Facies sequences of a semi-arid closed basin: the Lower Jurassic East Berlin Formation of the Hartford Basin, New England, U.S.A.

The Lower Jurassic East Berlin Formation exposed in the centre of the Hartford Basin can be divided into six facies: (1) laminated black mudstone is composed of very finely-laminated, organic-bearing clay-stone with common millimetre-scale lenses of dolomitic siltstone; (2) planar laminated mudstone is commonly mudcracked and composed of thickly-laminated, red, green or grey mudstone with common centimetre-scale lenses of sandstones; (3) disrupted mudstone has a complex, desiccation-cracked fabric; (4) planar- and large-scale trough cross-stratified sandstones are composed of moderately well-sorted medium- to coarse-grained arkoses; (5) small-scale, cross-stratified silty sandstones with common climbing-ripple structure; and (6) interbedded sandstones and mudstones which commonly carry desiccation cracks. Mudstone facies are organized into repetitive, metre-scale facies sequences which change gradationally upwards from laminated black mudstones to planar-laminated mudstones to disrupted mudstones. Facies sequences have sharp tops and bottoms and record increasing desiccation upwards. There are 15 such cycles in the upper 100 m of the formation in central Connecticut. They record long periods of dry playa mudflat aggradation punctuated by the rapid expansion and contraction of perennial lakes. The sandy facies occur as single, decimetre-scale sedimentation units or as two or more stacked sedimentation units up to 1 m thick. These record sheet floods across ephemeral floodplains.     

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.     

Microfacies, diagenesis, and depositional environments of the Tertiary carbonates of Usfan Formation in Haddat Ash Sham area, Western Arabian Shield, Saudi Arabia

The studied carbonates are present within the middle part of the Tertiary siliciclastic dominated succession in Haddat Ash Sham area. This succession consists of conglomerates, sandstones, siltstones, mudstones, and ironstones arranged in upward coarsening and fining cycles of intermittent depositional environments ranging from fluvial coastal plain to shallow marine. The carbonates represent deposition in slightly restricted depositional environments during periods of very low clastic input. The studied two carbonate sections show a pronounced lateral and vertical changes from predominantly dolostones in the west to mixed dolostones and limestones in the east. Both sections began by egg yellow dolomitic lime mudstones and fine crystalline dolomite which indicate the formation of dolomite by late depositional to early diagenetic recrystallization of precursor Fe and Mg lime mud. During this time period, the western part of the study area continues in the deposition of Fe and Mg lime mud in slightly restricted depositional environments and formation of interbedded fine and coarse crystalline dolostones in coarsening-upward cycles. In the eastern part, the depositional environments become deeper and more circulated with short-lived periods of fluctuation in sea level and hence the deposition of foraminiferal wackestone, bioclastic packstones, and bioclastic rudstone in coarsening and shallowing-upward cycles. Both the western and eastern parts of the study area are terminated by characteristic yellow coarse crystalline phosphatic dolomite which indicate ultimate stages of shoaling and increasing the level and concentration of phosphorous in the restricted water and hence the formation of in situ and reworked phosphatic components. The diagenetic processes affected the dolostones and limestones microfacies associations include: dolomitization of Fe and Mg-rich lime mud, hematitization, calcitization, gypsification, and phosphatization of dolomite. Neophormation and recrystallization of micritic matrix and micritic intraclasts as well as shell fragments are the main diagenetic processes affected the limestones.     

Lithofacies and environments of Bed I,Olduvai Gorge,Tanzania

Bed I in Olduvai Gorge spans the interval from about 1.7 to 2.0 m.y.a., and all evidences of hominid activity at Olduvai are within the latter half of this period. Bed I was deposited in a closed basin approximately 25 km in average diameter, and it can be subdivided into five lithologically different but partly time-equivalent rock assemblages, or lithologic facies, each of which was deposited in the same geographic environment or closely related series of environments. These lithofacies comprise lake deposits, lake-margin deposits, alluvial-fan deposits, alluvial-plain deposits, and lava flows.Alluvial-plain deposits form the lowermost part of Bed I, and they presumably interfinger northeastward with lake deposits in an area not now exposed. Discharge of the lavas diplaced the lake westward to a position it occupied through the latter half of the deposition of Bed I. The lake fluctuated greatly in salinity, level, and extent, and at times of low level it was highly saline and generally ranged between 7 and 10 km in average diameter. At times of high level it was as much as 15 km in diameter and was relatively fresh, at least along its southeastern margin. The lake-margin deposits accumulated on the zone of relatively flat terrain that was flooded at times of high level. Lake-margin deposits interfinger eastward with deposits of an alluvial fan of pyroclastic materials produced in an explosive phase of the volcano Olmoti. The climate at the time of Bed I was relatively dry although somewhat wetter than the present climate in the same region today.     

Depositional environments and diagenesis in Lake Parakeelya: a Cambrian alkaline playa from the Officer Basin, South Australia

Laminated and desiccated siliceous dolostones, dolomitic mudstones and dolomitic sandstones in the Cambrian Parakeelya Alkali Member of the Observatory Hill Formation accumulated in an alkaline playa. Four facies are recognized (from lake centre to lake edge): lake, saline mudflat, dry mudflat and sandflat facies. The facies occur in cycles. Cycles of tens of metres thickness record the gradual expansion and contraction of the playa. Superimposed smaller cycles of tens of centimetres thickness record minor oscillations in the position of the strandline in a shallow lake. The dominance of saline mudflat, dry mudflat and sandflat facies indicates that the lake was rimmed by broad flat areas with negligible relief. The high δ¹⁸O values of primary and penecontemporaneous diagenetic carbonates of +24 to +28‰ (SMOW) indicate strong evaporation of ground and surface waters within the lake system. Calcite pseudomorphs of the sodium carbonate minerals trona and shortite have δ¹⁸O values between + 19 and + 22.5‰, and contain fluid inclusions with variable salinites and homogenization temperatures up to around 110°C. This suggests that the euhedral alkaline evaporites were dissolved by heated waters; calcite pseudomorphs then precipitated from a mixed solution formed by the interaction of these incoming fluids with the relatively saline interstitial brines. The sodium bicarbonate solutions formed by dissolution of the evaporites would have been dispersed by the basinal brines so that despite the closed drainage, further groundwater concentration did not take place.     

Magnesite diagenesis in redbeds: a case study from the Permian of the Northern Calcareous Alps (Tyrol, Austria)

The Upper Permian Gröden Formation of the Northern Calcareous Alps (Austria) is composed of alluvial fan and playa lake sediments that were deposited in intramontane basins. A conspicuous feature of these redbeds is the abundance of magnesite in the form of nodules and discrete layers in mudstones as well as intergranular cement in sandstones. Sedimentological observations indicate that the bulk of these carbonates formed during early diagenesis and were probably syndepositional. Petrographically, most magnesites consist of micrite or, less commonly, microspar. An early non-ferroan magnesite is post-dated by later stage ferroan magnesites. Nodules consisting of recrystallized, sparry magnesite were observed only at one location. The general absence of relics of a non-magnesite precursor mineral and the occurrence of shrinkage features suggest that the fine grained magnesites formed by transformation of a hydrated magnesium carbonate mineral, e.g. hydromagnesite. Carbon, oxygen, sulphur and strontium isotope ratios in conjunction with sedimentological criteria support a model of (hydro)magnesite precipitation in an inland playa lake system, which was fed by run-off from the surrounding hinterland. The scarcity of evaporites and the dominance of magnesite over calcite and dolomite suggest that the playa lake brines were low in sulphate and had high Mg/Ca ratios. The source for the high magnesium concentrations is thought to be the weathering of Devonian dolostones and associated massive magnesite deposits in the catchment area.     

Sedimentary facies, depositional environments and palaeogeographic evolution of the Neogene Denizli Basin, SW Anatolia, Turkey

The Denizli Basin (southwestern Anatolia, Turkey) contains a record of environmental changes dating since the Early Miocene. Detailed facies analysis of the Neogene formations in this half-graben enables us to document successive depositional regimes and palaeogeographic settings. Sedimentation commenced in the Early Miocene with the deposition of alluvial-fan and fluvial facies (K?z?lburun Formation). At this stage, alluvial fans sourced from elevated areas to the south prograded towards the basin centre. The Middle Miocene time saw the establishment of marginal lacustrine and wetland environments followed by the development of a shallow lake (Sazak Formation). The uppermost part of this unit consists of evaporitic saline lake and saline mudflat facies that grade upward into brackish lacustrine deposits of Late Miocene-Pliocene age (Kolankaya Formation). The lake became shallower at the end of the Pliocene time, as is indicated by expansion shoreface/foreshore facies. In the Early Quaternary, the Denizli Basin was transformed into a graben by the activation of ESE-trending normal faults. Alluvial fans were active at the basin margins, whereas a meandering river system occupied the basin central part.Oxygen isotope data from carbonates in the successive formations show an alternation of wetter climatic periods, when fresh water settings predominated, and very arid periods, when the basin hosted brackish to hypersaline lakes. The Neogene sedimentation was controlled by an active, ESE-trending major normal fault along the basin's southern margin and by climatically induced lake-level changes. The deposition was more or less continuous from the Early Miocene to Late Pliocene time, with local unconformities developed only in the uppermost part of the basin-fill succession. The unconformable base of the overlying Quaternary deposits reflects the basin's transformation from a half-graben into a graben system.     

辽东湾西北部A区沙一、二段钻井层序地层和沉积相分析

利用辽东湾西北部A区6口井的录井、测井、岩心资料,通过细致的层序地层学及沉积学分析,将研究层段自下而上划分为SQs2和SQs1两个三级层序,每个层序均可划分出湖扩体系域(TST)和高位体系域(HST),并识别出三个层序边界和两个最大湖泛面,自下而上分别为SQs2底界面SBs2、最大湖泛面mfss2、SQs1底界面SBs1、最大湖泛面mfss1、SQs1顶界面SBd3。钻井揭示沙二段主要为砂岩、含砾砂岩,以粗碎屑岩发育为特征;沙一段主要为泥岩和白云岩,以泥岩发育为主要特征。研究区沉积相为湖泊相,滨浅湖亚相,微相发育泥滩、混合滩、砂质滩坝和钙质浅滩。低突起及其斜坡地区,在SQs2以混合滩沉积为主,在SQs1以泥滩沉积为主;陡坡地区,在SQs2发育砂质滩坝,在SQs1发育钙质浅滩。SQs2砂岩发育层段和SQs1的生物白云岩发育层段为良好的储层。     

Stream-dominated alluvial fan and lacustrine depositional systems in Cenozoic strike-slip basins, Denali fault system, Yukon Territory, Canada

Ancient stream-dominated (‘wet’) alluvial fan deposits have received far less attention in the literature than their arid/semi-arid counterparts. The Cenozoic basin fills along the Denali fault system of the northwestern Canadian Cordillera provide excellent examples of stream-dominated alluvial fan deposits because they developed during the Eocene-Oligocene temperate climatic regime in an active strike-slip orogen. The Amphitheatre Formation filled several strike-slip basins in Yukon Territory and consists of up to 1200 m of coarse siliciclastic rocks and coal. Detailed facies analysis, conglomerate: sandstone percentages (C:S), maximum particle size (MPS) distribution, and palaeocurrent analysis of the Amphitheatre Formation in two of these strike-slip basins document the transition from proximal, to middle, to distal and fringing environments within ancient stream-dominated alluvial-fan systems. Proximal fan deposits in the Bates Lake Basin are characterized by disorganized, clast-supported, boulder conglomerate and minor matrix(mud)-supported conglomerate. Proximal facies are located along the faulted basin margins in areas where C:S = 80 to 100 and where the average MPS ranges from 30 to 60 cm. Proximal fan deposits grade into middle fan, channelized, well organized cobble conglomerates that form upward fining sequences, with an average thickness of 7 m. Middle fan deposits grade basinward into well-sorted, laterally continuous beds of normally graded sandstone interbedded with trough cross-stratified sandstone. These distal fan deposits are characteristic of areas where C:S = 20 to 40 and where the average MPS ranges from 5 to 15 cm. Fan fringe deposits consist of lacustrine and axial fluvial facies. Palaeogeographic reconstruction of the Bates Lake Basin indicates that alluvial-fan sedimentation was concentrated in three parts of the basin. The largest alluvial-fan system abutted the strike-slip Duke River fault, and prograded westward across the axis of the basin. Two smaller, coarser grained fans prograded syntaxially northward from the normal-faulted southern basin margin. Facies analysis of the Burwash Basin indicates a similar transition from proximal to distal, stream-dominated alluvial fan environments, but with several key differences. Middle-fan deposits in the Burwash Basin define upward coarsening sequences 50 to 60 m thick composed of fine-grained lithofacies and coal in the lower part, trough cross-stratified sandstone in the middle, and conglomerate in the upper part of the sequence. Upward-coarsening sequences, 90–140 m thick, also are common in the fan fringe lacustrine deposits. These sequences coarsen upward from mudstone, through fine grained, ripple-laminated sandstone, to coarse grained trough cross-stratified sandstone. The upward-coarsening sequences are basinwide, facies independent, and probably represent progradation of stream-dominated alluvial-fan depositional systems. Coal distribution in the Amphitheatre Formation is closely coupled with predominant depositional processes on stream-dominated alluvial fans. The thickest coal seams occur in the most proximal part of the basin fill and in marginal lacustrine deposits. Coal development in the intervening middle and distal fan areas was suppressed by the high frequency of unconfined flow events and lateral channel mobility.     

四川会理—会东及邻区中元古界昆阳群沉积特征及演化

四川会理 会东及邻区中元古界昆阳群 ,由下而上可分为力马河组、凤山营组和天宝山组 ,与古元古界河口群为不整合接触 ,其代表年龄值为 1 70 0± 1 0 0Ma～ 1 2 0 0± 1 0 0Ma。对这套地层的沉积学研究 ,前人涉及甚少。笔者在野外考察和室内分析的基础上 ,对其沉积相和沉积环境进行了详细的研究。初步认为研究区的中元古界昆阳群可分为 7种沉积相 ,进而探讨了该区的沉积演化历史。     

A sedimentological and stable isotopic study of travertines and associated sediments within Upper Triassic lacustrine limestones, South Wales, UK

The Upper Triassic in South Wales is composed of up to 100 m of red, dolomitic mudstones of the Mercia Mudstone Group which overlie and are laterally equivalent to basin margin coarse clastic deposits. In the Sully Island and Dinas Powys areas, a series of carbonate deposits was laid down within small basins adjacent to the main Bristol Channel Basin. The rocks consist of dolomites containing replaced evaporites, overlain by perilittoral freshwater limestones. The limestones are fenestral intrasparites and contain abundant pedogenic and stromatolitic horizons, as well as locally developed travertines. Evidence for vadose diagenesis within the limestones is common. The travertines consist of sheets of fibrous calcite (flowstone) associated with pisoids and flöe calcite. Most of the travertines consist of single sheets several millimetres in thickness although ‘mounds’up to 1 m in height and 5 m in diameter are also present. The topmost metre of the limestones, which has been dolomitized, is deformed into tepee and megapolygonal structures. The carbon and oxygen stable isotopic composition of the limestones suggests that they were precipitated in low salinity waters. Successive samples from individual bands of flowstone show a covariance of δ¹⁸C and δ¹³C which is consistent with the mixing of resurgent groundwaters with pools of more evolved waters at the surface. The sedimentological and geochemical evidence suggests that the limestones were deposited in a small, enclosed basin fed by upwelling meteoric groundwaters in an environment distinct from that in which the laterally equivalent gypsiferous red mudstones were formed.     

湖缘峡谷及其含油性

在陆相断陷湖盆陡坡带,控盆断裂的剧烈活动导致在相对较短时期内形成盆地的快速沉降,与湖盆边缘地形形成巨大高差。沿此边缘,经过早期阵发性洪水及河流的强烈下蚀,并不断向源侵蚀,在古断面上形成宽达数km,深达上km的深切谷,称之为湖缘峡谷。东营凹陷北部陡坡带的Y921峡谷即为湖缘峡谷,其现今形态为长7000m、宽3500m、深3500m、剖面呈“U”型的特征。古构造及古生物分析认为,在古新世至渐新世时期,陈南断层剧烈活动,使断层两侧形成较大的高差,在干旱、阵发性洪水侵蚀下逐渐形成Y921峡谷,并在其底部形成侵蚀面。孢粉分析认为,仅沙四上段沉积时期就有近1000m的高差。后期,随湖平面上升,峡谷逐渐充填了古近系沙河街组四段、三段和部分二段地层,主要为辫状河粗碎屑砂砾岩、扇三角洲相交错层理砂岩和滨浅湖相泥岩、粉砂岩。这种峡谷的特点是短、宽、深,其充填模式主要为辫状河-扇三角洲-湖泊相沉积体系。由于峡谷前缘为深湖相泥岩作为生油岩,陈南断层和峡谷内的冲刷面作为油气运移通道,峡谷内砂砾岩作为储层,因此在峡谷内形成了多种非构造油气藏类型。     

Desert sand plain and sabkha deposits from the Bunter Sandstone Formation (L. Triassic) at the northern margin of the German Basin

Facies studies of well cores from the Bunter Sandstone Formation in the Tønder area, Denmark indicate, that the formation is composed of two desert sand plain sequences associated with sabkha and inland basin (lake?) mudstones. The lower desert sand plain sequence consists of subaerial sand flat deposits overlain by aeolian sand sheet and dune facies topped by interbedded aeolian and ephemeral river deposits. The upper desert sand plain sequence consists of ephemeral river deposits partly interbedded with and overlain by sabkha and inland basin mudstones. Two shoreline sandstones occur in the uppermost part. Both sequences are interpreted mainly in terms of tectonic subsidence of the basin and related upheavals of the source regions. The lower sequence represents a rather continuous progradation of the desert sand plain followed by a rapid transgression of the waters from the inland basin. The upper sequence represents brief periods of fluvial progradation followed by a gradual retreat of the river plain. The most distal part of the sand plain was finally reworked by weak wave-action.     

Alluvial fan–lacustrine association in the fault tip end of a half-graben, northern Triassic Cuyo basin, western Argentina

The Triassic deposits of Cerro Puntudo in the San Juan province of western Argentina constitute the northernmost exposures of the northern portion of the nonmarine Cuyo rift basin, also known as the Las Peñas-Tamberías half-graben. The local column, with an exposed thickness of approximately 400 m, consists of abundant basal and topmost coarse alluvial fan conglomerates and breccias (facies associations I and II) and a relatively thin (approximately 50 m) intervening sequence of marginal, shallow lacustrine deposits characterized by stromatolitic (domal) limestones, tuffaceous mudstones, and fine-grained sandstones (facies association III). Subaerial exposure in the lacustrine deposits is evidenced by desiccation cracks and brecciation. A very thin (0–6 m), laterally, discontinuous succession of lacustrine deposits with similar characteristics is interbedded with the basal conglomerates. Laterally, this lacustrine interval was eroded by overlying conglomerates. The basal conglomerates commonly show crude normal grading, faint cross-bedding, and b-axis clast imbrication. The predominance of coarse deposits and paleocurrents from NW to SE, indicative of an axial flow pattern, suggest that these exposures correspond to the northern end of the Cuyo basin, which is characterized by a shallow, alluvial fan-encased, carbonate-rich lake margin. This lacustrine interval can be correlated with the thicker lacustrine section exposed to the south at Quebrada del Tigre and Ciénaga Larga along the border fault margin of a nonmarine half-graben. The correlation with these sections suggests that the Cerro Puntudo lacustrine deposits are the shallowest equivalent of more profundal, organic-rich lacustrine sediments exposed in the deepest segment of the border fault margin. These thickness and facies variations are the result of differential subsidence along the border fault margin between the low accommodation, fault tip end represented by the Cerro Puntudo section and the high accommodation, central segment located to the south.     

羌塘盆地隆鄂尼-鄂斯玛古油藏带中侏罗统布曲组岩相古地理研究

羌塘盆地隆鄂尼-鄂斯玛古油藏带中侏罗统布曲组含油白云岩带主要由潮坪相及潮下浅滩相颗粒灰岩和藻纹层白云岩、颗粒白云岩组成。藻纹层白云岩与颗粒灰岩组成旋回性沉积,发育藻纹层构造、鸟眼构造;含油白云岩带之间为潟湖相暗色微泥晶灰岩、泥质灰岩、介壳灰岩。采用优势相原则,横向对比分析编制隆起剥蚀区、潮坪相带、潟湖相带和潮下浅滩相带古地理展布,以及研究区生油岩与储集层及油气藏的空间分布,预测覆盖区可能存在残存油气藏分布区。     

用Y／Ho比值指示俄罗斯乌拉尔南部晶质菱镁矿矿床的成因

乌拉尔省南部赋存有两种类型的晶质菱镁矿:1)白云岩地层中的层状矿体;2)白云质灰岩中的透镜状矿体。晶质菱镁矿矿体位于Riphean系列中下层的白云岩中,而在上层的白云岩单元中缺失。这两种类型的菱镁矿可通过矿体形态、晶体大小、石英和白云石含量不同来进行区分。第一种类型的菱镁矿储量巨大,菱镁矿呈粗粒结构,晶体粒径>10mm(最大达150mm);一般来说,矿体与白云岩围岩界限清楚,这种类型矿床以产在Riphean序列下部为特征。第二种类型的菱镁矿由于菱镁矿矿体穿插进入到白云岩围岩中,矿体很不规则,菱镁矿晶体也相对较小(1-5mm),这种类型的矿体主要产在Riphean中部层位中。这两种矿体都显示了交代成因的特征。但这两种菱镁矿矿石在一些主量元素和稀土元素的分布上具有不同的特征:与第二种类型相比,第一种菱镁矿具有较低的FeO,CaO和SiO2含量,与白云岩围岩(La／Lu>1)相比,具La／Lu<1的轻稀土亏损特征。第二种菱镁矿稀土分馏度较低,在稀土分配方面与白云岩围岩有差别。本文还特别讨论了Y／Ho值的重要性,因为该比值在菱镁矿和围岩中的类似性使得划分菱镁矿形成中的热液和成岩交代过程成为可能。因此我们认为,第一种类型菱镁矿,如具有高Y／Ho比值的Satka和Bakal矿床的形成属于沉积盆地发育过程中的早期成岩阶段;第     

Jet-efflux deposits of a subaqueous ice-contact fan,glacial Lake Rinteln,northwestern Germany

The coarse-grained, ice-contact, Porta Subaqueous Fan/Delta Complex was deposited in glacial Lake Rinteln at the margin of the Saalian ice sheet that advanced south of the Weser Chains, NW Germany. The ice-proximal depositional system was up to 15 km long and 10 km wide. The present study deals with ice-proximal subaqueous fan deposits, which are interpreted as products of a subcritical plane-wall outflow jet that periodically passed into a supercritical jet with hydraulic jump. The proximal facies assemblage consists of the coarse, clast-supported gravelly deposits of a hyperconcentrated (high-density) effluent and of related cohesionless debris flows attributed to the conduit or immediate proximal jet outflow zone of flow establishment. The intermediate facies assemblage, attributed to the outflow jet proximal zone of flow transition, is dominated by normally graded and cross-stratified gravels with scour structures at their bases; these gravels were deposited by a high-density effluent capable of forming mouthbar-like features. These deposits pass downcurrent into an assemblage of planar parallel-stratified and planar and trough cross-stratified sands and pebbly sands (partially interpreted as antidunes), with abundant scour structures and intercalated layers of fine sand/silt and silty mud, attributed to the jet distal zone of flow transition. The distal facies assemblage consists of trough cross-stratified sands and pebbly sands, and is attributed to the outflow jet proximal zone of established flow. The sedimentary succession as a whole has wedge-shape geometry, with a gentle fan-shaped inclination of the bedding from the southeast to the southwest. Repeated vertical alternations of supercritical and subcritical deposits and muddy interlayers can be attributed to temporary fluctuations in the meltwater outflow, whereas the overall upward fining of the succession indicates a net decline of meltwater discharges.     

Quantifying climatic change through the last glacial–interglacial transition based on lake isotope palaeohydrology from central Turkey

Questions remain as to the nature of climatic change through the last glacial–interglacial transition in the eastern Mediterranean region, particularly the relative contribution of evaporation and precipitation to regional water balance. Here changes in oxygen isotope values through this time period from Eski Acıgöl, a crater lake in central Turkey, are investigated using hydrological and isotope mass balance models. These allow changes in evaporation and precipitation to be quantified and their relative importance evaluated. We show that it is the volumetric flux rate of water passing through the lake system and not the precipitation-to-evaporation ratio per se which controlled the stable isotope record in Eski Acıgöl. Early Holocene precipitation is shown to be much greater than that during both the latter part of the last glaciation and the present day. We test these calculated values against other records in the same region, firstly with other lake records in Anatolia, the Konya basin and Lake Van, and secondly with isotope-inferred palaeo-precipitation data from Soreq cave in Israel. This reveals a contrast between pre- and post-LGM precipitation values in Turkey (wetter and drier, respectively) and also suggests that during the last glacial–interglacial transition there was a more marked precipitation gradient than at present between northern/interior and southern/coastal parts of the eastern Mediterranean region.     

准噶尔盆地乌夏地区二叠系风城组云质岩类成因研究

准噶尔盆地乌夏地区风城组发育的云质岩类是一套特殊成因的、重要的油气储层。岩石学、扫描电镜能谱和稳定同 位素分析表明,发生白云岩化作用的母岩是火山凝灰物质,白云岩化的流体来自风城组干旱气候条件下形成的咸化滨浅湖 卤水以及下伏佳木河组和石炭系残留的富镁海水。凝灰岩中富含大量的斜长石,其中的富钙长石在二氧化碳参与下水解蚀变, 沉淀方解石（即方解石化）。后期富镁卤水渗滤早期形成的方解石,成岩交代形成白云岩。富镁流体运移受火山喷发产生的 热流驱动,产生热对流环。同时,乌夏断裂同生逆掩活动加快深层富镁流体上侵,并使流体在层间快速渗透、流动。构造 作用产生的裂缝或断裂对白云岩的形成及优质储层分布起到决定性控制作用。