Origin of the Multiple-Sourced Cherts in Maokou Carbonates in Sichuan Basin, South China

Haofu Zheng,Hailei Tang,Junfeng Wu,Yixin Dong,Bo Liu,Kaiping Luo,Kaibo Shi,Qi Qiu,Xiangyang Yang

doi:10.3390/min11111269

Abstract

Cherts have been thought to originate from biosilicification, terrestrial inputs and hydrothermal activity. The study of cherts is helpful in understanding the paleo-ocean environment and tectonic–sedimentary processes. Large amounts of cherts occur widely in the Maokou Formation in the Sichuan Basin, which may be largely connected to the Permian Chert Event (PCE). However, the source of silica and the formation process of cherts remain debated. Here, we analyze the petrographic and geochemical features of the cherts from the Guadalupian Maokou Formation (~268–259 Ma) in six sections in the Sichuan Basin. Two main types of cherts, nodular and bedded, are recognized in the Maokou Formation. The formation of nodular cherts was mainly affected by hydrothermal fluids, whereas the bedded cherts are mainly of biogenetic origin. The Emeishan large igneous province (ELIP) caused the activation of deep faults, accompanied by intense hydrothermal activities. Correspondingly, the cherts of significant hydrothermal origin developed near the active deep faults. The intensified hydrothermal activities may provide extra silica supplies and flourish the silica-secreting organisms by the associated volcanogenic upwellings that facilitated the enrichment of cherts. The study of Maokou cherts can help to record the volcanic- and silicon-related biological activities in the eastern Paleo-Tethys Ocean and can provide significant implications for chert enrichment in analogous settings.

Highlights

Cherts have attracted wide attention because they were formed under specific geochemical conditions, which are of great significance in the reconstruction of the paleo-ocean environment, paleotectonic activity and paleogeography [1,2,3,4,5]
The Guadalupian cherts were formed under the influence of the silicon-rich hydrothermal fluids and volcanogenic upwellings, and they mainly accumulated in the stretched troughs related to the Emeishan large igneous province (ELIP) [5]
Systematic petrological and geochemical analyses were carried out to explore the siliceous sources and triggering factors for the formation of various types of cherts, and we propose a reasonable conceptual model for the origin of Guadalupian cherts in the Sichuan Basin

Summary

Introduction

Cherts have attracted wide attention because they were formed under specific geochemical conditions, which are of great significance in the reconstruction of the paleo-ocean environment, paleotectonic activity and paleogeography [1,2,3,4,5]. PCE has been reported in many regions around the world, such as New Zealand, Oman, Greece, Italy, Thailand, North America and China [6,7,8,9], and is believed to have been caused by the special paleo-ocean environment. Current studies overwhelmingly believed that the major formation of the Guadalupian cherts in the Upper Yangtze area was related to biosilicification and hydrothermal activity caused by regional tectonic and volcanic activity [4,22,23,24]. The Guadalupian cherts were formed under the influence of the silicon-rich hydrothermal fluids and volcanogenic upwellings, and they mainly accumulated in the stretched troughs related to the ELIP [5]

Methods

Results

Discussion

Conclusion