Dolomite crystal structure and geochemical characteristics in response to depositional environment: An example of dolomite from the Late Ediacaran Dengying Formation of the Yangzi Plateau

doi:10.13745/j.esf.sf.2023.6.16

Abstract

Abstract:

The crystal structure and geochemistry of dolomite in the Yangba section of the Late Ediacaran Dengying Formation on the Yangtze Platform are investigated to understand how they reflect the sedimentary environment in the paper. The study involves systematic sampling to analyze the evolution of the sedimentary environment based on petrological and geochemical characteristics. The research aims to elucidate the relationship between the crystal structure of dolomite, its geochemical properties, and the formation environment. The findings indicate the following: (1) The Yangba section of the Dengying Formation predominantly contains various types of microbial dolomite, including stromatolites, oncoids, foam asbestos, thrombolites, as well as some grain, particle, and breccia dolomite. The vertical sequence shows rhythmic layers of multi-stage microbial dolomite, primarily in restricted platform tidal flat and grain beach facies. (2) Geochemical analysis reveals that the Dengying Formation underwent sedimentary evolution in a shallow water environment characterized by arid conditions and high salinity, resulting in the deposition of mud and powder crystal dolomite. The lower part of the second section experienced deepening water conditions with increased humidity and lower salinity, leading to the prevalence of microbial dolomite. The middle and upper parts of the second section had relatively shallower water, decreasing humidity, and slightly higher salinity. In the fourth period, the water fluctuated between deepening and quick shallowing, accompanied by decreasing humidity and increasing salinity. (3) The dolomite crystal structure in the study area indicates the involvement of Mg²⁺-rich fluids. In arid, high salinity environments, there is a/c negative deviation, while in humid, low salinity conditions, there is a/c positive deviation. The order degree distribution suggests that a/c approaches ideal dolomite as the order degree increases. These results not only elucidate the connection between the crystal structure of contemporaneous dolomite and the formation environment but also provide insights into the ancient seawater environment of the late Proterozoic Dengying Formation.

Key words: crystal structure, geochemical characteristics, depositional environment, Yangtze Platform, Dengying Formation

CLC Number:

YANG Zhibo, JI Hancheng, BAO Zhidong, SHI Yanqing, ZHAO Yajing, XIANG Pengfei. Dolomite crystal structure and geochemical characteristics in response to depositional environment: An example of dolomite from the Late Ediacaran Dengying Formation of the Yangzi Plateau[J]. Earth Science Frontiers, 2024, 31(3): 68-79.

Figures/Tables 8

Fig.1 Comprehensive geological survey map of the study area

Fig.2 Typical dolomite types of the Dengying Formation in Yangba profile

Fig.3 Microscopic characteristics of microbial dolomite in the Dengying Formation of Yangba profile

Fig.4 Comprehensive strata histogram of the Dengying Formation in the Yangba profile

Fig.5 Crystal structure distribution map of dolomite in the Dengying Formation of Yangba profile

Fig.6 Geochemical histogram of dolomite in the Dengying Formation of the Yangba profile

Fig.7 Carbon isotope comparison of carbonate rocks in the Dengying Formation of the Yangtze Platform

Fig.8 Intersection diagram of crystal structure and geochemical characteristics of dolomite in Dengying Formation of Yangba section

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