unified imaging of multichannel seismic data combining traveltime inversion and prestack depth migration imaging 2d multichannel land seismic data can be accomplished effectively by a combination of traveltime inversion and prestack depth migration psdm referred to as unified imaging unified imaging begins by inverting the direct arrival times to estimate a velocity model that is used in static corrections and stacking velocity analysis the interval velocity model from stacking velocities is used for psdm the stacked data and the psdm image are interpreted for common horizons and the corresponding wide aperture reflections are identified in the shot gathers using the interval velocity model the stack interpretations are inverted as zero offset reflections to constrain the corresponding interfaces in depth the interval velocity model remains stationary we define a coefficient of congruence j that measures the discrepancy between horizons from the psdm image andtheir counterparts from the zero offset inversion a value of unity for j implies that the interpreted and inverted horizons are consisten

massive recrystallization of low mg calcite at high temperatures in hydrocarbon source rocks implications for organic acids as factors in diagenesis we document massive recrystallization of low mg calcite lime mudstone source rocks at moderately high temperatures in the smackover formation of mississippi this process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons secondary porosity generation in reservoirs and global environmental change this interpretation is based on contrasting the following petrographic and bulk rock geochemical characteristics of organic poor vs organic rich lime mudstones

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

volcanic rocks as prolific gas reservoir a case study from the qingshen gas field in the songliao basin ne china abstract the qingshen gas field with over 100 billion cubic meters bcms of proven gas reserves was discovered recently in the upper jurassic lower cretaceous strata of the songliao basin northeastern china the stratigraphic relationships and gas chemical compositions indicate mixed gas sources dominantly from the upper jurassic lower cretaceous coals and associated dark mudstones underlying the gas reservoirs with minor contribution from deep inorganic sources the gas reservoirs consist mainly of volcanic rocks rhyolite and tuff with some production also from the conglomerate gas charge into these largely volcanic rock reservoirs appears to coincide with the peak gas generation in the deep upper jurassic lower cretaceous coal measures the presence of several thick lacustrine mudstone beds in the upper cretaceous strata as regional caprocks and relatively mild structural deformation since the late cretaceous are among the favorable conditions for the preservation of large volume of natural gases in these relatively deep gas reservoirs the gas yields are the highest in the paleomorphological highs where fractures and secondary porosity are well developed in the gas reservoirs

micrometer scale carbon isotopic study of bitumen associated with athabasca uranium deposits constraints on the genetic relationship with petroleum source rocks and the abiogenic origin hypothesis abstract in situ analytical techniques fourier transform infrared microspectroscopy ftir and ion microprobe have been used to unravel the origin of solid bitumen associated with the uranium deposits of athabasca saskatchewan canada both aliphaticity and carbon isotopic compositions within the samples are heterogeneous but spatially organized in concentric zonations at the micrometer scale finally the 13 c values are positively correlated to the aliphatic contents over an extremely large isotopic range from 49 to 31 we infer that this positive correlation may be related to the carbon isotopic fractionations associated with the synthesis of bitumen through the catalytic hydrogenation of co 2 rather than the result of pre existing petroleum product precipitation and or alteration such as radiolysis this explanation is consistent with i published results of abiogenic synthesis experiments in which the differences in 13 c values between saturated and unsaturated hydrocarbons range from 2 and 19 in contrast to the differences systematically observed in conventional bitumen and petroleum ranging from 0 to 4 ii the absence of a similar positive correlation between aliphatic contents and 13 c values in the other bitumen analyzed in the present study for which a biogenic origin has been unequivocally established samples from oklo gabon and lodeve france uranium deposits iii the presence of co 2 and h 2 in the gas phase of fluid inclusions in the athabasca uranium deposits h 2 resulting from water radiolysis the present results suggest that the 13 c vs aliphaticity correlation could be used as a criterion to discriminate between abiogenic vs biogenic origin of macromolecular organic matter

late cretaceous cenozoic tectonic sedimentary evolution and u enrichment in the southern songliao basin abstract late cretaceous cenozoic tectonic sedimentary evolution is fundamental to u uranium migration and u enrichment in the southern songliao basin northeast china to establish the genetic connection between tectonic sedimentary evolution and u enrichment this paper presents a mineralogical study apatite fission track aft analysis and sem cl analysis of quartz grains two stages of mineralization were proposed including the u pre enrichment stage during the late cretaceous and the ore forming stage during the cenozoic based on the density plots of the aft ages paleoclimate studies and sem cl analysis of quartz grains it is inferred that the u pre enrichment was closely related to the rapid uplift of the great xing an range and the zhangguangcai range and the o2 rich atmosphere during 97 90 ma in the southern songliao basin the o2 rich atmosphere increased u mobility and led to the formation of red beds during the late cretaceous which widely developed u pre enrichment in the basins of northeast china the mineralogical study reveals that the qianjiadian uranium deposit developed in two stages the diagenetic process experienced the transition from early alkaline to late acidic conditions to promote the stage i mineralization u pre enrichment the dominant occurrence spaces for u were the dissolution pores of quartz tightly packed with calcite cement u enrichment during alkaline ambient conditions was mainly via adsorption with the increase of the buried depth the early alkaline diagenesis returned to acidic conditions due to the abundant organic material u vi was reduced to pitchblende due to the reducing capacity of the organic matter om stage ii ore forming stage mineralization was strictly related to the hydrocarbon re concentration according to the thermal history study of the cc1 and q2 boreholes the southern songliao basin experienced four episodes of rapid uplift during the cenozoic at 83 80 ma 68 52 ma 33 23 ma and 8 ma respectively the cenozoic uplifts led to hydrocarbon migration at 65 ma 23 ma and present the re concentration of hydrocarbon prompted the u mineralization in the qianjiadian uranium deposit in the southern songliao basin during the stable period of tectonic movements the reducing conditions caused by hydrocarbons promoted u mineralization the dominant spaces of coffinite were intergranular dissolved pores formed during the transformation from the feldspar to the kaolinite under acidic conditions the post rift phase and structural inversion phase directly controlled the u pre enrichment stage and the ore forming stage respectively overall the tectonic sedimentary evolution played an important role in controlling the u leaching from granites the dominant occurrence spaces and u recycling

seismic b value and the assessment of ambient stress in northeast india seismicity data of northeast india recorded between 1986 and 1999 by a local network are analysed for estimation of b values based on the obtained values viz low b 0 5 moderate 0 5 0 7 the study area is classified into different seismic domains an assessment of stress level is also carried out in identifying seismic domains seismic activities though mostly confined in some sectors are presumably triggered by mutual interaction of the shillong plateau mikir hills indo burman ranges and the easternmost part of the himalayas and the contributions from deep seated fractures cannot be ignored the results resemble the seismic character of a foreland setting adjacent to a convergent margin the b values estimated for 240 square grids of dimension 0 6 0 6 over five seismic domains indicate wide variation an analysis of cumulative seismic moment release m o in different layers also indicates an anomaly in reference to the total seismic energy budget of the five zones the lower b value and higher m o recorded at relatively lower depth 30 km towards the southwest of the study area might be associated with upward bulging of a strong lithosphere the bulging is perhaps regionally compensated by the downward flexing of the descending indian lithosphere beneath the upper assam area features unequivocally observed in any foreland setup towards the north and east of the study area random variations of in both b value and m o along the converging zone suggest a varied tectonic environment with active interaction between the tectonic elements in these areas

pop up structure in massive carbonate hosted fold and thrust belt insight from field mapping and 2d kinematic model in the central apennines abstract fold and thrust belts are characterized by the occurrence of foreland verging thrusts and antithetic backthrust which develop in the hangingwall of thrust sheets both thrust and backthrust bound the so called pop up structure which is a deformed zone characterized by thrust and backthrust related anticlines pop up structures mainly develop in fold and thrust belts characterized by a multilayered sedimentary sequence consisting of limestones marls and shales deformed above a weak decollement such as evaporites however in this work we combine field mapping stratigraphic constrains and structural analysis with 2d kinematic forward modeling to document a pop up structure developed within limestones dolostones deformed above a strong decollement consisting of dolostones in the central apennines italy in particular we describe a sw verging anticline and a ne verging anticline in the sw and ne margin of the serra lunga ridge respectively such folds were generated by a ne dipping backthrust and by sw dipping forethrust respectively therefore we suggest that the serra lunga ridge represents a pop up structure showing geometries similar to other pop up structures observed within fold and thrust belts characterized by a multilayered sedimentary sequence in addition backlimb tilting of backthrust related anticlines generates the forelandward dipping monoclines observed within thrust sheets in the central apennines and in several fold and thrust belts worldwide

deformation and kinematic evolution of the subsurface structures zagros foreland fold and thrust belt northern dezful embayment iran the dezful embayment is located in the foreland part of the zagros fold and thrust belt structural style of folding and thrusting vary in the dezful embayment in this study balanced cross sections and subsurface data including 2d seismic profiles and wells data decoded structural style of the subsurface structures in the northern dezful embayment presence of the multiple decollement horizons is the main controlling factor of the structural style in this area the subsurface anticlines have been formed between two main decollement horizons which include the miocene gachsaran formation as upper decollement and permian dashtak evaporites and lower cretaceous garau shales as the middle decollement horizons geometry of the subsurface anticlines differs much vertically and horizontally growth strata indicate folding is started in middle miocene time in this region anticlines formed as open wide and disharmonic structures active processes in the evolution of anticlines are limb rotation and hinge migration which was resulted in increase of inhomogeneous shortening rate more shortening rate indicates more structural relief in anticlines these anticlines are formed as a detachment folds in initiation and then during their evolution converted to fault propagation fold and fault bend fold final geometric shape of these anticlines depends on the geometry of thrusts propagation that formed in the forelimb

structural style and kinematic analysis of folding in the southern dezful embayment oilfields sw iran abstract compression of a region containing multiple detachment layers produces large scale disharmonic folding where individual competent units separated by detachment fold independently within the succession here we present a case study of the kinematic evolution of three subsurface structures the karanj paranj and parsi oilfields bounded by multiple detachments located in the southern dezful embayment a major petroleum province of the zagros fold thrust belt in sw iran interpretation of seismic sections and the construction of corresponding balanced cross sections reveals different geometries along the folds and the complete decoupling of these structures from the surface geology this is controlled by the reactivation of basement faults and flow of the gachsaran incompetent units miocene as the upper detachment and the kazhdumi upper cretaceous pabdeh gurpi and dashtak formations as the middle detachments respectively detachment folding with limb rotation started in the middle miocene and continued with the migration of the basal detachment horizon equivalent hormuz series into the core of the anticlines flow of both the basal and upper detachments continued until no more material is available whereupon the shortening is accommodated by fault development the development of a decoupled disharmonic folding style was controlled by the upper detachment surface through migration from the crests of the anticlines to the synclinal areas and by the reactivation of the basement faults from nw to se part of the area the total shortening amounts are changed between 21 and 12

apatite fission track analysis apatite fission track aft analysis has been widely used during the past 30 years to constrain the low temperature thermal histories of many igneous metamorphic and sedimentary rocks in a wide range of geological settings applicable geological settings include orogenic belts rifted margins faults sedimentary basins cratons and mineral deposits the types of geologic problems that can be addressed include the timing and rates of tectonic events sedimentary basin evolution the timing of hydrocarbon generation and ore mineralization the absolute age of volcanic deposits the effects of major climatic changes on the near surface geothermal gradient and long term landscape evolution early work by naeser 1967 and wagner 1968 1969 first established the basic procedures that enabled the fission track dating method to be applied routinely to these geologic problems fleischer et al 1975 summarized the early studies of the broader discipline of nuclear track detection in different solid state materials more recent comprehensive overviews of fission track applications have been provided by naeser and mcculloh 1989 wagner and van den haute 1992 gallagher et al 1998 van den haute and de corte 1998 dumitru 2000 and gleadow et al 2002 etched natural fission tracks in several apatite grains are shown in figure 1 successful aft analysis is limited by the following 1 the availability of apatite from which useful aft data can be obtained often due to a lack of apatite of sufficient grain size and quality within available rock types or alternatively the lack of available rock samples due to minimal outcrop exposure or other reasons 2 economic considerations in terms of the time and money required to obtain sufficient aft data 3 the inherent limitations of aft data to resolve geological thermal history information often related to limited numbers of accumulated spontaneous fission tracks due to

application of a ramp flat fault model to interpretation of the naga thrust and possible implications for petroleum exploration along the naga thrust front the assam arakan thrust belt extends along the india myanmar border from the chinese border on the north to the bay of bengal on the south tertiary nonmarine sediments dominate the stratigraphy within the frontal zone of this fold and thrust belt thrust fault flats occur in the upper barail group coaly interval and ramps are localized by preexistent normal faults and stratigraphic discontinuities as a result the frontal zone of the thrust belt is characterized by multiscale imbricate structures the jaipur anticline occurs at the foreland edge of the naga thrust imbricate zone at the northeastern end of the assam valley application of flat ramp geometric models with a limited data set from the jaipur anticline allows creation of geometrically viable models for interpreting the general structure of the jaipur anticline and for developing hydrocarbon exploration leads the results of this method indicate that 1 the proven productive foreland trend extends several kilometers beneath the naga thrust and 2 zones of high dip in the thrust belt mark the location of prospect leads probably related to local thrust imbrication the method provides a testable process of identifying prospective areas therefore it can minimize exploration expense and optimize exploration planning

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

magnetostratigraphy of the neogene siwalik group in the far eastern himalaya kameng section arunachal pradesh india abstract the siwalik group was deposited from the mid miocene to the pliocene in the foreland of the himalaya and records the unroofing history of the mountain belt in this study we provide the first magnetostratigraphic data for the eastern himalayan foreland basin we analyzed two sections of the lower to upper siwalik group along the kameng river in arunachal pradesh india magnetostratigraphic data were acquired from 395 sites within a 5 8 km thick molassic series thermal demagnetization and magnetic rock property analyses indicate a relatively low temperature 150 340 c characteristic remanent magnetization chrm yielding reliable primary directions carried by iron sulfides such as greigite the results show local counter clockwise rotation of the thrust sheets which is consistent with partitioning of arc normal and left lateral strain along the himalaya nineteen polarity zones have been identified in the two sections detrital fission track data from the top and bottom of the sections are used to constrain correlations with the geomagnetic polarity time scale gpts from chron c5ar 1n to chron c2an 2n from these results we propose that the siwalik formation in arunachal pradesh was deposited between 13 and 2 5 ma the transition between the lower and middle siwaliks is dated at about 10 5 ma and the middle to upper siwaliks transition is dated at 2 6 ma these results coupled with sedimentological observations suggest that the eastern himalayan chrono stratigraphic record is nearly synchronous with that analyzed in other parts of the neogene himalayan foreland basin nevertheless some differences in the evolution of the sedimentation rate and in the thickness of the middle siwaliks suggest that indian plate flexure in the east is different from that observed in other parts of the indian foreland basin and could be affected by the presence of the shillong plateau to the south

sedimentation and tectonics of the sylhet trough bangladesh the sylhet trough a sub basin of the bengal basin in northeastern bangladesh contains a thick fill 12 to 16 km of late mesozoic and cenozoic strata that record its tectonic evolution stratigraphic sedimentologic and petrographic data collected from outcrops cores well logs and seismic lines are here used to reconstruct the history of this trough the sylhet trough occupied a slope basinal setting on a passive continental margin from late mesozoic through eocene time subsidence may have increased slightly in oligocene time when the trough was located in the distal part of a foreland basin paired to the indo burman ranges oligocene fluvial deltaic strata barail formation were derived from incipient uplifts in the eastern himalayas subsidence increased markedly in the miocene epoch in response to western encroachment of the indo burman ranges miocene to earliest pliocene sediments of the surma group were deposited in a large mud rich delta system that may have drained a significant proportion of the eastern himalayas subsidence rates in the sylhet trough increased dramatically 3 8 times from miocene to pliocene pleistocene time when the fluvial tipam sandstone and dupi tila formation were deposited this dramatic subsidence change is attributed to south directed overthrusting of the shillong plateau on the dauki fault for the following reasons 1 pliocene and pleistocene strata thin markedly away from the shillong plateau consistent with a crustal load emplaced on the northern basin margin 2 the shillong plateau is draped by mesozoic to miocene rocks but pliocene and younger strata are not represented suggesting that the massif was an uplifted block at this time 3 south directed overthrusting of the shillong plateau is consistent with gravity data and with recent seismotectonic observations sandstone in the tioam has a marked increase in sedimentary lithic fragments compared to older rocks reflecting uplift and erosion of the sedimentary cover of the shillong plateau if the dauki fault has a dip similar to that of other himalayan overthrusts then a few tens of kilometers of horizontal tectonic transport would be required to carry the shillong plateau to its present elevation uplift of the shillong plateau probably generated a major 300 km westward shift in the course of the brahmaputra river

morphotectonic evolution of the majuli island in the brahmaputra valley of assam india inferred from geomorphic and geophysical analysis abstract the majuli island located in the upper reach of the brahmaputra valley in assam india has reduced in its areal extent from 787 9 km 2 to 508 2 km 2 during the period 1915 2005 35 5 reduction this amounts to severe average erosion of 3 1 km 2 yr all efforts so far to save the island have failed to achieve the desired redress the engineering approach of save majuli action plans has focused on quarantining the island from the influence of the brahmaputra river rather than designing long term process based solutions anchored on proper understanding of evolution of the relic island the existing geomorphic model for the evolution of the majuli island related its genesis to the great earthquake m 8 7 in 1750 during which a much smaller palaeo brahmaputra developed an anabranch and captured the burhi dihing river the intermediate land locked area thereby became the majuli island that is constituted primarily of the older floodplain deposits we demonstrate that the evolution of the majuli island has been influenced by fluvial morpho dynamics as well as basement configuration and tectonic controls thus the landform called the majuli island cannot be explained as a simple fluvial geomorphic feature rather it represents an outcome of tectono geomorphic process having strong subsurface control we have investigated the influence of geomorphic parameters including channel belt area chb channel belt width w braid bar area bb channel area ch thalweg changes and bankline migration on the trend of erosion of the majuli island integration of geophysical evidence from seismic data and the surface morphological changes suggest that the majuli island and other similar landforms represent structural highs morpho tectonic evolution of these islands has involved three stages pre bypass uplift majuli formation and abandonment the majuli island in the brahmaputra valley is presently passing through the abandonment stage and is gradually being incorporated within the flood plain of the valley

improved identification of pay zones through integration of geochemical and log data a case study from upper assam basin india the upper paleocene lower eocene clastic reservoirs constitute one of the most important hydrocarbon producing horizons in the upper assam basin of northeast india these reservoirs are characterized by the presence of 1 normal gravity oil 23 31 api 2 low to intermediate gravity oil 13 23 api and 3 gas and light oil condensate 31 api the sandstone reservoirs show complex wire line log signatures which are commonly misleading the main impediments to understanding the nature of reservoir fluid include 1 distinguishing low gravity intermediate gravity and normal gravity oil bearing zones and 2 resolving the problem of density rhob neutron porosity nphi crossover for gas bearing as well as oil bearing reservoirs geochemical analyses of sidewall core extracts by thin layer chromatography with flame ionization detection tlc fid and gas chromatography gc provide valuable cost effective input for reservoir fluid characterization the important parameters needed to identify the nature and composition of the reservoir fluid include 1 the bulk composition of the sidewall core extract i e saturated hydrocarbons aromatic hydrocarbons and resins asphaltenes 2 amount of extract in mg g of rock 3 gc fingerprint and 4 the ratio of pristane to n c17 these parameters integrated with geological and geophysical wire line logs evidence yield more accurate and reliable formation evaluation criteria the technique is simple and inexpensive and may find application as an additional formation evaluation tool in any geological setting

seismic imaging of the naga thrust using multiscale waveform inversion this case study images the structural features related to the naga thrust fault northeast india using a combination of multiscale waveform inversion and prestack depth migration psdm the waveform model and the psdm image complement each other the former provides a physical property map p wave velocity model and the latter provides a structural image the velocity model encompassing the starting model for waveform inversion is constructed using joint inversion of first and reflected traveltimes the 4 8 hz data are inverted consecutively in 1 hz bandwidths to yield the final waveform model which in turn is used for psdm the psdm image and the waveform model are consistent with the lithological interpretation of an inline exploratory well when interpreted jointly the psdm image and the waveform model reveal the presence of a conjugate fault system in the naga thrust and fold belt

hydrocarbon migration and accumulation in the upper cretaceous qingshankou formation changling sag southern songliao basin insights from integrated analyses of fluid inclusion oil source correlation and basin modelling abstract the upper cretaceous qingshankou formation acts as both the source and reservoir sequence in the changling sag situated in the southern end of the songliao basin northeast china an integrated approach involving determination of hydrocarbon charging history oil source correlation and hydrocarbon generation dynamic modeling was used to investigate hydrocarbon migration processes and further predict the favorable targets of hydrocarbon accumulations in the qingshankou formation the hydrocarbon generation and charge history was investigated using fluid inclusion analysis in combination with stratigraphic burial and thermal modeling the source rocks began to generate hydrocarbons at around 82 ma and the hydrocarbon charge event occurred from approximately 78 ma to the end of cretaceous 65 5 ma when a large tectonic uplift took place correlation of stable carbon isotopes of oils and extracts of source rocks indicates that oil was generated mainly from the first member of qingshankou formation k 2 qn1 suggesting that hydrocarbon may have migrated vertically three dimensional 3d petroleum system modeling was used to evaluate the processes of secondary hydrocarbon migration in the qingshankou formation since the latest cretaceous during the late cretaceous hydrocarbon mainly originated from the qianan depression migrated laterally to adjacent structural highs subsequent tectonic inversion defined as the late yanshan orogeny significantly changed hydrocarbon migration patterns probably causing redistribution of primary hydrocarbon reservoirs in the tertiary the heidimiao depression was buried much deeper than the qianan depression and became the main source kitchen hydrocarbon migration was primarily controlled by fluid potential and generally migrated from relatively high potential areas to low potential areas structural highs and lithologic transitions are potential traps for current oil and gas exploration finally several preferred hydrocarbon accumulation sites have been identified by this work like western slope southern uplift and eastern slope helping reduce the risk on targeting hydrocarbon potential reservoirs in changling sag

diagenesis and provenance of silurian quartz arenites in south eastern new york state abstract combined scanning electron microscopy cathodoluminescence and optical microscopy sem cl om of single quartz grains was used to determine the diagenetic history and provenance of framework grains in quartz arenites of the silurian shawangunk conglomerate and binnewater sandstone in south eastern new york state most sand sized sedimentary rocks of these two units experienced compaction and quartz cementation after deposition except for those with high matrix or pseudomatrix content no primary porosity is left today and secondary porosity is insignificant leaving the shawangunk conglomerate and binnewater sandstone with poor reservoir qualities the medium to coarse sand fraction of the shawangunk conglomerate and binnewater sandstone is dominated by quartz of plutonic origin of these usually sub rounded to rounded grains 10 15 carry remnants of inherited quartz cement indicating recycling from a sedimentary source such as quartz rich sedimentary rocks of the former iapetus passive margin in contrast polycrystalline vein quartz pebbles in the shawangunk conglomerate were most likely derived from a proximal crystalline source in the taconic orogen to the east formation of the shawangunk conglomerate and binnewater sandstone quartz arenites was likely supported by subtropical climatic conditions given the latitudinal position of eastern north america during the silurian with relatively high mean annual temperatures and high precipitation rates which accelerated the breakdown of unstable grains

plateau pop up in the great 1897 assam earthquake the great assam earthquake of 12 june 1897 reduced to rubble all masonry buildings within a region of northeastern india roughly the size of england and was felt over an area exceeding that of the great 1755 lisbon earthquake1 hitherto it was believed that rupture occurred on a north dipping himalayan thrust fault propagating south of bhutan2 3 4 5 but here we show that the northern edge of the shillong plateau rose violently by at least 11 m during the assam earthquake and that this was due to the rupture of a buried reverse fault approximately 110 km in length and dipping steeply away from the himalaya the stress drop implied by the rupture geometry and the prodigious fault slip of 18 7 m explains epicentral accelerations observed to exceed 1g vertically and surface velocities exceeding 3 m s 1 ref 1 this quantitative observation of active deformation of a pop up structure confirms that faults bounding such structures can penetrate the whole crust plateau uplift in the past 2 5 million years has caused the indian plate to contract locally by 4 2 mm yr 1 reducing seismic risk in bhutan but increasing the risk in northern bangladesh

porosity permeability and textural heterogeneity of reservoir sandstones from the lower cretaceous putaohua member of yaojia formation weixing oilfield songliao basin northeast china abstract with the granulometric analyses mineral composition x ray diffraction xrd analyses porosity and permeability measurements scanning electron microscopy sem observations and mercury porosimetry measurements of the reservoir sandstones from four wells in the weixing oilfield songliao basin ne china the porosity permeability and pore structural heterogeneity features of the putaohua member sandstone of the lower cretaceous yaojia formation have been investigated in this paper the sandstones are mostly characterized by a similar deposition in continental detrital environments with quartz and feldspar taking the majority 97 and argillaceous minerals illite kaolinite and chlorite the minority 3 however their granule size sorting index porosity and permeability vary significantly in contrast to the generality that high porosity permeability often corresponds to large grain sizes and sorting indexes the porosity and permeability here show no good correlations to the grain size and sorting index suggesting the presence of a remarkable textural heterogeneity in terms of sequential change in permeability along the well depth cyclic sedimentation modes have been identified in some sub layers despite the porosity data showing little response to those scenarios this may be ascribed to the sandstone s peculiar intergranular pore structures in which the cementation occurred in pore lining and filling manners to different extents depending on their depositional environments the distributary channel facies tends to have lowest detrital clay content and rather open packed texture in pore lining cementation manner whereas sand sheet facies has pore filling manner the hg porosimetry analytical data are in fairly good agreement with the heterogeneous pore structures observed by sem large sized pores and channels connecting them though only accounting for a low percentage of the total porosity are believed to contribute mostly to the effective permeability in the sandstone reservoir such textural heterogeneities should be closely associated with the dynamic changing sedimentary facies of sandstones in the continental environment

factors controlling reservoir properties and hydrocarbon accumulation of lacustrine deep water turbidites in the huimin depression bohai bay basin east china abstract lacustrine deep water turbidite plays are a novel area for exploration in the huimin depression bohai bay basin turbidites in the shang 847 block a typical turbidite play in the huimin depression provide an opportunity to study the factors controlling the reservoir properties and hydrocarbon accumulation in lacustrine turbidite sandstones the reservoir quality of turbidite sandstones very fine grained moderately to well sorted mainly lithic arkose in this study area are mainly controlled by the distribution patterns of carbonate cements and pseudomatrix significant inverse relationships exist between the volume of carbonate cement and both porosity and permeability of the turbidite sandstones carbonate cement is located preferentially near the margins of the sandstone bodies sandstones with distance from the sandstone mudstone contact surface less than 0 7 m or with thickness less than 1 2 m are commonly tightly cemented carbonate cement 15 with low porosity and permeability lower than 10 and 0 1 md respectively the source of carbonate cement was most likely external probably derived from the surrounding mudstone most pore filling carbonate cements occurred during late diagenesis at burial depths greater than 2200 m the petrophysical properties of turbidites have a positive relationship with the content of kaolinite and chlorite but have a negative relationship with the content of illite 2 d and 3 d reconstructions of non oil bearing and oil bearing layers indicate that dissolution of carbonate cement feldspars and unstable rock fragments was more developed in oil bearing layers than in non oil bearing layers and hance oil bearing layers have higher porosity and larger pore sizes petrophysical property appears to have a significant effect on the hydrocarbon accumulation in the turbidite sandstones sandstones with porosities lower than 9 and or permeabilities lower than 0 78 md are not prone to contain oil

geology geochemistry and origin of volcanic rock hosted uranium deposits in northwestern nevada and southeastern oregon usa abstract northwestern nevada and southeastern oregon have the largest uranium u deposits in tertiary volcanic rocks in the us most deposits are in or adjacent to calderas or rhyolite lava dome fields and are hydrothermal almost all are associated with rhyolites that have high primary u concentrations 9 to 20 ppm but the rhyolites range from peralkaline to peraluminous caldera related occurrences are hosted by peralkaline rocks in the mcdermitt and virgin valley calderas at mcdermitt major deposits are along or just inboard of the southwestern kings river and northern ring fractures bretz opalite of the caldera complex the kings river deposits are strongly enriched in trace elements associated with epithermal precious metal deposits e g as au ag mo and sb much of the u occurs as hydrothermal uraniferous zircon and whole rock samples contain as much as 5 zr gangue minerals include quartz adularia fluorite and numerous sulfides 40 ar 39 ar dating of adjacent volcanic rocks and adularia indicates that mineralization was contemporaneous with igneous activity the bretz opalite deposits which include the large aurora resource 7 5 106 kg u3o8 are less enriched in epithermal trace elements and contain uraninite coffinite chalcedony opal and numerous sulfides at virgin valley deposits are mostly in tuffaceous sediments adjacent to ring fracture rhyolites trace element enrichment is minor u is hexavalent in all identified u minerals and associated phases include opal organic material and pyrite deposits in the lakeview u district oregon are hosted by weakly peraluminous rhyolite domes and tuffs and are highly enriched in epithermal trace elements the mineral assemblage includes coffinite opal and numerous sulfides minor u occurrences at buff peak nevada the newly recognized westernmost topaz peraluminous rhyolite in the us are also trace element enriched gangue minerals include quartz adularia and sulfides on the basis of their geologic setting geochemistry age and mineralogy the mcdermitt lakeview and buff peak deposits are hydrothermal sparse published fluid inclusion data indicate temperatures between 200 c and 330 c virgin valley deposits most likely are hydrothermal minor deposits in outflow ash flow tuffs are distant from any intrusive heat source and probably formed from low temperature groundwater

biogenic and petroleum related ore forming processes in dongsheng uranium deposit nw china abstract sandstone hosted roll type u deposits has recently been found in the middle jurassic zhiluo formation in the dongsheng area north of the ordos basin in order to assess the origin of the uranium mineralization the host sandstone has been investigated with emphasis on 34s values of ore stage pyrite 13c of calcite fluid inclusion oil biomarkers x ray diffraction icp ms as well as studies by electron microprobe and scanning electron microscope the mineralization consists mainly of coffinite some of the coffinite is intimately intergrown with ore stage pyrite indicating co precipitation ore stage pyrite has 34s values from 34 to 17 suggesting the pyrite sulfur originated from bacterial sulfate reduction in the host sandstone calcite cement exhibits 13c values from 27 6 to 2 1 and fluid inclusion oils show evidence of biodegradation these lines of evidence indicate petroleum was likely oxidized by sulfate reducing bacteria srb and thus supplied a source of some of the carbon in the calcite microbial degradation of petroleum is partially supported by the low temperature diagenetic environment

recognition and significance of inherited quartz overgrowths in quartz arenites abstract inherited quartz overgrowths represent remnants of cement adhering to a grain s surface from a previous sedimentary cycle and can be recognized in petrographic studies on the basis of textural criteria they may occur as rounded double or penetrating overgrowths since these features occupy only a part of a grain s surface and are randomly positioned when studied in two dimensional sections the likelihood of their being transected and observed is significantly less than their whole rock abundance this has resulted in an underestimation of their importance as a provenance indicator probability that a random cut will transect a cap of inherited cement on any particular grain depends upon proportion of the grain s surface covered by the cap position of the cap on the grain s surfac and orientation of the cut through the grain an experiment was devised to analyze the relationship between size of a grain coating cap and likelihood that it will be transected in a random cut this involved using an eccentric stereonet one in which the origin is not at the projection sphere s center to project random planes results of the experiment were plotted as a curve and then derived mathematically since size of a coating cap is related to its projection angle measured from the sphere s center a second experiment was devised to determine the relationship between projection angles and equivalent apparent projection angles seen when a cut does not pass through a sphere s center it was found that the true projection angle equals the mode of apparent projection angles relati nships determined in these two experiments enable calculation of the whole rock proportion of grains with inherited overgrowths from petrographic data although at the present time results must be considered as estimates this capability leads to a more precise understanding of importance of inherited overgrowths as an indicator of sedimentary provenance the procedure was applied to samples of upper precambrian quartz arenites from the uinta mountain group the grand canyon supergroup and the belt supergroup resulting in calculated whole rock proportions of grains with inherited overgrowths that are in general twice the values observed in thin section this procedure may also be useful in a variety of other applications including studies of sediment distribution intrabasinal sedim nt maturation lithostratigraphic correlation and rates of grain surface abrasion

2 d traveltime and waveform inversion for improved seismic imaging naga thrust and fold belt india summary exploration along the naga thrust and fold belt in the assam province of northeast india encounters geological as well as logistic challenges drilling for hydrocarbons traditionally guided by surface manifestations of the naga thrust fault faces additional challenges in the northeast where the thrust fault gradually deepens leaving subtle surface expressions in such an area multichannel 2 d seismic data were collected along a line perpendicular to the trend of the thrust belt the data have a moderate signal to noise ratio and suffer from ground roll and other acquisition related noise in addition to data quality the complex geology of the thrust belt limits the ability of conventional seismic processing to yield a reliable velocity model which in turn leads to poor subsurface image in this paper we demonstrate the application of traveltime and waveform inversion as supplements to conventional seismic imaging and interpretation processes both traveltime and waveform inversion utilize the first arrivals that are typically discarded during conventional seismic processing as a first step a smooth velocity model with long wavelength characteristics of the subsurface is estimated through inversion of the first arrival traveltimes this velocity model is then used to obtain a kirchhoff pre stack depthmigrated image which in turn is used for the interpretation of the fault waveform inversion is applied to the central part of the seismic line to a depth of 1 km where the quality of the migrated image is poor waveform inversion is performed in the frequency domain over a series of iterations proceeding from low to high frequency 11 19 hz using the velocity model from traveltime inversion as the starting model in the end the pre stack depth migrated image and the waveform inversion model are jointly interpreted this study demonstrates that a combination of traveltime and waveform inversion with kirchhoff pre stack depth migration is a promising approach for the interpretation of geological structures in a thrust belt

post rift geodynamics of the songliao basin ne china origin and significance of t11 coniacian unconformity abstract the t11 unconformity lies between the qingshankou and yaojia formations in the post rifting sequence of the cretaceous songliao basin ne china it is intimately associated with petroleum reservoirs and considered to be a disconformity forming in the tectonic quiet stage we present the interpretations from new seismic surveys and cored sections of the cretaceous continental scientific drilling borehole ccsd sk 1 in order to resolve the nature and origin of t11 unconformity the t11 is often a low angle unconformity with underlying qingshankou formation having been deformed and eroded prior to deposition of the yaojia formation in the post rift evolution of the basin it marks an abrupt change from a deep lake to shallow lake or subaerial environment documented by reddening of the lacustrine mudstone extinction of the ostracod assemblages and a great increase of coarse detrital inputs the sharp change of depositional environment the truncation of gentle folds and the cluster of volcanic and paleoearthquake activities all happened simultaneously immediately before the development of t11 unconformity indicating a significant regional compressional uplift event in the basin the timing of the t11 unconformity formation is within the interval 88 86 2 ma correlations with coeval unconformities in other cretaceous sedimentary basins in eastern asia indicate that this compressional uplift coincided with an episode of global plate reorganization between the eurasian and paleo pacific plates that culminated at 88 87 ma during this short interval the northeast asian margin in eastern china south korea japan and russian far east experienced widespread violent volcanic and granite emplacement activity triggered by compression resulting from rapid and orthogonal slab subduction the post rift basin tectonic inversion occurred during t11 coniacian time thereafter the basin again evolved in an extension regime two subsidence phases in post rift history took place as the direct consequence of coniacian compression peak which defined the distribution of oil sources and reservoirs

detrital zircon u pb age and hf isotopic composition from foreland sediments of the assam basin ne india constraints on sediment provenance and tectonics of the eastern himalaya abstract synorogenic palaeogene neogene sediments of the assam foreland basin were derived by erosion of adjacent crustal and orogenic sources following the greater india eurasia collision since 55 ma to constrain source sediment influx and its relation to himalayan tectonics from pre to post collision time detrital zircon u pb geochronology and their hf isotopic compositions were carried out the varying detrital zircon spectral patterns analyzed from the paleogene jaintia barail and neogene surma and tipam groups with sediment petrography track source sediment derived from cratonic india gangdese and eastern transhimalayan batholiths and the eastern himalaya these sources are tested against cenozoic paleopositions proposed for the northeastward motion of the indian plate precollisional cratonic detritus to middle to late eocene sylhet formation shifted to tethyan himalaya and arc sources of the gangdese and eastern transhimalayan batholiths to late eocene kopili and barail formations consistent with the proposed paleoposition proximal to the indus yarlung suture this sylhet kopili formation transition within the jaintia group reflects one of the earliest himalayan hinterland exhumation stages during the late eocene major shift in provenance to higher himalayan crystalline and arc detritus is recorded from the surma group constraining mid miocene himalayan tectonic exhumation from the eastern himalaya late miocene tipam group preserves sediment of higher himalayan crystalline detritus ophiolite and likely lesser himalayan rocks

structural evolution in response to fold and thrust belt tectonics in northern assam a key to hydrocarbon exploration in the jaipur anticline area abstract the upper assam basin is an intermountain basin surrounded on two sides by eastern himalayan fold belt and the third side by assam arakan fold belt the basin has the contradictory characteristics of being a historic oil producing province in one of the most tectonically active areas of the world assam is a seismically active area and the location of major earthquakes yet contains one of the world s largest oil and gas fields an integrated study based on surface and subsurface data and relying on the sequence stratigraphic approach was undertaken to provide a re appraisal of the upper miocene to recent succession and its relationship to the region s structural history detailed data in the jaipur anticline region of the basin is viewed in regional context while the seismic database area includes only the northeastern part of the basin we suggest that the interpretations are applicable to the entire upper assam basin for interpreting the complex relationship between structural evolution and the generation and remigration of hydrocarbons in tectonically active regions a regional geo history analysis is a required component of the petroleum system description necessary for a successful exploration model

the tectonic stress field and deformation pattern of northeast india the bengal basin and the indo burma ranges a numerical approach abstract we performed numerical simulations to determine the contemporary maximum horizontal compressive stress hmax in the northeast india region the bengal basin bangladesh and the adjoining indo burma ranges with different boundary conditions the regional tectonic stress was simulated using the finite element method fem under the plane stress condition most of the study areas show ne sw regional stress orientation which is consistent with other stress indicators such as earthquake focal mechanism solutions the e w trending dauki fault which separates the shillong plateau to the north from the bengal basin to the south plays a major role in the stress distribution and regional deformation this fault alone accommodates 25 of the regional surface displacement rate of the study area the fault pattern of the study area was also simulated using rheological parameters and the mohr coulomb failure criterion the simulated results reproduce the observed tectonic state of the area including a strike slip regime along the dauki fault in the southwestern part of the bengal basin and in the tripura fold belt areas the modeling indicates that the brahmaputra valley to the north of the shillong plateau and to the south of the himalayan frontal thrust exhibits thrust reverse faulting with a strike slip component and in the indo burma ranges strike slip faulting is predominant with a reverse fault component

temperature distribution and its relation to hydrocarbon accumulation in upper assam valley india well log temperatures have been recorded in more than 400 wells drilled so far by oil india ltd in its concessions in the upper assam tertiary sedimentary basin at the northeastern corner of the indian subcontinent subsurface temperatures presented in the form of isogeothermal maps show 1 a general increase with the rise of basement configuration and 2 maximum values over the crests of local highs with gradual decrease toward the flanks the difference being on the order of 15 c geothermal gradients in the areas studied decrease with depth within argillaceous sediments but increase in the arenaceous group the geothermal gradients obtained for different areas of this sedimentary basin can be used in the hydrocarbon liquid window concept for oil exploration the study reveals that in the eastern part of this basin theoretically a considerable thickness of potentially hydrocarbon bearing section could be down to a depth of about 9 150 m which is yet to be explored by deep drilling

provenance interpretation of quartz by scanning electron microscope cathodoluminescence fabric analysis we used a cathodoluminescence cl detector attached to a scanning electron microscope sem to study patterns of variable intensity cl in quartz grains from a variety of igneous metamorphic sedimentary and shock deformed meteorite impact rocks distinctive fabrics in quartz grains revealed by sem imaged differential cl include zoning healed fractures complex shears planar features shocked quartz dark cl streaks and patches indistinct mottled texture and nondifferential low contrast cl zoning is common in volcanic quartz and some plutonic quartz zoned plutonic quartz is distinguished from volcanic quartz by the presence of closed fractures and dark cl streaks and patches metamorphic quartz displays either an indistinct mottled texture or nearly uniform nondifferential cl quartz from rocks severely deformed by tectonism displays a complex pattern of multiple small scale shears quartz from meteorite impact sites and some system boundaries is characterized by intricate patterns of planar features presumably created by shock metamorphism thus the sem cl fabric analysis technique provides a rapid method for distinguishing quartz from a variety of source rocks

uranium and organic matter in a paleodeltaic environment the coutras deposit gironde france the coutras uranium deposit located north of the aquitaine basin france was discovered by cogema in 1980 it is hosted by middle eocene arenaceous unconsolidated sediments at the surface the jean vincent area and down to 100 m depth the le fieu area the detrital components of the sediments are mainly quartz feldspars and granitic and metamorphic rock fragments the host sediments originated from the french massif central to the east orebodies are black tabular lenses occurring in sediments deposited in a delta plain environment where plant debris is abundant preservation of ligneous vegetation during burial established a reducing environment capable of concentrating uranium there is a good correlation between uranium total sulfur and organic carbon uranium is mainly fixed in organics as organo uranyl compounds uranium minerals detected include coffinite pitchblende and secondary hexavalent u minerals accumulation of uranium was favored by a permeable organic rich and slightly acid environment adsorption processes probably enhanced ore formation the lack of oxidized tongues may be the result of oxygen depleted uranium bearing solutions when they reached the organic rich zone the coutras uranium deposit is then a good example of a tabular type deposit which was deposited during early diagenesis

40ar 39ar and k ar dating on the volcanic rocks in the songliao basin ne china constraints on stratigraphy and basin dynamics precise 40ar 39ar and k ar ages were determined on sanidine and whole rock separates of volcanic rocks in the songliao basin sb the volcanism is characterized by a series of continual and episodic eruptions in the late jurassic 147 157 ma and early cretaceous 113 136 ma a fairly accurate chronostratigraphic column was first established based on those data the volcanic activities happened synchronously with closure of the mongolia okhotsk ocean north to the sb structures of the volcanogenic successions are s dipping or se dipping fault blocks coupled with n dipping or nw dipping major detachment systems distribution of the volcanics revealed by high resolution seismic reflections is neither restricted within nor in agreement with the framework of the overlying sedimentary sequence striking nne this new evidence fits the overlap model proposed in the present paper that formation of the volcanic successions in the sb is related to the subduction of the mongolia okhotsk plate under the mongolia north china block during the jurassic and early cretaceous whereas the overlying sedimentary sequence unconformably on the volcanics is tectonically controlled by the oblique subduction of the pacific plate under the eurasian plate since late aptian in addition the coal bearing epiclastic sediments intercalating the volcanics were deposited at the subduction quiescence episodes when extensional collapse occurred

tectonic effects of climate change on venus venusian plains regions are commonly crossed by small strain deformation features such as wrinkle ridges polygonal terrains and gridded terrains of these polygonal terrains are observed to have a relatively uniform spacing and are widely distributed on plains that formed during global resurfacing models of venusian climate that assume resurfacing occurred through massive volcanic events suggest that surface temperatures could have dramatically changed over nearly a billion years propagating thermal stresses into the surface and potentially causing small strain features we investigate this hypothesis by approximating the temperatures predicted by climate models as a step function and employ a fixed plate and strength envelope model to predict the resulting depth of failure and amount of strain our calculations indicate that strains due to temperature changes of 50 100 k which are favored for volcanic resurfacing events of 1 10 km thickness are consistent with the observed spacing of polygonal and gridded terrains as well as some wrinkle ridges the global nature of the climate change event is consistent with the global distribution and uniformity of such features and implies that such terrains may be a global stratigraphic marker

provenance analysis by single quartz grain sem cl optical microscopy abstract the integration of panchromatic scanning electron microscopy cathodoluminescence sem cl with optical microscopy analysis on single quartz grains is a new technique to interpret provenance of quartz rich sediments the combination of information gained from sem cl on textural features and cl response with information from optical microscopy allows distinction of different quartz types much more easily then with conventional microscopy or color cl analysis features visible by sem cl include zoning microcracks deformation fractures and lamellae diagenetic crushing recrystallization and strength and texture of cl response features visible by optical microscopy include embayments open fractures extinction behavior and mono poly and microcrystallinity the key is to integrate cl and optical properties of the same quartz grains in order to reduce ambiguities inherent in both techniques used on their own our technique is well suited for distinguishing between plutonic volcanic and metamorphic quartz in coarse to medium grained sand or sandstone this simple and inexpensive approach can easily be combined with other provenance techniques in this paper we outline the combined sem cl optical microscopy technique and demonstrate its application with examples from the south island of new zealand

exhumation of the dahinggan mountains ne china from the late mesozoic to the cenozoic new evidence from fission track thermochronology abstract zircon and apatite fission track ft analyses were used to reveal the exhumation of phanerozoic granitoid intrusions in the dahinggan mountains northeastern china zircon ft ages ranging from 84 5 to 97 8 ma and apatite ft ages from 47 3 to 67 4 ma with mean track lengths between 12 3 2 3 and 13 3 2 2 m respectively were obtained for the phanerozoic granitoids sampled along a south south west to north north east transect across the dahinggan mountains three cooling stages from the late mesozoic to the cenozoic have been identified in the studied region based on ft results and modeling stage one was a rapid cooling period from the closure temperature of zircon ft to the high temperature part of the apatite ft partial annealing zone 210 110 c during 90 57 ma stage two was a relatively slow cooling period 110 60 c occurred between 57 ma and 20 ma suggesting that the granitoids had been exhumed to depths of 1 2 km the final stage was a cooling period 60 20 c occurred since the miocene which bring studied samples to the earth s surface at an accelerated exhumation rate the estimated maximum exhumation is 5 km assuming a steady state geothermal gradient of 35 c km our results indicate that this exhumation is possibly led by the pacific plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling

development of phanerozoic sedimentary basins of india abstract phanerozoic sedimentation within the indian craton commenced essentially from late carboniferous with the opening of continental rift systems in east gondwana assembly of which india was a constituent member along with australia antarctica and madagascar late jurassic onward the fragmentation of east gondwana and the separation of india from its erstwhile neighbors triggered the formation of the eastern and western coastlines of the indian landmass with time the craton margin rifts turned into passive margins as the indian plate took a long northward drift the northward movement of india is accommodated by subduction of 4000 7000 km of the neotethys ocean crust leading to diachronous collision of the landmass first with kohistan ladakh arc and then with tibet the tethyan basins in kashmir lahul and spiti offer an opportunity to study the nature of deposition at the neotethys ocean margin with the continuing convergence of subducting plate and emplacement of himalaya tibet fold thrust belt the flexural buckling of the indian lithosphere resulted in the formation of foreland basins with varying dimension and character in conjunction with the evolution of the himalayan fold thrust system in post oligocene three mighty rivers viz indus ganges and brahmaputra drained the foreland and formed large scale submarine fan systems in the oceans surrounding the indian sub continent

evolution of uranium fractionation processes through time driving the secular variation of uranium deposit types uranium deposit types have evolved considerably from the archean to the present the major global drivers were 1 change of geotectonic conditions during the late archean 2 strong increase of atmospheric oxygen from 2 4 to 2 2 ga and 3 development of land plants during the silurian other significant variations of uranium deposit types are related to unique conjunctions of conditions such as those during phosphate sedimentation in the cretaceous earth s uranium fractionation mechanisms evolved through four major periods the first from 4 55 and 3 2 ga corresponds to formation of a thin essentially mafic crust in which the most fractionated trondheimite tonalite granodiorite ttg rocks attained uranium concentrations of at most a few parts per million moreover the uranium being essentially hosted in refractory accessory minerals and free oxygen being absent no uranium deposit could be expected to have formed during this period the second period from about 3 1 to 2 2 ga is characterized by several widespread pulses of highly fractionated potassic granite strongly enriched in u th and k late in this period peraluminous granite was selectively enriched in u and to a lesser extent k these were the first granite and pegmatite magmas able to crystallize high temperature uraninite the erosion of these granitic suites liberated thorium rich uraninite which would then be concentrated in placer deposits along with pyrite and other heavy minerals e g zircon monazite fe ti oxides within huge continental basins e g witwatersrand south africa and bind river canada the lack of free oxygen at that time prevented oxidation of the uraninite which formed the oldest economic uranium deposit types on earth but only during this period the third period from 2 2 to 0 45 ga records increased oxygen to nearly the present atmospheric level tetravalent uranium from uraninite was oxidized to hexavalent uranium forming highly soluble uranyl ions in water uranium was extensively trapped in reduced epicontinental sedimentary successions along with huge quantities of organic matter and phosphates accumulated as a consequence of biological proliferation especially during the late paleoproterozoic a series of uranium deposits formed through redox processes the first of these developed at a formational redox boundary at about 2 0 ga in the oklo area of gabon all known economically significant uranium deposits related to na metasomatism are about 1 8 ga in age the high grade large tonnage unconformity related deposits also formed essentially during the late paleoproterozoic to early mesoproterozoic the last period 0 45 ga present coincided with the colonization of continents by plants the detrital accumulation of plants within continental siliciclastic strata represented intraformational reduced traps for another family of uranium deposits that developed essentially only during this period basal roll front tabular and tectonolithologic types however the increased recognition of hydrocarbon and hydrogen sulfide migration from oil or gas reservoirs during diagenesis suggests potential for sandstone hosted uranium deposits to be found within permeable sandstone older than the silurian large uranium deposits related to high level hydrothermal fluid circulation and those related to evapotranspiration calcretes are only known during this last period of time probably because of their formation in near surface environments with low preservation potential

opposite verging chains sharing the same foreland kinematics and interactions through analogue models central po plain italy abstract in this study we investigate the potential role played by different geological factors on the development of a thrust system in particular our goal is to analyze how pre existing compressional structures located in the foreland of a thrust and fold belt may affect the kinematics of a thrust system we studied such circumstances both in a natural case and through analogue models as a natural case we selected the central po plain italy where the buried external fronts of the northern apennines and southern alps are very close to each other starting from a regional cross section representative of this tectonic setting we reconstructed the post messinian development of the apennines thrust fronts which includes out of sequence thrusting then we modeled this evolution through a set of analogue experiments to evaluate the possible relationships of the out of sequence thrusting with the burial of the syntectonic sediments and or the existence of the outer fronts of an opposite verging chain in its foreland the comparison between natural case and models highlights that the presence of opposite verging thrust fronts in the foreland of a belt limits the propagation of new thrusts favoring the out of sequence reactivation of inner thrusts an analysis of the study area with respect to adjacent tectonic settings coupled with analogue models revealed that syntectonic sedimentation as well has a role in the reactivation of the inner fronts although secondary in the po plain specific case this implies that the presence of the buried southern alps fronts affects the northern apennines kinematics even if the two fronts did not collide yet

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

influence of structural inheritance on foreland foredeep system evolution an example from the po valley region northern italy understanding the development of foreland foredeep systems and the influence exerted by pre existing structures on their evolution is an important step for defining the key factors that control long term basin and lithosphere dynamics comprehending the associated seismic hazard and assessing their economic potential in the domain of hydrocarbon exploration the po valley is a rather unique foreland basin for two major reasons a it developed intermittently at the front of two different mountain chains the northern apennines and the southern alps progressively converging one towards the other b the inherited structures mainly derived from the mesozoic extensional tectonics are oriented at high angle to the advancing belts the coexistence of these two factors and their various implications make the po valley basin a complex case study that deserves attention taking advantage of the recent building of a 3d structural model across the region we reconstructed the possible geometry and migration pattern of the tertiary basins that developed at the front of the northern apennines and the southern alps as part of the po valley tectonic evolution in addition a number of sections sliced from the 3d model across selected domains have then been used to restore the present day structural units to their pre compressional setting while highlighting the key stages of their geological history results from the model analysis show that the mesozoic extension related tectonics and the associated carbonate facies geometry and distribution localized and constrained the alpine structures inside around the basin their control on the cenozoic deformation and sedimentation is evident during the paleogene and the miocene whereas it becomes more subtle during the plio pleistocene when lithospheric scale mechanisms need to be invoked notwithstanding the model uncertainties and its explicit regional significance our results may be taken as reference for any foreland foredeep setting worldwide especially in complex systems where tectono sedimentary inhomogeneity is spatially and temporally dominant

estimating basal friction and fluid pressure from the geometry and spacing of frontal faults in naga fold thrust belt india abstract naga fold thrust belt is an emerging destination for petroleum exploration in eastern india it is a thin skinned ftb where new initiatives are being taken after a long gap of initial discoveries in absence of sufficient drilling or quality seismic data in the southern part of the fold thrust belt fluid pressure regimes remain largely speculative using the concept and the formulation for efficient coefficient of basal friction we have revisited the method and concept of pressure dependent coulomb wedge theory for thin skinned thrust belts for deriving the fluid pressure ratio in naga fold thrust belt the efficient coefficient of basal friction on the decollement and the fluid ratio of naga fold thrust belt are estimated to be 0 22 and 0 85 respectively this indicates an overpressure situation in the wedge this method of estimating basal friction and fluid pressure is more case specific and can be obtained from the data of thrust initiation angle and thrust spacing

mechanical controls on fluid flow during regional metamorphism some numerical models the control of fluid flow by plastic deformation during metamorphism is critical to our understanding of metamorphic processes various geological observations and field studies demonstrate the consequences of fluid flow control by deformation so that the concept appears to be accepted at least for small scale public for example faults and vein public however the concept appears to be less well recognized at regional scales considered here are examples of simple conceptual models based on fully coupled mechanical fluid flow concepts they include deformation of a section of fluid saturated crust containing a block or a layer of material of different properties from its surrounds in particular rheological and permeability contrasts between rock types during deformation associated with regional metamorphism are sufficient to control the form of fluid flow over the range of a few kilometres low contrasts and small strains allow pervasive fluid flow whereas greater contrasts and increasing strains cause focusing of the flow such focusing is generally associated with localization of the deformation especially for a strongly dilatant elastic plastic material however a rate of fluid flow much greater than the rate of deformation may result in pervasive flow although for most models pervasive flow is difficult to attain over regional distances furthermore lateral and downward fluid flow may occur demonstrated here by simple models for folding and for deformation of regions containing plutons therefore such modelling may be used as a means of testing the various hypotheses concerning the volumes of fluid predicted to have passed through some rock volumes numerical models of the future will become increasingly complex and powerful allowing greater coupling of thermal mechanical chemical and fluid flow effects and based more on the physical processes involved combined field and laboratory studies will provide correspondingly greater understanding and will permit the determination of the timing of fluid flow and structural controls on fluid flow patterns

fluid flow in extensional environments numerical modelling with an application to hamersley iron ores the mechanical feasibility of focusing both surface and basinal derived fluids towards sites of iron ore genesis during proterozoic deformation in the hamersley province is tested here by computer simulation finite difference modelling of porous media flow during extensional deformation of a mountain range shows that surface fluids are drawn towards areas of failure and focus into the centre of the mountain the addition of permeable structures such as a normal fault provides focused fluid pathways in which mechanical and geological conditions are particularly conducive to both upward and downward flow upward flow from the base of the fault within the model overall is favoured by low permeability basement materials and supra hydrostatic pore pressures downward migration of fluids becomes more prominent as extension progresses and upward fluid flow from the base diminishes the introduction of sedimentary layering into the models allows lateral fluid flow such that sites of potential fluid mixing may then occur within permeable iron formation units close to the fault zone allowing parts of the stratigraphy to become more permeable as a function of high fluid flux simulates permeability enhancement by silica dissolution as a mechanism for iron ore genesis the involvement of both basinal and surficial fluids in the genesis of the ore deposits is supported by the mechanical models and in addition provides an explanation for a progression from relatively reduced to oxidised conditions at the mt tom price deposit and possibly other large deposits with time

geochronology and thermochronometry of the jiapigou gold belt northeastern china new evidence for multiple episodes of mineralization the jiapigou gold belt one of the most important gold producing districts in china is located in the northern margin of the north china craton in this belt auriferous quartz vein types of gold deposits dominantly exist besides a few disseminated types of ore deposits though some research papers have been published about this belt the mineralization ages of the gold deposits within this region are still controversial this work uses zircon u pb fission track and 40ar 39ar dating methods to probe the timings and numbers of episodes of gold mineralization in the jiapigou gold belt the zircon u pb ages can be divided into four groups 166 170 ma 208 ma 228 9 230 0 ma and 2342 2536 ma the fission track ages on zircons from ores show three groups of ages 86 106 ma 120 138 ma and 153 155 ma the 40ar 39ar ages on biotite and k feldspar coincide with the ages mentioned above a total of five age groups have first been revealed 230 0 228 9 ma 208 ma 170 153 ma 138 120 ma and 106 88 ma because the samples come from mineralized and altered rocks or because the zircons belong to hydrothermal type the five age groups could indicate five episodes of gold mineralization with the three middle age groups being most plausible it is the multiple episodes of mineralization that resulted in the occurrence of large scale gold deposits in the jiapigou belt remarkably the ages of tectonic magmatic events coincide well with the dated mineralization periods therefore each episode of mineralization was closely related to regional plate activities in different epochs

morphotectonics and neotectonic activity of the schuppen belt of mokokchung nagaland india abstract a stretch of the schuppen belt trending ne sw in the western sector of the indo myanmar ranges represents a tectonically active zone deformed quaternary deposits and various geomorphic features lend evidence for the same in a portion of the footwall block of the sanis chongliyimsen thrust the nazira sandstone of the tipam group of mio pliocene age is thrust over tilted quaternary fluvial deposits near tzudikong with a displacement of more than 2 m along the plane of the thrust fault deformed quaternary deposits such as tilted terraces and faulted quaternary sediments are indicative of ongoing tectonic activity in the area the sediments are tilted towards the southeast by varying degrees 21 39 similar to the trend of stream migrations observed at four locations in and around tuli in some sections faulting has not only affected the underlying bedrock but also deformed the overlying fluvial sediments an important morphotectonic feature representing tectonic movement along the kongan thrust is evident from drainage migration in the hanging wall block of the thrust the stream has migrated towards the southeast as a result of nw verging along the kongan thrust which has left behind a trail of palaeochannels numerous palaeochannels mostly linear in nature associated with the scarp of the terrace are indicative of migration of the river stream migrations suggest that the two anticlines noted in the study area are possibly growing in the present tectonic regime multiple levels of strath terraces lend evidence to tectonic pulses in the study area each strath representing a tectonic phase lineaments have been extensively mapped in the area out of which around 70 are parallel to the regional ne sw trend and the other 30 are approximately perpendicular to this trend any movement along the nw se plane may be normal faults the mountain front sinuosity index of the emerging mountain front is close to 1 which is indicative of a relatively active mountain front steam length gradient index and steepness index correspond with each other with high values in the thrust zones which is indicative of a neotectonically active region

pop up tectonics of the shillong plateau in northeastern india insight from numerical simulations article i nfo the shillong plateau in northeastern india represents one of the most seismically active pop up structures within the peninsular shield area in order to constrain the role of the inferred oldham fault in the northern boundary of the plateau we performed 2 d finite element method fem simulations for convergent displacement caused by northeastward movement of the indian plate with respect to the eurasian plate various rock properties density poisson s ratio young s modulus cohesion and angle of internal friction and the mohr coulomb failure criterion are used to evaluate failure and faulting patterns two plane strain models with appropriate boundary conditions were also calculated the predicted maximum compressive stress 1 shows a preferred orientation that helps explain the tectonic environment and the fault pattern the best fit model suggests that a compressive stress regime is dominant in the study area everywhere except for the uppermost part of the crust where extensional stress dominates with increased progressive convergent displacement the modeled 1 are predicted to rotate counterclockwise around the fault zones the simulation results suggest that the oldham fault does not have a significant role in the development of stress and deformation distribution in the area we also infer that the tectonically induced deformation in both the plateau and the adjoining areas is restricted to mainly within the crust b30 km

petroleum geochemistry of a part of upper assam basin india a brief overview abstract the upper assam tertiary sedimentary basin is an important petroleum province with reservoir rocks ranging in age from upper paleocene to miocene the bulk of the oil production is from the barail oligocene and tipam miocene formations promising hydrocarbon pools have been discovered recently in upper paleocene lower eocene formations prolific source rocks occur within the barail oligocene formation langpar formation upper paleocene and lakadong theria member of sylhet formation of upper paleocene lower eocene age the source rocks contain predominantly type ii organic matter and are thermally immature to early mature biomarker ratios indicate the dominance of land plant derived kerogen the barail and tipam oils have moderate gravity and significant wax contents the physical and chemical characteristics of the paleocene eocene crude oil is similar to that produced from younger horizons within the basin with the exception of minor quantities of heavy viscous crude oils observed in a few wells multivariate analysis including principal components analysis and factor analysis of fluorescence data and principal components analysis of biomarker data indicate that the barail oligocene and tipam miocene oil have been derived from barail source rocks with a possible contribution from eocene source rocks these preliminary studies have not provided conclusive evidence for the source of the eocene oils although geological factors indicate that the source rocks are probably the interbedded shales coals occurring within the upper paleocene lower eocene sediments