The petrologic characteristics of Lower Cretaceous Tengeer Formation in Baiyin Chagan Sag, Erlian basin,China were systemically studied based on the data of drilling, well logging, cores, and analysis methods of QemScan,... [ view full abstract ]
The petrologic characteristics of Lower Cretaceous Tengeer Formation in Baiyin Chagan Sag, Erlian basin,China were systemically studied based on the data of drilling, well logging, cores, and analysis methods of QemScan, polarizing microscope, scanning electron microscope, electron probe and energy spectrum, whole rock X-ray diffraction, trace elements, etc.. It has a special mineral assemblage including ankerite- zeolite- sjogrenite- barite- pyrite and a special lithological combibation of mudstones, dolomitic mudstones, muddy dolostones, muddy zelolite and dolomicic zelolite. These petrologic characteristics indicate that Tengeer Formation of Lower Cretaceous was a set of ‘white smoke type’ hydrothermal deposition affected by thermal fluids. Based on vertical sequence features and the petrological variation of the hydrothermal sedimentation rocks, single hydrothermal sedimentation process could be divided into three stages: initial stage was the period when thermal fluids overflow, mainly forming dolomite and zeolitic laminaes, stripes or interlayers in normal lacustrine mudstones, corresponding rocks were dolomitic-zeolitic mudstone with low gamma; then as enhanced hydrothermal activity, exhalative stage began, making semi-solidified dolomitic–zeolitic laminaes formed in initial overflow deformed and crushed, dolomitic mudstone and dolomitic–zeolitic intraclasts grainstone with synsedimentary deformation structures occurred, logs were still characterized by low gamma; finally, due to hydrothermal energy descending ,slow overflow stage reactivated, forming high gamma, dolomite and partial dolomitic mudstone. Vertically, single hydrothermal sedimentation formed one cycle. Four obvious hydrothermal sedimentary cycles were observed in Lower Cretaceous Tengeer Formation of research area. Horizontally, hydrothermal sedimentary rocks mainly distributed along the fault, and were mainly located in the downsliping block of faults, hydrothermal sedimentary rocks were thin and undeveloped in the uplifting block or away from the faults.
