Abushan Fm

Qiangtang Basin. The Abushan Formation was named by Wu Ruizhong et al in 1986. Its type section is located on the east slope of the Abu Mountain at Shuanghu of Xizang (Tibet) (88°50′E; 33°10′N). In 1986 Wu Zhongrui et al named the intermontane molasse variegated clastic rock formation of Late Cretaceous in the Abu Mountainous area of Shuanghu the Abushan Group. In the Geological Record of Xizang compiled in 1993, the Abushan Group was renamed the Abushan Formation, and considered the upper part of the Xueshan Fm in the Hot Spring area of Qinghai as the same strata, being of Late Cretaceous age. The Abushan Formation is used in this lexicon, but the upper part of the Xueshan Fm is not considered to be of the same strata.

The Abushan Formation is composed of red sandstone, conglomerate, sandy conglomerate with marl, siltstone and clayey siltstone. Lower part is represented by dark purple boulder conglomerate and conglomerate interbedded with grit and dark purple conglomerate with sandstone and siltstone, measuring 249 m in thickness. Middle part is represented by dark purple sandy conglomerate with granule conglomerate, siltstone, conglomerate, sandy conglomerate and sandstone, earth red grit interbedded with gravel-bearing sandstone, and purple quartz sandstone with sandy conglomerate and marl, measuring 474 m in thickness, bearing floras and sporopollen grains. Upper part is represented by gray purple fine-grained sandstone, calcareous siltstone, gravel-bearing sandstone, fine sandstone, clayey siltstone interbedded with mudstone, and purple grey grit, fine sandstone constituting rhythms with siltstone, being 227 m thick and bearing sporopollen grains.

In the Shuanghu area, the middle and upper parts of the formation contain floras Cupressinocladus sp.; sporopollen grains such as Lycopodiumsporites sp., Concentricystis sp., Classopollis sp., etc.

Fluvial-lacustrine intermontane basin sediments deposited under the oxidized hot arid climatic conditions