Tashikula Fm

The type section is located in the Shirenzigou area about 12 km to the east of Urumqi, Xinjiang. It was named by the Xinjiang Regional Geological Survey Party in 1965.

Clastics and Limestone. Representing unequal interbeds of grey-black and grey-yellow medium- and thin-bedded siltstone, fine-grained sandstone and siltstone, intercalated with thin-bedded sandy limestone, micrite and oolitic limestone. Its basal part consists of black-shale, intercalated with the siliceous rock. The siliceous rock and limestone are possessed of distinct macro-stratifications characterized by convolute and olistostrome structures. Its lower part is composed mainly of siltstone, fine-grained sandstone and siltstone, and yields abundant plant fossils (phytolites). Its middle part is composed of sandstone and fine-grained sandstone with well-developed micro-stratifications, intercalated with a great amount of stromatolitic (cryptozon forma U) limestone and oolitic limestone layers. Its upper part is composed largely of medium-, and coarse-grained sandstones, intercalated with sandy limestone and calcareous sandstone with a good many of ripple marks, with a thickness of 1500 m. The formation is stable in both its lithology and thickness.

Among the spore and pollen fossils in the middle and lower parts of the formation it is the gymnosperm pollens that are the predominant absolutely, with the Protohaploxypinus having the highest content, less being the Striatoabietites, and the Hamiapollenites, etc. being the fewest, with the monosaccate and bivesiculate pollens being few as well, but with no Entylissa having been found. The salient features of spore-pollen assemblage are close to those of the spore-pollen assemblage of the Sakmarian-Kungurian Stages on the western slope of the Ural. The plant fossils (phytolites) occurring in the lower part of the formation comprise the Cordaianthus volkmannii, C. curtus, Walchia piniformis, etc.

It is interpreted as a marginal marine. It has a fairly high content of Mg, with the Sr/Ba ratio being a direct correlation, and the content of the latter two components is very high, indicating that the environment of their sedimentation is of a marine facies. The occurrence of stromatolite has proved that the middle and lower parts of the formation represent tidal-flat deposits, while the upper part of the formation may probably represent delta-facies deposit. Jin Huijuan et al. (1989) would think that the lower part of the formation belongs to bathyal slope-facies and basin-facies, while the middle and upper parts represent continental-shelf and tidal-flat deposits.