[HCG32-P07] Petrographic characteristics of Middle Permian sandstones in Southern Mongolia and their geological implications
Keywords:sandstone provenance, Middle Permian, Mongolia
Detrital grains of the studied samples consist of mineral grains and rock fragments. They are generally well-rounded and moderately sorted. Size of detrital grains ranges from 0.1 mm to 1.0 mm. Detrital minerals quartz and feldspar comprising 7-31% of the total constituents. Quartz comprises 13-24% and monocrystalline quartz dominates over polycrystalline quartz. In feldspar grains, plagioclase is more abundant than K-feldspar. Lithic fragment comprises 49-60%, of which volcanic rock fragments predominates. Cement is carbonates partly enriched in iron oxide, resulting in reddish color.
The sandstones of Middle Permian in Borteeg syncline are classified as litharenite suggesting that weathering intensity in source area was weak, probably due to relatively arid to semiarid climate conditions. Provenance analysis (Q-F-L, Qm-F-Lt, and Qp-Lvm-Lsm diagrams) suggests that the sandstones are recycled sediments derived from transitional arc and undissected arc that were formed during the closure of Paleoasian ocean between southern Mongolia and North China block.