Neptunian dykes and associated breccias (Southern Alps, Italy and Switzerland): role of gravity sliding in open and closed systems

Neptunian dykes and sills of Middle Jurassic pelagic limestone within Lower Jurassic shallow-water carbonate host rocks occur at many localities in the Southern Alps of Italy and Switzerland, especially on what were the upper slopes of tilted half-grabens created during the Early Jurassic rifting stage of a passive margin that faced the Middle and Late Jurassic Tethyan Ocean. The host rocks were dilated by cracking, folding, and brecciation during movements of shallow-based gravity-driven slides and slumps of semibrittle platform strata, commonly along décollement contacts between layers of different competence. In most places, the network of cavities in the dilated strata connected to the sea floor, and pelagic sediments trickled from above into the open spaces. In other places, the brittle strata were overlain by somewhat impermeable sediments that formed a partial seal. Sudden dilation of the brittle beds resulted in forceful injection of the overlying weakly consolidated or plastic sediments into open spaces. The filling in both open and closed systems was commonly episodic, resulting in complex internal-sediment stratigraphy and cross-cutting dykes. Stable isotopic data on internal sediments and early-formed cement lie within the field of normal sea water, and none of the sedimentological or stable isotopic data supports a subaerial, dissolution (karst) origin for the Jurassic neptunian dykes of this region.     

Nannofossils and biostratigraphy: An overview

Intensive biostratigraphic studies of calcareous nannofossils have been carried out for only about a decade, even though nannofossils have been known for over a century. Although coccoliths have been reported from various Paleozoic deposits, datable assemblages are known only from Liassic (early Jurassic) and younger strata. Today nannofossils are one of the best correlation tools available to the biostratigrapher in marine sediments that contain pelagic constituents. Precise age determinations and correlations can be made in Cretaceous and Cenozoic strata for which numerous reference sections have been studied. The Jurassic nannofossil succession is less completely known mainly because of a lack of good reference material.The very large number of specimens per sample and the minute size of calcareous nannofossils create both advantages and disadvantages in their utilization. Variability of synchronous assemblages may occur latitudinally as well as from the oceanic to the hemipelagic realms.     

论福建坂头组的时代及对比

<正> 坂头组系陈恺(1943)命名,未指定建组剖面,以永安城北坂头村一带的岩性为标准。当时称坂头系,时代为早白垩世。坂头组分布在崇安、永安和泰宁举岚等盆地,宁化、安溪、仙游、古田和霞浦等地亦有零星出露。对坂头组的时代归属存在二种意见:福建省区调队(1976—1985)、原福建石油地质队(1978)、顾知微(1980、1982)、王思恩等(1985)归于     

A carbonate submarine fan in a fault-controlled basin of the Upper Jurassic, Betic Cordillera, southern Spain

ABSTRACT The middle member of the Loma del Toril formation (Kimmeridgian-Lower Tithonian, Intermediate units, Betic Cordillera) consists of up to 250 m of resedimented carbonate material. Three units have been distinguished. The lower, Unit A, is composed of conglomerates that are interpreted as deposited in a major valley on the lower slope of a basin margin. Unit B, calcarenites with some conglomerate intercalation, is interpreted as distributary channel deposits and Unit C, calcarenites, as the result of poorly developed depositional lobes of a submarine fan. The three units form a recessional sequence. They cannot be related to a transgression because the Kimmeridgian-Lower Tithonian in the Prebetic zone, where epicontinental sediments exist, is clearly regressive. The upper member of the Loma del Toril formation, made up of pelagic limestones with sporadic calcarenites or even thin conglomerate intercalations, is best interpreted as a basin plain facies. Lateral facies relationships suggest that down-faulting of the basin floor controlled the development of the fan. The scarce occurrence of turbidite beds in the basin plain facies, the prevailing channelized facies and the obvious lack of overbank deposits, suggest a transport system of low efficiency, with fan deposition at the base of slope. The underlying Jurassic strata cropping out along fault scarps, coeval carbonate shelf material, and upper slope deposits were the main sources of turbiditic resediments. With respect to basin morphology sedimentary processes and fan geometry, this Jurassic turbidite basin can be compared with the modern California continental borderland. Ancient analogues have been described by Reinhart (1977) and Price (1977).     

Neptunian dykes along a drowned carbonate platform margin: an indication for recurrent extensional tectonic activity?

Three successive Mesozoic neptunian dyke generations and related unconformities suggest recurrent extensional fracturing and periods of relative sea-level rise along the NW Trento Plateau margin in the Southern Alps, Italy. The first neptunian dyke generation was induced by NNW–SSE directed extension of Early Jurassic skeletal oolitic periplatform deposits generating micritic early Middle Liassic neptunian dykes with orthogonal orientation. The second generation of neptunian dykes was possibly caused by marginal extension at the drowned platform edge penetrating Late Jurassic, red pelagic limestones with a pelagic matrix of Albian/Cenomanian age and nearly orthogonal fracture orientation. The third generation of neptunian dykes occurred after a prolonged period of submarine exposure and erosion (Aptian/Albian to Late Maastrichtian) during the rapid burial of the submarine Trento Plateau margin relief. The Late Maastrichtian neptunian dykes were caused by extension of Early to Middle Jurassic oolitic periplatform limestones along steep (inclination > 10°) submarine slopes. Generally successive neptunian dyke generations along drowned carbonate platform margins could be caused by repeated extensional brittle fracturing of lithified periplatform deposits and the filling of micritic matrix derived from overlying pelagic sediment sequences under substantial hydrostatic pressure. This would suggest that recurrent extensional fracturing is continuously recorded by neptunian dyke formation which could be used to indicate extensional tectonic activity at a foundering deep-marine carbonate platform edge.     

西藏沙丁、荣布地区三叠系—老第三系沉积地质特征

研究区从三叠纪到老第三纪,发育的岩石地层主要有确哈拉群（Ｔ３）、希湖群（Ｊ１－２）、拉贡塘组（Ｊ２－３）、多尼组（Ｋ１）、竟柱山组（Ｋ２）和牛堡组（Ｅ２－３）。在沉积相上,经历了从深水沉积到浅水直至陆相沉积的演变,发育有冲积扇、河流、湖泊、三角洲（潮汐）、障壁海岸、浅海、深海和火山碎屑流沉积。古地理分析表明,研究区晚三叠世古地理轮廓是一个从东南向西北和东北方向由浅水碳酸盐台地及深水陆层海底扇沉积共同发育的沉积盆地;早中侏罗世,演变成为一个由深水砂质浊积岩和细屑浊积岩组成的水下席状体沉积;进入中晚侏罗世,其古地理表现为一个陆屑浅海有障壁海岸;到了晚白垩世,研究区表现为以含煤沉积为特征的三角洲相沉积。     

The Geology of the Western Highlands of New Guinea

Abstract

The oldest rocks in the Western Highlands of New Guinea are granite and metamorphic rocks, and these are unconformably overlain by an incomplete marine succession of Permian, Upper Jurassic, Cretaceous, Eocene, Oligocene and Miocene sediments with a maximum thickness of 34,000 ft. The sedimentary succession in the east of the region is much thicker than in the west. Jurassic seas transgressed from the east. Studies of the faunas and petrology of the sediments show that the western part of the region was out of range of the sources of Cretaceous vulcanism and slow pelagic sedimentation continued into the Lower Miocene. By the Middle Miocene a volcanic island arc had developed in the vicinity of the Lai Syncline and the sediments are of shallow-water type, rich in volcanic debris.

Both sediments and basement were folded into a number of anticlines and synclines at the end of the Pliocene. Vigorous erosion was followed by extensive Pleistocene vulcanism in the west. Pleistocene glaciation occurred in the Bismarck Range down to about 13,000 feet above sea-level.     

Carbon and oxygen isotopes: a tool for Jurassic and early Cretaceous pelagic correlation (southern Spain)

The isotopic evolution of δ¹³C and δ¹⁸O is reported for the Jurassic and early Cretaceous in two pelagic sections of the External Zones in the Betic Cordilleras (SE Spain). Stable isotope curves from pelagic trough and swell sections display similar patterns. Variations in δ¹⁸O and δ¹³C values from strata at equivalent age probably reflect both early diagenetic cementation and later temperature‐related burial diagenesis. Comparison of global isotope curves with those presented in this work allows the differentiation of global from local events. Thus, the anoxic event during the early Toarcian (falciferum Zone) is characterized by elevated δ¹³C and depressed δ¹⁸O values. The isotopic record also allows the detection of the middle Oxfordian transgression. There are other peaks for the late Toarcian, early Bajocian, Callovian and early Berriasian that can also be used as tools for correlation purposes. Copyright © 2002 John Wiley & Sons, Ltd.     

Middle Jurassic—early Cretaceous radiolarian assemblages of the western Yarlung Zangbo Suture Zone: Implications for the evolution of the Neo-Tethys

Cherts in the Zhongba mélange of the western Yarlung Zangbo Suture Zone (YZSZ) contain well preserved radiolarian assemblages. These radiolarian assemblages indicate that the Zhongba mélange has middle Jurassic–early Cretaceous remnant, are coeval with those from the central and eastern parts of the YZSZ. Cherts from the Najiu area yield Aalenian to Aptian radiolarians, while cherts interbedded with siliceous mudstones from the Bielongjiala area yield Aptian radiolarians, indicating that terrigenous-derived sediments were deposited during early Aptian. The above observations indicate that the entire YZSZ have a similar geochronological framework and thus they underwent similar geological evolution: (1) during the Jurassic, the Neo-Tethys was a wide ocean with pelagic sediments distal from continents; (2) during the Cretaceous (around 130–120 Ma), the Neo-Tethys started to subduct along the southern margin of the Lhasa block, and terrigenous-derived siliceous mudstone began deposition.     

石臼坨凸起西南陡坡带扇三角洲锆石定年与源汇示踪

为了示踪渤海湾盆地石臼坨凸起西南陡坡带扇三角洲源汇体系,对其东三段层序（Ed₃）的6个砂岩样品进行碎屑锆石U-Pb定年分析.西部扇体（C6-4-4井）富含白垩纪（K）锆石并具有110 Ma峰值,母岩以白垩系义县组火成岩为主;中部（C6-4-3、C6-4-6D井）、东部扇体（C6-4-5D）富含侏罗纪（J）锆石并具有152 Ma或168 Ma峰值,母岩以侏罗系蓝旗组火成岩为主,古生代（Pz）锆石则来自中生界碎屑岩.所有样品都含有太古代（Ar）、元古代（Pt）锆石,母岩为花岗岩基底.研究表明,除古生界碳酸盐岩外,源区的母岩地层均可通过碎屑锆石U-Pb年龄示踪,各扇体物源的差异性是由母岩地层倾向控制的,由于中生界向西北倾斜,白垩系主控西部扇体沉积,侏罗系则是中部、东部扇体的主要物源区.      

Late Triassic rifting and Jurassic–Cretaceous passive margin development of the Southern Neotethys: evidence from the Adıyaman area,SE Turkey

Evidence of rifting and continental break-up to form the S Neotethys is found within the volcanic-sedimentary Koçali Complex. This is a folded, thrust-imbricated succession that includes lavas, volcaniclastic sediments, pelagic carbonates, radiolarites and manganiferous deposits. Interbedded ribbon cherts contain radiolarians of Late Triassic to Late Jurassic age. The lower part of the succession of Mid?-Late Triassic age (Tarasa Formation) is dominated by enriched mid-ocean ridge basalt (E-MORB). The overlying Late Triassic to Mid-Jurassic interval (Konak Formation) is characterised by intercalations of ocean island basalt and E-MORB. Taking account of structural position, the basalts erupted within the outer part of a continent–ocean transition zone. Continental break-up probably occurred during the Late Triassic (Carnian–Norian). Early to Mid-Jurassic lavas and volcaniclastic sediments record volcanism probably after continental break-up. In addition, the Karadut Complex is a broken formation that is located at a relatively low structural position just above the Arabian foreland. Pelagic carbonates, redeposited carbonates and radiolarites predominate. Radiolarians are dated as Early to Mid-Jurassic and Late Cretaceous in age. The pelagic carbonates include planktic foraminifera of Late Cretaceous age. The Karadut Complex resulted from the accumulation of calcareous gravity flows, pelagic carbonate and radiolarites in a relatively proximal, base-of-slope setting. After continental break-up, MORB and ophiolitic rocks formed within the S Neotethys further north. Tectonic emplacement onto the Arabian platform took place by earliest Maastrichtian time. Regional interpretation is facilitated by comparisons with examples of Triassic rifting and continental break-up in the eastern Mediterranean region and elsewhere.     

新疆准噶尔盆地侏罗系—白垩系生物地层和同位素年龄研究的新进展

研究的侏罗系—白垩系包括侏罗系头屯河组、齐古组、喀拉扎组和白垩系清水河组。清水河组的叶肢介、介形虫和孢粉化石组合研究的新成果表明:其地质时代为早白垩世早期(Berriasian)。齐古组下部的同位素年龄为164.6Ma±1.4Ma。此年龄值与国际地质年表对比,几乎与Callovian的底界年龄(164.7Ma±4.0Ma)相当。依据此年龄值和沉积厚度、沉积速率推算,齐古组的主要时代应为中侏罗世卡洛期(Callovian),其下部跨入巴通期最晚期;喀拉扎组的时代可能为牛津期最早期(early Early Oxfor-dian)。上列事实反映出在侏罗系与白垩系之间几乎缺失全部晚侏罗世的沉积,由此可以推断本区在晚侏罗世曾发生过一次较强烈的构造运动。     

Resedimented carbonate and volcanic rocks in the Berriasian-Hauterivian of the Subbetic (Alamedilla, Betic Cordillera, southern Spain)

Sedimentary rocks of the Lower Cretaceous in the Subbetic of the Alamedilla area (province of Granada) were studied. In this area, a significant amount of redeposited sediments within the Carretero Formation were recorded. Resedimented material is mainly composed of Jurassic oolitic limestones and volcanic rocks, as well as of Neocomian hemipelagic sedimentary rocks (marly limestones and marls). All these redeposited sediments corresponding to rock fall and debris flow originated as the result of significant slopes in a very sharp submarine topography. Volcanism and the resultant volcanic edifices created this sharp slopes making up in some cases guyots. The volcanism was mainly active in the Middle Jurassic, although it persisted locally until Late Jurassic and Early Cretaceous, and controlled the sedimentation in this area of the Subbetic basin during most of the Mesozoic. The proposed genetic model is in agreement with a base-of-slope apron model with two significant special features: (1) the provenance of the clasts mainly from Jurassic outcrops with oolites deposited in guyots and isolated marine platforms, and volcanic submarine rocks, and (2) the palaeobathymetry of the deposits, relatively shallow and sporadically affected by storm waves.     

西藏羌塘盆地中侏罗世布曲期及夏里期岩相古地理与油气远景

在露头剖面地层学及沉积学研究的基础上,采用单因素分析多因素综合作图法,编制了西藏羌塘盆地中侏罗世布曲期和夏里期的单因素图和岩相古地理图。布曲期以碳酸盐岩沉积为主,自北而南依次发育局限台地（潮坪、泻湖）、开阔台地（台盆、浅滩/点礁）、台缘礁/浅滩、台缘斜坡、盆地等沉积（亚）相;夏里期以陆源碎屑沉积为主,发育泻湖、潮坪、滨岸、陆棚等沉积（亚）相。布曲组台盆和泻湖相泥灰岩和泥晶灰岩是良好的烃源岩,台缘礁和浅滩相碳酸盐岩是良好的储集岩,而上覆的夏里组泻湖和潮坪相泥岩和膏盐层是良好的区域性盖层,共同构成良好的生、储、盖组合。该生储盖组合大都被上覆的上侏罗统、白垩系、第三系覆盖。因此,布曲组是盆地内最好的油气勘探目的层,沿中央隆起带两侧以及北羌塘地区的琵琶湖－半岛湖凸起一带应是油气勘探的有利区带。     

江西修水第四系网纹红土的地层学研究

根据大量野外观察和室内分析结果，较详细论述了江西修水地区第四系网纹红土的地貌地层、岩石地层、磁性地层和年代地层等方面的特征，并在此基础上，就有关网纹红土的形成时代、成因以及与黄土的对比等问题进行了讨论，提出１）网纹红土可分为强网纹化红土和弱网纹化红土两个岩性段，每个岩性段又由若干个密集网纹层与稀疏网纹层构成；网纹红土与下伏红色砾石层属同期产物；２）网纹红土中的密集网纹层的地质意义相当于北方黄土中的古土壤；３）网纹红土形成于早更新世末（约０．９ＭａＢ．Ｐ．）至晚更新世初（约０．１ＭａＢ．Ｐ．）；４）网纹红土发育于湿热气候条件下，地下水埋深浅，地表低洼、排水不畅的环境。     

Clastic heavy mineral assemblages in Permian-Mesozoic accretionary cherty and siliceous-clayey complexes of Sikhote Alin

The paper presents results of the study of assemblages of clastic heavy minerals and geochemical features of some assemblages in several Permian-Mesozoic cherty and siliceous-clayey sequences of Sikhote Alin. They are composed of pelagic and hemipelagic sediments of the Panthalassa (Paleopacific) Ocean. Four typical mineral assemblages and their environments are established. In one of the ocean segments, where sedimentary cover formed during the Late Paleozoic-Early Cretaceous, the Permian pelagic domain was characterized by the amphibole-pyroxene assemblage with heavy minerals derived from ophiolites. The Triassic-Jurassic stage was marked by development of the clinopyroxene assemblage with heavy minerals derived from intraplate alkaline volcanic complexes. Middle-Late Jurassic hemipelagic sediments host the zircon-clinopyroxene assemblage with a greater role of continental environments and the presence of volcanic products of the convergence zone. Another segment of the ocean accumulated red cherts and siliceous-clayey sediments during the Jurassic-Early Cretaceous under the influence of island-arc volcanism.     

桂林峰林平原、峰丛洼地残留中生代地层空间展布形成机制探讨

文章探讨了桂林峰林平原、峰丛洼地内中生代地层空间展布及形成机制,为查清桂林岩溶地貌发育演化过程提供参考.在前人研究基础上,通过调查地层、地貌的空间展布特征,结合区内构造发展史、岩相古地理环境变化及岩溶水文地貌过程等要素,对桂林峰林平原、峰丛洼地内中生代地层空间展布特征、形成机制,进行归纳总结与分析,认为:三叠纪地层和白...     

北黄海盆地中侏罗世-早白垩世构造体制转换期的古气候演化及元素地球化学响应

中侏罗世-早白垩世华北地台东部的北黄海盆地受古亚洲构造体制向滨太平洋构造体制转换的影响,其构造演化经历了伸展-反转挤压-伸展的转变.构造体制的差异不但表现在大地构造性质及其产生的地质效应上,也表现在盆地沉积特征、古生物及古气候等方面.本文以北黄海盆地东部坳陷X1井中侏罗统至下白垩统为研究对象,利用泥岩元素地球化学特征对...     

郯庐断裂带北延及中新生代构造体制转换问题的探讨

郯庐断裂带北段在进入东北地区后主要分为走向北东—北北东的三支断裂,由西向东依次为沈阳—长春—哈尔滨断裂、依兰—伊通断裂和敦化—密山断裂。由于不同时期的大地构造背景和地球动力学的不同,它们在中、新生代的构造体制转换主要表现有如下5个阶段:(1)早、中侏罗世直到早白垩世时以拉张为主,形成一系列断陷盆地或坳陷盆地,并伴有中-酸性岩浆侵入和喷发,形成了独特的火山-湖相沉积盆地;(2)早白垩世末,为北西—南东向的压缩构造应力场,使盆地内的中、上侏罗统地层发生走向近北东的逆冲推覆构造;(3)晚白垩世,为北东向左行剪切构造应力场,区内侏罗系和早白垩世早期的沉积物发生褶皱,与上覆地层呈明显的不整合;(4)古近纪时为北西—南东向拉张构造应力场,日本海从古近纪开始逐渐拉开,直到新近纪完成现在的格局;(5)新近纪时又转换为挤压构造应力场,以北西—南东向挤压为主,使古近系沉积物发生轻微的褶皱。     

The Middle Jurassic radiolarites and pelagic limestones of the Nieves unit (Rondaide Complex, Betic Cordillera): basin starvation in a rifted marginal slope of the western Tethys

Middle Jurassic radiolarites and associated pelagic limestones occur in the Rondaide Nieves unit of the Betic Cordillera, southern Spain. The Rondaide Mesozoic includes: (a) a thick succession of Triassic platform carbonates, comparable to the Alpine Hauptdolomit and Kössen facies; (b) Lower Jurassic pelagic limestones comparable to the Alpine Hierlatz and Adnet facies; (c) the Middle Jurassic Parauta Radiolarite Formation, described herein; and (d) a thin Upper Jurassic-Cretaceous condensed limestone succession. The Parauta Radiolarite Formation and associated limestones were studied with respect to stratigraphy, petrography, micropalaeontology (radiolarians, calcareous nanno- and microfossils) and facies. Radiolarite sedimentation occurred in the Middle Bathonian in a restricted and dysoxic deep Nieves basin, perched in the distal zone of a continental margin fringing the Tethyan ocean. This margin was adjacent to a young narrow oceanic basin between the South-Iberian margin and a continental block called Mesomediterranean Terrane. The Nieves basin was part of a marine corridor between the Proto-Atlantic and Piedmont-Ligurian basins of the Alpine Tethys. The regional tectonic position, the stratigraphical evolution since the Triassic, the age and the nature of the Mesozoic facies and the palaeogeographic relations to adjacent domains show striking analogies between the Betic Rondaide margin and coeval units of the Alps.