Biomarker Study of Depositional Paleoenvironments and Organic Matter Inputs for Permian Coalbearing Strata in the Huaibei Coalfield, East China

Abstract

This study presents detailed information regarding the organic geochemical and biomarker characteristics of the Permian coal-bearing strata in the Huaibei coalfield. The type of organic matter, sources input, depositional paleoenvironments, and thermal maturity are revealed by the organic molecular signatures study. These are of great significance to understand the coalification process and the generation of the coalbed methane. The extractable organic matter (EOM) in coal and coaly mudstone samples are 1.14% and 0.11% on average, respectively (polar compounds > aromatic hydrocarbons > saturated hydrocarbons). The midchain n-alkane (n-C 20 −n-C 24 ) is the dominant fraction for coal (42.33% on average) and coaly mudstone (44.91% on average). Compared to the continental coal-bearing basins, the Pr/Ph ratios (mostly <1.0) of both the coal and coaly mudstone in the Huaibei coalfield are lower. R o (%), Ts/(Ts + Tm), 22S/(22S + 22R) C 31 homohopane, 20S/(20S + 20R) C 27 diasteranes, and the Rock-Eval pyrolysis results demonstrate the organic matter in coals and coaly mudstones is at the mature to postmature stage. The coal-bearing strata were formed in a transitional zone of an open marine and estuarine environment. The interactive deposition of marine and terrestrial sediments in the weak oxidizing−reducing environment was favored for the accumulation of the organic matter and the appearance of multiple coal seams. The organic matter is primarily from terrestrial higher plants mixed with a certain amount of marine sources input for both coal and coaly mudstone. Biodegradation, waterwashing, and thermal maturation are all important factors which would change the distribution of saturated hydrocarbons significantly. As a result, some of the biomarker parameters may lose the meaning to differentiate sources input, depositional environment, and thermal maturity. Hence, the combination of the geological background and the strict screening of these biomarker parameters are very important and indispensable.

Geochemical characteristics, palaeoenvironment, and provenance of marine mudstone in Shanxi Formation of Huaibei Coalfield, southern North China Plate

“…The valence state of Ce and Eu changes when the environment changes, so the Ce anomaly (δCe) and Eu anomaly (δEu) can be used as indicators for determining the sedimentary environment (Li, Ju, et al, 2017;Wang, Chen, et al, 2020). The anomalies of Ce and Eu in all mudstone samples are between 1, with average values of 0.98 and 0.97, indicating an oxic-anoxic deposition environment.…”

Geological Controls on High Production of Tight Sandstone Gas in Linxing Block, Eastern Ordos Basin, China

“…Tight sandstone gas in some gas fields was thought to partly originate from carbonate because stable carbon isotope compositions indicate a coal-derived gas mixed with an amount of oil-derived gas (Dai et al, 2005;. However, because the sediments were deposited in a marine-continental transitional environment, a certain amount of OM in mudstone was sourced from marine aquatic-derived OM (Li Q et al, 2017;Qi et al, 2019aQi et al, , 2019b. As such, we believe that the oil-derived gas may partly originate from these transitional mudstones.…”

Biomarkers in Source Rocks from Barreirinha Formation (Devonian): Distribution and Paleoenvironment Significance

“…is generally used as a maturation parameter. [63][64][65][66] However, previous studies 67,68 have indicated that acidic (presence of clay minerals) or strongly oxidizing conditions catalyze conversion reactions from regular steranes to diasteranes, being related to deltaic marine deposition environments. In oil samples from evaporative carbonate or marine sources, diasteranes are in low relative abundance or even absent.…”