late pleistocene pinon pines in the chihuahuan desert abstract examination of late pleistocene packrat middens from the northern and central chihuahuan desert disclosed macrofossils of colorado pinon pinus edulis and texas pinon p remota radiocarbon dating indicates that texas pinon was widespread in trans pecos texas and northeastern mexico between 30 000 and 11 000 yr b p today it is found in small refugia east of its former range in the late pleistocene colorado pinon occurred at lower elevations on the northern edge of the chihuahuan desert both species occurred in the hueco mountains near el paso texas no clear evidence was found of the presence of mexican pinon p cembroides though today it is abundant in the davis and chisos mountains a paleoclimate is postulated that had the following characteristics increased winter precipitation from pacific frontal sources reduced summer temperatures and precipitation and milder winter temperatures due to a reduced frequency of arctic airmass incursion winter precipitation appears to have decreased from north to south while winter temperatures and possibly summer precipitation increased from north to south during the late pleistocene the northern chihuahuan desert was dominated by woodlands of pinon pines junipers and oaks the desert scrub communities that characterize the area today are a holocene phenomenon

marine geology of sohm basin canadian atlantic margin multichannel seismic reflection seismic refraction and magnetic anomaly data are used to interpret the mesozoic sea floor spreading history and subsequent sedimentary evolution of the sohm basin southeast of nova scotia observed m series mesozoic magnetic anomalies show that oceanic crust in the sohm basin was generated at very slow rates of sea floor spreading 5 15 mm yr half rates the slow spreading created very rough crustal topography but the crustal thickness and seismic velocity structure are typical of normal oceanic basement basement depths corrected for sediment loading fall below the predicted age depth curve in the anomaly m25 m4 interval these depth anomalies and an associated regional negative geoid anomaly suggest that the sohm basin is underlai by asthenosphere denser and possibly colder than normal correlation of seismic reflection profiles in the basin to regional seismic stratigraphy together with age constraints from reflection pinch outs on dated oceanic crust provides a chronology for interpreting the seismic sequences the jurassic to lower cretaceous sequences are similar in thickness and acoustic character to sequences observed along the united states atlantic margin suggesting that the new england seamount chain had little effect on sediment distribution patterns within the early western north atlantic basin upper cretaceous sediments in the sohm basin are thin probably because seaward transport of sediment was restricted by eustatic sea level rise and by a sedimentary ridge uplifted because of salt tectonics along the central and upper continental rise progradati nal sedimentary wedges and erosional unconformities characterize the tertiary and quaternary sedimentary record along the lower continental rise the prograding sequences generally correlate to sea level lowstands repeated episodes of erosion by abyssal currents are marked by seismic unconformities horizon au lower oligocene lm lower miocene mm middle miocene and l upper pliocene the deep currents also controlled local patterns of deposition and modified cross slope sediment transport and accumulation patterns thick supra horizon l sediments cover the sohm basin and reflect rapid sediment influx caused by glacio eustatic fluctuations in sea level during the quaternary

neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

the cretaceous tertiary boundary cocktail chicxulub impact triggers margin collapse and extensive sediment gravity flows a distinctive mixture of reworked microfossils impact derived materials and lithic fragments occurs in sediments at the cretaceous tertiary boundary in the basinal gulf of mexico and caribbean we have named this mixture the cretaceous tertiary boundary cocktail lithologic and paleontologic evidence suggests that the cocktail was deposited by giant sediment gravity flows apparently triggered by the collapse of continental margins around the gulf of mexico as a result of the chicxulub impact as most microfossils in the gravity flow units are reworked biostratigraphy provides only maximum ages recognition of the cocktail is a reliable way to identify cretaceous tertiary boundary deposits in the basinal gulf of mexico and caribbean

the global stratigraphy of the cretaceous tertiary boundary impact ejecta the chicxulub crater ejecta stratigraphy is reviewed in the context of the stratigraphy of underlying and overlying rock sequences the ejecta sequence is regionally grouped in a thick polymict and monomict breccia sequences inside the crater and within 300 km from the rim of the crater known from drill holes in and close to the breater and exposures near the border of yucatan and belize b gulf of mexico region 2500 m from the crater with up to 9 m thick complex tsunami wave influenced tektite bearing sequences in shallow marine 500 m deep environments and tektite bearing decimeter thick gravity flow deposits in deep water sites c an intermediate region between 2500 and 4000 km from the crater where centimeter thick tektite bearing layers occur and d a global distal region with a millimeter thin ejecta layer the distal ejecta layer is characterized by sub millimeter sized microkrystites often rich in ni rich spinels and altered clinopyroxene wherever present the ejecta layers mark exactly the sudden mass mortality horizon of the k t boundary what exactly caused the mass mortality is still uncertain but it appears the main event leading to the k t mass extinctions

sedimentary signatures and processes during marine bolide impacts a review abstract studies of submarine impact craters resulting from impacts of comets or asteroids demonstrate that the presence of water and the physical properties of target rocks have a major influence on sedimentary processes associated with meteorite impacts this results in difference in sedimentary signature of bolide impacts in marine environments compared to subaerial impact craters in subaerial impacts the targets are commonly hard rocks frequently of igneous and or metamorphic origin whereas in submarine impacts the targets are mostly unconsolidated or poorly lithified sediments or sedimentary rocks with high volumes of pore water such differences result in variability in crater morphology and in sedimentary processes inside and outside the impact area impacts in shallow water marine neritic environments produced craters with low or absent rims and wide and shallow brims as characterize by both the montagnais on the scotian shelf the mjolnir in the barents sea 45 and 40 km in diameter respectively and the chesapeake bay 90 km in diameter lack of elevated rims is thought to be the result of current reworking and resurge of the water back into the excavated cavity as the water in the crater is vaporized during this process resurge gullies can be cut across the rim while mass and debris flows turbidites and other gravity deposits are produced as results of tsunami and crater wall and central high collapse during and after the crater excavation stage such deposits are found both within and outside the crater structure the only difference between gravity deposits triggered by an impact or other rare events such as earthquakes is the admixture of various melt particles and possible enrichments in iridium in the former impacts near the shelf edge may cause partial collapse of the continental margin as shown by the montagnais and chicxulub impacts some of the gravity and debris flows generated by margin collapse may be channelized with final deposits up to several hundred meters thick extending for hundreds of kilometers from the impact site other impact features such as shatter cones tektites spherules and ni spinels shocked quartz isotropication and partial melts are common to both submarine and subaerial impacts theoretical calculations of the destructive forces of mega tsunami waves triggered by meteorite impact in the ocean greatly exceed those based on geologic evidence a dearth of gigantic tsunami evidence for the chicxulub impact outside of the gulf of mexico where from theoretical modelling the maximum near bottom orbital velocity of water flow crossing the deep north atlantic basin should have been 1 m s could be the result of the mitigating effect of the bathymetry of surrounding area causing wave diffraction and interference calculated maximum horizontal orbital velocity near the seafloor at the shelf for the montagnais impact is 22 m s for a 200 m high wave 5 5 m s for a 50 m high wave at 500 km decreasing to 0 5 m s at 1000 km strong enough to scour the deep ocean bottom and produce distinct erosion surfaces and disconformities in marine sedimentary record however lack of cores across impact horizon prevents confirmation of occurrence of such bottom water flows

high resolution records of the late paleocene thermal maximum and circum caribbean volcanism is there a causal link two recently drilled caribbean sites contain expanded sedimentary records of the late paleocene thermal maximum a dramatic global warming event that occurred at ca 55 ma the records document significant environmental changes including deep water oxygen deficiency and a mass extinction of deep sea fauna intertwined with evidence for a major episode of explosive volcanism we postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the earth s environment

late cretaceous and early paleogene nutrient and paleoproductivity records from blake nose western north atlantic ocean 1 we evaluate phosphorus p and biogenic barium bio ba as nutrient burial and export productivity indicators for the late cretaceous and early paleogene combining these with calcium carbonate caco3 organic carbon c and bulk caco3 c isotopes 13c sample ages span 36 71 ma 1 sample 0 5 m y for a depth transect of sites in the western north atlantic blake nose ocean drilling program leg 171b sites 1052 1051 and 1050 we use a multitracer approach including redox conditions to investigate export productivity surrounding the global paleocene 13c maximum 57 ma reducing conditions render most of the bio ba record not useful for export productivity interpretations p and organic c records indicate that regional nutrient and organic c burial were high at 61 and 69 ma and low during the paleocene 13c maximum a time of proposed global high relative organic c burial observed organic c burial changes at blake nose cannot explain this c isotope excursion

paleoclimatic changes during the late pleistocene holocene in laguna babicora near the chihuahuan desert mexico the paleoclimatic variability of northern mexico since the late wisconsinan is determined from sedimentological geochemical and stratigraphic studies of the lacustrine sequence of laguna babicora 29 4 n 107 7 w elevation 2100 m asl chronological control is based on 13 radiocarbon dates 6 from this study and 7 previously reported from four stratigraphic profiles that cover a range from 16 342 to 2800 bp two major periods of increased humidity are recognized by lake level variation during the late wisconsinan and early holocene the late wisconsinan humid period may be related to jet stream migration to southerly latitudes and the influence of the mobile polar high this period has been identified in the sedimentary record of el diablo profile with a radiocarbon date of 16 342 201 bp the early holocene humid period is recorded in el diablo 10 976 115 bp and cano profiles 9614 130 bp it is interpreted as a result of the younger dryas climatic anomaly characterized by a temperature decrease and cold paleoclimatic conditions similar to those for the late wisconsinan the early holocene was followed by an overall gradual drying that reached a maximum around 6000 bp during the middle holocene for the late holocene evidence of widespread erosion sedimentation changes flooded surfaces and paleosoils indicates that laguna babicora was subjected to short term climatic changes

gravity and magnetic studies of the subglacial grimsvotn volcano iceland implications for crustal and thermal structure the highly active subglacial grimsvotn volcano is associated with a 20 mgal bouguer gravity high and a broad magnetic low the magnetic low roughly coincides with the gravity high but short wavelength magnetic highs are superimposed on the low especially along caldera rims forward models of the gravity and magnetic fields show variable magnetization 0 12 a m 1 in the uppermost 1 2 km of the crust probably reflecting differences in the proportions of crystalline rocks and hyaloclastites and variations in hydrothermal alteration the models are consistent with but do not require a 10 km3 molten magma chamber in the shallow crust beneath the main caldera between 1 5 and 4 km depth a dense body 2 95 3 0 mg m 3 with a volume of 400 km3 is located probably composed of gabbro modeling suggests that this intrusive body is nonmagnetic which may imply that its temperature is at or above the curie point the distribution of geothermal activity at the glacier bed is consistent with heat extraction from this dense hot intrusive body it may be an important source for the presently observed geothermal heat output of 2000 4000 mw at grimsvotn this high heat transfer rate is difficult to reconcile with estimates of long term heat production in an icelandic rift zone volcano the heat flux may be a transient phenomenon caused by enhanced vertical permeability due to a recent caldera collapse and subsequent heat mining of the intrusive body

seismic and geologic evidence for early paleogene deepwater circulation in the western north atlantic previous studies of paleogeography global climate and foraminiferal stable isotopes have suggested that paleogene deepwater circulation was significantly different from that of today extracting details of deepwater history from the western north atlantic has been hampered by oligocene erosion and the lack of ideally located drill holes we report the discovery of a seismic disconformity on the sw bermuda rise that we have tied to a late paleocene erosional event in deep sea drilling project dsdp boreholes from this region distribution of this new seismic marker reflector ab indicates that it was formed by cyclonically circulating bottom water entering the western north atlantic from the south we attribute this vigorous deep circulation to a southern ocean source analogous to the effects of modern antarctic bottom water this interpretation is supported by isotopic comparisons that show the paleocene southern ocean was enriched in 13c relative to the pacific we distinguish reflector ab from the overlying reflector au on the basis of superposition and ages obtained at dsdp sites and piston cores using one of the cores we have estimated that the youngest age for reflector au is earliest oligocene 36 6 34 0 ma while its oldest age has been previously established as late eocene laminated sediments beneath reflector ab are enriched in organic carbon indicating that the early paleocene deep western north atlantic was occasionally anoxic these low oxygen levels may have been the result of sluggish deep circulation and or low latitude production of warm saline deep water wsdw sediments immediately above reflector ab show that deposition resumed on the western bermuda rise site 387 by the latest paleocene to earliest eocene biochron np10 57 2 0 6 ma while deposition resumed on the central bermuda rise site 386 during the late paleocene erosion nondeposition continued across much of the bermuda rise widespread resumption of pelagic deposition in the early eocene is consistent with 13c evidence for reduced southern ocean influence at this time however lower eocene sediments record well oxygenated conditions and 13c and 18o comparisons indicate that there were two early eocene deepwater sources the southern ocean and wsdw pak and miller this issue

geology of great abaco submarine canyon blake plateau observations from the research submersible alvin abstract nine dives in the research submersible alvin were made into great abaco submarine canyon to depths ranging from 1850 to 3666 m our observations indicate that the walls of this canyon are distinctly terraced consisting of nearly vertical to overhanging rock cliffs and intervening less steep sediment covered slopes the wall rock consists mostly of massive shallow water limestones and dolostones of cretaceous age coated on exposed surfaces with manganese oxides these rocks are heavily jointed fractured and thus very blocky to angular in appearance with sponges and other sessile organisms commonly attached talus slopes and sedimentary breccia deposits containing angular boulders are present at the base of these steep escarpments short term bottom current measurements in the axis of the eastern part of the canyon indicate that currents are relatively weak reaching velocities of only 10 cm sec this relatively placid setting is further corroborated by the abundance of turtle grass thalassia found along the canyon axis however abundant subdued symmetrical ripple marks and large scour depressions at the base of boulders indicate that high energy events sporadically impact the canyon axis contemporary erosional activity along the axis of the western headward part of the canyon appears to be more significant as evidenced by asymmetrical ripple marks sand waves and bioerosion great abaco canyon has evolved with time via a variety of processes including 1 faulting 2 subsidence 3 defacement and 4 erosional down cutting the location orientation and initiation of this canyon appear to be structurally controlled by the great abaco fracture zone during pre santonian time regional subsidence during the mesozoic allowed the walls of great abaco canyon to build vertically by accretion of shallow water limestones whereas joint controlled defacement has widened the canyon while maintaining steep walls erosional down cutting in the canyon axis by carbonate sediment gravity flows also appears to have been important episodically particularly during the miocene and pleistocene

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

the response of benthic foraminifera to the k pg boundary biotic crisis at elles northwestern tunisia abstract the high resolution quantitative study of benthic foraminifera from the elles section nw tunisia that contains one of the most complete cretaceous paleogene k pg boundary transition and spans about 357 kyr provides detailed data on the palaeoenvironmental turnover across the k pg boundary benthic foraminifera indicate outer neritic uppermost bathyal depths without perceivable bathymetrical changes throughout uppermost maastrichtian assemblages are well preserved and highly diversified indicating stable environment and mesotrophic to weakly eutrophic conditions during the latest cretaceous benthic foraminifera underwent a major faunal turnover in coincidence with the k pg boundary where a dramatic and sudden decrease in the percentage of both infaunal morphogroups and buliminids as well as in diversity heterogeneity and genus and species richness of the assemblages are recorded indicating overall oligotrophic conditions benthic foraminifera do not show significant extinction at the end of the cretaceous with only about 3 of the species clearly becoming extinct together with the temporary disappearance of some taxa a stepped pattern of faunal recovery and restructuring is recognizable during the lowermost danian reflecting the gradual restabilization of the environmental conditions after the k pg boundary event the nature and the abundance of food supply to the sea floor conditioned the faunal turnover in the earliest paleogene which reflects not only a sudden collapse of the food web due to the extinction of calcareous primary producers but also a major rapid change in composition and abundance of food supply just after the k pg boundary short term blooms of some opportunistic species within the g cretacea zone and the lowermost part of the ps pseudobulloides zone would reflect instability in the benthic assemblages that might be related to the transfer to the sea floor of food supply not easily used by the benthos through short term large blooms or changes in abundance of opportunistic various phytoplankton groups the major environmental instability at the sea floor that just follows the k pg boundary event may have been thus related to changes in the phytoplankton composition and abundance and would have taken place over a period of about 25 kyr benthic foraminiferal assemblages appear to stabilize in the lowermost part of zone ps pseudobulloides 65 kyr after the k pg boundary event the sea floor ecosystem at least at outer neritic uppermost bathyal depths may have recovered over a considerably shorter period than commonly suggested even if the food delivery to the sea floor had not fully recovered the pre k pg levels as indicated by the lower percentages of infaunal morphogroups and buliminids this would be also in agreement with the rapid recovery of terrestrial ecosystems following the biotic crisis at the k pg boundary the drastic change of benthic foraminiferal assemblages coincident with the k pg boundary at elles and their staggered reorganization during the lowermost paleogene are largely compatible with the catastrophic effects of a huge asteroid impact on earth at the k pg boundary that severely destabilized the oceanic phytoplankton based food web

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

cenozoic north atlantic deep circulation history recorded in contourite drifts offshore newfoundland canada abstract in the north atlantic ocean contour following deep currents have created regional erosional unconformities and deposited contourite drifts that exceed 2 km in thickness and extend for 100 s of km the stratigraphic records in the drifts have been used to reconstruct variations in north atlantic deep water circulation throughout the cenozoic however uncertainties remain about certain aspects of the timing intensity depth distribution and regional impact of these currents here we use an integrated dataset of seismic reflection profiles and iodp core data lithology biostratigraphy and magnetostratigraphy to document sedimentation history and the development of current effects in the cretaceous to present sedimentary record on the j anomaly ridge and southeast newfoundland ridge offshore newfoundland canada the newfoundland ridges are in a key location lying between well studied areas in the northern and western north atlantic and under the path of both the modern deep western boundary current and the gulf stream late cretaceous through early eocene sedimentation on the ridges was dominated by biogenic pelagic sedimentation but at 47 ma near the early middle eocene boundary well developed contourite drifts began to accrete in paleo water depths of 4000 4500 m accompanied by an order of magnitude increase in terrigenous sediment mass accumulation rates from this time forward drift deposition interrupted by brief episodes of erosion continued unabated this timing for the onset of persistent deep currents is coincident with reorganization of atlantic circulation inferred from a change from biosiliceous to non biosiliceous sedimentation in the western north atlantic horizon a c and with the current eroded intra eocene unconformity ieu in the northern north atlantic a change in sedimentation style occurred within the middle eocene to upper oligocene drift sequence and it likely was related to a shift to deeper more intense currents that eroded the widespread horizon a u along the margin of eastern north america about early oligocene time beginning in the late oligocene 25 ma a thick drift exhibiting seismically laminated mudwaves was deposited in a distinct belt at 3500 4500 m paleodepth on the southeast newfoundland ridge this development correlates with widespread late oligocene through miocene pliocene drift accumulation throughout the north atlantic the most recent phase of drift deposition since late pliocene time 3 ma occurred after a shift to the modern circulation system of deeper swifter currents and it includes mixed pelagic hemipelagic sediments and ice rafted debris that reflect glacial interglacial influences on sedimentation

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

benthic foraminifera and environmental turnover across the cretaceous paleogene boundary at blake nose odp hole 1049c northwestern atlantic sediments recovered at lower bathyal odp site 1049 on blake nose northwestern atlantic offer an opportunity to study environmental changes at the cretaceous paleogene k p boundary relatively close to the chicxulub impact structure on the yucatan peninsula mexico in hole 1049c the boundary is located at the base of a 9 cm thick layer with abundant spherules considered to be impact ejecta uppermost maastrichtian oozes below and lowermost danian pelagic oozes above the spherulebed contain well preserved bathyal benthic foraminifera the spherule bed itself in contrast contains a mixture of shallow neritic and deeper bathyal species and specimens vary strongly in preservation this assemblage was probably formed by reworking and down slope transport triggered by the k p impact across the spherule bed i e the k p boundary only f7 of benthic foraminiferal species became extinct similar to the low extinction rates of benthic foraminifera worldwide quantitative analysis of benthic foraminiferal assemblages and morphogroups in the 63 am size fraction indicates a relatively eutrophic stable environment during the latest maastrichtian interrupted by a sudden decrease in the food supply to the benthos at the k p boundary and a decrease in diversity of the faunas followed by a stepped recovery during the earliest danian the recovery was probably linked to the gradual recovery of surface dwelling primary producers d 2004 elsevier b v all rights reserved

lipid biomarkers in lacustrine sediments of subtropical northeastern mexico and inferred ecosystem changes during the late pleistocene and holocene abstract evolution of ecosystems in the northeastern mexico since the last glacial maximum lgm and through the holocene are yet to be fully characterised creating a gap in our understanding of the ecological response to climate change in this water scarce region here we explore the response of lacustrine and surrounding terrestrial habitats of this region to hydrological changes of the late pleistocene and especially the holocene biomarker based proxy data from the el potosi basin indicates dynamic and variable input of organic matter om into the basin with sources being the surrounding vegetation bacterial biomass and aquatic microfauna changes in these inputs reveal distinct stages of ecosystem development over the last 20 000 years overall low lipid abundances as a proportion of toc from 20 to 19 cal kyr bp mainly from aquatic in situ microbial biomass and degraded terrestrial om are attributed to relatively low runoff increasing lipid proportions during the deglaciation from 19 to 15 cal kyr bp were mostly derived from terrestrial sources like woodland vegetation soil and wetland vegetation and we attribute them to more rainfall and runoff subsequently the wetland biomarkers disappeared and woodland input began to dominate the om assemblage from 15 to 11 7 cal kyr bp during the early and mid holocene after about 11 7 cal kyr bp putative woodland and grass inputs decreased and the dominant vegetation appeared to shift to subtropical desert shrub which could have been due to increasing regional aridity the onset of the dry late holocene was characterised by gradual environmental transition and ecosystem adaption especially from 4 2 to 2 8 cal kyr bp the terrestrial vegetation comprised increasing proportions of c4 grasses documented by changes in leaf wax carbon isotopic compositions and potentially more open vegetation while the in lake bacterial production increased with increasing desertification from 2 8 cal kyr bp the terrestrial productivity decreased substantially the lake became shallower ephemeral and the surrounding soils became more alkaline changes of the limnic habitat from algal towards microbial communities occurred 300 years after the onset of terrestrial habitat changes during the last millennium the c3 components of the vegetation again dominated this implies an enhanced moisture supply possibly from agricultural activities overall this work reveals the marked sensitivity of northeastern mexico ecosystems to the climatic shifts that occurred since the lgm and this perhaps indicates their vulnerability to future global warming

benthic foraminiferal faunal turnover across the cretaceous tertiary boundary at agost southeastern spain paleoenvironmental inferences we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where v5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them 2003 elsevier science b v all rights reserved

effects of pleistocene environmental changes on the distribution and community structure of the mammalian fauna of mexico article i nfo biological communities in mexico experienced profound changes in species composition and structure as a consequence of the environmental fluctuations during the pleistocene based on the recent and fossil mexican mammal checklists we determine the distribution composition diversity and community structure of late pleistocene mammalian faunas and analyze extinction patterns and response of individual species to environmental changes we conclude that 1 differential extinctions occurred at family genus and species level with a major impact on species heavier than 100 kg including the extinction all proboscideans and several ruminants 2 pleistocene mammal communities in mexico were more diverse than recent ones and 3 the current assemblages of species are relatively young furthermore pleistocene relicts support the presence of biogeographic corridors important refugia existed as well as centers of speciation in isolated regions we identified seven corridors eastern usa sierra madre oriental corridor rocky mountains sierra madre occidental corridor central united states northern mexico corridor transvolcanic belt sierra madre del sur corridor western usa baja california corridor tamaulipas central america gulf lowlands corridor and sonora central america pacific lowlands corridor our study suggests that present mammalian assemblages are very different than the ones in the late pleistocene

late pleistocene paleohydrology near the boundary of the sonoran and chihuahuan deserts southeastern arizona usa abstract ground water discharge gwd deposits form in arid environments as water tables rise and approach or breach the ground surface during periods of enhanced effective precipitation where preserved these deposits contain information on the timing and elevation of past ground water fluctuations here we report on the investigation of a series of gwd deposits that are exposed in discontinuous outcrops along a 150 km stretch of the san pedro valley in southeastern arizona near the boundary of the sonoran and chihuahuan deserts chronologic isotopic geochemical faunal assemblage ostracodes and gastropods and sedimentological evidence collectively suggest that the elevation of the regional water table in the valley rose in response to a change in climate 50 ka ago and remained relatively high for the next 35 ka before falling during the bolling allerod warm period rebounding briefly during the younger dryas cold event and falling again at the onset of the holocene the timing of these hydrologic changes coincides closely with variations in 18o values of calcite from a nearby speleothem to the west and changes in lake levels at pluvial lake cochise to the east thus in southeastern arizona the assumption that changes in climate are reflected in all aspects of the hydrologic cycle of a region simultaneously is validated the timing of these changes also broadly coincides with variations in the gisp2 18o record which supports the hypothesis that atmospheric teleconnections existed between the north atlantic and the deserts of the american southwest during the late pleistocene

late quaternary lacustrine paleoenvironments in the cuenca de mexico abstract a late quaternary paleolimnological history from the mexican highlands has been obtained by diatom analysis of short cores and stratigraphic sections of lake and marsh sediments from the cuenca de mexico the large endorheic graben basin that holds mexico city the records dated by radiocarbon and tephrochronologic methods extend back to about 30 ka bp and document the presence of extensive saline lakes in the basin until 25 ka bp thereafter lake levels fell and marginal sites became shallow and fresh under the influence of surficial drainage and especially spring discharge a shallow saline lake existed 18 ka bp in texcoco the central and lowest basin in the system reflecting moderately increased effective moisture at that time by 16 ka bp lake texcoco had become so shallow that diatoms were no longer preserved however marginal sites nourished by spring flow recorded changes in the local hydrologic balance resulting from increased infiltration at higher elevations these changes appear to coincide with glacial advances between about 14 and 10 ka bp on the volcanic mountains surrounding the basin dry climates with reduced infiltration characterized the early holocene but by 5 ka bp a modest increase in precipitation established the modern climatic regime these lacustrine records offer important insights for evaluating the paleoenvironmental history of the cuenca de mexico based on other evidence they confirm glaciological stratigraphic and palynologic data that suggest dry climates and the absence of large pluvial lakes in the cuenca de mexico during and after the full glacial but document climates of significantly increased precipitation at least 10 ka prior to 18 ka bp

implications of reduced turbidity current and landslide activity for the initial eocene thermal maximum evidence from two distal deep water sites previous studies propose that submarine landslides and turbidity currents may become more likely due to future rapid global warming determining whether global warming increases likelihood assists in assessment of landslide triggered tsunami hazards and risk to seafloor structures other studies propose that landslides helped to trigger past rapid climate change due to sudden release of gas hydrates two deep water turbidite records show prolonged hiatuses in turbidity current activity during the initial eocene thermal maximum ietm at 55 ma the ietm represents a possible proxy for future anthropogenically induced climate change it is likely that our records mainly represent large and fast moving disintegrative submarine landslides statistical analysis of long term 2 3 myr records shows that turbidity current frequency significantly decreased after the ietm our results indicate that rapid climate change does not necessarily cause increased turbidity current activity and do not provide evidence for landslides as a primary trigger for the ietm

antarctic climate southern ocean circulation patterns and deep water formation during the eocene we assess early to middle eocene seawater neodymium nd isotope records from seven southern ocean deep sea drill sites to evaluate the role of southern ocean circulation in long term cenozoic climate change our study sites are strategically located on either side of the tasman gateway and are positioned at a range of shallow 500 m to intermediate deep 1000 2500 m paleowater depths unradiogenic seawater nd isotopic compositions reconstructed from fish teeth at intermediate deep indian ocean pelagic sites ocean drilling program odp sites 738 and 757 and deep sea drilling project dsdp site 264 indicate a dominant southern ocean sourced contribution to regional deep waters end t 9 3 1 5 iodp site u1356 off the coast of adelie land a locus of modern day antarctic bottom water production is identified as a site of persistent deep water formation from the early eocene to the oligocene east of the tasman gateway an additional local source of intermediate deep water formation is inferred at odp site 277 in the sw pacific ocean end t 8 7 1 5 antarctic proximal shelf sites odp site 1171 and site u1356 reveal a pronounced erosional event between 49 and 48 ma manifested by 2 end unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites this erosional event coincides with the termination of peak global warmth following the early eocene climatic optimum and is associated with documented cooling across the study region and increased export of antarctic deep waters highlighting the complexity and importance of southern ocean circulation in the greenhouse climate of the eocene

holocene aged human footprints from the cuatrocienegas basin ne mexico two sets of well preserved human footprints have been found in tufa sediments in the cuatrocienegas basin ne mexico and here we present their u series dates of 10 55 0 03 ka and 7 24 0 13 ka the former are the oldest known footprints in mexico although their exact location is unknown the latter form part of a trackway with eleven in situ human footprints oxygen and to a lesser extent carbon isotope data from the sediments suggest that the tufa with in situ footprints formed during a transition to a wetter less arid period while pollen evidence indicates the basin floor presence of pecan carya and willow salix sp before the onset of regional chihuahuan desert aridity these footprints confirm the presence of humans possibly nomadic hunter gatherer groups which persisted until the 18th century ad

tepexpan palaeoindian site basin of mexico multi proxy evidence for environmental change during the late pleistocene late holocene the tepexpan palaeoindian skeleton was discovered in 1947 close to the former lake texcoco margin in the basin of mexico the find has been the object of considerable interest and discussion over the last 60 years regarding its real age and archaeological interpretation here we report new ams radiocarbon dates associated with the sedimentary succession at tepexpan with ages between 19 110 90 and 612 22 14c years bp and a new uranium series date for the skeleton with an age of 4700 200 years bp that indicates a mid holocene age the sedimentary succession was studied in detail using stable isotopes diatoms organic geochemistry and tephrochronology the multi proxy evidence suggests large changes around the margins of lake texcoco in terms of the balance between aquatic and terrestrial plants c3 and c4 plants saline alkaline and freshwater conditions volcanic activity marginal reworking of lake sediments and input from the drainage basin through the late pleistocene late holocene these changes had large impacts on the prehistoric human populations living by the lake shores since the late pleistocene in the basin of mexico

changes in jokulhlaup sizes in grimsvotn vatnajokull iceland 1934 91 deduced from in situ measurements of subglacial lake volume a record of volumes of jokulhlaups from the subglacial grimsvotn lake vatnajokull iceland has been derived for the period 1934 91 the change in lake volume during jokulhlaups is estimated from the lake area ice cover thickness and the drop in lake level the jokulhlaup volumes have decreased gradually during this period of low volcanic activity and declining geothermal power the two jokulhlaups in the 1930s each discharged about 4 5 km peak discharge 25 30 10 3 m 3 s 1 in the 1980s jokulhlaup volumes were 0 6 1 2 km 3 peak discharge 2 10 3 m 3 s 1 the lake level required to trigger a jokulhlaup has risen as an ice dam east of the lake has thickened water flow in a jokulhlaup ceases when the base of a floating ice shelf covering grimsvotn settles to about 1160 m a s l apparently the jokulhlaups are cut off when the base of the ice shelf collapses on to a subglacial ridge bordering the lake on its eastern side the decline in melting rates has resulted in a positive mass balance of the 160 170 km grimsvotn ice drainage basin comparison of maps shows that the average positive mass balance rate was 0 12 km 3 a 1 25 of the total accumulation in the period 1946 87 a gradually increasing positive mass balance has prevailed since 1954 reaching 0 23 km 3 a 1 in 1976 86 48 of total accumulation

vegetation history along the eastern desert escarpment of the sierra san pedro martir baja california mexico abstract plant macrofossils from 38 packrat middens spanning the last 33 000 cal yr bp record vegetation between 650 and 900 m elevation along the eastern escarpment of the sierra san pedro martir northern baja california the middens span most of the holocene with a gap between 4600 and 1800 cal yr bp but coverage in the pleistocene is uneven with a larger hiatus between 23 100 and 14 400 cal yr bp the midden flora is relatively stable from the pleistocene to holocene exceptions include pinus californiarum juniperus californica and other chaparral elements that were most abundant 23 100 cal yr bp and declined after 14 400 cal yr bp despite being near the chaparral woodland desertscrub ecotone during glacial times the midden assemblages reflect none of the climatic reversals evident in the glacial or marine record and this is corroborated by a nearby semi continuous pollen stratigraphy from lake sediments regular appearance of c4 grasses and summer flowering annuals since 13 600 cal yr bp indicates occurrence of summer rainfall equivalent to modern jas average of 80 90 mm this casts doubt on the claim based on temperature proxies from marine sediments in the guaymas basin that monsoonal development in the northern gulf and arizona was delayed until after 6200 cal yr bp

biogeographic implications of a packrat midden sequence from the sacramento mountains south central new mexico abstract thirteen packrat neotoma spp and two porcupine erethizon dorsatum middens from 1555 to 1690 m elevation from the sacramento mountains new mexico provide an 18 000 yr vegetation record in the northern chiuahuan desert the vegetation sequence is a mesic wisconsin fullglacial 18 000 16 000 yr b p pinyon juniper oak woodland a xeric early holocene ca 11 000 8000 yr b p juniper oak woodland a middle holocene ca 8000 4000 yr b p desert grassland and a late holocene ca 4000 yr b p to present chihuahuan desertscrub the frequency of spring freezes and summer droughts in the late wisconsin probably set the northern limits of pinus edulis and juniperus monosperma at about 34 n or 6 south of today s limit rising summer tempratures in the early holocene eliminated pinyon and other mesic woodland plants from the desert lowlands and allowed the woodland to move upslope at this time pinyon juniper woodland and pine forest dominated by pinus ponderosa probably began their spectacular holocene expansions to the north continued warming in the middle holocene led to very warm summers with strong monsoons relatively dry cold winters and widespread desert grasslands desertscrub communities in the northern chihuahuan desert did not develop until the late holocene when the biseasonal rainfall shifted slightly back toward the winter catastrophic winter freezes decreased and droughts in all seasons increased the creosote bush desertscrub corridor across the continental divide between the chihuahuan and sonoran deserts was probably connected for the first time since the last interglaciation

stratigraphic evolution of blake outer ridge multichannel seismic data from a reconnaissance survey of the blake outer ridge reveal the seismic stratigraphy down to oceanic basement as well as intracrustal and mantle reflections the depositional history of the outer ridge can now be subdivided into four principal phases based on seismic stratigraphic style 1 jurassic early cretaceous sedimentation which filled in basement irregularities and leveled the sea floor by horizon s barremian time 2 early cretaceous late cretaceous deposition of a seaward thinning wedge typical of atlantic type margins its deeply eroded surface is probably equivalent to the late cretaceous miocene hiatus reflected by horizon au 3 earliest miocene current controlled deposits preferentially deposited along the xis of the incipient blake outer ridge these prograding strata which thin and dip downridge and laterally away from the ridge axis are attributed to the interaction of the florida current and western boundary undercurrent and 4 continuing early miocene preferential deposition on the ridge axis and sculpting by the western boundary undercurrent this phase is characterized by strata thinning and dipping upridge and toward the ridge axis the reversal of dip is explained to a first approximation by a steady state contour current model in which the current position is progressively shifted by the deposition five angular unconformities and associated bathymetric terraces west of the ridge crest are mapped using all lamont doherty seismic data and interpreted as having formed peneconte poraneously during phase four the areal extent of the gas hydrate clathrate horizon is also delineated it is continuous across the northern blake outer ridge and the multichannel seismic data presented here show it to extend onto the shallow blake plateau as well

biostratigraphic implications of mid latitude palaeocene eocene radiolarian faunas from hole 1051a odp leg 171b blake nose western north atlantic

late pleistocene woodlands in the bolson de mapimi a refugium for the chihuahuan desert biota abstract packrat middens radiocarbon dated at 12 280 345 and 12 700 165 yr b p record expansions of junipers and papershell pinyon pinus remota into the desert lowlands of durango and coahuila mexico 26 n extralocal trees and shrubs presently occur 24 580 km in nearly all directions including more subtropical areas to the northeast and southeast an equable late wisconsin climate marked by mild winters with increased precipitation and by cool summers with reduced summer monsoons is proposed the extensive playas of the bolson de mapimi probably held water at that time the bolson de mapimi was not a geographical refugium unaffected by glacial climates although many chihuahuan desert plants and animals probably remain in situ as members of equable woodlands equable climates low extinction rates and repeated rapid glacial interglacial climatic fluctuations may have been important in the evolution and accumulation of species at lower latitudes

paleoceanographic and paleoclimatic constraints on the global eocene diatom and silicoflagellate record abstract eocene diatom and silicoflagellate biostratigraphy are summarized and correlated with the most recent geologic time scale as well as with the global oxygen isotope and eustatic sea level curves the global distribution of eocene diatom silicoflagellate bearing sediments varies considerably reflecting changing oceanic gateways and paleoceanography with changing patterns that are punctuated by four major depositional events event 1 49 million years ago ma at the end of the early eocene climatic optimum eeco saw the cessation of diatom silicoflagellate deposition in epicontinental regions of the north sea region and in the northern russia and the onset of biosilica deposition in the arctic event 2 46 ma which coincided with intensification of the middle eocene cooling trend marked the widespread expansion of diatom silicoflagellate deposition in both the north and south atlantic a shift of diatom silicoflagellate deposition from the atlantic to the pacific began at event 3 at the end of the middle eocene climatic optimum meco 40 ma that was likely tied to the initial opening of the drake passage between antarctica and south america event 4 39 ma coincided with a major sea level fall and a widespread deep sea hiatus in the latest middle eocene late eocene diatom silicoflagellate deposition became more concentrated in middle to high latitude regions and coastal upwelling regions particularly in the pacific ocean tabulation of the first and last occurrences of 132 biostratigraphically important diatoms suggests increased species turnover during the latest paleocene to earliest eocene that may be in part due to a monographic effect an increasing rate of evolution of new diatom species between 46 and 43 ma and after 40 ma coincides respectively with the widespread expansion of diatom deposition in the atlantic and with an increased pole to equator thermal gradient that witnessed the expansion of diatoms in high latitude oceans and coastal upwelling settings

the source and fate of massive carbon input during the latest paleocene thermal maximum lithologic faunal seismic and isotopic evidence from the blake nose subtropical western north atlantic links a massive release of biogenic methane 55 5 million years ago to a warming of deep ocean and high latitude surface waters a large perturbation in the combined ocean atmosphere carbon cycle the largest of the past 90 million years a mass extinction event in benthic faunas and a radiation of mammalian orders the deposition of a mud clast interval and seismic evidence for slope disturbance are associated with intermediate water warming massive carbon input to the global exogenic carbon cycle pelagic carbonate dissolution a decrease in dissolved oxygen and a benthic foraminiferal extinction event these events provide evidence to confirm the gas hydrate dissociation hypothesis and identify the blake nose as a site of methane release

onset of north atlantic deep water production coincident with inception of the cenozoic global cooling trend here we show that the onset of deep water overflow from the norwegian greenland sea into the north atlantic interpreted to represent the onset of a modern style north atlantic deep water mass commenced close to the early to middle eocene boundary this finding is based on the identification of a large elongate contourite sediment drift the judd falls drift in the faeroe shetland basin through detailed mapping of high resolution two dimensional and three dimensional seismic data this sediment drift covers an area of 9000 km2 in one of the critical present day deep water gateways into the north atlantic ocean interpretation of the body as a contourite drift is based on standard seismic stratigraphic diagnostic criteria including tridirectional onlap lensoid sediment geometry upslope progradational configurations of stacked onlap units and an erosional base cut in a deepwater setting the internal reflection configuration indicates that the drift was deposited under a southwest flowing current regime which we propose represents the onset of north atlantic deep water production with continual deep water flow until at least the latest eocene ca 35 million years ago ma onset of drift deposition is dated by several key boreholes as occurring at ca 50 49 ma across the early to middle eocene boundary and is coincident with independent geochemical evidence for major changes in the configuration of deep sea circulation patterns global biological production and the onset of cenozoic climatic cooling these temporal concurrences suggest a strong link between the initiation of north atlantic deep water production and cenozoic global climate evolution

impact induced mass wasting at the k t boundary blake nose western north atlantic seismic reflection data combined with results from ocean drilling document regional scale slumping associated with the cretaceous tertiary k t impact event the k t boundary is biostratigraphically complete at three ocean drilling program sites 1049 1050 and 1052 located on blake nose 30 n 75 w off eastern florida in water depths of 1300 2600 m maastrichtian chalk is folded and fractured below the k t boundary at all three sites whereas lowermost paleocene clays and chalks are undeformed deformation is pervasive in maastrichtian at the deepest water site site 1049 whereas at the shallower water sites sites 1050 and 1052 thick intervals of structurally intact maastrichtian chalk are separated by thinner intervals of highly deformed sediments correlation of core to seismic reflection data indicates that the k t boundary immediately overlies seismic facies characteristic of mass wasting that extend across most of the 55 km distance of the depth transect maastrichtian sediments appear to have moved as large slump blocks on the upper part of blake nose but deformed more uniformly in the deeper water parts of the transect we suggest that mass wasting occurred on the blake nose 1600 km from the chicxulub crater in response to the cataclysmic seismicity generated by the impact

testing the cenozoic multisite composite δ18o and δ13c curves new monospecific eocene records from a single locality demerara rise ocean drilling program leg 207 until recently very few high quality deep ocean sedimentary sections of eocene age have been available consequently our understanding of eocene paleoceanography has become heavily reliant on composite records patched together from multiple sites in different ocean basins and generated using multiple taxa potential sources of local noise in the global signal here we test the reliability of the early to middle eocene composite 18o and 13c stratigraphies zachos et al 2001 by generating new monospecific records in benthic foraminiferal calcite from a single locality demerara rise in the tropical western atlantic ocean drilling program leg 207 we present new stable isotope correction factors for commonly used eocene benthic foraminiferal species we find that interspecies isotopic offsets are constant across the isotopic range supporting the notion that the inconstant intertaxa offsets reported elsewhere result from mixing species within genera in general the 18o stratigraphy from demerara rise supports the validity of the eocene 18o composite while revealing a temporary warming punctuating middle eocene cooling this warming may correspond to the so called middle eocene climatic optimum previously documented in the southern ocean the composite and demerara rise records for 13c differ substantially by removing the intersite and intertaxa sources of uncertainty in 13c we obtain a clearer picture of carbon cycling during the eocene secular change in interocean 13c gradients through the eocene reveals that intervals of climatic warmth especially the early eocene are associated with very small water mass ageing gradients

a silicon depleted north atlantic since the palaeogene evidence from sponge and radiolarian silicon isotopes despite being one of earth s major geochemical cycles the evolution of the silicon cycle has received little attention and changes in oceanic dissolved silica dsi concentration through geologic time remain poorly constrained silicon isotope ratios expressed as 30si in marine microfossils are becoming increasingly recognised for their ability to provide insight into silicon cycling in particular the 30si of siliceous sponge spicules has been demonstrated to be a useful proxy for past dsi concentrations we analysed 30si in radiolarian tests and sponge spicules from the blake nose palaeoceanographic transect odp leg 171b spanning the palaeocene eocene ca 60 30 ma our 30si results range from 0 32 to 1 67 and 0 48 to 0 63 for the radiolarian and sponge records respectively using an established relationship between ambient dissolved si dsi concentrations and the magnitude of silicon isotope fractionation in siliceous sponges we demonstrate that the western north atlantic was dsi deplete during the palaeocene eocene throughout the water column a conclusion that is robust to a range of assumptions and uncertainties these data can constitute constraints on reconstructions of past ocean circulation previous work has suggested ocean dsi concentrations were higher than modern ocean concentrations prior to the cenozoic and has posited a drawdown during the early palaeogene due to the evolutionary expansion of diatoms our results challenge such an interpretation we suggest here that if such a global decrease in oceanic dsi concentrations occurred it must predate 60 ma

rethinking the chronology of early paleogene sediments in the western north atlantic using diatom biostratigraphy abstract ocean drilling program odp site 1051 blake nose western north atlantic is of crucial importance for reconstructing diatom evolution and biosiliceous sedimentation patterns through the early cenozoic period of extreme greenhouse warmth followed by the progressive global cooling the magnetostratigraphy in hole 1051a however has been subject to divergent interpretations resulting in multi million year age control uncertainties especially for events surrounding the early to middle eocene transition to resolve these uncertainties we compare the stratigraphy of hole 1051a to the neighboring holes 1050a c we compile the published biomagnetostratigraphic data for both sites and identify three possible magnetostratigraphic solutions for hole 1051a the difference being the number of hiati and their duration in order to identify the most plausible magnetostratigraphic solution for hole 1051a we employ the graphic correlation method in which we compare the depth of individual magnetic reversals in both study sites against an independent proxy i e 49 diatom evolutionary events identified in holes 1050a c and 1051a the distribution of diatom bioevents lends strong support to the presence of two major hiati in both study sites the upper hiatus juxtaposes magnetozone c21n on c22n and the lower hiatus juxtaposes magnetozone c23n on c24n eliminating the record of the initial part of the early eocene climatic optimum diatom calcareous nannofossil and foraminiferal biostratigraphic markers also indicate that hole 1051a terminated within magnetozone c28n rather than c27n this age interpretation is strongly supported by the alignment of high resolution weight percent biogenic sio2 records from both study sites the revised age models developed here for holes 1050a c and 1051a have profound consequences for interpretations of western north atlantic paleoceanographic and paleoclimatic history through the early paleogene we propose a revised labelling of the early eocene carbon cycle perturbations identified to date in hole 1051a and show how published blake nose 30si records change when data from sites 1050 and 1051 are rescaled to the age models proposed herein we emphasize that these refinements to the stratigraphy of sites 1050 and 1051 are based on a study of diatom bioevents which are here identified and calibrated to the geomagnetic polarity timescale this successful application of diatom biostratigraphy is a substantial advance toward their future utility in providing high resolution age control for paleogene deep sea sites

widespread formation of cherts during the early eocene climate optimum radiolarian cherts in the tethyan realm of jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates however the widespread occurrence of cherts in the eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones in a new survey of the global spatio temporal distribution of cenozoic cherts in deep sea drilling project dsdp and ocean drilling program odp sediment cores we found that cherts occur most frequently in the paleocene and early eocene with a peak in occurrences at 50 ma that is coincident with the time of highest bottom water temperatures of the early eocene climatic optimum eeco when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity cherts occur less commonly during the subsequent eocene global cooling trend primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation this timing of peak eocene chert occurrence which is supported by detailed stratigraphic correlations contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and or volcanism in a supposedly sluggish ocean of the eeco followed during the subsequent middle eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification with the formation of chert as a result of biosilica transformation during diagenesis instead we suggest that basin basin fractionation by deep sea circulation could have raised the concentration of eeco dissolved silica especially in the north atlantic where an alternative mode of silica burial involving widespread direct precipitation and or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling deficient conditions of the eeco cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones 2007 elsevier b v all rights reserved

synchroneity of the k t oceanic mass extinction and meteorite impact blake nose western north atlantic a 10 cm thick layer of green spherules occurs precisely at the biostratigraphic boundary between the cretaceous and paleogene k t boundary at ocean drilling program site 1049 lat 30 08 n long 76 06 w the spherulitic layer contains abundant rock fragments chalk limestone dolomite chert mica books and schist as well as shocked quartz abundant large cretaceous planktic foraminifera and rounded clasts of clay as long as 4 mm interpreted as altered tektite glass probably derived from the chicxulub impact structure most of the cretaceous foraminifera present above the spherule layer are not survivors since small specimens are conspicuously rare compared to large individuals instead the cretaceous taxa in paleocene sediments are thought to be reworked the first paleocene planktic foraminifera and calcareous nannofossil species are recorded immediately above the spherule bed the upper part of which contains an iridium anomaly hence deposition of the impact ejecta exactly coincided with the biostratigraphic k t boundary and demonstrates that the impact event was synchronous with the evolutionary turnover in the oceans these results are consistent with a reanalysis of the biostratigraphy of the k t boundary stratotype which argues that shallow marine k t boundary sections are not biostratigraphically more complete than deep sea k t boundary sites

foraminiferal biostratigraphy and paleoenvironmental reconstruction at the yaxcopoil 1 drill hole chicxulub crater yucatan peninsula the yaxcopoil 1 yax 1 drill hole comprises cretaceous limestones and calcarenites the k p boundary cocktail unit including impact breccia and a danian marly clay layer overlain by calcareous marls the biostratigraphy paleobathymetry and environmental turnover across the k p interval were inferred after analyzing the planktic and benthic foraminiferal assemblages the cretaceous samples only contain a few poorly preserved planktic foraminifera of a middle campanian to maastrichtian age while low diversity benthic foraminiferal assemblages suggest a sufficient nutrient supply to the sea floor and a shallow neritic occasionally stressed environment the impact breccia and the redeposited suevite are overlain by a 46 cm thick dolomitic calcareous sandstone unit that contains scarce reworked planktic foraminiferal specimens this unit probably represents the uppermost part of the initial infill of the crater the uppermost centimeters of this unit are bioturbated and its top represents a hiatus that spans at least the g cretacea pv eugubina and part of the p pseudobulloides biozones this unit is overlain by a 3 4 cm thick marly clay layer that represents a condensed layer benthic foraminiferal assemblages suggest a low food supply to the sea floor and environmental instability during the deposition of the marly clay layer the increase in diversity of the assemblages indicates that the environmental conditions improved and stabilized from the g compressa biozone toward the a uncinata p2 biozone the danian planktic and benthic foraminiferal assemblages indicate a deeper probably bathyal environment