how paleosols influence groundwater flow and arsenic pollution a model from the bengal basin and its worldwide implication in the bengal basin the land surface exposed during the last lowstand of sea level around 20 ka and now buried by holocene sediment is capped by an effectively impermeable clay paleosol that we term the last glacial maximum paleosol lgmp the paleosol strongly affects groundwater flow and controls the location of arsenic pollution in the shallow aquifers of our study site in southern west bengal and by implication in shallow aquifers across the bengal basin and as polluted deltaic aquifers worldwide the presence of the lgmp defines paleointerfluvial areas it is absent from paleochannel areas a paleosol model of pollution proposed here predicts that groundwater in paleochannels is polluted by arsenic while that beneath paleointerfluvial areas is not paleointerfluvial aquifers are unpolluted because they are protected by the lgmp from downward migration of arsenic and from downward migration of organic matter that drives as pollution via reductive dissolution of as bearing iron oxyhydroxides horizontal groundwater flow carries arsenic from paleochannels toward paleointerfluvial aquifers in which sorption of arsenic minimizes the risk of pollution

facies and architectural element analysis of a meandering fluvial succession the permian warchha sandstone salt range pakistan abstract the 30 to 155 m thick early permian artinskian warchha sandstone of the salt range pakistan is a conglomerate sandstone and claystone succession within which seven lithofacies types gt st sp sr sh fl and fm occur in a predictable order as repeated fining upward cycles common sedimentary structures in the conglomerates and sandstones include planar and trough cross bedding planar lamination soft sediment deformed bedding compound cosets of strata with low angle inclined bounding surfaces and lags of imbricated pebbles structures in the finer grained facies include desiccation cracks raindrop imprints caliche nodules and bioturbation groups of associated facies are arranged into nine distinct architectural elements channels gravel bars sandy bedforms downstream and laterally accreting barforms sand sheets crevasse splays levees floodplain units and shallow lakes which is consistent with a fluvial origin for the succession the types of architectural elements present and their relationship to each other demonstrate that the warchha sandstone preserves a record of a meandering river system that drained the northern margin of gondwanaland the dominance of fine grained floodplain facies over gravel grade channel base facies and the widespread occurrence of large scale lateral accretion elements supports the interpretation of a high sinuosity meandering fluvial system in which channel bodies accumulated via the lateral accretion of point bars but in which the active channels covered only a small part of a broad floodplain at any time instant although the regional and temporal distribution of these deposits is complex in broad terms the lower part is dominated by stacked multistorey channel bodies whereas single storey channel elements isolated in abundant fine grained floodplain deposits dominate the middle and upper parts of the formation

internal structure of aeolian dunes in abu dhabi determined using ground penetrating radar a ground penetrating radar survey of aeolian dunes in the al liwa area of abu dhabi reveals a variety of dipping reflectors which are interpreted as primary sedimentary structures the interpretation of the radar profiles has been confirmed by bulldozing trenches through the study area and comparing logged sections in the trenches with the radar profiles nnw sse orientated radar profiles approximately parallel to the prevailing wind direction show two sets of dipping reflectors which are interpreted as sets of cross stratification and second and third order bounding surfaces radar profiles orientated wsw ene across the prevailing wind direction are dominated by concave up reflectors which are interpreted as trough shaped scours and sets of trough cross stratification produced by oblique progradation of barchanoid dunes nested troughs with small sets of trough cross stratification within larger troughs may be due to reactivation following wind reversal or the superposition of small dunes on larger dunes and the fill of large dune troughs by smaller dunes convex upwards reflectors are interpreted as linear spurs on the convex portions of sinuous dunes or erosional remnants between troughs overall there is a tendency for the larger second order bounding surfaces to dip downwind which confirms brookfield s ideas of the relative migration paths of dunes and draa

a sulfate control on marine mid depth euxinia on the early cambrian ca 529 521 ma yangtze platform south china abstract given the high oxygen demands of complex metazoans a sound understanding of marine redox conditions is essential to reconstruct the factors that lead to the dramatic increases in ecosystem complexity and biological diversity in the early cambrian in this study we report new fe mo c s geochemical data from black shale rich strata of the early cambrian continental margin yangjiaping section in the yangtze platform south china integrated fe speciation and mo abundance data from the yangjiaping section in combination with previously reported data from shatan inner shelf songtao slope and longbizui basinal sections suggest mid depth euxinic waters coexisting with ferruginous deep waters and oxic surface waters this redox structure is similar to conditions previously suggested for the ediacaran yangtze platform and other proterozoic marine basins indicating that proterozoic layered ocean redox structure in some basins persisted into the early cambrian furthermore the fe mo data demonstrate that the mid depth euxinia was widespread during a marine transgression but shrank gradually along with widespread shelf oxygenation when the basin evolved into subsequent regression excess highly reactive iron fe hr in deep water with a hydrothermal origin may have had a control on the mid depth euxinia given geochemical and geological evidence for basinal hydrothermal activities on the other hand a sulfate limitation on bacterial sulfate reduction bsr and sulfide generation was suggested by a weak correlation r 2 0 22 between pyrite iron versus fe hr and total organic carbon toc form anoxic deep water sections and high toc averagely 6 in the deepest ferruginous water longbizui section furthermore a spatial gradient was observed in sulfur isotopic composition of pyrite averagely from 0 2 to 21 0 consistent with a lateral gradient of sulfate in concentration or and in isotope from shore to distal waters on the transgressive yangtze platform we accordingly proposed that two distinct sources riverine input and ocean reservoir provided sulfate for bsr dominantly in near shore and distal areas respectively and the euxinic retreat observed for the regression can be explained as a response to the progressive sulfate consumption of the ocean reservoir by intensive bsr and pyrite formation during preceding transgression therefore our results support a sulfate control on the spatiotemporal distribution of mid depth marine euxinia on the yangtze platform in early cambrian when complex metazoans rapidly evolved

basinwide sedimentation and the continuum of paleoflow in an ancient river system kayenta formation lower jurassic central portion colorado plateau abstract utilizing detailed documentation of alluvial architecture to reconstruct the continuum of paleoflow perennial intermittent ephemeral a basinwide study of the kayenta formation lower jurassic reveals that the northern half of the basin is characterized by sandy low sinuosity fluvial systems which exhibit perennial assoc 1 to intermittent assoc 2 discharge indicators the rivers had headwaters east of the uncompahgre highlands western colorado and flowed southwest across the basin depositing a braidplain of channel sands with well preserved 3 dimensional macroforms one significant aspect of the macroform architecture is documentation of macroform climb in both an upstream and downstream direction the macroforms aggrade vertically by climbing maximum 10 dip in an upstream direction and migrating over the backs upstream ends of underlying macroforms the process of macroform climb records a minimum water depth of 8 m and a maximum of 16 m which places the kayenta perennial waterways assoc 1 within a mesothermal hydrologic regime the southern portion of the basin contains intermittent assoc 2 to ephemeral assoc 3 fluvial deposits extensive floodplain preservation and eolian dune and interdune sandsheet deposition assoc 4 a tributary drainage pattern to the northwest was established by smaller low to moderately sinuous streams eolian dune and interdune deposits migrated across this more arid windswept portion of the basin the range of alluvial architecture present in the kayenta attests to the diversity that can be found in a small continental sedimentary basin

reply to comment by k sugitani et al 2016 on the article archean coastal plain paleosols and life on land by g j retallack et al 2016 gondwana research 40 1 20

latest pleistocene and holocene dune construction at the north eastern edge of the rub al khali united arab emirates abstract optical dating of two dune pro les developed in linear dunes in ras alkhaimah united arab emirates has been used to establish the timing and rateof dune accretion one section at awa was over 17 m high while that at idhnwas over 40 m high the awa dune appears to have accumulated very rapidly 10 000 years ago with a vertical accumulation rate of about 3ae3mka 1 theidhn dune appears to have accumulated over the past 1000 years with 20 m ofsediment accumulating in a time period of about 270 years the awa dunemay have accumulated in response to the transgression of the persian gulf byrising sea levels in late pleistocene and holocene times the idhn dune mayhave accumulated rapidly because of intensi ed human activity a short livedclimatic event or because it may periodically be reactivated after erosion by uvial action at its base keywords linear dune optical dating rub al khali sand accumulation introductionthere remains some uncertainty surrounding thestyle and timing of deposition of large aeoliandunes with authors supporting both gradual andpunctuated models of dune development for adiscussion see thomas 1997 this divergence ofopinion results from both the general absence ofdating control within dunes in most studies anddif culties in gaining exposures within some ofthe larger dune bedforms the purpose of thispaper is to establish a chronology of dunedevelopment for two thick 10 m dune sectionsexcavated within large complex linear dunesfrom within the rub al khali near ras alkhaimah in the north of the united arabemirates fig 1 the sites were selected becauseof the availability of thick fresh sections inrecently excavated moist sand with an area of around 600 000 km

ephemeral fluvial deposits integrated outcrop and simulation studies reveal complexity ephemeral fluvial sandstones form the main reservoirs in many oil and gas fields production histories and development difficulties suggest these deposits are more complex than is commonly supposed in the petroleum industry there is inadequate published information to account for this observation relevant sedimentological literature on such deposits is qualitative and unsuitable for detailed reservoir characterization studies therefore integrated sedimentological petrophysical and fluid flow simulation studies have been conducted on outcrop analogs in the southwestern united states our key objectives were to define flow units and to find areas of sensitivity inherent both in the sediments and in the analytical and statistical procedures used to describe and model s ch systems we report results of integrated studies on the lower jurassic kayenta formation in southeastern utah the kayenta formation is a relatively proximal sand rich succession dominated by channel fill sandstones sedimentological analysis identified eight main genetic units in contrast reservoir simulations based on probe permeameter data collected at outcrop show that six of the main genetic units have uniform flow behavior intraformational mudclast conglomerates are the dominant permeability barriers both because of the clasts themselves and because they act as sites of preferential cementation stochastic permeability models conditioned to the outcrop data produce results little different from models based on averaged values for each facies the most sensitive feature of the mode s concerns the assumptions made about the mudclast conglomerates the model results show that only by integrating analytical approaches can we understand the full character of an outcrop analog in such a way that we can use it predictively

architectural features of the kayenta formation lower jurassic colorado plateau usa relationship to salt tectonics in the paradox basin abstract fluvial sandstones of the kayenta formation were analyzed using architectural element analysis paleocurrent trends the distribution of lacustrine facies and local silcrete development indicate that synsedimentary movement of evaporites in the underlying paradox basin created an unstable basin floor beneath the kayenta fluvial system this instability resulted in deflection of fluvial axes local basin development and local areas of interrupted fluvial deposition with eolian dunes paleocurrent trends in the kayenta system reflect periodic interruptions of southwesterly flow salt migrating laterally out of a rim syncline into an adjacent salt anticline resulted in a rim syncline of slight topographic relief the resulting basin was probably rapidly filled allowing the resumption of southwesterly flow differential movement of salt incipient solution collapse features resulted in the formation of small centripetal basins in which playa mudstones formed a laterally extensive resistant ledge underlies a horizontal surface suggestive of deflation to the water table of an exposed section of valley fill a channel scour in the top of one of these surfaces has margins much steeper 60 than the angle of repose for unconsolidated sand early cementation of the exposed floodplain could account for this resistance

event stratigraphy paleoenvironment and chronology of se arabian deserts the geological record of the se arabian desert is exhibited in a variety of geomorphic features and their characteristic sediments ranging from alluvial fans to inland and coastal dunes and sabkhas together they suggest a large range of environmental and climatic variability between periods of relative aridity and humidity sedimentary events in the emirates appear to correlate broadly with high latitude glaciations which affected both the shamal winds and the extent of exposure of the arabian gulf in general the aeolian sands in the rub al khali responded to glacial events as a consequence of exposure of the floor of the arabian gulf during glacials when global sea level was low quartz sands from across the exposed floor of the arabian gulf were transported by the shamal winds south eastwards to the emirates and then south to the rub al khali the supply of shamal transported sand from the floor of the arabian gulf was cut off by high stands of sea level during interglacial periods the new coastal dunes miliolite rich in foraminifera and other cement assisting calcareous shell fragments were deflated down to the water table as their sand was transported further to the south leading to the creation of coastal sabkhas studies on aeolianites and the lacustrine deposits provide evidence of phases of enhanced humidity prior to the last glacial maximum and during the holocene in contrast the bedding attitudes of miliolites in se oman suggest that the wahiba sands were transported from south to north by a branch of the sw monsoon the depositional ages of these dunes indicate a close connection between the winds and coeval fluctuations of the sw monsoon the interdunal lakes and underlying dune sands reflect an active sw monsoon during the holocene this is also indicated by the aeolian and lacustrine records of the thar desert in india which likewise are controlled by the sw monsoon south and west of the oman mountains is a broad alluvial fan bajada that is mostly inactive today the oldest fluvial sediments are undated but preliminary age estimates suggest that some correlate with more humid earlier interglacials

paleoproterozoic ca 1 9 ga megascopic life on land in western australia abstract controversial hairpin shaped trace fossils myxomitodes stirlingensis and discoid fossils cyclomedusa davidi are here reinterpreted in a reassessment of sedimentology and paleosols of the 1 9 0 1 ga stirling range formation of western australia paleosols in the stirling range formation were recognized from complex cracking patterns peds and cutans chemical and mineralogical zonation soil horizons and poikiloblastic crystals desert roses redox profiles of the paleosols are evidence of well drained profiles of a coastal plain under a low oxygen 433 116 ppmv and carbon dioxide 564 64 ppmv atmosphere gypsum pseudomorphs in paleosols that are deeply weathered chemically represent a persistence of acid sulfate weathering better known in archean paleosols before the great oxidation event at 2 45 ga chemical composition of the paleosols is evidence of a humid 1478 182 mm mean annual precipitation temperate 11 3 0 5 c mean annual temperature paleoclimate their paleoenvironmental setting was a coastal plain on a passive tectonic margin megafossils were found on paleosols of western red sandstones of the stirling range formation not in gray shales and sandstones of marine facies to the east trace fossils myxomitodes stirlingensis and discoid fossils are both found at the surface of well drained paleosols and so were not metazoan trails nor sea jellies myxomitodes was more likely a grex slug trail of soil slime molds and the cyclomedusa discoids were probably microbial colonies pervasive microfilamentous structures in the paleosol surface are additional evidence of paleoproterozoic microbial earth ecosystems

oceanic anoxia at the precambrian cambrian boundary the precambrian cambrian pc c boundary separates fossils representing two discrete evolutionary phases the neoproterozoic soft bodied ediacarian biotas and cambrian small shelly faunas the biological discontinuity is suspected to have been a result of mass extinction however recent discoveries of the ediacarian biotas in cambrian sediments have led to an understanding that the faunal change was gradual through the pc c transition th u ratios which are high in oxidizing conditions and low in reducing conditions show a considerable positive correlation with 13c values at all studied sites of the pc c boundary this correlation indicates that reported 13c variation across the pc c boundary from numerous localities corresponds to redox variation in the depositional environment the negative 13c anomaly that occurs worldwide at the pc c boundary therefore corresponds to the widespread development of an oxygen deficient shallow marine environment this finding suggests that widespread oceanic oxygen deficiency which has been interpreted to reflect phanerozoic mass extinction events also occurred immediately before the cambrian explosion

composition effects on pore structure of transitional shale a case study of the upper carboniferous taiyuan formation in the eastern uplift of the liaohe depression china abstract transitional shale is very different from marine shale with respect to mineral composition and pore structure insights into the effects of rock composition on pore structure can aid understanding of the storage and migration mechanisms of shale gas in a reservoir to investigate the compositional effects on pore structure a combination of geochemical and petrophysical experiments were conducted on four bulk shale samples and their corresponding extracted organic matter om and clay mineral samples the experimental results show that the removal of om using h2o2 during clay mineral extraction oxidizes and removes pyrite and siderite from the samples while other inorganic phases remain unaffected om hosted more abundant micropores compared with clay minerals while mesopores and fine macropores are dominant in clay minerals effects of the om and clay minerals on pore volume and surface area are quantitatively evaluated on the basis of weight normalized pore size distribution psd curves of extracted om and clay mineral samples in terms of the co2 adsorption contribution from om and clay minerals to micropore volume miv are 19 43 32 92 and 18 75 39 05 respectively and to micropore surface area mis are 19 30 32 28 and 16 42 35 72 other minerals other than organic matter and clay minerals account for 34 29 48 93 of the miv and 39 75 52 98 of the mis n2 adsorption results reveal that the pore volume and surface area are mainly attributable to the clay minerals providing 54 37 80 75 of the bjh pore volume bjhv average 65 83 and 70 68 87 04 of the bet surface area bets average 78 71 the primary medium for pore development in marine shale is om whereas pores in the transitional shale are mostly found in the clay and other inorganic minerals therefore the hydraulic fracturing design and drilling related operations involved in the exploitation of transitional shale gas should be appropriately adjusted and improved in order to accommodate intrinsic characteristics of the transitional shale gas reservoir

depositional environments architecture and controls of early cretaceous non marine successions in the northwestern part of kyongsang basin korea abstract in the northwestern part of kyongsang basin southeast korea non marine successions of interbedded sandstone and mudstone are divided into successive stratigraphic units on the basis of facies assemblages and sandstone architecture parts of the successions sinpyong anpyong and jotap units formed in southward or southeastward draining fluvial systems are documented in detail in terms of macroform scale to stratigraphic level architecture for the assessment of fluvial styles and evolution of non marine depositional environments the sinpyong anpyong unit consists of thick sandstone bodies 2 47 m thick thin sandstone bodies generally the jotap unit overlying the sinpyong anpyong unit comprises thick sandstone bodies 2 10 m thick interbedded sandstone siltstone bodies and siltstone dominated bodies the thick sandstone bodies are dominated by the deposits of small bars and dunes with common lenticular beds of purple siltstone and internal scour surfaces suggestive of bedform dominated channels with ephemeral discharges the channels are estimated at generally a few meters in depth and a few tens to hundreds of meters in width the interbedded sandstone siltstone bodies comprise thin sheet like and lenticular sandstone beds along with the marked change in fluvial styles the successions show systematic variations in the proportion and connectedness of channel sandstone bodies and the distribution of floodplain lake facies the basal and uppermost parts of the sinpyong anpyong unit are characterized by the sourceward expansion of distal poorly drained floodplain shallow lake facies and the low proportion and connectedness of channel bodies following these gray mudstone dominated sequences the middle part of sinpyong anpyong unit and jotap unit show increases in the proportion connectedness and grain size of channel bodies and basinward expansion of proximal well drained floodplain facies such a stratigraphic architecture can be attributed to the fluctuations in the ratio of accommodation space sediment supply regulated by repeated basin subsidence

cyanobacterial algal crusts from late ediacaran paleosols of the east european craton abstract the top surface of the ediacaran flood basalts of west ukraine volyn extruded during the break up of rodinia supercontinent is weathered into several meters thick paleosol covered by late ediacaran ca 550 ma sediments the paleosol grades from unaltered basaltic material into saprock and finally clay dominated saprolite with a minor content of the organic matter the upper parts are dominated by kaolinite and hematite sem images and sem eds analyses revealed in one of the paleosol profiles a horizon with significant amount of morphologically recognizable organic structures mineralized by silicates and iron oxides hf etching of the bulk rock samples revealed lithic fragments covered irregularly by a biocrust of colonial coccoid cyanobacteria associated with irregularly distributed unicellular algae the cyanobacteria are preserved as mineralized common mucilage sheaths glycocalyx which reproduce the original shape typical of sheaths of modern coccoidal cyanobacterial biofilms whereas the heavily mineralized algae show features characteristic of modern chlorococcaleans the preservation of morphologically distinguishable remnants of cyanobacterial biofilms and aggregates of unicellular algae in terrestrial weathering deposits is a rare preservational phenomenon requiring rapid post mortem permineralization of the dead microbiota one of the main factors facilitating such a unique fossilization was supposedly a copious excretion of extracellular polymeric substances eps by the biocrust forming biota in which early mineral nucleation occurred the colonization of the late ediacaran land by the presumably desiccation resistant cyanobacteria dominated crust communities associated with algae was of importance for creating fertile soils and a soil forming microbial ecosystem that later allowed a successful land invasion by the ancestors of vascular plants

architecture of a sandstone uranium reservoir and the spatial distribution of its internal carbonaceous debris a case study of the zhiluo formation eastern ordos basin northern china abstract the sandstone of the middle jurassic zhiluo formation in the eastern ordos basin provides the opportunity for conducting a critical case study of the architecture and internal carbonaceous debris cd distribution of a sandstone uranium reservoir located in a field outcrop in shiwan the 16 24 m thick outcrop section is a sandstone dominated subaqueous distributary channel succession in which six lithofacies types se st sm sp sh and fl occur in a predictable order of repeated fining upward cycles these facies emphasize that the dominant structures had been deposited under lower flow regime conditions various groups of associated facies have been identified as six distinct architectural elements intrachannel units longitudinal bar transverse bar diagonal bar dune complex and abandoned channel deposits within a framework of five orders of bounding surfaces these elements with specific lithofacies associations and spatial relationships indicate that the subaqueous distributary channel had involved in four stages of formation channel occurring channel flooding channel waning and channel abandonment moreover as one of the most significant reductants in the sandstone succession the cd occurs in the form of channel lags and is concentrated in the middle and lower parts of the lag deposit zones the spatial distribution of cd within the studied succession is controlled by the sandstone architecture and the cd rich zones are preserved exclusively upon the basal surfaces of intrachannel units longitudinal and transverse bars this study can be helpful for exploring the distribution of metallogenic flow field as well as the restriction of the reductants on interlayer oxidation

irreversible change of the oceanic carbon cycle in the earliest cambrian high resolution organic and inorganic carbon chemostratigraphy in the three gorges area south china the terminal neoproterozoic and its transition into the cambrian witnessed major evolutionary and geochemical changes large fluctuations in the carbon isotope ratio for inorganic carbon 13ccarb across the precambrian cambrian boundary pc c boundary indicate a significant change in the oceanic carbon cycle at that time this work presents the first high resolution 13corg chemostratigraphy of drill core samples across the pc c boundary in the three gorges area south china and discusses carbon cycles based on the relation between 13corg and 13ccarb we found that changes of 13corg and 13ccarb values were decoupled during the significant negative excursion of 13ccarb across the pc c boundary suggesting the presence of a huge organic carbon pool ocp previously the large ocp was inferred to have been established in the terminal proterozoic and to have disappeared at the end of the mid ediacaran shuram excursion in contrast our study suggests that the large ocp lasted until the early nemakit daldynian stage on the other hand in the middle nemakit daldynian to atdabanian the 13ccarb and 13corg changed in parallel as observed normally in the phanerozoic in order to evaluate these scenarios quantitatively we performed numerical simulations and calculated the time evolution of the 13ccarb masses of the inorganic and organic carbon pools and the fluxes between them as a result we show that the observed negative 13ccarb excursion with steady 13corg can be produced by enhanced primary productivity and remineralization of the large ocp if the rate constant for removal of organic carbon was considerably lower than that of today the end of the decoupled negative 13ccarb excursion is attributable to an increase in the removal rates of inorganic and organic carbon from the ocean the enhanced flux of organic carbon burials eliminated the large ocp so that the modern style carbon cycle was established by the early nemakit daldynian stage the inferred rapid increases of both organic and inorganic carbon burial rates in the middle nemakit daldynian stage were likely caused by the appearance of planktonic metazoans with guts making fecal pellets and by the first skeletal animals the biological innovations may have changed the oceanic carbon cycle irreversibly just after the pc c boundary

selenium arsenic and molybdenum variation and bio radiation in the ediacaran cambrian interval abstract the ediacaran early cambrian period is critical for the evolution of multicellular life however the distribution and enrichment patterns of biological trace elements and their correlations with the bio changes are not yet fully understood here we present the variation patterns of trace elements in the yangtze gorges area south china compared to the upper continental crust selenium se cadmium cd arsenic as and molybdenum mo are the most enriched and varied trace elements in the whole ediacaran and early cambrian formations the concentrations of which vary from 10 5 to 30 1 0 02 to 163 1 5 10 5 to 196 5 and 0 02 to 289 0 mg kg respectively with average values of 1 3 1 0 14 0 and 8 0 mg kg average enrichment factors ef of 27 0 10 7 9 7 and 5 4 and ef variations of 601 2 1663 6 131 0 and 192 6 respectively the significantly enriched ef 10 strata sequences of se and as mainly include the lower and upper ediacaran doushantuo member ii dst ii dst iv bottom and upper yanjiahe formation precambrian cambrian and shuijingtuo formation early cambrian mo displays similar significantly enriched strata with se and as from dst iv and above compared to the cryogenian nantuo formation se as and mo are enriched and concentrated in the whole ediacaran and early cambrian strata especially at the early ediacaran doushantuo formation the diachronous yanjiahe formation precambrian cambrian and the early cambrian shuijingtuo formation which are the horizons of the great bio changes moreover the significantly enriched strata of se as and mo are also consistent with intervals of great bio changes

late quaternary humidity and aridity dynamics in the northeast rub al khali united arab emirates implications for early human dispersal and occupation of eastern arabia the major driver of palaeoclimatic dynamics over the southeast arabian region is the varying latitudinal interface between the westerly driven shamaal winds and a northward branch of the southwesterly indian ocean summer monsoon iom at present this latter system is restricted in extent to the southern coastal regions of yemen and oman monsoonal winds are widely believed to have increased in strength and penetrated much further north across southeast arabia at various intervals during the quaternary resulting in a series of humid phases which early studies suggested focussed within mis 3 and mis 1 recent speleothem studies from oman and uae have indicated humidity within mis 5 which with current debates surrounding early human dispersal and occupation could be significant for affirming the regional potential for early occupation we investigate two new geoproxy suites from al ain and tawi asmar northern uae in the presently hyper arid rub al khali sand sea that preserve evidence of multiple episodes of aeolian deposition and humidity in the form of fluvial gravels sands and silts and dune sands 35 osl ages demonstrate humid episodes occurred in mis 5e 5a and the early holocene with a major dry dune building phase in late mis 3 and the onset of dry conditions again from 6 ka the fluvial sedimentary evidence from mis 5e and 5a suggest that the present hyper arid desert landscape of the northeastern rub al khali was at those times represented by an environment experiencing significant seasonal wadi flow this provides an environmental context that supports recent studies indicating archaeological visibility in arabia dating from mis 5 and the presence of anatomically modern humans in arabia at this time

biotically constrained palaeoenvironmental conditions of a mid holocene intertidal lagoon on the southern shore of the arabian gulf evidence associated with a whale skeleton at musaffah abu dhabi uae whale remains a left and right mandible scapula humerus and fragmentary radius and ulna as well as parts of the cranium and rostrum belonging to a probable humpback whale megaptera cf novaeangliae were found in the well described sabkha sequence exposed in the musaffah industrial channel abu dhabi united arab emirates more precisely the whale remains were found in a series of sediments representing a range of lagoonal facies the sediments surrounding the whale bones were age dated at approximately 5200 14 c yrs bp and are therefore interpreted to correspond to the previously documented late flandrian sea level peak preceding a fall in sea level which culminated in the supratidal sabkha overprint of the carbonates associated with the whale remains is an assemblage of molluscs foraminifera and ostracods together with the inferred presence of sea grass and algae these facies are interpreted to indicate a very shallow subtidal to intertidal lagoonal environment cirripede remains found associated with the skeleton were identified as those of the whale barnacle coronula diadema and hence had their origins with the whale significantly the low species diversity of microfossils suggests that higher salinities existed in the mid holocene lagoon than are present in modern counterparts this is here inferred to be related to the onset of continental aridity in arabia during the mid holocene

diagenetic constraints on the use of cerium anomalies as palaeoseawater redox proxies an isotopic and ree study of cambrian phosphorites seawater rare earth element ree distributions show heavy ree enrichment and cerium depletion but these characteristics are only rarely found in ancient marine authigenic minerals such as carbonate fluorapatite and calcite this enigma may be due to changing ree distributions in seawater through time or to post depositional redistribution of ree differentiating between these two factors is however far from straightforward as their relative importance is likely to vary and evidence is often ambiguous in this article we present ree as well as strontium and sulphur isotope data for basal cambrian phosphorites of south china which confirm the emerging rule of thumb that granular phosphorites seldom reveal extreme departures from the seawater norm and tend to undergo therefore less diagenetic alteration of ree spectra than skeletal apatites and other phosphate types this study reveals stratigraphic trends in ce anomalies ce ce that could be taken to imply the preservation of a palaeoenvironmental signal however further investigation of our data shows that such trends in phosphorites can also be caused by post depositional alteration which tends to 1 increase ree contents 2 reverse ce depletion 3 alter eu anomalies and 4 concentrate preferentially the middle ree mree further alteration which may be due to weathering has led to hree depletion and positive la and y anomalies tetrad effect this is the first study where ceanom and phosphate bound sulphate s isotope values could be compared for one particular stratigraphic section which provides us with an additional tool for the interpretation of diagenetic redox conditions least altered phosphorites from meishucun that yield a strongly negative ceanom constrain early cambrian seawater 34s to about 33 we conclude that phosphorite ceanom primarily records variations in the local conditions of diagenesis while outlining some special cases in which diagenetic redox conditions may broadly reflect local bottom water redox conditions

large scale bed configurations macroforms platte river basin colorado and nebraska primary structures and formative processes large scale current bed forms defined here as bed configurations having dimensions commensurate with the size of the turbulent boundary layer are considered by many workers to be hydrodynamically equivalent to the regime bed forms these bed forms were investigated at formative flows bankfull flows on the south platte and platte rivers in colorado and nebraska to determine structures and formative processes results of this study suggest that large scale bed forms here termed macroforms are not hydrodynamically equivalent to the regime bed forms but constitute a unique hierarchical class of bed configurations produced by turbulent vortices that involve the entire boundary layer macroforms are oriented obliquely to the mean flow direction and are attached to one or both channel banks three members of a continuum of geometries are recognized in the channels of the platte river basin the internal stratification for each of the three macroform types recognized in the basin is similar and in its simplest form consists of the coarsening upward sequence apron laminae foreset laminae topset laminae although it may not be possible to differentiate the three macroform types solely on the basis of internal stratification the presence of a distinctive coarsening upward sequence in coarse grained fluvial systems offers a potentially powerful tool for identifying these environments in the geologic record

incised valley fill interpretation for mississippian black hand sandstone appalachian basin usa implications for glacial eustasy at kinderhookian osagean tn2 tn3 boundary abstract lower mississippian strata of east central ohio are predominantly fine grained marine deposits of the cuyahoga and logan formations within these sediments is the black hand sandstone of the cuyahoga formation the black hand sandstone is a multistory crossbedded coarse grained conglomeratic sandstone the contact between the black hand sandstone and the subjacent cuyahoga formation is sharp and scoured with intraclasts of the cuyahoga formation incorporated into the basal black hand sandstone the black hand sandstone was previously thought to represent a distributary channel deposit however the combination of lithofacies and architectural elements indicates deposition in a braided stream setting the cuyahoga formation was deposited in a shallow marine setting the erosional basal contact of the black hand sandstone and the juxtaposition of fluvial and marine sediments suggests a sequence boundary the geographic distribution of the black hand sandstone combined with the evidence for a sequence boundary suggests deposition in an incised valley the age of the black hand sandstone is key to inferring the causes of valley incision the black hand sandstone is nearly devoid of body fossils necessitating a biostratigraphic analysis of the surrounding cuyahoga and logan formations analysis indicates the logan formation is early osagean age data from the cuyahoga formation suggest a kinderhookian age with a possible transition to the osagean in the uppermost cuyahoga formation this constrains the age of the black hand sandstone to the transition at the kinderhookian osagean boundary recent reports indicate late kinderhookian tournaisian tn2 gondwanan glaciation based upon tillites and sharp excursions in stable isotope curves a glacio eustatic fall in sea level is inferred to have caused incision of the cuyahoga formation followed by deposition of the black hand sandstone and logan formation during the subsequent sea level rise the associated unconformity correlates to the sequence boundary at the kinderhookian osagean boundary in the stratotype area of north america and the correlative tn2 tn3 boundary worldwide supporting the hypothesis of a global eustatic event at this time

the dynamics of mangrove ecosystems changes in sea level and the strategies of neolithic settlements along the coast of oman 6000 3000 cal bc abstract this paper focus on the holocene palaeogeography of the ja alan coast from the 6th to the 4th millennium cal bc integrating the dynamics of mangroves lagoons khors estuaries and deltas with sea level change and the evidence from neolithic shell middens the distribution and maturation of mangrove ecosystems along the arabian coasts has varied considerably affected by physical forces such as sea level changes climate tidal amplitude and duration as well as the quantity of fresh water inflow associated with the monsoon systems along the arabian coast palaeo mangroves and lagoons today replaced by large sabkhas appear to be correlated to mid holocene fossil deltas and estuaries that currently function episodically depending on the rhythm of winter rains all these parameters have determined and impacted the location of settlement networks and the economic strategies of the first arabian farmers along the eastern arabian coast the mid holocene sea level highstand stability 5th millennium bc can be considered to be an optimum period for mangrove development and can be correlated with neolithic sites around the mangroves the decline of mangroves since 3000 2500 cal bc and further degradation is mainly attributed to the prevailing arid climate that reduced summer monsoon effects in the tropical area by favouring the extension of sabkhas we discuss these aspects based on new archaeological surveys excavations and geoarchaeological studies

understanding erosion rates in the himalayan orogen a case study from the arun valley understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution denudation rates derived from terrestrial cosmogenic nuclides tcns are commonly used to quantify erosion and bridge tectonic myr and climatic up to several kiloyears time scales however how the processes of erosion in active orogens are ultimately reflected in 10be tcn samples remains a topic of discussion we investigate this problem in the arun valley of eastern nepal with 34 new 10be derived catchment mean denudation rates the arun valley is characterized by steep north south gradients in topography and climate locally denudation rates increase northward from 0 2 mm yr 1 to 1 5 mm yr 1 in tributary samples while main stem samples appear to increase downstream from 0 2 mm yr 1 at the border with tibet to 0 91 mm yr 1 in the foreland denudation rates most strongly correlate with normalized channel steepness r2 0 67 which has been commonly interpreted to indicate tectonic activity significant downstream decrease of 10be concentration in the main stem arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample this results in 10be concentrations and denudation rates that do not uniformly represent the upstream catchment area we observe strong impacts on 10be concentrations from local nonfluvial geomorphic processes such as glaciation and landsliding coinciding with areas of peak rainfall rates pointing toward climatic modulation of predominantly tectonically driven denudation rates

methane seepage patterns during the middle pleistocene inferred from molybdenum enrichments of seep carbonates in the south china sea abstract seepage of methane rich fluids are widespread along the continental margins of the world intense seepages of methane may lead to the emission of this powerful greenhouse gas into the hydrosphere and atmosphere with implications in the understanding of past dramatic marine environment changes and global warming however euxinic environments with sulfidic bottom water as a result of vigorous seepages at ancient cold seeps remain unidentified here we report trace element geochemistry and associated mineralogical and carbon and oxygen isotopic data in seep carbonates collected from long drill cores in the south china sea three distinct stages of methane seepages events probably caused by the dissociation of gas hydrates are discernible carbonates formed in stage 2 during the marine isotope stage 5 mis5 are mainly occurred as aragonite and show extremely high molybdenum mo contents up to 118 g g and strong enrichments of authigenic mo in relative to uranium these results suggest the presence of intermittent or even permanent euxinic conditions generated by sulfidic bottom water that result from intensive methane seepages in contrast mineral compositions and trace element patterns indicate that the carbonates before and after the mis 5 stages 1 and 3 form within sulfidic conditions restricted to pore water under relatively lower methane fluxes our results highlight extremely intense methane seepages that may potentially result in localized euxinic environments the inferred euxinic environments imply more amount of massive methane release into the water column than a previous estimation which was triggered by large scale dissociation of gas hydrates in the south china sea during mis 5

extreme enrichment of polymetallic ni mo pge au in lower cambrian black shales of south china an os isotope and pge geochemical investigation extreme metal enrichments occur in the lower cambrian niutitang formation a thick black shale sequence deposited on the yangtze platform of south china and form a regionally distributed conformable polymetallic ni mo pge au sulfide horizon the origin for the extreme enrichment of metals in these black shales is discussed based on a comprehensive geochemical investigation of re os isotopes and platinum group elements the black shales of the lower cambrian niutitang formation in guizhou province yielded an re os isochron age of 535 11 ma with an initial 187 os 188 os ratio of 0 80 0 04 which is similar to the initial 187 os 188 os ratio 0 78 0 19 of the ni mo sulfide ores but slightly lower than the initial 187 os 188 os ratio 1 18 0 02 of lower cambrian black shales from the lesser himalaya india a comparison of os isotope data among the chinese ni mo sulfide ores the seafloor massive sulfide deposits and contemporaneous seawater suggests a possible similar hydrothermal forming mechanism for these deposits the pge concentrations pt anomaly pt pt pt pd ir pd au pd ratios of the chinese ni mo sulfide ores are similar to those metal rich black shales of submarine volcanogenic hydrothermal origin from czech republic namibia and canada but are different from those data of the ocean floor fe mn crusts that have scavenged their pge and other metals directly from seawater it is therefore suggested that the ni mo sulfide ores from the niutitang black shale sequence in south china had a submarine hydrothermal origin the anoxic environments and abundant organic matter in the ocean basin also played a key role for the extreme metal enrichments the discharge of hydrothermal fluids into the cambrian ocean may have had a great effect on life during the cambrian explosion 2007 elsevier b v all rights reserved

high resolution organic carbon isotope stratigraphy from a slope to basinal setting on the yangtze platform south china implications for the ediacaran cambrian transition organic carbon isotope data from two slope to basinal sections across the ediacaran cambrian transition on the yangtze platform south china record secular variations in delta c 13 data supplement highly comparable organic carbon isotope profiles from time equivalent shallow shelf and slope settings no environmentally determined carbon isotope gradient across the yangtze platform is discernible suggesting that a transgressive anoxic event provided an isotopically homogenous carbon source for primary productivity that originated from the deeper part of an anoxic and or sulfidic basin c 2011 elsevier b v all rights reserved

holocene lakes from ramlat as sab atayn yemen illustrate the impact of monsoon activity in southern arabia abstract paleoecology and paleohydrology of the ramlat as sab atayn southern arabia are reconstructed from a comparative study including sedimentology mineralogy stable isotope ratios of carbonates and palynology of lacustrine sediments recovered from the al hawa depression the section dates from 8700 to 7200 yr b p and records an early phase of flooding followed by distinct lacustrine development from 7800 to 7200 yr b p coeval with maximum activity of the indian monsoon comparison of the pollen record with modern pollen deposition suggests that regional vegetation was then already of desert type and was related to strong seasonal trade winds

the mesozoic mogollon highlands arizona an early cretaceous rift shoulder the mogollon highlands have long been considered the southern source terrane for much of the early to middle mesozoic fluvial sedimentary rocks of the southern colorado plateau because of the lack of mesozoic sedimentary strata in the mogollon region many workers have suggested these highlands were located in central arizona and new mexico new evidence suggests that during the triassic and most of the jurassic a large highland did not exist in central arizona new mexico but was present as a continental margin volcanic arc in southern arizona and northern mexico at this time central arizona would be more aptly called the mogollon slope early jurassic navajo equivalent sands were blown south from the colorado plateau area across the mogollon slope to become intercalated with volcanics along the northeast side of the arc the first good evidence for a structural and topographic highland in the mogollon area is in the early cretaceous when the uplifted northeast flank of the bisbee rift basin tilted

sedimentological characteristics and morphology of the aeolian sand dunes in the eastern part of the uae a case study from ar rub al khali abstract the umm az zimul al wijan area is located in the southeastern part of the uae and covers about 1600 km 2 it is bounded to the east by the oman mountains and to the south and west by the extensive dune area of ar rub al khali field investigation revealed the common occurrence of parallel to sub parallel sand ridges with a general east west orientation also present but less frequent are barchan barchanoid and star dunes interdune areas are classified into four types that include dolomite mixed ancient sabkha and ophiolitic rock fragments mixed sand sheet and ophiolitic rock fragments and recent sabkha the textural characteristics of the sand forming the dunes are unimodal with a modal class in fine sand size moderately to very well sorted positively skewed and mesokurtic quartz grains are mainly subrounded to subangular the similarity in roundness properties in different dune types in the eastern province of the uae seems not to be influenced by dune form based on the heavy mineral suites and the angularity of quartz grains it is believed that the sand sediments are mostly derived from the ultrabasic rocks forming the ophiolitic sequence of the oman mountains acidic rocks of iran and from the coastal area

landform evolution in the arid northern united arab emirates impacts of tectonics sea level changes and climate abstract the interaction of wind and water may well be the key influence on the modern geomorphology of the arid regions of the world and has had a strong influence on long term landscape evolution in these areas this is the case for the landforms of the northern united arab emirates where aeolian landforms in the west lie on alluvial deposits and are adjacent to fluvial landforms in the east even within the aeolian forms there is evidence of modern and past water activity modern river flow is rare and largely confined to the mountains however rivers and alluvial activity were more important during certain periods in the past this study describes the landforms of the northern emirates ne and relates their form and evolution to alternating periods of arid and humid climates the study was initially carried out to provide a background for the soil survey of the ne details of landform character and materials were explored during the survey which involved detailed site and soil descriptions at 10 020 auger and geoprobe sites 2 m depth 200 backhoe pits 2 m depth and 150 drill observations 10 m depth the main landforms identified in the study area are the hajar mountains alluvial plains fans plains and wadis dunes ridges sand veneer rising dunes and coastal forms the influence of uplift and tilting of the hajar mountains during the miocene and more recently is considered sea level changes in the arabian gulf are also important the impacts of past climate change on the evolution of landforms is discussed and related to alternating periods of arid and wet climates the north westerly shamal wind is primarily responsible for the formation and continued evolution of the dune fields seen in the ne today

sandy high energy flood sedimentation some criteria for recognition with an example from the devonian of s w england abstract many modern sand deposits resulting from episodic floods in semi arid zones are dominated by parallel laminations but parallel laminated sands are not a major feature in perennial streams single flood events may deposit over 1 5 m of parallel laminated sand hence ancient parallel laminated sand dominated alluvial deposits may be the product of ephemeral flows the trentishoe formation hangman sandstone group middle devonian of north devon consists in part of laterally extensive beds of parallel laminated fine grained red sandstones that build multistorey sand bodies individual beds are little more than 1 m thick but may extend laterally for hundreds of metres a vertical sequence of erosion surface sparse silt clasts parallel laminations silt drape is often found suggesting high flow stage deposition of plane bedded sand followed by a very rapid waning of flow with silt fallout in the final stages of the flood this sequence bears marked similarity to certain modern ephemeral flow sands

holocene development of multiple dune generations in the northeast rub al khali united arab emirates it has been hypothesised that in sand seas where multiple dune generations occur each generation represents a distinct terrestrial response to contrasting palaeoatmospheric circulation conditions lancaster n kocurek g singhvi a pandey v deynoux m ghienne j f et al 2002 late pleistocene and holocene dune activity and wind regimes in the western sahara desert of mauritania geology 30 991 994 however reconstructing dunefield accumulation and preservation chronologies has often utilised a limited suite of samples because of the difficulties realised in accessing unconsolidated aeolian sands which has limited the capacity to test this hypothesis in the eastern united arab emirates artificial excavation for quarrying and construction have generated a unique opportunity to examine and sample the internal structures of dune systems and to generate data to test the hypothesis of dune generational development this paper presents new data and chronologies from a multigenerational analysis of dune

evolution of the composition of seawater through geologic time and its influence on the evolution of life abstract the redox state of the surface environment of the early earth is still controversial and a detailed and quantitative estimate is still lacking we carried out in situ analyses of major trace and rare earth elements of carbonate minerals in rocks with primary sedimentary structures in shallow and deep sea deposits in order to eliminate secondary carbonate and contamination of detrital materials and to estimate the redox condition of seawater through time based on the ce content and anomalies of the carbonate minerals at given parameters of atmospheric co2 content pco2 and ca content of seawater we calculated the oxygen contents of shallow and deep seawater respectively the results show that the oxygen content of the deep sea was low and constant until at least 1 9 ga the oxygen content of shallow seawater increased after 2 7 ga but fluctuated it became quite high at 2 5 and 2 3 ga but eventually increased after the phanerozoic in addition the calculation of a high pco2 condition shows that seawater was more oxic even in the archean than at present suggesting a relatively low pco2 through geologic time our detailed calculations from compositions of carbonate minerals in three gorge area south china show a low oxygen content of seawater after the snowball earth until the late ediacaran an increase in the late ediacaran and a significant decrease around the precambrian cambrian and nemakit daldynian tommotian boundaries these variations were possibly caused by global regression and dissolution of methane hydrates

a 160 000 year record of dune development and atmospheric circulation in southern arabia aeolian deposits in the wahiba sands sultanate of oman reveal patterns of atmospheric circulation over the past 160 000 years luminescence dating indicates a correlation of dune activity with periods of low global sea level and decreased monsoon intensity evidence from dune orientation and sedimentary structures shows exclusively northbound transport of sand during times of high latitude glaciation these results are in contrast to the current paleocirculation model that assumes an increase of northwesterly winds because of a southward shift of the intertropical convergence zone our results indicate that the circulation pattern during glacial times was comparable to that of the present

marine redox variations and nitrogen cycle of the early cambrian southern margin of the yangtze platform south china evidence from nitrogen and organic carbon isotopes the early cambrian is a crucial interval during which the marine environment encountered significant perturbations alongside key biological innovations the nitrogen isotopic composition of ancient sediments has the potential to record co variation between the marine ecosystem and environmental conditions here we report bulk nitrogen and organic carbon isotopic compositions accompanied by mo concentration data a proxy for redox conditions for a shelf marginal drill core section sancha and a deep basinal outcrop section yuanjia in hunan province south china for the cambrian fortunian stage variable delta n 15 bulk values 4 to 2 parts per thousand and low delta c 13 org values 35 parts per thousand to 33 from the yuanjia section indicate that anoxic waters shoaled into the photic zone with ammonia assimilation competing with anammox in the basinal area in the late cambrian stage 2 low delta n 15 bulk and delta c 13 org values together with high mo bulk concentrations delta n 15 bulk 5 to 0 parts per thousand delta c 13 org 33 5 to 31 0 parts per thousand 100 ppm mo bulk in sancha section and delta n 15 bulk 0 parts per thousand delta c 13 org similar to 33 parts per thousand 100 ppm mo bulk in yuanjia section reflect intense n 2 fixation accompanied by intermittent ammonia assimilation under expanded euxinic condition with shoaling chemocline possibly into the photic zone in the early cambrian stage 3 relatively high delta n 15 bulk values alongside positive delta c 13 org excursions at both sections indicate an increasing contribution from n 15 enriched nitrate assimilation and hence more oxic conditions shelf margin sediments from the middle and late parts of cambrian stage 3 are characterized bylaw delta n 15 bulk values similar to 0 parts per thousand being lowest in the basinal area 3 to 0 parts per thousand in combination with high mo bulk concentration 100 ppm and high mo tocbulk ratios averaging similar to 18 in deep basinal sediments these data suggest that the photic zone became anoxic again but that sulfidic conditions occurred in the basinal area only compared with stage 2 euxinia was less extensive during this interval with photosynthetic biomass dominating over chemoautotrophic biomass at both localities based on a combination of delta n 15 data from this study and published data from studies on contemporaneous sections in yunnan province and the three gorges area it is possible to reconstruct the spatial variability and temporal evolution of redox conditions in the various marine environments along the southern margin of the yangtze platform the basinal area appears to have been dominated by anoxia and intermittent euxinia in the photic zone during most of the early cambrian fortunian stage to stage 3 with the exception of more oxic conditions during early stage 3 on the platform oxygenated shallow water prevailed with the exception of the notable cambrian stage 2 anoxic event the outer shelf area experienced anoxia from stage 2 to stage 3 of the early cambrian although of possibly limited areal extent the high mo bulk concentrations and mo tocbulk ratios suggest that the south china basin was well connected with the considerably oxygenated open ocean and that the mean low delta n 15 bulk values similar to 1 6 parts per thousand from the basin may reflect generally lower delta n 15 composition for seawater nitrate in the early cambrian compared with modern value c 2015 elsevier b v all rights reserved

comparison of geochemical and distinctive mineralogical features associated with the kinzers and burgess shale formations and their associated units article i nfo article history accepted 12 august 2007 this paper compares two north american occurrences of fossils that exhibit burgess shale type preservation bst the middle cambrian burgess shale formation of southeastern british columbia and the lower to middle cambrian kinzers fm of southeastern pennsylvania redox sensitive trace elements mo ni co v sc indicate that palaeo oxygenation conditions varied with respect to faunal assemblage and location ogygopsis bearing fauna in both the burgess shale and kinzers formations are associated with a dysoxic metal signature burgess shale type preservation in the kinzers fm was deposited in a fluctuating oxycline whereas the bst fossil beds of fossil ridge and mt stephen burgess shale fm yield a geochemical signature that consistently indicates oxic conditions thus sustained low oxygen conditions do not correlate with higher quality of fossil preservation at these sites ogygopsis is associated with dysoxic conditions in both localities and may therefore be a faunal indicator of such environments in middle cambrian strata carbonate units associated with both the burgess shale and kinzers formations contain large generally concordant near surface cavities that contain herringbone calcite cements that show no significant enrichment in the potential calcite inhibitor ions such as reduced fe sr s pb and zn the abundance of micro inclusions of dolomite suggests that mg may have been the calcite inhibitor ion responsible for herringbone cement in these cambrian occurrences another distinctive mineralogical feature is the presence of doubly terminated euhedral zoned authigenic quartz as a conspicuous part of a carbonate host rock replacement assemblage the association of both herringbone calcite and zoned quartz crystals in units associated with the burgess shale and kinzers formations suggest a common feature in the depositional and diagenetic environment of these two regions in which burgess shale type fossil preservation occur syn depositional brine flow is the likely cause of these distinct mineralogical features brine seeps in the depositional environment may have provided nutrients for stable high abundance faunal communities in a slope setting thereby accounting for the abundance of fossil material furthermore high salinity brine in the pore waters of carcass bearing cambrian muds may have further limited shallow burrowing scavenging and decomposition rates accounting for the exceptional preservation in these two localities

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

hydrogen sulphide release to surface waters at the precambrian cambrian boundary changes in environmental conditions at the precambrian cambrian transition around 542 million years ago have been suggested as a possible explanation for the apparent rapid increase in abundance of multicellular organisms known as the cambrian explosion the nature of the environmental changes is still a matter of debate however wille et al now report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of about 542 million years with the help of a box model of the oceanic molybdenum cycle they find that intense upwelling of hydrogen sulphide rich deep ocean water best explains the observed early cambrian molybdenum isotope signal this suggests that the early cambrian animal radiation may have been triggered by a major change in ocean circulation following a long period during which the ocean was stratified with sulphidic deep water this paper reports molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 million years the findings suggest that the early cambrian animal radiation may have been triggered by a major change in ocean circulation terminating a long period during which the proterozoic ocean was stratified with sulphidic deep water animal like multicellular fossils appeared towards the end of the precambrian followed by a rapid increase in the abundance and diversity of fossils during the early cambrian period an event also known as the cambrian explosion 1 2 3 changes in the environmental conditions at the precambrian cambrian transition about 542 myr ago have been suggested as a possible explanation for this event but are still a matter of debate1 2 3 here we report molybdenum isotope signatures of black shales from two stratigraphically correlated sample sets with a depositional age of around 542 myr we find a transient molybdenum isotope signal immediately after the precambrian cambrian transition using a box model of the oceanic molybdenum cycle we find that intense upwelling of hydrogen sulphide rich deep ocean water best explains the observed early cambrian molybdenum isotope signal our findings suggest that the early cambrian animal radiation may have been triggered by a major change in ocean circulation terminating a long period during which the proterozoic ocean was stratified with sulphidic deep water

evaluating episodic hydrothermal activity in south china during the early cambrian implications for biotic evolution abstract the early cambrian 541 514 ma was a crucial interval for the evolution of life on earth popularly known as the cambrian explosion here we report the timing of changes in hydrothermal and depositional inputs as well as paleo redox state which may have influenced biogeochemical changes according to high resolution petrology fossil distributions isotopic records and inorganic geochemistry the lower cambrian of the south china can be subdivided into four intervals the lowermost cambrian zhujiaqing formation cam i the cambrian stage 2 shiyantou formation cam ii the lower part of the cambrian stage 3 yu anshan formation cam iii and the mid upper cambrian stage 3 and the middle upper part of the yu anshan formation continuing into the canglangpu formation cam iv hydrothermal events are detected during the early cam i cam ii and cam iii intervals during the early cam i and cam ii intervals these events coincided with extensive bottom water euxinia which in turn may have restricted the spread or proliferation of ediacaran fauna and small shelly fauna through the whole cam iii interval further hydrothermal events occurred concurrently with euxinic and ferruginous conditions probably within a single spatially stratified water column again plausibly restricting the spread of aerobic organisms in conjunction with the cessation of hydrothermal events and the gradual lowering of sea level during the late cam iii oxic water environments gradually spread into relatively deep water regions concurrent with the emergence of the chengjiang and qingjiang faunas these data suggest that periodic hydrothermal events may have had a significant impact on the spread radiation and extinction of macroscopic fauna during the early cambrian in south china

marine redox stratification on the earliest cambrian ca 542 529 ma yangtze platform abstract in order to explore the marine redox structure on the earliest cambrian ca 542 529 ma yangtze platform south china new fe mo c s geochemical data from the slope xugongping section for the liuchapo and the base of niutitang formation are reported here integrated fe speciation and mo abundance data from the xugongping section in combination with previously published data from slope basinal longbizui section and others suggest oxic surface waters and ferruginous deep waters coexisting with occasional mid depth euxinic waters during the fortunian stage and with widespread euxinic waters during the early stage 2 marine transgression a compilation of new and published sulfur isotope data of pyrite for the liuchapo and the base of niutitang formations presents high isotopic values mostly 10 and distinctly different spatiotemporal gradient characteristics during the fortunian stage and the beginning of the stage 2 we propose that redox stratification developed in the earliest cambrian protected basin and eustatic change and the connectivity of the protected basin with the open ocean controlled the materials supply from riverine input and open ocean reservoir and thus spatiotemporal variability of ocean chemistry

facies architecture and sedimentology of a meandering fluvial system a palaeogene example from the weisselster basin germany the schleenhain open pit coal mine located 30 km south of leipzig germany exposes upper eocene and oligocene non marine strata representing fluvial deposition in the centre of the weisselster basin active mining and successive cuts provided the rare opportunity to obtain a three dimensional perspective of laterally extensive surface outcrops these were used to construct a detailed fence diagram which provided the basis for recognition of key architectural elements in the weakly consolidated meandering stream deposits in addition to the eight basic architectural elements of miall 1985 the element sl shallow lake deposits was newly defined and the element ch channel was subdivided into chg palaeo river system and chk small channel the profiles contain parts of two fining upward cycles which are separated by an unconformity spanning the early oligocene deposits of the first cycle begin with transverse sand bars downstream accretion deposits da and point bars lateral accretion deposits la the upper part of the cycle is represented by overbank fines of and the element sl which consists of laterally discontinuous lenses of dark plant bearing kaolinite rich clays that were deposited in shallow lakes adjacent to the active channel coal seams interlayered with palaeosols are the main constituents of element of sheetlike bodies of medium to fine gravels gravel bars and bedforms gb on an erosive coal surface mark the beginning of the second cycle dissolution of underlying permian salts and sulphates prior to during and after the deposition of the palaeogene strata caused the development of two synclines within the outcrop coal seams and clay horizons which thicken and dip towards the centre of the synclines provide evidence for their chronological development

braided stream and flood plain architecture the rio vero formation spanish pyrenees early to middle miocene fluvial sandstones of the rio vero formation were studied in an area around the town of barbastro south central pyrenees spain the outstanding quality of outcrops in this area allows a three dimensional study of architectural elements six architectural elements are recognised described in detail and interpreted from three key localities seven main lithofacies were identified and sub divided into gravelly sandy and fine grained lithofacies the architectural elements and lithofacies have been combined with a hierarchy of depositional bounding surfaces to fully interpret the evolution of the depositional system at the meso and macro scale not only the different architectural elements and lithofacies of the complete braided fluvial system but also the lateral variation of the architectural elements were emphasised in this study differential tectonic movements seasonal climate change and their effect on vertical and lateral evolution of the area were the main control on basin sedimentation channel interconnection palaeocurrent patterns and consequently the fluvial architecture the presence of lateral ramp anticlines caused the fluvial system to be laterally restricted with the main channel belts being located in the areas of highest subsidence and lowest topography intervening topographic highs acted as both flood plains and lateral barriers between the main channel systems the proposed depositional model comprises broad low sinuosity perennial but seasonal moderate energy streams the sandstone architecture is dominated by channel fill and sheet sands and associated simple and more complex bars adjacent to the main channel belts fine grained sandstones siltstones and immature paleosols occur the along strike relationship between major fluvial systems and their outlets into a foreland basin has important implications for the infill of the basin and the modelling of fluvial systems along mountain belt fronts

cerium anomaly variations in ediacaran earliest cambrian carbonates from the yangtze gorges area south china implications for oxygenation of coeval shallow seawater abstract the late neoproterozoic ocean witnessed the naissance of animals which is believed to have been stimulated by an increase in oxygen levels in the ocean however apart from the emergence of animal fossils little supporting evidence has been found for the rise of oxygen in shallow seawater here we present ce anomaly data a redox proxy with a higher reduction potential than many other redox proxies for carbonates from well preserved marine successions the doushantuo formation dengying formation and lower yanjiahe formation of the ediacaran period and the upper yanjiahe formation of early cambrian on the neoproterozoic yangtze platform in the yangtze gorges area in order to constrain the redox evolution of the shallow marine environment calculated ce anomalies were screened using the following criteria al 36 in acetic acid leached carbonate to target samples that preserve primary seawater ree features and ce anomalies the samples satisfying this screening show seawater like ree distribution patterns in leached carbonates and may have recorded ce anomalies of the seawater from which the carbonates precipitated these data show that the doushantuo formation has ce ce values between 0 92 and 0 71 the dengying formation between 0 90 and 0 40 and the yanjiahe formation between 0 52 and 0 72 the ce ce values of the doushantuo formation suggest that shallow waters during the doushantuo stage 635 551 ma were anoxic to suboxic from the bottom to the top of the dengying formation ce ce values decrease systematically which cannot be explained by a change in depositional depth of the carbonate but suggests that the shallow waters became more oxygenated during the dengying stages from 551 ma to ediacaran cambrian boundary these results may provide direct evidence for an increase in oxygen levels in the shallow marine environment during the ediacaran period

temporal patterns of arid humid transitions in the south eastern arabian peninsula based on optical dating abstract the rub al khali aeolian system of the arabian peninsula is the world s largest erg while the region is presently hyper arid evidence for multiple past humid periods has been documented in previous studies radiocarbon dating of lacustrine travertine and palaeogroundwater deposits suggests that the climate was humid at 10 6 and 35 25 ka these phases have been associated with summer rainfall increases occurring in tandem with an intensification and northward migration of the monsoon system during northern hemisphere precessional maxima published optical dating studies have focused on preserved sand dune and aeolianite deposits to establish ages for the intervening arid phases here we present a summary of this work and additional optical dating results for samples of aeolian sediment from a deep drill core which provides insights into the style of barchan dune accretion in the liwa region of the united arab emirates the large dune accreted rapidly during the mid late holocene the results suggest that the transitions from humid to arid conditions and resulting accumulation of aeolian sediment in the form of large bedforms occurred abruptly at around 6 ka further aeolian sedimentation has not been constant since that time with initial gradual dune growth followed by rapid vertical accretion and possible termination of accumulation around c 2 ka

flaser and wavy bedding in ephemeral streams a modern and an ancient example abstract flaser and wavy bedding are sedimentary structures characterized by alternating rippled sand and mud layers these structures often are considered to form mostly in tidally influenced environments published examples from fluvial environments are rare flaser and wavy bedding were found in two ephemeral stream deposits the jurassic kayenta formation and the modern wash in seven mile canyon both located in southeastern utah usa these examples demonstrate that flaser bedding can form and be preserved in ephemeral streams

paleoclimatic reconstruction in northern oman based on carbonates from hyperalkaline groundwaters abstract a paleoclimatic reconstruction for the past 35 000 years for northern oman is based on an unusual approach using travertines and fracture calcites associated with hyperalkaline springs high ph groundwaters ph up to 11 9 discharge from the mantle sequence of the oman ophiolite as the product of modern low temperature serpentinization under arid climatic conditions hyperalkaline discharge occurs at the surface uptake of atmospheric co 2 precipitates characteristic laminated travertines accompanied by strong kinetic depletion of 13 c and 18 o pluvial climates supporting a shallow bicarbonate groundwater flow system and vegetation are recorded by fracture calcites with equilibrium stable isotope contents and calcite replaced roots and stems all such carbonates have modern initial 14 c contents allowing radiocarbon dating and paleoclimatic reconstruction for the late pleistocene and holocene our reconstruction shows a dominantly wet late pleistocene up to 19 000 yr b p when a phase of climatic deterioration began leading to a period of hyperaridity which dominated from ca 16 300 to 13 000 yr b p the early holocene pluvial occurred from 12 500 to ca 6500 yr b p and was followed by renewed climatic deterioration and the current phase of hyperaridity comparison of this paleoclimatic reconstruction with that for lacustrine deposits from the a rub al khali of central saudi arabia and the summer insolation driven monsoon record of east africa and the arabian sea is remarkably good

the nature and possible origin of mega dunes in liwa ar rub al khali uae abstract the liwa area is located in the south central part of the uae along the northeastern upwind margin of the ar rub al khali sand sea and covers about 3694 km 2 it has one type of dunes a mega barchan that is compound and complex in form characterized by the superimposition of smaller dunes due to the giant size of barchans interdune areas appear as closed depressions that vary in shape from irregular elongate triangular to circular or semi circular these depressions are mostly covered with small barchans or sabkha deposits with patches of gypcrete in their upper parts scattered flat top mounds are also observed in interdune areas the size of dunes in liwa is directly controlled by quaternary climatic changes multiple generations are superimposed on one another separated by calcretic horizons the climate during dune formation alternated between relatively arid to humid the dune sands are unimodal with a modal class of fine sand moderately to very well sorted and near symmetrical and mesokurtic quartz grains are mainly subrounded to subangular based on the heavy mineral suites the sand came mostly from the ultrabasic rocks that form the ophiolitic sequence of the oman mountains the acidic rocks of iran and from the arabian shield

trace and rare earth element geochemistry of black shale and kerogen in the early cambrian niutitang formation in guizhou province south china constraints for redox environments and origin of metal enrichments abstract early cambrian black shales of south china not only host important sponge arthropod and other soft bodied fossils that have helped to trace early metazoan diversification but also show extreme enrichments of a number of trace metals in particular ni mo and v in this study we use a new approach by analyzing rare earth elements in kerogen extracted from the black shales together with a number of redox sensitive trace element compositions and total organic carbon toc concentrations in an early cambrian black shale sequence in zunyi guizhou province south china to place better constraints on the oceanic redox conditions and the origin of the extreme metal enrichment our data show significant negative ce anomalies ce ce as low as 0 4 occurring in kerogen which indicate an oxygenated surface environment of primary productivity in consistent with the concept that the organic matter is mainly derived from organisms in the euphotic zone mass balance calculation suggests that the kerogen associated ree can dominate the measured black shale ree budget while similarity between our measured ree patterns and those of similarly aged phosphorites indicates that the ree content of ancient phosphorites may have also derived initially from organic matter the redox sensitive trace elements such as u v mo and their ratios of u al v al and mo al in black shales show different correlation patterns with toc contents the upper black shales show a good metal toc correlation but such a correlation is absent in the lower part the lower black shales exhibit much higher metal enrichments compared to black sea sulphidic euxinic sediment this is taken to indicate the presence of sulphidic bottom waters during the deposition of the lower black shales including the ni mo ore layer in contrast anoxic non sulphidic conditions occurred during the deposition of the upper black shales taking all these geochemical data together we suggest that the early cambrian south china seaway was strongly stratified and stagnant and that euxinic bottom water conditions may have led to enrichment of the redox sensitive metals such as u v and mo in the lower black shales and in one case the occurrence of a polymetallic ni mo sulphide ore bed bearing an extraordinarily extreme metal enrichment which according to the mo toc and ni toc ratios and much other geochemical evidence may have been additionally influenced by hydrothermal input of metals within the rift basin as suggested by a number of previous studies

submarine hydrothermal contribution for the extreme element accumulation during the early cambrian south china throughout the geological history of the earth submarine hydrothermal activity has played an important role in seawater chemistry biological evolution and enrichment of metals in the earth crust however the prospect of hydrothermal activity for extreme element accumulation during the early cambrian a key geological period in south china has not been well constrained this study reports geochemical e g ree and sr isotope investigations of a coarse grained limestone layer and associated calcite veins in zunyi and nayong areas guizhou province to constrain the hydrothermal activity and evaluate the significance of hydrothermal contribution to extreme element accumulation during the early cambrian south china our results reveal positive eu anomalies and higher initial 87sr 86sr ratios 0 7083 0 7150 for carbonate samples than those of early cambrian seawater indicating the presence of hydrothermal processes combined with constraints from the spatial relationships and coincidence with adjacent mineralization these hydrothermal processes provide the most probable contribution for polymetallic ni mo pge mineralization furthermore there are abundant hydrothermal dolomite and barite calcite veins in the dolostone of the dengying formation indicating the occurrence of a variety of hydrothermal fluids overall multi stage hydrothermal pulses with different fluid compositions spanned the ediacaran cambrian transition in south china in particular these hydrothermal fluids with positive eu anomalies and enriched radiogenic sr originating from proterozoic mafic ultramafic rocks may have flowed through the underlying precambrian silicate clastic rocks e g xiajiang banxi and lengjiaxi groups and may have been crucial for the marine environment biological diversity and extreme element accumulation during the early cambrian south china

geochemical evidence for oxygenated bottom waters during deposition of fossiliferous strata of the burgess shale formation abstract deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the burgess shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their preservation methods of paleo redox determination that are based upon trace fossils organic carbon content or size analysis of pyrite framboids are problematic when applied to the burgess shale fortunately patterns in redox sensitive trace elements hold great potential for determining paleo redox conditions for these greenschist facies rocks because they are independent of both age and metamorphic grade four burgess shale type bst fossil bearing sections were studied three lie within the burgess shale formation whereas one lies within the slightly younger duchesnay unit of the middle chancellor formation the geochemical proxies of seawater redox conditions that were used are mo u th v cr v v ni ni co and v sc each of these redox sensitive indices suggests that oxygenated conditions prevailed in the overlying seawater during deposition of beds within which bst preservation developed non fossiliferous beds at the base of the mt stephen trilobite beds yield three geochemical indices v v ni v sc ni co that indicate deposition under dysoxic to anoxic conditions thus the only beds to have been deposited under anoxic conditions are barren of fossils of soft bodied taxa further contradicting the notion that bottom water anoxia is a factor in bst preservation the laminated nature of the burgess shale and evidence for subsurface anoxia coupled with evidence for oxygenated bottom waters presence of bacterial mats and surficial trace fossils suggest that the burgess shale was deposited in the exaerobic zone oxic anoxic boundary at the water sediment interface implications of this reinterpretation of the depositional environment of the burgess shale include 1 taphonomic models for bst preservation must account for the presence of oxygen in bottom waters 2 paleoecological interpretations of the burgess shale need to account for a probable autochthonous benthic component in what is a complex assemblage of fossils that includes elements derived from the platform and 3 the possibility of burgess shale communities based upon chemosynthesis and or bacteria grazing must be considered

characterization of insoluble organic matter from the lower proterozoic huronian supergroup elliot lake ontario abstract elliot lake organic matter falls into two main groups 1 stratiform kerogens with reflectance from 2 63 to 7 31 ro max exhibit a high level of aromaticity and low atomic h c ratios 0 41 0 60 2 less aromatic disseminated globules most resembling solid bitumen are of lower maturity with ro max from 0 72 to 1 32 and atomic h c ratios 0 71 0 81 stratiform kerogens originated from cyanobacteria have 13c values from 15 to 25 one exception with 13c 31 8 may have originated from methanogenic source biota thus two genetically distinct populations of kerogen are tentatively recognized in elliot lake metasediments globular bitumens remobilized by hydrous pyrolysis from kerogen exhibit 13c values ranging from 25 tp 33 0 the overall isotopic bimodality among elliot lake organic material is explained by analogy to petroleum generation from particulate kerogen that matured under conditions of catagenesis to metagenesis and was subjected to radiation over a long time barium u th au pt pd and ree contents of elliot lake stratiform kerogen greatly exceed of average black shales except for as pt pd and au all metals ti v cr mn fe co ni zn se rb sr ag sb cs ba hf ta w hg th and u are more concentrated in stratiform kerogens than in the derivative bitumen this signals a significant role for a low temperature transfer of noble metals to migrating bitumen

trace elements and sr and c isotopic signatures in late neoproterozoic and earliest cambrian sedimentary organic matter from siliciclastic successions in the east european platform sedimentary organic matter deriving from tubes of sabelliditids vendotaenids sapropelic films and kerogens was extracted by acid processing from upper vendian siliciclastic successions in the east european platform elemental composition obtained by ins

boron paleosalinity proxy for deeply buried paleozoic and ediacaran fossils abstract boron content is an indicator of paleosalinity for mesozoic and cenozoic clayey sediments but is compromised by clay diagenesis in deeply buried sediments of paleozoic and ediacaran age this study of north american russian and australian paleozoic and ediacaran fossils showed tight covariance of b ppm and k wt confirming common wisdom that boron is carried largely by illlite smectite clays ratios of b k 40 g g distinguish modern marine and freshwater sediments but this discrimination threshold declines to 21 g g for sequences with bituminous coal just below the anchimetamorphic zone and to 5 g g for sequences within the anchimetamorphic zone toward greenschist facies marine and non marine threshold b k values can be predicted from weaver and kubler indices of illite crystallinity as a measure of b depletion during deep burial and metamorphism deviations from that expectation b k weaver and b k kubler are positive in marine rocks and negative in non marine rocks trilobites stromatolites and other marine fossils were correctly identified as marine by this proxy and fossil land plants identified as non marine though in some cases by small margins because of declining b content with increased clay crystallinity cryogenian to devonian problematic quilted fossils dickinsonia arumberia rangea pteridinium ernietta aspidella rutgersella protonympha are indistinguishable from devonian to triassic plants using this proxy and significantly different from trilobites brachiopods ammonites and other securely marine fossils

late quaternary chronology of major dune ridge development in the northeast rub al khali united arab emirates the northeastern sector of the rub al khali desert in the eastern united arab emirates uae is dominated by large ne sw trending dune ridges orientated perpendicular to the currently prevailing northwesterly wind regime in this study extensive use has been made of artificially exposed sections through these major dune ridges that reveal internal sedimentary structures and allow an intensive high resolution sampling programme to be carried out here we present the optical dating results for samples from 7 sections the results indicate that dune activity and preservation occurred within the periods 7 3 ka 16 10 ka and 22 20 ka with evidence of earlier preservation during marine oxygen isotope stages mis 3 and 5 with net accumulation rates in the range 2 2 25 m ka 1 in several instances hiatuses in the preserved record of dune accumulation coincide with stratigraphic bounding surfaces visible in the exposed section profiles with associated truncation of internal sedimentary structures caution must be exercised when interpreting such gaps in the recorded accumulation chronologies of these dunes since these may simply constitute phases of low preservation potential rather than phases of low aeolian activity other factors such as sediment supply and availability in relation to sea level dynamics may be significant and are also considered

alluvial eolian and lacustrine sedimentology of a paleoproterozoic half graben baker lake basin nunavut canada the northeast trending baker lake sub basin was a volcanically active half graben during deposition of ca 1 85 1 76 ga baker lake group drainage was oriented along transverse and axial directions with flow to playa lake and deeper perennial lacustrine depocentres basin marginal streamflow dominated alluvial fans were concentrated along the southern margin and provided sediment from archean crystalline basement rocks these fed transverse gravel and sand bed braided streams alluvial dynamics were characterized by channel aggradation and abandonment abandoned channel belts were sites of floodplain and eolian deposition basin axial braided streams fed northeast and southwest to a depocentre near christopher island where eolian playa and lacustrine environments were intimately linked felsic minette flows were initially erupted from localized centres contemporaneous sedimentary deposits typically contain minor volcaniclastic components that increase in abundance basinward voluminous and widespread younger minette flows prograded outward from volcanic centres contributing significant additional basin infill

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

early holocene paleosols at the southwestern ramlat as sab atayn desert margin new climate proxies for southern arabia abstract the ramlat as sab atayn desert margin near ma rib yemen displays well preserved early holocene paleosols which are documented by ams 14 c and soil data mollusc shells in bwk and bwkb horizons are dated to the period between 12 5 and 9 5 ka cal bp the buried soils above ahb and abwkb horizons indicate a period of soil formation mainly between 8 8 and 8 3 ka cal bp between 8 3 and 6 7 ka cal bp more weakly developed soils occur and those only locally in contrast to the paleosols sandy cover sediments c horizons without considerable signs of pedogenesis appear due to increasing aridity wind activity and sheet wash after 8 3 ka cal bp these results indicate an arid climate and the formation of cover sediments at the desert margin of yemen in the rain shadow of the yemen highlands after the main period of soil formation which ended around 8 3 ka cal bp at the latest at 6 7 ka cal bp calculating from geochemical data a palaeoprecipitation of about 400 to 600 mm a 1 235 mm a 1 from 12 5 to 8 3 ka bp is proposed accordingly after 8 3 ka cal bp the summer position of the itcz and the associated monsoon rain belt carrying rain to northeastern yemen is assumed not to go beyond 15 n in its whole amplitude

an allostratigraphic approach to a non marine basin the north western part of cretaceous kyongsang basin se korea the north western part of the cretaceous kyongsang basin south east korea comprises alluvial deposits of conglomerate gravelly sandstone sandstone and mudstone which can be grouped into four allomembers bounded by stratigraphic discontinuities the discontinuities trend nw se and are marked by distinct facies transitions abrupt emplacement of conglomerate and thin but persistent mudstone beds sedimentary facies and architectural analyses reveal that each allomember formed a depositional system of fluvial channel networks draining toward the south east with alluvial fans on the northern margin each allomember can be characterized by distinctive architecture of channel fills clast composition of conglomerate and sandstone mudstone ratio successive units show an eastward shift in the locus of deposition suggesting basinward relocations of alluvial systems such variations with time and space are interpreted to reflect changes in accommodation space and sediment supply during basin evolution probably caused by fault movements this study shows that detailed mapping combined with architectural analysis and the establishment of alluvial allostratigraphy can help assess changes in alluvial systems and structural development of the basin

architectural elements and bounding surfaces in fluvial deposits anatomy of the kayenta formation lower jurassic southwest colorado abstract three well exposed outcrops in the kayenta formation lower jurassic near dove creek in southwestern colorado were studied using lateral profiles in order to test recent regarding architectural element analysis and the classification and interpretation of internal bounding surfaces examination of bounding surfaces within and between elements in the kayenta outcrops raises problems in applying the three fold classification of allen 1983 enlarging this classification to a six fold hierarchy permits the discrimination of surfaces intermediate between allen s second and third order types corresponding to the upper bounding surfaces of macroforms and internal erosional reactivation surfaces within the macroforms examples of the first five types of surface occur in the kayenta outcrops at dove creek the new classifications is offered as a general solution to the problem of description of complex three dimensional fluvial sandstone bodies the kayenta formation at dove creek consists of a multistorey sandstone body including the deposits of lateral and downstream accreted macroforms the storeys show no internal cyclicity neither within individual elements nor through the overall vertical thickness of the formation low paleocurrent variance indicates low sinuosity flow whereas macroform geometry and orientation suggest low to moderate sinuosity the many internal minor erosion surfaces draped with mud and followed by intraclast breccias imply frequent rapid stage fluctuation consistent with variable seasonal monsonal ephemmeral flow the results suggest a fluvial architecture similar to that of the south saskatchewan river through with a three dimensional geometry unlike that interpreted from surface studies of that river

a 20 ka sediment record from the hajar mountain range in n oman and its implication for detecting arid humid periods on the southeastern arabian peninsula abstract playa like sediments from the hajar mountain range in northern oman 22 83 n 59 00 e 1050 m asl document variations of the paleoenvironmental and paleoclimate conditions over the last 20 ka based on high resolution sediment sampling and their osl dating sedimentation rates were calculated and used as a proxy for paleorainfall the results show that the glacial to lateglacial was characterized by arid conditions with a following transitional period of even less rainfall at 10 5 ka sedimentation rates increases abruptly indicating the onset of the early holocene humid period ehhp rainfall reaches its maximum at 9 8 ka ehhp 2 and a decreasing sedimentation rate after 8 ka characterizes the arid period of the middle to late holocene variations of the hydrological regime are associated with the intensity of the boreal summer indian monsoon and its related position of the itcz for the onset of the ehhp a northerly shift of the itcz is postulated thus confirming earlier results from the southern arabian peninsula

first evidence for episodic flooding events in the arid interior of central saudi arabia over the last 60 ka although evidence for quaternary environmental changes in the arabian peninsula is now growing research has mostly been conducted in the united arab emirates uae and in the sultanate of oman there have been virtually no recent studies in saudi arabia especially in the central region such as around al quwaiayh in this area there are a series of outwash plains developed along the eastern edge of the arabian shield that formed in the late quaternary four sedimentary sections which are representative of the deposits that have accumulated have been studied and five luminescence ages obtained these are the first luminescence ages acquired from quaternary sediments in central saudi arabia the preserved fluvial deposits in the study area have formed during humid events at ca 54 ka ca 39 ka and ca 0 8 ka in more recent times aeolian sands have been encroaching on to the distal parts of the outwash plains copyright 2008 john wiley sons ltd

ree and trace element patterns from organic rich rocks of the ediacaran cambrian transitional interval abstract it has been established that important changes in the marine environment and the biosphere occurred during the cambrian however the relationships between the so called cambrian explosion and the concomitant environmental changes are not yet fully understood this study presents new geochemical data from the black shale successions from different facies belts of the yangtze platform in south china variations in the concentrations of ree and trace elements varying ce ce th u v sc and v cr ratios in kerogen as well as in bulk rocks from different depositional environments along a transect from platform to basin indicate two oxidation events which led to the oxygenation of the water column in shallow marine environments and euxinic conditions weak correlation between toc v u and mo in the deeper sea during the first oxidation event in the late terreneuvian anoxic conditions in bottom waters rapidly changed to euxinic conditions subsequently the second oxidation event during the early epoch 2 of the cambrian led to oxic suboxic conditions in deeper seawater

controls on organic matter accumulation on the early cambrian western yangtze platform south china abstract the origin of widespread organic rich shales on the early cambrian yangtze platform of nanhua basin south china has been attributed to high primary productivity to test this hypothesis we generated multiple paleoproductivity ocar and par paleoredox corg p ratios upwelling restriction coef mnef co ppm mn mo toc and cd mo ratios and terrigenous flux proxies al and unreactive fe feu for the lower cambrian niutitang formation in the outer shelf jinsha section which records a typical transition from the organic rich black shales to overlying organic lean mudstones or siltstones these new data were integrated with published paleoredox proxies iron speciation and redox sensitive trace metals for the same section our results suggest that the organic rich toc 4 6 1 8 lower member lm 0 37 m of the niutitang formation records ferruginous conditions high productivity levels and low siliciclastic fluxes and that the organic poor toc 0 1 0 1 upper member um 37 329 m was characterized by dominantly oxic conditions declining productivity levels and high siliciclastic fluxes our results suggest a redox shift from ferruginous to oxic conditions and enhanced terrigenous fluxes in response to falling sea level from the lm to the um secular variations in primary productivity and redox conditions are strongly correlated which is consistent with a positive feedback high primary productivity led to increasing water column anoxia which enhanced organic p recycling stimulating further productivity variations in primary productivity may reflect variable upwelling intensity in a semi restricted shelf setting linked to sea level changes taken together these findings suggest that a combination of primary productivity redox conditions and terrigenous fluxes driven by sea level changes played a key role in organic matter accumulation on the early cambrian western yangtze platform

geochemical paleoredox indicators in devonian mississippian black shales central appalachian basin usa the degree of anoxia that existed during accumulation of devonian mississippian black shales in central kentucky has been debated widely in this study geochemical data were used to elucidate paleodepositional environments for these units using analyses from ten cores collected from the outcrop belt in central kentucky sulfur carbon and selected trace element relationships were compared the sunbury shale tournasian lower mississippian and the cleveland and huron members of the ohio new albany shale fammenian upper devonian show different relationships between carbon sulfur and trace elements c s fe relationships for the sunbury suggest anoxic possibly even euxinic conditions prevailed during sediment accumulation analysis of c s fe data suggests that the cleveland may have accumulated under anoxic conditions with intermittent dysoxia whereas the huron member may have accumulated under a relatively wide range of conditions from anoxic to dysoxic to possibly oxic these three units exhibit different degrees of trace element enrichment with the approximate order of enrichment relative to an average shale being mo pb zn v ni cu cr co the sunbury shows the highest levels of enrichment followed by the cleveland with the huron showing only slight enrichment for most of these trace elements differing degrees of enrichment may reflect differences in depositional environment during accumulation high mo concentrations in the sunbury generally 200 550 ppm may infer euxinic conditions prevailed during sediment accumulation the cleveland and the huron both show considerably lower mo contents averaging around 100 ppm geochemical ratios including ni co v cr and v v ni also indicate variable paleoredox conditions for these shales based on previously established thresholds v cr and ni co ratios infer at least anoxic conditions during accumulation of the sunbury anoxic to dysoxic conditions during cleveland accumulation and dysoxic to oxic conditions for the huron v v ni ratios tend to indicate consistently lower oxygen regimes than do other paleoredox indicators and this discrepancy is greatest for the huron member it is suggested that thresholds established for paleoredox indicators in previous studies should not be applied strictly but that relative differences in these indicators collectively can infer variations in the degree of anoxia in addition relationships between corg and redox elements may help elucidate the role of anoxia in om accumulation it may be concluded from this study that the devonian mississippian black shales of central kentucky accumulated under variable bottom water conditions at least anoxic conditions prevailed during accumulation of much of the sunbury shale and the upper part of the cleveland member and possibly euxinic conditions for the sunbury bottom water conditions may have been intermittently anoxic and dysoxic during deposition of the lower cleveland during accumulation of the huron member it is likely that conditions ranged from anoxic to dysoxic to marginally oxic possibly being close to normal marine conditions at times during accumulation of the lowermost huron sediments

are there ancient soils in the 3 7 ga isua greenstone belt greenland abstract a lens of black schist within 3 7 ga quartzites of greenland may be earth s oldest known alluvial paleosol the suspect metamorphic rock is a lens in orthoquartzite of berthierine schist with crystals of ripidolite but it has a truncated top above dark gray grading down to gray color ptygmatically folded surface cracks filled with silt grains and large sand crystals unusual for sedimentary or metamorphic rocks the paleosol hypothesis was tested with thin sections showing plausible mineral weathering trends and by chemical analysis showing molar weathering ratios and ree distribution like those of soils the schist is deeply weathered and at the culmination of weathering trends from analysis of other metasediments of the isukasia area the protolith can be reconstructed as a saponite clay with a salt rich horizon of kieserite like other acid sulfate paleosols of the early earth models for proton and electron consumption of paleosols applied to the profile reveal an atmosphere with only 36 510 ppm o2 and 820 201 ppm co2 and humid cool temperate paleoclimate the profile has organic 13cpdb consistently of 24 2 to 27 4 and modest raleigh distillation near the top similar consistent values and trends are produced by decay of organic matter in living soils but biotic carbon isotopic composition of sediments is erratic from bed to bed and abiotic carbon compounds of meteorites differ dramatically for each kerogen particle thus life in this very ancient soil is not precluded by our analyses but ultrastructural and geochemical testing of carbon particles would further test this hypothesis

architectural analysis of fluvial sequences in the northwestern part of kyongsang basin early cretaceous se korea abstract the northwestern part of kyongsang basin early cretaceous largely comprises interbedded sandstones and mudstones of fluvial depositional environments with local basin margin conglomeratic deposits of alluvial fan systems these non marine successions are divided into 5 successive stratigraphic units each of which is unique in facies assemblages and architecture of sandstone bodies one stratigraphic unit sinpyong anpyong unit is documented in this paper with detailed architectural analysis of sandstone bodies the deposits of the sinpyong anpyong unit are divided into three major components thick sandstone thin sandstone and mudstone dominated bodies the thick sandstone bodies 2 47 m thick comprise stacked element groups bounded by laterally persistent erosional surfaces probably representing superposition of channel belts within individual element groups elements are laterally superposed indicating growth and superposition of bars and movement of associated channels the thickness of bar deposits and dip angles of laterally inclined strata suggest that channels were a few to 10 m in depth and 9 m to several tens of meters in width paleocurrent data indicate southward or southeastward draining channel systems the thin sandstone bodies generally the thick sandstone bodies formed in major channels and channel belts are characterized by lateral superposition of numerous bar and channel deposits limited extent of individual lateral accretion sets and the presence of mid channel bar deposits suggesting deposition in braided rivers detailed reconstruction of bars and channels reveals a range of processes including growth coalescence and erosion of bars and migration switching and filling of channels lateral accretion of bars and the associated channel migration might have been principal processes in the sinpyong anpyong river systems bars were commonly coalesced by lateral superposition forming large bar complexes

how wet is wet precipitation constraints on late quaternary climate in the southern arabian peninsula it is generally recognized that the southern arabian peninsula has had two wet periods in the late quaternary to quantify wet a 28 000 year old capillary surface associated with a paleowater table was mapped and used as a surrogate for the water table in a ground water model analysis of this model suggests 1 4 mm year 1 of recharge is necessary to support the water table at the mapped elevations during the wet period climatic relations between rainfall and recharge in arid areas infer that annual rainfall during this wet period was approximately 200 50 mm year 1 or approximately five times the present rate

oxygenation history of bottom waters in the cariaco basin venezuela over the past 578 000 years results from redox sensitive metals mo v mn and fe we present results from analyses of the redox sensitive metals mo v mn and fe in sediment recovered from the cariaco basin ocean drilling program leg 165 site 1002 results are interpreted in the context of previous studies of 15n export production percent total organic carbon eolian input and hemipelagic deposition in the basin variations in redox metal ratios over the past 578 000 years were compared to variations in 18o at milankovitch frequencies and show a strong relationship between glacial interglacial cycles in sea level governed by the shallow sills encircling cariaco basin and bottom water oxygen content during 100 kyr and 41 kyr cyclicity enrichments of mo and v occur during highly productive interglacials indicating bottom water anoxia during glacials sediments are less depleted or enriched in mn and fe relative to the interglacials reflecting oxic conditions during 23 kyr and 19 kyr cyclicity however these redox metal patterns are not observed indicating that the cariaco basin responds differently to the higher frequency climate changes

a database approach for constraining stochastic simulations of the sedimentary heterogeneity of fluvial reservoirs quantitative databases storing analog data describing the geometry of sedimentologic features are commonly used to derive input for geostatistical simulations of reservoir sedimentary architecture however geometrical information alone is inadequate for the detailed characterization of sedimentary heterogeneity a relational database storing fluvial architecture data has been developed and populated with literature and field derived data from modern rivers and ancient successions the database scheme characterizes fluvial architecture at three different scales of observation recording style of internal organization geometries and spatial relationships of genetic units classifying data sets according to controlling factors e g climate type and context descriptive characteristics e g river pattern the database can therefore be filtered on both architectural features and boundary conditions to yield outputs tailored on the system being modeled to generate input to object and pixel based stochastic simulations of reservoir architecture when modeling heterogeneity with stochastic simulations the choice of input parameters quantifying spatial variation is problematic because of the paucity of primary data and the partial characterization of supposed analogs this database driven approach permits the definition of various constraints referring to either genetic units e g architectural elements or material units i e contiguous volumes of sediment characterized by the same value of a given categorical or discretized variable e g same lithofacies type clay and silt content and others which permit the realistic description of fluvial architecture heterogeneity applications of this database approach include the computation of relative dimensional parameters and the generation of auto and cross variograms and transition probability matrices which are necessary to effectively model spatial complexity

carbon isotopic evolution of the terminal neoproterozoic and early cambrian evidence from the yangtze platform south china profound geotectonic climatic and biological changes occurred during the terminal neoproterozoic and its transition into the early cambrian these changes are reflected in temporal variations of the carbon isotopic composition of seawater recorded in a sedimentary succession on china s yangtze platform however in addition to secular changes in carbon isotopes the studied succession reflects additional variations in accordance with the deposition in different sedimentary facies ranging from shallow water platformal to deeper water basinal settings likely a consequence of incorporation of variable amounts of 13 c depleted

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

ediacaran and cambrian paleosols from central australia abstract ediacaran to cambrian red sandstones of the northern territory including arumbera sandstone and grant bluff and central mount stuart formations have been reexamined and sampled in order to reconstruct paleoenvironments from sedimentary facies and paleosols sedimentary facies include green gray calcareous sandstone member iii of arumbera sandstone only red siltstone with calcareous nodules also only member iii and also non calcareous red green siltstone interbedded red siltstone and sandstone and trough bedded sandstone the green gray facies has diverse and distinctive cambrian marine trace fossils not found in the red beds which have instead an assemblage of problematic body fossils including arumberia noffkarkys hallidaya ernietta trepassia and dickinsonia the red facies are interpreted as fluvial paleochannels trough cross bedded fluvial levees interbedded siltstone and sandstone poorly drained floodplain red green siltstone and well drained floodplain or low terrace calcareous nodular the carbonate nodules have micritic replacive fabrics and a significant positive correlation of 13c and 18o characteristic of pedogenic carbonate of calcid soils other red beds have pseudomorphous sand crystals after gypsum like those of gypsid soils individual red beds show negative strain and mass transfer for cationic bases typical of soils as well as gradational alteration down from fossiliferous tops characteristic of soils their varied degree of pedogenic differentiation is identified as psamment aquent and ochrept paleosols phosphorus depletion in the paleosols is evidence that organisms lived in the paleosols and were not introduced by transient marine incursions the problematic quilted fossils arumberia noffkarkys and hallidaya formed a distinctive inland terrestrial polsterland during the ediacaran and early cambrian

palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest permian late triassic solway basin u k abstract the late permian to late triassic sediments of the solway basin consist of an originally flat lying laterally persistent and consistent succession of mature dominantly fine grained red clastics laid down in part of a very large intracontinental basin the complete absence of body or trace fossils or palaeosols indicates a very arid hyperarid depositional environment for most of the sediments at the base of the succession thin regolith breccias and sandstones rest unconformably on basement and early permian rift clastics overlying gypsiferous red silty mudstones very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary and their margins these pass upwards into thick bedded multi storied fine to very fine grained red quartzo felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter above thick trough cross bedded and parallel laminated fine grained aeolian sandstones deposited in extensive barchanoid dune complexes pass up into very thick multicoloured mudstones and gypsum deposited in marginal marine or lacustrine sabkha environments the latter pass up into marine lower jurassic shales and limestones thirteen non marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures the five associations can be compared with the desert pavement arid ephemeral stream sabkha saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as lake eyre and lake chad the accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent caused by climatic change and local variation and this promotes a large scale layer cake stratigraphy as exemplified in the solway basin here the dominant fine grained mature sandstones above the local basal reg breccias suggest water reworking of wind transported sediment as in the northern part of the lake chad basin growth faulting occurs in places in the solway basin caused by underlying evaporite movement but these faults did not significantly affect pre late triassic sedimentation and did not expose pre permian units above the basal breccias there is no evidence of post early permian rifting anywhere during deposition of the late permian to middle triassic british succession although the succession is often interpreted with a rift basin model the arid to hyperarid palaeoclimate changed little during deposition of the solway basin succession in contrast to lakes eyre and chad and this is attributed to tectonic and palaeolatitude stability unlike the later mesozoic cenozoic only limited plate movements took place during the triassic in western europe palaeolatitude changed little and the solway basin remained in the northern latitudinal desert belt from early to mid triassic times however the influence of the early triassic impoverished biota on environmental interpretations needs further study

recognizing products of palaeoclimate fluctuation in the fluvial stratigraphic record an example from the pennsylvanian to lower permian of cape breton island nova scotia tectonics and climate are the major extrinsic upstream controls on both the external and internal architectures of fluvial channels while the role of tectonics has been well documented the role of climate has received less attention because both tectonics and climate can produce similar stratigraphic architectures the ability to recognize and differentiate these has major ramifications for the interpretation of fluvial stratigraphy the pennsylvanian to permian succession of the maritimes basin complex on cape breton island is ca 5 km thick and is composed of predominantly non marine strata deposited within a series of depocentres characterized by different subsidence regimes basins in the west are transtensional depocentres characterized by episodic fault movement in contrast basins in the east were formed during prolonged periods of passive thermal subsidence the stratigraphy is composed of four second order sequences a to d each 5 to 10 myr in duration these sequences are composed of amalgamated fluvial channel deposits that fine upwards into extensive mud dominated floodplain deposits with isolated fluvial channel bodies a spectrum of fluvial styles is recorded within the study area including perennial perennial intermittent and ephemeral four stratigraphic intervals e1 to e4 are recognized in which the deposits of strongly seasonal perennial intermittent fluvial deposits are predominant these intervals 2 to 6 myr in duration are correlated across the study area between basins with differing tectonic regimes and do not correlate with a particular position in second order sequences this suggests that climate exerted the dominant influence on the formation of these intervals and can be differentiated from tectonic imprints while the tectonic regime of a particular basin exerted a fundamental control on the external architecture a coherent record of climate change is recognized in the internal architecture of fluvial units this study demonstrates that tectonic and climatic controls can be recognized and differentiated in vertical successions by evaluating the changes in fluvial architecture