present day kinematics of the mediterranean a comprehensive overview of gps results i combine recently published gps results to derive a geodetic horizontal velocity field consistent at the scale of the mediterranean and the surrounding alpine belts the velocity field is then used to discuss the boundary conditions around each major deforming area in the mediterranean to describe the main patterns of motion and deformation to critically review the existing kinematics models and to finally point out the main unresolved kinematics questions strain rate in europe north of the alpines belt is dominated by the signature of the glacial isostatic adjustment and tectonic strain remains below the current accuracy of gps results in the western mediterranean deformation is restricted to the betics the alboran and the morrocan rif with west to southwestward motion with respect to iberia which is part of stable europe shortening consistent with the relative nubia eurasia plate motion is found throughout the maghrebides but the distribution of deformation in northern africa remains largely unknown the central mediterranean is dominated by the counter clockwise rotation of the adriatic the junction between the southern adriatic domain and nubia has yet to be firmly established the deformation over a wide area east of the maghrebides in tunisia and the gulf of sirte in libya still remains to be quantified in the eastern mediterranean the velocity field is dominated by a general anti clockwise rotation and a general trend towards the hellenic trench with velocity magnitude increasing with decreasing distances from the trench this trend is observed not only in the aegean and anatolia but also in the southern balkans geodetic results emphasize that the convergence of the nubia and arabia plates towards eurasia directly controls the deformation across only very few segments along the plate boundary zone additional processes are therefore required to explain the observed velocity field and deformation pattern

evidence for enhanced aridity in the tarim basin of china since 5 3 ma abstract thick cenozoic deposits formed from the erosion of the northern evolving edge of the tibetan plateau provide opportunities to study the exhumation history and climatic changes within the region such deposits are important because they are located in an actively deforming mountain belt as well as in a rain shadow of the tibetan plateau multi proxy studies indicate that hyperarid climate has prevailed since 5 3 ma ago within the basin this information together with the geometry analysis of syntectonic deposits of the sanju anticline which indicate tectonic deformation at 5 3 ma enable us to better understand the interlay between climatic changes and tectonic uplift our results suggest that the tectonic uplift of the kunlun mountains at 5 3 ma must have been one of the significant regional tectonic events and the uplifted elevation of the kunlun mountains more effectively blocks the penetration of moisture from the indian monsoon into the tarim basin and thus enhances the rain shadow effect this can account for the increasing aridity as well as the formation of the world s second largest active sand desert the taklimakan desert in the tarim basin initiated at 5 3 ma ago

biogenic gas systems in eastern qaidam basin abstract several giant biogenic gas fields with proven gas reserves greater than 25 billion cubic meters have been discovered in recent years in the sanhu area of eastern qaidam basin this area has an average surface altitude of around 2800 m and forms the northern segment of the qinghai tibet plateau the biogenic gas fields occur mostly within or adjacent to the depocenter of approximately 3400 m of quaternary sediments the gas reservoirs with burial depth generally less than 1900 m are unconsolidated sandstones with approximately 24 40 porosity and are interbedded with mudstones containing on average 0 3 toc the occurrence of methanogens in the shallow quaternary sediments appears to depend on both the sedimentary facies and burial depths thus most of the biogenic gases in the sanhu area appears to have derived from the source kitchens in the central sag above a biogenic gas floor at the depth around 1800 m the key gas system elements for the formation of the giant biogenic gas accumulations include 1 secular low surface temperatures and lake water hypersalinity favor the preservation of suitable organic substrates for biogenic methane generation 2 well developed sand and mud interbeds 3 sufficient cumulative thickness of water saturated mudstones as caprocks 4 presence of syndepositional anticlines of pleistocene and later age 5 a regional hydrogeological system favoring northeastward gas migration and 6 ongoing dynamic gas migration and accumulation with abundant gas supply

climatic and tectonic controls on sedimentation and erosion during the pliocene quaternary in the qaidam basin china the qaidam basin is an internally drained basin located in the northeastern tibetan plateau presently over 50 of the basin floor exposes thick 1 km sections of pliocene quaternary strata that are deformed by folding and faulting we investigated this nearly continuous pliocene quaternary sedimentary record for the effects of global climate change and deformation on basin sedimentation new detailed stratigraphic magnetostratigraphic and stable isotope 18 o 13 c data from the pliocene shizigou and pleistocene qigequan formations along the southwestern flank of an intrabasin fold within the north central qaidam basin are presented here strata reveal climatically controlled meter scale parasequences within shallow lacustrine marginal lacustrine and deltaic lithofacies paleocurrents shift from eastward at the base to southwestward for the majority of the section but they abruptly shift toward the south southeast in the upper 400 m twenty two magnetozones constrain deposition between 5 2 ma and ca 0 8 ma and reveal that sedimentation rates were fairly constant 474 34 m m y from 5 2 to 3 0 ma after which time rates abruptly decreased to 154 40 mm yr before increasing again to 750 m m y since 1 2 ma the 18 o values shift from relatively constant values avg 6 8 range 9 6 to 4 5 relative to vienna peedee belemnite vpdb to less negative values avg 1 2 range 1 2 to 2 7 vpdb between 3 1 and 2 6 ma and to extremely variable values avg 2 9 range 8 3 to 4 0 after ca 2 6 ma the post 2 6 ma extreme variability in stable isotopes reflects the same timeframe of enhanced climatic cyclicity associated with northern hemisphere glaciation the 13 c values remain relatively constant average 4 0 range 5 7 to 1 0 until ca 0 9 ma when the values increase to 0 3 range 1 0 to 1 5 vpdb the appearance of growth strata at 3 0 ma shallow water evaporite deposition after 2 6 ma and the observation of paleoyardangs buried wind sculpted landforms within lake marginal strata at 2 4 ma imply that emergence of the adjacent anticline was followed by the shallowing and partitioning of the lake basin and subaerial exposure and erosion of marginal lake sediments these data reflect a significant change to a more arid climate in the qaidam basin between ca 3 1 ma and 2 6 ma overlapping with the onset of significant northern hemisphere glaciations and basin floor deformation lake level cycles were on 230 000 yr frequency from 2 6 ma to 1 2 ma before increasing to 12 000 yr frequency suggesting increased aridity and broad subaerial exposure of lake sediments after the pliocene quaternary transition deformation of intrabasin sediments by at least 3 0 ma caused uplift of the basin floor which provided an environment rich in friable material for wind deflation of the qaidam basin a likely source for sediments on the chinese loess plateau and nutrients for the pacific ocean carried by westerly winds by 2 6 ma deformation of the qaidam basin created closed depressions that facilitated evaporite sedimentation that continues today coeval intrabasin deformation combined with increasing aridity after 3 1 ma thus controlled both deposition and erosion within the region

multiproxy record for the last 4500 years from lake shkodra albania montenegro a multi proxy record is presented for approximately the last 4500 cal a bp from lake shkodra albania montenegro lithological analyses c n ratio and d 13 c of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic the d 18 o record of bulk carbonate indicates the presence of two prominent wet periods one at ca 4300 cal a bp and one at ca 2500 2000 cal a bp the latter phase is also found in southern spain and central italy and represents a prominent event in the western and central mediterranean in the last 2000 years four relatively wet intervals occurred between ca 1800 and 1500 cal a bp 150 450 ad 1350 1250 600 700 ad 1100 800 850 1150 ad and at ca 90 cal a bp 1860 ad between ca 4100 and 2500 cal a bp d 18 o values are relatively high with three prominent peaks indicating drier conditions at ca 4100 4000 cal a bp ca 3500 and at ca 3300 cal a bp four additional drier events are identified at 1850 ca 100 ad 1400 ca 550 ad 1150 800 ad and ca 750 cal a bp 1200 ad the pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment however since ca 900 cal a bp a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities copyright 2012 john wiley sons ltd

the radiocarbon age of organic carbon in marine surface sediments abstract long term carbon cycling and climate change are strongly dependent on organic carbon oc burial in marine sediments radiocarbon 14 c has been widely used to constrain the sources sinks and processing of sedimentary oc to elucidate the dominant controls on the radiocarbon content of total organic carbon 14 c toc accumulating in surface sediments we construct a box model that predicts 14 c toc in the sediment mixed layer measured as fraction modern fm our model defines three distinct oc pools degradable semi labile and refractory and assumes that 14 c toc flux to sediments is exclusively derived from surface ocean primary productivity and hence follows a generic surface ocean dissolved inorganic carbon dic bomb curve model predictions are compared to a set of 75 surface sediment samples which span a wide geographic range and reflect diverse water column and depositional conditions and for which sedimentation rate and mixed layer depth are well characterized our model overestimates the fm value for a majority 65 of these sites especially at shallow water depths and for sites characterized by depleted 13 c toc values the model is most sensitive to sedimentation rate and mixed layer depth therefore slight changes to these parameters can lead to a match between modeled and measured fm values at many sites yet in some cases we find that measured fm values cannot be simulated without large and unrealistic changes to sedimentation rate and mixed layer depth these results point to sources of pre aged oc to surface sediments and implicate soil derived terrestrial oc reworked marine oc and or anthropogenic carbon as important components of the organic matter present in surface sediments this approach provides a valuable framework within which to explore controls on sedimentary organic matter composition and carbon burial over a range of spatial and temporal scales

tectonic geomorphology and quaternary landscape development in the albania montenegro border region an inventory abstract young and recent tectonic activity can be discerned from instrumentally recorded seismic data as well as numerous geomorphological phenomena in the transition between the dinarides and hellenides fold and thrust belts we introduce a multiparametric approach using field remote sensing and seismic data from the region sw of shkodra lake between the towns of bar montenegro and lezha albania an area that offers unique opportunities of relating landscape development with tectonic deformation particularly we focus on windgap development on anticlines bound by pliocene quaternary active faults that allow statements on relative timing and rates of tectonic movement during the quaternary we propose an overall orogen perpendicular ne sw gradient from enhanced uplift and high tectonic activity in the hinterland to lower activity in the foreland an orogen parallel nw se gradient is added by the far field effects of shkodra peja transverse fault zone spfz these overall tendencies are valid despite a complex small scale mosaic of local differential uplift and subsidence recent gps studies and plate movement reconstructions are sparse providing rough estimates of 4 5 mm y horizontal and ca 1 mm y vertical movement geomorphological and paleoseismological studies are crucial to particularize recent and to estimate long term relative and absolute ground movement rates for this area

distribution of alkylated aromatic hydrocarbons and dibenzothiophenes in rocks of the upper rhine graben distributions of alkylated naphthalenes phenanthrenes and dibenzothiophenes and of selected non alkylated parent tri and tetra aromatic compounds were determined by capillary gas chromatography in extractable aromatic hydrocarbon fractions from 46 core samples from the middle upper rhine graben samples of palaeogene and jurassic ages at 250 2400 m depth were derived from four boreholes in the rastatt and kehl troughs assessment of thermal maturity based on the methylphenanthrene index mpi 1 was in agreement with mean random vitrinite reflectance rr only in the borehole closest to the graben centre where overmature stages were reached below 2000 m otherwise early thermal evolution of the organic matter inferred from rr 0 7 and rock eval pyrolysis data tmax 440 c was in contrast to the postmature stages indicated by the predominance of more stable type 2 methyl and 3 methylphenanthrenes mp s over less stable type 1 mp and 9 mp the 2 mp1 mp ratios 1 4 along with a predominance of phenanthrene fluoranthene and pyrene over alkylated tri and tetra aromatic hydrocarbons were attributed to pyrolytic like polycyclic aromatic hydrocarbons probably associated with reworked organic matter minor impregnations of migrated oil were revealed by elevated contents of methylated phenanthrenes dimethylnaphthalenes dmn s were mostly generated at 0 8 0 9 rr as indicated by 2 6 dmn 2 7 dmn 1 5 dmn ratios of 3 5 and then underwent extensive redistribution by upward migration the exceptional predominance of 4 methyldibenzothiophene mdbt and dibenzothiophene together with very high 4 mdbt1 mdbt ratios of 30 50 in certain samples from the rastatt trough were attributed to minor impregnations of hydrothermal petroleum

late cretaceous to early eocene deformation in the northern tibetan plateau detrital apatite fission track evidence from northern qaidam basin abstract unraveling the growth of northern tibet is crucial to understanding the geodynamic processes of the india eurasia collision evaluating plateau uplift models and reconstructing associated paleoclimate history however pre middle miocene deformation history of northern tibet remains poorly understood we use detrital apatite fission track detrital aft thermochronology of mesozoic and cenozoic sedimentary rocks from northern qaidam basin to constrain the early growth of northern tibet detrital aft ages of the mesozoic samples are younger than their depositional ages indicating that the mesozoic succession underwent two stages of exhumation after deep burial during 80 61 ma and 54 47 ma detrital aft ages of the cenozoic samples are older than their depositional ages and reveal that their source region experienced two periods of exhumation peak ages in 86 59 ma and 54 36 ma these results suggest that the northern tibet successively experienced late cretaceous early paleocene and early middle eocene deformation the late cretaceous early paleocene deformation implies that the extent of pre collisional india eurasia deformation region in the plateau were much larger than previously known the static detrital aft peak ages 54 51 ma based on lag time analysis for the paleogene samples demonstrate the early eocene deformation was a rapid and short lived event which was a far field response to the india eurasia collision hence we advocate synchronous deformation throughout the northern plateau at the collision time lag time analysis results also demonstrate absence of oligocene to early miocene cooling ages and post eocene decreasing exhumation rates in the cenozoic source regions this suggests relatively quiescent tectonic settings in the qilian mountains during the oligocene early miocene and agrees that the lateral strike slip movement of the altyn tagh fault was accommodated out of the plateau by the end of the early miocene

organic facies variations source rock potential and sea level changes in cretaceous black shales of the quebrada ocal upper magdalena valley colombia a 290 m thick middle cretaceous black shale sequence in the upper magdalena valley a present day intramontane basin located between the central and eastern cordilleras of colombia was investigated with organic geochemical and microscopic analyses as a result of the investigation we were able to 1 differentiate four organic facies types 2 estimate their source rock potential and 3 integrate these facies into a sequence stratigraphic framework the four organic facies types were type c bc b and d type c contains a distinct terrigenous organic matter component in lowstand or highstand deposits organic facies type bc is characterized by an increase and a better preservation of marine organic matter bc belongs to the lower part of the transgressive systems tract sediments of organic facies type b have the highest amount of marine organic matter due to excellent preservation under anoxic conditions the absence of bioturbation and the enrichment of trace metals are further implications for deposition under anoxic conditions facies type b is found in the upper part of the transgressive systems tract and contains the best petroleum source rock potential facies b occurrence coincides with sea level highstand and correlates especially with a maximum flooding in northern south america during the turonian organic facies type d is also related to highstand deposits but shows a high rate of reworking and degradation of organic matter

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

biogeochemical identification of the quaternary biogenic gas source rock in the sanhu depression qaidam basin abstract biogenic gas an important type of natural gas is produced by sedimentary organic matter via methanogenic processes through aerobic respiration nitrate reduction and bacterial sulfate reduction bsr after burial these diagenetic processes take place under special conditions and environments and produce specific products based on a study of tracers of different diagenetic stages this paper thoroughly examines various rocks of the quaternary gas producing province in the sanhu depression qaidam basin the possible source rocks for the biogenic gas were identified through investigating the special minerals characteristics of organic matter and their inter relationship the results demonstrated that the abundance of the primary active organic matter constrained the diagenetic stages of sediments mudstones with extremely low abundance of organic matter are at a stage of aerobic degradation and have not reached the reducing stage yet the organic carbon is dominated by recycled black carbon with low hydrocarbon generative potential mudstones containing a little more organic matter are mainly at the bsr stage the associated sedimentary organic matter is dominated by algae and chitin which have been converted into inert components due to extensive bsr bsr has thus reduced the hydrocarbon generative potential and the activity of organic matter leaving little reactive organic matter for the methanogenesis process carbonaceous mudstones with a high abundance of organic matter on the contrary contain abundant algae and higher plants that can largely survive bsr and remain active after the bsr stage these sediments constitute the primary gas source in the study area

controls on biogenic gas formation in the qaidam basin northwestern china abstract factors controlling biogenic gas generation were examined in the quaternary qaidam basin of china one of the youngest and largest biogenic gas producing basins in the world indicators of microbial activity were found in higher permeability stratigraphic intervals including high ratios of unresolved complex mixture resolved compounds u r as well as high ratios of methanogen biomarkers to normal alkanes such as 2 6 10 14 19 pentamethylicosane nc22 ipc25 nc22 and squalane nc26 ipc30 nc26 from solvent organic extracts from 86 samples samples with the highest concentrations of ipc25 nc22 and ipc30 nc26 were the most highly biodegraded as shown by u r ratios most intervals with high levels of methanogen biomarkers were characterized by groundwater with low total dissolved solids tds and low cl concentrations thought to be related to meteoric water recharge high h2 concentrations were also related to low tds and cl formation water results demonstrate that meteoric water invasion was important in stimulating microbial activity

cenozoic ostracoda and palaeoenvironments of the northeastern tarim basin western china abstract the paleogene rocks of the northeastern tarim basin in western china are composed mainly of reddish gypsum bearing coarse grained sediments and fossils are rare within these clastic facies however since the onset of the himalayan orogeny in the miocene continuous uplift of the tianshan mountains resulted in the rapid subsidence and appearance of a shallow lake environment as a result of this ostracods are widespread in the late cenozoic rocks of the tarim basin the brackish water ostracod cyprideis thrived from the mid to late miocene gypsum bearing sand and mud sediments were also deposited widely in the shallow brackish water lake environments this situation is similar to that of the qaidam basin which lies to the south of the altun mountains from the pliocene onwards the rates of subsidence and sedimentation increased the resulting regression of the lake led to disappearance of ostracods from a large part of the basin to the north of the kuqa depression the tianshan mountains underwent continuous uplift during the late himalayan orogeny as a result the quaternary lake deposits have a much greater extent than those of the pliocene and extend even further southward than those of the miocene consequently the brackish water ostracod cyprideis became dominant again during the quaternary from the end of the early pleistocene to present in this area an abundant and high diversity fauna of fresh to brackish water ostracods appeared alongside abundant cyprideis this situation is similar to that of the southern qaidam basin to the north of kunlun mountains the quaternary assemblages mainly consist of cyprideis torosa candoniella lactea candona neglecta candona arcina cypridopsis vidua limnocythere inopinata cypris subglobosa ilyocypris gibba ilyocypris biplicata eucypris inflata candoniella albicans darwinula sp and stenocypris sp under the extremely arid climate in the tarim basin freshwater originated mainly from snow melt this suggests that the tianshan mountains to the north were uplifted rapidly to above the snow line during the last million years the evolution of the ostracod assemblages indicates that the late himalayan orogeny not only controlled the deposition of biota assemblages but also took an important role in the hydrocarbon accumulation and migration

reworked triterpenoid and steroid hydrocarbons in a recent sediment abstract the distributions of steranes pentacyclic triterpanes and aromatic steroid hydrocarbons in core sections of a recent intertidal sediment bridgwater bay severn estuary u k have been examined by gas chromatography mass spectrometry depending on sample depth the distributions are explicable in terms of 1 i a reworked origin for these compounds from a geological source probably as a result of erosion of nearby organic rich sediments of lower liassic age or 2 ii a dual origin from both i and a more mature source probably an anthropogenic input of petroleum origin these results show that not all of these steroid and triterpenoid hydrocarbons in surface sediments necessarily result from fossil fuel pollution they indicate also that attention should be paid to the possibility of contributions from reworked components when using the distributions of these compounds in geochemical studies of sediments that are low in extractable organic matter

vertical gps ground motion rates in the euro mediterranean region new evidence of velocity gradients at different spatial scales along the nubia eurasia plate boundary we use 2 5 to 14 years long position time series from 800 continuous global positioning system gps stations to study vertical deformation rates in the euro mediterranean region we estimate and remove common mode errors in position time series using a principal component analysis obtaining a significant gain in the signal to noise ratio of the displacements data following the results of a maximum likelihood estimation analysis which gives a mean spectral index 0 7 we adopt a power law white noise stochastic model in estimating the final vertical rates and find 95 of the velocities within 2 mm yr with uncertainties from filtered time series 40 smaller than from the unfiltered ones we highlight the presence of statistically significant velocity gradients where the stations density is higher we find undulations of the vertical velocity field at different spatial scales both in tectonically active regions like eastern alps apennines and eastern mediterranean and in regions characterized by a low or negligible tectonic activity like central iberia and western alps a correlation between smooth vertical velocities and topographic features is apparent in many sectors of the study area glacial isostatic adjustment and weathering processes do not completely explain the measured rates and a combination of active tectonics and deep seated geodynamic processes must be invoked excluding areas where localized processes are likely or where subduction processes may be active mantle dynamics is the most likely process but regional mantle modeling is required for a better understanding

magnetostratigraphy and sedimentologically derived geochronology of the quaternary lacustrine deposits of a 3000 m thick sequence in the central qaidam basin western china the qaidam basin is a large basin in western china where the thickness of quaternary deposits has a range of 2000 3000 m at its subsiding depocentre this study investigated the chronology of the quaternary deposits including palaeomagnetics biostratigraphic correlation rates of sediment accumulation seismic reflection surveys and electrical property correlations the results give a full interpretation of ages for the sequence from bottom to top the oldest sequence age was defined by the first appearance of microlimnocythere sinensis huang and was placed in the gauss epoch estimated at approximately 3 ma by extrapolation of accumulation rates the m g boundary occurs at the base of the third fossil zone of ostracoda the first appearance of qinghaicypris crassa huang or at the marker layer k 10 of the electrical log in the sebei anticline area considered here to be 2 48 ma the olduvai event in the fifth fossil zone spanning electrical layers k 4 and k 3 in the sebei area occurs at reflection layer t 0 1 of seismic stratigraphy which could be stratigraphically correlated in the whole basin the boundary of early middle pleistocene such as the brunhes and matsuyama b m boundary falls within the eighth fossil zone and coincides with electrical marker k 0 1 two boundaries corresponding to middle late pleistocene and pleistocene holocene occur at the bases of the 11th and 12th biozones respectively neither of which can be correlated with seismic stratigraphy and electrical logs in the basin due to the lack of widely distributed lacustrine deposits since the middle pleistocene the ages of the boundaries can be tested by deposition rates of different facies derived from the varves and synchronous deposits as a result geochronological sequences of subsurface stratigraphy could be established within a basin wide area on the synchronology of seismic reflectors and correlations of electrical logs as well as biozones c 1998 elsevier science b v all rights reserved

quaternary exhumation history of the ne tibetan plateau revealed by peculiar distributions of polycyclic aromatic hydrocarbons in core extracts from the sanhu depression eastern qaidam basin

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

high resolution magnetostratigraphy of the neogene huaitoutala section in the eastern qaidam basin on the ne tibetan plateau qinghai province china and its implication on tectonic uplift of the ne tibetan plateau abstract the closed inland qaidam basin in the ne tibetan plateau contains possibly the world s thickest 12 000 m continuous sequence of cenozoic fluviolacustrine sedimentary rocks this sequence contains considerable information on the history of tibetan uplift and associated climatic change however work within qaidam basin has been held back by a paucity of precise time constraints on this sequence here we report on a detailed paleomagnetic study of the well exposed 4570 m huaitoutala section along the keluke anticline in the northeastern qaidam basin where three distinct faunas were recovered and identified from the middle miocene through pliocene constrained by these faunal ages the observed thirty three pairs of normal and reversed polarity zones can be readily correlated with chrons 2n 5br of the gpts this study assigns the age of the section to the interval between ca 15 7 ma to 1 8 ma in addition the widely used stratigraphic units the xia youshashan shang youshashan the shizigou and qigequan formations were formed at 15 3 ma 15 3 8 1 ma 8 1 2 5 ma and

influence of refractory organic matter on source rock hydrocarbon potential a case study from the second white specks and belle fourche formations alberta canada abstract dilution by inert refractory organic carbon can have a significant impact on the hydrocarbon potential of source rocks in this study a correction of total organic carbon based on petrographic observations is proposed to give a better indication of hydrocarbon generation potential this correction shows that although the second white specks formation is an excellent hydrocarbon source rock hydrogen index and total organic carbon are influenced by dilution from refractory organic carbon of various sources the results show that a higher degree of dilution occurs within the belle fourche formation than the second white specks formation this dilution can have a significant impact on the hydrocarbon potential of the rock volumetric calculation of the inert carbon fraction using organic petrographic methods provides a semi quantitative method to correct total organic carbon values for the refractory organic carbon dilution effect incorporation of the dilution corrected organic carbon value in hydrogen index calculations allows a greater understanding of source rock hydrocarbon potential this method provides better differentiation of the small scale variation between micro facies and formation as observed in the second white specks and belle fourche formations than traditional bulk geochemical methodologies and previously proposed correction methodologies degree of dilution either through transport of recycled allochthonous or autochthonous reworking of organic matter in situ is highly variable and represents a significant challenge in the characterization of heterogeneous source rocks this study investigates the organic petrology and geochemistry of a sediment core from the thermally immature area of the upper cretaceous second white specks formation and belle fourche formation reflectance and relative abundance of three maceral groups bituminite alginite and refractory organic carbon macerals showed significant organic matter compositional differences between micro facies in the second white specks formation a change is also observed in organic matter composition from the upper part of the belle fourche formation to the second white specks formation these compositional changes represent shifts in sediment source sea floor oxygen levels and depositional energy levels these changes can be episodic as observed between micro facies or longer time scale trends as observed between the studied formations

geochemistry and origin of the giant quaternary shallow gas accumulations in the eastern qaidam basin nw china abstract this study provided an overview of the geological setting and geochemical characteristics of the pleistocene shallow gas accumulations in the eastern qaidam basin nw china the five largest gas accumulations discovered in this region have a combined enclosure area of about 87 km 2 and 7 9 trillion cubic feet tcf of proven gas reserves the dominance of methane mostly more than 99 9 and the 13 c and d values of methane 68 51 to 65 00 and 227 55 to 221 94 respectively suggest that these gases are biogenic derived from the degradation of sedimentary organic matter by methanogens under relatively low temperatures 15 tds and strong stratification the deposition and extensive lateral occurrence of lacustrine shoreline sands silts in beach sand sheets and sand bars provided excellent reservoirs for the biogenic gas generated from adjacent rocks effective but dynamic gas seals are provided by a combination of factors such as the intermittent vertical variation in the sediment lithologies hydraulic trapping due to the mudstone water saturation the hydrocarbon gradient created as the result of gas generation from potential caprocks and the presence of a regional caprock consisting of 400 800 m of muds and evaporites it appears that the most favorable traps for large gas accumulations occur on structural slopes near the major gas kitchen and the prolific gas pools are often those large gentle anticlines with little faulting complication

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

geochemical study on a well in the western canada basin relation of the aromatic distribution pattern to maturity of organic matter abstract thirty one rock samples from a western canada basin well have been analysed for aromatics using glass capillary gas chromatography with simultaneous flame ionization and sulfur selective flame photometric detection a uniform aromatic distribution pattern with a marked predominance of di and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising cretaceous and jurassic sediments the very high relative abundance of sulfur aromatics at two narrow intervals in the triassic and mississippian is attributed to a major change in facies gradual changes with increasing depth have been observed for a series of compound ratios which had been calculated from the isomers of methyl and dimethylphenanthrene and their parent compounds these changes reflect the increasing thermal maturation of the sedimentary organic matter a methylphenanthrene index mpi has been introduced which exhibited a very good correlation with vitrinite reflectance data the mpi is the first maturity parameter which is based on a series of aromatic hydrocarbons this hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity e g vitrinite reflectance of source rocks

release of aliphatic aromatic and sulphur compounds from kimmeridge kerogen by hydrous pyrolysis a quantitative study abstract the results discussed in this paper form part of a larger study aimed at obtaining qualitative and quantitative data on the types and amounts of aliphatic and aromatic hydrocarbons including biological markers and sulphur containing heterocyclic compounds released when kerogens asphaltenes and the polar fractions of extracted bitumens and crude oils are heated in the presence of excess water some of the results from the experiments in which kimmeridge kerogen was heated in the presence of excess water at times ranging from 7 h to 3 months and at temperatures ranging from 200 to 340 c are reported here the maximum yield of pyrolysate was obtained in experiments conducted at 330 c for 72 h and became increasingly aromatic as pyrolysis temperatures increased aliphatic hydrocarbon distributions became increasingly oil like interestingly unsaturated isoprenoid hydrocarbons were present but only in the low temperature reaction mixtures quantitative estimates of individual hydrocarbon types showed that with increasing temperatures the n alkanes were approximately five to tenfold more abundant than the isoprenoid hydrocarbons by that the rate of release of the latter in the lower temperature work was greater than for the n alkanes the very small amoounts of c21 c22 steranes released increased for all reaction temperatures and with increased heating times unlike the c27 c29 steranes and hopanes they did not pass through a maximum yield at lower pyrolysis temperatures approximately five times more alkylnaphthalenes than phenanthrenes plus anthracenes were released the most abundant sulphur containing compounds in the pyrolysates were alkylbenzothiophnes and dibenzothiophenes the former being tenfold more abundant than the latter and almost double the total amount of alkylnaphthalenes produced at high pyrolysis temperatures microscopy of all of the kerogen residues indicated that vitrinite like material had been generated in the heated kerogens and this increased in rank with increased temperatures and times of heating

the transfer of organic signatures from bedrock to sediment abstract a case study in the canadian arctic demonstrates how an organic geochemical signature in the regional bedrock can be transferred by erosion and redeposition to younger geological formations and surface sediments the hydrocarbon composition recorded in laurentian lower palaeozoic carbonate bedrock was incorporated into overlying miocene and quaternary formations and modern mass waste alluvium snow ice and proglacial deposits and further distant in ice rafted detritus the retention of the original geological organic signature is reflected in consistent thermal maturities hopane ratios and environmental indicators sterane distributions in the modern sediments the geological signature is variably mixed with a modern microbial organic signature reflected in high values of carbon preference index and diploptene these data show that hydrocarbon occurrences in bedrock may be detected by the analysis of surface detritus especially in carbonate terrains however they also indicate that environmental signatures may be misleading if they are inherited from older geological units

alkylated phenanthrene distribution in artificially matured kerogens from kimmeridge clay and the brent formation north sea abstract kerogen and extractible organic matter from immature kimmeridge clay and brent coal were heated at different temperatures 270 500 c under conditions to mimic natural maturation aromatic fractions have been examined for their phenanthrene compound distribution phenanthrene indices based on methylphenanthrenes mp and dimethylphenanthrenes dmp exhibit very sensible changes in the applied temperature range however at high temperatures about 450 c and more possible thermal degradation of phenanthrene compounds produces a decrease in the values of the indices experimental data obtained in this study are compared and discussed with data obtained on thermal evolution performed on total rocks vitrinite reflectance values measured on artificially matured coals are also tentatively correlated with phenanthrene ratios theoretical thermodynamic calculations on mp compounds confirm also the relative thermal stability of the individual isomers

calibration of the mudrock compaction curve by eliminating the effect of organic matter in organic rich shales application to the southern ordos basin china abstract the mudrock log derived compaction curve is a significant tool for investigating the primary migration of hydrocarbon predicting fluid overpressure estimating formation erosion thicknesses and restoring the buried history and paleo structure of a basin however the presence of kerogen in organic rich shales can create typically high logging values of the acoustic transit time thus the abnormally high values of the acoustic transit time for organic rich rocks may not truly reflect the porosity variations of subsurface rocks leading to great uncertainties in the understanding of the mudstone compaction and a certain amount of error in the abnormal fluid pressure estimation when using the mudrock log derived compaction curve therefore it is necessary to recalibrate the mudstone compaction curve by eliminating the increment of the acoustic transit time caused by the kerogen content of organic rich mudstones taking the southwest ordos basin as an example this paper presents a new equivalent volume model based on the composition of organic rich shale in which the kerogen content is also considered based on the quantitative relationship between the rock composition and the acoustic transit time a quantitative formula for calculating the acoustic transit time increment caused by the kerogen is derived this formula shows that the increment depends not only on the organic content but also on the occurrence state pore size pore fluid composition and other factors x ray diffraction xrd data were used to determine the main mineral composition of the mudstone and to calculate the acoustic transit time of the rock skeleton then the mudstone compaction curve in the zhenjing area was calibrated by combining the measured porosity and total organic carbon toc of the mudstone based on the correction formula the compaction characteristics varied significantly between before and after the calibration the slope of the normal compaction trend nct line decreased by 30 55 and the acoustic transit time deviation from the nct in the undercompaction interval decreased significantly the overpressure at the maximum burial depth estimated by the equivalent depth method is in better agreement with the results obtained by numerical simulation after the calibration and the porosity determined from the well log after the calibration is also closer to the true measured value the method proposed in this paper is of great significance for improving the reliability and accuracy of compaction research on organic rich mudstones especially for the accurate estimation of abnormal pressure in the source rock layer additionally it can be used as an effective reference for mudstone compaction studies in similar geological settings areas or basins

scaling of intraplate earthquake recurrence interval with fault length and implications for seismic hazard assessment consensus indicates that faults follow power law scaling although significant uncertainty remains about the values of important parameters combining these scaling relationships with power law scaling relationships for earthquakes suggests that intraplate earthquake recurrence interval scales with fault length regional scaling data may be locally calibrated to yield a site specific seismic hazard assessment tool scaling data from small faults those that do not span the seismogenic layer suggest that recurrence interval varies as a negative power of fault length due to uncertainties regarding the recently recognized changes in scaling for large earthquakes it is unclear whether recurrence interval varies as a negative or positive power of fault length for large faults those that span the seismogenic layer this question is of critical importance for seismic hazard assessment

the adriatic region an independent microplate within the africa eurasia collision zone 1 we use gps measurements and block modeling to investigate the present day deformation of the adriatic region whose kinematics within the nubia eurasia plate boundary zone is not well constrained and remains controversial block modeling allows us to compute rigid plate angular velocities while accounting for elastic strain accumulation along block bounding faults results suggest that the adriatic is a microplate adria and that the southern boundary with the nubia plate and the aegean domain may be located along the apulia escarpment and the kefallinia fault geodetic data alone cannot discriminate between a single block ap or a two blocks gdap description of adria but the gdap model predicts boundary slip rates that are in better agreement with observations from previous studies

characterization of sedimentary organic matter in recent marine sediments from hudson bay canada by rock eval pyrolysis abstract a combination of rock eval pyrolysis and isotopic analyses is used to characterize the sources and distribution of organic matter in modern marine sediments from the subarctic hudson bay including hudson strait and foxe basin canada this approach reveals organic matter contributions from both marine and terrigenous sources with spatial patterns and varying degrees of degradation that are consistent with inferences from traditional geochemical tracers for modern organic matter rock eval parameters characterize hudson bay organic matter with low hydrogen index high oxygen index and a high degree of residual carbon that suggests heavily reworked materials locations of higher primary productivity in hudson strait foxe basin the northeast and far west of hudson bay and the concentration of watershed runoff in the southern part of hudson bay can be delineated using the ratios between hydrogen and oxygen indices and from the distribution of labile organic carbon relatively high temperatures of peak hydrocarbon yield identify an advanced state of om degradation or humic substances as important classes of organic carbon compounds in the majority of the sediment such highly degraded and oxygenated organic matter is unusual compared to that typically observed in other arctic shelf seas and is consistent with a strong role for sediment and organic matter recycling in hudson bay in the offshore region the source of highly oxidized and labile organic matter identified by rock eval parameters is resolved with 13 c and biomarker information that also permit examination of the sediment biogeochemical regime this approach suggests that a distinct association with mn enriched sediment contributes to the oxidization signal by abiotic or biological mn related processes these interpretations extend the limited information available on using rock eval analyses to characterize organic matter in recently deposited marine sediments and describe an important consideration to using this method in mn enriched environments

tectonic geomorphology of the qilian shan in the northeastern tibetan plateau insights into the plateau formation processes abstract we examined the regional scale topography of the qilian shan on the northeastern margin of the tibetan plateau longitudinal profiles and geomorphometric indices such as slope local relief and channel steepness reveal that the qilian shan was developed as a local plateau with high relief steep marginal ranges and interior low relief topography landscape mapping across this local plateau revealed spatially varied origins of the low relief landscape in the qilian shan north of the haiyuan fault universal massive intermontane aggradation was identified however the low relief plateau to the south of the haiyuan fault was dominated by relict erosional surfaces even though accompany basin filling still contributes the geomorphologic contrasts led us to integrate both the basin filling processes and antecedent low relief erosional surfaces into a new insight into the development of the qilian shan plateau in the northeastern tibet our present study highlights that explanation for the low relief plateau formation needs to consider the complex geological evolution of the qilian shan and the tibetan plateau itself

aromatic biomarkers as indicators of source depositional environment maturity and secondary migration in the oils of cambay basin india abstract aromatic biomarkers have been analysed for source depositional environment maturity and secondary migration in crude oils from different formations of paleocene to eocene age in the ahmedabad mehsana block of north cambay basin and the broach block of south cambay basin north cambay basin oils are characterized by a high abundance of 1 2 5 and 1 2 7 trimethylnaphthalenes tmn and low to medium ratio of dibenzothiophene phenanthrene and low ratio of pristane phytane indicates that these oils have been derived from a source containing predominantly higher plants and that the organic matter was deposited in restricted marine or lacustrine environments in anoxic to suboxic conditions the relative abundance of 1 2 7 tmn suggests that it was derived from the structural degradation of oleanane type triterpenoids present in angiosperms south cambay basin oils are less abundant in 1 2 5 and 1 2 7 tmns and low ratio of dibenzothiophene phenanthrene and high ratio of pristane phytane indicating that the oils were derived from higher plant source organic matter deposited under marine or fluvial deltaic environment in oxic conditions maturity sensitive ratios based on phenanthrene naphthalene dibenzothiophene and their alkyl substituted isomers have been used to calculate the equivalent vitrinite reflectance these parameters indicate a wide range of thermal maturity of the oils ranging from 0 60 to 0 93 vrc methylphenanthrene index and methyldibenzothiophene ratios indicate that the maturity of north and south cambay basin oils are different the north cambay basin oils are less mature than south cambay basin oils pyrrolic nitrogen distribution indicates that the alkylated carbazoles and benzocarbazoles are more abundant in south cambay basin oils as compared to north cambay basin oils these data indicate that north cambay basin oils are less migrated compared to south cambay basin oils this systematic investigation of the aromatic biomarkers in oils of cambay basin has resulted in a new generation migration and entrapment model that has led to the development of new exploration leads

cenozoic tectonic evolution of qaidam basin and its surrounding regions part 1 the southern qilian shan nan shan thrust belt and northern qaidam basin cenozoic qaidam basin the largest active intermountain basin inside tibet figures importantly in the debates on the history and mechanism of tibetan plateau formation during the cenozoic indo asian collision to determine when and how the basin was developed we conducted detailed geologic mapping and analyses of a dense network of seismic reflection profiles from the southern qilian shan nan shan thrust belt and northern qaidam basin our geologic observations provide new constraints on the timing and magnitude of cenozoic crustal thickening in northern tibet specifically our work shows that the southernmost part of the qilian shan nan shan thrust belt and contractional structures along the northern margin of qaidam basin were initiated in the paleocene early eocene 65 50 ma during or immediately after the onset of the indo asian collision this finding implies that stress was transferred rapidly through tibetan lithosphere to northern tibet from the indo asian convergent front located 1000 km to the south the development of the thrust system in northern qaidam basin was driven by motion on the altyn tagh fault as indicated by its eastward propagation away from the altyn tagh fault the eastward lengthening of the thrust system was spatially and temporally associated with eastward expansion of qaidam basin suggesting thrust loading was the main control on the basin formation and evolution the dominant structure in northern qaidam basin is a southwest tapering triangle zone which started to develop since the paleocene and early eocene 65 50 ma and was associated with deposition of an overlying southwest thickening growth strata sequence recognition of the triangle zone and its longevity in northern qaidam basin explains a long puzzling observation that cenozoic depocenters have been located consistently along the central axis of the basin this basin configuration is opposite to the prediction of classic foreland basin models that require the thickest part of foreland sediments deposited along basin edges against basin bounding thrusts restoration of balanced cross sections across the southern qilian shan nan shan thrust belt and northern qaidam basin suggests that cenozoic shortening strain is highly inhomogeneous varying from 20 to 60 both vertically in a single section and from section to section across the thrust belt the spatially variable strain helps explain the conflicting paleomagnetic results indicating different amounts of cenozoic rotations in different parts of qaidam basin the observed crustal shortening strain also implies that no lower crustal injection or thermal events in the mantle are needed to explain the current elevation 3000 3500 m and crustal thickness 45 50 km of northern qaidam basin and the southern qilian shan nan shan thrust belt instead thrusting involving continental crystalline basement has been the main mechanism of plateau construction across northern qaidam basin and the southern qilian shan nan shan region