Li G.S.,Wuhan University |
Wang Y.B.,Wuhan University |
Lu Z.S.,Wuhan University |
Liao W.,Natural History Museum of Guangxi Zhuang Autonomous Region |
And 3 more authors.
Science China Earth Sciences | Year: 2014
Gypsum-salt rocks and coccolith calcareous shale are widely deposited in the lower part of the Paleogene Shahejie Formation in the Dongying Sag, Shandong Province. The gypsum-salt rock is believed to be formed during the earlier deposition in salt lake, while the overlying coccolith shale in saline lake with relatively low salinity. By comparing the lake environment and lacustrine microbial communities between ancient and recent lakes, cyanobacteria are regarded as the main representative of productivity during the formation of gypsum-salt strata series, with the annual productivity of 1500-2000 gC m-2 yr-1. Based on the research of ultramicrofossils in the calcareous shale, coccolith is considered as the main contributor to the productivity during the formation of calcareous shale. On the basis of statistic data of sedimentary rates, shale laminations, and coccolith fossils in each lamination, the quantitative value of productivity is calculated, with the annual productivity of 2250-3810 gC m-2 yr-1 (averagely 3120 gC m-2 yr-1). Statistic data of large amount of pyrite framboids indicate that the lower water column was persistently in sulfidic or anoxic conditions during the deposition of gypsum-salt strata series, but it changed to be dysoxic when the coccolith calcareous shale was deposited. Both of these water conditions are favorable for the preservation of organic matter. It is estimated that the organic carbon burial efficiency of the Lower Paleogene salt lakes and saline lakes of Dongying Depression is about 10%-15%, which is calculated and analyzed using the multi-parameter geobiological model. © 2013 Science China Press and Springer-Verlag Berlin Heidelberg.
Tan X.-F.,Chongqing University of Science and Technology |
Tan X.-F.,Chengdu University of Technology |
Tian J.-C.,Chengdu University of Technology |
Li Z.-B.,Chongqing University of Science and Technology |
And 2 more authors.
Geological Bulletin of China | Year: 2010
Based on the analysis of thin-section analysis, scan electricitymicroscope observation, vitrinite reflectance-diffraction and geochemical analysis, the diagenesis evolution of shahejie formation in dongyingsag has been systematically researched. It is indicated that the original depositional environment of Es4 Member is alkali salt lake, and the calcareous and argillaceous were included in the rock. The diagenesis evolution is controlled by factors including alkali original depositional environment, sequence development, tectonic event, transformation of clay minerals, acid fluid provided by organic matter thermal evolution, which has experiences below stages including cryptocrystalline calcite cementation, early chlorite cementation, quartz dissolution, feldspar dissolution, phase II quartz increase, phase III quartz increase, Fe carbonate cementation, quartz and calcite vein filling. The conclusion has been verified that Es4 Member influenced by the original alkali fluid on early stage, cementation of the crypto-crystal carbonate, quartz solution and feldspar increase were occurred in the reservoir; influenced by the acid-fluid on the advanced stage, quartz increase, carbonate solution and feldspar solution were occurred in the reservoir of member 4 of shahejie formation in dongying sag.