Biomarker evidence for the depositional environment of basinal UK Mississippian mudstones

Abstract

Abstract The regional character of organic matter types and depositional conditions of Pendleian, Brigantian and Arnsbergian mudstones between the Craven Basin and the Widmerpool Gulf was compared through interpretation of biomarker and pyrolysis data from 201 samples recovered from nine boreholes. The Carboniferous seaways have been determined to commonly host dysoxic conditions, enabling the preservation of a mixture of marine and terrestrial organic matter types. Photic zone anoxia, established by the presence of aryl isoprenoids, was determined to be persistent during ‘marine’ conditions represented by marine band, high-sea-level and carbonate facies. The observation and correlation of diasteranes and trisnorneohopane/trisnorhopane ratios within the samples and to other maturity parameters highlighted a significant clay mineral catalytic and/or hydrocarbon retention effect in the samples. This influenced both biomarkers and programmed pyrolysis thermal maturity indices such as T max , reducing the reliability of such results for interpreting the burial depth, and ultimately reserve potential.