Sedimentary record of explosive silicic volcanism in a Cretaceous deep-marine conglomerate succession, northern Antarctic Peninsula

Lower Cretaceous conglomeratic strata exposed on southern Sobral Peninsula were deposited on a deep‐marine apron in the back‐arc Larsen Basin close to its faulted boundary with the Antarctic Peninsula magmatic arc. The succession is dominated by amalgamated beds of clast‐supported conglomerate, which, together with minor intercalated sandstones, consist of varied, but largely basaltic to andesitic, volcanic material and clasts derived from the Palaeozoic–Triassic (meta)sedimentary basement of the arc. Most of the volcanic clasts are thought to have been derived from lithified volcanic successions or older synvolcanic deposits, rather than from sites of coeval eruption. These mixed‐provenance strata enclose a number of intervals, consisting mainly of inverse–normally graded conglomerate and graded–stratified pebbly sandstone, in which the sand fraction is dominated by crystals and vitric grains considered to have been redeposited in the immediate aftermath of explosive silicic arc volcanism. Like syneruption deposits on non‐marine volcaniclastic aprons, these intervals are more sand‐prone than the enclosing strata and appear to show evidence of unusually rapid aggradation. Plagioclase from one such interval has yielded ⁴⁰Ar/³⁹Ar ages concordant at ≈121 Ma, similar to those obtained from the non‐marine Cerro Negro Formation, deposited within the magmatic arc. It is suggested that the two successions can be viewed as counterparts, both recording a history of mainly basaltic to andesitic volcanism, punctuated by relatively infrequent, explosive silicic eruptions. Whereas the Cerro Negro Formation consists mainly of syneruption deposits, most of the volcaniclastic material delivered to the eruption‐distal, deep‐marine apron appears to have been derived by normal degradation processes. Only rare silicic eruptions were capable of supplying pyroclastic material rapidly enough and in sufficient quantities to produce compositionally distinct syneruption intervals.     

Assessment of the oil source-rock potential of the Pedregoso Formation (Early Miocene) in the Falcón Basin of northwestern Venezuela

The early Miocene Pedregoso Formation is one of the numerous formations rich in organic matter within the stratigraphic record of the Urumaco Trough, in the central area of the Falcón Basin. Due to its lithological characteristics and stratigraphic position, this formation is of great interest regarding the basin's petroliferous systems. The evaluation of various inorganic and organic geochemical parameters indicates that the organic matter is primarily of marine origin, deposited in a marine carbonate environment typical of reefal systems, under oxic-to-dysoxic conditions. The low variability in the TOC concentrations and in the distributions of the biomarkers extracted from the samples suggests that the paleoenvironmental conditions and the organic-matter supply remained approximately constant throughout the sedimentation of this unit. The Pedregoso type-II organic matter (marine origin) and initial organic richness value (∼1.8%) suggest that this unit has probably generated hydrocarbons within the Urumaco Trough. However, present-day thermal maturity parameters reveal that the Pedregoso organic matter is overmature (dry gas window), indicating that this unit is only capable to generate gas. In addition, the geothermal gradient, maturity parameters, and the maximum paleotemperature estimated in this study suggest that the Pedregoso Formation reached a maximum burial depth the ∼6.5 km, consistent with the value obtained from data of stratigraphic thickness in the Urumaco Trough. This implies that the thermal anomaly that affected the basin during the Late Eocene–Early Miocene did not reach the central part of the basin, and therefore, the organic matter maturation in this unit is due to the sedimentary burial.     

浊流及相关重力流沉积研究综述

本文首先介绍了浊流及相关重力流的有关概念,并对浊流沉积研究历史进行了简要回顾,概括了当前浊流沉积的研究现状;随后,总结了浊积岩的沉积特征并对其成因进行了扼要解释;最后,对浊流及相关重力流沉积研究中两个有争议的问题－浊积相的划分和浊积相模式的建立进行了探讨。     

山东五号桩油田桩74块剩余油分布规律及挖潜措施

低渗透油田开发在中国石油工业中具有特别重要的意义。应用岩心、测井等资料将山东五号桩油田桩74块远岸浊积扇划分为扇根、扇中、扇缘3个亚相,其中扇中亚相划分为辫状水道、水道间、水道侧缘、扇中前缘及叶状体5个微相类型;阐明了研究区特低渗透油藏内储层的层内、层间及平面非均质特征;系统总结了微构造的类型及组合模式。在沉积微相、储层非均质性及微构造研究的基础上,采用动态、静态结合的分析方法阐明了研究区特低渗透油藏的剩余油分布规律及控制因素,揭示了沉积微相、储层非均质、微构造及井网条件等因素对剩余油分布的控制作用。根据剩余油分布的研究结果,结合相关资料,指出了剩余油潜力区,有针对性地确定了剩余油的挖潜措施,为增加剩余可采储量和提高采收率提供了科学依据。     

冲绳海槽的晚第四纪浊流沉积

冲绳海槽晚第四纪的浊流沉积发育在海底斜坡带和坡折处静水环境,属阵发性纵向浊流。物质来源于海槽中心斜坡区的滑塌沉积物、岛坡、陆坡和台湾宜兰浇滩的碎屑沉积物。受控于海底地形、滞流环境和构造岩浆活动以及伴生的浅源地震。 冲绳海槽海底表层浊流沉积物,形成在晚更新世末次冰期最盛期、末次冰期末和冰后期三个阶段,以末次冰期最盛期阵发频繁,浊积物最发育,与气候寒冷期有一定的相关性。     

山东灵山岛晚中生代滑塌沉积层的发现及区域构造意义初探

灵山岛位于青岛胶南市东南黄海近岸海域中,为中国北方第一高岛,构造上属于苏鲁造山带,但岛上很多重要的地质现象尚未在地质文献中披露过。本文作者对灵山岛进行了初步地质考察,在被看做早白垩世莱阳期的地层中发现远源浊积岩及其内部大量的滑塌沉积层,孢粉鉴定初步结果显示该地层的时代很可能为侏罗纪。滑塌构造以同沉积滑塌褶皱为主,而在滑塌体内部还发现有很多同沉积变形构造,如:同沉积布丁构造、同沉积拉伸线理、同沉积双重构造等。同沉积滑塌褶皱体的排列方向揭示了其物源来自南东方向,韵律层中弱粒序层单元颗粒为细砂到粉砂,反映出远源浊积岩的特征。根据滑塌体运移方向判断盆地的古地理特征为东南侧水体变浅而西北侧水体变深。滑塌沉积发育时,盆地为介于扬子板块和华北板块之间的残余洋盆。发育于砂质单元中的早期平面X剪节理指示了该套浊积岩在褶皱之前受到了SE—NW向的动态挤压,而后期的不对称褶皱构造记录了扬子板块自南东向北西侧的华北板块俯冲的历史。灵山岛中生代滑塌沉积层的发现不仅揭示了中国东部存在着晚中生代海相沉积,更为扬子板块与华北板块在郯庐断裂以东碰撞缝合的演化历史研究提供了珍贵的实际材料。     

Fluvial suspended sediment transfer and lacustrine sedimentation of recent flood turbidites in proglacial Eklutna Lake,western Chugach Mountains,Alaska

Suspended sediment delivery and deposition in proglacial lakes is generally sensitive to a wide range of hydrometeorologic and geomorphic controls. High discharge conditions are of particular importance in many glaciolacustrine records, with individual floods potentially recorded as distinctive turbidites. We used an extensive network of surface sediment cores and hydroclimatic monitoring data to analyse recent flood turbidites and associated sediment transfer controls over instrumental periods at Eklutna Lake, western Chugach Mountains, Alaska. Close to a decade of fluvial data from primary catchment tributaries show a dominating influence of discharge on sediment delivery, with various interconnections with other related hydroclimatic controls. Multivariate fluvial models highlight and help quantify some complexities in sediment transfer, including intra-annual variations, meteorological controls, and the influence of subcatchment glacierization. Sediments deposited in Eklutna Lake during the last half century are discontinuously varved and contain multiple distinctive turbidites. Over a 30-year period of stratigraphic calibration, we correlate the four thickest flood turbidites (1989, 1995, 2006, and 2012) to specific regional storms. The studied turbidites correlate with late-summer and early-autumn rainstorms with a magnitude of relatively instantaneous sedimentation 3–15 times greater than annual background accumulation. Our network of sediment core data captured the broad extent and sediment variability among the study turbidites and background sediment yield. Within-lake spatial modelling of deposition quantifies variable rates of downlake thinning and sediment focusing effects, and highlights especially large differences between the thickest flood turbidites and background sedimentation. This we primarily relate to strongly contrasting dispersion processes controlled by inflow current strength and turbidity. Sediment delivery is of interest for this catchment because of reservoir and water supply operations. Furthermore, although smaller floods may not be consistently represented, the lake likely contains a valuable proxy record of regional flooding proximal to major population centers of south-central Alaska including Anchorage.     

Physicochemical and biological influences on sedimentary‐fabric formation in a salinity and oxygen‐restricted semi‐enclosed sea: Gotland Deep,Baltic Sea

Two ca 8000 year long sediment cores from the Gotland Deep, the central sub‐basin of the Baltic Sea, were studied by means of digital images, X‐radiographs and scanning electron microscopy–energy‐dispersive X‐ray mineralogical analysis to gain understanding of the physicochemical and biological influences on sedimentary‐fabric formation in modern and ancient seas with a high flux of organic carbon, and associated oxygen stress and depauperate ichnofauna. Four lithofacies were recognized: (i) sharply laminated mud; (ii) biodeformed mud; (iii) burrow‐mottled mud; and (iv) sedimentation‐event bed. The sharply laminated and burrow‐mottled facies dominate the cores as alternating long intervals, whereas the biodeformed and sedimentation‐event facies occur as thin interbeds within the sharply laminated intervals. The sharply laminated mud comprises alternating diatom‐rich and lithic laminae, with occasional Mn‐carbonate laminae. Lamination discontinuity horizons within the laminites, where the regular lamination is overlain sharply by gently inclined lamination, challenge the traditional view of mud accumulation by settling from suspension, but indicate localized accumulation by particle‐trapping microbial mats and, potentially, by the rapid lateral accretion of mud from bedload transport. The biodeformed interbeds record brief (few years to few decades) oxic–dysoxic conditions that punctuated the anoxic background conditions and permitted sediment‐surface grazing and feeding by a very immature benthic community restricted to the surface mixed tier. The likely biodeformers were meiofauna and nectobenthic pioneers passively imported with currents. The sedimentation‐event interbeds are distal mud turbidites deposited from turbidity currents probably triggered by severe storms on the adjacent coastal areas. The turbidite preservation was favoured by the anoxic background conditions. The long burrow‐mottled intervals are characterized by intensely bioturbated fabrics with discrete Planolites, rare Arenicolites/Polykladichnus and very rare Lockeia trace fossils, as well as bivalve biodeformational structures which represent shallowly penetrating endobenthic feeding and grazing strategies and permanent dwellings. These burrowed intervals represent longer periods (several years to few centuries) of oxic–dysoxic conditions that permitted maturation in the benthos by means of larval settling of opportunistic worm‐like macrofauna and bivalves, resulting in the development of a transition tier. These observations imply more dynamic and oxic depositional conditions in Gotland Deep than previously thought. Comparison to previous zoobenthic studies in the area allowed discussion of the benthic dynamics, and the identification of probable biodeforming and trace‐producing species. Implications for current biofacies and trace‐fossil models are discussed.     

安徽西湾铅锌矿床闪锌矿原位微量元素组成及成矿流体特征

安徽西湾铅锌矿床位于长江中下游成矿带庐枞矿集区北部,是近年来在该地区发现的首个赋存于三叠系周冲村组碳酸盐地层中的大型隐伏铅锌矿床,目前该矿床的成矿流体演化及矿床成因研究较为薄弱,制约了该地区铅锌矿床成矿理论与地质勘探。文章根据矿床地质特征,结合镜下鉴定,认为矿床中硫化物主要形成于石英碳酸盐硫化物阶段及碳酸盐硫化物阶段。闪锌矿原位微量元素分析和包裹体测温数据显示,石英碳酸盐硫化物阶段闪锌矿Fe、Mn含量相对较高,Ga、Ge、Cd含量相对较低,该阶段闪锌矿的均一温度为207～236℃,流体盐度w(NaCl_eq)范围为7.45%～11.81%;碳酸盐硫化物阶段的闪锌矿相对贫Fe和Mn,Cd、Ga和Ge含量相对较高,其闪锌矿均一温度为164～189℃,流体盐度w(NaCl_eq)为0.88%～5.56%。此外,西湾矿床西南部的样品以石英碳酸盐硫化物阶段的闪锌矿为主,而东北部的样品以碳酸盐硫化物阶段为主,流体包裹体均一温度结果表明矿床成矿温度从西南(183～240℃)向东北方向呈降低趋势(160～209℃),说明成矿流体由西南向东北方向移动。西湾矿床闪锌...