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二叠纪-三叠纪之交重大地质转折期,海相地质记录指示全球发生了一系列显著的生物和环境事件,但是,该时期陆相古气候、古风化作用等方面的研究还很薄弱,争议较大.为了恢复新疆准噶尔盆地玛湖凹陷上二叠统乌尔禾组至中三叠统克拉玛依组的古气候、物源特征等,本研究对玛湖凹陷钻井岩心中的泥岩样品开展了全岩主量和微量元素测试,采用多种化学风化指数判定源区风化程度及古气候条件,通过多种地球化学比值及图解来恢复源岩岩性及其构造背景.化学蚀变指数(Chemical Index of Alteration,CIA)、化学风化指数(Chemical Index of Weathering,CIW)、Parker风化指数(Weathering Index of Parker,WIP)和斜长石蚀变指数(Plagioclase Index of Alteration,PIA)等多种化学风化作用指标均指示,玛湖凹陷自晚二叠世至早三叠世发生显著的风化作用变化,由低等程度的化学风化作用转变为中等程度的化学风化作用,某些季节可能会较为温暖湿润,且在整个早三叠世保持大致稳定,在早三叠世晚期稍减弱,这与锶同位素反映的全球风化作用变化趋势一致.中三叠世时的化学风化作用与早三叠世相比,并未降低,反而稍有增加,这可能代表了地区性事件.早三叠世化学风化作用显著增强的原因可能在于全球变暖、植被破坏及季节性降雨增加等.此外,上二叠统乌尔禾组至中三叠统克拉玛依组的物源岩性主要为长英质火成岩,源岩形成时的构造背景可能为大洋岛弧环境.
During the period of Permian-Triassic significant geologic transition, marine geological records indicate a series of significant biological and environmental events occurred in the world. However, studies on continental paleoclimate and paleoclimate in this period are still weak In order to restore the Paleoclimate and provenance characteristics of the Upper Permian Wuerhe Formation to the Middle Triassic Karamay Formation in the Mahu Sag, Junggar Basin, Xinjiang, the study carried out on mudstone samples in the drilling core of the Mahu Depression The whole rock mass and trace element tests were carried out and the weathering degree and palaeoclimatic conditions of the source area were determined by using a variety of chemical weathering indexes to restore the source rock lithology and its tectonic setting through various geochemical ratios and diagrams.The chemical alteration index Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Weathering Index of Parker (WIP) and Plagioclase Index of Alteration (PIA) Weathering indicators indicate that the Mahu sag experienced a significant change of weathering from Late Permian to Early Triassic and from a low degree of chemical weathering to a moderate degree The weathering effect may be warmer and humid in some seasons and stable in the whole of the Early Triassic and slightly weakened in the late Triassic, which is consistent with the trend of global weathering reflected by the strontium isotopes. The Middle Triassic Chemical weathering did not decrease but increased slightly during the Early Triassic, which may represent a regional event.The reason for the significant chemical weathering enhancement in the early Triassic may be due to global warming, vegetation damage and seasons In addition, the provenance of the Upper Permian Wuerhe Formation to Middle Triassic Karamay Formation is chiefly British igneous and the tectonic setting of the source rocks may be the oceanic arc environment.