petrology geochemistry and environmental significance of silcrete calcrete intergrade duricrusts at kang pan and tswaane central kalahari botswana calcrete silcrete intergrade duricrusts are an important component of the kalahari group sediments of central southern africa and yet have neither been analysed systematically nor in any detail in this study the petrological and geochemical characteristics of suites of calcrete silcrete and intergrade duricrusts from two fresh relatively deep exposures at kang pan and tswaane adjacent to the okwa valley in the central kalahari botswana are described the duricrust profile at kang pan consists of a highly indurated crystalline non pedogenic calcrete which has been extensively silicified by chalcedony and rarely cryptocrystalline silica or microquartz silicification is most extensive in lower parts of the profile where replacement is related to groundwater fluctuations and in upper sections due to periodic flooding by ephemeral surface water the exposure at tswaane consists of a sequence of pale green glauconitic non pedogenic silcrete and cal silcrete overlain by non pedogenic calcrete all of which have formed within sediments situated upon granitoid gneiss bedrock the siliceous duricrusts are dominated by cryptocrystalline silica cements and appear to have developed through the replacement of a preexisting non pedogenic calcrete these siliceous duricrusts have also been calcified at a later date during the formation of the overlying calcrete to produce a complex range of silica carbonate cements at both sites the style and type of silicification present appears to be determined by the duration of wetting and the permeability of the precursor calcrete geochemical evidence indicates a lack of chemical weathering profile development within the granitoid gneiss bedrock and considerable differences between the chemical signature of the bedrock and combined duricrusts from kang and tswaane this suggests that bedrock made a minimal contribution in terms of silica and carbonate species to duricrust formation and that the majority of cementing agents were non local it would therefore appear likely that the geomorphological context of each site had a major influence upon the development of calcrete silcrete and intergrade duricrust cements

climatic controls on late pleistocene alluvial fans cyprus alluvial fans are commonly associated with tectonically active mountain ranges and tectonism is frequently held responsible for abrupt coarsening and cyclical sedimentation of alluvial fan sequences whilst it is accepted that tectonism provides the opportunity for alluvial fan development through the creation of topography increasing gradients of fluvial systems supplying sediments and creating accommodation for the storage of sediment flux the role of climate in fan development is frequently neglected the hypothesis that climatically controlled events can produce recognisable sedimentary signatures in alluvial fan deposits is tested in the active supra subduction zone setting of the late pleistocene of southern cyprus this study demonstrates through architectural analysis and the reconstruction of palaeoflood hydrology a recorded pattern of increasing and decreasing palaeoflow dynamics with switches from a wetter to drier mode clearly exhibited by changes in the sedimentology of the fan at the present day cyprus has a semi arid climate and is influenced by a strongly seasonal rainfall pattern largely restricted to the winter months plus rare occurrences of summer cyclones however at precession minima increased activity of western mediterranean depressions produces wetter summers using inference we propose that longer term increases in rainfall increased river discharge as recorded in the fan palaeoflood hydrology and occurred at minima in the precession these periods correlate with the deposition of conglomeratic channels and open framework gravels drier periods are exhibited by sandier braided fluvial deposits shorter term or seasonal change is recorded in the form of 2nd and 3rd low order bounding surfaces this increased activity of mediterranean summer depressions increased precipitation to the wider levantine area and was coincident with increased intensity of the north african and indian ocean sw monsoons the resultant increase in river discharges at precession minima from both the nile and the wider levant resulted in the formation of sapropels in the eastern mediterranean and is recorded as wet periods in speleothem deposits in the soreq and peqiin caves of israel the predominant control of sedimentation on the late pleistocene alluvial fans of southern cyprus was climate

unconventional pattern of reservoir facies distribution in epeiric successions lessons from an outcrop analog lower keuper germany this article presents 1 a process oriented description of an outcrop analog for epeiric successions 2 a discussion of fundamental characteristics of epeiric basin fills and 3 a generic depositional model which may be used for improved reservoir prediction in epeiric settings the case study focuses on the upper ladinian mixed siliciclastic carbonate lower keuper formation it is composed of storm generated tide generated and bioturbated facies paleogeographically the succession shows an unusual lateral energy zonation comprising a seaward low energy zone close to wave base an intermediate reservoir prone high energy zone within wave base and a landward low energy zone above wave base stratigraphically the lower keuper formation is subdivided into meter scale transgressive regressive cycles correlatable over distances of more than 500 km cycle boundaries are interpreted to be isochronous within the resulting chronostratigraphic framework facies distributions have been mapped out in three dimensions revealing that reservoir prone facies are most extensive in shoreline detached positions reservoir bodies are thin have sheetlike geometries but extend for several tens of kilometers and are stacked in an aggradational facies architecture additionally the reservoir prone facies is thicker developed in zones of stronger subsidence a few kilometers wide linked to underlying basement blocks resulting unconventional reservoir prediction strategies for similar shallow marine epeiric settings should target shoreline detached high energy facies belts that are preferentially developed within zones of stronger subsidence controlled by basement tectonics

sedimentology of a marine intermontane pleistocene gilbert type fan delta complex in the crati basin calabria southern italy the crati basin is a pliocene holocene extensional basin filled by the progradation of different types of marine fan delta systems coarse grained gilbert type fan deltas developed during the pleistocene they represent the sedimentary response to a strong differential uplift involving the basin margins and the basin itself the differential uplift was responsible for the fragmentation of the basin into several sub basins into which these fan deltas prograded the protection and lateral confinement by structural highs steep coastlines and the absence of strong tidal action in the adjacent ionian sea allowed the regular progradation of these fan deltas in the restricted gulfs and narrow embayments of the crati basin for the classical gilbert type fan deltas in lacustrine settings homopycnal inflow favours a rapid mixing of water masses and deposition of sediment close to the river mouth in the case of the example described here the density contrast between the sea water and the inflowing river water caused the separation of the muddy fraction from the coarse sandy and conglomeratic part of the sediment this allowed the development of steep mud poor coarse grained delta foresets slope instability features slump scars conglomeratic flow slides are fairly scarce in the proximal parts of the san lorenzo del vallo system towards the north where protection from the ionian sea was less they increase in importance

modelling facies belt distribution in fan deltas coupling sequence stratigraphy and geostatistics the eocene sant llorenc del munt example ebro foreland basin ne spain abstract the eocene sant llorenc del munt fan delta complex developed in the ebro foreland basin the stratigraphy of this succession about 1000 m thick has been described as made up of several transgressive regressive composite sequences each composed of a stack of fundamental sequences in turn made up of a transgressive systems tract and an overlying regressive systems tract systems tracts are composed of several facies belts proximal alluvial fan distal alluvial fan fan delta front carbonate platform and fan delta slope and prodelta a 3d facies model of a 130 m thick stratigraphic succession was built using outcrop data from one of the composite sequences the modelling followed a hierarchical approach a deterministic method was used to reconstruct the surfaces bounding fundamental sequences and their constituent systems tracts data input was outcrop traces digitized on photorealistic terrain models the stacking trend and interfingering of adjacent facies belts within each systems tract was added by means of a geostatistical algorithm and was conditioned to measured stratigraphic logs the analysis of the resultant 3d facies distributions allows revising the architectural interpretation of the studied interval leading to the conclusion that the observed arrangements are accommodation not supply driven furthermore the 3d models were flow simulated in two injector producer scenarios up depositional and down depositional dip waterflooding flow simulation results show that the depositional architecture of the studied succession controls potential recovery efficiencies in that a considerable proportion of moveable oil is trapped at the dead ends in depositional pinch outs of the main potential reservoir fan delta front deposits also that up dip waterflooding predicts better recovery efficiencies than down dip the dataset methods and results herein make the sant llorenc del munt complex a ready for application analogue for marine transitional reservoirs

a retreating fan delta system in the neoproterozoic chattisgarh rift basin central india major controls on its evolution a thick wedge of immature siliciclastics characterizes the basal part of the basin fill succession in the eastern part of the neoproterozoic chattisgarh basin it comprises a mosaic of mass flow deposited conglomerate and pebbly sandstone coarse grained sandy braided stream deposits wave lag pebble sheets high energy wave dominated foreshore and upper shoreface facies and wave and tide dominated lower shoreface facies the succession is characterized by strong lateral and vertical facies variation the facies associations and stacking pattern point to the development of an alluvial fan to fan delta complex with outbuilding of delta lobes onto a high energy shallow marine shelf via a high gradient narrow delta plain the delta front deposits of coarse grained sand interfinger and grade into prodelta mud in the seaward direction the dominance of coarse grained sandy detritus with a high content of fresh feldspar grains points to mechanical weathering of granites and gneisses of the cratonic basement and a semiarid climate the sediment caliber and the climate exerted a major control on the facies and on processes of sediment transfer from the fan to the shelf a critical balance between progradation aggradation and retrogradation controlled the evolution of delta successions within an overall transgressive regime related to the extension of a cratonic rift basin repeated fault controlled uplift of the source followed by subsidence and transgression generated multiple fining upward cycles and a retreating fan delta system the marked variations in thickness of the delta succession and the stacking pattern in different measured profiles reflect the overriding tectonic controls on delta evolution the accumulated fault displacement in active sectors created higher accommodation and thicker delta sequences intermittent uplift of fault blocks exposed fresh bedrock to mechanical weathering generated a large amount of detritus and resulted in forced regressions repeatedly disrupting the fining upward pattern the controls of source rock lithology or climate were of secondary importance to tectonic effects retreating fan deltas are rarely reported and may be a stratigraphic response of marine connected rift basins at the early stage of extension the delta stratigraphy is analogous to the submarine fan stratigraphy in the case where basin shales act as hydrocarbon sources the fan deltas are potential hydrocarbon reservoirs the coarse grained lobes can be excellent reservoirs with the enclosing prodelta muds acting as seals to vertical migration of hydrocarbon the coarse grained deposits of the delta plain and proximal delta front occurring as laterally coalesced large sand bodies blanketed by transgressive prodelta mud might also form good reservoirs

depositional environments in an arid closed basin and their implications for oil and gas exploration the lower permian fengcheng formation in the junggar basin china the fengcheng formation is a nonmarine carbonate dominated succession that formed under arid climatic conditions in a hydrologically closed basin two transects and two seismic profiles were examined the characteristics and environmental significance of different lithofacies were studied and a model of depositional environment divisions was proposed the sedimentary model involved an alkaline lake in which the depositional environments consisted of a shallow saline lake margin slope saline lake center and steep lake margin from northeast to southwest the perennial central salty lake was located in the southwestern part of the study area whereas there were widespread low gradient lake margins in the northeast east southeast and southern parts of the study area lake level fluctuations had a major influence on the shallow saline lake system and complicated the depositional environments in these areas the deposits are derived from bedrock reworking volcanic eruptions and authigenic minerals that precipitated from brine during the hypersaline phase fine grained terrigenous clastic sediments volcanic ashes and dusts and authigenic minerals mixed in the depocenter concentration center of the brine pool which was covered by high salinity brines and the depositional environment was anoxic as a result of salinity based brine stratification a thick sodium carbonate succession occurred in the depocenter of the ancient mahu lake where bedded sodium carbonate alternated with fine grained organic rich tuff or tuffaceous hydrocarbon source rocks microorganisms bloomed in the alkaline high salinity brine and the organic matter was well preserved which is similar to those modern alkaline saline lakes in eastern africa and western north america thus the permian fengcheng formation contains source rocks that formed in an alkaline saline lake

groundwater dolocretes in a lake marginal environment an alternative model for dolocrete formation in continental settings danian of the provence basin france in the long continental history of the provence basin which extended from santonian to oligocene times a major period of palaeosol development occurred in the danian dolocretes developed within floodplain silts and partly from palustrine limestones dolocretes are overlain by pedogenic facies calcretes and palustrine limestones gradational lower and upper limits of profiles succession of nodular coalescent and massive horizons the epigenesis of quartz by dolomite the unimodal crystal size and the euhedral dolomite fabric as well as the absence of biogenic structures and vadose cements show that dolocretes formed in the phreatic zone the exclusive occurrence of dolocretes around the palaeolake or playa suggests that dolocrete formed by the mixing of groundwaters and lake brines which infiltrated the phreatic zone during periods of strong evaporation and lake level lowering the term halo dolocrete is proposed to describe this type of dolocrete deposit subsequent alteration of the dolocrete includes leaching of the central core of dolomite crystals and calcitization calcitization was either fabric destructive type i or fabric preserving type ii and took place during very early diagenesis i e concomitant with calcrete formation or palustrine limestone deposition fabric destructive calcitization is attributed to a drop in the lake level when the upper part of the dolocrete was subjected to vadose zone processes whereas the fabric preserving calcitization resulted from reactions with dilute lake and groundwaters during rise in lake level

kalahari valley calcretes their nature origins and environmental significance abstract calcretes that form in non pedogenic settings have been widely reported in the geomorphological and geological literature yet they are still poorly understood in comparison with pedogenic varieties this may be because there are assorted types of non pedogenic calcretes often loosely referred to as groundwater calcretes but encompassing groundwater phreatic open valley or confined channel calcrete types forming within vadose and phreatic environments in different geomorphological settings relatively few studies have described the detailed petrological characteristics of such calcretes leading wright and tucker calcretes international association of sedimentologists reprint series 1991 vol 2 blackwell scientific publications oxford p 10 to suggest that much more work is needed to define the groundwater calcrete facies and to devise criteria for its recognition so that the various non pedogenic calcretes can be identified within the quaternary as well as further back in the geological record most descriptions of groundwater calcretes are highly generalistic and do not take into account the variability that may occur as a result of calcretes forming in different positions within a landscape and affected by separate controls thus the range of groundwater calcretes that exists now needs to be studied individually to identify patterns within the distinct types as a step towards expanding our knowledge of the variety of non pedogenic calcretes this paper describes the petrology micromorphology and mode of development of one of these types of calcrete namely that which forms within valley locations but not in definite fluvial channels late quaternary to holocene valley calcretes are described from various dry valleys mekgacha across the kalahari region of central botswana with the majority of samples collected from trunk and tributary valleys of the okwa samples have been analysed in thin section and under scanning electron microscope in order to determine the carbonate matrix type and calcrete micromorphology in general most samples consist of grains of quartzose kalahari sand cemented by fine crystalline often glaebular grain coating and pore filling micrite cement types are fairly consistent and not as micromorphologically variable as has been noted for other kalahari calcretes biological inputs are prevalent in many samples and include networks of calcified rootlets these characteristics reflect the fact that the calcretes formed in a relatively near surface environment with relatively high rates of evaporation

pliocene pleistocene climate change sea level and uplift history recorded by the horingbaai fan delta nw namibia its location on a tectonically relatively stable passive margin and its degree of interaction with the sea make the horingbaai fan delta nw namibia an exceptional record of coastal activity providing insights into the response of ephemeral fluvial systems to changes in climate sea level and continent scale uplift the fan comprises upper middle and lower segments the upper fan and middle fan are dominated by a braided river system only in the upper fan are fluvial sediments interleaved with hyperconcentrated flow deposits plio pleistocene sea level highstands have left marine terraces on the fan surface which enable correlation with the offshore marine record and provide timelines to constrain fan growth the bulk of fan delta progradation took place at 2 7 2 4 ma between the formation of a widespread erosional surface incising the middle pliocene karpfenkliff and kamberg formations but prior to the emplacement of the warm water fauna bearing late pliocene oyster terrace 2 4 2 2 ma an equivalent of the 30 mp marine terrace package in coastal southwestern africa major fan progradation is contemporaneous with widespread regional uplift 12 5 m ma and climate change in southwestern africa the latter associated with intensification of northern hemisphere glaciations younger fan growth phases are weaker and constrained by 10 m asl marine terrace bodies that yield mostly cold water fauna corresponding to the onset of strong glacial interglacial climatic fluctuations superimposed on a general aridification trend and the introduction of colder sea surface temperatures after 2 2 ma

the role of detrital anhydrite in diagenesis of aeolian sandstones upper rotliegend the netherlands implications for reservoir quality prediction the rotliegend upper permian reservoir interval in the southern permian basin spb contains low permeability streaks corresponding to anhydrite cemented intervals an integrated study was conducted using core cuttings thin sections and well log data from a gas exploration well and two geothermal wells that target the zone of interest this study aims at understanding the origin and nature of these low permeability streaks as well as their impact on reservoir properties and to establish a predictive model of their spatial distribution high resolution xrf core scanning analysis allowed to extrapolate spot observations in thin sections to the entire core diagenetic history includes grain rearrangement and anhydrite haematitic clay coatings dolomite rims quartz overgrowths kaolinite and second generation carbonates as cementing phases coupling of all data reveals the detrital origin of the anhydrite gypsum grains which were deposited together with the coarse grained sand fraction in an aeolian sandflat environment such partially or completely dissolved grains acted as local sources of anhydrite cement and as nuclei for precipitation explaining its preferential occurrence in coarsegrained laminae thick gypscretes in the vicinity likely supplied the anhydrite gypsum grains a conceptual model is proposed including the location of nearby gypscretes and the prevailing west southwest aeolian transport direction on the southern rim of the spb

geochemical evolution and paleoenvironments of the eocene continental deposits in the paris basin abstract the continental and lacustrine deposits of eocene age in the paris basin form a geochemical sequence extending from clastic sediments characterized by aluminous clay minerals to chemical sediments with dolomite gypsum and magnesian clay minerals during the early eocene flood plains and lakes with large deltas extended across the southern margin of the paris basin the clays were derived from the weathered mesozoic rocks calcretes and smectitic vertisols developed within the flood plain deposits indicating that the climate was warm with an alternation of wet and dry seasons during the middle eocene lacustrine limestones and palygorskite clays developed in small lakes subject to periodic desiccation and pedogenesis landwards pedogenetic silcretes developed on the early eocenc pediments palygorskite is indicative of environments with high concentrations of silica and magnesium and the presence of opal in silcretes confirms a high silica concentration in the soils solutions the paleoclimate was warm with distinct dry seasons or periods during the late eocene gypsum was deposited in the basin center surrounded by a marly deposit in which dolomite and sepiolite are the characteristic minerals lacustrine limestone with alumino magnesian smectite and palygorskite formed on the margin of the basin the development of the evaporitic sequence was favored by the flatness of the palaeolandscape and its silcrete capping which restricted erosion and detrital input to the basin the climate was warm with a tendency to aridity thus the continental deposits of eocene age in the paris basin reflect a progressively more aric climate moreover each depositional pedogenetic and encrusting phase modified the palaeolandscape and thus influenced the next sedimentary episode

deposition and early diagenesis of playa glauberite in the karinga creek drainage system northern territory australia abstract glauberite na 2 ca so 4 2 in the form of discrete crystals nodules and lenses represents the second most common sulphate mineral type after gypsum in the chain of modern playa lakes located in the karinga creek drainage system northern territory these modern glauberite deposits exhibit textures and fabrics which reflect both syndeposition with gypsum within the playa phreatic zone and early diagenetic replacement of host gypsite in the playa vadose zone because the distribution of hydrological zones in individual playa lakes vary significantly the extent of glauberite facies development is highly irregular factors controlling glauberite deposition include the nature and extent of groundwater discharge from local and regional aquifers playa surface evaporation rates porewater geochemistry and the depth to basal aquicludes geochemical and petrographic evidence indicate that the paragenesis of sulphate minerals in the playa lakes of the study area is primarily dictated by the solubility of gypsum which in turn reflects the extent of dilution and concentration of playa porewaters on a regional scale brine dilution and concentration can be related to seasonal and longer term groundwater recharge discharge patterns but on a local scale the proximity to springs and ephemeral seepage creeks emanating from local calcrete aquifers is the dominating influence hence a thorough knowledge of groundwater hydrodynamics particularly the recharge discharge pattern in playa marginal areas must be an essential part of any detailed assessment of the role of depositional and early diagenetic processes in the genesis of glauberite facies in similar arid drainage basins the close relationship between glauberite facies development and the playa groundwater level has significant implications for interpretations of variation in the water table and other environmental conditions in the shallowing upwards sequences of ancient lacustrine deposits the presence of lacustrine glauberite facies may also mark a transition from depositional to early diagenetic evolution of the basinal sulphate mineral facies

muddy and dolomitic rip up clasts in triassic fluvial sandstones origin and impact on potential reservoir properties argana basin morocco abstract the significance of rip up clasts as sandstone framework grains is frequently neglected in the literature being considered as accessory components in bulk sandstone composition however this study highlights the great value of muddy and dolomitic rip up clast occurrence as a information source about low preservation potential from floodplain deposits and b key element controlling host sandstone diagenetic evolution and thus ultimate reservoir quality high resolution petrographic analysis on triassic fluvial sandstones from argana basin t6 and t7 t8 units highlights the significance of different types of rip up clasts as intrabasinal framework components of continental sediments from arid climates on the basis of their composition and ductility three main types are distinguished a muddy rip up clasts b dolomitic muddy rip up clasts and c dolomite crystalline rip up clasts spatial distribution of different types is strongly facies related according to grain size origin of rip up clasts is related to erosion of coeval phreatic dolocretes in different development stages and associated muddy floodplain sediments cloudy cores with abundant inclusions and clear outer rims of dolomite crystals suggest a first replacive and a subsequent displacive growth respectively dolomite crystals are almost stoichiometric this composition is very similar to that of early sandstone dolomite cement supporting phreatic dolocretes as dolomite origin in both situations sandstone diagenesis is dominated by mechanical compaction and dolomite cementation a direct correlation exists between 1 muddy rip up clast abundance and early reduction of primary porosity by compaction with irreversible loss of intergranular volume igv and 2 occurrence of dolomitic rip up clasts and dolomite cement nucleation in host sandstone occluding adjacent pores but preserving igv both processes affect reservoir quality by generation of vertical and 3d fluid flow baffles and barriers that compartmentalize the reservoir these findings may provide quantitative useful data for the better understanding of reservoir quality in analogous hydrocarbon bearing basins such as the bay of fundy nova scotia canada

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

depositional processes paleoflow patterns and evolution of a miocene gravelly fan delta system in se korea constrained by anisotropy of magnetic susceptibility analysis of interbedded mudrocks abstract anisotropy of magnetic susceptibility ams has been used as a proxy of grain fabrics and as a basis of interpretation of depositional processes and paleocurrent directions in sedimentary successions in this paper we present the results of the ams analysis of over 900 core specimens from the sandy to muddy deposits intercalated between the gravelly deposits of a miocene fan delta system in se korea analyses of the mean magnetic susceptibility thermomagnetic property and hysteresis show that paramagnetic minerals are the main contributors to the ams of the deposits the ams analysis shows that the deposits have four types of magnetic fabrics including 1 horizontal and type a imbricated fabrics characterized by girdle distributed to weakly clustered k 1 and k 2 axes on the bedding plane and subvertical to variably tilted k 3 axes 2 type b imbricated fabric characterized by well clustered k 1 and k 2 axes and subvertical to tilted k 3 axes and 3 rolling fabric characterized by streak distributed k 2 and k 3 axes along a plane perpendicular to the k 1 axes these fabric types are interpreted to have resulted from suspension settling horizontal and type a imbricated fabrics turbidity currents type b imbricated fabric and debris flows rolling fabric modification of the primary fabrics during sediment compaction on a slope resulted in a wide range of imbrication angles in all fabric types paleocurrent directions inferred from the ams data are generally consistent with those obtained by previous field studies of the gravelly sequences and provide additional information of the temporal change of the paleoflow pattern which is related to the growth exhumation and dissection of the fan delta system this study thus suggests that much information can be drawn from the ams analysis of mudrocks regarding not only the depositional processes and paleoflow pattern but also the evolution of a depositional system

the effect of drainage reorganization and climate on the sedimentologic evolution of intermontane lake systems the final fill stage of the tertiary ebro basin spain abstract stratigraphic and sedimentologic analyses and geochemical data from the middle and late miocene record in the southwestern central sector of the ebro basin have allowed the evolution of its neogene final fill stage to be characterized and its controlling factors to be discerned the focus of these analyses was the distinct depositional environments that occurred over time tecto sedimentary units t6 t7 and t8 twelve main associations of lacustrine palustrine fluvial and alluvial facies revealed that the sedimentary processes leading to the formation of the units occurred in different environments in units t6 and t7 middle and late aragonian i e langhian serravallian and in unit t8 vallesian turolian i e tortonian the depositional environments of units t6 and t7 encompassed a closed shallow carbonate lake system with wide palustrine fringes the lake was fed by small sandy and gravelly channels flowing from the southwest iberian range and a sandy fluvial system from the north pyrenees inputs were also received from a southeastward flowing axial fluvial system as the mouths of these systems commonly formed small deltaic sandy lobes on the northern lake margins the evolution of unit t6 and in particular that of unit t7 was greatly influenced by pyrenean tectonics the depositional environments of unit t8 included the occurrence of the as but this system was soon replaced by an open shallow carbonate lake surrounded by wide and shallow oncoid bearing channels and palustrine tufaceous areas on its west southwest margin distinct depositional events from the south and west which involved intra t8 erosion resulted in minor coarse alluvial deposits the carbonate system of unit t8 occurred in an open depression created after local erosion of the pre t8 deposits and subsequent northward shifting of the as since early deposition of unit t8 the origin of which was related to late contractile deformation in the northwestern iberian range bicarbonate and calcium rich water from the mesozoic carbonate rocks in the iberian range fed the t8 system sedimentologic 13c 18o and trace element data support the change from closed to open drainage and strongly suggest a general climate trend toward wetter and cooler conditions which is consistent with the middle late miocene climate evolution of other european regions despite the general timing coincidence between unit t8 deposition and the opening process of the ebro basin the attributes of the t8 deposits are inconclusive to support the previous hypothesis that the fluvial lacustrine palustrine system could be directly connected to the emptying drainage of the basin into the mediterranean sea instead the results of this study demonstrate the combined influence of tectonics and climate on the evolution of the final fill stage of this part of the ebro basin these results may be useful for assessing the influence of such allocyclic factors on the sedimentologic hydrologic and geochemical evolution of other intermontane lake basins

fan deltas and braid deltas conceptual problems the concept of fan deltas has been widely misinterpreted in the geologic literature a true fan delta is defined as an alluvial fan deposited into a standing body of water such sequences are of limited areal extent and are as expected uncommon in the rock record by contrast braid deltas herein defined formed by progradation of a braided fluvial system into a standing body of water are a common geomorphic feature in many modern settings and their deposits are common in the geologic record braid delta sequences are often identified as fan deltas on the false premise that coarse grained deposits in a deltaic setting are always part of an alluvial fan complex the authors find that most published examples of so called fan deltas contain no direct evidence for the presence of an alluvial fan even in examples where an alluvial fan could be documented the authors found that in many cases the alluvial fan complex was far removed from the shoreline separated by an extensive braid plain the authors suggest that such systems are better classified as braid deltas they consider that it is essential to distinguish the environmental setting of true fan deltas from that of braid deltas misclassificationmore will lead to incorrect interpretations of expected facies sandstone geometry reservoir quality and tectonic settings criteria based on geometry vertical and lateral lithofacies associations and paleocurrent patterns should be used to correctly identify and distinguish these depositional systems less

pedogenic and early diagenetic processes in palaeogene alluvial fan and lacustrine deposits from the sado basin s portugal abstract the palaeogene deposits of the sado basin were deposited in a continental basin that shows a typical pattern with alluvial fans system in the margins of the basin passing towards distal areas of mudflat facies where in some areas the installation of shallow water bodies favoured the development of palustrine conditions the deposits of this basin vary form coarse conglomerates and sandstones to palustrine carbonates these sediments were affected by pedogenesis and early diagenetic processes that promoted important modifications on their primary features these modifications have been studied by the analyses of four profiles developed on proximal middle and distal fan deposits and the fourth one on lacustrine deposits the overall analyses of the sedimentological pedogenic diagenetic features and their relationships indicate that three main processes took place throughout the basin soil formation palygorskite neoformation and dolomitization soil formation processes led to illuviation of clays and carbonate precipitation mostly around roots pedogenic carbonates increase towards distal areas whereas hydromorphic features are present throughout the basin palygorskite neoformation was partially diagenetic being maximum in proximal areas and palustrine deposits this neoformation is attributed to the percolation of alkaline mg rich soil and groundwaters through smectitic rich sediments promoting important clay transformation dolomitization was an early diagenetic process that occurred mainly in carbonate rich deposits of distal and lacustrine environments as a result of the increasing mg ca ratio of the percolating groundwaters in all these processes there has been a close spatial and temporal interplay between pedogenesis and diagenesis driven by the chemistry of soil particles and groundwaters

properties and development of channel calcretes in a mountain catchment tabernas basin southeast spain nonpedogenic channel calcretes of up to 3 5 m thick occur in a number of locations across the tabernas basin in almeria province southeast spain they represent the last major phase of late quaternary calcium carbonate cementation to affect this semiarid drainage basin channel calcretes are situated within the basal parts of sequences of 12 m thick poorly sorted coarse grained and schist dominated fluvial gravels that were deposited within confined bedrock channels channel calcretes occupy the full basal width of the bedrock channels within which they occur and mostly crop out near the mouths of tributary valleys to the main rambla de tabernas drainage system six profiles from five separate channel calcrete outcrops were logged and sampled all samples were analysed in thin section and under scanning electron microscope sem from these analyses the macro and micromorphological properties were identified and the mode of origin of channel calcrete profiles was assessed results indicate that all channel calcretes are massively cemented by calcite and appear uniform at the field profile scale microscale analyses reveal that detrital grains within the calcretes are initially coated by micrite which is overlain by grain coating and pore filling sparite a series of broad trends in cement type and micromorphology are recognised within individual field profiles all profiles exhibit an increasing degree of calcite crystal size in a down profile direction most field profiles predominantly contain micrite in upper parts with an increasing percentage of sparite towards the base some profiles are however dominated by sparite and show increasing crystal size and occurrence of euhedral crystals towards the profile base many profiles also contain evidence of postcalcite cementation diagenesis in the form of dissolution of calcite crystal faces or replacement of the calcite cement by amorphous silica with alteration mostly occurring in the lower parts of profiles the trends within the calcrete fabric appear to have developed in conjunction with a fluctuating water table with the increased crystal size and occurrence of euhedral crystals towards the base of profiles arising from greater duration of wetting in basal zones cementation in some field profiles occurred at depths of up to 12 m within the host sediment well below the zone of capillary rise and pedogenesis and in the absence of significant organic activity as such channel calcretes in the tabernas basin may represent an ideal opportunity to observe the influence of groundwater upon cementation of coarse grained sediments by carbonate

nonmarine sequence stratigraphy updip expression of sequence boundaries and systems tracts in a high resolution framework cenomanian dunvegan formation alberta foreland basin canada ten allomembers labeled j a have been mapped in the deltaic dunvegan formation using 2340 wells and 63 outcrop sections each allomember spans about 200 k y is bounded by regional transgressive surfaces and consists of 3 10 component shingles apparently of autogenic origin allomembers h e are discussed in this article their internal stacking patterns and bounding surfaces permit interpretation as depositional sequences sequences h f have a sigmoidal prismatic geometry downlap to the southeast and thin northwest onto the coastal plain no differential thickening exists toward the orogen in the southwest in contrast sequence e thickens markedly toward the northwest the tabular geometry of sequences h f suggests accommodation was controlled by sea level change whereas the wedge geometry of sequence e suggests significant tectonic tilting subaerial unconformities that bound valleys and extend onto adjacent interfluve paleosols can be traced 120 330 km updip into outcrop the base of each sequence is characterized by shoreline backstep of 80 150 km transgressive and highstand shingles in each sequence comprise marine deltaic deposits that pass landward into coastal plain strata falling stage shingles offlap seaward with little or no nonmarine equivalents updip whereas lowstand shingles show renewed coastal onlap in outcrop three nonmarine systems tracts are recognized 1 a channel dominated low accommodation systems tract fills valleys up to 35 m deep and is equivalent to the early transgressive systems tract begin page 1968 2 a lacustrine dominated high accommodation systems tract comprises mudstone enclosing ribbon channel sandstones blankets interfluves and forms the bulk of each sequence it is equivalent to late transgressive and early highstand systems tracts 3 a paleosol dominated low accommodation systems tract occupies the upper part of each sequence and is capped by the sequence boundary it is equivalent to the late highstand systems tract sequence bounding interfluve paleosols represent tens of thousands of years of pedogenesis related to slow aggradation followed by fluvial entrenchment and clastic bypass and represent the late highstand falling stage lowstand and early transgressive systems tracts coastal plain deposits record only part perhaps

a classification of rhizogenic root formed calcretes with examples from the upper jurassic lower cretaceous of spain and upper cretaceous of southern france reply abstract studies of fluvial sequences from the upper jurassic and lower cretaceous of the cameros basin spain and the upper cretaceous of the aquitaine basin france have revealed large numbers of calcrete profiles which have formed wholly or largely through the action of plant root calcification those from spain have formed by the calcification of root mats whereas those from france resulted from the accumulation of calcified root cells microcodium these root related rhizogenic calcretes developed in stages allowing developmental time series chronosequences to be identified contrasting with existing models for calcrete profile growth they provide unique examples where vegetation has been the dominant control on profile development and probably indicate specific vegetation types and palaeoecological settings the role of root activity in forming some quaternary calcretes is also discussed

characteristics evolution and distribution of quaternary channel calcretes southern jordan cemented and calcretized conglomerates of quaternary age are found within ancient river channels exposed at various heights between 1 and 125 m above the current bed of the wadi dana in southern jordan in cross section the calcrete deposits are typically lensoid in shape and are found in lling palaeochannels cut into the bedrock the fossilized channel sediments preserve evidence of past river conditions sediment loads source areas phases of river down cutting and sediment accretion as well as post depositional alteration processes samples have been analysed in thin section and under the scanning electron microscope in order to determine the calcrete micromorphology cement types and crystal sizes the results show that the river deposits have undergone signi cant displacement and replacement of the detrital grains by caco3 and this has resulted in the cementation in places of over 4 m of river material the cements display an alpha type fabric with no evidence of biogenic activity the nature of the cement fabric within and between deposits differs as a function of two key variables i the speci c location within the channel and ii height above the modern wadi oor firstly in many of the deposits cement crystal size varies with sparite dominating at depth within impermeable palaeowadi channels whereas on the anks of the channels and near the top of the channels micrite is the main type of cement these variations are thought to be a result of differences in the length of residence time of calcium carbonate rich uids in different parts of the channel and the spatially varying in uence of evaporation secondly distinct changes in cement fabric can be seen in channels of different ages with a reduction in the amount of micrite and an increase in the amount of secondary recrystallized pore lling spar over time copyright 2004 john wiley sons ltd

tectonic and climatic controls on fan systems the kohrud mountain belt central iran abstract late pleistocene to holocene fans of the kohrud mountain belt central iran illustrate the problems of differentiating tectonic and climatic drivers for the sedimentary signatures of alluvial fan successions it is widely recognised that tectonic processes create the topography that causes fan development the existence and position of fans along the kohrud mountain belt ne of esfahan are controlled by faulting along the qom zefreh fault system and associated fault zones these faults display moderate amounts of historical and instrumental seismicity and so may be considered to be tectonically active however fluvial systems on the fans are currently incising in response to low gavkhoni playa lake levels since the mid holocene producing incised gullies on the fans up to 30 m deep these gullies expose an interdigitation of lake deposits dominated by fine grained silts and clays with evaporites and coarse gravels that characterise the alluvial fan sediments the boundaries of each facies are mostly sharp with fan sediments superimposed on lake sediments with little to no evidence of reworking in turn anhydrite glauberite mirabilite and halite crusts drape over the gravels recording a rapid return to still water shallow ephemeral saline lake sedimentation neither transition can be explained by adjustment of the hinterland drainage system after tectonic uplift the potential influence in central iran of enhanced monsoons the northward drift of the intertopical convergence zone itcz and mediterranean climates for the early holocene 6 10 ka point to episodic rainfall during winter months associated with discrete high magnitude floods on the fan surfaces the fan sediments were deposited under the general influence of a highstand playa lake whose level was fluctuating in response to climate this study demonstrates that although tectonism can induce fan development it is the sensitive balance between aridity and humidity resulting from changes in the climate regime of central iran that influences the nature of fan sequences and how they interrelate to associated facies

pedogenic and groundwater processes in a closed miocene basin northern spain abstract the sepulveda ayllon basin sab was an episodically closed miocene basin adjacent to the tertiary duero basin northern spain the sediments studied here represent a depositional system developed from the margin to the centre of the basin by alluvial fan mud flat and saline mud flat ephemeral lacustrine environments an assemblage of authigenic lithotypes was formed in the basin their distribution being influenced by that of the depositional environments within the basin authigenesis took place mainly before sedimentation of the next set of beds in the distal alluuial fan authigenesis of smectite outer part palygorskite inner part and calcrete predominates and the original muddy deposits are still recognizable in the mud flat a more intense transformation of the sediments took place with predominant formation of palygorskite outer part interstitial gypsum calcrete outer part dolocrete inner part and brown silcrete in the saline mud flat ephemeral lake original sediment was extensively disturbed and replaced by magnesian clays sepiolite and magnesian smectite interstitial gypsum dolocrete and cream and white silcrete authigenic alteration within each cycle varied in time and place and was both pedogenic and groundwater related the authigenic assemblages point to a closed basin under evaporation in a seasonally dry climate at the end of this period the sab became connected with the duero basin to the northeast thus losing the endoreic regime consequently the authigenic evaporitic assemblages were then unstable and were partially replaced by a late sparry calcrete

genesis of calcrete in quaternary soil profiles hutt and leeman lagoons western australia abstract soil profiles exposed along the margins of hutt and leeman lagoons contain a succession of calcrete horizons that exhibit oolitic pisolitic grainstone lithoclast breccia and pelloidal wackestone mudstone stone lithologies the typical coastal profile consists of an upper laminar calcrete horizon which is usually overlain by a transitional pisolitic loose soil horizon underlying the laminar calcrete is breccia and or massive calcrete downward gradation into the host is through a mottled calcrete horizon structure textures and fabrics are utilized to classify the following different calcrete types pisolitic loose soil is composed of sandy soils calcrete ooids and pisolites eolianite clasts and shell fragments laminar calcrete is composed of parallel laminated sheets of micritic carbonate that develop by segregation processes massive calcrete is dense relatively structureless calcrete with a secondary mudstone fabric resulting from diagenetic alteration of primary constituents calcrete mottles form in response to localized diagenesis in the host sediment breccia calcrete develops as a result of prolonged weathering involving repeated episodes of calcretization dissolution and brecciation diminution of permeability of the host sediment by development of massive calcrete is a major process in genesis of the profile and occurs in the lowermost part of the zone of alternate wetting and drying where the effect of water input overcomes the cumulative effects of evapotranspiration profile development is thereafter topographically controlled and restricted to horizons overlying the massive calcrete redevelopment of zones of alternate wetting and drying in older deposits may produce multiple soil profiles

dual mechanisms for the formation of fluvial silcretes in the distal reaches of the okavango delta fan botswana silcretes exposed within river marginal or valley settings have been described in a number of studies but few models have been suggested for the development of these fluvial silcretes an exception is that proposed by mccarthy and ellery journal of sedimentary research 1995 vol a65 pp 77 90 to describe mechanisms of early stage near surface silica diagenesis in the okavango delta botswana this paper describes the characteristics and possible origins of massive surface and sub surface silcretes at samedupe and boro junction beyond the distal margin of the okavango delta and further downstream than the sites described by mccarthy and ellery morphological and petrological evidence from surface exposures and three sedimentary cores suggests that other modes of formation may also be applicable a dual model of formation is proposed surface silcretes are suggested to have developed by silica accumulation in seasonal pools remaining after the annual okavango flood whilst sub surface horizons appear to have formed under conditions of varying ph associated with fluctuating groundwater levels beneath the channel floor this model is reviewed in the context of the fluvial silcrete debate 1998 john wiley sons ltd

hydrogeochemistry and weathering on the yilgarn block western australia ferrolysis and heavy metals in continental brines abstract groundwater samples collected from salt lakes over the archean yilgarn block of western australia show the influence of climate on geochemical weathering patterns major element compositions in salt lake groundwaters show little systematic trend but there are marked differences in ph and fe cu and pb concentrations in the alkaline carbonated systems of the arid northeastern part compared to concentrations of the same elements in groundwater systems of the mediterranean type climatic region of the wheatbelt in the southwestern part of the block in this latter region in addition to higher rainfall input the groundwater systems have steeper hydraulic gradients weathering bedrock is closer to the surface and oxidation and hydrolysis of iron ferrolysis is evident in weathering profiles a combination of vertical diffusion and horizontal groundwater flow is thought to be responsible for the development of ferrolysis and acidity in groundwaters in this region anomalously high concentrations of heavy metals particularly lead are observed in some of the acid saline groundwaters the formation of laterite which is a ubiquitous feature of the yilgam block landscape is a process probably closely linked to ferrolysis

the west water formation hualapai plateau arizona usa as a calcrete paleosol sequence and its implications for the paleogene neogene evolution of the southwestern colorado plateau abstract analyses of stratigraphic sequences within the paleocanyons of the hualapai plateau arizona are important because these deposits offer the only evidence for the paleogene neogene geological history of the grand canyon area in this paper we focus on the origins and paleoenvironmental significance of the west water formation located within the milkweed and west water paleocanyons on the hualapai plateau we propose that the supposed limestone unit of the west water formation at and near its type section is not a limestone rather it is a 21 m thick valley calcrete overprinted by a 1 2 m thick pedogenic calcrete and subsequently dolomitized in its upper to middle sections with a superimposed 4 m thick red paleosol we also propose that this unit is not coeval in age or origin with the long point limestone on the coconino plateau and that the presence of a complex calcrete dolocrete paleosol alters previous interpretations associated with this unit evidence for a calcrete paleosol origin beyond the west water formation s lack of fossils includes its predominantly micritic calcite palygorskite composition its textures characteristic of valley and pedogenic calcrete deposits as exhibited by thin section sem and tem analyses and its association with a relatively thick overlying red paleosol that also contains abundant palygorskite stable carbon and oxygen isotope values from carbonate cements are also within the range expected of a near surface calcrete carbonate minerals within the calcrete dolocrete were precipitated at or near the water table in a valley setting due to evaporation and or co 2 degassing in a semi arid to arid environment of deposition high 87 sr 86 sr values within the calcrete were inherited from groundwater infiltrating through music mountain formation arkosic sediments which were derived from a precambrian source terrane to the south and southwest no absolute ages exist for the music mountain formation and west water formation in the milkweed and west water paleocanyons these sediments could range in age from the late cretaceous to the latest eocene earliest oligocene and may record the eocene oligocene transition in the grand canyon area

evaluation of paleohydrologic models for terrestrial inverted channels implications for application to martian sinuous ridges abstract fluvial systems can be preserved in inverted relief on both earth and mars few studies have evaluated the applicability of various paleohydrological models to inverted fluvial systems the first phase of this investigation focused on an extensive spanning 12 km inverted paleochannel system that consists of four sandstone capped carbonate cemented sinuous ridges within the early cretaceous cedar mountain formation located southwest of green river utah morphologic and sedimentologic observations of the exhumed paleochannels were used to evaluate multiple numerical models for reconstructing paleofluvial hydrological parameters another objective of the study was to determine whether aerial or orbital observations yield model results that are consistent with those constrained by field data the models yield an envelope of plausible dominant discharge values 100 500 m 3 s reflecting the limitations of the approach and no single model can be used to reliably estimate paleodischarge on mars landforms with attributes consistent with inverted channels have been identified in spite of differences in the formation history between these martian landforms and the terrestrial analog described here including potential differences in cement composition and the erosional agent that was responsible for relief inversion these numerical models can be applied with modification to the martian landforms and yield an envelope of plausible values for dominant discharge

pedogenic phreatic carbonates on a middle devonian givetian terrigenous alluvial deltaic plain gilwood member watt mountain formation northcentral alberta canada in the muskeg trough of northcentral alberta the gilwood member contains widespread carbonate deposits that formed within terrigenous mudstone and sandstone hosts stratigraphic depositional and petrographic relationships indicate that these carbonates represent calcretes and dolocretes calcretes observed best with cathodoluminescence display microcrystalline alpha fabrics circumgranular cracks root networks displacive growth fabrics elongate channel voids and rare coloform growths with flower spar similarly dolocretes have microcrystalline alpha fabrics brecciation gradational contacts with host mudstones extensive layered nodular horizons and are associated with anhydrite and pyrite 13c values range between 7 to 1 and 6 to 3 for calcretes and dolocretes respectively oxygen isotopes are more variable and differ with host lithologies 18o of calcretes ranges between 11 to 8 for sandstones and 8 to 3 for mudstones whereas 18o of dolocretes ranges between 3 to 1 for marine mudstones and 6 to 2 for pedogenic mudstones regional mapping indicates that calcretes thicken towards the deepest parts of the muskeg trough widespread dolocretes extend beyond the eastern and western limits of muskeg trough and are useful marker intervals for regional correlations dolocretes of restricted lateral extent are found within gleyed palaeosol mudstones next to calcretized channel sandstones calcrete isotopic values are interpreted as indicative of carbonate precipitation from waters with meteoric water input however the higher 18o values in dolocretes are indicative of a contribution from an isotopically heavier source such as seawater stratigraphically calcretes are most common along the western and northern edges of muskeg trough thus calcrete accumulation was further controlled by meteoric water in flow from the highland to the west and sluggish groundwater flow in muskeg trough in contrast regionally widespread dolocrete horizons appear to have formed from mixing of fresh waters derived from the highland to the west and seawaters introduced from the east regionally restricted dolocretes which are found next to channel sandstones formed from groundwater out flow from the permeable channel sandstones which resulted in calcretization in channel proximal mudstones and dolomitization in channel distal mudstones

junggar basin northwest china trapped late paleozoic ocean abstract the junggar basin originated during the late paleozoic as either a remnant lower to mid paleozoic ocean basin or a mid carboniferous back arc intra or inter arc basin bounded by emergent volcanic arcs south of the siberian craton the retreating junggar sea left behind a regressive sedimentary section comprising at least 3 4 km of marine volcaniclastics in the southern junggar area sandstones deposited in the junggar basin since the devonian are exclusively volcaniclastic demonstrating that precambrian basement rocks have never been exposed in the basin and supporting the hypothesis that the junggar is underlain by oceanic crustal materials the mid carboniferous junggar ocean may have been a remnant ocean basin of early to mid paleozoic age or alternatively may have been an extending intra or inter arc basin formed behind an emergent volcanic arc in the northern turpan region subsequent strike slip deformation and the general sparsity of geologic and geophysical data from the junggar area make it difficult to distinguish between these models late early permian through triassic sediments of the junggar basin are exclusively non marine deposited in a flexurally subsiding foreland basin during initial uplift of the ancestral tian shan mountains the sedimentary section deposited during the late permian early triassic appears to be inconsistent with a proposed rifting episode during this period

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

the qs problem sediment volumetric balance of proximal foreland basin systems although the stratigraphy of sedimentary basins depends on the balance between the magnitude and grain size characteristics of the sediment supply qs and the spatial distribution of tectonic subsidence generating accommodation x qs is problematical to measure in present day sediment routing systems and formidably difficult to predict in their ancient counterparts this challenge was tackled by treating the sediment discharge from the outlet of mountain catchments as the result of incision by a drainage network with a bulk diffusivity based on the length over which the mean annual rainfall is concentrated the size relief and slope of palaeo catchments acting as feeders for sediment routing systems are used to run simulations of sediment discharge and bulk diffusivity for a range of annual precipitation values a wide range of observable geological phenomena can be used to converge on the most likely solutions for qs including depositional volumes in the basin and bedrock thermochronology and detrital cosmogenic nuclide dating to constrain catchment erosion rates modelled sediment discharges can be checked with estimates derived from global regressions the sediment efflux of mountain catchments serves as a boundary condition for down system sediment transport and deposition variations in the volumetric ratio of sediment supply to available accommodation qs x determines patterns of transverse versus longitudinal axial sediment dispersal the volumetric ratio may change as a result of variations in climatic parameters tectonic uplift rate and catchment expansion an abrupt climate change to higher precipitation values promotes higher qs x but transient landscape response causes a return to values close to the baseline generating a distinctive down system extension of a gravel spike catchment expansion has a similar but more prolonged effect on gravel progradation in contrast a change in tectonic forcing such as an increase in slip rate on a border fault causes little change in qs x because increased subsidence compensates for the increased sediment supply studies of mid eocene oligocene sediment routing systems in the south central pyrenees allow the discrimination of different types of proximal wedge top sedimentary systems on the basis of the volumetric ratio of qs to accommodation x i small steep local fan systems in tectonically ponded underfilled basins supplied by low sediment discharges ii tectonically guided long range axial systems fed by large sediment discharges from widely spaced palaeovalleys and iii large shallow sloping transverse megafans burying underlying defunct or active tectonic structures supplied by high to very high sediment discharges understanding the role of variations in qs helps to explain the syntectonic evolution of proximal foreland basin systems the oligocene miocene north alpine foreland basin switzerland is qualitatively identified as a high qs example the miocene recent northern apennines of italy as a low qs example and the eocene oligocene southern pyrenees of spain as intermediate in character

sedimentary facies and the context of dolocrete in the lower triassic sherwood sandstone group corrib field west of ireland abstract the lower triassic sherwood sandstone group ssg reservoir in the corrib field is predominantly fine to medium grained fluvial sandstone with minor aeolian and playa sediments that formed under semi arid to arid conditions there is no evidence of roots burrows or organic rich soils in the ssg suggesting an environment with sparse vegetation in the catchment and sedimentation from a predominantly braided sand dominated river dolomite is the main porosity occluding cement

calcretes in semi arid alluvial systems formative pathways and sinks late quaternary deposits in gujarat western india show an abundant development of calcretes three major sinks of carbonate in the alluvial deposits are recognized 1 groundwater calcretes 2 pedogenic calcretes and 3 calcrete conglomerates groundwater calcretes originate from carbonate saturated waters travelling preferentially along stratification planes pedogenic calcretes form through soil forming processes typically in extra channel areas calcrete conglomerates occur as ribbons sheets and lenses due to the reworking of both pedogenic as well as groundwater calcretes as a result a pathway of calcretization develops that has the route groundwater calcrete to pedogenic calcrete to calcrete conglomerate the formation of pedogenic calcretes over sediments containing groundwater calcretes demonstrates that 1 apart from aeolian dust river waters are also a major source of carbonate and 2 pedogenic carbonates may attain large sizes at accelerated rates due to the presence of pre existing groundwater calcretes consequently the maturity of a soil may be overestimated if determined by following established morphogenetic sequences

a hydrogeological model for the early diagenesis of late triassic alluvial sediments the late triassic mercia mudstone group of southwest britain a problematic complex arid playa floodplain aeolian deposit contains a variety of mg clays and carbonates recent interpretations have invoked marine waters as a source of mg in clays however both the mg rich clays and other early diagenetic features seen in the late triassic in europe are directly analogous to those found in the inland drainage basins of australia a simple hydrogeological model is offered based on these basins where shallow groundwater evolution takes place within the basin producing a range of early diagenetic products including groundwater dolocretes and mg clays such a model as developed in australia is probably widely applicable to ancient arid alluvial systems the mercia mudstone group is a problematic sequence of predominantly red siltstones and mudstones with minor sand dolomite and limestone intercalations ruffell 1991 it has been extensively studied in outcrops in southwest and southern britain particularly in the bristol channel area the siltstones and mudstones of late triassic age are the distal equivalents to alluvial fan deposits and are associated at least locally with lake margin and spring travertine deposits leslie et al 1992 some workers have favoured a marine influenced setting for the deposition of the mudrocks or playa lakes see review in taylor 1983 most recently they have been interpreted as the deposits of complex floodplain playa systems with a signficant aeolian input talbot et al 1994 extensive evaporites occur locally in the unit including thick halite deposits and have been interpreted as evidence of marine

the character and genesis of calcrete in late quaternary alluvial deposits gujarat western india and its bearing on the interpretation of ancient climates late quaternary deposits in mainland gujarat contain sediments deposited in subhumid and semi arid climates the 30 35 m succession shows the presence of vertisols at the base and a red bed horizon ferric calcisol when pedogenic in origin that roughly bisects the succession a widespread development of calcretes is observed throughout the succession the various varieties of calcrete include pedogenic calcrete groundwater calcrete calcrete conglomerate transported calcrete and rhizogenic calcrete pedogenic calcrete nodules associated with vertisols and the red soil show marked differences in morphology dimensions and the distribution of microscopic features these differences arise due to contrasting climate controlled physicochemical environs under which they formed pedogenic calcrete nodules associated with vertisols acquire large 5 10 cm dimensions and are characterised by either showing the presence of a nucleus of soil matter or showing a dense micritic groundmass cut by thick sparitic veins in contrast calcrete nodules that formed in the red soil are 3 cm in size and do not exhibit dense networks of sparitic veins calcretes associated with vertisols and the ferric calcisol also exhibit differences in the morphology of rhizoliths these differences also show up in the distribution of microfabrics of calcretes grain coats are present in rhizogenic and pedogenic calcretes but absent in groundwater calcretes and less profuse in hydromorphic soil calcretes clotted micrite is present in all types except groundwater calcretes sparitic veins however are observed in each type but are relatively less developed in groundwater calcretes a similar distribution of displacive and replacive textures is also seen although some grains in groundwater calcretes showed signs of corrosion the vertisol associated calcretes represent a subhumid 500 700 mm climate whereas the red soil calcretes suggest a semi arid 100 500 mm climate calcretes from the vertisol association show a range in 13c composition constrained between 9 and 5 whereas the red soil calcretes exhibit the whole spectrum of values from 9 to 1 based on mineralogical associations calcretes usually taken to reflect semi arid episodes in the earth s history may be classified further calcretes when associated with sepiolite palygorskite suggest an arid climate mean annual rainfall 50 100 mm when associated with smectite haematite and the absence of hydromorphism a semi arid climate mean annual rainfall 100 500 mm and when found in smectitic vertisols subhumid climates mean annual rainfall 500 700 mm

calcrete and palustrine assemblages on a distal alluvial floodplain a response to local subsidence miocene of the duero basin spain abstract in the upper miocene of the eastern duero basin two carbonate units cu 1 and cu 2 display a lateral transition from distal alluvial floodplain red mudstones to calcrete and an upwards transition from calcrete to palustrine facies the carbonate content in the calcrete increases upwards as shown in sequences from red or reddish brown mudstones with diffuse calcification to nodular calcrete facies to massive calcretes the palustrine facies display a broad range of textures related to the degree of exposure peloidal intraclast textures formed during the most prolonged phases of exposure and are those most commonly seen in the palustrine facies the transition from calcrete to palustrine facies occurs in two ways 1 as an indurated limestone level with mixed features of calcrete and palustrine facies and 2 a well delimited boundary between the two facies which show very similar characteristics in the vicinity of this boundary the 13cpdb and 18opdb values of the calcretes are similar to those of the palustrine facies this is because their genesis was related to groundwaters which inherited the isotopic signature of meteoric waters good covariance between 13c and 18o palustrine values r 0 78 is typical of lakes in semi arid regions with long water residence times in closed basins the calcrete palustrine association records a progressive decrease in the terrigenous supply and a continuous elevation of the groundwater table until it intersected with the surface to create a pond the rise in the groundwater table resulted from local subsidence that was not compensated by terrigenous supply leading to a lowering of the floodplain changes in the thickness of palustrine facies from central to marginal pond areas with ubiquitous exposure features suggest that the pond was progressively filled up by bio chemical carbonate precipitation balancing the available space created by subsidence this maintained the shallow character of the pond deposits

characteristics and evolution of the late permian source to sink system of the beisantai area in the eastern junggar basin nw china abstract many studies have focused on the tectonic evolution and sedimentary processes of the beisantai uplift nw china during the late permian however the sedimentary characteristics of the area are still not well documented due to a complex tectonic evolution of the uplift and the limited distribution of core data to understand the sedimentary evolution of this study area a source to sink system research is adopted first the research redefines the sequence stratigraphic framework of the late permian which corresponds to a complete third order sequence that can be further divided into a transgressive system tract tst and a regressive system tract rst then the integration of three dimensional 3d seismic reflection data well logs mud logs and core data provides new insights into the transportation and sedimentary processes within the source to sink system the different characteristics of the source area transfer system and sedimentary paleogeomorphology between the tst stage and rst stage ultimately led to significantly different sedimentary characteristics in the two stages in the tst stage the source to sink system exhibited a continued transgressive depositional characteristic that matched the sediment discharge evolution the steeper sedimentary paleogeomorphology enabled the development of large scale fan deltas with few beach bars during the rst stage the source to sink system had low sediment discharge and a smooth sedimentary paleogeomorphology the source to sink system was predominantly characterized by small scale beach bars with few fan deltas with the decreasing level of sediment discharge and continued smoothing of the sedimentary paleogeomorphology the beach bars expanded

multiple calcrete profiles in the tabernas basin southeast spain their origins and geomorphic implications the paper describes a sequence of pliocene to quaternary age calcretes developed within alluvial fan and fluvial gravels in the tabernas basin almeria province southeast spain calcrete profiles are described from sites adjacent to major tributaries of the rambla de tabernas six distinct calcrete units are identified within the basin these have variable distributions but have developed in an identifiable evolutionary sequence two pairs of calcrete units are widely present across the basin preserving two former land surfaces each of the former land surfaces has been planated and subsequently buried by alluvial fan or fluvial gravels a massive calcrete unit is present at the base of each gravel sequence immediately in contact with the underlying bedrock with a less well developed calcrete unit situated at the top of the gravel sequence the lowest two calcrete units within the basin are more spatially restricted and are confined to the floors and flanks of incised drainage lines the geochemistry macro and micromorphological properties and geomorphological positions of the calcrete units are outlined and on the basis of this information their mode of origin identified two main modes of calcrete genesis appear to be present massive calcretes situated in direct contact with bedrock are suggested to have formed by groundwater processes whilst calcretes situated at the top of gravel sequences are likely to have developed by pedogenic processes calcrete genesis is subsequently considered in the context of the reconstruction of the early phases of landscape development and is suggested to have been controlled by phases of uplift and stability within the tabernas basin 1998 john wiley sons ltd

origin and palaeo environments of calcareous sediments in the moshaweng dry valley southeast botswana quaternary sedimentation in the moshaweng dry valley of southeastern botswana is evaluated on the basis of geomorphological evolution and sedimentological analyses stratigraphic evidence reveals an upper surface 1095 m containing abundant sil calcrete an intermediate surface 1085 m in which sil calcrete underlies nodular calcrete and lower 1075 m surface in which sil calcrete and nodular calcrete are interbedded this subdivision is reflected in the geochemical composition of the sediments which show an overall trend of decreasing sio2 content and increasing caco3 content with depth from the highest to the lowest surface levels the calcretes and sil calcretes represent modifications of pre existing detrital kalahari group sand and basal kalahari pebbles which thinned over a karoo bedrock high modification took place during wet periods when abundant ca rich groundwater flowed along the structurally aligned valley system with the onset of drier conditions water table fluctuations led to the precipitation of nodular calcretes in the phreatic layer to a depth of about 20 m a major geochemical change resulted in the preferential silicification of the nodular calcrete deposits conditions for silica mobilization may be related to drying induced salinity and in situ geochemical differentiation brought about by pebble dissociation towards the top of the sediment pile as calcretization and valley formation progressed to lower levels silica release took place on a diminishing scale thermoluminescence dating infers a mid pleistocene age for sil calcrete formation suggesting that valley evolution and original calcrete precipitation are much older late stage dissolution of caco3 from pre existing surface calcretes or sil calcretes led to the formation of pedogenic case hardened deposits during a time of reduced flow through the moshaweng system possibly during the upper or late pleistocene copyright 2002 john wiley sons ltd

palaeoclimatic and site specific conditions in the early permian fossil forest of chemnitz sedimentological geochemical and palaeobotanical evidence abstract as significant indicators of deep time palaeoclimate a number of new palaeontological pedological and geochemical characteristics are provided for the chemnitz fossil lagerstatte to depict more precisely its environmental conditions for the first time several lines of evidence indicate that this fossil forest instantaneously preserved by volcanic deposits once received an annual precipitation of around 800 1100 mm but grew on a nearly unweathered palaeosol although the composition of this rich and diverse t0 assemblage suggests a hygrophilous dense and multi aged vegetation dominated by conservative lineages the habitat was affected by environmental disturbances and pronounced seasonality repeated changes in local moisture availability are suggested by geochemical proxies the co occurrence to intergrowth of calcic and ferric glaebules in the palaeosol and developmental traits of perennial vegetational elements specific substrate adaptation is reflected by different root systems and cyclic growth interruptions recorded in the stems branches and roots of long lived woody plants many differentially adapted terrestrial animals complete the more comprehensive reconstruction of a late sakmarian ecosystem and its climatic and preservational controls albeit spatially confined this diverse in situ record may contribute to understand wetland dryland dynamics of sub tropical northern hemisphere pangaea

geochemistry of acid brines lake tyrrell victoria australia abstract pore water groundwater and sediments were collected from lake tyrrell to study the evolution of brines in an acidic environment lake tyrrell is a 150 km2 inland salt playa acid saline groundwater enters the playa through springs along the lake margin and is evapo concentrated past halite precipitation the brines were found to contain sea salts but some solutes do not follow the seawater evaporation curve processes that occur in neutral alkaline systems e g gypsum formation occur here but precipitation of alunite kal3 so4 2 oh 6 jarosite kfe3 so4 2 oh 6 and fe oxides also affect solute behavior processes that occur in the recharge area and along the groundwater flow path k uptake calcrete and gypcrete formation affect the brine s chemical signature regardless of the chemical variability found among the samples solutes have evolved from a common source sea salt acidification which appears to occur early in the evolution of the groundwater is related to pyrite oxidation and may be enhanced by precipitation of fe oxides alunite and jarosite and evaporation acidity is maintained in the system because of the lack of buffering capacity of aquifer minerals we suggest that this acid brine from australia is another end member in the eugster jones hardie model for the evolution of water by evaporation in closed basins

fan deltas and braid deltas varieties of coarse grained deltas two types of coarse grained deltas are recognized fan deltas and braid deltas fan deltas are gravel rich deltas formed where an alluvial fan is deposited directly into a standing body of water from an adjacent highland they occupy a space between the highland usually a fault bounded margin and the standing body of water in contrast braid deltas here introduced are gravel rich deltas that form where a braided fluvial system progrades into a standing body of water braid deltas have no necessary relationship with alluvial fans as exemplified by fluvioglacial braid deltas braid deltas have previously been classified as fan deltas even though the geomorphic and sedimentologic settings of the two systems can be vastly different braid deltas are a common present day geomorphic feature and are abundant in the geological record fan deltas and braid deltas can be distinguished in the rock record by distinctive subaerial components of these depositional systems the shoreline and subaqueous components of both are similar fan delta sequences have a subaerial component that is an alluvial fan facies comprising interbedded sheetflood debris flow and braided channel deposits fan deltas produce small a few tens of square kilometres wedge shaped bodies of sediment commonly displaying high variability in paleocurrent patterns and abrupt changes in facies the deposits are generally very coarse grained with large out sized clasts very poorly sorted matrix rich polymictic heterolithic partially cemented by penecontemporaneous carbonate and have low porosity and permeability braid deltas in contrast have a subaerial component consisting entirely of braided river or braidplain facies their deposits display better sorting roundness and clast orientation than do fan delta sediments they lack a muddy matrix they display size grading and bar migration they commonly have a sheet geometry with high lateral continuity tens to hundreds of square kilometres and they exhibit moderate to high porosity and permeability valuable paleogeographic and tectonic information concerning the proximity of highlands and major fault zones may be misinterpreted or lost if these two coarse grained deltaic systems are not differentiated

river avulsions and sedimentary evolution of the luanhe fan delta system north china since the late pleistocene abstract the luanhe fan delta lfd is one of the most important coastal deltas in north china numerous investigations on the late quaternary evolution of this fan delta system have been implemented during the 1980s however few detailed sedimentologic studies have been undertaken based on comprehensive analysis of sedimentary facies grain size microfossils radiocarbon dates ams14c and optically stimulated luminescence osl ages from three 30 m long cores along with recent reports from a series of cores and seismic profiles from the coastal areas we reconstructed the detailed late quaternary sedimentary evolution of the northern bohai coast which evolved from a coastal barrier lagoon system during mis5 to an alluvial plain with river channels and floodplains between mis4 and the early holocene a variety of transgressive coastal depositional environments freshwater marshes beach ridges sandy barriers shallow seas developed during the early holocene these environments were followed by delta progradation the delta system then gradually turned into a coastal barrier lagoon system under the combined impact of prevailing wave driven currents and local subsidence two dramatic 90 degree diversions of the lower luanhe river course likely influenced the sedimentary evolution of the lfd in its inner portion the first avulsion took place in qianxi probably at the end of the late pleistocene 15 000 cal a bp it led to the abandonment of the luanhe alluvial fan in the western part of the northern bohai coastal plain nbcp and to the formation of a new alluvial fan in the eastern nbcp this alluvial fan evolved into a fan delta system 7000 3500 cal a bp during the holocene transgression the second avulsion occurred at zhuacun during the late holocene probably at 3600 100 cal a bp following this latter avulsion the luanhe river shifted toward the east and formed a new fan delta system 3700 cal a bp present with its apex in luanzhou abrupt tectonic uplift in this highly seismic region likely controlled the two avulsions and the dramatic shift of the alluvial fan complexes climate and sea level changes may also have partly influenced the development of the lfd

controls and evolution of fan delta systems in the miocene pohang basin se korea abstract the miocene pohang basin southeastern korea occurs in the eastern part of the ne sw trending yangsan fault which has experienced right lateral strike slip deformation since the eocene during the miocene however the strike slip movement was negligible and instead was under extensional regime large scale drainage systems were developed at the junction between the strike slip zone and the oblique transfer faults acting as major sources for coarse grained sediments high rate of sediment supply and rapid subsidence of the hanging wall resulted in the progradation of large scale gilbert type fan deltas doumsan duksung and gohyun systems which all show a radial distributional pattern along the steeply inclined footwall scarps created by ne sw trending faults the drainage systems were relatively small here low rate of sediment supply formed scree apron type malgol and yugye systems and steep faced slope type maesan system fan deltas based on variations in sedimentary facies and distribution architecture and overlapping patterns the fan delta systems in the pohang basin can be divided into four stages of evolution during the early stage early miocene alluvial fans prograded into shallow marine setting in the doumsan and duksung systems high rate of sediment supply and rapid rise of relative sea level resulted in the transformation of shoal water type to gilbert type foresets in the malgol and maesan systems rapid sea level rise accompanied with low rate of sediment supply caused transformation of alluvial fans to scree apron type and steep faced slope type fan deltas respectively in the second stage subsidence of the hanging wall formed large scale truncation surfaces in the doumsan and duksung fan deltas coarse grained sediments were continuously supplied in the doumsan system whereas only fine grained sediments were deposited in the duksung system in the malgol system sediment supply was almost terminated in this stage in the third stage middle miocene sediment supply rate of the doumsan fan delta decreased abruptly and the system was overlain by fine grained gilbert type deposits the duksung fan delta was overlain by the maesan and gohyun systems the maesan system prograded further basinward during the last stage late miocene sediment supply of the doumsan and maesan systems was also terminated and the entire basin was draped by fine grained biogenic materials mainly diatoms

upper jurassic lower cretaceous morrison and cedar mountain formations ne utah nw colorado relationships between nonmarine deposition and early cordilleran foreland basin development abstract sedimentologic stratigraphic and petrologic analysis of the upper jurassic lower cretaceous morrison and cedar mountain formations of utah and colorado provides information on the timing and nature of early cordilleran foreland basin development the morrison formation can be subdivided into three depositional facies assemblages 1 lower progradational shallow marine lacustrine fluvial and eolian facies deposited during oxfordian kimmeridgian retreat of the stump sundance sea 2 a middle assemblage containing sandy gravelly braided fluvial deposits which are overlain by meandering fluvial channel and overbank facies and 3 an upper assemblage of laterally stable low sinuosity fluvial channel facies deposited during tithonian early neocomian time the upper part of this assemblage shows evidence of alteration and early diagenesis related to development of an early cretaceous unconformity the overlying cedar mountain formation is subdivided into two facies assemblages 1 the neocomian buckhorn conglomerate was deposited by northeast trending sandy gravelly braided rivers that were incised into the underlying morrison formation 2 an upper assemblage containing laterally stable low sinuosity fluvial channel facies deposited during late neocomian albian time the base of the unit contains a thick calcrete zone that formed during an unconformity following buckhorn deposition morrison and cedar mountain formation sandstones contain three petrofacies a feldspar rich lower morrison petrofacies qmflt 70 19 11 and chert rich upper morrison and buckhorn cedar mountain petrofacies qmflt 54 5 41 and 69 4 27 respectively sandstone composition and paleocurrent data indicate a cordilleran source area composed of proterozoic paleozoic and mesozoic sedimentary rocks the morrison formation and buckhorn conglomerate were deposited in the back bulge depozone of the late jurassic cordilleran foreland basin system and onlapped a flexural forebulge located in central utah late neocomian eastward migration of the forebulge uplifted areas in eastern utah producing an unconformity while the foredeep in central utah underwent flexural subsidence the upper part of the cedar mountain formation represents overfilling of the foredeep and deposition above the forebulge

a retreating fan delta system in the northwestern junggar basin northwestern china characteristics evolution and controlling factors abstract in this study we use seismic reflection logging and core data to investigate the depositional systems and their controlling factors in the lower triassic in the northwestern margin of junggar basin the succession shows strong lateral and vertical facies variation the facies associations indicate the development of conglomeratic fan delta system with characteristics of fining upward and landward migration of facies belts a critical balance between progradation aggradation and retrogradation controlled the evolution of delta successions within an overall transgressive regime migration of the locus of active faulting exerted the primary control on fan delta thickness variations on the sandy component and gravel type within the fan delta system among different units indicate the control of provenance the climate significantly influenced the mode of sediment transfer from the feeder system to the basin the significant climate change from arid to humid played a primary role in controlling the fan delta architecture our study suggests that in tectonic active basin the controls of tectonics on the sequence stratigraphy are still fundamental however during the tectonic quiescence or rift depression transition stage significant changes of climate would play a primary role in controlling the sediment dispersal the current study reveals that the hydrocarbon reservoir shows a landward migration trend within a retreating fan delta system

mid depth calcareous contourites in the latest cretaceous of caravaca subbetic zone se spain origin and palaeohydrological significance abstract deep marine carbonates of late campanian to early maastrichtian age that crop out in the subbetic zone near caravaca se spain contain a thick succession of dm scale levels of calcareous contourites alternating with fine grained pelagites hemipelagites these contourites characterised by an abundance and variety of traction structures internal erosive surfaces and inverse and normal grading at various scales were interpreted as having been deposited under the influence of relatively deep ocean currents based on these contourites a new facies model is proposed the subsurface currents that generated the contourites of caravaca were probably related to the broad circumglobal equatorial current system the strongest oceanic feature of cretaceous times these deposits were formed in the mid depth 200 600 m hemipelagic environments at the ancient southern margin of iberia this palaeogeographic setting was susceptible to the effects of these currents because of its position close to the narrowest oceanic passage through which the broad equatorial current system flowed in the westernmost area of the tethys seaway regional uplift related to the onset of convergence between iberia and africa probably favoured the generation of the contourites during the late campanian to the early maastrichtian

a gravel lobe deposit in the prodelta of the doumsan fan delta miocene se korea abstract the doumsan fan delta system in the pohang basin miocene se korea comprises tripartite components of gilbert type topset foreset and bottomset environments with an extended prodelta in the deeper part a few hundred metres deep the present study documents sedimentologic features and origin of a gravel body here interpreted as a gravel lobe formed in the prodelta region of the doumsan fan delta the gravel lobe lies on sandy mud deposits and is capped by a thick massive sand bed it extends for more than 1 5 km with a height of up to 30 m and shows a narrow tongue like geometry eight sedimentary facies have been distinguished to describe characteristic features of the gravel lobe and the associated deposits of these three types of gravelly sedimentary facies are important with regard to volumetric contribution and depositional processes 1 crudely stratified pebble grade conglomerate 2 disorganized clast rich pebble to cobble grade conglomerate and 3 matrix rich bimodal cobble grade conglomerate the former two types dominate the central part of the lobe where they are not accompanied by sand beds whereas the latter as subordinate units is prevalent in the fringe which otherwise is dominated by thick sandy mud deposits the stacked successions of crudely stratified pebble grade conglomerate are representative of the active aggradational phases of the gravel lobe whereas the occurrence of channels within the lobe reflects that the gravel lobe prograded under the influence of subaqueous channel systems the gravel lobe resulted from catastrophic disturbance slumping on the foreset region that further caused the development of channel systems promoting efficient transport of gravelly sediments this type of deposit may represent an important additional category of low efficiency subaqueous fans

controls on reservoir quality in fan deltaic conglomerates insight from the lower triassic baikouquan formation junggar basin china abstract fan delta sandy conglomerates form important oil and gas reservoirs recently a new giant oilfield was discovered in the lower triassic baikouquan formation t1b in the mahu sag of the junggar basin northwestern china however the fan delta sandy conglomerate reservoirs are strongly heterogeneous most have poor permeability and host little hydrocarbons while a subset at the delta front exhibit high porosity and permeability forming high quality reservoirs to explain this disparity the sedimentary facies diagenesis and reservoir quality of the sandy conglomerate strata and their interactions were studied detailed logging of 253m cores indicates that the t1b was deposited in a lacustrine fan delta complex comprising ten lithofacies from coarse matrix supported pebbly conglomerate gm to fine massive mudstone fm in four facies associations interpretation of optical microscope backscattered and scanning electron microscope imaging show that these ten lithofacies underwent differential diagenesis especially dissolution of minerals such as orthoclase dissolution was particularly prevalent in the subaqueous distributary channel deposits of sandstones st hyperpycnal flow massive sandstones sm and grain flow deposits of sandy gravelly conglomerates gcs at the delta front forming abundant secondary pores these pores enhanced the reservoir performance and led to high porosity and permeability within these three lithofacies for these reservoirs continuous winnowing at the delta front led to relatively high primary porosities and subsequent mineral dissolution during burial diagenesis closely related to acidic mn rich hydrocarbon bearing fluids significantly improved the porosities further migration of hydrocarbon bearing fluids was facilitated by faults cutting through the reservoir and underlying source rocks this led to the development of belts of high quality reservoir at the delta front near the fault conduits this model for reservoir development and charge suggests that further reservoirs can be expected within the t1b of the mahu sag

hydrochemical evolution of regional groundwaters to playa brines in central australia abstract a large scale groundwater system in central australia discharges to a chain of playas recharge in calcrete and fractured rock aquifers gives rise to relatively low salinity hco 3 cl so 4 groundwaters which evolve through regional saline groundwaters to highly saline playa brines the hydrochemical evolution of the groundwaters follows the anionic sequence hco 3 cl so 4 cl bhco 3 so 4 cl so 4 hco 3 cl so 4 cl with increasing salinity there is a relative increase in na k mg cl and so 4 however there is a relative decrease in hco 3 ca and sio 2 owing to the precipitation of carbonate sulphate and silicate minerals and the resultant brines are depleted in these ions significant chemical variation in the composition of playa brines is a result of complex processes of solution evaporative concentration precipitation and mineralogical change including dolomitisation thermodynamic calculations based on the pitzer equations have enabled a general model to be developed for these evolutionary processes in saline groundwaters up to the stage of halite saturation at an early stage the regional groundwaters are saturated with respect to the carbonate minerals dolomite first then calcite with increasing salinity sulphate minerals begin to precipitate saturation with respect to gypsum is attained at a chlorinity of 19 and saturation with respect to anhydrite is attained at 122 the playa brines attain saturation with respect to halite at a chlorinity of 144 solute budgets based on a chloride concentration factor show that final playa brines are 178 times more concentrated than recharge groundwaters and confirm the virtually complete loss of hco 3 ca and sio 2 through precipitation there are subtle differences in the hydrochemistry of different central australian playa brines and also vis a vis playa brines described from other parts of the world most australian playas have brines of the cl na type with so 4 and mg also important the generally accepted hardie eugster model for brine evolution and mineral precipitation sequences has therefore been modified and extended three pathways are defined following calcite precipitation on the basis of the ratio of molar ca to alkalinity these pathways lead to saline waters with different compositions subsequent evolution of the brines depends on the ratios between molar so 4 mg ca and alkalinity

chabazite and dolomite formation in a dolocrete profile an example of a complex alkaline paragenesis in lanzarote canary islands this paper studies the weathering and soil formation processes operating on detrital sediments containing alkaline volcanic rock fragments of the mirador del rio dolocrete profile the profile consists of a lower horizon of removilised weathered basalts an intermediate red sandy mudstones horizon with irregular carbonate layers and a topmost horizon of amalgamated carbonate layers with root traces formation occurred in arid to semiarid climates giving place to a complex mineralogical association including mg carbonates and chabazite rarely described in cal dolocretes profiles initial vadose weathering processes occurred in the basalts and in directly overlying detrital sediments producing stage 1 red smectites and dolomicrite dominant phreatic stage 2 conditions allowed precipitation of coarse zoned dolomite and chabazite filling porosities in stages 3 and 4 mostly pedogenic biogenic processes played an important role in dolomite and calcite accumulation in the profile overall evolution of the profile and its mineralogical association involved initial processes dominated by alteration of host rock to provide silica and mg rich alkaline waters suitable for chabazite and dolomite formation without a previous carbonate phase dolomite formed both abiogenically and biogenically but without a previous carbonate precursor and in the absence of evaporites dominance of calcite towards the profile top is the result of mg ca decrease in the interstitial meteoric waters due to decreased supply of mg from weathering and increased supply of ca in aeolian dust meteoric origin of the water is confirmed by c and o isotope values which also indicate lack of deep sourced co2 the dolocrete studied and its complex mineral association reveal the complex interactions that occur at surface during weathering and pedogenesis of basalt sourced rocks

sequence stratigraphy sedimentary systems and petroleum plays in a low accommodation basin middle to upper members of the lower jurassic sangonghe formation central junggar basin northwestern china abstract the lower jurassic junggar basin is a low accommodation basin in northwestern china because of low subsidence rates and a warm wet climate deposits of the central subbasin of the junggar basin formed from fluvial deltaic shallow lake facies sequence stratigraphy and sedimentary systems of the lower jurassic members of the sangonghe formation j1s were evaluated by observing cores interpreting wireline logs and examining seismic profiles two third order sequences were recognized in the strata the distribution of the sedimentary systems in the systems tracts shows that tectonic movement paleorelief paleoclimate and changes in lake level controlled the architecture of individual sequences during the development of the lowstand systems tract lst the intense structural movement of the basin resulted in a significant fall in the water level in the lake accompanied by rapid accommodation decrease braided rivers and their deltaic systems were also developed in the central junggar basin sediments carried by braided rivers were deposited on upward slopes of the paleorelief and braid delta fronts were deposited on downward slopes during the transgressive systems tract tst the tectonic movement of the basin was quiescent and the climate was warm and humid lake levels rose and accommodation increased quickly shoal lines moved landward and shore to shallow lake deposits sublacustrine fans and deep lake facies were deposited in shallow to deep lake environments during the highstand systems tract hst the accommodation no longer increased but sediment supply continued far exceeding accommodation hst deposits slowly formed in shallow lake to meandering river delta front environments relatively low rates of structural subsidence and low accommodation resulted in coarse grained successions that were fining upward deposits were controlled by structural movement and paleorelief within the lst to tst deposits in the central subbasin fine to medium grained coarsening upward successions developed during the hst the sand bodies of braid delta fronts on the downward slopes of the paleorelief in the lst and the sublacustrine fans in the tst became reservoirs for hydrocarbon accumulation petroleum plays have only been found in the sangonghe formation j1s located on structural ridges that consist of sand bodies comprising these sequences favorable conditions for petroleum plays in hst1 lst2 occur where the sand bodies have been fractured by faults and sealed by denudation and pinch out lines then overlain by deep lake mudstone in tst2 the favorable condition of the sand bodies within tst2 occurs where isolated sand bodies have been fractured by faults

influence of early diagenesis on reservoir quality of rotliegende sandstones northern netherlands reservoir quality of rotliegende sandstones lower permian in the northern netherlands was significantly affected by early diagenetic processes that are related to sedimentary facies in marginal desert playa lake environments in the past burial related products and processes have received more attention than early diagenetic processes neglecting the effects that early diagenesis can have on reservoir quality and well productivity of rotliegende sandstones shallow groundwater related diagenesis is a major factor affecting rotliegende reservoir sandstones the precipitation of the main porosity occluding cements dolomite anhydrite and quartz occurred early in the diagenetic history oxygen isotopes of dolomite d18o 18 4 to 23 4 smow suggest that meteoric water has played a major role throughout the diagenetic history and that precipitation of these cements occurred at low temperatures 80 c the strontium isotopes of dolomite cements 87sr 86sr 0 70935 0 71387 and the sulfur isotopes of anhydrite cements d34s 6 7 to 9 7 cdt rule out permian or younger seawater as a source for these cements and are consistent with formation from meteoric water within a continental basin an early diagenetic origin of the cements is also suggested by the fact that the majority of sandstone samples have lost more porosity due to cementation than through compaction most samples with high 20 amounts of porosity loss via cementation were affected by early dolomite and anhydrite the relative abundance of dolomite and anhydrite cements can be correlated with depositional environments wet depositional environments e g interdune and fluvial sandstones with water tables close to the surface show the highest amount of dolomite and anhydrite cements whereas dry environments with relatively deep water tables e g dune sandstones are characterized by low amounts of cements the precipitation of early diagenetic cements has strongly influenced the present day porosity patterns with depositional environments interpreted as drier showing less cements and significantly altering the porosity patterns formed during early diagenesis knowledge of the influence of sedimentology and paleogeography on the diagenetic patterns is a key element for improved understanding and prediction of reservoir quality in the rotliegende sandstones of the northern netherlands

dating inset terraces and offset fans along the dehshir fault iran combining cosmogenic and osl methods summary be and 36 cl cosmic ray exposure cre and optically stimulated luminescence osl dating of offset terraces have been performed to constrain the long term slip rate of the dehshir fault analysis of cosmogenic 10 be and 36 cl in 73 surface cobbles and 27 near surface amalgamscollectedfrominsetterracesdemonstratestheoccurrenceofalowdenudationrateof 1mm a 1 and of a significant and variable inheritance from exposure prior to the aggradation of these alluvial terraces the significant concentrations of cosmogenic nuclides measured in the cobbles collected within the riverbeds correspond to 72 20 ka of inheritance the mean creageofthesurfacesamplescollectedontheolderterracet3is469 88kabuttheanalysis of the distribution of 10 be concentration in the near surface samples discard ages older than 412 ka the mean cre age of the surface samples collected on terrace t2 is 175 62 ka but the 10 be depth profile discard ages older than 107 ka for each terrace there is a statistical outlier with a younger age of 49 9 3 3 and 235 5 35 4 ka on t2 and t3 respectively the late sediments aggraded before the abandonment of t2 and inset levels t1 b and t1a yielded osl ages of respectively 26 9 1 3 21 9 1 5 and 10 0 0 6 ka for a given terrace the osl ages where available provide ages that are systematically younger than the cre ages these discrepancies between the cre and osl ages exemplify the variability of the inheritance and indicate the youngest cobble on a terrace that minimizes the inheritance is the most appropriate cre age for approaching that of terrace abandonment however the upper bound on the age of abandonment of a terrace that is young with respect to the amount of inheritance is best estimated by the osl dating of the terrace material for such terraces the cre measurements are complementary of osl dating and can be used to unravel the complex historyofweatheringandtransportinthecatchmentofdesertalluvialfans thiscomprehensive set of dating is combined with morphological offsets ranging from 12 2t o 380 20 m to demonstrate the dehshir fault slips at a rate in the range 0 9 mm yr 1 1 5 mm yr 1 t he variable inheritance exemplified here may have significant implications for cre dating in arid endorheic plateaus such as tibet and altiplano

modal distribution of pore throat size in sandy conglomerates from an alluvial fan environment lower karamay formation junggar basin west china abstract alluvial fan exhibits various modal distribution of pore throat size which effectively control the oil displacement efficiency and fluid movement however the genetic mechanism of the modal distribution of the pore throat size and its macroscopic distribution within alluvial fan is poorly understood based on core analysis this paper which take the sandy conglomerate reservoir within the alluvial fan in junggar basin as an example aims to study the variations in modal distribution of pore throat size and controlling mechanisms the results reveal that 1 the modal distribution types of the pore throat size are complicated and can be classified into six subtypes including unimodal type uni unimodal type uni unimodal type uni bimodal type bi bimodal type bi and multimodal type multi uni uni and uni is dominated by intergranular pores intragranular dissolved pores and micropores respectively bi bi and multi are characterized by the combination of several pore types 2 diagenesis including compaction cementation and dissolution rock composition the mudstone fragment content and rock texture the clay content control the volume of each pore throat type which significantly influences the modal distribution of the pore throat size lithofacies with low mudstone fragment and clay content and great grain sorting tend to have experienced weak compaction thereby retaining a large volume of intergranular pores and have been subjected to strong dissolution when adequate acidic ions occur in the porewater resulting in a large volume of intragranular dissolved pores strong dissolution reduced the rock compressive strength and further enhanced the degree of mechanical compaction during the burial process cementation occurred later than compaction and dissolution and its intensity is controlled by the supply of co2 and ca2 and compaction intensity thus reducing the volume of intergranular pores the content of mudstone fragment and clay varies among different lithofacies of different origins for traction current deposits lithofacies with smaller median grain size contain fewer mudstone fragments resulting in fewer micropores the clay content decreased first and then increased with decreasing median grain size and lithofacies with lower clay content cause less volume of micropores 3 lithofacies types combined with porewater condition for dissolution and lithofacies location affect the diagenetic intensity rock composition and rock texture variations thus resulting in various modal distribution of pore throat size within the alluvial fan moreover the rock texture especially grain sorting is very important for compaction and facilitates percolation of meteoric water and dissolution

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

carnotite mineralization in inland drainage areas of australia abstract calcrete deposits developed adjacent to gypsite facies in arid inland drainage areas of australia contain several economic carnotite deposits major prospects and numerous minor occurrences the calcareous lithofacies located in the ponded sections of internal drainage systems are not only the main host for localization and concentration of uranium but they also offer the greatest number and variety of depositional environments for carnotite ore development factors identified as fundamental in carnotite mineralization include the physiographic and hydrologic setting of the individual uraniferous drainage systems and the solution chemistry pco2 co 3 hco 3 u v k concentrations eh ph however variation in several basic ore characteristics mineralogic textural and chemical variations radiometric disequilibrium and or distribution in some of the mineralized areas suggest that a major factor controlling the presence and ultimate extent of carnotite mineralization relates to the nature and extent of post depositional modification of earlier deposits due to changing chemical physical processes variation in the modes of carnotite precipitation relates directly to the textural and compositional characteristics of the host in different groundwater hydrologic zones hence the chemical modifications may be directly attributed to the contemporary hydrologic circulation pattern in individual drainage systems the physical processes mainly relate to the downward gradation of vadose modification into mineralized calcretes which may ultimately result in redistribution of ore zones within the drainages

distinguishing early groundwater alteration effects from pedogenesis in ancient alluvial basins examples from the palaeogene of southern portugal colour mottling and horizons of secondary carbonates are common in ancient alluvial sequences and are normally interpreted as pedogenic features they have been used to assess palaeoclimates soil drainage conditions and deposition rates palaeogene alluvial deposits in the sado and lisbon basins of portugal exhibit prominent colour variations and mottle patterns as well as carbonate accumulations both at the bases of fining upwards cyclothems and as thick units up to 20 m capping alluvial megasequences however these colour and carbonate features are interpreted as the products of shallow saline reducing groundwaters unrelated to pedogenesis such non pedogenic products are easily mistaken for soil formed ones and criteria for differentiating the two are reviewed to assist interpretations in other alluvial deposits key criteria are thickness gradational tops and bases absence of soil horizon features occurrence in coarser alluvium and prevalence of hydromorphic colour and mottling patterns

classification and genesis of calcrete and gypsite lithofacies in paleodrainage systems of inland australia and their relationship to carnotite mineralization calcrete and gypsite lithofacies are chemical sedimentary rocks irre spective of age and or stratigraphic position the depositional environments of these deposits indicate that since early tertiary silting up of inland drainage developed internal salt lake systems with gypsite as the dominant evaporitic lithotype elongate bodies of phreatic calcrete formed in paleochannels almost all primary calcretes and gypsites have been modified by phreatic and vadose diagenetic processes because the diagenetic processes are complex stratigraphic analysis is difficult carnotite mineralization is probably not contemporaneous with calcretization assuming that waters from fertile uraniferous sources are flowing through the sediments several controls will govern carnotite mineralization ponding by physical or chemical barriers solution chemistry p co2 co 3 hco 3 v u and k concentrations eh ph and postdepositional physical or chemical changes for significant carnotite bodies to remain primary deposition must have been followed by a freezing mechanism to preserve the deposit diagenetic conditions which may cause remobilization vary between deposits therefore it may be unwise to use a single deposit as the basis for a widely applicable exploration model modified journal abstract

evolution of calcrete in palaeodrainages of the lake napperby area central australia abstract carbonate lithofacies developed along the trunk valley of palaeodrainage channels as well as those adjacent to gypsite facies in the lake napperby drainage basin in central australia show wide ranges of sedimentary characteristics reflecting significant variation in depositional environments sedimentological and geochemical characterization of the calcrete lithofacies in this drainage area indicate that whereas variations in bedrock morphology are important in overall distribution of the phreatic and vadose calcrete varieties faulting and basin adjustments since the early quaternary may also have played a significant role in redistribution of the hydrologic zones and hence the evolution of these calcretes accordingly phreatic calcretes which initially precipitated from laterally moving groundwaters along the palaeodrainage channels undergo systematic mineralogical changes due to direct evaporative precipitation and diagenetic displacement replacement processes mainly dolomitization and silicification under present hydro chemical conditions within the zone of grounwater fluctuations however lateral and downward shifts in groundwater flow due to excessive volumetric expansion and reduction in effective permeability of calcrete may ultimately result in isolation of the calcrete like those observed from the eastern margins of the lake the evolution of the vadose calcretes is thereafter topographically controlled and relates to mobilization and redistribution of earlier deposited calcretes under present meteorological conditions