华南中生代岩相变化及海相地层时空分布

在搜集大量资料的基础上，分析了华南中生代地层时代、岩性、岩相对比关系，重点综述了中生代海相地层的时空分布特征。受所处构造部位的控制，华南中生代岩相时空变化总体上可分为3个区：东区(闽西南-粤东-粤北-粤中)、中区(粤西-桂东)、西区(滇西-滇东南)。中区在早三叠世以后完全隆升成陆，仅局部有山间盆地碎屑沉积。海相地层集中于东西两区，但存在明显的东西差异：海侵时间在东区为早三叠世、晚三叠世-早侏罗世和早白垩世，西区为中三叠世和中侏罗世；海侵方向在东区来自东南，西区则为中特提斯滇缅海的-部分。晚三叠世-早侏罗世的粤东海盆发育厚达5000m的海相和海陆交互相沉积，可能向南延伸到台西南盆地和南沙群岛东部，但它与南海西部围区的同时代海盆并不直接相通。     

加里曼丹岛和马来半岛中生代岩相古地理特征及其构造意义

印支运动以后,在现今的南海及其周围存在过2个古海洋,其中晚侏罗世一早白垩世消失于南海北部陆缘区、北巴拉望-礼乐滩-南沙地块以北的古海洋为“中特提斯”,而早第三纪期间消失于南沙地块以南沙捞越一带的古海洋为“古南海”。它们的结束时间和消失的古地理位置完全不同。对它们的正确识别和区分,对目前进行的南海周边地区中一新生代构造演化研究极为重要。对马来半岛、加里曼丹岛中生代岩相古地理资料的整理和分析结果支持如下结论：中特提斯洋的延伸是从苏门答腊的Woyla缝合线,过婆罗洲的Meratus缝合线。然后绕西南婆罗洲地块至加里曼丹岛的西北(Lupar带或者Boyan带),进入南海西南角(南沙-礼乐滩-北巴拉望地块等以北),再接南海北部陆缘区内的中特提斯缝合线。该区中生代海相地层的分布明显受构造演化的控制,整体趋势是向南退缩。印支运动以前、早-中三叠世的海侵广泛分布于古特提斯带及以南地区,涉及华南,中南地块,马来半岛及以南地区;印支运动基本结束了古特提斯带的海侵,因此晚三叠世一早侏罗世的海侵主要限于中特提斯海域及以南地区,如与中特提斯洋相邻的陆域,包括华南的湘赣粤海湾晚三叠世一早侏罗世的海侵、中南半岛东南部早侏罗世的海侵以及新加坡早侏罗世的海相地层。白垩纪海相地层主要分布于中特提斯以南地区,如加里曼丹岛。     

台西南盆地和北港隆起的中生界及其沉积环境

我国南海海域广泛存在中生代沉积地层，在南海寻找中生界油气藏潜力极大。台西南盆地和北港隆起有数十口井钻遇中生界，经过详细生物地层学工作确定了下白垩统（阿普特阶和下阿尔必阶）和侏罗系（？）两套中生代地层，是迄今南海北部中生界地层研究最为深入的地区，可作为对比的样板。介绍了台西南盆地和台湾西部中生界的岩性、岩相和生物地层学特征，指出晚侏罗世（？）与早白垩世之间沉积环境发生了显著变化，台西南盆地由深海至半深海变为内陆，而北港隆起由内陆变为海陆交互和浅海环境。     

南黄海西部海域高分辨率声学地层及其沉积环境

通过对高分辨率浅地层剖面的分析解译,对南黄海西部陆架区进行了声学地层划分。南黄海西部海域声学地层剖面可划分为5套地层Ⅰ、Ⅱ1、Ⅱ2、Ⅲ1、Ⅲ2,每套地层代表一次全球性(或区域性)海平面变化周期内的海进一海退这样一个完整的旋回变化过程所形成的海侵或海退沉积层序。将典型声学地层剖面与区内钻孔岩心的沉积地层岩性单元对比研究,得到各声学反射层的时代、岩性及沉积环境。并发现依据浅地层进行的声学地层划分与钻孔岩心的地质地层划分有较好的对应关系。结合区内钻孔岩心的分析结果,对晚更新世以来南黄海陆架区的沉积环境及沉积过程进行了探讨。     

东海陆架盆地中生代残留地层特征及其构造启示

东海陆架盆地是位于中国东部华南大陆边缘的一个中、新生代叠合盆地,具有较大油气潜力。目前东海陆架盆地油气的发现均来自于新生界,对中生代残留地层的各方面特征认识不足:在空间上通常集中于特定构造单元,且基本位于盆地西部;在时间上主要涉及白垩纪和侏罗纪,且多是定性或半定量的研究。本文在前人研究的基础上,收集、整理了研究区目前最新、最全的反射地震资料和钻井数据,从钻遇中生界井的标定出发,以地震资料的层序划分和解释为基础,进行残留地层的研究,空间上统一盆地东、西两大坳陷带,时间上统揽白垩纪、侏罗纪以及前侏罗纪三个时期。结果表明,东海陆架盆地中生代残留地层遭受了后期严重的剥蚀改造,总体呈现东厚西薄、南厚北薄的特征,残留地层范围随时间不断东扩。对比各时期残留地层平面展布特征,揭示了东海陆架盆地的演变过程:三叠纪时期盆地原型为被动大陆边缘坳陷型盆地,早、中侏罗世时期为活动大陆边缘弧前盆地,晚侏罗世—晚白垩世时期为大陆边缘弧后伸展盆地;与此相对应,古太平洋板块俯冲肇始于晚三叠世—早、中侏罗世时期,板块后撤始于晚侏罗世。东海陆架盆地在中生代的东侧边界位于钓鱼岛隆褶带的东侧。     

东海陆架盆地海相中生界及其与邻近古海洋关系探讨

多道反射地震、地磁、钻井资料表明，东海存在中生代地层。区域地层、古生物、古地理环境分析表明，东海陆架盆地南部赋存发育海相中生界的可能性。中生代期间，包括台西南、粤东、闽西在内的中国东南沿海一带存在一海相沉积环境，它可能是西太平洋、也可能是从南海东部或中部经过的中特提斯洋伸向陆地的一个支角。该支角北部可能抵达东海陆架盆地南部。     

Allochthonous salt, structure and stratigraphy of the north-eastern Gulf of Mexico. Part I: Stratigraphy

Major sequence boundaries associated with eustatic sea level changes are correlated to the general stratigraphy of the north-eastern Gulf of Mexico. The details of a Middle Cretaceous Flooding Surface, marking a major break in sedimentation, are documented. The sequence stratigraphic work provides an example of the ‘stratigraphic signature of the Neogene’. Three major episodes of sediment accumulation are represented by: (1) Late Jurassic (150.5 Ma) to Middle Cretaceous (94 Ma) aggradation and progradation of sediments with significant sediment accumulation in the present shelf and slope areas; (2) an extended period of starved sedimentation during 94-30 Ma corresponding to Middle Cretaceous flooding events (93.5 and 91.5 Ma) and the lack of sediment supply; and (3) since Late Oligocene time, unusually rapid sedimentation rates that characterize the deep water study area. These patterns of sediment accumulation directly affect the formation of allochthonous salt in the study area.     

山东及皖北上侏罗统及与邻区对比的大地构造意义

通过对研究区中生代地层典型剖面或代表性剖面系统考察和综合研究,对上侏罗统及其上覆、下伏岩石地层进行进一步系统清理和修订：（1）将济阳坳陷原上侏罗统蒙阴组划归下白垩统,与之相对应的是鲁西南地区为杨家庄组;将山东地区中—上侏罗统三台组界定为中侏罗统;（2）将皖北地区合肥盆地圆筒山组划入中—上侏罗统;原上侏罗统周公山组认为是跨时代地层单元（J3K1）。（3）大别山北麓北淮阳六安、金寨地区的凤凰台组、三尖铺组定为晚侏罗世早期。在此基础上建立了中国东部地区准确可行的地层对比关系,提出了与国际接轨的地层划分与对比表。对比结果表明中国东部晚侏罗世除了在南北缘存在沉积外,整个地区缺失上侏罗统。该现象表明中国东部在晚侏罗世仍为挤压应力环境甚至比早中侏罗世更为强烈,甚至一直维持到早白垩世初。     

珠江口盆地的形成与南海的构造演化

南海地块在中生代早期与华南大陆边缘发生了一次陆陆碰撞,这一碰撞形成了研究地区中生代近EW向为主的构造格局,珠江口盆地及整个南海的演化都是在南海地块各块体裂离华南陆缘后发生的。盆地自晚白垩世以来,先后经历了不同构造方向的两期张裂阶段及张裂后沉降阶段。     

南黄海盆地及邻区中生代地层对比

中生代地层广泛分布于南黄海盆地及邻区，包括胶莱盆地、苏北盆地、群山盆地、黑山盆地、庆尚盆地等。陆上和海域的三叠纪地层主要由灰岩组成。侏罗纪地层目前只发现陆上，主要由陆相碎屑岩组成，但从南黄海盆地某些地震剖面上可以看出，海域侏罗纪地层很可能存在。白垩纪地层在上述中生代盆地中分布最广，在许多钻井中，白垩纪地层的厚度在1000m以上，甚至2000m。其中，陆地上早白垩纪地层主要由暗色陆相碎屑岩组成，例如胶莱盆地的莱阳组、苏北盆地的葛村组，庆尚盆地的新洞群；而海域的早白垩纪地层通常由红色碎屑岩组成，例如，南黄海盆地东侧的Kachi-1和Inga-1井钻遇早白垩纪地层，其中Kachi-1井的早白垩纪地层为红褐色碎屑岩夹火山岩，而Inga-1井的早白垩纪地层为玄武岩。中白垩纪地层属氧化环境，岩石通常为红色或棕色。例如，胶莱盆地的王氏组、苏北盆地的浦口组和赤山组、庆尚盆地的河阳群。在南黄海盆地中，ZC7－2－1、Kachi-1和另外5口井均钻遇这套以红色为主的地层。苏北盆地和南黄海盆地的晚白垩纪地层称为泰州组，主要由暗色泥岩组成，而庆尚盆地的晚白垩纪地层称为榆川群，主要由火山岩组成。地层对比显示，南黄海盆地及邻区中生代地层具有东部沉积厚、西部沉积薄，东部沉积环境以氧化为主、岩石发红，西部以还原环境为主、岩石发暗，东部以火山岩为主、西部以碎屑岩为主的特征。     

华南陆缘中生界烃源岩条件评价

华南陆缘出露的上三叠统-白垩系,累计厚度超过10 000m,露头调查未见油苗,烃源岩主要为泥岩、碳质泥岩和煤线,有机质类型以Ⅱ-Ⅲ型为主。上三叠统小水组,发育较深水的海相、Ⅱ型良好烃源岩,TOC为1.17%～5.43%;下侏罗统桥源组发育海陆过渡环境的Ⅲ型良好烃源岩,TOC为1.36%～10.37%;下侏罗统其他层系(金鸡组、银瓶山组、上龙水组、长埔组、吉水门组)发育浅海-半深海相的中等-好的烃源岩,TOC为0.5%～1.76%。烃源岩均已处于成熟-过成熟阶段。小水组、蓝塘群烃源岩品质良好,厚度巨大,在南海北部海域开展中生界烃源岩研究时,值得重点关注是否有与之相当的烃源岩层系发育。     

Regional constraints of the Sørkapp Basin: A Carboniferous relic or a Cretaceous depression?

The Sørkapp Basin (NW Barents Shelf) contains a comprehensive sedimentary succession that provides insight into regional tectonics and depositional development of the shelf from the Devonian to the Cretaceous. With its location east of the mid-Atlantic spreading ridge and south of Svalbard, the Basin serves as an important link between the offshore and onshore realms.This study subdivides this sparsely studied basin into six main seismic units (three Paleozoic and three Mesozoic). A metamorphic basement together with assumed Devonian sedimentary deposits form the foundation for a chiefly Carboniferous basin. The Basin forms a syncline with infill showing limited fault-influence. Overlying the early infill are Late Carboniferous deposits which show less lateral variation in thickness but also active growth on the few faults showing significant displacement. The overlying platform deposits of the latest Carboniferous and Permian show a change in depositional geometry, with onlapping deposits towards the east probably resulting from uplift of the Stappen High and regional flooding. Subsequent, particularly Late, Triassic sedimentation shows a more distinctly progradational pattern with a dominantly southeastern source for sediments. During this shallow shelf-filling stage, the Sørkapp Basin is sheltered by the Gardarbanken High, blocking the Early Triassic clinoform development. The High was transgressed in the Middle Triassic and the platform-edge progressively approached the present Svalbard coastline.The youngest Mesozoic unit forms a separate saucer-shaped depocenter west of the Sørkapp Basin, where deposits are truncated by the seafloor in a mid-basin position and across the Gardarbanken High. The depositional pattern for this succession correlates with the outcrop pattern of the Adventdalen Group implying a post Middle Jurassic to Cretaceous age. The Sørkapp Basin has been referred to as a Cretaceous feature based in this depocenter. However, the foundations are much older and the Cretaceous depression is located west of the deeper basin. Accordingly, we propose the informal term Sørkapp Depression for the Cretaceous basin.     

南海北缘新生代盆地沉积与构造演化及地球动力学背景

南海北缘新生代沉积盆地是全面揭示南海北缘形成演化及与邻区大地构造单元相互作用的重要窗口。通过对盆地沉积-构造特征分析,南海北缘新生代裂陷过程显示出明显的多幕性和旋转性的特点。在从北向南逐渐迁移的趋势下,东、西段裂陷过程也具有一定的差异,西部裂陷活动及海侵时间明显早于东部,裂陷中心由西向东呈雁列式扩展。晚白垩世-早始新世裂陷活动应是东亚陆缘中生代构造-岩浆演化的延续,始新世中、晚期太平洋板块俯冲方向改变导致裂陷中心南移,印度欧亚板块碰撞效应是南海中央海盆扩张方向顺时针旋转的主要原因。     

南沙海区中生界岩相分布及构造特征

为了了解南中国海南部南沙群岛陆架-陆坡区中生代地层发育情况,作者通过综合分析该海区钻井、拖网及1987年以来采集的20000多公里的多道反射地震勘探等资料,得到了对该区中生界基本特征的如下新认识:空间分布上,南沙的中生界具有从北部的郑和-礼乐隆起南缘向南增厚的趋势;沉积岩相方面,东部三叠纪时为深海相,侏罗纪为浅海与三角洲相,白垩纪为浅海-内浅海相,而往西南部中生代的海水深度有变深的趋势;中-新生代变形上,在南沙西部的曾母盆地,中生界褶皱为复式的、非协调性的,南沙中部多为舒缓褶皱,东部仅在近巴拉望海槽地带出现小幅度的褶皱。结合围区中生界及特提斯构造域的发育特征,作者提出南沙地块上的海相中生界在大地构造上归属于残留在中特提斯洋北部减薄陆缘地壳上的中特提斯期海相沉积地层,是该海域油气资源勘探不可忽视的对象。     

Seismic stratigraphy and hydrocarbon prospectivity of the Lower Cretaceous Knurr Sandstone lobes along the southern margin of Loppa High,Hammerfest Basin,Barents Sea

The Lower Cretaceous Knurr Sandstone deposited along the southern slope of Loppa High and overlain by the Kolje and Kolmule seals forms an attractive play in the Hammerfest Basin of the Barents Sea. Late Jurassic organic-rich Hekkingen shale directly underlies the Knurr Sandstone and acts as a source to provide effective charge. Three wells, 7120/2-2, 7122/2-1 and 7120/1-2, have proven the Knurr-Kolje play in structural traps, with an oil discovery in 7120/1-2. Prospectivity related to stratigraphic traps is, however, highly under-explored.In order to document and map the reservoir distribution and stratigraphic-trap fairway, the Lower Cretaceous sedimentary package containing the Knurr Sandstone is divided into a number of depositional sequences and systems tracts using key regional seismic profiles calibrated with logs. Mapping of the key surfaces bounding the Knurr sandstone has been carried out using all the seismic vintages available from Norwegian Petroleum Directorate (NPD).The thick massive nature of the sandstone (123 m in well 7122/2-1), sedimentary features characteristic of gravity flow deposits, high-resolution internal seismic reflections and stratal geometries (truncations and lapout patterns), and sequence stratigraphic position of the Knurr Sandstone on seismic profiles confirm that the lobes identified on the seismic section are gravity driven base of the slope lobes. These Knurr lobes and slope aprons were formed as a result of uplift of the Loppa paleo-high in the Late Jurassic to Early Cretaceous times which caused subaerial exposure and incision. The characteristic mounded, lobate geometry evident on the seismic can be mapped along the toe-of-slope and records multiple stacked lobes fed by multiple feeder canyons. Lateral partitioning and separation of the lobes along the toe-of-slope could potentially create stratigraphic traps. The existing 2D seismic coverage is, however, not sufficient to capture lateral stratigraphic heterogeneity to identify stratigraphic traps. 3D seismic coverage with optimum acquisition parameters (high spatial and vertical resolution, appropriate seismic frequency and fold, long offsets and original amplitudes preserved) can allow for the reconstruction of 3D geomorphologic elements to de-risk potential stratigraphic traps prior to exploratory drilling.     

南海东北部陆架边缘第四纪高分辨率层序地层和沉积体系演化及其控制因素

The northeastern shelf margin of the South China Sea(SCS) is characterized by the development of large scale foresets complexes since Quaternary. Based on integral analysis of the seismic, well logging and paleontological data, successions since ～3.0 Ma can be defined as one composite sequence, consist of a set of regional transgressive to regressive sequences. They can be further divided into six 3 rd order sequences(SQ0–SQ5) based on the Exxon sequence stratigraphic model. Since ～1.6 Ma, five sets of deltaic systems characterized by development of wedge-shaped foresets complexes or clinoforms had been identified. High-resolution seismic data and the thick foresets allowed further divided of sub-depositional sequences(4 th order) of regression to transgression, which is basically consistent with published stacked benthic foram O-isotope records. Depositional systems identified in the study area include deltaic deposits(inner-shelf deltas and shelf-edge deltas), incised valleys, and slope slumping massive deposits. Since ～1.6 Ma, clinoforms prograded from the southern Panyu Lower Uplift toward the northern Baiyun Depression, shelf slope break migrated seaward, whereas the shelf edge of SQ0 migrated landward. The development of incised valleys in the continental shelf increased upward,especially intensive on the SB3 and SB2. The slumping massive deposits increased abruptly since SB2, which corresponds to the development of incised valleys. The evolution of depositional systems of continental slope mainly controlled by the combined influence of sea level changes, tectonic movements, sediment supply and climate changes. Since ～3.0 Ma, relative sea level of the northern SCS had been experienced transgression(～3.0 Ma BP) to regression(～1.6 Ma BP). The regional regression and maximum transgressions of the composite sequences were apparently enhanced by uplift or subsidence related to tectono-thermal events. In addition,climatic variations including monsoon intensification and the mid-Pleistocene transition may have enhanced sediment supply by increasing erosion rate and have an indispensable influence on the development of the incised valleys and 5 sets of deltaic systems since ～1.6 Ma.     

北黄海盆地中生代地层的地质特征和油气潜力(英文)

位于山东半岛东北部的北黄海盆地沿东北方向可以延伸到朝鲜的西朝鲜湾盆地和安州盆地 ,而沿西南方向可以延伸到中国的胶莱盆地。长期以来该盆地的找油重点为第三系 ,结果收效甚微。2 0世纪 80年代末朝鲜在西朝鲜湾靠北黄海盆地一侧钻井数口且在中生代地层中发现了商业性油气流 ,自此中生代地层替代新生代第三纪地层成为人们关注的焦点 ,人们希望在北黄海盆地的中生代地层中也能找出商业性油气流。本文以李四光 ( 1 979)划分的新华夏系第二隆起带理论为指导 ,将胶莱盆地、北黄海盆地、西朝鲜湾盆地和安州盆地作为一个整体进行考虑 ,在详细分析了安州盆地、西朝鲜湾盆地和胶莱盆地的中生代地层分布、油气潜力及其类比关系后认为 ,北黄海盆地在基底结构及其上覆盖层的沉积特征上应具有与安州盆地、西朝鲜湾盆地和胶莱盆地相似的特征。目前 ,西朝鲜湾盆地和胶莱盆地在中生代地层中已取得重要的油气发现和油气显示 ,而它们主要是由下白垩统和上侏罗统组成。因此 ,我们有理由相信 ,北黄海盆地的中生代地层很可能成为有远景的勘探靶区。     

南海区域岩石圈的壳-幔耦合关系和纵向演化

南海区域岩石圈由地壳层和上地幔固结层两部分组成。具典型大洋型地壳结构的南海海盆区莫霍面深度为９～１３ｋｍ,并向四周经陆坡、陆架至陆区逐渐加深;陆缘区莫霍面一般为１５～２８ｋｍ,局部区段深达３０～３２ｋｍ,总体呈与水深变化反相关的梯度带;东南沿海莫霍面深约２８～３０ｋｍ,往西北方向逐渐增厚,最大逾３６ｋｍ。南海区域上地幔天然地震面波速度结构明显存在横向分块和纵向分层特征。岩石圈底界深度变化与地幔速度变化正相关;地幔岩石圈厚度与地壳厚度呈互补性变化,莫霍面和岩石圈底界呈立交桥式结构,具有陆区厚壳薄幔—洋区薄壳厚幔的岩石圈壳－幔耦合模式。南海区域白垩纪末以来的岩石圈演化主要表现为陆缘裂离—海底扩张—区域沉降的过程,现存的壳－幔耦合模式显然为岩石圈纵向演化产物,其过程大致可分为白垩纪末至中始新世的陆缘裂离、中始新世晚期至中新世早期的海底扩张和中新世晚期以来的区域沉降等三个阶段。     

Different expressions of rifting on the South China Sea margins

Rifting of continental margins is generally diachronous along the zones where continents break due to various factors including the boundary conditions which trigger the extensional forces, but also the internal physical boundaries which are inherent to the composition and thus the geological history of the continental margin. Being opened quite recently in the Tertiary in a scissor-shape manner, the South China Sea (SCS) offers an image of the rifting structures which varies along strike the basin margins. The SCS has a long history of extension, which dates back from the Late Cretaceous, and allows us to observe an early stretching on the northern margin onshore and offshore South China, with large low angle faults which detach the Mesozoic sediments either over Triassic to Early Cretaceous granites, or along the short limbs of broad folds affecting Palaeozoic to Early Cretaceous series. These early faults create narrow troughs filled with coarse polygenic conglomerate grading upward to coarse sandstone. Because these low-angle faults reactivate older trends, they vary in geometry according to the direction of the folds or the granite boundaries. A later set of faults, characterized by generally E–W low and high angle normal faults was dominant during the Eocene. Associated half-graben basement deepened as the basins were filling with continental or very shallow marine sediments. This subsequent direction is well expressed both in the north and the SW of the South China Sea and often reactivated earlier detachments. At places, the intersection of these two fault sets resulting in extreme stretching with crustal boudinage and mantle exhumation such as in the Phu Khanh Basin East of the Vietnam fault. A third direction of faults, which rarely reactivates the detachments is NE–SW and well developed near the oceanic crust in the southern and southwestern part of the basin. This direction which intersects the previous ones was active although sea floor spreading was largely developed in the northern part, and ended by the Late Miocene after the onset of the regional Mid Miocene unconformity known as MMU and dated around 15.5 Ma. Latest Miocene is marked by a regional basement drop and localized normal faults on the shelf closer to the coast. The SE margin of the South China Sea does not show the extensional features as well as the Northern margin. Detachments are common in the Dangerous Grounds and Reed Bank area and may occasionally lead to mantle exhumation. The sedimentary environment on the extended crust remained shallow all along the rifting and a large part of the spreading until the Late Miocene, when it suddenly deepened. This period also corresponds to the cessation of the shortening of the NW Borneo wedge in Palawan, Sabah, and Sarawak. We correlate the variation of margin structure and composition of the margin; mainly the occurrence of granitic batholiths and Mesozoic broad folds, with the location of the detachments and major normal faults which condition the style of rifting, the crustal boudinage and therefore the crustal thickness.     

东海陆架盆地的前新生界

根据东海陆架盆地周边地质、地球物理和钻井资料,应用岩石学、古生物学、同位素年代学、层序地层学等分析方法,研究东海陆架盆地的前新生界.陆架盆地广泛发育中生界,其中盆地南部发育最全,以三叠—白垩系陆相碎屑岩为主,中部隆起带以发育侏罗—白垩系的陆相火山岩为主,以台湾海峡为中心的盆地南部有海相—海陆过渡相的中生界.在盆地南部钻遇的年龄为1680 Ma的黑云角闪斜长片麻岩和在北部钻遇的糜棱片麻岩分别为浙闽东部前震旦纪变质岩和浙北晚元古代变质岩在海中的延伸.陆架地区晚古生代可能属于亚洲大陆东缘优地槽带的冒地槽,在盆地内尤其在东部坳陷带可能有晚古生代浅变质岩.