Hydrocarbon potential, organisms, and depositional environments of the Lower Cambrian shales along the southern margin of the Ordos basin, Northern China

The dark shales of the Lower Cambrian Dongpo Formation, along southern margins Ordos Basin, were researched based on biomarkers and carbon isotope analyses outcrop samples to reveal their hydrocarbon potential, organism composition, depositional environment. Similar Yangtze Tarim blocks, in margin which is a part North China block, also deposited high abundance marine source rocks. displayed good excellent total organic (TOC) content (up 13.75%). crossplot phytane/ n C 18 vs. pristane/ 17 isotopes indicate kerogen be primarily type I-II. low Hydrogen index values, pyrobitumen reflectance (>3.0%) that are currently over-mature stage. thus exhibit generation potential might have produced discharged massive amounts hydrocarbons during geological history. G/C 30 H ratios (0.17–0.29) extended tricyclic terpanes Ratio (ETR) values (0.54–0.61) suggest sedimentary environments stratified water relatively moderate salinity. In addition, display Pr/Ph (<0.63), */C 29 Ts (<0.44), 35 22S/C 34 22 S (>0.47), abundant elemental sulfur. These parameters formed anoxic waters. steranes hopanes diversity organisms, including eukaryotes prokaryotes. composition (planktonic algae) consistent with but there obvious differences Oman, reflecting heterogeneity global distribution Early Cambrian. compared Tarim, contribution prokaryote shale low, may an important reason for enriched 13 kerogen. positive relationship between TOC 27 St (%) suggests primary productivity paleoenvironment probably attributed red algae. Pr/Ph, /C others indexes related conditions, preserving matter. • lower Basin quality enrichment OM prosperity environment been interpreted. kero -riched relative less prokaryote.