late miocene environmental change in nepal and the northern indian subcontinent stable isotopic evidence from paleosols neogene sediments belonging to the siwalik group crop out in the himalayan foothills along the length of southern nepal carbon and oxygen isotopic analyses of siwalik paleosols from four long siwalik sections record major ecological changes over the past 11 m y the carbon isotopic composition of both soil carbonate and organic matter shifts dramatically starting ca 7 0 ma marking the displacement of largely c3 vegetation probably semi deciduous forest by c4 grasslands by the beginning of the pliocene all the flood plains of major rivers in this region were dominated by monsoonal grasslands the floral shift away from woody plants is also reflected by the decline and final disappearance of fossil leaves and the decrease in coal logs in the latest miocene a similar carbon isotopic shift has been documented in the paleosol and fossil tooth record of pakistan and in terrigenous organic matter from the bengal fan showing that the floral shift was probably continentwide the latest miocene also witnessed an average change of 4 in the oxygen isotopic composition of soil carbonate as observed previously in pakistan the reasons for this are unclear if not diagenetic a major environmental change is indicated perhaps related to that driving the carbon isotopic shift recently described pollen and leaf fossils from the surai khola section show that evergreen forest was gradually displaced by semi deciduous and dry deciduous forest between 11 and 6 ma the gradual nature of this floral shift which culminated in the rapid expansion of c4 grasses starting 7 0 m y ago is difficult to explain by a decrease in atmospheric pco2 alone cerling et al 1993 but fits well with a gradual onset of monsoonal conditions in the late miocene in the northern indian subcontinent himalayan uplift driving both monsoonal intensification and consumption of co2 through weathering may be the common cause behind major late miocene environmental change globally however the decline of effective moisture associated with monsoon development has probably slowed not increased the rate of consumption of co2 by chemical weathering of himalayan sediments

reconstructing mid late holocene cyclone variability in the central pacific using sedimentary records from tahaa french polynesia abstract we lack an understanding of the geographic and temporal controls on south pacific cyclone activity overwash records from backbarrier salt marshes and coastal ponds have been used to reconstruct tropical cyclone strikes in the north atlantic basin however these specific backbarrier environments are scarce in the south pacific with cyclone records limited primarily to the period of modern observation this instrumental record suggests a correlation with the el nino southern oscillation enso but longer records are necessary to test this relationship over geologic timescales and explore other potential climate drivers of tropical cyclone variability deep lagoons behind coral reefs are widespread in the pacific and provide an alternative setting for developing long term sedimentary reconstructions of tropical cyclone occurrence coarse grained event deposits within the sediments of a back reef lagoon surrounding tahaa reveal a 5000 year record of cyclone occurrences timing of recent high energy deposits matches well with observed tropical cyclone strikes and indicates coarse deposits are storm derived longer records show tropical cyclone activity was higher from 5000 to 3800 and 2900 to 500 yrs bp comparison to records from the north pacific out of phase and north atlantic in phase suggests a coordinated pattern of storm activity across tropical cyclone basins over the mid late holocene the changes in tropical cyclone activity we observe in the south pacific and across other basins may be related to enso as well as precession driven changes in ocean atmosphere thermal gradients

eocene oligocene proto cascades topography revealed by clumped δ47 and oxygen isotope δ18o geochemistry chumstick basin wa usa the topography of the present day washington cascades impacts atmospheric circulation and precipitation patterns in the pacific northwest introducing a pronounced orographic rain shadow in the lee of the mountain range the temporal development of cascade topography however remains largely unconstrained for the early cenozoic based on coupled carbonate clumped isotope 47 and oxygen isotope 18o measurements we reconstruct 18o values of eocene groundwater 18owater in the chumstick basin central washington today located in the cascade rain shadow 47 paleo thermometry indicates a systematic change in basin burial temperatures from 110 c to 70 c depending on burial depth in the basin these data are in good agreement with low t thermochronological and vitrinite reflectance data and further constrain the basin burial and exhumation history in concert with field observations microstructural analysis and 18o values of the analyzed carbonates we suggest that the 47 temperatures and 18o values reflect open system carbonate cement recrystallization in meteoric derived groundwaters during early burial diagenesis assuming open system behavior reconstructed mean 18owater values of 7 middle eocene to 9 late eocene early oligocene are consistent with a low elevation origin of the corresponding meteoric waters that permeated the sandstone conglomerate members of the eocene sedimentary units in light of the paleogeographic setting of the chumstick basin the reconstructed 18owater values agree well with pacific derived moisture that did not experience strong rainout the absence of a rain shadow effect therefore permits only moderate eocene oligocene elevations at least for the southern part of the washington proto cascades

do stable isotopes in carbonate cement of mio pleistocene himalayan sediments record paleoecological and paleoclimatic changes non pedogenic carbonates such as carbonate cement and nodules in the sandstones are quite common in the terrestrial geological record unlike pedogenic carbonates their stable isotope ratios lack investigations for paleo climatic reconstructions the present investigation therefore explores the possibility of use of stable isotope studies of non pedogenic carbonates from the mb pleistocene siwalik group of sediments exposed in the ramnagar sub basin of the nw himalaya petrographic studies reveal the dominance of micrite fabric in carbonate nodules both of pedogenic and non pedogenic samples irrespective of specific stratigraphic unit however calcite as cement in the sandstones shows the dominance of micrite fabric in the younger in age sediments seventy two non pedogenic carbonate samples from the carbonate nodules and cement in the siwalik sandstones ranging in age between similar to 1 ma and 12 2 ma were analyzed for delta c 13 and delta o 18 values the delta c 13 values vary from 24 77 parts per thousand to 1 1 parts per thousand and delta o 18 values vary from 15 34 parts per thousand to 7 81 parts per thousand pedogenic and non pedogenic carbonates ranging in age between similar to 1 ma and 6 ma have largely similar delta c 13 values and the range of delta c 13 values indicate the dominance of c 4 type of vegetation however unlike pedogenic carbonates which showed the dominance of c 3 type of vegetation pre 7 ma on the basis of delta c 13 depleted isotopic values singh et al 2011 delta c 13 values are largely enriched in the corresponding aged non pedogenic carbonates revealing no information on specific type of vegetation likewise paleoprecipitational reconstructions from delta o 18 values in pedogenic carbonates showed a progressive increase in aridity from similar to 12 ma to recent excluding short term increases in rainfall monsoon intensity at around 10 ma 5 ma and 1 8 ma singh et al 2012 on the contrary such reconstructions are not possible from the delta o 18 values of non pedogenic carbonates and indeed the delta o 18 values of non pedogenic carbonates are largely depleted to as much as 6 parts per thousand from the corresponding pedogenic carbonates such differences in delta c 13 and delta o 18 values of non pedogenic carbonates from pedogenic carbonates are primarily due to the dependence of the former on groundwater conditions responsible for precipitating carbonate further a comparison of isotopic values between non pedogenic and pedogenic carbonates can be interpreted that post 6 ma and pre 6 ma non pedogenic carbonates were largely formed by shallow and deep groundwater conditions respectively the result of these investigative studies therefore suggests that the stable delta c 13 and delta o 18 values of non pedogenic carbonates unlike the pedogenic carbonates and irrespective of nature of calcite fabric showed their little importance in paleoclimatic and paleoecological reconstructions c 2014 elsevier b v all rights reserved

need for re apprehension of basin tectono depositional set up during initial stage of himalayan orogeny from pedogenic evidences abstract the collision and suturing of indian and eurasian plates about 50 ma ago closed the tethys ocean initiated himalayan orogen and a foreland basin developed towards its south the last phase of marine sedimentation in indian sub continent during paleocene eocene is represented by subathu formation overlain by continental dagshai sediments and nature of this transition named as passage beds sensu bhatia and mathur 1965 is controversial further it is poorly understood both in terms of depositional environment and age surprisingly these beds show evidences of pedogenesis but no such palaeopedological studies have been reported so far the degree and nature of pedogenesis is widely used in solving diverse geological problems in complex geological settings therefore pedogenesis of these beds exposed in the shimla hills of subathu sub basin has been worked out morphological and micromorphological studies divide them into older green greenish grey pedofacies gp and younger red reddish brown pedofacies rp units pedons are up to tens of centimeters thick structure largely comprises sub angular to sub rounded blocky peds a suite of pedogenic features include burrows root traces infillings mottling cutans segregations and nodules which vary in dominance from gp to rp unit greenish grey pedons are characterized by mottles fe mn oxide segregations whereas reddish brown pedons by root traces commonly filled with carbonates presence of carbonate segregations and cutans detailed field and laboratory studies at various local and regional exposures can reveal the nature and extent of pedogenesis which will be significant to enact depositional environment as well as stratigraphic position of passage beds co relatable at different localities throughout length of the himalaya from pakistan to nepal because of their distinctive lithology and stratigraphic position such studies bear global significance in demonstrating the use of palaeosols as a geologic archive in complex geological settings

tectonics or climate what drove the miocene global expansion of c4 grasslands investigations into the most plausible causes which triggered the late miocene global expansion of c4 grasslands have reached no consensus and are still being debated the global decline in co2 levels in the late miocene has been thought to be the most common driver although c4 grassland expansion was largely confined to the late miocene their first appearance varied significantly in different parts of the old and new world and therefore emphasizes role of local and or regional factors may or may not be in combination with one or more global factors the dynamic himalayan orogen constitutes a significant global tectonic event that is believed to have affected global climate hence a study of the himalayan foreland basin sediments could help in gleaning out possible causes behind this major paleoecologic event which could perhaps be directly or indirectly related stable carbon isotope analyses of a total of 141 pedogenic carbonates in the mio pleistocene siwalik paleosols of the ramnagar sub basin are coherent providing a better insight into paleovegetational changes across the sub basin on temporal and spatial scales furthermore paleovegetational history during oligocene is reconstructed from dagshai paleosols exposed in the subathu sub basin the isotopic results show dominance of c3 vegetation pre 7 ma and dominance of c4 vegetation post 5 ma percentage abundance of c4 vegetation was less than 20 pre 7 ma but increased to more than 40 post 5 ma reaching up to 100 in the youngest analyzed sediments there is exclusive dominance of c3 vegetation during oligocene these results conform to the pattern of change in vegetation documented in other parts of the himalayan belt the global expansion of c4 grasslands largely during late miocene have long been linked with then climate changes particularly brought by declining atmospheric co2 level large scale fires intensification of monsoon seasonality and aridity as demonstrated by various researchers these major hypotheses explaining expansion of c4 grasslands during late miocene are not very convincing due to significant shortcomings associated with them for example expansion of c4 grasslands in non monsoonal regions put serious constraints on the monsoonal intensification hypothesis likewise aridity as being the primary driver of c4 grassland expansion seems hard to support since there is no substantial evidence that could suggest global onset of arid conditions at about same geologic time and some most arid periods like the triassic show no evidence of c4 plants we suggest that the initial lowering of co2 below 450 ppmv created an environment for the beginning of c4 vegetation but the persistence of this threshold value for a considerable time during late miocene appears to be the probable cause of the late miocene global expansion of c4 grasslands irrespective of their time of first appearance it has been deduced through the correlation of himalayan tectonic events with atmospheric co2 levels and paleovegetational changes since upper miocene times that it was indeed the late miocene continuous intense tectonic instability of the himalayas that significantly decreased atmospheric co2 levels and which perhaps played a key role in changing the nature of photosynthetic pathways

the stable isotope composition of early ground water cements from sandstone in paleoecological reconstruction abstract the carbon isotope composition of soil carbonates in paleosols records the global expansion of cm4 biomass in the late miocene however soil carbonate is not present in many geological sections or if present is often difficult to distinguish from other carbonate cements here we report on the 13c values of sparry early ground water cements in sandstones from the siwalik group in pakistan that record like the soil carbonates from the same sections the dramatic late miocene expansion of c4 vegetation the early cements are confined to densely cemented nodules in the sandstones but can also be found reworked as nodules into adjacent paleo channels demonstrating their formation shortly after burial the early cements are isotopically distinct from later higher temperature calcite cements our results demonstrate that some early ground water cements can be used in a manner similar to soil carbonates to reconstruct vegetation and perhaps pco2 changes in the past

mio pliocene monsoonal record from himalayan foreland basin indian siwalik and its relation to vegetational change carbon and oxygen isotope ratios of soil carbonate nodules and carbon isotope ratio of associated organic matter were measured from three indian siwalik stratigraphic successions in order to reconstruct vegetational history and change in contemporaneous precipitation 13c values of soil carbonates show that from 10 5 to 6 ma the vegetation was c3 type and around 6 ma c4 grasses appeared the 18o variations of soil carbonates suggest that the monsoon system intensified with one probable peak at around 10 5 ma and a clear onset at 6 ma with peak at 5 5 ma after 5 5 ma monsoon strength decreased and attained the modern day condition with minor fluctuations which is supported by marine proxy of upwelling in the arabian sea and sedimentary morphology in siwalik the covariation between 18o and 13c data suggests that a change in precipitation pattern was partly responsible for expansion of c4 grasses in a mixed c3 c4 environment estimation of abundance of c3 and c4 plants using soil carbonate in one case and residual soil organic matter in another may differ this can be explained by assuming that the plant respired co2 is the main contributor of carbon in soil carbonate and may have different isotopic composition from that of the residual organic matter in the soil in addition the abundance estimate of c3 c4 plants also shows variation with time probably caused by change in growing season conditions through time

sedimentary facies of bora bora darwin s type barrier reef society islands south pacific the unexpected occurrence of non skeletal grains abstract barrier reefs when encircling small islands have been comparatively little noticed by voyagers but they well deserve attention in their structure they are little less marvelous than atolls and they give a singular and most picturesque character to the scenery of the islands they surround darwin 1842 p 2 sediment sampling revealed six modern sedimentary facies in the barrier reef system around the volcanic island of bora bora including mixed skeletal packstone peloidal packstone halimeda rich packstone to grainstone coralgal grainstone wackestone and mudstone whereas sediments rich in corals and coralline algae are abundant on reefs and carbonate shoals mud rich sediments with mollusks and foraminifera occur in deep lagoons 15 40 m carbonate mud is composed largely of aragonite needles probably derived from codiaceans like halimeda and coccoliths in moderate abundances despite the proximity to a volcanic island the content of siliciclastics in the sediments is low 10 on average which is a consequence of the absence of permanent water courses in addition to skeletal grains non skeletal grains cemented fecal pellets aggregates occur in high abundance 30 50 in shallow lagoons 5 m on the eastern side of bora bora this observation opposes the widely held concept that non skeletal carbonate grains are abundant on platforms from the atlantic ocean but virtually missing in recent indo pacific reefs and carbonate platforms in bora bora non skeletal grains and aggregates apparently form in warm shallow 5 m moderately agitated areas with relatively low sedimentation rates in addition early cementation is probably favored by elevated alkalinity and ph in surface waters in this part of the south pacific in the same area some 900 km to the southwest of the study area ooids and peloids have recently been discovered in the shallow lagoon of aitutaki cook islands more occurrences of abundant non skeletal grains probably exist in the indo pacific region however too few locations have been systematically studied a comparison of the new bora bora data with other modern reefs and platforms shows that sediment occurrence and distribution exhibits basic patterns in that marginal areas are dominated by coarse grained coralgal sediment whereas lagoons and platform interiors are characterized by mollusk foram halimeda and non skeletal grains and fines still grain abundances may vary significantly among locations and again suggest the need for more studies in order to fully understand the factors controlling occurrence and distribution of modern sediments

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

cyclone pumping sediment partitioning and the development of the great barrier reef shelf system a review abstract the modern great barrier reef gbr is part of the world s largest and best known mixed terrigenous carbonate continental margin the gbr shelf contains three shore parallel sedimentary belts an inner shelf zone of terrigenous sedimentation at depths of 0 22 m a middle shelf zone of sediment starvation at depths of 22 40 m and an outer shelf reef tract with its inner edge at ca 40 m depth these zones are controlled by the dynamics of northward fair weather along shelf drift driven by southeasterly trade winds and by the regular passage of tropical cyclones cyclones cause wind driven north directed middle shelf flows in excess of 130 cm s which erode the seabed concentrate the sparse mobile sediment into sand ribbons and advect suspended load onto the outer part of the nearshore terrigenous sediment prism and into inter reef depocentres within the outer shelf reef tract cyclones largely control the input of new sediment into the gbr system via river flooding seabed erosion or reef breakage they also help to control the partitioning and dispersion of the three main shore parallel belts of sediment and hence stratigraphic accumulation acting as a sediment pump especially during interglacial highstands cyclones have exerted great control on the development of the modern gbr province and its sediments by maintaining a broad shelf parallel zone of episodically mobilised sediment and scoured seabed upon which coral reefs have been unable to form cyclones may also have partly controlled the timing of initiation of the first gbr at 0 6 mybp contrary to current models gbr storm beds are most likely to be preserved intact close to the shoreline and become coarser grained away from the shoreline for the central gbr highstand shedding only applies to carbonate sediment at the scale of local reefs system wide oceanographic controls cause high rates of carbonate sedimentation on the slope during both sea level rise and highstand concomitantly terrigenous sediment accumulates fastest on the slope during sea level rise and slowest during sea level lowstand and highstand

tectono geomorphic and environmental set up deduced during deposition of mio pleistocene sediments in nw himalaya india detailed pedofacies characterization along with lithofacies investigations of the mio pleistocene siwalik sediments exposed in the ramnagar sub basin have been studied so as to elucidate variability in time and space of fluvial processes and the role of intra and extra basinal controls on fluvial sedimentation during the evolution of the himalayan foreland basin hfb dominance of multiple moderately to strongly developed palaeosol assemblages during deposition of lower siwalik similar to 12 10 8 ma sediments suggest that the hfb was marked by upland set up of thomas et al 2002 activity of intra basinal faults on the uplands and deposition of terminal fans at different times caused the development of multiple soils further detailed pedofacies along with lithofacies studies indicate prevalence of stable tectonic conditions and development of meandering streams with broad floodplains however the middle siwalik similar to 10 8 4 92 ma sub group is marked by multistoried sandstones and minor mudstone and mainly weakly developed palaeosols indicating deposition by large braided rivers in the form of megafans in a lowland set up of thomas et al 2002 significant change in nature and size of rivers from the lower to middle siwalik at similar to 10 ma is found almost throughout of the basin from kohat plateau pakistan to nepal because the himalayan orogeny witnessed its greatest tectonic upheaval at this time leading to attainment of great heights by the himalaya intensification of the monsoon development of large rivers systems and a high rate of sedimentation hereby a major change from the upland set up to the lowland set up over major parts of the hfb an interesting geomorphic environmental set up prevailed in the ramnagar sub basin during deposition of the studied upper siwalik similar to 4 92 to 1 68 ma sediments as observed from the degree of pedogenesis and the type of palaeosols in general the upper siwalik sub group in the ramnagar sub basin is subdivided from bottom to top into the purmandal sandstone 4 92 4 49 ma nagrota 4 49 1 68 ma and boulder conglomerate 1 68 ma formations on the basis of sedimentological characters and change in dominant lithology presence of mudstone a few thin gravel beds and dominant sandstone lithology with weakly to moderately developed palaeosols in the purmandal sandstone fm indicates deposition by shallow braided fluvial streams the deposition of mudstone dominant nagrota fm with moderately to some well developed palaeosols and a zone of gleyed palaeosols with laminated mudstones and thin sandstones took place in an environment marked by numerous small lakes water logged regions and small streams in an environment just south of the piedmont zone perhaps similar to what is happening presently in the upland region the upper gangetic plain this area is locally called the trai region pascoe 1964 deposition of boulder conglomerate fm took place by gravelly braided river system close to the himalayan ranges activity along the main boundary fault led to progradation of these environments distal ward and led to development of on the whole a coarsening upward sequence c 2014 elsevier b v all rights reserved

palaeovegetational reconstruction in late miocene a case study based on early diagenetic carbonate cement from the indian siwalik abstract carbon isotope ratio of early diagenetic carbonate cement edcc from sandstones was measured from mohand rao age 9 to 4 5 ma and haripur khol 6 to 1 8 ma sections of siwalik group of india to reconstruct palaeovegetation the 13 c of cement from mohand rao section varies from 10 5 to 0 2 with progressive increase in values from 9 to 7 3 ma indicating gradual change of existing c 3 type vegetation to c 4 type vegetation post 7 3 ma the 13 c value is anchored around zero per mil indicating mixed c 3 c 4 environment with c 4 dominating the ecosystem in haripur khol section the 13 c value of edcc from sandstone indicates presence of both c 3 and c 4 type of plants with dominance of c 4 in the ecosystem which corroborates the results of our previous study based on carbon isotope ratio of soil carbonates the oxygen isotope ratio of edcc from sandstones does not show any systematic variation with time the 18 o values of edcc from mohand rao section ranges from 8 9 to 13 6 and in haripur khol section from 9 9 to 13 6 at a given stratigraphic level the average 18 o value of edcc of sandstones is lower up to 4 compared to the average 18 o of soil carbonate from the same or adjacent level using our earlier published data from haripur khol section the depletion in 18 o of edcc may be due to contribution of contemporary river water infiltrating the groundwater system in the post monsoon period carbon and oxygen isotope ratio of soil carbonate nodules and carbon isotope ratio of associated organic matter from the same nodules were also measured from the mohand rao section in a few cases n 9 from 9 to 8 ma the carbon isotope ratio of soil carbonates varies from 10 8 to 7 8 indicating dominance of c 3 type vegetation in the flood plain in contrast from 5 4 to 4 8 ma the 13 c ranges from 0 1 to 4 3 indicating that the vegetation consisted of mixed c 3 c 4 plants with c 4 dominating the ecosystem the carbon isotope ratio of the organic matter from the same soil carbonate nodules ranges from 25 2 to 24 4 from 9 to 8 ma and 17 4 to 24 6 from 5 4 to 4 8 ma corroborating the above results the average 18 o value of soil carbonate nodules for the time period 9 to 8 ma is 8 8 for 5 4 to 4 8 ma the value is 7 9 these average 18 o values are comparable with previously published oxygen isotope results of soil carbonates from haripur khol and kangra valley

depositional origin of tuffaceous units in the pliocene upper siwalik subgroup jammu india nw himalaya during late pliocene times extrabasinally derived acidic volcanic ashes were deposited as distal pyroclastic fallout in upland interfluvial lacustrine settings in the northwestern part of the siwalik basin these ash beds occur as a bentonitized tuff band and tuffaceous mudstones in the jammu region of india we located and described 12 outcrops of this conspicuous geographically widespread bentonitized tuff band and tuffaceous mudstone association at the same stratigraphic level coincident with the gauss matuyama boundary at 2 48 ma this bentonitized tuff band and tuffaceous mudstone association represents a stratigraphic marker horizon in the diachronous and sporadic vertebrate fauna yielding siwalik strata the claystone siltstone and sandstone units and embedded bentonitized tuff band and tuffaceous mudstone beds represent a coarsening upward sequence reflecting deposition in lacustrine proximal and distal bottomsets pro delta foresets and mouth bar facies capped by fluvial topsets this study reports a chain of four contemporaneous palaeolake basins at this stratigraphic level which ranged in length from 2 to 7 km

the record of pliocene sea level change at enewetak atoll abstract detailed seismic stratigraphy lithostratigraphy and chemostratigraphy indicate that atoll wide subaerial exposure surfaces major disconformities developed during major sea level lowstands form prominent seismic reflectors and are coincident with biostratigraphic breaks in the plio pleistocene on enewetak atoll sea level models based on the stratigraphic position and age of major disconformities suggest a maximum sea level highstand elevation of 36 m above present sea level and a maximum sea level lowstand elevation of 63 m below present sea level for the pliocene

postglacial growth history of a french polynesian barrier reef tract tahiti central pacific bthe internal structure and growth pattern of tahiti reefs over the last 14 ka is reconstructed using sedimentological morphological and palaeobiological data coupled with radiometric dates in drill cores through the modern barrier reef flooding of the volcaniclastic deposits or the karst surface of a pleistocene reef started at 14 ka bp and coral growth began shortly after inundation the sequence in the tahiti barrier reef edge has formed predominantly through long term keep up growth controlled by stable environmental conditions while the adjacent backreef deposits did not start to accumulate before sea level stabilization around 6 ka the dominance of porites communities and the coeval occurrence of branching gracile lithophyllum in the lowermost part of the postglacial reef sequence 14 11 ka suggest the prevalence of uniformly moderate to low energy conditions and or growth in slightly deeper waters all over the drflled area during the early reef stages during the last 11 ka the reef frameworks developed in a high energy environment at maximum water depths of 5 6 m and were dominated by an acropora robusta danaihydrolithon onkodes association the local interlayering of other coralgal assemblages dominated by tabular acropora or domal porites reflects distinct diversification stages resulting either from the palaeotopographic control of the substrate or from slight and episodic environmental changes

contradicting barrier reef relationships for darwin s evolution of reef types the darwinian progressive subsidence model for the evolution of fringing reefs barrier reefs and atolls has been generally accepted following the indisputable proof of subsidence provided by drilling results in the pacific nonetheless there are data that do not fit the expectations of the model such as the similar lagoon depths of barrier reefs and atolls as opposed to the subsidence theory s implicit prediction that atolls should have significantly greater depths in contrast a great deal of evidence supports the influence of meteoric solution on barrier reef morphology for example the maximum lagoon depth of 56 modern barrier reefs is statistically correlated with the lagoon catchment area for modern annual rainfall these modern rainfall patterns would seem to be a reasonable proxy for relative geographic differences in glacial lowstand rainfall even though the absolute amounts of such rainfall are unknown the correlation therefore suggests the importance of pleistocene subaerial solution in contributing to barrier reef morphology further support for antecedent influence occurs in the form of barrier reef passes in which the depth of the reef pass is correlated with onshore drainage volumes on a larger scale the cook island of mangaia provides evidence that solution can produce barrier reef morphology independent of reef development in contrast there are no examples of the subsidence predicted lagoon transition of fringing reefs to barrier reefs to atolls moreover the common occurrence of fringing reefs within barrier reefs negates subsidence as a causal factor in their presumed progressive evolutionary development consequently the evidence to date suggests that a solution morphology template has been accentuated by reef construction to produce the diagnostic barrier reef morphology we see today the importance of subsidence would seem to be in accounting for the overall thickness of the resulting carbonate caps of oceanic examples and in contributing to lagoon depth variation among the larger continental entities

the distribution and discrimination of shallow authigenic carbonate in the pliocene pleistocene palomas basin southern rio grande rift nine types of authigenic carbonate are present in the pliocene pleistocene alluvial fan and axial fluvial sediment of the palomas half graben in the southern rio grande rift pedogenic and other vadose carbonate includes 1 pedogenic carbonate of stage ii and stage iii morphology underlying bw and bt horizons 2 mudstones in which the carbonate nodules may be pedogenic or the result of shallow groundwater invasion of the vadose zone 3 pedogenic calcic nodules and tubules in eolian sand and 4 gully bed cement of proximal fan conglomerates formed by infiltration and evaporation of surface runoff shallow groundwater carbonate exists as 5 thin 30 50 cm massive beds with an upper fringe of nodules and tubules precipitated at the water table and in the capillary fringe 6 thick 1 5 3 m massive beds deposited by lateral flow of groundwater or at springs and 7 thin 30 cm calcified root mats associated with near surface water saturated sediment or springs phreatic spar cements 8 occupy the interstices of conglomerates and sandstones and locally exist as 9 oriented concretions groundwater carbonates are best developed near the toes of the large hanging wall derived alluvial fans whereas phreatic cement preferentially exists in footwall derived alluvial fan conglomerates pedogenic carbonate is distinguished from groundwater carbonate by the association with other diagnostic paleosol horizons a predominantly vertical arrangement of root traces peds desiccation cracks and calcic tubules and by gradational contacts the 13 c and 18 o values are similar among pedogenic and shallow groundwater carbonate although locally nodules in eolian sand and gully bed cement have higher 18 o values perhaps due to the effects of evaporation some phreatic cements may be distinguished from pedogenic and shallow groundwater carbonate by lower values of 13 c and 18 o authigenic carbonate in footwall derived alluvial fan sediment has consistently higher values of 13 c than that in hanging wall derived sediment which may reflect differences in vegetative type and or density on either side of the basin

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

aeolian activity in northern amazonia optical dating of late pleistocene and holocene palaeodunes palaeodunes were examined on the eastern margin of the rio branco rupununi savanna northeast amazonia optical dating suggests that the onset of aeolian activity was between 17 000 and 15 000 yr ago just after the last glacial maximum both the palaeodune axes and modern dominant wind directions have northeast to east northeast directions implying no significant shift in atmospheric circulation patterns over northeast amazonia during the late pleistocene to holocene major regional climate change events such as the younger dryas do not appear to have had any effect on the rates of aeolian deposition at the study site aeolian activity appears to have continued to the present day showing a remarkably constant deposition rate of around 0 13 m kyr 1 initially increasing smoothly to the present until more palaeodunes in northern amazonia are dated it is impossible to determine if this record of gradual aeolian deposition is a reliable regional palaeoclimate indicator rather than being the result of local bioclimatic and geomorphological effects copyright 2004 john wiley sons ltd

early diagenesis atherton formation quaternary a guide for understanding early cement distribution and grain modifications in nonmarine deposits abstract the atherton formation represents an extensive sheet of outwash and related materials of quaternary age these sand q77f8r15 and gravel sediments are locally lithified and present an excellent opportunity for evaluating the effects of early diagenesis on a terrigenous deposit the principal cement present is calcium carbonate 98 occurring as euhedral to anhedral grain contact pore lining and porefilling varieties limonite and gypsum are present as rare cements cement distribution was controlled at various levels by 1 stratification character 2 grain size and sorting 3 framework grain composition and 4 proximity to near surface processes initial cement development and subsequent early growth were primarily parallel to laminae within beds this precipitation site preference is related to initially higher relative permeabilities estimated at 2 to 2 5 x parallel versus normal to stratification when associated with trough cross strata cements preferentially are located in the lower portion of troughs or directly below trough set boun aries there is a slight preference for early formed cements to be present along the axis instead of the flanks of a trough about 50 of pebble gravel and sandy pebble gravel units contain locally cemented zones while 17 of finer grain size strata are locally lithified over 95 of locally cemented units are within 7 m of the present ground surface suggestive of a causal relation to near surface perhaps soil related processes the sources for the various constituents composing cements are related to the dissolution of previously cemented layers and framework components such as carbonate rock fragments calcareous pelitic rock fragments and iron bearing silicate grains the examination of oversized voids elongate pores and intraparticle porosity suggests that at least locally multiple episodes of cementation followed by dissolution have taken place reactions between carbonate cement and limestone rock fragments have destroyed a high percentage of detrital carbonate grain boundaries such reactions combined with early dissolution can result in an information loss in excess of 50 of the limestone rock fragment component in a sandstone a combination of organic acids and co2 mixed with meteori waters is likely responsible for the dissolution and transportation of cement constituents

late pleistocene evolution of the mixed siliciclastic and carbonate southwestern new caledonia continental shelf lagoon abstract the main island of new caledonia nc is surrounded by the second largest barrier reef in the world after the australian great barrier reef the upper pleistocene evolution of this barrier reef lagoon complex offers the opportunity to examine the response of a modern mixed tropical siliciclastic carbonate system to relative sea level changes and to better constrain the relative role of lagoon backfilling and paleo drainage system in sediment transfer across the shelf this paper mainly focuses on the results of chronostratigraphic and sedimentological interpretations of new seismic bathymetric and coring data collected in the sw nc lagoon several significant points are highlighted from this study and allow the construction of a refined model which includes the evolution of both the sw nc mixed shelf and lagoon new results show that the nc lagoon has not recorded a reciprocal sedimentation during glacial interglacial sea level cycles but a unique mixed regime strong contrasts are observed and these depend above all on the two lagoon domains the outer coral plateau and the inner lagoon depression corresponding to a semi closed proximal basin which is separated from the plateau by a basement ridge in the depression clastic sediments remain dominant from early flooding to highstand stages while carbonate sedimentation continued through time across the coral plateau this spatial contrast between terrigenous and carbonate deposits was maintained throughout various sea level cycles thus even if spatial segregation is also observed for other examples of mixed shelf environments the sw nc shelf appears quite unique in comparison to the other mixed systems when considering conceptual models of reciprocal sedimentation moreover the presence of a semi enclosed lagoon depression allows the preservation of larger volume of terrigenous deposits this semi filled geometry of the lagoon is assumed to be the result of several factors a significant subsidence that offers accommodation for aggrading deposits evacuation through channels of sediments mobilized during storm events the tidal currents and fairweather wave dynamics lastly the inherited morphologic and structures may explain the geomorphic evolution of the escarpment margin type of the sw nc rimmed shelf and its differentiation with the opposite se nc ramp type shelf

seismic architecture and sediment distribution within the holocene barrier reef lagoon complex of mayotte comoro archipelago sw indian ocean twenty gravity cores and a large set of high resolution seismic profiles from various lagoonal settings were studied to determine the holocene sediment distribution and sequence architecture within the mayotte barrier reef lagoon complex the holocene seismic sequence comprises a type 1 sequence with lowstand transgressive and highstand systems tracts the lowstand systems tract consists of a paleosoil horizon formed during subaerial exposure the transgressive systems tract is composed of four depositional systems 1 inner transgressive layer 2 proximal and distal incised valley fills 3 mid lagoonal layer and 4 keep up or catch up fringing and barrier reef sequence the highstand systems tract comprises three depositional systems 1 of a proximal terrigenous wedge 2 mid lagoonal and distal carbonate sands or muds and 3 reefal carbonates our studies show that the nature of the holocene sequence is controlled by the rate and amplitude of sea level rise and environmental changes which are expressed by changes in clastic sediment supply and carbonate production the pre holocene topography and water dynamics steer the vertical and spatial sediment thickness distribution of the holocene additional important parameters are the proximity to a source area carbonate or terrigenous and the width of the depositional area climate dynamics are also of great importance while they determine carbonate production and terrigenous runoff sedimentation rates in the subtidal settings always lacked behind sea level rates thus a steep relief was created keeping most lagoonal parts within the deep subtidal realm in which sediment production was not efficient enough to fill up accommodation space in addition wave and or current energy might prevent the fill up of the lagoon this ultimately resulted in a typical empty bucket morphology only a high amplitude sea level fall would allow the subtidal lagoon to build up to base level unfilled accommodation space therefore must be a very common feature in the geologic record

a tracer study of the floridan aquifer in southeastern georgia implications for groundwater flow and paleoclimate distributions of stable isotopes of water radiocarbon noble gases and chloride c1 in groundwater from the upper floridan aquifer in southeastern georgia suggest that down gradient of the gulf trough this aquifer contains waters representative of both regional and local groundwater flow systems in this area locally recharged waters tend to remain near the top of the aquifer and do not mix substantially with the regional groundwater flow system noble gas temperatures suggest that this region of georgia was 4 0 0 6 c cooler during the last glacial period lgp similar temperature changes have been reported for southern texas and northern new mexico suggesting that the southern united states cooled uniformly during the lgp stable isotopes of water became enriched down gradient from the recharge area these enrichments which have been observed before appear to result from local influx of shallow groundwater into the regional aquifer system rather than representing a climate change signal an inland gradient of the stable isotope composition 0 60 0 14 100 km in 18o was found in young holocene water after correcting for the change in the stable isotope composition of the ocean during the lgp water that was recharged during the lgp was found to be slightly depleted in stable isotopes relative to modern recharge 18o 0 6 0 4 assuming the modern inland gradient the change in 18o is consistent with a shift in the coastline which was caused by the lower sea level during the lgp

dominant influence of volcanic loading on vertical motions of the hawaiian islands abstract rates of island vertical motion above intra plate hotspots record the processes that arise from interactions between lithospheric plates and mantle plumes to assess the contribution of mantle and lithospheric processes to surface motion above the hawaiian hotspot we compare simple models of lithospheric deformation to vertical motion rates measured from dated paleoshorelines and tide gauge records in the hawaiian islands our analysis shows that observed uplift and subsidence rates mainly record the flexural response of the lithosphere to volcanic loads the effective elastic plate thickness that best fits the spatial distribution of subsidence and uplift rates is 40 km consistent with previous estimates based on total vertical deflection because volcanic loading dominates the vertical motion signal hawaiian islands appear to follow a predictable trajectory of vertical motion when they reside within one flexural half wavelength of the active volcanic center islands initially subside at rapid and decreasing rates in the first 1 myr following their construction uplift relatively slowly 1 2 5 myr following their construction and eventually subside again but at slow rates within 5 myr of their construction this observed pattern of uplift and subsidence is consistent with the pattern of vertical motion predicted to result from volcanic loading at the hawaiian hotspot lithospheric migration over the long wavelength topographic swell associated with the hawaiian hotspot has a comparatively minor influence on island uplift and subsidence its contribution to island vertical motion is not readily observed in our data with the possible exception of some uplift observed in the past 500 kyr on o ahu that might correspond to non steady state behavior of the hawaiian plume

stable isotopic studies of palaeosol sediment from upper siwalik of himachal himalaya evidence for high monsoonal intensity during late miocene abstract palaeosols from sedimentary section exposed 2800 m at haripur kolar on somb river in himachal himalaya were studied for stable isotopes of carbon oxygen and hydrogen along with sr isotopic ratios stable isotopic studies of middle and upper siwalik sections from pakistan and nepal region have been used for inferring the palaeoclimate of the region during early and late miocene time the aim of our work was to extend this type of study to himachal himalaya india carbon isotopes in palaeosol carbonate nodule and associated organic matter indicate an abrupt transient of c3 vegetation dominance around 4 ma this transient disrupted the general trend of c4 ecological dominance observed from about 8 to 4 ma in this region of asian subcontinent we attribute this observation with the higher monsoonal intensity which also is supported by different archives from the region g bulloides abundance from dsdp core from the arabian sea and grass pollens abundances on land we propose that greater moisture availability around 4 ma due to higher monsoonal activity caused an abrupt transient of c3 dominance in this region the proposition is further supported by our data on 18o of carbonates and d of clay showing depletion around 4 ma observed high 87sr 86sr ratios in carbonates around the same time period suggest increased weathering and in turn higher rainfall activity

oxygen isotopic composition of carbonate concretions from the lower cretaceous of victoria australia implications for the evolution of meteoric waters on the australian continent in a paleopolar environment oxygen isotopic data from carbonate cements in concretions have been used to infer the isotopic composition of meteoric fluids present at the time of concretion growth in terrestrial sediments that were deposited within the early cretaceous south polar circle at 75 80 s carbon and oxygen isotope compositions have been determined on over 135 samples of carbonate from 45 concretions taken from 24 localities aptian albian in age in the terrestrial sedimentary basins associated with the otway and strzelecki groups southeastern australia the carbonate cements include calcite having 26 4 13c 19 6and3 6 18o 29 6 or siderite having17 6 18o 30 8 calcite cemented concretions are more abundant and are interpreted to represent early near surface cementation events on the basis of textural evidence such as high 30 porosities at the time of cementation and mineralogical evidence such as the preferential preservation within concretions of labile detrital grains including plagioclase pyroxene and amphibole the oxygen isotopic data indicate that meteoric fluids with very low 18o certainly less than 15 and probably on the order of 20 were involved in the precipitation of the early calcites the extremely low 18o values of the fluids involved in the early diagenesis of both the otway and strzelecki groups suggest that the catchment area of the river system that carried sediments to these basins had a cold high latitude climate with mean annual temperatures less than 5 c and quite possibly below freezing by analogy with the relationship between modern18o distribution of meteoric fluids and climate these new data suggest that the early cretaceous polar regions may not have been ice free

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

concretions in glacial sediments at seglvatnet norway abstract concretions in pleistocene glacial sediments at seglvatnet norway include a wide variety of forms the simplest of which apparently reflects relatively uniform growth rates in different directions the preferred orientation of others may be associated with water movement through the sediments concretion shape generally is influenced by the grain size and bedding of the enveloping sediments some concretions may have formed during or soon after deposition of the sediments others are forming at present

seismic evidence of glacial age river incision into the tahaa barrier reef french polynesia rivers have long been recognized for their ability to shape reef bound volcanic islands on the time scale of glacial interglacial sea level cycles fluvial incision of exposed barrier reef lagoons may compete with constructional coral growth to shape the coastal geomorphology of ocean islands however overprinting of pleistocene landscapes by holocene erosion or sedimentation has largely obscured the role lowstand river incision may have played in developing the deep lagoons typical of modern barrier reefs here we use high resolution seismic imagery and core stratigraphy to examine how erosion and or deposition by upland drainage networks has shaped coastal morphology on tahaa a barrier reef bound island located along the society islands hotspot chain in french polynesia at tahaa we find that many channels incised into the lagoon floor during pleistocene sea level lowstands are located near the mouths of upstream terrestrial drainages steeper antecedent topography appears to have enhanced lowstand fluvial erosion along tahaa s southwestern coast and maintained a deep pass during highstands upland drainages appear to contribute little sediment to refilling accommodation space in the lagoon rather the flushing of fine carbonate sediment out of incised fluvial channels by storms and currents appears to have limited lagoonal infilling and further reinforced development of deep barrier reef lagoons during periods of highstand submersion

foreland sedimentation in himalayan tectonic regime a relook at the orogenic process by raiverman v 2002 bishen singh mahendra pal singh publishers 23 a connaught place p o box 137 dehradun 248 001 india 378 pp price us 125

palaeoprecipitation record using o isotope studies of the himalayan foreland basin sediments nw india abstract the himalayan foreland basin sediments were deposited during a crucial time period in the himalayan orogeny this period in the tertiary has become major focus of research because of the large scale uplift of the himalayan range which has greatly modified the climate of the asian continent the present south asian monsoonal climate is believed to be a consequence of himalayan uplift during this period also the himalayan orogeny comprises a major regional tectonic event of the earth hence the study of these himalayan foreland basin sediments are not only significant in revealing the palaeoclimatic history of the asian continent but also paves a way for understanding of the effects of himalayan orogeny on global climate here we report a palaeoprecipitation history of the ramnagar sub basin since miocene times and its regional correlation to other sub basins of the himalayan mountain belt an attempt has been made to use oxygen isotope ratios of pedogenic carbonates in siwalik palaeosols as proxy palaeo recorders to deduce the palaeoclimatic history of the jammu region in the ramnagar sub basin for the first time a total of 141 pedogenic carbonates have been analyzed from three siwalik sections covering a lateral stretch of approximately 40 50km along strike the 18 o values vary from 12 31 to 5 89 and when plotted against age indicate that 18 o values on average become 2 enriched from the oldest to the youngest analyzed sediments except for largely depleted 18 o values around 10 ma 5 ma and 1 8 ma this 2 increase in calculated 18 o values could have been possible by an 3 c increase in mean annual air temperature conversely the largely negative 18 o values indicate periods of intense rainfall or stronger monsoonal conditions an increase of 2 6 in 18 o values has been found from the 10 ma rainfall event to that at 1 8 ma which indicates a reduction of 173 mm in rainfall intensity and amount hence precipitation reconstructions indicate a progressive increase in aridity from 12 ma to recent excluding a short term increases in rainfall or monsoon intensity at around 10 ma 5 ma and 1 8 ma this pattern of palaeoprecipitation change is similar to the changes documented in other sub basins of the himalayan mountain range further monsoon intensification at around 10 ma 5 ma and 1 8 ma is also observable in various other proxy records thereby suggesting the role of significant regional tectonism in the evolution and intensification of the present south asian monsoon climate our results indicate that from the mid miocene to recent except for the periods of largely depleted 18 o values the average 18 o value increased by 2 the general increase in average 18 o values from lower to upper siwalik sediments can be explained by changes in both continentality and latitude of the moisture source it seems likely that this long term increase in 18 o values was due to the uplift of the himalayas and the tibetan plateau in the north which acted as a barrier to the passage of airmasses from central asia in the north thereupon with time restricting the source of airmasses to the south from the indian ocean

contrasting diagenetic histories of concretions and host rock lion mountain sandstone cambrian texas white elliptical calcite cemented concretion nuclei up to 2 m long contrast markedly in color composition and diagenetic history from more glauconite rich concretion rinds and from dark green glaucarenite host rocks concretion nuclei are placers of loosely packed trilobite carapaces and minor quartz and glauconite tightly cemented with an average of 58 calcite cement the nuclei are shell lag deposits that were cemented by calcite at the sea floor or after burial of a few meters concretion rinds composed of sub equal amounts of quartz and compactionally deformed glauconite have an average of only 32 cement which consists of minor quartz overgrowths and later pore occluding calcite cement the rinds underwent burial for several million years to tens of million years to depths of several hundred meters before they were cemented the host rock is predominantly glauconite with very minor quartz and calcite cement 87 sr 86 sr ratios of host rock calcite cement are variable 0 7084 to 0 7093 but the lowest value suggests precipitation during the middle ordovician in the absence of significant amounts of carbonate cement the host rock underwent complete dissolution of trilobite carapaces and maximum compaction with total loss of porosity through squashing of glauconite grains maximum burial during this stage was completed by the end of ordovician time carbon and oxygen isotopic values of calcite from 16 samples show no differences between concretion nuclei rinds and host rocks 13 c ranges from 2 2 to 2 9 pdb and probably reflects derivation of carbon from trilobite carapaces and other skeletal grains 18 o ranges from 4 6 to 6 2 pdb and reflects either the original composition of the cement and trilobites or the modification of original grains by meteoric dominated ground water

oriented concretions ionian coast italy evidence of groundwater flow direction abstract highly elongate aligned calcite cemented concretions are present in exposed shallow marine pleistocene sands and gravels along the basilicata coast of the ionian sea southern italy concretions are shaped like rods pencils and cigars 0 5 3 cm in diameter and thin blades 031 cm thick and 1 5 cm wide most have aspect ratios greater than 5 and some reach 30 most concretions are in parallel laminated beds but a few are in cross stratified and ripple cross laminated beds concretions cut across foresets and inclined laminae the standard deviations of long axes at each of six localities with more than eight measurements are less than 7 the standard deviation of the orientation of concretions from 30 localities over a 400 km2 area is less than 17 previous interpretations for elongate carbonate concretions in sandstones include growth in the direction of groundwater flow growth parallel with current oriented grains and or paleocurrents and selective cementation in the troughs of wave ripples the basilicata concretions are oriented perpendicular to the local coastline and parallel with the direction of present day groundwater flow the groundwater flow direction was probably the same during the pleistocene the evidence indicates that the concretions grew parallel with groundwater flow and were not influenced by sedimentary structures or grain fabric the isotopic values 13c and 18o range from 10 to 1 pdb and from 5 to 3 pdb respectively and textures of calcite cement in the concretions indicate that the calcite was precipitated from meteoric groundwater nannobacteria may have mediated precipitation of calcite

paleomagnetic chronology fluvial processes and tectonic implications of the siwalik deposits near chinji village pakistan a 2800 m section of siwalik strata containing the stratotypes for both the chinji and nagri formations has been dated by magnetic polarity stratigraphy and the observed polarity zonation has securely been correlated with the chron 17 7 segment of the time scale the base of the section is the base of the kamlial formation which occurs near the top of chron 17 18 3 m y the kamlial chinji formation boundary occurs in the middle of chron 15 14 3 m y the chinji nagri boundary near the bottom of chron 10 10 8 m y and the nagri dhok pathan boundary at the chron 8 9 boundary 8 5 m y the siwalik deposits near chinji village consist of four distinct classes of fluvial cycles each with a characteristic periodicity a first order of 10 7 years a second order of 10 6 years a third order of 10 4 10 5 years and a fourth order of 10 0 10 4 years the river system responsible for siwalik sedimentation flowed from west to east and had properties much like the modern ganges river syste

depositional environment sediment provenance and oxygen isotope paleoaltimetry of the early paleogene greater green river basin southwestern wyoming u s a depositional process sediment provenance and paleotopography are critical to paleogeographic reconstruction during the coeval laramide and sevier orogenies in the cordillera orogenic system here we conduct lithofacies analysis sediment provenance and paleoelevation studies in the fluvial lower paleogene fort union and the main body of the wasatch formations in the center of the greater green river basin in order to reconstruct paleogeography the depositional environment changed from low energy floodplains and associated meandering river during the paleocene to braided rivers during the earliest eocene the lowermost eocene strata have more precambrian basement derived feldspar grains compared to the paleocene strata this change in sediment provenance was associated with the change to dominant northwestward paleoflow direction suggesting major uplift of the laramide uinta mountains during the earliest eocene the 18o values of authigenic carbonates were stable during the early paleocene but decreased gradually from 10 permil during the late paleocene to 18 permil during the earliest eocene suggesting the lack of highland precipitation in the basin catchment during the early paleocene and significant surface uplift and arrival of highland precipitation from the uinta mountains during the earliest eocene the reconstructed paleoelevation of the uinta mountains was at least 3 km possibly greater than 3 5 km and the paleoelevation of the greater green river basin floor was at most 1 km and the paleorelief between the greater green river basin and uinta mountains was 2 km during the earliest eocene our record of the earliest eocene establishment of high topography of the uinta mountains through renewed uplift is 4 to 6 myr older than previously thought if the carbonate cements in the fort union formation record the isotope compositions of surface water from the sevier orogen their high 18o values likely suggest that the sevier orogen had rugged topography during the paleocene

a 300 000 yr coral reef record of sea level changes mururoa atoll tuamotu archipelago french polynesia abstract the accurate dating of fossil coral reefs is of prime importance in determining the timing of deglaciation events and thus understanding the mechanisms driving glacial interglacial cycles so far the most useful coral reef records of past sea level changes are those related to the last deglaciation and the last interglacial period u th ages for older isotopic stages are more limited due to the scarcity of datable material reflecting diagenetic alteration most data are from emergent parts of reefs and reef terraces in active subduction zones where relative sea level records may be biased by variations in rates of tectonic uplift new constraints on sea level changes over the past 300 000 yr are based on high precision u series age measurements of successive reef units on mururoa these have been cored in four continuous 300 m long drill holes with seaward inclinations of 30 to 45 on the northeastern rim of the atoll past sea level positions have been calculated from the radiometric ages of corals by correcting the present depth of subsurface horizons both for thermal subsidence and for depositional palaeodepth the location of this atoll at a considerable distance from former ice sheets far field minimises the influence of glacio isostatic rebound prominent units formed during four periods of relative sea level highstands including the holocene and stages 5 125 ka 7 212 ka and 9 332 ka these are primarily composed of coralgal frameworks that grew in very shallow water three periods of relative low stand correspond to stages 2 17 23 ka 4 60 ka and 8 270 ka during which small reefs developed in association with large bioclastic accumulations good agreement with the timing of sea level changes based on oxygen isotope measurements in deep sea cores is noted for most of the dated reef units we report here the first accurate coral record of the last glacial maximum in the pacific 135 143 m below the present sea surface suggesting that sea level may have been lower than expected during this period

amazonian paleodunes provide evidence for drier climate phases during the late pleistocene holocene abstract recent studies on relict eolian dunes in the rio negro basin northern amazon brazil 00 35 n 63 14 w indicate a drier climate regime during the late pleistocene holocene transition that is different from the present humid climate the eolian sands form long chains of linear dunes bordering the rio negro river and some tributaries here we present thermoluminescence tl ages spanning the period 32 000 8000 yr b p the final dune stabilization took place after 8 000 yr b p and now the bases of the dunes are fixed by vegetation clustering of the tl dates suggests that the dry climate in the amazon basin occurred in distinct episodes and argues against current opinions that drastic ecological changes did not affect in the amazon during the last global glaciation

reply to terry j and goff j comment on late cenozoic sea level and the rise of modern rimmed atolls by toomey et al 2016 palaeogeography palaeoclimatology palaeoecology 4 51 73 83 this paper is not subject to u s copyright the definitive version was published in palaeogeography palaeoclimatology palaeoecology 469 2017 159 160 doi 10 1016 j palaeo 2016 11 028

methodological considerations in the optical dating of quartz abstract the optically stimulated luminescence from quartz grains extracted from sediments at two archaeological sites has been studied the sites were the upper palaeolithic site at hengistbury head dorset u k and the upper aterian site at chaperon rouge morocco problems associated with the technique of optical dating are discussed particularly the thermal treatment that is necessary to remove thermally unstable charge following artificial irradiation and the extrapolation of growth curves to estimate the equivalent dose the technique used is described and some preliminary dates are presented