partition between collision and subduction accretionary prisms along an inherited transcurrent fault zone new insights on the taiwan fold and thrust belt a new geotectonic framework of the taiwan orogen is presented in accordance with the hypothesis of an oblique arc arc collision the colliding luzon arc is physically connected to the eastern coastal range in which a subduction complex remnant is preserved and backthrust with intra arc sediments in a small retroforeland basin a southern and extinct extension of the ryukyu arc is characterized in western taiwan it displays a duplex structure tananao and backbone horses and lishan triangle zone between a buried floor thrust located in the arc crust and a roof thrust developed in the arc cover hsfiehshan range and south backbone range westward the basal thrust climbs in the sedimentary series of the western proforeland foothills and hengchun peninsula and dies out in a buried tip line the northern part of the orogen including all the tananao arc core is shown as an intra oceanic continental arc arc collision belt characterized by an unroofed duplex culmination above a leading floor thrust and both proforeland and retroforeland basins the southern part which displays a roof thrust sequence above a buried duplex is shown as an accretionary prism built in a transition zone between continent and oceanic subduction transition from the asian continental crust including the former ryukyu arc to the oceanic old philippine sea crust the partition is believed to be induced by a deep intracontinental transcurrent fault zone able to influence the difference in shortening duplex pattern and leading thrust depth the evolution was controlled by the ryukyu subduction backarc extension arc magmatism extinction and cooling and intra arc collapse until the early middle miocene around 15 ma and then it was controlled by the luzon arc progression continental subduction collision indentation and hinterland uplift and frontal thrust propagation

the stable isotopic composition of modern soil carbonate and its relationship to climate the oxygen isotopic composition of modern soil carbonate is well correlated with the isotopic composition of local meteoric water the carbon isotopic cycle for co 2 in soils can be described in terms of the proportion of biomass using the c 4 photosynthetic pathway and the co 2 respiration rate of the soil at low soil respiration rates significant atmospheric co 2 mixing can occur in general the carbon isotopic composition of soil carbonate is related to the proportion of c 4 biomass present in soil but soils that freeze to the depth of carbonate formation often have a significant atmospheric component this suggests that freezing of the soil solution should be considered as another important mechanism for soil carbonate formation because of these relationships the isotopic composition of soil carbonate may be a paleoclimatic and paleoecologic indicator in cases in which diagenetic alteration has not occurred

new insights on 3 d plates interaction near taiwan from tomography and tectonic implications abstract recent tomographic results are used to trace the south china sea and philippine sea subducting slabs south and northeast of taiwan along the manila and ryukyu trenches respectively in particular the 3 d plates interaction beneath taiwan is discussed based on a close up view of the tomographic sections together with earthquake hypocenters distribution our study indicates that 1 the east dipping south china sea slab can be followed to the north up to the latitude of hualien 2 the eurasian plate subducts beneath most part of the taiwan island down to the 670 km depth discontinuity 3 the north dipping philippine sea slab can be followed slightly west of the longitude of hualien both plates thus interact beneath northern taiwan where the arc continent collision is paroxysmal 4 slab detachment is envisaged at the northern edge of the subducted eurasian plate beneath the coastal range of taiwan which may facilitate the northwestward motion of the philippine sea plate with respect to eurasia slabs geometries obtained from tomographic sections allow us to reconstruct the late neogene plate kinematics and dynamics in this region our main conclusions are 1 the size of the original south china sea was about twice its present size 2 the subducted part of the west philippine basin i e the largest oceanic basin of the philippine sea plate extends only 400 km north of the ryukyu trench 3 slab detachment might have occurred 3 5 my ago beneath the central and northern ryukyu arc along a weak zone that is aligned with the gagua ridge an ancient plate boundary 4 the ryukyu trench has propagated westward from 126 e of longitude southeast of miyako island to the locus of the present arc continent collision along a major lithospheric tear that cut through the continent ocean boundary first and then through the continental lithosphere as a consequence the southern ryukyu margin developed progressively from east to west as a subduction zone during the last 8 my it has been elaborated onto a passive margin which corresponded to the edge of the eurasian continental shelf bordering the south china sea prior to pliocene 5 the southern okinawa trough rifted during the last 2 1 ma following the propagation of the subduction zone 6 subduction of the eurasian margin probably stopped recently beneath northern taiwan and a flip of subduction from west to east is being initiated near hualien

sedimentology and stable isotopes from a lacustrine to palustrine limestone deposited in an arid setting climatic and tectonic factors miocene pliocene opache formation atacama desert chile abstract field relations petrography gis and geochemistry of a late miocene pliocene limestone the opache formation calama basin atacama desert chile shows that depositional facies diagenetic histories and isotopes differ from eastern to western parts of the basin we recognize two facies lacustrine characterized by ostracod diatom mudstone and wackestone and palustrine characterized by both shallow water and pedogenic features gis analysis of the basin topography reveals an intrabasinal low in the eastern area and steeper hydrological gradients to the west with the calama constriction restricting flow between east and west petrography and geochemical results confirm that the calama constriction influenced depositional parameters ponding groundwater to the east forming a shallow lake and creating palustrine conditions to the west our analyses indicate that lake waters were less enriched in 13c or 18o than palustrine waters even though petrologic studies show that the lacustrine carbonates have a complex diagenetic history derived from groundwater rich in dissolved minerals this seemingly contrary observation can be reconciled if an important source of water for the western carbonates was sourced from the pacific ocean and was less evolved whereas eastern limestones precipitated from water which had become depleted in 18o during transport from the east today moisture from the pacific very rarely if ever reaches inland as far as calama indicating that during the late miocene mid pliocene breakdown in the temperature inversion due to weakened or absent upwelling in the cold coastal pacific current allowed moisture from the pacific to reach inland this changing atmospheric circulation pattern may have also affected upper level airflow that today blocks eastern sourced moisture from crossing the andes allowing it to reach farther westward into the atacama region during the late miocene pliocene together these moisture sources were sufficient to produce carbonate rich palustrine and lacustrine environments in the calama basin

equilibrium and disequilibrium stable isotope effects in modern charophyte calcites implications for palaeoenvironmental studies abstract stable isotopes in fossil charophyte calcite may record palaeoenvironmental information but at present very little is known about isotopic records in modern chara stem encrustations or gyrogonites this problem is addressed with isotopic data from present day chara from a wide spread of freshwater environments in britain and ireland 13 c values of stem encrustations from low water flow environments lakes ponds ditches are more positive than their coexisting gyrogonite values by between 0 6 and 3 0 reflecting microenvironmental metabolic effects caused by photosynthesis in stronger water flows where dissolved inorganic carbon is well mixed stem encrustation 13 c values are close to equilibrium 18 o values in chara stem encrustations are not equilibrium values being typically offset to isotopically lighter compositions by about 1 5 relative to equilibrium by kinetic effects during rapid calcification gyrogonite 18 o values are less negative than coexisting stem encrustation values by between 0 7 and 1 7 there is no clear evidence that gyrogonite 18 o or 13 c values are influenced by extensive disequilibrium but the data are difficult to interpret further without new experimental studies isotopic records in fossil lacustrine chara marls mainly stem encrustation calcites should be interpreted with caution environmental records essentially of relative changes in late summer water temperature or hydrology may be preserved but these are unlikely to represent true equilibrium values gyrogonite calcification probably happens on a timescale of weeks such that isotopic data represent snapshots of the environmental conditions at the time of calcification the timing of calcification in chara may itself be variable depending on environment and temperature it is a major unknown that currently hinders interpretation of isotopic data

late quaternary paleoclimate in the eastern mediterranean region from stable isotope analysis of speleothems at soreq cave israel abstract the eastern mediterranean continental paleoclimate during the past 25 000 years was determined by a high resolution petrographic stable isotopic and age study of speleothems from soreq cave israel 18o 13c trends indicate that all speleothems older than 7000 yr formed under conditions that differ from those of today the period from 25 000 to 17 000 yr b p was characterized by the highest 18o and 13c values which indicate deposition at temperatures of 12 16 c annual rainfall of 300 450 mm and vegetation typical of a mixed c3 c4type from 17 000 to 10 000 yr b p deglaciation in northern europe 18o values dropped progressively correlative with warming 2 3 c and a gradual increase in precipitation a simultaneous decrease in 13c gives a range expected for c3 type vegetation this period also shows significant 18o and 13c spikes which are correlatable with global events e g heinrich events and the younger dryas stade the speleothems that grew between 10 000 and 7000 yr b p have a unique petrography showing irregular thin laminae of various colors and much detritus they have the lowest 18o corresponding to 1000 mm rain coupled with the highest 13c caused by flooding events which stripped the soil cover from 7000 to 1000 yr b p conditions became closer to those of today this study demonstrates that global events which were recognized in northern europe and north africa are also evident in the eastern mediterranean and are reflected principally by large changes in the rainfall rate

do stable isotope data from calcrete record late pleistocene monsoonal climate variation in the thar desert of india late pleistocene terrestrial climate records in india may be preserved in oxygen and carbon stable isotopes in pedogenic calcrete petrography shows that calcrete nodules in quaternary sediments of the thar desert in rajasthan are pedogenic with little evidence for postpedogenic alteration the calcrete occurs in four laterally persistent and one nonpersistent eolian units separated by colluvial gravel thermoluminescence and infrared and green light stimulated luminescence of host quartz and feldspar grains gave age brackets for persistent eolian units i iv of ca 70 000 60 000 ca 60 000 55 000 ca 55 000 43 000 and ca 43 000 25 000 yr respectively the youngest eolian unit v is 10 000 yr old and contains no calcrete stable oxygen isotope compositions of calcretes in most of eolian unit i in the upper part of eolian unit iv and in the nonpersistent eolian unit range between 4 6 and 2 1 pdb these values up to 4 4 greater than values from eolian units ii and iii are interpreted as representing nonmonsoonal18o enriched normal continental waters during climatic phases when the monsoon weakened or failed conversely 25 000 60 000 yr old calcretes eolian units ii and iii probably formed under monsoonal conditions the two periods of weakened monsoon are consistent with other paleoclimatic data from india and may represent widespread aridity on the indian subcontinent during isotope stages 2 and 4 the total variation in 13c is 1 7 0 0 1 7 and 13c covaries positively and linearly with 18o 13c values are highest when 18o values indicate the most arid climatic conditions this is best explained by expansion of c4grasses at the expense of c3plants at low latitudes during glacial periods when atmosphericpco2was lowered c4dominance was overridingly influenced by global change in atmosphericpco2despite the lowered summer rainfall

mineralogy and sr mg geochemistry of charophyte carbonates a new tool for paleolimnological research abstract the carbonate biominerals formed in the oogonial cells and on stems of charophytes reveal intra specific and species to species variations within the genus chara calcite high magnesian calcite hmc and aragonite may be present in both oogonium and stem calcifications and for the first time evidence is presented of polymineral calcification hmc aragonite within single oogonial cells the data indicate strong specific differences in the biological mechanisms of mineralization within this group of plants among the various species of the genus chara studied there is no correlation between the charophyte carbonate mineralogy and the salinity of water where they formed calcite hmc and aragonite may all be present in charophyte calcifications formed in low salinity waters on the contrary there is an overall relationship between the mineralogy of these carbonates and the mg ca ratio of the water in which they formed sr content in charophyte calcite and high mg calcite reflect directly the sr ca ratio of the host water whereas mg content in these carbonates probably depends on the temperature and the mg ca ratio of the water partitioning coefficients for mg and sr for some widespread species are discussed our results indicate that charophyte carbonates may be used as paleohydrochemical proxies and imply that special attention must be paid to the mineralogical control of charophyte carbonates when they are to be used in isotopic studies

geochemical indicators of depositional and early diagenetic facies in holocene carbonate muds and their preservation potential during stabilisation holocene carbonate muds 63 m fraction and macro organic matter were collected from marine subtidal mudbanks and supralittoral mud islands of florida bay and freshwater marshes of the florida everglades u s a geochemistry sedimentology and mineralogy were used to determine whether carbonate mud formation in specific marine and freshwater environments was geochemically distinct and to assess the importance of early diagenetic reactions on mud chemistry and mineralogy significant variations were found in the relative amounts of carbonate minerals not just between the marine and freshwater environments but also within florida bay in particular mg calcite is enriched in crane key muds by 10 relative to nearby cross bank the mg calcite appears to precipitate in the surface living cyanobacterial mats of the key and seems to be linked to mg chelation by the cyanobacterial organic matter this mg calcite has a distinct 13c around 4 6 lighter than mg calcite derived from thalassia epibionts in the cross bank muds dolomite was found just below the cyanobacterial mats forming in the only part of the core where reactive organic carbon has been completely removed by sulphate reducing bacteria the 13c values of this dolomite at least 4 are consistent with previously published 13c values of dissolved inorganic carbon in pore waters at this horizon which support dolomite formation in situ mg supply for dolomite formation may be from dissolution of the overlying cyanobacterial mat mg calcite the various types of organic matter have distinctive 13c values ranging from 25 mangrove and sawgrass to 10 cyanobacterial mats and 8 thalassia seagrass values intermediate between these end members record mixing of the organic matter types which shows particularly the time when the bank muds became dominated by thalassia organic matter i e were relatively removed from mangrove vegetation five holocene mud suites bank key cyanobacterial mats mangrove swamp and freshwater everglades swamp show distinct chemical signatures in their mean 13c 18o mgco3 and sr values na distinguishes between seawater and non seawater influenced environments but fe mn and p are mainly controlled by non carbonate materials comparison with published stable isotope and elemental data for pleistocene limestones in the south florida area suggests that only the facies diagnostic signatures of 13c and mg will be resolvable once the muds have been stabilised to micrite alteration of the 18o and sr values during stabilisation will probably be more severe to the extent that original facies variations are destroyed

multi component stable isotope records from late weichselian and early holocene lake sediments at imiolki poland palaeoclimatic and methodological implications late weichselian and early holocene climatic and environmental changes are inferred from stable carbon and oxygen isotope records obtained on bulk and biogenic carbonates from the sediment sequence of lake lednica western poland along with sediment and pollen stratigraphic data a wide range of carbonate components occurring in the sediments was analysed for delta c 13 and delta o 18 including shells of several gastropod species and the bivalve genus pisidium carapaces of the ostracod subfamily candoninae and oogonia of the aquatic macrophyte genus chara the development of catchment soils and the onset of authigenic carbonate production in response to the climatic amelioration during the late weichselian are clearly reflected by rising carbonate content distinct isotopic shifts in bulk carbonates and decreasing delta c 13 values of bulk organic matter in the sediments the gi 1 gs 1 the bolling allerod interstadial complex younger dryas stadial and the gs 1 preboreal transitions are marked by significant shifts in delta o 18 values of 2 3 parts per thousand as well as by distinct changes in carbonate content indicative of a decrease and a subsequent increase in mean annual temperature corresponding delta c 13 records reflect primarily changes in aquatic productivity with favourable conditions for phytoplankton and macrophytes during gi 1 and the preboreal resulting in persistent c 13 enrichment the younger dryas stadial is characterised by depletions in c 13 and o 18 with indications of a climatic tripartition consistent offsets in delta c 13 and delta o 18 between records obtained on specific carbonate components reflect vital effects in combination with seasonal characteristics and habitat preferences of the respective carbonate precipitating biota largely parallel first order variations in delta c 13 and delta o 18 of the different carbonate components demonstrate that individual isotope records may provide important palaeoclimatic information although more detailed reconstructions can be obtained from multi component analysis copyright c 2009 john wiley sons ltd

japan sea opening history and mechanism a synthesis the respective tectonic effects of back arc spreading and continental collision in asia are considered either as two independent processes or as closely interrelated extrusion tectonics assumes that the opening of the south china sea and the left lateral motion along the red river fault are geometrically linked in a pull apart manner this model is not accepted by several workers because the structural link between the two processes is not clearly demonstrated in the case of the japan sea we can show without ambiguity that back arc opening was controlled by large intracontinental strike slip faults which can be easily understood as effects of the india asia collision far from the indenter the japan sea opened in the early miocene in a broad pull apart zone between two major dextral strike slip shear zones the first one extends from north sakhalin to central japan along 2000 km it has accommodated about 400 km of finite displacement deformation along it varies from dextral transpression in the north to dextral transtension in the south the second is between korea and sw japan and has accommodated a smaller displacement of about 200 km the extensional domain in between lies in the back arc region of japan distributed stretching of the arc crust resulted in the formation of most of the japan sea while localized oceanic spreading at the southern termination of the eastern transpressional shear zone shaped the japan basin the first oceanic crust was formed in a small triangle based on the eastern shear zone and spreading propagated westward inside the pull apart region timing of oceanic crust formation of formation of the dextral shear zones and of block rotation in between as well as the internal structure of the basins and the geometry of deformation along the master shear zones are used to reconstruct the opening history this evolution is discussed by comparison to other manifestations of the arc and back arc activity such as the history of sedimentation and volcanism the paper then suggests that the collision of india can have tectonic consequences as far north as japan and sakhalin and describes the geometrical relation of back arc opening there and diffuse extrusion

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

how was taiwan created abstract since the beginning of formation of proto taiwan during late miocene 9 ma the subducting philippine ph sea plate moved continuously through time in the n307 direction at a 5 6 cm year velocity with respect to eurasia eu tearing the eurasian plate strain states within the eu crust are different on each side of the western ph sea plate boundary extensional in the okinawa trough and northeastern taiwan versus contractional for the rest of taiwan island the b feature corresponds to the boundary between the continental and oceanic parts of the subducting eurasian plate and lies in the prolongation of the ocean continent boundary of the northern south china sea strain rates in the philippines to northern taiwan accretionary prism are similar on each side of b contractional though with different strain directions perhaps in relation with the change of nature of the eu slab across b consequently in the process of taiwan mountain building the deformation style was probably not changing continuously from the manila to the ryukyu subduction zones the luzon intra oceanic arc only formed south of b above the subducting eurasian oceanic lithosphere north of b the luzon arc collided with eu simultaneously with the eastward subduction of a portion of eu continental lithosphere beneath the luzon arc in its northern portion the lower part of the luzon arc was subducting beneath eurasia while the upper part accreted against the ryukyu forearc among the consequences of such a simple geodynamic model i the notion of continuum from subduction to collision might be questioned ii traces of the miocene volcanic arc were never found in the southwestern ryukyu arc we suggest that the portion of eu continental lithosphere which has subducted beneath the coastal range might include the miocene ryukyu arc volcanoes formed west of 126 e longitude and which are missing today iii the 150 km wide oceanic domain located south of b between the luzon arc and the manila trench above the subducting oceanic eu plate south china sea was progressively incorporated into the eu plate north of b

charophyte growth in small temperate water bodies extreme isotopic disequilibrium and implications for the palaeoecology of shallow marl lakes abstract a small pond containing the charophyte chara hispida was monitored over a one year period for changes in growth water chemistry water level and stable isotopic composition chara growth was found to be seasonal with maximum growth occurring from late april to july during this period ph rose to 10 while the dissolved inorganic carbon dic and calcium fell as a result of photosynthesis and calcification large gradients in ph water temperature and irradiance were found within the chara sward and measurements showed that most growth and photosynthesis occurred within the upper 20 cm of the water column chara oospore formation was also found to be seasonal but dependent upon environmental conditions 18 o w rose rapidly during summer as evaporation progressed and this was correlated with the 18 o dic and to some extent with 18 o c of the chara encrusted calcite however extreme isotopic disequilibrium was observed between the 18 o c and the 18 o w and also between the 13 c c and the 13 c dic this arose from the high ph allowing atmospheric co 2 to enter the water and combine directly with oh it is concluded that within shallow eutrophic lakes containing chara swards inferences of climate e g air temperature cannot be made from observations of the isotopic composition of chara carbonates however in combination with other geochemical data disequilibrium events may be identifiable in ancient lake basins and taken as evidence for lake shallowing and or eutrophication

detrital input to spring fed fen deposits a problem or an opportunity in palaeoenvironmental studies a holocene palaeoclimatic reconstruction from central europe detrital input to spring fed fen deposits

stable isotopic compositions of recent freshwater cyanobacterial carbonates from the british isles local and regional environmental controls recent 50 years old freshwater cyanobacterial carbonates from diverse environments streams lakes waterfalls throughout britain and ireland were analysed for their stable carbon and oxygen isotope compositions the mean 18o value of 5 9 pdb for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central britain 7 5 smow assuming a mean water temperature of 9 c the mean 18o of lake data 4 5 pdb is statistically different reflecting the effects of residence time and or variations in the oxygen isotopic composition of rainfall carbon isotopes have wide variations in both fluviatile and lake data sets 3 to 12 pdb these variations are principally controlled in the fluviatile samples by contribution of isotopically light soil zone carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution lake samples have the heaviest carbon isotope values reflecting a trend toward isotopic equilibrium between atmospheric co2 and aqueous hco 3 we infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information although the effects of stabilization and diagenesis on primary 18o values will need careful consideration primary carbon isotope compositions should be well preserved although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate

a 16 ka oxygen isotope record from genggahai lake on the northeastern qinghai tibetan plateau hydroclimatic evolution and changes in atmospheric circulation moisture source history and changes in atmospheric circulation are the most important attributes for portraying past climate changes and for estimating possible future trends however few climate records reflecting these attributes are available from the marginal zones of the asian summer monsoon here we present a record of the oxygen isotopic composition of authigenic carbonates delta 18 ocarb of sequential sediments from genggahai lake in the northeastern qinghai tibetan plateau qtp isotopic analyses were performed on the fine grained carbonate fraction 38 mu m mollusc shells and stem encrustations from submerged plants the stratigraphic variations of the delta o 18 record from the different carbonate components exhibit a remarkably similar pattern probably reflecting the fact that delta 18 ocarb variability was controlled primarily by changes in the oxygen isotopic composition of the lake water delta 18 olw disequilibrium effects and water temperature are precluded as major factors affecting the delta 18 ocarb variations genggahai lake is hydrologically open and characterized by a rapid discharge rate as indicated by analysis of the hydrological setting of the lake system and by the observed significant positive correlation between delta o 18 lw and the oxygen isotopic composition of the inflowing water delta o 18 1 under such hydrological conditions we argue that the isotopic signals of different moisture sources should be reflected in the carbonate isotopic composition furthermore placing the delta 18 ocarb record in the context of regional palaeoclimate archives we found that the isotopic signals particularly the negative shifts from the average values cannot be interpreted consistently despite a process of evaporative enrichment at the lake surface during the early to mid holocene low delta 18 ocarb values during 10 6 9 4 and 7 4 63 ka were associated with higher lake levels and thus the record may have been significantly affected by a strengthened asian summer monsoon at those times and hence by a positive moisture balance isotopic depletions with similar magnitudes occurred at 15 14 5 13 8 13 3 12 5 11 4 5 3 4 8 3 7 3 4 2 8 2 3 1 7 1 3 and 0 6 1 a i e within the lateglacial and the late holocene these negative shifts in delta 18 ocarb corresponded to lower lake level phases and most likely were a response to intensification of the mid latitude westerly circulation that may have transported significantly more o 18 depleted moisture to the region compared to that from the asian summer monsoon overall our results suggest that the alternating influence of the asian summer monsoon and the westerlies played a significant role in determining the pattern of atmospheric circulation on the northeastern qtp c 2017 elsevier ltd all rights reserved

slab breakoff as a mechanism for flipping of subduction polarity in taiwan we propose a model that involves breakoff of the east dipping eurasian slab beneath the taiwan orogen to account for the flipping of subduction polarity in northern taiwan the breakoff was initiated in southern ryukyu in the early pliocene and then propagated southwestward into taiwan like an opening zipper detachment of the eurasian slab has created a mantle window for the north dipping philippine sea plate to move in laterally causing a switch in the subduction polarity slab breakoff not only provides a testable model for the lithospheric structure of taiwan but also accounts for the high heat flow rapid uplift synorogenic extension deep focus earthquakes and north diminishing crustal contraction in the taiwan mountain belt

flexure and thickening of the lithosphere at the east pacific rise we have formulated a new class of plate bending equations which simulates the flexure of the lithosphere at mid ocean ridges the stress accumulation effect in a growing moving and thickening lithosphere significantly changes the flexural behavior it is shown that the growing plate flexes more easily than the conventional static plate due to the fact that the bending stress vanishes on the base of the plate we apply this new plate model to the east pacific rise compared with madsen et al 1984 the fits to the gravity and topography observations are improved assuming the thickness varies in proportion to the square root of distance from the ridge crest the best fitting thickening rate for the growing plate model is 0 7 km1 2 or 5 5 km m y 1 2 which further implies that the 600 or 700 c isotherm marks the bottom boundary of the effective elastic thickness of the lithosphere

evolutionary model for the taiwan collision based on physical modelling abstract 2 d and 3 d physical modelling of lithospheric convergence in the luzon taiwan ryukyu region is performed with properly scaled laboratory models the lithospheric model consists of two parts continental the asian plate ap and oceanic the philippine sea plate psp the oceanic lithosphere has one layer while the continental lithosphere includes both mantle and crustal layers the continental margin is covered by sediments a low viscosity asthenosphere underlies the lithosphere the opposing luzon and ryukyu subduction zones are initiated by inclined cuts made within the psp the subduction collision is driven by a piston pre collisional intraoceanic subduction along the luzon and ryukyu boundaries results in the formation of a transform zone between them with two tear faults at the ends the psp undergoes strong compression along this zone subduction of the chinese margin under the luzon boundary further increases the compression compressive stresses reach the yield limit of the psp in the arc area which is a weak zone in the experiments the plate fails at the western side of the arc along an eastward dipping fault the longitudinal valley fault underthrusting of the frontal wedge of the psp along this fault results in the closure of the fore arc basin and is then blocked the psp fails at the opposite side of the luzon arc along the westward dipping fault the failure releases lithospheric compression in this region and results in the initiation of southward propagating subduction of the psp under northeastern taiwan the incipient subduction zone becomes part of the southeastward retreating ryukyu subduction zone which allows the okinawa back arc rift to propagate into taiwan the taiwan collision thus includes the following succession of major processes over time or from south to north 1 an e w shortening of the psp in the luzon arc 2 a failure of this plate at the western side of the arc and the formation of the eastward dipping longitudinal valley fault the transient plate boundary 3 a closure of the fore arc basin and a rapid uplift of the orogen 4 a failure of the psp at the eastern side of the luzon arc partly overthrusting the orogen and the initiation of westward wn ward subduction of the psp 5 and finally back arc rifting in the rear of this incipient subduction zone i e in northern taiwan all these processes commence with some delay with respect to the preceding ones and propagate southwards

active detachment of taiwan illuminated by small earthquakes and its control of first order topography we use 110 000 small earthquakes to locate and map active faults in three dimensions within the taiwan arc continent collision the structure is dominated by a nearly horizontal band of small earthquakes at 10 km depth that is interpreted to seismically illuminate the main detachment zone of the mountain belt with other illuminated fault zones abutting the detachment zone the zone steepens below eastern taiwan to 30 90 and reaches depths of 30 60 km the three dimensional shape of the detachment zone in relation to topography allows a new test of critical taper wedge mechanics and suggests that the reversal of topographic slope across taiwan is controlled by the shape of the detachment

palaeoenvironmental records in holocene spanish tufas a stable isotope approach in search of reliable climatic archives tufa deposits are potential terrestrial archives of palaeoenvironmental and palaeoclimatic information this study assesses the potential of stable isotopic archives from two closely juxtaposed holocene tufa sites in se spain the ruidera site contains deep water lacustrine micrites and tufas whereas the nearby alcaraz site represents a shallow barrage tufa understanding site characteristics is critical to interpreting the stable isotopic variations these holocene lacustrine micrites have isotopic compositions consistent with modern european lake shore microbial carbonates where the isotopic chemistry is strongly influenced by hydrological and residence time effects all the lacustrine micrite d13c values were influenced by microenvironmental microbial effects to some degree because of these effects stable isotope data from lacustrine microbial micrites and tufas will not normally yield precise information on the isotopic composition of palaeoprecipitation temperature or vegetation composition of an area in contrast holocene tufas that formed in shallow fast flowing riverine settings may contain valuable palaeoclimatic archives the tufa deposits must be largely autochthonous as at alcaraz where in situ reed stem encrustations are present records of relative change in air temperature and changes in the source of airmasses are potentially resolvable in the d18o data these interpretations can be verified by other independent climatic data where chronology is constrained variations in riverine tufa d13c values probably record changes in local vegetation and or soil respiration covariation between d18o and d13c values may be intrinsically linked to climatic factors such as aridity tentative palaeoclimatic interpretations for the middle holocene at alcaraz based on the isotope data suggest warming or increasing influence of mediterranean sourced precipitation between approximately 5000 3000 radiocarbon years bp accompanied by increased aridity these interpretations are consistent with the sparse independent palaeoclimatic data and climate modelling results for the holocene of se spain this study supports the growing evidence that well chosen tufa sites could yield valuable palaeoclimatic information

constraints on backstop geometry of the southwest ryukyu subduction based on reflection seismic data abstract based on the analysis of 45 seismic reflection profiles the top of the ryukyu arc basement is mapped in the forearc region east of taiwan the ryukyu arc slope dips 10 trenchward while beneath the forearc basins the arc basement shows a series of morphologic along arc highs and lows one of the basement highs the nanao basement rise has been described as an area uplifted by the subduction of the gagua ridge the other one the hoping basement rise is suggested in this study to be an uplifted feature caused by the subduction or the underplating of some local asperity the nature of this asperity could either be a detached block of the luzon arc an isolated seamount or some material removed from the frontal part southernmost extremity of the ryukyu margin from seismic reflection profiles we infer that the right lateral transcurrent fault system located at the rear of the accretionary wedge defines the surface projection of the southern termination of the ryukyu arc basement two crustal sections across the ryukyu subduction system demonstrate that the backstop terminates in the form of a near vertical wall with its height over 5 km such an unusual geometry could be produced by crustal truncation at the toe of the backstop

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

oxygen isotopes in meteoric calcite cements as indicators of continental paleoclimate because meteoric water 18 o values decrease with decreasing ambient temperature and increasing latitude 18 o values of meteoric calcite cement should exhibit a similar relation with paleolatitude and be an indicator of continental paleotemperatures to test this we compiled isotopic and paleolatitude data for 20 meteoric cements and nine speleothems ranging in age from devonian to modern and in paleolatitude from 3 5 to 83 mean 18 o values for meteoric cements and speleothems both show the same negative correlation with paleolatitude the 18 o vs latitude trend for these carbonates is almost identical to that predicted for modern inland environments but differs from the trend for coastal environments this suggests that the ground water controlling the ultimate composition of meteoric cement is derived predominantly from inland recharge if it is assumed that the modern meteoric water 18 o vs temperature relation is valid for the past and that insignificant evaporation occurred prior to carbonate precipitation then coastal and inland paleotemperatures can be calculated from the 18 o values of meteoric calcite 18 o mcl and seawater 18 o sw by using the equations t coastal 13 3 32 6 0 231 0 0613 18 o mcl 18 o sw and t inland 17 8 16 2 0 572 0 1233 18 o mcl 18 o sw where t is temperature in c calcite precipitated from coastal meteoric water at temperatures between 0 and 25 c will exhibit a narrow range in 18 o 6 to 4 where 18 o sw 0 the 18 o of calcite precipitated from inland meteoric water will be sensitive to paleotemperature ranging from 14 to 5 where 18 o sw 0 for temperatures of 0 to 25 c

bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum abstract lacustrine shoreline depositional features in the bonneville basin western north america were investigated to chronicle paleolake expansion and contraction in response to climate change based on stratigraphy sedimentology geomorphology and radiocarbon dating this study identifies multiple intermediate to large lake intervals during marine isotope stage 3 and the last glacial maximum timing and magnitude of the bonneville basin lake size change are compared with those of hemispheric scale climate change events reported from the greenland ice sheet southwestern north america winter precipitation and east asian monsoon 18 o records the amount of precipitation received by surface water systems in the bonneville basin appears to have increased significantly during the greenland stades throughout the last half of mis 3 and early mis 2 the lake also underwent rapid large amplitude oscillations during the last glacial maximum

okinawa trough backarc basin early tectonic and magmatic evolution the okinawa trough lying between japan and taiwan is a backarc basin formed by extension within the continental lithosphere behind the ryukyu trench arc system stress directions associated with the two last extensional phases in the southwestern okinawa trough have been deduced from a comparison with analog modeling the direction of extension is n 150 o for the pleistocene phase of extension 2 0 1 ma and n 170 o for the late pleistocene holocene phase of extension 0 1 0 ma the present day ryukyu volcanic arc a narrow continuous feature extending from japan to taiwan is located on the eastern side of the okinawa trough 80 100 km above the wadati benioff zone the minimum depth for emplacement of arc magmatism scarce present day backarc volcanism appears in the middle and southern okinawa trough within linear en echelon bathymetric depressions a n045 o oriented seamount volcanic chain cuts across obliquely the southwestern okinawa trough and lies in the direct line of extension of the gagua ridge a n s linear volcanic feature of the philippine sea plate associated with this extension of the gagua ridge a large reentrant located at the base of the ryukyu prism the uplift of part of the nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross backarc volcanism could be tied to the subduction of the gagua ridge located there at a depth of 80 100 km beneath the backarc basin a second area of anomalous volcanism has been identified in the middle okinawa trough in the ene extension of the daito ridge a wnw ese 400 km long volcanic feature of the philippine sea plate we suggest that the gagua and daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere allowing magmas with arc affinities to erupt at the seafloor this excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts the okinawa trough is consequently still in an early stage of evolving from arc type to backarc activity

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

an oxygen isotope record of holocene climate change in the south central brooks range alaska abstract understanding the ecological and socio economic impacts of climatic warming requires knowledge of associated changes in moisture balance reconstructions of holocene moisture balance variation offer indispensible baseline information against which recent changes can be evaluated we analyzed chara stem encrustations in the sediments of takahula lake located in the south central brooks range of alaska for oxygen and carbon isotope composition to infer climatic change over the past 8000 years to help constrain climatic interpretations of the sediment 18 o record we also analyzed water samples from takahula and other lakes in the region for oxygen and hydrogen isotope composition results show that winter precipitation dominates the water balance of these lakes and that post input evaporation is a key control of lake water isotope composition of takahula lake stratigraphic patterns in chara 18 o supplemented by those in 13 c and sediment lithology reveal distinct changes in effective moisture precipitation minus evaporation over the past 8000 years effective moisture was relatively high from 8000 to 5000 cal bp with marked fluctuations between 6800 and 5000 cal bp it then decreased to reach a minimum around 4000 cal bp and increased with fluctuations from 4000 to 2500 cal bp followed by a decreasing trend toward the present that was interrupted by a wet little ice age centered at 400 cal bp aridity during the 20th century was among the highest of the entire 8000 year record at the millennial timescale the temporal patterns of moisture balance shifts at takahula lake are broadly coherent with those inferred from previous paleoclimate records from the region the chara 18 o values around 5600 cal bp and during the little ice age are up to 5 lower than at present and 3 6 lower than that of the modern input water to the lake these exceptionally low values suggest that factors other than effective moisture must have contributed to the pronounced variations in the takahula lake 18 o record increased winter precipitation associated with a westerly aleutian low position may account for 1 of the 18 o decrease other factors leading to the 18 o depletion during these periods probably include decreased temperatures as well as increased lake ice cover and associated reductions in evaporation

stable isotopes in charophyte incrustations relationships with climate and water chemistry abstract age gradients of stable c and o isotopes were found in modern chara hispida calcite incrustations allowing seasonal changes in water chemistry to be observed gradients resulted from apical calcification in growing charophytes in a regional study of 12 species and varieties of charophytes the carbonate 13c differed significantly with low value and high value species such as chara globularis and c baltica respectively samples from lakes and other stagnant waters had significantly higher 13c values than those sampled from flowing water the differences were related mainly to photosynthesis charophyte 18o carbonate was not significantly different between species but water chemistry was important for brackish water lamprothamnium papulosum the overall 18o carbonate was positively correlated with groundwater 18o and it is suggested that more reliable environmental information is available from 18o than 13c in charophyte marls the mean charophyte carbonate 13c and 18o was 5 7 and 6 4 vpdb respectively environmental temperature estimates suggested that at some sites the carbonate was deposited close to isotopic equilibrium but in others a slight to moderate disequilibrium was indicated

late holocene moisture balance variability in the southwest yukon territory canada abstract analyses of sediment cores from marcella lake a small hydrologically closed lake in the semi arid southwest yukon provides effective moisture information for the last 4500 years at century scale resolution water chemistry and oxygen isotope analyses from lakes and precipitation in the region indicate that marcella lake is currently enriched in 18 o by summer evaporation past lake water values are inferred from oxygen isotope analyses of sedimentary endogenic carbonate in the form of algal charophyte stem encrustations a record of the 18 o composition of mean annual precipitation at jellybean lake a nearby evaporation insensitive system provides data of simultaneous 18 o variations related to decade to century scale shifts in aleutian low intensity position the difference between the two isotope records represents 18 o enrichment in marcella lake water caused by summer effective moisture conditions results indicate increased effective moisture between 3000 and 1200 cal bp and two marked shifts toward increased aridity at 1200 and between 300 and 200 cal bp these prominent late holocene changes in effective moisture occurred simultaneously with changes in aleutian low circulation patterns over the gulf of alaska indicated by jellybean lake the reconstructed climate patterns are consistent with the topographically controlled climatic heterogeneity observed in the coastal mountains and interior valleys of the region today

what do we really know about early diagenesis of non marine carbonates abstract non marine carbonate rocks including cave spring stream calcrete and lacustrine palustrine sediments are susceptible to early diagenetic processes these can profoundly alter the carbonate fabric and affect paleoclimatic proxies this review integrates recent insights into diagenesis of non marine carbonates and in particular the variety of early diagenetic processes and presents a conceptual framework to address them with ability to study at smaller and smaller scales down to nanometers one can now observe diagenesis taking place the moment initial precipitates have formed and continuing thereafter diagenesis may affect whole rocks but it typically starts in nano and micro environments the potential for diagenetic alteration depends on the reactivity of the initial precipitate commonly being metastable phases like vaterite ca oxalates hydrous mg carbonates and aragonite with regard to the ambient fluid furthermore organic compounds commonly play a crucial role in hosting these early transformations processes like neomorphism inversion and recrystallization cementation and replacement generally result in an overall coarsening of the fabric and homogenization of the wide range of complex primary microtextures if early diagenetic modifications are completed in a short time span compared to the annual to millennial time scale of interest then recorded paleoenvironmental signals and trends could still acceptably reflect original depositional conditions however even compact non marine carbonate deposits may behave locally and temporarily as open systems to crystal fluid exchange and overprinting of one or more geochemical proxies is not unexpected looking to the future relatively few studies have examined the behaviour of promising geochemical records such as clumped isotope thermometry and non conventional stable isotopes in well constrained diagenetic settings ongoing and future in vitro and in situ experimental approaches will help to investigate and detangle sequences of intermediate diagenetic products processes and controls and to quantify rates of early diagenesis bridging a gap between nanoscale molecular lab studies and the fossil field rock record of non marine carbonates

extensional collapse of the northern taiwan mountain belt as an active collision zone between the luzon arc and the china continental margin the taiwan mountain belt particularly its south central part is undergoing crustal shortening and rapid uplift the northern part of the orogen is however subjected to crustal stretching and rifting as a result of flipping of subduction from the northwest facing luzon arc system to the south facing ryukyu arc system taiwan and its neighboring southern ryukyu used to be part of the rifted china continental margin before the collision started in late miocene time engineered by the northwest movement of the philippine sea plate in the past 5 m y the north south trending luzon arc obliquely overrode the northeast southwest trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest following the southwest propagating collision the north dipping philippine sea plate which was subducting beneath the ryukyu arc also extended westward and caused flipping of subduction in the northern part of the collision orogen in consequence the orogen lost the compressive support by the colliding plates and became subjected to lithospheric stretching induced by the trench suction the collision orogen collapsed as a result of crustal thinning and its central part foundered into a deep submerged basin a whole spectrum of active tectonic scenarios ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence can be readily observed in the taiwan ryukyu area and provides a vivid example for the process of orogenic collapse

centennial scale holocene climate variability revealed by a high resolution speleothem δ18o record from sw ireland evaluating the significance of holocene submillennial 18 o variability in the greenland ice cores is crucial for understanding how natural climate oscillations may modulate future anthropogenic warming a high resolution oxygen isotope record from a speleothem in southwestern ireland provides evidence for centennial scale 18 o variations that correlate with subtle 18 o changes in the greenland ice cores indicating regionally coherent variability in the early holocene evidence for previously undetected early holocene cooling events is presented but mid to late holocene ice rafting in the north atlantic appears to have had little impact on 18 o at this ocean margin site

stable isotope fossil coleoptera and pollen stratigraphy in late quaternary sediments from ontario and new york state stable oxygen isotope contents of marl deposits and molluscs from lakes and ponds in northern new york state u s a and southwestern ontario canada are remarkably uniform for carbonates formed between about 12 600 yr b p and 2000 yr b p this suggests relatively stable climatic conditions with slowly increasing temperatures throughout this time span an observation already indicated by fossil beetle data and re confirmed by additional data presented in this paper the variations seen in pollen diagrams probably are related to plant colonization and climatic parameters such as changing humidities this contrasts sharply with observations made in europe where variations in pollen diagrams are paralleled by changing 18o contents in lacustrine marls and molluscs which clearly reflect climatic temperature changes during late glacial and early postglacial times 13 500 9000 yr b p 13c contents in marls and molluscs are not directly dependent on climatic change but reflect changing environments with varying aquatic and terrestrial carbon contributions

significance of shallow marine and non marine algae stable isotope δ18o compositions over long periods example from the palaeogene of the paris basin in this study we test the potentiality of using dasycladales and charophytes calcareous shallow marine and non marine algae respectively as palaeoclimatic recorders these algae mineralize their carbonate during short periods in summer throughout the palaeogene we compare the 18o variation of these two taxa to identify a possible common factor influencing their isotopic composition i e temperatures variations from a local environmental signal we sampled and isotopically analyzed eight species of charophytes and seven species of dasycladales from 23 formations ranging from the palaeocene to the oligocene series of the paris basin by comparing the 18o of these two groups living in different environment with that of shallow marine mollusks from a previous study we show that temperature variations are the main factor influencing their 18o compositions and that local environmental effects do not screen the global thermal signal maximum annual palaeotemperatures are calculated from the 18o of the dasycladales and indicate by comparison with the data from mollusks previously analyzed that dasycladales species used probably mineralized their carbonate in equilibrium with sea water dasycladales recorded the global climatic events already known for the palaeogene with high temperatures reached during the early eocene and middle eocene climatic optimums and relative cooling intervals during the lutetian the priabonian and the rupelian charophyte gyrogonites also recorded temperature variations in their 18o compositions but reconstituting reliable temperature values in non marine environments is not directly possible and requires constraining 18o of local continental water using other proxies these promising results show that carbonates mineralized from algae constitute a reliable support for palaeoclimatic information and should be more widely used in the fossil record

east asia plate tectonics since 15 ma constraints from the taiwan region abstract 15 ma ago a major plate reorganization occurred in east asia seafloor spreading ceased in the south china sea japan sea taiwan sea sulu sea and shikoku and parece vela basins simultaneously shear motions also ceased along the taiwan sinzi zone the gagua ridge and the luzon ryukyu transform plate boundary the complex system of thirteen plates suddenly evolved in a simple three plate system eu ph and pa beneath the manila accretionary prism and in the huatung basin we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations these two patterns are rotated by 15 they were formed by seafloor spreading before 15 ma and belonged to the same ocean named the taiwan sea half spreading rate in the taiwan sea was 2 cm year from chron 23 to 20 51 to 43 ma and 1 cm year from chron 20 43 ma to 5b 15 ma five plate kinematic reconstructions spanning from 15 ma to present show implications concerning the geodynamic evolution of east asia amongst them the 1000 km long linear gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the ph sea plate the formation of taiwan was driven by two simple lithospheric motions i the subduction of the ph sea plate beneath eurasia with a relative westward motion of the western end a of the ryukyu subduction zone ii the subduction of eurasia beneath the philippine sea plate with a relative southwestward motion of the northern end b of the manila subduction zone the luzon arc only formed south of b the collision of the luzon arc with eurasia occurred between a and b east of a the luzon arc probably accreted against the ryukyu forearc

isotope signature of the younger dryas and two minor oscillations at gerzensee switzerland palaeoclimatic and palaeolimnologic interpretation based on bulk and biogenic carbonates oxygen and carbon isotope ratios in the carbonate of benthic ostracodes pseudocandona marchica and molluscs pisidium ssp were measured across the transitions bordering the younger dryas chronozone in littoral lacustrine cores from gerzensee switzerland the specific biogenic carbonate records confirm the major shifts already visible in the continuous bulk carbonate oxygen isotope record 18occ if corrected for their vital offsets oxygen isotope ratios of pisidium and juvenile p marchica both formed in summer are almost identical to 18occ this bulk carbonate is mainly composed of encrustations of benthic macrophythes chara ssp also mainly produced during summer adult p marchica which calcify in winter show consistently higher 18o larger shifts across both transitions and short positive excursions compared with the summer forms especially during early preboreal despite such complexity the 18o of adult p marchica probably reflects more accurately the variations of the 18o of former lake water because during winter calcification temperatures are less variable and the water column isotopically uniform the difference between normalised 18o of calcite precipitated in winter to that formed in summer can be used to estimate the minimum difference between summer and winter water temperatures in general the results indicate warmer summers during the late allerod and early preboreal compared with the younger dryas altogether the isotopic composition of lake water 18ol and of the dissolved inorganic carbonate 13cdic reconstructed from adult pseudocandona marchica as well as the seasonal water temperature contrasts indicate that the major shifts in the 18o of local precipitation at gerzensee were augmented by changes of the lake s water balance with relatively higher evaporative loss occurring during the allerod compared with the younger dryas it is possible that during the early preboreal the lake might even have been hydrologically closed for a short period we speculate that such hydrologic changes reflect a combination of varying evapotranspiration and a rearrangement of groundwater recharge during those climatic shifts

climate and environment during the younger dryas gs 1 as reflected by composite stable isotope records of lacustrine carbonates at torreberga southern sweden climatic and environmental changes during the younger dryas stadial gs 1 and preceding and following transitions are inferred from stable carbon and oxygen isotope records obtained from the sediments of ancient lake torreberga southern sweden event gs 1 is represented in the sediment sequence by 3 5 m of clay containing lacustrine carbonates of various origins comparison of isotopic records obtained on mollusc shells ostracod valves and chara encrustations precipitated during specific seasons of the year supports estimates of relative changes in both lake water and mean annual air temperatures variations in soil erosion rates can also be estimated from a simple isotope mass balance model to separate allochthonous and autochthonous carbonate contributions to the bulk carbonate content of the sediments the well known rapid climatic shifts characterising the last termination in the north atlantic region are clearly reflected in the isotopic data as well as longer term changes within gs 1 following maximum cooling shortly after the allerod younger dryas gi 1 gs 1 transition a progressive warming and a slight increase in aquatic productivity is indicated at the younger dryas preboreal gs 1 pb transition mean annual air temperature rapidly increased by more than 5 c and summer lake water temperature increased by ca 12 c the subsequent preboreal oscillation is characterised by an increase in soil erosion and a slight decrease in mean annual air temperature these results are in harmony with recent findings about large scale climate dynamics during the last termination copyright 1999 john wiley sons ltd

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

ecosystem response to lateglacial and early holocene climate oscillations in the great lakes region of north america abstract fossil pollen plant macrofossils gastropods and elemental and stable isotope geochemistry in a sediment core from twiss marl pond southern ontario canada were used to document climate oscillations during the last glacial interglacial transition 13 000 8500 14 c bp and understand their ecological effects chronology was provided by ams 14 c dating and regional pollen correlation oxygen isotope 18 o results from mollusc shells chara encrustations and bulk carbonates show a classic climate sequence of a warm bolling allerod boa at 12 500 10 920 14 c bp a cold younger dryas yd at 10 920 10 000 14 c bp the holocene warming at 10 000 14 c bp a brief preboreal oscillation pb at 9650 14 c bp and a possible gerzensee killarney g k cooling shortly before 11 000 14 c bp clay sediments at the base of the core contain high herb and shrub pollen and abundant arctic alpine plant macrofossils indicating a treeless tundra with severe soil erosion in watershed during the boa warm period authigenic marl began to be deposited and picea woodland became established the establishment of picea woodland after peaks of 18 o and of carbonate accumulation suggests a lagged response of upland vegetation to boa warming in contrast the occurrence of warmth loving aquatics najas flexilis and typha latifolia at that time indicates sensitive responses of aquatic plants the yd cooling is indicated by a 1 5 negative excursion in 18 o an increase in minerogenic matter and higher concentrations of erosion derived elements al na k ti and v pollen data show no forest transformation in response to yd cooling which is attributed to the insensitive nonecotonal vegetation at that time however more openings in the forests and increased erosion in the watershed are indicated by a slight increase of herb pollen high concentrations of erosion elements and a pediastrum peak the onset of the holocene was marked by an abrupt increase of 2 in 18 o and the replacement of picea woodland by pinus dominated forest the picea recurrence at 9650 14 c bp demonstrates sensitive response of ecotonal vegetation to the pb climate oscillation which is also indicated by 0 4 negative excursion of 18 o these new results suggest the importance of multiproxy records for reliable paleoclimate reconstruction reevaluation and revised chronologies of previously published sites gage street and nichols brook in the eastern great lakes region show their major 18 o shifts correlative to the yd and pb oscillations as documented from twiss marl pond and nearby crawford lake the sequence and magnitude of climatic oscillations from these sites match in detail with records from the atlantic seaboard suggesting that these oscillations are an expression of broad scale probably global climate change rather than local meltwater induced climate cooling