Age of metamorphic rock masses in Laba Basin,North Caucasus

A Neoarchaean sanukitoid pluton that was intruded into the base of the Guyang greenstone belt in the Yinshan Block of the North China Craton hosts a number of hornblendite enclaves. Geochemically, the pluton is characterized by high MgO, Mg#, Cr, Ni, large-ion lithophile element (LILE), and heavy rare earth element (HREE) contents and low TiO₂ and high-field strength element (HFSE) contents, and has relatively low Sr/Y ratios and negative Eu anomalies. Whole-rock Sr–Nd isotopic analyses indicate that it has ε_Nd(t) values of +1.4 to +2.0. These geochemical and isotopic characteristic suggest that the sanukitoid was formed under a low-pressure and high-temperature environment by slab melting and assimilation of hornblendite enclaves. The hornblendite enclaves show high MgO, Mg#, Cr, and Ni contents, high and variable K₂O, LREE, and Th contents, enrichment in LILEs and LREEs, and depletion in HFSEs. They have high Y contents and relatively low Sr/Y values, strongly negative Eu anomalies, and whole-rock ε_Nd(t) values of +1.0 to +1.9. The geochemical and isotopic characteristics indicate that these enclaves might have been derived from a mixed source of an enriched mantle, metasomatized by melts expelled from subducted sediments in a high-temperature, low-pressure environment. To explain these characteristics, a ridge subduction model is proposed for the formation of the sanukitoid and hornblendite in the Yinshan Block in the Neoarchaean.     

Sinian-Cambrian Tectonic Framework in the Tarim Basin and its Influences on the Paleogeography of the Early CambrianEI北大核心CSCD

Due to strong remodification and sparse trace remnants, tectonic restoration is critical for the reconstructing of the paleography and basin-prototype in the multiple-cycles superimposed basin, which is also fundamental for the hydrocarbon exploration of the deep marine carbonate in the Tarim Basin. This study presents the tectonic framework of the transition phase from the Sinian to the Cambrian Period and its constrains on the paleography of the Cambrian in the Tarim Basin based on comprehensive analysis of new geochronology data, seismic data and regional tectonic data. The results showed that (1) there is a large regional unconformity between the Cambrian and Precambrian, suggesting a discontinuous deposition from the Sinian to the Cambrian that is contrary to the major view; (2) a broad flattened paleotopography formed before Cambrian Period, which is favorable for the wide epicontinental sea environment and a gentle homoclinal ramp platform development in the early Cambrian, and the residual basement low relief uplifts that influence the microfacies differentiation in the carbonate platform; (3) the Cambrian carbonate platform has been involved much into the marginal orogenic belts, and the proto-platform is probably of 200 km out of the present basin in S-N direction; (4) there is a weak extensional setting in the Cambrian-Early Ordovician rather than a strong rifting setting with a large aulacogen into the platform, in which a inter-platform shallow depression and stable ramp platform developed in the Cambrian; (5) there is not troughs, but rather low relief uplifts developed in the Early Cambrian in the southwestern Tarim Basin, and lack of large uplifts along the carbonate platform margins; (6) it is showed a broad architecture of platform-wide slope-ocean basin from the inner Tarim plate to its margin in the Cambrian Period. Considering the basin prototype, the restoration of the tectono-paleography in the early Cambrian in the Tarim Basin is distinct from those of the previously proposed. We propose that a gentle pattern with “two platforms and one inter-depression” in E-W striking other than multiple small platform constrained in the basin, and further subdivision of the western platform with inner platform low uplift and sag in N-S striking, which is possibly inherited from the basement architecture. On the outer of the united platform, there is probably broad gentle slope for transition to ocean basin. We therefore argue that tectonic restoration is crucial for reconstruction of the paleogeography and basin prototype, especially for basins experienced multiphase of tectonic cycles. © 2018, Science Press. All right reserved.     

辽宁北部秀水盆地义县组烃源岩生物标志化合物特征及意义——以辽法D1井为例

正辽宁北部秀水盆地位于华北板块北缘陆缘活动带之上,地质构造复杂。秀水盆地是在海西褶皱基底和前寒武纪基底上发育起来的中生代断陷型盆地,面积710 km~2,是前人油气调查工作空白区。秀水盆地早白垩世义县组上部发育优质烃源岩。部署在秀水盆地中部的辽法D1井义县组沉积地层厚度为280 m,暗色泥岩厚度为128 m。本文通过对辽法D1井义县组泥岩样品分析,采用气相色谱、气相色谱—质谱技术,剖析秀水盆地义县组烃源岩     

南天山西段南缘断裂构造特征及对乌什凹陷发育的控制

乌什凹陷位于南天山西段以南,新生代受南天山崛起的陆内造山作用制约,与库车坳陷有相同的成盆动力学背景。因乌什凹陷南有温宿凸起阻挡了挤压应力的传播,东与库车坳陷间有北西向的构造变换带(西秋里塔格构造带)所隔,新生代变形与库车地区有不同的特征。以吉迪克组的泥岩层为滑脱面,乌什凹陷的中-新生界可分为上、下两个构造层,总体看上构造层以背冲构造为特征,下构造层则发育基底卷入的对冲构造。乌什凹陷的这一变形特征还与新生代挤压应力场自东向西迁移和走滑作用吸收了部分冲断变形有关,反映了南天山新生代构造对海西-印支期碰撞构造的继承性。文章简述了南天山造山带的构造演化,介绍了乌什凹陷周缘的主要断裂的特征,恢复了乌什凹陷中-新生代的演化并与库车坳陷进行了对比。在此基础上探讨了乌什凹陷的成盆动力学机制,分析了乌什凹陷与南天山造山带的耦合演化,指出该区的油气勘探应以三叠系为主要目的层。     

鄂尔多斯盆地东南缘延长组成岩作用及储层物性特征

通过成岩作用及储层物性的综合分析,该区主要油层组长9、长8、长6及长2的岩石成分成熟度和结构成熟度均较差,均经历了晚成岩A期。压实作用降低了储层的孔隙度,致密的碳酸盐岩胶结降低了孔隙度并阻止了次生孔隙的产生。该区储层为低孔低渗储层,孔隙度在4%~8%之间,渗透率多小于0.1×10^-3μm²。     

Sea Level Variations and Geomorphological Changes in the Coastal Belt of Pakistan

The UNEP in its regional seas program in 1989 has included Pakistan in a group of countries which are vulnerable to the impact of rising sea level. If the present trend of sea level rise (SLR) at Karachi continues, in the next 50 years the sea level rise along the Pakistan Coast will be 50 mm (5 cm). Since the rising rates of sea level at Karachi are within the global range of 1-2 mm/year, the trends may be treated as eustatic SLR. Historical air temperature and sea surface temperature (SST) data of Karachi also show an increasing pattern and an increasing trend of about 0.67°C has been registered in the air temperature over the last 35 years, whereas the mean SST in the coastal waters of Karachi has also registered an increasing trend of about 0.3°C in a decade. Sindh coastal zone is more vulnerable to sea level rise than Baluchistan coast, as uplifting of the coast by about 1-2 mm/year due to subduction of Indian Ocean plate is a characteristic of Baluchistan coast. Within the Indus deltaic creek system, the area nearby Karachi is more vulnerable to coastal erosion and accretion than the other deltaic region, mainly due to human activities together with natural phenomena such as wave action, strong tidal currents, and rise in sea level. Therefore, The present article deals mainly with the study of dynamical processes such as erosion and accretion associated with sea level variations along the Karachi coast and surrounding Indus deltaic coastline. The probable beach erosion in a decade along the sandy beaches of Karachi has been estimated. The estimates show that 1.1 mm/year rise in sea level causes a horizontal beach loss of 110 mm per year. Therefore, coast eroded with rise in sea level at Karachi and surrounding sandy beaches would be 1.1 m during a period of next 10 years. The northwestern part of Indus delta, especially the Gizri and Phitti creeks and surrounding islands, are most unstable. Historical satellite images are used to analyze the complex pattern of sediment movements, the change in shape of coastline, and associated erosion and accretion patterns in Bundal and Buddo Islands. The significant changes in land erosion and accretion areas at Bundal and Buddo Islands are evident and appear prominently in the images. A very high rate of accretion of sediments in the northwestern part of Buddo Island has been noticed. In the southwest monsoon season the wave breaking direction in both these islands is such that the movement of littoral drift is towards west. Erosion is also taking place in the northeastern and southern part of Bundal Island. The erosion in the south is probably due to strong wave activities and in the northeast is due to strong tidal currents and seawater intrusion. Accretion takes place at the northwest and western parts of Bundal Island. By using the slope of Indus delta, sea encroachment and the land area inundation with rising sea level of 1 m and 2 m have also been estimated.     

Summary of the fossil record of pinnipeds of Japan, and comparisons with that from the eastern North Pacific

Abstract The fossil pinniped record of the North Pacific Ocean includes both Phocidae and Otariidae ( sensu lato ), extends from the Late Oligocene to the Late Pleistocene, is taxonomically diverse, and is constantly becoming more complete owing to additional important discoveries. The earliest and most diverse fossil pinnipeds in the North Pacific are otariids, the phocids not appearing until the latest Pliocene. The theoretical center of otariid pinniped evolutionary history has been considered by some to be in the eastern North Pacific. New materials from the western North Pacific, however, including representatives of the subfamilies Enaliarctinae, Imagotariinae, Odobeninae and Otariinae, indicate that pinniped evolutionary patterns were basin-wide phenomena, and that a more complete record undoubtedly would reveal numerous trans-Pacific distributions. This would be expected considering the distributions of living species. The paucity of fossil Phocidae and their absence from pre-Pliocene deposits are consistent with theories that the family primarily evolved outside the North Pacific.     

1月北大西洋东部-乌拉尔山阻塞高压频次年际尺度偶极子模态特征

基于观测和再分析资料,本文研究了近几十年来1月北大西洋东部-乌拉尔山阻塞高压频次年际变异主导模态特征及与其相联的大气背景场。结果表明,1980—2019年冬季(12月—次年2月)该地区阻塞高压频次年际变异的主导模态存在明显月际差异:12月表现为北大西洋东部-欧洲西部地区阻塞高压频次的显著同位相变化,1月为北大西洋东部-欧洲西部与乌拉尔山地区阻塞高压频次的具有显著的反位相变化即偶极子模态,2月则为北大西洋东部-乌拉尔山阻塞高压频次的显著同位相变化。进一步研究表明:1月北大西洋东部-乌拉尔山阻塞高压频次偶极子模态与同期局地纬向西风、纬向风垂直切变、经向位涡梯度等大气背景场异常偶极型变化相联系。当乌拉尔山地区关键大气背景场为负异常,而北大西洋东部-欧洲西部为正异常时,两个地区阻塞高压频次分别增加和减少,呈现偶极子模态;反之亦然。阻塞高压频次偶极子模态及相关的背景环流异常可通过调节水平温度平流、垂直运动和水汽输送等来影响1月欧亚北部气温和降水,以及它们的极端事件频次。当阻塞高压频次偶极子模态处于正位相时,乌拉尔山北部(南部)和欧洲南部增温(降温),极端暖、冷事件频次分别增加(减少)和减少(增加...     

云南思茅盆地景谷地区下白垩统曼岗组风成砂岩沉积学特征及其古气候意义

本文通过野外剖面的观察和实测,室内薄片鉴定、阴极发光分析、粒度分析、扫描电镜及能谱测试分析,研究了云南思茅盆地景谷地区下白垩统曼岗组风成砂岩沉积学特征,详细了解了风成砂岩的发育特征,以期为研究区白垩纪古气候研究提供新的资料,为我国钾盐勘探提供一定的地质依据和新的思路。研究结果表明:1研究区曼岗组主要出露一套中—细粒石英砂岩、岩屑石英砂岩,发育中—大型交错层理、平行层理,碎屑颗粒分选中等-好,以次圆状-圆状为主,孔隙不发育,杂基含量少;2曼岗组中段发育具平行层理的石英砂岩,粒度分布呈双众数,带状分布,石英颗粒为浑圆状,颗粒表面见Fe、Mn质薄膜,颗粒表面具明显的碟形坑等特征,属于典型的风成砂岩,初步判定其沉积环境为风成沙丘和丘间沉积;3景谷地区下白垩统曼岗组风成砂岩,整体表现为干热型气候,曼岗组中段为丘间沉积,曼岗组上段和下段为沙丘沉积。其在搬运沉积成岩过程中经历了强烈的物理、化学风化作用,整体表现为氧化环境,风力较大,风速稳定,持续时间长。此外,可能还经历了一段时期的湿润性气候环境,这可能与大气降水、大气环流带的迁移,以及白垩纪海侵作用等有关。     

松辽盆地尚家—太平川地区石油地质条件及勘探方向分析

通过对尚家—太平川地区构造演化、烃源岩特征、沉积特征、储盖组合、油水关系及油藏类型和油气成藏特征的分析,研究了本区的石油地质条件,认为烃源岩具有较好的生、排烃能力,分流河道砂体为油气聚集提供较好的沉积环境,良好的储盖组合有利于油气的聚集与保存。研究区没有统一油水界面,尚家地区以岩性—构造油藏为主,太平川地区以构造—岩性油藏为主。区内扶余—杨大城子油层油气成藏受有效性圈闭、优势运移通道、过剩压力、储集条件和构造诱导作用控制。据上述认识确定了研究区下一步的勘探方向,并已在指导勘探实践中取得了较好的效果。