Original paper
Extinctions and recoveries in the Allgäu Basin (Northern Calcareous Alps) during the end-Triassic mass extinction
von Hillebrandt, Axel; Urlichs, Max
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 308 Heft 2 (2023), p. 91 - 111
53 references
published: May 31, 2023
manuscript accepted: Apr 16, 2023
manuscript received: Mar 31, 2023
ArtNo. ESP155030802000, Price: 29.00 €
Abstract
The late Rhaetian mass-extinction and recovery patterns are studied along three Triassic-Jurassic boundary sections in the Allgäu Basin (Northern Calcareous Alps). The sedimentological development of the Allgäu Basin from the late Rhaetian until the middle Hettangian is similar to the more ocean-ward and well-studied Eiberg Basin with some major palaeontological and sedimentological differences. This study reveals an at least two stepwise extinction pattern and a rather rapid faunal recovery. The uppermost limestone bed of the Rhaetian Kössen Formation in the Allgäu Basin shows an irregular corroded surface with an iron-manganese crust representing a hiatus. This hiatus coincides with the first step of the end-Triassic mass extinction. The arctic Trochammina sublapidosa group and Eoguttulina liassica, both interpreted as polymorphic pioneer species and opportunistic r‑type strategists, characterize a foraminifer repopulation during the overlying Schlossgraben Beds. The grey Schlossgraben Beds pass gradually into the red Schattwald Beds lacking both calcified organisms and agglutinated foraminifers. At their base, another extinction event occurred. The Schattwald Beds pass into the greyish marls of the Tiefengraben Beds containing layers of the gastropod Tricarilda and foraminifers of the genera Eoguttulina and Oberhauserella. In the middle and upper part of these marls, the foraminifer Praegubkinella turgescens occurs, which serves as a marker of the Triassic-Jurassic boundary. In the middle and upper Tiefengraben Beds, silty to finely sandy limestones and marls are intercalated in the western part of the Allgäu Basin, whereas marls predominate in the eastern part. Ecologically ubiquitous foraminifers Rheophax and Trochammina may be frequent; Eoguttulina is rare. The overlying Allgäu Formation is marked by the appearance of thick limestone beds with bivalves and rare ammonites. Intercalated marls yield ostracods and diverse foraminifer assemblages with a nodosariid dominance. Planularia inaequistriata and the ammonoid Analytoceras sp. indicate a late Hettangian age. Upsection, sponge spicules become more frequent thus indicating a deepening trend. The deposits of the Allgäu and Eiberg basins yield different microfaunas; thus, only a restricted faunal exchange was possible between these basins.
Keywords
Triassic-Jurassic boundary • Foraminifera • Ostracoda • lithostratigraphy • biostratigraphy • palaeoecology • palaeobiogeography