ABSTRACT
Mahu Sag, one of the most oil and gas bearing sags in Junggar basin, is in the
northwestern margin of the basin. On gentle slope region of the sag, a serial
of large scale coarse fan delta deposits were developed in Triassic Baikouquan
Formation. In order to understand the petrology characters of conglomerates
in Baikouquan Formation, based on lots of cores, grain size analysis, normal
thin sections, casting thin sections, scanning electron photomicrographs,
mineral composition identifications, clay mineral and bulk composition identifications
of X-ray diffraction, were comparatively studied for Xiazijie and
Huangyangquan fan-delta in Mahu Sag. Mineral composition of conglomerates
is main tuff, while eurite, dacite, rhyolite, andesite and granite are
common. However, more tuff and granite, less eurite and andesite in Xiazijie
fan-delta, there is no rhyolite in Huangyangquan fan-delta. Kaolinization and
chloritization of conglomerates are ubiquitous in the formation. The content
of chlorite and kaolinite is higher in Xiazijie fan-delta, with lower illite-smectite and illite. There is less feldspar of clastic and more calcite of cement
in Xiazijie fan-delta.