Upper Maastrichtian shallow marine environments and neoselachian assemblages in North Iberian palaeomargin (Castilian Ramp,Spain)

Upper Maastrichtian deposits formed in a nearshore subtidal environment within the Valdenoceda Formation (Castilian Ramp, North Iberian margin) are described together with two recently found selachian assemblages. Rare earth element concentrations (REE) have been used to assess the degree of taphonomic mixing and reworking, observing that it is minor or non-existent, and differences in degree of preservation and ecologic mixing can be explained by biostratinomic processes. The patterns of REE also helped to obtain a better understanding of the depositional environment, including the diagenetic history from burial to final degree of bone preservation.The fossil assemblages here described are close to that of the late Maastrichtian of Albaina (in the enclave of Condado de Treviño, Burgos), both in the Basque-Cantabrian Region, but their age may be slightly older (early late Maastrichtian). In total, the new assemblages consist of 17 taxa, assigned to 11 genera of shallow-water dwellers combined with individuals from the outer shelf. They represent cosmopolitan taxa (Squalicorax pristodontus, Serratolamna serrata and Rhombodus binkhorsti) together with local species (Rhinobatos echavei, Rhinobatos ibericus). Although there are not significant differences between Albaina and Quintanilla la Ojada faunas, the new assemblages add interesting taphonomic and geochemical information to the few existing uppermost Cretaceous deposits with fossil sharks in southwestern Europe.     

Atmospheric palaeo-CO2 estimates based on the carbon isotope and stomatal data of Cheirolepidiaceae from the Lower Cretaceous of the Jiuquan Basin,Gansu Province

The stable carbon isotope compositions and the stomatal parameters (stomatal density and stomatal index) of four Cheirolepidiaceae species, Brachyphyllum ningxiaensis, Brachyphyllum obtusum, Pseudofrenelopsis dalatzensis and Pseudofrenelopsis gansuensis, were analyzed to recover the late Early Cretaceous atmospheric CO₂ levels. The fossil plants were collected from 5 consecutive sedimentary members of the uppermost Zhonggou Formation. Based on the stomatal data, the estimated palaeo-atmospheric CO₂ concentrations in the Jiuquan Basin during the late Early Cretaceous were 1060–882 ppmv based on the carboniferous standardization and were 641–531 ppmv based on the recent standardization; the pCO₂ values present at first a decreasing and then an increasing trend within the sedimentary time of the five members. The δ¹³Cp values based on the 21 Brachyphyllum specimens showed a large variation, which ranged from −20.98‰ to −25.69‰, with an average of −24.2‰. The values also identified a C3 photosynthetic pathway for the Brachyphyllum specimens. The predicted δ¹³Ca values varied from −2.1‰ to −6.38‰, with an average of −5.03‰. These two proxies were irregular within the different members; therefore, the correlation with the change in atmospheric CO₂ concentrations was not significant. Moreover, a water-stressed environment was proposed based on the δ¹³C values of the present fossil plants, a proposal that was also supported by the previous palaeobotanical, palynological and stratigraphical evidence. In the present study, an inconsistent relationship between the stable carbon isotope and the stomata values was apparent, which most likely indicated that the stomata numbers of the plant were more sensitive to the variation in the concentration of the atmospheric CO₂, whereas the δ¹³C values were sensitive to the moisture conditions.     

Planktonic foraminifera and calcareous nannofossils record in the upper Campanian-Maastrichtian pelagic deposits of the Malatya Basin in the Hekimhan area (NW Malatya,eastern Anatolia)

The uppermost Cretaceous (upper Campanian-Maastrichtian) pelagic successions from the Malatya Basin (NW Malatya, eastern Anatolia) were studied by 688 samples, which were collected from five stratigraphic sections in the Hekimhan area. The pelagic deposits conformably overlie rudist bearing shallow-water limestones and are overlain conformably by Maastrichtian dolomites and unconformably by Paleocene-Eocene deposits, respectively.The pelagic successions in the Hekimhan area comprise the Kösehasan Formation at the base and the Zorbehan Formation at the top and reach up to 1100 m in thickness. The Kösehasan Formation rests over the neritic rudist-bearing limestones of the Güzelyurt Formation along a sharp contact and consists mainly of flysch-type sandstone-mudstone alternation with complete and partial Bouma sequences. The carbonate content of abundant planktonic foraminifera and nannoplankton-bearing 980-m-thick succession increases upwards and the formation passes gradually to the clayey limestones and marlstones of the Zorbehan Formation to the top. Occurrences of nannoplankton Lithraphidites quadratus Bramlette and Martini and Micula praemurus (Bukry) in the first beds of the Kösehasan Formation indicate that the age of the Kösehasan Formation and overlying Zorbehan Formation is of late Maasthrichtian. Another late Maastrichtian taxa Cribrosphaerella daniae Perch-Nielsen and Arkhangelskiella maastrichtiana Burnett are observed from the lowermost part of the succession. Maastrichtian planktonic foraminifera such as Contusotruncana walfischensis (Todd) and Globotruncanita pettersi (Gandolfi) were recorded through the successions. Although planktonic foraminifera are diverse and abundant particularly in the Kösehesan Formation, index late Maasthrichtian species were not encountered. Campanian and Santonian-Campanian planktonic foraminifera, e.g. Radotruncana calcarata (Cushman) and Globotruncanita elevata (Brotzen), obtained particularly from the lower part of the succession and calcareous nannofossils such as Broinsonia parca parca Bukry, Reinhardtites anthophorus (Deflanre) and Eiffellithus eximius (Stover) are interpreted as reworked from older strata. Trace fossils are common throughout the succession.Rareness of planktonic foraminifera and nannoplankton in the uppermost part of the succession (Zorbehan Formation) indicates maximum shallowing of the latest Maastrichtian sea in this part of the basin. Rare echinoids, bivalves and ammonites are observed in that part of the sequence.The obtained data indicate that sediment accumulation rate of the pelagic deposits is rather high and about 27.5 cm/ky for this part of the basin. Changes in thickness of the formations along short distances in the five stratigraphic sections analysed in this study should be related to the diachroneity of the depositional and erosional events.     

塔里木盆地西南凹陷古新统巨厚海相石膏岩沉积特征及环境意义

塔里木盆地(简称塔,下同)西南凹陷古新世阿尔塔什组发育巨厚层海相石膏岩,夹薄层泥岩、粉砂岩及灰岩,是塔西南凹陷断续海侵环境下多期次蒸发沉积的产物。野外调查显示,该层海相石膏岩出现于皮拉里、阿尔塔什、麻扎塔格及大山口地区的阿尔塔什组露头剖面。石膏岩在凹陷内分布广泛,在西昆仑山前、南天山山前及麦盖提斜坡带均有发育且沉积厚度比较稳定。石膏岩中主要盐类矿物为石膏、硬石膏。扫描电镜分析发现,石膏岩中尚含石盐、钙芒硝及含钾镁的硫酸盐等;石膏岩样品中石盐、石膏、硬石膏等多呈细晶或自形微晶,推测阿尔塔什组沉积期,古盐湖曾出现过富钾卤水;通过对皮拉里剖面石膏岩样品进行地球化学分析,揭示该地区古新世古盐湖演化过程中出现2个相对富钾峰值。在古盐湖演化过程中,由于多期次特提斯海水的侵入,凹陷内部阿尔塔时期发育了碎屑岩—巨厚层石膏岩—碎屑岩的沉积韵律,古盐湖卤水表现为淡—咸—淡的变化规律。伴随着阿尔塔时期4次大规模的海侵,石膏岩沉积从西昆仑山前扩展到麦盖提斜坡地带,海侵范围也逐渐扩大。在阿尔塔什组顶部发育中厚层灰岩,显示在阿尔塔什组沉积晚期,塔西南凹陷沉积环境从●湖相逐渐向浅海相环境演变。     

前陆盆地钾盐矿床成因及模式——以西班牙北部埃布罗盆地为例

前陆盆地蕴藏有巨量的钾盐资源,而对于其内的钾盐矿床成因和模式还欠缺系统的总结。西班牙埃布罗盆地是由于伊比利亚和欧亚块体碰撞而形成的前陆盆地。始新世晚期(约36 Ma)海水完全从盆地退出后,在极端干旱气候作用下,由于碰撞造山导致盆地的封闭作用,在南比利牛斯前陆盆地系统的前渊带(即埃布罗盆地北部)形成了典型的厚层含钾石盐_光卤石的正常海相蒸发岩序列。后期受到构造挤压作用,钾盐地层以盐底劈的形式出露在背斜核部。埃布罗盆地钾盐成因是构造、气候和物源三者耦合作用的结果,与中国库车前陆盆地有很大的相似性。据此,作者建议可重点关注盆地南北盐丘地带苏维依组蒸发岩以及卤水的迁移方向。     

A new titanosaur from the Lower Cretaceous of Brazil

Here we describe a new record of a sauropod dinosaur from the Lower Cretaceous (Hauterivian–Barremian) Rio Piranhas Formation, Sousa Basin, NE Brazil. Dinosaur fossil bones from this deposit were unknown until now. Thus, the discovery of a sauropod fibula from this locality is highly significant. Our discovery represents an indeterminate titanosaur and the earliest stratigraphic occurrence of this group in central Gondwana. When compared to chronocorrelate titanosaur trackmakers of this geological unit, this fossil specimen appears substantially smaller. Histological analysis of the fibula suggests that this is a relatively young individual (approximately 40–50% adult body size) that had passed its most rapid phase of early juvenile growth, but had not yet attained somatic maturity. Thus, the fibula recovered is from a young individual rather than from a small-bodied adult titanosaur.     

南美Oriente盆地北部海绿石砂岩油藏特征及成藏规律

南美厄瓜多尔Oriente盆地斜坡带发育的白垩系Napo组高伽马特征的UT海绿石砂岩段是成熟探区新发现的隐蔽含油层段。本文分析了海绿石砂岩储层的矿物组成、孔隙结构、成岩作用、物性特点,并结合烃源岩评价与石油空间分布探讨海绿石砂岩油藏的成藏特征。海绿石粘土矿物以颗粒形式存在,与石英共同构成海绿石砂岩的颗粒组分,海绿石砂岩的孔隙结构具有双峰特征,束缚水含量高,属于中-低孔、中-低渗储层类型,孔隙类型主要是剩余粒间孔。海绿石砂岩储层中石英次生加大属Ⅱ级,长石碎屑颗粒发生溶蚀作用,含铁碳酸盐类胶结物发育,结合泥岩低的I/S混层比和高的最高峰温值T_max,指示海绿石砂岩层段属于中成岩阶段A期的产物。与海绿石砂岩油藏紧邻的大面积分布的Ⅱ₁腐泥型成熟烃源岩就是缓翼斜坡带的生烃中心,大面积连续发育的海绿石砂岩与之构成优越的源储组合,有利于上生下储式成藏。海绿石砂岩油藏表现为近源性、成藏晚期性等特点,规模发育的海绿石砂岩储层得以成藏的主要运聚机制是体积流和扩散流运聚机制。这对盆地其它油区同类油藏的发现具有重要的借鉴意义。     

三塘湖盆地石炭系卡拉岗组火山岩岩相研究

三塘湖盆地石炭系卡拉岗组火山岩岩性揭示该区火山岩岩相主要包括火山爆发相、溢流相,火山沉积相不发育。为了明确不同岩相分布规律,本文系统利用测井、地质、地震等多种资料,建立测井岩性识别模板,以单井相作为约束,开展地震反演,明确火山岩岩相的平面分布规律。研究结果表明:该区火山喷发方式以裂隙式为主,火山口呈串珠状沿主断裂排列;溢流相平面呈层状分布,溢流相安山岩最为发育。研究结果可有效指导该区火山岩油藏的勘探评价工作,同时为火山岩岩相研究提供可借鉴的研究思路。     

四川盆地西南部第三纪盆地原型及其演化

第三纪是四川盆地大范围陆相沉积历史的最后阶段, 同时又是四川盆地重要的构造定形期.探究该时期原型盆地沉积充填规律与构造演化特征, 是揭示四川盆地形成演化过程, 还原其古地理、古气候演变的关键.在综合利用古地磁、地震、野外露头等资料的基础之上, 从盆-山结合的角度出发, 以地质历史时间为主要线索, 对第三纪原型盆地分阶段、分区域地进行了动态化分析研究.重建了各沉积时期原型盆地构造-古地理格局, 分析了盆地沉积充填规律并复原了不同阶段沉积相带的空间展布特征.主要受周缘山系逆冲推覆作用产生的构造负载和盆地基底构造的影响, 第三纪时期四川盆地沉积范围局限于西南部、南部地区, 以河、湖沉积环境为主, 处于持续地挤压、充填过程而具有萎缩消亡的趋势.现今残余第三系地层由老到新, 主要由名山组、芦山组、大邑砾岩组等地层组成(先后经历了: 受造山带挤压推覆作用和温暖干旱气候等因素影响, 发育湖盆边缘冲积扇和沙漠沉积环境, 处于快速沉降阶段的名山组沉积时期; 以及构造活动相对稳定, 湖盆面积不断减小, 以沙泥质沉积互层为特征的芦山组沉积时期; 和沿山前带由南向北迁移, 以发育大型冲积扇为特征的大邑砾岩组沉积时期).纵观整个第三纪构造演化历史, 反映出四川盆地西南部地区在第三纪时期表现为典型的陆内坳陷沉积盆地性质.同期的大地构造活动和气候变化等因素对原型盆地的形成与演化起到了重要的控制作用, 同时也对该时期盆地古地理格局和沉积充填规律产生了重要影响.     

松辽盆地大陆科钻二开段大井眼钻井液技术

CCSD-SK2井是一口钻穿松辽盆地白垩纪陆相沉积地层的中国大陆科学钻探井。二开段先以216mm口径钻至2806.20m,然后进行444.5mm口径扩孔。泥页岩地层大井眼钻进过程中粘土矿物含量高且易造浆,砂砾岩层渗透性强易粘卡,井壁稳定控制与钻屑携带难度大。选用了钾铵聚合物钻井液体系和聚磺钻井液体系,通过正交实验确定了钻井液配方。将钻井液控制在合适的密度、较低的失水量以及较强的封堵性,有效实现了井壁稳定;保持适当的环空返速、较高的动塑比以及定期打稠塞举砂等措施,有效实现了井眼净化。1086.45m~1147.56m与1182.74m~1256.01m井段累计收获岩心130.90m,取心率达到97.41%,平均机械钻速为0.84m/h;最终顺利钻至2806.20m。