sedimentology sequence stratigraphy and geochemical variations in the mesoproterozoic nonesuch formation northern wisconsin usa abstract we use core descriptions and portable x ray fluorescence analyses to identify lithofacies and stratigraphic surfaces for the mesoproterozoic nonesuch formation within the ashland syncline wisconsin we group lithofacies into facies associations and construct a sequence stratigraphic framework based on lithofacies stacking and stratigraphic surfaces the fluvial alluvial facies association upper copper harbor conglomerate is overlain across a transgressive surface by the fluctuating profundal facies association lower nonesuch formation the fluctuating profundal facies association comprises a retrogradational sequence set overlain across a maximum flooding surface by an aggradational progradational sequence set comprising fluctuating profundal fluvial lacustrine and fluvial alluvial facies associations middle nonesuch through lower freda formations lithogeochemistry supports sedimentologic and stratigraphic interpretations fe s molar ratios reflect the oxidation state of the lithofacies values are most depleted above the maximum flooding surface where lithofacies are chemically reduced and are greatest in the chemically oxidized lithofacies si al and zr al molar ratios reflect the relative abundance of detrital heavy minerals vs clay minerals greater values correlate with larger grain size vertical facies association stacking records depositional environments that evolved from fluvial and alluvial to balanced fill lake to overfilled lake and returning to fluvial and alluvial elsewhere in the basin where accommodation was greatest some volume of fluvial lacustrine facies is likely present below the transgressive stratigraphic surface this succession of continental and lake basin types indicates a predominant tectonic driver of basin evolution lithofacies distribution and geochemistry indicate deposition within an asymmetric half graben bounded on the east by a west dipping growth fault while facies assemblages are lacustrine and continental periodic marine incursions are probable especially across maximum transgressive surfaces we demonstrate a sequence stratigraphic approach may be applied to fine grained precambrian sediments using traditional rock description and supporting lithogeochemistry identification of a characteristic lithofacies succession in mesoproterozoic sediments demonstrates fundamental controls commonly interpreted for phanerozoic lake systems may be extended into the precambrian these controls result in a predictable association of lithofacies with distinct physical biological and geochemical properties this has regional significance for carbon sequestration and the distribution of mineral and hydrocarbon resources and broader significance for addressing mesoproterozoic paleogeographic reconstructions and questions related to the evolution of terrestrial life

placer mining along the fraser river british columbia the geomorphic impact we investigate the geomorphic impact of nineteenth century placer mining along the fraser river british columbia by estimating the volume and grain size distribution of excavated sediment evaluating the transport potential for the sediment in the river and discussing the relation between placer waste sediment and observed morphodynamics of the fraser river channel volume by area regression relations applied to 456 mapped mines estimate the total volume of material excavated to be 58 10 6 m 3 bulk volume sampling of mine scarp and mine lag sediments indicates that the discharged tailings consisted of 54 sand and finer material and 46 gravel and small cobbles modern observation and historical narratives indicate that the channel of the fraser between quesnel and laidlaw has been generally stable following placer mining application of a sediment transport function indicates that the river is capable of moving annually an amount of sediment comparable to the maximum loading from placer mining by applying established relations between channel scale and sediment virtual velocity we estimate the rate of downstream movement of the placer waste slug to be between 1 and 6 km yr 1 the predicted rates of sediment migration indicate that peak delivery of placer waste to the lower river below laidlaw likely occurred early in the twentieth century this predicted behavior agrees well with observed aggradation on the lower river the result emphasizes the importance of historical legacy in the appraisal of recent geomorphological processes and shows that widespread small scale disturbance has affected the fraser river with the effect concentrated where the gradient of the river is reduced

green river laminites does the playa lake model really invalidate the stratified lake model proponents of the playa lake model have proposed deposition of most of the green river formation microlaminated carbonates including oil shales in lakes that were not perennially stratified meromictic however there is a variety of evidence favoring a meromictic depositional environment 1 close similarity of much of the lamination to varves in modern meromictic lakes 2 evidence that hydrologic events favoring development of meromixis chemical stratification occurred prior to deposition of major accumulations of oil shale 3 mutually exclusive distribution of fossil nekton especially fish and normal lacustrine benthos including mollusks and 4 analogy with a quaternary playa that became a meromictic lake following increased inflow the playa lake model is untenable for the typical fish bearing kerogen rich microlaminated sediments these laminites were probably deposited in a large ectogenic meromictic lake a chemically stratified lake that formed when increased fresh water inflow drowned a saline playa complex

recognition and significance of sharp based mouth bar deposits in the eocene green river formation uinta basin utah sandstone bodies in the sunnyside delta interval of the eocene green river formation uinta basin previously considered as point bars formed in meandering rivers and other types of fluvial bars are herein interpreted as delta mouth bar deposits the sandstone bodies have been examined in a 2300 m long cliff section along the argyle and nine mile canyons at the southern margin of the uinta lake basin the sandstone bodies occur in three stratigraphic intervals separated by lacustrine mudstone and limestone together these stratigraphic intervals form a regressive transgressive sequence individual sandstone bodies are texturally sharp based towards mudstone substratum in proximal parts the mouth bar deposits only contain sandstone whereas in frontal and lateral positions mudstone drapes separate mouth bar clinothems the clinothems pass gradually into greenish grey lacustrine mudstone at their toes horizontally bedded or laminated lacustrine mudstone onlaps the convex upward sandstone bars the mouth bar deposits are connected to terminal distributary channel deposits together these mouth bar channel sandstone bodies accumulated from unidirectional jet flow during three stages of delta advance separated by lacustrine flooding intervals key criteria to distinguish the mouth bar deposits from fluvial point bar deposits are i geometry ii bounding contacts iii internal structure iv palaeocurrent orientations and v the genetic association of the deposits with lacustrine mudstone and limestone

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

depositional systems and sequence stratigraphy of mesozoic lacustrine rift basins in ne china a case study of the wulan hua sag in the southern erlian basin abstract the deltaic and lacustrine sediments respectively in the syn and post rift stages are recorded during the cretaceous at the wulan hua sag erlian basin inner mongolia in this study the mesozoic depositional system and sequence stratigraphic framework are recognized in the wulan hua sag using core well log and seismic data five sedimentary facies have been identified including fan delta braided delta shallow lacustrine deep lacustrine and sublacustrine fan during cretaceous at the wulan hua sag one first order sequence msq1 three second order sequences ssq1 ssq2 and ssq3 and five third order sequences sq1 sq2 sq3 sq4 and sq5 are classified by subaerial unconformities along the basin margins and correlative conformities in the central part of the basin during the depositional period of sq1 sq2 and sq3 the depocenter controlled by lake level fluctuations migrated from southern to northern part companying with multiple to single provenance supplies the characteristics of sedimentary facies and sequence stratigraphy in the wulan hua sag are commonly controlled by faults provenance and depocenters the development of the third order sequences is dominated by tectonism and sediment supplies as well as lake level changes driven by climate the favorable targets for hydrocarbon located in the lowstand system tract of sq1 sq2 and sq3 at the southern parts of the wulan hua sag

the sedimentary and environmental history of tortonian messinian lakes at the east mediterranean margins northern israel abstract during the late neogene the east mediterranean margins of the levant went through major morphological changes due to tectonic activity associated with the dead sea transform fault the regional fluvial systems inverted their flow direction from westward towards the mediterranean to eastward towards the jordan valley tectonic basins that developed at that time in northern israel were filled by lakes with intermittent connections to the sea the tectonic processes were accompanied by volcanism of alkali basalts this study focuses on the evolution of sedimentary volcanic sequences mainly included in the bira and gesher formations that were deposited in lacustrine and palustrine environments in northern israel the study presents a comprehensive dataset and interpretation integrating new and old lithological and paleontological records from outcrops and drill holes together with new petrographic and mineralogical data the bira formation of tortonian age which overlies the lower basalt unit consists mainly of lacustrine littoral limestone and dolostone and basinal marl sporadic occurrences of marine macrofauna indicate pulses of marine ingressions that reached the jordan valley depocenter where thick sequences of gypsum and salt were deposited the overlying gesher formation of messinian early zanclean age which has a similar lithology to that of the bira formation represents an environmental evolution from restricted shallow lakes into a larger lake or lakes and finally to shallow isolated water bodies the latter stage coincides with the messinian salinity crisis when climate became more arid in the levant pyroclasts and some lava flows recorded an ongoing volcanic activity during this period that intensified toward the eruption of the cover basalt unit that overlies the gesher formation overall the bira and gesher formations provide a detailed sedimentological tectonic and volcanic history of the continental margins of the east mediterranean and its connection to the tectonic evolution of basin associated with the dead sea transform fault

a quantitative approach to soil occurrence in alluvial deposits and its application to the old red sandstone of britain palaeosols fossil soils are a major component of alluvial deposits in the geological record not only do these typically show considerable variations in their degrees of development within single formations but they also exhibit highly complex stratigraphic relationships with one another a simple quantitative approach to these variations is presented which provides a graphical means of assessing differences in soil palaeosol development within a sequence with calcic or petrocalcic horizons to illustrate the approach a range of palaeosols from the siluro devonian old red sandstone of britain are characterized in terms of the likely frequency and magnitude of depositional events which occurred during their formation in particular two alluvial suites from the manorbier area of south wales are analysed using this approach the technique should be widely applicable to other alluvial successions and provides a means of graphicallv presenting relationships between multiple palaeosols although the wide range of rates of formation of calcic and petrocalcic horizons precludes their use to provide narrow estimates of deposition rates

laramide tectonics and humid alluvial fan sedimentation ne uinta uplift utah and wyoming abstract laramide uplift and erosion of the uinta mountains are recorded in a 10 km long outcrop of the lower eocene wasatch formation on the utah wyoming border this 750 m thick package of interbedded sandstones and conglomerates is dominated by a coarsening then fining upward megasequence 650 m thick that records the growth and abandonment of a humid alluvial fun system during a major cycle of uplift and unroofing of the thrust bounded northern flank of the uinta mountains grain size thickness and lateral extent of channel complex deposits increase upward in the lower 400 m of the sequence reflecting construction and northward progradation of the fan grain size and channel complex thickness decrease upward in the upper 250 m of the sequence reflecting gradual reduction of both sedime t yield and sediment caliber during postorogenic lowering of source area relief within the megasequence coarsening up sequences 10 100 m thick built mainly of channel complex deposits reflect progradation of fan lobes punctuated by periodic fan head avulsions these medium scale sequences in turn comprise small scale fining up cycles 1 10 m thick that reflect such fluvial processes on the fan as bar building discrete flood events and the filling and lateral migration of braided stream channels both the medium scale and small scale sequences are commonly underlain by paleosols evidence of debris flows or other mass movement processes is conspicuously lacking above the main megasequence a second thinner megasequence containing lacustrine mudstones and wave reworked conglomerates indicates that the fan persisted as a locus of coarse clastic deposition during the first of a series of lacustrine transgressions that began as ratios of sediment flux to subsidence rate decreased toward the end of the early eocene partial inundation of the fan during this transgression transformed it into a fan delta

quantifying denudation and sediment accumulation systems open and closed lakes basic concepts and first results abstract the quantitative aspects of denudation in the drainage areas and sediment accumulation in the corresponding closed or open lakes are approached using two methods 1 from known mean rates of mechanical and chemical denudation and the ratio of the drainage lake area average terrigenous and potential chemical biogenic and evaporites sedimentation rates in the lake are determined or 2 from known sedimentation rates the average denudation rate is found in closed systems the total mass denuded during a certain unit of time is deposited in the lake as terrigenous biogenic and evaporitic sediments whereas open lake systems lose a major part of the dissolved river input derived from chemical denudation applying elementary equations describing these relationships and using ratios between mechanical and chemical denudation weathering ratio established in other regions e g chemical weathering in the lake drainage can be estimated likewise the knowledge of the bio index ratio of biogenic sediment total dissolved mass allows the calculation of the loss of dissolved matter through the outflow from the lake etc in a first step existing data from modern lake systems are evaluated later idealized lake systems in various climatic and morphotectonic zones can be simulated and the results utilized to better understand ancient lake systems modern alpine lakes reflect increased mechanical denudation rates 100 to 300 mm ka in highly elevated drainage areas of the central alps mainly crystalline rocks and high chemical denudation up to ca 100 mm ka in carbonate rocks of the northern calcareous alps mechanical denudation is significantly enhanced by glaciation but transport of the detritus into lakes may be delayed until the time immediately after glacial retreat average rates of terrigenous lake sedimentation amount to 5 to 15 mm a crystalline rocks high relief or are 5 mm a carbonate rocks delta outbuilding was a main factor in the filling of many alpine lakes lakes draining low altitude semi arid parts along the eastern margin of the alps lake balaton in hungary have low sedimentation rates and reflect the influence of increased temperature and vegetation in east africa the transition from the late pleistocene arid to the early holocene humid and again back to somewhat drier conditions caused substantial rises in lake levels and changes from closed to open lake systems in such cases the calculation of denudation from accumulation rates is biassed as a result of intermittent sediment storage at the lake margins low sedimentation rates in the lake centre during lake highstands or redeposition of sediment during lowstands lowstand shedding the modern denudation rates of east african rift lake systems vary by a factor of 15 lake tanganyika crystalline rocks and more dense vegetation cover total denudation rate ca 4 mm ka lake turkana young volcanic rocks and tephra sparse vegetation mechanical denudation rate ca 60 mm ka

sequence stratigraphic distribution of coaly rocks fundamental controls and paralic examples significant volumes of terrigenous organic matter can be preserved to form coals only when and where the overall increase in accommodation approximately equals the production rate of peat accommodation is a function of subsidence and base level for mires base level is very specifically the groundwater table in paralic settings the groundwater table is strongly controlled by sea level and the precipitation evaporation ratio peat accumulates over a range of rates but always with a definite maximum rate set by original organic productivity and space available below depositional base level groundwater table below a threshold accommodation rate nonzero no continuous peats accumulate due to falling or low groundwater table sedimentary bypass and extensive erosion by fluvial channels this is typical of upper highstand lowstand fan and basal lowstand wedge systems tracts higher accommodation rates provide relatively stable conditions with rising groundwater tables mires initiate and copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received september 7 1995 revised manuscript received november 25 1996 final acceptance may 5 1997 2exxon production research company 3120 buffalo speedway houston texas 77096 3exxon production research company 3120 buffalo speedway houston texas 77096 present address conoco inc p o box 2197 houston texas 77252 we benefited from the input and assistance of many people of special assistance were the teams involved in collaborative studies with esso australia and esso malaysia p moore m sloan j emmett b burns a partridge s creaney hanif hussein r hill r lovell and m feeley we also thank the rock springs team r beauboeuf p mclaughlin w devlin a carroll y y chen g grabowski jr k miskell gerhardt m farley r webster and j schwalbach group members d curry and j yeakel were always helpful we also enjoyed and profited from many discussions of these concepts with our colleagues outside exxon c diessel r boyd k shanley b zaitlin p mccabe m hendricks a cohen and m kirschbaum we thank the reviewers of company reports whose careful comments on several generations of this work improved it s creaney m feeley j van wagoner f wehr j yeakel and a young f weber and j zullig provided extensive management support k linke translated our sketches into the fine figures herein we value all the help

a conceptual tectonostratigraphic model for seismic facies migrations in a fluvio lacustrine extensional basin one of the most fundamental differences between lacustrine basins and many marine basins is the stratigraphic response to differential tectonic subsidence because the water volume of a lake is finite tilting of the valley floor redistributes the lake water if the lake water level is below a hinge point fulcrum that experiences no net subsidence the lake shoreline is translated toward the site of subsidence and a deeper lake forms this tectonostratigraphic model for rift lake sedimentation is tested in a seismic and sequence stratigraphic study of deltaic and lacustrine deposits that accumulated in a cenozoic extensional basin beneath goshute valley nevada seismic sequences exhibit an internal cyclic stacking hierarchy of seismic reflections interpreted as the stratigraphic response of a lowstand paleolake to tectonism forced regression and subsequent lake level restoration transgressive and highstand systems tracts

anatomy of a lacustrine stratigraphic sequence within the fourth member of the eocene shahejie formation along the steep margin of the dongying depression eastern china a comprehensive study on rift stratigraphy requires a solid understanding of sequence architecture along the steep margins of rift basins this study analyzes an eocene lacustrine sequence along the steep margin of the dongying depression in eastern china through integrated core well log and three dimensional seismic analyses the lacustrine sequence is bounded by unconformities and their correlative conformities at the base and top and consists of three systems tracts namely an early expansion systems tract eest late expansion early contraction systems tract leecst and late contraction systems tract lcst which record a lake expansion contraction cycle these systems tracts differ in thickness and development of depositional systems the eest is the thickest and contains well developed marginal and basinal fan systems with an overall retrogradational stacking pattern the well developed fan systems are the most striking features within the sequence the leecst is the most widespread and contains dominantly profundal sublittoral deposits the lcst is the thinnest with poorly developed fan systems and is characterized by significant erosion by fluvial incision the variable thickness and development of depositional systems in the three systems tracts are the responses to the interplay of sediment supply and accommodation space accommodation space establishes the framework for sedimentary infill and sediment supply determines spatial distribution and temporal evolution of depositional systems within each systems tract this study provides a lake expansion contraction scheme to divide a lacustrine stratigraphic sequence into systems tracts and highlights the feasibility of applying this approach in studying sequence stratigraphy along the steep margin of a lacustrine rift basin the results also provide understandings for the development distribution and evolution of depositional systems and their controlling factors along the steep margin of other rift basins in the world

forced regressions in a large wave and storm dominated anoxic lake rhaetian sinemurian kap stewart formation east greenland during rhaetian sinemurian time a large wave and storm dominated lake was situated in the jameson land basin east greenland lake deposits consist of alternating black unfossiliferous mudstones and sheet sandstones anoxic conditions dominated at the lake bottom during deposition of the muds and the water column was probably stratified the sandstones were deposited by progradation of wave and storm dominated deltas in a water depth of less than 15 m sequence stratigraphic interpretation suggests that the mudstones were deposited in periods of rising and very high stands of lake level whereas progradation of the deltaic sheet sandstones took place during forced regressions caused by significant falls the lake thus underwent a large number of fairly high amplitude changes in level probably caused by climatic fluctuations the high order cycles can be grouped into several long period cycles that show the same number of major fluctuations as published eustatic sea level curves this similarity suggests a causal link between eustasy and long period variations in the lake the kap stewart formation represents one of the few ancient examples of a large wave and storm dominated lake and it is probably the first documented case of abundant well developed lacustrine forced regressions

paleolimnology and taphonomy of some fish deposits in fossil and uinta lakes of the eocene green river formation utah and wyoming abstract in four sections in the lacustrine eocene green river formation in utah lake uinta fish are preserved on carbonate mudflats along high energy carbonate shorelines in the littoral zone and in deeper profundal areas scattered bones and scales are found throughout dropped from disintegrating floating carcasses gar scales typify shallow water deposits partly due to habitat preference beach concentrations of greatly abraded bones and scales grade offshore into storm lag layers and lenses which grade to loosely packed horizons or patches of unworn remains littoral fish fossils range from dropped bones to good skeletons with much floating lifting and scavenging preservation improves away from the waterline not only into deep and cold profundal waters where the carcasses are protected from scavenging by anoxia and prevented from floating by temperature and pressure but also onto mudflats where stranding and burial of carcasses can also protect them a section through an isolated part of the green river formation in wyoming fossil lake also ranged from profundal to littoral with minor emergence dropped body parts were found throughout but preservation quality of the best specimens improved with presumed depth the beds with the best specimens seem to have accumulated at the bottom of a deep stratified warm monomictic lake our lake uinta sections were generally shallower and suggest more fluctuations in water level but this is not relevant to broad paleolimnological interpretations because they represent marginal zones which are necessarily more sensitive to changes in depth overall fish fossils are especially informative in deeper waters where sedimentary distinctions fail

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

terrestrial sediment yield and the lifetimes of reservoirs lakes and larger basins water reservoirs lakes and larger basins including their drainage areas represent sedimentologically closed to semi closed denudation accumulation systems the mean rates of mechanical denudation drme and clastic sedimentation srme are related by the ratio of the drainage lake area ad al if the latter is known drme or the specific sediment yield sy in t per km2 a can be calculated from srme or vice versa the best data for modern sy mainly come from the sediment fills of artificial reservoirs small drainage areas of mountainous regions show sy values up to two orders of magnitude higher than lowlands and approximately one order higher than larger regions of mixed relief this is also true of arid to semi arid zones which often provide approximately as much sediment sy as humid temperate and even tropical zones of comparable relief lithology and climate river runoff also may play some role for sy from catchments of limited size the importance of these factors is exemplified by perialpine lakes and two east african lakes sediment yields gained from some large reservoirs compare well with long term denudation rates derived from geological studies e g the tarbela dam reservoir along the indus river in many other cases human activities have raised sy by factors of 2 10 locally up to 100 artificial reservoirs in mountainous regions with sy in the range of 300 2000 t per km2 a tend to become filled within several tens to hundreds of years some have even shorter lifetimes perialpine lakes of the alps and british columbia are strongly affected by delta prograding and have lifetimes mostly between 15 and 40 ka closed lake systems in deep morphological depressions lake bonneville aral sea northern caspian sea have a high potential for sediment storage up to the level of spillover and therefore can persist over long time periods basins with markedly subsiding basin floors lakes of the east african rift zone the southern caspian sea and the black sea both on oceanic crust can survive for many ma in the future despite relatively high terrigenous input

sequence stratigraphy of lacustrine deposits a quaternary example from the bonneville basin utah the late quaternary lacustrine sedimentary record in the bonneville lake basin in the eastern great basin provides an excellent example of sequence stratigraphy two sequences referred to as the little valley and bonneville alloformations are exposed in the bluffs of the sevier river where it has entrenched its pleistocene delta between leamington and delta utah both alloformations contain offshore marl units and fine grained deltaic or underflow fan deposits they can be identified and mapped by tracing the unconformity separating them and employing a number of geochronometric tools including amino acid epimerization in fossil gastropods radiocarbon and thorium 230 ages and basaltic tephrochronology thin transgressive sand of the little valley alloformation is overlain by deeper water marl and down lapping regressive phase deltaic silt the bonneville alloformation lies unconformably above the little valley deposits fine grained deltaic sediments deposited during the transgressive phase of lake bonneville fill the entrenched sevier river valley that was eroded subsequent to the little valley lake cycle marl deposited during the deep water phase is overlain by down lapping deposits of the regressive phase below the provo shoreline but is the uppermost unit in the altitudinal range where the lake was lowered catastrophically during the bonneville flood the sequence stratigraphic interpretation leads to the conclusion that the sevier river delta as a whole is probably made up of a number of sediment sequences each composed of several facies recognition of this complexity could be important in potential applications of the stratigraphic model

comparative sequence stratigraphy of low latitude versus high latitude lacustrine rift basins seismic data examples from the east african and baikal rifts abstract lakes baikal malawi and tanganyika are the world s three largest rift valley lakes and are the classic modern examples of lacustrine rift basins all the rift lakes are segmented into half graben basins and seismic reflection datasets reveal how this segmentation controls the filling of the rift basins through time in the early stages of rifting basins are fed primarily by flexural margin and axial margin drainage systems at the climax of syn rift sedimentation however when the basins are deeply subsided almost all the margins are walled off by rift shoulder uplifts and sediment flux into the basins is concentrated at accommodation zone and axial margin river deltas flexural margin unconformities are commonplace in the tropical lakes but less so in high latitude lake baikal lake levels are extremely dynamic in the tropical lakes and in low latitude systems in general because of the predominance of evaporation in the hydrologic cycle in those systems evaporation is minimized in relation to inflow in the high latitude lake baikal and in most high latitude systems and consequently major sequence boundaries tend to be tectonically controlled in that type of system the acoustic stratigraphies of the tropical lakes are dominated by high frequency and high amplitude lake level shifts whereas in high latitude lake baikal stratigraphic cycles are dominated by tectonism and sediment supply variations

lacustrine turbidites in the green river formation northwestern colorado a preliminary study of drill cores of blebby and streaked oil shale from the green river formation eocene in the deep northern part of the piceance creek basin colorado shows sedimentary structures that suggest deposition by turbidity currents this type of oil shale composes about one half of the oil shale deposits at the saline depocenter of eocene lake uinta where it is interbedded with the well known laminated type of oil shale described previously in the literature episodic and rapid deposition by lake bottom currents of large amounts of carbonate silicate sediments that formed high grade oil shale is a new concept for the origin of a major part of the green river oil shale deposits in contrast the laminated oil shale as previously described accumulated very slowly as thin varves in a chemically stratified lake under stagnant conditions

quantitative filling model for continental extensional basins with applications to early mesozoic rifts of eastern north america in many half graben strata progressively onlap the hanging wall block of the basins indicating that both the basins and their depositional surface areas were growing in size through time based on these constraints we have constructed a quantitative model for the stratigraphic evolution of extensional basins with the simplifying assumptions of constant volume input of sediments and water per unit time as well as a uniform subsidence rate and a fixed outlet level the model predicts 1 a transition from fluvial to lacustrine deposition 2 systematically decreasing accumulation rates in lacustrine strata and 3 a rapid increase in lake depth after the onset of lacustrine deposition followed by a systematic decrease when parameterized for the early mesozoic basins of eastern north america the model s predictions match trends observed in late triassic age rocks significant deviations from the model s predictions occur in early jurassic age strata in which markedly higher accumulation rates and greater lake depths point to an increased extension rate that led to increased asymmetry in these half graben the model makes it possible to extract from the sedimentary record those events in the history of an extensional basin that are due solely to the filling of a basin growing in size through time and those that are due to changes in tectonics climate or sediment and water budgets

re sedimented deposits in the rift section of the campos basin abstract an integrated petrologic sedimentologic stratigraphic seismic study of the lagoa feia group rift section of the campos basin has shown that rift sedimentation was dominantly intrabasinal carbonate and stevensitic deposits with siliciclastic deposits restricted to the proximity of graben border faults the bivalve bioclastic rudstones coquinas that constitute the rift reservoirs show commonly limited abrasion of the bioclasts and were deposited both on basement highs and lows throughout the rift section although in situ deposits of stevensite ooids and peloids occur dominantly at the base of the succession these particles are ubiquitous to the entire rift section mixed in variable proportion with siliciclastic and carbonate sediments the environmental conditions required for the formation of stevensite and the growth of bivalves are mutually exclusive as stevensite forms only at ph greater than 10 while bivalves cannot tolerate ph greater than 9 the common mixture of well rounded basaltic rock fragments with angular granitic gneissic rock fragments and feldspars in the sandstones and conglomerates indicates recycling of epiclastic deposits from the early rift section combined with first cycle contribution from the plutonic basement the studied cores show no evidence of subaerial exposure and there is a lack of bioturbation suggesting harsh environmental conditions the rift deposits are dominantly massive or faintly laminated with diffuse facies boundaries structures indicative of unidirectional or oscillatory flow are subordinate integration of seismic sedimentologic and petrographic evidence indicates that the campos basin rift section is formed mostly by re sedimented gravitational deposits the onset of the rift sedimentation occurred in synformal depressions where bivalve banks or stevensite ooids were formed in shallow lacustrine environments under variable alkalinity conditions with the development of half grabens and concentration of the tectonic activity along the border faults recurrent tectonic events promoted the mixing and gravitational re deposition of stevensitic clastic and bioclastic sediments in deeper fault bounded troughs large scale units hundreds of meters thick were generated by major tectonic events whereas compositional variations in the scale of meters were possibly a product of lake level climatic fluctuations thus due to syn rift and mainly to post rift erosion the neo aptian unconformity the preserved rift section of the lagoa feia group comprises mostly sediments deposited in the central troughs of the half graben structures marginal sediments were extensively eroded and re sedimented as gravity driven mixed deposits this new model constructed form the integration of seismic stratigraphic sedimentologic and petrologic data diverges substantially from the presently accepted model for the sedimentation of the rift section opening new possibilities for the exploration of campos basin as well as of similar settings as in the adjacent santos basin

late quaternary lacustrine deposits of the dead sea basin high resolution sequence stratigraphy from downhole logging data abstract sequence architecture and depositional sequences of the quaternary lacustrine succession deposited in the northern dead sea sub basin were examined using logging data collected during the 2010 2011 icdp campaign methods borrowed from sequence stratigraphy techniques were used to investigate the characteristics of sediments deposited in the central part of the northern lake high resolution wire logging data combined with a detailed lithological description of the icdp 5017 1 a deep borehole were used to examine depositional systems and related processes controlling their formation analysis of sedimentary stacking patterns and stratal surfaces within the late pleistocene holocene lacustrine succession revealed 10 depositional sequences it was possible to identify key stratal boundaries and to discern between three sedimentary stacking patterns interpreted here as representing lowstand systems tracts lst transgressive systems tracts tst and highstand systems tracts hst examined together they may be interpreted in terms of relative lake level changes on the basis of the stratigraphic analysis complemented with new age dating this article presents a record of the sediment accumulation pattern and a relative lake level curve reconstructed for the last ca 225 ka results show that stratigraphic units and depositional and erosional surfaces examined in the deep 5017 1 a borehole can be correlated to the proximal area of the basin this means that changes in relative lake levels were generally synchronous and uniform across the dead sea basin the creation of accommodation space in the northern dead sea was found to generally be in phase with paleoclimatic modulating lake levels and not due to tectonics

synoptic reconstruction of a major ancient lake system eocene green river formation western united states numerous 40ar 39ar experiments on sanidine and biotite from 22 ash beds and 3 volcaniclastic sand beds from the greater green river piceance creek and uinta basins of wyoming colorado and utah constrain 8 m y of the eocene epoch multiple analyses were conducted per sample using laser fusion and incremental heating techniques to differentiate inheritance 40ar loss and 39ar recoil when considered in conjunction with existing radioisotopic ages and lithostratigraphy biostratigraphy and magnetostratigraphy these new age determinations facilitate temporal correlation of linked eocene lake basins in the laramide rocky mountain region at a significantly increased level of precision to compare our results to the geomagnetic polarity time scale and the regional volcanic record the ages of eocene magnetic anomalies c24 through c20 were recalibrated using seven 40ar 39ar ages overall the ages obtained for this study are consistent with the isochroneity of north american land mammal ages throughout the study area and provide precise radioisotopic constraints on several important biostratigraphic boundaries applying these new ages average sediment accumulation rates in the greater green river basin wyoming were approximately three times faster at the center of the basin versus its ramp like northern margin during deposition of the underfilled wilkins peak member in contrast sediment accumulation occurred faster at the edge of the basin during deposition of the balanced filled to overfilled tipton and laney members sediment accumulation patterns thus reflect basin center focused accumulation rates when the basin was underfilled and supply limited accumulation when the basin was balanced filled to overfilled sediment accumulation in the uinta basin at indian canyon utah was relatively constant at 150 mm k y during deposition of over 5 m y of both evaporative and fluctuating profundal facies which likely reflects the basin margin position of the measured section the most rapid sediment accumulation for the entire system 1 m k y occurred between 49 0 and 47 5 ma when volcaniclastic materials from the absaroka and or challis volcanic fields entered the green river formation lakes from the north our new ages combined with existing paleomagnetic and biostratigraphic control permit the first detailed synoptic comparison of lacustrine depositional environments in all the green river formation basins coupled with previously published paleocurrent observations our detailed correlations show that relatively freshwater lakes commonly drained into more saline downstream lakes the overall character of eocene lake deposits was therefore governed in part by the geomorphic evolution of drainage patterns in the surrounding laramide landscape freshwater overfilled lakes were initially dominant 53 5 52 0 ma possibly related to high erosion rates of remnant cretaceous strata on adjacent uplifts expansion of balanced fill lakes first occurred in all green river formation basins at 52 0 51 3 ma and again between 49 6 and 48 5 ma evaporative underfilled lakes occurred in various basins between 51 3 and 45 1 ma coincident with the end of the early eocene climatic optima and subsequent onset of global cooling defined from marine record however evaporite intervals in the different depocenters were deposited at different times rather than being confined to a single episode of arid climate evaporative terminal sinks were initially located in the greater green river and piceance creek basins 51 3 48 9 ma then gradually migrated southward to the uinta basin 47 1 45 2 ma this history is likely related to progressive southward construction of the absaroka volcanic province which constituted a major topographic and thermal anomaly that contributed to a regional north to south hydrologic gradient the greater green river and piceance creek basins were eventually filled from north to south with absarokaderived detritus at sedimentation rates 1 2 orders of magnitude greater than the underlying lake deposits

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

using fossil leaves as paleoprecipitation indicators an eocene example estimates of past precipitation are of broad interest for many areas of inquiry including reconstructions of past environments and topography climate modeling and ocean circulation studies the shapes and sizes of living leaves are highly sensitive to moisture conditions and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations however when tested on extant forests this method has consistently overestimated precipitation we present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set the significant relationship that results in addition to having value for paleoclimatic reconstruction refines understanding of the long observed positive relationship between leaf area and precipitation seven precipitation estimates for the eocene of the western united states are revised as lower than previously published but remain far wetter than the same areas today abundant moisture may have been an important factor in maintaining warm frost free conditions in the eocene because of the major role of water vapor in retaining and transporting atmospheric heat

estimated likelihood of observing a large earthquake on a continental low angle normal fault and implications for low angle normal fault activity the lack of observed continental earthquakes that clearly occurred on low angle normal faults lanfs may indicate that these structures are not seismically active or that these earthquakes are simply rare events to address this we compile all potentially active continental lanfs 24 in total and calculate the likelihood of observing a significant earthquake on them over periods of 1 100 years this probability depends on several factors including the frequency magnitude distribution for either a characteristic or gutenberg richter distribution we calculate a probability of about 0 5 that an earthquake greater than m6 5 large enough to avoid ambiguity in dip angle will be observed on any lanf in a period of 35 years which is the current length of the global centroid moment tensor catalog we then use bayes theorem to illustrate how the absence of observed significant lanf seismicity over the catalog period moderately decreases the likelihood that the structures generate large earthquakes

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

depositional setting and diagenetic evolution of some tertiary unconventional reservoir rocks uinta basin utah the douglas creek member of the tertiary green river formation underlies much of the uinta basin utah and contains large volumes of oil and gas trapped in a complex of fractured low permeability sandstone reservoirs in the southeastern part of the basin at pariette bench the eocene douglas creek member is a thick sequence of fine grained alluvial sandstone complexly intercalated with lacustrine claystone and carbonate rock sediments were deposited in a subsiding intermontane basin along the shallow fluctuating margin of ancient lake uinta although the uinta basin has undergone postdepositional uplift and erosion the deepest cored rocks at pariette bench have never been buried more than 9 800 ft 3 000 m the sandstones dominantly lithic arkoses and feldspathic litharenites were derived from source terranes south of the uinta basin secondary silica and several generations of authigenic calcite ca1 8 1 9 mg0 02 0 06fe0 02 0 06 co3 2 dolomite ca1 3 1 4 mg0 6 0 7fe0 02 0 04 co3 2 and ankerite ca1 2 1 3 mg0 2 0 3fe0 4 0 6 co3 2 form a replacive cement in the sandstones commonly syntaxial overgrowths of late iron bearing carbonate occur on detrital grains and preexisting relicts of iron free carbonate cement in sandstone where carbonate has been partly dissolved abundant authigenic illite partly ordered mixed ayer illite smectite and small amounts of chlorite partly to completely fill secondary pores isotopic composition of carbonate cement and grain supported rock range from 0 39 to 6 18 pmil for dgr13c and 7 80 to 13 98 pmil for dgr18o indicating that authigenic carbonate formed at low temperatures in the presence of meteoric waters by a process of solution precipitation enrichment of carbon and oxygen in early diagenetic calcite and fossiliferous rock relative to late diagenetic ankerite indicates a trend toward lighter isotopic carbonate compositions with increasing diagenesis kerogenous rocks at pariette bench are thermochemically immature and therefore are not the source of oil produced in the field hydrocarbons are compositionally similar to some of the oils produced from the green river formation in the bluebell altamont field and are interpreted to have migrated from mature green river source rocks through a network of open fractures the occurrence of small amounts of hydrocarbon in secondary pores indicates that its emplacement postdated carbonate dissolution

outcrop architecture of a fluvio lacustrine succession upper triassic yanchang formation ordos basin china abstract although several studies have considered the sedimentary facies of the upper triassic yanchang formation in terms of their hydrocarbon potential in the petroliferous ordos basin such studies have mostly interpreted subsurface data and few have systematically examined the detailed outcrop based anatomy of this succession this study characterizes a series of well exposed outcrop sections along an 80 km long e w oriented series of road cuttings in the southeast ordos basin to reconstruct the sedimentary architecture of a fluvio lacustrine succession and determine the principal controls that governed the style of accumulation and preservation the yanchang formation is divided into 10 depositional units chang 10 base to chang 1 top that record the sedimentary evolution of a series of large scale fluvial systems that constructed delta front and pro delta bodies as they entered a large interior draining lake detailed analysis of the internal architectures of the delta front bodies records the mechanism of growth of a large scale shallow water delta succession lacustrine subaqueous distributary channels are composed of 3 15 m thick sandstone fills such channelized bodies are highly elongate and many can be traced several kilometres such bodies can be shown to be commonly associated with thin bedded mouth bar and subaqueous interdistributary bay deposition the progradational architecture of the delta front elements is difficult to recognize on outcrop scale deposits of the chang 10 to 1 units record 4 major lacustrine transgressive regressive cycles during the late triassic transgressive events are signified by the widespread occurrence of 10 20 m thick oil shale prone intervals regressive events are signified by the progradational stacking towards the basin centre of sandstone prone facies associations mainly accumulated in fluvial channel delta plain and upper delta front environments the uppermost chang 1 interval records late stage filling of the lacustrine basin the transgressive regressive cycles equate to sequences that can be correlated across the region development of which was controlled by a combination of changes in the rate of tectonic subsidence the rate of sediment delivery from the basin margin hinterland and climate factors that were themselves influenced by intracontinental growth of the neighbouring qinling orogen

recognition of interfluve sequence boundaries integrating paleopedology and sequence stratigraphy in shallow marine and coastal plain strata sequence boundaries are easily recognized at the base of incised valley fills between valleys however it is more difficult to recognize sequence boundaries where they are expressed as interfluve paleosols we suggest that interfluve paleosols can be most reliably identified using a combination of 1 stratigraphic position 2 field observations such as thickness structure color and degree of rooting and 3 micromorphological features such as bioturbation fabric clay coatings ferruginous features and siderite and barite only micromorphology permits recognition of temporal changes in drainage surface stability and protracted pauses in sedimentation that typify these surfaces this three part approach has been successfully employed to identify interfluve sequence bounding paleosols in the cenomanian dunvegan formation in alberta and british columbia canada

stratigraphic evidence for a deep eocene lake uinta piceance creek basin colorado relief on a prograding clastic complex is used to estimate the water depth of eocene lake uinta in the piceance creek basin of western colorado relief of as much as 412 in is present today on the complex postdepositional compaction can account for only about 100 m of this relief therefore the remaining 312 m appear to represent paleorelief on the floor of lake uinta the lake was apparently more than 300 m deep authigenic saline minerals were precipitated in the unlithified sediments of the deeper areas of the lake suggesting that at least the lower part of the water column was highly saline the evidence presented here indicates that the deep stratified lake model is more appropriate than the more generally accepted shallow or playa lake model for lake uinta