evidence of methane and carbon dioxide migration to the near surface zone in the area of the abandoned coal mines in walbrzych district lower silesian coal basin sw poland based on periodical changes of molecular and isotopic compositions abstract the objective of this paper is to determine the reasons origin and character of periodical changes of methane and carbon dioxide concentrations in the near surface zone as well as emission of these gases to atmosphere after closing bituminous coal and anthracite mines in the former walbrzych coal district sw poland the measurements were performed during the period including the active impact of water piston effect on the migration of a coal bearing gases as well as the period of stabilization of water table of the pennsylvanian aquifer in the years 1997 2005 20 sampling sessions were completed during which 3210 soil gas samples were collected at a depth of about 1 2 m and along 4 measurement lines located in the gorce and the sobiecin depressions maximum methane and carbon dioxide concentrations measured in soil gas samples reached 32 4 and 15 7 vol respectively isotopic study shows that coal bed gases recent microbial methane and multigenetic carbon dioxide from degassing of ground waters of the upper pennsylvanian aquifer occur within the near surface zone of the walbrzych coal district within the serpukhovian walbrzych and upper bashkirian moscovian acle coal bearing formations three genetic types of coal bed gases occur variscan thermogenic methane higher gaseous hydrocarbons and carbon dioxide endogenic abiogenic carbon dioxide and late late cretaceous and recent microbial methane and carbon dioxide changes of mean concentrations of methane and carbon dioxide in the near surface zone recorded during years of studies demonstrated the influence of water piston effect which drives migration of coalbed gases towards the earth surface in both the gorce and the sobiecin depressions gas migrates with various intensity generally the lower methane emission measured in the years 2004 2005 and compared with the period 1999 2000 resulted from the stabilization of groundwater table whereas higher carbon dioxide emission confirms the degassing of shallow groundwaters anomalous concentrations of methane and carbon dioxide were related to numerous faults and fracture systems cutting the steeply dipping upper mississippian and pennsylvanian coal bearing formations and to the outcrops of these rocks however in the near surface zone multiproportional mixing of coal bed gases recent microbial methane and carbon dioxide is observed periodical changes of stable carbon isotope composition of methane and carbon dioxide of near surface zone in particular sessions are caused by the time related change of location of water table of pennsylvanian aquifer in the complicated structure of the gorce and sobiecin depressions persistently anomalous concentrations of methane and carbon dioxide in the near surface zone still observed after several years long stabilization of groundwater table seem to indicate a continuous supply of coalbed gases to the near surface zone through pervious dislocations such an interpretation is confirmed by the extreme value of methane emission detected at a particular sampling site after the cessation of the water piston effect it was presumably caused by the secondary intensification of gas flux from deep sources triggered by neotectonic movements in the study area

holocene aeolian activity in the southwestern kalahari desert southern africa significance and relationships to late pleistocene dune building events little is known about the timing of dune building episodes in the southwestern kalahari desert previously arid phases when dune activity occurred have been inferred from gaps in chronologies derived from information that attests to former humid periods to redress this optically stimulated luminescence osl dating was applied to sediment samples taken from a range of aeolian landforms in the sw kalahari four periods of dune building are identified in the late pleistocene and holocene holocene aeolian activity at 6 ka and 1 2 ka led to the construction of localised dune forms in contrast to late pleistocene times when the extensive field of linear dunes that dominates the region was emplaced late holocene aridity was however sufficient to allow rapid emplacement of the lunette dune at witpan the record of aeolian activity is evaluated in the context of humid chronologies and an ocean atmosphere model of holocene climate change with good agreement obtained it is concluded that the application of

the influence of surface and tectonic processes on landscape evolution of the iberian chain spain quantitative geomorphological analysis and geochronology abstract in tectonically active areas the landscape response to tectonic forcing is described and possibly quantified by regional topographic and hydrographic features as well as by spatial variation in rates of surface processes we investigated the recent landscape evolution of the iberian chain ne spain an intraplate thrust belt formed in cenozoic times and characterized by a dome shaped topography in its central sector the landscape is dominated by low relief surfaces late neogene in age presently standing at an average altitude of 1300 m a recent regional uplift controlled the organization of the present fluvial network and dissection of the landscape in this framework we investigated the geomorphic responses to tectonic forcing by the calculation of morphometric parameters focusing on topography map of local relief swath profiles and hydrography basin hypsometric curve and integral basin asymmetry factor river longitudinal profiles and relative indices and using srtm dem the results of morphometric analysis have been coupled with radiometric uranium series dating of calcareous tufas lying on fluvial strath terraces the obtained ages allow the estimation of incision rate along the high tajo and martin rivers our results indicate that uplift and rock type erodibility are the main factors influencing landscape evolution of the study area the incision rates are very similar throughout the central sector of the range indicating that despite subtle local variation the rivers are responding to a main tectonic input the regional uplift in conclusion the iberian chain landscape is in a transient state in response to a recent dome like uplift indeed the fluvial processes that weakly incised this landscape at a rate of 0 6 mm yr are approaching a radial pattern on the basis of geological and geomorphic constraints we hypothesize that the uplift started around or after 3 ma

warming phases in southern africa during the last 150 000 years an overview abstract firmly based palaeoenvironmental data for southern africa prior to 40 000 yr b p are sparse the only site which is likely to be able to provide useful information for isotope stage 6 is the pretoria saltpan warming at the end of this stage appears to have been rapid and to have been associated with increased precipitation in the interior of the sub continent in contrast dry conditions appear to have prevailed in the southwestern areas during the warmest phases of isotope stage 5 this regional difference first became apparent during the pliocene during the last glacial maximum temperatures based on isotope ratios reached their lowest values of 5 6 c below present in the southern part of the subcontinent and widespread dryness prevailed warming became quite rapid after 16 000 yr b p and was almost everywhere associated with a marked increase in wetness to around or even above present levels this warming phase continued until the beginning of the holocene the terminal pleistocene was however marked by desiccation in the arid western areas of special interest is the holocene altithermal which can be placed between 7000 and 6500 yr b p the extent of the temperature rise cannot be specified with any precision but probably did not exceed the holocene mean by more than 2 c in the southern cape and karoo more summer rain apparently occurred than during isotope stage 2 and in the early holocene and this trend towards year round rainfall appears to have become increasingly pronounced through the later holocene until about 2000 yr b p this argues in a general way for an increase in the proportion of summer rainfall with rising temperature in the present winter rainfall areas of southern africa

regional uplift and local tectonic deformation recorded by the quaternary marine terraces on the ionian coast of northern calabria southern italy abstract the setting of a flight of marine terraces along a 65 km long section of the ionian coast of northern calabria is the result of the interaction between interglacial sea levels regional uplift and local fault related elevation changes seven terraces with corresponding palaeoshoreline angles at elevations ranging from 12 m to 420 m were recognised by aerial photo interpretation and field surveying the terraces were correlated to the oxygen isotope stages 1 5a 5c 5e 7 9 15 which correspond to the 7 81 102 124 215 330 and 600 ka highstands of the palaeosea level curve the 600 ka long regional ascent of the terraces took place at an average uplift rate of 0 67 mm yr this value slightly but progressively increases southward along the coastline the elevation of the strandlines is related to the activity of tectonic structures three cases were analysed allowing us 1 to recognise the height anomalies of the terraces on the sibari plain as the result of cumulated coseismic deformation caused by the normal castrovillari fault and on this basis calculate a minimum slip rate and a mean recurrence time for a single event of deformation 2 to exclude the presence of significant vertical deformations and consequently activity on the easternmost section of the normal pollino fault and 3 to hypothesise the presence of an hitherto unknown active fault responsible for the strong vertical displacements of the flight of terraces near the river avena finally we find the ratio of the rate of regional uplift to the average rates of local tectonic deformation to be 2 to 3 1

the puglia uplift se italy an anomaly in the foreland of the apenninic subduction due to buckling of a thick continental lithosphere the apenninic foreland shows two distinct structural signatures comparing the central adriatic sea and the puglia region during the pliocene pleistocene the central adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping apenninic subduction the puglia region and the bradanic foredeep are located southward along strike in the same foreland but in contrast with the central adriatic after pliocene early pleistocene subsidence they underwent uplift since the middle pleistocene the geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas at the front of the central northern apennines off scraping and subsidence continued whereas the foredeep and foreland of the southern apennines were buckled those differences are interpreted as being due to the larger subduction hinge rollback rate since middle pleistocene of the central adriatic lithosphere 70 km thick with respect to the thicker puglia 110 km the different thicknesses of the continental crust and lithosphere were inherited from the mesozoic rifting that disrupted the adriatic plate the different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate the tremiti e w alignment is the right lateral lithospheric transfer zone of those different tectonic regimes the consequent different dip of the subduction in the two sections steeper west of puglia could also explain the lower elevation of the southern apennines compared to their central northern sector

an empirical stream power formulation for knickpoint retreat in appalachian plateau fluviokarst summary hydrologically abandoned caves on tributaries of the upper cumberland river tennessee usa record a wave of river incision that advanced up the drainage basin in the late pliocene and early pleistocene geomorphic and geologic evidence suggests that incision occurred as a migrating knickpoint generated by sudden base level lowering the passage of a knickpoint up the cumberland river tributaries was modeled as a perturbation to steady state incision according to the stream power law e kq m s n and tested using dated incision events recorded in cave sediments knickpoint migration rates generated by this model were 0 1 0 18 m yr over the entire stream network and 4 0 m yr for the mainstem cumberland river channel the ratio m n 0 79 was consistent with previously published parameters however the values of m 1 91 and n 2 39 were much higher than those reported in previous field studies these results suggest the stream power model may be used to model knickpoint migration in the study area provided values for the constants m and n are larger this may be due to the influence of fluviokarst where surface drainage is interrupted due to diversion into the underlying karst aquifer field measurements of channel and basin geometry in fluviokarstic tributaries to the upper cumberland river show 1 a stronger variance between channel slope and discharge 2 a nonlinear relationship between discharge and drainage area and 3 stream width to be nearly invariant as opposed to non karst watersheds because the stream power model relies heavily on the substitution of discharge for drainage area the behavior of channel incision and knickpoint migration in fluviokarst may differ substantially from that of non karst channels

evaluation of possible gas microseepage mechanisms petroleum microseepage anomalies over petroleum accumulations are commonly explained by rapid vertical migration of colloidal gas bubbles through fracture networks this article is a theoretical anal ysis of this mechanism and of continuous gas phase flow in frac tures the gas bubble ascent mechanism is much slower than re ported microseepage velocities so it cannot account for observed microseepage in contrast continuous gas phase flow through frac tures can equal or exceed reported microseepage velocity while maintaining total flux low enough so that petroleum accumulations can exist for geological lengths of time fracture entry pressure for bubbles is more than twice that of a continuous gas phase so con tinuous gas phase migration also requires a lower pressure threshold before initiating seepage vertical microseepage is therefore best explained by the same mechanism interpreted for macroseepage although this article provides a theoretically justified mecha nism for microseepage it also shows why interpretation of surface microseepage signals is problematic fracture geometry controls seepage velocity and flux so geochemical anomalies may indicate an increase in fracture aperture as well as possible subsurface ac cumulations larger fractures require very low gas capillary entry pressures so in some settings surface seepage could result from fractures over stratal migration pathways as well as over petroleum accumulations

natural seepage of shale gas and the origin of eternal flames in the northern appalachian basin usa abstract natural hydrocarbon gas seeps are surface expressions of petroleum seepage systems whereby gas is ascending through faults from pressurized reservoirs that are typically associated with sandstones or limestones a spectacular eternal flame in western new york state marks a gas macroseep of dominantly thermogenic origin emanating directly from deep shale source rocks which makes this a rare case in contrast to most petroleum seepage systems where gas derives from conventional reservoirs the main flaming seep releases about 1 kg of methane per day and may feature the highest ethane and propane c 2 c 3 concentration ever reported for a natural gas seep 35 vol the same gas is also released to the atmosphere through nearby invisible and diffuse seepages from the ground the synopsis of our data with available gas geochemical data of reservoir gases in the region and the stratigraphy of underlying shales suggests that the thermogenic gas originates from upper devonian shales without intermediation of a conventional reservoir a similar investigation on a second eternal flame in pennsylvania suggests that gas is migrating from a conventional sandstone pool and that the seep is probably not natural but results from an undocumented and abandoned gas or oil well the large flux of the emitted shale gas in new york state implies the existence of a pressurized gas pool at depth tectonically fractured shales seem to express naturally fracked characteristics and may provide convenient targets for hydrocarbon exploration gas production from tectonically fracked systems might not require extensive artificial fracking

segmentation and configuration of subducted lithosphere in italy an important control on thrust belt and foredeep basin evolution the apennine foredeep basin system located on continental crust consists of four roughly parallel basin segments each containing a flexural outer rise and an inner trough that deepens continuously toward the thrust belt flexural modeling of subsidence data across the basin indicates that this foredeep basin results mainly from deep subsurface loads acting on the subducted slab from within the subduction zone rather than from the topographic load of the apennine mountains the geometry of the four basin segments observed within the apennine foredeep is thus inferred to reflect subduction of segmented lithosphere where each lithospheric segment corresponds to a segment of the foredeep basin beneath the basin and in the foreland the lithosphere is continuous segmentation occurs only at depth beneath the thrust belt this pattern olf segmentation of the subducted lithosphere at depth is reflected in the large scale geometry of the outer part of the apennine thrust belt and appears to control it similarly the pattern of segmentation also appears to control the position of the eastern limit of back arc type extension in western italy these relations strongly suggest a genetic relation between subduction zone processes foredeep basin geometry and thrust belt evolution in which the configuration of the subducted lithosphere largely controls the large scale surface deformation observed in the apennine system

sediment hosted geothermal systems review and first global mapping abstract sediment hosted geothermal systems shgss are hybrid geological systems where volcanic and sedimentary domains interact leading to mixtures of inorganic and organic gases typically characterized by geothermal thermometamorphic or mantle derived co2 and biotic microbial or thermogenic ch4 shgss occur in sedimentary basins crossed by magmatic intrusions or involved in volcanic plumbing systems these systems can be of considerable interest for petroleum exploration and natural greenhouse gas emission studies but systematic studies for their characterization and worldwide distribution are missing here we provide a review of shgss identified so far and propose methodological criteria for their definition and identification based on integrated geological and gas geochemical parameters we find that shgss are typically characterized by a fluids dominated by mantle or decarbonation methamorphic co2 50 vol b considerable amounts of ch4 and heavier hydrocarbons at least 1 5 vol generally up to 30 40 vol produced by microbial or thermogenic degradation of organic matter hosted in sedimentary rocks c tectonically active sedimentary basins back arc rift zones and foredeep generally hosting petroleum fields and within 300 km from recent or ancient volcanic centers this analysis resulted in a global map including a first set of 33 shgss located in north america central and eastern europe far east eastern oceania and northern new zealand and a second set of potential shgs prone areas occurring also in south america north africa middle east and kamchatka the present shgs map can evolve on the basis of more detailed geological analysis and new gas geochemical data

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

geochemical constraints on the origin and volume of gas in the new albany shale devonian mississippian eastern illinois basin this study involved analyses of kerogen petrography gas desorption geochemistry microporosity and mesoporosity of the new albany shale devonian mississippian in the eastern part of the illinois basin specifically detailed core analysis from two locations one in owen county indiana and one in pike county indiana has been conducted the gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales gas origin was assessed using stable isotope geochemistry measured and modeled vitrinite reflectance values were compared depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail the shallower owen county location 415 433 m 1362 1421 ft deep contained significant additions of microbial methane whereas the pike county location 832 860 m 2730 2822 ft deep was characterized exclusively by thermogenic gas despite differences in the gas origin the total gas in both locations was similar reaching up to 2 1 cm3 g 66 scf ton lower thermogenic gas content in the shallower location lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures was compensated for by the additional generation of microbial methane which was stimulated by an influx of glacial melt water inducing brine dilution and microbial inoculation the characteristics of the shale of the maquoketa group ordovician in the pike county location are briefly discussed to provide a comparison to the new albany shale

reappraisal of the fossil methane budget and related emission from geologic sources converging evidence from new top down and bottom up estimates of fossil radiocarbon free methane emissions indicates that natural geologic sources account for a substantial component of the atmospheric methane budget comparing emission estimates based on atmospheric 14 ch 4 radiomethane with geologic emissions from seepage including terrestrial macroseeps microseepage marine seeps and geothermal volcanic emissions from the earth s crust shows that such geo ch 4 sources can be conservatively estimated at 53 11 tg yr 1 globally this makes geo ch 4 second in importance to wetlands as a natural methane source such a new appraisal can easily be accommodated within the uncertainty of the global methane budget as recently compiled and recognizes the importance of geophysical out gassing of methane generated within the lithosphere we propose a new coherent contemporary budget in which 30 5 based on atmospheric radiomethane measurements of the global source of 582 87 tg yr 1 has fossil origin both natural and anthropogenic

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

an active margin across the adriatic sea central mediterranean sea abstract new seismological and structural data from the central adriatic gargano promontory area demonstrate that the current models of an aseismic and slightly deformed adriatic block have to be revised a seismically active deformational belt is mapped along two main fault systems the tremiti islands and mattinata faults moreover geologic and geophysical evidence suggests that a more extensive lithospheric boundary may cut across the central italian peninsula to the tyrrhenian basin

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

emission of methane and heavier alkanes from the la brea tar pits seepage area los angeles natural hydrocarbon oil and gas seeps are widespread in los angeles california due to gas migration along faults from numerous subsurface petroleum fields these seeps may represent important natural contributors of methane ch4 and heavier alkanes c2 c4 to the atmosphere in addition to anthropogenic fossil fuel and biogenic sources we measured the ch4 flux by closed chamber method from the la brea tar pits park 0 1 km2 one of the largest seepage sites in los angeles the gas seepage occurs throughout the park not only from visible oil asphalt seeps but also diffusely from the soil affecting grass physiology about 500 kg ch4 d 1 is emitted from the park especially along a belt of enhanced degassing that corresponds to the 6th street fault additional emissions are from bubble plumes in the lake within the park order of 102 103 kg d 1 and at the intersection of wilshire boulevard and curson avenue 130 kg d 1 along the same fault the investigated area has the highest natural gas flux measured thus far for any onshore seepage zone in the usa gas migration oil biodegradation and secondary methanogenesis altered the molecular composition of the original gas accumulated in the salt lake oil field 300 m deep leading to high c1 c2 and i butane n butane ratios these molecular alterations can be important tracers of natural seepage and should be considered in the atmospheric modeling of the relative contribution of fossil fuel anthropogenic fugitive emission and natural geologic sources versus biogenic sources of methane on local and global scales

basement faults and seismicity in the appalachian basin of new york state abstract landsat lineaments identified by earth satellite corporation earthsat 1997 can be groundtruthed across the appalachian basin of new york state nys both fracture intensification domains fids and faults are observed in outcrop along the lineaments confirmation of deep structure associated with the surface structure is provided by both well log analyses and seismic reflection data primarily proprietary additional faults are proposed by comparing the lineament locations with gravity and magnetic data the result is a web of basement faults that crisscross new york state by overlaying epicenter locations on the fault lineament maps it is possible to observe the spatial correlation between seismic events and the faults every seismic event in the appalachian basin portion of nys lies on or near a known or suspected fault it thus appears that not only are there more faults than previously suspected in nys but also many of these faults are seismically active

the dip of the foreland monocline in the alps and apennines the foreland monocline dips underneath thrust belts and accretionary wedges both in oceanic and continental subduction zones we present new data on the dip of the monocline in the frontal part of two orogens the alps and the apennines there is an overall difference between the dip of the relative monoclines and there is also a strong lateral variation along both arcs in the alps the regional dip varies between 0 in the remote foreland to an average of 2 3 at the front of the thrust belt below the foredeep to about 5 beneath the external thrust sheets within 40 km from the leading edge of the accretionary wedge the regional dip of the monocline in the apennines has an average of 4 5 at the front of the thrust belt below the foredeep to about 10 beneath the external thrust sheets within 40 km from the leading edge of the accretionary wedge there are areas where the dip exceeds 20 the apennines though topographically lower than the alps present higher monocline dips and a deeper foredeep moreover there are variations in the dip of the monocline moving along the strike of the two belts the low values coincide with permian mesozoic inherited horsts whereas the steeper values correspond to basinal areas and they usually match the salients of the thrust belt front within the salients the distance between thrust ramps increases therefore there are two orders of mean values of the dip of the foreland monocline the first at the orogen scale more than 1000 km wavelength the second at the regional scale 100 200 km wavelength within the single orogen lateral variations in the lithospheric buoyancy due to the inherited mesozoic stretching may explain the second order variations in foreland dip but not the first order mean values which seem to be more sensitive to the geographic polarity of the subduction rather than to the lithospheric composition which is rather similar in the alpine and in the central northern apennines slabs

pleistocene sea level changes sapping processes and development of valley networks in the apulia region southern italy abstract the central area of the apulia region is characterized by a network of valleys with peculiar features locally called gravine or lame they are short straight valleys deeply incised in plio pleistocene calcareous sandstones and in mesozoic limestones these characteristic valleys cut a staircase of marine terraces a series of valley generations is recognisable each one of them leading to the internal margin of a marine terrace representing its base level morphological features and hydrogeological conditions suggest that sapping processes were responsible for the development of the valley network as the aquifer rests on seawater intruding from the nearby coastal area sapping processes were enhanced during interglacial high sea level stands so that each ancient coastline is marked by its own generation of valleys however the longest and deepest valleys formed at the ionian side during ois 7 this is due mostly to a fast sea level rise accompanied by very humid climatic conditions that increased the hydraulic head at the springs and the intensity of sapping processes sapping valleys could be useful for regional correlation of marine terraces and as indicators of relict coastlines at present placed below sea level

how flat is tibet high resolution digital topography three arc second grid for most of tibet provides new information to characterize the relief of the highest and largest plateau on earth the arid to semiarid central and northern part of the plateau interior has low relief average slopes of over 250 m windows and a mean elevation of 5023 m above sea level at moderate wavelengths of m relief is or less for most of tibet as opposed to the much higher relief of up to 6 km on the plateau edges where glacial and fluvial dissection is greater because of higher levels of precipitation the only faults manifesting significant topographic relief are the relatively small scale generally north trending graben systems primarily in southern tibet and several large scale fault systems near the edges of tibet the flatness of tibet implies that 1 there has been little deformation especially shortening of the uppermost crust north of the graben systems during the late cenozoic and 2 shallow crustal isostatic compensation has been acting to level the surface of the plateau

chemical and isotopic tracers of the contribution of microbial gas in devonian organic rich shales and reservoir sandstones northern appalachian basin in this study the geochemistry and origin of natural gas and formation waters in devonian age organic rich shales and reservoir sandstones across the northern appalachian basin margin western new york eastern ohio northwestern pennsylvania and eastern kentucky were investigated additional samples were collected from mississippian berea sandstone silurian medina sandstone and ordovician trenton black river group oil and gas wells for comparison dissolved gases in shallow groundwaters in devonian organic rich shales along lake erie contain detectable ch4 0 01 50 55 mol with low 13c ch4 values 74 68 to 57 86 and no higher chain hydrocarbons characteristics typical of microbial gas nevertheless these groundwaters have only moderate alkalinity 1 14 8 72 meq kg and relatively low 13c values of dissolved inorganic c dic 24 8 to 0 6 suggesting that microbial methanogenesis is limited the majority of natural gases in devonian organic rich shales and sandstones at depth 168 m in the northern appalachian basin have a low ch4 to ethane and propane ratios 3 35 mol c1 c2 c3 and high 13c and d values of ch4 53 35 to 40 24 and 315 0 to 174 6 respectively which increase in depth reservoir age and thermal maturity the molecular and isotopic signature of these gases show that ch4 was generated via thermogenic processes despite this the geochemistry of co produced brines shows evidence for microbial activity high 13c values of dic 10 slightly elevated alkalinity up to 12 01 meq kg and low so4 values 1 mmole l in select devonian organic rich shale and sandstone formation water samples suggest the presence of methanogenesis while low 13c dic values 22 and relatively high so4 concentrations up to 12 31 mmole l in many brine samples point to so4 reduction which likely limits microbial ch4 generation in the appalachian basin together the formation water and gas results suggest that the vast majority of ch4 in the devonian organic rich shales and sandstones across the northern appalachian basin margin is thermogenic in origin small accumulations of microbial ch4 are present at shallow depths along lake erie and in western ny

the role of quaternary environmental change in the evolution of landscapes case studies from southern africa abstract the paper begins by examining the importance of southern african quaternary environmental change the quaternary is characterised by repeated climatic changes of considerable amplitude analysis of these fluctuations reveals the ubiquity of change and the fundamental dynamism of earth systems change is normal and despite the fact that southern africa was not subject to quaternary glaciation per se the influence of variations in say amount and seasonality of rainfall has been very marked indeed the quaternary also represents the time period during which people have become a dominant environmental agent in the subcontinent southern africa has played a crucial role in the evolution of hominids and their development has been influenced strongly by accompanying environmental change the relationship between geomorphology and climate in southern africa is explored revealing the degree and extent to which its landscapes are determined by changing environmental conditions especially during the tertiary and quaternary how apparent is the legacy of the past this leads to a consideration of the types of geomorphological evidence some more reliable than others that can be utilised in order to reveal the details of quaternary environmental change arid and semiarid landscapes appear to preserve more evidence of former environmental conditions although high contemporary erosion rates and the paucity of long terrestrial sedimentary sequences hinder their complete elucidation two case studies of quaternary change in the subcontinent are presented from the southwestern cape and namibia these examples document the increasing intensity of human impact on landscapes to the extent that people now play the dominant geomorphological role especially in semiarid and coastal areas the conclusion offers pointers as to how geomorphological evidence of quaternary change can be used to assist in the better management of contemporary and future environmental conditions

relict landscape resistance to dissection by upstream migrating knickpoints expanses of subdued topographies are common at high elevation in mountain ranges they are often interpreted as relict landscapes and are expected to be replaced by steeper topography as erosion proceeds preservation of such relict fragments can merely reflect the fact that it takes time to remove any preexisting topography however relict fragments could also possess intrinsic characteristics that make them resilient to dissection we document here the propagation of a wave of dissection across an uplifted relict landscape in puerto rico using 10be 26al burial dating on cave sediments we show that uplift started 4 ma and that river knickpoints have since migrated very slowly across the landscape modern detrital 10be erosion rates are consistent with these long term rates of knickpoint retreat analysis of knickpoint distribution combined with visual observations along the streambeds indicates that incision by abrasion and plucking is so slow that bedrock weathering becomes a competing process of knickpoint retreat the studied rivers flow over a massive stock of quartz diorite surrounded by an aureole of metavolcanic rocks earlier studies have shown that vegetation over the relict topography efficiently limits erosion allowing for the formation of a thick saprolite underneath such slow erosion reduces streambed load fluxes delivered to the knickpoints as well as bed load grain size both processes limit abrasion compounding the effect of slow abrasion wide joint spacing in the bedrock makes plucking infrequent thus the characteristics of the relict upstream landscape have a direct effect on stream incision farther downstream reducing the celerity at which the relict subdued landscape is dissected we conclude that similar top down controls on river incision rate may help many relict landscapes to persist amidst highly dissected topographies

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

new chronological evidence for the nature and timing of linear dune development in the southwest kalahari desert abstract the age of the linear dunes in the southwest kalahari desert has not previously been directly established by applying the optical dating method to samples from the dunefield a number of questions relating to the timing and nature of linear dune development are addressed the last major period of simple linear dune development occurred 17 000 10 000 years ago probably from the reworking of earlier aeolian sediments dune emplacement occurred under more arid probably windier conditions than those prevailing today which are only responsible for episodic surficial dune sand movement as well as simple linear dunes the dunefield also contains more complex linear dune patterns samples from one area in the eastern dunefield demonstrate that multi phase development is more probable for complex dune patterns as opposed to single phase evolution under a complex wind regime

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

mixing of thermogenic natural gases in northern appalachian basin stable isotopic studies were undertaken to investigate the origin of 20 oil associated and non associated gases from western and central new york state in the northern appalachian basin gas wetness c2 c5 c1 c5 methane dgr13c and methane dgrd values range from 0 8 to 26 9 47 9 to 30 7 pmil and 305 to 143 pmil respectively corresponding ethane and propane dgr13c values range from 40 9 to 32 0 pmil and 34 9 to 27 9 pmil these data are interpreted to indicate a thermogenic origin with source rock maturities ranging from early mature equivalent vitrinite reflectance ro approximately 0 5 to post mature equivalent ro 2 0 inferred gas maturities generally in rease with increasing reservoir age from late to middle devonian marcellus and overlying rocks middle devonian to latest silurian oriskany onondaga akron silurian lockport herkimer medina to ordovician queenston and black river oil and gas in many late to middle devonian reservoirs may have migrated from interbedded organic rich shales in other reservoirs particularly those of ordovician and silurian age unusual isotopic reversals methane dgr13c ethane dgr13c suggest that gas generated locally from equivalent age rocks within the oil window mixed with post mature gas migrated from deeply buried sources to the south and southeast the post mature gas was probably sourced from middle to late ordovician shales regional migration of middle ordovician gas may have occurred along the middle ordovician knox unconformity gas was presumably channeled into overlying silurian and devonian reservoirs along faults and fractures

differential weathering and erosion in an inselberg landscape in southern zimbabwe a morphometric study and some notes on factors influencing the long term development of inselbergs abstract a morphometric analysis of inselberg systems in southern zimbabwe indicated that there are two types of inselberg systems that differ in the mode of development inselberg systems characterized by backwearing tend to occur on granitoid rocks that are foliated highly fractured and prone to grusification the inselbergs are mostly of the koppie type and are covered to a great extent with regolith or debris the second type of inselbergs consists of sparsely fractured granitoid rocks and areas underlain by these rocks are characterized by clusters of closely spaced rock domes in the case of these inselbergs backwearing is not indicated they appear to be the result of the exposure of structurally pre designed highly resistant rock compartments the hypothesis that differences in lithology and structure may influence the rate and style of inselberg development was tested by means of a simulation model the simulations are run under the same boundary conditions with differing assumptions concerning role of divergent weathering the results show that both modes of inselberg development may occur alongside one another as long as a critical relief is maintained the modelling provided also indicates that although the inselberg systems must have integrated several sequences of environmental changes during their development these changes were not able to divert the general trend of the process response system away from its steady course lithological and structural factors which are responsible for the differences in the mobility of material on the inselberg sideslopes are thus considered to be the primary source of influence of the different modes of inselberg development it is suggested that the compositional and structural diversity in granitoid rock terrains is what enables inselbergs to pass through different development modes and sequences as rocks of differing resistance become subject to weathering during the development of the landscape

significance of hydrocarbon seepage relative to petroleum generation and entrapment near surface indications of migrating hydrocarbons provide the petroleum systems analyst critical information about source organic matter type maturation organic maturity migration migration pathway delineation and in selected geologic settings specific prospect hydrocarbon charge all petroliferous basins exhibit some type of near surface signal but the hydrocarbon leakage to surface is not always detectable with conventional seep detection methods understanding the petroleum seepage system hence petroleum dynamics of a basin is key to understanding and using near surface geochemical methods for basin assessment and prospect evaluation the relationships between near surface hydrocarbon seepage and subsurface petroleum generation and entrapment are often complex the petroleum seepage system contain four key elements seepage activity qualitative expressions of relative leakage rates active vs passive and episodic vs continuous seepage type concentration of migrated thermogenic hydrocarbon relative to in situ material macro vs micro migration focus major direction of bulk flow leakage relative to the subsurface hydrocarbon generation and or entrapment and near surface seep disturbances near surface processes which can greatly alter or block seepage signals the rate and volume of hydrocarbon seepage to the surface greatly control near surface geological and biological responses and thus are the best method of sampling and analysis to detect hydrocarbon leakage effectively to properly predict subsurface petroleum properties interpretation of near surface geochemical data must recognize many potential problems including recent organic matter input transported hydrocarbons bacterial alteration mixing contamination and fractionation effects surface geochemical data should always be integrated with other geological data calibration datasets to determine the utility of near surface geochemical techniques within particular basinal settings are essential when evaluating prospects for hydrocarbon charge

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

evolution of fluviokarst canyons in response to the quaternary tectonic uplift of the apulia carbonate platform southern italy insights from morphometric analysis of drainage basins abstract the evolution of fluviokarst landscapes results from the interplay of karst and fluvial processes all driven by rock uplift or base level fall the fluviokarst landscape of the murge plateau in the central apulian region southeastern italy is characterized by narrow steep sided v shaped canyons locally called gravine and deeply incised into the plio pleistocene deposits of the bradanic trough and the underlying apulian limestone bedrock previous studies propose alternative models of canyons development however identifying a dominant morphogenetic process for the evolution of the gravine fluviokarst drainage basins remains an open question the results of our regional morphometric analysis reveal a marked transition from the relict low relief landscape preserved in the murge uplands to the steep channel reaches below prominent knickpoints showing evidence of a transient wave of river incision that is propagating inland we observe anomalies of mean local relief and channel steepness and the distribution of fluvial knickpoints consistent with a regional uplift affecting the murge plateau since middle late pleistocene these findings demonstrate that the history of landscape evolution was dominated by fluvial processes using transformed river profile analysis we show that anomalies in the gravine trunk channels indicate drainage basin instability by drainage area capture the convex shape of the hypsometric curves and high hypsometric integrals confirm that the disequilibrium state of the 13 analyzed basins results from a combination of regional uplift and subsequent river network reorganization and plateau area captures based on our results we propose a new model of landscape evolution for the gravine fluviokarst drainage basins

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

biomarker records of palaeoenvironmental variations in subtropical southern africa since the late pleistocene evidences from a coastal peatland abstract southern africa s unique global position has given rise to a dynamic climate influenced by large sea surface temperature gradients and seasonal fluctuations in the inter tropical convergence zone due to the semi arid climate of the region terrestrial palaeorecords are rare and our understanding of the long term sensitivity of southern african terrestrial ecosystems to climatic drivers is ambiguous a 810 cm continuous peat core was extracted from the mfabeni peatland with a 14 c basal age of c 47 thousand years calibrated before present kcal yr bp positioning it as one of the oldest known sub tropical coastal peatlands in southern africa this peat core provides an opportunity to investigate palaeoenvironmental changes in subtropical southern africa since the late pleistocene biomarker n alkane n alkanoic acid and n alkanol analysis in conjunction with previously published bulk geochemical data was employed to reconstruct organic matter om sources rates of om remineralisation and peatland hydrology our results showed that the principal om source into the peatland was emergent and terrestrial plants with exception of shallow lake conditions when submerged macrophytes dominated c 44 5 42 6 29 7 26 1 23 1 16 7 7 1 and 2 2 kcal yr bp n alkane proxies suggest that local plant assemblages were predominantly influenced by peatland hydrology by incorporating temperature sensitive n alkanoic acid and n alkanol proxies it was possible to disentangle the local temperature and precipitation changes we report large variations in precipitation intensities but subdued temperature fluctuations during the late pleistocene the holocene period was characterised by overall elevated temperatures and precipitation compared to the preceding glacial period interspersed with a millennial scale cooling event a close link between the mfabeni archive and adjacent indian ocean marine core records was observed suggesting the regional ocean surface temperatures to be the dominant climate driver in this region since the late pleistocene

knickpoint recession rate and catchment area the case of uplifted rivers in eastern scotland knickpoint behaviour is a key to understanding both the landscape responses to a base level fall and the corresponding sediment fluxes from rejuvenated catchments and must be accommodated in numerical models of large scale landscape evolution knickpoint recession in streams draining to glacio isostatically uplifted shorelines in eastern scotland is used to assess whether knickpoint recession is a function of discharge here represented by its surrogate catchment area knickpoints are identified using ds plots log slope versus log downstream distance a statistically significant power relationship is found between distance of headward recession and catchment area such knickpoint recession data may be used to determine the values of m and n in the stream power law e kamsn the data have too many uncertainties however to judge definitively whether they are consistent with m n 1 bedrock erosion is proportional to stream power and kps should be maintained and propagate headwards or m 0 3 n 0 7 bedrock incision is proportional to shear stress and kps do not propagate but degrade in place by rotation or replacement nonetheless the e scotland m and n values point to the dominance of catchment area discharge in determining knickpoint retreat rates and are therefore more consistent with the stream power law formulation in which bedrock erosion is proportional to stream power copyright 2005 john wiley sons ltd

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

abiotic methane flux from the chimaera seep and tekirova ophiolites turkey understanding gas exhalation from low temperature serpentinization and implications for mars abstract the emission of abiotic methane ch 4 into the atmosphere from low temperature serpentinization in ophiolitic rocks is documented to date only in four countries the philippines oman new zealand and turkey serpentinization produces large amounts of hydrogen h 2 which in theory may react with co 2 or co to form hydrocarbons fischer tropsch type synthesis ftt similar mechanisms have been invoked to explain the ch 4 detected on mars so that understanding flux and exhalation modality of ophiolitic gas on earth may contribute to decipher the potential degassing on mars this work reports the first direct measurements of gas ch 4 co 2 flux ever done on onshore ophiolites with present day serpentinization we investigated the tekirova ophiolites at cirali in turkey hosting the chimaera seep a system of gas vents issuing from fractures in a 5000 m 2 wide ophiolite outcrop at this site at least 150 190 t of ch 4 is annually released into the atmosphere the molecular and isotopic compositions of c 1 c 5 alkanes co 2 and n 2 combined with source rock maturity data and thermogenic gas formation modelling suggested a dominant abiotic component 80 90 mixed with thermogenic gas abiotic h 2 rich gas is likely formed at temperatures below 50 c suggested by the low deuterium hydrogen isotopic ratio of h 2 d h2 720 consistent with the low geothermal gradient of the area abiotic gas synthesis must be very fast and effective in continuously producing an amount of gas equivalent to the long lasting 2 millennia emission of 100 t ch 4 yr 1 otherwise pressurised gas accumulation must exist over the same ophiolitic formation 3 km away from chimaera we detected an invisible microseepage of abiotic ch 4 with fluxes from 0 07 to 1 g m 2 d 1 on mars similar fluxes could be able to sustain the ch 4 plume apparently recognised in the northern summer 2003 10 4 or 10 5 t yr 1 over the wide olivine bedrock and outcrops of hydrated silicates in the syrtis major and nili fossae just one seep like chimaera or more realistically a weak spatially sporadic microseepage would be sufficient to maintain the atmospheric ch 4 level on mars

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

relationship between antarctic sea ice and southwest african climate during the late quaternary here we compare late quaternary southwest african climate records from the west coast of southern africa published winter rainfall and trade wind intensity records from a core off the coast of namibia to records of antarctic sea ice extent this comparison reveals coherent changes between antarctic sea ice extent and the southwest african winter rain region since 45 k y b p with enhanced winter rainfall and trade wind vigor during periods of increased sea ice presence we propose an oceanic and atmospheric coupling between antarctic sea ice and the winter rainfall zone of southwest africa that may lead to increased desertification in the region if global warming persists

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

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

evidence for holocene sea level change at verlorenvlei western cape south africa abstract a series of sediment cores extracted from what is today a large freshwater coastal lake verlorenvlei has been sub sampled radiocarbon dated and subjected to a range of palaeoenvironmental techniques in particular pollen analysis sedimentology and geochemistry a mid late holocene higher sea level is evident in the cores indicating the rapidity with which sea level change can occur and invoke other forms of environmental response following a hiatus in sedimentation most probably around 3800 bp the marine conditions at the site were replaced by fresh water as the dominant hydrological and ecological influence laminated organic sediments in some of the cores suggest that around 300 years ago a fresh water lake characterised verlorenvlei since then the picture revealed by high resolution palynology is one of progressive levels of human disturbance both in and around the study area sedimentological and palaeoecological analyses of additional cores from the vlei two from the distal inland and one from the proximal coastal end of the system serve further to elucidate the precise nature of sea level change in the late holocene and facilitate the construction of a refined holocene sea level curve for the region environmental changes in the late holocene are shown to be especially dynamic

effect of drainage area on hypsometry from an analysis of small scale drainage basins in the siwalik hills central nepal hypsometry of drainage basins area elevation analysis has generally been used to infer the stage of geomorphic development and to study the influence of varying forcing factors i e tectonics climate lithology on topography however the scale dependence of hypsometry has generally been neglected in order to assess the scale dependence of hypsometry this study focuses on the sensitivity of hypsometry to different digital elevation model dem resolutions and on the influence of drainage area hypsometry inferred from different dems is shown to be robust against variations of their resolution however hypsometry appears to be dependent on drainage area we propose that this scale dependence may reflect the varying importance of river and hillslope processes with basin area copyright 1999 john wiley sons ltd

in situ low relief landscape formation as a result of river network disruption the relict landscapes of southeast tibet are being formed in situ as a result of river drainage reorganization that renders rivers unable to balance tectonic uplift so these landscapes may not provide an unaltered record of past geomorphic conditions high elevation low relief surfaces or relict landscapes are generally thought to be uplifted old landscapes that preserve past tectonic and environmental conditions rong yang et al have tested current models of landscape evolution using digital topographic analysis of so called relict landscapes in southeast tibet and yunnan province china dramatic scenery boasting up to 3 km of relief encompassing the gorges of the yangtze mekong and salween rivers they find that the region may not provide an unaltered record of past geomorphic conditions rather these landscapes form in situ as a result of river drainage reorganization that renders rivers unable to balance tectonic uplift landscapes on earth retain a record of the tectonic environmental and climatic history under which they formed landscapes tend towards an equilibrium in which rivers attain a stable grade that balances the tectonic production of elevation and with hillslopes that attain a gradient steep enough to transport material to river channels equilibrium low relief surfaces are typically found at low elevations graded to sea level however there are many examples of high elevation low relief surfaces often referred to as relict landscapes1 2 or as elevated peneplains3 these do not grade to sea level and are typically interpreted as uplifted old landscapes preserving former more moderate tectonic conditions4 here we test this model of landscape evolution through digital topographic analysis of a set of purportedly relict landscapes on the southeastern margin of the tibetan plateau one of the most geographically complex climatically varied and biologically diverse regions of the world we find that in contrast to theory the purported surfaces are not consistent with progressive establishment of a new steeper river grade and therefore they cannot necessarily be interpreted as a remnant of an old low relief surface we propose an alternative model supported by numerical experiments in which tectonic deformation has disrupted the regional river network leaving remnants of it isolated and starved of drainage area and thus unable to balance tectonic uplift the implication is that the state of low relief with low erosion rate is developing in situ rather than preserving past erosional conditions

the relief of the swiss alps and adjacent areas and its relation to lithology and structure topographic analysis from a 250 m dem abstract in this paper we discuss the large scale geomorphological characteristics of the swiss alps based on numerical analysis of a digital elevation model and compare these to an erodibility map constructed from a geotechnical map of switzerland and regional geomorphological studies comparing the erodibility map with the large scale morphometry shows an intimate relationship between mountain scale erodibility and topography on average higher mean elevations and steeper mean slopes correlate with regions where rocks of low erodibility prevail areas with high peaks as well as the main water divides are controlled by the presence of bedrock with low to very low detachability the drainage network of the swiss alps shows a close relationship to the lithological differences as well major longitudinal valleys follow easily erodible units in the eastern and western part of the swiss alps the highest values of local relief are located to the south of the main water divide whereas in the central part local relief is higher to the north of the main water divide the large scale geomorphic characteristics regarded in the framework of the geological history of uplift and denudation suggest that low and very low erodibilities lead to the development of areas of high elevations which are likely to persist over periods of 10 15 ma as the analysis of the lepontine area shows 20 ma after cessation of exhumation such high elevations are likely to be worn down and to manifest themselves as high relief only

historical contingency in fluviokarst landscape evolution abstract lateral and vertical erosion at meander bends in the kentucky river gorge area has created a series of strath terraces on the interior of incised meander bends these represent a chronosequence of fluviokarst landscape evolution from the youngest valley side transition zone near the valley bottom to the oldest upland surface this five part chronosequence not including the active river channel and floodplain was analyzed in terms of the landforms that occur at each stage or surface these include dolines uvalas karst valleys pocket valleys unincised channels incised channels and cliffs smaller features such as swallets and shafts also occur landform coincidence analysis shows higher coincidence indices ci than would be expected based on an idealized chronosequence ci values indicate genetic relationships common causality among some landforms and unexpected persistence of some features on older surfaces the idealized and two observed chronosequences were also represented as graphs and analyzed using algebraic graph theory the two field sites yielded graphs more complex and with less historical contingency than the idealized sequence indeed some of the spectral graph measures for the field sites more closely approximate a purely hypothetical no historical contingency benchmark graph the deviations of observations from the idealized expectations and the high levels of graph complexity both point to potential transitions among landform types as being the dominant phenomenon rather than canalization along a particular evolutionary pathway as the base level of both the fluvial and karst landforms is lowered as the meanders expand both fluvial and karst denudation are rejuvenated and landform transitions remain active

modeling of knickpoint retreat on the roan plateau western colorado 1 the roan plateau in western colorado constitutes a natural experiment for studying landscape response to a drop in base level late cenozoic incision of the upper colorado river led to elevational isolation of the plateau and initiation of a wave of incision into its southern edge knickpoints oversteepened reaches that contain waterfalls 60 110 m in height mark the upstream extent of this headward propagating wave that this incision has occurred in a laterally extensive well stratified and essentially flat lying bedrock and in an area with relatively uniform climate implies that it should serve as a good test of existing knickpoint propagation models we predict the locations of knickpoints by using a stream power based celerity model in which knickpoint recession rate is a power function of drainage area and is proportional to rock susceptibility to erosion models of the parachute and roan drainages 17 and 16 knickpoints respectively show expected rapid initial knickpoint propagation rates which decline as drainage area decreases stepwise at tributary junctions the modeled positions of knickpoints match well with observed features using a single combination of parameters to model retreat in both drainage basins we compare our celerity model results with past studies and explore how longitudinal profile analysis may be used to derive independently the exponent on drainage area in the celerity model

late holocene environments at verlorenvlei western cape province south africa abstract evidence on late quaternary palaeoenvironments of the western and southwestern cape of south africa has facilitated detailed reconstructions mainly for the mountains where organic sediment accumulation has been favoured by relatively humid climates on the lowlands particularly those of the west coast region the search for sites traditionally regarded as suitable for the accumulation of sediments containing preserved fossil pollen has commenced only more recently this area of the western cape province has however provided quaternary scientists with a rich archaeological record that has yet to be tested against independent lines of palaeoecological evidence a sequence of sediments which have accumulated in what is today a large freshwater coastal lake verlorenvlei has been sampled at grootdrift 15 km inland of the coast a series of seven sediment cores was extracted during 1991 and three of these have now been sub sampled radiocarbon dated and subjected to a range of palaeoenvironmental techniques in particular pollen analysis sedimentology and geochemistry three pollen diagrams are presented which reveal the vegetation history of both the immediate grootdrift environment and the wider catchment during several periods over the last 5500 years a mid holocene higher sea level is evident in two of the cores which were examined for pollen throughout their length the surrounding area appears at this time to have been somewhat more arid than today following a hiatus in sedimentation some time after 4300 bp the marine conditions at the site disappear and are replaced by fresh water as the dominant hydrological and ecological influence around the time of colonial occupation of the region some 300 years ago lacustrine conditions prevailed at grootdrift and greater moisture availability is indicated in the catchment during the last 300 years the picture revealed by high resolution palynology of the third core is one of progressive levels of human disturbance both in and around the verlorenvlei evidence from a textural and geochemical analysis of the sediments is consistent with the interpretation based on fossil pollen the implications of this information are examined against the archaeology and palaeoecology of several cave sites in the vicinity of the vlei the consistency apparent in the range of types of evidence suggests that some reliance can be placed on the mid late holocene palaeoenvironmental reconstruction at verlorenvlei the paper thus provides insight into the nature of the complex interactions between late holocene climate change sea level fluctuation vegetation change vlei hydrology and human activity in the western cape coastal region

late quaternary palaeoenvironments of the southwestern cape south africa a regional synthesis the contemporary uniqueness of the southwestern cape environemnt suggests that its response to the environmental perturbations of the late quaternary may have been correspondingly distinctive despite the wide variety of palaeoenvironmental evidence which has accumulated from within the region a coherent picture of the evolution and development of its environments has remained elusive since the publication of several regional reviews over the last decade or so a considerable body of palynological and other palaeoecological evidence has emerged which prompts a fresh synthesis as to the nature of late quaternary environmental changes in the southwestern cape s fynbos biome although there are few sediments which date to the appropriate period the last glacial maximum in contrast to the situation evident in the summer rainfall region is suggested to be a period characterised by considerably cooler and wetter conditions in certain parts of the biome the first half of the holocene appears to have been somewhat drier than much of the second half and the warmer temperatures of the holocene hypsithermal are associated with reduced moisture availability intra regional contrasts are evident in the response to late quaternary environmental changes furthermore it transpires that for much of the later quaternary and for large areas of the region precipitation may have fluctuated out of phase with changes in the interior of the subcontinent a situation which has great relevance to the prediction of future environmental changes and their impacts in the southwestern cape

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

revisiting the hypsometric curve as an indicator of form and process in transport limited catchment hypsometry has historically been used as an indicator of geomorphic form of catchments and landforms yet there has been little work aimed at relating hypsometry to landform process and scale this paper uses the siberia catchment evolution model to explore linkages between catchment process and hypsometry siberia generates results that are qualitatively and quantitatively similar to observed hypsometric curves for physically realistic parameters however we show that not only does the hypsometry reflect landscape runoff and erosion process but it is strongly dependent on channel network and catchment geometry we show that the width to length ratio of the catchment has a significant influence on the shape of the hypsometric curve though little on the hypsometric integral for landforms dominated by fluvial sediment transport the classic strahler mature hypsometric curve is only generated for catchments with roughly equal width and length narrow catchments show a hypsometric curve more similar to strahler s monadnock form for landscapes dominated by diffusive transport the simulated hypsometric curve is concave down everywhere this being consistent with curves reported for some example catchments in france because the transition between diffusive dominance to fluvial is scale dependent with larger catchments exhibiting greater fluvial dominance then the hypsometric curve is a scale dependent descriptor of landforms experimental results for simulated landforms from a small scale rainfall erosion simulator are reported it is shown that siberia yields satisfactory fits to the data confirming its ability to predict the form of the hypsometric curve from a simple model of geomorphic processes 1998 john wiley sons ltd

tectonic climatic and lithologic influences on landscape fractal dimension and hypsometry implications for landscape evolution in the san gabriel mountains california east west variation in tectonic activity and strong north south climatic gradients provide a unique opportunity to study tectonic climatic and lithologic influences on landscape evolution in the san gabriel mountains california the competing tendencies of constructive tectonic and degradational climatic effects act against lithologic resistance to influence fluvial systems and thus the nature of adjacent and nested drainage basins landscape fractal dimension d a measure of surface roughness over a variety of scales and the hypsometric integral i a measure of the distribution of landmass volume above a reference plane are useful measures of altitudinal variation with scale as such they may provide clues as to the relative influences of tectonism climate and rock type topographic analyses of the san gabriel mountains clearly indicate that tectonism strongly influences d at range wavelength scales while rock type variation apparently influences d and i at smaller scales tectonism is also shown to influence i across the mountain piedmont junction at all scales investigated tectonic activity shows strong negative correlation with both i and d because tectonically active portions of the mountain front do not allow time for much landscape dissection by lower order streams three dimensional topographic modeling suggests climatic parameters exert a stronger influence on d than does tectonism this modeling also suggests an inverse correlation between range scale d and i with varying climate and uplift rate a positive correlation is observed in the san gabriel mountains we suggest this difference results from 1 differences in uplift style between the san gabriel mountains and the models and or 2 variation in rock type erodibility present in the san gabriel mountains but which was not modeled we postulate that the interaction of tectonic climatic and lithologic parameters influences the stable i and d to which a landscape evolves key questions remaining include 1 the time required to reach a stable i or d after a climatic or tectonic change 2 what does the fractal nature of topography tell us about the scaling characteristics of major landforming processes 3 how does climate influence range scale i and both range and small scale d and 4 what are the effects on i and d of range scale lithologic variation both in the models and in real landscapes

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

the pretoria saltpan a 200 000 year southern african lacustrine sequence abstract the pretoria saltpan is a circular crater 1130 m in diameter and is situated some 40 km n of pretoria lat 25 34 30 long 28 04 59 e a recent tube sampling and core drilling programme has revealed an infilling consisting of some 90 m of fine lacustrine sediments chiefly organic muds underlain below 30 m depth by micrites which rest upon a further 61 m of coarse clastic debris granite bedrock was encountered at 151 m broad sedimentary zones correspond with major phases in the evolution of the crater lake superimposed cyclical patterns of accumulation reflect environmental changes on millenial to seasonal timescales 14c age determinations on algal debris from the upper 20 m of the core indicate a mean rate of sedimentation of about 1 m 2000 yr suggesting that the lacustrine sequence may span almost 200 000 yr over this period major environmental changes are apparent from sedimentological chemical mineralogical and isotopic analyses of the core and studies of the pollen spectra and diatom assemblages present within it this long continental sequence is therefore providing a high resolution palaeoenvironmental record for southern mid latitudes over much the same period as is covered by the vostok ice core in antarctica

landscape dissection isostatic uplift and the morphologic development of orogens we examine the morphologic factors that determine the isostatic response to landscape dissection in orogenic terrains in order to quantify the relative contributions of active tectonic uplift and passive isostatic uplift in generating mountain topography we demonstrate that although peaks many times the elevation of an assumed initial plateau can theoretically be generated only moderate amounts of peak uplift can be explained by isostatic rebound in real terrains analysis of topographic data from the european alps and other orogens indicates that isostatic uplift in response to dissection can account for about one fourth of the elevation of the highest peaks if local isostatic compensation is assumed and less if the lithosphere has significant flexural rigidity we conclude that although isostatic uplift can be significant in orogens high peaks are predominantly a consequence of tectonic processes in convergent settings

southwest african climate independent of atlantic sea surface temperatures during the younger dryas abstract to investigate land sea interactions during deglaciation we compared proxies for continental pollen percentages and accumulation rates and marine conditions dinoflagellate cyst percentages and alkenone derived sea surface temperatures the proxies were from published data from an ams radiocarbon dated sedimentary record of core geob 1023 5 encompassing the past 21 000 years the site is located at ca 2000 m water depth just north of the walvis ridge and in the vicinity of the cunene river mouth we infer that the parallelism between increasing sea surface temperatures and a southward shift of the savanna occurred only during the earliest part of the deglaciation after the antarctic cold reversal southeast atlantic sea surface temperatures no longer influenced the vegetation development in the kalahari stronger trade winds during the antarctic cold reversal and the younger dryas period probably caused increased upwelling off the coast of angola a southward shift of the atlantic anti cyclone could have resulted in both stronger trade winds and reduced impact of the westerlies on the climate of southwestern africa

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

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

extreme methane deuterium nitrogen and helium enrichment in natural gas from the homorod seep romania abstract methane ch 4 in terrestrial environments whether microbial thermogenic or abiogenic exhibits a large variance in c and h stable isotope ratios due to primary processes of formation isotopic variability can be broadened through secondary post genetic processes such as mixing and isotopic fractionation by oxidation the highest and lowest 13 c and 2 h or d deuterium concentrations in ch 4 found in various geologic environments to date are defined as natural terrestrial extremes we have discovered a new extreme in a natural gas seep with values of deuterium concentrations d ch4 up to 124 that far exceed those reported for any terrestrial gas the gas seeping from the small homorod mud volcano in transylvania romania also has extremely high concentrations of nitrogen 92 vol and helium up to 1 4 vol carbon isotopes in ch 4 c 2 h 6 and co 2 and nitrogen isotopes in n 2 indicate a primary organic sedimentary origin for the gas a minor mantle component is suggested by the 3 he 4 he ratio r ra 0 39 both thermogenic gas formation modeling and rayleigh fractionation modeling suggest that the extreme deuterium enrichment could be explained by an oxidation process characterised by a d ch4 and 13 c ch4 enrichment ratio h c of about 20 and may be accounted for by abiogenic oxidation mediated by metal oxides all favourable conditions for such a process exist in the homorod area where increased heat flow during pliocene quaternary volcanism may have played a key role finally we observed rapid variations within 1 h in c and h isotope ratios of ch 4 and in the h 2 s concentrations which are likely caused by mixing of the deep oxidized ch 4 n 2 h 2 s he rich gas with a microbial methane generated in the mud pool of one of the seeps we hypothesize that the unusual features of homorod gas can be the result of a rare combination of factors induced by the proximity of sedimentary organic matter mafic metal rich volcanic rocks and salt diapirs leading to the following processes a primary thermogenic generation of gas at temperatures between 130 and 175 c b secondary alteration through abiogenic oxidation likely triggered by the neogene quaternary volcanism of the eastern transylvanian margin and c mixing at the surface with microbial methane that formed through fermentation in the mud volcano water pool the homorod gas seep is a rare example that demonstrates how post genetic processes can produce extreme gas isotope signatures thus far only theorized and that extremely positive d ch4 values cannot be used to unambiguously distinguish between biotic and abiotic origin

sea surface temperature fluctuations during the holocene off the south coast of africa implications for terrestrial climate and rainfall models of southern african palaeoclimate implicate surface atmospheric circulation anoma lies as forcing large scale changes during the late quaternary the available proxy data are insufficient to test the models since they provide information about temperature and rainfall rather than surface circulation a conceptual model is proposed which links coastal ocean temperatures with atmospheric circulation and allows a history of surface circulation to be inferred from sea temperature data a holocene sea surface temperature sst record was constructed by measuring the oxygen isotope composition of marine mollusc shells preserved in an archaeological cave deposit on the coast of the eastern agulhas bank southern africa radiocarbon dating of individual shells allowed definition of the timing and timespan of events in the record by serially sampling along the growth axis of each shell information was obtained about intra annual variability as well as millennial scale trends during the early holocene th