Tracing of variabilities within a geological barrier by molecular organic geochemistry. Case of the Callovo-Oxfordian sedimentary series in the East of the Paris Basin (France)

摘要: Abstract The Callovo-Oxfordian claystones located at 500 m depth Bure (Meuse, France) are currently being investigated by Andra (the French National Radioactive Waste Management Agency) for testing the feasibility of long-term and deep geological nuclear waste disposal. In order to evaluate its potential as a barrier, it is very important study, assess describe physico-chemical variability. molecular biomarker composition 150 samples these their surrounding limestones carry diverse information on sources sedimentary organic matter, chemistry depositional environment, preservation diagenesis conditions. It also allows assessing degree lateral vertical variability matter within series. abundance unsaturated biomarkers, distribution steroids hopanoids CPI values >2 prove thermal immaturity matter. co-occurrence plankton, bacteria land plant biomarkers indicate that mixture marine continental contributions. data reveal was deposited under oxic open-sea conditions except brief event photic zone anoxia beginning Middle Callovian. claystones, geosynthesis diasterenes favored detriment formation steranes, especially in smectite-rich levels, rapidly isolated from oxidizing then reducing after deposition due protective effect clays. On scale investigated, characterized unique facies thus homogenous content point view. Yet, detailed investigation specific families indicates changes related major claystone–limestone transitions. homogeneity can be explained paleogeographic position setting plane sub-horizontal paleotopography which they were deposited. This study demonstrates efficiency geochemistry assessment barriers.