陆棚海泥岩的岩相特征及沉积过程

传统的沉积模式认为大部分细粒沉积岩（泥岩或页岩）的沉积发生在相对深水、低能的环境中。作为地表上分布最为广泛的沉积岩类型,泥页岩包含了对重构地质历史时期古地理、古气候的重要信息。泥页岩除了可以作为有效的烃源岩,勘探开发技术的进展更发掘出泥岩作为非常规油气储层的巨大潜力。近十年来,国内外对细粒沉积物的水槽实验、泥岩沉积微相的精细分析、以及泥岩岩相组成特征的研究取得了长足的进展。这些研究对泥岩的沉积过程和沉积模式在不同角度上提供了新的认知。大部分泥岩（甚至包括众多有机质含量高的泥岩）都可能沉积在相对浅水以及水动力条件相对较高的环境中。不同的沉积过程（底部水流）形成不同的泥岩沉积微相,并对有机质在泥岩中的埋藏富集具有重要的控制作用。以晚白垩纪北美西部内陆海道为例,总结在陆棚浅海环境中（最大水深< 200 m）,位于从近岸到远岸（> 500 km）不同沉积环境（包括前三角洲/下邻滨、内陆棚、中陆棚、和外陆棚环境）中的泥岩的主要沉积过程、沉积微相特征、以及富集有机质的潜力。由于沉积过程和沉积环境是决定泥岩成分、沉积相、和岩石物理特征非均质性的首要因素,不同浅海环境中的泥岩相特征和沉积模式可有助于利用泥岩地层进行古地理、古气候的重构,并能够对预测不同陆棚浅海环境中沉积的泥岩作为有效烃源岩或有效储层的潜力提供指导。     

From marine bands to hybrid flows: Sedimentology of a Mississippian black shale

Organic-rich mudstones have long been of interest as conventional and unconventional source rocks and are an important organic carbon sink. Yet the processes that deposited organic-rich muds in epicontinental seaways are poorly understood, partly because few modern analogues exist. This study investigates the processes that transported and deposited sediment and organic matter through part of the Bowland Shale Formation, from the Mississippian Rheic–Tethys seaway. Field to micron-scale sedimentological analysis reveals a heterogeneous succession of carbonate-rich, siliceous, and siliciclastic, argillaceous muds. Deposition of these facies at basinal and slope locations was moderated by progradation of the nearby Pendle delta system, fourth-order eustatic sea-level fluctuation and localized block and basin tectonism. Marine transgressions deposited bioclastic ‘marine band’ (hemi)pelagic packages. These include abundant euhaline macrofaunal tests, and phosphatic concretions of organic matter and radiolarian tests interpreted as faecal pellets sourced from a productive water column. Lens-rich (lenticular) mudstones, hybrid, debrite and turbidite beds successively overlie marine band packages and suggest reducing basin accommodation promoted sediment deposition via laminar and hybrid flows sourced from the basin margins. Mud lenses in lenticular mudstones lack organic linings and bioclasts and are equant in early-cemented lenses and in plan-view, and are largest and most abundant in mudstones overlying marine band packages. Thus, lenses likely represent partially consolidated mud clasts that were scoured and transported in bedload from the shelf or proximal slope, as a ‘shelf to basin’ conveyor, during periods of reduced basin accommodation. Candidate in situ microbial mats in strongly lenticular mudstones, and as rip-up fragments in the down-dip hybrid beds, suggest that these were potentially key biostabilizers of mud. Deltaic mud export was fast, despite the intrabasinal complexity, likely an order of magnitude higher than similar successions deposited in North America. Epicontinental basins remotely linked to delta systems were therefore capable of rapidly accumulating both sediment and organic matter.     

Carbon and oxygen isotopic composition and foraminifers of condensed basal Zechstein (Upper Permian) strata in western Poland: environmental and stratigraphic implications

The basinal facies of the Lopingian Zechstein Limestone in SW Poland consists of thin (often less than 1 m thick) limestones and/or dolomites, often containing the Kupferschiefer (few tens of centimetres thick) at their base, and local thick (up to 90 m) reefal carbonates. The δ¹³C curve of these basal Zechstein deposits strongly suggests that even when the Kupferschiefer is lacking, the thin (condensed) sequences record the entire interval of the Zechstein prior to the onset of evaporite deposition, in contrast to the thick reef sequences which lack the characteristic δ¹³C curve for the lowermost part of the Zechstein. The calcite samples show considerable ranges of δ¹⁸O values. If the maximum δ¹⁸O values are considered to be the closest to the pristine original ones and if δ¹⁸O_water value = 0 is assumed, then the calculated range of palaeotemperatures for the Kupferschiefer and Zechstein Limestone calcite ranges from 19 to 34 °C. The faunal restriction, common dwarf foraminifers and the predominance of lagenids in the foraminiferal assemblage indicate continual dysaerobic conditions and possibly elevated salinity of seawater during deposition of thin basinal Zechstein Limestone deposits. The mixing of shallow and deeper waters in the stratified Zechstein Basin caused by upwelling could result in prolific carbonate precipitation in reefs located at the slope of the marginal carbonate platform of the Zechstein Limestone and in isolated reefs related to palaeohighs within the basin; however, there is no isotopic record of eventual upwelling. Copyright © 2014 John Wiley & Sons, Ltd.     

Carbonate ramp-to-deeper shale shelf transitions of an Upper Cambrian intrashelf basin, Nolichucky Formation, Southwest Virginia Appalachians

The Nolichucky Formation (0–300 m thick) formed on the Cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton. Lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp. Peritidal facies of the regional shelf are cyclic, upward-shallowing stromatolitic carbonates. These grade toward the intrashelf basin into shallow ramp, cross-bedded, ooid and oncolitic, intraclast grain-stones that pass downslope into deeper ramp, subwave base, ribbon carbonates and thin limestone conglomerate. Ribbon limestones are layers and lenses of trilobite packstone, parallel and wave-ripple-laminated, quartzose calcisiltite, and lime mudstone arranged in storm-generated, fining upward sequences (1–5 cm thick) that may be burrowed. Shallow basin facies are storm generated, upward coarsening and upward fining sequences of green, calcareous shale with open marine biota; parallel to hummocky laminated calcareous siltstone; and intraformational flat pebble conglomerate. There are also rare debris-flow paraconglomerate (10–60 cm thick) and shaly packstone/wackestone with trace fossils, glauconite horizons and erosional surfaces/hardgrounds. A 15-m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin. Understanding the Nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the Lower Palaeozoic elsewhere. The study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation. Finally, recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks, whose trends may be unrelated to regional shelf-edge trends.     

The Rio Dell Formation: a Plio-Pleistocene basin slope deposit in Northern California

The Rio Dell Formation (Pleistocene and Pliocene), exposed south of Eureka, California, is a prograded sequence of basinal turbidites overlain by basin slope and shelf deposits. The slope deposits studied in the Centerville Beach section accumulated in a steadily shallowing environment delineated by analysis of palaeobathymetrically significant benthonic foraminiferal biofacies in turn suggesting deposition at depths of 1000–100 m. Lower slope deposits interfinger with basinal turbidites derived from the Eel River delta to the north. Slumped blocks of silty mudstone, and associated silt and mud beds, are common. The middle slope deposits are mudstones; coarser sediments bypassed this zone. Mudstones and muddy siltstones alternate on the upper slope. Shallow depressions, probably slump scars, that have been rapidly filled by upper slope sediment are common. The transition to shelf deposits is marked by an increase in sediment grain size, in the degree of oxidation, and in the abundance of megafossils. High percentages of benthonic foraminifera displaced from shelf depths indicate that resedimentation processes are most important on the upper slope.     

Facies and faunal changes in the Ludlovian rocks of Aymestrey,Herefordshire

The Aymestrey area displays changes in facies, faunas and thicknesses which can be related to its position on the shelf edge during later Silurian times. The Wenlock Limestone becomes an alternation of limestones and mudstones. The Lower and Middle Elton Beds, however, are substantially similar to their development at Ludlow. The Upper Elton Beds and the Bringewood Beds thin westwards within the area, probably due to non-deposition or erosion on a ridge at the hinge between shelf and basin. The most striking change is the rapid westward passage of the Aymestry Limestone facies of the Upper Bringewood Beds into siltstones, which are considered to be shallow-water deposits and not basinal. The Leintwardine Beds exhibit a westward thickening, and slumping is developed in the Lower Leintwardine Beds; the faunas relate more to the basin facies than to the shelf. The Whitcliffe Beds thicken markedly westwards but retain their shallow-water characteristics.     

Glacially-influenced deep-marine sedimentation of the Late Precambrian Gaskiers Formation, Newfoundland, Canada

The Late Proterozoic Conception Group, exposed on the Avalon Peninsula in Newfoundland, Canada, is a 4 km thick turbidite succession containing a conformable 300 m thick sequence of diamictites (the Gaskiers Formation) near the base. Massive and crudely-stratified diamictites form beds up to 25 m thick which have a tabular geometry with slightly erosive basal contacts and are interbedded with mudstones and fine-grained, thin-bedded turbidites. These diamictites are interpreted as submarine debris flow deposits. Disrupted diamictites form strongly deformed units that contain large, complexly folded rafts of mudstone and turbidite facies. These diamictite units are interpreted as submarine slumps. Diamictites contain glacially-striated and faceted clasts; clasts and matrix are predominantly of volcanic provenance. One outcrop shows interbedded volcanic agglomerate and diamictite, and volcanic bombs can also be identified. The interbedding of diamictites with turbidites and the stratigraphic context provided by the thick sequences of turbidites below (Mall Bay Formation) and above (Drook Formation) indicate a deep marine slope setting of diamictite deposition. Diamictite facies record remobilization and downslope transfer of large volumes of unstable volcanic and glacial debris initially deposited in a shallower water marginal marine zone. The regional tectonic framework suggests the Conception Group accumulated in a deep, southward-opening ensialic rift basin with active but waning volcanic centres to the north. The Gaskiers Formation may be representative of other Late Precambrian glacially-influenced diamictite sequences that were deposited around the North Atlantic region and in Europe. These deep marine diamictite sequences characterized by debris flows, turbidites, and slump deposits, can be contrasted with more extensive shallow marine shelf diamictite sequences found in association with dolomites and tidally influenced shallow water facies in other basinal settings.     

Three-dimensional sequence analysis of a subsurface carbonate ramp, Mississippian Appalachian foreland basin, West Virginia, USA

Well‐cuttings, wireline logs and limited core and outcrop data were used to generate a regional, three‐dimensional sequence framework for Upper Mississippian (Chesterian), Greenbrier Group carbonates in the Appalachian foreland basin, West Virginia, USA. The resulting maps were used to document the stratigraphic response of the basin to tectonics and to glacio‐eustasy during the transition into ice‐house conditions. The ramp facies include inner ramp red beds and aeolianites, lagoonal muddy carbonates, mid‐ramp ooid and skeletal grainstone shoal complexes, and outer ramp wackestone–mudstone, that grades downslope into laminated silty lime mudstone. The facies make up fourth‐order sequences, a few metres to over 90 m (300 ft) thick. The sequences are bounded along the ramp margin by lowstand sandstones and calcareous siltstones. On the ramp, sequence boundaries are overlain by thin transgressive siliciclastics and aeolianites, and only a few are calichified. Maximum flooding surfaces on the outer ramp lie beneath deeper water facies that overlie lowstand to transgressive siliciclastic or carbonate units. On the shallow ramp, maximum flooding surfaces overlie siliciclastic‐prone transgressive systems tracts, that are overlain by highstand carbonates with significant grainstone units interlayered with lagoonal lime mudstones. The fourth‐order sequences are the major mappable subsurface units; they are bundled into weak composite sequences which are bounded by red beds. In spite of differential subsidence rates across the foreland basin (1 to 3 cm/k.y. up to 25 cm/k.y.), eustatic sea‐level changes controlled regional sequence development. Thrust‐load induced differential subsidence of fault‐blocks, coupled with in‐plane stress, controlled the rapid basinward thickening of the depositional wedge, whose thickness and facies were influenced by subtle structures such as arches trending at high angles as well as parallel to the margin.     

Mapping the rise and demise of Urgonian platforms (Late Hauterivian - Early Aptian) in southeastern France and the Swiss Jura

Lower Cretaceous carbonate deposits historically called “Urgonian limestones” are widely exposed around the margins of the Vocontian basin in southeastern France and in the adjacent Swiss Jura. This paper presents the history of their rise, growth and sudden demise. Eleven maps were constructed for deposits ranging in age from the Late Hauterivian pro parte to the Early Aptian (Bedoulian) pro parte. Based on sequential interpretations, they illustrate the present geographical distribution of the inner platform facies (Urgonian limestones stricto sensu, with rudists), the outer platform facies (essentially bioclastic deposits) and the basinal facies (slope, hemipelagic, pelagic deposits). These maps depict only the final terms of each successive sequence (the late highstand intervals). Chronostratigraphy is constrained by ammonites found mainly in basinal deposits, by echinoids, by rudists and to a lesser extent by dinoflagellates and calcareous nannoplancton. Inner platform, outer platform and slope (talus) deposits are dated by rich assemblages of orbitolinids and dasycladalean algae. Currently 39 species of orbitolinids have been recognized and their ranges collated with those of the ammonites in the area.In the Jura and in Provence the oldest Urgonian deposits are dated early Late Hauterivian, thus showing the synchroneity of the onset of platform carbonates development on both the southern and northern margins of the basin. Thereafter, growth of the platforms led a clearly regressive shallowing-upward trend, resulting from a stepwise progradation toward the center of the Vocontian area, coordinated with cyclical exposures in the inner platform areas. The maximum reduction of the platform deposits occurred early in Late Barremian times, coeval with a noticeable turnover in the orbitolinids assemblages.Thereafter, carbonate platform deposition shifted toward the margins of the Vocontian basin. In Early Aptian time, a well-dated discontinuity of regional extent marks the sudden, almost synchronous disappearance of the Urgonian deposits.     

Geometry and sequence stratigraphy of the Late Eocene-Early Oligocene shelf and basin floor to slope turbidite systems, Lemnos Island, NE Greece

The Late Eocene-Early Oligocene sedimentary fill of the Lemnos Island, NE Greece, is represented by a submarine fan and shelf deposits. Turbidites in the system occur as a laterally isolated body, with one sediment influx center present. The influx center is a proximal distributary channel that occupies a position approximately in the fan’s center and displays the coarsest sediment in the study area. It also suggests in association with the main palaeocurrent direction toward NE a curved shape for the fan. The stratigraphic succession of the submarine fans indicates that their sedimentation started during the base level fall and completed shortly after the base level rise. As a consequence, the study area was filled by turbidites that correspond to forced regressive, lowstand normal regressive, and transgressive genetic units. The progradational bedsets, within the basal part of the turbidite deposits, recorded the history of the base level fall. The mixed progradational/aggradational style of the upper part of the submarine fan system suggests that the regression of the shoreline is driven by sediment supply during a period of base-level rise at the shoreline, or at a time of baselevel stillstand. The overlying shelf facies consist of thick to medium bedded sandstones and mudstones, which display a general thinning upward trend. The base of the mudstone facies that overlie the thick-bedded, amalgamated sandstones corresponds to a transgressive surface. This surface separates the low-stand deposits (thick-bedded sandstones) from the high stand deposits (mudstone facies), suggesting that deposition of shelf facies occurred during a transgressive system tract.     

鄂西—湘西北地区二叠纪栖霞期岩相古地理

对鄂西—湘西北地区多个沉积剖面的地层及沉积相进行了详细分析,结果表明,该区二叠纪栖霞期至茅口初期主要为内克拉通碳酸盐岩缓坡环境,发育内缓坡相、中缓坡相、外缓坡相和盆地相.内缓坡相以厚层至块状生物碎屑石灰岩为主,生物颗粒以绿藻和底栖有孔虫为主,缺乏高能沉积的生物颗粒.中缓坡相以中厚层含生物碎屑颗粒石灰岩以及厚层灰泥石灰岩...     

Probable distribution of Upper Jurassic and Lower Cretaceous deposits on the Laptev Sea shelf and their petroleum resource potential

The analysis of Upper Jurassic and Lower Cretaceous marine sections developed in surrounding structures of the Laptev Sea revealed that all of them are composed of terrigenous rocks, which enclose abundant concretions cemented by calcareous material. The Upper Jurassic portion of the section is the most variable in thickness and stratigraphic range of sediments usually including hiatuses. Its Lower Cretaceous part represented by the Boreal Berriasian (=Ryazanian) and lower Valanginian stages is most complete. The Upper Jurassic and Lower Cretaceous sections are usually composed of fine-grained rocks (clays and mudstones) in the west and coarser cemented varieties (siltstones and sandstones) with rare mudstone intercalations in the east. Practically all the investigated Upper Jurassic and Lower Cretaceous sections include readily recognizable age and facies analogs of the Bazhenovo Formation and Achimov sandstones, which are petroliferous in West Siberia. There are grounds to assume the occurrence of these formations also on the Laptev Sea shelf, which is confirmed by seismic records. Conditions favorable for the formation of potential hydrocarbon reservoirs could exist in the western part of the paleobasin along the Nordvik Peninsula coast and northeastern Tamyr Peninsula margin. Paleotectonic reconstructions presented in this work are well consistent with stratigraphic conclusions.     

中上扬子地区下志留统沉积演化与页岩气勘探方向*

通过录井、测井、地震、野外剖面与岩心资料的深入剖析, 探讨中上扬子地区下志留统页岩段的沉积相与总有机碳的关系, 预测页岩气有利勘探区。中上扬子地区下志留统龙马溪组为一套20～268 m厚的黑色页岩夹灰绿色泥质粉砂岩沉积, 在等时框架内自下而上可识别出2个三级层序即SQ1与SQ2, 它们分布稳定、可对比性好。下部层序(SQ1) 的海侵体系域(TST)发育一套有利于页岩气形成的富有机质页岩, 此时期呈现出“北面向次深海敞开、东西南三面受古陆围限、陆棚广布”的沉积格局, 深水陆棚相广泛发育, 面积为255000 km², 平均厚度35 m。受海平面下降的影响, 从下部层序至上部层序水体变浅, 岩相从深水陆棚相黑色页岩向中-浅水陆棚相沙纹层理粉砂质页岩转变。岩相的发育受海平面升降、古陆、海底地形、物源供给等因素的影响, 岩相类型有碳质或硅质或钙质页岩、纹层状页岩、生物扰动粉砂质页岩、沙纹层理的粉砂质页岩、块状砂岩或介壳灰岩薄夹层5类。研究表明, 沉积相对富有机质页岩的形成具有内在的控制作用, 高TOC含量页岩发育于深水陆棚相、中陆棚相和潟湖相中。目前, 已有多口井在龙马溪组页岩获得工业气流, 揭示了该区良好的页岩气勘探前景;综合分析认为涪陵-赤水-仁怀、威远-长宁、鄂西-渝东为中上扬子地区下志留统页岩气勘探的主要方向和有利目标区。     

Sedimentology,sequence stratigraphy and syn-rift model of younger part of Washtawa Formation and early part of Kanthkot Formation,Wagad, Kachchh basin,Gujarat

The 600 m thick prograding sedimentary succession of Wagad ranging in age from Callovian to Early Kimmeridgian has been divided into three formations namely, Washtawa, Kanthkot and Gamdau. Present study is confined to younger part of the Washtawa Formation and early part of the Kanthkot Formation exposed around Kanthkot, Washtawa, Chitrod and Rapar. The depositional architecture and sedimentation processes of these deposits have been studied applying sequence stratigraphic context. Facies studies have led to identification of five upward stacking facies associations (A, B, C, D, and E) which reflect that deposition was controlled by one single transgressive — regressive cycle. The transgressive deposit is characterized by fining and thinning upward succession of facies consisting of two facies associations: (1) Association A: medium — to coarse-grained calcareous sandstone — mudrocks alternations (2) Association B: fine-grained calcareous sandstone — mudrocks alternations. The top of this association marks maximum flooding surface as identified by bioturbational fabrics and abundance of deep marine fauna (ammonites). Association A is interpreted as high energy transgressive deposit deposited during relative sea level rise. Whereas, facies association B indicates its deposition in low energy marine environment deposited during stand-still period with low supply of sediments. Regressive sedimentary package has been divided into three facies associations consisting of: (1) Association C: gypsiferous mudstone-siltstone/fine sandstone (2) Association D: laminated, medium-grained sandstone — siltstone (3) Association E: well laminated (coarse and fine mode) sandstone interbedded with coarse grained sandstone with trough cross stratification. Regressive succession of facies association C, D and E is interpreted as wave dominated shoreface, foreshore to backshore and dune environment respectively. Sequence stratigraphic concepts have been applied to subdivide these deposits into two genetic sequences: (i) the lower carbonate dominated (25 m) transgressive deposits (TST) include facies association A and B and the upper thick (75m) regressive deposits (HST) include facies association C, D and E. The two sequences are separated by maximum flooding surface (MFS) identified by sudden shift in facies association from B to C. The transgressive facies association A and B represent the sediments deposited during the syn-rift climax followed by regressive sediments comprising association C, D and E deposited during late syn-rift stage.     

Deposition and derivation of clastic carbonates on a Mesozoic continental margin, Othris, Greece

The Othris Mountains of eastern Greece contain a calcareous continental margin/ocean basin sequence exposed in a stack of Cretaceous thrust sheets. Upper Triassic to Lower Cretaceous shelf, submarine fan and basinal successions overlie shallow marine units of Lower Triassic and Permian age. In off-shelf sequences the older sediments are separated from the younger by a horizon of alkaline ‘early-rifting’ basalts. Ophiolites overthrust the marginal sequence. Pre-rifting sediments are represented by a varied suite of limestones and clastics resting on metamorphic basement and include distinctive, green lithic arenites. In the thrust sheet immediately over the para-autochthonous shelf sequence, pre-rifting sediments are separated from the rift basalts by an intermittent horizon of calcareous sandstones and conglomerates reworked from uplifted basement and older sediments. Textural and petrographic immaturity suggests that these are probably deposits derived from fault scarps, produced in an early phase of rifting. Above the basalts in the same sheet is a suite of calciclastic sediment-gravity-flow deposits, apparently sedimented on a submarine fan. Progressive downslope modification of calcirudites suggests deposition from evolving, high concentration flows. Massive calcarenite facies (? grain flows) are unusually abundant; a possible reflection of a shallow palaeo-shelf break since provenance and palaeocurrent evidence proves the clastic carbonates to have been derived from a calcareous shelf. In addition to limestone lithoclasts the calcirudites, but not the massive calcarenites, contain fragments of pre-rifting lithologies including the distinctive arenites. Since the shelf sequence in Othris is totally nondetrital these clasts imply derivation of coarse sediment from an off-shelf position; probably the walls of a submarine canyon. This may have occurred either by direct erosion of wall rock, or by reworking of material from an older clastic sequence. In the latter case the inferred fault-scarp deposits are a likely source.     

Facies analysis of a Toarcian–Bajocian shallow marine/coastal succession (Bardas Blancas Formation) in northern Neuquén Basin,Mendoza province,Argentina

Strata of the Bardas Blancas Formation (lower Toarcian–lower Bajocian) are exposed in northern Neuquén Basin. Five sections have been studied in this work. Shoreface/delta front to offshore deposits predominate in four of the sections studied exhibiting a high abundance of hummocky cross-stratified, horizontally bedded and massive sandstones, as well as massive and laminated mudstones. Shell beds and trace fossils of the mixed Skolithos-Cruziana ichnofacies appear in sandstone beds, being related with storm event deposition. Gravel deposits are frequent in only one of these sections, with planar cross-stratified, normal graded and massive orthoconglomerates characterizing fan deltas interstratified with shoreface facies. A fifth outcrop exhibiting planar cross-stratified orthoconglomerates, pebbly sandstones with low-angle stratification and laminated mudstones have been interpreted as fluvial channel deposits and overbank facies. The analysis of the vertical distribution of facies and the recognition of stratigraphic surfaces in two sections in Río Potimalal area let recognized four transgressive–regressive sequences. Forced regressive events are recognized in the regressive intervals. Comparison of vertical distribution of facies also shows differences in thickness in the lower interval among the sections studied. This would be related to variations in accommodation space by previous half-graben structures. The succession shows a retrogradational arrangement of facies related with a widespread transgressive period. Lateral variation of facies let recognize the deepening of the basin through the southwest.     

湘中湘南地区奥陶纪达瑞威尔中晚期-凯迪早期岩相古地理及其油气地质意义

湘中湘南地区在早古生代时期,由于受海平面变化以及全球古气候的影响,形成了有利于烃源岩形成的沉积环境。笔者通过对湘中湘南地区的奥陶纪达瑞威尔中晚期-凯迪早期开展沉积相、岩相古地理和油气地质等研究,结合前人所取得的相关研究成果,将该区划分为陆架相、盆地相和陆架边缘相。陆架相主要由砂质板岩、砂岩、黑色页岩和硅质岩组成;陆架边缘相为粉砂-细粒石英砂岩、长石石英砂岩夹条带状板岩、炭质板岩和硅质岩等组成;而盆地相为一套炭质页岩和硅质岩组成的黑色岩系,代表了一种平静还原的滞流缺氧环境。该套岩性有机质含量高,具较高的生烃潜力,且分布范围广,是湘中湘南地区达瑞威尔-凯迪阶的富烃沉积区,也是下一步油气地质调查和勘探的重要层位。     

Carbonate platform growth and cyclicity at a terminal Proterozoic passive margin, Infra Krol Formation and Krol Group, Lesser Himalaya, India

Abstract The Infra Krol Formation and overlying Krol Group constitute a thick (< 2 km), carbonate-rich succession of terminal Proterozoic age that crops out in a series of doubly plunging synclines in the Lesser Himalaya of northern India. The rocks include 18 carbonate and siliciclastic facies, which are grouped into eight facies associations: (1) deep subtidal; (2) shallow subtidal; (3) sand shoal; (4) peritidal carbonate complex; (5) lagoonal; (6) peritidal siliciclastic–carbonate; (7) incised valley fill; and (8) karstic fill. The stromatolite-rich, peritidal complex appears to have occupied a location seaward of a broad lagoon, an arrangement reminiscent of many Phanerozoic and Proterozoic platforms. Growth of this complex was accretionary to progradational, in response to changes in siliciclastic influx from the south-eastern side of the lagoon. Metre-scale cycles tend to be laterally discontinuous, and are interpreted as mainly autogenic. Variations in the number of both sets of cycles and component metre-scale cycles across the platform may result from differential subsidence of the interpreted passive margin. Apparently non-cyclic intervals with shallow-water features may indicate facies migration that was limited compared with the dimensions of facies belts. Correlation of these facies associations in a sequence stratigraphic framework suggests that the Infra Krol Formation and Krol Group represent a north- to north-west-facing platform with a morphology that evolved from a siliciclastic ramp, to carbonate ramp, to peritidal rimmed shelf and, finally, to open shelf. This interpretation differs significantly from the published scheme of a basin centred on the Lesser Himalaya, with virtually the entire Infra Krol–Krol succession representing sedimentation in a persistent tidal-flat environment. This study provides a detailed Neoproterozoic depositional history of northern India from rift basin to passive margin, and predicts that genetically related Neoproterozoic deposits, if they are present in the High Himalaya, are composed mainly of slope/basinal facies characterized by fine-grained siliciclastic and detrital carbonate rocks, lithologically different from those of the Lesser Himalaya.     

贺兰奥拉槽早古生代深水重力流体系的沉积特征和充填样式

位于鄂尔多斯西缘的贺兰构造带为一中元古代一古生代的奥拉槽。在区内的中寒武和中奥陶统中识别了一套巨厚的深水重力流沉积,其中包括下斜坡滑塌泥石流复合体、浊积扇以及碳酸盐岩斜坡扇裙等沉积类型。主要的相单元包括充填沟道或进入扇面形成的泥石流钙质角砾岩和砾岩、充填辫状水道的多层叠置的砂岩和砂砾岩、上叠扇的砂、泥岩互层以及浊积砂屑或含砾砂屑灰岩等。在中奥陶世该奥拉槽发展成一深水一半深水海槽,沿盆地西侧发育有浊积扇,而东侧仅有碳酸盐岩滑塌扇裙。它们可能是沿深水盆地两侧深大断裂产生的陡坡或水下断崖分布的,代表了早古生代贺兰奥拉槽在强烈沉陷期特定的深水盆地充填。     

中上扬子地区晚奥陶世岩相古地理及其油气地质意义

中上扬子地区上奥陶统主要发育庙坡组、宝塔组、临湘组(涧草沟组)、五峰组和观音桥组。笔者通过对研究区野外露头及钻井剖面的考察,总结前人研究成果,利用岩石学、古生物学、生态学及室内分析等方法将其划分为潮坪相、浅海陆棚相和深水盆地相3种沉积相类型。潮坪相以沉积灰岩、白云岩、钙质粉砂岩和粉砂岩等为特征。浅海陆棚相主要沉积龟裂纹灰岩、瘤状灰岩、页岩和粉砂质页岩。深水盆地相主要岩性为黑色碳质页岩、粉砂质页岩与硅质页岩,产以营漂浮生活的笔石为主的生物组合。岩相古地理研究表明,晚奥陶世桑比-凯迪早中期,受加里东构造运动影响,华南板内碰撞挤压作用显著,汉南隆起、川中隆起、川西-滇中-黔中-雪峰隆起不断抬升扩大,中上扬子地区表现为海平面相对上升,原本镶边型碳酸盐台地被淹没,沉积了大范围的浅海陆棚相龟裂纹灰岩和瘤状灰岩。凯迪晚期-赫南特期,隆起面积继续扩大,构造围限作用加剧,中上扬子地区发育大面积黑色碳质页岩、粉砂质页岩和硅质页岩。尤其川东南宜宾-泸州,川北旺苍-南江及黔北渝东武隆道真地区五峰组黑色碳质和硅质页岩,具很好的生烃潜力,应视为下一步烃源岩及页岩气勘探开发的重点研究区域。