MORPHOLOGY AND STRATIGRAPHIC DISTRIBUTION OF PUTATIVE TINTINNID FOSSILS FROM THE TSAGAAN OLOM GROUP, MONGOLIA

Neoproterozoic carbonate successions have become an important new taphonomic window into the fossil record of eukaryotes. One of the most notable examples is the ca. 662–635 Ma Taishir Formation (Tsagaan Olom Group, Zavkhan Terrane, Mongolia), which has yielded multiple organic and agglutinated eukaryotic fossil forms. Here, we examine more closely the morphology and taxonomy of organic eukaryotic fossils interpreted as remains of putative ciliate loricae from the Taishir Formation and the overlying Ediacaran Ol Formation of the Tsagaan Olom Group. We document morphological diversity in fossils recovered from carbonate macerates through both external shape and size as well as wall ultrastructure, and compare our data to morphological studies on both fossil and modern tintinnid loricae. In addition, we document the occurrence and morphology of macroscopic organic warty sheets (MOWS) which are interpreted as putative red algae. We also present the first high resolution record of fossiliferous versus non-fossiliferous samples through 231 samples from the Taishir and Ol Formations; this record helps to reveal potential controls on fossil preservation in these cap carbonate successions. The Tsagaan Olom Group fossils increase the diversity of eukaryotic fossils from the Cryogenian and early Ediacaran and indicate the presence and persistence of diverse ecosystems during this critical period of Earth history.