Upper Cenomanian–Lower Turonian Ammonoids from the Saxonian Cretaceous (Lower Elbtal Group, Saxony, Germany)

Upper CenomanianLower Turonian ammonoids from the Saxonian Cretaceous (lower Elbtal Group, Saxony, Germany) MARKUS WILMSEN & EMAD NAGM The Upper Cenomanian to Lower Turonian ammonoid fauna of the Saxonian Cretaceous (Elbtal Group, Saxony, Ger- many) has been revised based on the study of 270 specimens hosted in the Museum für Mineralogie und Geologie (MMG) of the Senckenberg Naturhistorische Sammlungen Dresden. In total, 12 species have been identified and, based on this revision, a number of ammonoids are now reported and/or illustrated for the first time from the Elbtal Group of Saxony: Euomphaloceras septemseriatum, Neocardioceras juddii barroisi, Watinoceras coloradoense, Spathites (Jeanrogericeras) reveliereanus, Sciponoceras gracile and Scaphites equalis. The study demonstrated the presence of all Upper Cenomanian and Lower Turonian standard ammonite biozones in the lithostratigraphic succession of the lower Elbtal Group: the lower Upper Cenomanian Calycoceras naviculare Zone (represented by the Oberhäslich For- mation), the mid- and upper Upper Cenomanian Metoicoceras geslinianum and Neocardioceras juddii zones (represented by the Dölzschen Formation), and the Lower Turonian Watinoceras coloradoense and Mammites nodosoides zones (represented by the Brießnitz Formation). The ammonoid fauna from the Saxonian Cretaceous is dominated by strongly ornamented and widely distributed Acanthoceratidae. • Key words: Upper Cretaceous, Saxo-Bohemian Creta- ceous Basin, ammonites, taxonomic revision, biostratigraphy. WILMSEN,M.&NAGM, E. 2013. Upper Cenomanian–Lower Turonian ammonoids from the Saxonian Cretaceous (lower Elbtal Group, Saxony, Germany). Bulletin of Geosciences 88(3), 647–674 (18 figures). Czech Geological Sur- vey, Prague. ISSN 1214-1119. Manuscript received September 26, 2012; accepted in revised form January 25, 2013; published online July 3, 2013; issued July 3, 2013. Markus Wilmsen (corresponding author), Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie, Sektion Paläozoologie, Königsbrücker Landstr. 159, D-01109 Dresden, Germany; [email protected] • Emad Nagm, Geology Department, Faculty of Science, Al-Azhar University, Assiut, Egypt; [email protected] In Saxony, the area between Meißen, Dresden, Pirna and studied in considerable detail (e.g., Geinitz 1839–1843, the Czech border is characterized by sedimentary rocks of 1849, 1871–1875; Petrascheck 1902; Wanderer 1909; early Late Cretaceous (Cenomanian–Lower Coniacian) Tröger 1967, 1969, 2003). age, more-or-less following the river Elbe valley (Fig. 1A). The ammonites of the Saxonian Cretaceous have for The lithofacies of these Cretaceous strata is dominated by the last time been monographed by Petrascheck (1902) marine siliciclastics and marls or marly limestones over a century ago. Since those times, only some papers (so-called Pläner). Lithostratigraphically, they are combi- have been published dealing with individual taxa [e.g., ned in the so-called Elbtal Group (Tröger & Voigt in Nie- Tröger 1968 on Hyphantoceras reussianum (d’Orbigny); buhr et al. 2007), which forms an important link between Köhler 2001 on Turrilites (T.) cf. scheuchzerianus Bosc; the temperate Boreal shelf of northern and northwestern Wilmsen & Mosavinia 2011 on Schloenbachia varians Europe and the Tethyan warm-water areas to the south. (J. Sowerby)]. Thus, a comprehensive systematic revision The Elbtal Group was deposited in a relatively narrow was long overdue (for the Bohemian and Moravian part of strait between the Westsudetic and the Mid-European is- the Saxo-Bohemian Cretaceous Basin, Cenomanian– lands and shows strong relationships in terms of facies and Lower Turonian ammonites have been revised in more re- palaeontology to contemporaneous strata from the Bohe- cent times by Houša 1967; Konečný & Vašíček 1983, mian Cretaceous Basin towards the southeast. The Saxon- 1987; and Vašíček 1989). In this first part, we focus on the ian Cretaceous is a classical topic of geognostic research in Upper Cenomanian–Lower Turonian ammonite fauna. Germany and its palaeontology and stratigraphy have been The few ammonites from the Lower Cenomanian Meißen DOI 10.3140/bull.geosci.1390 647 Bulletin of Geosciences Vol. 88, 3, 2013 Formation have been excluded from the revision; they have (eustatic) rise of sea-level (plenus Transgression of au- already been treated in some recent papers (Dietze 1960, thors) resulted in the drowning of many islands and the Köhler 2001, Wilmsen & Mosavinia 2011). A second part onlap of the Dölzschen Formation (proximal fine-grained on the Middle–Upper Turonian ammonites of the Saxonian sandstones grading into silty spiculitic marlstones; Cretaceous will follow (Nagm & Wilmsen in prep.). “Unterer Pläner” or “plenus-Pläner”) onto formerly emergent basement areas, not only in Saxony but also in many parts of the Bohemian Cretaceous Basin (e.g., Žítt et al. Geological setting 1998, 2006, 2010) as well as on the opposite side of the Bo- hemian Massif in NE Bavaria (Wilmsen et al. 2010a, b; Palaeogeographically and in terms of (bio-)facies, the Elb- Richardt et al. 2013). tal Group is mediating between the Tethyan-influenced After the levelling of the pre-transgression topogra- Bohemian Cretaceous in the southeast and the Boreal phy during the Late Cenomanian, more uniform sedimen- North German shelf sea in the northwest (Fig. 1B, C). tation patterns became established during the Turonian. The Saxonian Cretaceous Basin has a special palaeogeo- In the Early Turonian, the still relatively narrow strait be- graphic position between the Westsudetic Island in the tween the Westsudetic Island and the Bohemian Massif northeast and the Osterzgebirge as an emergent part of the (Osterzgebirge) was characterized by cross-bedded, tid- central Mid-European Island in the southwest. Today, the ally influenced sands (Schmilka Formation; see Voigt basin fill is preserved in a tectonic halfgraben, the active 1999, Mitchell et al. 2010). These shallow-water deposits northeastern margin is represented by the Lausitz Fault grade, with a transitional facies of bioturbated, silty-argil- (Fig. 1A). The facies and thickness changes of the Creta- laceous, fine-grained sandstones and silts, into fine- ceous strata within the Saxonian Cretaceous Basin grained basinal deposits characterizing the “Pläner- show that at least from the Middle Turonian, deposition Fazies” of the Dresden area (calcareous siltstones and was influenced by syn-sedimentary activity of the Lau- silty marls of the Brießnitz Formation; Fig. 2). The sitz Fault (Voigt 1994, Kley & Voigt 2008). The Lausitz Brießnitz Formation ranges into the lowermost Middle Fault is joined by a number of other NW–SE-trending Turonian and is overlain by fine-grained, calcareous structural elements in Middle Europe (e.g., T. Voigt et basinal deposits (Pläner sediments of the Räcknitz For- al. 2006, Niebuhr et al. 2011) that have been characteri- mation) while in the Elbsandsteingebirge (“Saxonian zed by compression since Turonian times (Kley & Voigt Switzerland”), the sandstones, sandy marls and green- 2008). sands of the Postelwitz Formation have been deposited, The following brief geological overview follows the re- sourced from the rising Lausitz Massif. vised lithostratigraphy of the Elbtal Group (Tröger & Voigt in Niebuhr et al. 2007; see Fig. 2). A first marine transgression from the north took place in the late Early Ceno- Conventions manian, reaching the area of Meißen (Meißen Formation). Conglomeratic bioclastic limestones indicate high-energy More than 270 specimens have been studied, mostly well nearshore deposition. Marine Middle Cenomanian is un- to moderately well preserved (composite) internal known, but the back-filling of fluvial valleys (Nieder- moulds. All specimens, except one (Scaphites equalis So- schöna Formation; see Voigt 1998) indicates a continuing werby, M. Fengler collection, Dresden) are kept in the base-level rise. The major transgression occurred during Museum für Mineralogie und Geologie (MMG) of the the Late Cenomanian, submerging a pronounced relief of Senckenberg Naturhistorische Sammlungen Dresden depressions and cliffs related to the different erosional re- (SNSD), Germany (repository SaK). Most of the ammo- sistance of the basement. In that time, a chain of isolated noids are historical specimens that have been collected cliffs and islands was located at the southwestern margin of in the nineteenth and twentieth century, and some of the basin (Voigt 1994, Voigt et al. 1994, S. Voigt et al. them have already been illustrated in earlier publications 2006, Wilmsen et al. 2011). Clastic sediments were pre- (Geinitz 1839–1843, 1849, 1871–1875; Petrascheck 1902; dominantly sourced from the southwest (Osterzgebirge as Wanderer 1909). If a specimen is re-figured herein, this is a part of the Bohemian Massif) and the northeast (West- stated in the captions. sudetic Island). The Late Cenomanian transgression took Suture terminology follows Wedekind (1916) as put for- place in two major pulses: in the early Late Cenomanian ward by Kullman & Wiedmann (1970) and revised in parts (Calycoceras naviculare Zone), the shallow-marine con- by Korn et al. (2003): E = external lobe, A = adventive lobe glomerates, fossiliferous sands and argillaceous silts of the (= lateral lobe, L, of former nomenclature), U = umbilical Oberhäslich Formation (“Unterquader”) have been depos- lobe, I = internal lobe. A Vernier Caliper has been used to ited, usually missing on swells. The second

Load more