diagenesis and hydrocarbon accumulation brent sandstone jurassic bergen high area north sea diagenesis of brent group sandstones in the bergen high area was studied and related to the history of hydrocarbon maturation and pore fluid environment calcite and kaolinite are low temperature diagenetic precipitates that formed as meteoric pore water entered the brent at the end of brent deposition and later during late cimmerian erosion a major period of feldspar dissolution associated with quartz and illite cementation occurred at huldra field precipitation of diagenetic illite in brent sandstones was closely linked with hydrocarbon maturation in the adjacent viking graben and accumulation of generated fluids in traps at structural highs at huldra field illite k ar ages suggest onset of illite diagenesis in the latest cretaceous initial reservoiring of hydroca bons during the latest paleocene to early eocene 58 ma and filling of the reservoir by early oligocene 38 ma pore water character during illite diagenesis interpreted from oxygen isotope and quartz overgrowth fluid inclusion data was warmer than predicted by burial history analysis and one and a half to two times seawater salinity the incursion of saline isotopically evolved fluids at huldra suggests replacement of paleometeoric water by basin compaction fluid illite k ar ages from veslefrikk field indicate a minimum age of hydrocarbon accumulation at about 30 ma modern pore water chemistry in the brent at veslefrikk is unlike the suggested water chemistry at huldra and indicates that migrating compaction water did not completely displace older fresh connate water this sugge ts that hydrocarbons migrated into veslefrikk as a discrete phase without great volumes of associated compaction water

provenance of jurassic accretionary complex mino terrane inner zone of south west japan implications for palaeogeography of eastern asia provenance and tectonic history of the jurassic accretionary complex mino terrane located in the inner zone of south west japan were studied using sandstone framework composition and mudrock geochemistry modal analysis of sandstones shows that the tectonic setting of the source area for the studied mino terrane clastic rocks was uplifted basement largely dominated by high grade metamorphic terrain composed of quartz and feldspar especially plagioclase the textural and mineralogical immaturity extent of alkali and alkaline earth element leaching low chemical index of alteration values and depleted rare earth element ree contents suggest rapid uplift and erosion within the source terrain and a relatively weak weathering intensity factor analysis revealed that grain size effects governed compositional heterogeneity in the studied sediments provenance of the sediments is interpreted as being plagioclase enriched felsic basement rock such as granodiorite within a continental margin and evolved arc tectonic setting rather than active volcanic arc lack of a contribution from active volcanic arcs may have resulted from the cessation of volcanism during the reorganization of the subducting plate system and or erosion of arc volcanics and exposure of basement considering the previous studies on palaeogeography and palaeocurrent reconstruction the north eastern part of the yeongnam massif in the korean peninsula is interpreted as the most probable source area for the studied turbidites the results of mixing calculation for mino terrane sediments suggest that precambrian leucocratic granite and the basement rock of the cretaceous gyeongsang basin shed large amounts of sediments to the mino trench whilst precambrian granitic gneiss and the triassic pluton supplied lesser amounts the results of this study reveal that although active subduction accretion processes were occurring the mino trench was bordered by continental basement rocks this knowledge contributes to enhanced understanding of the jurassic palaeogeography of the east asia continental margin

stratigraphy and paleoenvironmental analysis of the frasnian famennian upper devonian boundary interval in tioga north central pennsylvania abstract two pulses of extinction in the late frasnian late devonian the lower and upper kellwasser lkw and ukw events coincided with the deposition of organic rich strata in many parts of the world including the appalachian basin here we describe two stratigraphic sections from tioga north central pennsylvania that span the frasnian famennian f f boundary interval the f f boundary and ukw equivalent strata are probably located in the covered interval between the two sections but the lkw equivalent pipe creek formation is well exposed we propose several stratigraphic revisions including raising the lock haven formation to group status and dividing it into formations as well as redefining the base of the canaseraga formation and subdividing it into members paleoenvironments at tioga range from offshore outer shelf to middle shoreface a regression follows the lkw transgression as evidenced by the sharp superposition of middle shoreface sands on outer shelf mudstones similar to large facies changes associated with the lkw in other settings the lkw is typically interpreted as representing deposition under dysoxic anoxic conditions and trace and body fossil content suggest that the pipe creek formation represents dysoxic but not permanently anoxic conditions these stratigraphic revisions and records of environmental change will provide the framework for more detailed studies of the lkw and ukw extinction events in the appalachian basin

the mesozoic and early tertiary tectonic evolution of the socotra area eastern gulf of aden yemen recent interpretation and mapping of seismic data covering the area to the south and west of the island of socotra have enhanced the understanding of the mesozoic and early tertiary tectonic history of the socotran platform lineament orientations after restoration to account for oligo miocene gulf of aden rifting indicate o 1 the most significant basin forming lineament has a 140 orientation basin initiation based on onshore yemen analogues occurred in the late jurassic early cretaceous oxfordian to hauterivian and is believed to be associated with neo tethys rifting between the afro arabian and laurasian plates 2 the presence of a 45 lineament orientation associated with the extension and subsequent opening of the north somali basin separation of the indian plate from the african plate during callovian oxfordian times resulted in the opening of a number of en echelon rift basins mozambique west somali and north somali basins offset by major north south orientated fracture zones davie ridge and a r s v l c c fracture zones 3 cretaceous post rift carbonate platform development in the study area was followed by several phases of later structural evolution these have characteristic translational aspects to their movements and occurred in the late cretaceous palaeocene further modifying the structural geometry of the socotran sub basins the majority of the translational features and faults evident on seismic data and mapped at late cretaceous and palaeocene time horizons suggest an 80 principal displacement zone pdz orientation seismically derived isochrons indicate that movement along this zone was intermittent

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

early neoproterozoic ca 900 ma rift sedimentation and mafic magmatism in the north lhasa terrane tibet paleogeographic and tectonic implications abstract the origin and evolution of the precambrian north lhasa terrane in the central tibetan plateau remain enigmatic here we present u pb age and hf isotopic data for detrital zircons from early neoproterozoic quartzites in the north lhasa terrane tibet an integrated petrological geochronological geochemical and sr nd hf isotopic study was also undertaken on amphibolites associated with the quartzites the depositional age of the quartzites is constrained to be between ca 931 ma youngest detrital igneous zircon core and 869 ma oldest metamorphic zircon rim the detrital zircons have a main age population from 1200 to 1000 ma and lack zircons with ages of 1000 900 ma zircons from the amphibolites yield concordant ages of ca 913 902 ma which are comparable to the depositional age of the quartzites the amphibolites have n morb like compositions and are characterized by high positive zircon ehf t 7 2 to 14 0 and whole rock end t 5 5 to 6 0 values their compositions have been modified by crustal contamination the formation of these quartzites and amphibolites was related to an early neoproterozoic rift adjacent to the african side of the northern east african orogen followed by opening of part of the mozambique ocean

pervasive early diagenetic dolomitization subsequent hydrothermal alteration and late stage hydrocarbon accumulation in a middle triassic carbonate sequence szeged basin se hungary abstract the middle triassic shallow marine carbonates of the se pannonian basin szeged dolomite formation show evidence for multistage dolomitization and a complex diagenetic history in first stage the whole sequence was completely dolomitized by reflux of slightly evaporated seawater this process took place from the near surface till shallow burial realms and resulted in the formation of both fabric preserving and fabric destructive dolomite types in the following stage nonplanar matrix dolomite and saddle dolomite cement were formed in the intermediate and or deep burial realm these later dolomite phases are likely generated by invasion of exotic fluids at relatively high temperature evidenced from the fluid inclusion homogenization temperatures and stable isotope compositions vuggy fracture and solution enhanced porosity are also related to this local hydrothermal event microthermometry performed on saddle dolomite hosted primary fluid inclusions confirm the presence of hot 138 235 c and moderately saline brines 4 1 8 7 mass nacl equivalent the calculated 18owater and the measured dwater values of the fluid inclusions from the saddle dolomite cement together with the relatively low salinity values indicate a metamorphogenic and or magmatic origin of the hydrothermal fluid that probably was channeled along the upper cretaceous subhorizontal overthrust zones the pores formed by the leaching effect of these hydrothermal fluids were subsequently partly occluded by meteoric calcite during the paleogene middle miocene subaerial exposure but a remarkable part was preserved and currently serves as reservoir space such an integrated study of the different dolomite and porosity types the understanding of their genesis and timing relative to hydrocarbon maturation and migration could aid in exploration and development

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

lhasa terrane in southern tibet came from australia the u pb age and hf isotope data on detrital zircons from paleozoic metasedimentary rocks in the lhasa terrane tibet defi ne a distinctive age population of ca 1170 ma with e hf t values identical to the coeval detrital zircons from western australia but those from the western qiangtang and tethyan himalaya terranes defi ne an age population of ca 950 ma with a similar e hf t range the ca 1170 ma detrital zircons in the lhasa terrane were most likely derived from the albany fraser belt in southwest australia whereas the ca 950 ma detrital zircons from both the western qiangtang and tethyan himalaya terranes might have been sourced from the high himalaya to the south such detrital zircon connections enable us to propose that the lhasa terrane is exotic to the tibetan plateau system and should no longer be considered as part of the qiangtang greater india tethyan himalaya continental margin system in the paleozoic reconstruction of the indian plate as current models show rather it should be placed at the northwestern margin of australia these results provide new constraints on the paleogeographic reconstruction and tectonic evolution of southern tibet and indicate that the lhasa terrane evolved as part of the late precambrian early paleozoic evolution as part of australia in a different paleogeographical setting than that of the qiangtang greater india tethyan himalaya system

changes in marine nitrogen fixation and denitrification rates during the end devonian mass extinction abstract the end devonian was a critical interval in earth history recording the transition from the early paleozoic greenhouse climate to the late paleozoic icehouse climate a mass extinction at this time the hangenberg extinction eliminated 21 of genera and 16 of families of marine invertebrates although its causes remain poorly understood the marine nitrogen cycle is intimately related to the nutrient status of seawater microbial community composition and the redox condition of the oceans and thus it may provide insights into the mechanism s of the end devonian mass extinction and climate change here we analyzed high stratigraphic resolution bulk sediment nitrogen isotope variation 15 n bulk in three sections from south china 1 long an an isolated carbonate platform section 2 qilinzhai a shallow water carbonate platform section between the yangtze oldland and the youjiang trough and 3 malanbian a shallow water carbonate platform section between the yangtze and cathaysia oldlands and distant from deep water areas our 15 n bulk records show a major perturbation to the marine nitrogen cycle in the middle siphonodella praesulcata zone which is marked by a decline in 15 n bullk from 4 to 0 at long an and from 4 5 to 2 5 at malanbian this perturbation coincided with the main end devonian mass extinction as well as with a negative shift in carbonate carbon isotopes 13 c carb the shift to lower 15 n values suggests locally enhanced nitrogen fixation possibly as a consequence of increased denitrification in response to globally expanded marine anoxia thus these 15 n bulk data are consistent with the hypothesis that intense anoxia was the immediate cause of the end devonian mass extinction the 15 n bulk records generated in this study suggest that there was significant spatial and temporal variation in the nitrogen isotope composition of seawater nitrate in the yangtze marginal sea during the latest devonian this variation may have been related to the complex paleogeography of the south china craton which contained numerous isolated and continent attached platforms and deep water basins that influenced watermass circulation nutrient inventories and primary productivity levels and watermass ventilation and redox conditions

late frasnian sedimentation cycles in the appalachian basin possible evidence for high frequency eustatic sea level changes abstract during the late frasnian 11 fourth order progradational retrogradational marine sedimentation cycles were deposited in the appalachian foreland basin mapping based primarily on subsurface data demonstrates the continuity of these cycles over a distance of 700 km cyclicity in distal facies occurs as alternations of organic rich and organic poor shales two of the organic shales can be correlated with the transgressive kellwasser beds of europe in more proximal facies recurring lobes of siltstone and sandstone were deposited based on lithologic indices the temporal pattern shows significant variation in the strength of relative facies change during deposition in particular two times of particularly pronounced progradation correspond to previously recognized eustatic sea level falls the correlation of portions of appalachian basin depositional cyclicity with global sea level events suggests that the entire sequence of 11 cycles with estimated average duration of around 100 150 ka were the result of high frequency eustatic sea level changes this in turn would be consistent with a brief period of late frasnian glaciation as others have previously suggested

intensified oceanic circulation during early carboniferous cooling events evidence from carbon and nitrogen isotopes abstract the early carboniferous was a climatic transition interval from a mid paleozoic greenhouse world into the late paleozoic ice age it was marked by a long term cooling trend that was punctuated by short glaciations in the tournaisian and visean early to mid early carboniferous here we generated organic carbon and nitrogen isotope profiles for two widely separated lower carboniferous sections arrow canyon range nevada and namur dinant basin belgium in order to assess the global nature and timing of changes in the carbon nitrogen cycles linked to oceanic productivity and redox conditions during this climatic transition interval the carbon and nitrogen isotope profiles of both study sections record major perturbations during the mid tournaisian and visean a mid tournaisian event tice is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 7 0 25 2 to 23 7 and 0 6 to 8 9 respectively and namur dinant from 0 3 to 4 7 27 9 to 22 2 and 5 7 to 5 2 respectively an early visean event vice named herein is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 3 1 28 4 to 23 6 and 1 4 to 9 4 respectively and namur dinant from 2 1 to 4 3 26 7 to 25 0 and 1 4 to 3 3 respectively the positive excursions in all three isotopic records during these events are consistent with increased fractional burial of organic carbon and enhanced denitrification implying intensification of marine productivity and expansion of hypoxia in the global ocean given that each event coincided with lowering of sea surface temperatures and increased glaciation as documented from published conodont 18o and sea level records we hypothesize that global cooling led to intensified oceanic circulation and upwelling on continental margins triggering increased marine productivity and attendant redox changes within the affected upwelling zones our results provide new insights into changes in early carboniferous oceanic conditions in response to the initial stages of cooling leading into the late paleozoic ice age

fluid inclusion evidence of petroleum migration through a buried metamorphic dome in the pannonian basin hungary some of the petroleum currently produced in the pannonian basin in hungary stems from buried metamorphic basement domes that form structural highs between neogene sedimentary sub basins in the bekes sedimentary sub basin the source rocks of the petroleum are known to be of middle to late miocene age whereas at least part of the petroleum in the adjacent szeghalom basement dome appears to be of lower miocene age or even older virtually nothing is known about the compositions distribution sources and migration history of this older petroleum although such variables are crucial to future exploration strategies this study addresses the first two of these gaps in knowledge by providing a basic characterization of the older petroleum trapped as fluid inclusions in fracture hosted quartz crystals within the szeghalom dome szd fluid inclusion samples from 9 wells at depths of 1900 to 2200 m were analysed by visible and cie calibrated uv microscopy microthermometry laser raman and 1 h nmr spectroscopy two major types of early miocene oils were found distributed over 5 distinct temporal generations an earlier immature brown oil succeeded by a light gas condensate the early petroleum was undersaturated with respect to methane gas and it migrated through the fracture network at temperatures between about 160 to 130 c entraining blebs of bitumen and flushed by weakly saline water the later gas condensate migration consisted of a heterogeneous mixture of volatile oil methane rich gas weakly saline water at slightly lower temperatures between 135 and 120 c the temperature evolution was caused by cooling of the metamorphic wall rocks during basement uplift culminating in middle miocene exhumation the various hydrocarbons are unevenly distributed across the szeghalom dome showing that pre middle miocene fluid migration through the fracture network was compartmentalized at the km scale 2007 elsevier b v all rights reserved

n2 fixing cyanobacteria supplied nutrient n for cretaceous oceanic anoxic events the abundance of specific membrane lipids 2 methylhopanoids indicates that cyanobacteria played a key role in the seemingly global deposition of black shales during the early aptian ca 120 5 ma and late cenomanian ca 93 5 ma oceanic anoxic events organic matter rich sediments deposited during these events are characterized by a 15n content typical of newly fixed n2 indicating that cyanobacterial n2 fixation was the main source for nutrient n we propose that denitrification and anaerobic ammonium oxidation effectively cut off the return of nutrient n from the anoxic deep waters to the photic zone in the oceans giving n2 fixing cyanobacteria a competitive advantage over algae during these oceanic anoxic events

structure and evolution of the himalaya tibet orogenic belt the 1981 french chinese expedition to tibet focused on the lhasa block extending earlier coverage 400 km north of the tsangpo suture the lhasa block stood between 10 and 15 n latitude over most of the upper cretaceous and eocene and if gondwanian in origin had detached from gondwana by early permian seismic profiles reveal a complex moho topography resulting both from multiple continental thrusting and large scale strike slip faulting subduction related granitoids representing mixtures of mantle and crustal components and anatectic granitoids have been analysed and dated this study emphasizes the role of smaller blocks in the accretion of the continental mosaic

characteristics and origin of the major authigenic minerals and their impacts on reservoir quality in the permian wutonggou formation of fukang sag junggar basin western china abstract this research is focused on the characteristics and origin of major authigenic minerals and the influences on the reservoir quality of the permian wutonggou formation sandstones in the eastern slope of fukang sag junggar basin western china authigenic cements were observed and described from thin sections scanning electron microscopy fluorescence and cathodoluminescence the elemental concentrations of the authigenic minerals were measured by electron probe microanalysis additional characterizations were obtained from o and c stable isotope ratios and from the homogenization temperature of aqueous fluid inclusions the results show that the sandstones in the wutonggou formation are dominated by volcanic lithic fragments carbonates and laumontites are the major authigenic minerals in the study area authigenic quartz and kaolinite can also be observed two types of carbonate cements are identified the first type is calcite with yellow fluorescent hydrocarbon inclusions the carbon and oxygen isotopes in the calcites are highly c depleted and o depleted the homogenization temperatures of the aqueous fluid inclusions in the calcite cements are higher than the highest paleogeotemperatures during the burial history combined with the presence of authigenic fibrous illites and the illitization of kaolinites it is determined that the precipitation of the calcites is related to the upwelling of deep fluids and was impacted by the co 2 from the thermal decarboxylation of organic matters during the middle late jurassic the second type is ferroan calcite with blue fluorescent hydrocarbon inclusions and higher contents of fe mn cr and mg than in the calcites the ferroan calcites in the beisantai uplift are rich in 13 c 13 c v pdb values are 22 10 and 22 16 the precipitation of these ferroan calcites was impacted by the co 2 from crude oil biodegradation after the late jurassic two types of laumontites are identified the first type is partially dissolved and is characterized by a high ca na ratio and low fe contents the second type is hardly dissolved has hydrocarbon inclusions with yellow and blue fluorescence and is characterized by a low ca na ratio and high fe contents the first type of laumontite was precipitated prior to hydrocarbon charging and the second type was formed after hydrocarbon charging and meteoric water leaching the hydration of the volcanic debris provided the source materials for both types of laumontite the authigenic quartz and kaolinite were formed by the alteration of feldspars laumontites and volcanic materials the evolution of the reservoir properties was impacted by various degrees of cementation and dissolution as a result the reservoir quality in the beisantai uplift was better than in the shaqiu area

platinum group element enrichments and possible chondritic ru ir across the frasnian famennian boundary western new york state the frasnian famennian boundary is recognized as the culmination of a global mass extinction in the late devonian in western new york state the boundary is a distinct horizon within a pyritic black shale bed of the upper hanover shale defined by the first occurrence of palmatolepis triangularis in the absence of frasnian conodonts the boundary is characterized by a minor disconformity marked by a lag concentration of conodonts iridium at the boundary is 0 11 0 24 ng g two to five times background levels of 0 05 ng g other ir enrichments of 0 38 ng g and 0 49 ng g occur within 50 cm of the conodont constrained boundary numerous ir enrichments in the boundary interval suggest extraterrestrial accretion and platinum group element pge concentration at disconformities or mobilization and concentration in organic rich pyritic rich laminations from cosmic or terrestrial sources pge ratios of pt pd and ru ir at the boundary horizon approximate chondritic ratios and are suggestive of an unaltered extraterrestrial source these values do not conclusively establish a single extraterrestrial impact as the ultimate cause of the frasnian famennian mass extinction especially given the presence of similar ir enrichments elsewhere in the section and the absence at the boundary of microtektites and shocked mineral grains

the north lhasa terrane in tibet was attached with the gondwana before it was drafted away in jurassic evidence from detrital zircon studies abstract it was commonly accepted that the north lhasa terrane of the present day central tibetan plateau in asia came from the northern gondwana but the timing of its northward drifting away from the gondwana remains controversial here we present for the first time u pb age and hf isotope data on detrital zircons from the cambrian metasedimentary rocks in the north lhasa terrane the detrital zircons display age peaks at ca 505 548 926 and 1104 ma and are interpreted to have gondwanan source regions these metasedimentary rocks were probably deposited in a collisional tectonic setting e g foreland basin related to the cambrian collisional accretion of microcontinents along the gondwanan proto tethyan margin the cambrian and carboniferous late triassic sedimentary rocks in the north lhasa terrane share the similar precambrian cambrian detrital zircon age and ehf t distributions indicating constant source accretion during the cambrian triassic time by contrast the precambrian cambrian detrital zircon age distribution of the late jurassic early cretaceous sedimentary rocks in the north lhasa terrane is distinctive from that of the adjacent cambrian triassic sedimentary rocks suggesting that the northward drifting of this terrane occurred in the jurassic

late jurassic early cretaceous palynofloras in the lhasa block central xizang china and their bearing on palaeoenvironments abstract as a part of the qinghai xizang plateau the lhasa block has experienced a very complicated geological history since it rifted from gondwana little is known about how terrestrial ecosystems evolved on this block during this time our new materials collected from this block reveal for the first time the palaeovegetation and palaeoclimate during the late jurassic to early cretaceous three distinct palynological associations are recognized including the late jurassic cyathidites classopollis association and the early cretaceous berriasian barremian dicheiropollis and dicheiropollis peak associations an additional classopollis cooksonites association recovered from qubsang which lacks dicheiropollis is coeval with the dicheiropollis association these associations are generally similar to those on the qiangtang block southern qinghai province which indicates that these blocks had merged before the late jurassic facilitating establishment of a common palynoflora across the two blocks and adjacent regions the palaeovegetation on the lhasa block in the late jurassic was characterized by abundant tree ferns whereas during the earliest cretaceous cheirolepidiacean communities were more dominant within these communities a new cheirolepidiacean plant that produced dicheiropollis pollen emerged implying a potential increase in temperature the palaeoclimate was generally warm and semi humid during the late jurassic and early cretaceous although fluctuations of temperature and humidity occurred a reduction in precipitation from the lhasa block to the inland qiangtang block and tarim basin is reflected in the palynoflora a brief history of the vegetation and climate of the lhasa block from late jurassic to early cretaceous is provided

connected fluid evolution in fractured crystalline basement and overlying sediments pannonian basin se hungary abstract uplifted crystalline basement highs have played an important role in the hydrologic history of the pannonian basin providing conduits for fluid migration during basin evolution petrographic stable isotope electron microprobe and fluid inclusion studies support a five step basin evolution 1 formation of crystalline core complexes 2 percolation of meteoric water through shear zones 3 basinwide thermal subsidence 4 hydrologic inversion and 5 tectonic inversion brittle fractures in the basement are the results of uplift during core complex formation and contain pyrite kaolin illite chlorite calcite and quartz hydrocarbon stains between calcite and quartz and yellow fluorescent primary hydrocarbon inclusions in quartz are indicative of migrations of hydrocarbon bearing fluids during uplift from mid crustal depth further uplift was associated with meteoric water infiltration along shear zones as recorded by light 13 c and 18 o values low trace element concentrations all liquid primary fluid inclusions and encased pollens and cuticules of terrestrial plants in a second fracture calcite crystallised after quartz a simultaneous meteoric influence in the overlying pannonian 12 7 3 ma sediments is indicated by extensive plagioclase dissolution calcite cement geochemistry and low salinity all liquid fluid inclusions the thermal subsidence of the basin led to isolation of the hydrologic system from the surface diminishing meteoric influence is recorded by increasing fluid inclusion salinities of secondary inclusions in calcite and quartz in the basement fractures and of primary inclusions hosted in late calcite and quartz in the sediments a sudden decrease of the fluid inclusion salinities from 4 5 to 1 wt nacl eq at 130 c both in burial cements and fracture filling minerals represents a newly established hydrological system which redistributed the interstitial fluids including hydrocarbons this hydraulic inversion is indicated by abundant fluorescent secondary fluid inclusions in fracture filling minerals finally the pliocene to recent tectonic inversion reopened fractures in the crystalline basement and induced a rapid crystallisation of laumontite these results support a long standing late miocene to recent hydraulic connection between fractured crystalline basement and overlying sediments in the central part of the pannonian basin

evidence for meteoric recharge in the san joaquin basin california provided by isotope and trace element chemistry of calcite abstract calcite cements were analysed petrographically and geochemically to document patterns of meteoric recharge into marine sandstones in the san joaquin basin california calcite cements in shallow marine sandstones in the eastern basin are pure 96 mol ca 32 and 18 o pdb 18 o and point counted volumes of 26 27 appear 5 m apart the purity of low temperature calcite 8 10 9 m 3 and rates of locally variable dissolution reactions and calcite crystallization exceeded the flushing rates of reservoirs if meteoric recharge began shortly after the deposition of marine shelf sandstones approximately 23 ma then calcite cements record downdip infiltration at an average rate of 1 mm year less than some recorded rates of gravity driven flow

from greenhouse to icehouse nitrogen biogeochemistry of an epeiric sea in the context of the oxygenation of the late devonian atmosphere ocean system abstract the late devonian emergence of extensive arborescent terrestrial ecosystems produced changes in the earth s atmosphere and climate that resulted in substantial changes to the biogeochemistry of marine ecosystems the biogeochemistry of nitrogen in epeiric seas was particularly susceptible to alteration because of its dependence upon the series of redox mediated reactions that comprise the marine n cycle in order to explore the impact of climate change on n biogeochemistry in a late devonian epeiric sea we sampled a core from the appalachian basin that spans the interval from the greenhouse climate at the base of the famennian period to glacial conditions near its conclusion based upon stable isotope analysis of n c and s as well as elemental analysis of n c p s and fe we contend that two distinct biogeochemical regimes obtained during the contrasting climates the greenhouse regime featured low seawater o2 and ph that served to significantly curtail the oxidation of ammonia i e nitrification resulting in an ammonium dominated water column and low sediment 15n values the greenhouse also featured more extensive recycling of c n and p in contrast the higher seawater o2 and ph of the icehouse regime permitted nitrification in the water column resulting in a nitrate dominated system and higher sediment 15n values we conclude that nitrification was the key component of the n cycle that differentiated the two climate biogeochemical regimes

sedimentary corg p ratios paleocean ventilation and phanerozoic atmospheric po2 the corg p ratios of organic rich facies tocn1 exhibit considerable variation through the phanerozoic from b10 1 in the permian phosphoria formation to n1000 1 in some devonian black shales relative to the composition of phytoplankton c p 106 1 which provide the bulk of organic c and p to organic rich marine sediments the range of phanerozoic sedimentary corg p ratios largely reflects the influence of benthic redox conditions on diagenetic pathways of c and p remobilization enhanced preservationoforganiccatlowerredoxpotentials combinedwithenhancedsedimentaryretentionofremineralizedorganicpathigher redox potentials results in a strong relationship between benthic redox conditions and sedimentary corg p ratios the strong secular coherence of the phanerozoic corg p record i e limited variation within narrow time slices suggests that these ratios are controlled primarily by factors influencing benthic redox conditions on a global scale such as atmospheric po2 inversion and scaling of the phanerozoic corg p record yields a new atmospheric po2 model that has strong similarities to existing models based on elemental and isotopic mass balances yet differs in some potentially significant respects in particular the new model suggests that atmospheric po2 wasmarkedlylowerduringtheearlytomiddlepaleozoicthanpreviouslyinferred duringmostofthedevonian atmospherico2levels mayhavebeensufficientlylow b13 astopreventthesustainedcombustionofplantmaterial thisfeatureofthemodelmayaccount for ananomalous gapinthefossilcharcoalrecordduringthedevonian theredox dependentburialofpintheoceanresults inpositive and negative feedback mechanisms that tend to stabilize atmospheric oxygen concentrations on geologic timescales temporal variations in the burial of p relative to c suggest that the strength of these feedback mechanisms varied over the phanerozoic 2007 elsevier b v all rights reserved

lipid biomarker stratigraphic records through the late devonian frasnian famennian boundary comparison of high and low latitude epicontinental marine settings abstract the pervasiveness of black shale preservation in association with late devonian biological crises suggests marine anoxia played a major role in driving ecological perturbations however devonian black shale deposition is still mechanistically poorly understood we have compiled detailed biomarker lipid chemostratigraphic records for 83 different rock samples using molecular constituents of bitumens of upper kellwasser equivalent black shales from two foreland basins from the low paleolatitude appalachian basin new york state and from the high paleolatitude madre de dios basin bolivia in order to better understand local environmental conditions and organic source inputs during this depositional event despite strong indications from stable nitrogen isotopic signatures for fixed nitrogen nutrient limitation the biomarker assemblages with consistently low moderate hopane sterane ratios 28 c 29 sterane ratios at higher paleolatitude in the more nutrient replete madre de dios basin suggest prasinophyte microalgae flourished in this setting in accordance with palynological evidence for high contributions of tasmanites cysts in these strata all samples contain only very low absolute amounts of aryl isoprenoids with 2 3 6 trimethyl substitution and other aromatic carotenoids up to several orders of magnitude lower than concentrations reported from other phanerozoic euxinic basins these data are consistent with local marine paleo redox models for both basins lacking a persistently shallow sulfidic aquatic zone and demonstrate that temporally persistent or spatially pervasive photic zone euxinia is not necessarily associated with all black shale sequences in the late devonian

mesozoic cenozoic rift drift sequence of asian fragments from gondwanaland abstract the university of cambridge atlas map plotting computer program has been used to plot a reconstruction of the dispersal of continental blocks from eastern gondwanaland from the late jurassic 160 ma until the late miocene 10 ma the geological basis for the reconstruction rests on the concept of south tibet burma western thailand malaya and sumatra having been part of the eastern gondwana continent during the late palaeozoic and early mesozoic the reconstruction is also based on the view that these asian continental blocks were rifted from eastern gondwanaland in the late jurassic this rifting episode gave rise to the continental margin of central new guinea and northern australia it was associated with the sea floor spreading anomalies preserved in the floor of the northeastern indian ocean the model considers the indication of crustal uplift in the middle jurassic followed by profound subsidence in the cretaceous and palaeogene exposed in the islands of the outer banda arc from seram to timor and the similar jurassic cretaceous facies in eastern sulawesi implies that these areas formed part of this rifted northern margin of australia in the jurassic subsequent tectonic collision and associated major strike slip movements have deformed and disrupted these rock sequences during the cainozoic the date of the rifting that removed south tibet burma western thailand and malaya from gondwanaland is controversial the indications in favour of the rifting episode having occurred in the jurassic rather than in the permo triassic are stratigraphie structural observations on the northwestern australian shelf in the banda arc and in central new guinea the identification of the continental blocks removed by this rifting is based partly on stratigraphie correlation with the banda arc and new guinea and partly on indications that the age of collision of tibet burma western thailand and malaya with asia was a late cretaceous event and not triassic jurassic as is generally held there are very few reliable land based palaeomagnetic measurements to constrain the movements of these dispersed continental fragments from gondwanaland the computer generated map reconstructions put forward here fit the available indian ocean sea floor spreading data although they are not unique solutions much of the critical ocean floor data associated with the rifting and dispersal of these continental fragments has been destroyed in the tectonic collision processes that occurred at the asian continental margin

are systematic variations in thrust belt style related to plate boundary processes the western alps versus the carpathians within the mediterranean region cenozoic deformation of the western alps and the west to east carpathians has resulted in two different styles of foreland fold and thrust belt the most prominent difference between the two belts is the presence carpathians or absence western alps of contemporaneous back arc extension but other important differences in structure topography and metamorphism also exist these differences in thrust belt style developed mainly during the final stages of thrust belt evolution and appear to reflect fundamental differences in the tectonic settings of the western alps and the carpathians in middle and late cenozoic time in particular they appear to be the result of convergence that is in the first case driven primarily by major plate motions and in the second case only by local motions of small lithospheric flakes or fragments we suggest that the structural styles developed in these two mountain belts may be useful in identifying mountain belts that have evolved in similar tectonic settings elsewhere in the world in this respect the western alps and the carpathians can be regarded as typical examples of two different styles of foreland fold and thrust belt or more properly as end member examples within a broad spectrum of foreland fold and thrust belt styles we propose that continental subduction zones and orogenic belts can be loosely divided into segments that show no major back arc extensional deformation adjacent to the belt the western alps and segments that exhibit back arc extension contemporaneously with thrusting the carpathians the former are found in areas where the rate of overall plate convergence exceeds the rate of subduction and are commonly typified by extensive involvement of crystalline basement in thrusting exposure of high grade metamorphic rocks at the surface high topographic elevation and large amounts of erosion tens of kilometers the latter are found in areas where the rate of subduction exceeds the rate of overall plate convergence and are commonly typified by thrust belts with little to no involvement of crystalline basement in thrusting low grade to no metamorphism low topographic elevation little erosion and in some instances an anomalously deep foredeep basin system

brittle tectonothermal evolution in the forsmark area central fennoscandian shield recorded by paragenesis orientation and 40ar 39ar geochronology of fracture minerals in this paper we show how studies of fracture mineral paragenesis their orientation and ar 40 ar 39 geochronology can be applied in order to recognise the brittle tectonothermal evolution in an area samples were selected from nearly 18 km of drill cores from the upper i km of the fennoscandian shield obtained during the site investigation for a repository of spent nuclear fuel in forsmark central sweden four major events of fracturing and or reactivation of fractures associated with fracture mineralisation have been distinguished the first event was characterised by precipitation of epidote quartz and chlorite along preferably sub horizontal and gently dipping fractures or steep wnw ese to nw se fractures precipitation occurred between 1 8 and 1 1 ga possibly during the late stage of the svecokarelian orogeny close to 1 8 1 7 ga the second event is associated with precipitation of hematite stained adularia and albite prehnite laumontite calcite and chlorite preferably along steep ene wsw to nne ssw and nnw sse fractures precipitation occurred around 1107 7 to 1034 3 ma probably due to effects from the sveconorwegian orogeny this event was followed by a period with dissolution of fracture minerals and subsequent precipitation of mainly calcite quartz pyrite and asphaltite during the palaeozoic the formation fluid emanated from an overlying organic rich sedimentary cover precipitation occurred during reactivation of proterozoic fractures but formation of new fractures is also inferred possibly due to far field effects of the caledonian orogeny or elevated hydrostatic pressure due to its foreland basin the latest event is dominated by clay minerals chlorite and calcite along hydraulically conductive fractures these minerals are prominent along sub horizontal and gently dipping fractures but also occur in sets of steeply dipping fractures it is inferred that the hydraulically conductive fractures are proterozoic structures in which mineral precipitation has occurred during a long period however some of the near surface sub horizontal fractures may be quaternary in age c 2009 elsevier b v all rights reserved less

evolution of the pannonian basin system 1 tectonics the carpathian arc formed during cretaceous to miocene time by continental collision between europe and smaller continental fragments following southward and westward subduction of ocean floor during the last stages of thrusting in the outer carpathians a set of discrete basins formed behind the carpathian loop these basins are regions of middle to late miocene extension and are connected to each other and to areas of coeval shortening in the outer carpathian thrust belt by a system of strike slip faults sinistral northeast trending and dextral northwest trending sets of conjugate shears reflect overall east west extension of the intra carpathian region during middle to late miocene time palinspastic reconstruction of the basins indicates about 100 50 km of east west extension across the intra carpathian region during this time we interpret the vienna basin which is superimposed partly on the flysch nappes of the outer west carpathians as the result of thin skinned extensional tectonics above a shallow detachment surface within the crust extension of upper crustal rocks above this detachment was probably accomodated by thrusting of the outermost nappes of the west carpathians over the european platform extension of basins farther inside the carpathian loop probably involved rocks at deeper crustal levels and within the upper mantle the most internally situated basins formed by extensional processes that involved the entire lithosphere thus the depth to which extension occurred seems to be closely related to the proximity of each basin to the active thrust front in the carpathians this can be related to the geometry of the subduction zone extension within the intra carpathian basins began first in the northernmost basins and migrated southward and eastward over a ten million year period palinspastic reconstruction of the basins at three different times during the miocene 17 5 16 5 and 13 0 ma predicts eastward migration of the zone of thrusting and shortening within the carpathian mountains to accomodate the synchronous eastward and southward migration of areas of extension from these reconstructions about 120 60 km of east west shortening is predicted across the outer east carpathians from about 17 5 ma until present both predictions are in good agreement with the timing and magnitude of shortening in the carpathian thrust belt as determined directly from rocks within the belt from this we infer a close relationship for middle to late miocene extension of the intra carpathian region and middle to late miocene crustal shortening within the outer carpathians during middle and late miocene time deformation of the pannonian fragment was dominated by extensional and wrench tectonics except along a narrow zone in the outer carpathian thrust belt middle and late miocene thrusting in the carpathians is interpreted as the result of simple shear caused by relative motion between europe and the overriding pannonian fragment at the subduction boundary rather than of regional compression of lithospheric rocks at depth the initiation of extensional tectonics within the intra carpathian region in middle miocene time can be related to reorganization of major fragment boundaries of the eastern european alpine system

origin chemical and isotopic evolution of formation water in geopressured zones in the pannonian basin hungary abstract in the central part of the pannonian basin we investigate formation waters from two deep sub basins with sedimentary sequences up to 7000 m thick and from fields above basement highs where the total thickness of the sediments is only 2000 m in each study region the depth interval involves the lower lower part of the upper miocene and upper upper part of the upper miocene and pliocene pannonian sediments separated with a widespread aquitard named the algy formation at the top of the lower pannonian however in the fields above basement highs it occasionally contains sand lenses sedimentological discontinuities faults and fractures resulting in a more conductive character we investigate the sources and evolution of the formation waters in two geological settings in sub basins and in fields above an elevated basement we distinguish nahco3 type water in the sub basins and nacl dominated water in the fields above the elevated basement the isotopic composition of most nahco3 type samples indicates a pure paleometeoric origin while a few samples are a mixture of paleometeoric and non meteoric waters the nacl type samples all have a non meteoric contribution we have developed a model for the origin and evolution of the formation water that operates for both water types and both geological conditions the cl dominated water is a mixture of ascending pre pannonian evaporated water and freshening lake pannon water trapped during the late miocene and pliocene sedimentation in the area above the elevated basement where in some places the algy formation is conductive the source and evolution of the nahco3 non meteoric water in the sub basins are similar to those of the nacl water with the main difference being the aquitard character of the algy formation in the sub basins the aquitard consists of siltstone and clay marl which has resulted in overpressure in the layers under the algy formation the ascending pre pannonian water which mixes with in situ pore water squeezed through the compacted clay by overpressure is exposed to microfiltration the cl remains behind and the squeezed water is depleted of the heavier isotopes these processes are shown by recent chemical and isotopic data 18o and d as well as by archival chemical and hydrological data

evidence from chlorin nitrogen isotopes for alternating nutrient regimes in the eastern mediterranean sea abstract nitrogen isotopes of chlorins degradation products of chlorophyll reflect the isotopic composition of nutrient n utilized by marine phytoplankton communities here we show that in sediments of the eastern mediterranean pleistocene and holocene values of 15n for chlorins and total nitrogen vary in concert with a consistent offset of 5 reflecting the fractionation imparted during chlorophyll biosynthesis samples from the integrated ocean drilling program sites 964 and 969 were analyzed at a sampling resolution of 4 10 cm clustered around sapropel events 2 3 4 and 5 100 170 ka in low organic content sediments chlorin values of 0 coincident with total nitrogen values of 5 indicate that the latter reflects the original biomass and is not a consequence of diagenetic isotope enrichment in sapropel horizons the chlorin and total nitrogen values are 5 more negative 5 and 0 respectively resembling previously reported modern day water column particulates 0 we suggest that nutrient conditions in the eastern mediterranean correspond to three scenarios and that the similarity between sapropel and modern day bulk 15n is coincidental organic poor marl sediments formed under oligotrophic conditions where surface productivity resulted from upwelling of atlantic sourced nitrate sapropels were characterized by enhanced diazotrophy that was likely fueled by increased riverine p fluxes to surface waters present day conditions are dominated by anthropogenic n sources these scenarios agree with a model of sapropel formation in which stratification caused by increased fresh water inputs led to n fixation due to p n nutrient imbalance enhanced production combined with stratification promoted and maintained anoxic deep waters consequently increasing organic matter preservation such a model may be relevant to interpreting other episodes of intense organic matter deposition in past oceans

hyperpycnal transport of carbonaceous sediment example from the upper devonian rhinestreet shale western new york u s a abstract the upper devonian rhinestreet shale of the western new york region of the appalachian basin contains centimeter scale composite beds comprised of a thin black shale layer overlain by several cm of gray shale that are interpreted to have been deposited from hyperpycnal turbidity currents evidence for this explanation includes 1 the presence of planar parallel and cross lamination within some layers and 2 zr al profiles consistent with an inversely graded lower unit overlain by normally graded deposits diminished k al values of the inferred hyperpycnites suggest that they were generated during periods of increased precipitation and consequent intensified continental weathering of the source region within the tectonically active acadian highlands the transition to a wetter climate reflected in these deposits perhaps a response to astronomically induced variations in tropical monsoonal dynamics would have increased the frequency and magnitude of floods within the catskill delta complex thereby enhancing the likelihood that hyperpycnal flows would have been produced organic matter contained within the hyperpyncites probably reflects the entrainment of carbonaceous detritus perhaps much of it in the form fecal pellets from estuarine and shallow marine settings during flood related discharges post depositional oxygen depletion within the organic rich sediment and related bacterial sulfate reduction resulted in the precipitation of abundant diagenetic pyrite intense bioturbation of gray shale intercalated with the dark layers suggests that oxygenated conditions prevailed during accumulation of the sturgeon point section alternatively these deposits reflect a history of repeated early diagenetic burn down events that resulted in the strongly reworked nature of the organic lean gray shale and the sharp upper contacts of the black shale layers the present study offers an alternative explanation of thin black shale beds hosted within organic deficient successions beyond models involving marked changes in productivity on the one hand and the establishment of a stratified water column on the other

damage phenomenon and petrophysical properties of sandstones at the phnom bakheng temple angkor cambodia first investigations and possible conservation measures sandstones clay in the form of bricks and laterite are the building materials used by the khmer to construct the imposing and magnificent temples in southeast asia many of these monuments suffer from fracturing sanding contour scaling crust formation and salt weathering the affinity to weathering is closely connected to the type of material two sandstone types classified as feldspathic arenite and quartz arenite of angkor as well as two arkosic sandstones from thailand are described and investigated in this study important petrophysical properties determined for the different sandstones consist of hydric expansion thermal expansion pore radii distribution and ultrasonic velocity different investigations such as capillary water uptake surface hardness hygroscopic water sorption and salt resistance tests were undertaken in the laboratory to characterize the various rock types observations and quantified damage mapping were done onsite at the phnom bakheng temple contour scaling in the form of weathering crusts is one of the main deterioration features observable at the angkor monuments comparisons are made between the building stone the crust material from the phnom bakheng temple and fresh stone material used for restoration significant differences in hydric and especially in thermal expansion of the crust and sandstone have been determined the results seem to indicate that extensional processes occur which can be considered a force for detachment i e contour scaling flaking in an experimental trial the hydric and thermal expansion of the weathering crust and the building stone was significantly reduced by using a weak acid for the crust and a swelling inhibitor for the original building stone

structural evolution of mesozoic peninsular malaysia field evidence from upper palaeozoic and mesozoic strata exposed in peninsular malaysia demonstrates that the structural style degree and orientation of folding axial plane cleavage and faulting in the triassic jurassic and cretaceous rocks of the central basin are remarkably similar in contrast the upper palaeozoic strata especially the carboniferous rocks exposed in the eastern part of the peninsula show multiple phase folding and regional metamorphism unlike anything seen in the mesozoic rocks these observations demonstrate that two important compressional events affected peninsular malaysia one in late permian times and the other in the mid to late cretaceous the late palaeozoic compressional event was a major orogenic mountain building phase with associated emplacement of major permo triassic granite plutons that form the eastern and main ranges no indications were found of the widely reported triassic orogenic compression the palaeotectonic and palaeogeographical implications of these discoveries are important for interpreting the evolution of eastern gondwana and tethys the raub bentong line was an important fault zone active during the mesozoic but does not appear to have been a major tectonic suture since the late palaeozoic we postulate that the permo triassic granites of the eastern belt and those presently exposed in the main range were originally about 30 50 km apart and that triassic and jurassic crustal attenuation and subsidence led to the separation of these two granitic belts by more than 100 km

role of alternating redox conditions in the formation of organic rich interval in the middle devonian marcellus shale appalachian basin usa abstract geochemical isotopic and petrographic analyses were performed on a 30 m core of the marcellus shale obtained from greene county pennsylvania to understand the dominant controls on organic matter deposition in the black shale study units our study suggests that the regeneration of nutrients such as nitrogen n and phosphorous p may have played a key role in the formation of organic carbon oc rich intervals in the marcellus shale the decomposition of organic matter is likely to have released n and p into the water column and the episodic upward mixing of these nutrient enriched waters enhanced primary production the ratios of corg nbulk and corg ptot are significantly higher in the oc rich zone of the core i e defined as toc 4 and located between 2393 and 2406 5 m depth the high corg ptot and corg nbulk ratios of the preserved organic matter may reflect the release of n and p by microbial processes indicating the recycling of nutrients during deposition of the oc rich interval in addition our data show a positive relationships between the corg ptot and corg nbulk ratios and the organic carbon content which indicate that the recycled nutrients may have promoted primary productivity resulting in higher oc accumulation in some intervals the geochemical and stable isotopic results also suggest that the alternating redox conditions in the water mass were favorable for nutrient regeneration highly variable trace metal concentrations e g u mo and v in the oc rich zone and a wide range of 15n and 34spyr values towards the top of the oc rich zone suggest fluctuations between anoxic and suboxic water conditions finally sedimentary features and agglutinated benthic foraminifera in the oc rich zone support the existence of short term fluctuations between suboxic and anoxic conditions near the sediment water interface multiple lines of evidence suggest that nutrient regeneration due to alternating redox conditions may have played an important role in the formation of oc rich intervals in the marcellus shale

paleogene retroarc flexural basin beneath the neogene pannonian basin a geodynamic model abstract the neogene middle miocene recent pannonian basin is superimposed on an earlier paleogene middle eocene early miocene basin complex as a result of back arc extension although the stratigraphy of the latter is very well known due to raw material exploration its formation and structural evolution is much less understood a transtensional origin was generally proposed for the paleogene basin of hungary assuming an origin analogous to that of the overlying neogene pannonian basin we suggest an alternative geodynamic scenario for the development of the paleogene basin complex as we think that the observations are better understood in terms of a retroarc foredeep basin model according to this a flexural basin developed south of the backthrust inner west carpathian units the thrust load resulted in a generally deep underfilled flysch basin during middle eocene early oligocene times in the late oligocene early miocene predominantly shallow marine and continental deposition occurred indicating the gradual cessation of thrusting in the adjacent thrust fold belt and the beginning of molasse sedimentation throughout the whole paleogene a shift can be observed of the bathyal dominantly siliciclastic in the axis of the foredeep and neritic partly carbonate in the foreland flank of the foredeep facies belts this migration of the middle eocene early miocene depocenters of the hpb hungarian paleogene basin to the east northeast in present day coordinates is the result of two processes 1 1 the advancement of backthrusting to the southeast 2 2 along strike shift of thrusting to the northeast while a thin skinned thrust front can be reconstructed for the late eocene buda anticline the diosjeno hurbanovo line is interpreted as the result of a major thick skinned thrusting event at the base of the np24 zone 31 ma the subsidence pattern the distinct depositional environments and the structural observations can be more easily integrated into a flexural basin model than into a wrench basin model based on the flexural basin model of this work the early tertiary western carpathians formed a compressional arc while this arc probably developed above a b subduction zone during the late eocene with a corresponding trench magura a forearc basin central carpathian or podhale and a retroarc flexural basin hungarian paleogene from the early oligocene to the early miocene it was characterized by a subduction with a corresponding peripheral foredeep dukla and silesian and a retroarc flexural basin hungarian paleogene

interpretation of subhorizontal crustal reflections by metamorphic and rheologic effects in the eastern part of the pannonian basin summary the geologic origin of subhorizontal reflections often observed in crustal seismic sections was investigated by establishing metamorphic facies and strength of rocks in depth and correlating these properties to seismic reflection sections from eastern hungary estimation of the depths of metamorphic mineral stability zones utilized the principles developed by fyfe et al and known geothermal data of the area the strength versus depth profile was derived by relating local seismic p wave interval velocities to meissner et al s activation energy the results show that the series of subhorizontal reflections observed in the pannonian basin are a consequence of combined metamorphic and rheologic changes in depths the synthesis of the integrated data set suggests that the retrograde alteration of the pre tertiary basement above the percolation threshold was made possible by the softening effect of shear zones and their water conducting capacity the subhorizontal reflections of highest energy of the consolidated crust below the percolation threshold originate in the depths of greenschist amphibolite and granulite metamorphic mineral facies which were formed in geothermal and pressure conditions similar to those existing today these results imply the overprint of earlier variscan metamorphic sequences of the crust by more recent retrograde metamorphic processes

age of the banda sea eastern indonesia the age of the banda sea is critical for palaeogeographical reconstructions of eastern indonesia assumed ages for its formation range from mesozoic to neogene1 10 however geophysical evidence shows that the banda sea is floored by oceanic crust11 12 with a minimum age of eocene4 evidence for a sequence of events involving continental breakup and the initiation of spreading that led to the formation of the banda sea should be found in the microcontinents around the margins of the sea reinterpretation of the geological history of these microcontinents based on new data reported here from western irian jaya9 13 shows that they separated from gondwana during the jurassic and strongly supports the suggestion of bowin et al 4 that the banda sea is trapped mesozoic oceanic crust of indian ocean affinities

15n 14n variations in cretaceous atlantic sedimentary sequences implication for past changes in marine nitrogen biogeochemistry at two locations in the atlantic ocean dsdp sites 367 and 530 early to middle cretaceous organic carbon rich beds black shales were found to have significantly lower 15n values lower15n 14n ratios than adjacent organic carbon poor beds white limestones or green claystones while these lithologies are of marine origin the black strata in particular have 15n values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools in contrast black organic carbon rich beds at a third site dsdp site 603 contain predominantly terrestrial organic matter and have c and n isotopic compositions similar to organic matter of modern terrestrial origin the recurring15n depletion in the marine derived cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry existing isotopic and other data indicate that the low15n relative abundance is the consequence of pelagic rather than post depositional processes reduced ocean circulation increased denitrification and hence reduced euphotic zone nitrate availability may have led to cretaceous phytoplankton assemblages that were periodically dominated by n2 fixing blue green algae a possible source of this sediment15n depletion lack of parallel isotopic shifts in cretaceous terrestrially derived nitrogen site 603 argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment

the application of isotope and chemical analyses in managing transboundary groundwater resources abstract managing transboundary groundwater resources requires accurate and detailed knowledge of aquifers and groundwater bodies the pannonian basin is the largest intracontinental basin in europe with a continuous succession of more than 7 km of miocene to quaternary sediments and with an average geothermal gradient of about 5 c 100 m geographically the pannonian basin overlaps eight countries hungary romania serbia croatia slovenia austria slovakia and ukraine so the issue of transboundary cold and thermal water resources is regionally very important the t jam bilateral hungarian slovenian hu slo project is the first to apply modern isotopic and chemical analyses in the characterization and correlation of a number of shared groundwater resources in the mura zala sub basin of the pannonian the aims of this work were the identification of groundwater flow paths the delineation of transboundary aquifers based on thermal and cold groundwater geochemical and isotope properties in the mura zala basin and providing input to calibrate a hydraulic numerical model following a common groundwater sampling campaign 24 cold and thermal groundwater samples from seven aquifers were collected for chemical isotope gas and noble gas analyses chemical analyses and d o and c isotopes were used to correlate cross border aquifers a regional groundwater flow is hydrogeologically possible in some aquifers in the mura zala basin and has been confirmed by hydrogeochemistry the ujfalu hu and mura slo formations are a part of the active regional thermal groundwater flow system probably hydraulically separated from the shallower flow system of the ptuj grad slo zagyva and somlo tihany hu formations the thermal water is of meteoric origin reductive and alkaline the predominant water type in the quaternary and pliocene aquifers is ca mg hco3 changing to na hco3 in the main pannonian geothermal aquifer and na cl brine in deeper and older miocene aquifers total dissolved solids and na content generally increase with depth deuterium is in the range 87 to 75 18o from 11 9 to 10 4 while 14c values are less than 6 1 pmc in the samples of the active regional thermal groundwater flow system these and results of noble gas analyses indicate recharge during the pleistocene interglacial period with temperatures around 6 7 c regional thermal water resources are limited and environmental isotopes can be used as an early warning in the management of thermal water

new window on tibetan tectonics the latest reports from the sino french expedition in tibet show a rich and surprising harvest of discovery has not the time come for more open access to this important region

ichnological constraints of palaeoenvironmental and palaeoclimatological features of the middle palaeozoic palaeo asian ocean evidence from the western junggar nw china abstract late devonian to early carboniferous deep sea deposits of the western junggar nw china contain 21 ichnotaxa arenituba verso chamberlain chondrites cf intricatus brongniart chondrites targionii brongniart chondrites isp gordia marina emmons halopoa imbricata torell helminthoidichnites isp helminthopsis cf hieroglyphica wetzel and bromley laevicyclus isp lophoctenium comosum richter multina isp nereites missouriensis weller phycodes cf bilix ksi zkiewicz phycosiphon incertum fischer ooster phycosiphon isp planolites isp cf taenidium thalassinoides isp zoophycos isp undetermined short ridges and undetermined tubular structures they form three typical ichnoassemblages i e the helminthopsis helminthoidichnites arenituba ichnoassemblage characteristic of upper bathyal probably hyperpycnal flow influenced deposits zoophycos nereites phycosiphon ichnoassemblage in typical slope deposits and the phycosiphon nereites ichnoassemblage featuring bottom current influenced lower slope or basin floor muddy deposits they can be ascribed to the cruziana zoophycos and the nereites ichnosubfacies respectively comparison with contemporaneous deep water facies foremost the kulm facies in western and central europe reveals significant loss in the western junggar of otherwise common element dictyodora liebeana geinitz combining the global palaeozoic tectonic evolution we propose that dictyodora was probably originated from peri gondwana terranes and the larvae juveniles of dictyodora producers hadn t migrated to the northern palaeolatitudes open ocean kazakhstan archipelago in the early carboniferous the relatively global distribution of the phycosiphon nereites association indicates efficient larval dispersal of their producers intensive bioturbation in deposits dominated by the phycosiphon nereites ichnoassemblage implies a high level of food supply at certain stratigraphic levels most likely related to surface blooms and enhanced plant detritus input the monsoonal palaeoclimatic model is integrated with the archipelagic palaeogeography to account for the deep sea ichnofauna in the western junggar during the late devonian to early carboniferous the most important factors include seasonal climatic perturbations such as monsoon derived upwelling events and enhanced primary production and efficient food nutrients transport in the dotted island scenario

basinward nitrogen limitation demonstrates role of terrestrial nitrogen and redox control of δ15n in a late devonian black shale the depleted nitrogen isotope values observed in devonian black shales have been ascribed to the dominant role of marine diazotrophic n fixation in providing new reactive n for the productivity that generated the organic matter preserved in these organic rich facies however the emergence of substantial terrestrial ecosystems in the middle to late devonian introduced an additional source of reactive n to shallow epicontinental seas we examined three sites along a deepening transect of the late devonian appalachian basin eastern united states employing element ratios of c n and p degree of pyritization and stable isotope analyses of c n and s in order to determine whether basinward changes in n biogeochemistry and 15 n reflect the dominant source of new reactive n high degrees of pyritization and depleted 34 s indicate a persistently dysoxic to euxinic water column sediment n p rises basinward indicating that p was relatively more abundant than n in the water column with increasing distance from the shore nitrogen isotope values however are very consistently 0 at all three sites despite the evidence of distally increasing n limitation suggesting that terrestrially derived reactive n was an important source of reactive n and that marine n fixation was not sufficient to address the stoichiometric deficit depleted 15 n values in these black shales do not provide a reliable record of diazotrophy rather they are a product of the reducing state of the water column and underlying sediments

biogeochemical controls on black shale deposition during the frasnian famennian biotic crisis in the illinois and appalachian basins usa inferred from stable isotopes of nitrogen and carbon abstract the frasnian famennian biotic crisis is marked by two distinct intervals known as the lower and upper kellwasser events kwes that in many locations are associated with deposition of organic rich shales sedimentary nitrogen and carbon isotopes offer insight into the biogeochemical processing of nutrients production of organic matter and palaeoceanographic conditions during the kwes here we present new bulk nitrogen 15nbulk and organic carbon 13corg isotope data from the late devonian appalachian and illinois basins ab and ib with a focus on intervals encompassing the kwes black shales from the ib and ab including the kwes are 15n depleted 1 0 2 0 and have significantly lower 15nbulk than interbedded grey shales 0 5 4 0 a trend consistent with many instances of black shale deposition in the phanerozoic organic carbon isotopes exhibit the broad positive excursions 3 5 from background that are typical of the kwes globally superimposed over these positive excursions in 13corg are sharp decreases of up to 3 0 within the black shale beds to as low as 30 5 the pattern of 15nbulk and 13corg values suggests that the depth of the chemocline and the degree of water column stratification exert a primary control on both 15nbulk and 13corg during black shale deposition in the context of the frasnian famennian biotic crisis the oscillating redox state and changing temperatures would have likely placed extreme stress on organisms within the marine environment of the ab and ib and may potentially have been a contributing factor to diversity loss over this time period

phases of compression during the evolution of the pannonian basin and its bearing on hydrocarbon exploration abstract progress in understanding the structural evolution of the pannonian basin is reported this has been driven by the application of seismic stratigraphy constrained by magnetostratigraphic data and the recent release of a great amount of hydrocarbon exploration data this has led to a redefinition and better understanding of the syn rift period and style of rifting in addition a complex structural evolution history during the post rift phase has been recognized two compressive events are defined one in the early stage and another in the late stage of evolution the importance of these findings for hydrocarbon exploration includes an improved knowledge of the timing of trap formations and a possible explanation for remarkably variable reservoir pressures in pools of the great hungarian plain

the lhasa terrane record of a microcontinent and its histories of drift and growth article i nfo the lhasa terrane in southern tibet has long been accepted as the last geological block accreted to eurasia before its collision with the northward drifting indian continent in the cenozoic but its lithospheric architecture drift and growth histories and the nature of its northern suture with eurasia via the qiangtang terrane remain enigmatic using zircon in situ u pb and lu hf isotopic and bulk rock geochemical data of mesozoic early tertiary magmatic rocks sampled along four north south traverses across the lhasa terrane we show that the lhasa terrane has ancient basement rocks of proterozoic and archean ages up to 2870 ma in its centre with younger and juvenile crust phanerozoic accreted towards its both northern and southern edges this finding proves that the central lhasa subterrane was once a microcontinent this continent has survived from its long journey across the paleo tethyan ocean basins and has grown at the edges through magmatism resulting from oceanic lithosphere subduction towards beneath it during its journey and subsequent collisions with the qiangtang terrane to the north and with the indian continent to the south zircon hf isotope data indicate significant mantle source contributions to the generation of these granitoid rocks e g 50 90 0 70 and 30 100 to the mesozoic magmatism in the southern central and northern lhasa subterranes respectively we suggest that much of the mesozoic magmatism in the lhasa terrane may be associated with the southward bangong nujiang tethyan seafloor subduction beneath the lhasa terrane which likely began in the middle permian or earlier and ceased in the late early cretaceous and that the significant changes of zircon ehf t at 113 and 52 ma record tectonomagmatic activities as a result of slab break off and related mantle melting events following the qiangtang lhasa amalgamation and india lhasa amalgamation respectively these results manifest the efficacy of zircons as a chronometer u pb dating and a geochemical tracer hf isotopes in understanding the origin and histories of lithospheric plates and in revealing the tectonic evolution of old orogenies in the context of plate tectonics

basement structures underneath the northern south yellow sea basin east china implications for the collision between the north china and south china blocks abstract the south yellow sea basin sysb as the eastern part of the yangtze block has undergone multiple tectonic events since the formation of its basement the north china south china collision affected intensely the structures of the basin the relationship between the deep structures in the basement and collisional orogeny has long been a matter of debate in this paper 2d seismic magmatic gravity and drilling data were integrated to unravel the basement structures in the interpreted seismic sections the basement can be subdivided into three seismic facies the seismic facies i and iii correspond to two basement layers the seismic facies ii is interpreted as shear zones that were formed during the mesozoic collision and exhumation the influence of the north china south china collision propagated from north to south in the sysb according to observations from drill holes and seismic sections the northern part of the basin the yantai depression uplifted during the earlier stage of the collision resulting in the erosion of the upper paleozoic and triassic strata in the middle and southern parts the laoshan uplift and qingdao depression the compression was obviously after that in the yantai depression the exhumation of the qianliyan basement metamorphic complex of the yangtze block occurred gradually the shear zones were initially developed during the collision during early mesozoic the exhumation process of metamorphic rocks lasted till late mesozoic and the jurassic cretaceous strata were deposited in the hanging wall of the northern boundary fault

why are the δ13corg values in phanerozoic black shales more negative than in modern marine organic matter the 13corg values of phanerozoic black shales average 27 whereas those of modern marine organic matter average 20 the black shale isotopic values mimic those of continental organic matter yet their organic geochemical properties mandate that they contain predominantly marine organic matter hypotheses that proposed to explain the low 13c values of black shales include diagenetic losses of isotopically heavier organic matter components releases of isotopically light carbon from methane clathrates or extensive magmatic events greater photosynthetic discrimination against 13c during times of higher atmospheric pco2 and greenhouse climate stratification of the surface ocean that magnified photic zone recycling of isotopically light organic matter although the last possibility seems contrary to the vertical mixing that leads to the high productivity of modern oceanic upwelling systems it is consistent with the strongly stratified conditions that accompanied deposition of the organic carbon rich pliocene pleistocene sapropels of the mediterranean sea because most phanerozoic black shales contain evidence of photic zone anoxia similar to the sapropels well developed surface stratification of the oceans was likely involved in their formation existence of isotopically light land plant organic matter during several episodes of extensive magmatism that accompanied black shale deposition implies massive release of mantle co2 that added to the greenhouse conditions that favored oceanic stratification the 13c depletion common to most phanerozoic black shales apparently resulted from a greenhouse climate associated with elevated atmospheric pco2 that led to a strongly stratified ocean and photic zone recycling of organic matter in augmented by magmatic co2 releases

the frasnian famennian boundary in central and eastern united states abstract the frasnian famennian f f boundary in the northern appalachian basin is found in the hanover shale and equivalent strata where it is locally associated with a black shale interval equivalent to the upper kellwasser interval in europe the boundary is immediately below the dunkirk huron black shale that represents the iie t r cycle transgression in the southern appalachian basin the southern edge of the cincinnati arch and the southeastern illinois basin the f f boundary is at or near the base of the gassaway member of the chattanooga shale or the morgan trail member of the new albany shale or was eroded during the iie t r cycle beginning in the middle triangularis zone in the western illinois basin grassy creek shale michigan basin lachine member of antrim shale and southern continental margin woodford shale the f f boundary is within black shale strata indicative of an earlier development of the iie t r transgression inboard of the appalachian basin or the juxtaposition of the iie t r transgression over the upper kellwasser black shale interval without significant or recognizable lithologic change

nitrogen cycling during the cretaceous cenomanian turonian oceanic anoxic event ii low 15n values ranging from 1 2 to 3 9 and atomic carbon nitrogen c n ratios of 25 50 are characteristic of black shales deposited during the cenomanian turonian boundary interval and oceanic anoxic event ii oae ii an observed antithetic relationship between c n ratios and 15n could suggest a predominance of terrestrially derived organic matter or a diagenetic control on 15n variability shifting bulk 15n values lower however hydrogen indices hi generally 450 and a positive correlation of hi with c n mitigates against a significant terrestrial organic matter fraction high c n values are likely the result preferential degradation of labile n rich compounds during early diagenesis and loss of n as ammonium from sediments through time a hypothetical model that considers the degradation of a 15n enriched labile protein fraction yields only small 1 2 negative shifts in 15n however 15n depletion during diagenesis is contrary to normal isotope kinetics which should result in 15n enrichment of bulk organic matter therefore we conclude that the bulk 15n values in this study reflect primary changes in the nitrogen cycle the 15n data support the hypothesis of expanded nitrogen fixation driven by upwelling of nutrient nitrogen poor phosphorus replete waters during oae ii and from the mid cenomanian to santonian at demerara rise the low 15n values which are significantly lower than bulk 15n values in modern regions where nitrogen fixation is known to be important probably result from a more significant fraction of dissolved inorganic nitrogen being produced by nitrogen fixation during the peak of oae ii a marked shift to lower 15n values is observed this shift possibly reflects greater utilization of 15n depleted ammonium during a chemocline upward excursion cue dominance of low 15n values from other periods of more widespread marine anoxia is likely the result of similar processes

paleoceanographic and paleoclimatic similarities between mediterranean sapropels and cretaceous black shales pliocene quaternary sapropels of the mediterranean sea and mid cretaceous black shales share many distinctive properties organic carbon concentrations that often exceed 5 in both types of sequences record episodes of exceptional accumulation of organic matter although both are rich in marine organic matter they have high c n ratios that mimic those of land plant organic matter which suggests less efficient organic matter recycling than in the modern ocean the coupled presence of isorenieratene derivatives and low 15n values that result from microbial primary productivity indicates that photic zone anoxia existed during their formation and implies strong stratification of the surface ocean enrichments of redox sensitive metals and sediment laminations indicate that anoxia existed deeper in the water column and at the seafloor multiple proxies indicate freshening of surface waters of the mediterranean and imply periods of wetter climate during times of sapropel deposition episodes of black shale deposition similarly coincide with times of wetter climate these comparisons suggest that the wetter climate created similar conditions of surface salinity stratification that enhanced microbial primary production and magnified organic matter export during deposition of both the mediterranean sapropels and mid cretaceous black shales

evaluation of high frequency paleoenvironmental variation using an optimized cyclostratigraphic framework example for c s fe analysis of devonian mississippian black shales central appalachian basin u s a abstract stratigraphic successions are rarely sampled at sufficiently dense spacing to permit evaluation of paleoenvironmental variation at the shortest fundamental frequency operative in the depositional system of interest often because that frequency remains undetermined here we provide an example of a sampling strategy optimized for recovery of high frequency paleoenvironmental signals based on 1 full core analysis using a continuous survey tool such as x radiography followed by 2 fine sampling of selected small scale cycles that record significant short term paleoenvironmental variation we show that this strategy results in recovery of high frequency paleoenvironmental signals that are completely missed by low density sampling protocols permitting key insights into depositional and early diagenetic processes that may otherwise by overlooked the present case study is based on c s fe systematics of the cleveland and sunbury shales which belong to the upper devonian lowermost carboniferous black shale succession of the central appalachian basin in eastern north america in these units the fundamental scale of paleoenvironmental variation is recorded by pervasive decimeter scale 5 to 20 cm thick compositional cycles that are readily visible in outcrop in which high organic layers weather out as resistant ledges we identified these cycles in drillcores using x radiography which proved to be an effective proxy for compositional variation owing to control of bulk density primarily by total organic carbon toc content we then sampled selected dm scale cycles n 21 at a centimeter spacing generating short high resolution multiproxy chemostratigraphic records including toc sulfur and fe concentrations fepy fehr a redox proxy 34spyrite and organic maceral content this analysis yielded the novel insight that all proxies related to authigenic iron sulfides e g stotal and spyrite fetotal and fepyrite fepy fehr and 34spyrite covary negatively with toc within the dm scale cycles we interpret the unusual pattern of negative toc pyrite covariation in the cleveland and sunbury shales to have resulted from differential distributions of labile organic matter om which drove h2s production via microbial sulfate reduction msr and reactive fe which controlled pyrite formation labile om was concentrated in high toc layers whereas reactive fe was concentrated in low toc layers possibly as fe oxyhydroxide coatings on silt grains as a consequence of which part of the h2s generated in the high toc layers diffused upward into the low toc layers before becoming fixed as pyrite this process is evidenced by several contrasts between high toc and low toc layers 1 higher spyrite concentrations and fepy fehr values in the latter 2 concentration of pyrite in the lower part of low toc layers immediately above high toc layers and 3 higher 34spyrite values in the latter reflecting late diagenetic formation of the h2s that diffused upward into the low toc layers to our knowledge this process has not been documented previously in ancient marine shales probably owing to insufficiently high resolution analysis in earlier studies

reconstruction of eastern gondwanaland substantial additions of large continental blocks to the smith et al 1 model of eastern gondwanaland are proposed here largely on the basis of the distribution of key land floras tropical and subtropical marine faunas lithofacies patterns and the identification of a triassic magmatic arc that characterized all the eastern margin of gondwanaland the continental fragments that must have been rifted from northern australia new guinea in the jurassic are identified as south tibet burma thailand malaya and sumatra the original site of deposition of the subtropical permian limestones and tropical late triassic limestones overthrust onto the northern margin of australia by the late cenozoic collision2 is located in this greater gondwanaland palaeomagnetic data except those from malaya3 support this reconstruction

styles of extension in the pannonian basin abstract structural interpretation of reflection seismic profiles reveals distinct modes of upper crustal extension in the pannonian basin while some subbasins in the pannonian basin complex show little extension planar rotational normal faults others are characterized by large magnitude of extension detachment faults metamorphic core complexes gravitational collapse of the intra carpathian domain combined with subduction zone roll back is thought to be the driving mechanism of the neogene back arc extension the very heterogeneously distributed extension is accommodated by transfer faults which bound regions characterized by different polarity direction or amount of extension in cross section these transfer faults are characterized by flower structures typical for strike slip faults seismic stratigraphic interpretations indicate that the non marine post rift sedimentary fill of the pannonian basin can be described in terms of sequence stratigraphy the exceptionally good seismic sequence resolution allows recognition of third order and also fourth order depositional sequences which may reflect the interplay of tectonics and eustasy and milankovitch scale climatic variations respectively

nitrogen isotope compositions of the upper triassic chang 7 shale ordos basin north china implications for depositional redox conditions abstract nitrogen isotope 15n analysis has been used to evaluate depositional redox conditions in well preserved sedimentary systems however fewer n isotope studies have been performed to reconstruct the redox conditions in lacustrine shales in this paper we report the 15n data from the upper triassic chang 7 shale of the ordos basin north china sedimentary 15n values are significantly higher in the chang 73 and the lower part of the chang 72 submembers zone a average 9 4 1 3 than in the upper part of the chang 72 and the chang 71 submembers zone b average 5 4 1 5 previous geochemical measurements i e u and toc p of both zones show wide redox variation however the average values of these redox proxies are relatively higher in zone a than those of zone b combined with lithological aspects of the chang 7 shale our study suggest that zone a was mainly deposited under suboxic bottom water conditions whereas zone b deposits accumulated within an oxygenated water column stable organic carbon isotopes 13corg and total nitrogen tn values of the two zones display little variation that could be attributed to changing organic matter sources and or post depositional alteration of 15n thus we suggest that variations in 15n throughout the chang 7 shale primarily reflect differences in depositional redox conditions and 15n values of the shale that can provide important details regarding the depositional history of unconventional resource plays

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

the triassic of the thakkhola nepal ii paleolatitudes and comparison with other eastern tethyan margins of gondwana during the triassic the thakkhola region of the nepal himalaya was part of the broad continental shelf of gondwana facing a wide eastern tethys ocean this margin was continuous from arabia to northwest australia and spanned tropical and temperate latitudes a compilation of permian triassic and early jurassic paleomagnetic data from the reconstructed gondwana blocks indicates that the margin was progressively shifting northward into more tropical latitudes the thakkhola region was approximately 55 s during late permian 40 s during early triassic 30 s during middle triassic and 25 s during late triassic this paleolatitude change produced a general increase in the relative importance of carbonate deposition through the triassic on the himalaya and australian margins regional tectonics were important in governing local subsidence rates and influx of terrigenous clastics to these gondwana margins but eustatic sea level changes provide a regional and global correlation of major marine transgressions prograding margin deposits and shallowing upward successions a general mega cycle characterizes the triassic beginning with a major transgression at the base of the triassic followed by a general shallowing upward of facies during middle and late triassic and climaxing with a regression in the latest triassic

chemical osmosis reverse chemical osmosis and the origin of subsurface brines abstract calculations using recently tabulated values of density and osmotic coefficient for nacl h2o indicate that overpressuring is more than adequate to overcome chemical osmosis and drive reverse chemical osmosis in sedimentary sequences the best demonstrated overpressuring mechanism is the rapid deposition of fine grained sediments the dehydration of gypsum contributes to overpressuring for brief time intervals at shallow depths whereas water evolved during the protracted conversion of smectite to illite is probably a subordinate but continuing contributor to overpressuring at greater depth occurrences of overpressuring in sedimentary sections older than cretaceous indicate that post depositional mechanisms such as tectonic compression and aquathermal pressuring must also operate the latter may be of major importance in geothermal areas with adequate low permeability seals and a nontrivial contributor in areas of normal geothermal gradient because of shales that sharply decrease normal fluid flow the strongest arguments for the importance to present day brine compositions of membrane concentration of sea water solutes are 1 1 the correlation of d values of water molecules of pore fluid with those of local meteoric water 2 2 the need for major sources of mg2 and cl in apparently evaporite free basins even where dissolution of halite is a major contributor of solute reverse chemical osmosis still operates to leak relatively dilute water of the associated diagenetic chemical reactions that of mg2 with limestone to form dolomite is particularly effective in generating concentrated cl brines rich in ca2 it decreases the concentration of mg2 increases that of ca2 and decreases those of both so42 and co32 by precipitating caco3 and caso4 because of the ca2 common ion effect

changes of palaeoenvironmental conditions recorded in late devonian reef systems from the canning basin western australia a biomarker and stable isotope approach abstract although the late devonian extinctions were amongst the largest mass extinction events in the phanerozoic the causes nature and timing of these events remain poorly restrained in addition to the most pronounced biodiversity loss at the frasnian famennian f f boundary and the end famennian there were also less extensively studied extinction pulses in the middle to late givetian and the frasnian here we used a combination of palynological elemental molecular and stable isotope analyses to investigate a sedimentary record of reef systems from this time period in the canning basin western australia the acquired data generally showed distinct variations between sediments from i the time around the givetian frasnian g f boundary and ii later in the frasnian and indicated a distinct interval of biotic stress particularly for reef builders in the older sediments alterations of pristane phytane ratios gammacerane indices chlorobi biomarkers dkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column simultaneous excursions in 13c profiles of carbonates organic matter om and hydrocarbons in the older sediments reflect the stratification induced enhancement of om recycling by sulfate reducing bacteria alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans mttcs and perylene indicate an increased terrigenous nutrient input via riverine influx which would have promoted stratification phytoplankton blooms and the development of lower water column anoxia the detected palaeoenvironmental conditions around the g f boundary may reflect a local or global extinction event our data furthermore suggest a contribution of the higher plant expansion and photic zone euxinia to the late devonian extinctions consistent with previous hypotheses furthermore this work might contribute to the understanding of variations in devonian reef margin and platform top architecture relevant for petroleum exploration and development in the global devonian hydrocarbon resources

postglacial early permian late sakmarian early artinskian shallow marine carbonate deposition along a 2000 km transect from timor to west australia abstract late sakmarian to early artinskian early permian carbonate deposition was widespread in the marine intracratonic rift basins that extended into the interior of eastern gondwana from timor in the north to the northern perth basin in the south these basins spanned about 20 of paleolatitude approximately 35 s to 55 s this study describes the type section of the maubisse limestone in timor leste and compares this unit with carbonate sections in the canning basin nura nura member of the poole sandstone the southern carnarvon basin callytharra formation and the northern perth basin fossil cliff member of the holmwood shale the carbonate units have no glacial influence and formed part of a major depositional cycle that in the southern basins overlies glacially influenced strata and lies a short distance below mudstone containing marine fossils and scattered dropstones perhaps indicative of sea ice in the south marine conditions became more restricted and were replaced by coal measures at the top of the depositional sequence in the north the carbonate deposits are possibly bryozoan crinoidal mounds whereas in the southern basins they form laterally continuous relatively thin beds deposited on a very low gradient seafloor at the tops of shale limestone parasequences that thicken upward in parasequence sets all marine deposition within the sequence took place under very shallow inner neritic conditions and the limestones have similar grain composition bryozoan and crinoidal debris dominate the grain assemblages and brachiopod shell fragments foraminifera and ostracod valves are usually common tubiphytes ranged as far south as the southern carnarvon basin albeit rarely but is more common to the north gastropod and bivalve shell debris echinoid spines solitary rugose corals and trilobite carapace elements are rare the uniformity of the grain assemblage and the lack of tropical elements such as larger fusulinid foraminifera colonial corals or dasycladacean algae indicate temperate marine conditions with only a small increase in temperature to the north the depositional cycle containing the studied carbonate deposits represents a warmer phase than the preceding glacially influenced asselian to early sakmarian interval and the subsequent cool phase of the mid artinskian that is followed by significant warming during the late artinskian early kungurian the timing of cooler and warmer intervals in the west australian basins seems out of phase with the eastern australian succession but this may be a problem of chronostratigraphic miscorrelation due to endemic faunas and palynofloras

sedimentology palaeoecology and palaeoenvironmental evolution of the 1985 lhasa to golmud geotraverse vertical and horizontal measurements of almost 30 km of sections were made along the geotraverse route at 113 localities ranging in age from ordovician to tertiary over 280 palaeocurrent measurements were taken and 200 thin sections were studied ordovician strata occur only in the kunlun terrane w here thick metamorphosed sequences of elastics and carbonates occur these are tentatively interpreted as platform margin and slope deposits during carboniferous times in the kunlun terrane transgressive late dinantian marine limestones with tropical to subtropical eurasian reefoidal faunas overlie fluviatile redbeds derived from an unroofed orogenic belt the lhasa terrane contains shelf basin elastics with low diversity faunas succeeded by thick late carboniferous early permian glacio marine mixtites deposited by iceberg meltout permian carbonate ramp and shelf facies with reefoidal developments occur over both the lhasa and qiangtang terranes with coal bearing elastics and fluviatile redbeds also occurring in the latter

arsenic iron and organic matter in sediments and groundwater in the pannonian basin hungary in the central part of the pannonian basin factors controlling the distribution of as in sediments and groundwater of the upper 500 m were studied in core samples the amounts of as fe and mn extractable with hydroxylamine hydrochloride nh2oh hcl in 25 acetic acid the proportion of the 0 063 mm size fraction and the sediment organic c corg contents were measured in the groundwaters concentrations of as humic substances and selected major chemical components were determined in most core samples extractable fe as feooh and corg are correlated but some samples have excess fe or organic matter in cases where either excess fe or excess organic matter is found the amount of as is also elevated the spatial distribution of as in the groundwater and the lack of a consistent correlation of as with a single component indicate that there is no single factor controlling the concentration of dissolved as over the entire study area the only consistent feature is enrichment of as relative to fe in the groundwater compared to the sediments this suggests that the dissolution of fe minerals which primarily adsorb as is not congruent in reducing conditions fe iii oxyhydroxides together with adsorbed as dissolve and siderite with little or no as precipitates when sub regions are separated and studied individually it can be shown that hydrogeological features of the sediments the proportions of fe minerals and sedimentary organic matter and the concentration of dissolved humic materials all influence the accumulation and mobilization of as the significance of the different mobilizing processes however and the mean concentration of as is different in the recharge through flow and discharge areas

the origin and pre cenozoic evolution of the tibetan plateau different hypotheses have been proposed for the origin and pre cenozoic evolution of the tibetan plateau as a result of several collision events between a series of gondwana derived terranes e g qiangtang lhasa and india and asian continent since the early paleozoic this paper reviews and reevaluates these hypotheses in light of new data from tibet including 1 the distribution of major tectonic boundaries and suture zones 2 basement rocks and their sedimentary covers 3 magmatic suites and 4 detrital zircon constraints from paleozoic metasedimentary rocks the western qiangtang amdo and tethyan himalaya terranes have the indian gondwana origin whereas the lhasa terrane shows an australian gondwana affinity the cambrian magmatic record in the lhasa terrane resulted from the subduction of the proto tethyan ocean lithosphere beneath the australian gondwana the newly identified late devonian granitoids in the southern margin of the lhasa terrane may represent an extensional magmatic event associated with its rifting which ultimately resulted in the opening of the songdo tethyan ocean the lhasa northern australia collision at similar to 263 ma was likely responsible for the initiation of a southward dipping subduction of the bangong nujiang tethyan oceanic lithosphere the yarlung zangbo tethyan ocean opened as a back arc basin in the late triassic leading to the separation of the lhasa terrane from northern australia the subsequent northward subduction of the yarlung zangbo tethyan ocean lithosphere beneath the lhasa terrane may have been triggered by the qiangtang lhasa collision in the earliest cretaceous the mafic dike swarms ca 284 ma in the western qiangtang originated from the panjal plume activity that resulted in continental rifting and its separation from the northern indian continent the subsequent collision of the western qiangtang with the eastern qiangtang in the middle triassic was followed by slab breakoff that led to the exhumation of the qiangtang metamorphic rocks this collision may have caused the northward subduction initiation of the bangong nujiang ocean lithosphere beneath the western qiangtang collision related coeval igneous rocks occurring on both sides of the suture zone and the within plate basalt affinity of associated mafic lithologies suggest slab breakoff induced magmatism in a continent continent collision zone this zone may be the site of net continental crust growth as exemplified by the tibetan plateau c 2012 international association for gondwana research published by elsevier b v all rights reserved

a global marine fixed nitrogen isotopic budget implications for holocene nitrogen cycling 1 a nitrogen stable isotopic model was constructed in order to constrain the holocene marine fixed nitrogen budget the primary sources and sinks considered were riverine and atmospheric sources nitrogen fixation sedimentary and water column denitrification and sediment burial the source budget was found to be insensitive to changes in nitrogen fixation rates and thus could not be used to constrain this term however the isotopic value of fixed nitrogen losses was very sensitive to the amount of sedimentary denitrification if the isotopic value of marine fixed nitrogen has not changed during the holocene as supported by sedimentary records then in order to balance the isotopic value of sinks and sources approximately 280 tg n yr 1 of sedimentary denitrification is required if such a high rate of denitrification has been sustained throughout the holocene it implies that present day estimates of marine nitrogen fixation are grossly underestimated it also implies that the marine nitrogen budget has a residence time of less than 2000 years

geochemistry and arsenic behaviour in groundwater resources of the pannonian basin hungary and romania abstract groundwater resources in the pannonian basin hungary romania croatia and serbia are known to contain elevated naturally occurring as published estimates suggest nearly 500 000 people are exposed to levels greater than the eu maximum admissible concentration of 10 g l in their drinking water making it the largest area so affected in europe in this study a variety of groundwaters were collected from romania and hungary to elucidate the general geochemistry and identify processes controlling as behaviour concentrations ranged from so 4 2 reduction containing low as levels so 4 2 ongoing so 4 2 reduction will release s2 removing as from solution either by the formation of as sulfides or from sorption onto fe sulfide phases in methanogenic waters as released by reductive dissolution is not removed from solution and can rise to the high levels observed levels of organic c are thought to be the ultimate control on the redox conditions in these 2 groups high levels of organic c as found in group 1 would quickly exhaust any so 4 2 present in the waters driving the system to methanogenesis and subsequent high levels of as group 2 has much lower concentrations of organic c and so so 4 2 is not exhausted therefore as levels in waters of the pannonian basin are controlled not by release but by retention mechanisms ultimately controlled by levels of toc and so 4 2 in the waters d and 18o analysis showed that groundwaters containing elevated as dated mostly from the last ice age and are sourced from late pliocene to quaternary aquifers the importance of toc and retention capabilities of so 4 2 reduction have only previously been suggested for recent holocene sediments and groundwater most notably those in se asia as these are the most likely to contain the right combination of factors to drive the system to a redox situation leading to high aqueous as concentrations in contrast it is shown here that a much older system containing as bearing fe oxides also has the potential to produce elevated levels of as if the toc is suitable for the microbial population to drive the system to the correct redox situation and so 4 2 is either absent or wholly consumed