【作者】 万秋；

【导师】 李双应；

【作者基本信息】 合肥工业大学 ， 矿物、岩石、矿床学， 2011， 博士

【摘要】 本文以中扬子地区二叠系实测剖面为基础,综合运用岩石学、沉积学及地球化学等方法,利用微相分析作为基本的研究手段,将实测剖面及微相分析等有机结合,对中扬子地区二叠系的地层特征、岩石学特征、沉积特征及古地理演化进行了系统的研究,并就沉积与构造演化的关系进行了深入探讨。研究区下二叠统部分缺失,仅在鄂东南及鄂西、湘西北的部分地区发育;中二叠统发育广泛,在研究区均有分布,总体南厚北薄,岩相呈渐变关系,从南到北由浅海相的灰岩向半深海及深海相的硅质灰岩、硅质岩转变,沉积水体南浅北深;上二叠统以碳酸盐岩为主,吴家坪组与龙潭组、长兴组与大隆组均为同期异相,地层穿时明显,反映出晚二叠世沉积的分异。通过实测剖面的微相分析,识别出12个微相类型,主要由生物碎屑颗粒灰岩、泥晶灰岩、泥晶粉屑灰岩、砾屑灰岩、硅质岩等组成。从微相分析及粒度分析的角度证明了在研究区中二叠统广泛发育的砾屑灰岩为异地沉积成因,而非差异压实成因。沉积体相分析表明,研究区二叠纪主要发育碳酸盐岩台地、缓坡和盆地沉积,其中,早二叠世发育碳酸盐岩台地,中二叠世发育碳酸盐岩缓坡沉积和盆地沉积,鄂西地区发育重力流沉积,自上而下分为滑塌沉积、碎屑流沉积、颗粒流沉积;晚二叠世发育台地、斜坡和盆地沉积,早-中二叠世和晚二叠世分别构成两个大的海侵海退旋回。早二叠世,海水还未完全侵入研究区,部分地区为古陆,在鄂西及研究区东南部发育局限台地-开阔台地沉积;栖霞期研究区遭受广泛海侵,中扬子北缘为外缓坡-盆地沉积,中扬子克拉通主体为缓坡沉积,局部为碳酸盐岩台地相沉积,鄂西海槽为外缓坡沉积;茅口期海侵进一步加剧,北缘为欠补偿深水盆地沉积且范围进一步扩大,中扬子主体依然为缓坡沉积,鄂西地区发育盆地相沉积。研究区中二叠世从南到北的台地-缓坡-盆地沉积构成一个碳酸盐岩斜坡沉积体系,并与区域构造格局相吻合,同沉积断裂的活动,对研究区的沉积有一定的控制作用,中扬子北缘深水盆地的发育受南秦岭海活动的制约,沉积受其控制。晚二叠世主要发育碳酸盐岩开阔台地、陆棚及盆地沉积,吴家坪期以台地相沉积为主,深水盆地范围较小,长兴期发育台地相及盆地相,深水盆地范围变大,研究区晚二叠世的沉积主要受南秦岭海活动控制,受盆地演化影响,沉积分异在晚二叠世较发育。古地理演化表明,吴家坪期中扬子北缘为深水盆地沉积,中扬子克拉通主体开阔台地沉积与陆棚沉积并存,鄂西海槽范围缩小,变为孤立海盆;长兴期海侵加剧,中扬子南部为浅海台地沉积,北缘为欠补偿深水盆地沉积且范围进一步扩大,长兴晚期达到高潮,中扬子变为克拉通边缘盆地。此外,通过碳酸盐岩微相分析,将研究区发育的成岩作用类型分为交代作用、胶结作用、压实-压溶作用及重结晶作用等,结合碳氧同位素特征,得出本区成岩环境主要为海水-大气淡水-埋藏环境,并就成岩阶段做了划分,从δ13C和δ18O值计算出古盐度及古温度,表明研究区二叠纪为温暖气候。更多还原

【Abstract】 Based on the measured Permian section in the middle Yangtze region, according to stratigraphic, lithofacies and sedimentary facies analysis, petrology, sedimentary and geochemical and other methods, microfacies analysis as a basic means of the measured profile, combination of measured profile and microfacies analysis, Permian in the Yangtze region characteristics, lithology, sedimentary characteristics and palaeogeographic have been systemly studied. Evolution of sedimentary environments and deposition models have been founded and the relationship beween sedimentary and tectonic evolution has been dephly discussed.Lower Permian is missing in a part of study area, only exposed in the southeastern and western Hubei, northwestern Hunan. The thickness of Middle Permian is gradually thinning from south to north, lithofacies show a gradient relations from south to north by the shallow marine limestone to the bathyal and deep-sea siliceous limestone, siliceous rock, depth of sea gradually becomes deeper from south to north. Upper Permian mainly formed by the carbonate rocks, Longtan and Wujiaping formation, Changxing and Dalong formation is same phase different facies, which reflecting the deposition of the Late Permian differentiation.According to the sedimentary environment analysis, three primary kinds of sedimentary environments were identified, which include ramp, platform and basin. Lower and Upper Permian have mainly deposited on the carbonate platform, the Middle Permian have mainly deposited on the ramp and basin. Types of gravity-flow deposits have been found in Maokou Formation Middle Permian, western Hubei, from top to bottom slump deposits, debris flow deposits. The sedimentary evolution indicates that two sedimentary cycles of transgression and regression occurred in the Permian:Lower-Middle Permian and Middle-Upper Permian. By use of measured section and microfacies analysis, 12 kinds of microfacies can be recognized:bioclastic grainstone, mudstone, micrite calcisiltite, bcalcirud, silica and etc. Microfacies analysis shows widely developed calcirudite in the study area is allochthonous instead of differential compaction causes.Early Permian, the sea has not yet fully penetrated the study area, part of study area is still land, southeast of the study area is restricted platform - open platform deposition. Qixiaian suffers extensive transgression in the Middle Permian, in the northern margin of the Middle Yangtze is the outer ramp– deep water basin, in the main Middle Yangtze craton is ramp deposition, some area is carbonate platform facies, western Hubei trough is outer ramp; Maokouan transgression is aggravated, the northern margin of the Middle Yangtze is deep basin and the compensation is extended. Ramp remains in the main Middle Yangtze area, western Hubei becomes to deep water basin. platform-ramp–deep water basin from south to north build up a carbonate ramp depositional system in the study area, and is consistent with the regional tectonic framework. Syndepositional fault activity is a certain control element of the deposition in the study area, deposition of the northern margin of Middle Yangtze basin is by the constraints of the South Qinling sea and under its control.Late Permian mainly developed open platform, shelf and basin, Wuchiapingian developed shallow marine sediments, deep-water basin range becomes small, Changxing developed platform and basin facies, deep-water basin range is expanding. Sedimentary facies of the Late Permian is controlled by the activities of the South Qinling sea, an obvious sedimentary facies differentiation occurred during Late Permian, which is controlled by basin evolution. Palaeogeographic evolution shows that the northern margin of the Middle Yangtze Wujiapingian is deep basin, in the main Middle Yangtze craton open platform developed, western Hubei trough is an isolated basin; Changhsingian transgression intensified and reach a climax in Late Changxingian, the northern margin of the Middle Yangtze is deep basin and the scope further expanding, the Yangtze craton come into craton margin basin.Carbonate facies analysis shows that diagenesis of Daxiakou section is consist of metasomatism, cementation, compaction pressure solution, dissolution and recrystallization, with characteristics of carbon and oxygen isotope, the diagenetic environment could be distinguished marine-atmospheric fresh water-burial environment,correlation of porosity and diagenetic phasis has been dissised. Paleotemperature and pale salinity fromδ¹³C andδ¹⁸O value suggests that study area is stable open sea and warm climate in Permian.更多还原