Flora and phytostratigraphy from Noyonsum Formation, Late Triassic, Mongolia

Abstract

The distribution of plant bearing Triassic continental strata is limited in Mongolia. The of these formations is thought to be the Middle-Upper Triassic Noyon synclinal formation, a Triassic geological cross section in Southern Mongolia. There are fossilized plant remains in the Noyonsum Formation, and paleobotanical study is required to establish a phytostratigraphic basis for the age. The formation is a the base for studies on stratigraphy and sedimentation as well as being rich in fossils of bygone animals and plants. Before this study, phyto stratigraphic research hasn’t been done based on the Noyon sum Formation's ancient flora and its classification. First time phyto stratigraphic research done based on the Noyonsum Formation's ancient flora and its classification by this study. During the collaborative geological research between Russia and Mongolia in the 1970s, fossils of extinct leafy plants, including ferns, seed ferns and horsetail, found and preliminary definitions of classification were completed. The researchers of our Institute have gone out in the field several times (2008, 2020) in different regions of the syncline and in the Sain-Sar and Muu-Sar canyons of the Noyon Formation, and found and determined Equisetites sp., Neocalamites carrerei, Cladophlebis sp., Pityophyllum sp., which also was discovered and determined by Russian scientists previously. According to the results of field research conducted in 2023, seven genera out of ten species of plants belonging to the horsetail, fern, seed fern and ginkgo groups, among of them Neocalamites aff minensis, N. ex. gr carrerei, Schizoneura ex. gr. ornata, S. ex.gr. grandifolia, Cladophlebis sp., Todites princeps, Danaeopsis marantacea, D. petchorica, Lepidopteris toretiziensis and Toretzia ex.gr. angustifolia were identified. According to these plants the Middle-Upper Triassic Noyonsum Formation sediments were deposited at the early stages of the Late Triassic.

Ноёнсум формацын хожуу триасын ургамал, фитостратиграфи