A Spore‐Pollen Assemblage from the Damoguaihe Formation in the Tamutsag Basin, Mongolia and Its Geological Implication

Abstract

AbstractBased on the palynological data from Well Ta‐19–36 and Well Ta‐19–37 in the Ta'nan Sag, and Well Ta‐22–1 and Well Ta‐21–1 in the Bayin Gobi Sag, a spore‐pollen assemblage from the Damoguaihe Formation is named as Cicatricosisporites minutaestriatus – Aequitriradites spinulosus – Protopinus sp. assemblage in the Tamutsag Basin, Mongolia. The assemblage is characterized by abundant gymnosperm pollen and diverse fern spores, counted 46.35%‐65.57% and 34.43%‐52.58% in percentage respectively. Among the gymnosperm pollen, Pinuspollenites sp. (2.66%‐16.94%), Protopinus sp. (0–11.38%) and Protopicea sp. (0–10.81%) are dominant; and Alisporites sp., Cerebropollenites sp., Podocarpidites sp., and Abietineaepollenites sp. are common. Some important elements, such as Chasmatosporites sp., Callialasporites prominulus, Parvisaccites sp., Parcisporites sp., Jiaohepollis cf. annulatus, J. bellus, J. verus, Polycingulatisporites sp., Schizaeoisporites certus, Classopollis annulatus are seen. Within the fern spores, Osmundacidites wellamanii (0.85%‐4.93%), Appendicisporites sp. (0–4.45%), Baculatisporites comaumensis (0.80%‐2.87%), Cicatricosisporites sp. (0.51%‐2.66%), C. minor (0–2.14%), Foraminisporis asymmetricus (0–2.40%), Aequitriradites sp. (0–2,19%) and Cyathidites minor (0–2.13%) are dominant; and some specie of Densoisporites, Cooksonites, Impardecispora, Pilosisporites, Schizaeosprites, Fixisporites, Leptolepidites, Trilobosporites, Kuylisporites, Klukisporites, Hsuisporites, Couperisporites, Maculatisporites are seen. The angiosperm pollen are rare in the assemblage, characterized by Clavatipollenites sp. (0–0.80%) and Songipollis sp. (0–0.27%). The geological age of the Damoguaihe Formation is assigned to Hauterivian – Barremian of Early Cretaceous according to the palynological data, due to the fact that there existed a lot of diverse spores of the family Schizaeaceae and prosperous gymnosperm saccat pollen which the corpus and sacci are differentiated completely, and the presence of early angiosperm pollen of Clavatipollenites. However, the zircon U‐Pb isotopic dating of the volcanic rocks in the Nantun Formation indicated that the overlying strata of the Nantun Formation, i.e. the Damoguaihe Formation must be younger than 127.0±2,0–137.9±1.5 Ma. This is consistent with the palynological data. Furthermore, the vegetation reconstructed on the palynological data of the Damoguaihe Formation is conifer forest with shrubs and grassland, belonging to the semi‐humid or humid middle to south subtropical climate. Moreover, three new species, namely Biretisporites punctatus sp. nov., Chasmatosporites reticulates sp. nov. and Concentrisporites contractus sp. nov. are described here.