«Coniacian and Santonian inoceramid bivalves from the Gosau-Group (Cretaceous, Austria) and their biostratigraphic and palaeobiogeographic ...»
180 Annalen des Naturhistorischen Museums in Wien 96 A The Santonian inoceramid fauna reflects a more differentiated paleogeographic pattern. In particular, sphenoceramids of the Sph. pachti-cardissoides-group, of the Sph. pinniformisgroup and the Sph. patootensiformis-group, common and widespread in the Northern Temperate Realm are apparently missing in the Gosau-group. They are regarded as a boreal element. Further research in the higher parts of the Grabenbach formation (p. 187) and in the Hochmoos formation (p. 187) is needed for palaeogeographical conclusions. On the other hand, cordiceramids of the C. muelleri-group seem to be tethyan. Sphenoceramus cardissoides (GOLDFUSS) together with the occurrence of Cladoceramus undulatoplicatus (ROEMER) could indicate migrations directed from north to south in the Lower Santonian. The scarcity of Cordiceramus muelleri (PETRASCHECK) in the NW German-Polish basin could be interpreted as an indication of migrations from south to north in the Upper Santonian. In this context the rare occurrence of nerineids (BAF collection, unregistered; collection of the Staatliches Museum für Mineralogie und Geologie zu Dresden; NHMW collection) and the solitary coral Cyclolites (BAF collection) in the Upper Santonian Heidelberg- and Heimburg Formations (GEINITZ 1848-1849: AÌ-A2, SCHROEDER & DAHLGRÜN 1927) of the southern Subhercynian Cretaceous basin near Blankenburg should be mentioned.
Short description of the localities investigated:
A) T h e S t. W o l f g a n g basin 1., 2.
Bad Ischi (tunnel section):
Tunnel section N of Bad Ischi approximately 600 metres long. Fossils were collected by Wolf-Peter MAHERNDL (Bad Ischi) while construction was in progress. Bed by bed collecting and measurement of the section was impossible. Investigation of inoceramids revealed two different faunas: one of Lower Coniacian, the other of Middle Coniacian age. Predominant Forreste ria (F.) alluaudi (BOULE, LEMOINE & THÉVENIN) is thought to belong to the Lower Coniacian (1.) because none of the Middle Coniacian ammonite sites in the neighbourhood yields even a single specimen of Forresteria. Peroniceratidae represent the Middle Coniacian (2.).
Peroniceras (Peroniceras) tridorsatum (SCHLÜTER) Volviceramus koeneni (G. MÜLLER) Platyceramus mantelli mantelli (MERCEY) A g e : Lower to Middle Coniacian; assemblage-zones 21 and 22 according to the scheme established by TRÖGER (1989).
Tetragonites cf. superstes VAN HOEPEN 1921 Peroniceras (P.) tridorsatum (SCHLÜTER) Tissotia sp.
A g e : Middle Coniacian; assemblage-zone 22 (TRÖGER 1989).
4. Schmolnauer Alpe la This site is probably the type locality of Tissotioides haplophyllus. Several individuals and fragments were recently collected by one of us (H. S.) together with Tetragonites, Pseudophyllites, Jimboiceras, Peroniceratidae, Scaphitidae, Baculitidae and large inoceramids. The exposure of about 2 metres thickness is separated by unexposed area from Schmolnauer Alpe Ib. No measurable sequence.
Platyceramus mantelli beyenburgi (SEITZ) Platyceramus mantelli cf. subrhenanus (SEITZ) Mytiloides cf. sublabiatus (G. MÜLLER) Volviceramus koeneni (G. MÜLLER) A g e : Middle Coniacian; assemblage-zone 22 (TRÖGER 1989).
5. Schmolnauer Alpe lb Bivalves are the dominating faunal elements. Barroisiceras haberfellneri and Tissotioides haplophyllus do not occur here. There is no exposure at this site. The fossils were collected near the surface from a layer of less than half a meter thickness. There is no measurable sequence at this site.
Tetragonites cf. superstes VAN HOEPEN Metatissotia sp.
Hauericeras schlueteri (REDTENBACHER) Peroniceratidae, Scaphitidae, Baculitidae Volviceramus koeneni (G. MÜLLER) A g e : Middle Coniacian; assemblage-zone 22 (TRÖGER 1989).
D i s c u s s i o n : The faunas of Schmolnauer Alpe la and lb were still considered as coeval by SUMMESBERGER (1985, p. 150: "Strobl H") and are for the first time separated here.
According to the inoceramids it seems likely that the fauna of Schmolnauer Alpe la with Tissotioides haplophyllus is older than that of Schmolnauer Alpe Ib.
Text-fig. 4. Correlation of Coniacian/Santonian sections of the Gosau basin (Upper Austria/Salzburg) by the local marker fossil "Hemitissotia" randoi GERTH, the appearance of Texanites and by Cladoceramus undulatoplicatus (ROEMER). Numbers indicate excursion stops in KOLLMANN & SUMMESBERGER (1982).
A) Stöcklwaldgraben section: About 120 m of continuously exposed section were measured by KOLLMANN & SUMMESBERGER (1982). The Coniacian/Santonian boundary is based on the first appearance of Texanites quinquenodosus. Nr. 341 indicates the sample number of WAGREICH (1992: 509, fig. 3).
B) The Grabenbach section of about 230 m was measured by KOLLMANN & SUMMESBERGER (1982 and unpublished data).
C) The faulted and not continuously exposed Randobach section is compiled by indication of fossils.
D) The thickness of the inaccessible Edlbach section is estimated. Accessible outcrops are in the riverbed and tributaries.
SANTONIAN -*I-CON I AC I A N ?-?«;S=5;j; »T quinquenodosus I ZIMMERGRABEN) m
SANTONIAN ] CONIACIAN
GRABENBACH FORMATION STREITECK FM. FORM.FORM 184 Annalen des Naturhistorischen Museums in Wien 96 A
6. Schmolnauer Alpe 2 (fauna Strobl III of SUMMESBERGER 1985: 151).
Outcrop on the side of the forest road. There is also no measurable sequence at this site.
Metatissotia robini THIOLLIÈRE Platyceramus mantelli subrhenanus (SEITZ) Platyceramus mantelli cf. subrhenanus (SEITZ) A g e : Middle Coniacian; assemblage-zone 22 (TRÖGER 1989).
7. Paß Gschütt Graben:
Site N of the Paß Gschütt. No ammonites from this locality. Streiteck Formation.
Volviceramus sp. aff. involutus (SOWERBY)
8. Stöcklwaldgraben (Gosau) (Stop 22 of KOLLMANN & SUMMESBERGER 1982: 68, 69).
The section was measured and sampled by KOLLMANN & SUMMESBERGER (1982: 69). Additional collecting was done in 1982 by SUMMESBERGER and KOLLMANN and in 1993 by SUMMESBERGER and TRÖGER. The boundary of the Streiteck and Grabenbach Formations is tentatively drawn above disappearance of the conglomerates and sandstones. Upper Coniacian is recognized on the basis of the presence of Volviceramus involutus (SOWERBY).
9. Stöcklwaldgraben (Gosau) (Stop 21 of KOLLMANN & SUMMESBERGER 1982: 68, 69).
Basal Santonian is indicated by the appearance of Texanites quinquenodosus (REDTENBACHER) and Sphenoceramus cardissoides (GOLDFUSS) ssp. indet. Actaeonella laevis (SOWERBY), common in the Streiteck Formation, becomes abundant in the basal Grabenbach Formation and disappears before "Hemitissotia" randoi GERTH appears at the top of the section.
Volviceramus involutus (SOWERBY) Sphenoceramus cardissoides (GOLDFUSS) A g e : Evidence is present for Upper Coniacian, assemblage-zone 23 and for Lower Santonian, assemblage-zone 26 (TRÖGER 1989).
10. Randobach (Stop 25/26 and 29 of KOLLMANN & SUMMESBERGER 1982): Several metres of Grabenbach Formation are exposed in the riverbed of the Randobach. Stratigraphically lower parts of the outcrop yielded Parapuzosia daubreei (GROSSOUVRE) approximately at the level of the first appearance of Texanites quinquenodosus (REDTENBACHER). Higher up in the section is the type locality of "Hemitissotia" randoi GERTH. This is also the level in which Cladoceramus undulatoplicatus (ROEMER) occurs, the former is of local value for correlation, the latter is widely used to indicate the base of the Santonian. It seems likely that Texanites quinquenodosus and Cladoceramus undulatoplicatus co-occurring in the Mühlbach section of Brandenberg (Tyrol) are separated by few metres of sediment in the Gosau basin (text-fig. 4). Platyceramus cycloides cycloides (WEGNER) was observed by the authors (1993) in the riverbed.
A g e : Lower Santonian; assemblage-zone 26 (TRÖGER 1989) TRÖGER & SUMMESBERGER: Coniacian and Santonian inoceramid bivalves 185 Cladoceramus undulatoplicatus (ROEMER) Platyceramus cycloides cycloides (WEGNER) Sphenoceramus cardissoides (GOLDFUSS)
In the easily accessible basal parts of the large outcrops of the Edelbachgraben, "Hemitissotia" randoi GERTH occurs together with Cladoceramus undulatoplicatus (ROEMER).
A g e : Lower Santonian; assemblage-zone 26 (TRÖGER 1989)
Five sections separated by faults were measured by KOLLMANN & SUMMESBERGER (1975/76) before dam construction destroyed large parts of these formerly excellent outcrops. The Grabenbach Formation is exposed throughout up to the confluence with the Tauerngraben (basal Hochmoos Formation). The absence of Actaeonella laevis indicates, together with a single specimen of "Hemitissotia" randoi GERTH, that the basal parts of the Grabenbach section more or less continue the section of the Stöcklwaldgraben. Here the occurrence of Texanites quinquenodosus (REDTENBACHER) does not represent the first appearance of the species.
Platyceramus cycloides ahsenensis SEITZ and Cordiceramus cordiinitialis (SEITZ) collected in 1993 by the authors indicate assemblage-zone 27 (TRÖGER 1989), which is tentatively middle Santonian. Higher up in the section, Muniericeras gosauicum (HAUER) allows correlation with the downstream locality of the Randobach (stop 29 of KOLLMANN & SUMMESBERGER 1982).
Muniericeras gosauicum (HAUER) "Hemitissotia" randoi GERTH Texanites quinquenodosus (REDTENBACHER) "Muramotoceras" sp. indet.
Platyceramus cycloides ahsenensis (SEITZ), Cordiceramus cordiinitialis (SEITZ) A g e : Middle Santonian
13. Bibereck (local name "Finstergrabenwandl" at the Zwieselberg forest road; stop 11 of & SUMMESBERGER 1982).
KOLLMANNAmmonites were published by WIEDMANN (1978) and SUMMESBERGER (1979, 1980, 1992), gastropods by KOLLMANN (1980) and bivalves including inoceramids by DHONDT (1987).
The Sandkalkbank Member of the Hochmoos Formation, about 20 m thick, is well exposed along the forest road. Fossils were collected from 1971-1975 while and immediately after the road was constructed.
Placenticeras polyopsis (DUJARDIN) Placenticeras paraplanum WIEDMANN Placenticeras maherndli SUMMESBERGER.
Boehmoceras arculus (MORTON) Boehmoceras krekeleri (WEGNER) Cordiceramus muelleri muelleri (PETRASCHECK), Cordiceramus muelleri germanicus (HEINZ), Platyceramus cycloides ahsenensis (SEITZ).
186 Annalen des Naturhistorischen Museums in Wien 96 A Placenticeras polyopsis (DUJARDIN) is indicative for Santonian, the genus Boehmoceras for Upper Santonian (KENNEDY & COBBAN 1991:185; SUMMESBERGER 1979:122). The association of inoceramids confirms a top Santonian age (lower part of assemblage-zone 29;
Lithologie units (Upper Turonian through Santonian) of the Gosau basin
Streiteck Formation (WEIGEL 1937: 14) The Lower Streiteck Formation comprises nearshore marine conglomerates with sandstone intercalations (offshore transition) of a fan delta environment (WAGREICH 1988: 669). A coal seam with freshwater mollusks indicates paralic to lacustrine environments (STOLICZKA 1860). A recently discovered (H. S. together with P. SKOUMAL 1993) shaly intercalation with Barroisiceras haberfellneri (HAUER) and other marine mollusks (Inoceramus ex aff. kleini G. MÜLLER; det. K.-A. TRÖGER) is a strong indication for Late Turonian age (SUMMESBERGER & KENNEDY, in prep.).
The Upper Streiteck Formation consists mainly of shales with sandy layers. It represents an offshore shelf environment with occasional storm events. The greater part of the formation is of Coniacian age based on the presence of late Coniacian Volviceramus involutus (SOWERBY) and subsequent appearance of Texanites quinquenodosus (REDTENBACHER) near the top of the sequence (Text-fig. 4). Fossils are abundant and concentrated into shell beds.
Grabenbach Formation (WEIGEL 1937: 16) The Grabenbach Formation consists of pelitic shales with occasional sandy/silty storm layers. It was built up under normal shelf conditions (WAGREICH 1988: 670). Fossils are scarce and never occur in lumachelles. Assuming an equal sedimentation rate, the Grabenbach Formation comprises approximately one half of the Santonian (Tab. 15).
Hochmoos Formation (WEIGEL 1937: 16) The Hochmoos Formation is a complex series of fossiliferous shales, sandstones, conglomerates, bioclastic storm layers and the first rudist bioherms and biostromes occurring in the Gosau basin. Conglomerates and sandstones are compared by WAGREICH (1988: 674) with the fan deltas of the Streiteck Formation. Rudists indicate shallow marine environments. In this paper only the top Santonian Sandkalkbank member (WEIGEL 1937, geol. map) is taken into consideration (see above; locality Bibereck).
AcknowledgementsOur thanks are due to Dr. Peter SKOUMAL (Vienna) and Wolf-Peter MAHERNDL (Bad Ischi) who generously gave access to their outstanding private collections. Financial support was provided by the IGCP project 362 "Tethyan and Boreal Cretaceous" and by the Naturhistorisches Museum Wien (K.-A. T.). Both authors are deeply indebted to Dr. H. A. KOLLMANN (NHMW) and Dr. W. J. KENNEDY (Oxford), who helped with discussions, suggestions and corrections. Thanks are due to Dr. O. SCHULTZ (NHMW) for editorial support and to the staff of the Naturhistorisches Museum Wien and the Bergakademie Freiberg. We are especially grateful to Dr. A. V. DHONDT for her detailed review of the paper.
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