Portal de Periódicos da CAPES

C20-C21-C23 tricyclic terpanes abundance patterns: Origin and application to depositional environment identification

2023; Frontiers Media; Volume: 11; Linguagem: Inglês

10.3389/feart.2023.1128692

2296-6463

Aiguo Wang, Chunyu Li, Long Li, Renhai Pu, Zeguang Yang, Zhu Nan, Kai Guo,

Geological formations and processes

Reconstruction of paleo-depositional environments in a sedimentary basin is often obstructed by the absence of typical environmental indicators in sedimentary rocks. Here, we propose a biomarker method using C 20 -C 21 -C 23 tricyclic terpanes (TTs) as a tracer, which is simple in analysis but robust to provide reliable and detailed environmental information. Based on the analysis of 271 C 20 -C 21 -C 23 TT data from 32 basins in 18 countries, we observed a relationship between C 20 -C 21 -C 23 TT abundance patterns and depositional environments. This relationship was attributed to the control of depositional environments on the input proportions of plankton and terrigenous plants, which act as two end-member precursors for the TTs in a depositional system. The various mixing proportions between these two end-members result in different C 20 -C 21 -C 23 TT abundance patterns associated with different depositional environments, e.g., C 20 >C 21 >C 23 TT in river-lake transitional, C 20 <C 21 <C 23 TT in marine or saline lacustrine environments, C 20 <C 21 >C 23 TT in freshwater lacustrine and C 20 >C 21 <C 23 TT in marine-continental transitional environments. In addition, the C 23 /C 21 TT ratio increases with elevated salinity of depositional water, and the C 21 /C 20 TT ratio increases with increasing water depths. Based on these observations, a discrimination diagram using C 23 /C 21 TT vs. C 21 /C 20 TT was developed for environmental identification. The validity of this C 20 -C 21 -C 23 TT biomarker method is well demonstrated by the rock samples with typical environmental indicators. This method is applicable in a broad spectrum of rocks and in maturities up to 2.4%Ro. Its strength was shown by a case study of a complex depositional system in the East China Sea Basin, which has been strongly affected by eustasy.