palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

the last glacial maximum and late glacial environmental and climate dynamics in the baikal region inferred from an oxygen isotope record of lacustrine diatom silica abstract the last glacial maximum and late glacial environmental and climatic variability in the baikal region southern siberia russia has been studied in a sediment sequence from lake kotokel located 2 km east of lake baikal using the oxygen isotope composition of diatom silica 18 o diatom the purification of diatom frustules involved the process of trimethylsilylation which has been shown to be suitable for preparation of diatoms for oxygen isotope analysis the lake kotokel 18 o diatom record presented here spans intervals from about 24 6 to 22 9 ka bp further referred to as last glacial maximum and 16 7 11 5 ka bp further referred to as late glacial displaying variations in the oxygen isotope composition between 26 7 and 31 2 overall high 18 o diatom values of about 29 to 31 during the two investigated intervals characterize a strongly evaporative lake system in a dry environment and suggest a lower than present lake level due to enhanced evaporation the lake kotokel diatom isotope record is roughly in line with the 60 n summer solar insolation pointing to a linkage to broader scale climate change but displays weaker reaction to short term climatic oscillations i e bolling allerod or younger dryas the climate warming at 14 3 ka bp is marked by negative spikes in the 18 o diatom record due to isotopically low melt water input from the mountainous hinterland

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

changes in carbon and nitrogen cycling during tree line retreat recorded in the isotopic content of lacustrine organic matter western taimyr peninsula russia bulk organic and cellulose stable carbon isotope and bulk organic nitrogen isotope profiles from the sediments of a small tundra lake on the western taimyr peninsula russia show changes that are correlated with climate cooling and treeline retreat at c 4000 14 c years bp increased soil organic matter decomposition combined with a moist climate probably provided a 13 c depleted source of co2 aq to lake phytoplankton thriving under favourable conditions during the forest interval increased concentration of co 2 aq and re utiliz ation of respired co2 aq from organic matter settling through the water column may have also contributed to the relatively low d 13 c values in the lower part of the lake sediment record bulk organic and cellulose carbon are more enriched in 13c after the boreal forest retreated probably because co2 from the atmosphere became the dominant source of carbon to the lake as soil organic decomposition rates declined the lake became more oligotrophic and the climate became colder and drier reduced concentration of co2 aq may have also led to 13 c enrichment interpretation of the bulk organic d15n record is somewhat more speculative but changes in drainage basin terrestrial vegetation soil decomposition and hydrology also appear to have strongly influenced the lake water nitrogen cycling although considerably more effort is required to assess modern carbon and nitrogen isotope systematics these promising results suggest that lake sediment organic matter d 13

assessment of δ13c and c n ratios in bulk organic matter as palaeosalinity indicators in holocene and lateglacial isolation basin sediments northwest scotland carbon isotopes 13c and c n ratios from bulk organic matter have recently been used as alternative proxies for relative sea level rsl reconstruction where there are problems associated with conventional biological indictors a previous study on a single isolation basin upper loch nan eala in northwest scotland has shown a clear relationship between 13c c n ratios and palaeosalinity from younger dryas and holocene aged sediments in this paper we present results of 13c and c n ratio analyses from other isolation basins in northwest scotland over the holocene and the lateglacial period in order to validate this technique the results from the holocene sequences support the earlier findings that this technique can be used to identify rsl change from isolation basins over the holocene in this region the relationship between 13c c n ratios and rsl change is not apparent in sediments of lateglacial age other environmental variables such as atmospheric co2 concentration poor vegetation development and temperature influence 13c values during this period

evolution of the indian summer monsoon during the interval 32 7 11 4 cal ka bp evidence from the baoxiu peat yunnan southwest china abstract there have been few investigations of the phase relationship between the indian summer monsoon ism and the east asian summer monsoon easm during the last glacial period we present multi proxy mineralogical and geochemical records from a peat core taken from the baoxiu basin central yunnan southwest china to investigate changes in chemical weathering and climate associated with the ism in southwest china spanning the interval 32 7 11 4 ka bp the results suggest that the lgm period 23 18 ka bp was characterized by cold and dry climatic conditions a comparison of proxy data from baoxiu peat with other related proxy climate records reveals that broadly synchronous variations in the ism and easm on orbital timescales can be attributed to solar radiation forcing in the northern hemisphere in addition four synchronous weak millennial scale monsoonal events coincide well with cooling events recorded in the ngrip ice core corresponding to the younger dryas and heinrich events h1 h2 and h3 significantly the strengths of the two asian monsoons show an inverse relationship during the interval 23 19 ka bp probably resulting from el nino like conditions in the tropical pacific

vegetation and climate history inferred from a qinghai crater lake pollen record from tengchong southwestern china abstract a palynological investigation of a 514 cm long continuous core section from qinghai crater lake western yunnan province southwestern china was performed in order to reconstruct regional vegetation and climate from 15 8 cal kyr bp to the present the results show that the area was covered with deciduous broadleaved forest dominated by deciduous quercus between 15 8 and 12 8 cal kyr bp suggesting slightly cold and dry conditions from 12 8 to 8 3 cal kyr bp the vegetation continued to be dominated by deciduous broadleaved forest but there was also a sudden increase in castanopsis lithocarpus and a slight drop in deciduous quercus and alnus reflecting a gradual increase in both temperature and humidity during the period 8 3 4 6 cal kyr bp the mixed deciduous forests became more diverse and dense with thermophilous and hygrophilous species expanding to their maximum extents implying a warm and rather humid climate from 4 6 to 0 5 cal kyr bp the vegetation was succeeded by open mixed deciduous forest dominated by alnus with a retreating evergreen broadleaved forest indicating a cool and slightly dry climate after 0 5 cal kyr bp the vegetation became less diverse and more open but evergreen broadleaved trees increased their spread markedly suggesting that the climate had become warmer and drier in recent decades human activity resulted in a large increase in alnus and pinus around this lake basin specifically we concluded that the warm and moist climate detected between 8 3 and 4 6 cal kyr bp may have occurred in response to the high sea surface temperatures and high sea levels in the bay of bengal existent at that time

hydroclimatic changes over the past 900 years documented by the sediments of tiewaike lake altai mountains northwestern china abstract the reconstruction of variations in effective moisture over the past millennium are important for assessing potential future climatic trends in environmentally sensitive arid central asia aca especially in the context of ongoing global warming however high resolution time series reflecting past moisture variability in the region are scarce thus preventing a full understanding of the hydroclimatic evolution here we present the results of multi proxy analysis of a sediment core spanning the past 900 years from tiewaike lake in the altai mountains northern xinjiang the climatic proxies measured include grain size organic matter and carbonate content c n ratio and the stable carbon isotope composition of bulk organic matter the results show that over the past 900 years the climatic evolution of the study area can be divided into distinct hydroclimatic phases the arid medieval climate anomaly mca 1090 1430 ad the humid little ice age lia 1430 1940 ad and the arid current warm period cwp 1940 2012 ad during the lia the water level at tiewaike lake was overall higher than during the other climatic intervals in addition the lia climate was unstable and characterized by six intervals with the occurrence of heavy precipitation events on a multi decadal timescale a humid unstable climate during the lia is also suggested by climatic records from adjacent regions our results support the view that over the past millennium on a multi centennial timescale the moisture variations in aca were generally out of phase with those in the region affected by the asian summer monsoon the humid unstable lia climate in aca may have been associated with changes in the north atlantic oscillation nao index and or with variations in solar irradiance

in situ u pb hf and re os isotopic analyses of the xiangshan ni cu co deposit in eastern tianshan xinjiang central asia orogenic belt constraints on the timing and genesis of the mineralization abstract the timing and genesis of the major ni cu co sulfide deposit in the xiangshan intrusion have been studied based on newly obtained in situ u pb hf and re os isotopic analyses the sims u pb zircon ages of the gabbro hosting the ni cu co sulfide deposit indicate that the xiangshan intrusion was emplaced at 279 6 1 1 ma 95 confidence level mswd 1 30 n 15 on the basis of combined geological and geochronological evidence we suggest that the xiangshan and other adjacent ni cu deposits were formed in the same period sulphides have low common os concentrations and high re os ratios similar to sulphide ores from the duluth sally malay and voisey bay complexes the re os isotopic data from the disseminated and massive ores from the xiangshan intrusion do not form a single isochron as they have different initial os ratios the hf and os isotopic data suggest that the xiangshan intrusion and associated ni cu co mineralization were derived from crustally contaminated mantle melts the geochemical data show a tholeiitic affinity and a strong suprasubduction zone signature with negative nb sr and ti anomalies similar to n morb and e morb we suggest that the mafic ultramafic rocks and associated ni cu mineralization of the eastern tianshan orogen formed in an alaska type subduction zone arc setting some diagnostic features of ridge trench interaction are present in the chinese east tianshan orogen e g granites adakites high mg andesites near trench magmatism alaskan type mafic ultramafic complexes high temperature metamorphic belts that prograde rapidly from low grade belts and orogenic gold deposits the above distinctive rock groups are probably related to the same thermal event ridge subduction as in the cenozoic orogen of alaska we suggest that ridge subduction is the most plausible mechanism to provide the necessary heat ridge subduction provides an important promising model for understanding many aspects of the evolution of the chinese eastern tianshan orogen and by inference throughout much of central asia

short term biomarker variability in the monterey formation santa maria basin abstract forty eight samples of a 370 ft miocene monterey formation core from the union leroy 51 18 well santa maria basin california are examined for source rock potential and molecular distributions total organic carbon content rock eval pyrolytic yield vitrinite reflectance and distribution of regular steranes tricyclic and pentacyclic terpanes and aromatic steroids are measured the present day temperature range through the sampled interval is estimated to be less than 5 c maturity differences among samples are negligible source rock potential and molecular distribution differences are considered to arise entirely from the effects of source input diagenesis including lithologic effects and migration the sampled section is comprised of siliceous and phosphatic carbonate lithofacies and covariances between geochemical parameters source potential and biomarker distribution and lithofacies are recognized several molecular parameters change systematically with depth lithology including ethylcholestane ratios and c 20 and c 22 sterane and hopane epimer ratios the siliceous lithofacies possesses higher moretane hopane tricyclic pentacyclic terpane and sterane terpane ratios and lower mono mono tri aromatic steroid ratios bisnorhopane hopane ratios are up to 40 times higher in the phosphatic carbonate lithofacies than in the siliceous lithofacies increased relative concentrations of aromatic steroids are attributed to sulfur sterol reactions during very early diagenesis whereas increased relative bisnorhopane amounts are considered to result from massive input of specific anaerobic biota although kerogen elemental ratios change abruptly at the lithofacies boundary molecular distributions within the extractable organic matter change gradually beginning about 30 ft 9m above this interface this gradual change is tentatively attributed to upward migration of hydrocarbons originating in the phosphatic carbonate lithofacies probably through fractures within the lower part of the siliceous lithofacies interval

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

haynesville and bossier mudrocks a facies and sequence stratigraphic investigation east texas and louisiana usa abstract upper jurassic haynesville and bossier shale gas plays of the northwestern gulf of mexico gom basin produce from organic rich marine transgressive to highstand mudrocks within mixed carbonate clastic depositional systems modern wireline log suites from 200 deep wells were used for detailed correlations and 10 cores throughout the upper kimmeridgian to lower tithonian basin were incorporated into detailed facies stratigraphic and lithologic analyses the haynesville shale lies within a 2nd order transgressive systems tract tst that encompasses back stepping ramp carbonates proximal and marine shales distal below a maximum flooding surface mfs this shale onlaps retrogradational carbonates and basement highs and is capped by the 2nd order mfs bossier shales and local sandstones prograde basinward above the haynesville shale and downlap the 2nd order mfs they grade upward and updip into the thick highstand systems tract hst fluvio deltaic sandstones of the cotton valley group distally organic rich facies developed in restricted bossier environments creating another productive gas shale opportunity several preexisting basement highs in the south and carbonate platforms in the northwest and west restrict and partition the basin thus influencing deposition of highly organic versus nonorganic and siliciclastic dominated versus carbonate dominated lithologies haynesville and bossier shales each compose three upward coarsening cycles that probably represent 3rd order sequences within the larger 2nd order tst and early hst respectively most of the three bossier 3rd order cycles are dominated by varying amounts of siliciclastics deposition of the haynesville mudrocks occurred below storm wave base under mostly dysoxic conditionsm allowing settlement of benthic bivalve communities and bioturbating organisms and oscillating periodically to more anoxic conditions on the seafloor however most of the sparse faunae found in these mudrocks are of planktonic origin bossier mudrocks exhibited more oxygenated and clastic rich lithologies related to progradation of the clastic shoreline and sea level highstand knowledge of lithologic stratigraphic geochemical and faunal variations across mudrock basins needs to be detailed so that shale gas basins might be successfully explored

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

the permian huangshanxi cu ni deposit in western china intrusive extrusive association ore genesis and exploration implications the permian huangshanxi cu ni deposit is the second largest magmatic sulfide deposit discovered to date in a major ni cu province related to protracted basaltic magmatism in eastern xinjiang china it is hosted by a small mafic ultramafic intrusion comprised predominantly of lherzolites olivine websterites gabbronorites and gabbros the huangshanxi intrusion is coeval with permian basalts of tholeiitic and alkaline affinities in the tuha and tarim basins respectively to evaluate a possible genetic relationship between the huangshanxi intrusion and a specific type of coeval basalt in the region as well as ore genesis in the intrusion we have carried out an integrated mineralogical petrological and geochemical study our data reveal that the huangshanxi intrusive rocks are characterized by relatively flat chondrite normalized ree patterns depletion in nb and ta and elevated end values varying between 6 and 10 these features are similar to those of coeval tholeiitic basalts in the nearby tuha basin but are significantly different from those of coeval alkaline basalts in the relatively remote tarim basin the geochemical similarities and differences suggest that the huangshanxi intrusion is genetically related to the tholeiitic basalts in the tuha basin not to the alkaline basalts in the tarim basin as suggested previously by some researchers this implies that regional exploration for the huangshanxi type cu ni deposits should be centered in the tuha basin instead of the tarim basin more specifically the uplifted areas around the tuha basin where similar intrusions may have been brought close to the surface should be carefully examined for mineralization potential intrusive relations and mass balance constraints from incompatible trace elements and sulfide abundances suggest that the huangshanxi intrusion represents a dynamic magma conduit through which multiple pulses of magma ascended to higher levels or to the surface numerical simulation of magma evolution and mixing calculations using sr nd isotopes indicate that selective assimilation of s bearing crustal materials is important for sulfide saturation during the early stages of magma evolution when lherzolites formed fractional crystallization may have also played a role in the attainment of sulfide saturation during the later stages of magma evolution when olivine websterites and gabbronorites formed in both cases immiscible sulfide droplets were retained in the conduit to form disseminated sulfide lenses while the fractionated silicate liquids and buoyant phases such as plagioclase continued to ascend extremely low pge tenors in the sulfide ores of the huangshanxi deposit suggest that the parental magma was highly depleted in chalcophile elements possibly due to previous sulfide segregation at depth

late quaternary carbon cycling responses to environmental change revealed by multi proxy analyses of a sediment core from an upland lake in southwest china stable carbon isotope 13c values of organic matter in lacustrine sediments are commonly used to trace past changes in terrestrial and aquatic carbon cycles here we use a high resolution well dated 13c record from lake tengchongqinghai tcqh in southwestern china together with other proxy indices to reconstruct the paleolimnological history over the past 18 5 ka organic matter in the sediments of lake tcqh is derived predominately from aquatic macrophytes the lacustrine primary productivity is closely linked with lake level changes affected by variations in the strength of the asian summer monsoon and modified by evapotranspiration similar to lake sediments world wide a ca 3 shift occurred in the 13c values of lake tcqh in response to the significant increase in atmospheric co2 concentration during the last deglaciation in the holocene the availability of dissolved co2 in the lake water of lake tcqh was determined by variations in hydraulic energy low water turbulence creates a thick stagnant boundary layer around aquatic plants which will restrict the rate of co2 diffusion and result in more positive 13c values of aquatic plants in contrast significant water turbulence dramatically reduces the boundary layer thickness leading to more negative 13c values of aquatic plants

tectonic evolution of the south tianshan orogen and adjacent regions nw china geochemical and age constraints of granitoid rocks geochemical and geochronological evidence was obtained from granitoids of the south tianshan orogen and adjacent regions which consist of three individual tectonic domains the kazakhstan yili plate the central tianshan terrane and the tarim plate from north to south the central tianshan terrane is structurally bounded by the early paleozoic nikolaev line north nalati fault and late paleozoic atbashy inyl chek south nalati qawabulak fault zones against the kazakhstan yili and tarim plates respectively the meta aluminous to weakly peraluminous granitic rocks which are exposed along the kekesu river and the bikai river across the central tianshan terrane have a tholeiitic calc alkaline or high potassium calc alkaline composition i type geochemical trace element characteristics and the y versus rb nb or y versus nb discrimination diagrams favor a continental arc setting for these granitoid rocks shrimp u pb and la icp ms u pb zircon age data indicate that the magmatism started at about 480 ma continued from 460 to 330 ma and ended at about 275 ma the earlier magmatism 470 ma is considered to be the result of a simultaneous southward and northward subduction of the terskey ocean beneath the northern margin of the tarim plate and the kazakhstan yili plate respectively the later magmatism 460 330 ma is related to the northward subduction of the south tianshan ocean beneath the southern margin of the kazakhstan yili central tianshan plate the dataset presented here in conjunction with previously published data support a late paleozoic tectonic evolution of the south tianshan orogen not a triassic one as recently suggested by shrimp u pb zircon dating for eclogites

a lateglacial and holocene lake record from the nianbaoyeze mountains and inferences of lake glacier and climate evolution on the eastern tibetan plateau abstract our 12 81 m long record from lake ximencuo provides insight into the lateglacial and holocene evolution of the lake and the nianbaoyeze glacier in its catchment and the regional climate history since 19 kyr lake ximencuo was a permanent deep lake throughout its history in contrast to numerous lakes on the tibetan plateau which experienced shallow lake levels or even desiccation during the lateglacial lake ximencuo was fed by large quantities of meltwater in the lateglacial the existence of glaciated upper catchment areas is apparently a prerequisite for lakes on the tibetan plateau which maintained relatively high water levels during the generally cold and dry periods following the global lgm 21 kyr a minor re advance of the nianbaoyeze glacier was recorded coeval with the greenland stadial 2a 16 4 and 14 5 kyr followed by rapid warming apparently synchronous with the greenland interstadial 1 warmest conditions were recorded at lake ximencuo during the early holocene which was punctured by a remarkable pulse of climate deterioration around 8 3 kyr this spell represents probably the 8 2 kyr event of the north atlantic region suggesting that it had a significant impact on the tibetan plateau colder conditions of longer duration occurred from 4 7 to 3 7 kyr apparently in phase with numerous records signalling colder and drier conditions on the tibetan plateau two minor spells of colder conditions and probably catchment erosion were recorded in the late holocene between 2 0 and 1 4 kyr and between 0 5 and 0 1 kyr with the latter representing the little ice age it is unclear whether human activities may have accelerated or even solely triggered the late holocene erosion events

the early permian mafic ultramafic complexes in the beishan terrane nw china alaskan type intrusives or rift cumulates abstract the petrogenesis and geodynamic setting of the early permian mafic ultramafic complexes in the beishan terrane nw china have important bearing on the prospects of ni cu pge sulfide and ti fe oxide deposits as well as in understanding the history of evolution of the southern central asian orogenic belt caob here we present results from a detailed study on a representative suit of a mafic ultramafic rocks from the bijiashan complex in the beishan terrane the complex is composed of dunite troctolite olivine gabbro and gabbro without clinopyroxenite or hornblendite in addition to olivine and clinopyroxene orthopyroxene and plagioclase are also present in all these rock types in the absence of chromite or primary hornblende the minerals display marked compositional variations with the fo content in olivines ranging from 66 to 83 and the clinopyroxenes ranging from diopside to augite the whole rock geochemistry shows good correlations among the major elements and the trace elements are characterized by flat ree patterns with eu positive anomalies and hfse depletion relative to lile these features are comparable to other mafic ultramafic complexes in the beishan and eastern tianshan terranes but obviously deviate from the typical features of alaskan type intrusives the present study suggests that the beishan complexes were formed in a post orogenic extensional environment with potential for ni cu mineralization rather than in arc related setting with alaskan type pge mineralization our study confirms that the beishan area does not conform to an arc related setting but was located within a rift setting in permian probably related to permian mantle plume event suggesting that the subduction of the paleo asian ocean had culminated by this time and the southern caob witnessed a post orogenic extensional regime in late paleozoic

lignin biomarker and isotopic records of paleovegetation and climate changes from lake erhai southwest china since 18 5kabp abstract a sound knowledge of paleovegetation is fundamental to better understanding of past climate variability and provides necessary background for improving predictions of future climate changes in the present study stable isotopes 13c and 15n and lignin biomarker of sedimentary organic matter som from lake erhai 25 50 n 100 10 e southwest china were determined to reconstruct paleovegetation and to find vegetation climate relationships the stable carbon isotope signatures suggested that the organic matter mostly derived from c3 plants throughout the depositional periods since 18 5 ka bp the variability of isotopic values of carbon 13c 28 8 to 23 9 and nitrogen 15n 1 2 4 1 might be related to changes in terrestrial runoff i e precipitation compositions of the alkaline cuo oxidation products of lignin showed a significant change in terrestrial vegetation from gymnosperm rich to angiosperm rich plants at lake catchments in the early holocene the lignin phenol vegetation index lpvi also indicated changes in terrestrial vegetation with few more subtle changes during the last 18 5 ka as a single proxy of entire characteristic of terrestrial vegetation in comparison to past asian monsoon records 18o record in stalagmite of dongge cave lpvi suggested a direct linkage between vegetation changes and asian monsoon variability that might be influenced by global climate changes

kerogen based characterization of major gas shales effects of kerogen fractionation abstract research into the origin and the mode of entrapment and expulsion of natural gas from unconventional plays requires the isolation and separation of kerogen in its purest and most intact form from the rock matrix this study expands on the comparative analysis of the effects that isolation methods conservative closed system versus conventional open system have on kerogen s elemental isotopic and physical properties four major gas shales including the barnett the marcellus the haynesville and a polish gas shale were chosen in addition the monterey shale though not strictly a gas shale was included to address the effects on sulfur rich type ii s kerogen results indicate that the kerogen residues from the conventional open system method showed lower recovery and higher mineral content than those from the conservative closed system method differences were manifested in the elemental analysis data where kerogens isolated using the open system method showed a significant deficit in the organic c h o s and n material balance furthermore the recovered residues show different sulfur content and 34s composition most likely attributable to differences in pyrite content nevertheless the relative abundances of the various macerals in the kerogen residues from the same parent shale are not very different neither was the bulk 13c composition of the recovered residues this is not particularly surprising considering that in all the five cases examined in this study the organic matter was fairly homogeneous

discrimination of ophiolitic from nonophiolitic ultramafic mafic allochthons in orogenic belts by the al ti ratio in clinopyroxene in mafic igneous suites typical of anorogenic igneous provinces mid ocean ridges back arc basins continental rifts and hotspots clinopyroxenes of tholeiitic and silica undersaturated rocks incorporate al in clinopyroxene chiefly via the charge coupled substitution vimgivsi2 vitiival2 as the catial2o6 molecule this substitution is promoted by high titania activity relative to silica in the melt and hence is particularly characteristic of silica undersaturated mafic rocks mafic igneous suites of convergent plate margins i e arc tholeiites and calc alkalic gabbros and basalts characteristically incorporate al in clinopyroxene largely as the cafe3 alsio6 molecule the vimgivsi vife3 ival substitution is promoted by relatively high fugacities of h2o and o2 a characteristic feature of arc axis magmas recognition of cumulates that are complementary to compositions of eruptive rocks in arcs is crucial to development of valid petrogenetic models for arc magmas plots of tetrahedrally coordinated al vs octahedral ti in augite of gabbroic and ultramafic cumulates show that augite data arrays for arc related cumulates have a trend of substantially higher al ti in clinopyroxene than do those from rift related tholeiites the al ti ratio in clinopyroxene may be utilized to discriminate ophiolitic from nonophiolitic ultramafic mafic allochthons in orogenic belts

vegetation history climatic changes and indian summer monsoon evolution during the last glaciation 36 400 13 400 cal yr bp documented by sediments from xingyun lake yunnan china abstract we obtained a 9 74 m long sediment core xy08a from xingyun lake in central yunnan province southwest china and used ams radiocarbon dating of terrestrial plant macrofossils to provide a chronology here we present the results of pollen and grain size analyses of the interval 36 400 13 400 cal yr bp and discuss the vegetation history and record of climate change associated with the evolution of the indian summer monsoon ism three stages of regional vegetation change are documented i during the late marine isotope stage 3 36 400 29 200 cal yr bp the study region was occupied by mixed coniferous and evergreen broad leaved forest dominated by pinus and evergreen quercus with tsuga abies picea growing on the surrounding mountains ii during the last glacial maximum lgm 29 200 17 600 cal yr bp cold temperate coniferous forest dominated by species of abies picea expanded and reached a maximum extent and at the same time the extent of evergreen broadleaved forest increased iii from 17 600 to 13 400 cal yr bp the hemlock forest and abies picea forest began to decline until they disappeared completely in the early phase of the last deglaciation while pine forest and evergreen broadleaved forest dominated the surrounding areas the vegetation history indicates a generally drying climate from 36 400 to 13 400 cal yr bp suggesting a gradual weakening of the ism with the weakest ism influence occurring during the early part of the last deglaciation when the climate was the driest the regional temperature first decreased intermittently and then increased gradually being mild and wet during the late mis3 stage followed by the coldest but not the driest climate during the lgm when the temperature was at least 3 c lower than at present

paleoclimate of southwestern china for the past 50 000 yr inferred from lake sediment records abstract long sediment cores 12 5 and 13 5 m from two lakes in yunnan province were used to infer the paleoclimate of southwest china over the past 50 000 yr during the holocene and marine isotope stage mis 3 bio induced carbonate precipitation and organic matter om production was high suggesting warm temperatures and high primary productivity in contrast sediment inorganic carbon ic and organic carbon oc concentrations were low in last glacial deposits from 38 000 to 12 000 cal yr b p indicating cool temperatures and low productivity the 50 000 yr record has alternating peaks of carbonate and coarse grain 38 m quartz that reflect warm moist interglacial or interstadial conditions alternating with cold dry glacial or stadial conditions respectively spectral analysis of the carbonate and quartz signals reveals power concentrated at periods of 7200 and 8900 cal yr respectively that may reflect a nonlinear climate response to precessional forcing at a time of reduced eccentricity modulation mcintyre and molfino 1996 oxygen isotope values of calcite from yunnan lake cores indicate the summer monsoon was weak during the last glaciation from 50 000 to 12 000 cal yr b p the summer monsoon intensified between 12 000 and 8000 cal yr b p but weakened gradually in response to insolation forcing during the mid to late holocene our results support the overpeck et al 1996 model that posits a weak summer monsoon during the last glaciation that responded nonlinearly to insolation forcing when its intensity was affected by eurasian snow cover and ice sheet extent the summer monsoon intensified and responded linearly to seasonal insolation forcing in the holocene when ice volume diminished

new insights on late quaternary asian palaeomonsoon variability and the timing of the last glacial maximum in southwestern china abstract a 6 35 m core 06sd was retrieved from lake shudu yunnan province china the sediments spanning the period 22 6 10 5 kcal yr bp 6 35 1 44 m were analysed using a combination of variables including pollen charcoal particle size magnetic susceptibility and loss on ignition the resulting palaeorecord provides a high resolution reconstruction of late pleistocene to early holocene climatic and environmental changes in southwestern china our findings indicate that from c 22 6 to 17 7 kcal yr bp vegetation assemblages were primarily aligned to sparse xerophytic grassland tundra or cold tolerant boreal pinus forest indicating that climatic conditions in southwestern china were cold and dry however from c 17 7 to 17 4 kcal yr bp the lake shudu record is punctuated by marked environmental changes these include the establishment of denser vegetation cover a marked expansion of boreal pinus forest and enhanced hydrological activity in the catchment over centennial timescales perhaps suggesting that stepwise variations in the asian monsoon were triggering fundamental environmental changes over sub millennial timescales thereafter the pollen record captures a period of environmental instability reflected in fluctuations across all of the variables which persists until c 17 1 kcal yr bp after c 17 1 kcal yr bp the expansion of steppe vegetation cover and cold cool mixed forest consisting of mesophilous vegetation such as tsuga and picea thermophilous trees including ulmus and deciduous quercus inferred from the lake shudu pollen record point to the establishment of warmer wetter and perhaps more seasonal conditions associated with a strengthening asian summer monsoon during the shift from pleistocene to holocene climatic conditions

topsoil c n ratios in the qilian mountains area implications for the use of subaqueous sediment c n ratios in paleo environmental reconstructions to indicate organic sources abstract sediment carbon nitrogen c n ratios can play an important role in reconstructing lacustrine and coastal paleo environments because significantly different c n ratios result from aquatic phytoplankton versus organic matter derived from terrestrial plants however researchers have not yet taken into account the fact that topsoil organic matter is another important terrestrial organic source for lacustrine and coastal sediments a study of topsoil c n ratios from the heihe and shiyang river drainage basins located in the qilian mountains on the northeast margins of the tibetan plateau shows that topsoil c n ratios can be as low as those of subaqueous sediments 80 4 of total topsoils in the heihe river drainage basin and 67 7 of total topsoils in the shiyang river drainage basin have c n ratios below 12 while 18 8 of all samples in the heihe river drainage basin and 29 2 of all samples in the shiyang river drainage basin possess c n ratios between 12 and 20 traditionally researchers have considered that low c n ratios indicate subaqueous deposition however these sediments are terrestrial and most of the organic matter is derived from land plants furthermore topsoil c n ratios from both the heihe and shiyang river drainage basins correlate significantly with altitude and local vegetation our results indicate that not all c n ratios of terrestrial organic matter including plants and soil organic matter equal 20 or more nor can one distinguish subaqueous sediment organic sources solely on the basis of c n ratios low subaqueous sediment c n ratios may not simply result from a greater proportion of aquatic plants versus terrestrial organic matter but also from low end member terrestrial organic matter c n ratios which are lowered by the addition of soil organic matter with its own low c n ratios

lake ecosystem dynamics and links to climate change inferred from a stable isotope and organic palaeorecord from a mountain lake in southwestern china ca 22 6 10 5 cal ka bp abstract a detailed understanding of long term climatic and environmental change in southwestern china is hampered by a lack of long term regional palaeorecords organic analysis toc tn c n ratios and 13c values of a sediment sequence from lake shudu yunnan province ca 22 6 10 5 cal ka bp indicates generally low aquatic palaeoproductivity rates over millennial timescales in response to cold dry climatic conditions however the record is punctuated by two marked phases of increased aquatic productivity from ca 17 7 to 17 1 cal ka bp and from ca 11 9 to 10 5 cal ka bp we hypothesise that these shifts reflect a marked stepwise lacustrine response to asian summer monsoon strengthening during the last deglaciation

comparative analysis and geological significance of kerogen isolated using open system palynological versus chemically and volumetrically conservative closed system methods abstract characterization of kerogen the insoluble organic fraction of sedimentary rocks is of key importance in investigations of the geochemistry of ancient depositional systems paleo climates basin thermal history and petroleum generation systematics furthermore exploitation of organic rich oil shales as unconventional petroleum resources requires understanding of the physical chemistry of the kerogen conversion reactions and the coking behavior these issues can be effectively addressed only if pure representative kerogen is obtained from the rock matrix using chemically and volumetrically conservative methods that preclude losses alteration or fractionation of the organic matter isolation of representative and pure kerogen concentrates from the rock matrix is difficult many methods have been used over the years with various degrees of success most are based on traditional palynological processing approaches in open systems that commonly yield fractionated products generally contaminated with pyrite and insoluble neo fluorides a few are based on complex sealed system procedures that purport to conserve the entire kerogen with no fractionation no alteration and no contamination this study focuses on a comparative analysis of kerogens isolated with the conventional open system approach hcl hf heavy liquid separation and kerogens concentrated with a fully automated conservative closed system method hcl hf crcl 2 under an inert n 2 atmosphere source rock samples of various richness kerogen types ages depositional environments lithologies and thermal histories were selected for kerogen isolation using the two approaches kerogen recovery efficiency progress of the processes and quality of the isolated kerogens were monitored via mass balance calculations organic elemental analysis and x ray diffraction analysis the inherent inadequacy in the open system approach for geochemical research and the improved features of the chemically and volumetrically conservative method are documented

pollen evidence of changing holocene monsoon climate in sichuan province china pollen evidence from lake shayema mianning county was obtained to examine postglacial vegetation and climatic change in southwestern sichuan china the sclerophyllous character of the region s warm temperate vegetation today is a reflection of extreme drought in spring before the onset of the asian monsoons the pollen record displays several changes in the vegetation over the last 11 000 yr from 11 000 to 9100 yr b p cold tolerant species such as abies betula and deciduous oaks dominated the vegetation between 9100 and 7800 yr b p the abundance of deciduous oaks decreased and evergreen oaks increased as did tsuga and mesic deciduous species this change suggests a warming climate with increased precipitation from 7800 to 4000 yr b p sclerophyllous species increased at the expense of mesic deciduous species an indication that precipitation was becoming more seasonal except for increased disturbance starting ca 1000 yr b p the predominance of sclerophyllous vegetation continued until today the pollen results are compatible with proposed global circulation hypotheses of a strengthened monsoon system during the early to mid holocene

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

the southwest indian monsoon over the last 18 000 years previously published results suggest that the strength of the sw indian monsoon can vary significantly on century to millenium time scales an observation that has important implications for assessments of future climate and hydrologic change over densely populated portions of asia we present new well dated multi proxy records of past monsoon variation from three separate arabian sea sediment cores that span the last glacial maximum to late holocene to a large extent these records confirm earlier published suggestions that the monsoon strengthened in a series of abrupt events over the last deglaciation however our data provide a somewhat refined picture of when these events took place and suggest the primacy of two abrupt increases in monsoon intensity one between 13 and 12 5 ka and the other between 10 and 9 5 ka this conclusion is supported by the comparisons between our new marine data and published paleoclimatic records throughout the african asian monsoon region the comparison of data sets further supports the assertion that maximum monsoon intensity lagged peak insolation forcing by about 3000 years and extended from about 9 5 to 5 5 ka the episodes of rapid monsoon intensification coincided with major shifts in north atlantic european surface temperatures and ice sheet extent this coincidence coupled with new climate model experiments suggests that the large land sea thermal gradient needed to drive strong monsoons developed only after glacial conditions upstream of and on the tibetan plateau receded cold north atlantic sea surface temperatures european ice sheets and extensive asian snow cover it is likely that abrupt changes in seasonal soil hydrology were as important to past monsoon forcing as were abrupt snow related changes in regional albedo our analysis suggests that the monsoon responded more linearly to insolation forcing after the disappearance of glacial boundary conditions decreasing gradually after about 6 ka our data also support the possibility that significant century scale decreases in monsoon intensity took place during the early to mid holocene period of enhanced monsoon strength further highlighting the need to understand paleomonsoon dynamics before accurate assessments of future monsoon strength can be made

kerogen asphaltene sulfur relationships in sulfur rich monterey oils abstract monterey oils in the santa maria basin onshore and offshore are generally low maturity oils because of low thermal exposure relatively shallow burial for short times they are generated as heavy high sulfur oils because of the composition of the unusual type ii source kerogens which are exceptionally rich in organic sulfur 8 14 these high sulfur kerogens which we designate type ii s appear to generate oil at significantly lower thermal exposures than ordinary type ii kerogens with less than 6 s in contrast to common type ii kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon carbon bonds eliminating co2 h2o and hydrocarbon fragments type ii s kerogens have an additional complement of weak bonds associated with bound sulfur the preferential cleavage at weak sulfur linkages tends to produce larger fragments leading to high initial amounts of asphaltenes resins and sulfur rich aromatics together with smaller amounts of saturated hydrocarbons elemental analyses of monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics this sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties initial asphaltenes have essentially the same atomic h c ratios as the source kerogen but have significantlyy lower o c ratios and slightly lower s c ratios the n c ratios are nearly the same for kerogens and their derived asphaltenes with increasing maturity the h c ratios in asphaltenes decrease much like maturation changes in kerogen the s c ratio also decreases significantly however the o c ratios initially low in asphaltenes and n c ratios increase slightly due to material balance caused by other losses these element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone this can be useful when potential source rock samples are not available for analysis and or when a choice between alternate source rock possibilities must be made

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

paleoclimate changes of the past 30 cal ka bp inferred from lipid biomarkers and geochemical records from qionghai lake southwest china abstract multi proxy records of paleoclimate changes spanning the past 30 cal ka bp were obtained from qionghai lake sediment core sichuan province southwest china where southwest summer monsoon prevails the core was studied for molecular compositions of n alkanes stable carbon isotope ratios 13c of organic matter om total organic carbon toc total nitrogen tn and trace elements evidence from n alkanes cross chart of c n 13c values and trace elements indicated the organic matter derived from a mixed source composed of autochthonous aquatic organisms and allochthonous terrestrial plants and the sediments mainly deposited in reducing conditions which is in favor of preservation and accumulation of om variations of n alkanes biomarker proxies 13c of organic matter and mo concentrations reflected three stages of paleoclimate evolution during the past 30 cal ka bp a relatively warm and humid climate between 29 1 and 22 9 cal ka bp corresponding to a strong southwest summer monsoon climate shifted towards cold and dry condition during the period of 22 9 15 7 cal ka bp in response to the reduced insolation and weakened southwest summer monsoon temperature and humidity gradually increased in the holocene with fluctuations broadly track the strengthening trend of southwest summer monsoon our findings further confirm that variations in solar activity may primarily affect the strength of southwest summer monsoon resulting in the shifts of paleoclimate conditions further studies are needed to better constrain the detailed forcing drivers which may amplify the intensity of southwest summer monsoon particularly in the holocene period

loss of apatite caused irreversible early holocene lake acidification lakes created by retreating ice at the end of the last glaciation underwent rapid acidification during the first few thousand years of their existence a phenomenon attributed in part to progressive leaching of soil bases since it was discovered more than 80 yeas ago though a role for leaching is still acknowledged the most recent studies see this as subordinate to the effects of biological and climatic changes initiated by deglaciation chiefly primary vegetation succession and species immigration until now there has been no quantitative test of the relative importance of these different mechanisms here i use geochemical modelling of runoff acidity to show that the extent and timing of early holocene lake acidification in eight published palaeoecological records can be explained by leaching of the calcium phosphate mineral apatite from the granitic till soils of their catchments at a rate controlled by simple dissolution kinetic factors this shows that a single progressive abiotic process is capabl

permian bimodal dyke of tarim basin nw china geochemical characteristics and tectonic implications abstract this study reports for the first time the occurrence of bimodal dyke in the shuigongtuan area of bachu county tarim basin nw china here quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature the quartz syenitic porphyry is metaluminous enriched in k2o na2o 10 11 wt and total rare earth elements ree with low mg mg fe ratios high lree hree and negative eu anomalies the chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with a type granites the diabase dyke shows 45 52 wt sio2 and mg mg fe ratio in the range of with high total ree high lree hree ratios and lack of eu anomalies broadly corresponding to tholeiitic composition based on low y nb as low as 0 4 and less than 1 2 enrichment in lile and hfse and uniform nb enrichment patterns in spider diagram for the quartz syenitic porphyry together with the geochemical patterns of the diabases this biomodal association is interpreted to be derived from a mantle source and formed under typical within plate environment the quartz syenitic porphyry and diabase have daly gap of 46 wt 67 wt in sio2 which is explained through formation under bimodal rifting the quartz syenitic dyke probably formed during early permian 277 ma and has geochemical affinity with the xiaohaizi syenitic body we propose that magmas sourced from the mantle intruded into middle upper crust and were emplaced as dykes which indicate large scale extension during the permian in tarim basin the bimodal dyke has genetic affinity with the huge volume of permian basalts and igneous rocks 248 292 ma that occur in the tarim basin the magmatism manifests the culmination of the major thermal event in the tarim basin

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

climate and tectonic effects on holocene development of an alpine lake muge co se margin of tibet south west china is an important area for determining variability of the sw asian monsoon it is however also tectonically very active palaeolimnological studies in this region generally focus on climate as a direct driver of ecological change rarely considering the effects of tectonic activity and catchment ontogeny we present diatom and organic matter data from a holocene sediment record from muge co an alpine lake located on an active fault zone in the southeast margin of tibet and explore the possible drivers of ecological change a major change occurred at 9000 cal bp when the diatom assemblage switched from benthic to predominantly planktonic forms and organic matter content decreased rapidly comparison of the holocene diatom record with a regional data set of lake surface sediments using detrended canonical correspondence analysis dcca suggests that this change in diatom development was mainly associated with changing water depth most likely linked to a seismically triggered landslide

palaeoclimate dynamics in continental southeast asia over the last 30 000calyrs bp abstract although the asian monsoon is the dominant source of precipitation across continental southeast asia projections of future climate trends in this region remain unclear this is partly because historic climate records are relatively short precluding our ability to understand long term climate dynamics and potential drivers of change in this synthesis 17 palaeorecords from sites located in continental southeast asia provide a synopsis of regional palaeoclimate dynamics over the last 30 000 cal yrs bp the results indicate that over millennial timescales the dominant control on asian monsoon intensity is solar insolation linked to orbital changes from ca 30 to 11 9 cal kyr bp climatic conditions are interpreted to have been cold and arid most probably dominated by a strong asian winter monsoon marked changes occurred during the pleistocene holocene transition including a shift to warmer wetter climatic conditions at ca 11 5 cal kyr bp which was apparently synchronous across the region during the early to mid holocene warmer wetter climatic conditions were established consistent with a strong asian summer monsoon inferred from the dongge cave 18o speleothem record intriguingly contrasting sub regional palaeoclimatic trends are captured in the synthesis most notably during the holocene possibly due to differing sub regional climatic and environmental influences including differences in the role of the asian monsoon the westerlies and or topographical effects however because of uncertainties relating to the age control of many of the palaeorecords it is not possible to make this interpretation with confidence further work involving comprehensive radiocarbon dating of sequences and the development of high resolution palaeoclimatic reconstructions are urgently required if we are to identify decadal to centennial scale changes across continental southeast asia and test hypotheses of synchroneity in the region

late glacial vegetation and climate oscillations on the southeastern tibetan plateau inferred from the lake naleng pollen profile we present a late glacial pollen record 17 700 to 8500 cal yr bp from a lake naleng sediment core lake naleng is located on the southeastern tibetan plateau 31 10 n 99 75 e 4200 m along the upper tree line variations in the summer monsoon are evident from shifts in vegetation that correspond to late glacial climate trends from other monsoon sensitive regions alpine steppe was recorded between 17 700 and 14 800 cal yr bp indicating low effective moisture at the study site expansion of alpine meadows followed by advances in the position of tree line around lake naleng suggest that climate became warmer and wetter between 14 800 and 12 500 cal yr bp probably representing an enhancement of the asian monsoon climatic cooling and reduced effective moisture are inferred from multivariate analysis and the upward retreat of tree line between 12 500 and 11 700 cal yr bp the timing and nature of these shifts to warm wet and then cold dry climatic conditions suggest that they correspond to the bolling allerod and younger dryas intervals abies betula forests representing warm and moist conditions spread during the early holocene

hydrological and ecosystem response to abrupt changes in the indian monsoon during the last glacial as recorded by sediments from xingyun lake yunnan china abstract the indian summer monsoon ism is the major moisture source of precipitation in southwest china and plays an important role in regional environmental change and in economic and social development since abrupt changes of the ism can cause crop failures and flooding that impact the livelihood of a large population however with the exception of speleothem records abrupt changes of the ism during the last glacial are not well documented in terrestrial records here we present a sediment record from xingyun lake in yunnan province southwest china spanning the interval 36 4 ka bp to 13 4 ka bp 1 ka 1000 cal a which documents the occurrence of a series of millennial scale episodes which may reflect the abrupt weakening of the ism seven ams 14c dates from terrestrial wood fragments provide a robust chronology the results demonstrate that increases in the coarse sediment fraction 30 m correspond to increases in the concentration of pediastrum the grain size of magnetic minerals carbonate content and c n ratios which together indicate episodes of low lake level in addition pollen analysis indicates that quercus oak increased and that ferns decreased during intervals of abrupt weakening of the ism indicating a drier environment nine abrupt shifts to a low lake level are documented for the studied interval and three of them are correlative with heinrich events 1 to 3 our study supports the hypothesis that in response to the cold events in the north atlantic associated with massive iceberg influxes and the corresponding slowing down of atlantic meridional overturning circulation the mean latitudinal extent of the itcz shifted southwards as a result of an atmospheric teleconnection there was a corresponding decrease in precipitation associated with ism precipitation which caused reduced fluvial runoff in yunnan

diatom response to climate forcing of a deep alpine lake lugu hu yunnan sw china during the last glacial maximum and its implications for understanding regional monsoon variability abstract the yunnan plateau of southwest china is strongly influenced by the asian monsoon and is a critical area in terms of determining its development and variability since the last glacial maximum high resolution diatom analysis of a 14c dated sediment core retrieved from lugu lake yunnan provides a detailed history of palaeoenvironment changes from 30 000 to 10 000 cal yr bp a model of climate diatom interactions linking thermal stratification ice cover and catchment derived nutrients is proposed to explain the observed changes prior to 24 500 cal yr bp the dominance of the planktonic cyclotella rhomboideo elliptica indicates a period of stable stratification and low nutrient levels with a moderate change of temperature and precipitation in the southwest monsoon region during the lgm 24 500 14 500 cal yr bp the loss of the planktonic diatoms and a switch to small fragilaria spp suggest an altered thermal regime in the lake i e weaker stratification and possibly ice cover from 18 000 cal yr bp the expansion of planktonic taxa stephanodiscus and the asterionella formosa and increased toc are indicative of increased nutrient availability reflecting altered vegetation and soil processes due to rising regional temperatures after 14 500 cal yr bp a rapid reversal to dominance by planktonic diatoms indicates a further increase in temperature and continued development of catchment vegetation and soils the abrupt changes in diatom species composition around 24 500 and 14 500 cal yr bp suggest that the ecological status of the lake exceeded limnological thresholds interestingly however the younger dryas event is not clearly recognizable in either the diatom or pollen records in the lugu lake sediment record in a partial redundancy analysis 44 2 of the variability in the total diatom assemblages in the period 30 000 10 000 cal yr bp was accounted for by changes in summer solar radiation the relationships between the diatom assemblages and the c n and pollen data are further evidence of climate catchment vegetation interactions and their impact on lake functioning the composition of diatom assemblages in the lugu lake sediment core reflects direct and indirect i e via catchment processes climate forcing and in particular the strength of the southwest monsoon which in turn corresponds to orbitally induced variability in northern hemisphere summer solar insolation from 30 000 cal yr bp to 10 000 cal yr bp

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

distinct climate change synchronous with heinrich event one recorded by stable oxygen and carbon isotopic compositions in stalagmites from china abstract uranium series dating of oxygen and carbon isotope records for stalagmite sj3 collected in songjia cave central china shows significant variation in past climate and environment during the period 20 10 ka stalagmite sj3 is located more than 1000 km inland of the coastal hulu cave in east china and more than 700 km north of the dongge cave in southwest china and despite minor differences displays a clear first order similarity with the hulu and dongge records the coldest climatic phase since the last glacial maximum which is associated with the heinrich event 1 in the north atlantic region was clearly recorded in sj3 between 17 6 and 14 5 ka in good agreement in timing duration and extent with the records from hulu and dongge caves and the greenland ice core the results indicate that there have been synchronous and significant climatic changes across monsoonal china and strong teleconnections between the north atlantic and east asia regions during the period 20 10 ka this is much different from the holocene optimum which shows a time shift of more than several thousands years from southeast coastal to inland china it is likely that temperature change at northern high latitudes during glacial periods exerts stronger influence on the asian summer monsoon relative to insolation and appears to be capable of perturbing large scale atmospheric oceanic circulation patterns in the northern hemisphere and thus monsoonal rainfall and paleovegetation in east asia climatic signals in the north atlantic region propagate rapidly to east asia during glacial periods by influencing the winter land sea temperature contrast in the east asian monsoon region

deposition models for chronological records abstract long term sedimentary sequences provide a wealth of useful information for research into the palaeo environment especially in relation to past climate change shorter records provide similar information in many archaeological contexts however if such records are to be used to provide precise timing of events and more critically the relative timing between different records methods are needed to provide accurate and precise age depth models for these sequences given the imprecision of individual calibrated radiocarbon determinations it is necessary to use the information we have about the deposition process to refine our chronologies and also to provide interpolation between dated levels in any sequence even with layer counted chronologies the uncertainties are sometimes hard to quantify this paper outlines a range of bayesian models for deposition which have been implemented in the computer programme oxcal these models can be used to combine information from the sediments themselves with radiocarbon or other direct dating information such models have the potential to integrate information between different records and provide a coherent chronology on which to base environmental or archaeological research