Lithofacies classification and sedimentary description of the Khüren Dukh (Choir Basin) fossil site

In this study, we redescribe the geology of fossil-bearing rocks, exposed in the Lower Cretaceous Khuren Dukh locality. This study is based on new data collected during the Mongolian Expedition (ME) in 2019. Previously, the Khuren Dukh Formation at the Khuren Dukh locality had been subdivided into three members (lower, middle, and upper) based on textural features and sedimentary structure of dominant lithofacies assemblages. This study shows that the lower member can be further subdivided into two major lithofacies associations (lithofacies association-1 and 2). Association-1 is characterized by a combination of the interbedded crossbedding of small-grained pebbles and coarse-grain-size sandstones. Association-2 consists of a medium to coarse grained, white-grayish sandstone, which is characterized as thick and structureless. A precise contact boundary between these two associations is ambiguous, however, it is distinguishable depending on the granular types and the color of the sediments regarding the studied areas. A horizontally oriented thin layer of dolomite and a carbonate black-grayish mud is exposed at the north of the study area and has been interpreted as the middle member of the Khuren Dukh Formation. We interpret this member as a lakebed (Figure-6A) and suggest additional geochemical work would contribute greatly to understanding the nature of the lake. Хүрэн Дух (Чойрын Хотгор) олдворт газрын хурдас хуримтлалын литофацийн ангилал