Abstract: The late Precambrian dolomites are widely developed in the Yangtze Craton and its periphery areas in the Dengying
Formation. As the diagenetic assemblages and sedimentary sequences of the Dengying Formation in the northern Yangtze Craton are
quite different from those in the Yangtze Craton, it is critical to study the formation process and paleoclimatic implications of the
dolomites. Based on the field profile measurement, thin section observation, cathodoluminescence, and X-ray diffraction study of the
Dengying Formation in Xichuan area, the dolomite can be divided into four types, i.e., anhedral mud-powder crystalline dolomite,
euhedral-subhedral fine crystalline dolomite, subhedral-xenotropic fine-coarse crystalline dolomite, and saddle to karst breccia
dolomite. The anhedral mud-powder crystalline dolostone is the product of dolomitization related to high salinity seawater in the
penecontemporaneous stage. The euhedral-subhedral fine crystalline dolostone was deposited in the early diagenetic stage related to
shallow-buried dolomitization, which was caused by the infiltrating reflux of high salinity seawater. The subhedral-xenotropic
fine-coarse crystalline and saddle dolostone are the product of hydrothermal dolomitization or recrystallization of carbonate minerals in
the middle-deep burial environment in the late diagenetic period. The karst breccia dolomite is related to the dissolution-collapse of
early dolomite. Changes in diagenetic environment resulted in the development of different types of dolomites in the study area.

Key words: Southwestern Henan, Sinian, Dengying Formation, dolomite, genesis