Marine and Continental Ichnology of Permian-Triassic, High-Latitude Depositional Systems During Greenhouse Conditions: Victoria Group (Beacon Supergroup), Central Transantarctic Mountains, Antarctica

Abstract

Global climate has varied from greenhouse and icehouse conditions, with the vast majority of time spent under greenhouse conditions. We are familiar with the distribution of tracemaking organisms (and the lack of them) at high-latitude (> 60 degrees) settings during this interglacial period. For example, continental macrofauna and flora diversity in Antarctica are depauperate, whereas marine diversity is high with large bodied crustaceans present and abundant and diverse bioturbation. During greenhouse conditions, however, global temperatures are much warmer, with little or no ice present on land or in oceans at high-latitude. As ice sheets collapse and runoff and sediment discharge significantly increase, nearshore and shallow marine settings are overwhelmed with freshwater and terrestrial sediments. The Victoria Supergroup preserves the greenhouse transition and climatic conditions that shaped the ichnology of Permian-Triassic Antarctic environments. Transitional to shallow marine environs of the Lower Permian Mackellar were deposited at ~75–85 degrees S in fluvial-dominated, freshwater-stressed and high sediment input, deltaic environments. Traces are of low diversity, high abundance, and small sized, dominated by vermiform animals and mollusks, and lack such marine indicators as Ophiomorpha, Rhizocorallium, and Zoophycos. Strata typically exhibit low ichnofabric indices (1–3) and very shallow tiering (< 2 cm deep). The Upper Permian Buckley Formation is fully continental in deposition and contains interbedded coal and alluvial sediments of braided river and floodplain environments, deposited at ~75 degrees S latitude during humid, temperate climates. Trace fossils are few and simple in alluvial deposits due to high water tables; however, they are abundant in lacustrine deposits with higher diversity of arthropods and fishes. The Lower to Middle Triassic Fremouw Formation contains strata of alternating alluvial channel and overbank sediments deposited at ~65–70 degrees S latitude. Invertebrate trace fossils show similar patterns in occurrence, diversity, and abundance as those found in low latitude channel deposits, which are low overall. In contrast, traces of plants, invertebrates, and vertebrates in levee, crevasse-splay, proximal and distal overbank settings are much more diverse, abundant, and penetrative in weakly to moderately developed paleosols. Greenhouse conditions produce greater ichnodiversity, and penetration in continental deposits.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015