palaeoenvironmental reconstruction of a middle miocene alluvial fan to cyclic shallow lacustrine depositional system in the calatayud basin ne spain the middle miocene sedimentary fill of the calatayud basin in north eastern spain consists of proximal to distal alluvial fan floodplain and shallow lacustrine deposits four main facies groups characteristic of differentsedimentary environments are recognized 1 proximal and medial alluvial fan facies that comprise clast supported gravel and subordinate sandstone and mudstone the latter exhibiting incipient pedogenic features 2 distal alluvial fan facies formed mainly of massive mudstone carbonate rich palaeosols and local carbonate pond deposits 3 lake margin facies which show two distinct lithofacies associations depending on their distribution relative to the alluvial fan system i e front lithofacies a comprising massive siliciclastic mudstone and tabular carbonates or lateral lithofacies b showing laminated and or massive siliciclastic mudstone alternating with tabular and or laminated carbonate beds and 4 mudflat shallow lake facies showing a remarkable cyclical alternation of green grey and or red siliciclastic mudstone units and white dolomitic carbonate beds the cyclic mudflat shallow lake succession as exposed in the orera composite section ocs is dominantly composed of small scale mudstone carbonate dolomite cycles the mudstone intervals of the sedimentary cycles are interpreted as a result of sedimentation from suspension by distal sheet floods the deposits evolving either under subaerial exposure or water saturated conditions depending on their location on the lacustrine mudflat and on climate the dolomite intervals accumulated during lake level highstands with mg rich waters becoming increasingly concentrated lowstand to highstand lake level changes indicated by the mudstone dolomite units of the small scale cycles reflect a climate control from dry to wet conditions on the sedimentation in the area the spatial distribution of the different lithofacies implies that deposition of the small scale cycles took place in a low gradient shallow lake basin located in an interfan zone the development of the basin was constrained by gradual alluvial fan aggradation additional support for the palaeoenvironmental interpretation is derived from the isotopic compositions of carbonates from the various lithofacies that show a wide range of 1 8 o and 1 3 c values varying from 7 9 to 3 0 pdb and from 9 2 to 1 7 pdb respectively more negative 1 8 d and 1 3 c values are from carbonate rich palaeosols and lake margin carbonates which extended in front of the alluvial fan systems whereas more positive values correspond to dolomite beds deposited in the shallow lacustrine environment the results show a clear trend of 1 8 o enrichment in the carbonates from lake margin to the centre of the shallow lake basin thereby also demonstrating that the lake evolved under hydrologically closed conditions

palustrine carbonates and the florida everglades towards an exposure index for the fresh water environment abstract palustrine carbonates are shallow fresh water deposits showing evidence of subaqueous deposition and subaerial exposure these facies are common in the geological record the intensity of modification is highly variable depending on the climate and the length of emergence palustrine limestones have previously been interpreted as marginal lacustrine deposits from fluctuating low salinity carbonate lakes but several problems remain with existing facies models 1 palustrine carbonates possess a lacustrine biota but commonly display fabrics similar to those of calcretes and peritidal carbonates 2 the co occurrence of calcrete horizons and karst like cavities is somewhat unusual and appears to indicate contemporaneous carbonate precipitation and dissolution in the vadose zone 3 the dominance of gray colors indicates water saturation apparently inconsistent with the evidence for strong desiccation overprint 4 profundal lake deposits are generally absent from palustrine sequences and sublittoral facies commonly make up only a small proportion of total thicknesses 5 no good modern analogue has been identified for the palustrine environment analogy with the florida everglades suggests a re interpretation of palustrine limestones not as pedogenically modified lake margin facies but as the deposits of extensive very shallow carbonate marshes the distribution of environments in the everglades is determined by the local hydrology reflecting the control of seasonal water level fluctuations and topography climate and topography were the main controls on deposition of ancient palustrine carbonates as in peritidal sequences aggradational cycles are capped by a range of lithologies evaporites desiccation and microkarst breccias calcretes lignite or coal horizons etc permitting interpretation of the climate careful analysis of lateral facies variations may permit reconstruction of subtle topography consideration of the florida everglades as a modern analogue for the palustrine environment has suggested the development of an exposure index for fresh water carbonates

facies and facies architecture of paleogene floodplain deposits willwood formation bighorn basin wyoming usa abstract paleogene deposits of the willwood formation were analyzed in two areas of the bighorn basin to provide a better understanding of the facies and facies arrangement of floodplain deposits and the various processes that influence floodplain construction and facies variability despite similar facies and facies organization floodplain deposits in the two areas differ in grain size hydromorphy and maturity of the paleosols and scale and organization of ribbon sandstones in the avulsion deposits these differences appear to be controlled by basin position of the study areas and differences in avulsion between the areas two kinds of cumulative floodplain paleosols red and purple paleosols formed on overbank deposits the red paleosols were better drained and formed on less clay rich parent material intense mottling and iron oxide nodules indicate that the purple paleosols which formed on more clay rich parent material were poorly drained the grain size differences reflect basin position in particular distance from a local sediment source avulsion deposits are volumetrically important comprising about half of the floodplain deposits in both areas the avulsion deposits resemble the stage iii splays described by smith et al 1989 smith n d cross ia dufficy j p clough s r 1989 anatomy of an avulsion sedimentology 36 1 24 in terms of characteristics of their ribbon sandstones and the presence of thin sheet sandstones or siltstones paleosols that formed on the fine grained facies show morphologic differences interpreted as developmental differences and attributed to differing rates of avulsion in the two study areas this study shows that avulsion belt paleosols provide a key to understanding avulsion rate in the stratigraphic record other differences between the willwood avulsion deposits in the two areas and between these ancient deposits and the modern avulsion deposits described by smith et al may reflect 1 problems in clearly recognizing ancient avulsion deposits in the field and 2 sampling bias resulting from the areally restricted view provided by the stratigraphic record of an areally extensive modern depositional feature at the same time because exposures are three dimensional the willwood strata reveal aspects of the facies and facies arrangement of avulsion belts not readily observed in the modern ones

paleosols of the upper cretaceous lower tertiary maghra el bahari formation in the northeastern portion of the eastern desert egypt their recognition and geological significance the upper cretaceous lower tertiary maghra el bahari formation at gabal ataqa and gabal shabrawet in the northeastern portion of the eastern desert of egypt is subdivided into two informal lithostratigraphic parts lower and upper the lower part has common features of alluvial floodplain dominated deposits with occasional occurrences of crevasse splay deposits the upper part has sediments typical of marginal lacustrine environments both the floodplain and marginal lacustrine deposits exhibit pedogenic features comprising various types of paleosols among other soil forming processes diversity in the paleosols studied is mainly attributed to paleoclimatic and paleohydrologic changes the paleosol criteria suggest two climatic regimes a subhumid semiarid one succeeded by a semiarid arid one the continental depositional environments recognized floodplain and lacustrine with their associated paleosols helped in the recognition of a marine regression in the area studied in a regional perspective comparison of the data presented in this study with paleosol data spanning the same time period in other localities suggests that the proposed paleoclimatic changes may have been of regional extent d 2005 elsevier b v all rights reserved

stratigraphy and facies architecture of the fluvial aeolian lacustrine sergi formation upper jurassic reconcavo basin brazil abstract the sergi formation encompasses an upper jurassic fluvial eolian lacustrine succession deposited within a wide intracratonic basin its sand bodies represent the largest and more important reservoirs in the reconcavo basin hosting 362 million m 3 of oil in place the main goal of this paper is to provide a detailed stratigraphic analysis of the sergi formation based on core and outcrop data it was achieved through the recognition and correlation of regional surfaces that have allowed the subdivision of this unit into distinct depositional sequences and the reconstruction of its depositional history the studied succession can be subdivided into three unconformity bounded sequences sequence i is composed of lacustrine mudstone at its base which is overlain by fine to medium grained sandstone related to aeolian dune and sand sheet and ephemeral fluvial stream deposits fluvial strata indicate northeastward flowing streams whereas aeolian dune deposits suggest the action of southwestward blowing winds the regional unconformity bounding sequences i and ii denotes both a climate change and tectonic rearrangement of the basin this surface delineates a change in the depositional style from fluvial aeolian lacustrine sequence i to entirely fluvial sequence ii the latter includes coarse grained to conglomeratic sandstone deposited within northwestward flowing braided channel belts changes in fluvial palaeocurrent from sequence i to ii indicate rearrangement of the drainage system related to basin tectonism furthermore a change in the fluvial discharge regime took place as a result of a change from a drier to a wetter climate fluvial deposition in sequence i was related to ephemeral streams whereas fluvial facies architecture of the sequence ii deposits indicates perennial braided streams with significant discharge variation another regional unconformity this time related to a stratigraphic base level fall and consequent widespread basinwide aeolian deflation separates the braided fluvial facies of sequence ii from the fine to medium grained sandstones ascribed to sheet floods aeolian dunes and aeolian sand sheets of sequence iii the resumption of aeolian sedimentation indicates a return to drier conditions in the basin the abrupt change from fluvial aeolian deposits to the lacustrine deposits of the overlying itaparica formation suggest a rapid rise of the water table and consequent basinwide flooding

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

floodplain palaeosols of the cenomanian dunvegan formation alberta and british columbia canada micromorphology pedogenic processes and palaeoenvironmental implications

paleosols spanning the cretaceous paleogene transition eastern montana and western north dakota paleosols occur in exposures of the latest cretaceous hell creek and paleocene tullock ludlow formations in montana and western north dakota these units are composed mainly of interbedded siltstones and sandstones of meandering fluvial origin the paleosols indicate that changes in ancient soil development occurred concomitantly with the better known faunal transition in order of decreasing abundance silty soils sandy soils organic soils and volcanic soils are preserved pedogenic features present in these soils include roots microscopic segregations of amorphous material birefringence fabric and soil structures the features suggest that throughout the cretaceous paleogene transition pedogenic processes in the region produced immature profiles an observation consistent with the unstable fluvial setting in which the ancient soils formed gleization was a dominant process in this setting and podzolization modified some sandy soils the association of the features enables recognition of o a e btg bhs bg bc cg and c horizons during middle hell creek time soils formed in a poorly drained setting that was only stable enough to permit incipient pedogenesis the bulk of the pedogenesis occurred in levee and flood plain deposits soils also occurred on point bar and crevasse splay deposits in topographically depressed regions organic accumulations formed with minimal soil development matted plant debris is the product of this environment gley features and segregations of iron oxides around voids suggest fluctuation of the water table by latest hell creek time the mean level of the water table rose and in the lowest tullock ludlow exposures extensive ponded deposits are preserved vegetation accumulated at a rate sufficient for coal formation the amount of fluctuation apparently was reduced and pedogenesis was further inhibited as indicated by the virtual absence of illuviated clays in the sediments

large scale architecture in non marine basins the response to the interplay between accommodation space and sediment supply sedimentary successions of non marine basins can be considered in terms of accommodation space and sedimentary supply changes changes in accommodation space controlling the large scale architecture of non marine basins are different in areas with high and low sedimentary supplies uplift of intrabasinal monoclines and anticlines reduced the available accommodation space resulting in changes in both the geometry of the depositional sequences and the large scale architecture of fluvial mudflat and shallow carbonate lacustrine deposits main drainage fluvial systems record areas with a high sedimentary supply while mudflats and shallow fluctuating lakes represent areas that received less sediment two end members in the large scale architecture of main drainage fluvial system in the almazan basin spain are i ribbon shaped channel fills with low interconnectivity which pass laterally into mudflats dominated by mudstones and evaporites and into palustrine and shallow carbonate lacustrine deposits mainly in the a2 depositional sequence and ii sheet like channel fills with high interconnectivity laterally correlated with stacked calcretes in the marginal mudflats in the upper part of a3 ribbon shaped channel fills formed in areas of high accommodation space and sheet like channel fills formed in areas of reduced accommodation space

mid eocene alluvial lacustrine succession at gebel el goza el hamra shabrawet area ne eastern desert egypt facies analysis sequence stratigraphy and paleoclimatic implications abstract this study aims to provide the depositional facies sequence stratigraphic and paleoclimatic characteristics of the mid eocene bartonian continental succession exposed at gebel el goza el hamra shabrawet area ne eastern desert egypt the studied succession consists of siliciclastic rocks followed upward by carbonate rocks detailed field observation and petrographic investigation indicate accumulation in floodplain dominated alluvial and shallow lacustrine systems the floodplain dominated alluvial facies 45 m thick is composed mainly of carbonate nodules bearing mottled mudrock with subordinate sandstone and conglomerate beds the conglomerate and pebbly sandstone bodies interpreted as ephemeral braided channel deposits the massive laminated planner cross bedded fine to medium grained sandstone bodies interlayered within mudstone reflect sheet flood deposits the mudrocks associated with paleosols represent distal floodplain deposits the shallow lacustrine facies 15 m thick is made up of an alternation of marlstone micritic limestone dolostone and mudrock beds with charophytes and small gastropods both the alluvial and lacustrine facies show evidence of macro and micro pedogenic features pollen assemblages stable 18 o and 13 c isotopes and paleopedogenic features reflect prevalence of arid to semi arid climatic conditions during the bartonian the sequence stratigraphic framework shows an overall fining upward depositional sequence consisting of low and high accommodation systems tracts last hast and is bounded by two sequence boundaries sb 1 sb 2 conglomerate and pebbly sandstone deposits braided channel and sheet flood deposits of the lower part of the alluvial facies reflect a last mudrock and silty claystone facies distal floodplain deposits of the upper part of alluvial facies and its overlying lacustrine facies correspond to a hast the last hast and sb were formed during different accommodation to sediment supply a s ratio phases the variation in a s ratios was mainly controlled by sea level change as well as by local tectonic subsidence and uplift of the basin coincident with the reactivation of the syrian arc system during the bartonian

unconfined flow deposits in distal sectors of fluvial distributary systems examples from the miocene luna and huesca systems northern spain abstract thin sheet sandstone beds in a continental succession may be the products of unconfined overbank flow or deposition in lacustrine environments in the distal parts of fluvial distributary systems these two settings may be intercalated recording fluctuations in lake level in response to climatic changes field studies of the luna and huesca fluvial distributary systems in the miocene of the ebro basin spain are here used to characterise sheet sandstone deposited in distal fluvial and lake margin environments in this study we document the facies and relationships between 322 individual sandbodies deposited in both alluvial settings as sheetfloods and in lacustrine settings as deltaic lobes the alluvial sandstone sheets were deposited from lateral and frontal sheetflood events when unconfined flow replaced channelised flow as the main transport mechanism the term sheetflood is used here to refer to sub aerial unconfined turbulent flow events that undergo expansion thinning and deceleration with increasing radial distance from source the depositional process is similar to modern floodouts and terminal splays of the channel country and lake eyre central australia such a process was thought to be the dominant depositional mechanism during lake lowstands the sheets formed in the lacustrine setting are interpreted as deltaic sediments deposited in a shallow gradient lake similar to the modern day volga delta caspian sea shallow water friction dominated deltaic processes are thought to have been the primary depositional mechanism in the distal sectors of the fluvial systems during lake highstands

microbially mediated carbonates in the holocene deposits from sarlieve a small ancient lake of the french massif central testify to the evolution of a restricted environment both the mineralogy and facies of lacustrine bio induced carbonates are controlled largely by hydrological factors that are highly dependent upon climatic influence as such they are useful tools in characterizing ancient lake environments in this way the study of the sedimentary record from the small ancient sarlieve lake limagne massif central france aims to reconstruct the hydrological evolution during the holocene using petrographical mineralogical and geochemical analyses the fine grained marls mainly calcitic display numerous layers rich in pristine ca dolomite with small amounts of aragonite which are clearly autochthonous as these minerals are rather unusual in the temperate climatic context of western europe the question arises about their forming conditions and therefore that of the lacustrine environment ca dolomite prevails at the base of the sequence as a massive dolomicrite layer and in the middle part it builds up most of the numerous laminae closely associated with organic matter scanning electron microscope observations reveal the abundance of tiny crystals tens to hundreds of nanometres mainly organized as microspheres looking like cocci or bacilli such a facies is interpreted as resulting from the fossilization of benthic microbial communities by dolomite precipitation following organic matter consumption and extracellular polymeric substance degradation these microbial dolomites were precipitated in a saline environment as a consequence of excess evaporation from the system as is also suggested by their positive 18o values the facies sequence expresses the following evolution i saline pan i e endorheic stage with a perennial lowstand in lake level boreal to early atlantic periods ii large fluctuations in lake level with sporadic freshening of the system atlantic iii open lake stage sub boreal and iv anthropogenic drainage sub atlantic

palaeoclimate interpretation of stable isotope data from lake sediment archives the isotope composition of authigenic and biogenic carbonates and diatom silica are commonly used as palaeoclimate proxies from lake sediments this article reviews the controls on the isotope composition of lacustrine skeletal and non skeletal deposits and illustrates how stable isotope studies contribute to an understanding of changes in temperature precipitation patterns evaporation and the carbon cycle it highlights the differences in the palaeoclimate potential of a wide range of lakes ranging from open to closed lake basins a large number of the case histories but not all are drawn from studies of temperate lakes from europe large closed lake systems in the tropics and elsewhere lose water predominantly through evaporation and contain sediments with variable and generally high 18o values fluctuations in the isotope composition of authigenic or biogenic minerals are mainly a function of long term changes in the precipitation evaporation ratio in contrast small open lakes which have a degree of through flow typically contain sediments with 18o values that vary by no more than a few these variations are generally ascribed to variations in temperature or the isotope composition of precipitation p from which either an annual or seasonally specific signal can be gained these types of lakes are common in northern europe and at high altitudes the interpretation of isotope data from a lacustrine succession requires a knowledge of the local processes that might control and modify the signal their effects need to be quantified and a robust calibration using the modern lake system is necessary to establish the relationship between the measured signal the isotopic composition of the host waters and climate

facies architecture and sequence stratigraphy of an early post rift fluvial succession aptian barbalha formation araripe basin northeastern brazil abstract the barbalha formation aptian records deposition in a fluvial and lacustrine environment accumulated in an early post rift sag basin characterization of the facies architecture and sequence stratigraphic framework of the alluvial succession was carried out through detailed description and interpretation of outcrops and cored wells the development of depositional sequences in this unit reflects variation in the accommodation to sediment supply a s ratio two depositional sequences showing an overall fining upward trend are preserved within the succession the sequences are bounded by regional subaerial unconformities formed during negative a s ratio and may be subdivided in low accommodation systems tracts last positive a s ratio close to zero and high accommodation systems tracts hast a s ratio between 0 5 and 1 sequence 1 with a minimum thickness of 100 m is characterized by amalgamated multi storey braided fluvial channel sand bodies defining a last these are interlayered with crevasse splay and floodplain deposits toward the top passing to open lacustrine deposits defining a hast sequence 2 with minimum thickness ranging from 50 to 90 m overlies the organic rich lacustrine deposits at the base this sequence is composed of amalgamated multistorey braided fluvial channel sand bodies last similar to sequence 1 overlain by well drained floodplain with fixed fluvial channel deposits interpreted as an anastomosed fluvial system which are in turn capped by lacustrine deposits both grouped in a hast paleocurrent data on fluvial deposits of sequences 1 and 2 show a consistent paleoflow to the se sedimentological evidence indicates humid to sub humid climatic conditions during deposition of sequences 1 and 2 accumulation of fluvial sequences 1 and 2 was mainly controlled by tectonics variation in a s ratios must be related to tectonic subsidence and uplift of the basin

radiocarbon age of late glacial deep water from the equatorial pacific radiocarbon age differences for pairs of coexisting late glacial age benthic and planktic foraminifera shells handpicked from 10 sediment samples from a core from a depth of 2 8 km in the western equatorial pacific are not significantly different from that of 1600 years calculated from measurements on prenuclear seawater this places a lower limit on the depth of the interface for the hypothetical radiocarbon depleted glacial age seawater reservoir required to explain the 190 drop in the 14c c for atmospheric co2 which occurred during the mystery interval 17 5 to 14 5 calendar years ago these measurements restrict the volume of this reservoir to be no more than 35 that of the ocean further 14c measurements on a single last glacial maximum age sample from a central equatorial pacific core from a depth of 4 4 km water fail to reveal evidence for the required 5 to 7 kyr age difference between benthic and planktic foraminifera shells if the isolated reservoir occupied only one third of the ocean nor does the 13c record for benthic forams from this abyssal core yield any evidence for the excess respiration co2 expected to be produced during thousands of years of isolation nor as indicated by the presence of benthic foraminifera was the dissolved oxygen used up in this abyssal water

direct dating of the oxygen isotope record of the last deglaciation by 14c accelerator mass spectrometry major trends of quaternary global climate are reflected in the continental ice volume changes which have been reconstructed by oxygen isotope analysis1 2 18o records from deep sea sediments show that the net glacial build up occurs relatively slowly3 but that the end of an ice age occurs quickly in less than 10 000 yr implying a nonlinear response4 5 to simple milankovitch theory6 the latter observation suggests that the cause of the most recent deglaciation was the maximum in summer calorific radiation at the upper latitudes of the northern hemisphere centred around 11 000 yr ago a view supported by early studies7 later work has produced conflicting dates the main source of confusion being problems with obtaining accurate and reliable dates here by using accelerator mass spectrometry we have measured 14c for various species of foraminifera to produce a reliable timescale for the oxygen isotope record our results show that at the end of the last ice age continental ice sheets began to melt more than 4 000 yr before the northern hemisphere maximum of summer calorific radiation

overlapping of pedogenesis and meteoric diagenesis in distal alluvial and shallow lacustrine deposits in the madrid miocene basin spain the miocene distal alluvial fan and palustrine deposits of the madrid basin paracuellos de jarama area were examined to establish the sequence of its pedogenic diagenetic processes and the main factors controlling them in this area the diagenetic processes operated not only on carbonates as commonly studied but also in high magnesium clays and opaline cherts this paper provides a dynamic model for saline alkaline lake margins that complements the existing freshwater palustrine model three sections ber pel and upc containing limestones sepiolite dolostones and opaline cherts were examined these represent the entire transition from alluvial fan deposit to lake environment the alluvial fan deposits pel section show the most complex sequence of processes after a weak edaphic imprint the primary mudstone and siltstones are affected by silicification opaline levels formed mainly by selective replacement of sepiolites and later dolomitization several types of dolomite are present rounded crystals spherules and globular bodies being the most characteristic in the ponds situated at the foot of the alluvial fans or in interfan areas sepiolite precipitated within free water bodies ber section and an intense pedogenesis led to the formation of palustrine sepiolite deposits later the intense silicification of the sepiolite produced lenticular opaline levels that were locally transformed to quartz by aging in the shallow lakes upc section palustrine limestones and sepiolite were deposited the carbonates are partially affected by silicification the sepiolite becoming completely silicified the opaline levels clearly preserve the structure of the limestones and sepiolite host rocks all the opaline levels show local aging processes the silicification processes were different in the three settings due to the interplay of groundwater with sedimentary environments and facies in the distal alluvial fan sediments of the pel section the initial host rock affected by silicification is not preserved due to the later dolomitization that erased both it and its textures the silicification environment was therefore not easy to determine in the ber and upc section the main silicification took place in groundwater influenced environments but evidence was seen of cements and silicifications in vadose environments in all study settings the overlapping of pedogenic vadose and groundwater processes was controlled by changes in the position of the water table four stages were concluded to explain the transformation from the primary deposits to the later dolomitization process and the formation of vadose cements the majority of the silicifications seen occurred as responses to changes in the water table position linked to the aggradation of this closed basin in all the studied environments the sepiolite deposits were preferentially silicified their fibrous structure and high absorption capacity helping to retain interstitial fluids moreover sepiolite and opal are stable under relatively similar geochemical conditions in arid environments the dissolution of the sepiolite caused an increase in silica in the interstitial fluids favouring silicification and ruling out the need of a biogenic source the replacement of limestones by silica is usually driven by variations in ph and salinity which are very common in surface environments such as shallow lakes and soils

alluvial fan lacustrine sedimentation and its tectonic implications in the cretaceous athgarh gondwana basin orissa india abstract the athgarh formation is the northernmost extension of the east coast upper gondwana sediments of peninsular india the formation of the present area is a clastic succession of 700 m thick and was built against an upland scarp along the north and northwestern boundary of the basin marked by an e w ene wsw boundary fault a regular variation in the dominant facies types and association of lithofacies from the basin margin to the basin centre reveals deposition of the succession in an alluvial fan environment with the development of proximal mid and distal fan subenvironments with the distal part of the fan merging into a lake several fans coalesced along the basin margin forming a southeasterly sloping broad and extensive alluvial plain terminating to a lake in the centre of the basin aggradation of fans along the subsiding margin of the basin resulted in the athgarh succession showing remarkable lateral facies change in the down dip direction the proximal fan conglomerates pass into the sandstone dominated mid fan deposits which in turn grade into the cyclic sequences of sandstone mudstone of the distal fan origin further downslope thick sequence of lacustrine shales occur the faulted boundary condition of the basin and a thick pile of lacustrine sediments at the centre of the basin suggest that tectonism both in the source area and depositional site has played an important role throughout the deposition of the athgarh succession of the present area the vertical succession fines upward with the coarse proximal deposits at the base and fine distal deposits at the top suggesting deposition of the succession during progressive reduction of the source area relief after a single rapid uplift related to a boundary fault movement the nw se trending fault defining the son mahanadi basin of lower gondwana sediments are shear zones of great antiquity and these were rejuvenated under neo tensional stress during lower gondwana sedimentation the e w ene wsw trending fault of the athgarh basin on the other hand define tensional rupture of much younger date in the early cretaceous period there was a reversal of palaeoslope in the athgarh basin southward slope with respect to the son mahanadi basin northward slope during the phase drifting of the indian continent and with the evolution of indian ocean in the early cretaceous period the tectonic events in the plate interior was manifested by formation of new grabens like the athgarh graben

interaction of typhoons with the taiwan orography part ii continuous and discontinuous tracks across the island abstract numerical model simulations of west moving tropical cyclones approaching and crossing the taiwan orography are shown to contain many of the observed surface features vortices tend to track continuously around the northern end of the island due to the deflection of the deep layer mean flow and the vortex circulation is modified less because the higher winds to the right of the center do not have a strong interaction with the barrier discontinuous tracks predominate for vortices approaching the central southern portions of the taiwan orography severe distortions of the inner core circulation occur and the surface pressure and surface wind centers become decoupled and may be dissipated at different rates numerical sensitivity studies demonstrate that more intense and rapidly moving vortices are more like to cross directly over the barrier and thus maintain a continuous track in one special case of a weak but fast moving vortex approaching the southern end the model simulates the existence of

sedimentary and tectonic evolution of plio pleistocene alluvial and lacustrine deposits of fucino basin central italy abstract the fucino basin was the greatest lake of the central italy which was completely drained at the end of 19th century the basin is an intramontane half graben filled by plio quaternary alluvial and lacustrine deposits located in the central part of the apennines chain which was formed in upper pliocene and in quaternary time by the extensional tectonic activity the analysis of the geological surface data allows the definition of several stratigraphic units grouped in lower units and upper units the lower units upper pliocene are exposed along the northern and north eastern basin margins they consist of open to marginal lacustrine deposits breccia deposits and fluvial deposits the upper units lower pliocene holocene consist of interbedded marginal lacustrine deposits and fluvial deposits thick coarse grained fan delta deposits are interfingered at the foot of the main relief with fluvial lacustrine deposits most of the thickness of the lacustrine sequences more than 1000 m thick is buried below the central part of the fucino plain the basin is bounded by e w wsw ene and nw se fault systems velino magnola fault e w and tremonti celano aielli fault wsw ene and s potito celano fault nw se in the north the trasacco fault the pescina celano fault and the serrone fault nw se in the south east the geometry and kinematic indicators of these faults indicate normal or oblique movements the study of industrial seismic profiles across the fucino basin gives a clear picture of the subsurface basin geometry the basin shows triangular shaped basin fill geometry with the maximum deposits thickness toward the main east boundary fault zones that dip south westward serrone fault trasacco fault pescina celano fault on the basis of geological surface data borehole stratigraphy and seismic data analysis it is possible to recognize and to correlate sedimentary and seismic facies the bottom of the basin is well recognized in the seismic lines available from the good and continuous signals of the top of meso cenozoic carbonate rocks the shape of sedimentary bodies indicates that the filling of the basin was mainly controlled by normal slip along the nw se boundary faults in fact the continental deposits are frequently in on lap contact over the carbonate substratum several disconformable contacts occurred during the sedimentary evolution of the basin the main faults with antithetic and synthetic fault planes displace the whole sedimentary sequence up to the surface indicating a recent faults activity 1915 avezzano earthquake ms 7 0 the stratigraphic and tectonic setting of the fucino basin and neighboring areas indicates that the extensional tectonic events have had an important role in driving the structural sedimentary evolution of the plio quaternary deposits the geometry of the depositional bodies of the fault planes and their relationships indicate that the fucino basin was formed as a half graben type structure during plio quaternary extensional events some internal complexities are probably related to the fold and thrust structures of the apenninic orogeny formed in messinian time in this area and to a different activity timing of the e w and wsw ene fault systems and the nw se fault systems we believe based on the similarity of the surface characteristics that the structural setting of the fucino basin can be extrapolated to the other great intramontane basins in central italy e g rieti l aquila sulmona sora isernia basins

loss of carbon from the deep sea since the last glacial maximum deep ocean carbonate ion concentrations co32 and carbon isotopic ratios 13c place important constraints on past redistributions of carbon in the ocean land atmosphere system and hence provide clues to the causes of atmospheric co2 concentration changes however existing deep sea co32 reconstructions conflict with one another complicating paleoceanographic interpretations here we present deep sea co32 for five cores from the three major oceans quantified using benthic foraminiferal boron calcium ratios since the last glacial period combined benthic 13c and co32 results indicate that deep sea released co2 during the early deglacial period 17 5 to 14 5 thousand years ago was preferentially stored in the atmosphere whereas during the late deglacial period 14 to 10 thousand years ago besides contributing to the contemporary atmospheric co2 rise a substantial portion of co2 released from oceans was absorbed by the terrestrial biosphere

lower eocene alluvial paleosols pedogenic development stratigraphic relationships and paleosol landscape associations abstract two kinds of cumulative floodplain paleosols red and grey paleosols formed on overbank deposits of the willwood formation in the sand coulee area of the bighorn basin wyoming although both kinds experienced down profile iron movement due to seasonal saturation of a clay rich a horizon the red paleosols were better drained and their b horizons were rubified various redoximorphic features indicate that the grey paleosols were poorly drained the red paleosols show progressive increases in the degree of profile development away from an associated channel sandstone a paleosol landscape relationship termed pedofacies by bown and kraus 1987 although the grey paleosols show relatively systematic changes in hydromorphy consistent pedofacies changes were not recognized furthermore no lateral relationship between the red and grey paleosols was observed these features suggest that because of the retarding effects of poor drainage on soil weathering poorly drained soils are not amenable to pedofacies modelling and that the landscape associations of well drained and poorly drained soils may be difficult to document without unusually extensive exposures results of this study also show that the pedofacies model is limited by sediment accumulation rates and the kind of fine grained facies on which paleosols developed although readily observable in sand coulee pedofacies are difficult to recognize in the elk creek area where accumulation rates were approximately half as rapid as in sand coulee the attainment of steady state conditions is believed to have obscured pedofacies in the elk creek area finally pedofacies are only developed on true overbank deposits which in the willwood formation and probably many other ancient alluvial sequences make up only a fraction of the fine grained deposits only immature soils formed on the remainder of the fine grained facies because they were deposited very rapidly as a result of channel avulsion

devising quality assurance procedures for assessment of legacy geochronological data relating to deglaciation of the last british irish ice sheet this contribution documents the process of assessing the quality of data within a compilation of legacy geochronological data relating to the last british irish ice sheet a task undertaken as part of a larger community based project britice chrono that aims to improve understanding of the ice sheet s deglacial evolution as accurate reconstructions depend on the quality of the available data some form of assessment is needed of the reliability and suitability of each given age s in our dataset we outline the background considerations that informed the quality assurance procedures devised given our specific research question we describe criteria that have been used to make an objective assessment of the likelihood that an age is influenced by the technique specific sources of geological uncertainty when these criteria were applied to an existing database of all geochronological data relating to the last british irish ice sheet they resulted in a significant reduction in data considered suitable for synthesis the assessed data set was used to test a bayesian approach to age modelling ice stream retreat and we outline our procedure that allows us to minimise the influence of potentially erroneous data and maximise the accuracy of the resultant age models

δ13c δ18c covariance as a paleohydrological indicator for closed basin lakes the relationship between 18o and 13c in a closed basin lake is a function of hydrological change vapor exchange lake productivity and total co2 or carbonate alkalinity concentration covariance of 18o and 13c usually occurs in lake sediments under the condition of hydrological closure for time periods of the order of 5000 yr or longer on shorter time scales however certain subtleties in the use of the 13c 18o covariance as a hydrology history indicator must be recognized the covariant trend may not be found in hyper alkaline lakes because of the insensitivity of 13c to lake volume changes for less alkaline closed basin lakes covariance of 13c 18o will result from relatively rapid increase or decrease of lake volume with the rapid decrease condition giving rise to heavy and narrow ranged isotopic values for both 13c and 18o due to the coupled evaporation productivity effect when the lake volume remains stable as is the case for an over flowing open lake poor 13c 18o covariance will ensue due to the effect of vapor exchange with the atmosphere we have used the measured 13c 18o covariance in carbonate sediments of mono lake california to deduce paleo hydrological and lake water alkalinity and salinity variations and found the results in consonance with holocene lake level history derived from the 18o and other information

high frequency environmental changes and deposition processes in a 2 kyr long sedimentological record from the cap breton canyon bay of biscay the core md03 2693 43 39 258 n 01 39 805 w 431 m water depth was collected on an abandoned meander of the capbreton canyon se bay of biscay filled over the last millennia by very high sedimentation rates mean sedimentation rate of 1 2 cm yr linked to its specific environmental location and fine grained clayed sediment decantation from the proximal canyon axis this archive thus permits to undertake the study of late holocene regional climatic patterns at a decadal temporal resolution in the present work we use data derived from planktonic foraminifera assemblages coupled to a multiproxy approach that associates grain size measurements x ray fluorescence xrf elemental analysis and stable oxygen isotope on globigerina bulloides shells to infer sea surface temperature sst and sea surface salinity sss changes over the last two millennia signals reconstructed in the bay of biscay show significant oscillations that are consistent with well known temperature anomalies such as the little ice a

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

search for a glacial age 14c depleted ocean reservoir 1 measurements of the radiocarbon age difference between mixed benthic foraminifera and several coexisting planktic entities were made in hopes of finding evidence for the existence of an isolated glacial age abyssal ocean reservoir whose demise would explain the large drops in the 14 c to c ratio in atmosphere and surface ocean carbon which occurred during the period of deglaciation forty six new radiocarbon results were obtained at seven depths covering the full range of glacial time i e 27 to 15 14 c kyrs from an equatorial pacific sediment core at 4 4 km water depth even though age reversals for foraminifera but not for coccoliths at two of the eight depths and large age differences between g sacculifer and three submixed layer planktic species mar this data set there remains little likelihood that such a reservoir existed

use of micromorphology for palaeoenvironmental interpretation of complex alluvial palaeosols an example from the mill creek formation albian southwestern alberta canada abstract field observations are often not sufficient for process based interpretations of palaeosols particularly where they form parts of thick aggradational pedocomplexes within alluvial successions under such conditions micromorphology provides genetic temporal and spatial information on soil forming processes that is critical to an understanding of past environmental conditions thick alluvial successions of the albian mill creek formation contain abundant evidence of pedogenesis but few well developed palaeosol profiles and therefore provide an ideal case study in which to demonstrate the usefulness of micromorphological data for palaeoenvironmental interpretation the micromorphological features of greatest interpretive value are types of clay coatings and ferruginous segregations structure and fabric papules evidence of bioactivity and ferruginous concretions provide information on geomorphic surface stability and assist in reconstructing temporal changes in drainage conditions while individual features can provide some palaeoenvironmental information the relationships of features to one another and assemblages of features provides additional information when analysed hierarchically to establish a sequence of sedimentologic and pedogenic events a common recurring sequence of palaeoenvironmental events subject to local variations can be recognized throughout the mill creek formation the presence of illuvial clay requires that water percolated through the soil and that the soil periodically dried out so that the translocated clay was retained dark reddish clay coatings indicate clay illuviation under freely drained conditions while pale yellow and silty clay coatings suggest that phases of free drainage alternated with phases of poorly drained or saturated soil conditions the presence of iron depletion coatings iron nodules and quasiferrans indicates that these units were at least periodically saturated and the occurrence of multiple overlapping phases within single thin sections demonstrates that redox conditions fluctuated strongly suggesting development in the vadose zone recent soils containing similar assemblages of features develop under warm temperate seasonal climates alternating phases of well drained and saturated conditions on the mill creek floodplains are attributed to changing sediment supply and local palaeogeomorphology rather than to any major regional climate change this type of process based micromorphological analysis should have broad application in other complex pedogenically modified alluvial successions and similar studies would lead to a more detailed understanding of ancient palaeoenvironments

petrography geochemistry and primary origin of spheroidal dolomite from the upper cretaceous lower tertiary maghra el bahari formation at gabal ataqa northwest gulf of suez egypt abstract field petrographical and geochemical studies of the maghra el bahari formation at gabal ataqa in egypt indicate an occurrence of spheroidal dolomite as a primary precipitate petrographically this dolomite is microcrystalline 10 40 m in diameter and lacks any direct or indirect evidence of a precursor mineral each dolomite spherule is composed of a cluster of coalesced incomplete rhombohedral sub units exhibiting a globular body with a hollow core this dolomite is commonly associated with authigenic palygorskite and gypsum based on its associations the spheroidal dolomite occurs in two modes i siliciclastic disseminated dolomite and ii evaporitic associated dolomite on the basis of its elemental and stable isotopic signature the spheroidal dolomite is subdivided into two types type a and type b type a is ca rich with average caco3 and mgco3 equal to 58 20 and 39 91 mol respectively and with average sr 108 ppm average na 656 ppm average mn 72 ppm and 18o ranges from 0 4 to 0 9 pdb type b compared with type a is nearly stoichiometric with average caco3 and mgco3 equal to 49 32 and 43 75 mol respectively with higher average sr 508 ppm average na 3008 ppm average mn 171 ppm and 18o 0 98 to 1 8 pdb slightly positive values of 13c 0 18 to 2 10 pdb are recorded for the two types of dolomite type a belongs to the siliciclastic disseminated dolomite whereas type b is of the evaporitic associated dolomite it is interpreted that the spheroidal dolomite directly precipitated from a solution that was supersaturated with respect to dolomite components and did not develop by dolomitization of precursor carbonates two main sources are suggested for dolomite precipitation hypersaline water and mixed saline fresh water

is the core top modern observations from the eastern equatorial pacific abstract a compilation of ages from 67 core tops in the eastern equatorial pacific eep does not display an easily discernible regional pattern the ages range from 790 to over 15 000 years the youngest core tops with the highest sediment focusing factors are located in the panama basin there are weak but statistically significant inverse relationships between core top age and age model based mass accumulation rates bioturbation depth linear sedimentation rate and sediment focusing factors however we found no statistically significant relationship between core top age and calcite dissolution in sediments or 230th normalized mass accumulation rates we found evidence suggesting that greater amount of sediment focusing helps to preserve the carbonate fraction of the sediment where focusing is taking place when focusing factors are plotted against percent calcite dissolved we observe a strong inverse relationship and core tops younger than 4500 years tend to occur where focusing factors are high and percent calcite dissolved values are low using labile organic carbon fluxes to estimate bioturbation depth in the sediments results in the observation that where bioturbation depth is shallow

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

stable isotopes of planktonic foraminifera from tropical atlantic caribbean core tops implications for reconstructing upper ocean stratification abstract 18o values of nine tropical subtropical planktonic foraminiferal species with different preferential habitat depths collected from 62 core top samples along an east west transect across the tropical atlantic caribbean were used to test the applicability of interspecific 18o gradients for reconstructions of tropical upper ocean stratification in general the 18o difference 18o between intermediate and shallow dwelling species decreases and 18o between deep and intermediate dwellers increases with increasing thermocline depth towards the west the statistical significance of regional differences in 18o highlights 18o between the intermediate dwellers in particular globorotalia scitula and globorotalia tumida and the shallow dweller globigerinoides ruber pink as well as 18o between the deep dwellers globorotalia crassaformis or globorotalia truncatulinoides dextral and intermediate dwellers as most sensitive to changes in tropical atlantic thermocline depth based on the observed regional variations in interspecific 18o we propose a multispecies stratification index stratrop 18ointermediate 18oshallow 18odeep 18oshallow for the tropical ocean statistically significant differences in stratrop values between the e atlantic and the caribbean suggest that this index may be a useful tool to monitor variations in tropical upper ocean stratification in the geological record

palynology and palynofacies analyses of the gray fossil site eastern tennessee their role in understanding the basin fill history abstract the gray fossil site gfs includes multiple karst sub basins that are filled with lacustrine sediments early paleontologic work on one of the sub basins gfs 2 indicates a late miocene early pliocene age based on an assemblage of well preserved vertebrate fossils however detailed palynological analysis of the 38 7 m deep gfs 1 core recovered from another sub basin indicates an older age the presence of caryapollenites imparalis c inelegans and c prodromus association suggests a paleocene to eocene age for the gfs 1 core section this age is also supported by the absence of pollen of the poaceae the grass family that is not commonly present until the neogene age constraints from palynologic data suggest that the gfs has a more complex basin fill history than previously suspected and that multiple depo centers within the basin may have been periodically active through the cenozoic palynofacies analysis of the gfs 1 core indicates that phytoclasts and opaques are the most abundant organic constituents and have diluted both the palynomorph population and amorphous organic matter two possible scenarios can account for this observation 1 an oxidizing depositional paleoenvironment and 2 a localized high flux of charcoal following wildfires and subsequent increased runoff

near constancy of the pacific ocean surface to mid depth radiocarbon age difference over the last 20 kyr although 13c to 12c and cadmium to calcium ratios provide information regarding the distribution of deep water masses during late glacial time and during the period of deglaciation our knowledge of the rate at which these water masses were ventilated comes mainly from the difference in radiocarbon age between coexisting bottom and surface dwelling foraminifera paired benthic planktonic foraminiferal radiocarbon age differences covering last 20 kyr in a high deposition rate western equatorial pacific core md01 2386 from a water depth of 2 8 km show no significant climate related variations over this period this result is surprising for we would have expected a change in this age difference between the last glacial maximum lgm and the holocene and also during the mystery interval 17 5 14 5 kyr ago when the waters in a radiocarbon depleted abyssal reservoir were presumably being mixed back into the remainder of the ocean

early forest soils and their role in devonian global change a paleosol in the middle devonian aztec siltstone of victoria land antarctica is the most ancient known soil of well drained forest ecosystems clay enrichment and chemical weathering of subsurface horizons in this and other devonian forested paleosols culminate a long term increase initiated during the silurian from silurian into devonian time red clayey calcareous paleosols show a greater volume of roots and a concomitant decline in the density of animal burrows these trends parallel the decline in atmospheric carbon dioxide determined from isotopic records of pedogenic carbonate in these same paleosols the drawdown of carbon dioxide began well before the devonian appearance of coals large logs and diverse terrestrial plants and animals and it did not correlate with temporal variation in volcanic or metamorphic activity the early paleozoic greenhouse may have been curbed by the evolution of rhizospheres with an increased ratio of primary to secondary production and by more effective silicate weathering during silurian time

carbonate deposition in an ephemeral siliciclastic alluvial system jurassic shuttle meadow formation newark supergroup hartford basin usa abstract nonmarine carbonate accumulation from a sedimentologic perspective has multiple possible origins clastic load springs groundwater discharge soil development biochemical seasonal changes cave speleothems and eolian influx many of these carbonates contain diagnostic textures from which origin is easy to ascertain however differentiating between clastic and spring groundwater carbonates especially in depositional systems dominated by siliciclastics is not always simple here criteria for recognition are developed subsurface hydrology and tectonic origin of the depositional basin source rocks surrounding the basin sedimentologic packaging and extent of the carbonates in question as well as their sedimentary structures and fossil content and stable isotopic analyses of the carbonates can all aid in determining carbonate origin and correctly assessing sedimentary and basin evolution the present study focuses on a nonmarine carbonate deposit found within the jurassic shuttle meadow formation of the hartford basin one of many rift basins which formed as a result of the opening of the north atlantic ocean during the late triassic to early jurassic the upper 50 m of the formation at plainville connecticut is interpreted as continental in origin and is composed of five facies red ripple cross laminated muddy siltstones to sandstones fr sr massive red siliciclastic mudstones fm buff fine to medium grained horizontally laminated sandstones sh red to white disrupted calcareous shales fl3 and rare micritic carbonates pm facies fr sr sh and fm are interpreted as an alluvial plain system in an ephemeral setting with bedload sheetflooding as the dominant depositional mechanism similar to the channel country drainage system of central australia in addition preservation of lateral accretion sandstone sheets accretionary benches indicate that the shuttle meadow alluvial system was rapidly accreting the anomalous existence of carbonate beds in facies fl3 and pm in the smf bedload dominated siliciclastic sequence is attributed mainly to the unique nature of the clastic sediment load in the basin no direct evidence for a spring groundwater input is apparent the shallow carbonate lake margin or a pond with vegetation and periodic exposure is envisioned as the depositional environment the intraclastic texture of the micrites with rare primary relict lamination indicates early diagenetic alteration from root penetration desiccation cracks and burrowing

major controls on sedimentation during the evolution of a continental basin pliocene pleistocene of the guadix basin betic cordillera southern spain abstract sequence stratigraphy based on climatic tectonic and base level parameters can be used to understand carbonate sedimentation in continental basins the uppermost continental fill of the guadix basin betic cordillera containing both siliciclastics and carbonates is investigated here in its central sector a thick succession of fluvio lacustrine sediments appear hosting several important pliocene and pleistocene macrovertebrate sites fonelas project the need to characterize the stratigraphic and sedimentologic context of these important paleontologic sites has lead to litho magneto and biostratigraphic studies these data together with the sedimentologic analysis of the pliocene and pleistocene siliciclastic and carbonate successions establish a sedimentary model for the fluvio lacustrine sedimentation of the two last stages of sedimentation in the guadix basin units v and vi unit v comprises mostly fluvial siliciclastic sediments with less abundant carbonate beds interpreted as floodplain lakes or ponds the latter unit vi is dominated by vertically stacked carbonate palustrine successions using two pre existent continental stratigraphic models the influence of climate tectonism and stratigraphic base level during the last 3 5 ma on the sedimentary evolution of the fluvio lacustrine system in the guadix basin especially the carbonate sedimentation patterns is outlined

late miocene to plio pleistocene fluvio lacustrine system in the karacasu basin sw anatolia turkey depositional paleogeographic and paleoclimatic implications abstract the sedimentary record of the late cenozoic karacasu basin a long lived continental half graben from southwestern turkey is characterized by siliciclastic and carbonate deposits sedimentation was controlled by an active nw se trending major normal fault along the basin s southern margin and by climatically induced lake level changes detailed facies analysis subdivides the entire neogene quaternary basin fill into three distinct litostratigraphic units representing paleogeographic changes and sedimentation patterns throughout the basin evolution sedimentation commenced in the late miocene with the deposition of proximal medial alluvial fan and fluvial facies damdere formation fa1 at this stage alluvial fans developed in elevated areas to the south prograding towards the basin center at the beginning of the pliocene fresh to slightly alkaline shallow lake deposits fa2a of the karacaoren formation formed the lake became open and meromictic conditions developed fa2b pollen data from the fa2b facies show that climate was arid to humid climate probably changed cyclically through time producing alternation of artemisia steppe cold and dry periods and more forested vegetation warm and wet the open lake facies passes upwards into lake margin facies fa2c but it was still dominated by alkaline to slightly saline lake conditions sedimentation was almost continuous from the late miocene to pleistocene in the early quaternary the basin was dissected by the re activation of basin bounding faults the unconformable base of the overlying quaternary deposits karacasu formation fa3 reflected the basin s transformation from a half graben into a full graben system oxygen isotope data from carbonates show an alternation of humid climatic periods when freshwater settings predominated and semiarid arid periods in which the basin hosted alkaline and saline water lakes neotectonic activity has rejuvenated many of the basin bounding faults causing development of talus aprons and local alluvial fans the basin was progressively incised by modern rivers that have largely smoothed out the topographic relief of the graben margins

radiocarbon evidence for a possible abyssal front near 3 1 km in the glacial equatorial pacific ocean abstract we investigate the radiocarbon ventilation age in deep equatorial pacific sediment cores using the difference in conventional 14c age between coexisting benthic and planktonic foraminifera and integrate those results with similar data from around the north pacific ocean in a reconstruction for the last glaciation 15 to 25 conventional 14c ka most new data from both the equatorial pacific and the emperor seamounts in the northwestern pacific come from maxima in abundance of benthic taxa because this strategy reduces the effect of bioturbation although there remains considerable scatter in the ventilation age estimates on average ventilation ages in the equatorial pacific were significantly greater below 3 2 km 3080 1125 yrs n 15 than in the depth interval 1 9 to 3 0 km 1610 250 yrs n 12 when compared to the average modern seawater c 14 profile for the north pacific the equatorial pacific glacial data suggest an abyssal front located somewhere between 3 0 and 3 2 km modern water depth above that depth the data may indicate slightly better ventilation than today and below that depth glacial equatorial pacific data appear to be as old as last glacial maximum lgm deep water ages reported for the deep southern atlantic this suggests that a glacial reservoir of aged waters extended throughout the circumpolar southern ocean and into the equatorial pacific renewed ventilation of such a large volume of aged and by corollary carbon rich water would help to account for the rise in atmospheric pco2 and the fall in c 14 as the glaciation drew to a close

radiocarbon dating of planktonic foraminifer shells a cautionary tale 1 sedimentation rate bioturbation winnowing and calcite dissolution produce significant radiocarbon age offsets among multiple species of coexisting planktonic foraminifers and pteropod fragments we compare the radiocarbon age of foraminifer species and pteropod fragments with estimates of percent calcite dissolved made with a sedimentary proxy globorotalia menardii fragmentation index mfi to delineate the effect of dissolution on radiocarbon age of foraminifers data from two core top transects on the rio grande rise rio and ontong java plateau ojp and from down core sediments of varying sedimentation rates in the tropical pacific me 27 md98 2177 and mw91 9 56ggc reveal that sediments with the greatest accumulation rates produce the least age offsets among coexisting species age offsets among coexisting foraminifers are about 3500 years on rio and 1000 years on ojp two core tops from rio yield an age of the last glacial maximum possibly due to mass displacement of younger sediments downslope foraminifer age increases with increasing dissolution and there is a consistent pattern of older foraminifer fragments coexisting with younger whole shells of the same species the only exception is sediments which have experienced high dissolution where fragments are younger than whole shells the age offset between fragments of g menardii and its coexisting whole shells does not exceed the age offset among other coexisting foraminifer species in the same core tops

alluvial and lacustrine facies in an extensional basin the miocene of malatya basin eastern turkey abstract during the neogene both strike slip and extensional regimes coexisted giving rise to a number of fault bounded basins in eastern turkey one of these basins the malatya basin contains a thick sequence up to 2000 m of alluvial and lacustrine deposits this paper focuses on the miocene alluvial and lacustrine deposits in the northern part of the basin alluvial and lacustrine deposits in the study area having a thickness over 1200 m are divided into three units on the basis of their vertical sequential changes and lithologic characteristics these are the lower alluvial unit lacustrine unit and upper alluvial unit the lower alluvial unit is composed of stratified conglomerate gm planar cross stratified conglomerate gp trough cross stratified sandstone st planar cross stratified sandstone sp horizontally stratified sandstone sh ripple cross laminated sandstone sr red mudstone fm carbonaceous claystone fl1 and rarely limestone pf facies gm gp and sh characterize alluvial fan to sheetflood deposits facies st sp sh and sr are interpreted as braided stream to sheetflood deposits facies fm fl1 and siltstone are interpreted as deposits in an alluvial plain system with an ephemeral setting carbonaceous claystone fl1 and limestone pf are interpreted as a shallow lake situated as a distal environment in alluvial plain the middle unit interpreted as channel crevasse splay swamp and lacustrine deposits is composed of interbedded sandstone siltstone grey claystone sf low angle cross stratified sandstone sl planar cross stratified sandstone sp limestone pf carbonaceous claystone fl1 marl fl2 and coal c the upper alluvial unit is composed of gm gp st sp sh sr and fm characterizing a low sinuosity river most of the alluvial input into the basin was from the north northeast and east soft sediment deformation structures slump folds which indicate seismically active areas were formed within the lacustrine facies the sediment supply lake level fluctuation and facies architecture were mainly controlled by synsedimentary tectonism

a high resolution micromorphological record of the late quaternary paleosols from ganga yamuna interfluve stratigraphic and paleoclimatic implications abstract this study reports the micromorphological record of a continuous set of samples from paleosol bearing intervals of two subsurface cores of 50 m depth representing typical pedosedimentary sequences of the ganga yamuna interfluve in the western ganga plains micromorphology microstructures rhizocretes fe mn features pedogenic carbonate illuvial clay coatings and relict pedofeatures was used to characterize pedogenic processes in the 13 paleosols in the iitk core and the 10 paleosols in the bhognipur core formation of these paleosols took place through incipient to moderate weathering on relatively stable surfaces of the ganga yamuna interfluve over the last 100 ka these paleosols range in character from simple ones having weakly developed pedofeatures to mature paleosols with strongly developed pedofeatures and are similar to modern entisols inceptisols alfisols and vertisols of the ganga plains pedosedimentary evolution in the two interfluve successions differs in terms of stratigraphic stacking of paleosols types of paleosols and heterogeneous nature of sediments in the northern part the iitk interfluve core is marked by a thick mature paleosol with a strongly developed argillic bt horizon at 41 45 m depth and weakly developed paleosols in the remaining part of the core the mature paleosol represents a major discontinuity when prolonged pedogenic activity took place on stable surfaces with little or no deposition on the other hand thin simple thick cumulic paleosols with weakly developed pedogenic features even with some preservation of sedimentary laminations indicate short stratigraphic breaks in rapidly aggrading sediments in the southern part the bhognipur core is marked by the heterogeneous nature of sediments with a predominance of cratonic sediments in the lower part and the himalayan sediments in the upper parts in contrast the iitk core shows a himalayan source throughout the entire interfluve succession in the bhognipur region is marked by rapid sedimentation and short pedogenic intervals of weakly developed paleosols excepting one mature paleosol with well developed argillic bt and vertic bss horizons at 10 14 m depth this mature paleosol possibly formed synchronously with a mature paleosol from the northern part of this interfluve the mature paleosol in both the cores represents a major stratigraphic break of 8000 10 000 years when prolonged pedogenesis occurred over large areas of the ganga yamuna interfluve following regional degradation and local gullying in response to climate change from sub humid to semi arid conditions during the mis 5 4 transition

radiocarbon age offsets of foraminifera resulting from differential dissolution and fragmentation within the sedimentary bioturbated zone 1 shells of coexisting species of planktonic foraminifera from the ontong java plateau reveal radiocarbon age offsets of up to 2200 years similar offsets are found between fragments and whole shells of single species steady state modelling of dissolution and bioturbation within the sedimentary mixed layer predicts age differences of up to several kiloyears due to the interplay between differential dissolution and fragmentation of foraminifer shells and bioturbation the observation that fragile foraminiferal shells are systematically older than those of more robust species is more difficult to explain mechanisms of chemical erosion interface dissolution and sediment redistribution are all apparently unable to explain this phenomenon a possible solution is presented in which a particular species may be represented by two distinct classes of shells which are more or less robust in this case differential dissolution and fragmentation causes an increase in the mean age as the fragile class contributes less to the remaining intact shells this study highlights the vulnerability of low sedimentation rate cores to the effects of dissolution and bioturbation

discriminating between tectonism and climate signatures in palustrine deposits lessons from the miocene of the teruel graben ne spain the upper miocene vallesian turolian unit ii of the teruel graben comprises at its top a 25 m thick sequence of palustrine deposits deposition of the entire unit commenced some 9 to 7 ma ago in a halfgraben basin here via a recent quarry we examine in detail the lateral and vertical distribution of unit ii s palustrine facies and their features to determine the palaeogeography and main controls on deposit formation our findings suggest the deposits formed at a low gradient lake margin with different energy levels these energy levels controlled the type of primary deposit within the lake wackestone to packstone sediments formed in low energy conditions whereas cross bedded rudstones to floatstones formed under higher energy conditions by erosion and redeposition of prior lacustrine deposits pedogenic and diagenetic modifications of the primary sediments took place during sedimentary discontinuities sd when the lacustrine sediments were subaerially exposed these processes serve to explain the formation of eight different palustrine limestones limestones with root traces mottled limestones brecciated limestones flat pebble breccias granular limestones micro karstified limestones with laminar calcretes carbonate mounds and clayey limestones with laminar calcretes based on the features and thicknesses of the modified sediments five different morphological stages i to v of palustrine carbonates are defined stage i is characterized by incipient mottling and brecciation stage ii shows mottling and strong brecciation that lead to the formation of intraclast breccias in which the fragments are mostly in situ in stage iii the primary fabric is totally changed intraclasts have moved and may have lost their initial morphology this stage iii may also be characterized by the formation of micro karst stage iv is typified by the presence of coated grains and thin root mats the chronological data available suggest that the formation of stage iii lacustrine deposition palustrine modification would require about 40 000 yr facies and the sd record changes across short horizontal distances and thus reflect the topography of prior sedimentation modification events small 50 cm highs with micro karst have their sd counterparts in lower areas of the lake in which the sd is indicated by desiccation and mottling the topographic differences of the micro karst were filled by intraclastic rudstones sourced by the adjacent carbonate flats the example examined not only clearly sketches the morphology of ancient palustrine systems or wetlands it also provides evidence that recycling of previous carbonate deposits played an important role as a sediment source apart from biogenic or physical chemical production processes our geochemical data indicate lmc low magnesian calcite as the main component and fe contents lower than 1 except for the mottled areas that are richer in feo stable isotope compositions provide 18o values close to 6 5 vpdb and more varied 13c 3 39 to 6 97 pdb oxygen and carbon values reveal no covariation and clear trends are lacking the homogeneity of 18o values reflects the intense effects of meteoric waters the deposition of these palustrine limestones took place under suitable semi arid to sub humid climates climate could also have a role in determining subaerial exposure periods however its imprint is not easy to detect neither in the geochemical signals nor in the vertical arrangement of the facies this could be attributed to climate changes probably occurring over shorter periods than those that can be recorded in this type of sediment such as the astronomical precession cycles and suggests the unsuitability of palustrine carbonates for detailed palaeoclimate analyses tectonism controlled the location of the main lacustrine depocentre close to the basin s main fault the activity of this normal fault during the sedimentation of unit ii determined long and short term sedimentary sequences such sequences are the response to small scale subsidence pulses followed by the infill of the created accommodation space by shallow lacustrine deposits which underwent early pedogenic and diagenetic processes after subaerial exposure

western pacific thermocline structure and the pacific marine intertropical convergence zone during the last glacial maximum paleoclimate proxy evidence suggests a southward shift of the intertropical convergence zone itcz during times of northern hemisphere cooling including the last glacial maximum 19 23 ka before present however evidence for movement over the pacific has mainly been limited to precipitation reconstructions near the continents and the position of the pacific marine itcz is less well constrained in this study we address this problem by taking advantage of the fact that the upper ocean density structure reflects the overlying wind field we reconstruct changes in the upper ocean density structure during the lgm using oxygen isotope measurements on the planktonic foraminifera g ruber and g tumida in a transect of sediment cores from the western tropical pacific the data suggests a ridge in the thermocline just north of the present day itcz persists for at least part of the lgm and a structure in the southern hemisphere that differs from today the reconstructed structure is consistent with that produced in a general circulation model with both a northern and southern hemisphere itcz

caco3 size distribution a paleocarbonate ion proxy lysocline reconstructions play an important role in scenarios purporting to explain the lowered atmospheric co2 content of glacial time these reconstructions are based on indicators such as the caco3 content the percent of coarse fraction the ratio of fragments to whole foraminifera shells the ratio of solution susceptible to solution resistant species and the ratio of coarse to fine caco3 all assume that changes with time in the composition of the input material do not bias the result however as the composition of the input material does depend on climate none of these indicators provides an absolute measure of the extent of dissolution in this paper we evaluate the reliability of the ratio of 63 m caco3 to total caco3 as a dissolution indicator we present here results that suggest that in today s tropics this ratio appears to be determined solely by co3 ion concentration and water depth i e the saturation state of bottom waters this finding offers the possibility that the size fraction index can be used to reconstruct co3 ion concentrations for the late quaternary ocean to an accuracy of 5 mol kg 1

radiocarbon age differences among coexisting planktic foraminifera shells the barker effect 1 for slowly accumulating sediments a major contrast exists in the radiocarbon age differences among coexisting shells of planktic foraminifera between those experiencing little dissolution and those experiencing significant dissolution in the former the ages generally agree to within a couple of hundred years in the latter age differences as large as 1000 years are common the most likely explanation appears to be the barker effect which involves the preferential fragmentation of dissolution prone g sacculifer and g ruber the whole shells of these species picked for radiocarbon dating have shorter residence times in the bioturbation zone than those for dissolution resistant species including benthics as low accumulation rate sediment cores often fail to yield reliable radiocarbon based ocean ventilation ages where possible such studies should be conducted on high accumulation rate cores

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

alluvial to lacustrine systems in a pull apart margin southwestern eumsung basin cretaceous korea abstract in the pull apart margin of pull apart basins sedimentation patterns are poorly known compared with those in rift basins the rhomb shaped eumsung basin cretaceous mid west korea was formed in an overstep of the kongju fault system and provides significant information on how sedimentary bodies dynamically filled the pull apart margin according to a detailed analysis of sedimentary facies palaeoflow directions clast compositions and downstream changes in clast size the southwestern basin fills comprise three facies associations representing distinctive depositional environments 1 facies association f a i volcaniclastics dominated alluvial fan 2 f a ii alluvial plain and 3 f a iii floodplain lake the matrix supported and clast supported conglomerate f a i is indicative of deposition in alluvial fans the hollow fill or sheetlike deposits encased in purple siltstone f a ii are suggestive of channel or sheetflood deposition in an alluvial plain the dominant purple and green mudstone f a iii indicates deposition in floodplain and lacustrine environments the distribution of facies associations represents a basinward change in depositional environments from alluvial fan to lacustrine systems the succession is divisible into three large scale lateral and partly vertical units the southernmost ochang 1 5 km thick the medial baeti 1 km thick and the northernmost kugokri units 0 5 km thick on the basis of basinal structure and changes in clast composition and lithofacies the ochang baeti transition reflects synchronous development of the alluvial to lacustrine systems in a pull apart margin this succession development is attributable to the basinal faults progressed during the basin development the baeti kugokri transition recorded the changes in clast composition and lithofacies which was due to the progressive shifting in basinal setting from a pull apart margin to a strike slip margin unlike that of the strike slip margins clast composition of the pull apart marginal fills reflects adjacent source rock lithology in the pull apart margin alluvial to lacustrine systems show a transverse to margin channel network 060 135 converging into the southwestern depocentre although the basin is of strike slip origin sedimentation patterns in the pull apart margin are suggestive of relatively synchronous developments of the alluvial to lacustrine systems reflecting the lithology of the adjacent source rock and subsurface structure of normal slip dominant faults

toward better paleocarbonate ion reconstructions new insights regarding the caco3 size index 1 the reconstruction of paleocarbonate ion concentrations provides an important constraint on the contribution of the caco3 cycle to the decrease in atmospheric co2 content during glacial time such reconstructions have been challenging because each of the existing paleo co32 indices has serious limitations in this study we reexamine the broecker clark caco3 size index by analyzing the 20 m 20 to 38 m and 38 to 63 m fractions in sediments from the ontong java plateau and the ceara rise scanning electron microscope analyses demonstrate that the less than 20 m caco3 is dominated by coccoliths and the greater than 20 m caco3 is dominated by foraminifera our results clearly indicate that the coccoliths are far more resistant to dissolution than the foraminifera referenced to a core top sample from 2 31 km depth in a core top sample from 4 04 km depth on the ontong java plateau 70 of the foraminifera caco3 was dissolved as opposed to only 7 of the coccolith caco3 we found that the dissolution of foraminifera shells did not produce a significant amount of fragments smaller than 63 m in size and thus the broecker clark size index is not a measure of the extent of fragmentation rather it is a measure of the extent of differential dissolution of foraminifera relative to coccoliths on the basis of these results we propose a new dissolution index which involves the ratio of dissolution susceptible foraminifera caco3 to total caco3

sequence stratigraphy and marine to nonmarine facies architecture of foreland basin strata book cliffs utah u s a the desert member of the blackhawk formation and the castlegate sandstone in the book cliffs of utah and colorado were analyzed to develop a model of sequence stratigraphy and facies architecture in foreland basins stratal architecture of these rocks is controlled by two regionally extensive surfaces of incision and subaerial exposure interpreted as major sequence boundaries and at least six surfaces of incision and subaerial exposure with more limited lateral extent interpreted as minor sequence boundaries each sequence boundary is a regionally correlatable single surface major sequence boundaries can be traced from marine into proximal alluvial plain environments sequence boundaries have different physical expressions depending upon where in the basin they are observed strata beneath sequence boundaries are unrelated to strata above and time lines cannot be carried across these boundaries flooding surfaces called parasequence or parasequence set boundaries also exert an important control on facies architecture based on parasequence stacking patterns position of sequence boundaries and facies associations the desert member and castlegate sandstone have been divided into sequences with durations of 200 000 to 300 000 yr there are an order of magnitude more sequences in this interval than are predicted by the global sea level chart of haq et al 1988 the major sequences have been divided into the following systems tracts or sequence sets 1 grassy highstand sequence set below the desert sequence boundary named for the grassy member of the blackhawk formation 2 desert lowstand transgressive and highstand systems tracts between the desert and castlegate sequence boundaries 3 castlegate lowstand sequence set resting on the castlegate sequence boundary and 4 castlegate transgressive systems tract parasequence stacking patterns suggest that the grassy highstand sequence set and the desert highstand systems tract were deposited during a relative rise in baselevel the grassy highstand sequence set is punctuated by minor relative falls in baselevel both of these stratal units contain thick

ventilation of the glacial deep pacific ocean measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial pacific deep sea cores suggest that during peak glacial time the radiocarbon age of water at 2 kilometers depth was no greater than that of today these results make unlikely suggestions that a slowdown in deep ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon 14 14c to carbon in the atmosphere and surface ocean during glacial time comparison of 14c ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14c to c ratio difference was not substantially different from today s

sedimentological and palaeohydrological responses to tectonics and climate in a small closed lacustrine system oligocene as pontes basin spain a small closed lacustrine system developed during the restraining overstep stages of the oligocene as pontes strike slip basin spain the increase in basin accommodation and the headward spread of the drainage which increased the water input triggered a change from shallow holomictic to deeper meromictic conditions the lower shallow lacustrine assemblage consists of mudstone carbonate cycles recording lacustrine palustrine ramp deposition in a saline lake high sr content in some early diagenetic calcites suggests that aragonite and calcite made up the primary carbonate muds early dolomitization took place together with widespread pedogenic activity the upper deep freshwater lacustrine assemblage includes bundles of carbonate clay rhythmites and fine grained turbidite beds primary calcite and diagenetic siderite make up the carbonate laminae the mg content of the primary carbonates records variations in mg ca ratios in lacustrine waters d 18 o and d 13 c covariance trends in calcite reinforce closed drainage conditions d 18 o data indicate that the lake system changed rapidly from short lived isotopically light periods i e from seasonal to pluriannual to longer steadystate periods of heavier d 18 o i e from pluriannual to millennial the small d 13 c changes in the covariant trends were caused by dilute inflow changing the contributions of dissolved organic carbon in the system and or internal variations in lacustrine organic productivity and recycling in both shallow and deep carbonate facies sulphate reduction and methanogenesis may account respectively for the larger negative and positive d 13 c shifts recorded in the early diagenetic carbonates calcite dolomite and siderite the lacustrine system was very susceptible to high frequency climatically forced water balance variations these climatic oscillations interfered with the lowfrequency tectonic and morphological changes in the basin catchment this resulted in the superposition of high order depositional mineralogical and geochemical cycles and rhythms on the lower order lacustrine infill sequence

tectonic event stratigraphy in a fluvio lacustrine strike slip setting the boss point formation westphalian a cumberland basin maritime canada abstract the boss point formation westphalian a was deposited in a rapidly subsiding strike slip basin the formation about 800 m thick comprises alternate braidplain and lacustrine facies associations sixteen megacycles defined by sharp but nonerosive lacustrine flooding surfaces each comprise a lower lacustrine and an upper braidplain package braidplain deposits invariably scour deeply into lacustrine strata the lacustrine facies association consists of very fine sandstone mudstone claystone coal and limestone deposited in shallow hydrologically open freshwater lakes lakes were filled by small elongate river dominated deltas and by suspended and biogenic sediment sand rich deltaic facies represent mouth bar subaqueous levee crevasse channel and splay and straight and sinuous distributary channel subenvironments evidence of wave reworking is very scarce interdeltaic areas accumulated platy gray mudstone as interdistributary bays aggraded to water level they were subject to oxidation and pedogenic modification forming bright colors prismatic desiccation fabrics pseudo anticlines and calcretes thin but laterally extensive possibly up to 40 km abandonment facies comprising black organic rich mudstones coals and ostracod limestones suggest periods of clastic starvation dunes current ripples and rarely adhesion ripples are common on the top surfaces of braidplain sandstone packages preserved beneath a blanket of lacustrine mudstone rare oscillation ripples attest to localized reworking of the fluvial sand during or soon after flooding flooding surfaces can be traced for 12 km and possibly up to 40 km and are attributed to instantaneous subsidence along the northwest margin of the basin during major earthquakes one locality preserves evidence of abrupt 180 paleoflow reversals above and below a lacustrine unit this is interpreted to record abrupt basin tilting first to the northwest forming a lake that filled from the southeast followed by tilting to the southeast we interpret boss point megacycles to reflect the interaction of episo ic tectonic subsidence with longer term changes in sediment supply controlled by cyclical climatic variation in the milankovitch band during periods of pronounced wet dry seasonality when clastic supply was high sandy and gravelly braidplain deposits prevailed and any lakes that formed by earthquake related subsidence were rapidly filled during more humid periods higher vegetative cover greatly reduced clastic supply and lakes persisted for many thousands of years hydrologic changes accompanying the transition from relatively humid to strongly seasonal wet dry periods might have resulted in the deep fluvial erosion observed at the base of each braidplain package

climatic and environmental indications of carbon and oxygen isotopes from the lower cretaceous calcrete and lacustrine carbonates in southeast and northwest china abstract carbon and oxygen isotopic ratios were determined from 100 lower cretaceous samples from four carbonate bearing facies in southeast se and northwest nw china for palaeoclimatic and palaeoenvironmental analyses the samples were interpreted as sediments within sublithofacies of distal alluvial ponds sf1 open shallow lakes sf2 littoral lakes sf3 and marshes sf4 results of analyses show in se china 13c values range between 5 0 and 3 0 with a negative trend through time and 18o values are all negative 19 3 7 4 in nw china 13c values range from 4 0 to 4 0 with periodic change and 18o values range between 18 0 and 1 5 both relatively heavy values and pronounced covariances of most 13c and 18o indicate semiarid climate and domination of closed brackish lakes marshes and ponds in nw and se china during the early cretaceous of them positive 13c 0 0 to 4 0 and relatively heavy 18o 5 0 to 1 5 values suggest interruptions of arid evaporation in intermittences of the early hauterivian in sw fujian of the middle aptian in west jiuquan basin of the late aptian in sw ordos basin and of the late aptian early albian in liupanshan basin in a short interval of the early aptian the hot and humid climate occurred in local sw zhejiang by high kaolinite content and in west jiuquan basin by warm flora could be an exception particularly extremely negative 18o values mainly 19 0 9 0 indicate relatively low temperature in se fujian in the berriasian barremian in liupanshan basin in the late aptian in sw ordos basin in the late albian and in west jiuquan basin in the mid late aptian which is supposed to attribute to the presence of 2500 m 4500 m in elevation more positive values and more covariance ratios of 13c and 18o in nw china than in se china and in mainland china than in america indicate a arider climate in former than in later probably attributing to the palaeogeography in distance to sea a tentative correlation of the early cretaceous 13c value excursion of calcretes shows a good compatibility between marine oaes and terrestrial carbonate sediments and between nw china and america continents implying a global response to carbon cycle in both marine and terrestrial environments the feature suggests the potential of global correlation and application of terrestrial calcrete 13c excursions in pre cenozoic