Search Results (2)

Located in the eastern Paleo-Tethys Ocean and near the equator, carbonate sedimentation widely developed in the Sichuan Basin in the Permian Guadalupian period. Although the growth and decline of carbonate particles are closely related to the surrounding sedimentary environment, the relationships between the grain composition and distribution of the northwest Sichuan Basin and the sedimentary environment are not clear. This study explored the particle type, particle content, and sedimentary structure of 300 thin sections from 19 wells and seven field profiles of the Guadalupian period in the northwest Sichuan Basin, identified seven microfacies and four microfacies associations, analyzed the sedimentary environment, and established a sedimentary evolution model. The results show that there was a warm-water Dasycladaceae-dominated and foraminifera-dominated open platform developed in the early Roadian era in the research area. As the climate cooled during the late Roadian era, the warm-water carbonate sedimentary environment was replaced by a cold-water bryozoan-dominated and echinoid-dominated marginal sedimentary environment. As the climate continued to cool and the sea level dropped, the platform margin grain beach sediment underwent further development in the early Wordian era. In the late Wordian era stage, the sedimentary environment was influenced by the Dongwu movement, resulting in sea level changes and acidification caused by hydrothermal activities, which reduced the degree of grain beach development. During the Capitanian era, the climate became warmer due to the eruption of the ELIP. The uplift caused by the Dongwu movement resulted in a relative shallowing of the platform margin region, and hence, the grain beach sediment only developed in the southwest, while the northeast was dominated by deepwater basin sediments. The sudden transition from a warm-water, autotroph-dominated carbonate open platform to a cold-water, heterozoan-dominated carbonate platform margin resulted from a combination of tectonic movements, rapid sea level changes, and sedimentary environment changes during the Guadalupian era. Full article

The Upper Permian Changhsingian Jiantissanba reef complex is a well-known platform marginal reef, located in the western Hubei Province, China. Based on field observations and lithological analysis of the entire exposed reef complex, 12 reef facies have been distinguished according to their sedimentary components and growth fabrics. Each of the lithofacies is associated with a specific marine environment. Vertically traceable stratal patterns reveal 4 types of the lithologic associations of the Jiantianba reef: (1) heterozoan reef core association: developed in the deep marginal platform with muddy composition; (2) photozoan reef core association developed within the photic zone; (3) tide-controlled reef crest association with tidal-dominated characteristic of lithofacies in the shallow water; and (4) reef-bank association dominated by bioclastic components. The entire reef complex shows a complete reef succession revealing a function of the wave-resistant and morphological units. This study displays a complete sedimentary succession of Jiantianba reef, which provides a more accurate and comprehensive description of the reef lithofacies and a better understanding of the structure and composition of organic reefs. Full article