【作者】 张妮；

【导师】 林春明；

【作者基本信息】 南京大学 ， 矿物学、岩石学、矿床学， 2012， 博士

【摘要】 由于沉积岩的复杂性,一直以来,沉积盆地的物源研究发展缓慢,研究方法单一且主要集中在碎屑岩类分析法、重矿物法、沉积法等传统方法上,而元素地球化学和同位素地球化学方法等现代分析手段在物源研究中的应用较少；前人对苏北盆地沉积岩方面的研究主要集中在古生物、层序地层、沉积相以及对油气成藏的控制等方面,而物源研究程度较低；且苏北盆地所在的下扬子地区的构造演化一直是研究热点,但其新生代以来的构造演化研究相对缺乏。随着苏北盆地高邮凹陷古近系戴南组(E2d)勘探和研究程度的提高,展示其具备较好的构造-岩性油气藏的勘探前景,而物源供给量的变化决定了与油气藏有密切关系的沉积体的发育能力,因此,本文将传统方法和现代分析手段相结合,以苏北盆地高邮凹陷E2d地层为研究对象进行物源综合研究。此研究一方面可对弄清高邮凹陷E2d的有利沉积相带、恢复沉积盆地与源区之间的耦合关系、深化该区的油气勘探具有实际意义；另一方面,为沉积盆地的物源研究提供新的思路并起到示范作用;同时丰富了古近系沉积盆地的源岩信息,为下扬子地区的构造演化过程提供沉积物源、原生建造等地球化学方面的证据,对沉积盆地常规和非常规油气勘探和物源研究的发展具有重要意义。本文在综合、借鉴前人研究成果的基础上,以亚段为基本单位,对大量样品进行碎屑组分分析、石英阴极发光观察、锆石U-Pb测年和元素地球化学测试,并对数据进行筛选、统计、分析,对研究区在E2d沉积时期的物源方向、蚀源区位置、母岩性质(岩石类型、发育年龄和形成期次)、不同蚀源区对沉积盆地的贡献、古湖泊环境的恢复(风化作用、古地理特征和古气候特征)及构造背景等进行了较为系统和深入的探讨。碎屑组分分析显示,高邮凹陷E2d碎屑岩以岩屑长石砂岩和长石岩屑砂岩为主,母岩主要来自再旋回造山带物源区,并混合较多来自其他源区的物质。高邮凹陷各地区E2d时期的母岩类型略有差异,凹陷南部和西北部的沉积物主要来自变质岩源区；凹陷东部和西部的沉积物主要来自火成岩源区；凹陷西南部的沉积物则同时受到变质岩源区和火成岩源区的影响。该时期物源主要来自柘垛低凸起、吴堡低凸起、通扬隆起和菱塘桥低凸起这4个方向。高邮凹陷东部的周庄地区主要受到来自吴堡低凸起方向的物源影响；凹陷西部的沙埝、永安和富民北部地区的沉积物主要来自柘垛低凸起方向；凹陷南部的富民南部、曹庄、真武、邵伯、黄珏以及马家嘴南部地区的沉积物主要来自通扬隆起方向,而马家嘴北部地区的沉积物主要来自菱塘桥低凸起方向,以上地区的物源方向较为稳定。相比而言,花庄和联盟庄地区的物源方向较为复杂,主要表现为：在E2d13沉积时期,花庄地区东部沉积物主要来自吴堡低凸起方向,西部沉积物则来自柘垛低凸起方向；联盟庄地区主要受到来自柘垛低凸起方向的物源影响。至E2d12沉积时期,物源方向开始发生变化,来自柘垛低凸起方向的物源对花庄地区的影响逐渐占主导,而联盟庄南部地区开始接受来自菱塘桥低凸起方向的物源,北部地区则仍然接受来自柘垛低凸起方向的物源,这种变化一直持续至E2d11沉积时期。稀土元素(REE)的物源方向分析结果与碎屑组分分析较为一致,且在分析过程中发现,轻重稀土元素分馏值[(La/Yb) N]与矿物成熟度指数(MMI)可形成较好的吻合,(La/Yb)N值结合稀土元素总量(ΣREE),δEu值等REE参数以及沉积相分析,可对物源方向起到较好的指示作用。(Gd/Yb) N平均值也可较好的反映沉积相特征,即近岸水下扇、扇三角洲和三角洲相随其碎屑岩的平均成熟度逐渐升高,(Gd/Y>b) N平均值呈逐渐增高的趋势,这一趋势同样表现在各沉积相中的沉积亚相之间。微量和主量元素分析结果表明,高邮凹陷E2d碎屑岩的矿物成分成熟度较高,源区岩石主要为受再旋回沉积物质的影响,其次为长英质物质,受中基性物质的影响较小。随着E2d的沉积演化,再旋回沉积物源对研究区的影响一直持续,但长英质物源和基性物源对研究区的影响逐渐减弱。源区所经历的风化作用以物理风化为主,化学风化作用较弱。高邮凹陷南部陡坡带的大部分地区(黄珏、邵伯除外)所经历风化作用一般,且风化作用较为稳定,受构造运动的影响较小；北部缓坡带以及黄珏、邵伯地区所经历的风化作用差异较大,沉积物部分来自经历了较强的风化作用或较远距离搬运的源岩,部分来自近处由于强烈的构造运动抬升剥蚀后迅速再沉积的源岩。虽然苏北盆地在E2d沉积时期已演变为内陆湖泊环境,但在阜宁组四段(E1f4)沉积时期发生海侵形成的海相特征仍残留在不整合于其上的戴南组一段(E2d1)地层中,且该海相特征主要残留在高邮凹陷南部陡坡带富民南部-肖刘庄-真武-马家嘴一线的海陆交界线上。构造背景研究表明,由于地史及动力学机制的差异,位于下扬子地块西南缘的苏北盆地在E2d1时期所具有的安第斯型活动大陆边缘构造背景可反映我国东部地区由较多地体拼贴的特殊构造特征,这有别于东太平洋典型的安第斯型活动大陆边缘。锆石U-Pb测年证实扬子克拉通确实存在非常古老的早太古代地壳物质。研究区晚白垩纪-古近纪时期的沉积物物源主要形成于4个时期：①晚古生代-中生代(100～300Ma),指示物源为张八岭隆起区南段的多期岩浆活动形成的火成岩(100～200Ma)、大别-苏鲁造山带的超高压变质岩(200～250Ma)；②新元古代(700～850Ma),大别-苏鲁造山带的新元古代片麻状变质花岗岩和对Rodinia超大陆裂解事件的响应；③古元古代(1700～1900Ma),研究区对Columbia超大陆裂解作用的响应,指示扬子地块在约1850Ma发生了与Columbia超大陆由碰撞挤压向伸展作用的构造转换作用；④新太古代—古元古代(2450～2600Ma),指示扬子地块结晶基底。另外,研究区在阜宁组(E1f和泰州组(K2t)发现的400-500Ma的锆石U-Pb年龄峰是对加里东运动时期华夏地块与扬子地块碰撞所发生构造-热事件的响应,研究区对该构造热事件的响应最晚发生在白垩纪晚期,至E2d时期,该响应逐渐消失。结合REE的物源对比分析结果认为,研究区内晚白垩纪-古近纪时期的碎屑物源主要来自沉积盆地内部(结晶基底)及盆地周边再旋回造山带,沉积物主要来自扬子地块的新太古代-古元古代结晶基底和大别-苏鲁造山带广泛分布的新元古代的浅变质岩基底,具体母岩可能为高钾Ⅰ型花岗片麻岩,研究区同时还受到张八岭隆起区南段的中生代侵入岩的物源影响,源岩曾经历多期全球性构造-热事件。锆石U-Pb年龄体现了研究区的物源具有较好的继承性和再旋回沉积的特征,大别-苏鲁造山带和张八岭隆起区对研究区的物源影响最晚至白垩纪晚期便已在持续进行。E1f沉积时期发生的大规模湖盆扩张,导致研究区内不同地区所受到的物源影响存在差异。更多还原

【Abstract】 Because of the complexity of sedimentary rocks, provenance researches on sedimentary basin developed slowly. The traditional mothods including mineral composition analysis, heavy mineral analysis, sedimentary method, etc., were often used, while the geochemical method utilized was scarce. Previous researches on the North Jiangsu Basin were focused on paleontology, sequence stratigraphy, hydrocarbon reservoir, sedimentary facies, and so on, with low t degree of research.Constructive evolvement in the lower Yangtze region, where the North Jiangsu Basin located in, was research focus all along. However, the research of constructive evolvement since Cenozoic was scarce. At present, the Gaoyou Depression in the North Jiangsu Basin has been shown good exploration prospect, in which the Paleogene Dainan Formation (E2d) is the target of hydrocarbon exploration and research. The amount of the supplying source rocks can decide the size of sediment body. This paper will combine the traditional methods with modern means and select the E2d of the Gaoyou Depression in the north Jiangsu Basin as an example for provenance study. On one hand, making clear the provenance system of the E2d deposits would provide theoretical supports to further gas and oil exploration in this region, and reconstruct relationship between the sedimentary basin and provenance, on the orther hand, would provide new thought and act as an example for provenance research of sedimentary basin. This research would also enrich the information of source rock and offer geochemical evidence for constructive evolvement in the lower Yangtze region, which is also helpful to the oil and gas exploration in sedimentary basin or the development of provenance study.In this thesis, based on the previous fruits and sub-member is selected as basic unit, a systematic study with mineral composition, quartz observation in Cathodoluminescence (CL), isotope geochemistry and element geochemistry are carried out with abundant samples. Based on the results, we studied the provenance directions, the location of source, the type of mother rocks and the tectonic setting of the E2d Gaoyou Depression. After dealing with the data, we made a systemetic and embedded research on the source direction, location of source region, characteristics of mother rocks (type, age, and forming stage), contribution of different source region to sedimentary basin, reconstruction of the paleo-environment (weathering degree, characteristics of paleogeography and paleoclimate), and the tectonic background. Analysis on mineral composition displays the main composition of debris-feldspar rocks and feldspar-debris rocks in clastic rocks from the E2d Gaoyou Depression and the characteristics of source form recycled orogenic region. In the E2d Gaoyou Depression, there exists diverse source rocks in different area, for example, sediments in the southern and west-northern depression are from source of metamorphic rocks; deposits in the eastern and western depression are from source of igneous rocks; while the west-southern depression are effected by sources of both metamorphic rocks and igneous rocks. Source rocks in this period are mainly from four source directions:the northwestern Zheduo Salient, the eastern Wubao Salient, the southern Tongyang Uplift and the southwestern Lingtangqiao Salient. Weathering deposits in the eastern Gaoyou Depression such as Zhouzhuang area were mainly from direction of the Wubao Salient; sediments in Yong’an and the northern Fumin in the western depression were mostly from direction of the Zheduo Salient; deposits in the southern Fumin, Caozhuang, Zhenwu, Shaobo, Huangjue and the southern Majiazui came from direction of the Tongyang Uplift; And the sediments in the northern Majiazui are mainly from direction of the Lingtangqiao Salient. Not being like the stable source direction in the above areas, source directions in areas of Huazhang and Lianmengzhuang were relatively complex. In the E2d13, sediments in the eastern and the western Huazhuang area are respectively from direction of the Wubao Salient and the Zheduo Salient, while Lianmengzhuang area was influenced by provenance from direction of the Zheduo Salient. In the E2d12, the source direction changed and persisted to the E2d11, with influence of sediments from direction of the Zheduo Salient becoming greater in Huazhuang area, and the southern Lianmengzhuang area begining to receive sediments from direction of the Lingtangqiao Salient. The result of source direction in REE analysis is concord with that of mineral composition analysis. We found that the degree of fractionation between light REE and heavy REE [(La/Yb)N] can correspond well with the mineralogical maturity index (MMI). Combing with the REE gross (∑REE) and δEu values,(La/Yb)N values can well instruct the source direction. Correlative analysis show that, from delta facie to fan delta facie and to nearshore subaqueous fan facie, the average (Gd/Yb)N values present increasing trend with the decreasing average maturity of facies. This trend is also revealed in different sub-facies of the same facies.Trace and major elements data display the mature mineral composition in studied area, and show that the source rocks are mainly recycled metasediments and felsic materials, with being effected little by the basic rocks. The source area had experienced strong physical weathering and weak chemical weathering. Except for the areas of Shaobo and Huangjue, the majority of the southern step-fault zone underwent persistent weathering, because the deposits in these areas came from distant sources and underwent weak tectonic impact. On the contrast, in the northern slope zone, weathering diversified place to place and time to time, the provenance underwent strong weathering or severe tectonic movement for having caused rapid denudation and fast sedimentation in the depression. Although the E2d North Jiangsu Basin had become the inland lake, the marine characteristics in the E2d1inherit from the older E1f4, because of marine ingression, with these characteristics distributing in the paralic line (the southern Fumin-Xiaoliuzhuang-Zhenwu-Majiazui). Because of the divergence in geological history and dynamics mechamism, tectonic setting in the North Jiangsu Basin reflects the special tectonics of the eastern China, which is different from the typical Andean active continental margin of the eastern Pacific Ocean and needs deeper research. We deem that this is worth further investigating and deeper research for better understanding the tectonic evolvement of these Cenozoic rift basins in eastern China.Zircon U-Pb ages approve that there exist the Early Archean materials in Yangtze Craton and show that there are fore episodes of detrital zircons from the Late Creataceous-Paleogene studied area:1) Late Paleozoic-Mesozoic (100-300Ma):igneous rocks from the Southern Zhangbaling uplift (100-200Ma), uhp-metamorphic rocks in Dabie-Sulu orogenic belt (200-250Ma);2) Late Proterozoic (700-850Ma):the Late Proterozoic low-grade metamorphic granite widely distributed in the Dabie-Sulu orogenic belt;3) Early Proterozoic (1700-1900Ma):respond to the tectonic events in the cracking of the Yangtze platform and supercontinent;4) Late Archean-Early Proterozoic (2450-2600Ma): crystalline basement of the Yangtze platform. In addition, the zircon U-Pb ages of400-500Ma that found in E1f and K2t can respond to the tectonic events in the collision of of the Huaxia platform and Yangtze platform. Combined with the result of REE analysis, we deem that the sediments of the Late Archean-Early Proterozoic Gaoyou Depression mainly come from the internal part of studied basin and the recycled orogen around it, with the provenances mainly composed of the crystalline basement of the Yangtze platform, the shallow metamorphic basement of the Dabie-Sulu orogen, and some Mesozoic igneous rock from the southern part of Zhangbaling uplift. The source rocks had ever underwent multiple-episode global magma tectonic events. The zircon U-Pb ages in studied area reflect a well successive characteristics and recycled orogenic region. The large-scale expanding of ancient lake in E1f leads to the divergence among different areas in Gaoyou Depression.更多还原