structure of the vakhsh fold and thrust belt tadjik ssr geologic mapping on a landsat image base an enhanced landsat image of the northeastern tadjik depression in the soviet union was combined with field data to produce a 1 250 000 geologic map of the vakhsh fold and thrust belt and adjacent autochthon mapping of the relatively continuous geologic structure in this region first required recognizing marker beds and contacts at or near the resolution of the landsat sensor and then defining mappable units satellite image mapping was complemented by field study which was necessary in this recently deformed area both to verify the image mapping and to obtain more accurate structural dips deformation of the cretaceous and tertiary strata of the fold and thrust belt is in the western half of the mapped area conspicuously absent north of a buried basement fault that marks the hinge zone of the late mesozoic passive margin in the eastern half of the mapped area however the major thrusts displacing rocks northward have moved coherent sheets over the block fault these sheets now lie flat atop the autochthon to the north tectonically these observations indicate that 1 the crustal structure inherited from the mesozoic extensional phase has strongly influenced the late cenozoic pattern of deformation 2 the thrust sheets that are displaced over the paleo hinge zone actively load the basement rocks to the north and 3 the development of the fold and thrust belt which is markedly asymmetric has included the progressive overlapping of thrusts the later thrusts apparently formed internal to the older thrusts and subsequently overrode them

kinematics of active deformation in the sulaiman lobe and range pakistan the western margin of the indian plate is highly oblique to the direction of convergence between india and asia and represents an excellent example of large scale oblique continent continent collision determining the strain field in western pakistan and how it relates to the plate motion and plate margin geometry affords an exceptional opportunity for understanding oblique margin processes in general through the inversion of regional and teleseismic body waves we have determined the source parameters of 10 moderate sized earthquakes that occurred between 1964 and 1985 in and around the sulaiman range pakistan the earthquakes are dominantly thrust events with slip vectors that are approximately perpendicular to the lobate sulaiman mountain front slip vector orientations rotate 60 70 from a n s to a wnw ese direction of compression consistent with the geometries of the complex festoon shaped mountain belts of this margin we have estimated the spatial variation of the horizontal strain rate and velocity fields within sulaiman using vertically averaged models that accommodate plate motion constraints within a deforming layer the most important factors determining the style of strain rotation in the sulaiman lobe and range are the presence of pure strike slip motion along the chaman fault and the relatively rigid and undeformed katawaz basin that is therefore allowed to translate obliquely relative to india this same conclusion is obtained using either a three dimensional frictional analogue model with significant basal tractions or a thin sheet viscous numerical model without basal tractions thrusting in a predominantly nw se direction in the sulaiman range accommodates 5 14 mm yr of n s motion between india eurasia and 3 6 mm yr of e w shortening seismic moment release this century within the india eurasia plate boundary zone west of the western himalayan syntaxis constitutes roughly 40 of the expected total seismic moment release for this time period particularly significant moment rate deficits exist within the sulaiman range and along the chaman fault

late quaternary variability of precipitation in southern california and climatic implications clay mineral evidence from the santa barbara basin odp site 893 abstract clay mineral assemblages have been investigated in a sequence of late quaternary age sediments 160 ka from the santa barbara basin off california these predominantly terrigenous sediments contain an assemblage of clay minerals dominated by smectite mostly derived from discharges of the santa clara river together with illite and kaolinite from adjacent relief besides its characteristic clay mineral signature the santa clara river has the largest drainage basin in this region and contributes most of the terrigenous load to the santa barbara basin smectite contents of the sediments in the basin may therefore be used as a proxy for precipitation and run off distinct changes in the relative abundance of smectite allow reconstruction of the pattern of precipitation and its relations with regional environments and global climate this showed that major intervals of precipitation coincide with local development of pine during glacials and oak during terminations and interglacials some expansion of mountain glaciers in the sierra nevada especially when they occur during local minima of insolation and lacustrine developments in the now arid continental interior of california major precipitation intervals started during glacials and persisted during terminations and early interglacials associated with a weak california current and subsequent expansion of warm pacific surface waters in detail major precipitation intervals consist of alternating episodes of higher and lower rainfall modulated by orbital precession with a significant correlation between episodes of high rainfall and minima in precession which were times of increased meridional gradients enhanced poleward heat transfer and northward expansion of tropical waters

late pleistocene and early holocene rivers and wetlands in the bonneville basin of western north america abstract field investigations at dugway proving ground in western utah have produced new data on the chronology and human occupation of late pleistocene and early holocene lakes rivers and wetlands in the lake bonneville basin we have classified paleo river channels of these ages as gravel channels and sand channels gravel channels are straight to curved digitate and have abrupt bulbous ends they are composed of fine gravel and coarse sand and are topographically inverted i e they stand higher than the surrounding mudflats sand channels are younger and sand filled with well developed meander scroll morphology that is truncated by deflated mudflat surfaces gravel channels were formed by a river that originated as overflow from the sevier basin along the old river bed during the late regressive phases of lake bonneville after 12 500 and prior to 11 000 14c yr b p dated samples from sand channels and associated fluvial overbank and wetland deposits range in age from 11 000 to 8800 14c yr b p and are probably related to continued sevier basin overflow and to groundwater discharge paleoarchaic foragers occupied numerous sites on gravel channel landforms and adjacent to sand channels in the extensive early holocene wetland habitats reworking of tools and limited toolstone diversity is consistent with theoretical models suggesting paleoarchaic foragers in the old river bed delta were less mobile than elsewhere in the great basin

the interaction of two indenters in analogue experiments and implications for curved fold and thrust belts abstract scaled analogue experiments are used to investigate the indentation of two basement blocks into a sedimentary basin and the formation of a fold and thrust belt the experimental set up has two adjacent indenters moving in parallel with a velocity difference the slow indenter moves with a relative velocity ranging from 40 to 80 of that of the fast one in a first experimental series quartz sand and low friction glass beads represent the sediment stack and its basal detachment respectively silicone oil simulates a viscous detachment in the second series of experiments the surface evolution and the spatio temporal strain distribution are derived from particle image velocimetry piv together with the 3d finite structure derived by cutting the models at the end of each experiment this allows the analysis of the structural evolution of the experimental wedges thrusting wedge development depends crucially on the relative velocity when the slow indenter moves with a velocity of more than 55 of the fast indenter a single curved thrust wedge develops the wedge becomes decoupled along strike slip zone at large velocity differences i e when the slow indenter moves slower than 55 of the faster indenter consequently the thrust front is strongly curved at high 55 60 and smoothly curved at low velocity differences 70 80 in all cases curvature increases during indentation along the most strongly curved portion of the thrust wedge the transfer zone rises particle rotation and material transport oblique to the indentation direction occur directed toward the front of the slow indenter thrusting cycles are timed by the fast indenter and influence thrusting in front of the slow indenter thrusts nucleate in front of the fast indenter wedge and propagate laterally to the slow indenter front this implies distant effects of wedge growth active hundreds of kilometres along strike of orogens silicone oil as a detachment induces a low angle wedge which is less curved than in the glass beads experiments and shows variable thrust vergence with fore and back thrusts we compare our experimental results with the curved fold and thrust belts of the tajik basin in front of the hindu kush and pamir indenters our results are able to explain several first order features

tajik basin and southwestern tian shan northwestern india asia collision zone 1 structure kinematics and salt tectonics in the tajik fold and thrust belt of the western foreland of the pamir

factors affecting 14c ages of lacustrine carbonates timing and duration of the last highstand lake in the lahontan basin abstract two processes contribute to inaccurate 14c age estimates of carbonates precipitated within the lahontan basin nevadacalifornia low initial 14c c ratios in lake water reservoir effect and addition of modern carbon to calcium carbonate after its precipitation the mast reliable set of 14c ages on carbonates from elevations 1310 m in the pyramid and walker lake subbasins indicate that lakes in all seven lahontan subbasins coalesced 14 200 14c yr b p forming lake lahontan lake lahontan achieved its 1330 m highstand elevation by 13 800 14 c yr b p and receded to 1310 m by 13 700 14c yr b p calculations based on measured carbonate accumulation rates of the amount of time lake lahontan exceeded 1310 and 1330 m 500 and 50 yr are consistent with this chronology the timing of the lake lahontan highstand is of interest because of the linkage of highstand climates with proximity to the polar jet stream the brevity of the lahontan highstand is interpreted to indicate that the core of the southern branch of the polar jet stream remained only briefly over the lahontan basin

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

multispectral remote sensing as stratigraphic and structural tool wind river basin and big horn basin areas wyoming stratigraphic and structural analyses of the wind river basin and big horn basin areas of central wyoming are in progress one result has been the development of an approach to stratigraphic and structural analysis that uses photogeologic and spectral interpretation of multispectral image data to characterize the attitude thickness and lithology of strata new multispectral systems that have only been available since 1982 are used with topographic data to map upper paleozoic and mesozoic strata exposed on the southern margin of the bighorn mountains landsat acquired thematic mapper tm data together with topographic data are used to map lithologic contacts measure dip and strike and develop a stratigraphic column that is correlated with conventional surface and subsurface sections aircraft acquired airborne imaging spectrometer ais and thermal infrared multispectral scanner tims data add mineralogic information to the tm column including the stratigraphic distribution of quartz calcite dolomite smectite and gypsum results illustrate an approach that has general applicability in other geologic investigations that could benefit from remotely acquired information about areal variations in attitude sequence thickness and lithology of strata exposed at the earth s surface application of our methods elsewhere is limited primarily by availability of multispectral and topographic data and quality of bedrock exposures

evidence of temperature depression and hydrological variations in the eastern sierra nevada during the younger dryas stade sediment records from two lakes in the east central sierra nevada california provide evidence of cooling and hydrological shifts during the younger dryas stade yd 12 900 11 500 cal yr bp a chironomid transfer function suggests that lake water temperatures were depressed by 2 c to 4 c relative to maximum temperatures during the preceding bolling allerod interstade ba 14 500 12 900 cal yr bp diatom and stable isotope records suggest dry conditions during the latter part of the ba interstade and development of relatively moist conditions during the initiation of the yd stade with a reversion to drier conditions later in the yd these paleohydrological inferences correlate with similar timed changes detected in the adjacent great basin vegetation response during the yd stade includes the development of more open and xeric vegetation toward the end of the yd the new records support linkages between the north atlantic the north pacific and widespread yd cooling in western north america but they also suggest complex hydrological influences shifting hydrological conditions and relatively muted vegetation changes may explain the previous lack of evidence for the yd stade in the sierra nevada and the discordance in some paleohydrological and glacial records of the yd stade from the western united states

millennial scale deep water oscillations reflections of the north atlantic in the deep pacific from 10 to 60 ka northeast pacific benthic foraminiferal 18o and 13 reveal repeated millennial scale events of strong deep sea ventilation associated with nutrient depletion and or high gas exchange during stadial cool high ice volume episodes from 10 to 60 ka opposite the pattern in the deep north atlantic two climate mechanisms may explain this pattern north pacific surface waters chilled by atmospheric transmission from a cold north atlantic and made saltier by reduced freshwater vapor transports could have ventilated the deep pacific from above alternatively faster turnover of pacific bottom and mid depth waters driven by southern ocean winds may have compensated for suppressed north atlantic deep water production during stadial intervals during the younger dryas event 11 6 13 0 cal ka ventilation of the deep ne pacific 2700 m lagged that in the santa barbara basin 450 m by 500 years suggesting that the ne pacific was first ventilated at intermediate depth from above and then at greater depth from below this apparent lag may reflect the adjustment time of global thermohaline circulation

a new greenland deep ice core the polar ice sheets are rich sources of information on past atmospheric conditions including paleoclimates a new deep ice core has been drilled in south greenland comparison of the oxygen isotopic profile with that from camp century and with a deep sea foraminifera record indicates that the new core reaches back to about 90 000 years before present in a continuous sequence the details in the wisconsin part of the ice core records seem to be climatically significant and the general trends reveal all of the relevant emiliani stages recorded in deep sea cores the redated camp century record suggests a dramatic termination of the eem sangamon interglacial

palynological evidence for early holocene aridity in the southern sierra nevada california sediments of balsam meadow have produced a 11 000 yr pollen record from the southern sierra nevada of california the balsam meadow diagram is divided into three zones 1 the artemisia zone 11 000 7000 yr b p is characterized by percentages of sagebrush artemisia and other nonarboreal pollen higher than can be found in the modern local vegetation vegetation during this interval was probably similar to the modern vegetation on the east slope of the sierra nevada and the climate was drier than that of today 2 pinus pollen exceeded 80 from 7000 to 3000 yr b p in the pinus zone the climate was moister than during the artemisia zone 3 fir abies cupressaceae and oak quercus percentages increased after 3000 yr b p in the abies zone as the modern vegetation at the site developed and the present cool moist climatic regime was established decreased fire frequency after 1200 yr b p is reflected in decreased abundance of macroscopic charcoal and increased concentration of abies magnifica and pinus murrayana needles

geomorphic expression of abrupt climate change in southwestern north america at the glacial termination eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern north america drying of pluvial lake estancia central new mexico occurred after ca 12 000 14c yr b p thereafter eolian landforms on the old lake floor constructed of gypsum sand were overridden by rising lake water modified by subaqueous processes and organized into beach ridges along the lake s eastern shore preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the younger dryas yd stade the beach ridges provide information about lake surface area which was 45 of the lake area reached during the maximum highstands of the late pleistocene a similar proportional response has been reported for yd climate changes outside the north atlantic region

thirty thousand years of vegetation changes in the alabama hills owens valley california abstract twenty packrat neotoma middens recovered from three sites 1265 1535 m in the alabama hills inyo county california provide a ca 31 450 yr record of vegetation change located ca 7 km east of the sierra nevada the middens document that utah juniper juniperus osteosperma joshua tree yucca brevifolia and bitterbush purshia tridentata occupied the site between 31 450 and 19 070 yr b p joshua tree and bitterbush departed by ca 17 760 yr b p with cliffrose purshia mexicana and joint fir ephedra viridis appearing by 13 350 yr b p blackbush coleogyne ramosissima and cholla opuntia echinocarpa entered the record between 9540 and 7990 yr b p utah juniper and other species now extralocal to the sites departed and modern components such as wolfberry lycium andersonii and rubber rabbitbrush chrysothamnus teretifolius appeared the middle holocene records little variation in plant macrofossil composition however pollen analysis reflects an increase in aquatic pollen types which might suggest more open conditions the transition to the modern vegetation associations at the sites occurred after ca 2800 yr b p the record from the alabama hills correlates well with that of other regional vegetation data but documents conditions of increasing aridity earlier than many other packrat midden sites a shift in understory vegetation between 19 070 and 17 760 yr b p may reflect a transition from glacial maximum to post maximum conditions in the eastern sierra nevada

a holocene pollen record of persistent droughts from pyramid lake nevada usa pollen and algae microfossils preserved in sediments from pyramid lake nevada provide evidence for periods of persistent drought during the holocene age we analyzed one hundred nineteen 1 cm thick samples for pollen and algae from a set of cores that span the past 7630 years the early middle holocene 7600 to 6300 cal yr b p was found to be the driest period although it included one short but intense wet phase we suggest that lake tahoe was below its rim for most of this period greatly reducing the volume and depth of pyramid lake middle holocene aridity eased between 5000 and 3500 cal yr b p and climate became variable with distinct wet and dry phases lake tahoe probably spilled intermittently during this time no core was recovered that represented the period between 3500 and 2600 cal yr b p the past 2500 years appear to have had recurrent persistent droughts the timing and magnitude of droughts identified in the pollen record compares favorably with previously published y 18 o data from pyramid lake the timing of these droughts also agrees with the ages of submerged rooted stumps in the eastern sierra nevada and woodrat midden data from central nevada prolonged drought episodes appear to correspond with the timing of ice drift minima solar maxima identified from north atlantic marine sediments suggesting that changes in solar irradiance may be a possible mechanism influencing century scale drought in the western great basin d 2004 university of washington all rights reserved

thrusting of the hindu kush over the southeastern tadjik basin afghanistan evidence from two large earthquakes we infer from the mechanisms and depths of two large earthquakes that the hindu kush is actively thrusting northwest over the tadjik basin and that the basin is closing rather than being displaced to the west teleseismic body waves were used to determine focal mechanisms and depths for the two largest shallow earthquakes on the southern edge of the basin the two earthquakes on june 24 1972 mb 6 0 and december 16 1982 mb 6 2 have seismic moments of 2 1018 n m and 6 1018 n m respectively focal mechanisms of both events indicate almost pure thrust faulting with nodal planes striking northeast southwest the inferred fault planes dip southeast at 20 for the first event and 50 for the second the p axes for both events are oblique to the direction of relative motion between india and asia suggesting that the pamir is overthrusting the basin to the west depths for both earthquakes are between 20 and 25 km and place them well below the tadjik basin sediments the depths and steep fault planes suggest that these earthquakes represent a downdip extension within the basement of shallow folding and thrusting seen in the sediments northwest of the events thus convergence in afghanistan between india and eurasia is taken up along southeast dipping thrust faults north of the hindu kush as well as by northward subduction under the southern part of the range

seismic domains within the gissar kokshal seismic zone soviet central asia by evaluating seismological data from the belt of shallow intraplate seismicity known as the gissar kokshal seismic zone in soviet central asia in conjunction with recent data on the shallow crustal structure and longer term geologic deformation we show that certain size classes of earthquakes are characteristic of adjacent and in some places overlapping geologic tectonic settings we call these settings seismic domains they are both geologically and seismologically distinct i e they contain different rocks and structures and have different frequency magnitude relationships for example in terms of number of events gissar kokshal seismicity is dominated by the microearthquakes that have occurred within the sedimentary rocks of the vakhsh fold thrust belt these are all shallow and have occurred mostly within the frontal portions of the thrust sheets more rarely moderate size m 5 5 earthquakes have ruptured the thrust ramps on the other hand the major strain release in this region has accompanied the large 5 5 m 8 1 shallow earthquakes on basement faults in the southern gissar range adjacent to the fold thrust belt within these ranges there is relatively little microearthquake activity that dichotomy indicates that a significantly different seismic hazard is associated with each of these areas but the seismological distinction is obscured along the front of the fold thrust belt where the domain of small shocks in the sedimentary rocks overlaps the domain of large earthquakes on basement faults to explain the localization of the large basement events along the southern flank of the fold thrust belt adjacent to the fold thrust belt we hypothesize a mechanism of thrust sheet loading thrust loads are greatest in this region since thrust sheets have overridden large basement block uplifts beneath the illiac and peter the first range faults

pollen analysis of a late glacial and holocene sediment core from mono lake mono county california pollen analysis of a 752 cm core from mono lake mono county california indicates generally high lake levels 11 600 7000 14c yr b p moderate lake levels until ca 4000 14c yr b p and fluctuating levels to the present drying events with lake levels near or below the historic minimum are dated ca 8800 4000 2400 and 1100 14c yr b p chronologic control is provided by six radiocarbon dates and six volcanic ashes the rate of upland vegetation change is greatest 11 000 4000 and 1130 14c yr b p juniperus and sequoaidendron pollen declines 11 000 yr b p marking the transition from late glacial juniper woodland to holocene steppe high values 5 20 of sequoaidendron pollen are unique to this study and may indicate the presence of these trees east of the sierra crest the pollen based reconstructions of climate are generally cooler and wetter than today with relatively dry but cool climate during the early holocene the contrast between higher lake levels and more arid vegetation during the early holocene can be explained by insolation driven seasonality greater summer insolation produced summer drought but lower winter insolation led to greater snowpack greater spring runoff and higher lake levels increased artemisia and other compositae pollen percentages mark the establishment of modern vegetation ca 2000 14c yr b p during the late holocene the pollen based reconstructions of climate generally match the mono lake fluctuations proposed by stine 1990 but fewer fluctuations are recorded

paleoclimatic interpretations of meadow sediment and pollen stratigraphies from california a comparison of sediment stratigraphies from nine meadow cores in the sierra nevada california with fossil pollen reconstructions of paleoclimates shows excellent correlation between these parameters and confirms the results of recent paleoclimatic models colluvium and alluvium dominate early holocene sedimentary deposits and undoubtedly originated from greater erosion on dry basin side slopes fossil pollen suggests that species characteristic of dry microclimates flourished the transition to peats after 4 5 ka is concurrent with increases in pollen of plants that require abundant soil moisture during the dry summer these results confirm the importance of analysis of the physical stratigraphy of holocene deposits in pollen based reconstructions

pollen and oxygen isotope analyses on late and post glacial sediments of the tourbiere de chirens dauphine france the sequence of vegetation phases in the late glacial was studied in a sediment section from the bog tourbiere de chirens by means of pollen analysis 18o16o ratios of samples of lacustrine marl obtained from the same profile reflect variations of 18o16o in precipitation and thus provide an additional independent paleoclimatic record the observed 18o16o variations agree well with the climatic history as deduced from pollen analysis the climatic transition from the oldest dryas to the bolling period sensu lato as well as the beginning and end of the younger dryas cold phase is marked by abrupt changes in the 18o16o ratio which were observed also in other regions of the alps these drastic climatic changes probably took place simultaneously over large areas of central europe and occurred within short time spans

geomorphology and late holocene morphogenesis of tchinguiz tepe hill old termez uzbekistan central asia tchinguiz tepe hill is the southernmost outcrop interrupted at the shores of the amu darya of the cenozoic sediments that form the baysuntau kugitangtau alignment the initiation points of the recent morphogenesis are the slopes and a pediment controlled structurally by the unequally weathered substrate the hill is covered by sediments of varying thickness on the south side which is exposed to dominant winds from the se and was occupied by humans at least during kushan times 1st and 2nd centuries ad its form is derived from two systems of natural processes slope and aeolian and an anthropic one which have operated under arid to semiarid conditions these processes have mobilized sands from the weathered substrate and from the afghan dunes and pebbles and gravels from early kushan time constructions such as the fortress of the tchingiz tepe hill slope wash processes have contributed materials which have evolved as slope aeolian sediment in the mantled pediment part of the aeolian sand has been re exported together with primary autochthonous sand outside the hill towards the north thus in tchinguiz tepe the current morphogenesis has slowed down considerably and is currently in dynamic equilibrium with a slow increase in sediments the carbonate crusts which are not very well developed have formed a complex host sediment anthropic morphogenetic action has modified the natural shape of the hill from the earliest times of occupation to the present day and has generated materials that are now incorporated in the slope wash and govern the current topography and the distribution of sediments from the wall of the fortress and other buildings

the geology and petroleum potential of the north afghan platform and adjacent areas northern afghanistan with parts of southern turkmenistan uzbekistan and tajikistan the north afghan platform has a pre jurassic basement unconformably overlain by a jurassic to paleogene oil and gas bearing sedimentary rock platform cover unconformably overlain by neogene syn and post orogenic continental clastics the pre jurassic basement has four units 1 an ordovician to lower devonian passive margin succession developed on oceanic crust 2 an upper devonian to lower carboniferous tournaisian magmatic arc succession developed on the passive margin 3 a lower carboniferous visean to permian rift passive margin succession 4 a triassic continental magmatic arc succession the mesozoic palaeogene cover has three units 1 a late triassic to middle jurassic rift succession is dominated by variable continental clastics thick coarse lenticular coal bearing clastics were deposited by braided and meandering streams in linear grabens while bauxites formed on the adjacent horsts 2 a middle to upper jurassic transgressive regressive succession consists of mixed continental and marine bathonian to lower kimmeridgian clastics and carbonates overlain by regressive upper kimmeridgian tithonian evaporite bearing clastics 3 a cretaceous succession consists of lower cretaceous red beds with evaporites resting unconformably on jurassic and older deposits overlain usually unconformably by cenomanian to maastrichtian shallow marine limestones which form a fairly uniform transgressive succession across most of afghanistan 4 a palaeogene succession rests on the upper cretaceous limestones with a minor break marked by bauxite in places thin palaeocene to upper eocene limestones with gypsum are overlain by thin conglomerates which pass up into shales with a restricted brackish water upper oligocene lower miocene marine fauna the neogene succession consists of a variable thickness of coarse continental sediments derived from the rising pamir mountains and adjacent ranges almost all the deformation of the north afghan platform began in the miocene oil and gas traps are mainly in upper jurassic carbonates and lower cretaceous sandstones across the entire north afghan block upper jurassic carbonate traps sealed by evaporites occur mainly north of the southern limit of the upper jurassic salt lower cretaceous traps consist of fine grained continental sandstones sealed by aptian albian shales and siltstones upper cretaceous palaeocene carbonates sealed by palaeogene shales are the main traps along the northern edge of the platform and in the tajik basin almost all the traps are broad anticlines related to neogene wrench faulting in this respect like similar traps along the san andreas fault hydrocarbon sources are in the mesozoic section the lower middle jurassic continental coal bearing beds provide about 75 of the hydrocarbons the callovian oxfordian provides about 10 the neocomian a meagre 1 and the aptian albian about 14 the coal bearing source rocks decrease very markedly in thickness southwards cross the north afghan platform much of the hydrocarbon generation probably occurred during the late cretaceous paleogene and migrated to structural traps during neogene deformation since no regional structural dip aids southward hydrocarbon migration and since the traps are all structural and somewhat small then there is little chance of very large petroleum fields on the platform nevertheless further studies of the north afghan platform should be rewarding because a the traps of strike slip belts are difficult to find without detailed exploration b the troubles of the last 20 years mean that almost no exploration has been done and c conditions may soon become more favorable there should be ample potential for oil and particularly gas discoveries especially in the northern and western parts of the north afghan platform

reappraisal of the relative importance of dynamic topography and andean orogeny on amazon landscape evolution abstract the cenozoic landscape of northern south america evolved under the influence of different geodynamic processes culminating in the formation of the largest drainage basin on earth the amazon drainage system the orogeny of the andean cordillera and the increase in surface denudation induced an asymmetric influx of sediments in amazonia which caused an eastward propagation of the andean sedimentary wedge reversing the topographic gradient and driving the drainage flow towards the atlantic equatorial margin the low relief topography of lowlands in amazonia is also a factor that propitiates this reversal concomitantly variations in the subduction angle of the nazca plate under the continental lithosphere during the miocene also contributed to create dynamic topography that perturbed the surface and modified the drainage pattern through time in the last decade both surface processes during andean orogeny and dynamic topography were invoked independently to explain the formation of the present amazon drainage system connecting the andes and the equatorial margin however hitherto these mechanisms were not considered in a single model hampering the evaluation of the contribution of each factor on the evolution of the amazon river to quantify the combined effect of the different geodynamic processes in the present work we used numerical models that integrate orogeny surface processes dynamic topography and flexural isostasy of the lithosphere in our results we present new numerical scenarios for the cenozoic landscape evolution of amazonia showing that the dynamic topography may have affected the environmental evolution in western amazonia favoring the development of a megawetland in this region before the establishment of the amazon river as a transcontinental river we conclude that although the formation of the amazon drainage system can be explained without the influence of mantle convection variations in dynamic topography may have anticipated the establishment of the transcontinental drainage system a few million years furthermore the stratigraphic evolution and the total cenozoic sedimentation preserved in the solimoes basin is a function of the temporal variations in the amplitude of dynamic topography in northern south america

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

cenozoic intracontinental deformation and exhumation at the northwestern tip of the india asia collision southwestern tian shan tajikistan and kyrgyzstan along the ghissar alai range of the southwestern tian shan southwestern kyrgyzstan northern tajikistan the deformation front of the india asia collision the pamir tibet orogen is interacting with the intra continental tian shan orogen without the intervening tarim craton apatite fission track n 33 3 3 145 6 ma 27 10 ma and u th he n 32 1 9 26 1 ma 56 10 ma thermochronologic ages suggest approximate isothermal holding very slow cooling to weak reheating during relative tectonic quiescence between 150 15 ma accelerated exhumation 0 2 1 0 km myr median 0 5 km myr and cooling 11 16 c myr occurred over the last 10 myr geomorphologic parameters incision and river steepness and concavity confirm the youth of the southwestern tian shan s mountain building high exhumation cooling rates correlated with pronounced local relief produced by cenozoic faults reactivating inherited late paleozoic structures regions with similarly young exhumation are centered along rims of rigid crustal blocks in the central and eastern tian shan structurally the ghissar alai range is a broad east trending zone of dextral transpression that includes the northern tajik basin illiak fault zone and the pamir thrust system of the frontal northern pamir it is the particular deformation field at the northwestern tip of the india asia collision the interaction of the westward gravitational collapse of the pamir plateau into the tajik basin with the bulk northward motion of the pamir that transformed the southwestern tian shan into a dextral transpression belt the dextral transpression in the southwestern tian shan contrasts with sinistral strike slip shear localized along inherited fault zones accommodating dominant north south shortening in the central and eastern tian shan the deformation field influenced by the pamir and the associated young exhumation make the ghissar alai range a unique feature in the tian shan orogen

the wetar back arc thrust belt eastern indonesia the effect of accretion against an irregularly shaped arc the 350 km long east west trending wetar back arc thrust belt in eastern indonesia is a result of the collision of australia with the indonesian island arc along the northwest margin of wetar island a short 50 km section of the thrust belt trends northeast coincident with the offset of the indonesian arc by the newly discovered left lateral wetar atauro fault which runs along the shelf region and trends northeast the wetar atauro fault may be viewed as a large scale lateral ramp or wrench fault separating the eastern wetar thrust belt from the western wetar thrust belt the interaction of strike slip faulting and back arc thrust faulting creates several arc blocks whose geometry strongly affects the structure of the deformed wedge of sediment accreting in the wetar back arc thrust belt the varying orientations of the arc backstop make the wetar back arc thrust belt a perfect laboratory for the study of oblique convergence along most of its length the wetar thrust belt parallels the arc slope however along the northeast trending offset in the thrust belt seamarc ii side scan sonar plus seismic reflection data show that the trend of the thrust belt is not parallel to the trend of the arc slope rather it is intermediate between the trend of the arc slope and the perpendicular to the expected convergence direction the side scan images allow us to map the geometry of four main thrust faults the wetar liran atauro and alor faults the wetar liran and atauro faults trend northeast parallel to the thrust front and do not have an en echelon relationship the westernmost fault in the survey area the alor fault trends almost east west the orientation of the wetar atauro fault is consistent with a maximum principal stress within the arc oriented between 8 and 23 west of north depending on the internal coefficient of friction this agrees well with the p axes of nearby earthquake focal mechanisms which trend consistently west of north suggesting that the regional principal tectonic compression is oriented west of north because the thrust belt is oblique to the arc slope we infer the structural directions are influenced by both the arc backstop and by the regional tectonic stress the tectonic compression due to arc continent collision in this region may be modified by the arc geometry in several ways 1 the stress necessary to support the arc topography may be significant close to the arc 2 the change in thickness of the elastic part of the lithosphere may cause a concentration of tectonic stress and 3 the difference in material properties between the relatively rigid arc bulldozer and the weak basin sedimentary fill may be an important factor in producing a thrust belt that conforms roughly to the shape of the arc the structure of the wetar back arc thrust zone demonstrates that the development of small rigid blocks within a major collision zone may produce complex structural patterns and local directions of shortening that are highly oblique to the main direction of plate convergence

packrat midden evidence of late quaternary vegetation change in the white mountains california nevada packrat neotoma spp middens from the white mountains indicate climatic and plant community conditions for the last 19 000 yr during full glacial times ca 19 000 yr b p and at the pleistocene holocene boundary juniper woodlands were 600 m lower in elevation than at present midden assemblages and stable isotope data suggest lower temperatures and increased precipitation relative to the present into the early holocene two early holocene middens ca 8000 yr b p from lower elevations of the white mountains contain fragments of pinyon pine and indicate that both pinyon and juniper grew at a site that today supports only a pinyon woodland two middle holocene middens ca 5000 yr b p indicate that there was an upward migration of pinyon juniper woodlands along a high elevation ecotone but little change in the middle of the pinyon juniper woodland middens from the late holocene indicate that present day plant communities were in place by ca 2000 yr b p or before

spatial and temporal patterns of earthquake distribution in soviet central asia application of pair analysis statistics we have examined the soviet regional earthquake catalog for central asia for the period 1962 to 1983 to characterize the spatial and temporal structure of the earthquake process in this highly active continental collision zone three areas of apparently homogeneous earthquake distribution were identified as characteristic of distinct seismic regimes 1 a segment of the range bounding gissar kokshal fault zone 2 the interior of the crystalline massif of the tien shan mountain range and 3 the tadjik depression fold thrust belt the pair analysis technique applied in our study compares the spatial and temporal distribution of pairs of earthquakes with those determined by uniformly distributed events in the same area and time interval we have found the earthquake distribution in this region to be dominated by significant nonrandomness in both space and time the spatial nonrandomness is manifested in two major ways spatial clustering appears to characterize the overall structure of the earthquake process in the region as it is observed regardless of the scale considered and even upon removal of foreshocks aftershocks and swarms from the catalog anomalies at larger distances could also be distinguished suggesting the existence of a regular spatial alternation of subareas of higher and lower levels of seismic activity the nonrandomness in temporal distribution of earthquakes is also characterized by clustering at short time intervals in contrast with the spatial patterns earthquakes appear to be randomly distributed in time after removal of foreshocks aftershocks and swarms

intracontinental subduction beneath the pamir mountains constraints from thermokinematic modeling of shortening in the tajik fold and thrust belt american philosophical society american association of petroleum geologists geological society of america exxon mobil corporation

out of the tropics the pacific great basin lakes and late pleistocene water cycle in the western united states the water cycle in the western united states changed dramatically over glacial cycles in the past 20 000 years higher precipitation caused desert lakes to form which have since dried out higher glacial precipitation has been hypothesized to result from a southward shift of pacific winter storm tracks we compared pacific ocean data to lake levels from the interior west and found that great basin lake high stands are older than coastal wet periods at the same latitude westerly storms were not the source of high precipitation instead air masses from the tropical pacific were transported northward bringing more precipitation into the great basin when coastal california was still dry the changing climate during the deglaciation altered precipitation source regions and strongly affected the regional water cycle

precursory seismicity changes preceding moderate and large earthquakes in the garm region central asia this study reports on variations in seismic activity preceding moderate and large earthquakes in a highly active portion of the india eurasia collision zone the study is based on the catalog of earthquake locations from the complex seismic expedition cse network in the garm region central asia the local seismic network was established in the mid 1950s and recorded and located over 85 000 earthquakes from 1955 to 1988 two main approaches were used to evaluate variations in seismic activity associated with 12 moderate to large magnitude ml 5 0 to 6 3 mainshocks that occurred in the study area 1 a qualitative approach involving examination of maps cross sections space time plots and earthquake histograms for the area identified as the rupture area of the mainshock and 2 a quantitative approach based on magnitude frequency relations estimated for small space time windows within the seismic network in addition to temporal variations in seismicity three long term gaps were identified 1 in the western peter the first range near the city of garm 2 in the central peter the first range and 3 in the northeastern part of the study area approximately coinciding with a gap identified by other authors using different approaches the potential magnitude of future gap filling events is estimated to be in the range 6 7 to 7 0 evidence of precursors has been found to varying extent for 9 out of the 12 mainshocks studied these include quiescence or low activity before the mainshock foreshock activity before the mainshock and a sequence of low activity high activity quiescence before the mainshock for the quantitative analysis the level of seismic activity in small space time windows is quantified by the parameter a 2 defined as the a value at magnitude 2 in the gutenberg richter magnitude frequency relation log n a bm the a 2 values were calculated for 30 12 12 minute spatial cells with a moving time window of five years from this analysis only one earthquake the m 6 3 dzhirgital earthquake of 26 october 1984 shows a significant decrease by a factor of 45 in activity level a 2 the results of the quantitative analysis also show strong spatial variations the central portion of the study area which includes the peter the first range fold thrust belt shows high but relatively stable seismic activity the tien shan basement uplift in the north has a tendency of decreasing activity and the northeastern part of the study area shows increasing activity the october 1984 earthquake is located near the transition between the two tendencies

erosional processes as a control on the structural evolution of an actively deforming fold and thrust belt an example from the pamir tien shan region central asia the foreland of the pamir mountains displays an unusual orogenic topography in which an active north vergent thin skinned fold and thrust belt shows no topographic foredeep in advance of the thrust sheets instead the thrusts are impinging on a topographic barrier formed by the southern edge of the tien shan the deformation front of this thrust belt is coincident with a deeply incised river valley occupied by a large river the surkhob we suggest that this river played a key role in the evolution of this orogenic system by acting as a lateral conveyor belt for the transport of mass delivered to the deformation front by thrusting on the basis of reconnaissance geologic mapping it is clear that the present system developed in the late miocene or pliocene when the tien shan were uplifted within an existing foreland basin as the tien shan highland developed a longitudinal river within the foreland basin was trapped between the north directed thrusts and the tien shan highland with continued deformation the river was squeezed into a narrow canyon and since that time the system has been in an unusual equilibrium where thrusting acts to push the deformation front northward toward the tien shan but fluvial erosion and transport act to keep it in a constant position geologic relationships indicate that the vakhsh thrust the frontal thrust of the north directed system is now emerging on an erosion surface beneath a thin quaternary cover throughout the canyon suggesting that the river has been unable to keep pace with the tectonic mass flux and the thrust front as well as the river have been pushed northward across the beveled edge of what was originally the southern edge of the tien shan we suggest that the original deformation front of the tien shan now lies 10 km south of the present day topographic front of the tien shan beneath the north vergent vakhsh thrust as indicated by 1 a near vertical zone of intense basement seismicity the petrovsky seismic zone 2 an en echelon array of backthrusts along the south flank of the peter the first range and 3 footwall cutoff relationships of the vakhsh thrust system order of magnitude mass balance considerations based on sediment budgets support this conclusion but suggest that the mass imbalance may be small thus large volumes of material may have passed through the thrust fron and been carried out of the system by erosion a relationship that may account for the narrow 30 50 km wide band of deformed sedimentary rock between the pamir salient and the tien shan the present near equilibrium is maintained by long term tectonic transport rates and fluvial transport rates the latter closely linked to climate particularly precipitation thus although there is apparently a mass pile up within this system other systems of this type might show grossly different structural and stratigraphic relationships depending on the amount of rainfall and corresponding variations in rates of fluvial sediment transport similar settings can be recognized in the active thick skinned thrust systems of the tien shan and ancient systems like the laramide belt of western north america

paleoproduction and environmental change at mono lake eastern sierra nevada during the pleistocene holocene transition abstract the late quaternary limnological history of mono lake 16 6 4 3 cal kyr bp a hydrologically closed basin in the eastern sierra nevada california is inferred based on a multi indicator analysis of a long 10 8 m composite sediment core constructed from overlapping deepwater piston cores the composite core dated by 14c and tephra correlation shows variations in sedimentology magnetic susceptibility elemental geochemistry and stable isotopes through time consistent with changes in aquatic productivity hydroclimate and volcanism in the late pleistocene deepwater stratigraphy was influenced by high amplitude water level changes and runoff from a glaciated watershed in contrast mono lake s elevation was lower in the early to middle holocene low amplitude water level changes wave reworking of the shoreline and water column stratification were important controls on facies during that time the data suggest that the chief controls on organic facies development in mono lake productivity preservation and dilution dynamics are sensitive to climate changes that influence lake level elevation water chemistry and the position of deltas the study shows that deepwater sediments from certain locales in mono lake are well preserved continuous and can be reliably dated with 14c applied to terrestrial materials when paired with precisely dated paleoshoreline data these sediments provide a high resolution archive of deglacial and holocene environmental information for the eastern sierra nevada

cosmogenic 3he age estimates of plio pleistocene alluvial fan surfaces in the lower colorado river corridor arizona usa abstract plio pleistocene deposits of the lower colorado river lcr and tributary alluvial fans emanating from the black mountains near golden shores arizona record six cycles of late cenozoic aggradation and incision of the lcr and its adjacent alluvial fans cosmogenic 3he 3hec ages of basalt boulders on fan terraces yield age ranges of 3 3 2 2 ma 2 2 1 1 ma 1 1 ma to 110 ka

sedimentary charcoal as an indicator of late holocene drought in the sierra nevada california and its relevance to the future a holocene record of climate fire and vegetation regimes was reconstructed for siesta lake yosemite national park california using fossil pollen and charcoal from lake sediments these reconstructions were generated to provide a long term perspective on drought in the sierra nevada the sedimentary record is in agreement with other long term records of climate and vegetation from the sierra nevada and the records of climate and fire for the last c 1000 years are in agreement with tree ring and hydrological studies this correspondence suggests that sedimentary charcoal and pollen are reliable indicators of change in climate vegetation and fire frequency through time the fire frequencies associated with the droughts of the mediaeval warm period are only half as great as those recorded during the early holocene insolation maximum model results suggest that the temperature increases associated with the insolation maximum are a good analogue for those expected with global warming if this is the ca

late quaternary environments in ruby valley nevada abstract palynological data from sediment cores from the ruby marshes provide a record of environmental and climatic changes over the last 40 000 yr the modern marsh waters are fresh but no deeper than 3 m a shallow saline lake occupied this basin during the middle wisconsin followed by fresh and perhaps deep waters by 18 000 to 15 000 yr b p no sediments were recovered for the period between 15 000 and 11 000 yr b p possibly due to lake desiccation by 10 800 yr b p a fresh water lake was again present and deeper than modern conditions lasted until 6800 yr b p the middle holocene was characterized by very shallow water and perhaps complete desiccation the marsh system deepened after 4700 yr b p and fresh water conditions persisted until modern times vegetation changes in ruby valley were more gradual than those seen in the paleolimno logical record sagebrush steppe was more widespread than at present through the late pleistocene and early holocene giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr b p shadscale steppe contracted by 4000 yr b p but had greater than modern coverage until 1000 to 500 yr ago pinyon juniper woodland was established in the southern ruby mountains by 4700 yr b p

the mescal cave fauna san bernardino county california and testing assumptions of habitat fidelity in the quaternary fossil record abstract the late pleistocene and holocene vertebrate fossil record for the northern mojave desert southwestern usa is known primarily from five sites until now only two of these have been radiometrically dated and temporal placement of the others has been based on stratigraphic or biostratigraphic correlation leading to circular interpretations of mammal extirpations in the mojave here i report a revised and complete faunal list for mescal cave along with 22 ams radiocarbon dates from 5 vertebrate taxa recovered from its deposits the results reported here demonstrate time averaging in mescal cave encompassing around 34 ka a maximum age 14 ka older and minimum age 10 ka younger than previously thought furthermore radiocarbon analyses suggest local extirpation of marmota flaviventris around 3 6 cal ka bp considerably younger than expected based on regional patterns of warming and aridification in the mojave conversely radiocarbon dates from another presumably boreal species neotoma cinerea are considerably older than expected suggesting either that climate change at this site did not directly mirror regional patterns that habitat requirements for these two species are not strictly boreal or cool mesic as has often been assumed or that local edaphic conditions and or competitive interactions overrode the regional climatic controls on theses species distribution

earthquake focal mechanisms deformation state and seismotectonics of the pamir tien shan region central asia this paper presents a review of the seismotectonics of the pamir tien shan collision zone in the garm region tajikistan based on geological structure seismicity and focal mechanism solutions the region is dominated by horizontal compression manifested by imbricate low angle thrust faults that separate the upper crust into a series of tectonic sheets these thrust systems verge northward from the tajik depression toward the southern tien shan and southward toward the northern pamir the pattern of seismicity across the region suggests that similar low angle thrust faults exist within the crystalline basement as well in order to reconstruct the present day stress strain state of the region we used data from over 15 000 earthquake focal mechanism solutions for small earthquakes m 1 0 gathered over the 27 year period 1963 1989 the method of reconstruction of the seismotectonic deformation std field involves dividing the data set into small spatial windows and summing the individual focal mechanism solutions to form an average earthquake mechanism tensor for each cell the std state of that cell can then be represented by the orientation of the principal axes of compression and tension the intensity or relative uniformity of the average mechanism and the lode nadai coefficient which defines the relation between the magnitudes of the principal strain components we observe throughout the study area a general predominance of subhorizontal compression manifested in a mixture of thrust and strike slip deformation normal fault deformation is observed in only two small portions of the study area the orientation of principal compression varies from nearly n s in the northern pamir and the southern tien shan to nw se in the peter the first range in general the std field has a clearly developed mosaic structure defined by spatial groupings of nearly uniform orientations of compression and tension axes the boundaries of these groups cannot in most cases be directly correlated with known geological contacts the std structure also shows some variation with depth with more or less uniform std orientation in the upper crust 0 14 km depth changing significantly at greater depths examination of various subsets of the focal mechanism catalog shows the spatial structure of the std field to be largely stable with respect to both time and magnitude the reliability of the reconstructed std field was verified using three approaches 1 comparison of individual focal mechanism determinations for a large subset of the data using both soviet and u s algorithms 2 comparison of std reconstruction results using the two independent focal mechanism catalogs and 3 examination of the effect of spatial sampling on the results the dominance of generally north oriented subhorizontal compression is interpreted to be primarily the result of convergence between the pamir and tien shan ranges in turn caused by the ongoing collision of india and eurasia

late glacial vegetation and climate change in western oregon abstract pollen records from two sites in western oregon provide information on late glacial variations in vegetation and climate and on the extent and character of younger dryas cooling in the pacific northwest a subalpine forest was present at little lake central coast range between 15 700 and 14 850 cal yr b p a warm period between 14 850 and 14 500 cal yr b p is suggested by an increase inpseudotsugapollen and charcoal the recurrence of subalpine forest at 14 500 cal yr b p implies a return to cool conditions another warming trend is evidenced by the reestablishment ofpseudotsugaforest at 14 250 cal yr b p increased haploxylonpinuspollen between 12 400 and 11 000 cal yr b p indicates cooler winters than before after 11 000 cal yr b p warm dry conditions are implied by the expansion ofpseudotsuga a subalpine parkland occupied gordon lake western cascade range until 14 500 cal yr b p when it was replaced during a warming trend by a montane forest a rise inpinuspollen from 12 800 to 11 000 cal yr b p suggests increased summer aridity pseudotsugadominated the vegetation after 11 000 cal yr b p other records from the pacific northwest show an expansion ofpinusfrom ca 13 000 to 11 000 cal yr b p this expansion may be a response either to submillennial climate changes of younger dryas age or to millennial scale climatic variations

velocity structure and seismicity of the garm region central asia summary we have examined arrival time data from two seismic networks operating within the pamir tien shan region of central asia in order to evaluate crustal structure and earthquake distribution in one of the most seismically active zones in the region the data are from two networks surrounding the soviet earthquake prediction laboratory at garm tadjikistan a 15 station local network operated by the soviet complex seismological expedition cse since the mid l950s and a dense telemetered network nested within the larger cse network operated jointly by the us geological survey usgs and the cse since 1975 a simultaneous inversion procedure was used to calculate l d layered velocity models and station corrections independently for each of the two networks using a variety of data subsets and starting models we obtained stable estimates of the velocity structure independent of the initial velocity models for both the cse and the usgs network data the velocities of two upper crustal layers proved to be indistinguishable from a model with a single layer over a half space for the cse network the best p wave velocity model comprises an 8 km thick upper crustal layer of 5 2 km sk overlying a 5 9 km sk half space using data from the usgs network alone a similar velocity model was obtained with the exception of a significantly higher velocity v 6 3 km sk for the mid crustal half space these results contradict previously published velocity models featuring anomalously low or high seismic velocities in the upper to mid crust hypocentral parameters were redetermined for approximately 26 000 events occurring during the period 1975 82 using the newly obtained velocity models and station corrections most of the seismicity in the study area is associated with active deformation of the sedimentary rocks of the peter the first range the distribution of hypocentres within the range suggests the presence of a southeastdipping zone of seismicity that can be traced updip to the petrovsky thrust fault beneath this upper crustal seismicity at a depth of 12 17 km is an aseismic zone that may be related to the presence of low strength evaporites at the base of the sedimentary section this aseismic zone is in turn underlain by anomalously deep crustal seismicity at a depth of 17 30 km the deeper seismicity appears to be associated with a southeast dipping feature approximately 10 km in thickness this dipping seismic zone is interpreted as a zone of intracontinental subduction whose surface expression is the vakhsh thrust fault at the frontal edge of the peter the first range

a 180 000 year pollen record from owens lake ca terrestrial vegetation change on orbital scales abstract pollen from the upper 90 m of core ol 92 from owens lake is a climatically sensitive record of vegetation change that indicates shifts in the plant associations representing warm and cold desertscrub pinyon juniper woodland and pine fir forest during the past 180 000 years these changes are synchronized with glacial interglacial cycles during glacial and stadial climates juniper woodland expanded downslope and replaced warm desert shrubs while upper montane and subalpine forests in the arid inyo mountains also expanded and those in the sierra nevada were displaced by the ice cap and periglacial conditions conversely during interglacial and interstadial climates warm desert plants expanded their range in the lowlands juniper and sagebrush retreated upslope and montane and subalpine forests expanded in the sierra nevada the reconstructed vegetation history demonstrates a regional climatic response and the congruence of the pollen sequence with marine and ice cap oxygen isotope stratigraphies suggests a link between regional vegetation and global climate change at orbital scales

vegetation fire and climate history of the northwestern great basin during the last 14 000 years the northwestern great basin lies in the transition zone between the mesic pacific northwest and xeric intermountain west the paleoenvironmental history based on pollen macroscopic charcoal and plant macrofossils from three sites in the northwestern great basin was examined to understand the relationships among the modern vegetation fire disturbance and climate the vegetation history suggests that steppe and open forest communities were present at high elevations from ca 11 000 to 7000 cal yr bp and were replaced by forests composed of white fir western white pine and whitebark pine in the late holocene over the last 11 000 years fires were more frequent in mid elevation forests 10 25 fire episodes 1000 years and rare in high elevation forests 2 5 fire episodes 1000 years applying modern pollen climate relationships to the fossil pollen spectra provided a means to interpret past climate changes in this region in the past 9000 years summer temperatures decreased from 1 to 41c and annual precipitation has increased 7 15 these results indicate that the millennial scale climate forcing driving vegetation changes can be quantified within the intermountain west in general and northwestern great basin in particular in addition fire can be considered an important component of these ecosystems but it does not appear to be a forcing mechanism for vegetation change at the resolution of these records r 2007 elsevier ltd all rights reserved

a late wisconsin 32 10k cal a bp history of pluvials droughts and vegetation in the pacific south west united states lake elsinore ca continuous sub centennially resolved paleo terrestrial records are rare from arid environments such as the pacific south west united states here we present a multi decadal to centennial resolution sediment core lake elsinore ca to reconstruct late wisconsin pluvials droughts and vegetation in general the late wisconsin is characterized by a wetter and colder climate than during the holocene specifically conditions between 32 3 and 24 9k cal a bp are characterized by large amplitude hydrologic and ecologic variability highlighting this period is a 2000 year glacial mega drought 27 6 25 7k cal a bp during which the lake shallowed 3 2 4 5 m depth this period is approximately coeval with a lake manix regression and an increase in xeric vegetation in the san bernardino mountains baldwin lake the local last glacial maximum llgm is bracketed between 23 3 and 19 7k cal a bp a 3000 year interval characterized by reduced run off relative to the glacial colder conditions and vegetative stability maximum sustained wetness follows the llgm beginning at 19 7 and peaking by 14 4k cal a bp a two step decrease in runoff characterizes the lateglacial to holocene transition however the vegetation change is more complex particularly at the beginning of the younger dryas chronozone by 12 6 12 4k cal a bp the climate achieved near holocene conditions

tajik basin and southwestern tian shan northwestern india asia collision zone 3 preorogenic to synorogenic retro foreland basin evolution in the eastern tajik depression and linkage to the pamir hinterland

nearly synchronous climate change in the northern hemisphere during the last glacial termination the climate of the north atlantic region underwent a series of abrupt cold warm oscillations when the ice sheets of the northern hemisphere retreated during the last glacial termination 17 7 11 5kyr ago evidence for these oscillations which are recorded in european terrestrial sediments as the oldest dryas bolling older dryas allerod younger dryas vegetational sequence1 2 has been found in greenland ice cores3 4 the geographical extent of many of these oscillations is not well known5 6 but the last major cold event the younger dryas seems to have been global in extent7 8 9 10 here we present evidence of four major oscillations in the hydrological balance of the owens basin california that occurred during the last glacial termination dry events in western north america occurred at approximately the same time as cold events recorded in greenland ice with transitions between climate regimes in the two regions taking place within a few hundred years of each other our observations thus support recent climate simulations which indicate that cooling of the north atlantic ocean results in cooling of the north pacific ocean11 which in turn leads to a drier climate in western north america12

continental margin tectonics submarine accretionary prisms submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted deformed and ultimately transformed to continental crust accretionary prisms develop at sites of lithospheric convergence that is subduction zones commonly accretionary prisms form along continental margins although accretionary prisms may also occur adjacent to island arcs which are ultimately coalesced into continental landmasses here we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the united states

modelling teleconnections between the north atlantic and north pacific during the younger dryas evidence for a cooling event synchronous with the younger dryas 12 000 calendar years before present has been found in the north pacific ocean north of 30 n in records of surface1 5 and subsurface water properties6 7 these changes may be related to a temporary shut down of north atlantic deep water formation and associated surface cooling over the north atlantic it has remained unclear however whether this north atlantic cooling was communicated to the north pacific ocean through the atmosphere or the ocean here we report results of a sensitivity experiment with a coupled ocean atmosphere general circulation model that support a primarily atmospheric forcing of north pacific climate variations changes in wind strongly affect coastal upwelling at the north american west coast and surface cooling by the atmosphere causes better ventilation of the thermocline waters of the northeast pacific this effect is amplified by oceanic progagation to the pacific of the signal arising from collapse of north atlantic deep water formation these teleconnections may also explain earlier north pacific and western north american millenial scale cooling events of a similar nature8 12

last glacial maximum and holocene lake levels of owens lake eastern california usa abstract stratigraphic investigations of fluvio deltaic and lacustrine sediments exposed in stream cuts quarry walls and deep trenches east of the sierra nevada in owens valley near lone pine california have enabled the reconstruction of pluvial owens lake level oscillations age control for these sediments is from 22 radiocarbon 14 c dates and the identification and stratigraphic correlation of a tephra which when plotted as a function of age versus altitude define numerous oscillations in the level of pluvial owens lake during the latest pleistocene and early holocene we have constructed a lake level altitude curve for the time interval 27 000 cal yr bp to present that is based on the integration of this new stratigraphic analysis with published surface stratigraphic data and subsurface core data pluvial owens lake regressed from its latest pleistocene highstands from 27 000 to 15 300 cal yr bp as recorded by 15 m of down cutting of the sill from the altitudes of 1160 to 1145 m by 11 600 cal yr bp the lake had dropped 45 m from the 1145 m sill this lowstand was followed by an early holocene transgression that attained a highstand near 1135 m before dropping to 1120 m at 7860 7650 cal yr bp that had not been recognized in earlier studies the lake then lowered another 30 m to shallow and near desiccation levels between 6850 and 4300 cal yr bp fluvial cut and fill relations north of lone pine and well preserved shoreline features at 1108 m indicate a minor lake level rise after 4300 cal yr bp followed by alkaline and shallow conditions during the latest holocene the new latest quaternary lake level record of pluvial owens lake offers insight to the hydrologic balance along the east side of the southern sierra nevada and will assist regional paleoclimatic models for the western basin and range

least squares restoration of tertiary thrust sheets in map view tajik depression central asia the tajik depression located west of the pamirs and south of the tien shan is a compressional intermontane basin bounded by basement overthrusts and filled with mesozoic and cenozoic sediments the internal structure is typical of a thin skinned tbld and thrust belt kinematic data available in the literature suggest that indentation of the pamirs into asia durino the cenozoic collision of india and asia has been accommodated in various ways within the depression including westward extrusion thickening combined with wrenching along n s tblds and thrusts and counterclockwise rotations these various detbrmation processes can be analyzed and quantified by reconstruction of the predeformed state of the depression however the combina tion of thrusting wrenching and block rotations implies a nonplane deformation which cannot be restored properly using balanced cross sections alone we have therefore developed a numerical method for restoration of stratigraphic surfaces designed for regions of nonplane compressional tectonics the deformed region is represented in map view as a mosaic of fault bounded blocks overlapping each other along the faults blocks are separately unfolded and then numerically packed together by least squares minimization of overlaps yielding fields of finite horizontal translations and rotations about vertical axes to analyze the deformation postdating the collision of india and asia we have restored a stratigraphic surface at the base of the cenozoic first in order to test the numerical method we restored a map that had previously been restored by a purely manual method restoration of a second map drawn from newly available subsurface data leads to geometrical inconsistencies overlaps and gaps which cannot be reduced remain in the restored state after correction of these inconsistencies restoration yields a complex mode of deformation for the depression individual thrust slices have undergone counterclockwise rotations about verti cal axes the magnitudes increasing from west to east up to a maximum of 40 o near the pamirs horizontal shortening is 150 km 35 in the center of the depression and 240 km 85 in the northeastern part between the pamirs and the tien shan strike slip motions commonly not revealed by balancing cross sections are associated with thrusting on faults striking n s inde pendent paleomagnetic data and slip directions on small scale faults provide positive checks on the results of our restoration

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

dense gnss profiles across the northwestern tip of the india asia collision zone triggered slip and westward flow of the peter the first range pamir into the tajik depression

environmental changes of a shallow kettle lake catchment in a young glacial landscape sumowskie lake catchment north central poland abstract on the basis of detailed analysis sedimentological palynological macroremains geochemical and gis analysis the development of the sumowskie paleolake was reconstructed obtained results led to distinguish three main stages of the evolution of the basin and its catchment during the late glacial and the holocene the lacustrine stage the lake overgrowth stage and the post lacustrine stage study site is located in the western part of the brodnica lakeland north eastern poland within the former sumowskie lake bottom multidisciplinary research was conducted for two cores sedimentological palynological plant macroremains sum a 149 cm and sum c 51 cm and the soil profile sum 3 sedimentological geochemical gis analyses land cover and water level changes were carried out for the nowadays sumowskie lakes catchment it was confirmed that climate was the most important factor influencing the evolution of the lake and its surrounding although the role of this factor decreased in the neo holocene period in favor of rapidly growing human impact changes of the water level were much more abrupt and lasted longer e g 9500 5000 bp hiatus caused by the water level decrease than in other described basins of the region due to the specific geomorphologic situation shallow kettle basins could alternately act as lakes and wetlands as they are well spread in the young glacial area the strong influence of this abrupt and long term events should be reconsidered

late glacial and early holocene vegetation and climate change near owens lake eastern california abstract pollen and algae from owens lake in eastern california provide evidence for a series of climatic oscillations late in the last glaciation juniper woodland which dominated the owens valley from 16 200 to 15 500 cal yr b p suggests much wetter conditions than today although still wetter and cooler than today the area then became fairly warm and dry with woodland being replaced by shrubs mainly sagebrush from 15 500 to 13 100 cal yr b p next chenopodiaceae shadscale increased woody species declined and lake levels fell all evidence for a brief ca 100 200 yr drought about 13 000 cal yr b p the climate continued to oscillate between wet and dry from 13 000 to 11 000 cal yr b p after 11 000 cal yr b p low lake levels and the increased dominance of desert shrubs indicate the beginning of warm dry holocene conditions the region s climate was unstable during the younger dryas but uncertainities in dating prevent identification of the younger dryas interval in the owens lake record comparison of the owens lake record with studies in the sierra nevada and great basin suggest that the climate was generally wetter between 13 000 and 11 000 cal yr b p with warmer summers although no consistent pattern of climate change emerges

interactive processing of satellite images for structural and lithological mapping in northeast africa interactive digital processing of multispectral satellite images landsat mss using principal components transformations and spatial filtering has clarified the position of continuous sutures linking apparently isolated pan african late proterozoic ophiolites these have been field checked and an arrangement of pan african suture zones is proposed spatial filtering has also highlighted faults with various trends which can be related to the late precambrian tectonics of the horn of africa region

nonlocal sediment transport on steep lateral moraines eastern sierra nevada california usa available for download is the author s version of the paper the final publisher s version is available at https dx doi org 10 1002 2017jf004325 the dataset doi is https doi org 10 15695 vudata cee 1

episodic late quaternary slopewash deposition as recorded in colluvial aprons southeastern wyoming abstract colluvial aprons found along fluvial terraces of the laramie river and sybille creek in southeastern wyoming are interpreted as late quaternary slopewash deposits each apron studied contained multiple buried soils interpreted to indicate that slopewash activity was episodic and short lived and was followed by relatively long periods of landscape stability and soil development apron deposits were described and subsequently correlated based on their internal stratigraphy and their relative degree of soil development optical dating was used to chronologically constrain periods of slopewash deposition and based on 17 optical ages taken from five aprons aggradation occurred at 65 56 16 0 12 9 11 8 8 1 7 3 5 0 and 1 7 ka several of these events correspond with climatic transitions such as the termination of heinrich event 1 the onset and termination of the younger dryas and the 8 2 ka event suggesting that apron aggradation was driven by changes in climatic regime although either increased aridity or a change in precipitation regime could result in increased erosion of terrace scarps apron aggradation events do not correlate with regional records of aridity instead periods of increased precipitation intensity and or frequency that occur during climatic transitions most likely drive apron aggradation events

late wisconsin paleoecologic record from swamp lake yosemite national park california a 7 86 m sediment core from swamp lake in yosemite national park california provides a continuous record of environmental change over the last ca 16 000 yr as inferred from pollen macrofossil and microscopic charcoal analyses the core stratigraphy documents late wisconsin tioga stage deglaciation between 16 000 and 13 700 yr b p approximately 6000 3500 yr earlier than higher elevation sierra nevada records the core includes five volcanic ash layers chemically identified as four mono craters ashes and the tsoyawata ash mt mazama oregon the fossil record shows that herbs and sagebrush dominated the glacial environment at swamp lake by 12 000 yr b p a mixed conifer forest composed of high and mid elevation conifers grew around the lake suggesting a cool wet late glacial environment the modern sierra montane forest did not become established until ca 10 400 yr b p when maximum charcoal concentrations and minimum fir pollen percentages indicate an early holocene xeric period the record suggests that a cooling trend began ca 6500 yr b p and persisted until ca 3700 yr b p when the modern climatic regime was established

multibeam study of the flores backarc thrust belt indonesia using the seamarc ii seafloor mapping tool in conjunction with closely spaced seismic reflection profiles we have mapped a segment of the flores back arc thrust zone structural irregularities along the deformation front of the thrust zone result from changing stratigraphy and basement structure of the lower plate ne trending faults cutting the outer slope of the flores basin are easily mapped because they truncate dense drainage patterns obliquely mud diapirs probably indicating elevated fluid pressures have formed throughout the accretionary wedge but appear to be concentrated as do back arc thrust earthquakes at the ends of thrust faults the overall orientation of the deformation front of the accretionary wedge is 100 suggesting a nne sense of thrust motion and supporting an origin of the thrust zone by collision of the arc with australia rather than by magmatic forcing or gravitational sliding or spreading orientations of faults and folds close to the arc are not consistent with the trends of the frontal thrusts however and the difference may be due to either different initial orientations or to later rotations of structural features as the accretionary wedge grew

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

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

the impact of cold north atlantic sea surface temperatures on climate implications for the younger dryas cooling 11 10 k the sensitivity of global climate to colder north atlantic sea surface temperatures is in vestigated with the use of the giss general circulation model north atlantic ocean temperatures 18 000 b p resembling those prevalent during the younger dryas were incorporated into the model of the present climate and also into an experiment using orbital parameters and land ice characteristic of 11 000 b p the results show that with both 11 000 b p and present conditions the colder ocean temperatures produce cooling over western and central europe in good agreement with younger dryas paleoclimatic evidence cooling also occurs over extreme eastern north america although the precise magnitude and location depends upon the specification of ocean temperature change in the western atlantic despite the presence of increased land ice and colder ocean temperatures the younger dryas summer air temperatures at northern hemisphere midlatitudes in the model are warmer than those of today due to changes in the orbital parameters chiefly precession and atmospheric subsidence at the perimeter of the ice sheets

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

evidence for younger dryas age cooling on the north pacific coast of america abstract a review of the palynological evidence from the olympic peninsula of washington state north to the alaska panhandle strongly supports the existence of a climatic oscillation similar in timing and effect to the younger dryas cooling 11 10 ka bp of europe and eastern north america the evidence includes many late glacial pollen peaks of mountain hemlock tsuga mertensiana an indicator of cool and moist climate reversals from forest to non arboreal vegetation and paleoclimate analysis using pollen climate transfer functions on the queen charlotte islands evidence of cooler ocean waters based on fossil foraminifera in cores from the continental shelf also supports an interpretation of a younger dryas age climatic reversal on the other hand geological evidence of glacier readvances during the younger dryas chronozone is weak and poorly dated although more and better constrained ams dates are needed to confirm the timing of the pacific northwest cold oscillation results so far point to maximum cooling and increased moisture between ca 10 7 10 ka bp followed by rapid warming in the early holocene additional late glacial sites need to be investigated in detail to confirm the geographical pattern of vegetation and climate change during this interval which is best expressed in hypermaritime and maritime climate regions similar to the younger dryas event around the north atlantic these results suggest that the search for causal mechanisms to drive the younger dryas cooling cannot be limited to events in the north atlantic region but should focus on possible hemispheric or global processes

radiocarbon chronology of lake bonneville eastern great basin usa abstract lake bonneville occupied a series of connected topographically closed structural basins in the eastern great basin from about 30 ka to 12 ka the following synthesis of lake bonneville history is based on a critical evaluation of the stratigraphic and geomorphic contexts of 83 radiocarbon ages of a variety of samples including wood charcoal dispersed organic matter mollusk shells and tufa the lake began to rise from levels close to average holocene levels after about 28 ka by 22 ka it had transgressed approximately 100 m between 22 and 20 ka it regressed about 45 m in the stansbury oscillation and the stansbury shoreline was formed transgression after 20 ka proceeded in two phases a rapid phase from 20 to 18 ka and a slower phase from 18 to 15 ka the lake overflowed intermittently at its highest level the bonneville shoreline from about 15 to 14 5 ka then catastrophically dropped 100 m during the bonneville flood to the level of the provo shoreline which it occupied until about 14 ka subsequent closed basin regression was rapid and complete by 12 ka and was followed by a modest transgression to form the gilbert shoreline between 10 9 and 10 3 ka the lake bonneville record is an accurate proxy of the changing water balance in the bonneville basin during the late pleistocene although the nature of the climatic changes during this period are still uncertain

stalagmite records of hydroclimate in central california during termination 1 abstract the last deglaciation is marked by large and abrupt hydroclimatic changes in the great basin and the american southwest however comparatively little is known about how hydroclimate varied on the western side of the sierra nevada we present new evidence for abrupt changes in precipitation amount in the central sierra nevada during the last deglaciation our new record from mclean s cave overlaps with a previously published record from nearby moaning cave oster et al 2009 and extends the record of hydroclimatic change in the region through heinrich stadial 1 mclean s cave speleothem 18o 13c mg ca and sr ca indicate a shift to drier conditions at the beginning of heinrich stadial 1 from 16 1 to 17 5 ka followed by wetter conditions at the end of heinrich stadial 1 when the majority of great basin lakes reached their deglacial highstands during the last deglaciation coincident shifts in the moaning and mclean s cave proxy records indicate drier conditions in the western sierra nevada during millennial scale intervals of warming at high latitudes such as the bolling and allerod and wetter conditions during cooler intervals such as the older and younger dryas thus the sierra nevada speleothem records are consistent with other regional records that document increased winter rainfall during millennial scale cold periods of the last deglaciation however regional differences exist in the hydroclimatic response to the younger dryas with central californian and interior southwestern sites indicating an increase in winter storms that is not apparent in southern california dynamic simulations of atmospheric circulation indicate that wetter conditions during the younger dryas relative to the bolling at mclean s cave may have resulted from a stronger storm track in the north pacific at the latitude of northern california

late pleistocene california droughts during deglaciation and arctic warming abstract recent studies document the synchronous nature of shifts in north atlantic regional climate the intensity of the east asian monsoon and productivity and precipitation in the cariaco basin during the last glacial and deglacial period yet questions remain as to what climate mechanisms influenced continental regions far removed from the north atlantic and beyond the direct influence of the inter tropical convergence zone here we present u series calibrated stable isotopic and trace element time series for a speleothem from moaning cave on the western slope of the central sierra nevada california that documents changes in precipitation that are approximately coeval with greenland temperature changes for the period 16 5 to 8 8 ka from 16 5 to 10 6 ka the moaning cave stalagmite proxies record drier and possibly warmer conditions signified by elevated 18 o 13 c mg sr and ba and more radiogenic 87 sr 86 sr during northern hemisphere warm periods bolling early and late allerod and wetter and possibly colder conditions during northern hemisphere cool periods older dryas inter allerod cold period and younger dryas moaning cave stable isotope records indicate that wet conditions persisted in this area well beyond 11 5 ka suggesting the effects of the younger dryas event may have been longer lived in the western sierra nevada than in greenland however a shifting drip center and corresponding change in seepage water routing may have influenced the trace element records between 10 6 and 9 6 ka linkages between northern high latitude climate and precipitation in the sierra nevada suggested here could indicate that under conditions of continued global warming this drought prone region may experience a reduction in pacific sourced moisture

lake bonneville fluctuations and global climate change lake bonneville the largest late pleistocene closed basin lake in the north american great basin fluctuated widely in response to changes in climate the geochemistry and mineralogy of endogenic calcium carbonate deposited in deep water and stratigraphic studies of shore zone deposits provide evidence of millennial scale lake level fluctuations that had amplitudes of about 50 m between 30 and 10 ka falling lake events occurred at 21 18 5 19 17 5 16 15 5 14 13 and 10 ka radiocarbon years synchronously with the terminations of heinrich events h1 and h2 and other smaller scale iceberg rafting events a b c and younger dryas in the north atlantic ocean the lake bonneville results thus support other climate records that suggest that late pleistocene millennial scale climate change was global in extent the size and shape of the northern hemisphere ice sheets which determined the mean positions of storm tracks may have been the primary control on late pleistocene water budgets of great basin lakes

fluvial tufa evidence of late pleistocene wet intervals from santa barbara california u s a abstract past pluvials in the western united states provide valuable context for understanding regional hydroclimate variability here we report evidence of conditions substantially wetter than today from fluvial tufa deposits located near zaca lake santa barbara county california that have been dated by radiocarbon 14c and infra red stimulated luminescence irsl two successions of tufa deposition occur within a small catchment that drains miocene monterey formation bedrock 1 a fluvial deposit 0 0 5 m thick 200 m in extent that formed along a narrow valley below a modern spring and 2 a perched deposit 10 m higher 2 m thick 15 m in extent irsl and radiocarbon dating of the perched carbonates suggest at least two episodes of carbonate growth one at 19 4 2 4 1 through 17 8 2 8 1 ka and another at 11 9 1 5 1 ka verified with a charcoal 14c age of 10 95 0 12 2 cal ka bp the relationship between the perched and fluvial spring deposits is inferred to represent a drop in the water table of more than 10 m associated with a transition from a wet climate in the late glacial to a dry holocene today the wet period indicated by the perched tufa deposit between 19 4 and 17 8 ka is relatively consistent with other california climate records both north and south of zaca lake however tufa growth ca 12 to 11 ka demonstrates wet conditions occurred as far south as zaca lake during the younger dryas event in contrast to climate records farther south in lake elsinore that indicate a drying trend through this interval a small shift north in the average position of the winter season storm track could explain wet winters at zaca while at the same time generating dry winters at lake elsinore 275 km southwest of zaca if true these data indicate that rather small latitudinal shifts in the average winter season storm track can produce large changes in regional hydroclimate

spatial patterns of atmospheric pollen transport in a montane region abstract annual pollen deposition pollen cm 2 yr 1 was sampled for 6 yr in the southern sierra nevada the owens valley and the inyo mountains of central california spatial pollen distributions were examined for anemophilous plants which are limited to growth sites 1 at high elevations on one or both mountain ranges 2 on lower mountain slopes and 3 on the owens valley floor pollen deposition values for high and low elevation plants changed by a factor of 5 to 10 between adjacent sample sites which straddle boundaries of the plant communities in which the source plants grow pollen deposition values were high and variable within communities in which the species grew pollen deposition beyond source populations was low and uniform despite great differences in distance of sites from pollen sources the step function that seems to characterize pollen distribution patterns implies that pollen from distant populations may be of little value in interpreting vegetation stability and change reflected by fossil pollen stratigraphy the physical isolation of pollen embedded in the local mountain valley wind system from that in the prevailing westerlies may explain part of the spatial distribution of the pollen

tracking regional and global teleconnections recorded by western north american speleothem records abstract speleothem proxy records are useful for interrogating past climates in the low and mid latitudes given their ability to provide continuous high resolution and long lived records that can be dated with high precision several speleothem oxygen isotope records from western north america have recently been developed that highlight the importance of this archive in documenting past changes in atmospheric circulation taken individually these records hint at teleconnections between western north american hydroclimate and climate changes in the high northern latitudes and tropics however there has been no systematic investigation of global climate teleconnections to this region that draws upon the body of north american speleothem records as a whole here we review the dominant controls on precipitation oxygen isotopes across the region and conduct statistical comparisons and network visualizations of high resolution speleothem oxygen isotope records from western north america to investigate the regional response to pronounced climate changes of the last deglaciation and to determine the pattern of global teleconnections to this region we find that most western north american speleothem oxygen isotope records demonstrate a robust and consistent response to the events of the last deglaciation despite differing controls on the oxygen isotope ratio of precipitation across the region one record that receives a strong influence from the gulf of mexico exhibits a contrasting pattern in oxygen isotopes relative to most of the other records which are dominated by westerly storms generated in the pacific during the studied interval major shifts in western north american speleothem records appear broadly synchronous at least within the uncertainty of age models we also find strong statistical linkages between western north american speleothem records and speleothem records of asian monsoon variability and other records from regions directly influenced by movement of the intertropical convergence zone demonstrating that nearly synchronous changes in atmospheric circulation measurably altered precipitation dynamics in these regions during the last deglaciation further multi proxy investigations are needed to determine how such changes in atmospheric circulation recorded by speleothem oxygen isotope ratios influenced precipitation amounts in drought prone western north america

a reassessment of u th and14c ages for late glacial high frequency hydrological events at searles lake california u th isochron ages of tufas formed on shorelines suggest that the last pluvial event in lake lahontan and searles lake was synchronous at about 16 500 cal yr b p equivalent to a radiocarbon age of between 14 000 and 13 500 yr b p whereas the timing of this pluvial event determined by radiocarbon dating is on the order of 1000 yr younger the timing of seven distinct periods of near desiccation in searles lake during late glacial time has been reinvestigated for u th age determination by mass spectrometry u th dating of evaporite layers in the interbedded mud and salt unit called the lower salt in searles lake was hampered by the uncertainty in assessing the initial230th 232th of the samples the resulting ages corrected by a conservative range of initial230th 232th ratios suggest close correlation of the abrupt changes recorded in greenland ice cores dansgaard oeschger events and wet dry conditions in searles lake between 35 000 and 24 000 cal yr b p

pluvial lakes in the great basin of the western united states a view from the outcrop abstract paleo lakes in the western united states provide geomorphic and hydrologic records of climate and drainage basin change at multiple time scales extending back to the miocene recent reviews and studies of paleo lake records have focused on interpretations of proxies in lake sediment cores from the northern and central parts of the great basin in this review emphasis is placed on equally important studies of lake history during the past 30 years that were derived from outcrop exposures and geomorphology in some cases combined with cores outcrop and core records have different strengths and weaknesses that must be recognized and exploited in the interpretation of paleohydrology and paleoclimate outcrops and landforms can yield direct evidence of lake level facies changes that record details of lake level fluctuations and geologic events such as catastrophic floods drainage basin changes and isostatic rebound cores can potentially yield continuous records when sampled in stable parts of lake basins and can provide proxies for changes in lake level water temperature and chemistry and ecological conditions in the surrounding landscape however proxies such as stable isotopes may be influenced by several competing factors the relative effects of which may be difficult to assess and interpretations may be confounded by geologic events within the drainage basin that were unrecorded or not recognized in a core the best evidence for documenting absolute lake level changes lies within the shore nearshore and deltaic sediments that were deposited across piedmonts and at the mouths of streams as lake level rose and fell we review the different shorezone environments and resulting deposits used in such reconstructions and discuss potential estimation errors lake level studies based on deposits and landforms have provided paleohydrologic records ranging from general changes during the past million years to centennial scale details of fluctuations during the late pleistocene and holocene outcrop studies have documented the integration histories of several important drainage basins including the humboldt amargosa owens and mojave river systems that have evolved since the miocene within the active tectonic setting of the great basin these histories have influenced lake levels in terminal basins many pre late pleistocene lakes in the western great basin were significantly larger and record wetter conditions than the youngest lakes outcrop based lake level data provide important checks on core based proxy interpretations we discuss four such comparisons in some cases such as for lakes owens and manix outcrop and core data synthesis yields stronger and more complete records in other cases such as for bonneville and lahontan conflicts point toward reconsideration of confounding factors in interpretation of core based proxies

black mats spring fed streams and late glacial age recharge in the southern great basin black mats are prominent features of the late pleistocene and holocene stratigraphic record in the southern great basin faunal geochemical and sedimentological evidence shows that the black mats formed in several microenvironments related to spring discharge ranging from wet meadows to shallow ponds small land snails such asgastrocopta tappanianaandvertigo berryiare the most common mollusk taxa present semiaquatic and aquatic taxa are less abundant and include catinellids fossaria parva gyraulus parvus and others living today in and around perennial seeps and ponds the ostracodescypridopsis okeechobiandscottia tumida typical of seeps and low discharge springs today as well as other taxa typical of springs and wetlands are common in the black mats several new species that lived in the saturated subsurface also are present but lacustrine ostracodes are absent the 13c values of organic matter in the black mats range from 12 to 26 reflecting contributions of tissue from both c3 sedges most shrubs and trees and c4 saltbush saltgrass plants carbon 14 dates on the humate fraction of 55 black mats fall between 11 800 to 6300 and 230014c yr b p to modern the total absence of mats in our sample between 6300 and 230014c yr b p likely reflects increased aridity associated with the mid holocene altithermal the oldest black mats date to 11 800 11 60014c yr b p and the peak in the14c black mat distribution falls at 10 00014c yr b p as the formation of black mats is spring related their abundance reflects refilling of valley aquifers starting no later than 11 800 and peaking after 11 00014c yr b p reactivation of spring fed channels shortly before 11 20014c yr b p is also apparent in the stratigraphic records from the las vegas and pahrump valleys this age distribution suggests that black mats and related spring fed channels in part may have formed in response to younger dryas yd age recharge in the region however the inception of black mat formation precedes that of the yd by at least 40014c yr and hydrological change is gradual not rapid