paleovegetation simulations of lowland amazonia and implications for neotropical allopatry and speciation paleovegetation modeling simulations of the lowland amazon basin were made to assess the relative importance of glacial climate and atmospheric co2 for altering vegetation type and structure as well as to explore the potential physiological mechanisms underlying these ecosystem level responses modeling results support the view that widespread invasion of grasslands into the amazon lowlands during the last glaciation was not likely glacial cooling was probably responsible for maintaining glacial forest cover via its effects in reducing photorespiration and decreasing evapotranspiration which collectively improve plant carbon and water relations modeling results confirm that leaf area index lai a common proxy for canopy density is highly sensitive to independent and interactive changes in climate and low concentration of atmospheric co2 and the results show considerable region to region variation during the last glaciation heterogeneous variations in glacial vegetation lai may have promoted allopatric speciation by geographically isolating species called vicariance in the forest sub canopy the proposed vicariance hypothesis incorporating spatial variations in canopy density conforms to many of the essential tenets addressed by previous neotropical speciation models but also helps to overcome some of their inconsistencies c 2001 university of washington

development of single crystal σ shaped quartz porphyroclasts by dissolution precipitation creep in a calcite marble shear zone abstract within a greenschist facies calcite marble shear zone isolated quartz grains change shape across the shear zone profile whereas quartz grains have a spherical to elongated shape in the coarse grained marble protolith and protomylonite they are asymmetric shaped porphyroclasts with wedge shaped appendages wings in ultramylonites in all cases quartz grains are single crystals they are sometimes twinned but never recrystallized stress induced dissolution precipitation creep is the favourable shape controlling process during deformation providing a relatively undeformed core truncation of pre existing cathodoluminescence cl patterns and syntaxial precipitation of wings the necessary fluids may have been released from fluid inclusions during dynamic recrystallization of the calcite matrix the development of shape is not related to the crystallographic orientation of the quartz porphyroclasts crystallographic orientation analysis by electron backscatter diffraction ebsd and cl analyses exclude crystal plasticity as a shape controlling mechanism of quartz grains during mylonitisation however in ultramylonites quartz clasts have a strong crystallographic preferred orientation cpo with c axes sub parallel to the shear direction this fabric is uncommon for quartz under greenschist facies conditions it might be explained by a strengthening of a pre existing weak cpo during mylonitisation by rigid particle rotation of elongated quartz grains

40ar 39mineral ages from the scituate granite rhode island implications for late palaeozoic tectonothermal activity in new england j i gil ibarguchi abstract the alkalic scituate granite was emplaced into crystalline sequences within the new england esmond dedham terrane in the late devonian c 370 ma variably recrystallized amphibole iron rich hastingsite hastinpitic hornblende from four variably deformed samples of the pluton record south westerly younging ar ar plateau ages ranging between 276 and 263 ma these are interpreted to date diachronous cooling through temperatures appropriate for intracrystalline retention of argon following late palaeozoic orogenic activity iron rich biotite concentrates from the samples record only slightly younger ages and therefore suggest relatively rapid post metamorphic cooling the ar ar ages indicate that the late palaeozoic tectonothermal overprint was much more regionally pervasive than was previously considered the apparent timing of this activity is similar to previous estimates for the chronology of high grade metamorphism throughout the adjacent hope valley terrane and for phases of ductile movement on the intervening lake char honey hill fault system

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

fluctuations of eolian flux and ocean productivity in the mid latitude north pacific during the last 200 kyr abstract in order to understand fluctuations in terrestrial and marine environments a sedimentary core h3571 was investigated from the hess rise located in the mid latitude north pacific under the north westerly wind system the 18 o grain size and grain shape of type 1 quartz suggest that this quartz is of aerosol origin good correlation between al and aerosol quartz in content and mass accumulation rate mar indicates that the alumino silicate minerals in the sediments are mainly transported by wind mar of mineral aerosol maraerosol varies from 156 to 732 mg cm 2 kyr 1 during the last 200 kyr the maraerosol maxima occur in oxygen isotope stage ois 4 to latest ois 5 middle ois 6 moderate maxima occur in early ois 1 2 late ois 3 and middle ois 3 these maxima are ascribed to reduced precipitation during the summer monsoon and to strengthened wind speed during the winter monsoon the mean organic carbon total nitrogen atomic ratio is 7 2 suggesting that the organic matter in the core h3571 is also mainly of marine origin the mar of organic carbon marorganic exhibits two prominent maxima in ois 2 and 4 and relatively high values in middle and late ois 6 enhanced primary productivity is most likely to be responsible for the high burial rate of organic carbon in the sediments carbonate and phosphorus inputs with aerosol into sea surface have played a minor role through dissolution in diminishing pco2 in surface water during glacial times on the other hand the aerosol silica supply to the ocean may have some potential to affect the burial of biogenic silica into sediments the effect of mineral aerosol on the ocean carbon cycle would be greater in the coastal and hemipelagic regions of the western pacific and equatorial atlantic as compared with that in the hess rise regime

tropical atlantic coral oxygen isotopes glacial interglacial sea surface temperatures and climate change abstract we have generated a detailed oxygen isotope time series from the fossil coral reefs from offshore barbados the barbados coral based record is a unique paleoceanographic data set with an equivalent sedimentation rate in excess of 600 cm kyr where not only is the annual signal uniquely preserved but seasonality as well oxygen isotope values during the late glacial and lgm 16 20 14c kyrs 19 24 calendar kyrs are 2 3 heavier than corresponding living specimens and indicate a regional cooling on the order of 4 5 c there is also an isotopic expression of the bolling pre boreal climate oscillation with values reflecting a cooling during the younger dryas seasonality a key diagnostic of the state of the climate system remained the same or slightly less than present and indicates that the observed coolings were a change in the mean state of the western tropical atlantic pan tropic cooling during the last glaciation is best explained by a change in the radiative balance of the tropics variable tropical sea surface temperatures during climate oscillations such as the younger dryas challenge the paradigm that climate change only cascades from variations in north atlantic deep water production

synmagmatic deformation patterns in the old woman mountains se california abstract synmagmatic structures within granitic plutons may provide insight into the interplay between plutonism and regional deformation at mid crustal levels within the late cretaceous old woman pluton mojave desert se california synmagmatic structures include magmatic fabrics parallel to wall rock foliations melt filled shear zones folded gneissic xenoliths and schlieren with axial planar magmatic fabric deformation continued below granite solidus temperatures in shear zones on the pluton margins these structures permit reconstruction of a sheet like pluton that was emplaced under regional extension taken together with published thermochronometric data the synmagmatic structures constrain the role played by magmatic events in the collapse of a thickened crustal section the post plutonic cooling history suggests rapid uplift and denudation ending by 65 ma we argue that extensional deformation overlapped and post dated pluton emplacement and may have contributed to tectonic unroofing we suggest that magma emplacement can trigger subsequent extensional collapse in overthickened crustal blocks

glacial interglacial organic carbon record from the makassar strait indonesia implications for regional changes in continental vegetation abstract recent studies convincingly show that climate in the western pacific warm pool and other equatorial tropical regions was significantly colder by 3 4 c during glacial periods prompting a reexamination of the late pleistocene paleoenvironments of these regions this study examines changes in continental vegetation during the last two deglaciations terminations i and ii using a sediment core md9821 62 recovered from the makassar strait indonesia evidence based on the lignin phenol ratios suggests that vegetation on borneo and other surrounding islands did not significantly change from tropical rainforest during the last two glacial periods relative to subsequent interglacial periods this supports the hypothesis that the winter monsoon increased in strength during glacial periods allowing indonesia to maintain high rainfall despite the cooler conditions

terrestrial organic carbon accumulation on the amazon deep sea fan during the last glacial sea level low stand abstract sediment cores from the amazon deep sea fan recovered during r v meteor cruise 16 2 show in detail the modern areal distribution of sedimentary organic carbon stable organic carbon isotopes of the organic matter om as well as variations in the depositional processes in addition we studied up to 300 m long drilled sediment records recovered during odp leg 155 which allow evaluation of temporal variations on the amazon fan our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea level change over the middle and lower amazon fan to estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the amazon fan we used stable organic carbon isotopes of the om 13 c org organic carbon content corg and age models based on oxygen isotopes faunal data and magnetic excursions following our results the organic carbon accumulation on the amazon deep sea fan is controlled by glacio eustatic sea level oscillations interglacial sea level high stand sediments are dominated by marine om whereas during glacial sea level low stands terrestrial organic carbon is transported beyond the continental shelf through the amazon canyon and deposited directly onto the amazon deep sea fan glacial sediments of the amazon fan stored approximately 73 1015 g terrestrial corg in 20 000 years or 3 7 1012 g terrestrial corg yr 1 equivalent to 7 12 of the riverine organic carbon discharge assuming constant paleo discharge which is about the same amount of terrestrial organic carbon as deposited on the amazon shelf today 3 1 1012 g terrestrial corg yr 1 or 6 10 of the modern riverine organic carbon discharge

timing of intrusion of the narragansett pier granite relative to deformation in the southwestern narragansett basin rhode island the pennsylvanian sediments of the narragansett basin rhode island were deformed during the al leghanian orogeny and record the effects of alleghanian deformation in southeast new england without the complication of earlier structures during this deformation the basin was intruded at its southwestern corner by the narragansett pier granite which has a crystallization age of 273 ma mapping of basin metasediments along the narragansett bay shore in the southwestern portion of the basin reveals features formed by several episodes of deformation two generations of isoclinal folds along north trending axes f1a and f1b are the earliest structures in the area followed by a set of small closed folds f2 also on north trending axes the fla f1b and f2 folds are the result of east west closure of the basin minor sinistral and more significant dextral motion on faults within the beaverhead shear zone produced local east trending crenulations s3 and open folds with north trending axes f4 in the study

palaeoenvironmental developments in the lake tondano area n sulawesi indonesia since 33 000 yr b p abstract geo morpho logical sedimentological and ecological developments in the lake tondano area since 33 000 yr b p and limnological changes in the moderately sized lake situated at 680 m asl in the northern part of sulawesi indonesia are discussed first the environmental setting of the lake is presented study of the regional distribution of lacustrine sediments and a detailed analysis of their sedimentary facies texture organic matter content suggest major changes in size and depth of the lake and in past sedimentation insight into the long term development of the lake sedimentation processes is highly relevant for sustainable use of the present lake analysis of diatom assemblages provides further detail of the changing aquatic settings of the lake lake levels rise quickly around 33 000 and 12 000 yr b p fall dramatically between 30 000 and 13 000 yr b p and are lowered gradually since approximately 6000 yr b p following early holocene high lake levels drainage of the lake is affected by both volcanic depositional events and regional climatic events palynological analysis is indicative of local palaeoecological settings in the lake area and regional climatic change a distinct late pleistocene phase with lower precipitation and lowered mean temperatures is inferred furthermore progressive deforestation of the tondano uplands is evident as well as diffuse anthropogenic volcanic vegetation disturbance from the early mid holocene onwards information from sedimentary facies diatom assemblages and local palaeoecology pollen are integrated to reconstruct palaeoenvironmental settings and processes in the lake area this record of environmental change as well as the pollen based record of regional vegetation and climate change corroborates other palaeoenvironmental data derived from the few terrestrial sites in the region the data attribute a greater magnitude of temperature and precipitation change in the region than is commonly deduced in studies based on marine faunal and sedimentary records the lake tondano sedimentary record is highly suitable for further analysis aimed at determining the exact timing and amplitudes of environmental change in the se asian equatorial region

supplemental material zircon and monazite geochronology in the palmer zone of transpression south central new england usa constraints on timing of deformation high grade metamorphism and lithospheric foundering during late paleozoic oblique collision in the northern appalachian orogen analytical methods for zircon u pb and monazite th pb sims geochronology zircon u pb la icp ms geochronology data tables and supporting previous work

late devonian carboniferous detachment faulting and extensional tectonics in western cape breton island nova scotia canada abstract shallow dipping detachment faults have played a key role in the evolution of the late devonian to carboniferous maritimes basin of western cape breton island the faults are responsible for large scale post orogenic crustal thinning and denudation of mid crustal levels tournaisian and westphalian clastic sedimentation can be related to detachment faulting along the margaree shear zone msz and the ainslie detachment ad respectively the msz consists of thick shallow dipping retrogressive mylonite overprinted by cataclastic horizons brittle detachment faults and chloritic breccia the shear zone crosscuts and transports low grade late devonian bimodal volcanic rocks and redbeds of the fisset brook formation in its hanging wall towards the west and juxtaposes them against exhumed medium to high grade metamorphic rocks and basement in its footwall locally the mylonite is 200 700 m thick and outcrops along strike from north to south for approximately 60 km tournaisian coarse clastic units and debris flow deposits of the horton group unconformably overlie ductile mylonite of the msz due to incision of brittle faults into the msz regional transgression and marine flooding of the extensional complex and exhumed units are marked by the thick visean carbonate and evaporite deposits of the windsor group the carbonates reflect a relatively quiescent tectonic regime and widespread subsidence was likely due to the cessation of extension related thermally induced buoyancy in a tectonically thinned crust the ainslie detachment nucleated as a regional flat lying fault along the carbonate evaporite contact at the top of the macumber formation forming calc mylonite near the base of the windsor group significant stratigraphic omissions in the windsor group above the detachment provide clear evidence of an extensional regime during faulting clastic deposits of the westphalian cumberland group are bounded by the detachment and sedimentation is related to listric normal faults which cut down section towards the west southwest the documentation of detachment faults has widespread implications for the interpretation of the post orogenic evolution of the northern appalachians an extensional regime can now be recognized deep reflection seismic data are interpreted in light of the new findings and can be related to late devonian carboniferous basin formation

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

regional differences in pb isotopic compositions of feldspars in plutonic rocks of the northern appalachian mountains u s a and canada a geochemical method of terrane correlation feldspar pb isotopic compositions from paleozoic tonalitic to leucogranitic caledonian plutons from the northern appalachian mountains of the u s a and canada range from nonradiogenic to radiogenic relative to the evolution curve of stacey and kramers 1975 pb isotopic values in the feldspars are generally independent of modal and major and trace element contents of the plutons plutons with the least radiogenic pb isotopic signatures northern group have intruded allochthonous rocks closest to the north american craton and plutons with the most radiogenic pb southern group have intruded avalonian basement feldspars from plutons in the central group have intermediate pb isotopic compositions between the northern and southern groups and do not define an isotopically unique group the predominant source of the felsic magmas was the continental lithosphere as indicated by the general pb isotopic similarity of the plutonic feldspars with either grenville or chain lakes basement in the case of the northern group and with avalonian basement rocks in the case of the southern group the source region for plutons in the central group may have contained a mixture of grenvillian and avalonian components plutons in the northern appalachians are as a group more evolved in their pb isotopic compositions relative to caledonian plutons in the british isles

a comparison of quartz c axis preferred orientations in experimentally deformed aplites and quartzites the effect of feldspar on the development of quartz c axis preferred orientations was investigated by experimentally deforming aplite 30 quartz and pure quartzite under equivalent conditions and comparing the quartz c axis patterns axial compression experiments were performed at temperatures of 800 and 900 c strain rates of 10 6 and 10 5s 1 and a confining pressure of 1500 mpa under these conditions both quartz and feldspar deform by dislocation creep with only minor syntectonic recrystallization the quartz c axis preferred orientations produced in the two rock types at equivalent deformation conditions and quartz grain strains were found to be essentially identical in pattern and strength these results indicate that the presence of feldspar has little or no effect on the operative slip systems in adjacent quartz grains in quartzo feldspathic rocks and that quartz c axis preferred orientation analyses can be performed on a wide range of crustal rock types

palaeoecology and climate of the amazon basin during the last glacial cycle our interpretation of the available palynological data from the amazon basin is that they show a long history of continuous occupation by forest we have thoroughly reviewed the accumulated data leading to this conclusion elsewhere but briefly recapitulate the arguments here one implication of this botanical reconstruction if correct is that interpretations of geomorphological features requiring an arid land surface for glacial age amazonia require reassessment copyright 2000 john wiley sons ltd

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

palynology of eastern indonesian marine piston cores a late quaternary vegetational and climatic record for australasia abstract pollen analyses of late quaternary sediments from nine marine piston cores reveal a continuous vegetation and environmental record for eastern indonesia and northern australia on the island of halmahera a montane oak forest largely replaced the tropical lowland vegetation during the last glacial period while fern cover was strongly reduced during its maximum 18 000 yr b p climate was cooler and slightly drier than today around 10 000 yr b p mangrove vegetation expanded following the rising sea level in our western new guinea record at 14 000 yr b p climate grew warmer and slightly wetter until it stabilised around 10 000 yr b p at that time the mid to upper montane forests expanded to their full altitudinal range and fern cover increased while montane oak forest grassland and woodland areas had contracted in our marine pollen records during the last glacial the climate of northern australia was distinctly drier than today grassland vegetation with sedges increased considerably at 38 000 and 24 000 yr b p replacing eucalypt forest and culminating in a maximum grassland cover at the height of the last glaciation 18 000 yr b p the rapid sea level rise allowed the expansion of mangrove forests and salt bush marshes which had become established on the large tidal flats of the drowning sahul shelf around 12 000 yr b p one piston core g6 4 extends to 300 000 yr b p and shows that glacial periods are characterized by high pollen concentrations in marine sediments recording expanding grassland vegetation during interglacial woodland and fern cover increased while pollen concentrations in the sediments were low after 190 000 yr b p a more open vegetation suggests that conditions were in general much more arid than before repeated mangrove vegetation expansions suggest major rises in sea level at around 244 000 220 000 and 130 000 yr b p

differential response of zircon u pb isotopic systematics to metamorphism across a lithologic boundary an example from the hope valley shear zone southeastern massachusetts usa a detailed morphological chemical and isotopic study of zircons from a single outcrop of two mineralogically and chemically distinct units of the late precambrian ponaganset gneiss was undertaken to investigate the effects of mylonitization and metamorphism on u pb isotopic systematics late paleozoic amphibolite grade approx 600 c mylonitization of the ponaganset gneiss at this locality is associated with movement along the hope valley shear zone the response of zircon to metamorphism in each gneiss unit is distinct zircons in gray augen gneiss are uncorroded and not overgrown whereas zircons from fluorite bearing pink granitic gneiss are variably corroded and over 50 bear opaque overgrowths the zircon overgrowths are chemically distinct from the primary cores and contain high conentrations of hf u hree and th mylonite derived from the gray gneiss contains only a small population of hf u rich metamorphic zircon but zircons in the pink gneiss derived mylonite are dominated by the hf u rich metamorphic component in terms of their u pb isotopic systematics overgrowth free zircons from both units are markedly discordant gray 10 20 pink 35 but overgrown zircons from the pink gneiss are up to 70 discordant zircons from the mylonites yield younger pb pb and u pb ages than those of the protolith gneisses and isotopic data from each gneiss mylonite pair define a linear array on concordia plots upper intercept ages of the gray gneiss 621 27 ma and the pink gneiss 635 50 ma indicate that the crystallization of both units was coeval and the lower intercept ages gray 270 92 ma pink 285 26 ma fall within the range of other published age estimates for alleghanian metamorphism in southeastern new england e g zartman et al 1988 new growth of zircon suggests that zr was mobile during metamorphism the presence of fluorite in the pink gneiss and a discontinuity in log left f text h text 2 text o mathord left vphantom f text h text 2 text o f text hf right kern nulldelimiterspace f text hf right values obtained from biotite across the pink gneiss gray gneiss contact indicates that dissolution and reprecipitation of zircon may be related to local variations in hf fugacity zircon dissolution reprecipitation in the pink gneiss and the lack of similar features in the contiguous gray gneiss suggests that the degree of isotopic perturbation of zircon during metamorphism is related to bulk chemistry fluid chemistry and or the degree of fluid rock interaction

south and southeast brazilian grasslands during late quaternary times a synthesis fourteen pollen records from the south s and the southeast se brazilian regions have been synthesised late glacial records from s brazilian highlands document the predominance of grassland campos where today araucaria forests occur records from se brazil show that during pre and full glacial times modern tropical semideciduous forest and cerrado savanna to dry forest were mostly replaced by grassland and some subtropical gallery forest modern montane araucaria forests and cloud forests in se brazil were mostly replaced by grassland during pre and full glacial times there is evidence that the modern tropical atlantic rainforest in s brazil was significantly reduced and replaced by cold adapted forest taxa or grassland during glacial especially during full glacial times the synthesis indicates that grasslands dominated the s and se brazilian landscape during the late pleistocene where today different forest ecosystems exist grassland extended over 750 km from s to se brazil from latitudes of about 28 27 s to at least 20 s these results indicate that climates in the region were markedly drier and 5 7 c cooler during glacial times antarctic cold fronts must have been much stronger and more frequent than today studies from s brazil show that huge areas of late pleistocene campos vegetation were still found on the s brazilian highlands during early and mid holocene times reflecting dry climatic conditions with an annual dry period of probably 3 months modern wet climatic conditions with no or only short dry periods were not established until the late holocene period when araucaria forests replaced large areas of grassland vegetation after about 3000 14c yr b p and especially after 1500 1000 14c yr b p

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

millennial reoccurrence of century scale abrupt events of east asian monsoon a possible heat conveyor for the global deglaciation high resolution sediment records from the south china sea reveal a winter monsoon dominated glacial regime and a summer monsoon dominated holocene regime during the last glacial cycle a fundamental change between regimes occurred during deglaciation through a series of millennial reoccurrences of century scale changes in the east asian monsoon eam climate these abrupt events centered at 17 0 15 9 15 5 14 7 13 5 13 9 13 3 12 1 11 5 and 10 7 14c ka correlate well with the millennial scale events in the santa barbara basin and the arabian sea i e a relationship between eam and el nino southern oscillation systems the abrupt increases in summer monsoon imply enhanced heat transport from low latitude sea area to the midlatitude high latitude land area the phase relationship between events of eam and ice sheet may reflect a faster eam response and a slower ice sheet response to the insolation change a far reaching conclusion is that the eam might have triggered the northern hemisphere deglaciation

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

phase boundary mobility in naturally deformed high grade quartzofeldspathic rocks evidence for diffusional creep abstract grain shape fabrics and optical microstructures of some quartzofeldspathic rocks deformed under upper amphibolite facies conditions in the southwestern grenville province ontario canada suggest that quartz and feldspar have accommodated intracrystalline plastic strains by both diffusional and dislocation creep in these rocks quartz and feldspar form polycrystalline domains separated by gently curved and locally cuspate phase boundaries whose morphology is similar in certain respects to the phase boundary morphology of rocks annealed experimentally under hydrostatic stress conditions in the naturally deformed rocks however phase boundary cusps consistently point along the foliation and parallel to the mineral fibre lineation i e in directions of inferred finite extension which implies that phase boundary motion and cusp formation occurred during deformation optical microstructures in feldspar and crystallographic preferred orientations in quartz are consistent with the accommodation of some intracrystalline plastic strains by dislocation creep however the morphology of quartz feldspar phase boundaries cannot be explained by either dislocation creep or static annealing alone we propose that phase boundary motion resulted from a diffusion assisted process involving dissolution at foliation parallel quartz feldspar phase boundaries mass transfer over length scales of the order of feldspar domain size 200 m or greater and precipitation at quartz feldspar phase boundary cusps this study extends the range of natural deformation conditions under which diffusional creep has been identified in quartzofeldspathic rocks it also has important implications for the natural rheological behavior of the mid and lower continental crust

sense of shear in high temperature movement zones from the fabric asymmetry of plagioclase feldspars abstract a new method for determining the sense of shear in plagioclase bearing tectonites from the 010 orientation of plagioclase feldspar is presented the method is based on the asymmetry of the 010 plane with respect to the structural frame foliation and lineation and the dominant activity of the 010 slip plane in the high temperature plasticity of plagioclase feldspar using examples from the zabargad gneisses red sea the method is applied to plagioclases of an25 an45 and compared with other methods of shear sense determination quartz c axis fabrics and microstructural criteria

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

alleghanian polyphase deformation of the hope valley shear zone southeastern new england structural petrographical and rb sr isotopic studies in the highly deformed basement rocks of southern rhode island have allowed the identification of the southern continuation of the hope valley shear zone hvsz previous work recognized the hvsz as an alleghanian tectonic boundary separating the distinct late precambrian esmond dedham and hope valley terranes in southeastern new england two important components of the esmond dedham terrane the late precambrian ponaganset gneiss and the devonian scituate granite gneiss now have been traced with structural continuity into southern rhode island the distribution of these gneissic units and their structures shows that the southern segment of the hvsz has been strongly deformed abruptly deflecting it from a nw se orientation to a n s trend the deflection of the hvsz marks an abrupt structural boundary between two distinct regionally developed mineral lineation domains a northwestern domain with north to nnw trends characteristic of most of the hvsz and a southeastern domain with ne trends structural relations suggest that all mineral lineations were originally parallel along the hvsz with a north to nnw trend the deflection formed during a subsequent phase of ductile right lateral shear producing a clockwise rotation of both lineations and the hvsz in southern rhode island thus basement gneisses in southeastern new england have suffered polyphase alleghanian deformation at high metamorphic grades it has been argued that during the late paleozoic southern new england was located in a structural transition zone between convergent tectonics in the central and southern appalachians and wrench tectonics in the northern appalachians the structural link between these two distinct tectonic regimes is an e w right lateral transcurrent fault the late dextral shear deformation described in southern rhode island basement rocks appears to have resulted from right lateral movement at depth within this transcurrent fault zone

diffusion creep and partial melting in high temperature mylonitic gneisses hope valley shear zone new england appalachians usa field petrographic microstructural and isotopic studies of mylonitic gneisses and associated pegmatites along the hope valley shear zone in southern rhode island indicate that late palaeozoic deformation c 275 ma in this zone occurred at very high temperatures 650 c high energy cuspate lobate phase boundary microstructures a predominance of equant to sub equant grains with low internal lattice strain and mixed phase distributions indicate that diffusion creep was an important and possibly predominant deformation mechanism field and petrographic evidence are consistent with the presence of an intergranular melt phase during deformation some of which collected into syntectonic pegmatites rb sr isotopic analyses of tightly sampled pegmatites and wall rocks confirm that the pegmatites were derived as partial melts of the immediately adjacent isotopically heterogeneous mylonitic gneisses the presence of syntectonic interstitial melts is inferred to have permitted a switch from dislocation creep to melt enhanced diffusion creep as the dominant mechanism in these relatively coarse grained mylonitic gneisses 200 500 lm syn deformational grain size a switch to diffusion creep would lead to significant weakening and may explain why the hope valley shear zone evolved into a major regional tectonic boundary this work identifies conditions under which diffusion creep operates in naturally deformed granitic rocks and illuminates the deformation processes involved in the development of a tectonic boundary between two distinct late proterozoic avalonian basement terranes

fluid inclusion evidence for basement decompression during permo triassic extension se new england usa co2 bearing fluid inclusions in strongly lineated but weakly foliated late precambrian gneisses within the hope valley shear zone of connecticut and rhode island are of mixed composition xco2 0 1 7 wt nacl equivalent and variable density 0 59 0 86 g ml and occur mainly as isolated inclusions also present are dilute 3 wt nacl equivalent aqueous inclusions which occur on healed fractures related to greenschist facies retrograde metamorphism isochores for dense isolated co2 bearing inclusions indicate pressures of 7 5 9 kbar at 500 600 c the estimated temperature conditions of peak metamorphism published 40ar 39ar hornblende plateau age spectra indicate cooling through about 500 c at 265 5 ma isochores for low density co2 bearing inclusions and aqueous inclusions intersect at the conditions of retrograde metamorphism 325 400 c and indicate pressures of 3 4 kbar published 40ar 39ar biotite plateau ages indicate cooling through about 300 c at 250 5 ma these data define a p t uplift curve for the region which is convex towards the temperature axis and indicate uplift rates between 0 4 and 3 3 mm year in permian time exhumation of basement gneisses was coeval with normal west down motion along the regional basement cover contact honey hill lake char willimantic fault system and is interpreted as due to post orogenic extensional collapse of the alleghanian orogeny

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

late quaternary palaeoecology palynology and palaeolimnology of a tropical lowland swamp rawa danau west java indonesia abstract sedimentological limnological and palynological analyses of a sediment core from a lowland site in west java indonesia provide a detailed palaeoenvironmental record for the late glacial and the holocene the record suggests open vegetation under inferred drier climatic conditions for the late glacial however there is no unequivocal evidence for cooler conditions at this time the onset of the holocene coincides with a change to more humid climatic conditions with the development of a fern rich closed forest vegetation type dramatic changes in diatom community composition provide a striking record of habitat change associated with lake shallowing but this process appears to be a result of basin in filling rather than variations in precipitation evaporation balance associated with climatic fluctuations evidence for human impact on the vegetation development is restricted to the last few hundred years

late paleozoic orogenies in western africa and eastern north america the diachronous closure of theic ocean the carboniferous evolution in western morocco southeastern canada and new england was dominated by intracontinental processes the subsidence of pull apart sedimentary basins and their subsequent deformation during middle carboniferous to early permian times with the development of autochthonous structures and mainly low to medium grade metamorphism on the other hand the structural style of the late carboniferous deformation in the southern appalachians and to a substantial degree also in new england that is related to a continental collision is characterized by deep seated northwest vergent thrusts and medium to high grade metamorphism the mauritanides structures are symmetrically east vergent thrusts this pattern is explained by the diachronous closure of the theic ocean that separated the avalon and carolina microcontinental blocks from paleo gondwana the closure of the theic ocean occurred during devonian times between the northern appalachians and the northwestern edge of paleo gondwana morocco whereas it was achieved only at the end of carboniferous times between the southern appalachians and western africa mauritania senegal the late devonian to early carboniferous counterclockwise rotation of gondwana induced the opening of the pull apart basins of canada new england and morocco as well as later the oblique collision in the southern appalachians and the generalized late paleozoic dextral transcurrent faulting along the northern edge of paleo gondwana

environmental change in the late pleistocene and later holocene at wanda site soroako south sulawesi indonesia abstract this paper reports the pollen analysis of an 8 m core from a mire at 445 m altitude and 2 s latitude on ultramafic soils near the western shore of lake matano south sulawesi the area is almost undisturbed by humans and the record is believed to cover about 50 75 000 yr b p with some breaks in the record a section from 17 000 to around 5500 yr b p and the last 1000 years of the record may be missing or disturbed the results show that montane forest grew around the site continuously through the late pleistocene with a maximum increase in higher altitude taxa from 35 000 to after 17 000 yr b p the time of glacial maxima elsewhere also in this period increases in grass and casuarina indicate possible drier conditions the holocene sections record lower altitude forest with increased taxonomic diversity including secondary species the results show that vegetation in the region has been sensitive to climatic change the pleistocene ecology being consistent with a temperature change of about 2 5 3 5 c with a phase up to 50 drier than present the site climate was possibly affected by shelf exposure in the gulf of bone due to lower sea levels however the tropical forest demonstrates overall long term stability in which changes in dominance may reflect minor shifts in disturbance and tree longevity a distinctive record of fine charcoal occurs throughout the deposit this shows that the forest has never been continuously fire free for a very long time the cause of the fires may be natural as no evidence for human occupation was discerned

late pleistocene sea level variations derived from the argentine shelf 1 neritic littoral marine sedimentary deposits from the argentine shelf provide a record of late pleistocene sea level variation sediments interpreted to reflect the last glacial maximum low stand are 150 m below present using a simple airy isostatic model for hydroisostatic compensation and correcting for a minor tectonic component yields a local eustatic sea level lowering of 105 m at the last glacial maximum the deglacial sea level curve records two rapid sea level rises consistent with mwp1 a and 1 b as documented by the barbados coral based sea level curve comparison with relative sea level variations predicted by the ice4g vm2 viscoelastic model have highlighted a deficiency in the model s predicted sea level history for this region detailed data model comparisons of late pleistocene sea level variations are necessary in the face of climate change induced sea level perturbations to determine regional and or systematic biases in the treatment of lithosphere viscosity and accurate predictions of future sea level

a 135 000 year record of vegetational and climatic change from the bandung area west java indonesia sedimentological and palynological analyses of sediment cores from the intramontane bandung basin west java indonesia provide a first palaeoclimatic record for the indonesian region covering continuously the last 135 000 years our data on palaeosol development indicate anomalously dry conditions for the final part of the penultimate glacial period around 135 000 yr b p and very warm and humid interglacial conditions from 126 000 to 81 000 yr b p during the transition to the last glacial period around 81 000 yr b p freshwater swamp forest of the bandung plain was replaced by an open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier conditions possibly related to reduced moisture uptake by the nw monsoon as a consequence of lower sea levels at the onset of glacial conditions a strong reduction in asplenium ferns from 81 000 to 74 000 yr b p suggests that drier conditions may also have occurred in the mountains of the bandung area while increased numbers indicate that from 74 000 to 47 000 yr b p it was slightly wetter again inferred depression of montane vegetation zones and reduced fern percentages suggests distinctly cooler and possibly drier climatic conditions prevailed in the bandung area from 47 000 to approximately 20 000 yr b p for the last glacial maximum 4 7 c lower temperatures are recorded

40ar 39ar ages of detrital muscovite and whole rock slate phyllite narragansett basin ri ma usa implications for rejuvenation during very low grade metamorphism late pennsylvanian sedimentary rocks in the narragansett basin were metamorphosed lower anchizone to sillimanite grade during late paleozoic regional metamorphism at ca 275 280 ma twenty five variably sized concentrates of detrital muscovite were prepared from samples collected within contrasting low grade areas diagenesis lower greenschist facies microprobe analyses suggest that the constituent detrital grains are not chemically internally zoned however some grains within several concentrates display very narrow 25 m compositionally distinct low grade epitaxial peripheral overgrowths detrital muscovite concentrates from the lower anchizone are characterized by internally concordant 40ar 39ar age spectra which define plateau ages of ca 350 360 ma these are interpreted to date post devonian acadian cooling within proximal source areas concentrates from lower grade sectors of the middle anchizone display slightly discordant spectra in which apparent ages systematically increase from ca 250 275 ma to define intermediate and high temperature plateaus of ca 360 400 ma detrital muscovite within samples from higher grade sectors of the middle anchizone and the upper anchizone are characterized by systematic low age discordance throughout both low and intermediate temperature increments high temperature ages only range up to ca 330 ma six size fractions of detrital muscovite from a sample collected within the lower greenschist facies have similarly discordant spectra in which apparent ages increase slightly throughout the analyses from ca 250 ma to 275 ma the detrital muscovite results are interpreted to reflect variable affects of late paleozoic regional metamorphism however it is uncertain to what extent the systematic low age spectra discordance reflects intracrystalline gradients in the concentration of 40ar and or experimental evolution of gas from relatively non retentive epitaxial overgrowths however low age discordance occurs regardless of the extent of epitaxial overgrowth intermediate temperature increments evolved during 40ar 39ar whole rock analyses of five slate phyllite samples are characterized by internally consistent apparent k ca ratios these are attributed to gas evolved from constituent very fine grained white mica samples from lower grade portions of the middle anchizone are characterized by intermediate temperature apparent ages which systematically increase from ca 275 300 ma to ca 360 375 ma before evolution of a high temperature contribution from detrital plagioclase feldspar this age variation may reflect partial late paleozoic rejuvenation of very fine grained detrital material with a source age similar to that for the detrital muscovites slate phyllite samples from upper sectors of the middle anchizone and from the upper anchizone were completely rejuvenated during late paleozoic metamorphism and record intermediate and high temperature plateau ages of ca 270 290 ma these data document that metamorphic conditions of the lower to middle biotite zone ca 325 350 c are required to completely rejuvenate intracrystalline argon systems of detrital muscovite therefore the 40ar 39ar dating method may be useful in determination of detrital muscovite provenance and in resolution of the metamorphic evolution of low grade terranes

contrasting p t t paths thermochronologic evidence for a late paleozoic final assembly of the avalon composite terrane in the new england appalachians strongly contrasting pressure temperature time paths for the avalon composite terrane and the structurally overlying putnam nashoba zone in eastern new england obtained from thermochronologic and thermobarometric data are best explained by a late paleozoic underthrusting of cover rocks by the avalon composite terrane we present new ar and u pb thermochronologic data that show that in the southern hope valley zone permian 280 ma anatectic metamorphic conditions of 700 c and 6 kbar were quenched by relatively rapid cooling 12 c m y and exhumation 0 5 km m y for 40 m y in contrast peak metamorphic conditions in the putnam nashoba zone predate silurian intrusions and slower cooling 3 5 c m y began at about 400 ma one dimensional thermal modeling suggests that these two belts were not in thermal equilibrium during the permian metamorphism of the avalon composite terrane because of the absence of high grade alleghanian metamorphism in rocks overlying the avalon terrane we conclude that high grade alleghanian metamorphism in the avalon terrane occurred east of rocks now overlying it and that significant motion between avalon and this cover occurred after peak alleghanian metamorphism similarly contrasting metamorphic histories between avalon inliers willimantic window massabesic complex gneiss pelham dome and their cover rocks reveals the regional significance of this boundary the core rocks all show permian cooling but the cover rocks show post acadian cooling ages decreasing from east to west to the pelham area where hornblende ages in avalon and cover differ by only 35 rather than 80 m y model calculations show that thermal equilibrium between instantaneously thrusted blocks of rocks is generally obtained in tens of millions of years consequently underthrusting of avalon is constrained to be middle mississippian or younger because the leading edge of the underthrusting block would have been heated the longest and would have most closely approached thermal equilibrium with its cover core rocks of the pelham dome must have been relatively close to this leading edge thus carboniferous to permian underplating from a generally eastward direction best explains these thermochronologic relationships

vegetation and climate change in west java indonesia during the last 135 000 years abstract sedimentological and palynological analyses of two sediment cores from the intramontane bandung basin java indonesia provide the first palaeoclimatic record for the indonesian region covering the last 135 000 years our data indicate anomalously dry conditions for the penultimate glacial and very warm and humid conditions during the last interglacial during the last glacial period fresh water swamp forests of the bandung plain were replaced by open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier climatic conditions possibly as a consequence of lower sea levels at the onset of glacial conditions for the last glacial maximum temperatures 4 7 c lower than at present are recorded

changes in monsoon and ocean circulation and the vegetation cover of southwest sumatra through the last 83 000 years the record from marine core bar94 42 abstract we present the palynological record from deep sea core bar94 42 taken offshore of southwest sumatra in the indian ocean refinement of a previous age model for the core has been made using 7 additional radiocarbon ages and 29 additional oxygen isotope measurements these analyses have substantially improved the previously published chronology which has enabled revision of the results of sedimentological studies of the core the pollen and re interpreted biogenic and terrigeneous data were used to reconstruct monsoon circulation and vegetation of southwest sumatra over the last 83 000 years 83 kyr during marine isotope stage mis 5a southwest sumatra was covered by rainforest with open herbaceous swamps lining river courses and surrounding lakes the se component of the monsoon was stronger than the nw component resulting in a humid climate with a short dry season during mis 4 conditions were drier fire activity increased and the monsoon was generally weaker this latter pattern persisted until mis1 the vegetation was most open during mis 3 between 52 and 43 kyr identifying this phase as the driest of the last glacial an increase in montane trees from 52 kyr indicates the onset of cooler conditions which lasted until the transition to mis 1 at about 11 9 kyr after 43 kyr an everwet climate gradually developed as monsoonal circulation intensified and the se monsoon component became stronger during this time closed canopy rainforest became dominant regionally over southwest sumatra increased monsoonal activity during the early holocene resulted in increased precipitation river runoff sediment discharge and offshore sediment transport from the continental shelf

tropical climate changes at millennial and orbital timescales on the bolivian altiplano tropical south america is one of the three main centres of the global zonal overturning circulation of the equatorial atmosphere generally termed the walker circulation1 although this area plays a key role in global climate cycles little is known about south american climate history here we describe sediment cores and down hole logging results of deep drilling in the salar de uyuni on the bolivian altiplano located in the tropical andes we demonstrate that during the past 50 000 years the altiplano underwent important changes in effective moisture at both orbital 20 000 year and millennial timescales long duration wet periods such as the last glacial maximum marked in the drill core by continuous deposition of lacustrine sediments appear to have occurred in phase with summer insolation maxima produced by the earth s precessional cycle short duration millennial events correlate well with north atlantic cold events including heinrich events 1 and 2 as well as the younger dryas episode at both millennial and orbital timescales cold sea surface temperatures in the high latitude north atlantic were coeval with wet conditions in tropical south america suggesting a common forcing

the flooding of sundaland during the last deglaciation imprints in hemipelagic sediments from the southern south china sea abstract during the last 30 ka the south china sea scs experienced pronounced palaeogeographic changes associated with the postglacial sea level rise which significantly modified the hydrography of this marginal sea the most crucial effects in the southern part of the basin were the submergence of sundaland and the opening of the southern channels connecting the scs to the tropical indo pacific isotopic sedimentological and organic geochemical parameters determined in two sediment cores from the southern scs one in the open sea and the other close to the continental shelf sites 17961 and 17964 respectively show that the main hydrographical changes during this period were related to critical thresholds in sea level rise the main changes occurred at about 15 13 5 ky bp coincident with meltwater pulse mwp ia when sea surface temperatures ssts at both sites experienced a rapid 1 5 c rise and the clay content and n nonacosane concentrations dropped significantly both trends reflect a rapid retreat of the coastline and an initial flooding of sundaland at that time a second important change starting with the beginning of mwp ib at about 11 5 ky bp and culminating at 10 ky bp involved the establishment of modern hydrographic conditions this is evident from the rapid convergence of the foraminiferal oxygen isotope records and the establishment of holocene sst values these results highlight the need to include the flooding emergence of sundaland as an important boundary condition in future modelling studies of asian palaeomonsoons

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

lignin biomarkers and pollen in postglacial sediments of an alaskan lake abstract we analyzed a 12 000 yr sediment core from wien lake central alaska for a suite of phenolic products from cuo oxidation of lignin polymers and compared their composition with pollen data from the same core to assess lignin phenols as sedimentary biomarkers inferences of the gross taxonomic origin of sediment organic matter from lignin phenol composition agree with vegetational reconstructions based on pollen assemblages in particular the ratios of syringyl to vanillyl phenols are consistently higher before 6500 yr bp when angiosperms dominated or codominated the regional vegetation than after 6500 yr bp when gymnosperms dominated however the ratios of cinnamyl p coumaric and ferulic acids to total vanillyl phenols c v do not show patterns expected from the abundance of woody plants c v ratios are particularly high 0 7 0 85 after 6500 yr bp when pollen spectra suggest closed boreal forests dominated by picea and the stratigraphic patterns are strikingly similar between c v and picea pollen concentrations cuo oxidation of modern pollen of p glauca and p mariana yields exceptionally high amounts of cinnamyl phenols 8 90 and 6 41 mg 100 mg oc for p glauca and p mariana respectively in particular p coumaric acid is obtained in large amounts 8 87 and 6 41 mg 100 mg oc for p glauca and p mariana respectively versus vanillyl phenols 0 25 and 0 49 mg 100 mg oc for p glauca and p mariana respectively and ferulic acid 0 03 and 0 00 mg 100 mg oc for p glauca and p mariana respectively thus lignin phenols derived from fossil picea pollen preserved in sediments likely drive the c v profile of the wien lake core these data imply that if picea pollen concentrations are sufficiently high the amount of nonwoody tissue in sediments may be grossly overestimated when the lignin composition of gymnosperm needles is used as the end member of nonwoody tissues given that pollen grains are among the most resistant components of sedimentary organic matter and that p coumaric acid is labile it is important to consider pollen as a nonwoody tissue type when lignin biomarkers are used to determine the sources of vascular plant material in sediments

constancy in the vegetation of the amazon basin during the late pleistocene evidence from the organic matter composition of amazon deep sea fan sediments analyses of more than 60 sediment samples from the amazon deep sea fan show remarkably constant terrigenous biomarkers lignin phenols and cutin acids and stable carbon isotopic compositions of organic matter batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document 13 c om end document deposited from 10 to 70 ka sediments from the nine amazon deep sea fan channel levee systems investigated in this study yielded relatively narrow ranges for diagnostic parameters such as organic carbon oc normalized total lignin yields 3 1 1 1 mg 100 mg oc syringyl vanillyl phenol ratios s v 0 84 0 06 cinnamyl vanillyl phenol ratios c v 0 08 0 02 isomeric abundances of cutin derived dihydroxyhexadecanoic acid f10 16 oh 0 65 0 02 and batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document 13 c om end document 27 6 0 6 our measurements support the hypothesis that the vegetation of the amazon basin did not change significantly during the late pleistocene even during the last glacial maximum moreover the compositions obtained from the amazon deep sea fan are similar to those of modern amazon river suspended sediments such results strongly indicate that the current tropical rainforest vegetation has been a permanent and dominant feature of the amazon river watershed over the past 70 k y specifically we found no evidence for the development of large savannas that had been previously postulated as indicators of increased glacial aridity in amazonia climate models need to be modified to account for the uninterrupted input of moisture to the tropical amazon region over the late pleistocene holocene period

io galileo evidence for major variations in regolith properties galileo ssi images taken at different times early in the jupiter orbital tour show striking widespread changes in io s color and albedo patterns that result from observing the satellite s surface at different lighting and viewing geometries such changes indicate significant variations in the photometric or light scattering behavior of the ionian surface from region to region and thereby provide strong evidence for major lateral variations in regolith properties in particular the regolith particles in io s bright equatorial band appear to be larger than or have a higher density of internal scatterers than those in the satellite s higher latitude regions such heterogeneity is not surprising on io given the rapid rate of volcanic resurfacing

late quaternary peat formation and vegetation dynamics in a lowland tropical swamp nee soon singapore abstract cores of sediment from nee soon a peat forming freshwater swamp located in the perimarine zone of singapore have yielded a record of vegetation history that comprises parts of the last glacial and holocene periods the evidence includes two conventional and four ams radiocarbon dates the oldest of which is 23 050 330 b p uncalibrated radiocarbon years and variations in the abundances of sub fossil pollen and spores and charcoal the results of a study of the relationship between contemporary vegetation and modern pollen accumulation facilitated interpretation of sub fossil tree pollen data peat formation occurred at nee soon during the last glacial when sea levels on the sunda continental shelf were well below those at present the occurrence of montane pollen types notably podocarpaceae in sediment samples dated to the late glacial and early holocene suggests either temperatures substantially lower than those of the present and possibly humid conditions or cold seasonally dry climates and reduced levels of atmospheric co 2 the abundance of charcoal indicates the widespread occurrence of fires throughout the entire period represented by the cores for the mid holocene the evidence indicates an increased saline influence presumably as a result of relatively high sea levels falling sea levels during the late holocene appear to have preceded the onset of the most recent period of peat formation at nee soon the evidence confirms that long last glacial interglacial records of lowland vegetation history are available from terrestrial locations in the humid core of southeast asia and suggests that the complexity of perimarine swamp dynamics is not captured fully by anderson s model which assumes a close relationship between peat formation and sea level

structural analysis of progressive deformation within complex transcurrent shear zone systems southern narragansett basin rhode island abstract complex progressive ductile deformation on dutch island narragansett basin rhode island is localized along a system of non parallel intersecting shear zones with opposite senses of strike and oblique slip motion the structural intensity and complexity of this area can be attributed in part to the proximity of nne ne and ene trending pre existing basement faults bounding early horsts and grabens reactivation of these faults caused the formation of shear zones within the overlying metasediments structural superposition of non coaxial mesoscopic folds and crenulation cleavages formed as a result of progressive movement along these shear zones provide unusual and accurate kinematic indicators that track movement along individual zones through time sinistral motion on nne trending zones preceded dextral motion on ne trending zones dextral oblique slip motion on ene trending zones followed deformation became increasingly brittle with time the deformation is the result of two transcurrent shear systems with opposite senses of motion that formed adjacent to the north american and african plate boundary after plate collision

synchronous tropical south china sea sst change and greenland warming during deglaciation the tropical ocean plays a major role in global climate it is therefore crucial to establish the precise phase between tropical and high latitude climate variability during past abrupt climate events in order to gain insight into the mechanisms of global climate change here we present alkenone sea surface temperature sst records from the tropical south china sea that show an abrupt temperature increase of at least 1 c at the end of the last glacial period within the recognized dating uncertainties this sst increase is synchronous with the bolling warming observed at 14 6 thousand years ago in the greenland ice sheet project 2 ice core

the massabesic gneiss complex new hampshire a study of a portion of the avalon terrane geochemical data from the 625 ma massabesic gneiss complex of southern new hampshire show strong affinities for other avalonian rocks of southern new england and suggest continental rifting in the late proterozoic migmatized paragneiss the dominant rock type in the complex has major and trace element compositions that are compatible with graywackes from continental arcs the para gneiss also has strong lithologic metamorphic and isotopic similarities to the rocks of the hope valley zone of connecticut avalon suggesting a possible hope valley massabesic correlation at 625 ma the paragneiss end values are similar to avalonian crust in other locations of the orogen two types of amphibolite are present in minor amounts in the paragneiss of the massabesic gneiss complex the first type is a paramphibolite and consists of calc silicate layers in the massabesic paragneiss the second type is metaigneous major and trace element abundances reveal that the protoliths of the orthoamphibolites range from continental rift alkaline basalts and tholeiites to n type morbs orthoam phibolite end 625 ma values range from 2 4 to 4 as expected of rift related magmas derived from partial melting of a depleted mantle source and have the same values as iapetus ocean floor rocks of similar age orthoamphibolite major and trace element geochemical characteristics overlap those of the middlesex fells amphibolites of the esmond dedham zone of eastern massachusetts avalon which range from alkaline to transitional basalts erupted in a continental rift setting the compositions of orthoam phibolites define a potential magmatic continuum produced by batch partial melting of the mantle initiated during continental rifting and proceeded to ocean basin forma tion the inferred continuity of mafic magmatism from the esmond dedham mid dlesex fells formation to the massabesic gneiss complex and hope valley zone suggests that these zones are not distinct lithotectonic zones but are parts of a single landmass massachusetts avalon esmond dedham represents the continental section of avalon where the alkaline to transitional magmas of the early rifting stages are preserved according to our tectonic reconstruction the massabesic gneiss complex is the oceanward continental margin represented by volcanoclastic sediments with the morbs representing the initiation of ocean basin development the leading edge of this landmass of which the massabesic gneiss complex is the only observable remnant collided with laurentia during the acadian orogeny the inboard thicker more continental trailing edge that is platform avalon esmond dedham collided later during the alleghanian orogeny

glacial conditions in the northern molucca sea region indonesia abstract palynological planktonic foraminiferal and stable isotope data from a sediment core in the northern mollucca sea have been used to evaluate regional glacial climatic and hydrographic conditions the palynological record shows that in glacial time the climate was drier than today indicating a weakened influence of the northwesterly winds at that time the drier climatic conditions at glacial time were associated with a higher lapse rate which together with a lower sea level resulted in a large expansion of the lower montane oak forests on the nearby island of halmahera glacial mollucca sea surface water salinities were probably higher than today while glacial surface water temperatures might have been close to present day values the deep chlorophyll maximum dcm layer in the northern molucca sea at glacial time was more productive and cooler than today probably the result of the inflow of cooler and nutrient enriched subtropical lower water from the pacific the less asymmetrical high latitude ice coverage at glacial time and the particularly strong increase in the pole to equator thermal gradient on the northern hemisphere provides theoretical evidence that the intertropical convergence zone itcz shifted equatorwards and oscillated over a more narrow latitudinal range than today this inferred configuration of the itcz at glacial time however fails to explain the observed increased aridity in the study area at that time we propose therefore that the drier glacial climatic conditions are related to a possible disturbance in the el nino southern oscillation enso system

foraminiferal faunal estimates of paleotemperature circumventing the no analog problem yields cool ice age tropics the sensitivity of the tropics to climate change particularly the amplitude of glacial to interglacial changes in sea surface temperature sst is one of the great controversies in paleoclimatology here we reassess faunal estimates of ice age ssts focusing on the problem of no analog planktonic foraminiferal assemblages in the equatorial oceans that confounds both classical transfer function and modern analog methods a new calibration strategy developed here which uses past variability of species to define robust faunal assemblages solves the no analog problem and reveals ice age cooling of 5 o to 6oc in the equatorial current systems of the atlantic and eastern pacific oceans classical transfer functions underestimated temperature changes in some areas of the tropical oceans because core top assemblages misrepresented the ice age faunal assemblages our finding is consistent with some geochemical estimates and model predictions of greater ice age cooling in the tropics than was inferred by climate long range investigation mapping and prediction climap 1981 and thus may help to resolve a long standing controversy our new foraminiferal transfer function suggests that such cooling was limited to the equatorial current systems however and supports climap s inference of stability of the subtropical gyre centers

the vegetation and climate at the last glaciation on the emerged continental shelf of the south china sea studies on the dispersal mechanism and source areas of pollen from hemipelagic sediments recovered from the continental slopes of the south china sea scs reveal that vegetation existed on the exposed shelves at the last glacial maximum lgm and the latter part of the marine isotope stage 3 at the low sea level stand artemisiadominated grassland covered the northern continental shelf and tropical lowland rainforest and mangroves grew on the southern shelf sunda land consequently the climate in the northern scs must have been much colder and drier during the last glacial period compared to the present sunda land experienced only a marginally lower temperature but was not drier than today the enhanced contrast between the northern and southern parts of the scs in vegetation and climate during the lgm may be ascribed at least partly to the strengthening of winter monsoon during the last glacial period 2000 elsevier science b v all rights reserved

the last glacial cycle from the humid tropics of northeastern australia comparison of a terrestrial and a marine record a detailed pollen record from the ocean drilling program site 820 core located on the upper part of the continental slope off the coast of northeast queensland was constructed to compare with the existing pollen record from lynch s crater on the adjacent atherton tableland and allow the production of a regional picture of vegetation and environmental change through the last glacial cycle some broad similarities in patterns of vegetation change are revealed despite the differences between sites and their pollen catchments which can be related largely to global climate and sea level changes the original estimated time scale of the lynch s crater record is largely confirmed from comparison with the more thoroughly dated odp record conversely the lynch s crater pollen record has assisted in dating problematic parts of the odp record in contrast to lynch s crater which reveals a sharp and sustained reduction in drier araucarian forest around 38 000 yrs bp considered to have been the result of burning by aboriginal people the odp record indicates most likely a stepwise reduction dating from 140 000 yrs bp or beyond the earliest reduction shows lack of a clear connection between araucaria decline and increased burning and suggests that people may not have been involved at this stage however a further decline in araucarian forest possibly around 45 000 yrs bp which has a more substantial environmental impact and is not related to a time of major climate change is likely at least partially the result of human burning the suggestion from the odp core oxygen isotope record of a regional sea surface temperature increase of around 4 degrees c between about 400 000 and 250 000 yrs bp may have had some influence on the overall decline in araucaria and its replacement by sclerophyll vegetation c 2000 elsevier science b v all rights reserved

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr