stratigraphic and sedimentological evidence for late wisconsinan sub glacial outburst floods to laurentian fan abstract sub glacial meltwater produces a distinctive stratigraphic and sedimentological response on the continental margin seismo stratigraphy of laurentian channel reveals thick till deposits at its seaward end that pass laterally into stratified sediment in deeper basins that may record periods of water build up beneath the ice two scales of meltwater discharge are recognised large scale that caused catastrophic erosion and transported large volumes of coarse sediment to the abyssal plain and smaller scale yielding principally muddy sediment sub glacial outburst floods from the laurentian channel ice stream delivered distinctive red sediment derived from permian carboniferous strata of the gulf of st lawrence directly to laurentian fan between ca 17 and 14 14 c ka separate from north atlantic heinrich events on levees of laurentian fan three major pulses of meltwater plume muds are separated by intervals dominated by hemipelagic sediments these meltwater intervals are recognised distally as periods of plume sedimentation on the scotian slope and ice rafting of hematite stained quartz to the north atlantic ocean in channels of laurentian fan at least one major sediment transport event is recognised that eroded the upper slope and the major fan valleys depositing a bed of gravel at least 3 m thick in the characteristically wide fan valleys and thick sand on the sohm abyssal plain the same event was probably responsible for giant flute like scours the age of the gravel bed is directly constrained only by the presence of local overlying holocene sediment much of the surface of the gravel bed was re worked by the 1929 grand banks turbidity current an erosional event on the upper slope likely correlative with the flood generated gravel bed has been dated at 16 5 14 c ka such large scale erosional flood events can be recognised back through several glacial cycles and have played an important role in the architectural evolution of laurentian fan

the influence of shelf crossing glaciation on continental slope sedimentation flemish pass eastern canadian continental margin abstract flemish pass is a small perched slope basin seaward of the grand banks on the eastern canadian continental margin glacial ice crossed the grand banks to reach the upper continental slope during some mid to late quaternary glaciations but terminated on the middle shelf 200 km distant at the last glacial maximum this study investigates the effect of ice extent on slope sedimentation processes sediment in flemish pass comprises muds of hemipelagic and proglacial plume origin minor thin bedded turbidite sands and thick bedded mass transport deposits mtds a regional stratigraphy based on 500 km of high resolution seismic profiles and 60 piston cores up to 11 m long was dated using 30 radiocarbon dates the presence of ash zone ii and oxygen isotope stratigraphy this provided stratigraphic control for till tongues in water depths

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

on using carbon and oxygen isotope data from glendonites as paleoenvironmental proxies a case study from the permian system of eastern australia abstract glendonites calcite pseudomorphs after ikaite caco3 6h2o feature prominently in fine grained glacially influenced permian marine strata of eastern australia which accumulated in a series of extensional basins that occupied polar to temperate latitudes along the southeastern margin of gondwana because ikaite formation in the marine environment requires near freezing temperatures high alkalinity and elevated concentrations of orthophosphate the presence of glendonites in ancient strata implies a particular array of paleoenvironmental conditions a petrographic and geochemical study was carried out to assess the veracity of isotopic data from glendonites as proxy indicators of ancient ocean chemistry sea floor temperature and diagenesis in thin section glendonites consist of inclusion zoned equant to bladed calcite crystals interpreted as the ikaite replacement phase enclosed in a matrix of calcite and minor chalcedony and pyrite cements carbon and oxygen isotope data show a negative covariance with 18o values ranging from 22 5 to 0 3 and 13c values from 27 7 to 4 5 v pdb of the calcite phases examined the ikaite replacement phase is the most enriched in 18o and most depleted in 13c enclosing cements possess lower 18o and higher 13c values and are interpreted to have formed during later stages of burial diagenesis the 18o values of the ikaite replacement phase do not correspond to formation with permian seawater at near freezing temperatures unless isotopic disequilibrium is assumed the 13c values are similar to the carbon isotope composition of bulk organic matter in the host sediment and suggest that the alkalinity and orthophosphate necessary for ikaite stability were generated in the zone of suboxic to anoxic diagenesis results indicate that although 18o and 13c values from glendonites are useful for understanding early to late diagenetic processes they are not ideal proxies for seawater chemistry and temperature

rare earth patterns with positive cerium anomaly in alkaline waters from lake van turkey abstract the distribution of rare earth elements has been studied for aerobic alkaline ph 9 6 carbonate rich waters from lake van turkey shale normalized ree ree sn patterns display an almost linear increase from the light to the heavy rees and strong positive ce sn anomalies there exist neither positive nor negative gd sn anomalies the ree sn patterns are consistent with domination of ree speciation in solution by poly carbonato complexes generating enrichment of the heavy rees that is even more pronounced than that seen in seawater this is the first report of positive ce sn anomalies observed in ree sn patterns of aerobic natural waters these anomalies apparently result from stabilization of penta carbonato ce iv complexes in solution leading to enhanced abundances of ce in comparison with its trivalent ree neighbours thus in remarkable contrast to seawater positive ce sn anomalies may be general features of alkaline carbonate rich and aerobic lake waters

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

late quaternary stratigraphy and sedimentology of orphan basin implications for meltwater dispersal in the southern labrador sea abstract orphan basin is a deep water basin on the continental margin off newfoundland which throughout the late quaternary received proglacial sediment from local ice that crossed the continental shelf sediment from more distant sources was transported southward in the labrador current as proglacial plumes and in icebergs five sedimentary facies related to glacial processes are distinguished in cores recovered from orphan basin hemipelagic sediment nepheloid layer deposits layered mud beds rich in ice rafted detritus ird sand and mud turbidites and glaciogenic debris flow deposits ird rich beds correspond to periods of intensified iceberg calving and layered mud turbidites and glaciogenic debris flow deposits with glacial meltwater discharge in the late wisconsinan eight periods of meltwater discharge and iceberg calving from the newfoundland ice sheet are interpreted from the sediment facies in orphan basin these discharges coincide with the terminations of the colder periods of the d o cycles recorded in greenland ice cores the oldest minor meltwater event 27 5 28 5 cal ka corresponds to the first late wisconsinan ice advance across the grand banks and ne newfoundland shelf the following three meltwater discharges 23 23 5 23 8 24 5 and 25 27 cal ka deposited sand turbidites and glaciogenic debris flow deposits seaward of trinity trough which was occupied by an ice stream at this time and mud turbidites in the southern part of the basin derived from a mid shelf ice margin on the grand banks four periods of meltwater discharge occurred during the deglaciation and are centered at 15 18 5 19 75 and 20 75 cal ka the youngest is correlated to heinrich event 1 in the literature the 18 5 and 20 75 cal ka events have been recorded in multiple glacial settings in the north atlantic and therefore are interpreted as large scale events of meltwater discharge and iceberg calving but in orphan basin the 19 75 cal ka event is also of similar scale

carbon isotopic evidence of methane oxidation through sulfate reduction in sediment beneath cold seep vents on the seafloor at nankai trough during the kaiko tokai project we took a total of 15 near surface sediment push cores from inside and outside seafloor clam colonies and bacterial mats in the nankai trough in this study we present the chemical and isotopic composition of pore fluids extracted from the sampled cores with special emphasis on those taken at the ryuyo canyon and discuss a the chemical relation between the seeping fluid and biological communities and b the origin of cold seep fluids compared with bottom seawater up to 5 depletion of chloride concentration extremely high ch4 concentration of more than 300 mol kg and slight dh2o depletion are observed in pore fluids at the ryuyo canyon which suggests that the ryuyo canyon is an active seep zone of low chloride ch4 rich low dh2o fluid from the sea bottom remarkable depletion of sulfate and significant enrichment of dissolved inorganic carbon and of hydrogen sulfide are also observed in the pore fluids particularly those taken within bacterial mats while the carbon isotopic composition of pore fluid dissolved methane 13cch4 shows large heterogeneity up to 30 in and around the vents these chemical and isotopic characteristics might be due to active anaerobic methane oxidation and hydrogen sulfide production methane oxidation through sulfate reduction in the sedimentary layer just below within 30 cm the vents on the seafloor the carbon isotopic composition of methane can be considered direct evidence of the mediation process between methane enriched cold seep fluid and the h2s dependent biological community on the cold seep vent after correcting for the effect of methane oxidation at the sediment surface we estimate the end member carbon isotopic composition of methane as less than 90 pdb and the end member ch4 c2h6 ratio as more than 103 which suggests a microbial shallow layer is the origin of methane in the fluid

ocean atmosphere responses to climatic change in the labrador sea pleistocene plankton and pollen records abstract pleistocene climate change is examined using proxy climatic records from oxygen isotope data calcareous and organic walled marine microfossils pollen and terrestrial spores deposited during the past 0 9 ma at odp site 646 in the labrador sea 500 km north of the present polar front paleotransfer functions applied to planktonic foraminiferal assemblages show relative increases in interglacial summer 3 7 and winter 3 5 temperatures and in winter salinity 0 5 2 for the past 0 4 ma but only two earlier intervals early stage 11 and stage 17 have changes of comparable magnitude coccolith and dinoflagellate cyst accumulation rates show that primary productivity is generally correlated with temperature and salinity changes at the start of interglacials these productivity peaks lag the ice volume changes by 2 4 ka dinocyst blooms seem to precede coccolith peaks reflecting the tolerance of opportunistic species for large variations in temperature and salinity peaks in pollen and spore abundance are strongly correlated with ice volume which controls the position and stability of the polar jet stream in addition to the northern extent of forest vegetation time series analysis was made of 7 oceanographic variables sst summer and winter surface salinity coccoliths dinocysts planktonic and benthic foraminifera and 5 other variables 18 pollen spores percent sand foraminiferal test fragmentation and reworked palynomorphs most variables showed significant power peaks at 100 ka and or at 41 ka however sea surface responses showed minor peaks at 26 and 16 ka and microfossil productivity also showed significant peaks at 68 ka the high latitude labrador sea records thus display large non linear regional responses to climate changes in addition to the effects of orbital insolation forcing at 41 and 23 ka

mid late pleistocene glacimarine sedimentary processes of a high latitude deep sea sediment drift antarctic peninsula pacific margin the effects of glaciation on sediment drifts is recognised from marked sedimentary facies variation in deep sea cores taken from the continental rise of the antarctic peninsula pacific margin nineteen sediment cores were visually described logged for magnetic susceptibility and x radiographed about 1000 analyses were performed for grain size clay minerals and biostratigraphy foraminifera nannofossils and diatoms four sediment types associated with distinct sedimentary processes are recognised based on textural compositional analysis 1 hemipelagic mud forms the bulk of the interglacial sediment and accumulated from the pelagic settling of bioclasts and ice rafted wind transported detritus 2 terrigenous mud forms the bulk of the glacial sediment and accumulated from a combination of sedimentary processes including turbidity currents turbid plumes and bottom current reworking of nepheloid layers 3 silty deposits occurring as laminated layers and lenses represent the lateral spillout of low density turbidity currents 4 lastly glacial interglacial gravelly mud layers derive from settling of ice rafted detritus five depositional settings are interpreted within sediment drift 7 each characterised by the dominance interaction of one or several depositional processes the repetitive succession of typical sedimentary facies is inferred to reflect a sequence of four climatic stages glaciation glacial deglaciation and interglacial each one characterised by a distinctive clay mineral assemblage and bioclastic content variations in clay mineral assemblage within interglacial stage 5 core sed 06 suggest minor colder climatic fluctuations possibly correlatable with substages 5a to 5e

canyons and late quaternary sedimentation on the north norwegian margin the presence of erosive canyons on high latitude passive margins is unusual such margins are more normally dominated by subsidence and glacially influenced deposition however ten canyons are identified at the edge of the narrow shelf on the north norwegian margin off the lofoten islands between the traenadjupet and andoya slides on the basis of gloria long range side scan sonar and contemporaneous 3 5 khz profiler data combined with a detailed bathymetry the canyons are located down stream of sediments transported through the lofoten drift and the margin is characterized by an absence of cross shelf troughs canyons are up to 420 m deep u shaped display steep gradients in their upper parts and sediments derived from them have short runout distances onto the continental rise the canyons are estimated to be 20 30 ma old being incised into only thinly covered lithified pre miocene sediments as a response to cenozoic uplift late quaternary sedimentation processes associated with the canyons are inferred to occur during both glacials and interglacials glacial sedimentation is probably in the form of direct subglacial debris input in addition to turbid subglacial meltwater plumes interglacial sedimentation processes are probably dominated by the along shelf transport of sediments by strong ocean currents canyon heads capture sediment from the shelf the remobilization of this coarse material and erosion of the canyons occurs through debris flows and turbidity currents canyon preservation and continued development can be attributed directly to the comparatively low sedimentation rates during full glacial conditions as ice streams located to the north and south produce regional depocentres away from this area of relatively slow flowing ice

gas seepage from tokamachi mud volcanoes onshore niigata basin japan origin post genetic alterations and ch4 co2 fluxes abstract methane and co 2 emissions from the two most active mud volcanoes in central japan murono and kamou tokamachi city niigata basin were measured in from both craters or vents macro seepage and invisible exhalation from the soil mini and microseepage molecular and isotopic compositions of the released gases were also determined gas is thermogenic 13 c ch4 from 32 9 to 36 2 likely associated with oil and enrichments of 13 c in co 2 13 c co2 up to 28 3 and propane 13 c c3h8 up to 8 6 suggest subsurface petroleum biodegradation gas source and post genetic alteration processes did not change from 2004 to 2010 methane flux ranged within the orders of magnitude of 10 1 10 4 g m 2 d 1 in macro seeps and up to 446 g m 2 d 1 from diffuse seepage positive ch 4 fluxes from dry soil were widespread throughout the investigated areas total ch 4 emission from murono and kamou were estimated to be at least 20 and 3 7 ton a 1 respectively of which more than half was from invisible seepage surrounding the mud volcano vents at the macro seeps co 2 fluxes were directly proportional to ch 4 fluxes and the volumetric ratios between ch 4 flux and co 2 flux were similar to the compositional ch 4 co 2 volume ratio macro seep flux data in addition to those of other 13 mud volcanoes supported the hypothesis that molecular fractionation increase of the bernard ratio c 1 c 2 c 3 is inversely proportional to gas migration fluxes the ch 4 emission factor total measured output divided by investigated seepage area was similar to that derived in other mud volcanoes of the same size and activity the updated global emission factor data set now including 27 mud volcanoes from different countries suggests that previous estimates of global ch 4 emission from mud volcanoes may be significantly underestimated

a new estimate of global methane flux from onshore and shallow submarine mud volcanoes to the atmosphere a new estimate of global methane emission into the atmosphere from mud volcanoes mvs on land and shallow seafloor is presented the estimate considered a lower limit is based on 1 new direct measurements of flux including both venting of methane and diffuse microseepage around craters and vents and 2 a classification of mv sizes in terms of area km2 based on a compilation of data from 120 mvs the methane flux to the atmosphere is conservatively estimated between 6 and 9 mt y 1 this emission from mvs is 3 6 of the natural methane sources and is comparable with ocean and hydrate sources officially considered in the atmospheric methane budget the total geologic source including mvs seepage from seafloor microseepage in hydrocarbon prone areas and geothermal sources would amount to 35 45 mt y 1 the authors believe it is time to add this parameter in the intergovernmental panel on climate change official tables of atmospheric methane sources

recognising biodegradation in gas oil accumulations through the δ13c compositions of gas components a large suite of natural gases 93 from the north west shelf and gippsland and otway basins in australia have been characterised chemically and isotopically resulting in the elucidation of two types of gases about 26 of these gases have anomalous stable carbon isotope compositions in the c1 c4 hydrocarbons and co2 components and are interpreted to have a secondary biogenic history the characteristics include unusually large isotopic separations between successive n alkane homologues up to 29 pdb and isotopically heavy co2 up to 19 5 pdb irrespective of geographic location these anomalous gases are from the shallower accumulations 600 1700 m where temperatures are lower than 75 c the secondary biogenic gases are readily distinguishable from thermogenic gases 74 of this sample suite which should assist in the appraisal of hydrocarbons during exploration where hydrocarbon accumulations are under 2000 m while dissolution effects may have contributed to the high 13c enrichment of the co2 component in the secondary biogenic gases the primary signature of this co2 is attributed to biochemical fractionation associated with anaerobic degradation and methanogenesis correlation between biodegraded oils and biodegraded dry gas supports the concept that gas is formed from the bacterial destruction of oil resulting in secondary biogenic gas furthermore the prominence of methanogenic co2 in these types of accumulations along with some isotopically depleted methane provides evidence that the processes of methanogenesis and oil biodegradation are linked it is further proposed that biodegradation of oil proceeds via a complex anaerobic coupling that is integral to and supports methanogenesis

facies characteristics of a proglacial turbiditic sand lobe at svalbard abstract a shallow marine turbiditic lobe inferred to be associated with an ice contact delta was deposited during the last glaciation weichselian at svalbard the norwegian arctic the postglacially raised sandy lobe is exposed in a 200 m long river section and exhibits six units that reflect an early phase of glaciomarine mud deposition followed by three episodes dominated by deposition from sandy turbidity currents the lobe is characterized by a complex pattern of turbidite filled erosional features from thin scour fills reflecting a highly mobile flow pattern to stacked chute fill deposits showing confined flow the sandy turbidites show rhythmic deposition of massive to graded laminae deposited from suspension alternating with faint laminae or ripple cross lamination deposited from tractional transport semi continuous turbidity currents are thought to have been generated by retrogressive slumping of ice proximal well sorted sandy deposits on the delta front and slope the lateral and vertical changes of lithofacies within the sandy lobe are mainly attributed to normal mechanisms of turbiditic lobe growth with only minor effect from synsedimentary glacier terminus movement and minor changes in the meltwater outflow position this detailed mapping of facies changes allows a fairly accurate reconstruction of the axis of the former discharge outlet

geophysical evidence of a late pleistocene glaciation and paleo ice stream on the atlantic continental shelf offshore massachusetts usa abstract interpretations of seismic reflection data collected offshore massachusetts usa reveal the first conclusive geophysical evidence of a pre wisconsinan glaciation that extended beyond the limits of the last glacial maximum lgm in the region the data image numerous glacial geomorphic features that define the extent of a paleo ice stream including 1 a regionally distributed erosion surface that forms a 50 km wide trough with steeply eroded sidewalls 4 18 and nearly 100 m in relief at the margins 2 a network of sub ice sheet meltwater channels and 3 a transparent glacigenic seismic unit the orientation of the paleo ice stream trough indicates that the ice stream flowed to the south southwest toward the shelf break this suggests that the ice stream formed further to the north where it appears that georges bank southeast of the gulf of maine usa redirected ice flow limited well data constrain the glacial erosion event up to 300 m below sea level to occur within the pleistocene the glacial event represents a time of larger ice volume on the northern atlantic continental shelf as compared to the lgm thus we suggest that the event corresponds to marine oxygen isotope stage 12 late pleistocene when the first major pleistocene shelf crossing glaciation began offshore southeastern canada these geophysical constraints on a late pleistocene glaciation offshore massachusetts have important implications for 1 models of the laurentide ice sheet as the geomorphic evidence of pre lgm ice streams are difficult to characterize yet account for most of the ice sheet s mass flux and 2 the pore water salinity pattern offshore new england as sedimentary basins near an ice sheet margin often contain large volumes of glacially emplaced freshwater

oxygen isotopes in lacustrine carbonates of west china revisited implications for post glacial changes in summer monsoon circulation five lakes in the qinghai tibet plateau and north xinjiang have provided oxygen isotope records covering the past 17 11 cal kyr bp the modern lakes are first presented within the major atmospheric circulation and climate patterns of china with the climate related isotope composition of input water equations used to extract hydrological and climatic information from 18o in carbonates are then given after a discussion on potential causes for 18o changes each of the five isotope profiles is interpreted in the light of its specific environmental data the most significant event observed in all records occurred at 12 11 cal kyr bp an abrupt intensification of summer rainfall associated with an extremely rapid 1000 1500 km westward migration of the monsoon fronts the monsoon regime weakened in stages after 8 7 cal kyr bp holocene maximal aridity is recorded at all sites between about 4 5 and 3 5 cal kyr bp long term changes in monsoon strength as inferred from our isotopic interpretation are in good agreement with climate model reconstructions in the tibet qinghai plateau while observed hydrological changes in north xinjiang are not simulated by the models also the non linearity of the holocene monsoon variations cannot be accounted for by orbital forcing

evidence for wisconsinan glaciations in the verrill canyon area scotian slope a composite thickness of about 25 m of sediment has been cored from the verrill canyon on the scotian slope it is interpreted that the majority of this sequence was deposited in a glaciomarine environment during oxygen isotopic stage 2 and the top of stage 3 these sediments as seen in high resolution seismic reflection profiles are well stratified become thicker upslope are laterally variable in thickness and pass upslope into possible outer shelf tills three wedge shaped units of incoherent reflections interfinger with the parallel reflections and terminate in water depths greater than 700 m these wedge shaped units are interpreted as slumped diamict and outwash deposits the age of the uppermost wedge shaped unit is 26 000 21 000 yr based on extrapolation of radiocarbon dates this unit documents a late wisconsinan glacier readvance on the outer scotian shelf the underlying wedge shaped unit estimated to be 70 000 yrs old extends further west along the continental slope and may represent a more extensive early wisconsinan ice advance a third wedge shaped unit inferred to have formed during isotopic stage 6 is possibly a remnant of the first glaciation in the study area

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

interbedded late quaternary turbidites and contourites in flemish pass off southeast canada their recognition origin and temporal variation abstract the recognition of contourite and turbidite deposits in deep marine sequences can be challenging as deposits may show similar sedimentary characteristics in flemish pass a small 1100 m deep perched basin along the southeast canadian continental margin both types of deposits occur late quaternary sediments include thin sand layers interbedded with hemipelagic muds the distribution age sedimentary structures and petrology of these sands were used to distinguish between turbidite and contourite deposits which were then characterized by detailed grain size distribution for understanding the conditions leading to deposition of each type seven sediment facies each with a distinctive grain size distribution were recognized they are 1 transported contourites 2 winnowed beds 3 possible jokulhlaup deposits 4 sandy turbidites 5 muddy turbidites 6 hemipelagic sediment and 7 turbidites from well sorted materials sand packets comprised of several stacked turbidite sand beds some with erosive contacts were correlated from the margin to the basin floor showing clear distal fining and creating a small lobe the temporal distribution of the sand beds indicates that most turbidites and contourites were deposited at stadial to interstadial transitions this linkage may be related to variations in the oceanic circulation in flemish pass which winnowed turbidites and may have triggered turbidity currents by moving sands into canyon heads

till tongue stratigraphy seismostratigraphic studies on the scotian and mid norwegian continental shelves have led to the development of a conceptual model for glacial deposition and erosion by ice sheets in a marine environment till tongue model some of the terminal deposits of the marine ending glaciers are composed in part of acoustically incoherent wedge shaped bodies the wedges are thought to be part of a grounding line system associated with a floating terminus according to the model the sedimentary wedges are formed through the accumulation of glacial debris by subglacial processes proximal to the grounding line together with a penecontemporaneous proglacial contribution from sediment gravity flows sedimentation rates appear to be highest near and proximal to the grounding line that is within a grounding line zone ice proximal stratified glaciomarine sediment accumulates from plumes within the water column and rain out of ice rafted debris the glaciomarine sediment interfingers with the till tongues resulting from oscillations of the grounding line till tongues represent discrete stratigraphic units formed in both vertical and lateral successions marginal to massive till deposits major till tongues can be correlated regionally for hundreds of kilometers and thus can provide a basis for stratigraphic correlation on the mid norwegian shelf lateral and vertical successions of till tongues delineate several large scale till units which represent major advances and retreats of the ice that probably were of both stadial and glacial rank we refer to this type of succession as a till tongue stratigraphy it appears that till tongue formation is limited to intermediate water depths which range from 75 to 1 000 m present water depth but those formed in water depths 600 700 in may not be strictly subglacial in origin we speculate that processes leading to the development of till tongues possibly give rise to the formation of subglacial undermelt till together with thin flow tills near the grounding line it is also possible that another type of subglacial till embracing concepts inherent in the expression deforming basal tills as described by alley and others 1989 may contribute to the formation of till tongues boundaries between the major till units of the mid norwegian shelf are mainly depositional in the zone of maximum glaciation near the shelf edge and upper slope proximal to this zone of major deposition intraformational erosional processes dominate and give rise to smooth widespread time transgressive erosional surfaces erosion progressively increases in a proximal direction beveling the earlier glacial deposits and ultimately reaches and modifies the bedrock surface these regional surfaces are analogous to the ross sea unconformity which was also formed by glacial erosion morainic deposits within a till tongue stratigraphy are termed grounding zone moraines and are subdivided into advance and retreat varieties with linear tabular and hummocky attributes fields of small morainic ridges lift off moraines form in basinal areas during recession

proglacial sediment instability features on the scotian slope at 63 w abstract a small area of the scotian slope has been investigated in detail as a type example of a high latitude continental slope adjacent to a major ice outlet the geologic framework has been defined by airgun seismic profiles which show that late tertiary shales have irregular dips but overlie undisturbed strata these shales form a zone of diapirs at around 1200 m water depth which have ponded the prograding quaternary sediments upslope high resolution sparker profiles seamarc i mid range sidescan imagery and piston cores have been used to investigate the late quaternary sedimentary sequence a prominent gullied horizon about 40 m subbottom that is overlain by acoustically unstratified sediments sands is correlated with the occurrence of an early middle wisconsinan grounded icesheet at the top of the continental slope it is overlain by a thick sequence of proglacial muds and a thin veneer of holocene sediments much of the late wisconsinan sequence has been dissected by a series of closely spaced gullies both sidescan and subbottom profiler data show that slumping is common in the late wisconsinan sequence as a result of high sedimentation rates and local gully erosion piston cores provide evidence for debris flows and turbidity currents depositional sediment mounds in the diapir zone have accumulated sediment at three times the regional sedimentation rate suggesting that large amounts of fine sediment reached the slope in suspension and that much of the proglacial sediment by passed the continental slope

geological history of the flemish pass basin offshore newfoundland in this paper we present a seismic stratigraphic interpretation of the mesozoic and tertiary geologic history of the flemish pass basin offshore newfoundland based on seismic data and data from seven wells that were integrated on the bp subsurface integrated interpretation system siis four megasequences are identified megasequence 1 ms1 is triassic to lower berriasian and includes poorly known sediments associated with triassic early jurassic rifting prior to spreading between the north african and american continents the uppermost mappable unconformity bounded unit within ms1 contains major kimmeridgian to portlandian marine source rocks deposited in two east west trending subbasins in the baccalieu and gabriel areas during the early berriasian pronounced rif ing linked to the subsequent spreading of iberia from the grand banks barremian aptian led to regional deepening and deposition of clastic sediments ms2 in two northeast southwest trending fault bounded subbasins in the baccalieu and gabriel areas in the aptian early cretaceous subbasins were inverted due to strike slip movement as extension assumed a northeast southwest orientation prior to movement of greenland europe away from labrador albian ms3 sediments fill northwest southeast trending fault bounded depocenters typically located on areas that had formed highs during the early cretaceous postrift sedimentation continued from the albian to the present with upper cretaceous pelagic limestone and later clastic sediment deposition

wisconsinan glacial and sea level history of maritime canada and the adjacent continental shelf a correlation of land and sea events the wisconsinan glacial history of maritime canada records the interaction of land based glaciers with the sea which dissects the region along the deep embayments of the bay of fundy and the laurentian channel ice centers collectively termed the appalachian ice complex shifted in a clockwise manner across the varied bedrock terranes of the region producing cross striated bedrock outcrops and compositionally distinct till sheets on land offshore glacial sediments can be correlated to their terrestrial counterparts on the basis of provenance thus establishing crucial land sea links in the glacial record five glacier flow events have been recognized during the caledonia phase in early to middle wisconsinan time ice from eastern appalachian upland sources crossed nova scotia and extended to the continental shelf edge where a calving margin was established slumping at this margin produced proximal wedge shaped bodies of diamicton that interfinger with glaciomarine sediments the caledonia phase glacier retreated during middle wisconsinan time to the inner scotian shelf during the escuminac phase in late wisconsinan time 22 19 ka an ice center formed over the magdalen shelf escuminac ice center and transported large quantities of local red bed material southward to the outer shelf slope margin this glacier retreated about 18 ka to a tidewater margin at sable island bank and banquereau sea level during this time was falling as a result of isostatic recovery from earlier escuminac phase maximum ice loads just after 18 ka ice wasted back across the midshelf basins to the tidewater margin of the scotian shelf end moraine complex and was stabilized by falling sea levels escuminac ice was reorganized into the scotian ice divide scotian phase over mainland nova scotia and the continental shelf south of cape breton island between 15 and 13 ka another period of glacier retreat ensued and the margin settled close to the present day land areas between 13 and 12 5 ka an ice margin was established from local terrestrial ice centers in northern nova scotia chignecto phase into the bay of fundy and just beyond the present day atlantic coast responding to increasing climatic warming these smaller glaciers dissipated and their margins retreated landward a sea level lowstand of 65 m on the inner shelf occurred ca 11 7 ka isolated terrestrial remnants of chignecto phase glaciers were reactivated as a result of cooling during the collins pond phase younger dryas ca 10 8 ka enhanced ice rafting evident in the north atlantic deep oceanic record appears to correlate with periods of glacier retreat in the appalachian ice complex during melting and sea level rise both the quantity and thickness of icebergs increased due to grounding line retreat within the magdalen shelf thereby increasing the net flux of hematite stained quartz to the north atlantic

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

dansgaard oeschger events is there a signal off the hudson strait ice stream abstract it is generally accepted that the dramatic heinrich h events were principally sourced from the major hudson strait drainage basin of the laurentide ice sheet but it is not known whether the higher frequency dansgaard oeschger d o events have an imprint on sediments deposited during the inter h intervals in ice proximal slope sediments this paper examines this question by an analysis of data from cores on the se baffin slope because the proxies for heinrich events are so massive in scale we removed the major h events h 1 h 2 and h 4 from the records so as to better examine the structure of data in the intervening hemipelagic sediments the period of interest extends between 15 and 40 cal ka interstadial events 2 8 resolution varies with the proxy to between 210 and 700 yrs per sample in hu87033 009 from the lower slope a total of twelve variables for example 18o mass magnetic susceptibility calcite dolomite ratio number of ird 2 mm show a variety of multi millennial oscillations although not all of the same amplitude nor frequency several parameters show little correlation with the gisp2 18o record however a comparison of cie sediment color l from hu87033 009 and hu97048 007 from the upper slope with the gisp2 oxygen isotope record suggests that a substantial correlation exists between the records such changes might be associated with either detrital carbonate content or foraminiferal concentrations analysis suggests however that the first possibility is correct hence suggestive of a glaciological response of the hudson strait ice stream with d o events in the nw labrador sea the sediment records from around h 3 time 30 cal ka show excursions which might be correlative within this event but its amplitude is not unusual compared to events both before and after this reaffirms the argument that h 3 represents a different glaciological response a significant issue discussed in this paper is the inherent ambiguity of correlating records whose errors in the time domain approach that of a dominating periodicity in this case ca 1 5 kyr

late cenozoic sea level changes and the onset of glaciation impact on continental slope progradation off eastern canada abstract late cenozoic sedimentation from four varied sites on the continental slopes off southeastern canada has been analysed using high resolution airgun multichannel seismic profiles supplemented with some single channel data biostratigraphic ties are available to exploratory wells at three of the sites uniform slow accumulation of hemipelagic sediments was locally terminated by the late miocene sea level lowering which is also reflected in changes in foraminiferan faunas on the continental shelf data are very limited for the early pliocene but suggest a return to slow hemipelagic sedimentation at the beginning of the late pliocene there was a change in sedimentation style marked by a several fold increase in accumulation rates and cutting of slope valleys this late pliocene cutting of slope valleys corresponds to the onset of late cenozoic growth of the laurentian fan and the initiation of turbidite sedimentation on the sohm abyssal plain although it corresponds to a time of sea level lowering the contrast with the late miocene lowstand indicates that there must also have been a change in sediment delivery to the coastline perhaps as a result of increased rainfall or development of valley glaciers high sedimentation rates continued into the early pleistocene but the extent of slope dissection by gullies increased gully cutting episodes alternated with sediment draping episodes throughout the southeastern canadian continental margin there was a change in sedimentation style in the middle pleistocene that resulted from extensive ice sheets crossing the continental shelf and delivering coarse sediment directly to the continental slope

the age and chronostratigraphical significance of north atlantic ash zone ii rhyolitic tephra with the geochemical characteristics of north atlantic ash zone naaz ii are described from the giant piston core md95 2006 from the northeast atlantic ocean shard size distribution indicates that the tephra represent a wind sorted primary air fall deposit but with a mode close to 200 m they are too coarse to be air fall deposits at the core site which lies ca 1000 km from the possible tephra source randomly sampled shards reveal a single geochemical population belonging to the icelandic transitional alkali magma series suggesting that they are unlikely to represent ice rafted debris derived from icelandic icebergs the tephra probably represent air fall deposits transported to the core site by sea ice within the northeast atlantic gyre the naaz ii peak coincides with the rapid climate transition cooling at the end of interstadial 15 which can be assigned an age of 53 260 2660 yr bp from direct correlation with the greenland ice core gisp2 record a comparison of the md95 2006 neogloboquadrina pachyderma sinistral relative abundance and gisp2 18o records relative to the naaz ii isochron suggests that this climatic event was synchronous across the north atlantic by direct correlation of interstadial maxima between the two records the gisp2 time scale is transferred to md95 2006 comparison of corrected and calibrated radiocarbon ages derived from monospecific foraminifers with the gisp2 ages at the same stratigraphical horizon suggest major age differences these probably result from large variations in atmospheric 14c concentration and highlight the significant uncertainties associated with radiocarbon calibration during marine isotope stage 3 copyright 2004 john wiley sons ltd

terrestrial methane seeps and mud volcanoes a global perspective of gas origin abstract a global database of gas composition and methane stable isotopes of 143 terrestrial mud volcanoes from 12 countries and 60 seeps independent from mud volcanism from eight countries was compiled and examined in order to provide the first worldwide statistics on the origin of methane seeping at the earth s surface sixteen seep data were coupled with their associated subsurface reservoirs the surface seepage data indicate that at least 76 of the mud volcanoes release thermogenic gas with only 4 biogenic and 20 with mixed character the average 201 data of methane concentration and methane carbon isotope ratios 13 c 1 of mud volcanoes are 90 v v and 46 4 respectively the other types of seeps which are independent from mud volcanism have an average 13 c 1 value that is slightly higher 42 9 gases from mud volcanoes are generally lighter more methane less ethane and propane than their associated reservoir gases suggesting a molecular fractionation during advective fluid migration other types of seeps especially dry seeps maintain the reservoir c 1 c 2 c 3 bernard ratio mud volcanoes behave like a natural refinery and the origin of gas more isotopically enriched than 50 and with c 1 c 2 c 3 500 should be attributed to a thermogenic source rather than partial oxidation of biogenic gas some data that appear biogenic in the bernard diagram can be explained by molecular fractionation of mixed gas consequently the bernard parameter may be misleading when applied to mud volcanoes since it does not always reflect the original gas composition the mechanisms of the molecular advective segregation should be studied quantitatively by specific models and experiments

geothermal regime and jurassic source rock maturity of the junggar basin northwest china abstract we analyze the thermal gradient distribution of the junggar basin based on oil test and well logging temperature data the basin wide average thermal gradient in the depth interval of 0 4000 m is 22 6 c km which is lower than other sedimentary basins in china we report 21 measured terrestrial heat flow values based on detailed thermal conductivity data and systematical steady state temperature data these values vary from 27 0 to 54 1 mw m 2 with a mean of 41 8 7 8 mw m 2 the junggar basin appears to be a cool basin in terms of its thermal regime the heat flow distribution within the basin shows the following characteristics 1 the heat flow decreases from the luliang uplift to the southern depression 2 relatively high heat flow values over 50 mw m 2 are confined to the northern part of the eastern uplift and the adjacent parts of the eastern luliang uplift and central depression 3 the lowest heat flow of smaller than 35 mw m 2 occurs in the southern parts of the basin this low thermal regime of the junggar basin is consistent with the geodynamic setting the extrusion of plates around the basin the considerably thick crust the dense lithospheric mantle the relatively stable continental basement of the basin low heat generation and underground water flow of the basin the heat flow of this basin is of great significance to oil exploration and hydrocarbon resource assessment because it bears directly on issues of petroleum source rock maturation almost all oil fields are limited to the areas of higher heat flows the relatively low heat flow values in the junggar basin will deepen the maturity threshold making the deep seated widespread permian and jurassic source rocks in the junggar basin favorable for oil and gas generation in addition the maturity evolution of the lower jurassic badaowan group j 1b and middle jurassic xishanyao group j 2x were calculated based on the thermal data and burial depth the maturity of the jurassic source rocks of the central depression and southern depression increases with depth the source rocks only reached an early maturity with a r 0 of 0 5 0 7 in the wulungu depression the luliang uplift and the western uplift whereas they did not enter the maturity window r 0

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

trinidad mud volcanoes where do the expelled fluids come from abstract in order to establish the origin of fluids expelled from mud volcanoes in trinidad we analyzed their major element trace element and isotopic h o sr compositions the mineralogical chemical and sr isotope compositions of associated expelled muds were also determined on the basis of their chemical and sr isotope compositions the fluids were divided into two groups those southwest and northeast of a major right lateral wrench fault the los bajos fault that both controls the chemical quality of the fluids and acts as a drain strontium isotopes were derived via mixing between a radiogenic source 0 71135 and a nonradiogenic source 0 70671 for both southwest and northeast groups however the nonradiogenic source possibly feeding the northeast group showed a lower sr concentration than that of the southwest group h and o isotope data show that the fluids became enriched in 18 o through interaction with wall rocks the fluids were originally oceanic but their properties were subsequently modified by diagenesis as evidenced by chemical data and mixing between fluids issued from two deep seated reservoirs and surface aquifer end members the gas phase expelled with the mud and the fluid through the mud volcanoes is composed mainly of methane with minor carbon dioxide the amount of expelled gas seems the same in samples from both sides of the los bajos fault the almost unique methane content of the gas phase and the large positive 18 o shifts of the reservoir end member as well as b li and ba contents reveal that the fluids from the deep seated reservoirs inherited their chemical compositions at high temperature fluid rock interactions estimates of equilibrium temperatures of the two deep seated reservoirs suggest that to acquire the estimated higher temperature 150 c the mud volcanoes must have been fed partly by a reservoir located at a depth of more than 3 km this depth corresponds to previous geologic information which located the deep seated reservoir in miocene sediments at such a comparable depth the mixing of the original fluids with a less deep seated reservoir and meteoric waters on the ascending path suggests the presence of a recharge mechanism and contributes to the dynamics of the expulsion itself

geotechnical aspects of seabed pits in the grand banks area ice created seabed pits found on the grand banks of newfoundland can be analysed in terms of probable range of soil strength properties and failure mechanisms to determine the ice loads transmitted to the seabed almost all pits are less than 3 m deep their existence can be explained by indentation failures caused by rolling icebergs about 3 5 of the pits are more than 5 m deep and cannot be explained by iceberg impact this paper presents a possible mechanism for their formation consisting of two actions 1 the hard grounding of an iceberg such that the keel becomes embedded in the seabed and 2 the passive failure of the soil after the grounding event predominantly caused by the loads associated with wave forces on the iceberg at the time of grounding or shortly thereafter a 10 m deep pit located in the hibernia area is analysed with respect to its configuration and soil parameters calculations have shown that though waves in the grand banks area cause forces on the iceberg of a sufficient m

rare earth element distributions among coexisting granulite facies minerals scourian complex nw scotland the major rock forming mineral phases pyroxenes plagioclase garnet hornblende of a suite of granulite facies gneisses from the scourian complex nw scotland have been analyzed for their rare earth element ree content although host rock compositions range from felsic to ultramafic ree abundances and patterns for each mineral group show only limited variation the rees exhibit regular and consistent distribution patterns for each mineral which suggest together with major element and textural considerations that the observed distribution coefficients approach equilibrium total ree content follows the sequence hornblende clinopyroxene garnet plagioclase orthopyroxene and mass balance calculations show that even in the felsic gneisses 60 of the rees reside in the major rock forming minerals comparisons of both relative ree abundances and distribution coefficients with those in other rock types reveal a striking resemblance with patterns observed in mineral liquid pairs of dacitic rocks these similarities may have arisen during a partial melting episode in which granite granodiorite melts were generated and removed from the scourian complex leaving a residuum which is severely depleted in the incompatible elements including the rees

a geochemical study on mud volcanoes in the junggar basin china abstract a comprehensive study was performed to characterize for the first time the mud water and gases released from onshore mud volcanoes located in the southern margin of the junggar basin northwestern china chemical compositions of mud along with the geology of the basin suggest that a source of the mud is mesozoic or cenozoic shale oxygen and h isotope compositions of the released water suggest a local meteoric origin combined with the positive eu anomalies of the water a large 18 o shift of the water suggests extensive interaction with rocks gases discharged from the mud volcanoes are predominantly thermogenic hydrocarbons and the high 13 c values 20 vpdb for co 2 gases and dissolved carbonate in muddy water suggest secondary methanogenesis with co 2 reduction after oil biodegradation the enrichments of eu and 18 o in water and the low thermal gradient of the area suggest that the water rock interactions possibly occur deeper than 3670 200 m on the other hand considering the relationship to the petroleum reservoir around the mud volcanoes the depth of the gases can be derived from about 3600 m a depth that is greater than that generally estimated for reservoirs whose gas is characterized by 13 c enriched co 2 oil biodegradation with co 2 reduction likely occurs at a shallower depth along the seepage system of the mud volcano the results contribute to the worldwide data set of gas genesis in mud volcanoes moreover they further support the concept that most terrestrial mud volcanoes release thermogenic gas produced in very deep sediments and may be early indicators of oil biodegradation an important problem in the petroleum industry

sulphur isotope and elemental geochemistry studies of the hemlo gold mineralization ontario sources of sulphur and implications for the mineralization process discussion undoubtedly geochemical studies can provide key information on the genesis of an ore deposit but it is important to constrain these studies by reliable ore paragenesis this is particularly important for the hemlo gold deposit which is characterized by a long history of deformation and metamorphism in their paper the authors have used sulfur isotope studies to determine the temperature of isotopic equilibrium and to speculate on the possible source of sulfur of barite and sulfides in our opinion the methodology of their study is very questionable because they seem to give no consideration to the ore paragenesis and the relative timing of deformation metamorphism and gold mineralization in the golden giant mine michibayashi 1991 has recorded the presence of two distinct types of barite highly folded and sheared banded barite and massive barite filling fractures within the feldspathic altered ore bodies the massive barite appears to have formed after the potassic alteration as a result of syntectonic remobilization of the banded barite the massive barite is characterized by microstructures polygonal to dynamically recrystallized indicating that barite was deformed plastically based on the mesoscopicand microscopic scale structures the pyrite grains can be divided into three types sub to euhedral pyrite polygonal pyrite and elongate pyrite with their long axes parallel to the schistosity onetching the individual pyrite grains commonly show zoned structure with a core overgrown by a later generation of possibly metamorphic pyrite in the golden giant mine microstructural studies reveal a difference in the timing of formation of molybdenite and stibnite molybdenite has formed synchronously with the development of s and s cleavages and was associated with the formation of potash feldspar and muscovite stibnite occurs along rnicrofractures that cut across both s and s cleavages and is coeval with the development of s michibayashi 1991 gold is associated with both molybdenite and stibnite mineralization and appears to be unrelated to barite the authors have used the equilibrium fractionation between barite and pyrite to determine the temperature according to them the temperatures determined by sulfur isotope fractionation varying between 492 and 557 c are close to those determined by the oxygen isotope fractionation between quartz and muscovite although the oxygen isotope geothermometer

a 200 ka geomagnetic chronostratigraphy for the labrador sea indirect correlation of the sediment record to specmap abstract a chronostratigraphic framework for the last 200 ka based on relative variations of geomagnetic paleointensity has been derived for the labrador sea where 18o stratigraphies are compromised by lack of benthic foraminifera and environmental perturbations of the planktic record relative paleointensity records derived from three labrador sea piston cores are correlated to a recently developed 200 ka paleointensity composite sint 200 y guyodo j p valet earth planet sci lett 143 1996 23 36 the chronology for sint 200 was derived by correlating oxygen isotope stratigraphies from individual paleointensity records to the specmap chronostratigraphy the correlation of sint 200 to labrador sea paleointensity records allows the specmap chronology to be imported into the labrador sea although comparisons of the chronostratigraphy based on paleointensity correlations with those derived from ams 14c dates and 18o data indicate significant discrepancies support for the new chronostratigraphic framework is provided by 1 consistent correlation of labrador sea detrital layers to north atlantic heinrich layers 2 general consistency between planktic 18o values and the specmap reference curve and 3 feasible prediction for the age of ash layer 2 as the new chronostratigraphy is tied to specmap labrador sea sediment cores can now be directly compared with any specmap dated record

late cenozoic architecture of the st pierre slope the late cenozoic seismic stratigraphy of the continental slope south of western newfoundland is interpreted using new seismic reflection profiles new miocene pliocene biostratigraphic palynology age determinations on the hermine e 94 well on the northwestern grand banks of newfoundland are correlated to the study area the quaternary section of st pierre slope is disrupted by numerous failure scarps and mass transport deposits but correlation from the mid slope to the continental rise is achieved using major mass transport deposits as markers on the upper slope stacked downslope thinning wedges of acoustically incoherent sediment are interpreted as till deposits of mid to late pleistocene age sedimentation rates in the youngest part of the succession are estimated from a 30 ka radiocarbon date 25 m below the horizon of the youngest till tongue which is exposed on a 60 m deep failure surface extrapolation of sedimentation rates and comparison with dated sections on the j anomaly ridge and bermuda rise provides a consistent interpreted age model for the till tongues that corresponds to marine isotope stages 2 4 6 8 10 and 12

diagenesis and origin of calcite cement in the flemish pass basin sandstone reservoir upper jurassic implications for porosity development abstract the flemish pass basin is a deep water basin located offshore on the continental passive margin of the grand banks eastern newfoundland which is currently a hydrocarbon exploration target the current study investigates the petrographic characteristics and origin of carbonate cements in the ti 3 member a primary clastic reservoir interval of the bodhran formation upper jurassic in the flemish pass basin the ti 3 sandstones with average q 86 0 f 3 1 r 10 9 contain various diagenetic minerals including calcite pyrite quartz overgrowth dolomite and siderite based on the volume of calcite cement the investigated sandstones can be classified into 1 calcite cemented intervals 20 calcite and 2 poorly calcite cemented intervals porous petrographic analysis shows that the dominant cement is intergranular poikilotopic 300 500 m calcite which stared to form extensively at early diagenesis the precipitation of calcite occured after feldspar leaching and was followed by corrosion of quartz grains intergranular calcite cement hosts all liquid inclusions mainly in the crystal core but rare primary two phase liquid and vapor fluid inclusions in the rims with mean homogenization temperature t h of 70 2 4 9 c and salinity estimates of 8 8 1 2 eq wt nacl the mean 18 o and 13 c isotopic compositions of the intergranular calcite are 8 3 1 2 vpdb and 3 0 1 3 vpdb respectively whereas fracture filling calcite has more depleted 18 o but similar 13 c values the shale normalized rare earth element ree sn patterns of calcite are generally parallel and exhibit slightly negative ce anomalies and positive eu anomalies fluid inclusion gas ratios co 2 ch 4 and n 2 ar of calcite cement further confirms that diagenetic fluids originated from modified seawater combined evidence from petrographic microthermometric and geochemical analyses suggest that 1 the intergranular calcite cement precipitated from diagenetic fluids of mixed marine and meteoric riverine waters in suboxic conditions 2 the cement was sourced from the oxidation of organic matters and the dissolution of biogenic marine carbonates within sandstone beds or adjacent silty mudstones and 3 the late phases of the intergranular and fracture filling calcite cements were deposited from hot circulated basinal fluids calcite cementation acts as a main controlling factor on the reservoir quality in the flemish pass reservoir sandstones over 75 of initial porosity was lost due to the early calcite cementation the development of secondary porosity mostly enlarged moldic pores and throats by later calcite dissolution due to maturation of organic matters e g hydrocarbon and coals was the key process in improving the reservoir quality

glacigenic debris flows on the north sea trough mouth fan during ice stream maxima abstract numerous short sediment cores which penetrate through the glacimarine section and into glacigenic debris flow debrites gdfs on the north sea fan are investigated the sampled gdfs represent the uppermost of several sequences of these stacked bodies many hundreds of metres thick the gdfs occurred over slopes from 0 3 to 0 7 and examples are found from the shelf break at the mouth of the norwegian channel to the norway basin floor 300 km distant the gdf diamicts are structureless and homogeneous in terms of grain size magnetic susceptibility nrm bulk density water carbonate foraminiferal and rock fragment content this applies both from gdf to gdf across the fan and in a proximal distal sense comparison of the investigated lithologic parameters with weichselian till from a borehole in the norwegian channel 200 km up ice shows striking similarity to the gdf debrites ams 14c dates at the gdf glacimarine contact and stratigraphic relationships indicate voluminous deposition before 18 ka continuing possibly uninterrupted until ca 16 ka and a final phase halting just before 15 ka when the norwegian channel became ice free this chronology the comparable lithologic character between till and gdf debrites and a seismic continuity confirms inferences that the gdfs are directly associated with glacial ice at the shelf break the glacial efflux has not been subject to subsequent sorting and the homogeneity of the gdf is thought to reflect thorough mixing in a deforming till layer beneath a fast flowing ice stream the glacimarine section subsequent to gdfs shows no indications of turbidity flow observations are compatible with a slow non disintegrating cohesive plug flow transport mechanism with little sediment water interaction on the upper surface minor distal differentiation might reflect a change in flow process deposition on the fan margins from water borne glacimarine processes simultaneous with gdf deposition is limited

slope instability on a shallow contourite dominated continental margin southeastern grand banks eastern canada abstract submarine sediment failures and related mass transport deposits mtds are widespread on the eastern canadian continental slope settings and in general have been related to ice sheets crossing the outer shelf the southeastern grand banks margin was not glaciated in the last 10 5 years and has a deep shelf break as a result the upper continental slope consists principally of sediment transported from the north by the labrador current high resolution seismic profiles and 10 m long piston cores show widespread sediment failure and mtds in a plastered contourite drift from 500 to 1000 m water depth this study documents the stratigraphy of the past 48 000 years and the record of sediment failure events heinrich layers h1 to h5 have been recognized from distinctive petrology physical properties and bulk geochemistry and are constrained by numerous 14 c ams dates the geotechnical analysis shows that the latest quaternary sediment section is mildly underconsolidated perhaps related to high sedimentation rates up to 0 5 m ka enhanced by some leakage of deep fluids nevertheless factor of safety calculations using su p 0 and friction angles from triaxial testing suggest the slope is statically stable up to gradients of 9 atterberg limit measurements of silty contourite sediments indicate susceptibility to liquefaction under cyclic loading there is evidence that apparently synchronous failure occurred over many tens of kilometres of the slope probably as a result of rare passive margin earthquakes these shallow water contourite deposits have a higher sand and coarse silt content much less biogenic material and more rapid variations in sediment and geotechnical properties than those of the deep water equivalents all of which make them more susceptible to sediment failure

late cenozoic evolution of sackville spur a sediment drift on the newfoundland continental slope the sackville spur is a sediment drift feature that forms a northeastward extension of the grand banks continental slope between the 900 and 2500 m isobaths near latitude 48 n at present the labr

two phase syntectonic gold mineralization and barite remobilization within the main ore body of the golden giant mine hemlo ontario canada abstract structural analysis of the central part of the hemlo gold deposit in the hemlo heron bay greenstone belt has revealed four generations of deformation structures d1 d4 the second d2 and fourth d4 deformations significantly influenced the orebody and controlled the localization of gold mineralization development of d3 dextral shearing during retrogressive conditions resulted in strain partitioning around the feldspathic orebody such that this deposit appears to be controlled by the hemlo shear zone however the orebody dominantly preserves vertical d2 parasitic folds rather than d3 structures the earliest occurrence of gold is with molybdenite as s1 inclusion trails in vanadium muscovite grains that grew during d2 this suggests that the gold deposit was emplaced by at least early d2 syngenetic banded barite was partially dissolved transported and redeposited during each deformation event and in particular in association with brittle deformation that occurred during d4 microstructural relationships indicate two distinct generations of gold the first generation is associated with molybdenite and potassic alteration and was deposited before or early in d2 during progressive amphibolite facies metamorphism the second generation formed by redistribution and concentration of gold together with stibnite in ductile brittle d4 structures after peak metamorphic conditions

composition and origin of coalbed gases in the upper silesian and lublin basins poland abstract coalbed gases in the upper silesian coal basin uscb are highly variable in molecular and stable isotope composition geochemical indices and stable isotope ratios for coalbed gases from uscb vary within the following ranges ch4 c2h6 c3h8 hydrocarbon index from 122 to more than 10 000 cdmi carbon dioxide methane index cdmi co2 co2 ch4 100 from 0 0 to 21 0 13c ch4 from 79 9 to 44 5 d ch4 from 202 to 153 13c c2h6 from 24 6 to 22 3 13c c3h8 24 7 one sample and 13c co2 from 27 2 to 2 8 only two coalbed gases were collected from the lublin coal basin lcb geochemical indices and stable isotope ratios for these samples show the following values hydrocarbon index more than 10 000 cdmi 4 3 and 34 6 13c ch4 67 3 and 52 5 d ch4 201 one sample and 13c co2 13 7 and 11 9 methane higher gaseous hydrocarbons c2 to c5 and carbon dioxide occurring in the coalbed gases in both the uscb and the lcb were generated during the bituminous stage of the coalification process and probably during microbial reduction of carbon dioxide however depth related isotopic fractionation which has resulted from physical e g diffusion and adsorption desorption processes during gas migration cannot be neglected in both basins the coalification process lasted no longer than several ma and was completed at the end of the variscan orogeny at the turn of carboniferous and permian

late quaternary sedimentation on the southwestern scotian slope eastern canada relationship to glaciationgeological survey of canada contribution 20070176 the sedimentary record on continental slopes has the potential to preserve a record of glacial retreat on the adjacent continental shelf the glacial history of the southwestern part of the scotian shelf is poorly known air gun and high resolution sparker profiles and numerous sediment cores up to 10 m long have been used to determine the character of sedimentation on the southwestern scotian slope since the last glacial maximum lgm seismic reflection profiles show that glacial till was deposited at shallow depths on the upper continental slope and correlation to dated piston cores farther downslope show that this till dates from the lgm slope sedimentation at this time was dominated by local ice and deposited as plume fallout and turbidites progressively increasing importance of red brown sediment derived from glacial supply to laurentian channel indicates retreat of ice from the shelf edge and diminishing supply of proglacial sediment from the calving embayment in the mid scotian shelf with the

geochemistry of oils from the junggar basin northwest china the junggar basin of northwestern china is a structural basin containing a thick sequence of paleozoic pleistocene rocks with estimated oil reserves of as much as 5 billion bbl analyses of 19 oil samples from nine producing fields and two oil stained cores in the junggar basin revealed the presence of at least five genetic oil types the geochemistry of the oils indicates source organic matter deposited in fresh to brackish lake and marine environments including coaly organic matter sources the volumetrically most important oil type discovered to date is produced from late carboniferous middle triassic reservoirs in the giant karamay field and nearby fields located along the northwestern margin of the junggar basin oil produced from the mahu field located downdip in a depression east of the karamay field is from a different source than karamay oils unique oil types are also produced from an upper permian reservoir at jimusar field in the southeastern part of the basin and from tertiary oligocene rocks at dushanzi field and lower jurassic rocks at qigu field both located along the southern margin of the basin previous studies have demonstrated the presence of upper permian source rocks and the possibility of mesozoic or tertiary sources has been proposed but not tested by geochemical analysis although analyses of some possible jurassic coal source rocks have been reported our findings indicate that several effective source rocks are present in the basin including local sources of mesozoic or younger age for oil accumulations along the southern and southeastern margins of the basin future exploration or assessment of petroleum potential of the basin can be improved by considering the geological relationships among oil types possible oil source rocks and reservoirs

late quaternary sedimentation in central flemish pass flemish pass is a basin in 1000 m water depth on the continental slope off the grand banks of newfoundland and has a quaternary fill principally of turbidites the late quaternary history of the pass has been investigated using mid range side scan sonargraphs high resolution seismic profiles and cores dated using c 14 the sequence of facies in the cores reveals six lithostratigraphic units deposited in the past 40 ka at 15 19 ka and 25 30 ka sedimentation was dominated by debris flow and turbidite deposits together with hemipelagic deposits of similar clay size mineralogy derived from the grand banks at other times ice rafting and hemipelagic sedimentation principally of carbonate rich sediment transported by the labrador current predominated a late quaternary regional unconformity on the slope may reflect the effects of ice sheets reaching the shelf break probably in the early wisconsinan late wisconsinan resedimentation was not related to ice marginal processes and probably resulted from

evidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud volcanoes abstract the assessment of gas origin in mud volcanoes and related petroleum systems must consider post genetic processes which may alter the original molecular and isotopic composition of reservoir gas beyond eventual molecular and isotopic fractionation due to gas migration and microbial oxidation investigated in previous studies we now demonstrate that mud volcanoes can show signals of anaerobic biodegradation of natural gas and oil in the subsurface a large set of gas geochemical data from more than 150 terrestrial mud volcanoes worldwide has been examined due to the very low amount of c 2 in mud volcanoes isotopic ratios of ethane propane and butane generally the best tracers of anaerobic biodegradation are only available in a few cases however it is observed that 13 c enriched propane is always associated with positive 13 c co2 values which are known indicators of secondary methanogenesis following anaerobic biodegradation of petroleum data from carbon isotopic ratio of co 2 are available for 134 onshore mud volcanoes from 9 countries azerbaijan georgia ukraine russia turkmenistan trinidad italy japan and taiwan exactly 50 of mud volcanoes all releasing thermogenic or mixed methane show at least one sample with 13 c co2 5 pdb thermogenic ch 4 associated with positive carbon isotopic ratio of co 2 generally maintains its 13 c enriched signature which is therefore not perturbed by the lighter secondary microbial gas there is however high variability in the 13 c co2 values within the same mud volcanoes so that positive 13 c co2 values can be found in some vents and not in others or not continuously in the same vent this can be due to high sensitivity of 13 c co2 to gas water rock interactions or to the presence of differently biodegraded seepage systems in the same mud volcano however finding a positive 13 c co2 value should be considered highly indicative of anaerobic biodegradation and further analyses should be made especially if mud volcanoes are to be used as pathfinders of the conditions indicative of subsurface hydrocarbon accumulations in unexplored areas

upper permian lacustrine organic facies evolution southern junggar basin nw china abstract the jingjingzigou lucaogou and hongyanchi formations of the southern junggar basin together comprise over 1000 m of organic rich lacustrine facies they record an overall evolution from relatively shallow evaporative lakes to freshwater lakes associated with fluvial systems the jingjingzigou formation is characterized by low toc and hi and biomarker features such as abundant carotane consistent with a specialized saline or hypersaline biota biomarker distributions in jingjingzigou formation extracts most closely resemble oils from the giant karamay oilfield the lucaogou formation represents one of the richest and thickest lacustrine source rock intervals in the world yet it contradicts conventional lacustrine source rock models in at least two important aspects first deposition occurred at middle paleolatitudes 39 43 n rather than in the tropics second limited nutrient supply in a drainage basin dominated by intermediate volcanic rocks appears to have caused low to moderate primary productivities stable salinity stratification and low inorganic sedimentation rates in a deep lake nonetheless resulted in deposits with up to 20 toc and hi near 800 the overlying hongyanchi formation has 1 5 toc but low hi and was deposited in freshwater oxic to sub oxic lakes

the hemlo gold deposit ontario canada principal deposit characteristics and constraints on mineralization abstract the archean world class hemlo lode gold deposit has been overprinted by deformation and metamorphism resulting in part in several proposed depositional models for its emplacement no single model clearly accounts for all of the characteristics of the deposit most proposed models are inappropriate in terms of timing with respect to host rock deformation intrusion or metamorphism or require inappropriate geometry metal tenors or metal ratios the deposit is spatially associated with high strain zones a restraining bend in the hemlo greenstone belt and the volcanic sedimentary contact of the moose lake volcanic complex mlvc the restraining bend correlates with changes in the style of mineralization and or alteration hence the deposit is subdivided into two segments the west segment is west striking and consists of numerous low grade erratically mineralized west to west northwest striking zones mineralization is locally dominantly fracture controlled or disseminated the main segment strikes approximately 290 contains the majority of the ore and consists of two main tabular zones of dominantly disseminated mineralization the main mineralized zone within the lake superior shear zone and the lower mineralized zone within the moose lake fault zone a broad zone of alteration about 4 km long and as much as 400 m wide asymmetrically surrounds the deposit there is ample evidence at a variety of scales of d 2 structural control on the various mineralized zones tabular zones of alteration and or disseminated mineralization are parallel to the predominant s 2 fabric in the west segment and a composite mylonitic s 2 s 2m s 3c fabric in the main segment tabular mineralized zones of fracture controlled alteration and pervasive alteration are paraconcordant with lithotectonic units the deposit is ductilely deformed by d 2 and d 3 strains which are associated with sinistral and dextral transpression respectively the deposit was emplaced after f 2 folding synchronous with the incipient development of high strain zones during mid d 2 strain post deposit overprinting by deformation and regional metamorphism has resulted in remobilization and modification of some of the original deposit characteristics the hemlo gold deposit is interpreted as an atypical mesozonal orogenic disseminated replacement stockwork deposit broadly synchronous with d 2 and middle stage granitoid plutonism prior to or synchronous with peak regional metamorphism and involving magmatic metamorphic fluids its emplacement is poorly constrained between 2694 and 2677 ma u pb systematics are consistent with field evidence for a history of protracted episodic progressive strain intrusive activity and an evolving hydrothermal system the chief emplacement controls specifically appear to have been the restraining bend competency contrast at a major lithologic contact and permeability in a fragmental unit with general more broadly developed steady state permeability in ductile zones enigmatic barite associated with the deposit is considered an intrinsic product of the hydrothermal system the orientation of the major part of the deposit is consistent with statistically preferred orientations for large gold deposits in other gold camps of the superior province other examples of alteration and mineralization in the hemlo greenstone belt share some common attributes with the hemlo deposit these factors provide a basis for selecting favourable exploration targets in the greenstone belt

the influence of meltwater on the labrador current in heinrich event 1 and the younger dryas abstract the labrador current transports freshwater from the arctic regions to the northern atlantic and the freshwater flux can influence the meridional overturning circulation the response of the labrador current to meltwater processes is unclear during the deglaciation of the ice sheets around the northwest atlantic this study utilized cores from flemish pass to monitor variations in the strength of the labrador current by using the sortable silt proxy the carbonate content the amount of ice rafted detritus and xrf chemical data were measured to identify the main meltwater events during the last deglaciation this study observed a clear enhancement of the flow strength of the labrador current in heinrich event 1 and the younger dryas with the greatest flow strength during the younger dryas event the onset of the current enhancement was dated at ca 13 cal ka bp which preceded the enhanced ice rafted deposition in hudson strait by about one thousand years the current enhancement in flemish pass during the younger dryas event corresponds to the freshening of the surface water thus meltwater preceding significant iceberg supply has an important effect on the labrador current in heinrich events on the laurentide ice sheet margin

linking continental slope failures and climate change testing the clathrate gun hypothesis it has been suggested that the release of clathrates rather than expansion of wetlands is the primary cause of the rapid increases observed in the ice core atmospheric methane record during the pleistocene because submarine sediment failures can involve as much as 5000 gt of sediment and have the capacity to release vast quantities of methane hydrates one of the major tests of the clathrate gun hypothesis is determining whether the periods of enhanced continental slope failure and atmospheric methane correlate to test the clathrate gun hypothesis we have collated published dates for submarine sediment failures in the north atlantic sector and correlated them with climatic change for the past 45 k y more than 70 by volume of continental slope failures during the past 45 k y was displaced in two periods between 15 and 13 ka and between 11 and 8 ka both these intervals correlate with rising sea level and peaks in the methane record during the bolling allerod and preboreal periods these data support the clathrate gun hypothesis for glacial interglacial transitions the data do not however support the clathrate gun hypothesis for glacial millennial scale climate cycles because the occurrence of sediment failures correlates with heinrich events i e lows in sea level and atmospheric methane a secondary use of this data set is the insight into the possible cause of continental slope failures glacial period slope failures occur mainly in the low latitudes and are associated with lowering sea level this finding suggests that reduced hydrostatic pressure and the associated destabilization of gas hydrates may be the primary cause the bolling allerod sediment failures were predominantly low latitude suggesting an early tropical response to deglaciation e g enhanced precipitation and sediment load to the continental shelf or warming of intermediate waters in contrast sediment failures during the preboreal period and the majority of the holocene occurred in the high latitudes suggesting either isostatic rebound related earthquake activity or reduced hydrostatic pressure caused by isostatic rebound causing destabilization of gas hydrates

the kaliningrad west russia earthquakes on the 21st of september 2004 surprise events in a very low seismicity area abstract the earthquakes in kaliningrad west russia on the 21st of september 2004 were unexpected in a seismically quiet area the main shock of magnitude m b 5 was widely felt around the baltic sea a comparison with some historic earthquakes in northern europe shows that its perceptibility area is smaller than that of the 1904 oslo graben earthquake of an estimated magnitude m l 5 4 but larger than those of the 1759 kattegat and 1819 luroy earthquakes the latter are claimed to have had magnitudes m s in the range of 5 7 6 0 an analysis of the lg phase of the kaliningrad earthquakes as recorded at a number of european stations accords only weakly with the macroseismic intensity pattern that shows fast attenuation towards west northwest and southeast the strike slip focal mechanism of the main shock is discussed in the context of remnant glacial rebound stresses in generating present day seismicity in n europe

mapping hydrocarbon induced mineralogical alteration in the northern tian shan using aster multispectral data seepage from hydrocarbon reservoirs can cause a number of chemical and or mineralogical changes in overlying rocks and soils these surface changes can be detected by remote sensing imaging systems the advanced spaceborne thermal emission and reflection radiometer aster is an advanced multispectral imaging system in the visible and near infrared vnir to shortwave infrared swir region band ratios of aster vnir and swir data to detect red bed bleaching and secondary carbonate formation induced by hydrocarbon seepage are proposed through analysis of the spectral properties of rock samples results show that aster band ratios of 2 1 and 4 8 can discriminate bleached red beds and secondary carbonate minerals due to hydrocarbon seepage in the northern tian shan they are in good agreement with mineral identification using x ray diffraction the ratio technique derived from aster data may provide a potential approach for hydrocarbon exploration in areas with sparse vegetation cover

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

whole rock geochemistry and sr isotopic compositions of phanerozoic sedimentary rocks in the inner zone of the southwest japan arc abstract pre cretaceous metasedimentary rocks occurring in the inner zone of the southwest japan arc can be divided into three major groups namely high p t metamorphic renge and suo belts low p t metamorphic hida oki ryoke and higo belts and accretionary terranes akiyoshi maizuru mino tamba and ashio belts major and trace element compositions of most of the sedimentary rocks are typical of relatively mature sedimentary rocks although abundances of ferromagnesian elements also suggest the presence of a significant mafic to intermediate igneous component the sedimentary rocks with older nd model ages 2 0 ga have high esr values and major and trace element geochemical signatures typical of mature sediments whereas those with younger model ages

w and m type tetrad effects in ree patterns for water rock systems in the tono uranium deposit central japan abstract abundances of rare earth elements plus y ree were determined for granitic rocks tertiary sedimentary rocks and related groundwater in the tono area central japan tetrad effects concave curves in ree patterns were found for these rocks and groundwater samples conjugate m and w types of tetrad effects were simultaneously observed in these specimens which constitute the water rock system the granitic rocks show the m type tetrad effects while the groundwater and the sedimentary rocks exhibit the w type tetrad effects non chondritic y ho ratios were found especially in the groundwater y ho ratios showed larger values than the chondritic value for the samples showing w type tetrad effects and vice versa these results suggest that 1 preference of the groundwater for a w type tetrad effect and larger y ho ratio than chondrite produces an m type tetrad effects and lower y ho ratios in the granitic rocks during weathering processes 2 the w type tetrad effect and larger y ho ratio for the sedimentary rocks is brought about by the fixation of groundwater ree onto the sedimentary rocks the variation of the tetrad effect and y ho ratio was confirmed by laboratory experiments on the leaching of ree from the granitic rocks the w type tetrad effect and large y ho ratio in the u mineralization zone in the sedimentary rocks were also found by sims analysis which is consistent with the w type tetrad effect and larger y ho ratio in the whole rock abundances of the sedimentary rocks disequilibrium of the u series 234 u 238 u analyzed by sims in the u mineralization zone suggests that the u bearing minerals were formed through precipitation from groundwater as it became reducing these results suggest that the ree in the sedimentary rocks were transported by the groundwater from the granitic rocks in the tono area based on this study it is implied that the degree of the tetrad effects and the variation of y ho ratio can be valuable tools to investigate the migration of ree during water rock interactions in natural systems

fine scale sediment structure and geochemical signature between eastern and western north atlantic during heinrich events 1 and 2 abstract heinrich iceberg rafting events 1 and 2 h1 and h2 in the labrador sea are identified by their typical nepheloid flow deposit sedimentary structure high bulk carbonate increase in iceberg rafted detritus ird and depletion of 18o in the surface dwelling foraminifer neogloboquadrina pachyderma s h layers in this region have sedimentological characteristics different than those in the north atlantic and consist of ird interspersed in pelagic sediments high resolution 14c ams dates allowed us to delineate the leads and lags in instability between different ice streams of the former laurentide ice sheet lis our data suggest that the discharge from the hudson strait ice stream was followed by cumberland sound ice sheet during h1 and h2 new radiogenic isotopes from the ice proximal and surficial sediments of the greater hudson strait region and labrador sea h0 h1 and h2 layers suggest that carbonate rich layers were only derived from hudson strait not baffin bay fine scale structure of h1 and h2 intervals in labrador sea slope cores is characterized by two lithic peaks dominated by detrital carbonate grains and a single peak in cores from the central labrador sea a similar pattern in the structure of h1 and h2 is observed along the western european margin these findings contrast with north atlantic h1 and h2 intervals which are characterized by a peak of carbonate rich grains followed by a peak of quartz and volcanic grains this comparison with north atlantic and western european margin cores leads us to suggest that the coupling or lack thereof between the lis and european ice sheet is related to the depositional processes occurring along the margins as well as the distance from the sources and the ability of the oceanic currents to disperse icebergs any significant change in ice sheet dynamics would be recorded close to the ice sheet margin while distal locations would only record extreme events we hypothesize that the discordance between the findings reported in the literature is most likely similar to the difference between the upper slope deep labrador sites and the flemish pass site described in this contribution but requires vigorous testing

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

yttrium the immobility mobility transition during basaltic weathering trace elements have been used as provenance indicators of igneous rocks for many years even though the conditions under which they remain immobile during subaerial weathering have not been thoroughly defined we have used a novel geochemical and quantitative mineralogical data set of variably weathered basaltic rocks from northeast ireland to investigate the immobility of various elements titanium and niobium seem to be the most immobile of all elements relative to these elements zirconium is predominantly depleted but is also locally enriched yttrium displays a marked depletion from the early stages of weathering during the growth of clay minerals yttrium zirconium and their ratios with other elements should thus be used with caution as provenance indicators unless the rocks show no detectable signs of weathering

characteristics of selected petroleum source rocks xianjiang uygur autonomous region northwest china 1 the sedimentary basins of xinjiang uygur autonomous region china are moderately to poorly explored for petroleum volumetric adequacy of petroleum source rocks is a critical exploration risk in these basins particularly because source rock data are limited this study provides new source rock data and speculatively assesses the source rock potential of xinjiang basins the junggar zhungaer basin the best explored of the xinjiang basins and containing a giant oil field is underlain in many areas by an upper permian lacustrine oil shale sequence remarkable for its organic richness and oil source quality depending on its position in the basin the permian section ranges from immature to overmature and is inferred to be the principal source of oil in the basin upper triassic middle jurassic coal measures including lacustrine rocks constitute a secondary source rock sequence in the basin the smaller intermontane turpan tulufan basin contains a very similar upper triassic middle jurassic sequence which where sufficiently buried probably comprises the only significant oil source sequence in the basin the vast tarim talimu basin offers the greatest variety of potential source rocks of all xinjiang basins but remains the least well documented from limited but geologically planned and focused sampling cambrian carboniferous and permian strata are not considered major oil contributors in the dominantly shallow marine paleozoic section of the northern tarim basin only ordovician black shales appear to have significant potential the upper triassic middle jurassic sequence of the northern tarim basin is similar to that of the junggar and turpan basins a section rich in coal and lacustrine shale that constitutes another potentially significant oil source due to the size stratigraphic packaging and structural relief of the northern tarim basin paleozoic and mesozoic potential il source beds range from immature to overmature

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

quaternary seismic stratigraphy of the north sea fan glacially fed gravity flow aprons hemipelagic sediments and large submarine slides abstract approximately 1000 km of high resolution sleeve gun array transects on the north sea fan located at the mouth of the norwegian channel reveal three dominant styles of sedimentation within a thick 900 m quaternary sediment wedge comprising numerous sequences these are interpreted as terrigenous hemipelagic sedimentation large scale translational slides and aprons of glaciogenic debris flow deposits contributing to considerable fan construction four large buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned first storegga slide on the ne fan flank several thick 100 m terrigenous hemipelagic deposits apparently represent long lived 150 200 kyr periods of sedimentation whose distribution indicates fan input via the norwegian channel the upper sequences are each made upper sequences are each made up of one or several thick 100 m aprons comprising stacked lensoid and or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness they characterize debris flows attributed to periodic input from several phases of a norwegian channel ice stream reaching the shelf edge subsidence in the outer norwegian channel allowed preservation of several glaciation cycles represented by sheet erosion bounded tills and progradational units much of the shelf slope transition has been preserved allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the norwegian channel debris flows which signal the initial shelf edge glaciation are not recognized from the initial glaciation in the channel 1 1 myr but are associated with a middle pleistocene and all following glacial erosion surfaces ges in the outer norwegian channel this was followed by six further sequences probably totalling over 13 000 km 3 of sediment at least four of these were shelf edge ice maximum events the last of which was late weichselian age 14 c ams considering earlier glaciation related hemipelagic sedimentation material since removed by the large slides and extensive unmapped areas total quaternary fan sedimentation was in the vicinity of 20 000 km 3

provenance of sediment in the labrador current a record of hinterland glaciation over the past 125 ka the labrador current flows southward along the continental margin off eastern canada and is the principal source of sediment to the outer continental margin areas where ice sheets did not cross the continental shelf we present multi proxy mineralogical and geochemical records based principally on x ray diffraction and x ray fluorescence for core 2011031 059 from northern flemish cap to determine changes in supply and hence to reconstruct provenance evolution during the last glacial cycle the calcite to dolomite ratios in heinrich layers ranged from 2 to 4 suggesting carbonate layers derived from hudson strait as early as marine isotope stage mis 5a d mineral abundance shows three time dependent predominant sediment sources other than in heinrich layers i baffin bay shelves and adjacent land in mis 5 and 1 with high ca sr kaolinite and feldspars and low clay minerals and calcite dolomite ratios ii labrador in mis 3 with low clays and grey color and iii north east newfoundland shelf in mis 2 and 4 with higher concentrations of clay minerals red sandstones and transition elements these results allow a reconstruction of principal ice streams supplying the north west atlantic over the last full glacial cycle

using geochemical fingerprinting to determine transpressive fault movement history application to the new zealand alpine fault 1 geochemical fingerprinting of conglomerate clasts from depocenters adjacent to a strike slip fault and of source areas on the opposite side of the fault provides a method of determining fault movement history in instances where potential piercing points have been removed by erosion or buried in pull apart or down warp basins our example demonstrating this method is the neogene maruia basin adjacent to the new zealand alpine fault the on land australian pacific plate boundary which shows permian pelorus caples terrane offset by 480 km twenty six sandstone and schist conglomerate clasts from the maruia basin rappahannock group were analyzed for major elements and 18 trace elements by x ray fluorescence and compared to similar analyses from potential regional source areas significant source terranes the caples group and the torlesse terrane were identified both located southeast of the fault dextral movement on the fault provided a conveyor belt of material to the maruia basin first supplying at 11 5 ma caples sandstone then caples schist followed by torlesse schist from 9 5 ma which translates to an average neogene movement rate of 36 37 mm yr 1 the increase in metamorphic grade reflects accelerated exhumation of source rocks as they passed through a restraining bend adjacent to the maruia basin and from later regional uplift from a change in the australian pacific plate motion vector and more transpressive movement from 5 ma this robust method of geochemical fingerprinting could be readily applied to determining movement history of transpressive faults of other regions

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

mineral chemistry petrogenesis and tectonic setting of the wateranga layered intrusion southeast queensland australia the wateranga layered mafic intrusion 28 km2 in area 500 m thick is a tholeiitic undeformed unmetamorphosed permo triassic layered gabbroic pluton intruded into the late carboniferous goodnight beds of the goodnight block in southeast queensland the intrusion mainly consists of gabbro and norite associated with subordinate amounts of troctolite anorthosite and orthopyroxenite and rare picrite olivine gabbro is the dominant rock type of the intrusion fractionation followed a tholeiitic trend with iron enrichment in the liquid petrographic mineral chemical and whole rock geochemical data have been used to divide the intrusion into lower middle and upper zones which are interpreted as reflecting magma chamber replenishment the observed changes in the crystallization order between the zones reveal that a single parental magma is inadequate to explain the data the common differentiation indices such as an content of plagioclase mg s of olivine clinopyroxene orthopyroxene and whole ro

methanogenic biodegradation of petroleum in the west siberian basin russia significance for formation of giant cenomanian gas pools approximately 1700 tcf 48 trillion m3 of dry gas 99 methane reserves and resources occur in western siberia mostly in shallow 1500 m 4921 ft cenomanian pools in the northern part of the basin this dry gas constitutes about 11 of the world s conventional gas endowment and about 17 of the annual gas production the origin of the dry gas has been debated extensively over the last 45 yr but remains controversial widely discussed hypotheses on the origin include early mature thermogenic gas from coal primary microbial gas from dispersed organic matter or coal and thermogenic gas from deep source rocks however all these hypotheses are in some ways inconsistent with the molecular or isotopic composition of the gases or the results of basin and petroleum systems modeling here i present geochemical and geological evidence that a significant although yet not quantified part of the shallow dry gas in the northern west siberian basin originated from methanogenic biodegradation of petroleum circumstantial evidence includes the occurrence of heavily biodegraded oil legs and residual oil in many cenomanian gas pools as well as geochemical evidence of heavy to slight biodegradation in jurassic albian reservoirs commonly underlying the cenomanian pools direct evidence includes most importantly 13c enriched co2 in pools with biodegraded oil although data are limited which indicates 40 70 wt conversion of oil derived co2 to secondary microbial methane distinctive hydrocarbon molecular and isotopic compositions of most gases in cenomanian pools average dryness c1 sum c1 c5 is 0 9976 average 13c of methane is 51 8 suggest that they represent mixtures of biodegraded thermogenic gases from deep mainly jurassic source rocks and secondary microbial methane with an occasional small addition of primary microbial methane contribution of early mature coal derived gas is possible in areas with the most significant thermal stress of hauterivian aptian sediments but remains speculative review of petroleum habitats of five representative oil gas condensate fields in western siberia including the world s second largest gas field urengoyskoe suggests that methanogenic biodegradation may best explain the observed distribution and properties of fluids in the shallow reservoirs of those fields recognition of secondary microbial gas in western siberia helps explain the observed dominance of gas in the shallow cool northern part of the basin where conditions were more favorable for prolonged petroleum biodegradation than in the central and southern parts of the basin secondary microbial gas has been recognized worldwide and may 1 represent a volumetrically significant exploration target in shallow reservoirs perhaps more significant than primary microbial gas and 2 indicate effective thermogenic petroleum systems in the deeper sections large volumes up to 66 500 tcf 1884 trillion m3 of secondary microbial methane could have been generated from biodegraded petroleum accumulations worldwide although a part of that gas accumulated as oil dissolved free and hydrate bound gas most gas apparently escaped into the overburden atmosphere and ocean and could have affected global climate in the geologic past