geochemical constraints on mode of extension in the death valley region the petrographic chemical and isotopic characteristics of synex tensional miocene pliocene volcanic rocks of the nova formation death valley area record interaction of three components two of these are ancient crust and enriched mantle they have been recognized previously in the basin and range province the third component is isotopically similar to rocks of the sierra nevada batholith exposed to the west of the study area the authors interpret this source to be the mantle lithosphere and or lower crust of the sierra nevada batholith that was emplaced beneath the death valley area by extensional deformation this is consistent with 150 to 250 km of extension across the southern basin and range province inferred from other evidence and supports the conclusions of workers who suggest that the dominant mode of crustal extension in this area is simple shear with large amounts of lateral lithospheric transport

core and intact polar glycerol dialkyl glycerol tetraethers gdgts in sand pond warwick rhode island usa insights into the origin of lacustrine gdgts branched and isoprenoidal glycerol dialkyl glycerol tetraethers gdgts are abundant in lake sediments and have potential use for determining past changes in climate and limnology however emerging evidence suggests that both classes of gdgts can be associated with both allochthonous soil organic matter and in situ production potentially complicating interpretation of these compounds in lacustrine sedimentary environments here we investigate the dual source issue surrounding lacustrine gdgts with an emphasis on the branched gdgts by studying both core and intact polar gdgts within a pond and its watershed in warwick ri significant differences in both absolute concentrations of branched gdgts and the percent of branched gdgts present as ipls between the soils and shallow lake sediments suggests in situ production of these compounds within the lake environment principal components analysis of gdgt lipid concentrations and environmental parameters in sand pond sediments and soils highlights two prominent trends in the data one related to the absolute concentrations of type i branched gdgts brgdgt i ib ic and the majority of the isoprenoidal gdgts and another related to the concentration of the more methylated type iii branched gdgts brgdgt iii iiib iiic and isoprenoidal gdgt 0 the latter trend exhibits a subsurface maximum in the sediment column potentially indicating in situ production of more highly methylated branched gdgts and gdgt 0 within the lacustrine sediment column trends in the distributions of branched gdgts as reflected by the mbt and cbt indices imply mixing of two distinct sources of branched gdgts soil derived and in situ or alternatively two or more different microbial producers both possibilities present a challenge to the application of brgdgt based paleoenvironmental proxies in lakes this study highlights the importance of determining the sources of gdgts to the lacustrine environment prior to paleoenvironmental application

a lacustrine gdgt temperature calibration from the scandinavian arctic to antarctic renewed potential for the application of gdgt paleothermometry in lakes quantitative climate reconstructions are fundamental to understand long term trends in natural climate variability and to test climate models used to predict future climate change recent advances

a retreating fan delta system in the neoproterozoic chattisgarh rift basin central india major controls on its evolution a thick wedge of immature siliciclastics characterizes the basal part of the basin fill succession in the eastern part of the neoproterozoic chattisgarh basin it comprises a mosaic of mass flow deposited conglomerate and pebbly sandstone coarse grained sandy braided stream deposits wave lag pebble sheets high energy wave dominated foreshore and upper shoreface facies and wave and tide dominated lower shoreface facies the succession is characterized by strong lateral and vertical facies variation the facies associations and stacking pattern point to the development of an alluvial fan to fan delta complex with outbuilding of delta lobes onto a high energy shallow marine shelf via a high gradient narrow delta plain the delta front deposits of coarse grained sand interfinger and grade into prodelta mud in the seaward direction the dominance of coarse grained sandy detritus with a high content of fresh feldspar grains points to mechanical weathering of granites and gneisses of the cratonic basement and a semiarid climate the sediment caliber and the climate exerted a major control on the facies and on processes of sediment transfer from the fan to the shelf a critical balance between progradation aggradation and retrogradation controlled the evolution of delta successions within an overall transgressive regime related to the extension of a cratonic rift basin repeated fault controlled uplift of the source followed by subsidence and transgression generated multiple fining upward cycles and a retreating fan delta system the marked variations in thickness of the delta succession and the stacking pattern in different measured profiles reflect the overriding tectonic controls on delta evolution the accumulated fault displacement in active sectors created higher accommodation and thicker delta sequences intermittent uplift of fault blocks exposed fresh bedrock to mechanical weathering generated a large amount of detritus and resulted in forced regressions repeatedly disrupting the fining upward pattern the controls of source rock lithology or climate were of secondary importance to tectonic effects retreating fan deltas are rarely reported and may be a stratigraphic response of marine connected rift basins at the early stage of extension the delta stratigraphy is analogous to the submarine fan stratigraphy in the case where basin shales act as hydrocarbon sources the fan deltas are potential hydrocarbon reservoirs the coarse grained lobes can be excellent reservoirs with the enclosing prodelta muds acting as seals to vertical migration of hydrocarbon the coarse grained deposits of the delta plain and proximal delta front occurring as laterally coalesced large sand bodies blanketed by transgressive prodelta mud might also form good reservoirs

distributions and temperature dependence of branched glycerol dialkyl glycerol tetraethers in recent lacustrine sediments from china and nepal 1 glycerol dialkyl glycerol tetraether gdgt membrane lipids in surface sediments from 24 lakes in china and nepal were analyzed the result shows that branched gdgt lipids occur widely in the studied lake sediments the different distribution of branched gdgts between the chinese soils from weijers et al 2007b and the chinese lake sediments indicates that the branched gdgts in the lacustrine sediment are the mixture of allochthonous and autochthonous branched gdgts our result supports the suggestion that temperature is the principal factor affecting the distribution of gdgts seasonality sources and precipitation increase the uncertainty of the correlation between the methylation index of branched tetraethers mbt cyclization ratio of branched tetraethers cbt proxy and the temperature the correlations of the mbt cbt index with mean annual air temperature t for the global lakes are t 6 803 7 062 cbt 37 090 mbt n 139 p 0 0001 r2 0 62 and rmse 5 24 c for the global lakes with ph 8 5 t 3 949 5 593 cbt 38 213 mbt n 100 p 0 0001 r2 0 73 and rmse 4 27 c the significant correlation suggests that the mbt cbt proxy might be used as a potential paleotemperature proxy in the limnic environment the mbt cbt proxy provides an independent way to evaluate and verify the sensitivities of the different proxies for paleotemperature reconstruction from lacustrine sediments

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

middle and late holocene paleotemperatures reconstructed from oxygen isotopes and gdgts of sediments from lake pupuke new zealand abstract quantitative holocene temperature reconstructions for southern hemisphere terrestrial environments are still restricted to few records and multi proxy methods are rarely applied to the same system here we test the applicability and comparability of temperature reconstructions inferred from different methodological approaches we combined sedimentary cellulose and diatom oxygen isotope data from lake pupuke north island new zealand to derive a record of lake water temperatures this record is complemented with mean annual air temperatures derived from the branched gdgt index mbt measured on the same sedimentary record the datasets of both reconstructions show little temperature variation for the period 1320 7110 cal bp the exceptions are a warmer period culminating between 1700 and 1600 cal bp reflected in both proxies and centennial scale intervals with cooler water temperatures at 3380 and 2750 cal bp recorded in the oxygen isotope based temperature reconstruction but not in the mbt inferred air temperature estimates we suggest that variations in lake circulation are the likely reason for deviations between temperature reconstructed from different proxies

a 15 ka ph record from an alpine lake in north china derived from the cyclization ratio index of aquatic brgdgts and its paleoclimatic significance abstract a well dated sediment core from an alpine lake in north china gonghai lake was used for analysis of branched glycerol dialkyl glycerol tetraether lipids brgdgts based on the cyclization ratio index cbt of the brgdgts and using different terrestrial and lacustrine cbt ph empirical relationships the reconstructed ph records over the past ca 15 ka exhibited similar trends of variation although the absolute ph values were different in order to better understand the reconstructed ph record samples of surface soils from the dust source area and the catchment of gonghai lake as well as surface sediments from the lake were collected for instrumental ph measurements and modern brgdgt analysis the instrumental ph results demonstrated that the surface soils from the dust source area were alkaline while those from the catchment of gonghai lake were acidic in addition the instrumental ph results for the surface sediments from the lake were slightly alkaline and the corresponding ph values were intermediate between those of the two surface soil source groups this may reflect the effect of the input of material from different sources on the sedimentary ph record however the results from modern brgdgts in some of the surface soils and surface sediment samples demonstrate that brgdgts in the core sediments from gonghai lake are predominantly of aquatic origin therefore the cbt derived ph record over the past ca 15 ka from the lake can be interpreted as a record of the lake water ph history which is consistent with the carbonate content record from a parallel core from the same lake in addition using the modern lacustrine calibration the cbt derived ph values for surface sediments of gonghai lake are consistent with instrumental modern lake water ph values for the lake further comparison indicates that the lake water ph is controlled mainly by the degree of humidity of the local climate which is closely related to the intensity of the east asian summer monsoon easm therefore the ph record can be used as an indicator of easm intensity our results demonstrate that on the basis of careful analysis of its origins the cbt index of aquatic brgdgts can be used for lake water ph reconstruction and subsequent paleoclimate reconstruction and that in north china the lake water ph is controlled mainly by the degree of humidity of the local climate

temperature fluctuations during the common era in subtropical southwestern china inferred from brgdgts in a remote alpine lake abstract documenting climate change over the past 2000 years or the common era is critical to understand how the climate system evolved from one controlled by natural forcings alone to one influenced by anthropogenic greenhouse gas forcing however global and regional temperature changes during this interval are still poorly understood largely due to the limited geographical coverage and scarcity of data here we report a well dated quantitative mean annual air temperature maat record with 10 yr resolution for the common era derived from a sediment core collected at a small alpine lake in remote subtropical southwestern china and based on a site specific temporal calibration between down core analyses of brgdgts and instrumental data for the interval 1959 2015 ad the record reveals distinct multicentennial scale temperature fluctuations including a relatively cold interval from 0 800 ad followed by warmer temperatures during the so called medieval climate anomaly mca 800 1400 ad cooling during the little ice age lia 1400 1900 ad and abrupt and rapid warming into the late 20th century after 1900 ad superimposed on these large scale features are three short term cold events centered on 250 310 ad 0 06 c 570 650 ad 0 87 c and 1800 1823 ad 0 83 c respectively the temperature variations captured in the record are supported by historical documents and existing regional and global paleoclimate records and correspond in time to a number of the major chinese dynastic transitions importantly the record captures large magnitude up to 4 c centennial scale temperature fluctuations documents cold conditions during the first millennium ad and demonstrates that the post 1989 ad warmth is greater than any other time during the past 2000 years the results suggest that high elevation areas have been more sensitive than low elevation regions to climate variations during the common era

environmental controls on branched tetraether lipid distributions in tropical east african lake sediments abstract quantifying past continental temperature changes is an important aspect of paleoclimate research as it allows us to constrain the amplitude of natural variability test predictive climate models and provide a proper context for changes that may arise in response to anthropogenically induced climate change the recently developed biomarker based methylation index of branched tetraethers cyclization ratio of branched tetraethers mbt cbt proxy shows potential as a new method for continental temperature reconstruction but thus far it has only been applied successfully in ocean margin sediments to assess whether this proxy is also applicable to the sedimentary record in tropical lacustrine systems we investigated the distribution of branched glycerol dialkyl glycerol tetraethers gdgts in recently deposited sediments from 46 lakes in tropical east africa these lakes span a substantial range in surface elevation 770 4500 m above sea level and thus also a wide gradient of mean annual temperature we find that saline lakes excepted branched gdgts are universally abundant in the lakes investigated and can be used to predict mean annual air temperature maat with a high degree of accuracy however the existing global mbt cbt calibration for maat based on soils predicts inaccurate temperatures when applied to our african lake dataset this observation together with the fact that surface water ph and to lesser extent lake depth appear to influence the distribution of branched gdgts among sites leads us to conclude that in situ production of branched gdgts in lakes is likely the robust relationship between branched gdgt distribution and the temperature and ph of african freshwater lakes makes these compounds suitable for paleoenvironmental reconstruction however we urge caution in using branched gdgts in lake sediments to infer past temperatures unless their exact origin can be determined

temperature variations in the southern great lakes during the last deglaciation comparison between pollen and gdgt proxies abstract our understanding of deglacial climate history in the southern great lakes region of the united states is primarily based upon fossil pollen data with few independent and multi proxy climate reconstructions here we introduce a new well dated fossil pollen record from stotzel leis oh and a new deglacial temperature record based on branched glycerol dialkyl glycerol tetraethers brgdgts at silver lake oh we compare these new data to previously published records and to a regional stack of pollen based temperature reconstructions from stotzel leis silver lake and three other well dated sites the new and previously published pollen records at stotzel leis are similar but our new age model brings vegetation events into closer alignment with known climatic events such as the younger dryas yd brgdgt inferred temperatures correlate strongly with pollen based regional temperature reconstructions with the strongest correlation obtained for a global soil based brgdgt calibration r2 0 88 lending confidence to the deglacial reconstructions and the use of brgdgt and regional pollen stacks as paleotemperature proxies in eastern north america however individual pollen records show large differences in timing rates and amplitudes of inferred temperature change indicating caution with paleoclimatic inferences based on single site pollen records from 16 0 to 10 0ka both proxies indicate that regional temperatures rose by 10 c roughly double the 5 c estimates for the northern hemisphere reported in prior syntheses change point analysis of the pollen stack shows accelerated warming at 14 0 1 2ka cooling at 12 6 0 4ka and warming from 11 6 0 5ka into the holocene the timing of bolling allerod b a warming and yd onset in our records lag by 300 500 years those reported in syntheses of temperature records from the northern mid latitudes this discrepancy is too large to be attributed to uncertainties in radiocarbon dating and correlation between pollen and brgdgt temperature reconstructions rules out vegetation lags as a cause however the yd termination appears synchronous among the brgdgt record regional pollen stack and northern hemisphere stack the cause of the larger and lagged temperature changes in the southern great lakes relative to northern hemisphere averages remains unclear but may be due to the effects of continentality and ice sheet extent on regional climate evolution

petrological and geochemical evidence of the paleoproterozoic and the meso neoproterozoic sedimentary rocks of the bastar craton indian peninsula implications on paleoweathering and proterozoic crustal evolution the petrology and geochemistry of the sandstones and shales of the meso neoproterozoic chattisgarh and indravati basins and the pelites and quartzites of the paleoproterozoic sakoli and sausar basins of the bastar craton have been studied for the paleoweathering tectonic setting and to delineate sediment source components and finally to trace the proterozoic crustal evolution in the bastar craton indian peninsula the geochemical data shows decrease in the abundance of mafic major elements and transition elements and an increase in the large ion lithophile elements liles from the paleoproterozoic pelites to the meso neoproterozoic shales this suggests partial exposure of granitoids in the paleoproterozoic and unroofing of the granitoids by the complete removal of mafic rocks in the provenance as the meso neoproterozoic sedimentation progressed overall the study of the meso neoproterozoic sandstones and shales show homogeneity in the source rock composition with strong felsic component however the paleoproterozoic pelites and quartzites show heterogeneity in the source rock composition with mixture of the felsic and mafic components geological geochemical and petrographic evidences indicate that the sediments in the paleoproterozoic sakoli and sausar basins and the meso neoproterozoic chattisgarh and indravati basins have been deposited in passive margin tectonic settings cratonic basins or intra cratonic rifts the relationship among alkali and alkaline earth elements cia pia and the th u ratio indicate that the source area was affected by moderate to intense weathering history

isoprenoid and branched gdgt based proxies for surface sediments from marine fjord and lake environments in chile abstract proxies based on glycerol dialkyl glycerol tetraether gdgt lipids from archaea isoprenoid gdgts and bacteria branched br gdgts in 33 surface sediments from marine fjord and lake systems between 25 s and 50 s in chile were analyzed the regional texh86 calibration obtained from the marine and fjord sediments and mean annual surface temperature t 59 6 texh86 33 0 r2 0 9 n 23 is statistically identical to the global ocean calibration based on suspended particulate material in terms of slope but not in terms of intercept the regional surface and subsurface texh86 calibrations were statistically different from the existing global ocean core top calibrations the tex86 calibration model based on most of the relatively large lakes studied here t 50 7 tex86 11 8 r2 0 9 n 5 is statistically identical to the global lake calibration the relatively high tex86 values from smaller lakes suggested an additional source for isoprenoid gdgts likely terrestrial or aquatic methanogenic archaea application of the soil calibrated mbt cbt methylation and cyclization of br gdgts respectively temperature proxy to the marine and fjord sediments resulted in an overestimation of continental mean annual air temperature maat suggesting in situ production of certain br gdgts in the water column or surface sediment for the lakes mbt cbt based surface air temperature estimates were 3 6 c below maat however temperature estimates from the lake specific mbt cbt global calibration were in good agreement with mean annual surface temperature for all the lakes the results highlight the need for testing local vs global calibrations of gdgt based proxies before their application for palaeoenvironmental reconstruction

coupled thermal and hydrological evolution of tropical africa over the last deglaciation we analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the congo river outflow and the results enabled us to reconstruct large scale continental temperature changes in tropical africa that span the past 25 000 years tropical african temperatures gradually increased from 21 to 25 c over the last deglaciation which is a larger warming than estimated for the tropical atlantic ocean a direct comparison with sea surface temperature estimates from the same core revealed that the land sea temperature difference was through the thermal pressure gradient an important control on central african precipitation patterns

fluxes and distribution of tetraether lipids in an equatorial african lake constraints on the application of the tex86 palaeothermometer and bit index in lacustrine settings abstract the distribution of isoprenoid and branched glycerol dialkyl glycerol tetraether gdgt lipids was studied in material from various sources in and around lake challa a crater lake on the southeastern slope of mt kilimanjaro tanzania to examine the provenance of gdgts in lake sediments and their potential application as palaeoenvironmental and palaeoclimatic proxies the study material included samples collected at monthly intervals in a sediment trap over one complete annual cycle particles suspended in the stratified water column profundal surface sediments and soils surrounding the lake the sediment trap time series revealed that crenarchaeol and related isoprenoid gdgts were predominantly produced in january and february following the locally prominent short rain season november december the tex 86 inferred temperature derived from sedimenting particles corresponded well with lake surface water temperature at this time of largest crenarchaeol flux molecular ecological analysis showed that group 1 1a and 1 1b crenarchaeota are the most likely source organisms of these gdgts gdgt 0 in the lake sediments does not only originate from lake surface dwelling crenarchaeota but seems predominantly derived from archaea residing in the deeper anoxic part of the water column the main flux of branched gdgts to the sediment was during the short rain season and is most probably derived from eroded catchment soils in surface run off however a contribution from in situ production of branched gdgts in the lake sediment or water or in groundwater cannot be fully excluded we conclude that palaeoclimatic reconstruction based on branched gdgt distributions in lake sediments should only be performed when the origin of those branched gdgts is well constrained

fluvial architecture of early permian barakar rocks of korba gondwana basin eastern central india abstract the early permian barakar formation of the korba basin represents repeated deposition of fining upward sequences of coarse to medium grained sandstone fine grained sandstone shale shale and coal the sandstones are channel sheet like multistory and profusely cross bedded the shale beds are lens as well sheet like and laminated coal facies is thin to moderately thick and shows splitting paleocurrent analysis suggests a northwesterly paleoslope during barakar sedimentation however the deflection of paleoslope towards northeast in the eastern part of the basin supports the existence of a watershed in the depositional area the barakar paleochannel were 4 05 m deep and 176 m wide single channel with an average sinuosity of 1 27 the average flow velocity and sediment load during flood stage are in the order of 1 77 m s and 4 15 these results indicate bed load braided to mixed load nature of the barakar streams of the korba basin the study suggests that the early permian braided barakar streams deposited the coal measure sequence subsequent to deglaciation in a northwesterly slopping paleovalley the basin floor was highly uneven marked by the presence of a basement high in the northwestern part that bifurcates the paleostreams into northwestern and northeastern branches

evaluation of leaf wax δd and soil brgdgts as tools for paleoaltimetry on the southeastern tibetan plateau abstract the orogenic history of the tibetan plateau tp and surrounding mountain ranges continues to be a major source of disagreement among geologists particularly concerning the uplift models for the cenozoic evolution of the tp and estimates for when the highest and largest plateau on earth reached its current elevation quantitative reconstructions of past elevation from geologic samples are necessary to document the uplift history of tp and examine the interactions between tectonic relief and climate over geological time scales several studies establishing lipid biomarker based paleoaltimetry based on leaf wax d values and brgdgts have been reported in recent years for the tp and surrounding regions but have yet to be synthesized into a regional framework for paleoelevation determination and uncertainty analysis here we report new leaf wax d and brgdgts data developed from surface soil samples along an elevation transect spanning 1250 3900 m a s l in the hengduan mountains on the southeastern edge of the tp we find that the abundance weighted mean leaf wax d n c27 n c29 and n c31 values dwax lapse rates determined for the hengduan mountains and for five other nearby study locations are statistically indistinguishable and can be combined to provide a regional dwax lapse rate of 1 97 0 04 1 100 m for use in regional paleoelevation studies across the southeastern tp we also find a strong correlation r2 0 71 between brgdgts and elevation dependent mean annual air temperature which contributes to a number of studies in the region that support the use of fossil brgdgts as a paleoelevation proxy our results reveal that dwax and brgdgts for the hengduan mountains provide similar empirical uncertainty in paleoelevation reconstruction with standard errors of elevation estimation se of 483 m 1 and 394 m 1 respectively we propose a paleoaltimetric approach that combines dwax and brgdgt data in order to derive paleoelevation estimates with lower uncertainties in the hengduan mountains data set the approach yields a se 286 m 1 that is 27 40 lower than when dwax values and brgdgts are applied separately

distributions of branched gdgts in soils and lake sediments from western uganda implications for a lacustrine paleothermometer bacterially produced branched glycerol dialkyl glycerol tetraethers gdgts are ubiquitous in soils and lake sediments and can potentially be used to reconstruct past temperatures in lakes however it is still unclear if these compounds are derived from eroded soils or if they are produced in situ to better understand environmental controls on the distributions of these compounds and the sources of branched gdgts to lake sediments we compare branched gdgt distributions and concentrations in lake sediments and catchment soils within a 3600 m altitudinal transect in western uganda reconstructed mean annual air temperature maat determined from the degree of methylation mbt and cyclisation cbt of branched gdgts in soils decreases with increasing altitude as is expected from the air temperature gradient in our transect however we observe significant offsets between observed and reconstructed temperatures in soils from wet high elevation soils but not in most dry low elevation soils branched gdgt distributions differ significantly between lake sediments and soils at all elevations with greater differences at low elevations than at high elevations these data support previous hypotheses that branched gdgts are produced in situ in lakes and suggest that the abundance of water in soil environments may play a role in controlling the distribution of branched gdgts while branched gdgts in lacustrine sediments can be used to reconstruct temporal temperature variations in lakes we urge caution in utilizing this proxy in lacustrine systems with high soil loadings especially if there is evidence of changing clastic fluxes through time

impact of riverine suspended particulate matter on the branched glycerol dialkyl glycerol tetraether composition of lakes the outflow of the selenga river in lake baikal russia branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids found in several environments including soils rivers and lakes whose distribution varies with temperature and ph although this dependence is apparently not the same for the different environments mixing of brgdgt sources may thus complicate palaeoenvironmental reconstruction the extent to which brgdgts in a lake outflow reflect the distribution delivered by upstream rivers was studied for lake baikal russia one of the largest freshwater lakes worldwide fifteen brgdgts in suspended particulate matter spm of the selenga river and its outflow from the lake were quantified the river and lake spm had rather different distributions the riverine distribution was still apparent in the spm of the lake surface water 5 km from the river mouth but shifts in the distribution were already apparent in the spm of the surface water after 1 km based on the brgdgt distributions of the spm of the selenga outflow and that of the lake conservative mixing between the river and the lake brgdgt distributions could not fully explain the observed shifts in distributions both preferential degradation and in situ production of brgdgts in the surface and especially bottom water of the river outflow were potentially responsible this implies that a riverine lipid distribution delivered to a lake can be modified prior to being transported downstream the lacustrine brgdgt distribution that possibly could have reflected a mixture of mountainous and selenga river spm was not recognized in downstream yenisei river spm the watershed of lake baikal thus does not seem to contribute to the brgdgts transported to the marine system as many large rivers have major lakes in their watershed this has implications for palaeoclimate reconstruction from river fan sediments globally

decoupled warming and monsoon precipitation in east asia over the last deglaciation our understanding of the continental climate development in east asia is mainly based on loess paleosol sequences and summer monsoon precipitation reconstructions based on oxygen isotopes delta o 18 of stalagmites from several chinese caves based on these records it is thought that east asian summer monsoon easm precipitation generally follows northern hemisphere nh summer insolation however not much is known about the magnitude and timing of deglacial warming on the east asian continent in this study we reconstruct continental air temperatures for central china covering the last 34 000 yr based on the distribution of fossil branched tetraether membrane lipids of soil bacteria in a loess paleosol sequence from the mangshan loess plateau the results indicate that air temperature varied in phase with nh summer insolation and that the onset of deglacial warming at similar to 19 kyr bp is parallel in timing with other continental records from e g antarctica southern africa and south america the air temperature increased from is c at the onset of the warming to a maximum of 27 degrees c in the early holocene similar to 12 kyr bp in agreement with the temperature increase inferred from e g pollen and phytolith data and permafrost limits in central china comparison of the tetraether membrane lipid derived temperature record with loess paleosol proxy records and stalagmite 5180 records shows that the strengthening of easm precipitation lagged that of deglacial warming by ca 3 kyr moreover intense soil formation in the loess deposits caused by substantial increases in summer monsoon precipitation only started around 12 kyr bp ca 7 kyr lag our results thus show that the intensification of easm precipitation unambiguously lagged deglacial warming and nh summer insolation and may contribute to a better understanding of the mechanisms controlling ice age terminations

vertical and temporal variability in concentration and distribution of thaumarchaeotal tetraether lipids in lake superior and the implications for the application of the tex86 temperature proxy abstract this study investigated the vertical and temporal distribution of thaumarchaeota derived core isoprenoid glycerol dialkyl glycerol tetraether gdgt lipids through sampling and analysis of both suspended particulate matter from the water column at different times in the annual cycle and a 3 year long record of settling particles in two sediment traps at different depths at an open lake location in lake superior results from these analyses suggest that thaumarchaeota were present throughout the water column during times of overturning but mainly resided below the depth of the thermocline 20 40 m during the period of thermal stratification fluxes of thaumarchaeotal produced gdgts were highly periodic and mainly occurred during two periods of the annual cycle winter and late spring early summer a covariance of both branched and isoprenoid gdgt fluxes with the mass accumulation flux combined with the observation that those periods of maximum fluxes were associated with increased bit index values however suggest that these two periods of elevated fluxes may be related to an influx of resuspended particles transported from shallower near shore regions of lake superior during all sampling periods tex 86 inferred temperatures from spm were in good agreement with in situ water temperatures of the depths at which the spm was sampled the observed range of tex 86 inferred temperatures in 3 years of settling particles is relatively small and does not show significantly higher inferred temperatures during the thermally stratified period indicating that the sedimentary tex 86 signal during the summer thermally stratified period mainly originated from depths below the relatively shallow thermocline additionally tex 86 values during the winter period of increased fluxes did not capture the decrease in water temperatures observed throughout the water column during this period and thus may be a further indication that the thaumarchaeotal lipid flux was the result of sediment focusing flux weighted tex 86 inferred temperatures from both sediment traps were in good agreement with tex 86 temperatures from surface sediments from the same location in lake superior both flux weighted tex 86 temperatures from the sediment traps and average tex 86 temperatures from surface sediments were similar to averaged measured water temperatures at below 40 m depth within the error of the lacustrine tex 86 calibration based on the observed depths of thaumarchaeota in the water column tex 86 values in sediments of lake superior likely reflect a combination of mixed season and sub thermocline temperatures this is effectively the same as the annual averaged water temperature observed at depths below 40 m in lake superior thus trends in tex 86 inferred temperatures in sediment records of lake superior and similar lakes are likely to reflect subsurface temperature variability rather than that of surface temperatures

evidence from the lamarck granodiorite for rapid late cretaceous crust formation in california strontium and neodymium isotopic data for rocks from the voluminous 90 million year old lamarck intrusive suite in the sierra nevada batholith california show little variation across a compositional range from gabbro to granite data for three different gabbro intrusions within the suite are identical within analytical error and are consistent with derivation from an enriched mantle source recognition of local involvement of enriched mantle during generation of the sierran batholith modifies estimates of crustal growth rates in the united states these data indicate that parts of the sierra nevada batholith may consist almost entirely of juvenile crust added during cretaceous magmatism

extended megadroughts in the southwestern united states during pleistocene interglacials the potential for increased drought frequency and severity linked to anthropogenic climate change in the semi arid regions of the southwestern united states us is a serious concern1 multi year droughts during the instrumental period2 and decadal length droughts of the past two millennia1 3 were shorter and climatically different from the future permanent dust bowl like megadrought conditions lasting decades to a century that are predicted as a consequence of warming4 so far it has been unclear whether or not such megadroughts occurred in the southwestern us and if so with what regularity and intensity here we show that periods of aridity lasting centuries to millennia occurred in the southwestern us during mid pleistocene interglacials using molecular palaeotemperature proxies5 to reconstruct the mean annual temperature mat in mid pleistocene lacustrine sediment from the valles caldera new mexico we found that the driest conditions occurred during the warmest phases of interglacials when the mat was comparable to or higher than the modern mat a collapse of drought tolerant c4 plant communities during these warm dry intervals indicates a significant reduction in summer precipitation possibly in response to a poleward migration of the subtropical dry zone three mat cycles 2 c in amplitude occurred within marine isotope stage mis 11 and seem to correspond to the muted precessional cycles within this interglacial in comparison with mis 11 mis 13 experienced higher precessional cycle amplitudes larger variations in mat 4 6 c and a longer period of extended warmth suggesting that local insolation variations were important to interglacial climatic variability in the southwestern us comparison of the early mis 11 climate record with the holocene record shows many similarities and implies that in the absence of anthropogenic forcing the region should be entering a cooler and wetter phase

northeast african temperature variability since the late pleistocene abstract the development and application of lacustrine paleotemperature proxies based on microbial membrane lipid structures including the tex86 and branched glycerol dialkyl glycerol tetraether brgdgt paleothermometers have greatly advanced our understanding of the late glacial and postglacial temperature history of africa however the currently available records are from equatorial and southern hemisphere sites limiting our understanding of the spatial patterns of temperature change here we use the brgdgt paleotemperature proxy to reconstruct late pleistocene and holocene temperatures from lake tana ethiopia 12 n 37 e following the termination of heinrich stadial 1 at 15 ka lake tana experienced a 3 7 c oscillation over 1 2 ky temperatures then increased abruptly by nearly 7 c between 13 8 and 13 0 ka followed by a slow warming trend that peaked during the mid holocene temperatures subsequently cooled from 6 ka to 0 4 ka these data indicate that temperature at lake tana was sensitive to climate changes caused by variations in the atlantic meridional overturning circulation during the late pleistocene as well as to regional hydroclimatic changes and reorganizations of the monsoons our record suggests that late glacial temperature changes in northeast africa were linked to high latitude northern hemispheric climate processes but that subsequent post glacial temperature variations were strongly influenced by tropical hydrology

carbonate rocks and related facies with vestiges of biomarkers clues to redox conditions in the mesoproterozoic ocean abstract the raipur group of the chattisgarh basin preserves two major late mesoproterozoic carbonate platforms the lower platform is about 490 m thick separated from the upper platform 670 m thick by a 500 m thick calcareous shale carbonate strata cover almost 40 of the chattisgarh basin outcrop and represent two major platform types a a non stromatolitic ramp the charmuria sarangarh limestone and b a platform developed chiefly in the intertidal to shallow subtidal environment with prolific growth of stromatolites the chandi saradih limestone the first platform consists primarily of the black timarlaga limestone that is locally replaced by early diagenetic dolomite this carbonate platform experienced strong storm waves and was subsequently drowned by a major transgression during which extensive black limestone marl rhythmite was deposited followed by deposition of the gunderdehi shale the carbonate factory was later re established with development of an extensive stromatolite dominated charmuria sarangarh platform that ranged from restricted embayment to open marine conditions sea level change played a major role in controlling the broad facies pattern and platform evolution the 13 c signatures of the chattisgarh limestones falling within a relatively narrow range 0 to 4 are typical for upper mesoproterozoic carbonate rocks 18 o values however have a greater range 5 7 to 13 3 indicating significant diagenetic alteration of some samples likely dysoxic or anoxic conditions prevailed during deposition of the black timarlaga limestone and well oxygenated conditions during deposition of the gunderdehi shale and saradih chandi stromatolite the lack of 17 21 moretanes and high t max values suggest mature organic matter in the non stromatolitic ramp a paucity of diagnostic eukaryotic steroids indicates that algae were rare in the chattisgarh basin a high content of hopanes supports a generally bacterially dominated proterozoic ocean in which various stromatolites flourished

seasonal variability of branched glycerol dialkyl glycerol tetraethers brgdgts in a temperate lake system quantitative climate reconstructions are crucial for understanding the magnitude of and mechanisms behind natural and anthropogenic climate change yet there are few proxies that can reliably reconstruct terrestrial temperature branched glycerol dialkyl glycerol tetraethers brgdgts are bacterial membrane lipids that are increasingly used to reconstruct paleotemperature from lake sediments but despite their potential we have a poor understanding of 1 autochthonous vs allochthonous sources of brgdgts in lakes and 2 the seasonality of and environmental controls on brgdgt production within lakes to investigate these factors we examined water column suspended particulate matter spm and settling particles from a sediment trap collected on a biweekly to monthly basis over a period of three years at lower king pond a small kettle lake in northern vermont usa we also compared the concentration and fractional abundances of brgdgts in spm and settling particles with those of catchment soils river sediments and lake surface sediments to constrain the relative importance of brgdgts derived from the landscape versus brgdgts produced within the lake itself we find significant differences in concentrations and fractional abundances of brgdgts between soil and river sediment samples from the catchment and lake sediments indicating a mostly autochthonous source for lacustrine brgdgts brgdgt concentrations fluxes and fractional abundances in spm vary over the annual cycle indicating that brgdgts are produced throughout the year and respond to changes within the water column the total annual flux of brgdgts settling through the water column is comparable to the brgdgt accumulation rates in surface sediments indicating that in this lake brgdgts are mostly produced within the water column not in the sediment itself while brgdgts are produced in all seasons within the water column the flux to the sediments is highest during periods of spring and fall isothermal mixing potentially biasing paleotemperature reconstructions towards mixing season temperature because the seasonal timing and frequency of lake mixing varies as a function of regional climate lacustrine brgdgt calibrations should be regional in nature and comprise lakes with similar mixing regimes

origin of cratonic basins tectonic subsidence curves show that the illinois michigan and williston basins formed by initial fault controlled mechanical subsidence during rifting and by subsequent thermal subsidence thermal subsidence began around 525 ma in the illinois basin 520 460 ma in the michigan basin and 530 500 ma in the williston basin in the illinois basin a second subsidence episode middle mississippian through early permian was caused by flexural foreland subsidence in response to the alleghanian hercynian orogeny resurgent permian rifting in the illinois basin is inferred because of intrusion of well dated permian alnoites such intrusive rocks are normally associated with rifting processes the process of formation of these cratonic basins remains controversial past workers have suggested mantle phase changes at the base of the crust mechanical subsidence in response to isostatically uncompensated excess mass following igneous intrusions intrusion of mantle plumes into the crust or regional thermal metamorphic events as causes of basin initiation cratonic basins of north america europe africa and south america share common ages of formation around 550 to 500 ma histories of sediment accumulation temporal volume changes of sediment fills and common dates of interregional unconformities their common date of formation suggests initiation of cratonic basins in response to breakup of a late precambrian super continent this supercontinent acted as a heat lens that caused partial melting of the lower crust and upper mantle followed by emplacement of anorogenic granites during extensional tectonics in response to supercontinent breakup intrusion of anorogenic granites and other partially melted intrusive rocks weakened continental lithosphere thus providing a zone of localized regional stretching and permitting formation of cratonic basins almost simultaneously over sites of intrusion of these anorogenic granites and other partially melted intrusive rocks

lithospheric mantle deformation beneath the indian cratons abstract the nature of deformation of the deep continental roots beneath the archean early proterozoic terrains opens the question whether these ancient terrains have had stable roots since the precambrian or whether recent plate motions have deformed them in view of this we make an attempt to study the thermal structure beneath the cratonic regions of the indian shield which vary in lithospheric thickness from 65 km in the singhbhum craton to 148 km in the archean dharwars the average depth of 104 km to the top of the underlying asthenosphere is consistent with other termination methods and is in fact less than half the 200 400 km depth found in other stable areas of the earth similarly the average reduced heat flow of about 35 mw m2 and moho temperature of about 550 c range 400 730 c for the indian cratons are also much higher than their counterparts elsewhere our study indicates a large scale deformation of the cratonic mantle lithosphere beneath the indian shield since the mesoproterozoic c

lead isotopic evidence for synextensional lithospheric ductile flow in the colorado river extensional corridor western united states this is the published version copyright 1998 american geophysical union all rights reserved

lithostratigraphy of the neoproterozoic chattisgarh sequence its bearing on the tectonics and palaeogeography abstract the neoproterozoic purana succession in the eastern part of chattisgarh basin around sarangarh has been classified into a conglomerate sandstone shale dominated proximal assemblage and a lithographic limestone shale dominated distal assemblage the proximal assemblage constitutes the chandarpur group and unconformably overlies the archean crystalline basement complex the chandarpur succession has been classified into three formations that were deposited in fan fan delta deep water prodelta and storm tide dominated prograding shelf environments the distal assemblage the raipur group conformably overlies the chandarpur group and may be subdivided into two shale dominated formations separated by a limestone dominated formation the limestone sequence the sarangarh limestone comprises a lower member of mixed carbonate siliciclastic succession deposited in a storm dominated shallow water platform and an upper member of pelagic limestone that grades upward into a deep water shale the gunderdehi shale the rapid transition from shallow water platformal succession to deep water pelagic limestone and shale points to abrupt deepening of the basin and drowning of the craton the peak of transgression is represented by a persistent horizon of black limestone a product of basin wide anoxia disposition of facies belts in proximal and distal assemblages and palaeocurrent directions measured from different facies belts point to a north northwesterly palaeoslope of the basin signatures of intense storm and tidal currents in different litho units collectively point to an open marine circulation condition it has been inferred that the basin was connected to a major seaway that skirted the northern and north western margin of the craton development of thick fan delta sequence at the base of the succession occurrence of felsic welded tuff within the gunderdehi shale thick sandstone mudstone cyclothems in the chandarpur group and abrupt drowning of the carbonate platform leading to pelagic sedimentation collectively point to major tectonic control on basin evolution the basin developed as a cratonic rift and evolved into a deeply subsiding one without any major stratigraphic hiatus through episodic tectonic pulses

calibration and application of the branched gdgt temperature proxy on east african lake sediments branched glycerol dialkyl glycerol tetraethers brgdgts are a novel proxy for mean annual air temperature maat and have the potential to be broadly applicable to climate reconstruction using lacustrine sediments several calibrations have been put forth relating brgdgt distributions to maat using a variety of linear regressions including the methylation mbt and cyclization cbt indices of brgdgts the relative abundances of the major non cyclized brgdgts mbrgdgts and best subsets regression bsr of the fractional abundances of the nine most common brgdgts however these calibrations have rarely been applied to lake sediment cores to reconstruct temperatures and test the applicability of this proxy as a paleothermometer we present an expanded east african lakes surface sediment brgdgt dataset based upon 111 lakes and examine three methods of calibrating brgdgts to maat these methods include recalculations of the east african lake mbt cbt calibration and mbrgdgts calibrations as well as a new stepwise forward selection sfs calibration that uses the four combined brgdgts that explain the most variance in temperature in our calibration set we apply these new calibrations as well as five previously published lacustrine brgdgt calibrations to the brgdgt distributions of our surface sediment dataset and a 48 kyr sediment core from sacred lake mt kenya producing the first brgdgt temperature reconstruction available from a small tropical lake we compare the reconstructed temperatures to previously published paleotemperature records from east africa to help us assess the performance of the brgdgt calibrations we find that the sfs calibration has a consistently low root mean squared error of prediction rmsep over the entire range of maat while the mbt cbt and mbrgdgt calibrations have relatively large rmseps particularly between lakes with similar temperatures but variable ph this suggests that these techniques do not properly deconvolve the temperature and ph signals recorded in the distributions of the brgdgts we further find that only the sfs calibration produces a credible reconstructed temperature history from sacred lake when compared to other last glacial maximum paleotemperature estimates from east africa thus we advocate for the use of the sfs calibration when reconstructing paleotemperatures from brgdgts in east africa

distributions of branched gdgts in a tropical lake system implications for lacustrine application of the mbt cbt paleoproxy branched glycerol dialkyl glycerol tetraether gdgt lipids are abundant and ubiquitous in lake sediments potentially allowing for a paleolimnological application of the so called mbt cbt proxy methylation index of branched tetraethers cyclization ratio of branched tetraethers to investigate the origin and characteristics of these compounds in lacustrine environments we examined the distributions of gdgts in soils river sediments and lake sediments from lake towuti on the island of sulawesi indonesia we found significant differences in the degree of methylation and cyclization expressed by way of the mbt and cbt indices between the soil samples and the aquatic samples suggesting that there may be in situ production of gdgts in the aquatic environment based on these findings we urge caution in the application of the mbt cbt paleoproxy to lake sediments and encourage more rigorous study of these compounds in freshwater environments

depositional history of the chhattisgarh basin central india constraints from new shrimp zircon ages a reply abstract the indian shield includes the singhbhum bastar and east and west dharwar cratons proterozoic sedimentary basins formed on these cratons have preserved rocks with a range of degrees of metamorphism and deformation in the chhattisgarh basin within the bastar craton the ca 2200 2500 m thick chhattisgarh supergroup has been preserved in nearly pristine condition previous work has shown that the sukhda tuff located about 2200 m from the base of the section was formed ca 1007 ma new u pb shrimp age determinations show that the singhora tuff located about 100 m above the base of the basin is not older than ma thus most of the chhattisgarh supergroup was deposited between 1400 and 1000 ma age data for detrital zircons from sandstones show that regardless of their stratigraphic position there is a unimodal age peak near 2500 ma the typical age of adjacent granitic and rhyolitic basement rocks indicating that these constituted the principal provenance of the sediments in the chhattisg

time vs composition trends of magmatism at sunlight volcano absaroka volcanic province wyoming sunlight volcano is a dissected but well preserved eruptive center in the eastern high k belt of the absaroka volcanic province on the basis of high precision 40ar 39ar ages magmatism at the volcano commenced prior to 49 6 ma and continued until ca 48 1 ma stratigraphic relationships along with geochemical and 40ar 39ar data distinguish three principal stages of effusive volcanism that are interpreted to reflect the inception climax and decay of a crustal magmatic system related to three major pulses of basalt and high eruptive rates during the first two stages shoshonitic and latitic lavas with small but distinct compositional ranges accumulated the third stage included eruption of picritic basaltic lavas and intrusion and solidification of magmas in the volcanic edifice as this stage produced magmas compositionally more evolved and diverse basalts to trachytes than in previous stages it likely represents the terminal pulse of basalt to the system followed by cooling protracted differentiation and cessation of eruptive activity petrographic geochemical and sr and nd isotope data for sunlight igneous rocks indicate that crystallization differentiation was the dominant magma evolution process although phenocryst accumulation and crustal contamination also occurred evidence for phenocryst accumulation is most pronounced in final stage rocks this relationship is interpreted to reflect recharge of late magmas into mature chambers laden with crystals deposited during earlier stages the importance of crystallization differentiation at sunlight volcano contrasts with recent petrogenetic models for calc alkaline magmas in the absaroka volcanic province which require a more important role for early magma mixing the results presented here indicate that across strike increases in k2o contents of rocks in the field derive from variations in the conditions of crustal differentiation rather than from mantle processes involving a subducting slab

the neoproterozoic cratonic successions of peninsular india abstract the peninsular india hosts extensive record of mesoproterozoic and neoproterozoic successions in several mobile belts and cratonic basins the successions provide excellent opportunities for chronostratigraphic classification in tune with the chronometric classification adopted by iugs for inter regional correlation on a global scale major tectono thermal events at 1000 950 ma in the mobile belts correlatable with the grenville orogeny may be considered as the datum for meso neoproterozoic classification in india principles of chronostratigraphic classification however can not be applied yet to the cratonic successions of india because of inadequate radiometric data paucity of biostratigraphic studies and lack of regionally correlatable stratigraphic or palaeoclimatic datum the kimberlite magmatism which affected the peninsular india on a continental scale at about 1100 ma holds the key to the identification of neoproterozoic successions of the cratonic basins thus the stratigraphically confined diamond bearing conglomerates and or the tuffs associated with kimberlites may be considered as the datum to define the base of the neoproterozoic fixed at about 1000 ma accordingly the rewa and bhander groups in the vindhyan basin the kurnool group in the cuddapah basin the jagdalpur formation in the indravati basin and the sullavai group in the pranhita godavari basin are taken to represent the neoproterozoic successions in the peninsular india the chattisgarh group in the central india the lower part of the marwar supergroup in western rajasthan the badami group in the kaladgi basin and the bhima group are the other possible neoproterozoics in the peninsula the closing phase of the mesoproterozoic in all these basins are characterised by stable shelf lithologic associations attesting to high crustal stability the neoproterozoic basins by contrast mark a new phase of rifting and extension and the basin fills exhibit signatures of initial instability which evolved with time into a more stable platformal condition a major episode of sea level rise has been recorded in most of the basins the riftogenic origin and evolution of the basins are comparable with the history of neoproterozoic basins of australia though there is no unequivocal record of glaciation in the indian formations

late quaternary vegetation climate and fire history of the southeast atlantic coastal plain based on a 30 000 yr multi proxy record from white pond south carolina usa the patterns and drivers of late quaternary vegetation dynamics in the southeastern united states are poorly understood due to low site density problematic chronologies and a paucity of independent paleoclimate proxy records we present a well dated 15 accelerator mass spectrometry 14 c dates 30 000 yr record from white pond south carolina that consists of high resolution analyses of fossil pollen macroscopic charcoal and sporormiella spores and an independent paleotemperature reconstruction based on branched glycerol dialkyl tetraethers between 30 000 and 20 000 cal yr bp open pinus picea forest grew under cold and dry conditions elevated quercus before 26 000 cal yr bp however suggest warmer conditions in the southeast before the last glacial maximum possibly corresponding to regionally warmer conditions associated with heinrich event h2 warming between 19 700 and 10 400 cal yr bp was accompanied by a transition from conifer dominated to mesic hardwood forest sporormiella spores were not detected and charcoal was low during the late glacial period suggesting megaherbivore grazers and fire were not locally important agents of vegetation change pinus returned to dominance during the holocene with step like increases in pinus at 10 400 and 6400 cal yr bp while charcoal abundance increased tenfold likely due to increased biomass burning associated with warmer conditions low intensity surface fires increased after 1200 cal yr bp possibly related to the establishment of the mississippian culture in the southeast

proterozoic felsic volcanism in the pranhita godavari valley india its implication on the origin of the basin abstract the proterozoic sedimentary rocks in the pranhita godavari valley pg valley south india were deposited in diverse environments ranging from continental shallow shelf to deep basin and occur as several unconformity bound sequences the sedimentary rocks also include felsic pyroclastics in different formations and at different stratigraphic levels repeated occurrences of intrabasinal pyroclastic rocks of similar composition suggest that the detritus might have been erupted from a common chamber which was activated at different times throughout the basin filling episode it is postulated that the mature proterozoic crust of indian craton acted as a heat lens resulting in extensive partial melting at the lower crustal levels localized stretching and rifting of the craton leading to the formation of the intracratonic basin the sedimentological attributes also support extensional setting and the hypothesis may be extended for several meso neoproterozoic cratonic basins in the indian shield the mechanism operated over the time span of 1 6 0 7 ga and overlaps with the age of development of an extensive granite rhyolite province in north america the process of accumulation of heat at the lower crustal levels generating a heat lens is typical of the stationary phase of supercontinental cycles and the origin of the cratonic basins the origin of the pg valley basin may be related to the fragmentation of a supercontinent of which the indian craton was a part

assessment of branched gdgts as temperature proxies in sedimentary records from several small lakes in southwestern greenland this study of five small 3 0 ha lakes in southwestern greenland examines the veracity of branched glycerol dialkyl glycerol tetraethers br gdgts as a temperature proxy in lacustrine systems the proximity 5 km of the lakes suggests that their temperature history and thus their br gdgt records should be similar distributions of br gdgts in i surface sediments from all five lakes ii 14c dated sediment cores from two lakes upper and lower evv lakes and iii soil samples from the area surrounding the lakes were examined the temporal records of br gdgt based temperature for the two cores exhibited both similarities and major discrepancies the differences between the paleotemperature records for the two lakes suggest that br gdgts are not solely soil derived reflecting air temperature but also indicate an additional br gdgt contribution from another source among the broader suite of lake sediments there was a strong correlation r2 0 987 between br gdgt based surface sediment temperatures and measured summer bottom water temperatures for the four lakes with hypoxic anoxic bottom waters including upper evv lake the correlation suggests production of br gdgts by anaerobic bacteria within the bottom water and or sediment water interface reflecting environmental temperature for the individual lakes and augmenting the uniform soil derived signal hence assessment of br gdgts in greenland lake sediments provides evidence for their origin from anaerobic autochthonous bacteria and indicates that interpretation of lacustrine br gdgt based paleotemperature records requires contextual knowledge of individual lake systems and potential source s of sedimentary br gdgts

almandine garnet phenocrysts in a 1 ga rhyolitic tuff from central india we report on the newly discovered almandine garnet phenocrysts in rhyolitic ignimbrites sukhda tuff in the precambrian churtela shale formation of the chhattisgarh supergroup in central india shrimp ages of igneous zircon from the ignimbrites range from 990 ma to 1020 ma these ignimbrites exhibit characteristic eutaxitic texture with compacted curvilinear glass shards with triple junctions quartz commonly embayed bluish cathodoluminescence and albite altered but retaining ghosts of twinning are common phenocrysts others are apatite ilmenite rutile magnetite zircon monazite and garnet there are no metamorphic or granitic xenoliths in the ignimbrites garnet grains occur as isolated broken isotropic crystals with sharp or corroded boundaries in a very fine grained groundmass of volcanic ash that consists principally of albite quartz magnetite and glass they do not have any systematically distributed inclusions a few have penetratively intergrown phenocrysts of apatite ilmenite rutile and zircon which we interpret as subophitic texture extensive sem bse imaging of more than 100 grains and electron microprobe traverses across about 30 grains showed no zoning or systematic compositional variability common metamorphic garnets are usually zoned with respect to fe mg mn and typically have mineral inclusions we infer therefore that these observed garnets are not metamorphic xenocrysts the average major oxide composition of analysed garnets from five different horizons within the sukhda tuff spanning approximately 300 m of the stratigraphic section have very small standard deviation for each element which is suggestive of a single magmatic source phenocrysts of quartz including those in contact with coexisting garnets show blue scanning electron cl indicating rapid cooling from high temperature this suggests that adjacent coexisting garnets are not slowly cooled restites we conclude on the basis of texture mineral chemistry and absence of any indicative xenoliths or xenocrysts that these almandine garnets al 78 7 py 12 3 gr 7 4 sp 1 6 are phenocrysts within the sukhda tuff almandine of such composition is stable under high pressure we infer that almandine crystallized at lower crustal depths in a magma that ascended very rapidly and may have erupted explosively

recycled detrital quartz grains are sedimentary rock fragments indicating unconformities examples from the chhattisgarh supergroup bastar craton india abstract recycled detrital quartz grains are unequivocally identified if there are overgrowths on abraded overgrowths we argue that the presence of such recycled grains even in small quantities in successions of quartz arenites indicates derivation from one or more sedimentary units from below an intrabasinal unconformity or an extrabasinal unroofing surface as do detritus from characteristic rock fragments in polymict clastic rocks in fact detrital grains with inherited overgrowths are sedimentary rock fragments we apply this petrographic criterion to evaluate the presumed unconformities that bound the singhora chandarpur raipur and the kharsiya groups of the essentially mesoproterozoic chhattisgarh supergroup in the bastar craton a critical ur craton vis a vis columbia and rodinia optical examination of about 6000 grains in 12 thin sections reveal few recycled quartz grains in sandstone samples of the chandarpur group but about 4 recycled quartz grains with inherited abraded overgrowths in a sandstone unit of the raipur group characteristic rock fragments from a tuffaceous unit at the top of the raipur group are found in the basal sandstone of the kharsyia group the data indicate that the presumed unconformities below the kharsyia group and the raipur group are real but the one above the singhora group cannot be confirmed on the basis of recycled grains published age spectra of detrital zircons from these sandstones are compatible with the above inferences drawn from detrital quartz and rock fragment petrography

microbial lipid records of highly alkaline deposits and enhanced aridity associated with significant uplift of the tibetan plateau in the late miocene saline alkaline sediments and soils are widespread in arid and semiarid regions but their occurrence in ancient dry periods remains unknown due to the lack of a suitable proxy on the basis of investigations of modern chinese soils with a wide ph range of 3 5 9 1 we suggest that the microbial lipid ratio r i b i e the abundance ratio of archaeal isoprenoid gdgts glycerol dialkyl glycerol tetraethers to bacterial branched gdgts indicates the presence of drought induced alkaline deposits in terrestrial settings the r i b is invariant in modern soils with ph 600 mm but it increases sharply at higher ph values and lower mean annual precipitation i b ratio in a fluviolacustrine section in the zhada basin of the southwestern tibetan plateau covering the time period 9 2 2 6 m y ago the r i b ratio remains relatively stable in most intervals but exhibits maxima in some horizons indicative of the occurrence of severe drought and alkaline deposits in the basin catchment these occur in fluvial sediments deposited 9 m y ago a critical time with respect to the intensification of the east asian and indian monsoons and the significant uplift of the plateau that has previously been associated with enhanced aridity in central asia

the purana basins of southern cratonic province of india a case for mesoproterozoic fossil rifts abstract since its cratonization in the palaeoproterozoic southern peninsular india witnessed the development of a number of large intracratonic sedimentary basins traditionally referred to as purana basins spanning in age from late palaeoproterozoic through neoproterozoic the localization of these intracratonic basins namely pranhita godavari pg chattisgarh and cuddapah basins is apparently controlled by pre existing sutures and or weak zones the pg basin and the cuddapah basin host unconformity bound thick sediment dominated successions attesting to several cycles of fluvial shallow marine to shelf slope basin sedimentation deposition was punctuated by block uplifts resulting in local hiatuses and or volcanic upheavals leading to intercalation of thin but persistent basaltic flows and acid tuffs and ignimbrites basin margin deep faults apparently played a role in the facies distribution in these basins based on these features we propose that these basins initiated as continental rifts which however never opened up into a full fledged ocean basin but links with open seaway are evident from frequent occurrence of deposits representing tidal and storm influence particularly in upper part of the chattisgarh succession spatial distribution of facies and sediment thickness in the cuddapah and pg basins suggest that an open seaway existed to the east of the south indian cratonic province during the mesoproterozoic while similar criteria point to the existence of an open seaway north of the chattisgarh basin development history including nature of inversion suggest that the southern cratonic province of india existed as a single large continental mass since the mesoproterozoic in spite of episodes of supercontinent build up and fragmentation involving india and east gondwana during the proterozoic

a refined paleotemperature calibration for new zealand limnic environments using differentiation of branched glycerol dialkyl glycerol tetraether brgdgt sources branched glycerol dialkyl glycerol tetraethers brgdgts were abundant in surface sediments of freshwater lakes and in catchment soils at altitudes from 10 to 2020m in new zealand significant differences in brgdgt compositions between lake sediments and soils indicate sources from separate microbial habitats an expanded modern calibration dataset comprising 33 lakes has enabled a revised calibration function for determining past mean annual air temperature mat from brgdgts in new zealand lake sediments mat degrees c 31 664 x mbtm 16 252 n 30 the function uses a modified methylation index of branched tetraethers mbtm that incorporates brgdgt iii in the numerator to overcome the lower correlation found between our larger dataset and the unmodified mbt which had been used for previous calibrations calibrations combining the cyclization index of branched tetraethers cbt and the mbtm or using only certain brgdgts are possible but have limitations the revised function shows slightly higher correlation with mat r 2 0 75 than previous calibrations which were based on nine sites the refined calibration function is applied to a similar to 16 000 year lake sediment sequence from northern south island new zealand and yields temperature reconstructions that are consistent with independently derived climate trends from the same sequence copyright c 2016 john wiley sons ltd

branched glycerol dialkyl glycerol tetraethers in lake sediments can they be used as temperature and ph proxies a series of surface sediments from 82 lakes of variable water depth and size was analyzed for glycerol dialkyl glycerol tetraethers gdgts in order to investigate the potential of the mbt cbt methylation ratio cyclization ratio of branched tetraethers as a continental palaeothermometer in lacustrine environments branched gdgts dominated in most sediments as indicated by the high branched vs isoprenoid tetraether bit values we observed that cbt and mbt varied substantially mean annual air temperature maat reconstructed and ph values were calculated using the cbt and mbt values and the calibration from the global soil data set the mbt cbt inferred temperatures were considerably lower than measured values nevertheless there was a significant correlation between maat reconstructed and maat observed on site although there was still considerable scatter r2 0 47 lacustrine sediments integrate organic remains of organisms in a lake and its drainage basin thereby offering a unique opportunity for calibrating mbt and cbt as small scale variability is averaged out since the source of the branched gdgts in the lake sediments is ambiguous it is not clear whether only temperature and ph in the catchment area are the driving factors therefore even in lake sediments with high concentrations of branched gdgts the straightforward application of mbt cbt as palaeoproxies may be difficult given the uncertainties regarding their source and origin

late paleozoic to jurassic silicic magmatism at the gondwana margin analogy to the middle proterozoic in north america a vast region of upper paleozoic to middle jurassic 300 150 ma silicic magmatic rocks that erupted inboard of the gondwana margin is a possible phanerozoic analogue to the extensive middle proterozoic 1500 1350 ma silicic magmatic province that underlies much of the southern mid continent of north america like the north american rocks the gondwana silicic magmas appear to be melts of crust that formed about 200 300 m y earlier in the north american case this older crust formed and was accreted to the continent during a major period of crustal formation 1700 1900 ma whereas in the gondwana case the crust that melted consisted mainly of magmatic are terranes accreted to the continental margin during the paleozoic in both cases basic to intermediate magmatic rocks are extremely rare and magmatism is less abundant in regions that contain older and previously melted crust the similarities between the north american and gondwana silicic rocks suggest that both suites formed in extensional settings where basaltic magmas ponded at the base of the preheated crust caused extensive crustal melting that inhibited upward passage of the basalts in both cases silicic volcanism occurred after major assembly of a supercontinent by subduction and accretion processes and before breakup of the supercontinent by analogy with the polar wander curves for gondwana the granite rhyolite provinces may have formed during a period of very slow motion of the supercontinents relative to the poles

stratigraphic architecture of the proterozoic succession in the eastern chattisgarth basin india tectonic implications abstract the basin fill succession of the proterozoic eastern chattisgarth basin comprises a sandstone shale conglomerate dominated shallow marine assemblage and an assemblage of limestone shale pyroclastics deposited in off shelf slope base of slope environments the proximal and distal lithologic assemblages developed as lateral equivalents and show signatures of sea level fluctuations amenable to chronostratigraphic correlation the stratigraphic architecture of the proximal assemblage is characterized by cyclic deposition on different scales the largest order cyclicity is represented by alternating sandstone sequences and mudstone dominated sequences of the order of several tens of metres the smallest order cyclicity is represented by metre scale units punctuated aggradation cycles pac bounded by isochronous surfaces the lowermost large scale sandstone sequence the lohardih sandstone unconformably overlies the highly deformed rocks of the gneissic basement complex the sequence was deposited as alluvial fan fan delta complexes controlled by basin margin faulting the upper two sandstones the daihan sandstone and the kansapathar sandstone represent two different phases of major sand accumulation in fan or river deltas their rapid emplacement over muddy shelf deposits along erosional surfaces signaled abrupt sea level fall and basinward migration of facies belts generation and accumulation of very large volumes of sand and their rapid influx into the basin accompanied by major changes in depositional motif and in the circulation system in the basin collectively indicate that larger order sand depositing cycles were caused by tectonic uplift of the cratonic basement the smallest order cycles the pacs on the other hand may be attributed to glacioeustacy though tectonic control cannot be ruled out the sand deficient mud dominated large scale sequences are attributed to major transgression during periods of relative tectonic quiescence and subsidence of the cratonic hinterland episodic tectonic uplift and derivation of sands from similar quartzo feldspathic sources suggest repeated rifting of the cratonic basement and expansion of the rift into a major marine basin

proterozoic evolution of eastern dharwar and bastar cratons india an overview of the intracratonic basins craton margins and mobile belts abstract based on critical analysis of stratigraphic succesions in the proterozoic intracratonic basins geochronological data and possible connections or disconnections with adjacent fold belts and craton margin mobile belts an overview of the proterozoic evolution of the eastern dharwar and bastar cratons in india is presented the chattisgarh and cuddapah basins in these cratons with archean nuclei host sedimentary successions ranging in age from the paleoproterozoic to the ediacaran period and representing several silicilastic and carbonate cycles the proterozoic successions of the pranhita godavari valley pgv basin along the dharwar bastar join record multiple rifting since late neoarchean suturing of the two cratons we postulate a first order stratigraphic correlation across the cratons and their join and discuss how major sea level fluctuations coupled with regional tectonic events shaped the development of unconformity bound successions adjoining fold belts and the mobile belts with supposed global tectonic connections the oldest paleoproterozoic intracratonic sedimentation is preserved in the cuddapah and pgv basins while sedimentation in the bastar craton is largely mesoproterozoic the fluviodeltaic to shallow marine neoproterozoic sedimentation followed emplacement of end mesoproterozoic kimberlites and lamproites indicating thermal rejuvenation of the indian continental crust the allochthonus nallamalai fold belt in eastern cuddapah basin and the early mesoproterozoic fold belt in pgv basin point to craton margin crustal convergences which punctuated the paleoproterozoic sedimentation widespread development of carbonate bearing sequences in the mesoproterozoic to neoproterozoic successions point to peneplanation of the cratons and stable platformal sedimentation the neoproterozoic sedimentation was terminated following the docking of the eastern ghats belt to the eastern margin of the dharwar bastar ensemble and possible final tectonic hiccups in the central indian tectonic zone bordering the bastar craton the available data and their analysis rule out any foreland basin type connection between the eastern ghats belt and cratonic sedimentation in bastar and eastern dharwar

forced regressive wedges on a neoproterozoic siliciclastic shelf chandarpur group central india abstract outcrop based sequence analysis across the transition from the chaporadih to the kansapathar formation of chandarpur group chattisgarh supergroup central india resolved a long standing uncertainty on occurrence of depositional discontinuity through undoubted identification of a forced regressive wedge and associated intraformational unconformity process based facies analysis identified eleven different facies types that are grouped into five different facies associations paleoenvironments range from shelf shoreface foreshore and beach tide influenced estuary and delta bounded between the surface of marine erosion at its base and subaerial unconformity marked by paleosol development at its top the coarse grained wedges of shoreface sandstone is interpreted as forced regressive in origin the basinward downstepping of two such regressive wedges bears evidence for lowering of wavebase in connection with relative fall in sea level the valley created during the falling sea level was filled by sediments in lowstand transgressive and highstand depositional motif the aggradational to weakly progradational bedsets of foreshore beach sediments record the history of early slow rise in base level with steepening in the rate of relative sea level rise the coastline transformed from wave dominated to tide dominated wide variability in the balance between sediment supply and accommodation is recorded in the facies types and stacking motif of transgressive estuarine sections at different studied locations the highstand tidal delta is a supply driven normal regressive product at stable or marginally rising base level

the dharwar craton and the assembly of peninsular india peninsular india can be separated into five discrete crustal areas the bhandara singhbhum and aravalli bundelkhand cratons the eastern ghats and a block in southern india containing the dharwar craton and adjoining granulite terrain these areas are separated by four major joins eastern ghats front godavari rift mahanadi rift sukinda thrust and narmada son lineament and associated thrusts all joins except the godavari rift are former orogenic belts where thrusts juxtapose rocks of different metamorphic grade these thrusts and the absence of clear correlation of suites among different cratons suggest that the indian shield formed by accretion of separate continental fragments epicontinental late archean early pro terozoic sediments throughout india however may indicate that the joins are intracontinental formed within a coherent block the term dravidian shield is used for the southernmost of the five crustal blocks including all of india south of the deccan basalts and godavari rift

effects of temperature ph and nutrient concentration on branched gdgt distributions in east african lakes implications for paleoenvironmental reconstruction branched glycerol dialkyl glycerol tetraethers brgdgts are membrane lipids found in soils and sediments and their relative abundance correlates with temperature and ph enabling them to be used as proxies in reconstructing past climatic and environmental conditions however the potential for other environmental variables such as nutrient concentration to affect brgdgt distributions remains largely unexplored we have examined the influence of a suite of environmental factors including temperature lake water and sediment chemistry and lake morphometry on brgdgt concentration and distributions in the surface sediments of 111 lakes in east africa we found that temperature was the major control on the distributions while the influence of ph was relatively minor water depth also had a minor but statistically significant influence perhaps due to the relationship between lake depth and deep water anoxia water column nutrient concentration did not have a significant effect on the distributions or concentration we further explored the potential for these variables to affect brgdgt temperature reconstruction by examining the correlation between them and the residuals of our brgdgt temperature calibration we found that while the distribution of some cyclized brgdgts may be influenced by ph and other environmental variables they are necessary in brgdgt calibration equations in order to accurately reconstruct temperature likely due to covariation between temperature and other environmental variables while surface water ph correlated with the relative abundance of certain brgdgts caution should be exhibited when using brgdgts as a ph proxy because of systematic calibration errors

radioactivity heat flow and rifting of the indian continental crust the relationship between heat flow q and heat production a in india is quite different for the northern and southern parts of the peninsula in the north locations in a variety of tectonic settings including gondwana rifts show a linear relationship between q and a with a common reduced heat flow q about 40 mwm 2 in southern india the heat production of surface rocks is greater than is expected for the measured heat flow relative to other continental shields g is high in northern india and about average in the south apparently the indian crust evolved with a content of radioactive elements higher than in most shields and the southern part of the peninsula has undergone regional depletion in the lower crust and possibly upper mantle this depletion may coincide with a regional granulite event about 2 500 m y ago the high heat flow and heat production in northern india may explain several unique characteristics of the indian peninsula one feature is the continued reactivation of rif

deformation pattern and evolution of the structures in the penganga group the pranhita godavari valley india probable effects of grenvillian movement on a mesoproterozoic basin abstract recent studies reveal imprints of tectonic deformation in the mesoproterozoic rocks of the pranhita godavari p g valley india outcrop scale structures that record a progressive sequence of deformation can thus be used to clarify the kinematic evolution of the penganga group a mesoproterozoic succession in the northern and central parts along the sw marginal proterozoic belt of the pg valley overprinting relationships among the structures in the northern part indicate three distinct structural stages 1 layer parallel shortening 2 thrusting and folding in combination and 3 extensional joint and fracture opening the former two stages are explained in the framework of a progressive deformation model the extensional structures were produced during exhumation similar structures are also developed in the central part of the sw belt of the pg valley though the two areas slightly differ in the overall pattern of deformation the geometry of the progressive deformation structures from both regions of the belt suggests that they were produced under a regime of ne sw ene wsw directed regional compression the deformation in the proterozoic basin is possibly related to the grenvillian orogeny recorded in the eastern ghats mobile belt and may represent a small scale meso neoproterozoic convergence event