南海北部深水区东西构造差异性及其动力学机制

南海北部深水区位于南海洋陆转换带,构造运动活跃,构造特征复杂。同时,南海北部深水区石油、天然气、天然气水合物等矿产资源丰富。因此,加强南海北部深水盆地构造特征分析,揭示南海北部陆缘构造属性与南海形成演化机制,对于南海深部过程演变研究、油气资源评价与地质灾害防治等具有重要的意义。本论文通过对南海北部深水区陆架-陆坡结构、盆地构造特征与演化规律的分析,指出研究区东西存在明显的构造差异性,并分析了其动力学机制。南海北部深水区东部陆架-陆坡结构为宽洼窄隆型,而西部为窄洼宽隆型。东部珠江口盆地深水凹陷均为半地堑结构,剖面上呈不对称的箕状;西部琼东南盆地除北礁凹陷为南段北超的小型半地堑外,其它凹陷均为地堑结构,为南北双断式沉积体系。在构造演化方面,东部中中新世末结束裂后期进入新构造活动期,白云凹陷构造活动性增强,表现为快速的沉降和显著的晚期断裂作用;而西部晚中新世末才进入新构造活动期,深水区表现为快速沉积作用,断裂活动较弱。     

Controls on forearc basin architecture from seismic and sequence stratigraphy of the Upper Cretaceous Great Valley Group,central Sacramento Basin,California

Seismic and sequence stratigraphic analysis of deep-marine forearc basin fill (Great Valley Group) in the central Sacramento Basin, California, reveals eight third-order sequence boundaries within the Cenomanian to mid-Campanian second-order sequences. The third-order sequence boundaries are of two types: Bevelling Type, a relationship between underlying strata and onlapping high-density turbidites; and Entrenching Type, a significantly incised surface marked by deep channels and canyons carved during sediment bypass down-slope. Condensed sections of hemipelagic strata draping bathymetric highs and onlapped by turbidites form a third important type of sequence-bounding element, Onlapped Drapes. Five tectonic and sedimentary processes explain this stratigraphic architecture: (1) subduction-related tectonic tilting and deformation of the basin; (2) avulsion of principal loci of submarine fan sedimentation in response to basin tilting; (3) deep incision and sediment bypass; (4) erosive grading and bevelling of tectonically modified topography by sand-rich, high-density turbidite systems; and (5) background hemipelagic sedimentation. The basin-fill architecture supports a model of subduction-related flexure as the principal driver of forearc subsidence and uplift during the Late Cretaceous. Subduction-related tilting of the forearc and growth of the accretionary wedge largely controlled whether and where the Great Valley turbiditic sediments accumulated in the basin. Deeply incised surfaces of erosion, including submarine canyons and channels, indicate periods of turbidity current bypass to deeper parts of the forearc basin or the trench. Fluctuations in sediment supply likely also played an important role in evolution of basin fill, but effects of eustatic fluctuations were overwhelmed by the impact of basin tectonics and sediment supply and capture. Eventual filling and shoaling of the Great Valley forearc during early Campanian time, coupled with dramatically reduced subsidence, correlate with a change in plate convergence, presumed flat-slab subduction, cessation of Sierran arc volcanism, and onset of Laramide orogeny in the retroarc.     

珠江口盆地白云凹陷深水扇沉积相特征

珠江口盆地深水扇的发现为中国油气勘探中的重大突破,并以其宏大的规模、典型的结构及巨大的勘探前景引起国内外的关注。在区域地质背景研究基础上,通过白云凹陷X-1气田岩石学特征、地球化学特征和地球物理特征研究,识别出该盆地内深水扇沉积体,将深水扇划分为内扇、中扇和外扇三个亚相和水道颗粒流、碎屑流、水道间、近源和远源浊流等微相。对各微相作了较为详细的描述,结果表明水道砂质碎屑流微相是最有利于优质储集砂体发育的沉积微相。在此基础上提出深水扇理想沉积模式。     

晚三叠世鄂尔多斯盆地湖盆沉积中心厚层砂体特征及形成机制分析

晚三叠世延长组长6、长7油层组沉积期鄂尔多斯盆地湖盆中部深水区稳定发育厚层砂岩,局部地区连续厚度可达上百米。在盆地西南沉积体系,巨型砂带北西—南东向平行于相带界线展布,与三角洲前缘砂体呈现出“断根”的现象;在东北沉积体系,砂带围绕三角洲呈群状、带状分布。厚层砂体成因复杂,总体上可称作深水重力流—牵引流沉积复合体,包括滑塌砂体、砂质碎屑流砂体、浊积砂体、三角洲砂体及底流改造砂体5种成因类型,其中以重力流沉积组合为主,但白豹及其北部主要为三角洲沉积夹重力流沉积。不同成因的砂体纵向叠加,横向复合连片形成了稳定分布、规模宏大的砂带。厚层砂体的形成、展布方向、分布范围主要受控于沉积物的供给速率、湖盆底形及构造活动等因素。     

Structural characteristics of central depression belt in deep-water area of the Qiongdongnan Basin and the hydrocarbon discovery of Songnan low bulge

The Qiongdongnan Basin has the first proprietary high-yield gas field in deep-water areas of China and makes the significant breakthroughs in oil and gas exploration. The central depression belt of deep-water area in the Qiongdongnan Basin is constituted by five sags, i.e. Ledong Sag, Lingshui Sag, Songnan Sag, Baodao Sag and Changchang Sag. It is a Cenozoic extensional basin with the basement of pre-Paleogene as a whole. The structural research in central depression belt of deep-water area in the Qiongdongnan Basin has the important meaning in solving the basic geological problems, and improving the exploration of oil and gas of this basin. The seismic interpretation and structural analysis in this article was operated with the 3D seismic of about 1.5×10~4 km~2 and the 2D seismic of about 1×10~4 km. Eighteen sampling points were selected to calculate the fault activity rates of the No.2 Fault. The deposition rate was calculated by the ratio of residual formation thickness to deposition time scale. The paleo-geomorphic restoration was obtained by residual thickness method and impression method. The faults in the central depression belt of deep-water area of this basin were mainly developed during Paleogene, and chiefly trend in NE–SW, E–W and NW–SE directions. The architectures of these sags change regularly from east to west: the asymmetric grabens are developed in the Ledong Sag, western Lingshui Sag, eastern Baodao Sag, and western Changchang Sag; half-grabens are developed in the Songnan Sag, eastern Lingshui Sag, and eastern Changchang Sag. The tectonic evolution history in deep-water area of this basin can be divided into three stages,i.e. faulted-depression stage, thermal subsidence stage, and neotectonic stage. The Ledong-Lingshui sags, near the Red River Fault, developed large-scale sedimentary and subsidence by the uplift of Qinghai-Tibet Plateau during neotectonic stage. The Baodao-Changchang sags, near the northwest oceanic sub-basin, developed the large-scale magmatic activities and the transition of stress direction by the expansion of the South China Sea. The east sag belt and west sag belt of the deep-water area in the Qiongdongnan Basin, separated by the ancient Songnan bulge, present prominent differences in deposition filling, diaper genesis, and sag connectivity. The west sag belt has the advantages in high maturity, well-developed fluid diapirs and channel sand bodies, thus it has superior conditions for oil and gas migration and accumulation. The east sag belt is qualified by the abundant resources of oil and gas. The Paleogene of Songnan low bulge, located between the west sag belt and the east sag belt, is the exploration potential. The YL 8 area, located in the southwestern high part of the Songnan low bulge, is a favorable target for the future gas exploration. The Well 8-1-1 was drilled in August 2018 and obtained potential business discovery, and the Well YL8-3-1 was drilled in July 2019 and obtained the business discovery.     

Late Pleistocene deep-water circulation in the subantarctic eastern Atlantic

We present three new benthic foraminiferal δ¹³C, δ¹⁸O, and total organic carbon time series from the eastern Atlantic sector of the Southern Ocean between 41°S and 47°S. The measured glacial δ¹³C values belong to the lowest hitherto reported. We demonstrate a coincidence between depleted late Holocene (LH) δ¹³C values and positions of sites relative to ocean surface productivity. A correction of +0.3 to +0.4 [‰ VPDB] for a productivity-induced depletion of Last Glacial Maximum (LGM) benthic δ¹³C values of these cores is suggested. The new data are compiled with published data from 13 sediment cores from the eastern Atlantic Ocean between 19°S and 47°S, and the regional deep and bottom water circulation is reconstructed for LH (4–0 ka) and LGM (22–16 ka) times. This extends earlier eastern Atlantic-wide synoptic reconstructions which suffered from the lack of data south of 20°S. A conceptual model of LGM deep-water circulation is discussed that, after correction of southernmost cores below the Antarctic Circumpolar Current (ACC) for a productivity-induced artifact, suggests a reduced formation of both North Atlantic Deep Water in the northern Atlantic and bottom water in the southwestern Weddell Sea. This reduction was compensated for by the formation of deep water in the zone of extended winter sea-ice coverage at the northern rim of the Weddell Sea, where air–sea gas exchange was reduced. This shift from LGM deep-water formation in the region south of the ACC to Holocene bottom water formation in the southwestern Weddell Sea, can explain lower preformed δ¹³C_DIC values of glacial circumantarctic deep water of approximately 0.3‰ to 0.4‰. Our reconstruction brings Atlantic and Southern Ocean δ¹³C and Cd/Ca data into better agreement, but is in conflict, however, with a scenario of an essentially unchanged thermohaline deep circulation on a global scale. Benthic δ¹⁸O-derived LGM bottom water temperatures, by 1.9°C and 0.3°C lower than during the LH at deepest southern and shallowest northern sites, respectively, agree with the here proposed reconstruction of deep-water circulation in the eastern South Atlantic Ocean.     

济阳坳陷车15井区浊积扇沉积及油气勘探意义

根据岩心、地震、测录井资料,在济阳坳陷车镇凹陷车15井区的沙三下砂砾体中识别出滑塌浊积扇和深水浊积扇。其中,车古25井以具水道补给的(有根的)滑塌浊积扇为特色;内扇及水道最发育,为碎屑流夹浊流的巨砾岩、中细砾岩(厚10～20 m)与砾质砂岩夹薄层深灰、灰色泥岩;崩塌成因的巨砾(大小1.06 m)反映了陡的斜坡;地震上呈楔状外形,内扇为弱反射,中扇与外扇为发散、亚平行的连续反射。车57井以粒度偏细且有根的深水浊积扇与深湖相互层为特色;中扇发育,为厚(5～11 m)的水道碎屑流细砾岩与砾质砂岩,夹深灰色泥岩;水道沉积表现为钟型测井曲线。顺水道方向滑塌浊积扇由北而南产生进积,向盆出现深水浊积扇;2类扇体沿主构造线串珠状排列,包裹于大片的深湖相中,呈现"深湖包扇"的沉积格局。不同类型浊积扇的识别及其边界的确定,对于该区隐蔽圈闭勘探具有重要意义。     

基于ADCP反向散射强度估算悬沙浓度在洋山港的应用研究

洋山深水港地形差异大,流态复杂,在宽阔的西口门和窄深东口门,以传统方法同步开展悬沙输移监测十分困难。详述了在颗珠山汊道应用ADCP走航测沙的实现方法,结论显示,与传统代表垂线法成果相比,通过ADCP声反向散射信号计算的垂线平均含沙量,其对比标准差约为6%,随机不确定度在12%(置信水平为95%)左右,误差分布基本成正态,两种方法之间的断面输沙率相关系数达到0.96,可见,利用ADCP的声反向散射信号,只要标定得当,在洋山港区得到的垂线平均含沙量和断面输沙率是可信的,该技术将为洋山港区关键控制断面悬沙监测提供新思路。     

利用AVO正反演技术识别深水凹陷气层

针对深水凹陷莺二段地质条件复杂,地震资料信噪比较低、烃检困难等难点,利用琼东南盆地陵水凹陷地气勘探阶段的钻孔资料及测井资料,应用zoeppritz方程进行射线数字模拟,研究该区典型气层及水层段的反射特征和AVO特征,对深水区坡折带低信噪比资料进行了保幅去噪及道集拉平处理,对常规的碳氢指示因子进行了改进.经结果表明:改进的碳氢指示因子对第三类及第四类AVO异常检测卓有成效,第四类AVO异常对于深水勘探有重要意义.     

湖相深水块状砂岩特征、成因及发育模式——以南堡凹陷东营组为例

块状砂岩因其厚度大、储层物性较好而成为深水沉积油气勘探开发中最重要的目标。沉积构造相对简单,但变化迅速且组构特征多变。为了探索不同块状砂岩的成因及其联系,建立预测性地质模型,首先将南堡凹陷东营组深水块状砂岩分为2类8种岩相和10种岩相组合,其中单期砂层顶部常含漂浮状砾石,形态多变、内外源均有。本区块状砂岩成分成熟度差,结构成熟度不稳定,粒度累积概率曲线反映了3种搬运过程:多流体改造型、三角洲前缘继承型和混杂快速冻结型。成因分析认为,块状砂岩以砂质碎屑流搬运为主,真正碎屑流和颗粒流次之,并见部分砂质滑塌成因;常与浊流、泥流、泥质滑塌沉积伴生,发育5种相序组合,其中砂质碎屑流-浊流、砂质碎屑流-泥流组合最常见。高密度流体内沉积物浓度分层与特殊的流速剖面共同控制下塑性层流与牛顿紊流间的界面控制了漂浮状砾石搬运和沉积。最后,建立了陡坡带外源型、陡坡带内源型和缓坡地内源型深水沉积过程及块状砂岩发育模式,为断陷盆地深水沉积砂岩储层的预测提供了新思路。