STRUCTURAL DEFORMATION OF BLACK SHALE BEDS RESULTING FROM THEIR LOSS OF ORGANIC MATTER

Abstract

Any significant decrease in volume or thickness of rocks may lead to the formation of weakened zones (decomposition) and subsequent structural deformation. Rock decarbonization as one of the factors controlling the self-deformation of the environment can be illustrated by the Middle Ordovician shale-bearing sequence of the Baltic region. This sequence is about 30 m thick and consists mainly of carbonate rocks. They are enriched to a different extent in organic matter (OM) and clastic material and have numerous intercalations of oil shale, a highly carbonaceous marl with as much as 40 percent OM or more. OM is the main component of the shales studied by volume and, therefore, is the main potential factor controlling first the decrease in thickness of the economic bed, and then its deformation when the shales were decarbonized and/or disintegrated. This leads to self-faulting and contributes markedly to the amplitude and intensity of existing disruptions.