New palaeoclimatic insights on the Late Cretaceous environments of Mongolia based on the isotope data (δ13C,δ18O) of dinosaur eggshells and pedogenic carbonates from Bayn Dzak section

• 作者: S.V.Naugolnykh V.N.Kuleshov
• 来源期刊: 世界地质（英文版）
• 年，卷（期）: 2020,（4）
• 页码范围: 199-213
• 页数: 15页
• 语种: 英文
• DOI: 10.3969/j.issn.1673-9736.2020.04.01

摘要

Isotopic data obtained from the dinosaur eggshells and pedogenic nodules ( pedonodules) are inter-preted in terms of palaeoclimatology. The material studied originated from the Bayn Dzak locality, Southern Gobi Aimak, Mongolia, having Late Cretaceous ( Campanian) age. Stratigraphically the Bayn Dzak locality belongs to the Djadokhta Formation. All the present data ( lithology, type of paleosols, FPS-profiles, geochemistry) , and the isotopic characteristics of the selected samples show unequivocally that the environments of the Bayn Dzak area in Late Cretaceous ( Campanian) time were warm to summer-hot, seasonally dry. Wet seasons ( most probably, which took place in the winter time) were not longer than two months with not more than 400 mm precipitation per year. The distribution of isotope data in the dinosaur eggshells show the main relation, which is the dependence of δ13C and δ18O values, i. e. specimens with heavy carbon isotope ratios are characterized by lighter oxygen isotope composition and conversely. Thus, the δ13C and δ18O values of the dinosaur eggshells display a clear positive correlation. It may be consequent both with the difference of the isotope composition of diet of the egg-lying animals modified by physicochemical isotope fractionation due to metabolism and changes in the isotope environment, and/or diagenetic alteration of the eggshell carbonate. Obtained isotopic data on the studied dinosaur eggshell fragments and the soil carbonates lend support to our assumption that diagenesis did not play significant role in changing the isotopic values. The distribution of δ13C and δ18O values in eggshells and in pedogenic carbonates shows the visible opposite dependencies.