中国科学院南京地质古生物研究所机构知识库

The opening time of the Bangong-Nujiang Ocean has been a contentious issue for a long time. The correlations of sequences and paleobiogeography can constrain the opening time of the Bangong-Nujiang Ocean. From the viewpoint of the depositional sequences, the whole Lhasa Block has evidenced a stable transition from elastic rocks to carbonates after the Late Paleozoic glaciation. By contrast, the South Qiangtang Block varies a lot in depositional sequences. The western South Qiangtang Block has uplifted after the deposition of the Lower Permian Tunlonggongba Formation that results in an unconformity between the Tunlonggongba Formation and the Upper Permian Jipuria Group. The eastern South Qiantang Block, however, is characterized by a sequence of basalts and carbonates during the Middle Permian. In paleobiogeography, the South Qiangtang Block yields the fusuline Palaeofusulina fauna during the Late Permian. This fauna is absent in the whole Lhasa Block. During the Middle Permian, the fusuline Eopolydiexodina fauna in the South Qiangtang Block contrasts with the dominant Nankinella-Chusenella fauna in the Lhasa Block. In addition, the South Qiangtang Block is dominated by warm-water fusulines, brachiopods and corals during the late Early Permian. But, these warm-water taxa have not been documented from the Lhasa Block so far. The Bangong-Nujiang Ocean is considered to have formed a considerable width during the Middle Permian based on their contrast differences in depositional sequences and paleobiogeography between the South Qiangtang Block and the Lhasa Block. Consequently, the Bangong-Nujiang Ocean is considered to have opened before the Middle Permian but after the Early Permian deglaciation event.