豫西济源谭庄组河流沉积中的Stipsellus遗迹组构

豫西济源盆地上三叠统谭庄组下段为曲流河沉积。本文通过描述和分析谭庄组河流沉积特征，划分了4种不同河流沉积组合类型，识别出Stipsellus遗迹组构，并发现该遗迹组构常与曲流河沉积物伴生，可作为此类沉积的典型生物遗迹标志。其中，Stipsellus sp．A代表发育在河漫滩较浅水体下或潮湿的软底细粒沉积物中的一种遗迹组构类型；Stipsellus sp．B则代表发育在曲流砂坝上部的男一种遗迹组构类型。     

Fluvial sedimentation in the lower carboniferous of Clew Bay,County Mayo,Ireland

A succession of about 300 m of fluvial sediments from the Lower Carboniferous of northwest Ireland is described and interpreted. A lower, mainly red, formation contains fluvial channel deposits dominated by flat laminated sandstone. These are separated by interbedded sandstones and mudrocks with local caliche horizons and abundant mudcracks interpreted as levee and flood basin deposits. An upper, mainly non-red, formation contains fluvial channel deposits with common trough cross-stratification and epsilon cross-stratification also separated by interbedded sandstones and mudrocks. Evidence of desiccation is less common in the uppermost beds which pass transitionally upwards into marine sediments.The change in fluvial channel style is interpreted as due to increasing sinuosity and permanence of flow which may have been partly temporally and partly spatially controlled. The predominance of coarse sediments is thought to be largely controlled by limited subsidence. The Lower Carboniferous transgression was the major overall control of alluviation.     

Upper Aptian mixed carbonate-siliciclastic sequences from Tucano Basin,Northeastern Brazil: Implications for paleogeographic reconstructions following Gondwana break-up

The evolution of the Cretaceous basins of the Brazilian northeastern hinterland was associated with the Gondwana rifting and opening of the South Atlantic Ocean. The first marine ingression in northeastern Brazil occurred in the late Aptian and was recorded as the Santana Group of the Araripe Basin, which is currently an isolated basin, located hundreds of kilometers away from the Brazilian marginal basins. Bellow the first upper Aptian marine deposits, an important section of fossiliferous limestone (Lagerstätte) was deposited and preserved in the Crato Formation transitioning upward into evaporites of the Ipubi Formation. The direction of the marine ingression is controversial, with several possibilities being suggested, mainly due to the absence of other areas of upper Aptian marine sections within the hinterland. Serra do Tonã is a sedimentary mesa with scarped edges where the upper part of the Marizal Formation crops out, displaying laminated limestones, litho- and chrono-correlated with those of the Crato Formation, is preserved. Therefore, this mixed upper Aptian section, at the North Tucano Basin (Serra do Tonã), is a unique occurrence of utmost importance to the definition of sedimentary events and paleogeographical reconstruction of northeastern Brazil during the late Aptian. A detailed stratigraphic analysis allowed the definition and characterization of two upper Aptian depositional sequences bounded by regional disconformities. Both sequences are dominantly transgressive and carbonate-siliciclastic in composition. The lower sequence comprises the basal portion of the Marizal Formation and consists of a succession of fluvial sandstones, ending on a laterally continuous thin interval (<15 m) of interbedded shales and limestones bearing exposure features and paleosols on the top. The limestones show a diversity of microfacies, including microbialites, organized in high-frequency deepening-upward cycles. The recognized sequence stratigraphic architecture resembles the lower part of the Barbalha Formation in the Araripe Basin, positioned in the same palynological zone, suggesting the correlation of the shale-carbonate interval in the Serra Tonã with the Batateira Beds in the Araripe Basin. The upper sequence also exhibits a fining upward pattern, with a vertical succession starting with sandstones and shales deposited in fluvial and deltaic environments, culminating upward in laminated limestones and lacustrine shales. The stratigraphic succession is very similar to the upper portion of the Barbalha Formation in the Araripe Basin, and the laminated limestones are lithostratigraphically classified as the Crato Formation. These limestones also comprise several microfacies, organized in a transgressive-regressive cycle with the maximum flooding surface positioned on relatively deep-water carbonates. Fluvial paleocurrent directions, which are similar to those of the Araripe Basin, suggest that both basins were part of the same continental paleodrainage, flowing to the south, where the South Atlantic proto-ocean was located. Fish fossils found in shales of the Marizal Formation, further south in the Central Tucano Basin and in the same stratigraphic interval of those of the lower sequence, were interpreted as marine forms. Indeed, some of them were considered to have Tethyan affinity, probably coming from an incipient Equatorial Atlantic gateway, supporting the interpretation based on the paleocurrents. The limestones at the top of the Serra do Tonã, which are also found in inselbergs in the Jatobá Basin, are relicts of a once extensive cover of Aptian carbonate deposits, now restricted because of uplifting and erosion events from the Late Cretaceous to the Cenozoic.     

Lithofacies,palynofacies, and sequence stratigraphy of Palaeogene strata in Southeastern Nigeria

Integrated sedimentologic, macrofossil, trace fossil, and palynofacies data from Paleocene-Middle Eocene outcrops document a comprehensive sequence stratigraphy in the Anambra Basin/Afikpo Syncline complex of southeastern Nigeria. Four lithofacies associations occur: (1) lithofacies association I is characterized by fluvial channel and/or tidally influenced fluvial channel sediments; (2) lithofacies association II (Glossifungites and Skolithos ichnofacies) is estuarine and/or proximal lagoonal in origin; (3) lithofacies association III (Skolithos and Cruziana ichnofacies) is from the distal lagoon to shallow shelf; and (4) shoreface and foreshore sediments (Skolithos ichnofacies) comprise lithofacies association IV. Five depositional sequences, one in the Upper Nsukka Formation (Paleocene), two in the Imo Formation (Paleocene), and one each in the Ameki Group and Ogwashi-Asaba Formation (Eocene), are identified. Each sequence is bounded by a type-1 sequence boundary, and contains a basal fluvio-marine portion representing the transgressive systems tract, which is succeeded by shoreface and foreshore deposits of the highstand systems tract. In the study area, the outcropping Ogwashi-Asaba Formation is composed of non-marine/coastal aggradational deposits representing the early transgressive systems tract. The occurrence of the estuarine cycles in the Palaeogene succession is interpreted as evidence of significant relative sea level fluctuations, and the presence of type-1 sequence boundaries may well be the stratigraphic signature of major drops in relative sea level during the Paleocene and Eocene. Sequence architecture appears to have been tectono-eustatically controlled.     

Depositional environment and sedimentary of the basinal sediments in the Eibiswalder Bucht (Radl Formation and Lower Eibiswald Beds), Miocene Western Styrian Basin,Austria

The Eibiswald Bucht is a small subbasin of the Western Styrian Basin exposing sediments of Lower Miocene age. In the past the entire sequence exposed in the Eibiswalder Bucht has been interpreted as being of fluvial/lacustrine origin; here, results are presented of detailed sedimentological investigations that lead to a revision of this concept. The lowermost siliciclastic sedimentary unit of the Eibiswalder Bucht sequence is the Radl Formation. It is overlain by the Eibiswald Beds, which are subdivided into the Lower, Middle and Upper Eibiswald Beds. The Radl Formation and the Lower Eibiswald Beds are interpreted as a fan delta complex deposited along NNW-SSE striking faults. Based on the sedimentary facies this fan delta can be subdivided into a subaerial alluvial fan facies group, a proximal delta facies group and a distal delta/prodelta facies group. The Radl Formation comprises the alluvial fan and proximal delta facies groups, the Lower Eibiswald Beds the distal delta/prodelta facies group. The alluvial fan and the proximal delta consist of diverse deposits of gravelly flows. The distal delta/prodelta consists of wave-reworked, bioturbated, low density turbidites intercalated with minor gravelly mass flows. The prodelta can be regarded as as the basin facies of the small and shallow Eibiswalder Bucht, where marine conditions prevailed. The basin was probably in part connected with the Eastern Styrian Basin, the contemporary depositional environment of the Styrian Schlier (mainly turbiditic marine offshore sediments in the Eastern Styrian Basin). Analysis of the clast composition, in conjunction with the paleotransport direction of the coarse delta mass flows of the Radl Formation, shows that the source rocks were exclusively crystalline rocks ranging from greenschists to eclogites.     

Palaeoshoreline for the Late Cretaceous marine platform in the Iberian Trough (Leonese Area, Spain) deduced from outcrop and subsurface analysis

The location of the Late Cretaceous paleoshoreline in the Leonese Area (Iberian Trough, Spain) has been investigated by seismic analysis through isobath and isopach maps. The succession can be divided into two depositional sequences: DS-1 and DS-2. These sequences are composed of fluvial systems at the base, with paleocurrents that flowed eastward and north-eastward. The DS-1 sequence (Late Albian-Middle Turonian) shows intertidal to subtidal and offshore deposits at the top, while the DS-2 sequence (Late Turonian-Campanian) presents intertidal to subtidal, tidal flat and shallow marine and lacustrine deposits at its top. The stratigraphic cyclicity based on systems tracts shows that these two depositional sequences exhibit remarkable eustatic control. Both sequences start at the base with a significant sedimentary supply from fluvial systems, related to eustatic fall episodes, and conclude at the top with transgressive periods. The evolution of the basin reveals the history of base-level changes and associated shifts in depositional trends during successive stages. The deeper sectors of the DS-1 sequence are located towards the northeastern part of the study area while the proximal portion of the basin-margin is located to the southwest. The paleoshoreline is placed in a direction oriented at 120. The variations in thickness are elongated in orientations between 030 and 050 and are mainly related to paleovalleys and tributary fluvial networks that supply sediment through the shoreline. It is possible that these variations may be related to active synsedimentary faults. Depocenters move toward the northeast and east during the DS-2 sequence while the proximal portion of the basin-margin moves to the southwest. The paleoshoreline has an orientation of 155 direction and moves basinward. The isopach maps show a group of corridors oriented at 130?C140 and 165?C170, interpreted as result of accumulation of sandy bodies such as inter and subtidal bars. The fluvial systems are transversal to the paleoshoreline direction.     

渤海湾盆地垦东凸起北坡新近系馆陶组上段沉积相模式探讨

主要通过岩心观察、粒度分析、参数计算、录井及测井分析等手段,充分吸收国内外河流研究成果,结合研究区区域地质背景,总结出渤海湾盆地垦东凸起北坡新近系馆陶组上段沉积相模式。研究认为：馆上段为河流相沉积,从沉积物特征和平面形态角度可以将研究区馆上段河流理解为介于辫状河与曲流河之间的过渡河型。其平均河道弯曲度大于1.7,垂向层序表现为泥多砂少,具有曲流河的特征;但沉积层序顶部常直接覆盖河漫/洪泛平原沉积,特别是河道内砂坝发育造成河道分汊河,砂坝沉积物粒度特征反映的受洪水控制的震荡性特点而与曲流河有重要差别。作者借用在水利学界和地貌学界广为使用的分汊河概念,建立了馆上段沉积相模式,包括河床、堤岸、河漫/洪泛平原和废弃河道等4个亚相,其沉积物组成下粗上细的正韵律。其中,河道砂坝是其主要砂体,顶部常被洪泛平原直接覆盖;决口扇是仅次于河道砂坝的次要砂体。     

Aeolian/fluvial interactions and high-resolution sequence stratigraphy of a non-marine lowstand wedge: the Avilé Member of the Agrio Formation (Lower Cretaceous), central Neuquén Basin, Argentina

Abstract Accumulation within the unconformity‐based Hauterivian Avilé Sandstone of the Neuquén Basin, Argentina, was characterized by a close interaction between fluvial and aeolian processes developed after a major relative sea‐level drop that almost completely desiccated the entire basin and juxtaposed these non‐marine deposits on shallow‐ and deep‐marine facies. Aeolian deposits within the Avilé Member include dune (A1) and sand sheet (A2) units that characterize the lower part of the unit. Fluvial deposits comprise distal flood units (F1) interbedded with aeolian dune deposits in the middle part of the succession, and low‐ (F2) and high‐sinuosity (F3) channels associated with floodplain deposits (F4) towards the top. The internal characteristics of the aeolian system indicate that its accumulation was strongly controlled by water‐table dynamics, with the development of multiple horizontal deflation super surfaces that truncate dune deposits and form the basal boundary of flood deposits and sand sheet units. A long‐term wetting‐upward trend is recorded throughout the entire unit, with an increase in fluvial activity towards the top and the development of a more permanent fluvial system overlying a major erosion surface interpreted as a sequence boundary. The upward increase in water‐table influence might be related to relative sea‐level rise, which controlled the position of the water table and allowed the accumulation of tabular aeolian units bounded by horizontal deflation surfaces. This high‐frequency, eustatically driven process acted together with a long‐term climatic change towards wetter conditions.     

鄂尔多斯盆地北部侏罗系直罗组沉积特征与演化*

鄂尔多斯盆地东北部发现的多个砂岩型铀矿床均赋存于侏罗系直罗组下段砂岩中。前人对已知铀矿床分布区直罗组的沉积学研究程度相对较高,但对盆地北部直罗组大区域沉积体系展布与演变、物源供给特征等的研究仍较为薄弱。文中在大量钻井资料分析、野外剖面实测等基础上,将盆地北部砂岩型铀矿含矿层段直罗组下段细分为2个亚段。在直罗组中识别出河流和三角洲相沉积,认为直罗组下段下亚段主要发育砾质、砂质辫状河沉积,东北部地区发育辫状河三角洲沉积;直罗组下段上亚段主要发育砂质辫状河和曲流河沉积;直罗组上段则以曲流河沉积为主。结合前人研究工作,认为源岩物质组成、有利沉积相带和气候条件对鄂尔多斯盆地北部砂岩型铀矿的成矿均具有重要控制作用。对盆地北部直罗组沉积特征及其演化的整体认识,可为该区砂岩型铀矿床的进一步勘查提供重要的沉积学依据。     

Sedimentology of the upper Karoo fluvial strata in the Tuli Basin, South Africa

The sedimentary rocks of the Karoo Supergroup in the Tuli Basin (South Africa) may be grouped in four stratigraphic units: the basal, middle and upper units, and the Clarens Formation. This paper presents the findings of the sedimentological investigation of the fluvial terrigenous clastic and chemical deposits of the upper unit. Evidence provided by primary sedimentary structures, palaeontological record, borehole data, palaeo-flow measurements and stratigraphic relations resulted in the palaeo-environmental reconstruction of the upper unit.The dominant facies assemblages are represented by sandstones and finer-grained sediments, which both can be interbedded with subordinate intraformational coarser facies. The facies assemblages of the upper unit are interpreted as deposits of a low-sinuosity, ephemeral stream system with calcretes and silcretes in the dinosaur-inhabited overbank area. During the deposition of the upper unit, the climate was semi-arid with sparse precipitation resulting in high-magnitude, low-frequency devastating flash floods. The current indicators of the palaeo-drainage system suggest flow direction from northwest to southeast, in a dominantly extensional tectonic setting.Based on sedimentologic and biostratigraphic evidence, the upper unit of the Tuli Basin correlates to the Elliot Formation in the main Karoo Basin to the south.     

Architecture and morphodynamics of a 1·6 Ga fluvial sandstone: Ellice Formation of Elu Basin,Arctic Canada

Precambrian fluvial deposits have been traditionally described as architecturally simple, forming shallow and wide braidplains with sheet‐like geometry. The varied architecture and morphodynamics of the 1·6 Ga Ellice Formation of Elu Basin, Nunavut, Canada, are examined from detailed studies of section and planform exposures along coastal platforms and stepped cliffs. The Ellice Formation overlies older Proterozoic sandstones and Archean crystalline rocks, recording sedimentation in fluvial, aeolian, coastal and nearshore‐marine environments. The fluvial deposits display palaeoflow towards the west/north‐west, while overlying shallow‐marine deposits record transgression towards the east/south‐east. The Ellice Formation displays dispersed palaeoflow at its base, and also at higher stratigraphic levels, where fluvial and aeolian deposits are associated. Elsewhere, mainly unimodal palaeoflow points to extensive low‐sinuosity fluvial deposition. Within the terrestrial deposits, fluvial, fluvial–aeolian and coastal architectural elements are recognized. Fluvial elements comprise cross‐bedded sandstone and minor conglomerate, exhibiting an overall fining‐upward trend with associated decrease in preservation, dimension and amalgamation of channel bodies. These motifs are interpreted to portray a shift in depositional environment from proximal trunk rivers to distal alluvial plains. Low‐sinuosity fluvial elements are the most common, and include major channel bodies, elongate side bars and mid‐channel bars with well‐developed scroll topography. High‐sinuosity channel‐bar complexes exhibit upbar‐flow rotation and yield evidence of bar expansion coupled with rotation and translation. Fluvial–aeolian elements are composed of aeolian dunes juxtaposed with isolated channel bodies and bank‐attached bars. Minor mixed fluvial–aeolian sheets record local deposition in unconfined settings (possibly floodbasins) or inter‐distributary highlands. Finally, coastal elements comprise small deltaic complexes composed of sand‐rich distributary‐channel bodies feeding heterolithic mouth bars. Overall, the sedimentary record of the Ellice Formation demonstrates an example from the Precambrian where alluvium was locally characterized by a higher geomorphic variability than previously recognized.     

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.     

渤海湾盆地垦东凸起北坡馆上段沉积相模式探讨

主要通过岩心观察、粒度分析、参数计算、录测井分析等手段,充分吸收国内外河流研究成果,结合研究区区域地质背景,揭示垦东凸起北坡馆上段沉积相模式。得到以下认识：研究区馆上段地层为河流相沉积,从沉积物特征和平面形态角度可以将研究区馆上段河流沉积理解为介于辫状河及曲流河之间的过渡河型。其平均河道弯曲度大于1.7,垂向层序表现为泥多砂少,具有曲流河的特征;但沉积层序顶部常直接覆盖河漫/洪泛平原沉积,特别是河道内砂坝发育造成河道分汊河,砂坝沉积物粒度特征反映受洪水控制的震荡性特点而与曲流河有重要差别。本文借用在水利学界和地貌学界广为使用的分汊河概念建立了研究区馆上段沉积相模式,包括河床、堤岸、河漫/洪泛平原、废弃河道等4个亚相,组成下粗上细的正旋回。其中,河道砂坝是其主要砂体,顶部常被洪泛平原直接覆盖;决口扇是仅次于河道砂坝的第二大砂体。     

Pliocene sedimentation in a shallow, cool-water, estuarine gulf, Murray Basin, South Australia

The Pliocene Norwest Bend Formation is a well‐preserved succession of terrestrial and shallow‐marine deposits in the Murray Basin, South Australia. Sediments in this unit consist of two discrete terrigenous clastic‐rich, decametre‐scale sequences, or informal members, which record episodes of marine incursion during the Early and Late Pliocene respectively. The base of each sequence is a transgressive lag and/or strandline deposit that is transitional upwards into a highstand, subtidal, terrigenous clastic and cool‐water carbonate sediment accumulation. The top of each sequence is incised by fluvial channels that are filled by river deposits which formed as relative sea‐level fell and terrestrial environments prograded basinward. Sedimentological data suggest that gross stratigraphic architecture was primarily determined by glacioeustasy. Differences in sedimentary style between these two sequences, however, reflect a major climatic change that took place in southern Australia during the mid‐Pliocene. The lower quartzose sand member is formed of siliciclastic sediment derived from prolonged, deep, subaerial weathering and contains a bivalve‐dominated, cool‐temperate, open‐marine mollusc assemblage. These sediments accumulated under an equitable, relatively warm, humid climate. The Murray Basin during this time, because of high fluvial discharge, was a salt‐wedge estuary with typical estuarine circulation. In contrast, the upper, oyster‐rich member is typified by large monospecific oyster buildups that grew in restricted coastal environments. Strandline deposits contain a warm‐temperate skeletal assemblage. Contemporaneous aeolian sediments accumulated under warm, semi‐arid climatic conditions. Well‐developed ferricrete, silcrete and calcrete horizons reflect cyclic conditions of rainwater infiltration and evaporation in the seasonally dry climate that typifies southern Australia today. Highly seasonal rainfall produced an estuary that fluctuated annually from being well to partially mixed. These Pliocene sediments support the notion that mollusc‐rich facies are the signature of cool‐water carbonate accumulations in inboard neritic environments. Unlike bryozoans that dominate the outer parts of Cenozoic cool‐water carbonate shelves, molluscs evolved to exploit an array of coastal ecosystems with wide salinity variations and variable sedimentation rates.     

Stratigraphy and tectono-sedimentary evolution of the Upper Cretaceous–Tertiary sequence in the southern part of the Malatya Basin, East Anatolia, Turkey

The Malatya Basin is situated on the southern Taurus-Anatolian Platform. The southern part of the basin contains a sedimentary sequence which can be divided into four main units, each separated by an unconformity. From base to top, these are: (1) Permo-Carboniferous; (2) Upper Cretaceous–Lower Paleocene, (3) Middle-Upper Eocene and (4) Upper Miocene. The Upper Cretaceous–Tertiary sedimentary sequence resting on basement rocks is up to 700 m thick.The Permo-Carboniferous basement consist of dolomites and recrystallized limestones. The Upper Cretaceous–Lower Paleocene transgressive–regressive sequence shows a transition from terrestrial environments, via lagoonal to shallow-marine limestones to deep marine turbiditic sediments, followed upwards by shallow marine cherty limestones. The marine sediments contain planktic and benthic foraminifers indicating an upper Campanian, Maastrichtian and Danian age. The Middle-Upper Eocene is a transgressive–regressive sequence represented by terrestrial and lagoonal clastics, shallow-marine limestones and deep marine turbidites. The planktic and benthic foraminifers in the marine sediments indicate a Middle-Upper Eocene age. The upper Miocene sequence consists of a reddish-brown conglomerate–sandstone–mudstone alternation of alluvial and fluvial facies.During Late Cretaceous–Early Paleocene times, the Gündüzbey Group was deposited in the southern part of a fore-arc basin, simultaneously with volcanics belonging to the Yüksekova Group. During Middle-Late Eocene times, the Yeşilyurt Group was deposited in the northern part of the Maden Basin and the Helete volcanic arc. The Middle-Upper Eocene Malatya Basin was formed due to block faulting at the beginning of the Middle Eocene time. During the Late Paleocene–Early Eocene, and at the end of the Eocene, the study areas became continental due to the southward advance of nappe structures.The rock sequences in the southern part of the Malatya Basin may be divided into four tectonic units, from base to top: the lower allochthon, the upper allochthon, the parautochthon and autochthonous rock units.     

The infill of a supradetachment(?) basin: the continental to shallow-marine Upper Permian succession in the Dolomites and Carnia (Italy)

In the Dolomites and Carnia (eastern Southern Alps), the Upper Permian succession is represented by red beds of Val Gardena Sandstone, grading upwards and eastwards into the evaporitic and carbonate deposits of the Bellerophon Formation.

An overall transgressive pattern is shown by the general trend of the depositional setting, which evolved from flashy alluvial fans, through multiple-channel bedload rivers, mixed-load sinuous rivers, terminal fans, coastal sabkha and evaporitic lagoon, to a shallow, low-gradient marine ramp. The inferred fluvial regime was subject to rapid and erratic fluctuations in discharge. Palaeosols are represented by calcic soils, and suggest a warm to hot, semi-arid or dry subhumid climate with strongly seasonal rainfall. Vertic features are associated with more inland alluvial complexes: they are missing in the terminal-fan deposits, suggesting greater aridity in lowland (coastal) areas.

The Bellerophon Fm. consists of two units: a lower evaportte-bearing unit, deposited in a barred basin, and an upper shallow-marine carbonate unit, laid down on a very low-energy, low-gradient ramp.

Five third-order sequences and the lower part of a sixth sequence, collectively showing a backstepping pattern, have been identified in the succession. Due to the presence of a very low-gradient ramp margin, and the consequent ineffectiveness of relative sea-level falls in producing large-scale erosion in coastal areas, it is suggested that, rather than eustatic changes, degradational episodes marking sequence boundaries in the red-bed succession reflect changes in the climate-modulated intrinsic variables of discharge and sediment supply, and/or tectonic uplift.

Base level rises in, red-bed sequences are recorded by upward change from thick channel-belt sandstone bodies with an often high connectedness ratio, to progressively thinner channel deposits, ranging from isolated ribbons to channel-belt sandstone bodies potentially reaching high width/thickness ratios, encased in a comparably greater volume of overbank fines. This trend is thought to reflect the change from a confined geomorphic setting, with a limited area of potential avulsion, to an unrestricted setting with rivers free to move extensively; in addition, it documents the transition from an inland fluvial system with laterally migrating perennial or semi-perennial channels, to an ephemeral network of randomly migrating and frequently avulsing small terminal-fan distributaries, through a drastic downstream decrease in channel depth and discharge.

Identification of key sequence-stratigraphic relationships within the red-bed succession was mostly aided by the presence of easily recognizable and regionally correlated marine and marginal marine bed packages, traceable landwards into alluvial deposits showing faint traces of tidal activity, interpreted as the equivalent of marine maximum-flooding sediments. They may grade upwards into progradational fluvial packages showing basinward increase in thickness.

The Upper Permian deposits of the Southern Alps are considered part of an Upper Permian-Lower Triassic, second-order, structurally controlled sequence. The location of the basin on a thickened, previously active crust, affected by thermal perturbance after the last stages of the Variscan orogeny, the relatively reduced thickness of the basin fill, and predominantly long, transverse drainage networks, mostly derived from the denuded Insubric footwall, all suggest that sedimentation took place in a supradetachment basin, with a major detachment fault located in the palaeo-Insubric belt.     

Sedimentology,stratigraphy and palynological occurrences of the late Cretaceous Erlian Formation,Erlian Basin,Inner Mongolia,People's Republic of China

The Erlian Basin is one of the non-marine Cretaceous basins of north-east China that developed during the late Mesozoic continental extension in eastern Asia. This basin experienced two major tectonic events: (i) a syn-rift stage that was dominated by a fluvial–lacustrine depositional environment and (ii) a post-rift stage that was dominated by a fluvial environment. A new sedimentological study performed on Erlian Formation drill cores has led to the determination of an architectural model and to the subsequent characterisation of the stratigraphic evolution of this sedimentary unit during the late Cretaceous. The palynological occurrences that were identified in samples provided a possible stratigraphical age for the Erlian Formation.Sediments of the Erlian Formation occur at the top of the Cretaceous stratigraphic column of the Erlian Basin and were deposited during the post-rift stage. Facies architecture and the ideal succession of facies that were identified for this formation exhibit two different members, both dominated by a fluvial depositional environment: (i) the lower member, which is dominated by channels of a braided river system and (ii) the upper member, which is dominated by overbank deposits. The lower member expresses a tectonically induced uplift as indicated by channels clustering under negative accommodation, whereas a period of stratigraphic base-level rise that is associated with an increase of accommodation is identified in the upper member. Therefore the Erlian Formation highlights an alternation of short uplifts that were dominated by braided fluvial channel deposits with periods of stratigraphic base-level rise that were dominated by overbank deposits. This sedimentological architecture has significant metallogenic implications for the origin of confined permeable sandstone layers, which represent adequate host-rocks for roll front-type uranium deposits.The palynological assemblage Exesipollenites, Ulmipollenites/Ulmoideipites, Buttinia and Momipites that were recognised in two samples of the Erlian Formation has revealed a post-late Campanian age therefore more likely indicating a late Cretaceous age of deposition for the sediments of the Erlian Formation.     

成都金沙遗址区全新统震积岩的发现及其地质意义

震积岩是灾变性事件岩的典型代表,是具有震积构造和震积岩序列有一定成因联系的一组岩石的总称。成都金沙遗址区全新统地层中首次发现震积岩,该地层自下而上为底部砾石层、中部暗色(含炭)泥质层、上部褐黄色土壤层,整体属河流冲积物。通过野外观察,研究区发育一组走向SE120°的正断层,断层两盘的底部砾石层顶界面有明显的错断。构成地垒构造;在IT6511、IT6610层位中的断层带中见明显阶梯状断裂,其以张性正断层为主,断距约为10~90cm。在靠近阶梯状断裂的IT6512、IT6613-6614层位中发现一系列地震成因的软沉积物变形标志及破裂构造,包括砂土液化(脉)、液化卷曲变形构造、负载构造、微断裂、地裂缝、震塌岩等。分析认为这些软沉积物变形标志及破裂构造是由同期地壳活动引起的地震作用形成的。金沙遗址区震积岩的发现,对研究四川盆地全新世以来的古环境有重要意义。     

Sequence stratigraphic framework for mixed aeolian,peritidal and marine environments: Insights from the Pennsylvanian subtropical record of Western Pangaea

Due to difficulties in correlating aeolian deposits with coeval marine facies, sequence stratigraphic interpretations for arid coastal successions are debated and lack a unifying model. The Pennsylvanian record of northern Wyoming, USA, consisting of mixed siliciclastic–carbonate sequences deposited in arid, subtropical conditions, provides an ideal opportunity to study linkages between such environments. Detailed facies models and sequence stratigraphic frameworks were developed for the Ranchester Limestone Member (Amsden Formation) and Tensleep Formation by integrating data from 16 measured sections across the eastern side of the Bighorn Basin with new conodont biostratigraphic data. The basal Ranchester Limestone Member consists of dolomite interbedded with thin shale layers, interpreted to represent alternating deposition in shallow marine (fossiliferous dolomite) and supratidal (cherty dolomite) settings, interspersed with periods of exposure (pedogenically modified dolomites and shales). The upper Ranchester Limestone Member consists of purple shales, siltstones, dolomicrites and bimodally cross‐bedded sandstones in the northern part of the basin, interpreted as deposits of mixed siliciclastic–carbonate tidal flats. The Tensleep Formation is characterized by thick (3 to 15 m) aeolian sandstones interbedded with peritidal heteroliths and marine dolomites, indicating cycles of erg accumulation, preservation and flooding. Marine carbonates are unconformably overlain by peritidal deposits and/or aeolian sandstones interpreted as lowstand systems tract deposits. Marine transgression was often accompanied by the generation of sharp supersurfaces. Lags and peritidal heteroliths were deposited during early stages of transgression. Late transgressive systems tract fossiliferous carbonates overlie supersurfaces. Highstand systems tract deposits are lacking, either due to non‐deposition or post‐depositional erosion. The magnitude of inferred relative sea‐level fluctuations (>19 m), estimated by comparison with analogous modern settings, is similar to estimates from coeval palaeotropical records. This study demonstrates that sequence stratigraphic terminology can be extended to coastal ergs interacting with marine environments, and offers insights into the dynamics of subtropical environments.     

Fluvial deposits within the Pleistocene Crag at Thorpe St Andrew,Norwich, England

This paper records the findings at a temporary exposure at Thorpe St Andrew near Norwich, Norfolk, UK in Early and early Middle Pleistocene Crag deposits. The British Geological Survey (BGS) describes the particular formation exposed as Norwich Crag consisting of Early Pleistocene shallow marine sediments. The section shows a succession of sorted sands and gravels overlain by a sandy diamicton. Based on field evidence and clast analysis, the sands and gravels are interpreted as the product of point bar and overbank sedimentation and represent the product of a river cutting into and aggrading within the more widespread shallow marine deposits. Composition of the sediments indicates derivation, primarily from Wroxham Crag Formation, with a contribution from Norwich Crag. The sandy diamicton is interpreted as late Middle Pleistocene Corton Till that is recorded in the area. A distinct pattern of colour changes at the top of the sands and gravels is interpreted as a soil that developed on the fluvial sediments before being overridden by the glacier that deposited the Corton Till. The existence of the fluvial sediments within the regional shallow marine deposits suggests that a fall of sea-level, possibly due to climate cooling, while the elevation of the sediments and the adjacent Crag implies that the site has been uplifted since sedimentation. This is the first observation of terrestrial sediments within the shallow marine Crag. The paper also makes a contribution to understanding the diagenetic processes that give deposits within this region some distinctive colour and sediment patterns.