late quaternary climate variability and vegetation response in ziro lake basin eastern himalaya a multiproxy approach abstract pollen phytolith and stable carbon isotopic records provide new insights into the palaeoenvironmental and palaeoclimatic changes in ziro lake basin sub himalayan arunachal pradesh india since pre lgm time phytoliths record a minor change in grass woodland cover and appear to be more sensitive than pollen grains to climate fluctuations both pollen and non pollen palynomorph data suggest prevalence of a dense c3 species dominated moist semi evergreen forest in the area until the lgm which shows conformity with 13c data the phytolith assemblage indicates an alteration in forest cover with expansion of c4 grasses during the lgm the study further indicates a climatic amelioration with intensification of south west monsoon during 10 2 3 8 ka and an expansion of forest cover after 3 8 ka there was a rising trend of dryness shrinkage in forest cover and a slight increase in c4 species while c3 plants dominated ecosystem variability also points towards a hydrological transformation in the area since pre lgm time application of coexistence approach on pollen data reveals that prior to the lgm the mean annual temperature and mean annual precipitation were approximately 19 3 0 001 c and 1925 15 mm respectively between 10 2 and 3 8 ka mat was about 19 4 0 5 c while map was 1901 41 3 mm between 3 8 and 1 2 ka and onwards a slight increase in mat 0 3c was observed with further decrease in map to 1861 33 4 mm during pre and post lgm times mat was more or less similar in the ziro lake basin which increased gradually after 3 8 ka and was 1 2 c higher than today prior to the lgm map was higher than the present day by 94 mm between 10 2 and 3 8 ka by 70 mm and since 3 8 ka onwards by 30 mm showing a tendency of gradual decline suggesting a consequent increase in dryness

intensified monsoon and spatiotemporal changes in precipitation patterns in the nw himalaya during the early mid holocene we have undertaken a high resolution palaeoclimate reconstruction on radiocarbon dated palaeolake sediments from the spiti valley nw himalaya this site lies in the climatically sensitive winter westerlies and indian summer monsoon ism transitional regime and provides an opportunity to reconstruct the precipitation seasonality and extreme precipitation events that are characterised by intensified erosion the lake sediments reveal distinct lithofacies that provide evidence of changes in depositional environment and climate during early to mid holocene 8 7 6 1 cal ka bp we have identified three stages during the period of lake s existence the stage i 8 7 7 6 cal ka bp is marked by lake establishment stage ii 7 6 6 8 cal ka bp by sustained cooler periods and weakened summer monsoon and stage iii 6 8 6 1 cal ka bp by a shift from colder to warmer climate with stronger ism we have identified several short term cooler periods at ca 8 7 8 5 8 3 and 7 2 6 9 cal ka bp based on an overview of regional climate records we show that there is an abrupt switch in precipitation seasonality ca 6 8 cal ka bp that is followed by the onset of the intensified monsoon in the nw himalaya

topography relief and trmm derived rainfall variations along the himalaya 1 along the southern himalayan topographic front the indian summer monsoon modulates erosive processes and rates to investigate the influence of topography and relief on rainfall generation and resultant erosion we processed satellite rainfall amounts for the last 8 years 1998 2005 from the tropical rainfall measurement mission trmm based upon a spatial resolution of 5 5 km for the himalaya we identify 1 the spatial distribution of rainfall and 2 the large scale relationships between topography relief and rainfall locations our results show two distinct rainfall maxima along strike in the himalaya the first outer rainfall peak occurs along the southern margin of the lesser himalaya within a narrow band of mean elevation 0 9 0 4 km and mean relief 1 2 0 2 km the second discontinuous inner band typically occurs along the southern flank of the greater himalaya elevation and relief both 2 1 0 3 km

clinoforms and clinoform systems review and dynamic classification scheme for shorelines subaqueous deltas shelf edges and continental margins abstract clinoforms are inclined and normally basinward dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems the study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir seal and source rocks along shoreline to basin floor profiles here we review clinoform research and propose a more systematic description and classification of clinoforms this is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions together with the genesis drivers and dynamics of their constituent sedimentary units four basic clinoform types are here distinguished in delta shorelines lacustrine and marine environments on the basis of their overall spatial and temporal scale morphology outbuilding dynamic and geodynamic and depositional setting 1 2 delta scale clinoforms which in turns are sub divided into shoreline and delta scale subaqueous clinoforms 3 shelf edge clinoforms and 4 continental margin clinoforms delta scale clinoform sets are tens of metres high and typically represent 1 103 kyr with progradation rates ranging from 1 000 100 000 m kyr for shorelines and subaerial deltas to 100 20 000 m kyr for subaqueous deltas shelf edge clinoform sets are hundreds of metres high and are nucleated and accreted in 0 1 20 myr usual progradation rates of 1 100 m kyr by successive cross shelf transits of delta scale clinoforms continental margin clinoform sets are thousands of metres high hallmark key geodynamic crustal boundaries e g continent ocean transition and slowly prograde basinwards in ca 5 100 myr with typical rates of 0 1 10 m kyr as a consequence of the very different progradation rates and of the difficulty of large scale clinothems to backstep during transgressions shorelines are the most dynamic clinoforms with regards to position continental margins the least and shelf edges are intermediate shortly after a transgression therefore the four clinoform types may prograde synchronously along shoreline to abyssal plain transects forming compound clinoform systems during the subsequent regressive cycle however due to the dissimilarity in progradation rates different clinoform types will normally merge progressively with each other giving rise to hybrid clinoforms e g shelf edge deltas and fewer depositional breaks in slope are distinguished along a single shoreline to abyssal plain transect overall all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum regulated by the cyclical backstepping of the smaller scale system within natural progradational retrogradational cycles of larger scale clinothem outbuilding all clinothem types may show either an accretionary active or draping passive style depending on the proximity to the sediment source draping clinothems are nearly always composed of condensed fine grained sediments while actively accreting clinothems can be composed of predominantly coarse grained i e reservoir forming or predominantly fine grained i e non reservoir lithotypes a novel hierarchical classification scheme for both recent and ancient clinoforms is here proposed consisting of 12 classes the four basic clinoform types delta scale shoreline delta scale subaqueous shelf edge and continental margin are sub divided into eight accretionary active and draping passive sub types 8 division each accretionary sub type is then sub divided into a sandstone prone and mudstone prone variant 12 division which can be at least tentatively predicted on the basis of the clinoform morphology even in the absence of direct stratigraphic logs

holocene vegetation and climatic variations in central india a study based on multiproxy evidences palynology texture mineralogy geochemistry and magnetic susceptibility analysis of a 2 m deep sediment core from padauna swamp southeastern madhya pradesh infers that between 8600 and 7500 cal yr bp a warm and relatively less humid climate prevailed with open tree savannahs dominated by grasses followed by sedges artemisia and members of chenopodiaceae amaranthaceae with scanty trees viz schrebera aegle marmelos and sterculia urens this is well supported by lower organic to carbonate carbon ratio coarser texture having relatively low cia and magnetic susceptibility values and presence of some primary minerals between 7500 and 6250 cal yr bp the tree savannahs were succeeded by open mixed deciduous forests with the invasion of a few more trees viz madhuca indica holoptelea emblica officinalis mitragyna parvifolia and members of anacardiaceae in response to onset of a warm and humid climate a considerable rise in organic carbon generated from the degradation of plentiful biomass along with increase in clay content with signs of kaolinite and increase in immobile over mobile elements with slightly higher cia and magnetic susceptibility values also suggest climatic amelioration the presence of ruderal plants such as artemisia cannabis sativa and cheno am further infers initiation of human activities in the region between 6250 and 2800 cal yr bp the mixed deciduous forests became more diverse and dense subduing grasses and other herbaceous elements sporadic incursion of shorea robusta sal in forest floristic was recorded around 5000 cal yr bp the overall change in the vegetation mosaic reflects that a warm and more humid climate prevailed in the region probably on account of invigoration of southwest monsoon this observation is further corroborated by other proxy data showing a spurt in organic inorganic carbon ratio increase in clay content with matured mineralogy significantly higher cia and magnetic susceptibility values since 2800 cal yr bp onwards the modern sal dominated deciduous forests were established indicating continuation of warm and more humid climate including timely arrival of sw monsoon coinciding with the shedding of sal seeds as they are viable for a very short period

compositional variations in calciturbidites due to sea level fluctuations late quaternary bahamas piston cores in tongue of the ocean bahamas revealed an alternating sequence of periplatform ooze and bankderived turbidites of the past 5 glacial and interglacial periods by using the point count method we have analyzed the composition of the turbidite sediment variations in the bank derived fraction are clearly linked to the glacial interglacial cycles nonskeletal components pellets ooids grapestones are most abundant in interglacial turbidites while skeletal components calcareous algae peneroplids and reef builders dominate in glacial turbidites we attribute this pattern to the exposure and flooding of the surrounding carbonate platforms during late quaternary sea level cycles because nonskeletal sediment is produced in the interior of the platforms its growth and subsequent export to the flanks are at a maximum when the banks are flooded i e during interglacial periods during glacials skeletal grains dominate because the banks are exposed and carbonate production is limited to a narrow belt of skeletal sands and fringing reefs the resulting compositional signal appeared to have a good correlation with aragonite variations in the periplatform ooze between the turbidites further compositional variation parallels the change in turbidite frequency described earlier highstand bundling frequency and composition of turbidites are both unaffected by diagenesis and therefore provide an excellent monitor of sealevel fluctuations

facies changes in the triassic jurassic boundary interval in an intraplatform basin succession at csővar transdanubian range hungary a continuous pelagic marine triassic jurassic boundary section is exposed in newly excavated trenches in the surroundings of cso var ne of budapest hungary in the late triassic this area was located close to the offshore margin of the dachstein carbonate platform system that was segmented by intraplatform basins based on detailed facies analysis of the rhaetian hettangian platform foreslope basin succession a long term second order and superimposed shorter term third and fourth order changes of the relative sea level could be revealed after a period of highstand platform progradation in the late norian large amounts of larger plant fragments and sporomorphs of continental plants mark a significant sea level drop in the early rhaetian presumably exposing large parts of the platform a renewed transgression led to the formation of smaller build ups fringing the higher parts of the previous foreslope crinoid meadows may have occupied the slopes a potential source area of the bioclastic carbonate turbidites rising relative sea level that followed the marked early rhaetian lowstand is also reflected in the general facies trend from lithoclastic debris flows and proximal to the very distal turbidites and radiolarian basin facies up to the earliest hettangian meter scale high frequency probably fourth order deepening upward cycles probably indicating sea level oscillation could also be recognized within this interval at the base of the last rhaetian cycle about 10 m below the assumed tr j boundary the amount of bioclasts including conodonts drastically decreases biotic decline in the radiolarian basin facies characterizing the topmost part of this cycle a significant negative shift in both the d 13 ccarb and d 13 corg and a marked decrease in the organic material toc was recognized that can be interpreted to reflect reduced productivity in connection with the triassic jurassic boundary event it is overlain by a lithoclastic horizon then by laminites where the last conodonts were found the next significant facies change in the early hettangian is marked by appearance of redeposited oncoid grapestone beds suggesting survival of shallow marine carbonate factories in the neighborhood of the basin and the end of the rhatian to earliest hettangian sequence third order the recurrence of basin facies above this interval indicates a new short term third order transgression and continuation of the long term second order deepening trend in the early hettangian d 2004 elsevier b v all rights reserved

monsoon variability and chemical weathering during the late pleistocene in the goriganga basin higher central himalaya india stable isotope analysis along with radiocarbon and luminescence dating of late pleistocene lacustrine deposits at burfu in the higher central himalaya are used to interpret hydrologic changes in the lake basin from 15 5 ka to 14 5 ka the burfu lake was largely fed by melting glaciers a warming event at 14 5 ka suggests an enhanced monsoon and increased carbonate weathering from 13 5 ka to 12 5 ka the isotopic data suggest large amplitude climate variability following this the isotope data suggest a short lived abrupt cooling event comprising a 300 yr intense cool period followed by a 500 yr interval of moderate climate a shift in isotope values at 11 3 ka may signify a strengthening monsoon in this region the inferred climatic excursions appear to be correlative at least qualitatively with global climatic events and perhaps the burfu lake sequence provides regional evidence of globally recorded excursions this study also suggests a potential use of radiocarbon ages in specific environments as a paleoenvironmental proxy

the continental margin of the mesozoic tethys in the western alps abstract most of the structural units of the western alps were derived from the european continental margin of the ligurian ocean a segment of the mesozoic tethys ocean their mesozoic palaeotectonic and stratigraphic evolution bears witness of the following main stages 1 deposition of the triassic platform carbonates essentially prerift but nevertheless bearing the imprint of some extensional movements 2 the liassic middle jurassic rifting corresponds to the creation of a horst and graben system with especially tilted blocks and hence a shoal and basin palaeogeography but without a preliminary doming event 3 the late jurassic early cretaceous opening and spreading of the ligurian ocean began with a general collapse of the continental margin thermal subsidence latest middle jurassic and earliest late jurassic in this paper emphasis is given to the refting derived structures more especially to the major tilted crustal blocks a few tens of kilometres wide which can be either reconstructed or directly observed the rifting stage lasted roughly 40 m y with the alternation of extensional tectonic phases and of relatively quiet periods during the extensional phases movements along fault planes and related episodes of tilting were followed by sudden and rapid episodes of subsidence the latter may be interpreted as resulting from the isostatic and thermal readjustment that follows a phase of stretching of the crust and of the lithosphere the tectonic evolution of the margin continued but decreased during the late jurassic early cretaceous oceanspreading stage tectonic activity resumed in the late cretaceous this probably resulting from the beginning of contraction of both the ocean and the continental margin leading progressively to the continental collision in the tertiary

holocene aridification of india 1 spanning a latitudinal range typical for deserts the indian peninsula is fertile instead and sustains over a billion people through monsoonal rains despite the strong link between climate and society our knowledge of the long term monsoon variability is incomplete over the indian subcontinent here we reconstruct the holocene paleoclimate in the core monsoon zone cmz of the indian peninsula using a sediment core recovered offshore from the mouth of godavari river carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the cmz and document a gradual increase in aridity adapted vegetation from 4 000 until 1 700 years ago followed by the persistence of aridity adapted plants after that the oxygen isotopic composition of planktonic foraminiferglobigerinoides ruberdetects unprecedented high salinity events in the bay of bengal over the last 3 000 years and especially after 1 700 years ago which suggest that the cmz aridification intensified in the late holocene through a series of sub millennial dry episodes cultural changes occurred across the indian subcontinent as the climate became more arid after 4 000 years sedentary agriculture took hold in the drying central and south india while the urban harappan civilization collapsed in the already arid indus basin the establishment of a more variable hydroclimate over the last ca 1 700 years may have led to the rapid proliferation of water conservation technology in south india

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

sea level highstand and lowstand shedding related to shelf margin aggradation and emersion upper eocene oligocene of maiella carbonate platform italy abstract sequence stratigraphic analysis of the upper eocene lower oligocene of the maiella carbonate platform allows the timing of shelf aggradation and erosion to be linked to shedding onto the slope and relative sea level stands the shelf was eroded during lowstands and the lowstand slope sediments are thin channelized lithic breccias with clasts eroded from an emerged reef tract highstand shedding of skeletal sands from the inner shelf resulted in thick coarsening and thickening upward successions of turbidites

late holocene drought responsible for the collapse of old world civilizations is recorded in an italian cave flowstone a severe drought in parts of low latitude northeastern africa and southwestern asia 4200 yr ago caused major disruption to ancient civilizations stable isotope trace element and organic fluorescence data from a calcite flowstone collected from the well watered alpi apuane karst of central western italy indicate that the climatic event responsible for this drought was also recorded in mid latitude europe although the timing of this event coincides with an episode of increased ice rafted debris to the subpolar north atlantic the regional ocean atmosphere response seems atypical of similar holocene ice rafting events furthermore comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer term climate anomaly

late quaternary environmental and sea level changes from kolleru lake se india inferences from mineral magnetic geochemical and textural analyses abstract the present study employs mineral magnetic geochemical and textural parameters to elucidate the climate and sea level change signatures from kolleru lake sediments representing the inter deltaic part of the krishna godavari sedimentary basin kg basin for this purpose four cores were obtained which included significant peat the conventional radiocarbon dating suggested that the peat formation took place during 9 ka 6 ka with an average sedimentation rate of 0 31 cm y thermomagnetic analysis identifies titanomagnetite magnetite and hematite as the dominant magnetic mineralogy of the kg basin sediments the variation in magnetic mineralogy is related to paleoclimatic and paleoenvironmental processes the transitions between titano magnetite and hematite coincide with peat layers of the cores as indicated by sirm saturation isothermal remanent magnetization magnetic susceptibility and s ratio defined by irm 0 3t sirm values the various mineral magnetic parameters and s ratio along with major elemental concentrations of ti al fe and zr show signatures of an arid event before 10 ka between 9 ka 8 ka periods and during the last 5 5 ka the overall climate of warm and humid type was inferred from 10 ka to 9 ka which correlates with early holocene optima and 6 ka to 5 5 ka of middle holocene the presence of evaporite crystals in the lowermost part of the cores corroborated by mineral magnetic and geochemical proxies indicates sub aerially weathered facies of the arid late pleistocene similarly the peat layers rich in mangrove pollen indicate sea level changes between 10 ka and 6 ka the sub surface position of the pleistocene weathered layer and the holocene peat layer suggests tectonic subsidence of the area which is situated over the basement graben known as gudiwada sub basin

evolution of a high relief carbonate platform slope using 3d digital outcrop models lower jurassic djebel bou dahar high atlas morocco abstract seismic scale continuous exposures of an early jurassic carbonate platform located in the southern high atlas of morocco provide detailed quantitative information about the lithofacies and stratal geometries of an aggrading retrograding and prograding steeply inclined slope system that evolved in an active intracratonic rift basin aggradational backstepping and progradational outer platform to slope transects are each characterized by distinct lithological features and stratal patterns a digital outcrop model was constructed using real time kinematic global positioning system and lidar storing information on recorded stratal surfaces including lithofacies information from these data 3d models of the slope system could be built in the study area four stages of slope development are recognized stage 1 corresponds to a low relief carbonate platform characterized by widespread sub wave base depositional conditions stage 2 developed as an aggrading to retrograding platform during which the platform built considerable relief in addition a massive organically bound upper slope fringe formed dominated by coral sponge microbial boundstone the in situ boundstone consisted of irregular wedges that accreted on the upper slope down to 140 m below the platform break after a period of sediment starvation stage 3 involved a major backstepping of sediment deposition seventy meter high clinoforms prograded from the center of the platform across the platform top until reaching the relict platform break of stage 2 subsequently progradation occurred basinward as indicated by the spilling of lobes down the existing slope deposits of stage 2 limited progradation along with the reestablishment of the in situ coral sponge microbial boundstone on the upper slope led to the progressive steepening of the slope profile to dips of 23 clinoforms are planar in the upper part of the slope and concave upwards in the lower part with a total relief of over 460 m stage 4 is observed only in the lower slope and adjacent basin coarse detrital carbonate deposits form lens shaped aprons that grade basinward into kilometer scale lobes that alternate with thick wedges of basinal fallout sediments syndepositional extensional faults operating in the subsurface affected sedimentation along the lower slope profile throughout the four stages and are expressed in the stratal patterns through growth strata in monoclinal folds three dimensional digital outcrop models reconstructing the architecture of the slope system allowed quantification of slope geometries and stratal relationships and spatial distribution of sedimentary bodies the digital model enhanced the understanding of the depositional changes during slope evolution and also led to observations on for example angular relationships that would have been difficult to detect without the digital approach the evolution from aggrading to retrograding prograding and retrograding was strongly influenced by synsedimentary tectonics within an intracratonic rift basin the tectonics generated irregular distribution of accommodation space variably interfering with eustatic sea level movement this in combination with the character of lithofacies types and style of sedimentary processes along the slope such as in situ boundstone growth and gravity driven resedimentation processes directly controlled carbonate slope architecture and stratigraphy of the djebel bou dahar and influenced stratal anatomy and lithofacies distribution

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

late pleistocene holocene vegetation and indian summer monsoon record from the lahaul northwest himalaya india abstract the high resolution holocene paleomonsoon records from northwest nw himalaya are limited the carbon isotope 13 c total organic carbon toc and pollen analysis were therefore carried out from a peat lake sediment sequence developed in alpine meadows of the chandra valley lahaul nw himalaya in order to reconstruct centennial to millennial scale vegetational changes and indian summer monsoon ism variability during the holocene the chronology of peat lake sediments is constrained with 9 ams 14 c dates the recovered non arboreal pollen nap suggested that during holocene alpine desert steppe meadows and shrubs growing along the stream had developed in the lahaul valley whereas arboreal pollens ap e g pinus quercus cedrus and ulmus presently growing in the southern hill slopes of pir panjal range indicated moisture carrying monsoonal air flow from the south the increased 13 c and low toc values between 12 880 and 11 640 calibrated years before present cal yr bp suggested weakening of ism and low organic carbon production corresponding to the younger dryas yd cold event the gradual depletion in carbon isotope ratio from 11 640 to 8810 cal yr bp indicated enhanced precipitation in the chandra valley in response of increased ism strength in early holocene the short spell of cold and dry climate with gradual decrease in ism intensity between ca 10 398 and 9778 cal yr bp is closely linked with bond event 7 the other prominent cold dry events recorded in present study are i 8810 to 8117 cal yr bp roughly corresponding to global 8 2 ka cold event ii 4808 to 4327 cal yr bp closely preceding the global 4 2 ka cold arid period and iii 1303 to 1609 cal ad corresponding to little ice age lia event the expansion of thermophillous broad leaved taxa viz betula utilis alnus nepalensis quercus semicarpifolia and juglans regia and effective growth of meadow vegetation such as grasses caryophyllaceae and artemisia along with marshy elements i e polygonum and liliaceae between 6732 and 3337 cal yr bp marked warm and wet holocene climate optimum hco period the warm and moist climate from 1158 647 cal yr bp corresponded with global medieval warm period mwp

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

understanding the geological record of carbonate platform drowning across rifted tethyan margins examples from the lower jurassic of the apennines and sicily italy abstract in the geological record a drowning process is documented by various types of shallow water to pelagic or shallow water to mixed benthic pelagic carbonate transitions drowning unconformities are paraconformities to disconformities to angular unconformities and their drowning surfaces range from planar to highly irregular morphologies drowning successions display a mix of products of both the benthic and pelagic carbonate factories these successions can be also bounded by unconformities drowning unconformities and drowning successions are contrasted through a description and discussion of examples of escarpment bounded platforms from the jurassic of the northern apennines and subordinately from sicily and other tethyan sectors the areal distribution of drowning unconformities and successions is discussed with reference to a complex depositional system whose architecture was the product of the rift induced fragmentation of a regional hettangian carbonate megabank the examples in this study show drowning unconformities to be exclusive to intrabasinal highs while drowning successions are found both on highs and in hangingwall basins drowning unconformities with their long associated hiatuses and drowning successions are often seen to merge laterally into one another over very short distances on the same intrabasinal high the deposits of the drowning succession are sometimes missing on the top of the platform while they are found forming clinoforms along its flanks evidence that sediment could be permanently swept from the highs in these depositional systems at this stage

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

environmental gradients in carbonate sediments and rocks detected by correspondence analysis examples from the recent of norway and the dinantian of southwest england continuous sedimentary gradients are only crudely expressed by standard facies and microfacies methods which are more appropriate to situations where changes occur in relatively discrete steps in carbonate sediments and rocks continuous gradients are often represented by the arrangement of component grain types in a relay that is a systematic shifting of the relative importance of the components subdivision of such relays into micro facies can only be arbitrary correspondence analysis is shown to be useful for detecting isolating and describing relays particular use is made of the arch effect in which samples and components from data sets with a strong unidimensional structure a relay plot in the form of an arch in the plane of the first two factor axes a relay index indicating the position of samples in the relay can be extracted from the analysis and plotted on maps and stratigraphic logs to reveal details of the sedimentary gradient in areal and or stratigraphic context examples are given from i recent shallow marine carbonate sediments from northern norway illustrating a relatively simple depositional setting where surface sediments are viewed in plan and ii lower carboniferous carbonates of southwest england representing a more complex regional study of a particular stratigraphic interval viewed in cross section in both examples the relays can be related to identifiable environmental gradients

systems tracts and depositional sequences in a carbonate setting a study of continuous outcrops from platform to basin at the scale of seismic lines abstract the application of sequence stratigraphy concepts to carbonates is feasible and this paper presents an example of its successful application the continuity and lateral extent of outcropping sedimentary sections observed at the scale of a seismic line from platform to basin in the southern vercors plateau western alps france confirm the validity of sequence stratigraphy concepts when applied to carbonate depositional systems from the stratal patterns displayed in outcrop we determined that carbonate lowstand systems tracts are major components in the basin even in the deep pelagic realm transgressive and highstand systems tracts are very thin a response to starvation in contrast on the shelf transgressive and highstand systems tracts are the major components carbonate lowstand and shelf margin systems tracts pinch out in the vicinity of the offlap break it clearly appears that the stratal patterns and stratal termination patterns of carbonate systems tracts especially of carbonate lowstand systems tracts are basically similar to those of siliciclastic systems tracts this study documents that carbonate platforms may provide the basin with carbonate clastics during periods of relative sea level falls and lowstand this is one of the most controversial aspects of the application of sequence stratigraphy concepts in carbonate environments a second controversial aspect of the application of sequence stratigraphy concepts to carbonate rocks is the distinction between transgressive and regressive facies cycles and depositional sequences and systems tracts this paper demonstrates that the shoreline position for carbonates which indicates the facies transgression or regression is independent of prograding or retrograding shelf breaks the stratal pattern and facies within systems tracts vary depending on the overall evolution of the accommodation space i e on their position within the transgressive and regressive cycles

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

holocene vegetation and climate change in central ganga plain a study based on multiproxy records from chaudhary ka tal raebareli district uttar pradesh india abstract pollen sediment texture and organic inorganic carbon analyses of a 2 1 m thick sediment profile from chaudhary ka tal lake of raebareli district reveals that around 8470 to 6422 cal bp grasslands comprising grasses asteraceae cheno am with interspersed forest groves of madhuca indica holoptelea integrifolia shorea robusta and acacia thrived in the region under a warmer and moderately humid climate than today this is also substantiated by the finer clay sediment with increasing concentrations of moisture and organic carbon the appearance of cerealia pollen 7500 cal bp suggests incipient agrarian practice the record of aquatic elements lemna and typha reflects the existence of lake between 6422 and 3150 cal bp the forest groves became diversified with the invasion of more trees capparis butea monosperma and symplocos reflecting a warm and more humid climate compared to the previous phase attributed to the strengthening of the sw monsoon the higher concentration of organic carbon further confirms good vegetation cover and an increase in aquatic flora depict the expansion of lake a similar vegetation scenario existed 3150 to 1110 cal bp however the forest groves became less varied due to prevailing moderately humid climate owing to weakening of the sw monsoon this is also validated by more carbonate in the sediments from 1110 cal bp a further diminishing trend of trees implies that the region supported open grasslands owing to reduced rainfall under a warm and less humid climate which is corroborated by a further increase in carbonate content

compositional variations during phases of progradation and retrogradation of a triassic carbonate platform picco di vallandro durrenstein dolomites italy in this paper data are presented on the composition of sediments deposited at the toe of slope during progradation or retreat of triassic carbonate platforms in the dolomites italy for this purpose a succession was studied from the toe of slope of a triassic carnian carbonate platform picco di vallendro durrenstein dolomites italy the microfacies analysis of selected calciturbidites sequences revealed a reduced input of oncolites and ooids during progradation and an increase in clasts the main input however was derived from the reefs on the platform retrogradation of the platform showed an increase of filaments and radiolarians open ocean biota as well as carbonate mud and a reduced input of grains that originated within the reefs on the platform both during progradation and retrogradation parts of the platform were flooded and could produce excess sediment that could be exported to the surrounding basins however the absence of platform interior biota documents that progradation occurred from sediments of the reefal belt probably during relative sea level lowstands carbonate composition varies systematically with toe of slope progradation retrogradation and thus argues for carbonate production as the main driver of the geometries observed at the toe of slope

facies architecture of an early jurassic carbonate platform slope jbel bou dahar high atlas morocco the plateau of jbel bou dahar high atlas morocco represents an outstanding example of a well preserved early mesozoic carbonate platform field observations of the large scale sedimentary structures and the arrangement of lithofacies associations within the mid and lower slope were combined with detailed microfacies analyses and gamma ray measurements the investigations were carried out in order to 1 resolve the sequence stratigraphic architecture of the slope and 2 reconstruct the sediment export patterns and depositional processes related to high frequency sea level variations the slope strata are arranged into two different types of lithofacies associations that are bounded by characteristic discontinuities and show a specific occurrence along the investigated slope section the steep 8 18 mid slope is dominated by thick to medium bedded limestone successions that were able to maintain a high angle of repose due to their detrital composition the sediment packages are bounded by basal low angle unconformities and wedge out within the lower slope or thin into the adjacent basin as single carbonate layers the sediments are characterized by coarse grained and poorly sorted floatstones to rudstones which show low gamma ray values and contain components derived mainly from the platform edge the facies associations were interpreted as debris flow deposits that were exported during sea level lowstands when the flattened platform top and extended parts of the margin were exposed and sediment production was restricted mainly to the outer margin and upper slope section in contrast the gently dipping lower slope 4 18 is characterized by rhythmic limestone marl alternations that show increasing thicknesses with increasing distance from the platform from the lower part of the mid slope down the successions onlap the debris flow deposits forming a characteristic interfingering pattern of different lithofacies associations the medium to thin bedded carbonates of the limestone marl alternations comprise two different microfacies types 1 mudstones to wackestones with high gamma ray values and a mixed shallow marine to deep marine microfacies overlain by 2 well sorted arenitic packstones to grainstones with low gamma ray values and a shallow marine component composition the latter points to the platform interior and margin as primary source areas the shallow marine material was exported during sea level highstands when the carbonate factory included the entire platform margin and the flooded lagoons of the platform top during these periods the exported fine grained sediments could maintain only low angles of repose thus they bypassed the steep upper and mid slope sections developed into turbidites during downslope transport and were finally redeposited on the gently dipping lower slope and in the adjacent basin the architecture of the investigated slope area shows a characteristic interfingering of different facies associations that can be interpreted as genetic highstand and lowstand stratigraphic sequences the arrangement of these sequences along the slope as well as their composition were controlled by high frequency sea level fluctuations affecting the primary sediment production source area export patterns and sedimentary processes resulting in a shift of the depositional centers during different sea level stands

stratal patterns sediment composition and sequence stratigraphy at the margin of the vercors carbonate platform lower cretaceous se france abstract conventional sequence stratigraphic concepts relate the large scale stratal architecture of sediment bodies to changes in relative sea level this paper evaluates the relationship between stratal geometry and sea level stand based on a study of large semicontinuous outcrops of cretaceous carbonate platform strata in the vercors southeastern france multiple lines of evidence for sea level change are combined including stratal geometry detailed quantitative microfacies analyses and diagenetic patterns at platform top hardground surfaces the studied outcrops of the cirque d archiane show two main prograding platform tongues both over 100 m thick the stratal geometries at the boundary between these platform tongues including an apparent pinchout of a wedge of slope sediments suggest the presence of a major lowstand unconformity however this stratal boundary does not coincide with the horizon containing the most extensive meteoric alteration furthermore detailed platform to basin correlation shows that the wedge of slope sediments is not basin restricted but makes a thin drape over the platform top the sedimentologic and diagenetic evidence suggest incipient drowning of the platform at the boundary between the two main platform tongues preceded by a minor exposure event only internally the main platform tongues consist of smaller 10 30 m thick units that prograde towards the basin and aggrade on the platform top and which are interpreted as stacked highstand wedges these wedges are usually topped by hardground surfaces with minor evidence for subaerial exposure the platform top horizon with the most extensive subaerial diagenesis and erosion correlates with a distinct but relatively thin unit of lithoclastic debris on the slope a pronounced scour in the clinoforms of the vercors does not correlate with a major exposure surface on the platform top this study shows that stratal geometries alone are a rather ambiguous guide to sea level history without the accompanying sedimentologic and diagenetic evidence for sea level change most of the stratal architecture of the vercors platform can be explained by either changes in accommodation or changes in carbonate production

basin to platform chemostratigraphy and diagenesis of the early cretaceous vercors carbonate platform se france abstract cathodoluminescence petrography has been combined with bulk rock and micro sampled 87 sr 86 sr 18 o and 13 c analyses to reconstruct the diagenetic history of lower cretaceous barremian limestones exposed at the southern margin of the vercors carbonate platform in southeastern france stratigraphic and geographic trends in these analyses coupled with mass balance water rock interaction modeling have been used to constrain the chemical composition source and relative timing of the groundwaters responsible for diagenetic alteration this study was completed on the montagnette outcrop which is composed of two stacked 70 m thick units of prograding platform margin limestones that interfinger with marly basinal sediments the montagnette exposure is exceptional in that it is a single complete outcrop of basin to platform limestones that are preserved in their original lateral depositional continuity cathodoluminescence petrography indicates that the limestones have experienced a complex sequence of carbonate dissolution precipitation and fracturing events over one hundred bulk rock and micro sampled 87 sr 86 sr 18 o and 13 c analyses were completed to characterize each major event of deposition and diagenesis bulk rock analyses from the montagnette basin to platform transect exhibited no significant variations in 87 sr 86 sr 0 707523 to 0 707555 these values are consistent with estimated barremian seawater 87 sr 86 sr ratios in contrast micro sampled shell material in the platform margin and platform top deposits exhibit large variations in 87 sr 86 sr 0 706910 to 0 707450 the least radiogenic sr lowest 87 sr 86 sr occurs in shell material located toward the platform while the more seawater like ratios occur in sections without shells that are located toward the basin this pattern implies that selective diagenetic alteration of the shell material took place after basinal brines flowed up into the platform and spread out laterally the sr in the diagenetic waters was probably derived from water rock interaction with jurassic basinal sediments in the vocontian trough this conclusion is based on 1 the extremely low 87 sr 86 sr composition of shell material in the platform limestone 2 modeled co variation trends in 87 sr 86 sr 13 c and 18 o and 3 the absence of another nearby source of less radiogenic sr in the vercors region

early holocene monsoonal fluctuations in the garhwal higher himalaya as inferred from multi proxy data from the malari paleolake abstract a 4 9 m thick lake sequence formed due to the landslide damming of a stream in the semiarid garhwal himalaya was studied to understand past monsoonal variations in the region the optically stimulated luminescence osl chronology indicates that the lake existed between 12 and 7 ka ago chronologically constrained trends of sand percent organic phosphorus op apatite inorganic phosphorus aip and parameters of environmental magnetism were measured in the paleolake profile measured proxies indicate that the indian summer monsoon ameliorated in the early holocene after 12 ka cooling and it appears that all the proxies from the lake have captured this globally recognized early holocene warming four phases of wet conditions intensified monsoon are recognized at 11 5 ka 11 10 5 ka 10 9 ka and 8 7 ka with maximum uncertainties of 1000 years the wet phases are characterized by high magnetic susceptibility increased op and reduced aip in an attempt to understand the primary forcing of the sharp fluctuations in monsoonal activity in the region we show that changes in magnetic susceptibility match variations of residual atmospheric 14c suggesting a role for solar variability as an explanation of climatic variability

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

clinoform composition and margin geometries of a lower cretaceous carbonate platform vercors se france the concept of sequence stratigraphy uses the stratal geometries at the margins of carbonate platforms to define depositional sequences and systems tracts the aim of this study was to research if prograding purely aggrading and retrograding phases of a cretaceous carbonate platform showed differences in the composition and facies type of the slope sediments the vercors plateau in se france provides excellent outcrops to study this relationship continuous exposure of the platform to basin transition allowed direct examination of the margin geometries five successions were measured and sampled in great detail samples were thin sectioned and point counted using point count groups characterizing palaeoenvironments along the platform to basin transect the composition logs as well as the numerical analysis of the point count data both show a clear relationship between grain composition and stratal geometry the prograding and purely aggrading intervals are similar in composition as they are both relatively coarse grained and enriched in platform biota and limeclasts retreating units are relatively fine grained and rich in basinal grains small benthic foraminifers sponge spicules non carbonate grains and embedding material these observations suggest that the retreating intervals represent incipient drownings of the platform however rather than distinctly separated groups the different phases of platform development form a continuous range of variation between high platform input and high basinal input compared to the prograding units the purely aggrading intervals are relatively rich in peloids which may be suggestive of relatively low energy conditions on the platform during aggradation the compositional analysis also revealed significant variation in the frequency of ooids but these variations showed no relationship with the progradation aggradation or retreat of the platform

the interactions of sea level change terrigenous sediment influx and carbonate productivity as controls on upper cambrian grand cycles of western newfoundland canada the upper cambrian stratal record in western newfoundland is complex and reflects the interplay and feedback between 1 changes in third order sea level 2 episodic incursion of terrigenous fines onto the paleoshelf and 3 productivity levels of the ancient carbonate factory mixed carbonate and terrigenous clastic rocks of western newfoundland are configured in large scale third order stratal patterns called grand cycles such cycles are tens to hundreds of meters in stratigraphic thickness and appear to span millions of years grand cycles are divided here into ribbon half cycles composed principally of ribbon rock and oolitic half cycles dominated by oolite stratigraphic distribution of shale in these rocks however is not everywhere coincident with large and small scale patterns in carbonate lithofacies and it suggests that the incursion of terrigenous clay and silt onto the ancient platform must be evaluated separately in part from the dynamics of carbonate accumulation areal and stratigraphic distribution of rock cycles record shifts in facies belts on the ancient platform presumably in response to third order changes in accommodation potential meter scale cycles in carbonate lithofacies are of two types peritidal cycles that fine upward and shelf cycles that coarsen upward thick successions of shelf cycles composed of ribbon rock are interpreted as highstand deposits and are separated by a sequence boundary marked by peritidal cycles from lowstand deposits comprising thick successions of ootite shelf cycles the former mid grand cycle transitions of previous workers are thereby reinterpreted in this study as sequence boundaries the long term position of sea level and thus the degree of platform inundation influenced the health of the platform carbonate factory during times of low sea level the platform was bathed in water more saline than open ocean sea water and it had a robust non skeletal carbonate factory that was resilient to poisoning by episodic influx of terrigenous fines onto the shelf in contrast the carbonate factory during highstands was less resilient to terrigenous poisoning and was susceptible to localized drowning by the reduction in the rate of carbonate sediment production the thick shale units are therefore interpreted to represent the coincidence of and interaction between 1 incursion of terrigenous fines onto the ancient platform and 2 a weakened highstand carbonate factory unable to recover from this terrigenous poisoning

interpreting compositional variations of calciturbidites in relation to platform stratigraphy an example from the paleogene of se spain abstract in the sierra de aitana betic cordilleras southern spain a sequence of massive platform limestones outcrops study of these limestones indicates a late eocene age and has resulted in distinguishing four lithofacies associations several features suggest tilting uplift and partial exposure of this carbonate platform at the end of the eocene in a more basinward section this time interval is represented by calciturbidites the composition of which has been analysed microscopically the upper eocene turbidites are mainly composed of loose skeletal grains derived from the platform interior around the eocene oligocene boundary the composition changes abruptly and the lower oligocene turbidites mainly consist of platform derived limestone clasts and skeletal debris from the platform margin this compositional change is accompanied by a large decrease in volume of turbidite input it is concluded that both composition and amount of calciturbidites reflect the history of the adjacent carbonate platform this case study therefore provides new evidence for the mechanism of highstand shedding in carbonate depositional systems

late quaternary sediments minerals and inferred geochemical history of didwana lake thar desert india abstract variations in clastic sediment texture mineralogy of both evaporites formed at the surface and precipitates formed below the lake floor and the relative chemical activities of the major dissolved components of the chemical precipitates have allowed reconstruction of the history of salinity and water level changes in didwana lake thar desert india hypersaline conditions prevailed at about the last glacial maximum with little evidence of clastic sediments entering the lake between ca 13 000 and 6000 b p the lake level fluctuated widely the lake alternately hypersaline and fresh and clastic sediments were delivered to the lake at a low rate deep water conditions occurred ca 6000 b p and clastic influx increased abruptly the water level dropped towards 4000 b p when the lake dried briefly since 4000 b p the lake has been ephemeral with a lowered rate of sedimentation and mildly saline conditions rather like those of today this sequence of changes documented in the lake parallels changes in vegetation recorded in published pollen diagrams from both the thar and the arabian sea correlation of the various lines of evidence suggests that the climate of the last glacial maximum at didwana was dry and windy with a weak monsson circulation the monsson was re established between ca 13 000 and a little before 6000 b p and when winter rainfall increased ca 6000 b p the lake filled to its maximum depth

mid late holocene monsoonal variations from mainland gujarat india a multi proxy study for evaluating climate culture relationship a multi proxy study involving palynology phytoliths sedimentology clay mineralogy carbon isotopes and magnetic mineralogy was carried out on wadhwana lake sediments from sub humid zone of mainland gujarat to determine the mid holocene climatic fluctuations and its possible impact on the harappan culture the 1 03 m sediment profile of wadhwana lake shows five paleoclimatic phases the study reveals high lake stand during phase i 7500 5560 cal yr bp a considerable cool and moist climatic condition during phase i is inferred due to the presence of pollen belonging to wet evergreen taxa and high phytolith climatic index ic later part of phase i show gradual replacement of evergreen to deciduous pollen taxa decrease in ic value and dominance of smectite over kaolinite indicating a reduction in wet climatic condition due to decline in the precipitation and prevalence of seasonally dry climate however a large variety of madhuca meliaceae asteraceae pollen taxa abundant fresh water algae chrozophora and ceralia pollen in this period provides evidence of intensified arboriculture and agricultural activity low lake level and dry climate have been documented during phase ii 5560 to 4255 cal yr bp and are synchronous with the lake records of western indian region high values of phytolith aridity index iph high primary minerals increase in the i 13c values provide evidence for excessive dry climatic conditions at 4255 cal yr bp phase iii shows a gradual strengthening of sw monsoon after 3500 cal yr bp phase iv shows a short pulse of dry climatic conditions 3238 to 2709 cal yr bp followed by somewhat similar to present day climate for phase v the study concludes that onset of dry climate after 5500 cal yr bp is a regionally spread synchronous event that has been documented in several lake records of western india it is surmised that the urbanization in harappan civilization in north west india was coincident with the initial phase of declining rainfall of mid holocene the emergence of cultural complexity of harappan civilization should be seen as an initial adaptation to earliest phase of environmental deterioration and its subsequent decline is probably linked with the changing seasonality pattern and excessive dry climate of later phase 4200 4255 cal yr bp of mid holocene

carbonate platform to basin correlation by means of grain composition logs an example from the vercors cretaceous se france quantitative logs of grain composition for several sections of platform top and flank of the vercors carbonate platform early cretaceous se france provide platform to basin correlation with a resolution of a few metres over an area of 70 km2 grain composition was determined by point counting thin sections point count groups that characterize palaeoenvironmental realms i e open sea platform margin were defined for the platform basin trajectory grain composition logs revealed marked peaks in the number of open sea biota and peaks in ooid abundance the peaks in open sea biota correspond to back stepping intervals and deepening upward facies successions at the platform margin these peaks probably relate to incipient drowning of the platform and may be used to delineate marine flooding surface bounded sequences peaks in ooid occurrence show no relationship with the progradation aggradation or retreat of the platform apparently the oolitic sands were not part of a facies tract that shifted up and down the platform instead they represent a depositional mode that was either on or off times of prolific ooid production and shedding probably occurred during wide but shallow submergence of the platform accompanied by suitable water chemistry peaks in both ooids and open sea biota are excellent markers for platform to basin correlation as they are recorded in successions on the platform top as well as on the flank altogether the grain composition logs show that each of the lithologically rather similar platform tongues of the vercors has a unique signature or compositional fingerprint these compositional fingerprints are most helpful in evaluating the lateral extent of different stratigraphic units in outcrops of the vercors platform the physical tracing of bedding surfaces delineate wedges of toe of slope sediments that show a conspicuous thinning towards the platform however our correlation shows that these sediment bodies are not truly basin restricted wedges but have a platform top equivalent this implies that these units were at least partly deposited during high stands of sea level that flooded the platform

hydrological evolution during the last 15 kyr in the tso kar lake basin ladakh india derived from geomorphological sedimentological and palynological records abstract the tso kar lake basin in ladakh northwestern himalayas 33 18 n 78 e 4527 m a s l is located close to the modern boundary of effective moisture transport from the indian summer monsoon in order to reconstruct the possible monsoonal impact on the hydrology of the lake basin during the last 15 kyr we studied the geomorphology of the basin and combined the results with multi proxy records from tso kar lake sediments major analyses comprise geochemical data high resolution x ray fluorescence xrf mineral composition xrd aquatic pollen and non pollen palynomorphs npp although the chronological framework based on 41 14c ams dates remains speculative for the lateglacial and late holocene periods our results indicate major hydrological phases linked to regional climate variations and tectonic activity the maximum glacier advance falls within the period between the global lgm and ca 15 kyr bp while the basin remained open and may have drained along the paleo tso kar river tectonic pulses may have triggered terrace development and the closure of the lake the estimated mean vertical displacement rate accounts for 7 9 mm yr considerable summer monsoon moisture supply occurred for the periods around 12 5 kyr bp and between ca 11 5 and 8 6 kyr bp indicated by deposition of more profundal lake facies and the development of aquatic fauna and flora the lake level rise about 11 8 kyr bp was due to intensified glacier melt and summer monsoon effective moisture supply the lake reached its maximum level and extent between 8 5 and 7 kyr bp under warm moist climate conditions permafrost was absent from the basin summer monsoon influence weakened after 8 kyr bp with a short reverse trend at ca 5 6 kyr bp the lake shrank gradually after 7 kyr bp towards its lowest stand at about 4 2 kyr bp with return of permafrost activity subsequent terrace formation was probably amplified by tectonic movement the lake remained at a low level with minor fluctuations the results indicate that the orbitally driven regional climate variability is well reflected in the tso kar basin by hydrological variations considerable summer monsoon moisture seems to have influenced the area only during the early holocene the late quaternary evolution of the tso kar was controlled by the interplay of climate forces local morphodynamics and tectonic impact

hydrography and climate of the last 4400 years in a sw greenland fjord implications for labrador sea palaeoceanography a multiproxy record including benthic foraminifera diatoms and xrf data of a marine sedi ment core from a sw greenland fjord provides a detailed reconstruction of the oceanographic and cli matic variations of the region during the last 4400 cal years the lower part of our record represents the final termination of the holocene thermal maximum after the onset of the neoglaciation at approxi mately 3 2 ka cal bp the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the labrador sea and the north atlantic region our data show that increased advection of atlantic water irminger sea water from the west greenland current into the labrador sea was a typical feature of northeast atlantic cool ing episodes such as the little ice age and the european dark ages while the advection of irminger sea water decreased significantly during warm episodes such as the mediaeval warm period and the roman warm period whereas the mediaeval warm period was characterized by relatively cool climate as suggested by low meltwater production the preceding dark ages display higher meltwater runoff and consequently warmer climate when compared with european climate these regional climate anomalies indicate persisting patterns of advection of colder respectively warmer air masses in the study region dur ing these periods and thus a long term seesaw climate pattern between west greenland and europe

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

holocene climate records from lake sediments in india assessment of coherence across climate zones abstract holocene lake records constitute an important archive for the reconstruction of paleoclimate despite the overall climatic stability of the holocene the monsoons in india both summer and winter show various episodes of weakening and strengthening during this time interval as the holocene lake records are distributed across the various geomorphic and climatic zones of india they offer the possibility of understanding regional scale variations in terms of both qualitative and quantitative assessment of the available proxy data the present day precipitation in india varies from

a holocene pollen record from the northwestern himalayan lake tso moriri implications for palaeoclimatic and archaeological research this paper presents a new fossil pollen record from tso moriri 32 54 n 78 19 e 4512 m a s l and seeks to reconstruct changes in mean annual precipitation map during the last 12 000 years this high alpine lake occupies an area of 140 km2 in a glacial tectonic valley in the northwestern himalaya the region has a cold climate with a map 300 mm and open vegetation the hydrology is controlled by the indian summer monsoon ism but winter westerly associated precipitation also affects the regional water balance results indicate that precipitation levels varied significantly during the holocene after a rapid increase in map a phase of maximum humidity was reached between ca 11 and 9 6 cal ka bp followed by a gradual decline in map this trend parallels the reduction in the northern hemisphere summer insolation comparison of different palaeoclimate proxy records reveal evidence for a stronger holocene decrease in precipitation in the northern versus the southern parts of the ism domain the long term trend of ism weakening is overlaid with several short periods of greater dryness which are broadly synchronous with the north atlantic cold spells suggesting reduced amounts of westerly associated winter precipitation compared to the mid and late holocene it appears that westerlies had a greater influence on the western parts of the ism domain during the early holocene during this period the westerly associated summer precipitation belt was positioned at mediterranean latitudes and amplified the ism derived precipitation the tso moriri pollen record and moisture reconstructions also suggest that changes in climatic conditions affected the ancient harappan civilisation which flourished in the greater indus valley from approximately 5 2 to 3 cal ka bp the prolonged holocene trend towards aridity punctuated by an interval of increased dryness between ca 4 5 and 4 3 cal ka bp may have pushed the mature harappan urban settlements between ca 4 5 and 3 9 cal ka bp to develop more efficient agricultural practices to deal with the increasingly acute water shortages the amplified aridity associated with north atlantic cooling between ca 4 and 3 6 and around 3 2 cal ka bp further hindered local agriculture possibly causing the deurbanisation that occurred from ca 3 9 cal ka bp and eventual collapse of the harappan civilisation between ca 3 5 and 3 cal ka bp

probabilistic hazard analysis of impulse waves generated by multiple subaerial landslides and its application to wu gorge in three gorges reservoir china abstract subaerial landslides can generate impulse waves in reservoirs fjords and other water bodies and cause severe damage to the shipping industry infrastructure and human communities along the shorelines compared with deterministic hazard models probabilistic hazard analysis is an important tool for assessing the intensity and exceedance probability of impulse waves generated by multiple landslide sources which are essential for evidence based risk mitigation and contingency planning this paper proposes a methodological procedure for systematic probabilistic hazard analysis of impulse waves generated by subaerial landslides considering all relevant landslide sources and multiple uncertainties i e landslide mechanisms triggering scenarios and material parameters the main steps include 1 definition of the source parameters by parameterizing the epistemic and aleatory uncertainties in this respect the logic tree event tree and monte carlo models were used to organize the uncertainties of landslide mechanism models parametric scenarios and material parameters respectively 2 estimation of generated waves based on a landslide dynamic analytical model and previously validated empirical wave models derived from prototype scaled experiments and 3 aggregation of the hazard analysis results in the form of hazard maps and probability maps under parametric scenarios and a specific scenario considering the wu gorge in the three gorges reservoir as a case study soil slides and unstable rock slopes were analyzed to quantify the wave hazard along the reservoir under parametric and specific scenarios while considering rainfall and water level fluctuations the results show considerable wave hazard in the wu gorge for a 20 year return period the maximum expected height of propagation waves is 14 41 m the probability of experiencing propagation waves higher than 2 m in 20 years is over 50 in the river segment with high landslide density the results of the probabilistic wave hazard analysis could be aggregated and disaggregated to accommodate specific requirements of wave risk management

calciturbidite composition related to exposure and flooding of a carbonate platform triassic eastern alps the compositional variation of calciturbidites pedata potschen formation deposited adjacent to the dachstein formation carbonate platform in the triassic hallstatt basin was analysed using detailed field measurements and point counting of thin sections the 35 m long section is located in the northern calcareous alps of austria six point count groups were distinguished separating basinal from platform derived input summary statistics cluster and correspondence analysis of the point count data reveals a close relationship between the biota present on the dachstein carbonate platform and the calciturbidite composition the variations in turbidite composition are attributed to fluctuations in sea level and resulting flooding and exposure of the platform which alternately created and destroyed shallow water habitats on the platform top

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

tropical rainforest vegetation climate and sea level during the pleistocene in kerala india abstract the southwestern ghats region of the indian peninsula is unique for its extant endemic rainforest flora supported by high rainfall throughout the year the record of tropical rainforest corresponding to the dynamic series of pleistocene interglacial glacial cycles is poorly known from peninsular india this communication discusses the palynological study of organic matter om deposits 40 ka bp in two well sections chaganachery kerala from the indian peninsula west coast a rich archive of tropical rainforest pollen spores and marine dinoflagellate cysts indicates anoxic fluvio marine estuarine depositional environments during warmer climates with an intensified asian monsoon the geochemical fingerprinting of glass shards indicates the presence of youngest toba ash of 74 ka from northern sumatra and therefore establishes a time controlled stratigraphy thus the depositional time period of the om is related to the sea level highstand of marine isotopic stage 5 1 80 ka which was the host to the ytt shards the late quaternary pollen spores diversity suggests that the modern climatic conditions in the southwestern ghats have facilitated the conservation of moist evergreen rainforest and dry moist deciduous forest the pollen grains show its lineage with the extant flora and some of the fossil pollen recorded during the mesic tertiary period from the indian peninsula thus it appears that the tropical rainforest survived here as plant refugia in xeric glacial quaternary periods perhaps as riparian vegetation and was rejuvenated during the holocene as modern extant flora

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

compositional changes in sigmoidal carbonate clinoforms late tithonian eastern sardinia italy insights from quantitative microfacies analyses quantitative analysis of sediment composition was performed on a kilometre wide section of upper tithonian low relief up to 70 m gently inclined 3 to 15 sigmoidal carbonate clinoforms eastern sardinia to identify changes in sediment composition along the slope and across the studied succession these changes may reflect modifications of the carbonate factory and of processes responsible for sediment transport point count analysis of carbonate microfacies q mode r mode cluster analysis and spearman s rank provided a composition based classification of microfacies and highlighted relationships among sediment components the studied clinoforms are mainly composed of non skeletal grains 70 such as peloids and lithoclasts together with micrite and cements and only a limited contribution from coated grains 2 among skeletal grains 28 the greatest contribution derives from a coral stromatoporoid encruster reef that provided 15 of the components crinoids brachiopods and other along slope thriving biota provided nearly 5 of the allochems whilst fragments of molluscs gastropods bivalves and diceratids from the backreef sourced another 2 the contribution of platform interior biota is negligible 1 the association of composition based facies varies along the slope the upper slope beds consist of coral stromatoporoid grainstone to rudstone the middle slope deposits are dominated by encruster lithoclast grainstone and packstone at the lower slope peloidal lithoclastic packstone as well as brachiopod crinoidal wackestone prevail also the association of skeletal grains changes along the slope the encruster frame builder association typifies the upper slope whilst encrusters characterize the middle slope sediments in the lower slope encrusters are equally represented as the brachiopod crinoid association along slope compositional changes evidence a scarce downslope transport of frame builders and a progressive enrichment in along slope thriving biota quantitative analysis of microfacies allowed the sigmoidal clinoforms to be grouped into six sets each set gathers sigmoids with a similar sediment composition coated grains are dominant in the first set whilst they are lacking in the overlying sets reflecting a change in the carbonate factory other major compositional changes among the sets concern the relative amounts of peloids micrite frame builders corals and stromatoporoids and encrusters the contribution of peloids varies inversely to that of cements and micrite as evidenced in the third and fifth sets which respectively record the highest occurrence of peloids or cement and micrite variations in the amount of frame builders and encrusters are instead non linear high percentages of both frame builders and encrusters as recorded in the second and fifth sets are related to low amounts of peloids and lithoclasts that probably reflect episodes of reduced background sedimentation this study demonstrates that quantitative analysis of carbonate microfacies represents a powerful tool that can improve the reconstruction of the stacking pattern in carbonate slope successions both in outcrop and in subsurface settings

reconstructed late quaternary hydrological changes from lake tso moriri nw himalaya abstract we present the results of our investigations on the radiocarbon dated core sediments from the lake tso moriri nw himalaya aimed at reconstructing palaeohydrological changes in this climatically sensitive region based on the detailed geochemical mineralogical and sedimentological analysis we recognise several short term fluctuations superimposed upon seven major palaeohydrological stages identified in this lake since 26 cal ka stage i 20 2 cal ka shallow lake characterised by input of coarse grained detrital sediments stage ii 20 2 16 4 cal ka lake deepening and intensification of this trend ca 18 cal ka stage iii 16 4 11 2 cal ka rising lake levels with a short term wet phase 13 1 11 7 cal ka stage iv 11 2 8 5 cal ka early holocene hydrological maxima and highest lake levels inferred to have resulted from early holocene indian monsoon intensification as records from central asia indicate weaker westerlies during this interval stage v 8 5 5 5 cal ka mid holocene climate deterioration stage vi 5 5 2 7 cal ka progressive lowering of lake level stage vii 2 7 0 cal ka onset of modern conditions the reconstructed hydrological variability in lake tso moriri is governed by temperature changes meltwater inflow and monsoon precipitation increased runoff a regional comparison shows considerable differences with other palaeorecords from peninsular india during late holocene

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

multiproxy record of monsoon variability from the ganga plain during 400 1200 a d abstract understanding on the indian summer monsoon ism variability is chiefly based upon the marine proxies and a few continental records the ganga plain one of the most densely populated regions of the world marked by intensive cultivation of monsoon dependent crops and a rich cultural history is not yet well understood in the context of monsoon variability we present here a 400 1200 a d ams radiocarbon dated record of ropan chhapra tal in the central ganga plain using sedimentology environmental magnetism and stable isotope of oxygen for ism variability the environmental magnetic parameters lf arm sirm lf s ratio b 0 cr and hirm inferred antiferromagnetic mineralogy hematite and or goethite independent of grain size variation during 400 900 a d depicting climate variability within warm humid to warm arid conditions favouring stronger ism seasonality prevalence of ferrimagnetic mineralogy under less oxygenated conditions intermittently demonstrates an altered catchment regime or possibly in response to stronger winter monsoon the higher 18 o values around 500 580 and 740 a d indicate warm and arid conditions under weak ism the lower 18 o values around 480 540 and 700 a d and from 900 to 1200 a d occur during warm and humid conditions indicating maximum intensity of the ism increased silt content from 800 a d onwards is due to increased surface runoff in response to enhanced precipitation and the higher clay percentage around 500 580 and 740 indicates low energy ponding conditions under weak ism the well sorted nature of sediment indicates consistency of the lacustrine environments under fairly uniform energy and constant bottom water conditions under varied monsoonal intensity combinations of sediment textures and stable isotope indicate intense ism at 480 and 540 a d with flooding around 700 a d and a weak monsoon at 580 and 740 a d with drought at 500 a d during 900 1200 a d the multiproxy record suggests strong summer monsoon synchronous with medieval warm period mwp whereas after 1200 a d the weak monsoon phase coincides with the onset of the little ice age lia

record of vegetation and climate during late pleistocene holocene in central ganga plain based on multiproxy data from jalesar lake uttar pradesh india pollen organic inorganic carbon ratio clay mineral texture analyses and radiocarbon dating of a 2 8 m sediment profile from jalesar lake demonstrate that from prior to 42 490 until 13 560 cal bp the central ganga plain supported grassland with scanty trees under a cool and dry climate the sediments deposited during 13 560 5260 cal bp are palynologically barren and coarser in nature with increased inorganic organic carbon ratio depicting the upwarping phase of the ganga plain between 5260 and 4760 cal bp the immigration of more trees including holoptelea acacia and bombax accompanied by higher clay and organic carbon indicate establishment of forest groves under an ameliorating climate the debut of cerealia pollen denotes the initiation of agricultural practices around 4760 3260 cal bp forest groves became diversified substantiated by higher clay with increasing kaolinite and organic carbon indicating warm and humid climate owing to an active sw monsoon the consistent presence of aquatics and rising trend of cerealia pollen suggest lake expansion and acceleration in agricultural practices respectively between 3200 and 1200 cal bp the forest groves became sparse allowing coarser sediments with less organic carbon which implies that climate became less humid since 1200 cal bp diminution of arboreals signifies a weak sw monsoon

a facies distribution model controlled by a tectonically inherited sea bottom topography in the carbonate rimmed shelf of the upper tithonian valanginian southern tethyan continental margin nw sicily italy the upper tithonian valanginian shallow water carbonates outcropping in the palermo mts nw sicily consist of several facies associations reflecting different depositional environments of a carbonate rimmed shelf pertaining to the southern tethyan continental margin the reconstructed depositional model based on the sedimentological features cyclic facies arrangement and biota distribution shows that a wide protected lagoon dominated by algae molluscs and scattered patch reefs was bordered landward by a tidal flat where stromatolitic algal mats were cyclically subaerial exposed and seaward by a marine sand belt and reef complex oolitic packstone grainstone lithofacies cyclically subjected to subaerial exposure suggests the occurrence of a barrier island located nearly to the lagoonal carbonate shoreline allowing the development of narrow embayments with restricted circulation in the outer platform the oolitic lithofacies of the marine sand belt pass landward into the protected lagoon where washover oolite sands occur and seaward into a high energy zone back reef apron gradually merging in the reef complex in the latter coral framestone occupied the inner sector reef flat while the facies association dominated by boundstone with ellipsactinia sp developed in the outer sectors reef wall adjacent to the fore reef and upper slope environments stratigraphic evidence associated with the recognized facies associations helped to reconstruct the geo tectonic setting of the carbonate platform where the distribution of the depositional facies along the shelf and their extension were influenced by the tectonically inherited sea bottom topography in a regime of extensional tectonics localized and thin succession of high energy prograding oolite sand belt depositional facies occupied structural highs footwall uplift while the largely diffused and thick low energy aggrading peritidal to lagoonal depositional facies developed in subsiding hanging wall the reef complex and the fore reef depositional facies exhibiting lateral migration and prograding geometries with clinoforms and downlap stratal terminations developed on a subsident stepped margin adjacent to a faulted shelf break this morphostructural setting can be comprised in a model where the tilted and faulted blocks inner platform and stepped margin outer platform paleo topography inherited from the rifting tectonics was the most important factor controlling the geometry and depositional architecture of a carbonate platform growing on the southern tethyan passive margin

stable isotopes in bulk carbonates and organic matter in recent sediments of lake qinghai and their climatic implications abstract multi proxy indices on annual decadal scales during the past 600 years were developed from the surface sediments of lake qinghai based on 210pb and 137cs geochronology the 13ccarb 18ocarb and total carbonate content are consistent with one another in trends and their variations have been mainly ascribed to regional temperature it is suggested that the strong evaporation contributes in modifying 18o of lake water and 13c of the dissolved inorganic carbon of the surface water and appears to be responsible for the covariance between 13ccarb and 18ocarb photosynthesis of the aquatic plants appears to have played a significant role in determining 15n of organic matter the discrimination of 14n and 15n during photosynthesis may have triggered a positive linkage between temperatures and 15norg after removal of the stratigraphic trend variations of total organic carbon toc c n ratio and 13corg have been ascribed to local precipitation toc after removal of the stratigraphic trend is positively correlated with the c n ratio r 0 45

pliocene pleistocene platform facies transition recorded in calciturbidites exuma sound bahamas abstract the composition of pliocene pleistocene calciturbidites of odp hole 632a exuma sound bahamas has been determined by point count analysis of thin sections in order to correlate basin platform events which influenced sedimentation strontium isotope chronostratigraphy has been used to correlate basin turbidite compositional variations to the evolution of the platform as documented by magnetostratigraphy magnetostratigraphy of great bahama bank cores shows that between 3 4 and 2 5 ma late pliocene ooids and peloids became the dominant sediments across the platform after this period the platform has been subjected to a series of subaerial exposure events this led to slow accumulation on the platform and starvation of the basin around 1 ma the platform was reflooded the transgression being followed by an increased production of ooids there is a change in calciturbidite composition in the earliest pleistocene coinciding with a regional unconformity pleistocene turbidites containing abundant skeletal material and ooids overlie pliocene early pleistocene turbidites rich in mud and skeletal material the duration of the hiatus represented by the unconformity based on 87 sr 86 sr dating is 1 0 0 7 ma prior to this hiatus sedimentation rates in the basin are an order of magnitude lower than present day accumulation rates we conclude that reflooding of the platform around 0 8 ma led to shedding of both non skeletal and skeletal sediments the change of great bahama bank from a pliocene reef rimmed skeletal platform to the present day flat topped bank dominated by non skeletal sediments can be correlated with the observed change in turbidite composition