Based on core observation,five types of conglomerates are divided in the Triassic Lower Karamay Formation,Karamay Oilfield,i.e., the matrix-supported breccias,weak-cemented conglomerates(strictly speaking,this type is still uncemented),mud-supported conglomerates,sand-supported conglomerates and well sorted granule-conglomerates. Compared to the sediments of modern alluvial fans,the depositional environment of each conglomerate in the Lower Karamay Formation can be determined as following:in the early stage,due to all arid climate,the conglomerates have similar characteristics to that of modern arid alluvial fans in Zaier Mountain area. However,in the late stage a humid climate prevailed, and the fluvial process become dominant, with the deposited conglomerates showing similar characteristics to that of Baiyanghe alluvial fans in Fukang. So,vertically,the alluvial fans showed a retrogradational sequence towards the ancient Zaier Mountain.

Giant ooids are commonly seen in the Precambrian and Lower Triassic,while they are hardly reported in the Cambrian. Recently,we found giant ooid limestone with about 35 cm thick in the Lower Cambrian Tianheban Formation at the Shiliu section in Shizhu area,Chongqing. The diameter of these giant ooids is generally 5-7mm,with a maximum diameter of 9mm. The giant ooids make up 55％ of rock components. Meanwhile,the recrystallized normal ooids and calcareous shells are relatively common in the limestone. The cements of sparry calcites can be found between the grains. Abundant Cyanobacteria fossils found in the outermost laminae of a giant ooid,form a sort of protruberance-shaped laminae named as “abortive laminae”,with which the microbial cause of giant ooids is clearly revealed. The recrystallized inner dark laminae of giant ooids similarly contain messy girvanell fossils. So it is thought that the active involvement of microorganisms and frequent strong storms are the necessary conditions for the formation of giant ooids.