Biostratigraphy, magnetostratigraphy, and geochronology of lower Miocene Aoerban strata in Central Inner Mongolia

摘要

The Aoerban region of central Inner Mongolia, China is an important early Miocene fossil site that contains a diverse mammalian record unrivaled by other Asian sites of similar age. In this paper, we present lithostratigraphic, iostratigraphic, and magnetostratigraphic data from Aoerban Formation to better understand faunal changes between the Xiejian and Shanwangian Chinese Land Mammal ages. With new biochronological constraints, magnetochrons in the Aoerban Formation can be correlated to C6An.2n to C5Cr with an age range of 20.71-16.72 Ma of the Astronomically Tuned Neogene Timescale (ATNTS2012). The strata of the Aoerban region contain a number of important mammalian First Appearance Data, including several morphotypes of deer (Cervidae), horses (Anchitherium), pika (Alloptox), cricetid rodents (Megacricetodon), and possibly the local earliest record of gomphotheres (i.e., the Proboscidea event). Although the ranges for most of these taxa are still poorly known, some of them, alone or in combination, are useful in defining the base the Shanwangian Land Mammal Age. Within this finely calibrated chronologic framework, the faunas of the Aoerban region are important for better understanding mammalian evolution, biogeography, and paleoenvironment.