Sedimentary Environment and Tectonic Significance of the Upper Triassic Rigain Pünco Formation in the Rongma Region, Tibet, China

doi:10.19657/j.geoscience.1000-8527.2021.164

Abstract

Abstract:

The Upper Triassic Rigain Pünco Formation is composed of thick carbonate sequences with some clastic interbeds in Rongma (Nima, Tibet). A total of 13 carbonate microfacies were identified through thin-section microscopic analysis. According to the petrological characteristics and assemblage types, six sedimentary facies were recognized, i.e., detrital littoral, restricted-platform, open-platform, platform-edge bank, platform-edge reef, and slope facies. The results show that the Late Triassic Rongma was dominated by shallow-marine carbonate platform environment with local bathyal slope facies. During this period, four major transgression-regressive cycles may have occurred, together with several smaller sea-level fluctuations at intervals. Regionally, the sedimentary environment in the northern margin of the Bangong-Nujiang Ocean was similar to that in the Late Triassic, and the regional unconformity between the Upper Permian and Upper Triassic sequences was widely developed. Therefore, we considered that the Bangong-Nujiang Ocean was opened in an east-west quasi-simultaneous mode before the Late Triassic.

Key words: Rongma area, Tibet, Rigain Pünco Formation, sedimentary environment, Bangong-Nujiang Ocean

CLC Number:

P534.631

CHEN Yaofei, HOU Engang, GAO Jinhan, XIAO Hongji, WANG Genhou. Sedimentary Environment and Tectonic Significance of the Upper Triassic Rigain Pünco Formation in the Rongma Region, Tibet, China[J]. Geoscience, 2022, 36(01): 48-57.

Figures/Tables 5

Fig.1 Geological sketch map of the Rongma region, Tibet

Fig.2 Photos of Nagangri section, Rongma, Tibet

Fig.3 Photos of carbonate structure microfacies in the Nagangri section in Rongma, Tibet

Fig.4 Column graph of the Upper Triassic Rigain Pünco Formation in Rongma, Tibet

Fig.5 The carbonate rock and clastic rock sedimentary model of the Upper Triassic Rigain Pünco Formation in Rongma, Tibet(Modified by Hou et al.[20])

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