The Upper Jurassic of the Laptev Sea: interregional correlations and paleoenvironments

The Late Jurassic evolution of Boreal and Arctic basins is reflected in the widespread deposition of organic-rich black shales (source rocks). In this connection, the priority should be placed on the development and refinement of zonal schemes for the Upper Jurassic of the Laptev Sea coast based on ammonites, foraminifers, ostracods, dinocysts, and spores and pollen from reference sections as the basis for stratigraphic, paleogeographic, and facies studies. The Upper Jurassic and Lower Cretaceous reference section of interest is located on the left side of the Anabar Bay of the Laptev Sea (Nordvik Peninsula, Urdyuk-Khaya Cape). An uninterrupted and continuous section from Upper Oxfordian to Lower Valanginian is exposed in coastal cliffs and consists mainly of silty clay deposits with abundant macro- and microfossils. A reliable biostratigraphic subdivision of the Upper Jurassic interval of this section was taken as the basis for the assessment of the correlation potential of different fossil groups and subsequent interregional correlations, facies analysis, and detailed paleogeographic reconstructions of the study area. The analysis of variations in the composition of macrobenthic communities and microphytoplankton and terrestrial palynomorph assemblages and the biofacies analysis allowed the reconstruction of the evolution of marine paleoenvironmental settings in the western part of the Anabar–Lena sea and in the terrestrial settings in the adjacent land area of Siberia.     

Mid-Cretaceous Tuor-Yuryakh Section of Kotelnyi Island,New Siberian Islands: How Does the Probable Basement of Sedimentary Cover of the Laptev Sea Look on Land?

The model of geological structure of sedimentary cover of the Laptev Sea accepted by most geologists suggests that the lower seismic complex of the cover begins by the Aptian–Albian sedimentary rocks. They can be studied in natural outcrops of Kotelnyi Island. The section of the Tuor-Yuryakh Trough, which exposes the lower part of the Cretaceous complex, is described in the paper. It is composed of continental coaliferous rocks ~100 m thick. The marking beds divide it into five members, which are traced along the western wall of the trough at the distance up to 3 km. The spore–pollen complexes and plant megafossils indicate that almost the entire visible section of the mid-Cretaceous is Albian. Only its lower part no more than 14 m thick can probably belong to the Aptian. Marine facies with Albian foraminifers were found 15 m above the bottom of the Cretaceous complex. The section of the Cretaceous rocks is underlain by the Lower Jurassic marine clays and siltstones. The foraminifer assemblages of this part of the section are typical of the upper Sinemurian–Pliensbachian and fossil bivalves indicate late Sinemurian age of the host rocks. The hiatus ~70 Ma duration has no expression in the section and this boundary can de facto be substantiated only by microfossils. This vague contact between the Lower Jurassic and mid-Cretaceous rocks does not correspond to geophysical characteristics of the bottom of the lower seismic complex of the cover of the eastern part of the Laptev Sea. The latter is described as the most evident seismic horizon of the section of the cover, suggesting unconformable occurrence of the lower seismic complex on a peneplenized surface of lithified and dislocated rocks. This is mostly similar to the bottom of the Eocene sediments, which were observed on Belkovsky and Kotelnyi islands. The paper discusses possible application of our land results for interpretation of the shelf seismic sections of the Laptev Sea. It is concluded that local reasons are responsible for a vague boundary between the Lower Jurassic and mid-Cretaceous sequences in the section studied. Our observations support ideas on possible Aptian–Albian age of the rocks of the basement of the lower seismic complex; however, it is proposed to use also the previously popular idea on the Eocene age of the lower seismic complex of sedimentary cover of the eastern part of the Laptev Sea as one of the possible working scenarios.     

民和盆地侏罗系地层划分与对比

民和盆地是一个油、煤、气伴生的中新生代陆相盆地,侏罗系地层层序自下而上划分为下侏罗统炭洞沟组(大西沟组)、中侏罗统窑街组、红沟组、上侏罗统享堂组。中侏罗世早、中期气候温暖湿润,形成了以沼泽相煤系地层和湖相暗色泥岩、油页岩为主的生油建造,晚侏罗世至白垩纪气候较为干燥,形成了以河流相为主的砂砾岩储集建造。根据古生物、岩性、电性、含煤性、构造、古气候等地层划分对比标志,重新确立了盆地的地层系统,建立了盆地中新生界地层标准剖面,为盆地石油勘探奠定了坚实的基础。     

西藏江孜-浪卡子一带的侏罗-白垩纪界线地层

侏罗系/白垩系界线是显生宙所有系级界线中存在问题最多的一个。西藏南部出露有良好的侏罗-白垩纪地层,本次工作在喜马拉雅地层区的康马隆子地层分区开展了海相侏罗系/白垩系的界线研究。江孜地区的界线地层被划分为维美组和甲不拉组;浪卡子地区的甲不拉组之下发育一套含大量火山岩层的火山－沉积地层,被称为桑秀组。该地层分区的地层系统由下至上为：维美组浅灰色厚层状粗-细粒石英砂岩;桑秀组黑色页岩、安山岩和玄武岩;以及甲不拉组黑色页岩、硅质泥页岩夹砂岩和砂质灰岩。维美组中含化石稀少,仅在江孜地区发现零星菊石Haplophylloceras、Himalayites等。桑秀组下部页岩和粉砂岩中找到少量菊石化石,属于Spiticeras、Berriasella、Haplophylloceras的一些种,和富集成层的双壳类Inoceramus everesti等。江孜甲不拉组下部化石丰富,划分为Spiticeras-Berriasella下组合和Himalayaites-Haplophylloceras上组合。本研究区的生物地层可与聂拉木地区的菊石化石组合对比。通过生物地层学对比,江孜-浪卡子地区的维美组时代为晚侏罗世Tithonian期,江孜地区甲不拉组下部和浪卡子地区的桑秀组均属于下白垩统。桑秀组下部的页岩段与江孜甲不拉组的最下部地层相当,上部火山岩的同位素年龄为133 Ma。据此,桑秀组的时代为Berriasian至Hauterivian期,侏罗系/白垩系的界线位于该组之底,以Virgatosphinctes、Aulocosphinctes的消失和Spiticeras的出现为标志。侏罗纪末期西藏特提斯海区普遍形成大规模海退,表现为维美组和门卡墩组顶部砂岩的同期沉积。     

中原油气区侏罗系地层特征

综述中原油气区侏罗系地层古生物特征,提出该区存在下侏罗统—中侏罗统,未确证存在上侏罗统,过去所称上侏罗统—下白垩统归入下白垩统为宜。提出了区内北部临清坳陷的下侏罗统—中侏罗统地层可划分为中一下侏罗统的坊子组和中侏罗统的三台组、西南部济源凹陷下侏罗统的鞍腰组和中侏罗统马凹组、东南部黄口凹陷仅存在中侏罗统的三台组、南部中牟凹陷的侏罗纪地层与济源凹陷的相近,并提出了它们之间的对比意见。     

合肥盆地中生代地层时代与源区的碎屑锆石证据

合肥盆地位于大别造山带北侧、郯庐断裂带西侧,其发育过程与这两大构造带演化密切相关。本次工作对合肥盆地南部与东部出露的中生代砂岩与火山岩进行了锆石年代学研究,从而限定了各组地层的沉积时代,确定了火山岩喷发时间,指示了沉积物的源区。这些年代学数据表明,合肥盆地南部的中生代碎屑岩自下而上分别为下侏罗统防虎山组、中侏罗统圆筒山组或三尖铺组、下白垩统凤凰台组与周公山组(或黑石渡组)与上白垩统戚家桥组,其间缺失上侏罗统。盆地东部白垩系自下而上为下白垩统朱巷组与响导铺组和上白垩统张桥组。该盆地出露的毛坦厂组或白大畈组火山岩喷发时代皆为早白垩世(130～120 Ma)。盆地南部的下——中侏罗统及白垩系源区皆为大别造山带,分别对应该造山带的后造山隆升与造山后伸展隆升。而盆地东部白垩系的源区始终为东侧的张八岭隆起带,后者属于郯庐断裂带伸展活动中的上升盘。     

北黄海盆地东部坳陷中生界烃源岩特征及其指示的油气勘探方向

为了量化表征北黄海盆地东部坳陷中生界主力烃源岩生、排烃特征,综合利用镜质体反射率(R_o)、残余有机碳含量(TOC)、岩石热解、干酪根镜检及饱和烃色谱等资料,在总结研究区烃源岩地化特征的基础上,通过油源对比明确主力烃源岩层并依托盆地模拟方法量化其生、排烃贡献.结果表明,北黄海盆地东部坳陷中生界的两类原油均来源于区内中侏罗统和上侏罗统两套主力烃源岩层,其中,中侏罗统烃源岩的有机质丰度整体处于"好-最好"级别,上侏罗统烃源岩的有机质丰度则以"中等-好"为主;二者均存在早白垩世末期和早中新世两次生、排烃高峰,但上侏罗统的排烃速率[q_e(max)=27.3×106 t/Ma]远高于中侏罗统的排烃速率[q_e(max)=4.2×106 t/Ma],对研究区油气成藏的贡献更大.虽然下白垩统暗色泥岩的生烃潜力有限,但其底部砂岩与紧邻上侏罗统主力烃源岩层构成的"下生上储"式的源储配置关系是区内最重要的勘探目的层,其次为中、上侏罗统内部"自生自储"式的有利成藏组合,同时,中侏罗统下部"上生下储"式的成藏组合也应予以重视.      

From back-arc rifting to arc accretion: the Late Jurassic–Early Cretaceous evolution of the Guerrero terrane recorded by a major provenance change in sandstones from the Sierra de los Cuarzos area,central Mexico

The Guerrero terrane is composed of Middle Jurassic–Lower Cretaceous arc assemblages that were rifted from the North American continental mainland during Late Jurassic–Early Cretaceous back-arc spreading within the Arperos Basin, and subsequently accreted back to the continental margin in the late Aptian. The Sierra de los Cuarzos area is located just 50 km east of the Guerrero terrane suture belt and, therefore, its stratigraphic record should be highly sensitive to first-order tectonic changes. Two Upper Jurassic–Lower Cretaceous clastic units were recognized in the Sierra de los Cuarzos area. The Sierra de los Cuarzos Formation is the lowermost exposed stratigraphic unit. Petrographic data and U-Pb zircon ages suggest that the Sierra de los Cuarzos Formation was derived from quartz-rich sedimentary and igneous sources within the North American continental mainland. The Sierra de los Cuarzos Formation is overlain by the Pelones Formation, which is composed of volcanoclastic sandstones derived from a mix of sources that include the mafic arc assemblages of the Guerrero terrane and quartz-rich sedimentary and volcanic rocks exposed in the continental mainland. The provenance change documented in the Sierra de los Cuarzos area suggests that the Pelones Formation was deposited when the Arperos Basin was closed and the Guerrero terrane was colliding with the North American continental mainland. Based on these data, we interpret the Pelones Formation as the syn-tectonic stratigraphic record associated with the accretion of the Guerrero terrane.     

Stratigraphy and Mesozoic–Cenozoic tectonic history of northern Sierra Los Ajos and adjacent areas,Sonora, Mexico

Geologic mapping in the northern Sierra Los Ajos reveals new stratigraphic and structural data relevant to deciphering the Mesozoic–Cenozoic tectonic evolution of the range. The northern Sierra Los Ajos is cored by Proterozoic, Cambrian, Devonian, Mississippian, and Pennsylvanian strata, equivalent respectively to the Pinal Schist, Bolsa Quartzite and Abrigo Limestone, Martin Formation, Escabrosa Limestone, and Horquilla Limestone. The Proterozoic–Paleozoic sequence is mantled by Upper Cretaceous rocks partly equivalent to the Fort Crittenden and Salero Formations in Arizona, and the Cabullona Group in Sonora, Mexico.Absence of the Upper Jurassic–Lower Cretaceous Bisbee Group below the Upper Cretaceous rocks and above the Proterozoic–Paleozoic rocks indicates that the Sierra Los Ajos was part of the Cananea high, a topographic highland during the Late Jurassic and Early Cretaceous. Deposition of Upper Cretaceous rocks directly on Paleozoic and Proterozoic rocks indicates that the Sierra Los Ajos area had subsided as part of the Laramide Cabullona basin during Late Cretaceous time. Basal beds of the Upper Cretaceous sequence are clast-supported conglomerate composed locally of basement (Paleozoic) clasts. The conglomerate represents erosion of Paleozoic basement in the Sierra Los Ajos area coincident with development of the Cabullona basin.The present-day Sierra Los Ajos reaches elevations of greater than 2600 m, and was uplifted during Tertiary basin-and-range extension. Upper Cretaceous rocks are exposed at higher elevations in the northern Sierra Los Ajos and represent an uplifted part of the inverted Cabullona basin. Tertiary uplift of the Sierra Los Ajos was largely accommodated by vertical movement along the north-to-northwest-striking Sierra Los Ajos fault zone flanking the west side of the range. This fault zone structurally controls the configuration of the headwaters of the San Pedro River basin, an important bi-national water resource in the US-Mexico border region.     

中国东南海域中生界油气地质条件与勘探前景

中国东南海域中生代地处欧亚板块东南缘, 夹持于欧亚板块、太平洋板块与印度澳大利亚板块之间。以往对于该区域的油气勘探多集中于新生代。笔者在前人研究的基础之上, 结合新近获得的地震资料, 开展了中国东南海域及周缘油气地质条件研究。结果表明:中国东南海域中生界分布广, 东海南部、台湾岛以及台西南盆地发育中生界深海相硅质岩, 可能与冲绳缝合带和菲律宾巴拉望缝合带形成有关;南海北部及周缘陆区发育上三叠统下侏罗统海相和海陆交互相碎屑岩及上侏罗统白垩系陆相碎屑岩, 可能与印支期缝合带的形成有关。从海域钻井及周缘陆区沉积层序资料推断, 中国东南海域有两套发育良好的烃源岩, 具有较强的生烃潜力:上三叠统下侏罗统海相泥页岩, 有机碳质量分数为0.28%~14.96%, 干酪根类型主要以Ⅱ₂型和Ⅲ型为主;下白垩统海相泥页岩, 有机碳质量分数为0.60%~2.00%, 干酪根类型以偏Ⅱ₂Ⅲ型为主。该海域发育两套生储盖组合:一套以上三叠统下侏罗统泥页岩为烃源岩, 中、上侏罗统砂岩为储层, 下白垩统泥页岩为盖层;另一套以下白垩统泥页岩为烃源岩, 白垩系砂岩为储层, 上白垩统泥页岩为盖层。它们相互可以形成"古生新储"、"自生自储"油气藏组合。因此, 中国东南海域中生界是值得关注的油气勘探新领域。     

PALAEOMAGNETIC STRATIGRAPHIC STUDIES OF THE JURASSIC AND LOWER CRETACEOUS ROCKS FROM THE QIANGTANG BASIN, NORTHERN TIBET

The Qiangtang Basin located in northern Tibet is a Jurassic foreland basin, whereas the sedimentation for the arc\|basin system during the Late Triassic. Paleomagnetic sampling sites and sections include the Lower Jurassic section in Juhuashan, Shuanhu district, the Middle and Upper Jurassic section in Nadigangri Mountain and the Lower Cretaceous section in Abushan, Shuanhu district. The Lower Jurassic Nadigangri Fm. is composed of tuffaceous volcanic rocks and turbidite (lower) and purple clastic rocks. The Middle Jurassic consists of Quemocuo Fm. purple clastics , Buqu Fm. carbonates and Xiali Fm. gypsum\|bearing varicolored clastics.The Upper Jurassic includes Suowa Fm. carbonates and Xueshan Fm. purple clastics. The Lower Cretaceous Abushan Fm. is lacustrine clastics.1723 oriented paleomagnetic samples of Jurassic and Cretaceous strata were collected in 1997.The sampling sections is located in Shuanhu district of northern Tibet. Although it is unlikely that the sections studied formed by constant and continuous deposition, field evidence indicates no major breaks in the Jurassic sedimentation, except early Bajocian stage. Based on sections of actual survey, all sampling was done using a portable gas\|powered core drill, and cores were oriented with magnetic compass and inclinometer. Samples were obtained at common stratigraphic spacing of 0 5～5m, partly 5cm at some important geological boundary\|surfaces and beds/members. 25mm diameter and 20～50mm length paleomagnetic core samples were drilled in cropping field. The measuring of most samples was completed at the China Academy of Geosciences Paleomagnetic Laboratory using a type DSM\|2 digital rotational magnetometer (its sensitivity of reaching 10 -5 A/m) made by SCHONSTEDT Company of U.S.A., and SCHONSTEDT TSD\|1 for thermal demagnetization. The apparatus used for AF demagnetization was a commercial (SCHONSTEDT GSD\|5)instrument, capable of reaching 100mT peak field. 10% of total measuring samples were completed at the Beijing Geological Institute Paleomagnetic Laboratory of China Academy of Sciences using a type 2G\|755R magnetometer made by Superconducting Technology for weak magnetized samples (sensitivity of reaching 10 -8 A/m). Most samples were stepwise thermally demagnetized, at 50℃ intervals from 100 to 700℃.     

High-resolution stratigraphy of the Upper Jurassic section(Laptev Sea coast)

Jurassic strata are widespread through Arctic Siberia and host oil and gas fields. However, in most cases, the geology of such vast areas still remains unexplored, and study of the Jurassic stratigraphy and reconstructions of geologic history are possible only through analysis of sediment cores. In this connection, there is a clear need for detailed studies of microfaunas (foraminifera, ostracods) and palynomorphs (dinocysts, spores, and pollen). The studied reference section of the Upper Jurassic and Lower Cretaceous is located on the left side of Anabar Bay of the Laptev Sea (Nordvik Peninsula, Cape Urdyuk-Khaya). An uninterrupted and continuous section from the Upper Oxfordian to the Lower Valanginian is exposed in coastal cliffs and consists mainly of silty clay deposits with abundant macro- and microfossils. Integrated field studies (biostratigraphy, lithostratigraphy, sedimentology) allow a more detailed characterization of the regional geologic framework. A detailed subdivision of the section is based on the systematic composition of ammonites from Upper Oxfordian and Kimmeridgian deposits. Several foraminiferal zones of the Upper Oxfordian and Lower Volgian are defined, and some of them are denfined for the first time. The distribution of ostracods in the section is analyzed for the first time. The section is also studied using palynological analysis, that results in its detailed subdivision on palynological data and recognition of two sequences of palynostratigraphic units. The integrated stratigraphy is used to establish the precise position of stage and substage boundaries. The continuity of the section is defined based on micropaleontological and palynological data.     

塔里木盆地西南部下白垩统克孜勒苏群沉积特征与成矿成藏作用*

通过对塔里木盆地西南部(塔西南)江格结尔地区下白垩统克孜勒苏群地层剖面测量,该地区的克孜勒苏群分为5个岩性段,岩性主要为泥质粉砂岩、岩屑砂岩、含砾砂岩、砾岩等,沉积相主要为辫状河三角洲相;其上覆的上白垩统库克拜组为介壳灰岩、膏质泥岩,沉积相为浅海相、滨海潟湖相; 下伏的上侏罗统库孜贡苏组岩性主要为杂砾岩、含砂杂砾岩和石英砂岩等,沉积相为冲积扇相;三者呈整合接触。从该区下白垩统克孜勒苏群的沉积特征来看,早白垩世为陆源碎屑沉积环境,在晚白垩世转入海相沉积环境。对比该区北侧陆内造山带中的拉分断陷盆地(萨热克巴依盆地)中下白垩统克孜勒苏群的地层层序,该区仅沉积了下白垩统克孜勒苏群下部3个岩性段而缺失上部岩性段,表明在早白垩世后期塔里木盆地北侧西南天山发生过一次抬升作用。下白垩统克孜勒苏群是铜铅锌铀矿等金属矿产的赋矿层位,同时也是塔里木盆地石油和天然气的重要储集层位,在铜铅锌等矿石中常可见大量的沥青等有机质,这些有机质主要源于下伏侏罗系的煤系烃源岩,并通过成矿流体参与了金属矿产的成矿作用,因而这种多矿种“同盆共存”的现象,在沉积盆地的研究中作为整体的成矿系统来研究将更有意义。     

塔里木盆地西南部下白垩统克孜勒苏群沉积特征与成矿成藏作用*

通过对塔里木盆地西南部(塔西南)江格结尔地区下白垩统克孜勒苏群地层剖面测量,该地区的克孜勒苏群分为5个岩性段,岩性主要为泥质粉砂岩、岩屑砂岩、含砾砂岩、砾岩等,沉积相主要为辫状河三角洲相;其上覆的上白垩统库克拜组为介壳灰岩、膏质泥岩,沉积相为浅海相、滨海潟湖相; 下伏的上侏罗统库孜贡苏组岩性主要为杂砾岩、含砂杂砾岩和石英砂岩等,沉积相为冲积扇相;三者呈整合接触。从该区下白垩统克孜勒苏群的沉积特征来看,早白垩世为陆源碎屑沉积环境,在晚白垩世转入海相沉积环境。对比该区北侧陆内造山带中的拉分断陷盆地(萨热克巴依盆地)中下白垩统克孜勒苏群的地层层序,该区仅沉积了下白垩统克孜勒苏群下部3个岩性段而缺失上部岩性段,表明在早白垩世后期塔里木盆地北侧西南天山发生过一次抬升作用。下白垩统克孜勒苏群是铜铅锌铀矿等金属矿产的赋矿层位,同时也是塔里木盆地石油和天然气的重要储集层位,在铜铅锌等矿石中常可见大量的沥青等有机质,这些有机质主要源于下伏侏罗系的煤系烃源岩,并通过成矿流体参与了金属矿产的成矿作用,因而这种多矿种“同盆共存”的现象,在沉积盆地的研究中作为整体的成矿系统来研究将更有意义。     

1D PetroMod software modeling of the Basrah oil fields, Southern Iraq

1D (Petromod) hydrocarbon charge modeling and source rock characterization of the Lower Cretaceous and Upper Jurassic underlying the prolific Cretaceous and Tertiary reservoirs in the Basra oilfields in southern Iraq. The study is based on well data of the Majnoon, West Qurna, Nahr Umr, Zubair, and Rumaila oil fields. Burial histories indicate complete maturation of Upper Jurassic source rocks during the Late Cretaceous to Paleogene followed by very recent (Neogene) maturation of the Low/Mid Cretaceous succession from early to mid-oil window conditions, consistent with the regional Iraq study of Pitman et al. (Geo Arab 9(4):41–72, 2004). These two main phases of hydrocarbon generation are synchronous with the main tectonic events and trap formation associated with Late Cretaceous closure of the neo-Tethys; the onset of continent–continent collision associated with the Zagros orogeny and Neogene opening of the Gulf of Suez/Red Sea. Palynofacies of the Lower Cretaceous Sulaiy and Lower Yamama Formations and of the Upper Jurassic Najmah/Naokelekan confirm their source rock potential, supported by pyrolysis data. To what extent the Upper Jurassic source rocks contributed to charge of the overlying Cretaceous reservoirs remains uncertain because of the Upper Jurassic Gotnia evaporite seal in between. The younger Cretaceous rocks do not contain source rocks nor were they buried deep enough for significant hydrocarbon generation.     

西昆仑山前地区白垩系分布研究

白垩系是西昆仑山前地区最重要的储层,受区域构造演化控制,其岩性与分布在纵、横向上均发生变化。下白垩统为冲积扇辫状河相沉积的红色砾岩、砂岩夹泥岩;上白垩统英吉沙群在研究区西部为一套海相碳酸盐岩地层。白垩系在喀什凹陷最厚,往西、往东、往北均逐渐变薄,并发生相变与尖灭,控制储层发育。本文在研究区域首次通过地震相研究,根据白垩系反射特征精细追踪对比其层位,确定尖灭位置,进而确定白垩系分布范围。研究认为,地震相能在区域上宏观地反映白垩系的沉积特征与分布范围,进而指导油气勘探,具有很重要的现实意义。     

南海南沙海域沉积盆地构造演化与油气成藏规律

据钻井、地震剖面、区域地质及磁异常条带分析解释,南沙海域及其邻区的主要沉积盆地的形成演化受裂谷起始不整合面和破裂不整合面分隔,可分为前裂谷期、裂谷期和后裂谷期3个构造阶段。大中型油气藏相关数据的统计表明,南沙海域及邻区大中型油气藏的成藏要素和油气田发育受构造阶段控制。(1)烃源岩发育具有分期、分区特征,礼乐盆地发育前裂谷期、裂谷1幕烃源岩;万安、曾母、西北巴拉望盆地发育裂谷2幕烃源岩,文莱-沙巴盆地发育后裂谷期烃源岩。(2)储层发育具有分期、分带特征,表现为外带老(裂谷2幕)、内带新(后裂谷期)。(3)圈闭类型包括构造、岩性地层圈闭及构造-岩性地层等因素形成的复合圈闭,大致具有内带以地层圈闭为主,外带以构造圈闭为主的特征。(4)大中型油气田分布具有外带砂岩富油气、内带碳酸盐岩富气特点。(5)南沙海域及邻区发育两个后裂谷期主含油气区,即东部巴兰三角洲砂岩背斜油气区和西部卢卡尼亚碳酸盐台地气区。其中,大中型气田的成藏要素组合为裂谷2幕烃源岩、后裂谷期碳酸盐岩储层和地层圈闭;大中型油气田则为后裂谷期烃源岩、砂岩储层和背斜圈闭。     

Sedimentary provenance of the Hengyang and Mayang basins,SE China,and implications for the Mesozoic topographic change in South China Craton: Evidence from detrital zircon geochronology

Detrital zircon U–Pb data from sedimentary rocks in the Hengyang and Mayang basins, SE China reveal a change in basin provenance during or after Early Cretaceous. The results imply a provenance of the sediment from the North China Craton and Dabie Orogen for the Upper Triassic to Middle Jurassic sandstones and from the Indosinian granitic plutons in the South China Craton for the Lower Cretaceous sandstones. The 90–120 Ma age group in the Upper Cretaceous sandstones in the Hengyang Basin is correlated with Cretaceous volcanism along the southeastern margin of South China, suggesting a coastal mountain belt have existed during the Late Cretaceous. The sediment provenance of the basins and topographic evolution revealed by the geochronological data in this study are consistent with a Mesozoic tectonic setting from Early Mesozoic intra-continental compression through late Mesozoic Pacific Plate subduction in SE China.     

Lower–Middle Jurassic foraminiferal and ostracode biostratigraphy of the Barents Sea shelf

The Barents Sea shelf is an attractive target as a prospective large petroleum province. Further development of geological and geophysical exploration in the area requires high-resolution biostratigraphic constraints and update stratigraphic charts. The zonal succession of Lower and Middle Jurassic assemblages of foraminifers and ostracodes of the Barents Sea fits well the division for northern Siberia based on correlated independent Jurassic and Cretaceous zonal scales on all main microfossil groups, of which some scales were suggested as the Boreal Zonal Standard. The stratigraphic range of the Barents Sea microfossil assemblages has been updated through correlation with their counterparts from northern Siberia constrained by ammonite and bivalve data. Joint analysis of foraminiferal and ostracode biostratigraphy and lithostratigraphy of the sections allowed a revision to the stratigraphic position and extent of lithological and seismic units. The discovered similarity in the Lower and Middle Jurassic lithostratigraphy in the sections of the Barents Sea shelf and northern Siberia, along with their almost identical microfossil taxonomy, prompts similarity in the Early and Middle Jurassic deposition and geological histories of the two areas.