Evolution of carbonaceous formations in Devonian sedimentation basins

Based on geodynamic data, we consider paleogeographic positions of basins w here sediments rich in organic matter (black-shale facies) accumulated in t hree Devonian epochs. A brief description is given to black-shale Formation s (series, members, and horizons) and the position of zones of their accumu lation in the basins and in the cycles of sedimentation. We study the evolu tion of the geologic positions of these zones and their dependence on the a rrangement of continents and the sequence of transgressive events. In the Early Devonian, when the continents were located relatively close to each other, black-shale sedimentation basins existed on their periphery, i n the area transitive between shoal and pelagic zones. In the Middle Devoni an, such basins also appeared in pre-orogeny zones, and black-shale formati ons accumulated in more shallow-water settings as compared with the Early D evonian black shales. In the Late Devonian, the shelf areas expanded, and t he number of black-shale zones and their areas considerably increased. In s tratigraphic sections, black-shale facies occur in the middle parts of sedi mentation cycles, which are the most transgressive and subsided.