NEW TYPE OF KARST IN BLACK SHALE BEDS

Abstract

Oil shale is a slightly transformed analog of black shales - a large group of sedimentary rocks, rich in organic matter and often ore-bearing. Previous investigations have shown that ore-generating processes in oil shale can also occur in the early stages of lithogenesis and, moreover, under subsurface karst conditions. Organic matter is thereby decomposed as well. Carbonate, sulfate and salt types of karst differ, depending on the composition of disintegrating material. In karst disruptions in the Baltic shale basin, along with carbonate material in oil shales, organic (carbonaceous) matter, which accounts for 40 to 60 percent of their volume, is also decomposing. Thus a new, carbonaceous type of karst can be identified. In intervals where conditions are favorable for karstification of oil shale, carbonaceous karst develops earlier and more intensively than carbonate karst. Thus, observations in open pits and underground workings showed that oil shale decomposes faster than the host limestone and the carbonate intercalations in the shale itself. Such changes in the productive horizon within karst disruptions, which were noticed by many authors while oil shale was being mined, have caused a reduction in the thickness and volume of shale-bearing deposits. Oil shales of the Baltic region are not decomposed in all karst disruptions. These and other aspects of the subject are discussed.