Clay mineral and inorganic geochemical characteristics of Eocene Huadian formation in Huadian basin and their paleoenvironment implications.

Clay mineral and inorganic geochemical characteristics of Eocene Huadian formation in Huadian basin have been found through X-ray diffraction, scanning electron microscopy and inorganic geochemical element tests. Clay minerals of Huadian formation of the study area contain montmorillonite, kaolinite and illite. The content of montmorillonite is the highest, and illite/smectite mixed layer is rare. Mn, Sr, P, Cd, Sr/Cu, B/Ga, Sr/Ba and Ca/(Ca+Fe) change with an exactly similar trend vertically, and Cu, Cs, Rb/Sr, V/(V+Ni) and 8Ce change with another similar trend. Clay minerals and inorganic geochemical evidence reveal the characteristics of paleoclimate and paleolimnology:the upper section containing coal and the lower section containing pyrite of Huadian formation belong to terrestrial sedimentary environment under the condition of warm and humid climate and low salinity ; the middle section containing oil shale belongs to frequently alternating freshwater and saltwater environment, alternating humid and drought climate. The largest expansion phase of lacustrine basin which was under reduction condition with alternating humid and drought climate and salinity stratification developed semi-deep lake and deep lake facies which formed oil shale; the shrinkage phase of lacustrine basin with warm and humid climate developed delta plain with peat swamp which formed coal. [ABSTRACT FROM AUTHOR]