YOU Jiyuan1, ZHOU Xiaohu2*, YANG Yiyao2, BAI Yunyun1, ZHANG Peng3,
YANG Guilin1, LIANG Zhengzhong1, LI Jie4
(1. The Youth Innovation Team of Shaanxi Universities, School of Energy Engineering, Yulin University, Yulin 719000, China;
2. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi'an 710069, China;
3. Shaanxi Yulin Energy Group Co., Ltd., Yulin 719000, China;
4. Mineral Resources Investigation Center in Xi’an, China Geological Survey, Xi'an 710100, China)
Abstract: The coprolite is an important kind of trace fossils. Its inclusions often preserved the remains of prey organisms and some microbial, soft tissue and even ancient DNA information, which are of great significance to interpret the ecological information of lakes in geological history. Fish coprolites discovered in shale of the lower part of Chang 7 member of Triassic Yanchang Formation in the Tongchuan area of the southern Ordos Basin are slightly flattened, spindle-shaped, sharp and thin fossils, with obvious spiral lines on the surface. By observing inclusions of the coprolite, it is found that they are mainly composed of incompletely digested animal and plant residues, including fish scales and bone fragments, and a large number of mineral aggregates based on the phosphorus-containing dolomite. Fish coprolites were formed in the semi-deep to deep parts of the open freshwater lake. They were mostly well preserved as the typical in-situ burial. The fish coprolite was biologically sourced from a kind of large carnivorous fish with many spiral valves in its intestine. A complex multi-layer nutrition lake system, appeared in Late Triassic, was mainly composed of producers and consumers, with relatively complicated food chain. The research results show that the multi-level nutrient lake ecosystem in Late Triassic was basically recovered after the end-Permian mass extinction. In addition, the participation of microorganisms and the anaerobic environment of high argillaceous content resulted in the well preservation of coprolites. An important basis can be provided by using the well preserved coprolite for the restoration and reconstruction of the lake ecosystem in Carnian period in Late Triassic.
Keywords: fish coprolite; lacustrine organic-rich shale; lake ecosystem; palaeoenvironment; Late Triassic; Ordos Basin
