shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

early mesozoic tectonics of the south china block insights from the xuefengshan intracontinental orogen abstract intracontinental orogens remain less understood than accretionary or collisional orogens that are related to plate margin interactions in the center of the south china block the xuefengshan belt provides a well exposed example of such an intracontinental orogen of early mesozoic age detailed field tectonic observations indicate that the xuefengshan belt can be divided into a western outer zone characterized by km scale box fold structures and an eastern zone separated from the western outer zone by the se dipping main xuefengshan thrust in the eastern zone nw verging folds coeval with a pervasive slaty cleavage and a nw se trending lineation are the dominant structures from west to east the dip of the cleavage surface exhibits a fan like pattern the bulk architecture of the xuefengshan belt results from polyphase deformation d 1 is characterized by a top to the nw ductile shearing d 2 corresponds to se directed back thrusting and folding d 3 consists of upright folds with vertical cleavage and lineation at depth a high strain zone characterized by greenschist facies metamorphic rocks and a top to the nw ductile shearing corresponds to a ductile decollement zone that accommodated the deformation of the neoproterozoic to early triassic sedimentary series kinematic compatibility suggests that the synmetamorphic ductile shearing was coeval with the d 1 event in the sedimentary cover the xuefengshan belt is interpreted as an early mesozoic intracontinental orogen which possibly originated from the se directed continental subduction of a piece of the south china block in response to northwestwards subduction of the pacific plate

island ecosystem and biodiversity dynamics in northeastern australia during the holocene unravelling short term impacts and long term drivers vegetation changes of tropical lizard island great barrier reef world heritage area australia over the last 8000 years are derived from palaeoenvironmental analysis of a 475 cm long sediment core during early holocene sea level rise flooding of the continental shelf and thus isolation of lizard island the pollen record shows the gradual establishment of a mangrove forest paralleled by contraction of the near coastal palm and grass dominated vegetation subsequently mid holocene relative environmental stability supported a diverse rhizophora dominated mangrove and open mixed sclerophyll vegetation inland around 6000 years ago a profound disturbance of the mangrove is recorded by a siliciclastic layer and we hypothesise that this deposit documents the impact of a storm or cyclone postevent environmental conditions were strongly altered with enhanced estuarine conditions supporting a sonneratia and bruguiera dominated mangrove forest during late holocene sea level fall and stabilisation prograd

environmental context for late holocene human occupation of the south wellesley archipelago gulf of carpentaria northern australia a 2400 year record of environmental change is reported from a wetland on bentinck island in the southern gulf of carpentaria northern australia three phases of wetland development are identified with a protected coastal setting from ca 2400 to 500 years ago transitioning into an estuarine mangrove forest from ca 500 years ago to the 1940s and finally to a freshwater swamp over the past 60 years this sequence reflects the influence of falling sea levels development of a coastal dune barrier system prograding shorelines and an extreme storm cyclone event in addition there is clear evidence of the impacts that human abandonment and resettlement have on the island s fire regimes and vegetation a dramatic increase in burning and vegetation thickening was observed after the cessation of traditional indigenous kaiadilt fire management practices in the 1940s and was then reversed when people returned to the island in the 1980s in terms of the longer context for human occupation of the south wellesley archipelago it is apparent that the mangrove phase provided a stable and productive environment that was conducive for human settlement of this region over the past 1000 years

high frequency of super cyclones along the great barrier reef over the past 5 000 years understanding long term variability in the occurrence of tropical cyclones that are of extreme intensity is important for determining their role in ecological disturbances1 2 3 4 5 for predicting present and future community vulnerability and economic loss6 and for assessing whether changes in the variability of such cyclones are induced by climate change7 our ability to accurately make these assessments has been limited by the short less than 100 years instrumented record of cyclone intensity here we determine the intensity of prehistoric tropical cyclones over the past 5 000 years from ridges of detrital coral and shell deposited above highest tide and terraces that have been eroded into coarse grained alluvial fan deposits these features occur along 1 500 km of the great barrier reef and also the gulf of carpentaria australia we infer that the deposits were formed by storms with recurrence intervals of two to three centuries8 9 10 11 and we show that the cyclones responsible must have been of extreme intensity central pressures less than 920 hpa our estimate of the frequency of such super cyclones is an order of magnitude higher than that previously estimated which was once every several millennia12 13 14 and is sufficiently high to suggest that the character of rainforests and coral reef communities were probably shaped by these events

palaeomagnetic constraints on the collision and rotation of north and south china the eastern half of china is dominated by the north china block ncb and south china block scb separated by a complex fold system that trends roughly east west interpretation of the geology of this fold belt has led to a variety of estimates of the age of amalgamation of these two blocks1 7 palaeomagnetic results are few and have also been subject to conflicting interpretations8 11 here we present our own palaeomagnetic results for late permian rocks for both the scb and ncb and summarize other relevant palaeomagnetic data by reinterpreting the polarity given in some previous studies we are able to synthesize the results for the widespread emeishan basalts of the scb and to suggest a new model for the collision and relative rotation of the two blocks

vegetation change in the coastal lowland rainforest at avai o vuna swamp vava u kingdom of tonga avai o vuna swamp a small coastal wetland in vava u kingdom of tonga produced a 4500 year pollen and sediment record results are 1 a mid holocene sea level highstand is confirmed for tonga between about 4500 and 2600 14 c yr b p marine clay contains pollen from mangroves rhizophora mangle coastal forest trees barringtonia asiatica and cocos nucifera and rainforest trees alphitonia rhus hedycarya and calophyllum 2 microscopic charcoal first appeared at 2600 14 c yr b p coincident with the arrival of polynesians 3 cocos pandanus excoecaria macaranga and elaeocarpaceae pollen reflects the establishment of a mixed coastal lowland rainforest in the last 2500 years 4 the loss of hedycarya elaeocarpus calophyllum and guettarda and the reduction of terminalia and taxa in the papilionaceae family by about 1000 years ago may be due to habitat destruction and the loss of dispersal capabilities of some species through the extinction of the two largest pigeons in tonga d 2005 university of washington all rights reserved

long shelf sediment transport and storm bed formation by cyclone winifred central great barrier reef australia three major sediment facies belts occur on the great barrier reef shelf an inner shelf prism of holocene terrigenous sand and mud a patchy middle shelf veneer of palimpsest muddy shelly calcsand 1 m thick above a weathered pleistocene erosion surface and an apron of modern carbonate mud and sand around reefs of the main reef tract these sediments were mobilized and strongly affected by the passage of severe tropical cyclone winifred central pressure 958 hpa which traversed the central great barrier reef shelf on february 1 1986 re surveys after the passage of cyclone winifred showed that i a storm induced shell lag and or a normally graded bed of terrigenous fine sand mud had been deposited at depths down to 20 m ii middle shelf longitudinal bedforms were widespread at depths of 28 35 m and comprised a furrowed substrate of palimpsest muddy shell gravel surmounted by 40 150 m wide ribbons of quartzose and bioclastic sand up to 15 cm thick iii fields of northward facing 1 2 m wavelength megaripples were present adjacent to zones of ribbons and in the alleys between ribbons iv five days after the cyclone mud was still settling from suspension and large parts of the inner shelf were bathed in muddy hypopycnal river plumes some of which reached 30 km seaward to the inner edge of the reef tract and v suspended mud derived in part by unmixing of the seabed was present throughout the shelf water column and a seaward thinning mud drape up to 40 cm thick had accumulated on and seawards of the inshore sediment prism tapering seawards to a few mm thick only over most of the middle shelf it is inferred that storm waves and currents associated with the passage of cyclone winifred caused widespread unmixing of bottom sediments offshore long shelf transport of bedload sand ribbons and megaripples was affected by powerful shelf parallel currents of velocity 1 3 m s as the storm passed the graded seaward thinning sand mud bed was deposited over the inner middle shelf on the middle shelf bioturbation and downward mixing of the mud drape started immediately after the passage of the cyclone and was well advanced after 3 months in this way the ephemeral seabed features produced by passage of a cyclone are gradually degraded and the storm layer stratigraphy becomes incorporated within a thin middle shelf veneer of muddy shelly calcsand

insight into craton evolution constraints from shear wave splitting in the north china craton the multi episodic tectonic activities from the precambrian to cenozoic including nucleus formation cratonic amalgamation and rejuvenation make the north china craton ncc an ideal natural laboratory for studying craton evolution spatial change in the upper deformation records is an important aspect for understanding cratonic formation and rejuvenation in this study we performed seismic shear wave splitting analysis using sks phases from 50 portable stations two different methodologies shear wave splitting measurement and amplitude analysis of transverse radial components produced mutually consistent splitting results these results showed that the seismic anisotropy beneath the ordos block can be divided into three subgroups reflecting the tectonic control combining these results with those from previous splitting studies in the eastern ncc we suggest that the proterozoic amalgamation generated the seismic anisotropy in the boundary zone between the ordos block and the trans north china orogen while the anisotropy in the eastern trans north china orogen and eastern ncc were possibly associated with the lithospheric rejuvenation during the late mesozoic to cenozoic

frequency dependent shear wave splitting beneath the japan and izu bonin subduction zones abstract despite its importance for our understanding of physical processes associated with subduction the geometry of mantle flow in subduction zones remains poorly understood particularly in the mantle wedge above subducting slabs constraints on mantle flow and deformation can be obtained by measurements of shear wave splitting a valuable tool used to characterize the geometry and strength of seismic anisotropy a complete characterization of shear wave splitting is particularly important for understanding the mantle wedge beneath japan which overlies multiple subduction zones with complex slab morphologies previous studies indicate that the upper mantle beneath japan exhibits complicated anisotropy that manifests itself in complex splitting patterns to characterize better the geometry of mantle anisotropy beneath japan we analyzed direct s waves from local earthquakes originating in the subducting slabs for evidence of shear wave splitting using data from 54 broadband seismic stations in japan s f net array in addition both local s and teleseismic sks phases were examined using data from four f net stations in the izu bonin arc in order to characterize any frequency dependence of splitting parameters that may indicate the presence of complex anisotropy we carried out our splitting analysis in two different frequency bands 0 02 0 125 hz and 0 125 0 5 hz our measurements indicate that shear wave splitting due to upper mantle anisotropy beneath japan is highly complex and exhibits both dramatic spatial variations and a strong dependence on frequency

the palaeoenvironmental development of the northeastern vietnamese mekong river delta since the mid holocene three radiocarbon dated sediment cores from the northeastern vietnamese mekong river delta have been analysed with a multiproxy approach grain size pollen and spores macro charcoal carbon content to unravel the palaeoenvironmental history of the region since the mid holocene during the mid holocene sea level highstand a diverse zoned and widespread mangrove belt dominated by rhizophora covered the extended tidal flats the subsequent regression and coeval delta progradation led to the rapid development of a back mangrove community dominated by ceriops and bruguiera but also represented locally by e g kandelia excoecaria and phoenix along rivers this community seems to have endured even when the adjoining floodplain had already shifted to freshwater vegetation generally this freshwater vegetation has a strong swamp signature but locally arecaceae fabaceae moraceae urticaceae and myrsinaceae are important and mirror the geomorphological diversity of the delta plain the macro charcoal record

sequence architecture during the holocene transgression an example from the great barrier reef shelf australia abstract the application of sequence stratigraphic analysis to post glacial sediments requires the correct identification of sequence boundaries flooding surfaces and systems tracts the nature of coastal sediments deposited during sea level cycles is complex and misinterpretation is easy particularly in ancient sequences for which eustasy is inferred rather than demonstrated a large core seismic and radiocarbon database from cleveland bay in tropical queensland allows detailed analysis of the systems tracts and parasequences developed during the late holocene despite the large database a unique sequence stratigraphic interpretation is not possible because oscillations in the sea level curve apparently occurred at a frequency higher than the resolving power of radiocarbon dating our best estimate is that the final stages of the holocene sea level rise comprise four parasequences each deposited during episodic slowdowns in sea level rise and or a pulse of rapid sediment supply sea level pauses probably occurred at 12 10 m below modern levels at 8 5 ka bp followed by a fall to ca 17 m at 8 1 ka bp a very rapid transgression to ca 10 m at 7 9 ka bp a further transgression to ca 5 m at 6 8 ka bp and a final rise to the holocene highstand at 1 65 m at 5 5 ka bp the stratigraphic record of these sea level rises is complex occurs within the modern shore connected sedimentary wedge and comprises parasequences associated with shorelines at 11 m p11 17 m p17 10 m p10 5 m p5 and 1 65 m p 1 7 each parasequence comprises in ascending order onlapping estuarine shoreline sediment including mangrove mud and beach sand and progradational shallow bay muddy sand across the bay units up to and including the lower parts of the shallow bay mud correspond to the transgressive systems tract tst of the last 18 ka glacial interglacial cycle the particular parasequence represented being dependent upon location especially depth bay mud above this level corresponds to the post 5 5 ka bp highstand systems tract hst which comprises sand cheniers on the coastal plain and bioturbated muddy sand in the shallow bay the junction between the tst and the hst lies within the bay mud and corresponds approximately to the local flooding surface for the p 1 7 parasequence deposited at the 1 65 m shoreline offshore terrigenous tst strata do not occur over most of the middle and outer shelf which instead is veneered with a thin mid cycle shellbed the lower part of this shellbed is time equivalent to the later part of the tst and the upper part is time equivalent to the hst offshore the maximum flooding horizon mfh and peak eustatic sea level horizon pesh of the late pleistocene holocene sea level cycle lie at some level within the mid cycle shellbed nearshore the mfh and pesh lie within the shore connected sediment wedge at levels near the tst hst boundary however at no locality do either the mfh and pesh necessarily correspond to a physical boundary within the stratigraphy

evidence for smoothly falling sea level relative to north queensland australia during the past 6 000 yr post glacial sea level curves are expected to differ between different parts of the world as a result of global isostatic changes1 or perhaps other forms of geoidal changes2 i report here results from the inner part of the northern great barrier reef which seem to show a pattern of smoothly falling sea level during the past 6 000 yr the results are consistent with stratigraphical results from prograded mangrove coasts on the nearby north queensland mainland the region is remote from the tectonically active margin of the south west pacific ocean and the results contribute to the global data set relevant to isostatic changes being assembled by the international sea level project igcp project no 61 they also provide a baseline relevant to holocene coral reef growth in the inner great barrier reef

abnormal pollen grains an outcome of deteriorating atmospheric conditions around the permian triassic boundary records of abnormal gymnosperm pollen morphotypes from coeval localities in russia and nw china provide independent and unique evidence of deteriorating atmospheric conditions at the close of the permian although at similar palaeolatitude the vologda region of european russia and the junggar basin of xinjiang province china were thousands of kilometres apart and on different tectonic plates the co occurrence of the megaspore otynisporites eotriassicus fuglewicz 1977 and its restricted distribution elsewhere in marine sections with either late permian ammonoids or the basal triassic conodont marker hindeodus parvus confirms the age range and correlation of the russian and nw chinese sections in three chinese sections rapid changes in carbon isotopic 13 c org composition of between 4 and 10 occur over the intervals showing abnormal pollen these patterns reflect bioclastic facies contributions responding to local environmental changes they are nevertheless coincident with global perturbations in the atmosphere caused by extensive volcanic activity around the permian triassic boundary

dislocation damping and anisotropic seismic wave attenuation in earth s upper mantle crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves although these defects known as dislocations potentially contribute to the attenuation of seismic waves in earth s upper mantle evidence for dislocation damping from laboratory studies has been circumstantial we experimentally determined the shear modulus and associated strain energy dissipation in pre deformed synthetic olivine aggregates under high pressures and temperatures enhanced high temperature background dissipation occurred in specimens pre deformed by dislocation creep in either compression or torsion the enhancement being greater for prior deformation in torsion these observations suggest the possibility of anisotropic attenuation in relatively coarse grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in earth s upper mantle

testing models of mid to late holocene sea level change north queensland australia understanding the nature of global ice equivalent eustatic sea level changes during the mid to late holocene is important to our understanding of how ice sheets will respond to future climate change this study re analyses the indicative meaning and age control of existing relative sea level rsl data from cleveland bay north queensland australia and presents new rsl data from a foraminifera based transfer function as a preliminary test of global geophysical models in this region during the mid to late holocene the foraminifera based transfer function produces reliable rsl estimates consistent through the mid to late holocene at different locations in cleveland bay analysis of the combined rsl database reveals that rsl rose above present between 8 and 6 2 ka cal bp with the peak of the sea level highstand c 2 8 m above present at c 5 ka cal bp remaining relatively stable above 1 5 m from 6 2 until at least 2 3 ka cal bp falling to present in the last millennia this long period of sea level above present in the mid to late holocene suggests a gradual rather than abrupt end to global ice melt which must have continued into the late holocene this new analysis also shows no evidence for episodic fluctuations within the highstand although they cannot be entirely ruled out by this study this study demonstrates that more sea level data needs to be collected from locations uncontaminated by glacio isostasy hydro isostasy and tectonic effects in order to better constrain the late holocene melt histories of the large polar ice sheets

a two dimensional hybrid method for modeling seismic wave propagation in anisotropic media national science foundation of china 40504006 40434012 90814002 ear 0609717 chinese academy of sciences

complex seismic anisotropy at the border of a very low velocity province at the base of the earth s mantle 1 we constrain the anisotropy associated with a very low velocity province vlvp at the base of the earth s mantle using the sks and skks waves sampling the region our selected high quality data sets consist of 415 sks and 111 skks waveforms for 127 deep earthquakes recorded at distances between 90 and 150 by the seismic stations in three temporary broadband passcal seismic arrays the kaapvaal seismic array 1997 1999 the tanzania seismic array 1994 1995 and the ethiopia kenya seismic array 1999 2001 as well as the permanent stations in the global seismographic network these seismic data provide good sampling coverage for some portion of the vlvp and its surrounding areas our results show when the sks or skks phases sample the regions away from the border of the vlvp inside or outside the vlvp the apparent splitting parameters inferred from the sks phases are consistent with those inferred from the skks phases and their variations strongly correlate with seismic stations but not with the exit points at the core mantle boundary of these seismic phases however when the sks or skks phases sample near the border of the vlvp the apparent splitting parameters inferred from the sks phases and skks phases are different and their variations no longer correlate with seismic stations these features indicate that part of the shear wave splitting for the seismic data sampling the border of the vlvp has to originate from deep mantle most likely near the border of the vlvp we assume that the anisotropy in the shallow mantle beneath seismic stations has a horizontal hexagonal symmetry axis and infer the splitting parameters associated with the shallow anisotropy beneath the seismic stations using the sks and skks waveforms for the seismic data sampling the regions away from the border of the vlvp we then obtain the splitting parameters associated with the lowermost mantle anisotropy using the sks and skks waveforms corrected for the inferred shallow anisotropy beneath seismic stations assuming that the medium in the lowermost mantle also has a horizontal hexagonal symmetry axis our results reveal a complex anisotropy pattern near the border of the vlvp such a complex anisotropy pattern may be explained by lattice preferred orientation of anisotropic mantle aggregates aligned by a complex mantle flow near the vlvp margins the complex flow pattern near the vlvp margins may indicate strong interactions between the vlvp a compositional anomaly and the surrounding normal mantle and may provide an explanation to the concentration of some hot spots geographically near the borders of the vlvps in the lowermost mantle

where is the north china south china block boundary in eastern china the qinling dabieshan belt results from the collision of the north china and south china blocks the eastern extension of the belt the sulu area consists of several stacked units from top to bottom these are 1 a weakly metamorphosed slate sandstone unit of neoproterozoic paleozoic age 2 a gneiss quartzite unit metamorphosed under high pressure p conditions 3 a marble amphibolite unit 4 an ultrahigh p unit that was very deeply subducted and then exhumed and 5 a migmatitic dome resulting from the melting of ultrahigh p rocks all these units underwent the same deformation which was characterized by a top to the northwest extensional ductile shearing during their exhumation granulite facies restites in the migmatite are not significantly different from granulitized eclogites derived from the ultrahigh p rocks the migmatite exhibits the same structural and petrologic evolution as that determined for the other units the resemblance of petrologic and structural features and the lack of ocean basin rock shows that the boundary between the north china block and south china block must be placed north of the sulu area

mantle flow pattern and geodynamic cause of the north china craton reactivation evidence from seismic anisotropy 1 we investigate the mantle flow pattern and geodynamic cause of north china craton ncc reactivation using shear wave splitting measurements from 140 broadband stations using a newly developed method for simulating wave propagation in a two dimensional anisotropic medium we first examined the influence of sedimentary structures on sks splitting measurements the simulations show that a sedimentary layer whether isotropic or anisotropic significantly influences the waveform however the shear wave splitting parameters can be retrieved with negligible errors as a result this study included new splitting measurements at stations which were deployed within basins and not used previously among 121 broadband stations that contribute valid splitting results 55 stations are newly added which were deployed within basins this significantly improved the sampling coverage on the ncc the complicated spatial patterns of the splitting parameters indicate that complex upper mantle deformation has occurred in the ncc to obtain both deep kinematic and geometric information we interpret our splitting measurements in the context of new high resolution tomographic results for the ncc by comparing our observations with three end member conceptual models upwelling wedge flow and lithospheric delamination we found that the observed anisotropy pattern beneath the ncc is not completely consistent with any of them thus we prefer a hybrid mantle flow model where the subduction of the pacific plate causes a mantle wedge flow beneath the eastern archean block and a regional upwelling beneath the central block which has been imaged as a low velocity anomaly in seismic tomography thus we speculate that the subduction of the pacific plate compared to the ncc yangtze craton amalgamation and the india eurasian collision is most likely the geodynamic cause of the reactivation of the ncc eastern block during the late mesozoic to cenozoic

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

small scale sublithospheric continental mantle deformation constraints from sks splitting observations summary it is generally believed that azimuthal seismic anisotropy is an important property of the subcontinental mantle and that this is a relatively small scale phenomenon compared with anisotropy of the oceanic mantle during recent years shear wave splitting has come to be viewed as the most direct diagnostic of azimuthal anisotropy the magnitude of the splitting delay times can often rule out a crustal source of anisotropy however it is not yet clear whether the source of anisotropy lies within the lithosphere or the sublithosphere it is essential to know the scale of lateral variations and the distribution of anisotropy with depth in order to understand the origin of this phenomenon here we describe a way to constrain the depth of the anisotropy by studying the lateral variation of the splitting parameters at neighbouring seismic stations we use sks and skks phases recorded at the nars nl array a relatively dense network of broad band stations separated by about 50 km fresnel zones at different depths are calculated for these phases the depth of the anisotropy is constrained by the criterion that fresnel zones corresponding to different splitting observations should not overlap variability in the splitting measurements for events with different directions of approach recorded at one station and for single events recorded at various stations provides evidence for a non homogeneously distributed source of anisotropy located below the array at different depths we show that this variability in the measurements cannot be due to effects of crustal scattering our results indicate that the anisotropy is partly located in the sublithospheric mantle at about 400 km depth this suggests that the deformation in this region is subject to significant lateral variations

the late quaternary decline and extinction of palms on oceanic pacific islands late quaternary palaeoecological records of palm decline extirpation and extinction are explored from the oceanic islands of the pacific ocean despite the severe reduction of faunal diversity coincidental with human colonisation of these previously uninhabited oceanic islands relatively few plant extinctions have been recorded at low taxonomic levels recent faunal extinctions on oceanic islands are concentrated in larger bodied representatives of certain genera and families fossil and historic records of plant extinction show a similar trend with high representation of the palm family arecaceae late holocene decline of palm pollen types is demonstrated from most islands where there are palaeoecological records including the cook islands fiji french polynesia the hawaiian islands the juan fernandez islands and rapanui a strong correspondence between human impact and palm decline is measured from palynological proxies including increased concentrations of charcoal particles and pollen from cultivated plants and invasive weeds late holocene extinctions or extirpations are recorded across all five of the arecaceae subfamilies of the oceanic pacific islands these are most common for the genus pritchardia but also many sedis fossil palm types were recorded representing groups lacking diagnostic morphological characters

quaternary gomphotheres mammalia proboscidea gomphotheriidae from the continental shelf pearl islands panama abstract fishermen have recovered four quaternary proboscidean teeth from the continental shelf in the vicinity of the pearl islands about 50 80 km offshore from the southern coast of panama two upper third molars m3 and one lower third molar m3 are similar to comparable teeth of the pleistocene gomphothere cuvieronius based on the presence of 4 to 5 lophs lophids that are either horizontal or slightly inclined to long axis of the tooth and rather complicated enamel with single trefoils incipient double trefoils and numerous small accessory cusps cuvieronius is also known from the pleistocene el hatillo and la trinidaita sites from the azuero peninsula in panama the teeth of cuvieronius from the pearl islands are referred to c hyodon following recent taxonomic revisions indicating a single pan american species of this genus was present in both north america and south america the oldest records of cuvieronius are from early pleistocene early irvingtonian faunas in el salvador florida and new mexico cuvieronius dispersed to south america in the early pleistocene during the great american biotic interchange with the earliest record of c hyodon on that continent from the early to middle pleistocene ensenadan tarija fauna in bolivia the two late pleistocene populations of c hyodon in the neotropical region have a disjunct biogeographic distribution with the population from southern mexico and central america separated from the second population in the andean highlands of ecuador peru and bolivia by a distance of about 1000 km the intervening region comprising the lowland tropics of northern south america was populated by the gomphothere notiomastodon during the late pleistocene although notiomastodon is also known from andean localities in ecuador and peru two of the cuvieronius teeth from the pearl islands were recovered in nets by shrimp fisherman from depths of about 90 m likely indicating they date to the last glacial maximum between 30 and 15 ka when sea level was as much as 120 m lower than present and the gulf of panama was dry land these teeth represent the first record of late pleistocene fossils of terrestrial mammals from the continental shelf in central america

middle pleistocene age of the fossiliferous sedimentary sequence from tarija bolivia abstract the highly fossiliferous sediments of the tolomosa formation from tarija southern bolivia represent one of the most important localities in south america that documents the great american biotic interchange over the past several decades chronostratigraphic studies have indicated a middle pleistocene age for the tolomosa formation from 1 1 to 0 7 ma this interval correlates to the ensenadan south american land mammal age as it is characterized from classic localities in argentina recently however a new interpretation based on ams 14c ages indicates that the fossiliferous sediments from tarija are latest pleistocene i e

late quaternary cycles of mangrove development and decline on the north australian continental shelf mangrove communities in the australian tropics presently occur as narrow belts of vegetation in estuaries and on sheltered muddy coasts palynological data from continental shelf and deep sea cores indicate a long term cyclical component of mangrove development and decline at a regional scale which can be linked to specific phases of late quaternary sealevel change extensive mangrove development relative to today occurs during periods of marine transgression whereas very diminished mangrove occurs during marine regressions and during rarer periods of relative sea level stability episodes of flourishing mangrove cannot be linked to phases of humid climate as has been suggested in studies elsewhere rather the cycle of expansion and decline of mangrove communities on a grand scale is explained in terms of contrasting physiographic settings characteristic of continental shelf coasts during transgressive and regressive phases in particular by the existence or lack of well developed tidal estuaries copyright c 1999 john wiley sons ltd

azimuthal anisotropy of lg attenuation in eastern tibetan plateau 1 the q of seismic phase lg is measured to approach the crustal q which can be used to infer crustal rheology a reverse two station event method is used to measure the interstationqlg which theoretically eliminates effects from the source and site response strong azimuthal anisotropy of 1 qlg in northern tibet is observed which approximately correlates with the seismic velocity anisotropy observed using both surface waves and teleseismic s waves both the intrinsic and scattering attenuation contribute the isotropic q whereas the anisotropic q may be associated with the fractures and faults in the crust strong 1 qlgis observed in the northwestern songpan ganzi fold belt where the high qdirections correspond with the orientations of major strike slip faults intrinsic and scatteringq values are estimated for different tectonic terranes in eastern tibetan plateau the intrinsic qvalues are approximately 500 in the northern tibetan plateau which suggests a hot 700 c crust consistent with low seismic velocity measurements our result suggests that the crust of northwestern songpan ganzi fold belt may be hotter than that of the qiangtang terrane which may be related to the strain heating along the major strike slip fault zones that dominate the northernmost tibet

evidence for a mid holocene tsunami deposit along the andaman coast of thailand preserved in a mangrove environment abstract klong thap lamu a large mangrove fringed tidal channel along the northern andaman coast of thailand provides an ideal location to test the hypothesis that a paleotsunami record can be preserved in the sediments of a mangrove forest the 2004 indian ocean tsunami destroyed local swaths of mangrove forest with highly variable widths up to 300 m left in the wake of the tsunami is a thin mantling of laterally discontinuous sand macerated shells and localized coral rubble that is being mixed rapidly into the underlying mangrove peat transects across the channel s tsunami modified shore show that the sand layer thins abruptly at the border of the undisturbed mangroves suggesting that the energy of the wave dissipated quickly as it entered the forest the distribution and sedimentology of the 2004 tsunami deposit unit ti suggest that any paleotsunami deposit within this mangrove environment should be spatially restricted and thoroughly bioturbated sediment cores collected from within the 2004 tsunami zone penetrate a buried coral shell peat unit unit tiii that tapers inland unit tiii is strikingly similar to unit ti except for unit tiii s diffuse sedimentology which we attribute to extensive bioturbation unit tiii also cross cuts an identified facies boundary that is traceable across the width of the 2004 tsunami zone rather than a facies boundary associated with the regional early to late holocene sea level regression stratigraphic correlations suggest that unit tiii represents an event horizon i e tsunami ams 14 c dates on material from within unit tiii combined with an upper bracketing age suggest that the tsunami event occurred sometime between 2720 and 4290 cy bp if correct this tsunami predates the 3 4 tsunami events recognized to the north at koh phra thong unit tiii is however a potential far field equivalent of a recently recognized paleotsunami deposit on the southwestern indian coast ca 3 710 years before present nair et al 2010

frequency dependent anisotropy in wellington new zealand shear wave splitting measurements are made using teleseismic s scs and sks waveforms recorded at the gdsn broadband station snzo situated in south karori new zealand the average s and sks delay times are around 2 to 3 s among the highest in the world the average scs delay time is significantly smaller around 1 s this discrepancy appears to be due to differences in dominant frequency the most likely cause of frequency dependent anisotropy is oriented heterogeneities with a scale length much smaller than the wavelength the fast polarizations range between 21 and 79 with an average ne sw direction which is sub parallel to the trend of the local geologic structure and the strike of the hikurangi subduction zone azimuthal variations in delay time which cannot be explained by differences in period may be due to a dipping axis of symmetry or laterally varying anisotropy or a more complicated symmetry system

distinct upper mantle deformation of cratons in response to subduction constraints from sks wave splitting measurements in eastern china abstract interaction between the subducting slab the overriding continental lithosphere and mantle flow are fundamental geodynamic processes of subduction systems eastern china is an ideal natural laboratory to investigate the behavior and evolution of cratonic blocks within a subduction system in this study we investigate deformation of the upper mantle beneath eastern china we present seismic shear wave splitting measurements from three networks consisting of over 483 broadband stations with 157 stations giving a total of 516 results the splitting parameters exhibit complex regional patterns but are relatively coherent within individual tectonic units tectonic blocks exhibited distinctive fast directions relative to regional features the dominant attitude of fast directions for the north china craton was subparallel to the direction of subduction whereas fast directions for southeastern china were perpendicular to the direction of subduction the shear wave splitting measurements were interpreted according to a high resolution tomographic body wave velocity model combining these two datasets showed that the predominant geodynamic models for the region mantle plume mantle wedge and flat slab subduction models are incompatible with the observations presented here we suggest that the north china craton yangtze craton and the cathaysia block have undergone different deformational events due to differing mantle flow patterns and distinct spatial and temporal subduction histories of the pacific and philippine sea plates

seismic anisotropy in the lower mantle a comparison of waveform splitting of sks and skks 1 we have carried out a global investigation on seismic anisotropy in the lower mantle by comparing the waveform splitting of sks and skks found at the same seismogram the two shear waves have very similar ray paths in the upper mantle but different ones in the lower mantle we collected a total of 104 sks skks waveform data recorded at 76 stations the sks skks data are first matched with a single anisotropic model 2 parameters the fast polarization direction and delay time t and two independent anisotropic models 4 parameters we then applied an f test to examine whether the 4 parameter models are better than the 2 parameter ones based on error improvement we found that the data from most of the stations can be explained by the simple 2 parameter models while this observation provides compelling evidence that the vast part of the lower mantle below 1000 km including the d region is transversely isotropic it is still arguable that the uppermost lower mantle and the transition may partly contribute the sks skks splittings we also found that the 4 parameter models provide a better fitting to the sks and skks splitting at 8 stations suggesting the existence of transverse anisotropy or anomalous dipping structures in some part of the lower mantle

middle pleistocene climate change recorded in fossil mammal teeth from tarija bolivia and upper limit of the ensenadan land mammal age fossiliferous middle pleistocene sediments of the tarija basin of southern bolivia contain a classic ensenadan land mammal fauna new carbon isotopic data reported here for 50 specimens of the grazing mammals equus horse and cuvieronius mastodon documented from eight stratigraphic levels at tarija vary significantly in the 13c values of their teeth the pattern of variation appears to reflect the proportion of c3 and c4 grasses eaten during colder more c3 and warmer more c4 times within age limits set by associated magnetostratigraphy the cold periods can be correlated with particular even numbered stages in the marine oxygen isotope record and the warm periods can be correlated with odd numbered stages the oldest fossil teeth analyzed from the tarija section can thereby be assigned to stage 29 and the youngest to stages 17 or 15 that is the teeth range in age from about 1 1 myr to as young as 0 7 myr based on correlation of the upper part of the tarija beds to the isotopic stages the upper limit of the ensenadan land mammal age is between 0 7 and 0 6 myr which is younger than stated in most previous studies

shear wave splitting from local events beneath the ryukyu arc trench parallel anisotropy in the mantle wedge we present shear wave splitting measurements from local slab earthquakes at eight seismic stations of the japanese f net array located in the ryukyu arc we obtained high quality splitting measurements for 70 event station pairs and found that the majority of the measured fast directions were parallel to the strike of the trench and perpendicular to the convergence direction splitting times for individual measurements ranged from 0 25 to 2 s most values were between 0 75 and 1 25 s both the fast directions and the split times were similar to results for teleseismic s k ks and s wave splitting at the same stations which suggests that the anisotropy is located in the mantle wedge above the slab we considered several mantle deformation scenarios that would result in predominantly trench parallel fast directions and concluded that for the ryukyu subduction system the most likely explanation for the observations is corner flow in the mantle wedge combined with b type olivine fabric in this model the flow direction in the wedge is perpendicular to the trench but the fast axes of olivine crystals tend to align perpendicular to the flow direction resulting in trench parallel shear wave splitting

high resolution body wave tomography models of the upper mantle beneath eastern china and the adjacent areas 1 we present new 3 d tomographic models of vp vs and vp vsratio anomalies in the upper mantle beneath ec and adjacent areas this data was collected and interpreted with the goal of clarifying geodynamic processes that caused spatially variable event histories throughout eastern china ec during mesozoic to cenozoic time the tomographic images were constructed by inverting body wave travel times recorded at 1300 stations within the upgraded china national seismic network and 9 temporary arrays resolution tests for different depths and the featured velocity anomalies verify that the tomographic images capture the velocity heterogeneities in the upper mantle to depths of 700 km the salient features of vp vs and vp vsratio anomalies can be clearly identified these include strong multiscale heterogeneities occupying the upper mantle beneath ec and differences in the spatial scale of anomalies found beneath northern and southern areas of ec these features demonstrate a degree of spatial variability in the geodynamic evolution of ec we propose two mechanisms to explain these patterns first the western front of the subducted slab may have imparted greater horizontal compressional stress in areas where it impinged further eastward into ec these areas would experience stronger convection and an altered stress regime in the upper mantle creating significant thermal anomalies beneath the south china block scb relative to the eastern north china craton ncc second differing thermal states and viscosities for the eastern ncc and the cathaysia block cab resulted in differing responses to regional deformation the archean hinterland of the eastern ncc specifically has a colder thermal state and higher viscosity and therefore exhibits only small scale heterogeneities due to the effect of shear localization the neoproterozoic cab has a relatively warm thermal state with lower viscosity and thus deformed more continuously

the magnitude symmetry and origin of upper mantle anisotropy based on fabric analyses of ultramafic tectonites summary seismic anisotropy within the upper mantle originates from the preferred orientation of highly anisotropic single crystals the symmetry and magnitude of anisotropy depend upon 1 the volume percentages of the minerals constituting the upper mantle 2 the degree and symmetry of preferred orientation of each mineral and 3 the alignment of the minerals crystallographic axes relative to one another the nature of upper mantle anisotropy can be examined by studying mineral orientations within ultramafic rocks which were once part of the mantle petrofabric data for olivine and pyroxene have been used to obtain velocity anisotropy patterns over large regions of ultramafic rocks from the samail ophiolite oman the troodos ophiolite cyprus the bay of islands ophiolife newfoundland the twin sisters ultramafic washington usa the dun mountain ophiolite new zealand the red hills ophiolite new zealand and the red mountain ophiolite new zealand the compressional wave anisotropy calculated for these massifs ranges from 3 to 8 per cent in excellent agreement with observed seismic anisotropy in the upper continental and oceanic mantle the symmetry varies from orthorhombic to axial with the axial symmetry axis corresponding to the olivine a axes maxima and subparallel to spreading directions in oceanic upper mantle pyroxene a b and c axes maxima generally parallel olivine b c and a axes respectively and anisotropy decreases with increasing pyroxene content shear wave splitting is predicted for all propagation directions within the upper mantle symmetry is also orthorhombic or axial with the minimum difference in velocity between the two shear waves parallel to the maximum compressional wave velocity

attenuation anisotropy and the relative frequency content of split shear waves summary the variation of frequency dependent seismic wave attenuation with direction attenuation anisotropy contains additional information to that contained in velocity anisotropy in particular it has the potential to distinguish between different mechanisms that can cause velocity anisotropy for example aligned fracturing might be expected to cause measurable velocity and attenuation anisotropy while preferred crystal orientation leads to significant velocity anisotropy but may cause only small amounts of attenuation attenuation anisotropy may also contain useful information about pore fluid content and properties we present a methodology for analysis of attenuation anisotropy and apply it to a microseismic data set previously analysed for shear wave splitting by teanby et al 2004 attenuation anisotropy values obtained show a temporal variation which appears to correlate with the temporal variation in the velocity anisotropy the comparison of the relative frequency content of fast s1 and slow s2 split shear waves is a convenient method for examining seismic attenuation anisotropy provided that s1 and s2 initially have the same spectral colouring that no spectral distortion is introduced by the differences between receiver responses of geophone components and that spectral distortion due to background noise can be ignored or corrected for we can attribute any differences in their frequency content to attenuation anisotropy attenuation anisotropy where present should be detected by the different approximately orthogonal polarizations of s1 and s2 as they pass through the anisotropic medium in the presence of attenuation anisotropy s1 and s2 should experience different levels of frequency dependent attenuation we quantify the differential attenuation of s1 and s2 using a scheme based on a spectral ratio method we present results from a microseismic data set acquired in an abandoned oil well at valhall a north sea oil field the results are surprising in that sometimes the slower arrival s2 is richer in high frequencies than the faster s1 this appears to be contrary to results predicted by theoretical crack models for attenuation anisotropy e g hudson 1981 the mechanism responsible for these observations is not clear our differential attenuation attribute correlates with the angle between the strike of the inferred initial shear wave source polarization and the fast shear wave polarization which suggests that the split shear wave with the larger amplitude is preferentially attenuated our attribute also correlates with the event backazimuth and the minimum percentage anisotropy

contrasting holocene sedimentary geologies of lower daly river northern australia and lower sepik ramu papua new guinea abstract the estuarine plain of the macrotidal daly river in monsoonal northern australia is underlain by extensive mid holocene mangrove swamp sediments which accumulated during the last stages of post glacial sea level rise sediment yield from the catchment is too low to account for the volume which accumulated during sea level rise and onshore transport is invoked this is supported by radiocarbon ages and facies analysis of the transgressive sediment tract beneath the maximum flooding surface mfs and of the tract of vertical sedimentation which extends from the mfs to the surface of estuarine fluvial transition the eft the eft occurred about 5000 to 6000 bp throughout the estuarine plain a contrasting situation exists in the lowland holocene basin of the microtidal sepik and ramu rivers in papua new guinea which derive sediment from highly tectonic catchments a tectonic basin which was a shallow brackish inland sea after post glacial transgression is separated by a low divide from a deltaic plain progradation of the deltaic plain commenced about 3500 bp after regressive sedimentation eclipsed the inland sea in the tectonic basin contrasting organic facies mangrove in the daly and freshwater swamp deposits in the sepik ramu highlight differences between facies models of the two systems differences between fluvio tidal regimes are reflected by the eft which is synchronous in the daly and diachronous in the sepik ramu and possibly by the mfs which is diachronous in the daly and may be synchronous in the sepik ramu

seismic anisotropy and mantle dynamics beneath china abstract we analyzed the shear wave splitting at 138 permanent seismograph stations to study seismic anisotropy and mantle dynamics under mainland china to obtain reliable results we used three different methods to measure the shear wave splitting parameters using core phases sks skks skiks and pks as well as the direct s waves from regional and distant earthquakes our results show that the fast orientations of the anisotropy wnw ese in eastern china are generally consistent with the absolute plate motion apm direction of the eurasian plate suggesting that the anisotropy is mainly located in the asthenosphere resulting from the lattice preferred orientation of olivine due to the shear deformation there the fast axes in western china generally agree with the strikes of the orogens and active faults while they are perpendicular to the direction of the maximum horizontal stress suggesting that the anisotropy in the lithosphere contributes significantly to the observed shear wave splitting the fast axes in western china are also consistent with the apm direction suggesting that the apm driven anisotropy in the asthenosphere is another source of the shear wave splitting there these results suggest that apm driven anisotropy commonly exists under continents similar to that under oceanic regions even though the continental lithosphere has suffered extensive deformation

preliminar correlation of the pleistocene sequences of the tarija valley bolivia with the pampean chronological standard most of the mammal collections of the pleistocene from the tarija valley bolivia lack precise stratigraphic data some fossil collections were made under stratigraphic control but have not been described however mammals were used for correlation and comparison with the pattern established for the pampean region of argentina the bearing units have been referred either to the ensenadan and bonaerian stages the belgranan the ensenadan or the lujanian in a broad sense corresponding to the middle upper pleistocene or the upper pleistocene studies during the last twenty five years accomplished by american authors and based on magnetostratigraphy and absolute dating suggest that the tarija sequence corresponds to the ensenadan early middle pleistocene of the pampean standard recently italian scientists based on radiometric dating discarded this age and considered that the whole sequence belongs to the late pleistocene new biostratigraphic and systematic studies allowed the recognition of glyptodon munizi arctotherium angustidens and hippidion devillei exclusive taxa of the mesotherium cristatum biozone the biostratigraphic base for the ensenadan of the pampean region however collections include mostly putative endemic species or those characteristic of the equus amerhippus neogaeus biozone the biostratigraphic base for the lujanian of the pampean area in sum from a biostratigraphic point of view the tarija sequence has taxa from the lower to middle pleistocene ensenadan and the upper pleistocene lower holocene lujanian of the pampean area from a paleofaunistic standpoint the association recovered from the tarija valley shows significant differences with the typical pampean association the high frequency of remains of gomphotheriidae and equidae and in lower proportion of hydrochoeriidae and tapiridae are noteworthy members of these two latter families are restricted today to warm and wet climates most glyptodontidae records belong to glyptodon and in the pampean region this family is much more diversified

cyclone frequency during the last 5000 years at curacoa island north queensland australia abstract a series of storm deposits at curacoa island a steep bedrock island in the palm group north queensland record the passage of cyclonic events storm ridge accretion occurs when cyclonic waves and surge combine to transport coarse sediment mostly broken coral onto the shore and deposit it above normal tidal levels narrow fringing reefs at curacoa act as a rapidly replenished sediment source augmented by lithic gravel transported longshore beachface stormberm ridge platform and washover deposits can accrete during a single event a series of storm ridges were examined via stratigraphic pits and trenches on two traverses deposits from 22 events were identified and their ages were determined using 68 radiocarbon dates from coral clasts most dates from each storm deposit formed statistically accordant groups only 15 of the dates were older than the group ages and were interpreted as reworked specimens accordant ages within each group were combined and converted to calibrated radiocarbon ages ridge ages decrease uniformly with distance from the oldest ridge indicating uniform depositional processes over the last 5000 years a time series of storm deposit ages indicates that cyclone frequency was statistically constant over the last 5000 years this suggests that cyclone frequency may not have been affected by sea surface temperatures in the region which appear to have been about 1 c warmer about 5000 years ago gagan m k ayliffe l hopley d cali j mortimer g chappell j mcculloch m head m j 1998 temperature and surface water balance of the mid holocene tropical western pacific science 279 1014 1018

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

coastal wetlands reveal a non synchronous island response to sea level change and a palaeostorm record from 5 5 kyr to present here we describe environmental change on lord howe island lhi 31 30 s 159 05 e over the last 5500 cal bp derived from the analysis of the accumulating sediments in four coastal wetlands grain size analyses loss on ignition loi and micrometre resolution x ray fluorescence xrf geochemical data were combined with 10 accelerator mass spectrometry ams 14c dates to determine a chronology of environmental change sedimentary coastal features were initiated on the drowned lhi basalt coastline after 4500 cal bp which was followed by gradual development of wetland environments from 4200 cal bp to present within this period a series of high intensity storm events are recorded perhaps related to low pressure systems including cyclones and east coast low ecl events a lack of synchronicity between the studied sites resulted from their position in the landscape relative to the coast features within the lagoon and greater sediment availability after 2800 cal bp as sediment filled sinks in the

seismic anisotropy in the eastern united states deep structure of a complex continental plate we have analyzed shear wave splitting recorded by portable and permanent broadband and long period stations located in the eastern united states teleseismic shear waves sks skks and pks were used to retrieve the splitting parameters the orientation of the fast wave polarization plane and the delay time t in total 120 seismic events were processed allowing for more than 600 splitting measurements within the appalachians stations located in the western external part are characterized by t 1s and trending n50 70 e in the south and central regions and n30 40 e in the north closely following the trend of the orogenic belt in these areas the transition region between north and central is characterized by t 1 1 3 s and by e w trending that are at a high angle to the regional geologic trend measurements at two stations located in the eastern internal part of the belt indicate very weak anisotropy the large scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate splitting along the southern and eastern margins of the continent is consistent with that expected for grenvillian deformation an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out within the cratonic core the correlation between t and lithospheric thickness suggests a lithospheric anisotropy smaller length scale variations also argue for a significant contribution of lithospheric structures the fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern united states i e the grenville and appalachian orogenies and the subsequent rifting of the north atlantic ocean our observations in the western appalachians suggest that the anisotropy may be preserved since the grenvillian orogeny the absence of detectable splitting in the two stations in the eastern appalachians is attributed to the igneous intrusions related to the atlantic rifting the measurements in the transition between the northern and central southern appalachians constitute an intriguing anomaly whose e w have little obvious relation to the regional surface geology we suggest two possible causes 1 the local dominance of asthenospheric flow motivated by the proximity of a pervasive low velocity anomaly and 2 lithospheric deformation in a transcontinental strike slip fault zone active during the appalachian collision

two anisotropic layers in central orogenic belt of north china craton abstract we present evidence of two layers of anisotropy in earth s upper mantle beneath the central orogenic belt of the north china craton from teleseismic shear wave splitting analysis a one layer model is in disagreement with the well constrained azimuth dependent splitting parameters for stations in the central orogenic belt however two layers of anisotropy improve the fit to the data at the bottom layer the fast polarization directions are subparallel to the absolute plate motion indicating the presence of the current strain within the subcratonic asthenosphere related to the interactions between the surrounding plates in contrast at the top layer the fast polarization directions are consistent with the strikes of the local surface faults confirming a combined contribution of the past orogenies in the lithosphere

vegetation change following mid holocene marine transgression of the torres strait shelf a record from the island of mua northern australia the pollen and sedimentary record from a coastal backdune swamp on the island of mua torres strait australia is presented a 4 55 m core collected from the swamp centre provides a record of vegetation and landscape change spanning the postglacial marine transgression to present prior to 6000 radiocarbon years before present yr bp results show mangrove vegetation encroaching on the core site periodically displacing non mangrove taxa until the establishment of an extensive mangrove forest between 6000 yr bp and 3000 yr bp within the mangrove community a transition from lower tidal rhizophora forest to an upper intertidal ceriops community is evident this is followed by the development of the current herbaceous freshwater swamp in the late holocene the dryland vegetation record is dominated by sclerophyll and rainforest elements with strongest forest representation occurring around the mid holocene before a decline in tree density and the establishment of open woodlands in the late holocene the data suggest vegetation change accompanied marine transgression and a humid mid holocene climate before stabilization of sea levels and the initiation of dominant on shore catchment processes signalling drier climatic conditions and possible human activity

magnetic polarity stratigraphy of the middle pleistocene ensenadan tarija formation of southern bolivia abstract the tarija formation of southern bolivia which is well known for its classic vertebrate faunas is of prime importance in understanding of the chronology of the ensenadan land mammal age this formation consists of well exposed and relatively fossiliferous sections of clays clayey silts sands gravels and tuffs which were deposited in a predominately fluviatile regime in a pleistocene structural basin four stratigraphic sections each measuring 110 m or less were studied to establish a magnetic polarity stratigraphy paleomagnetic samples were collected from the finer grained sediments at 100 sites spaced at stratigraphic intervals of 5 m or less all paleomagnetic specimens were demagnetized in alternating fields of least 250 oersteds oe some specimens were also thermally demagnetized at 200 c or more of the 100 sites 77 were ultimately used to determine the magnetic polarity zonation based on the four sections sampled the tarija formation spans a time interval from about 1 my to about 0 7 my b p or perhaps younger the lower half of the composite section is of reversed polarity punctuated by a short normal event this sequence probably represents the late matuyama chron with the jaramillo subchron the upper part of the section is of normal polarity and represents early brunhes time a tuffaceous unit 43 m above the brunhes matuyama boundary yielded a fission track zircon age of 0 7 0 2 by b p these data indicate that the classic tarija fauna is middle pleistocene ensendan in age

sand beach ridges record 6000 year history of extreme tropical cyclone activity in northeastern australia sand beach ridges are considered to be derived either from aeolian processes and or waves but their deposition by individual or multiple storms has not been investigated in any detail we use numerical meteorological and oceanographic models to determine the origin of a sequence of 29 shore parallel sand beach ridges in northeastern australia the results suggest that the ridges were constructed by waves and that the final form or height of the ridges is a function of high energy tropical cyclone generated waves plus storm tides hence these landforms archive a nearly 6000 year long history of intense tropical cyclones the record implies that these extreme tempests occur considerably more frequently than that suggested by the short historical record for this region the genesis of this sand beach ridge plain has implications for the interpretation of similar sequences elsewhere along the northeast coast of australia and in comparable environments globally if other similar sand beach ridge plains have also been deposited by like processes it stands to reason that these long term records of high intensity tropical cyclones can be used to ascertain a regional scale risk assessment from this hazard

glacial to holocene climate changes in the se pacific the raraku lake sedimentary record easter island 27 s abstract easter island se pacific 27 s provides a unique opportunity to reconstruct past climate changes in the south pacific region based on terrestrial archives although the general climate evolution of the south pacific since the last glacial maximum lgm is coherent with terrestrial records in southern south america and polynesia the details of the dynamics of the shifting westerlies the south pacific convergence zone and the south pacific anticyclone during the glacial interglacial transition and the holocene and the large scale controls on precipitation in tropical and extratropical regions remain elusive here we present a high resolution reconstruction of lake dynamics watershed processes and paleohydrology for the last 34 000 cal yrs bp based on a sedimentological and geochemical multiproxy study of 8 cores from the raraku lake sediments constrained by 22 ams radiocarbon dates this multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake high lake levels and clastic input dominated sedimentation in raraku lake between 34 and 28 cal kyr bp sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the glacial period between 28 and 17 3 cal kyr bp including the lgm period colder conditions contributed to a reduction of the tree coverage in the island the coherent climate patterns in subtropical and mid latitudes of chile and eastern island for the lgm more humid conditions suggest stronger influence of the antarctic circumpolar current and an enhancement of the westerlies the end of glacial period occurred at 17 3 cal kyr bp and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments deglaciation termination 1 between 17 3 and 12 5 cal kyr bp was characterized by an increase in lake productivity a decrease in the terrigenous input and a rapid lake level recovery inaugurating a period of intermediate lake levels dominance of organic deposition and algal lamination the timing and duration of deglaciation events in easter island broadly agree with other mid and low latitude circum south pacific terrestrial records the transition to the holocene was characterized by lower lake levels the lake level dropped during the early holocene ca 9 5 cal kyr bp and swamp and shallow lake conditions dominated till mid holocene partially favored by the infilling of the lacustrine basin during the mid to late holocene drought phases led to periods of persistent low water table subaerial exposure and erosion generating a sedimentary hiatus in the raraku sequence from 4 2 to 0 8 cal kyr bp the presence of this dry mid holocene phase also identified in low andean latitudes and in patagonian mid latitudes suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by el nino like dominant conditions have occurred at a regional scale the palm deforestation of the easter island attributed to the human impact could have started earlier during the 4 2 0 8 cal kyr bp sedimentary gap our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the polynesian people to the island if it occurred at ca ad 800 it coincided with the warmer conditions of the medieval climate anomaly whereas if it took place at ca ad 1300 it was favored by enhanced westerlies at the onset of the little ice age changes in land uses farming intensive cattle during the last century had a large impact in the hydrology and limnology eutrophication of the lake

smooth or oscillating late holocene sea level curve evidence from cross regional statistical regressions of fixed biological indicators abstract what if any is the pattern of change of the late holocene sea level curve if a common pattern exists can it be better discerned in the non glaciated tectonically stable regions of the southern hemisphere and is sea level data more reliable from one type of marine sample than another to begin an investigation of these questions we present a review of regressing time elevation plots from the low to mid latitudes of the southern hemisphere based upon the differential between modern and past levels of various fixed biological indicators mainly calcareous tubeworms and corals stranded up to 2 m above present relative sea levels the sample sets come from our work in southeast australia and comparable work from north east australia the pacific islands and brazil we show that using evidence obtained from fixed intertidal tubeworm species there is no statistical exclusivity between the smooth and oscillating polynomials but corals are more problematic in situ tubeworm species with their reduced error bars in comparison to corals fulfil the condition of providing more robust results for statistical analysis regression curves based on these species point to cross regional similarities in the pattern of sea level movement of the last 6000 years across the lower latitudes of the southern hemisphere these statistical exercises while not able to yield definitive conclusions can highlight statistically equally likely alternative patterns of sea level movement which can then be tested by field evidence they can also give useful indications of the quality of sea level data obtained from different biological sources as in the difficulties in the use of corals compared to common intertidal tubeworm species

holocene palaeoenvironments and change at three quarter mile lake silver plains station cape york peninsula australia pollen and diatom analyses of organic sediments from three quarter mile lake a perched lake on cape york peninsula north queensland indicate that significant changes in vegetation and hydrology occurred during the holocene early holocene grass dominated landscapes were replaced in mid holocene times by increasingly woody vegetation comprising tropical heathlands savanna and rainforest early holocene lake levels fluctuated widely from mid holocene times lake levels stabilized and water became increasingly acidic as a mature swamp forest developed adjacent to the lake and contributed tannins to the lake water the timing and character of changes are consistent with those described from the atherton tableland in wet tropical queensland holocene dry phases described from the northern territory and the western shores of cape york cannot be identified from three quarter mile lake rainforest is currently close to its greatest holocene extent suggesting that the rainforest dependent endemic fauna of no

holocene evolution of coastal wetlands in wet tropical northeastern australia pollen in sediments drilled from the innisfail coastal plain northeast queensland australia was examined to reconstruct the evolution of holocene wetlands in a wet tropical environment in contrast to monsoonal australia stable environmental conditions created by year round rainfall and low tidal range caused abrupt unidirectional transitions in wetland zonation as marine influence changed this has enabled a detailed reconstruction of the marine transgression and subsequent progradation mangroves colonized in response to marine transgression at c 7400 bp as riverine mangroves of low salt tolerance migrated up the mulgrave river these were replaced around 7000 bp by extensive rhizophora dominated mangroves coinciding with the development of a rhizophora dominated community in wyvuri embayment mangroves reached their greatest extent as sea level rise slowed towards 6000 bp with a stillstand indicated by a brief return to terrestrial conditions at one site high freshwater input depressed salt i

strong intracontinental lithospheric deformation in south china implications from seismic observations and geodynamic modeling abstract classical plate tectonics theory predicts concentrated deformation at plate boundaries and weak deformation within plates yet the existence of intracontinental orogens shows that highly deformed regions can occur within continental plates which is geodynamically incompletely understood shear wave splitting measurements in south china show belt parallel i e ne sw fast directions beneath the wulingshan xuefengshan belts while no dominant fast direction is found in the cratonic sichuan basin tomographic studies in the mantle in the same area show that the thickness of lithosphere beneath the intracontinental orogen is larger than that beneath the cratonic sichuan basin in order to better understand these seismic observations we performed numerical experiments of intracontinental lithospheric deformation with the presence of cratonic basin by comparing systematic model results with topography data and constraints on the accumulated amount of shortening in the study region we find that the best fitting result is obtained for models with a strong upper and a wet lower crust and with a weak mantle lithosphere beneath the orogen belt which has an effective viscosity that is 2 orders of magnitude smaller than that of the craton our numerical model successfully explains the belt parallel anisotropy and high velocity anomaly beneath intracontinental orogen and suggests that significant intracontinental lithospheric deformation occurred in south china

paleoenvironmental analysis of the neotropical fossil mammal site of cerdas bolivia middle miocene based on ichnofossils and paleopedology abstract the early middle miocene langhian age site of cerdas in the southern bolivian altiplano has produced a diverse fauna of extinct mammals 15 species in seven orders and 11 families in this study we use paleosols and ichnofossils to reconstruct its paleoenvironment and the conditions in which its fossils were preserved the described paleosols represent three pedotypes and three distinct landscape surfaces in an alluvial system type 1 paleosols are interpreted as haplusteps inceptisols that formed on a proximal floodplain in a subhumid to humid patchy shrubland with seasonal variation in precipitation and associated changes in soil moisture conditions landscape 1 type 2 paleosols are interpreted as dystrudepts that formed on a well vegetated distal floodplain in a seasonal humid climate with ground covering shrubland vegetation landscape 2 type 3 paleosols are interpreted as calciustolls mollisols that formed in a shifting alluvial environment in a seasonal sub humid to semi arid open environment landscape 3 ichnofossil assemblages of cerdas include skolithos planolites macanopsis parowanichnus rhizohaloes and rhizotubules these were produced by detritivorous herbivorous and faunivorous soil arthropods as well as plant roots and represent soil communities not normally preserved as body fossils that were living within a heterogeneous alluvial environment the physical and geochemical properties of the paleosols and associated ichnofossil assemblages indicate that the paleolandscapes were composed of shrublands and open environments that experienced changes in moisture regimes due to seasonal precipitation and flooding events and had varying degrees of temporal stability our analysis is the first detailed study of pre pleistocene cenozoic paleosols and trace fossils from the southern tropics mid latitudes of south america and one of the few focused on important fossil mammal bearing sediments

u series dates of great barrier reef corals suggest at least 0 7 m sea level 7000 years ago strong evidence from field observation and high precision tims u series dating of exposed in situ massive corals and exposed microatolls on magnetic island great barrier reef indicates that the relative sea level was at least 0 7 m higher than present 7000 calendar years cal yr ago and culminated to at least 1 6 m higher than present 5800 cal yr ago the present sea level was probably first reached around 7300 7100 cal yr ago together with the youngest age 2236 27 cal yr of an exposed microatoll colony the data suggest past sea level highstands occurred between 7200 and 2200 cal yr ago lasting for 5000 years this study represents the first attempt to date sea level indicators from the great barrier reef by the high precision u series method the results are broadly consistent with a sea level reconstruction based on a compilation and re examination of 115 calibrated 14c dates from eastern australia by lewis et al 2008

correlation of late cenozoic sequences of southeastern buenos aires province biostratigraphy and magnetostratigraphy abstract correlations among stratigraphic sequences of the continental late cenozoic of southeastern buenos aires province have been historically based on lithostratigraphy and paleontological content recent magnetostratigraphic studies supplied new evidence which together with biostratigraphy allowed improvement of the chronostratigraphic framework recent studies were conducted at four localities of southeastern buenos aires province playa santa elena punta hermengo mar del sur and centinela del mar the studied sequences at santa elena and mar del sur show normal magnetic polarity while punta hermengo and centinela del mar display levels of reverse polarity discontinuities in the sequence of mar del sur might explain the absence of sediments of reverse polarity thus some units the lower ones could correspond to the normal magnetic events c1r1n and or c2n as the fossil fauna collected here has no typical pliocene components that could suggest an age older than the gauss matuyama boundary i e 2 58 ma the basal levels of the profile at punta hermengo with reverse polarity display ensenadan fauna this may be the most recent section of c1r c1r1r 0 90 0 78 ma which took place after the normal jaramillo event c1r1n the lower unit of playa santa elena of normal polarity c1n bears mammal remains suggesting a late ensenadan age

storm impact and evolution of a mangrove fringed chenier plain shoal bay darwin australia abstract storms are considered to have significant impacts on the development of chenier plains particularly through the devastation of mangrove vegetation but also in terms of winnowing sand and shell from mudflats and forming chenier ridges shoal bay in the beagle gulf northern australia contains a small chenier plain which was struck by a severe tropical cyclone cyclone tracy on christmas day 1974 as it devastated the city of darwin the morphology vegetation and stratigraphy of the plain are described the plain is underlain by lower intertidal sand with shell hash a radiocarbon age of 6130 years bp indicates mangrove colonisation of this flat at the time that sea level stabilised around its present level after the postglacial transgression subsequently progradation of mudflats has occurred especially around 2300 years ago and shells of this age are found both in growth position from within the mudflats and incorporated into the shelly chenier ridges a further phase of build out and subsequent erosion is reflected by stumps and in situ bivalves being excavated presently on the foreshore radiocarbon dating about 900 1100 years bp within this context of evolution cyclone tracy can be seen to have had severe consequences upon the patterning of mangroves with extensive windthrow of ceriops and defoliation of rhizophora at the western end of the plain recovery of the mangrove vegetation has been gradual and is still incomplete however the storm had little influence on the pattern of landform development indeed the aerial photographic sequence indicates a trend by which sand shoals are gradually reworked landwards in places moving through mangrove vegetation the study suggests that rather than pronounced regional episodes of alternative mudflat buildout and erosion both processes occur simultaneously at different points along this foreshore

post glacial evolution of the indo pacific warm pool and el nino southern oscillation recent research has revealed new insights into the temperature size and variability of the indo pacific warm pool ipwp and the nature of the el nino southern oscillation enso since the last glacial maximum lgm sea surface temperature sst reconstructions from foraminiferal mg ca alkenone and revised coral sr ca palaeothermometry agree that ssts in the ipwp during the lgm were similar to 3degreesc cooler than at present in the central portion of the ipwf the rapid post glacial rise in sst led the deglaciation by similar to 3000 years to produce near modern ssts by the early holocene in contrast further west and north post glacial shifts in ssts in the south china and sulu seas are synchronous with abrupt climate changes in the north atlantic new evidence for the nature of the little ice age in the tropics has been obtained from a 420 year record of coral sr ca and 6180 from the great barrier reef australia this indicates that ssts and salinity were higher in the 18th century than in the 20th century the results suggest that the tropical pacific played a role as a source region of water vapour during the global expansion of little ice age glaciers the onset of modern enso periodicities is identified by palaeo enso records throughout the tropical pacific region similar to 5000 years ago with an abrupt increase in enso magnitude similar to 3000 years ago individual enso events recorded by corals reveal that the precipitation response to el nino temperature anomalies was subdued in the mid holocene the apparent non linear onset of enso in the late holocene appears to reflect abruptly enhanced interaction between the southern oscillation and the pacific intertropical convergence zone comparisons of precipitation variability recorded by great barrier reef corals with enso indices for the last 350 years confirms that non stationarity of enso teleconnections is a natural characteristic of modern climate c 2003 elsevier ltd and inqua all rights reserved