Geochemical Characteristics and Geological Significance of Permian Reef Limestone in the Northwest of Tarim Basin

In the northwest of Tarim basin, the Early Permian section exposed thick layer of algae reef limestone, which is an important target layer for the oil-gas prospecting areas. The trace elements of the algae reef limestone showed a seawater-like pattern of LREE depletion, negative Ce anomaly and positive Gd anomaly. The high Y/Ho and Er/Nd, and the extremely low Th indicate that it was not affected by terrestrial debris. δCe had moderate to weak negative anomalies, δU<1, V/(V+Ni) between 0.16~0.20 and V/Sc between 4.28~5.14 indicate that algal reef limestone formed in an oxidizing environment. Sr/Ba is between 16.19~25.77, indicating that the seawater was in a saline environment. Sr/Cu is between 176.42~361.54, indicating the arid climatic condition. Based on various geochemical characteristics, it is inferred that the algae reef limestone in the northwest of Tarim basin was formed in a limited carbonate platform environment.