The Upper Triassic deposits of the west Bangong-Nujiang suture zone and their paleogeographic implications

Guichun Wu,Jianxin Yao,Zhansheng Ji,Gary G Lash

doi:10.1038/s41598-021-98257-5

Guichun Wu, Jianxin Yao + Show 2 more

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https://doi.org/10.1038/s41598-021-98257-5

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Abstract

The Bangong-Nujiang Suture Zone (BNSZ) of Tibet (Xizang) has been interpreted to represent a relic of the Bangong-Nujiang Ocean. However, the existence of this ocean during Triassic time remains a point of contention. A sedimentary succession spanning the Upper Permian through Triassic described from the central BNSZ suggests that the Lhasa and South Qiangtang terranes were contiguous thus negating the existence of a terrane-separating ocean during Triassic time. However, the apparent lack of Triassic deposits in the west BNSZ has called into question the existence of Triassic deposits in the central region of the BNSZ. Our biostratigraphic work in the Wuga Formation of the Gaize area has yielded abundant Norian conodonts thus confirming the existence of Upper Triassic deposits in the west BNSZ. The clastic deposits of the Wuga Formation are herein interpreted to be of Rhaetian age. Moreover, intercalated limestone and chert are termed the Dongnale Formation of Norian age. The Norian to Rhaetian succession can be correlated with strata of the central BNSZ as well as with deposits of the Lhasa Terrane and the South Qiangtang Terrane. Similar stratigraphies among these regions through the Late Triassic suggests a shared depositional setting and that the BNSZ was not an ocean in Norian and Rhaetian time.

Highlights

The Bangong-Nujiang Suture Zone (BNSZ) of Tibet (Xizang) has been interpreted to represent a relic of the Bangong-Nujiang Ocean
In order to demonstrate the existence of Triassic deposits in the west BNSZ, we carried out a biostratigraphic investigation of the Wuga Formation east of Gaize (Fig. 1B)
The existence of Upper Triassic deposits in the west BNSZ has been debated in previous research[17,18]

Summary

Introduction

The Bangong-Nujiang Suture Zone (BNSZ) of Tibet (Xizang) has been interpreted to represent a relic of the Bangong-Nujiang Ocean. More recent biostratigraphic results stemming from an analysis of radiolarians, conodonts, and corals suggests that Triassic deposits are more widespread within the BNSZ, especially its central and eastern regions, than heretofore believed (Fig. 1B) These deposits include cherty strata that host Carnian radiolarians and conodonts described from the Dingqing a rea[16]; chert-dominated deposits containing Ladinian radiolarians in the Gajia a rea[14]; and dolomite-dominated rocks bearing Late Permian corals and Early Triassic to Anisian conodonts and limestone that yields Norian corals documented from the Ban’ge a rea[12]. Our goal is to elucidate the Triassic nature of the BNSZ in its western region

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