estimation of the hydrocarbon loss through major tectonic events in the tazhong area tarim basin west china abstract the tazhong area located in the central part of the tarim basin is the major commercial oil and gas province in the tarim basin hydrocarbons have been discovered in the ordovician silurian and carboniferous reservoirs most of the hydrocarbon reservoirs in the tazhong area have experienced post charge and accumulation readjustment or loss associated with multiple post charge tectonic movements the relationship between the destroyed hydrocarbon proportion dhp caused by tectonic events and tectonic movement intensity tmi in 15 well blocks has been established for the entire tazhong area using tmi analysis tmi can be quantitatively characterized by the denudation thickness and effective caprock thickness ratio whereas the dhp can be quantitatively determined by the variations of the palaeo and current oil water contacts there appears to be a good relationship between dhp and tmi with a correlation coefficient of 0 9 most of the original ordovician hydrocarbon accumulations formed in the late ordovician had been lost with an average dhp of up to 70 the tectonic movement is much weaker in the late silurian and late permian period with the dhps for the silurian reservoirs and carboniferous reservoirs in the eastern tazhong area averaging 50 all the dhps show a gradual increase from west to the east figure 17 figure 18 figure 19 the preservation condition of the reservoirs is generally better in west than in the east

determination of trapping pressure and temperature of petroleum inclusions using pvt simulation software a case study of lower ordovician carbonates from the lunnan low uplift tarim basin abstract we report a case study carried out on lower ordovician reservoir carbonates of the lunnan low uplift tarim basin to determine trapping pressures and temperatures of petroleum inclusions from the intersection of isochores of coeval petroleum and aqueous fluid inclusions using pvt sim software there are four types of petroleum inclusions from this sequence their trapping pressures and temperatures are type i 80 105 c 199 230 bar type ii 135 145 c 235 250 bar type iii 155 165 c 344 360 bar and type iv 220 252 c 345 390 bar respectively which are consistently higher than their homogenization temperature and saturation pressures by about 5 15 c and 25 70 bar to confirm the reliability of the pvt simulation approach fluid inclusions were synthesized in calcite under controlled temperature and pressure conditions and studied using the same methods the calculated trapping pressure and temperature of the synthetic petroleum inclusions closely match the actual pressure and temperature applied in the experiment by reference to the burial and geothermal history of the tarim host rocks it was inferred that types i ii and iii petroleum inclusions represent fluids associated with three distinct phases of petroleum emplacement in the lower ordovician strata of this area occurring during late silurian to early devonian cretaceous to early tertiary and late tertiary respectively type iv petroleum inclusions occur only in some fine calcite veins from few samples and are believed to be related to an anomalous thermal event in this area on the basis of the trapping pressures and trapping temperatures of the petroleum inclusions three main phases of the petroleum filling of the lower ordovician reservoirs can be delineated phase i and phase iii petroleum events were related to petroleum migration and accumulation from the lunnan low uplift or nearby area the petroleum of the phase ii petroleum event appears to have originated from middle and upper ordovician source rocks in the northern slope area of the manjiaer depression with a long distance migration

interlaminated ice proximal glacimarine sediments in muir inlet alaska muir inlet in glacier bay alaska is a glacial fjord receiving a tremendous volume of sediment annually the rate of sediment accumulation is greatest proximal to muir glacier about 9 m yr 1 and decreases away from the glacier the primary sediment sources are meltwater streams discharging at subglacial and ice marginal positions to form overflows interflows and underflows continuous turbidity currents overflows and interflows interact with diurnal tidal currents and their volume and sediment concentration varies diurnally and annually with meltwater discharge these effects produce cyclic deposits of a thin fine grained sand or silt lamina that grades normally to a thicker poorly to very poorly sorted mud lamina this lamina couplet is termed a cyclopel underflows are suggested to occur in this glacimarine environment because of conditions unique to subglacial fluvial systems underflow deposits occur only in proximal positions 0 5 km from glacier face and are coarse grained reverse to normal graded and exhibit an increase in sorting and sand content up layer ice rafted debris identified as particles 177 m is ubiquitous though low 5 by weight and occurs as isolated particles frozen pellets or as lenses that in cores may have a lamina appearance proximally ice rafted debris is difficult to identify because proximal sediment is often as coarse grained deposited sediment may be reworked by tidal currents and sediment gravity flows depositional processes operating in muir inlet produce interlaminated sand silt clay that characterizes sediment proximal to a glacier and fines seaward to mud sediment is classified into one of three sediment types 1 1 type i sediment is very fine grained mean 8 65 7 17 o low in sand 0 1 11 2 and very poorly to poorly sorted it is the dominant sediment type in muir inlet and is transported by plumes and deposited by suspension settling 2 2 type ii sediment is fine to coarse grained mean 6 70 3 12 o low to high in sand 5 1 86 6 and very poorly to moderately sorted it represents reworked sediment proximal plume deposits or coarse grained laminae of cyclopels 3 3 type iii sediment is coarse grained mean 3 89 2 38 o high in sand 58 0 100 0 and poorly to well sorted it is deposited by sediment gravity flows or underflows

calibration and validation of reservoir models the importance of high resolution quantitative outcrop analogues rapidly developing methods of digital acquisition visualization and analysis allow highly detailed outcrop models to be constructed and used as analogues to provide quantitative information about sedimentological and structural architectures from reservoir to subseismic scales of observation terrestrial laser scanning lidar and high precision real time kinematic gps are key survey technologies for data acquisition 3d visualization facilities are used when analysing the outcrop data analysis of laser scan data involves picking of the point cloud to derive interpolated stratigraphic and structural surfaces the resultant data can be used as input for object based models or can be cellularized and upscaled for use in grid based reservoir modelling outcrop data can also be used to calibrate numerical models of geological processes such as the development and growth of folds and the initiation and propagation of fractures

seismic stratigraphy of the central bransfield basin nw antarctic peninsula interpretation of deposits and sedimentary processes in a glacio marine environment abstract the central bransfield basin is a deep narrow trough between the northern tip of the antarctic peninsula and the south shetland islands analyses of single channel high resolution seismic reflection data are used to characterise the seismic stratigraphy of the central bransfield basin the tectonised acoustic basement is overlain by a 1 s thick sedimentary cover composed of two main sedimentary sequences the lower sequence which shows synsedimentary deformation has only been identified on the antarctic peninsula margin the upper sequence is a complex sedimentary package composed of eight seismic units whose distribution geometry and seismic facies allow two types of seismic units to be distinguished slope and basinal units the slope units constituted by progradational stratified seismic facies form a sedimentary wedge extending from the shelf edge the basinal units fill the basin floor showing chaotic and undulated seismic facies that change basinward into stratified seismic facies both types of seismic units display an interfingering pattern at the base of the slope suggesting an alternating shift of the sedimentary depocentre from the slope to the basinfloor and vice versa this alternate pattern indicates that the sedimentary processes responsible for the infilling of the central bransfield basin followed a cyclic pattern which has likely been associated with the advance and retreat of the ice sheets over the margins during glacial and interglacial episodes during glacial periods the ice sheets advanced eroded the shallower sea floor areas and deposited diamicton and debris flow deposits along the moving grounding line resulting in a progradational sedimentary wedge on the slope at the end of glacial periods coinciding with the retreat of the ice sheets extensive sediment failures affected the continental margin during interglacial periods the ice sheets remained restricted to coastal locations and glacial troughs where processes of meltwater formation might have been significant sediment laden underflows are generated within these troughs from where they flow and spread over the shelf and down the slope to the basinfloor as sediment gravity flow deposits the combined effect of these processes is a progradational build up of the shelf and an aggradational infilling of the basin floor together with the development of the interfingering pattern at the base of the slope

high resolution holocene climate record from maxwell bay south shetland islands antarctica the highest resolution holocene sediment core from the antarctic peninsula to date was collected during the first shaldril cruise nbp0502 drilling yielded a 108 2 m long core 87 recovery site nbp0502 1b from maxwell bay south shetland islands this high resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat such records can help to constrain the nature of past climate change and causal mechanisms and to provide a context for evaluating current climate change and its impacts the base of the drill site sampled till and or proximal glacimarine sediments resting directly on bedrock glacimarine suspension deposits composed of dark greenish gray silty mud with variable diatom abundance and scattered very fine sand laminations make up the majority of the sedimentary section detailed sedimentological and geochemical analyses including magnetic susceptibility total organic carbon toc content carbon and nitrogen isotopic composition pebble content and biogenic silica content allow subdivision of the glacimarine section into nine units and seismic facies analyses resulted in the identification of six distinct seismic units we used 29 radiocarbon ages to construct an age model and calculate sedimentation rates that vary by two orders of magnitude from 0 7 mm a to 30 mm a radiocarbon ages from glacimarine sediments just above the till date back to between 14 1 and 14 8 ka thus ice was grounded in the fjord during the last glacial maximum and eroded older sediments from the fjord following initial retreat of grounded ice from maxwell bay the fjord was covered by a permanent floating ice canopy probably an ice tongue the highest sedimentation rate corresponds to an interval that contains abundant sand laminations and gravelly mud intervals and likely represents a melt out phase or period of rapid glacial retreat from 10 1 ka to 8 2 ka there is no evidence for an early holocene climatic reversal as recorded farther south at the palmer deep drill site minimum sea ice cover and warm water conditions occurred between 8 2 and 5 9 ka from 5 9 to 2 6 ka there was a gradual cooling and more extensive sea ice cover in the bay after 2 6 ka the climate varied slightly causing only subtle variation in glacier grounding lines there is no compelling evidence for a little ice age readvance in maxwell bay the current warming and associated glacial response in the northern antarctic peninsula appears to be unprecedented in its synchroneity and widespread impact

lithogenic and biogenic particle deposition in an antarctic coastal environment marian cove king george island seasonal patterns from a sediment trap study abstract particulate suspended material was recovered over a 23 month period using two sediment traps deployed in shallow water 30 m deep off the king sejong station located in marian cove of king george island west antarctica variability in seasonal flux and geochemical characteristics of the sediment particles highlights seasonal patterns of sedimentation of both lithogenic terrigenous and biogenic particles in the coastal glaciomarine environment all components including total mass flux lithogenic particle flux and biogenic particle flux show distinct seasonal variation with high recovery rates during the summer and low rates under winter fast ice the major contributor to total mass flux is the lithogenic component comprising from 88 during the summer months about 21 g m 2 d 1 up to 97 during the winter season about 2 g m 2 d 1 the lithogenic particle flux depends mainly on the amount of snow melt snow accumulation delivered into the coastal region as well as on the resuspension of sedimentary materials these fine grained lithogenic particles are silt to clay sized composed mostly of clay minerals weathered on king george island biogenic particle flux is also seasonal winter flux is 0 2 g m 2 d 1 whereas the summer contribution increases more than tenfold up to 2 6 g m 2 d 1 different biogenic flux between the two summers indicates inter annual variability to the spring summer phytoplankton bloom the maximum of lithogenic particle flux occurs over a short period of time and follows the peak of biogenic particle flux which lasts longer the seasonal warming and sea ice retreat result in change in seawater nutrient status and subsequent ice edge phytoplankton production meanwhile the meltwater input to marian cove from the coastal drainage in january to february plays a major role in transporting lithogenic particles into the shallow water environment although the tidal currents may be the main agents of resuspension in this kind of sheltered bay

relationship between continental rise development and palaeo ice sheet dynamics northern antarctic peninsula pacific margin abstract acquisition of swath bathymetry data west of the north antarctic peninsula nap between 63 s and 66 s and its integration with the predicted seafloor topography of smith and sandwell global seafloor topography from satellite altimetry and ship depth soundings science 277 1956 1962 reveal the links between the continental rise depositional systems and the nap palaeo ice sheet dynamics the nap pacific margin consists of a wide continental shelf dissected by several troughs tens of kilometres wide and long the biscoe trough which has been almost entirely surveyed with multibeam sonar shows spectacular fan shaped streamlining sea floor morphologies revealing the presence of ice streams during the last glacial maximum in the study area the continental rise comprises the six northernmost sediment mounds of the nap pacific margin and the canyon channel systems between them these giant sediment mounds have developed since the early neogene by southwest flowing bottom currents which have redistributed along the margin the fine grained component of the turbiditic currents flowing down canyon channel systems the widespread evidence of shallow slope instability within the sediment mounds has been identified from both swath bathymetry and topographic parametric sonar seismic reflection profiles bathymetric data show that the heads of all the rise canyon channel systems coincide geographically with the mouths of the major glacial troughs on the continental shelf edge this suggests a close genetic link between these morphological features and allows considering a glacio sedimentary model for the western nap outer margin seascape development this model considers the availability of depositional space on the continental rise as the limiting factor for mound development the depositional space in turn is controlled by the spacing between glacial maxima shelf edge reaching ice streams this model takes into account both glacial and interglacial scenarios and gives new insights on evaluating the palaeoenvironmental record of the continental rise sediment mounds

the cenozoic subduction history of the pacific margin of the antarctic peninsula ridge crest trench interactions new magnetic anomaly identifications w of the shackleton fracture zone show 5 spreading sections separated by fracture zones in the 2 most southerly the ridge crest collided with a trench at the margin of the antarctic peninsula only 6 5 and 4 ma ago the latest of a series of collisions starting at the base of the peninsula so ma ago following each collision spreading and subduction both stopped opposite the south shetland trench and actively extending bransfield strait spreading also stopped 4 ma ago but before the spreading centre reached the trench the tendency of the subducting plate to continue sinking probably initiated the opening of the bransfield strait the parallelism between fracture zone orientation on the descending plate and convergence direction previously thought responsible for the tectonic segmentation of the peninsula was effective for only 10 30 ma before collision before that either the fracture zones did not extend to the trench or the subducting ocean floor formed at the farallon phoenix nazca aluk boundary with fracture zones oblique to the subduction direction the aleutian arc kula ridge model in which arc magmatism virtually ceases when ocean floor younger than 25 30 ma occurs beneath the arc fits the distribution of antarctic peninsula radiometric dates explaining a 50 60 ma gap between collisions and youngest ages in the s and possibly the migration of the youngest activity towards the trench thus gaps in the geologic record of arc magmatism need not imply cessation of subduction the progressive steepening of the peninsular margin towards the 4 ma collision site suggests tectonic erosion of the fore arc as the ridge crest approached

glaciomarine sedimentation and palaeo glacial setting of maxwell bay and its tributary embayment marian cove south shetland islands west antarctica abstract high resolution 3 5 khz and multi channel seismic profiles and piston cores were collected from maxwell bay and its tributary embayment marian cove in the south shetland islands antarctica during the korea antarctic research program 1992 93 and 1995 96 to elucidate the glaciomarine sedimentation processes and recent glacial history of the area seismic data from maxwell bay reveal a rugged bay margin and flattened basin floor covered with well stratified hemipelagic muds on the base of slope acoustically transparent debris flows occur indicating downslope resedimentation of glaciomarine sediments despite the subpolar and ice proximal settings of marian cove the seafloor is highly rugged with a thin sediment drape suggesting that much of the area has been recently eroded by glaciers sediment cores from the cove penetrated three distinct fining upward lithofacies 1 basal till in the lower part of the core accumulated just seaward of the grounding line of the tidewater glacier 2 interlaminated sand and mud in the middle part deposited in ice proximal zone by a combination of episodic subglacial meltwater inflow and iceberg dumping and 3 pebbly mud in the upper part deposited in ice distal zone by both surface meltwater plume and ice rafting from the glacier front a reconstruction of the glacial history of these areas since the late glacial maximum shows an ice sheet filling maxwell bay in late wisconsin time and grounding of the tidewater glacier in marian cove until about 1300 yr bp

magnetic stratigraphy and sedimentology of holocene glacial marine deposits in the palmer deep bellingshausen sea antarctica implications for climate change abstract the palmer deep is a closed bathymetric depression on the antarctic peninsula continental shelf it contains three separate sub basins these basins lie along a northeast southwest axis with water depths ranging from 1400 m to the southwest basins ii and iii to just over 1000 m to the northeast basin i six sediment piston cores were collected from the study region these cores clearly demonstrate the varied sediment character for each basin sediments in basin i are laminated and thinly bedded consisting of diatomaceous pelagic hemipelagic sediments siliciclastic terrigenous sediments and ice rafted hemipelagic sediments in concurrence with other investigators we propose that these laminations and thin beds represent climatically forced productivity cycles basin ii and basin iii sediments alternate between pelagic hemipelagic units and bio siliceous mud turbidites correlations between cores are based on their remarkable magnetic susceptibility ms records which indicate alternating biogenic low ms and siliciclastic high ms dominated sedimentation the bio siliceous mud turbidites are characterized by intermediate to low ms values cores taken from within the main axis of the basins are expanded ultra high resolution sections a core collected on the sill between basins ii and iii represents a condensed sediment section and may contain a complete holocene record of changing paleoenvironments one that records the transition from a glacial ice shelf environment to an open marine holocene environment a sharp drop in magnetic susceptibility at mid core is a common sedimentological feature of each basin presently we favor a climate change hypothesis for this magnetic lithostratigraphic transition which may reflect the termination of the holocene hypsithermal and a marked change in productivity dated ca 2500 years bp

late holocene glacial advance and ice shelf growth in barilari bay graham land west antarctic peninsula three marine sediment cores were collected along the length of the fjord axis of barilari bay graham land west antarctic peninsula 65 55 s 64 43 w multi proxy analytical results constrained by high resolution geochronological methods 210 pb radiocarbon 137 cs in concert with historical observations capture a record of holocene paleoenvironmental variability our results suggest early and middle holocene 7022 2815 cal calibrated yr b p retreated glacial positions and seasonally open marine conditions with increased primary productivity climatic cooling increased sea ice coverage and decreased primary productivity during the neoglacial 2815 to cal 730 cal yr b p this climatic cooling culminated with glacial advance to maximum holocene positions and expansion of a fjord wide ice shelf during the little ice age lia ca 730 82 cal yr b p seasonally open marine conditions were achieved and remnant ice shelves decayed within the context of recent rapid regional warming 82 cal yr b p to present our findings agree with previously observed late holocene cooling and glacial advance across the antarctic peninsula suggesting that the lia was a regionally significant event with few disparities in timing and magnitude comparison of the lia antarctic peninsula record to the rest of the southern hemisphere demonstrates close synchronicity in the southeast pacific and southern most atlantic region but less coherence for the southwest pacific and indian oceans comparisons with the northern hemisphere demonstrate that the lia antarctic peninsula record was contemporaneous with pre lia cooling and sea ice expansion in the north atlantic arctic suggesting a global reach for these events

glaciomarine sedimentation in disraeli fiord high arctic canada abstract disraeli fiord represents a glaciomarine environment unique to the north coast of ellesmere island featuring floating glacier tongues multi year landfast sea ice and a strongly stratified water body which results from enclosure of the fiord by ward hunt ice shelf it is a very low energy depositional environment even at sites proximal to glaciers sediment enters the fiord by interflow and is deposited through suspension settling ice rafting is precluded by the year round sea ice cover sedimentation rates in the inner fiord since about 7000 yrs b p are estimated to be 5 10 cm ka a reflection of the limited sediment influx from the cold based glaciers which contact the fiord changes in sediment structure through the holocene reflect changes in the rate and process of sediment input as well as changes in fiord circulation all of which relate to regional climate during deglaciation early holocene sedimentation rates were orders of magnitude greater than at present subglacial meltwater was the dominant source of inflow with sediment transported in turbid plumes as over or interflow and deposited through suspension settling this is supportive of other studies indicating that a pronounced climatic amelioration led to warm based glaciers at this time

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

benthic foraminiferal distributions in chilean fjords 47 s to 54 s abstract surface sediment samples collected from the fjord region of southern chile 47 to 54 south were analyzed for benthic foraminifera a total of 175 species were identified including agglutinated and calcareous benthic taxa hierarchical cluster analysis of the foraminiferal data resulted in the recognition of three distinct biofacies inner fjord intermediate fjord and channel and oceanic biofacies geographically controlled by relative position between the pacific ocean and fjord heads similarity percentage simper analysis identified key taxa in the definition of the biofacies that include globocassidulina rossensis cassidulina laevigata and bulimina notovata principal components analysis resulted in two principal components representing sediment size and bottom water temperature and salinity regional distributions are strongly controlled by the oceanographic conditions influenced from the pacific in the west and the glacial freshwater input from the east localized distributions of foraminifera are controlled by conditions influenced by the physiography of the individual fjords and channels the distribution of chilean fjord foraminifera and their environmental associations are consistent with results from other temperate to high latitude fjord foraminiferal studies

marine sedimentation at a calving glacier margin a 2 month study at a subpolar tidewater glacier was conducted at anvers island antarctic peninsula lat 64 s to improve understanding of sedimentary processes and associated deposits in glacial marine settings data collected in the ice proximal environment were 1 brash ice size distribution and melt rates to assess sediment source and transport mechanisms 2 conductivity temperature turbidity depth cttd profiles water samples and sediment trap catches to study processes and patterns of sediment dispersal 3 bottom cores and grabs to document recent glacial marine sedimentation and 4 remotely operated vehicle video surveys of the ice terminus and sea bottom to obtain images of physical and biological processes the water column is stratified and a halocline occurs at 20 30 m water temperature ranged from 1 to 1 6 c salinity was 32 34 and suspended solids were 3 5 mg l well above the bottom ephemeral turbid horizons contain 8 15 mg l suspended solids rare surface plumes and a quasipermanent turbid layer produced by resuspension during calving events reach 25 35 mg l meltwater drains from the glacier surface but no subglacial meltwater was detected directly entering the sea the most important sources of sediment appear to be the direct melting of the submerged ice front and melting of calved glacial ice most fragments of floating ice melt within 1 km of the ice front some sediment may be contributed as low density 1 1 g cm 3 algae bound sediment pellets by meltwater streams draining the ablating ice surface sediment enters the stratified water column and is moved by tidal and wind driven circulation marine sedimentation rates are low 3 mm yr relative to depth of bioturbation resulting in unstratified sandy mud with dispersed clasts

the study on the contributing factors of phase state of gas condensate examples from tarim basin abstract the gas condensate is a particular type of hydrocarbon system two methods are presented here to study the origin of gas condensate method 1 is based on the thermal simulation of two typical source rocks humuic organic material and sapropelic material we can get the compositions of generated product and calculate the mole percentages of hydrocarbon the ro values come from the residue generated during the thermal simulation after these data are put into the software package for the pr equation a series of phase diagrams of the generated product can be exported which shows the pvt phase parameters at different thermal evolution stages corresponding to different ro the model of gas condensate formation then could be built it is proved that gas condensate generated from terrestrial humic source rocks with thermal maturities equivalent to vitrinite reflectance ro values between 0 5 and 1 9 and from marine sapropelic source rock with thermal maturities ranging from 1 5 to 1 9 method 2 is based on the analysis of the gas condensate sample from the reservoir the 13 c 1 value of sample determined by sample analysis is used to distinguish the type of the source rock and its maturities by the formula the conversion between 13 c 1 of hydrocarbon system to ro so we can get the ro value of the gas sample and figure out its depth d temperature t and pressure p and then get a phase diagram of the generated product according to our model in method 1 at the same time a present phase diagram of the hydrocarbon systems generated from source rocks can be calculated by pvt analysis the difference between the two phase diagrams can be used to explain the formation mechanism of the gas condensate reservoir the condensate gas reservoirs can be classified into three primary types according to their formation mechanism

the marine record of deglaciation of the south shetland islands antarctica since the last glacial maximum abstract the marine geological record of the glacial retreat history of the south shetland islands is derived from the integration of seismic data core lithofacies radiocarbon ages and geomorphological data from two study areas on the northern shelf we present one of the first published multibeam bathymetric images of the seafloor this new image combined with descriptions of new and existing short sediment cores and high resolution seismic data from the continental shelf north of king george island are used to map a grounding zone wedge that marks the minimum seaward extent of the south shetland ice cap during the last glacial maximum seismic data multibeam bathymetry and sediment cores from maxwell bay on the opposite side of king george island are used to provide further spatial constrains on the history of grounding and retreat of the ice cap along the southern margin of the south shetland islands during the last glacial maximum the south shetland ice cap extended onto the outer continental shelf some 50 km north of its present location the ice grounded on the shelf in troughs in present water depths of almost 400 m it had a minimum thickness of 570 m and was also grounded in the deepest part of fjords and straits between the islands to the south the ice cap extended seaward of the mouths of fjords and straits to the steep northern boundary of the bransfield strait sediment eroded from the fjords and straits was deposited in prominent fans that extend into the bransfield strait and show evidence for an ice shelf that covered the bransfield strait during the last glacial maximum a long drill core shaldril in maxwell bay and several jumbo piston cores yielded carbonate material used to constrain the timing and spatial extent of glacial retreat within maxwell bay the oldest glacimarine sediments in the fjord date back to 14 1 to 14 8 ka and suggest an initial deglaciation earlier than most previous studies of the south shetland islands upper maxwell bay was ice free by 9 1 ka and most of maxwell bay proper was ice free by 5 9 ka except for the smaller tributary fjords of maxwell bay these smaller tributary fjords were ice free by 1 7 ka but may have been ice free earlier but reoccupied by a neoglacial advance that ended approximately 1 7 ka

integrated geological geophysical characterizations of deeply buried fractured vuggy carbonate reservoirs in ordovician strata tarim basin abstract the central uplift region of the tarim basin contains a series of thick ordovician carbonates that form fractured vuggy hydrocarbon rich reservoirs along an unconformity these fractured vuggy reservoirs are difficult to characterize using traditional well logging and seismic interpretation methods because these carbonates feature complex and heterogeneous lithologies and variations in scale geometry and spatial distribution in this paper a series of deeply buried fractured vuggy carbonate reservoirs are characterized on micro macro and mega scales these characterizations are based on previous studies detailing the carbonate sedimentation diagenesis and tectonic processes in the study area and abundant geological and geophysical data including core samples thin sections and well logging and seismic datasets which have been obtained and upscaled using the choosing classification evaluation generalizing upscaling ccegu method in this area different facies can be identified at different scales 1 detailed core and thin section observations performed based on the dunham classification demonstrate that 7 lithofacies and 19 rock types are present at the micro scale 0 01 m 2 logging data and assorted reservoir characteristics indicate that these 19 different rock types consist of 9 different electro facies at the macro scale 0 1 m 1 m and the presence of electro facies in individual wells can be recognized and 3 these 9 different electro facies comprise 6 distinct seismic facies at the mega scale 10 m and can be used to delineate the spatial outlines of potential reservoirs and evaluate their properties the targets of particular interest in the study area are a series of partially dissolved dolomites located near large faults and a series of vuggy soluble limestones located near ne trending strike slip faults this study combines geological and geophysical response data from fractured vuggy carbonate reservoirs to achieve seamless connections among micro scale macro scale and mega scale observations to effectively characterize a series of strongly heterogeneous fractured vuggy reservoirs this method can also be applied to characterize other deeply buried paleokarst reservoirs in the tarim basin as well as other strongly heterogeneous reservoirs

climatic control of sedimentation in bays and fjords of the northern antarctic peninsula abstract the northern antarctic peninsula is dominated by strong climatic gradients which are locally enhanced by subsidiary orographic and topographic effects these gradients are reflected in the sediments of the bays and fjords of the region the climate of the south shetland islands is relatively warm with high levels of precipitation this leads to a temperate glacial setting in which many glaciers terminate on land and bay waters which are turbid with terrigenous debris sediments which consist of terrigenous muds and sands with a low ice rafted debris ird content are relatively thick 70 m and have now filled in and almost completely mask the underlying basement topography the palmer archipelago is colder than the south shetland islands and is the wettest area of the antarctic it is heavily glaciated and all major glaciers are grounded below sea level only rarely have sediment plumes been seen the sediments which are primarily terrigenous muds and sands with a variable ird component are thin maximum 40 m but are ponding in every available bathymetric depression the pristine nature of the ice visible above sea level indicates that terrigenous debris is entering the bays from below sea level sediment gravity flows are important in redistributing sediment the danco coast lies within the precipitation shadow of the graham land plateau its climate is slightly colder and is the driest in the study area with less than half of the precipitation of the palmer archipelago nevertheless it is also heavily glaciated with few exceptions sediments here are diatomaceous muds and oozes they are very thin and drape across the rugged basement topography rather than ponding in lows sediment gravity flow deposits are rare these observations indicate a lower rate of production of terrigenous sediment here a consequence of the drier climatic setting

ice formed intertidal boulder pavements in the sub antarctic abstract boulder pavements are flat tightly packed mosaics of ice smoothed and striated boulders that occur in low gradient intertidal and lacustrine areas in polar regions in the sub antarctic intertidal boulder pavements are located in three morphogenetic environments spanning l0 of latitude some boulder pavements are composed of ice pushed or ice rafted boulders which have been forced into the substrate by the pressure of grounding ice blocks other pavements may result from wave winnowing of glacial till at sea level which has been subsequently modified by grounding ice shallow depressions in the pavement surface may correspond to the loci of large grounded ice blocks and this interpretation is supported by striation and boulder orientations on the ridges between the depressions the occurrence of the pavement appears to depend on the following factors a a boulder supply b frequent onshore movement of floating ice and c a low gradient intertidal zone given such conditions the degree of development of the pavement seems to be controlled by the frequency of onshore ice movement because the best formed pavements occur in areas subject to the highest frequencies of freely moving floating ice the occurrence of raised pavements in the south shetland islands suggests that little morphogenetic change has occurred in the area since 9 000 years ago radiocarbon dating indicates that where the frequency of ice grounding is relatively low periods in excess of 200 years are necessary for pavement development whereas at locations where the ice grounding frequency is high pavements are well formed within 300 years

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 1 oil family classification abstract a series of palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the tarim basin nw china have been examined to delineate oil families crude oils from the mesozoic foreland kuqa depression were also analyzed for comparison the genetic family was assessed using bulk hydrocarbon isotopic composition alkylation pattern of polycyclic aromatic hydrocarbons pahs and biomarker distributions detailed oil oil correlation suggests two distinct families occur in the cratonic region despite the diversity of the reservoir rocks and some variability in oil physical properties the tabei and tazhong oils are classified in general into a single family with a possible indication for secondary subdivision these oils are characterized by low pristane phytane pr ph ratio high dibenzothiophene phenanthrene dbt p ratio light bulk isotopic composition high degree of pah alkylation high proportion of c23 and c24 tricyclic terpanes and low abundance of c24 tetracyclic terpane and triaromatic dinosteroids this family is inferred to have a middle upper ordovician source rock the tadong family distinctly different from the tabei and tazhong families is characterized by relatively high pr ph ratio low dbt p ratio slightly heavier bulk isotopic compositions and low degree of pah alkylation it also has a unique biomarker signature with a high proportion of triaromatic dinosteroids possibly indicating cambrian lower ordovician source rocks the oils from the kuqa depression are easily distinguished from the other two families due to their terrigenous origin the major characteristics of the kuqa oils are high pr ph ratio very low dbt p ratio heavy bulk isotopic composition low pah alkylation degree high proportion of c20 and c21 tricyclic terpanes and c24 tetracylic terpane and abundance of triaromatic dinosteranes and 4 methyl 24 ethyltriaromatic cholestanes these characteristics are consistent with terrestrial organic source rocks deposited under sub oxic conditions

glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and the barents sea a review abstract studies of glacigenic and associated marine sediments in the weddell sea fjords of spitsbergen and barents sea show that during periods of limited glacial coverage interstadials large amounts of material may be brought into the sea mainly by meltwater the major load is deposited relatively close to the icefront 1 at times of maximum glacial extent grounded ice extends onto the shelf with the shelf edge as the outer limit and land and inner shelf areas are eroded main glacial depositional sites are then the outer shelf and shelf edge the sedimentary environment outside an ice shelf is characterized by low clastic supply mainly deposited from icebergs due to low turbidity and a supply of nutrient rich water biogenic matter accumulates leading to a glaciomarine sequence rich in bioclastics sea level lowering results in grounding and seaward expansion of the ice shelf subsequent eustatic rise causes the grounded ice to float deglaciation and sea level rise reduces clastic input to the shelves glacial sediments are reworked and carbonates may accumulate forming tillite carbonate sequence e g late precambrian break up of marine ice sheets such as the barents sea ice sheet seems to have taken place stepwise in response to eustatic rise and climatic changes

marine record of holocene climate ocean and cryosphere interactions herbert sound james ross island antarctica abstract the sediment record offshore james ross island northeast antarctic peninsula presents an unparalleled opportunity to directly compare marine and terrestrial climate records spanning the holocene in maritime antarctica an 11 m drill core was collected between herbert sound and croft bay as part of the shaldril nbp 0502 initiative and produced the southernmost sediment record from the eastern side of the ap thirty eight radiocarbon ages are used to construct an age model of centennial scale resolution multi proxy records including magnetic susceptibility pebble content particle size total organic carbon and diatom assemblages were interrogated in the context of nearby holocene age ice core lake and drift records from james ross island differences in the timing and expression of holocene events reflect marine controls on tidewater glaciers such as water mass configurations and sea ice glacial behavior mimics ice core paleotemperatures during the holocene with the exception of distinct ocean warming events herbert sound was fully occupied by grounded ice during the last glacial maximum and experienced rapid lift off followed by a floating ice phase the canopy of floating ice receded by 10 2 4 cal kyr bp presumably in response to early holocene warming herbert sound and croft bay fully deglaciated by 7 2 cal kyr bp when the mid holocene hypsithermal commenced and the sound became open and productive an extreme peak in productivity 6 1 cal kyr bp indicates an oceanic warming event that is not reflected in atmospheric temperature or lacustrine sediment records increase in sea ice cover and ice rafting mark the onset of the neoglacial 2 5 cal kyr bp when pronounced atmospheric cooling is documented in the james ross island ice core our comparison facilitates more holistic understanding of atmosphere ocean cryosphere interactions that may aid predictions of glacial response to future warming and sea level scenarios

upper oligocene to lowermost miocene strata of king george island south shetland islands antarctica stratigraphy facies analysis and implications for the glacial history of the antarctic peninsula the cape melville formation cmf exposed on southeastern king george island south shetland islands provides rare evidence of extensive earliest miocene glaciation in the antarctic peninsula region the formation records the presence of regional marine based grounded ice on the continental shelf it overlies disconformably the upper oligocene destruction bay formation which consists of sandstones recording nonglacial shallow marine conditions four units have been identified within the approximately 150 m thickness of the cmf the basal unit a consists of coarse glacigenic debris flow facies interbedded with glaciomarine mudstone and sandstone the overlying unit b is mainly fine grained this succession may represent relatively ice proximal deposition followed by glacial retreat and or relative sea level rise the upper cmf units c and d was deposited in an ice distal marine environment with intermittent input of coarse glacigenic debris mainly from ice rafting thin beds of pelagic carbonate ooze within unit c indicate periods of low terrigenous sediment input and high productivity lithologically diverse glacigenic gravel clasts mainly ice rafted debris in the cmf had a wide regional source area suggesting that ice cover was widespread regionally and included calving ice margins for a small proportion of clasts the nearest known source is the mountains fringing the southern weddell sea such clasts were presumably transported north in debris laden icebergs by a strong cold weddell sea surface current a temperate glacial setting is tentatively inferred from the cmf palynological results confirm and enhance the paleoenvironmental interpretation from the sedimentology and include the first early miocene dinoflagellate cyst assemblages recorded on the antarctic peninsula this reappraisal of the glacial record from the cmf provides valuable constraints on the antarctic cryosphere and regional paleoenvironments in the mid cenozoic

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

the dynamics of ice sheet outlets a comparison of data from aircraft altimetry landsat imagery and radia echo sounding has shown characteristic surface topographies associated with sheet and stream flow the transition between the two is abrupt and occurs at a step in the subglacial topography this marks the onset of basal sliding and high velocities caused by subglacial water it results in crevassed amphitheatre like basins round the head of outlet glaciers it is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase this abrupt transition appears to be topographically controlled since basal temperatures are at the pressure melting point well inland of the change in regime the marie byrd land ice streams exhibit qualitative differences from other ice sheet outlets however the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice the repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion this is concentrated towards the heads of outlet glaciers up stream of the region where significant basal decoupling occurs this may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls

crustal growth of the antarctic peninsula by accretion magmatism and extension a subduction accretion model incorporating new geophysical data is presented to explain the geology of the antarctic peninsula from late palaeozoic to cenozoic time according to the model the peninsula consists of overlapping accretionary magmatic and extensional regimes that were diachronous across the peninsula and have built the crust to its present form the crust which contains a small proportion of sialic basement was mainly formed by accretionary and magmatic processes and modified to its present shape by extension the gondwanide orogeny for the antarctic peninsula is interpreted in terms of the accretionary processes

controlling factors and genesis of hydrocarbons with complex phase state in the upper ordovician of the tazhong area tarim basin china seven hydrocarbon reservoirs have been discovered to date in the upper ordovician of the tazhong area a region in which hydrocarbon phase distribution is complex in the present study the genesis and controlling factors of the hydrocarbons with complex phase in the tazhong area were investigated on the basis of the geological and geochemical conditions required for the formation and distribution of hydrocarbon reservoirs integrated with the source rock geochemistry natural gas and oil properties and oil and gas reservoir fluid tests pvt i e pressure volume and temperature tests the results indicate that hydrocarbon reservoir types in the upper ordovician of the tazhong area transition from unsaturated to saturated condensate gas reservoirs from west to east and from condensate gas reservoirs to unsaturated oil reservoirs from north to south the crude oil in the region originated primarily from the mixing of lower middle cambrian and middle upper ordovician source rocks while the natural gas

a model for sedimentation by tidewater glaciers sampling of sediment from the fjord floor in front of tidewater glaciers in glacier bay alaska has provided information about processes in this restricted glacimarine dreimanis 1979 setting sediment sampling in conjunction with oceanographic and glacial dynamics data has also enabled the discrimination of sediment types and their facies associations deposits are strongly controlled by sea water characteristics position and sediment discharge of melt water streams iceberg calving and rate of glacierfront retreat five distinct facies associations have been found to reflect glacier fjord regimes the facies associations and ice fjord conditions responsible for them form the basis for constructing a preliminary model for glacimarine sedimentation by tidewater glaciers the model can be used to predict i rapid retreat of an actively calving ice front ii slow retreat or stabilization of a calving ice front at a channel constriction iii stabilization of a melting very rarely calving ice front when the glacier base is near tidewater elevation and iv large outwash delta progradation into a fjord when the ice front retreats onto land this model can be used to interpret facies associations found in a stratigraphic record

diatom assemblages from coastal settings of west antarctica abstract diatom assemblages from 33 core tops collected along a 2500 km transect of the northern antarctic peninsula and pine island bay areas were examined for their use as paleoenvironmental proxies environmental affinities of assemblages were interpreted within a broad geographical context and a wide range of ecological conditions four major assemblages were identified three pelagic assemblages related to different sea ice duration sst and other conditions affecting primary production and one benthic and epiphytic dominated assemblage typical of near shore shallow water habitats chaetoceros resting spores are an important component of diatom assemblages their high concentrations may reflect increased primary production and are associated with low total assemblage diversities the lowest diversities are observed at sites with increased resting spore percentages along the nw coast of the antarctic peninsula sedimentation rates strongly influence total diatom concentrations by contrast relative abundances of chaetoceros resting spores remain mostly unaffected by terrigenous flux and may serve as a reliable proxy for primary production this broad sampling of antarctic coastal environments fills a gap in our knowledge of phytoplankton communities in polar regions and helps establish the framework for reconstructing paleoenvironments from the paleorecord