Whole rock geochemistry and Sr isotopic compositions of Phanerozoic sedimentary rocks in the Inner Zone of the Southwest Japan Arc

Pre-Cretaceous metasedimentary rocks occurring in the Inner Zone of the Southwest Japan Arc can be divided into three major groups, namely, high P/T metamorphic (Renge and Suo belts), low P/T metamorphic (Hida-Oki, Ryoke and Higo belts), and accretionary terranes (Akiyoshi, Maizuru, Mino-Tamba, and Ashio belts). Major and trace element compositions of most of the sedimentary rocks are typical of relatively mature sedimentary rocks, although abundances of ferromagnesian elements also suggest the presence of a significant mafic to intermediate igneous component. The sedimentary rocks with older Nd model ages (> 2.0 Ga) have high εSr values and major and trace element geochemical signatures typical of mature sediments, whereas those with younger model ages (< 1.45 Ga) have low εSr values and immature geochemical characteristics. With the exception of Hida samples, the sedimentary rocks from other districts have geochemical and isotopic features intermediate between the rocks with old and young Nd model ages. Some of the Hida samples have old Nd model ages, but others are influenced by younger rock fragments and have immature geochemical features. Based on combined isotopic and geochemical evidence, Inner Zone sedimentary rocks with older Nd model ages are interpreted to have been derived from felsic upper continental crustal materials such as Sino-Korean or northwest Yangtze craton granitoids. Compositions of rocks with younger Nd model ages reflect addition of mafic to intermediate detritus, such as island arc basalts and andesites. The rocks with intermediate Nd model ages may have formed in and around the Asian continental margin. The Hida metasedimentary rocks may have been derived from several terranes of varying age and geochemical composition.     

鄂尔多斯盆地胡尖山-耿湾地区延长组长4+5油层组沉积特征及有利相带预测

以岩心观察为依据,结合储集层岩性、沉积构造和粒度分析等方法对鄂尔多斯盆地胡尖山—耿湾地区长4 5油层组进行沉积相分析.研究结果表明:研究区长4 5油层组为三角洲前缘沉积,水下分流河道、河口坝、分流间湾、远砂坝及前缘席状砂构成其主要沉积微相.长4 52期水下分流河道砂体之间交叉叠合连片,但水下分流河道、叠置水下分流河道分割性较强,随着湖盆短暂的扩张,长4 51期水下分流河道缩小,分流间湾进一步扩大.在沉积相研究的基础上对长4 52期进行有利相带预测,共预测出5个有利储集相带发育区,为该地区进一步勘探提供依据.     

L'Arenig–Llanvirn du Haut Atlas occidental et central (Maroc). Environnements sédimentaires,paléogéographie et contrôle de la sédimentation

The sedimentological study of Arenig–Llanvirn successions of Aït Lahsen (western High Atlas), Tizi-n-Tichka and Imini (central High Atlas) allow us to recognise two independent epeiric seas. In the western High Atlas, the sedimentation occurred in a wave- and storm-influenced delta, alimented by a source situated at the present-day location of the Argana corridor, under the control of sea-level fluctuations and subsidence. In the central High Atlas, the sedimentation occurred in an influenced tide and episodic storm delta, alimented by sources situated at the present-day location of the Siroua and Ouzellagh Massifs under the control of sea-level fluctuations and tectonics. To cite this article: C. Chacrone, N. Hamoumi, C. R. Geoscience 337 (2005).     

Fluid-dynamics driving saline water in the North East German Basin

In several areas of the North German Basin, saline water comes close to, or even reaches the surface. Available data from wells indicate that brine stratification is under unstable conditions in the deeper underground. In order to analyse the possible transport mechanisms, 3D thermohaline simulations have been carried out for two different scenarios. The 3D regional model (230×330 km) indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands. In addition, a smaller scale model (10×10 km) has been constructed with a grid resolution accounting for possible convective flow. The results indicate that convective flow may play a dominant role in areas with minor topography. In summary, the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces.     

The northern Upper Rhine Graben: basin geometry and early syn-rift tectono-sedimentary evolution

A large-scale transfer zone subdivides the northern parts of the Upper Rhine Graben into a northern and a southern sub-basin. These sub-basins display the geometry of asymmetric half-grabens with opposing tilt directions. The transfer zone connects the western master fault of the northern half-graben with the eastern master fault of the southern half-graben. In the northern Upper Rhine Graben early syn-rift sedimentation (Late Priabonian to Late Rupelian) was controlled by the tectonically induced subsidence of these half-grabens (autogenetic), as well as by regional third-order sea level variations (allogenetic). Within the graben, lateral changes in subsidence rates (in dip and strike direction of fault blocks) controlled the development of accommodation space and thus, sediment thickness and facies. Furthermore, a low-displacement segment along the western border fault acted as a sediment entry point. Tectonics controlled the distribution of early syn-rift deposits and the palaeogeography of the northern Upper Rhine Graben.     

Refinement of three-dimensional multilayer models of basins and crustal environments by inversion of gravity and magnetic data

The sensitivity of gravity and magnetic data to deep structures and the broad availability of regional data sets and surveys of high resolution make them suitable for determining detailed three-dimensional (3D) models of the subsurface. However, the sole consideration of gravity and magnetic information cannot properly resolve heterogeneous 3D environments. Advocated to solve this problem, we present an automated refinement technique for three-dimensional multilayer models as conditioned by gravity and magnetic data and by meaningful geometrical and physical constraints. We construct our model by an aggregate of rectangular prisms and aim to estimate their bottom depths, which define the geological layers. We summarize mathematically our concept of refinement in an objective function that includes the misfit to the data, the similitude to an a priori geological–geophysical model, and the smoothness of the relief of the layers. Importantly, our objective function also includes inequality constraints that prevent the superposition of layers and integrate the surface and borehole geology with the multilayer deep model. The objective function is solved using quadratic programming in a stable iterative scheme. The resulting algorithm is tested on synthetic data and applied to crustal and sedimentary basin environments from southern Baja California, Mexico. The assimilation of the geological and geometrical constraints to the inversion process produces models that correlate with the surface geology and reveal the three-dimensional features of the subsurface.     

Geochemical characterisation, provenance, source and depositional environment of ‘Roches Argilo-Talqueuses’ (RAT) and Mines Subgroups sedimentary rocks in the Neoproterozoic Katangan Belt (Congo): Lithostratigraphic implications

The chemical characteristics of sedimentary rocks provide important clues to their provenance and depositional environments. Chemical analyses of 192 samples of Katangan sedimentary rocks from Kolwezi, Kambove–Kabolela and Luiswishi in the central African Copperbelt (Katanga, Congo) are used to constrain (1) the source and depositional environment of RAT and Mines Subgroup sedimentary rocks and (2) the geochemical relations between the rocks from these units and the debate on the lithostratigraphic position of the RAT Subgroup within the Katangan sedimentary succession. The geochemical data indicate that RAT, D. Strat., RSF and RSC are extremely poor in alkalis and very rich in MgO. SD are richer in alkalis, especially K₂O. Geochemical characteristics of RAT and Mines Subgroups sedimentary rocks indicate deposition under an evaporitic environment that evolved from oxidizing (Red RAT) to reducing (Grey RAT and Mines Subgroup) conditions. There is no chemical difference between RAT and fine-grained clastic rocks from the lower part of the Mines Subgroup. The geochemical data preclude the genetic model that RAT are syn-orogenic sedimentary rocks originating from Mines Group rocks by erosion and gravity-induced fragmentation in front of advancing nappes.     

福建省泉州市第四纪沉积物粒度特征及沉积环境分析

对福建省泉州市钻孔,进行详细的第四纪沉积物粒度分析,同时结合地质背景、岩性等资料,得出了研究区第四纪以来沉积环境及其演变的认识。采用MS-2000型激光粒度分析仪进行测试,所测数据利用计算机整理,绘制出沉积物粒度频率曲线、概率累积曲线和粒度众数分布曲线图。根据曲线变化情况,进行沉积环境及其演变解释。区内第四纪沉积环境和沉积物的成因类型分为3个类型,晋江河道以冲积相为主,山前高地以洪冲积为主,盆地主体区域以海湾相为主。第四纪以来泉州盆地环境演化经历了:更新统中期龙海组洪积和洪冲积→更新统晚期东山组洪积和洪冲积→全新统长乐组海湾相沉积。     

新疆罗布泊罗北洼地CK—2孔盐类沉积特征

新疆罗布泊罗北洼地主要有粉砂、粘土沉积 ,硫酸盐沉积和氯化物沉积。其中硫酸盐 (主要为钙芒硝 )沉积占主导地位 ,钻孔岩芯中微细层理发育。研究分析表明 ,罗北洼地为一长期动荡的浅水沉积环境 ;钾资源以液体矿为主 :2 5 ka B.P.- 10 Ka B.P.为该洼地湖泊的演化末期 ,属于盐湖阶段     

河口、海湾沉积磷在全球变化区域响应研究中的意义

通过探讨海陆交互作用带近代沉积磷的生物地球化学循环过程及与大气圈氧气和二氧化碳等的相关关系 ,综述了用环境生物地球化学的理论和方法研究海陆边缘近代沉积磷随时间的变化规律、赋存形态、与相关元素的耦合关系等生物地球化学特征及其在全球变化区域响应研究中的特殊意义。藉此追溯过去气候和环境变化的驱动因素 ,区分自然因素和人类活动作用的影响 ,揭示河口、海湾近代沉积磷对过去气候和环境变化的指示作用 ,为预测未来区域和全球变化趋势及建立模型提供科学依据。