central baffin electromagnetic experiment cbex mapping the north american central plains nacp conductivity anomaly in the canadian arctic abstract over the summers of 2001 and 2002 a 45 station 500 km long regional magnetotelluric mt profile was acquired on central baffin island in the eastern canadian arctic this central baffin electromagnetic experiment cbex profile traverses the northern margin of the paleoproterozoic trans hudson orogen tho in its southern segment within the juvenile rocks of the orogen the profile lies on paleoproterozoic meta sedimentary strata known as the piling group and the profile extends northwards onto the archean rae craton the primary goal of the experiment was to determine the subsurface geometry of major geological boundaries and to define regional electrical structures field observations and laboratory analyses show that one particular horizon within the piling group the sulphidic graphitic astarte river formation is highly conductive and can be mapped and used as structural proxy for the base of the piling group the laboratory results imply that the source of the enhanced conductivity in the astarte river formation is the high content of interconnected graphite and that the host rocks are highly anisotropic due to bedding mapping this formation in depth images the base of the piling group basin well there is high contrast in electrical conductivity between the piling group meta sedimentary rocks and the archean granites and gneissic complexes of the rae craton to the north the lower crust of the rae craton in this area is moderately conductive some 100 s m in contrast to rae lower crust observed elsewhere in canada and this observation is not readily explained the lithospheric mantle beneath the profile exhibits a strong north to south gradient in decreasing resistivity suggesting resistive archean mantle 3000 m subducted beneath moderately resistive proterozoic mantle 300 m

evolution of the indian summer monsoon and terrestrial vegetation in the bengal region during the past 18 ka the indian summer monsoon ism is a major global climatic phenomenon long term precipitation proxy records of the ism however are often fragmented and discontinuous impeding an estimation of the magnitude of precipitation variability from the last glacial to the present to improve our understanding of past ism variability we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower ganges brahmaputra meghna catchment and the indo burman ranges over the last 18 000 years 18 ka the records derive from a marine sediment core from the northern bay of bengal nbob and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the bengal region the isotopic composition of terrestrial plant waxes dd and d13c of n alkanes are compared to results from an isotope enabled general atmospheric circulation model isocam for selected time slices pre industrial mid holocene and heinrich stadial 1 comparison of proxy and model results indicate that past changes in the dd of precipitation and plant waxes were mainly driven by the amount effect and strongly influenced by ism rainfall maximum precipitation is detected for the early holocene climatic optimum ehco 10 5 6 ka bp whereas minimum precipitation occurred during the heinrich stadial 1 hs1 16 9 15 4 ka bp the isocam model results support the hypothesis of a constant moisture source i e the nbob throughout the study period relative to the pre industrial period the model reconstructions show 20 more rain during the mid holocene 6 ka bp and 20 less rain during the heinrich stadial 1 hs1 respectively a shift from c4 plant dominated ecosystems during the glacial to subsequent c3 c4 mixed ones during the interglacial took place vegetation changes were predominantly driven by precipitation variability as evidenced by the significant correlation between the dd and d13c alkane records when compared to other records across the ism domain precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ism from the last glacial to the present

a 25 ka indian ocean monsoon variability record from the andaman sea recent paleoclimatic work on terrestrial and marine deposits from asia and the indian ocean has indicated abrupt changes in the strength of the asian monsoon during the last deglaciation comparison of marine paleoclimate records that track salinity changes from asian rivers can help evaluate the coherence of the indian ocean monsoon iom with the larger asian monsoon here we present paired mg ca and d 18 o data on the planktic foraminifer globigerinoides ruber white from andaman sea core rc12 344 that provide records of sea surface temperature sst and d 18 o of seawater d 18 osw over the past 25 000 years ka before present bp age control is based on nine accelerator mass spectrometry ams dates on mixed planktic foraminifera mg ca sst data indicate that sst was 31c cooler during the last glacial maximum lgm than the late holocene andaman sea d 18 osw exhibited higher than present values during the lateglacial interval ca 19 15 ka bp and briefly during the younger dryas ca 12 ka bp lower than present d 18 osw values during the bolling allerod ca 14 5 12 6 ka bp and during the early holocene ca 10 8 5 5 ka bp are interpreted to indicate lower salinity reflect some combination of decreased evaporation precipitation e p over the andaman sea and increased irrawaddy river outflow our results are consistent with the suggestion that iom intensity was stronger than present during the bolling allerod and early holocene and weaker during the late glaciation younger dryas and the late holocene these findings support the hypothesis that rapid climate change during the last deglaciation and holocene included substantial hydrologic changes in the iom system that were coherent with the larger asian monsoon r 2007 elsevier ltd all rights reserved

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

metamorphosed carbonate platforms and controls on the genesis of sapphire gem spinel and lapis lazuli insight from the lake harbour group nunavut canada and implications for gem exploration abstract baffin island s lake harbour group lhg a paleoproterozoic granulite facies metasedimentary sequence rich in carbonates contains occurrences of the gemstones sapphire corundum spinel including vivid blue cobalt enriched spinel and lapis lazuli hauyne bearing rock most occurrences of these gem minerals are uniquely metasedimentary carbonates and calc silicate rock while a few spinel occurrences formed from metasomatic reactions between si al rich rock syenogranite or gneiss and marble the metasedimentary corundum spinel and hauyne occurrences have similar protoliths primarily dolomitic marls with a high al si relative abundance interpreted as sandy mud to clay siliciclastic fraction in the protolith kimmirut type sapphire deposits formed via a multi step metamorphic process under three different and specific p t conditions lapis lazuli formation required the presence of evaporites to provide na and possibly s for the blue mineral hauyne in addition to high al si calc silicate rocks spinel also occurs in impure dolomitic marbles with very low k al potential for kimmirut type sapphire deposits is expected to be restricted to metacarbonate sequences proximal to the thrust fault separating the lhg from the narsajuaq arc where retrograde upper amphibolite facies mineralization is most pervasive spinel and kimmirut type sapphire deposits are expected to be found in dolomitic marble sequences rich in calc silicate layers the potential occurrence of lapis lazuli is more difficult to predict but deposits could be identified thanks to large geographical footprints and their color similar gem occurrences or deposits to those in the lhg may be found in other metacarbonate bearing terranes with similar metamorphic conditions and for kimmirut type sapphire a similar metamorphic history aerial hyperspectral and photographic surveys are well suited to gemstone exploration on southern baffin island thanks to excellent rock exposure with minimal sediment or plant lichen cover spectral mapping of dolomite diopside phlogopite and scapolite rich domains in lhg metacarbonate sequences using airborne hyperspectral data is expected to provide exploration targets remote sensing exploration could be used in other metacarbonate bearing upper amphibolite to granulite facies metamorphic terranes found in polar climates arid climates or at high elevation in mountainous regions where such rocks are well exposed with minimal vegetative cover

variations of indian monsoon precipitation during the last 32 kyr reflected in the surface hydrography of the western bay of bengal hydrography of the bay of bengal is highly influenced by the river runoff and rainfall during the southwest monsoon we have reconstructed 18 osw sea surface salinity and sea surface temperature sst changes in the bay of bengal by using paired measurements of 18 o and mg ca in a planktonic foraminifera species globigerinoides ruber from core sk218 1 in the western bay of bengal in order to understand the rainfall variability associated with southwest monsoon over the past 32 kyr our sst reconstructions reveal that bay of bengal was 3 2 c cooler during the lgm as compared to present day temperature and a 3 5 c rise in sst is documented from 17 to 10 ka both sst and 18 osw exhibit greater amplitude fluctuations during mis 2 which is attributable to the variability of ne monsoon rainfall and associated river discharge into the bay of bengal in association with strong seasonal temperature contrast on set of strengthening phase of sw monsoon was started during bolling allerod as evidenced by the low 18 osw values 14 7 ka 18 osw show consistently lower values during holocene with an exception around 5 ka which suggests that the freshening of bay of bengal due to heavy precipitation and river discharge caused by strong sw monsoon results of this study signify that the maximum fluctuations of the ne monsoon rainfall during mis 2 appear to be controlled by the

three dimensional structure of the torngat orogen ne canada from active seismic tomography the crustal velocity structure and the moho depth of the proterozoic torngat orogen ne canada is determined by active seismic tomography using travel times of crustal turning rays and moho reflections the orogen developed during oblique convergence of the archean superior and nain provinces which trapped an interior belt of archean crust core zone between them with the torngat orogen evolving between the core zone and the nain province beneath the central orogen a crustal root is found with a preserved depth of 52 km and a width of 100 km to the north the root shallows to 44 km and narrows to a width of 45 km the root correlates with a set of major late orogenic shear zones that accommodated oblique convergence of the superior and nain provinces this correlation suggests that the transpressional shearing focused strain in the region of the root and contributed to the crustal thickening absence of postorogenic magmatic activity prevented reworking or thermal relaxation of the root the lack of late magmatism is probably related to the depleted and refractory nature of the archean lithosphere underlying the orogen upper crustal velocities are lowest in the core zone 5 7 km s at the surface and are compatible with laboratory measurements carried out on gneissic rock samples from that area higher velocities in the nain province 5 9 km s correlate with felsic gneiss and anorthosite rock samples a high velocity region immediately to the north of the crustal root is associated with a moho uplift 34 km this is explained by extension along the ungava transform fault and possibly in hudson strait at 55 ma when rifting in the labrador sea was transferred into baffin bay

sedimentological and geochemical basin analysis of the paleoproterozoic penrhyn and piling groups of arctic canada abstract paleoproterozoic metasedimentary successions on the western churchill province record a history of regional tectonic events spanning the breakup and amalgamation of supercontinents metasedimentary successions in the northeastern part of the trans hudson orogeny including the penrhyn and piling groups of melville peninsula and baffin island respectively have been understudied with respect to their basin evolution records we present new sedimentological geochemical and geochronological data for the penrhyn and piling groups that record deposition on the rae craton new detrital zircon u pb age data indicate that deposition of the penrhyn group started after 1897 ma and post dates deposition of most of the piling group the new maximum age constraints and stratigraphy of the penrhyn group do not support previous lithostratigraphic correlation with the piling group deposition of the lower piling group likely occurred in an epicontinental basin setting the occurrence of detritus from the meta incognita microcontinent in the upper piling group bravo lake and longstaff bluff formations is interpreted to signal the onset of foreland basin deposition the details of sedimentation in the piling foreland basin provide an additional constraint to discerning the polarity of subduction between the rae craton and meta incognita microcontinent that closed the piling basin we conclude that the piling foreland system shows characteristics of a pro foreland basin implying that the rae craton was the lower plate in the collision with the meta incognita microcontinent finally with new stratigraphic and detrital zircon geochronological data for the penrhyn and piling groups we provide a comparison with other sedimentary successions on the rae craton whose histories were influenced by similar regional tectonic events

a late miocene early pliocene biogenic silica crash in the andaman sea and bay of bengal abstract variations in the mass accumulation rate of biogenic silica bsi in continental margin sediments can be used to reconstruct relative changes in productivity through time in these settings in the northern bay of bengal a lack of long sedimentary records has historically precluded this type of reconstruction the acquisition of 21 new long sedimentary records during the 2006 indian national gas hydrate program nghp expedition 01 has made it possible for the first time to reconstruct paleoproductivity in this important region of the world that is dominated by intense changes in the geological and biological fluxes largely driven by tectonic and climate related mechanisms in the research presented here fluctuations in the mass accumulation rate of biogenic opal during the past 9 4 myrs are reconstructed using continental margin sediment cores from the andaman sea site nghp 01 17a and the northern bay of bengal site nghp 01 19 within these records a biogenic silica crash is recorded at 6 ma and is consistent with previous geotectonic geochemical and paleontological studies of the southern indian ocean and pacific ocean that suggest connectivity and thus exchange of nutrient rich water masses between the eastern tropical indian ocean and western tropical pacific ocean was diminished as a result of the tectonic restriction of the northerly sector of the indonesian throughflow itf the biogenic silica crash at sites 17 and 19 is consistent with a decrease in surface water productivity that may have been driven by the reduction of nutrient rich pacific waters delivered to the andaman sea and bay of bengal via the northerly route of the itf following the bsi crash at 6 ma subsequent recovery of the bsi mass accumulation rates at sites 17 and 19 occurred and was perhaps renewed by an enhanced supply of nutrient rich freshwater from the nearby irrawaddy and mahanadi rivers which could have occurred during a documented increase in the intensity of the indian monsoon at 5 ma although recovery is noted at both core locations biogenic silica mass accumulation rates did not fully recover in the andaman sea this could be explained by the restricted nature of the andaman basin and its more distal location from a major source of nutrient rich freshwater

terrane accretion in the internal zone of the ungava orogen northern quebec part 2 structural and metamorphic history the tectonic history of the early proterozoic ungava orogen is marked by structural metamorphic episodes that both predate and postdate a collision between a magmatic arc terrane and the northern c

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

upper and lower plate juxtaposition deformation and metamorphism during crustal convergence trans hudson orogen quebec baffin segment canada abstract the lower plate of the quebec baffin segment of paleoproterozoic trans hudson orogen comprises parautochthonous archean crystalline basement of the superior province 3 22 2 74 ga and imbricated paleoproterozoic rift margin strata 2 04 1 92 ga the collisional upper plate contains 1 allochthonous ophiolitic units 2 00 ga 2 a continental arc terrane narsajuaq arc 1 86 1 82 ga 3 shelf sequence strata ca 1 86 ga and basement orthogneisses ca 1 95 ga 4 foreland basin deposits 1 86 ga and 5 a batholith which intrudes the shelf and foreland basin rocks cumberland batholith 1 86 1 85 ga lower and upper plate assemblages were juxtaposed during a 1 82 1 79 ga accretion collision event and deformed into regional scale folds during two post collisional folding episodes ca 1 76 1 74 ga as a result of the structural relief generated by the post collisional folding and subsequent exhumation all orogenic elements can be directly examined along a 400 km across strike transect in the external zone northern quebec lower plate rift margin units were internally imbricated cape smith belt and translated southward across the superior province basement paleoproterozoic amphibolite facies mineral growth is syn to post thrusting tectonic imbrication has resulted in a structural inversion of the accreted i e upper plate ophiolite stratigraphy north of the cape smith belt mid crustal plutonic units of the narsajuaq arc form an upper plate crystalline wedge whose sole thrust is localized near the thrust belt s basal decollement within narsajuaq arc syn magmatic granulite facies assemblages are retrogressed to amphibolite facies assemblages in proximity to major accretion collision faults in the internal zone southern baffin island a tripartite orogen scale tectonostratigraphy is exposed on the flanks of the post collisional fold structures at the lowest structural level lower plate superior province orthogneisses are imbricated with paleoproterozoic rift margin units and mineral growth is syn thrusting at intermediate structural level upper plate orthogneisses are correlated with the narsajuaq arc in northern quebec at the highest structural level a north facing shelf sequence is structurally overlain by an assemblage of clastic rocks interpreted as a foreland basin sequence dominantly monzogranite plutons of the cumberland batholith are restricted to the upper structural level and indicate pre emplacement imbrication of tectonostratigraphic units within both upper and lower plates granulite facies assemblages are retrogressed to upper amphibolite assemblages in proximity to 1 82 1 79 ga accretion collision structures exposures of superior province basement across the orogen document a progressive increase in the extent of reworking during accretion of upper plate units from a narrow shear zone in the external zone to km scale imbrication and more pervasive shear deformation in the internal zone a minimum of 160 km of basement underthrusting is constrained by the structural overlap of upper plate allochthons on lower plate units basement involvement during post collision shortening is manifest as thick skinned folding indicating coupling across the collisional basal decollement

a high resolution absolute dated deglacial speleothem record of indian ocean climate from socotra island yemen abstract stalagmite m1 5 from socotra island yemen in the northwest indian ocean provides a robust high resolution paleoclimate record from 27 4 11 1 ka based on 717 stable isotope and 28 230 th measurements variations in m1 5 oxygen isotope ratios 18 o are interpreted to be primarily driven by an amount effect related to changes in the mean position and or intensity of convection of the intertropical convergence zone the island s only source of precipitation the m1 5 18 o time series is strongly correlated to the greenland ice cores similar to an older socotra speleothem deposited from 53 40 ka s j burns d fleitmann a matter j kramers a al subbary indian ocean climate and an absolute chronology over dansgaard oeschger events 9 to 13 science 301 2003 1365 1367 indicating that a north atlantic indian ocean cold dry warm wet teleconnection persisted through the end of the last glacial period peak aridification occurred at 23 ka and a gradual increase in moisture thereafter was interrupted by an abrupt drying event at 16 4 ka perhaps related to heinrich event 1 indian ocean rainfall increased dramatically during the bolling period and then decreased continuously and gradually through the allerod and younger dryas the holocene began abruptly with increased precipitation at 11 4 ka and was followed by a major but short lived drying during the preboreal oscillation at 11 2 ka m1 5 is highly correlated to the dongge cave record from 15 5 11 ka suggesting much of the indian ocean monsoon region responded similarly to the major climate changes of the last deglaciation the transitions into the younger dryas and to a lesser extent the bolling are remarkably gradual in m1 5 as they are in all other asian speleothem records occurring over several centuries these gradual transitions are in striking contrast to high resolution records from around the north atlantic basin where the transitions are extremely abrupt and generally occur in under a century this spatially variable pattern of climate change is consistent with an atlantic origin for these deglacial climate events

processes controlling the geochemical composition of the south china sea sediments during the last climatic cycle abstract sediments of the upper 28 2 m of ocean drilling program odp site 1145 from the northern south china sea scs were analyzed for their geochemical composition most of the major and trace elements exhibit significant fluctuations at glacial interglacial scales implying a close relation with regional and global climate change al normalized elemental ratios can be subdivided into three principal components pc pc1 e g ca al ba al sr al displays significant glacial interglacial variation and is related to paleoproductivity in the northern scs pc2 e g k al mg al rb al is associated with the degree of chemical weathering in the source regions and shows little glacial interglacial variation pc3 e g ti al zr al reflects the relative contribution of coarse and fine grained materials in the terrigenous components of the scs sediments likely associated with changes in sea level and monsoon induced fluvial input spectral analyses indicate that paleoproductivity i e ba al in the south china sea lags hulu sanbao speleothem 18o record an indicator of annual average meteoric precipitation by 102 and indian summer monsoon multi proxy stack by 23 at the precession band indicating a close relationship with the indian summer monsoon however the chemical weathering degree in the source area pc2 is not sensitive to monsoon related changes at the precession band during the last climatic cycle

climate change at the 4 2 ka bp termination of the indus valley civilization and holocene south asian monsoon variability 1 planktonic oxygen isotope ratios off the indus delta reveal climate changes with a multi centennial pacing during the last 6 ka with the most prominent change recorded at 4 2 ka bp opposing isotopic trends across the northern arabian sea surface at that time indicate a reduction in indus river discharge and suggest that later cycles also reflect variations in total annual rainfall over south asia the 4 2 ka event is coherent with the termination of urban harappan civilization in the indus valley thus drought may have initiated southeastward habitat tracking within the harappan cultural domain the late holocene drought cycles following the 4 2 ka bp event vary between 200 and 800 years and are coherent with the evolution of cosmogenic 14c production rates this suggests that solar variability is one fundamental cause behind holocene rainfall changes over south asia

inverse phase oscillations between the east asian and indian ocean summer monsoons during the last 12 000 years and paleo el nino abstract the inverse phase variations between the east asian and indian ocean summer monsoons on the interannual timescale result from the el nino southern oscillation activity in the tropical pacific which potentially provides a new way for studying paleo enso here we reconstruct a 12 000 yr proxy record for the east asian summer monsoon from 13 c time series of the plant cellulose of the hani peat bog in the northeastern china the comparison of it with the peat proxy record of the indian ocean summer monsoon suggests that the el nino conditions are coincident with strong east asian summer monsoons weak indian summer monsoons and drift ice events in the north atlantic at both orbital and millennial time scales the orbital scale inverse phase relationships between the monsoons indicate the occurrence of a long term enso like pattern confirming the sensitivity of the monsoon systems associated with enso to insolation forcing the nine inverse phase variations on the millennial time scales may suggest the nine el nino like patterns superimposing the long term enso like pattern the inverse phase variations between the monsoons also show close correspondence to the drift ice events at high northern latitudes in every case when the abrupt ice rafted debris events occurred in the north atlantic the inverse phase relationship established and the el nino like pattern occurred in the tropical pacific correspondingly the discussions on the influence of ocean thermohaline circulation on these global linkages have been made

deciphering the paleoproterozoic cooling history of the northeastern trans hudson orogen baffin island canada using 40 ar 39 ar step heating and uv laser thermochronology abstract the previously unstudied cooling and exhumation history of mid crustal rocks exposed on southeastern baffin island canada provides new insights into the post orogenic evolution of the paleoproterozoic trans hudson orogen tho new 40 ar 39 ar step heat analyses of biotite muscovite and phlogopite and core to rim intra grain 40 ar 39 ar analyses of muscovite have a range of apparent ages compatible with slow regional cooling following peak metamorphism twenty nine amphibolite to granulite facies rocks were dated using the 40 ar 39 ar step heating laser co 2 method 40 ar 39 ar spot analyses were performed across muscovite grains from three samples using an ultraviolet uv laser to investigate intra grain 40 ar 39 ar age variations step heating apparent ages range from ca 1788 1622 ma for biotite 1720 1630 ma for phlogopite and 1729 1657 ma for muscovite uv spot 40 ar 39 ar analyses in the three muscovite grains range from ca 1661 1640 ma 1675 1645 ma and 1680 1652 ma with core to rim apparent age gradients of 20 30 myr previous studies resolved peak metamorphism in this region to between ca 1860 and 1820 ma and identified late to post tho zircon and monazite populations at ca 1800 1750 ma numerical diffusion models for ar in muscovite were conducted to test different proterozoic cooling and exhumation scenarios comparisons with our 40 ar 39 ar ages attest to cooling rates of 1 2 c myr following peak metamorphism and 1 5 2 5 c myr after ca 1740 ma anomalously old apparent 40 ar 39 ar ages in cases equivalent to u pb zircon rim and monazite ages likely result from incorporation of excess ar the results suggest that mid crustal rocks on southeastern baffin island remained hotter than 420 450 c for 150 200 myr after peak metamorphism with subsequent slow cooling and denudation rates that are typical of proterozoic orogens the apparent absence of orogenic collapse implies that despite high temperatures and estimated maximum crustal thicknesses comparable to those of large hot orogens the tho remained gravitationally stable during its terminal phase

wave transformation and swash oscillation on gentle and steep slopes the numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches the numerical model is one dimensional in the cross shore direction and is based on the finite amplitude shallow water equations including the effect of bottom friction which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint the slight modification is related to the effect of the time averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes the modified numerical model is compared with available small scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope additional comparisons are made with small scale tests conducted using transient monochromatic and grouped waves on a 1 8 smooth slope with and without an idealized nearshore bar at the toe of the 1 8 slope as a whole the numerical model is shown to be capable of predicting both time varying and time averaged hydrodynamic quantities in the surf and swash zones on gentle as well as steep slopes

major ash eruptions of barren island volcano andaman sea during the past 72 kyr clues from a sediment core record barren island andaman sea is the northernmost active volcano of the indonesian arc to construct the eruptive history of this little studied volcano we measured 14c dates of inorganic carbon in sediment beds and sr and nd isotopic ratios of seven discrete ash layers in a marine sediment core collected from 32 km southeast of the volcano the study reveals that the volcano had seven major ash eruptions at 70 69 61 24 19 15 and 10 ka the ash layers erupted from 70 ka through 19 ka have highly uniform nd isotopic composition and since the 15 ka eruption to the present the isotopic composition has been highly variable between 24 ka and 10 ka the volcano had large ash eruptions spaced at 4 500 year intervals isotopically correlating the precaldera lavas and ash exposed on the volcano to the uppermost ash layer in the core we infer that the caldera of barren island volcano is younger than 10 ka

glacial interglacial indian summer monsoon dynamics the modern indian summer monsoon ism is characterized by exceptionally strong interhemispheric transport indicating the importance of both northern and southern hemisphere processes driving monsoon variability here we present a high resolution continental record from southwestern china that demonstrates the importance of interhemispheric forcing in driving ism variability at the glacial interglacial time scale as well interglacial ism maxima are dominated by an enhanced indian low associated with global ice volume minima in contrast the glacial ism reaches a minimum and actually begins to increase before global ice volume reaches a maximum we attribute this early strengthening to an increased cross equatorial pressure gradient derived from southern hemisphere high latitude cooling this mechanism explains much of the nonorbital scale variance in the pleistocene ism record

distinguishing between archean and paleoproterozoic tectonism and evolution of the isortoq fault zone eqe bay area north central baffin island canada structural metamorphic and u pb geochronological data bear on the distinction between archean and paleoproterozoic tectonism along the southeastern margin of the rae province on baffin island archean rocks include ca 3 0 2 8 ga gneiss two greenstone belts of the mary river group and various younger granitoid intrusions in the greenstone belts intermediate felsic volcanism 2 74 2 725 ga was accompanied and outlasted by calc alkaline plutonism 2 73 2 715 ga deformation low to medium pressure metamorphism and peraluminous plutonism followed at ca 2 7 ga archean rocks and the locally overlying piling group ca 2 2 1 9 ga were deformed and metamorphosed together during development of the paleoproterozoic foxe fold belt tectonism is linked to the isortoq fault zone a major southeast dipping structure marking an abrupt northwestward transition to granulite facies within a 5 km wide zone tight folds of the archean mary river group give way down section to moderately southeast dipping high

irregular wave transformation processes in surf and swash zones a frequency domain model is developed for elucidating the nonlinear transformation processes of the fourier amplitudes and phases of normally incident random waves in surf and swash zones the verticallyintegrated continuity and momentum equations which have been used to describe a turbulent bore on a beach are rearranged to derive the equations expressing the cross shore variations of the fourier components of normally incident random waves the derived equations are solved numerically using forcing terms computed from a previously developed time domain model the frequencydomain model attempts to quantify the importance of the nonlinear forcing due to the cross shore variations of instantaneous radiation stress and bottom shear stress as well as the seaward boundary condition related to incoming low frequency waves for generating two dimensional surf beat in the surf and swash zones

age constraints on the paleoproterozoic tectonometamorphic history of the committee bay region western churchill province canada evidence from zircon and in situ monazite shrimp geochronology in situ u pb sensitive high resolution ion microprobe shrimp analyses of monazite from upper amphibolite facies paragneiss of the committee bay supracrustal belt central rae domain canada reveal three age populations ca 2350 1850 and 1780 ma the ca 1850 ma age also corresponds to growth of low th u zircon as indicated by u pb shrimp analyses of zircon separates from melanosome and leucosome the contextual advantage of the in situ monazite analysis allows evaluation of the geochronological data in terms of the regional structural and metamorphic evolution the region is dominated by a northeast striking s2 s1 fabric axial planar to tight northwest vergent f2 folds early garnet is enveloped by this biotite sillimanite cordierite s2 fabric garneti hosts ca 1850 ma monazite inclusions with ca 2350 ma cores placing a maximum age on garneti growth and s2 development d2 metamorphic conditions progressed through 3 5 kbar 1 kbar 100 mpa and 600 c to near peak conditions of 5 kbar and 675 c a minimum age for s2 is provided by unstrained ca 1820 ma monzogranite that locally and regionally truncates s2 dominantly ca 1780 ma matrix monazite is interpreted to date post s2 garnetii and cordierite which record 5 kbar and 675 c these data indicate that the committee bay region experienced penetrative d2 tectonometamorphism at ca 1850 1820 ma with a subsequent static overprint the absence of a ca 1 85 ga plutonic suite in the region suggests that low pressure metamorphism was a response to thick skinned crustal thickening initiated at ca 1870 ma the new data highlight the importance of paleoproterozoic reworking of the central rae domain in the hinterland of the trans hudson orogen

the holocene indian monsoon variability over the southern tibetan plateau and its teleconnections abstract a high resolution stalagmite oxygen isotope record from tianmen cave located in the south central tibetan plateau characterizes detailed climatic variations between 8 7 and 4 3 ka bp on centennial and decadal time scales with a temporal resolution of 3 to 7 years the tianmen record is in good agreement with speleothem records from asian monsoon regions i e dongge cave dykoski et al 2005 wang et al 2005 qunf cave fleitmann et al 2003 upwelling records from the arabian sea gupta et al 2003 gupta et al 2005 and peat bog records from southeast tibetan plateau hong et al 2003 indicating that the indian summer monsoon ism gradually weakened as northern hemisphere summer insolation declined during the early mid holocene and that ism intensity rather than temperature dominates the precipitation 18o on centennial to decadal time scales in the southern tp on centennial to decadal time scales the detrended tianmen record correlates well with the greenland ice core record further confirming the mechanistic connection between the ism and high northern latitude temperature changes meanwhile the tianmen record bears significant solar activity cycles suggesting that the solar output changes may affect the variability of the ism and likely the position of the intertropical convergence zone itcz as well moreover due to joint effects of changes in monsoon precipitation moisture source and temperature the tianmen 18o record shows much larger amplitude changes than speleothem 18o records from low elevation asian monsoon regions which is similar to the previously reported marine isotope stage mis 5 record cai et al 2010 suggesting heightened sensitivity of precipitation isotope composition to climate changes over the high elevation regions and further demonstrating that the stable isotope lapse rate may change under different climatic conditions

variability of southwest indian summer monsoon precipitation during the bolling allerod we have generated a high resolution 20 yr 2 3 0 th dated stalagmite oxygen isotope record from timta cave in the western himalaya in india that documents southwest indian summer monsoon ism precipitation variations during the bolling allerod interstadial from 15 2 to 11 7 ka compared with the glacial and younger dryas ism precipitation was enhanced during the bolling allerod ism precipitation was apparently coupled to variations in the east asian monsoon and north atlantic climate on millennial and multicentennial time scales during the deglaciation analyses of a high growth rate interval 2 5 yr resolution encompassing the late bolling early alterod suggest that multidecadal monsoon variability was an important aspect of ism behavior at that time the frequency spectrum of ism precipitation during this time interval is similar to that of the 1 4 c record and other ism precipitation records during the latest holocene this raises the hypothesis that multidecadal climate dynamics during the late boiling early allerod may have been similar to those that operated during the last several millennia even though the boundary conditions of these two time intervals were very different

an overview of the upb geochronology of the paleoproterozoic torngat orogen northeastern canada abstract the paleoproterozoic torngat orogen northern labrador and northeastern quebec canada is the result of oblique collision between the nain north atlantic and rae cratons a comprehensive set of u pb ages allows the chronology of events to be closely bracketed subduction occurred below the nain craton from ca 1910 1870 ma and collision between the cratons may have occurred between 1869 and 1844 ma sinistral deformation continued along the intervening abloviak shear zone until ca 1824 ma and convergence was ultimately impeded by the partial subduction of the southern rae craton post collisional isostatic uplift of the southern rae craton initiated deformation in the komaktorvik zone ca 1798 ma a prominent bend in the abloviak shear zone may be the result of differential uplift of the western side of the orogen in the south sinistral strike slip and east as well as west side up deformation continued episodically in the komaktorvik zone until at least 1710 ma the tectonic development of the orogen can be explained in terms of modern plate tectonic processes

higher erosion rates in the himalaya geochemical constraints on riverine fluxes the modern erosion rate of continental scale mountains is difficult to estimate and is usually based on measurement of the suspended load flux of rivers combined with assumptions about river bedload transport and sedimentation in flood plains these two parameters are very difficult to measure directly in continental scale basins in this paper we examine the chemical composition of the suspended load bedload and dissolved load of the ganga and brahmaputra rivers and compare them with the average composition of himalayan source rocks a mass balance equation of erosion fluxes shows that a si rich component is needed in addition to suspended and dissolved load fluxes to account for the composition of the source rock it corresponds to bedload sediment and flood plain deposits which are enriched in quartz by mineral sorting during transport the combined budget of si al and fe in the river system allows us to estimate this si rich flux by this method the total himalayan erosion is estimated to be twice the measured flux of suspended load the comparison between the brahmaputra and the ganga shows that the eastern himalaya has a higher erosion rate 2 9 mm yr than the western himalaya 2 1 mm yr this is likely the result of the higher runoff in the brahmaputra basin the intensity of the monsoon acts as a first order control of the erosion rate in the range

himalayan sedimentary pulses recorded by silicate detritus within a ferromanganese crust from the central indian ocean a central indian ocean deep water seamount hydrogenous ferromanganese crust ss663 crust contains variable 7 23 amounts of detrital material silicate detritus taking into account the growth rate of the authigenic component the accumulation rate of the silicate detritus has been calculated which shows an overall decrease during the past 25 7 2 ma growth history of the specimen this silicate detritus displays ond 0 between 37 7 and 312 7 and 87 sr 86 sr between 0 7083 and 0 7215 the sr nd isotopic compositions record the variation in the mixture of two detrital end members throughout the growth history of the ss663 crust while one end member clearly appears to be himalayan derived material the other component is less well defined but could be related to the volcanogenic component from the indonesian back arc basin we have unscrambled the proportion of these two components in the silicate detritus of the ss663 crust to quantify the variation in the accumulation rate of the himalayan derived silicate detritus during the last 25 ma the result shows three periods of high accumulation rates modern around 10 ma and prior to 16 ma these sedimentary pulses have already been recognised and described in the turbidites from the distal bengal fan which is located more than 1000 km away from the ss663 crust location suggesting that these sedimentary pulses are of regional significance rather than of local importance the timings of elevated contents of the himalayan derived silicate detritus in the specimen during the neogene closely superimpose the periods of the himalayan uplift along the main central thrust the main boundary thrust and the main frontal thrust this further emphasises the tectonic control of the sediment production by the erosion of an active orogenic range and its distribution over a vast area additionally close superimposition of the early miocene detritus pulse in the ss663crust on the riverine sr isotopic positive excursion suggests that the physical and chemical weathering of the himalaya was strongly coupled during the early miocene while the spatial decoupling appears to have taken place only around 12 14 ma 2002 elsevier science b v all rights reserved

sedimentary responses to the indian summer monsoon variations recorded in the southeastern andaman sea slope since 26ka abstract paleoenvironment and paleoclimate change in the andaman sea during the last 26 ka were reconstructed from high resolution records of grain size major elements and sr nd isotopes in core adm 9 the values of end 0 and 87sr 86sr were in good agreement with those of irrawaddy river sediments indicating a common source of origin two sensitive grain size intervals 3 4 7 5 and 16 8 21 2 m were identified the former was controlled primarily by sea level change whereas the latter was related to irrawaddy river discharge and south west current transport driven by the indian summer monsoon ism proxies of chemical weathering k al and terrigenous input ti ca coupled with sensitive grain size interval 16 8 21 2 m population revealed that the ism was weak during 15 26 ka bp and then strengthened gradually to a maximum during 7 9 ka bp subsequently the ism exhibited a generally declining trend to 2 ka bp the variation in the ism recorded in this work is consistent with ism variations observed in an open area in the northern indian ocean and adjacent continents implying the evolution of the asia summer monsoon since 26 ka

u pb geochronology of a paleoproterozoic continental magmatic arc on the western margin of the archean nain craton northern labrador canada the paleoproterozoic torngat orogen in northernmost labrador and northeastern quebec records the collision between the western margin of the nain province and the eastern margin of the rae province six samples from a suite of calc alkaline plutonic rocks that intrude the nain craton have been dated using the u pb method at 1895 2 1888 2 1885 2 two samples and 1859 ma and support the interpretation that east dipping subduction occurred below the nain craton during this interval a granitic dyke that truncates the sinistral shear fabric in the abloviak shear zone is 1824 2 ma placing a younger limit on the timing of this deformation in the area a second granitic dyke emplaced synchronously with dextral deformation in the bend in the abloviak shear zone is 1798 3 ma a model is proposed in which subduction occurred beneath the nain craton along its entire exposed length from 1 91 to 1 86 ga and collision occurred between 1 86 and 1 84 ga followed by oblique uplift of the southern

magnetic properties of sediments in the bay of bengal and the andaman sea impact of rapid north atlantic ocean climatic events on the strength of the indian monsoon abstract the results of a high resolution mineral magnetic study combined with major element geochemistry analysis oxygen isotopes and 14c ams stratigraphy are reported for deep sea gravity cores md77 169 and md77 180 located in the andaman sea and the bay of bengal respectively core md77 169 covers the last 280 kyr and core md77 180 covers the last 160 kyr in both cores rock magnetic parameters indicate that the magnetic assemblage is dominated by pseudo single domain titanomagnetite grains with grain size variations following a strong 23 kyr periodicity smaller magnetic grain sizes are observed during periods characterized by a strong summer monsoon in addition in core md77 180 we observe a correlation between magnetic grain size and a chemical index of alteration this suggests that these magnetic grain size changes are related to chemical weathering driven by summer monsoon rainfall a comparison of the gisp2 ice core isotopic record and the magnetic grain size record of the bay of bengal shows that rapid temperature variations documented in the ice core dansgaard oeschger cycles and heinrich events during the last glacial period are also present in the magnetic grain size record heinrich events and cold stadial events are characterized by relatively large magnetic grain sizes furthermore heinrich events are characterized by lower values of the chemical index of alteration implying a lower degree of chemical weathering related to significantly drier conditions on the continent we suggest that rapid cold events of the north atlantic heinrich events during the last glacial stages are characterized by a weaker summer monsoon rainfall over the himalaya via an atmospheric teleconnection

timing of proterozoic deformation and magmatism in a tectonically reworked orogen rayner complex colbeck archipelago east antarctica abstract the high grade metamorphic rocks of the colbeck archipelago comprise granulite facies metasedimentary gneisses and charnockitic gneisses of three ages a suite of rocks previously mapped as the colbeck gneiss is shown to be composite in age and origin consisting of metasedimentary and orthogneiss that are intruded by granitic gneiss and charnockitic gneiss an archaean granulite facies s1 gneissosity is preserved in the metasedimentary gneisses and early orthogneiss the development of s1 was followed by isobaric cooling from peak metamorphic conditions of t 750 c and p 5 1 0 8 kbar younger intrusions cut rocks containing s1 structures but were deformed by a 1200 ma granulite facies d2 event that resulted in reclined isoclinal f2 folds oriented parallel to a pervasive east trending l2 mineral and stretching lineation rocks bearing s2 structures are cut by the areally extensive 960 ma mawson charnockite which was affected by two upright folding events d3 and d4 at 920 ma events d2 4 comprise the proterozoic rayner structural episode which is characterized regionally by the retrogression of archaean assemblages the two pulses of extensive intermediate to felsic magmatism accompanied or immediately preceded the proterozoic orogenies evident as d2 4 and it is tempting to infer causal links however field relationships are consistent with intrusion having been contemporary with anomalously high conductive heat fluxes which could be due to advective heating from larger intrusions not exposed at the present structural level the formation of extensional granulite facies d5 ultramylonite pseudotachylite zones is the last deformation event in the area

tropical east african climate change and its relation to global climate a record from lake tanganyika tropical east africa over the past 90 kyr abstract forcing mechanisms of tropical climate in continental areas remain poorly understood due in large part to a lack of continuous long term high fidelity records sediment core t97 52v from lake tanganyika provides new insight into the timing and mechanisms behind east african climate change over the past 90 kyr this record is particularly important because other than a recently recovered scientific drill core from lake malawi there are no other continuous well dated records from east africa prior to 60 ka the high resolution age model presented here provides a large degree of age certainty for the past 45 kyr and our suite of proxies allows a thorough examination of lake tanganyika s dynamics from core stratigraphy and chemical analyses we present evidence of a lake level drop greater than 400 m sometime prior to 90 ka much greater than that inferred for the lgm suggesting a period of intense aridity sometime around 100 ka additionally core t97 52 v preserves evidence of worm burrows detected by x radiographic imagery as indicated by burrow shaped deposits of iron oxide indicating a shallow lake at the time of deposition of that material intermittently high lake levels between 78 ka and 72 ka developed at the same time as a weakened asian monsoon and a pluvial phase in northeast brazil suggesting a global reorganization of climate possibly forced by a reduction in orbital eccentricity over the past 60 ka this core preserves the same events recorded in a core collected 100 km away in the southern basin of lake tanganyika including an unexplained increase in biogenic silica at 37 ka suggesting that this vast lake is responding coherently across both major bathymetric basins to regional and global climate forcing

reconstruction of last glacial to early holocene monsoon variability from relict lake sediments of the higher central himalaya uttrakhand india abstract proglacial lake sediments at goting in the higher central himalaya were analyzed to reconstruct the summer monsoon variability during the last glacial to early holocene sedimentary structures high resolution mineral magnetic and geochemical data suggest that the lacustrine environment experienced fluctuating monsoonal conditions optically stimulated luminescence osl dating indicates that the lake sedimentation occurred before 25 ka and continued after 13 ka during this period goting basin witnessed moderate to strengthened monsoon conditions around 25 ka 23 5 ka 22 5 ka 22 ka 18 ka 17 ka 16 5 ka and after14 5 13 ka the last glacial phase ended with the deposition of outwash gravel dated at 11 ka indicating glacial retreat and the onset of holocene condition additionally centennial scale fluctuations between 16 5 ka and 12 7 ka in the magnetic and geochemical data are seen a close correspondence at the millennial scale between our data and that of continental and marine records from the indian sub continent suggests that goting basin responded to periods of strengthened monsoon during the last glacial to early holocene we attribute the millennial scale monsoon variability to climatic instability in higher northern latitudes however centennial scale abrupt changes are attributed to the result of albedo changes on the himalaya and tibetan plateau

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

provenance of the proterozoic thelon basin nunavut canada from detrital zircon geochronology and detrital quartz oxygen isotopes abstract the paleoproterozoic thelon basin in nunavat canada is one of several large quartz dominated sedimentary basins developed on paleoproterozoic and archean rocks of the canadian shield coarse grained quartz to sub feldspathic sandstones and conglomerates of the thelon formation comprise the basin fill detrital zircons from the thelon formation have lam icp ms 207 pb 206 pb ages ranging from 3 94 to 1 78 ga but most are neoarchean 2 70 2 50 ga the 18 o values of quartz range from 7 7 to 13 9 and are typically 10 12 ages u zr ratios and oxygen isotopic compositions of detrital quartz are consistent with a predominantly neoarchean metasedimentary source such as surrounds the eastern thelon basin and comprises the bulk of basement rocks within the rae domain the three stratigraphic sequences of the thelon formation have 18 o ranges for detrital quartz and zircon ages that further constrain the source areas and support previous sequence stratigraphic interpretations the lower sequence contains reworked siltstone and sandstone clasts and 2 50 1 85 ga zircons indicating a contribution from paleoproterozoic terranes detrital quartz 18 o values range from 9 8 to 13 9 indicating a metamorphic source also which is consistent with a proximal source for the lower sequence the middle sequence contains zircons exhibiting the widest range of ages 3 94 1 78 ga a 3 4 ga paleoarchean zircon population cannot be correlated to the immediately surrounding basement and therefore indicates a distal source possibly in the order of 1000 2000 km away the upper sequence contains relatively few zircons due to extensive alteration but ages are predominantly early paleoproterozoic and neoarchean the upper sequence strata contain the lowest 18 o values of quartz indicating an influx of granitic material late in the depositional history of the basin the geochronology and geochemistry of detrital grains within the thelon formation indicate that the source areas evolved from predominantly proximal to distal and back to proximal as the basin filled

a 900 year 600 to 1500 a d record of the indian summer monsoon precipitation from the core monsoon zone of india 1 we present a near annually resolved record of the indian summer monsoon ism rainfall variations for the core monsoon region of india that spans from 600 to 1500 a d from a 230th dated stalagmite oxygen isotope record from dandak cave our rainfall reconstruction which spans the medieval warm period mwp and the earliest portion of the little ice age lia indicates that the short instrumental record of ism underestimates the magnitude of monsoon rainfall variability periods of severe drought lasting decades occurred during the 14th and mid 15th centuries and coincided with several of india s most devastating famines

tidal influence on suspended sediment distribution and dispersal in the northern andaman sea and gulf of martaban abstract surface and water column profiles of suspended matter collected during april may 2002 and satellite images were used to study factors influencing suspended sediment concentrations sscs and dispersal in the northern andaman sea and gulf of martaban one of the largest highly turbid areas of the world s oceans perennial high ssc in the gulf of martaban is due to a combination of factors including resuspension of sediments by strong tidal currents shallow bathymetry and seasonal sediment influx from rivers from satellite images it was observed that in the central portion of the gulf of martaban the turbidity front oscillates about 150 km in phase with spring neap tidal cycles and the area covered by the turbid zone ssc 15 mg l 1 increases from less than 15 000 km2 during neap tide to more than 45 000 km2 during spring tide the sediment discharged by the ayeyarwady river is transported mainly eastward along the coast into the gulf of martaban occasionally during the winter monsoon period sediment plumes are seen heading westward into the bay of bengal turbidity profiles show that bottom nepheloid layers are actively transporting some of the sediments into the deep andaman sea via the martaban canyon

constraints on pb closure temperature in titanite based on rocks from the ungava orogen canada implications for u pb geochronology and p t t path determinations on the basis of multiequilibrium metamorphic pressure temperature p t estimates we have determined that 660 700 c is a reasonable minimum estimate of the closure t of pb diffusion in titanite a temperature significantly higher than previously suggested activity corrected reactions that produce titanite define narrow t stability fields 40 c that correspond closely to metamorphic p t determinations derived for coronitic garnet clinopyroxene hornblende samples growth of titanite occurring between 1789 and 1814 ma in the underthrust archean basement of the paleoproterozoic ungava orogen northern quebec is associated with retrograde metamorphism during underthrusting of the archean basement approx 1 b y after formation of the original granulitic assemblages

the 8 2 ka event from greenland ice cores we present a collection of high resolution chemistry and stable isotope records from the plateau of the greenland ice cap during the cold event 8200 yr ago using a composite of four records the cold event is observed as a 160 5 yr period during which decadal mean isotopic values were below average within which there is a central event of 69 yr during which values were consistently more than one standard deviation below the average for the preceding period four cores in north south and central greenland show differences at decadal and shorter timescales it is not yet clear if this represents significant spatial differences in response the results show clear evidence for colder temperatures and a decrease in snow accumulation rate however the changes in chemical concentrations for the ions looked at here are small suggesting only minor changes in atmospheric circulation for this event apart from the decrease in methane concentration greenland ice cores give only weak evidence for effects outside the north atlantic region

reconstruction of environmental changes using a multi proxy approach in the ulleung basin sea of japan over the last 48 ka based on elemental geochemical data we reconstructed the sediment provenance surface productivity and bottom water redox conditions for the last 48 ka in the ulleung basin sea of japan and inferred the factors controlling them al2o3 tio2 ratio and chemical index of alteration cia suggest that sediment provenance changed during the glacial period 48 18 ka compared to the deglacial ca 18 11 ka and holocene mass accumulation rates of total organic carbon toc caco3 phosphorus cadmium and excess barium reveal low paleoproductivity during low sea stand during 18 11 ka productivity increased due to increasing inflow of nutrient rich water masses the oyashio and the east china sea coastal water in tandem with the rising sea level maximum productivity occurred during younger dryas and pre boreal periods when sea level was at 60 m and then gradually decreased as the tsushima warm current inflow kicked off at ca 9 3 ka consistent with other paleoredox proxies which reveal the presence of anoxic bottom water during ca 12 9 ka with the changes in paleoredox proxies and their ratios toc mo u mn c s ratio and uauthigenic and mo contents we hypothesized that the redox changes were mainly ventilation driven and were superimposed on the influence of circulation induced productivity changes the global climate and sea level changes on a millennial timescale play a major role in enhancing paleoproductivity and restrict bottom water advection subsequently driving the oxygenation of bottom water in the ulleung basin copyright 2012 john wiley sons ltd

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

early partitioning of quebec microcontinent formation in the paleoproterozoic the distribution of allochthonous versus parautochthonous carbonate platforms combined with the timing of initial continental rift magmatism versus the timing of subsequent rifting of the continental margin provides tectonostratigraphic evidence for the formation and isolation of the oldest documented microcontinent perhaps as a consequence of the impingement of a mantle plume onto a cratonic margin during the paleoproterozoic initial rifting of the archean nucleus of north america in eastern canada is constrained to have been diachronous between 2 17 and 2 03 ga renewed rifting of a segment of the continental margin 292 to 120 m y later was accompanied by the emplacement of ultramafic layered sills the accumulation of komatiitic and alkalic basalts the deposition of banded iron formations and the isolation of a microcontinent and its 1 93 ga continental shelf succession subsequently accreted to the telescoped continental margin during collisional orogenesis

u pb and lu hf isotopes of the archean orthogneiss complex on eastern hall peninsula southern baffin island nunavut identification of exotic paleo to mesoarchean crust beneath eastern hall peninsula abstract eastern hall peninsula on southeastern baffin island lies at the junction of a complex paleoproterozoic collision between the rae craton meta incognita microcontinent and the north atlantic craton from ca 1 88 to 1 80 ga several different interpretations of crustal correlations and the location of intervening sutures have been proposed based on reconnaissance scale geologic investigation therefore in this study complex zircon grains from archean orthogneiss units on eastern hall peninsula were analyzed in situ to elucidate the detailed magmatic history of the region and assess crustal provenance magmatic zircons yielded u pb crystallization ages between ca 2976 and 2720 ma and metamorphic zircons record tectonothermal disturbances between ca 2740 and 2700 ma a period coinciding with metamorphism documented in adjacent crustal blocks e g west greenland and northern labrador magmatic rocks older than ca 2740 ma generally have positive ehf t signatures between 0 and 7 2 and depleted mantle model ages of ca 3 1 3 0 ga indicating the time that protolith melt was extracted from the mantle the oldest granodioritic crust crystallized at ca 2976 ma and was then reworked periodically at ca 2 93 2 84 2 81 and 2 77 2 69 ma zircons from two orthogneiss samples with u pb crystallization ages younger than ca 2740 ma yielded negative ehf t values ranging from 4 to 12 and mean depleted mantle model ages of ca 3 4 and 3 3 ga respectively indicating derivation from an older potentially exotic crustal source yet to be identified in outcrop on hall peninsula synthesizing regional u pb data we propose a new regional correlation model that retains the essentials of previous models and incorporates new data from eastern hall peninsula and other recent studies this new tectonic correlation model groups eastern hall peninsula southern cumberland peninsula and the aasiaat domain into a core zone that shared a geologic history prior to 1 90 ga and potentially prior to 2 75 ga

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

age and provenance of early precambrian metasedimentary rocks in the lapland kola belt russia evidence from pb and nd isotopic data 207pb 206pb ages are presented for detrital zircons laser ablation microprobe icp ms and whole rock nd isotopic determinations tims from samples of neoarchean and palaeoproterozoic metasedimentary rocks from the umba granulite terrane and the keivy domain of the central kola composite terrane kola peninsula north western russia three are samples of rocks from the umba granulite terrane that were deposited 2 20 1 90 ga they contain archaean detritus much of it older than 3 0 gyr as well as abundant 2 20 1 95 gyr old material deposition may have occurred on the margin of an archaean craton with an exposed palaeoproterozoic magmatic arc source possibly during orogenesis two samples from the keivy domain have remarkably similar dominantly archaean detrital zircon age spectra one was deposited pre 2 4 ga whereas the other was probably deposited post 2 01 ga both had similar sources compatible with the proximal country rocks and possible shallow water cratonic margin depositional settings

geology u pb and pb pb geochronology of the lake harbour area southern baffin island implications for the paleoproterozoic tectonic evolution of northeastern laurentia geological and geochronological results of an investigation of the paleoproterozoic siliciclastic and carbonate supracrustal rocks of the lake harbour group lhg and surrounding tonalitic gneisses on southern baffin island are presented conventional u pb geochronology of monazite from rocks of the lhg suggest that penetrative deformation of these rocks occurred prior to or during peak metamorphic conditions at ca 1845 1840 ma conventional u pb zircon results indicate that much of the tonalitic gneiss ranges in age from to 1827 the tonalitic gneisses and lake harbour group units were tectonically imbricated by ca 1805 ma and are part of a southwest verging thrust belt interpreted from regional considerations to represent the northern continuation of the ungava orogen the present results indicate that current tectonic models for the evolution of northeastern laurentia that involve a dominantly archean southeastern rae province require revision it is proposed that much of the metaigneous mate

multi stage zircon and monazite growth revealed by depth profiling and in situ u pb geochronology resolving the paleoproterozoic tectonics of the trans hudson orogen on southeastern baffin island canada abstract understanding the growth and recrystallization of zircon and monazite during regional metamorphism is important for identifying the nature and timescales of tectonic processes in continental crust we present extensive in situ u pb monazite geochronology and u pb zircon depth profiling analyses from the mid crust exposed on southeastern baffin island canada in the internal zone of the paleoproterozoic trans hudson orogen in situ la icp ms u pb monazite dating on ten metasedimentary rocks totalling 300 analyses from different paleodepths reveals a dominant ca 1860 1820 ma monazite population that records regional mid amphibolite to granulite facies metamorphism with coeval fabric development subordinate monazite with ages between ca 1800 1750 ma are interpreted to have formed through dissolution reprecipitation the sims u pb depth profiling technique allowed dating of ca 1861 1833 ma zircon rims and less abundant ca 1800 1764 ma zircon rims that would be unresolvable using conventional spot dating trace element depth profiling via la icp ms shows that zircon rims typically have lower th u values higher hf contents and different ree compositions than zircon interiors zircon rim compositions are highly variable with no apparent link to u pb age and are interpreted as the combined result of metamorphic zircon growth and dissolution reprecipitation our data demonstrate that the timing of peak metamorphism is recorded by both monazite and zircon and that they are both sensitive to u pb age resetting at lower temperatures during late orogenic tectonism regional mid amphibolite to granulite facies metamorphism and east directed crustal shortening are bracketed between ca 1860 1820 ma these events are interpreted to result from the accretion of cratonic blocks in the internal zone of the trans hudson orogen the integrated geochronological approach on regionally distributed samples enabled us to document ca 1800 1750 ma monazite domains and zircon rims which we interpret to result from the terminal collision with the lower plate superior craton followed by late to post orogenic tectonothermal activity that continued for at least 70 myr after thermal peak this prolonged history is characteristic of the northeastern trans hudson orogen and implies that orogenic collapse may not be a hallmark of all hot thickened orogens

review of crustal architecture and evolution in the ungava peninsula baffin island area connection to the lithoprobe ecsoot transect within the trans hudson orogen in northern quebec and southern baffin island parautochthonous archean basement and paleoproterozoic cover as well as allochthonous accreted paleoproterozoic units are exposed in a series of antiformal culminations and complementary synclinoria the parautochthonous rocks of the superior province margin and two assemblages of accreted paleoproterozoic units ungava and meta incognita crustal terranes define a basic tripartite crustal architecture which is characterized by polyphase deformation and metamorphic histories early structures and mineral assemblages are recognized in all three crustal components and shown to be temporally distinct the earlier structures and assemblages are overprinted by younger elements and mineral assemblages that are related to at least three regional contraction episodes and one thermal event that are common to all crustal components of the orogen close correlation of regional aeromagnetic data in northern quebec and southern baffin island with the three crustal components offers a first order approximation of the distribution of basement lithological units across hudson strait continuation of the aeromagnetic domains beneath ungava bay to northeastern quebec and northern labrador allows for the southward extrapolation of the tripartite trans hudson orogen crustal architecture into the lithoprobe eastern canadian shield onshore offshore transect area

u pb geochronology of detrital zircons in metasedimentary rocks from southern baffin island implications for the paleoproterozoic tectonic evolution of northeastern laurentia a geochronological investigation of metasedimentary rocks from southern baffin island using the geological survey of canada shrimp ii sensitive high resolution ion microprobe has characterized the ages of detrital zircon populations to determine their provenance bracket timing of deposition and distinguish potentially distinct sequences of rocks four lithologically and structurally distinct metasedimentary packages have been identified each appears to have been derived from a different source region in the structurally lowest package all analysed zircons are archean and 90 have ages between 2 83 and 2 63 ga these rocks are interpreted as the northernmost exposures of the paleoproterozoic povungnituk group of the cape smith belt northern quebec with detritus derived from the superior craton occupying the intermediate structural levels the most abundant supracrustal rocks on southern baffin island are siliciclastic and carbonate units of the lake harbour group and the tasiuyak paragneiss

mid late holocene monsoonal variations from mainland gujarat india a multi proxy study for evaluating climate culture relationship a multi proxy study involving palynology phytoliths sedimentology clay mineralogy carbon isotopes and magnetic mineralogy was carried out on wadhwana lake sediments from sub humid zone of mainland gujarat to determine the mid holocene climatic fluctuations and its possible impact on the harappan culture the 1 03 m sediment profile of wadhwana lake shows five paleoclimatic phases the study reveals high lake stand during phase i 7500 5560 cal yr bp a considerable cool and moist climatic condition during phase i is inferred due to the presence of pollen belonging to wet evergreen taxa and high phytolith climatic index ic later part of phase i show gradual replacement of evergreen to deciduous pollen taxa decrease in ic value and dominance of smectite over kaolinite indicating a reduction in wet climatic condition due to decline in the precipitation and prevalence of seasonally dry climate however a large variety of madhuca meliaceae asteraceae pollen taxa abundant fresh water algae chrozophora and ceralia pollen in this period provides evidence of intensified arboriculture and agricultural activity low lake level and dry climate have been documented during phase ii 5560 to 4255 cal yr bp and are synchronous with the lake records of western indian region high values of phytolith aridity index iph high primary minerals increase in the i 13c values provide evidence for excessive dry climatic conditions at 4255 cal yr bp phase iii shows a gradual strengthening of sw monsoon after 3500 cal yr bp phase iv shows a short pulse of dry climatic conditions 3238 to 2709 cal yr bp followed by somewhat similar to present day climate for phase v the study concludes that onset of dry climate after 5500 cal yr bp is a regionally spread synchronous event that has been documented in several lake records of western india it is surmised that the urbanization in harappan civilization in north west india was coincident with the initial phase of declining rainfall of mid holocene the emergence of cultural complexity of harappan civilization should be seen as an initial adaptation to earliest phase of environmental deterioration and its subsequent decline is probably linked with the changing seasonality pattern and excessive dry climate of later phase 4200 4255 cal yr bp of mid holocene

east asian monsoon variability since the mid holocene recorded in a high resolution absolute dated aragonite speleothem from eastern china abstract paleoclimatic conditions associated with the east asian monsoon are reconstructed for the mid to late holocene using 18o values 819 measurements from a precisely dated 10 230th dates aragonite stalagmite from lianhua cave hunan province china 18o values 1 6 to 7 0 are interpreted to reflect the precipitation amount effect related to the strength of summer monsoonal circulation throughout this period the intensity of east asian summer monsoonal circulation declined in response to changes in insolation and a southward shift in the intertropical convergence zone itcz punctuating this first order trend are abrupt millennial to decadal scale fluctuations the most prominent of which occurred around 3337 5 yr bp and records a dramatic weakening in summer monsoonal circulation that coincides with the beginning of neoglacial conditions comparisons between the 18o values of stalagmite a1 and previously published data from stalagmite hs 4 from heshang cave and stalagmites d4 and da from dongge cave china demonstrate a similar regional response to changes in east asian monsoonal circulation several spectral analysis techniques and wavelet analysis were applied to these stalagmite records to evaluate the nature and character of cyclicity in the east asian monsoon during the holocene multi taper method mtm lomb scargle and single spectrum analysis ssa results reveal common periodicities that are unlikely to be artifacts of any single technique the periodicities expressed in the stalagmite 18o records occur at both solar and non solar frequencies and support previous interpretations that variability in monsoonal circulation responds to both solar forcing and internal climatic mechanisms wavelet analysis demonstrates that some of these frequencies are intermittent and recur at semi regular intervals which may indicate long term cyclicity that is unconstrained by the chronology of the record

u pb geochronology of deformation and metamorphism across a central transect of the early proterozoic torngat orogen north river map area labrador1 the early proterozoic torngat orogen resulted from the oblique collision of the archean nain and southeastern rae provinces and evolved in four stages 0 deposition of platformal supracrustal assemblages followed by subduction related arc magmatism in the margin of the rae province i crustal thickening and nappe tectonics ii sinistral transpression and formation of the abloviak shear zone iii uplift on steeply dipping east verging mylonites along the eastern orogenic front u pb geochronology on zircon and monazite from major rock units and syntectonic intrusions indicates that arc magmatism at ca 1880 ma was followed by 40 ma of deformation and high grade metamorphism from ca 1860 to 1820 subsequent uplift and final cooling occurred ca 1795 1770 ma several ages of mineral growth that correspond to distinct structural and metamorphic events have been recognized 1 1858 1853 ma zircon and monazite dates are interpreted as the minimum age of stage i and peak metamorphic conditions 2

modulation and amplification of climatic changes in the northern hemisphere by the indian summer monsoon during the past 80 k y high frequency suborbital variations dansgaard oeschger cycles characterize the climatic history of the northern hemisphere as observed in greenland ice cores deep sea sediments of the north atlantic the californian borderland the arabian sea the south china sea and the chinese loess area paleoceanographic data from core kl126 from the bay of bengal in combination with data from the other asian monsoonal areas indicate that the feedback processes involving snow and dust of the tibetan plateau vary the summer monsoon capacity to transport moisture into central south asia and into the atmosphere we postulate that the summer monsoon initiates amplifies and terminates these cycles in the northern hemisphere

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

terrane boundaries within trans hudson orogen quebec baffin segment canada changing structural and metamorphic character from foreland to hinterland within the trans hudson orogen in northern quebec and southern baffin island parautochthonous archean basement and paleoproterozoic cover as well as allochthonous accreted paleoproterozoic units are exposed in a series of antiformal culminations and complementary synclinoria the parautochthonous rocks and two assemblages of accreted paleoproterozoic units crustal terranes are separated by major tectonic boundaries and associated deformation zones field petrological and isotopic data document an increase in the width of the deformation zones and a concomitant increase in p t conditions of metamorphism from orogenic foreland to hinterland tectonostratigraphic and geochronological criteria allow footwall and hangingwall units to be consistently distinguished in spite of the changing structural and metamorphic aspect of the terrane boundaries across the width of the orogen

swash on a gently sloping beach waves observed in the inner surf and swash zones of a fine grained gently sloping beach are modeled accurately with the nonlinear shallow water equations the model is initialized with observations from pressure and current sensors collocated about 50 m from the mean shoreline in about i m depth and model predictions are compared to pressure fluctuations measured at five shoreward locations and to run up run up was measured with a vertical stack of five wires supported parallel to and above the beach face at elevations of 5 10 15 20 and 25 cm each 60 m long run up wire yields time series of the most shoreward location where the water depth exceeds the wire elevation as noted previously run up measurements are sensitive to the wire elevation owing to thin run up tongues not measured by the more elevated wires as the wire elevation increases the measured mean run up location moves seaward low frequency infragravity energy decreases and higher frequency sea swell energy increases these trends as well as the variation of wave spectra and shapes e g wave skewhess across the inner surf zone are well predicted by the numerical model

coherence between solar activity and the east asian winter monsoon variability in the past 8000 years from yangtze river derived mud in the east china sea ams 14 c dating and grain size analysis for core pc 6 located in the middle of a mud area on the inner shelf of the east china sea ecs were used to rebuild the holocene history of the east asian winter monsoon eawm the 7 5 m core recorded the history of environmental changes during the postglacial transgression the core s mud section the upper 450 cm has been formed mainly by suspended sediment delivered from the yangtze river mouth by the ecs winter coastal current ecswcc since 7 6 kyr bp using a mathematical method called grain size vs standard deviatiow we can divide the core pc 6 s grain size distribution into two populations at about 28 mu m the fine population 28 mu m is considered to be transported by the ecswcc as suspended loads content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation thus variation of mean grain size from the fine population would reflect the strength of ecswcc which is mainly controlled by the east asian winter monsoon abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ecswcc which was caused by the strengthened eawm thus the high resolution mean grain size variation might serve as a proxy for reconstruction of the eawm a good correlation between sunspot change and the mean grain size of suspended fine population suggests that one of the primary controls on centennial to decadal scale changes of the eawm in the past 8 ka is the variations of sun irradiance i e the eawm will increase in intensity when the number of sunspots decreases spectral analyses of the mean grain size time series of core pc 6 show statistically significant periodicities centering on 2463 1368 128 106 100 88 91 7678 and 70 72 years the eawm and the east asian summer monsoon easm agree with each other well on these cycles and the east asian monsoon eam and the indian monsoon also share in concurrent cycles in holocene which are in accord with the changes of the sun irradiance c 2005 elsevier b v all rights reserved

deep sea records of the continental weathering and erosion response to east asian monsoon intensification since 14 ka in the south china sea we analyzed sediment from ocean drilling program odp site 1144 in the northern south china sea to examine the weathering response of se asia to the strengthening of the east asian monsoon eam since 14 ka our high resolution record highlights the decoupling between continental chemical weathering physical erosion and summer monsoon intensity mass accumulation rates ti ca k rb hematite goethite and sr 87 sr 86 show sharp excursions from 11 to 8 ka peaking at 10 ka clay minerals show a shorter lived response with a higher kaolinite illite chlorite ratio at 10 7 9 5 ka however not all proxies show a clear response to environmental changes magnetic susceptibility rises sharply between 12 and 11 ka grain size becomes finer from 14 to 10 ka and then coarsens until similar to 7 ka but is probably controlled by bottom current flow and sealevel sr and nd isotopes show that material is dominantly eroded from taiwan with a lesser flux from luzon while clay mineralogy suggests that the primary sources during the early holocene were reworked via the shelf in the taiwan strait rather than directly from taiwan erosion was enhanced during monsoon strengthening and caused reworking of chemically weathered pleistocene sediment largely from the now flooded taiwan strait which was transgressed by similar to 8 ka cutting off supply to the deep water slope none of the proxies shows an erosional response lasting until similar to 6 ka when speleothem oxygen isotope records indicate the start of monsoon weakening although more weathered sediments were deposited from 11 to 8 ka when the monsoon was strong these are reworked and represent more weathering during the last glacial maximum lgm when the summer monsoon was weaker but the shelves were exposed c 2012 elsevier b v all rights reserved

40ar 39ar and pb pb study of individual hornblende and feldspar grains from southeastern baffin island glacial sediments implications for the provenance of the heinrich layers lead isotope analysis of individual feldspar grains and 40ar 39ar analysis of individual hornblende grains from three samples taken from baffin island ice proximal till deposits are consistent with a provenance recording a two stage geologic history including formation of continental crust in the late archean and partial isotopic resetting and or reequilibration during major paleoproterozoic regional metamorphism and magmatism significantly although the populations are small and the two stage archean paleoproterozoic history of their sources are similar the pb isotope compositions of samples from baffin island do not match the results from heinrich layer h2 in core hu87 033 009 from northeast of the hudson strait in the labrador sea specifically in h2 samples from hu87 033 009 the 207pb 204pb is high for a given value of 206pb 204pb additionally the range in 206pb 204pb is greater in hu87 033 009 samples and there are two distinct trajectories of 208pb 204pb the steeper of the 208pb 204pb versus 206pb 204pb trends is not seen in the studied baffin island glacial sediment samples samples of feldspar grains from heinrich layers h1 h2 h4 and h5 from core v28 82 in the eastern north atlantic have a 207pb 204pb versus 206pb 204pb relation similar to that of baffin island till samples but there is also a high 208pb 204pb that we have not captured in this suite of glacial sediment samples our results highlight the strength of a combined radiogenic isotope approach to characterizing the geological history of sediment sources and provide a first step in assessing the variability in isotope character in this region of dynamic glacial events during the late quaternary period

observations and predictions of run up for a significant range of offshore wave conditions and foreshore slopes run up observations are compared to semiempirical formulations and predictions of an existing numerical model based on the depth averaged one dimensional nonlinear shallow water equations with bore like breaking wave dissipation and quadratic bottom friction the numerical model is initialized with time series of sea surface elevation and cross shore velocity observed in 80 cm mean water depth approximately 50 m offshore of the mean shoreline on a gently sloping beach and in 175 cm water depth 100 m offshore of the shoreline on a steep concave beach run up was measured with a stack of resistance wires at elevations 5 10 15 20 and 25 cm above and parallel to the beach face at sea swell frequencies nominally 0 05 f 0 18 hz run up energy is limited by surf zone dissipation of shoreward propagating waves so that increasing the offshore wave height above a threshold value does not substantially increase the predicted or observed sea swell run up excursions e g run up is saturated existing semiempirical saturation formulations are most consistent with the observations and numerical model predictions of run up excursions nearest the bed in contrast at infragravity frequencies 0 004 f 0 05 hz where surf zone dissipation is relatively weak and reflection from the beach face is strong e g saturation formulas are not applicable the run up excursions increase approximately linearly with increasing offshore wave height the numerical model also accurately predicts that the tongue like shape of the run up results in sensitivity of run up measurements to wire elevation for instance run up excursions and mean vertical superelevation above the offshore still water level increase with decreasing wire elevation and continuous thinning of the run up tongue during the wave uprush can result in large phase differences between run up excursions measured at different wire elevations numerical model simulations suggest that run up measured more than a few centimeters above the bed cannot be used to infer even the sign of the fluid velocities in the run up tongue

empirical wave run up formula for wave storm surge and berm width abstract an empirical model to predict wave run up on beaches considering storm wave and surge conditions and berm widths dry beach has been derived through a synthetic data set generated from a one dimensional boussinesq wave model the new run up equation is expressed as a function of a new iribarren number composed of three regions the foreshore the berm or dry beach width and the dune the dissipative effect of the berm is included as a reduction factor expressed as a function of the berm width normalized by the offshore wavelength the equation is relatively simple but is shown to be applicable for a fairly wide variety of berm widths and storm wave conditions associated with extreme events such as hurricanes and it is shown to be an improvement over existing empirical run up models that do not consider the berm width explicitly in addition the new parameterization of the iribarren number considering the three regions and the berm width reduction factor are shown to improve other empirical models

u pb geochronology of the eastern hall peninsula southern baffin island canada a northern link between the archean of west greenland and the paleoproterozoic torngat orogen of northern labrador abstract a corridor east of iqaluit that crosses several regionally significant lithologic boundaries has been mapped and sampled for geochronology zircon monazite and titanite were analysed by the isotope dilution u pb method to characterize igneous and metamorphic events and pb pb ages of detrital zircons were determined by laser ablation microprobe icp ms tonalitic gneisses at the eastern end of the corridor are archean with emplacement ages of 2920 8 6 2848 3 2844 6 5 and 2797 27 15 ma these samples record variable tectonothermal overprints at ca 2 77 ga and between 1844 and 1736 ma and may be related to similar rocks in west greenland a sequence of quartzites and semipelites associated with the archean gneisses contains exclusively archean detrital zircons and was metamorphosed at 1 88 ga in the central part of the corridor semipelitic and psammitic rocks contain almost exclusively paleoproterozoic detritus deposited after 1 93 0 05 ga and are interpreted as the northern continuation of the tasiuyak gneiss of the torngat orogen at the western end of the corridor monzogranites of the cumberland batholith intruded at 1869 9 3 1857 5 3 and 1850 3 2 ma the present data suggest that the north south nagssugtoqidian collision

terrane accretion in the internal zone of the ungava orogen northern quebec part 1 tectonostratigraphic assemblages and their tectonic implications the tectonostratigraphic record of the ungava orogen contains evidence for the interaction of divergent transform and convergent plate boundaries over a 0 2 ga period in the early proterozoic three principal tectonic domains are recognized 1 autochthonous basement plutonic and supracrustal rocks of archean age 2 autochthonous and allochthonous sedimentary and volcanic units associated with a ca 1 99 1 92 ga rift to drift margin and 3 suspect crustal components of a ca 2 00 ga ophiolite and ca 1 90 1 83 ga island arc terrane domain 1 is the stratigraphic or structural basement to domains 2 and 3 field relationships indicate that domain 2 units were accumulated on or near domain 1 whereas no tectonostratigraphic linkages are known between domain 3 and the others accumulation of continent derived sedimentary rocks continental tholeiites komatiitic basalts and mafic lavas equivalent to modern normal mid oceanic ridge basalts n morb s in domain 2 is interpreted as recording continental rifting leading to the possible formation of oceanic crust pillowed basalts sheeted dykes and cumulate rocks suggest that the crustal portion of an ophiolite is preserved within domain 3 the ophiolite is interpreted as a suspect fragment of oceanic crust which may represent an earlier rifted portion of domain 2 possibly juxtaposed by transform plate boundary motions within domain 3 calc alkaline volcanic and plutonic units and sequences of volcanogenic and siliciclastic sedimentary rocks are thought to indicate the development of a magmatic arc and fore arc basin and thus the establishment of a convergent plate boundary the most internal lithotectonic packages in domain 3 are predominantly crystalline thrust sheets containing i an older intrusive suite interpreted as the plutonic foundation of the magmatic arc and ii younger plutons interpreted as the result of a reversal in subduction polarity the reversal may have followed attempted subduction of domains 1 and 2 beneath the upper plate arc assemblage of domain 3

upb geochronology of the northern torngat orogen labrador canada a record of palaeoproterozoic magmatism and deformation abstract the palaeoproterozoic torngat orogen located in northeastern quebec and northern labrador canada records the sinistral transpressional collision of the western margin of the archaean nain province and the eastern margin of the rae province u pb age determinations are presented for twelve samples from the northern part of the orogen and used to evaluate models for its tectonic evolution voluminous granitoid plutonic rocks which in part intrude gneisses interpreted as the northern extension of the nain province and are possibly related to subduction below it have zircon ages of 1910 2 ma 1895 3 ma 1891 2 ma 1890 2 ma 1869 3 2 ma and 1864 2 ma suggesting at least 45 m y of convergence between the rae and nain provinces granulite facies conditions may have existed in the northern part of the area at 1 84 ga these plutonic rocks as well as tonalitic gneisses of the nain province were reworked at amphibolite facies conditions within a north south corridor referred to as the komaktorvik zone zircon age determinations of two granitic veins which were intruded synchronously with ongoing deformation in the komaktorvik zone are 1789 2 ma and 1719 2 ma suggesting that deformation within the zone may have lasted for up to 70 m y metamorphic titanite from samples within the komaktorvik zone have ages of 1776 4 ma 1774 4 ma 1767 4 ma 1710 4 ma and 1632 4 ma and support the interpretation of long lived deformation in the komaktorvik zone palaeoproterozoic subduction beneath the nain province has not been widely recognized in southern parts of the orogen suggesting that a distinct tectonic regime existed in the study area

trans hudson orogen of north america and himalaya karakoram tibetan orogen of asia structural and thermal characteristics of the lower and upper plates 1 the trans hudson orogen tho of north america and the himalaya karakoram tibetan orogen hkto of asia preserve a paleoproterozoic and cenozoic record respectively of continent continent collision that is notably similar in scale duration and character in tho the tectonothermal evolution of the lower plate involves 1 early thin skinned thrusting and barrovian metamorphism 2 out of sequence thrusting and high t metamorphism and 3 fluid localized reequilibration anatexis and leucogranite formation the crustal evolution of the indian lower plate in hkto involves 1 early subduction of continental crust to ultrahigh pressure uhp eclogite depths 2 regional barrovian metamorphism and 3 widespread high t metamorphism anatexis and leucogranite formation the shallow depths of the high t metamorphism in hkto are consistent with early to mid miocene ductile flow of an indian lower plate midcrustal channel from beneath the southern tibetan plateau to the greater himalaya melt weakening of the lower plate in tho is not observed at a similar scale probably due to the paucity of pelitic lithologies tectonothermal events in the upper plate of both orogens include precollisional accretion of crustal blocks emplacement of andean type plutonic suites and high t metamorphism syncollisional to postcollisional events include emplacement of garnet biotite muscovite leucogranites anatectic granites and sporadic metamorphism up to 90 myr following the onset of collision in tho comparing the type and duration of tectonothermal events for tho and hkto supports the notion of tectonic uniformitarianism for at least the later half of dated earth history and highlights the complementary nature of the rock record in an older exhumed orogen compared to one undergoing present day orogenesis

sensitive grain size records of holocene east asian summer monsoon in sediments of northern south china sea slope changes in paleoenvironments over the last 17 500 yr have been documented by a high resolution clay mineralogy and grain size records of core kng5 from the northern slope of the south china sea our results indicate that clay minerals are mainly from the pearl river from 17 500 to 12 500 cal yr bp and the south china sea modern current system began to form since 12 500 cal yr bp as a result taiwan turns to be the major contributor of clay minerals after 12 500 cal yr bp two grain size populations with high variability through time were identified in the 13 28 mu m and 1 2 2 mu m grain size intervals the 1 2 2 mu m grain size population are mainly controlled by provenance supply and current transport the 13 28 mu m grain size fraction could be controlled mainly by the sea level change the 1 2 2 mu m grain size population record demonstrates that east asian summer monsoon intensity generally follows changes in insolation and that the response is similar for a large area of china and other northern low latitude records implying the globality of the monsoon evolution since holocene the anomalous environmental conditions in the northern south china sea may imply intensified enso activity during the late holocene c 2011 university of washington published by elsevier inc all rights reserved

a new greenland ice core chronology for the last glacial termination 1 we present a new common stratigraphic timescale for the north greenland ice core project ngrip and grip ice cores the timescale covers the period 7 9 14 8 kyr before present and includes the bolling allerod younger dryas and early holocene periods we use a combination of new and previously published data the most prominent being new high resolution continuous flow analysis cfa impurity records from the ngrip ice core several investigators have identified and counted annual layers using a multiparameter approach and the maximum counting error is estimated to be up to 2 in the holocene part and about 3 for the older parts these counting error estimates reflect the number of annual layers that were hard to interpret but not a possible bias in the set of rules used for annual layer identification as the grip and ngrip ice cores are not optimal for annual layer counting in the middle and late holocene the timescale is tied to a prominent volcanic event inside the 8 2 kyr cold event recently dated in the dye 3 ice core to 8236 years before a d 2000 b2k with a maximum counting error of 47 years the new timescale dates the younger dryas preboreal transition to 11 703 b2k which is 100 150 years older than according to the present grip and ngrip timescales the age of the transition matches the gisp2 timescale within a few years but viewed over the entire 7 9 14 8 kyr section there are significant differences between the new timescale and the gisp2 timescale the transition from the glacial into the bolling interstadial is dated to 14 692 b2k the presented timescale is a part of a new greenland ice core chronology common to the dye 3 grip and ngrip ice cores named the greenland ice core chronology 2005 gicc05 the annual layer thicknesses are observed to be log normally distributed with good approximation and compared to the early holocene the mean accumulation rates in the younger dryas and bolling periods are found to be 47 2 and 88 2 respectively

reconstructing chemical weathering physical erosion and monsoon intensity since 25 ma in the northern south china sea a review of competing proxies reconstructing the changing strength of the east asian summer monsoon has been controversial because different proxies many being indirect measures of rainfall tell contrasting stories about how this has varied over long periods of geologic time here we present new sr isotope grain size and clastic flux data and synthesize existing proxies to reconstruct changing chemical erosion in the northern south china sea since the oligocene using the links between weathering rates and monsoon strength established in younger sediments as a way to infer intensity chemical proxies such as k rb l al and the chemical index of alteration cia together with clay proxies like kaolinite illite chlorite show a steady decline in alteration after a sharp fall following a maximum at the mid miocene climatic optimum mmco 15 5 17 2 ma probably as a result of cooling global temperatures in contrast physical erosion proxies including bulk ti ca and clastic mass accumulation rates mar show peaks at 21 23 ma similar to 19 ma and 15 5 17 2 ma implying faster run off in the absence of drainage capture rates increase again likely driven by slightly increased run off after 13 ma but decrease after 8 ma which is identified as a period of summer monsoon weakening sr isotope composition correlates with hematite goethite and the spectral proxy crat to show stronger weathering linked to more monsoonal seasonality these proxies argue for a strengthening of the east asian monsoon after 22 23 ma followed by an extended period of monsoon maximum between 18 and 10 ma then weakening there is some suggestion that the summer monsoon may have strengthened since 3 4 ma after reaching a minimum in the pliocene c 2014 elsevier b v all rights reserved

proterozoic orogens of the northeastern canadian shield new information from the lithoprobe ecsoot crustal reflection seismic survey as part of the eastern canadian shield onshore offshore transect ecsoot lithoprobe acquired 1250 km of deep seismic reflection data along the coast of labrador and across ungava bay to image evidence of proterozoic crustal accretion to the archean nuclei of the nain and superior provinces of the canadian shield the relatively pristine archean crust of the nain province has low reflectivity and generally lacks systematic reflector orientations reworking of archean crust on the margins of the makkovik province has little effect on this weak signature in contrast the archean crust in the eastern churchill rae province appears to have been overprinted by a strongly developed whole crustal easterly dipping reflection fabric interpreted to result from proterozoic collision of the nain and superior provinces in the paired new quebec and torngat orogens juvenile proterozoic crust in the makkovik and grenville provinces also shows strong whole crustal dipping reflection fabrics interpretable as outw

turbulence in the swash and surf zones a review this paper reviews mainly conceptual models and experimental work in the field and in the laboratory dedicated during the last decades to studying turbulence of breaking waves and bores moving in very shallow water and in the swash zone the phenomena associated with vorticity and turbulence structures measured are summarised including the measurement techniques and the laboratory generation of breaking waves or of flow fields sharing several characteristics with breaking waves the effect of air entrapment during breaking is discussed the limits of the present knowledge especially in modelling a two or three phase system with air and sediment entrapped at high turbulence level and perspectives of future research are discussed

bar generating cross shore flow mechanisms on a beach random waves normally incident on a dissipative beach induce a variety of cross shore flows such as asymmetric oscillatory flow wave grouping induced long wave flow breaking induced turbulent flow and momentum decay induced undertow these flows are identified analyzed and hindcasted in a set of laboratory experiments with the aim of revealing the role of each of the flow mechanisms in the two dimensional case of bar generation on a beach

upb geochronology of the western cape smith belt canada new insights on the age of initial rifting and arc magmatism abstract the cape smith belt of northern quebec is the foreland to hinterland transition of the ungava orogen a component of the paleoproterozoic trans hudson orogen of north america u pb ages for rift and volcanic arc related units from the cape smith belt are presented and used to evaluate models of its tectonic evolution a gabbroic sill intrusive into the rift related sediments near the base of the povungnituk group is 2038 2 4 ma old indicating that rifting of the superior province was initiated prior to that time 80 m y earlier than previously reported a granodiorite intrusive into the volcanic rocks of the povungnituk group is dated at 1991 2 ma indicating that magmatism associated with the rifting event was active at that time 30 m y earlier than formerly thought the age of parent group arc related magmatism ranges from 1874 3 4 ma the age of a diorite intrusion to 1860 2 ma the age of another diorite intrusion and of a rhyolite a granodiorite intrusive in the parent group yields an age of 1845 6 ma magmatism of the parent group is thought to be related to northward dipping subduction of the superior province margin below the watts group a gabbroic intrusion in the 2000 ma old watts group is dated at 1858 2 ma these ages are consistent with a tectonic model in which the rocks of the cape smith belt formed in a single continental rift to oceanic progression followed by subduction which led to an arc continent collision a comparison of u pb ages for similar events in different sectors of the trans hudson orogen in canada reveals that early events are diachronous and range from 2169 ma to 2038 ma the main collisional events are coeval in the ungava and new quebec orogens and in some of the western sectors at 1830 1860 ma younger ages of 1800 1820 ma are obtained for the late collisional stages throughout the trans hudson orogen

the irrawaddy river sediment flux to the indian ocean the original nineteenth century data revisited the irrawaddy ayeyarwady river of myanmar is ranked as having the fifth largest suspended load and the fourthhighest total dissolved load of the world s rivers and the combined irrawaddy and salween thanlwin system is regarded as contributing 20 of the total flux of material from the himalayan tibetan orogen the estimates for the irrawaddy are taken from published quotations of a nineteenth century data set and there are no available published data for the myanmar reaches of the salween apart from our own field studies in 2005 and 2006 no recent research documenting the sediment load of these important large rivers has been conducted although their contribution to biogeochemical cycles and ocean geochemistry is clearly significant we present a reanalysis of the irrawaddy data from the original 550 page report of gordon covering 10 yr of discharge 1869 1879 and 1 yr of sediment concentration measurements 1877 1878 we describe gordon s methodologies evaluate his measurements and calculations and the adjustments he made to his data set and present our revised interpretation of nineteenth century discharge and sediment load with an estimate of uncertainty the 10 yr average of annual suspended sediment load currently cited in the literature is assessed as being underestimated by 27 on the basis of our sediment rating curve of the nineteenthcentury data on the basis of our sampling of suspended load the nineteenth century concentrations are interpreted to be missing about 18 of their total mass which is the proportion of sediment recovered by a 0 45 mm filter the new annual irrawaddy suspended sediment load is mt our revised estimate of the annual sediment load 364 60 from the irrawaddy salween system for the nineteenth century 600 mt represents more than half the present day ganges brahmaputra flux to the indian ocean since major chinese rivers have reduced their load due to damming the irrawaddy is likely the third largest contributor of sediment load in the world

sea surface temperatures during the sw and ne monsoon seasons in the western arabian sea over the past 20 000 years abstract the western arabian sea is influenced by the seasonal southwest and northeast monsoon wind systems in the modern day sw monsoon induced upwelling of cold water leads to lowest ssts in summer while in glacial periods weakened upwelling and increased cooling by ne monsoon winds may have resulted in lowest sst in winter in order to reconstruct the western arabian sea seasonal sea surface temperature sst evolution during the monsoons over the past 20 000 years a novel proxy is used that captures the contrast in seasonal ssts the presented proxy concerns the difference in 18o between two shallow dwelling species of planktonic foraminifera globigerinoides ruber which calcifies throughout the year and globigerina bulloides which mainly calcifies during sw monsoon driven upwelling we convert this 18o difference to the difference in calcification temperature tcrub bul and use it in combination with mg ca derived temperatures to reconstruct seasonal ssts we present the monsoon evolution record of core niop929 located nw of the island of socotra based on our results we distinguish three distinct modes i a glacial monsoon mode 20 13 ka bp characterised by weakly negative tcrub bul values and sw monsoon ssts tsw that are 2 c higher than ne monsoon ssts tne this pattern is indicative for a weak sw monsoon and stronger cooling by glacial ne monsoon winds compared to the modern situation ii a transitional mode 13 8 ka bp characterised by tcrub bul values around 0 and thus a reduced difference between tsw and tne iii the modern monsoon mode which started at 8 ka bp with the main shift toward low summer ssts and high winter ssts the modern mode is characterised by tcrub bul values around 4 c indicative of a strong sw monsoon associated with strong upwelling and weak influence of the ne monsoon on sst we propose that measuring mg ca on both species will improve the accuracy of the sst estimates

major and trace element variations of the sediments at odp site 1144 south china sea during the last 230 ka and their paleoclimate implications abstract we present here the major and trace element data of the sediments at odp site 1144 of the last 230 ka with time resolution about 1 5 kyr to investigate their relations to the climate changes estimated from tio2 and cao contents over 70 in weight of the sediments are terrestrial materials and caco3 abundance ranges between 7 and 19 the variation patterns of some of the major elements such as al fe k mg and mn and some of the trace elements such as the alkali elements such as rb and cs the alkali earth elements such as ba and most transition metals such as sc v co cr zn well match that of the oxygen isotopes of the planktonic foraminifer after normalized with ti with higher values during interglacial periods and lower values during glacial periods whilst the na abundance exhibits inverse variation patterns with lower values during interglacial periods and higher values during glacial periods however most refractory elements such as y zr nb hf ta rees th and u do not show such patterns these agree well with the behaviors of these elements during chemical weathering therefore the changes of chemical weathering intensity in south china the source area of these sediments may account for such variation patterns during interglacials wet and warm climate might occur at south china which resulted in stronger chemical weathering and dry climate might occur during glacials which resulted in weaker chemical weathering such paleoclimate interpretation agrees with those from other paleoclimate proxies such as pollen records indicating that change of the east asian monsoon especially change of the winter monsoon is the key for such paleoclimate variation patterns

late quaternary climatic control on erosion and weathering in the eastern tibetan plateau and the mekong basin abstract high resolution siliciclastic grain size and bulk mineralogy combined with clay mineralogy rubidium strontium and neodymium isotopes of core md01 2393 collected off the mekong river estuary in the southwestern south china sea reveals a monsoon controlled chemical weathering and physical erosion history during the last 190 000 yr in the eastern tibetan plateau and the mekong basin the ranges of isotopic composition are limited throughout sedimentary records 87 sr 86 sr 0 7206 0 7240 and e nd 0 11 1 to 12 1 these values match well to those of mekong river sediments and they are considered to reflect this source region smectites illite chlorite and smectites kaolinite ratios are used as indices of chemical weathering rates whereas the bulk kaolinite quartz ratio is used as an index of physical erosion rates in the eastern tibetan plateau and the mekong basin furthermore the 2 5 6 5 m 15 55 m siliciclastic grain size population ratio represents the intensity of sediment discharge of the mekong river and in turn the east asian summer monsoon intensity strengthened chemical weathering corresponds to increased sediment discharge and weakened physical erosion during interglacial periods in contrast weakened chemical weathering associated with reduced sediment discharge and intensified physical erosion during glacial periods such strong glacial interglacial correlations between chemical weathering erosion and sediment discharge imply the monsoon controlled weathering and erosion

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