Full
WANG Yuan,born in 2002,is a master degree candidate,and is mainly engaged in unconventional oil and gas geological research. E-mail: 17836061727@163.com.
Outline
The Qiongzhusi Formation in the Upper Yangtze Region is currently a key target for shale gas exploration. To reconstruct the sedimentary paleoenvironment of the Lower Cambrian Qiongzhusi Formation in southern Sichuan Basin,this study takes the Qiongzhusi Formation shales from Well A1 as the research object,and explores the weathering intensity,paleoclimatic characteristics,tectonic setting,and provenance features during their deposition through geochemical analyses of major elements,trace elements,and rare earth elements. The results reveal enrichment of TFe2O3,MgO,and K2O,and depletion of SiO2,Al2O3,and Na2O in major elements. Among trace elements,Mo and Cd are strongly enriched,whereas Sr is significantly depleted. The REE distribution patterns are comparable to those of the upper continental crust,showing a right-inclined “V”shape with LREE enrichment,flat HREE trends,distinct LREE-HREE fractionation,and notable negative Eu anomalies. CIA values range from 48.16 to 69.36(average 64.03),and A-CN-K diagrams indicate moderate chemical weathering under a warm and humid climate. The Th/Sc-Zr/Sc plot suggests a first-cycle sedimentary origin for the shale,with no evidence for significant sedimentary recycling. Provenance diagrams(K2O-Rb,TiO2-Zr,Co/Th-La/Sc,and Th/Sc-Zr/Sc)consistently imply intermediate to acidic felsic igneous sources. Major element discrimination and REE abundances(ΣREE=136.51~297.68×10-6,avg. 189.23×10-6,higher than average continental crust)support a passive continental margin setting. Based on paleoclimatic conditions,provenance characteristics,and tectonic setting,it is inferred that the Lower Cambrian Qiongzhusi Formation shales in southern Sichuan were deposited in a passive continental margin under a warm,humid climate with moderate chemical weathering,predominantly sourced from intermediate-acidic felsic igneous rocks of the Kangdian-Yunnan craton with negligible hydrothermal influence.
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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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