REGIONAL PALEOECOLOGY OF NEAR-FIELD MARINE FAUNAS DURING THE LATE PALEOZOIC ICE AGE, WESTERN ARGENTINA

The late Paleozoic Ice Age (LPIA) has long been known as an important climatic event in Earth’s history. The end of the LPIA is the only example in Earth’s history where a vegetated and biologically complex Earth transitioned from a bipolar icehouse to a greenhouse state. Recent studies show that LPIA climate changes broadly affected marine invertebrate faunas: glaciations decreased origination and extinction, and long-term, gradual global warming during the final deglaciation altered paleocommunity composition. Regional far-field studies demonstrate that LPIA shallow tropical paleocommunities were stable or weakly distinguishable, and comprised of similar sets of eurytopic taxa.

Regional effects of LPIA glaciation and glacial retreat on high paleolatitude (“near-field”) marine biotas have received very little attention. We hypothesized that glacial to post-glacial fluctuations in near-field settings were not conducive for community stability. It was predicted that near glacial margins, faunas would exhibit characteristics indicative of low oxygen and high sedimentation, including low diversity, small body size, and opportunistic behavior.

The southwestern margin of Gondwana (present-day Argentina) has been shown to have a complex history of interacting tectonism, climate, and sea-level changes. Glacial and post-glacial faunal assemblages were examined in the Paganzo, Río Blanco, and Tepuel-Genoa basins of northwestern and southwestern Argentina. These were compared in order to gain environmental perspectives on the effects of deglaciation on biota.

Diversity and abundance data from northwestern Argentina reflects that ice-proximal environments proved physiologically stressful to organisms; however, opportunistic assemblages successfully exploited ice-distal settings. Following glaciation, the fauna of northwestern Argentina diversified and became increasingly ecologically complex during two marine transgressions. In comparison, ice-distal faunal assemblages in southwestern Argentina were compositionally different than those in northwestern Argentina, yet maintained high diversity. It is interpreted that paleocommunity establishment and diversification in western Argentina during the LPIA was mostly dependent upon localized environmental conditions.