a 33 ma lithostratigraphic record of tectonic and paleoceanographic evolution of the south china sea abstract the 853 m thick sediment sequence recovered at odp site 1148 provides an unprecedented record of tectonic and paleoceanographic evolution in the south china sea over the past 33 ma litho bio and chemo stratigraphic studies helped identify six periods of changes marking the major steps of the south china sea geohistory rapid deposition with sedimentation rates of 60 m ma or more characterized the early oligocene rifting several unconformities from the slumped unit between 457 and 495 mcd together erased about 3 ma late oligocene record providing solid evidence of tectonic transition from rifting slow spreading to rapid spreading in the south china sea slow sedimentation of 20 30 m ma signifies stable seafloor spreading in the early miocene dissolution may have affected the completeness of miocene pleistocene succession with short term hiatuses beyond current biostratigraphical resolution five major dissolution events d 1 to d 5 characterize the stepwise development of deep water masses in close association to post oligocene south china sea basin transformation the concurrence of local and global dissolution events in the miocene and pliocene suggests climatic forcing as the main mechanism causing deep water circulation changes concomitantly in world oceans and in marginal seas a return of high sedimentation rate of 60 m ma to the late pliocene and pleistocene south china sea was caused by intensified down slope transport due to frequent sea level fluctuations and exposure of a large shelf area during sea level low stands the six paleoceanographic stages respectively corresponding to rifting 33 28 5 ma changing spreading southward 28 5 23 ma stable spreading to end of spreading 23 15 ma post spreading balance 15 9 ma further modification and monsoon influence 9 5 ma and glacial prevalence 5 0 ma had transformed the south china sea from a series of deep grabens to a rapidly expanding open gulf and finally to a semi enclosed marginal sea in the past 33 ma

vegetation zones in nw africa during the brunhes chron reconstructed from marine palynological data abstract six east atlantic sites between 9 and 35 n allow the reconstruction of the latitudinal position and extension of the nw african vegetation zones during the last 0 7 ma the response of the vegetation to alternating glacial dry and interglacial humid climatic conditions has been recorded the vegetation response to a climatic amelioration starts with the northward expansion of the tropical rain forest followed by the northward shift of the saharan sahelian boundary and ends with the southward shift of the saharan mediterranean transitional steppes and the expansion of the mediterranean oak forests most sensitive is the reaction of the saharan sahelian boundary to climatic change large shifts of the saharan sahelian boundary seem to occur faster than small ones annual precipitation estimates for the latitude of dakar 15 n range from 100 to 1000 mm at 24 n yearly precipitation probably ranged from 0 to 150 mm smallest extent of the guinean tropical rain forest probably occurred during the arid conditions of isotope stages 2 and 6 reducing the carbon fixation of these forests to a minimum large extent of the guinean tropical rain forest occurred during most of the odd isotope stages more humid interglacials

the seawater osmium isotope record of south china sea implications on its history and evolution abstract the south china sea is the largest marginal basin in the world and is located in the confluence of three major tectonic plates pacific philippine sea indo australia eurasia its tectonic history and evolution throughout the cenozoic has been the subject of much discussion with regards to its mechanism timing and relationship to neighboring geological features we conducted the first re os isotope study of the south china sea cores recovered from ocean drilling odp ocean drilling program and iodp international ocean discovery program and from philippine oil exploration wells in order to investigate whether or not the basin s tectonic evolution will be reflected in the seawater os isotope record these cores represent the northern and southern conjugate margins of the south china sea and should have complementary records of the tectonic events in the basin we found three important negative anomalies in the south china sea s seawater os isotope record at 35 33 ma 26 23 ma and 13 6 ma which are temporally related to tectono magmatic events at the northern margin the record starts with the lowest 187os 188os i values of 0 37 and 0 32 for the oldest samples which then progresses to more radiogenic values for younger sediments the trend is consistent with the start of seafloor spreading at 33 ma that saw the peak in the flux of mantle derived material which later slowed down until the second peak between 26 and 23 ma however these unradiogenic values also mark the eocene oligocene transition and more likely implies south china sea connectivity to global ocean circulation since pre oligocene in both margins slight to marked decrease in 187os 188os i values deviate from the global trend and coincides with the ridge jump at 23 ma in the southern conjugate margin 187os 188os i show a general decreasing tendency opposite that of the northern margin and the global trend starting from mid to late miocene 13 6 ma mass balance modeling suggests that the two younger negative excursions may be accounted for by mantle and hydrothermal os inputs of 372 mol my at 23 ma and post 13 ma we suggest that the post 13 ma protracted decrease in 187os 188os i values for the southern margin reflects localized input of mantle derived lithogenic os from the luzon arc combined with post spreading magmatic intrusions and possibly gradual changes in paleoceanographic condition at the southern east sub basin

tectonics of short lived intra arc basins in the arc continent collision terrane of the coastal range eastern taiwan the coastal range in eastern taiwan was originated from an oblique collision between the luzon volcanic arc and asian continent since the late neogene in this collision terrane two intra arc basins the pliocene chingpu and pleistocene chengkung basins were developed on the eastern part of the neogene chimei and chengkuangao volcanic islands respectively prior to their accretion to eastern taiwan the tectonic evolution of these neogene volcanic islands and associated intra arc basins is reconstructed by stratigraphic and sedimentological analysis igneous rock geochemistry and comparison with observations in modern collision zone in the regions off southeastern taiwan in the coastal range the intra arc basin sequences are 1 5 10 km wide and 40 km long comparable in size to their modern analogues in the active collision zone the basin axis trends subparallel to the volcanic ridge in both basins deepwater flysch overlies shallow marine reef carbonates which in turn rest on volcanic basement indicating rapid arc collapse minimum rate of 1 km m y soon after the arc continent collision the arc collapse occurred earlier in the north chimei between 5 1 and 3 5 ma and later in the south chengkuangao between 2 9 and 1 8 ma in concert with a southward propagation of the oblique collision sedimentation ended about 2 ma and 1 ma in the chingpu and chengkung basins respectively coeval with rotation of the neogene volcanic islands this suggests that the rotation inverted the intra arc basin into thrusting uplifting and final emergence thus the duration of sedimentation for the intra arc basins spanned only about 0 8 3 1 m y on the basis of land geology offshore observations and a clay model experiment simulating oblique arc continent collision a model for the intra arc basin evolution in eastern taiwan is proposed during the collision strike slip faults would have been developed in the eastern part of volcanic islands to induce transtension movements thus forming pull apart intra arc basins on the collapsed volcanic island this mechanism is believed to be responsible for the formation of the pliocene chingpu and pleistocene chengkung basins as well as the present day offshore intra arc basins found on the lutao and lanhsu volcanic islands the two intra arc basins on lutao and lanhsu are predicted to be short lived as collision continues these two basins together with their underlying northern part of the luzon arc will be rotated thrust and uplifted in the next 1 m y and finally will become part of the southern extension of the coastal range

effect of the formation of the isthmus of panama on atlantic ocean thermohaline circulation the late cenozoic closure of the seaway between the north andsouth american continents is thought to have caused extensive changes in ocean circulation and northern hemisphere climate1 2 but the timing and consequences of the emergence of the isthmus of panama which closed the seaway remain controversial1 2 3 4 5 here we present stable isotope and carbonate sand fraction records from caribbean sediments which when compared to atlantic and pacific palaeoceanographic records indicate that the closure caused a marked reorganization of ocean circulation starting 4 6 million years ago shallowing of the seaway intensified the gulf stream and introduced warm and saline water masses to high northern latitudes these changes strengthened deep water formation in the labrador sea over the next million years as indicated by an increased deep water ventilation and carbonate preservation in the caribbean sea and favoured early pliocene warming of the northern hemisphere the evaporative cooling of surface waters during north atlantic deep water formation would have introduced moisture to the northern hemisphere although the pronounced intensification of northern hemisphere glaciation between 3 1 and 2 5 million years ago substantially lagged the full development of north atlantic deep water formation we propose that the increased atmospheric moisture content was a necessary precondition for ice sheet growth which was then triggered by the incremental changes in the earth s orbital obliquity

mapping of c4 plant input from north west africa into north east atlantic sediments abstract mapping the abundance of 13c in leaf wax components in surface sediments recovered from the seafloor off northwest africa 0 35 n reveals a clear pattern of 13c distribution indicating systematic changes in the proportions of terrestrial c3 and c4 plant input at 20 n latitude we find that isotopically enriched products characteristic of c4 plants account for more than 50 of the terrigenous inputs this signal extends westward beneath the path of the dust laden sahara air layer sal high c4 contributions apparently carried by january trade winds also extend far into the gulf of guinea similar distributions are obtained if summed pollen counts for the chenopodiaceae amaranthaceae and the poaceae are used as an independent c4 proxy we conclude that the specificity of the latitudinal distribution of vegetation in north west africa and the pathways of the wind systems trade winds and sal are responsible for the observed isotopic patterns observed in the surface sediments molecular isotopic maps on the marine sedimentary time horizons e g during the last glacial maximum are thus a robust tool for assessing the phytogeographic changes on the tropical and sub tropical continents which have important implications for the changes in climatic and atmospheric conditions

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

the tectonic history of drake passage and its possible impacts on global climate this study provides an integrated review of plate tectonic models of the evolution of the antarctica patagonia connection compared to geological records collected on land in patagonia and tierra del fuego and offshore along the northern edge of the scotia sea a temporal framework for the sedimentary and tectonic events of the north scotia ridge and tierra del fuego is constructed with additional data compiled from entire patagonia and the austral basin this review provides robust correlations of seaways and tectonic events along the scotia and south america plates and indicates that the opening of the drake passage was not steady state since ca 30 ma rather the regions forming the present day northern limit of this gateway experienced important paleogeographic changes from deep marine basins to shallow ridges and emerged regions during the late oligocene and early middle miocene time our compilation of geological data shows that emergence along the north scotia ridge and tierra del fuego was achieved at 23 22 ma and has been followed by elimination of the patagoniano sea in patagonia starting at 22 23 ma and achieved at 20 ma this transition towards more continental sedimentation in southern south america is correlated with more shallow marine conditions in the austral basin this succession of events had a strong influence on the general geometry of the drake passage corresponding to a constriction of its northern limit starting in the window 29 22 ma and achieved at 21 ma this period of active deformation in southern south america also corresponds to a period of the global climate having two anomalies well known from the isotopic records the late oligocene warming around 26 ma and the mid miocene climatic optimum which ended between 15 and 14 ma the possible effects of the post oligocene tectonic evolution of the drake passage region on general oceanic circulation are discussed causes for the synchronicity between tectonic events and these global warming events are examined

late quaternary palaeoenvironments in the lake barombi mbo west cameroon deduced from pollen and carbon isotopes of organic matter abstract a sediment core 23 5 m long was recovered from a water depth of ca 110 m in lake barombi mbo a maar crater of the cameroon volcanic chain this paper presents a carbon isotopic curve of organic matter linked to the main results of the pollen analysis interpretation of this carbon isotopic curve is simplified 1 because of the weak role played by the phytoplankton in the balance of the organic particle flux and 2 because of the presumed absence of diagenetic alteration of the isotopic composition the carbon isotopic curve exhibits an almost linear correlation with that of total grass pollen which form the main part of the c4 biomass the major fluctuations of isotopic and pollen curves allow four main phases to be distinguished from ca 25 000 to 20 000 yr b p 13c values of 25 to 30 pdb are related to a forest environment associated with a montane floral element from 20 000 to 13 000 yr b p the 13c values are between 23 and 28 and are linked to openings of landscape with a mosaic of forest and savanna and a fall of lake level with colonization of the shores by cyperaceae and other aquatic plants from 13 000 to 10 000 yr b p the forest extended again reaching a maximum density during the period from 9500 until 3000 yr b p and with an average 13c value of 32 a new dry phase at around 2500 2000 yr b p with temporary openings in the forest marked by a 13c excursion above 30 but during the last 2 millennia the forest developed again with 13c values of 32

origin of the rhythmic reddish brown and greenish gray sediments in the abyssal south china sea implications for oceanic circulation in the late miocene abstract during international ocean discovery program iodp expedition 368 a series of drillings were conducted in the northern south china sea scs at the abyssal drilling site 1502 hole a 3764 m below sea level successive core sections were recovered from 442 to 497 m below sea floor these cores were placed into the late miocene period and the most remarkable feature of these 50 m long cores were the consecutive occurrences of the rhythmic reddish brown and greenish gray sediments such color transitions during the late miocene period were not remarkable for the cores at the adjacent shallower iodp 368 sites 1501 and 1505 in this study we aimed to determine the origin of these cyclicity like color transitions at site 1502 in the abyssal scs we conducted experiments dealing with sediment color reflectance nannofossil key element content and clay minerals we inferred that the in situ formed amorphous hematite caused the coloration of the reddish sediments in which ferrum and manganese contents were high and carbonate was not poorly preserved we suggest that the occurrence of the cyclicity like color transitions could result from the extent of deep water ventilation in the abyssal scs such changes in deep water ventilation were possibly related to an orbital forced rearrangement of deep oceanic circulation in the pacific ocean

subsidence of the northern south china sea and formation of the bashi strait in the latest miocene paleoceanographic evidences from 9 myr high resolution benthic foraminiferal δ 18 o and δ 13 c records abstract we present astronomically tuned high time resolution 3 4 kyr benthic foraminiferal 18o and 13c records between 9 ma and 5 ma from ocean drilling program odp site 1143 in the southern south china sea scs we found that the late miocene ocean carbon shift lmocs which was linked with the late miocene early pliocene biogenic bloom also occurred in the northern and southern scs a marked deep water 13c gradient as much as 1 0 of the northern and southern scs was observed between 6 5 ma and 5 9 ma which was probably caused by the significant difference in paleoproductivity between the northern and southern scs the deep 13c gradient was likely produced by rapid tectonic subsidence in the northern scs at 6 0 ma and the final formation of the bashi strait at 6 5 ma a reversed benthic 13c gradient of the northern and southern scs was also observed between 1 2 ma and 0 35 ma which was probably caused by the consecutive closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma closures of the interarc water gates within the bashi strait at 3 0 ma and 1 2 ma further semi enclosed the scs basin and made the paleoproductivity the major factor influencing the deep water 13c leading to the reversed deep water 13c gradient of the northern and southern scs between 1 2 ma and 0 35 ma

pliocene pleistocene stable isotope and paleoceanographic changes in the northern south china sea abstract based on the stable isotopic analysis of planktonic and benthic foraminifers from ocean drilling program core 1148 of the northern south china sea scs pliocene pleistocene isotope stratigraphy and events have been reconstructed the benthic foraminiferal 18o record shows that the pacific intermediate water had a greater influence upon the scs or the pacific deep water above 2600 m was warmer before 3 2 ma than at present after that the benthic 18o conspicuously increased during the 3 2 2 5 ma period in correspondence to the formation of the northern hemisphere ice sheet whereas the planktonic 18o signal suggests a stepwise overall decrease of sea surface temperature during the 2 2 0 9 ma period compared to the equatorial pacific records the decrease in planktonic globigerinoides ruber 13c during the 3 2 2 2 ma period is particularly striking suggesting that fertility of surface water increased noticeably according to the modern 13c distribution of g ruber in the northern scs it is inferred that the east asian winter monsoon strengthened during this interval afterwards there were several conspicuous decreases of g ruber 13c at 1 7 1 3 0 9 0 45 and 0 15 ma bp that is about every 0 4 ma suggesting that the east asian winter monsoon became episodically stronger this is confirmed by changes in relative abundance of planktonic foraminifer species neogloboquadrina dutertrei a typical east asian winter monsoon proxy the deep water 13c of the scs is close to that of the pacific but lighter than that of the atlantic implying that the pattern of deep water originating mainly from the atlantic and through the pacific entering the scs existed at least since the early pliocene after 1 4 ma the benthic 13c signal decreased conspicuously but with a periodicity of 100 ka suggesting that the deep water ventilation of the scs was reduced probably corresponding to a decrease of the north atlantic deep water and or further isolation of the scs deep basin from the pacific during glaciations

glacial and interglacial wind regimes over the eastern subtropical atlantic and north west africa analysis of aeolo marine dust deposits in the subtropical eastern atlantic enables the strength of the major wind patterns during the late quaternary to be evaluated and gives an insight into the climate of north africa

paleoceanography of the mid pleistocene south china sea high frequency fluctuations in paleoenvironmental proxies from the south china sea including stable isotopes and abundance of planktonic foraminifers nannofossils radiolarians and palynomorphs reveal a dynamic local response to the stepwise development of the mid pleistocene climate transition mpt these proxies indicate a dramatic drop in sea surface temperature sst at about 900 ka the first largest sst decrease in the region during the quaternary estimated winter sst declined from 24 25 degrees c to 17 18 degrees c in the northern and from 26 27 degrees c to 23 24 degrees c in the southern south china sea subsequent changes in the thermocline depth and faunal floral turnovers imply a period of about 300 ka in the final stage of the mpt winter monsoons increased at similar to 900 ka and reached a maximum strength toward the end of the mpt when summer monsoons also strengthened in interglacials as a result thermal gradient between the northern and southern south china sea increased substantially with stronger winter monsoon influence in the north and warm and saline conditions in the south especially during glacial periods these n s paleoceanographic contrasts indicate an initial establishment of the modern styled semi enclosed south china sea about 900ka ago when passages in the south started to become completely exposed during glacial lowstands coupled with deep water cooling and ventilation uplift of the sill depth in the bashi strait to near the present 2400 m during this period caused sudden decline and extinction of pacific deep water benthic foraminifers in the isolated deep sea basin together with data from the oceanic western pacific these results further imply a considerable weakening of the western pacific warm pool during mis 23 22 and in subsequent glacial periods while the mpt may have invoked high latitude processes especially an increased ice volume tropical processes more likely have facilitated the restoration of heat and energy to the western pacific in each interglacial rebound planktonic delta c 13 maxima on eccentricity periocities leading major cooling events during the quaternary indicate the important role of global carbon reservoir changes due to low as well as high latitude processes in past climate change c 2008 elsevier ltd all rights reserved

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

marine geology in the arc continent collision zone off southeastern taiwan implications for late neogene evolution of the coastal range abstract marine geology in the region between taiwan and luzon is characterized by a convergent tectonics in the south and an oblique arc continent collision in the north in the collision zone six geologic provinces are recognized they are the manila trench the accretionary prism of the hengchun ridge the sutural basin of the southern longitudinal trough the subduction melange of the huatung ridge the forearc basins of the taitung and the north luzon troughs and the volcanic arc of the north luzon ridge the oceanic crust of the south china sea is subducting eastward beneath the philippine sea plate along the manila trench south of 20 n further to the north the trench has changed progressively its axis toward the west from the subduction melanges off southeastern taiwan at 3 ma to the hengchun peninsula of southern taiwan at 2 1 ma and then to the present day location off southwestern taiwan because of the continuing collision and the westward shifting of the manila trench sediments deposited in the region are passively incorporated into the accretionary prism and deformed to the hengchun ridge after the collision the southern longitudinal trough consisting of a 2 km thick of orogenic sediments represents a sutural basin superposed on the plate boundary between the accretionary prism of the hengchun ridge asian continent and the subduction melange of the huatung ridge philippine sea plate the huatung ridge is a bathymetric high connected to the southern coastal range and is characteristic of low negative free air gravity and magnetic anomalies the ridge contains deeply weathered sedimentary blocks with abraded deep water late pliocene foraminifera and identical clay mineral compositions as those in the onshore lichi melange this implies that at least a portion of the huatung ridge is composed of melange materials and represents a former subduction zone extending from the lichi melange of the southern coastal range the north luzon trough and the taitung trough are the constructed foreac basins with 2 km of orogenic sediments unconformably overlying the volcanic islands and the subduction melange the taitung trough is southward connected to the north luzon trough through a bathymetric passage which was formed by narrowing the north luzon trough as a consequence of clockwise rotation of the lutao volcanic island during the late pleistocene a detailed study of the four neogene tectonostratigraphic units in the coastal range shows that the overall history of the formation of the range can be related to the present day geologic provinces and the on going collision processes in the region off southeastern taiwan the range had evolved from a southward accretion of the shuilien loho remnant forearc basin and the chimei volcanic pair at 2 ma followed by the chengkung taiyuan remnant forearc basin and the chengkuangao volcanic island pair at 1 ma and the taitung trough and the lutao volcanic island pair presently in process by analogy the northern part of the north luzon trough and the lanhsu volcanic island will be accreted to the coastal range in the next million years the paired forearc basin volcanic island accretion model proposed in this study may thus have implications for mountain ranges that evolved from similar tectonics of oblique arc continent collision

environmental control of pollen grain distribution patterns in the gulf of guinea and offshore nw africa the areas of marine pollen deposition are related to the pollen source areas by aeolian and fluvial transport regimes whereas wind transport is much more important than river transport pollen distribution patterns ofpinus artemisia chenopodiaceae amaranthaceae and asteraceae tubuliflorae trace atmospheric transport by the northeast trades pollen transport by the african easterly jet is reflected in the pollen distribution patterns of chenopodiaceae amaranthaceae asteraceae tubuliflorae andmitracarpus grass pollen distribution registers the latitudinal extension of sahel savannas and dry open forests marine pollen distribution patterns of combretaceae melastomataceae alchornea andelaeis reflect the extension of wooded grasslands and transitional forests pollen from the guinean congolian zambezian forest and from the sudanian guinean vegetation zones mark the northernmost extension of the tropical rain forest rhizophora pollen in marine sediments traces the distribution of mangrove swamps only near the continent pollen ofrhizophora mitracarpus chenopodiaceae amaranthaceae and pollen from the sudanian and guinean vegetation zones are transported by the upwelling under current and the equatorial under current where those currents act as bottom currents the distribution of pollen in marine sediments reflecting the position of major climatic zones desert dry tropics humid tropics can be used in tracing climatic changes in the past

tectonic and paleoceanographic conditions during the formation of ferromanganese nodules from the northern south china sea based on the high resolution geochemistry mineralogy and isotopes abstract deep water ferromanganese fe mn nodules cumulate trace elements from the underlying sediment pore water and seawater during the concentric mineral layers growth process over millions of years they can record long term tectonic movements and paleoceanographic changes to systematically ascertain paleoceanographic evolution of the deep south china sea scs since the last 3 2 ma we comprehensively investigated microstructure mineralogy geochemical element concentrations as well as sr nd and pb isotopic compositions in the fe mn nodules nearby the dongsha islands in the northern scs results indicate that these deposits were formed in a continental marginal environment by a mixture of diagenetic and hydrogenetic processes overall the studied nodules can be divided into three stages with different microstructures and chemical compositions which indicate different formation environments stage 1a is the innermost and oldest layer with a porous mottled texture and has the lowest mn fe ratio cu ni and zn which implies comparatively high oxidization conditions in contrast the mn mineralogy of stage 2 shows conditions similar to those of buserite formed under less oxidative conditions between stage 1a and 2 stage 1b represents a mixture of stage 1a and 2 and has inhomogeneous growth structures based on the nd and sr isotopic composition of the detrital phases and pb isotopes three potential terrigenous source regions including south china luzon and taiwan that discharge into the northern scs from 3 2 ma to 1 06 ma after 1 06 ma the terrigenous fraction in the fe mn deposits on the northern slope of the scs is a two end members mixture of fluvial input from taiwan islands and eolian dusts from the chinese loess our study indicates that scs bottom water variation occurred at 3 2 ma 2 1 ma and 1 06 ma respectively which could be attributed to global cooling and the influence of luzon arc forearc uplift

molecular and isotopic biogeochemistry of the miocene clarkia formation hydrocarbons and alcohols the miocene lacustrine deposit at clarkia northern idaho u s a is well known for its rich and exceptionally well preserved higher plant leaf fossils in the present study the distributions abundance and isotopic compositions of aliphatic hydrocarbons and alcohols isolated from two sediment samples and from two associated fossils magnolia latahensis and platanus dissecta are investigated the general similarity of these characteristics in the sediments suggests a relatively uniform depositional environment and consistent terrestrial input the sediment hydrocarbons are comprised mainly of compounds derived from higher plants and bacteria whereas the alcohols reflect contributions from both higher plants and algae a notable feature of the higher plant derived terpenoid hydrocarbons is the prevalence of des a triterpenes largely in the absence of their pentacyclic precursors indicating the dominance of a ring degradation for these pentacyclic triterpenoids the des a triterpenes include several novel compounds namely 19 h and 19 h 28 nor des a lup 17 ene and des a oleana 9 13 18 diene the sediment samples contain high abundances of c24 c32 long chain alkanediols consisting of a series of diols 1 diols 1 15 diols and an unusual series of 1 3 diols both fossil leaves show clear differences in their compound distributions and concentrations from the associated sediments which suggests that they retain a composition distinct from the sediment groundmass the 13c values of c25 c33 n alkanes and c24 c32 n alcohols in sediments and fossils are consistent with an origin from terrestrial c3 higher plants algal lipids in the two sediments are represented by dinostanol 24 6 and 25 9 inherited from dinoflagellates and long chain 1 15 alkanediols 26 4 to 29 7 derived from microalgae the long chain 1 and 1 3 alkanediols are more enriched in 13c 21 8 to 26 4 suggesting an origin from sources other than higher plants probably aquatic photoautotrophic organisms the 13c depletion of some hopanoids 35 9 to 61 0 attests to contributions from methanotrophic bacteria and suggests an active methane cycle at the time of deposition

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

source areas and transport mechanisms for freshwater and brackish water diatoms deposited in pelagic sediments of the equatorial atlantic abstract distributions of freshwater and brackish water diatoms from dust samples and modern sediments of the equatorial atlantic demonstrate different transport mechanisms and source areas both melosira spp and stephanodiscus spp are transported via winds from the southern sahara and sahel in northern hemisphere winter the core top distribution of cyclotella striata delineates the extent of the low salinity plume formed by runoff from the zaire river into the extreme eastern atlantic the transport mechanism and source areas for melosira spp during arid phases have not changed appreciably in the last 130 000 yr there is no evidence for long distance transport of freshwater diatoms by the southeast trade winds this study confirms the validity of paleoclimatic research which inferred eolian transport of melosira spp in the winter dust plume from source regions north of the equator although fluviatile input of melosira valves into nearshore sediments cannot be ruled out

development of tectonostratigraphy in distal part of foreland basin in southwestern taiwan abstract in the young and active tectonic belt of southwestern taiwan reconstructed stratigraphy in the distal part of the foreland basin reveals at least two regional unconformities with the younger ones covering the areas farther from the mountain belt in contrast with the previously proposed monotonous basin development the temporal spatial distribution of the unconformities indicates the back and forth migration of the foreland basin margin three distinct episodes of rapid subsidence during the foreland basin development have also been identified the onset of the basin development can be well constrained by the initial rapid subsidence at 4 4 4 2 ma which happened only in the proximal part of the basin this was followed by two younger episodes of rapid subsidence events at 2 1 8 ma and 0 45 ma which were encountered initially in the areas progressively farther from the orogenic belt we propose a model of episodic tectonic evolution in the distal part of the foreland basin in southwestern taiwan during each episode of rapid subsidence uplifting that corresponds to the forebulge began with a concurrent rapid subsidence in the areas closer to the basin center and was followed by rapid subsidence and deposition of widespread strata onlapping toward the basin margin part of the widespread strata and its overlying deposits would be eroded in the beginning of the next episode when the forebulge shifted toward the orogenic belt in general rate of forebulge migrating away from the orogenic belt during the early stage was slower than that derived from a previously proposed kinematic model of a steady migration of the orogenic belt this might be due to a rifted and weaker lithosphere beneath the foreland basin once the foreland basin migrated onto the less stretched lithosphere the basin would expand rapidly into the craton

the 14c dates and 13c 12c ratios of soil organic matter as a means of studying the past vegetation in intertropical regions examples from colombia south america abstract the 14 c ages and 13 c 12 c values were obtained on soil organic matter of various soils sampled in the guasca valley adjacent to the high plain of the sabana de bogota in the colombian cordillera oriental a soil distribution is observed as a function of climatic and altitudinal changes in the lowest parts of the valley planosols are found from the bottom of the valley to 2700 2800 m at altitudes up to 2900 m brunizems and ferrisols occur above 3000 m andic soils are almost everywhere present in more humid mountain zones at present the landscape is widely open without any natural forest nevertheless it was proved by pollen analytical data that at altitudes up to 3000 m the andean forest replaced a paramo formation 13 000 yr ago to conciliate the facts with the known evolution of the vegetal population a first hypothesis consists of admitting that open landscapes were due to a recent anthropogenic destruction of the forest the forest degradation hypothesis was tested by determination of the 13 c 12 c ratio because the trees have a 13 c of 25 to 28 influence of plants with c 3 photosynthesis pathway whereas herbs characteristic of open vegetation such as tropical grasses may have a 13 c of 23 to 16 due to a c 4 photosynthetic cycle the organic matter dated at 13 000 30 000 yr has 13 c close to 25 in the andic soil zone this indicates that at elevations of around 3000 m a cold paramo vegetation was probable for organic matter dated at 12 000 6000 yr 13 c shows a variation from 23 to 21 that does not indicate forest conditions it is uncertain that a forest stage occurred in the past for the planosols brunizem and ferrisol organic matter dated at 13 000 20 000 yr has a 13 c 23 compatible with the paramo vegetational phase occurring at that time for organic matter dated at 9500 yr and less 13 c varies from 20 to 17 these values do not confirm the evidence of forest conditions but rather the existence of open vegetation typified by a mixture of c 3 plants shrubs and rare trees and tropical graminaea thus the 13 c values prove that the valley has known drier and warmer influences that prevented the forest from developing during the holocene to explain the origin of the open landscapes of the valley the hypothesis of recent human deforestation must be discarded moreover the valley appears as a persistent dry enclave in the oriental cordillera

on the wave current interaction during the passage of a tropical cyclone in the bay of bengal abstract the impact of waves on currents and vice versa is an integral part of the complex coastal dynamics the wave current interaction is prominent in the coastal shelf slope regions particularly during the passage of a tropical cyclone in the present study we describe the importance of wave current interaction in the northern bay of bengal bob using a fully coupled three dimensional coupled ocean atmosphere wave sediment transport coawst modelling system the coawst model is applied to the case of a very severe cyclonic storm phailin that passed over the bob basin during 10 15 october 2013 to represent the interaction between waves and currents we utilized the newly implemented vortex force method in the coupled model numerical experiments with different coupling configuration within the coawst modelling framework were performed to separately identify the effects of wind tide and wave current interaction process a comparison of model results with the buoy observations of water elevations currents and wave measurements shows a good agreement between model and observed data various terms of the momentum balance were calculated from the model simulated and diagnosed parameters a comparison of the horizontal momentum balance term identifies the wave breaking induced acceleration as one of the leading terms along the storm affected the east coast of india further an increase in the apparent bed roughness caused by waves found to affect the values and distribution of the bottom shear stress the pressure gradient term showed significant changes to the pure tidal case the study highlights that the changes in the momentum balance caused by waves includes contributions from the variations in the water level and currents the most relevant effect on the coastal hydrodynamics was in the form of a wave induced setup near the location of landfall of the cyclone

review and revision of cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale planktonic foraminifera are widely utilized for the biostratigraphy of cretaceous and cenozoic marine sediments and are a fundamental component of cenozoic chronostratigraphy the recent enhancements in deep sea drilling recovery multiple coring and high resolution sampling both offshore and onshore has improved the planktonic foraminiferal calibrations to magnetostratigraphy and or modified species ranges this accumulated new information has allowed many of the planktonic foraminiferal bioevents of the cenozoic to be revised and the planktonic foraminiferal calibrations to be reassessed we incorporate these developments and amendments into the existing biostratigraphic zonal scheme in this paper we present an amended low latitude tropical and subtropical cenozoic planktonic foraminiferal zonation we compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the cenozoic and have incorporated these recalibrations into a revised cenozoic planktonic foraminiferal biochronology we review and synthesize these calibrations to both the geomagnetic polarity time scale gpts of the cenozoic and astronomical time scale ats of the neogene and late paleogene on the whole these recalibrations are consistent with the previous work however in some cases they have led to major adjustments to the duration of biochrons recalibrations of the early middle eocene first appearance datums of globigerinatheka kugleri hantkenina singanoae guembelitrioides nuttalli and turborotalia frontosa have resulted in large changes in the durations of biochrons e7 e8 and e9 we have introduced upper oligocene zone o7 utilizing the biostratigraphic utility of paragloborotalia pseudokugleri for the neogene period major revisions are applied to the fohsellid lineage of the middle miocene and we have modified the criteria for recognition of zones m7 m8 and m9 with additional adjustments regarding the globigerinatella lineage to zones m2 and m3 the revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress of the cenozoic time scale

isotope evidence for pleistocene climatic changes in kashmir india stable carbon isotope ratios of organic carbon from palaeosols in loess and oxygen isotope ratios of pedogenic and lacustrine carbonates reveal significant pleistocene climatic changes in the kashmir basin the extreme 13c values of 16 and 25 reported here indicate a shift from arid to sub humid conditions the 18o values of pedogenic carbonates is 2 higher than that of the underlying lacustrine carbonates suggesting that they were deposited in different climatic conditions

geodynamic processes of taiwan arc continent collision and comparison with analogs in timor papua new guinea urals and corsica abstract the taiwan arc continent collision involves four geodynamic processes intra oceanic subduction initial arc continent collision advanced arc continent collision and arc collapse subduction these processes now occur simultaneously in 19 24 30 n but have operated sequentially southward since the late miocene although the geological and geophysical features appear to change progressively from north to south across the island they are distinct within individual tectonic regimes using the present scenario as a basis for comparison it is suggested that timor is at the initial arc continent collision stage while papua new guinea and urals proceeded to the advanced arc continent collision stage however corsica represents an even more advanced stage than in taiwan where a previously accreted arc has collapsed and been totally removed

transition from oblique subduction to collision in the northern luzon arc taiwan region constraints from bathymetry and seismic observations we systematically study the detailed bathymetry seismicity and source parameters of large and moderate sized earthquakes that occurred in the northern luzon arc taiwan region between 1964 and 1996 the purpose is to characterize the transition from oblique subduction to regional collision in terms of the distribution of morphological features the characteristics of seismogenic structures and the corresponding state of strain to the south of 21 5 n the existence of a subduction zone is clearly shown by both bathymetry and seismicity the subducted eurasia slab reaches a maximum depth of 200 km and the depth decreases sharply as it approaches taiwan focal mechanisms indicate that the subducted slab is in downdip extension for depths 150 km but switches to downdip compression at greater depths to the north of 23 n collision is clearly the predominant process with broad deformation on both sides of the suture in between the transition is accommodated by a distributed thrust deformation zone in the frontal portion of the accretionary prism closure of the forearc basin and the right lateral ne sw striking taitung canyon fault zone tcfz these structures resolve the differential movements between the subduction and collision zones and will repeatedly change their positions as the collision propagates southwestward the present day plate boundary follows the axis of the manila trench in the south broadens significantly in the zone of transition and finally becomes a zone of several tens of kilometers in width across eastern taiwan the deformation front on the other hand is located between the western foothills and coastal plain in taiwan then connects to the manila trench to the south seismic strain tensors indicate that the region to the north of tcfz has a compression rate 15 times larger than that to the south the northern luzon arc shows characteristics of oblique subduction but the effects of collision are not as significant within the subducted eurasian lithosphere as comparing to the subducted philippine sea plate beneath the southernmost ryukyu arc

deep water circulation in the luzon strait deep water circulation in the luzon strait which connects the pacific deep circulation with the south china sea throughflow is investigated using a set of oceanographic observations combined with results from three numerical experiments both the in situ observations and the model show a deep water overflow in the luzon strait their results suggest that the deep pacific water first flows into the luzon strait through the bashi channel 1 2 sv 1 sv 1 106 m3 s 1 and the taltung canyon 0 4 sv then turns southward along the luzon trough and finally enters the south china sea primarily through two gaps in the heng chun ridge overall the mean transport of the luzon strait overflow is about 1 5 sv results from numerical experiments suggest that strong diapycnal mixing in the south china sea and luzon strait which sustains the baroclinic pressure gradient across the luzon strait is the primary driving mechanism of the deep circulation in the luzon strait

observation of luzon strait transport using recently collected current and hydrographic data we provide a high resolution picture of the subinertial flow and estimate the volume transport through the luzon strait the distribution of the subinertial flow shows a strong westward flow around 100 m in the northern part of the luzon strait while the eastward flow is confined to the deeper layers mostly at depths around 1000 m the total volume transport is estimated to be 6 3 sv during the period of observations from october 4 to 16 2005 the observations also confirm that the luzon strait transport has a sandwiched vertical structure the net westward volume transport in the deep 1500 m layer of the luzon strait reaches 2 sv

late miocene atmospheric co2 concentrations and the expansion of c4 grasses the global expansion of c4 grasslands in the late miocene has been attributed to a large scale decrease in atmospheric carbon dioxide co2 concentrations this triggering mechanism is controversial in part because of a lack of direct evidence for change in the partial pressure of co2 pco2 and because other factors are also important determinants in controlling plant type distributions alkenone based pco2 estimates for the late miocene indicate that pco2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago the estimates presented here provide no evidence for major changes in pco2 during the late miocene thus c4 plant expansion was likely driven by additional factors possibly a tectonically related episode of enhanced low latitude aridity or changes in seasonal precipitation patterns on a global scale or both

neogene overflow of northern component water at the greenland scotland ridge in the north atlantic ocean flow of north atlantic deep water nadw and of its ancient counterpart northern component water ncw across the greenland scotland ridge gsr is thought to have played an important role in ocean circulation over the last 60 ma the iceland plume has dynamically supported an area which encompasses the gsr consequently bathymetry of the gsr has varied with time due to a combination of lithospheric plate cooling and fluctuations in the temperature and buoyancy within the underlying convecting mantle here we reassess the importance of plate cooling and convective control on this northern gateway for ncw flow during the neogene period following wright and miller 1996 to tackle the problem benthic foraminiferal isotope data sets have been assembled to examine 13c gradients between the three major deep water masses i e northern component water southern ocean water and pacific ocean water composite records are reported on an astronomical timescale and a nonparametric curve fitting technique is used to produce regional estimates of 13c for each water mass confidence bands were calculated and error propagation techniques used to estimate ncw and its uncertainty despite obvious reservations about using long term variations of 13c from disparate analyses and settings and despite considerable uncertainties in our understanding of ancient oceanic transport pathways the variation of ncw through time is consistent with independent estimates of the temporal variation of dynamical support associated with the iceland plume prior to 12 ma 13c patterns overlap and ncw cannot be isolated significant long period variations are evident which are consistent with previously published work from 12 ma when lithospheric cooling probably caused the gsr to submerge completely long period 13c patterns diverge significantly and allow reasonable ncw estimates to be made our most robust result is a dramatic increase in ncw overflow between 6 and 2 ma when dynamical support generated by the iceland plume was weakest between 6 and 12 ma a series of variations in ncw overflow have been resolved

an assessment of 40ar39ar dating for the whole rock volcanic samples from the luzon arc near taiwan from electron microprobe petrographic and image analyses of samples from the northern tip of the luzon arc the effects of various alteration reactions phenocryst and groundmass assemblages on the whole rock 40ar39ar step heating spectra have been delineated the alteration of primary hornblende to an assemblage of zoisite chlorite sphene the palagonitization of glass and the crystallization of phillipsite tends to cause discordant 40ar39ar dates in the low temperature steps of the age spectra discordant 40ar39ar dates in the high temperature steps appear to result from degassing of inherited or trapped 40ar from coarse grained phenocrysts samples in which most of the k resides in groundmass plagioclase tend to yield meaningful plateau dates whereas samples in which most of the k resides primarily in palagonitized glass tend to yield meaningless plateau and isochron dates substantial loss of 39ar 13 40 occurred from irradiated samples prior to 40ar39ar step heating analysis which appears to be correlated with the abundance of groundmass and the degree of alteration this argon loss is attributed to thermally induced argon diffusion from the fine grained groundmass plagioclase glass and alteration phases during the pre step heating bakeout

high resolution benthic foraminifer δ13c records in the south china sea during the last 150 ka abstract high resolution 13c ratios of benthic foraminifer cibicidoides wuellerstorfi in core md97 2151 from the southern south china sea scs and core so50 31kl from the northern scs indicate deep water variations in the scs during the last 150 ka the 13c records of both show a general variation pattern with higher 13c during interglacial periods than glacial periods and rapid increases during terminations this variation pattern resembles those of the west pacific intermediate deep water the sources of the scs deep water and the general variation of global deep water indicating that the variation of the scs deep water is largely controlled by global factors such as carbon cycles and global deep water circulation spectra analysis exhibits robust milankovitch cycles in the scs deep water 13c again supporting global controls significant semi precession cycles can also be seen in the spectra implying that changes of local surface productivity also influence the scs deep water 13c

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

east asian monsoon evolution since the late miocene from the south china sea abstract the south china sea scs has become a global focus for paleoclimatic and paleoceanographic studies due to its location which makes it highly sensitive to the east asian monsoon and to pacific ocean changes we present here a refined magnetostratigraphy for the last 6 5 ma for hole u1431d which was recovered during iodp expedition 349 in the central scs magnetic analyses demonstrate that magnetite is the dominant magnetic carrier except for within a greigite bearing layer at 130 5 132 0 meters below sea floor the greigite layer coincides with the timing of intensification of northern hemisphere glaciation and records an oceanographic response to this event environmental magnetic results indicate that the east asian summer and winter monsoon were stable from 6 5 to 5 ma the summer monsoon intensified at 5 ma and then weakened gradually since 3 8 ma in contrast the winter monsoon weakened at 5 ma and has then been enhanced since 3 8 ma and more stable from 0 6 ma spectral analysis indicates that the east asian summer monsoon was driven directly by low latitude insolation changes before 3 2 ma and that it has been affected by both low latitude insolation and high latitude ice volume changes since 3 2 ma

depleted deep south china sea δ13c paleoceanographic events in response to tectonic evolution in taiwan luzon strait since middle miocene abstract the most distinctive feature of the deep south china sea scs paleoceanography is the occurrence of long term depleted deep sea benthic foraminiferal 13c values they are lower than the global and the pacific composite records in the last 16 ma especially at 13 2 10 5 6 5 3 0 and 1 2 0 4 ma this distinct deep scs paleoceanograhic history coincides with the subduction collision history in the taiwan region where waters of the west pacific wp and the scs exchange the depleted deep sea benthic foraminiferal 13c events indicate that the scs deep basin became progressively a stagnant environment in the last 16 ma due to either closure of the connection with the wp bottom water or temporary reduction of the wp deep water flowing into the deep scs both the taiwan accretionary prism and the luzon arc became the main tectono morphological barriers for the wp bottom water flowing into the scs deep basin when eastward subduction of the scs oceanic lithosphere beneath the philippine sea plate started from the middle miocene 18 16 ma this began a long term trend of depleted scs deep sea benthic 13c values in the last 16 ma the oblique arc continent collision since 6 5 ma uplifted the taiwan accretionary prism rapidly above sea level and further isolated the scs from the open pacific the collision simultaneously causes backthrusting deformations in the north luzon trough forearc basin and sequentially closes interarc water gates between volcanic islands from north to south the loho and the taitung interarc water gates in the advanced collision zone were closed at 3 0 ma and 1 2 ma coinciding with the very low scs deep sea benthic 13c events at 3 0 and 1 2 0 4 ma respectively the taitung canyon between the lutao and lanyu volcanic islands in the incipient collision zone is semi closed presently these closure events also lead to the result that the wp deep water intrudes westward into the scs principally through the bashi channel between the lanyu and batan volcanic islands in the subduction zone

glacial interglacial environmental changes inferred from molecular and compound specific δ13c analyses of sediments from sacred lake mt kenya abstract molecular stratigraphic analyses including lipid distributions and compound specific 13c measurements have been performed at 15 levels in a sediment core from sacred lake mt kenya a high altitude 2350 m a s l freshwater lake with a record extending from the last glacial 40 000 cal yr bp through the present interglacial terrestrial and aquatic organic matter sources were independently assessed using source specific biomarkers 13c values of long chain n alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts those from the last glacial maximum lgm 20 to 18 indicate a terrestrial vegetation dominated by c4 grasses or sedges whereas those from the early holocene 34 to 27 reflect recolonization of the catchment area by c3 plants consistent with a rapid rise in the upper treeline specific algal biomarkers including five unsaturated hydrocarbons of novel structure ascribed to the microalga botryococcus braunii were abundant as confirmed by scanning electronic microscopy sem an extreme 13c shift of over 25 is displayed by the algal biomarkers an elevated value of 5 1 at the last glacial maximum lgm contrasting with a minimum value of 30 3 at the beginning of the holocene a major change in the molecular distributions of the algal biomarkers parallels this large 13c shift with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the holocene the low atmospheric partial pressure of co2 pco2 at the lgm would favour photosynthetic organisms possessing co2 concentrating mechanisms including terrestrial c4 grasses and freshwater green algae hence glacial interglacial changes in pco2 and in the co2 o2 ratio in particular had a significant impact on both terrestrial and aquatic ecosystems on mt kenya in addition to the effects of climate and local environmental factors

a high resolution palaeoclimatic record for the last 27 500 years in tropical west africa from the carbon and nitrogen isotopic composition of lacustrine organic matter variations in the carbon and nitrogen isotopic composition of bulk organic matter in the sediments of lake bosumtwi ghana reflect climatically induced changes to the lake and the catchment flora cores spanning the last 27 5 kyr of sedimentation in the lake show large oscillations in 13corg pdb and 15norg air the late pleistocene record is particularly detailed showing changes of ca 20 in carbon and ca 10 in nitrogen isotopic compositions these variations are of complex origin although different in magnitude major isotopic excursions in the two records are generally in phase and reveal the occurrence of two major dry intervals at and immediately following the last glacial maximum the allerod younger dryas period also seems to have been marked by generally dry conditions in this part of tropical west africa nitrogen isotopic evidence suggests that during the period 9 2 3 2 kyr the lake had an extremely stable water column probably due to the absence of a windy or cool dry season or both regular circulation of the water column recommenced during the late holocene and has persisted until the present day

the importance of atmospheric input of terrestrial organic material to deep sea sediments the concentrations of lipids were determined in atmospheric particle gas and rain samples collected from the tropical north pacific to assess lipid sources transport mechanisms and fluxes to the ocean surface four lipid compound classes aliphatic hydrocarbons fatty alcohols fatty acid esters and salts all unequivocally show a terrestrial vascular plant source these aerosol lipids originate from wind erosion of asian and american soils and direct emission from vegetation the major fluxes result from rain rather than dry deposition these fluxes are large enough to have a major potential impact on the inventory of terrestrially derived lipid material found in deep sea sediments this has been showm for n alkanes fatty alcohols fatty acids total lipids and for organic carbon by comparing atmospheric and sediment trap fluxes with sediment accumulation rates it is suggested that some biogenic terrestrial material is more protected from degradation than marine derived material

δ13c of organic carbon in the bengal fan source evolution and transport of c3 and c4 plant carbon to marine sediments carbon isotopic measurements on organic carbon oc in sediment cores from the bengal fan odp leg 116 show a dramatic 10 increase beginning ca 7 ma ago and a rapid decrease after 0 9 ma these shifts reflect changes in the mixing ratio of terrigenous carbon derived from c3 and c4 plants the rapid increase in 13c of bengal fan oc at 7 ma shows that late miocene expansion of c4 plants already documented in the siwaliks was widespread over all the himalayan foreland after 7 ma relations of 13c with sedimentological parameters show that c4 plants dominate in the foreland whereas c3 plants remain abundant in the mountain range variations in the source of the sediments and of the oc appear to be sensitive to climate hydrologic conditions in the basin major changes in the isotopic composition of the carbon flux in one of the worlds largest river systems modify the isotopic budgets of both marine dissolved carbon and the sedimentary carbon mass

terrestrial vegetation change inferred from n alkane σ13c analysis in the marine environment abstract we report gas chromatography isotope ratio monitoring mass spectrometry gc irm ms measurements of the 13c values of individual biomarker compounds n alkanes extracted from a 3 m marine sediment core taken near the mouth of the johnstone river north queensland australia the technique allows a purely terrestrial isotope signal to be discerned despite mixing of terrestrial and marine derived carbon the results indicate that there has been a 2 increase in the 13c values of terrestrially derived n alkanes c29 c33 since clearing of the forested johnstone river drainage basin for sugarcane and pasture began in the late 19th century a much slower 1 increase in 13c values after 6 000 years bp and prior to european settlement may be related to a decrease in rainfall in the basin or to an increase in the abundance of c4 plants as a result of increased aboriginal burning the results from the sediment core are consistent with data obtained for modern river sediments from forested and cleared subcatchments within the basin and demonstrate that the 13c values of terrestrially derived n alkanes in the marine environment can be used to assess basin wide vegetation changes in adjacent river catchments on geological timescales

structural evolution and significance of a melange in a collision belt the lichi melange and the taiwan arc continent collision the analysis of melanges of various types sedimentary diapiric tectonic and polygenetic is generally difficult and depends on a variety of criteria however understanding the nature and origin of melanges is crucial to deciphering the evolution of some mountain belts the lichi melange of the taiwan coastal range is juxtaposed against remnant forearc basin sequences by thrust faults and is composed of exotic ophiolite and sedimentary blocks with sizes ranging from metres to kilometres and coherent turbidite beds all embedded in a sheared scaly argillaceous matrix the lichi melange has been interpreted either as a subduction complex or as an olistostrome by separating four main deformation levels based on the degree of disruption within the lichi melange and adjacent sedimentary rocks we have made new detailed geological maps and structural profiles in two key areas of the lichi melange we paid particular attention to the original stratigraphic relationships between the melange and the adjacent flysch formation our field results compared with submarine seismic profiles suggest that the present day structure of the lichi melange results mainly from the shearing of lower forearc basin sequences rather than from a subduction complex or a mere olistostrome in late miocene time because lithospheric subduction turned into arc continent collision in the southern taiwan area the site of the proto manila trench changed from an active plate boundary into a deformation zone with several thrusts a new plate suture zone between the eurasian plate eastern central range and the philippine sea plate coastal range was therefore formed along the longitudinal valley the longitudinal valley originated as a submarine arc prism boundary an innate weak zone within the overriding plate and has become a prominent tectonic feature of the arc continent collision this inference is supported by observations on the lichi melange in the coastal range and the huatung ridge off southeastern taiwan

δ13c analyses of individual lignin phenols in quaternary lake sediments a novel proxy for deciphering past terrestrial vegetation changes this study of the sediments from sacred lake mount kenya demonstrates that 13 c analyses of individual lignin phenols can be used to assess past changes in the proportion of c 3 and c 4 plants within different plant groups in the lake catchment vegetation changes resulting from climatic and atmospheric changes since the last glacial maximum can be deduced from specific lignin phenols lignin a major biopolymer in vascular plants differs from n alkyl lipids in 1 its higher specificity and more quantitative representation of vascular plant input and 2 its major transport mechanism into the sediments by fluvial runoff as opposed to the greater importance of eolian transport for leaf waxes and pollen lignin 13 c data support the hypothesis that atmospheric co 2 concentration is an important factor controlling the vegetation in tropical mountain ecosystems and provide additional insights into past changes in vegetation structure specifically the 13 c values of p coumaric acid indicate the persistence of c 4 grasses during the late glacial when the lake level was lower than today suggesting that aridity also played a role in controlling the abundance of c 4 plants

paleomagnetic evidence for a diachronic clockwise rotation of the coastal range eastern taiwan abstract paleomagnetic results obtained from over 2100 cores sampled at 132 early pliocene to late pleistocene sites in the coastal range of eastern taiwan indicate that since the late pliocene the margin of the philippine sea plate has undergone a clockwise rotation of about 30 as a direct consequence of the plio pleistocene collision of this plate with the chinese continental plate the rotation is diachronic and started between 3 and 4 ma ago in the northern coastal range then propagated southward at an average speed of the order of 70 10 km ma this value is in very good agreement with estimates of the southward propagation of the collision between the philippine sea plate and the eurasian margin in taiwan it is suggested that the rotation reflects the deformation of the philippine sea plate at depth and does not results from the shallow deformations involved in the building of the coastal range orogen

juxtaposed sequence stratigraphy temporal spatial variations of sedimentation and development of modern forming forearc lichi melange in north luzon trough forearc basin onshore and offshore eastern taiwan an overview abstract the south china sea oceanic lithosphere has been subducting eastward beneath the huatung basin philippine sea plate since the early miocene 18 ma the subduction is followed by the oblique collision between the luzon arc and the subducting eurasian plate from 6 5 ma the north luzon trough forearc strata and the luzon arc are then obducted northwestward as the coastal range eastern taiwan in the last 1 ma the collision propagates southward and is presently active in the region offshore se taiwan integrating seismic surveys offshore and a detailed forearc stratigraphy study onshore the coastal range this paper overviews the characteristics of forearc deformation dynamic sequence stratigraphy temporal spatial variations of forearc sedimentation and stratigraphic correlation onshore and offshore forearc sequences in response to the oblique convergent tectonics north of 20 n combining onshore and offshore forearc geology together allows us to reconstruct a structural evolution of the north luzon trough forearc basin from subduction through collision to obduction and to discuss the mechanism and processes responsible for developments of the modern forming forearc lichi melange during the active taiwan orogeny seismic surveys offshore show that forearc deformation in the subduction zone is primarily caused by increase of rear prism slope and west vergent thrusting of forearc strata along the prism top since the early forearc sedimentation east vergent backthrusting occurs during the late forearc sedimentation and propagates arcward when the volcanic arc collides with the accretionary prism in the collision zone bivergent thrusting leads to a development of the forearc huatung ridge popup as a bathymetric high which further controls the sedimentation of the younger forearc sequence in the collision zone in response to the syn sedimentation deformation forearc depocenter shifts progressively eastward forearc stratigraphy thus changes from two mega sequences bounded by an unconformity in the subduction zone to three mega sequences juxtaposed from west to east unconformably in the collision zone as a consequence the forearc deformation and stratigraphy in the oblique collision zone off se taiwan show a characteristic temporal spatial pattern that the lowest mega sequence with the most intensive deformation occurs restrictedly in the west whiles the middle and the upper mega sequences with mild deformation crop out in the center and the eastern part of the forearc basin respectively detailed biostratigraphy study using planktonic foraminifera and calcareous nannoplanktons indicates that the forearc strata onshore the coastal range are also composed of three sequences lower unit s 1 6 5 5 8 ma middle unit s 2 5 8 3 0 ma and upper unit s 3 a structure reconstruction reveals that the north luzon trough forearc strata have experienced multiple stages of thrust deformation from subduction through collision to obduction these deformations account for the mechanism and processes to develop the modern forming highly sheared ssz bearing forearc lichi melange tectonically in the western coastal range during the last 1 ma

freshwater diatom influx in intertropical atlantic relationships with continental records from africa diatom assemblages from modern west african rivers and from lacustrine sediments subjected to deflation represent the present day sources of continental diatoms to the sea diatom productivity in large rivers is high especially for the genus melosira windblown diatoms derive mainly from the central and northern sahara summer dust plume where saline chloride water assemblages are widespread or from the southern edge of the sahara winter dust plume where melosira rich assemblages of dilute water predominate freshwater diatom peaks in atlantic cores may reflect 1 phases of increased river influx correlated with humid episodes on the continent or 2 phases of enhanced deflation and wind transport during arid episodes the single hypothesis for fine sediments from mid ocean sites genus melosira dominates the freshwater assemblages of many modern and fossil marine samples whatever the transport agent is therefore it is not an accurate paleoclimate indicator by itself but associated taxa may provide information on the environmental and geographical origin of the displaced diatoms this tentative approach shows that freshwater diatoms in atlantic cores may be a good tool for reconstructing paleoclimates and for establishing continent ocean correlations if species analyses are made and if the continental distribution of the taxa encountered is considered

the influence of oceanographic processes on contourite features a multidisciplinary study of the northern south china sea abstract this study examines how multiscale oceanographic processes interact with the seafloor to influence the development of contourite features in northern part of the south china sea the multidisciplinary approach used in this study combines physical oceanographic monitoring numerical simulation multibeam echosounding seismic reflection profiling and sediment core interpretation the contourites detected and interpreted herein include depositional drifts and sediment waves erosional channels moats and furrows and mixed erosional and depositional features terraces and irregular depressions this study finds that climatic variation influences the intensity of quasi steady along slope regional water circulation which in turn influences the long term development of primary 10 100 km contourite depositional systems energetic but intermittent oceanographic processes such as eddies and internal waves generate smaller secondary features within the contourite depositional systems resulting in a complex local seafloor morphology westward to south westward migrating mesoscale eddies locally enhance regional water mass circulation and trigger sub mesoscale flows which can generate 1 10 km irregular depressions along their paths westward propagating internal solitary waves form sedimentary waves with the aid of numerical modelling results a sedimentary model is proposed to explain how oceanographic processes influence sedimentary processes and determine a hierarchy of associated feature formation this model can help advance understanding of how bottom currents influence sedimentary processes along continental margins and abyssal plains

astronomically modulated neogene sediment records from the south china sea 1 general global cooling over the neogene has been modulated by changes in earth s orbital parameters investigations of deep sea sediment sequences show that various orbital cycles can dominate climate records for different latitudes or for different time intervals however a comprehensive understanding of astronomical imprints over the entire neogene has been elusive because of the general absence of long continuous records extending beyond the pliocene we present benthic foraminiferal 18o and 13c records over the past 23 ma at ocean drilling program site 1148 in the northern south china sea and construct an astronomically tuned timescale tj08 for these records based on natural gamma radiation and color reflectance data at this site our results show that a 41 ka cycle has dominated sediment records at this location over the neogene displaying a linear response to orbital forcing a 100 ka cycle has also been significant however it is correlated nonlinearly with earth s orbital variations at the 100 ka band the sediment records also display a prominent 405 ka cycle although this cycle was coherent with orbital forcing during the oligocene and the early miocene it was not coherent with earth s orbital variations at the 405 ka band over the whole neogene amplification of northern hemisphere and southern hemisphere glaciation since the middle miocene may be responsible for this change in sedimentary response our benthic foraminifera 18o and 13c records further exhibit amplitude variations with longer periods of 600 1000 1200 and 2400 ka apparently these cycles are nonlinear responses to insolation forcing

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities