QUANTITATIVE BIOSTRATIGRAPHIC ANALYSIS OF CENTRAL ASIA UNDERSCORES THE REGION’S IMPORTANCE AS A BIOGEOGRAPHIC PROVINCE

Central Asia lies at a nexus both in terms of geology and evolutionary biogeography. With the convergence of the Indian and Asian plates creating high rates of deformation over broad regions, shortening of the Paleozoic and Mesozoic basement rocks has created a rich history of late Cenozoic sedimentary basins. Additionally, the region remains a biogeographic crossroad, facilitating the intercontinental migrations of distant faunas from North American, Europe, Africa, and Southern Asia. With such an active geological and biological evolution, the utility of temporal constraints is evident. However, the surrounding region has provided few volcanic rocks suitable for radiometric dating. Therefore, while less precise, the biostratigraphic analysis of Central Asia I present is an ideal method for both establishing ages and correlating between disparate basins. The last several decades provided great advancements in quantitative biostratigraphic methods applied to marine microfossils from drill cores. While these newer methods such as RASC (ranking and scaling) and CONOP (constrained optimization) provide a clear improvement over older methods such as graphic correlation, they have yet to be applied to terrestrial vertebrate faunas. Graphic correlation only allows comparison between two stratigraphic columns at a time and is heavily weighted by the initial selection of a type section. Both RASC and CONOP compare all stratigraphic sections simultaneously, eliminating type section bias. Previous vertebrate biostratigraphy methods attempted to predict FADs and LADs with the assumption they are generally minimum estimates. RASC instead establishes average stratigraphic ranges for each taxon and with the add-on of the sister program CASC actually provides confidence intervals for each prediction, reducing the potential error resulting from reworking. Used in conjunction, RASC, CASC, and CONOP provide both a solid evaluation of land mammal ages or zones for Central Asia and a predictive composite column for new late Cenozoic fossil localities. With a high degree of endemicity and migration, Central Asia cannot rely on the European Neogene Mammal Zones. This study aims to support and evaluate the emerging Asian biostratigraphic and geochronologic framework.