Lithostratigraphy of a long, fossiliferous Oligocene sequence: Revisiting Saint Jacques, Nei Mongol, China

For a hundred years the Saint Jacques area has been known to produce rich Oligocene vertebrate fossils, yet only handful of previous studies have focused on this area. Since 2010, we conducted 12 field expeditions Jacques, and here report findings from our paleontological excavations stratigraphical investigations. Twenty-two fossiliferous blocks across are recognized chronostratigraphic framework established aid fossil collection. Fossil-mammal materials recovered in situ 1635 localities additionally surface sediments. Fossiliferous correlated by lithological similarity lateral tracing. Lithologically, is mainly composed reddish silty mudstone muddy siltstone, with three distinctive layers grayish white sandstone. The measured composite stratigraphic column spans 239 meters divided into lithostratigraphic units. Contrary knowledge that contains two mammalian assemblages, preliminary biostratigraphic analysis small mammals shows documents successive faunal transition Eocene possibly early Miocene. hyracodontid perissodactyl Ardynia , ctenodactyloid rodent Gobiomys basal Glires Gomphos bottom litho-units imply presence Eocene–Oligocene boundary, while mammal assemblage top units similar Miocene faunas northern China Mongolia. Thus, rock strata likely span through Miocene, bracketing an entire sequence within. In sum, re-exploration greatly expanded taxonomic coverage collection This long, makes important record for studying Transition. Further study will contribute range paleoenvironmental questions.