lithospheric uplift in eastern gondwana evidence for a long lived mantle plume system recent work has demonstrated that modern drainage systems on rifted continental margins may be the product of ancient lithospheric doming in areas of flood basalt magmatism this uplift is thought to reflect the existence of widespread mafic underplating and excess melt generation at rift zones here i show that uplift due to the initiation of a thermal anomaly plume head in the asthenosphere may be evidenced by the formation of discrete rift structures and persistent paleodrainage sediment dispersal patterns for up to 150 m y prior to the commencement of igneous activity and final continental breakup volcanism thus occurs as a comparatively late stage geochemical response to the long term residence of hot plume material beneath continental mantle lithosphere

polyphase deformation in a fore arc back arc basin salin subbasin myanmar burma the salin subbasin of myanmar part of the larger central basin is a fore arc back arc basin couplet situated between an oblique subduction zone to the west and a major right lateral strike slip fault to the east surface and subsurface expressions of folds and faults suggest that the basin experienced north northwest directed extensional deformation in the miocene followed by east northeast directed pliocene pleistocene transpressional deformation resulting in a variety of structural styles including thrust faults oblique reverse faults strike slip faults and normal faults fault propagation folds cored by west dipping thrust faults in the basin center are located above steps in the top of basement surface most likely fault controlled unconformities at the base of and within the pliocene pleistocene synorogenic section indicate that the thrust faults were active during the pliocene pleistocene the southeastern region contains broad north northwest trending uplifts and east northeast striking normal faults associated with thickened miocene synorogenic deposits pliocene pleistocene sedimentary rocks lie unconformably above the miocene section and are folded above the uplifts reflecting pliocene pleistocene compression in the southern part of the basin miocene sedimentary rocks thicken dramatically over the 20 n uplift and the yedwet uplift suggesting that the north northwest striking faults that bound them represent pliocene pleistocene inversion of miocene normal faults during the miocene the burma plate acted as a fore arc sliver coupled with the india plate subducting obliquely underneath it and moved northward relative to asia along the sagaing fault normal faulting and local basin formation took place at this time when the northern part of the burma plate collided with eastern asia in the pliocene transpressional deformation predominated creating thrust and reverse faults positive flower structures and inverted basins

timing of intraplate deformation northeastern indian ocean abstract seismic stratigraphy and dsdp and odp drilling have demonstrated that two unconformities of early eocene and latest miocene age can be traced over much of the northeastern indian ocean the eocene event was a major hiatus in sedimentation following collision of india with asia and was the time of termination of deposition of a continental rise off the east side of india and the initiation of proximal bengal fan deposition the miocene event was the onset of north south compression in the indian plate during rapid uplift in tibet and the himalayas

sequence stratigraphy and the evolution of the ganges brahmaputra delta complex 1 a seismic stratigraphic analysis of 2600 km of data covering part of the ganges brahmaputra delta has shown that it evolved in three stages 1 the proto ganges delta developed immediately after the breakup of gondwana at approximately 126 ma the indian plate then moved rapidly northward ultimately crossing more than 50 degrees of latitude because the catchment area was small sedimentation was relatively restricted and the early delta consists of relatively small scale prograding clastic bodies alternating with mixed carbonate clastic and carbonate platform assemblages 2 the transitional delta developed following a major eustatic sea level low at 49 5 ma initially sedimentation was relatively restricted but at about 40 ma the flux of water and clastic sedime ts dramatically increased and the delta grew rapidly with the development of major prograding clastic depositional sequences abundant evidence of lobe switching suggests that the delta was stream dominated at that time the abrupt change in the morphology of the delta appears to be a direct response to the collision of the indian plate with the eurasian plate and the rise of the himalayas the delta remained stream dominated some time after the major plate collision and until the bay of bengal became a well developed deep embayment at about 21 ma the bengal fan began to accumulate during this interval as turbidity currents carried the increased sediment load into deeper water 3 the modern delta began to appear in its present form following a major eustatic sea level low and erosio at 10 5 ma by this time the delta had become tidally dominated and had prograded well beyond the study area into the now deeply embayed bay of bengal

regional tectonics of myanmar burma and adjacent areas analysis of 38 contiguous landsat multispectral scanner scenes acquired over myanmar burma reveals numerous large scale features associated with margins of the burman plate previously unidentified northeast southwest trending discontinuities important extensions of previously mapped fault trends and numerous structural features that appear favorable for petroleum exploration a mosaic of these scenes at 1 1 000 000 scale shows a large number of tectonic elements and their spatial relationships within the area of investigation are portions of the indian burman lhasa and shan thai plates and perhaps other smaller plates the himalayan front and indo burman ranges manifest effects of current and recently past plate movement the complexity of the kinematic history accounts for the diversity of structural features in the area the last major event in this long and violent saga which began in middle miocene approximately 11 ma time and continues to the present is the recent change from a collisional to a right lateral strike slip transform margin between the indian and burman plates the complexity of the structures visible is the product of multiple plate collisions rotation of the indian plate and parts of the asian plate and long continued convergence that changed velocity and direction tbrough time the most obvious evidence of this complexity which ismore immediately apparent on geologic maps or the landsat mosaic of the region is the almost right angle relationship of the folds of the indo burman ranges and the frontal thrusts and suture zones of the himalaya these two sets of compressive features imply maximum compressive stress axes that lie at right angles to each other the implications are either that the orientation of the stress field changes rapidly over a short distance or that the stress field has changed through time both occurrences seem to be true less

palaeomagnetism of cretaceous to tertiary sediments from southern tibet evidence for the extent of the northern margin of india prior to the collision with eurasia abstract palaeomagnetic studies have been carried out on mid cretaceous to latest palaeocene sediments from the tethyan himalaya on the northern margin of the indian plate near the localities of gamba 28 3 n 88 5 e and duela 28 0 n 89 2 e in southern tibet a total of 61 sites more than 700 cores have been sampled mainly from limestones zongshan formation jidula formation member ii zongpu formation sandstones jidula formation member iii and graywackes gamba group member ii with ages well defined from detailed lithological and biostratigraphic analyses carriers of characteristic remanences are magnetite in limestones and graywackes and hematite in sandstones reliable palaeodirections were obtained from 35 sites 356 specimens positive fold tests antiparallel normal and reverse polarities a northward trend of the palaeolatitudes with decreasing age and absence of any metamorphic overprint indicate a primary origin for the characteristic remanences the results have been compared with expected palaeodirections according to available data for the indian subcontinent based on its present day geometry the late maastrichtian sites fourteen sites 156 specimens and the middle late palaeocene sites fourteen sites 113 specimens yield palaeolatitudes of 5 7 s and 4 0 n for the sampling localities in southern tibet respectively these palaeolatitudes are much further north than expected and imply that crustal shortening between the tethyan himalaya and the indian shield since the time of india eurasia collision has occurred on the order of 1500 km at the longitude of gamba duela comparison of our observed palaeolatitudes with palaeolatitudes for the lhasa block during cretaceous and palaeocene times indicate that initial contact of the northern indian margin with the lhasa block was already established at 65 60 ma with suturing completed at about 55 50 ma

tectonic framework of the northern junggar basin part i the eastern luliang uplift and its link with the east junggar terrane abstract the luliang uplift preserves relatively complete carboniferous strata and is an important region to study the spatio temporal framework and tectonic evolution of the junggar basin here we report new shrimp sims u pb ages whole rock sr nd data and in situ zircon hf isotopic compositions for carboniferous strata samples in the eastern luliang uplift the gravity and magnetic data suggest that the carboniferous volcanics are distributed as nw trending bands and also bring out n s oriented parallel amalgamation the sedimentary units and structural deformation of the eastern luliang uplift suggest that the basin evolution involved late carboniferous extensional graben stage and latest carboniferous early permian compressional stage the carboniferous batamayineishan formation is divided into the lower volcanic unit followed up sedimentary unit and an upper volcanic unit as inferred from the lithology and unconformities the lower volcanic unit from the drill cores mainly consists of andesite dacite rhyolite and tuff intercalated with minor basalt the middle sedimentary unit is made up of sandstone and mudstone with tuff and tuffaceous sandstone and the upper volcanic unit is composed of basalt rhyolite tuff and breccia with minor clastic sedimentary rocks zircon shrimp u pb age 337 2 ma for the tuff and sims u pb age 308 6 ma for basalt suggest that the lower and upper volcanic units belong to lower carboniferous and upper carboniferous respectively the basalts from upper volcanic unit in the eastern luliang uplift show typical calc alkaline affinity with low nb y ratios 0 17 0 28 and sio2 contents 47 54 and moderate th abundances 0 45 3 74 ppm enrichment in lree and liles and depletion in nb ta and ti they have low initial 87sr 86sr ratios 0 703571 0 705122 and positive end t values 5 5 8 6 and constant sm yb ratios 1 56 2 03 and variable trace element ratios e g ba th ba la and ba nb suggesting that the parental magmas were mainly derived from 2 to 8 partial melting of a spinel iherzolite mantle source metasomatized by hydrous fluids and melts of subducted sediments furthermore relatively high tio2 1 52 3 76 and zr contents 172 414 ppm indicate that they were formed in an extensional setting taking into account the occurrence of coeval island arc related volcanics we propose an intra arc rift basin model for the eastern luliang uplift the eastern luliang uplift and east junggar terrane display different tectonic features during the closure of the junggar ocean during the late carboniferous continued northward subduction prevailed and generated a fault controlled intra arc basin in the eastern luliang uplift intra arc basin contraction in permian is probably indicative of the closure of junggar ocean in the northern junggar basin our study confirms the important role of subduction accretion process associated with the carboniferous crustal growth in the junggar terrane

origin of the rajmahal traps and the 85 e ridge preliminary reconstructions of the trace of the crozet hotspot the 85 e ridge is a buried aseismic ridge approximately parallel to and west of the ninetyeast ridge in the northeastern indian ocean it was previously shown to be of probable volcanic origin emplaced on very young oceanic crust but no satisfactory model of emplacement of the rocks was offered we propose a model of origin of the rajmahal traps of northeastern india the 85 e ridge and afanasy nikitin seamount as the trace of the hotspot that now lies beneath the crozet islands in the southern indian ocean this reconstruction places the kerguelen hotspot which formed the ninetyeast ridge at the triple junction between greater india australia and antarctica before the breakup of eastern gondwana

a coordinated investigation of the gravity wave breaking and the associated dynamical instability by a na lidar and an advanced mesosphere temperature mapper over logan ut 41 7 n 111 8 w the impacts of gravity wave gw on the thermal and dynamic characteristics within the mesosphere lower thermosphere especially on the atmospheric instabilities are still not fully understood in this paper we conduct a comprehensive and detailed investigation on one gw breaking event during a collaborative campaign between the utah state university na lidar and the advanced mesospheric temperature mapper amtm on 9 september 2012 the amtm provides direct evidence of the gw breaking as well as the horizontal parameters of the gws involved while the na lidar s full diurnal cycle observations are utilized to uncover the roles of tide and gws in generating a dynamical instability layer by studying the changes of the oh layer peak altitude we located the wave breaking altitude as well as the significance of a 2 h wave that are essential to this instability formation by reconstructing the mean fields tidal and gw variations during the wave breaking event we find that the large amplitude gws significantly changed the brunt vaisala frequency square and the horizontal wind shear when superimposed on the tidal wind producing a transient dynamic unstable region between 84 km and 87 km around 11 00 ut that caused a subsequent small scale gw breaking

characterization of exceptionally strong mesospheric wave events using all sky and zenith airglow observations 1 two unusually clear mesospheric gravity wave events were observed by the boston university all sky imager and the argentine airglow spectrometer on two consecutive nights at the el leoncito observatory argentina 31 8 s 69 3 w during august 2001 both events exhibited brightness amplitudes an order of magnitude above typical values the first event had the appearance of a large amplitude 60 in oh 6 2 22 in o 2 and 37 in o 1 s emissions peak to peak compared to 1 5 typically upward propagating gravity wave with pronounced nonlinear behavior the waves also showed noticeably curved wavefronts indicating that they had originated from a relatively small source region within 180 km of el leoncito estimates of the vertical flux of horizontal energy and momentum for the wave event in the oh and o 2 emissions were very large compared to typical values and they also indicated a high degree of flux divergence over the nominal 8 km altitude between the two layers the second event occurred on the following night and exhibited a frontal morphology and behavior consistent with an internal ducted gravity wave showing nonlinear behavior akin to a mesospheric bore the disturbance also had several interesting characteristics in particular the propagation speed decreased during its passage across the sky in addition a strong vertical temperature gradient due to the semidiurnal tide appeared to influence the occurrence of the bore event

evolution of the eastern indian ocean since the late cretaceous constraints from geosat altimetry we propose a new model for the tectonic evolution of the eastern indian ocean from the late cretaceous to the present two types of data are used to improve previously published reconstructions first recent reinterpretations of seafloor magnetic anomalies between australia and antarctica and in the wharton basin provide new constraints on spreading rates and the timing of major reorganizations second vertical deflection profiles i e horizontal gravity anomaly derived from 22 repeat cycles of geosat altimeter data reveal the tectonic fabric associated with fracture zones these new geosat data provide tight constraints on paleospreading directions for example three prominent fracture zones can be traced from south of tasmania to the george v basin antarctica providing an important constraint on the relative motions of australia and antarctica through the late eocene in addition the geosat profiles are used to locate the conjugate continental margins and continent ocean boundaries of australia and antarctica as well as the conjugate rifted margins of kerguelen plateau and broken ridge based on a compilation of magnetic anomaly data from the crozet basin the central indian basin the wharton basin and the australian antarctic basin ten plate tectonic reconstructions are proposed reconstructions at chrons 5 11 ma 6 21 ma 13 36 ma and 18 43 ma confirm that the southeast indian ridge behaved as a single plate boundary since chron 18 the constraints from the geosat data provide an improvement in the fit of the kerguelen plateau and broken ridge at chron 20 46 ma to avoid overlaps between broken ridge and the kerguelen plateau prior to their breakup our model includes relative motions between the northern and southern provinces of the kerguelen plateau finally we examine the implications of our model for the relative motions of india australia and antarctica on the tectonic evolution of the kerguelen plateau and broken ridge and the adjacent labuan basin and diamantina zone as well as the emplacement of the ninetyeast ridge and the kerguelen plateau over a fixed hot spot

geologic influence on groundwater salinity drives large seawater circulation through the continental shelf observations of offshore freshened groundwater and saline groundwater discharge along continental shelves have important implications for water resources ecosystem function and the composition of the ocean but they cannot be explained by basic theory we show that these independent observations are linked and result from processes that drive variable density groundwater flow through the spatial heterogeneity that is ubiquitous in geologic formations we use lithologic data to develop geostatistical models that mimic the architecture of coastal aquifers simulation of groundwater flow and salt transport through these random realizations shows that heterogeneity produces spatially complex subsurface salinity distributions that extend tens of kilometers offshore even at steady state the associated density gradients drive high saline groundwater circulation rates that cannot be predicted by equivalent homogeneous models results suggest that these phenomena may be common along continental shelves potentially altering estimates of ocean chemical budgets and impacting coastal water management for future generations

cretaceous eocene sedimentation tectonism and biofacies in the bengal basin india abstract the bengal basin located in the eastern part of the indian subcontinent is one of the thickest sedimentary basins in the world the basin started downwarping in the early cretaceous and the sedimentation has since been continuous from an initial transgressive marine phase lasting almost up to end of the eocene the basin has evolved through a subsequent regressive marine and a later continental deltaic phase in the absence of detailed information available from the deeper basinal parts an analysis of the sedimentary and tectonic history and biofacies of the regions forming the western and northwestern shelves of the bengal basin pertaining to the initial phase of its evolution is attempted this is achieved through the synthesis of all the geological information available on the basis of recent exploration and research conducted on the sequences developed in west bengal meghalaya mikir hills and assam india the subsidence of the bengal basin was the result of differential adjustments of the crystalline basement along certain well established trends and was initiated soon after the gondwana tectonism sedimentation and volcanicity the earlier sediments were not typically marine but were more paralic to estuarine in nature the entire bengal basin except the area now comprising assam came under the influence of the first regional marine transgression during the late campanian maestrichtian the coarse clastic sediments were deposited under shallow coastal marine conditions a more widespread marine transgression took place during the early middle eocene which covered almost the entire shelf area including assam during this transgression the sediments belonging to the orthoquartzite carbonate association were formed in the shelf the sea started receding in the late eocene during which the entire bengal shelf came under the influence of heavy unloading of fine clastics the top of this fine clastic shaly sequence is an important sedimentary datum in the bengal shelf which marks the end of the first phase in the evolutionary history of the basin

cretaceous cenozoic tectonic events in the western myanmar burma assam region correlation of late mesozoic mafic and ophiolitic rocks suggests that in the late lower cretaceous a northeasterly facing mafic arc was emplaced onto southeast borneo western sumatra western myanmar burma then 1100 km south of its present position the mogok belt of myanmar and the denqen bangong co ophiolite zone in tibet all then situated on the southwestern margin of asia reversal in tectonic polarity and eastward subduction generated a late cretaceous magmatic arc in western myanmar and sumatra and its continuation through the mogok belt into the gandise batholith of tibet magmatism interrupted in the latest cretaceous probably resumed in the western myanmar tibet and sumatra arc segments in the early palaeogene it was again interrupted in the mid eocene when an east vergent ophiolite nappe overrode the indo burman ranges deforming lower eocene turbidites derived from the magmatic arc to the east following renewed northward and eastward subduction of ocean floor in the latest eocene india collided with northern myanmar and with tibet along a suture south of the jurassic triassic flysch and adjacent yarlung ophiolite in the mogok segment of the late cretaceous arc crust thickened in the early cretaceous orogeny underwent extension to form a metamorphic core complex as myanmar west of the sagaing fault moved northward more than half of this northward movement preceded the well documented 450 km of post early miocene dextral displacement on the sagaing fault and related spreading in the andaman sea generation of late cretaceous to early eocene i and s type granites in and east of the mogok belt was related either to crustal shortening or more probably to subsequent extension in the mogok belt

mesozoic anomalies in the bay of bengal abstract the analysis of 8200 line km of total magnetic intensity data in the bay of bengal northeastern indian ocean revealed the presence of approximately n30 e trending seafloor spreading type magnetic anomalies these anomalies resemble the mesozoic anomaly series m11 m0 reported elsewhere the oldest anomaly m11 132 5 ma identified close to the east coast of india is followed by the younger series of mesozoic anomalies towards the offshore some of the anomalies are offset by 60 80 km the configuration of the offsets of the isochrons allowed us to propose approximately n120 e trending oceanic fracture zones the mesozoic crust of 132 5 118 ma is estimated to evolve with an average half spreading rate of 3 5 cm yr except for the ocean floor between the m9 and m4 magnetic isochrons this part of the crust appears to be affected by the buried subsurface 85 e ridge

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

strain rate dependency of oceanic intraplate earthquake b values at extremely low strain rates we discovered a clear positive dependence of oceanic intraplate earthquake oceq b values on the age of the oceanic lithosphere oceq b values in the youngest 20 ma oceanic lithosphere exceed 1 5 which is significantly higher than the average worldwide earthquake b value around 1 0 on the other hand the b value of intraplate earthquakes in the ninety east sumatra orogen where oceanic lithosphere has an anomalously higher strain rate compared with normal oceanic lithosphere is 0 93 which is significantly lower than the oceq b value about 1 9 with the same age 50 110 ma thus the variation in b values relates to the strain rate of the oceanic lithosphere and is not caused by a difference in thermal structure we revealed a negative strain rate dependency of the b value at extremely low strain rates 1 5 in oceanic lithosphere 20 ma old imply that future improvement in seismic observation will capture many smaller magnitude oceqs which will provide valuable information on the evolution of the oceanic lithosphere and the driving mechanism of plate tectonics

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

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

latest cretaceous himalayan tectonics obduction collision or deccan related uplift abstract diverging interpretations and incompatible scenarios have been proposed for the early stages of himalayan history numerous researchers have postulated that northern india was involved in ophiolite obduction arc continent or continent continent collision during the late cretaceous or early paleocene but firm geological evidence was never produced in this article we argue against orogenic events predating the late paleocene when the neotethys ocean was still open the tethys himalayan sedimentary record testifies to anorogenic evolution primarily controlled by dynamic uplift of the passive margin prior to the massive outburst of deccan lavas and eventually followed by thermal subsidence major stratigraphic gaps in pelagic sediments suggest that such tectono magmatic episode started to affect the base of the indian plate in the campanian or possibly even in the santonian 10 to 20 ma before the climax of deccan flood basalt eruptions the abrupt increase in siliciclastic supply and accumulation rates recorded in sedimentary basins all around the indian subcontinent during the maastrichtian was followed by progradation of coastal quartzarenites along the northern indian margin in the early paleocene sandstones derived from the rejuvenated craton and uplifted inner continental margin in the south are dominantly but not exclusively quartzose felsitic volcanic rock fragments and cr spinels many of which with the same geochemical fingerprint as deccan spinels and newly found throughout the maastrichtian to danian succession resisted the combined effect of subequatorial weathering and subsequent diagenesis and testify that detritus from deccan basalts reached the indian passive margin as far as south tibet at the close of the early paleocene india drifted away from the seychelles block and thermal subsidence led to widespread carbonate deposition along the tethys himalaya this article illustrates how mega events of magmatic upwelling followed by lithospheric cooling may control passive margin sedimentation and stratigraphic patterns as occurred in northern india first in the early cretaceous and next in the latest cretaceous paleocene

post eocene biofacies palaeoenvironments and palaeogeography of the bengal basin india abstract the bengal basin is known for the extensive development of a thick cretaceous tertiary sedimentary sequence in the eastern part of india the basin has undergone several phases of transgressions regressions periodic uplifts and localised negative movements throughout the period of its evolution the sedimentation up to the end of the eocene was largely under the influence of a major transgressive phase which was later replaced by a regressive phase on account of the uplift and resulting marine retreat in this paper an analysis of the microfaunal distribution biofacies and sedimentary and tectonic history is made for reconstruction of the palaeoenvironmental conditions and palaeogeography of the bengal basin relating to the post eocene regressive phase of evolution during the oligocene early miocene the open marine conditions existing since the eocene were progressively modified on account of the regression into more brackish lagoonal and estuarine types a typical prograding delta started to spread over a large part of the marginal area of the basin the rocks of the barail group formed under the transitional environments of the delta are found to occur in almost all the major geo provinces of the basin the sedimentary environments and characteristics of the rocks were ultimately controlled by the configurations of the respective geo provinces the negative movements in the miocene along certain marginal areas were associated with the marine transgressive phase giving rise to the surma group this transgressive phase was however short lived and its impact was not equally felt in all areas the northeastern region was still uplifted which favoured an almost continuous existence of the deltaic phase by the end of miocene a greater part of the basin underwent a strong tectonic upheaval which was possibly the precursor of the main himalayan orogeny the intermontane depressions formed in the uplifted areas were the depositional sites for the tipam group and younger beds in plio pleistocene times the rapidly eroded debris from the highlands spread over a wide area towards the south under the influence of the river system of the ganga and brahmaputra which has transformed the original basinal areas into a large modern delta complex

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

an early india asia contact paleomagnetic constraints from ninetyeast ridge odp leg 121 new paleomagnetic results from sedimentary rock and basement of the ninetyeast ridge ocean drilling program leg 121 sites 756 758 detail the northward movement of the indian plate for the past 80 m y analysis of the combined paleolatitude age profile indicates a distinct reduction in india9s northward movement rate at 55 ma interpreted as completion of suturing of greater india and asia india9s northward motion slowed from 18 19 5 cm yr to 4 5 cm yr for the location of site 758 comparison of this profile with paleomagnetic data from the wider himalayan region indicates that initial contact between northwestern greater india and southern asia was already established by cretaceous tertiary time this supports a possible causal link between the india asia convergence and the deccan traps extrusion

the configuration of asia prior to the collision of india cretaceous paleomagnetic constraints paleomagnetic data from central asia show that 1700 610 km of shortening of southern asia since cretaceous time have been absorbed by distributed deformation between southern tibet and the siberia craton this result is based on a compilation of cretaceous poles from the junggar tarim tibet indochina south china north china and mongolia blocks complementing the recent compilation of enkin et al 1992a we propose a paleogeographic reconstruction of asia in the cretaceous in which the position of siberia is derived from the synthetic apparent polar wander path of besse and courtillot 1991 the resulting map which likely represents asia as it remained throughout the cretaceous until the collision with india began features an unbent tibet with an east west trending andean margin at tropical latitudes and a rather continuous belt of continental red bed basins extending from sichuan to tarim through tibet the map allows one to estimate continental shortening and rotations between the blocks which are attributed to the collision despite large uncertainties these have amounts and senses which are in all cases compatible with some recent kinematic models such as that of avouac 1991 appendix is available with entire paper on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b93 007 2 50 payment must accompany order

lateral variations in the crustal structure of the indo eurasian collision zone we thank michael ritzwoller and two anonymous reviewers for constructive comments that have helped improve the manuscript the majority of the seismic data used in this study were downloaded from iris dmc data for the ngri stations in india were provided by s s rai and zahid ra provided the pmd pakistan data kajal borah provided the ambient noise cross correlations for the uttaranchal network figures were prepared using generic mapping tools gmt software wessel and smith 1998 we thank robert herrmann for making the computer programs in seismology freely available

geological structure of an arsenic contaminated aquifer at sonargaon bangladesh abstract continuous sediment core samples and groundwater were collected in the northern part of sonargaon central bangladesh to document the hydrogeological constraints on as contaminated aquifers the study area spans the alluvial plain of the old brahmaputra river and a pleistocene terrace the madhupur tract the quaternary sequence comprises plio pleistocene sand upper pleistocene mud and holocene sand units highly as contaminated groundwater 50 1000 g l is found in the upper aquifer corresponding to the holocene sand unit that underlies the alluvial plain and it plausibly appears to be closely related to the distribution of lenses of silt to fine sand as free 1 g l groundwater occurs only within sediments coarser than medium sand highly as contaminated groundwater is characterized by low concentrations of cl and documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepac

crustal structure of the western bengal basin from joint analysis of teleseismic receiver functions and rayleigh wave dispersion teleseismic data recorded at the broadband seismological observatory of the indian institute of technology iit kharagpur are analyzed to determine the seismic characteristics of the crust beneath the western bengal basin receiver functions calculated from the teleseismic p waveform for a range of back azimuths show little variation in the moho ps arrival time indicating a nearly one dimensional crustal structure beneath kharagpur transforming the time domain receiver functions into the h v p v s domain for a stack of all receiver functions reveals a 38 2 km thick crust with a v p v s of 1 73 0 01 receiver functions stacked in narrow bins of back azimuth and great circle arc distance were inverted jointly with group velocity dispersion data for periods from 15 to 45 sec joint inversion results reveal a near surface sedimentary layer of 1 5 km thickness a 13 km thick upper crust and a 23 km thick lower crust with the moho at a depth of 37 5 km the average crustal s wave velocity is 3 7 km sec the top 0 5 km of the sedimentary layer has very low s wave velocity and a large impedance contrast with the underlying layer this represents the thin layer of unconsolidated sediments and weathered laterites near the surface as seen from deep seismic sounding dss studies across the region the s wave velocity structure of the crust beneath kharagpur is the first such result for the western bengal basin and is broadly similar to that of the indian shield crust a comparison of the crustal thickness and lower crustal velocities between kharagpur and agartala seperated by the eocene hinge zone shows remarkable differences crustal models beneath agartala reveal 36 km thick crust with the presence of a high velocity lower crust 6 km thick possibly oceanic in nature which is absent beneath kharagpur the hinge zone therefore separates the continental crust of the western bengal basin from the eastern deep basinal oceanic crust both being overlain by sediments derived from the himalayas

geology and depositional history of cenozoic sediments of the bengal basin of bangladesh abstract the bengal basin lies on the eastern side of the indian subcontinent and occupies the northern part of the bengal geosyncline sedimentation started with the breakup of gondwanaland cretaceous fluvial and deltaic sedimentation was slowly taken over by open marine and deep sea fan sedimentation by the mid eocene the basin was witnessing the maximum marine transgression and most of the stable shelf was in carbonate regime as part of the extended tethyan carbonate shelf the deeper part of the basin was dominated by deep sea fan sedimentation fed by clastic turbidites from the northeast with limited carbonate turbidites from the shelf the collision of the indian plate with the tibetan plate and with the burmese plate in the miocene resulted in a rapid switch in sedimentation pattern in the bengal basin the basin structure and sedimentation were both strongly influenced by the collision pattern of the plates and by the uplift of the himalayas with the miocene collision of the indian plate there was a change from flysch to molasse sedimentation the present day basin configuration with the ganges bramaputra delta on the north and the bengal deep sea fan on the south was established in the pliocene the stratigraphic and tectonic framework of the bengal basin suggest that the deposition of hydrocarbon source rocks was associated with the flysch sedimentation whereas formation of traps and deposition of most of the reservoir rocks in the basin was associated with mid pliocene tectonic movements and with the molasse sedimentation the pre mid miocene sediments now deeply buried in the deeper part of the bengal basin and in the eastern folded belt are the major source of gas of the eastern folded belt of the basin

sedimentation and basin fill history of the neogene clastic succession exposed in the southeastern fold belt of the bengal basin bangladesh a high resolution sequence stratigraphic approach abstract the tertiary basin fill history of the bengal basin suffers from oversimplification the interpretation of the sedimentary history of the basin should be consistent with the evolution of its three geo tectonic provinces namely western northeastern and eastern each province has its own basin generation and sediment fill history related mainly to the indo burmese and subordinately to the indo tibetan plate convergence this paper is mainly concerned with facies and facies sequence analysis of the neogene clastic succession within the subduction related active margin setting oblique convergence in the southeastern fold belt of the bengal basin detailed fieldwork was carried out in the sitapahar anticline of the rangamati area and the mirinja anticline of the lama area the study shows that the exposed neogene succession represents an overall basinward progradation from deep marine through shallow marine to continental fluvial environments based on regionally correlatable erosion surfaces the entire succession 3000 m thick has been grouped into three composite sequences c b and a from oldest to youngest composite sequence c begins with deep water base of slope clastics overlain by thick slope mud that passes upward into shallow marine and nearshore clastics composite sequence b characteristically depicts tide dominated open marine to coastal depositional systems with evidence of cyclic marine regression and transgression repetitive occurrence of incised channel tidal inlet tidal ridge shoal tidal flat and other tidal deposits is separated by shelfal mudstone most of the sandbodies contain a full spectrum of tide generated structures e g herringbone cross bedding bundle structure mud couplet bipolar cross lamination with reactivation surfaces tidal bedding storm activities appear to have played a subordinate role in the mid and inner shelf region rizocorallium rosselia planolites and zoophycos are the dominant ichnofacies within the shelfal mudstone this paralic sedimentation of neogene succession in the study area can serve as a good point of reference for tide dominated regressive shelf depositional systems the top of the composite sequence b is marked by a pronounced erosion surface indicating the final phase of marine regression followed by the gradual establishment of continental fluvial depositional systems represented by composite sequence a in this composite sequence stacked channel bars of low sinuosity braided rivers gradually pass upsequence into high sinuosity meandering river deposits a sequence stratigraphic approach has been adopted to interpret the basin fill history with respect to relative sea level changes and to subdivide the rock record into several sequences and units systems tracts and parasequences based on identified bounding discontinuities such as transgressive erosion surface tes regressive erosion surface res marine flooding surface mfs and incised valley floor ivf this approach provides new insight for both exploration and exploitation strategy for hydrocarbon plays that may prove vital to the oil companies engaged in exploration activities in the bengal basin it is strongly recommended here that the traditional lithostratigraphic classification of this part of the basin which is based on the assam stratigraphy be abandoned or at least revised a tentative allostratigraphic scheme is presented and it is suggested that to formalize the scheme further study both surface and subsurface is needed

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

the diagenesis of neogene clastic sediments from the bengal basin bangladesh abstract the diagenetic history of the neogene clastic sediments of the bengal basin is described based on petrological analysis of samples from four boreholes in the shales evidence has been found of progressive illitization of the mixed layer illite smectite with increasing depth of burial unlike other studies notably of the tertiary gulf coast sediments there is no evidence of the illite smectite changing from a random to a regular mixed layer phase during diagenesis other diagenetic changes in the shales include the decrease in the proportions of kaolinite and calcite with increasing burial diagenesis in the sandstones principally involves the progressive development of various types of cements in the following order chlorite authigenesis siderite crystallization illite rim formation quartz overgrowths and late fe calcite cements after the formation of the cementation phases there was a dissolution phase creating secondary porosity via the dissolution of carbonate and feldspars and this was accompanied by the generation of a late kaolinite cementing phase the latter processes are thought to arise from the generation of acidic pore waters generated by the maturation of organic matter in the neogene and paleogene shales in some of the sandstones an early poikilotopic fe calcite cement formed and halted further diagenesis beyond the formation of the chlorite and early siderite crystallization

ref changing river courses in the western part of the ganga brahmaputra delta by kalyan rudra 2014 geomorphology 227 87 100 abstract research on river dynamics of the gb delta is in the early stages and it is a topic of multidisciplinary interest a narrow sectoral approach of research may lead to much confusion the discussion has a declared vision of offering corrected information against inconsistencies improper understanding and misrepresentation of facts in my paper but in reality the critics arguments are based on the wrong premise and those may create much confusion this reply is designed sequentially to address issues raised in the discussion

fabry perot imaging observations of oh 8 3 rotational temperatures and gravity waves ground based observations of lower thermospheric emission originating from oh 8 3 rotation lines p1 2 at 7316 4 a and p2 3 at 7330 a were made with an intensified imaging fabry perot interferometer from santa cruz california on september 25 and 26 1987 during a cedar campaign the rotational lines were imaged simultaneously from four different atmospheric volume elements which were separated by 15 km north to south and 30 km east to west two types of analysis are performed on the data first traditionally observed temporal structure in the rotational temperature showed acoustic gravity wave like periods which are compared to other experimental data spectral analysis on the data shows the traditional gravity wave characteristics for specific periods in four separated atmospheric volumes which were sampled simultaneously second the simultaneous multiple point sample provides a measurement of horizontal phase velocity spectral components of temperature variation exhibited phase coherence in all four spatial regions indicating wave phenomena of length scales 30 km gravity wave versus period data are compared with the theories of schubert and walterscheid 1988 and hickey 1988a b

an overview of the sedimentary geology of the bengal basin in relation to the regional tectonic framework and basin fill history abstract the bengal basin in the northeastern part of indian subcontinent between the indian shield and indo burman ranges comprises three geo tectonic provinces 1 the stable shelf 2 the central deep basin extending from the sylhet trough in the northeast towards the hatia trough in the south and 3 the chittagong tripura fold belt due to location of the basin at the juncture of three interacting plates viz the indian burma and tibetan eurasian plates the basin fill history of these geo tectonic provinces varied considerably precambrian metasediments and permian carboniferous rocks have been encountered only in drill holes in the stable shelf province after precambrian peneplanation of the indian shield sedimentation in the bengal basin started in isolated graben controlled basins on the basement with the breakup of gondwanaland in the jurassic and cretaceous and northward movement of the indian plate the basin started downwarping in the early cretaceous and sedimentation started on the stable shelf and deep basin and since then sedimentation has been continuous for most of the basin subsidence of the basin can be attributed to differential adjustments of the crust collision with the various elements of south asia and uplift of the eastern himalayas and the indo burman ranges movements along several well established faults were initiated following the breakup of gondwanaland and during downwarping in the cretaceous by eocene because of a major marine transgression the stable shelf came under a carbonate regime whereas the deep basinal area was dominated by deep water sedimentation a major switch in sedimentation pattern over the bengal basin occurred during the middle eocene to early miocene as a result of collision of india with the burma and tibetan blocks the influx of clastic sediment into the basin from the himalayas to the north and the indo burman ranges to the east rapidly increased at this time and this was followed by an increase in the rate of subsidence of the basin at this stage deep marine sedimentation dominated in the deep basinal part while deep to shallow marine conditions prevailed in the eastern part of the basin by middle miocene with continuing collision events between the plates and uplift in the himalayas and indo burman ranges a huge influx of clastic sediments came into the basin from the northeast and east throughout the miocene the depositional settings continued to vary from deep marine in the basin to shallow and coastal marine in the marginal parts of the basin from pliocene onwards large amounts of sediment were filling the bengal basin from the west and northwest and major delta building processes continued to develop the present day delta morphology since the cretaceous architecture of the bengal basin has been changing due to the collision pattern and movements of the major plates in the region however three notable changes in basin configuration can be recognized that occurred during early eocene middle miocene and plio pleistocene times when both the paleogeographic settings and source areas changed the present basin configuration with the ganges brahmaputra delta system on the north and the bengal deep sea fan on the south was established during the later part of pliocene and pleistocene and delta progradation since then has been strongly affected by orogeny in the eastern himalayas pleistocene glacial activities in the north accompanied sea level changes in the bay of bengal

a paleo brahmaputra subsurface lithofacies analysis of miocene deltaic sediments in the himalayan bengal system bangladesh abstract the bengal foreland basin contains a succession of up to 16 km of dominantly deltaic deposits eroded from the eastern himalayas and the indo burman ranges and carried by major river systems similar to the present day ganges and brahmaputra analysis of electric logs and core descriptions acquired during oil and gas exploration in bangladesh allows construction of lithofacies maps which constrain depositional patterns of miocene strata compilations of sand thickness and sand shale ratio of the miocene surma group show that lower to middle miocene strata of the bhuban formation accumulated in a large elongate trough sand thickness and percentage both decrease markedly away from this depocenter which describes a large scale bend running initially westward from rashidpur northeast bengal basin and curving southward toward the bengal fan middle to upper miocene strata of the boka bil formation show a similar geographic trend in deposition of coarsest and thickest sediment but the major depocenter had shifted northward relative to that of the bhuban formation by some 30 km passing near beani bazar these trends suggest that deltaic deposits of the surma group filled the sylhet trough of the northeast bengal basin from the east published seismic data from western bangladesh show that additional large channels also contributed materials to the bengal basin from the northwest during the late miocene but these channels resulted in very little accumulation in the northwestern part of the basin probably due to restricted subsidence of underlying continental crust this study suggests that there was a major drainage system similar to the modern brahmaputra river during miocene time which carried orogenic sediments eroded from the uplifted terranes of the eastern himalayas and indo burman ranges to the eastern bengal delta

the potential for giant tsunamigenic earthquakes in the northern bay of bengal the sumatra andaman earthquake and indian ocean tsunami of 2004 came as a surprise to most of the earth science community while it is now widely recognized that the risk of another giant earthquake is high off central sumatra just east of the 2004 earthquake there seems to be relatively little concern about the subduction zone to the north in the northern bay of bengal along the coast of myanmar formerly burma phil cummins suggests however that giant earthquake activity is possible in this region and that a large and vulnerable population may be facing a significant earthquake and tsunami hazard there is a high potential for giant earthquake activity along the coast of myanmar indications that this may be the case include the tectonic environment historical earthquake activity and stress and crustal strain observations these findings suggest that giant earthquakes do occur off the coast of myanmar and that a very large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard the great sumatra andaman earthquake and indian ocean tsunami of 2004 came as a surprise to most of the earth science community although it is now widely recognized that the risk of another giant earthquake is high off central sumatra1 just east of the 2004 earthquake there seems to be relatively little concern about the subduction zone to the north in the northern bay of bengal along the coast of myanmar here i show that similar indicators suggest a high potential for giant earthquakes along the coast of myanmar these indicators include the tectonic environment which is similar to other subduction zones that experience giant megathrust earthquakes stress and crustal strain observations which indicate that the seismogenic zone is locked and historical earthquake activity which indicates that giant tsunamigenic earthquakes have occurred there in the past these are all consistent with active subduction in the myanmar subduction zone and i suggest that the seismogenic zone extends beneath the bengal fan i conclude therefore that giant earthquakes probably occur off the coast of myanmar and that a large and vulnerable population is thereby exposed to a significant earthquake and tsunami hazard

characteristics of atmospheric waves in the tidal period range derived from zenith observations of o2 0 1 atmospheric and oh 6 2 airglow at lower midlatitudes from about 100 nights of ground based measurements of fluctuations in airglow brightness and rotational temperature taken from two sites at 32 s and 37 n a considerable number of new determinations of complex values of krassovsky s are derived and compared with observations by other investigators and model predictions our findings support the model of hines tarasick and shepherd hts which leads to practical consequences regarding the usefulness of airglow observations for deriving vertical propagation of atmospheric waves in the mesopause region it is shown at least in part that the vertical wave propagation can be inferred from zenith observations of one airglow emission alone and that consistent information can be obtained simultaneously for the two airglow layers the analysis presented comprises the range of observed periods between 3 and 24 hours the salient feature is that values are essentially limited to the fourth quadrant for both the o2 and oh emissions which means according to the hts model that the majority of the waves observed propagate upward with vertical wavelengths between 20 and 60 km and only a few are possibly evanescent this would not contradict the interpretation that most if not all of the wave signatures may be due to the semidiurnal tide or tidal transients

deep structure and tectonics of the burmese arc constraints from earthquake and gravity data abstract active subduction of the indian plate is currently occurring beneath the burmese arc along an east dipping benioff zone which extends to a depth of about 180 km the overriding burma plate has an appearance of an inland seismic slab that is deflected downwards in the vicinity of the benioff zone a crustal seismic zone some 60 80 km east of the benioff zone correlates to backarc activity a triangular aseismic wedge in the top part of the crust outlines the central belt molasse basin east of the burmese foldbdt fault plane solutions show that the burmese benioff zone is characterized by shallow angle thrusting at its upper edge whereas down tip tensional events dominate its lower edge most of the backarc seismicity is accounted for by the sagaing transform or by the activity of the shan scarp normal fault zone at the margin of the asian plate a gravity anomaly pair with amplitude of 175 mgal coincides with the 1100 km long burmese arc lying in a north south direction the gravity anomalies along a profile in central burma and in adjacent areas of the bengal basin are interpreted in terms of plate subduction as well as near surface mass anomalies this suggests that sediments below the central belt may have an average thickness of the order of 10 km but may be as thick as 15 km at the subduction zone the oceanic crust underlying deeper parts of the bengal basin experiences phase transition at about 30 km depth in a benioff zone environment east of the burmese foldbelt several thrust planes are present within the folded and deformed cretaceous tertiary sediments of the fold belt these are often associated with ophiolites and basic to ultrabasic rocks a low density zone at least 60 km wide underlies the andesitic volcanic axis in the overriding plate

trench slope controlled deep sea clastics in the exposed lower surma group in the southeastern fold belt of the bengal basin bangladesh abstract deltaic to shallow marine neritic depositional settings have until now been the accepted interpretation for the neogene surma group of rocks exposed throughout the southeastern fold belt of the bengal basin the present study revises the earlier views and proposes some new insights on the basis of detailed field studies carried out in the sitapahar anticline rangamati area and in the mirinja anticline lama area it is here proposed that the surma group succession represents an overall basinward progradation from deep marine to coastal marine depositional settings sedimentological evidence strongly suggests that the lower part of the surma group represents a slope apron the growth of which is thought to have been governed by a westward migrating accretionary prism complex within the active margin setting of the indo burmese plate convergence thin packages of distinct turbidity current generated deposits together with some slump and debris flow deposits contained within thicker intervals of mudstone characterize the lowermost exposed unit of the surma group in the sitapahar anticline the overlying slope deposits are essentially mudstone dominated comparable deep sea clastics with thicker intervals of sandstone turbidites contained within a submarine canyon are present in the mirinja anticline this new model suggests that it may be timely to re evaluate the existing stratigraphic and tectonic framework of the eastern bengal basin