The sulfur and strontium isotopic compositions of Permian evaporites from the Zechstein basin, northern Germany

The sulfur isotopic composition of stratigraphically well constrained samples from five evaporitic cycles of the German Zechstein (upper Permian) displays no systematic lateral variation and no significant temporal trend. With an average δ³⁴S value close to 11‰, results confirm the previously determined sulfur isotope minimum for Phanerozoic seawater. Least radiogenic ⁸⁷Sr/⁸⁶Sr ratios for these sulfates define a clear temporal variation with a minimum value at 0.707008. A conclusive assessment of this temporal trend in comparison with other data sets for upper Permian seawater is not possible due to substantial differences in (bio)stratigraphic assignments.     

A facies analysis of the Pucara Group (Norian to Toarcian carbonates,organic-rich shale and phosphate) of Central and Northern Peru

The Pucará Group contains an excellent record of marine uppermost Triassic and basal Jurassic sedimentation. New biostratigraphic and lithostratigraphic studies have led to a reassessment of the regional internal correlation of the group and thus to a new understanding of the facies relationships. There is a relatively complete record of sedimentation from late Norian to late early Jurassic, the only notable omissions apparently occurring in the latest Norian and at the Hettangian-Sinemurian boundary. The oldest constituent formation, the Chambará, which is locally of great thickness, consists largely of dark cherty limestones representing basinal conditions of sedimentation. The succeeding Aramachay Formation marks widespread recommencement of sedimentation in the Semicostatum Zone of the Sinemurian, with organic-rich shales passing up into phosphatic deposits. It is proposed that this event is the consequence of a significant eustatic rise of sea level. The record of sedimentation of the youngest, Condorsinga, formation is restricted to Central Peru and no other middle-upper Lias units are identified. Alternating marginal marine and shallow neritic conditions are inferred with high carbonate production rates and dolomitizing environments. The character of the sediments, particularly the phosphatic deposits, suggests a tectonically quiescent continental margin with unrestricted access to the palaeo-Pacific Ocean, in contrast to earlier palaeogeographic interpretations. As such the Pucará Group represents unusual conditions in the development of the Andean regime.     

滇黔桂盆地及其邻区石炭纪至二叠纪层序地层格架及三级海平面变化的全球对比

属于被动大陆边缘裂谷盆地的滇黔桂盆地，自加里东运动之后，泥盆纪开始拉开，整个晚古生代延续发展。受同生断裂的控制，在深水盆地中发育大小不等的孤立碳酸盐台地，因而在滇黔桂盆地及其邻区形成特殊的“台-盆-丘-槽”的古地理格局。对不同古地理背景下的典型剖面进行三级层序划分并对其进行空间追索和对比，在滇黔桂盆地及其邻区的石炭纪和二叠纪地层中可以识别出12个三级层序，相当于晚古生代25个三级沉积层序(2-5Ma；SQ1至SQ25)中的SQ24至SQ25；以地层记录中的的两种相变面和两种穿时性为基本要素，可以建立研究区石炭系和二叠系的层序地层格架；层序地层格架反映了三级层序的基本特征：空间上相序的有序性和时间上环境变化的同步性。研究区的石炭系和二叠系，主要为一套碳酸盐岩地层，其中在连陆台地上发育3套煤系地层，它们分别组成石炭纪三级层序SQ15跨系的三级层序SQ19的HST以及二叠纪吴家坪期的三级层序SQ24；而且在连陆台地边缘和孤立台地上，于阳新世的茅口亚世以及乐平世的长兴期发育海绵生物礁，海绵生物礁分别构成了以下二叠系三级层序即阳新世的SQ22和SQ23以及长兴期的SQ25。3套煤系地层和两套海绵生物礁的发育，使研究区的石炭系和二叠系形成了一个与欧美地区完全不同的层序地层序列。在研究区石炭系和二叠系所识别出的12个三级层序中，石炭纪一二叠纪船山世地层可以划分出6个三级层序。这种划分与Busch等对北美相同层位的划分相似，也就是说该6个三级层序的形成时限大于10Ma；较长的形成时限可能反映了形成在联合古陆汇聚时期即全球构造相对稳定时期三级海平面变化的一个特性。因此，研究区的石炭系和二叠系所识别和划分出的12个三级层序，其数量比Ross和Ross(1985)对欧美地区石炭系和二叠系所划分出的50多个三级层序要少得多。     

内蒙古西部银额盆地及邻区二叠系隆林阶—冷坞阶层序地层格架

依据露头层序地层学原理,对银额盆地及邻区二叠系隆林阶—冷坞阶露头剖面进行层序界面的识别和层序划分,共划分为2个Ⅲ级层序。在对东西、南北向层序地层对比的基础上,初步建立了研究区的层序地层格架。隆林期—罗甸期全区发生大范围的海侵接受海相沉积,以滨海—浅海陆棚相为主,局部发育碳酸盐岩台地相,盆地边缘发育过渡相沉积,有2个沉积中心,黑鹰山-额济纳旗坳陷带的沉积中心在碧云泉南-芦草井地区,柳园-巴丹吉林坳陷带的沉积中心在卡路山-杭乌拉一带。祥播期-冷坞期继承了前期的沉积格局,只是沉积范围向北西缩小,黑鹰山-额济纳旗坳陷带的沉积中心在芦草井地区,柳园-巴丹吉林坳陷带水体变浅,沉积中心在古硐井地区。     

内蒙古西部银额盆地及邻区二叠系隆林阶—冷坞阶层序地层格架

依据露头层序地层学原理,对银额盆地及邻区二叠系隆林阶—冷坞阶露头剖面进行层序界面的识别和层序划分,共划分为2个Ⅲ级层序。在对东西、南北向层序地层对比的基础上,初步建立了研究区的层序地层格架。隆林期—罗甸期全区发生大范围的海侵接受海相沉积,以滨海—浅海陆棚相为主,局部发育碳酸盐岩台地相,盆地边缘发育过渡相沉积,有2个沉积中心,黑鹰山-额济纳旗坳陷带的沉积中心在碧云泉南-芦草井地区,柳园-巴丹吉林坳陷带的沉积中心在卡路山-杭乌拉一带。祥播期-冷坞期继承了前期的沉积格局,只是沉积范围向北西缩小,黑鹰山-额济纳旗坳陷带的沉积中心在芦草井地区,柳园-巴丹吉林坳陷带水体变浅,沉积中心在古硐井地区。     

Controlling factors of reservoir quality in low-permeability reservoir within a sequence stratigraphic framework: a case study of the lower Jurassic sandstones in the Northern margin of the Qaidam Basin,China

The Qaidam Basin, one of China’s most prolific petroliferous basins, is located in the northeastern corner of the Qinghai-Tibet Plateau. Using analytical data from cores, thin-sections and seismic data, and combined with the previous sequence stratigraphy research results, research on the reservoir characteristics was undertaken. The main controlling factors of reservoir quality in the sequence stratigraphy framework in the Lenghu area are discussed. The Lower Jurassic includes lowstand system tract (LST) and transitional systems tract (TST); the highstand systems tract are missing owing to tectonic uplift. The Lower Jurassic sandstones are composed of moderately to poorly sorted, subrounded sandstone representing several representative environments, including fan-delta and lacustrine facies. The main types of the Lower Jurassic sandstones are mostly feldspathic litharenite and lithic sandstone. The pore types of the Lower Jurassic sandstones are mainly secondary dissolution pores with few fracture types. The Lower Jurassic sandstones have experienced strong compaction that resulted in the loss of primary porosity. Carbonate cementation of the LST sandstones is greater than in the TST sandstones. Dissolution, which has an important role in reservoir development, is mainly caused by acidic fluids from the matured source rocks in the LST and meteoric water ingression from the top sequence boundary in the TST. Distributary channel sandstones adjacent to coal and mudstones are favourable reservoirs with turbidite sandstones adjacent to the sequence boundary less favourable reservoirs.     

Variations in stratigraphic and reservoir properties adjacent to the Mid-Paleocene sequence boundary, Campo section, Pyrenees, Spain

The Paleocene of the Campo section, Spain has different sedimentological characteristics above and below the Mid-Paleocene Unconformity. Beneath the unconformity sediments are dominated by evaporitic carbonates and collapse breccias. Above it they are characterized by continental detrital beds alternating with paleosols. Different subaerial features are observed and correspond to different porosity values, pore–throat sizes and micrite morphologies. Unexposed or intertidal facies have low porosity, low throat–pore size (mesoporosity) and well preserved rhombic crystals. Intermediate exposed facies (paleosols) possess medium porosity, medium pore–throat size (microporosity) and mainly micro-rhombic crystals. Finally, the facies corresponding to high exposure intensity and to evaporitic original facies presents high porosity, permeability, large pore–throat size and rounded micritic crystals. These observations show that the emersion phase caused important dissolution, especially when associated with an easily dissolved original lithofacies.     

Application of sequence and genetic stratigraphic concepts to Carboniferous coal-bearing strata: an example from the Black Warrior basin,USA

Carboniferous strata provide an excellent example on which to test the application of genetic stratigraphic and sequence stratigraphic concepts. Both approaches are employed in the evaluation of the coal-bearing strata of the Black Warrior basin, south-eastern USA. Bounding hiatal surfaces have been recognized in the succession of rock that includes the Mary Lee coal zone. Within the framework of genetic stratigraphy, one genetic sequence has been identified comprised of offlap (progradational and aggradational facies) and onlap (aggradational and transgressive facies) components. Seven parasequence sets have been delimited according to the concepts of sequence stratigraphy. These have been ascribed to transgressive, highstand and shelf margin systems tracts. The identification of components of these contrasting frameworks provide the basis for evaluating other Carboniferous strata. Correspondence to: R. A. Gastaldo     

The anatomy of a sulphate platform and adjacent basin system in the Leba sub-basin of the Lower Werra Anhydrite (Zechstein, Upper Permian), northern Poland

The Lower Werra Anhydrite (Zechstein, Upper Permian) deposits of the teba area originated in a deep basin setting, in shallow to deep water conditions. Facies changes occur within small distances and suggest fluctuating boundaries between well defined basins and platforms. This pattern of local platforms and adjacent basins developed during deposition. In basinal areas, the sequence is clearly transgressive, whereas on platforms accumulation kept pace with subsidence after an initial transgression. Nodular anhydrite represents a polygenetic deposit which formed at different times with respect to deposition. Massive anhydrite with pseudomorphs after upright-growth gypsum crystals suggest rapid precipitation in a subaqueous environment and/or fluctuating, but generally high, salinity conditions. Massive clastic sulphate originated due to periodic high energy events and resedimentation, or due to brecciation possibly connected with salinity fluctuations and the dissolution of halite. Massive, textureless anhydrite is locally porous and passes upward into breccia, indicating a strongly saline environment. Bedded anhydrite is considered to form in shallow water environments and laminated anhydrite in deep water. Bedded anhydrites contain portions which are graded. Intercalations of sulphate turbidites and upright-growth gypsum suggest fluctuating water depths, with comparatively deep water during turbidite deposition, but shallower conditions during upright-growth gypsum deposition. The sequence observed in slope zones at platform-basin margins, detrital (parautochthonous) sulphate sand to graded beds to basinal laminites, indicates that redistribution processes were important. At the onset of the Lower Werra Anhydrite deposition bathymetric relief existed between the central part of the basin and its margins, where carbonate platforms remained subaerially exposed. Formation of local platforms and adjacent basins required a relatively high subsidence rate, as pre-existing relief cannot account for the total accumulated thickness of the Lower Werra Anhydrite deposits. One implication of this is that the main argument against ‘the shallow water - shallow basin’ evaporite basin model, i.e.,a very fast rate of subsidence, may not be valid for the Łeba Lower Werra Anhydrite basin.     

Diagenesis of spiculites and carbonates in a Permian temperate ramp succession – Tempelfjorden Group,Spitsbergen, Arctic Norway

This paper explores little investigated diagenesis of spicule‐dominated sediments, based on Permian spiculites and cool‐water carbonates of the Tempelfjorden Group in central Spitsbergen. Field observations, petrography, stable isotope geochemistry, and mineralogical and chemical analyses reveal that the strata have been subjected to multistage diagenesis as the result of silica phase transitions at medium burial depths and deep‐burial overprinting. The growth of silica concretions occurred during the opal‐A/opal‐CT conversion and was controlled by the content and distribution of clay and spicules in the sediment, resulting in a variety of megascopic silica fabrics. Opal‐CT was subsequently dissolved, and all silica is now in a stable quartz stage. Petrographically, the rocks are characterized by a variety of chalcedony and quartz cements which perfectly preserve precursor textures. Most cements precipitated from silica‐oversaturated fluids, and their shapes reflect the silica saturation state and geometry of the pore space. Some microquartz and cryptoquartz also formed by a solid–solid inversion (recrystallization) of chalcedony. The cements have δ ¹⁸O values between +30‰ and +20‰ Standard Mean Ocean Water and display a systematic depletion in ¹⁸O from the first to the last crystallized, interpreted to reflect a gradual increase in temperature during burial. The precipitation of quartz cements started in the Middle Triassic when the strata passed the 19°C isotherm at burial depths of ca 600 m, and was completed in the mid‐Cretaceous, 2·3 km beneath the sea floor at temperatures of 75°C. Late diagenetic overprinting of the chert includes fracturing, brecciation and cementation with carbonate cements having δ ¹⁸O values between +2‰ and −30‰ Pee Dee Belemnite and δ ¹³C values between +4‰ and −14‰ Pee Dee Belemnite; they are linked to hot solutions introduced during Cretaceous volcanism or Palaeogene tectonism. This study illustrates the diagenetic pathway during burial of spicule‐rich sediments in a closed system and thereby provides a baseline for studies of more complexly altered chert deposits.     

西藏札达盆地上新统古格组和托林组的厘定与层序地层划分

根据札达盆地剖面中地层的接触关系、沉积旋回、沉积体系和岩相岩性特征,可将上新统河湖相地层划分为2个组、5个沉积相、8个岩段。古格组(N22g)一岩段为砾岩,属河流相沉积;二、三、五岩段以细碎屑岩为主,属浅湖相沉积;四岩段以含粘土质细碎屑岩为主,属深湖相沉积。托林组(N21t)一、二、三岩段为一套砾岩、含砾中粗粒钙质长石岩屑砂岩和中细粒砂岩的碎屑岩,为典型冲(洪)积扇沉积物。ESR法和古地磁法测年结果表明,古格组形成时代为上新世晚期(4.40～2.47Ma);托林组形成时代为上新世早期(5.44～4.40Ma)。札达盆地为一同生断陷盆地,在上新世时期的构造运动过程中,盆地演化经历了水进体系域—湖泊扩张体系域—湖泊收缩体系域3个发展阶段。     

Mineralogy,genesis and diagenesis of a brecciated shaly clay from the Zechstein evaporite series of Germany

20 core samples from the dolomite-anhydrite sequence overlying the Werra-anhydrites (Zechstein 1) were examined. The formation consists of brecciated shaly clay in a groundmass of dolomite and anhydrite with small amounts of rocksalt. The drillhole is located near the village Bruennighausen (N. Germany) on the south west flank of a saltdome.Chlorites and illite are the only clay minerals present. Chlorites: three different varieties could be distinguished, predominate in the upper portion whereas the content of illite increases in the lower part. A regeneration of illite in the upper part of the profile has been found by comparison of the K₂O-content of the illite (9–10%=upper part, 8%=lower part). Diagenetic formation of quartz and feldspars was also observed throughout the profile. The ratio of authigenic quartz/detrital quartz deoreasss in lower part. At least two generations of dolomite have been found and also pseudomorphs of dolomite after gypsum.The investigations have shown, that the shaly clay was deposited in a saline environment. Diagenetic changes after deposition were due to increasing salinity of the pore solution of the sediment. Brecciation took place long after compaction of the clay. It was accompanied and followed by further diagenetic changes.     

Anatomy, geometry and sequence stratigraphy of basin floor to slope turbidite systems, Tanqua Karoo, South Africa

The Tanqua area of the Karoo basin, South Africa, contains five Permian deep-water turbidite fan systems, almost completely exposed over some 640 km². Reconstruction of the basin-fill and fan distributions indicates a progradational trend in the 450 m+ thick succession, from distal basin floor (fan 1) through basin-floor subenvironments (fans 2, 3 and 4) to a slope setting (fan 5). Fans are up to 65 m thick with gradational to sharp bases and tops. Facies associations include basin plain claystone and distal turbidite siltstone/claystone and a range of fine-grained sandstone associations, including low- and high-density turbidite current deposits and proportionally minor debris/slurry flows. Architectural elements include sheets of amalgamated and layered styles and channels of five types. Each fan is interpreted as a low-frequency lowstand systems tract with the shaly interfan intervals representing transgressive and highstand systems tracts. All fans show complex internal facies distributions but exhibit a high-frequency internal stratigraphy based on fan-wide zones of relative sediment starvation. These zones are interpreted as transgressive and highstand systems tracts of higher order sequences. Sandy packages between these fine-grained intervals are interpreted as high-frequency lowstand systems tracts and exhibit dominantly progradational stacking patterns, resulting in subtle downdip clinoform geometries. Bases of fans and intrafan packages are interpreted as low- and high-frequency sequence boundaries respectively. Facies juxtapositions across these sequence boundaries are variable and may be gradational, sharp or erosive. In all cases, criteria for a basinward shift of facies are met, but there is no standard 'motif' for sequence boundaries in this system. High-frequency sequences represent the dominant mechanism of active fan growth in the Tanqua deep-water system.     

Some evidence for the base-metal potential of the Pretoria Group: stratigraphic targets,tectonic setting and REE patterns

The Timeball Hill and Silverton Formations of the 2.1–2.3 Ga Pretoria Group have regional lithological associations which are thought to have been favourable for the genesis of stratiform sulphide deposits. The observed association of carboniferous and pyritic black shales, tuffaceous material, stromatolitic carbonates and inferred turbidity current deposits is common in stratiform sulphide deposits of the sedimentary exhalative group. Massive sulphides in the Silverton Formation are compatible with a syngenetic brine discharge, probably related to deep fracture systems. The basal shales of the Timeball Hill Formation are significantly enriched in base-metals and Ba. Interlayered tuff beds at this stratigraphic level have PGE-contents of up to 1 g/t. The REE-geochemistry of Pretoria Group sedimentary rocks supports hydrothermal activity as an important factor in both stratigraphic units.     

新疆博格达地区早二叠世软沉积物变形构造:弧后碰撞前陆盆地地震记录

早二叠世下岌岌槽子群发育于博格达弧后碰撞前陆盆地缓坡带,为一套长石含量较高的陆源碎屑岩。古流向、沉积相带分布研究表明,当时的古坡向向南。岌岌槽子群中首次发现大量软沉积物变形构造,包括链环层理、水塑性褶皱、液化沙脉、沙侵蘑菇、碟状泄水构造、球枕构造、流化砾岩、底辟流化砾岩坨、滑混层、同沉积断层等,均是与地震驱动相适配的变形构造。这些变形构造常沿限定的岩层发育,上、下均为未变形的岩层,显示事件变形特征。大量滑混层褶皱枢纽和球枕构造轴面实测结果显示,它们既没有优势方位,其位态也与古坡向无关,进一步证实最有可能的驱动机制是地震。由于古地震活动直接与东天山造山活动密切相关,因此,研究软沉积物变形构造的时、空发育特征能够成为认识天山造山过程和相关盆地发育的一个新视角。     

Palynological and sequence stratigraphic analysis of the Napo Group in the Pungarayacu 30 well, Sub-Andean Zone, Ecuador

The study of palynomorphs and calcareous nannofossils from the Albian–Campanian Napo Group in the Pungarayacu 30 well in the Subandean Zone of Ecuador has led to a new biostratigraphic framework revealing the existence of several hiatuses for this area. The palynological and palynofacies data are used together with other fossils and lithological evidence to define a sequence stratigraphic framework. The distribution of palynomorphs and palynofacies indicates a strong terrestrial input for the lower part of the Napo Group (Napo Basal and Lower Napo formations). In the upper part (Middle and Upper Napo formations), terrestrial input is reduced and a restricted marine environment with several dysoxic–anoxic intervals can be inferred. The hydrocarbons present in the well studied have traditionally been regarded as locally sourced. However, several lines of evidence (TAS, Tmax and VR) prove the immature stage of the source rock in this borehole as well as in a larger area.     

藏北达杂迪扎错中二叠世鲁谷组地层层序及沉积环境浅析

西藏北部达杂迪扎错出露的中二叠世鲁谷组，是西亚尔岗中央隆起带的组成部分，对其地层层序和沉积环境的研究，有助于对羌塘盆地的从新认识。