【作者】 詹润；

【导师】 朱光；

【作者基本信息】 合肥工业大学 ， 矿物学、岩石学、矿床学， 2013， 博士

【摘要】 青东凹陷位于华北克拉通东部渤海湾盆地东南部,是郯庐西支断裂控制形成的一个新生代断陷一坳陷型盆地。由于凹陷内部断裂十分发育,并经历了长期、复杂而强烈的活动,使得该凹陷不仅具有复杂的演化历史,同时也呈现出复杂的构造特征,从而给进一步确定含油气圈闭及具体的勘探选区带来了困难。因而,对该盆地新生代构造特征、演化规律及成盆机制的分析具有十分重要的理论和实际意义。本论文以青东凹陷新生代构造演化为主线,重点对该盆地沉积和构造特征进行了详细的研究。在对区域地球物理资料分析基础上,本文确定了青东凹陷的盆地结构特征和边界断裂特征。研究发现,剖面上该盆地具有古近纪断陷和新近纪一第四纪坳陷的二元结构。平面上盆地四周被凸起所围限,凸起与盆地之间通过大型断裂带或超覆边界过渡。受盆地东边界上郯庐西支断裂强烈活动影响,其古近纪构造格局整体呈现为北北东向带状展布,东西方向上表现为“东断西超”的构造格局。其内部二级构造带由西向东可以分为北北东向延伸的西部斜坡带、中部洼陷带和东部郯庐断坡带。南北方向上剖面显示该凹陷受一系列东西向和北西一北西西向断裂控制而形成“南北分割,隆洼相间”的构造格局。通过对青东凹陷沉积特征的分析发现,新生代期间四周的凸起为盆地的沉积充填提供了充足的物源,从盆地边缘至内部横向上沉积类型与沉积相变化较大。古近纪时期,盆地内部沉积展布格局从早到晚总体上经历了由北(北)东向、北(北)西向→近东西向→北(北)东向的变化的规律,且盆地沉积范围和沉积厚度不断缩小,古近纪后期沉积、沉降中心主要集中在中部洼陷带北部郯庐断裂带附近。新近纪—第四纪时期盆地主要表现为披盖式沉积,沉积厚度变化不大。本论文通过对青东凹陷沉降特征的定量分析,揭示其新生代沉降具有明显的时空差异,从早至晚可以划分为古近纪初始沉降阶段、古近纪快速沉降阶段至新近纪—第四纪缓慢沉降阶段,古近纪的沉降曲线具有典型伸展盆地的特征。孔店期青东凹陷沉降作用主要发生在南部地区；沙四上—沙二期沉降作用逐渐向凹陷东北部迁移;沙一至东营期沉降中心集中在凹陷北部郯庐断裂带附近,南部则处于相对抬升状态。依据整个渤海湾盆地古近纪的沉积与沉降演变规律,本文认为正是区域性构造迁移作用导致了青东凹陷从渐新世时开始就逐渐抬升,盆地萎缩,广泛缺失古近系顶部地层。青东凹陷古近纪共发育三组优势方位的断裂,分别是以郯庐西支断裂为代表的北北东向(包括北东向)断裂系统、北西向(包括北北西向和北西西向)断裂系统和东西向断裂系统。古近纪期间从早到晚该凹陷内北北东向和北西向断裂逐渐减少,而东西向断裂不断增多且规模变大。根据地球物理物理资料解释及区域构造演化分析,本文认为青东凹陷内的北北东向和北西向两组断裂系统为复活的基底断裂,分别起源于晚侏罗世郯庐左行平移断裂系和中三叠世印支期前陆变形。通过对青东凹陷古近纪不同方位断裂运动学规律的详细分析发现,复活的北北东向断裂在古近纪表现为右行平移正断层活动,北西向断裂表现为左行平移正断层活动。除较大型的基底断裂古近纪表现为持续、强烈的活动外,多数基底断裂呈现出早期活动较强、晚期活动减弱或停止的特点。青东凹陷内大量存在的东西向断裂是古近纪断陷期新生的正断层,不具有平移分量,由早到晚数量不断增多,活动逐渐增强,最终在盆地内占主导地位。根据古近纪断裂格局和活动规律,并结合前人构造应力场研究成果,本文认为青东凹陷古近纪成盆期处于近南北向的伸展应力状态。在此区域应力作用下,北北东向和北西向基底断裂呈现为斜向拉张活动,表现为直接复活、派生雁列式断裂、扩展与连接断裂三种复活方式。直接复活者主要出现在接近于正向拉张的基底断裂中,而派生雁列状断裂多出现在平移分量大的大型基底断裂带上(如郯庐西支断裂)。通过对青东凹陷与渤海海域新近纪构造特征分析发现,该时期断裂格局与古近纪相似,但构造活动明显减弱,主要受控于岩石圈热沉降作用。这期间盆地内活动的断层多是下覆较大型断裂的再活动,新生断裂较少且规模较小。郯庐断裂带在新近纪表现为右行平移正断层活动,旁侧北西向断裂为左行平移正断层活动,近东西向断裂为正断层活动。这三组断裂的几何学与运动学特征指示该时期区域应力状态为近南北向弱拉伸。综合分析表明,青东凹陷在新生代经历了孔店至沙四下期的早期断陷→沙四下末期盆地反转抬升→沙四上至沙二期的强烈断陷→沙一至东营期的弱断陷→古近纪末盆地反转抬升→新近纪弱伸展→第四纪以来区域性挤压七个主要演化阶段。太平洋区大洋板块的俯冲作用与印度-欧亚板块碰撞的远程效应在不同时期的变化是该地区新生代构造演化的动力来源。华北克拉通东部破坏的深部过程是导致青东凹陷及周边地区古近纪-新近纪期间发生构造迁移的主要原因。更多还原

【Abstract】 The Qingdong sag in the southeast of the Bohai Bay basin in eastern North China Craton is an Cenozoic rift-type to depression-type basin controlled by the western branch of the Tan-Lu fault zone. It has long, complex and intensive tectonic activities, well-developed faultsand complex structural features due to its suffering complicated structural evolution, and also presents, which make it more difficult to determine hydrocarbon traps and selection of exploration areas. Therefore, it is of great theoretical and practical significance to analyze its Cenozoic structural features, evolution history and the formation mechanism. With the Cenozoic structural evolution as a main clue, characteristics of sedimentation and structures in the sag are studied in detail.Based on analysis of regional geophysics materials, structural features and boundary faults of the basin have been recognized. The studies find that the basin has a dual texture which consists of the Paleogene rift and Neogene-Quaternary depressions on its profile. It is surrounded by uplifts on the plane. Boundaries between the basin and uplifts are large faults and overlap lines. Controlled by strong activities of the western branch of the Tan-Lu fault zone, the basin framework of Paleogene shows NNE-SSW trend in general, with faults at the eastern margin and overlap at the western margin on its E-W profiles. Secondary structure units of the basin can be divided into the western slop belt, central sub-sag belt and the Tan-Lu fault fault-slope belt from west to east, which are all NNE-trending. The sag is controlled by series of E-W and NW-NWW faults on the NS profiles, forming the tectonic framework of division in the N-S direction accompanied by alternating uplifts and depressions.Based on the analysis of Cenozoic sedimentary characteristics in the Qingdong sag, we can find that abundant sediments of the sag were supplied by surrounding uplifts during the rifting period. The sedimentary sequences vary obviously from boundaries to centre of the basin. Generally, the sedimentary distribution underwent a change process of N(N)E and N(N)W→nearly EW→N(N)E from the early to late stage during Paleogene in the interior of the basin, Meanwhile, the depositional area and thickness continued to decrease. The depocenter and subsidence centers mainly focused on the vicinity of the Tan-Lu fault zone in the sub-sag belt at the end of Paleogene. The basin deposition is uniform and sediment thicknesses have little variations during Neogene and Quaternary.After quantitative analysis on subsidence history of the Qingdong sag, the paper reveals that the sag subsidence differ greatly in space and time during Cenozoic, which can be classified into initial subsidence and rapid subsidence stages during Paleogene and the slow subsidence from Neogene to Quaternary. Their subsidence curves indicate a typical extensional basin of Paleogene. The subsidence mainly concentrated in the southern areas during deposition of the Kongdian Formation, then migrated to the northeastern areas gradually during deposition of the upper Sha-4and Sha-2members. Finally, the subsidence center focused on the vicinity of the Tan-Lu fault zone in the northern basin during deposition of the Sha-1member and Dongying Formation, meanwhile, the southern areas were be under the regional uplifting relatively. According to the sedimentary and subsidence evolution rules of the whole Bohai Bay basin during Paleogene, the paper proposes that it is the tectonic migration that leads to the basin uplifting gradually during the Oligocene together with basin shrinking and the wide absence of the top Paleogene strata.There are three sets of predominant fault systems developed during Paleogene in the Qingdong sag, including the NNE-trending fault system (including NNE, NE and NEE) represented by the west branch of Tan-Lu fault zone, NW-trending (including NNW,NW and NWW) and E-W trending fault systems. From analyses of many geophysical data and regional tectonic evolution, it is proposed that the NNE-and NW-striking faults belong to basement faults, and result from the Tan-Lu sinistral faulting in Late Jurassic and foreland deformation in the Indosinian period respectively.By analysis of kinematic characteristics of Paleogene for faults with different orientations in the Qingdong sag, it is found that the reactivated NNE and NW basement faults show dextral and sinistral normal faulting respectively. Majority of the basement faults show intensive reactivity in the earlier stage, and became weak or dying in the later stage except for some large-scaled faults which have strong and sustained activities. A large number of E-W faults formed during the Paleogene rifting are newly-formed normal faults without strike-slip components, and they show increase in quantities and activity intensity gradually from the earlier to later stage and predominated in the basin finally.According to the distribution pattern and activity features of the Paleogene faults and comparing with previous results about regional stress fields, it is proposed that the basin was under N-S extension during the Paleogene basin formation period. The NNE and NW basement faults reactivated by a way of oblique extension. Reactivity methods of the basement faults can be classed into three types, i.e. the direct reactivity, formation of new en echelon faults and direct reactivity plus propagating into E-W faults. The direct reactivity faults mainly appear in some basement faults close to orthogonal extension while the deriving en echelon faults usually in the major basement with larger strike-slip components, such as the western branch of the Tan-Lu fault zone.By analysis of Neogene structural characteristics in the Qingdong sag and Bohai region, it is found that the fault framework formed during this period is similar to that of the underlying Paleogene strata, but activity intensity, mainly controlled by lithospheric thermal subsidence, became weaker. Active faults of Neogene in the basin were reactivity of pre-existing ones mostly. Newly-formed faults of Neogene were few and often small-scale. The Tan-Lu fault zone showed dextral normal faulting while the NW-and E-W striking faults showed sinistral normal faulting and normal faulting respectively. Geometry and kinematics of the three sets of faults indicate that the region was under a weaker, N-S extension setting during Neogene.Comprehensive studies show the Qingdong sag experienced seven phasesof evolution, i.e. the early rifting stage during deposition of the Kongdian Formation and lower sha-4member, basin inversion and uplifting stage at the end of deposition of the lower sha-4member, intensive rifting stage from deposition of the upper sha-4to sha-2members, weak rifting stage during deposition of the sha-1member and Dongying Formation, basin inversion and uplifting stage at the end of Paleogene, weak extension stage during the Neogene and regional compression stage since the latest Neogene. Geodynamics for the basin evolution might come from changes in oceanic plate subduction in the Pacific Ocean as well as far-field influence of the India-Eurasiancollision in different periods. It is the destruction deep processes of the eastern North China Craton that lead to the structural migration in the Qingdong sag and its surrounding areas during Paleogene-Neogene.更多还原