四川盆地侏罗纪至早白垩世沉积旋回与构造隆升的关系

为弄清四川盆地在侏罗至白垩纪的演化及古气候特征, 对该时期的沉积相及生物特征进行了综合分析.研究证明, 侏罗纪至白垩纪四川盆地周边山系的构造活动可分为两个旋回.早、中侏罗世为第一个旋回, 晚侏罗至早白垩世为第二个旋回.每个旋回的早期多以湖相泥页岩、砂岩夹介壳灰岩的广泛发育为特征, 沉积物颗粒细、厚度较小, 反映出相对稳定的构造背景.晚期则以大套杂色的河流相砂泥岩、巨厚的河流相及洪冲积相砂泥岩、砂砾岩及砾岩的出现为特征, 且厚度巨大, 反映出盆地周边山系强烈的构造隆升.从沉积物及生物特征上分析, 第一个旋回期间, 四川盆地处在一个温暖湿润的环境之下, 而从第二个旋回开始, 总体则以潮湿、炎热的气候为特征      

The Maesan fan delta, Miocene Pohang Basin, SE Korea: architecture and depositional processes of a high-gradient fan-delta-fed slope system

The Maesan fan-delta-fed slope system in the Miocene Pohang Basin occurs between two Gilbert-type fan deltas. Detailed analysis of sedimentary facies and bed geometry reveals that the sequence is represented by 13 sedimentary facies. These facies can be organized into three facies associations, representing distinct depositional environments: alluvial fan (facies association I), steep-faced slope (facies association II), and basin plain (facies association III). Subaerial debris flows and dense, inertia-dominated currents were transformed into subaqueous sediment gravity flows in steep-faced slope environments. Further downslope, these flows were channelized and formed lobate conglomerate and sandstone bodies at the terminal edge of the channels (or chutes). Interchannel and interlobe areas were dominated by homogeneous mudstone and muddy sandstone, deposited by suspension settling of fine-grained materials. Part of the steep-faced slope deposits experienced large-scale slides and slumps. The chutes/channels, lobes and splays on the steep-faced slope of the Maesan system are similar to those in modern subaqueous coarse-grained fan-delta systems.     

The Cretaceous Uhangri Formation, SW Korea: lacustrine margin facies

The Uhangri Formation forms part of the Cretaceous sedimentary sequence deposited in a series of inland basins in the south-western Korean Peninsula. It comprises an approximately 400-m-thick epiclastic sequence of conglomerate, (gravelly) sandstone, cherty mudstone and black shale. The entire sequence can be represented by 16 distinctive sedimentary facies organized into four facies associations. Facies association I is characterized by thick homogeneous brownish siltstone, wedge-shaped disorganized conglomerate and thinly interlayered gravelly sandstone units. The siltstone units were formed by large floods submerging the alluvial fan fringe (floodplain), whereas the conglomerate and gravelly sandstone units were deposited by sheetfloods and debris flows. Facies association II consists of stratified conglomerate — gravelly sandstone, laminated sandstone and sandstone/siltstone couplets which form fining-upward cycles. Some facies units are low-angle trough cross-bedded and show broad channel geometries. This association represents subaqueous delta lobes fed by high- and low-concentration turbidity currents in the distal delta realm. Facies association III is characterized, by wedged conglomerate and gravelly sandstone facies with interfingered massive sandstone bounded by scoured bases. It represents a delta front where distributary channels and mouth bars are dominant. Facies association IV consists of laterally continuous sequence of laminated black shale, crudely stratified sandstone and convoluted sandstone/cherty mudstone. This facies association is suggestive of depositional processes controlled by chemical equilibrium resulting from an interaction between density inflows and lake water. The cherty mudstone resulted from inorganic precipitation from siliceous solution provided by acidic volcanism. The Uhangri sequence generally shows a fining-upward trend with a transition from alluvial fan fringe, coarse-grained subaqueous delta, to shallow lake. The retrogradation was probably due to continuous subsidence related to continental rifting in the oblique-slip mobile zone.     

Submarine fan facies of the Upper Cretaceous Great Valley sequence,northern and central California

The Upper Cretaceous part of the Great Valley Sequence provides a unique opportunity to study deep-marine sedimentation within an arc-trench gap. Facies analysis delineates submarine fan facies similar to those described from other ancient basins. Fan models and facies of Mutti and Ricci-Lucchi allow reconstruction of the following depositional environments: basin plain, outer fan, midfan, inner fan, and slope. Basin plain deposits are characterized by hemipelagic mudstone with randomly interbedded thin sandstone beds exhibiting distal turbidite characteristics. Outer fan deposits are characterized by regularly interbedded sandstone and mudstone, and commonly exhibit thickening-upward (negative) cycles that constitute depositional lobes. The sandstone occurs as proximal to distal turbidites without channeling. Midfan deposits are characterized by the predominance of coarse-grained, thick, channelized sandstone beds that commonly are amalgamated. Thinning-upward (positive) cycles and braided channelization also are common. Inner fan deposits are characterized by major channel-fill complexes (conglomerate, pebbly sandstone, and pebbly mudstone) enclosed in mudstone and siltstone. Positive cycles occur within these channel-fill complexes. Much of the fine-grained material consists of levee (overbank) deposits that are characterized by rhythmically interbedded thin mudstone and irregular sandstone beds with climbing and starved ripples. Slope deposits are characterized by mudstone with little interbedded sandstone; slumping and contortion of bedding is common. Progressions of fan facies associations can be described as retrogradational and progradational suites that correspond, respectively, to onlapping and offlapping relations in the basin. The paleoenvironments, fan facies associations, and tectonic setting of the Late Cretaceous fore-arc basin are similar to those of modern arc—trench systems.     

内蒙古银根盆地下白垩统沉积相

在对盆地周缘大量野外地质剖面详细测量的基础上结合室内分析，研究了银根盆地下白垩统巴音戈壁组的沉积相类型及其分布、演化。银根盆地下白垩统为典型的内陆湖盆沉积，形成了厚度达2000m以上的砂砾岩、泥岩夹碳酸盐岩、中基性火山岩，局部见油页岩和蒸发岩沉积，发育冲积扇、河流（以辫状河为主）、扇三角洲、三角洲、湖泊等沉积相类型。沉积体系的分布及演化主要受区域构造的影响，大致可以划分为三个沉积阶段，反映了断陷湖盆由发生、发展直至萎缩的一个完整旋回。早白垩世早期为湖盆初始断陷阶段，中期为强裂断陷阶段，晚期为湖盆萎缩阶段，每一沉积阶段在湖盆的不同部位发育了特定的沉积相类型及组合。     

鄂尔多斯盆地白垩系洛河组至环河华池组沉积相特征研究

通过研究构造背景、野外露头、岩性组合、沉积构造、古生物特征和测井曲线特征,分析和总结鄂尔多斯盆地白垩系洛河组至环河华池组沉积相、相带分布范围和沉积特征。洛河组主要沉积了冲积扇相、风成沉积相、辫状河相和沙漠相;而在环河华池组主要沉积了湖相、三角洲相、曲流河相及风成砂岩夹层。平面上沉积相带的变化规律性较强,由盆地边缘的冲积相、冲积—河流相砾岩向盆内渐变为河流相—滨浅湖—半深湖相泥岩。沉积特征受构造运动影响和沉积相带控制,洛河组是从山缘向盆地内砂岩厚度迅速变薄、尖灭;环河华池组岩性变化表现为北粗南细、东粗西细,在北部砂体呈现东薄西厚,东北向西南增厚,在南部砂体呈近南北向展布,东薄西厚,南薄北厚。     

江西象山地质公园丹霞地貌成景地层沉积环境分析

随着旅游地学的兴起和地学科普的需求,红层与丹霞地貌正在吸引着越来越多的关注。赣东北贵溪市象山地质公园发育以赤壁丹崖为特色的丹霞地貌景观,成景地层为上白垩统圭峰群河口组以砾岩为主的红色碎屑岩,冲刷侵蚀界面、粒序层理和交错层理等沉积构造发育,这为沉积环境分析提供了良好的判断标志。对该套成景地层进行厘米级实测,另外选择2处砾岩露头进行砾石统计以获取碎屑颗粒粒径、岩性、磨圆度和风化程度等信息。在实测厚度为40余米的地层柱状图上,识别出7种岩相类型,即正粒序砾岩、逆粒序砾岩、无沉积构造砾岩、平行层理砾岩、交错层理砾岩、聚集状砾岩、砂岩。砾石以中砾(2~5 cm)为主,磨圆度低,风化程度中等,成分以凝灰岩为主(58%~665%),其次为石英、花岗岩、砂岩。砾石成分和砾向分析结果说明,盆地南部早白垩世凝灰岩提供了主要的碎屑物质。根据野外实测红层剖面和砾石统计分析,认为成景地层为冲积扇沉积体系的产物。河口组红层沉积时期,盆地边缘断层活跃,间歇性强降雨事件导致冲积扇朵叶上洪泛河流搬运的沉积物供应充足,最终在剖面上形成砾岩和砂岩频繁互层及其厚度横向不稳定的现象。在中国东南地区晚白垩世总体干燥的古气候背景下,河口组中河流作用主导的冲积扇沉积体系可能指示了古气候向湿润转变,降水增加,相对丰富的水系将粗碎屑搬运到盆地区发生沉积。     

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.     

塔中地良奥陶系地层格架与沉积演化

塔里木中部地区奥陶系大致以Ⅰ号断裂为界分东北和西南两个地层分区,自下而上分白云岩段、灰岩段、泥质灰岩段、泥岩夹灰岩段、泥岩夹砂岩段、砂砾岩段、泥岩夹砂岩段、泥岩灰岩互层段和砂岩段等9个岩性段。早奥陶世,塔中地区以碳酸盐岩台地相为主,自西向东为局限台地相、开阔台地相、台地边缘相和深水斜坡相。中——晚奥陶世,塔中地区西部以混积陆架相为主,东部以深水斜坡相为主。中—晚奥陶世,塔中东部及塔东地区在构造上具弧后前陆盆地性质。中—上奥陶统地层完整地记录了该盆地从形成发展到消亡的过程,即早期为深水斜坡相复理石活动沉积,晚期演化为浅海陆架相稳定沉积。     

江西信江盆地白垩系沉积体系及其与丹霞地貌的关系

根据野外沉积层序、岩石学特征、古生物资料和地貌景观特征,本文对江西信江盆地白垩系沉积相进行了初步分析,首次探讨了沉积体系与丹霞地貌发育特征之间的内在联系。信江盆地白垩系主要发育4种沉积体系,即冲（洪）积、三角洲、湖泊和扇三角洲。早白垩世主要发育半深湖-深湖、扇三角洲相沉积,晚白垩世从盆地南缘到北缘大致为洪冲积相→辫状河流→三角洲→滨浅湖→三角洲→辫状河流→洪冲积相的展布方式。研究表明,该区丹霞地貌形成的物质基础主要是上白垩统冲积扇、辫状河相沉积产物,丹霞地貌的空间分布与盆地冲积扇、辫状河沉积相的平面展布具有较好的一致性,同时,沉积亚相、微相类型对丹霞地貌的发育起到一定的控制作用。     

江西龙虎山地区红层沉积相分析及与丹霞地貌发育关系研究——以仙人城景区为例

江西龙虎山地区以发育老年期丹霞地貌为特色,其成景地层为晚白垩世河口组红层,目前对这套红层的沉积相认识程度还比较低。龙虎山仙人城景区河口组出露厚度达百余米,沉积构造发育,且人工开凿的台阶可以直达山顶,这为沉积相分析提供了便利条件。根据野外露头岩性组成、沉积构造等特点,识别出6种岩相单元:无沉积构造砾岩、正粒序层理砾岩、逆粒序层理砾岩、平行层理砾岩、含砾砂岩、古土壤。砾石统计结果表明,砾石粒径范围主要为3~4 cm,最大可达12.5 cm,成分以紫红色凝灰岩为主,砂岩、花岗岩和石英次之、变质岩（主要是片岩）较少,磨圆度主要为次棱角状,其次为棱角状。在显微镜下,砂岩碎屑颗粒主要呈棱角-次棱角状,分选性较差,粒径为0.05~2.00 mm,主要由石英、长石和岩屑组成,总体具有结构和成分成熟度中等偏低的特点。野外露头宏观和室内显微分析结果表明,仙人城丹霞地貌的成景地层为河流主导的冲积扇沉积体系的产物。在龙虎山地区,丹霞地貌的空间分布与盆地冲积扇沉积相的平面展布具有较好的一致性,盆地边缘冲积扇成因的厚层砾岩为后期丹霞地貌的形成和演化提供了物质基础。      

Paleoenvironment of deposition of the Dupi Tila Formation,Lalmai Hills,Comilla, Bangladesh

The Dupi Tila Formation is composed of yellow to light brown medium to very fine moderately hard to loose sandstone, siltstone, silty clay, mudstone and shale with some conglomerates with clasts of petrified wood. The lithofacies of matrix supported conglomerate, trough cross bedded conglomerate, massive sandstone, trough cross bedded sandstone, planar cross bedded sandstone, ripple cross laminated sandstone-siltstone, flaser laminated sandstone-shale, lenticular laminated sandstone-siltstone-shale, parallel laminated sandstone-siltstone, wavy laminated shale, parallel laminated blue shale, and mudstone are delineated within this formation. Based on the grain size, sedimentary structures, water depth and genesis of individual facies, facies are grouped into three types of facies associations like (i) coarse-grained conglomerate facies association in relation to tractive current deposits of alluvial fan set up at the base of litho-succession (FAC), (ii) medium to fine-grained sandstone-siltstone-mudstone facies association or facies association in relation to strong tide (FAT) characterizing the middle part of litho-succession, (iii) very fine-grained sandstone-siltstone-mudstone facies association in relation to less frequent weak tide or heterolithic facies association (FAHL) characterizing upper part of litho-succession and shallow marine facies association (FASM) composing the uppermost litho-succession. Presence of gluconite indicates that the depositional environment was shallow to deep marine. The dominant paleoflow direction during the deposition of Dupi Tila Formation was toward southeast to southwestern direction. The rivers were of braided type at the piedmont alluvial depositional set up at the lower part, which later changed to estuarine-tidal flat type environmental set up in the middle part to upper part and paleo-environment was shallow marine in the uppermost part.     

Terrestrial-marine transition in the Cambrian rocks of Kangaroo Island, South Australia

The upper part of the Lower Cambrian succession in northeast Kangaroo Island comprises three interbedded facies associations. The fine-grained association is composed of siltstone, mudstone and minor sandstone. It contains flat lamination and abundant ripple cross-lamination which shows bipolar palaeocurrents, and occurs in combinations of flaser bedding, lenticular bedding and wavy lamination. Although body fossils are relatively rare, trilobite traces and desiccation cracks are common, and the association is interpreted as a predominantly subtidal to intertidal deposit. The conglomerate facies association contains horizontally bedded cobble to boulder conglomerate, with subordinate trough cross-stratified coarse sandstone to granule/pebble conglomerate. Fabrics and structures in the coarse conglomerates are consistent with alluvial transport (stream and debris flow), but not beach deposition. The conglomerate association is attributed to tectonic uplift and erosion of a Precambrian-Lower Cambrian succession developed adjacent to the present north coast of Kangaroo Island. Southward progradation of an alluvial fan complex occurred across east-west oriented tidal flats on which limited wave activity reworked sand and fine gravel, but not coarser material. The sandstone facies association mainly comprises trough cross-stratified and plane-laminated sandstone, the latter with current lineation predominantly sub-parallel to the east-west shoreline. Trough cross-stratification is ascribed to onshore waves and longshore currents, and current lineation to predominantly shore-parallel tidal currents, augmented by longshore drift and storm surge. Tectonic movements gave rise to cycles of transgression and regression as tidal and alluvial processes dominated alternately.     

西藏阿里札达盆地下更新统香孜组地层厘定与层序地层划分

根据札达盆地香孜组河湖相地层剖面的接触关系、沉积旋回、沉积体系和岩相岩性特征,可将札达盆地下更新统香孜组河湖相地层划分为2个沉积相、3个岩段。香孜组一、二岩段为一套砾岩夹砂岩的粗碎屑岩,属典型的冲（洪）积扇沉积物;第三岩段为砾岩与砂岩互层,属冰水冰缘相沉积。ESR法和古地磁法测年结果表明,札达盆地香孜组河湖相地层的形成时代为早更新世早期（2．68—1．36Ma）。札达盆地为一同生断陷盆地,在后期重新复活的过程中,盆地只经历了冲积体系域和水进体系域。冲积体系域形成于札达盆地早更新世早期重新复活层序发育的早、中期,水进体系域形成于札达盆地早更新世早期重新复活层序发育的晚期。     

金宝屯盆地晚侏罗世含煤地层沉积环境

金宝屯盆地是一中生代内陆盆地。含煤地层为上侏罗统协尔苏组,主要由灰绿色、灰色砾岩和砂岩,灰黑色、黑色细砂岩和粉砂岩、泥岩及灰白色中—粗砂岩组成,平均厚110m。区内不同沉积环境,出现在盆地演化的不同阶段和盆地的不同部位。下部砾岩段沉积期以冲积扇环境为主;含煤段沉积期为冲积扇-河流-湖泊环境组合;成煤后演化为曲流河环境;上部砂岩砾岩段沉积期以辫状河沉积为主。聚煤作用发育于盆地中的湖泊分布区,发生于盆地快速沉降之后的整体稳定、缓慢沉降阶段的早期,煤层直接覆于湖相厚层泥岩之上。盆地仅经历了一个快—慢沉降旋回,煤层的形成受控于这种“无振荡聚煤作用”。     

Facies architecture of a submarine fan channel–levee complex: the Juniper Ridge Conglomerate, Coalinga, California

The Upper Cretaceous Juniper Ridge Conglomerate (JRC) near Coalinga, California, provides a rare, high-quality exposure of a submarine channel to overbank transition. The facies architecture of the JRC comprises a thick, predominantly mudstone sequence overlain by a channellized conglomerate package. Conglomeratic bounding surfaces truncate successions of interbedded turbiditic sandstones and mudstones both vertically and laterally. Thick-bedded, massive sandstones are interbedded with conglomerates. Facies architecture, palaeocurrent indicators, slump features, sandstone percentages and sandstone bed thickness trends lead to the interpretation that these elements comprise channel and overbank facies. A vertical sequence with conglomerate at the base, followed by thick-bedded sandstone, and capped by interbedded turbiditic sandstone and mudstone form a fining-upward lithofacies association that is interpreted as a single channel-fill/overbank system. Three similar lithofacies associations can be related to autocyclic processes of thalweg migration and submarine fan aggradation or to allocyclically driven changes in sediment calibre.     

Synorogenic alluvial-fan – fan-delta deposition in the Papuan foreland basin: Plio-Pleistocene Era Formation,Papua New Guinea

The Pliocene to possibly Pleistocene uppermost Orubadi and Era Formations, southwest margin of the Papuan Peninsula, are interpreted as having been deposited in alluvial-fan, fan-delta and shallow-marine environments. The alluvial-fan facies consists primarily of lenticular, coarse-grained conglomerate (up to 2 m boulders) and cross-bedded and horizontally laminated sandstone. Conglomerate and sandstone were deposited in shallow fluvial channels and by overbank sheetfloods. The facies also contains thick mudflow diamictite and minor tuff and terrestrial mudstone. The shallow-marine and fan-delta facies, in contrast, consists of heterogeneously interbedded marine and terrestrial mudstone, sandstone, diamictite, conglomerate and limestone. Marine mudstone is calcareous, sandy, bioturbated, and contains marine shells. Limestone is mostly packstone that has a varied, open-marine fauna. Rare coral boundstone is also present. Marine sandstone is burrowed to bioturbated and is hummocky cross-stratified in places. Some marine mudstone contains sandstone pillows formed by loading of unconsolidated sand by storm waves. Other sandstone in the fan-delta facies is cross-bedded, lacks shells and was probably deposited by fluvial processes. Several conglomerate beds in the fan-delta facies are well sorted and imbricated and were also deposited by stream floods. The synorogenic Orubadi and Era Formations were deposited in a foreland basin formed from loading of the Papuan–Aure Fold and Thrust Belt on the edge of the Australian craton. Deformation in the fold and thrust belt was probably related to docking and compression of the Finisterre Terrane–Bismarck Arc against the New Guinea Orogen. The Era Formation interfingers with the reefal Wedge Hill Limestone in which reef facies likely grew on a deforming anticline. Era Formation siliciclastics were sourced from volcanic, metamorphic and sedimentary rocks that were uplifted in the orogen to the northeast. Volcanic sediment was derived mostly from a then-active volcanic arc likely related to southward subduction at the Trobriand Trough.     

Anatomy and evolution of a Lower Cretaceous alluvial plain: sedimentology and palaeosols in the upper Blairmore Group, south-western Alberta, Canada

The Lower Cretaceous (Albian) upper Blairmore Group is part of a thick clastic wedge that formed adjacent to the rising Cordillera in south-western Alberta. Regional transgressive intervals are superimposed on the overall regressive succession. Alluvial conglomerates, sandstones and mudstones were deposited in east-north-eastward draining fluvial systems, orientated transverse to the basin axis. Five facies associations have been identified: igneous pebble conglomerate, thick sandstone, interbedded lenticular sandstone and mudstone, thick mudstone with thin sandstone interlayers, and fossiliferous sandstone and mudstone. The facies associations are interpreted as gravelly fluvial channels, sandy fluvial channels, sand-dominated floodplains, mud-dominated floodplains, and marine shoreline deposits, respectively. Five types of palaeosols are recognized in the upper Blairmore Group based on lithology, the presence of pedogenic features (clay coatings, root traces, ferruginous nodules, slickensides, carbonate nodules) and degree of horizonization. The regional distribution of the various types of palaeosols enables a refinement of the palaeoenvironmental reconstruction permitting an assessment of the controls on floodplain evolution. In source-proximal areas, palaeosol development was inhibited by high rates of sedimentation. In source-distal locations, poor drainage resulting from high watertables, low topography and lower rates of sedimentation also inhibited palaeosol development. The best-developed palaeosols (containing Bt horizons) occur in intermediate alluvial plain positions (tectonic hinge zone) where the floodplains were most stable due to a balance between sedimentation, erosion and subsidence rates. Extrapolating from the upper Blairmore Group suggests that the tectonic hinge zone of continental foreland basins can be established by palaeosol analysis. At the hinge zone, soil development is controlled primarily by climate and tectonics and their effect on sediment supply, whereas closer to the palaeoshoreline, relative sea level fluctuations, resulting in poor drainage, may have a more significant influence.     

柴北缘牦牛山地区牦牛山组沉积相组合特征

柴达木盆地北缘牦牛山地区出露的牦牛山组是一套由冲积扇和扇三角洲相共同构成的陆相沉积组合,冲积扇相砾岩-粗砂岩组合主要分布于研究区SE侧,扇三角洲相砂岩-泥岩组合主要分布于研究区NW侧。古水流分析表明牦牛山组沉积物主要来自其SE侧古隆起,但后期扇三角洲相包含少量来自NW和NE向的沉积物。该套沉积组合序列特征与区域上分布在牦牛山西侧同时期形成的湖泊相、滨浅海相沉积共同表明,柴达木盆地北缘在晚志留-早泥盆世时期存在一NW向倾斜的古斜坡,且晚期北侧发生抬升。砾岩和砂岩碎屑组成与区域岩石组合类型对比表明,牦牛山组沉积碎屑物主要来自于滩间山群。沉积组合序列特征、碎屑组成和区域构造背景综合研究表明,牦牛山组可能为柴达木板块向北俯冲过程中形成的局部断陷盆地的充填物。     

俄罗斯北极地区前寒武纪岩相古地理特征

本文基于大量文献资料,系统研究俄罗斯北极地区前寒武纪的岩相古地理。俄罗斯北极地区前寒武纪共识别出半深海-深海区、浅海区、滨海区、冲积区和隆起剥蚀区5种古地理单元,其中,隆起剥蚀区沉积记录缺失;冲积区以砾岩+砂岩+泥岩和变质碎屑岩+碳酸盐岩为主;滨浅海区沉积则以变质碎屑岩+碳酸盐岩、蒸发岩+碳酸盐岩、砂岩+泥岩+碳酸盐岩3种岩性组合为主,局部有蒸发岩、砾岩+砂岩+泥岩发育;而半深海-深海区为大洋。俄罗斯北极地区前寒武纪古地理以滨浅海区为主,主要分布在东西伯利亚台地、西西伯利亚盆地、鄂霍茨克地块、楚科奇板块和巴伦支海北部地区;半深海-深海区的分布仅次于滨浅海区,此时西西伯利亚盆地尚未完全形成,其东侧为半深海-深海区;隆起剥蚀区分布范围小于半深海-深海区,主要分布在波罗的地盾及其周缘地区,以及东西伯利亚台地的阿纳巴尔地块和阿尔丹地盾地区;冲积区分布范围最为局限,仅在蒂曼-柏朝拉盆地中部发育。研究表明,俄罗斯北极地区广泛发育前寒武纪地层,岩性以碳酸盐岩和变质碎屑岩为主,部分构造单元中的前寒武纪地层已成为陆壳基底,前寒武纪岩相古地理特征研究可为前寒武纪地质研究提供依据,为其余地质时期的岩相古地理研究奠定基础。