the philippine sea new survey results reveal the structure and the history of the marginal basins the hydrographic department of japan initiated a long term geological and geophysical survey of the philippine sea in 1983 we here summarize the bathymetry and magnetic anomalies of this area focusing on the structure and the evolutionary process of the marginal basins the shikoku and parece vela basins developed as one backarc system in the later phase of their formation the significant difference between the two basins however is clearest near the extinct spreading centers the steep oki daito escarpment located in the northern west philippine basin was mapped for the first time during this survey the n s trending spreading fabric north of the escarpment is in striking contrast to the nw se to e w lineament in the south our data reveal a more complicated history of the western philippine sea than has been proposed in previous studies

origin and emplacement of mariana forearc seamounts large seamounts occur on the outer half of the mariana forearc they represent a new class of seamounts consisting of horsts and diapirs of metamorphosed forearc material the degree of metamorphism in this material depends on the amount of water available and the pressure temperature regime of the forearc wedge the major source for the water involved in the metamorphism is most likely the descending slab theoretical models for thermal regimes in convergent margins suggest that the lower grade metamorphic facies will be restricted to the outermost part of a forearc zeolite and chlorite facies rocks predominate in dredge hauls from horsts on the outer 50 km of the mariana forearc thermal models indicate that higher grade greenschist facies should occur farther from the trench seamounts that were probably formed in response to diapiric emplacement of serpentinite predominate from 50 to 120 km from the trench uplift of the horsts and emplacement of the serpentinite diapirs were probably facilitated by vertical tectonic movement in response to subduction of plate seamounts and by fracturing of the mariana forearc

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

petrographic and trace element analysis of uranium rich tufa calcite middle miocene barstow formation california usa an integrated petrographic and spectroscopic x ray diffraction phosphor imaging and synchrotron x ray absorption spectroscopy study of tufas from the miocene barstow formation california relates sample morphology mineralogy and geochemical composition the tufas composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters have textures similar to those of microbially mediated terrestrial stromatolites and travertines the tufas have elevated concentrations of a number of trace elements including mn fe sr and u synchrotron x ray fluorescence analyses show that u concentrations can exceed 500 p p m x ray absorption spectroscopy indicates that the u in these samples is incorporated as u iv it is suggested here that alkaline lake waters had a high u ca ratio and tufa calcite formed where groundwater or possibly epithermal springs brought in ca and trace elements such as sr the rapid and possibly microbially mediated precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine scale inclusions

temporal benchmarks for modeling phanerozoic flow of basinal brines and hydrocarbons in the southern midcontinent based on radiometrically dated calcite fluid inclusion studies of radiometrically dated u pb th pb calcite samples document the presence of hydrothermal fluids at ca 251 137 67 and probably 39 ma within the tri state zn pb mining district of missouri kansas and oklahoma fluid inclusions indicate minimum temperatures and equivalent salinities ranging from highs of 122 c and 24 wt nacl ca 251 ma to lows of 52 c and 0 wt nacl ca 39 ma the two earliest calcites contain primary petroleum inclusions but these are absent in samples younger than ca 137 ma when combined with information on metal rich shales paleomagnetism and modern groundwater flow our results are most readily explained by periodic influxes of hydrothermal fluids of diverse compositions for 200 m y and sporadic migration of hydrocarbons for at least 100 m y in the southern midcontinent

u pb dating of a speleothem of quaternary age we demonstrate that u pb dating is a promising method for secondary carbonate materials of quaternary age and older by obtaining a 206pb 238u age for a speleothem with high u 10 g g 1 and very low pb 10 ng g 1 that is supported by an independent 230th age thermal ionisation mass spectrometry was used to determine the u and pb isotopic ratios and concentrations for subsamples of a stalactite from winnats head cave peak district uk we obtained 206pb 204pb ratios up to 50 and determined a 206pb 238u age of 248 10 ka which is within error of the 207pb 235u age of 333 79 ka and a spectrometric u th age of 255 ka for samples of tertiary and quaternary age the initial state of u series disequilibrium is an important consideration and as with most radiometric dating techniques the mineral must have remained closed to u th pb and all intermediate daughters we show that dense calcite speleothems are ideal in this respect and that no loss of rn has occurred unlike u series disequilibrium methods u pb dating has no upper limit and hence materials of quaternary age older than 0 6 ma can be analysed to investigate landscape development paleoclimate hominid evolution or hydrogeochemistry in carbonate terrains

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

extraordinary hydro climatic events during the period ad 200 300 recorded by slackwater deposits in the upper hanjiang river valley china abstract the hanjiang river a major tributary of the yangtze river in china is noted for the current national south to north water diversion project palaeo hydrological investigations were carried out along the upper reach gorges of the hanjiang river that drains the qinling and the dabashan mountains a set of palaeoflood slackwater deposit beds swds was identified in holocene pedo stratigraphy of the riverbanks along the valley these swds are interbedded in the eolian loess soil profiles in the cliffy riverbanks and they thin out toward the upper slopes the palaeoflood swds were differentiated from eolian loess and soil by the sedimentary criteria and analytical results the minimum flood peak discharges were estimated to be 65 400 65 830 m 3 s 1 by using palaeo hydrological methods they are about twice of the largest gauged flood 34 300 m 3 s 1 that has ever been measured they represent the largest flood events in the upper reaches of the hanjiang river over the holocene these extraordinary flood events were dated to 1810 1710 a ad 200 300 with the optically stimulated luminescence method and checked by archaeological dating of the human remains retrieved from the profiles this indicates that the extraordinary floods occurred during the dynasties of eastern han to western jin ad 25 316 in chinese history during which severe droughts and floods were recorded in documents in the reconstructed 2000 year temperature time series based on high resolution climatic proxies from tree rings stalagmites ice cores and lake sediments from over the world these extraordinary palaeoflood events are correlated with an increased climatic variability characterized by cooling and drying during the period ad 150 350 this result is important for understanding the effects of global change on river system dynamics

the response of transitional pedogenic characteristics of loess in the yunxian basin to abrupt climatic events in the northern subtropics since the last glacial maximum abstract the transitional pedogenic characteristics of loess deposits in the yunxian basin have provided solid evidence for understanding the mechanisms of dust transportation deposition and detailed documentation of climate instability since the last glacial maximum lgm in the northern subtropics of china the heinrich stadial 1b hs 1b 16 9 14 7 ka b p event b lling aller d b a 13 9 13 ka b p period younger dryas yd 12 9 11 7 ka b p event and an environmental event 5 4 ka b p during the holocene optimum were imprinted by the high resolution multi proxy of loess paleosol in the yunxian basin china based on granularity and chemical analyses the loess in the yunxian basin can be classified as a fine clayey loess zone that experienced a moderate degree of chemical weathering the mechanism forming the transitional pedogenic characteristics was explained by the dust storm frequency data 1957 2007 particle size data and multi proxy records of chemical weathering extent which was mainly caused by the moderate transport distance from the common provenance and the transitional climatic characteristics of the northern subtropical zone

accelerated pleistocene coral extinctions in the caribbean basin shown by uranium lead u pb dating ages of corals and shallow marine sequences define rates of marine invertebrate evolution tectonic uplift and paleoclimate change yet accurate ages are difficult to obtain prior to the late pleistocene we report a new approach for combining uranium lead u pb and uranium series dating for middle pleistocene corals from the caribbean side of costa rica two corals have 230 th 238 u in secular equilibrium small excesses in 234 u and 206 pb 238 u ages of 1 02 0 07 ma and 1 288 0 034 ma the latter coral age dates a recognized geomagnetic event to ca 1 3 ma a time at which no polarity events had been identified the new ages also show that the major coral extinction in the caribbean basin occurred shortly after 1 0 0 9 ma much more recently than previously thought this coral extinction now coincides with the global change at 1 0 0 8 ma to the current pattern of glacial interglacial cycles and amplified changes in sea level these factors may have provided a new strong environmental mechanism for rapid habitat modification and coral extinction

u pb isotopic age of the stw 573 hominid from sterkfontein south africa sterkfontein cave south africa has yielded an australopith skeleton stw 573 whose completeness has excited great interest in paleoanthropology stw 573 or little foot was found 25 meters below the surface in the silberberg grotto 238u 206pb measurements on speleothems immediately above and below the fossil remains corrected for initial 234u disequilibrium yield ages of 2 17 0 17 million years ago ma and 2 24 0 07 0 09 ma respectively indicating an age for stw 573 of close to 2 2 ma this age is in contrast to an age of approximately 3 3 ma suggested by magnetochronology and ages of approximately 4 ma based on 10be and 26al but it is compatible with a faunal age range of 4 to 2 ma

direct radiometric age determination of carbonate diagenesis using u pb in secondary calcite abstract carbonate rocks and corals from the middle devonian lucas formation ontario have 238 u 204 pb values ranging from 132 to 559 and give concordant apparent 206 pb 238 u and 207 pb 235 u ages in approximate agreement with the primary age of sedimentation a carbonate rock from one part of the section gives an anomalously young age and contains patches of secondary calcite spar this spar is predominantly pale purple under cathodoluminescence cl and contains 250 600 ppb u and 15 22 ppb pb the values range from 2 10 3 10 4 making the pb very radiogenic apparent 206 pb 238 u ages range from 208 to 249 ma and 232 th 238 u values are from 0 005 to 0 040 the younger ages are correlated with an increase in orange cl and higher apparent values the age scatter is attributed to mixing of a subordinate calcite spar which infiltrated the older spar the young calcite is bright orange under cl has 7200 ppb u of 6 2 10 4 a of 0 23 and is dated at 45 ma the age of the older spar has been determined by a sequential dissolution technique the resulting u pb data can be plotted as u pb age spectra and yield lplateau dates ranging from 231 5 1 4 to 244 9 1 6 ma and an integrated 206 pb 238 u age of 238 2 1 1 ma also the sequential dissolution increases the values progressively to a5 10 4 making these ages independent of the initial pb correction the occurrence of two young ages of diagenetic calcite in these strata is consistent with the idea of recurrent fluid activity along fracture zones in subsurface sediments in the michigan basin this study shows that it is now possible to date secondary carbonate diagenesis by u pb and by inference to determine precisely the timing of activity on ancient fracture zones in carbonate rocks

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

age and evolution of the grand canyon revealed by u pb dating of water table type speleothems the age and evolution of the grand canyon have been subjects of great interest and debate since its discovery we found that cave mammillaries water table indicator speleothems from nine sites in the grand canyon showed uranium lead dating evidence for an old western grand canyon on the assumption that groundwater table decline rates are equivalent to incision rates samples in the western grand canyon yielded apparent water table decline rates of 55 to 123 meters per million years over the past 17 million years in contrast to eastern grand canyon samples that yielded much faster rates 166 to 411 meters per million years chronology and inferred incision data indicate that the grand canyon evolved via headward erosion from west to east together with late stage 3 7 million years ago accelerated incision in the eastern block

high resolution mapping of uranium and other trace elements in recrystallized aragonite calcite speleothems from caves in the pyrenees france implication for u series dating abstract aragonite and calcite speleothems were sampled in the cave of pierre saint martin pyrenees atlantiques france these speleothems contain significant amounts of uranium and strontium which were measured spatially and chemically by nuclear microprobe analysis sr and u distributions are highly varied with a marked contrast between aragonite and calcite because the aragonite concentrates sr and u on the other hand zn is preferentially located in calcite and in layers of organic matter trapped in caco 3 sr contents ranged from 440 to 1100 g g in the calcite and 4900 to 18 500 g g in the aragonite u concentrations show remarkably high values from 11 to 19 g g in the calcite and 89 to 350 g g in the aragonite these u and sr concentrations are amongst the highest measured in supergene speleothems deposited by infiltrating meteoric waters x ray absorption experiments with synchrotron radiation suggested that uranium was incorporated in its hexavalent oxidation state in both aragonite and calcite recrystallization from aragonite into calcite was indicated by micromorphological observations for some of the samples this recrystallization process may explain the uranium loss in neogenic calcite deposits and consequently the opening of the geochemical system which can lead to errors in age dating with the u series dating method uranium loss in recrystallized calcite is one of the important aspects to be considered in u series dating and more generally for u geochemical stability in caco 3

u pb dates of paleosols constraints on late paleozoic cycle durations and boundary ages u pb ages of paleosol samples from cyclothemic sections in the sacramento mountains of new mexico and the permian basin of west texas bracket the pennsylvanian permian and carboniferous permian boundaries linear interpolation and extrapolation to boundaries are accomplished by using cyclothems as periodic subdivisions the carboniferous permian boundary is 301 2 ma 2 the pennsylvanian permian boundary is 302 2 4 2 and the missourian virgilian boundary is 307 3 ma 2 these ages are within the uncertainties of recent estimates for the boundaries but are significantly more precise the average cycle duration for this upper pennsylvanian and lower permian interval is 143 64 ka 2 within the uncertainty of the 100 k y cycle that dominated pleistocene sea level history this new estimate which is much shorter than those published previously suggests that the pennsylvanian and early permian cyclothems may have been driven in a manner similar to that which caused glacio eustatic cycles of the pleistocene

u pb dating of discordant 0 1 ma old secondary u minerals abstract a modified tera wasserburg u pb concordia plot which takes care of initial disequilibrium of radioactive daughter nuclides has been applied to date discordant torbernite samples from hohenstein northeast bavaria to 137 11ka lower intercept and 66 27ma upper intercept the secondary u pb age is supported by the 230 th 234 u disequilibrium age of 132 4 ka

the younger dryas cold interval as viewed from central greenland abstract greenland ice core records provide an exceptionally clear picture of many aspects of abrupt climate changes and particularly of those associated with the younger dryas event as reviewed here well preserved annual layers can be counted confidently with only 1 errors for the age of the end of the younger dryas 11 500 years before present ice flow corrections allow reconstruction of snow accumulation rates over tens of thousands of years with little additional uncertainty glaciochemical and particulate data record atmospheric loading changes with little uncertainty introduced by changes in snow accumulation confident paleothermometry is provided by site specific calibrations using ice isotopic ratios borehole temperatures and gas isotopic ratios near simultaneous changes in ice core paleoclimatic indicators of local regional and more widespread climate conditions demonstrate that much of the earth experienced abrupt climate changes synchronous with greenland within thirty years or less post younger dryas changes have not duplicated the size extent and rapidity of these paleoclimatic changes

topographic and sedimentary features in the yap subduction zone and their implications for the caroline ridge subduction abstract the yap subduction zone in the western pacific presents some unique features compared to normal intra oceanic subduction zones such as the subduction of an oceanic plateau however due to the relative paucity of geophysical data the detailed structure remains unknown in this area in this study we present the latest high quality swath bathymetry and multi channel seismic data acquired synchronously in 2015 across the yap subduction zone the topographic and sedimentary features are intensively investigated and a modified evolutionary model of the yap subduction zone is proposed the two stage evolution of the parece vela basin pvb produced fabrics that are n s trending and nw se trending our seismic data clearly reveal landslide deposits at the upper slope break of the forearc to the north of the yap island which was identified as the fault notch denoting a lithological boundary in previous work the swath bathymetry and seismic profile reveal detailed horst and graben structures including a crescent shaped fault zone near the contact between the yap trench and the caroline ridge a simple geometric model is proposed to explain the structure formation indicating that the higher topography of the caroline ridge resulted in enhanced bending related extension a seismic angular unconformity named r1 is identified in the sorol trough marking the onset of rifting in the trough based on the sequence thickness and deposition rate by deep sea drilling project dsdp it is deduced that the sorol trough formed at 10 ma or even earlier a modified model for the yap subduction zone evolution is proposed incorporating three major tectonic events the proto yap arc rupture in the oligocene the collision of the caroline ridge and the yap trench in the late oligocene or middle miocene and the onset of the sorol trough rifting in the late miocene

upb dating of calcite concretions from cambrian black shales and the phanerozoic time scale the u pb dating of carbonate offers considerable potential for accurate and direct dating of sedimentary rocks here we show that carbonate concretions from the upper cambrian black shales in southern scandinavia have remarkably high u to pb ratios 238u204pb up to 288 000 permitting precise geochronology a fine crystalline early diagenetic concretion yields an age of 509 8 5 1 ma providing an accurate age for the late cambrian whereas a coarse cone in cone concretion has yielded an age of 478 2 4 9 ma defining the final stage of sediment compaction and indicating a protracted dewatering and diagenetic history these results demonstrate the power of this method for directly calibrating the geological time scale and constraining diagenetic histories

preservation of particulate non lithogenic uranium in marine sediments particulate non lithogenic uranium pnu excess u above detrital background levels found in marine particulate matter is formed in surface waters throughout the ocean previous studies have shown that pnu is regenerated completely prior to burial of particles in sediments within well oxygenated open ocean regions however the fate of pnu has never been examined in ocean margin regions or in anoxic basins here we evaluate the preservation of pnu in ocean margin sediments and within semi enclosed basins using samples from sediment traps deployed at multiple depths and surface sediments organic carbon fluxes at the sediment trap locations ranged from 0 1 to 4 3 g cm 2 kyr while the dissolved oxygen concentration in the water column ranged from 3 mt o 270 m preservation of pnu increases with decreasing dissolved oxygen concentration approaching 100 preservation at oxygen concentration 25 m pnu contributes as much as 40 to 70 of the total authigenic u in sediments in the santa barbara basin and seasonally anoxic saanich inlet and some 10 to 50 of the total authigenic u in sediments off the central california margin copyright 2002 elsevier science ltd

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

was scotland deglaciated during the younger dryas recent work has produced data that challenges the canonical view that the younger dryas c 12 9 11 7 ka was a time of glacier expansion across the north atlantic boulders on moraines located within the inner sector of the scottish loch lomond stadial younger dryas ice cap yield cosmogenic exposure ages 12 8 11 3 ka with a best estimate moraine age of 11 5 0 6 ka this age contradicts the interpretation that scotland was completely deglaciated as early as 12 580 cal yr bp and no later than 12 200 cal yr bp our data supports the previously accepted scenario supported by a wide variety of data that final deglaciation of scotland did not occur until late in the loch lomond stadial or the early holocene

high resolution evidence from southern china of an early holocene optimum and a mid holocene dry event during the past 18 000 years abstract computer models suggest that the holocene optimum for east asian summer monsoon precipitation occurred at different times in different regions of china previous studies indicate that this time transgressive holocene optimum should have been experienced about 3000 yr ago in southern china in this study we describe a section which allows us to test this timing directly we have closely examined high resolution eutrophic peat mud sequences covering the past 18 000 cal yr at dahu jiangxi on the southern boundary of the mid subtropical zone in china late pleistocene successions in the dahu record indicate cooler and much wetter conditions relative to synchronous events in north central china our results indicate that the holocene optimum occurred between ca 10 000 and 6000 cal yr ago in southern china consistent with the global pattern conditions were relatively dry and cold from 6000 to 4000 cal yr ago our data also support the conclusion that the last deglaciation to early holocene in the south was much wetter resulting in the formation of dense broad leaved forests which could have acted to moderate land temperature 10 000 to 6000 cal yr ago yielding a stable early holocene climate after 6000 cal yr forest reduction led to unstable land temperatures and possibly to a northerly shift of the subtropical high pressure system whatever the mechanism these changes resulted in decreased precipitation between 6000 and 4000 cal yr b p in southern china

early human settlements in the southern qinling mountains central china abstract china is a key area of early human settlement in east asia with numerous paleolithic localities indicating an early pleistocene presence of hominins in northern and southern china considerable research has been devoted to determining possible migration routes for hominins linking the two areas in this paper we report the discovery of several loess covered paleolithic sites in the hanzhong and ankang basins along the hanjiang river in the southern piedmont of the qinling mountains qlm in central china a chronology is developed for these sections using a combination of detailed optically stimulated luminescence dating magnetostratigraphic analyses and pedostratigraphic correlation with the well dated loess paleosol sequence of the central chinese loess plateau the results indicate that the age of the oldest lithic assemblage at the longgangsi locality 3 paleolithic site in hanzhong basin is 1 20 ma thus making this locality as one of the oldest sites in central china our work also indicates that hominins occupied the hanjiang valley at several times 1 2 0 9 0 6 and 0 1 ma we propose that the hanjiang river valley was a probable hominin routeway through the qlm because many sites corresponding to these different phases were also discovered to the north of the qlm future study on the hanjiang river valley is important for verifying the hypothesis of an early human migration route between southern and northern china

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

th pb and u pb dating of ore stage calcite and paleozoic fluid flow thorium 232 lead 208 and uranium 238 lead 206 radiometric ages for ore stage calcite show that mississippi valley type mvt ore deposits can form in distinct tectonic settings an age of 251 11 million years for the jumbo mine in kansas united states is in agreement with other ages for mvt deposits in the midcontinent of north america the similarity of ages of these deposits supports the concept that they formed in response to fluid flow during the late paleozoic alleghenian ouachita orogeny an age of 351 15 million years for twelve mile bore and bloodwood kapok deposits in australia indicates that these mvt ores were deposited in a rifting environment

u pb calcite age of the late permian castile formation delaware basin a constraint on the age of the permian triassic boundary abstract organic rich calcite laminated with gypsum in the evaporitic non fossiliferous castile formation of the delaware basin southwest usa yields a total pb u isochron age of 251 5 2 8 ma mswd 1 3 the castile formation is almost certainly late permian based on its 87 sr 86 sr value of 0 706923 identical to the distinct minimum in the late permian sr curve in this paper we explore the potential for using u pb calcite ages to date traditionally undatable sections and show how this southern midcontinent usa far west texas and southeast new mexico deposit can be correlated to the type section in china we accept that diagenetic alteration can bias u pb results but the data set we present shows no evidence for such alteration clearly with alteration the age we present would represent a minimum age for the castile formation if the age actually dates the castile formation then it requires the permian triassic boundary to be younger than 251 5 2 8 ma

morphological studies of the ayu trough philippine sea caroline plate boundary the ayu trough lies on the southern boundary between the philippine sea plate and caroline plate although this trough may be the best place to study the evolution and kinematics of the philippine sea plate the origin and evolution of this trough are poorly understood our geophysical and morphological surveys in the northern part of the ayu trough revealed that the trough shares morphological similarities with slow spreading lid ocean ridges the seafloor ages and an average spreading rate of the trough were inferred from the avcrage length of the ridge segments distribution of sediment thickness and basement subsidence based on the seismic section at 3 30 n the opening of the trough started about 25 ma with an average half spreading rate 4 1 mm yr this spreading rate is much slower than some previous estimates the present magma production rate and activity of the trough is estimated to be even lower than the 25 m y average the seafloor depth of the trough axis and relief of the axial valley are approximately twice as deep as that of active lid ocean ridges the trough axis valley is covered with sediment in contrast with the axial valleys of active lid ocean ridges sedimentation at the trough axis shows that the spreading rate has been quite slow for the last 2 5 ma

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

the asian monsoon over the past 640 000 years and ice age terminations oxygen isotope records from chinese caves characterize changes in both the asian monsoon and global climate here using our new speleothem data we extend the chinese record to cover the full uranium thorium dating range that is the past 640 000 years the record s length and temporal precision allow us to test the idea that insolation changes caused by the earth s precession drove the terminations of each of the last seven ice ages as well as the millennia long intervals of reduced monsoon rainfall associated with each of the terminations on the basis of our record s timing the terminations are separated by four or five precession cycles supporting the idea that the 100 000 year ice age cycle is an average of discrete numbers of precession cycles furthermore the suborbital component of monsoon rainfall variability exhibits power in both the precession and obliquity bands and is nearly in anti phase with summer boreal insolation these observations indicate that insolation in part sets the pace of the occurrence of millennial scale events including those associated with terminations and unfinished terminations records of the asian monsoon have been extended to 640 000 years ago and confirm both that the 100 000 year ice age cycle results from integral numbers of precessional cycles and that insolation influences the pacing of major millennial scale climate events prior records of the asian monsoon have revealed cyclic variations over hundreds of thousands of years probably driven by variations in insolation caused by the precession of earth s orbit hai cheng and colleagues now provide a speleothem record from chinese cave samples that extends earlier records to 640 000 years ago close to the maximum age possible with uranium thorium dating this spectacular record confirms that the characteristic 100 000 year ice age cycle corresponds to an integral number four or five of precession cycles and that insolation influences millennial scale variations in monsoon strength

the impact of diagenesis on high precision upb dating of ancient carbonates an example from the late permian of new mexico we have applied upb trace element and sr isotopic analyses to subsamples of a single specimen of the capitan formation from the permian reef complex of new mexico with the goal of calibrating the late permian time scale and understanding the factors that set and later alter the initial u pb ratio and pb isotopic composition of the limestone the data indicate a limestone upb isochron age of 249 8 4 7 ma 2 and a pbpb age of 249 18 ma in addition with values 238u 204pb ranging up to 4200 among the highest ever recorded for a limestone we also obtain precise single sample 206pb 238u 207pb 235u and 207pb 206pb ages indicating averages of 250 2 3 2 ma 250 0 2 8 ma and 256 3 3 5 ma respectively comparison of the average pb u age of 250 3 ma for the latest guadalupian with published radiometric constraints for the late permian suggests preservation of essentially the depositional age trace element and sr isotopic analyses highlight four samples that preserve a chemical signature expected for primary marine aragonite including high sr 3000 g g high u 2900 ng g low initial pb 26 g g and 87sr 86sr 0 7073 as well as the lower u and higher pb mg and fe expected for a diagenetically altered carbonate these data clearly delineate the diagenetic alteration of the limestone and allow us to demonstrate the critical importance of diagenesis in controlling the spread in values primarily through the expulsion of u but with some incorporation of pb the high are simply a function of preservation of original carbonate chemistry and not of u scavenging by fe oxyhydroxides or phosphates although it has long been suspected that limestone upb and pbpb isochron ages reflect the timing of early diagenesis as opposed to a strictly depositional age this is the first study in which this is conclusively demonstrated to be the case the upb data also suggest a late stage neogene alteration that disturbed the system mainly via the redistribution of u intriguingly the four samples that best retain their primary marine aragonitic geochemistry also best maintained a closed upb system most of the subsamples with comparably high values but clearly altered trace element compositions showed upb systematics indicating late disturbance unfortunately it is not yet possible to determine which processes are responsible for this late stage alteration and it is unclear exactly how to avoid such alteration in future work

pedostratigraphy of aeolian deposition near the yunxian man site on the hanjiang river terraces yunxian basin central china abstract since 2010 we have found stone artifacts at the houfang and dishuiyan loess sections on the second terrace of the hanjiang river and the wolonggang thick natural loess section on the fifth terrace of the same river near the xuetangliangzi site we dated dishuiyan and houfang loess sections by optically stimulated luminescence osl and thermally transferred osl tt osl methods respectively dating results showed that the loess paleosol deposited on the second hanjiang river terrace as l1 s1 l2 and s2 in sequence we dated the wolonggang loess section by high resolution paleomagnetostratigraphic analyses the jaramillo subchron was found at this section correlating with the central loess plateau we recognized the continuous loess paleosol sequence from l9 to l15 investigations showed that loess was continuously deposited on the terraces of the hanjiang river at yunxian basin since at least 1200 ka

holocene paleofloods related to climatic events in the upper reaches of the hanjiang river valley middle yangtze river basin china abstract holocene slackwater deposits along the river channels were used to study the magnitude and frequency of the paleofloods that occurred prior to gaged and historical data sets all over the world paleoflood hydrological investigations were carried out in the upper reaches of the hanjiang river china four bedsets of paleoflood slackwater deposits were found interbedded in the holocene loess soil sequence within the cliff riverbanks they were studied by field observations and laboratory analysis including magnetic susceptibility particle size distribution and optically stimulated luminescence osl dating these provide a complete catalog of holocene flood events at a watershed scale that is very important in understanding the regional hydrological response to monsoonal climatic change four episodes of holocene overbank flooding have been recorded over the basin these hydroclimatic events were dated to 8500 8400 4200 4000 3200 2800 and 1800 1700 ybp by using the osl method in combination with pedostratigraphic correlations with the previously studied holocene pedostratigraphy in the hanjiang river basin the peak discharges of these flood episodes vary in a range from 26 610 to 47 900 m 3 s 1 as estimated by using the slope area method of streamflow measurement these flood events are therefore considered a regional expression of known climatic events and demonstrate holocene climatic instability the study provides a solid reference that magnitudes and recurrence frequencies of floods are highly sensitive to climate change in the monsoonal zone in other parts of the world

distribution and origin of igneous rocks from the landward slopes of the mariana trench implications for its structure and evolution the landward slope of the mariana trench is composed largely of igneous rocks serpentinites and serpentinized ultramafic rocks occur at nearly all structural levels on the slope from depths of 8000 to 1200 m seamountlike features on the trench slope break are the surface expression of serpentinite diapirs cumulate and massive gabbros are found several varieties of volcanic rocks are common including boninites altered and metamorphosed basalts andesites and dacites the chemical characteristics of the volcanic rocks indicate that nearly all are products of island arc volcanism together with the gabbros these volcanic rocks represent what is probably a late eocene arc complex these rocks were probably the first volcanic products to result from the subduction of the pacific plate beneath the phillippine sea plate their exposure on the trench slope today implies a significant amount of tectonic erosion of the landward slope since eocene time most of this removal of material appears to have occurred during the early stages of subduction there are isolated occurrences on the landward slope of rock assemblages including alkalic basalts chert hyaloclastites upper cretaceous siliceous sediments and shallow water limestones these assemblages are very similar to rocks dredged from seamounts on the offshore flankmore of the trench and their presence on the landward slope suggests that since the cessation of vigorous tectonic erosion there has been episodic accretion of seamount fragments to the landward slope less

high resolution multi proxy evidence for millennial and centennial scale climate oscillations during the last deglaciation in jeju island south korea abstract millennial and centennial scale climate and vegetation changes during the last deglaciation from hanon maar paleolake on jeju island south korea were reconstructed by high resolution multi proxy data pollen anhysteretic remanent magnetization arm total organic carbon toc total nitrogen tn carbon nitrogen c n ratio carbon and nitrogen isotope compositions 15 n and 13 c major element geochemistry and sediment grain size the resolution of our multi proxy data was sufficiently high to enable the detection of millennial and even centennial scale climate change in the study area during the last deglacial transition we found centennial scale cold reversals between 14 650 and 12 900 cal yr bp possibly corresponding to the bolling allerod ba oscillations hanon pollen data implied that climate amelioration around 11 900 cal yr bp terminated the younger dryas yd in the study area and that a cold event around 11 300 cal yr bp probably correlated with the pre boreal oscillation pbo cooling event our results indicate that rising summer insolation and northward expanding low latitudinal warm currents exerted a strong influence on climatological teleconnection via westerlies between the north atlantic and the east asian region during the last deglaciation presumably causing a decoupling between temperature and east asian summer monsoon easm precipitation during the last deglaciation

paleomagnetism geochronology and possible tectonic rotation of the middle miocene barstow formation mojave desert southern california the barstow formation of the central mojave desert in the mud hills consists of 965 m of epiclastic and volcanic sediments deposited in an extensional rift this widespread unit is of importance because its mammalian faunas characterize the barstovian land mammal age previous isotopic ages on interbedded tuffs have been used to calibrate middle miocene time and it was deposited in a tectonically active region volcanic ash samples were collected from the barstow formation for isotopic dating using conventional 40 k 40 ar and 40 ar 39 ar single crystal laser fusion methods multiple analyses on minerals from 5 superposed tuffs yielded the following mean 40 k 40 ar ages rak tuff at 16 3 0 3 m y oreodont tuff at 15 9 0 2 m y dated tuff at 14 8 0 2 m y hemicyon tuff at 14 0 0 1 m y and lapilli tuff at 13 4 0 2 m y similar mean ages were also obtained on the following tuffs using single crystal 40 ar 39 ar laser fusion methods oreodont tuff at 15 9 0 06 m y dated tuff at 14 8 0 06 m y and hemicyon tuff at 14 0 0 09 m y in order to develop a local magnetostratigraphy 272 paleomagnetic sites were collected from 7 important sections within the mud hills saturation isothermal remanence experiments suggested the presence of either hematite or magnetite as carriers of remanence after either stepwise alternating field or thermal demagnetization characteristic directions were usually isolated between 30 and 50 mt or 300 and 500 c positive reversal and fold tests indicate a stable remanence acquired prior to folding there are 21 magnetic polarity zones interpreted from the continuous part of the barstow formation in the study area by using the 5 isotopic ages determined from interbedded tuffs the local composite polarity pattern is correlated to the top of chron c5d through the bottom of c5ab on the magnetic polarity time scale or an age range from 17 6 to 13 4 m y the boundary between hemingfordian and barstovian land mammal ages herein occurs 30 m below the oreodont tuff 15 8 0 2 m y within c5b and is taken at about 16 0 m y ago the barstow formational mean declination is 347 1 inc 47 5 95 6 51 d 7 97 suggesting negligible or possibly slight counterclockwise rotation r 4 1 r 10 5 for this part of the mojave block during the past 18 m y a 40 ar 39 ar mean age of 19 3 0 02 m y for the red tuff which is near the local base of the barstow formation and unconformably underlying our composite section constrains a minimum age for the beginning of local basin filling with principally epiclastic sediments

cyclic variations of uranium concentrations and oxygen isotopes in tufa from the middle miocene barstow formation mojave desert california uranium concentrations of 42 to 169 ppm in fibrous calcite from spring deposited tufa in the middle miocene barstow formation california are among the highest reported for calcite fission track maps of multiple bands of uniformly dull luminescent fibrous calcite show that the concentration of u increases in the outward growth direction of the calcite of each individual band homogeneous dull luminescence in the fibrous calcite indicates no change in redox conditions of the fluid from which the calcite was precipitated it is proposed that the cyclic pattern of increase in u concentration reflects a cyclical change in the u ca ratio in the fluid episodic mixing between ca rich spring water with a low u ca ratio and ca poor saline alkaline lake water with a high u ca ratio could produce the episodes of formation of fibrous calcite with increasing u concentrations the spring water supplies the ca for calcite precipitation and the u concentrations increase with the decreasing fraction of spring water and increasing fraction of lake water these cycles reflect a variable recharge of groundwater into the lake by springs the large variation in u concentrations suggests mixing of 0 to 45 spring water with the lake while the narrow range in 18 o of 6 37 to 6 87 limits the variation of the proportions of spring and lake water to 5

pedostratigraphy of chinese loess deposits and climatic cycles in the last 2 5 myr summary the pedostratigraphy and magnetostratigraphy of several sections in the loess plateau of north central china have been investigated and correlated the most complete and distinct loess paleosol sequence occurs in the baoji section of the southern part of the plateau thirty seven pedostratigraphic units are identifiable in the baoji section and correlated with those in other parts of the plateau the sequence represents thirty seven major cold to warm climatic cycles in the last 2 5 myr at about the time of the matuyama gauss magnetic reversal an abrupt climatic event occurred in north china represented by the shift of the well weathered red clay formation below the m g boundary to the alternating loess and paleosol units above marking the beginning of a new epoch in the course of climatic evolution in addition there are two other major shifts of dominant periods of climatic cycles recorded in the loess paleosol sequences one occurring at about 1 5 myr and another at about 0 8 myr the pedostratigraphy of loess deposits in north central china provides an independent measure of the world wide climatic fluctuations and is now the most complete and reliable record of the major climatic cycles in the last 2 5 myr

reconstructing the palaeoflood events from slackwater deposits in the upper reaches of hanjiang river china abstract through investigation in the upper reaches of hanjiang river china an aeolian loess soil profile with four palaeoflood slackwater deposit swd interbeds was found on the cliffed riverbanks in yunxian county reach of hubei province based on field observation and laboratory analysis including magnetic susceptibility and particle size distribution the four palaeoflood swds were differentiated from aeolian loess and soil by sedimentary criteria and analytical results and recorded four episodes of palaeoflood events in the upper reaches of hanjiang river by using stratigraphic correlation and osl dating the four palaeofloods were dated to 12 600 12 400 a b p 11 600 11 400 a b p 5500 5000 a b p and 1000 900 a b p respectively according to the calculated maximum palaeoflood stage the maximum peak discharges of the palaeofloods events were reconstructed by using the hec ras one dimensional model the same hydrological method was used to calculate the peak discharge of the 2010 flood in the same reach the error between the calculated and gauged discharges was 4 9 showing that the reconstructed four palaeoflood discharges were reliable the flood peak discharge frequency relationship at 10 000 year timescale was established by a combination of the gauged flood historical flood and palaeoflood hydrological data in the upper reaches of the hanjiang river assessing reliability of peak discharge data in flood design for the water conservancy construction and flood mitigation

caribbean chronostratigraphy refined with u pb dating of a miocene coral an exceptionally well preserved aragonitic coral of the extinct species goniopora hilli was collected from late cenozoic sedimentary deposits in the dominican republic and dated using u pb techniques nine coralline subsamples yielded a 238 u 206 pb 207 pb 206 pb three dimensional 3 d inverse linear concordia age of 5 52 0 15 2 ma which when coupled with 87 sr 86 sr ratios obtained from the same coral allows for tighter constraints on temporal variability of marine species diversity prior to closure of the central american seaway the recognition that pre quaternary aragonitic corals can be suitable for u pb dating creates new possibilities for refining the chronologies of late cenozoic marine sedimentary sequences

concurrent u pb age and seawater 87sr 86sr value of a marine cement the purpose of this contribution is to show that it is possible to obtain accurate depositional u pb ages and original marine 87sr 86sr values from the same sample of marine cement altered marine aragonite cements from algal mounds of the late carboniferous bursum stage laborcita formation yield a u pb age of 300 2 3 8 ma consistent with the existing chronostratigraphic framework we use fluid rock interaction models to extrapolate to original seawater 87sr 86sr values based on sr isotope and trace element analyses of multiple petrographically identified components that should represent mixes of primary and diagenetic fluids such modeling provides a range of 0 70807 0 70820 for the 87sr 86sr value of the marine end member these data combined with a 87sr 86sr value of 0 70849 0 00001 for unaltered aragonite from algal plates and bivalves in the underlying holder formation show a decreasing trend in 87sr 86sr toward the end of the carboniferous whereas the range in 87sr 86sr values from the laborcita formation is consistent with existing sr curves the 87sr 86sr values of the aragonite are appreciably higher than these curves at least 0 0001 the aragonite from the holder formation has greater than 6000 ppm sr and thus these components should reflect the original marine value data from marine cements and biogenic aragonite from other sections are necessary to evaluate whether the 87sr 86sr values from the sacramento mountains truly record the global value

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

u pb systematics and alteration trends of pennsylvanian aged aragonite and calcite abstract carbonate allochems from the mid pennsylvanian buckhorn fauna of the boggy formation oklahoma usa consist of primary aragonite preserved in nautiloids and of secondary low mg calcite present in crinoids and corals unaltered nautiloids contain 11 38 ppb u and 23 422 ppb pb and have low 238 u 204 pb values from 4 1 14 8 they give a 238u 206pb isochron age of 311 48 ma 2 which is in agreement with the assigned stratigraphic age mid desmoinsian 305 ma of the boggy formation sediments their initial lead isotope ratios are 206 pb 204 pb 19 11 0 08 207 pb 204 pb 15 70 0 04 and 208 pb 204 pb 38 7 and reflect an upper crustal source for pb in mid pennsylvanian seawater these values are similar to those of coals of this age the contents of both u and pb in the buckhorn nautiloids are significantly higher than those found in the modern nautilus nautilus pompilius these enrichments are attributed to bitumen which was added to the carbonates during diagenesis the diagenetic transformation of aragonite to low mg calcite in the buckhorn nautiloids was apparently associated with a net loss of pb thereby increasing their values the secondary carbonates of crinoids contain 265 352 ppb u 136 262 ppb pb and their values range from 68 111 consequently their present day uranogenic lead isotopic ratios are higher than those of the buckhorn nautiloids the u pb data for some diagenetic low mg components indicate an age of 280 ma suggesting an early timing for the post depositional alteration process the apparent initial lead isotope ratios of crinoids are variable and some are significantly higher than the coexisting aragonite 206 pb 204 pb 20 50 207 pb 204 pb 15 73 this very radiogenic signature is similar to those of mississippi valley type ore deposits and both types may share a similar genesis

grain size magnetic susceptibility and geochemical characteristics of the loess in the chaohu lake basin implications for the origin palaeoclimatic change and provenance abstract rare studies on the aeolian deposit located in north bank of the yantgze river are documented recently it is found in the field investigations and in bore sections that the loess in the chaohu lake basin has the largest thickness of over 40 m in this study the probability cumulative curves frequency distribution the grain size distributions and the discriminant function of the grain size suggest that the loess in the chaohu lake basin is of eolian origin the magnetic susceptibility curves of the loess in the basin coincide perfectly with those of the loess in the northern china and the marine isotope stages mis and show that paleoclimatic cycles and sub cycles were documented since l3 during middle late pleistocene in the basin the ms curve of paleosol s1 paleosol s2 and loess l3 in the basin coincide perfectly with mis5 mis 7 and mis 8 respectively the good correspondence indicates that the loess in the basin has given a sensitive response to the globe paleoclimatic change since l3 on the other hand the climate changes in some stages recorded by the loess has regional characteristics obviously which might be the result of the dual effect of globe climate changes and east asia monsoon climate changes the result of geochemical characteristics suggests that the loess in the basin has undergone moderate to strong chemical weathering most elements are mobilized during chemical weathering na and ca of the loess are markedly lost and the removal of k is also evident and chemical weathering doesn t evidently turn into the si removal stage the chemical weathering of the loess is more intensive than that of the loess deposits in northwestern china and the upper reaches of the yantgze river the intensive chemical weathering has been documented by the loess might be related to strong monsoon climate in chaohu lake basin the provenance of the loess also differs from that in northern china and is discussed firstly with the lithofacies palaeogeography the well developed alluvial lacustrine deposits in the huaihe floodplain seem to be the major source materials of the loess

subduction erosion crustal structure and an evolutionary model of the northern yap subduction zone new observations from the latest geophysical survey the yap subduction zone is a distinctive erosive margin with an extremely slow convergence rate the high relief of the subducting plate generated by horst and graben structures and seamounts leads to attenuation of the crust in this study we present the latest geophysical data collected by the chinese research vessel kexue to investigate subduction erosion at the yap subduction zone and develop subduction models for yap subduction zone structures we show an anomalous distance between the yap trench and the adjacent volcanic arc the steep slope of the trench arcward a frontal prism and rare sediment in the trench all typical features of erosive margins we propose that the high relief subducting plate has led to erosion of the overlying plate and that different subduction processes controlled locally by the topography of the subducting plate have modified the yap subduction zone numerous normal faults increase the relief of the seafloor entering the trench and an anomalously large slope angle along the trench reflects uplift of the fore arc high via seamount subduction in addition the thin crust of the subducted horst and graben structures along with the normal faults might have eroded the fore arc crust and subsequently eroded the yap arc crust during subduction these subduction erosional processes at the yap trench provide one of the best cases of an erosive margin in the world particularly for a subduction zone with an extremely slow convergence rate

post 8 ma reconstruction of papua new guinea and solomon islands microplate tectonics in a convergent plate boundary setting papua new guinea and the solomon islands are located in a complex tectonic setting between the converging ontong java plateau on the pacific plate and the australian continent here we present a late neogene to quaternary plate tectonic reconstruction for this region the reconstruction was performed using gplates software and is based on data derived from multiple geological datasets including seafloor magnetic isochrons 3d models of subducted slabs paleomagnetic data deformation patterns and the spatio temporal distribution of arc magmatism the reconstruction shows that since ca 6 ma the crustal elements that comprise papua new guinea and the solomon islands began interacting in advance of the impending collision between the ontong java plateau and australian continent leading to the inception of regional microplate tectonics and escalation in tectonic complexity the bismarck sea initially formed as a back arc basin behind the new britain arc but was later modified during arc continent collision following collision the west bismarck sea developed into a transpressional zone associated with subduction of the caroline plate and north bismarck microplate at the new guinea trench farther east seafloor spreading occurred in response to the clockwise rotation of the south bismarck microplate relative to the australian plate the solomon sea plate was subjected to anticlockwise rotation relative to papua new guinea primarily due to the west dipping subduction at the new britain trench which resulted in initiation of subduction at the trobriand trough and extension in the woodlark basin from ca 5 ma crustal shortening in the upper plate which now forms the solomon islands resulted from the resistance of the relatively hot and buoyant woodlark basin lithosphere to subduction at the san cristobal our reconstruction shows that tectonism at convergent plate boundaries could involve an intricate relationship between microplate rotations seafloor spreading and subduction segmentation over timescales considerably 10 ma by unraveling the tectonic evolution of this complex region we provide insights into the development of microplate tectonics at convergent margins in general and the possible diagnostic geological records that might be preserved in ancient orogenic systems

asynchronous holocene optimum of the east asian monsoon abstract the spatial and temporal distribution of summer monsoon precipitation or effective moisture during the holocene has been reconstructed on the basis of geological data including lake levels pollen profiles and loess paleosol records in addition the summer july precipitation increment effective precipitation and monsoon strength index have been obtained from numerical modeling experiments both geological data and numerical modeling indicate that the holocene optimum as defined by peak east asian summer monsoon precipitation was asynchronous in central and eastern china reaching a maximum at different times in different regions e g ca 10 000 8000 yr ago in northeastern china 10 000 7000 yr ago in north central and northern east central china ca 7000 5000 yr ago in the middle and lower reaches of the yangtze river and ca 3000 yr ago in southern china in southwestern china the maximum appeared ca 11 000 yr ago but probably was related to the maximum landward extension of the indian summer monsoon the regional shift in the maximum precipitation belt from northwest to southeast over the past 10 000 yr is interpreted as a response to changing seasonality related to orbital forcing of the climate the southeastward shift of the east asian summer monsoon maximum is consistent with the progressive weakening of the summer monsoon as the summer solar radiation anomaly decreased progressively through the holocene and the east asian monsoon index declined while the early maximum in southwestern china matches the maximum of the indian monsoon index

seismic observations at the yap islands and the northern yap trench abstract we conducted two seismic surveys in the yap region to investigate tectonic activity in this area one was conducted in the northern yap trench for ten days using ocean bottom seismometers the other was conducted on the yap islands for eight months using a small array from these observations we detected many earthquakes beneath the yap region and found a characteristic pattern of seismicity many earthquakes occurred in the inner trench slope no seismicity was observed in the axial region of the trench and a few earthquakes occurred in the outer trench slope this pattern is similar to the typical pattern in active subduction zones this result indicates that the yap trench is still actively subducting we did not detect earthquakes deeper than 40 km during the observations

tectonics of the southern tip of the parece vela basin philippine sea plate we report new geophysical and petrological data collected at the southern tip of the parece vela basin in the philippine sea the parece vela basin which was formed as a backarc basin behind proto mariana arc trench system from late oligocene to middle miocene provides us a good opportunity to study the nature of successive backarc basin formations in the philippine sea and the relationship between are and backarc magmatisms regional bathymetric map derived from satellite altimetry shows that the southern tip of the basin now located just west of the yap arc trench system has unique morphological and tectonic features which include 1 the absence of spreading center or its trace 2 shallow average depth and 3 enigmatic curved structures our newly collected high resolution bathymetric data reveal that the spreading fabric similar to the central parece vela basin exists to the north of 9 degrees 20 n thus it appears that the present day yap arc and backarc region represent the western half of the seafloor that was produced by the early e w and the following ne sw spreading in the northern and central parece vela basin and that the eastern counterpart now lies west of the west mariana ridge unlike the northern parece vela basin there appears to be no evidence for a systematic propagation of spreading center in the southern part instead two rift segments one which extends from the central parece vela basin and the other which lies within the western remnant arc kyushu palau ridge overlap at the southern tip of the basin producing a complex seafloor that includes curvilinear deeps and deformed topographic highs c 2007 elsevier b v all rights reserved

direct dating of phanerozoic sediments by the 238 u 206 pb method direct radiometric age determination of phanerozoic carbonates has been a long standing problem in geochronology rb sr and k ar dating schemes commonly used to constrain the chronology of phanerozoic sediments have so far proved to be unsuccessful in dating these rocks because of their poor enrichment in radiogenic 87sr and 40ar and also because of analytical difficulties recent studies1 2 have demonstrated that large amounts of radiogenic pb exist in some carbonates and that they could be dated by the pb pb method however the precision of this method is severely limited to samples having very high uranium to lead ratios because by the beginning of the phanerozoic 590 myr ago 98 of 235u originally present in the earth had decayed to 207pb here we report the first isochron age of carbonates using the 238u 206pb method on corals this method which gives good accuracy even for low u concentrations has great potential for the direct dating of sedimentary sequences and should be valuable for refining the phanerozoic timescale

summer monsoon variations over the last 1 2 ma from the weathering of loess soil sequences in china the loess soil sequence in northern china contains a near continuous record of quaternary paleoclimate magnetic susceptibility and grain size have so far been the only proxies available to address the long term changes of the east asian paleomonsoon extending back to more than one million years in this study the ratio of cbd citrate bicarbonate dithionite extractable free fe2o3 fed a measure of iron liberated by chemical weathering versus the total fe2o3 available fet was measured on samples at 10 cm intervals taken from two loess sections deposited over the last 1 2 ma variations of this index are highly consistent with other pedological indicators but in addition provide a quantitative measurement of the degree of pedogenesis in the loess plateau since chemical weathering in the region mainly depends upon summer precipitation and temperature weathering intensity primarily reflects changes in the east asian summer monsoon the new proxy has been used to document a series of summer monsoon changes of global significance which are not necessarily recorded by magnetic susceptibility

construction of the mississippian pennsylvanian and permian seawater 87sr86sr curve abstract the estimated path of seawater 87 sr 86 sr during the mississippian pennsylvanian and permian is based on 228 analyses the samples are largely from the southern interior of the u s a where rocks of this age are widely exposed multiple analyses from single rock units are used to define the seawater ratio for different time periods the seawater 87 sr 86 sr declines from 0 70812 sw 95 mississippian to an estimated low in the early meramecian of near 0 70755 sw 152 the value rises to near 0 70812 sw 95 in latest mississippian the ratio rises to 0 70830 sw 77 in mid pennsylvanian and decreases to near 0 70809 sw 98 during virgilian time the earliest permian value is near 0 70793 sw 114 after rising to 0 70804 sw 103 in the early leonardian the seawater 87 sr 86 sr falls sharply to reach a low of 0 70672 sw 235 in ochoan time the end of the paleozoic is estimated to be near 0 70707 sw 200 based on samples from china analysis of the paleozoic curve shape shows an alternating dominance of oceanic and continental sr contributions the extended and precipitous decline in the 87 sr 86 sr during mid permian is unmatched during the phanerozoic the contrast of the paleozoic seawater sr curve shape to that in the mesozoic and cenozoic indicates a potentially fundamental change in the balance of oceanic and continental sr contributions at the end of the permian

using u pb ages of miocene tufa for correlation in a terrestrial succession barstow formation california sedimentary rocks and associated fossils are the direct record of past life and its environmental context few methods allow direct and precise dating of this important archive making it diffi cult to correlate climate biologic and tectonic events preserved in terrestrial records we sampled lacustrine tufa calcite from the middle member of the miocene barstow formation to further test the feasibility of uranium lead dating of terrestrial carbonates five samples yield u pb ages 2 of 14 81 0 39 ma 15 30 0 25 ma 15 39 0 15 ma 16 14 0 40 ma and 16 24 0 23 ma these precise ages are consistent with existing ages from k ar and 40 ar 39 ar dating of intercalated volcanic ashes our most precise u pb age on tufa has an uncertainty of 1 150 ka which is equivalent to uncertainties for k ar ages from the same time period our results indicate that u pb dating of carefully sampled and screened sedimentary carbonates provides much needed age constraints in purely terrestrial sequences and can be a powerful tool for correlation even in deposits with structural complexity and rapid facies changes

high resolution multi proxy climate records from chinese loess evidence for rapid climatic changes over the last 75 kyr the loess paleosol sequence in loess layer l1 malan loess is investigated in three regions of the western chinese loess plateau nine pedogenic layers are found in l1 and three proxy climate indices magnetic susceptibility ms grain size gs and caco3 content are measured at intervals of 0 2 kyr in order to recover records of monsoon climate variations time series of ms gs and caco3 content document the high resolution history of summer and winter monsoon climate variations over the last 75 kyr the records show a high degree of similarity to the warm interstadials recorded in ice cores from greenland and the antarctic and with heinrich events in the north atlantic during the last glacial cycle bond cycles are also recorded by the chinese loess records overall our results indicate that numerous rapid changes in climate occurred in china during the last glacial cycle but that the range of climate variations was smaller than recorded in greenland

chinese loess and the paleomonsoon abstract this paper presents a general review of the recent research advances of the east asian paleomonsoon based mainly on studies of the loess soil sequences in the chinese loess plateau in the last 2 6 million years the paleomonsoonal history may be divided into about 166 events on a time scale of the earth s orbital variations during the last glacial period millenial scale oscillations of the monsoon system were prominent which can be fairly well correlated with the dansgaard oeschger cycles recognized in the greenland ice cores the monsoonal rainfall belt has experienced a wide repeated advance retreat change during the glacial interglacial cycles of the pleistocene both temporal and spatial changes of the monsoon system in the quaternary could have been linked closely to global ice volume variations

baoji type pedostratigraphic section loess plateau north central china abstract the baoji section is judged to be the most complete pedostratigraphic section on the loess plateau of north central china it is located about 5 km north of the city of baoji and consists of 37 paleosols formed during more than the last 2 5 ma it is designated here as the type pedostratigraphic section with formally named geosols following the rules of the north american commission on stratigraphic nomenclature geochronological control is based largely on magnetostratigraphy with the brunhes matuyama and gauss epochs and jaramillo and olduvai events clearly recognized the baoji geosols can be correlated with equivalent pedostratigraphic units throughout the loess plateau by a combination of magnetostratigraphy and character position and the association of the pedostratigraphic units within the quaternary succession the variation of the geosols suggests climatic cycles of varying intensity and duration but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods

peridotites and volcanics from the yap arc system implications for tectonics of the southern philippine sea plate satellite altimetry reveals a continuous n20 e trending bathymetric feature extending from the yap trench through the north yap escarpment nye to the parece vela rift suggesting a genetic relationship we report the results of submersible observations and geochemical study of peridotites and volcanics from the yap trench and the north yap escarpment and use these to understand the genesis and evolution of the yap arc system metamorphosed rocks and gabbros of the parece vela basin origin predominate on the yap islands and for the upper part of the forearc although minor remnant arc volcanics of 25 ma age exist there are also arc volcanics of 11 7 ma age in the forearc whereas depleted arc type mantle peridotites are exposed along faults in the lower part of the forearc landward slope the results show that the yap arc north yap escarpment system might form as an incipient arc system at the propagating tip of the parece vela rift at 25 ma and that the overall yap arc forearc region is composed of several different units

petrology geochemistry and tectonic implications of volcanics dredged from the intersection of the yap and mariana trenches abstract rocks dredged from the forearc very close to the intersection of the yap and mariana trenches include a suite of highly depleted arc tholeiites and several samples of transitional to slightly alkaline basalt the tholeiites range from magnesian quartz tholeiites with 0 46 0 6 tio2 to andesites with up to 62 sio2 and 8 2 feo all show pronounced lree depletion and have very low contents of ba and sr they are postulated to have been produced by partial melting of upper mantle peridotite residual after morb extraction following influx of hydrous fluids from the subducted slab while these fluids were responsible for small enrichments in ba k rb and sr in melts generated lree were not involved in the metasomatism and the strong lree depletion probably reflects the unmodified depleted source peridotite the second lava suite includes slightly ne normative ti augite bearing basalts with convex upward ree patterns showing slight lree depletion la sm n 0 76 the chemical features of these basalts support affinities with basalts erupted during the earliest stages of backarc basin opening a k ar age on one sample 7 8 1 3m y is in good agreement with the initial opening of the mariana trough the tectonic significance of the dredged arc tholeiite suite is less obvious a k ar age of10 8 0 4 my on one andesite and the occurrence of similar lavas in dredges from at least 300 km along the length of the yap arc suggest that subduction was occurring beneath the yap arc in the late miocene after overthrusting of the yap greenschist allochthon and while calc alkaline arc magmatism was occurring further north on the west mariana ridge we suggest that the depleted arc tholeiites in dredge 1438 were generated by abnormally shallow melting of upper mantle beneath the yap forearc following subduction beneath this area of young hot sorol trough crust these arc tholeiites represent a magma type transitional between more typical arc tholeiites e g tongan and high mg andesites and boninites

u pb zircon and titanite systematics of the fish canyon tuff an assessment of high precision u pb geochronology and its application to young volcanic rocks a large data set of single and multi grain zircon and titanite analyses from a sample of the oligocene fish canyon tuff fct a voluminous ash flow from the san juan mountains of colorado and widely used 40ar 39ar geochronological standard has been used to evaluate the influence of various sources of analytical and geological uncertainty on the calculated age of this tuff by the isotope dilution u pb zircon method twenty three single zircon grains and seven small multi grain fractions of the fct yield an inverse variance weighted mean 206pb 238u date of 28 402 0 023 ma 2 mswd 0 93 and a slightly older weighted mean 207pb 235u date of 28 529 0 030 ma mswd 0 74 which are insensitive to common pb corrections initial 230th disequilibria calculated from a newly measured th u 2 2 for fct pumice shards indicate th deficiency for these zircons its correction brings the weighted mean 206pb 238u date to 28 478 0 024 mswd 0 97 minimizing the discordance of the fct zircon analyses these calculations culminate in concordia ages ludwig 1998 for the crystallization of the fct zircons of 28 476 0 029 ma mswd 1 50 without propagating decay constant errors or 28 498 0 035 ma mswd 1 03 with propagated decay constant errors these results are in close agreement with a previous single grain 206pb 238u zircon date of 28 41 0 05 ma for the fct oberli et al 1990 however they do not corroborate the discordia lower intercept date of 27 52 0 09 put forth by lanphere and baadsgard 2001 the 28 476 0 064 ma concordia age for fct zircons including systematic decay constant errors and uncertainty in pb u tracer calibration is substantially older than all published 40ar 39ar sanidine ages which range from 27 5 to 28 05 ma lanphere and baadsgaard 1997 renne et al 1998 a lengthy period 400 k y of zircon residence in the magma chamber before eruption is commonly called upon to explain the age discrepancy however fct titanite which may remain open to pb diffusive exchange until quenching upon eruption yield a minimum 230th disequilibrium corrected weighted mean 206pb 238u age of 28 395 0 049 ma 0 078 with tracer uncertainty weakening residence time arguments and supporting recent calls for re evaluation of the 40k decay constant and the accepted ages for commonly used 40ar 39ar mineral standards the fct zircon concordia age also provides an empirical constraint on the decay constants of the u isotopes indicating the relative accuracy of the currently accepted decay constants to within the original counting statistic errors of jaffey et al 1971

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

uranium series chronology and environmental applications of speleothems an increasing number of scientists recognize the value of speleothems1 as often extremely well preserved archives of information about past climate vegetation hydrology sea level nuclide migration water rock interaction landscape evolution tectonics and human action well constrained data are required to document past changes reconstruct past patterns and predict future responses of the earth system at a wide range of spatial and temporal scales speleothems are particularly useful in this regard because they can be found in many locations of the globe sampled at high resolution and reliably dated using high precision uranium series techniques speleothems are bodies of mineral material formed in caves as the result of chemical precipitation from groundwater flowing or dripping in a cave most speleothems are composed of calcite formed by slow degassing of co2 from supersaturated groundwater but aragonite and gypsum forms are also common particularly near cave entrances where evaporative effects are important a host of different speleothem types decorate the walls ceilings and floors of caves and their mineralogy and morphology is a function of fluid flow and chemistry of waters feeding a particular location as well as the ambient conditions temperature chemistry light in the air or water filled void subaerial forms include the familiar stalagmites stalactites draperies flowstones subaqueous forms include rimstone pools rafts mammillary calcite wall coatings and dog tooth spar for an extensive review of the types of speleothem that have been observed see hill and forti 1997 speleothems are used in a multitude of ways to explore past environmental conditions perhaps the most fundamental of which is their very presence or absence deposition of speleothems relies on sufficient water supply and soil co2 to enable dissolution and transport of reactants in the vadose zone to underlying caves in arid or glacial times conditions may not have been favorable for speleothem formation

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

asian summer monsoon instability during the past 60 000 years magnetic susceptibility and pedogenic evidence from the western chinese loess plateau abstract the 28 m high resolution shajinping loess section in lanzhou on the western chinese loess plateau records a 60 ka millennial summer monsoon variation the record shows that asian summer monsoons have rapid episodic pulse enhancements spanning only ca 1 2 ka in high frequency domain and having sub milankovitch cycles of progressive weakening in low frequency domain in the last glaciation soil formation seems to occur with a surprisingly fast response to these summer monsoon enhancements resulting in weakly or moderately developed paleosol sequences both the pattern and timing of the summer monsoon enhancements show that they can be correlated to most major warm dansgaard oeschger episodes and long term cooling bond cycles of the north atlantic climatic records indicating a possible teleconnection between tropic oceanic air masses and the north atlantic climatic system but differences exist for the transition of mis 2 3 and the holocene where extraordinarily heavy dust input events and fairly variable climatic fluctuations occur for the former and latter respectively a westerlies swing model is proposed to interpret this link

chronology of newly discovered paleolithic artifact assemblages in lantian shaanxi province central china abstract the homo erectus cranium mandible and hundreds of associated lithic artifacts found in lantian central china in the 1960s demonstrate that the area was important for hominin habitation during the early to middle pleistocene however the region which was not adequately researched until the early 2000s still poses several questions regarding hominin behavior and lithic technology development in this study three loess paleosol sequences the jijiawan ganyu and diaozhai sites from which in situ stone artifacts were recovered are investigated and dated by optically stimulated luminescence osl magnetostratigraphy and stratigraphic correlation the results demonstrate that the artifacts are located within paleosol layers s4 correlative with marine oxygen isotope stage mis 11 s3 mis 9 s2 mis 7 and s1 mis 5 and within loess layer l1 mis 2 4 the main stone knapping technique used was direct hard hammer percussion in addition the technological features of the stone tools found at these sites exhibit little variation indicating the presence of a long established stable technology in the lantian area our observations show that the ancient humans lived episodically on the terraces of the bahe river from the early pleistocene indicating a long history of hominin occupation of the region

source fingerprinting loess deposits in central asia using elemental geochemistry with bayesian and glue models abstract the provenance of loess deposits in central asia is largely unexplored accordingly the goals of this research were to test and compare the performance of two different models generalized likelihood uncertainty estimation glue and a bayesian model for quantifying the uncertainty in source apportionment estimated for 46 target loess samples collected in the ili basin in eastern central asia model performance was evaluated using goodness of fit gof mean absolute fit maf and virtual mixtures vm in combination with root mean square error rmse and mean absolute error mae our dataset comprised 132 surficial samples collected from three potential sources comprising river alluvium n 29 sand dunes n 35 and topsoils n 68 all samples were analysed for elemental geochemistry six geochemical properties co er y ga dy and pb were selected in a composite fingerprint which classified 83 of the samples from the three source categories correctly based on both models source contributions to the loess samples were in the following order topsoils river alluvium sand dunes based on the gof and maf tests both models were accurate in predicting measured tracer concentrations in the loess samples the bayesian model was slightly more accurate mean rmse 1 6 mean mae 1 8 than the glue mean rmse 5 0 mean mae 4 7 model in predicting known source contributions overall our results provide confirmation that application of source fingerprinting with elemental geochemistry and uncertainty modelling techniques is useful for identifying the provenance of loess sediments in arid and desert environments

origin and tectonic evolution of the caroline ridge and the sorol trough western tropical pacific from admittance and a tectonic modeling analysis abstract an independent caroline sea plate surrounded by prominent seismotectonic features is said to exist in the western tropical pacific the caroline sea plate is a transient feature existing only when the caroline philippine sea plate boundary is jumping to the caroline pacific boundary the origin and the tectonic evolution of the caroline ridge sorol trough region which forms the northern part of the caroline pacific plate boundary are examined using a standard admittance analysis a tectonic modeling study and additional direct gravity and magnetic analyses the observed admittance function is fitted well by shallow airy model in the 250 125 km 0 025 k 1 wavelength region whose average crustal thickness t c is 20 km and also by thin plate flexure model of isostasy within the diagnostic waveband of 250 80 km 0 025 k 1 with an effective elastic thickness t e of 5 7 km a simple interpretation of the observed admittance function is that the local airy model of isostasy is the main support mechanism in the study region for the longer wavelength more fundamental topography corresponding to that of the caroline ridge the caroline ridge is inferred to have formed in a near ridge tectonic setting on top of oceanic lithosphere which was young thin and weak at the time of emplacement the tectonic model study after an explanation for rifting along the mendana fracture zone in the nazca plate suggests that the sorol trough formed in the 17 7 ma interval splitting the caroline ridge into two longitudinal halves the rifting along the sorol trough which took place in the manner described in weissel and karner 1989 flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension j geophys res 94 13 919 13 950 necking of unbroken lithosphere post dated the formation of the caroline ridge by 10 15 m y during which time t e in the region increased to 5 10 km the rifting necking along the sorol trough represents a second loading event in the region the combined gravity effects of the rifting as well as the increase in the t e in the region from essentially nil to 5 10 km is reflected in the agreement between the observed admittance and the regional model with a 5 7 km t e in the wavelength region 80 km these results are consistent with the findings and the suggestions of the previous investigators in the region in that 1 the caroline ridge was constructed in the late oligocene by hot spot volcanism on top of oligocene seafloor of the caroline sea back arc basin 2 the eauripik rise genetically related to the caroline ridge formed on young and weak caroline basin lithosphere and is supported by airy manner crustal thickening and that 3 the lithosphere of the caroline ridge was young at the time of rifting necking along the sorol trough on the basis of the current results and the findings of the previous workers a tentative hypothetical rheological model for the crustal density structure of the caroline ridge sorol trough is also given the caroline sea plate appears to be bounded in the north and south by e w trending boundaries that deform diffusely while more normal narrow n s trending boundaries exhibiting more localized albeit slow deformation bound the plate in the east and west

geochemical constraints on provenance of the mid pleistocene red earth sediments in subtropical china abstract the source of mid pleistocene red earth sediments in the middle to lower reaches of the yangtze changjiang river was investigated based on their geochemical characteristics the xuancheng and jiujiang red earth sediments have similar major and trace element distribution patterns compared to the loess and paleosol deposits of the chinese loess plateau the upper continental crust ucc and the post archean australian average shale paas the sediments display notable depletion of cao mgo na2o and accumulation of tio2 al2o3 and fe2o3 t the trace element distribution patterns of the red earth sediments are also different from those of loess and the paas but are similar to those of the loess deposits except for lower values of mobile trace elements sr ba and ni and higher values of zr and y the red earth samples have uniform la th ratios of 2 8 compatible with those of the ucc loess and paleosol they also have similar chondrite normalized ree patterns characterized by enriched lree and relatively flat hree profiles and consistent negative eu anomalies similar to those of the ucc the loess and paleosol and the yangtze deposits these results suggest that the red earth sediments have been subject to considerable mixing prior to deposition and strong subsequent chemical weathering the sediments have very uniform 143nd 144nd and 147sm 144nd ratios this points to well mixed and multi recycled sediments the 143nd 144nd and 87sr 86sr values of the red earth sediments match well with those of the deposits in the middle to lower reaches of the yangtze river but are different from those of the loess and paleosols this suggests that the red earth sediments are derived from the drainage basins of the middle to lower yangtze river and might have experienced more intense chemical weathering relative to the yangtze deposits as reflected by their higher rb sr ratios intense depletion of mobile elements and accumulation of immobile elements as well as their well developed net like structure

provenance of loess deposits in the eastern qinling mountains central china and their implications for the paleoenvironment loess deposits in the eastern qinling mountains central china provide a detailed archive for reconstructing the paleoenvironment during early hominin occupation the study of the loess deposits also provides a unique opportunity to understand pleistocene atmospheric circulation in this transitional climatic zone however the provenance and formation of the loess deposits were not well understood until now in this paper we report on new geomorphologic investigations and depositional analyses of the loess deposits the results suggest that gobi deserts and drylands in northern and northwestern china were one of the dust sources these loess deposits show similar geochemical composition as the average upper crust ucc and may indicate that they experienced multiple sedimentary processes with the dust being well mixed before deposition however the higher sr 87 sr 86 ratios between 0 719650 and 0 721043 and extremely low nd 0 values between 11 98 and 18 97 which are different from the typical loess of the chinese loess plateau demonstrate that proximal clastic sediments that were apparently derived from the weathered qinling orogen bedrocks form the other important source for the loess deposits the chemical index of alteration cia al2o3 al2o3 cao na2o k2o x 100 and chemical proxy of alteration cpa 100 x al2o3 al2o3 na2o both in molar proportions show that the loess has experienced intense pedogenesis we conclude that the loess deposit has a mixed provenance the palaeoclimate in the eastern qinling mountains remained mild in the glacial periods due to the topography and unique geographic locations providing a suitable place for hominine occupation c 2012 elsevier ltd all rights reserved

cenozoic tectonic and depth age evolution of the indonesian gateway and associated back arc basins abstract we reconstruct the tectonic and paleo age and depth history of the indonesian seaway and associated southeast asian back arc basins to create a comprehensive paleogeographic framework for the region during the cenozoic we combine published tectonic models with revised models of the evolution of back arc basins based on available marine magnetic anomaly data and a recently published high resolution 1 min marine gravity anomaly grid which reveals many fine scale tectonic features previously not resolved reconstructions of the now subducted ceno tethys ocean floor are integrated with a revised absolute plate motion reference frame for the indian ocean based on moving hotspots all marginal seas north of australia formed in a back arc setting with the caroline and celebes seas opening north of a northward dipping subduction zone and the solomon sea south of a southward dipping subduction zone north of australia we suggest that the evolution of the two sub basins of the caroline sea from 36 to 25 ma followed different seafloor spreading patterns with the western sub basin being influenced by the manus hotspot our model suggests that collision between the melanesian and the caroline arcs led to cessation of oceanic crustal production in the caroline basin shortly before 25 ma combined geophysical and geological observations suggest that several major tectonic events occurred north of australia at around 45 ma roughly at the time when australia started moving northwards at fast rates similar to the present we suggest that this event is related to a relocation of the subduction zone nw of australia under the philippine sea plate due to a collision and subsequent accretion of old pacific plate material to the northward subducting australian plate our gridded oceanic paleo depth maps capture the history of marginal seas north of australia and the stepwise destruction of the ceno tethys ocean floor in the northern wharton basin and the west pacific providing boundary conditions for both paleoceanograpic and geodynamic models a regional analysis of basement depth anomalies reveals that median negative anomalous depth of several back arc basins is of the order of 650 800 m with a range of 300 1100 m accompanied by negative regional heatflow anomalies suggesting that mantle driven dynamic topography plays a larger role in modulating regional basement depth than previously suggested regional shear wave mantle tomography cross sections highlight that all marginal basins that exhibit large negative dynamic topography are underlain by massive buried slab material in the lower portion of the upper mantle and or below the transition zone supporting the notion that the observed paired negative dynamic topography and heatflow anomalies are due to basin formation above slab burial grounds

a three dimensional upb discordia plane to evaluate samples with common lead of unknown isotopic composition abstract the concordia method introduced by g w wetherill or in a modified fashion by f tera and g j wasserburg which can only be applied to the radiogenic leead fraction of u containing minerals can be extended to the measured total pb isotope ratios by a three dimensional discordia plane the three dimensional model does not require knowledge of the isotope ratios of the common pb used for correction if the assumption of only one type of common pb with an a priori unknown isotopic composition for the investigated samples is justified the theory is derived and formulae for calculation of best fit plane parameters as well as for their errors are derived with one synthetic set of data the applicability of the method is demonstrated

upb dating of a carbonate subaerial exposure event ten samples of the dolomite fraction from the lower ordovician oneota formation directly below the sauk tippecanoe unconformity in wisconsin define a 238u 206pb age of 504 14 ma mswd 190 206pb204pb 27 85 238u204pb 84 795 which is in agreement with the 500 4 ma depositional age based on conodont biostratigraphy the u pb age is interpreted as recording u enrichment of the carbonate during the early stages of subaerial exposure shortly following deposition variable initial pb isotope ratios prolonged interaction with meteoric fluids and later recrystallization associated with the influx of fluids that produced the permian upper mississippi valley pb zn sulfide deposits are likely factors in producing scatter about the isochron however the substantial u enrichment that can be associated with subaerial exposure of carbonates apparently allows precise u pb ages to be obtained despite some isotope mobility that occurs during later diagenetic events dolomite samples have 232th238u 0 3 much lower than that of average silicate crust consistent with the low solubility of th in low temperature systems and the high solubility of u in oxidized fluids 204pb206pb 208pb206pb variations in dolomite and oxide fractions from the oneota formation are linearly correlated 208pb206pb 38 955 204pb206pb 0 050 r2 0 9996 and are interpreted as indicating that the u and common pb were derived from penokean 1 8 ga crust exposed to the north i e the wisconsin dome or from its derivative sediments

origin of the palau and yap trench arc systems summary this paper attempts to account for several unique morphological and geological characteristics of the palau and yap trench arc systems in the northwestern pacific ocean using a new hydrodynamic model postulated herein the model is a simple mathematical treatment of a stationary viscous flow pattern in the asthenosphere that causes an appreciable amount of mechanical resistance against a vertically subducted rigid slab moving horizontally together with the flat plate a couple of thrusting forces comprising uplifting pressure generated in the frontal edge of the overriding lid and a new type of tectonic erosion along the surface of the vertical slab seem to reasonably explain apparently contradictory features of the palau and yap trench arcs long term gps measurements show that the palau and yap trench arcs are moving over the viscous asthenosphere toward the nww with velocities as great as 10 cm yr 1 stresses along the trench arcs predicted by the model would be sufficiently large to maintain their present morphology 1 water depths greater than 8000 m in spite of the extremely small plate convergence rates and relatively young ages of subducted plate 2 v shaped cross section of the axial bottom of these trenches implying little cover of slumped deposits in spite of very steep landward slopes 3 serpentinized peridotites gabbros basalts and limestones are exposed on the landward slope with neither sediment cover nor ferromanganese hydro oxide coatings 4 abnormally close proximity of the palau and yap islands to the trench axis 5 predominant distribution of barrier reefs in their western periphery apparently opposite to the easterly to northeasterly prevailing wind

abrupt climatic events recorded by the ili loess during the last glaciation in central asia evidence from grain size and minerals abstract the loess record of central asia provides an important archive of regional climate and environmental changes in contrast to the widely investigated loess deposits in the chinese loess plateau central asian loess paleosol sequences remain poorly understood here we present an aeolian loess section in the southern ili basin based on granularity and mineralogical analyses we reconstruct climatic changes during the last glaciation the results indicated that most of the abrupt climatic events such as dansgaard oeschger events and heinrich events were imprinted in this loess section although their amplitudes and ages showed some differences compared with the millennial oscillations recoded in loess and stalagmites in east asia the arid central asia responded more sensitively to the warming events than to the cooling events the shifting trajectory of westerlies across central asia played an important role in dust deposition during the stadials the north atlantic climatic signals may have been transmitted from central asia to the east asian monsoon regions via the westerlies

u pb calcite age of the late permian castile formation delaware basin a constraint on the age of the permian triassic boundary reply to a comment by ian metcalfe