Deposition of Oil Shale and Coal in China: the Eocene Fushun and Huadian Basins
Research output: Thesis › Doctoral Thesis
The Fushun and Huadian basins, located along the DunMi fault zone (NE China), are filled with non-marine oil shale- and coal-bearing sediments of Eocene age. Despite similar tectonic setting and age, the habitat of oil shale and coal differs significantly in terms of thickness, distribution and quality. The Fushun Basin hosts world-class coal and oil shale deposits, which are mined in a huge open-pit mine. In contrast, the Huadian Basin hosts several relative thin oil shale and coal seams, which are mined underground. During this study the depositional environment of coal and oil shale in both basins and factors controlling differences between them were investigated mainly based on detailed bulk geochemical, organic petrographical and organic geochemical data. In the Fushun Basin, a single sub-bituminous coal seam, up to 120-m-thick (Guchengzi Formation), formed during the early transgressive stage of basin evolution. It is overlain by an up to 300-m-thick oil shale unit (Jijuntun Formation). During the deposition of oil shale, excellent preservation conditions of organic matter were established in a more than 100-m-deep lake with a stable stratified water column and photic zone anoxia. Especially in the upper unit of the Jijuntun Formation, the organic matter is dominated by algal and bacterial biomass. Relative high thermal maturity is due to high paleo-heat flow related to magmatic activity. In the Huadian Basin 13 oil shale layers intercalated with fan delta sediments (Oil Shale Member) were deposited in a lake with relative low water depth (a few tens of meters) preventing stable water column stratification. Nevertheless, algal blooms and oxygen-depleted conditions resulted in high quality oil shale (e.g. oil shale layer 4). In contrast, strong input of terrestrial plants reduces the quality of the lower oil shale layers (e.g. oil shale layers 13-11). Thin coal layers accumulated during the late regressive stage of basin evolution (Carbonaceous Shale Member). The main factor controlling differences in stratigraphic position, thickness and quality of oil shale and coal deposits in the Fushun and Huadian basins is tectonic subsidence. The subsidence rate was significantly higher in the Fushun Basin than in the Huadian Basin. This resulted in the formation of a thick coal seam during the transgressive phase of basin evolution. Similar coal is missing in the Huadian Basin. In addition, a single thick high quality oil shale unit developed under deep lacustrine conditions in the Fushun Basin, whereas several thin oil shale layers were deposited in a relative shallow lake in the Huadian Basin. During the regressive stage of basin evolution, thin coal layers accumulated in the Huadian Basin, whereas equivalent coal is missing in the Fushun Basin. In general, the organic matter of the oil shale within the Fushun Basin mainly composed of algae and bacteria, whereas terrestrial organic matter is more abundant in the Huadian Basin. Moreover, differences in paleo-vegetation (gymnosperms prevail in Fushun; angiosperms prevail in Huadian) may indicate different climatic conditions.
|Translated title of the contribution||Ölschiefer- und Kohleablagerungen in China: Die eozänen Fushun und Huadian Becken|
|Publication status||Published - 2014|