Local versus global effects on changes of fossil diversity: paleoenvironmental interpretation of Triassic faunas of the Balaton Highland (Hungary)

Vörös, Attila (2009) Local versus global effects on changes of fossil diversity: paleoenvironmental interpretation of Triassic faunas of the Balaton Highland (Hungary). Central European Geology, 52 (3-4). pp. 343-358. ISSN 1788-2281

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Abstract

Abstract The formations of the Balaton Highland provide a high-resolution record of various fossil groups (ammonoids, bivalves, brachiopods) from the Early Triassic to the Carnian, with remarkable changes in taxonomic diversity. The local data differ considerably from the gradually increasing global diversity trends of the respective fossil groups. Ammonoids are rare in the Early Triassic; during the Anisian they reach a diversity maximum and remain rather diverse until the Carnian. This is connected to the considerable deepening of the sedimentary basin in the Middle Triassic. The benthic fossil groups show almost inverse local trends. In the Early Triassic, the proliferation of bivalves largely follows the transgressive pulses in the shallow marine setting; brachiopods are represented solely by Lingula specimens. Both the bivalve and the brachiopod diversity culminate in the middle Anisian what is interpreted in terms of extensional tectonic movements: the rocky escarpments of the disintegrated carbonate platforms provided favorable biotopes for sessile benthic organisms. The benthic diversities decreased significantly in the rest of Middle Triassic, which is due to the significant deepening of the local basin floor. The benthic groups reached maximum diversity in the Carnian. This is attributed partly to the filling up and shallowing of the local basin, partly to redeposition in the course of platform progradations, carrying rich fossil shell material from the neighboring shallow marine environments to the basin. Simultaneously, the sudden increase of the humidity (“Carnian pluvial event”) created extensive river systems in the European continent; the increasing supply of organic matter was favorable for the benthos in the marine environments.

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