the geomorphic dynamics and environmental history of an upper deltaic floodplain tract in the sacramento san joaquin delta california usa a multi proxy approach was used to examine the geomorphic dynamics and environmental history of an upper deltaic oodplain tract in the sacramento san joaquin delta california three long cores were collected from the mccormack williamson tract mwt and these cores were analyzed for bulk density loss on ignition ne clay and silt content al concentration magnetic susceptibility pollen and charcoal radiocarbon dates obtained for the cores were converted into calendar years and an age depth model was constructed long term vertical accretion and sedimentation rates were estimated from the age depth model cross core relations show that coarse sediment generally accumulates more rapidly and has greater magnetic susceptibility compared to ne sediment percentage ne and loi data show a strong linear relationship that indicates ooding is the primary mechanism for the deposition of particular organic matter on the oodplain and that landscape wash load has contributed a highly consistent fraction of persistent organic matter averaging 5 5 per cent to the site down core grain size pro les show two hydrological domains in the cores namely millennial ne coarse uctuations superimposed on general up core ning coarse sediment is viewed as channel or near channel overbank deposits whereas ne deposits are considered to be distal overbank ood deposits the coarse ne uctuations are indicative of changing depositional settings as channels migrated laterally across mwt whereas the upward ning trend re ects a combination of self limiting overbank deposition as oodplain elevation increased and decreasing competence as sea level rise reduced ood pulse energy slopes mwt has been cross cut and incised numerous times in the past only to have the channels abandoned and subsequently lled by ne sediment the channels around mwt attained their modern con guration about 4000 years ago mwt likely came under tidal in uence at about 2500 cal bp wetlands have recently developed on mwt but they are inorganic sediment dominated copyright 2004 john wiley sons ltd

late pleistocene and holocene vegetation changes and anthropogenic impacts in the cauvery delta plains southern india abstract a 5 m long core from uttarangudi in the distal plain of cauvery delta in south india provides evidences of vegetation climate and anthropogenic activities during the late pleistocene and holocene the pollen catchment area for this region is the localised sources including the adjoining tertiary upland plateau the recorded variation in pollen assemblages and sediments indicates that the environmental conditions have changed over time from aerial oxidising to lacustrine or ponded environment the lack of pollen records from 17 802 cal bp until 11 535 cal bp suggests severe drier conditions and an extremely patchy species poor tropical dry evergreen forest tdef vegetation community associated with an arid climate between 11 535 and 8487 cal bp partial climatic amelioration appears to have occurred and the trend become humid until 7034 cal bp characterised by the expansion of the tdef vegetation and strengthening of the monsoon precipitation the period from 7034 3553 cal yr bp recorded a regressive transition of the forest taxa influenced by a weakened monsoon precipitation and enhanced anthropogenic activity the subsequent increase of disturbance signals post 3553 cal yr bp is in agreement with independent archaeological evidences obtained from this region

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

a less humid climate since ca 3500 yr b p from marine cores off karwar western india abstract a marked change in the vegetation of the western ghats at ca 3500 yr b p has been observed from a study of two marine cores taken from the inner shelf off karwar karnataka western india at the mouth of the kalinadi river this change is indicated by a decrease in forest pollen particularly from evergreen forests and by a corresponding increase in savanna pollen as well as by a reduction in mangrove pollen at the same time the values of the stable isotope 13 c of sedimentary organic matter increased suddenly due to a higher contribution of organic matter of margine origin all these modifications were probably induced by a less humid climate the term drier can hardly be used for an area where the annual rainfall still attains 6 m in the hills above this clear limit the same trends steady but considerably weaker also resulting a reduction in the humid conditions were recorded up to ca 2200 yr b p reduction in forest vs increase in savannas decrease in the mangrove vegetation higher 13 c values from there onwards the pollen assemblages have remained uniform up to the present day it may be deduced that a climate quite similar to the present conditions was established about 2200 yr ago and still prevails the curves representing the percentages of marine microfossils dinoflagellates organic tests of foraminifera eggs of copepods show little variation at the 3500 yr b p boundary the marine assemblages were modified drastically only at about 2200 yr b p these sharp modifications are probably due to an increase in the marine influence as a result of a reduction in the fresh water supply from the kalinadi the stability in the representation of marine assemblages which has persisted from about 2200 yr b p to the present confirms the establishment of the present day climate around that date this paleoclimatic reconstruction is in conformity with the evidence for the beginning of drier conditions recorded at about the same time in the low latitudes in many parts of the world india northern arabian sea africa sahara tropical forest east african lakes australia and the carribbean

high resolution holocene environmental changes in the thar desert northwestern india sediments from lunkaransar dry lake in northwestern india reveal regional water table and lake level fluctuations over decades to centuries during the holocene that are attributed to changes in the southwestern indian monsoon rains the lake levels were very shallow and fluctuated often in the early holocene and then rose abruptly around 6300 carbon 14 years before the present 14c yr b p the lake completely desiccated around 4800 14c yr b p the end of this 1500 year wet period coincided with a period of intense dune destabilization the major harrapan indus civilization began and flourished in this region 1000 years after desiccation of the lake during arid climate and was not synchronous with the lacustral phase

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

weathering of charnockites and sediment production in the catchment area of the cauvery river southern india abstract in the cauvery catchment area charnockites are making high hills compared to gneisses in situ static weathering of a charnockitic boulder shows lesser extent of chemical weathering relative to that developed into a profile this difference is seen both in clay mineral composition their ree patterns and in the a cn k and a cnk fm triangular plots based on the chemical changes relative to ti three groups of elements are recognized ba si k na sr ca and mg show increasing depletion as the weathering intensity increases in listed order al remained relatively immobile whereas fe followed by mn cr ni ree and p show a variable extent of enrichment with increasing chemical weathering the sediment occurring on the foothills of the charnockite hills have a very uniform composition and texture without any depositional features reworking of these sediments in a first order stream has caused only minor compositional changes by the local segregation of heavy minerals on the channel bed and by the removal of small amount of clay materials as suspended load the ree pattern of the reworked channel bed sand is nearly identical to that of the channel wall sediments but with lower by 25 abundance although the rocks are 2500 ma and now located in tropical latitudes and probably had experienced several periods of warm and wet climate the soils and the sediments derived from them are chemically very immature suggesting their exposure to denudational processes very recently by tectonic uplift

sediment transport in the cauvery river basin sediment characteristics and controlling factors abstract during the monsoon period 75 of the annual rainfall 73 of the annual water discharge and 85 of the annual sediment transport takes place in the cauvery river basin geology and river water discharge are the major natural factors controlling the sediment transport sediment transport in the cauvery river is greatly influenced by the presence of two major dams built across the river an examination of the particle size distribution of the suspended sediments shows that the less than 20 m fraction accounts for nearly 60 of the total sediment transported by the river at dam sites coarse sediments are selectively removed from the suspended load the suspended mineralogy is dominated by quartz and feldspar followed by clay minerals and carbonates clay minerals average about 30 and are dominated by the montmorillonite type the results of our study also demonstrate the importance of such sediment characteristics as particle size and mineralogy in controlling the trace metal distribution in sediments

a 200 ka pollen and oxygen isotopic record from two sediment cores from the eastern arabian sea abstract we present here a pollen record from the northern indian ocean that goes back to 200 ka the boundary between marine isotopic stages mis 7 and 6 pollen oxygen isotopic composition and organic carbon have been examined for two sediment cores from the eastern arabian sea 15 02 n and 71 41 e 13 16 n and 71 00 e to reconstruct the long term palaeoclimate and palaeovegetation of the indian subcontinent oxygen isotope data suggest that glacial periods mis 2 4 and 6 are characterised by low precipitation because of a weak southwest monsoon and a strong northeast monsoon in contrast interglacial periods mis 1 3 and 5 are marked by high fresh water input resulting from a strong southwest monsoon during the last glacial interglacial cycle sea surface temperature and surface salinity changed as a result of variations in the evaporation precipitation e p balance throughout the core the dominant pollen types are poaceae and chenopodiaceae and or amaranthaceae 50 their dominance during glacial periods mis 2 4 and 6 suggests that the climate was cold and dry this dominance is also suggestive of salinity tolerant vegetation colonizing large areas near seashore due to lower sea level or high e p conditions during interglacial periods mis 1 3 and 5 when there was high precipitation the arid taxa were sparse whereas poaceae and piperaceae were abundant hence chenopodiaceae and or amaranthaceae and artemisia are suggestive of cold and arid semi arid climate and poaceae and piperaceae of warm and wet conditions mangrove pollen is not well represented in the cores

ree geochemistry of recent clastic sediments from the kaveri floodplains southern india implication to source area weathering and sedimentary processes abstract the kaveri river drains through archean gneissic and charnockitic terranes in south india the rare earth element ree chemistry of the floodplain sediments along with their major and trace element composition in different size fractions are discussed we observe a strong coherence between ree and tio2 contents in the sediments which is suggestive of strong control by titanite or its weathered products on the ree chemistry ree concentrations also show a general increase with decreasing size of bulk sediments different size fractions and of light and heavy mineral fractions this suggests the presence of ree in the fe oxy hydroxide surface coatings on clastic grains formed by the weathering of hornblende and titanite in the granodioritic to dioritic protoliths we also interpret the data as showing that ree patterns of clastic sediments notably eu anomaly are affected by the degree of source rock weathering as well as by the fluvial processes of sorting and mineral differentiation therefore for provenance study sediments having all granulometric grades such as the floodplain sediments are preferable because they most closely represent the source particularly when the source region suffered little chemical weathering in the present case the sediments were derived from the high standing hills of archean charnockites because of their recent uplift and physical denudation

agriculture and environmental change at qingpu yangtze delta region china a biomarker stable isotope and palynological approach rice oryza sp agriculture sustains vast numbers of people and despite great advancements made in recent years questions about its origins and spread throughout asia remain unanswered this study uses sedimentary biomarker stable carbon isotope and palynological analyses to investigate early rice agriculture in the yangtze delta a region where rice agriculture emerged at least 7000 years ago accelerator mass spectrometer ams 14c dating reveals the age of sedimentary section to be between c 6000 and 1800 cal bp widespread clearing of forest vegetation c 2400 cal bp is the earliest major human influence detected in the qingpu record following this rice agriculture probably dominated the qingpu area evidence supporting rice agriculture after c 2400 cal bp is provided by increased poaceae and cereal type taxa which occur with high concentrations of plant wax n alkanes with a dominant c3 plant origin c27 c31 with odd even preference 13c 29 8 to 36 3 also high concentrations of a

a δ 13 c record of late quaternary climate change from tropical peats in southern india stable isotope ratios of carbon in soils or lake sediments1 3 and of oxygen and hydrogen in peats4 5 have been found to reflect past moisture variations and hence to provide valuable palaeoclimate records previous applications of the technique to peat have been restricted to temperate regions largely because tropical climate variations are less pronounced making them harder to resolve here we present a 13c record spanning the past 20 kyr from peats in the nilgiri hills southern india because the site is at high altitude 2 000 m above sea level it is possible to resolve a clear climate signal we observe the key climate shifts that are already known to have occurred during the last glacial maximum 18 kyr ago and the subsequent deglaciation in addition we observe an arid phase from 6 to 3 5 kyr ago and a short wet phase about 600 years ago the latter appears to correspond to the mediaeval warm period which previously was believed to be confined to europe and north america6 7 our results therefore suggest that this event may have extended over the entire northern hemisphere

magnetic properties of sediments in the bay of bengal and the andaman sea impact of rapid north atlantic ocean climatic events on the strength of the indian monsoon abstract the results of a high resolution mineral magnetic study combined with major element geochemistry analysis oxygen isotopes and 14c ams stratigraphy are reported for deep sea gravity cores md77 169 and md77 180 located in the andaman sea and the bay of bengal respectively core md77 169 covers the last 280 kyr and core md77 180 covers the last 160 kyr in both cores rock magnetic parameters indicate that the magnetic assemblage is dominated by pseudo single domain titanomagnetite grains with grain size variations following a strong 23 kyr periodicity smaller magnetic grain sizes are observed during periods characterized by a strong summer monsoon in addition in core md77 180 we observe a correlation between magnetic grain size and a chemical index of alteration this suggests that these magnetic grain size changes are related to chemical weathering driven by summer monsoon rainfall a comparison of the gisp2 ice core isotopic record and the magnetic grain size record of the bay of bengal shows that rapid temperature variations documented in the ice core dansgaard oeschger cycles and heinrich events during the last glacial period are also present in the magnetic grain size record heinrich events and cold stadial events are characterized by relatively large magnetic grain sizes furthermore heinrich events are characterized by lower values of the chemical index of alteration implying a lower degree of chemical weathering related to significantly drier conditions on the continent we suggest that rapid cold events of the north atlantic heinrich events during the last glacial stages are characterized by a weaker summer monsoon rainfall over the himalaya via an atmospheric teleconnection

new insights on permafrost genesis and conservation in talus slopes based on observations at fluelapass eastern switzerland abstract the talus slope at fluelapass was the first mountain permafrost study site in switzerland in the 1970s and the presence of ice rich permafrost at the foot of the slope has been investigated in the context of several studies focusing on the role of snow cover distribution we review previously developed hypotheses and present new ones using various data sources such as temperature measurements in boreholes a subaquatic dem generated from unmanned aerial system uas photogrammetry terrestrial laser scan measurements of snow depth geophysical ground investigations and automatic time lapse photography from this combination of data sources together with observations in the field an interesting sequence of geomorphologic processes is established at fluelapass as a result we show how mass wasting processes can initiate the genesis and long term conservation of ice rich permafrost at the base of a talus slope

importance of flood plain sedimentation for river sediment budgets and terrigenous input to the oceans insights from the brahmaputra jamuna river recent authors have suggested that a significant proportion of the worldwide terrigenous sediment budget is trapped landward of the river ocean boundary in high load tectonically active basins to test this idea modern flood plain sediment accumulation rates were determined along a 110 km reach of the brahmaputra locally jamuna river using 137cs geochronology of sediment cores and geographic information system gis extrapolation to adjacent areas 137cs accumulation rates decrease exponentially away from the channel from 4 cm yr on the natural levees to 1 cm yr within a few tens of kilometers basinward important controls on sedimentation in this area include proximity to distributary channels local topography and interannual variability of the flood pulse model results indicate that an average of 23 m t yr of sediment are sequestered in this section of the flood plain extrapolated basinwide as much as 39 71 of the river sediment budget may be trapped landward of the ganges brahmaputra mouth

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

atmospheric summer circulation and coastal upwelling in the arabian sea during the holocene and the last glaciation accumulation rates of biogenic and lithogenic components were studied in 39 turbidite free well dated sediment cores from the northern indian ocean to define the proportions of fluvial and eolian input and to reconstruct quaternary patterns of coastal upwelling the majority of dust deposited in the western arabian sea during the holocene about 100 106 t yr 1 is advected from arabia by northwesterly winds which overlie the low level southwest monsoon the glacial increase in dust flux to 160 106 t yr 1 culminated in the northern arabian sea most probably due to i entrainment of dust rich in chlorite dolomite and lithogenic carbonate in the then dry persian gulf and ii a southward shift of the mean position of the southwest monsoon during glacial summer this shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off somalia and oman both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27 000 yr as well as the asian continental summer heat low however the glacial seasonal time span of the southwest monsoon season was much reduced most likely because of a delay in the seasonal onset of the southwest monsoon

late holocene mangrove dynamics and coastal environmental changes in the northeastern cauvery river delta india abstract a palaeoclimate and palaeoecological study was carried out using sedimentological palynological and thecamoebian evidence in a 5 m deep sediment core deposited since 3630 cal bp from tspettai mangrove wetland northeastern part of cauvery river delta textural analysis shows the overall predominance of fine clay with intermittent phases of sand the palynological climatic period inferred in phase i 3630 3170 cal bp shows a stabilized estuarine ecosystem conducive for mangroves along with a good percentage of hinterland forest indicating a warm and humid climate with strengthened monsoon phase iia 3170 2600 cal bp shows abundance of salt tolerant mangroves along with a mixed forest suggesting climatic amelioration from warm and humid to dry and arid phase iib 2600 1300 cal bp shows the dominance of salt tolerant species indicating enhanced dry and arid climate coupled with weakened monsoon phase iii since 1300 cal bp is characterized by rejuvenation of true mangroves and high percentages of salinity tolerant mangroves with a low percentage of thecamoebians thereby indicating increased salinity induced by weakened monsoon and enhanced anthropogenic activity it is inferred that during the past 3 millennia climate changed from warm and humid to cool and arid conditions with an evolution of vegetation from moist to dry deciduous forest the qualitative and quantitative study shows a decline in the true mangroves and an increase in the salt tolerant vegetation which is attributed to the increased salinity in the wetland due to high salt accumulation in the root zone which is vulnerable for mangroves

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

holocene and late pleistocene relative sea level fluctuations along the east coast of india abstract hermatypic coral colonies and intertidal fossil bearing grainstone packstone and sandstone beds of holocene and of a late pleistocene highstand are exposed above the present high tide level htl at a number of locations along the east coast of india from cape comorin to rameswaram being a passive margin boundary free from indications of late quaternary seismogenic movements this sector provides a benchmark for defining minor relative sea level perturbations during the late pleistocene and holocene highstands along a tropical coast lying between latitudes 5 n and 10 n a series of marine terraces carved on and locally blanketted by late pleistocene biotic and terrigenous accumulations occur at different elevations up to 4 4 m above ltl at manappad point possibly signifying discrete stillstand episodes followed by abrupt intervals of rising falling sea level sea level indicators of the holocene highstand occur in this sector as well as along the fringes of the godavari delta further north the holocene highstand reached nearly 3 m above ltl at 7 3 ka remained stable for approximately 1 7 kyr and was followed by a relative sea level fall between 5 2 and 4 2 ka there was a second pulse of relative sea level rise of a few metres leading to a fresh spurt in coral growth along the northern coast of mandapam and rameswaram this was nearly contemporaneous with fresh melting of ice sheets of antarctica the little ice age lia witnessed a minor 1 m relative sea level fall along this coast resulting in rapid diagenetic hardening and infiltration of goethite into the emerged foreshore sand at karikovil and its neighbourhood this was followed by a rise of the sea level during the last few centuries

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