The Late Visean (Early Carboniferous) goniatite ...

News!. Stratigr.

4 Fig.

Berlin· Stuttgart, 31. 7. 1997

The Late Visean (Early Carboniferous) goniatite stratigraphy in the South Portuguese Zone, a comparison with the Rhenish Massif by DIETER KoRN and KATHARINA HoRN''· with 4 figures

Abstract.

In the South Portuguese Zone, sections located in the Bordeira Antiform (localities Praia de Murras;ao, Praia das Quebradas, and Rocha da Lagoa) show a Late Visean fauna! succession of goniatites, which principally resembles that of Northwestern and Central Europe (e. g. the Rhenish Massif). The fol lowing goniatite zones were identified in South"(est Portugal: Goniatites hudsoni Zone, Goniatites spiri fer Zone, and the zones b�tween the Arnsbergites gracilis Zone and the Lyrogoniatites liethensis Zone. On the bas.is of goniatites, a ptoposal for a subdivision of the Late Visean into the three substages Late Visean A, B and C: is given. Zusammenfassung.

In der Sudportugiesischen Zone zeigen Profile in der Antiform von Bordeira (Lokalit�ten Praia de Murras;ao, Praia das Quebradas und Rocha da Lagoa) eine Faunenabfolge von Go niatiten im Ober-Vise, welche grundsatzlich mit derjenigen aus Nordwest- und Mitteleuropa (z.B. dem Rheinischen Schiefergebirge) ubereinstimmt. Die folgenden Goniatiten-Zonen konnten in Sudwestpor tugal nachgewiesen werden: Goniatites hudsoni-Zone, Goniatites spirifer-Zone sowie die Zone zwischen der Arnsbergites gracilis-Zone und der Lyrogoniatites liethensis-Zone. Ein Vorschlag zur Untergliederung des Ober-Vise in die drei Unterstufen Ober-Vise A, B und C wird unterbreitet. Resume. Des coupes clans l'antiforme de Bordeira (coupes Praia de Murras;ao, Praia das Quebradas et Rocha da Lagoa), clans la Zone Sud-Portuguese, compartent une succession de goniatites du Viseen superieur. Elle correspond essentiellement a celle de !'Europe nord-occidentale et mediane (par example le Massif Rhenan). La presence des zones suivantes a pu etre demontree: Zone a Goniatites hudsoni, Zone a Goniatites spirifer ainsi que les zones entre celles a Arnsbergites gracilis et a Lyrogoniatites liethensis. La . subdivision du Viseen superieur en sous-etages A, B et C est proposee.

1.

Introduction

The South Portuguese Zone marks the southvi�stern margin of the European Variscides, being mainly composed of Late Devonian and Carboniferous sedimentary rocks. These sediments are predominantly Flysch-like deposits which cover a large area of the Baixo Alentejo and Algarve regions. Autochthonous rocks, such as fine-grained claystones, black shales and lime'

,,. Authors' addresses: DIETER Ko RN, Institut und Museum fur Geologie und Palaontologie der EberhardKarls-Universitat, Sigwartstrafle 10, D-72076 Tubingen. KATHARINA HoRN, Ernst-Toepfer-Strafle 3, D- 65110 Idstein. 0078-00421/97/0035-0097$4.25

© 1997 Gebriider Borntraeger, D-14129 Berlin· D-70176 Stuttgart

D. KoRN and K. HoRN

98

stones, which compose the Carrapateira Group, consisting of the Bordalete, Murra,.ao, and Quebradas Formations, frequently occur in the antiforms of Aljezur and Bordeira. These for mations contain ammonoid faunas which are usually rich in individuals, but rather poor in spe Cies. Petrographical and palaeontological similarities between the Early Carboniferous succes sions of South Portugal and Central Europe have been known since the beginning of the pio neering research by NERY DELGADO (1870, 1876) as well as RoEMER (1876), and were later con firmed by intensive investigations of the Flysch series (OLIVEIRA, HoRN & PAPROTH 1979). In that paper it was demonstrated that the development of the South Portuguese Basin closely resembles that of the Rhenohercynian Basin, even in stratigraphical timing of the clastic depo sition. Up to now, however, an attempt to correlate the fauna! succession of the Early Carboni ferous goniatites from the South Portuguese Zone with that described from other regions has not been made. Hence the purpose of this paper is to describe sections with goniatite-bearing beds to allow comparison of these with sections in Ireland (MoORE & HoDSON 1958, BRAN DON & HoDSON 1984), North England (BrsAT 1924, 1934, 1952, MooRE 1936, RrLEY 1990), the Harz Mountains (KoBOLD 1933), and the Rhenish Massif (HAUBOLD 1933, RuPRECHT 1937, KuucK 1960, NrcoLAUS 1963, KoRN 1988, 1996). 2.

Historical review

The first reference of Early Carboniferous ammonoids from the South Portuguese Zone can be found in the note written by RoEMER (1876), who mentioned "Goniatites crenistria", "Go niatites sphaericus", and "Goniatites mixolobus", which were collected by J. F. NERY DELGADO from various localities of the Baixo Alentejo and Algarve regions. RoEMER already noticed that there is a surprising consistency in petrography and palaeontology of the Posidonia shales in the Rhenish Massif and South Portugal. From almost the beginning of this century, Early Carboniferous goniatites and goniatite bearing localities have been described in the papers by PRUVOST (1914), PEREIRA DE SousA (1923, 1924, 1926), CARRINGTON DA CosTA (1943), and FEro (1946). DELEPINE (1957) listed 10 Tournaisian as well as 19 Visean goniatite-bearing fossil localities within the South Portuguese Zone, and was the first who provided a stratigraphical scheme in which he placed the different faunas known so far. Also, he tried to correlate the Portuguese faunas with those known from England, Russia and North America. In 1978, PERDIGAO listed a number of goniatite localities from various regions within South Portugal, and revised the stratigraphical scheme developed earlier by DELEPINE. During mapping fieldwork in the South Portuguese Zone, J. T. 0LIVEIRA assembled a col lection of Late Visean goniatites from the Alcoutim and Castro Verde areas, which were stud ied by WAGNER-GENTIS in 0LIVEIRA & WAGNER-GENTIS (1983). Due to the field work by E. PAPROTH, M. HoRN and J. T. 0LIVEIRA between 1977 and 1982, five stratigraphical sections in the Bordeira and Aljezur areas have been studied in detail for the first time. Numerous goniatite specimens were collected during these campaigns, and the results summarized in a subsequent article (OLIVEIRA, HoRN, KuLLMANN & PAPROTH 1985). Further ammonoid material was found by K. HoRN in the years 1982 to 1984 and by D. KoRN

Goniatite stratigraphy in South Portuguese Zone

99

in 1993 and 1994. The promising results of these explorative collections led the authors to a more extended field campaign in 1995 with the aim to correlate the ammonoid bearing strata of the South Portuguese Zone with the existing stratigraphical scheme developed in the Rhen ish Massif. This comparison of the sections under examination will be presented in the follow mg. 3.

Stratigraphical sections in the Rhenish Massif

3.1

In den Dieken

The section along the road from Affeln to Langenholthausen has been known for 60 years (RuPRECHT 1937, ScHMIDT 1942), but a modern description of this very fossiliferous outcrop is still lacking. With the widening of the road in the early 1970s, the exposure conditions improved, so that within a trench in the cutting slope a complete section throughout the entire Late Visean strata could be examined. The In den Dieken section is located at the southern flank of the Liidenscheid Syncline. Here, sedimentation was hardly influenced by the turbidity currents which led to sedimenta tion of the Kulmplattenkalk Formation, exposed in sections in the Remscheid-Altena Anti cline only a few kilometer towards the North. Hence the rock column is almost exclusively composed of fine grained clastics, with only very few carbonate intercalations. The columnar profile (Fig. 1) shows the vertical organisation of the section, which is rela tively reduced in thickness. Above the grimmeri Bed, the predominant cherts and cherty lime stones of the upper part of the Kulmkieselkalk Formation are replaced by an almost pure alum shale succession with only few cherts of the so-called "Kieselige Ubergangsschichten" in terms of NrcoLAUS (1963). In the grimmeri Bed, in addition to the very common species Entogon ites grimmeri (KITTL 1904), Goniatites hudsoni BrsAT 1934 as well as Girtyoceras sp. occur. 2.60 m above the grimmeri Bed, Goniatites (?) globostriatus (ScHMIDT 1925) is found very frequent in the alum shales. The first occurrence of Goniatites crenistria PHILLIPS 1836 has not been discovered, but the three-fold Crenistria Limestone lies 10 m above the grimmeri Bed, a distance that resembles the situation of the eastern margin of the Rhenish Massif (NrcoLAUS 1963). Above the Creni stria Limestone, claystones are dominant, with only few interbedded limestones, usually dis tant calciturbidites, and a tuffitic layer at 3.40 m from the upper bed of the Crenistria Lime stone. The claystones are very rich in goniatites, and some horizons even yield three dimensionally preserved silicified material. 40 and 60 cm above the top bed of the Crenistria Limestone, Goniatites fimbriatus (FooRD & CRICK 1897) is common, and Paraglyphioceras (?) semistriatum (NrcoLAUS 1963) is simi larly frequent. Nomismoceras vittiger (PHILLIPS 1836) is found abundantly on some bedding surfaces. At 80 cm, the fauna! composition is still the same, except for the new entry of Goniatites spirifer RoEMER 1850, providing an indication of the Goniatiies spirifer Zo'ne. Gim. spirifer and Paragl. (?) semistriatum also eo-occur at 1.40 m, and at 2.75 m Paraglyphioceras radiatum (HonsoN & MooRE 1959) is very frequent in only one horizon. The Goniatites spirifer Zone may still be present at 3.70 m, where only poorly preserved goniatites have been collected.

Late Visean B

Late Visean A hudsoni Zone

I

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fzm..

crenistria

globostriatus Zone

Zone

spirifer Zone

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faZe.

gr. Zone Z.

spirale

rotundum

suerlandense

Zone

Zone

Zone

I C I L.V. I post. I Zone I S"

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[ Goniatites crenistria-------

• Entogonites grimmeri • Goniatites hudsoni • Girtyoceras sp.

-Neoglyphioceras spirale • Praedaraelites culmiensis

Goniatitesjimbriatus--Paraglyphioceras semistriatus-

• Goniatites (?) globostriatus

..... Paraglyphioceras rotundum

Nomismoceras vittiger ••1--••-----••

• Hibernicoceras striatosphaericum

Goniatites spirifer ....

250cm

• Sulcogirtyoceras burhennei

Paraglyphioceras radiatum •

• Girtyoceras brueningianum •Neoglyphioceras sp.

Amsbergitesfalcatus • Paraglyphioceras cf. elegans • Amsbergites cf. gracilis •

Hibernicoceras sp . ....

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Sudeticeras crenistriatum •


101

Arnsbergites falcatus (RoEMER 1850) enters at 4.60m, and at 5.20m goniatites of the genus Pa.raglyphioceras are common, comparable to Paragl. elegans (BrsAT 1928). The Arnsbergites gracilis Zone begins at 5.50m, where the first Hibernicoceras is accompanied by Arnsbergites sp. The same occur together with Nom. vittiger at 5.80m. From 6.20 to 7.20m, Neoglyphioceras spirale (PHILLIPS 1836) indicates the Neoglyphioce ras spirale Zone, and is extremely frequent on some bedding surfaces. In between these hori zons, individuals of Arnsbergites cf. gracilis as well as different species of Hibernicoceras occur. A rather rich fauna could be collected especially in the marly claystone at 7.20m, where

Nom. vittiger and Praedaraelites culmiensis (KoBOLD 1933) are also common, providing a good index horizon for supraregional correlations. At 8.50 and 8.90m, several claystone horizons yielded a fauna composed of Paraglyphio ceras rotundum BRUNING 1923, Hibernicoceras striatosphaericum (BRtiNING 1923), Girtyoce ras brueningianum (ScHMIDT 1925), and Sulcogirtyoceras burhennei (BRUNING 1923), a fauna well known from one distinct calciturbidite bed from the Kulmplattenkalk region (KoRN 1988). Neoglyphioceras spirale and Hibernicoceras ultimum KoRN 1988 have been collected 40 cm above this horizon. On a few bedding planes at 10.20m, Neoglyphioceras sp. gives a weak indication of the Neoglyphioceras suerlandense Zone, and higher in the section, the Lusitanoceras poststriatum Zone is present at the silicified carbonate beds at 14.50m. Here, Lusitanoceras poststriatum (BRUNiNG 1923) is very abundant and accompanied by Sudeticeras crenistriatum (BrsAT 1928). 3.2

Berge, Wenne River section

Already described by RuPRECHT (1937), this section best exposes a fossil-rich succession of upper Late Visean sedimentary rocks. It is located 1.2 km southwest of Wennemen on the right bank of the Wenne river. The section is mainly composed of claystones, marly shales and cal citurbidites, which decrease in frequency towards the top of the section (Fig. 2). Near the base, the Actinopteria Shale is intercalated as an approximately 2.50m thick portion, consisting mainly of alum shales. The section begins in the rotundum Zone [observation by RuPRECHT, who mentioned "Goniatites striatus" from a bed 2.50m above the base of the section]. Between 6.50m and 7.50m above the base, crushed specimens of Neoglyphioceras (probably N. suerlandense KoRN 1988) were collected from three different shaly horizons, giving an indication of the Neogly phioceras suerlandense Zone. Actinopteria persulcata (MeCoY 1851) occurs frequently in an alum shale horizon at 9 m [RuPRECHT (1937) mentioned this index fossil from three layers between 8.00m and 10.40m]. Lusitanoceras poststriatum (BRUNING 1923) is frequent in two claystone layers of 14.50 and 15 m above the base. Especially the higher horizon contains numerous specimens, which are accompanied here by a species of Lusitanites (most probably L. circularis KoRN 1988). Higher horizons yielded only few goniatite remains, which can be attributed to the genus Lyrogonia-

Fig. 1. The Late Visean In den Dieken section along the road Affeln - Langenholthausen with its con tent of ammonoid species. Abbreviations: fim. Z. =fimbriatus Zone, falc. falcatus, gr. =gracilis, post. = poststriatum, L.V. C. Late Visean C. =

=

Late Visean B

Late Visean C suerlandense Zone

rotundum Zone

• [Paraglyphioceras sp.] Neoglyphioceras cf. suerlandense ___.

Lusitanoceras poststriatum ....._.. Lusitanites circularis •

�

�

•

Lyrogoniatites sp. •

• Sudeticeras splendens •

Lyrogoniatites liethensis

Actinopteria persulcata •

Caenolyroceras chalicum Cousteauceras costatum Girtyoceras cf. goii

Late Visean C poststriatum Zone

liethensis Zone

• • •

Namurian A chalicum Zone

navalis Zone tr:l

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250cm

Caenolyroceras chalicum Cousteauceras costatum Girtyoceras sp.

-

Edmooroceras wedekindi

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Emstites navalis

Emstites schaelkensis ... Edmooroceras pseudocoronula- Edmooroceras tornquisti ....... Cousteauceras? involutum • Edmooroceras medusa

._.__


103

tites (at 19.80 and 22 m). Lyrogoniatites liethensis KoRN 1988 and Sudeticeras splendens (BrsAT 1928) were found at 25.50 m. A shaly horizon very rich in goniatites is exposed at the top of the section (27.60 m), where Caenolyroceras chalicum KoRN 1988 is associated with Cousteauceras costatum (RuPRECHT 1937) and Girtyoceras cf. goii KoRN 1988. 3.3

Edelburg section

In the abandoned quarry southeast of Edelburg between Menden and Hemer, the highest part of the Kulmplattenkalk Formation and its transition to the Hangende Alaunschiefer was ex posed. Especially at this transition, many different horizons yielded crushed ammonoids of three successive zones (Fig. 2). Lusitanoceras poststriatum (BRUNING 1923) could be collected in crushed specimens in the middle of the exposed succession, about 20 meters above the Actinopteria Shale. A conspicuous horizon, which can be used for orientation, is the 65 cm thick limestone bed near the top of the section. 9.9 m below this bed, impressions of Caenolyroceras chalicum KoRN 1988 as well as Cousteauceras costatum (RuPRECHT 1937) could be collected, providing evidence of the Caenolyroceras chalicum Zone. From 2.75 m to directly below the thick limestone, a fauna consisting of Emstites navalis KoRN"1988 and Edmooroceras wedekindi (BRliNING 1923) was found in several shaly horizons. Above the limestone bed, only the first of these two species occurs in a single horizon, and Emstites schaelkensis (BRUNING 1923) enters immediately above it. At 20 cm, the fauna con sists also of Edmooroceras pseudocoronula (BrsAT 1950) as well as Edmooroceras tornquisti (WOLTERSTORFF 1899), which both have their first occurrences. A similar fauna could be detected at 80 and 135 m. 4:

Stratigraphical sections in South Portugal and their stratigraphical interpretation

4.1

Praia de Murra�ao

This section, which best exposes the Late Visean succession of the South Portuguese Zone, and which is regarded as a standard section for the fauna! succession, is located at the cliff immedi ately above the Murrac;.:ao Bay (FEro & LOMBARD 1958), 6 km southwest of Bordeira (Figs. 3, 4). The beds dip steeply towards the north and are slightly overturned. The profile begins at the top of the cliff with marly, dolomitic shales of the lower of the two members composing the Murrac;.:ao Formation, the Pedra das Safias Member. From this member, goniatites could not be collected from this unit. The upper of the two members, the Vale Figueira Member, is exposed with a thickness of about 36 meters. The contact with the Pedra das Safias Member is sharp; towards the top of the section, the outcrop ends in a fault zone, which does not allow to study the continuation

Fig. 2. The Late Visean Berge and Edelburg sections with their content of ammonoid species. Abbrevi ations: eh. Z. chalicum Zone. =

D. KoRN and K. HoRN

104 200m

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Brejeira Formation Legend for the Quebradas and Murra�ao sections

Quebradas Formation Vale Figueira Member Pedra das Safias Member Bordalete Formation

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Murra�ao Formation

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nodular limestone mar!

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platy shale

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