Preservation of aeolian genetic units by lava flows in the Lower Cretaceous of the Paraná Basin, southern Brazil

The Lower Cretaceous geological record of the intracratonic Paraná Basin in southern Brazil comprises a thick succession of aeolian sandstones and volcanic rocks. The intercalation between aeolian sandstone and volcanic floods allowed the preservation of distinct aeolian genetic units. Each genetic unit represents an accumulation episode, bounded by supersurfaces, that coincides with the base of lava flood events. The entire package can be subdivided into a Lower Genetic Unit, which corresponds to aeolian sandstones preserved below the initial lava flows (Botucatu Formation), and an upper set of genetic units, which comprises interlayered aeolian deposits and lava floods (Serra Geral Formation). The Lower Genetic Unit is up to 100 m thick. Its base is composed of ephemeral stream and aeolian sand sheet deposits that are overlain by cross‐bedded sandstones whose origin is ascribed to simple, locally composite, crescentic and complex linear aeolian dunes. Aeolian accumulation of the lower unit was possible as a result of the existence of a wide topographic basin, which caused wind deceleration, and a large sand availability that promoted a positive net sediment flux. The Upper Genetic Units comprise isolated sand bodies that occur in two different styles: (1) thin lenses (<3 m thick) formed by aeolian sand sheets; and (2) thick sand lenses (3–15 m) comprising cross‐bedded cosets generated by migration and climbing of simple to locally composite crescentic aeolian dunes. Accumulation of the aeolian strata was associated with wind deceleration within depressions on the irregular upper surface of the lava floods. The interruption of sedimentation in the Lower and Upper Genetic Units, and related development of supersurfaces, occurred as a result of widespread effusions of basaltic lava. Preservation of both wind‐rippled topset deposits of the aeolian dunes and pahoehoe lava imprints indicates that lava floods covered active aeolian dunes and, hence, protected the aeolian deposits from erosion, thus preserving the genetic units.     

中国南方中、新生代盆地对海相中、古生界的迭加、改造分析

本文主要论述了我国南方中、新生代四期构造变格发育的主要盆地原型及其在主要盆地的迭加特征, 并根据中、新生代盆地原型的迭加方式和构造改造特点, 将南方主要探区的海相中、古生界后期改造形式划分为五种类型, 即:持续前渊*迭加型、渊-滑-断-拗迭加型、渊-滑断迭加型、推覆构造及影子盆地型、残留改造型, 进而分别探讨了它们的主要构造特点和在油气保存条件上的差异。分析认为, 以四川盆地为代表的持续前渊迭加是海相天然气在中、新生代得到有效保存的最有利类型; 其次应为中下扬子地区以江汉盆地、皖南-苏北盆地为代表的渊-滑-断-拗迭加型, 它们在早期(T₃-J₂)前渊盆地迭加和晚期(K₂以来)的断陷-拗陷迭加下曾先后为海相中、古生界构建了区域封盖条件, 尽管在第二变格期(J₃-K₁)遭受到燕山运动强烈挤压-走滑作用的改造, 但在晚期断-拗盆地迭加下可为海相中、古生界二次生烃油气提供有效保存; 而以楚雄盆地、十万大山盆地为代表的渊-滑断迭加型, 尽管早期(T₃-J₂)前渊盆地迭加为海相中古生界构建了区域封盖条件, 但自第二变格期以来由于受到冲断与走滑联合作用影响, 使盆地整体形成高块断构造, 对海相油气保存造成不利影响; 同时指出, 要注意推覆构造中的“影子盆地”尤其是区域滑脱层之下的油气保存条件, 以及像南盘江拗陷这类残留改造型的弱变形带。      

川东-武陵构造带下古生界海相页岩构造变形特征及对页岩气保存的影响

川东-武陵构造带下古生界发育的两套海相页岩层系(下寒武统牛蹄塘组和上奥陶统五峰组—下志留统龙马溪组)不仅是区域内重要的滑脱层,也是页岩气勘探开发的重点层位。通过野外详细的构造解析及室内显微观察,从宏观露头—显微尺度分析了页岩的变形特征,认为页岩至少存在两期构造变形:早期顺层向北西或南东的逆冲和晚期的切层断层作用。页岩的变形强度随着与断裂带距离的变化而发生改变,远离断裂带的地区页岩变形主要表现为近直立的微裂隙,属脆性域;靠近断裂带,页岩的变形特征逐渐表现为脆-韧性过渡,开始发育糜棱化构造;在断裂带内部,页岩强烈面理化,发育大量的糜棱化构造,属韧性域。通过氩离子抛光和扫描电镜技术,分析了变形页岩内部的孔隙演化特征,认为随着变形作用从脆性—脆-韧性过渡—韧性的转变,页岩内部的孔隙类型不仅可以发生转换,而且页岩内部孔隙的大小、分布特征也随之改变。在此基础上,进一步讨论了中国南方复杂构造区下古生界页岩变形对页岩气保存的影响,认为顺层剪切滑脱作用会改变页岩内部的孔隙体系,有利于页岩气的富集;切层的伸展或走滑剪切作用不仅会破坏先前形成的油气圈闭,而且会导致油气沿着断裂带从高势区向低势区运移,进而造成油气散失。      

三峡工程库区公路复建工程主要地质病害及防治对策

三峡工程建成后, 库水回水将淹没沿江(河) 地带的公路约1 000 km. 随着库区的开发, 不仅需要复建被淹没的公路, 恢复其功能, 而且还将大量修建新公路. 通过实例对三峡工程库区公路复建工程中的主要地质病害进行了论述, 指出已发生的地质病害主要是山区常见的滑坡、崩塌、泥石流, 而潜在的地质病害是由于水库库岸再造对公路工程的不利影响; 分析了产生病害的原因, 并提出了防治对策. 对三峡工程库区今后的公路建设、相似地质条件地区的道路建设均具有一定的参考和借鉴意义.      

水滴冻结实验测量降水物中的冻结核含量

文中介绍了一套新研制的均匀水滴冻结实验装置 ,实验水滴与周围环境同步冷却 ,其温度梯度很小 ,可控制降温速率 ,并能自动记录冻结事件 ,从而提高了实验的精度。用此装置对北京地区 1995年底至 1998年出现的各类降水样品进行了实验 ,由水滴冻结温度谱推算了降水的冻结核浓度 温度谱 ,并对结果进行了分析和讨论     

Porosity preservation due to grain coating illite/smectite: Evidence from Buchan Formation (Upper Devonian) of the Ardmore Field,UK North Sea

The Buchan Formation sandstone reservoirs from the Ardmore Field in the UK Central North Sea are fluvial-aeolian deposits and provide examples of porosity preservation in deeply-buried reservoirs (2.7–3.2?km) caused by grain-coating illite/smectite (I/S). Here, high reservoir quality commonly correlates with the occurrence of grain-coating I/S and consequent inhibition of quartz cementation in the aeolian dune and interdune sandstones. Porosity is lower in fluvial sandstones lacking grain coating I/S but with intense quartz overgrowths. We propose that the presence of I/S reflects concentration of the smectitic-rich clay bearing water which would have been the deposits of the interdune and/or distal sector of fluvial distributary system, and were introduced into aeolian deposits by mechanical infiltration. Petrographic relationships indicate that these coatings grew mainly before the mechanical compaction as the clays occur at grain contacts. The use of empirical model suggested that about 6–7% porosity have been preserved. The burial-thermal history of the Ardmore area contributed to the high quality reservoir because throughout much of the time since deposition, the Devonian sandstones have been little buried. Only from the Palaeogene the reservoir temperatures exceeded about 70?°C and rapidly buried to today’s maximum depth, which have minimized the negative effect generally ascribed to smectitic clays on reservoir quality. The circumstances of porosity preservation shown in this study may be unusual, but nonetheless have profound consequences for exploration. It is possible to identify new Buchan Formation prospects in areas hitherto dismissed because they were generally assumed to be poor reservoir.     

冻结作用下非饱和黄土水分迁移试验研究

通过室内大尺寸非饱和黄土冻结作用下水分迁移试验,开展了土体密度、含水量、冻结温度、冻结方式对非饱和黄土水分迁移影响的研究.试验结果表明:冻结过程中土样温度变化分为3个阶段:急剧降温阶段,缓慢降温阶段,稳定阶段; 干密度越大,稳定冻结锋面的水分迁移量越大,但冻结区的整体水分增量越小; 初始含水量越大,水分迁移量越大,并且在冻结锋面处含水量增幅越大; 在未冻结区,从邻近冻结锋面到暖端,含水量先增大后减小,初始含水量越小,这种现象越明显.此现象是冻结界面抽吸力、温度梯度和基质吸力梯度共同作用的结果.冻结方式直接影响已冻结区的含水量分布和水分迁移总量.     

甲壳动物精子生物学的研究进展(英文)

甲壳动物精子生物学的研究对于甲壳动物的人工繁育及遗传育种等工作有重要意义。本文归纳了甲壳动物精子生物学的最新研究进展,包括精子的形态结构、发生、活力、体外保存及顶体反应等方面,并对该领域今后的研究方向提出了展望。     

矿床四维时空定量评价的新认识——以西藏玉龙斑岩铜矿床为例

大型、超大型斑岩铜矿的定量研究正在受到广泛关注,集中体现在现代矿产资源勘探模式趋向于从经验找矿、理论找矿和信息找矿3大传统找矿方法向集成信息技术方向发展。本项研究以青藏高原典型的玉龙斑岩铜矿床为例进行分析,提出了矿床定量评价的4个方面的新认识:(1)区域矿床发生、发展的年代与消亡速率的确定是研究矿床规模与保存环境的重要参数;(2)研究区的古地理、古气候特征有利于斑岩体的剥蚀起始时间的估算,研究区不同时代地层剖面的对比分析以及成矿古地理环境的模拟有利于正确评价斑岩矿床的形成与保存现状;(3)地层、岩体、构造和DEM数据的三维空间定量研究是正确评价"多位一体"成矿模式的重要因素;(4)3S技术发展了三维可视化技术、数据融合和模拟技术,能够最大限度地利用各种多元数据(地质、地球物理、地球化学和遥感等)资料,有助于提高发现大型矿床或潜在矿床的成功率。     

石西油田石炭系水动力特征及其与含油性关系

利用油层流体的物化参数对油藏所处的水动力环境、油气运移方向及断层的封闭性进行了分析判断。研究结果表明，石西油田供水区在石007井东断裂西侧，并且由西向东渗人；石007井东断裂具有良好的封闭性，断裂东侧较西侧封闭，水动力也较西侧弱，使东断块油气较西侧易于保存，东断块含油显示也明显好于西断块。石西油田原油的物理性质与水动力环境有一定关系，但在平面上原油性质的变化主要受油气运移层析效应的控制。西断块水动力强，原油性质变化速率大；东断块水动力弱，原油性质变化速率小。油气运移方向为东、东北向西、西南，原油性质也沿该方向降低。