hydrocarbons in mississippi fan and intraslope basin sediments abstract aliphatic and aromatic hydrocarbons in sediments of the middle and lower mississippi fan and two intraslope basins in the gulf of mexico are derived from terrestrial organic matter and thermogenic mature hydrocarbons the terrestrial hydrocarbon component consists primarily of terrigenous plant biowaxes n alkanes with 21 to 33 carbons the occurrence of thermogenic hydrocarbons in immature near surface sediments their molecular distributions and concentration variations with depth suggest that the majority of these mature hydrocarbons have migrated from a source much deeper in the sediment column a portion of the thermogenic hydrocarbons may be derived from recycled material and includes phenanthrene methyl phenanthrenes chrysene and benzopyrenes the migrated thermogenic hydrocarbons include normal and isoprenoid alkanes with less than 21 carbons naphthalene methyl naphthalenes ethyl naphthalenes and other aromatics of similar volatility i e biphenyl acenaphthene and fluorene triterpane sterane and aromatized sterane distributions suggest that the thermogenic hydrocarbons at both sites have a common source and are overprinted with immature sediment hydrocarbons the biomarker distributions and carbon isotopic compositions of the thermogenic hydrocarbons are atypical for petroleum produced in the gulf of mexico molecular distributions of the hydrocarbons are constant regardless of the present depth of occurrence suggesting that they have migrated in a separate phase the upward migration of hydrocarbons from deeper sources is a wide spread phenomenon in the gulf of mexico with several documented cases of massive seepage visible oil as well as the more diffuse permeation of pleistocene sediments of the mississippi fan and two intraslopes reported here

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

nothofagus forest dynamics and palaeoenvironmental variations during the mid and late holocene in southwest patagonia southern patagonia intersects the core of the southern westerlies providing a unique opportunity for palaeo reconstructions and the implication of past wind variations there is a strong link between the strength of the westerlies and precipitation which impacts vegetation communities the palaeoenvironmental changes that occurred since the middle holocene to present days are reconstructed from a peat record recovered in peninsula avellaneda 50 15 57 s 72 50 33 w interpretations are based on pollen charcoal and sediment analyses closed nothofagus forest together with low fire activity characterized the region during the period c 5500 3500 cal yr bp related to an increased in precipitation through an intensification of the westerlies after 3500 cal yr bp shrub and grass communities became dominant at the expense of nothofagus forest suggesting a climatic shift to dry conditions as a result of weaker westerlies this patchy forest steppe vegetation has favoured the occurrence of fire events

a record from lake cardiel of climate change in southern south america southern south america the only continental land mass lying between 38 s and the antarctic circle presents a rare opportunity to reconstruct terrestrial records of palaeoclimate in an area that is subject to shifts of polar and mid latitude wind and pressure belts in the bulk of this region patagonia are many hydrographically closed lakes which despite the palaeoclimatic significance of the region and the proven utility of lake level records in reconstructing past climates1 2 have escaped detailed study using sedimentary and geomorphic evidence together with 14c dating we present here a detailed lake level record for lake cardiel fig 1 the highest level of the past 21 000 years occurred at about 9 780 bp reminiscent of tropical lakes rather than those in northern mid latitudes1 2 the lake cardiel record corroborates and clarifies the timing of the wetness record inferred from pollen studies in patagonia

methane related carbonate cements in pockmarks of the north sea abstract some pockmarks on the norwegian continental shelf contain patches of cemented sediment that can provide hardgrounds attractive to a variety of benthonic organisms detailed examination of a sandstone sample from a pockmark in norwegian block 25 7 in the north sea has revealed the presence of mg calcite and aragonite cements some of the latter forming botryoids all cement types are characterized by extremely light carbon isotopic compositions with a mean 13c value of 56 1 pdb which shows that the cements contain carbonate produced by oxidation of biogenic methane oxidation occurred in both the oxic and anoxic diagenetic zones trace amounts of interstitial methane mean 13c 40 8 and higher hydrocarbon gases up to c5 with a c1 cn ratio of 0 855 0 874 in the pockmark sediments indicate that some thermogenic methane may be mixed with the biogenic gas

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

near surface hydrocarbon anomalies in shelf sediments off spitsbergen evidences for past seepages 1 as global warming occurs the dissociation of bound methane on arctic shelves due to ocean current temperature changes may become a major contributor to the global methane budget and thus contribute to strong positive climate feedback mechanisms however little is known about the magnitude and fate of methane emissions from shallow submarine sediments to the atmosphere in the peculiar area in this paper we present one of the first direct evidences for seepage on the northwestern barents sea shelf by studying the molecular and isotopic signatures of low molecular weight hydrocarbons in seawater near surface sediment pore space and the sediment matrix at 26 locations we provide a detailed view on the partitioning of gaseous hydrocarbons in the sediment water interface off spitsbergen in the free gas phase low concentration of methane 28 ng g wet sediment paired with constantly high isotopic values 65 is consistent with high impact of methane oxidation on the isotopic composition in contrast high concentrations of adsorbed ch4 up to 5292 ng g wet 63 m and c2 ethane through pentane up to 1724 ng g wet 63 m in the sediment matrix suggest that the adsorbed gas is reasonably well protected against microbial degradation moreover the isotopic and molecular signatures of adsorbed ch4 38 60 100 5300 ng g wet 63 m and c2h6 20 36 30 1700 ng g wet 63 m indicate an integrated but strongly varying signal of historic thermally derived hydrocarbon plumes plus in situ adsorbed gas of biological origin this suggests a minimal exchange and unlike histories of free and adsorbed gas the majority of gaseous hydrocarbons in the adsorbed pool may be the result of past seepages past upward flow of thermogenic gas and impregnation with mature hydrocarbons was particularly strong along tectonic lineaments active petroleum source rocks along the continental margin and migration of gaseous hydrocarbons at re activated fault systems might explain the anomalies along these conduits

surface geochemical studies in the norwegian barents sea comparison with drilling results during the last 4 years a number of surface geochemical studies have been undertaken in the barents sea acreage in all of the areas has subsequently been licensed for exploration sampling for surface geochemistry has been undertaken using a gravity corer where samples were taken 2 m below the seafloor the sampling grids were either regular or irregular based on known geological features in the areas or a combination of the two the samples were analyzed for interstitial gas adsorbed gas grain size distribution organic and inorganic carbon content fluorescence of the hexane extract and heavy hydrocarbons in the hexane extract the results from the different areas ranged from barren i e no indication of petrogenic hydrocarbons at the surface anomalies of petrogenic hydrocarbons i e indicating the generation of gas condensate or oil to extremely strong anomalies of oil interpreted as indicators of direct leakage from source rocks or a defective caprock

abrupt cooling of antarctic surface waters and sea ice expansion in the south atlantic sector of the southern ocean at 5000 cal yr b p antarctic surface waters were warm and ice free between 10 000 and 5000 cal yr b p as judged from ice rafted debris and microfossils in a piston core at 53 s in the south atlantic this evidence shows that about 5000 cal yr b p sea surface temperatures cooled sea ice advanced and the delivery of ice rafted detritus ird to the subantarctic south atlantic increased abruptly these changes mark the end of the hypsithermal and onset of neoglacial conditions they coincide with an early neoglacial advance of mountain glaciers in south america and new zealand between 5400 and 4900 cal yr b p rapid middle holocene climate changes inferred from the taylor dome ice core antarctica cooling and increased ird in the north atlantic and the end of the african humid period the near synchrony and abruptness of all these climate changes suggest links among the tropics and both poles that involved nonlinear response to gradual changes in northern hemisphere insolation sea ice expansion in the southern ocean may have provided positive feedback that hastened the end of the hypsithermal and african humid periods in the middle holocene

hydrocarbons from near surface sediments of the barents sea north of svalbard indication of subsurface hydrocarbon generation abstract the barents sea is considered as an important target for oil and gas exploration but the petroleum potential of its shelf and slope regions is unknown here we present results of a research cruise to the northern hinlopen margin at the transition to the southern nansen basin and the eastern yermak plateau multichannel reflection seismic data acquisition heat flow measurements and geochemical analyses of near surface sediments obtained by gravity coring were conducted to study the northern barents sea shelf and the early opening of the nansen basin and decipher their petroleum potential seismic data indicate high thicknesses of up to 2000 m of cenozoic sediments heat flow density values in the study area range between 67 and 108 mw m 2 the sediment samples were analysed for bulk geochemistry and sorbed hydrocarbon gases and for two sites for extractable hydrocarbons data from extractable n alkanes n c 25 and bulk hi and oi from rock eval organic matter demonstrate predominantly terrigenous organic material most likely derived from ice transported allochthonous sediments none of the sediments revealed substantial amounts of methane in pore waters arguing against active hydrocarbon seepage in the studied areas however thermogenic gases sorbed to the sediment matrix clay minerals organic matter and or carbonates were found in concentrations of up to 600 ppb on sediment wet wt basis for the samples from the northern hinlopen margin and particularly from the adjacent nansen basin a paleo fluid flow of thermogenic gas is indicated and accompanied by higher n alkanes with a modal petroleum like distribution 13 c values of methane ethane and propane and gas compositions point at a mainly marine source rock origin of all studied gases with early oil window maturities of the associated rocks 0 6 0 9 vr from this data an admixture of type iii derived thermogenic gases is indicated for some of the yermak plateau sediments for which also the lowest abundances of sorbed gases 50 100 ppb were observed gas geochemical characteristics in the samples with low gas abundances can partially be explained by an input of gases through ice transport of allochthonous hydrocarbons which were bound to mature organic matter for a site on the northern hinlopen margin ne of svalbard right at the southern termination of the nansen basin a different situation is indicated in this area the highest concentrations of sorbed gases most likely derived from sediments with an early oil window maturity and a marine kerogen type ii typical isotopic distribution at this location a pseudo well was constructed from 2d seismic data for reconstruction of thermal and maturity evolution the simulation results indicate that an early to middle eocene source rock would be in the early oil window since the early miocene a possible source rock here and in the circum arctic region could have been formed by azolla algae and other flourishing primary producers

hydrocarbon provinces in the swiss southern alps a gas geochemistry and basin modelling study abstract in order to evaluate the petroleum potential of southern switzerland south alpine fold and thrust belt gas geochemical investigations including free and adsorbed gases were combined with a basin modelling analysis the palaeotectonic setting and alpine orogenic movements were recognized as main controls in the evolution of the petroleum generation potential three main hydrocarbon provinces are distinguished 1 the arbostora anticline which developed from an early jurassic high has excellent but immature source rocks which probably at no time generated hydrocarbons because of their swallow level in the nappe edifice 2 the stabio anticline south of the arbostora anticline in southernmost switzerland where wet gases are observed at the surface that are likely to have been generated from late cretaceous to present day from triassic source rocks occurring deeper in the nappe pile and 3 the m generoso basin with prevailing petroleum generation in the early jurassic and possible minor generation in marginal areas during cretaceous and tertiary times

palaeoenvironmental conditions during the early peopling of southernmost south america late glacial early holocene 14 8 ka b p abstract environmental conditions in southernmost south america the patagonian andes and the extra andean plains during the early peopling of the region in late glacial early holocene times are herein described different glacial advances or stabilization phases in valley glaciers occurred several millennia after the last glacial maximum lgm as a consequence of regional cold climatic episodes according to clapperton 1993 two advances during the late glacial took place ca 15 14 14 c ka and 12 10 14 c ka b p a cold event during this last period probably correlative with the younger dryas episode in the northern hemisphere has been observed in the palynological record a tundra environment dominated until ca 13 10 14 c ka b p afterwards a gramineous steppe with forest refuges developed the transition steppe forest lasted to the middle holocene when the nothofagus forest took over the arrival of man in southernmost south america ca 13 14 c ka b p or even before probably took place while glaciers were still present in most andean valleys sea level was much lower than today and tundra environments dominated the extra andean plains moreover peopling in the isla grande de tierra del fuego would have occurred not later than 11 8 14 c ka b p when the present magellan straits valley was still occupied by a meltwater discharge braided stream fed by the receding magellan glacier

hydrocarbon geochemistry in surface sediments of alaskan outer continental shelf part 2 distribution of hydrocarbon gases the distribution of c1 to c4 hydrocarbon gases in surficial sediments from the alaskan continental shelf was determined as part of a regional environmental survey sponsored by national oceanic and atmospheric administration and bureau of land management noaa blm methane ethane ethene propane propene n butane and iso butane were observed in low concentrations 0 1 10 ppb as weight gas to dry weight sediment in nearly all of the 190 sediment samples examined with methane exceeding c2 to c4 hydrocarbons in abundance by about a factor of 10 no gasoline range c5 to c8 hydrocarbons were detected above blank levels ethene was found generally to be more abundant than ethane while propane was slightl more abundant than propene the correlation between these hydrocarbons suggests a common possibly biogenic origin sediments from norton sound have anomalously high methane concentrations probably as a result of biological methanogenesis in subsurface organic rich peat layers most of the regions sampled showed median values of the c1 c2 c3 ratio of 20 the generally low c1 concentrations probably resulted from the selective loss of c1 by biologic oxidation or ebullition from the surface sediments no major c2 to c4 hydrocarbon anomalies were discovered however at some stations in kachemak bay kodiak shelf and norton sound anomalously high c3 c3 1 ratios indicated the poss ble presence of thermogenic gases at depth

changes in lithic technology and environment in southern continental patagonia the chico and santa cruz river basins abstract changes in artifact technology and environment during the holocene are documented within an organization of technology framework for three different regions of patagonia possible relationships between environmental changes and changes in artifact technology are explored we examine past vegetation and geomorphic evidence of holocene climate conditions in the three regions studied and what technologies were used during particular wetter and drier intervals our results suggest that many of the observed changes in technology use occurred at times of rapid climate change particularly towards much drier conditions

cold climatic episode of younger dryas age in tierra del fuego pronounced climatic change during the last glacial maximum is recognized as global in extent and has been attributed to orbital forcing1 not readily explained in a global context because of the equivocal nature of the evidence are the late glacial climatic events of short 100 1 000 yr duration the cold climate of the younger dryas chron 11 000 10 000 yr bp for example is known to have been particularly pronounced over the north atlantic and parts of europe and north america2 3 whereas in the southern hemisphere cold conditions for that time are not well established here we present evidence for late glacial climatic cooling in southernmost south america from studies of radiocarbon dated glacial and pollen stratigraphy at sites along the beagle channel in tierra del fuego where a forest tundra tension zone in the region is especially sensitive to shifting climate we conclude that the cold episode corresponds with the time of the younger dryas in europe when a drop in temperature ascribed most recently to colder sea surface temperatures and production rate of deep water in the north atlantic4 5 apparently occurred worldwide

habitat of hydrocarbons on the norwegian continental shelf eds a m spenceret al norwegian petroleum society graham and trotman 1986 isbn 0 86010 833 3 price 65 00

geochemical surface exploration for hydrocarbons in north sea approximately 350 sediment samples were taken in the central part of the north sea and hydrocarbon composition methane c1 and ethane c2 yields and carbon isotope composition of the methane dgr13c1 adsorbed in the sediment were determined methane generation or oxidation by bacterial activity can not be deduced from the analytical data this fact is explained by the assumption of a threshold of methane concentration in sediments below which methane oxidizing bacteria are inactive and that this threshold was not reached in the area investigated background gases in the surface sediments characterized by low c1 yields and dgr13c1 37 ppt can be distinguished from thermal sediment g ses which are obviously derived from a hydrocarbon generating source rock in the subsurface source rock data obtained from several wells situated on a cross section through the investigated area were compared to the geochemical patterns of the sediment gases and used to define profile sections with good dgr13c1 approx 40 ppt yield c1 approx 217 ppb and poor source rock properties dgr13c1 approx 33 ppt yield c1 approx 24 ppb an assessment of the source rock potential of the whole area under investigation has been carried out using the geochemical data of the surface sediment gases and taking into account that the c1 and c2 yields are generally higher in clay sediments than in sand samples the number of producing wells was related to the number of all wells 271 in the areas characterized by surface geochemistry as good or poor source rock areas the comparison showed that the relative number of producing wells is higher in areas geochemically characterized as good hydrocarbons in surface sediments of good north sea areas are not generated by bacteria at shallow depth they are formed thermally from the organic carbon of deep source rocks and migrate to the surface therefore they are indicative of thermal hydrocarbon generation in the subsurface

holocene glacier history of the lago argentino basin southern patagonian icefield abstract we present new geomorphic stratigraphic and chronologic data for holocene glacier fluctuations in the lago argentino basin on the eastern side of the southern patagonian andes chronologic control is based on 14c and surface exposure 10be dating after the lateglacial maximum at 13 000 cal yrs bp the large ice lobes that filled the eastern reaches of lago argentino retreated and separated into individual outlet glaciers this recession was interrupted only by a stillstand or minor readvance at 12 200 cal yrs bp the eight largest of these individual outlet glaciers are from north to south upsala agassiz onelli spegazzini mayo ameghino perito moreno and grande formerly frias holocene recession of upsala glacier exposed brazo cristina more than 10 115 100 cal yrs bp and reached inboard of the holocene moraines in agassiz este valley by 9205 85 cal yrs bp ice remained in an inboard position until 7730 50 cal yrs bp several subsequent glacier readvances are well documented for the upsala and frias glaciers the upsala glacier readvanced at least seven times the first being a relatively minor expansion documented only in stratigraphic sections between 7730 50 and 7210 45 cal yrs bp the most extensive holocene advances of upsala glacier resulted in the deposition of the pearson 1 moraines and related landforms which are divided into three systems the pearson 1a advance occurred about 6000 5000 cal yrs bp and was followed by the slightly less extensive pearson 1b and 1c advances dated to 2500 2000 and 1500 1100 cal yrs bp respectively subsequent advances of upsala glacier resulted in deposition of the pearson 2 moraines and corresponding landforms also separated into three systems pearson 2a 2b and 2c constructed respectively at 700 400 and

relation between shallow sediment bitumens and deeper reservoired hydrocarbons offshore santa maria basin california u s a abstract detailed molecular and isotopic analysis of near surface liquid hydrocarbon seepage is useful not only in determining the presence of petroleum hydrocarbons but also to indicate the type and quality of deeper seated hydrocarbons near surface sediment bitumens collected over known production in the offshore santa maria basin were shown to be similar to reservoired petroleum in the adjacent onshore triterpane sterane and aromatized sterane compositional similarities between oils and near surface sediment bitumens suggest a common source in the monterey formation an empirical model based on the relation between oil composition pristane phytane and bisnorhopane hopane ratios and api gravity was applied to the near surface bitumens and accurately predicted the api gravity of the nearest known production the improvement and refinement of geochemical prospecting techniques has greatly enhanced their use and reliability as exploration tools

an examination of possible relationships between paleoenvironmental conditions during the pleistocene holocene transition and human occupation of southern patagonia argentina east of the andes between 46 and 52 s abstract spatial and temporal variations in evidence for human occupation of argentinian south patagonia closely resemble changes in past vegetation reconstructed from pollen records the antarctic cold reversal was cold and dry in the deseado massif and there is little evidence of humans at this time in contrast the younger dryas interval was warmer and slightly wetter and this was when humans moved into the deseado area increasing temperatures during the early holocene brought higher precipitation to much of patagonia east of the andes except the northern deseado massif explaining the increase in evidence of human occupation in western areas and the decrease in evidence in the massif spatial and temporal variations in the frequency of radiocarbon dates indicating human presence show that in southern patagonia humans were not only influenced by the major climate shifts of the pleistocene holocene transition but possibly also by distinct short term changes lasting only a few to several centuries that are apparent in the high resolution antarctic byrd ice core water availability may have had the greatest influence on human use of the landscape rather than temperature however as temperature is crucial in controlling the latitude of the core of the southern westerly winds associated with reduced precipitation over most of eastern patagonia it is difficult to separate water from temperature in examining impacts on the first humans in southernmost south america

gas hydrate and free gas indications within the cenozoic succession of the bjornoya basin western barents sea multichannel seismic data containing high amplitude reflections from cenozoic sediments of the bjornoya basin southwestern barents sea have been studied inferring the existence of gas hydrate and free gas the cenozoic succession comprises late palaeocene and early eocene claystones and siltstones and locally also some sandstones overlain by late pleistocene glaciogenic sediments the inferred gas hydrate and free gas accumulations are mainly located in the vicinity of larger faults which can be followed up to base tertiary level and which seem to have controlled the geographical distribution of the accumulations free gas accumulations are inferred to occur most frequently within the late palaeocene strata that occur below the gas hydrate stability zone and indicate that relatively small gas leakages from deeper accumulations have dominated larger gas leakages have probably led to gas migration up into the gas hydrate stability zone and together with the increasing thickness of the hydrate stability zone towards the north control the distribution of the suspected gas hydrates the inferred gas leakages are closely related to the cenozoic evolution of the barents sea and are probably caused by gas expansion due to the removal of up to 1 km of sediments from the barents sea shelf and or reservoir tilting during the late cenozoic glaciations which affected this area

raw material circulation at broad scales in southern patagonia argentina the cases of the chico and santa cruz river basins abstract the purpose of this paper is to begin to understand human mobility through rock transport at different times in two areas with different environmental characteristics the southern deseado massif and the basaltic canyons north of the santa cruz river we focus on obsidian which has a clear geochemical signature and an uneven distribution additionally we use macroscopic information on siliceous rocks which at present have only been identified in northern areas although they may also be recovered randomly and in low frequencies in southern ones during the initial peopling of the southern deseado massif ca 10 800 bp inhabitants were transporting black obsidian as well as translucent chalcedony probably as part of the individual gear during the late holocene the number of obsidian artifacts decreased in the southern deseado massif related to a better knowledge of the high quality local lithic resources and or to the existence of higher population densities obsidian artifacts are more abundant in the northern santa cruz river basin than in the southern deseado massif suggesting the existence of a relationship with areas located to the northwest close to the obsidian source as other lines of evidence suggest in addition the presence in the basaltic canyons of artifacts made from high quality siliceous rocks more abundant and predictable in northern areas could also be the result of human movements following a north south direction

recent distribution and accumulation of organic carbon on the continental margin west off spitsbergen the study compiles the controlling factors for organic matter sedimentation patterns from a suite of organogeochemical parameters in surface sediments off spitsbergen and direct seabed observations using a remotely operated vehicle rov in addition we assess its storage rates as well as the potential of carbon sinks on the northwestern margin of the barents sea with short sediment cores from a selected fjord environment storfjord while sedimentation in the fjords is mainly controlled by river meltwater discharge and coastal erosion by sea ice glaciers resulting in high supply of terrigenous organic matter atlantic water inflow and thus enhanced marine organic matter supply characterizes the environment on the outer shelf and slope local deviations from this pattern particularly on the shelf are due to erosion and out washing of fine grained material by bottom currents spots dominated by marine productivity close to the island have been found at the outer isfjord and west off prins karls forland as well as off the kongsfjord krossfjord area and probably reflect local upwelling of nutrient rich atlantic water derived water masses accumulation rates of marine organic carbon as well as reconstructed primary productivities decreased since the middle of the last century negative correlation of the isfjord temperature record with reconstructed productivities in the storfjord could be explained by a reduced annual duration of the marginal ice zone in the area due to global warming extremely high accumulation rates of marine organic carbon between 5 4 and 17 2 g m 2 yr 1 mark the storfjord area and probably high latitude fjord environments in general as a sink for carbon dioxide

predictions of oil or gas potential by near surface geochemistry recent advances in surface geochemical prospecting have enabled age old seep detection technology to be used to determine the gas versus oil character of a potential fairway extensive field work has demonstrated that the chemical compositions of near surface hydrocarbon soil gases measured by flame ionization gas chromatography are largely determined by the hydrocarbons in nearby underlying reservoirs by using compositions and ratios of the light hydrocarbons methane ethane propane and butane one may predict whether oil or gas is more likely to be discovered in the prospect area near surface hydrocarbons are best represented by normalized histograms of composition data these histograms are strongly correlative with those of reservoir gas and with compositions o gas from shows recorded in downhole mud logging this correspondence with the actual formation gases suggests that the upward migration of reservoired light hydrocarbons into near surface soils represents a viable mechanism allowing surface geochemical exploration to be utilized for regional hydrocarbon evaluations geochemical profiles over known production areas are shown for the sacramento and san joaquin basins in california and for the utah wyoming overthrust belt geochemical predictions were documented by subsequent drilling near the pineview field in utah the data imply that the pineview field should extend westward into an area containing a dry hole in addition a new gas discovery on the intersection of a landsat lineament and a large methane anomaly was made 6 5 km 4 mi northeast of the pineview field by amoco in 1981 most of the geochemical examples reported show direct anomalies over known fields however seeps can be laterally displaced in certain geologic settings in addition geochemical investigations indicate that seep magnitudes depend on tectonic activity to aid gas migration along faults and fractures which appear to provide the major migration pathways this fault association suggests that diffusion is of secondary importance geochemical prospecting must be used with caution and only in conjunction with geologic and geophysical tools because the location and shape of many geochemical anomalies are governed more by the local tectonic structure of the region than by the position and shape of the actual deposit regional groundwater flow is less significant thus geochemical prospecting when used alone cannot predict whether a particular soil gas anomaly is associated with a commercial deposit it can only be used to verify the presence of petroleum hydrocarbons and to predict whether gas or oil is likely to occur in a potential structure geochemical prospecting yields excellent regional evaluations of hydrocarbon potential

structural and stratigraphic controls on subsurface fluid flow at the veslemoy high sw barents sea abstract subsurface and seafloor fluid flow anomalies are gaining large interest after the finding of five new hydrocarbon discoveries and observation of large gas flares in the sw barents sea in the present study we have analysed structural and stratigraphic controls on fluid flow towards the seafloor using gravity cores selected based on subsurface gas anomalies observed on seismic data from the veslemoy high sw barents sea the subsurface fluid flow at the veslemoy high is observed to be controlled by 1 the morphology and orientation of regional faults structural highs and sedimentary basins 2 the presence of paleocene silica ooze deposits that changes microstructure with temperature thereby controlling fluid flow and 3 the location of regional and local open faults formed by glacial loading and unloading analysis of extractable organic matter in subsurface holocene sediments corroborates the active migration pathways inferred from seismic data micropalaeontological studies on benthic foraminifera reveal methane seep associated assemblages that confirm the interpretation of subsurface gas anomalies in seismic data we ultimately link these new results to the geological evolution history of the region to give a comprehensive model for the fluid flow system within the study area

origin of near surface hydrocarbon gases bound in northern barents sea sediments abstract in the southern part of the norwegian barents sea extensive hydrocarbon exploration and drilling has led to several oil and gas discoveries yet little is known on the petroleum systems and potential hydrocarbon reservoirs in the northern norwegian barents sea if hydrocarbons generated by thermogenic processes deep in the subsurface migrate to the surface traces of these hydrocarbons can remain in the near surface sediments and provide indirect information on potential petroleum systems near surface hydrocarbon prospecting is a method frequently used in hydrocarbon exploration of frontier areas where no direct geochemical information from drilling is available to improve knowledge of subsurface structures and the evolution of potential petroleum systems in the northern barents sea seismic data and near surface sediment samples were collected analysis of bound hydrocarbon gases extracted from these sediments revealed concentrations significantly above background in areas along the hornsund knollega fault complex as well as near margins of the olga basin generally the compositional and stable carbon isotope signatures of bound gases indicate thermogenic origins from source rocks of oil window maturity for near surface gases with anomalous high concentrations whereas for sediments with low concentration of bound gases mixture of thermogenic and microbial gas is indicated amount and composition of bound gas extracted from source rock samples from spitsbergen indicate that contribution of transported material may have influenced the bound gas in near surface marine sediment of the barents sea in areas where presence of mature organic matter is indicated in the knolegga fault complex near the western barents sea margin high concentrations of thermogenic gas in near surface sediments are associated with fault bound basins and most likely originate from the paleocene eocene torsk formation in the olga basin higher bound gas concentrations occur near the southern border of the basin corresponding to sub cropping late jurassic early cretaceous shales whereas elevated concentrations in the northern olga basin are associated with reactivated faults reaching close to the surface sediments above the center of the basin show significantly lower bound gas concentrations these observations indicate that the jurassic shales act as a regional seal for hydrocarbons and that reactivated faults at the basin margin represent pathways for migration to the surface 1d basin and petroleum systems modeling for the olga basin indicates that early to middle triassic sediments reached oil window maturity and represent the most likely source for thermogenic near surface gas in that area