redox control of arsenic mobilization in bangladesh groundwater abstract detailed hydrochemical measurements 34sso4 and 3h analyses were performed on 37 groundwater samples collected during february 1999 january and march 2000 from 6 locations in eastern and southeastern bangladesh to examine redox processes that lead to as mobilization in groundwater the study sites were chosen based on available nation wide as surveys to span the entire spectrum of as concentrations in bangladesh groundwater and to represent 3 of 5 major geological units of the ganges brahmaputra delta uplifted pleistocene terrace fluvial flood plain and delta plain arsenic was found to be mobilized under fe reducing conditions in shallow aquifers 50 g l or 0 7 m were always accompanied by high dissolved hco3 4 mm and were close to saturation with respect to calcite groundwater enriched in as 200 800 g l or 2 7 10 7 m and phosphate 30 100 m but relatively low in dissolved fe 5 40 m probably resulted from re oxidation of reducing as and fe enriched water this history was deduced from isotopic signatures of 34sso4 and 3h2o 3h to delineate the nature of redox changes for some of the reducing groundwaters in contrast as is not mobilized in presumed pleistocene aquifers both shallow 30 60 m and deep 150 270 m because conditions were not reducing enough due to lack of sufficient o2 demand

texture and mineralogy of sediments from the ganges brahmaputra meghna river system in the bengal basin bangladesh and their environmental implications the bengal basin bangladesh represents one of the most densely populated recent floodplains of the world the sediment flux through the basin is one of the highest on a global scale a significant portion of this sediment load find its sink in the basin itself because of its lower elevation and frequent flooding the textural mineralogical and chemical nature of the sediments thus have an important bearing on the environmental quality of the basin as well as for the bay of bengal

spatial vertical and temporal variation of arsenic in shallow aquifers of the bengal basin controlling geochemical processes a detailed understanding of the geochemical processes that regulate the spatial temporal and vertical variation of dissolved arsenic as in shallow aquifers 50m is a prerequisite for sustainable drinking water management in the bengal basin the present study conducted at chakdaha block of the nadia district west bengal india combined a high resolution hydrogeochemical monitoring study over 20months from two sets of piezometers 2 5 to the sediment geochemistry at areas with high average 146 g l n 5 and relatively low average 53 3 g l n 10 dissolved as concentrations in groundwater the determination of the isotopic composition of 2h and 18o in groundwater of the two sites indicated the recharge of evaporative surface water to the aquifer the concentrations of major aqueous solutes ca2 mg2 na k hco3 and cl and electrical conductivity were considerably higher in wells at the high as site compared to the low as site additionally at the high as site the major ions fe so4 2 electrical conductivity 2h and 18o showed markedly greater enrichment in the shallowest part 24m of the aquifer compared to the deeper part reflecting vertical layering of groundwater composition within the aquifer the oxidation of pyrites has been attributed to the high rate of mineral dissolution resulting in such greater enrichments in this part of the aquifer in addition the anthropogenic input with recharge water possibly increased the concentrations of cl in this part of the aquifer the vertical layering of groundwater was absent in the aquifer at the low as site the absence of such layering and relatively low major ion concentrations and electrical conductivity could be linked to the enhanced aquifer flushing and decreased water sediment interactions influenced by local scale groundwater abstraction the seasonal variations of as concentrations in groundwater were observed only in the shallowest part of the aquifers 30m furthermore the as concentrations in groundwater at the uppermost part of the shallow aquifers 21m increased continuously over the monitoring period at both sites this study supports the view that the reductive dissolution of fe oxyhydroxides coupled with competitive po4 3 sorption reactions in the aquifer sediment enriches as in groundwater of the bengal basin however the additional fe released by the weathering of silicate minerals especially biotite or the precipitation of fe as secondary mineral phases such as siderite vivianite and acid volatile sulfides may result in the decoupling of as and fe enrichment in groundwater the redox zonation within the aquifer possibly regulates the vertical distribution of as in the groundwater

the effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments abstract the natural optically stimulated luminescence osl response of quartz grains extracted from a range of recent glaciofluvial and other glaciogenic sediments from western greenland is presented all samples were deposited within the last 10 years many only days or hours before collection consequently we would expect to measure zero or very small d e values had optical resetting of the osl signal been complete in the case of most samples d e values in the range 0 5 10 gy are observed while higher values are observed for a handful of samples however the regenerated osl growth curves constructed after daylight exposure of at least several hours also show large apparent d e values negative x axis intercepts corresponding samples from four different locations in the indian himalaya display similar osl characteristics the measurement of several regenerated osl growth curves omitting the preheat procedure which normally precedes osl measurement confirms that a significant degree of thermal transfer is occurring during the preheating it is this thermal transfer of charge during the preheat which is responsible for a significant contribution to the large apparent d e values observed for the regenerated osl growth in this paper we describe combined osl and tl measurements which have been used to monitor the charge transfer in detail for one sample an attempt is made to describe the charge transfer behaviour and we discuss methods appropriate to eliminating the unwanted effects of this phenomenon during osl dating preliminary results from the application of these techniques are presented and the implications of these observations for the osl dating of glaciogenic sediments are discussed

high energy coastal sedimentary deposits an evaluation of depositional processes in southwest england sediments left by coastal flooding have been observed worldwide and have been variously ascribed to the action of storm surges and tsunami waves to date no study has attempted to unequivocally establish on stratigraphical sedimentological and palaeoecological grounds the means by which these two different processes might be distinguished in coastal sedimentary sequences this paper examines the evidence for historical storm surges and tsunamis and shows that both high magnitude events have been documented over the past 250 years in southwest england sand layers of varying thickness are present within holocene lagoonal and peat sequences of several shallow lakes of the scilly isles detailed analysis of big pool st agnes indicates that the basal peats date from around 1000 bp within the basal peats are numerous thin sand layers above the basal peat is an extensive sand layer 15 to 40 cm thick the base of this latter layer probably dates from the early to mid 18th century particle size grain surface morphology diatom and mineral magnetic studies are used to try and determine the most likely mode of deposition the results of all analyses are inconclusive but the weight of evidence suggests that the increasing frequency of thin sand layers in the upper part of the basal peat may be related to the increasing frequency and intensity of atlantic storms during the little ice age superimposed upon a rising sea level the thick sand layer may have been deposited by the tsunami wave generated by the lisbon earthquake of november 1 1755 due to the difficulties in distinguishing depositional processes in coastal environments known to have been affected by storm surges and tsunami waves it is suggested that generally accepted sedimentological techniques are inadequate for discriminating depositional processes in coastal environments

analysis of environmental controls on tsunami deposit texture abstract tsunamis transport large amounts of sediment and can leave recognisable signatures in the landscape the form and composition of onshore tsunami deposits are a function of wave dynamics sediment availability and characteristics of the local environment the latter of which also partially controls preservation of the deposit this research reviews these relationships in a global context and assesses the connection between tsunami deposit particle size and four controlling parameters climate temperature and rainfall density of tsunami sediments degree of coastal protection and distance between tsunami source and sediment deposition an international dataset of tsunami deposit locations and texture was compiled from published literature and existing databases values for environmental variables were calculated for each location from global datasets of temperature rainfall coastline shape and tsunami source locations spearman s rank order correlation principal component analysis pca and hierarchical cluster analysis ca were used to analyse relationships between these variables pca results show an inverse relationship between particle size and sediment density climate variables and distance from source ca results support this suggesting a cluster structure controlled primarily by particle size and secondly by climate and sediment density these relationships can be explained by the influence of the environment on antecedent morphology and the composition of sediments available for tsunami transport

quartz as a natural luminescence dosimeter abstract luminescence from quartz is commonly used in retrospective dosimetry in particular for the dating of archaeological materials and sediments from the quaternary period the phenomenon of luminescence is related to the interaction of natural radiation with mineral grains by the activation of and subsequent trapping of electrons at defects within the quartz lattice the latent luminescence signal i e the trapped electrons is released when the grains are exposed to stimulation energy in the form of light or heat despite the fact that quartz is most nominally pure sio2 the mineral forms in several different geological settings i e under different pressure and temperature conditions the luminescence emitted from quartz is complex and shows a variety of different components with diverse physical properties this complexity is explained by the variety of defects in quartz that are either intrinsic e g si and o vacancies or related to impurity atoms e g al or ti the concentration of impurity related defects is dependent on the conditions of mineral formation or subsequent alteration experimental data have shown that the luminescence properties of quartz are highly variable with geological source and vary even at a grain to grain level within a sediment as a consequence caution is needed when making any general statements about the luminescence properties of quartz when using luminescence measurements as a dating technique it is necessary to adjust the measurement procedures for each geological provenance furthermore some quartz has luminescence properties that make it problematic or even unsuitable for certain applications these problems can arise from low and changing luminescence sensitivity thermal transfer of trapped electrons thermal instability of the trapped electrons and low saturation dose reviewing the present knowledge reveals that insufficient information is available either to unambiguously link distinctive lattice defects with characteristic luminescence components or even to explain problems observed in application studies by potential dynamics of the defects within the crystal this paper gives some ideas on how future research could utilise innovative analytical tools to identify or map the distribution of lattice defects and how practitioners could relate lattice defects to measured luminescence properties of quartz

geomorphological effects of tsunami run up and backwash abstract geomorphological processes associated with tsunami run up and backwash are highly complex to date most studies have considered the sedimentology of palaeo tsunamis while almost no detailed studies have been undertaken in areas known to have been affected by tsunamis in recent times research on contemporary tsunamis show that coastal landscapes may be greatly altered not only by direct tsunami run up orthogonal to the shoreline but also by episodes of vigorous backwash and by water flow sub parallel to the coastline the combined effect of these processes produces hitherto unrecognised coastal landforms that are dominated by the effects of high magnitude erosion and deposition deposition of large boulders is also associated with severe tsunamis while in adjacent areas run up processes often result in the deposition of continuous and discontinuous sediment sheets in many instances the upper limit of sediment deposition lies well below the upper limit of wave run up which is frequently marked by a well defined zone of stripped vegetation and soil the processes described have considerable implications for models of coastal evolution it may even be the case that the evolution of particular stretches of coastline are dominated by such high magnitude low frequency events

aquifer system for potential groundwater resources in hanoi vietnam predictions in ungauged basins pub mainly focus on surface water but there are much higher prediction uncertainties inherent in groundwater hanoi depends entirely on groundwater for its domestic water supply however the characteristics of the entire hanoi aquifer system remain poorly understood due to the lack of available data recently we were nominated to construct a hydrogeological database using the valuable data contained in this database this paper comprehensively analyzed the best number of 240 boreholes including well logs and their hydrogeological parameters obtained from pumping tests for the first time in order to identify the entire hanoi aquifer system and characterize the hydrogeological conditions for potential groundwater resources great efforts have been made to establish and analyze the hydrogeological maps cross sections and the isopach maps of main aquifers thickness and transmissibility as for the results we found that groundwater mainly exists in the topmost holocene unconfined aquifer and the shallow pleistocene confined aquifer pca while cleft and karst water exists in the neogene water bearing layer and the mesozoic fractured zones these aquifers are adequately quantitatively characterized and evaluated from the viewpoint of potential groundwater resources we found the pca serving as the highest groundwater potential and the most important aquifer for the water supply the findings are indispensable for further groundwater analyses contributing to ensuring the sustainable groundwater development not only in hanoi but also in poorly gauged or ungauged neighboring basins copyright 2012 john wiley sons ltd

middle to late holocene storminess in brittany nw france part ii the chronology of events and climate forcing this study focuses on the recurring climate conditions required for the largest storms occurring in nw france brittany it is based on the analysed records of storm events along western brittany coast see part i in this manuscript part ii storm recurrence is explored along with forcing mechanisms periods of more frequent storm events over the two last centuries are analysed first in order to link these events with possible forcing mechanisms north atlantic oscillation nao and atlantic multidecadal oscillation amo modes triggering the most destructive storms then palaeostorm events are discussed at the holocene scale from 6000 yr bp to present to verify the forcing mechanisms most recorded events appear to be linked with cooling episodes mostly in winter a transition to or from a negative winter nao mode a positive amo mode extreme storms occur immediately prior to the medieval warm period mwp maximum effects are reached prior to the onset of the mwp and during the maunder and dalton solar minima low storm activity occurred during the sporer minimum linked to an acceleration of the atlantic meridional overturning circulation amoc main storm triggers seem to correspond to a positive amo mode with an unstable jetstream configuration driving a negative nao in this study four specific weather configurations were defined to explain each type of recorded storminess the strongest storms correspond to low amo and decennial negative nao modes e g little ice age or high amo in association with dominant low nao modes as during the early middle age and present day period fresh or warm oceans in association with a positive nao mode are stormy but with very low sting storms frequency although in agreement with the orbital forcing and the holocene glacial history increasing storm frequency and intensity is most probably partly biased by continuous sea level rise and resulting erosion

controls on facies distribution and stratigraphic preservation in the ganges brahmaputra delta sequence abundant sediment supply and accommodation space in the bengal basin have led to the development of a major late quaternary delta sequence this sequence has formed in a tectonically active setting and represents an important example of a high energy marine and fluvial high yield continental margin deposit recent studies have detailed the delta s stratigraphy and development noting that tectonics and sediment supply control the ganges brahmaputra more significantly than in many other delta systems these ideas are developed here through a discussion of the effects that spatial and temporal variations in tectonics and sediment supply have had on deltaic processes and sequence character unique and differing stratigraphies are found within thedeltasystem suchthatfine grainedsedimentpreservationisfavoredinareasofactivetectonicprocessessuchasfolding block faulting and subsidence coarse grained deposits dominate the stratigraphy under the control of high energy fluvial processes and mixed fine coarse stratigraphies are found in areas dominantly influenced by eustatic sea level change overlaid upon these spatially varying stratigraphic patterns are temporal patterns related to episodic events e g earthquakes and rivers avulsions and long termchangesinclimate andsediment supply modelingisalsousedtoinvestigatethe influenceofavariable sedimentsupply on sequence character results show that the timing and magnitude of sediment input relative to sea level rise is a significant control on the subaerial extent of the delta and the relative dominance of alluvial and marine facies within the sequence d 2002 elsevier science b v all rights reserved

mobility of arsenic in a bangladesh aquifer inferences from geochemical profiles leaching data and mineralogical characterization aquifer geochemistry was characterized at a field site in the munshiganj district of bangladesh where the groundwater is severely contaminated by as vertical profiles of aqueous and solid phase parameters were measured in a sandy deep aquifer depth 150 m below a thick confining clay 119 to 150 m a sandy upper aquifer 3 5 to 119 m above this confining layer and a surficial clay layer 3 5 m in the deep aquifer and near the top of the upper aquifer aqueous as levels are low 10 g l but aqueous as approaches a maximum of 640 g l at a depth of 30 to 40 m and falls to 58 g l near the base 107 m of the upper aquifer in contrast solid phase as concentrations are uniformly low rarely exceeding 2 g g in the two sandy aquifers and never exceeding 10 g g in the clay layers solid phase as is also similarly distributed among a variety of reservoirs in the deep and upper aquifer including adsorbed as as coprecipitated in solids leachable by mild acids and reductants and as incorporated in silicates and other more recalcitrant phases one notable difference among depths is that sorbed as loads considered with respect to solid phase fe extractable with 1 n hcl 0 2 m oxalic acid and a 0 5 m ti iii citrate edta solution appear to be at capacity at depths where aqueous as is highest this suggests that sorption limitations may in part explain the aqueous as depth profile at this site competition for sorption sites by silicate phosphate and carbonate oxyanions appear to sustain elevated aqueous as levels in the upper aquifer furthermore geochemical profiles are consistent with the hypothesis that past or ongoing reductive dissolution of fe iii oxyhydroxides acts synergistically with competitive sorption to maintain elevated dissolved as levels in the upper aquifer microprobe data indicate substantial spatial comapping between as and fe in both the upper and deep aquifer sediments and microscopic observations reveal ubiquitous fe coatings on most solid phases including quartz feldspars and aluminosilicates extraction results and xrd analysis of density magnetic separates suggest that these coatings may comprise predominantly fe ii and mixed valence fe solids although the presence of fe iii oxyhydroxides can not be ruled out these data suggest as release may continue to be linked to dissolution processes targeting fe or fe rich phases in these aquifers copyright 2004 elsevier ltd

geologic geomorphic and hydrologic framework and evolution of the bengal basin india and bangladesh abstract the bengal basin the largest fluvio deltaic sedimentary system on earth is located in bangladesh and three eastern states of india sediment accumulates in the basin from the ganges brahmaputra and meghna gbm river systems and is dispersed into the bay of bengal forming the largest submarine fan in the world the basin is located in the himalayan foreland at the junction of the indian eurasian and burmese plates the basin is bounded by the indian craton on the west and the indo burmese fold belts on the east it can be broadly divided into a stable shelf and a foredeep separated by a deep seismic hinge zone basin sediments overlie gondwanan basement and vary in thickness from a few kilometers on the stable shelf to more than 16 km in the foredeep the basin was initiated at the breakup of gondwanaland in the late mesozoic and evolved through the formation of the proto gbm delta to the present delta starting around 10 5 ma the stratigraphy of the different parts of the basin differs considerably because of contrast in depositional history within the several sub basins that were produced by intra plate tectonic activities associated with ongoing himalayan orogeny the present day geomorphology is dominated by the extensive holocene gbm floodplain and delta the vertical succession of the deltaic plain can be classified into five units on the basis of differences in grain size which reflect differing depositional environments the initiation of the modern gbm delta at the onset of the pleistocene glacial maximum and its evolution to the present configuration are intricately related to holocene fluvio dynamic processes eustatic sea level changes and tectonic movements the sedimentology and mineralogy of the different parts of the basin reflect differences in sediment provenance the mineralogy is dominated by detrital quartz some feldspar and minor amounts of carbonates illite and kaolinite are the main clay minerals the basin has profuse groundwater resources but the architecture of the aquifers is not yet well resolved different classification schemes have been proposed on the basis of lithology regional groundwater flow follows a low hydraulic gradient from north to south but pumping for irrigation during the past several decades appears to have severely distorted regional flow recharge occurs primarily during the monsoon season groundwater chemistry is dominated by anoxic ca hco 3 type water with relatively high concentrations of fe mn and as carbonate dissolution silicate weathering feooh reduction and mixing with saline water are the primary processes controlling hydrochemistry

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

stratigraphic evolution of the late holocene ganges brahmaputra lower delta plain sediment cores from the ganges brahmaputra delta in bangladesh were examined for sedimentological character clay mineralogy elemental trends c n s and 14c geochronology to develop a model for the sedimentary sequence resulting from lower delta plain progradation in the late holocene a widespread facies succession from muddy sand to interbedded mud records progradation of shoal island complexes and the transition from subtidal to intertidal conditions mangrove vegetated islands and peninsulas represent the final phase of progradation a mottled mud that is deposited by penetration of turbid coastal water into the mangroves during high water events organic matter preservation is generally low 1 toc in most of these well drained deposits that are characterized by a permeable silt dominated granulometry clay mineralogy in the cores records the relative influence of smectite and kaolinite rich ganges sediments and illite and chlorite rich brahmaputra material the lower delta plain west of the modern river mouths was deposited as a ganges dominated delta in three phases since 5000 cal years bp with brahmaputra influence confined to the meghna estuary area and to the supratidal section of western delta deposits evolution of the lower delta plain in the late holocene was influenced by regional subsidence patterns in the tectonically active bengal basin which controlled distributary channel avulsion and migration and the creation of accommodation space

effects of an imposed quasi biennial oscillation in a comprehensive troposphere stratosphere mesosphere general circulation model a 48 yr integration was performed using the geophysical fluid dynamics laboratory skyhi troposphere stratosphere mesosphere gcm with an imposed zonal momentum forcing designed to produce a quasi biennial oscillation qbo in the tropical stratosphere in response to this forcing the model generates a qbo in the tropical circulation that includes some very realistic features notably the asymmetry between the strength of the descending easterly and westerly shear zones and the tendency for the initial westerly accelerations to appear quite narrowly confined to the equator the extratropical circulation in the northern hemisphere nh winter stratosphere is affected by the tropical qbo in a manner similar to that observed in particular the polar vortex is generally weaker in winters in which there are easterlies in the tropical middle stratosphere roughly twothirds of the largest midwinter polar warmings occur when the equatorial 30 mb winds are easterly again in rough agreement with observations despite this effect however the total interannual variance in the zonalmean extratropical circulation in the model apparently is slightly decreased by the inclusion of the tropical qbo the observed qbo dependence of the winter mean stratospheric extratropical stationary wave patterns is also quite well reproduced in the model the qbo was also found to have a profound influence on stratospheric stationary waves at low latitudes near and above 10 mb the nh stationary waves were found to penetrate across the equator during the westerly qbo phase but to be restricted to latitudes poleward of 108n during the easterly phase this means that the equatorial qbo in prevailing wind near and above 10 mb has a significant zonally asymmetric component if this is also true in the real atmosphere there are important implications for the adequacy of the current observational rawindsonde network near the equator analysis of the zonal mean zonal momentum budget in the tropical stratosphere reveals that the resolved waves in the model are strong enough to force the realized accelerations through much of the qbo cycle the exception appears to be the easterly acceleration phase below about 20 mb the implications of this for the generation of a self consistent qbo by gcms will be considered the effects of the imposed qbo on the troposphere were found to be very modest there does appear to be a statistically significant weakening by 1ms 21 of the high latitude winter vortex in the middle and upper troposphere given the very high predictability of the stratospheric qbo itself this effect could possibly be used to enhance the skill of seasonal weather forecasts no significant qbo influence was found in the model precipitation field

mineralogy of the ganges and brahmaputra rivers implications for river switching and late quaternary climate change late quaternary sediments of the bengal basin contain a history of river switching and climate change as revealed from sand and clay size mineralogy of boreholes and modern riverbed grabs epidote to garnet ratios e g in sand fraction sediments are diagnostic of source with high 1 e g indicating brahmaputra provenance and low 1 e g indicating ganges provenance in the clay fraction of surficial sediments smectite is diagnostic with high values 39 in the ganges and low values 3 in the brahmaputra in contrast the brahmaputra contains more kaolinite 29 vs 18 more illite 63 vs 41 and more chlorite 3 vs 1 than the ganges analysis of mineralogic and stratigraphic data indicates that the two rivers have changed position several times during the holocene extended periods of mixed river inputs appear to be isolated to the early holocene suggesting rapidly migrating braided channels during sea level lowstand tectonically driven accommodation in the sylhet basin may have contributed to the favored easterly course of the brahmaputra during much of the holocene relative abundances of illite and chlorite ic vs smectite and kaolinite sk record varying degrees of physical and chemical weathering respectively high ic values in early post glacial deposits suggest a dominance of physical weathering at that time however a general increase in sk concentrations throughout the holocene appears to reflect enhanced chemical weathering under increasingly warmer and more humid conditions notably a peak in sk concentrations that corresponds to an early holocene warm period 10 7 ka suggests that weathering patterns in the catchment respond quickly to climatic shifts

brahmaputra river assam india physiography basin denudation and channel aggradation the brahmaputra river in assam india characterized by high seasonal variability in flow sediment transport and channel configuration experienced a secular period of aggradation from 1971 to 1979 the suspended load budget indicates an overall aggradation of the 607 km assam reach of the brahmaputra by about 16 cm during that period with about 70 of the suspended sediment inflow into the reach being retained in the channel expressed as a percentage of the change in storage for the different reaches computed errors due to sampling variability in sediment discharge generally lie within about 5 15 and do not appear to be large enough to affect the conclusions drawn from the suspended load budget for a 145 km reach of the brahmaputra an alternative method based on measurement of channel cross sections suggests 21 cm of aggradation somewhat more than estimated by the suspended load budget based on the suspended load carried by trans himalayan rivers the present rate of denudation of the eastern himalayas is estimated to be 73 157 cm 103 years the average rate for the last 2 3 million years estimated from the volume of alluvial fill in the brahmaputra valley in assam the sediment yield of the himalayan rivers and assuming a total yield to deposition ratio of 1 4 present study is 3 cm 103 years the current high rate of denudation of the himalayas may be attributed mainly to the rapid uplift of the mountain system recent earthquake activity and high susceptibility of geologic formations to erosion by running water coupled with the effectiveness of the monsoon rainfall regime

seismic history of a bedrock fault scarp using quantitative morphology together with multiple dating methods a case study of the luoyunshan piedmont fault southwestern shanxi rift china abstract the study of bedrock fault scarps is a useful approach to identify paleo earthquakes and acquire the faulting history in bedrock areas where traditional trench techniques are not applicable here we report a study on the luoyunshan piedmont fault lyspf southwestern shanxi rift china although several studies have analyzed the lyspf its faulting behavior is still under debate for example the tectonic geomorphology fails to determine the frequency of past slips and the elapsed time to address these problems we investigated two bedrock fault surfaces luoyuncun northern segment and weicun southern segment using quantitative morphology analyses together with multiple quaternary dating techniques quantitative morphology analysis shows that both bedrock fault surfaces have the characteristics of vertical segmentation this kind of segmentation indicates that the fault surfaces are exhumed intermittently likely owing to periodic faulting earthquakes therefore earthquake events can be identified as morphological segments and the corresponding co seismic displacement can be determined by the height of these segments according to the results from the quantitative morphology and dating techniques four seismic events with a co seismic vertical displacement of 0 9 m 0 82 m 1 64 to 2 38 m and 2 30 to 2 54 m on the northern segment occurred during the late pleistocene whereas two seismic events with a co seismic vertical displacement of 1 33 m and 1 to 1 08 m are identified on the southern segment occurred during the holocene combined with the results of knickpoint series and trench techniques of the lyspf eight paleo earthquake events were identified since 45 ka with an average recurrence interval of 5 8 kyr the more complete paleo earthquake sequence also showed the possibility that the variation of the slip rate along the lyspf depends on the segment and that the displacement produced by the linfen m 7 earthquake of 649 ce has been recorded at the wc fault surface

major ion chemistry of the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal the ganga brahmaputra one of the world s largest river systems is first in terms of sediment transport and fourth in terms of water discharge a detailed and systematic study of the major ion chemistry of these rivers and their tributaries as well as the clay mineral composition of the bed sediments has been conducted the chemistry of the highland rivers upper reaches of the ganga the yamuna the brahmaputra the gandak and the ghaghra are all dominated by carbonate weathering ca mg and hco3 account for about 80 of the cations and anions in the lowland rivers the chambal the betwa and the ken hco3 excess over ca mg and a relatively high contribution of na k to the total cations indicate that silicate weathering and or contributions from alkaline saline soils and groundwaters could be important sources of major ions to these waters the chemistry of the ganga and the yamuna in the lower reaches is by and large dictated by the chemistry of their tributaries and their mixing proportions illite is the dominant clay mineral about 80 in the bedload sediments of the highland rivers kaolinite and chlorite together constitute the remaining 20 of the clays in the chambal betwa and ken smectite accounts for about 80 of the clays this difference in the clay mineral composition of the bed sediments is a reflection of the differences in the geology of their drainage basins the highland rivers weather acidic rocks whereas the others flow initially through basic effusives the ganga brahmaputra river system transports about 130 million tons of dissolved salts to the bay of bengal which is nearly 3 of the global river flux to the oceans the chemical denudation rates for the ganga and the brahmaputra basins are about 72 and 105 tons km yr 1 respectively which are factors of 2 to 3 higher than the global average the high denudation rate particularly in the brahmaputra is attributable to high relief and heavy rainfall

the sedimentological and environmental footprint of extreme wave events in boca do rio algarve coast portugal abstract in 1755 ce a strong earthquake followed by a transatlantic tsunami destroyed large coastal areas it also left its sedimentary imprints in the boca do rio valley western algarve portugal this tsunami layer is very well preserved and has been analysed in several studies deposits of preceding extreme wave events however have rarely been described for the entire algarve coast in this study we present a multiproxy analysis of seven sediment cores from the boca do rio region organized in two crossing transects one parallel and the other perpendicular to the coastline the geochronological framework has been established by combining radiocarbon and optically stimulated luminescence dating with sedimentological and geochemical analyses xrf c n magnetic susceptibility granulometry micropalaeontology and covers the palaeogeographical evolution of that area for the last four millennia as expected the 1755 ce tsunami was easily identified at all coring sites as a sandwiched stratum between fine grained alluvium this event layer presents several tsunami characteristics such as erosive basal contact rip up clasts a fining upward sequence and a mud cap at one coring site a second extreme wave event layer of marine origin was detected within floodplain deposits due to its granulometric xrf magnetic susceptibility and micropalaeontological properties it is stratigraphically located below the 1755 ce lisbon tsunami layer and can be associated with another yet undocumented extreme wave event most likely dating to the mid or late 1st millennium ce

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

regional scale stable isotopic signatures of recharge and deep groundwater in the arsenic affected areas of west bengal india summary samples of deep groundwater river water and rainwater were collected for 18o and 2h analyses from an area of 22 000 km2 in the arsenic affected districts of west bengal india in order to examine groundwater recharge a plot of 18o versus 2h of groundwater falls subparallel to the constructed local meteoric water line 2h 7 2 18o 7 7 suggesting a predominance of meteoric recharge with some evaporation the stable isotopic signature of groundwater from the deeper part of the semiconfined main aquifer is similar to that of shallower groundwater which suggests that deeper groundwater has been recharged in the present day climatic regime mostly from monsoonal rainfall groundwater in deeper isolated aquifers falls within the isotopic range observed for the main aquifer a trend of isotopic depletion of groundwater that extends northward and westward from the bay of bengal the monsoonal moisture source area indicates a rain out process following rayleigh type distillation some recharge may have taken place from the rivers ganges and bhagirathi hoogly with minimal inflow from other rivers jalangi and ichamati

holocene loess sedimentation along the qilian shan china significance for understanding the processes and timing of loess deposition abstract we present optical ages for well preserved loess deposits along the qilian shan a 500 km long mountain belt forming the tectonically active northeastern margin of the tibetan plateau loess on tectonically controlled fill terraces along the shiyou and baiyong rivers was dated by applying the single aliquot regeneration sar technique to coarse grained 90 160 m quartz samples additional measurements on polymineralic fine grained 5 10 m samples were carried out to allow a comparison between various optical dating techniques currently in use the results demonstrate that i loess accumulation started between 13 and 11 ka b p continuing to the present ii mean loess accumulation rates range between 9 and 16 cm ka 1 and iii holocene loess is not restricted to certain sites only but is a prevalent phenomenon along the qilian shan mountain front the absence of loess deposits of late pleistocene age is a result of a combination of cold and dry climate conditions strong winds and the absence of a vegetation cover during the last glacial period only with the change to a warmer and moister climate at the onset of the holocene did a plant cover develop which acted as a dust trap thus initiating the formation of loess

the southern oscillation part v the anomalies in the lower stratosphere of the northern hemisphere in winter and a comparison with the quasi biennial oscillation abstract the mean anomalies of 50 mb height in the northern winter for seven warm events in the southern oscillation show a weak polar vortex and an enhanced aleutian high in the mean for six cold events the polar vortex is unusually strong and the aleutian high is weakened and displaced far to the southwest these anomalies are consistent with the corresponding anomalies in sea level pressure pattern the warm events of 1963 and 1982 did not fit this pattern as in both years the polar vortex was cold and intense these events happened in years when volcanoes injected large amounts of gases and aerosols into the stratosphere and the temperature of the tropical stratosphere became unusually high in other warm events the temperature of the tropical stratosphere was abnormally low the mean anomalies of the quasi biennial oscillation for the winter as a whole west minus east phase computed from years with no cold or warm events are zonally symmetrical and shaped as four concentric regions with alternatin

the southern oscillation in the stratosphere abstract the signal of the southern oscillation in the lower half of the northern hemisphere stratosphere in winter appears to be as follows in the extreme of the southern oscillation when the trade winds are comparatively weak in the south pacific ocean stratospheric geopotential heights and temperatures tend to be higher over the arctic and lower in middle latitudes than in the opposite extreme at the same time the polar night stratospheric jetstream tends to be weaker and the subtropical westerlies to be stronger the conclusions are based on 11 extremes within a 15 year period and on data at standard pressure levels as high as 10 mb

weathering processes in the ganges brahmaputra basin and the riverine alkalinity budget abstract we present river chemistry data for a network of rivers draining the western and central nepal himalaya our sampling locations cover the system from the sources of rivers in tibet to the gangetic plain water samples were collected throughout the year including the monsoon season for rivers in nepal and for the ganges and brahmaputra in bangladesh rivers draining the north himalaya are characterized by low discharge under a cold and arid climate main stream waters have 13 c dic near 0 and high so42 so42 hco3 ratios xso4 with values around 40 eq and high cl ca is the dominant cation ca2 cations 55 to 75 eq after correction of sodium by chloride dissolved sulfate is produced in waters from the tethian sedimentary series whereas chlorine is related to thermal waters dissolved sulfate is primarily derived from sulfide oxidation rather than evaporite dissolution 13 c dic values of up to 3 9 show that metamorphic co2 is an important weathering agent rivers of the north himalayan basins have about 50 of their alkalinity derived from carbonate dissolution 20 from biogenic activity and 30 from metamorphic co2 on the south flank of the himalaya rivers are more depleted in 13 c and have on average lower xso4 most rivers have 13 c dic and xso4 values compatible with a simple mixing between soil co2 and sulfate derived from sulfide oxidation during the monsoon discharge increases by a factor 20 but the total dissolved concentration is only slightly reduced xso4 and 13 c decrease while ca cations increases implying enhanced dissolution of pedogenic calcite as a whole the g b riverine flux of alkalinity derived from silicate weathering is around 2 7 1011 mol year modest at the global scale sulphuric acid controls 20 30 of the weathering reaction in the brahmaputra and 6 to 9 in the ganges na and k balance 60 to 65 of the silicate derived alkalinity flux and the long term co2 consumption by ganges and brahmaputra is near 6 4 1010 mol year the flux of metamorphic co2 converted to alkalinity via weathering reactions is ca 1 1010 mol year

geochemical evolution of groundwater in the quaternary aquifer of calcutta and howrah india abstract groundwater in the quaternary aquifer of the twin city calcutta and howrah occur in a confined condition coarse clastic deposits consisting of fine to coarse sand at places mixed with gravels form the aquifer above and below lie clay sequences the average thickness of the top confining clay bed is 40 m and the aquifer continues down to a depth of at least 296 m below which the bottom clay bed of pliocene age occurs during the last five decades there is a distinct lowering of piezometric head in calcutta and howrah the groundwater flow pattern changed from an open system which was from north to south in the mid 1950s to a closed one in the mid 1980s with the formation of a groundwater trough this closed flow system persisted in the 1990s with the increase in the area of the trough detailed geochemical investigation of groundwater samples n 57 along with statistical analyses viz correlation principal component and mixing analyses on these chemical data reveal i that the groundwater samples can be categorised into eight hydrochemical facies which may be assigned to the three broad types fresh blended and brackish water ii a pronounced and well defined trend of variation of chemistry of the groundwater iii modified connate water and or interaction with the aquifer matrix was possibly responsible for the evolution of the brackish water iv mixing of fresh water and brackish water in ca 48 52 proportion is presently taking place due to heavy groundwater withdrawal and v such mixing will cause deterioration in quality from fresh water to the blended variety mean tds 724 mg l

oceanographic processes and morphosedimentary products along the iberian margins a new multidisciplinary approach abstract our understanding of bottom currents and associated oceanographic processes e g overflows barotropic tidal currents including intermittent processes e g vertical eddies deep sea storms horizontal vortices internal waves and tsunamis is rapidly evolving many deep water processes remain poorly understood due to limited direct observations but can generate significant depositional and erosional features on both short and long term time scales this paper represents a review work which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the iberian continental margins this review explores the implications of the studied processes given their secondary role relative to other factors such as mass transport and turbiditic processes and highlights three major results a contourite depositional and erosional features are ubiquitous along the margins indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation b the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient including the contourite terraces development and c contourites deposits exhibit greater variation than the established facies model suggests therefore a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development an integrated interpretation of these oceanographic processes requires an understanding of contourites seafloor features their spatial and temporal evolution and the near bottom flows that form them this approach will synthesize oceanographic data seafloor morphology sediments and seismic images to improve our knowledge of permanent and intermittent processes around iberia and evaluate their conceptual and regional role in the margin s sedimentary evolution given their complexes three dimensional and temporally variable nature integration of these processes into sedimentary oceanographic and climatological frameworks will require a multidisciplinary approach that includes geology physical oceanography paleoceanography and benthic biology

luminescence dating of well sorted marine terrace sediments on the southeastern coast of korea abstract along the southeastern coastline of the korean peninsula well developed marine terraces are found at various elevations the ages of these terraces and the time of deposition of the terrace sediments are important to our understanding of the geological history of this area during the quaternary period and represent a unique record of the regional tectonic activity previous efforts to establish a chronology using optically stimulated luminescence osl methods have produced controversial results particularly because of stratigraphic inconsistency and poor reproducibility in this paper the application of osl dating based on the single aliquot regenerative dose sar protocol for quartz is investigated the dependence of equivalent dose on the preheat and cut heat temperatures thermal treatment of the regeneration and test doses respectively are examined linearly modulated luminescence signals from chemically cleaned quartz samples are used to identify the presence of a thermally unstable component with a large optical cross section component a which in part affects the ability to correct for sensitivity changes during measurements and thus the reliability of the equivalent dose estimates in some samples a higher heat treatment after the test dose is shown to improve our ability to measure a dose given in the laboratory before any heat treatment dose recovery test this higher temperature treatment effectively removes component a and hence improves sensitivity correction furthermore the samples were broadly divided into poorly sorted and well sorted based on field evidence the poorly sorted samples contain friable weathered gravel clasts which is a likely post depositional source of quartz grains in general these grains will not have been zeroed prior to deposition and so the poorly sorted samples are rejected from further age studies results obtained from the well sorted samples are reproducible at each sampling location and give ages grouping broadly into 50 70 and 110 120 ka but laterally discontinuous on a scale of tens of km our osl results for the younger group are supported by radiocarbon ages from overlying terrestrial deposits it is concluded that these results point to considerable tectonic activity in the southeast of korea during the late pleistocene

indian ocean tsunami recurrence from optical dating of tsunami sand sheets in thailand abstract sand sheets deposited by the 2004 indian ocean tsunami and three holocene tsunami predecessors in western thailand have been dated by optically stimulated luminescence osl ages from the modern indian ocean tsunami sand sheet allow an assessment of the suitability of osl to date tsunami deposited sediment in tropical beach ridge plain depositional environments they show that provided appropriate precautions are taken to correct for incomplete bleaching of sediments osl can provide a robust chronology of tsunami recurrence ages from the tsunami deposited sand sheets underlying the 2004 tsunami deposits provide a chronology of the largest tsunamis in western thailand over the late holocene three sand sheets likely deposited by tsunamis of similar magnitude to the 2004 event were dated by luminescence to 380 50 990 130 1410 190 and 2100 260 years before ad 1950 at 1 sigma precision the youngest of these compares with previous radiocarbon ages of detrital bark high in buried soils jankaew et al 2008 which suggest that the most recent large scale predecessor to the 2004 tsunami occurred soon after 550 700 cal bp the osl ages from the lower two sand sheets provide constraint on tsunami recurrence that was not previously available from radiocarbon dating the ages imply that between 350 and 1100 years separate successive tsunamis on the andaman coast of thailand with an average tsunami recurrence interval of around 550 years these results contribute to the growing body of research on tsunami recurrence in the indian ocean region and show that osl can provide independent estimates of tsunami recurrence for hazard analysis particularly in areas where suitable material for radiocarbon dating is unavailable

seismic driving of nationwide changes in geomorphology and prehistoric settlement a 15th century new zealand example abstract we propose a model for the seismic driving of environmental changes and illustrate it using a case study from new zealand dated to the 15th century ad a seismic staircase shows a chronological progression of environmental outcomes that includes tsunami rock avalanches vegetation disturbance rapid coastal dune building river aggradation and abandonment of prehistoric coastal settlements the 15th century event appears to be unique in the past millenium and is most notable for its period of rapid coastal dune building the coincidence of a catastrophic el nino episode in the mid 15th century ad may have served to move sediments rapidly through the terrestrial system thus delimiting clearly separate geomorphological after effects we contend that seismic driving is a major factor in determining paleoenvironmental change in tectonically active areas during the holocene and provides the palaeoenvironmental context within which smaller scale events operate

coastal and sea level changes during the holocene in bangladesh abstract the aim of the study is to reconstruct the holocene sea level history along a section of the coast of bangladesh detailed litho bio and chronostratigraphic techniques have been applied to unveil the nature of sedimentary sequences in association with the events of the holocene marine transgressions and regressions samples were collected from panigati near khulna the study provides evidence of five periods of marine transgression each followed by a regression during the holocene each minerogenic sediment layer indicates a marine episode and the sediments were deposited under intertidal to estuarine conditions each peat layer is in situ and indicates a regression of the sea it is difficult to separate the regional eustatic components contributing to these relative sea level movements although processes operating locally and regionally are clearly evident a sea level curve together with possible error ranges has been proposed for this part of bangladesh since the early to mid holocene an average relative sea level rise of 1 07 mm yr has been estimated

optically stimulated luminescence dating of holocene relict foredunes guichen bay south australia abstract optically stimulated luminescence osl dating of quartz sand 106 150 or 150 200 m in bioclastic carbonate quartz sediments sampled from coastal relict foredunes beach ridges was undertaken to evaluate the utility of the osl method for studies of dune dynamics and to quantify rates of coastal progradation twelve sediment samples from a 4 km transect across a holocene embayment fill at guichen bay south australia were measured for their luminescence characteristics apart from one age inversion attributed to recent disturbance associated with mining the osl ages are in sequential order when considered in the context of their associated error terms the osl ages indicate an extremely rapid initial phase of sedimentation i e 1600 m within a few hundred years approximately 5 ka ago followed by a constant rate of progradation for the past 4 ka of 0 39 m a with a high level of association between distance across the embayment fill and luminescence age for this time interval an average rate of dune development of one dune every 80 yr from 3900 yr ago to the present day is apparent the osl ages for the late holocene indicate that the present beach state is largely in equilibrium with sediment supply

reconnaissance of historic post ad 1000 high energy deposits along the atlantic coasts of southwest britain ireland and brittany france abstract sand and gravel deposits from the atlantic coasts of southwest britain brittany and western ireland are identified as potential indicators of historic post ad 1000 ocean sourced high energy events such as storm surges and tsunami this is an important historic period as it includes the climatic perturbations of the medieval warm period and the little ice age and also seismogenic events such as the lisbon tsunami of 1755 ten new sites are identified from various coastal settings and dated using eight new radiocarbon dates alongside previously published data generally sites do not appear to record multiple high energy events suggesting that either only the most extreme and or recent events are registered a number of radiocarbon dates from marine shell yield modern ages when corrected for the marine reservoir effect rather than necessarily indicating recent deposition this may reflect a poor understanding of terrestrial carbon input into coastal and estuarine waters and the practice of applying broad regional r values at the local scale two groupings of radiocarbon dates are recognised a medieval group and a post medieval group which might reflect events within known climatic perturbations and or tsunami occurrences these events may include the lucia flood of 1287 the all saint s day flood of 1570 the 1607 flood the great storm of 1703 and the lisbon tsunami some older pre ad 1000 deposits indicate the potential to construct frequency magnitude records of high energy events throughout the holocene data presented here support the view that salt marshes within the bristol channel and severn estuary were completely eroded away early in the 17th century

the composition of suspended matter from ganges brahmaputra sediment dispersal system during low sediment transport season abstract suspended matter supplied from the ganges brahmaputra river system was sampled in waters of the adjacent shelf area in times of low suspended matter load november december 1997 the absolute amount of suspended matter ranges between 500 mg l near the river mouth and chemical and mineralogical analyses of the suspended matter show changes in its composition with distance from the source compositional changes are based on grain size partitioning quartz and heavy minerals are precipitating sooner leaving the suspended matter from the outer shelf depleted in quartz ree zr hf nb ta w u th y and ca the other part of the compositional changes is based on the reaction of suspended matter with seawater manganese hydroxide is producing coatings on suspended matter grains and adsorbing elements out of the seawater as a consequence enrichment of mn zn ni cr co li cs as sb pb tl and cd can be observed in the suspended matter from the outer shelf arsenic is accumulating on the inner shelf by a factor of 2 chemical partitioning in sequential leaching experiments shows that arsenic does not follow the enrichment mechanism of manganese and other transition metals more than 90 of the total arsenic is bound to nearly insoluble phases of the suspended matter e g crystalline iron oxides residual minerals for comparison with suspended matter adjacent surface sediments were sampled and analysed in this sediment the dominating phase is the one which settled down during the times of high suspended load with more quartz and heavy minerals and consequent chemical composition the enrichment of manganese oxide and adsorbed transition metals gets lost because of anaerobic conditions in the bottom near seawater they dissolve from the sediment and get recycled in seawater arsenic is found in nearly insoluble parts of the sediment as it is the case in the suspended matter

middle to late holocene storminess in brittany nw france part i morphological impact and stratigraphical record our study aims to understand the recurring climatic conditions prevailing during the largest storms reaching nw france brittany these storms are responsible for the breaching of coastal barriers and major flooding of lowlands in a first part of our work we examine the morphological impact and stratigraphic record of storm events along western brittany rocky coasts with a special focus on the southern coast of the bay of audierne the most exposed coast of the region in a second paper middle to late holocene storminess in brittany nw france part ii we shall focus on the chronology of storm events and their climate forcing conditions drilling transects and stratigraphic analyses were first undertaken to constrain chronology strength and wind direction during the main holocene storm events new dates observations and a relative sea level rsl curve were then used to inform discussion of the necessary climatic and morphologic conditions leading to destructive storm events most recorded events appear to be linked with cooling episodes of the holocene and a rsl close to present some storms are clearly responsible for breaching and dune building or remobilisation we demonstrate that storm frequency and intensity appear to rise in a stepwise manner during the late holocene maximum efficiency is reached during the little ice age with clustered events probably lasting several days but major storms also occurred immediately prior to the medieval warm period we suggest that recent coastal dune building from c ad 1100 until now despite a sea level close to present and continuously rising may be a direct consequence of the restoration of beaches after periods of recurrent storminess this building activity often occurred during dry negativ

chemistry of uranium thorium and radium isotopes in the ganga brahmaputra river system weathering processes and fluxes to the bay of bengal abstract the most comprehensive data set on uranium thorium and radium isotopes in the ganga brahmaputra one of the major river systems of the world is reported here the dissolved 238u concentration in these river waters ranges between 0 44 and 8 32 1 and it exhibits a positive correlation with major cations na k mg ca the 238 u cations ratio in waters is very similar to that measured in the suspended sediments indicating congruent weathering of uranium and major cations the regional variations observed in the 234 u 238 u activity ratio are consistent with the lithology of the drainage basins the lowland tributaries chambal betwa ken and son draining through the igneous and metamorphic rocks of the deccan traps and the vindhyan bundelkhand plateau have 234 u 238 u ratio in the range 1 16 to 1 84 this range is significantly higher than the near equilibrium ratio 1 05 observed in the highland rivers which drain through sedimentary terrains the dissolved 226ra concentration ranges between 0 03 and 0 22 dpm 1 the striking feature of the radium isotopes data is the distinct difference in the 228ra and 226ra abundances between the highland and lowland rivers the lowland waters are enriched in 228ra while the highland waters contain more 226ra this difference mainly results from the differences in their weathering regimes the discharge weighted mean concentration of dissolved 238u in the ganga at patna and in the brahmaputra at goalpara are 1 81 and 0 63 1 respectively the ganga brahmaputra river system constitutes the major source of dissolved uranium to the bay of bengal these rivers transport annually about 1000 tons of uranium to their estuaries about 10 of the estimated global supply of dissolved uranium to the oceans via rivers the transport of uranium by these rivers far exceeds that of the amazon although their water discharge is only about 20 of that of the amazon the high intensity of weathering of uranium in the ganga brahmapura river system can also be deduced from the 232 th 238 u and 230 th 238 u activity ratios measured in the suspended sediments 230th is enriched by about 19 in the suspended sediments relative to its parent 238u the flux of excess 230th supplied to the bay of bengal via these river sediments is 980 1012 dpm a about six times more than its in situ production from seawater in the entire bay of bengal

late quaternary sedimentary environments and landforms in the ganges delta abstract late quaternary sediments deposited since the lowest stand of sea level during the last glacial maximum in the ganges delta and its surrounding region were classified into five units according to their sedimentary facies these are the lowest unit of sandy gravels the lower unit of sand with a few gravels and the middle upper and uppermost units consisting mainly of sand and silt with occasional peat layers the contact between the lower and middle units is fairly sharp and the upper part of the lower unit is oxidized in some places this suggests a period of subaerial exposure after the deposition of the lower unit during the low stand of sea level about the time of the last glacial maximum rivers in the ganges delta and its surrounding region dissected the surfaces of the region and deposited the lowest unit on the valley floors the lower unit was deposited over the lowest unit during an early stage of the post glacial transgression between ca 12 000 yr bp and 10 000 yr bp the surface of the delta was slightly dissected and the top of the lower unit was weathered and oxidized following this period the middle and upper units of alluvial or deltaic sand and silt with occasional peat were deposited the coastline in the early holocene retreated towards the central part of the present ganges delta in the middle and late holocene the silt and clay with occasional peat layers of the uppermost unit indicate that the lowland gradually became marshy and poorly drained as the rate of transgression became slower

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

strong sea forcing and warmer winter during solar minima 2765 yr b p recorded in the growth bands of crassostrea sp from the confluence of river ganges eastern india abstract long term variation of solar activity plays a key role in controlling climatic oscillations during glacial interglacial cycles the records of such climatic shifts can be retrieved from sedimentary archives in overbank deposits found in the estuary regions of major rivers in the tropics which are fed by glaciers in this study we have shown the effect of solar variability on regional climate by altering the river discharge and incursion of warm water pool into the region adjoining bay of bengal during seasonal dry period the incremental growth bands present in the modern day meretrix sp and late holocene crassostrea sp were examined for reconstruction of temperature and water composition at the head bay region of the river ganges the conventional c14 techniques on fossil oyster yielded age of 2765 130 yr b p which coincides with a solar minima analysis of clumped isotope thermometry on the growth bands provided temperature estimates for the growth of shells the temperature estimates for the modern shell suggesting range of values showed a range between 13 and 42 c close to the observed temperatures recorded in the climatological data while the fossil shell had a range of values between 22 and 38 c the 18o measured in the aragonite together with the estimated temperature were used to deduce the water composition during growth at equilibrium condition the water 18o varied between 4 8 and 1 2 for the modern sample close to the observed values of water measured near this locality while the range in water composition inferred for the paleo samples was from 2 37 to 0 82 suggesting a stronger influence of sea water throughout the year the results are consistent with the argument of infiltration of water from neighbouring warm water pool into the estuary a similar approach can be extended to evaluate the effects of climate variability due to differential action of river discharge into the sea at seasonal time scales based on available mollusc shells in the sedimentary successions from the region

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

historical tsunami deposits in peru sedimentology inverse modeling and optically stimulated luminescence dating the entire coast of peru was surveyed to document deposits of historical tsunami evidence of four tsunami was found at puerto casma in northern peru a graded heavy mineral rich layer with shell and rock fragments was detected osl dating revealed an age of 0 37 0 03 ka 1615e1667 ad inverse modelling of tsunami onshore flow parameters indicates a flow depth of w 6ma nd aflow speed of w8 m s at a distance of w60 m from the shoreline for the chimbote earthquake of 1619 ad a tsunami was not listed in the historical tsunami catalogues although it is seen as a predecessor of the 1996 chimbote earthquake and tsunami hence this study may provide the first evidence of a local tsunami triggered by this event a graded shell rich event layer that contains cobbles with attached marine organisms was found at vila vila in southern peru this layer was dated to 0 17 0 04 ka 1797e1871 ad and is most probably the result of the 1868 arica tsunami two additional event layers found in boca del rio southern peru were dated 2 26 0 37 ka 615 bce119 ad and 1 98 0 23 ka 207 bce255 ad thus the layers record for the first time tsunami much older than the events listed in tsunami catalogues these two events exhibit similar parameters with flow speeds of 7e8 m s and depths of 6 m in a distance of 460 m from the present shoreline the time that passed between the events is similar to the recurrence interval of the two arica tsunami of 1604 and 1868 ad hence giving evidence of another prehistoric earthquake and tsunami couplet

soils of the high mountain region of eastern nepal classification distribution and soil forming processes abstract eleven soil profiles of the mt everest region dudh kosi and beni khola valley between 2 700 and 4 900 m a s l were investigated to provide information about soil classification zonal distribution and changes in the chemical and mineralogical properties with elevation and climatic conditions the soils are mainly developed from deposits of the last main glaciation which are predominated by paragneisses they were classified as entisols inceptisols and spodosols according to the u s soil taxonomy soil survey staff 1990 detailed chemical and clay mineralogical analyses indicate a strong influence of the elevation integrating several factors of climatic conditions and bioclimatic zones on soil types and soil forming processes inceptisols predominate in the hill zone and lower tropical mountain zone between 2 000 and 3 000 m a s l they are replaced by spodosols in the subalpine forest and alpine shrub zone up to 4 500 m on eroded sites and locations above 4 500 m shallow and stony soils classified as entisols are present a linear decrease in the intensity of weathering with increasing elevation is shown by the decreasing clay content of the main weathering horizon

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

mineralogical profiling of alluvial sediments from arsenic affected ganges brahmaputra floodplain in central bangladesh abstract mineral assemblages heavy and light fractions and sedimentological characteristics of the quaternary alluvial aquifers were examined in the central bengal basin where as concentrations in groundwater are highly variable in space but generally decrease downward chemical compositions of sediment samples from two vertical core profiles 2 150 m below ground level bgl were analyzed along with groundwater in moderately as enriched aquifers in central bangladesh manikganj district and the as mobilization process in the alluvial aquifer is described heavy minerals such as biotite magnetite amphibole apatite and authigenic goethite are abundant at shallow 4 reduction mediated by so 4 reducing bacteria in manikganj groundwater is limited in contrast to the southeastern bengal basin where precipitation of arsenian pyrite is thought to sequester as from groundwater

unroofing history of the eastern himalaya and the indo burman ranges heavy mineral study of cenozoic sediments from the bengal basin bangladesh abstract upper eocene to neogene fill of the bengal basin provides an earlier unroofing history of the eastern himalaya and indo burman ranges than that provided by drilling of the bengal fan and analysis of heavy minerals in these sequences provides useful provenance constraints quartzose sandstones of the eocene kopili and oligocene barail formations contain only 0 2 heavy minerals comprising abundant opaque minerals and stable minerals such as tourmaline garnet rutile and zircon this assemblage suggests sediment sources dominated by low to intermediate grade metamorphic silicic igneous and metasedimentary rocks the low heavy mineral content and abundance of stable minerals suggest intense chemical weathering these sediments may have been derived in part from incipient uplifts of the proto himalaya and or the indo burman ranges but a more likely source is the indian craton immediately to the west miocene sandstones of the surma group contain more abundant and more diverse heavy mineral assemblages than oligocene sandstones these include abundant opaque minerals and garnet mostly almandine and moderate to minor amounts of tourmaline kyanite zircon calcic amphibole rutile chlorite zoisite staurolite epidote sillimanite and clinopyroxene indicating a broad range of mostly metamorphic source rocks upper strata of the surma group also contain abundant blue green amphibole orthopyroxene and sparse chromite suggesting exhumation of arc and ophiolitic rocks sands and sandstones from the upper miocene to pliocene tipam group and the pliocene to pleistocene dupi tila formation contain assemblages similar to those of the underlying miocene sandstones along with more abundant orthopyroxene and sillimanite in dupi tila sands temporal variations in heavy mineral assemblages in the bengal basin suggest that orogenic detritus first appears in the eastern himalayan foredeep much later early miocene than in the western part of the foredeep eocene the appearance of high pressure phases in upper miocene strata reflects continued unroofing of deeper crustal metamorphic and silicic to ultramafic plutonic rocks

shelf sedimentation off the ganges brahmaputra river system evidence for sediment bypassing to the bengal fan the nature of shelf sedimentation seaward of the world9s largest sediment dispersal system is examined by using sedimentological and geochronological techniques on a unique suite of sediment cores and grab samples sediments from the ganges brahmaputra river system are currently accumulating on the shelf in water depths of less than about 80 m forming a clinoform like deposit similar to subaqueous deltas found off other major river systems the highest sediment accumulation rates on the shelf occur near the head of the swatch of no ground a major submarine canyon that indents the shelf west of the present river mouths this observation together with textural data suggests that river sediments are transported seaward and westward and that the swatch of no ground is currently a major conduit for the transport of sediments from the bengal shelf

neogene himalayan weathering history and river87sr86sr impact on the marine sr record abstract clastic sediments in the bengal fan contain a neogene history of erosion and weathering of the himalaya we present data on clay mineralogy major element stable and radiogenic isotope abundances from lower miocene pleistocene sediments from odp leg 116 nd and sr isotope data show that the himalayan provenance for the eroded material has varied little since 17 ma however from 7 to 1 ma smectite replaces illite as the dominant clay while sediment accumulation decreased implying an interval of high chemical weathering intensity but lower physical erosion rates in the ganges brahmaputra gb basin o and h isotopes in clays are correlated with mineralogy and chemistry and indicate that weathering took place in the paleo gangetic flood plain the87sr86sr ratios of pedogenic clays vermiculite smectite record the isotopic composition of sr in the weathering environment and can be used as a proxy for87sr86sr in the paleo gb basin the sr data from pedogenic clays shows that river87sr86sr values were near 0 72 prior to 7 ma rose rapidly to 0 74 in the pliocene and returned to 0 72 in the middle pleistocene these are the first direct constraints available on the temporal variability of87sr86sr in a major river system the high87sr86sr values resulted from intensified chemical weathering of radiogenic silicates and a shift in the carbonate silicate weathering ratio modeling of the seawater sr isotopic budget shows that the high river87sr86sr values require a ca 50 decrease in the sr flux from the gb system in the pliocene the relationship between weathering intensity 87sr86sr and sr flux is similar to that observed in modern rivers and implies that fluxes of other elements such as ca na and si were also reduced increased weathering intensity but reduced sr flux appears to require a late miocene pliocene decrease in himalayan erosion rates followed by a return to physically dominated and rapid erosion in the pleistocene in contrast to the view that increasing seawater87sr86sr results from increased erosion mio pliocene to mid pleistocene changes in the seawater sr budget were the result of reduced erosion rates and sr fluxes from the himalaya

groundwater flow in the ganges delta basu et al 1 1 reported that 2 1011 m3 year of groundwater flows directly into the bay of bengal an outflow equivalent to 19 of the discharge from the ganges brahmaputra river system they showed that this estimate of flow could have important consequences for the interpretation of

seismicity and tectonics of the bay of bengal evidence for intraplate deformation of the northern indian plate abstract seismicity and fault plane solutions of several earthquakes in the bay of bengal have been studied to focus attention on the nature of intraplate deformation in the northern indian plate a widely dispersed diffuse seismicity provides evidence that the intraplate region of the entire bay of bengal and peninsular india of the indian plate are seismically active of which the gangetic delta and the eastern flank of the ninety east ridge show somewhat higher seismicity in comparison to the thickly populated epicenters at the eastern plate boundary predominance of thrust faulting earthquake mechanisms with consistent north dipping fault planes and more or less n s pressure axes imply that n s compression is more prevalent in the intraplate region of the bay of bengal which is analogous to the himalayan arc this intraplate seismicity and n s compressive deformation is presumed to be the result of collisional resistance to the north moving indian plate with the eurasian plate at the himalayas where subduction of the indian lithosphere in mantle has stopped recently as a result to compensate the horizontal compressive force by ridge push at the carlsberg ridge the intraplate region of the northern indian plate in continuation to the central indian ocean basin no longer remains passive due to a strong repulsive force at the collisonal plate boundary himalaya that causes stress transmission towards south and makes the intraplate region seismically active

dating tsunami deposits present knowledge and challenges abstract dating approaches for fine sediment tsunami deposits can be divided into two categories 1 dating directly using materials from within a tsunami deposit and 2 dating indirectly using materials from above and below it for the former optically stimulated luminescence osl dating has a possible advantage in that is can directly date the burial age of sediments laid down by a tsunami however because of methodological limitations osl dating cannot always provide a reliable age although 14c and u th dating of reworked material from within a tsunami deposit are possible means of determining the age of the event the results merely represent a maximum age of deposition for these reasons dating is commonly achieved indirectly from 14c dates taken from samples in sections immediately above and below a tsunami deposit however indirectly dated results do not provide a precise timing of the event therefore there are distinct limitations in the ability to obtain high precision dating of past tsunamis recent methodological developments including the application of bayesian statistical analysis to radiocarbon dating results and the selection of appropriate dating materials has significantly improved the accuracy of age determination by reducing errors this review presents several methodological improvements that have enhanced tsunami deposit age estimation the most important points for a more precise tsunami age estimation are the numbers of 14c samples dated coupled with the use of bayesian statistical analysis these points are applicable not only to tsunami deposits but also to many other past geohazard events

geochemical study of arsenic release mechanisms in the bengal basin groundwater 1 to investigate arsenic mobility in the bengal basin groundwater we sampled water wells and sediments throughout the region there are strong correlations among high levels of dissolved arsenic and iron ammonia and methane especially in samples from a single site laxmipur no linkage is seen between as and agricultural tracers such as phosphate the association of as and fe occurs because arsenic strongly adsorbs onto feooh particles in river water they flocculate with other fine grained particles at the freshwater saltwater transition zone subsequent bacterially mediated reduction of feooh in the clay releases the adsorbed arsenic weathering of as bearing mica plays a significant role in the as budget the correlated presence of as ch4 and nh4 in water supply wells is the result of diffusion out of organic rich clay into the more permeable zones arsenic is mainly released from recent sediments at 50 m depth deposited in the gbr floodplain as sea level rose throughout the holocene

optical dating of tsunami laid sands abstract the ages of some tsunami deposits can be determined by optical dating a key requirement being that the deposits are derived from sediment that was reworked and exposed to daylight by tidal currents waves wind or bioturbation during the last years before the tsunami measurements have been made using 1 4 ev infrared excitation of k feldspar grains separated from samples of prehistoric tsunami sand sheets and modern analogs of tsunami source sediments at four sites in washington state and british columbia source sands gave equivalent doses indicative of recent exposure to daylight tsunami sand at cultus bay washington yielded an optical age of 1285 95 yr calendric years before a d 1995 1 at 2 this age overlaps the range of from 1030 to 1100 yr determined through a combination of high precision radiocarbon dating and stratigraphic correlation tsunami sands at three sites near tofino and port alberni on vancouver island british columbia have optical ages of 260 20 325 25 and 335 45 yr historical records and radiocarbon dating show that the sand at each of the three sites is between 150 and 400 yr old these optical ages support the hypothesis that the vancouver island sands were deposited by a tsunami generated by a large earthquake on the cascadia subduction zone about 300 yr ago

nonlinear relation of the arctic oscillation with the quasi biennial oscillation a nonlinear principal component analysis nlpca is applied to a set of monthly mean time series from january 1956 to december 2007 consisting of the arctic oscillation ao index derived from 1 000 hpa geopotential height anomalies poleward of 20 n latitude and the zonal winds observed at seven pressure levels between 10 and 70 hpa in the equatorial stratosphere to investigate the relation of the ao with the quasi biennial oscillation qbo the nlpca is conducted using a new compact neural network model the nlpca modeling of the dataset of the ao index and qbo winds offers a clear picture of the relation between the two oscillations in particular the phase of covariation of the oscillations defined by the two nonlinear principal components of the dataset progresses with a predominant 28 4 month periodicity this predominant cycle is modulated by an 11 year cycle the variation of the ao index with the qbo phase also shows that the average ao index is positive when the westerly qbo phase descends past 30 hpa and conversely the average ao index is negative when the easterly qbo phase descends past 30 hpa this relationship is evident during the boreal cold season from november to april but non existent during the boreal warm season from may to october

distribution of c n and p in the sediments of the ganges brahmaputra meghna river system in the bengal basin the bengal basin is one of the geologically youngest and tectonically active drainage regimes of the world which includes the total lower ganges brahmaputra meghna gbm river system one of the highest sediment dispersal systems in the world the sediment load in this system comprises exclusively fine sand silt and clay river bed sediments and suspended matter from stations situated uniformly all over the basin have been analyzed in order to understand the spatial distribution and biogeochemical processing of the c n and p in the system among the ganges brahmaputra and meghna subbasins variations in total phosphorus tp and nitrogen tn contents in the bulk and 63 m fraction of the bed sediments are statistically insignificant but total carbon tc content varies significantly among the three subbasins there is a gradual increase in the concentration of tc from the meglna towards the ganges subbasin attributable to the nature of the floodplain and bank materials which supply major sediment load to the river channels the tp concentration is 2 to 5 times more in the suspended matter than that in any particle size fraction of the sediments although excellent correlation between corg and tn suggests their coorigin the influence of inorganic nitrogen is evident in very low c n ratios the c n ratio varies from 2 to 11 suggesting complete degradation of the organic matter and or enrichment of inorganic nitrogen in the sediments the plant available phosphorus pap varies from 1 78 to 6 98 of tp and indicates a significant anthropogenic contribution the corg tn and c n ratio in the bed sediments of the lower gbm system are in the range comparable with other river basins of the subcontinent

scilly isles uk optical dating of a possible tsunami deposit from the 1755 lisbon earthquake abstract we present the results of optical dating of quartz from marine and aeolian deposits on st agnes island scilly isles uk the single aliquot regenerative dose protocol was used to estimate the equivalent dose in these samples proposed tsunami laid deposits at big pool provided ages of 230 40 and 380 60 years both are consistent with an expected age of 244 years an osl age of 6 3 years was obtained on a modern sub aqueous beach deposit these results suggest that the osl signal in the tsunami laid quartz was completely reset before deposition and that these sediments can be dated accurately by optical dating techniques sand dunes at bergecooth 250 m south of big pool were also dated using osl these ages indicate phases of aeolian activity at 300 a and 1000 a in the scilly isles

diagnosing the qbo s influence on circumpolar vortex variability using msu brightness temperatures and msu derived winds abstract using brightness temperatures from channels 3 and 4 of the microwave sounding unit msu as approximations to mean layer temperatures the geostrophic winds at 50 mb can be computed through a bottom up approach when this method is applied at high latitudes during austral winter and spring it is found that accurate descriptions of the seasonal evolution and interannual variability of the lower stratospheric circumpolar vortex are obtained variations in early spring vortex strength from year to year appear to relate well to variations in the timing of the first large late winter wavenumber one event in the lower stratosphere since wave forcing of the mean flow in the lower stratosphere is known to be weak the variability in vortex strength may result from variations in wave induced subsidence through the downward control principle previous studies have demonstrated a biennial harmonic in both extratropical wave forcing and the mean flow suggesting a link with the equatorially confined quas

distribution of stress axes orientation in the andaman nicobar island region a possible stress model and its significance for extensional tectonics of the andaman sea abstract composite plots of pressure and tension axes of the available focal mechanism solutions of earthquakes are used to investigate the nature and process of the stress system and their bearing on tectonics in the andaman nicobar island region the composite plots show that the andaman nicobar island arc and the andaman sea are subjected to ssw nne directed compressive force in response to the ne drifting motion and or oblique subduction of the indian plate beneath the andaman nicobar island arc stress study also reveals that the andaman sea at the same time is experiencing an ese wnw tensile stress analogous to active back arc opening extension based on this stress pattern a strain ellipse model is proposed to explain the extensional tectonics of the andaman sea it is suggested that the oblique subduction of the indian plate invokes ne sw directed compression as well as north south directed shear stress these combined stresses are transmitted to or act on the andaman sea plate and result in stretching of the andaman sea plate in a nw se least stress direction on the strain ellipse this stretching leads to ne sw directed fracture zones normal to stretching where ascending magmas are emplaced to form active mid oceanic spreading ridges and thus active back arc extension or opening of the marginal basin takes place nearly n s dominated fracture zones which form ridge ridge type transform faults by offsetting the spreading ridges are thought to originate chiefly along the plane of maximum shear of the strain ellipse that makes an angle of 45 5 with the greatest horizontal stress component 1 and both have a close resemblance

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

nature of solute loads in the rivers of the bengal drainage basin bangladesh the bengal drainage basin is geologically one of the youngest and tectonically most active denudation regimes of the world and encompasses the total lower reaches of the ganges brahmaputra meghna gbm drainage basin the gbm river system contributes around 4 5 of the total annual global freshwater flux to the oceans the solute load of the gbm river system is dominated by the carbonate weathering products of the transport limited denudation regime however in the meghna basin which drains a mountainous region silicate weathering is slightly more predominant and the solute load tends to be more influenced by the atmospheric contribution the river system represents about 5 152 106 t yr 1 of the annual global chemical flux to the world s oceans the chemical denudation rate of the gbm system in the bengal basin is one of the world s highest 79 114 t km 2 yr 1 suggesting intensive weathering and erosion in the drainage basin both in bangladesh as well as in the hinterlands of india and china

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

a 13 000 year climate record from western tibet although the tibetan plateau is important in influencing the atmospheric circulation of the northern hemisphere1 3 there are only a few continuous palaeoclimate records available and these are limited to the plateau s northeastern margin4 6 here we present a 13 000 yr record from sumxi co western tibet constructed from both lake core and shoreline studies which shows that conditions in the early middle holocene were warmer and wetter than at present these results confirm model predictions of an intensified monsoon over the region at 9 000 yr bp owing to an orbitally induced increase in summer insolation7 8 we also find evidence for warm humid pulses at 12 500 and 10 000 yr bp in phase with the steps of the last deglaciation and for a return to cold dry conditions at 11 10 000 yr bp none of which can be explained by orbital variations the existence of the cold episode confirms that the cooling associated with the younger dry as event occurred in continental china6 9 and provides further evidence of the global nature of this event10

optical dating of young coastal dunes on a decadal time scale we explore the use of quartz optically stimulated luminescence osl dating for reconstructing coastal evolution on a time scale of decades to a few hundred years samples are taken from the accretionary south west coast of texel a barrier island just offshore of the northern netherlands the ages of dune ridges are known from historical sources an excellent chronology with a decadal accuracy exists for the past 260 years osl ages of less than 10 years on the youngest samples indicate that the osl signal of the quartz grains is very well zeroed prior to deposition and burial osl ages of five samples from a 250 year old dune ridge are indistinguishable and the osl ages on 17 out of 20 samples are in excellent agreement with the well known independent age controls our results highlight the potential of osl dating for high resolution reconstruction of coastal evolution over the past few centuries

arsenic toxicity of groundwater in parts of the bengal basin in india and bangladesh the role of quaternary stratigraphy and holocene sea level fluctuation arsenic toxicity in groundwater in the ganges delta and some low lying areas in the bengal basin is confined to middle holocene sediments dissected terraces and highlands of pleistocene and early holocene deposits are free of such problems arsenic rich pyrite or other arsenic minerals are rare or absent in the affected sediments arsenic appears to occur adsorbed on iron hydroxide coated sand grains and clay minerals and is transported in soluble form and co precipitated with or is scavenged by fe iii and mn iv in the sediments it became preferentially entrapped in fine grained and organic rich sediments during mid holocene sea level rises in deltaic and some low lying areas of the bengal basin it was liberated subsequently under reducing conditions and mediated further by microbial action intensive extraction of groundwater for irrigation and application of phosphate fertilizer possibly triggered the recent release of arsenic to groundwater this practice has induced groundwater flow mobilizing phosphate derived from fertilizer as well as from decayed organic matter which has promoted the growth of sediment biota and aided the further release of arsenic however the environment is not sufficiently reducing to mobilize iron and arsenic in groundwater in the ganges floodplains upstream of rajmahal thus arsenic toxicity in the groundwater of the bengal basin is caused by its natural setting but also appears to be triggered by recent anthropogenic activities

deeper groundwater chemistry and geochemical modeling of the arsenic affected western bengal basin west bengal india abstract a regional scale hydrogeochemical study of a 21 000 km2 area in the western bengal basin shows the presence of hydrochemically distinct water bodies in the main semiconfined aquifer and deeper isolated aquifers spatial trends of solutes and geochemical modeling indicate that carbonate dissolution silicate weathering and cation exchange control the major ion chemistry of groundwater and river water the main aquifer water has also evolved by mixing with seawater from the bay of bengal and connate water the isolated aquifers contain diagenetically altered water of probable marine origin the postoxic main aquifer water exhibits overlapping redox zones metal reducing sulfidic and methanogenic indicative of partial redox equilibrium with the possibility of oxidation in micro scale environments the redox processes are depth dependent and hydrostratigraphically variable elevated dissolved as in the groundwater is possibly related to fe iii reduction but is strongly influenced by coupled fe s c redox cycles arsenic does not show good correlations with most solutes suggesting involvement of multiple processes in as mobilization the main river in the area the bhagirathi hoogly is chemically distinctive from other streams in the vicinity and probably has little or no influence on deep groundwater chemistry arsenic in water of smaller streams jalangi and ichamati is probably introduced by groundwater discharge during the dry season

arsenic mobilization in a freshening groundwater system formed within glaciomarine deposits abstract arsenic release to groundwater and conditions favoring as mobility are investigated in a system of aquifers formed within unconsolidated quaternary sediments the studied groundwater system is comprised of unconfined aquifers formed in glaciofluvial sediments with ca mg hco3 groundwater and confined aquifers formed within glaciomarine sediments with high as above 10 g l na hco3 or na cl groundwater a positive relationship of as concentrations with the na ca mg ratio of groundwater indicates that as release occurs in glaciomarine sediments concurrent to cation exchange reactions related to groundwater freshening arsenic is mobile in confined aquifers as a result of groundwater basic ph which prevents arsenate from adsorbing to mineral surfaces and reducing conditions that favor speciation to arsenite selected extractions applied to sediment core samples indicate that as occurs in sediments predominantly in sulfide minerals and in mn oxides and or fe oxyhydroxides general positive relationships between as and the reduced species fe2 nh3 and dissolved s2 suggest that as release occurs at increasingly reducing conditions despite likely as release via fe oxyhydroxide reductive dissolution fe remains at relatively low concentrations in groundwater up to 0 37 mg l as a result of possible fe adsorption and fe reprecipitation as carbonate minerals favored by basic ph and high alkalinity the presence of s2 in some samples a negative relationship between 34s of so4 and so 4 2 concentrations and a positive relationship between 34s and 18o of so4 indicate that groundwater in confined aquifers is undergoing bacterial so4 reduction

distribution of major stratospheric warmings in relation to the quasi biennial oscillation data from 1953 to the present indicate that major warmings in the northern hemisphere winter have not occurred when the equatorial monthly mean zonal winds are deep westerly i e westerly over more than about 5 8 of the 10 85 mb layer sixteen winters have had a major warming in the last 35 years six january february periods had deep equatorial westerlies but did not experience a major warming major warmings do not require deep equatorial easterlies nor is the occurrence of a major warming significantly correlated with the sign of the zonal mean wind at any particular level between 10 and 50 mb although as noted by previous investigators more than half of the observed major warmings have occurred when the equatorial flow is easterly at a given level between 10 and 50 mb we suggest that a more relevant qbo statistic may be found in the depth of qbo wind regimes the previously proposed connection between the equatorial quasi biennial oscillation and the major warmings of the northern hemisphere winter is supported by these observations

natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water the example of west bengal and its worldwide implications in order to investigate the mechanism of as release to anoxic ground water in alluvial aquifers the authors sampled ground waters from 3 piezometer nests 79 shallow 80 m wells in an area 750 m by 450 m just north of barasat near kolkata calcutta in southern west bengal high concentrations of as 200 1180 mug l 1 are accompanied by high concentrations of fe 3 13 7 mgl 1 and po4 1 6 5 mg l 1 ground water that is rich in mn 1 5 3 mg l 1 contains 50 mug l 1 of as the composition of shallow ground water varies at the 100 m scale laterally and the metre scale vertically with vertical gradients in as concentration reaching 200 mug l 1 m 1 the as is supplied by reductive dissolution of feooh and release of the sorbed as to solution the process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit in well waters thermotolerant coliforms a proxy for faecal contamination are not present in high numbers 10 cfu 100 ml in 85 of wells showing that faecally derived organic matter does not enter the aquifer does not drive reduction of feooh and so does not release as to ground water arsenic concentrations are high much greater than50 mug l 1 where reduction of feooh is complete and its entire load of sorbed as is released to solution at which point the aquifer sediments become grey in colour as feooh vanishes where reduction is incomplete the sediments are brown in colour and resorption of as to residual feooh keeps as concentrations below 10 mug l 1 in the presence of dissolved fe sorbed as released by reduction of mn oxides does not increase as in ground water because the as resorbs to feooh high concentrations of as are common in alluvial aquifers of the bengal basin arise because himalayan erosion supplies immature sediments with low surface loadings of feooh on mineral grains to a depositional environment that is rich in organic mater so that complete reduction of feooh is common c 2004 published by elsevier ltd

climatology of the equatorial lower stratosphere abstract twenty years of radiosonde data have been analyzed in an attempt to develop a latitudinal structure climatology of winds temperature and geopotential at 30 and 50 mb in the equatorial stratosphere the fine latitudinal resolution provided by the wmo station network reveals several interesting features in the latitudinal structure of the annual and quasi biennial cycles which dominate this region for example the westerly and easterly acceleration phases of the quasi biennial oscillation are markedly different westerly accelerations appear first at the equator spreading outward with time to higher latitude and an more intense on average than the easterly accelerations the easterly accelerations are more uniform in latitude but leer uniform in time sometimes occurring in two stages the quasi biennial wind and temperature oscillations are symmetric about the equator while the annual harmonic in zonal wind is antisymmetric about the equator but is not proportional to the coriolis paramete

the groundwater geochemistry of the bengal basin weathering chemsorption and trace metal flux to the oceans sixty eight groundwater samples from the ganges brahmaputra floodplain in the bengal basin were analyzed to assess the groundwater geochemistry the subsurface hydrology the buffering effects of sediments on trace metal concentrations and their isotopic compositions and the magnitude of the subsurface trace element flux to the bay of bengal and to the global ocean samples obtained from depths of 10 to 350 m were measured for major and trace elements dissolved gas and tritium on the basis of the 3he 3h ages the groundwater at depth 30 150 m appears to be continually replenished indicating that this recharge of groundwater to depth must ultimately be balanced by a significant quantity of submarine discharge into the bay of bengal using the 3he 3h groundwater age depth relationship to calculate a recharge rate of 60 20 cm yr we estimate a subsurface discharge into the bay of bengal of 1 5 0 5 1011 m3 yr or 15 of the surface ganges brahmaputra river gbr flux several trace elements especially sr and ba display elevated concentrations averaging 7 to 9 times the surface gbr water values the submarine groundwater fluxes of sr and ba to the oceans are 8 2 2 108 and 1 5 0 3 108 mol yr or 3 3 and 1 2 respectively of the world total or equal to the surface gbr sr and ba estimated fluxes our groundwater flux for ba agrees with the estimate of moore 1997 3 108 3 109 mol yr on the basis of measured ba and ra excesses in the bay of bengal other trace metals such as u and mo are at low but measurable levels and are not major contributors to the global flux in this river system a comparison of the sr and ba concentrations plus 87sr 86sr ratios in groundwater to the oxalate extractable fractions of a coastal sediment core suggests that weathering of carbonates and minor silicates coupled with cation exchange plus adsorption and desorption reactions controls the trace element concentrations and 87sr 86sr isotopic compositions in both the groundwater and river water our data also imply that other coastal floodplains e g the mekong and the irrawaddy rivers that have high precipitation rates and rapid accumulation of immature sediments are likely to make significant contributions to the global oceanic trace metal budgets and have an impact on the sr isotopic evolution in seawater

deltaic land subsidence and sea level fluctuations along the east coast of india since 8 ka a palynological study the consequences of climate change and land subsidence are often related to sea level rise fall mangrove extinction and migration were assessed through palynological studies in two sedimentary cores in order to address climate relative sea level rsl and its relation to geomorphology since 8420 cal yr bp from kanuru 500 cm deep and since 5850 cal yr bp from machilipatnam 118 cm deep krishna delta india four units nine phases of sediment depositional environment were identified on the basis of marine terrestrial palynomorphs in unit 1 the marine palynomorphs indicate palaeoshoreline in kanuru from 8420 to 8300 cal yr bp which is now 4 5 km from the present day shoreline but after a short span a retreat in sea level took place between 8300 and 7040 cal yr bp about three to four short term intermittent rise fall in rsl were recorded in unit 2 between 7040 and 3980 cal yr bp in kanuru and between 5225 and 3240 cal yr bp in machilipatnam during this period the diversity of mangroves was

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

arsenic in groundwater testing pollution mechanisms for sedimentary aquifers in bangladesh in the deltaic plain of the ganges meghna brahmaputra rivers arsenic concentrations in groundwater commonly exceed regulatory limits 50 m gl 21 because feooh is microbially reduced and releases its sorbed load of arsenic to groundwater neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution the most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat concentrations of ammonium up to 23 mg l 21 come from microbial fermentation of buried peat and organic waste in latrines concentrations of phosphorus of up to 5 mg l 21 come from the release of sorbed phosphorus when feooh is reductively dissolved and from degradation of peat and organic waste from latrines calcium and barium in groundwater come from dissolution of detrital and possibly pedogenic carbonate while magnesium is supplied by both carbonate dissolution and weathering of mica the 87 sr 86 sr values of dissolved strontium define a two component mixing trend between monsoonal rainfall 0 711 6 0 001 and detrital carbonate 0 735

optical dating using inclusions within quartz grains a sequence of stranded beach dunes in the southeast of south australia which resulted from the advance and retreat of the sea over a tectonically rising land surface during the past 800 ka has been securely dated by geological means and successfully used to test thermoluminescence dating based on quartz we have now obtained a series of promising results from the same sequence with a test of optical dating on inclusions within the quartz grains the innovative aspect of the measurements is the use of infrared irradiation to stimulate emission from the inclusions rather than conventional stimulation of the quartz itself by light of shorter wavelength satisfactory ages were found for seven dunes covering the time span 0 400 ka

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

the significance of large sediment supply active tectonism and eustasy on margin sequence development late quaternary stratigraphy and evolution of the ganges brahmaputra delta abstract borehole data from the ganges brahmaputra delta system unveil an intriguing late quaternary history controlled by immense sediment discharge tectonics and eustasy sea level first intersected a major portion of the lowstand surface 10 000 11 000 cal yr bp marking the onset of sediment trapping and delta growth despite rapid sea level rise 1 cm yr sediment load was sufficient to maintain relative shoreline stability during this time by 7000 cal yr bp accommodation was quickly infilled with slowed sea level rise leading to upstream channel migration and widespread dispersal of sands this forced coastal progradation along the western delta front where the ganges was situated and much of the river s fine grained discharge bypassed the subaerial delta and formed a prograding deltaic clinoform on the shelf concurrently brahmaputra sediments were sequestered to an inland tectonic basin thus starving the adjacent shoreline and leading to transgression along the eastern delta by 5000 cal yr bp the two rivers had migrated or changed course to discharge along the eastern delta shoreline which began to prograde into what is now the modern river mouth estuary present delta configuration appears to have developed by 3000 cal yr bp evolution of the tectonically active ganges brahmaputra g b system reveals important similarities and differences with other deltas overall facies succession follows that of basic models progressing from an alluvial valley to coastal marine delta front to a prograding subaerial delta plain however the timing thickness and controls of these deposits differ immense sediment discharge from the ganges and brahmaputra rivers allowed initial delta growth 2000 3000 yr earlier than the global average despite debouching onto a canyon incised high energy margin subsequently a thick 50 m transgressive systems tract was formed during the early holocene phase of delta aggradation contrasting with extensive shoreline retreat documented along most margins highstand progradation of coastal and shelf sequences ensued by the middle holocene but subsiding inland basins also favored accumulation of a thick to 40 m highstand sequence in the lower floodplains unlike many other delta systems subsidence in the subaerial g b delta is not dominated by compaction but rather by plate driven tectonic processes that generate rates up to 4 mm year overall the huge sediment load tectonic subsidence major seismic events and a nearshore canyon system have led to widespread sediment dispersal and sequence formation across the subaerial delta shelf and deep sea bengal fan throughout the late quaternary

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