Geological characteristics of the Lower Carboniferous Heshirafu Formation reef in the Artashi section in the Southwest Tarim Basin

Abstract

Objective Research on reefs is highly important for determining sedimentary environments and for oil and gas exploration, but relatively few studies have been conducted on Carboniferous reefs in the Southwest Tarim Basin. Methods Early Carboniferous reefs of the Heshirafu Formation in the Artashi section in the Southwest Tarim Basin formed in the Middle-Late Visean section of the Early Carboniferous. Reef-building organisms and accessory organisms were not quite diversified; the former mainly consisted of colonial corals of different kinds and solitary corals of a small number, and the latter were mostly echinoderms. Results Their growth was suspended due to less supply of terrigenous materials largely related to the frequent sea level changes in the Early Carboniferous in the piedmont structures of the Southwest Tarim Basin. These reefs are among the products of the recovery of metazoan skeleton reefs across the globe after the Late Devonian mass extinction; their occurrence was accompanied by mid- to late-stage Visean climate warming and global sea level rise. These reefs are common in the Early Carboniferous Visean reefs worldwide. In addition, according to the overall sedimentary facies of the Heshirafu Formation in the Artashi section and the adjacent Hantiereke Formation in the Kushanhe section, it is speculated that a transgression occurred from southwest to northeast in the Visean period of the Early Carboniferous in the Southwest Tarim Basin when the global sea level was rising and a passive continental margin was simultaneously forming and beginning to sink. As a result, a narrow platform margin facies belt gradually took shape in the piedmont structure of the Southwest Tarim Basin. This belt was conducive to the development of biological reefs. Then, when the Heshirafu Formation formed, a depositional system of "shore facies-lagoon facies-platform margin facies-slope facies-continental shelf facies" developed in a seaward direction. Conclusion The classification of sedimentary systems can provide a reference for Carboniferous sedimentary environments and oil and gas exploration in the Southwest Tarim Basin.

Keywords

• artashi
• reef
• early carboniferous
• coral
• sea level
• heshirafu formation