a holocene pollen record of vegetation and coastal environmental changes in the coastal swamp forest at batulicin south kalimantan indonesia abstract pollen analysis of a coastal peat swamp core representing 9100 bp from batulicin south kalimantan indonesia shows that mangrove forest with rhizophora as its main element has been established since the early holocene vegetation development in general and particularly mangrove forest was influenced by holocene environmental changes the highest value of rhizophora at ca 8200 bp indicates an early holocene sea level drop and implies sea level at ca 9 m subsequently mangrove forest was severely disrupted by rapid sea level rise at ca 6400 bp prior to the holocene maximum however it quickly recovered following a lower rate of sea level rise or subsequent sea level drop at ca 6000 bp and flourished until ca 1000 bp from ca 6000 bp the environmental setting around the site seems to have gradually become more terrestrial and changed from mangrove forest to peat swamp forest due to higher precipitation and intensive progradation human influence is recognized from ca 1600 bp

causes of recent himalayan uplift deduced from deposited patterns in the ganges basin the hypothesis1 that late cenozoic uplift of many of the world s mountain ranges was a response to climate change rather than to tectonic processes is based on the premise that enhanced erosion in an altered climate led to a reduction in both the total mass of a mountain range and its mean elevation this reduction was coeval with increased regional relief and with passive isostatic uplift of the remaining summits the hypothesis is difficult to evaluate because both climate and tectonic forces affect uplift in many active ranges in the absence of sufficient denudational and uplift data from the mountains themselves depositional patterns in adjacent basins may sometimes be used to distinguish between uplift arising from erosional or from tectonic processes in foreland basins uplift of the proximal basin and a reduction or absence of asymmetric subsidence are predicted responses to erosionally driven uplift2 here i show that patterns of sediment accumulation and the position of major rivers in the neogene gangetic foreland basin seem to have changed markedly in plio pleistocene times these changes lend support to the hypothesis that the importance of erosional unloading has increased in the himalayas during the past 4 myr

2 d modelling of the anticlinal structures and structural development of the eastern fold belt of the bengal basin bangladesh abstract structural architecture of the bengal basin has been strongly controlled by the collision pattern of the indian plate with the burma and tibetan plates the eastern fold belt efb of the basin comprising a series of north south trending curvilinear anticlines and synclines represents a fold and thrust belt that constitutes the westward continuation of arakan chin fold system of the indo burman ranges the present study is mainly concerned with the 2 d modelling of the anticlinal structures in order to develop an understanding about the process response relationships between the structural style and tectonic evolution of the eastern fold belt the dominant fold generating mechanism is believed to be the east west directed compressional force arising from oblique subduction of the indian plate beneath the burma plate that resulted in the growth of fault propagation folds above a detachment or decollement at depth giving rise to the neogene accretionary prism complex development a prominent feature of the region is the major east dipping thrusts separating successive accretionary wedges in seismic sections evidence for several phases of compressional deformation suggests that multiphase stress conditions were responsible for the structural expression of the fold belt deep seismic sections reveal that the base of folding is characterized by a low interval velocity horizon that represents a detachment separating the upper folded zone from the lower seismically coherent nearly unfolded zone this detachment coincides with the undercompacted pressured shale unit which is thought to have played an important role in the structural development of the eastern fold belt clay mineralogical analysis reveals the presence of a low density shale horizon within the dense and thick shale sequence that is thought to be an undercompacted pressured shale during the geological past and was responsible for the initiation of decollement and incipient diapirism involving thin skinned tectonics it is suggested that the salient structural features of the eastern fold belt e g multiphase fold development series of east dipping thrusts and a basal zone of detachment or decollement are the products of thin skinned tectonics resulting from the indo burmese plate convergence

high energy ephemeral stream deltas an example from the upper silurian holmestrand formation of the oslo region norway abstract the late orogenic deposits of the upper silurian holmestrand formation of the oslo region norway comprises sharply alternating ephemeral stream and sandy beach face deposits the formation is divided into three units reflecting the down slope change on an extensive ephemeral stream delta system the lower unit of the formation comprises ephemeral stream sediments as stacked sheet sandstone bodies deposited on a broad coastal floodplain each sheet is bounded by a lower intraclast strewn scoured surface overlain by massive horizontally stratified low angle and trough cross bedded sandstones in the medial and upper units of the formation the ephemeral stream sediments alternate with beach face deposits forming ephemeral stream deltas the ephemeral stream deltas are marked by intraclast strewn scoured surfaces and dominated by trough cross bedded sandstones they may contain escapement burrows marine bioturbation and wave working of the delta surfaces the beach face deposits are composed of alternating irregular horizontally stratified sandstones with current and wave ripple cross lamination and tabular cross bedded sandstones deposition took place in a coastal non to micro tidal shallow water environment influenced by longshore currents and low palaeo wave energy seven ichnotaxa are recognized and support the sedimentary record of a transitional environment between a broad coastal floodplain and a shallow marine environment the presence of calcretes indicate an arid to semi arid palaeo climate

model for turbidite to contourite continuum and multiple process transport in deep marine settings examples in the rock record abstract petrological analysis of geological sections in st croix in the caribbean the niesenflysch in switzerland and the annot sandstone in the french maritime alps sheds light on multiple process transport in deep marine settings a model depicting a turbidite to contourite continuum of stratal types is applied to these three rock units recognition of a diverse suite of bedforms coupled with analysis of paleocurrents helps to better interpret depositional origin and basin paleogeography the st croix strata record emplacement by gravity flows and subsequently by bottom currents flowing parallel to the base of slope these sediments accumulated on a lower slope apron a niesenflysch section in the swiss alps west of adelboden includes turbidites which were deposited at fairly regular intervals beyond the base of slope in a setting more distal than that of the st croix sequences most of these turbidites appear to have been partially reworked by bottom currents related to basin circulation or to density flows from the basin margins in the annot sandstone reworked turbidites termed transitional variants and packets of entirely rippled strata are observed in submarine fan and slope sequences in the peira cava area in contrast to those in st croix and the niesenflysch the current emplaced deposits of the annot sandstone are directly associated with fan valley deposits such rippled strata in channels are deposits of gravity flow origin which were subsequently reworked downslope by currents generated by successive gravity flows they also occur on levees by overbank flow consideration of multiple process transport is of special help to interpret sections which are poorly exposed or which can be examined in cores or which are located in sequences that have been highly deformed structurally

the boundary layer character of tidal currents in the eastern irish sea abstract the vertical profile of the tidal currents observed by a ship borne adcp at a site in the eastern irish sea where the water depth is 50 m was logarithmic with height above the bed in the lower 50 60 of the water column except for periods of about 1 h either side of slack water the maximum height of the boundary layer reached 40 m during the flood tide the shearing stress determined by the method of bowden et al 1959 showed a tendency to be uniform with height in the lower half of the water column while the eddy viscosity increased linearly away from the bed scaling on u z where u is the friction velocity both of these features are characteristic of the logarithmic profile region of a boundary layer flow estimates of zo the roughness length and cd the bottom drag coefficient were around 10 3 m and 2 4 10 3 consistent with the known character of the bed the scatter in the derived boundary layer parameters was reduced significantly by averaging the data within 30 min intervals which suggests the presence of tidal eddies having periods comparable to the 5 min sampling period of the adcp short period fluctuations in the flow were coherent over the lower 20 m of the water column and propagated vertically away from the bed

episodic granite plutonism in the scottish caledonides boulders from a lower devonian conglomerate complete the record of a phase of ordovician plutonism associated with island arcs and blue schist metamorphism indicating high angle subduction following a phase of sedimentary accretion late silurian plutonism was the result of low angle subduction the two granite suites have distinct isotopic trends

10 be profiles in seawater a knowledge of the marine geochemical cycle of 10be is basic to the use of this long lived cosmogenic radioisotope half life 1 5 myr in geochronological and geophysical studies1 3 the first attempts at measuring 10be in seawater were made only recently using nuclear accelerator spectrometry and six concentration values from four locations have been reported4 6 this data base must be expanded to include detailed water column profiles so that the behaviour of 10be in the ocean can be more fully described a parallel case in point is the recent measurement7 of a detailed oceanic profile for the stable 9be we report here two water column profiles of 10be one in the drake passage near antarctica and the other in the san nicolas basin about 100 km off the coast of southern california the san nicolas basin profile clearly demonstrates the regulation of 10be distribution by particulate cycling the data confirm the earlier suggestion4 of particle uptake of 10be in the surface ocean they also furnish evidence for regeneration of 10be across the thermocline and near the sea floor and for mid water scavenging

neogene syn tectonic sedimentation in the eastern margin of arakan bengal basins and its implications on for the indian asian collision in western myanmar abstract the arakan basin is one of the major sedimentary basins formed in the frontal part of the himalayan orogenic belt since the late cenozoic defining one of the four major sedimentary basins of myanmar it is geomorphologically and tectonically differentiated from the others the study area along the westernmost edge of myanmar is separated from the arakan yoma indo burman ranges by a narrow coastal strip and is bordered by the bay of bengal to the west regional stratigraphic correlation and the geological age of the siliciclastic sequences were established based on planktonic foraminiferal zonation deep marine slope and shelf environments during early to middle miocene ca 21 5 11 ma and a southward prograded shelf delta environment during late miocene to pliocene time were determined the early miocene underthrusting along the himalayan front is well documented by the forced regressive sedimentation patterns in the slope and shelf systems sediments of which derived from the paleo ganges brahmaputra river systems in the bengal arakan basins sequential evolution of the miocene successions manifests in forced regressive wedged systems tracts these evolved through slope by passing and slumping and following deep marine channel in filling began to accumulate an increasing sediment load due to the rapid fall of sea level by the uplift in the hinterlands during the early to early middle miocene the formation of a shelf delta systems marks a dramatic shift in the evolution of the southward prograding delta systems following a eustatic sea level low in the foreland areas erosional off loading with foreland uplifting caused a wide active fluvial systems and formed transverse rivers distally in the late middle to late miocene

neogene evolution of the himalayan tibetan region constraints from odp site 758 northern ninetyeast ridge bearing on climatic change abstract magnetic susceptibility remanence and lithostratigraphic profiles for the neogene quaternary sequence at site 758 odp leg 121 on the northern ninetyeast ridge show distinct changes dated from biostratigraphy and detailed magnetostratigraphy at 17 5 10 4 10 0 8 8 6 5 5 4 5 1 2 7 2 5 1 9 and 1 2 1 1 ma these magnetic and lithologic changes appear to reflect changes in the supply and character of terrigenous material from the himalayan tibetan region resulting from changes in gradient of the ganges brahmaputra and probably the ancient indus drainage systems the sedimentary changes can be correlated with changes in uplift sensitive markers such as the oceanic 87 sr 86 sr ratio and monsoonal induced upwelling but not clearly so with sealevel variations we interpret these sedimentary changes therefore to primarily reflect changes in the tectonic evolution of the himalayan tibetan region the changes in the distal marine sedimentary record of the northern ninetyeast ridge are compared with isotopic control on the timing of himalayan tibetan tectonic phases and magnetostratigraphic control on their reflection in the proximal siwalik molasse record this comparison indicates that the distal ninetyeast ridge record can be used to detail and to place minimal age constraints on tectonic phases in the wider himalayan region and on evolution of the proximal molasse sequence with a time lag determined for the four earliest changes at less than 1 m y the changes at 17 5 ma and 5 4 5 1 ma can be interpreted in terms of the causative chain enhanced plate motion uplift and sedimentation change climatic change supporting arguments that the late cainozoic global climatic deterioration is driven by uplift of large plateaus such as the himalayan tibetan region and the western cordillera

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

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone 1 the nordfjord sogn detachment zone nsdz is widely cited as one of the primary structures responsible for the exhumation of norwegian ultra high pressure uhp rocks here we review data from the considerable volume of research describing this shear zone and compile a strikeparallel cross section along the nsdz from the solund basin in the south to the soroyane uhp domain in the north this cross section highlights several previously unrecognized patterns revealing a shear zone with top to the west asymmetric fabrics that 1 initiated at amphibolite facies 2 overprints metamorphic breaks and tectonostratigraphic contacts and 3 has a gradational continuum of muscovite cooling ages these patterns constrain the kinematic evolution of the nsdz and suggest a new three step model for the exhumation of norwegian u hp rocks the initial stages of exhumation were characterized by the rise of crustal rocks from u hp depths to the base of the crust by buoyancydriven mechanisms not specified in this paper mantle exhumation was followed by top to thewest normal sense displacement within a broad noncoaxial ductile shear zone near the base of the crust that overprinted tectonostratigraphic contacts formed previously during mantle exhumation in the final stages of crustal exhumation top w brittleductile detachments soled into and partially excised this ductile shear zone dropping the devonian basins into contact with rocks of varying tectonostratigraphic levels this new interpretation of the nsdz is significant as it accounts for the extreme crustal excision observed in western norway using three sequentially overprinting structures active at different stages of uhp rock exhumation citation johnston s m b r hacker and t b andersen 2007 exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone tectonics 26 tc5001

forced regressions in a sequence stratigraphic framework concepts examples and exploration significance sequence stratigraphic concepts suggest that stratal geometries develop and are largely controlled by changes in relative sea level on the shelf lowstand deposits which form during falls and subsequent stillstands of relative sea level can be recognized by the presence of an unconformity at the base the isolated and basinward position relative to the previous shoreline and the abrupt seaward translation of shallow water and shoreline facies into the basin across an unconformity surface this seaward translation of facies and shoreline regression in response to relative sea level lowering is termed a forced regression a forced regression is independent of variations of sediment flux and is in contrast with normal regressions that occur in response to excess sediment flux relative to space available on the shelf i e accommodation forced regressions commonly are associated with a zone of sedimentary bypass subaerial exposure and possible fluvial erosion between the newly formed and preceding shorelines certain shelf sands previously interpreted as offshore or mid shelf sand bodies thus can be reinterpreted as stranded lowstand shorelines associated with forced regressions this alternative interpretation has economic significance insofar as it suggests different subsurface correlations and reservoir geometries with the potential for development of new play types and enhanced recovery in o der fields examples of forced regression can be observed at a variety of scales and ages several such examples include the modern east coulee fan delta and the lower cretaceous viking formation in alberta canada the quaternary rhone delta and the quaternary hudson valley system

biological controls on resuspension and the relationship between particle size and the kolmogorov length scale in a shallow coastal sea abstract measurements of suspended particle matter spm and turbulence have been obtained over five tidal surveys during spring and summer 2010 at station l4 50 25 n 04 22 w depth 50 m in the western english channel the relationship between turbulence intensity and bed stress is explored with an in line holographic imaging system evaluating the extent to which material is resuspended image analysis allows for the identification of spm above a size threshold of 200 m capturing particle variability across tidal cycles and the two seasons dissipation of turbulent kinetic energy which exceeds 10 5 w kg 1 yields maximum values of bed stress of between 0 17 and 0 20 n m 2 frequently resulting in the resuspension of material from the bed resuspension is shown to promote aggregation of spm into flocs where the size of such particles is theoretically determined by the kolmogorov microscale lk during the spring surveys flocs of a size larger than lk were observed though this was not repeated during summer it is proposed that the presence of gelatinous biological material in spring allows flocculated particles to exceed lk this suggests that under specific circumstances the limiting factor on the growth of flocculated spm is not only turbulence as previously thought but the presence or absence of certain types of biological particle

comment on the paper systematic variation in chemistry and nd sr isotopes across a caledonian calc alkaline volcanic arc implications for source materials by m f thirlwall

intermittent stability and frontogenesis in an area influenced by land runoff a frontal structure in liverpool bay was studied using conductivity temperature depth ctd and current meter data at times of weak vertical mixing by wind and tides a density driven gravity flow induced by river discharge distorts the thermohaline field so that an expanding stratified region develops bounded offshore by a surface front expansion of this frontal structure is increasingly curbed by rotation as a near geostrophic balance is attained owing to friction the space scale and time scale of frontogenesis are somewhat greater than two internal rossby radii and an inertial period respectively at times of increased mixing the frontal structure is destroyed and the enhanced friction between layers inhibits gravity flow hampering the frontogenesis mechanism large variability in mixing conditions results in an intermittent frontal structure

tectonics of the northern himalaya since the india asia collision abstract the india asia collision resulted in the construction of the vast himalayan orogen the northern himalayan domain began to experience extensional tectonics since eocene oligocene transition eot when the himalayan orogeny was still in progress major structures generated by the extension in the northern himalaya include the south tibet detachment system stds the north himalayan gneiss domes nhgd and the north south trending rifts nstr the earliest emplacement of syn deformational leucogranite at 36 32 ma along the stds marks the initial transformation from thickening to thinning in the northern himalayan domain at eot the thickening before eot caused crustal partial melting which formed the weak root of the thickened orogen or the so called channel flow this channel flow triggered the collapse of the orogen extrusion of the greater himalayan crystalline complex ghc and the onset of extensional tectonics of the stds the similarities in tectono thermal history and geochemistry of rocks between the stds and nhgd suggest that the formation of the nhgd has a direct relationship to the activity of the stds the extension of stds and the resultant thinning caused further partial melting of the crust leading to the larger scale emplacement of leucogranite during miocene 27 13 ma diapirism of these plutons shaped the domes in nhgd exposing the ghc and the shear zones of the stds in the northern himalaya in gyirong another tectonic transform from extension to shortening occurred after 18 7 ma in dinggye region the stds was offset by the nstr culminating the deformation at 13 ma when the nstr began to be active this indicates another tectonic transform in the northern himalaya at 13 ma when the n s extension of the stds ceased and gave way to e w extension of the nstr marking the end of the peak granitic magmatism in northern himalaya multiple episodes of deformation in the major structures such as the stds mct and nstr and superposition of different structures indicate a multiphase orogenic process in the himalayas in which mountain building and collapse occurred alternately with the formation of nstr and conjugate shear zones in tibet this tectonic scenario was possibly controlled by the india asia convergent rate we propose that the extension was an integral part of the orogenic process rather than a simple marker of the culmination of the orogeny

influence of overpressure on formation velocity evaluation of neogene strata from the eastern bengal basin bangladesh abstract interpretation of sonic log data of anticlinal structures from eastern bangladesh reveals significant variations of acoustic velocity of subsurface strata the amount of variation in velocity is 32 from miocene to pliocene stratigraphic units in titas and bakhrabad structure whereas 21 in rashidpur structure velocity fluctuations are influenced by the presence of gas bearing horizons with velocities of gas producing strata 3 7 lower than laterally equivalent strata at similar depth average velocities of miocene boka bil and bhuban formations are respectively 2630 and 3480 m s at titas structure 2820 and 3750 m s at bakhrabad and 3430 and 3843 m s at the rashidpur structure from the overall velocity depth distribution for a common depth range of 915 3000 m the titas bakhrabad and rashidpur structures show a gradual increase in velocity with depth in contrast the sitakund anticline in se bangladesh reveals a decrease in velocity with depth from 3000 to 4000 m probably due to the presence of overpressured mudrocks of the bhuban formation tectonic compression associated with the indo burmese plate convergence likely contributed the most toward formation of subsurface overpressure in the sitakund structure situated in the chittagong tripura fold belt of the eastern bengal basin bangladesh

tectonic evolution of the mogok metamorphic belt burma myanmar constrained by u th pb dating of metamorphic and magmatic rocks 1 the mogok metamorphic belt mmb extends for over 1500 km along the western margin of the shan thai block from the andaman sea north to the eastern himalayan syntaxis previous geochronology has suggested that a long lasting jurassic early cretaceous subduction related event resulted in emplacement of granodiorites and orthogneisses 171 120 ma and a poorly constrained tertiary metamorphic event on the basis of new u pb isotope dilution thermal ionization mass spectrometry and u th pb laser ablation multicollector inductively coupled plasma mass spectrometer geochronology presented here we propose two tertiary metamorphic events affected the mmb in burma the first was a paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at 59 ma a second metamorphic event spanned late eocene to oligocene at least from 37 possibly 47 to 29 ma this resulted in the growth of metamorphic monazite at sillimanite grade growth of zircon rims at 47 43 ma sillimanite muscovite replacing older andalusite and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45 5 0 6 ma and 24 5 0 7 ma these data imply high temperature sillimanite muscovite metamorphism peaking at 680 c and 4 9 kbar between 45 and 33 ma to around 606 656 c and 4 4 4 8 kbar at 29 3 0 5 ma the later metamorphic event is older than 24 5 0 3 ma the age of leucogranites that crosscut all earlier fabrics our structural and geochronological data suggest that the mmb links north to the unexposed middle or lower crust rocks of the lhasa terrane south tibet and east to high grade metamorphic core complexes in northwest thailand

when and why the continental crust is subducted examples of hindu kush and burma abstract the indian subcontinent has been colliding against asia along the himalayas hindu kush and burma in this collision zone have intermediate depth seismicities beneath them with most of the continental crust subducted into a few hundred km depth the subduction not collision in these regions is an enigma long time we show that the continental lithosphere subducted beneath hindu kush and burma traveled over the reunion and kerguelen hotspots from 100 ma to 126 ma and is likely to have been metasomatized by upwelling plumes beneath those hotspots the devolatilization of the metasomatized lithosphere impinging on the collision boundary would have provided a high pore fluid pressure ratio at the thrust zones and made the subduction of the continental lithosphere in these regions possible the subducted lithosphere could give intermediate depth seismicities by devolatilization embrittlement such subduction of hotspot affected lithosphere without accompanying any oceanic plate would be one candidate for producing ultrahigh pressure metamorphic rocks by deep subduction of the continental crust

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

episodic rapid uplift in the himalaya revealed by 40ar 39ar analysis of detrital k feldspar and muscovite bengal fan detrital k feldspar and muscovite samples from ocean drilling program leg 116 cores have been dated by the sup 40 ar sup 39 ar technique and have depositional ages from 0 to 18 ma from 4 to 13 individual k feldspars and 1 to 12 individual muscovites have been dated from 7 stratigraphic levels in every level at least one k feldspar and one muscovite yielded a minimum age identical within uncertainty to the age of deposition these results indicate that a significant portion of the material in the bengal fan is first cycle detritus derived from the himalaya therefore the substantial amount of sediment deposited in the distal fan in early to middle miocene time can be ascribed to a significant pulse of uplift and erosion in the collision zone at this time moreover these data indicate that throughout the neogene some part of the himalayan orogen was undergoing rapid erosion 1 to 10 mm yr this erosion must have been less than or equal to uplift relative to sea level the lack of granulite facies rocks in the eastern himalaya and tibetan plateau suggests to us that very rapid uplift must have been distributed in brief pulses over different parts of the mountain belt these datamore are incompatible with tectonic models in which the himalaya and tibetan plateau are uplifted either uniformly over the past 40 m y or mostly within the past 2 to 5 m y less

comparisons of measured and predicted sediment transport rates in tidal currents abstract this paper describes bedload transport measurements in a large scale sedimentary system on the british continental shelf steady flow sediment transport theories are applied to oscillatory tidal currents and various equations are compared with measured transport rates from tracer dispersion experiments the effects of waves on both measured and predicted rates are briefly considered and the predicted directions of sediment movement compared with those inferred from sedimentological data