Paleoclimate and Paleoenvironmental Study of the Lower Cretaceous Tevshiingovi Formation, Mongolia

The study is focused on the sediments of the Tevshingovi Formation. The Tevshingovi Formation in Choir-Nyalga basin is composed of many coal-bearing lignite deposits, including the Tugrug nuur-Khovil, Baganuur, and Shivee-Ovoo, which are with widespread spores and pollen of Lower Cretaceous in Central Mongolia. During the field work in 2016-2020, we were collected 82 samples from mudstone and siltstone. 46 samples were analyzed for palynology and 59 samples were analyzed for geochemistry. Palynological analysis was carried out by comparative morphological study of spore-pollen from previously identified spore and pollen genera and species. We have reconstructed the paleoclimate and paleoenvironment of Choir-Nyalga basin during Lower Cretaceous. The spore pollen assemblages of Tugrug nuur-Khovil, Baganuur and Shivee-Ovoo deposits calculated in detail by spectral analysis, and defined 17 new palynozones. In the palynoassemblages of Choir-Nyalga basin gymnosperm pollen is dominated, most abundant in Baganuur deposit, 63%. In Tugrug nuur-Khovil deposit is 48%, in Shivee-Ovoo deposit is 37%. Spores are most abundant in Shivee-Ovoo deposit, 61%. In Tugrug nuur-Khovil deposit is 48%, and in Baganuur deposit is the lowest, 32%. Sediments of the Tevshingovi Formation may have been accumulated in tropical and subtropical highlands, rivers’ banks, shores of lakes, grassy swamps and along the coniferous forest edge. The main groups of coal-producing plants were conifers and ferns. The palynoassemblages of Choir Nyalga basin are well correlated to the Lower Cretaceous Aptian-Albian palynoassemblages of northeastern China and south of Siberia in Russia (Kotova, 1970; Brattseva et al., 1975; Bolchovitina, 1979; Ichinnorov, 2003, 2009; Nichols et al., 2006; Yang, 2007; Wang, 2014; Lebedeva, 2012; Odgerel et al., 2018).