The Cretaceous of the Eastern Bangong-Nujiang Suture Zone (Tibet):Tectono-Sedimentation

1IntroductionThe Tibet plateau consists of terranes which were accreted in a southward-younging succession from Late Permian to Mid-Eocene (Dewey etal., 1988; Mattern etal., 1998; Mattern and Schneider, 2000). The Songpan-Ganzi terrane was accreted to the Kunlun during Late Permian along Kunlun-Qin-ling suture. The Qiangtang block was added onto the Songpan-Ganzi terrane at the Jinsha suture dur-ing Late Triassic-Early Jurassic. The Lhasa block became attached to the Qia…     

RESPONSE OF TRIASSIC SEQUENCE STRATIGRAPHY OF LOWER YANGTZE TO THE COLLISION BETWEEN THE YANGTZE PLATE AND THE NORTH CHINA PLATE

The characteristics of the Triassic sequences developed in the Lower Yangtze area display some great changes in both environment and climate. The change of environment was a transition from marine to continent via alternating environments. The change of climate was a transition from tropic （torrid） to warm and wet climate via subtropic dry climate. The type variations of the sequences were from the marine sequences to the continental sequences, corresponding to the changes of environments and climates. Sequence 1 is a type II of sequence of mixed elastic and carbonate sediments; sequence 2 is a type I of sequence of carbonate platform; sequence 3 is a type I of sequence of carbonate tidal flat-salt lagoon, sequence 4 is a type iI of sequence of lacustrine within marine layers, and sequence 5 is a sequence of lacustrine-swamp. The development, distribution and preservation of those sequences reveal the tectonic controls and their changes in the background. The collision between the Yangtze plate and the North China plate was a great geological event in the geological history, but the timing of the collision is still disputed. However, the characteristics of Triassic sequence stratigraphy and sea level changes in the Lower Yangtze area responded to this collision. The collision started at the beginning of middle Triassic and the great regression in the Lower Yangtze area started 22Ma earlier than those in the world. The tectonic conditions occurred before and during the collision controlled the development of sequences and type changes.     

油页岩中生物及有机质与金属元素富集的关系及机理探讨

松辽盆地白垩系油页岩中的Ｍｎ、Ｃａ、Ｂａ、Ｓｒ、Ｐ、Ｎａ、Ｚｎ、Ｔｈ等元素含量高于国际标样（ＳＤＯ－１）２～１００倍，呈明显富集趋势。有机质（干酪根）中Ｚｎ、Ｂａ、Ｃｕ、Ｍｏ、Ｐｂ、Ｎｉ、Ｙ、Ｃｏ、Ｍｇ、Ｂ等元素含量高于其页岩平均含量１．５～２００倍，说明有机质相是它们的＂富集相＂。油页岩物相分析显示，只有Ｚｎ和Ｂａ等少数元素是以有机质相为＂载体相＂（即有机相中所含元素的量占岩石中该元素总含量的５０％以上）。据上述研究作者认为，油页岩中生物有机质对多种金属元素都具有显著富集作用；但只有当有机质相既是金属元素的＂富集相＂同时又是该元素的＂载体相＂时，生物有机质对它的矿化作用才具有实际意义。     

松辽盆地乾安地区青山口组三段沉积微相特征

乾安地区位于松辽盆地南部中央坳陷区长岭凹陷的东北部。本区发育青三段高台子油层,顶界最浅埋深1518m,底界埋深2072m,青三段厚度平均97m,最大244m。青三段上部主要为泥岩,中、下部以粉砂岩为主和少量细砂岩、中粒砂岩和含砾砂岩,为一套湖泊三角洲相沉积。利用360口井的声波时差、自然电位、自然伽玛和视电阻率等曲线和20余口井的录井资料,识别出研究区青三段的沉积微相类型有:水下分流河道、席状砂、远砂坝、水下扇、河道间和前三角洲,总结了各微相特征,并建立了沉积微相地质—测井综合模式,完成了青三段早、中、晚期三期沉积微相平面图,分析沉积微相平面分布规律。早、中期三角洲为叶状三角洲,在此沉积时期,湖岸线相对稳定,河湖均有一定能量。物源供应较丰富,湖盆水体对河流带来的沉积物也有一定改造作用,属一般建设型三角洲。晚期三角洲体为伸长状三角洲,为典型的河控三角洲。在此沉积时期,湖盆开始较快速地水退,侵蚀基准面下降,河流搬运能力增大,物源供给充足。而湖能很弱,对河流带来的沉积物改造作用小。在不同的沉积时期,物源方向也有明显变化,说明保康沉积体系在此沉积期间物源的不稳定性。早期,物源来自南部;中期,物源来自西部;晚期,物源来自西北部。     

云南泸水市压扭性构造对银厂坪白云岩岩溶系统发育控制作用

银厂坪岩溶系统由溶蚀洼地和溶洞系统组成,溶蚀洼地内发育15个规模和形态不同的落水洞以及多条溶沟。根据断层面擦痕反演构造应力张量和共轭剪节理反映的应力场特征, 结合区域地质背景,认为研究区于始新世—早中新世主要受 SEE-NWW 向挤压和 NNE-SSW 向拉张应力场控制,形成 NW 向左旋压扭性构造,其几何学和运动学特征符合里德尔剪切模式。走滑拉分阶区所形成凹陷具有汇水功能,利于岩溶作用形成溶蚀洼地,内部发育的共轭节理交汇部位是良好的导水构造,叠加在走滑微拉分阶区内,促进白云岩溶蚀作用形成落水洞。地下岩层受构造挤压发生层间滑动形成微裂隙,经溶蚀扩大,形成顺倾斜岩层发育的岩溶洞穴。左行走滑断裂造成地表河流和山脊发生系统左旋位错,发育断层崖于山脚处形成倒石堆,在构造抬升和剥蚀作用下,岩壁不断后退,地下河频繁袭夺使早期溶洞成为干洞,现代地下河于斜坡下游通过地下河出口转为明流。     

Reassessment of the Distribution of Mantle CO2 in the Bohai Sea, China: The Perspective from the Source and Pathway System

Research on the distribution of mantle CO₂should involve comprehensive analysis from CO₂source to accumulation.The crust-mantle pathway system is the key controlling factor of the distribution of mantle CO₂,but has received little attention.The pathway system and controlling factors of CO₂distribution in the Bohai Sea are analyzed using data on fault styles and information on the mantle and lithosphere.The relation between volcanic rocks and the distribution of mantle CO₂is reassessed using age data for CO₂accumulations.The distribution of mantle CO₂is controlled by uplift of the asthenosphere and upper mantle,magma conduits in the mantle and fault systems in the crust.Uplifted regions of the asthenosphere are accumulation areas for CO₂.The area with uplift of the Moho exhibits accumulation of mantle CO₂at depth.CO₂was mainly derived from vertical migration through the upper mantle and lower crust.The fault style in the upper crust controls the distance of horizontal migration and the locations of CO₂concentrations.The distribution of mantle CO₂and volcanic rocks are not the same,but both probably followed the same pathways sometimes.Mantle CO₂in the Bohai Sea is concentrated in the Bozhong sag and the surrounding area,particularly in a trap that formed before 5.1 Ma and is connected to crustal faults(the Bozhang faults)and lithospheric faults(the Tanlu faults).     

The Cretaceous volcanic succession around the Songliao Basin,NE China: relationship between volcanism and sedimentation

With volume ratio of 8:1:1.5 amongst acidic, intermediate and basaltic rocks, the Cretaceous volcanics around the Songliao Basin are a series of high‐K or medium‐K, peraluminous or metaluminous, calc‐alkaline rocks, lacking typical basalts and peralkaline members of typical rift‐related types. Their eruption ages range between 133 and 127 Ma, 124 and 122 Ma and 117 and 113 Ma respectively. They are high in total (Rare earth element) REE contents (96.1–326 ppm), enriched in LREE and depleted in HREE (LREE/HREE = 4.6–13.8), with negative Eu and Ce anomalies (Eu/Eu* = 0.04–0.88; Ce/Ce* = 0.60–0.97). They have enriched large‐ion lithophile elements (e.g. K, Ba, Th) and depleted high field strength elements (e.g. Nb, Ti and Y), suggesting a subduction‐related tectonic setting. The volcanic activities migrated from south to north, forming a successively northward‐stepping volcanic series and showing a feature significantly different from the overlying sedimentary sequence striking northeast. Thus, an overlap basin model was proposed. Accompanied by opening of the basin, the volcanogenic succession was formed at the block‐faulting stage (131–113 Ma) owing to the closure of the Mongolia–Okhotsk ocean in the Jurassic and early Cretaceous, while the overlying sedimentary sequence was unconformably deposited at the spreading stage (Albian–Maastrichtian) owing to the oblique subduction of the Pacific plate under the Eurasian plate. The volcanic succession constitutes the lower unit of basin filling and is the forerunner of further basin spreading. Copyright © 2002 John Wiley & Sons, Ltd.