The Guadalupian (Permian) Gufeng Formation on the North Margin of the South China Block: A Review of the Lithostratigraphy, Radiolarian Biostratigraphy, and Geochemical Characteristics

Abstract

The Guadalupian (Permian) Gufeng Formation, distributed over the north margin of the South China block, is characterized by siliceous rock and muddy rock and yields several representative radiolarian fossils. The lithostratigraphy, radiolarian occurrences and biostratigraphy, and geochemical characteristics of the Gufeng Formation are reviewed and summarized in this paper. The distributional area of the Gufeng Formation is subdivided into the Lower, Middle, and Upper Yangtze regions. The Gufeng Formation in the Lower Yangtze region is lithostratigraphically characterized by muddy rock, chert, and nodule-bearing muddy rock in descending order. The Gufeng Formation in the Middle Yangtze region is lithostratigraphically characterized by chert, muddy rock with carbonate, and muddy rock in ascending order. The lithostratigraphic characteristics of the “Gufeng Formation” in the south margin of the South China block greatly differ from the typical Gufeng Formation in containing fewer siliceous rocks and a large amount of clastic rocks and in having a significantly greater total thickness; therefore, this article considers that the “Gufeng Formation” in the block's south margin should be isolated from the Gufeng Formation in the block's north margin. The radiolarian biostratigraphy of the Lower and Middle Yangtze regions is composed of the Pseudoalbaillella globosa, Ps. monacantha, and Follicucullus scholasticus-Ruzhencevispongus uralicus assemblage zones in ascending order. The lower Gufeng Formation has abundantly yielded the Albaillellaria; however, its occurrence ratio with respect to other radiolarian orders decreases stratigraphically upward. The geochemical characteristics indicate the following facts: (1) the siliceous rocks are generally biogenic; (2) even though a previous study concluded that the organic matter within the chert was originated from terrestrial or reworked organic matter, the origin remains debatable; and (3) the Gufeng Formation was formed on a continental shelf. The geochemical characteristics, in addition to the lithological characteristics, indicate that the redox conditions of the Gufeng Formation in the Lower Yangtze region changed from aerobic to suboxic to anoxic, while that in the Middle Yangtze region changed from oxic to anoxic to suboxic.