the white stone band of the kimmeridge clay formation an integrated high resolution approach to understanding environmental change the kimmeridge clay is a jurassic mudrock succession that shows milankovitch band climatic cyclicity a key issue is to determine how the subtle changes that define this cyclicity result from climatic change using material from the natural environment research council rapid global geological events rgge kimmeridge drilling project boreholes the white stone band was investigated at the lamination scale using backscattered electron imagery and quantitative palynofacies fabric analysis shows the lamination to represent successive deposition of coccolith rich and organic matter rich layers individual laminae contain unsorted palynological debris with a consistent ratio of marine and terrestrial components such mixed organic matter input is interpreted as the result of storm transport linking water column processes to laminae deposition suggests seasonal input with a coccolith bloom followed by a more diverse assemblage including dinoflagellates and photosynthetic chlorobiacean bacteria as the photic zone extended into the euxinic water column organic matter export to the sea bed underwent minimal cycling through oxidation and subsequently became preserved through sulphurization with greatly increased sequestration of carbon this was significantly increased by late season storm driven mixing of euxinic water into the photic zone increased frequency of storm systems would therefore dilute the coccolith input to give an oil shale hence climatically induced changes in storm frequency would progressively vary the organic content of the sediment and generate the climate cycle signal

seismic stratigraphy and sediment distribution on the wilkes land and terre adelie margins east antarctica abstract seismic reflection data show the existence of two major sedimentary basins along the continental margin of wilkes land and terre adelie east antarctica that contain more than 5 s twt 9 km of sediments four seismic megasequences are identified ms4 to ms1 that are bounded by basement unconformities of interpreted turonian maastrichtian and early middle eocene age and the seafloor the 4 5 km thick rift and pre rift sediments are concentrated in a margin parallel basin sabrina basin on the basis of seismic correlation with the australian margin this basin is interpreted to be of late jurassic to mid cretaceous age the post rift sediments are generally thick along the margin and in the adjacent deep ocean basin but are particularly thick in a major depocentre off west wilkes land named here the budd coast basin bcb the bcb contains a maximum observed thickness of 5 s twt 9 km of post rift sediments and its location suggests that the sediments were largely derived from a sub glacial basin currently occupied by the totten glacier within the post rift sediments a major regional unconformity is identified that is interpreted to be of early middle eocene age 45 ma while some previous interpretations have suggested that this unconformity marks the onset of the glaciation of east antarctica the unconformity is interpreted here to be the product of the major global plate reorganisation in the middle eocene and the coincident sharp increase in the sea floor spreading rate between australia and antarctica a seismic unconformity that can be correlated with the onset of glaciation is not identified and the position of glacial onset within the sedimentary section can only be estimated through the extrapolation of sedimentation rates from the underlying section and from deep sea drilling project site 269 the post middle eocene section is much thicker than the underlying post rift section and this is interpreted to be largely due to the very high sediment fluxes associated with the period of polythermal glaciation from 34 9 ma sediment isochron and isopach maps derived from a regional seismic grid show that the depocentre of the bcb trends approximately north south beneath the continental slope but is deflected to the east beneath the deep ocean basin this distribution indicates that deep marine processes were important in lateral along margin sediment transport a west to east direction of movement is inferred by the sediment distribution this direction is opposite to the present day marginal currents along the continental slope and rise

uncommon steranes in brazilian marginal crude oils dinoflagellate molecular fossils in the sergipe alagoas basin brazil comprehensive two dimensional gas chromatography with time of flight mass spectrometry gc gc tofms was used to identify unusual steranes in branched cyclic hydrocarbon fractions of crude oils from sergipe alagoas basin brazil and infer the geochemical settings of their cretaceous source rocks hopane sterane and sterane ratios and the presence of gammacerane and carotane in the oil samples indicates a saline source rock depositional environment and predominantly marine organic matter om input steroidal hydrocarbons were represented by alkyl steranes and several sterane series including abundant short chain steranes c21 and c22 regular steranes c27 c29 and diasteranes c21 c23 c27 c29 the ring a methyl sterane series contained 3 methyl steranes c22 and c23 c28 c30 abundant 3 methyldiginane c22 and 3 methyldiacholestanes c28 including 4 methyl steranes with abundant c30 4 23 24 trimethylcholestanes in the branched cyclic fraction of these crude oils the c29 sterane isomers 23 24 dimethylcholestane and 24 ethylcholestanes were resolved by gc gc tofms and a c29 dinosterane derivative was identified for the first time in brazilian crude oils the 23 24 dimethyl and 4 23 24 trimethyl steroids can be related to dinoflagellate om and abundant dinosteranes suggests dinoflagellate blooms during source rock deposition in this brazilian marginal basin additionally the detection of c28 c32 3 alkyl cholestanes c29 c33 3 alkyl 24 methylcholestanes and c30 c34 3 alkyl 24 ethylcholestane with ethyl to pentyl groups at c 3 resulted in a complex sterane fingerprint as expected for petroleum generated from source rocks deposited under predominantly marine saline conditions with high microalgal input these biomarker results provide additional insight into the character and geologic processes responsible for the source rocks of crude oils in the brazilian marginal basins this information will be a valuable exploration tool that can be used to constrain the distribution of different oil types in these basins

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

photic zone euxinia in the central rhaetian sea prior the triassic jurassic boundary abstract shortly after the deposition of black shales in the rhaetian sea central european basin ceb the triassic jurassic tr j boundary witnessed one of the big five mass extinction events in earth s history aiming at a better understanding of paleoenvironmental changes in the geochemically less well known middle to late rhaetian german subdivision we studied samples from a cored borehole from the central rhaetian sea in nw germany hebelermeer 2 biomarkers palynomorphs and bulk geochemistry all support a marine brackish setting with inputs from terrestrial plants dinosteranes were found throughout the core most likely suggesting the spread of dinoflagellates it is widely accepted that volcanic exhalations during the development of the central atlantic magmatic province camp had a major impact on marine and terrestrial environments in the earliest jurassic e g the development of photic zone euxinia and h2s poisoning of benthic life there is evidence from the studied core however that comparable conditions already thrived in the central rhaetian sea during the middle rhaetian a first indication of euxinia anoxia is evident from low to very low total organic carbon versus total sulfur toc ts ratios

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

scratching the surface a marine sediment provenance record from the continental slope of central wilkes land east antarctica the geology of wilkes land east antarctica is masked by kilometers of ice and remains largely unexplored defining the sediment provenance adjacent to this hidden region is important for distinguishing the proximal subglacial basement terranes and refining the dynamic regional glaciological history this study presents a detrital sediment provenance record spanning c 23 5 ka from the continental slope of central wilkes land sediment provenance was characterized using u pb geochronology and trace element geochemistry from detrital zircon titanite and apatite and pb isotopic signatures from detrital feldspar these data were compared with new feldspar pb isotopic signatures and existing u pb zircon datasets from rare nearby coastal outcrop a principally igneous source was revealed with dominant age populations between c 1360 1100 ma and c 1620 1490 ma characteristic of rocks of the proximal wilkes and banzare provinces respectively minor detritus was additionally sourced from the proximal nuyina province c 1450 1390 ma temporal variation in the climate and ice sheet configuration are likely responsible for subtle downcore changes observed in detrital sediment provenance high sedimentation rates during the glacial period suggest reworking of continental shelf sediments and downslope transport in debris flows during ice sheet advance glacial meltwater fluxes fed largely by the totten glacier were responsible for supplying detritus during deglaciation during interglacials detritus was derived from a broad coastal region and delivered to the slope via multiple glacial outlets these results present the first substantial offshore evidence to support recent interpretations that the subglacial crust of central wilkes land has a dominantly mesoproterozoic history

structure and significance of c30 4 methyl steranes in lacustrine shales and oils abstract the structure of the abundant c 30 4 methyl steranes of ancient freshwater lacustrine sediments and derived oils is of interest as their precursors the 4 methyl and in particular 4 23 24 trimethyl sterols dinosterols are reported to be specific to dinoflagellates this study employs a novel liquid crystal gc phase combined with gc ms and gc ms ms to separate and characterise mixtures of c 30 4 methyl sterane standards not resolvable on non polar phases this technique is then applied to identify the c 30 4 methyl steranes in an ancient freshwater sediment a freshwater lacustrine and a marine derived oil a comparison is also made with the 4 methyl steranes in marine sediments containing varying amounts of dinoflagellate cysts the c 30 4 methyl steranes of the freshwater lacustrine samples have been shown to possess a 4 methyl 24 ethylcholestane structure while both 4 methyl 24 ethylcholestanes and 4 23 24 trimethyl 5 h cholestanes dinosteranes were found in the marine dinoflagellate rich sediments while still indicative of dinoflagellates 4 methyl 24 ethyl sterols are generally not the major dinoflagellate sterol and alternative explanations for the abundance of 4 methyl 24 ethylcholestanes in ancient lacustrine sediments should be considered possibly ancient freshwater dinoflagellates synthesised principally the 4 methyl 24 ethyl form alternatively a source from an unrecognized algal class is possible while a source from bacteria which are known to synthesise certain 4 methylsterols is discussed

organic matter of the mulhouse basin france a synthesis the lower oligocene evaporite sequence of the mulhouse basin france contains organic matter rich marl deposits these marls display an overall cyclic variation of sedimentation rate organic carbon content hydrogen index and selected molecular parameters over a 30 m thick stratigraphic interval the integration of all sedimentological and geochemical parameters has allowed the reconstruction and characterization of the paleoenvironment of deposition the marls were deposited in a perennial lake that was at times connected to the sea two organic facies end members could be assigned to a lake stage with a marine connection and a lake stage that received dominantly continental water input the overall stratigraphic variation in the organic matter content is interpreted to reflect the adaptation of the oligocene flora to the changing paleoclimate and environmental conditions

late winter oceanography off the sabrina and banzare coast 117 128 e east antarctica abstract we report on the late winter oceanography observed beneath the antarctic sea ice offshore from the sabrina and banzare coast of wilkes land east antarctica 117 128 e in september october 2007 during the sea ice physics and ecosystem experiment sipex a pilot program using specifically designed through ice conductivity temperature depth ctd and acoustic doppler current profiling adcp systems was conducted to opportunistically measure water mass properties and ocean currents at major ice stations additional water mass properties across the survey region were collected from ice argo floats deployed during the voyage north of the 3000 m isobath the mean drift of the floats was along the slope to the west with the antarctic slope current vertical profiles of the potential temperature reveal the deepest 350 400 m winter mixed layer wml in the western sector of the survey northwest of the dalton iceberg tongue polynya the meridional structure of the antarctic slope front i e the monotonic shoaling of the wml across the upper continental slope is found to be similar to the previous observations in summer a strong bottom intensified intrusion of modified circumpolar deep water mcdw as warm as 0 c was detected beneath the fast ice south of the continental shelf break at 118 e an mcdw intrusion of similar strength was detected near this location in the austral summer of 1996 we hypothesise that there is a persistent supply of mcdw and associated ocean heat flux to this region of the continental shelf that is capable of migrating to the grounding lines of the nearby totten glacier and moscow university ice shelf there was no detection of locally formed dense shelf water capable of forming antarctic bottom water at the shelf break locations sampled despite the number of minor polynyas across this region ocean current measurements limited to a maximum period of 24 h and 50 100 m depth by the relative scarcity of backscatter found increased mean vertical speeds at the offshore stations 6 17 cm s 1 relative to the shelf break 2 3 6 4 cm s 1 the diurnal variation in the adcp range reflected the diel migration of zooplankton occurring beneath the sea ice in late winter with greater range abundance offshore concurrent time series of wind ocean current and their influence on sea ice drift from global positioning system gps compass measurements were examined but the length of data acquisitions limited the applicability of this analysis

evidence of a hydrological connection between the ice divide and ice sheet margin in the aurora subglacial basin east antarctica subglacial hydrology in east antarctica is poorly understood yet may be critical to the manner in which ice flows data from a new regional airborne geophysical survey icecap have transformed our understanding of the topography and glaciology associated with the 287 000 km2 aurora subglacial basin in east antarctica using these data in conjunction with numerical ice sheet modeling we present a suite of analyses that demonstrate the potential of the 1000 km long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin we present results from our analysis of basal topography bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures although no clear cut subglacial lakes are found within the aurora basin itself dozens of lake like reflectors are observed that in conjunction with other results reported here support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the dome c ice divide to reach the coast via the totten glacier

bathymetric control of warm ocean water access along the east antarctic margin observed thinning of the totten glacier in east antarctica has cast doubt upon the stability of the east antarctic ice sheet recent oceanographic observations at the front of the totten ice shelf have confirmed the presence of modified circumpolar deep water mcdw which likely promotes enhanced melting details of how this water accesses the shelf remain uncertain here we present new bathymetry and autumnal oceanographic data from the outer continental shelf north of the totten glacier that show up to 0 7 c mcdw in a 100 km wide and 500 m deep depression within the shelf break in other parts of east antarctica a shelf break bathymetry shallower than 400 m prevents these warmer waters from entering the shelf environment our observations demonstrate that detailed knowledge of the bathymetry is critical to correctly model the across shelf exchange of warm water to the various glaciers ice shelves of antarctica for future sea level prediction

post miocene sedimentation at the continental rise of southeast greenland the interplay between turbidity and contour currents southeast greenland continental rise depositional sequences have been studied by means of high resolution reflection seismic data major depositional features of this glaciated margin have been compared with comparable seismic architectures at the antarctic margin two seismic units with an estimated age of early to mid pliocene and mid pliocene to recent have been analysed in detail it is concluded that episodic turbidity currents interacting with more continuous contour currents have controlled the location and architecture of the sedimentary mounds found off southeast greenland in the early pliocene turbidite sediment input significantly surpassed the amount of sediments reworked and transported by southbound contour currents as a result an overbank deposit developed oriented perpendicular to the continental slope at the proximal part and parallel to the continental slope in the distal part where the effect of the turbidity processes decreased contour current action further resulted in a southward migration of the overbank deposit from the mid pliocene a relatively stronger impact of the contour current on the sedimentation pattern is observed suggesting a relative decrease of downslope sediment transport processes stronger contour current activity may have been related to generally enhanced north atlantic deep water circulation this resulted in formation of elongated contourite deposits trending parallel to the continental slope both in proximal and distal settings the morphology and seismic expression of the sedimentary mound structures at the southeast greenland margin display several features also observed at the antarctic margin it is concluded however that the sedimentary mounds in the latter area formed in a different way which is principally attributed to persisting contour current activity off antarctica during glacial stages when currents off southeast greenland had virtually ceased

glacial retreat patterns and processes determined from integrated sedimentology and geomorphology records abstract although hundreds of cores have been collected on the antarctic continental shelf over the past five decades definitive interpretations of depositional environments associated with marine based ice advance and retreat are hindered by similarities in sediment facies and a lack of geomorphic context the recent use of an advanced multibeam bathymetry system allows for more detailed ice sheet reconstructions from glacial landforms that were previously not resolved with older generation systems here we present results from a recent cruise to the ross sea antarctica that focuses on integrating sediment facies analyses into a geomorphic framework to confidently determine depositional environments and sedimentological processes since the last glacial maximum grain size analysis geotechnical properties and micropaleontology from targeted sediment cores are used to develop improved criteria for making the distinction between subglacial diamictons and ice proximal diamictons which can be applied to geomorphically blind sediment cores our consideration of geomorphic context while interpreting sediment facies has also allowed us to determine that most debris melted out of the base of paleo ice shelves in the ross sea only 1 2 km seaward of the grounded ice margin additionally we find that agglutinated foraminifera specimens are characteristic of sluggish marine currents and a resulting accumulation of siliceous detritus rich in organic matter however calcareous specimens dominate in higher energy current settings and in ice proximal environments with lesser amounts of siliceous detritus and associated organic material overall sedimentary successions record contrasting behaviors of the west antarctic and east antarctic ice sheets that extended onto the continental shelf during the last glacial maximum not only is this coupled geomorphic and sedimentologic approach useful for understanding glacimarine processes and ice sheet retreat patterns but it is essential for selecting appropriate facies transitions for chronological constraints of past ice sheet behavior

sea level change and facies development across potential triassic jurassic boundary horizons sw britain the late triassic to early jurassic aged succession of sw britain the penarth and lower lias groups comprises mudstone sandstone and limestone strata deposited in a variety of marine to non marine environments faunal and floral characteristics of these successions have led to the proposal that one location in sw england st audrie9s bay should serve as the global stratotype section and point gssp for the base of the hettangian stage and thus for the triassic jurassic tr j boundary the sections of sw britain have also been used previously to infer sea level change history and relate this to potential kill mechanisms associated with the tr j boundary mass extinction chemostratigraphic biofacies and lithofacies data are used here to suggest alternative models of sea level change in relation to possible tr j boundary horizons in the sections of sw britain a sea level lowstand surface of erosion is inferred to occur within the cotham member of the lilstock formation a unit deposited in an environment that was often subaerially exposed in contrast to previous interpretations the top surface of the overlying langport member here inferred to be deposited on a carbonate ramp of depositional or tectonic origin represents a drowning event of at least regional extent all horizons regarded as plausible levels at which to place the tr j boundary based on fossil distributions lie within strata deposited during relative sea level rise however it is doubtful whether the higher horizons proposed to mark the boundary faithfully record times of true biotic change on a global scale and additionally there is no positive evidence that sea level fall had any relation to the genesis of proposed tr j marker horizons it is unlikely that sea level fall played a significant role in the tr j boundary extinctions in either a local or a global context

origin of nama basin bitumen seeps petroleum derived from a permian lacustrine source rock traversing southwestern gondwana abstract biodegraded bitumens associated with quartz and calcite veins in the cambrian fish river subgroup sediments of the nama group of southern namibia have a geochemical signature diagnostic for organic matter that was deposited in a saline lacustrine palaeoenvironment in particular they contain abundant gammacerane carotane and 3 methylhopanes while 24 isopropyl cholestanes and dinosteroids are not detectable sealed tube hydrous pyrolysis of asphaltene and polar fractions yielded saturated hydrocarbons amenable to c isotopic analysis and these analyses show unusually low 13 c values these combined characteristics are also present in immature bitumens from the permian irati formation of brazil and a saline lacustrine facies of the whitehill formation in the karoo basin south africa we conclude that the bitumens originated from whitehill equivalent strata of the kalahari basin deposited in what was an extensive saline lacustrine basin in southwestern gondwana during the early permian in southern africa source rocks of the whitehill formation are generally immature for petroleum generation and it is therefore likely that the nama bitumens were expelled by contact metamorphism during emplacement of karoo dolerite sills and dykes in the jurassic

product distributions from chemical degradation of kerogens from a marl from a miocene evaporitic sequence vena del gesso n italy abstract lithium in ethylamine li etnh 2 treatment has been carried out on sulphur rich kerogens from 10 sub samples of the cycle iv marl from the vena del gesso evaporitic sediments upper miocene italy the treatment releases after chromatography of the resulting solvent extracts up to 30 of the kerogen total organic carbon the biomarkers released are dominated by components of algal origin the concentrations of the aliphatic hydrocarbons obtained are of the same order of magnitude as the bound alkanes released upon desulphurization of polar fractions from organic extracts and show similar distributions the presence of diaromatic isoprenoids derived from chlorobiaceae indicates that photic zone anoxia occurred during the deposition of the cycle iv marl such conditions being more prevalent at the middle of the section polar material makes up by far most of the organic material released and contains in particular alcohols and amides which may result from the cleavage of ester bonds present in these immature kerogens the amides being secondary products formed by reaction with the etnh2 in the case of the alcohols however these components could also arise from cleavage of sulphide bound moieties

geological constraints on antarctic palaeo ice stream retreat submarine landforms preserved in bathymetric troughs on the antarctic continental shelf show that the style of ice stream retreat across the shelf following the last glacial maximum varied between different troughs three styles of retreat are inferred from the geological evidence rapid episodic and slow rapid retreat by ice stream floatation and calving is recorded by the preservation of a landform assemblage of unmodified streamlined subglacial bedforms including mega scale glacial lineations msgls that record streaming flow along these troughs these elongate bedforms are not overprinted by recessional glacial landforms formed transverse to ice flow such as moraines or grounding zone wedges and overlying deglacial sediments are thin a second type of landform assemblage consists of msgls overprinted or interrupted by transverse grounding zone wedges this assemblage implies episodic retreat between successive grounding zone positions the third type of landform assemblage is that of numerous closely spaced recessional moraines and intermittent grounding zone wedges that overlie and interrupt msgls this assemblage records the slow retreat of grounded ice across the shelf variation in the style of ice stream retreat between the different bathymetric troughs indicates that antarctic palaeo ice streams did not respond uniformly to external forcing at the end of the last glacial cycle rather their diachronous retreat reflects the dominance of local controls in the form of bathymetry and drainage basin size more broadly these data show that retreat of marine based ice sheets in areas of reverse bed slope is not necessarily catastrophic and they provide important constraints for numerical models that attempt to predict the dynamics of large polar ice sheets copyright 2008 john wiley sons ltd

geomorphic signature of antarctic submarine gullies implications for continental slope processes five quantitatively distinct gully types are identified on the antarctic continental margin from swath bathymetric data of over 1100 individual features the gullies differ in terms of length width depth width depth ratio cross sectional shape branching order sinuosity and spatial density quantitative analysis suggests that antarctic gully morphology varies with local slope character i e slope geometry gradient regional factors i e location of cross shelf troughs trough mouth fans subglacial meltwater production rates drainage basin size sediment yield and ice sheet history in keeping with interpretations of previous researchers most gullies are probably formed by hyperpycnal flows of sediment laden subglacial meltwater released from beneath ice sheets grounded at the continental shelf edge during glacial maxima the limited down slope extent of gullies on the western antarctic peninsula is explained by the steep gradient and slope geometry at the mouth of marguerite trough which cause flows to accelerate and entrain seawater more quickly resulting in a reduction of the negative buoyancy effect of the sediment load due to pressure gradients at the ice sheet bed caused by variations in ice thickness inside and outside palaeo ice stream troughs subglacial meltwater flow was generally focussed towards trough margins this has resulted in gullies with larger cross sectional areas and higher sinuosities at the trough margins a unique style of gullying is observed off one part of the western antarctic peninsula corresponding to an area in which the ice sheet grounding line is not thought to have reached the shelf edge during the last glacial maximum we interpret the features in this area as the cumulative result of slope processes that operated over a long period of time in the absence of hyperpycnal meltwater flows

pregnanes as molecular indicators for depositional environments of sediments and petroleum source rocks steroids with unconventional side chains have increasingly been applied as diagnostic markers for geological source and age assessments however one of the most distinctive characteristics the abnormal abundance of pregnane and homopregnane in ancient sediments and petroleum remains unresolved higher pregnane and homopregnane as well as c23 c26 20 n alkylpregnanes relative to the regular steranes were observed in samples collected from different petroleum basins in china these included precambrian marine carbonate derived petroleum nw sichuan basin lower paleozoic marine marl derived crude oils tarim basin and eocene hypersaline lacustrine carbonate source rocks and associated petroleum bohai bay basin however all of the samples have many common biomarker characteristics such as pristane phytane ratios 1 low amounts of diasteranes and high c29 c30 hopane 0 6 1 c35 c34 hopane mostly p 1 and dibenzothiophene phenanthrene dbt phen mostly 0 5 1 ratios revealing a contribution from anoxic carbonate marl source rocks deposited in restricted clastic starved settings we suggest that 5a l4b l7b pregnane and homopregnane as well as their higher c23 c26 homologues are geological products derived from steroids bound to the kerogen by a sulfurized side chain carbon or carbonate minerals are considered to be natural catalysts for this cracking reaction via preferential cleavage of the bond between c 20 and c 22 similar distributions occur in the short chain analogues of 4 methylsterane triaromatic steroid and methyltriaromatic steroid hydrocarbons providing circumstantial evidence for this proposal the ratio of pregnane and homopregnane to the total regular steranes and the ratio of c27 diasteranes to cholestanes can be sensitive indicators of sedimentary environments and facies in general high diasteranes and low pregnanes with homologues indicate an oxic water column or significant input of terrigenous organic matter in clay rich source rocks and some organic lean carbonate rocks low diasteranes with high pregnanes implies restricted sulfur rich conditions typical of anoxic carbonate source rocks furthermore the two ratios may be useful to assess the variation of mineralogy and openness of source rock depositional settings

organic geochemical and mineralogical characterization of the lower silurian longmaxi shale in the southeastern chongqing area of china implications for organic matter accumulation abstract abundant in organic matter the lower silurian longmaxi shale in the upper yangtze platform south china has been demonstrated to play important roles in the petroleum system as both a good source rock and a shale gas reservoir in order to better understand the heterogeneous organic matter accumulation of such shales in the southeastern chongqing area the vertical variations of total organic carbon toc contents mineral concentrations and biomarker distributions were systematically analyzed in this study the longmaxi formation consists of fine grained siliciclastic rocks deposited in a restricted marine shelf environment and it can be further subdivided into two members the lower member is enriched in toc whereas a diminished toc content is documented in the upper member laterally the toc content gradually drops southeast ward in the study area the mineralogical compositions dominated by quartz and clay and to a lesser extent feldspar and carbonate show good correlations with toc contents vertically especially in the lower member saturated and aromatic hydrocarbon biomarkers indicate a dominant organic matter origin from lower hydrobionts algae and bacteria in a reducing marine environment negative correlation relationships between toc contents and terrigenous clastic minerals indicate the predominant role of dilution of terrigenous clastic materials in controlling the organic matter accumulation the sea level drop combined with the continuously active xuefeng uplift contributed to more terrigenous clastic inputs into the study area which resulted in a significant reduction of toc content in the upper longmaxi member

upper slope processes and seafloor ecosystems on the sabrina continental slope east antarctica abstract this study applies detailed seafloor bathymetry data and seafloor images to understand upper slope features and how these influence the distribution of seafloor biota on the east antarctic margin the east antarctic slope on the sabrina margin has been shaped by diverse processes related to repeated glaciation differences in the morphology of gullies on the upper slope enable an understanding of the likely processes that have been active on this margin gully morphology varies according to changes in slope gradient which may have driven variations in sedimentation areas of lower slope angles may have led to rapid sediment deposition during glacial expansion to the shelf edge and subsequent sediment failure typically gullies in these areas are u shaped initiate well below the shelf break are relatively straight and long and have low incision depths consistent with formation due to mass wastage areas of higher slope angles likely experienced enhanced flow of erosive turbidity currents during glaciations associated with the release of sediment laden basal meltwaters sediment laden subglacial meltwater flows typically create gullies such as those we observe that initiate at or near the shelf break are v shaped in profile and have high sinuosity deep incision depths and a relatively short downslope extent the short downslope extent reflects a reduced sediment load associated with increased seawater entrainment as the slope becomes more concave in profile these differences in gully morphology have important habitat implications associated with differences in the composition and beta diversity of the seafloor communities this upper slope region also supports seafloor communities that are distinct from those on the adjacent shelf highlighting the uniqueness of this environment for biodiversity conservation strategies therefore need to consider slope and shelf communities as distinct and equally important components of the antarctic ecosystem

reconnaissance paleomagnetic results from western cuba abstract a paleomagnetic study of mesozoic rocks from the sierra de los organos and sierra del rosario fold belts of western cuba revealed postfolding magnetisation in diabases of the late jurassic el sabalo formation and carbonates of the middle cretaceous pons and the late cretaceous carmita and moreno formations steep components with inclinations of about 70 were isolated from all three formations at the same time postfolding shallow components were also found in a few samples of the pons limestones we rule out a possibility to account for these results by either horizontal movements or non dipole field anomaly neither very appealing is a hypothesis of a post remagnetization tilt of the entire region all the components appear to be confined to a plane perpendicular to the main structural trends we hypothesize that the remanences might have been distorted or re aligned during deformation this assumption however is far from being proven in contrast well defined characteristic components were isolated from basalts of the aptian albian encrucijada d i 247 23 k 14 a95 9 0 and the late cretaceous orozco d i 228 22 k 110 a95 4 7 formations from the bahia honda zone in the north of western cuba the remanence in the encrucijada formation is shown to predate deformation mean inclinations in both formations match those in cretaceous volcanics from central cuba and all the results show lower latitudes than expected from the reference data for the north american plate thus implying that volcanic domains of cuba were displaced northward by about 1000 km prior to the middle eocene cretaceous declinations in western and central cuba differ by about the same amount as the major structural trends of these two areas suggesting oroclinal bending of cuba at the same time both areas are rotated counterclockwise with respect to north america thus implying movements on a broader scale

observations of a street of cyclonic eddies in the indian ocean sector of the antarctic divergence hydrographic and drifting buoy data from japanese cruises show that the antarctic divergence in the indian ocean sector is composed of a street of cyclonic eddies these eddies measure about 500 km in the zonal direction and 200 km in the meridional part of the eastward flowing antarctic circumpolar current acc meanders southward in the regions between the eddies in the eddy regions warm saline circumpolar deep water is upwelled into the shallow layers while cold dense coastal water advects into the deep layers the advection occurs along the isobaths of ridges which extend north from the coast the combination of the advection with the upwelling produces a water column denser than the surrounding water and leads to the formation and maintenance of the cyclonic eddies presence of the northward extending ridges approximately governs the location of eddy formation the eddy formation recurs year after year although eddy locations can vary somewhat a polynya was observed to persistently occur and corresponded with one of the eddies in location size and form the oceanographic observations also suggest that the primary meridional exchanges of heat and salt in the antarctic are caused through the eddies and acc meanders within the antarctic divergence

retreat of the east antarctic ice sheet during the last glacial termination the east antarctic ice sheet retreated at the end of the last glacial period terrestrial and marine data suggest that the retreat began 14 000 years ago indicating that the east antarctic ice sheet probably did not contribute to meltwater pulse 1a 14 700 years ago

sulfur rich petroleum derived from lacustrine carbonate source rocks in bohai bay basin east china abstract crude oils produced from the zhanhua depression bohai bay basin are high in sulfur and differ from most lacustrine oils in this basin and elsewhere physical properties biomarker ratios and aromatic hydrocarbon assemblages reveal that they are derived from carbonate source rock horizons representative source rock samples with abundant organic matter toc 1 and s 2 5 mg hc g rock were selected for further correlation and their high bitumen contents indicated their indigenousness to saline or carbonate depositional environments the results of oil source rock correlation suggest that these sulfur rich heavy oils originate from es 3 4 carbonates and marls limited to the bonan sag maturity assessments with burial history showed that they were expelled at the early oil generation window high levels of 20s 5 14 17 and 5 14 17 steranes together with low values for the ts ts tm ratio and two methylated aromatic ratios mdr and mpi 1 were observed in these oils sulfur associated with evaporite and carbonate environments is a significant factor not only in controlling the occurrence of biomarker isomers but also for petroleum formation at abnormally low thermal stress levels

dinosteranes 4 23 24 trimethylsteranes and other biological markers in dinoglagellate rich marine sediments of rhaetian age abstract alkane biological marker distributions and concentrations have been determined in 18 samples from a section of rhaetian age from the bristol trough and a quantitative micropalaeontological analysis carried out taking into account previous geological investigations of the sequence three end member depositional settings have been recognised from changes in total organic carbon content the biological markers and the micropalaeontological composition these depositional environments are attributed as follows the first which occurs in the lower part of the section corresponds to deposition in a supratidal sabkha type setting with the major organic input being of allochthonous origin the second also in the lower part of the section indicates the occurrence of periods of marine incursion with enhanced salinity resulting from evaporation in the upper part of the section marginal marine conditions are apparent with higher organic carbon biological marker and amorphous organic matter contents at the top suggesting the establishment of more stable conditions of oxygen depletion some sediments in the sequence are notable for containing an abundance of cysts of rhaetogonyaulax rhaetica one of the oldest marine dinoflagellates comparison of microfossil abundances with hydrocarbon abundances extends the circumstantial evidence for the dinophyceae being the major biological source of dinosteranes 4 23 24 trimethylcholestanes and some other 4 methyl steranes in marine sediments the presence of dinosteranes and their 24 ethyl counterparts extends the stratigraphic range of occurrence of such components back to the rhaetian c 31 methyl steranes in the sediments from the second depositional setting are tentatively assigned a 4 22 23 24 tetramethyl sterane skeleton and a dinoflagellate origin

ocean access to a cavity beneath totten glacier in east antarctica totten glacier has the largest thinning rate in east antarctica a derivation of the sea floor bathymetry reveals entrances to the ice cavity beneath the glacier that could allow deep warm water to enter and enhance basal melting

deglacial history of the west antarctic ice sheet in the western amundsen sea embayment abstract the amundsen sea embayment ase drains approximately 35 of the west antarctic ice sheet wais and is one of the most rapidly changing parts of the cryosphere in order to predict future ice sheet behaviour modellers require long term records of ice sheet melting to constrain and build confidence in their simulations here we present detailed marine geological and radiocarbon data along three palaeo ice stream tributary troughs in the western ase to establish vital information on the timing of deglaciation of the wais since the last glacial maximum lgm we have undertaken multi proxy analyses of the cores core description shear strength x radiographs magnetic susceptibility wet bulk density total organic carbon nitrogen carbonate content and clay mineral analyses in order to 1 characterise the sedimentological facies and depositional environments and 2 identify the horizon s in each core that would yield the most reliable age for deglaciation in accordance with previous studies we identify three key facies which offer the most reliable stratigraphies for dating deglaciation by recording the transition from a grounded ice sheet to open marine environments these facies are i subglacial ii proximal grounding line and iii seasonal open marine in addition we incorporate ages from other facies e g glaciomarine diamictons deposited at some distance from the grounding line such as glaciogenic debris flows and iceberg rafted diamictons and turbates into our deglacial model in total we have dated 78 samples mainly the acid insoluble organic aio fraction but also calcareous foraminifers which include 63 downcore and 15 surface samples through careful sample selection prior to dating we have established a robust deglacial chronology for this sector of the wais our data show that deglaciation of the western ase was probably underway as early as 22 351 calibrated years before present cal yr bp reaching the mid shelf by 13 837 cal yr bp and the inner shelf to within c 10 12 km of the present ice shelf front between 12 618 and 10 072 cal yr bp the deglacial steps in the western ase broadly coincide with the rapid rises in sea level associated with global meltwater pulses 1a and 1b although given the potential dating uncertainty additional more precise ages are required before these findings can be fully substantiated finally we show that the rate of ice sheet retreat increased across the deep up to1600 m basins of the inner shelf highlighting the importance of reverse slope and pinning points in accelerated phases of deglaciation

secular and environmental constraints on the occurrence of dinosterane in sediments abstract the distribution patterns of sedimentary a ring methylated steranes have changed markedly over geological time although dinosterane and its isomer 24 ethyl 4 methylcholestane have been tentatively identified in three proterozoic rock units they are either not detectable or occur in low abundance relative to 3 methyl steranes throughout most of the palaeozoic between permian and middle triassic times 260 220 ma ago 4 methyl sterane abundances in marine sediments increased markedly the presence of dinosterane in some middle triassic marine sediments is contemporaneous with the appearance of fossil cysts of uncontested dinoflagellate affinity 4 methyl steranes including dinosterane or their precursor sterenes and sterols then show a continuous presence often in high abundance in marine sediments from the late triassic through to the present day assemblages of 4 methyl steranes and their precursors but with dinosterane absent or in low relative abundance are often the predominant steroids in lacustrine sediments in the cainozoic dinosterane appears to arise predominantly from marine dinoflagellates and as a consequence is a useful biological marker for mesozoic and cainozoic marine organic matter the isomer 24 ethyl 4 methylcholestane is likely to have multiple origins although its very high abundance in tertiary lacustrine sediments and oils compared to older materials suggests that dinoflagellates could also be the source in these cases

the distribution of molecular fossils derived from dinoflagellates in paleogene lacustrine sediments bohai bay basin china steroids with unconventional side chains in ancient sediments and petroleum have been increasingly used as age diagnostic markers triaromatic dinosteroids and dinosteranes occur widely throughout the eocene oligocene shahejie formation in the southeastern bohai bay basin china consistent with its abundant fossil dinoflagellate assemblages in addition 24 norcholestane biomarkers which commonly appear in marine oils have been found in this lacustrine formation although a firm link has not been established between 24 norcholestane and specific modern taxa both diatoms and dinoflagellates are shown to be likely sources of 24 norcholestanes although the shahejie strata lack intact diatom frustules they do exhibit a good relationship between 24 norcholestane other molecular fossils of dinoflagellates and dinocysts dinoflagellates are important precursor taxa of 24 norcholestanes and the various species identified in eocene oligocene lacustrine shales and mudstones of the shahejie formation are all potential sources of the 24 norcholestanes

a dynamic early east antarctic ice sheet suggested by ice covered fjord landscapes the east antarctic ice sheet has played a fundamental part in modulating climate and sea level during the past 30 million years understanding its history is crucial to evaluating its future behaviour and response to global warming airborne ice penetrating radar studies now reveal a fjord like landscape beneath several kilometres of ice in the east antarctic aurora subglacial basin the data confirm and provide a new constraint on the magnitude and dynamics of the oscillations of the east antarctic ice sheet during the late cenozoic which had previously been supported only by marine cores the first cenozoic ice sheets initiated in antarctica from the gamburtsev subglacial mountains1 and other highlands as a result of rapid global cooling 34 million years ago2 in the subsequent 20 million years at a time of declining atmospheric carbon dioxide concentrations2 and an evolving antarctic circumpolar current2 sedimentary sequence interpretation3 and numerical modelling4 suggest that cyclical periods of ice sheet expansion to the continental margin followed by retreat to the subglacial highlands occurred up to thirty times these fluctuations were paced by orbital changes and were a major influence on global sea levels5 ice sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of antarctic topographic lowlands here we show that the basal topography of the aurora subglacial basin of east antarctica at present overlain by 2 4 5 km of ice is characterized by a series of well defined topographic channels within a mountain block landscape the identification of this fjord landscape based on new data from ice penetrating radar provides an improved understanding of the topography of the aurora subglacial basin and its surroundings and reveals a complex surface sculpted by a succession of ice sheet configurations substantially different from today s at different stages during its fluctuations the edge of the east antarctic ice sheet lay pinned along the margins of the aurora subglacial basin the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level although the timing of the channel incision remains uncertain our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions each of which would have over deepened existing topographic depressions reversing valley floor slopes

major environmental change and bonebed genesis prior to the triassic jurassic mass extinction we present new geochemical and sedimentological data from marginal marine strata of penarth bay south wales uk to elucidate the origin of widespread but enigmatic concentrations of vertebrate hard parts bonebeds in marine successions of rhaetian age late triassic sedimentological evidence shows that the phosphatic constituents of the bonebeds were subjected to intense phosphatization in shallow current dominated settings and subsequently reworked and transported basinward by storms interbedded organic rich strata deposited under quiescent and poorly oxygenated conditions record enhanced phosphorus regeneration from sedimentary organic matter into the water column and probably provided the main source of phosphate required for heavy bonebed clast phosphatization the stratigraphically limited interval showing evidence for oxygen depletion and accelerated p cycling coincides with a negative 4 organic carbon isotope excursion which possibly reflects supra regional changes in carbon cycling and clearly predates the initial isotope excursion characterizing many triassic jurassic boundary strata our data indicate that rhaetian bonebeds are the lithological signature of profound climatically driven changes in carbon cycling and redox conditions and support the idea of a multi pulsed environmental crisis at the end of the triassic possibly linked to successive episodes of igneous activity in the central atlantic magmatic province supplementary material sample positions data table and a detailed stratigraphic log from the upper triassic of penarth bay south wales uk are available at http www geolsoc org uk sup18510

a molecular stratigraphic approach to palaeoenvironmental assessment and the recognition of changes in source inputs in marls of the mulhouse basin alsace france principal components analysis pca has been used to investigate changes in concentrations of the components of the hydrocarbon fractions extracted from 71 marl samples selected to cover two total organic carbon toc maxima in the lower part of the salt iv formation a lower oligocene evaporitic sequence from the mulhouse basin france the analysis indicates that the fractions can be ascribed as lying between two end member distributions the changes in these distributions are gradual suggesting that they resulted from fairly gradual changes in the depositional palaeoenvironment these changes are related to increased algal productivity associated with the evolution of a restricted lacustrine environment through to one with a greater marine influence systematic variations in the concentrations of selected components relative to the toc profile point to a repeated sequential evolution in the biological assemblage during deposition of the sequence

observations beneath pine island glacier in west antarctica and implications for its retreat thinning ice in west antarctica is currently contributing about 10 of the observed rise in global sea level observations obtained from an autonomous underwater vehicle operating beneath pine island glacier west antarctica reveal that the glacier was recently grounded on a transverse ridge in the sea floor but now warm sea water flows through the widening gap above the ridge thinning ice in west antarctica resulting from acceleration in the flow of outlet glaciers is at present contributing about 10 of the observed rise in global sea level1 pine island glacier in particular has shown nearly continuous acceleration2 3 and thinning4 5 throughout the short observational record the floating ice shelf that forms where the glacier reaches the coast has been thinning rapidly6 driven by changes in ocean heat transport beneath it as a result the line that separates grounded and floating ice has retreated inland7 these events have been postulated as the cause for the inland thinning and acceleration8 9 here we report evidence gathered by an autonomous underwater vehicle operating beneath the ice shelf that pine island glacier was recently grounded on a transverse ridge in the sea floor warm sea water now flows through a widening gap above the submarine ridge rapidly melting the thick ice of the newly formed upstream half of the ice shelf the present evolution of pine island glacier is thus part of a longer term trend that has moved the downstream limit of grounded ice inland by 30 km into water that is 300 m deeper than over the ridge crest the pace and ultimate extent of such potentially unstable retreat10 are central to the debate over the possibility of widespread ice sheet collapse triggered by climate change11 12

morphology and sedimentary processes on the continental slope off pine island bay amundsen sea west antarctica morphology and sedimentation on the pine island bay continental margin eastern amundsen sea is investigated using swath bathymetry parametric subbottom profiler topas records and sediment cores a major cross shelf trough extends to the continental shelf edge at 114 w through which fast flowing ice drained the west antarctic ice sheet under full glacial conditions the slope adjacent to the trough mouth is 4 whereas to the east and west it is steeper a bulge in bathymetric contours beyond and east of the trough mouth indicates some slope progradation elsewhere seismic reflection profiles indicate major shelf aggradation and minor slope progradation networks of gullies and channels dominate the slope adjacent to pine island bay in front of the trough mouth gullies at the shelf edge and uppermost slope connect directly with channels that continue to the continental rise other gullies connect indirectly with channels further downslope topas records indicate that gully channel systems acted as conduits for coarse grained sediment transfer cores comprise turbidites representing channel deposits and diamicton facies deposited by debris flows sandy turbidites interbedded with hemipelagic muds occur on the rise and abyssal plain the west antarctic ice sheet extended to the shelf edge during full glacials delivering water saturated till and turbid water directly to the continental slope along a line source gully channel systems are probably a product of sediment gravity flows derived from the release of water saturated till and turbid water along the ice sheet margin perhaps augmented subsequently by downslope flow of dense cold and saline water associated with sea ice production during the holocene the gully channel systems enable sediment to bypass the continental slope spatial variations in gully channel system morphology along the amundsen sea continental slope are probably linked to differences in sediment gravity flow processes and the rate and composition of sediment delivered to the shelf edge from the ice sheet cored sediments on the slope and abyssal plain record the widespread presence of turbidite sands indicating that downslope transfer of glacier derived sediments has taken place this supports our interpretation that submarine channels are derived from and are conduits for mass wasting submarine channels on the upper slope continue into the abyssal plain as far north as 67 s they are separated by sediment drifts and sediment waves resulting from the interaction between downslope turbidity current processes and along slope bottom currents similar deep sea sedimentary processes operate along much of west antarctica and the western side of the antarctic peninsula

marine transgressional events in the gigantic freshwater lake songliao paleontological and geochemical evidence abstract the fossil remains of euryhaline organisms in the mesozoic cenozoic non marine sedimentary records of eastern china may have resulted from either marine transgressions or inland hypersaline lacustrine environments paleontological and organic geochemical results of this study have provided new evidence for marine transgressional events in the gigantic freshwater lake songliao during the late cretaceous

repeated large scale retreat and advance of totten glacier indicated by inland bed erosion climate variations cause ice sheets to retreat and advance raising or lowering sea level by metres to decametres the basic relationship is unambiguous but the timing magnitude and sources of sea level change remain unclear in particular the contribution of the east antarctic ice sheet eais is ill defined restricting our appreciation of potential future change several lines of evidence suggest possible collapse of the totten glacier into interior basins during past warm periods most notably the pliocene epoch causing several metres of sea level rise however the structure and long term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice sheet extents here we show that deep ice sheet erosion enough to expose basement rocks has occurred in two regions the head of the totten glacier within 150 kilometres of today s grounding line and deep within the sabrina subglacial basin 350 550 kilometres from this grounding line our results based on icecap aerogeophysical data demarcate the marginal zones of two distinct quasi stable eais configurations corresponding to the modern scale ice sheet with a marginal zone near the present ice sheet margin and the retreated ice sheet with the marginal zone located far inland the transitional region of 200 250 kilometres in width is less eroded suggesting shorter lived exposure to eroding conditions during repeated retreat advance events which are probably driven by ocean forced instabilities representative ice sheet models indicate that the global sea level increase resulting from retreat in this sector can be up to 0 9 metres in the modern scale configuration and exceeds 2 metres in the retreated configuration

sediment delivery and depositional patterns off adelie land east antarctica in relation to late quaternary climatic cycles article i nfo this study focuses on the understanding of depositional patterns over late quaternary glacial interglacial cycles and of the influence of diagenesis on geochemical sedimentary records from the continental margin off adelie land east antarctica we provide a complete analysis of the 30 m long sediment core md03 2603 collected on a deep sea sediment mound deposit the lr04 benthic oxygen isotope stack vs down core records of ba al and ba ti atomic ratios reflectance data and micropaleontological evidence allow to determine a detailed chronology back to 490 ka bp long lived uranium and thorium 238 u 234 u 232 th and 230 th provide an assessment of lateral vs vertical sediment advection by constraining the sediment focusing factor is high in most glacial intervals when mostly detrital material was transported down slope and focused to the core area interglacials display highs in ba al and ba ti coupled to low values related to stronger contour current flow biogenic fractions are more abundant during interglacials and more diluted by detrital fractions during glacials the diatom assemblage is dominated by the open ocean species fragilariopsis kerguelensis but glacial intervals display an increase of sea ice related and coastal species the integrated approach high resolution record of major and minor elements uauth 15 n norg 13 c and corg provides key insights into how redox conditions affect glacial interglacial sedimentation processes our evidence shows that diagenetic effects due to development of reducing conditions and consequent higher preservation of organic matter may overprint the paleoclimatic significance of some proxies involved into a sequence of diagenetic remineralization pathways comparison of the marine record to ice core data epica dome c edc allows to extend the information to the whole east antarctic margin sediment proxies of increased burial of biogenic material or increased preservation of organic matter are linked to climatic amelioration on the continent highs in edc dust flux correlate with high mn al and mo al ratios within the sediment record confirming that establishment of colder conditions on the continent triggered changes in sedimentation rates at the glacial interglacial transition which in turn affected the development of reducing redox fronts within the sediment

the significance of 24 norcholestanes triaromatic steroids and dinosteroids in oils and cambrian ordovician source rocks from the cratonic region of the tarim basin nw china abstract two oil families in ordovician reservoirs from the cratonic region of the tarim basin are distinguished by the distribution of regular steranes triaromatic steroids norcholestanes and dinosteroids oils with relatively lower contents of c 28 regular steranes c 26 20s c 26 20r c 27 20s and c 27 20r regular triaromatic steroids dinosteranes 24 norcholestanes and triaromatic dinosteroids originated from middle upper ordovician source rocks in contrast oils with abnormally high abundances of the above compounds are derived from cambrian and lower ordovician source rocks only a few oils have previously been reported to be of cambrian and lower ordovician origin especially in the east region of the tarim basin this study further reports the discovery of oil accumulations of cambrian and lower ordovician origin in the tabei and tazhong uplifts which indicates a potential for further discoveries involving cambrian and lower ordovician sourced oils in the tarim basin dinosteroids in petroleum and ancient sediments are generally thought to be biomarkers for dinoflagellates and 24 norcholestanes for dinoflagellates and diatoms therefore the abnormally high abundance of these compounds in extracts from the organic rich sediments in the cambrian and lower ordovician and related oils in the cratonic region of the tarim basin suggests that phytoplankton algae related to dinoflagellates have appeared and might have flourished in the tarim basin during the cambrian period steroids with less common structural configurations are underutilized and can expand understanding of the early development history of organisms as well as define petroleum systems

past ice stream and ice sheet changes on the continental shelf off the sabrina coast east antarctica abstract our understanding of the response of the antarctic ice sheet to climate and ocean changes requires the improvement of current ice atmosphere ocean models and the accurate determination of boundary conditions such as ice thickness and extent at key time intervals so that satellite gravity observations and isostatic models can be adjusted however large portions of the antarctic margin remain understudied or lack suitable data one key area where data are lacking is the sabrina coast portion of the east antarctic ice sheet eais margin where the totten glacier which has the largest ice discharge in east antarctica is accelerating thinning and loosing mass at high rates in this work we present the results of the first geological and geophysical marine survey to the continental shelf offshore of the dalton ice tongue and moscow university ice shelf east of the totten glacier the data presented include multibeam swath bathymetry and multichannel seismic focusing on the sea floor morphology and sedimentary section above a regional angular unconformity separating pre and post miocene glacial strata sea floor scouring and iceberg keel marks on the outer shelf associated with gullies on the upper slope indicate that ice expanded in the past and grounded 5 km from the shelf edge at 450 500 mbsl extending 155 km north of the current moscow university ice shelf a nearly 1000 m deep area in the inner middle shelf oriented nw with paleo ice flow direction indicated by mega scale glacial lineations msgl and drumlins is interpreted as a cross shelf glacial trough a series of geomorphic associations on the north eastern side of the glacial trough includes glacial lobes grounding zone wedges gzw glacial lineations and transverse ridges which indicates slower ice grounding line stabilization and collapse these geomorphic associations are organized in 4 four sets representing different past ice flow configurations reflecting changes in ice flow direction grounding line position location of fast and slow ice areas and retreat pattern some of the geomorphic features identified are compatible with the presence of an organized subglacial drainage and others are with rapid grounding line collapse a well preserved series of gzws occurring at different water depths implies they were formed during different glacial stages or cycles the inferred diminishing ice thickness for consecutives gzws indicates that the margin of the antarctic ice sheet evolved to a less extensive coverage of the continental shelf through successive glacial stages or cycles the identification of different ice flow configurations evidence of subglacial water and past ice margin collapse indicates a dynamic ice sheet margin with varying glacial conditions and retreat modes we observe that some of the described morphological associations are similar to those found in the amundsen sea sector of the west antarctic ice sheet wais where they are associated with ice sheet and ice stream collapse although further studies are needed to assess the precise timing and rates of the glacial processes involved we conclude that there is enough evidence to support the hypothesis that the eais margin can behave as dynamically as the wais margin especially during glacial retreat and icesheet margin collapse

characterization of eocene lacustrine source rocks and their oils in the beibuwan basin offshore south china sea two hundred twenty five rock samples and thirty seven oil samples from the beibuwan basin south china sea were analyzed with geochemical and organic petrological techniques to evaluate the eocene lacustrine source rocks and investigate controls on their properties and the distribution of different oil families in the basin two types of organic facies are recognized in the liushagang ls formation the first organic facies is algal dominated and mainly occurs in the organic rich laminated mudstones of the middle member of the ls ls 2 that were deposited in an anoxic stratified medium deep lake environment it is geochemically identified by its high abundance of c30 4 methylsteranes and heavy 13c values in the range of 22 4 to 27 5 the organic matter in this organic facies comprises type i and ii1 kerogens with its macerals dominated by fluorescent amorphous organic matter aom and exinites indicating a highly oil prone character the second organic facies is of terrestrial algal origin and is mainly identified in the non laminated mudstones of the upper ls 1 and lower ls 3 members of the liushagang formation that were deposited in shallow dysoxic weakly stratified fresh water environments source rocks of the second organic facies mainly contain type ii1 ii2 kerogens with mixed macerals of aom internites and vitrinites it is geochemically differentiated from the algal dominated organic facies by its relatively low abundance of c30 4 methylsteranes and lighter 13c values in the range of 27 20 to 28 67 three oil groups are identified by their biomarkers and stable carbon isotopes the first two groups a and b are probably end members of two major oil families a and b that correspond to the algal dominated organic facies and algal terrestrial organic facies respectively most of the discovered oils belong to group a oils that are characterized by a high abundance of c30 4 methylsteranes and heavy 13c values and show a good correlation with the algal dominated organic facies in ls 2 group b oils are found only within the ls 1 and ls 3 reservoirs and they are recognized by their relatively low content of c30 4 methylsteranes and lighter 13c values showing a close relation to the algal terrestrial source facies within the ls 1 and ls 3members respectively group c oils display intermediate biomarker features and stable carbon isotope values and are interpreted to be a mixture of group a and b oils the oil source correlation reveals a strong control of organic facies on the geographic distribution of oil groups or oil fields in the basin

climatic influences on the paleogene evolution of alkenones application of the alkenone paleotemperature proxy uk 37 for marine sediments is typically constrained by three factors i an absence of alkatrienones in sediments deposited where ocean temperatures exceed 28 c ii loss of alkenones in thermally altered sediments and iii poor preservation of alkenone signals due to oxidative degradation in addition there appears to be a temporal limit on the occurrence of alkatrienones which are conspicuously absent in all alkenone containing sediments from the early aptian to the immediate aftermath of the early eocene climatic optimum eeco when they first appeared in arctic ocean sediments compilation of reported and previously unpublished alkenone distributions for the paleogene coupled with assessment of co occurring calcareous nannoplankton genera within the noelaerhabdaceae provide evidence that evolutionary developments in alkenone occurrences include biosynthetic responses likely triggered by climate change the timing of emergence of alkatrienones post eeco and their subsequent appearance at all latitudes during the middle eocene accompanies expansion of the calcareous nannoplankton genus reticulofenestra coincident with significant climate driven changes in oceanic conditions including i modification of trophic structure associated with weakened thermal stratification ii higher productivity facilitated by enhanced nutrient influx and iii changes in seasonality initially at high latitudes related to greater latitudinal temperature gradients collectively these changes would serve to favor eurythermal eurytrophic algae like reticulofenestra with a biomechanism to store energy through production of lipid bodies rich in alkenones during episodes of higher nutrient availability this ability likely enhanced the viability of this marine haptophyte when nutrients were limiting ultimately ensuring its evolutionary success

a hierarchical tectonic model of the gulf of mexico and caribbean region abstract a quantitative computer graphic methodology hierarchical tectonic analysis has been used to model the tectonic evolution of the gulf of mexico and caribbean region this method employs a highly structured hierarchical description of the relative motions of pairs of tectonic elements in order to quantify the timing and style of plate interactions the main features described in this model are 1 1 a revised fit of pangea 2 2 the opening of the gulf of mexico in the middle late jurassic 3 3 the formation of a proto caribbean ocean due to the separation of north and south america during the early cretaceous 4 4 the formation of the greater antilles arc along the western margin of the proto caribbean ocean 5 5 the insertion of the farallon plate between north and south america during the middle cretaceous resulting in the northeastward advance of the greater antilles arc and the subduction of proto caribbean oceanic crust 6 6 the complete subduction of the proto caribbean ocean and the collision of the greater antilles arc with the bahamas platform in the late cretaceous 7 7 the truncation of the caribbean section of the farallon plate from its pacific counterpart and the formation of the panama arc latest cretaceous and 8 8 the westward movement of north and south america with respect to the caribbean plate resulting in the opening of the yucatan basin paleocene and subsequently in the evolution of the cayman trough and e w zone of strike slip

the international bathymetric chart of the southern ocean ibcso version 1 0 a new bathymetric compilation covering circum antarctic waters the international bathymetric chart of the southern ocean ibcso version 1 0 is a new digital bathymetric model dbm portraying the seafloor of the circum antarctic waters south of 60 degrees s

geochemical characteristics palaeoenvironment and formation model of eocene organic rich shales in the beibuwan basin south china sea abstract lacustrine organic rich shales in the eocene are the most important source rock in the beibuwan basin palynological petrographical and geochemical data were applied to define their palaeoenvironment formation and petroleum potential toc values range from 2 84 to 14 77 and the kerogens of these dark gray or brown shales with numerous lamalginites can be classified as oil prone type i and type ii1 biomarkers are characterized by a high abundance of c30 4 methylsteranes a low content of oleanane and diterpanes relatively abundant pentacyclic terpanes which indicate that the organic matter in the shales is typically algal and microbial origin abundance of amorphous organic matter the presence of low level gammacerane small amounts of pyrite pr ph ratios of 1 38 2 42 and v v ni ratios of 0 74 0 84 suggest that the organic rich shales were formed in a less oxic to anoxic stratified fresh brackish lake environment with a relatively low sedimentation rate for this starved lake basin the bloom and death of algae in nutrient rich surface water supplied a large amount of organic matter to the lacustrine sediments the oxygen depleted bottom waters of the palaeo lakes favored the accumulation and preservation of sedimentary organic matter resulting in the formation of the organic rich shale a high quality source rock future exploration or assessment of the petroleum potential of the basin could be assisted by considering the proposed formation model of the organic rich shales and their distribution relative to potential traps

continental slope and rise geomorphology seaward of the totten glacier east antarctica 112 e 122 e abstract the continental slope and rise seaward of the totten glacier and the sabrina coast east antarctica features continental margin depositional systems with high sediment input and consistent along slope current activity understanding their genesis is a necessary step in interpreting the paleoenvironmental records they contain geomorphic mapping using a systematic multibeam survey shows variations in the roles of downslope and along slope sediment transport influenced by broad scale topography and oceanography the study area contains two areas with distinct geomorphology canyons in the eastern part of the area have concave thalwegs are linked to the shelf edge and upper slope and show signs of erosion and deposition along their beds suggesting cycles of activity controlled by climate cycles ridges between these canyons are asymmetric with crests close to the west bank of adjacent canyons and are mostly formed by westward advection of fine sediment lofted from turbidity currents and deposition of hemipelagic sediment they can be thought of as giant levee deposits the ridges in the western part of the area have more gently sloping eastern flanks and rise to shallower depths than those in the east the major canyon in the western part of the area is unusual in having a convex thalweg it is likely fed predominantly by mass movement from the flanks of the adjacent ridges with less sediment input from the shelf edge the western ridges formed by accretion of suspended sediment moving along the margin as a broad plume in response to local oceanography supplemented with detritus originating from the totten glacier this contrasts with interpretations of similar ridges described from other parts of antarctica which emphasise sediment input from canyons immediately up current the overall geomorphology of the sabrina coast slope is part of a continuum of mixed contourite turbidite systems identified on glaciated margins

morphology and acoustic character of the antarctic wilkes land turbidite systems ice sheet sourced versus river sourced fans the wilkes land continental slope contains an intricate network of submarine canyons that on the continental rise develop into a series of channel and overbank deposits of turbidite systems we can define upper fan middle fan and lower fan provinces the wilkes land upper fans are characterized by large channels with relief up to 900 m distances between levee crests up to 18 km and channel floor widths up to 6 km middle fan channels also have high relief 300 m and locally interchannel areas exhibit mounded contourite style deposits with high relief up to 490 m within middle fan sediment mounds there are acoustic facies of channel overbank deposits from turbidity currents and of sediment waves from contour current sedimentation the lower rise is characterized by small shallow channels 50 75 m relief and by interchannel areas of low relief both characteristic of a lower fan environment the wilkes land turbidite systems show the following significant morphological differences compared to most river sourced fans 1 multiple large tributary channels across the upper and middle fan 2 channel relief several times greater 900 m than typical relief 100 200 m for channels on fans less than 300 km in diameter and 3 steep middle fan and lower fan gradients we interpret the differences in channel network patterns channel size and middle fan and lower fan gradients between the wilkes land fans and other fans to result from the continental ice sheet feeding glacial ice streams that reached the outer continental shelf at times of glacial maxima the wilkes land canyon channel network patterns are comparable with the high latitude laurentian fan and labrador sea channels the laurentian fan also has large upper fan channels with larger relief 800 m than typical relief 200 300 m expected for fans that are 600 km in diameter both the labrador sea and laurentian fan are fed by continental ice sheets at the shelf edge

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

paleoenvironmental implications of novel c30 steranes in precambrian to cenozoic age petroleum and bitumen petroleums and bitumens from early proterozoic 1800 ma to miocene 15 ma age marine strata contain 24 isopropylcholestanes a novel group of c30 steroids the abundance of these compounds relative to 24 n propylcholestanes varies with source rock age late proterozoic vendian and early cambrian oils and or bitumens from siberia the urals oman australia and india have a high ratio of 24 isopropylcholestanes to 24 n propylcholestanes 1 while younger and older samples have a lower ratio 0 4 temporal changes in this parameter may reflect the relative abundance of certain porifera sponges and certain marine algae through time geochemical indicators such as this which can constrain the source rock age of a migrated oil are useful in source rock identification during petroleum exploration

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

significance of the fine drainage pattern for submarine canyon evolution the foix canyon system northwestern mediterranean sea abstract submarine gullies are relatively small valleys that occur in a variety of submarine slopes they are very common in continental slopes and in submarine canyon heads and flanks where they often form tributary networks gullies are smaller than submarine canyons though there is no standardised size criterion to distinguish between them gullies and gully networks have been often viewed as initial steps in the development of larger submarine canyons and more mature drainage networks the shelf incising submarine foix canyon system fcs is located in the northwestern mediterranean sea numerous well developed and morphologically diverse gullies carve its two heads and flanks the objective of this study is to analyse the drainage network of the fcs and decipher the role of gullies in its evolution submarine gully and canyon networks were extracted from swath bathymetry data of 50 m grid size using geographic information systems gis a systematic morphometric analysis was carried out on drainage network of the fcs by using the horton strahler method our results show that the fcs is formed by 1660 streams 1000 km in total length which can be classified to six stream orders to detect relevant morphological changes along valley sections the drainage density the stream frequency and the drainage area relief parameters were applied furthermore a branching index i b was developed to characterise the geometry of the submarine drainage network in the canyon heads i b values are 1 7 which correspond to a dendritic network whereas i b in the canyon branches displays values of 2 2 corresponding to a pinnate one at a finer scale we have identified two types of canyon flank gullies namely rim gullies and toe gullies 1 rim gullies form large dendritic networks that extend from the canyon thalweg up to the canyon rim and 2 toe gullies form smaller pinnate networks restricted to the lower part of the canyon flanks the formation and development of rim gullies are interpreted as the main process responsible for canyon head growth and across flank transport of material from the continental shelf toe gullies on the other hand are the morphological expression of the rejuvenation of rim gullies and the canyon itself axial incision and toe gully formation are interpreted as the result of bottom to top erosive processes acting at different scales in response to regional and local changes of the factors controlling the system respectively this study helps to identify a variety of gullies and the processes they result from and provides a morphometric methodology to characterise submarine drainage networks at fine resolution scales

interrelationship of the terranes in western and central cuba comment k piotrowska s paper piotrowska 1993 addresses some of the fundamental problems of cuban and western caribbean geology these include the definition original position and later displacement of suspect terranes in the area problems that have been controversial for many years the model presented by k piotrowska her fig 4 is extremely simple in her model tectonic terranes such as los organos and escambray originally formed part of the yucatan borderland from which they were detached and transported northward during the cretaceous the farallon plate pushed the escambray terrane until it reached its present position finally the escambray terrane was overthrust and pressed into the zaza zone ophiolites and cretaceous volcanic arc suites later during the middle eocene the los organos terrane detached from the yucatan and overthrust the farallon plate zaza zone in this case in order to support this scenario piotrowska 1993 relies on opinions rather than observa

on the circulation and water masses over the antarctic continental slope and rise between 80 and 150 e abstract the circulation and water masses in the region between 80 and 150 e and from the antarctic continental shelf to the southern boundary of the antarctic circumpolar current acc 62 s are described from hydrographic and surface drifter data taken as part of the multi disciplinary experiment baseline research oceanography krill and the environment broke two types of bottom water are identified adelie land bottom water formed locally between 140 and 150 e and ross sea bottom water ross sea bottom water is found only at 150 e whereas adelie land bottom water is found throughout the survey region the bottom water mass properties become progressively warmer and saltier to the west suggesting a westward flow all of the eight meridional ctd sections show an antarctic slope front of varying strength and position with respect to the shelf break in the water formation areas between 140 and 150 e and 104 e the antarctic slope front is more v shaped while elsewhere it is one sided the shape of the slope front and the presence or absence of water formation there are consistent with other meridional sections in the weddel sea and simple theories of bottom water formation gill 1973 deep sea research 20 111 140 whitworth et al 1998 in jacobs and weiss eds ocean ice and atmosphere interactions at the antartic continental margin antarctic research series american geophysical union washington pp 1 27 adcp surface velocities and buoy drift tracks show a strong westward flow over the shelf and slope regions in the region 90 100 e there is a strong eastward flow of the waters just south of the southern boundary of the acc suggesting a recirculation of the westward slope current and the presence of a weak cyclonic gyre using the adcp velocities as a reference for the ctd data the average westward transport in this region is 29 4 14 7 sv

lipids of aquatic organisms as potential contributors to lacustrine sediments ii abstract the relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments previously examined for n alkanols and steroids is now reported for hydrocarbons ketones and carboxylic acids the n c7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment bacterial biomarkers including hopenes and i ai branched fatty acids were detected in the photosynthetic bacterial layer occurring just above the sediment water interface within the sediment the apparent conversion of free n alkanes alkan 2 ones and hydroxy acids to the corresponding bound form is noted microbiological oxidation of n alkanes to alkan 2 ones is supported by the detection of the intermediate alkan 2 ols with a distribution similar to that of the ketones the geochemistry of sediment deposited c 1900 prior to biological study of the site was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition a qualitative difference in algal input to the older sediment is inferred from the low 7 sterol content and presence of 2 6 10 trimethyl 7 3 methylbutyl dodecane however there was still significant dinoflagellate input as indicated by the presence of 4 methylsterols a difference in higher plant input to the older sediment indicated from the n alkane alkene and triterpenoid ketone distributions is consistent with the recent development of tree cover

molecular indicators of palaeoenvironmental conditions in an immature permian shale kupferschiefer lower rhine basin north west germany from free and s bound lipids a study of the distributions of free and s bound biomarkers and their 13c values in the extract of a bulk sample of the permian kupferschiefer from the lower rhine basin has been carried out to provide a more detailed characterization of the biological inputs the distributions and isotopic compositions of selected components released from nickel boride desulphurization have been compared with those of components in the free fraction the free biomarkers occur in greater abundance than their s bound counterparts the distribution and carbon isotopic composition of both free and bound components in the extract indicate a major cyanobacterial and algal input likewise the free and bound aromatic hydrocarbons contain components which reveal an origin from the carotenoids of chlorobiaceae green sulphur bacteria providing molecular evidence for the occurrence of photic zone anoxia in the water column most of the components in the complex mixture of mono di tri and tetra aromatics in the free aromatic hydrocarbon fraction result from cyclization and aromatization reactions

end triassic calcification crisis and blooms of organic walled disaster species the triassic jurassic t j mass extinction event is marked by isotope anomalies in organic 13 corg and carbonate carbon 13 ccarb reservoirs these have been attributed to a rapid 4 fold rise in pco2 as a result of massive flood basalt volcanism and or methane hydrate dissociation here we examine the response of marine photosynthetic phytoplankton to the proposed perturbation in the carbon cycle our high resolution micropalaeontological analysis of t j boundary beds at st audrie s bay in somerset uk provides evidence for a bio calcification crisis that is characterized by 1 extinction and malformation in calcareous nannoplankton and 2 contemporaneous blooms of organic walled green algal disaster species which comprise in one case n70 of the total palynomorph fraction blooms of prasinophytes and acritarchs occur at the onset and in association with a prominent negative shift in 13 corg values close to the first appearance of the early jurassic ammonite psiloceras planorbis across the same interval we obtained palaeotemperature and palaeosalinity estimates from oyster low mg calcite based on mg ca sr ca and 18 o records the results of our palynological and geochemical analyses strongly suggest that shallow marine basins in nw europe during this period became salinity stratified inducing anoxic conditions the t j boundary event shows similarities with the permian triassic p t mass extinction event which was also marked by extensive flood basalt volcanism negative excursions in carbon isotope records a bio calcification crisis the development of shallow marine anoxia and mass abundances of acritarchs in the early triassic this leads us to suggest that the proliferation of green algal phytoplankton may be symptomatic of elevated carbon dioxide levels in the atmosphere and oceans during mass extinction events 2007 published by elsevier b v

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

interhemispheric ice sheet synchronicity during the last glacial maximum the timing of the last maximum extent of the antarctic ice sheets relative to those in the northern hemisphere remains poorly understood we develop a chronology for the weddell sea sector of the east antarctic ice sheet that combined with ages from other antarctic ice sheet sectors indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of northern hemisphere ice sheets surface climate forcing of antarctic mass balance would probably cause an opposite response whereby a warming climate would increase accumulation but not surface melting our new data support teleconnections involving sea level forcing from northern hemisphere ice sheets and changes in north atlantic deep water formation and attendant heat flux to antarctic grounding lines to synchronize the hemispheric ice sheets

antarctic ice sheet sensitivity to obliquity forcing enhanced through ocean connections deep sea geological records indicate that antarctic ice sheet growth and decay is strongly influenced by the earth s astronomical variations known as milankovitch cycles and that the frequency of the glacial interglacial cycles changes through time here we examine the emergence of a strong obliquity axial tilt control on antarctic ice sheet evolution during the miocene by correlating the antarctic margin geological records from 34 to 5 million years ago with a measure of obliquity sensitivity that compares the variance in deep sea sediment core oxygen isotope data at obliquity timescales with variance of the calculated obliquity forcing our analysis reveals distinct phases of ice sheet evolution and suggests the sensitivity to obliquity forcing increases when ice sheet margins extend into marine environments we propose that this occurs because obliquity driven changes in the meridional temperature gradient affect the position and strength of the circum antarctic easterly flow and enhance or reduce ocean heat transport across the antarctic continental margin the influence of obliquity driven changes in ocean dynamics is amplified when marine ice sheets are extensive and sea ice is limited our reconstruction of the antarctic ice sheet history suggests that if sea ice cover decreases in the coming decades ocean driven melting at the ice sheet margin will be amplified the sensitivity of the antarctic ice sheet to obliquity increases when ice sheet margins are exposed to the ocean suggests an analysis of sediment core oxygen isotope records

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

occurrence and composition of solid bitumens from the bulonggoer devonian paleo oil reservoir north xinjiang china abstract the bulonggoer paleo oil reservoir bpr on the northwest junggar basin is the first devonian paleo oil reservoir discovered in north xinjiang china solid bitumens occur within sandstone pores and as veins filling fractures samples of both types were analyzed using stable carbon isotope and reflectance measurements as well as molecular biomarker parameters the extremely positive 13 c values and biomarker indicators of depositional environment lithology such as pristane phytane pr ph c 29 c 30 hopane diasteranes regular steranes and dibenzothiophene phenanthrene ratios indicate a siliciclastic source for the bpr and their deposition in a highly reducing hypersaline environment the presence of long chain n alkanes and abundant tetracyclic diterpanes c 20 c 21 tricyclic terpanes and perylene are indicators of higher plant organic matter input moreover the bimodal distribution of c 27 c 28 29 regular steranes and abundant methyltriaromatic steroids also support a contribution of microalgae as well as higher plants organic matter the similar molecular composition and thermal maturity parameters indicate that the reservoir and veined solid bitumens were altered from a common paleo petroleum which originated from peak oil window matured source rocks all solid bitumens from the bpr are characterized by relatively low bitumen reflectance values rb

organic facies variations in the westbury formation rhaetic bristol channel sw england abstract despite their dark colour laminated fabric and dysoxic character the thermally immature shales of the rhaetic westbury formation of the bristol channel area typically have total organic carbon toc values of only 1 0 1 5 and hydrogen indices hi 200 variations in toc and hi are correlated with the amorphous organic matter aom fluorescence but not the aom suggesting that redox related variations in aom preservation control the organic facies the diameter of equidimensional black wood phytoclasts decreases in intervals with higher toc and hi suggesting an association with lower energy depositional conditions such intervals also show a relative increase in light brown wood probably a reflection of more humid onshore conditions and lower phytoclast oxidation at source phytoc values suggest the input of terrestrial om was relatively low and stable during westbury deposition indicating a distal setting removed from fluviodeltaic sediment sources

sedimentary processes in the wilkes land margin a record of the cenozoic east antarctic ice sheet evolution multichannel seismic data collected off wilkes land east antarctica reveal four main units that represent distinct phases in the evolution of the cenozoic depositional environment a cretaceous synrift succession is overlain by hemipelagic and distal terrigenous sequences deposited during phase 1 sediment ridges and debris flow deposits mark the transition to phase 2 unit 3 records the maximum sediment input from the continent and is characterized by the predominance of turbidite deposits during phase 4 the sediment supply from the continental margin was reduced and draping and filling were the dominant processes on the continental rise unit 4 also contains the deposits of sediment wave fields and asymmetric channel levee systems these four units are a response to the cenozoic evolution of the east antarctic ice sheet during phase 1 small ice caps were formed in the innermost continental areas the ice volume increased under temperate glacial regimes during phases 2 and 3 when large volumes of melt water production led to high sediment discharge to the continental rise change to a polar regime occurred through phase 4 when a thick prograding wedge developed on the continental shelf and slope and the sediment transport to the rise diminished producing general starvation conditions

organic carbon as a palaeoenvironmental indicator in the marine realm recent developments in biogeochemistry have made accessible all information currently known to be present in sedimentary organic compounds i e the carbon skeleton structure the positions of functional groups and stable carbon isotope ratios this combined information has strengthened the applications of sedimentary organic compounds as biomarkers and palaeoenvironmental indicators this review summarizes the most important biomarkers and their applications in reconstructing marine palaeoenvironments and processes the marine environment is characterized by the combined presence of specific compounds such as organic sulphur compounds dinosteroids 24 n propylsteroids even in trace amounts high amounts of c hbi hydrocarbons and the absence of long chain n alkanes with odd over even predominance bicadinanes and specific higher plant triterpenoids e g oleanane furthermore palaeoenvironmental conditions such as photic zone anoxia hypersalinity microbial sulphate reducing activity algal blooming palaeo upwelling and palaeo surface seawater temperature are indicated by molecular and or isotopic characteristics biomarkers from terrestrial sources are included because land derived organic matter is an important contributor to coastal and shallow marine environments a short case study within a holocene terrestrial marine setting florida bay usa is also presented to illustrate the reconstruction of transgressive regressive trends using selected organic compounds

geochemical evidence of organic matter source input and depositional environments in the lower and upper eagle ford formation south texas abstract late cretaceous source rocks in the south texas eagle ford formation were characterized based on geochemical features of the iona 1 core which penetrates the lower and upper eagle ford formation this set of immature samples provides a detailed record of the variation of organic matter om sources across different depositional facies our results show that organic matter rich shales are dominated by marine type ii kerogen lower eagle ford lef contains high sulfur kerogen type ii s with s c 0 04 and a minor contribution of terrestrial om is evident in the upper eagle ford uef combined geochemical data from iona 1 core samples based on bulk geochemical rock properties residual oil chromatography and biomarker analyses reveal that the total organic carbon content and extractable bitumen content in the lef are higher than in the uef redox sensitive biomarkers demonstrate that sulfur rich photic zone anoxia euxinia developed in the lef and that persistent oxygenation occurs during deposition of the uef sulfur rich kerogen in the lef in turn generates medium high sulfur containing oils up to 2 6 as a consequence of the elevated sulfur contents in the lef oil bitumen generation initiated earlier and at lower maturity levels than in the uef high levels of anomalous 22s 22s 22r homohopane ratios and 20s 5 14 17 steranes have been observed in the lef interval which is controversial because of the low maturity level indicated by most bulk geochemical thermal maturity parameters including tmax calculated ro 0 45 and ts ts tm as well as c29ts c29ts c29 hopane and c29 sterane ratios these anomalously high thermal maturity parameters are more likely caused by enhanced isomerisations due to high organic sulfur content under reducing depositional environments in the lef rather than by thermal maturation hypothetical diagenetic pathways for the sulfurisation of homohopanoids and steroids are proposed to explain their abnormal isomerisations in the lef

depositional and erosional signatures in sedimentary successions on the continental slope and rise off prydz bay east antarctica implications for pliocene paleoclimate abstract the prydz bay region of antarctica is the immediate recipient of ice and sediments transported by the lambert glacier the single largest outflow from the east antarctic ice sheet the continental slope and rise provide records covering multiple glacial cycles and containing paleoclimatic information marine geological and geophysical data collected from the continental shelf and adjacent slope of prydz bay antarctica including seismic reflection data bathymetry and core records from odp drilling sites reveal the history of glacial sediment transport and deposition since the early pliocene times seismic facies are interpreted in terms of episodes of slope progradation contourite turbidite trough mouth fan and mass transport deposition two seismic units with estimated age of early to late pliocene and late pliocene to recent have been analyzed in detail for the area immediately offshore the lambert glacier and prydz bay and the adjacent mac robertson margin the upper slope is dominated by episodic mass transport deposits many of which accumulated to form a trough mouth fan since early pliocene times the trough mouth fan contrasts with the adjacent steep 4 6 continental slope of the mac robertson margin where glacigenic sediments have been transported down slope as high velocity turbidity currents via submarine channels the distal region exhibits evidence for contrasting effects of high energy traction dominated versus lower energy fallout dominated suspension flows the counter clockwise coriolis force modifies the erosion and deposition patterns of turbidity currents creating an asymmetric channel levee architecture since the early pliocene turbidite sedimentation surpassed the amount of sediment reworked and transported by westward flowing contour currents along the base of slope on the continental rise contourites and sediment waves were deposited in response to enhanced bottom water formation which is consistent with climatic cooling since late pliocene times this study based on existing seismic reflection and odp data highlights the need for a future scientific ocean drilling proposal on the prydz bay continental slope and rise in order to more accurately determine the timing of the important events that have influenced the evolution of this margin

the age fauna and palaeoenvironment of the late triassic fissure deposits of tytherington south gloucestershire uk important vertebrate faunas occur in fissure deposits of late triassic jurassic age in sw britain although the faunas are well described their age and palaeoenvironment remain poorly understood one such fissure system was documented in detail during quarrying operations at tytherington and has yielded in situ palynomorphs that add much information concerning its age and palaeoenvironment significantly the tytherington fauna is of the sauropsid type that has generally been dated as norian or pre penarth group transgression and was also regarded as representing a distinct upland fauna the palynomorphs which include a significant marine component demonstrate that the tytherington triassic fissures are infilled with late triassic rhaetian sediments that match specific levels in the westbury formation in addition many of the tytherington solutional fissures probably formed during the rhaetian and are consistent with a fluctuating saline to freshwater environment there is no prima facie evidence of solutional formation and infilling of the reptile bearing deposits before the rhaetian trangression the fissure reptile fauna which includes the early dinosaur thecodontosaurus inhabited a small fire swept limestone island in the rhaetian sea the features of the herpetofauna are entirely consistent with this island model which has quaternary analogues

interrelationship of the terranes in western and central cuba abstract present day cuba is a complex of terranes in the western and central parts of the island the sierra de los organos and the escambray terranes which are genetically related and the volcanosedimentary cretaceous sequences of the greater antilles arc are distinguished the escambray and sierra de los organos massifs are terranes that were detached from their source areas near the yucatan a rift separating the yucatan from the florida bahama plate was involved separation of the escambray sequence from that of the sierra de los organos took place in the early cretaceous along a ne sw trending transform fault the escambray sequence was transported together with the greater antilles island arc in front of the farallon plate about 80 ma ago the volcanosedimentary cretaceous sequence of the greater antilles island arc was thrust over the ophiolitic association in this way the zaza zone was formed at that time some overthrusting and metamorphism took place in the escambray massif which was then overthrust and pressed into the zaza zone at about 45 50 ma ago detachment and nappe overthrusting took place in the sierra de los organos and overthrust units reached the margin of the margin of the florida bahama plate various structures are involved in the zaza zone including 1 the volcanosedimentary cretaceous sequences of the greater antilles arc which is a tectonized and overthrust terrane and 2 the ophiolitic association the greater antilles arc terrane is thrust over this association both of these tectonic units were folded together the sierra de los organos and the escambray terranes were thrust onto the zaza zone and then deformed together with it during later phases

trough mouth fans palaeoclimate and ice sheet monitors abstract trough mouth fans are fans at the mouth of transverse troughs channels on glaciated continental shelves on the northwest european glaciated continental margin eight trough mouth fans varying in size between 2700 and 215 000 km 2 have been identified the trough mouth fans are depocentres dominated by debris flows accumulated in front of ice streams draining the former large northwest european ice sheets the debris flow units are separated by hemmipelagic interglacial interstadial sediments it is inferred that the number of debris flow units record the number of shelfbreak positions of the ice sheet margins the number found varies between three in the south and eight in the north typical trough mouth fans and related debris flow units seem to have been formed later than the early mid pleistocene thus the north european ice sheets did not form ice streams extending to the shelfbreak in any appreciable length before the mid pleistocene besides being loci for sediment deposition the trough mouth fans were also the main sites of fresh water supply to the ocean in the form of icebergs during the mid late pleistocene ice ages

new geochemical evidence for the onset of volcanism in the central atlantic magmatic province and environmental change at the triassic jurassic boundary the late triassic early jurassic was a time of major global change however the fundamental processes driving these changes are less than clear we have determined the re and os abundances and os isotope compositions of marine mudrock samples that span the triassic jurassic boundary in the uk and have established that major isotopic and geochemical shifts in the composition of seawater took place in the latest triassic we argue that these shifts were caused by the sudden initiation of widespread igneous activity within the central atlantic magmatic province associated with rifting of the supercontinent pangea the os isotope composition of seawater responded rapidly to these events demonstrating that the seawater os isotope system has great potential in identifying the nature and precise timing of major environmental change