ELSEVIER
Marine Micropaleontology 3 1 (1997) 65-95
Dinoflagellate biostratigraphy and sequence stratigraphy of the Type Maastrichtian (Upper Cretaceous), ENCI Quarry, The Netherlands Poul Schioler a,*, Henk Brinkhuis b, Lucia Roncaglia”,
Graeme J. Wilson d
a Geological Survey of Denmark and Greenland, Thoravej8, DK-2400 CopenhagenNL! Denmark b Laboratoryof Palaeobotanyand Palynology,Universityof Utrecht, Budapestlaan4. 3584 CD Utrecht,The Netherlands ’ Dipartimento di Scienze della Terra, University of Modena, via Universitci 4, 41100 Modena, Italy d Institute of Geological and Nuclear Sciences, RO. Box 30368, Lower Hun, New Zealand
Received 3 March 1996; accepted 24 October 1996
Abstract The upper Maastrichtian strata in ENCI Quarry contain rich assemblages of marine palynomorphs, especially dinoflagellate cysts. A quantitative study shows that a marked change from dinoflagellate-dominated assemblages to assemblages dominated by the acrltarch genus Paralecaniella occurs at the base of the Lanaye Member, indicating a change from open marine to marginal marine conditions. A sequence stratigraphic breakdown into systems tracts based on an interpretation of the changes in the palynological assemblages and lithology suggests the presence of parts of four sedimentary cycles in the ENCI section. Three of the cycles may be correlated with the third-order cycles UZA 4.5, TA 1.1 and TA 1.2 of Haq et al. (1988), the fourth cycle is probably of higher order. Three dinoflagellate cysts are new: Laciniadinium? aquiloniforme Schioler et al., sp. nov., Leberidocysta? verrucosa Schioler et al., sp. nov. and Pulchrasphaera minuscula Schioler et al., gen. et sp. nov. The description of Rottnestia wetzelii is emended and the new combination Cribroperidinium wilsonii (Slimani) Schioler et al., comb. nov. is proposed. The Triblastula utinensis Zone, Isabelidinium cooksoniae Zone and the Palynodinium grallator Zone with its two subzones, Tanyosphaeridium magdalium Subzone and Thalassiphora pelagica Subzone can be recognized in the ENCI section. Keywords: Maastrichtian; stratotype; biostratigraphy; sequence stratigraphy; palynology
1. Introduction The ENCI Quarry in South Limburg, The Netherlauds (Fig. l), is the type locality for the Maastrichtian Stage and has been the subject of extensive litbological and biostratigraphical study (see review in Zijlstra, 1994a). Dinoflagellates from the ENCI *Corresponding author. Address: GEUS, Thoravej 8, DK2400 Copenhagen NV, Denmark. Fax: +45 38142050. E-mail:
[email protected].
section have been studied by De Wit (1943), Wilson (197 la, 1974) and Schumacker-Lambry (1977); however, these studies were based on few and scattered samples and their biostratigraphic conclusions were unclear. The present study reports on the qualitative and quantitative distribution of dinoflagellates and selected acritarchs in the ENCI section based on a study of 64 samples. The dinoflagellate biostratigraphy is documented and correlated with other macroand microfossil zonations of the ENCI section and
0377-8398/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SO377-8398(96)00058-S
66
R Schi@ler et al/Marine
Micropaleontology
31 (1997) 65-95
5km ‘45
45’
’ 6O
Fig. 1. Map of the Limburg area, The Netherlands, showing the location of the ENCI Quarry.
with dinoflagellate zonation schemes of northern Germany, Denmark, and the Central North Sea. In recent years palynology has been increasingly used as a support for sequence stratigraphic models (e.g., Partridge, 1976; Brinkhuis and Zachariasse, 1988; Habib and Miller, 1989; Gorin and Steffen, 1991; Eshet et al., 1992; Versteegh, 1993; Brinkhuis, 1994; Habib et al., 1994; Hart et al., 1994; Fauconnier, 1995; Huault et al., 1995; Powell et al., 1995; Sue et al., 1995). We propose here a sequence stratigraphic model for the ENCI section, based on changes in the composition of the palynological assemblage (palynofacies) and variations in the distribution of dinoflagellate morpho-groups. The model is supported by previously published sedimentological evidence. 2. Lithostratigraphy The Maastrichtian strata in ENCI Quarry belong to the Gulpen and Maastricht formations. The latter
was established as the type section for the Maastrichtian Stage by Dumont (1849) and is separated from the underlying Gulpen Formation by the Lichtenberg Horizon (Fig. 2). The Gulpen Formation extends below the base of the exposed section. At ENCI, the Maastricht Formation is overlain unconformably by the Oligocene Tongeren Formation. The Maastrichtian strata in the quarry consist of ca. 81 m of rhythmically bedded coarsening-upwards yellowish white carbonate ranging from mud to coarse sand in grain size, with common nodular flint layers in the lower half of the section. A description of the lithology may be found in Felder and Jagt (1992). A detailed lithostratigraphy was established by Felder (1975a,b) who defined a number of members separated by prominent sediment surfaces (‘horizons’); his subdivision is used here (Figs. 2-4 and 6). The horizons were studied in detail by Zijlstra (1988, 1994b,c) who concluded that the eight major horizons separating the Lanaye-Meerssen members (Maastricht Formation, Fig. 2) are encrusted and
F! Schieler el al. /Marine Micropaleontology 31 (1997) 65-95
bored hardgrounds. The hardgrounds are overlain directly by coarser grained sediment. Vertical fissures are associated with the Nivelle Horizon (Gulpen Formation, Fig. 2), and vertical flint nodules from an overlying flintlayer (Zijlstra, 1988) indicate intensive burrowing. Thus this flint layer may also be interpreted as occupying a bored hardground. The stratigraphic distribution of bioclasts, derived mainly from fossil invertebrates, has been used for correlation between the various chalk exposures in the area (Felder et al., 1985a,b; Felder, 1988). The petrography and sedimentology were discussed in detail by Zijlstra (1988, 1994a), who divided the ENCI section into a lower, middle and upper part (Zijlstra, 1994~). The lower part, encompassing the Lixhe 2, Lixhe 3 and Lanaye members (Fig. 2) consists of homogeneously bioturbated coarsening-upwards coccolithic biomicrite with planar bedded layers of flint nodules. The middle part encompasses the Valkenburg, Groensveld and Schiepersberg members (Fig. 2) and consists of fining-upward beds of occasionally crossbedded bioclastic silt and fine-grained sand. The top part of the section, encompassing the Emael, Nekum and Meerssen members (Fig. 2) consists of finingupward bioclastic sand beds with crossbedding or crosslamination in their lower parts (Zijlstra, 1994~). The overall coarsening-upwards in the ENCI section indicates a gradual increase in hydrodynamic energy and deposition rate. Zijlstra recognized more than one hundred individual beds in the interval from the base of the Lixhe members to the Vroenhoven Horizon (slightly above the top of the ENCI section). The apparent cyclic bedding led Zijlstra to suggest a Milankovitch-driven depositional model in which each bed reflects periods of relatively high deposition rates during periods with calm weather. The beds are separated by encrusted and bored hardgrounds developed during intervals of storm maxima; each cycle is thought to represent a 20 kyr precession cycle (Zijlstra, 1994a). In Zijlstra’s model it is assumed that all the strata at the ENCI section were deposited in a shallow water shelf environment.
67
inition of the base of the Maastrichtian (first occurrence of Belemnitella Zanceolata) of Jeletzky (195 1) and Birkelund (1957). These authors also suggested a four-fold subdivision of the Maastrichtian Stage based on belemnites; their subdivision was revised and refined by Schultz (1979) who subdivided the lower Maastrichtian into six belemnite zones and Schultz and Schmid (1983) who subdivided the upper Maastrichtian below the uppermost casimirovensis belemnite Zone of Jeletzky (195 1) into four zones based on invertebrate macrofossils. The first occurrence (FO) of B. lanceolata is below the Type Maastrichtian and also below the base of the exposed section in the ENCI Quarry. In the South Limburg area the top of the Maastrichtian Stage (i.e., the K/T boundary) occurs at the Berg en Terblijt Horizon, a hardground slightly below the Vroenhoven Horizon (see papers in Brinkhuis and Smit, 1996). Neither of these horizons are exposed in the ENCI section. Therefore, the Maastrichtian strata in the ENCI Quarry represent only a part of the Maastrichtian Stage. Based on belemnite biostratigraphy the larger part of the section, up to the Caster Horizon (Fig. 2) may be correlated with the junior belemnite Zone of Jeletzky (1951) (Felder and Jagt, 1992); the overlying part (Meerssen Member) is assigned to the casimirovensis Zone (Colins et al., 1995; Jagt, 1996). Both zones are of late Maastrichtian age. The members exposed in the ENCI Quarry were correlated with the tegulatusljunior, argentaljunior, danicalargenta and balticaldanica zones established in northern Germany (Schultz and Schmid, 1983). In a major study on the stratigraphic distribution of foraminifera Hofker (1966) established a zonation covering the South Limburg area; the ENCI section falls within the foraminiferal zones E-M. Cepek and Moorkens (1979) recognized the presence of the Lithraphidites quadratus and Nephrolithus frequens nannofossil zones in the ENCI section. The belemnite, foraminiferal and nannofossil zones recognized in the section are shown in Fig. 2. 4. Material and methods
3. Biostratigraphy Most biostratigraphers now have a more extended concept of the Maastrichtian Stage than that defined by Dumont (1849), and use the belemnite based def-
Sixty four samples were collected from the ENCI section: from the Hallembaye Horizon I (base of studied section) to directly below the contact with the Tongeren Formation. The sample interval hence
l? Schider et al. /Marine Micropaleontology 31 (1997) 65-95
.,8 . .
.gI
***
’
pOUIJaddn
. 8,.
.. .
”
.,.
5:
.
I
.
.
.
.
s
. . ..
..”
3
.s
P
, . . .... . ... ... .. . .““.m..i
&3ouJJaMo~
L
a-
P
I
HST
LST
TST
Fig. 4. Relative abundance of dinoflagellate groups and dinoflagellate diversity from the ENCI section based on the counting shown in Fig. 5. The plotted groups together constitute 100%. Very rare occurrences (less than 0.5%) are asterisked. Calculation of the diversity index is based on the counting listed in Fig. 5, excluding very rare occurrences (‘x’ in Fig. 5). Abbreviations as in Fig. 3. For further explanation, see text. Lithology after Felder et al. (1978). see Fig. 2 for legend.
fi
HST
LST
TST
HST
LST
TST
SEQUENCE XRATIGMP
P Schi#ler et al/Marine
Micropaleontology 31 (1997) 65-95
covers the upper part of the Gulpen and the Maastricht formations (Fig. 2). The samples were processed by the Laboratory of Palaeobotany and Palynology (LPP), University of Utrecht, following standard palynological preparation procedures for chalk samples (cf. Wilson, 1971b). The palynodebris (sensu Boulter and Riddick, 1986; Boulter, 1994) was sieved on 15 pm filters. Heavy liquid separation (using ZnClz) was carried out on all samples. In order to avoid possible damage to the palynomorphs, treatment with oxidative agents and hydroxides was avoided. The palynodebris was stained with safranine and mounted in glycerine jelly on microscope slides after extensive mixing to obtain homogeneity. At least 200 palynodebris specimens were counted from each sample. Whenever possible, counting was continued until 200 dinoflagellate specimens were counted; however, due to low abundance of dinoflagellates in the upper two thirds of the section less than 200 specimens were counted in the higher samples. The counted palynodebris specimens were grouped in the following way: dinoflagellates, Paralecaniella spp., other and indeterminate marine algae (encompassing acritarchs other than Paralecaniella, Palambages spp. and indeterminate algae), foraminiferal linings, sporomorphs, and brown wood debris (including rare leaf cuticles). Using 15 Km filters, some of the smaller acritarchs and spores are probably lost. Amorphous organic matter (AOM) is rare throughout the section and was not counted. Opaque matter was not counted as this group may include inorganic mineral grains. Fragments (halves and quarters) of palynomorphs were counted and added up to entire specimens. The results of the palynodebris countings are shown in Fig. 7. The relative distribution of the palynodebris groups is shown in Fig. 3. A separate quantitative analysis was undertaken for the dinoflagellates which were identified to species level and placed in the following groups: (1) the Spiniferites group, combining all species of Spiniferites and species of the morphologically similar genus Achomosphaera; (2) the Areoligera group, combining all Areoligera spp. and the morphologically comparable Glaphyrocysta spp., Heterosphaeridium spp. as well as representatives for the genera Neonorthidium, Palynodinium and Senoniasphaera; (3) the Hystrichosphaeridium group,
71
wherein all Hystrichosphaeridium spp. are combined with the morphologically similar Oligosphaeridium spp.; (4) Cribroperidinium spp.; and (5) the Cordosphaeridium group, combining all Cordosphaeridium spp. with the morphologically comparable Disphaerogena carposphaeropsis, Fibrocysta spp. and Exochosphaeridium bijidum. In the lower part of the succession, representatives of Prolixosphaeridum? cf. nanum are also quantitatively important. All other taxa as well as indeterminate dinoflagellate taxa have been grouped in ‘Other and indeterm. dinoflagellates’. The relative distribution of the dinoflagellate groups is shown in Fig. 4. The encountered dinoflagellate taxa as well as acritarchs and green algae are listed in Table 1. The stratigraphic distribution of the dinoflagellates is shown in Fig. 5, which also gives the counting results for this category. In both Figs. 3 and 4 the plotted groups together constitute 100%. The dinoflagellate diversity is shown in Fig. 4, and was calculated using Brillouin’s index (see Pielou, 1969, for discussion and algorithm) using the computer program MVSP (Kovach, 1990). Basis for the diversity calculation is the count of determinate dinoflagellates from Fig. 5, excluding very rare occurrences (‘ x ’ in Fig. 5). 5. Palynology Dinoflagellate cysts constitute the dominating palynodebris group in the lower ca. 25 m of the section (approx. 70% of the counted palynodebris in the Lixhe 2 and 3 members). The acritarch genus ParaZecaniella (Plate IV, 1) has a gradual but conspicuous frequency increase starting from the lower part of the Lanaye Member (at ca. 21 m) and often dominates the palynodebris above ca. 30 m. Other acritarchs are very rare. Terrestrial palynomorphs are rare throughout the section. Brown wood debris constitute ca. 20% in the Lixhe members, but only 5-10% in the overlying members (Fig. 3). 5.1. DinojIagellate biostratigraphy
Fig. 2 correlates the ENCI section with the dinoflagellate zonation schemes of Wilson (1974), Schumacker-Lambry (1977), Marheinecke (1992) and Schioler and Wilson (1993), and with foraminifera, nannofossil and belemnite zones recognized
P. Schiqder et al. /Marine Micropaleontology 31 (1997) 65-95
72
tWP-auo3
u-m--
~“~~.I I 95s
IIIIIIII I IIIIIIIII
I
II
II I I IIII II II I IIIII IIII
73
P Schider et al. /Marine Micropaleontology 31 (1997) 65-95
E
r*dumww-eNJ
zasBlwwPur)ugldulIIIIlIIIl/IIIIlIIlIIII
2 2?
-
z! 3 -2
YMI
2 - 33233 s..
XI
-
I I-M
I I I I I I-/415/ TM
Ix/ I I I I 151 I I ISISI ISISI I I
P Schi@ler et af. /Marine Micropaleontology 31 (1997) 65-95
I
pvobiqwd~l I t I I I I I I i I I I I i I I I I I I I I I I I I I I / I I I I I
P Schieler et al. /Marine Micropaleontology 31 (1997) 65-95
in the section. The application of the dinoflagellate zones in Fig. 2 is briefly discussed below, and is based mainly on the following five events: last occurrence (LO) of Triblastula utinensis, FO of Gluphyrocysta per&rata, LO of Isabelidinium cooksoniae, FO of Palynodinium grallator and FO of Thalassiphora pelagica. Except for the FO of G. perforutu, which is only rarely reported, these events seem to have a largely similar distribution pattern in the boreal Maastrichtian (cf. Hansen, 1977; Firth, 1987; Aurisano, 1989; Kirsch, 1991; Costa and Davey, 1992; Schioler and Wilson, 1993), and thus may be important inn-a-Maastrichtian events, as noted by Schioler and Wilson (1993). The LOS are positioned at the last consistent occurrence in the ENCI section. The events are indicated by shading in Fig. 5. Wilson (1974) proposed a zonation for the Maastrichtian strata in the region; his zonation was partly based on samples from the ENCI Quarry. The base of Wilson’s Zone Va is identified on the FO of G. per$orutu at 25.05 m. This event more or less coincides with the LO of i? urinensis (at 23.75 m), in agreement with Wilson’s description of the boundary between zones IV and Va. Zone Vb of Wilson is identified at the FO of P grullator (at 64.6 m) and ranges to the top of the section (Fig. 2). Schumacker-Lambry (1977) proposed a zonation of the ENCI section which is largely comparable to that of Wilson: the base of her Zone IVb coincides with the base of Wilson’s Zone Va. The base of the underlying Zone IVa of Schumacker-Lambry cannot be determined in the section as the index fossils are present from the base of the section. Schumacker-Lambry did not clearly define the base of Zone IVc, but positioned it at the Caster Horizon (Fig. 2). Marheinecke (1992) proposed a zonation for the Maastrichtian interval in the Hemmoor Quarry section in northern Germany; Marheinecke’s zones were correlated with the macrofossil zones of Schultz and Schmid (1983) which were also established in the Hemmoor section, and thus serve as an important link between macrofossil and dinoflagellate biostratigraphy. The base of Marheinecke’s Zone C may be recognized on the FO of dinoflagellates similar to G. peflorata ( = Cyclonephelium expansum and Cyclonephelium castelcasiense of Marheinecke, 1992). The strata below the FO of G. per$orutu in the ENCI
75
section are hence tentatively assigned to Zone B. The C2/Cl Zone boundary cannot be identified with certainty in the ENCI section due to absence of the index fossils, but the boundary coincides with the LO of I. cooksoniae judged from the range chart provided by Marheinecke. Thus the C2/Cl Zone boundary is correlated with that event (at 47.5 m) in the ENCI section (Fig. 2). The LO of I. cooksoniae occurs close to the boundary between the lower and upper part of the upper Maastrichtian (sensu Surlyk, 1970) in the Hemmoor section (Schultz and Schmid, 1983), and close to the Romontbos Horizon in the ENCI section. Zone D cannot be identified in the ENCI section and is tentatively correlated with the interval above the LO of Z. cooksoniae and below the FO of P. grallator. The dinoflagellate based correlation between the Hemmoor and ENCI sections shown in Fig. 2 is in agreement with the correlation based on macrofossils suggested by Schultz and Schmid (1983). Schioler and Wilson (1993) subdivided the Maastrichtian strata in the Dan Field, Danish North Sea Sector into eight units, using two Maastrichtian subzones of Hansen (1977) and six additional events. The LOS of T. utinensis and I. cooksoniae, and the FOs of P. grallator and T. pelagica may be used to apply the Central North Sea zonation to the ENCI section (Fig. 2). The interval between the LO of I. cooksoniae and the FO of P grallator is tentatively assigned to the Palaeocystodinium denticulatum and Hystrichostrogylon borisii zones which occupy this interval in the Central North Sea. Alterbidinium acutulum, which marks the top of the lower Maastrichtian Alterbidinium acutulum Subzone has a single occurrence at 47.35 m and otherwise occurs scattered in the lowermost 10 m of the ENCI section (three specimens encountered here) and is considered reworked. 5.2. Significance of quantitative changes in the palynomorph categories The relative distribution pattern of the broad groups of palynomorphs (Fig. 3) indicates that the assemblages can be characterized as being dominated either by specimens of Parulecaniella or by dinoflagellates. Paralecaniella becomes more abundant upsection, while rich and diverse dinoflagellate
76
R Schi#ler et al. /Marine Micropaleontology 31 (1997) 65-95
associations are mainly recovered from the majority of samples from the lower part of the succession (see Fig. 4 for dinoflagellate diversity index). The boundaries between the dinoflagellate or Purulecaniellu dominated assemblages are in most cases conspicuously associated with the various hardgrounds, indicating environmental change (Fig. 3). In their review of the possible palaeoecological significance of abundance of Purulecuniellu, Brinkhuis and Schioler (1996) suggest this probably indicates extremely marginal marine, possibly stressed environments. Thus high relative abundance of Purulecuniellu may indicate marginal marine to restricted marine influence, or may reflect increased transport from such settings. Alternatively, as also suggested by Brinkhuis and Schioler (1996), high relative abundance of Purulecuniellu may be related to sediments deposited under higher hydrodynamic energy conditions. The assemblages characterized by rich and relatively high diversity dinoflagellate associations probably reflect outer neritic conditions, or hydrodynamically lower energy deposits. In both models the recorded pattern indicates an overall neritic setting for the analyzed succession, with a shoaling trend upsection. The alternation of the two assemblage types may be explained in terms of relative sea-level fluctuations, subdivided in phases of relative lowstand, transgression, and highstand phases, in turn related to high, high to low, and low to high hydrodynamic conditions, respectively. So the analyzed succession may tentatively be subdivided into (parts of) four short-term cycles on a scale of several to tens of meters of section, superposed on the longer-term general shallowing trend. Intervals interpreted to reflect relative sea-level lowstand are taken as the base of each cycle (cf. Haq et al., 1988) for third-order cyclicity, or sequence stratigraphy). Boundaries between cycles are accordingly placed at the horizons of Nivelle, Romontbos and Kanne (Fig. 3). 5.3. Dinojlugellutes The dinoflagellate distribution is plotted in Fig. 4. Typically, a few groups of morphologically related taxa make up some 5060% of the associations. In general, representatives of the Spiniferites group dominate the associations in the lower and mid-
dle part of the succession, and reach high relative abundances in some levels from the upper part. In most of the relatively low diversity samples from the upper part of the succession, the Areoligeru and Hystrichosphaeridium groups reach high relative abundances (Fig. 4). The encountered dinoflagellate cysts are probably all of marine origin. However, taxa typically representing relatively offshore and/or oceanic conditions, e.g., Impagidinium spp., or the morphologically similar Pterodinium spp. (see, e.g., Wall et al., 1977; Head and Wrenn, 1992) have only been recorded in low numbers. Dinoflagellate cysts presumably derived from heterotrophic dinoflagellates (i.e., the peridinioids) are not quantitatively pronounced in any of the investigated samples. They are, like Impugidinium and Pterodinium spp. only consistently present in the lower part of the succession. The most abundant groups of morphologically related taxa recorded from the ENCI succession (Fig. 4) are usually found in similar abundances in relatively marginal marine, neritic successions throughout the Mesozoic and Cenozoic (compare, e.g., Downie et al., 1971; Hultberg and Malmgren, 1987; Brinkhuis and Zachariasse, 1988; Brinkhuis, 1994; Brinkhuis and Schioler, 1996). Thus, in general, the composition of the association supports the inferred neritic setting for the analyzed succession. Of the dinoflagellate cyst groups, only representatives of the Spiniferites group still occur today. This group typically occupies outer neritic waters (e.g., Wall et al., 1977; Head and Wrenn, 1992). The Spiniferites group may tentatively be regarded as the most offshore quantitatively important category of dinoflagellate cysts present in the ENCI section. The Areoligeru group is often abundant in coastal sediments (e.g., Downie et al., 1971; Brinkhuis, 1994; Powell et al., 1995). High numbers of the Hystrichosphaeridium group have been widely reported from Mesozoic to Eocene neritic sediments. Dinoflagellates producing Hystrichosphueridium-type cysts are apparently able to tolerate stressed environments; judging from their total dominance in extremely marginal marine, possibly lagoonal settings in the Ypresian of the North Sea Basin (Bujak and Mudge, 1994). High numbers of the Cordosphaeridium group have also been widely reported from Mesozoic to Miocene neritic sediments,
P Schider et al. /Marine Micropaleontology 31 (1997) 65-95
while elevated numbers of the equally long ranging genus Cribroperidinium are often recorded from ancient coastal deposits (e.g., Wilpshaar and Leereveld, 1994; Leereveld, 1995). On the paleoecology of Prolixosphaeridium species little is known; they are usually present in Mesozoic neritic sediments. The distribution pattern of the probably more marginal marine Areoligera and Hystrichosphaeridium groups in the ENCI section relative to the slightly more offshore Spiniferites group is similar to the overall pattern of Puralecaniellu vs. dinoflagellates, a situation previously encountered in the chalk deposits from the Maastrichtian type area (compare, e.g., Herngreen et al., 1986; Brinkhuis and Schioler, 1996). Moreover, their distribution patterns support the inferred shallowing upsection. The cyclicity as recognized on the basis of the distribution patterns of the dinoflagellate and Paralecaniella categories and the corresponding proposed successive alternation of relative lowstands, transgressions and highstands can be correlated with the distribution pattern of the individual dinoflagellate groups. Optima of the ,Spiniferites group are in most cases associated with a sea-level high and/or an energy low (Fig. 4). 5.4. Origin and age model for the recorded cyclicity The amount of time represented in the ENCI succession is still difficult to assess. Neither detailed, unequivocal nannofossil or planktic foraminifer zonation nor magnetostratigraphy are available. The most significant stratigraphic information comes from macrofossils (see overview by Jagt, 1996), particularly belemnites. The upper Maastrichtian is subdivided into the junior and casimirovensis belemnite zones (Jeletzky, 1951; Birkelund, 1957; Christensen, 1988); both these zones are identified in the ENCI section suggesting that it spans much of the upper Maastrichtian. Although not exposed in the ENCI section, only two underlying upper Maastrichtian lithological units (Vijlen and Lixhe 1 members of the Gulpen Formation) have been described from the region (Felder, 1975b; Zijlstra, 1994a), totalling some 25 m of section. These units were also assigned to the junior belemnite Zone (Robaszynski et al., 1983, 1985). Latest age-models place the late Maastrichtian between 65.3 and 69.3 Ma, a duration of 4.0 myr
71
(Gradstein et al., 1994). If the ENCI section represents ca. 3 myr, the four inferred sea-level fluctuations (Figs. 3, 4, and 6) may be compared to the third-order sea-level changes of Haq et al. (1988). These authors plot only three third-order sequences in the upper Maastrichtian; one at the base (‘71 Ma’), and two closely spaced together near the CretaceousfTertiary boundary, at ‘68’ and ‘67’ Ma on their timescale. The lowermost upper Maastrichtian, the Vijlen Member of the Gulpen Formation, may be seen as deposits laid down during a transgression in the last phase of a major episode of blockfaulting and tectonic inversion in the Maastricht area (Robaszynski et al., 1983, 1985; Bless et al., 1987; Gras, 1995). The base of the Vijlen Member often unconformably overlies Campanian deposits, or in some cases, it conformably overlies a part of the lower Maastrichtian Buitenaken Member of the Gulpen Formation (see Robaszynski et al., 1983, 1985). Since the Vijlen Member represents the basal upper Maastrichtian in the region, this transgression may be correlated with the transgressive part of the earliest late Maastrichtian cycle UZA 4.5 of Haq et al. (1988), with a corresponding maximum flooding (mfs) at the top of the Vijlen Member. The overlying Lixhe members may be regarded as the highstand deposits of this cycle which, according to Haq et al. (1988) is of relatively long duration (‘3 myr’). The results of our study indicate that subsequent sequence boundaries may be positioned at Nivelle, Romontbos and Kanne horizons at ENCI, all underlying lowstand deposits (Figs. 3 and 4). The inversion tectonics eased off during the early late Maastrichtian and a final episode is inferred to have occurred during the middle late Maastrichtian (e.g., Robaszynski, 1981; Bless et al., 1987; Bless, 1989; Gras, 1995). This episode may be associated with the base of the Maastricht Formation, and thus with the formation of the Lichtenberg Horizon (Fig. 6). The Maastricht Formation is widespread and laterally continuous, and can be traced in seismic profiles across major structural elements into the North Sea Basin (Gras, 1995). Thus it may represent the final drowning phase caused by tectonic relaxation following the episode of local inversions of the entire area. Tectonics could therefore have affected the middle part of the analyzed succession, causing
-- 70,.
Relative sea level (This study)
Hz.“.H*llembay.?1
Hz. v. Schiepersberg
HL.V.ROmO”tbos
_---.-
.
.---.w..
___
..,...
___~
.
-.:
.
_.
.
.
I
50
..
-.I I’.
. . . .. .
.. .,
o
IO
*.:..I: i:_k:':1: 40
.:~-.7..=.+2:.‘=..
..I,,*..-.--
: ._
..:-.:-~:
_.
,...‘l’C - . :
. . - ._ .- 60 HZ.".h"rnO"l. -V.--n...' cHI"Lava G. I- A-.
.a_.. I -
_ __ __. =I+
Hz.".Ka"ne m-
.
-_--7
I-
Short term eustatic curve (Haq et al., 1988)
Fig. 6. Comparison between the relative sea level changes inferred from the present study and the short-term (third-order) eustatic cycles of Haq et al. (1988). A higher-order cycle occurs between Romontbos and Kanne horizons in the ENCI section. Geochronology based on astronomical calibration from Zijlstra (1994a). For further explanation, see text. US = highstand; Ls = lowstand; MFS = maximum flooding surface; SB = sequence boundary; TR = transgression. Lithology after Felder et al. (1978), see Fig. 2 for legend.
_ixhe2
_lxhe 3
i,O”S”d
