Advances in the study of 'black shales': source rocks for bricks and hydrocarbons

Recent advances in methods and concepts in the study of organic-rich mudroc ks are reviewed. Organic biomarkers, especially derivatives of isorenierate ne, unambiguously identify anoxia within the photic zone of the water colum n in several well-known black shales. This demands a re-interpretation of m uch palaeoecological data in terms of intermittent anoxia, rather than only dysoxia, an endeavour aided by increased understanding of the life strateg ies of benthic invertebrates. The role of sulphur compounds in diagenesis, both organic-bound and as pyrite, is increasingly recognized. Pyrite studie s afford anoxicity indices based on pyrite framboids and sulphur geochemist ry. The role of organic sulphur is in stabilizing organic matter during ker ogen formation, and in 'fixing' biomarker molecules. Recycling of nutrients is probably more important than previously thought in forming epicontinent al black shales. Reworking of primary organic matter by heterotrophic organ isms: especially bacteria, is indicated by isotopic studies on individual o rganic molecules. All these factors must be integrated with constraints fro m stratigraphical relationships and basin evolution. Some of these points a re illustrated by reference to work by members of the Oxford Clay Working G roup in understanding the palaeo-environment of the organic-rich Peterborou gh Member of that Jurassic formation, a famous source material for bricks a nd an analogue for hydrocarbon source-rock studies.