direct determination of the timing of sea level change during termination ii an outcrop within the last interglacial terrace on barbados contains corals that grew during the penultimate deglaciation or termination ii we used combined 230th and231pa dating to determine that they grew 135 8 0 8 thousand years ago indicating that sea level was 18 3 meters below present sea level at the time this suggests that sea level had risen to within 20 of its peak last interglacial value by 136 thousand years ago in conflict with milankovitch theory predictions orbital forcing may have played a role in the deglaciation as may have isostatic adjustments due to large ice sheets other corals in the same outcrop grew during oxygen isotope 18o substage 6e indicating that sea level was 38 5 meters below present sea level about 168 0 thousand years ago when compared to the 18o signal in the benthic v19 30 v19 28 record at that time the coral data extend to the previous glacial cycle the conclusion that deep water temperatures were colder during glacial periods

a new ordovician silurian boundary section in san juan province argentina and its definitive graptolite fauna bed by bed collecting of the la chilca formation at talacasto san juan argentina has revealed a sequence spanning the ordovician silurian boundary and the recognition of the following graptolite zones glyptograptus persculptus probable parakidograptus acuminatus and possible atavograptus d the talacasto section thus allows the closest definition of the ordovician silurian boundary in south america the shales of the la chilca formation are 3 65 m thick rich in graptolites and have allowed us to recognize for the first time in south america several stratigraphically important forms glyptograptus persculptus climacograptus angustus c normalis c acceptus c rectangularis and paraclimacograptus innotatus also identified for the first time are rhaphidograptus and lagarograptus the following are described talacastograptus leanzai gen et sp nov pseudoclimacograptus metaclimacograptus robustus sp nov and lagarograptus praeacinaces sp nov the closest affinity of the new biserial genus is considered to be with pseudoclimacograptus the evolutionary relationships of the three new graptolites are briefly discussed

ice sheet sources of sea level rise and freshwater discharge during the last deglaciation we review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation the last glacial maximum 26 19 ka was terminated by a rapid 5 10 m sea level rise at 19 0 19 5 ka sourced largely from northern hemisphere ice sheet retreat in response to high northern latitude insolation forcing sea level rise of 8 20 m from 19 to 14 5 ka can be attributed to continued retreat of the laurentide and eurasian ice sheets with an additional freshwater forcing of uncertain amount delivered by heinrich event 1 the source of the abrupt acceleration in sea level rise at 14 6 ka meltwater pulse 1a 14 15 m includes contributions of 6 5 10 m from northern hemisphere ice sheets of which 2 7 m represents an excess contribution above that derived from ongoing ice sheet retreat widespread retreat of antarctic ice sheets began at 14 0 15 0 ka which together with geophysical modeling of far field sea level records suggests an antarctic contribution to this meltwater pulse as well the cause of the subsequent younger dryas cold event can be attributed to eastward freshwater runoff from the lake agassiz basin to the st lawrence estuary that agrees with existing lake agassiz outlet radiocarbon dates much of the early holocene sea level rise can be explained by laurentide and scandinavian ice sheet retreat with collapse of laurentide ice over hudson bay and drainage of lake agassiz basin runoff at 8 4 8 2 ka to the labrador sea causing the 8 2 ka event

the ordovician silurian boundary on cornwallis and truro islands arctic canada preliminary data four sections of the lower part of the cape phillips formation two outcrops on northeastern cornwallis island and one outcrop and one drill core from truro island northwest territories canada provide significant new data on the ordovician silurian boundary they show evidence of continuous sedimentation through the boundary interval and a continuous sequence of graptolite zones including the bohemicus and persculptus zones which have not been previously found in arctic canada strata yield graptolites including uncompressed specimens and conodonts through most of the sections the ordovicicus conodont zone occurs within the pacificus to lower persculptus graptolite zones the nathani conodont zone contains a transitional fauna a mixing of species typical of the preceeding ordovicicus zone and those generally regarded as silurian indicators this conodont zone ranges from the middle of the persculptus graptolite zone into the lower acuminatus graptolite zone and thus spans the ordovician silur

structural grain mud volcanoes and other features on the barbados ridge complex revealed by gloria long range side scan sonar abstract a long range side scan sonar survey of the broad band of deformed sediments east of the antilles volcanic arc has revealed the detailed structural trends of folds and reverse faults or thrusts in plan view for the first time the prevalent trend lies substantially parallel with the arc and is simplest near to the deformation front at the eastern edge of these deformed sediments these trends are interrupted locally by more or less transverse zones of disturbance associated with ridges in the oceanic basement that are obstructing the relative eastward movement of the deformation front local rough surfaced mounds interpreted as mud volcanoes underlain by diapirs are common and occur much further to the north than the mud diapir field already described near trinidad only one large sediment slide has been identified

cuyania an exotic block to gondwana review of a historical success and the present problems abstract a review of the early history of the cuyania terrane and the numerous pioneering works of the past century provides the present robust framework of evidence supporting a derivation from laurentia travel towards gondwana as an isolated microcontinent and final amalgamation to the protomargin of western gondwana in middle to late ordovician times the major remaining uncertainties and inconsistencies such as the time of deformation and collision with gondwana the lack of evidence of famatinian derived zircons the effects of strike slip displacements proposed along the suture as well as the potential sutures defined by ophiolite assemblages are discussed the precise boundary along the northern and southern limits is not yet well defined the most suitable hypothesis based on present data is that cuyania originated as a conjugate margin of the ouachita embayment south of the appalachian platform during early cambrian times the subsequent travel toward the gondwana protomargin is clearly depicted by the changing faunal assemblages in the carbonate platform new geochemical and age data on k bentonites presented by several authors reinforce the strong connection between cuyania ash fall tuffs and famatina volcanics by 468 470 ma indicating cuyania and gondwana were in close proximity at that time extension related to flexural subsidence preceded by the drowning of the carbonate platform in early llanvirnian times is recorded by abrupt facies changes in the sedimentary cover during late llanvirnian and early caradocian times this episode marked the beginning of contact between cuyania and gondwana the subsequent evolution of the foreland basin indicates that deformation lasted until latest silurian early devonian times the time of collision is tracked by the cessation of arc related magmatic activity in the upper plate gondwana protomargin at about 465 ma in western sierras pampeanas and ages around 454 ma corresponding to syncollisional and postcollisional magmatism the age of the collision is also preserved in the lower plate cuyania where both angular unconformities in the sedimentary cover and the ages of peak of regional metamorphism in the basement rocks point to 460 ma as the most probable age for the beginning of the collision evidence from the upper plate is essentially identical with an age of 463 ma thermal gradients along this suture vary from 13 c km in the lower plate to 18 c km in the fore arc upper plate reaching more than 30 c km along the famatinian arc based on these data a llandelian caradocian age for the collision can be postulated on firm grounds deformation continued through most of the early paleozoic until amalgamation of the chilenia terrane by the late devonian

quaternary reef response to sea level and environmental change in the western atlantic the tropical subtropical western atlantic realm harbours abundant fringing reefs two major barrier reefs belize florida several atolls and large reef fringed carbonate platforms bahamas data from belize and south florida indicate that major barrier reefs were established during the high sea levels of the long and warm marine isotope stage 11 reefs formed during pleistocene sea level highstands whereas erosion non deposition and the formation of subaerial exposure surfaces prevailed during lowstands of sea level florida bahamas exposed reefs and platforms with siliciclastic hinterlands were characterized by deposition of clays and sands on fluvial plains belize elevated terraces and outcrops of reefs of the last interglacial of marine isotope stage 5e are evidence of higher than present sea level and temperature that sustained large reef fringed carbonate platforms and ramps in the florida bahamas region and central america belize mexico including ooid deposition in warm and shallow waters during the highstands of marine isotope stages 5c and 5a at sea levels several metres lower than today fringing reefs developed in parts of the caribbean for example in south florida outlier reefs data from the island of barbados support the contention that the postglacial sea level rise from about 120 m was rapid and punctuated by two meltwater pulses ia and ib which bracket the beginning and end of the younger dryas respectively after reflooding of shelves in the early holocene reefs developed preferentially on highs of the underlying karstified pleistocene limestone surface and on former river channel bars many reefs in the western atlantic region kept pace with holocene sea level rise whereas some were drowned reasons for reef drowning are debated and include sea level rise elevation of antecedent topography and deterioration of environmental conditions such as high nutrient input apart from sea level and antecedent topography factors such as exposure to waves and currents storms and sedimentation have controlled reef development the historical decline of acroporid corals in the caribbean realm has been attributed to cooling following the holocene thermal optimum however historical die offs of reef building corals and other reef organisms suggest that some if not all recent declines were unprecedented during the holocene rising temperatures decreasing carbonate saturation increased frequency of major storms high nutrient concentrations and sedimentation overfishing and disease certainly played a role in decline but systematic studies relating these environmental factors to holocene reef building are only in the early stages

seismicity of the forearc marginal wedge accretionary prism three different types of seismic data have been examined for seismic events occurring within the zone called the accreted wedge or forearc marginal wedge that underlies the inner trench wall of some arcs these types of data are 1 teleseismically recorded earthquakes that have been reported in the literature as occurring in major arc trench regions these events fail to demonstrate that earthquakes occur within the accreted wedge because the uncertainty of focal depth usually exceeds the depth dimension of the accreted wedge these data include many tsunamigenic earthquakes 2 local earthquakes located by combined ocean bottom seismograph and land networks in the arc trench region in the new hebrides and the central and eastern aleutian trench none of the more reliable of these hypocenters lies within the accreted wedge 3 s p intervals measured at stations on islands located on the outer ridge or at ocean bottom seismograph stations on the forearc marginal wedge these data do not show the existence of events occurring within the accreted wedge e g from 18 ocean bottom seismograph stations with a cumulative operation time of about 1 year the smallest s p time is about 2 5 s for events in the new hebrides and about 4 s for events in the adak and kodiak regions we found no s p time smaller than 2 s from 6 years of seismograms recorded at middleton island alaska and no s p time smaller than 4 s from 25 years of seismograms recorded on barbados all of the events could have occurred outside the forearc marginal wedge although we have located no events with hypocenters which are situated unambiguously within the accreted wedge we have located many events which occurred in the vicinity of the accreted wedge some occur in the upper portion of the benioff zone shallower than about 40 km and others occur in the leading edge of the overriding plate these locations reported in this paper which are within or close to the seismic networks comprise some of the most reliably located shallow events ever reported in convergent margins of island arcs the absence of seismic activity within the accreted wedge in any island arc that we studied suggests that the deformation evident in this region occurs aseismically

amino acids and stable carbon isotope distributions in taihu lake china over the last 15 000 years and their paleoecological implications amino acid organic nitrogen and stable carbon isotope 13c 12c profiles through a core from east taihu lake are interpreted in terms of paleoecology and paleoclimate over the last ca 15 000 yr lower amino acid contents and higher 13c values at the base of the core represent a cool and arid climate and coincide with low organic productivity a marked increase in total amino acids and organic nitrogen with a decrease in 13c values from 193 to 90 cm ca 6500 6000 yr b p indicates a warmer and moist climate and greater organic productivity amino acids then decrease in abundance while 13c values increase progressively beginning at 73 cm ca 6000 yr b p reflecting cooling and lower organic productivity the average 13c values from a core from west taihu lake are evidently higher than values from east taihu lake the latter may reflect a stream environment whereas the high 13c values from west taihu lake likely reflect autotrophic carbon sources and a lacustrine environment since 11 000 yr b p

liquefaction and flowage at archaeological sites in the inner belt of central japan tectonic and hazard implications abstract all archaeological data gathered at 55 archaeological sites excavated in the alluvial plains and basins of the inner belt of central japan revealed the occurrence and age of events of liquefaction and flowage the alluvial plains and basins are bounded on one or both sides by active faults representing tectonic or block boundary lines the excavated sites with liquefaction and flowage events identified are found distributed within a 15 km wide zone along the tectonic or block boundary lines of the alluvial plains and basins this suggests that seismic hazards caused by liquefaction and flowage mainly occur within this 15 km wide zones along the tectonic lines sand filled dikes of various shapes were found and are thought to represent evidence of liquefaction and flowage the sand filled dikes can be classified into two main types a lenticular type arrangeden echelon and a cylindrical type opening upward in a fan shape archaeological age estimates indicate that the liquefaction and flowage were induced by earthquakes which occurred during three periods around 1000 b c between 0 and 500 a d and after 1500 a d suggesting that active seismic periods occurred at an interval of approximately 1000 years

hirnantian ordovician through wenlock silurian conodont biostratigraphy bioevents and integration with graptolite biozones cape phillips formation slope facies cornwallis island canadian arctic islands cornwallis island in the canadian arctic archipelago provides one of the world s best areas for establishing an integrated graptolite conodont biozonation for the late ordovician silurian given the well exposed interfingering relationship of the basinal shale and carbonate platform facies building on earlier graptolite work 180 samples were collected from nine sections of the cape phillips formation of which 118 yielded approximately 7600 conodont elements representing 54 species in 25 genera including one new genus and species mayrodus melchini the conodonts are well preserved with minimal thermal alteration colour alteration index cai 1 nine conodont zones are recognized and defined for this region namely the amorphognathus ordovicicus distomodus kentuckyensis aspelundia expansa as fluegeli and pterospathodus celloni interval zones pt a amorphognathoides taxon range zone pt pennatus procerus and kockelella ranuliformis highest occurrence zones and k ortus absidata taxon range zone an integration of graptolite and conodont zones is documented earlier paleontological and isotope geochemical studies have demonstrated the dynamic nature of the silurian ocean climate system and identified major faunal turnovers or events five of these are recognized in the cornwallis fauna and related to oceanographic and climate changes in part referring to recent oxygen isotope data from conodonts from the cornwallis collections hirnantian extinction event sandvika event late aeronian llandovery snipklint primo episode early telychian llandovery ireviken event late telychian llandovery sheinwoodian wenlock and mulde event early homerian wenlock

actively evolving microplate formation by oblique collision and sideways motion along strike slip faults an example from the northeastern caribbean plate margin abstract the pattern of folding faulting and late quaternary coral reef uplift rates in western and central hispaniola haiti and dominican republic suggest that the elongate gonave microplate a 190 000 km2 area of the northeastern caribbean plate is in the process of shearing off the caribbean plate and accreting to the north american plate late cenozoic transpression between the southeastern bahama platform and the caribbean plate in hispaniola has inhibited the eastward motion of the northeastern corner of the plate transpression is manifested in western and central hispaniola by the formation of regional scale folds that correspond to present day anticlinal topographic mountain chains continuous with offshore anticlinal ridges areas of most rapid quaternary uplift determined from onland coral reefs 125 ka and younger coincide with the axial traces of these folds offshore data suggest recent folding and faulting of the seafloor onshore reef data do not conclusively require late quaternary folding but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the northwest peninsula of haiti 0 37 mm yr to to the central part of the coast of western haiti 0 19 mm yr to the south central part of western haiti 0 mm yr formation of the 1200 km long enriquillo plantain garden walton fault zone as a bypass strike slip fault has isolated the southern edge of the gonave microplate and is allowing continued unimpeded eastward motion of a smaller caribbean plate past the zone of late neogene convergence and quaternary uplift of coral reefs in hispaniola offshore seismic reflection data from the jamaica passage the marine strait separating jamaica and haiti show that the enriquillo plantain garden fault zone forms a narrow but deep active fault bounded trough beneath the passage the active fault is continuous with active faults mapped onshore in western haiti and eastern jamaica the bathymetric deep is present because the jamaica passage fault segment represents a 50 km wide transtensional left step of the fault trace between haiti and jamaica onshore satellite imagery and field observations suggest that the enriquillo plantain garden fault forms a continuous trace extending from central hispaniola east of lake enriquillo dominican republic to the westernmost end of the southern peninsula of haiti the regional lineament corresponds to a recent fault scarp in quaternary alluvium of the clonard pull apart basin in the central part of the southern peninsula of haiti and suggests that at least this part of the lineament has undergone recent slip calmus 1983 has suggested a total offset of 30 50 km of the enriquillo plantain garden fault zone in the southern peninsula of haiti using the apparent offset of lithologic units seismic reflection data from lake enriquillo document recent deformation of quaternary lake sediments where the lineament crosses the lake leveling of the crest of a late holocene coral reef and associated algal tufa around lake enriquillo demonstrate late holocene vertical movement and tilting in a 1500 m wide zone parallel to the fault trend lateral offset is difficult to show in the enriquillo valley area because of rapid recent sedimentation into the valley the pattern of inactive strike slip faults and fold belts of cenozoic age in cuba and the yucatan basin suggest that two elongate microplates were sheared off the proto caribbean plate and accreted to the north american plate by a similar process in paleocene and eocene times age of terminal deformation in western central and eastern cuba is consistent with southeastward younging and migration of arc collision the similarity of the size and sequence of events in cuba suggests that the process of oblique collision and sideways motion of the plate along a new strike slip fault towards a free face may be an important process of microplate formation and interplate transfer in other areas

the holocene drowned reef of les saintes plateau as witness of a long term tectonic subsidence along the lesser antilles volcanic arc in guadeloupe abstract resulting from the interplay between tectonics and eustatism reef terraces are powerful markers of vertical movements at a scale of 1000 to 100 000 years in the lesser antilles they grow around every island of the archipelago and record both local and subduction related tectonics the recent acquisition and interpretation of very high resolution bathymetry of les saintes submarine plateau french west indies together with seismic reflection profiles are a unique opportunity to study one of these submarine structures at metric to kilometric scales addressing the questions of its nature age and growth environment but also of the control of active tectonics on its formation the 20 km wide les saintes reef plateau lies at about 45 mbsl it is crosscut by nw se striking north dipping normal faults that belong to les saintes fault system and graben which produced a mw 6 3 earthquake in 2004 the plateau is composed of four 20 m thick reef units piled up in layer cake morphology down to 110 mbsl the upper unit has a fresh morphology and presents typical reef features like barrier and lagoon spurs and grooves pinnacles etc from its morphology we propose that it grew during the holocene last transgression below the three other units likely formed during pleistocene sea level highstands and were eroded during the low stands as evidenced in seismic reflection profiles this scenario would imply that les saintes plateau formed in a context of subsidence with a rate we evaluate to be of the order of tenths of mm yr probably linked to local tectonics we believe that this deformation is also related to plate scale subduction processes similarly to deformations occurring on the other islands of the guadeloupe archipelago

late quaternary folding of coral reef terraces barbados uplifted late ouaternary coral reefs on the island of barbados record folding of the emergent crest of the lesser antilles accretionary prism barbados ridge complex since ca 1 ma three northeast striking folds are defined by systematic changes in altitudes in the crest of first high cliff a mostly constructional reef terrace about 125 ka and second high cliff a partially erosional reef terrace about 500 ka the folds have wavelengths of 6 to 8 km and fold axes extend about 10 km the largest anticline rises to the northeast where it has been breached by erosion exposing highly deformed eocene to lower miocene rocks of the scotland district uplift rates based on heights of the last interglacial first high cliff range from 0 07 to 0 44 mm yr quaternary folding on barbados indicates that the crest of the accretionary prism continues to be an active fold belt undergoing northwestsoutheast shortening

a test of alternative caribbean plate relative motion models two contrasting models have been proposed to describe the present day motions between the caribbean plate and neighboring plates one model based on both north america caribbean and cocos caribbean data assumes that north america caribbean motion is reflected by the spreading rate approximately 2 cm yr inferred from magnetic anomalies at the cayman spreading center and the azimuths of nearby transforms jordan 1975 this geometry was used by minster and jordan 1978 in deriving global plate motion model rm2 the other model based only on north america caribbean data uses rates and azimuths inferred from the geometry of the lesser antilles wadati benioff zone sykes et al 1982 the cayman spreading center data were discounted assuming that they underestimate the full north america caribbean motion owing to the complex tectonics of the greater antilles the latter model assumes plate convergence at the lesser antilles at a rate about twice as fast as and an azimuth differing by 25 from the jordan model the two models also differ in their predictions of south america caribbean motion the jordan model predicts oblique convergence whereas sykes et al predict oblique divergence we use the nuvel 1 global relative motion data set which incorporates recent data not used in earlier studies to discriminate between the alternative models we find that the jordan geometry provides a better fit to the direction of north america caribbean motion moreover we find that models based on this geometry better fit the direction of cocos caribbean motion observed in earthquake slip vectors along the middle america trench since the prediction of this direction depends strongly on the rate of north america caribbean motion we conclude that the jordan model better describes caribbean plate motions the discrepancy between the two models results from the different methods of estimating plate motions sykes et al 1982 report that they determined a caribbean north america convergence rate of approximately 4 cm yr from the length of the lesser antilles wadati benioff zone we employ a similar procedure and obtain a rate closer to 2 cm yr we also find that the method they report using to determine the convergence direction is unable to distinguish between the alternative azimuths we thus conclude that estimates of the rate and direction of plate motion from wadati benioff zone configurations are insufficiently robust and that such estimates are better derived using rates from magnetic anomalies and azimuths from transform faults and slip vectors we further conclude that successful estimates of relative motion require internal consistency between the euler vectors of all relevant plates as demonstrated by the powerful cocos caribbean constraint not incorporated in the sykes et al model

two new graptolites from the early silurian llandovery aeronian of central wales an origin for monoclimacid thecal morphology

a preliminary radiolarian biozonation for the lower silurian of the cape phillips formation nunavut canada radiolaria from the lower silurian of the cape phillips formation nunavut canada allow the definition of four biostratigraphic assemblages the haplotaeniatum assemblage extends from the basal llandovery to topmost coronograptus cyphus graptolite biozone the base is taken as the first occurrence of haplotaeniatum nunavutensis no samples were collected below the ordovician silurian boundary the top of the assemblage is defined by the first occurrence of orbiculopylorum the orbiculopylorum assemblage is marked by the first occurrence of orbiculopylorum the boundary between this assemblage and the overlying plussatispila assemblage is unclear because of a break in stratigraphy upper spirograptus turriculatus through monograptus crispus graptolite biozones the last occurrence of orbiculopylorum defines the top of the assemblage the base of the plussatispila assemblage is defined by the last occurrence of orbiculopylorum a barren interval cyrtograptus insectus to lower monograptus instrenuus cyr

younger dryas sea level and meltwater pulse 1b recorded in barbados reef crest coral acropora palmata the younger dryas climate event occurred during the middle of the last deglacial cycle and is marked by an abrupt shift in the north atlantic polar front almost to its former glacial position trending east to west using high precision and high accuracy u th dated barbados reef crest coral acropora palmata we generate a detailed sea level record from 13 9 to 9000 years before present kyr b p and reconstruct the ice volume response to the younger dryas cooling from the mid allerod 13 9 kyr b p to the end of the younger dryas 11 65 kyr b p rates of sea level rise decreased smoothly from 20 mm yr 1 to 4 mm yr 1 culminating in a 400 year slow stand before accelerating into meltwater pulse 1b mwp 1b the mwp 1b event at barbados is better constrained as beginning by 11 45 kyr b p and ending at 11 1 kyr b p during which time sea level rose 14 2 m and rates of sea level rise reached 40 mm yr 1 we propose that mwp 1b is the direct albeit lagged response of the northern hemisphere ice sheets to the rapid warming marking the end of the younger dryas coinciding with rapid warming in the circum north atlantic region and the polar front shift from its zonal to meridional position 11 65 kyr b p as predicted by glaciological models the ice sheet response to rapid north atlantic warming was lagged by 400 years due to the thermal inertia of large ice sheets the regional circum north atlantic younger dryas climate event is elevated to a global response through sea level changes starting with the global slowdown in sea level rise during the younger dryas and culminating with mwp 1b no meltwater pulses are evident at the initiation of the younger dryas climate event as is often speculated

coastal tectonics on the eastern margin of the pacific rim late quaternary sea level history and uplift rates channel islands national park california usa abstract the pacific rim is a region where tectonic processes play a significant role in coastal landscape evolution coastal california on the eastern margin of the pacific rim is very active tectonically and geomorphic expressions of this include uplifted marine terraces there have been however conflicting estimates of the rate of late quaternary uplift of marine terraces in coastal california particularly for the northern channel islands in the present study the terraces on san miguel island and santa rosa island were mapped and new age estimates were generated using uranium series dating of fossil corals and amino acid geochronology of fossil mollusks results indicate that the 2nd terrace on both islands is 120 ka and the 1st terrace on santa rosa island is 80 ka these ages correspond to two global high sea stands of the last interglacial complex marine isotope stages mis 5 5 and 5 1 respectively the age estimates indicate that san miguel island and santa rosa island have been tectonically uplifted at rates of 0 12 0 20 m ka in the late quaternary similar to uplift rates inferred from previous studies on neighboring santa cruz island the newly estimated uplift rates for the northern channel islands are however an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the last glacial period the differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment gia effects that were not known at the time of the earlier study set in the larger context of northeastern pacific rim tectonics channel islands uplift rates are higher than those coastal localities on the margin of the east pacific rise spreading center but slightly lower than those of most localities adjacent to the cascadia subduction zone the uplift rates reported here for the northern channel islands are similar to those reported for most other localities where strike slip tectonics are dominant but lower than localities where restraining bends such as the big bend of the san andreas fault result in crustal shortening

holocene climate change in the western part of taihu lake region east china abstract the taihu lake basin is one of the most sensitive areas to climate change in the east asian summer monsoon easm influenced region there are significant differences regarding the interpretation of climate history for this area during the holocene due to a lack of high resolution paleoclimate records to better understand this scientific issue here we provide a new record of holocene climate change from the western part of taihu lake region east china a 4 m depth profile from gaochun has provided a 13 200 year record of climate change holocene climate change was reconstructed for the western part of taihu lake area based on various proxy records including pollen charcoal degree of humification doh and loss on ignition loi from the gaochun site the results indicate that climate during the late pleistocene 13 200 10 700 cal yr b p and early holocene 10 700 8000 cal yr b p was warm and humid alternated with several cold and dry intervals the late pleistocene and early holocene was a transitional period from cold dry to warm wet climates the middle holocene 8000 4400 cal yr b p was still warm and humid with a relatively stable climate the period between 8000 and 5300 cal yr b p was the holocene climate optimum hco during the late holocene 4400 0 cal yr b p the climate was cool but still humid in addition climate change at the western part of taihu lake during the late pleistocene and holocene was unstable containing several short term climate events such as younger dryas yd 8 2 ka and 4 2 ka events these abruptly occurred climate events were indicated by various paleoclimatic proxy indicators and can be compared with related records from other regions our findings suggest that the easm strength was strongest during the middle holocene between 8000 and 5300 cal yr b p which can be depicted as the period of hco

late quaternary uplift along the north america caribbean plate boundary evidence from the sea level record of guantanamo bay cuba abstract the tectonic setting of the north america caribbean plate boundary has been studied intensively but some aspects are still poorly understood particularly along the oriente fault zone guantanamo bay southern cuba is considered to be on a coastline that is under a transpressive tectonic regime along this zone and is hypothesized to have a low uplift rate we tested this by studying emergent reef terrace deposits around the bay reef elevations in the protected inner part of the bay are 11 12 m and outer coast wave cut benches are as high as 14 m uranium series analyses of corals yield ages ranging from 133 ka to 119 ka correlating this reef to the peak of the last interglacial period marine isotope stage mis 5 5 assuming a span of possible paleo sea levels at the time of the last interglacial period yields long term tectonic uplift rates of 0 02 0 11 m ka supporting the hypothesis that the tectonic uplift rate is low nevertheless on the eastern and southern coasts of cuba east and west of guantanamo bay there are flights of multiple marine terraces at higher elevations that could record a higher rate of uplift implying that guantanamo bay may be anomalous southern cuba is considered to have experienced a measurable but modest effect from glacial isostatic adjustment gia processes thus with a low uplift rate guantanamo bay should show no evidence of emergent marine terraces dating to the 100 ka mis 5 3 or 80 ka mis 5 1 sea stands and results of the present study support this

uncompressed specimens of monograptus turriculatus barrande 1850 from cornwallis island arctic canada isolated specimens of monograptus turriculatus barrande 1850 have been recovered from calcite concretions of the turriculatus zone late llandovery from the cape phillips formation canadian arctic islands the sicula shows ventral as well as dextral lateral curvature and the thecae show a pronounced lateral asymmetry this asymmetry is manifest as a tear shaped aperture a long laterally directed spine on the outer apertural margin and a shorter ventrally directed spine on the inner apertural margin the latter spine is totally absent on the proximal thecae monograptus sedgwickii portlock 1853 is suggested as a possible ancestor to m turriculatus

the generative phase and the first radiation event in the early silurian monograptid history abstract the generative phase in the monograptid history that is a period between the appearance of the uniserial colony the persculptograptus persculptus biozone and the first radiation event the cystograptus vesiculosus biozone shows neither morphological nor taxonomical variety in the rhabdosomal and thecal structure it is characterized by the speciation events in the single atavograptus linage these events coincide with the recovery phase of the early silurian diplograptids and are associated mostly with deep water environments within the marginal basins in the low latitude equatorial belt the monograptid radiation in the c vesiculosus biozone is well represented in the bornholm and south urals sections koren and bjerreskov 1997 it resulted in a significant increase in diversity of derived thecal morphologies based on a simple atavograptus primitivus morphotype some important morphological novelties that were typical for almost all early monograptids such as the position of the theca 1 bud at the metasicula were also introduced in several akidograptid and dimorphograptid lineages within the parakidograptus acuminatus and c vesiculosus biozones the vesiculosus radiation led to geographical and ecological expansion of monograptids which became globally recognizable within the epipelagic and marginal basins in the low to moderate palaeolatitudes

dolomite formation in caribbean islands driven by plate tectonics abstract postdepositional dolomite occurs in the shallow subsurface of several caribbean islands in tertiary and pleistocene carbonates e g on barbados grand cayman jamaica and st croix recent investigations have interpreted these dolomites as relatively early diagenetic formations from chemically modified seawater mainly on the basis of petrography stratigraphic association and stable isotope values interpretations of the hydrologic regimes during dolomitization vary and usually include freshwater seawater mixing thermal or density driven convection of seawater or a combination thereof this paper offers two alternative interpretations based on the relatively low sr isotope ratios of the dolomites 0 7085 to 0 7092 and their proximity to active plate margins dolomitization may have been driven by plate tectonics i e either by thermal convection of pore fluids at active spreading centers or by tectonic expulsion of fluids from accretionary prisms the dolomitizing solution was seawater that was enriched in 86sr by magmatic hydrothermal solutions or by interaction with siliciclastics in an accretionary prism respectively

hirnantian strata identified in major intracratonic basins of central north america implications for uppermost ordovician stratigraphy carbon isotopes are analyzed for the first time from the ordovician silurian boundary interval in the williston and hudson bay basins of manitoba revealing a prominent positive excursion the nature of this excursion and its co occurrence with the appearance of the ozarkodina hassi conodont zone and a distinctive coral dominated macrofauna indicate that this is the upper portion metabolograptus persculptus graptolite zone of the globally recognized hirnantian isotopic carbon excursion hice as a result the ordovician silurian boundary is placed at a higher position than previously thought at the disconformable stonewall fisher branch formational boundary in the williston basin and probably the port nelson severn river formational boundary in the hudson bay basin disconformities within sections suggest periods of nondeposition due to subaerial exposure as sea level fluctuated during the late ordovician glaciation latest ordovician hirnantian deposition was far more widespread on the laurent

uranium series ages of marine terrace corals from the pacific coast of north america and implications for last interglacial sea level history abstract few of the marine terraces along the pacific coast of north america have been dated using uranium series techniques ten terrace sequences from southern oregon to southern baja california sur have yielded fossil corals in quantities suitable for u series dating by alpha spectrometry u series dated terraces representing the 80 000 yr sea level high stand are identified in five areas bandon oregon point arena san nicolas island and point loma california and punta banda baja california terraces representing the 125 000 yr sea level high stand are identified in eight areas cayucos san luis obispo bay san nicolas island san clemente island and point loma california punta bands and isla guadalupe baja california and cabo pulmo baja california sur on san nicolas island point loma and punta bands both the 80 000 and the 125 000 yr terraces are dated terraces that may represent the 105 000 sea level high stand are rarely preserved and none has yielded corals for u series dating similarity of coral ages from midlatitude erosional marine terraces with coral ages from emergent constructional reefs on tropical coastlines suggests a common forcing mechanism namely glacioeustatically controlled fluctuations in sea level superimposed on steady tectonic uplift the low marine terrace dated at 125 000 yr on isla guadalupe baja california presumed to be tectonically stable supports evidence from other localities for a 6 m sea level at that time data from the pacific coast and a compilation of data from other coasts indicate that sea levels at 80 000 and 105 000 yr may have been closer to present sea level within a few meters than previous studies have suggested

high resolution stable isotope stratigraphy of the upper cambrian and ordovician in the argentine precordillera carbon isotope excursions and correlations abstract we report the occurrence of important carbon isotope excursions in early paleozoic formations of the eastern and central argentine precordillera the steptoean positive isotope carbon excursion spice is known from north america kazakhstan south china australia and south america and the negative isotope carbon excursion snice has been described for the first time in south america we report here the record of the spice and snice in a single section in the eastern precordillera in the central precordillera a minor middle darriwilian positive carbon isotope excursion mdice and a late sandbian positive isotope carbon excursion the gice 3 c bicornis biozone are reported from two sections one pre gice positive carbon isotope excursion sandbian sa1 n gracilis biozone in the central precordillera with a 13c peak of 2 is perhaps equivalent to the positive spechts ferry 13c excursion of north america a positive 13c excursion 6 n persculptus biozone recorded at the base of the late hirnantian la chilca formation probably corresponds to hice these carbon isotope excursions resulted from more than one factor where paleoceanographic events probably played a major role a sea level fall and vigorous fluctuations in the steptoean spice b sea level rise in the sunwaptan snice c important transgression in the sandbian pre gice and gice and d sea level fall in the late hirnantian hice in the darriwilian and sandbian stages organic burial has led to a large 12c sequestration in the deep anoxic ocean with saline bottom water recorded by the graptoliferous black shales of the gualcamayo and los azules formations in central precordillera helped the building of the mdice and gice anomalies 18o values for the upper cambrian carbonates are likely near primary isotope signals that point to progressive cooling from the spice to the snice whereas for sandbian carbonates they suggest strong temperature fluctuations the 13c peak of the gice coincides with a cooler period with temperatures warming up towards the late hirnantian to rhuddanian the upper cambrian to the middle ordovician of the precordillera recorded a decrease of seawater 87sr 86sr ratios in accordance to the global picture this decrease probably reflects the influence of widespread volcanic activity from arc terranes in low latitude settings along eastern margins of laurentia and in the argentine precordillera in the early to middle ordovician five carbonate samples from san juan gualcamayo and los azules formations yielded end values that along seven already published values seem to plot along the nd isotopic evolution trend of the iapetus ocean together the record of global upper cambrian and ordovician carbon isotope excursions in the argentine precordillera is a valuable proxy in refining early paleozoic stratigraphy establishing of regional global high resolution correlations and sea level change history in south america

a revised morpho and chronostratigraphy of the late and middle pleistocene coral reef terraces on southern barbados west indies the barbados coral reef terraces are one of the few type localities worldwide that provide insights into interglacial sea level change during the late and middle pleistocene several sea level estimates have been established since the late 1960s and each has contributed to the barbados model of sea level change this paper presents new morpho and chonostratigraphic data from the barbados coral reef terraces developed over the last 12 years the work is based on significant advances in electron spin resonance esr dating of fossil coral air photo interpretation and a greatly improved geomorphic map of preserved fossil beach formations and reef terraces above present sea level the need for a revision of past published morpho and chronostratigraphies is best demonstrated on the southern part of the island the morpho and chronostratigraphic sequence in this region is both more complex and diverse than has been assumed so far the revised morphostratigraphy presented here includes a differentiation of coral reef terraces wave cut platforms and other erosive features such as notches and cliffs our study of these geomorphic features combined with new numeric dating results esr u th enable a revised estimate of the spatial and temporal variation in tectonic uplift rate within south barbados these new rates are an essential requirement for more precise glacio eustatic sea level reconstructions during the late and middle pleistocene from this region

u th dating of marine isotope stage 7 in bahamas slope sediments in order to understand the driving forces for pleistocene climate change more fully we need to compare the timing of climate events with their possible forcing in contrast to the last interglacial marine isotope stage mis 5 the timing of the penultimate interglacial mis 7 is poorly constrained this study constrains its timing and structure by precise u th dating of high resolution n 18 o records from aragonite rich bahamian slope sediments of odp leg 166 sites 1008 and 1009 the major glacial interglacial cycles in n 18 o are distinct within these cores and some mis 7 substages can be identified these sediments are well suited for u th dating because they have uranium concentrations of up to 12 ppm and very low initial 230 th contributions with most samples showing 230 th 232 th activity ratio of s 75 u and th concentrations and isotope ratios were measured by thermal ionisation mass spectrometry and multiple collector inductively coupled plasma mass spectrometry with the latter providing dramatically better precision twenty nine of the 41 samples measured have a n 234 u value close to modern seawater suggesting that they have experienced little diagenesis ages from 27 of the 41 samples were deemed reliable on the basis of both their u and their th isotope ratios ages generally increase with depth although we see a repeated section of stratigraphy in one core extrapolation of constant sedimentation rate through each substage suggests that the peak of mis 7e lasted from v237 to 228 ka and that 7c began at 215 ka this timing is consistent with existing low precision radiometric dates from speleothem deposits the beginning of both these substages appears to be slightly later than in orbitally tuned timescales the end of mis 7 is complex but also appears to be somewhat later than is suggested by orbitally tuned timescales although this event is not particularly well defined in these cores fl 2002 elsevier science b v all rights reserved

barbados architecture and implications for accretion the island of barbados exposes the crestal zone of the remarkably broad accretionary prism of the lesser antilles foreacrc the architecture of barbados is three tiered an upper arched cap of pleistocene reefs that record rapid and differential uplift of the island an intermediate zone of nappes of mainly abyssal or deep bathyal pelagic rocks and a basal complex whose lithotypes extend to substantial depth and may be representative of the bulk of the western or inner accretionary prism the exposed basal complex consists of generally steeply dipping ene to ne striking fault bounded packets which contain rocks of one of three lithic suites terrigenous quartzose turbidite and mudstone debris flow and hemipelagic chiefly radiolarite present but imcomplete rock dating indicates that the terrigenous and hemipelagic suites and the pelagic rocks of the intermediate zone are age overlapping in early and middle eocene time deformation within packets of the basal complex is systematic pre or synfault and indicative of shortening that is generally normal to packet boundaries a unit of terrigenous materials that probably underwent local resedimentation in the miocene is recognized in wells but its relationship to exposed rocks is uncertain the packet bounding faults of the basal complex are interpreted to have been primary accretionary surfaces which may have been reactivated by later intraprism movements exposed sedimentary rocks of barbados can be successfully assigned to contemporaneous depositional sites associated with an accretionary prism terrigenous beds to a trench wedge that was connected to south american sediment sources debris flow to trench floor or slope basin accumulations of material derived from the lower slope hemipelagic to atlantic plain strata and pelagic rocks of the intermediate zone to deep outer forearc basin sites the decollement at the base of the intermediate zone is probably due to uplift and arcward motion of the crestal zone of the accretionary prism with respect to the forearc basin during progressive prism growth principal uplift of the prism seems to have started apparently abruptly in the miocene quaternary uplift of barbados may be due partly to local diapirism paleogene subduction that created the arcward region of the prism probably occurred in a differently configured zone from the present one

episodic fluid flow and dolomitization by methane bearing pore water of marine parentage in an accretionary prism setting barbados west indies abstract barbados is a small island located on the crest of an accretionary prism at the eastern edge of the caribbean sea dolomite occurs in relatively small amounts in pleistocene carbonates and in the underlying oligocene miocene chalk which also contains a few small caves distinctive authigenic calcites and oil that ascended through a dense networks of fractures the stable isotopes of calcites form a positive trend while those of the dolomites form a negative trend dolomite 18o values range from about 1 to 8 pdb and 13c values range from about 2 to 25 pdb sr isotope ratios range from 0 7079 to 0 7094 which corresponds to a secular range from the oligocene to the holocene the data presented in this study support the notion that the barbados accretionary wedge has undergone a prolonged history of compression with concomitant expulsion of fluids that varied through time and space at times these fluids were diluted relative to seawater and also undersaturated with respect to calcite which resulted in limited dissolution along fractures and in their immediate vicinity at other times the expelled pore fluids were prone to limited dolomitization forming pods of dolomite at yet other times the expelled fluids formed calcite as interstitial cements and around submarine points of exit in what appears to be cold seeps with calculated temperatures as low as 4 c the expelled fluids were chemically slightly modified seawater that contained thermogenic methane calculated temperatures of dolomitization range between 4 and 25 c which suggest fluid expulsion from sub sea depths of zero to about 650 m a temperature of 4 c is the lowest ever determined for dolomite formation the sr isotope data suggest that the hypogene fluids were expelled episodically between about 8 and 2 my ago this study provides support for the hypothesis that dolomitization can result from fluid expulsion in an accretionary prism setting however the volumes of dolomite formed in barbados are small and probably are similarly small in most other accretionary prism settings thus regionally extensive pervasive dolomitization is not to be expected from the dolomitizing process identified here if elevated to the status of a model dolomitization via fluid expulsion from an accretionary prism would be comparable in importance to the mixing zone model of dolomitization

morphology and classification of some early silurian monograptids graptoloidea from the cape phillips formation canadian arctic islands exquisitely preserved early to mid llandovery monograptids have been chemically isolated from calcareous concretions sampled from the cape phillips formation central canadian arctic archipelago they provide morphological information critical in refining the definition of four of the earliest known monograptid genera and in the elucidation of their phylogenetic dispersal through the llandovery monograptid radiation these primitive monograptid genera are defined primarily on the basis of derived thecal form the specific derived thecal and thecal apertural character states used in generic diagnoses are as follows species of atavograptus possess simple geniculate to slightly sigmoidal thecae with a large dorsoventral overlap species of pribylograptus possess thecae bearing lateral apertural lappets that may occur with atavograptus style thecae proximally species of coronograptus possess flared thecal apertures at least part way along the rhabdosome species of lagarograptus have conspicuous tongue

llandovery graptolite biostratigraphy and paleobiogeography cape phillips formation canadian arctic islands llandovery graptolites have been collected from 11 sections in the cape phillips formation of the canadian arctic archipelago melville bathurst truro cornwallis devon and ellesmere islands the cape phillips formation appears to have been deposited in a distinct subbasin here termed the cape phillips basin under deep shelf to shallow basin conditions intermediate in position between the arctic platform to the south and east and the deeper hazen trough to the northwest a total of 170 graptolite species and a further 25 subspecies have been identified their stratigraphic distribution allows the recognition of 11 graptolite zones the acuminatus atavus acinaces cyphus curtus convolutus minor turriculatus crispus griestoniensis and sakmaricus zones the curtus zone can be subdivided into the pectinatus and orbitus subzones the zones can be correlated with graptolite sequences worldwide the canadian arctic faunas show strong affinities with those of siberia china and the northern canadian

precise timing of the last interglacial period from mass spectrometric determination of thorium 230 in corals the development of mass spectrometric techniques for determination of 230 th abundance has made it possible to reduce analytical errors in 238 u 234 u 230 th dating of corals even with very small samples samples of 6 x 10 8 atoms of 230 th can be measured to an accuracy of 3 percent 2 and 3 x 10 10 atoms of 230 th can be measured to an accuracy of 0 2 percent the time range over which useful age data on corals can be obtained now ranges from about 50 to about 500 000 years for young corals this approach may be preferable to 14 c dating the precision with which the age of a coral can now be determined should make it possible to critically test the milankovitch hypothesis concerning pleistocene climate fluctuations analyses of a number of corals that grew during the last interglacial period yield ages of 122 000 to 130 000 years the ages coincide with or slightly postdate the summer solar insolation high at 65 n latitude which occurred 128 000 years ago this supports the idea that changes in pleistocene climate can be the result of variations in the distribution of solar insolation caused by changes in the geometry of the earth s orbit and rotation axis

structure of the accretionary complex of barbados i chalky mount the island of barbados is underlain by a basal tectonic complex that may be representative of rocks and structures of the structural high of the accretionary prism of the lesser antilles arc at chalky mount the complex consists of six fault bounded packets of east northeast strike and steep dips the packets are composed of deformed but generally coherent cenozoic sedimentary rocks terrigenous turbidite in five of the packets and hemipelagic rocks in the sixth there is no evident stratigraphic affiliation among beds in any of the six packets rocks in fault packets underwent sequential deformations most of which can be timed as early contemporaneous or late with respect to cessation of interpacket motions early structures in packet 1 consist of a main fold train with easterly striking axial planes and related thrusts broken formation and homoaxially refolded folds packet 1 also contains later open folds with northeast strikes packets 2 4 are relatively thin slices within a fault complex the chalky mount fault zone in which late left oblique slip occurred on two of the four faults of the zone packet 5 contains three phases of deformation an early near recumbent major fold marginal belts of fault related second folds and open post fault third folds packet 6 includes early folds that are tightened and reoriented toward its northern fault boundary where it is locally a thrust early structures in each packet are the most pervasive and record the major stratal shortening shortening in each packet is approximately normal to packet boundaries and early axes lie in the plane of the boundaries packet boundaries are interpreted as surfaces of accretion and early structures as deformations generated during transfer of layer successions from an ocean floor to the front of the accretionary prism contemporaneous and post fault structures are local and are due to displacements during reactivation of faults mainly inter packet within the accretionary prism early structures at chalky mount developed in the brittle state apparently with displacements taken up by sliding between grains and along layer boundaries all structures record distinctly nonmetamorphic environments

origin of convex accretionary wedges evidence from barbados the surface slopes of submarine accretionary wedges generally decrease away from the toe or defor mation front toward the arc this paper presents evidence that this characteristic convex cross sectional shape is a direct mechanical response to the lithification of sediments during accretion the recently accreted sediments near the toe which are typically unconsolidated and therefore very weak must deform until a critical taper is attained at which they are stable in the presence of the horizontal tectonic compression this critical wedge taper and thus the bathymetric slope of the accretionary prism is relatively high for the porous weak sediments near the toe in contrast the compacted sediments farther back in the wedge are stronger so they require a relatively modest critical taper and therefore a lower bathymetric slope to be stable under the same tectonic compression the result is a convex cross sectional wedge shape we investigate several possible causes of the increase in sediment strength within the wedge and conclude that the primary cause is an increase in cohesive strength with decreasing porosity a straightforward generalization of the exact critical taper model is combined with empirical cohesion porosity velocity relations to infer the distribution of porosity and p wave velocity within the barbados accretionary wedge we estimate that the porosity decreases from its near toe value of 70 to approximately 30 at a depth of 3 km below the seafloor and a distance of 60 km arcward from the front of the wedge

deglacial meltwater pulse 1b and younger dryas sea levels revisited with boreholes at tahiti reconstructing sea level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets the resolution of the few sea level records covering the critical time interval between 14 000 and 9 000 calendar years before the present is still insufficient to draw conclusions about sea level changes associated with the younger dryas cold event and the meltwater pulse 1b mwp 1b we used the uranium thorium method to date shallow living corals from three new cores drilled onshore in the tahiti barrier reef no significant discontinuity can be detected in the sea level rise during the mwp 1b period the new tahiti sea level record shows that the sea level rise slowed down during the younger dryas before accelerating again during the holocene

dating open systems by the 238 u 234 u 230 th method application to quaternary reef terraces abstract the sedimentation conditions and diagenetic processes of biogenic and inorganic carbonates are such that the assumptions of a closed system evolution and the absence of initial th invoked in classical 238 u 234 u 230 th dating methods are very often not fulfilled for such material this problem is of interest for all studies requiring accurate dating of corals or aragonite rich sediments as in palaeoclimatology or neotectonics extending the approach of henderson and slowey nature 404 2000 61 66 we propose a consistent model that takes into account possible initial 230 th excess and where continuous selective redistribution gain or loss of 234 u 234 th and 230 th is controlled by recoil processes this model applied to quaternary marine terraces in barbados marie galante lesser antilles arc and pacific islands is able to explain the large scatter in isotopic compositions observed in the series of cogenetic corals or sediments we show that recoil processes generally tend to increase the 234 u 238 u and 230 th 234 u ratios with time leading to an overestimation of the apparent ages calculated using classical methods on the basis of simple assumptions identical marine initial 234 u 238 u 0 and 230 th 232 th 0 ratios we propose a method for calculating a best estimate of the age of cogenetic series our model offers an alternative way to date old reef terraces where corals are almost systematically altered and where classical dating methods do not apply it may also explain the apparent variations of the 234 u 238 u seawater initial ratio estimated from corals formed in the last 300 ka and the apparent uncoupling between sea level highstands and high latitude northern hemisphere summer insolation our set of equations can be applied to all weathering processes where the mobility of u series isotopes is controlled by recoil

crustal and uppermost mantle velocity structure along a profile across the pamir and southern tien shan as derived from project tipage wide angle seismic data summary utilizing seismic refraction wide angle reflection data from 11 approximately in line earthquakes 2 d p and s velocity models and a poisson s ratio model of the crust and uppermost mantle beneath the southern tien shan and the pamir have been derived along the 400 km long main profile of the tipage tien shan pamir geodynamic program project these models show that the crustal thickness varies from about 65 5 km close to the southern end of the profile beneath the south pamir through about 73 6 km under lake karakul in the north pamir to about 57 7 km 50 km south of the northern end of the profile in the southern tien shan average crustal p velocities are low with respect to the global average varying from 6 26 to 6 30 km s 1 the average crustal s velocity varies from 3 54 to 3 70 km s 1 along the profile and thus average crustal poisson s ratio varies from 0 23 beneath the central pamir in the south central part of the profile to 0 265 towards the northern end of the profile beneath the southern tien shan the main layer of the upper crust extending from about 2 km below the earth s surface to 27 km depth below sea level b s l has average p velocities of about 6 05 6 1 km s 1 except beneath the south central part of the profile where they decrease to around 5 95 km s 1 this is in contrast to the s velocities which range from 3 4 to 3 6 km s 1 and exhibit the highest values of 3 55 3 6 km s 1 where the p velocity is lowest thus for the main layer of the upper crust is 0 26 beneath the profile except beneath the south central part of the profile where it decreases to 0 22 the low value of 0 22 for under the central pamir the along strike equivalent of the qiangtang terrane in tibet is similar to that within the corresponding layer beneath the northern lhasa and southern qiangtang terranes in central tibet and is indicative of felsic rocks rich in quartz in the state the lower crust below 27 km b s l has p velocities ranging from 6 1 km s 1 at the top to 7 1 km s 1 at the base further for this layer is 0 27 0 28 towards the northern end of the profile but is low at about 0 24 beneath the central and southern parts of the profile which is similar to the situation found in the northeast tibetan plateau the low values can be explained by felsic schists and gneisses in the upper part of the lower crust transitioning to granulite facies and possibly also eclogite facies metapelites in the lower part within the uppermost mantle the average p velocity is about 8 10 8 15 km s 1 and is about 0 26 assuming an isotropic situation then a relatively cool 700 800 c uppermost mantle beneath the profile is indicated this would in turn indicate an intact mantle lid beneath the profile an upper mantle reflector dipping from 104 km b s l 120 km from the southern end of the profile to 86 km b s l 155 km from the northern end of the profile has also been identified the preferred model presented here for the crustal and lithospheric mantle structure beneath the pamir calls for nearly horizontal underthrusting of relatively cool indian mantle lithosphere the leading edge of which is outlined by the pamir seismic zone this cool indian mantle lithosphere is overlain by significantly shortening warm asian crust the moho trough that is a feature seen beneath some other orogenic belts for example the alps and the urals beneath the northern pamir may mark the southern tip of the actively underthrusting tien shan crust along the main pamir thrust

the tectonic fabric of the barbados ridge accretionary complex abstract a map showing near surface structure and other surficial geological features on the barbados ridge accretionary complex has been constructed from gloria long range side scan sonographs detailed bathymetric surveys using seabeam and single and multichannel seismic reflection sections the map shows major variations in the size orientation and style of structures across the accretionary complex that are principally related to the increasing thickness of the complex and the sediment drape upon it and variations along the complex that derive from the northward thinning of sediment accreted from the ocean floor and the effects of ridges in the oceanic basement the development of crossfaulting is mainly associated with basement ridges mud diapirism is abundant in the southern part of the complex and is characteristic of that part of the complex into which turbidites from the orinoco submarine fan are accreted slumping on a variety of scales is another feature of the complex the map is presented at a scale of 1 1063415 4 inches per degree of longitude and also shows bathymetry at 200 m contour intervals

mid holocene coastal hydrology and salinity changes in the east taihu area of the lower yangtze wetlands china abstract during the mid holocene the eastern taihu area on china s yangtze delta plain was populated by advanced late neolithic cultures supported by intensive domesticated rice cultivation this agricultural system collapsed around 4200 cal yr bp with severe population decline the end of the liangzhu culture and about half a millennium of very low scale human activity in the area before the re establishment of agricultural production microfossil analyses from six sedimentary sequences supported by ams 14c dating has allowed reconstruction of mid holocene hydrological conditions and salinity changes which would have had a major influence on agricultural viability and cultural history in the coastal wetlands these data allied to existing stratigraphic and sea level records show that chenier ridges that developed after ca 7000 cal yr bp in the east of the area sheltered it from marine inundation and although still connected to the sea through tidal creeks low salinity conditions persisted throughout the neolithic period there is no evidence that marine flooding caused the collapse of liangzhu culture marine influence was stable and evolved slowly social and cultural causes may also have been important but if environmental change triggered the collapse of neolithic agricultural society here other natural forces must be sought to explain this event

the timing of high sea levels over the past 200 000 years the 230 th ages and 234 u 238 u ratios were determined for barbados corals that grew during periods of high sea level within the last 200 000 years the similarity of the initial 234 u 238 u ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine 234 u 238 u ratio 83 000 and 200 000 years ago was within 2 per mil of the modern value the accuracies of the 230 th ages are evaluated on the basis of the 234 u 238 u values and a model of the behavior of uranium and thorium isotopes during diagenesis for the last three interglacial and two intervening interstadial periods sea level peaked at or after peaks in summer insolation in the northern hemisphere this overall pattern supports the idea that glacial interglacial cycles are caused by changes in earth9s orbital geometry the sea level drop at the end of the penultimate interglacial the last interglacial and a subsequent interstadial period lagged behind the decrease in insolation by 5 000 to 10 000 years

investigation of late quaternary fault block uplift along the motagua swan islands fault system implications for seismic tsunami hazard for the bay of honduras abstract uplifted and warped coastal landforms fossil coral reef and beachrock wave cut and beach terraces on the western part of roatan island off the northern honduran coast record at least two late holocene earthquakes that we estimate to have had magnitudes of m7 uplift has been primarily related to a fault that follows the southern coast of western roatan herein termed the flowers bay fault a subsidiary fault of the motagua swan islands fault system which marks the boundary between the north american and caribbean plates using electron spin resonance esr and radiocarbon ages of calcium carbonate samples and a late quaternary sea level elevation curve that is compatible with caribbean sea level data we constrain the ages and long term uplift rates of the displaced landforms on roatan caused by the vertical component of slip on the flowers bay fault the fossil reef that is uplifted along the fault grew between 43 and 34 ka and the beachrock horizon and lowest uplifted terrace along the southern and western coasts developed between 1000 and 1700 ad we describe evidence of one earthquake that raised the south coast 3 m as much as 5 m locally and that post dates 1700 ad we interpret this event to be the great earthquake of august 1856 that generated a tsunami which ran as much as 24 km onto the mainland another earthquake circa 900 ad produced a similar amount of uplift as the 1856 event and likely generated a similar tsunami the age and elevation of the fossil reef suggest a long term uplift rate of 3 mm year consistent with a recurrence interval of 1000 years for these large earthquakes

decreasing uplift rates and pleistocene marine terraces settlement in the central lesser antilles fore arc la desirade island 16 n this study investigates the lesser antilles fore arc at the latitude of guadeloupe archipelago and evidences that la desirade island the eastermost island of the forearc displays a staircase coastal sequence including four uplifted marine terraces and an upper reefal platform with mean shoreline angle elevations ranging from 10 to 210 m above sea level asl the platform paleobathymetry is constraint by a detailed analysis of the sediments we propose a revised morphostratigraphy for this coastal sequence including 5 paleo shorelines based on six u th dating from aragonitic corals from the three lowest terraces combined with paleobathymetric analysis of the fossil corals present in the upper platform terrace and upper platform carving of construction periods occurred during marine isotopic stages mis 5e mis 9 and during the intervals mis 15 17 mis 19 25 and mis 31 49 upper coral reef platform our results evidence a bulk decreasing uplift rate since early calabrian to present day clearly documented since 310 ka mis 9 from 0 14 to 0 19 to ca 0 mm y our data are consistent with first the transient influence of the subducting oceanic tiburon ridge during calabrian then with other parametres of the subduction zone since late calabrian to present day dip of the slab basal erosion of the upper plate inherited structures

coral indicators of past sea level change a global repository of u series dated benchmarks fossil corals provide valuable data for reconstructing past sea levels as they are often well preserved in the fossil record and can be dated with u series methods here we present a global and internally consistent database of usingle bondth dated fossil coral sea level indicators including full consideration of all known associated uncertainties both vertical and chronological we include carefully determined taxon specific depth distributions rather than blanket depth uncertainty terms as used in most previous work this is based on a synthesis of extensive modern ecological information on depth ranges these ranges are found to be spatially variable between ocean basins between regions and on sub regional scales because depth itself is not limiting instead depth distributions arise from complex physical chemical and biological interactions with coral reef growth distribution and composition one of the main causes for recognition of the greater depth variability of coral taxa has been the routine inclusion of deep diving and rov surveys in coral ecological studies over the past few decades which has broken through the shallow water bias of early surveys by adding frequent observations on deeper occurrences although more are needed it is also clear from our assessment that coral habitat depth distributions must be determined on the species level to reduce uncertainties in reconstructions of past sea levels and that application to sea level studies then requires these studies also to identify fossil corals to the species level samples identified only to the genus level give rise to wide uncertainties in habitat depth and hence sea level our database contains extensive metadata to assist evaluations of dating quality as well as geomorphic and stratigraphic metadata we demonstrate with examples how such metadata can help to evaluate sea level reconstructions for example by identifying outlier points one example discusses the last interglacial lig where we use the available data with their uncertainties to assess probabilistically the time at which local sea levels exceed that of the present which yields a mean age of 124 6 ka with 95 probability bounds at 118 5 and 129 5 ka we conclude with identification of key outstanding issues relating to i current incomplete understanding of tectonic setting including the current lack of independent verification of uplift subsidence rates and reliance of somewhat unsatisfactory and circular use of the elevation of last interglacial deposits ii the depth distributions of coral taxa and iii the complete documentation of stratigraphic geomorphological and other contextual information with suggestions for strategies to address these issues

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

late ordovician to earliest silurian graptolite and brachiopod biozonation from the yangtze region south china with a global correlation late ordovician to earliest silurian is an important geological period marked by large geological and biological events however the strata and fossils of this interval are not complete in many parts of the world based on studies of 43 sites in south china in particular the continuous sections on the yangtze platform we recognize a complete succession including seven graptolite zones and two shelly faunas in ascending order the graptolite zones are the dicellograptus complanatus dicellograptus complexus paraorthograptus pacificus including lower subzone tangyagraptus typicus subzone and diceratograptus mirus subzone normalograptus extraordinarius normalograptus ojsuensis normalograptus persculptus akidograptus ascensus and parakidograptus acuminatus zones the shelly faunas are the foliomena nankinolithus and hirnantia faunas which may be correlated with d complanatus zone and n extraordinarius n ojsuensis to part of n persculptus zones respectively the biozonation through this interval from the yangtze region can be correlated with that of other parts of the world such as dob s linn in scotland spain and portugal thuringia saxonia bavaria bohemia poland kazakhstan kolyma malaya peninsula yukon canadian arctic islands nevada argentina niger and victoria australia the hirnantian substage which has been proposed by us recently includes the n extraordinarius n ojsuensis zone hirnantia fauna and n persculptus zone the base of the hirnantian substage is marked by the first appearance data fads of n extraordinarius and n ojsuensis which have been determined to be synchronous on a global scale

geochemical evidence for african dust inputs to soils of western atlantic islands barbados the bahamas and florida 1 we studied soils on high purity limestones of quaternary age on the western atlantic ocean islands of barbados the florida keys and the bahamas potential soil parent materials in this region external to the carbonate substrate include volcanic ash from the island of st vincent near barbados volcanic ash from the islands of dominica and st lucia somewhat farther from barbados the fine grained component of distal loess from the lower mississippi river valley and wind transported dust from africa these four parent materials can be differentiated using trace elements sc cr th and zr and rare earth elements that have minimal mobility in the soil forming environment barbados soils have compositions that indicate a complex derivation volcanic ash from the island of st vincent appears to have been the most important influence but african dust is a significant contributor and even mississippi river valley loess may be a very minor contributor to barbados soils soils on the florida keys and islands in the bahamas appear to have developed mostly from african dust but mississippi river valley loess may be a significant contributor our results indicate that inputs of african dust are more important to the genesis of soils on islands in the western atlantic ocean than previously supposed we hypothesize that african dust may also be a major contributor to soils on other islands of the caribbean and to soils in northern south america central america mexico and the southeastern united states dust inputs to subtropical and tropical soils in this region increase both nutrient holding capacity and nutrient status and thus may be critical in sustaining vegetation

comment on younger dryas sea level and meltwater pulse 1b recorded in barbados reefal crest coral acropora palmata by n a abdul et al based on new u th ages of corals drilled offshore barbados abdul et al 2016 have confirmed the existence of the abrupt stratigraphic feature called meltwater pulse 1b mwp 1b which they interpret as being due to a very large and global sea level step change dated at about 11 3 kyr before present approximately 15 m and equivalent to twice the amount of water stored in the present greenland ice sheet this contrasts with the tahiti record in which mwp 1b is essentially absent or very small as carlson and clark 2012 and lambeck et al 2014 also conclude in their recent reviews of deglacial sea levels at the global scale however the evidence provided by abdul et al and their main conclusions are not convincing as they are affected by the following three main problems which may explain the apparent discrepancies problem 1 barbados is located in a subduction zone which was also active throughout the late glacial period furthermore the barbados cores studied by abdul et al were drilled on both sides of the extension of a tectonic feature identified at the southern tip of barbados south point as underlined by several studies of the barbados stratigraphy problem 2 fossil samples of acropora palmata may not be reliable sea level markers during rapid and large sea level rises indeed the asexual reproduction strategy of this species may not be optimal to keep up when the water depth is increasing very rapidly this may in part explain why the living depth of a palmata at barbados was significantly greater than 5 m during some periods of the last deglaciation notably between 14 5 and 14 kyr b p and possibly between 14 and 11 5 kyr b p problem 3 the slow glacio isostatic adjustment and the rapid responses due to gravitational changes of ice and water masses complicate the interpretation of individual relative sea level rsl records at specific locations therefore the barbados and tahiti record cannot be compared directly in terms of absolute sea level values as done by abdul et al in addition different glaciohydroisostatic adjustments at the two sites may also have contributed to the observed discrepancy between their deglacial rsl records

amino acids and hexosamines in the hess rise core during the past 220 000 years abstract core sediment samples collected from the hess rise north pacific were analyzed for 20 common amino acids aa and two hexosamines ha to understand the relation between glacial interglacial variations and deposition preservation of sedimentary organic matter om the sediments are predominantly carbonaceous carbonates 35 80 aa based parameters aspartic acid glycine ratio and serine threonine relative mole content suggest that calcareous plankton was the major source of om in these sediments this inference is supported by the similarity in distribution patterns of aa and ha contents with that of organic carbon low values of aa ha and glucosamine galactosamine ratios average 4 4 and 1 1 respectively imply that much of the planktonic om was replaced by microbial om the relative molar concentration of two nonprotein aa alanine and aminobutyric acid varied with age of sediments i e they were less abundant in recent sediments and more abundant in the oldest sediments this trend is an indicator of extremely slow but continuous enzymatic degradation of proteinaceous om within the sediments so far bulk om has been believed to be one of the best proxies for estimation of primary productivity however it may be an underestimate even for the late quaternary sediments comparison of aa and ha content variations with specmap stack revealed their enhanced deposition and preservation during glacial periods relative to interglacial periods this in turn affected not only the planktonic production in surface waters but also the benthic community including bacteria on the seafloor

palynology and palynofacies analysis of a silurian llandovery wenlock marine succession from the precordillera of western argentina palaeobiogeographical and palaeoenvironmental significance abstract a comprehensive survey of the marine and terrestrial palynomorphs from the la chilca formation exposed in the central precordillera of san juan argentina is presented twenty four samples from the quebrada ancha section were analysed marine phytoplankton predominated in the entire stratigraphic unit while the contribution of terrestrial palynomorphs was much less acritarchs and chlorophytes represent a highly diversified assemblage including stratigraphically relevant taxa such as domasia trispinosa tylotopalla caelamenicutis tylotopalla digitifera crassiangulina variacornuta stellinium rabians and percultisphaera cf stiphrospinata terrestrial palynomorphs are exclusively represented by six cryptospore species namely gneudnaspora divellomedia pseudodyadospora laevigata rugosphaera cerebra tetrahedraletes medinensis cf imperfectotriletes vavdovae and velatitetras retimembrana comparisons with coeval phytoplankton assemblages from gondwana and other palaeoplates such as laurentia baltica and avalonia show strong similarities suggesting a cosmopolitan distribution pattern during the llandovery and wenlock the first palynofacies analysis for the early silurian of argentina was performed depositional environments based on palynofacies match with those previously suggested based on sedimentological data two main palynofacies associations are recognised association b occurs in the lower part of the la chilca formation and is mostly composed of amorphous organic matter aom representative of low energy inner shelf environments association a is recognised in the upper part of the formation where sandstone beds become more frequent and is characterised by a greater amount of possible palynomorph remains ppr indicating a proximal platform to shoreface environment three excursions of total organic carbon toc were identified in the section probably as a result of sea level rise episodes that produced anoxic conditions and preservation of organic matter