Full
SHI Shuyuan,born in 1987,Ph.D.,is currently a senior engineer at the PetroChina Research Institute of Petroleum Exploration & Development(RIPED). His primary research focuses on Carbonate sedimentology,sedimentary geochemistry,deep-time palaeogeography reconstruction,sedimentary tectonics,and integrated petroleum geology. E-mail: shi18yuan@163.com.
Outline
The Longmen Mountains region is one of the key areas for Devonian geological research in China. However,controversies persist concerning stratigraphic correlation and paleoenvironmental studies in this area. This study focuses on the Middle Devonian Guanwushan Formation and the Lower Carboniferous Zongchanggou Formation in the northwestern Sichuan Basin. Systematic field surveys of outcrop sections were conducted,complemented by thin-section petrographic analyses. A total of 210 carbonate rock samples were analyzed for carbon and oxygen isotope compositions. The results indicate that the middle part of the Guanwushan Formation in the northwestern Sichuan Basin was deposited under relatively higher paleosalinity and shallow-water conditions,representing a favorable stage for dolomite formation. The Guanwushan Formation exhibits conformable contacts with the overlying Shawozi Formation and the underlying Jinbaoshi Formation. The Devonian-Carboniferous boundary is marked by a regional unconformity,resulting in the absence of the upper Guanwushan Formation and the lower Zongchanggou Formation. Within the Guanwushan Formation,δ13C values range from -3.72‰ to 3.19‰(average: 0.61‰),while δ18O values vary between -7.30‰ to-1.11‰(average: -4.49‰). In the Zongchanggou Formation,δ13C values range from-4.47‰ to 2.08‰(average: -0.92‰),and δ18O values range from-5.83‰ to-0.64‰(average: -3.52‰). Paleoenvironmental reconstruction indicates that both the Guanwushan and Zongchanggou formations were deposited in typical marine settings. During deposition of the Guanwushan Formation,seawater temperatures ranged from 15 ℃ to 40 ℃,with an average of 25.32 ℃,suggesting a subtropical to tropical climate. In contrast,during deposition of the Zongchanggou Formation,seawater temperatures varied between 15 ℃ and 34 ℃,averaging 23.71 ℃,reflecting a temperate-tropical climate transition and revealing a cooling event across the Devonian-Carboniferous boundary. Furthermore,the multi-stage positive and negative excursions in δ13C were controlled by high-frequency sea-level fluctuations and periodic exposure of continental shelves,reflecting perturbations in the paleo-oceanic carbon cycle. The overall trends in carbon isotope variations across three measured outcrops in the study area show consistency and are broadly comparable to those documented in sections from Guangxi(China),France,and Germany,demonstrating their utility for global Devonian-Carboniferous stratigraphic correlation and subdivision. This study reveals the carbon isotope geochemical characteristics of the Devonian-Carboniferous strata in the northwestern Sichuan Basin,providing key evidence for regional isochronous stratigraphic correlation. It reconstructs the evolution of paleo-seawater temperatures and the mechanisms of carbon cycle fluctuations,identifies the favorable period for dolomite development,and holds significant implications for understanding paleoenvironmental evolution along the eastern Paleo-Tethyan margin and for hydrocarbon reservoir prediction.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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