| Popis: |
Our work on the dark pelitic sediments of the Polish Carpathians and eastern Alps shows that these Jurassic through Lower Cretaceous sediments owe their organic content to a combination of global processes, such as climatic changes and changes to the carbonate compensation depth (CCD), and local controls, such as basin morphology, input of terrestrial organic material, and local volcanic activity. These sediments developed in basins both floored by oceanic crust as well as within the continental crust (North European platform). Our data show that these anoxic or poorly oxygenated deposits (average total organic carbon [TOC] value is around 2.5 wt. %) were laid down in the individual basins at different times, from the Late Jurassic to the Barremian and almost continuously up to the early Cenomanian, a period of 30 to 50 m.y., and their thickness reached hundreds of meters. This long time span made it impossible to distinguish precisely the known Aptian and Albian oceanic anoxic events (OAE). Our data show that sedimentation of dark organic-rich deposits was not only controlled by global events such as climatic and CCD changes, but also by local ones as a result of differences in their basin morphology and development, input of land-plant detritus, and local volcanic activity. As an example of the anoxic succession, a detailed description of the black sediments of the proto-Silesian basin is presented. Some of these anoxic shales were buried to a depth of a few thousand meters during the folding and overthrusting movements. We propose that these shales could represent a unique shale-oil and shale-gas resource in an intensely structured basin. |
