【作者】 孔为伦；

【导师】 李双应；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2011， 博士

【摘要】 通过对中上扬子北缘地区中晚二叠世地层剖面的野外勘测、室内碳酸盐岩薄片粒度和成分统计分析,碳酸盐岩微相分析,以及碳酸盐岩同位素地球化学、烧失量、碎屑岩地球化学等的综合研究,得出如下结论:研究区中晚二叠世的岩石类型包括碳酸盐岩、碎屑岩、硅岩和煤四类,其中以碳酸盐岩为主,碎屑岩、硅质岩次之,煤较少。碳酸盐岩主要为石灰岩,其次是白云岩。石灰岩包括颗粒灰岩、泥粒灰岩、粒泥灰岩、灰泥石灰岩、礁灰岩、砾屑灰岩。根据微相特征,碳酸盐岩进一步分为生物碎屑颗粒灰岩、团块颗粒灰岩、核形石颗粒灰岩、含生物碎屑灰泥灰岩、生物碎屑粒泥灰岩、生物碎屑泥粒灰岩、鲕粒灰岩、砂屑生物碎屑、泥晶粉屑灰岩。白云岩包括泥-粉晶白云岩和细-中晶白云岩。碎屑岩包括砂岩、粉砂岩和泥页岩。硅岩包括薄层硅岩、似层状硅岩、透镜状和团块状硅岩。通过碳酸盐岩定量分析,赋予平均粒径、簸选率和颗粒/基质比权值后得出的水动力指数能反映灰岩沉积时的水动力强弱程度。根据簸选率和水动力指数的相关性,并参照前人的研究结果将水动力条件划分为五类:I、II类水动力指数<4.90,为未簸选或簸选很差;III类在4.90~6.37之间,为略有簸选;IV类在6.37~9.01之间,为簸选较强;V类>9.01,为簸选强。研究区中晚二叠世沉积相类型主要为碳酸盐岩台地相、碳酸盐陆棚相、碳酸盐斜坡相、盆地相和滨岸碎屑岩相。碳酸盐台地主要发育于陕西镇安西口剖面三里冲组、石门垭组、垭子组、熨斗滩组、龙洞川组,陕西汉中梁山剖面栖霞组-长兴组大部分层位,四川广元上寺剖面栖霞组-吴家坪组的部分层位,重庆华蓥山剖面长兴组以及栖霞组-吴家坪组的部分层位;碳酸盐陆棚主要发育于陕西镇安西口剖面水峡口组和西口组,四川广元上寺剖面栖霞组-吴家坪组的大部分层位;碳酸盐斜坡主要发育于陕西汉中梁山剖面茅口组-吴家坪组部分层位,四川广元上寺剖面吴家坪组-长兴组的部分层位,重庆华蓥山剖面栖霞组-茅口组的部分层位;盆地主要发育于四川广元上寺剖面长兴组的部分层位,重庆华蓥山剖面吴家坪组部分层位;滨岸碎屑岩主要发育于陕西汉中梁山剖面吴家坪组底部,四川广元上寺剖面栖霞组和吴家坪组底部,重庆华蓥山剖面栖霞组和吴家坪组底部。根据碳酸盐岩薄片定量分析结果,二叠纪栖霞期和吴家坪期生物因素对沉积厚度的控制作用大于水动力因素,茅口期和长兴期水动力因素和生物因素对沉积厚度的控制作用相似。陕西镇安西口二叠系灰岩巨大的沉积厚度可能是与特殊的古地理位置和区域构造背景密切相关的。陕西镇安西口剖面碳酸盐岩碳氧同位素计算出的古盐度结果显示其均为海相灰岩,与沉积环境的研究结论一致。二叠纪古海水温度范围为13.4℃~35.1℃,平均22.3℃,基本属二叠纪正常海水温度。该地区在整个二叠纪期间,生物碳酸盐岩加工厂生产力较高但存在波动,古海水盐度变化不大,古海水温度、水动力条件和洋流强度存在变化,有机质埋藏速率也存在变化。δ13C平均值明显超过了Keith和Weber总结的海相碳酸盐岩δ13C值变化范围-0.99-2.11‰的上界,表明二叠系碳酸盐岩相对富含13C。镇安西口地区二叠系碳同位素总体呈现的持续高值现象为地史上碳同位素的演化规律作了重要的补充。研究区砂岩碎屑组分物源分析表明,物源具多源性,构造背景以再旋回造山带为主,但不排除弧和俯冲带的可能性。地球化学数据显示源岩风化程度低到中等,碎屑岩沉积旋回和分选程度低,成熟度不高,为陆源碎屑组分的低等重组,源岩主要为中酸性长英质火山岩,也可能含有其它复杂成分,物源主要来自上部大陆壳。非迁移性微量元素和稀土元素显示碎屑岩的构造背景主要为大陆岛弧-活动大陆边缘,但不排除抬升基底和构造高地的影响。更多还原

【Abstract】 By field reconnaissance, grain size and composition statistic on thin sections, carbonate microfacies, isotope geochemistry, loss of ignition, geochemistry of calstic rocks on middle and later Permian sections in the northern margin of middle and upper Yangtze region, followed results has been educed:Middle and late Permian rock styles in studied area can be divided into four categories, with carbonate rocks being the major component, clastic rocks and siliceous rocks being subordinate, and coal being the least. Carbonate rocks include limestones and dolostones, with former being the main composition. Limestones include grainstone, packstone, wackstone, mudstone, reef limestone, calcirudite. By characteristics of microfacies, carbonate rocks could further be compartmentalized as followed categories: bioclastic mudstone, bioclastic wackstone, bioclastic packstone, bioclastic grainstone, peloid grainstone, oncoid grainstone, oolitic grainstone, detritus-bioclastic sparite, reef limestone, micrite calcisiltite. Dolostones include mud-silt-sized crystalline dolostone and fine-medium-sized crystalline dolostone. Clastic rocks includes sandstone, siltstone, mudstone and shale. Siliceous rocks include thin-bedded siliceous rocks, stratoid siliceous rocks and lenticular, nodular siliceous rocks.By assigning weights to mean grain size, winnowing ratio and grain/matrix in quantitative analysis of carbonate rocks, we obtain the index of hydrodynamatic force which could reflect the hydrodynamatic condition of limestone during its deposition time. Combining former research and correlation between winnowing ratio and the index, the conditions could be divided into five categories, with I、II<4.90 being no or poor winnowing, 4.90<III<6.37 being slight winnowing, 6.37<IV<9.01 being strong winnowing, 9.01<V being violent winnowing.The types of Middle and late Permian sedimentary facies in the studied area were carbonate platform facies, shelf facies, slope facies, basin facies, littoral facies. Carbonate platform facies mainly developed in Sanlichong Formation, Shimenya Formation, Yazi Formation, Yundoutan Formation, Longdongchuan Formation of Xikou section in Zhen’an county, Shanxi province, parts of Qixia-Wujiaping Formation of Shangsi section in Guangyuan county, Sichuan province, parts of Qixia-Wujiaping Formation and Changxing Formation of Huayingshan section in Chongqing county; Shelf facies mainly developed in Shuixiakou Formation and Xikou Formation of Xikou section in Zhen’an county, Shanxi province, majority parts of Qixia-Wujiaping Formation of Shangsi section in Guangyuan county, Sichuan province; Slope facies mainly developed in parts of Maokou-Wujiaping Formation of Liangshan section in Hanzhong county, Shanxi province, parts of Wujiaping -Changxing Formation of Shangsi section in Guangyuan county, Sichuan province, parts of Qixia-Maokou Formation of Huayingshan section in Chongqing county; Basin facies mainly developed in parts of Changxing Formation of Shangsi section in Guangyuan county, Sichuan province, parts of Wujiaping Formation of Huayingshan section in Chongqing county; Littoral facies mainly developed in base of Wujiaping Formation of Liangshan section in Hanzhong county, Shanxi province, base of Qixia Formation and Wujiaping Formation of Shangsi section in Guangyuan county, Sichuan province, base of Qixia Formation and Wujiaping Formation of Huayingshan section in Chongqing county.Research has shown that the controlling factor on sedimentary thickness might be biology more than hydrodynamatic condition in Qixia Formation and Wujiaping Formation, while they were similar in Makou Formation and Changxing Formation. Contrast to the other three sections, the Permian carbonates rocks of Xikou section in Zhen’an county, Shanxi province were huge thick and might relate to its special geographical location and regional tectonic background.Paleosalinity of Xikou section in Zhen’an county, Shanxi province calculated by oxygen and carbon stable isotopes showed that these carbonates deposited in marine environment, which agreed with the result of the sedimentary environment. The paleotemperatures of the seawater, which the carbonate deposited, were in the range of 13.4℃~35.1℃with mean value being 22.3℃within Permian normal scope. Combining LOI, oxygen and carbon stable isotopes, paleotemperatures, paleosalinity, and quantitative analysis stratigraphic distribution curve, it was thought that biologic carbonate plant had higher productivity with variation in paleotemperatures, hydrodynamatic condition, ocean currents intensity and organic matter buried rate, with gentle fluctuation in paleosalinity and productivity itself. The mean value ofδ13C surpassing upper limit of -0.99-2.11‰of marine carbonate rocks summarized by Keith and Weber indicated that Permian carbonates enriched 13C. The persistent high value ofδ13C of Permian carbonate rocks in Xikou section in Zhenan county made a supplement to the evolving regulation during geological time.Detrital model of studied area showed the provenances were diverse and tectonic settings were dominantly orogenic recycling source, with arc orogenic belt source and subduction mixing zone source should not be ruled out. Geochemistry showed parent rocks had low to moderate weathering degree, low degree of recycling and sorting of souce materials, low maturity and low reworking degree of terrigenous clastic rocks. Souce rocks were mainly acid and intermediate felsic volcanic rocks with other complex components should not be ruled out, and might derived mainly from upper continental crust. Immobile trace elements and REE showed that the tectonic settings was dominantly continental island-arc--active continental margins, with uplift base and tectonic highland should not be ruled out.更多还原