Weiach, Benken, Leuggern) and Southern Germany (Weizen, Freudenstadt)
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Rivista Italiana di Paleontologia e Stratigrafia (Research in Paleontology and Stratigraphy) vol. 126(2): 363-394. July 2020 PALYNOLOGY AND CHEMOSTRATIGRAPHY OF MIDDLE TRIASSIC SUCCESSIONS IN NORTHERN SWITZERLAND (WEIACH, BENKEN, LEUGGERN) AND SOUTHERN GERMANY (WEIZEN, FREUDENSTADT) PETER A. HOCHULI1†, ELKE SCHNEEBELI-HERMANN1*, PETER BRACK2, KARL RAMSEYER3 & DANIEL REBETEZ3 1Palaeontological Institute and Museum, University of Zurich, Karl Schmid-Strasse 4, CH-8006 Zurich, Switzerland. E-mail: [email protected] 2Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, CH-8092 Zurich, Switzerland. E-mail: [email protected] 3Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, CH-3012 Bern, Switzerland. E-mail: [email protected] *corresponding author To cite this article: Hochuli P.A., Schneebeli-Hermann E., Brack P., Ramseyer K. & Rebetez D. (2020) - Palynology and chemostratigraphy of Middle Triassic successions in Northern Switzerland (Weiach, Benken, Leuggern) and Southern Germany (Weizen, Freudenstadt). Riv. It. Paleontol. Strat., 126(2): 363-394. Keywords: Palynology; Palynofacies; Germanic Basin; Middle Triassic; Anisian; Ladinian. Abstract. New Anisian to Ladinian palynology, palynofacies and stable carbon isotope records are reported for the Middle Triassic from deep Swiss wells (Weiach, Benken, Leuggern), well B3/13 (Weizen, S-Germany) and the type area of the Freudenstadt Formation in southern Germany. A wide spectrum of moderately to well-preserved palynomorphs represent a high Middle Triassic plant diver- sity. Based on the distribution of diverse spore-pollen assemblages five Anisian Palynozones (A–E) and two Ladinian ones (F, G) are differentiated. Throughout these Palynozones the occurrence of spores and pollen, assigned to plant groups so far known only from the Palaeozoic, shed a new light on the evolution of plant assemblages during the Triassic. The comparison of Palynozones A–G with palynostratigraphic schemes from the central part of the Ger- manic Basin and from the Tethyan realm demonstrate the regional variability of marker species ranges – especially for the Anisian. In agreement with the lithological record, two prominent transgressive events (Lower Muschelkalk, Upper | downloaded: 3.6.2020 Muschelkalk) are indicated by increased abundances of marine particulate organic matter in palynofacies data. Mar- ginal marine influence is documented at the base of the studied interval, comprising the Buntsandstein and the base of the Lower Muschelkalk. Carbonate carbon isotopes data show a negative shift at the boundary between Lower and Middle Muschelkalk. Coincidently, a prominent change in relative abundances of climate-sensitive plant groups (e.g. Triadispora spp. vs. Pteridophytes) indicate a change to relatively dryer climatic conditions during the Middle Muschelkalk. STATUS OF ANISIAN PALYNOLOGICAL (e.g., Looy et al. 1999). Palynology is an important RESEARCH AND GOAL OF THE PRESENT tool to assess the diversity of floras, since plant STUDY macro-remains are comparatively rare and show a more erratic geographic and stratigraphic distribu- The Middle Triassic is often considered to tion. In most areas, the Early Triassic is character- represent the time when plants had fully recovered ised by poorly diversified palynofloras. In the Ger- after the Permian–Triassic and Early Triassic crises manic Basin and in the Southern Alps Early Triassic https://doi.org/10.7892/boris.143983 palynological assemblages often consist of a few Received: July 1, 2019; accepted: March 24, 2020 species, mostly spores (e.g., Orłowska-Zwolińska source: 364 Hochuli P.A., Schneebeli-Hermann E., Brack P., Ramseyer K. & Rebetez D. 1984; Reitz 1988; Spina et al. 2015), whereas in oth- outcrops of Middle Triassic (Anisian – Ladinian) er areas, parts of the Early Triassic yield well-diver- Muschelkalk successions of the southernmost part sified assemblages (e.g., Barents Sea, see Vigran et of the Triassic Germanic Basin (northern Swit- al. 2014 and refs. therein; and Antarctica, Lindström zerland and southern Germany) (Fig. 1). Unfortu- & McLoughlin 2007). In contrast Middle Triassic nately, the temporal calibration of data from marine palynomorphs seem to be much more diversified, sections in the epicontinental Germanic domain but for some reasons Anisian assemblages of the is hampered by poor and only punctual age-diag- Germanic Basin are relatively poorly known, and nostic biostratigraphic constraints. In spite of this studies including more than a few marker species shortcoming, we consider the few ammonoid data are rare (i.e., Heunisch 1999, in press; Orłowska- from this domain as principal guides for a reliable Zwolińska 1985). Kürschner & Herngreen (2010) chronostratigraphic comparison with open marine compiled the biostratigraphic results of numerous counterparts of Western Tethys where well-defined studies from the Germanic realm and proposed a Middle/Upper Anisian (Pelsonian - Illyrian) to La- new zonation scheme (for additional references see dinian (Fassanian - Longobardian) successions have Kürschner & Herngreen 2010). Attempts have been been described (e.g., Brack et al. 1999, 2005). Thus, a made to correlate the palynological successions of combination of available stratigraphic information the Germanic realm with the better-calibrated zona- from southern Germany and northern Switzerland tion scheme from the Southern Alps and Hungary allows us to compare the new data within a larger (e.g., Van der Eem 1983; Brugman 1986; Kürschner framework of Triassic successions throughout the & Herngreen 2010), but this correlation is ham- Germanic Basin and even further. pered by pronounced regional differences in the composition of the palynological assemblages and STRATIGRAPHIC FRAMEWORK AND AGE by possibly diverging ranges of the marker species CONSTRAINTS (van der Eem 1983; Brugmann 1986; Kustatscher & Roghi 2006; Hochuli et al. 2015). Moreover, the The Triassic System was established in south- ranges of most of the few stratigraphic marker spe- western Germany on the basis of the classical tri- cies generally mentioned lack independent age con- partition of Buntsandstein, Muschelkalk and Keu- trol. per (e.g., Hagdorn & Nitsch 2009). The assembly of For some markers similar ranges are generally clastic and carbonate sediments and evaporite inter- assumed over distant areas (e.g., Densoisporites nejbur- vals extends over a vast area of central and northern gii and Stellapollenites thiergartii); other markers are Europe and characterizes the infill of the epiconti- restricted to the Tethyan realm (e.g., Strotersporites nental Germanic Basin. Connections between the tozeri) or to the Germanic Basin (e.g., Tsugaepollenites restricted basin and open marine shelf areas sur- oriens), respectively. rounding western Tethys existed temporarily during Contrary to the Anisian, terrestrial or mar- Middle Triassic times (e.g., Brack et al. 1999; Ber- ginal marine sections of the Ladinian and younger nasconi et al. 2017). intervals attracted more interest and were exten- Middle Triassic sediments of southern Ger- sively studied (e.g., Scheuring 1970; Heunisch 1986; many and northern Switzerland (Fig. 1) formed in a Mädler 1964; Klaus 1964; Orłowska-Zwolińska somewhat peripheral portion of the Germanic Ba- 1983). Numerous reports have been generated by sin, far away from the marine gates. Stratigraphic Dutch palynologists although only relatively few intervals in this sector are thus generally thinner publications are accessible in the literature (for lists when compared with successions in basin portions see Kürschner & Herngreen 2010 and Heunisch in of central/northern Germany. press). Detailed range charts are essentially missing. Outcrops of Middle Triassic sediments are Thus, in this study reference is made only to pub- scattered throughout the eastern Jura mountains lished reports. and somewhat more continuous along a rim south In an attempt to improve coverage and age and east of the Black Forest Massif (Fig. 1). In ad- calibration in this article we present and discuss jacent areas of northern Switzerland Triassic suc- new palynological and palynofacies results along cessions are known from a number of shallow and with stable carbon isotope data from cores and deep boreholes. Palynology and chemostratigraphy in Middle Triassic successions in N. Switzerland and S. Germany. 365 Fig. 1 - Distribution of Lower to 8° E FREUDENSTADT Haas Middle Triassic outcrops 50 km (Buntsandstein and Mu- Glatten schelkalk) in northern outcrops Switzerland and southern well data Germany (after Rupf & 55 m Kaiseraugst Fm. Nitsch 2008 [in Hagdorn & F r a n c e (Lower Muschelkalk) Nitsch 2009]; Jordan 2016). isopachs Isopachs of the Lower Muschelkalk are modified Rhein and extended after Jordan (2016, Fig. 5). The locations of outcrops and well data 50 m G e r m a n y referred to in this study are FREIBURG Donau indicated. The thick brown 48° N Muschelkalk line perpendicular to the Buntsandstein 45 m isopachs marks the trace of 40 m the pannel of projected stra- Wutach- 35 m tigraphic data of Fig. 2 a,b. schlucht 30 m 25 m Weizen Siblingen Black Forest (Schwarzwald) Basement Ühlingen 20 m Benken 15 m Leuggern Thur Böttstein Weiach BASEL Riniken ZÜRICH Aare Switzerland The correlation of the borehole and outcrop ing reports, e.g., by Nagra (National Cooperative for successions of this study relies on the tracing of the Disposal of Radioactive Waste). marker beds and cycles along with general strati- In the