 (313.2 m)/1, F17; high and low focus, respectively. Figures 6, 7, 8. ?Florisphaeridium sp. VA 44 (338.8 m)/1, K44/1. Figures 9, 10. Hoegklintia visbyensis (Eisenack 1959) Dorning 1981. VA 38 (313.2 m)/1, M36; low and high focus, respectively. Figure 11. Estiastra magna Eisenack 1959. VA 38 (313.2 m)/2, P33/1.

15


Palynology

Plate 7. All scale bars represent 20 mm when not specified. The photomicrographs were all taken using plain transmitted light. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. Likropalla adiazeta Colbath 1979. VA 46 (345.6 m)/1, E19/3. Figures 2, 3, 4. Likropalla adiazeta Colbath 1979. VA 44 (338.8 m)/2, M18/2; low, median and high focus, respectively. Figures 5, 6, 7. Navifusa punctata Loeblich & Tappan 1978. VA 38 (313.2 m)/1, M31/2; low, median and high focus, respectively. Figures 8, 9, 10. Lophosphaeridium edenense Loeblich & Tappan 1978. VA 46 (345.6 m)/1, S27/1; high, median and low focus, respectively.

A. Delabroye et al.


16

Plate 8. All scale bars represent 20 mm when not specified. The photomicrographs were all taken using plain transmitted light. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2. Orthosphaeridium insculptum Loeblich 1970. VA 46 (345.6 m)/1, M27; low and high focus, respectively. Figure 3. Orthosphaeridium insculptum Loeblich 1970. VA 38 (313.2 m)/1, B29. Figures 4, 5, 6. Orthosphaeridium vibrissiferum Loeblich & Tappan 1971. VA 44 (338.8 m)/1, R34/1; high, median and low focus, respectively. Figures 7, 8, 9. Orthosphaeridium rectangulare (Eisenack 1963) Eisenack 1968. VA 44 (335.5 m)/1, H34/2; low and high focus and magnification of the vesicle, respectively. Figures 7, 8 Baltisphaeridium sp. A. VA 38 (313.2 m)/2, P35/1; low and high focus, respectively.

17


Palynology

Plate 9. All scale bars represent 20 mm when not specified. Figures 1–2, 4–5 and 7 were taken using plain transmitted light; figures 3, 6 and 8–10 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2. Peteinosphaeridium accinctulum Wicander, Playford & Robertson 1999. VA 38 (313.2 m)/2, O42; low and high focus, respectively. Figure 3. Peteinosphaeridium accinctulum Wicander, Playford & Robertson 1999. VA 38 (313.2 m)/ SEM stub. Figures 4, 5. Peteinosphaeridium septuosum Wicander, Playford & Robertson 1999. VA 46 (345.6 m)/1, S28; high and low focus, respectively. Figure 6. Peteinosphaeridium septuosum Wicander, Playford & Robertson 1999. VA 40 (320.0 m)/SEM stub. Figure 7. Multiplicisphaeridium sp. A. VA 46 (345.6 m)/1, M18. Figures 8, 9. Multiplicisphaeridium sp. A. VA 46 (345.6 m)/ SEM stub. Figure 10. Evittia porkuniensis Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/SEM stub.

A. Delabroye et al.


18

Plate 10. All scale bars represent 20 mm when not specified. Figures 1–6 and 8–9 were taken using plain transmitted light; figures 7 and 10 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. Helosphaeridium tongiorgii Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/2, Paratype, S21/4. Figure 2. Helosphaeridium tongiorgii Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/1, Paratype, J18. Figure 3. Helosphaeridium tongiorgii Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/2, Paratype, J43. Figures 4, 5. Helosphaeridium tongiorgii Delabroye, Vecoli, Hints & Servais sp. nov. VA 38 (313.2 m)/2, Holotype, E36/2; high and low focus, respectively. Figure 6. Helosphaeridium tongiorgii Delabroye, Vecoli, Hints & Servais sp. nov. VA 38 (313.2 m)/2, Paratype, L22/2. Figure 7. Helosphaeridium tongiorgii Delabroye, Vecoli, Hints & Servais sp. nov. VA 38 (313.2 m)/SEM stub. Figures 8, 9. ?Carminella sp. VA 46 (345.6 m)/2, J24/4; low and high focus, respectively. Figure 10. Leiofusa sp. aff. L. granulicatis Loeblich 1970 forma quincunx Uutela 1989. VA 38 (313.2 m)/SEM stub.

19


Palynology

Plate 11. All scale bars represent 20 mm when not specified. Figures 3, 6 and 7 were taken using plain transmitted light; figures 1–2 and 4–5 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2. Leiofusa granulicatis Loeblich 1970 forma quincunx Uutela 1989. VA 46 (345.6 m)/ SEM stub. Figure 3. Leiofusa granulicatis Loeblich 1970 forma quincunx Uutela 1989. VA 38 (313.2 m)/1, O24. Figures 4, 5. ?Ferromia sp. A. VA 44 (338.8 m)/SEM stub. Figures 6, 7. Oppilatala sp. VA 40 (320.0 m)/2, E29; low and high focus, respectively.

A. Delabroye et al.


20

Plate 12. All scale bars represent 20 mm when not specified. Figures 1–2 and 5–6 were taken using plain transmitted light; figures 3–4 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2. Poikilofusa obliquipunctata (Uutela & Tynni 1991) Delabroye, Vecoli, Hints & Servais comb. nov. VA 40 (320.0 m)/2, J31. Figures 3, 4. Poikilofusa obliquipunctata (Uutela & Tynni 1991) Delabroye, Vecoli, Hints & Servais comb. nov. VA 44 (338.8 m)/SEM stub. Figures 5, 6. Ordovicium sp. A. VA 40 (320.0 m)/2, H28; high and low focus, respectively.

21


Palynology

Plate 13. All scale bars represent 20 mm when not specified. Figures 1–2, 5–7 and 10–12 were taken using plain transmitted light; figures 3–4 and 8–9 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figures 1, 2. Ordovicium sp. A. VA 38 (313.2 m)/1, O26/3; low and high focus, respectively. Figures 3, 4. Ordovicium sp. A. VA 38 (313.2 m)/ SEM stub. Figures 5, 6, 7. Ordovicium sp. B. VA 38 (313.2 m)/1, O39/2; high, median and low focus, respectively. Figures 8, 9. Ordovicium sp. B. VA 38 (313.2 m)/ SEM stub. Figures 10, 11. Nexosarium leherissei Delabroye, Vecoli, Hints & Servais sp. nov. VA 38 (313.2 m)/2), Holotype, K21; high and low focus, respectively. Figure 12. Nexosarium leherissei Delabroye, Vecoli, Hints & Servais sp. nov. VA 45 (340.6 m)/2, Paratype, K35/2.

A. Delabroye et al.


22

Plate 14. All scale bars represent 20 mm when not specified. Figures 5–10 were taken using plain transmitted light; figures 1–4 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. Nexosarium leherissei Delabroye, Vecoli, Hints & Servais sp. nov. VA 44 (338.8 m)/SEM stub. Figures 2, 3, 4. Nexosarium leherissei Delabroye, Vecoli, Hints & Servais sp. nov. VA 38 (313.2 m)/ SEM stub. Figures 5, 6, 7. ?Veryhachium bulliferum Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/1, Holotype, O20/1; high, median and low focus, respectively. Figures 8, 9, 10. ?Veryhachium bulliferum Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/1, Paratype, O34; high, median and low focus, respectively.

23


Palynology

Plate 15. All scale bars represent 20 mm when not specified. Figures 1–10 were taken using plain transmitted light; figures 11–12 were taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. ?Veryhachium bulliferum Delabroye, Vecoli, Hints & Servais sp. nov. VA 38 (313.2 m)/1, Paratype, D19/2. Figures 2, 3. Evittia sp. A. VA 40 (320.0 m)/2, F37; low and high focus, respectively. Figures 4, 5, 6. Evittia sp. A. VA 45 (340.6 m)/1, N38/2; low, median and high focus, respectively. Figure 7. Evittia porkuniensis Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/ 1, Paratype, X20. Figures 8, 9, 10. Evittia porkuniensis Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/1, Holotype, W31/1; high, median and low focus, respectively. Figures 11, 12. Evittia porkuniensis Delabroye, Vecoli, Hints & Servais sp. nov. VA 40 (320.0 m)/SEM stub.

A. Delabroye et al.


24

Plate 16. All scale bars represent 20 mm when not specified. Figures 2–10 were taken using plain transmitted light; figure 1 was taken using the SEM. The sample/slide numbers and the England Finder coordinates are indicated for all specimens. Figure 1. Buedingiisphaeridium balticum Uutela & Tynni 1991. VA 44 (335.5 m)/SEM stub. Figures 2, 3. Buedingiisphaeridium balticum Uutela & Tynni 1991. VA 45 (340.6 m)/1, L45/4; low and high focus, respectively. Figures 4, 5. Buedingiisphaeridium balticum Uutela & Tynni 1991. VA 46 (345.6 m)/2, G31; low and high focus, respectively. Figures 6, 7. Nanocyclopia sp. A. VA 40 (320.0 m)/1, E43/1; low and high focus, respectively. Figure 8. Nanocyclopia sp. A. VA 44 (335.5 m)/1, N40/2. Figure 9. Nanocyclopia sp. A. VA 46 (345.6 m)/1, O21/1. Figure 10. Nanocyclopia sp. A. VA 46 (345.6 m)/1, K18/1.

Palynology (Plate 13, figures 10–12; Plate 14, figures 1–4), Orthosphaeridium insculptum (Plate 8, figures 1–3), Peteinosphaeridium accinctulum (Plate 9, figures 1–3), P. septuosum (Plate 9, figures 4–6) and Stellechinatum helosum (Plate 5, figures 5–9). AS3 is represented by VA 40 (320.0 m) and VA 38 (313.2 m). It is characterised by the first occurrences of several taxa, including Evittia porkuniensis (Plate 9, figure 10, Plate 15, figures 7–12) which has not been observed elsewhere excluding some imprecisely dated Ordovician erratics from Finland. AS4 is represented by one productive sample, VA 38 (312.2 m), at the base of the Silurian succession. It is characterised exclusively by the occurrence of Leiosphaeridia sp.


6.

Systematic palaeontology

Group ACRITARCHA Evitt 1963 Genus Carminella Cramer 1968 ? Carminella sp. Plate 10, figures 8–9

Description. Vesicle spherical, shagrenate, bearing numerous, thin filaments less than 5 mm. Process distribution bipolar; +30, simple, thin, long processes present on the two opposite sides of vesicle and surrounded by a diaphanous membrane; processes of equal length, apparently solid; processes attached to vesicle only at periphery; no processes present on the central part of vesicle. No excystment structure observed. Dimensions. (1 specimen observed) Vesicle diameter 35 mm; process length 25–27 mm; vesicle filament length 55 mm. Discussion. This specimen differs from Carminella Cramer 1968 by having the processes distributed only at the periphery of the vesicle and not covering the entire vesicle surface. Occurrence. Lower Jelgava Formation, Pirgu regional Stage (upper Katian), Valga-10 drill-core, southern Estonia.

25

Repository. ‘Geosyste`mes’ Laboratory, SN5 building, University of Lille 1, France. Type locality. Valga-10-drill core, southern Estonia. Stratigraphical horizon. Porkuni Regional Stage (Hirnantian), uppermost Ordovician. Etymology. After the Ordovician regional Stage Porkuni. Diagnosis. Vesicle spherical, reticulate, bearing numerous processes; processes short, conical, heteromorphic (simple to multifurcate), equal in length, regularly distributed, well delimited from the vesicle and freely communicating with the interior, showing numerous small spaced grana on their trunk; vesicle/process contact curved. When simple, processes thin with acuminate tips; when multifurcate, processes with wider base but showing a short distal, multifurcate part (a quarter of the process length). No opening structure observed. Dimensions. (20 measured specimens) Vesicle diameter 20–30 mm; process length 7–11 mm; width at the base of the process 1.4–4 mm; number of visible processes 25–50. Discussion. This species is morphologically close to the Silurian–Devonian species E. sanpetrensis (Cramer 1964) Lister 1970, but has much more numerous processes, which are regularly distributed and equal in length. The specimen figured by Uutela (1989) as Multiplicisphaeridium raspa Cramer 1964 clearly shows the same gross morphology and wall microsculpture (grana on process wall) as the present specimens. However, Multiplicisphaeridium raspum (Cramer 1964) Eisenack, Cramer & Dı´ ez 1973 as originally named and illustrated, differs from the specimens herein by having a smaller vesicle diameter (10–20 mm), a laevigate vesicle wall, and laevigate processes which are variable in length. Occurrence. Kuldiga Formation, middle Edole Member, Porkuni Regional Stage (Hirnantian), Valga-10drill core, southern Estonia. Distribution. Upper Ordovician Baltic erratics, southwestern Finland (Uutela 1989). Evittia sp. A Plate 15, figures 2–6

Genus Evittia (Brito 1967) emend. Lister 1970 Evittia porkuniensis sp. nov. Plate 9, figure 10; Plate 15, figures 7–12 Multiplicisphaeridium raspa Cramer, 1964; Uutela 1989, p. 34, plate 7, figure 59

Evittia sp. 1, Eiserhardt, 1992, p. 24, plate 2, figures 6– 8 Evittia sp. 2, Eiserhardt, 1992, p. 25, plate 2, figures 9– 10

Holotype. Sample VA 40 (320.00), slide no. 1, E.F., W31, Plate 15, figures 8–10. Paratype. Sample VA 40 (320.00), slide no. 1, E.F., X20, Plate 15, figure 7.

Description. Vesicle subspherical to tetrahedrical, grano-reticulate, bearing few short and broad processes not well delimited from the vesicle. Processes conical, variable in length and distally acuminate to


26

A. Delabroye et al.

slightly digitate and rounded, freely communicating with the vesicle interior. On the vesicle, grana or rounded spines present at the intersection of the muri. On the processes, longitudinal ridges with grana or rounded spines present. Ridges originate by extensions of some of the vesicle muri. No opening structure observed. Dimensions. (2 specimens measured) Vesicle diameter 28–35 mm; process length 8–20 mm; width at the base of the processes 3.5–8 mm; number of processes 4–5. Discussion. This species is rare in the samples from Valga but it has biostratigraphical potential, as similar morphotypes have been observed from the Hirnantian Ellis Bay Formation at Anticosti Island, Que´bec, Canada. Specimens assignable to the present species have been also described and figured at Gotland (Ordovician–Silurian boundary strata of the Na¨r borehole; Le He´risse´ 1989a, and Upper Ordovician erratic boulders; Eisehardt 1992). This species is morphologically close to Evittia robustispinosa (Downie 1959) Lister 1970 and E. sampetrensis (Cramer 1966) Lister 1970 (two similar Silurian species), from which it differs by having fewer processes which are not clearly set out from the vesicle. The digitate process tips of Evittia sp. A are also more rounded than those of the Silurian species. These three species have globally the same dimensions and could be phylogenetically linked. Occurrence. Middle Jelgava Formation, Pirgu Regional Stage (upper Katian) and base of the Kuldiga Formation, Porkuni Regional Stage (Hirnantian), Valga-10-drill core, southern Estonia. Distribution. Uppermost Ordovician of the Na¨r borehole, southern Gotland, Sweden (Le He´risse´ 1989a); Ellis Bay Formation, Hirnantian, western Anticosti, Canada; O¨jlemyrflint erratic boulders, Middle-Upper Ordovician, northwestern shore of Gotland, Sweden (Eiserhardt 1992). Genus Ferromia Vavrdova´ 1979 emend. Martin 1996 ? Ferromia sp. A Plate 11, figures 4–5 Description. Vesicle originally spherical, sculptured with numerous small conical spines regularly spaced and bearing twelve flattened and flexible laevigate processes. Processes, by a majority in the equatorial plane, simple or slightly bifurcate at their distal end, basally constricted, equal in length to the vesicle diameter, showing basal longitudinal ridges converging toward their trunk. Spines of vesicle ornamentation with relatively wide base but narrowing rapidly to reach the small diameter of their trunk; one spine shows a bifurcation; spines with wider base show tiny ridges or crests converging toward their trunk; between

each spines, presence of rather randomly distributed and closely packed elevated grana or papillae, that align according to the basal process ridges in this area. No excystment structure observed. Dimensions. (1 observed specimen) vesicle diameter 19 mm; process length 18–20 mm; wide at the base of the process 1.15–1.25 mm; width in the half of the processes 1.7–1.9 mm; length of the spines 2.5–3.7 mm; width at the base of the spines 0.6 mm; width of the spine trunk 0.3 mm; diameter of the elevated grana 0.1 mm. Discussion. Only one specimen has been observed with SEM (Figure 2). No information can be given on the communication between processes and vesicle interior. Also, some processes arise perpendicularly to the equatorial plane. According to the diagnosis of Ferromia Vavrdova´ 1979 emend. Martin 1996, processes communicate freely with the vesicle interior and are preferentially oriented in one plane. For these reasons, we prefer to assign this specimen to ?Ferromia sp. A. Ridges at the base of the processes and at the base of the spines of vesicle ornamentation, basal constriction of the processes and vesicle ornamentation with two different kinds of elements (spines and elevated grana or papillae) are the characteristic features of the present species. Ferromia pellita (Martin 1977) Martin 1996 from the Lower Ordovician of western Europe differs from ?Ferromia sp. A by having hair-like ornamentation which shows minute, possibly anastomosed, lateral ramifications, pilose to microgranulate processes and no basal constriction of the processes. Ferromia clavula Vecoli 1999 from the Llanvirn of North Africa has no basal constriction at the base of the processes. The vesicle ornamentation is similar to those of ?Ferromia sp. A by the presence of spine-like elements but differs by having no closely packed grana between the spines. Occurrence. Uppermost Jelgava Formation, upper Pirgu Regional Stage (uppermost Katian), Valga-10 drill-core, southern Estonia. Genus Helosphaeridium Lister 1970 Helosphaeridium tongiorgii sp. nov. Plate 10, figures 1–7 ?Helosphaeridium clavispinulosum Lister 1970; Smelror, 1987, plate 2, figure 3, plate 5, figure 1 ?Multiplicisphaeridium borracherosum f. regulare Uutela & Tynni, 1991, p. 88, plate 20, figure 208 ?Multiplicisphaeridium aff. M. borracherosum (Cramer) Lister 1970 [sic]; Uutela and Tynni, 1991, pp. 88–89, plate 19, figure 194

Holotype. Sample VA 38 (313.2), slide no. 2, E.F., E36/ 2, Plate 10, figures 4–5.


Palynology Paratypes. Sample VA 40 (320.0), slide no. 2, E.F., S21/4, Plate 10, figure 1; Sample VA 40 (320.0), slide no. 1, E.F., J18, Plate 10, figure 2; Sample VA 40 (320.0), slide no. 2, E.F., J43, Plate 10, figure 3; Sample VA 38 (313.2), slide no. 2, E.F., L22/2, Plate 10, figure 6. Repository. ‘Geosyste`mes’ Laboratory, SN5 building, University of Lille 1, France. Type locality. Valga-10 drill core, southern Estonia. Stratigraphical horizon. Porkuni Regional Stage (Hirnantian), uppermost Ordovician. Etymology. In honour of Professor Marco Tongiorgi (Pisa, Italy), palynologist. Diagnosis. Vesicle subcircular, thick-walled, laevigate, bearing numerous, thick walled, highly heteromorphic, closely-spaced, very short and stout laevigate processes. Distal end of processes flat, rounded, capitate, or slightly digitate with two or three equifurcate pinnae. Communication between process and vesicle cavities difficult to define; narrowest processes appearing as solid whereas larger processes showing a thin median longitudinal hollow portion. Mode of excystment by simple splitting. Dimensions. (27 measured specimens) vesicle diameter 20–49 mm; process length 1.8–7.3 mm; process width 1.3–3.5 mm. Discussion. The present specimens closely resemble H. clavispinulosum Lister 1970 from the Ludlow of England (Lister 1970, p. 76; plate 8, figures 8, 12, 16). Nevertheless, the latter has more widely-spaced, thinner processes which, according to Turner (1984, p. 129), ‘are open to the vesicle cavity’. It is worth noting that Palaiosphaeridum sp. A of Turner (1984) has the same general morphology as Helosphaeridium clavispinulosum and could be a junior synonym of the latter. Helosphaeridium clavispinulosum Lister 1970 in Smelror (1987) seems identical to Helosphaeridium tongiorgii sp. nov. by having tightly-arranged processes but no more information can be given on their potential synonymy as Smelror (1987) only figured one SEM specimen, which prevented observing the communication between processes and vesicle. If the specimens of Smelror (1987) have free communication between process and vesicle cavities, based on Turner (1984), the attribution by Smelror (1987) would be correct and synonymy with our new species would be rejected. Multiplicisphaeridium borracherosum f. regulare Uutela & Tynni 1991, of which the type specimen is figured by a SEM photograph (Uutela and Tynni 1991, plate 20, figure 208), is also, however, identical to our specimens. Uutela and Tynni (1991, p. 89) did not specify the kind of communications present between the process and vesicle cavities. Multiplicisphaeridium aff. M. borracherosum (Cramer) Lister 1970 in Uutela and Tynni (1991, pp. 88–89; plate 19, figure 194) is also

27

morphologically close to Helosphaeridium tongiorgii sp. nov. but has more complexly ramified processes, and no information is available concerning the process–vesicle communication. Recent investigation of acritarch assemblages from the uppermost Vaureál and Ellis Bay formations of Anticosti Island shows that Helosphaeridium tongiorgii sp. nov. is also present in these uppermost Ordovician strata from eastern Laurentia. Occurrence. Porkuni Stage (Hirnantian), Valga-10drill core, southern Estonia. Distribution. Western Anticosti: uppermost Vaureal Formation sensu Petryk (1981); Eastern Anticosti: Lousy Cove Member, Ellis Bay Formation, uppermost Katian–Hirnantian. Genus Leiofusa Eisenack 1938 emend. Combaz, Lange and Pansart 1967 Discussion. Distinction between the fusiform (or netromorph) acritarchs is based on the general shape of the vesice and the type and arrangement of wall sculpture (Combaz et al. 1967; Cramer 1970). Leiofusa has distinct processes drawn out from the opposite ends of the vesicle, and can possess fine sculptural elements. Dactylofusa Britos & Santos 1965 and Poikilofusa Staplin, Jansonius & Pocock 1965, have fusiform vesicles ending in acuminate tips, but no clearly demarcated processes. The former has digitate or branched ornamentation, the latter has simple ornamentation. Leiofusa granulicatis forma quincunx Uutela 1989, Plate 11, figures 1–3 ?Eupoikilofusa aff. E. ampulliformis (Martin 1965); Duffield and Legault 1981, plate 1, figure 8; Duffield and Legault 1982, plate 1, figures 1–2 ?Leiofusa aff. L. tumida Downie 1959; Duffield and Legault 1981, plate 1, figure 11; Duffield and Legault 1982, plate 1, figures 3–4 Eupoikilofusa aff. E. ampulliformis, sensu Duffield and Legault 1981; Martin 1988 p. 304, figures 3–14a, b Leiofusa granulicatis forma quincunx Uutela 1989, p. 31, plate 5, figure 41; Uutela and Tynni 1991, p. 74, plate 17, figure 161 Poikilofusa aff. P. ampulliformis (Martin) Cramer 1970; Martin 1989, figure 151B Dimensions. (20 measured specimens) vesicle width 21– 26 mm; vesicle length 36–45 mm; process length 14–24 mm; width at the base of the processes 2.5– 3.7 mm. Discussion. The specimens observed have a slightly larger vesicle and slightly shorter processes than


28

A. Delabroye et al.

specimens from the Pirgu and Porkuni strata from Rapla, northern Estonia (Uutela and Tynni 1991). The specimens attributed to Leiofusa aff. L. tumida and Eupoikilofusa aff. E. ampulliformis by Duffield and Legault (1981) from the Ellis Bay and Becsie formations of Anticosti Island, Que´beć, Canada, do not show any recognisable ornamentation, based on their illustrations, and thus their taxonomic attribution is considered questionable. However, Martin (1988) who restudied Duffield and Legault’s (1981) Anticostan material, figured a specimen which is clearly assignable to L. granulicatis forma quincunx. Our investigation of acritarchs from the Ellis Bay Formation at Anticosti confirms the occurrence of the species at this locality. Leiofusa granulicatis forma quincunx differs from L. granulicatis forma granulicatis Loeblich 1970 by having ‘scattered tubercles with a regularly quincuncial pattern’. The tubercles of L. granulicatis forma granulicatis are not regularly arranged according to the diagnosis of Loeblich (1970), although it is not so evident on the only one specimen figured with SEM (Loeblich 1970, p. 767, figure 18E). Notwithstanding, the specimens of L. granulicatis forma granulicatis from the Mapplewood Shale Formation (Middle Silurian, New York) studied by Loeblich (1970) are twice as long as all the specimens of L. granulicatis forma quincunx considered here. Leiofusa ampulliformis Martin 1966 from the Silurian of Belgium differs from L. granulicatis forma quincunx by having papillae rather than small granular tubercles. No information is given on the pattern of these papillae and no SEM pictures are available to further compare the two species, which could be synonyms based on the available information. Poikilofusa sp. A of Playford and Wicander (2006), from the Sylvan Shale Formation (Oklahoma, upper Richmondian, upper Katian), is similar to the present specimens but is much larger. Disparifusa borea Jacobson & Achab 1985 (Vaureal Formation, upper Katian, Anticosti Island) has an elongated vesicle ornamented with numerous small grana and closely and regularly-spaced but randomly distributed coni. However, D. borea is twice as long as L. granulicatis forma quincunx and its processes are not clearly delimited from the vesicle. Disparifusa psakadoria Loeblich & Tappan 1978 from the Upper Ordovician (Richmondian) Sylvan Shale of Oklahoma (USA) differs only from L. granulicatis forma quincunx by its asymmetric fusiform vesicle and its larger size (128 mm long) and could represent two ecophenotypic expressions of the same species relating to different environmental factors as are generally found in coeval strata.

Occurrence. Pirgu Regional Stage (upper Katian) and Porkuni Regional Stage (Hirnantian), Valga-10-drill core, southern Estonia. Distribution. Ellis Bay (Hirnantian) and Becsie formations (Rhuddanian), Anticosti Island, Canada (Duffield and Legault 1981, 1982; Martin 1988; Ordovician Baltic erratics, southwestern Finland (Uutela 1989); Pirgu Regional Stage (upper Katian) and Porkuni Regional Stage (Hirnantian), Rapla borehole, north Estonia (Uutela and Tynni 1991); Clemville Formation, Baie des Chaleurs area, Gaspe´, Canada, Rhuddanian, Llandovery (Martin 1989). Leiofusa sp. cf. L. granulicatis forma quincunx Uutela, 1989 Plate 10, figure 10 Description. Small, rounded vesicle bearing two small processes at each pole, not exceeding the vesicle length and distally rounded. Vesicle ornamented by numerous small papillae regularly arranged in a quincuncial pattern; papillae also present at the base of the processes and decreasing in size to progressively disappear at about half of the process length. Dimensions. (1 specimen measured) vesicle width 18 mm; vesicle length 23 mm; process length 16 mm; width at the base of the processes 2.4 mm. Discussion. This specimen assigned to Leiofusa sp. cf. L. granulicatis forma quincunx differs from L. granulicatis forma quincunx by its smaller dimensions, less elongate shape, and by showing papillae rather than small grana/tubercles on the vesicle. Without more specimens, we prefer to separate L. granulicatis forma quincunx from L. sp. cf. L. granulicatis forma quincunx based on vesicle ornamentation although it is possible that the first represents less well-preserved specimens of the second. Occurrence. Uppermost Porkuni Regional Stage (Hirnantian; Saldus Formation, Broceni Member), Valga10 drill core, southern Estonia. Distribution. Uppermost Ellis Bay Formation and lowermost Becsie Formation (Hirnantian–Rhuddanian), Anticosti Island, Canada. Genus Nexosarium Turner 1984 Nexosarium leherissei sp. nov. Plate 13, figures 10–12, Plate 14, figures 1–4 ?Multiplicisphaeridium granulabrachium 1992, p. 50–51, Plate 5, figures 6–7, 10

Eiserhardt

Holotype. Sample VA 38 (313.20), slide no. 2, E.F., K21, Plate 13, figures 10–11. Paratype. Sample VA 45 (340.6), slide no. 2, E.F., K35/2, Plate 13, figure 12.


Palynology Repository. ‘Geosyste`mes’ Laboratory, SN5 building, University of Lille 1, France. Type locality. Valga-10-drill core, southern Estonia. Stratigraphical horizon. Porkuni Regional Stage (Hirnantian), uppermost Ordovician. Etymology. In honour of Dr Alain Le He´risse´ (Brest, France). Diagnosis. Vesicle globally spherical in shape, thinwalled, sculptured with muri, bearing about eleven hollow, heteromorphic, multifurcate processes up to fourth order, exceptionally to sixth order, appearing granulate under SEM. Plug at the base of the processes without proximal constriction. Opening structure by simple rupture. Description. Vesicle spherical to slightly polygonal. In transmitted light, vesicle muri easily observable unlike grana on processes, only identifiable under SEM observation. In vicinity of processes, reticulum progressively replaced by converging ridges directed toward the base of processes; granular sculptural elements, up to 0.25 mm high, present on entire process trunks from a few microns above process–vesicle contact and decreasing gradually in size towards process distal ends; process base laevigate, wider than the mid and distal parts, and without proximal constriction but showing a clear basal plug. Processes slightly longer than the vesicle diameter, heteromorphic, usually branched up to fourth order, exceptionally to sixth order; distal terminations of pinnulae acuminate. Excystment by simple rupture of vesicle wall. Dimensions. (25 specimens measured) vesicle diameter 15–28 mm; process length 14–40 mm; width at the base of the processes 2.5–5.5 mm; width at the mid-processes 0.9–1.9 mm; number of processes 8–15; rank of bifurcation 3–6. Discussion. Nexosarium leherissei sp. nov. differs from N. parvum Turner 1984, from the Caradoc of England by having more complexly branched processes (up to the sixth order) than N. parvum, which typically bears ‘processes having one or two orders of bifurcation, rarely a trifurcate process’ (Turner 1984). Multiplicisphaeridium granulabrachium Eiserhardt, 1992 from O¨jlemyrflint erratic boulders (Middle-Upper Ordovician?, Gotland, Sweden) clearly shows the same overall morphology as N. leherissei sp. nov. (reticulate vesicle, spines on the processes, heteromorphic and multifurcated processes), but, according to Eiserhardt (1992), it has free communication between process and vesicle cavities. However, on the only figured specimen of M. granulabrachium in optical micrograph (Eiserhardt 1992, plate 5, figure 6), communication between process interior and vesicle caviy is not evident, however, a plug is possibly present at the base of one process.

29

Hapsidopalla multifida Uutela and Tynni 1991 (Middle Ordovician to Lower Silurian, Rapla borehole, north Estonia) is also similar to Nexosarium leherissei sp. nov. but has microgranulate processes that communicate freely with the vesicle interior. Occurrence. From the upper Pirgu Regional Stage (Jelgava, Paroveja and Kuili formations; upper Katian) to the uppermost Porkuni Regional Stage (Kuldiga and Saldus formations; Hirnantian), Valga10-drill core, southern Estonia. Distribution. Uppermost Ordovician of the Na¨r borehole, southern Gotland, Sweden (Le He´risse´ 1989a). Genus Oppilatala Loeblich & Wicander 1976 Oppilatala sp. Plate 11, figs 6–7 Description. Vesicle circular, double-layered, laevigate, bearing six processes. Processes thin-walled, laevigate, hollow, long, slender and flexible, equal in length to vesicle diameter, bifurcated or trifurcated to first order at 65 to 50% along their length, and tapering to thin sharp point; small pinnae of second order present sometimes at process extremities; presence of a solid plug with flat proximal face and concave distal face near process base making them slightly constricted at this point. Process–vesicle contact forming an acute angle. Opening structure not observed. Dimensions. (1 specimen observed and measured) vesicle diameter 19.5 mm; process length 20–22 mm; width of the plugs 1.5–2 mm; height of the plugs 1.4– 1.5 mm; number of processes 6. Discussion. This species is also present in the Ellis Bay Formation of the western and eastern parts of Anticosti Island, Canada. Even if one specimen of Oppilatala sp. has been recovered in the Porkuni strata at Valga (Figure 2), future investigations on uppermost Ordovician strata from Baltica could reveal the importance of this species for uppermost Ordovician biostratigraphy at low latitudes. Occurrence. Middle Kuldiga Formation, middle Edole Member, Porkuni Regional Stage (Hirnantian), Valga10 drill-core, southern Estonia. Distribution. Ellis Bay Formation, Hirnantian, Anticosti Island, Canada. Genus Poikilofusa Staplin, Jansonius & Pocock 1965 Poikilofusa obliquipunctata (Uutela & Tynni 1991) comb. nov. Plate 12, figures 1–4 Basionym: Leiofusa obliquipunctata Uutela & Tynni 1991, p. 75, plate 15, figure 150


30

A. Delabroye et al.

Description. Vesicle long and slender, varying considerably in length and width. From central part of vesicle, width decreasing progressively to end in an acuminate tip. Under optical microscope, fine granulation observed on vesicle wall appearing under SEM, as microgranulate to microfossulate sensu Tappan and Loeblich (1971); microgranules organised in a regular quincuncial pattern according to two perpendicular axes forming a 458 angle relatively to the longitudinal axis of vesicle, and diminishing in the distal part of acuminate tips. Mode of opening structure not observed. Dimensions. (6 measured specimens) total length 190– 440 mm (average 285 mm); width of the body 27–44 mm (average 35 mm). Discussion. This species is attributed to Poikilofusa because of its fusiform shape without processes and the presence of simple ornamentation. The granulation of Poikilofusa obliquipunctata is close to those observed on Leiofusa granulicatis Loeblich 1970 forma quincunx Uutela 1989. In the Ellis Bay Formation at Anticosti, specimens of Poikilofusa are similar to Poikilofusa obliquipunctata herein. They only differ by their microstructure composed of long uninterrupted longitudinal costae. Occurrence. From the middle Jelgava Formation (upper Pirgu Regional Stage; upper Katian) to the middle Kuldiga Formation (Porkuni Regional Stage; Hirnantian), Valga-10 drill-core, southern Estonia. Distribution. Vormsi Regional Stage (upper Katian), Rapla borehole, northern Estonia (Uutela and Tynni, 1991). Genus Veryhachium Deunff 1954 emend. Sarjeant & Stancliffe 1994 ?Veryhachium bulliferum sp. nov. Plate 14, figures 5–10, Plate 15, figure 1 ?Veryhachium hamii Loeblich, 1970; Wright and Meyer 1981, pp. 29–30, plate 3, figure N Holotype. Sample VA 40 (320.00), slide no. 1, E.F., O20/1, Plate 14, figures 5–7. Paratypes. Sample VA 40 (320.00), slide no. 1, E.F., O34, Plate 14, figures 8–10; Sample VA 38 (313.20), slide no. 1, E.F., D19/2, Plate 15, figure 1. Repository. ‘Geosyste`mes’ Laboratory, SN5 building, University of Lille 1, France. Type locality. Valga-10-drill core, southern Estonia. Stratigraphical horizon. Porkuni Regional Stage (Hirnantian), uppermost Ordovician. Etymology. Lat., bulla, bubble; Lat., ferum, bear; referring to the several small hollow parts on the processes. Diagnosis. Vesicle rhombohedral in shape, thick walled, laevigate, bearing around six homomorphic processes expanding from each corner of vesicle.

Because of flattening of specimens, sometimes one to three processes arise perpendicularly from both sides of vesicle body. Vesicle–process junction curved and progressive. Process base large but thinning down rapidly to show acuminate extremity. Processes filled by same material as vesicle wall from the beginning of their narrowing to tip, with several small circular hollow parts. Opening structure by simple rupture. Dimensions. (23 measured specimens) vesicle diameter 21–30 mm (average: 25.5 mm); process length 23–43 mm (average: 33 mm); width at the half of the process 1.1– 1.8 mm (average: 1.4 mm); number of processes 6–7 (average: 6.3). Discussion. The attribution to Veryhachium is questionable because the processes do not communicate freely with the vesicle interior. This species appears in the uppermost Ordovician strata in the Na¨r borehole, southern Gotland, Sweden (Le He´risse´ 1989a) and also exhibits small hollow parts in the processes. Consequently, these hollow parts seem an original feature rather than being preservational. ?Veryhachium bulliferum differs from Dorsennidium hamii (Loeblich 1970) Sarjeant & Stancliffe 1994 by having a rhombohedral shape rather than a bell-shape. The processes are homomorphic, not hollow because they are filled by the same material as the vesicle wall, and variable in shape and size. Among the specimens figured by Wright and Meyer (1981) as Veryhachium hamii, one shows the same gross morphology as the specimens herein of ?Veryhachium bulliferum (see Wright and Meyer 1981, Plate 3, figure N) but the small hollow parts in the processes cannot be confirmed. Occurrence. From the upper Pirgu Regional Stage (Jelgava, Parojeva and Kulli formations; upper Katian) to the top of the Porkuni Regional Stage (Kuldiga and Saldus formations; Hirnantian), Valga10-drill core, southern Estonia. Distribution. Topmost Ordovician of the Na¨r borehole, southern Gotland, Sweden (Le He´risse´ 1989a). 7. Distribution patterns of the major palynomorph groups The distributional patterns of palynomorphs were analysed based on absolute and relative countings. Acritarchs were grouped into morphological classes as follows: Micrhystridium group (small acritarchs 520 mm), veryhachid group (all polygonomorph acritarchs such as Veryhachium Deunff 1954), sphaeromorph group (acritarchs devoid of processes, prasinophytes included), baltisphaerid group (large acanthomorph acritarchs typical of Late Ordovician strata; see Le He´risse´ in Paris et al. 2000, p. 97), non-ramified acanthomorph acritarch group (baltisphaerids excluded), ramified acantomorph acritarch

31

Palynology group (e.g. Multiplicisphaeridium Staplin 1961) and Polygonium/Goniosphaeridium group (large specimens typical of carbonaceous environments). Netromorphs and peteinosphaerids (e.g. Tongiorgi et al. 2003, p. 13) were not retained as independent classes because they proved to be rare. Based on inferred similar hydrodynamic properties, we included the netromorphs into the sphaeromorph class, and the peteinosphaerids were deemed acanthomorphic. In addition, the following groups of palynomorphs were also counted: chitinozoans, scolecodonts, cryptospores (land plant-derived palynomorphs) and melanosclerites (black rodlets of uncertain origin).


7.1.

Absolute frequency

Absolute frequency of Palaeozoic palynomorphs, and particularly of acritarchs, has been previously used as a productivity proxy (e.g. Stricanne et al. 2006). The absolute frequency (abundance) of palynomorphs (specimens per gram of rock) in the study material is shown in Figure 4C. The maximum value was recorded in samples VA 46 (345.6 m); (argillaceous marl: 6998 palynomorphs/g), VA 44 (338.8 m); (argillaceous limestone: 4708 palynomorphs/g), VA 38 (313.2 m); (argillaceous dolomitic limestone: 4389 palynomorphs/g), VA 40 (322.7 m); (argillaceous dolomitic marl: 1462 palynomorphs/g), VA 40 (320.0 m); (argillaceous dolomitic marl: 1210 palynomorphs/g) and VA 44 (335.5 m); (argillaceous crystalline limestone: 1056 palynomorphs/g). The remaining samples contained few palynomorphs, such as VA 45 (340.6 m); (dolomitic marl: 302 palynomorphs/g), VA 38 (312.2 m); (dolomitic marl: 196 palynomorphs/g) and VA 42 (328.9 m); (dolomitic marl: 140 palynomorphs/g). The following samples proved barren: VA 41 (324.1 m); (dolomitic marl), VA 37 (310.7 m); (microcrystalline dolostone), VA 39 (316.7 m); (microcrystalline dolostone), VA 43 (331.9 m), VA 39 (316.7 m); (microcrystalline dolostone) and VA 38 (314.4 m); (dolomitic sandstone). The more argillaceous and less dolomitic samples were more productive, indicating that palynomorph abundance is primarily controlled by original depositional environments, but is secondarily affected by diagenetic processes (e.g. dolomitisation and crystallisation). There are many factors other than original phytoplanktonic productivity which influence the concentration of acritarchs in the sediments, such as diagenesis, differences in palaeoenvironment and sedimentation rate (Tongiorgi et al. 2003, p. 22), differential preservation of organic matter leading to selective degradation of palynomorphs due to the original differences in biochemical composition (Versteegh and Zonneveld 2002), and varying oxidation conditions in the water column during palynomorph transport (Tongiorgi et al. 2003, p. 26).

In particular, dilution and concentration effects are common in limestone–marl alternations (Westphal et al. 2000), which are typically represented in the Valga-10 section. The marls underwent a volume decrease due to aragonite depletion during their burial. This dissolution provided the carbonate for the lithification of the limestones, which escaped further compaction by cementation (Munnecke and Samtleben 1996). Compacted layers show a concentration of palynomorphs 1.5 to 7 times higher than uncompacted layers (Westphal et al. 2000), which is totally independent from the original phytoplanktonic productivity signal. Hence, caution must be taken when interpreting absolute palynomorph concentration in the sediments in terms of palaeoproductivity. 7.2.

Relative frequency

Figure 4B shows the variations of relative abundances of selected palynomorph groups in the productive samples. Within the limits of the sampling resolution, general compositional trends of the palynomorph assemblages are evident. Before the onset of the carbon isotopic excursion, the palynomorph assemblages are dominated by simple, non-ramified acanthomorphs (e.g. Cheleutochroa gymnobrachiata; Plate 3, figure 12) in the upper Jelgava Formation, with an increasing abundance of baltisphaerids in the Kuili Formation. The other groups of palynomorphs do not vary significantly before the isotopic excursion. Major compositional changes occur within the Porkuni strata (Hirnantian). Close to the base of the Porkuni Stage (lower Kuldiga Formation), scolecodont abundance increases abruptly. These data are corroborated by abundance analyses by Hints (2001, p. 13, appendix 11) on scolecodont assemblages. At the same stratigraphical interval, relative abundance of sphaeromorphs slightly increases whereas acanthomorphic acritarchs show a net decrease compared to those of the underlying Pirgu strata. ‘Non-ramified acanthomorphs’ are not present in this palynomorph assemblage. In the middle Kuldiga Formation (sample VA 40, 320.0 m), in correspondence of maximum d13C values, the relative abundance of ramified acanthomorphs increases for the first time in the studied section, up to twice the abundance of baltisphaerids and ‘non-ramified acanthomorphs’. At the same time, the presence of cryptospores in the assemblages begins to be noticeable. Similar increases in cryptospores in Hirnantian sediments seems to be of regional significance, having been described from uppermost Ordovician beds of the Na¨r borehole in Gotland, Sweden (Le He´risse´ 1989a) and from the Borenshult-1 borehole in O¨stergo¨tland, Sweden (M. Vecoli, unpublished data). Cryptospores reach their highest abundance in the

Figure 4. (A) The stratigraphical section studied in the Valga-10 drill core showing lithofacies, carbon isotope curve according to Kaljo et al. (2007), and positions of the samples; (B) relative frequency of selected palynomorph groups throughout the sampled section; (C) comparison of absolute frequency of the total palynomorphs (acritarchs, chitinozoans, scolecodonts, melanosclerites, cryptospores) with the lithology of the samples from the section studied from the Valga-10 drill core.



Palynology


Saldus Formation (sample VA 38 (313.2 m)), together with the melanosclerites. Sample VA 38 (312.2 m), ~ from the base of the Ohne Formation (base of the Juuru Regional Stage, Early Silurian), is dominated by one morphotype of Leiosphaeridia. The other palynomorph groups (Micrhystridium, veryhachids, Goniosphaeridium and chitinozoans) do not display significant changes in relative abundance throughout the section. The major palynological compositional changes and trends are as follows: (1) The Jelgava and Kuili formations are dominated by non-ramified acanthomorphs and baltisphaerids. (2) The base of the Kuldiga Formation exhibits an increase in relative abundance of scolecodonts. (3) The middle Kuldiga Formation is characterised by an increase in abundance of ramified acanthomorphs and a significant inception of cryptospores. (4) The Saldus Formation shows a peak in cryptospore abundance. ~ (5) The Ohne formation is distinguished by an acme of Leiosphaeridia. These observations can be compared with the Late Ordovician Baltic sequence stratigraphy of Harris et al. (2004). The regressive strata of the Porkuni Stage are characterised by increasing abundance of benthonic palynomorphs (scolecodonts and melanosclerites), consistently with the establishment of a shallower marine environment as observed by comparing diversity trends of the different microorganisms. The increasing abundance of cryptospores might also be associated with the Hirnantian, glacially-driven sealevel drops providing new biotopes favourable for the colonisation of cryptospore plant-parents in the transitional belt lying between the Estonian/Lithuanian Shelves and the Livonian Basin (Figure 1A). Two other localities yielding Hirnantian cryptospores in Baltica (Gotland, Na¨r borehole; Le He´risse´ (1989a) and O¨stergo¨tland, Bohrenshult-1 borehole; Sweden; M. Vecoli, unpublished data) were located at these times in this transitional belt. The most significant change in the acritarchs is the transition from high relative abundance of non-ramified acanthomorphs (including baltisphaerids) in Pirgu strata to high relative abundance of ramified acanthomorphs in Porkuni strata (i.e. Multiplicispaheridium ramispinosum, Plate 6, figures 2–3; or Nexosarium leherissei sp. nov., Plate 13, figures 10–12, Plate 14, figures 1–4). The development and growth of processes in extant (Kokinos and Anderson 1995), sub-recent (Mertens

33

et al. 2009) or Tertiary dinoflagellate cysts (Pross 2001) appears to be directly related to salinity and oxygenation conditions in the water column. In a morphometrical and statistical study of the dinoflagellate cyst Lingulodinium machaerophorum Wall 1977, Mertens et al. (2009) demonstrated that the specimens having ‘the longest processes occur in high water density environments where flotation would be easier, which is counterintuitive [. . .] because longer processes [. . .] increase floating ability according to Stokes’ law’. According to the same authors, the longer processes in dinoflagellate cysts ‘biologically function mainly as a clustering device to enhance sinking rates’ in environments with high water salinity and density. In the Valga-10 section, the predominance of highly ramified acritarchs into the Porkuni strata could be the result of selective pressure linked to an increasing salinity in the Baltic tropical epicontinental marine basin during the Hirnantian glacially-driven sea-level drop. 8. Palaeobiogeographical implications The section studied stratigraphically extends from the middle Pirgu to the lowermost Juuru regional stages, comprising the upper Katian (Time Slice 6b in Webby et al. 2004), the Hirnantian (Time Slice 6c in Webby et al. 2004), and the lowermost Rhuddanian (one productive sample: VA 38, 312.2 m; see Figure 2). A comparison with other acritarch assemblages described from several uppermost Katian and Hirnantian (Time Slices 6b–6c in Webby et al. 2004) levels worldwide has been performed (Figures 5 and 6), complementing previous similar comparisons on older upper Katian strata (Time Slice 5a in Webby et al. 2004) by Wicander et al. (1999), Playford and Wicander (2006) and Wicander and Playford (2008). Comparison of earliest Silurian acritarch assemblages is hindered by the scarcity of published data and the extremely low diversity of the only one Rhuddanian productive sample from Valga. This extremely low diversity seems to be a general feature of phytoplanktonic assemblages of the beginning of the Silurian which are mainly dominated by sphaeromorphs (Leiosphaeridia spp., Tasmanites spp.) and environmentally tolerant acritarchs like Veryhachium spp., Micrhystridium spp., Multiplicisphaeridium spp. or Evittia spp. (Vecoli 2008). This could be related to the establishment of eutrophic palaeoenvironmental conditions favourable to monospecific algal blooms possibly linked to a rapid post-glacial transgression (Vecoli 2008). Globally, more diverse acritarch associations developed at the Rhuddanian/Aeronian transition (Duffield and Legault 1981; Martin 1989; Le He´risse´ 2000). Eleven localities have been retained for comparison of published data on uppermost Katian–Hirnantian


34

A. Delabroye et al.

Figure 5. Latest Ordovician palaeogeography showing the position of latest Katian–Hirnantian sections (time slices 6b–6c in Webby et al. 2004) that have been previously studied for their palaeophytoplankton content, and discussed in the text. Numbers and symbol as follows: 1, Morocco, Anti-Atlas; 2, northeast Libya; 3, northeast Algerian Sahara; 4, Czech Republic, Prague Basin; 5, northwest Argentina, Puna Region; 6, China, northwestern Zheijiang; 7, south Turkey; 8, Canada, Quebec, Anticosti Island; 9, Sweden, Gotland Island; 10, northern Estonia, Rapla; 11, Poland, Holy Cross Mountains; Star, south Estonia, Valga. This map is adapted from Scotese and McKerrow (1991). Reproduced with the permission of Natural Resources Canada, courtesy of the Geological Survey of Canada.

acritarch assemblages from different tectonic plates of low to high palaeolatitudes (Figures 5 and 6) in order to better understand the spatial distribution of acritarch floras during the time of the Late Ordovician glaciation. However, it was sometimes impossible to accurately compare our material from Valga with other studies due to the lack of complete figured assemblages. The present analysis shows that two phytoplanktonic provinces can be easily distinguished during latest Katian–Hirnantian times: (1) The low latitude eastern Laurentian and Baltican assemblages are characterised by the presence of numerous large forms of Baltisphaeridium spp., ‘giant’ acritarchs such as Hoegklintia spp. or Estiastra spp. typical of low to mid-latitude carbonate environments, several large species of the Goniosphaeridium– Stellechinatum – Polygonium plexus, and Dilatisphaera wimani (Eisenack 1968) Le He´risse´ 1989, a ‘giant’ ascendant of smaller Dilatisphaera species, like D. williereae (Martin 1966) Lister 1970, evolving during the Silurian (Le He´risse´ 1989b, p. 112); (2) The high latitude Gondwanan and ‘peri-Gondwanan’ (e.g. Perunica, Arabian Plate) assemblages are dominated by netromorph acritarchs: Poikilofusa spinata Staplin et al.

1965, Dactylofusa cabotii (Cramer 1971) Fensome et al. 1990, Dactylofusa cucurbita Jardine´ et al. 1974, Dactylofusa striatifera (Cramer 1964) Fensome et al. 1990, Dactylofusa striatogranulata Jardine´ et al. 1974, and other characteristic forms such as Tylotopalla caelamenicutis Loeblich 1970, Beromia clipeata Vavrdova´ 1986, Neoveryhachium carminae (Cramer 1964) Cramer 1970 and Neoveryhachium sp. A in Molyneux 1988. Some of these species display a Silurian ‘affinity’ sensu Le He´risse´ in Paris et al. (2007, p. 103) (i.e. Neoveryhachium spp. and Tylotopalla sp.) (Le He´risse´ in Paris et al. 2000, p. 98). (3) South China is difficult to compare with these two provinces. Only one published Hirnantian acritarch assemblage from this area (Time Slice 6c) has been analysed (Yin and He 2000). Unfortunately, this material is poorly preserved, preventing reliable identifications. More south Chinese uppermost Ordovician assemblages are thus needed to analyse the biogeographical affinities of these assemblages. South China is located at low latitudes on Late Ordovician palaeogeographical maps. It would be interesting to know precisely these affinities. As phytoplanktonic organisms, acritarchs would be expected to be distributed according to latitudinal gradients.


Palynology

35

Figure 6. Comparison of the acritarchs from the Valga-10 core with published coeval (latest Katian–Hirnantian) palynofloras. Numbers and symbols as follows: 1, northern Gondwana, Morocco, Anti-Atlas, upper Ktaoua, Lower 2nd Bani and Upper 2nd Bani formations; uppermost Katian–Hirnantian (Elaouad-Debbaj 1988; 16 acritarch species recognised for the stratigraphical interval considered); 2, northern Gondwana, northeast Libya, uppermost Ordovician strata of the Well El-81; uppermost Katian? (Molyneux and Paris 1985; Hill and Molyneux 1988 (AS1–AS2); Molyneux 1988; Paris 1988; 32 acritarch species recognised for the stratigraphical interval considered); 3, northern Gondwana, northeast Algerian Sahara, Hassi el Hadjar and M’Kratta formations; uppermost Katian–Hirnantian (Vecoli 1999; Le He´risse´ in Paris et al. 2000; 19 acritarch species recognised for the stratigraphical interval considered in Vecoli 1999); 4, Perunica (Northern Gondawana adjacent terranes), Czech Republic, Prague Basin, uppermost Kosov Formation; Hirnantian (Dufka and Fatka 1993; 25 acritarch species recognised for the stratigraphical interval considered); 5, Western Gondwana, northwest Argentina, Puna Region, upper Salar del Rincoń Formation; Hirnantian (Rubinstein and Vaccari 2004; 21 acritarch species recognised for the stratigraphical interval considered); 6, South China Palaeoplate, China, northwestern Zheijiang, Wenchang Formation; latest Ordovician (Hirnantian?) (Yin and He 2000; 22 acritarch species recognised for the stratigraphical interval considered); 7, Northern Arabian Plate, south Turkey, Halevikdere Formation; Hirnantian (Le He´risse´ in Paris et al. 2007; 50 acritarch species recognised for the stratigraphical interval considered); 8, Eastern Laurentia, Canada, Quebec, Anticosti Island, Ellis Bay Formation; Hirnantian (Duffield and Legault 1981, 1982; Duffield 1982; Martin 1988; Delabroye et al. 2007; number of acritarch species ca. 80); 9, Western Baltica, Sweden, Gotland Island, uppermost Ordovician strata from the Na¨r borehole; late Katian?–Hirnantian (Le He´risse´ 1989a; 45 acritarch species recognised for the stratigraphical interval considered); 10, Western Baltica, north Estonia, Rapla borehole, Adila and A¨rina formations; uppermost Katian–Hirnantian (Uutela and Tynni 1991; personal observation, 2007; 86 acritarch species recognised for the stratigraphical interval considered); 11, South-western Baltica, Poland, Holy Cross Mountains, uppermost Zalesie Beds–lowermost Bardo Beds; uppermost Katian–Hirnantian (Kremer 2001; Masiak et al. 2003; 18 acritarch species recognised for the stratigraphical interval considered).


36

A. Delabroye et al.

Based on the present data, it is possible to propose a scenario accounting for the differentiation of these two palaeophytoprovinces during the Late Ordovician. Wilde (1991) reconstructed the palaeogeography of surface current circulation and surface water masses during the Late Ordovician (Ashgill). All landmasses located between 308 N and 308S (i.e. Laurentia, Baltica, Siberia, south China, Australia) are in the zone of warm water masses, where as the northern and western Gondwana are in the zone of cold water masses. Major oceanic currents allowing for biological exchanges and migrations between the two zones might have been blocked by ‘the bathymetric ridge-rise associated with the opening of the Rheic ocean’ (Wilde 1991). This barrier effect could have been intensified by the sea level drawdown during the end-Ordovician glaciation and could still have been present at the beginning of the Late Ordovician–Early Silurian diversity and biogeographical patterns observed in palynomorph assemblages. Such a scenario is further corroborated by the analyses of the time of appearance and the spatial distribution of ‘Silurian affinity genera’ (genera that developed and diversified during the Silurian) during late Katian–Hirnantian times. Indeed, ‘Silurian affinity genera’ which appeared during the glaciation and the associated regressive phase (e.g. Neoveryhachium, Cymbosphaeridium, Visbysphaera, Tylotopalla s.s.; see Paris et al. 2000, 2007; Rubinstein et al. 2008) are only present in the Gondwanan province. However, some ‘Silurian affinity genera’ which appeared before the glaciation have a cosmopolitan distribution such as Oppilatala and Evittia ( ¼ Diexallophasis ) (Le Herisse´ in Paris et al. 2000). Dilatisphaera seems to be an exception: this ‘Silurian affinity genus’ appears before the glaciation but has been recognised only in the Laurentian/Baltic province. 9. Late Katian–Hirnantian palaeobiogeographical differentiation versus biostratigraphy The existence of two distinct palaeophytoprovinces has significant implications for the use of palynomorphs in global biostratigraphical correlation of Uppermost Ordovician (upper Katian–Hirnantian) sequences. Late Katian–Hirnantian graptolites and chitinozoans show similar limitations. Legrand (2003) discussed the problem of the use of the Hirnantian extraordinarius and persculptus graptolite zones, in northern Gondwana (Delabroye and Vecoli 2010). In this region, the endemism of graptolite assemblages prevents correlation of the northern Gondwana sections with the Hirnantian GSSP in south China, in particular for the lower Hirnantian (Chen et al. 2006). In Baltica and eastern Laurentia, graptolites are absent or scarce, thus preventing reliable correlation with the GSSP (Riva

1988; No˜lvak et al. 2006; Pasˇ kevicius 2007). Similarly, the late Katian and Hirnantian chitinozoan biozonation from northern Gondwana (Paris 1990), cannot be precisely correlated with those available for Baltica (No˜lvak and Grahn 1993), Laurentia (Achab 1989), as demonstrated by Delabroye and Vecoli (2010). The chitinozoan biostratigraphical framework established in Avalonia (Vandenbroucke 2008) appears to be intermediate between that used in Baltica and that of northern Gondwana, with the northern Gondwanan merga chitinozoan Zone (upper Katian), lying between the two Baltic zones rugata and taugourdeaui (Vandenbroucke 2008, figure 6), probably reflects the presence of plankton migration corridors between northern Gondwana and Avalonia before the sea level fall associated with the Hirnantian glaciation. In summary, it appears that Baltic/Laurentian microfloras and microfaunas significantly differ from Gondwanan and peri-Gondwanan ones, limiting the use of palynomorphs and graptolites for long-distance correlations between low and high latitudes; climatic and physical barriers probably caused these differences. Nevertheless, this study demonstrates that some acritarchs have potential for future improvement of correlations between uppermost Ordovician strata at low to mid latitudes. These include Evittia porkuniensis sp. nov., Evittia sp. A, Leiofusa granulicatis Loeblich 1970 forma quincunx Uutela 1989, Leiofusa sp. aff. L. Granulicatis Loeblich 1970 forma quincunx Uutela 1989, Helosphaeridium tongiorgii sp. nov., Nexosarium leherissei sp. nov., Oppilatala sp., and ?Veryhachium bulliferum sp. nov. At Valga some of these species have been identified based on few specimens, e.g. Leiofusa granulicatis forma quincunx or Oppilatala sp. Nevertheless, they are all present in high abundances in coeval strata from eastern Laurentia (Anticosti) or in other Baltic sections (Rapla borehole, Uutela and Tynni 1991; Na¨r borehole, Le He´risse´ 1989a), which have been investigated at higher sampling resolution than the presently studied strata from Valga. Future palynological investigations of the numerous boreholes available from Estonia would help in clarifying their biostratigraphical potential. 10. The Ordovician-Silurian boundary crisis in the phytoplankton realm In contrast to other Ordovician fossil groups (e.g. brachiopods, graptolites, trilobites) which drastically suffered during the Hirnantian Glaciation, acritarch standing diversity increased through the glacial interval, evidencing a major turnover in phytoplankton assemblages rather than a mass extinction (Vecoli and Le He´risse´ 2004; Vecoli 2008). This diversity increase is due to the first appearance during the latest Ordovician of some taxa of Silurian ‘affinity’ which will further

37


Palynology diversify during the Early–Middle Silurian (Le He´risse´ in Paris et al. 2000, 2007; Vecoli and Le He´risse´ 2004; Vecoli 2008), such as Cymbosphaeridium spp., Tylotopalla spp., Visbysphaera spp., Oppilatala spp., Evittia spp., Dilatisphaera sp., Hoegklintia spp. and Neoveryhachium spp. At Valga, similar species include Dilatisphaera wimanii, Evittia porkuniensis, Evittia sp. A, Evittia denticulata denticulata, Hoegklintia visbyensis and Oppilatala sp. Typical Ordovician taxa such as Baltisphaeridium, Peteinosphaeridium spp., Ordovicidium spp., Dicommopalla spp., Leprotolypa sp. and Orthosphaeridium spp. disappeared during the earliest Silurian, and lowermost Silurian strata are characterised by an abundance of sphaeromorphs and other ecologically tolerant acritarchs (Vecoli 2008). A change in nutrient supply and anoxic conditions (Armstrong and Coe 1997; Le He´risse´ in Paris et al. 2000; Vecoli et al. 2009), coupled with possible decreasing light penetration into the water masses during the earliest Silurian transgression might be related to this early Silurian ‘crisis’. The Late Ordovician is considered to be an icehouse period (Saltzman and Young, 2005; Cherns and Wheeley 2007; Ghienne et al. 2007), culminating with the Hirnantian glaciation, although some authors have challenged this interpretation (Fortey and Cocks 2005). The gradual Late Ordovician atmospheric cooling could have favoured productivity by increasing thermohaline circulation and water-mass oxygenation (e.g. Armstrong and Coe 1997; Sheehan 2001; Cherns and Wheeley 2007). Phytoplankton of K-type reproductive strategy would have adapted to the gradual environmental modifications. Phytoplankton of R-type reproductive strategy should have also been favoured in a slowly changing environment. The ‘Silurian-type’ acritarchs would have radiated just before and during the Hirnantian and survived the Early Silurian transgression because of a wider range of tolerance (R-type?) as opposed to the typical Ordovician taxa (K-type?) that suffered extinction (for information on reproductive strategies of extant phytoplankton see Sandgren 1988; Alvez-de-Souza et al. 2008). 11.

Event stratigraphy

11.1. Local event stratigraphy The available biostratigraphical and chemostratigraphical data allow for a precise chronology of the different biological events recorded across the Ordovician–Silurian boundary in the Valga-10 section. Based on Po˜ldevere (2001), diversity trends of the different microorganisms studied from the core are presented in Figure 7. All the microfossil groups (ostracods, conodonts, chitinozoans, scolecodonts and acritarchs) show a clear diversification trend within Porkuni strata. However, differences of timing can be observed. Ostracods and scolecodonts are of low diversity in

Pirgu strata and in the overlying Bernati Member of the Kuldiga Formation (lowermost Porkuni). Diversity increased in the early Porkuni (scabra chitinozoan Biozone; early Hirnantian) with the appearance of numerous new taxa (Hints 2001; Meidla 2001). Both chitinozoans (planktonic or nektonic) and conodonts (nektonic), show moderate to high diversity in the Pirgu strata, a decreasing diversity trend at the base of the Porkuni Stage (taugourdeaui and scabra chitinozoan biozones), which correlates with the ascending leg of the local carbon isotopic curve, and a further diversification pulse in the overlying sediments. Seven chitinozoan taxa appeared in the late Porkuni. These taxa have never been observed in other upper Porkuni strata of Baltica, and may be reworked. Only conodonts are present in the dolomitised Silurian ~ sediments of the Ohne Formation. Conodonts are a well-preserved group; the completeness of the fossil record largely reflects the lack of fossiliferous rock rather than the preservation of the skeletal remains (Barrick and Ma¨nnick 2005). A similar situation is observed in the Hirnantian reefal Laframboise Member at Anticosti Island (Canada, Que´bec) (McCracken and Barnes 1981) and could be related to the high fossilisation potential of conodonts (Barrick and Ma¨nnick 2005). The acritarchs do not exhibit any major diversity changes in Pirgu and basal Porkuni strata (Assemblages AS1–AS2). A slight increase in diversity is observed in assemblage AS3 in upper Porkuni strata with appearances of nine taxa (Figures 2 and 7) representing a turnover. This stratigraphical interval was also characterised by abundant occurrences of cryptospores. A dramatic change occurs in the Early Silurian (AS4, sample VA 38, 312.2 m, Figures 2 and 7) where the assemblage consists of one morphotype of Leiosphaeridia sp. (Prasinophyceae). In the section studied, benthonic organisms (ostracods and scolecodonts) increase in diversity at the beginning of the positive carbon isotopic excursion (Figure 7) with appearances of several new taxa, whereas the planktonic acritarchs displayed a turnover slightly later, during maximum HICE values. Zooplanktonic and nektonic organisms (chitinozoans and conodonts) exhibit a different pattern: their diversity decrease abruptly during the ascending leg of the HICE to finally revive during the descending leg of the HICE with appearances of new taxa. 11.2.

Discussion

Harris et al. (2004) analysed the sequence stratigraphy of Upper Ordovician strata (from the Nabala to the Porkuni regional stages) from the Livonian Basin of western Estonia (Figure 1A). They identified seven depositional sequences (Figure 3). Sequence 5 (Figure 3), represented by the Jelgava and Parojeva formations

Figure 7. Comparison of distributions of microfossils (ostracods, conodonts, chitinozoans, scolecodonts and acritarchs) in the uppermost Ordovician of the Valga-10 drill core.



39


Palynology (Mid-Pirgu, rugata chitinozoan zone), and sequence 6 (Figure 3), Kuili Formation (topmost Pirgu, anticostiensis and gamachiana chitinozoan zones), record a progressive deepening (Harris et al. 2004). Below the Porkuni strata, part of sequence 6 is truncated by submarine erosion or slumping in the Gulf of Riga area (Ruhnu well; Harris et al. 2004). In the Valga-10 section, the absence of the anticostiensis and gamachiana chitinozoan Biozones (No˜lvak 2001; Figure 2) could possibly indicate this truncation, although higher sampling resolution might have potentially allowed the recognition of the two zones (No˜lvak in Kaljo et al. 2008, p. 208). Sequence 7 (Figure 3) is represented by the Kuldiga and Saldus formations (Porkuni, taugourdeaui and scabra chitinozoan zones) and records a shallowing event corresponding to the Hirnantian glaciations according to Harris et al. (2004), culminating during the deposition of sediments assigned to the scabra Biozone. This sequence is bracketed by two unconformities which have been interpreted by Harris et al. (2004) as the Baltic equivalent of the two large Hirnantian glacially-driven sea-level falls observed in north Gondwana (Ghienne et al. 2007; Loi et al. 2010). Curiously, in the Valga section, no major evidence of a discontinuity surface has been recognised at the base, or at the top of the Porkuni strata (Figure 2). Burrows into the Pirgu and Porkuni strata are the only sedimentary structures indicating sedimentation breaks (Figure 2). The presence of a previously unrecorded chitinozoan assemblage (No˜lvak in Po˜ldvere 2001; Delabroye et al. 2008) in the upper Kuldiga and Saldus formations (Porkuni), overlying the scabra Zone, could indicate a more continuous section across the Ordovician–Silurian boundary at Valga compared to other Estonian sections and boreholes previously studied. The two productive samples from Porkuni strata, VA 38 (313.2 m) and VA 40 (320.0 m) (Figure 2), bracketing the peculiar chitinozoan assemblage (No˜lvak in Po˜ldevere 2001), confirm a Late Ordovician age without evidence of reworking. Also, the carbon isotopic signal in the Porkuni strata from Valga-10 is one of the most complete Porkuni d13C profiles in Estonia, with those of Ruhnu and Taagepera (see Brenchley et al. 2003; Kaljo et al. 2007; Figure 2). The opposing diversity trends observed between benthonic and primary producers (scolecodonts and ostracods and acritarchs) and planktonic/nektonic (chitinozoans and conodonts) microfossils in Porkuni strata in the Valga section could be linked to sea-level variations, causing establishment of shallow water environments during the Hirnantian (sequence 7) more favourable to the development and proliferation of benthonic organisms and acritarchs while zooplanktonic/nektonic organisms would have migrated into deeper environments. As an alternative interpretation, organisms like chitinozoans and conodonts might have been affected by the

oceanographic and climatic changes linked to the latest Ordovician glaciations earlier and stronger than the benthonic organisms and the phytoplankton. Such a scenario has been proposed for the faunal crisis observed during the major carbon isotopic excursions at the Llandovery/Wenlock boundary (Ireviken Event; Gelsthorpe 2004) and during the late Ludlow (Lau Event, Ludfordian; Stricanne et al. 2006) at Gotland (Sweden). In these situations, the deep migrating zooplankton and nekton (graptolites and conodonts) were affected at the beginning or even prior to the increase of the carbon isotopic excursions (Stricanne et al. 2006) whereas the phytoplankton was affected later. Faunal dynamics across the HICE event shows a similar pattern, with graptolites declining rather suddenly at the base of the Hirnantian (beginning of the ascending leg of the HICE; Fan and Chen 2007) and chitinozoans declining before the onset of the glaciation and the isotopic excursion (Achab and Paris 2007). 12.

Summary (1) The data herein show the potential of acritarch biostratigraphy and its application for correlation between uppermost Katian to Hirnantian strata from eastern Laurentia and Baltica. Future investigations of coeval strata from other Baltic localities could contribute to a formal acritarch-based palynozonation. (2) The analysis of global palaeogeographical distribution of latest Katian–Hirnantian palynofloras reveals the existence of two distinct Baltic/Laurentian and Gondwanan phytoplanktonic palaeoprovinces. (3) This Late Ordovician palaeobiogeographical differentiation was possibly caused by limited water masses exchange between Gondwana and Laurentia/Baltica due to the presence of a bathymetric ridge associated with the opening of the Rheic Ocean. This effect would have been intensified during the Hirnantian glacially-driven sea-level drop. (4) Biodiversification trends have been established for acritarchs and then compared with those of ostracods, scolecodonts, chitinozoans and conodonts. All these groups show an increase in diversity during Hirnantian times (Porkuni), which is preceded by a strong diversity drop in chitinozoans (zooplanktonic organisms) and conodonts (nektonic organisms). This significant diversity drop is not recorded in ostracods and scolecodonts (benthonic organisms) as well as in the acritarchs (phytoplankton). This implies that the Hirnantian glacially influenced palaeoenvironments of the shallow-water carbonate platforms in Baltica were more favourable to the

40

A. Delabroye et al.


development and proliferation of benthonic organisms adapted to stronger hydrodynamic conditions. Sequence stratigraphy data as well as the increasing abundance of cryptospores in the Hirnantian strata at Valga and in other Baltic localities (Gotland, O¨stergotland; Sweden) and the presence of highly ramified acritarchs, indicate the establishment of shallower proximal environment with dense and salty water masses at regional scale in Baltica, supporting the above interpretation.

Acknowledgements Grateful acknowledgement is expressed to Dr Jaak No˜lvak (Tallinn University of Technology) for discussion and for providing data on Upper Ordovician–Lower Silurian chitinozoan biostratigraphy. Evelyne Rogie (Laboratoire Geósyste`mes, Lille, France) is also thanked for help in palynological preparations as well as Philippe Recourt (Laboratoire Geósyste`mes, Lille, France) for SEM assistance. The authors also acknowledge the Parrot Program No. 14539UL (Diversity patterns of Ordovician organicwalled microfossils) for having supported numerous visits to our respective laboratories in France and Estonia. Research in Estonia was also supported by the Estonia Science Foundation, Grant 7640. The authors thank Reed Wicander (Central Michigan University, Mount Pleasant, USA and Claudia Rubinstein (CONICET, IANIGLA, CRICyT, Mendoza, Argentina) for their critical reading and remarks which improved the manuscript. This is a part of the Ph.D. investigation of A. Delabroye at the University of Lille 1 (France) and a contribution to the IGCP 503. Author biographies AURE´LIEN DELABROYE obtained an MSc in palaeontology from the University of Lille 1, France in 2006. In his MSc Thesis, he focused on palaeobiological and palaeoenvironmental analyses of some Ordovician trilobites from western France using morphometric and statistical approaches. He received his Ph.D. in Geosciences from the same university in 2010, in which he analysed the phytoplankton dynamics across the Ordovician–Silurian boundary at low latitudes for comparison with the high-latitude glacial areas. His research interests include studies on Palaeozoic microphytoplankton reactivities to palaeoenvironmental stresses.

MARCO VECOLI graduated in geology from the University of Pisa, Italy in 1993, and received his Ph.D. from the University of Queensland, Australia in 1999 with a thesis on the Cambro-Ordovician acritarchs of the Sahara Platform, North Africa. After a first postdoctoral position funded by the European Commission at the Martin-Luther-Universita¨t of Halle/Saale, Germany, he pursued his career as Marie Curie Postdoctoral Fellow at the University of Western Brittany in Brest, France. Subsequently he obtained a postdoctoral position at the University of Lille, France, where he became a permanent senior researcher of the Centre National de Recherche Scientifique (CNRS) in 2004. Marco’s research focuses on Lower Paleozoic palynology, and its use in solving geological and paleobiological questions, from high resolution biostratigraphy to provenance studies, the evolution of oceanic plankton and early land plants. He also works as a consultant to the oil industry.

]>

OLLE HINTS is senior researcher and scientific secretary at the Institute of Geology at Tallinn University of Technology. He graduated from the University of Tartu in geology (palaeontologystratigraphy) and received his Ph.D. in applied geology from Tallinn University of Technology in 2002. His main research has been focused on Early Palaeozoic scolecodonts (jaws of polychaete annelids), which are a common but mostly neglected group of organicwalled microfossils. In recent years he has been working in close collaboration with specialists of other microfossil groups, particularly chitinozoans, acritarchs and conodonts, and also on stable isotope geochemistry. He is currently Chairman of the Estonian Commission on Stratigraphy and Vice Chairman of the Expert Board of National Scientific Collections. THOMAS SERVAIS is a research director at the French Centre of Scientifical Research (CNRS). He was trained as geologist at the universities of Namur and Lie`ge (Belgium), where he received a Ph.D. on Ordovician acritarchs in 1993. After post-doctoral studies in Belgium, Germany and the United Kingdom, he was recruited as a CNRS research associate at the University of Lille 1 in 1997. Most of his research is

Palynology


concentrated on Lower Palaeozoic microphytoplankton, but other fields of interest include regional geology, macropalaeontology (collaboration in graptolite, trilobite, and coral studies) and micropalaeontology (in particular calcareous microfossils). After having occupied the posts of Secretary of the Acritarch Subcommission (CIMP), General Secretary of the CIMP (Commission Internationale de Microflores du Paleózoı¨ que), President of the APLF (Association de Palynologues de Langue Française), President of the Association Paleóntologique Française (APF) and leader of the IGCP (International Geoscience Programme) project n8 503 ‘‘Ordovician Palaeogeography and Palaeoclimate’’, he is currently President of the IFPS (International Federation of Palynological Societies), and Vice-President of the Palaeontological Association.

References Achab A. 1989. Ordovician chitinozoan zonation of Quebec and western Newfoundland. Journal of Paleontology, 63: 14–24. Achab A., Paris F. 2007. The Ordovician chitinozoan biodiversification and its leading factors. Palaeogeography, Palaeoclimatology, Palaeoecology, 245: 5–19. Achab A., Asselin E., Desrochers A., Riva J., Farley C. 2011. Chitinozoan contribution to the development of a new Upper Ordovician stratigraphic framework for Anticosti Island. Geological Society of America, Bulletin, 123: 186– 205. Alves-de-Souza C., Gonzales M.T., Iriarte J.L. 2008. Functional groups in marine phytoplankton assemblages dominated by diatoms in fjords of southern Chile. Journal of Plankton Research, 30: 1233–1243. Armstrong H.A., Brasier M.D. 2005. Microfossils. . 2nd ed. Malden, Oxford, Carlton: Blackwell Publishing. 296 p. Armstrong H.A., Coe A.L. 1997. Deep sea sediments record the geophysiology of the end Ordovician glaciation. Journal of the Geological Society, 154: 929– 934. Barrick J.E. 1986. Conodont faunas of the Keel and Cason formations. In: Amsden T.W., Barrick J.E., editors. Late Ordovician–Early Silurian strata in the Central United States and the Hirnantian Stage. Oklahoma Geological Survey Bulletin, 139: 57–89. Barrick J.E., Ma¨nnick P. 2005. Silurian conodont biostratigraphy and paleobiology in stratigraphic sequences. Special Papers in Palaeontology, 73: 103–116. Bergstro¨m S.M., Saltzman M.M., Schmitz B. 2006. First record of the Hirnantian (Upper Ordovician) d13C excursion in the North American Midcontinent and its regional implications. Geological Magazine, 143: 657–678. Brenchley P.J, Carden G.A.F., Hints L., Kaljo D., Marshall J.D., Martma T., Meidla T., No˜lvak J. 2003. Highresolution stable isotope stratigraphy of Upper Ordovician sequences: constraints on timing of bioevents and environmental changes associated with mass extinction and glaciation. Geological Society of America Bulletin, 115: 89–104.

41

Chen X., Rong J., Fan J.-X., Zhan R, Mitchell C.E., Harper A.T., Melchin M.J., Peng P., Finney S.C., Wang X. 2006. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Hirnantian Stage (the uppermost of the Ordovician System). Episodes, 29: 183–196. Cherns L., Wheeley J.R. 2007. A pre-Hirnantian (Late Ordovician) interval of global cooling – The Boda event re-assessed. Palaeogeography, Palaeoclimatology, Palaeoecology, 251: 449–460. Cocks L.R.M., Torsvik T.H. 2004. Major terranes in the Ordovician. In: Webby B.D., Paris F., Droser M.L., Percival I.G., editors. The Great Ordovician biodiversification event. New York: Columbia University Press. p. 61–67. Combaz A., Lange F.W., Pansart J. 1967. Les ‘‘Leiofusidae’’ Eisenack, 1938. Review of Palaeobotany and Palynology, 1: 291–307. Cramer F.H. 1970. Distribution of selected Silurian Acritarchs. An account of the palynostratigraphy and paleogeography of selected Silurian acritarch taxa. Revista Espanola Micropaleontologia, Numero Extraordinario, 1: 1–203. Dale B. 1996. Dinoflagellate cyst ecology: modeling and geological applications. In: Jansonius J., McGregor D.C., editors. Palynology: principles and applications. American Association of Stratigraphic Palynologists Foundation, 3: 1249–1275. Delabroye A., Vecoli M. 2010. The end-Ordovician glaciation and the Hirnantian Stage: A global review and questions about Late Ordovician event stratigraphy. Earth Science Reviews, 98: 269–282. Delabroye A., Vecoli M., Servais T. 2007. Acritarch assemblages from the Normalograptus persculptus graptolite biozone (Upper Hirnantian) from Anticosti Island, Quebec, Canada. In: Pereira Z., Oliveira J.T., Wicander R., editors. The CIMP Lisbon0 07, joint meeting of the spores/pollen and acritarch CIMP subcommissions, Abstract book: 9–12 (abstract). Lisbon (Portugal): iNETi. Delabroye A., No˜lvak J., Vecoli M., Hints O. 2008. New latest Hirnantian acritarch and chitinozoan assemblages of Baltica (topmost Porkuni Stage, Valga-10 drill core, southern Estonia): biostratigraphical interest. 12th International Palynological Congress (IPC-XII), 8th International Organisation of Palaeobotany Conference (IOPCVIII), Abstract Volume. Terra Nostra, 2: 60 (abstract). Desrochers A., Farley C., Achab A., Asselin E., Riva. J.R. 2010. A far-field record of the end-of-the-Ordovician glacaition: the Ellis Bay Formation, Anticosti Island, Eastern Canada. Palaeogeography, Palaeoclimatology, Palaeoecology, 296: 248–263. Duffield S.L. 1982. Late Ordovician–Early Silurian acritarch biostratigraphy and taxonomy, Anticosti Island, Que´bec [unpublished Ph.D. thesis]. [Ontario (Canada)]: University of Waterloo, 296 p. Duffield S.L., Legault J.A. 1981. Acritarch biostratigraphy of Upper Ordovician–Lower Silurian rocks, Anticosti Island, Que´bec: preliminary results. In: Lespe´rance P.J., editor. Field Meeting, Anticosti-Gaspe´, Que´bec 1981 (Stratigraphy and Paleontology) 2 (I.U.G.S. Subcommission on Silurian Stratigraphy, Ordovician–Silurian Boundary Working Group). Montreál, p. 91–99. Duffield S.L., Legault J.A. 1982. Gradational morphological series in Early Silurian acritarchs from Anticosti Island, Quebec. In: Mamet B., Copeland M.J., editors. Third North American Paleontological Convention, Proceedings, Montreal, 1: 137–141.


42

A. Delabroye et al.

Dufka P., Fatka O. 1993. Chitinozoans and acritarchs from the Ordovician–Silurian boundary of the Prague Basin, Czech Republic. Special Papers in Palaeontology, 48: 17–28. Eiserhardt K.-H. 1992. Die Acritarcha des O¨jlemyrflintes. Palaeontographica Abteilung B, 226: 1–132. Elaouad-Debbaj Z. 1988. Acritarches de l’Ordovicien supe´rieur (Caradoc, Ashgill) de l’Anti-Atlas, Maroc. Revue de Micropaleóntologie, 30: 232–248. Ellegaard M. 2000. Variations in dinoflagellate cyst morphology under conditions of changing salinity during the last 2000 years in the Limfjord, Denmark. Review of Palaeobotany and Palynology, 109: 65–81. Fan J.-X., Chen X. 2007. Preliminary report on the Late Ordovician graptolite extinction in the Yangtze region. Palaeogeography, Palaeoclimatology, Palaeoecology, 245: 82–94. Fortey R.A., Cocks L.R.M. 2005. Late Ordovician global warming – The Boda event. Geology, 33: 405–408. Gelsthorpe D.N. 2004. Microplankton changes through the early Silurian Ireviken extinction event on Gotland, Sweden. Review of Palaeobotany and Palynology, 130: 89–103. Ghienne J.-F., Le Heron D., Moreau J., Denis M., Deynoux M. 2007. The Late Ordovician glacial sedimentary system of the North Gondwana platform. In: Hambrey M., Christoffersen P., Glasser N., Janssen P., Hubbard B., Siegert M., editors. Glacial sedimentary processes and products. Oxford: Blackwells (Special Publication of the International Association of Sedimentologists). p. 295– 319. Harris M.T., Sheehan P.M., Ainsaar L., Hints L., Ma¨nnik P., No˜lvak J., Rubel M. 2004. Upper Ordovician sequences of western Estonia. Palaeogeography, Palaeoclimatology, Palaeoecology, 210: 135–148. Hill P.J., Molyneux S.G. 1988. Biostratigraphy, palynofacies and provincialism of Late Ordovician – Early Silurian acritarchs from northeast Libya. In: El-Arnauti A., Owens B., Thusu B., editors. Subsurface palynostratigraphy of northeast lybia. Benghazi (Libya): Garyounis University. p. 27–43. Hints L., Oraspo˜ld A., No˜lvak J. 2005. The Pirgu Regional Stage (Upper Ordovician) in the East Baltic: lithostratigraphy, biozonation, and correlation. Proceedings of the Estonian Academy of Sciences. Geology, 54: 225–259. Hints L., Hints O., Kaljo D., Kiipli T., Ma¨nnik P., No˜lvak J., Pa¨raste H. 2010. Hirnantian (latest Ordovician) bio- and chemostratigraphy of the Stirnas-18 core, western Latvia. Estonian Journal of Earth Sciences, 59: 1–24. Hints O. 2001. Distribution of scolecodonts. In: Po˜ldvere A., editor. Valga (10) drill core. Geological Survey of Estonia, Tallinn. Estonian Geological Sections Bulletin, 3: 12–14. Jaanusson V. 1995. Confacies differentiation and upper Middle Ordovician correlation in Baltoscandian basin. Proceedings of the Estonian Academy of Sciences. Geology, 44: 73–86. Kaljo D., Hints L., Martma T., No˜lvak J., Oraspo˜ld A. 2004. Late Ordovician carbon isotope trend in Estonia, its significance in stratigraphy and environmental analysis. Palaeogeography, Palaeoclimatology, Palaeoecology, 210: 165–185. Kaljo D., Martma T., Saadre, T. 2007. Post-Hunnebergian Ordovician carbon isotope trend in Baltoscandia, its environmental implications and some similarities with that of Nevada. Palaeogeography, Palaeoclimatology, Palaeoecology, 245: 138–155.

Kaljo D., Hints L., Ma¨nnik P., No˜lvak J. 2008. The succession of Hirnantian events based on data from Baltica: brachiopods, chitinozoans, conodonts, and carbon isotopes. Estonian Journal of Earth Sciences, 57: 197–218. Kiipli E., Kallaste T., Kiipli T. 2004. Metabentonites of the Pirgu Stage (Ashgill, Upper Ordovician) of the East Baltic. In: Hints O., Ainsaar L., editors. WOGOGOB 2004 Conference Materials. Tartu: Tartu University Press. p. 53–54 (abstract). Kokinos J.P., Anderson D.M. 1995. Morphological development of resting cysts in cultures of the marine dinoflagellate Lingulodinium polyedrum ( ¼ L. machaerophorum). Palynology, 19: 143–166. Kremer B. 2001. Acritarchs from the Upper Ordovician of southern Holy Cross Mountains, Poland. Acta Palaeontologica Polonica, 46: 595–601. Le He´risse´ A. 1989a. Acritarches et kystes d’algues prasinophyceés de l’Ordovicien Supe´rieur et du Silurien de Gotland, Sue`de [unpublished Ph.D. thesis]. [Brest (France)]: Universite´ de Bretagne Occidentale, 409 pp. Le He´risse´ A. 1989b. Acritarches et kystes d’algues Prasinophyceés du Silurien de Gotland, Sue`de. Palaeontographia Italica, 76: 57–302. Le He´risse´ A. 2000. Characteristics of the acritarch recovery in the Early Silurian of Saudi Arabia. In: Al-Hajri S., Owens B., editors. Stratigraphic Palynology of the Palaeozoic of Saudi Arabia. Manama, Bahrain. GeoArabia Special Publication, 1: 57–81. Legrand P. 2003. Paleógeógraphie du Sahara alge´rien l’Ordovicien terminal et au Silurien infe´rieur. Bulletin de la Socie´te´ Geólogique de France, 174: 19–32. Lister T.R. 1970. The acritarchs and chitinozoa from the Wenlock and Ludlow Series of the Ludlow and Millichope areas, Shropshire. Palaeontographical Society Monographs, 1: 1–100. Loeblich A.R., Jr. 1970. Morphology, ultrastructure and distribution of Paleozoic acritarchs. Proceedings of the North American Paleontological Convention, Chicago 1969, G: 705–788. Loi A., Ghienne J.F., Dabard M.P., Paris F., Botquelen A., Christ N., Elaouad-Debbaj Z., Gorini A., Vidal M., Videt B., Destombes J. 2010. The Late Ordovician glacio-eustatic record from a high-latitude storm-dominated shelf succession: the Bou Ingarf section (AntiAtlas, southern Morocco). Palaeogeography, Palaeoclimatology, Palaeoecology, 296: 332–358. Ma¨nnik P. 2001. Distribution of conodonts. In: Po˜ldvere A., editor. Valga (10) drill core. Geological Survey of Estonia, Tallinn. Estonian Geological Sections Bulletin, 3: 10–12. Ma¨nnik P. 2007. Recent developments in the Upper Ordovician and lower Silurian conodont biostratigraphy in Estonia. Estonian Journal of Earth Sciences, 56: 35–46. Martin F. 1988. Late Ordovician and Early Silurian acritarchs. In: Cocks L.R.M., Rickards R.B., editors. A global analysis of the Ordovician–Silurian Boundary. Bulletin of the British Museum (Natural History), Geology Series, 43: 299–309. Martin F. 1989. In: Holland C.H., Bassett M.G., editors. A global standard for the Silurian System (Natural Museum of Wales, Geological Series). Vol 9, Chapter 20: Acritarchs. p. 207–215. Masiak M., Podhalanska T., Stempien-Sałek M. 2003. Ordovician–Silurian boundary in the Bardo Syncline, Holy Cross Mountains, Poland – new data on fossil assemblages and sedimentary succession. Geological Quarterly, 47: 311–330.


Palynology McCracken A.D., Barnes C.R. 1981. Conodont biostratigraphy and paleoecology of the Ellis Bay Formation, Anticosti Island, Quebec, with special reference to Late Ordovician–Early Silurian chronostratigraphy and the systemic boundary. Geological Survey of Canada Bulletin, 329: 51–134. Meidla T. 2001. Distribution of ostracodes. In: Po˜ldvere A., editor. Valga (10) drill core. Geological Survey of Estonia, Tallinn. Estonian Geological Sections Bulletin, 3: 14–16. Mertens K.N, Ribeiro S., Bouimetarhan I., Caner H., Combourrieu-Nebout N., Dale B., De Vernal A., Ellegaard M., Filipoya M., Godhe A., Goubert E., Grøsfjeld K., Holzwarth U., Kotthoff U., Leroy S.A.G., Londeix L., Marret F., Matsuoka K., Mudie P.J., Naudts L., Penã-Manjarrez J.L., Persson A., Popescu S.-M., Pospelova V., Sangiorgi F., Van de Meer M.T.J., Vink A., Zonneveld K.A.F., Vercauteren D., Vlassenbroeck J., Louwye S. 2009. Process length variation in cysts of a dinoflagellate, Lingulodinium machaerophorum, in surface sediments: investigating its potential as salinity proxy. Marine Micropaleontology, 70: 54–69. Molyneux S.G. 1988. Late Ordovician acritarchs from northeast Lybia. In: El-Arnauti A., Owens B., Thusu B., editors. Subsurface palynostratigraphy of northeast Lybia. Benghazi (Libya): Garyounis University. p. 45–59. Molyneux S.G., Paris F. 1985. Late Ordovician palynomorphs. Journal of Micropalaeontology, 4: 11–26. Molyneux S.G., Raevskaya E., Servais T. 2007. The messaoudensis–trifidum acritarch assemblage and correlation of the base of Ordovician Stage 2 (Floian). Geological Magazine, 144: 143–156. Munnecke A., Samtleben C. 1996. The formation of micritic limestones and the development of limestone–marl alternations in the Silurian of Gotland, Sweden. Facies, 34: 159–176. No˜lvak J. 2001. Distribution of chitinozoans. In: Po˜ldvere A., editor. Valga (10) drill core. Geological Survey of Estonia, Tallinn. Estonian Geological Sections Bulletin, 3: 8–10. No˜lvak J., Grahn Y. 1993. Ordovician chitinozoan zones from Baltoscandia. Review of Palaeobotany and Palynology, 79: 245–269. No˜lvak J., Hints O., Ma¨nnik P. 2006. Ordovician timescale in Estonia: recent developments. Proceedings of the Estonian Academy of Sciences, Geology, 55: 95–108. Paris F. 1988. New chitinozoans from the Late OrdovicianLate Devonian of northeast Lybia. In: El-Arnauti A., Owens B., Thusu B., editors. Subsurface palynostratigraphy of northeast Lybia. Benghazi (Libya): Garyounis University. p. 73–87. Paris F. 1990. The Ordovician chitinozoan biozones of the Northern Gondwana Domain. Review of Palaeobotany and Palynology, 66: 181–209. Paris F., No˜lvak J. 1999. Biological interpretation and paleobiodiversity of a cryptic fossil group: the ‘‘chitinozoan animal’’. Geobios, 32: 315–324. Paris F., Bourahrouh A., Le He´risse´ A. 2000. The effects of the final stages of the Late Ordovician glaciation on marine palynomorphs (chitinozoans, acritarchs, leiospheres) in well Nl-2 (NE Algerian Sahara). Review of Palaeobotany and Palynology, 113: 87–104. Paris F., Le He´risse´ A., Monod O., Kozlu H., Ghienne J.-F., Dean W.T., Vecoli M., Gnay Y. 2007. Ordovician chitinozoans and acritarchs from southern and south eastern Turkey. Revue de Micropaleóntologie, 50: 81–107.

43

Pasˇ kevicius J. 2007. Correlation of the Ordovician regional stages of the Baltic palaeobasin with new global stages. Geologija, 57: 30–36. Petryk A.A. 1981. Stratigraphy, sedimentology and paleogeography of the upper Ordovician–lower Silurian of Anticosti Island, Quebec. In: Lespe´rance P.J., editor. Field Meeting, Anticosti-Gaspe´, Que´bec 1981 (I.U.G.S. Subcommission on Silurian Stratigraphy, Ordovician– Silurian Boundary Working Group). Stratigraphy and Paleontology, 2: 11–39. Playford G., Wicander R. 2006. Organic-walled microphytoplankton of the Sylvan Shale (Richmondian: Upper Ordovician), Arbuckle Mountains, Southern Oklahoma. U.S.A. Oklahoma Geological Survey Bulletin, 148: 1–116. Po˜ldvere A. 2001. General geological setting and stratigraphy. In: Po˜ldvere A., editor. Valga (10) drill core. Geological Survey of Estonia, Tallinn. Estonian Geological Sections Bulletin, 3: 5–6. Pross J. 2001. Paleo-oxygenation in Tertiary epeiric seas: evidence from dinoflagellate cysts. Palaeogeography, Palaeoclimatology, Palaeoecology, 166: 369–381. Riva J. 1988. Graptolites at and below the Ordovician–Silurian boundary on Anticosti Island, Canada. In: Cocks L.R.M., Rickards R.B., editors. A global analysis of the Ordovician– Silurian Boundary. Bulletin of the British Museum (Natural History), Geology Series, 43: 221–237. Rochon A., Lewis J., Ellegaard M., Harding I.C. 2009. The Gonyaulax spinifera (Dinophyceae) ‘‘complex’’: Perpetuating the paradox? Review of Palaeobotany and Palynology, 155: 52–60. Rubinstein C.V., de la Puente G.S., Delabroye A., Astini R.A. 2008. New palynological record of the Ordovician/ Silurian boundary in the Argentine Cordillera Oriental, Central Andean Basin. 12th International Palynological Congress (IPC-XII), 8th International Organisation of Palaeobotany Conference (IOPC-VIII), Abstract Volume. Terra Nostra, 2: 239 (abstract). Rubinstein C.V., Vaccari N.E. 2004. Cryptospore assemblages from the Ordovician–Silurian boundary in the Puna Region, north-west Argentina. Palaeontology, 47: 1037–1061. Saltzman M.R., Young S.A. 2005. Long-lived glaciation in the Late Ordovician? Isotopic and sequence-stratigraphic evidence from western Laurentia. Geology, 33: 109–112. Sandgren C.D., editor. 1988. Growth and reproductive strategies of freshwater phytoplankton. Cambridge (UK): Cambridge University Press. 452 pp. Scotese C.R., McKerrow W.S. 1991. Ordovician plate tectonic econstructions. In: Barnes C.R., Williams S.H., editors. Advances in Ordovician Geology. Geological Survey of Canada Paper, 90(9): 271–282. Servais T., Stricanne L., Montenari M., Pross J. 2004. Population dynamics of galeate acritarchs at the Cambro–Ordovician transition in the Algerian Sahara. Palaeontology, 47: 395–414. Sheehan P.M. 2001. The late Ordovician mass extinction. Annual Review of Earth and Planetary Sciences, 29: 331– 364. Smelror M. 1987. Early Silurian acritarchs and prasinophycean algae from the Ringerike district, Oslo region, Norway. Review of Palaeobotany and Palynology, 52: 137–159. Soufiane A., Achab A. 2000. Chitinozoan zonation of the Late Ordovician and the Early Silurian of the island of Anticosti, Quebec, Canada. Review of Palaeobotany and Palynology, 109: 85–111.


44

A. Delabroye et al.

Stockmarr J. 1971. Tablets with spores used in absolute pollen analysis. Pollen et Spores, 13: 615–621. Stricanne L., Munnecke A., Pross J. 2006. Assessing mechanisms of environmental change: palynological signals across the Late Ludlow (Silurian) positive isotope excursion (d13C, d18O) on Gotland, Sweden. Palaeogeography, Palaeoclimatology, Palaeoecology, 230: 1–31. Stricanne L., Munnecke A., Pross J., Servais T. 2004. Acritarchs along an inshore-offshore transect in the Gorstian (lower Ludlow) of Gotland, Sweden. Review of Palaeobotany and Palynology, 130: 195–216. Tappan H., Loeblich A.R., Jr. 1971. Surface sculpture of the wall in Lower Paleozoic acritarchs. Micropaleontology, 17: 385–410. Tongiorgi M., Yin L., Di Milia A. 2003. Lower Yushanian to lower Zhejiangian palynology of the Yangtze Gorges area (Daping and Huanghuachang sections), Hubei province, South China. Palaeontographica Abteilung B, 266: 1–160. Torsvik T.H., Rhenstro¨m E.F. 2003. The Tornquist Sea and Baltica–Avalonia docking. Tectonophysics, 362: 67– 82. Turner R.E. 1984. Acritarchs from the type area of the Ordovician Caradoc Series, Shropshire, England. Palaeontographica Abteilung B, 190: 87–157. Tynni R. 1982. On Paleozoic microfossils in clastic dykes in the A˚land Islands and in the core samples of Lumparn. Geological Survey of Finland Bulletin, 317: 35–114. Uutela A. 1989. Age and dispersal of sedimentary erratics on the coast of southwestern Finland. Bulletin of the Geological Survey of Finland, 349: 1–100. Uutela A., Tynni R. 1991. Ordovician acritarchs from the Rapla borehole, Estonia. Bulletin of the Geological Survey of Finland, 353: 1–135. Vandenbroucke T.R.A. 2008. An Upper Ordovician chitinozoan biozonation in British Avalonia (England and Wales). Lethaia, 41: 275–294. Vecoli M. 1999. Cambro–Ordovician palynostratigraphy (acritarchs and prasinophytes) of the Hassi-R’Mel area and northern Rhadames Basin, North Africa. Palaeontographia Italica, 86: 1–112. Vecoli M. 2008. Fossil microphytoplankton dynamics across the Ordovician–Silurian boundary. Review of Palaeobotany and Palynology, 148: 91–107. Vecoli M., Le He´risse´ A. 2004. Biostratigraphy taxonomic diversity, and patterns of morphological evolution of Ordovician acritarchs (organic-walled microphytoplankton) from the northern Gondwana margin in relation to palaeoclimatic and palaeogeographic changes. EarthScience Reviews, 67: 267–311. Vecoli M., Riboulleau A., Versteegh G.J.M. 2009. Palynology, organic geochemistry and carbon isotope analysis of a latest Ordovician through Silurian clastic succession from borehole Tt1, Ghadamis Basin, southern Tunisia, North Africa: Palaeoenvironmental interpretation. Palaeogeography, Palaeoclimatology, Palaeoecology, 273: 378–394. Versteegh G.J.M., Zonneveld K.A.F. 2002. Use of selective degradation to separate preservation from productivity. Geology, 30: 615–618. Webby B.D., Cooper R.A., Bergstro¨m S.M., Paris F. 2004. Stratigraphic framework and time slices. In: Webby B.D., Paris F., Droser M.L., Percival I.G., editors. The great Ordovician biodiversification event. New York: Columbia University Press. p. 41–47.

Westphal H., Head M.J., Munnecke A. 2000. Differential diagenesis of rhythmic limestone alternations supported by palynological evidence. Journal of Sedimentary Research, 70: 715–725. Wicander R., Playford G. 2008. Upper Ordovician microphytoplankton of the Bill’s Creek Shale and Stonington Formation, Upper Peninsula of Michigan, USA: Biostratigraphy and Paleogeographic significance. Revue de Micropaleóntologie, 51: 39–66. Wicander R., Playford G., Robertson E.B. 1999. Stratigraphic and paleogeographic significance of an Upper Ordovician acritarch flora from the Maquoketa Shale, Northeastern Missouri, USA. Paleontology Society, Memoir 51 (Journal of Paleontology), 73: 1–38. Wilde P. 1991. Oceanography in the Ordovician. In: Barnes C.R., Williams S.H., editors. Advances in Ordovician geology. Geological Survey of Canada Paper, 90(9): 283–298. Wright R.P., Meyers W.C. 1981. Organic-walled microplankton in the subsurface Ordovician of Northeastern Kansas. Kansas Geological Survey, Subsurface Geology Series, 4: 1–53. Yin L., He S. 2000. Palynomorphs from the transitional sequences between Ordovician and Silurian of northwestern Zhejiang, South China. Palynofloras and palynomorphs of China. Hefei: Press of University of Science and Technology of China. p. 186–202.

Appendix 1. List of acritarch and prasinophytes recovered from the Valga-10 section Prasinophyte phycomata (1) Cymatiosphaera sp. (2) Leiosphaeridia spp. (Plate 4, figures 10–11) (3) Tasmanites sp. (Plate 4, figure 12)

Acritarchs (4) Ammonidium sp. (Plate 4, figure 3) (5) Aremoricanium squarrosum Loeblich & MacAdam 1971 (Plate 1, figures 1–2) (6) Baltisphaeridium adialstaltum Wicander, Playford & Robertson, 1999 (Plate 2, figures 5–6) (7) Baltisphaeridium aliquigranulum Tappan & Loeblich 1971 (Plate 2, figures 7–8) (8) Baltisphaeridium curtatum Playford & Wicander 2006 (Plate 1, figures 6, 9–10) (9) Baltisphaeridium perclarum Tappan & Loeblich 1971 (Plate 2, figures 9–11) (10) Baltisphaeridium sp. A (Plate 1, figures 3–5, 7–8) (11) ?Baltisphaeridium sp. (Plate 2, figures 1–4) (12) Baltisphaeridium sp. aff. B. aspersilumiferum Tappan & Loeblich 1971 (Plate 3, figures 1–6) (13) Buedingiisphaeridium balticum Uutela & Tynni 1991 (Plate 16, figures 1–3) (14) ?Carminella sp. (Plate 10, figures 8–9) (15) Cheleutochroa gymnobrachiata Loeblich & Tappan 1978 (Plate 3, figure 12) (16) Cheleutochroa sp. aff. C. venosa Uutela & Tynni 1991 (Plate 3, figures 7–9) (17) Comasphaeridium williereae (Deflandre & Deflandre-Rigaud 1965 ex Lister 1970) Sarjeant & Stancliffe 1994 (Plate 5, figure 8)


Palynology (18) Comasphaeridium lanugiferum Jacobson & Achab 1985 (Plate 4, figures 1–2) (19) Comasphaeridium sp. A (Plate 6, figure 1) (20) Dilatisphaera wimanii (Eisenack 1968) Le He´risse´ 1989 (Plate 3, figure 10) (21) Dorsennidium hamii (Loeblich 1970) Sarjeant & Stancliffe 1994 (Plate 3, figure 11) (22) Dorsennidium sp. cf. D. europaeum (Stockmans & Willie`re 1960) Sarjeant & Stancliffe 1994 (Plate 5, figure 10) (23) Estiastra magna Eisenack, 1959 (Plate 6, figure 11) (24) Evittia denticulata denticulata (Cramer 1970) Le He´risse´ 1989 (Plate 4, figures 4–5) (25) Evittia porkuniensis Delabroye, Vecoli, Hints & Servais sp. nov. (Plate 9, figure 10, Plate 15, figures 7–12) (26) Evittia sp. A (Plate 15, figures 2–6) (27) ?Florisphaeridium sp. (Plate 6, figures 6–8) (28) ?Ferromia sp. A (Plate 11, figures 4–5) (29) Goniosphaeridium sp. A (Plate 5, figures 1–4) (30) Helosphaeridium tongiorgii Delabroye, Vecoli, Hints & Servais sp. nov. (Plate 10, figures 1–7) (31) Hoegklintia visbyensis (Eisenack 1959) Dorning 1981 (Plate 6, figures 4–5, 9–10) (32) Leiofusa granulicatis Loeblich 1970 forma quincunx Uutela 1989 (Plate 11, figures 1–3) (33) Leiofusa sp. aff. L. granulicatis Loeblich 1970 forma quincunx Uutela 1989 (Plate 10, figure 10) (34) Likropalla adiazeta Colbath 1979 (Plate 7, figures 1– 4) (35) Lophosphaeridium edenense Loeblich & Tappan 1978 (Plate 7, figures 8–10) (36) Micrhystridium spp. (37) Micrhystridium taeniosum Uutela & Tynni 1991 (Plate 4, figures 7–9) (38) Multiplicisphaeridium irregulare Staplin, Jansonius & Pocock 1965

45 (39) Multiplicisphaeridium ramispinosum Staplin 1961 (Plate 6, figures 2–3) (40) Multiplicisphaeridium sp. A (Plate 9, figures 7–9) (41) Navifusa punctata Loeblich & Tappan, 1978 (Plate 7, figures 5–7) (42) Nexosarium leherissei Delabroye, Vecoli, Hints & Servais sp. nov. (Plate 13, figures 10–12, Plate 14, figures 1–4) (43) Oppilatala sp. (Plate 11, figures 6–7) (44) Ordovicidium sp. A (Plate 12, figures 5–6, Plate 13, figures 1–4) (45) Ordovicidium sp. B (Plate 13, figures 5–9) (46) Orthosphaeridium insculptum Loeblich 1970 (Plate 8, figures 1–3) (47) Orthosphaeridium rectangulare (Eisenack 1963) Eisenack 1968 (Plate 8, figures 7–9) (48) Orthosphaeridium vibrissiferum Loeblich & Tappan 1971 (Plate 8, figures 4–6) (49) Peteinosphaeridium accinctulum Wicander, Playford & Robertson 1999 (Plate 9, figures 1–3) (50) Peteinosphaeridium septuosum Wicander, Playford & Robertson 1999. (Plate 9, figures 4–6) (51) Poikilofusa obliquipunctata (Uutela & Tynni 1991) Delabroye, Vecoli, Hints & Servais comb. nov. (Plate 12, figures 1–4) (52) Nanocyclopia sp. A (Plate 16, figures 6–10) (53) Stellechinatum helosum Turner 1984. (Plate 5, figures 5–7, 9) (54) Veryhachium oklahomense Loeblich 1970 (Plate 5, figure 11) (55) ?Veryhachium bulliferum Delabroye, Vecoli, Hints & Servais sp. nov. (Plate 14, figures 5–10, Plate 15, figure 1)