environmental change during the early cretaceous in the purbeck type durlston bay section dorset southern england a biomarker approach abstract the purbeck type section durlston bay dorset uk exhibits littoral lagoonal to lacustrine facies it shows a gradual climatic environmental change from semi arid conditions associated with evaporites at the jurassic cretaceous transition to a more humid climate at the end of the berriasian though generally organic poor total organic carbon toc the distribution of alkanes hopanes and steranes indicates that the origin of the om is mainly algal bacterial and only changed moderately with the climatic evolution the saline and anoxic bottom water conditions indicated for most of the samples point to the recurrence of salinity stratification within the basin a high contribution of odd numbered c 23 c 31 n alkanes from algaenan containing freshwater algae in particular botryococcus is noted for all the samples despite the low abundance of these organisms in the corresponding palynofacies this prominence probably results from the high resistance to degradation and the selective preservation of botryococcus related lipids the subtle balance of aridity and freshwater inputs favoured both an abundance of botryococcus and the development of anoxia leading to the enhanced preservation of om during the intermediate climatic episode while the conditions were less favourable during the semi arid and more humid episodes

growth and deformation of the ladakh batholith northwest himalayas implications for timing of continental collision and origin of calc alkaline batholiths abstract the calc alkaline ladakh batholith nw himalayas was dated to constrain the timing of continental collision and subsequent deformation batholith growth ended when collision disrupted subduction of the tethyan oceanic lithosphere and thus the youngest magmatic pulse indirectly dates the collision both u pb ages on zircons from three samples of the ladakh batholith and k ar from one subvolcanic dike sample were determined magmatic activity near leh the capital of ladakh occurred between 70 and 50 ma with the last major magmatic pulse crystallizing at ca documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand tex

building the biomarker tree of life it is the great challenge of geomicrobiology to study microorganisms in the context of their environments both in earth s distant past and in the present planet earth and its biosphere have evolved together and a chronicle of earth s ecosystems and their geochemical cycles is recorded in sedimentary rocks spanning billions of years a relatively new and very powerful approach to read these subtle microbial and environmental signatures in ancient rocks is the study of molecular fossils or biomarkers within the context of the biochemistry and phylogeny of their origins biomarkers are organic compounds primarily lipids that have particular biosynthetic origins and can be preserved in sediments and sedimentary rocks the most valuable biomarkers are taxonomically specific i e they can be assigned to a defined group of organisms and are resistant to degradation reading the biomarker signatures in rocks can give information about the ancient record of anoxic conditions in the water column e g summons and powell 1986 the intensity of uv radiation penetrating lakes leavitt et al 1997 hypersalinity in evaporitic environments grice et al 1998 and the function of microbial communities at methane seeps hinrichs et al 1999 biomarkers have helped to reconstruct the first appearance of major groups of organisms e g mccaffrey et al 1994 moldowan et al 1994 moldowan and talyzina 1998 brocks et al 2005 elucidate events of global climate change e g brassell et al 1986 record major perturbations and reorganization of geochemical cycles e g logan et al 1995 kuypers et al 1999 and document catastrophic losses in biodiversity e g grice et al 2005 they are even used as tools to help in the discovery of major new petroleum reservoirs for a review see peters et al 2004 the field of biomarker research is young and many new applications wait to be

reply to comment on interplay of deformation and magmatism in the pangong transpressional zone eastern ladakh india implications for remobilization of the trans himalayan magmatic arc and initiation of the karakoram fault abstract in the eastern part of ladakh the right lateral karakoram fault zone kfz bifurcates into two strands called the pangong strand and the tangtse strand these two strands bound a region called the pangong transpression zone ptz which consists of migmatitic dioritic gneiss calc silicates and the durbuk pluton a pluton of two mica leucogranite outcrop scale observations suggest pervasive migration of leucogranitic melt through the existing tectonic structures of the gneiss magnetic fabric from both the tectonized and undeformed parts of the durbuk pluton show parallelism with the tectonic fabric of the host gneiss which along with pervasive melt migration indicates syn kinematic relationship between deformation along the kfz leucogranite magmatism and emplacement of the durbuk pluton u pb geochronology of zircons from the dioritic gneiss yields a crystallization age of 63 6 1 5 ma and also shows younger zircon growth down to 13 ma which suggest arc magmatism at 65 ma followed by partial melting and leucogranite magmatism in the kfz till 13 ma one two mica leucogranite sample from the durbuk pluton gives a crystallization age of 22 7 0 5 ma as the durbuk pluton is syn tectonic with deformation along kfz it is inferred that the kfz initiated at least 23 ma ago

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

highly isotopically depleted isoprenoids molecular markers for ancient methane venting abstract we propose that organic compounds found in a miocene limestone from marmorito northern italy are source markers for organic matter present in ancient methane vent systems cold seeps the limestone contains high concentrations of the tail to tail linked acyclic c20 isoprenoid 2 6 11 15 tetramethylhexadecane crocetane a c25 homolog 2 6 10 15 19 pentamethylicosane pme and a distinctive glycerol ether lipid containing 3 7 11 15 tetramethylhexadecyl phytanyl moieties the chemical structures of these biomarkers indicate a common origin from archaea their extremely 13c depleted isotope compositions 13c 108 to 115 6 pdb suggest that the respective archaea have directly or indirectly introduced isotopically depleted methane derived carbon into their biomass we postulate that a second major cluster of biomarkers showing heavier isotope values 13c 88 is derived from sulfate reducing bacteria srb the observed biomarkers sustain the idea that methanogenic bacteria in a syntrophic community with srb are responsible for the anaerobic oxidation of methane in marine sediments marmorito may thus represent a conceivable ancient scenario for methane consumption performed by a defined two membered bacterial consortium 1 archaea that perform reversed methanogenesis by oxidizing methane and producing co2 and h2 and 2 srb that consume the resulting h2 furthermore the respective organic molecules are unlike other compounds tightly bound to the crystalline carbonate phase the marmorito carbonates can thus be regarded as cold seep microbialites rather than mere authigenic carbonates

new u th pb constraints on timing of shearing and long term slip rate on the karakorum fault 1 zircons and monazites from 6 samples of the north ayilari dextral shear zone nasz part of the karakorum fault zone kfz have been dated with the u th pb method using both id tims and sims techniques the ages reveal 1 inheritance from several events spanning a long period between the late archean and the jurassic 2 an eocene oligocene magmatic event similar to 35 32 ma 3 an oligo miocene magmatic event similar to 25 22 ma at least partly synkinematic to the right lateral deformation and 4 a period of metamorphism metasomatism similar to 22 14 ma interpreted as thermal and fluid advection in the shear zone the labhar kangri granite located similar to 375 km farther southeast along the kfz is dated at 21 1 0 3 ma such occurrence of several oligo miocene granites along the kfz some of which show evidence for synkinematic emplacement suggests that the fault zone played an important role in the genesis and or collection of crustal melts we discuss several scenarios for the onset and propagation of the kfz and offset estimates based on the main sutures zones our preferred scenario is an oligo miocene initiation of the fault close to the na range and propagation along most of its length prior to similar to 19 ma in its southern half the averaged long term fault rate of the kfz is greater than 8 to 10 mm a in good agreement with some shorter term estimates based on the indus river course or quaternary moraines and geodesy our results show the kfz cannot be considered as a small transient fault but played a major role in the collision history

branched aliphatic alkanes with quaternary substituted carbon atoms in modern and ancient geologic samples a pseudohomologous series of branched aliphatic alkanes with a quaternary substituted carbon atom baqcs specifically 2 2 dimethylalkanes and 3 3 and 5 5 diethylalkanes were identified in warm 65 c deep sea hydrothermal waters and late cretaceous black shales 5 5 diethylalkanes were also observed in modern and holocene marine shelf sediments and in shales spanning the last 800 million years of the geological record the carbon number distribution of baqcs indicates a biological origin these compounds were observed but not identified in previous studies of 2 0 billion to 2 2 billion year old metasediments and were commonly misidentified in other sediment samples indicating that baqcs are widespread in the geological record the source organisms of baqcs are unknown but their paleobiogeographic distribution suggests that they have an affinity for sulfides and might be nonphotosynthetic sulfide oxidizers

water column euxinia and wildfire evidence during deposition of the upper famennian hangenberg event horizon from the holy cross mountains central poland a palynological study of the uppermost famennian section from kowala quarry holy cross mountains central poland allowed recognition of two miospore zones lv retispora lepidophyta apiculiretusispora verrucosa and ln retispora lepidophyta verrucosisporites nitidus based on palynology and sedimentology the black shale within the upper part of the section is identified as equivalent to the hangenberg black shale which is known globally this black shale contains compounds characteristic of photic zone euxinia including isorenieratane and its derivatives such compounds are absent in the organic poor marls and shales occurring below the ln zone and are present only as traces in the layers just above the black shale indicating fluctuations in the oxygen minimum zone during uppermost famennian sedimentation palynofacies show high amounts of amorphous organic matter and prasinophyte concentrations in the black shale and a subsequent significant decrease of amorphous organic matter concomitant with a rapid increase of terrestrial input mainly miospores with common tetrads in the layers above the black shale this supports the relatively rapid change in the taxonomic composition of phytoplankton caused by fluctuations of the chemocline the whole succession corresponds to one sea level rise and fall the presence of high concentrations of peri condensed polycyclic aromatic hydrocarbons and large amounts of small charcoal particles at the hangenberg event horizon indicate the occurrence of wildfires such observations suggest that atmospheric o2 levels had exceeded the critical threshold of 13 above which wildfires may occur by latest famennian time

seismotectonic model of the kangra chamba sector of northwest himalaya constraints from joint hypocenter determination and focal mechanism the existing seismological network in the kangra chamba sector has been upgraded with 12 three component digital seismometers to obtain new insight on the nature and sources of continued clustered seismicity in this part of northwest himalaya a combination of travel time distance plots and travel time inversion of p and s phases have been used to derive a 1d velocity model for the region the mini mum 1d velocity model divides the average 44 km thick crust into four layers the top 10 km thick layer represents the metamorphosed sediments of the chamba nappe that dominates the surface geology of the study area suggestion of a thin low velocity layer at 15 km depth possibly marks the detachment zone separating the downgoing indian plate from the overriding wedge the improved locations of epicenters show close clustering of seismic events immediately northeast of the epicenter of the 1905 kangra earthquake while away from this zone the seismicity in the chamba sector has more even distribution in the later sector space depth distribution of hypocenters suggests that strain resulting from the ongoing collision of the indian plate with asia is being consumed by reverse fault movement on the chamba thrust the clustered seismicity in the kangra sector has three distinct source regions and mechanisms 1 southward displacement of the thick chamba nappe sheet over the panjal imbricate zone along the panjal thrust accounts for the seismicity at shallow depths of less than 7 km 2 the nucleation of strains where the northeast dipping main boundary thrust mbt merges with the detachment plane produces focused seismicity near this junc tion and 3 the seismicity in a small pocket below the plane of detachment appears to be a consequence of stresses generated at the base of the northeast dipping detachment plane by the transverse structure

magma ponding in the karakoram shear zone ladakh nw india granitic melt migration and pluton emplacement are commonly closely associated with transcurrent shear zones the processes that link granites to shear zones are not yet fully understood the dextraltranspressive karakoram shear zone in ladakh nw india exposes anatectic rocks where synkinematic melt migration and ponding at kilometer scale were controlled by competency contrasts metasedimentary rocks and a dominantly granodioritic calcalkaline intrusion underwent fl uid present partial melting at upper amphibolite facies to produce leucogranite sheets and irregular intrusive masses dated at 21 14 ma leucogranitic magmas ponded in the lowpressure strain shadow of the competent grano dioritic calc alkaline pluton giving rise to a migmatitic rocks that are pervaded by irregular leucogranite intrusions at a scale of meters or tens of meters and b the growth of the tangtse pluton a kilometer scale sheeted complex thus magmas accumulated during shearing and anatexis in a low pressure strain shadow within the karakoram shear zone this magma provided a readily available magma source that could have been tapped to feed larger plutons at shallower levels by modifi cations in the pressure distribution accompanying changes in shear zone geometry and kinematics we conclude that shear zones tapping anatectic regions act as magma pumps creating and destroying magma traps at depth as they evolve and leading to incremental magma addition to upper crustal plutons

composition and origin of hydrothermal petroleum and associated lipids in the sulfide deposits of the rainbow field mid atlantic ridge at 36 n the lipid components in hydrothermal sulfide deposits from the rainbow vent field mid atlantic ridge at 36 n were studied by gas chromatography mass spectrometry the rainbow vent field is one of two known active hydrothermal systems related to abyssal circulation where high temperature fluids are formed during serpentinization of ultrabasic crustal rocks the major amount of the extractable organic matter from the sulfides consists of normal and branched alkanes ucm pahs terpenoids and fatty acids the branched alkanes are comprised of unique gem diethylalkane series possibly from sulfide oxidizing bacteria and biphytanes from archaea the characteristic lipid and biomarker compounds found in the hydrothermal samples support a predominantly biological origin of the bitumens from the thermal transformation of the biomass of microorganisms bacteria and archea and minor macrofauna of this vent field a search for molecular evidence for abiogenic thermocatalytic synthesis of organic compounds was negative however methane in the hydrothermal fluids and possibly a minor amount of the alkanes in the sulfides may be of an abiogenic origin in the rainbow vent field

large scale geometry offset and kinematic evolution of the karakorum fault tibet the total offset lifespan and slip rate of the karakorum fault zone kfz western tibet are debated along the southern fault half ongoing oblique slip has exhumed dextrally sheared gneisses intruded by synkinematic leucogranites whose age v23 ma u pb on zircon indicates that right lateral motion was already in progress in the late oligocene ar ar k feldspar thermochronology confirms that rapid cooling started around 12 ma likely at the onset of the present dextral normal slip regime correlation of suture zones across the fault requires a total offset greater than 250 km along the active northern fault branch an average long term slip rate of 1 0 3 cm yr is inferred assuming that this offset accrued in a time span of 23 34 ma southwest of the ladakh karakorum range the large scale boudinage of ophiolitic units suggests that an offset of several hundreds of kilometers exists along another southern branch of the kfz towards the southeast in the mount kailas region the fault zone does not end at gurla mandatha but continues eastwards as a transpressive flower structure along the indus tsangpo suture our new data thus suggest that the kfz contributed to absorb hundreds of kilometers of india asia convergence

iterative deconvolution of regional waveforms and a double event interpretation of the 2003 lefkada earthquake greece the moment tensor inversion for multiple point sources based on kikuchi and kanamori 1991 was extended to full waveform data at regional or local distances the new code proved to be efficient for retrieving major source contributions of the 2003 lefkada greece earthquake the source model was derived from five three component regional stations epicentral distances 140 km at periods 10 20 s two main events dominated the rupture process one at the lefkada island comprising three subevents of total moment 0 9 1018 n m and the other at the cephalonia island comprising one subevent of 0 5 1018 n m their spatial and temporal separation is 40 km and 14 s respectively they can be understood as two earthquakes the uncertainty estimate based on reduced data sets repeatedly excluding a station shows that the cephalonia subevent and the major lefkada subevent are very well resolved regarding their position time and focal mechanism the source model explains well the aftershock distribution characterized by two clusters at the lefkada and cephalonia islands respectively the focal mechanisms of the two main subevents are predominantly right lateral strike slip of south southwest north northeast orientation the cephalonia subevent occurred on a less steeply dipping fault with a small thrust component large deviations from pure double couple were found but interpreted as artifacts the new software developed in this article fortran code and matlab graphic user interface is freely available online material color graphics and 3d visualization of the 2003 lefkada earthquake sequence

formation and evolution of strike slip faults rifts and basins during the india asia collision an experimental approach the processes which have governed the formation and evolution of large tertiary strike slip faults during the penetration of india into eastern asia are investigated by means of plane strain indentation experiments on layered plasticine models the steady state deformation of plasticine obeys a power creep flow law e c t n the stress exponent n is between 6 and 9 at 25 c uniaxial plane strain tests on cubic specimens show that the growth of faults in layered plasticine results from strain softening a process observed for strain rates ranging from 3 5 10 5 to 3 6 10 3 s 1 fault or shear zones form after only 7 10 bulk strain subsequent deformation is controlled by the geometry of the fault pattern rather than the physical properties of the plasticine a series of nine plane strain indentation experiments shows the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence the ubiquity of strain softening in experimental deformation of a variety of rocks as well as the widespread occurrence of shear zones in nature suggest that long term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain the deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision induced strikeslip faulting in asia particularly to total offsets and rates of movements on the faults the experiments simulate the evolution of the western ends of the strike slip faults which have probably been analogous to trench fault fault triple junctions the experiments also illustrate mechanisms for the formation of extensional basins such as the south china sea north china basin and andaman sea near active continental margins the basins which appear to absorb terminal offsets along major strike slip faults near such margins may result from mismatch between the sharply angular shape of the deformed continental edge and the more regularly curved trench along which the smoothly flexed oceanic lithosphere subducts the existence of distinct phases of strike slip extrusion corroborates the idea that the discontinuities in time which typify intracontinental tectonics and orogenic cycles may often result from strain localization and the ensuing discontinuous non steady state deformation of the continental lithosphere

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

tectonics of the southern asian plate margin along the karakoram shear zone constraints from field observations and u pb shrimp ages abstract new geological observations recent published data and u pb shrimp zircon dating from the karakoram mountains along the nubra and shyok rivers reveal that the initial subduction of the tethyan oceanic lithosphere took place 110 ma beneath the paleozoic mesozoic platform of the southern edge of the asian plate this has produced the i type plutons within the karakoram batholith complex well before the juxtaposition of the asian plate along the karakoram shear zone within this shear zone u pb zircon crystallisation ages of 75 ma from mylonitised granitoids and 68 ma from undeformed tirit granodiorite constrain the timing of suturing of the karakoram terrain with the trans himalaya between 75 and 68 ma post shearing leucogranite was episodically generated within frontal migmatised karakoram metamorphic belt and emplaced between 20 and 13 ma within the shear zone presence of a low resistivity zone as a possible indication of mid crustal partial molten crust underneath the higher himalaya ladakh karakoram terrains manifests the impingement of the indian plate along the main himalayan thrust at depth physical continuity of the baltoro granite belt into the karakoram batholith is established as well as the continuity of the shyok suture as the shiquanhe suture zone in western tibet through the chushul dungti sector the karakoram shear zone therefore displays a complex geological history of movements since 75 ma and plays a very significant role in the overall india asia convergence rather than merely being a strike slip fault for eastward extrusion of a segment of asia in tibet

isotopic biogeochemistry of the oxford clay formation jurassic uk a total of 165 samples was obtained from the oxford clay formation at seven different sites nearly all were from the peterborough member lower oxford clay but seven were from the stewartby and weymouth members middle and upper oxford clay respectively five samples from the underlying kellaways formation were also examined stratigraphic relationships were estimated on the basis of ammonite subzones and results from all locations can be placed along a single stratigraphic scale the following were determined for all samples abundance and isotopic composition of organic carbon abundances of carbonate carbon and total sulphur and the rock eval pyrolysis parameters hydrogen index oxygen index and t max for a subset of eight samples selected to be representative of geochemical and apparent palaeoenvironmental variations soluble organic compounds were extracted and the isotopic composition of pristane phytane and long chain n alkanes determined by isotope ratio monitoring gas chromatograph mass spectrometry concentrations of organic carbon in samples from the peterborough member ranged from 0 5 to 16 6 and values of total organic carbon toc ranged from 27 7 to 23 1 v pdb shales dominated by epifaunal bivalve assemblages have high concentrations of toc and values of h index approaching 800 indicating preservation of hydrogen rich organic material conversely shell beds and calcareous and silty clay beds have lower abundances of toc and values of h index dropping below 100 indicating extensive oxidation of the organic matter isotopic composition of pristane and phytane in the peterborough and stewartby members average 31 7 those in the weymouth member average 29 8 values of for long chain n alkanes average 28 together these results indicate values for primary inputs as follows terrestrial vascular plants 23 5 peterborough member algae 28 2 stewartby member algae 29 1 weymouth member algae 26 6 comparison of primary values to those of toc indicates that in some cases secondary processes enriched toc relative to primary inputs by as much as 4 palaeontological evidence in these same beds indicates development of extensive food webs and supports attribution of this isotopic enrichment to heterotrophic reworking

configuration of the indian moho beneath the nw himalaya and ladakh 1 teleseismic receiver function analysis of seismograms recorded on a 700 km long profile of 17 broadband seismographs traversing the nw himalaya shows a progressive northward deepening of the indian moho from 40 km beneath delhi south of the himalayan foredeep to 75 km beneath taksha at the karakoram fault similar studies by wittlinger et al 2004 to the north of the karakoram fault show that the moho continues to deepen to 90 km beneath western tibet before shallowing substantially to 50 60 km at the altyn tagh fault the continuity of the indian moho imaged in the receiver functions reported here along with those of wittlinger et al 2004 suggest that in this part of the himalayan orogen the indian plate may penetrate as far as the bangong suture and possibly as far north as the altyn tagh

terminal proterozoic mid shelf benthic microbial mats in the centralian superbasin and their environmental significance abstract a combined sedimentological and biogeochemical study has been conducted on several terminal proterozoic mid shelf microbial mat facies from the centralian super basin isotopic and organic geochemical analysis of the bitumen and kerogen indicated that two sources of organic matter from planktonic and benthic microbial mat populations contributed to the sediment the planktonic source provided a suite of n alkanes with c20 whereas the benthic source contributed an overlay of n alkanes c20 with a strong even preference together with mid chain methyl alkanes kerogen and biomarkers derived from the microbial mat were found to be depleted in 13c relative to planktonic material pyrite in the micorbial mats was also found to be depleted in 34s compared to surrounding facies the combination of these observations suggested that the mats may have been at least partly composed of sulfide oxidising bacteria these organisms have specific environmental tolerances that set limits on palaeo environment their requirement for oxygen indicates that the water column above the mid shelf could not have been anoxic accordingly from the results and age determinations reported here it would appear that mid shelf environments of the centralian superbasin of australia were seeing significant levels of oxygen through the ediacarian

methane related microbial gypsum calcitization in stromatolites of a marine evaporative setting munder formation upper jurassic hils syncline north germany fossil stromatolites may reveal information about their hydrochemical palaeoenvironment provided that assignment to a specific microbial community and a corresponding biogeochemical mechanism of formation can be made tithonian stromatolites of the munder formation at thuste north germany have traditionally been considered as formed by intertidal cyanobacterial communities however thin sections of the stromatolites show elongated angular traces of former gypsum crystals in a dense arrangement but no algal or cyanobacterial filament traces moreover high fe 2 and mn 2 contents oxygen isotope and sulphur isotope ratios of carbonate bound sulphates and sulphurized hydrocarbon biomarkers of the stromatolitic carbonate indicate that caco3 precipitation occurred near the oxic anoxic interface as a result of intensive bacterial sulphur cycling rather than photosynthetic activity furthermore anaerobic oxidation of methane by archaea may have driven caco3 precipitation in deeper parts of the biofilm community as reflected by high concentrations of squalane with a strongly negative d 13 c in conjunction with evaporite pseudomorphs showing extremely low d 13 ccarb ratios consequently the thuste stromatolites are now interpreted as having initially formed by gypsum impregnation of biofilms subsequently early mg calcitic calcitization within the biofilms occurred because of combined bacterial iron manganese and sulphate reduction with an increasing contribution of anaerobic oxidation of methane with depth this model plausibly explains the prominent preservation of signals derived from oxygen independent metabolic pathways whereas virtually no geochemical record exists for an aerobic community that may nevertheless have prevailed at the stromatolite surface photic zone stromatolites with a prominent signal of anaerobic oxidation of methane may be common in and indicative of oxygen depleted sulphate bearing environments with high rates of methane production conditions that possibly were fulfilled at the archaean to proterozoic transition

the boundary between the indian and asian tectonic plates below tibet the fate of the colliding indian and asian tectonic plates below the tibetan high plateau may be visualized by in addition to seismic tomography mapping the deep seismic discontinuities like the crust mantle boundary moho the lithosphere asthenosphere boundary lab or the discontinuities at 410 and 660 km depth we herein present observations of seismic discontinuities with the p and s receiver function techniques beneath central and western tibet along two new profiles and discuss the results in connection with results from earlier profiles which did observe the lab the lab of the indian and asian plates is well imaged by several profiles and suggests a changing mode of india asia collision in the east west direction from eastern himalayan syntaxis to the western edge of the tarim basin the indian lithosphere is underthrusting tibet at an increasingly shallower angle and reaching progressively further to the north a particular lithospheric region was formed in northern and eastern tibet as a crush zone between the two colliding plates the existence of which is marked by high temperature low mantle seismic wavespeed correlating with late arriving signals from the 410 discontinuity poor sn propagation east and southeast oriented global positioning system displacements and strikingly larger seismic sks anisotropy

freshwater and atlantic water inflows to the deep northern barents and kara seas since ca 13 14 c ka foraminifera and stable isotopes foraminiferal stable isotopes and assemblages from franz victoria and st anna troughs provide a valuable record of freshwater and atlantic water flows to the northern barents and kara seas from deglaciation to present the d 18 o and d 13 c of planktonic neogloboquadrina pachyderma s and benthic elphidium excavatum were up to1 4 lower than present at ca 13 11 5 and 10 14 c ka global sea level corrected mostly reflecting substantial freshwater inputs coincident with glacial marine sediment deposition cassidulina teretis exceeded 40 of benthic foraminifera ca 13 and 10 14 c ka indicating subsurface penetrations of atlantic water the transition to postglacial marine conditions is marked by a 1 rise in foraminiferal d 18 o and a sharp fall in c teretis soon after 10 14 c ka these changes imply reduced inputs of freshwater and atlantic water subsequent isotopic and foraminiferal assemblage variations reflect changing atlantic water conditions upstream in the nordic seas and shifts between the warm fram strait and cold barents sea branches of atlantic water we hypothesize that glacial isostatically induced deepening by up to 150 m influenced atlantic water inflows to the northern barents sea during deglaciation and the holocene thus effects of isostatic recovery have to be factored into paleoceanographic reconstructions 2001 elsevier science ltd all rights reserved

crustal rheology of the himalaya and southern tibet inferred from magnetotelluric data the collision between the indian and asian continents which began about 70 million years ago involved a convergence of at least 1 400 km and raised the tibetan plateau since crustal material is too buoyant to be transported downwards into the earth s interior the mechanisms at work in plateau formation are important in understanding the evolution of the continents yet still a matter of debate geophysical observations in the himalaya and tibet using ultra low frequency radio waves now reveal that a partially molten layer is present along the entire length of the himalaya this weak layer implies that widespread crustal flow is occurring and explains many features of plateau evolution the cenozoic collision between the indian and asian continents formed the tibetan plateau beginning about 70 million years ago since this time at least 1 400 km of convergence has been accommodated1 by a combination of underthrusting of indian2 and asian lithosphere crustal shortening3 horizontal extrusion4 and lithospheric delamination5 rocks exposed in the himalaya show evidence of crustal melting1 6 and are thought to have been exhumed by rapid erosion and climatically forced crustal flow7 8 magnetotelluric data can be used to image subsurface electrical resistivity a parameter sensitive to the presence of interconnected fluids in the host rock matrix even at low volume fractions here we present magnetotelluric data from the tibetan himalayan orogen from 77 e to 92 e which show that low resistivity interpreted as a partially molten layer is present along at least 1 000 km of the southern margin of the tibetan plateau the inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in southern tibet

first indications of the formation of kerogen amorphous fractions by selective preservation role of non hydrolysable macromolecular constituents of eubacterial cell walls abstract two marine kerogens supposed to contain an important bacterial component were analysed and their spectroscopic and pyrolytic features compared with those of the amorphous non hydrolysable macromolecular materials bacterans isolated from extent bacteria examination by transmissio electron microscopy revealed that dontrien lower toarcian shales paris basin is essentially composed of amorphous organic matter and osb3 marl slate formation n e england is exclusively amorphous the formation upon kerogen pyrolysis of series of products 3 methylalkanes dimethylalkanes ethylesters and alcohols characteristic of bacteran pyrolysates is consistent with the contribution of bacterans to the formation of these two kerogens the nature and distribution of the acids of the pyrolysates indicate that bacterial biomass was implicated in osb3 and dontrien kerogen formation via two pathways bacteran selective preservation and incorporation of partly degraded lipids comparison between dontrien and osb3 indicates a weaker contribution of the selective preservation pathway to osb3 kerogen whereas bacteria lipid incorporation may have been more significant in osb3 kerogen the selective preservation pathway was so far considered as restricted to the formation of kerogens having retained some of the morphological features of the source organisms an important point derived from this study is therefore the ability of this pathway to also contribute to the formation of amorphous kerogens

tibetan plate overriding the asian plate in central and northern tibet at the southern boundary between india and tibet the indian tectonic plate subducts northwards beneath the tibetan plateau seismic imaging shows that at the northern boundary of tibet the asian plate is also subducting southwards beneath the plateau and the tibetan lithosphere is separate

mantle fluids in the karakoram fault helium isotope evidence abstract the karakoram fault kkf is the 1000 km long strike slip fault separating the western himalaya from the tibetan plateau from geologic and geodetic data the kkf is argued either to be a lithospheric scale fault with hundreds of km of offset at several cm a or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper crustal localization of distributed deformation at depth here we show 3he 4he ratios in geothermal springs along a 500 km segment of the kkf are 3 100 times the normal ratio in continental crust providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle mantle enrichment is absent along the indus yarlung suture zone isz just 35 km southwest of the kkf suggesting that the mantle fluids flow only within the kkf within the last few ma the kkf must have accessed tectonically active tibetan mantle northeast of the mantle suture which we therefore locate vertically beneath the kkf very close to the surface trace of the isz hence in southwestern tibet indian crust may not now be underthrusting substantially north of the isz even though miocene underthrusting may have placed indian crust north of the isz in the lower half of the tibetan plateau crust this is in significant contrast to central and eastern tibet where underthrust indian material not only forms the lower half of the tibetan crust but is also currently underthrusting for 200 km north of the isz our new constraint on kkf penetration to the mantle allows an improved description of the continuously evolving karakoram fault as a tectonically significant yet perhaps geologically ephemeral lithospheric structure

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

occurrence and origin of mono di and trimethylalkanes in modern and holocene cyanobacterial mats from abu dhabi united arab emirates n alkanes highly branched isoprenoids monomethylalkanes mmas dimethylalkanes dmas and trimethylalkanes tmas are the most abundant components in the hydrocarbon fractions of extracts of four modern and two holocene cyanobacterial mats t1500 and 5110 170 y bp collected in abu dhabi united arab emirates the homologous families of mmas dmas and tmas were identified by comparison of mass spectral and relative retention time data with published data dmas were also identified by synthesis of authentic standards 3 9 dimethyltricosane 5 9 dimethyltricosane and 11 15 dimethylheptacosane mmas dmas and tmas of the cyanobacterial mats can be separated into two groups on the basis of their distribution patterns and structures mmas and dmas in the c16 c22 range are characterized by methyl substituents mainly located at c 6 or 6 and c 7 or 7 and are derived from cyanobacteria they are relatively abundant components in the modern cyanobacterial mats but with increasing age of the mats they become much less abundant on the contrary mmas dmas and tmas in the c24 c45 range are exclusively found in the holocene cyanobacterial mats their longest chains mainly contain an odd number of carbon atoms and they always carry the methyl substituents at odd numbered carbon atoms the similarity in composition of this very specific group of branched alkanes with that encountered in insect epicuticular waxes suggests that these sedimentary hydrocarbons originate from insects which probably grazed on the cyanobacterial mats

evidence for ancient halophiles testing biomarker syngeneity of evaporites from neoproterozoic and cambrian strata molecular fossils from evaporites can provide significant insights into the biotic composition of ancient hypersaline ecosystems however hydrocarbon contamination can mask the true nature of this composition and potentially result in misleading interpretations in this study drill core samples of neoproterozoic and cambrian age dolomite anhydrite and halite from the amadeus basin in central australia contain distinctive and varied hydrocarbon signatures the results are consistent with previous studies of ancient hypersaline settings and include elevated concentrations of heptadecane n c17 docosane n c22 a diverse range of acyclic isoprenoids hopanes and steranes including high concentrations of pregnanes furthermore several samples yielded hydrocarbon signatures with high concentrations of mono and dimethylalkanes relative to n alkanes which is characteristic of many cambrian and precambrian bitumens by quantifying the exterior interior concentration differences of biomarkers in these evaporites considerable insight into the syngeneity of these molecules was obtained in most samples the majority of biomarkers were only detected in the exterior demonstrating that they are contaminants and not indigenous to the evaporites these include biomarkers typically assigned to hypersaline environments demonstrating in this case that their presence is not necessarily an indicator of syngeneity we show that even in combination these molecules can have a wide variety of sources that are not necessarily indigenous to the host rocks nevertheless some neoproterozoic evaporites while also marred by contamination contain demonstrably indigenous biomarkers with equal concentrations on the rock exterior and interior we show that the ability to discern biomarker syngeneity in a complex mix of contaminated and indigenous hydrocarbons requires the need for each compound in every sample to be separately evaluated this study provides an example of how to unravel such a complex series of contamination and obtain more accurate insights into biomarkers of ancient evaporites the approach outlined herein can be readily applied to biomarker studies of other ancient settings

detailed waveform inversion for moment tensors of m 4 events examples from the corinth gulf greece moment tensors mts of weak events are often calculated by a single agency network thus lacking independent validation this article investigates how to increase reliability of the single agency solutions through various multiple checks it deals with the inversion of complete waveforms for six representative events mw 3 4 4 6 in the range of 0 08 0 15 hz several three station sets at near regional distances 8 103 km are used the mts are repeatedly calculated for two independent locations from a regional and local network the source depth is held fixed at the hypocenter and also grid searched to optimize the waveform match initially large variations instability of the mt solution with the approach we used were found for some events later the difficulties were understood and the solutions stabilized it led to practical recommendations on how to detect or even avoid problematic mt solutions first avoid mt solutions for a single fixed depth hypocenter second optimize mt solutions by the depth grid search below epicenter or better for at least two alternative epicenters third carefully analyze i any rapid variation of the so lution ii major misfit of the first motion polarities iii low double couple percen tage often correlating with ii iv low values of the min max eigenvalue ratio and v departures of the mt preferred depth from the location derived depth the mt preferred depths hence also the focal mechanism may be misleading due to data problems e g long period disturbances clipping hidden in the band pass wave forms the location derived depth may be especially wrong for very shallow earth quakes if the crustal model is inadequate in its shallow part and or near stations are lacking on the other hand near stations 20 km should not be used in the wave form inversion together with distant stations because of their large amplitudes the inversion can be easily biased due to instrumental data errors and small location errors online material color figures and waveform match

bimodal stable isotope signatures of zildat ophiolitic melange indus suture zone himalaya implications for emplacement of an ophiolitic melange in a convergent setup zildat ophiolitic melange zom of the indus suture zone himalaya represents tectonic blocks of the fragmented oceanic metasediments and ophiolite remnants the zom is sandwiched between the zildat fault adjacent to a gneissic dome known as tso morari crystalline tmc and thin sliver of an ophiolite called as the nidar ophiolitic complex the zom contain chaotic low density lithologies of metamorphosed oceanic sediments and hydrated mantle rocks in which carbonates are present as mega clasts ranging from 100 meters to few centimeters in size in this work calcite microstructures fluid inclusion petrography and stable isotope analyses of carbonates were carried out to envisage the emplacement history of the zom calcite microstructure varies with decreasing temperature and increasing intensity of deformation intense shearing is seen at the marginal part of the melange near zildat fault these observations are consistent with the melange as a tectonically dismembered block formed at a plate boundary in convergent setup the 18o and 13c isotope values of carbonates show bimodal nature from deeper interior to the shallower marginal near the zildat fault part of the melange carbonate blocks from deeper part of the melange reflect marine isotopic signature with limited fluid rock interaction which later on provide a mixing zone of oceanic metasediments and or hydrated ultramafic rocks carbonates at shallower depths of the melange show dominance of syn deformation hydrous fluids and this has later been modified by metamorphism of the adjacent tmc gneisses above observations reveal that the melange was emplaced over the subducting indian plate and later on synchronously deformed with the tmc gneissic dome

40ar 39ar dating of volcanic rocks of the shyok suture zone in north west trans himalaya implications for the post collision evolution of the shyok suture zone abstract 40 ar 39 ar geochronological studies carried out on the khardung volcanics of ladakh india and our earlier ar ar results from the volcanics of the shyok suture along with the available geological and geochemical data provide good constraints for post collision evolution of the shyok suture zone whole rock samples from the shyok volcanics yielded disturbed age spectra and we have demonstrated earlier that the youngest tectonic event in the shyok suture zone responsible for the thermal disturbance of these samples is karakoram fault activation at 14 ma contrastingly whole rock samples from the khardung volcanics which are in tectonic contact with these shyok volcanics and are exposed in the form of thick rhyolitic and ignimbritic flows yielded undisturbed age spectra and good plateau ages the whole rock plateau ages of two rhyolite samples are 52 8 0 9 and 56 4 0 4 ma we interpret these ages to be the time and duration of emplacement of these volcanics over thickened margin of the continental crust which appears to be coeval with the initiation of the collision between the indian and asian plate the lesser extent of post emplacement isotopic re equilibration in these samples unlike the shyok volcanics indicate that these samples were present in different tectonic settings away from the karakoram fault at the time of deformation in the shyok suture zone we propose that the two volcanic belts of contrasting nature were brought together in juxtaposition by the karakoram strike slip faulting at 14 ma

unusual distribution of hydrocarbons in a hydrothermally altered phosphorite nodule from kusu basin northern kyushu japan abstract lacustrine phosphorite nodules occur in diatomaceous mudstone from the kusu basin northern kyushu japan most of these phosphorite nodules have been hydrothermally altered features of the extractable hydrocarbons in an altered nodule are n alkanes with an even carbon number predominance and unusual suites of dimethyalkanes and alkylcyclopentanes maturity indicators based on hopanes show that this non altered sample is much more mature than a hydrothermally altered one the hydrocarbons in the altered phosphorite were produced during the alteration process and dimethylalkanes and alkylcyclopentanes can be regarded as specific biological markers for hydrothermal environments

a review of the discrete wavenumber method we present a review of the discrete wavenumber dwn method the method introduced by bouchon and art 1977 allows the simple and accurate calculation of the complete green s functions for many problems in elastodynamics

late pleistocene changes in terrestrial biomarkers in sediments from the central arctic ocean abstract biomarkers in late pleistocene sediments collected from the integrated ocean drilling program iodp arctic coring expedition acex hole m0004c central arctic ocean were investigated the major biomarkers are long chain n alkanes n fatty acids and n alkan 1 ols indicating fresh organic matter om derived predominantly from higher plants the dominance of terrestrial biomarkers is attributed to severe om degradation caused by slow sedimentation in oxygen rich benthic water and or low primary production due to permanent sea ice coverage hopanes representing thermally altered om tend to be abundant in samples with abundant ice rafted debris ird an om rich dark grey layer deposited during marine isotope stage mis 6 contains a significant amount of branched glycerol dialkyl glycerol tetraethers branched gdgts suggesting ice erosion of organic rich continental soil followed by transportation to the central arctic by drifting ice the labile refractory index i e the abundance ratio of long chain n alkan 1 ols to the sum of long chain n alkanes and long chain n alkan 1 ols decreases above the dark grey layer indicating that the om became more refractory this change suggests that coverage of the source region by om rich soil decreased because of extensive glacial erosion during mis 6

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

magmatism and metamorphism in the ladakh himalayas the indus tsangpo suture zone abstract ladakh india provides a complete geological section through the northwestern part of the himalayas from kashmir to tibet within this section the magmatic metamorphic and geotectonic evolution of the northern himalayan orogeny has been studied using petrographic geochemical and isotope analytical techniques the beginning of the himalayan cycle was marked by large basaltic extrusions panjal trap of permian to lower triassic age at the northern margin of the gondwana continent indian shield these continental type tholeiitic basalts were followed by a more alkaline volcanism within the triassic to jurassic lamayuru unit of the gondwana continental margin lower jurassic to cretaceous oceanic crust and sediments ophiolitic melange s s accompany the triassic to cretaceous flysch deposits within the indus tsangpo suture zone the major structural divide between the indian shield high himalaya and the tibetan platform so far no relic of paleozoic oceanic crust has been found subduction of the tethyan oceanic crust during upper jurassic and cretaceous time produced an island arc represented by tholeiitic and calc alkaline volcanic rock series dras volcanics and related intrusives accompanied by volcaniclastic flysch deposits towards the tibetan continental margin subsequent to the subduction of oceanic crust large volumes of calc alkaline plutons trans himalayan or kangdese plutons intruded the tibetan continental margin over a distance of 2000 km and partly the dras island arc in the ladakh region the collision of the indian shield and tibetan platform started during the middle to upper eocene and caused large scale still active intracrustal thrusting as well as the piling up of the himalayan nappes the tectonically highest of these nappes is built up of oceanic crust and huge slices of peridotitic oceanic mantle spongtang klippe in the high himalayas the tectonic activity was accompanied and outlasted by a barrovian type metamorphism that affected triassic sediments of the kashmir nun kun synclinorium up to kyanite staurolite grade and the deeper seated units up to sillimanite grade cooling ages of micas are around 20 m y muscovite and 13 m y biotite towards the indus tsangpo suture zone metamorphism decreases with no obvious discontinuity through greenschist prehnite pumpellyite to zeolite grade remnants of possibly an eo himalayan blueschist metamorphism have been found within thrust zones accompanying ophiolitic melange in the suture zone

the eocene rusayl formation oman carbonaceous rocks in calcareous shelf sediments environment of deposition alteration and hydrocarbon potential paralic carbonaceous series intercalated among calcareous shelf sediments have seldom been investigated during the early eocene calcareous and siliciclastic sediments were deposited on a wide shelf in front of low reliefed hinterland in the al khawd region in ne oman the siliciclastic calcareous sediments originated from strongly reworked debris of the arabic shield the underlying semail ophiolite did not act as a direct source of debris but provided some heat to increase the maturity of carbonaceous rocks and modify the isotope signal of the calcareous minerals in the rusayl formation a multidisciplinary approach involving sedimentology mineralogy chemistry coal petrography and paleontology resulted in the establishment of nine stratigraphic lithofacies units and provides the reader with a full picture from deposition of the mixed carbonaceous calcareous siliciclastic rocks to the most recent stages of post depositional alteration of the paleogene formations the calcareous jafnayn formation lithofacies unit 1 developed in a subtidal to intertidal regime influenced episodically by storms deepening of the calcareous shelf towards younger series was ground to a halt by paleosols developing on a disconformity lithofacies unit 11 and heralding the onset of the rusayl formation the stratigraphic lithofacies units iii and iv reflect mangrove swamps which from time to time were flooded through washover fans from the open sea the presence of spinozonocolpites and the taxon avicennia which today belong to a coastal marsh vegetational community furnish palynological evidence to the idea of extensive mangrove swamps in the rusayl formation el beialy s y 1998 stratigraphic and palaeonenvironmental significance of eocene palynomorphs from the rusayl shale formation al khawd northern oman review of palaeobotany and palynology 102 249 258 during the upper rusayl formation lithofacies units v through vii algal mats episodically flooded by marine incursions make up a greater deal of the sedimentary record than mangrove swamps terra rossa paleosols mark the end of accumulation of organic material om and herald supratidal conditions at the passage of rusayl formation into the overlying seeb formation in the subtidal supratidal cycles of lithofacies unit viii the terra rossa horizons are thining upwards and become gradually substituted for by deep water middle ramp sediments of lithofacies unit ix framboidal pyrite ferroan dolomite with very little siderite are indicative of an early diagenetic alteration stage i under rather moderate temperatures of formation

assessing biomarker syngeneity using branched alkanes with quaternary carbon baqcs and other plastic contaminants biomarker molecules are valuable for the elucidation of ancient microbial ecosystems and the characterization of petroleum source rocks for such studies acquisition of reliable hydrocarbon data and proof of their syngeneity are essential however contamination of geological samples with anthropogenic petroleum products during drilling storage and sampling can be particularly problematic because these hydrocarbons may over print an original indigenous biomarker profile to evaluate the extent of contamination of drill core and outcrop material we studied the distribution of hydrocarbons in 26 rocks from different locations in the world all rocks had petroleum products on their exterior surfaces twenty two samples also contained surficial hydrocarbons derived from polyethylene plastic including branched alkanes with quaternary carbon centers baqcs and alkylcyclopentanes with pronounced even over odd carbon number preference using three examples from the paleoproterozoic tawallah and mcarthur groups in northern australia we show how indigenous biomarkers can be recognized by comparing hydrocarbon distributions between exterior rock surfaces and the rock interior and how infiltration of allochthonous hydrocarbons can be assessed through the spatial distribution of characteristic polyethylene derived hydrocarbons in the rock the methods outlined in this paper give confidence in the interpretation of biomarkers in particularly sensitive applications such as the first occurrences of certain organisms in the geological record and the provenance of organic matter in meteorites

molecular fossil constraints on the water column structure of the cenomanian turonian western interior seaway usa abstract bulk geochemical and biomarker molecular fossil data were collected for four cenomanian turonian sections in the western interior basin usa the four sections represent a 900 km wide transect across the basin from kansas to new mexico rock eval and biomarker analyses indicate an east west thermal maturity trend due to progressive deeper burial associated with the tectonic flexure of the foreland basin since the cenonamian turonian at each site the source of extractable organic matter is dominantly marine with minor terrestrial contribution the presence of isorenieratene derivatives in samples from bunker hill ks pueblo co and red wash nm indicates the presence of the green sulfur bacterium chlorobium in the water column and shows that the southern part of the western interior seaway wis experienced events of photic zone anoxia at maximum transgression sedimentary features indicative of water column oxygenation occur within single beds with geochemical evidence of photic zone anoxia this is consistent with a scenario in which bottom waters experienced alternating oxic dysoxic and anoxic conditions these so called intermittent anoxic events underline the high variability in redox conditions in the wis the distribution of isorenieratene derivatives shows a dynamic water column structure of the wis and indicates that anoxia was a permanent feature of the transgressive and regressive intervals of the greenhorn cyclothem rather than at maximum transgression hence the oceanographic circulation is dominated by near field effects inherent to the seaway rather than by direct proto atlantic elements such as the oceanic anoxic event oae

productivity contribution of paleozoic woodlands to the formation of shale hosted massive sulfide deposits in the iberian pyrite belt tharsis spain the geological materials produced during catastrophic and destructive events are an essential source of paleobiological knowledge the paleobiological information recorded by such events can be ric

biogeochemistry of the 1640 ma mcarthur river hyc lead zinc ore and host sediments northern territory australia abstract the formation of the mcarthur river lead zinc deposit involves thermogenic or biologic oxidation of sedimentary organic matter the products of which generated a massive stratiform sulfide ore body and secondary carbonate and silica precipitates formed within the sediment pile down the flow pathway and above the reaction zone the fine grained texture of the mineralization indicates that primary ore texture is preserved and coupled with the regional thermal maturity indicate that this deposit is an ideal location to study organic matter signals related to ore formation and the sedimentary environment biomarker data point to a marine environment of deposition and are consistent with data previously collected from the host barney creek formation in the adjacent glyde subbasin an unusual biomarker distribution found in some samples from within two orebody is considered to be related to the presence of sulfide oxidizing bacteria these organisms flourished after turbidite deposition when oxygen in the upper part of the water column was mixed down to the sediment water interface the biomarker data are supported by micropalaeontologic observations from the same samples and are consistent with intermittent oxygenation of the water column to the sediment water interface this observation suggests an extension of the known occurrence of sulfide oxidizing bacteria back in time by 800 million years to 1640 ma

geochemical and isotopic constraints on the age and origin of the nidar ophiolitic complex ladakh india implications for the neo tethyan subduction along the indus suture zone abstract the nidar ophiolite complex is exposed within the indus suture zone in eastern ladakh india the suture zone is considered to represent remnant neo tethyan ocean that closed via subduction as the indian plate moved northward with respect to the asian plate the two plates ultimately collided during the middle eocene the nidar ophiolite complex comprises a sequence of ultra mafic rocks at the base gabbroic rocks in the middle and volcano sedimentary assemblage on the top earlier studies considered the nidar ophiolite complex to represent an oceanic floor sequence based on lithological assemblage however present study based on new mineral and whole rock geochemical and isotopic data on bulk rocks and mineral separates indicate their generation and emplacement in an intra oceanic subduction environment the plutonic and volcanic rocks have nearly flat to slightly depleted rare earth element ree patterns the gabbroic rocks in particular show strong positive sr and eu anomalies in their ree and spidergram patterns probably indicating plagioclase accumulation depletion in high field strength elements hfse in the spidergram patterns may be related to stabilization of phases retaining the hfse in the subducting slab and or fractional crystallization of titano magnetite phases the high radiogenic nd and low radiogenic sr isotopic ratios for these rocks exclude any influence of continental material in their genesis implying an intra oceanic environment nine point mineral whole rock sm nd isochron corresponds to an age of 140 32 ma with an initial 143nd 144nd of 0 513835 0 000053 end t 7 4 this age is consistent with the precise early cretaceous age of hauterivian 132 2 to 127 1 6 ma to aptian 121 1 4 to 112 1 1 ma for the overlying volcano sedimentary radiolarian bearing chert sequences based on well preserved radiolarian fossils kojima s ahmad t tanaka t bagati t n mishra m kumar r islam r khanna p p 2001 early cretaceous radiolarians from the indus suture zone ladakh northern india in news of osaka micropaleontologists nom spec vol 12 257 270 and cooling ages of 110 130 ma based on 39ar 40ar for nidar spontang ophiolitic rocks maheo g berttrand h guillot s villa i m keller f capiez p 2004 the south ladakh ophiolites nw himalaya india an intra oceanic tholeiitic arc origin with implications for the closure of the neo tethys chem geol 203 273 303 as these gabbroic and volcanic rocks are interpreted to be arc related the new sm nd age data may indicate that intra ocean subduction in the neo tethyan ocean may have started much before 140 32 ma as this date is interpreted as the age of crystallization of the arc magma present and published age data on the arc magmatic rocks from the indus suture zone may collectively indicate episodic magmatism with increasing maturity of the arc from more basic during 140 32 ma when the arc was immature through intermediate andesitic granodioritic at 100 ma to more felsic rhyolitic dioritic magmatism at 50 45 ma when the indian and the asian plates collided

exhumation of the ultrahigh pressure tso morari unit in eastern ladakh nw himalaya a case study exhumation processes of the ultra high pressure uhp tso morari dome nw himalaya are investigated using structural petrological and geochronological data the uhp tso morari unit is bounded by the low grade metamorphic indus suture zone to the ne and mata unit to the sw three deformation phases d1 d2 and d3 are observed only d3 is common to the uhp unit and the surrounding units in the uhp unit the first deformation phase d1 produced upright folds under eclogitic conditions 20 kbar 580 60 c d1 is overprinted by d2 structures related to a nw se trending open anticline this phase is characterized by blueschist mineral associations and corresponds to the quasi isothermal decompression from a depth of 90 km eclogitic conditions up to 30 40 km the final exhumation phase of the tso morari unit is dominated by tectonic denudation and erosion d3 associated with a slight temperature increase radiochronological analyses indicate that the uhp exhumation process began during the eocene exhumation was fast during d1 d2 and slowed down through d3 in oligocene time the change in the deformation style from d1 d2 to d3 in the tso morari unit coincides with changes in the exhumation rates and in the metamorphic conditions these changes may reflect the transition from an exhumation along the subduction plane in a serpentinized wedge to the vertical uplift of the tso morari unit across the upper crust

seismotectonics of the trans himalaya eastern ladakh india constraints from moment tensor solutions of local earthquake data abstract the seismotectonic scenario of the northwest part of the india asia collision zone is studied by analyzing the local earthquake data m 1 4 4 3 recorded by a broadband seismological network consisting of 14 stations focal mechanism solutions fmss of 13 selected earthquakes were computed through waveform inversion of three component broadband records depth distribution of the earthquakes and fmss of local earthquakes obtained by waveform inversion reveal kinematics of the major fault zones present in eastern ladakh a most pronounced cluster of seismicity is observed in the karakoram fault kf zone down to a depth of 65 km the fmss reveal a transpressive environment with an inferred strike slip fault plane parallel to the kf it is argued that the kf penetrates down to the lower crust and is a manifestation of active underthrusting of indian lower crust beneath tibet two clusters of microseismicity are observed at a depth range 5 20 km at the northwestern and southeastern fringes of the tso morari gneiss dome which can be correlated to the activities along the zildat fault and karzok fault respectively the fmss obtained for representative earthquakes show thrust fault solutions for the karzok fault and normal fault solutions for the zildat fault it is suggested that the zildat fault is acting as a detachment facilitating the exhumation of the tso morari dome on the other hand the tso morari dome is underthrusting the karzok ophiolite at its southern margin along the karzok fault due to gravity collapse

the crustal structure of the western himalayas and tibet we present new high resolution shear velocity models for the western himalayas and west tibet from the joint inversion of p receiver functions recorded using seismic stations from four arrays in this region and fundamental mode rayleigh wave group velocity maps from 5 70 s covering central and southern asia the tibetan plateau is a key locality in understanding large scale continental dynamics a large number of investigations has examined the structure and processes in eastern tibet however western tibet remains relatively understudied previous studies in this region indicate that the western part of the tibetan plateau is not a simple extension of the eastern part the areas covered by these arrays include the karakoram and altan tagh faults and major terrane boundaries in west tibet and the himalayas the arrays used include broadband data collected by the west tibet array a u s china deployment on the western side of the tibetan plateau between 2007 and 2011 we use the shear wave velocity models to obtain estimates of moho depth the moho is deep 68 84 km throughout west tibet we do not observe significant steps within the moho beneath west tibet a large step in moho depth is observed at the altyn tagh fault where moho depths are 20 30 km shallower to the north of the fault compared to those to the south beneath the lhasa terrane and tethyan himalayas we observe a low velocity zone in the midcrust this feature is not interrupted by the karakoram fault suggesting that the karakoram fault does not cut through the entire crust

imaging the indian subcontinent beneath the himalaya new seismic images reveal the geometry of the indian plate as it passes beneath the himalayan plateau several important subsurface features of vanished india are revealed including a shear zone above the base of the indian crust beneath the himalaya and conversion of the deep indian crust into denser rock the rocks of the indian subcontinent are last seen south of the ganges before they plunge beneath the himalaya and the tibetan plateau they are next glimpsed in seismic reflection profiles deep beneath southern tibet1 yet the surface seen there has been modified by processes within the himalaya that have consumed parts of the upper indian crust and converted them into himalayan rocks2 3 the geometry of the partly dismantled indian plate as it passes through the himalayan process zone has hitherto eluded imaging here we report seismic images both of the decollement at the base of the himalaya and of the moho the boundary between crust and mantle at the base of the indian crust a significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths north of the himalaya the lower indian crust is characterized by a high velocity region consistent with the formation of eclogite a high density material whose presence affects the dynamics of the tibetan plateau

abundance and carbon isotopic composition of neo pentane in australian natural gases abstract here we report the abundance and carbon isotopic composition of neo pentane or 2 2 dimethylpropane in australian natural gases derived from source rocks of late proterozoic to early tertiary age in australian natural gases neo pentane abundance is low ranging from 6 to 295 ppm the 13cneo pentane shows a strong source control and together with the other gaseous hydrocarbons a maturity effect albeit less pronounced than the source effect in severely biodegraded natural gases neo pentane abundance is similar to that in non biodegraded gases as a result of a counter balance between preservation of neo pentane relative to other wet gases and the addition of biogenic methane nevertheless neo pentane can become the most abundant pentane isomer with neo pentane iso n pentane ratios up to 9 9 here the 13cneo pentane is identical between biodegraded and non biodegraded natural gas from the same source providing strong evidence that neo pentane is resistant to biodegradation even within severely biodegraded gases where the carbon isotopic composition of all the other gaseous hydrocarbons has been altered the carbon isotopic composition of neo pentane ranges from 13c 50 8 to 24 4 vpdb and is typically isotopically more depleted in 13c up to 9 7 than iso pentane and n pentane this wide carbon isotopic variability between the pentane isomers most likely results from the interplay between decomposition isomerisation and methylation mechanisms for neo pentane formation in biodegraded gases the iso pentane and n pentane become progressively enriched in 13c resulting in much larger isotopic differences 13cneo pentane iso pentane values of up to 16 6 in this paper we show how the carbon isotopic composition of neo pentane is related to source rock type and age and demonstrate the usefulness of neo pentane in gas gas correlation particularly in biodegraded accumulations

massive expansion of marine archaea during a mid cretaceous oceanic anoxic event biogeochemical and stable carbon isotopic analysis of black shale sequences deposited during an albian oceanic anoxic event 112 million years ago indicate that up to 80 weight percent of sedimentary organic carbon is derived from marine nonthermophilic archaea the carbon 13 content of archaeal molecular fossils indicates that these archaea were living chemoautotrophically their massive expansion may have been a response to the strong stratification of the ocean during this anoxic event indeed the sedimentary record of archaeal membrane lipids suggests that this anoxic event marks a time in earth history at which certain hyperthermophilic archaea adapted to low temperature environments

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

teleseismic imaging of subducting lithosphere and moho offsets beneath western tibet teleseismic images suggest that the tarim plate plunges 45 s down to 300 km depth beneath nw tibet the 410 km discontinuity shallows by 10 km under the plateau implying 100 c cooler upper mantle the deepest moho on record 90 km lies under w qiangtang it rises abruptly by 20 and 10 km beneath the altyn tagh fault and bangong suture respectively vp vs ratios are normal except in the yecheng flexural basin and deep under the south karakax volcanics 1 92 w kunlun s neogene tectonics are simply accounted for by oblique subduction of lithospheric mantle beneath an upward extruding thrust wedge of the tarim crust

upb geochronology of gangdese transhimalaya plutonism in the lhasa xigaze region tibet abstract a series of different plutons from the lhasa xigaze segment of the gangdese transhimalaya belt has been studied by high resolution u pb analyses of zircon using zircon fractions of 5 100 grains each selected upon specific grain characteristics for two diorites located east of xigaze dazhuka the zircons yield concordant ages of 93 4 1 0 and 94 2 1 0 m y respectively also concordant ages of 41 1 0 4 and 41 7 0 4 m y have been obtained for two granodiorites collected southwest of lhasa qushui the precision on the ages of two granites from the xigaze and lhasa area is limited by two factors the presence of inherited radiogenic lead and the occurrence of subsequent lead loss however some concordant zircons detected in both granites define approximate ages of about 67 and 53 m y respectively the inherited lead components show that melting of precambrian material was involved in magma genesis the u pb ages substantiate a magmatic activity lasting from mid cretceous cenomanian to eocene lutetian time such a period of plutonism at the southern margin of eurasia as well as the occurrence of magma generation from continental crust suggest that the gangdese range results from the subduction of tethys oceanic lithosphere indian plate underneath eurasia eurasian plate if this model is true the collision of india with eurasia along the lhasa xigaze sector postdates the emplacement of the 41 m y old gangdese granodiorites i e the collision occurred after lutetian time

restoration and evolution of the intermontane indus molasse basin ladakh himalaya india abstract collision of the indian plate with the karakorum plate lhasa block during the eocene ca 55 50 ma created predominantly a s or sw verging thrust culmination across the himalaya during the late tertiary two molasse basins existed the siwalik bain formed in the late miocene to present on the indian foreland south of the himalaya and the mid eocene to late miocene indus basin along the indus suture zone north of the high himalaya the indus basin is approximately 2000 km long extending eastwards from ladakh across south tibet a balanced cross section along the zanskar river shows a minimum 36 km shortening in the eocene late miocene molasse and suggests that the minimum basin width was approximately 60 km in ladakh more than 2000 m of post eocene alluvial fan fluvial and fluvio lacustrine sediments accumulated in the ladakh sector with petrographies suggesting derivation mainly from the deeply dissected and uplifted northern granodioritic ladakh batholith aptian eocene with only minor amounts of debris derived from the deformed southern tethyan passive margin palaeocurrents show predominant e w axis parallel sediment transport with subordinate lateral input paths being preserved the indus molasse basin is deformed by numerous post eocene n directed backthrusts many of which cut the entire stratigraphy and therefore were active at least into late tertiary times

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

association between catastrophic paleovegetation changes during devonian carboniferous boundary and the formation of giant massive sulfide deposits abstract the iberian pyrite belt sw iberia is one of the largest sulfur anomalies in the earth s crust in the southern iberian pyrite belt more than 820 mt of exhalative massive sulfides were deposited in less than one million years at the devonian carboniferous boundary the shale of the ore bearing horizon contains biomarkers indicating major biogenic activity in a methanogenic setting including a five fold increase in typical vascular plant biomarkers and a significant anomaly in those probably indicating the presence of thermophilic archaea this contrasts with signatures in the average sedimentary rocks of the basin that indicate the sediments settled in oxic to sub oxic environments and that they have only minor biomarkers derived from continental paleoflora these data show that the formation of the mineralization was not only related to major hydrothermal activity synchronous with volcanism but may also have been controlled by the input of large amounts of organic matter mostly derived from the degradation of woodland detritus sourced in the nearby continent this massive influx of organic matter could have accelerated extremophilic microbial activity that used short chain hydrocarbons as electron donors for seawater sulfate reduction resulting in concomitant massive sulfide precipitation we propose that the giant massive sulfide deposits resulted from overlapping of geological and biological processes that occurred at the devonian to carboniferous transition including 1 continent collision during the onset of the variscan orogeny leading to major paleogeographic changes and volcanism 2 dramatic stress of continental ecosystems due to the combination of climatic change volcanism variations in the sea level and erosion on a regional scale 3 major biomass destruction and increase of organic supply to marine environments and 4 generation of anoxic conditions and the thriving of sulfate reducing microorganisms under these conditions massive sulfide deposits formed where venting sulfur poor but metal rich hydrothermal brines flowed into a hydrogen sulfide rich anoxic water column the data presented strongly suggest that there was a temporal and causal relationship between the devonian carboniferous geotectonic climatic and biological crises and the formation of the giant volcano sedimentary massive sulfide deposits of the southern iberian pyrite belt

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

water column structure during deposition of middle devonian lower mississippian black and green gray shales of the illinois and michigan basins a biomarker approach abstract the extractable organic matter of organic rich black shales and associated organic poor bioturbated green gray shales of the illinois and michigan basins of north america is analyzed to constrain the water column structure during their deposition all black shale samples contain derivatives of the biomarker isorenieratene a diaromatic carotenoid pigment produced exclusively by the brown strain of the green sulfur bacteria chlorobiaceae chlorobiaceae are phototrophic organisms requiring euxinic anoxic and sulfidic conditions to survive and the presence of isorenieratene derivatives indicates that the middle devonian early mississippian epeiric seas of north america experienced bottom water euxinic conditions during black shale deposition analysis of green gray shales also reveals the presence of isorenieratene derivatives and in some cases isorenieratane the highly bioturbated fabric of these sediments indicates the presence of oxygen in bottom waters during their deposition thus we suggest that short term shoaling of the oxycline across the basin slope may have occurred during their deposition though they were deposited predominantly under an oxygenated water column i e above the chemocline most green gray shales contain three pseudohomologous series of branched alkanes with quaternary substituted carbon atoms baqcs which are absent in black shale samples recent studies suggest that baqcs are produced by benthic chemoautotrophs dwelling at the redox boundary separating anoxic sediments from moderately oxygenated waters comparison of the biomarker content i e regular isoprenoid baqcs between black and green gray shales indicates different sources of organic matter and suggests that phytoplanktonic productivity in the upper water column was enhanced during black shale deposition the results of this study indicate that the alternation of green gray and black shales in these basins results from the vertical fluctuations of the chemocline these fluctuations seem to be driven by changes in phytoplanktonic productivity our data when associated to previous studies of other black shales from canada and europe confirm that photic zone euxinia was a widespread feature of low latitude epeiric seas during the middle devonian lower mississippian

magma migration folding and disaggregation of migmatites in the karakoram shear zone ladakh nw india effi cient extraction of granitic magma from crustal sources requires the development of an extensive permeable network of melt bearing channels during deformation we investigate rocks that have undergone deformation and melting within the karakoram shear zone of ladakh nw india in which leucosome distribution is inferred to record the permeable network for magma extraction delicate structures preserved in these rocks record the development of this permeable magma network and its subsequent destruction to form a mobile mass of melt and solids resulting from the interplay between folding and magma migration during folding magma migrated from rock pores into layer parallel and axial planar sheets forming a stromatic migmatite or metatexite with two communicating sets of sheets intersecting parallel to the fold axis once the network was developed folding and stretching was eased by magma migration and slip along axial planar magma sheets folding and magma migration led to layer disaggregation transposition and the formation of a diatexite where rock coherency and banding were destroyed a number of structures developed during this process such as cuspate fold hinges disharmonic folds truncated layering shear along axial planar leucosomes and fl ow drag and disruption of melanosomes in this system magma migration was an integral part of deformation and assisted the folding and stretching of metatexites while folding gave rise to a magma sheet network now preserved as leucosomes as well as the pressure gradients that drove magma migration and the breakup of the metatexite thus metatexite folding increased melt interconnectivity while magma mobility increased strain rate and released differential stresses

structure and distribution of branched aliphatic alkanes with quaternary carbon atoms in cenomanian and turonian black shales of pasquia hills saskatchewan canada abstract twelve pseudohomologous series of branched alkanes with one or two quaternary carbon atoms baqcs c14 c33 range are present in the extractable organic matter of cenomanian and turonian black shales of pasquia hills saskatchewan canada five of these pseudohomologous series are also observed in a holocene sample from the russian arctic three of the pseudohomologous series were identified by kenig et al pnas 100 2003 12554 12558 as 3 3 and 5 5 diethylalkanes deas and 2 2 dimethylalkanes dmas the nine other pseudohomologous series of baqcs are tentatively identified on the basis of their characteristic mass spectral fragmentation and retention indices as 3 3 dimethylalkanes dmas 3 ethyl 3 methyl and 5 ethyl 5 methylalkanes 9 9 7 7 and 6 6 diethylalkanes deas 3 3 3 3 and 5 5 5 5 tetraethylalkanes and 5 butyl 5 ethylalkanes pseudohomologous series of branched alkanes with tertiary carbon atoms such as monomethyl and monoethylalkanes are also present in the same carbon number range all these pseudohomologous families share the particularity of including isomers with exclusively odd or exclusively even carbon numbers clearly indicating a biosynthetic origin baqcs such as 5 5 deas 3 3 deas and 3 ethyl 3 methylalkanes seem to be widespread in sediments and sedimentary rocks ranging from modern to 2 1 billion years a xenobiotic source for baqcs can be excluded at this point baqcs seem to have a very low biodegradability in part explaining their widespread occurrence in ancient sediments

late cretaceous cenomanian to campanian paleoenvironmental history of the eastern canadian margin of the western interior seaway bonebeds and anoxic events abstract upper cretaceous strata in the pasquia hills of the northern manitoba escarpment eastern saskatchewan canada provide a detailed paleoenvironmental and sea level record of the eastern margin of the western interior seaway sediments deposited during the cenomanian turonian greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column with bottom water anoxia recurrently reaching into the photic zone a middle cenomanian sea level lowstand event followed by transgression left a series of bonebeds within the belle fourche member of the ashville formation indicating a sedimentary environment starved of coarse siliciclastics maximum sea level resulted in the formation of limestone beds within the favel formation further favoured by reduced terrigenous sediment input compared to the western margin limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions and reducing zoo and phytoplankton diversities during final greenhorn regression eastern saskatchewan probably turned into a restricted basin severely limiting marine circulation poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the cenomanian turonian transgressive regressive cycle this was caused either by a freshwater lid stratification of boreal and tethyan derived watermasses or both to various intensities affected by changing sea level basin oxygenation during niobrara time varies between localities along the eastern margin as documented by presence absence of benthic and planktic foraminifera

sedimentology of the indus group ladakh northern india implications for the timing of initiation of the palaeo indus river the upper reaches of the indus river form a longitudinal network that drains a large portion of the western himalaya it plays an important role as a sediment routing system feeding the indus delta and submarine fan and has played a controlling role in the denudational history of the western himalaya given the rivers long term significance its timing of initiation remains poorly constrained the facies palaeocurrents and provenance of the post early eocene indus group preserved along the upper reaches of the modern indus reveal a history of fluvial deltaic and deep water sedimentation in an intermontane basin dominated by internal drainage hence the indus group is not considered to represent the deposits of a palaeo indus river as previously thought illite crystallinity values and apatite fission track dating of the indus group suggest that the succession was buried to temperatures of 155 280 c and that unroofing started in early miocene times and proceeded at 0 1 0 4 mm a 1 to the present the youngest sedimentary rocks preserved along the indus basin are early miocene in age from the tectonostratigraphically equivalent deposits around kargil to the west of the study area the transition from sediment accumulation to erosional unroofing in early miocene times coincides with accelerated regional unroofing of the high himalayas to the south and the initiation of the indus delta submarine fan to the west differential uplift between the northward thrusting of the zanskar and indus sedimentary succession against the undeformed ladakh batholith provides a mechanism for post early miocene initiation of a major longitudinal river hence early miocene times is believed to represent the earliest possible age of initiation of the palaeo indus river following this course

an organic geochemical study of cenomanian turonian sediments from the western interior seaway canada abstract bulk geochemical and biomarker data were collected for three cenomanian turonian late cretaceous sections in the western canada sedimentary basin western interior seaway canada rock eval and biomarker analyses indicate an east west thermal maturity trend due to progressive deeper burial associated with the tectonic flexure of the foreland basin the source of extractable organic matter is dominantly marine with a minor terrestrial contribution a pseudohomologous family of 2 2 dimethylalkanes 2 2 dmas in the c 16 c 28 range with an even number of carbon atoms exclusively was tentatively identified from mass spectral data in samples from the pasquia hills region easternmost section the specific origin of 2 2 dimethylalkanes remains unclear the presence of isorenieratene derivatives indicates that the northern part of the western interior seaway experienced photic zone euxinic events throughout the transgressive highstand and regressive phases of the greenhorn cycle the differential occurrence of isorenieratane between the canadian sections and the united states transect at maximum sea level high stand indicates that the water column of the northern part of the wis was less oxygenated whereas the water column in the southern wis was more dynamic and well mixed

a deterministic probabilistic approach for seismic hazard assessment abstract a recurrent criticism of the deterministic approaches for seismic hazard analysis sha is that they make use of a controlling earthquake usually the maximum to have occurred within a given time and space domain instead of the frequency of earthquake occurrence we propose a deterministic method for sha in which instead of a fixed controlling earthquake the earthquake frequency is used the method is based on the deterministic procedure developed by costa et al costa et al 1993 j appl geophys 30 149 160 this procedure computes synthetic seismograms over a regular grid of receivers the input for these estimations consists of available earthquake sources and structural models the earthquake sources are modelled as follows the seismogenic zones are divided into cells of dimension 0 2 0 2 and a point source is placed in the centre of each cell the magnitude of the maximum observed earthquake in the cell and the available focal mechanisms are then used to assign the seismic moment and the double couple orientation to the source in this study the rate of earthquake occurrence is taken into account using the recently computed molchan et al 1997 bull seismol soc am 87 1220 1229 gutenberg richter parameters in each seismogenic zone in italy an annual probability of exceedance and an average return period are calculated for each event of a given magnitude the average annual number of events producing ground motion exceeding a given value and therefore an annual probability of exceedance are then calculated at each receiver the methodology allows us to estimate both the ground motion due to large and rare events as well as that due to small and frequent earthquakes and the obtained results can be easily compared with the probabilistic studies if available for standard return periods the approach for seismic hazard analysis proposed here has two outputs a deterministic i e fixed ground motion due to a fixed event and a probabilistic i e annual average number of events or probability of ground motion exceedance over a given time period the method we propose overcomes one of the most recurrent criticism of the deterministic approaches for sha and at the same time maintains their advantages clear and realistic estimation of engineering parameters needed in the calculation of seismic risk as an example the deterministic probabilistic approach has been applied to estimate the seismic hazard for the region of eastern sicily in italy

abundance and geochemical significance of c2n dialkylalkanes and highly branched c3n alkanes in diverse meso and neoproterozoic sediments several series of branched alkanes with quaternary carbon centers have been detected by gc ms in the saturated hydrocarbon fractions of neoproterozoic sedimentary rocks associated with fossilised microbial mats officer basin south australia and of shallow water carbonates spitsbergen east greenland and baffin island canada a series of 5 5 diethylalkanes was predominant in most of these sediments and was typically accompanied by related series in lower abundance which based on mass spectral characteristics are tentatively assigned as 6 6 diethylalkanes 5 butyl 5 ethylalkanes and 6 butyl 6 ethylalkanes each series displays strong odd or even carbon number preferences several of the sediments contained additional series of structurally undefined c3n alkanes notable for very negative retention time factors which become more negative with increasing molecular weight indicating that branching increases with each c3 addition the strongly sequential carbon preference of the respective c2n and c3n branched alkane series and a predominantly light 13c signature of the 5 5 diethylalkanes cf co occurring n alkanes are consistent with an origin from organisms with a distinct physiology and or carbon source the relatively wide occurrence and high abundance of these branched alkanes in proterozoic sediments containing benthic microbial mats suggests a relationship with specific paleoenvironmental conditions for example strong water column redox gradients that may have been more prevalent than in the phanerozoic