Discovery of late Early Triassic tempestite in Tongren area, Qinghai, China and its significance

Tongren area of Qinghai Province is located on the copulae of Qilian and West Qinling orogene, which has undergone a long enduring tectonic evolution process. A well disclosed Triassic section in the Longwuhe area was surveyed in detailed during this work. According to the fossils collected from this section, this paper has ascertained the chronology of this stratum roughly. A tempestite set was discovered in the upper member of the Jiangligou formation, which belongs to late Early Triassic by geologic timing, the hummocky bedding structure is well developed here. Major sedimentary combination of the lower part of the tempestite set belongs to relative deep water sediments, namely Sc, Sd and Sc, Sd, Se combination, accompanied by the stormy turbid deposition, while the upper part is Sa1, Sc, Sd, Se and Sa2, Sc combination, which belongs to sediments formed closed to the base level of storm wave. It’s indicated by these features reflected from the sedimentary structure and basic sedimentary sequence that it belongs to distal type or proximal type B tempestite. The lower part of the section is a set of distal tempestite from relative deeper water environment which gradually transit into a near source type B tempestite upwards. Occurrence of these tempestite indicates that the sedimentary environment of late Early Triassic in this area was somehow closed to the base level of storm wave. The sea level went down at the beginning, and then there was a small-scale transgression.