stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

sr and 87sr 86sr in rivers draining the deccan traps india implications to weathering sr fluxes and the marine 87sr 86sr record around k t the concentration of dissolved sr and its 87sr 86sr has been measured in the headwaters of the krishna river system and west flowing western ghat rivers all of which have their drainage almost entirely in the deccan traps the sr concentration follows that of ca and mg with sr ca and sr mg ratios similar to that of deccan basalts suggesting that all these alkaline earths are released to waters nearly congruently from the deccan basalts during chemical weathering the 87sr 86sr range from 0 70614 to 0 70986 within that reported for the deccan basalts the dissolved sr flux from the deccan calculated from the measured data is 1 35 108 moles yr 1 0 4 of the global riverine flux which is nearly the same as the proportion of area covered by deccan basalts relative to the global drainage the flux however is a factor of 3 lower than that reported for the narmada tapti wainganga ntw rivers draining the northern deccan this difference in sr flux among rivers draining the various regions of deccan could be natural spatial temporal variations and or due to supply of sr to ntw rivers from nonbasaltic sources model calculations on the role of emplacement and weathering of deccan on marine sr isotope evolution around ktb and late tertiary show that deccan basalts can be an important contributor to the decline in 87sr 86sr during these periods it is shown that to account for the pre ktb dip in 87sr 86sr the flux requirement from deccan at that time would have to be several times the contemporary flux with 87sr 86sr of 0 705 0 708 considering that the area of deccan at ktb was about thrice the present area and that the weathering rate of deccan basalts may have been much higher in early stages following eruption such high fluxes at about ktb seem feasible the disproportionately higher flux requirement for sr is similar to that invoked to explain the pre ktb decrease in 187os 188os the calculations also show that the supply of unradiogenic sr from basalts can have significant control on the long term 66 to 55 ma decline of marine 87sr 86sr

holocene climatic fluctuations in the gujarat alluvial plains based on a multiproxy study of the pariyaj lake archive western india abstract a sediment core from pariyaj lake from the vatrak river basin located at the desert margin in the gujarat alluvial plains of western india was investigated in a multidisciplinary aspect the goal was to reconstruct the palaeoclimate palaeoenvironment and tectonic history and to understand the role these factors played in the geomorphological evolution of the area during the holocene palaeoclimatic interpretations also shed light on the factors responsible for the rise and fall of the harappan civilisation the results obtained based on multiproxy studies show five climatic phases during the last 11 000 yr bp phase 1 11 000 cal yr bp represents a very humid climate and high precipitation discharge leading to high lake stand as attested by the high pollen concentration of semi evergreen tree taxa phytoliths belonging to cool and moist grasses and large proportion of algae marking the onset of holocene in phase 2 8000 to 9000 cal yr bp a significantly reduced yield of pollen phytoliths and aquatic algae indicates shrinkage of the lake phase 3 7630 cal yr bp shows moderate yield of pollen and phytolith pointing towards fluctuating precipitation conditions phase 4 5864 to 4680 cal yr bp shows very low pollen and phytolith counts indicating a very dry spell finally phase 5 4680 to 3500 cal yr bp shows a good density and diversity of flora the wet climate and high lake stand 11 000 cal yr bp 7630 cal yr bp and after 4680 cal yr bp are synchronous with the lacustrine marine and aeolian records of western india the contribution of winter precipitation at 7630 cal yr bp and after 4680 cal yr bp can be correlated with similar records from rajasthan lake decrease in the precipitation activity the low lake stand and the onset of dry climatic condition between 8000 and 9000 cal yr bp corresponds to a near global anomaly of this period another dry event between 5864 and 4680 cal yr bp documented in pariyaj lake record is synchronous with various proxy records of the mid late holocene afro asiatic monsoonal belt

geochemistry of the palitana flood basalt sequence and the eastern saurashtra dykes deccan traps clues to petrogenesis dyke flow relationships and regional lava stratigraphy recent studies of large mafic dyke swarms in the deccan traps flood basalt province india indicate that some of the correlative lava flows reached several hundred kilometers in length here we present field petrographic mineral chemical and whole rock geochemical including sr nd isotopic data on the palitana lava sequence and nearby dykes in the saurashtra region of the northwestern deccan traps these rocks are moderately evolved many with low ti nb characteristics we infer that most dykes are notably and systematically less contaminated by ancient continental crust than the palitana flows but four dykes are equally or significantly more contaminated with some of the most extreme sr nd isotopic compositions seen in the entire deccan traps initial end is as low as 18 0 a bhimashankar type and a poladpur type dyke are present several hundred kilometers from the type section of these magma types in the western ghats escarpment we find no geochemical correlations between the palitana sequence and three subsurface sequences in ne saurashtra containing abundant picritic rocks surface lavas previously studied from saurashtra or the western ghats sequence intriguingly the eastern saurashtra dykes cannot have been feeders to any of these lava sequences feeder dykes of these sequences may be located in southwestern or central saurashtra or in the dhule nandurbar dediapada areas across the gulf of cambay 200 300 km east of palitana our results indicate polycentric flood basalt eruptions not only on the scale of the deccan traps province but also within the saurashtra region itself

signatures of climate vs sea level change within incised valley fill successions quaternary examples from the texas gulf coast abstract the passive margin texas gulf of mexico coastal plain consists of coalescing late pleistocene to holocene alluvial deltaic plains constructed by a series of medium to large fluvial systems alluvial deltaic plains consist of the pleistocene beaumont formation and post beaumont coastal plain incised valleys a variety of mapping outcrop core and geochronological data from the extrabasinal colorado river and the basin fringe trinity river show that beaumont and post beaumont strata consist of a series of coastal plain incised valley fills that represent 100 kyr climatic and glacio eustatic cycles valley fills contain a complex alluvial architecture falling stage to lowstand systems tracts consist of multiple laterally amalgamated sandy channelbelts that reflect deposition within a valley that was incised below highstand alluvial plains and extended across a subaerially exposed shelf the lower boundary to falling stage and lowstand units comprises a composite valley fill unconformity that is time transgressive in both cross and down valley directions coastal plain incised valleys began to fill with transgression and highstand and landward translation of the shoreline paleosols that define the top of falling stage and lowstand channelbelts were progressively onlapped and buried by heterolithic sandy channelbelt sandy and silty crevasse channel and splay and muddy floodbasin strata transgressive to highstand facies scale architecture reflects changes through time in dominant styles of avulsion and follows a predictable succession through different stages of valley filling complete valley filling promoted avulsion and the large scale relocation of valley axes before the next sea level fall such that successive 100 kyr valley fills show a distributary pattern basic elements within coastal plain valleys can be correlated with the record offshore where cross shelf valleys have been described from seismic data falling stage to lowstand channelbelts within coastal plain valleys were feeder systems for shelf phase and shelf margin deltas respectively and demonstrate that falling stage fluvial deposits are important valley fill components signatures of both upstream climate change vs downstream sea level controls are therefore interpreted to be present within incised valley fills signatures of climate change consist of the downstream continuity of major stratigraphic units and component facies which extends from the mixed bedrock alluvial valley of the eroding continental interior to the distal reaches wherever that may be at the time this continuity suggests the development of stratigraphic units and facies is strongly coupled to upstream controls on sediment supply and climate conditions within hinterland source regions signatures of sea level change are critical as well sea level fall below the elevation of highstand depositional shoreline breaks results in channel incision and extension across the newly emergent shelf which in turn results in partitioning of the 100 kyr coastal plain valleys moreover deposits and key surfaces can be traced from continental interiors to the coastal plain but there are downstream changes in geometric relations that correspond to the transition between the mixed bedrock alluvial valley and the coastal plain incised valley channel incision and extension during sea level fall and lowstand with channel shortening and delta backstepping during transgression controls the architecture of coastal plain and cross shelf incised valley fills

reconstruction of the late quaternary environment of the lower luni plains thar desert india geomorphological processes in the thar desert of india are largely climate driven in the lower reaches of the river luni the only major drainage system in the thar desert a fluvio aeolian sequence was located at a site called khudala sediments of this sequence represented a variety of depositional environments namely aeolian fluvially reworked aeolian overbank deposits gravels and occasional evidence of pedogenesis this provided a good opportunity to study aeolian fluvial interaction in the region and for deducing climatic records from the luminescence dating standpoint these sequences offered a good opportunity for a comparative study of thermoluminescence tl blue green light stimulated luminescence bgsl and infrared light stimulated luminescence irsl on different mineral separates of identical provenance but deposited under different environments broadly within experimental errors the tl ages agreed with bgsl and irsl ages on aeolian sands but differed substantially in the case of fluvially reworked and proximally deposited sands and silts the sequence provided a record spanning more than 100 ka with an aeolian phase at 100 ka a channel activation phase between 70 and 30 ka and a phase of climate instability between 13 and 8 ka this appears consistent with the records of monsoon performance during this period which includes the younger dryas it is also inferred that during the last glacial epoch geomorphological processes in the thar both aeolian and fluvial were dormant largely on account of their relationship with the southwest monsoon copyright 2001 john wiley sons ltd

review of recent developments in mineral magnetism of the chinese loess mineral magnetism of the chinese loess has been investigated for more than 20 years although there is a consensus that the neoformation of fine grained maghemite particles in the superparamagnetic sp and single domain sd grain size regions accounts for the magnetic enhancement in the chinese paleosols quantitative retrieval of paleoclimatic signals in terms of rock magnetic proxies is still a subject of debate the ambiguities arise from the inherent complexities of magnetic proxies as well as the multiple factors that control the pedogenic processes therefore a better description of the magnetic assemblage including its mineralogy grain size distribution and stoichiometry of two distinct origins pedogenic and eolian can help us better understand mechanisms behind variations in magnetic proxies at different timescales in order to link them to the paleoclimatic processes this review focuses on recent developments in loess magnetism and carefully evaluates merits and limitations of rock magnetic proxies furthermore several currently unsolved problems are addressed

control of dust emissions by geomorphic conditions wind environments and land use in northern china an examination based on dust storm frequency from 1960 to 2003 the degree to which dust emissions are controlled by geomorphic conditions wind environments and land use was investigated using the dust storm frequency dsf and data from more than 300 meteorological stations throughout northern china our analysis showed that most dust emissions originated in gobi deserts that developed in piedmont alluvial fans of the kunlun qilian and helan mountains dust emissions are low from other gobi desert regions such as the northern gurbantunggut and eastern taklimakan where high vegetation coverage restrained dust emissions or where dust size particles are not abundant after a long period of strong wind erosion sandy deserts with relatively high vegetation coverage or an extensive cover by mobile sands are not a major dust source although the highest dust emissions did not appear in regions with the highest wind energy dsf trends in each region from 1960 to 2003 were closely related to local wind activity dsf was low in regions with high levels of human activity where the mean dsf from 1960 to 2003 did not exceed 4 days year even from the 1960s to the early 1970s the period with the greatest dsf frequency did not exceed 8 days year which indicates that extensive land use did not contribute to dsf the low dsf in these areas might result from the fact that although land use could produce abundant fine soil fractions vegetation coverage and soil moisture remained higher than in the gobi deserts of arid china thereby decreasing dust storm occurrence

holocene paleoclimates of india we present a comprehensive summary of the available palaeoclimate records from india and compare the results from different proxies the results indicate i fluctuating lake levels during the early holocene the period of relatively higher lake levels from increased precipitation efficiency was reached only 7 2 6 0 cal kyr bp possibly due to increased contribution from winter rainfall ii the onset of aridity in nw india could have begun as early as 5 3 cal kyr bp subsequently there were multiple wet events but of shorter duration and smaller magnitude than during the mid holocene iii there is evidence of several short term climate events in the proxy record however in the absence of a rigorous chronological framework a detailed regional correlation is not possible at this stage finally a comparison between marine and terrestrial records indicates that episodes of strongest and weakest monsoon winds were not always associated with wettest and driest episodes respectively in the nw indian lakes

geochemistry of surface sediments from the arabian sea we report new geochemical data si al na k rb sr mn cu ni fe zn co and pb for 126 surficial sediments and base metal partition data for limited samples from the deep arabian sea and discuss the controls affecting these elemental concentrations the geochemical nature of and differences between sediments from three physiographically tectonically distinct regions have been identified the spatial resolution allows us to discern the various processes operative in the deep arabian sea during the holocene epoch r mode factor analysis on the geochemical data suggests that four dominant factors are responsible for the observed geochemical variations in the samples namely carlsberg ridge hydrothermal activity terrigenous contribution hydrogenous authigenic precipitates and biological contribution

holocene sea level change on the southeast coast of australia a review a revised holocene sea level curve for the southeast coast of new south wales australia is presented based on a review of previously published geochronological results for fossil molluscs organi

chronology of late pleistocene environmental changes in the lower mahi basin western india sediments exposed in the lower mahi basin at the southern fringe of the thar desert rajasthan india provide evidence of three distinct depositional environments namely marine aeolian and fluvial these have been used to reconstruct late pleistocene environmental and tectonic history of the region infrared stimulated luminescence irsl chronology of the fluvial and aeolian litho units provides evidence of two major fluvial aggradation phases in the region corresponding to oxygen isotopic stages 5 and 3 the basal marine clay is inferred to represent the last interglacial stage and its present elevation at 20 m a s l is attributed to post depositional tectonism comparison of fluvial records from other regions indicates interhemispherically documented wetter phases during oxygen isotope stages 5 and 3 copyright 2000 john wiley sons ltd

luminescence dating of loess palaeosol sequences and coversands methodological aspects and palaeoclimatic implications abstract of the terrestrial archives loess palaeosol sequences provide a most complete record of climatic change this may be compared with the marine oxygen isotope stratigraphy and may help in the reconstruction of past atmospheric circulation patterns numerical chronometry of loess palaeosol sequences has generally been based on correlation of variations in climatic proxies such as magnetic susceptibility and particle sizes with marine isotopic data such chronometric assignments involve implicit assumptions about the constancy of sedimentation rates and particle fluxes through time this review presents a brief survey of the present status methodology outstanding problems and interpretational aspects of luminescence techniques and discusses the import of luminescence ages on global land sea correlations statistical analysis of the ages suggests episodicity of loess accumulation with extended periods of quiescence recent luminescence dating studies on closely spaced samples also lead to a similar inference luminescence ages imply high variability in loess sedimentation rates this conflicts with the assumption made in some current attempts to correlate loess records with marine records of almost constant particle fluxes a review of source proximal coversand deposits of northwest europe is also presented evidence of the onset of coversand deposition at 15 ka with a peak in accretion during the younger dryas and subsequent minor reactivation episodes is discussed

fluvial response to late quaternary climate changes western india we review here the fluvial response to late quaternary climatic changes in the semi arid regions of western india i e the thar desert and its margins and maharashtra the rivers in the thar desert show a spectrum of environments from gravel bedload braided to ephemeral sand bed streams to sheet flows and sheet floods while those in the thar margin and maharashtra show dominantly two modes i e braided and meandering rivers the streams became defunct and aeolian sands were deposited during periods of relatively greater aridity in the thar desert and its margins incisions occurred during the wet phases in ois 1 it is inferred that changes in the monsoon precipitation led to relative changes in the discharge and sediment supply which were routed through those in the vegetation cover and played a key role in determining the fluvial style an inter comparison of the late quaternary alluvial deposits in the semi arid regions of western india suggests a continuum of fluvial environments interrelated through a precipitation gradient further a global comparison indicates that the response of semi arid western indian rivers was synchronous with the rivers in other climatic settings

source regions and formation of the loess sediments on the high mountain regions of northwestern china loess on the high mountains of northwestern china is largely controlled by the topographic features distributed mainly on the northern slopes of the tianshan and kunlun mountains as well as in the ili valley between the northern and central tianshan ranges loess distributed in different regions has different ages with the oldest early pleistocene loess occurring in the ili valley geochemical mineralogical and granulometric analyses demonstrate that the loess in the three different regions has different provenance the loess on the northern tianshan and kunlun mountains is mainly derived from the junggar and taklimakan deserts respectively whereas the loess in the ili valley is derived mainly from the sary ishikotrau desert located in the republic of kazakhstan however these deserts serve mostly as holding areas for the silts rather than original source regions the production of the silt sized particles is mainly associated with glacial abrasion and tectonic induced rock denudation thus the loess in the studied regions can be described as mountainous loess rather than simply glacial loess or desert loess it is unlikely that the mechanisms of loess formation are the same in different regions given their dependence on specific geomorphological conditions and associated processes

fluvial systems of the drylands of western india a synthesis of late quaternary environmental and tectonic changes abstract the fluvial systems and landscape of the drylands of western india have preserved evidence of late quaternary environmental and tectonic changes data on the fluvial systems of mainland gujarat saurashtra and kachchh have been synthesised to evaluate the roles of geological factors in the evolution of these drylands mainland gujarat is largely underlain by the flat alluvial plain and has a structurally controlled fluvial system that originates in the eastern uplands the fluvial system of mainland gujarat shows deeply incised valleys entrenched meanders extensively developed ravines and uplifted terraces which have preserved a late quaternary succession of continental fluvial and aeolian and marine sediments dating back to 125 ka marine sediments correspond to the transgressive phases of the last interglacial 125 ka and post glacial maximum 6 ka the overlying alluvial sediments suggest deposition by ephemeral rivers in varied fluvial depositional environments under a semi arid to sub humid climatic regime with periods of intense pedogenesis the sedimentation can be correlated with marine isotopic stages mis 5 and 3 the fluvial sediments are buried under a thick blanket of aeolian sediments which are indicative of enhanced dune building activity in the thar desert and are correlatable to the global arid phase of the last glacial maximum the post aeolian tectonic uplift triggered severe erosion of late pleistocene sediments and 40 50 m deep incised fluvial valleys were formed this erosional phase suggests a resumption of fluvial activity which coincided with the rapidly rising sea level on the west coast during the early holocene the holocene marine and fluvial aggradation was initiated within the incised fluvial valleys around 6 ka and continued uninterrupted until 2 ka these sediments now occur as raised valley fill terraces suggesting a late holocene uplift further corroborated by low to moderate seismic activity during historical times the landscape of saurashtra is marked by flat topped basaltic trappean ridges and a highly varied coastline where a narrow belt of low ridges and cliffs of miliolite limestones and other shore deposits are found the fluvial system of saurashtra shows a radial drainage pattern the channels have steep banks in the hilly regions and show significant deflections before meeting the sea evidence of last interglacial high sea levels 125 ka are found on the coastal cliffs of southern saurashtra in the form of oyster reefs and notches of various types which now occur at higher levels a net sea level rise of 7 m consistent with the global sea level estimates at 125 ka has been obtained by recent studies after decoupling the tectonic component dating of late pleistocene and holocene sea levels on this coast suggest continued uplift of saurashtra since 125 ka even though the sea level continued to fluctuate the holocene high sea submerged a considerable stretch of land including the okha rann on the northern saurashtra coast and isolated patches in and around the river mouths on the southern coast the short straight and parallel courses of rivers in the direction of tectonic slope incised and confined channel belts also suggest a strong component of tectonic uplift the continental sediments exposed in these river valleys have however remained uninvestigated leading to lack of palaeoclimatic data a remarkable control of structure on landscape evolution is depicted by the kachchh peninsula the fluvial system exhibits the characteristics of drainage flowing along tectonically provided slopes the overall drainage pattern of kachchh shows excellent correlation with n s trending transverse fault patterns the transverse fault system has brought out changes in the landscape of kachchh though the kachchh rift basin evolved along e w latitudinal faults the quaternary deposits occur in the form of miliolite limestones colluvial and alluvial fans fluvial sands and silts and rann sediments significant sedimentologic details on these sediments are lacking however the marine incursions seem to correlate with the adjacent saurashtra and mainland gujarat

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

mineralogic and climatic interpretations of the luochuan loess section china based on diffuse reflectance spectrophotometry we examined the top 135 m that is the entire pleistocene of the classic luochuan section on the chinese loess plateau with a diffuse reflectance spectrophotometer from the near ultraviolet through the visible and into the near infrared from the reflectance data we calculated sample brightness which with some caveats is a reasonable proxy for magnetic susceptibility mineralogic changes were identified by factor analyzing the first derivative of the percent reflectance data and examining samples with high factor scores two factors which explain about 96 of the cumulative variance are distinguished by the relative proportion of hematite and goethite the minerals that are responsible for the color changes in the loess sequence both hematite and goethite are present in both loess and paleosol but goethite dominates in loess whereas hematite dominates in paleosol the goethite factor exhibits an inverse correlation with magnetic susceptibility the hematite factor exhibits a weak positive correlation with susceptibility paleoclimatic interpretations are drawn from comparison of susceptibility to the concentration of spectrally identified hematite based on this comparison paleosols in the early pleistocene wucheng formation are characterized by conditions that are drier than today a dry summer monsoon whereas later pleistocene paleosols are characterized by a wet summer monsoon

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

lower eocene alluvial paleosols pedogenic development stratigraphic relationships and paleosol landscape associations abstract two kinds of cumulative floodplain paleosols red and grey paleosols formed on overbank deposits of the willwood formation in the sand coulee area of the bighorn basin wyoming although both kinds experienced down profile iron movement due to seasonal saturation of a clay rich a horizon the red paleosols were better drained and their b horizons were rubified various redoximorphic features indicate that the grey paleosols were poorly drained the red paleosols show progressive increases in the degree of profile development away from an associated channel sandstone a paleosol landscape relationship termed pedofacies by bown and kraus 1987 although the grey paleosols show relatively systematic changes in hydromorphy consistent pedofacies changes were not recognized furthermore no lateral relationship between the red and grey paleosols was observed these features suggest that because of the retarding effects of poor drainage on soil weathering poorly drained soils are not amenable to pedofacies modelling and that the landscape associations of well drained and poorly drained soils may be difficult to document without unusually extensive exposures results of this study also show that the pedofacies model is limited by sediment accumulation rates and the kind of fine grained facies on which paleosols developed although readily observable in sand coulee pedofacies are difficult to recognize in the elk creek area where accumulation rates were approximately half as rapid as in sand coulee the attainment of steady state conditions is believed to have obscured pedofacies in the elk creek area finally pedofacies are only developed on true overbank deposits which in the willwood formation and probably many other ancient alluvial sequences make up only a fraction of the fine grained deposits only immature soils formed on the remainder of the fine grained facies because they were deposited very rapidly as a result of channel avulsion

late quaternary climate and seismicity in the katrol hill range kachchh western india abstract a channel fill sequence in the upper catchment of the khari river in the south of the katrol hill fault khf has been investigated to understand the role of climate and tectonics in the evolution of fluvial landforms detailed sedimentology and limited optical chronology suggest that the channel incision occurred during weak summer monsoon prior to 19 9 ka and is attributed to the activity along the khf and its subsidiary faults the post glacial to early holocene was a phase of landscape stability subdued tectonics which persisted until around 7 1 ka particularly between 9 4 ka and 7 1 ka an enhanced monsoon activity is inferred a renewed phase of uplift is suggested after 7 1 ka that probably continues till present

climatic imprints in quaternary valley fill deposits of the middle teesta valley sikkim himalaya abstract quaternary alluvial sediments occur as distinct terrace and fan deposits in the middle teesta valley in the belt between the main central thrust and the main boundary thrust in the sikkim himalaya these sequences are characterized by lithofacies deposited by braided river channels debris flows and hyperconcentrated flows the channel flow deposits constitute relatively well sorted well imbricated and clast supported gravels with coarse to medium sand matrix mostly poorly sorted weakly imbricated to disorganized matrix supported pebble to boulder gravels with silty sand represent debris flow deposits hyperconcentrated flow deposits consist of clast supported poorly developed sorted polymodal gravel facies with poorly developed imbricated fabric and generally occupy the lower parts of the terrace and fan sequences the alternation from hyperconcentrated flow to channel flow deposits is predominant in the sequence and is possibly the response to different climate modes the high discharge and supply of sediments as well as the dispersal and deposition of these materials in the trunk stream is attributed to millennial multimillennial climatic perturbations during the quaternary climate change has a dominant role in the valley aggradation and incision cycle

scour fill and burial depth of coarse material in gravel bed streams scour fill and burial depths of coarse particles were examined in two ephemeral streams using magnetically tagged particles and scour chains the burial depth varied within a bedform and from one bedform to another the maximum burial depth was recorded in bars but differences in the mean burial depth in the pools bar and thalweg were insignificant mean burial depth was three to six times the median size of material on bar surfaces and ten to thirty times that in the pools and thalweg more than eighty per cent of the tagged particles which were located on or close to the bed surface moved in each event although previously buried particles were moved by flood events others which were initially exposed remained stationary on the surface or were buried in situ the data indicate that the mean burial depth was intermediate between the mean depths of scour and fill deeply buried particles probably reflect the development of scour holes during flood flows aggradation and degradation changed the recorded burial depth relative to the local bed surface of stationary tracer particles these observations indicate that scour and fill processes during a flow event are sporadic and change with water discharge

aggradation history and luminescence chronology of late quaternary semi arid sequences of the sabarmati basin gujarat western india the gujarat alluvial plain in the semi arid desert margin of the thar desert contains a record of continental quaternary sequences these sequences were built by drainages originating in the aravalli hills and flowing westward into the indian ocean stratigraphic studies of a part of the late quaternary succession in the sabarmati basin have resulted in a fourfold lithostratigraphic scheme the waghpur formation conglomeratic member sand member the mahesana formation lower heterolithic member upper sand member the akhaj formation and the sabarmati formation facies analysis distribution of conglomerates and cross bed azimuths of the clastic facies of the waghpur formation were used to infer ne sw trending semi arid alluvial fans the deposition of the overlying heterolithic member took place in ephemeral streams influenced by episodic flows and aeolian reworking the upper member of the mahesana formation represents aeolian and older levee deposits feasibility studies of thermoluminescence tl and infra red stimulated luminescence irsl dating on the sabarmati succession yielded stratigraphically consistent ages ranging from 5 ka to 300 ka for two samples tl ages on quartz and irsl ages on feldspar separates were consistent these results together with the stratigraphic and petrographic data reveal the following events in the accumulation history of the sabarmati sequence 1 1 significant aggradation at 300 ka gravel sand and at 58 ka sand and 2 2 pedogenesis bracketed to 58 39 ka the sabarmati river in its middle stretches follows a regional slope deviatory course interpreted previously to be a neotectonic adjustment within the cambay graben our chronological data suggest that this adjustment occurred possibly within the past 39 ka

late quaternary geomorphic evolution of the lower narmada valley western india implications for neotectonic activity along the narmada son fault geomorphic data combined with stratigraphic studies provide significant information to constrain timing and amount of fault movement the lower narmada valley lies astride the narmada son fault nsf an important ene wsw trending tectonic element responsible for the current intraplate seismicity being experienced in the central part of the indian plate varying nature and degree of tectonic movements along the nsf during late pleistocene and holocene have produced four geomorphic surfaces in the lower narmada valley the alluvial plain s1 ravine surface s2 a gravelly fan surface s3 and the valley fill terrace surface s4 two major phases of tectonic movements in a compressive stress regime are recorded along the nsf slow synsedimentary subsidence of the basin during late pleistocene due to differential movement followed by inversion of the basin during the holocene marked by differential uplift along the nsf the study suggests that the inversion of the basin is in response to the significant increase in the intensity of compressive stresses in the indian plate mainly during the early holocene the present incisive drainage and recent seismic activity indicate that the compressive stresses continue to accumulate along the nsf due to continued northward movement of the indian plate

nebkha formation implications for reconstructing environmental changes over the past several centuries in the ala shan plateau china abstract sediments of chinese tamarisk tamarix chinensis lour nebkhas in china s arid ala shan plateau document both the formation processes of these vegetated dunes and the environmental changes and geomorphological evolution in this region dating of the nebkhas showed that after surface water disappeared the wadis and playas evolved into gobi deserts desert pavements within two centuries the 13c trends in the litter deposited within the nebkhas revealed three stages of fluctuating moisture conditions during the past five centuries before the 1580s between the 1580s and the late 1990s and from the early 2000s to the present however changes in the coarse fraction of the nebkha sediments show that this region experienced at least five phases of aeolian sediment transport during the same period the early stages of nebkha formation coincided with the initial stage when the wadis and playas evolved into gobi deserts and nebkha sizes increased rapidly due to the abundant sediment supply provided by the playas however after the playa surfaces stabilized the nebkha sediments documented environmental changes in adjacent regions our results also show that the formation of the tamarix nebkhas in this region was not controlled by the groundwater table because in most periods the water table depth remained above the depth that limits tamarix survival in the ala shan plateau nebkha formation was mainly controlled by aeolian processes and revealed the integrated effects of environmental changes thereby providing possibilities for climate and environment reconstructions with a relatively high resolution in extremely arid areas

geochronology of palaeolithic cultures in the hiran valley saurashtra india abstract the u and th concentrations of 16 miliolite samples from the hiran valley in saurashtra ranged from 0 3 to 2 14ppm and 0 12 to 0 82ppm respectively the 234 u 238 u activity ratio ranged from 1 09 to 1 16 with a mean of 1 12 0 02 it agrees well with the seawater value of 1 14 0 02 within the quoted errors nine of the samples were datable by the 230 th 234 u method and the ages ranged from 56 8 to 190 kyr the problem of chronology of palaeolithic artifacts is interlinked with the miliolite and other coastal formations the present investigations permit the development of a chronological framework for the palaeolithic cultures in the hiran valley in particular and generally in saurashtra peninsula on the basis of radiometric dates and relative chronology the lower palaeolithic cultures fall in a time bracket of 190 69 kyr bp the middle palaeolithic industry is much older than 56 8 kyr bp the dates obtained for the lower palaeolithic cultures are perhaps the oldest reported to date

major and trace element geochemistry of bay of bengal sediments implications to provenances and their controlling factors major and trace elements of sediments from a 13 m long piston core sk187 pc33 from the western bay of bengal have been investigated in this study to infer about the changes in provenances and related controlling factors during the last glacial interglacial period factor analysis of these geochemical dataset ascertains dominant role of riverine supply of sediments in regulating the geochemistry of sk187 pc33 sediments the al normalized major k and ti and trace elemental cu and cr ratios of these marine sediments fall within the ranges observed for their major provenances viz ganga brahmaputra and the godavari krishna gk rivers and depth profiles of these ratios showed significant variations with synchronous excursion at around the last glacial maxima lgm implying a change in their provenances with relatively reduced himalayan contribution during this climatic event relatively higher cia and ti ca ratios with lower k al ratios of these sediments during the holocene hint intense chemical weathering in the river basins in response to strengthened monsoon during this period inverse model calculation of al normalized elemental ratios of the sediments estimated an average sediment contribution of 66 13 and 34 13 from the himalayan and the peninsular indian rivers to the core site respectively consistent with the depth profiles of elemental ratios the estimated sediment contributions from the himalayan rivers are observed to decrease by 20 from the himalayan rivers particularly that of the ganga to the studied location during the lgm lowering of sediment supply from the himalaya ganga during the lgm is due to weakening of south west monsoon and reduction in available exposure area for weathering due to extent of glacier cover outcomes of this study underscore the strong linkage between erosion and climate

sedimentology geochemistry and osl dating of the alluvial succession in the northern gujarat alluvial plain western india a record to evaluate the sensitivity of a semiarid fluvial system to the climatic and tectonic forcing since the late marine isotopic stage 3 abstract the alluvial successions in the northern gujarat alluvial plain western india have been investigated for reconstructing the climatic fluctuations during the last 40 ka alluvial architecture and geochemical proxies indicate prevalence of a strengthened indian summer monsoon ism with fluctuations between the late marine isotopic stage 3 mis 3 37 ka to the early mis 2 27 ka a gradual onset of aridity declining ism after 27 ka with peak aridity at 22 ka is observed a gradual strengthening of ism at around 18 and 12 ka followed by a short reversal in ism intensity between 12 and 11 ka is attributed to the younger dryas yd cooling event the aeolian sand sheet dated to 6 and 3 5 ka represents the onset of regional aridity following this a short lived humid phase was observed after 2 ka which includes the medieval warm period mwp the study suggests that the variability in the ism to the latitudinal migration of the inter tropical convergence zone was caused by insolation driven cooling and warming events in the north atlantic the incision of the valley fill alluvium occurred in two distinct phases the older incision phase occurred after 11 ka and before 6 ka whereas the younger incision phase that led to the development of present day topography is bracketed between 3 5 ka and before 1 ka the older incision phase is ascribed to the early to mid holocene enhanced ism climatically driven whereas the younger incision seems to be modulated by the activation of basement faults tectonically driven

fluvial response to tectonic activity in an intra continental dryland setting the neales river lake eyre central australia abstract geomorphological studies in the centre of the australian continent have emphasised the antiquity of the australian landscape typically considered tectonically stable evidence from the neales river on the western shore of lake eyre indicates that mild epeirogenic forces have deformed sediments of miocene age deformed bedding planes small scale folds and fracture systems reflect consistent miocene and younger tectonic activity in central and southern australia this compression was mild resulting in broad gently plunging folds these folds are evident in the miocene strata but not in the overlying quaternary strata elsewhere in the study area the landscape has been rearranged to preserve features in the geomorphic record that indicate a second phase of tectonic activity in the early to mid pleistocene these include stream diversions preserved on alluvial fans and floodplains formed downstream of faults

mid holocene climate and land sea interaction along the southern coast of saurashtra western india abstract the relict mudflat from the southern saurashtra coast of gujarat was investigated using geochemical and palynological analyses supported by radiocarbon dating to understand whether climate fluctuations and sea level operated in tandem during mid holocene the study revealed that the saurashtra coast experienced relatively wet climatic conditions with simultaneous occurrence of marginally high sea level between 4710 and 2825 cal yr bp subsequently a gradual onset of aridity and lowering of the sea level was observed between 2825 and 1835 cal yr bp and further a slight decrease in aridity is observed after 1835 cal yr bp the present day coastal configuration was probably achieved after around 1500 cal yr bp considering the tectonic instability of saurashtra coast land level changes the effective mid holocene sea level was estimated to be 1 m higher than the present the study demonstrates that sea level changes climate variability and land level changes were coupled during the mid holocene

mid holocene sedimentation and landscape evolution in the western great rann of kachchh india abstract this study is an attempt to reconstruct the history of sedimentation and landform evolution in the western great rann of kachchh field stratigraphy sedimentology geochemistry optical and radiocarbon dating suggest dominance of tidal flat sedimentation with subordinate contribution coming from the southern draining streams during 5 5 to 2 ka variability in the geochemical proxies are interpreted as a surrogate for tidal energy viz zr and cr which along with the major elemental ratios tio 2 al 2 o 3 and k 2 o al 2 o 3 indicate enhanced tidal energy condition during 5 5 to 5 ka and around 3 ka a close correspondence of the major and trace elements with those of the indus river sediment and the dominance of illite suggest the indus river was a major contributor for western rann sedimentation during the mid holocene these sediments were routed through the kori creek during marginally high sea level until around 2 2 ka and the present landscape was largely sculptured after the 1819 allah bund earthquake

characteristics of deformation and past seismicity associated with the 1819 kutch earthquake northwestern india the 1819 earthquake in kutch northwestern india is one of the most significant events to have occurred in a plate interior setting despite being the second largest among the stable continental region scr earthquakes this event has not been analyzed within the context of present day understanding of earthquake seismology coseismic changes related to this earthquake include massive ground deformation in a wide low lying tidal flat area although detailed historic accounts of this earthquake exist many questions regarding the mode of deformation and the seismic history of the region remain unresolved we explored the region nearly 180 years after the earthquake and the information gathered adds to our understanding of this event and provides a fresh perspective on this unique intraplate seismogenic zone a 90 km long tract of elevated land with a peak height of 4 3 m is the most visible surface expression of this earthquake we surveyed and analyzed the morphological features of this scarp and also carried out exploratory trenching in this region the scarp morphology is suggestive of a growing fold related to a buried north dipping thrust rather than a discrete fault that could have resulted from a surface rupture the extensive liquefaction field associated with the earthquake offered an ideal setting to explore the paleoearthquake history age data of liquefaction features suggest that a previous event of comparable size must have occurred 800 1000 years ago seismic activity appears to be related to the reactivation of an ancient rift in a stress regime that is dominated by nearly north south compression

late pleistocene holocene uplift driven terrace formation and climate tectonic interplay from a seismically active intraplate setting an example from kachchh western india abstract fluvial terrace formation is often regulated by external forcings like climate tectonic and eustatic changes these terraces particularly in a dryland environment preserves the discrete signatures of these external forcings thus enabling us to reconstruct the fluvial response to the late quaternary palaeoenvironmental changes and factors governing them the present study focuses on reconstructing the aggradation incision phases in the lotia river which is located in the eastern segment of the northern hill range nhr of the kachchh peninsula the lotia river drains through mesozoic rocks before cutting across the kachchh mainland fault kmf and finally debouch in the banni plains reconstruction based on tectonic geomorphology sedimentology sediment geochemistry mineral magnetic and osl chronology suggests the fluvial response to monsoon variability archived during the last 15 ka the time frame was also marked by incision enhanced by uplift along the kmf which led to strath terrace formation the accommodation space thus created was filled by an aggradational event between 14 8 ka and 10 6 ka sedimentological and geochemical parameters have also suggested that the time period between 12 5 ka and 11 5 ka showed a decline in the monsoon strength which coincides with younger dryas it has been observed that the sediments spanning between 10 6 ka and 7 8 ka are absent from the archive which is most likely the manifestation of the early holocene optimum that led to severe erosional processes the period between 7 8 ka and 3 3 ka is marked as another aggradational phase with fluctuating climatic conditions at 3 3 ka the region has experienced an incision of 4 m which led to the formation of holocene terrace t 1 most likely due to tectonic uplift during the last 3 3 ka another pulsative uplift has occurred which led to the formation of unpaired holocene terrace t 2 along with tilting of the lotia basin based on the osl chronology of bedrock strath terrace we reported a minimum uplift rate of 1 04 mm a for the eastern kmf during the late pleistocene holocene period hinting seismically active nature of the kmf during this period the terrace formation in the eastern northern hill range is mostly regulated by tectonic uplifts along the kmf

continental record of the southwest monsoon during the last 130 ka evidence from the southern margin of the thar desert india abstract field stratigraphy sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka the sedimentary architecture and textural attributes of the sediments belonging to the period 130 120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions a shift from a meandering to a braided pattern during 120 100 ka indicates a phase of reduced precipitation presence of flood plain fines and bedded calcretes during 100 70 ka suggest a period of enhanced monsoon with seasonality following this a phase of weak monsoon activity was observed during 70 60 ka regional flood plain aggradation and pedogenesis during the period termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20 11 ka suggest that the present rivers occupied their course between 11 ka drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf the incision intensified with the re establishment of monsoon during the early holocene

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

mid late holocene monsoonal records from the partially active mudflat of diu island southern saurashtra gujarat western india abstract the mid late holocene period is seldom known for any drastic climatic perturbations but witnessed significant anthropogenic growth and thus has been a subject of scientific importance in this study sediment core raised from an active mudflat of diu island southern saurashtra coast gujarat with a climatic history for the last 4100 yr bp has been investigated based on geochemical proxies productivity weathering and detrital results indicate warm and humid conditions during holocene climate optimum hco between 4105 and 2640 cal yr bp as a result of monsoon intensification followed by an arid conditions between 2640 and 1930 cal yr bp later during 1930 355 cal yr bp the region regained warm and humid conditions the mudflat responded in accordance with the global climatic perturbations during last 2000 yr witnessing signatures of roman warm period and medieval warm period additionally cool and humid climatic conditions persisted during little ice age followed by modern warming period witnessed during last 300 yr

influences of eolian and pedogenic processes on the origin and evolution of desert pavements well developed desert pavements are present above eolian deposits that mantle flows of the cima volcanic field located in the mojave desert california soil stratigraphic data and geochemical data demonstrate that eolian and pedogenic processes play major roles in the evolution of these pavements eolian dust 1 accelerates mechanical fragmentation of flow rock providing the source material for pavements and 2 accumulates slowly below basaltic colluvium in flow depressions eventually promoting development of cumulate soils below the evolving stone pavement an increase in dust flux during the holocene has raised ancient pleistocene pavements as much as 20 cm above the former land surface the results of our studies demonstrate for the first time that most desert pavements do not form by deflation by overland flow or by upward migration of stones through a slowly formed clayey argillic horizon desert pavements are born and maintained at the surface

tracing dust input to the mid atlantic ridge between 14 45 n and 36 14 n geochemical and sr isotope study abstract a geochemical and sr isotope study was carried out on sediment cores collected from the logatchev hydrothermal vent site 14 45 n on the mid atlantic ridge with the aim of identifying aeolian inputs into the overlying water column the logatchev vent site lies beneath the ne trade winds which transport large amounts of detrital material across the north atlantic sequential dissolution of the sediments has been used to discriminate the detrital fraction from other types of sediment ree patterns for the acetic acid fraction at the logatchev site record contributions from biogenic carbonate seawater like ree pattern and oxy hydroxides which exhibit positive eu and negative ce anomalies typical of hydrothermal origin the logatchev site leach fractions have similar major element compositions to terrigenous al fe mn oxides whose ree patterns show strong positive ce and negative eu anomalies that are comparable to those of preformed fe mn oxides of continental origin based on major element and ree data and 87sr 86sr ratios 0 7197 0 7236 the residue fractions at the logatchev site contain a significant contribution from aeolian sources whose chemical composition is virtually identical to oligotrophic settling particles in the equatorial atlantic ocean in comparison residues from the rainbow hydrothermal site 36 14 n have geochemical composition controlled by hydrothermal anhydrite chavagnac v german c r milton j a palmer m r 2005 sources of ree in sediment cores from the rainbow vent site 36 14 n mar chem geol 216 329 352 they are characterised by 87sr 86sr ratios of 0 7087 0 7093 which are significantly less radiogenic than those of the saharan dust hence the data suggest 1 a significant contribution of aeolian material to the sediments at 14 45 n that is not present at 36 14 n 2 that this material is most likely of north african origin and 3 that this source of aeolian material has remained relatively constant over the last 13 kyr

reconstruction of the variability of the southwest monsoon during the past 3 ka from the continental margin of the southeastern arabian sea from temporal variation in 18o in globigerinoidesruber and g sacculifer and geochemical indices of weathering erosion chemical index of alteration al and ti we infer rapid southwest monsoon swm deterioration with dwindling fluvial and detrital fluxes at ca 450 650 1000 and 1800 2200 cal a bp during the late holocene we have evaluated the role of solar influx reconstructed and high latitude climate variability archived in grip and gisp 2 cores on swm precipitation broadly our 18o climate reconstruction is concordant with grip and gisp 2 and supports a teleconnection through atmospheric connection between the swm and the north atlantic climate albeit temporal extents of the little ice age and medieval warm period from high latitude are not entirely coeval moreover there is a humid climate and enhanced precipitation during the terminal stages of the little ice age the medieval warming ca ad 800 1300 is not synchronous either and is punctuated by an arid event centred at 1000 a bp although the delineation of the specific influence of solar influx on swm precipitation is elusive we surmise that swm precipitation is a complex phenomenon and local orography along southwestern india may have a role on the entrapment of moisture from the southwest trade winds when these hit land copyright 2009 john wiley sons ltd

fluvial geomorphology and neotectonic activity based on field and gpr data katrol hill range kachchh western india abstract the largely rocky and rugged landscape of the katrol hill range composed of mesozoic rocks and structurally controlled occurrences of quaternary sediments is delimited to the north by north facing range front scarps of the seismically active e w trending katrol hill fault khf the landscape and drainage characteristics of the katrol hill range are documented together with ground penetrating radar gpr investigations along the khf to delineate its nature for understanding neotectonic activity in the contemporary tectonic setting the overall geomorphology is controlled by the south oriented tilt block structure of the range indicated by its pronounced influence on the morphology and drainage network the drainage comprises north flowing and south flowing rivers with the drainage divide located close to the northern edge of the range which also marks the highest topographic elevations the narrow zone between the crest line and the drainage divide has been identified as the zone of gorges where gorges and deeply incised fluvial valleys have been formed within quaternary sediments by the various north flowing streams the quaternary sediments consist of bouldery colluvial deposits in front of the range front scarps valley fill miliolites and alluvial deposits of late pleistocene age within the back valleys and scarp derived colluvium forming the youngest deposit based on the geomorphic and stratigraphic evidence three major phases of quaternary tectonic uplift in the katrol hill range are inferred the oldest pre miliolite phase middle pleistocene was followed by a prominent phase of fluvial incision with formation of gorges during early holocene and then by the last one during late holocene continuing at present uplift of the range occurred in well marked phases during the quaternary in response to differential uplift along the khf under an overall compressive stress regime gpr investigations at selected sites show that the khf is a steep south dipping reverse fault near the surface which becomes vertical at depth this suggests neotectonic reactivation of the khf under a compressive stress regime responsible for active southward tilting of the katrol hill range

zr rb ratio in the chinese loess sequences and its implication for changes in the east asian winter monsoon strength abstract the long term dust accumulation sequences on the chinese loess plateau clp provide a valuable opportunity to study the evolution of east asian winter monsoon strength grain size of bulk samples of loess deposits though widely used is a modified measure of the strength of winter monsoon wind due to modification by post depositional weathering and pedogenesis this study proposes a new and reliable geochemical climate proxy that records the variability of the east asian winter monsoon on the clp six loess paleosol sections on the plateau were selected for measuring concentrations of the trace elements zr and rb as well as grain size variations of the zr rb ratio in all the sections encompassing the last 130 ka display a generally similar pattern to that of mean grain size of bulk samples mgsb though a positive correlation exists between the zr rb ratio and mgsb the correlation coefficient decreases in southern and eastern sections where intense pedogenesis occurred in the relatively warm and humid climates long term zr rb variation in the lingtai section exhibits amplitudes and frequencies similar to those in mgsb and the mean grain size of quartz particles mgsq accepted as a more reliable proxy than mgsb in the upper loess paleosol sequence over the past 2 6 ma however for the underlying red clay formation in the interval from about 7 2 6 ma b p the mgsb record is relatively stable whereas both the zr rb ratio and mgsq show distinct variability and display amplitudes similar to those observed in the overlying loess paleosol sequence these results demonstrate that the zr rb ratio reflects original eolian grain size and may serve as a reliable index of the strength of east asian winter monsoon winds

climatic and hydrologic oscillations in the owens lake basin and adjacent sierra nevada california oxygen isotope and total inorganic carbon values of cored sediments from the owens lake basin california indicate that owens lake overflowed most of the time between 52 500 and 12 500 carbon 14 14 c years before present b p owens lake desiccated during or after heinrich event h1 and was hydrologically closed during heinrich event h2 the magnetic susceptibility and organic carbon content of cored sediments indicate that about 19 sierra nevada glaciations occurred between 52 500 and 23 500 14 c years b p most of the glacial advances were accompanied by decreases in the amount of discharge reaching owens lake comparison of the timing of glaciation with the lithic record of north atlantic core v23 81 indicates that the number of mountain glacial cycles and the number of north atlantic lithic events were about equal between 39 000 and 23 500 14 c years b p

mineral magnetic record of the chinese loess and paleosols variations in the magnetic susceptiblity of the chinese loess and its interbedded paleosols correlate strikingly well with the deep sea oxygen isotope record low susceptibility values are found for the loess layers and high values are found for the soil horizons two interpretative models have been advanced to account for these magnetic variations both of these models discount any significant in situ formation of magnetite during soil forming periods instead they infer relative concentration of detrital or atmospheric magnetite at these times we critically examine the assumptions made in these models and on the basis of some new mineral magnetic data and fromalized magnetic flux calculations offer an alternative explanation of the loess magnetic record our model identifies pedogenic formation of magnetite as the major contributor to the high magnetic susceptibility of the paleosols the formation and preservation of this pedogenic magnetite is dependent on soil froming conditions and hence reflects the regional climate

fluvial landforms and their implication towards understanding the past climate and seismicity in the northern katrol hill range western india abstract the tectonically active kachchh peninsula in western india lies in the southwest monsoon trajectory and hence provides a rare opportunity to decipher the temporal changes in climate tectonics interaction in the evolution of the fluvial landforms reconstructions based on geomorphology sedimentology and geochemistry supported by optical chronology suggest that the fluvial aggradation in the region was initiated during the onset of the indian summer monsoon ism after the last glacial maximum lgm the sedimentary characteristics and major elemental concentrations suggest that the sediments are dominated by fluvially reworked miliolites with subordinate contribution from the mesozoic sandstones and shales and were deposited with the initiation of the ism after the lgm temporal changes in facies architecture and major element concentrations suggest a progressive strengthening of the monsoon between 17 and 12 ka this was succeeded by an overall strengthened ism phase with fluctuations after 12 ka and based on the morphology of the fluvial landforms two major events of enhanced uplift can be suggested the geomorphic expression of the older uplift event dated to 17 ka is represented by the beveled mesozoic bedrock surfaces which accommodated the post lgm valley fill aggradation the younger event of enhanced uplift which is assigned to

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

holocene environmental changes and cultural patterns in coastal western india a geoarchaeological perspective abstract geomorphological studies carried out around coastal sites at hazira kanmer padri and sanjan in gujarat and chaul and kelshi in maharashtra indicate human activity throughout the holocene the offshore site at hazira of early holocene age is the only submerged prehistoric site at a depth of 20 40 m below the present sea level in the entire 7000 km long coastline of india protohistoric harappan sites at kanmer and padri are of mid holocene age the sites of sanjan chaul and kelshi represent an early historic cultural phase belonging to the late holocene age the site of hazira was located on the banks of a buried channel adjusted to the low sea level phase of the early holocene cultural development of the harappan site at kanmer in the present semi arid rocky landscape of kachchh was closely related to the existence of 2 5 m deep water in the presently dried up part of rann of kachchh throughout the mid holocene on the other hand the economy of the harappan site of padri depended on salt manufacturing in a stable estuarine environment close to the present sea level of the gulf of cambay sanjan chaul and kelshi appear to have depended on a trading economy these sites are situated in estuarine environments involving lateral transgressive regressive phases more or less within the present intertidal zone of arabian sea in a humid environment

regional tectonic framework structure and evolution of the western marginal basins of india abstract the kutch saurashtra cambay and narmada basins are pericontinental rift basins in the western margin of the indian craton these basins were formed by rifting along precambrian tectonic trends interplay of three major precambrian tectonic trends of western india dharwar nnw sse aravalli delhi ne sw and satpura ene wsw controlled the tectonic style of the basins the geological history of the basins indicates that these basins were formed by sequential reactivation of primordial faults the kutch basin opened up first in the early jurassic rifting was initiated in late triassic along the delhi trend followed by the cambay basin in the early cretaceous along the dharwar trend and the narmada basin in late cretaceous time along the satpura trend the evolution of the basins took place in four stages these stages are synchronous with the important events in the evolution of the indian sub continent its breakup from gondwanaland in the late triassic early jurassic its northward drifting during the jurassic cretaceous and collision with the asian continent in the early tertiary the most important tectonic events occurred in late cretaceous time the present style of the continental margins of india evolved during early tertiary time the saurashtra arch the extension of the aravalli range across the western continental shelf subsided along the eastern margin fault of the cambay basin during the early cretaceous it formed an extensive depositional platform continuous with the kutch shelf for the accumulation of thick deltaic sediments a part of the saurashtra arch was uplifted as a horst during the main tectonic phase in the late cretaceous the present high thermal regime of the cambay bombay high region is suggestive of a renewed rifting phase

on postglacial sea level summary an exact method is presented for calculating the changes in sea level that occur when ice and water masses are rearranged on the surface of elastic and viscoelastic non rotating earth models the method is used to calculate the instantaneous elastic and delayed vi scoelastic sea level changes following the partial melting of late quaternary ice sheets we find that there can be large errors in the usual assumption that changes in sea level are uniform over the ocean basins if a quantity of ice equivalent to a uniform 100 m rise in sea level melts from the laurentide and fennoscandian ice sheets then in the south pacific the instantaneous rise in sea level can be as large as 120m in the north atlantic the instantaneous rise is always less than 100 m there is a zone in the north atlantic with almost no sea level change and near greenland and norway the sea level falls rather than rises by over 100 m one thousand years after the melting a forebulge migrating towards the ice loads causes water to flow from the south pacific into the north pacific suggesting that raised beaches should occur in the south pacific the gravitational attraction of an ice mass upon a nearby ocean tends to hold sea level high in the vicinity of the ice this extra load near the ice may have a significant influence on postglacial isostatic adjustment

assessing the climatically triggered aggradation incision processes in a dryland environment during the late quaternary period from shetrunji river basin saurashtra india abstract the present study is an attempt to infer the response of the dryland fluvial sequences to paleoenvironmental change since the last glacial maximum lgm from the semi arid saurashtra region a basaltic terrain of the late cretaceous age deccan trap of western india we employed a conventional sedimentological analysis supported by sediment geochemistry which was constrained by optical dating based on detailed field investigation we identified five terrace sequences from the valley fill deposit in the shetrunji river basin since 18 ka i e post lgm the sedimentary archives expose the deposition during three alternate phases of aggradation and incision marked on the basis of morphostratigraphy and timing of landform evolution the coastal region of western india experienced a widespread valley aggradation in response to the rising sea stand and under gradual strengthening of the monsoonal conditions around the 18 9 ka period the early holocene climatic optima 9 7 5 ka coupled with lower than present but rising sea stand triggered the intense erosion in the valleys of shetrunji river basin leading to erosion lack of sediment preservation this was followed by the middle holocene period 7 5 5 ka which experienced valley aggradation this was ended by the incision post 5 5 ka in the lower reaches of the shetrunji river the sea stand was similar to present day stand as evidenced by the change from fluvial to the estuarine environment in the top sequence of site sl at 5 5 ka the late holocene relative sea stand lowering 3 ka led to an incision in the estuarine terrace of about 2 m the causal mechanism for triggering of this incision is most likely the relative fall in sea stand to present day level from its middle holocene high stand the late holocene period 3 1 ka shows aggradation in upper reach in fluctuating hydrodynamic conditions with seasonality followed by a relatively good monsoonal condition at

geochemical and isotopic studies of aeolian sediments in china the sr and nd isotopic rare earth element ree and major element compositions together with mineral and grain size proportions are reported for aeolian loess deposits and desert sands from several chinese localities the study was carried out in order to examine regional variations in the isotopic and geochemical features of these aeolian sediments and to constrain the provenance of chinese loess samples include loesses from the tarim and junggar basins and desert sands from the taklimakan desert in north west china loess from the ordos area and desert sands from the tengger and mu us deserts in north central china as well as loess and desert sands from the naiman area north east china ree distributions show minimal variation among the chinese loess deposits whereas those for the desert sands show regional variations new isotopic data document a latitudinal variation in sr and nd isotopic features for the loesses and desert sands the naiman and junggar loesses have distinctly lower 87sr 86sr ratios and higher end 0 values than the loesses from the tarim basin the ordos area and the loess plateau among the desert sands the naiman samples have higher end 0 values than the taklimakan tengger and mu us samples isotopic data suggest that loesses of the loess plateau were supplied from the tarim basin loesses and taklimakan desert sand and that the naiman loesses were supplied from the junggar basin loesses the latitudinal variation in the loesses and desert sands may be partly explained by isotopic variations reported previously for moraines from the tianshan and west kunlun mountains which are possible sources for the loesses and desert sands these inferences on the provenance of the loesses and desert sands are consistent with the dust transport pattern over east asia

geochemical and magnetic characteristics of fine grained surface sediments in potential dust source areas implications for tracing the provenance of aeolian deposits and associated palaeoclimatic change in east asia abstract we investigated the geochemical and magnetic characteristics of fine grained surface sediments fractions

late pleistocene holocene climate and sea level changes inferred based on the tidal terrace sequence kachchh western india abstract an estuarine tidal terrace sequence at the mouth of the kharod river kachchh western india is investigated for pleistocene to holocene climate and sea level changes based on sedimentology major element geochemistry mineralogy supported by optical dating the study reports a lowered sea level during 13 8 ka followed by gradual rise in the sea level until around 6 ka this is ascribed to a combination of enhanced melt water discharge and strengthened indian summer monsoon ism the temporal changes in major elements detrital proxies suggest a fluctuating to an overall arid monsoon conditions during 5 7 to 3 1 ka with a rapidly rising sea level this is further supported by the dominance of fine textured sediment along with the occurrences of shell rich horizon in the absence of any evidence of land level changes the study suggests that at around 6 ka to 3 ka the sea was approximately 2 m higher then present the decline in the concentration of geochemical proxies and occurrence of aeolian sand after 3 ka is interpreted as the onset of aridity and present day like conditions the three levels of sea stands during early middle and late holocene are synchronous with various archeological harappan settlements in the region

mapping thin resistors and hydrocarbons with marine em methods insights from 1d modeling the use of marine controlled source electromagnetic em csem sounding to detect thin resistive layers at depths below the seafloor has been exploited recently to assess the resistivity of potential hydrocarbon reservoirs before drilling we examine the sensitivity of the csem method to such layers with forward and inverse modeling in one and three dimensions the 3d modeling demonstrates that if both source and receivers are over a tabular 3d target 1d modeling predicts the observed response to very high accuracy experimental design can thus be based on 1d analysis in which hundreds of range and frequency combinations can be computed to find the optimal survey parameters for a given target structure modeling in three dimensions shows that the vertical electric field response is largest over the edges of a 3d target the 3d modeling also suggests that a target body needs to have a diameter twice the burial depth to be reliably seen by csem sounding a simple air wave model energy propagating from source to receiver via the atmosphere allows the effects of the target layer and atmosphere to be separated and shows where sensitivity to the target is diminished or lost because of finite water depth as a function of range frequency and seafloor resistivity unlike dc resistivity sounding the marine csem method is not completely t equivalent and in principle can resolve resistivity and thickness separately smooth inversion provides an estimate of the method s resolving power and highlights the fact that although the radial csem fields contain most of the sensitivity to the thin resistive target inverted alone they produce only increasing resistivity with depth inclusion of the radial mode csem data forces the recovery of the thin resistor but magnetotelluric data can be used more effectively to achieve the same result

interpreting the response of a dryland river system to late quaternary climate change abstract a u series calcrete chronology has been constructed for three late quaternary terrace units termed the d1 d2 and d3 terraces in age descending order from the rio aguas river system of the sorbas basin southeast spain the d1 terrace formed between 30 300 4400 year bp and 12 140 360 year bp correlating well with the last glacial maximum when rates of sediment supply would have increased greatly because of higher rates of weathering reduced vegetation cover and weak soil development the d2 terrace formed between 12 800 1100 year bp and 9 600 530 year bp correlating well with the younger dryas event the d3 terrace could only be poorly constrained to the early holocene and no unequivocal cause could be assigned to this period of aggradation the sedimentology and geomorphology of the d2 terrace suggests however that the aggradation of this unit was a response to diapirism karstic processes occurring within the underlying messinian gypsum strata and the subsequent damming of the aguas system therefore despite its coincident occurrence with the younger dryas aggradation of the d2 terrace is unrelated to climate change the style of this response controlled predominantly by the characteristics of the underlying bedrock makes correlating the terrace record of the aguas with other systems in the mediterranean unreliable this study therefore highlights the problems of correlating fluvial sequences in regions of variable tectonics climatic history and bedrock geology and emphasises the need to properly understand the main controls on individual fluvial systems before any attempt is made to correlate their depositional histories

reconstruction of late quaternary monsoon oscillations based on clay mineral proxies using sediment cores from the western margin of india abstract in order to reconstruct the variations in the intensity of summer monsoon precipitation during the late quaternary two sediment cores from the southwestern continental margin of india were studied for their clay mineral composition and grain size parameters kaolinite illite and gibbsite were dominant in a core off cochin illite with increasing kaolinite content towards the core top was found to dominate in a core from the continental slope off goa major sources of clays at both the core sites were from the hinterland rocks and soils careful evaluations of several factors that could complicate the clay distribution in marine environment indicate that the clay mineral parameters can be used as proxies for the intensity of summer monsoon precipitation in the past the relatively low values of humidity proxies kaolinite content k c and k i ratios and higher illite crystallinity with significant variations indicate that the summer monsoons in general were weaker during the late glaciation with distinct events of intensification at 28 000 and 22 000 yr bp the last deglaciation was characterised by an increased terrigenous input with high values of humidity proxies during 15 700 14 800 cal yr bp indicating an early strengthening of summer monsoon activity in the region the most remarkable increase in kaolinite content k c and k i ratios associated with much reduced values of chlorite and illite and illite crystallinity however occur between 8800 and 6400 cal yr bp it appears that the holocene precipitation maxima occurred after 9000 cal yr bp and lagged behind the precessional forcing the late holocene witnessed reduced rainfall activity and resultant decrease in hydrolysis starting at 5600 cal yr bp