pressure core analysis of geomechanical and fluid flow properties of seals associated with gas hydrate bearing reservoirs in the krishna godavari basin offshore india abstract physical properties of the sediment directly overlying a gas hydrate reservoir provide important controls on the effectiveness of depressurizing that reservoir to extract methane from gas hydrate as an energy resource the permeability of overlying sediment determines if a gas hydrate reservoir s upper contact will provide an effective seal that enables efficient reservoir depressurization compressibility stiffness and strength indicate how overlying sediment will deform as the in situ stress changes during production providing engineering data for well designs assessing these properties requires minimally disturbed sediment india s national gas hydrates program expedition 2 nghp 02 provided an opportunity to study these seal sediment properties reducing disturbance from gas exsolution and bubble growth by collecting a pressure core from the seal sediment just above the primary gas hydrate reservoir at site nghp 02 08 in area c of the krishna godavari basin the effective stress chamber esc and the direct shear chamber dsc devices in the suite of pressure core characterization tools pccts were used to measure permeability compressibility stiffness and shear strength at the in situ vertical stress geotechnical properties of the predominantly fine grained seal layer at in situ vertical stress are in typical clay sediment ranges with low measured permeability 0 02 md high compressibility c c 0 26 0 33 and low shear strength 404 kpa though pressure and temperature were maintained throughout the collection and measurement process to stabilize gas hydrate the lack of effective stress in the pressure core storage chamber and the chamber pressurization with methane free water caused core expansion and gas hydrate in a thin coarser grained layer to dissolve the pccts can reapply in situ stress with incremental loading steps during a consolidation test to account for sediment compaction gas hydrate dissolution can be limited by storing cores just above freezing temperatures and by using solid spacers to reduce the storage chamber s free volume

application of k ϵ turbulence models to enclosed basins the role of internal seiches 1 a numerical model was developed for the prediction of the density stratification of lakes and reservoirs it combines a buoyancy extended k model with a seiche excitation and damping model to predict the diffusivity below the surface mixed layer the model was applied to predict the seasonal development of temperature stratification and turbulent diffusivity in two medium sized lakes over time periods ranging from 3 weeks to 2 years depending on the type of boundary condition for temperature two or three model parameters were optimized to calibrate the model the agreement between the simulated and the observed temperature distributions is excellent in particular if lake surface temperatures were prescribed as surface boundary condition instead of temperature gradients derived from heat fluxes comparison of different model variants revealed that inclusion of horizontal pressure gradients and or stability functions is not required to provide good agreement between model results and data with the aid of uncertainty analysis it is shown that the depth of the mixed surface layer during the stratified period could be predicted accurately within 1 m the sensitivity of the model to several parameters is discussed index terms 4211 oceanography general benthic boundary layers 4255 oceanography general numerical modeling 4568 oceanography physical turbulence diffusion and mixing processes keywords lake turbulence model seiche stratification simulation turbulence kinetic energy

india national gas hydrate program expedition 02 operational and technical summary abstract the india national gas hydrate program is being steered by the government of india s ministry of petroleum and natural gas mopng with participation of directorate general of hydrocarbons dgh oil and natural gas corporation limited ongc and the national oil companies and research institutes of india the india national gas hydrate program expedition 01 nghp 01 established the presence of gas hydrate in the krishna godavari kg and mahanadi basins and in the offshore area of the andaman sea basin however the gas hydrates discovered during nghp 01 were mainly distributed as fracture filling material in fine grained clay rich sediments the india national gas hydrate program expedition 02 nghp 02 was carried out with an objective to discover gas hydrate in sand rich sediment along the eastern offshore margin of india ongc planned and executed nghp 02 on the behalf of the mopng nghp 02 started on march 3 2015 and was completed on july 28 2015 total 147 days using the japanese scientific drilling vessel chikyu d v chikyu during nghp 02 42 holes at 25 sites were drilled cored and or surveyed with downhole logging tools these sites were located in four areas along the eastern margin of india and formally named area a mahanadi basin three sites area b northern part of the kg basin twelve sites area c central part of the kg basin six sites and area e southern part to the kg basin four sites all 25 sites established during nghp 02 were first drilled and logged with logging while drilling lwd tools and an additional 17 holes were then drilled and or cored with conventional coring tools hpcs escs or pressure coring tools pctb wireline logging was conducted in 10 holes and formation tests using a dual packer modular formation dynamics tester mdt tool were carried out in two holes the onboard science team used the laboratory facilities on the d v chikyu to examine and analyse the physical properties geochemistry and sedimentology of all the cores collected during the expedition core samples were also analysed in additional post expedition shore based studies conducted in numerous domestic and international gas hydrate research laboratories the nghp 02 sediment cores were archived at the national gas hydrate core repository in mumbai india which is associated with the ongc gas hydrate research and technology centre ghrtc the necessary data for characterizing the occurrence of gas hydrate such as interstitial water chlorinities core derived gas chemistry physical and sedimentological properties thermal images of the recovered cores pressure core and downhole measured logging data lwd and or conventional wireline log data were obtained from most of the drill sites established during nghp 02 almost all the drill sites yielded evidence for the occurrence of gas hydrate however the inferred in situ concentration of gas hydrate varied substantially from site to site for the most part the interpretation of downhole logging data core thermal images interstitial water analyses and pressure core images from the sites established during nghp 02 indicate that the occurrence of concentrated gas hydrate is mostly associated with coarser grained sand rich sediments this paper presents the operational and technical summary of nghp 02

up gully flow in the great plains region a mechanism for perturbing the nighttime lower atmosphere 1 studies using data gathered during cases 99 show that when the near surface nighttime wind direction shifts through the up gully direction of a significant gully near the tower the flow produces a pronounced but localized upward surge of vertical velocity up to at least 55 m this surge generates an outward propagating wave packet having horizontal and vertical wavelengths on the order of 100 250 m with tilted wave fronts consistent with upward phase propagation the wave packet is observable with significant delays by other sensors out to 850 m as a working hypothesis we assume that the up gully flow is constricted and strengthened as it progresses up the narrowing gully we theorize that upon exiting the gully the flow has a pronounced and tightly confined vertical component that in turn produces a packet of internal propagating gravity waves

water and gas chemistry at lake kivu drc geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure 1 waters and dissolved gases collected along vertical profiles in the five basins main kabuno bay kalehe ishungu and bukavu forming the 485 m deep lake kivu democratic republic of the congo were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry the measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by 1 different contribution from long circulating fluid system containing magmatic co2 responsible of the huge co2 ch4 rich reservoir hosted within the deep lake water 2 spatial variations of the biomass distribution and or speciation and 3 solutes from water rock interactions the kabuno bay basin is characterized by the highest rate of magmatic fluid input accordingly this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the nyiragongo and nyamulagira volcanoes located a few kilometers north of the lake

holocene aridification of india 1 spanning a latitudinal range typical for deserts the indian peninsula is fertile instead and sustains over a billion people through monsoonal rains despite the strong link between climate and society our knowledge of the long term monsoon variability is incomplete over the indian subcontinent here we reconstruct the holocene paleoclimate in the core monsoon zone cmz of the indian peninsula using a sediment core recovered offshore from the mouth of godavari river carbon isotopes of sedimentary leaf waxes provide an integrated and regionally extensive record of the flora in the cmz and document a gradual increase in aridity adapted vegetation from 4 000 until 1 700 years ago followed by the persistence of aridity adapted plants after that the oxygen isotopic composition of planktonic foraminiferglobigerinoides ruberdetects unprecedented high salinity events in the bay of bengal over the last 3 000 years and especially after 1 700 years ago which suggest that the cmz aridification intensified in the late holocene through a series of sub millennial dry episodes cultural changes occurred across the indian subcontinent as the climate became more arid after 4 000 years sedentary agriculture took hold in the drying central and south india while the urban harappan civilization collapsed in the already arid indus basin the establishment of a more variable hydroclimate over the last ca 1 700 years may have led to the rapid proliferation of water conservation technology in south india

paleomagnetic constraints on the late cretaceous and cenozoic tectonics of southeastern asia abstract many features of the cenozoic tectonic history of central and southeastern asia can be understood as direct consequences of the thrust and penetration of india into asia recent indentation experiments with plasticine tapponnier et al 7 have extended this idea and have led to the prediction of a pattern of large rotations and displacements of continental blocks that can be tested by paleomagnetism the available cretaceous and cenozoic paleomagnetic data from this part of the world have been reviewed and a new apwp for eurasia has been constructed for reference the negligible rotation of south china and large clockwise rotation of indochina are consistent with the model i e with an history of large scale left lateral strike slip motion along the altyn tagh and red river faults data from malaya and borneo can be reconciled with the model although in a less straightforward fashion the large counter clockwise rotation of south tibet implies that it rotated in sympathy with india during the collision and suggests that future indentation experiments should include this feature finally a middle cretaceous reconstruction of the south margin of asia is proposed one interesting result is the restored continuity of geological features in tibet and indochina with active subduction of oceanic indian plate crust taking place to the south at subtropical latitudes

rise of the base of the gas hydrate zone since the last glacial recorded by rock magnetism gas hydrate a clathrate of methane and water widespread on continental margins has been implicated as a trigger of climate change and submarine slides as a result of methane release when the base of its stability zone moves upward rapidly direct tests of these hypotheses are made difficult by the ephemeral record of gas hydrate in sediment in places a seismic reflector double bottom simulating reflector bsr appears to mark the old base of the gas hydrate layer but the occurrence of this feature is patchy and its interpretation is controversial microbial activity is stimulated in the presence of gas hydrate and results in the production of magnetic iron sulfides the base of the gas hydrate interval is marked by a sharp reduction in the magnetic hysteresis parameter d j h at hydrate ridge on the cascadia margin sampled during ocean drilling program leg 204 this signature occurs between 20 and 65 m below the present day base of the gas hydrate zone at a depth consistent with predictions for the base of gas hydrate stability given water depths and bottom water temperatures appropriate for the last glacial maximum seismic evidence for a double bsr over part of hydrate ridge corroborates the rock magnetic interpretation

the evolution of the east coast of india abstract the evolution of the east coast of india from the permian up to the end of the cretaceous is traced peninsular india had an imprint of hercynian epeirogeny manifested in the formation of some regional geofracture and rift systems the east coast basins mahanadi godavari krishna palar and cauvery basins are pericratonic the structural style and regional trends during the jurassic are ne sw the basin architecture during the late jurassic is of horst graben type the close of the mesozoic was marked by regional easterly regression basinal tilt and formation of monoclinal post mesozoic sedimentary cover the oldest sequence in these basins is of permian age and is known in the palar basin the triassic sediments are not known in the land area from the faunistic and floristic evidence the uppermost jurassic lower cretaceous gondwana sediments are paralic the occurrence of marine permian palynofossils in the indian east coast sediments points to the presence of a narrow paleo shelf to the east prior to the break up and drift of gondwanaland different continental fits offered by various authors are analysed to understand the evolution of the indian ocean the structural grain and basin architecture of the pre drift and post drift basins of the east coast of india are similar to that of the western and northwestern coastal basins of australia it is postulated that permian sediments were extensive and have since been eroded such a pattern of erosion of permian beds is also observed in northwestern australia the most favoured fit of western australia against northern india does not conform to the regional geotectonic pattern and the nature of sediments that are present in india and the australian counterparts in addition to geological evidence palaeo biological evidence has been considered which favours the juxtaposition of the east coast of india with western australia the authors are of the opinion that palaeomagnetic interpretations which have of late gained importance fail to explain the pre drift geological similarities of the east coast of india and western coast of australia

an overview of indian sedimentary basins with special focus on emerging east coast deepwater frontiers this article will provide an overview of the current indian petroleum exploration scenario with special focus on the east coast deepwater basins an attempt has been made to distinguish the hydrocarbon system and play types for both rift related and other structural styles using high quality 2d and 3d seismic imaging information integrating the geologic information with state of the art seismic data has generated a large portfolio of play types e g channel levee complex lobes synrift structural closures and wedge outs against basement highs worthy of exploration

tectonic geomorphology of the southernmost sagaing fault and surface rupture associated with the may 1930 pegu bago earthquake myanmar abstract the sagaing fault is a continental transform fault between the india and sunda plates that connects spreading centers in the andaman sea and the continental convergence zone along the himalayan front several m 7 earthquakes occurred along the fault in the last century and global positioning system campaigns revealed a right lateral slip rate of 18 mm yr about half of the total india sunda displacement rate of 35 mm yr however there are few fundamental geologic data on the sagaing fault such as detailed fault trace locations information on late quaternary slip rate or spatial extent of surface ruptures during historical earthquakes we conducted geologic field investigations along the southernmost 120 km long stretch of the fault zone that ruptured during the m 7 3 1930 pegu bago earthquake we found well defined tectonic geomorphic features across a deltaic lowland including fault scarps tectonic depressions stream offsets and pressure ridges the sense of displacement is predominantly right lateral strike slip with vertical motion less than 1 5 of horizontal motion based on right lateral offsets of stream channels terrace risers and property boundaries we estimate coseismic displacement during the 1930 earthquake as 3 0 m this in turn gives us a preliminary recurrence interval of surface rupturing earthquakes on the sagaing fault east of yangon as 160 yr coulomb stress change induced by the may 1930 pegu bago earthquake may have triggered the december 1930 pyu earthquake immediately to the north this study demonstrates that detailed geomorphic investigations are key for a better assessment of seismic hazard for the sagaing fault

origin of gas in gas hydrates as interpreted from geochemistry data obtained during the national gas hydrate program expedition 02 krishna godavari basin offshore india abstract this report presents the result of geochemical studies carried out on cores recovered from krishna godavari basin k g basin during the national gas hydrate program expedition 02 nghp 02 nghp 02 targeted gas hydrate accumulations in sand facies in the k g basin off the east coast of the indian peninsula three areas area b area c and area e in the k g basin were investigated during this expedition 10 research sites in k g basin were cored and samples for geochemistry analysis were collected high toc tn ratios indicate an input from terrestrial organic matter analysis of gas samples from pressure cores also acquired during nghp 02 were composed of mostly methane carbon isotopic studies show that methane gas sampled from recovered gas hydrate samples were derived from biogenic microbial sources this list of factors appears to indicate that the gas associated with the recovered hydrate bearing core samples were derived from a microbial source however the biogeochemical processes responsible for generating the microbial gases found with the recovered gas hydrates may not have been limited to current limits off the gas hydrate stability zone it is important to note here that microbial process likely extend to more than 1 km deep into the basin so gas coming from below the gh stability zone can still be from a microbial source in addition the microbial gas within the stability zone was likely in part recycled from hydrate accumulations that has passed through the base of the gas hydrate stability zone as a product of sedimentation with the dissociated microbial gas migration again vertically in the section entering the gas hydrate stability zone and reforming gas hydrates although the organic carbon required for in situ methanogenesis and gas hydrate formation is abundant in the shallow sedimentary section of the kg basin the faulted fractured and deformed stratigraphy observed in the kg basin coupled with high pore filling gas hydrate saturations at many sites suggests that advective processes may be contributing to the supply of methane to the gas hydrates in the kg basin the possible migration of gas from greater depths is also supported by seismic evidence of through going migration pathways that can connect the gas hydrate system with deeper petroleum systems it is important to note here that the deep conventional gas accumulations in the basin also contain microbially sourced gas

multi measurement approach for establishing the base of gas hydrate occurrence in the krishna godavari basin for sites cored during expedition nghp 02 in the offshore of india abstract the 2015 national gas hydrate program of india s second expedition nghp 02 acquired logging and coring datasets for constraining the base of the gas hydrate occurrence zone deepest gh and the theoretical base of gas hydrate stability zone bghs these data are used here for two primary goals to constrain the deepest occurrence of gas hydrate relative to predicted stability limits and the observed bsr and to characterize the nature of the contact between gas hydrate bearing sediment and the underlying gas hydrate free sediment a consensus depth for the deepest gh is derived for each nghp 02 coring site from downhole indicators of gas hydrate occurrence obtained from well log electrical resistivity and acoustic data pressure core compressional wave velocity measurements and conventional core measurements of anomalously low temperatures to establish the theoretical bghs models of gas hydrate phase stability with depth are compared with downhole temperature profiles derived from 1 assuming a constant geothermal gradient consistent with downhole temperature measurements and 2 assuming constant heat flow using a geotherm through the downhole temperature measurements and incorporating thermal conductivity calculated from borehole logging data although the deepest nghp 02 gh occurrences are controlled at several sites by a lithologic boundary most sites have deepest gh occurrences within a single coarse grained lithology cutoffs within a single coarse grained lithology which occur for the primary nghp 02 area b gas hydrate reservoir will inhibit pore pressure drawdowns used to extract methane from gas hydrate as an energy resource

evidence for middle triassic to miocene dual subduction zones beneath the shan thai terrane western thailand from magnetotelluric data abstract kanchanaburi province western thailand is in the middle of shan thai terrane paleomagnetic and geological data support the hypothesis of dual subduction zones beneath the shan thai terrane during the late triassic there was a westward subduction in the east where the lampang chiang rai block subducted beneath the shan thai terrane in addition in the early tertiary the western burma terrane subducted underneath the shan thai in the west resulting in an eastward subduction a pioneer survey of this region was therefore conducted using magnetotelluric mt techniques with the aim of finding deep structures associated with these ancient subduction zones 39 mt stations were deployed to cover most of the province resistivity structures are obtained from the 3 d inversion the near surface resistivity structures correspond well with the surface geology the mid and lower crusts are conductive and this is interpreted as the crusts being composed of mafic granulites of 3 porosity in which the remnant dehydrated fluid was accumulated during the subduction in addition the westward and eastward subduction zones generated mafic ultramafic intrusions which appear as two conductive zones on the east and west respectively these two conductors and the conductive lower crust support the hypotheses of the middle triassic to miocene dual subduction zones

analysis of ducted motions in the stable nocturnal boundary layer during cases 99 abstract data obtained with multiple instruments at the main site of the 1999 cooperative atmosphere surface exchange study cases 99 are employed to examine the character and variability of wave motions occurring in the stable nocturnal boundary layer during the night of 14 october 1999 the predominant motions are surprisingly similar in character throughout the night exhibiting largely westward propagation horizontal wavelengths of 1 to 10 km phase speeds slightly greater than the mean wind in the direction of propagation and highly coherent vertical motions with no apparent phase progression with altitude additionally vertical and horizontal velocities are in approximate quadrature and the largest amplitudes occur at elevated altitudes of maximum stratification these motions are interpreted as ducted gravity waves that propagate along maxima of stratification and mean wind and that are evanescent above and occasionally below the altitudes at which they are ducted modal structures for ducte

magnetotelluric studies in the central india tectonic zone implications for intraplate stress regimes and generation of shallow earthquakes abstract the central india tectonic zone citz dissects the indian peninsula into the northern and southern crustal blocks the citz has been a seismically active region since the precambrian whereas the relatively deep crustal earthquakes near the narmada faults in the eastern part of the citz have been well investigated the mechanisms for the shallow earthquakes in the western part remain unknown here we present results from a new magnetotelluric study to derive the crustal structure and to understand its implications our data show a thick and highly resistive 500 ohm m crust in the south of tapti river as against a less resistive one in the north these results in conjunction with heat flow values indicate that the crust below the southern part has stable continental cratonic signatures on the northern side of the tapti river we infer the ascent of basaltic magmas from the mantle into the shallow crust and crystallization into layered intrusions these mafic ultramafic bodies could be a potential cause for the shallow earthquakes in the western part of the citz the mafic ultramafic bodies below the crust of citz would locally modify the intraplate stresses which in turn would facilitate the occurrence of earthquakes due to reactivation of pre existing faults thus the large accumulation of strain energy in the deep crust beneath the region can be attributed to the presence of high stress bodies emplaced at depth during the deccan volcanic activity

sediment transport of the godavari river basin and its controlling factors abstract the mean annual water flow and sediment transport of the godavari river are estimated to be 92 km 3 and 170 10 6 ton t respectively in terms of sediment transport and the rate of physical erosion 555 t km 2 yr 1 the position of the godavari would be ninth and fifth respectively among the world rivers geology of the basin is the main controlling factor of the sediment transport the sedimentary rocks located in the lower part of the basin and constituting 7 of the total basin area are responsible for 33 of the sediment load more than 67 of sediment load is silt and clay annual monthly and daily variations in sediment transport indicate that a few selected days in the hydrological year control the annual sediment budget our latest estimates are nearly twice that of our earlier values the presently available global estimates on sediment transport need to be re evaluated

electrical imaging of narmada son lineament zone central india from magnetotellurics the narmada son lineament nsl zone is the second most important tectonic feature after himalayas in the indian geology magnetotelluric mt studies were carried out in the nsl zone along a 130 km long nne ssw trending profile the area of investigation extends from edlabad 20 46 16 7 5 59 05 in the south to khandwa 21 53 51 7 6 18 05 i n the north the data shows in general the validity of a two dimensional 2d approach besides providing details on the shallow crustal section the 2d modeling results resolved four high conductive zones extending from the middle to deep crust spatially coinciding with the major structural features in the area namely the gavligarh tapti barwani sukta and narmada south faults the model for the shallow section has brought out a moderately resistive layer 30 150 m representing the exposed deccan trap layer overlying a conductive layer 10 30 m inferred to be the subtrappean gondwana sediments the latter resting on a high resistive basement upper crust the deccan trap thickness varies from around a few hundred meters to as much as 1 5 km along the traverse a subtrappean sedimentary basin like feature is delineated in the northern half of the traverse where a sudden thickening of subtrappean sediments amounting to as much as 2 km is noticed the high resistive upper crust is relatively thick towards the southern end and tends to become thinner towards the middle and northern part of the traverse the lower crustal segment is conductive over a major part of the profile considering the generally enhanced heat flow values in the nsl region coupled with characteristic gravity highs and enhanced seismic velocities coinciding with the mid to lower crustal conductors delineated from mt presence of zones of high density mafic bodies intrusives with fluids presumably associated with magmatic underplating of the crust in the zone of major tectonic faults in nsl region are inferred 2004 elsevier b v all rights reserved

3 d magnetotelluric imaging of the phayao fault zone northern thailand evidence for saline fluid in the source region of the 2014 chiang rai earthquake abstract seismicity in thailand had been relatively low for decades prior to the mw 6 5 earthquake of 5 may 2014 which came as a surprise and was followed by thousands of aftershocks most of the epicenters were located in the transition region between the mae lao segment mls and the pan segment ps of the phayao fault zone pfz we conducted a 3 d magnetotelluric mt survey 31 sites to image the deep pfz structure the shallow 3 d resistivity structure matches very well with the surface geology while the deeper structures disclose many interesting resistive and conductive anomalies however the most interesting feature of this study is the large conductive anomaly ml located at a depth of 4 km to the mid crust beneath the mls near the seismogenic zone our current hypothesis is that the ml conductor has a highly interconnected aqueous fluid content and also plays crucial role in the earthquake sequence of the 5 may 2014 event as our previous seismic waveform study revealed that the mls has a relatively high fault plane instability the fluid within the fractured fault would further reduce the fault strength the accumulated pre existing tectonic stress from the north can therefore overcome the maximum frictional strength of the mls and hence cause it to slip and produce the main shock with the local structural heterogeneities and fluid in the fractured fault zones the aftershocks then occurred on both the ps and mls this is in contrast to the mae chan fault zone mcfz in the north which many scientists expected to generate a larger magnitude earthquake than any other faults since instrumental record it has only generated a few mw 4 earthquakes some of our mt stations were located within the mcfz however there is no deep conductor as the conductor lies beneath the mls a lack of interconnected fluid within the deep fault beneath the mcfz might be one of the reasons for the lower seismic activity from the mcfz other geophysical methods such as seismic tomography are necessary in order to confirm the presence of the fluid beneath the mls and also the lack of a deep conductor beneath the mcfz

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

a collision boundary imaged by magnetotellurics hidaka mountains central hokkaido japan magnetotelluric mt data were acquired across the hidaka mountains which are thought to have formed by collisional orogenic processes a regional electrical strike of n18 w consistent with surficial geology was derived from impedance tensor decomposition two dimensional resistivity models were constructed by forward model fitting with preference for reducing the misfit of transverse magnetic mode the final modeling imaged a collision boundary between cretaceous forearc basin rocks and continental crust the major features of the model are 1 a 5 km thick surficial conductive layer corresponding to cretaceous forearc basin and the underlying resistive basement that shallows and is exposed to the east where sorachi formations characterized by oceanic crustal rocks crop out therefore we interpret the underlying resistive layer as oceanic crust 2 a thin 500 m thick conductive 3 m anomaly corresponds to serpentinite exposure in the kamuikotan metamorphic belt 3 exposed deep crustal rocks in the hidaka belt showed high resistivity 1000 2000 m at the surface the subsurface westward extension inferred from the mt data is supported by seismic refraction data 4 in the hidaka mountains a relatively conductive 500 1000 m layer implying accretionary prism sequences was inferred at 2 to 10 km depth beneath a more resistive 1000 2000 m surface layer 5 a wedge shaped resistivity anomaly was found at 5 to 50 km depth beneath the hidaka belt the resistivity of this wedge decreases eastward from 30 000 m to 2000 m consistent with the surface decrease of metamorphic grade the spatial distribution is also consistent with a seismic high velocity anomaly 6 the western side of the resistive wedge is fringed by a dipping conductor correlations with a low velocity anomaly and high seismicity suggest that this conductor is an enhanced porosity region and that it may be working as a detachment zone at the collision boundary the high resistivity contrast between oceanic crust and high temperature metamorphosed continental crust permitted us to image the interfingered complex structure beneath the hidaka mountains from 300 m to 50 km depth

cenozoic plate reconstruction of southeast asia abstract the india eurasia collision alone set up a series of chain reactions and caused the formation and destruction of sedimentary basins within the domain of the collision belt changes in the rate and angle of convergence between the india and eurasia plates reflect different stages of tectonic development in southeast asia for example extrusion of the indochina block induced the consumption of the pre existing proto south china sea along northeastern kalimantan and led to the eventual opening of the south china sea along the south china margin subsequent motions of the sino burma thailand malay peninsula sumatra and kalimantan blocks have produced a succession of basins stretching from north sumatra to central thailand and on to the natuna area we present reconstructions of the southeast asia region at 60 ma 50 ma 40 ma 30 ma 20 ma 15 ma 10 ma and 5 ma it is clear from the reconstructions that the impact between greater india and southeast asia took place in the northwestern part of southeast asia the duration for the impact was probably from the middle eocene to early miocene this timing is in good agreement with the dating of the main red river fault motion wu et al 1989 scharer et al 1990 since the impact between greater india and southeast asia was basically west of the burma block there is no reason to assume that the sumatra malay peninsula and kalimantan should extrude to the southeast first along the left laterally displaced mae ping and three pagodas fault zones as suggested by peltzer and tapponnier 1988 if the opening of the central thailand basins the gulf of thailand and the malay basin are taken into consideration a dextral megashear zone is required to compensate the relative motion between indochina and the malay peninsula this dextral megashear zone might even extend into western kalimantan and serve as a boundary between the indochina block and kalimantan

national gas hydrate program expedition 01 offshore india gas hydrate systems as revealed by hydrocarbon gas geochemistry abstract the national gas hydrate program expedition 01 nghp 01 targeted gas hydrate accumulations offshore of the indian peninsula and along the andaman convergent margin the primary objectives of coring were to understand the geologic and geochemical controls on the accumulation of methane hydrate and their linkages to underlying petroleum systems four areas were investigated 1 the kerala konkan basin in the eastern arabian sea 2 the mahanadi and 3 krishna godavari basins in the western bay of bengal and 4 the andaman forearc basin in the andaman sea upward flux of methane at three of the four of the sites cored during nghp 01 is apparent from the presence of seafloor mounds seismic evidence for upward gas migration shallow sub seafloor geochemical evidence of methane oxidation and near seafloor gas composition that resembles gas from depth the kerala konkan basin well contained only co2 with no detectable hydrocarbons suggesting there is no gas hydrate system here gas and gas hydrate from the krishna godavari basin is mainly microbial methane with 13c values ranging from 58 9 to 78 9 with small contributions from microbial ethane 52 1 and co2 gas from the mahanadi basin was mainly methane with lower concentrations of c2 c5 hydrocarbons c1 c2 ratios typically 1000 and co2 carbon isotopic compositions that ranged from 70 7 to 86 6 for methane and 62 9 to 63 7 for ethane are consistent with a microbial gas source however deeper cores contained higher molecular weight hydrocarbon gases suggesting a small contribution from a thermogenic gas source gas composition in the andaman basin was mainly methane with lower concentrations of ethane to isopentane and co2 c1 c2 ratios were mainly 1000 although deeper samples were

along strike variations in the electrical structure of the san andreas fault at parkfield california magnetotelluric exploration has been used to image along strike variations in the electrical resistivity structure of the san andreas fault at parkfield california a low resistivity wedge extending to a depth of several kilometers is continuous over a horizontal distance of 8 km the base of the wedge is coincident with the shallowest microearthquakes a change in the electrical and fluid connection of the san andreas fault with a low resistivity zone in the franciscan formation is observed along the parkfield segment

exploration for unconformity type uranium deposits with audiomagnetotelluric data a case study from the mcarthur river mine saskatchewan canada unconformity type deposits supply a significant amount of the world s uranium and consist of uranium that is generally codeposited with graphite in a fault zone the low resistivity of the graphite produces a significant contrast in electrical resistivity which can be located with electromagnetic em methods the athabasca basin in western canada hosts significant uranium deposits and exploration in deeper parts of the basin has required the application of new em methods this paper presents an evaluation of the audiomagnetotelluric amt exploration method at the mcarthur river mine in the athabasca basin amt data were collected at 132 stations on a grid and two dimensional 2d and three dimensional 3d inversions were used to generate resistivity models these models showed two major results 1 a significant conductor coincident with a major basement fault p2 and the uranium deposits this conductor begins at the unconformity at a depth of 550 m and extends to a depth of at least three km an

magnetotelluric imaging of fluids in intraplate earthquake zones ne japan back arc intraplate earthquake zones in the back arc of ne japan were imaged by wide band magnetotelluric mt soundings the 90km long mt profile of 34 stations extends over the two topographic features the dewa hills and the ou backbone range which were uplifted by thrust faults mt data show two dimensionality and strong te tm anisotropic responses at the periods around 100 s after tensor decompositions with regional strike of n12 e two dimensional inversion was carried out where static shift was also a model parameter the final model is characterized by conductive blocks in the mid crust to account for the anisotropic responses correlation of the conductors to the seismic scatterers and to the low velocity anomalies suggests that the conductors represent fluids high seismicity clustering near the rims of conductors suggests that the intraplate seismicity results either from the migration of the fluids to less permeable crust or from local stress concentration near the structural boundary

structure and significance of s wave velocity and poisson s ratio in the crust beneath the eastern side of the qinghai tibet plateau the receiver functions of body waves of distant earthquakes obtained for the regions beneath 41 digital stations lhasa and ganz in tibet mandalay and rangoon in myanmar shio in india chto in thailand and station network in sichuan and yunnan were used to invert for s wave structure in the crust and upper mantle in sichuan yunnan and their surrounding areas meanwhile the distribution characteristics of the poisson s ration and the crustal thickness in sichuan and yunnan areas were also obtained results indicate that the depth of moho beneath the eastern side of qinghai tibetan plateau varies strikingly it is obvious that the greatest changes in crustal thickness occur in a north south direction the crustal thickness decreases from north to south being as thick as 70 km in eastern tibet the northern portion of our area of interest and less than 30 km in chaing mai and rangoon the southern portion of our area there are however exceptions regarding the trend the thickness exhibits an east west variation trend in the area from ma erkong kongding in sichuan to lijiang in yunnan in general the jinpingshan longmenshan fault and anninghe fault can be taken as the boundaries of this exception area the thickness in kongding in the west is 68 km while it is only 39 km in yongchuan in the east moreover the poisson s ratio values in the blocks of central sichuan and sichuan yunnan diamond are high and a low velocity layer in the crust of this area can be obviously detected the distribution characteristics of the high poisson s ratio and the low velocity of the crust in this block correspond to the tectonic structure being in contrast with the surrounding areas combining with the distribution features of the modern tectonic stress field it is deduced that the sichuan yunnan area is probably the channel through which the materials of the lithosphere flow eastward

sedimentation stratigraphy and petroleum potential of krishna godavari basin east coast of india the krishna godavari basin is located in the central part of the eastern passive continental margin of india the structural grain of the basin is northeast southwest exposures of upper cretaceous sedimentary rocks demarcate the basin margin toward the north west where the northwest southeast trending pranahita godavari graben abuts the basin the basin contains thick sequences of sediments with several cycles of deposition ranging in age from late carboniferous to holocene a major delta with a thick argillaceous facies that has prograded seaward since the late cretaceous is a hydrocarbon exploration target magnetic and gravity data predicted the basin architecture which was subsequently confirmed by a multichannel seismic sur vey the basin is divided into subbasins by fault controlled ridges sediments accumulated in subbasins more than 5 km thick above the basement ridges thin sediments are found until the jurassic period sediments were deposited in the rift valley and in topo graphic lows this sequence is completely overlain by a lower cretaceous transgressive sedimentary wedge later continued delta progradation characterized basin sedimentation with an areal extent of approximately 45 000 km2 this proven petroliferous basin has potential reservoirs ranging in age from the permian to the pliocene exploratory drilling of more than 350 wells in more than 160 structures has resulted in the discovery of 42 oil and gas bearing structures good source rocks are known from sequences ranging in age from permian carboniferous to early miocene because the reservoir sand bodies have limited lateral variation understanding the stratigraphy and depositional sub environments in different sequences is essential to decipher the favorable locales for reservoir sands tilted fault blocks growth faults and related rollover anticlines provide the structural traps begin page 1624

origin of low chloride fluid in sediments from the eastern continental margin of india results from the national gas hydrate program expedition 02 abstract national gas hydrate program expedition 02 was conducted in 2015 by d v chikyu in the western bay of bengal india analyses of interstitial water in sediment from four drilling sites along the eastern and western transect in the krishna godavari basin show that dissolved chloride cl concentrations decreased with depth from seawater values 550 mm near the sediment surface to 300 400 mm at 350 400 m below seafloor mbsf suggesting the upward advection of low cl fluid excursions of cl concentrations toward low values in gas hydrate zones were attributed to the presence of fresh water released by dissociation of gas hydrate during core recovery at sites in the western transect cl concentrations below the gas hydrate reservoir around 280 mbsf were ca 60 mm and ca 45 mm lower than those from above the reservoir and 18o and d values were 1 2 and 0 7 1 3 higher than those from above the reservoir respectively these results suggest that a fraction of migrating low cl fluid is trapped in the gas hydrate zone causing decreases of 18o and d in the residual water due to isotopic fractionation during gas hydrate formation from mass balance calculations we estimated that 10 20 of the advected fluid is trapped at the gas hydrate zone at all sites the 18o and d values below the gas hydrate zone representing relatively unaltered low cl fluid were 0 5 1 higher and ca 13 15 lower than those of seawater respectively this trend is consistent with water derived from the dehydration of clay minerals which generally occurs in deeply buried sediments the contribution of clay mineral dehydration is relatively large at the western transect compared to that in the eastern transect our results imply that fluid advection contributes to the accumulation of gas hydrate in the study area

gas hydrate reservoir identification delineation and characterization in the krishna godavari basin using subsurface geologic and geophysical data from the national gas hydrate program 02 expedition offshore india abstract during the national gas hydrate program expedition 02 nghp 02 logging while drilling conventional coring and pressure coring wire line logging vertical seismic profiling and formation pressure measurements were carried out in deep water portions of the krishna godavari k g and mahanadi basins along the eastern continental margin of india a total of 42 research holes were completed for comprehensive data collection and measurements related to gas hydrate reservoir and host sediments properties with an objective to identify producible gas hydrate in sand rich reservoirs that would be suitable for a future pilot production test shipboard and post cruise evaluation of physical properties measurements pressure core dissociation studies and gas analysis of recovered core samples have confirmed the occurrence of sand hosted gas hydrate deposits in three operational areas named during nghp 02 as area b area c and area e in the deep water portion of the k g basin the energy resource potential of the discovered gas hydrate deposits in the k g basin depends on many factors including the quantity of available gas trapped as gas hydrate in the basin therefore this study was undertaken to identify characterize and delineate the discovered and confirmed gas hydrate prospects in the k g basin based on the integrated analysis of regional seismic data and nghp 02 acquired borehole data a total of 8 sand rich reservoir constrained gas hydrate prospects have been identified and mapped in the k g basin areas b c and e as described in this report

seabed morphology and gas venting features in the continental slope region of krishna godavari basin bay of bengal implications in gas hydrate exploration abstract increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of mahanadi krishna godavari kg and cauvery basins which are promising petroliferous basins along the eastern continental margin of india in this paper we analyze the high resolution sparker subbottom profiler and multibeam data in kg offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration we identified and mapped prominent positive topographic features in the bathymetry data these mounds show fluid gas migration features such as acoustic voids acoustic chimneys and acoustic turbid layers it is interesting to note that drilling coring onboard joides in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate further geological and geochemical study of long sediment cores collected onboard marion dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo expulsion of methane and sulfidic fluid from the seafloor to understand the origin of the mounds and their relationship with gas hydrate cold seep formation we analyzed the multi channel seismic reflection mcs data close to the mounds the mcs data show that the subsurface layers beneath the mounds are folded below the folded overburden we observe zones of no coherent reflections probably originating from miocene sequence since the study area is located in shale tectonics regime where miocene sequences are known to be overpressured we interpret the zones of no coherent reflections as miocene shale diapirs the upward movement of shale diapirs has folded the overburden layer and resulted in the formation of numerous faults fractures these faults act as permeable pathways for fluid gas movement facilitating the formation of gas hydrate and cold seeps close to shale diapiric mound

crustal structure beneath the indochina peninsula from teleseismic receiver functions 1 we analyze teleseismic receiver functions to determine the crustal structure beneath the indochina peninsula which is located immediately south east of the eastern himalayan syntaxis basin we found that the indochina peninsula is characterized by a thin 31 km crust with a low vp vs ratio 1 68 the intra lower crustal low velocity zone lvz is observed beneath the northwestern part of our study region we hypothesize that it is an extension of the lower crustal lvz observed beneath the southeastern tibet and the south china block and that it terminates at the dien bien phu fault dbpf a lvz observed in the upper crust beneath southeast of the dbpf indicates that the crust is ductile and earthquakes are rare citation bai l x tian and j ritsema 2010 crustal structure beneath the indochina peninsula from teleseismic receiver functions geophys res lett 37 l24308 doi 10 1029 2010gl044874

the phuket terrane a late palaeozoic rift at the margin of sibumasu abstract it is widely accepted that sibumasu rifted from gondwana in the late palaeozoic but the rifts themselves have not previously been documented in southeast asia this paper identifies the pre middle permian kaeng krachan group of upper peninsular thailand as the infill of one such rift which is given the name phuket terrane indirect evidence suggests the rift infill is several kilometres thick and glacially influenced diamictites are conspicuous in the succession there are significant similarities with the 3 km thick pre middle permian rift infill of the carnarvon basin of western australia east of the khlong marui fault belt the succession is thinner and diamictites are a minor component a tectono stratigraphic model is proposed involving gondwana glaciers dropping their load at the present western margin of the phuket terrane from where it was re sedimented in the rapidly subsiding marine rift basin it is suggested that the khlong marui fault formed part of the eastern boundary of the rift system the three pagodas fault belt similarly juxtaposes different pre middle permian successions rifting ceased in the early permian and a passive margin formed as the mesotethys ocean widened the upper part of the kaeng krachan group and the overlying ratburi limestone representing the post rift sequence

thailand s crustal properties from tele seismic receiver function studies abstract thirty three seismic stations throughout thailand were used to infer the crustal thickness vp vs ratio and poisson s ratio of thailand using the receiver function technique the crustal thickness increases from around 31 km in the shan thai terrane stt in the west to around 38 km in the khorat plateau kp ict located in the indochina terrane ict in the east similarly the mean vp vs and poisson s ratios derived here show that vp vs increases from 1 69 to 1 73 from the stt to the kp ict while poisson s ratio increases from 0 23 to 0 25 from the stt to the kp ict our results are well supported by geological evidence found at the surface in addition we incorporate gravity and magnetic data to constrain the crustal properties of thailand the low poisson s ratios show that the crust of thailand is mostly felsic only the lower crust of kp ict is different as it is thicker denser and has higher mafic composition than the other terranes of thailand this special feature in the kp ict is required to explain the lower bouguer anomaly in the kp ict in addition we interpret the crustal evolution and deformation of these terranes and compare our results with the results from the vietnam network of the ict

electromagnetic heterogeneity of the seismogenic region of 1962 m6 5 northern miyagi earthquake northeastern japan magnetotelluric surveys were carried out to in vestigate the electrical resistivity structure of the seismo genic region of the 1962 northern miyagi earthquake m6 5 in miyagi prefecture northeastern japan a 2 d inversion reveals the existence of a deep conductive zone and overly ing re sistivezonein theuppe r crust a positiveae romag netic anomaly is also recognized above the resistive zone which is interpreted as a buried kitakami granitoid pluton by comparison with these ismicity wefound that themi croearthquakes occur just above the deep conductor and in the resistive zone and that several s wave reflectors are just above the deep conductor since the s wave reflectors sug gest the existence of fluid beneath them the deep conduc tor can be interpreted as a fluid filled zone moreover we suggest that the seepage of the fluid from the conductive fluid filled zone to the resistive granitoid pluton can become a trigger of the earthquakes

geochemical and geological constraints on the composition of marine sediment pore fluid possible link to gas hydrate deposits abstract pore water sulfate consumption in marine sediments is controlled by microbially driven sulfate reduction via organo clastic and methane oxidation processes in this work we present sediment pore fluid compositions of 10 long sediment cores and high resolution seismic data from the krishna godavari k g basin bay of bengal our results show occurrence of transient s and kink types and steady state quasi linear sulfate concentration profiles which are attributed partly to the anaerobic oxidation of methane 13 c ch 4 84 8 to 100 1 vpdb and organo clastic sulfate reduction influence of aom on alkalinity is evident from the presence of authigenic carbonate layers with highly depleted carbon isotope ratios in core md161 8 the authigenic carbonates represent the paleo smtzs and suggest marked fluctuation in vertical methane flux our geophysical data show the acoustic signatures of upward fluid migration from shallow sub surface whereas coring during nghp expedition 01 confirms the presence of sub surface gas hydrate deposits in k g basin which can be linked to deep methane sources the geochemical analysis suggests that shallow methane source can be attributed to high burial flux of labile organic matter due to high sedimentation rate sampling sites with high methane flux from the shallow gas source are characterized by quasi linear sulfate concentration profile and a shallow sulfate methane transition zone smtz and may not be necessarily linked to deeper gas hydrate deposits in contrast the deep methane source results in a transient kink type sulfate profile and a deeper smtz we have observed a close link between the occurrence of gas hydrate and the s kink type sulfate profile we interpret the short lived kink in the sulfate profiles as a result of recent enhancement in vertical methane flux possibly driven by reactivation of fault fractures systems which provide the conduits for fluid flow

magnetotelluric imaging beneath the taiwan orogen an arc continent collision 1 the taiwan orogen has formed since the late miocene by oblique collision between the luzon volcanic arc on the philippine sea plate and the eurasian continental margin this oblique collision has produced an orogen that decreases in age from north to south and permits study of the temporal evolution of an arc continent collision these factors make taiwan a favorable location to study the process of arc continent collision the first long period magnetotelluric mt measurements were recorded in taiwan as part of the taiwan integrated geodynamics research taiger project in 2006 7 measurements were made at 82 sites on three transects across south central and north taiwan that span the breadth of the orogen and cross all major tectonic boundaries robust remote reference processing of the mt time series data resulted in high quality soundings that were modeled in both 2 and 3 dimensions these mt models support predictions of lithospheric deformation i e thick skinned tectonics beneath the central ranges in south and central taiwan but are inconsistent with predictions of orogen scale thin skinned models the mt resistivity model for northern taiwan is consistent with dewatering of the subducting philippine slab and with deformation described by the subducting indenter tectonic model modeling the taiger mt data has definitively shown that conductive and seismically active crustal structures exist to 30 km beneath the orogen these conductive regions interpreted as interconnected fluid map pervasive zones of collisional deformation that are lithospheric in scale

evidence of paleo cold seep activity from the bay of bengal offshore india 1 we report evidence of paleo cold seep associated activities preserved in methane derived carbonates in association with chemosynthetic clams calyptogena sp from a sediment core in the krishna godavari basin bay of bengal visual observations and calculations based on high resolution wet bulk density profile of a core collected on board r v marion dufresne may 2007 show zones of sharp increase in carbonate content 10 55 vol within 16 20 meters below seafloor mbsf the presence of calyptogena clam shells chimneys shell breccias with high mg calcite cement and pyrite within this zone suggest seepage of methane and sulfide bearing fluid to the seafloor in the past highly depleted carbon isotopic values 13c ranges from 41 to 52 vpdb from these carbonates indicate carbon derived via anaerobic oxidation of methane extrapolated mean calendar age 58 7 ka b p of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the u th based depositional age 46 2 3 7 and 53 0 1 6 ka of authigenic carbonates sampled from this level thereby constraining the younger age limit of the carbonate deposition methane expulsion events the observed carbonate deposition might have resulted from the flow of methane enriched fluids through the fracture network formed because of shale diapirism

sedimentation rates from calcareous nannofossil and planktonic foraminifera biostratigraphy in the andaman sea northern bay of bengal and eastern arabian sea abstract in this study we determined calcareous nannofossil and planktonic foraminifera events in sediments recovered during the 2006 indian national gas hydrate program nghp expedition 01 selected bioevents permitted the assignment of orbitally calibrated ages derivative sedimentation rate estimates and identification of sedimentary discontinuities in the andaman sea at hole nghp 01 17a a late miocene to recent record was recovered but with a significant hiatus during the latest miocene and pliocene sedimentation rates here vary from 50 m myr during the pleistocene to 130 m myr for the late miocene in the northern bay of bengal at hole nghp 01 19a the base of the cored record also reaches the late miocene and extends to recent but the same hiatus missing the pliocene is present at this hole a the early pleistocene at hole nghp 1 19a shows sensible variation in sedimentation rates ranging between 130 m myr and 10 m myr during the last 0 5 ma for the late miocene the sedimentation rate was ca 50 m myr in the western bay of bengal at hole nghp 01 10b d calcareous nannofossils were sparse and only foraminifera datums are available the base of the section is latest early pliocene to late pliocene and the majority of the record is considered younger than late pliocene due to the scarcity of calcareous nannofossils and the few foraminifera datums sedimentation rates were not determined here however hole nghp 01 16a in the same region recorded the highest occurrence of pseudoemiliania lacunosa an event that confirms a pleistocene age allowing us to estimate a sedimentation rate between 110 m myr and 450 m myr along the western peninsular indian margin at hole nghp 01 01a a continuous record from the holocene to the early oligocene indicates sedimentation rates of ca 25 m myr until the middle miocene and a sensible reduction downward reaching 4 m myr in the early miocene to the early oligocene no hiatuses were observed the large changes in sedimentation rates observed in these cores reflect long timescale changes in the environment likely induced by changes in the strength of the indian monsoon system

basin architecture and petroleum system of krishna godavari basin east coast of india krishna godavari basin is a peri cratonic passive margin basin on the east coast of india figure 1 the onland part consists of 28 000 km2 and is mostly alluvium covered krishna and godavari are the two major river systems which drain the area and discharge in the bay of bengal the offshore basinal area covers 24 000 km2 to the isobath of 200 m however the basin extends into deeper water and covers a much larger area the basin s characteristic feature is its en echelon horst and graben system which is filled with a thick pile of sediments of permian to recent age and emerging as one of india s most promising petroliferous areas commercial accumulation of hydrocarbons occurs in sediments from the permian to as young as the pliocene

lithospheric characterization of the central pyrenees based on new magnetotelluric data terra nova 23 213 219 2011 abstract the pyrenees resulted from the continent continent collision between the iberian and european plates during the alpine orogeny although the subduction of the iberian lower crust is currently accepted the physical processes that occur at the boundary between the plates are still a topic of open discussion today as illustrated by the debate about the presence or absence of partial melting in the iberian subducted lower crust long period magnetotelluric data acquired for the first time in the central pyrenees constrain the low electrical resistivity structure in the iberian subducted lower crust better than previous studies plotting their upper limit 9 km deeper this new upper limit reinforces the hypothesis of partial melting additionally long period magnetotelluric data constrain the lithosphere asthenosphere boundary at 90 and 130 km deep below the iberian and european plates respectively and are compatible with electrical resistivity values between 10 and 18 ohm m for the asthenosphere

techno economic forecasting of a hypothetical gas hydrate field in the offshore of india abstract the national gas hydrate program 01 expedition 2006 and the national gas hydrate program 02 expedition 2015 have established the presence of large deposits of gas hydrates in deep water areas offshore india this paper presents the results of a techno economic study carried out for the development of a hypothetical gas hydrate field in the krishna godavari kg basin located along the eastern margin of india standard industry approaches have been used to carry out capital cost and operational cost estimates based on initial reservoir simulation modelling results three cases have been considered to encompass the possible range of reservoir production responses in the first case 18 mmscmd of gas is envisaged to be produced from 120 wells for a production period of 10 years in the second case 12 mmscmd of gas is envisaged to be produced from the 120 wells for 16 years in the third case 6 mmscmd of gas is envisaged to be produced from the 120 wells for 30 years the production rates assumed in case 3 best represents what is believed to be the most reasonable production rates as modeled for a gas hydrate accumulation nghp 02 area b site nghp 02 16 drilled during nghp 02 for case 1 an initial determination is that field development is economically viable for prevailing gas price of usd 7 67 mmbtu with npv of 1921 mmusd and irr of 27 87 with a cost of production of usd 4 74 mmbtu for case 2 the study indicates that field development is viable with npv of usd 986 mmusd and irr of 20 27 and cost of production of usd 5 8 mmbtu for case 3 the cost of production is usd 9 mmbtu no production data is available for the gas hydrate accumulations discovered during nghp 02 in the offshore of india therefore these techno economic results generated in this study can only be validated after matching the results from future pilot production testing under actual field conditions

composition and origin of authigenic carbonates in the krishna godavari and mahanadi basins eastern continental margin of india abstract the mineralogical and stable isotopic composition of authigenic carbonates from the krishna godavari kg and mahanadi basin provide a deeper insight into the processes inducing carbonate formation in the sediments of the eastern continental margin of india in the bay of bengal authigenic carbonate cements micro nodules bioturbation casts and tubes from 12 core locations drilled during the indian national gas hydrate program nghp expedition 01 were investigated for this study three main processes responsible for authigenic carbonate precipitation are identified organoclastic sulfate reduction anaerobic oxidation of methane and methanogenesis evidence of vigorous methane seepage is indicated in carbonates recovered at sites 7 10 12 kg basin and 19 mahanadi basin these methane derived carbonates display typical paragenetic carbonate mineralogies aragonite high mg calcite with 15 mol mgco 3 ca rich dolomite two separate horizons of methane derived carbonates are correlated between 4 drill holes up to 16 km apart the upper horizon has been dated with 14 c 40 100 51 600 a bp 1950 and clearly indicates that methane seepage has been much more vigorous in the past possibly due to the effect of lower sea level on the gas hydrate stability zone across the margin

electrical structure of the tectonically active kalabsha fault aswan egypt in this work we use the magnetotelluric mt method to detect geoelectrical conductivity anomalies in the earth s crust and link them to local seismic activity this application affords the unusual opportunity to study the percolation of water from a lake into a fault system and its effect on the induced seismicity mt measurements were carried out in the period range 0 0046 420 s at nine sites along a 15 km long north south profile crossing the kalabsha fault on the western bank of lake aswan data were analysed by 2d simultaneous inversion of both polarisations the resulting model is compared with the local seismicity map and reveals the conductive signature of the fault as well as geological and tectonic stresses prevailing in the aswan area our mt investigations show the following features the measured mt strike aligns with the seismic epicentre axis corresponding to the kalabsha fault while crossing the fault enhanced conductivity is found down to depths of 5 km on a 1 2 km profile segment at mid crustal depths 20 km a very high conductive body is found to coincide with the main seismic cluster in the aswan area these observations indicate that seismic activity and high electrical conductivity are related the link between them is the presence of crustal fluids which are presumably the cause of the high conductivity observed their presence is also required to trigger the observed seismicity in addition we explain the lower conductivity of the local upper crust in terms of stress modulated rock porosity we believe that these results are of general significance as they could explain the mid crustal seismicity of tectonically active zones d 2005 elsevier b v all rights reserved

physical property characteristics of gas hydrate bearing reservoir and associated seal sediments collected during nghp 02 in the krishna godavari basin in the offshore of india abstract india s national gas hydrate program expedition 02 nghp 02 was conducted to better understand geologic controls on gas hydrate occurrence and morphology targeting coarse grained sediments along the lower continental slope offshore eastern india this study combines seismic logging while drilling data and a petroleum system approach to provide a regional geologic and lithologic context for 1 gas hydrate morphology and distribution and 2 effects of fine grained sediments clays and other grains smaller than 63 m on gas production in nghp 02 area b in the krishna godavari basin area b seismic data show a buried anticline syncline structure with strong reflectors r1 and r2 that delineate two of the five lithologic units unit i shallowest ii r1 iii iv r2 and v below the bas of gas hydrate stability throughout area b gas hydrate morphology depends on its placement within these units specifically core and grain scale measurements indicate fines content exerts a primary control on the gas hydrate distribution and morphology units i ii and iii are generally fine grained on the anticline crest these units host primarily grain displacing gas hydrate veins linked to pore occupying gas hydrate in thin localized coarser grained deposits diatoms in unit iii increase porosity with depth reaching 70 where it contacts unit iv the gas hydrate reservoir associated with reflector r2 the unit iii lithology and porosity allow fluid and dissolved phase methane to escape unit iv and form gas hydrate in the fine grained overburden within unit iv fine grained layers are interbedded with coarser grained gas hydrate reservoir sands and the fines content even in the sands is high enough to impact hydraulic and mechanical properties during gas production fluid motion during gas production can mobilize fines which can then clog pore throats limiting production rates pore water freshening during gas hydrate dissociation can increase fines mobilization particularly given the smectite identified in the fine grained interbeds

magnetotelluric image of the fluid cycle in the costa rican subduction zone fluids entering the subduction zone play a key role in the subduction process they cause changes in the dynamics and thermal structure of the subduction zone1 and trigger earthquakes when released from the subducting plate during metamorphism fluids are delivered to the subduction zone by the oceanic crust and also enter as the oceanic plate bends downwards at the plate boundary however the amount of fluids entering subduction zones is not matched by that leaving through volcanic emissions4 or transfer to the deep mantle implying possible storage of fluids in the crust here we use magnetotelluric data to map the entire hydration and dehydration cycle of the costa rican subduction zone to 120 km depth along the incoming plate bend we detect a conductivity anomaly that we interpret as sea water penetrating down extensional faults and cracks into the upper mantle along the subducting plate interface we document the dehydration of sediments the crust and mantle we identify an accumulation of fluids at 20 30 km depth at a distance of 30 km seaward from the volcanic arc comparison with other subduction zones5 14 indicates that such fluid accumulation is a global phenomenon although we are unable to test whether these fluid reservoirs grow with time we suggest that they can account for some of the missing outflow of fluid at subduction zones

seismic imaging of a fractured gas hydrate system in the krishna godavari basin offshore india gas hydrate was discovered in the krishna godavari kg basin during the india national gas hydrate program nghp expedition 1 at site nghp 01 10 within a fractured clay dominated sedimentary system logging while drilling lwd coring and wire line logging confirmed gas hydrate dominantly in fractures at four borehole sites spanning a 500 m transect three dimensional 3d seismic data were subsequently used to image the fractured system and explain the occurrence of gas hydrate associated with the fractures a system of two fault sets was identified part of a typical passive margin tectonic setting the lwd derived fracture network at hole nghp 01 10a is to some extent seen in the seismic data and was mapped using seismic coherency attributes the fractured system around site nghp 01 10 extends over a triangular shaped area of 2 5 km2 defined using seismic attributes of the seafloor reflection as well as seismic sweetness at the base of the gas hydrate occurrence zone the triangular shaped area is also showing a polygonal nearly hexagonal fault pattern distinct from other more rectangular fault patterns observed in the study area the occurrence of gas hydrate at site nghp 01 10 is the result of a specific combination of tectonic fault orientations and the abundance of free gas migration from a deeper gas source the triangular shaped area of enriched gas hydrate occurrence is bound by two faults acting as migration conduits additionally the fault associated sediment deformation provides a possible migration pathway for the free gas from the deeper gas source into the gas hydrate stability zone it is proposed that there are additional locations in the kg basin with possible gas hydrate accumulation of similar tectonic conditions and one such location was identified from the 3d seismic data 6 km nw of site nghp 01 10

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

gas hydrate distribution and carbon sequestration through coupled microbial methanogenesis and silicate weathering in the krishna godavari basin offshore india abstract the national gas hydrate program expedition 01 cored ten sites in the krishna godavari basin located on the southeastern margin of india a comprehensive suite of pore water solute concentrations and isotope ratios were analyzed to investigate the distribution and concentration of gas hydrate along the margin in situ diagenetic and metabolic reactions and fluid migration and flow pathways gas hydrate was present at all of the sites cored and in situ microbial methanogenesis leads to estimates of depth integrated average gas hydrate saturations that are typically

eastern termination of the altyn tagh fault western china constraints from a magnetotelluric survey the left lateral altyn tagh fault forms the northern boundary of the tibetan plateau the strike slip rate of the active altyn tagh fault decreases northeastward and reduces close to zero as it passes north of the qilian shan this geometry raises controversies on whether and how the fault terminates or extends further east to address these controversies wide band magnetotelluric data were collected along four profiles across the altyn tagh fault ranging from 135 to 261 km in length all four profiles are located in the foreland of the qilian shan ranges and are oriented perpendicular to the inferred fault zone that could be the continuation of altyn tagh fault both the two dimensional and three dimensional electrical resistivity models derived from our magnetotelluric data show that the hexi corridor crust is generally of low resistivity whereas the crust of the huahai jinta basin is in general of high resistivity with a local and isolated low resistivity anomaly within the mid lower crust the generally high resistivity crust of the huahai jinta basin may be rheologically unfavorable for the altyn tagh fault passing through the basin toward the northeast the entirely different electrical structure between the hexi corridor and its northern neighbors indicates the existence of a tectonic boundary that coincides with the altyn tagh fault in the west and reverse faults in the east the two dimensional electrical conductivity models suggest that the altyn tagh fault transfers from a single fault in the west to a branching set of mainly dip slip faults in the east

internal deformation of the shan thai block inferred from paleomagnetism of jurassic sedimentary rocks in northern thailand abstract paleomagnetic samples of red sandstones were collected at 16 sites from the lower to upper jurassic phu kradung formation and the upper jurassic phra wihan formation around nan city 19 2 n 101 0 e in the southern region of the shan thai block after stepwise thermal demagnetization a high temperature component with an unblocking temperature of about 680 c is isolated from 11 sites we interpret this to be a prefold characteristic remanent magnetization because of a positive fold test at the 95 confidence level the tilt corrected mean paleomagnetic direction from 11 sites is d 32 3 i 33 3 95 12 2 k 15 0 which gives a paleomagnetic pole for this area of 60 1 n 186 5 e with a95 11 7 compared with a jurassic paleopole for the stable part of the yangtze block we observe a clockwise tectonic rotation of 12 8 which is similar to the observed rotation 18 28 of the northern region of the shan thai block this amount contrasts with a large rotation of more than 45 that is estimated from the narrow zone extending from luxi to mengla in the central region of this block this declination aspect suggests that a coherent whole block rotation by about 20 of the shan thai block took place in an earlier phase during indentation of india into asia and that an internal deformation with additional local rotation between 25 and 77 followed within a limited zone in the central part the internal deformation of the shan thai block absorbed the stress on the asian continent induced by indentation of india as well as its coherent whole block motions of clockwise rotation and southward displacement

deep electrical structure over the igneous arc of the indo burman orogen in sagaing province myanmar from magnetotelluric studies abstract magnetotelluric studies over the igneous arc of the indo burman range in the sagaing province of myanmar have delineated the high resistivity indian plate subducting westwards beneath the burmese block to depths of 30 km and beyond the thick moderately resistive 20 100 m layer overlying the subducting indian plate may be due to the low resistivity sediments the entire region is covered with prominent sedimentary layer with a conductance varying between 20 and 3000 s showing a general increase from the east to west suggesting that their thickness increases toward the west the large unsystematic variations in the conductance are indicative of the widely varying depositional environments and also possible vertical block movements during the course of their deposition a west dipping low resistivity zone to the east of burmese block seems to demarcate its eastern limit suggesting the possibility of a hitherto unknown deep seated fault which is also supported by the several earthquake foci located over this zone the nature of the crustal movements over this fault is not immediately apparent possibility exists that the sagaing fault is an en echelon fault and the present feature observed here is a part of this en echelon fault the possibility of channel flows of the weakened rocks in the deep crust observed in the vicinity of the eastern himalayan syntaxis may also cause such low resistivity zones

a tectonic model for the tertiary evolution of strike slip faults and rift basins in se asia abstract models for the tertiary evolution of se asia fall into two main types a pure escape tectonics model with no proto south china sea and subduction of proto south china sea oceanic crust beneath borneo a related problem is which if any of the main strike slip faults mae ping three pagodas and aliao shan red river asrr cross sundaland to the nw borneo margin to facilitate continental extrusion recent results investigating strike slip faults rift basins and metamorphic core complexes are reviewed and a revised tectonic model for se asia proposed key points of the new model include 1 the asrr shear zone was mainly active in the eocene oligocene in order to link with extension in the south china sea the asrr was less active during the miocene tens of kilometres of sinistral displacement with minor amounts of south china sea spreading centre extension transferred to the asrr shear zone 2 at least three important regions of metamorphic core complex development affected indochina from the oligocene miocene mogok gneiss belt doi inthanon and doi suthep around the asrr shear zone hence paleogene crustal thickening buoyancy driven crustal collapse and lower crustal flow are important elements of the tertiary evolution of indochina 3 subduction of a proto south china sea oceanic crust during the eocene early miocene is necessary to explain the geological evolution of nw borneo and must be built into any model for the region 4 the eocene oligocene collision of ne india with burma activated extrusion tectonics along the three pagodas mae ping ranong and klong marui faults and right lateral motion along the sumatran subduction zone 5 the only strike slip fault link to the nw borneo margin occurred along the trend of the asrr fault system which passes along strike into a right lateral transform system including the baram line

the central india tectonic zone a geophysical perspective on continental amalgamation along a mesoproterozoic suture abstract the central india tectonic zone citz is a prominent divide and a major suture zone between the north indian and south indian crustal blocks the resistive upper crust as modeled in the magnetotelluric data from citz suggests a dominant tonalite trdondhjemite granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components the highly conductive bodies in this zone might represent mafic ultramafic layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the cretaceous deccan flood basalts the uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of archaean and paleoproterozoic subducted slabs we redefine the nature of deep faults traversing the citz which were described as steep and penetrating the moho by previous workers and classify them as listric faults with gentle dips at depth seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the bhandara craton reflection data from the central part of the citz show northerly dip in the southern part suggesting northward subduction of the dharwar craton however an opposite trend is observed in the northern part of the suture with a southward dip of the bundelkhand craton based on these features and in conjunction with existing magnetotelluric models we propose a double sided subduction history along the citz this would be similar to the ongoing subduction accretion process in the western pacific region which possibly led to the development of paired collision type and pacific type orogens one important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust the high resistivity felsic domain suggests underplated sediments felsic crust that would have caused the doming our model also accounts for the extrusion of regional metamorphic belts at the orogenic core and the occurrence of high pressure ultrahigh temperature paired metamorphic belts within the suture

an alternative plate tectonic model for the palaeozoic early mesozoic palaeotethyan evolution of southeast asia northern thailand burma abstract an alternative model for the geodynamic evolution of southeast asia is proposed and inserted in a modern plate tectonic model the reconstruction methodology is based on dynamic plate boundaries constrained by data such as spreading rates and subduction velocities in this way it differs from classical continental drift models proposed so far the different interpretations about the location of the palaeotethys suture in thailand are revised the tertiary mae yuam fault is seen as the emplacement of the suture east of the suture we identify an indochina derived terrane for which we keep the name shan thai formerly used to identify the cimmerian block present in southeast asia now called sibumasu this nomenclatural choice was made on the basis of the geographic location of the terrane eastern shan states in burma and central thailand and in order not to introduce new confusing terminology the closure of the eastern palaeotethys is related to a southward subduction of the ocean that triggered the eastern neotethys to open as a back arc due to the presence of late carboniferous early permian arc magmatism in mergui burma and in the lhasa block south tibet and to the absence of arc magmatism of the same age east of the suture in order to explain the presence of carboniferous early permian and permo triassic volcanic arcs in cambodia upper triassic magmatism in eastern vietnam and lower permian middle permian arc volcanites in western sumatra we introduce the orang laut terranes concept these terranes were detached from indochina and south china during back arc opening of the poko song ma system due to the westward subduction of the palaeopacific this also explains the location of the cathaysian west sumatra block to the west of the cimmerian sibumasu block

nan river suture zone northern thailand the nan river suture zone consists of a belt of ophiolitic mafic and ultramafic rocks formed in a back arc or inter arc setting and metasedimentary rocks including epidote crossite blueschists that may represent an inner trench sequence these rocks are probably pre permian in age the nan river belt forms part of the suture between the indosinian and shan thai cratonic blocks and is inferred to correlate with the changning shuangjiang suture zone in southern china

application of 3d inversion to magnetotelluric profile data from the deccan volcanic province of western india abstract using synthetic data siripunvaraporn et al 2005b demonstrated possible advantages of interpreting single profile mt data with a three dimensional 3d inversion program here we explore this idea further using real mt data from two profiles on the indian subcontinent the first profile 330 km long cuts across the deccan volcanic province of peninsular india the second 130 km long is in the narmada son lineament zone approximately 100 km further north using the data space occam inversion code of siripunvaraporn et al 2005a 3d inversion is carried out on each of these profiles independently and results are compared with previously published two dimensional 2d interpretations in addition to inversion of the full impedance tensor we consider 3d inversion of only the off diagonal components we also experiment with variants on the model covariance in particular allowing for longer smoothing length scales along the geoelectric strike not surprisingly the 3d inversion finds models that fit the data better than had been possible with the 2d programs many of the features inferred from these previous 2d interpretations are also present in the 3d inverse solutions but the positions and amplitudes of individual conductive features are in some cases changed the 3d models suggest substantial non uniqueness in the single profile data even without explicit or special treatment we find that the relatively modest near surface distortion effects in these datasets were well fit by the 3d inversion by inserting small scale conductive and resistive features in surface layers mostly off profile

permian tectonic framework and palaeogeography of se asia abstract the principal continental lithospheric terranes now comprising se asia and that existed in the permian are the south china indochina super terrane and the sibumasu simao west burma and sw borneo semitau terranes the simao terrane is here regarded a separate terrane derived from south china by back arc spreading in the lower carboniferous rather than as an extension of indochina the main palaeo tethys ocean in thailand is identified as being represented by the chiang mai and sra kaeo sutures and the eastern boundary of the sibumasu terrane is thus interpreted to lie farther west in thailand than previously inferred the nan uttaradit suture is interpreted as representing a marginal back arc basin and contiguous with the ailaoshan and jinshajiang sutures in sw china the south china indochina super terrane and the simao terrane were located within the palaeo tethys in equatorial latitudes during the permian where they together with north china exhibit cathaysian floras and faunas the sibumasu terrane was located on the nw australian margin of gondwana until the sakmarian major shifts in faunal affinities from gondwana province faunas to an independent sibumasu province and then to assimilation into the cathaysian province records the separation and rapid northward drift of sibumasu after the late sakmarian the principal permian palaeogeographic models for the region are assessed for internal consistencies and conflicts

the impact of upstream blocking drainage flow and the geostrophic pressure gradient on the persistence of cold air pools idealized numerical simulations are performed to investigate dynamical mechanisms affecting the persistence of cold air pools in basins and valleys the first orography type considered is a shallow elongated basin located upstream of a mountain ridge for sensitivity tests the mountain ridge is removed the second type is a basin embedded in a plateau like mountain ridge in part of the simulations this basin has an outflow towards the lee side plain so as to assess the impact of the drainage flow the large scale flow is taken to be in geostrophic balance in the standard setting it is perpendicular to the basin and the ridge the main effect of a large scale pressure gradient is to induce a circulation within a cold air pool until the upper boundary of the cold pool is inclined such as to compensate for the ambient pressure gradient the cold air accumulates where the ambient pressure is lowest for a shallow basin this means that part of the cold air may be lost due to advection out of the basin the upstream influence of a mountain ridge in the lee of a shallow basin is found to be twofold it tends to deflect the low level flow towards the lower pressure leading to an additional ridge parallel force on the cold air pool on the other hand the absolute wind speed is reduced diminishing the turbulent mixing near the top of the cold pool the simulations show that the first effect prevails for ridge normal flow while second effect may dominate for other flow directions drainage flow out of a valley is found to be very important as it promotes the penetration of warm air into valleys very effectively it may cause a cold pool in a deep valley to disappear more quickly than a cold pool in a shallow basin sensitivity tests show that the persistence of a cold pool depends on its depth on its vertically integrated heat deficit and on the maximum heat deficit at the bottom of the cold pool copyright 2003 royal meteorological society

formation of methane related authigenic carbonates in a highly dynamic biogeochemical system in the krishna godavari basin bay of bengal abstract we report the abundant occurrence of authigenic fe rich carbonate high mg calcite hmc and low mg calcite from 11 cores recovered from the krishna godavari basin k g basin bay of bengal the cores were collected as part of the indian gas hydrate exploration program on board r v marion dufresne md 161 may 2007 in different environments including mounds mud diapirs mass flows and hemipelagic sediments over a range of water depths from 647 to 2079 m authigenic carbonates range in size from 1 mm to 12 cm and display various morphologies like roundish or platy micro nodules and tube like forms from the cores 173 carbonate samples have been investigated for their depth distribution mineralogy geochemical and stable isotopic composition the stable carbon isotopic composition of 46 out of 88 measured carbonate samples are around 50 which allows the differentiation into methane related carbonates hmc especially at sites 8 and 15 but also in low abundance at sites 1 5 9 and 12 results indicate that the carbonates at site 8 and 15 represent paleo methane seepage locations the fe rich carbonates occur abundantly at many sites in the k g basin their varying carbon isotopic composition indicates that probably not only sulfate reduction through organic matter degradation but also methanogenesis are the responsible processes for their formation

fluid and deformation regime of an advancing subduction system at marlborough new zealand newly forming subduction zones on earth can provide insights into the evolution of major fault zone geometries from shallow levels to deep in the lithosphere and into the role of fluids in element transport and in promoting rock failure by several modes the transpressional subduction regime of new zealand which is advancing laterally to the southwest below the marlborough strike slip fault system of the northern south island is an ideal setting in which to investigate these processes here we acquired a dense high quality transect of magnetotelluric soundings across the system yielding an electrical resistivity cross section to depths beyond 100 km our data imply three distinct processes connecting fluid generation along the upper mantle plate interface to rock deformation in the crust as the subduction zone develops massive fluid release just inland of the trench induces fault fracture meshes through the crust above that undoubtedly weaken it as regional shear initiates narrow strike slip faults in the shallow brittle regime of interior marlborough diffuse in width upon entering the deeper ductile domain aided by fluids and do not project as narrow deformation zones deep subduction generated fluids rise from 100 km or more and invade upper crustal seismogenic zones that have exhibited historic great earthquakes on high angle thrusts that are poorly oriented for failure under dry conditions the fluid deformation connections described in our work emphasize the need to include metamorphic and fluid transport processes in geodynamic models

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

high resolution numerical studies of stable boundary layer flows in a closed basin evolution of steady and oscillatory flows in an axisymmetric arizona meteor crater 1 we describe high resolution numerical simulations of flow within and over an axisymmetric approximation of the arizona meteor crater under stable boundary layer conditions motivations included guidance of and comparisons with observations during the meteor crater experiment metcrax performed in october 2006 modeling objectives were to assess the dynamical processes accounting for cold pool breakup various initial stable boundary layer sbl flows were considered on the basis of observed sbl flows and responses forcing conditions include impulsive sbl startups constant sbl accelerations and oscillatory sbl flows dominant responses include kelvin helmholtz shear instability at the top of the crater cold pool gravity waves arising from the crater geometry and seiches within the crater cold pool shear instability at the cold pool top exhibits a range of behaviors in response to different initial conditions including vortex shedding from the inflow crater lip vortex pairing strong mixing and erosion of the cold pool stratification and secondary vortex formation at the top of the mixing layer gravity wave responses depend on the flow speed are strongly three dimensional and time dependent and impact flow structure within and above the crater seiches arise from transient or oscillatory forcing and exhibit complex responses and spatial structures including upward phase progression multiple periods and vertical structures and sloshing that ejects cold pool air into the external sbl we conclude that both sloshing of cold pool air and mixing accompanying shear instability represent efficient dynamical mechanisms by which cold pool stratification can be eroded in response to external sbl motions

magnetotelluric observations across the juan de fuca subduction system in the emslab project a magnetotelluric mt transect has been obtained near latitude 45 n from the active juan de fuca spreading center across the subduction zone and cascades volcanic arc and into the back arc deschutes basin region this paper presents the mt data set and describes its major characteristics as they pertain to the resistivity of the subduction system in addition we discuss the measurement and processing procedures employed as well as important concerns in data interpretation broadband audiomagnetotelluric amt mt soundings approx 0 01 500 s period were collected on land with considerable redundancy in site location and from which 39 sites were selected which constrain upper crustal heterogeneity but sense also into the upper mantle fifteen long period mt recordings about 50 10 000 s on land confirm the broadband responses in their common period range and extend the depths of exploration to hundreds of kilometers on the juan de fuca plate offshore 33 out of 39 sea floor instruments at 19 locations gave good results of these locations five magnetotelluric soundings plus two additional geomagnetic variation sites covering the period range 200 105 s approximately constitute the ocean bottom segment of our profile the feature of the land observations which probably relates most closely to the subduction process is a peak in the impedance phase of the transverse magnetic mode around 30 50 s period this phase anomaly with a corresponding inflection in the apparent resistivity is continuous eastward from the seacoast and ends abruptly at the high cascades it signifies an electrically conductive layer in otherwise resistive lower crust or upper mantle with the layer conductance decreasing eastward from the coast to a minimum under the coast range but increasing suddenly to the east of the central willamette basin the higher conductance to the east is corroborated by the vertical magnetic field transfer function whose real component shows negative values in the period range 100 1000 s over the same distance the transverse electric mode apparent resistivity and phase on the land display a variety of three dimensional effects which make their interpretation difficult conversely both modes of the ocean floor soundings exhibit a smooth progression laterally from the coastal area to the spreading ridge indicating that the measurements here are reflecting primarily the large scale tectonic structures of interest and are little disturbed by small near surface inhomogeneities the impedance data near the ridge are strongly suggestive of a low resistivity asthenosphere beneath resistive juan de fuca plate lithosphere approaching the coastline to the east both impedance and vertical magnetic field responses appear increasingly affected by a thick wedge of deposited and accreted sediments and by the thinning of the seawater

deep electrical conductivity structures of the appalachian orogen in the southeastern u s long period magnetotelluric data across the southeastern appalachians image deep crustal and upper mantle relics of ancient orogenic events inversions of the responses show 1 beneath the appalachian mountains there is a sub horizontal conductor at 15 20 km depth which dips to the southeast at the surface trace of the brevard fault 2 at the location of the central piedmont suture there is a crustal conductor which dips towards the southeast interpreted as a structure related to the acadian suture 3 upper mantle conductors were found at 80 km depth northwest of the blue ridge and at 140 km depth southeast of the eastern piedmont between these there is a northwest dipping resistive gap possibly representing the remnant structure of the alleghanian collision

assessment of gas hydrate accumulations using velocities derived from vertical seismic profiles and acoustic log data in krishna godavari basin india abstract the second indian national gas hydrate program expedition nghp 02 was executed in 2015 in four areas termed as areas a b c and e during this expedition twenty five research sites were drilled and or cored in krishna godavari kg and mahanadi basins eastern indian offshore during nghp 02 zero offset vertical seismic profile vsp data were acquired at three sites sites nghp 02 17 19 and 22 in area b of the kg basin in this study we focus on the three sites in area b of the kg basin where zero offset vsp and downhole acoustic log data are used to assess and characterize the gas hydrate deposits zero offset vsp data are correlated with wireline log surface seismic and synthetic seismic data to characterize and delineate gas hydrate accumulations in the kg basin low velocities ranging from 1500 to 1650 m s are observed in the unconsolidated shallow sedimentary section above gas hydrate bearing units whereas very high velocities are observed in the acquired acoustic log and vsp data in the gas hydrate bearing sedimentary sections the vsp derived interval velocities range from 2000 to 3000 m s in the depth interval between 267 and 287 m below sea floor mbsf at site nghp 02 17 between 1650 and 1750 m s in the depth interval between 306 and 366 mbsf at site nghp 02 19 and between 1700 and 1800 m s in the depth interval between 198 and 290 mbsf at site nghp 02 22 gas hydrates are distributed both as pore filling and fracture filling at all three sites however high concentrations are only observed as pore filling morphology we estimate the amount of gas hydrate considering both isotropic pore filling and anisotropic fracture filling acoustic reservoir models our estimations of gas hydrate saturation match well with the available pressure core data and suggest that high gas hydrate concentrations to nearly 85 of pore space are distributed in a load bearing morphology

lithofacies characterization of gas hydrate prospects discovered during the national gas hydrate program expedition 02 offshore krishna godavari basin india abstract lithofacies of host sediments associated with gas hydrate reservoirs may have a significant influence on the formation of hydrates the type of sediments and the depositional processes responsible for the gas hydrate bearing sediments along the eastern margin of the india have been studied by integrating core data and logging while drilling downhole logs borehole data correlated with seismic data were used for the interpretation of geological process responsible for gas hydrate formation the acquired seismic profiles were correlated with the downhole logs by identifying the shape of the well logs curves that indicate finning up and blocky patterns turbidite sands and debris flows were also identified from the log and core sediment studies this study identified two prominent types of depositional systems 1 turbidity currents and 2 debris flows were mainly responsible for the deposition of gas hydrate bearing reservoirs in the study area based on these studies two well developed gas hydrate systems have been identified in the krishna godavari basin and hydrates were determined to be distributed mostly in sand dominated facies fine grained sand in the identified turbidite deposits were shown to be a good hydrate reservoir the hydrate bearing sediments in the central part of the krishna godavari basin area c in d6 block consist of mostly debris flows which is consistent with scattered gravel and sand silt sized grains in channel levee systems

geologic implications of gas hydrates in the offshore of india krishna godavari basin mahanadi basin andaman sea kerala konkan basin gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the gas hydrate petroleum system that control the occurrence of gas hydrates in nature the primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of india and to document the application of the petroleum system approach to the study of gas hydrates national gas hydrate program of india executed the national gas hydrate program expedition 01 nghp 01 in 2006 in four areas located on the eastern and western margins of the indian peninsula and in the andaman sea these areas have experienced very different tectonic and depositional histories the peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of gondwanaland to form the present indian ocean the andaman sea is bounded on its western side by a convergent margin where the indian plate lithosphere is being subducted beneath southeast asia nghp 01 drilled logged and or cored 15 sites 31 holes in the krishna godavari basin 4 sites 5 holes in the mahanadi basin 1 site 2 holes in the andaman sea and 1 site 1 hole in the kerala konkan basin holes were drilled using standard drilling methods for the purpose of logging while drilling and dedicated wireline logging as well as through the use of a variety of standard coring systems and specialized pressure coring systems nghp 01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the krishna godavari basin the mahanadi basin and in the andaman sea the site drilled in the kerala konkan basin during nghp 01 did not yield any evidence of gas hydrate most of the downhole log inferred gas hydrate and core recovered gas hydrate were characterized as either fracture filling in clay dominated sediments or as pore filling or grain displacement particles disseminated in both fine and coarse grained sediments geochemical analyses of gases obtained from sediment cores recovered during nghp 01 indicated that the gas in most all of the hydrates in the offshore of india is derived from microbial sources only one site in the andaman sea exhibited limited evidence of a thermogenic gas source the gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of india

terrane boundary and spatio temporal distribution of ore deposits in the sanjiang tethyan orogen insights from zircon hf isotopic mapping abstract the sanjiang tethyan orogen sjto of the eastern tethyan tectonic belt in china records a transition from late paleozoic tethys realm to cenozoic continental collision associated with the formation of large metallic mineral deposits this contribution combines geological and hf isotopic data for igneous rocks from the sjto together with the salient features associated with mineralization to gain insights into the crustal architecture and metallogeny integrating the available information from tectonic events sedimentary successions paleobiogeography and paleolatitude based on paleomagnetic data the hf isotopic maps that we construct highlight the changning menglian suture as an important tectonic boundary between the gondwana and cathaysian continents the changning menglian suture separates two distinct hf isotopic domains with an old reworked crustal block to the southwestern part of the sjto and a juvenile crustal block with significant mantle derived components to the northeastern part of the orogen the hf isotopic mapping of the sjto also provides important indications on the location of different deposits the jinshajiang ailaoshan suture appears to have exerted a first order control on the localisation of cenozoic magmatism and intrusion related mineral systems the magmatic source for intrusions in the eastern high ehf low tdmc domain is dominated by mantle components and gave rise to porphyry and porphyry skarn cu mo mineralization in contrast the magma sources for intrusions in the low ehf high tdmc domains contain an old and reworked crustal component and gave rise to granite related sn w mineralization those for the intrusions characterized by variable ehf and tdmc are dominantly reworked older crustal components together with subordinate juvenile material which generated the granite related pb zn cu ag mineralization