the organic and mineral matter contents in deposits infilling floodplain basins holocene alluviation record from the klodnica and osobloga river valleys southern poland the work examines the timing and environmental conditions of floodplain sedimentation in the valleys of the upland klodnica and piedmont osobloga rivers in the upper odra river basin a distribution of 52 14c ages shows relatively high floodplain sedimentation at the late glacial holocene transition more stable floodplain environments since the early in the klodnica valley and middle holocene in the osobloga valley and a gradual increase in floodplain deposition in the late holocene since 3 4 kyr bp organic matter om and mineral matter mm fluctuations were correlated with variables responsible for the activation of erosion i e vegetation changes human impact and hydrological events as well as factors affecting the local record of sedimentation i e valley morphology hydrologic conditions and episodes of local erosion a clear relationship is shown between an increase in alluviation and climate or human induced extension of unforested areas the deposition of mineral rich sediments increases rapidly during periods characterized by non arboreal pollen values exceeding approximately 8 in pollen diagrams on the other hand the results obtained do not confirm significant interactions between holocene changes in forest composition and alluviation despite the settlement of agrarian groups the sedimentary record of human activity in the osobloga catchment is very poor during the neolithic and early bronze age a large scale alluviation of the osobloga and klodnica valleys was initiated during the settlement of people of the lusatian culture from the middle bronze age and escalated in the early middle ages and modern times the deposition of products of soil erosion was limited to between ca 1 9 1 2 kyr bp probably due to demographic regression during the migration period comparison of om mm fluctuations with phases of increased fluvial activity does not show a relationship between holocene wetter phases and catchment sediment yield sedimentary episodes in the upper odra basin also show a low degree of correlation with the probability density curve of the 14c ages the results obtained in the klodnica and osobloga valleys indicate a strong to moderate correlation between the spatial distribution of the study sites and the origin of mm rich deposits but a weak correlation between the spatial distribution of the study sites and toc content such a pattern suggests that om mm fluctuations relate predominantly to the changes in sediment yield although morphological conditions have a significant impact on the capture potential of sedimentary basins during phases of alluviation additionally high om content is not a simple function of an increase in wetness of the sedimentary environment on the other hand hydrologically conditioned hiatuses as well as erosion episodes impoverish the sedimentary record complicating the consideration on the geochronology of deposits and making it difficult to calculate reliable accumulation rates however they do not reduce the value of om mm fluctuations as an indicator of alluviation events for a preserved series of sediments

an 15 000 year record of el nino driven alluviation in southwestern ecuador debris flows have deposited inorganic laminae in an alpine lake that is 75 kilometers east of the pacific ocean in ecuador these storm induced events were dated by radiocarbon and the age of laminae that are less than 200 years old matches the historic record of el nino events from about 15 000 to about 7000 calendar years before the present the periodicity of clastic deposition is greater than or equal to 15 years thereafter there is a progressive increase in frequency to periodicities of 2 to 8 5 years this is the modern el nino periodicity which was established about 5000 calendar years before the present this may reflect the onset of a steeper zonal sea surface temperature gradient which was driven by enhanced trade winds

history of laurentide meltwater flow to the gulf of mexico during the last deglaciation as revealed by reworked calcareous nannofossils the history of meltwater flow from the laurentide ice sheet to the gulf of mexico during the last deglaciation which holds possible implications for the cause of the younger dryas cold episode is not well understood we propose a new chronology based on using the percentage of reworked calcareous nannofossils in orca basin sediments as a proxy for erosion the period of greatest meltwater flow to the gulf was between 12 7 and 12 1 ka during the bolling warm interval and flow remained high until the beginning of the younger dryas cold episode at 11 3 ka this corresponds to meltwater pulse ia a sharp meltwater decrease at 12 2 ka may represent the older dryas glacial readvance little or no meltwater is inferred to have flowed to the gulf from 10 to 9 ka which is the time of the second major meltwater pulse ib therefore meltwater must have been permanently diverted away from the gulf of mexico at the beginning of the younger dryas

holocene soft sediment deformation of the santa fe sopetran basin northern colombian andes evidence for pre hispanic seismic activity abstract the detailed study of four deformed intervals from the holocene fluvio lacustrine deposits of the santa fe sopetran basin in northern colombia shows 17 types of soft sediment deformation ssd structures evidence indicates that seismic activity was responsible for the ssd structures a conclusion reached after considering the environmental conditions at the time of sediment deposition and shortly after and the detailed analysis of the driving force systems other triggers i e overloading and rapid sedimentation however are not discarded intervals showing ssd structures occurred at centennial frequencies and apparently resulted from mw 6 7 earthquakes the holocene age of these major shaking events should be seriously considered when evaluating the seismic hazard and risk for the middle cauca valley and the nearby city of medellin with 3 million inhabitants

the mediaeval warm period drought recorded in lake huguangyan tropical south china the geochemistry of dated sediment cores from lake huguangyan 21o9 n 110o17 e tropical south china reveals distinct stratigraphical patterns in total organic and inorganic carbon toc tic biogenic silica bs and total nitrogen tn over the past 1400 years in this hydrologically closed lake tic variations may reeect changes in the precipitation evaporation ratio which controls the evaporative enrichment of carbonate toc bs and tn in the sediment are proxy indicators of lake productivity and nutrient input which we believe are linked to local precipitation high tic content correlates with low concentrations of toc bs and tn and indicates two drought episodes dated to ad 670 760 and ad 880 1260 in the sediments of lake huguan gyan local historical chronicles support these data suggesting that the climate of tropical south china was dry during the mediaeval warm period mwp and wet during the little ice age lia the detected mwp drought is temporally correlated with evidence for lower precipitation on the guliya china and quelccaya peru ice caps and with increased salinity in moon lake us great plains

biomarker distributions in australian oils predominantly derived from terrigenous source material oils found in many australian sedimentary basins contain a relatively high input of terrigenous organic source material a study of a large number of these oils has permitted a number of biomarker distributions to be determined that appear to be characteristic for oils derived from terrigenous source material these features include the presence of sesquiterpanes absence of tricyclic terpanes relatively high concentrations of a c24 tetracyclic terpane predominance of c29 steranes presence of two unidentified c27 and c30 terpanes and virtual absence of 18 h oleanane the latter observation is significant since it appears that 18 h oleanane appears only in oils of tertiary age derived from terrigenous source material an attempt has also been made to compare the results for the australian oils with published results for oils derived from terrigenous source material in other parts of the world the number of reports in the literature for these oils is fairly limited but it appears that some of the observations for the australian oils can be extended to them this study is an initial attempt to devise a classification scheme that can be used to determine the origin of an oil unambiguously from biomarker parameters in order for this approach to be successful a relatively large number of biomarker parameters need to be assigned as characteristic of a particular type of source material

evolution of the holocene mississippi river floodplain ferriday louisiana insights on the origin of fine grained floodplains abstract the alluvial architecture and soil characteristics of holo cene mississippi river floodplain deposits in the southern lower mississippi valley provide evidence for significant changes in floodplain development in response to sea level rise floodplain cores acquired near ferriday louisiana show that holocene deposits consist of 15 30 m ave 20 m of sands silts and clays which overlie late wisconsin sands and gravels on the basis of differences in sediment grain size sediment body geometry and the abundance of soil features the holocene deposits are subdivided into lower and upper holocene units lower holocene deposits 5000 yr b p consist of lacustrine and poorly drained backswamp muds that contain authigenic siderite pyrite and vivianite and show little evidence of soil formation muds encase crevasse splay and floodplain channel sand bodies 1 km wide and collectively these deposits represent a mosaic of shallow lakes poorly drained backswamps and multichannel streams similar to modern examples in the atchafalaya basin 100 km south of ferriday upper holocene deposits 5000 yr b p are represented by large mississippi river meander belt sand bodies that are up to 15 km wide and 30 m thick natural levee silts and sands and well drained backswamp muds are present between meander belt sands upper holocene deposits contain abundant soil features and sandy and silty soils are entisols inceptisols and alfisols whereas clayey soils are vertisols the presence of isolated sand bodies surrounded by mud and the scarcity of soil features suggest that lower holocene sediments reflect a period of rapid floodplain aggradation during which crevassing lacustrine sedimentation and avulsion dominated floodplain construction no evidence of large meandering mississippi river channels represented by buried thick tabular sands exists near ferriday and discharge in lower mississippi valley flow was probably conveyed by a network of small multichannel floodplain streams upper holocene sediments record a dramatic change ca 5000 yr b p from rapid to slower floodplain aggradation which was accompanied by extensive lateral channel migration overbank deposition and soil formation on the basis of differences in meander belt dimensions and numbers of abandoned channels upper holocene meander belts are subdivided into simple and complex forms relative age relationships suggest that the smaller and older simple meander belts represent periods of divided mississippi river flow and early attempts to establish a large single channel meandering regime this type of meandering regime is represented by the larger and younger complex meander belts and includes the modern meander belt similarities in the timing of changes in floodplain processes and fluvial style and decreasing rates of holocene sediment accumulation in the southern lower mississippi valley strongly suggest that decelerating holocene sea level rise in the gulf of mexico affected floodplain development at least 300 km inland from the present day coast the alluvial architecture of the lower holocene deposits and the absence of large meandering mississippi river channel deposits older than 5000 yr b p near ferriday indicates that most of the floodplain muds were deposited by avulsion related crevassing and lacustrine sedimentation rather than by overbank flooding of large mississippi river channels similarities between the floodplain history of the mississippi river and those of modern and ancient rivers elsewhere further suggest that avulsion rather than simple overbank deposition contributes to the construction of fine grained floodplains to a greater degree than generally recognized

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

climate variations in europe over the past 140 kyr deduced from rock magnetism rapid shifts in climate during the last glacial are now well documented particularly from the oxygen isotope records of the two greenland ice cores grip1 2 and gisp23 in the grip record1 2 these climate events are also seen during the preceding eemian interglacial which may be an analogue for the future climate warmed by the greenhouse effect but these shifts are not found in the eemian section of the gisp2 core3 casting doubt on whether the rapid shifts in the grip oxygen isotope record really do represent a climate signal here we present magnetic susceptibility pollen and organic carbon records from maar lake deposits in the massif central france these data provide an independent record of past climate and we find that they correlate well with the ice core records during the last glacial during the eemian two rapid cooling events seen in our record also correlate with those seen in the grip ice core supporting the idea that rapid climate change did occur in the eemian interglacial and demonstrating that it extended to continental europe

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

variations of the amazonian rainforest environment a sedimentological record covering 30 000 years abstract two cores css 2 and css 10 were collected from two lakes situated in the carajas area 6 35 s 49 30 w that show different stages of silting up the results of geochemical and petrographic organic analyses backed up by 14 c radiometric dating lead to a reconstruction of the variations in the hydrological regime of these lakes over the last 30 000 years evidence is revealed for a period of drying up characterized by a sedimentary hiatus between 22 000 and 13 000 14 c years bp followed by a period of refilling between 13 000 and 11 000 14 c years bp 15 400 12 900 cal years bp the latter interval is primarily characterized by a mainly clastic sedimentary input rich in quartz kaolinite and iron hydroxides leading on to the authigenic formation of siderite this type of sedimentation implies the erosion of the small catchment basin during periods of transition between arid and humid climatic regimes from 8000 to 4000 14 c years bp 8900 4500 cal years bp as well as from 2700 to 1500 14 c years bp 2780 1360 cal years bp special hydrological conditions prevailed they are characterized in the sedimentary record by the presence of micro laminae containing wood charcoal interlayered with sponge spicule material this interlamination reflects the rapid alternation of dry and humid periods a comparison with the results obtained by pollen analysis shows that sedimentological indicators once filtered for strictly local effects can provide a full record of the regional scale variations in the environment

middle pleistocene palaeolimnology of a dammed tropical river the zarzal formation cauca valley colombia abstract the plio pleistocene zarzal formation zf offers one of the few examples of alternation between fully lacustrine to fluvial conditions in a major tropical intramontane river in the northern andes i e the cauca river the zf is mainly composed of diatomites mudstones and tuffaceous sandstones deposited in an intramontane depression located between the western and central cordilleras of colombia and associated with the cauca romeral fault system stratigraphic sedimentological micropalaeontological diatoms and geochronological analyses independent u th he dating of apatite and zircon have been performed on two sections of the zf these analyses reveal a fluctuation between volcanic fluvial and lacustrine deposits during the middle pleistocene in addition the presence of soft sediment deformation structures reflects the synergetic effect of tectonism and volcanism on the sedimentation patterns in the cauca river valley our data show that between about 0 48 0 52 ma ionian depositional facies varied from a fluvial dominated environment to a palaeo lake suggesting the impoundment of the river once the lake was formed full lacustrine conditions were frequently interrupted by river pulses bringing terrigenous and previously deposited volcanic material into the lake diatom based palaeolimnological reconstructions and comparisons with the sedimentological records indicate that river episodes played a decisive role on nutrient supply and sediment input controlling important ecological dynamics in the newly formed lake although we cannot unambiguously pinpoint to the influence of volcanic activity on nutrient cycling within the lake our data exhibit a strong relationship between volcanic deposits and changes in flora the latter are possibly linked to the increase in phosphorous availability the combined effects of tectonism and volcanism had major environmental implications in the quaternary evolution of the cauca river causing unprecedented damming of a one of the major torrential tropical rivers in northern south america therefore are of utmost importance when considering risk assessment and management for riverine communities and infrastructure such as dam buildings

source rock heterogeneity of the upper jurassic draupne formation north viking graben and its relevance to petroleum generation studies abstract the upper jurassic draupne formation in the north viking graben north sea has been studied to identify lateral and vertical variations in source rock characteristics and their effect on the timing of petroleum generation fourteen source rock samples from the western flank of the graben and five from the eastern flank were analysed using rock eval analysis microscopy open system pyrolysis gas chromatography and kinetic experiments two major organic facies with different petroleum generation characteristics were identified a stratigraphically higher thermally less stable facies corresponding to a type ii kerogen with hi hydrogen index values of 350 mg hc g toc and a stratigraphically lower more stable type ii iii facies with hi values

tree ring analysis of ancient baldcypress trees and subfossil wood abstract ancient baldcypress trees found in wetland and riverine environments have been used to develop a network of exactly dated annual ring width chronologies extending from the southeastern united states across mexico and into western guatemala these chronologies are sensitive to growing season precipitation in spite of frequently flooded site conditions and have been used to reconstruct moisture levels the southeastern united states and mexico for over 1000 years the el nino southern oscillation enso is a major influence on the climate reconstructions derived from these baldcypress chronologies especially in mexico where some of the most extreme reconstructed droughts occurred during el nino events in the southeast the enso influence on climate and tree growth changes sign from spring to summer and this change in dynamical forcing is recorded by sub seasonal chronologies of earlywood and latewood width most existing baldcypress chronologies have been extended with tree ring data from subfossil wood recovered from surface and submerged deposits well preserved subfossil logs have also been recovered in quantity from buried deposits of great age and may permit development of long continuously dated holocene chronologies and discontinuous floating pleistocene chronologies the extensive subfossil baldcypress swamp discovered 6 m below the streets of washington d c was overrun by a transgression of the potomac estuary possibly during the previous super interglacial marine ois 5e and provides direct evidence for one potential impact of unmitigated anthropogenic warming and sea level rise

high resolution tropical climate record for the last 6 000 years 1200 800 cal yrs b p the initial d 18 oi ncrease centered at 5 500 years ago is coincident with the development of arid conditions in the caribbean region and the end of the african humid period indicating a global drying of the northern tropics at this time synchronous with the aridification of the caribbean region are the onset of wetter conditions in the south american altiplano and the reoccupation of this region by humans this combination of contrasting climate conditions is attributed to a southward displacement of the intertropical convergence zone itcz that would have resulted in decreased precipitation and increased trade wind intensity in the caribbean region and increased rainfall over the altiplano index terms 4267 oceanography general paleoceanography 4231 oceanography general equatorial oceanography 4870 oceanography biological and chemical stable isotopes 4802 oceanography biological and chemical anoxic environments citation tedesco k and r thunell high resolution tropical climate record for the last 6 000 years geophys res lett 30 17 1891 doi 10 1029 2003gl017959 2003

megaflood erosion and meltwater plumbing changes during last north american deglaciation recorded in gulf of mexico sediments submicrometer variations in the median diameter of siliciclastic mud in orca basin northern gulf of mexico sensitively monitor laurentide ice sheet runoff to the gulf during early stages of the last deglaciation grain size data document a prominent pulse of very fine grained sediment to the northern gulf from 12 6 to 12 0 ka corresponding with the well known sea surface meltwater spike in 18 o records meltwater megafloods at this time eroded and transported large volumes of clay to the gulf via the mississippi river system the nonquartzose megaflood sediments appear to have been derived from clay rich midcontinental terrace deposits rather than from glacial outwash supplied by the laurentide ice margin sediment grain size data in combination with other terrigenous proxies clay minerals and reworked calcareous nannofossils indicate substantial variability in deglacial meltwater discharge and associated sediment load of meltwater runoff this variability reflects changes in continental plumbing consistent with terrestrial records of north american deglaciation

the mississippi delta region past present and future the mississippi delta region of south louisiana houses a wealth of resources within a dynamic subsiding landscape foundations for the delta region reflect neogene evolution of the depocenter whereas details of the modern landscape reflect late pleistocene to holocene evolution of the alluvial deltaic plain the holocene delta plain was constructed by cyclical growth of deltaic headlands followed by avulsion and relocation of the fluvial sediment source abandoned headlands were then submerged and reworked while a new headland was created at the site of active fluvial sediment input historic period levees have decoupled the delta plain from its fluvial sediment source at the same time global sea level rise was accelerating which has accelerated delta plain submergence diversions of mississippi river water and sediment are necessary to achieve delta plain sustainability but upstream dams trap 50 of the total sediment load and there is not enough supply to keep pace with subsidence and accelerated

lacustrine organic fluxes and palaeoclimatic variations during the last 15 ka lac du bouchet massif central france to assess the influence of climatic changes on organic lacustrine sedimentation two cores recovered from the centre of the lac du bouchet were studied by petrographical palynofacies and geochemical methods only core ldb h was used for estimation of the organic fluxes the variation of these fluxes with climo stratigraphic periods showed low organic fluxes during the lateglacial an increase at the beginning of the holocene a minimum at the end of the atlantic period resulting from the climatic cooling and a maximum at the end of the sub boreal related to the installation of the present climatic conditions

age limits on the late quaternary evolution of the upper loire river abstract the loire river is one of the largest rivers in europe draining a basin area of southern france which exceeds 100 000 km 2 despite its significance the loire remains poorly studied and has a very limited amount of chronological control on the deposited sedimentary record of fluvial activity these factors coupled with the availability of a set of 10 radiocarbon dates on younger c

annual and inter annual variability of the present climate in northern south america and southern mesoamerica abstract present climate of northwestern south america and the southern isthmus is detailed in terms of major hydro climatic controls supported by evidence from station records reanalysis data and satellite information in this tropical region precipitation is the principal hydro climatological variable to display great variability the primary objective is to view the controls that operate at intra seasonal to inter decadal time scales this is a topographical complex region whose climate influences range in provenance from the south atlantic to the canadian prairies and from the north atlantic to the eastern pacific the situation is further complicated by interactions and feedbacks in time and space between these influences which are interconnected over various scales the greatest single control on the annual cycle is the meridional migration of the inter tropical convergence zone and its pattern of associated trade winds consideration of these alone and their interaction with the cordilleras of the andes and central america produce a variety of unimodal and bimodal regimes regionally two low level jet streams the westerly choco jet 5 n and the easterly san andres jet 12 14 n and their seasonal variability have tremendous significance as do mesoscale convective storms and mid latitude cold fronts from both the northern nortes and southern friagems hemispheres there are many examples of hydro climatological feedbacks within the region of these the most notable is the interaction between evaporation over the amazon precipitation onto the eastern andes and streamflow from the headwaters of the amazon this is further compounded by the high percentages of recycled precipitation over large areas of the tropics and the potential impacts of anthropogenic modification of the land surface the el nino southern oscillation phenomenon enso is the greatest single cause of interannual variability within the region yet its effects are not universal in their timing sign or magnitude a set of regional physical connections to enso are established and their varying local manifestations are viewed in the context of the dominant precipitation generating mechanisms and feedbacks at that location in addition some potential impacts of longer run variations within the ocean atmosphere system of the atlantic are examined independently and in conjunction with enso this review of the climatic controls and feedbacks in the region provides a spatial and temporal framework within which the highly complex set of factors and their interactions may be interpreted from the past

early cenozoic two phase extension and late cenozoic thermal subsidence and inversion of the bohai basin northern china abstract the bohai basin is one of a family of early cenozoic extensional basins that lie along the eastern margin of asia from russia to vietnam initial extension was probably triggered by subduction roll back of the oceanic pacific plate from the asian continent there were two phases in the bohai basin s rift history the earlier paleocene early eocene phase resulted in the deposition of the kongdian formation and the fourth lowest member of the shahejie formation in a series of elongate half grabens these half grabens have master faults with a nne ssw orientation secondary normal faults are typically clockwise oblique to the master faults indicating a component of dextral transtension deposition was focused in the west and south of the present basin these rocks are mainly alluvial fan and fluvial red beds the architecture of the basin underwent an important change at ca 43 45 ma middle eocene beginning with the deposition of the third member of the shahejie formation in part these sediments were deposited in the same half grabens as the kongdian formation but the bozhong depression in the central part of the basin originated at this time and became the major depocentre the bozhong depression superficially resembles a pull apart basin it formed when continued transtension of the earlier tertiary fault systems to the east and west created an extensional overlap between them during this phase the basin as a whole had a geometry with elements typical of both pull apart and transtensional basins regional extension in many east asian basins ended at the end of the oligocene probably because of the onset of transpression within eastern asia caused by the collision of australia with the philippine sea plate dextral transpression caused minor inversion of some of the earlier normal faults in bohai but as a whole the basin began to subside in a post rift phase of thermal subsidence that has lasted until the present day

a contemporary appraisal of some key fiskian concepts with emphasis on holocene meander belt formation and morphology abstract looking back five decades and reflecting on the contributions of harold fisk to lower mississippi valley lmv geological knowledge it is apparent that he was highly successful in making engineers aware of the critical role of glacial advance and retreat sea level changes valley slope and river gradient and time in affecting geomorphic processes sedimentary patterns and river regimes perhaps his greatest contribution to river engineering was in recognizing and elaborating on the effects of bed and bank materials on stream meandering fisk however could only work within the prevailing geological theory and method of his time with regard to glacial chronology and stratigraphy and such matters as global structure and tectonics major advances in these areas with new concepts and techniques have shown his lmv glacial response model to be oversimplified and invalid in some respects more cycles of valley filling and cutting are now known to be represented in the alluvial sequence and his concept of deep valley entrenchment as a direct response to sea level changes is untenable in light of substantial new data the presence of a regional rectilinear fracture pattern with a corresponding network of major fault zones has not been substantiated by subsurface data the most widely known aspect of fisk s work is his detailed interpretation and colorful depiction of the complex pattern of overlapping cross cutting and discontinuous holocene meander belts and their hundreds of abandoned channels however it is now recognized that fisk s elaborate chronological reconstruction is largely invalid both because of some incorrect basic assumptions and his lack of radiocarbon and other numerical dating techniques for precise control a newly emerging model of meander belt formation is more generalized and relies heavily on archaeological evidence it places emphasis on episodes of multiple active river courses partial flow channels frequent formation of distributary channels and the significant influence of mississippi river tributaries and minor basin drainage interesting regional variations over time in meander belt configurations and morphology may reflect climate changes but at present broad scale variations in the lithology of the quaternary alluvial sequence appear to be the dominant control

fluvial activity in major river basins of the eastern united states during the holocene in the eastern united states existing paleo reconstructions in fluvial environments consist primarily of site specific investigations of climate and human impacts on riverine processes this paper

palynofacies and geochemical analysis of the triassic yanchang formation ordos basin implications for hydrocarbon generation potential and the paleoenvironment of continental source rocks abstract the petroliferous basins that have formed in china since the mesozoic are characterized by non marine organic matter input a characteristic that is significantly different from that of marine organic sources the triassic yanchang formation in the ordos basin is a suite of typical intra continental lacustrine sediments that comprise the most important source rocks for the triassic oil reservoirs the yanchang formation is divided into ten subsections from top to bottom chan 1 to chan 10 three borehole successions in the southern ordos basin located in the huachi zhidan and yichuan areas cross the chan 4 5 to chan 10 subsections and have been studied using the palynofacies method combined with organic geochemistry data palynofacies analysis indicates that the sediments are rich in amorphous organic matter aom and phytoclasts the aom content in all of the samples positively correlated with the hydrogen index hi in contrast the transparent ligno cellulosic fragments tlf opaque particles op content are negatively correlated with the hi values additionally the gelified particles gp content has no linear correlation with the geochemistry data based on the quantitative composition of the particulate organic matter three palynofacies types are identified reflecting depositional settings in a distal dysoxic anoxic deep basin a shelf to basin transition zone and a proximal suboxic shelf the palynofacies total organic carbon toc and rock eval data together indicate that type i and ii kerogen are abundant in the d48 and w22 wells in the zhidan and yichuan areas respectively these kerogen types are uncommon in the l94 well in the huachi area which suggests low hydrocarbon generation potential in detail the chan 7 and chan 9 subsections of the three wells contain abundant type i and ii kerogen indicating that these layers are likely the two primary source rocks in the southern ordos basin

applications of ichnology in lacustrine sequence stratigraphy potential and limitations abstract in comparison with their marine counterparts lacustrine ichnofaunas have not been extensively used in sequence stratigraphy application of trace fossils in continental sequence stratigraphy cannot be based simply on the extrapolation of marine sequence stratigraphy marine substrate controlled ichnofacies in particular the firmground glossifungites ichnofacies develop in stable and cohesive substrates reflecting erosive exhumation of the sediment in contrast in lacustrine sequences substrate controlled ichnofossils only rarely indicate erosional exhumation because they are commonly related to desiccation of water bodies the tripartite division of overfilled balanced fill and underfilled lakes provides a comprehensive framework to evaluate the potential and limitations of lacustrine ichnofaunas in sequence stratigraphy based on a number of case studies spanning the three lake basin types a model of trace fossil distribution in overfilled balanced fill and underfilled basins is proposed overfilled lake basins contain well developed softground trace fossils mermia and skolithos ichnofacies and the softground suite of the scoyenia ichnofacies that are useful to delineate parasequences and parasequence sets fluvial discharge into overfilled lakes usually generates density currents that oxygenate lake bottoms allowing the establishment of epifaunal and infaunal communities additionally these are freshwater lakes where no stress due to hypersalinity occurs leading to the development of a relatively diverse benthos land plant derived organic matter is the prime source of nutrients favoring the development of a deposit feeding benthic fauna in permanently subaqueous low energy zones firmground suites are rare because such large lakes usually do not experience desiccation abundant firmground trace fossil suites of the scoyenia ichnofacies occur in balanced fill lakes but softground assemblages are usually depauperate lowstand deposits contain abundant and widespread ichnofaunas commonly meniscate trace fossils and arthropod trackways of the scoyenia ichnofacies lake hydrology is closed during lowstands and salinity usually increases imposing a stress factor on the lake biota and therefore softground ichnofaunas are depauperate ichnofaunas from turbidite systems in balanced fill lakes are less abundant and diverse than those from overfilled lacustrine turbidites freshwater conditions are common during transgression but dysaerobic conditions may prevail imparting a stress factor on the benthic biota in hydrologically closed lakes the scoyenia ichnofacies is widespread but the mermia ichnofacies is commonly absent or impoverished the scoyenia ichnofacies is associated with lowstand desiccated substrates in underfilled lakes the density of arthropod trackways may be high forming tracked omission surfaces some of these omission surfaces may represent sequence boundaries expressed by co planar surfaces of lowstand and subsequent flooding rapid changes in depositional conditions reflecting desiccation during vertical aggradation can lead to the formation of composite ichnofabrics that reflect successive bioturbation events

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

lacustrine source rock deposition in response to co evolution of environments and organisms controlled by tectonic subsidence and climate bohai bay basin china three paleogene syn rift intervals from the bohai bay basin the most petroliferous basin in china were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions the third es3 and first es1 members of the eocene shahejie formation and the oligocene dongying formation ed display widely variable total organic carbon contents hydrogen indices and visual kerogen compositions suggesting changes in organic facies from deep to marginal sediments carefully selected deep lake facies samples from any interval however display fairly uniform biomarker composition these three intervals have distinctly different biomarker assemblages which indicate weakly alkaline freshwater lakes with a moderately deep thermocline during es3 deposition alkaline saline lakes with shallow chemocline during es1 deposition and acidic freshwater lakes with deep unstable thermocline during the deposition of the dongying formation such environmental changes corresponded to changes in subsidence rate and paleoclimate from rapid subsidence and wet climate during es3 deposition through slow subsidence and arid climate during es1 deposition to rapid subsidence and wet climate during ed deposition and resulted in synchronous changes in terrigenous organic matter input phytoplankton community and primary productivity the co evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn rift evolutions the models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins

circum arctic petroleum systems identified using decision tree chemometrics source and age related biomarker and isotopic data were measured for more than 1000 crude oil samples from wells and seeps collected above approximately 55n latitude a unique multitiered chemometric multivariate statistical decision tree was created that allowed automated classification of 31 genetically distinct circum arctic oil families based on a training set of 622 oil samples the method which we call decision tree chemometrics uses principal components analysis and multiple tiers of k nearest neighbor and simca soft independent modeling of class analogy models to classify and assign confidence limits for newly acquired oil samples and source rock extracts geochemical data for each oil sample were also used to infer the age lithology organic matter input depositional environment and identity of its source rock these results demonstrate the value of large petroleum databases where all samples were analyzed using the same procedures and instrumentation

causes of river avulsion insights from the late holocene avulsion history of the mississippi river u s a abstract the emphasis on gradient advantages in studies of avulsion is misleading while gradient advantages are necessary for an avulsion to occur the late holocene avulsion history of the mississippi river in louisiana suggests that factors such as substrate composition and floodplain channel distributions are more important cross valley to down valley slope ratios of the modern floodplain range from 16 to 110 and are typically 30 the slope ratio is 35 at the location of the mississippi atchafalaya diversion old river yet slope ratios are 83 to 110 immediately upvalley of old river all values of mississippi river floodplain slope ratios are significantly larger than values of avulsion threshold calculated by numerical models shallow floodplain cores 14c dating of organic remains and geologic mapping show that the mississippi river has avulsed only four times over the past 5 ky in the southern lower mississippi valley lmv gradient advantages are widespread yet avulsions are rare these observations indicate that factors other than gradient advantage control mississippi river avulsion several examples of mississippi and red river avulsion by channel reoccupation support the idea that channel distributions and substrate compositions are primary influences on avulsion incipient mississippi river avulsion and development of the atchafalaya river involved reoccupation of abandoned mississippi river channels and a red river crevasse splay complex the modern atchafalaya river also incises buried mississippi river channel belt sands abandoned channel belts and crevasse splay complexes consist of sandy substrates that facilitate scour and the development of channels capable of capturing the mississippi river abandoned channels provide ready made conduits for mississippi river flow that can efficiently develop into avulsive channels multi storied sheet sandstones in ancient fluvial deposits may provide additional support for the idea that erodible substrates and floodplain channel distributions are critical influences on avulsion these features record episodic reoccupation of channel belts which at least in some cases may simply reflect successive avulsions rather than major changes in aggradation rate or extrabasinal factors such as climate

multiple oil families in the west siberian basin two major oil families are identified in the west siberian basin twenty six of 32 analyzed oils occur in jurassic and cretaceous reservoirs and are derived from anoxic marine upper jurassic bazhenov source rock based on geochemical comparison of oils and source rock extracts these oils are widely distributed both north and immediately south of the ob river and their biomarker ratios indicate a wide range of source rock thermal maturity from early to middle oil window van egan russkoye samotlor sovninsko sovyet olyenye ozynornoye and kogolym to peak oil window srednekhulym yem yegov vostochno surgut khokhryakov fedorov and urengoi to late oil window salym some of these oils have been mildly e g fedorov 75 to heavily e g russkoye biodegraded n the reservoir the bazhenov sourced oils show different compositions that support regional variations of organic facies in the source rock for example the anoxic marine bazhenov facies which generated the oils in the samotlor fedorov and nearby fields was particularly clay poor and sulfur rich six nonbiodegraded highly mature oils show geochemical characteristics that suggest they were derived from clastic rich lacustrine or nearshore marine source rocks dominated by terrigenous higher plant input like those in the lower to middle jurassic tyumen formation although no correlation was observed between the oils and a single rock sample yem yegov 15 from the formation the six oils occur in the tyumen taitym geologiche and cheremshan and fractured basement paleozoic gerasimov yagyl yakh and verchnekombar reservoirs in positions readily accessible to any oil migrating from the tyumen source rock for example at the gerasimov location the tyumen formation lies unconformably on weathered basement paleozoic reservoir rocks most of the probable tyumen sourced oils ar from south of the ob river but the occurrence of geologiche oil to the north suggests that related oils may be widespread in the basin

organic and isotope geochemistry of the early cretaceous rift sequence in the camamu basin brazil paleolimnological inferences and source rock models abstract the camamu basin located at the eastern brazilian continental margin is characterized by a thick early cretaceous organic rich rift sequence the integration of bulk geochemical isotopic and biomarker data with paleontological and geological information provided the basis for a better assessment of rift lake evolution hydrological regime redox potential salinity etc and its impact on source rock development pyrolysis and visual kerogen analyses reveal the dominance of lipid rich algal bacterial type i kerogen through the entire rift sequence paleolimnological reconstruction suggests that the lower rift sequence morro do barro formation neocomian was deposited in a fault bounded deep lake with fresh to brackish water stable water column stratification and water bottom anoxia high hydrogen indices 700 900 mg hc gtoc and 13c depleted carbon isotopic composition of the organic matter 13c values around 30 might reflect enhanced organic preservation the recycling of light ch4 generated by methanogenesis and the incorporation of isotopically light lipid rich bacterial biomass on the other hand the upper rift sequence rio de contas formation barremian was probably deposited within a broader shallower lake with a higher frequency of water column overturn and a deeper thermocline high organic carbon contents and strong 13c enrichment of the organic matter 13c excursions of up to 23 are interpreted to have resulted from enhanced primary productivity triggered by an increased input recycling of nutrients favored by lake morphology and humid climate

charging of oil fields surrounding the shaleitian uplift from multiple source rock intervals and generative kitchens bohai bay basin china abstract this paper discusses origin and charging directions of oil fields on the shaleitian uplift bohai bay basin the shaleitian uplift is a footwall uplift surrounded by three sags containing mature source rocks the origins of the four oil fields on the shaleitian uplift both in terms of source rock intervals and in terms of generative kitchens were studied using biomarker distributions for 61 source rock samples and 27 oil samples hierarchical cluster analysis using 12 parameters known to be effective indicators of organic matter input and or depositional conditions allowed the identification of six oil types or classes these six oil classes could then be linked to three distinct source rock intervals ranging in age from 43 0 ma to 30 3 ma the third member 43 0 38 0 ma in age and first member 35 8 32 8 ma of the eocene shahejie formation and the third member of the oligocene dongying formation 32 8 30 3 ma each sourced one class of oil the other three classes represent mixtures of oil generated from multiple source rock intervals traps on the shaleitian uplift were charged in the east by oil generated from the eocene shahejie formation in the bozhong sag in the southeast by oil generated from the eocene shahejie and then oligocene dongying formations in the southwestern part of the bozhong sag and or in the eastern part of the shanan sag and in the southwest by oil generated from the eocene shahejie formation in the western part of the shanan sag the estimated migration distances range from less than 5 km to about 20 km the compositional heterogeneity within fields and multiple parameter comparisons between oils from nearby wells in different fields have proven to be a powerful tool to determine the in filling histories of oil fields in cases where multiple source rock intervals and multiple generative kitchens exist

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

the younger dryas cool episode in the gulf of mexico data are presented from orca basin piston core en32 pc4 in the gulf of mexico that confirm the existence of surface water cooling during the younger dry as chronozone 11 10 ka late glacial planktonic foraminiferal species made a reappearance between 11 4 and 9 8 ka an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer globigerinoides ruber the presence of the younger dryas event in the gulf at 27 n demonstrates that surface water cooling extended to mid latitude regions in the north atlantic the cool surface water interval is bracketed by rapid shifts in 18o related to changes in the influx of meltwater to the gulf of mexico a chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a 500 year period and ended in less than 200 years these results are among the first deep sea sediment data documenting the climatic transitions bracketing the younger dryas with a rapidity observed in ice core records a rapid decrease in 18o values measured in the white form of gs ruber at 10 2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures surprisingly a similar decrease is not observed in the pink form of gs ruber a summer surface water dweller in the gulf this discrepancy may be explained by continued meltwater influx throughout the younger dryas during the summers only such that there was no change in the 18o of the pink form at the end of the episode an additional possibility is that warming at the end of the younger dryas raised year average temperatures and summer temperatures remained constant the coincidence of rapid shifts in 18o with the younger dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the younger dryas cooling based on changes in the routing of laurentide glacial meltwater

late holocene paleoenvironmental changes in northeast brazil recorded by organic matter in lacustrine sediments of lake boqueirao northeast brazil represents a key area in terms of holocene environmental changes in south america due to its distinct semi arid climate at near equatorial latitudes as well as to a wetter early and middle holocene paleoclimate in comparison with other south america regions which also experienced a reduced monsoon at that time we studied the lacustrine sediments of lake boqueirao which is located at 5 s latitude on the brazilian atlantic coast it is directly influenced by displacement of the intertropical convergence zone itcz a short 1 m core boqc0701 was collected at a 7 5 m water depth during a seismic survey organic matter om geochemical rock eval total organic carbon toc hydrogen index hi oxygen index oi and petrographical studies allowed us to distinguish five sedimentary intervals during the last 3 kyrs phase e 3000 to 2050 cal yr bp presents the largest toc hi and oi fluctuations in the entire core the most probable cause of these variations is a great instability in the lake level during this period phase d 2050 to 1830 cal yr bp is marked by an increase in sedimentation rate and a higher contribution from a well preserved om with an algal origin this was interpreted as a higher and more stable lake level during phase c 1830 to 1550 cal yrs bp low hi and high oi indicate the input of more oxidized degraded and detrital om reflecting a lower lake level in phase b 1550 to 1470 cal yr bp the om quality and quantity hi and toc indicate an algal contribution during phase a 1470 to 570 cal yr bp the high stability of the proxies may be due to a deep environment where om fluctuations are strongly buffered these changes in lake level can be compared with other tropical south america high resolution records a correspondence seems to exist between phases of low enso cool north atlantic ocean and boqueirao wet phases we did not encounter this same pattern during the last 1050 years during which the 1050 570 cal yrs bp interval was generally wet although probable fluctuations are buffered in our proxies while the north atlantic was warm mann et al 2009 a prolonged dryness occurred in lake boqueirao from 570 cal yrs bp until recent decades this phase corresponds to the little ice age characterized by a cooler north atlantic ocean mann et al 2009 these data indicate that the teleconnection pattern between the tropical atlantic enso and northeast brazil rainfalls has changed in the past

refining the link between the holocene development of the mississippi river delta and the geologic evolution of cat island ms implications for delta associated barrier islands abstract the geologic evolution of barrier islands is profoundly influenced by the nature of the deposits underlying them many researchers have speculated on the origin and evolution of cat island in mississippi but uncertainty remains about whether or not the island is underlain completely or in part by deposits associated with the past growth of the mississippi river delta in part this is due to a lack of comprehensive geological information offshore of the island that could augment previous stratigraphic interpretations based on terrestrial borings an extensive survey of cat island and its surrounding waters was conducted including shallow water geophysics e g high resolution chirp seismic side scan sonar and swath and single beam bathymetry and both terrestrial and marine vibracoring high resolution seismic data and vibracores from south and east of the island show two horizontally laminated silt units marine radiocarbon dates indicate that they are st bernard delta complex sbdc deposits furthermore seismic data reveal that the sbdc deposits taper off toward the southern shoreline of cat island and to the west morphology consistent with the distal edge of a delta complex the sedimentology and extent of each unit suggest that the lower unit may have been deposited during an earlier period of continuous river flow while the upper unit may represent reduced or sporadic river flow osl dates from the island platform beneath beach ridge complexes indicate three stages of terrestrial evolution island emergence resulting from relative sea level rise 5400 ybp island aggradation via littoral transport 2500 4000 ybp and island degradation due to delta mediated changes in wave direction present 3600 ybp finally the combination of terrestrial and marine data shows that portions of cat island that are lower in elevation than the central part of the island are younger and are likely underlain by a thin layer of deltaic sediments this underscores the potential for increased future vulnerability of barrier islands that develop adjacent to major river delta complexes

application of organic facies studies to sedimentary basin analysis a case study from the yitong graben china abstract an organic facies is defined in this paper as a mappable stratigraphic unit containing organic matter om of a particular genetic type in certain abundance several concepts concerning organic facies are proposed and their significance in basin analysis is discussed in detail a combined sedimentological and organic geochemical investigation has been carried out in the yitong graben and four organic facies and one organic parafacies have been recognized distinct organic basin fill sequences obfs and organic facies association ofa were developed in different sub units of this graben which indicates that the yitong graben had undergone two tectonic subsidence cycles such tectonic subsidence patterns could not have been found out without detailed organic facies analysis confirming that organic facies especially obfs and ofa study is a very useful tool not only for prediction and three dimensional mapping of petroleum source rocks but also for sedimentary basin analysis

palynofacies analysis of the late holocene san nicolas terrace of the cauca paleolake and paleohydrology of northern south america abstract the detailed palynofacies analysis of the late holocene laminated succession of the san nicolas terrace in the middle cauca valley northern colombia is interpreted as the product of sedimentation in a lacustrine to fluvial dominated setting radiocarbon analyses reveal that the succession was deposited between 3500 and a few hundreds of years with sedimentary rates in excess of 600 cm ka the milimetric laminae and the high frequency fluctuations in the content of the palynodebris of terrestrial origin i e the high altered ligno cellulosic debris amorphous organic matter ratio together with diatoms typical of fluvial conditions such as aulacoseira granulata do suggest an intermittent and continuous hydrological and biological connectivity with the cauca river akin to a varzea lacustrine environment drier to wetter conditions appear to occur moving upward in the succession this might reflect regional precipitation conditions all along the cauca valley and the southern migration of the intertropical convergence zone

geochemical comparison of fluid inclusion and present day oil accumulations in the papuan foreland evidence for previously unrecognised petroleum source rocks abstract petroleum production in papua new guinea is limited to the papuan fold belt present day oil accumulations in fields such as iagifu hedinia and gobe are thought to be mainly derived from clay rich jurassic marine source rocks containing terrestrially derived organic matter that were deposited under oxic conditions in this study other generative source rocks in the papuan foreland are indicated using fluid inclusion fi oil data from three wildcat wells koko 1 bujon 1 and kimu 1 which were drilled on the bosavi arch detailed organic geochemistry of these fi oils and associated free oils or oil stains suggests that none of these were generated from the aforementioned jurassic source rocks instead at least three different generative source rocks are indicated firstly a marine probably late cretaceous or younger source rock deposited under reducing conditions is indicated by the bujon 1 fi oil this source rock had a moderate contribution from higher plant organic matter including oleanane and or lupane the bujon 1 fi oil has similarities with fi oils from the iagifu 7x and p nyang 2x wells in the papuan fold belt secondly an algal dominated lacustrine source rock is indicated by the biodegraded koko 1 rft crude oil the unbiodegraded fi oil from koko 1 and the bujon 1 oil stains from the toro and imburu formations these lacustrine oils have high abundances of tricyclic terpanes pregnane homopregnane and gammacerane contain carotane and have high c26 c25 tricyclic terpane ratios the source of the lacustrine oils is inferred to contain moderate amounts of terrestrial organic matter indicated by a dominance of c29 steranes and abundant aromatic higher plant biomarkers and could be gypsiferous shales embedded in oligocene miocene carbonates or triassic age sediments deposited on igneous basement during early rifting associated with the break up of gondwana the kimu 1 fi oil was generated from a mature marine suboxic source rock but has a different geochemical composition to free oil from a similar interval which was derived from a carbonate rich source rock none of the fi oils correlate well with oil families previously described in papua new guinea accordingly the oils recovered from fis in this part of the papuan basin support the presence of laterally varying source rock compositions and qualities and indicate that there are opportunities to develop new charge models for features across the papuan foreland furthermore koko 1 bujon 1 and kimu 1 fi oils have different geochemical compositions compared to the associated free oils or oil stains indicating that each of these localities has a multi phase charge history further work to lower exploration risk in the papuan foreland should be directed to understanding the distribution maturity and expulsion history of these newly recognised potential source rocks

palaeoenvironmental changes during the last ca 8590 calibrated yr 7800 radiocarbon yr in the dry forest ecosystem of the patia valley southern colombian andes a multiproxy approach two sediment cores were recovered from two swamps in the dry forest lowland ecosystem of the patia valley colombia the 500 cm long core el patia 1 was analysed using diatoms pollen lithostratigraphy geochemistry charcoal and radiocarbon dates the 270 cm long core patia 2 was analysed using pollen lithostratigraphy and radiocarbon dates the environmental reconstruction includes the local development and history of the patia 1 swamp and the regional vegetation history of the two swamps the environmental reconstruction shows a fluvial system in the area before 7830 14c yr bp ca 8590 cal yr bp after this date the river gradually moved away leading to the formation of the swamp patia 1 open vegetation with patches of dry forest surrounded the swamp between 7670 and 6860 14c yr bp 8350 7690 cal yr bp the swamp become partially isolated from the river and was a permanent water body which was alkaline and mesotrophic during this period the surroundings were covered by dry forest from 6860 to 5870 14c yr bp 7690 6690 cal yr bp the swamp was totally isolated from the river and suffered from frequent periods of desiccation and erosion from 5870 to 3570 14c yr bp 6690 3890 cal yr bp the swamp turned into a marsh terrestrial environment and in the surrounding area the dry forest alternated with open vegetation it is possible that there were human impacts on the environment during this period between 3570 and 1990 14c yr bp 3890 2000 cal yr bp unstable conditions prevailed after 1990 14c yr bp 2000 cal yr bp swamp conditions of permanent water were re established open vegetation surrounded the swamp agriculture and human activities were present and have continued since then the climatic reconstruction suggests an increase in humidity at ca 7670 14c yr bp 8350 cal yr bp and a dry climate between 6860 and 5870 14c yr bp 7690 6690 cal yr bp

multiple scale hydraulic characterization of a surficial clayey aquitard overlying a regional aquifer in louisiana abstract the vertical hydraulic conductivity k v of a 30 m thick surficial clayey aquitard overlying a regional aquifer at an industrial site in the mississippi river valley in louisiana was investigated via intensive hydraulic characterization using high resolution vertical hydraulic head profiles with temporal monitoring and laboratory tests a study area was instrumented with a semi circular array of piezometers at many depths in the aquitard at equal distance from a large capacity pumping well including replicate piezometers profiles showed negligible head differential to 20 m bgs below which there was an abrupt change in vertical gradients over the lower 8 10 m of the aquitard hydraulic characteristics are strongly associated with depositional environment the upper zone of minimal head differentials with depth and minimal variation over time correlates with paleo mississippi river backswamp deposits while the lower zone with large head differentials and slow but moderate head changes correlates with lacustrine deposits the lower zone restricts groundwater flow between the surface and underlying regional aquifer which is hydraulically connected to the mississippi river lab tests on lacustrine samples show low k v 8 10 11 4 10 9 m s bracketing field estimates 6 10 10 m s from 1 d model fits to piezometric data in response to large aquifer head changes the slow response indicates absence of through going open fractures in the lacustrine unit consistent with geotechnical properties high plasticity normal consolidation suggesting high integrity that protects the underlying aquifer from surficial contamination the lack of vertical gradients in the overlying backswamp unit indicates abundant secondary permeability features e g fractures rootholes consistent with depositional and weathering conditions 2 d stylized transient flow simulations including both units supports this interpretation other published reports on surficial aquitards in the gulf coast region pertain to pleistocene deposits that lack laterally extensive lacustrine units and where k v is enhanced by secondary permeability features resulting in clayey aquitards with poor integrity

late pleistocene evolution of the lower mississippi river valley southern missouri to arkansas the mississippi river served as the principal conduit for meltwaters discharging from the southern margins of north american ice sheets the northern half of the mississippi river alluvial valley in missouri and arkansas can be subdivided into two distinct channel courses the western and eastern lowlands which are separated by crowleys ridge the eastern lowlands contain two entry points the bell city oran and thebes gaps the latter is a narrow bedrock gorge that contains the modern river this paper summarizes a model for evolution of channel courses in the western and eastern lowlands during the illinoian and wisconsin glacial stages for the western lowlands stratigraphic relations between loess units and subjacent fluvial deposits show that major continuous terrace surfaces or valley trains are illinoian or late wisconsin in age investigations of tributary valley fills further show the western lowlands were deeply incised during the early to middle wisconsin stage then aggraded during the late wisconsin stage to such an extent that tributary valleys were backfilled with slackwater deposits moreover analysis of loess thinning and fining trends shows that early to middle wisconsin roxana silt and the late wisconsin peoria loess covers on western lowlands valley trains were derived from deflation of valley trains in the eastern lowlands we conclude that the western lowlands were the primary mississippi river course during illinoian deglaciation but were abandoned shortly thereafter then episodically reoccupied during the late wisconsin stage for the eastern lowlands course valley trains of early to middle wisconsin age are not preserved with the exception of a small remnant where the mississippi river broke through a gap in the southern margins of crowleys ridge and reentered the western lowlands all valley trains in the eastern lowlands are late wisconsin age a series of discontinuous terrace surfaces in the bell city oran gap represent dissected remnants of the primary late wisconsin full glacial and early late glacial course of the mississippi river or combined mississippi and ohio rivers whereas younger continuous braided stream surfaces in the bell city oran and thebes gap courses represent valley trains of latest wisconsin and earliest holocene age hence the bell city oran gap was the primary course during the entire wisconsin stage and the thebes gap was permanently occupied in earliest holocene time as much as 5 m difference in elevation between successive late wisconsin terrace surfaces of the eastern lowlands indicates that valley trains were rapidly constructed incised and abandoned in response to fluctuations in the delivery of meltwater and outwash from the former ice margin moreover a variety of data indicates that deglacial meltwater floods were commonly of sufficient magnitude to overflow from the primary course in the bell city oran gap throughout the late wisconsin substage floodwaters overflowed into the western lowlands constructed a series of secondary valley trains and filled tributary valleys with slackwater deposits during the latest wisconsin stage perhaps in association with the drainage of glacial lake agassiz floodwaters overflowed into the western lowlands and broke through the thebes gap the charleston fan represents the initial deposits of the thebes gap course following deposition of a large crevasse splay at the western lowlands entrance that course was no longer active but flow was routed through the thebes gap during periods of high magnitude flooding until the bell city oran gap was abandoned and the thebes gap course was permanently occupied during earliest holocene time

the character and origin of lacustrine source rocks in the lower cretaceous synrift section congo basin west africa lower cretaceous synrift lacustrine shales from the congo basin west africa have been analyzed with sedimentological and geochemical techniques to characterize source rock quality and identify triggers for deposition of intervals richest in organic carbon the sequence includes a lower active rift section deposited during active faulting and subsidence overlain by an upper late rift section deposited during reduced faulting and subsidence total organic carbon toc averages 2 3 wt throughout the active rift siliciclastic shale section 6 in marls in the lower part of the late rift section and 1 2 in deltaic shales in the upper part of the late rift section organic matter consists of mixed types i and iii kerogen in the active rift shales pure type i kerogen in the late rift marls and a type i and iii mixture in the late rift deltaic shales redox proxies indicate that the deep lake was relatively reducing throughout deposition of the active rift and lower late rift sections therefore enhanced anoxia did not trigger deposition of the richest source rocks decreased sedimentation rates in the late rift do not account for the full increase in toc nor the shift on organic matter type the richest source rocks are associated with high rates of organic productivity and chemical sedimentation indicating that flux of dissolved components to the rift lake including nutrients for algae growth was critical we propose that reduced topography associated with the late rift was necessary for efficient cycling of plant derived carbon into soil carbonate and ultimately the rift lake and for enhancing chemical weathering and nutrient flux

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

oil families and their potential sources in the northeastern timan pechora basin russia oil and rock samples collected throughout the northeastern timan pechora basin identify key oil families and correlate these oil families to stratigraphic units that sourced them based on distinctive molecular characteristics three distinctive hydrocarbon systems have been identified within the northeastern timan pechora basin hydro carbons both oil and gas are found in clastic and carbonate reservoirs from the lower silurian to the triassic three major oil families have been identified based on physical properties gas chromatography liquid chromatography and gas chromatography mass spectrometry family a oils are found in permian silurian reservoirs within the sorokin swell and upper devonian reservoirs within the eastern and western edges of the khoreyver depression this oil family is sourced from an upper devonian bitumen laminated carbonate mudstone informally known as the domanik facies family b oils are found only in upper devonian reservoirs within the central khoreyver depression this oil family is most likely sourced from upper devonian hypersaline marine mudstones with significant bacterial input many of the family b oils were generated at temperatures less than that for peak oil generation family c oils are found in carboniferous lower devonian reservoirs within the northern sorokin swell this family is sourced from marine mudstones that have gloecapsamorpha prisca as well as other marine algae present organic rich lower devonian and silurian shales contain similar molecular characteristics and are potential sources for the family c oils

pollen analysis of a long upper pleistocene continental sequence in a velay maar massif central france abstract a new 20 m sequence is presented which is based on 279 spectra derived from a coring at le bouchet lake massif central france the vegetational history of this region is described back to the end of the last interglacial ribains interglacial the two preglacial early glacial forested interstadials st geneys 1 and st geneys 2 are evidence for the first time in the massif central in spite of the altitude of the site 1200 m they suggest a quite temperate vegetation with the same mesophilous character as during the holocene the pleniglacial appears to be threefold with two cold episodes lower and upper pleniglacial divided by a long complex period of moderate climatic improvement the vegetation history of this mountain region is compared with that evidenced for the same period on the basis of the sequence of les echets at a lower altitude 267 m botanical and climatic inferences are discussed

geochemical characterisation and genetic origin of oils and condensates in the south viking graben norway abstract geochemical analysis of oil and condensate samples from all major fields and discoveries in the norwegian south viking graben as well as source rock extracts of upper and middle jurassic source horizons was carried out to characterise reservoired hydrocarbons and establish genetic relationships the south viking graben is in a mature phase of exploration and this study aims at unravelling regional trends to improve predictions in exploration and will show the significance of the play models in the area seven hydrocarbon families have been identified based on interpretation of molecular and isotopic characteristics and multivariate analysis of biomarker data these families can be linked to three source horizons three families originate from different facies of the draupne formation and are characterised by pr ph ratios below 2 dominance of c 27 regular steranes over the c 29 homologues and carbon isotopic values for saturate and aromatic fraction lighter than 28 and 27 respectively the upper jurassic heather formation and the middle jurassic vestland group each source one group of hydrocarbons typical for heather sourced hydrocarbons are elevated pr ph ratios between 2 35 and 3 08 low ratios of c 27 c 29 regular steranes and average isotopic values of 28 4 13 c sat and 26 8 13 c aro hydrocarbons from a middle jurassic source are characterised by very heavy isotopic composition highest pr ph ratios of the data set and dominance of c 29 regular steranes over the c 27 homologues among other factors the two remaining families represent mixtures from upper and middle jurassic sources and are mainly encountered in the greater sleipner area the available data in this study allowed characterisation of 84 of the recoverable oil resources which proved that the main source rock in the area is the upper jurassic draupne formation the play concept including a draupne source and tertiary reservoir proves to be most prolific with 239 10 6 s m 3 of recoverable oil equalling 88 of the total characterised oil resources oils in these tertiary reservoirs are however likely to be affected by biodegradation based on the available data the zone of biodegradation in the south viking graben appears to be limited to depths above 2140 m and temperatures below 70 c

mechanisms of petroleum accumulation in the bozhong sub basin bohai bay basin china part 1 origin and occurrence of crude oils the origin of the fourteen major oil fields in the bozhong sub basin bohai bay basin was studied based on the results of rock eval pyrolysis on more than 700 samples and biomarker analysis on 61 source rock samples and 87 oil samples the three possible source rock intervals have different biomarker assemblages and were deposited in different environments the third member of the oligocene dongying formation e3d3 32 8 30 3 ma in age is characterized mainly by high c19 c23 tricyclic terpane 0 75 high c24 tetracyclic terpane c26 tricyclic terpane 2 5 low gammacerane c30 hopane 0 15 and low 4 methyl steranes c29 steranes 0 15 ratios and was deposited in sub oxic to anoxic environments with significant terrigenous organic matter input the first e2s1 35 8 32 8 ma and third e2s3 43 0 38 0 ma members of the eocene shahejie formation have low c19 c23 tricyclic terpane and low c24 tetracyclic terpane c26 tricyclic terpane ratios and were deposited in anoxic environments with minor terrestrial organic matter input but have different abundances of 4 methyl steranes and gammacerane the hydrocarbon generating potential and biomarker associations of these three source rock intervals were controlled by tectonic evolution of the sub basin and climate changes three oil families derived from e2s3 e2s1 and e3d respectively and three types of mixed oils have been identified all large oil fields in the bozhong sub basin display considerable heterogeneities in biomarker compositions and originated from more than one source rock interval which suggests that mixing of oils derived from multiple source rock intervals or multiple generative kitchens and or focusing of oils originated from a large area of a generative kitchen is essential for the formation of large oil fields in the bozhong sub basin e2s3 and e2s1 derived oils experienced relatively long distance lateral migration and accumulated in traps away from the generative kitchen e3d3 derived oils had migrated short distances and accumulated in traps closer to the generative kitchen such a petroleum distribution pattern has important implications for future exploration there is considerable exploration potential for dongying derived oils in the bozhong sub basin and traps close to or within the generative kitchens have better chance to contain oils generated from the dongying formation

relationships between organo mineral supply and early diagenesis in the lacustrine environment a study of surficial sediments from the lac du bouchet haute loire france the relationships between organo mineral composition and early diagenetic processes in surface 50 cm sediments from the lac du bouchet haute loire france are presented parallel pore water studies reveal downcore increases in dissolved organic carbon inorganic carbon and ch4 illustrating the dominant methanogenetic degradation but also highlighting regions of enhanced degradation due to sulphate reduction confirmed by solid phase sulphur and pyrite distributions three sedimentary facies are observed ia 0 25 cm where the majority of compaction and degradation of the organic matter by diagenesis occurs in the absence of any significant change in the type of organic material or sedimentation rate ib 25 40 cm characterised by an increased grain size and diatom abundance ii below 40 cm whose base dates at 2500 350 bp i e within the sub atlantic shows high organic carbon contents and large grain size autochthonous amorphous organic matter is the dominant petrographical organic component whereas pedogenetic allochthonous amorphous organic matter is slightly enriched in facies ii and ia this is coincident with the disappearance of the spores and pollen and suggests a greater continental runoff from the surrounding basin at these times proportions of kaolinite chlorite and illite content do not vary greatly indicating that the detrital input has not changed significantly over the last 2500 years downcore decreases in the sial curve proxy for biogenic silica parallel those of total organic carbon suggesting the dissolution of solid phase silica over time the anthropogenic deforestation and consequent greater nutrient runoff into the oligotrophic lake encouraged an increased production of diatoms around 30 cm the increased sedimentation rate at the beginning of the sub atlantic facies ii as a result of greater continental runoff due to installation of present climatic conditions enhanced the preservation of the organic material by reducing the dia genetic effects and by increasing the proportion of diagenetically inert and relatively resistant organic matter these findings underline the critical role that bulk sedimentation rate and the nature of organic matter play in the final determination of sediment composition both in terms of input and in post depositional degradation

characteristic of source rocks and origin of crude oils in the raoyang sag and baxian sag bohai bay basin china insights from geochemical and geological analyses abstract three potential source rock intervals were evaluated based on the results of rock eval pyrolysis on nearly 700 rock samples and the origin of the twenty two oil fields was studied by the biomarker analysis on 62 source rock samples and 93 oil samples in the raoyang sag and baxian sag bohai bay basin the first member of the shahejie formation es was deposited in an anoxic and salted water column with the dominant contribution of algal organic matters reflected by its rock samples with high gammacerane c30 hopane high etr high c35 c34 hopane high steranes hopanes low pristane phytane low c27 diasterane c27 sterane and low c19 c23 tricyclic terpane characterized by higher c19 c23 tricyclic terpane higher pristane phytane lower steranes hopanes and lower c35 c34 hopane than the es1 rock samples the biomarkers of rocks suggest that the third and forth members of the es were deposited in the sub oxic to anoxic environments with a significant terrestrial organism input further studies suggest that the best source rock interval for oil generation is the es1 source rock interval in the raoyang sag and is the es3 source rock interval in the baxian sag by organic facies analysis of source rocks three source related oil groups have been identified there are two oil groups for the discovered oils in the raoyang sag group i oil dominated by the es1 derived oils has been found in all the oil fields in the raoyang sag and group ii oil mainly derived from the es3 source rock interval only distributes in the north east area and in the south end of the raoyang sag however the three oil groups have been found in the baxian sag but the es3 derived oils are dominant in them and have been found in the major oil fields in the east area and the wen an slope in the west area furthermore the es4 derived oils group iii oil mainly distribute in the baxian sag without any findings in the raoyang sag because of the absence of the es4 source rocks as our studies oils almost accumulate near their source rocks without a long distance migration except the slope areas in the raoyang sag and baxian sag therefore the source rock distribution is a key factor to oil accumulations in the raoyang sag and baxian sag especially the efficient source rock distributions which mainly developed in the organic facies a and b based on the geochemical and geological researches

organic facies variability in the posidonia black shale from luxembourg implications for thermal maturation and depositional environment abstract posidonia shale lias e lower toarcian schiste bitumineux samples were obtained from a well in southern luxembourg esch sur alzette elemental composition and organic facies were studied along the cores and accordingly the thermal maturity and depositional environment were evaluated the organic matter content is high with an average of 7 2 ranging between 2 8 and 13 5 the average vitrinite reflectance value is ca 0 55 indicating an early stage of oil generation several biomarker based maturity parameters support the low thermal maturity including oep values and c 29 5 14 17 h steranes 20s 20s 20r rock eval data and microscopy observations reveal that the organic matter is composed of hydrogen rich type ii kerogen derived from alginite small algal bodies derived from nannoplankton predominate but large telalginite tasmanales also occurs pyrites are abundant and fish bones are frequently observed characterizing a marine depositional environment where strong sulfate reduction occurred small amount of autochthonous vitrinite observed microscopically combined with predominance of short chain n alkanes over long chain n alkanes as well as a low terrigenous aquatic ratio tar indicate a low input of terrigenous organic matter sterane distribution is in good agreement with an origin from a marine carbonate depositional environment which corresponds to the general marlstone lithology additionally c 30 24 propyl 14 h 17 h cholestane 20r was detected supporting the marine origin the depositional environment was strongly oxygen depleted in bottom water as indicated by low concentrations of c 35 homohopane fair to low pr ph ratios slightly less than 1 0 and high sulfur content ca 3 wt on average and sulfur organic carbon ratios with only few interruptions of dysoxic to suboxic conditions during deposition of the posidonia shale in luxembourg gammacerane detected in low abundance reveals that a stratified water column existed and water salinity was slightly enhanced in the paleoenvironment the highest c 27 c 29 sterane ratio due to more algal input indicates a maximum flooding during the upper falciferum zone of the lower toarcian in luxembourg which fits well to the global sea level curve and might correspond to a productivity oceanic anoxic event p oae furthermore toarcian greenhouse climate led to generally low oxygen concentration in bottom water of the shallow sea

molecular organic geochemistry of the tarim basin northwest china we conducted organic geochemical analyses on the largest suite of oils and source rock extracts from the tarim basin northwest china currently available statistical cluster analysis of the entire suite of tarim oils distinguishes at least seven genetic groups of oils the largest group of oils was collected from the tazhong and tabei uplifts and originated from marine middle upper ordovician anoxic marls that mark slope facies at the margins of structural uplifts two other genetic groups most likely originated from marine middle upper ordovician source rocks but of distinct facies with one an oxic shale rich source west of the bachu uplift and the other an anoxic shale source at tazhong

extension of the lac du bouchet palaeomagnetic record over the last 120 000 years a high resolution profile of the palaeomagnetic variations recorded in the upper 20 m of the lac du bouchet sedimentary sequence has been reconstructed from several parallel mackereth and livingstone type cores inter core correlations were established by comparing individual core profiles of magnetic susceptibility individual records of af cleaned directions were then stretched to a common depth scale and merged the mean record was then filtered and smoothed in order to reduce the background noise accelerator radiocarbon determinations and pollen analyses show that the sequence covers the last interglacial glacial cycle back to ca 120 kyr b p and allow to perform a depth to time transformation there is a noted absence of widely divergent directions back to 90 kyr b p it is estimated that the recorded signal a pdrm signal represents the geomagnetic input signal attenuated by about 19 it follows that the excursions reported for the laschamp and olby lavas if they existed at all must have been of rather short duration two durable excursions appear in narrow diameter sections at the base of three independent cores b c and d while a reverse to normal transition is possibly documented in the lowermost meter core d this part of the sequence is dated from the recognition of major climatic events related to the 18 o isotopic stages defined in the oceanic record between 116 and 95 kyr this introduces the possibility of new excursions at ca 104 and 95 kyr i e immediately after the recovery of normal polarity documenting the end of the blake event

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

possible relict meanders of the pliocene mississippi river and their implications abstractalthough the late quaternary history of the mississippi river the largest north american river has been intensely studied its pliocene history is largely unknown we assert that large relict meander bends oxbows of the pliocene mississippi river are preserved as arcuate valleys of local streams in the northwest area of the state of mississippi these arcuate valleys are within the pliocene upland complex stratigraphic unit that occurs as a high level alluvial terrace along the lower mississippi river valley outside these arcuate valleys the upland complex is a braided river gravel deposit that shows southward downvalley paleoflow directions interiors of the arcuate valleys are occupied by upland complex point bar deposits with large scale cross bedding showing a range of paleoflow directions commonly upvalley flow indicative of a meandering regime we used measurements of the radii of the putative relict meander bends and of their paleochannel widths to estimate paleodischarge of the pl

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

a revised holocene geochronology for the lower mississippi valley data from two locations 1 a hydrodam site at the old river diversion structure south of the latitude of natchez ms and 2 eight water wells from the latitude of baton rouge la are the basis for a revised holocene geochronology of the lower mississippi river floodplain based on 84 radiocarbon dates analyses of 64 borehole logs and 75 grain size analyses which together provide major insight into questions concerning the complexity of meander belt movement the influence of the younger dryas on the lower valley and on the pleistocene holocene interface following the younger dryas the early holocene was characterized by periodic flooding and deposition separated by times of little or no deposition

evidence of late glacial runoff in the lower mississippi valley abstract thousands of cubic kilometers of massive coarse grained glacial outwash underlie the alluvial plain of the lower mississippi valley between cairo illinois and the gulf of mexico however valley trains deposited by braided streams characterize less than one third of the valley area and those attributable to runoff from the laurentide ice sheet cover less than 15 000 km2 mostly in the st francis basin segment of the valley there they form a series of subdued terraces that reflect episodes of meltwater release and possibly catastrophic flood events radiocarbon dated sediment cores establish that the initial runoff entered the basin about 16 3 ka bp and continued without a significant lull for about 5000 years the distribution of archeological sites tends to support an effective brief cessation of runoff to the valley about 11 0 ka bp when meltwater is thought to have been diverted from the mississippi river valley to the st lawrence valley both radiocarbon dates and archeological evidence document a final pulse of outwash to the lower mississippi valley about 10 0 ka bp when the mississippi river occupied thebes gap near cairo and created the charleston fan all outwash deposition ended and the river adopted a meandering regime not later than 9 8 ka bp

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

controls of oil family distribution and composition in nonmarine petroleum systems a case study from the turpan hami basin northwestern china controls on oil family distribution in tectonically complicated nonmarine petroliferous basins are commonly difficult to isolate because of the varying ages of potential source rocks the complex assemblage of organic rich sedimentary facies and the geographic variability of burial histories the turpan hami basin of northwestern china is an oil bearing intermontane basin where stratigraphic sedimentologic and geochemical controls are sufficient to address each of these issues independently and to determine how they influence the current distribution and composition of liquid hydrocarbons source rock age is one of three major statistically significant discriminators affecting oil family composition both lower middle lower or middle jurassic and upper permian rocks are important source rocks for the basin a newly developed diterpane biomarker parameter can distinguish permian rocks and their correlative oils from jurassic coals and mudrocks and their derivative oils source facies is a second key control on petroleum occurrence and character a variety of biomarker parameters that reflect source rock depositional conditions are indexed to rock samples from interpreted depositional environments by erecting rock to oil correlation models the biomarker parameters separate oil families into end member groups group 1 oils lower middle jurassic peatland swamp facies high land plant input less reducing conditions group 2 oils lower middle jurassic profundal lacustrine facies high algal input more reducing conditions and group 3 oils upper permian lacustrine facies high algal stratified anoxic conditions burial history exercises a third major control on petroleum distribution source rock maturation modeling can demonstrate that relatively uninterrupted burial in the asymmetrically subsiding northern turpan hami area taibei depression exhausted upper permian sourced rocks by the late cretaceous which led to southward migration of upper permiansourced oils group 3 into triassic reservoirs of southern and southwestern turpan hami tainan and tokesun depressions subsequent to uplift of the central basin thrust that currently partitions taibei from tainan lower middle jurassicsourced oils were expelled in the taibei depression by paleoceneeocene time which locally charged jurassic and cretaceous reservoirs groups 1 and 2 forming turpan hami s largest oil accumulations in the basin

deltas radiocarbon dating and measurements of sediment storage and subsidence in holocene marine deltaic sequences there is no simple relationship between radiocarbon age and depth of sampling the nile and ganges brahmaputra deltas show remarkably similar radiocarbon age depth relationships 1 most radiocarbon dates by conventional and accelerator mass spectrometric ams analyses are older some by 4000 yr than reasonably expected 2 dates are commonly inverted i e older upcore and 3 sample dates at delta surfaces commonly exceed 2000 yr b p these anomalous age depth phenomena are in part a response to reservoir effects introduction of old carbon and emphasized herein influence of sediment storage and remobilization that prevail in fluvial and delta plains in fluvial systems sediment generally is not transported in a single episode from its original source area to the sea rather material transported from upland reaches and river valley to coast is subject to a repeated series of depositional burial and erosional events induced by episodic flooding overbank sedimentation and channel migration because sediment is likely to be temporarily stored in the delta plain it is difficult to determine the time of a sediment9s final deposition and burial at a delta site a successful strategy requires use of several independent dating methods including ams analyses of in situ basal peats and fossils and where possible archaeological evaluation of associated artifacts that are in place accurate dates are needed for reliable measurement of rates of delta plain aggradation and land subsidence information to help implement effective coastal protection measures

oil source rock correlations limitations and recommendations a rigorous defensible and causal oil source rock correlation definitively ties an individual source rock sample to an individual crude oil using genetically based internally consistent parameter matches such a correlation is a relationship established between the two components which is consistent with all known chemical geochemical and geological information and meets three criteria a the relationship must be causal the oil must arise at least in part from the specified source rock s b chemical data used in the correlation must be comparable the elemental molecular and isotopic data derived from the source rock must be of the same type as that derived from the oil and c all available geological data must be supportive clear geological evidence must exist which allows the proposed source rock to have sourced the oil the three points of this definition are satisfied and the correlation is successful if we solve one analytical and three geological problems natural extraction of crude oil from its source rock i e expulsion differs mechanically and temporally from laboratory extraction leading to a correlation problem referred to as extraction differences and representing the single greatest analytical uncertainty in correlation efforts geologically three aspects confound oil source correlations occurrence of multiple source units and or source units at differing maturity levels lateral and vertical depositional variations in source unit s organic matter and lateral and vertical variation in reservoir unit s organic matter these concerns are overcome by taking five actions for each oil source correlation effort 1 select representative samples using statistically defensible methods 2 establish the inherent compositional variability laterally and temporally due to depositional and maturation processes in each prospective source unit 3 assess the extent of migration induced changes in oil composition including post migration changes such as in reservoir alteration 4 support each correlation with migration histories derived from 4d models 5 iterate correlation results with new data gathered from ongoing exploration efforts these five actions will a allow correlation success to be measured more objectively b establish risking parameters for direct use in basin assessment and c provide baseline criteria for use in assessing the reliability of oil source rock correlations although these approaches will improve conventional oil source rock correlation efforts ultimately they may not be needed if inversion methods become more reliable the ability to invert compositional data for crude oil i e predict the age lithology maturity and other characteristics of a source rock solely through chemical analysis of its expelled oil could eventually result in successful oil source rock correlations in which source rock analysis for oil source rock correlation purposes is less critical

selective organic matter preservation in burn down turbidites on the madeira abyssal plain 1 oxidized intervals of five organic rich madeira abyssal plain map turbidites deposited during the miocene pliocene and pleistocene all displayed comparable major loss of total organic carbon toc 84 3 1 accompanied by a negative isotopic 13c shift ranging from 0 3 to 2 9 major but significantly lower loss of total nitrogen ntot 61 7 1 also occurred leading to a decrease in toc relative to ntot c ntot and a 1 3 to 2 7 ntot isotopic 15n shift compound specific isotopic measurements on plant wax n alkanes indicate the terrestrial organic component in the unoxidized deposits is 13c enriched owing to significant c4 contribution selective preservation of terrestrial relative to marine organic carbon could account for the 13c behavior of toc upon oxidation but only if a 13c depleted component of the bulk terrestrial signal is selectively preserved in the process although the c ntot decrease and positive 15n shift seems inconsistent with selective terrestrial organic preservation results from analysis of a modern eolian dust sample collected in the vicinity indicate these observations are compatible regardless of the specific explanation for these isotopic observations however our findings provide evidence that paleoreconstruction of properties such as pco2 using the 13c of toc is a goal fraught with uncertainty whether or not the marine sedimentary record considered is contaminated with significant terrestrial input nonetheless despite major and selective loss of both marine and terrestrial components as a consequence of postdepositional oxidation intensive organic geochemical proxies such as the alkenone unsaturation index u37k appear resistant to change and thereby retain their paleoceanographic promise

a revised chronology for mississippi river subdeltas radiocarbon measurements by accelerator mass spectrometry relating to three of the four late holocene mississippi river subdeltas yielded consistent results and were found to differ by up to 2000 carbon 14 years from previously inferred ages these geological dataare in agreement with archaeological carbon 14 data and stratigraphic ages based on ceramic seriation and were used to develop a revised chronologic framework which has implications for prehistoric human settlement patterns coastal evolution and wetland loss and sequence stratigraphic interpretations

marine evidence for episodic holocene megafloods in north america and the northern gulf of mexico hemipelagic muds deposited during the past 5 3 cal kyr in the northern gulf of mexico orca basin contain seven intervals punctuated by relatively coarse siliciclastic grain size peaks planktonic faunal turnovers and negative 13c excursions we believe these episodes represent megaflood deposits reflecting historically unprecedented outfall of north american floodwater and terrigenous mud plumes into the gulf resulting in collapse of the open ocean pelagic ecosystem the deposits record multidecadal episodes of high continental precipitation and large mississippi river floods at 4 7 3 5 3 0 2 5 2 0 1 2 and 0 3 cal ka 500 1200 year recurrence interval variations in tropical plankton frequencies define submillenial warming intervals that culminate in these fluvial episodes strengthened tropical currents in the gulf at these times appear to have increased sea surface temperatures and associated flow of moist gulf air to the midwest terrestrial paleohydrologic records support the marine evidence for millennial scale changes in recurrence of large midwest flood episodes

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

two pool to pool spacing periods on large sand bed rivers mega pools on the madeira and mississippi abstract the madeira river thalweg includes two pool to pool spacing periods first standard pool crossing sequences form 6 to 8 m deep pools these pool crossing sequences recur approximately every six channel widths 9 7 km or 6 8 w on average however the madeira study reach between manicore and porto velho in northern brazil is relatively straight making these pools more frequent than meanders second much deeper pools 13 to 30 m deep also form at relatively regular but much longer spacing 50 60 km about 40 channel widths apart the deeper mega pools occur where the river reaches the edge of the holocene alluvium encountering resistant units e g granite mud clasts and conglomerates in the confining pleistocene units these two pool scales also occur on the lower mississippi river downstream of tarbert landing this study identified pool formation processes responsible for these two pool depth and spacing scales on two large sand bed rivers the analyses computed pool statistics and correlated the deepest pools with planform controls two distinct pool formation hypotheses explain the two pool types the standard pools are rhythmic features developed by macro turbulent feedbacks while the mega pools are forced features imposed by the regional geology the former are fundamentally periodic the latter are not however periodogram analysis indicates that mega pools on the madeira form a second relatively regular pool period the regional geology including the confining pleistocene bluffs and potentially orthogonal neotectonic lineaments imposed periodic regularity to these mega pools on the madeira river that is not observed on the mississippi river a comparably sized sand bed river with mega pools

heterogeneities of organic matter and its occurrence forms in mudrocks evidence from comparisons of palynofacies abstract mudrocks buried at different depths in a single well exhibiting different sedimentary environments and lithologies were collected from the dongying sag of the jiyang depression of eastern china to investigate the heterogeneities of organic matter om and its occurrence forms in this study both bulk rocks and their organo clay composites i e

mechanisms for oil depletion and enrichment on the shijiutuo uplift bohai bay basin china the shijiutuo uplift is a major uplift to the north of the bozhong depression the largest generative kitchen in the bozhong subbasin bohai bay basin although the n35 2 trap on this uplift contains a medium size oil accumulation and the q32 6 trap contains china s third largest offshore oil accumulation the q31 1 trap between the n35 2 and q32 6 traps with very similar evolution history was confirmed to be dry biomarker associations of crude oil and source rock samples were analyzed and three dimensional migration pathway modeling was conducted to investigate the origin of oils and mechanisms for oil enrichment and depletion on the uplift multiple parameter oil source correlation and hierarchical cluster analysis using 10 selected biomarker parameters allowed the identification of four source related oil classes almost all oils from the shijiutuo uplift are derived from the eocene shahejie formation whereas oils found between the shijiutuo uplift and the bozhong depression either are derived from or have important contributions from the oligocene dongying formation variations in oil classes and biomarker parameters suggest sequential migration of oil generated from the shahejie and then dongying formations in the bozhong depression which is reasonably supported by petroleum migration pathway modeling oil charge from two oil prone source rock intervals and more importantly focusing of oil originating from a large area of the bozhong generative kitchen into the same trap accounted for oil enrichment and formation of china s third largest offshore oil field in the q32 6 structure the complexity and primary control of the sealing surface top surface of the carrier bed morphology on the positions of migration pathways caused the q31 1 trap to be shielded from migration of oil originating from the bozhong depression resulting in oil depletion in this trap shadows to petroleum migration may occur because of the three dimensional behavior of petroleum migration and two dimensional migration modeling may be misleading in predicting petroleum occurrences

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator lagoa do caco ne brazil sediment samples collected along a 6 m core drilled in the deepest part of the lagoa do caco ne brazil have been investigated in order to determine source s and degradation conditions of the organic matter om with special emphasis on paleoenvironmental implications bulk organic geochemistry rock eval pyrolysis c n determination 13c and 15n measurement and petrography combined with sedimentological evidence and radiocarbon dates allowed to identify four major intervals documenting major environmental changes that occurred during the last 20 000 years the first interval dating back to the end of the last glacial maximum lgm contains well preserved om derived from higher plants this material was most probably produced in an ephemeral palustrine system and rapidly buried by sands this level is thought to have been deposited under relatively arid climate conditions associated with strong but episodic rainfalls between 19 240 and 17 250 cal years bp the climate appears to have been more humid and seasonality more pronounced as suggested by the presence of a permanent lake after a drastic environmental change dating back to 17 250 cal years bp the sediment became truly lacustrine with restricted mineral input and highly degraded higher plant derived organic matter after that a stepwise improvement in the preservation of om occurred as revealed by several pronounced shifts in the rock eval tps2 signal these changes could document abrupt climatically driven changes during the late glacial finally around 5610 cal years bp environmental conditions approaching those prevailing today were established minor climatic changes during the holocene were probably buffered by a high water table which might explain the lack of paleoenvironmental fluctuations

holocene flood plain soil formation in the southern lower mississippi valley implications for interpreting alluvial paleosols holocene mississippi river flood plain soils in central louisiana provide important insights on alluvial pedogenesis in an aggradational setting insights that are useful for interpreting alluvial paleosols the flood plain soils are younger than ca 5400 yr b p and are grouped into two categories 1 meander belt and 2 backswamp soils meander belt soils are entisols inceptisols and alfisols developed on point bar ridges and natural levee crests they consist of 3 5 m thick brown silty and sandy moderately well drained profiles with multiple parent materials common yellow brown and gray mottles and a few iron and calcite nodules backswamp soils are vertisols formed in flood plain depressions away from active and abandoned mississippi river channels and consist of up to 10 m thick gray clayey poorly drained profiles that have abundant yellow brown mottles iron and calcite nodules gypsum accumulations and slickensides the thickness of the soils and the presence of multiple parent materials show that as the flood plain aggrades concurrent or alternating episodes of sedimentation and pedogenesis produce cumulative profiles profile thickness is more closely related to sediment accumulation rates than to the depth of chemical weathering and the cumulative nature of the soils explains the difficulty of recognizing discrete paleosol profiles in many ancient alluvial deposits comparisons of soils formed on the three youngest holocene mississippi river meander belts saucier and snead 1989 show that the soils record episodes of meander belt growth abandonment and relocation meander belt 1 soils form as the active meander belt develops and consist of either vertically stacked entisols or a single inceptisol the soils contain few calcite nodules and form over intervals of a few hundred years meander belt 2 soils are alfisols lack free carbonates and form over intervals of a few thousand years following meander belt abandonment and soil leaching meander belt 3 soils are alfisols or vertisols that contain common calcite nodules and the profiles are developed in 1 to 2 m of backswamp mud that overlies meander belt silt and sand the mud inhibits profile leaching and leads to poor drainage and calcite precipitation this change in soil hydrology complicates interpretations of the effects of time on meander belt soil development backswamp soils are strongly influenced by seasonal episodes of soil wetting and drying as demonstrated by the gray colors and the abundance of mottles nodules and slickensides in the soils the distribution of calcite nodules in the backswamp and meander belt soils is more closely related to seasonal water table position than to mean annual precipitation which suggests that not all calcic paleosols in ancient alluvial deposits represent semiarid or arid climates slickensides attest to seasonal rainfall but the composition of the backswamp soils primarily reflects source area lithology and depositional influences rather than the effects of chemical weathering in general these soils provide an incomplete record of the humid subtropical climate of louisiana although short term sediment accumulation rates decrease away from mississippi river channels the backswamp soils are not better developed i e more mature than the meander belt soils because poor drainage and slow but continuous sedimentation inhibits weathering collectively these observations suggest that flood plain soils that developed in aggradational settings such as that of the mississippi river flood plain are best suited for interpreting depositional and hydrologic histories of ancient alluvial deposits rather than paleoclimates

definition and characterization of petroleum compositional families in williston basin north america using principal component analysis abstract petroleum hydrocarbons in the gasoline range grh and saturate sfh 210 c boiling point fractions carry information that is often obscured by compositional diversity and multiple processes working simultaneously multivariate statistical methods can enhance the analysis and interpretation of compositional data from these fractions especially in conjunction with independent geological information in the present study principal component analysis pca was applied to the grh and sfh data for 171 oil samples from the williston basin these oils were previously classified using polycyclic terpane and sterane biomarker traits our results indicate that only family a oils can be uniquely classified using pca families b c and d oils show grh and sfh characteristic compositions consistent with biomarker defined families but these characteristics are insufficient for independent classification however the pca analyses of the grh and sfh compositional traits proves to be a useful technique in recognizing the effect of mixing of oils derived from different sources

paleoenvironmental reconstruction based on palynofacies analysis of the aptian albian succession of the sergipe basin northeastern brazil abstract palynofacies analyses were carried out on 272 core samples from two wells gtp 17 se and gtp 24 se in the sergipe basin with the aim of reconstructing the paleoenvironments of the upper aptian middle albian for the palynofacies analysis the kerogen categories were counted and subjected to cluster analyses for detailed environmental analysis kerogen distribution trends and parameters were applied based on percentages of kerogen categories total organic carbon analysis was also used the stratigraphic distribution of palynofacies associations that defined eight palynofacies units in well gtp 17 se and ten in well gtp 24 se reflects a continuous terrestrial influx throughout the succession amorphous organic matter aom and palynomorph groups show moderate to high percentages especially in well gtp 24 se the increase in relative abundance of these groups suggests that a long term a transgression and or a decreasing terrestrial influx occurred in the area from the bottom to top six depositional environments were identified in wells gtp 17 se and gtp 24 respectively and they reflect the progressive increase in marine influence as the basin evolved brackish lagoon conditions changed to more open marine conditions as sea level changed during the separation of south america from africa

alluvial pedogenesis in pleistocene and holocene mississippi river deposits effects of relative sea level change comparison of pleistocene and holocene soils developed in mississippi river meander belt deposits in louisiana illustrates the influence of relative sea level change on pedogenesis holocene and pleistocene meander belts have similar landscape morphologies lithofacies and soil characteristics and probably formed under similar hydrologic regimes the pleistocene avoyelles prairie meander belt is now terraced but it was originally graded to a lower relative sea level position than the holocene flood plain holocene alluvial soils are generally weakly expressed cumulative profiles with abundant redoximorphic features and formed on an aggrading flood plain with a shallow fluctuating water table the soil morphology varies with respect to landscape position and overbank lithofacies pleistocene alluvial paleosols show evidence for two stages of pedogenesis during the first stage of pedogenesis water table fluctuations and flood plain aggradation produced profiles with color mottles iron and carbonate nodules and weak b and c horizons similar to holocene flood plain soils the second stage of pedogenesis occurred after the avoyelles prairie was terraced and the regional water table fell a minimum of 30 m improved soil drainage created oxidizing and acidic conditions removed free carbonates dehydrated iron oxides and transformed clay minerals this stage produced pleistocene profiles with brighter matrix and mottle hues lower ph values larger and harder iron nodules and greater kaolinite contents than comparable holocene flood plain soils the primary influence on regional water table lowering in the southern lower mississippi valley was relative sea level fall mississippi river flood plain lowering adjacent to the avoyelles prairie most likely occurred between the end of oxygen isotope stage 3 and the maximum period of valley entrenchment during oxygen isotope stage 2 water table fall affected pedogenic processes a minimum of 400 km upvalley of the continental shelf margin pleistocene mississippi river paleosols represent excellent analogs for interpreting ancient alluvial paleosols formed during episodes of base level fall and valley incision as fluvial entrenchment terraced the meandering avoyelles prairie a pedogenic threshold was crossed that altered the pathway of chemical weathering the complexity of a multiple step pedogenic history also highlights the fact that interpretation of relative profile development as a function of time can be problematic

inventory of sedimentary organic matter in modern wetland marais vernier normandy france as source indicative tools to study holocene alluvial deposits lower seine valley france palynofacies analysis was developed for petroleum exploration but it is now commonly used to differentiate the major constituents of the sedimentary organic matter som in postglacial deposits our work aimed at studying the som distribution in a present wetland of the seine estuary vernier marsh in order to provide comparative elements to interpret the composition of som in the lower seine valley alluvial infilling in the vernier marsh the distribution of major constituents is heterogeneous thus for each depositional environment studied soils drainage ditches channels ponds the composition of som has been characterized by using two ternary diagrams amorphous om preserved phytoclasts transformed phytoclasts and opaque amorphous gelified particles op ap gp this approach allowed us to define four optical indices that can be used to estimate the relative abundances of principal organic fractions in mixed deposits based on the origin of som aquatic terrestrial its source areas vegetation soils river and controls of early diagenetic changes aerobic anaerobic conditions advanced oxidation amorphous om contents increase from terrestrial environments to fluvial deposits and evaluate the abundance of planktonic contribution preserved transformed phytoclasts ratio decreases from sites of production to those of deposition indicating the degree of degradation of terrestrial materials op contents allow one to define fluvial high values and palustrine low values environments gp ap ratio allows one to discern soil low values and plant high values supplied areas finally these optical compositional indices are measured in holocene deposits and used to complete palaeoenvironmental reconstructions

fluid inclusion evidence for an early marine sourced oil charge prior to gas condensate migration bayu 1 timor sea australia the distribution of oil bearing fluid inclusions fi in currently gas bearing jurassic reservoir sandstones from bayu 1 northern bonaparte basin timor sea is consistent with the bayu gas condensate field originally containing a palaeo oil column beneath a thick palaeo gas cap in order to assess the origin of the oil trapped in the fis and its relationship if any to the gas condensate a detailed molecular geochemical study was carried out on a fi oil extract and a condensate sample recovered from a similar interval by modular formation dynamics tester mdt compared to the condensate the fi oil was generated from a more marine influenced less clay rich source rock or source facies which was deposited in a less oxic environment with greater eukaryotic input the source rock of the condensate was more terrigenous and had greater microbial input the bayu fi oil contains a greater amount of c28 and c29 tricyclic terpanes than the bayu condensate and particularly compared to the elang plover sourced oils from further to the northwest e g corallina and laminaria which are more terrestrially dominated the bayu condensate has previously been attributed to either the marine cretaceous echuca shoals formation or mixed sourcing from the less terrestrially influenced facies of the jurassic elang and plover formations together with the marine flamingo group analysis of the fi oil confirms a more marine influenced source facies of the palaeo oil with the echuca shoals formation being the most likely source based on oil oil and oil source correlations the fi oil appears to represent a marine source end member and it is likely that mixing of this oil sourced from the echuca shoals formation with hydrocarbons sourced from the more terrestrially dominated plover elang source facies could account for the intermediate composition of the currently reservoired condensate a discrete flamingo group is not required and this oil family may not be present in the bayu area the differences are nevertheless subtle and a contribution from the flamingo group cannot be completely discounted the fi oil has a mid oil window maturity 0 75 vitrinite reflectance equivalent vre whereas the currently reservoired condensate has a higher maturity 0 9 vre these maturity data are consistent with early expulsion from the more labile marine derived organic matter in the echuca shoals formation followed by expulsion of large amounts of condensate from the more terrestrially dominated elang and plover formations three possible transition mechanisms from gas over oil to condensate are consistent with the fi petrographical and geochemical data the first charge may have 1 been lost by breaching of the seal 2 been displaced by the condensate or 3 been partly dissolved in the later condensate charge a combination of factors 2 and 3 is considered most likely but further investigation is required to assess these options the fi oil at bayu 1 predominantly represents a different hydrocarbon charge compared to the condensate liquid and so by analogy the large residual oil columns that are observed elsewhere in the northern bonaparte basin are unlikely to be due to water washing of a pre existing gas condensate column similar to bayu undan

palynofacies as useful tool to study origins and transfers of particulate organic matter in recent terrestrial environments synopsis and prospects palynofacies analysis is based on transmitted light microscope study of organic constituents isolated and concentrated by acid and basic digestions published results of studies of present day terrestrial environments show that two complementary approaches successfully characterize particulate organic matter om from palynofacies analyses the first method is based on the identification and the quantification of some typical particles optical markers according to their origin i e aquatic or terrestrial their nature i e biogenic anthropogenic fossil and or their formation i e biodegradation combustion oxidation the second approach is based on the use of binary or ternary diagrams in order to define petrographical signatures from the relative proportions of significant organic constituents this approach can be used for tracking i changes in om composition during humification in soil profiles ii transport of reworked terrestrial particles iii diagenesis of peaty deposits or iv weathering of geological substratum the more advanced approach is based on the use of some predefined optical markers and their optical signatures to establish the relation between the om compositions palynofacies and their depositional environments in addition this kind of study aims to define a modern frame of reference that can be applied in paleoenvironmental reconstructions this paper combines a bibliographic review with previously unpublished data from palynofacies analyses the aim is to present some applied examples illustrating 1 the main approaches developed for characterization of the particulate om in surficial deposits and 2 the study of om transfers in terrestrial geosystems