The start‐up of the Dolomia Principale/Hauptdolomit carbonate platform (Upper Triassic) in the eastern Southern Alps

Wide carbonate platform environments developed on the western passive margin of the Tethys during the Late Triassic, after a major climate change (Carnian Pluvial Episode) that produced a crisis of high‐relief microbial carbonate platforms. The peritidal succession of this epicontinental platform (Dolomia Principale/Hauptdolomit, Dachstein Limestone) is widespread in the Mediterranean region. However, the start‐up stage is not fully understood. The original platform to basin depositional geometries of the system have been studied in the north‐eastern Southern Alps, close to the Italian/Slovenian boundary where they are exceptionally preserved. Sedimentological features have been investigated in detail by measuring several stratigraphic sections cropping out along an ideal depositional profile. The analysis of the facies architecture allowed reconstruction of the palaeoenvironments of the Dolomia Principale platform during its start‐up and early growth stages in the late Carnian. The carbonate platform was characterized by an outer platform area, connected northward to steep slopes facing a relatively deep basin. Southward, the outer platform was connected to inner sheltered environments by a narrow, often emerged shelf crest. Behind this zone, carbonate sedimentation occurred in shallow lagoons and tidal flats, passing inward to a siliciclastic mudflat. The Dolomia Principale platform was initially aggrading and able to keep pace with a concomitant sea‐level rise, and then prograding during the late Carnian. This stratigraphic interval was correlated with the Tuvalian succession of the Dolomites, allowing depiction of the depositional system on a wide scale of hundreds of kilometres. This large‐scale depositional system presents features in common with some Palaeozoic and Mesozoic carbonate build‐ups (for example, the Permian Capitan Reef complex, Anisian Latemar platform), both in terms of architecture and prevailing carbonate producers. A microbial‐dominated carbonate factory is found in the outer platform and upper slope. The recovery of high‐relief microbial carbonate platforms marks the end of the Carnian Pluvial Episode in the Tuvalian of Tethys.     

Sedimentation in shallow to deep water carbonate environments across a sequence boundary: effects of a fall in sea-level on the evolution of a carbonate system (Ladinian-Carnian, eastern Lombardy, Italy)

In the Concarena‐Pizzo Camino Massif (Lombardy Basin, Southern Alps, Italy) the lateral transition from Ladinian‐Carnian carbonate platforms to coeval intraplatform basins is preserved. The succession records the sedimentological evidence of a sea‐level fall on a flat‐topped platform with a narrow marginal reef rim and its effects in the adjacent deeper‐water basin. Repeated high‐frequency exposures of the platform top are recorded by a peritidal–supratidal succession that overlies subtidal inner platform facies of the former highstand system tract (HST). On the slope and in the basin, the sea‐level fall is recorded by a few metre thick succession of bioclastic packstones. These facies directly lie on coarse clinostratified breccia bodies (slope facies of the former HST) or on resedimented, well‐bedded, dark laminated limestones (basinal facies of the HST). This facies distribution indicates that during the sea‐level fall carbonate production on the platform top decreased rapidly and that sedimentation in the basin was mainly represented by condensed facies. Microfacies record an enrichment, during low stand, in pelagic biota (packstones with radiolarians and spiculae), whereas the occurrence of platform‐derived, shallow‐water materials is limited to thin lenses of reworked and micritized Fe‐rich oolites and bioclasts (mainly pelecypods and echinoderms). The facies association in the Concarena‐Pizzo Camino Massif demonstrates that a highly‐productive carbonate factory was almost completely turned off during the emergence of the platform top at a sequence boundary, leading to low‐stand starvation in the basin. The reconstruction of the stratigraphic evolution of the Concarena‐Pizzo Camino carbonate platform therefore represents a significant case history for the study of the behaviour of ancient carbonate systems during a fall in sea‐level, independent of its origin (eustatic or tectonic).     

Lateral variations in sediment composition and bedding in Middle Triassic interplatform basins (Buchenstein Formation, southern Alps, Italy)

ABSTRACT Hemipelagic deposits are widespread in Triassic sequences of the Alpine belt and provide important data for stratigraphy and the study of bedding rhythms. The area of the western and central Dolomites of northern Italy escaped strong alpidic deformation and preserves such deposits in their original palaeogeographic setting. The Buchenstein Formation, the object of this study, was deposited in up to 1000 m deep, Middle Triassic interplatform basins, which extend over an area of 500 km² within the Dolomites. Excellent outcrops and volcaniclastic markers allow a detailed correlation of the formation in both laminated (anoxic) and bioturbated facies down to a bed scale, and show its relationship to coeval carbonate platforms. Correlation of lithostratigraphically well‐constrained intervals in the bioturbated facies reveal that lateral thickening and thinning of the deposits depends on the amount of shallow‐water debris in the succession and is a function of the distance to coeval carbonate platform sources. In the laminated background deposit, thickness variations in limestones and marls parallel the thickness variations in ash layers, and were caused by local redeposition of sediment on the basin floor. Lateral persistence of laminae indicates that bottom currents were weak in the Buchenstein basin, but were able to redeposit mud in a significant way. In the area around Seceda and Geisler (western Dolomites), a lateral transition from dark‐grey laminated to grey bioturbated to red bioturbated facies is observed, which is probably linked to local relief with different oxygenation conditions on the sea floor. A comparison shows that decimetre‐scale bedding is preserved in all facies types and that the bedding rhythm is partly the result of different cementation of the sediment during early diagenesis. Correlation of individual layers in the bioturbated facies reveals that beds are thicker and enriched in lime mud in the western part of the basin, and decrease in thickness and contain less micrite towards the east, further away from the main shallow‐water areas. Nearslope calciturbidites change gradually from distinct layers into lateral arrays of micrite nodules and bands further out in the basin. These observations point to a platform source of lime mud in the Buchenstein basin.     

Facies interfingering and synsedimentary tectonics on late Ladinian–early Carnian carbonate platforms (Dolomites, Italy)

A stratigraphic model for carbonate platform evolution in the Dolomites during the late Ladinian-early Carnian is presented. New light on pre-Raibl growth of individual carbonate platforms of the western Dolomites was shed by biostratigraphic data combined with a revised lithostratigraphy. At the Schlern, Langkofel and Sella, the carbonate factory (Upper Schlern Dolomite) remained productive into the lowermost Carnian (Cordevolian = Aon Zone), and caused a levelling-out of the former steep platform-to-basin relief. In the eastern Dolomites, platforms were producing till basal Julian 2 (Austriacum Zone). At the Sella and Langkofel, the sedimentation pattern after deposition of the Upper Schlern Dolomite was strongly influenced by synsedimentary tectonics. A first phase of extensional tectonics led to local fissures, block-tilting, graben structures and breccia deposits. Composition and fabric of the reworked clasts argue for local-source sediments and short transport distances. The extensional structures are sealed by sediments of Lower Carnian age. Two facies belts (Schlernplateau beds and Dürrenstein Dolomite), which interfinger at the western side of the Sella, reflect the shallow marine environment with terrigenous-volcanoclastic input in the western Dolomites. A second generation of breccias at the Sella documents local fracturing of the Dürrenstein and Upper Schlern Dolomite. Depositional environments across the western and eastern Dolomites were largely dependent on differential subsidence. The sediments of early Carnian age on top of the Schlern platform are a few metres thick only, whereas, in the eastern Dolomite, up to 400-m-thick carbonate sediments ('Richthofen reef' and Settsass platform) were deposited. The most incomplete stratigraphic record is present at the Mendel platform in the west, where Ladinian volcanics are unconformably overlain by late Carnian 'Raibl beds'. The increase in sediment thickness towards the eastern Dolomites becomes partly visible at the eastern flank of the Sella platform. Differential subsidence across western and eastern Dolomites caused local fracturing of platform sediments. Synsedimentary extensional tectonics was a significant controlling factor to the lithofacies and thickness variations of early Carnian platform sediments in the Dolomites.     

Anatomy of an Upper Triassic continental to marginal‐marine system: the mixed siliciclastic–carbonate Travenanzes Formation (Dolomites,Northern Italy)

The Travenanzes Formation is a terrestrial to shallow‐marine, siliciclastic–carbonate succession (200 m thick) that was deposited in the eastern Southern Alps during the Late Triassic. Sedimentary environments and depositional architecture have been reconstructed in the Dolomites, along a 60 km south–north transect. Facies alternations in the field suggest interfingering between alluvial‐plain, flood‐basin and shallow‐lagoon deposits, with a transition from terrestrial to marine facies belts from south to north. The terrestrial portion of the Travenanzes Formation consists of a dryland river system, characterized by multicoloured floodplain mudstones with scattered conglomeratic fluvial channels, merging downslope into small ephemeral streams and sheet‐flood sandstones, and losing their entire discharge subaerially before the shoreline. Calcic and vertic palaeosols indicate an arid/semi‐arid climate with strong seasonality and intermittent discharge. The terrestrial/marine transition shows a coastal mudflat, the flood basin, which is usually exposed, but at times is inundated by both major river floods and sea‐water storm surges. Locally coastal sabkha deposits occur. The marine portion of the Travenanzes Formation comprises carbonate tidal‐flat and shallow‐lagoon deposits, characterized by metre‐scale shallowing‐upward peritidal cycles and subordinate intercalations of dark clays from the continent. The depositional architecture of the Travenanzes Formation suggests an overall transgressive pattern organized in three carbonate–siliciclastic cycles, corresponding to transgressive–regressive sequences with internal higher‐frequency sedimentary cycles. The metre‐scale sedimentary cyclicity of the Travenanzes Formation continues without a break in sedimentation into the overlying Dolomia Principale. The onset of the Dolomia Principale epicontinental platform is marked by the exhaustion of continental sediment supply.     

Compositional variations during phases of progradation and retrogradation of a Triassic carbonate platform (Picco di Vallandro/Dürrenstein, dolomites, Italy)

In this paper data are presented on the composition of sediments deposited at the toe of slope during progradation or retreat of Triassic carbonate platforms in the Dolomites (Italy). For this purpose a succession was studied from the toe of slope of a Triassic (Carnian) carbonate platform (Picco di Vallendro/Dürrenstein, Dolomites, Italy). The microfacies analysis of selected calciturbidites sequences revealed a reduced input of oncolites and ooids during progradation and an increase in clasts. The main input, however, was derived from the reefs on the platform. Retrogradation of the platform showed an increase of filaments and radiolarians (open ocean biota) as well as carbonate mud and a reduced input of grains that originated within the reefs on the platform. Both during progradation and retrogradation parts of the platform were flooded and could produce excess sediment that could be exported to the surrounding basins. However, the absence of platform interior biota documents that progradation occurred from sediments of the reefal belt, probably during relative sea-level lowstands. Carbonate composition varies systematically with toe-of-slope progradation/retrogradation and, thus, argues for carbonate production as the main driver of the geometries observed at the toe of slope.     

Internal architecture of mass‐transport deposits in basinal carbonates: A case study from southern Italy

Submarine mass‐transport deposits represent important stratigraphic heterogeneities within slope and basinal sedimentary successions. A poor understanding of how their distribution and internal architecture affect the fluid flow migration pathway may lead to unexpected compartmentalization issues in reservoir analysis. Studies of modern carbonate mass‐transport deposits mainly focus on large seismic‐scale slope failures; however, the near‐platform basinal depositional environment often hosts mass‐transport deposits of various dimensions. The small‐scale and meso‐scale (metres to several tens of metres) carbonate mass‐transport deposits play a considerable role in distribution of sediment and therefore have an impact on the heterogeneity of the succession. In order to further constrain the geometry and internal architecture of mass‐transport deposits developed in near‐slope basinal carbonates, a structural and sedimentological analysis of sub‐seismic‐scale mass‐transport deposits has been undertaken on the eastern margin of the Apulian carbonate platform in the Gargano Promontory, south‐east Italy. These mass‐transport deposits, that locally comprise a large proportion (50 to 60%) of the base of slope to basinal sediments of the Cretaceous Maiolica Formation, typically display a vertically bipartite character, including debrites and slump deposits of varying volume ratios. A range of brittle and ductile deformation styles developed within distinct bed packages, together with the presence of both chert clasts, folded chert layers and spherical chert nodules, suggest that sediments were at different stages of lithification prior to downslope movement associated with mass‐transport deposits. This study helps elucidate the emplacement processes, frequency and character of subseismic‐scale mass‐transport deposits within the basinal carbonate environment, and thereby reduces the uncertainties in the characterization of subsurface carbonate geofluid reservoirs.     

Progradation geometries of carbonate platforms: examples from the Triassic of the Dolomites, northern Italy

Various types of progradation of Triassic carbonate platforms are described from the Dolomites of the Southern Alps. The internal and external geometric relationships are exposed in spectacular natural sections and, moreover, their scale (500–1000 m of thickness) is such that they can be compared with features found in seismic profiles. The different types of progradation are controlled by a number of factors which, normally, interact with each other. These factors include: rate of basinal sedimentation, rate of subsidence, width of the platform, depth of the surrounding basin and eustatic variations of sea-level. Progradation is not a continuous process but episodic. Moments of massive debris input, during which the platform advances, alternate with long periods of negligible progradation, during which basinal sediments accrete and onlap the toe of slope. Upper boundary relationships of the prograding platforms include offlap, toplap and erosional truncation. Lower boundary relationships are horizontal, climbing and descending progradations. A variety of phenomena and circumstances have caused the cessation of progradation of the Triassic platforms. They include volcanism, collapse of margins, drowning (rapid relative rise of sea-level), subaerial exposure (relative fall of sea-level) and, probably, a natural decay of the system. In the Triassic of the Dolomites, two main progradation models can be put forward: in the Ladinian model, progradation took place simultaneously with aggradation (relative rise of sea-level), whereas the characteristic feature of the Carnian model is toplap (relative stillstand of sea-level).     

Lower carboniferous (Dinantian) stratigraphy and structure in the Kingscourt Outlier,Ireland

Logging of 55 recent boreholes, together with remapping, has resulted in a fundamental reassessment of the stratigraphy and sedimentology of the Dinantian Kingscourt Outlier. Despite the present isolated position of the outlier within the Longford-Down Massif, the Kingscourt rocks are an integral part of the Dublin Basin succession. The newly defined Ardagh Platform marks the most northerly limit to basinal sedimentation in the Dinantian Dublin Basin. The Courceyan is a typical but thinner, north Dublin Basin succession with two new formal units: the Rockfield Sandstone Member and the Kilbride Formation. The latter, a coarse-grained, well washed limestone of latest Courceyan to early Chadian (late Tournaisian) age is the shallow water equivalent of the Feltrim Formation (Waulsortian facies), which is absent in the outlier. The Courceyan interval in the north of the outlier is markedly attenuated. In the succeeding Chadian-Brigantian interval basinal facies predominate in the south, but on the Ardagh Platform an almost complete coeval Viséan shallow water sequence is found. A new platform unit (Deer Park Formation) of latest Asbian to Brigantian age is defined in the Ardagh area. The Dee Member (Chadian) is newly defined for the lower part of the basinal Tober Colleen Formation and the Altmush Shale Member is formally defined for the upper part of the Loughshinny Formation. Two major structures dominate the Kingscourt Outlier: the NE-SW trending Moynalty Syncline in the south and the N-S trending Kingscourt Fault. Both are Hercynian structures, but probably represent reactivated Caledonide basement-controlled structures. Dinantian syn-depositional faulting is indicated in both the Courceyan (‘Kingscourt Sag’) and Chadian-Asbian. The latter period of faulting in the Ardagh area separates platform facies in the north from basinal facies to the south. In the late Asbian, platform facies with carbonate build-ups prograded south into the basin as far south as Nobber, but in the latest Asbian to Brigantian, basinal facies extended northwards over the collapsed platform margin.     

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.     

四川盆地及其邻区中上寒武统洗象池群沉积相与沉积模式特征研究

近年来,我国海相碳酸盐岩油气勘探正处于大发现期,其中四川盆地龙王庙组气藏的突破,使得寒武系碳酸盐岩储层越来越获得研究者的重视。洗象池群作为寒武系有利储集层段目前还处于勘探初期,地质研究程度相对滞后。为此,基于前人的研究成果,通过综合分析露头、钻井、地震和测井等资料,研究了四川盆地及邻区洗象池群沉积相、沉积体系模式,编制岩相古地理图,建立洗象池群“三滩夹两凹”沉积模式,指出了该区下一步天然气勘探的方向。研究结果表明:(1)四川盆地洗象池群呈现碳酸盐岩镶边台地的古地理格局,发育蒸发台地、局限台地、半局限台地、台地边缘、斜坡盆地等5种沉积相;(2)建立了洗象池群“三滩夹两凹”沉积模式,其中一条为台地边缘颗粒滩,分布于该盆地东缘,另外两条为台内颗粒滩,分布于局限台地相的东西两侧,分属局限台地相和半局限台地相;(3)台内颗粒滩发育主要受古地貌及高频海平面升降变化所控;台地边缘颗粒滩主要分布于盆地的东缘,发育受沉积古地貌坡折控制。结论认为:台内颗粒滩和台地边缘滩储层质量好,是天然气勘探的重要领域;洗象池群“三滩夹两凹”沉积模式和颗粒滩带分布的新认识,对古老地层的沉积体系研究具有重要的理论意义。     

Geology of the Dolomites

The Dolomites region is a spectacularly exposed portion of the Southern Alps, a northern Italian chain derived from the comparatively gentle deformation of the Tethyan passive continental margin of Adria. The regionhad an active Permo-Jurassic tectono-magmatic evolu-tion, leading from Permian magmatism, through a Mid-die Triassic episode offast subsidence and volcanism, to the Jurassic oceanic break-up. Although the sedimentary succession ranges in age from Middle Permian to Creta-ceous, the geological landscape is largely dominated by the majestic Triassic carbonates, making the area a clas-sical one for the early Mesozoic stratigraphy. Particu-larly noteworthy are the Anisian to Carnian carbonate platforms, recording an evolution from regional muddy banks to isolated high-relief builduos. The hlline of the various basins and the development of a last generation of regional peritidal platform followed. The carbonate platforms of the Dolomites bear witness to a remarkable set of changes in the carbonate production and to signif-icant palaeoclimatic fluctuations,from arid to moist con-difions and vice versa; a great range of margin and slope depositional styles is therefore recorded. Alpine tectonic shortening strongly affected the area, with a first Eocenede formation, followed by later Neogene overthrusting and strike-slip movements.     

Architecture and depositional development of the Eocene deep‐marine Morillo and Coscojuela Formations,Aínsa Basin,Spain

The Aínsa Basin of northern Spain contains a deep‐marine succession comprising up to 24 sandstone bodies separated by thick marl‐rich units. A detailed analysis of nine outcrops (>900 m of sediment profiles) from the Morillo Formation of the San Vicente Group, from the upper part of the basin succession, has enabled a reappraisal of the unit. Within the Morillo Formation, sediment transport was to the NW, and a range of environments are recognized including channels, lobes and pelagic deposits. The overlying Coscojuela Formation, which partly cuts into the Morillo Formation, shows W‐directed palaeocurrents in its proximal reaches, with flows being deflected to the N along an adjacent slope. Destabilization of the adjacent carbonate platform resulted in a significant input of carbonate material into the flow. The final phases of sedimentation within the Aínsa Basin were more complex than previously suspected, probably as a result of a combination of factors, including tectonic activity, resulting in basin narrowing due to anticlinal growth, as well as encroachment and/or destabilization of the adjacent regional carbonate platforms. Copyright © 2013 John Wiley & Sons, Ltd.     

新化—城步地区泥盆纪沉积相及台盆演化

新化—城步地区泥盆纪沉积相类型较丰富,可划分7个相组、17个相。最突出的特征是在两个碳酸盐台地之间发育有一较深水的盆地,即台盆。西部的碳酸盐台地与台盆之间的边缘无明显的陡坡,属于J.F.Read所称的碳酸盐等斜缓坡。区内沉积相,尤其是在棋梓桥晚期——佘田桥期,大体上呈北北东向展布。构成这一特殊沉积格局的主要原因是该区沉积相受加里东运动期间形成的基底断裂控制。区内台盆演化可分为初始台盆、台盆扩展、台盆稳定、台盆最大扩展、台盆收缩变浅、台盆残余凹陷等六个阶段。     

Organic Carbon Isotope Geochemistry of the Neoproterozoic Doushantuo Formation, South China

The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South China, documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata, exquisitely preserved fossils have been discovered： the Weng＇an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng＇an section of a carbonate platform （shelf of the Yangtze Platform, Guizhou Province） from the Songtao section and Nanming section of a transition belt （slope of the Yangtze Platform, Guizhou Province） and from the Yanwutan section （basin area of the Yangtze Platform, Hunan Province）. Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon （mean δ^13Corg = -35.0‰） from the uppermost Nantuo Formation are followed by an overall increase in δ^13C up-section. Carbon isotope values vary between -9.9‰ and 3.6‰ for carbonate and between -35.6‰ and -21.5‰ for organic carbon, respectively. Heavier δ^13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity （such as the Weng＇an biota）. The δ^13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin, reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.     

Storm-influenced siliciclastic and carbonate ramp deposits, the Lower Ordovician Dumugol Formation, South Korea

The Dumugol Formation (Lower Ordovician) in the southern part of the Baegunsan syncline, South Korea, contains mixed siliciclastic and carbonate ramp deposits. The ramp sediments were frequently influenced by storm events resulting in tempestites of sandstone-mudstone couplets, bioclastic grainstones to packstones, flat-pebble conglomerates, a skeletal lag layer and laminated calcisiltites. All tempestites are characterized by an erosive to sharp base, poor grading and a transitional upper boundary. The difference in lithology of tempestites appears to have been controlled by the nature of substrates and by proximality. For example, laminated calcisiltites have developed on the shallow carbonate ramp, flat-pebble conglomerates are closely associated with nodular limestones on shallow and deep ramps, and thin skeletal lag layers from fossiliferous argillaceous sediments formed in a basinal setting. The stratigraphic succession of the Dumugol Formation represents an initial transgression followed by a regression. The vertical facies change records the transition from a shallow siliciclastic ramp to a deep carbonate ramp, to a basin, shallowing to a deep carbonate ramp, and to a shallow carbonate ramp. Storm effects are mostly well preserved in shallow to deep ramp deposits.     

安徽巢湖二叠系栖霞组碳酸盐岩斜坡沉积

长期以来,人们均认为下扬子地区广泛发育的栖霞组碳酸盐岩属于浅海碳酸盐岩台地沉积。但以巢湖地区为例研究表明,栖霞组主要为碳酸盐岩斜坡沉积。碳酸盐岩碎屑流沉积物形成了臭灰岩段和顶部灰岩段的层状石灰砾岩,分布于斜坡上部;等深流沉积物形成了上、下硅质层段的砂屑硅质粒泥灰岩,主要分布于斜坡下部。而上、下硅质层段中的钙、硅质页 (泥 )岩属于斜坡远端和盆地沉积;唯有本部灰岩段可能属于浅海碳酸盐岩台地沉积。这一认识不仅突破了传统观念,而且有助于重新认识下扬子板块二叠纪的古地理特征和盆地构造演化。     

峡东地区寒武系岩石学、沉积学特征及储集性

研究区位于扬子板块中段,地层发育齐全,构造层次清晰,交通方便(图1),因此早在本世纪初就有不少地质学家涉足此地(李四光、赵亚曾,1924)。该区地质研究程度较高,尤其在古生物地层学研究方面成果甚丰,其中前寒武系和寒武系的界线剖面已被国际地科联确定为该界线层型的主要参考点;寒武系和奥陶系亦被确定为我国南方寒武系、奥陶系的主要标准剖面;奥陶系与志留系界线剖面正在争取成为国际层型剖面。寒武系的研究有     

Chadian faunas and flora from dyserth: Depositional environments and palaeogeographic setting of Viséan strata in northeast wales

New floral and faunal data from the oldest Dinantian limestones (Foel Formation) in the Dyserth area, suggest that these sediments are of Chadian age, rather than the Asbian age concluded by earlier workers. The basal late Chadian limestones rest conformably on Dinantian Basement Beds of ?Chadian age or older. The initial inundation of St. George's Land occurred during Chadian times, when shallow-water marine limestones accumulated in the Dyserth area and further to the south, together with terrestrially derived siliciclastics, containing drifted plant fragments. Periodically, a restricted hypersaline lagoonal environment was established but an open marine, neritic environment with abundant stenohaline fauna prevailed in this area. These Chadian sediments accumulated on the proximal part of a carbonate ramp and are presumed to have passed laterally downslope into deeper water basinal facies with Waulsortian buildups of the Irish Sea Basin. In the later Arundian, a carbonate ramp–to–platform transition occurred, with widespread deposition of shallow-water carbonates. In the Asbian this platform developed a rimmed margin, with buildups forming a linear belt between platform and basin. An almost complete Chadian to Brigantian Lower Carboniferous sequence can now be recognized in North Wales. This succession is comparable with the shelf succession in south Cumbria on the northern margin of the Irish Sea Basin.     

安徽泾县-南陵地区二叠纪沉积相与沉积环境分析

安徽泾县—南陵地区二叠系较发育,主要由碳酸盐岩、硅质岩和碎屑岩组成。二叠系船山组为浅水碳酸盐台地相;栖霞组底部碎屑岩段是滨海沼泽相,臭灰岩段和上、下富硅质灰岩段是水体较深的斜坡中部相,中部灰岩段是浅水开阔碳酸盐台地相,而顶部灰岩段是缓斜坡上部相;孤峰组和大隆组是缺氧滞流环境下的深水盆地至盆地边缘相;武穴组是碳酸盐台地相,银屏组属于滨海潟湖相;龙潭组是一套海陆交互的三角洲相沉积,包括从三角洲前缘到三角洲平原两个亚相,而泾县昌桥龙潭组顶部发育的生物碎屑灰岩属于开阔碳酸盐台地相。纵观二叠纪有三次大的海侵和两次大的海退旋回,海侵时间分别是:栖霞早期、茅口早期和长兴早期,海退时间分别是:紫松—隆林期末和茅口期末,其中栖霞期还包含两个海侵海退的亚旋回。