holocene history of fire vegetation and land use from the central pyrenees france located on a mountain pass in the west central pyrenees the col d ech peat bog provides a holocene fire and vegetation record based upon nine 14c ams dates we aim to compare climate driven versus human driven fire regimes in terms of frequency fire episodes distribution and impact on vegetation our results show the mid holocene 8500 5500 cal yr bp to be characterized by high fire frequency linked with drier and warmer conditions however fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution wetter and colder conditions at the mid to late holocene transition 4000 3000 cal yr bp led to a decrease in fire frequency probably driven by both climate and a subsequent reduction in human land use on the contrary from 3000 cal yr bp fire frequency seems to be driven by agro pastoral activities with a very regular distribution of events during this period fire was used as a prominent agent of landscape management

review and test of reproducibility of subdecadal resolution palaeoenvironmental reconstructions from microfossil assemblages abstract very high even annual resolution quantitative palaeoenvironmental reconstructions have been generated from microfossil assemblage data using transfer functions evidence of the utility of some of these reconstructions is given by the high correlations between the reconstructions and instrumental records such performance is despite several ecological and taphonomic issues that can become more problematic at subdecadal resolution than at multidecadal resolution this paper explores these timescale dependent issues and tests the reproducibility of the several of published reconstructions it demonstrates that the previously reported exceptionally good performance of several published chironomid based reconstructions is not reproducible

origin of the late early cretaceous granodiorite and associated dioritic dikes in the hongqilafu pluton northwestern tibetan plateau a case for crust mantle interaction we present a detailed study of geochronology mineral chemistries bulk rock major and trace element abundances and sr nd hf isotope compositions of the granodiorite and associated dioritic dikes in the hongqilafu pluton at the northwestern margin of the tibetan plateau the granodiorite and dioritic dikes yielded zircon u pb ages of similar to 104 ma and similar to 100 ma respectively the dioritic dikes comprise varying lithologies of gabbroic diorite diorite porphyry and granodiorite porphyry exhibiting a compositional spectrum from intermediate to felsic rocks their mineral compositions display disequilibrium features such as large major element compositional variations of plagioclase clinopyroxene and amphibole crystals these dioritic dikes are enriched in incompatible elements ba rb th u k and sr nd hf isotopes sr 87 86 sri 0 7066 to 0 7071 epsilon nd t 5 3 to 7 4 epsilon hf t 3 6 to 6 2 we suggest that the dioritic dikes were most likely derived from partial melting of mantle wedge metasomatized by the subducted subducting seafloor with a sediment component followed by afc processes with fractional crystallization of clinopyroxene amphibole and plagioclase and assimilation of lower continental crust the mantle wedge derived magma parental to the dioritic dikes underplated and induced the lower continental crust to melt forming the felsic crustal magma parental to the granodiorite with mantle melt signatures and having more enriched isotope compositions sr 87 86 sri 0 7087 to 0 7125 epsilon nd t 9 5 to 11 6 epsilon hf t 10 3 to 14 1 than those of the dioritic dikes the hongqilafu pluton is thus the product of mantle crust interaction at an active continental margin subduction setting over the period of several million years this understanding further indicates that the closure timing of the shyok back arc basin and the collision between the kohistan ladakh arc and the karakoram terrane may have taken place later than similar to 100 ma c 2016 elsevier b v all rights reserved

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

episodic unroofing of the kohistan batholith pakistan implications from k feldspar thermochronology new 40ar 39ar and u pb mineral ages from plutonic rocks help constrain the thermal and tectonic evolution of the kohistan island arc terrane following its collision with india in early tertiary time kohistan has experienced a prolonged tectonomagmatic history extending from the early cretaceous through the tertiary thermal histories derived from multi diffusion domain analyses of k feldspar within the kohistan batholith reveal rapid cooling events 70 140 c m y distributed through space and time the cooling histories show a systematic variation along the length of the batholith suggesting that kohistan experienced differential unroofing an episode of rapid cooling in the middle eocene is recognized in western kohistan whereas rapid cooling occurs substantially later during the middle and late miocene in eastern kohistan rapid cooling in western kohistan might have been caused by postemplacement cooling of hot magma against cold country rocks at relatively shallow crustal levels within the nw region of eastern kohistan rapid cooling at 13 12 ma is recorded in k feldspars 60 km from the contact with the nanga parbat haramosh massif nphm whereas cooling does not occur until 11 ma only 2 5 km from the contact this temporal and spatial variation in cooling histories may record differential unroofing in response to the development and propagation of the nphm structure beneath kohistan the nphm has experienced rapid cooling and unroofing over the last 10 m y and our results are consistent with this mid late miocene event

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

comparing fire history interpretations based on area number and estimated volume of macroscopic charcoal in lake sediments sedimentary charcoal particles from lakes are commonly used to investigate fire history fire history reconstructions are based on measuring the surface area or counting the number of charcoal fragments in adjacent samples recently the volume of charcoal particles was advised as a more accurate method for quantifying past charcoal production large charcoal datasets used to synthesize global fire history include these different types of charcoal measurements and implicitly assume that they provide comparable fire history information however no study has demonstrated that this assumption is valid here we compare fire frequency reconstructions based on measurements of charcoal area and number and estimates of charcoal volume from two lake sediment records from the eastern canadian boreal forest results indicate that the three proxies provide comparable fire history interpretations when using a locally defined threshold to identify fire events

collision tectonics in the nw himalayas west himalayan tectonics involve the collision of microplates between the indian and asian plates the kohistan complex consists largely of tightly folded basic volcanics and sediments generated as late jurassic to late cretaceous island arcs these were intruded by post folding mid cretaceous eocene plutonics produced from continued subduction of the indian plate after closure of a suture between kohistan and the karakorum the himalayan structures show major thrust sheets and the kohistan arc is essentially a crustal pop up with southward upright and northward verging structures developed above a thick ductile decoupling zone the indus suture which can be traced for 100 km beneath kohistan on large reentrants this pop up formed by a two stage process closure of the northern suture followed by closure of the southern indus suture granitic rocks of the kohis tan ladakh batholith dated at 100 40 ma post date most of the structures related to the northern suture but were deformed and carried southwards on shear structures related to the indus suture postcollisional deformation carried this kohistan complex on deep decoupling zones over the indian plate on a series of imbricated gneiss sheets the thrusts climbing up section in the movement direction so that in the far s some override their own molasse debris folds above these deep decoupling zones deformed their overlying thrust sheets into large antiforms i e the nanga parbat and hazara syntaxes the nanga parbat syntaxis probably formed due to a shear couple near a branch line where one of the main himalayan thrusts joined the indus suture beneath kohistan crustal delamination to produce the imbricated gneiss sheets could not account for all the displacement of india into asia suggested by palaeomagnetic data there must also have been lateral displacement as demonstrated by the large oblique slip shear zone in the hunza valley n of kohistan

rock assemblages in central asia and the evolution of the southern asian margin by looking in detail at the rock record in central asia it is possible to map rock assemblages that are diagnostic of particular plate settings simplest of the assemblages include the rocks of the tadjik depression where mesozoic and paleogene sediments record the development of a south facing passive continental margin analysis of igneous activity in central asia and of the timing of deformation of these miogeoclinal rocks indicates that the paleotethyan ocean to the south was in the mesozoic subducting to the south beneath a migratory arc consisting of parts of iran afghanistan and the pamir only in the late tertiary does the tadjik depression develop a peripheral foreland assemblage which indicates any deformation of the miogeocline this presumably occurred as a result of the closing of the paleotethyan ocean and accretion of this portion of the arc to the southern margin of asia it appears unlikely that the depression passive margin sequence developed in a normal rift margin setting analysis of assemblages in the hercynian orogen tien shan to the north indicates that unlike the uralian section of the orogen the deformation here occurred due to the closure of a marginal basin and overthrusting of its basement rocks over a south facing arc thus considering depression basement composition it appears that the passive margin assemblage is superimposed over either a late paleozoic forearc or paleozoic ocean floor paleozoic rocks exposed north of the herat suture in afghanistan may require the forearc basement interpretation noting that the geometry of subduction and the timing of paleotethyan suturing seem to have varied along strike in the orogen a more complicated model of tectonic accretion is required

a signal to noise index to quantify the potential for peak detection in sediment charcoal records article i nfo charcoal peaks in lake sediment records are commonly used to reconstruct fire histories spanning thousands of years but quantitative methods for evaluating the suitability of records for peak detection are largely lacking we present a signal to noise index sni that quantifies the separation of charcoal peaks signal from other variability in a record noise we validate the sni with simulated and empirical charcoal records and show that an sni n3 consistently identifies records appropriate for peak detection the sni thus offers a means to evaluate the suitability of sediment charcoal records for reconstructing local fires matlab and r functions for calculating sni are provided

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

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

warm mediterranean mid holocene summers inferred from fossil midge assemblages reconstructions of holocene summer temperatures differ between models and vegetation based proxies a quantitative reconstruction for the mediterranean region based on fossil midge assemblages suggests warm summers in line with climate models

sedimentary charcoal pattern in a karstic underground lake vercors massif french alps implications for palaeo fire history knowledge on processes of charcoal transportation is crucial for fire reconstruction based on sedimentary charcoal charcoal is susceptible to long distance transport by water a lake basin with a large and long catchment area is likely to accumulate charcoal from many fires not only those produced by fires nearby the lakeshore here we test the potential of charcoal transportation by analysing sedimentary charcoal accumulated in an underground lake within a karstic massif fires cannot spread around the lake nor within the karstic massif organic materials including charred particles are generated several kilometres from the lake on the karstic plateau above the pattern of sedimentary charcoal shows that the underground lake records continuously produced charcoal by wild fires or human made biomass burning slash and burn charcoal kilns over centuries and millennia but also stored charcoal from eroded soils although the charcoal series shows a certain high variability signal fire frequency reconstruction cannot be performed owing to chronological uncertainties the charcoal accumulation corresponds to a more or less regular background input such background input is empirically well described in palaeo fire reconstruction but was never experimentally displayed this study provides evidence that the pattern surface length slope etc of catchment areas is crucial for interpreting sedimentary charcoal series large catchment areas draining long rivers are not suitable for high resolution and spatially precise fire reconstructions

reactivated tibetan block in a tethyan context abstract the tibetan block originated during the late palaeozoic early mesozoic by separation from gondwanic india and the opening of neo tethys the event which was responsible for reactivating the tibetan basement closed palaeo tethys lying to the north of it and created the kun lun fold system as a consequence of the collision of the north moving tibetan block with the tarim tsaidam block during the late cretaceous south tibet developed into an andean type foldbelt nyenchen thangla by subduction of neo tethyan lithosphere beneath tibet which had begun in the late triassic mesozoic sedimentary sequences in tibet are the response to an extensional regime behind an active margin a neo tethys island arc system at this margin was crushed during the early eocene with the development of the transhimalayan ophiolite and plutonic belts final collision during mid eocene times between the himalayan microcontinent a fragment of india and reworked tibet in the mid eocene produced the indus tsangpo suture zone a large part of the microcontinent with an unconsumed segment of neo tethys oceanic crust attached to it presumably underthrust tibet prior to the himalayan orogeny this feature is responsible for the double thickness of tibetan crust and its young volcanism

rbsr dating of the kohistan arc batholith in the trans himalaya of north pakistan and tectonic implications the kohistan arc batholith in northern pakistan is situated between the indus suture and the northern suture it belongs to the trans himalayan belt which continues eastwards as the ladakh arc batholith in northwest india and the kangdese batholith in southern tibet in kohistan the island arc consists upward sequence of the chilas stratiform complex of norites noritic gabbros and chromite layered dunites which formed in the sub arc magma chamber plutons of tonalite and diorite one of which has a rbsr isochron age of 102 12 ma the chalt volcanics of basaltic tholeiites succeeded by andesites to rhyolites and the yasin group sediments which formed in overlying intra arc basins and which contain albian aptian faunas all these rocks were deformed by major fold structures which are correlated with the formation of the northern suture ne sw trending basic jutal nomal dykes north of gilgit cross cut all the above structures and have a39ar 40ar hornblende age of 75 ma thus the northern suture must have formed in the period 102 12 to 75 ma with the island arc attached to the eurasian plate further northward subduction of the tethyan plate gave rise to an andean type batholith two plutons of which have rbsr isochron ages of 54 4 ma and 40 6 ma the dir utror group of calc alkaline lavas and sediments with eocene fossils are remnants of the volcanic cover of the andean type batholith we suggest that late cretaceous blueschists formed during subduction under the active continental margin and that continental collision and formation of the indus suture was in the eocene the batholith was intruded by layered aplite pegmatite sheets at 34 14 ma and 29 8 ma rbsr ages in post collisional times the87sr 86sr initial ratios of all the dated rocks range between 0 7039 and 0 7052

relationships between charcoal particles in air and sediments in west central siberia production and size of charred particles determine transport and deposition in lakes lack of such data is a principal obstacle to interpretation of past fire from charcoal profiles our two part a

the indus tsangpo suture zone in ladakh northwest himalaya further palaeomagnetic data and implications abstract a total of 81 samples 244 specimens from upper cretaceous indus molasse and middle to upper cretaceous dras flyschoids of the indus tsangpo suture zone in ladakh northwest himalaya has been studied by thermal demagnetization methods both formations showed a characteristic magnetization component indicative for equatorial to low northern palaeolatitudes of acquisition similar palaeolatitudes have been obtained before from secondary magnetization components of early tertiary age in the ladakh intrusives and in the tibetan sedimentary series of central nepal the present characteristic components are interpreted likewise as secondary magnetizations which stabilized between 50 and 60 m y ago during greater india s collision with asia s southern margin the dras flyschoids show another magnetic component which in case of primary origin indicates acquisition at a low southern palaeolatitude if correct this interpretation supports recent suggestions for late cretaceous obduction of an island arc on greater india s northern margin

mesozoic and cenozoic volcanic rocks from central and southern tibet 39ar 40ar dating petrological characteristics and geodynamical significance field relations radiometric ages and mineralogical and chemical characteristics of the orogenic volcanic rocks from the lhasa block tibet are studied volcanic activity started before the deposition of the albian aptian sedimentary units takena formation and xigaze group volcanism is volumetrically limited in the northern part of the lhasa block basalts andesites and dacites are present while ignimbrites are scarce radiometric ages of these rocks range between 110 and 80 ma conversely in the southern part of the lhasa block volcanism is largely developed gangdese belt there paroxysmal activity occurred later than in the north between 60 and 50 ma lingzizong formation this volcanism is mainly represented by andesites and ignimbrites a younger episode at about 15 10 ma took place in this southern region the mineralogical and geochemical characteristics indicate that as a whole the volcanic rocks from the lhasa block belong to a calc alkaline continental margin series enriched in k20 and other incompatible elements subordinate potassic alkaline lavas are present in the northern margin of the gangdese belt some basalts exhibit a tholeiitic affinity daquin area southern region the geodynamic significance of these cenozoic volcanic rocks lies in the relative motion of india and the lhasa block after accretion of the latter to the northern qantang block a geodynamic model based on changes of the type of subduction of the indian oceanic crust beneath the lhasa block for the period 120 40 ma is proposed to account for the abundance age and magmatic affinity of the volcanic products

the age and nature of mesozoic tertiary magmatism across the indus suture zone in kashmir and ladakh n w india and pakistan we report the following new40ar 39ar ages 130 150 and 90 100 ma from monzodiorite and tremolite actinolite schist of the kohistan complex 44 0 5 39 7 0 2 ma from dikes cutting the ladakh deosai batholith complex 130 145 ma from a diorite in the shyok melange and 7 8 0 1 ma from a late stage monzogranite of the karakorum batholith a 261 13 ma age from gneiss of the karakorum batholith is of uncertain significance

a comparison of charcoal measurements for reconstruction of mediterranean paleo fire frequency in the mountains of corsica fire history reconstructions inferred from sedimentary charcoal records are based on measuring sieved charcoal fragment area estimating fragment volume or counting fragments similar fire histories are reconstructed from these three approaches for boreal lake sediment cores using locally defined thresholds here we test the same approach for a montane mediterranean lake in which taphonomical processes might differ from boreal lakes through fragmentation of charcoal particles the mediterranean charcoal series are characterized by highly variable charcoal accumulation rates results there indicate that the three proxies do not provide comparable fire histories the differences are attributable to charcoal fragmentation this could be linked to fire type crown or surface fires or taphonomical processes including charcoal transportation in the catchment area or in the sediment the lack of correlation between the concentration of charcoal and of mineral matter suggests that fragmentation is not linked to erosion reconstructions based on charcoal area are more robust and stable than those based on fragment counts area based reconstructions should therefore be used instead of the particle counting method when fragmentation may influence the fragment abundance

tectonic environment and geodynamic significance of the neo cimmerian donqiao ophiolite bangong nujiang suture zone tibet the bangong nujiang suture zone is underlain by a discontinuous and roughly ew ophiolite belt around donqiao gyanco ophiolitic and metasedimentary palaeozoic series form nappes thrusted over jurassic flysch series all these series have undergone a late symmetrical folding accompanied by generally northward reverse faulting although strongly dismembered a complete ophiolitic sequence comprising harzburgites with large podiform type chromite deposits wehrlites cumulate gabbros sheeted dolerite dykes foliated garnet bearing amphibolites and pillow lavas has been found

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

the four plutonic belts of the transhimalaya himalaya a chemical mineralogical isotopic and chronological synthesis along a tibet nepal section

climatic controls of holocene fire patterns in southern south america holocene fire climate vegetation linkages are mostly understood at individual sites by comparing charcoal and pollen records with other paleoenvironmental proxy and model simulations this scale of reconstruction often obscures detection of large scale patterns in past fire activity that are related to changes in regional climate and vegetation a network of 31 charcoal records from southern south america was examined to assess fire history along a transect from subtropic to subantarctic biomes the charcoal data indicate that fire activity was greater than present at ca 12 000 cal yr bp and increased further and was widespread at 9500 cal yr bp fire activity decreased and became more spatially variable by 6000 cal yr bp and this trend continued to present atmospheric circulation anomalies during recent high fire years show a southward shift in westerlies and paleoclimate model simulations and data syntheses suggest that such conditions may have prevailed for millennia in the early holocene when the pole to equator temperature gradients were weaker and annual temperatures were higher than present in response to orbital time scale insolation changes

creation and preservation of subduction related inverted metamorphic gradients peak metamorphic temperatures and recrystallization increase structurally upward in the lower plate of several paleosubduction zones in the westernmost u s cordillera inverted metamorphic gradients are preserved in the pelona orocopia schist southern california the catalina schist california borderland the central metamorphic belt klamath province the south fork mountain schist northern california coast ranges and possibly the shuksan suite northern washington with the exception of the south fork mountain schist peak metamorphic temperatures increase structurally upward from 400 c to 650 c over 1 2 km indicating metamorphic gradients in excess of 100 c km 1 estimates of metamorphic gradients in some terranes such as the catalina schist depend critically on the effects of postmetamorphic faulting the tectonic settings and high metamorphic pressures 800 mpa suggest that the inverted metamorphic gradients formed in paleosubduction zones four out of five inverted metamorphic gradients lie structurally beneath ultramafic hanging walls whereas the pelona orocopia schist formed beneath granitic crystalline rocks the high temperatures recorded by the metamorphic rocks strongly suggest that inverted metamorphic gradients form during the early stages of subduction and thus provide insight into the early thermal history of subduction zones two separate two dimensional numerical models were constructed in order to constrain the thermal conditions under which inverted metamorphic gradients are created and preserved rapid subduction 10 cm yr 1 beneath young oceanic lithosphere 10 ma results in rapid heat conduction downward from the hanging wall and the creation of inverted thermal gradients in excess of 100 c km 1 in the top portion of the downgoing slab in order to be preserved in the geologic record the inverted metamorphic gradient must be accreted to the base of the hanging wall accretion of the upper portion of the subducting slab may occur because of declining temperatures that cause downward migration of the viscous slip zone and or greenschist facies devolatilization reactions that weaken the descending slab alternatively inverted metamorphic gradients may represent the continuous accretion of material at rates of 1 10 mm yr 1 under conditions of declining temperature continuously accreted inverted metamorphic gradients could form in oceanic lithosphere as old as 30 ma continued subduction of 1000 km of oceanic lithosphere effectively refrigerates the early accreted inverted metamorphic gradient synsubduction uplift and or moderately fast postsubduction uplift rates of 1 mm yr 1 are required to preserve the inverted metamorphic gradient the models predict that 1 the high grade metamorphic rocks in inverted metamorphic gradients form early in the subduction process and therefore effectively date the initiation of subduction and 2 inverted metamorphic gradients mark sites of major plate convergence in excess of 1000 km

the intercept is a poor estimate of a calibrated radiocarbon age intercept based methods of generating a point estimate of a calibrated radiocarbon date are very popular but exhibit undesirable behaviour they are highly sensitive to the mean of the radiocarbon date and to adjustments of the calibration curve other methods give more stable results the weighted average of the probability distribution function is recommended as the best central point estimate but more consideration should be given to using the full probability distribution rather than a point estimate in developing age depth models

the 8k event cause and consequences of a major holocene abrupt climate change abstract a prominent abrupt climate event about 8200 years ago brought generally cold and dry conditions to broad northern hemisphere regions especially in wintertime in response to a very large outburst flood that freshened the north atlantic changes were much larger than typical climate variability before and after the event with anomalies up to many degrees contributing to major displacement of vegetative patterns this 8k event provides a clear case of cause and effect in the paleoclimatic realm and so offers an excellent opportunity for model testing the response to north atlantic freshening has the same general anomaly pattern as observed for older events associated with abrupt climate changes following north atlantic freshening and so greatly strengthens the case that those older events also reflect north atlantic changes the north atlantic involvement in the 8k event helps in estimating limits on climate anomalies that might result in the future if warming caused ice melt and hydrologic cycle intensification at high latitudes lead to major changes in north atlantic circulation few model experiments have directly addressed the 8k event and most studies of proxy records across this event lack the time resolution to fully characterize the anomalies so much work remains to be done

increased northeast pacific climatic variability during the warm middle holocene 1 we use a pair of decadally resolved planktonic foraminiferal 18o records from santa barbara basin sbb to show that the warmest interval of the current interglacial the middle holocene was characterized by increased decadal to centennial scale climatic variability modern relationships between the pacific decadal oscillation pdo the el nino southern oscillation enso and upper water conditions in sbb also suggest a preference of the northeast ne pacific climate during the warm mid holocene toward the warm phase of the pdo and more intense enso warm events el ninos in the context of future climate this study suggests increasing decadal to centennial scale climatic variability in a globally warmed world

holocene fire and vegetation along environmental gradients in the northern rocky mountains abstract holocene records of fire vegetation and climate were reconstructed from four sites in the bitterroot range region of the northern rocky mountains in order to examine the vegetation and fire histories and evaluate the hypothesis proposed by whitlock and bartlein 1993 regarding the effects of increased summer insolation on precipitation patterns vegetation history in the series of sites was broadly similar in the late glacial period the pollen data suggest open parkland dominated by picea or alpine meadow which reflect conditions cooler and drier than present these open forests were replaced in the early to middle holocene by forests composed mainly of pinus and pseudotsuga which suggest conditions warmer than present modern forest compositions were in place by ca 3000 cal yr bp and small variations in the timing of the vegetation shifts reflect local differences among sites the long term trends in fire occurrence support the hypothesis proposed by whitlock and bartlein 1993 that precipitation regimes were sharpened during the early holocene summer insolation maximum but their location has remained unchanged as a result of topographic constraints sites located in areas currently summer dry were drier than present during the early holocene and fires were more frequent conversely sites located in the areas that are summer wet at present were wetter than present in the early holocene and fires were less frequent on millennial time scales it appears that the climate boundary is controlled by topography and does not shift

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

the northern suture pakistan margin of a cretaceous island arc the northern suture is a fault separating the cretaceous kohistan island arc terrain northwest himalayas from palaeozoic sediments of the asian plate to the north the kohistan arc includes volcanic and sedimentary rocks andesitic lavas tuffs volcaniclastics slates and limestones metamorphosed to greenschist facies and intruded by the two phase kohistan batholith asian continental margin sediments are mainly of shelf type are variably metamorphosed and intruded by the karakoram batholith the northern suture is a zone of melange from 150 m to 4 km wide and contains blocks of volcanic greenstone limestone red shale conglomerate quartzite and serpentinite in a slate matrix it has a strong planar fabric but in many places bedding is preserved in blocks and matrix and depositional rather than tectonic contacts are seen between the two the melange is inferred to be an olistostrome largely derived from the kohistan arc formed in a small back arc basin between kohistan and asia limestone blocks in the melange are dated as aptian albian post tectonic intrusions yield radiometric ages from 111 to 62 ma the northern suture therefore probably formed in the early late cretaceous during closure of the back arc basin the tethys ocean lay south of kohistan where the main mantle thrust represents the westward continuation of the indus tsangpo suture

peak analysis of sedimentary charcoal records some underlying assumptions and potential pitfalls abstract fire histories are derived from sedimentary charcoal sequences using a suite of statistical techniques that has become increasingly complex here we outline the various assumptions that underpin these methods and highlight potential sources of error that must be considered we hope to spur debate on the circumstances in which such methods are appropriate and highlight areas needing further research

stratigraphic charcoal analysis on petrographic thin sections application to fire history in northwestern minnesota results of stratigraphic charcoal analysis from thin sections of varved lake sediments have been compared with fire scars on red pine trees in northwestern minnesota to determine if charcoal data accurately reflect fire regimes pollen and opaque spherule analyses were completed from a short core to confirm that laminations were annual over the last 350 yr a good correspondence was found between fossil charcoal and fire scar data individual fires could be identified as specific peaks in the charcoal curves and times of reduced fire frequency were reflected in the charcoal data charcoal was absent during the fire suppression era from 1920 a d to the present distinct charcoal maxima from 1864 to 1920 occurred at times of fire within the lake catchment fire was less frequent during the 19th century and charcoal was substantially less abundant fire was frequent from 1760 to 1815 and charcoal was abundant continuously fire scars and fossil charcoal indicate that fires did not occur during 1730 1750 and 1670 1700 several fires occurred from 1640 to 1670 and 1700 to 1730 charcoal counted from pollen preparations in the area generally do not show this changing fire regime simulated sampling of the thin section data in a fashion comparable to pollen slide methods suggests that sampling alone is not sufficient to account for differences between the two methods integrating annual charcoal values in this fashion still produced much higher resolution than the pollen slide method and the postfire suppression decline of charcoal characteristic of my method but not of pollen slides is still evident consideration of the differences in size of fragments counted by the two methods is necessary to explain charcoal representation in lake sediments

cooling history of the nw himalaya pakistan fission track and 40ar 39ar cooling ages indicate that the late tertiary cooling history of the himalayan ranges of northern pakistan is largely a function of uplift and erosion interpretation of cooling ages which range from under 0 5 ma to over 80 ma suggests that during the late tertiary long term uplift rates at least doubled from under 0 2 mm yr to in some cases well over 0 5 mm yr uplift rates show strong and systematic regional variations as well which reflect the greater uplift of eastern and northern regions the association of very rapid uplift and erosion with the nanga parbat haramosh massif can be explained by a locally vigorous collision of india with eurasia near a promontory of indian crust the resultant rapid uplift of the nanga parbat haramosh massif reactivated the main mantle thrust melange zone with a reversed sense of motion discontinuities in the coolingage distribution along the main mantle thrust in the southern swat hazara region may be the result of the thermal effects of overthrusting

estimating the mass flux of charcoal from sedimentary records effects of particle size morphology and orientation reconstructing past fire requires ways to compare concentration estimates obtained by different charcoal analysis methods these methods estimate concentrations from area measurements or particle counts on pollen slides on sieves and on thin sections and they do so at different magnifications depending on particle properties each method might give substantially different results image analysis of charred particles in thin sections of lake sediments is used to parameterize relationships among different concentration estimators we determined distributions of particle size shape and orientation in undisturbed sediments and assessed how those distributions affect concentration estimates particle diameter distributions were conservative across different magnifications particle shape was also conservative with major minor axis ratios near 2 5 our derived relationships among estimators could be used to improve comparability for all but the smallest particle classes which tended to be unpredictable

corrigendum to comparison between chironomid inferred mean august temperature from varved lake żabinskie poland and instrumental data since 1896 ad quat sci rev 111 2015 35 50

karakoram fault zone rocks cool in two phases the karakoram fault zone of ladakh india is a major strike slip boundary along which the tectonic evolution of tibet has been accommodated in this paper 40 ar 39 ar isotopic age data are integrated with structural and metamorphic data to infer an exhumation history for granites and low to intermediate grade metamorphic rocks exposed adjacent to two strands of the fault zone near tangtse leucogranites which crystallized c 17 ma ago are cut by the karakoram fault zone indicating that fault movement was initiated subsequent to 17 ma the 40 ar 39 ar data give temperature time histories which indicate that the two phases of rapid cooling of karakoram fault zone rocks are evident one at c 17 ma to c 13 ma and another following an intervening period of relatively slow cooling starting at c 8 ma and continuing until at least 7 ma uplift since c 17 ma via dextral oblique thrusting has resulted in exhumation from amphibolite facies metamorphic conditions possibly with a larger thrust component from 17 to 13 ma followed by a change to dominant strike slip motion at about 13 ma rapid cooling starting at c 8 ma at greenschist facies temperatures is probably the result of renewed oblique thrusting it is notable that the two episodes of rapid cooling recorded in karakoram fault zone rocks coincide with episodes of exhumation in the pakistani karakoram and also in southern tibet

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

paleofire reconstruction for high elevation forests in the sierra nevada california with implications for wildfire synchrony and climate variability in the late holocene abstract here we present two high resolution records of macroscopic charcoal from high elevation lake sites in the sierra nevada california and evaluate the synchroneity of fire response for east and west side subalpine forests during the past 9200 yr charcoal influx was low between 11 200 and 8000 cal yr bp when vegetation consisted of sparse pinus dominated forest and montane chaparral shrubs high charcoal influx after 8000 cal yr bp marks the arrival of tsuga mertensiana and abies magnifica and a higher than present treeline that persisted into the mid holocene coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the sierra nevada after 3800 cal yr bp independent fire response occurs between 9200 and 5000 cal yr bp and significant synchrony at 100 to 1000 yr timescales emerges between 5000 cal yr bp and the present especially during the last 2500 yr indistinguishable fire return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late holocene fires after 1200 cal yr bp are often synchronous and corroborate with inferred droughts holocene fire activity in the high sierra nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the el nino southern oscillation

40ar 39ar age constraints on deformation and metamorphism in the main central thrust zone and tibetan slab eastern nepal himalaya in eastern nepal structural and petrologic observations suggest that movement on the main central thrust mct the development of an inverted metamorphic sequence and leucogranite plutonism were genetically related samples from across the mct zone and its hanging wall the tibetan slab were collected from four locations in the everest region for 40ar 39ar studies 1 the mct zone 2 the lower tibetan slab 3 the upper tibetan slab away from intrusive rocks and 4 the upper tibetan slab adjacent to and including leucogranitic material within the mct zone muscovite and hornblende yield cooling ages of 12 0 0 2 ma and 20 9 0 2 ma respectively k feldspar gives a minimum age of 8 0 0 2 ma closure temperature tc 220 15 c in the lower tibetan slab a sample from a sheared pegmatite yields muscovite and biotite isochron ages of 7 7 0 4 ma and 7 5 0 6 ma and a k feldspar minimum age of 6 4 0 8 ma tc 225 20 c an adjacent gneiss yields a 9 1 0 2 ma biotite isochron and a k feldspar minimum age of 3 6 0 2 ma tc 210 50 c in the upper tibetan slab samples collected 200 m from visible intrusives yield a biotite isochron age of 20 2 0 2 ma and a complex hornblende age spectrum suggestive of excess argon at the fourth location an augen gneiss a pegmatite and a tourmaline bearing leucogranite all in mutual contact yield indistinguishable mineral ages the average biotite and muscovite isochron ages for these samples are 17 0 1 4 and 16 6 0 2 ma respectively the minimum age for k feldspar from the leucogranite is 15 5 1 8 ma as thermobarometric data from the mct zone in this area suggest synmetamorphic deformation at temperatures of 500 550 c the mct hornblende tc 500 c dates this event at 21 ma diffusion experiments on hornblendes from the mct zone provide data which support a maximum duration of peak metamorphic temperatures of 2 ma biotite ages as old as 20 ma from the upper tibetan slab near leucogranites indicate that leucogranite intrusion was essentially coeval with deformation and metamorphism in the mct zone very young ages in a ductile shear zone in the lower tibetan slab suggest that there has been deformation within the tibetan slab that postdates major movement on the mct

holocene multidecadal and multicentennial droughts affecting northern california and nevada abstract continuous high resolution 18 o records from cored sediments of pyramid lake nevada indicate that oscillations in the hydrologic balance occurred on average about every 150 years yr during the past 7630 calendar years cal yr the records are not stationary during the past 2740 yr drought durations ranged from 20 to 100 yr and intervals between droughts ranged from 80 to 230 yr comparison of tree ring based reconstructions of climate change for the past 1200 yr from the sierra nevada and the el malpais region of northwest new mexico indicates that severe droughts associated with anasazi withdrawal from chaco canyon at 820 cal yr bp calendar years before present and final abandonment of chaco canyon mesa verde and the kayenta area at 650 cal yr bp may have impacted much of the western united states during the middle holocene informally defined in this paper as extending from 8000 to 3000 cal yr bp magnetic susceptibility values of sediments deposited in pyramid lake s deep basin were much larger than late holocene 3000 0 cal yr bp values indicating the presence of a shallow lake in addition the mean 18 o value of caco 3 precipitated between 6500 and 3430 cal yr bp was 1 6 less than the mean value of caco 3 precipitated after 2740 cal yr bp numerical calculations indicate that the shift in the 18 o baseline probably resulted from a transition to a wetter 30 and cooler 3 5 c climate the existence of a relatively dry and warm middle holocene climate in the truckee river pyramid lake system is generally consistent with archeological sedimentological chemical physical and biological records from various sites within the great basin of the western united states two high resolution holocene climate records are now available from the pyramid and owens lake basins which suggest that the holocene was characterized by five climatic intervals tic and 18 o records from owens lake indicate that the first interval in the early holocene 11 600 10 000 cal yr bp was characterized by a drying trend that was interrupted by a brief 200 yr wet oscillation centered at 10 300 cal yr bp this was followed by a second early holocene interval 10 000 8000 cal yr bp during which relatively wet conditions prevailed during the early part of the middle holocene 8000 6500 cal yr bp high amplitude oscillations in tic in owens lake and 18 o in pyramid lake indicate the presence of shallow lakes in both basins during the latter part of the middle holocene 6500 3800 cal yr bp drought conditions dominated owens lake desiccated and lake tahoe ceased spilling to the truckee river causing pyramid lake to decline at the beginning of the late holocene 3000 cal yr bp lake tahoe rose to its sill level and pyramid lake increased in volume

a 14 000 year sedimentary charcoal record of fire from the northern sierra nevada lake tahoe basin california usa this research examines how the controls of fire episode frequency in the northern sierra nevada have varied at different temporal scales through the holocene a 5 5 m long sediment core was collected from lily pond a 2 5 ha lake in the general creek watershed on the west shore of lake tahoe in the northern sierra nevada in california usa dendrochronology was used to reconstruct the recent history of fire and high resolution charcoal analysis was used to reconstruct fire episodes for the last 14 000 cal yr bp fire episode frequency was low during the lateglacial period but increased through the middle holocene to a maximum frequency around 6500 cal yr bp during the late holocene fire episode frequency generally declined except for noted peaks around 3000 cal yr bp and 1000 800 cal yr bp these variations track major climatic and vegetation changes driven by millennial timescale variation in the seasonal cycle of insolation and regional decadal and centennial scale variation in effective moistur

miocene 40ar 39ar ages from the karakorum batholith and shyok melange northern pakistan indicate late tertiary uplift and southward displacement brookfield m e and reynolds p h 1990 miocene raar 39ar ages from the karakorum batholith and shyok melange northern pakistan indicate late tertiary uplift and southward displacement tecmnophysics 172 155 167 the magmatic arc of the karakorum mountains is separated from the cretaceous tertiary kohistan arc sequence by an ophiolitic melange the shyok melange two views of the age of the shyok melange and karakorum arc are a that they represent a mid mesozoic arc trench complex which collided with the kohistan arc in the cretaceous before the closure of the main tethys ocean to the south and b that they represent a late tertiary arc trench complex which closed in the late miocene representing final subduction of tethyan sea floor whether final destruction of ocean crust took place in the mesozoic or tertiary has important implications for current models of the development of the indian asian collision zone here we wish to report ages of between 20 and 8 ma suggesting that final assembly and uplift did not occur until the late tertiary and that the shyok melange is the structural equivalent of the main central thrust of the himalaya to the east like the main central thrust the shyok melange appears to mark intraplate continental subduction which is mainly responsible for tertiary granitoid intrusion deformation and uplift in the high himalaya and karakorum to the north

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

woody vegetation fuel and fire track the melting of the scandinavian ice sheet before 9500 cal yr bp abstract new studies indicate the presence of early holocene ice free areas far north in scandinavia post glacial fire and vegetation were investigated based on sedimentary charcoal and pollen from two small lakes in northern sweden accumulation of organic sediment started around 10 900 and 9200 cal yr bp showing that both lake valleys were ice free extremely early given their northerly location fire events started after 9600 cal yr bp and became less common around the 8 2 ka event woody vegetation provided fuel that contributed to fires the first vegetation in our pollen record consisted of hippophae dryas grasses and sedges subsequently broadleaved trees betula salix increased in abundance and later pinus alnus ferns and lycopodium characterized the vegetation pollen from larix picea and malus were also found the change in vegetation composition was synchronous with the decrease in lake water ph in the region indicating ecosystem scale processes this occurred during a period of net global and regional warming the changes in fire frequency and vegetation appear independent of regional trends in precipitation the reconstructed fire history and vegetation support the scenario of early ice free areas far north in scandinavia during early holocene warming creating favorable conditions for woody plants and wildfires

fire climate and the origins of agriculture micro charcoal records of biomass burning during the last glacial interglacial transition in southwest asia this study investigates changes in climate vegetation wildfire and human activity in southwest asia during the transition to neolithic agriculture between ca 16 and ca 9 ka in order to trace the fire history of this region we use microscopic charcoal from lake sediment sequences and present two new records one from south central turkey akgol and the other from the southern levant hula these are interpreted primarily as the result of regional scale fire events with the exception of a single large event ca 13 ka at akgol which phytolith analysis shows was the result of burning of the local marsh vegetation comparison between these and other regional micro charcoal stable isotope and pollen records shows that wildfires were least frequent when the climate was cold and dry glacial lateglacial stadial and the vegetation dominated by chenopod artemisia steppe and that they became more frequent and or bigger at times of warmer wetter but seasonally dry climate lateglacial interstadial early holocene warmer and wetter climates caused an increase in biomass availability with woody matter appearing to provide the main fuel source in sites from the levant while grass fires predominated in the interior uplands of anatolia southwest asia s grasslands reached their greatest extent during the early holocene and they were maintained by dry season burning that helped to delay the spread of woodland by up to 3 ka at the same time as neolithic settlement became established across this grass parkland landscape although climatic changes appear to have acted as the principal pacemaker for fire activity through the last glacial interglacial climatic transition lgit human actions may have amplified shifts in biomass burning fire regimes therefore changed markedly during this time period and both influenced and were influenced by the cultural economic transition from hunter foraging to agriculture and village life copyright 2009 john wiley sons ltd

variation in holocene el nino frequencies climate records and cultural consequences in ancient peru analysis of mollusks from archaeological sites on the north and central coasts of peru indicates that between ca 5800 and 3200 2800 cal yr b p el nino events were less frequent than today with modern rapid recurrence intervals achieved only after that time for several millennia prior to 5 8 ka el nino events had been absent or very different from today the phenomena called el nino have had severe consequences for the modern and colonial historically recorded inhabitants of peru and el nino events also influenced prehistoric cultural development the onset of el nino events at 5 8 ka correlates temporally with the beginning of monumental temple construction on the peruvian coast and the increase in el nino frequency after 3 2 2 8 ka correlates with the abandonment of monumental temples in the same region

geo tectonic framework of the himalaya of n pakistan in the karakorum range there is a structurally complicated cretaceous are comprising the kohistan sequence on its northern side the northern suture consists of a mega melange and is bounded to the s by tightly folded pillow bearing volcanics and sediments to the s the kohistan plutonic belt consists of southwards a early foliated and late post tectonic tonalites and diorites b aplites and pegmatites up to 30 of rock volume c basic dykes up to 10 m thick d the chilas complex a stratiform cumulate body over 300 km long and 8 km thick chromite layered dunites gabbros and norites with a low pressure granulite facies mineral fabric of tectonic origin e an amphibolite belt with a complex mixture of other rocks and f the jijal complex a 200 km 2 tectonic wedge of high pressure granulites and chromite layered dunites cumulate graded units in the chilas complex show that it is folded by an isoclinal anticline f 1 the mid upper crust of the are is folded by a 50 km half wavelength f 2 syncline the whole kohistan sequence with its two phases of isoclinal folds was tilted during himalayan collision so that the structures are now subvertical the southern suture main mantle thrust has a wedge of glaucophane schists the indian plate contains a basement of psammites and schists intruded by cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales

structural evolution and sequence of thrusting in the high himalayan tibetan tethys and indus suture zones of zanskar and ladakh western himalaya reply abstract the timing of motion on major thrusts in the western himalaya shows an extremely complex sequence that spans approximately 70 ma from the latest cretaceous throughout the tertiary three major phases of thrusting can be distinguished the earliest phase t1 is associated with emplacement of tethyan basin thrust sheets lamayuru sediments and spontang ophiolite south and south westwards onto the submerged northern passive margin of india 75 60 ma collision between india and asia occurred at 50 36 ma and was followed immediately by the major phase t2 of crustal shortening involving large scale south and south westward directed thrusting of the complete palaeozoic mesozoic and late tertiary tibetan tethys zone rocks preliminary balanced cross sections show a minimum shortening of 126 km of these rocks across the zanskar range the late collision phase t3 involved re thrusting of the previously stacked pile breaching or leap frog thrusting reversing the earlier stacking order in places and widespread steepening overturning and backthrusting along the whole northern margin of the tibetan tethys zone and throughout the indus suture zone

particle size evidence for source areas of charcoal accumulation in late holocene sediments of eastern north american lakes abstract two methods of analyzing charcoal in sediment reveal changes in charcoal accumulation across temperate eastern north america during the last several hundred years in one method the analyst counts mostly small particles that reflect regional emissions in the other the analyst counts only larger particles derived mostly from such local sources as catchment fires we used these methods to compare charcoal accumulation at 14 lakes from the prairie forest border in minnesota to eastern maine the two methods gave concordant accumulation rates for sediments of pre 1850 age at each of 4 lakes analyzed by both methods this concordance is consistent with the interpretation that pre 1850 emissions were controlled by broad scale factors such as climatically controlled regional differences in fuels and moisture since 1900 large particles decreased greatly and small particles decreased slightly in minnesota and wisconsin by contrast in the northeast the large particle accumulation has remained at the low values measured in pre 1900 sediments at most sites while small particles increased everywhere east of central new york and pennsylvania the observed patterns suggest that 1 large particles primarily reflect local fires that were common in the midwest before fire suppression became effective 2 large particles were rare in the northeast especially before extensive land clearance 3 small particles reflect regional combustion that increased in the northeast after extensive use of fire for land clearance and wood burning for industrial purposes of the 19th century and 4 small particles remain abundant in the midwest long after effective fire suppression probably because these well dispersed small particles have a large source area that extends beyond the local wildfires that account for large particles before european settlement

granites of western karakorum and northern kohistan pakistan a composite mid cretaceous to upper cenozoic magmatism abstract the petrography the chemical mineralogical typology and the ages of six plutonic units four from the karakorum axial batholith darkot pass ghamu bar batura and hunza units and two of northern kohistan gindai and nomal plutons are defined and compared based on field data and analyses of up to 78 samples major elements ree rb s sbnd sr and k ar isotopes the karakorum axial batholith is a composite body three major intrusive stages occurred 1 around mid cretaceous times ca 110 95 ma with the emplacement of subalkaline i e monzonitic darkot pass and calc alkaline hunza ghamu bar units 2 during palaeogene maybe up to 43 ma batura subalkaline unit a strong tectonommetamorphic event recorded in the gneissification of the cretaceous intrusives occurred between these two stages it may be of palaeocene age p t estimates of the highest metamorphic grade rocks of the hunza unit have yielded values of 580 640 c and 5 0 5 kbar and 3 during upper miocene ca 9 ma baltoro subalkaline unit debon et al 1986c in addition a conspicuous network of aplo pegmatitic dykes emplaced into the hunza area possibly from the eocene up to the upper cenozoic with a maximum during the middle miocene ca 15 ma most of these major magmatic stages are met again among the acidic intrusives and dykes of northern kohistan the first one as blastomylonitic tholeiitic plutons nomal ca 102 ma petterson and windley 1985 the second one as subalkaline plutons gindai ca 59 ma and a third one as leucocratic dykes of oligocene age ca 30 ma petterson and windley 1985 these data may be related to the geodynamic evolution of the nw part of the india eurasia suture zone thus allowing better constraints on the major steps of this evolution the partly synchronous closures by n dipping subduction of the two tethys branches which are assumed to have encircled the kohistan arc in upper mesozoic times may have generated both the karakorum and the kohistan intrusives of cretaceous and palaeogene ages the northern branch very likely closed before the southern one at the time of the second intrusive stage palaeogene a kohistan and karakorum had already collided were welded and had suffered the same major tectonometamorphic event b subduction of the southern tethys floor beneath the welded kohistan karakorum was still active c however collision between india and kohistan karakorum may have already begun particularly at the level of the nanga parbat promontory finally it is emphasized that the intrusive processes continued in the karakorum long after the collision e g baltoro granite

thermochronology of the modern indus river bedload new insight into the controls on the marine stratigraphic record 1 the indus river is the only major drainage in the western himalaya and delivers a long geological record of continental erosion to the arabian sea which may be deciphered and used to reconstruct orogenic growth if the modern bedload can be related to the mountains in this study we collected thermochronologic data from river sediment collected near the modern delta u pb ages of zircons spanning 3 gyr show that only 5 of the eroding crust has been generated since india asia collision the greater himalaya are the major source of zircons with additional contributions from the karakoram and lesser himalaya the 39ar 40ar dating of muscovites gives ages that cluster between 10 and 25 ma differing from those recorded in the bengal fan biotite ages are generally younger ranging 0 15 ma modern average exhumation rates are estimated at 0 6 km m y or less and have slowed progressively since the early miocene 20 ma although fission track ft dating of apatites may indicate a recent moderate acceleration in rates since the pliocene 1 0 km m y driven by climate change the 39ar 40ar and ft techniques emphasize the dominance of high topography in controlling the erosional flux to the ocean localized regions of tectonically driven very rapid exhumation e g nanga parbat s karakoram metamorphic domes do not dominate the erosional record

plate tectonic models for indian ocean intraplate deformation abstract the equatorial region of the conventionally defined indo australian plate has long been recognized as containing a type example of intense intraplate deformation we trace the development of tectonic models for the area to illustrate techniques for the analysis of such deformation the identification of anomalous seismicity near the ninetyeast and chagos laccadive ridges demonstrated the existence of the deformation focal mechanisms from recent and historic earthquakes showed strike slip motion occurring along the ninetyeast ridge seismic moment data allowed the rate to be estimated similar studies showed north south tension in the chagos bank region and north south compression in the region between the ninetyeast and chagos ridges global plate motion studies indicated non closure of the indian ocean triple junction suggesting the conventional plate geometry was inadequate for a rigid plate description of the area gravity and marine geophysical data indicated intense north south compressional deformation south of the bay of bengal these observations are reconciled by a plate motion model in which australia and india lie on distinct plates divided by a boundary that intersects the central indian ridge near the equator in this model arabia usually considered a separate plate has negligible motion relative to india the resulting euler vector for australia relative to indo arabia lies just east of the central indian ridge and predicts approximately 0 5 1 5 cm yr compression in the central indian basin and 1 5 2 cm yr strike slip motion along the northern ninetyeast ridge consistent with the seismological and geophysical data in contrast to conventional oceanic plate boundaries the boundary deformation is distributed over a wide zone this diffuse nature may reflect either the boundary s recent inception or slow rate of motion analysis of seismicity and deformation in the boundary zone should offer insights into the mechanics of its development and its implications for the evolution of plate boundaries

a late quaternary chironomid inferred temperature record from the sierra nevada california with connections to northeast pacific sea surface temperatures chironomid remains from a mid elevation lake in the sierra nevada california were used to estimate quantitative summer surface water temperatures during the past 15 000 yr reconstructed temperatures increased by 3 c between lake initiation and the onset of the holocene at 10 600 cal yr bp calibrated years before present temperatures peaked at 6500 cal yr bp displayed high variability from 6500 to 3500 cal yr bp and stabilized after 3500 cal yr bp this record generally tracks reconstructed santa barbara basin sea surface temperatures ssts through much of the holocene highlighting the correspondence between sst variability and california land temperatures during this interval

suppression of el nino during the mid holocene by changes in the earth s orbit a number of recent reports have interpreted paleoproxy data to describe the state of the tropical pacific especially changes in the behavior of the el nino southern oscillation enso over the holocene these interpretations are often contradictory especially for the eastern tropical pacific and adjacent areas of south america here we suggest a picture of the mid holocene tropical pacific region which reconciles the data enso variability was present throughout the holocene but underwent a steady increase from the mid holocene to the present in the mid holocene extreme warm el nino events were smaller in amplitude and occurred less frequently about a mean climate state with a cold eastern equatorial pacific and largely arid coastal regions as in the present climate this picture emerges from an experiment in which a simple numerical model of the coupled ocean atmosphere system in the tropical pacific was driven by orbital forcing we suggest that the observed behavior of the tropical pacific climate over the mid to late holocene is largely the response to orbitally driven changes in the seasonal cycle of solar radiation in the tropics which dominates extratropical influences

40ar 39ar incremental release ages of biotite from a progressively remetamorphosed archean basement terrane in southwestern labrador abstract gneisses within an archean basement terrane adjacent to the southwestern portion of the labrador trough were variably retrograded during a regional metamorphism of grenville age ca 1000 ma biotites from non retrograded segments of the gneiss terrane record 40 ar 39 ar plateau and isochron ages which date times of cooling following an episode of the kenoran orogeny 2376 2391 ma a suite of gneiss samples displaying varying degrees of retrograde alteration was collected across the grenville metamorphic gradient biotites in these samples show no petrographic evidence of retrograde alteration however they do record internally discordant 40 ar 39 ar age spectra although the extent of internal discordance is variable the overall character of the release patterns is similar with younger apparent ages recorded in intermediate temperature gas fractions the total gas dates range from 2257 27 ma northwest to 1751 23 ma southeast suggesting that variable quantities of radiogenic argon were lost from the archean biotites during grenville metamorphism the saddle shaped nature of the discordant spectra indicates that argon loss was not accomplished through single stage volume diffusion processes biotites in portions of the gneiss terrane which were completely recrystallized during grenville metamorphism are petrographically and texturally distinct a representative of this phase records a 40 ar 39 ar plateau age of 2674 28 ma this date is markedly inconsistent with regional constraints on the timing of grenville metamorphism and indicates the presence of extraneous argon components both the extraneous and radiogenic argon components must have been liberated in constant proportions during experimental heating because the argon isotopic data yield a well defined 40 ar 36 ar vs 39 ar 36 ar isochron corresponding to an age 2658 23 ma similar to that defined by the plateau portion of the spectrum the 40 ar 39 ar biotite dates suggest that the effects of grenville metamorphism extent 15 20 km northward into the superior province the limit of this overprint is approximately coincident with the northernmost development of grenville age thrust faults in the archean terrane therefore it is proposed that the northern margin of the grenville province in southwestern labrador should be located along the northernmost grenville thrust fault because this represents both a structural and a thermal discontinuity

climate and biomass control on fire activity during the late glacial early holocene transition in temperate ecosystems of the upper rhone valley france abstract the main objective of this study is to document paleofire activity during the late glacial early holocene transition in temperate ecosystems for this purpose we cored lakes paladru and moras rhone valley france and quantified sedimentary charcoal accumulation rate and fire frequency to assess the role of climate and vegetation in paleofire activity charcoal data were compared to vegetation dynamics based on pollen analyses and to climate reconstructions the first increase in paleofire activity occurred at the beginning of the bolling allerod interstadial period 14 500 cal yr bp synchronous with temperature and fire prone vegetation increases during the younger dryas paleofire activity first decreased 12 600 12 200 cal yr bp and then abruptly increased 12 200 11 600 cal yr bp this change corresponds to a known climate partitioning that occurred during the younger dryas and implies that a sufficient quantity of biomass was available during the second period at the beginning of the holocene fire activity remained high this is in agreement with the increases in temperature and vegetation density the change in forest composition since ca 11 200 cal yr bp partly explains the decrease in paleofire activity whereas warm climate conditions seem suitable for fire ignition and propagation

charcoal deposition and redeposition in elk lake minnesota usa sedimentary charcoal diatom and phytolith records of the past 1500 years at elk lake minnesota in combination with sediment trap studies and a transect of surface sediment samples document the mechanisms by which previously deposited charcoal is redeposited and finally buried in this lake the frequent correspon dence of high diatom concentrations and peaks of phytolith and charcoal fragments suggests that currents and turbulence related to lake circulation are responsible for winnowing charcoal and phytoliths from shallow water depositional sites to deeper areas of the lake high diatom concentrations in the record relate to increased nutrient fluxes also supplied by circulation despite the fact that the watershed and area around elk lake has not been burned since ad 1922 charcoal continues to reach the profundal zone from littoral source areas in elk lake the variable redeposition of within lake charcoal requires evaluation before fire history records can be related to global regional or even lo

metamorphism of an obducted island arc example of the kohistan sequence pakistan in the himalayan collided range in northern pakistan the extraordinary 40 km thick kohistan sequence of metamorphosed mafic ultramafic and calc alkaline layered plutonic and volcanic mainly andesitic to rhyodacitic rocks has been recently reinterpreted as the only complete vertical section of an intra oceanic island arc presently exposed anywhere in the world plate scale models have been suggested to explain the origin and the tectonic evolution of this arc in the himalayan collision range despite some noticeable differences in the models there is general agreement that the kohistan sequence represents the crust of an arc obducted onto the northern edge of the indian plate before the oligocene collision of india against asia new data on the tectonometamorphic evolution of the kohistan sequence have led to the conclusion that a first major d 1 event developed with increasing metamorphic grades oriented downward the kohistan pile but also toward ensandwiched basic ultrabasic granulitic rocks rare geochronological data and petrological evidence indicate that the latter granulites pyriclasites and various plagiopyrigarnites pyrigarnites metatroctolites metawebsterites metadunites etc were parts of enormous lower to middle cretaceous layered calc alkaline plutons emplaced during the arc building stages as the d 1 metamorphic event is correlated with the upper cretaceous obduction process of the kohistan onto india it is proposed that the d 1 thermal structure was strongly controlled by remnant magmatic heat source s within the obducted arc this interpretation fits nicely with recent theoretical thermal models since the obduction of the arc was probably shortly after 10 20 ma the emplacement of the former plutonic arc rocks a blueschist tectonic melange underlying the obducted arc was possibly synchronous to the obduction and not clearly linked to the older subductive process the oligocene collision of india against asia was associated with a barrovian overprinting metamorphism in the kohistan arc during this second event the dynamo thermal structure was much more classical and not controlled by the occurrence of the cretaceous metaplutonic rocks a tentative model of the thermal structures during the major events which affected the kohistan arc is proposed

estimating phytolith influx in lake sediments abstract so far no phytolith extraction protocols have been tested for accuracy and repeatability here we aim to display a phytolith extraction method combining the strengths of two widely used protocols supplemented with silica microspheres as exogenous markers for quantifying phytolith concentrations phytolith concentrations were estimated for samples from two sedimentary sequences in which numerical age depth models make it possible to calculate phytolith influxes phytolith numbers per cm2 per yr analysis of replicates confirmed the statistical robustness the repeatability and the very few biases of our extraction technique for small phytoliths since the relationship between grass silica short cells and microspheres was kept stable furthermore we demonstrated that silica microspheres are robust exogenous markers for estimating phytolith concentrations the minimum number of items i e phytoliths plus silica microspheres that must be counted to estimate phytolith concentrations and thus influxes depends on the ratio of phytoliths to microspheres r and is minimized when r 1 nevertheless we recommend using ratios r 1 in order to avoid having the counting process become excessively time consuming because microspheres are easier to identify and count than phytoliths

a 1000 year record of temperature and precipitation in the sierra nevada abstract tree ring data from subalpine conifers in the southern sierra nevada were used to reconstruct temperature and precipitation back to a d 800 tree growth of foxtail pine pinus balfouriana and western juniper juniperus occidentalis ssp australis is influenced by nonlinear interactions between summer temperature and winter precipitation reconstruction of the separate histories of temperature and precipitation is feasible by explicitly modeling species and site differences in climatic response using response surfaces the summer temperature reconstruction shows fluctuations on centennial and longer time scales including a period with temperatures exceeding late 20th century values from ca 1100 to 1375 a d corresponding to the medieval warm period identified in other proxy data sources and a period of cold temperatures from ca 1450 to 1850 corresponding to the little ice age precipitation variation is dominated by shorter period decadal scale oscillations the long term record presented here indicates that the 20th century is anomalous with respect to precipitation variation a tabulation of 20 and 50 yr means indicates that precipitation equaling or exceeding 20th century levels occurred infrequently in the 1000 yr record