鄂尔多斯盆地西南缘上奥陶统平凉组岩石特征及沉积环境

为研究鄂尔多斯盆地西南缘上奥陶统平凉组岩石特征及沉积环境,基于沉积学相关理论和方法,根据野外露头、古生物及粒度分析等资料,对研究区岩石特征、沉积相及主控因素开展了研究。结果表明：①研究区平凉组可划分3种岩相和2种岩相组合。②通过综合研究岩性、古生物、沉积构造及粒度参数等资料,确定平凉组沉积环境为深水斜坡。③沉积相为海底扇,在此基础上可划分为中扇和下扇2个亚相,近端朵叶和远端朵叶2个微相。④海底扇的主控因素为相对海平面升降、构造运动和物源供给。     

东阿拉伯海拉克希米盆地浊流沉积序列的粒度变化及其对中更新世气候转型的响应

阿拉伯海印度沉积扇是世界第二大海底扇,保存着来自喜马拉雅和喀喇昆仑等山系的新生代风化沉积物,是研究印度季风和南亚地区环境演化的理想材料。通过对2015年3~5月完成的IODP 355航次U1456钻孔A段总长345.36 m沉积物（约1.8 Ma以来）的沉积特征分析,发现其为典型的浊流沉积。通过对757个样品高分辨率的粒度测试,揭示研究区沉积序列在构造时间尺度上的粒度变化主要受到印度季风降水控制,阿拉伯海深海沉积物的粒度变化可作为一个新的季风演化的替代指标。从1.80~1.18 Ma到1.18~0.10 Ma,浊流沉积物的堆积速率降低,粒度变细,揭示了更新世印度季风强度的阶段性减弱。在沉积序列上,砂组分的变化周期从约41 ka向更长周期转化,推测东阿拉伯海U1456A钻孔沉积物序列在中更新世的粒度变化可能是对印度季风气候转型的响应。

     

江汉盆地西南缘原油中含硫化合物的分布特征及其地球化学意义

对江汉盆地西南缘12个原油样品中含硫化合物分布特征的研究表明,原油中二苯并噻吩系列化合物和苯并萘并噻吩系列化合物分别占芳烃总量的4.61%～9.79%和0.27%～1.32%,与烃源岩中含硫化合物的含量一致,反映原油中含硫化合物的含量与沉积环境有关.原油含硫化合物的内组成表明,咸水环境有利于二甲基二苯并噻吩和三甲基二苯并噻吩系列化合物的相对富集.4-甲基二苯并噻吩/1-甲基二苯并噻吩峰面积比值(MDR)在低成熟阶段(Ro＜0.7%)的变化范围较小,当成熟度进一步增加时,因热稳定性较差的1-甲基二苯并噻吩向其他化合物转化的速度加快,相对丰度降低,而4-甲基二苯并噻吩的相对丰度增加,致使MDR值随成熟度的增加而很快增大.同时,DR值受到沉积条件的影响,可能指示沉积环境的咸水化程度.2 3-甲基二苯并噻吩/二苯并噻吩峰面积比值与4-甲基二苯并噻吩/二苯并噻吩峰面积比值之间表现为正相关,说明2 3-甲基二苯并噻吩与4-甲基二苯并噻吩的形成机理相似,同样受沉积环境和成熟度的影响.     

柴达木盆地西南区震积岩的发现及其引发的勘探启迪

随着勘探和开发的需要,岩性油气藏成为柴达木盆地西南区石油勘探的一个重要领域,然而由于受多期的构造叠加改造,致使柴达木盆地西南区岩性油气藏分布规律不清,勘探接替领域不明确。笔者通过研究发现,由于受盆缘及其北西向二级断裂的影响,盆地西南区地震活动强烈,深、浅层均发现一系列与地震有关的震积岩,可见阶梯状小断层、液化砂岩脉、振动液化卷曲变形构造、砂火山、火焰状构造、假结核、震积砂枕、震积砂球构造、串珠状构造及震褶层等原地震积岩的软沉积物变形特征,另外可见地震引起的重力滑塌或泥石流形成的滑塌构造和角砾岩化变形特征,诸如震裂岩、震塌岩、自碎屑角砾岩、液化角砾岩、内碎屑副角砾岩等异地震积岩。事实上这些震积岩能够极大地改善储集层渗透性,使渗透率大幅度增加,为油气勘探和开发提供了新的视角和领域。更为重要的启迪是形成震积岩的古地震具有重要的触发机制,很容易引起三角洲前缘相的岩性发生滑塌,进而形成滑塌扇、浊积等一系列沉积现象,这种储集体将成为油田储量增长的新亮点,本着这种思想,笔者通过叠前地震多属性的预测及先进的叠前AVO反演预测,在柴达木盆地西南区跃东斜坡带发现这种滑塌体的存在,并建立了相应的沉积模式图。这样将可能突破以往该区"...     

藏北荣玛乡亚丹地区下二叠统曲地组的厘定及大地构造意义

西藏羌塘中部增生杂岩的不断解体对于该区古生代—三叠纪地层格架的厘定及特提斯洋演化研究具有重要的指示意义。对西藏荣玛乡亚丹地区的增生杂岩进行实测剖面时,发现一段早二叠世大陆斜坡相深水重力流形成的海底扇细碎屑岩沉积,北侧被新生代康托组红层覆盖,南侧与玄武岩等基性岩块呈断层接触,沉积序列不完整,主体为一套海底扇中扇-外扇厚层粉砂岩夹水道砂岩透镜体。碎屑岩层中垮塌沉积的生屑灰岩夹层含Parafusulina,Pseudofusulina,Schwagerina,Chalaroschwa-gerina parampla共4属10种（䗴）类化石,指示地层时代为早二叠世亚丁斯克期。1:25万日干配错幅区域地质调查将该地层归为吞龙共巴组,主要为混积陆棚相沉积。依据岩石地层及化石组合时代,厘定本套海底扇沉积为下二叠统曲地组。结合前人报道的早—中二叠世含（䗴）灰岩建造,以及羌塘中部晚石炭世—早二叠世基性岩的大陆裂谷背景,认为羌塘中部早二叠世沉积代表了中特提斯洋演化的初始阶段,并推测在空谷阶之后发育小规模洋盆。     

Very Low-grade Metamorphic Evolution of Pelitic Rocks under High-pressure/Low-temperature Conditions, NW New Caledonia (SW Pacific)

The P–T gradient in a Late Eocene low-T high-P metamorphicbelt in northern New Caledonia increases from SW to NE. Metapelitesin the pumpellyite–prehnite and blueschist zones containlawsonite, Mg-carpholite, Fe-stilpnomelane and Fe-glaucophane.Thermodynamic calculations indicate a progression of metamorphicconditions from less than 0·3 GPa and 250°C in akaolinite-bearing rock in the SW, up to 1·5 GPa and 410°Cin a lawsonite–glaucophane-bearing sample in the NE ofthe Diahot terrane. Through a multi-method investigation ofphyllosilicates, organic matter and fluid inclusions, we demonstratethat the evolution of organic matter and illite crystallinitydepends strongly on the evolution of the P–T path withtime. In addition, we show that the illite–muscovite bcell dimension provides a robust estimate of maximum pressurereached in low-temperature domains with polyphase metamorphichistories, despite subsequent high-temperature–low-pressureevents. Fluid inclusion study reveals an isothermal decompressionin the Diahot terrane. KEY WORDS: low-temperature/high-pressure metapelites; illite crystallinity; coal rank; illite–muscovite b cell dimension; New Caledonia     

Morphotectonic evolution of the New Caledonia ridge (Pacific Southwest) from post-obduction tectonosedimentary record

The tectonostratigraphic and geomorphic study of two post-obduction fluvial sedimentary systems on mainland New Caledonia and imaged offshore on seismic reflection lines provides a new perspective on the post-orogenic evolution of the New Caledonia ridge. Relations between sedimentary sequence boundaries, erosion surfaces and faults, both on land and on offshore seismic reflection profiles indicate that an episode of extensional tectonics initiated in the Early Neogene led to the disruption and collapse of the island landsurface previously shaped during a Latest Oligocene phase of planation. Microtectonic analysis further suggests early slip on the normal faults was associated with ridge-normal extension. A later set of faults accompanied ridge-parallel to ridge-oblique extension that is interpreted to result from a shift toward a transtensional regime driven by the initiation of east-verging subduction of the Australian plate beneath the Pacific plate starting at least in the late Mid-Miocene.     

Evolution of Micropterigidae (Lepidoptera) in the SW Pacific

The distribution and possible evolutionary history of two major lineages of Micropterigidae in Australia, New Caledonia and New Zealand are presented. In Australia a simple vicariant evolutionary model is applied to the data and it is noted that the development of micropterigids is paralleled by the evolutionary history of eastern Australian rainforests. In New Zealand there appear to be distinct patterns of evolution in the different micropterigid lineages, a situation which is interpreted in terms of separate evolutionary histories, possibly on different land masses. In New Caledonia a species swarm exists which is also interpreted in terms of a former more complex geography. It is concluded that micropterigid evolution in the SW Pacific supports the idea of a composite origin for both New Zealand and New Caledonia.

     

Late Holocene paleoenvironment in northern New Caledonia, southwestern Pacific, from a multiproxy analysis of lake sediments

Lithostratigraphic and palynological analysis of two cores recovered from the ‘Grand Lac’ (New Caledonia), combined with 35 ¹⁴C AMS dates, yields a paleoenvironmental record spanning the last 2000 yr. The lithology is represented mainly by clayey or laminated layers. A catastrophic event, which is marked by very coarse deposits, occurred probably between ca 1070-960 cal yr B.P. and possibly is associated with an unusually severe La Niña event. Before and after this event, a similar combination of the two main sediment types is recorded. The repeated alternation of laminated and clayey layers is interpreted as the response to local hydrologic forcing, which may reflect a shift from relatively wet to relatively drier conditions, respectively. Variable amount of micro-charcoal is detected all along the profile. Without additional evidence, notwithstanding the initial local human settlement documented since ca 2900 ¹⁴C yr B.P., micro-charcoal occurrence and variability cannot be linked directly to an anthropogenic origin. No distinct palynological zonations in relation to the lithology are observed, and the vegetation changes may only represent minor transitions across environmental limits.     

Ni-Cu-Co-rich hydrothermal manganese mineralization in the Wallis and Futuna back-arc environment (SW Pacific)

The Wallis and Futuna back-arc system is a complex area composed of at least two active oceanic spreading centers (the Futuna and Alofi spreading centers) and young volcanic zones characterized by diffuse magmatism locally affected by the Samoan hotspot. This geological setting is favorable to the establishment of hydrothermal systems, in the form of either high-temperature (HT) hydrothermal venting or low-temperature (LT) diffuse flow. During the 2010 Futuna cruise aboard the R/V L'Atalante, three remarkable inactive LT Fe-Si-Mn deposits were discovered (Utu Uli, Anakele and Utu Sega). Some of the Mn-rich precipitates discovered exhibit the highest base metals concentrations so far recorded in ferromanganese rocks, including in the well-documented hydrogenetic crusts and polymetallic nodules. The deposits lie on top of volcanoes and formed in close association with the volcanic facies. The manganese mineralization occurs in the form of massive layered crusts and Mn-rich cements within strongly altered basaltic pyroclastic rocks, brecciated lavas and, more rarely, in sediments. Field observations and mineralogical and chemical studies support a hydrothermal origin for the mineralization and show that nickel, cobalt and copper enrichments are controlled by the precipitation of 7 Å and 10 Å manganates. The conventional geochemical classifications (e.g. Bonatti et al., 1972) used to decipher the origin of Mn mineralization cannot be used for this new type of deposit and new robust discrimination diagrams need to be established. We suggest that the unusual enrichment of metals recorded in our samples is due to (i) a lack of precipitation of high-temperature massive sulfides at depths that would have retained metals (e.g. Cu, Ni, Co); (ii) isolation of the hydrothermal system, thereby avoiding Ni, Co and Cu losses in the water column; and (iii) the ability of birnessite and buserite/todorokite to scavenge Co, Ni, and Cu from aqueous fluids. The Utu Uli and Anakele deposits share certain characteristics with the active hydrothermal system at Loihi seamount (e.g. the depth of mineralization, relationships with pyroclastic volcanoes, and the influence of a mantle plume source) and thus might represent late-stage products of this specific type of hydrothermal activity. Elsewhere, the Co-rich mineralization of the Calatrava volcanic field (CVF) in Spain may be a potential analog of the Utu Sega deposit. The Mn-(Co) deposits of the CVF formed in close proximity to Pliocene volcanic rocks. Metals were transported by epithermal hydrothermal solutions with high fO₂ and cobalt was scavenged by Mn oxides. Together with the well-documented stratabound Mn deposits (González et al., 2016; Hein et al., 2008; Hein et al., 1996), the Mn deposits discovered in the Wallis and Futuna back-arc provide crucial insights into LT hydrothermal activity in the deep ocean. The metal-rich character of this LT hydrothermal activity may be of major importance for future research on the net flux of hydrothermally derived metals (e.g. Ni, Co, Cu) to the open ocean.     

Palaeoecology of Late Triassic marine assemblages from the proto-Atlantic Basin (Ayamonte,SW Spain)

The Triassic represents a critical period that attests to the diversification of marine ecosystems. This paper analyses the stratigraphy of the easternmost Mesozoic series of the Algarve Basin in the Ayamonte sector (SW Spain). Two sets forming this series are described. The first, mainly siliciclastic, was deposited in continental contexts represented by fluvial and lacustrine environments with bioturbation associated with swamp-like environments (Taenidium) or with plain alluvial sediments (Labyrintichnus terrerensis, Planolites). This ichnoassemblage corresponds to the ichnofacies of Scoyenia. The second set, is carbonate-dominated and shows a remarkable palaeontological content comprising bivalves and gastropods, which made it possible to review our current knowledge of the regional stratigraphy of the Triassic in this area. Trigonodus-Isocyprina form this association for bivalves and Coeslostylina and Coeslostylina-Spirostylus-Mathilda for gastropods allowing to infer a Late Triassic (Carnian-Rhaetian) age for the Ayamonte area. The characteristic trace fossils of the carbonate sections are represented by Thalassinoides Treptichnus pollardi and Helminthoidichnites tenuis, which belong to the proximal expression of the Cruziana ichnofacies. Shallow marginal, low energy, and brackish and locally lacustrine conditions are inferred for this carbonate-dominated set, alternating with episodes of normal salinity, and towards the top, with punctuated episodes of higher energy. This palaeoenvironmental context is congruent with the palaeogeographical scenario conditioned by the existence of a threshold of major order that would indicate the initial breaking of Pangea and the opening of the Tethys in the eastern Mediterranean.     

南极普里兹湾海域的近现代沉积速率

沉积速率主要受上层海洋生物生产的影响,而在湾口浅滩区沉积速率则主要受底栖生物的影响。此外,水流、水体稳定度、冰封期长短和海底地形等条件也对沉积速率产生一定的利用中国第21次南极科学考察获得的普里兹湾海域的沉积物样品,运用沉积地层同位素210Pb测年技术,探讨了该海域沉积物的近现代沉积速率及其影响因素。研究结果表明,南极普里兹湾海域的近现代沉积速率变化范围在0.47～1.88 mm/a之间,平均值为1.06 mm/a,高于南极罗斯海而低于威德尔海,总体上与南、北极多个海区的沉积速率相当。在湾内和冰架边缘区影响,沉积速率的分布是多种因素共同控制的结果。在生物量较高、水体条件较为稳定的湾内中心区域,沉积速率较高,而冰架边缘区的沉积速率则较低     

新疆乌伦古湖的210Pb、137Cs测年与现代沉积速率

通过对乌伦古湖2个沉积柱样的²¹⁰Pb和¹³⁷Cs剖面的观测,运用²¹⁰Pb过剩法和¹³⁷Cs时标法估算了近几十年来的平均沉积速率。研究结果表明：²¹⁰Pb过剩法的CRS模式测定的沉积速率的变化范围为0.018～0.071 g/(cm²·a),137Cs时标法测定沉积速率的变化范围为0.034～0060 g/(cm²·a),两者具有较高的一致性。20世纪60年代以前,人类活动对本区影响相对较小,湖泊的沉积速率主要受自然因素的影响;20世纪60年代以后,随着乌伦古河中、下游农业的发展和调水工程的实现,人类活动逐渐成为主导湖泊演化的因素,从而影响乌伦古湖沉积速率。     

Character of Sedimentation in the Potassium-Bearing Basin of the Gremyachinskoye Field(The Volga Monocline)

正1 Introduction The Gremyachinskoye potassium salt field lies within the Safronovskaya area and is confined to the preoverthrust zone–the 20-25 kilometer band conventionally recognized in the southern termination of the Volga     

Blueschist ophiolites in the melange zone,northern New Caledonia

A regional melange zone, 150 km long and 30 km wide, forms the southern boundary and structural capping to a high-pressure blueschist belt in northern New Caledonia. The disrupted country rocks in the melange zone are Mesozoic metagrey-wackes and Eocene chert-limestone sequences which have been penetrated from below by tectonically-injected ophiolite slivers containing metamorphosed serpentinite, gabbro, dolerite, basalt, tuff, chert and shale. An ocean crust origin for these rocks is indicated by chemical, mineralogical and radiometric data from coastal outcrops at Anse Ponandou on the northeast coast. The age (41 m.y.), metamorphic environment (350 ° C at 7 kb), and mineral association (acmitic jadeite-riebeckite-pyropic spessartine-pistacitic epidote-lawsonite-high Si phengite) are significantly different from those of the adjacent regional high-pressure schist belt, indicating a separate structural site for blueschist metamorphism of buried ophiolitic ocean crust during early Tertiary orogenesis.