Effect of Rheology and Thickness Variation of Basal Detachment on Fold-and-Thrust Belts: Numerical SimulationEI北大核心CSCD

Detachment is the prime factor affecting the fold-and-thrust belts. In order to investigate the effect of rheology and thickness variation of basal detachment on fold-and-thrust belts, numerical simulations are carried out by using two dimensional plane strain mechanical models with elastoplastic or viscoelastoplastic material behavior solved with the finite difference software FLAC. Universal mudstone detachment has frictional property. Such fold-and-thrust belts are simulated with elastoplastic constitutive model. In contrast, salt detachment has creep property, so viscoelastoplastic constitutive models are employed for these fold-and-thrust belts. The results show that rheology and thickness of basal detachment influence the fold-and-thrust belts greatly. When the detachment is mudstone, the typical structural style of imbricate fan will develop, also the propagating forward piggy-back thrust sequence; however, when the detachment is salt, structural style will show Jura-type consisted of a series of anticlines and synclines, and out-of-sequence thrusts will appear. Varieties of thickness of basal mudstone detachment will change eventual surface slope of the fold-and-thrust belts, but have little effect on the structural styles and thrust sequence. For salt detachment, the effect is significant, no matter where the thickest detachment distributes, most strongly deformation and the highest surface will be located there. Thickening of salt detachment combined with slight thinning of overburden strata from hinterland to foreland will result in uncommon structural style and thrust sequence: back thrusts and backward propagating. These differences are mainly due to the much smaller shear strength of salt than that of mudstone. © 2017, Science Press. All right reserved.     

Syn-depositional continental rifting of the Southeastern Neo-Tethys margin during the Albian–Cenomanian: evidence from stratigraphic correlation

ABSTRACT

Albian–Cenomanian successions (Kazhdumi and Sarvak formations) represent remarkable variations in thickness, facies, fauna, and environments throughout the Zagros area. In the Coastal Fars (Charmu section), sedimentological and paleontological data evidence an intrashelf, with depths of 10s–100s m, surrounded by a shallow carbonate platform. Due to its depth, deposition of sequences in this setting has been controlled by eustatic sea-level changes rather than eurybathic changes, and several condensation episodes occurred related to marine transgressions. These observations are different from those in the adjacent sections in the Coastal Fars which recorded subaerial exposures instead. Combined with previous studies, this study denotes several intrashelf basins enclosed by a shallow carbonate platform on the southeastern margin of the Neo-Tethys during the Albian–Cenomanian. Development of intrashelf basins corresponds to basement faults in the Fars Salient. Likely, an extensional tectonic regime associated with a rifting event created horst–graben architecture by exerting extension along the basement faults and reactivating salt structures. Deposition on these troughs and highs led to the facies and thickness variations of the concomitant sequences. Development of several intrashelf basins on the southeastern margin of the Neo-Tethys indicates that syn-depositional continental rifting event could occur during the Albian–Cenomanian, prior to the tectonic inversion around the earliest Turonian.     

福建漳州牛头山火山地质公园火山喷发层序及岩相

牛头山火山地质公园位于风景壮观秀丽的闽南漳州市海滨，构造位置处于平潭一东山北东向断裂带中段，火山口坐落在龙海市隆教乡白塘村附近，涨潮时古火山口部分被海水淹没成为孤立于海中的小岛，退潮时，火山口全貌再露海面，火山口附近有一深槽（凹地），直径约8m，低于周围岩石3m，火山岩地层为新第三纪佛昙组上段玄武岩，根据岩性分布特征及岩石结构构造和岩层的产状等。可划分为喷溢相和火山颈相，是省内保存较完好的新生代古火山机构。     

东海陆架盆地西湖凹陷渐新世海侵作用与潮控体系沉积特征*

西湖凹陷位于东海陆架盆地东部坳陷带,是该盆地规模最大的富油气凹陷。然而,西湖凹陷渐新世沉积环境与沉积体系类型一直存在较大争议。本文以井、震为基础,岩心为核心,结合地球化学指标,通过泥岩甾烷与自生海绿石的特征,明确了渐新世西湖凹陷南部整体处于海陆交互的过渡环境,且发生5次主要的海侵事件。西湖凹陷南部渐新统以厚层砂岩与薄层泥岩互层为特征,发育典型的双向交错层理、双黏土层、透镜状层理及泥质披覆,共识别出4种主要的岩相类型: 含泥砾块状中粗粒砂岩相、交错层理中细粒砂岩相、沙纹层理粉细砂岩相、纹层状泥岩相。渐新世,西湖凹陷南部主要发育潮控河口湾体系,其中包括潮汐水道、潮汐沙坝、沙质潮坪及泥质潮坪等多个沉积微相,其沉积地形在SW向逐渐变为开阔的展布特征,说明研究区河流供源来自东北部,而潮汐水流来自西南部。渐新世西湖凹陷南部与开阔海连通,受到海侵作用下潮汐水流的强烈改造,且由于地形坡度较缓,无大规模的河流携带碎屑物质注入,易形成潮汐作用为主的河口湾体系。     

Cycles of passive versus active diapirism recorded along an exposed salt wall

Although it has long been recognised that passive salt diapirism may encompass sub-ordinate cycles of active diapirism, where sedimentary overburden is periodically shed off the roof of the rising salt, there has been very little study of this process around exposed salt (halite) diapirs. However, the Late Miocene-Pliocene Sedom salt wall, on the western side of the Dead Sea Basin, presents an opportunity for detailed outcrop analysis of diapiric salt and the associated depositional and deformational record of its movement during both passive and active phases of diapirism. The sub-seismic scale record of diapirism includes sedimentary breccia horizons interpreted to reflect sediments being shed off the crest of the growing salt wall, together with exceptional preservation of rotated unconformities and growth faults. Areas of more pronounced dips directed towards the salt wall are capped by unconformities, and interpreted to represent withdrawal basins within the overburden that extend for at least 1500 m from the salt margin. Elsewhere, broad areas of upturn directed away from the salt extend for up to 1250 m and are marked by a sequence of rotated unconformities which are interpreted to bound halokinetic sequences. The margins of the salt wall are defined by steep extensional boundary faults that cut upturned strata, and have enabled rapid and active uplift of the salt since the Holocene. The Sedom salt wall therefore charts the transition from passive growth marked by withdrawal basins, growth faults and unconformities, to more active intrusion associated with major boundary faults that enable the rapid uplift of overburden deposited on top of the salt to ∼100 m above regional elevations in the past 43 ka. Individual cycles of passive and active diapirism occur over timescales of <30 ka, which is up to an order of magnitude less than typically suggested for other settings, and highlights the dynamic interplay between salt tectonics and sedimentation in an environment undergoing rapid fluctuations in water level.     

松辽东缘中生代含煤盆地充填序列及在能源勘探中的意义

松辽东缘在晚侏罗世一早白垩世期间发育一系列ＮＥ向含煤断陷盆地。主要含煤层位是晚侏罗世沙河子组和早白垩世大羊草沟组。盆地的充填特征具有明显的规律性．基本上为三段式。反映在拉张裂陷－萎缩抬升的背景下盆地的演化特点。聚煤作用发生在特定的演化阶段。对盆地充填序列的研究有助于指导能源资源的勘探。     

歧口凹陷西坡白水头构造沙一段下部油气成藏期次研究

根据储层的成岩序次、油气包裹体特征及含烃盐水包裹体均一温度,结合构造活动特征及烃源岩的演化史,对歧口凹陷西坡白水头构造沙一段下部油气藏进行了成藏期次综合研究。认为该油气藏有三期油气充注过程:第一期发生在馆陶组末到明化镇组下段沉积早中期,约为11.5～8Ma,源区沙三段烃源岩有机质处于低成熟阶段,油气来源不足,成藏规模小;第二期发生在明化镇下段沉积末期到明化镇上段沉积初期,约为5Ma±,白水头构造各主要断层活动强烈,沙三段烃源岩开始进入生排烃高峰,油气运聚规模较大;第三期发生在明化镇上段沉积中晚期到第四系初期,约为3.5～2Ma,烃源岩整体处于生排烃高峰,各大断层活动有所减弱,但仍控制着油气的大规模垂向运移,成藏规模大。     

准噶尔盆地西南缘构造模式、演化及其油气

通过地震勘探、钻井、地面地质资料综合分析,列出了6点依据,认为,盆地南缘西部构造特征是3个深浅层次的北凸孤形滑脱体。它们分别为燕山和喜山运动由南向北的侧向挤压造就而成。圈闭的含油气性,总的说来西段较东段好。     

藏南日喀则群复理石的层序、沉积流体性质和沉积模式分析

日喀则群砂泥质复理石的浊积层序非常发育,包括富泥的粘性高密度浊流、砂质高密度浊流、低密度浊流和Pickering及Hiscott (1986)的限制性泥质高密度浊流的沉积层序。其中,低密度浊流沉积层序的组合与鲍马(Bouma)层序很相似,两者的区别在于沉积的粒度、粒级分布范围、层序厚度和相组合等特征的不同。沉积相序、古流向和物源分析表明,日喀则群复理石盆地的南侧主要发育单向物源的海底扇体系,而盆地北侧以发育双向物源和多种沉积流体的复合沉积为特征。值得指出的是,特殊的浊积类型——限制性泥质高密度浊流沉积的发现为论证日喀则群复理石盆地属残留盆地又提供了一条有力的依据。     

大陆架科学钻探CSDP-2井科学目标及初步成果

大陆架科学钻探（CSDP）,是一个在我国大陆架上实施的以钻探我国陆架区深部地层为目的的科学计划,是介于大陆科学钻探（ICDP）和大洋科学钻探（DSDP,ODP,IODP）之间的大陆架地球科学探索计划。首批两口科学钻探井布设在南黄海陆架上,CSDP-1井的主要目标为第四纪及其环境演化,CSDP-2井则瞄准中-古生界海相地层及其资源环境效应。CSDP-2井的科学目标为揭示中-古生界的地层时代、沉积环境、构造演化,详细标定钻遇地层的地球物理性质,系统评价其油气生储盖特征,以及开发和探索钻探与井中观测等技术。CSDP-2井完井深度2 843.18 m,创造了全球陆架全取心钻探的最深记录,综合取心率97.7%,其中中-古生界取心2 198.10 m,取心率99.3%,先后钻遇第四系-新近系,下三叠统青龙组,二叠系大隆组、龙潭组、孤峰组和栖霞组,石炭系船山组、黄龙组和高骊山组,泥盆系五通组,志留系坟头组和高家边组。初步建立钻遇中-古生界的岩性剖面、地球物理性质剖面、地层时代和沉积环境格架,厘定印支期和加里东期两个不整合面,以及孤峰组和龙潭组之间的断层滑脱面,并通过对烃源岩系统评价发现4套好的烃源岩。下一步工作将在进一步厘定地层年龄的基础上,深入探讨沉积环境演化、构造和热演化历史,以及结合区域资料恢复古地理环境。