calculated mineral equilibria for eclogites in cao na2o feo mgo al2o3 sio2 h2o application to the pouebo terrane pam peninsula new caledonia the high p medium t pouebo terrane of the pam peninsula northern new caledonia includes barroisite and glaucophane bearing eclogite and variably rehydrated equivalents the metamorphic evolution of the pouebo terrane is inferred from calculated p t and p t xh2o pseudosections for bulk compositions appropriate to these rocks in the model system cao na2o feo mgo al2o3 sio2 h2o the eclogites experienced a clockwise p t path that reached p 19 kbar and t 600 c the eclogitic mineral assemblages are preserved because reaction consequent upon decompression consumed the rocks fluid extensive reaction occurred only in rocks with fluid influx during decompression of the pouebo terrane

multistage crack seal vein and hydrothermal ni enrichment in serpentinized ultramafic rocks koniambo massif new caledonia sets of fractures and breccia sealed by ni rich silicates and quartz occur within saprock of the new caledonian regolith developed over ultramafic rocks the crystallization sequence in fractures is as follows 1 serpentine stage lizardite polygonal serpentine white lizardite 2 ni stage ni mg kerolite followed by red brown microcrystalline quartz and 3 supergene stages the red brown microcrystalline quartz corresponds to the very last stage of the ni sequence and is inferred to have precipitated within the 50 95 c temperature range it constitutes also the main cement of breccia that has all the typical features of hydraulic fracturing the whole sequence is therefore interpreted as the result of hydrothermal fluid circulation under medium to low temperature and fluctuating fluid pressure although frequently described as the result of a single downward redistribution of ni and mg leached in the upper part of the regolith under ambient temperature the ni silicate veins thus appear as the result of recurrent crack and seal process corresponding to upward medium temperature fluid convection hydraulic fracturing and subsequent fluid mixing and mineral deposition

new caledonia obducted peridotite nappe offshore extent and implications for obduction and postobduction processes one of the largest ophiolitic peridotite masses in the world covers a quarter of the island of grande terre new caledonia the peridotite nappe was obducted during the eocene is weakly deformed and corresponds to the highest of a structurally simple pile of thrust nappes we present new marine seismic data that allows us to track the offshore continuation of the peridotite nappe along strike for a distance of more than 500 km south of new caledonia and to image its pre syn and post obduction sedimentary records offshore the peridotite nappe underlies a c 150 km wide and 2 km deep basin flat topped horsts of peridotite are clearly bounded by major normal faults in contrast faults are obscure onland to the east the peridotite nappe roots along the eastern margin of the felicite ridge new name a c 300 x 25 km dome shaped ridge which we interpret as being the southern extension of the hp lt metamorphic core complex observed in new caledonia two alternative tectonic models address the relative timing and relationships between peridotite nappe emplacement uplift of a metamorphic core complex and extensional tectonics these models provide new ideas for the understanding the formation of the eastern margin of the zealandia continent our results contribute to an understanding of how oceanic mantle is emplaced onto continental margins

the metamorphic sole of new caledonia ophiolite 40ar 39ar u pb and geochemical evidence for subduction inception at a spreading ridge amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of new caledonia termed peridotite nappe recrystallized in the high temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the eocene metamorphic complex amphibolites mostly display the geochemical features of morb with a slight nb depletion and thus are similar to the youngest late paleocene eocene babb components of the allochthonous poya terrane thermochronological data from hornblende 40ar 39ar zircon and sphene u pb suggest that these mafic rocks recrystallized at 56ma using various geothermobarometers provides a rough estimate of peak recrystallization conditions of 0 5gpa at 800 950c the thermal gradient inferred from the metamorphic assemblage 60 ckm 1 geometrical relationships and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction obduction system and recrystallized when they subducted below young and hot oceanic lithosphere they were detached from the down going plate and finally thrust onto unmetamorphosed poya terrane basalts this and the occurrence of slab melts at 53ma suggest that subduction inception occurred at or near to the spreading ridge of the south loyalty basin at 56ma 2012 american geophysical union all rights reserved

eocene and oligocene basins and ridges of the coral sea new caledonia region tectonic link between melanesia fiji and zealandia this paper presents 34 geochemical analyses 24 ar ar ages and two u pb ages of igneous rocks from the back arc basins and submarine ridges in the coral sea new caledonia region the d entrecasteaux ridge is a composite structural feature primitive arc tholeiites of eocene age 34 56 ma are present along a 200 km length of the ridge and arguably were part of the initial line of subduction inception between fiji and the marianas substantial eocene arc edifices are only evident at the eastern end where bougainville guyot andesite breccias are dated at 40 2 ma the south rennell trough is confidently identified as a 28 29 ma early oligocene fossil spreading ridge and hence the flanking santa cruz and d entrecasteaux basins belong in the group of sw pacific eocene early miocene back arc basins that include the solomon sea north loyalty and south fiji basins the rate and duration of spreading in the north loyalty basin is revised to 43 mm yr between 28 and 44 ma longer and faster than previously recognized the direction of its opening was to the southeast that is parallel to the continent ocean boundary and perpendicular to the direction of coeval new caledonia ophiolite emplacement medium and high k alkaline lavas of 23 25 ma late oligocene age on the northern norfolk ridge are an additional magmatic response to pacific trench rollback

a drastic lower miocene regolith evolution triggered by post obduction slab break off and uplift in new caledonia a lower miocene coarse conglomerate that crops out in the nepoui peninsula does not represent the base of the marine transgression that followed obduction in new caledonia instead the conglomeratic alluvial fan that contains peridotite cobbles and reworked weathering products records a short lived episode of terrestrial erosion intercalated between two intervals of subsidence marked by marine carbonate deposition considering the miocene sea level evolution reported in the literature it is concluded that neither lower miocene transgression nor erosion were driven by sea level variation in contrast a southeastward propagating slab tear that initiated at the latitude of the high pressure low temperature metamorphic complex of northern new caledonia likely generated east to west tilting of new caledonia subsidence along the west coast and hence fringing reef development together with moderate erosion of older regolith coincidence between conglomerate deposition and hence prominent erosion that closely followed emplacement of postobduction granitoids influenced by a slab window suggests a genetic link therefore it is concluded that short lived lower miocene erosion was due to slab breakoff and subsequent uplift that occurred at 22 ma lower miocene erosion profoundly dissected the peridotite nappe and in the northern half of new caledonia only left isolated klippes along the west coast

the north fiji basin basalts and their magma sources part ii sr nd isotopic and trace element constraints abstract sr nd isotope and trace element data are reported for basalts from the north fiji basin nfb nfb basalts are characterized by extreme variations in isotopic ratios and trace element abundances which are related to mantle heterogeneities values of 87 sr 86 sr for basalts from the northern segments n160 and triple junction range from 0 7029 to 0 7041 whereas 143 nd 144 nd values vary from 0 51281 to 0 51313 most of the basalts from these segments are characterized by strong relative enrichments in rb ba sr k nb ta la ce and ti that are comparable to oib components the central segments n15 and n s have 143 nd 144 nd ratios between 0 51298 and 0 51363 and 87 sr 86 sr ratios between 0 7029 and 0 7033 and are depleted in large ion lithophile light rare earth and high field strength elements similar to n morb covariation between trace element and isotopic ratios among nfb basalts supports a model in which melts from the nfb rift system are derived by mixing of oib type and depleted n morb mantle components the sr nd isotopic and trace element variability indicates that the nfb basalt source is heterogeneous on the scale of individual melt batches

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

u pb zircon dating of post obduction volcanic arc granitoids and a granulite facies xenolith from new caledonia inference on southwest pacific geodynamic models in new caledonia the occurrence of one of the world s largest and best exposed subduction obduction complex is a key point for the understanding of the geodynamic evolution of the whole southwest pacific region within the ophiolite pre and post obduction granitoids intrude the ultramafic allochthon and provide new time constraints for the understanding of obduction processes at 27 4 ma a new east dipping subduction generated the active margin magmatism along the western coast of the island saint louis massif at 24 3 ma the eastward shift of the magma activity and slightly different geochemical features koum borindi massif was either related to the older slab break off or alternatively due to the eastward migration of the mantle wedge following the collision of the eastern margin of the low howe rise finally the occurrence of a granulite facies xenolith in the koum borindi massif with comparable 24 5 ma u pb zircon age and isotopic features initial end 5 1 suggests that these evolved magmas were generated within the lithospheric mantle beneath a continental crust of normal thickness geochronological evidence for continuous convergence during the oligocene infers an east dipping eocene oligocene subduction obduction system to have existed in the southwest pacific from the d entrecasteaux zone to the north island of new zealand

detritus feeding as a buffer to extinction at the end of the cretaceous at the end of the cretaceous the principal animals that became extinct such as dinosaurs marine animals that lived in the water column and benthic filter feeders were in food chains tied directly to living plant matter animal groups less affected by extinction including marine benthic scavengers and deposit feeders small insectivorous mammals and members of stream communities were in food chains dependent on dead plant material the proposal that an asteroid or comet impact at the end of the cretaceous produced a dust cloud that cut off photosynthesis for several months is consistent with this pattern of extinction food chains dependent on living plant matter crashed while food chains based on detritus were buffered from extinction because there was a food supply adequate for the interval when photosynthesis was halted

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

geochemical evolution and tectonic significance of boninites and tholeiites from the koh ophiolite new caledonia the central chain ophiolites in new caledonia are fragments of a supra subduction zone ssz ophiolite now preserved from the upper layered gabbros through to volcanics and overlain by pelagic cherts and a thick middle triassic to upper jurassic volcaniclastic sequence most of the fragments were formed by a single tholeiitic magmatic episode but one of these the koh ophiolite was formed by two tholeiitic magmatic episodes separated by boninites the first event in the koh ophiolite formed cumulate gabbros dolerites plagiogranites and the first pillow lava sequence from a tholeiitic magma with strong depletion in the light rare earth elements lree and abnormally low tio2 0 5 at mg 60 shortly after their eruption these tholeiitic lavas were overlain by a high ca boninitic unit with a basal section of boninite pillows flows and breccias and an upper section of boninitic dacites and tuffs the last magmatic phase involved eruption of evolved tholeiitic basalts as pillows above the boninites and as dykes and sills intruding the older plutonic and volcanic sections of the ophiolite this second phase of tholeiitic magmatism is compositionally distinct from the first and is closest to back arc basin basalts babb erupted during the early rifting history of modern back arc basins the boninitic volcanics belong to a high ca series with slightly lower sio2 al2o3 and tio2 compared to those from modern island arc systems and they lack the positive zr spike relative to adjacent rare earth elements ree in normalised element variation patterns these boninites were formed shortly after the production of back arc basin crust represented by the depleted tholeiites and shortly before a second spreading event which caused 40 60 extension of the initial basin crust and eruption of the upper tholeiites the dominance of babb like tholeiites throughout the central chain ophiolites in new caledonia the restricted occurrence of boninites and the stratigraphy and chemistry of the koh ophiolite suggest that the boninites were erupted in response to an exceptional tectonic situation we suggest that this boninite generation event was driven by adiabatic decompression of hot depleted mantle residual from the production of the lower tholeiites during initiation of rifting of young oceanic crust intimately associated with propagation of a back arc basin spreading centre the occurrence of a thick blanket of calc alkaline volcaniclastic sediments above the ophiolite indicates proximity to a mature arc and suggests that the koh boninites were not associated with the initiation of subduction a close modern analogy for the koh ophiolite exists on the hunter ridge protoisland arc between southernmost vanuatu new hebrides island arc and the fijian islands there high ca boninites lacking positive zr spikes occur together with low ti tholeiites and more typical babb tholeiites where the southern spreading centre of the north fiji basin is propagating into the protoarc crust of the hunter ridge

seagrass related carbonate ramp development at the front of a fan delta burdigalian new caledonia insights into mixed carbonate siliciclastic environments abstract past shallow water carbonate environments of the main island of new caledonia nc have been subject to high terrigenous influx derived from the erosion of ultramafic obducted nappes and are therefore a relevant case study for characterizing neritic carbonate production in mixed carbonate siliciclastic systems under a tropical climate more particularly we focused on burdigalian carbonate sedimentary records cropping out on the western coast of nc in the nepoui area based on a comprehensive sedimentological study of cores and outcrops we established a new depositional model of an alluvial fan to carbonate ramp transition shallow water euphotic carbonate production was dominated by seagrass related biota and corals derived from small sized bioconstructions extensional tectonics and associated normal faulting driven by post obduction isostatic rebound favored carbonate ramp aggradation and preservation the carbonate ramp was incised by conglomerate filled terminal distributary channels which indicate that terrigenous inputs remained significant during marine transgression and did not inhibit the development of seagrass and scleractinian carbonate factories phytal substrates induced by seagrass and or macro algae seafloor colonization strongly controlled the nature of carbonate production and promoted the accumulation of foraminiferal coralline algal sediments seagrass development at the front of the fan delta is interpreted to have controlled the preservation of a diverse and significant carbonate production by reducing water turbidity and by limiting the risk of suffocation for filter feeding biota in such a high terrigenous influx setting

groundwater in the celtic regions this book covers a diverse range of hydrogeological environments that occur in the celtic regions of britain and ireland these include hard rock aquifers of lower palaeozoic and precambrian age generally dominated by fracture flow within a shallow zone of weathering carboniferous limestone aquifers often characterized by conduit flows in karstic systems dual porosity permo triassic sandstone aquifers and quaternary deposits many of which form shallow granular aquifers the papers presented here address a number of current issues common to the celtic regions including groundwater protection policies groundwater management in karst aquifers groundwater development in quaternary aquifers groundwater evaluation in data scarce aquifers and groundwater supplies to small island communities

paired stable isotopes o c and clumped isotope thermometry of magnesite and silica veins in the new caledonia peridotite nappe abstract the stable isotope compositions of veins provide information on the conditions of fluid rock interaction and on the origin of fluids and temperatures in new caledonia magnesite and silica veins occur throughout the peridotite nappe in this work we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore forming laterization focusing on the koniambo massif for magnesite veins occurring at the base of the nappe the high 18 o values between 27 8 and 29 5 attest to a low temperature formation clumped isotope analyses on magnesite give temperatures between 26 c and 42 c that are consistent with amorphous silica magnesite oxygen isotope equilibrium the meteoric origin of the fluid is indicated by calculated 18 o water values between 3 4 to 1 5 amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of 18 o values between 29 7 and 35 3 for quartz veins occurring at the top of the bedrock and at the saprolite level commonly in association with ni talc like minerals the 18 o values are lower between 21 8 and 29 0 and suggest low temperature hydrothermal conditions 40 95 c thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and or influence of exothermic reactions of serpentinization could be the source s of heat needed to form quartz veins under such conditions

the impact of lithification on the diversity size distribution and recovery dynamics of marine invertebrate assemblages lithified marine sediments are not equitably distributed through time raising the possibility that lithification masks biological signals when data from unlithified and lithified sediments are compared or combined using mollusk dominated assemblages from the early cenozoic of the gulf coastal plain we find that lithification conceals small taxa decreases taxonomic resolution and exacerbates the undersampling of rare taxa lithified assemblages appear less diverse and have less even abundance distributions than coeval unlithified samples these limitations cannot be overcome by standardization procedures nor are they likely to be circumvented by collecting larger samples the effects of this bias however can be mitigated by restricting analyses to a single lithification state or to specific size classes since lithification selectively obscures small taxa the magnitude of this bias will be most severe when organisms are particularly small such as in the aftermath of mass extinctions in the study area lithification artificially protracts the recovery period following the cretaceous paleogene mass extinction by 7 m y

mercury as a proxy for volcanic activity during extreme environmental turnover the cretaceous paleogene transition abstract the usually low geological background concentrations of hg makes this trace element suitable for identifying accumulation pulses in sediments that can be tentatively related to weathering processes and thus to climatic changes intense volcanism has witnessed the cretaceous paleogene transition ktb and was perhaps responsible for dramatic climatic changes and decrease in biodiversity and mass extinction we have used hg concentrations as a proxy for volcanic activity and atmospheric hg and co2 buildup across the ktb at three localities in the salta basin argentina hg contents display several spikes across the ktb with a maximum value of 250 ng g 1 in three drill cores across the ktb in the paraiba basin northeastern brazil hg contents increase from the late maastrichtian to early danian and hg spikes predate the ktb perhaps as a record of volcanic activity before but very close to this transition at stevns klint denmark hg contents reached almost 250 ng g 1 within a 5 cm thick clay layer the fiskeler member fish clay that comprises the ktb some co variation between hg and al2o3 contents has been observed in all of the studied sections across the ktb suggesting that hg is probably adsorbed onto clays thermo desorption experiments in selected samples from the yacoraite formation showed hg 2 as the major species present which is in agreement with a volcanic origin combined hg and c isotope chemostratigraphy may become a powerful tool for the eventual assessment of the role of volcanic activity during extreme climatic and biotic events such as those during the ktb

faunal evidence for reduced productivity and uncoordinated recovery in southern hemisphere cretaceous paleogene boundary sections the mass extinction at the cretaceous paleogene boundary is generally explained by a severe crisis in primary productivity following a catastrophic bolide impact consistent with this scenario danian mollusk dominated benthic shelf ecosystems of southern middle paleolatitudes neuquen basin argentina are characterized by 1 a stratigraphically limited low in macrofossil abundances 2 an increase in starvation resistant nonplanktotrophic deposit feeders and chemosymbionts 3 a reduction in the average body size of individuals and 4 individuals with inactive lifestyles being more common than in the late maastrichtian return to pre extinction conditions of the various synecological attributes occurred over unequal time spans indicating that recovery was uncoordinated with respect to ecological traits global comparison of ecological patterns suggests that reduced food supply 1 was a controlling factor in both hemispheres 2 affected macrobenthic marine faunas at various distances from the chicxulub impact site and 3 was more effective in siliciclastic environments as compared to oligotrophic carbonate settings

tectonic history of northern new caledonia basin from deep offshore seismic reflection relation to late eocene obduction in new caledonia southwest pacific new high quality multichannel seismic reflection data from the western new caledonia offshore domain allow for the first time the direct continuous connection of seismic reflectors between the deep sea drilling project 208 drill hole on the lord howe rise and the new caledonia basin a novel seismic interpretation is hence proposed for the northern new caledonia basin stratigraphy which places the eocene oligocene unconformity deeper than previously thought and revisits the actual thickness of the pre oligocene sequences a causal link is proposed between the obduction of the south loyalty basin over new caledonia nc and the tectonic history of the northern new caledonia basin here it is suggested that as the south loyalty basin was being obducted during early oligocene times the nc basin subsided under the effect of the overloading and underthrusted to accommodate the compressional deformation which resulted in 1 the uplift of the northern fairway ridge and 2 the sinking of the western flank of new caledonia this event also had repercussions farther west with the incipient subsidence of the lord howe rise

regional implications of u pb shrimp age constraints on the tectonic evolution of new caledonia abstract u pb shrimp ages for zircons from plagiogranites indicate a late carboniferous age of formation for ophiolitic basement of the koh terrane in the central chain mountains of new caledonia samples from ophiolites at koh and koua yielded ages of 302 7 ma and 290 5 ma respectively the similarity of these ages to those of plagiogranites in the dun mountain ophiolite belt maitai terrane of new zealand and the comparable structural positions of the two terranes potentially constrain reconstructions of the cretaceous sw pacific margin detrital zircons from late mesozoic sediments that overlap the koh terrane also provide potential constraints on the location of new caledonia prior to its break up and dispersal from eastern australia

first palaeomagnetic dating of ferricrete in new caledonia new insight on the morphogenesis and palaeoweathering of grande terre terra nova 24 77 85 2012 abstract comparing palaeolatitudes estimated from remanent magnetization data of ferricrete developed over laterite at two sites goro and tiebaghi against the apparent polar wandering path of australia provides new time constraints for the peridotite weathering in new caledonia the tiebaghi massif of the west coast klippes displays a single episode of ferricrete development during latest oligocene times by contrast the goro site in the southern part of the massif du sud reveals a more complex history with several episodes of ferricrete development from latest oligocene to pliocene quaternary times these data have made it possible to constrain the post obduction geodynamics and associated morphogenesis of new caledonia since related uplift probably prevented regolith development until latest oligocene times moreover the later uplift and deep erosion of the west coast klippes during the early miocene probably prevented further regolith preservation

quantification of the water balance and hydrogeological processes in the vicinity of a small groundwater fed wetland east anglia uk abstract badley moor fen exists in a region of the uk where potential evapotranspiration exceeds annual rainfall the wetland is maintained by an input of chalk groundwater in an area where the groundwater aquifer is regionally confined below boulder clay the large groundwater contribution to the water balance arises from a unique local geological situation on the margin of the valley floor that allows the vertical movement of groundwater to the surface under a strong upward head gradient the groundwater contribution is the dominant water input and maintains saturation within the immediate vicinity of the source of groundwater surface water outflow via adjacent drainage channels is the major output the groundwater component is also important in that as a result of hydrochemical change in the groundwaters with flow towards the surface tufa has been precipitated the calcium bicarbonate rich groundwater and tufa accumulation have given the site a unique character with an exceptionally rich calcareous fen community

on impact and volcanism across the cretaceous paleogene boundary the cause of the end cretaceous mass extinction is vigorously debated owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing impact and extinction we used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing we found support for major outgassing beginning and ending distinctly before the impact with only the impact coinciding with mass extinction and biologically amplified carbon cycle change our models show that these extinction related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide thus limiting the global warming otherwise expected from postextinction volcanism

slab derived origin of tremolite antigorite veins in a supra subduction ophiolite the peridotite nappe new caledonia as a case study hydration of mantle peridotites provides information on the exhumation history and on the fluid regime accompanying exhumation of these rocks reservoirs involved fluid rock ratios temperature of interaction highly depleted harzburgites and dunites of the peridotite nappe of new caledonia are crosscut by fractures which have been pervasively serpentinized producing lizardite brucite magnetite and minor chrysotile in a near static environment probably by sea water circulating in cooling joints this event is generally referred to as primary serpentinization in a next step already serpentinized joints were re opened to produce tension and shear cracks sealed by higher temperature synkinematic fibrous minerals locally tremolite bearing veins and pockets which do not display evidence for void infill were generated by metasomatic replacement of the wall rock peridotite most veins only contain fibrous antigorite but some display tremolite antigorite intergrowths or even pure tremolite the latter rocks yield high contents of ca and incompatible elements which contrast with the overall depletion of the peridotite host rock and suggest contribution of an external source whole rock geochemical and isotopic features 87sr 86sr 18o and h suggest that antigorite veins which bear highly radiogenic sr isotope signatures were strongly influenced by fluids emitted by the subducted slab and associated sediments in contrast the geochemical and isotopic signatures of tremolite bearing rocks suggest a genetic link with early eocene supra subduction dykes and fluids that leached them calcium strontium and ree bearing oxidized fluids reacted with already serpentinized fracture wall rock as shown by fibre nucleation chromite alteration and high cr contents in tremolite the bulk of syn tectonic fluid rock interaction associated with shear and tensile fracture development probably occurred at the onset of eocene intra oceanic subduction when the buoyant lower plate the south loyalty basin obliquely forced its way beneath the nascent loyalty fore arc mobile elements extracted from supra subduction dykes temporarily enriched the circulating fluids and generated tremolite antigorite mg chlorite and magnetite instead of antigorite and magnetite solely tremolite crystallization probably ceased due to the exhaustion of ca rich fluids in a globally cooling fore arc environment

stable isotope records across the cretaceous paleogene transition stevns klint denmark new insights from the chromium isotope system abstract late cretaceous to early paleogene time represents a critical transitional period in earth history global events include short term instability in climate and ocean circulation large igneous province emplacement and catastrophic extinction of marine and terrestrial fauna due at least in part to a bolide impact event the response of the ocean system to cretaceous paleogene k pg global events has been the subject of much research yet fundamental questions remain regarding carbon cycling climate ocean mixing and redox conditions to help elucidate paleoceanographic changes across the k pg transition we revisit the classic maastrichtian to danian chalk limestone succession at stevns klint denmark with a suite of new geochemical data including insights from the redox sensitive chromium isotope system we use carbon and oxygen isotope trends to form a well constrained framework for the succession before presenting strontium isotope chromium isotope and rare earth element data for the units deposited both before and after the k pg event carbon isotopes show only minor perturbation across the k pg boundary and oxygen isotopes record a prominent positive excursion with both of these trends standing in contrast to many k pg boundary sections worldwide strontium isotopes record a spike towards more radiogenic values which is consistent with a globally observed short term weathering pulse the chromium isotope profile of maastrichtian chalk begins with strongly positive values followed by a sharp negative excursion associated with a facies shift and initiation of bottom currents in the chalk sea 53 cr values then recover before falling steadily across the k pg boundary and into the danian limestone chromium isotope trends do not correspond to changes in hydrothermal input or basin redox conditions instead we propose that mixing of water masses with distinct chromium isotope signatures controlled temporal chromium isotope variability the local mixing event inferred from our maastrichtian chromium isotope data could be related to a temporary inflow of tethyan bottom waters or the shift from end maastrichtian greenhouse warming associated with deccan volcanism to the worldwide cooling phase that immediately preceded the k pg boundary no immediate change in chromium isotopes is recorded across the k pg boundary indicating that the bolide impactor did not substantially perturb the marine chromium cycle at least at the scale resolvable by our data instead chromium isotope trends continued to be controlled by local oceanographic processes highlighting the potential of the chromium isotope system to record isotopic heterogeneity and mixing events in ancient oceans

high resolution hg chemostratigraphy a contribution to the distinction of chemical fingerprints of the deccan volcanism and cretaceous paleogene boundary impact event abstract there is a renewed interest in volcanism as the major trigger for dramatic climatic changes at the cretaceous paleogene transition ktb which were accompanied by a decrease in biodiversity and mass extinction we have used hg contents as proxy for volcanic activity at the classical localities of gubbio italy and stevns klint denmark where the ktb layer is easily recognizable and at a near complete succession exposed at the bajada del jaguel locality in the neuquen basin argentina these three localities display similar 13ccarb trends with markedly negative excursion at the ktb layer bulk rock oxygen isotopes yielded similar pathways across the ktb layers in these localities and if considered near primary the negative 18o excursion at the ktb in gubbio and bajada del jaguel suggest warming temperatures during this transition whereas the negative excursion immediately followed by positive one at stevns klint points to a cycle of warm followed by colder climate at stevns klint hg contents reach 250 ng g 1 within the ktb layer fiskeler member and 45 ng g 1 at 1 5 m above that while within the scaglia rossa formation at gubbio three hg peaks across the ktb are observed one of them within the ktb layer 5 3 ng g 1 hg shows several peaks across the ktb in the neuquen basin with up to 400 ng g 1 in the jaguel formation the phenomena that caused dramatic changes at the ktb probably expelled huge amounts of hg into the atmosphere as recorded by these high hg levels a co variation between hg and al2o3 in the studied sections suggest that hg is adsorbed onto clays hg concentrations and also hg isotopes are perhaps a powerful tool in the assessment of the role of volcanic activity during extreme climatic and biotic events and in assessing the role of meteorite impact versus volcanism as the predominant cause of past global catastrophes and mass extinction

eocene arc continent collision in new caledonia and implications for regional southwest pacific tectonic evolution new caledonia preserves evidence that constrains models for the tectonic evolution of the southwest pacific region onland geology reflects four main tectonic phases 1 early mesozoic development of subduction related terranes and their accretion to the gondwana margin 2 cretaceous passive margin development and sea floor spreading during the gondwana breakup 3 foundering of an oceanic basin and the eocene arrival of thinned gondwana margin crust at a southwest facing subduction zone resulting in collisional orogenesis and obduction of an ophiolitic nappe from the northeast and 4 detachment faulting during extensional collapse resulting in unroofing of metamorphic core complexes the last phase explains supposedly anomalous metamorphic gradients in the northeast of the island

the emplacement of the peridotite nappe of new caledonia and its bearing on the tectonics of obduction the peridotite nappe of new caledonia is one of the few ophiolites worldwide that escaped collisional orogeny after obduction here we describe the deformation associated with serpentinization in two klippes of the nappe in northwestern new caledonia the klippes are flat lying and involve s sw vergent reverse slip shear zones which are true compressional structures in origin further northeast the nappe is folded in association with the development of a steep schistosity in low grade metasediments this difference in structural style indicates that the peridotite nappe experienced compression at greater depths toward its root zone suggesting a push from the rear mechanism of emplacement this supports the view that the nappe has been emplaced through horizontal contraction sustained by plate convergence we establish a crustal scale cross section at the end of the obduction event before neogene extension this involves a large fold nappe of high pressure rocks bounded from below by a major thrust furthermore we show that obduction in new caledonia occurred through dextral oblique convergence oblique convergence probably resulted from the initial obliquity between the subduction trench and the continental ribbon that became incorporated in it this obliquity can solve the paradox of the peridotite nappe seemingly being emplaced at the same time the high pressure rocks were exhumed oblique convergence together with focused erosional denudation on the northeastern flank of the island led to exhumation of the metamorphic rocks in a steep fold nappe rising through the rear part of the orogen

palaeoecology of the late triassic extinction event in the sw uk a high resolution palaeoecological study of the shelly invertebrate macrofauna across two marine triassic jurassic boundary sections in the uk st audrie9s bay and lavernock point is presented loss of taxonomic richness occurs in the upper westbury formation to lower lilstock formation late rhaetian but if sample size is taken into account there is little convincing evidence of a catastrophic marine extinction there is however good evidence for significant palaeoecological change in the benthic marine ecosystem at this time the immediate post event recovery interval in the upper lilstock formation is characterized by assemblages of low abundance low diversity high dominance and low evenness body sizes of taxa that survived the event and originated afterwards were low until the later hettangian recovery to higher abundance higher diversity and higher evenness is recorded in the psiloceras planorbis zone recovery of the benthic ecosystem in the aftermath of the late triassic event was disrupted by marine anoxia and shows additional similarities to the much slower recovery that followed the late permian event the pattern of body size changes recorded in the shelly fossil record closely matches that of the trace fossil record shell thickness trends do not support a biocalcification crisis during the late triassic biotic event

seasonal variability and simulation of groundwater flow in a prairie wetland wetlands in regional discharge areas of the red river valley of eastern north dakota provide runoff flood protection and wildlife habitat two years of groundwater and soil water monitoring were used to characterize the hydrology of a 500 ha wetland 24 km north west of grand forks the objective was to describe monitor and model important water budget processes from november through march 1990 and 1991 the water table dropped as water flowed towards frost in the vadose zone where saturated soils occurred near the surface the water table rose quickly in the spring a later larger rise occurred where the water table and capillary fringe were deeper during the summer precipitation was rapidly depleted by evapotranspiration et the low hydraulic conductivity of the clayey lacustrine sediments 0 1 2 m yr combined with a small horizontal hydraulic gradient results in minimal lateral and maximum vertical flow the us geological survey modflow code was used to simulate vertical saturated flow by including actual et estimated from potential evaporation and using the recharge option to represent vadose flow the model provided good correspondence between observed and simulated hydrographs these results suggest that a shallow vertical flow of ground and soil water dominates the hydrological budget simulation of unusually dry conditions such as those experienced during the 1930s indicates that water levels in the wetland would reach a steady state about 0 3 m lower than normal within two to three years less winter vadose storage would decrease the water level rise in spring and early summer but would have a minimal impact on the overall yearly water budget

modelling the effects of climate change and its uncertainty on uk chalk groundwater resources from an ensemble of global climate model projections projections of climate for the 2080s from an ensemble of global climate models gcms run under a medium high a2 emissions scenario are used to simulate changes in groundwater resources of a chalk aquifer in central southern england few studies that have investigated the impacts of climate change on groundwater resources have addressed uncertainty in this paper the uncertainty associated with use of a suite of gcm outputs in catchment scale impact studies is quantified a range of predictions is obtained by applying precipitation and temperature change factors derived from thirteen gcms to a distributed recharge model and a groundwater flow model of the chalk aquifer of the marlborough and berkshire downs and south west chilterns in the uk the ensemble average suggests there will be a 4 9 reduction in annual potential groundwater recharge across the study area although this is not statistically significant at the 95 confidence level the spread of results for simulated changes in annual potential groundwater recharge range from a 26 decrease to a 31 increase by the 2080s with ten predicting a decrease and three an increase whilst annual recharge is not found to change significantly the multi model results suggest that the seasonal variation in the groundwater resource will be greater with higher recharge rates during a reduced period of time in winter the spread of predictions for changes in river baseflow at the bottom of the largest river sub catchment is from 16 to 33 in march and from 68 to 56 in october the effects of climate change are shown to depend significantly on the type of land use it is concluded that further research is required to quantify the effect of different vegetation types on chalk covered by different thicknesses of soil and their response to a changing climate

syn tectonic meteoric water derived carbonation of the new caledonia peridotite nappe exceptional outcrops recently exposed in the koniambo massif allow the study of the serpentine sole of the peridotite nappe of new caledonia southwest pacific ocean many magnesite veins are observed with characteristics indicating that they were emplaced during pervasive top to the southwest shear deformation the oxygen isotope composition of magnesite is homogeneous 27 4 18o 29 7 while its carbon isotope composition varies widely 16 7 13c 8 5 these new data document an origin of magnesite from meteoric fluids laterization on top of the peridotite nappe and carbonation along the sole appear to represent complementary records of meteoric water infiltration based on the syn kinematic character of magnesite veins we propose that syn laterization tectonic activity has enhanced water infiltration favoring the exportation of leached elements like mg which has led to widespread carbonation along the serpentine sole this calls for renewed examination of other magnesite bearing ophiolites worldwide in order to establish whether active tectonics is commonly a major agent for carbonation

fabric of the cretaceous tertiary marine macrofaunal transition at braggs alabama abstract the record of latest cretaceous and earliest tertiary macroinvertebrates in the k t boundary sequence at braggs alabama is documented by high resolution stratigraphic data latest maastrichtian and earliest danian strata lie within a reversed magnetic interval identified as chron c29r the faunal decline across this interval is abrupt and severe with 50 of the terminal cretaceous species dropping out of the record a pronounced lazarus effect is displayed across the boundary however persistently high cretaceous and low tertiary diversity coupled with good stratigraphic resolution and comparable quality of preservation of both cretaceous and tertiary faunas in similar lithologies all argue for a relatively abrupt decline the lazarus effect is most likely the result of local extinction and or migration rather than taphonomic or collection difficulties if only previously published species lists were used in this study either a gradual extinction pattern or a larger scale lazarus effect could have been invoked to explain the observed diversity changes extensive collecting however has revealed a persistently high diversity throughout the latest maastrichtian no stepwise extinctions were observed and most taxa represent widespread and long ranging clades the braggs faunal transition is consistent with proposed catastophic extinction hypotheses but a limit in temporal resolution of up to 0 8 ma for the faunal turnover at this site allows ample time for other longer term extinction processes and patterns to have developed this resolution is perhaps as good as can be expected with current methods and the shallow marine character of the sequence

southwest pacific absolute plate kinematic reconstruction reveals major cenozoic tonga kermadec slab dragging tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench parallel slab motion through the mantle recently defined as a form of slab dragging we investigate here long term slab dragging components of the tonga kermadec subduction system driven by absolute pacific plate motion to this end we develop a kinematic restoration of tonga kermadec trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle estimating tonga kermadec subduction initiation is challenging because another new caledonia subduction zone existed during the paleogene between the australia and pacific plates we test partitioning of plate convergence across the paleogene new caledonia and tonga kermadec subduction zones against resulting mantle structure and show that most if not all tonga kermadec subduction occurred after ca 30 ma since then tonga kermadec subduction has accommodated 1 700 to 3 500 km of subduction along the southern and northern ends of the trench respectively when placed in a mantle reference frame the predominantly westward directed subduction evolved while the tonga kermadec trench underwent 1 200 km of northward absolute motion we infer that the entire tonga kermadec slab was laterally transported through the mantle over 1 200 km such slab dragging by the pacific plate may explain observed deep slab deformation and may also have significant effects on surface tectonics both resulting from the resistance to slab dragging by the viscous mantle

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

impact dust not the cause of the cretaceous tertiary mass extinction most of the 3 mm thick globally distributed chicxulub ejecta layer found at the cretaceous tertiary k t boundary was deposited as condensation droplets from the impact vapor plume a small fraction of this layer 14 g was submicrometer size dust the global mass and grain size distribution of the clastic debris indicate that stratospheric winds spread the debris from north america over the pacific ocean to europe and little debris reached high southern latitudes these findings indicate that the original k t impact extinction hypothesis the shutdown of photosynthesis by submicrometer size dust is not valid because it requires more than two orders of magnitude more fine dust than is estimated here furthermore estimates of future impact hazards which rely upon inaccurate impact dust loadings are greatly overstated

nickel dispersion and enrichment at the bottom of the regolith formation of pimelite target like ores in rock block joints koniambo ni deposit new caledonia in new caledonian ni deposits the richest ni silicate ores occur in fractures within the bedrock and saprolite generally several tens of meters to hundred meters below the present day surface fracture related ni silicate ore accounts for high ni grades at least a few weight percent above the average exploited grade 2 5 these ni rich veins are affected by active dissolution precipitation processes at the level of the water table ni in solution is precipitated as silicates in thin layer cementing joints this mineralization is characterized by chemical and mineralogical concentric zoning with an outer green rim around an inner white zone composed from the edge to the centre of the block i a highly oxidized and altered zone ii a green pure ni rich pimelite zone iii a zone limited to a few centimetres with a mixture of ni poor kerolite and ni rich pimelite and intermediate colours and iv a large white mg kerolite mineralization zone this study proposes that the concentric zonation results from evapo precipitation process related to alternate periods of hydration and drying induced by water table movements this extensive dispersion of ni in concentrically zoned ores can partly explain the rather monotonous ni grade of the bulk exploitation at the base of the regolith with values between 2 and 3 wt

origin of the new caledonian ophiolites based on a french australian seismic transect abstract the origin age and nature of the new caledonian ophiolites are still debated recently as part of the joint french australian seismic transect faust program the australian research vessel rig seismic recorded a series of multichannel deep seismic profiles between the new hebrides arc and the australian margin these profiles which ran south of new caledonia image the southern prolongation of the overthrusted ophiolites and allow a new interpretation of the eocene compressive tectonism along the new caledonia norfolk ridge a model involving abduction of the whole oceanic lithosphere of the loyalty basin is consistent with the age and origin of the ophiolite variations in tectonic style along strike in the north south trending part of the norfolk ridge have produced ophiolite exposures related to uplifted and partially overthrust upper mantle slivers within the southern part of the loyalty basin

observation of sections of oceanic crust and mantle cropping out on the southern wall of kane fz n atlantic the objective of the 20 nautile dives of the recent kanaut cruise was to study the southern wall of the kane fracture zone from its eastern intersection with the mid atlantic ridge mar to 5 myr in age the geological mapping shows four successive massifs wrench faulted and slightly tilted the transform facing walls of these massifs exhibit outcrops of fresh and serpentinized peridotites gabbros and basalts the entire crustal exposure is cataclased and metamorphosed to greenschist facies

development of a numerical model for nitrates in groundwater in the reservoir area of the komesu subsurface dam okinawa japan a numerical model consisting of simplified equations was developed to simulate nitrate concentrations in groundwater in a reservoir area of a subsurface dam in a quaternary limestone region the model was composed of a water balance sub model and a nitrogen balance sub model the water balance sub model was built from tank models which can express the quick dilution near caves and the effect of dam construction and the nitrogen balance sub model was made to represent changes in nitrogen forms and movement of nitrogen in the soil and aquifer zones the model was calibrated and verified by observed data before and after the dam construction and then applied to a predictive simulation under a simple assumption that rainfall descends gradually the model seemed applicable to long term prediction of changes in no3 n in the reservoir area

geochemistry and tectonic setting of matakaoa volcanics east coast allochthon new zealand suprasubduction zone affinity regional correlations and origin in north eastern new zealand the late cretaceous to eocene submarine volcanic rocks of the east coast allochthon referred to as matakaoa volcanics formed a dominantly mafic melange with minor abyssal sediments during the subduction of oceanic crust accreted and melanged pillow lavas and dolerites display the geochemical and isotopic features of tholeiites with some diversity referred to as midocean ridge basalts island arc tholeiites and back arc basin basalts the association of supra subduction tholeiitic magmas abyssal sediments and polymetallic volcanogenic sulphide deposits is typical of many back arc basins therefore a correlation with the alkaline and transitional basalts of the hikurangi manihiki ontong java plateau may be ruled out these petrological features and the fossil ages as well are closely similar to those of the tangihua complex northland allochthon and allow matakaoa and tangihua mafic volcanic rocks now separated by the modern havre trough to be correlated within one single late cretaceous to eocene 2 basin the consideration of possible younger ages oligocene is also discussed the occurrence of late cretaceous eocene oceanic crust with supra subduction zone affinities to the east of the norfolk ridge poses the problem of the intervening southwest dipping subduction the missing late cretaceous eocene arc and their relationship with southeast gondwana marginal break up

lower danian bivalves stevns klint denmark continuity across the k t boundary abstract the paleoenvironmental change at the k t boundary at stevns klint is a change from an upper maastrichtian bryozoan bioherm environment with different faunas from the bioherms and from the interbiohermal basins to an early danian environment comparable to the biohermal basins except for a nearly complete lack of bryozoans in the lowermost danian the bivalves exhibit a drastic reduction in species number when the complete faunas are compared however a within habitat comparison between the maastrichtian interbiohermal basins and the danian shows an increase in the number of infaunal species across the boundary a decline in the number of epifaunal species is related to the lack of bryozoans acting as substrates for epibyssate bivalves comparison with other k t boundary sections rich in marine mesobenthos does not support the presence of general patterns in the faunal change at the boundary

selective extinction and survival across the cretaceous tertiary boundary in the northern atlantic coastal plain the inner atlantic coastal plain in new jersey and the delmarva peninsula is underlain by an upper cretaceous lower tertiary sequence of marine and paralic sand clay and glauconitic beds campanian maastrichtian danian and thanetian deposits are especially fossiliferous and yield a succession of marine faunas that reveal a pattern of selective extinction and survival across the cretaceous tertiary k t boundary in this area cretaceous benthic invertebrate communities are dominated by oysters and other semi infaunal and infaunal molluscs with planktotrophic larval stages these are replaced in the danian by brachiopod dominated communities that are composed of epifaunal benthos with a variety of nonplanktotrophic reproductive strategies a similar pattern is observable in the nektonic cephalopod populations in this sequence the typical ammonites of the cretaceous became extinct at the k t boundary whereas the nautilids survived ammonites are thought to have had a planktotrophic larval stage whereas nautilids are known to lay large lecithotrophic eggs this pattern of differential survival is attributed to the planktonic population crash at the k t boundary which placed planktotrophically reproducing species at a disadvantage while favoring the varied groups that practiced alternative reproductive strategies

terrestrial evidence for the lilliput effect across the cretaceous paleogene k pg boundary abstract recent research has demonstrated that the lilliput effect reduction of body size in biota associated with the aftermath of mass extinctions affected all trophic levels in the marine realm following the cretaceous paleogene k pg event however it is unclear if this size change was strictly a marine signal or a global phenomenon that also affected continental ecosystems herein we present the results of an ichnological proxy for body size of soil dwelling insects across the k pg boundary in big bend national park texas u s a quantitative efforts focused on naktodemasis bowni which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci these traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments as an approximation for the body size of the subterranean insects this dataset indicates that a smaller n bowni diameter dn is statistically correlated

patterns of bivalve biodiversity from early to middle triassic in the southern alps italy regional vs global events abstract the triassic records the severe effects of the end permian mass extinction and the beginning of the mesozoic modern adaptive radiation of marine invertebrates as far as bivalves are concerned a group which was relatively unaffected by the extinction diversification started in the middle triassic more particularly during the anisian thus the interval between the basal triassic induan and anisian is crucial in analysing the biodiversity changes and diversification patterns of these molluscs this analysis is discussed at genus level and based on the regional records of the southern alps biodiversity changes are examined in connection with palaeogeographic evolution the conquest of vacated ecologic niches and climatic changes the lowest point of generic richness as an immediate aftermath of the p t mass extinction is recorded in the induan units mazzin and siusi mbs of the werfen formation which include only five genera numerically dominated by claraia and unionites twelve genera are represented in the olenekian campil val badia and cencenighe members such an increasing richness is mostly connected with the recovery of pectinids and endobyssate bakevellids typical marine biota such as ammonoids tirolites and dinarites fauna and crinoids also appear in this time the richness and structure of the early anisian bithynian bivalve assemblages contained in the gracilis formation and equivalent units of southern alps do not significantly change 15 genera in comparison with those from olenekian the most relevant increase in bivalve genera 31 genera occurs in the late anisian mostly in the pelsonian calcare di recoaro and equivalent units when a strong tectonic phase considerably differentiated the marine habitats and ecological niches in the southern alps however bivalve pelsonian radiation is recorded in other tethyan and peri tethyan areas and coincides with the reappearance of marine stenotopic hard bottom dwellers and reef communities including scleractinian corals therefore it represents a global bioevent which indicates the fully recovery of the physical and chemical limiting factors of the sea water in the southern alps the diversification of bivalves after the end permian extinction occurred in two steps at the end of smithian early olenekian when their recovery began and in the pelsonian late anisian when their radiation parallels with the recovery of hard bottom communities and metazoan reefs both the events occurred at the end of humid phases

productivity across the cretaceous tertiary boundary in high latitudes in low and middle latitudes the cretaceous tertiary boundary is marked by a sudden and pronounced decrease in 13c values of near surface water carbonates and a reduction in the surface to bottom 13c gradient these isotopic data have been interpreted as evidence of a decline in surface water productivity that was responsible for the extinction of many planktic foraminiferal species and other marine organisms at or near the k t boundary we present planktic and benthic foraminiferal isotopic data from two almost biostratigraphically complete sections at ocean drilling program site 738 in the antarctic indian ocean and at nye klov in denmark these data suggest that planktic carbonate 13c values in high latitudes may not have decreased dramatically at the k t boundary thus surface water productivity may not have been reduced as much as in low and middle latitudes comparison of the records of site 738 with those of odp sites 690 and 750 indicates a pronounced decline in 13c values of planktic and benthic foraminifera and fine fraction bulk carbonate 200 000 yr after the k t boundary this reflects a regional shift in the carbon isotopic composition of oceanic total dissolved carbon tdc and correlates with a similar change in benthic foraminiferal 13c values at mid and low latitude deep sea drilling project sites 527 and 577 this oceanographic event was followed by the ecosystem s global recovery 500 000 yr after the k t boundary these data suggest that the environmental effects of the k t boundary may have been less severe in the high latitude oceans than in tropical and subtropical regions

a new miniaturized extraction chromatography method for precise u pb zircon geochronology abstract in this paper we describe a new method for the concomitant separation of u and pb in zircons for radiometric dating purposes the proposed separation scheme is based on a blend of two extraction chromatographic materials referred to as tru spec and sr spec respectively these afford a straightforward separation of u and pb with high yield good purity and satisfactory blank levels on micro columns using very small volume 5 l of mixed resins owing to the selectivity and high capacity of the specific extraction chromatographic materials for u and pb this new technique could be further scaled down the validity of the method is illustrated by measurements of u pb isotopic ratios and determination of corresponding ages in 0 2 0 8 mg fragments of the zr91500 zircon standard