Preliminary results of biostratigraphic studies of Lower Cretaceous sediments in the Ergel-Khaliv area, SE Mongolia

Batkhuyag Enkhbaatar,Batsaikhan Buyantegsh,Bayasgaa Ganzorig,Byambaa Purevsuren,Enkhtaivan Zorig,Jalbaa Undarya,Luvsantseden Uranbileg,Sukhbat Purevsuren

doi:10.5564/mgs.v50i0.1326

Abstract

The research area is located in the territory of Khatanbulag soum, Dornogovi province, in the Great Govi Province (coordinates: 108°25'39.04"E and 43°10'11.43"N). Here, the authors studied the composition of sediments that had previously been classified as Lower Cretaceous Khukhteeg Formation, forming Mt. Ergel-Khaliv during earlier mapping work. The authors revealed fossils of faunas and floras, processing some data of biostratigraphic survey works taken on fossil-bearing sediments of the area. The fieldwork was conducted in April 2019 by researchers from the Institute of Paleontology, Mongolian Academy of Sciences. The area is very rich in fossils of mollusca, therefore, the local communities named it Dun-Ovoo (Conch hill). During the previous studies, the sediments outcropping around the Ergel-Khaliv were classified as Khukhteeg Formation (K1ht, Aptian-Albian) based on lithological characteristics and comparing them to the type section of the Khukhteeg Formation sediments. Our research revealed biostratigraphic basements and recorded previous data of collected fossils two types of mollusca; we have studied plant fossils, turtles, ostracods, fish and dinosaur bones had been revealed at first in that area. The results of the research work, the fossils that found in the mountain, were amended by more and new types and families of fauna and flora and their constituents. These new findings were helpful in the precise determination of the age of the sediments and provided some information on the paleoenvironmental conditions of the sedimentation period.

Highlights

Location and geomorphology of the site: The Ergel-Khaliv fossil-bearing area is located in 80 km to the North of Mongolia’s southern border, in more than 60 km south-west of Khatanbulag, Dornogovi province, and 100 km to the East of Khanbogd, Umnugovi province (Fig. 1)
The main result of the study was the findings and the age determination for many classes and groups of animals and plant fossils from the Ergel-Khaliv area. They had been existing, spreading there for quite a long geological time, during the Lower Cretaceous, Barriamian-Lower Aptian stages. This may indicate the need for further review of the summaries determining the Lower Cretaceous sediments of the site, into Aptian-Albian sediments of the Khukhteeg Formation
The sediments contain fossils such as molluscs, fish, amphibians and continental leaf plants, which are important for the paleo-ecosystem studies evidencing of their accumulation on lake shores

Summary

INTRODUCTION

Location and geomorphology of the site: The Ergel-Khaliv fossil-bearing area is located in 80 km to the North of Mongolia’s southern border, in more than 60 km south-west of Khatanbulag, Dornogovi province, and 100 km to the East of Khanbogd, Umnugovi province (Fig. 1). The sediment package is composed of gray, bluish gray mud, coaly mudstone and siltstone, containing 4 coal seams (layers), of which thickness ranges from 2 m up to 18 m. 19 in Plate II) well-preserved and in Mid coalbearing package, which have the richest fossils (Fig. 9), as mentioned above, in siltstone and mudstone layers, belonging to the genus and species of gastropods mainly Viviраrus rоbustus Martinson, Campeloma yihsiensis Grabau, C. mongolica Martinson, Lioplax sp. The period was sometimes referred to as the 'Lacustrine basin phase' (Berkey and Morris, 1927) In this regard, ancient species of the Lycoptera genus, which are widespread in the Early the Cretaceous sediments are found in most of East Asia, such as Mongolia, China, and. Peipiaosteus-type fish from upper-mid layers of lower package belonging to the Ergel-Khaliv section. The researchers have determined that these fossils belong to Cypridea copulenta Lubimova, Limnocypridea grammi Lubimova and Lycopterocypris infantilis Lubimova indicating they belong to the mid to late part of the Lower Cretaceous Barremian stage

DISCUSSION

CONCLUSION