luminescence chronology of aeolian deposition during the late quaternary on the southern margin of thar desert india abstract aeolian deposits constitute the uppermost lithostratigraphic unit in the southern margin of the thar desert they occur as poorly organized dunes resting on the upper part of a major fluvial sequence considerable evidence exists to show that the southern margin witnessed fluvial aggradation before the onset of dune accretion transition from a dominantly fluvial phase to aeolian deposition was gradational blue green light stimulated luminescence chronometry of six fossil dunes indicates that the dune building activity started around 26 ka and continued episodically until around 5 ka evidence of a phase of landscape stability is seen corresponding to the interval 11 9 ka this is also reflected by the presence of stone age artifacts microliths and fluvially reworked aeolian sand and corresponds to the strengthening of the southwest monsoon in the region a progressive northward shift through time in the parameters controlling dune building activity is seen aeolian accretion in the southern part mahi basin ended around 10 ka whereas in the northern sabarmati it continued until around 5 ka and in the case of core regions of thar it continued until 0 6 ka the southern margins of the thar desert thus have not experienced any major aeolian deposition since 5 ka

water chemistry and caco3 dissolution in the saline part of an open flow mixing zone coastal yucatan peninsula mexico along the caribbean coast of the yucatan peninsula brackish ground water mixed fresh water and sea water is channeled through upper pleistocene limestone via fracture controlled caverns in caves cenotes and caletas at xcaret yalku and tancah this open flow coastal mixing zone comprises three major layers 1 an upper dilute zone of gradually increasing salinity with depth slow mixing 2 a thin intermediate zone of rapidly increasing salinity with depth rapid mixing and 3 a lower saline zone of gradually increasing salinity with depth the intermediate layer occurs at different absolute salinities at different localities and it generally corresponds to the level of a notch apparently related to dissolution in the wall rock of the caverns chemical composition of the mixed ground water is consistent with that predicted from theoretical conservative mixing of fresh water and sea water end members sampled in the yucatan coastal region inorganic c alkalinity mg ca and sr ca and 18o and 13c of the mixed water give no indication of dissolution or precipitation of cac03 as the ground water flows rapidly seaward field and petrographic observations however show that aragonite is preferentially dissolving throughout the modern mixing zone and in particular in the saline portion comparison of saturation indices to calculated mixing curves shows that the coastal mixing zone of the eastern yucatan peninsula is undersaturated with respect to cac03 over a wide range of salinity including mixtures of as much as 95 sea water for aragonite and 90 sea water for calcite supersaturation with respect to stoichiometric dolomite is maintained over the whole range of salinities but super saturation with respect to calcian dolomite ca57mg43 can be confined to high salinity mixtures depending on the thermodynamic data base used in calculations these data suggest that 1 dissolution of coastal limestone can take place in the sea water dominated portion of the mixing zone and 2 the mixing zone model for dolomitization can be extended to much higher salinities than is indicated by the widely accepted dorag model

late holocene mangrove development and onset of sedimentation in the yax chen cave system ox bel ha yucatan mexico implications for using cave sediments as a sea level indicator abstract this study examines the relationship between the flooding of cenotes and formation of coastal mangrove with holocene sea level rise and the onset of aquatic sedimentation in yax chen a cave system in quintana roo on mexico s yucatan peninsula sediment depth measurements n 180 were collected along 2 7 km of an underwater cave passage and three cores were radiocarbon dated to examine both the extent and timing of sedimentation in the cave basal radiocarbon ages 4 ka for aquatic sediments in the cave show that holocene sea level rise flooded cenotes creating sunlit open water conditions with associated mangroves on the upper karst surface these conditions initiated abundant and widespread sedimentation in the cave cenote surface area controlled the long term sediment accumulation in the cave passages through primary productivity in the sunlit open water areas of the cenotes this primary productivity was enhanced with mangrove formation which causes funneling of precipitation and nutrient rich waters into the cenotes from the mangroves accumulation histories from the radiocarbon dated sediment cores n 3 were compared with accumulation histories in previously published studies including actun ha mexico and green bay cave gbc bermuda

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

thermoluminescence chronology of sand profiles in the thar desert and their implications thermoluminescence chronology of three sand profiles in western rajasthan indicates a peak in sand accretion rate at ca 14 ka and a period of dormancy during 13 6 ka bp this observation shows a general correlation with pollen and geochemical records from lakes in thar and demonstrates the potential of desert sands in paleoclimatic reconstruction thermoluminescence ages of 36 ka and 40 ka on two samples suggest that the aeolian sand mobilization activity in this regions is at least as old

estimation of shape factor and depth from gravity anomalies due to some simple sources the gravity anomalies over some simple geometry sources have been inverted to compute the shape factor and depth using a hybrid algorithm involving simulated annealing followed by non linear curve fitting the shape factors for a point an infinite horizontal line and a semi infinite vertical line source are 1 5 1 0 and 0 5 respectively a procedure to determine the depth and the horizontal or vertical extent of a line source has been developed a ribbon of finite vertical extent is characterized by a shape factor varying between 0 1 and 1 0 a symmetrical syncline can be distinguished from an anticline on the basis of the shape factor as this assumes values greater than 1 0 for a syncline and less than 1 0 for an anticline interpretation schemes are presented to compute the depth to the horizontal base and its radius for models of a 2d dome and a 2d depression the efficiency and potential of the proposed technique has been evaluated by applying it to three published field examples a chromite anomaly in cuba the mobrun orebody and the louga anomaly

orbital and internal forcing of climate on the yucatan peninsula for the past ca 36 ka abstract a 19 6 m sedimentary sequence from lake quexil guatemala is presented as a proxy record of climatic change on the low lying yucatan peninsula over the last ca 36 ka long term climatic fluctuations are attributed to orbital forcing of insolation while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled gcms simulating meltwater cooling of the gulf of mexico may predict some but not all climatic responses in the circum caribbean lake quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones q lg 1 and 2 which were drier only in comparison with holocene conditions q lg 1 appears to have been colder than expected based on insolation alone and is contemporary with the younger dryas event between meltwater pulses 1a and 1b thus other feedbacks also may have cooled surface temperatures in the gulf of mexico such as unique late glacial circulation patterns increased albedo for the florida and yucatan peninsulas or surface temperatures on the north american continent additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub regional climatic variability in the circum caribbean

thermoluminescence dating of sand dunes in rajasthan india we report here a new application of thermoluminescence tl for dating sand dunes this application assumes that exposure to sunlight causes bleaching of the geological tl of a sediment to a residual value and that tl accumulation starts again when the sediment is buried under fresh deposit and is thus shielded from the sun although the tl method has been applied to loess1 2 and ocean sediments3 4 the application of this technique to sand dunes provides the first reliable dating control for dune dynamics palaeoclimatology and spread of deserts

luminescence chronology of river adjustment and incision of quaternary sediments in the alluvial plain of the sabarmati river north gujarat india river adjustment and incision in the sabarmati basin gujarat india have been examined at a site near mahudi towards this the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated the upper fluvial sequence along with the overlying aeolian sand and riverbed scroll plains provide clues to the evolution of the present sabarmati river sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase luminescence chronology bracketed this sequence to between 54 and 30 ka which corresponds to oxygen isotope stage 3 during which the sw monsoon was enhanced the overlying aeolian sand has been dated to 12 ka indicating that dune accretion occurred simultaneously with the strengthening of the sw monsoon during the early holocene adjustment of the sabarmati along a n s transect is placed around 12 ka and the incision is bracketed between 12 and 4 5 ka river adjustment could have been tectonic however the incision was facilitated by the availability of continuous flow in the river caused by the sw monsoon the basin experienced two tectonic events at about 3 and 0 3 ka as demonstrated by the morphology of the scroll plains

a new concept in euler deconvolution of isolated gravity anomalies euler s homogeneity equation has been used to develop a new technique to interpret the gravity anomalies over some simple geometrical sources namely a finite horizontal line vertical line a finite vertical ribbon a semicircular dome basin and an isosceles triangle approximating an anticline syncline a linear over determined system of equations has been solved to compute the depth the horizontal location and the structural index all treated as free parameters the concept of a variable structural index provides better depth estimates and helps to identify the source geometry nomograms have been prepared to compute an additional model parameter namely the horizontal vertical extent of a line the vertical extent of a ribbon and the radius of a dome basin the efficacy of the proposed method has been evaluated using two real field examples

hurricane ingrid and tropical storm hanna s effects on the salinity of the coastal aquifer quintana roo mexico abstract there is a lack of information on aquifer dynamics in anchialine systems especially in the yucatan peninsula of mexico most of our knowledge is based on spot measurements of the aquifer with no long term temporal monitoring in this study spanning four years 2012 2016 sensors water depth and conductivity salinity were deployed and positioned 9 and 10 m in the meteoric water mass wm close to the transition with the marine wm halocline in 2 monitoring sites within the yax chen cave system to investigate precipitation effects on the salinity of the coastal aquifer the results show variation in salinity 95 mm such as hurricane ingrid 2013 and tropical storm hanna 2014 shows meteoric water mass salinity rapidly increasing approx 6 39 to 8 6 ppt but these perturbations have a shorter duration weeks and days wavelet analysis of the salinity record indicates seasonal mixing effects in agreement with the wet and dry periods but also seasonal effects of tidal mixing meteoric and marine water masses occurring on shorter time scales diurnal and semi diurnal these results demonstrate that the salinity of the freshwater lens is influenced by precipitation and turbulent mixing with the marine wm the salinity response is scaled with precipitation larger more intense rainfall events 95 mm create a larger response in terms of the magnitude and duration of the salinity perturbation 1 ppt the balance of precipitation and its intensity controls the temporal and spatial patterning of meteoric wm salinity

morphology and late quaternary sedimentation on the north faeroes slope and abyssal plain north atlantic whilst the interplay between tectonics glaciation and oceanography is reasonably well understood on some high latitude margins relatively little is known about the nature of quaternary processes affecting the continental margin north of the faeroe islands we therefore present side scan sonar gloria and tobi and 3 5 khz data in combination with a new regional bathymetry in order to characterise and analyse the margin s physiography and the sedimentary processes that have occurred in the area during the late quaternary seven acoustic facies are identified and interpreted in combination with published core records the margin is subject to differing sedimentation regimes over glacial interglacial cycles relating to the changing importance of contouritic hemipelagic glacimarine and mass movement processes mass movement is much more extensive than previously thought with a total sediment volume of 2000 km3 similar to that of the storegga slide 5500 km3 and may occur primarily at glacial terminations the downslope limit of instabilities is associated with a series of channels focusing the deposition of distal turbiditic sediments into the regional deep beyond together with glacigenic debris flows from the western margin of the north sea fan mass movement processes are identified to have affected 52 70 of the north faeroes margin area in contrast distal glacimarine sedimentation alternating with hemipelagic and contouritic development is found on the remaining 30 48 of the margin during glacials and hemipelagic and contouritic sedimentation are active across 90 of the margin in interglacial conditions despite a lack of any local direct glacial influence these observations on the relative importance of sedimentation processes are comparable with other glacially influenced passive margins

paleoenvironmental implications of fixed dune systems in southern africa extensive systems of fixed linear dunes occur in the kalahari region of southern africa from 28 s to 16 30 s they provide evidence for large scale expansion of arid climates in the subcontinent during the quaternary on the basis of differing dune morphologies and alignments three periods of upper pleistocene aridity are recognised patterns of dune alignments reflect paleosand flow regimes and permit deduction of past winds and circulation patterns leading to the conclusion that arid episodes were associated with and probably caused by greater strength and persistence of the south african anticyclone a tentative chronology of the arid periods tends to support the hypothesis that subtropical aridity was contemporaneous with glacial conditions in high latitudes

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

very high resolution seismic stratigraphy of pleistocene eustatic minima markers as a tool to reconstruct the tectonic evolution of the northern latium shelf tyrrhenian sea italy this paper analyzes depth variations of seismically detected lowstand features i e paleo shelf break and lowstand submerged depositional terraces lsdts in order to define vertical movements along a continental margin narrowly spaced high resolution two dimensional reflection seismic data were used collected along a segment of the continental shelf of latium eastern tyrrhenian sea italy seismostratigraphic analysis allowed us to identify the six most recent fourth order depositional sequences formed in the past 500 k y they have a different degree of preservation in the outer and middle shelf with almost no continuation in the inner shelf some wedge shaped bodies interpreted as lsdts can be identified in these units the depth of paleo shelf break and lsdts of marine isotope stage 12 ca 435 ka was measured and gradually varies along the margin between 220 m and 131 m below current sea level differential subsidence rates have been estimated for the area varying from 0 to 0 21 mm a the spatial variations agree with studies of uplifted coastal terraces on land controlled by localized volcanic activity along the latium section of the tyrrhenian coast the comparison of deformation onshore and offshore has proven to be a promising approach for understanding the evolution of uplifting continental margins

reconstructing water level in hoyo negro quintana roo mexico implications for early paleoamerican and faunal access abstract the skeletal remains of a paleoamerican naia hn5 48 and extinct megafauna were found at 40 to 43 mbsl in a submerged dissolution chamber named hoyo negro hn in the sac actun cave system yucatan peninsula mexico the human remains were dated to between 12 and 13 ka making these remains the oldest securely dated in the yucatan twelve sediment cores were used to reconstruct the holocene flooding history of the now phreatic cave passages and cenotes ich balam oasis that connect to hn four facies were found 1 bat guano and seed sf 2 lime mud mf 3 calcite rafts crf and 4 organic matter calcite rafts om crf which were defined by their lithologic characteristics and ostracod foraminifera and testate amoebae content basal radiocarbon ages ams of aquatic sediments sf combined with cave bottom and ceiling height profiles determined the history of flooding in hn and when access was restricted for human and animal entry our results show that the bottom of hn was flooded at least by 9850 cal yr bp but likely earlier we also found that the pit became inaccessible for human and animal entry at 8100 cal yr bp when water reaching the cave ceiling effectively prevented entry water level continued to rise between 6000 and 8100 cal yr bp filling the cave passages and entry points to hn cenotes ich balam and oasis analysis of cave facies revealed that both holocene sea level rise and cave ceiling height determined the configuration of airways and the deposition of floating and bat derived om guano and seeds calcite rafts which form on the water surface are also dependent on the presence of airways but can also form in isolated air domes in the cave ceiling that affect their loci of deposition on the cave bottom these results indicated that aquatic cave sedimentation is transient in time and space necessitating extraction of multiple cores to determine a limit after which flooding occurred

short note source geometry identification by simultaneous use of structural index and shape factor a cross plot of the shape factors and the structural indices determined from gravity anomalies over various idealized sources namely horizontal vertical lines and vertical ribbons with various strike lengths and depth extents forms a closed loop different segments of this loop termed the source geometry identification loop sgil correspond to different source geometries combined use of the structural index and the shape factor determined from an isolated gravity anomaly reduces the ambiguity in characterizing the source geometry a simulated example and three field examples namely a cuban chromite anomaly an indian example over manganese ore and a sulphide ore from quebec have been analysed by the proposed method in order to identify their respective source geometries

chronology of expansion and contraction of four great basin lake systems during the past 35 000 years abstract during the past 35 000 years lake bonneville lake russell and lake searles underwent a major period of lake level change the lakes were at moderate levels or dry at the beginning of the period and seem to have achieved highstands between about 15 000 and 13 500 yr b p the rise of lake lahontan was gradual but not continuous in part because of topographic constraints intrabasin spill lake lahontan also had an oscillation in lake level at 15 500 yr b p radiocarbon age estimations for materials that were deposited in the lake basins indicate that lake bonneville rose more or less gradually from 32 000 yr b p and had major oscillations in level between 23 000 and 21 000 yr b p and between 15 250 and 14 500 yr b p lake russell and lake searles had several major oscillations in lake level between 35 000 and 14 000 yr b p the timing and exact magnitude of the oscillations are difficult to decipher but both lakes may have achieved multiple highstand states all four lakes may have had nearly synchronous recessions between about 14 000 and 13 500 yr b p after the recessions the lakes seem to have temporarily stabilized or experienced a minor increase in size between about 11 500 and 10 000 yr b p these data provide circumstantial evidence that the younger dryas event affected climate on at least a hemispheric scale during the holocene the four lakes remained at low levels and small oscillations in lake level occurred an important aspect of the lake level data is the accompanying expansion of lake surface area at the time of the last highstand lake bonneville and lake lahontan had surface areas about 10 times larger than their mean historical reconstructed areas whereas lake russell and lake searles had surface areas about 5 times larger than their mean historical reconstructed areas differences in the records of effective wetness may have been due to the locations of the basins relative to the position of the jetstream or they may have resulted from lake atmosphere feedback processes

late quaternary geomorphological evolution and erosion rates in the clayey peri adriatic belt central italy abstract this study analyses the geomorphological evolution during the last 20 000 years in two areas representative of the peri adriatic belt of central italy mt ascensione in the high hilly sector 600 1100 m a s l and the atri district in the hilly coastal sector up to ca 500 m a s l in both areas the lithostructural setting is characterized by an east verging monocline mainly composed of clayey formations the two areas are compared in relation to their morpho chronological aspects and geomorphological dynamics the results suggest two fundamental evolutionary phases 1 about 20 000 yr bp sedimentation occurred along the main valleys when the middle to upper portions of slopes were covered by colluvial deposits and 2 at the beginning of the holocene the climatic improvement triggered erosion along rivers producing deep and narrow valleys estimated denudation rates during the last 20 000 yr are 7 8 mm yr 1 for the mt ascensione area and 2 4 3 0 mm yr 1 for the atri district reflecting frequent landslides and fluvial erosion the rates are consistent with the data available in literature denudation rates double if we assume most of the erosion process took place after the beginning of the holocenic warming phase

lignite deposits of the kutch basin western india carbon isotopic and palynological signatures of the early eocene hyperthermal event etm2 abstract this study presents new results of combined palynological and stable carbon isotope 13 c investigations carried out in the well known lignite sequence at panandhro district kutch in the gujarat state of western india dinoflagellate cysts and associated spore pollen assemblage assign an early eocene ypresian age to the lignitic succession at panandhro furthermore a pronounced negative carbon isotope excursion cie of about 2 7 correlated to the second eocene thermal maximum 53 7 ma a globally recognized hyperthermal event was discovered in the middle part of the succession consistent with the palynological constraints this is the first record of an eocene hyperthermal event etm2 from the kutch basin our data has regional implications for the age of the lignitic sequences across western india as it demonstrates that there is no significant age difference between the lignite deposits of the kutch and cambay basins our results also support a lutetian age for the previously described vertebrate fossils including whales from the panandhro mine section

the influence of the south west indian monsoon on continental deposition over the past 130 kyr gujarat western india ocean and ice core records of the intensity of the south west indian monsoon swim show rapid shifts in most proxy indicators of climate over the past 125 kyr on decadal to millenial scales however the responses of continental environments to such perturbations remain unknown due to the absence of a suitable long term continental record the stratigraphic record from gujarat western india an area where all sedimentological processes are governed by the vagaries of the swim reveals three aggradation phases that represent deposits of seasonal rivers ap1 ephemeral rivers ap2 and dust storms ap3 based on a review of available dates and new esr dates on the oldest exposed calcretes from palaeovertisols these phases are assigned the time brackets 135 100 kyr bp ap1 100 20 kyr bp ap2 and 20 6 kyr bp ap3 these results suggest that continental depositional environments respond in a subdued manner and are separated by thresholds for climate shifts to effect durable changes in the continental depositional environment a period between 5 kyr and 16 kyr is the minimum time required to permanently change the landscape of an area alternatively catastrophic changes in terrestrial depositional environments may also be effected by abrupt climatic shifts that are beyond the tolerance limits of the depositional systems

regional response of the coastal aquifer to hurricane ingrid and sedimentation flux in the yax chen cave system ox bel ha yucatan mexico abstract coastal karst aquifers are an important source of potable water which can be affected by external forcing on various temporal and spatial scales e g sea level but there is a lack of long term data to understand their response sediment cores and their proxy records have been used in lakes and oceans to assess past environmental change but haven t been extensively applied to anchialine caves where there is less known about the physical biological and chemical processes affecting sedimentation over fifty sediment traps were placed in yax chen which is part of the ox bel ha cave system near tulum mexico and four water level sensors were placed in two additional cave systems ponderosa sac actun for comparative water table fluctuations data collected over the past three years 2011 2013 captured seasonal and spatial sediment flux including the effect of an intense rainfall associated with hurricane ingrid september 18 2013 the data indicates that sediment deposition was controlled by cenote size and the presence of mangrove areas upstream of cenote gemini had negligible sediment accumulation as there were few cenotes and the terrain is dominated by lowland tropical forest while areas downstream from cenote gemini were dominated by mangrove forests and larger cenotes which resulted in higher sediment accumulation rates 0 014 vs 0 22 mg cm 2 day bi annual sedimentation rates in 2013 2014 were higher in the months after the rainy season 0 2 vs 0 5 mg cm 2 day indicating that cenote productivity was likely controlling sedimentation mangrove areas with their peat accumulations occlude the porous karst causing funneling of nutrient rich rainwater into the sunlit cenotes enhancing primary productivity and sedimentation in downstream areas hurricane ingrid had little effect on the yearly sediment rate even though water table fluctuations were high 0 7 m compared to the yearly values 0 3 m this likely is due to water bypassing the cenotes with little residence time to enhance productivity and sedimentation in downstream areas

holocene variations of monsoon rainfall in rajasthan two reconstructed histories of the monsoon rainfall in rajasthan show that the monsoon was weak or absent in latest glacial time with the advent of holocene climatic patterns fresh water lakes formed in dune fields and the pollen rain preserved in these reservoirs provides a basis for the reconstruction of the monsoon history the two reconstructions separated by only 150 km have some features in common and some striking differences both show maximum monsoon amounts in the early holocene with a roughly two thirds decrease to the present both show salinization in sub boreal time both show long intervals of near complete desiccation in the last four millennia the shorter term variations however are not closely parallel these shorter term variations may be explained in terms of the behavior of the present day interannual variability