a tsunami deposit at the cretaceous tertiary boundary in texas at sites near the brazos river texas an iridium anomaly and the paleontologic cretaceous tertiary boundary directly overlie a sandstone bed in which coarse grained sandstone with large clasts of mudstone and reworked carbonate nodules grades upward to wave ripple laminated very fine grained sandstone this bed is the only sandstone bed in a sequence of uppermost cretaceous to lowermost paleocene mudstone that records about 1 million years of quiet water deposition in midshelf to outer shelf depths conditions for depositing such a sandstone layer at these depths are most consistent with the occurrence of a tsunami about 50 to 100 meters high the most likely source for such a tsunami at the cretaceous tertiary boundary is a bolidewater impact

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

multiple impacts across the cretaceous tertiary boundary abstract the stratigraphy and age of altered impact glass microtektites microkrystites ejecta layers from the chicxulub crater are documented in late maastrichtian and early danian sediments in mexico guatemala belize and haiti in northeastern mexico two to four ejecta layers are present in zone cf1 which spans the last 300 ky of the maastrichtian the oldest ejecta layer is dated at 65 27 0 03 ma based on sediment accumulation rates and extrapolated magnetostratigraphy all younger ejecta layers from the maastrichtian and early danian parvularugoglobigerina eugubina zone pla l may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity the k t boundary impact event 65 0 ma is not well represented in this area due to widespread erosion an early danian pla l ir anomaly is present in five localities bochil actela coxquihui trinitaria and haiti and is tentatively identified as a third impact event at about 64 9 ma a multiimpact scenario is most consistent with the impact ejecta evidence the first impact is associated with major deccan volcanism and likely contributed to the rapid global warming of 3 4 c in intermediate waters between 65 4 and 65 2 ma decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations the k t boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species the early danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity

proximal cretaceous tertiary boundary impact deposits in the caribbean trace element isotopic and mineralogic studies indicate that the proposed impact at the cretaceous tertiary k t boundary occurred in an ocean basin although a minor component of continental material is required the size and abundance of shocked minerals and the restricted geographic occurrence of the ejecta layer and impact wave deposits suggest an impact between the americas coarse boundary sediments at sites 151 and 153 in the colombian basin and 5 to 450 meter thick boundary sediments in cuba may be deposits of a giant wave produced by a nearby oceanic impact on the southern peninsula of haiti a approximately 50 centimeter thick ejecta layer occurs at the k t boundary this ejecta layer is approximately 25 times as thick as that at any known k t site and suggests an impact site within approximately 1000 kilometers seismic reflection profiles suggest that a buried approximately 300 km diameter candidate structure occurs in the colombian basin

in situ velocities in pelagic carbonates new insights from ocean drilling program leg 130 ontong java plateau ocean drilling program leg 130 returned an extensive suite of in situ borehole logging and closely spaced shipboard physical properties measurements from four sites drilled in carbonate rich pelagic oozes and chalks on the ontong java plateau using these data we evaluated factors responsible for observed differences between laboratory data and in situ values laboratory and log differences for bulk density porosity are small and nearly constant and can be accounted for by hydraulic rebound of pore fluid following sediment recovery evidence for mechanical rebound of sediments was not observed velocity porosity relationships cannot be used to indirectly correct laboratory velocities to in situ because fundamental assumptions required for rebound corrections are not satisfied velocity porosity systematics are also complicated by foraminiferal intraparticle porosity variations we derived empirical laboratory velocity corrections using log and laboratory velocity differences expressed as functions of depth and effective pressure we tested the velocity corrections using data for carbonates recovered from ocean drilling program sites 704 722 and 762 comparisons with logs show that corrected velocities accurately estimate in situ values for oozes and chalks caco3 60 for applications to unlogged deep sea drilling project leg 85 sites igneous basement travel times calculated using corrected velocities agree with acoustic basement travel times from seismic records implying that corrected velocities are realistic in situ estimates at site 574 we used our corrected velocities to reevaluate previous lithostratigraphic and seismostratigraphic correlations based on mechanical rebound corrected velocities the new velocities correlate reflectors to progressively greater core depths although changes are minor above 200 m below seafloor the lowest assigned reflector is shifted 36 m deeper to more closely coincide with a diagenetic boundary and acoustic basement correlates with igneous basement instead of with postulated high impedance reflectors within the sediments

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

age chemo and biostratigraphy of haiti spherule rich deposits a multi event k t scenario examination of two new expanded k t transitions and reexamination of road outcrops near beloc haiti reveals that deposition of the glass spherule rich deposit srd occurred within the early danian parvularugoglobigerina eugubina pla 1 zone followed by an ir anomaly and 50 cm above it a second pd dominated platinum group element pge anomaly the k t boundary is at an erosional unconformity between the base of the srd and underlying maastrichtian limestone where an interval representing about 100 250 thousand years appears to be missing juxtaposition of planktic foraminiferal zones pla 1 and plummerita hantkeninoides cf1 it is possible that the spherule layers are reworked from original deposits at or below the k t boundary the ir anomaly is of roughly chondritic type and compatible with an impact event whereas the pd dominated pge anomaly is a more basalt type and compatible with a magmatic origin this suggests a multi event scenario consistent with one impact followed by a major vol

late cretaceous sea level changes in tunisia a multi disciplinary approach a multi disciplinary study of sea level and climate proxies including bulk rock and clay mineral compositions carbon isotopes total organic carbon toc sr ca ratios and macro and microfaunal associations reveals seven major sea level regressions in the southwestern tethys during the last 10 million years of the cretaceous late campanian c 74 2 ma 73 4 72 5 ma and 72 2 71 7 ma early maastrichtian 70 7 70 3 ma 69 6 69 3 ma and 68 9 68 3 ma and late maastrichtian 65 45 65 3 ma low sea levels are generally associated with increased terrigenous influx low kaolinite chlorite mica ratios high toc and high sr ca ratios whereas high sea levels are generally associated with the reverse conditions these sea level changes may be interpreted as eustatic as suggested by the global recognition of at least four of the seven major regressions identified 74 2 ma 70 7 70 3 ma 68 9 68 3 ma and 65 45 65 3 ma climatic changes inferred from clay mineral contents correlate with sea level changes warm or humid climates accompany high sea levels and cooler or arid climates generally accompany low sea levels

tektites in cretaceous tertiary boundary rocks on haiti and their bearing on the alvarez impact extinction hypothesis relic tektites are associated with a pt group metal abundance anomaly and shocked minerals in a thin marl bed that marks the k t boundary on haiti the presence of these three impact produced materials at the precise k t boundary enormously strengthens the alvarez impact extinction hypothesis the tektites occur in smectite spherules that have external shapes typical of tektites their chemical and physical properties are broadly similar to those of other tektite groups except that the haitian tektites have lower si and higher fe ca and na on average they contain more sc v cu zn ga sr sn and ba and less cr ni co b mn and hf than other tektite groups amounts of rare earth elements ree in the tektites indicate that their progenitor materials were not melted mafic or ultramafic oceanic crust rather they were sedimentary deposits having a bulk composition of andesite rare tektites contain unusually high amounts of cao 20 and s 0 4 and these data suggest that some target materials consisted of caso4 anhydrite beds occur in the subsurface at two candidate impact sites chicxulub and manson sm nd isotopic data for the tektites indicate that the melted precursor sediments were most likely deposited less than 400 m y between the late cretaceous and silurian periods major chemical changes accompanied the diagenetic change of glass to smectite the haitian tektites are the first datable impact products in k t boundary rocks and 40ar 39ar ages of the glass show that the k t boundary and impact event are coeval at 64 5 0 1 ma

observations on attenuation and shear wave velocity in fine grained marine sediments compressional p wave attenuation shear s wave attenuation and shear s wave velocity measurements compiled for fine grained unconsolidated sediments show trends that do not support empirical relationships hamilton j acoust soc am 68 1313 1340 1980 in acoustics and ocean bottom f a s e specialize conf madrid 1987 commonly used for geoacoustic modeling the exception is compressional wave attenuation data from 10 hz to 500 khz that essentially follow a frequency dependence of f1 2 standard deviations p wave attenuation with depth is difficult if not impossible to predict given the variability in the data examination of several attenuation depth profiles indicates that those of mitchell and focke j acoust soc am 67 1582 1589 1980 may be the best choice for predicting p wave attenuation with depth at the present time the assumption that s wave and p wave attenuations are proportional hamilton j acoust soc am 60 334 338 1976c in acoustics and ocean bottom

equatorial pacific seismic reflectors as indicators of global oceanographic events the origin of a series of regionally correlatable seismic horizons in the neogene sediments of the central equatorial pacific is examined through seismic modeling and the detailed analyses of stratigraphic and physical property relationships in deep sea drilling project cores these regionally traceable reflectors are synchronous the younger reflectors are the direct result of carbonate dissolution events the older ones of stratigraphically selective diagenetic processes the changes in ocean chemistry associated with these events appear to be linked to global reorganizations of surface and bottom water circulation patterns the most dramatic of which are associated with reorganizations of north atlantic bottom waters these deepwater seismic horizons appear to correlate with the major events on the relative sea level curve of vail et al for the neogene

yaxcopoil 1 and the chicxulub impact csdp core yaxcopoil 1 was drilled to a depth of 1 511 m within the chicxulub crater an organic rich marly limestone near the base of the hole 1 495 to 1 452 m was deposited in an open marine shelf environment during the latest cenomanian uppermost rotalipora cushmani zone the overlying sequence of limestones dolomites and anhydrites 1 495 to 894 m indicates deposition in various carbonate platform environments e g sabkhas lagoons a 100 m thick suevite breccia 894 794 m identifies the chicxulub impact event above the suevite breccia is a dolomitic limestone with planktic foraminiferal assemblages indicative of plummerita hantkeninoides zone cf1 which spans the last 300 ky of the maastrichtian an erosional surface 50 cm above the breccia dolomite contact marks the k t boundary and a hiatus limestones above this contact contain the first tertiary planktic foraminifera indicative of an upper p eugubina zone p1a 2 age another hiatus 7 cm upsection separates zone p1a 2 and hemipelagic limestones of planktic foraminiferal zone p1c planktic foraminiferal assemblages of zone plc to p3b age are present from a depth of 794 04 up to 775 m the cretaceous carbonate sequence appears to be autochthonous with a stratigraphic sequence comparable to late cretaceous sediments known from outside the chicxulub crater in northern and southern yucatan including the late cenomanian organic rich marly limestone there is no evidence that these sediments represent crater infill due to megablocks sliding into the crater such as major disruption of sediments chaotic changes in lithology overturned or deep dipping megablocks major mechanical fragmentation shock or thermal alteration or ductile deformation breccia units that are intercalated in the carbonate platform sequence are intraformational in origin e g dissolution of evaporites and dykes are rare major disturbances of strata by the impact therefore appear to have been confined to within less than 60 km from the proposed impact center yaxcopoil 1 may be located outside the collapsed transient crater cavity either on the upper end of an elevated and tilted horst of the terrace zone or even outside the annular crater cavity the chicxulub site thus records a large impact that predates the k t boundary impact and mass extinction

cretaceous paleogene boundary deposits at loma capiro central cuba evidence for the chicxulub impact a newly discovered upper cretaceous to lower paleogene section at loma capiro central cuba has provided new evidence for a cretaceous paleogene boundary age for the chicxulub impact the studied sediments at loma capiro consist of a foraminifera rich marl and sandstone hemipelagic sequence and a 9 6 m thick intercalated clastic complex planktic foraminifera indicate an upper maastrichtian age for the sediments below the clastic complex and a lowermost danian age for those just above this complex small benthic foraminifera from below and above the clastic complex indicate deposition at middle to lower bathyal depths the fining upward clastic complex consists of a basal breccia that is overlain by microconglomerates and coarse to fine grained sandstones the clastic complex contains reworked foraminifera from different ages and different paleoenvironments and toward the top impact material such as altered microtektites shocked quartz terrestrial chondrules and accretionary lapilli these microfacies suggest deposition from gravity flows that eroded sediments from upper slope and shelf settings and redeposited them in deeper bathyal environments we suggest that the origin of the clastic complex may be linked to the collapse of the cuban platform triggered by the cretaceous paleogene impact at chicxulub

flow variation in layered rocks subjected to bulk flow of various kinematic vorticities theory and geological implications abstract flow variation is studied analytically in rocks with layers of varied competence and varied orientation with respect to constant bulk flow fields of given kinematic vorticity 0 w k 1 the results explicitly demonstrate that flow varies significantly from layer to layer and with time in any individual layer even though the bulk flow is constant any flow regime can occur and the instantaneous stretching axes isa spin all the time reverse sense of non coaxiality can occur in the same layer at different times and in different layers at the same time this study further reveals the significance of heterogeneity and non steadiness in natural flows the assumption of a time independent flow history for natural deformation is highly unrealistic the spinning of the instantaneous stretching axes isa and the variation of flow regimes have bearings on the progressive development of fabrics and structures such as folded boudins refolded folds in shear zones and double rotation of porphyroclasts that are often interpreted as being due to multi deformational events

spherule deposits in cretaceous tertiary boundary sediments in belize and guatemala large spheroid deposits at albion island and armenia in northern and central belize and the spherule deposits of southern belize and eastern guatemala have the same glass origin based on the presence of almost pure cheto smectite derived from alteration of impact glass from the chicxulub impact on yucatan mexico the same origin has also been determined for altered glass spherules in mexico haiti and the caribbean however the spherule layers have variable ages as a result of erosion and redeposition with an early danian parvularugoglobigerina eugubina zone pla 1 age in southern belize guatemala haiti southern mexico and the caribbean and a pre k t plummerita hantkeninoides zone cf1 age of 65 27 0 03 ma in ne mexico a pre k t age for the chicxulub impact has now also been determined from the new yaxcopoil 1 core drilled in the impact crater these data show that chicxulub was not the k t impact that caused the end cretaceous mass extinction but an earlier impact event a multiple impact hypothesis volcanism and climate change appears the likely scenario for the end cretaceous mass extinction

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

seismic interpretation of pelagic sedimentation regimes in the 18 53 ma eastern equatorial pacific basin scale sedimentation and infilling of abyssal valleys understanding how pelagic sediment has been eroded transported and deposited is critical to evaluating pelagic sediment records for paleoceanography we use digital seismic reflection data from an integrated ocean drilling program site survey amat03 to investigate pelagic sedimentation across the eastern central equatorial pacific which represents the first comprehensive record published covering the 18 53 ma eastern equatorial pacific our goals are to quantify 1 basin hill scale primary deposition regimes and 2 the extent to which seafloor topography has been subdued by abyssal valley filling sediments the eastern pacific seafloor consists of a series of abyssal hills and basins with minor late stage faulting in the basement ocean crust rarely outcrops at the seafloor away from the rise crest both hills and basins are sediment covered the carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data overall we recognized three different sedimentation regimes depositional high sedimentation rate transitional and minimal sedimentation low sedimentation rate regimes in all areas the sedimented seafloor mimics the underlying basement topography although the degree to which topography becomes subdued varies depositional regimes result in symmetric sedimentation within basins and subdued topography whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief regardless of sedimentation regime enhanced sediment deposition occurs within basins however we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills if this variation is due to sediment focusing the focusing factor in the basins as measured by 230th is no more than a factor of 1 3 of the total vertical particulate rain

empirical reflection travel time versus depth and velocity versus depth functions for the deep sea sediment column numerous correlations of one way reflection travel times and depths to reflecting horizons have been proposed in the initial reports of the deep sea drilling project dsdp having carefully reviewed proposed correlations we selected 233 correlated depths ranging from 27 m to 1 4 km and one way travel times ranging from 0 02 to 0 7 s from 154 dsdp sites worldwide assuming that the velocity depth function for deep sea sediments can be approximated by an exponential form we have used these data to establish statistically well constrained global models relating depth to travel time and velocity to depth there is remarkably little scatter in the data based on nonlinear least squares fits the best depth time function is z km 3 03 1n 1 0 52t s the rms error in depth is 26 m the corresponding average velocity depth function is v km s 1 59exp 0 33z we estimate that the real site to site variability of velocities at depth is less than 0 20 km s any dependence of velocity on composition is below the resolution of the data and available evidence suggests that age has no significant effect these results imply that to a depth of 1 4 km the physical state of sediments depends on in situ overburden pressure and temperature which are related to depth of burial and that chemical and mechanical equilibrium is achieved in a period of time that is geologically short our results are consistent with laboratory measurements of p wave velocities in deep sea sediments but velocity depth functions for terrigenous and calcareous sections derived from sonobuoy wide angle reflection surveys are incompatible with the time and depth data and overestimate velocities by as much as 10 and 30 respectively these systematic errors may result from the fact that the marked anisotropy of deep sea sediments is neglected in the interpretation of reflection data

the cretaceous palaeogene boundary at gorgonilla island colombia south america the discovery of a new cretaceous palaeogene k pg bathyal marine sequence on gorgonilla island sw colombia extends the presence of chicxulub impact spherule deposits to the pacific region of northern south america and to the eastern pacific ocean the gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well preserved glass spherules up to 1 1 mm in diameter about 70 90 of the spherules are vitrified and their chemical composition is consistent with haiti beloc impact glass spherules normal size grading delicate spherule textures welded melt components and an absence of bioturbation or traction transport suggest that the gorgonilla spherule layer represents an almost undisturbed settling

is the transition impact to post impact rock complete some remarks based on xrf scanning electron microprobe and thin section analyses of the yaxcopoil 1 core in the chicxulub crater the transition from impact to post impact rocks in the yaxcopoil 1 core is marked by a 2 cm thick clay layer characterized by dissolution features the clay overlies a 9 cm thick hardground overlying a 66 cm thick crossbedded unit consisting of dolomite sandstone alternating with thin micro conglomerate layers with litho and bioclasts and the altered remains of impact glass now smectite the micro conglomerates mark erosion surfaces microprobe and backscatter sem analysis of the dolomite rhombs show an early diagenetic complex zoned idiomorphic overgrowth with mn rich zones possibly formed by hot fluids related to cooling melt sheet in the crater the pore spaces are filled with several generations of coelestite barite k feldpar and sparry calcite xrf core scanning analysis detected high mn values in the crossbedded sediments but no anomalous enrichment of the siderophile elements cr co fe and ni in the clay layer shocked quartz occurs in the crossbedded unit but is absent in the clay layer the basal paleocene marls are strongly dissolved and do not contain a basal paleocene fauna the presence of a hardground the lack of siderophile elements shocked quartz or ni rich spinels in the clay layer and the absence of basal paleocene biozones p0 and pa all suggest that the top of the ejecta sequence and a significant part of the lower paleocene is missing due to the high energy sedimentation infill a hiatus at the top of the impactite is not unexpected but there is nothing in the biostratigraphy geochemistry and petrology of the yaxcopoil 1 core that can be used to argue against the synchroneity of the end cretaceous mass extinctions and the chicxulub crater

garnet rotation and the development of axial plane crenulation cleavage rotated helicitic garnets syntectonically overgrowing axial plane crenulation cleavage on the limbs of folds show the opposite sense of rotation to that undergone by the folded foliation during the development of the fold the garnet rotation is inconsistent with simple minded shear models for the development of the crenulation cleavage and it is useful to consider this problem in order to understand the development of crenulation cleavage better various models are considered in an attempt to explain both garnet rotation and cleavage morphology earlier models were based on the assumption that garnet rotation is driven by shear parallel to s2 they were mostly unsatisfactory but one involving migration of the crenulation hinges is viable when combined with other models described here the new models proposed here are based on the assumption that garnet rotation is driven by shear on the crenulated surface s1 the new foliation s2 is considered to be a passive structure at least in the early stages of its development these models satisfactorily explain garnet rotation and development of the cleavage including differentiation and they can be used to predict the morphological evolution of the cleavage microstructure as it should be preserved in garnets comparison of observed and predicted helicitic structures strongly supports the proposed models evidence is presented to show that where a garnet has an se that is a schistosity and an si that is a crenulation cleavage the schistosity can have developed by unfolding of the crenulations

the k pg boundary at brazos river texas usa an approach by marine palynology two cores and one outcrop section from the cretaceous palaeogen k pg boundary interval at the brazos river area texas usa have been high resolution sampled and analysed fully quantitatively by marine palynology the results have been compared and integrated with data from micropalaeontology sedimentology and isotope geochemistry from the same sections within all three sections the k pg boundary defined as the base of the p0 foraminifera zone and the onset of a negative carbon isotope anomaly closely corresponds to the appearance of lowermost danian organic walled dinocysts based on various palynological proxies as well as on sedimentologic features a sequence stratigraphic subdivision of the sections is proposed from a synopsis of all three sections a long term punctuated drop of relative sea level is indicated starting at about the top of the upper cretaceous cf2 foraminifera zone and reaching a minimum within the upper p1a zone of the lower palaeogene this is followed by a prominent transgression starting within the p1a p1b boundary interval the event deposit ed a siliciclastic unit located well below the base of the p0 foraminifera zone in the present sections most probably represents a combination of both episodic relative sea level fall and lag deposit due to initial transgression it is preceded by significant fluctuations of climatic boundary conditions with cool climates correlating to heavier 13c values and increased p g ratio of dinocysts suggestive of higher marine primary productivity across the k pg boundary a prominent increase and spike of the warm temperate waters dinocysts fraction is documented represented mainly by trithyrodinium evittii which is accompanied by climatic warming and an episodic relative sea level rise thus prominent paleo environmental changes and sea level fluctuations precede and coincide with the k pg boundary proper these data are inconsistent with a single catastrophic impact as the cause for the k pg boundary event but suggest relative longer term environmental stress as finally leading to end cretaceous crisis of the biosphere between the ed and the k pg boundary proper the gradual increase to peak abundance in trilete spores demonstrates a significant time lag between these two horizons according to the distinct distribution of this peak abundance it cannot be excluded that an impact tsunami event is related to the lower portion of the ed in contrast no significant changes within most palynologic proxies are documented across the yellow clay layer below the ed documented within one of the sections and recently suggested as the original chicxulub impact ejecta horizon this questions the impact origin of this horizon or at least suggests only little consequences of this event on the ecosystem

in situ acoustic properties of pelagic carbonate sediments on the ontong java plateau the ontong java plateau with its thick capping sequence of cretaceous and cenozoic pure pelagic carbonate sediments forms an ideal setting for the study of the acoustic properties of this lithology on an oceanic rise borehole logs recorded on deep sea drilling project leg 89 at site 586 provided detailed data on in situ acoustic properties of pleistocene to early miocene sediments to a depth of 623 m below seafloor comparison of these logging results and the sonobuoy based results of johnson et al 1978 with previous laboratory measurements from the ontong java plateau shows that velocity depth functions determined from the logging and sonobuoy methods are concordant but diverge significantly from functions derived from laboratory measurements log densities and compressional velocities exceed those measured by laboratory techniques the density discrepancy is strongly influenced by laboratory method the differences between log and laboratory compressional velocities are greater than and extend to greater depths than those between densities these differences can be attributed to reductions in the frame bulk modulus and dynamic rigidity caused by the removal of overburden pressure in the absence of significant porosity rebound agreement of site 586 log velocities with velocities derived from the earlier sonobuoy measurements across the plateau argues for the interpretation that both methods measure in situ values the disagreement between the site 586 log results and the sonobuoy results with both the empirical velocity depth function of carlson et al 1986 and the empirical velocity porosity function of raymer et al 1980 supports the conclusion that pelagic carbonate sediments on oceanic plateaus and rises have unique acoustic properties primarily arising from the presence of intraparticle porosity and should not be grouped with other oceanic lithologies in acoustic modeling studies

late maastrichtian paleoclimatic and paleoceanographic changes inferred from sr ca ratio and stable isotopes abstract milankovitch scale cycles can be recognized in high resolution 13c 18o sr ca mineralogical and magnetic susceptibility data in hemipelagic sediments that span the last 700 kyr of the maastrichtian at elles tunisia oxygen isotope data reveal three cool periods between 65 50 and 65 55 ma 21 5 23 5 m 65 26 and 65 33 ma 8 11 m and 65 04 and 65 12 ma 1 5 4 m and three warm periods between 65 33 and 65 38 ma 12 16 m 65 12 and 65 26 ma 4 8 m and 65 00 and 65 04 ma 0 1 5 m the cool periods are characterized by small surface to deep temperature gradients that reflect intensive mixing of the water column the surface to deep sr ca gradient generally correlates with the oscillating t trend temperature difference between surface and bottom waters the carbon isotope composition of planktonic foraminifera indicates a continuous decrease in surface bioproductivity during late maastrichtian decreasing 13c values difference between the 13c values of surface and bottom dwelling foraminifera and the carbon isotope ratios of the planktonic species at the onset of gradual warming at 65 50 ma reflect a reduction in surface productivity as a result of decreased upwelling that accompanied global warming and possibly increased atmospheric pco2 related to deccan trap volcanism time series analysis applied to magnetic susceptibility 18o and sr ca data identifies the 20 kyr precession 40 kyr obliquity and 100 kyr eccentricity milankovich cycles

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

physical property changes as a monitor of pelagic carbonate diagenesis an empirically derived diagenetic model for atlantic ocean basins a new physical model of carbonate diagenesis has been derived based on physical property measurements from 81 dsdp odp deep sea drilling project ocean drilling project drill sites in the atlantic ocean changing depth gradients of porosity bulk density p wave velocity vertical and horizontal and acoustic impedance characterize five successive diagenetic stages 1 compaction of ooze 2 breakage and dissolution of fossil tests 3 formation of chalk through precipitation of calcite 4 cementation and 5 compaction of calcite crystals age depth information from the drill sites was used to calculate the average duration of these processes in atlantic ocean basins the model can predict carbonate sediment physical properties down to a burial depth of 1000 m the model is presented for both lab and in situ conditions and thus can serve as a standard for comparison with lab log and seismic measurements an acoustic impedance vs age curve derived from the model allows estimation of the initial and present day diagenetic potential of carbonate sediments and chalk reservoirs

changes in attenuation with depth in an ocean carbonate section ocean drilling program sites 806 and 807 ontong java plateau changes of in situ seismic attenuation with depth are estimated from full waveform acoustic logs in a soft formation rock with shear velocity less than borehole fluid velocity the relative attenuation qp 1 is computed from the variation with depth of the p wave amplitude spectrum of a single source receiver pair the method is applicable when unknown source and receiver responses of the sonic tool make other methods difficult to apply tests with synthetic data generated by a full waveform method verify that in a soft formation the decay of the p wave amplitude spectrum depends mainly on attenuation the method is applied to ocean drilling program data from holes 806b and 807a on the ontong java plateau in the western pacific ocean four attenuation logs were computed independently using data from four source receiver pairs agreement of the four logs at each site and agreement of results from the two sites suggest that the method is robust and practical the attenuation logs show a maximum attenuation between 300 and 500 m below the seafloor they agree well with compilations of high frequency attenuation versus porosity and frequency in marine sediments but are somewhat greater than results from seismic experiments possibly owing to the presence of sedimentary microbeds and the three decade difference between the seismic and sonic frequency bands

late maastrichtian age of spherule deposits in northeastern mexico implication for chicxulub scenario in the la sierrita area of nuevo leon mexico three spherule layers are present and separated from the overlying siliciclastic deposits by up to 6 m of pelagic marls the marls are of latest maastrichtian age plummerita hantkeninoides cf1 zone micula prinsii zone and deposited under normal pelagic conditions with no significant evidence of reworking or slumping original deposition of the spherule layers occurred during the last 300 ka of the maastrichtian and well prior to the cretaceous tertiary k t boundary event thus if the spherules in northeastern mexico provide critical evidence of an impact at chicxulub this impact predates the k t boundary

relationships between foliation development porphyroblast growth and large scale folding in a metaturbidite suite snow lake canada ahstractxomplex relationships exist between cleavage development metamorphism and large scale folding in the well bedded polydeformed staurolite grade metaturbidite of the burntwood suite internal paleoproterozoic trans hudson orogen at snow lake manitoba canada it is demonstrated a that cleavage in anisotropic pelitic rock develops whenever microfolding is possible and that commonly initiation of a cleavage which is pervasive on the scale of a fold predates folding b how a new axial planar fabric can develop on one fold limb of a symmetrical fold and not on the other and c how two cleavages of different generations can be present in adjacent beds it is further shown that porphyroblasts rotate with respect to geographical coordinates during folding finally dissolution of cleavage septa is suggested here as an alternative mechanism for the generation of schistosity the burntwood suite is exposed on the dismembered limb of a macroscopic isoclinal f2 structure and preserves a domainal cleavage sz which locally grades into a schistosity s developed from crenulation of a generally bedding parallel s cleavage that is axial planar to f isoclinal folds formed at 1 84 ga porphyroblast growth coincided with crenulation of st early during f2 folding at 1 815 1 8 ga early stages of development are recorded by inclusion trails sj in the porphyroblasts during fz flexural flow folding variations in magnitude of bedding parallel shear in lithologies of different competency resulted in a strong s refraction and thus heterogeneous strains between beds independent of shear magnitude and resulting j s angle s and s2 remained sub orthogonal everywhere and thus porphyroblasts and the enveloping s rotated by equal amounts with respect to ss as the different magnitudes of porphyroblast rotation in different beds could not be exactly balanced by the counteracting rotation of the fold limbs same magnitude for all beds during fold tightening most porphyroblasts also rotated with respect to geographical coordinates s2 was crenulated prior to f3 large scale folding where favourably oriented f3 crenulations were tightened on the eastern f3 limb and unfolded by sinistral layer parallel shear on the western limb where f2 and f3 layer parallel shears were of opposite and the same sense respectively as a result the initial developmental stages of an ss are developed only on the eastern f3 limb and there only in incompetent layers whereas sz is preserved in the competent layers on the western limb s2 is preserved and appears axial planar to the f3 structure the s domainal fabric was locally transformed into a schistosity by dissolution of the septa during widespread fluid activity which endured until syn or post fa 5c 1998 elsevier science ltd

proximal impact deposits at the cretaceous tertiary boundary in the gulf of mexico a restudy of dsdp leg 77 sites 536 and 540 restudy of deep sea drilling project sites 536 and 540 in the southeast gulf of mexico gives evidence for a giant wave at cretaceous tertiary boundary time five units are recognized 1 cenomanian limestone underlies a hiatus in which the five highest cretaceous stages are missing possibly because of catastrophic k t erosion 2 pebbly mudstone 45 m thick represents a submarine landslide possibly of k t age 3 current bedded sandstone more than 2 5 m thick contains anomalous iridium tektite glass and shocked quartz it is interpreted as ejecta from a nearby impact crater reworked on the deep sea floor by the resulting tsunami 4 a 50 cm interval of calcareous mudstone containing small cretaceous planktic foraminifera and the ir peak is interpreted as the silt size fraction of the cretaceous material suspended by the impact generated wave 5 calcareous mudstone with basal tertiary forams and the uppermost tail of the ir anomaly overlies the disturbed interval dating the impact and wave event as k t boundary age like beloc in haiti and mimbral in mexico sites 536 and 540 are consistent with a large k t age impact at the nearby chicxulub crater

modelling of porosity evolution and mechanical compaction of calcareous sediments a continuum mechanics model for the gravitational compaction of sediments is derived by assuming that the sediments are normally pressured and in a one dimensional state of stress sediment strength is characterized in terms of effective stress laws adopted from soil mechanics the model is a relatively simple mathematical formula that gives the porosity as a function of burial depth the shape of the porosity profile is controlled by two mechanical parameters the compression index and the void ratio at an effective stress of 100 kpa the model was verified by analysing the porosity depth data of oozes and chalk from the ontong java plateau gathered during leg 130 of the ocean drilling program the mechanical parameters of the sediments were estimated using a least squares method to fit the theoretical profile to the porosity data the theoretical profile described accurately the ooze porosity data over depth ranges of 100 m or more however over smaller length scales of 10 50 m there were systematic deviations between the theoretical porosity values and the ooze porosity data the porosity deviations correlated with variations in the mean grain size of the sediments due in part to changes in the foraminifera abundance in the case of the oozes the estimated mechanical parameters were consistent with published values obtained from one dimensional compression tests in contrast the estimated mechanical properties for the chalks differed from published values the chalk porosities were lower than could be explained by mechanical compaction this explanation is supported by the compressional p wave velocity data in the chalk sections the p wave velocity increases more rapidly with burial depth than it does in the ooze sections suggesting that sediment elastic properties are increasing due to interparticle binding

slumping and a sandbar deposit at the cretaceous tertiary boundary in the el tecolote section northeastern mexico an impact induced sediment gravity flow slumps affecting uppermost mendez formation marls as well as the spherulitic layer and basal part of the sandy deposits of the cretaceous tertiary k t boundary clastic unit are described at the new k t el tecolote section northeastern mexico these k t clastic deposits represent sedimentation at middle bathyal water depths in channel and nonchannel or levee areas of reworked materials coming from environments ranging from outer shelf to shallower slope via a unidirectional high to low density turbidite flow we emphasize the development and accretion of a lateral bar in a channel area from a surging low density turbidity current and under a high flow regime the slumps discovered on land and the sedimentary processes of the k t clastic unit reflect destabilization and collapse of the continental margin support the mechanism of gravity flows in the deep sea and represent important and extensive evidence for the impact effects in the gulf of mexico triggered by the chicxulub event

back rotation during crenulation cleavage development implications for structural facing and cleavage forming processes abstract structural facing can be a useful tool for understanding macroscale structural geometries particularly where poor outcrop inhibits the mapping of fold closures however in some situations facing must be determined with considerable care in graded metaturbidites where bedding and a near parallel foliation have been overprinted by a crenulation cleavage the earlier foliation in the metapelitic layers can be substantially back rotated in the hinges of the overprinting crenulation cleavage thus the rotation in the crenulation hinges is opposite to the rotation in the crenulation limbs when viewed in the metapelitic layers relative to a bedding surface back rotation can cause an apparent reversal in the structural facing and vergence on the rotated foliation to avoid such misinterpretation structural facing on the earlier foliation should be determined in the metapsammitic layers where the effects of the overprinting crenulation cleavage are minimal because foliations that intersect bedding at a low angle are commonly hard to identify in metapsammitic outcrops microstructural analysis may be required the back rotation process provides important constraints on mechanisms and kinematics of crenulation cleavage development and may also have important implications for porphyroblast rotation folding mechanisms and issues of strain compatibility in compositionally interlayered rocks

fe rich and k rich mafic spherules from slumped and channelized chicxulub ejecta deposits in the northern la sierrita area ne mexico spherule deposits commonly interpreted as ejecta from the chicxulub impact at yucatan mexico are present in many k t cretaceous tertiary sections geological mapping of the northern la sierrita area ne mexico revealed the presence of 1 multiple spherule deposits embedded in late maastrichtian marls which are folded or disaggregated breccia like they are up to 6 m thick locally present in two outcrop areas and show limited lateral continuity these deposits consist of mm cm sized spherical to drop shaped vesiculated spherules angular to filamentous ejecta fragments and abundant carbonate they are interpreted as primary ejecta fallout deposits that have been affected by subsequent local slumps slides liquefaction and debris flows welded components suggest an initial ground surge like ejecta dispersion mode 2 a spherule deposit 10 60 cm thick that constitutes the base of a channelized sand siltstone deposit at or close to the k t boundary and is characterized by wide lateral continuity it is of similar petrologic composition to deposit 1 though slightly enriched in terrigeneous detritus thus reflecting influx from proximal shelf areas it is interpreted to result from debris flows and turbidite currents though no size sorting and abrasion of ejecta has been observed petrological mineralogical and geochemical criteria suggest that ejecta components from both types of spherule deposits are similar and originated from the chicxulub impact with multiple deposits produced by subsequent remolding reworking and redeposition spherules and fragments have an fe 25 30 wt al mg rich and si poor 25 wt sio2 composition and are altered to chlorite and iron oxides though rare k rich mafic glass 50 wt sio2 5 8 wt k is also present they contain ti fe k rich schlieren fe mg rich globules and rare m sized metallic and sulfidic ni co rich inclusions carbonate as clasts and within spherules and fragments shows textures indicative of quenching and or liquid immiscibility although potential ejecta fractionation and alteration make accurate evaluation difficult this composition suggests an ejecta origin mainly from mafic lithologies and carbonaceous sediments in addition to a contribution from intermediate felsic rocks and the possibility of meteoritic contamination

deposition of channel deposits near the cretaceous tertiary boundary in northeastern mexico catastrophic or normal sedimentary deposits investigation of cretaceous tertiary k t boundary channel deposits in three sections in northeastern mexico reveal three lithologically and mineralogically distinct units separated by three or more disconformities the units include a spherule rich layer unit 1 laminated sandstone unit 2 and rippled sand and shale layers unit 3 on the basis of paleontological mineralogical and geochemical evidence the k t boundary is just above the top of unit 3 although the deposits have previously been interpreted as a tsunami deposit related to a presumed k t impact at chicxulub on yucatan we have found no evidence of a nearby impact we suggest that deposition occurred in an incised valley setting and over an extended period of time

a geologic perspective on the miocene evolution of the antarctic circumpolar current system abstract the dominant geologic feature of pelagic sediment accumulation patterns at intermediate water depths in the southern ocean is the sequential northward migration and replacement of a calcareous ooze sedimentary facies by a siliceous ooze facies following the late oligocene opening of the drake passage and the subsequent initiation of the antarctic circumpolar current closely spaced whole core measurements of bulk density are evaluated for four sites drilled in the southern ocean during ocean drilling program odp legs 113 sites 689 and 690 and 120 sites 747 and 751 these sites are all located on submarine rises in open ocean pelagic depositional environments south of the polar front a major oceanographie and sedimentologic boundary high resolution profiles of bulk density are used to correlate between adjacent drill holes on the maud rise where multiple overlapping sedimentary sequences were recovered using the advanced hydraulic piston core barrel apc stratigraphie age models have been applied to the bulk density data to provide a temporal framework for a discussion of the sedimentologic basis for paleoceanographic interpretations and also to constrain future acoustic research studies the early to middle miocene intervals at sites 689 and 690 are marked by distinct sequences of meter scale alternating carbonate and siliceous units separated by several proposed stratigraphie hiatuses at least six dissolution productivity events are identified in the middle to late miocene on the maud rise and others are noted at the odp sites on the kerguelen plateau the downhole profiles are used to identify the density signature and position of sediment facies changes and proposed stratigraphie hiatuses in sediment cores of late oligocene to late miocene age based on the reversals inflections and discontinuities in the downhole bulk density trends an analysis of the observed bulk density trends at these sites is combined with a review of other tectonic sedimentologic oceanographie and modeling studies to develop a hypothesis for explaining the observed sediment accumulation patterns at intermediate water depths of the southern ocean

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

sonostratigraphy of tropical indian ocean giant piston cores toward a rapid and high resolution tool for tracking dissolution cycles in pleistocene carbonate sediments abstract during the seymama expedition of the french r v marion dufresne in the equatorial indian ocean we retrieved giant piston cores 30 53 m long as part of a high resolution palaeo oceanographic and stratigraphic study of pliocene pleistocene pelagic carbonates major changes in the compressional wave p wave velocity profiles recorded in these cores appear to be correlatable from the madingley rise western equatorial indian ocean to the southeast of the maldives archipelago central equatorial indian ocean about 1700 km away thus emphasizing the stratigraphic potential of acoustic records in uncemented pelagic carbonates as expected in deep sea carbonate deposits changes in p wave velocity parallel past changes in coarse fraction content 63 m changes in grain size appear to be mainly controlled by carbonate dissolution as evidenced by a strong relationship between sand content and a foraminifer preservation index thus in uncemented pelagic carbonates p wave velocities provide quick and easy to obtain qualitative information on carbonate dissolution pulses as diagenesis takes place however compaction and cementation change the dynamic rigidity of the sediments and may conceal the original grain size signal due to the strong positive relationship between p wave velocity and coarse fraction content in uncemented pelagic carbonates p wave velocity profiles can be tied to a precise chronologic framework by correlating them to the composite grain size index curve cgsi established by bassinot et al for the tropical indian ocean 1 2 this composite curve has been constructed by stacking the normalized coarse fraction records from odp site 722 owen ridge arabian sea 3 and odp site 758 ninetyeast ridge central equatorial indian ocean 4 in these two sites detailed 18 o records provide the basis for precise inter site correlations they ensure the accuracy of the stacking procedure which tends to reduce most of the local grain size signals and enhances the regional signal related to carbonate dissolution pulses 1 2 a detailed chronostratigraphy of cgsi curve was developed by correlating the 18 o records of sites 722 and 758 to the orbital chronology recently developed from odp site 677 5 the cgsi may be used as a reference curve for developing a sonostratigraphy in the tropical indian ocean

acoustic and mechanical properties of nankai accretionary prism core samples we studied undeformed sediment and accreted strata recently recovered by ocean drilling program integrated ocean drilling program odp iodp drilling in nankai trough convergent margin to unravel the changes in physical properties from initial deposition to incipient deformation we have derived acoustic vp and mechanical uniaxial poroelastic compliance compaction amplitude properties of samples from various drill sites along the muroto odp 1173 and kii transects iodp c0001 c0002 c0006 and c0007 from isotropic loading tests where confining and pore pressure were independently applied we quantified the dependence of vp on both effective peff and confining pc pressure which can be used to correct atmospheric pressure measurements of vp experimental vp obtained on core samples extrapolated to in situ conditions are slightly higher than logging derived velocities which can be attributed either to velocity dispersion or to the effect of large scale faults and weak zones on waves with longer wavelength in the high porosity 30 60 tested sediments velocities are controlled at first order by porosity and not by lithology which is in agreement with our static measurements of drained framework incompressibility much smaller than fluid incompressibility rather than framework incompressibility shear modulus is probably the second order control on vp accounting for most of the difference between actual vp and the prediction by wood s 1941 suspension model we also quantified the mechanical state of nankai samples in terms of anisotropy diagenesis and consolidation both acoustic and mechanical parameters reveal similar values in vertical and horizontal directions attesting to the very low anisotropy of the tested material when considering the porous samples of the upper shikoku basin sediments site 1173 as examples of diagenetically cemented material several mechanical and acoustic attributes appeared as reliable experimental indicators of the presence of intergrain cementation we also detected incipient cementation in samples from iodp site c0001 accretionary prism unit in terms of consolidation we distinguished two classes of material response shallow deformable samples and deep hardly deformable ones based on the amount of compaction upon application of a peff large with respect to the inferred in situ value with a transition that might be related to a critical porosity

carbon isotopes rare earth elements and mercury geochemistry across the k t transition of the paraiba basin northeastern brazil the parao ba basin northeastern brazil is divided into three sub basins olinda alhan dra and miriri which encompass the formations beberibe coniacian santonian itamaraca campanian and gramame and maria farinha maastrichtian to danian respectively in the olinda sub basin the cretaceous palaeogene transition ktb has been recorded by the carbon ates of the gramame and maria farinha formations this study focus on the behaviour of c and o isotopes major and rare earth elements and mercury in carbonates from three drill holes in the olinda sub basin the climate was fairly cold during the marine transgression in which carbonates of the itamaracaformation were deposited a temperature and bioproductivity increase has been registered in the early maastrichtian gramame formation with a gradual fall during the rest of this period a positived 13 c 2 excursion near the ktb is followed by a drop to values around 1 immediately after this transition in one drill hole several negative d 13 c anomalies predate the ktb possibly related to either multiple impacts or volcanic activity that preceded this tran sition in two of the three drill holes the total mercury increases immediately after the ktb and in two of them mercury spikes four of them in one case precede this transition which has been interpreted as an indication that volcanic activity predated the transition rare earth element patterns support a marine origin for the carbonates in the campanian maastrichtian tran sition and ktb in the olinda sub basin in carbonates from one of the drill holes absent to weakly positive ce anomalies 20 1 and 0 002 in the ktb coincide with a fall in d 13 c values followed by an increase from 2 3 to 1 8 and back to 2 3 and in increment in mercury values from 0 4 to 2 7 ng g 21 the presence of pyrite nodules associated with a weakly negative eu anomaly point to slightly reducing conditions around the ktb

more evidence that the chicxulub impact predates the k t mass extinction yaxcopoil 1 yax 1 drilled within the chicxulub crater was expected to yield the final proof that this impact occurred precisely 65 myr ago and caused the mass extinction at the cretaceous tertiary k t boundary instead contrary evidence was discovered based on five independent proxies sedimentologic biostratigraphic magnetostratigraphic stable isotopic and iridium that revealed that the chicxulub impact predates the k t boundary by about 300 000 years and could not have caused the mass extinction this is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest maastrichtian zone cf1 and is corroborated by magnetostratigraphic chron 29r and characteristic late maastrichtian stable isotope signals these results were first presented in keller et al 2004 in this study we present more detailed evidence of the presence of late maastrichtian planktic foraminifera sedimentologic and mineralogic analyses that demonstrate that the chicxulub impact breccia predates the k t boundary and that the sediments between the breccia and the k t boundary were deposited in a normal marine environment during the last 300 000 years of the cretaceous

beloc haiti revisited multiple events across the kt boundary in the caribbean examination of new expanded k t boundary sections near beloc haiti reveals deposition of a glass spherule rich deposit srd and two pge anomalies one ir dominated and one pd dominated during the early danian parvularugoglobigerina eugubina zone pla l the presence of the haiti srd within the early danian is interpreted as being due to reworking ir is only slightly elevated within the srd but forms an anomaly at the top of the srd extending into the overlying pelagic limestones it is unclear at present whether this ir anomaly results from mechanical reworking of an impact at the k t boundary or an additional impact event in the early danian the second pge anomaly upsection is dominated by pd and pt and is more compatible with a magmatic origin this suggests a multi event scenario consistent with one and possibly two impact s followed by a pge enriched volcanic event in the caribbean

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

near orthogonal foliation development in orogens meaningless complexity or reflection of fundamental dynamic processes abstract orogenic belts are geometrically complex owing to repeated deformation within this complexity there is evidence that may suggest a common pattern of sequential steeply dipping and gently dipping foliations seven possible explanations are presented for the sequential development of these foliations which can probably be reduced to four of general importance 1 the passage of thrust sheets over flats and ramps 2 switching of the maximum and minimum compressive stress orientations during orogenesis 3 reversal of structural development owing to strong rheological anisotropy and 4 back rotation of crenulation hinges during crenulation cleavage development it is suggested that all four of these reflect fundamental dynamic processes at work to build an orogen and therefore that sequentially overprinted steeply and gently dipping foliations also reflect such fundamental processes this illustrates that detailed geometrical analysis at the meso and microscales can provide valuable input to dynamic models of orogenesis

miocene benthic foraminiferal isotope records a synthesis abstract 18 o 16 o and 13 c 12 c ratios of miocene benthic foraminifera from a number of atlantic pacific and indian ocean dsdp sites 71 77b 206 208 238 279 289 296 329 357 and 366a have been compiled these provide a rather detailed history of miocene deep water especially in the pacific ocean bottom water temperatures rose during the early miocene and then declined rapidly during the middle miocene this decline was accompanied by an increase in antarctic glaciation late miocene bottom temperatures and antarctic ice volumes are inferred to be similar to today s but exhibited some fluctuation the early miocene ocean was less thermally stratified at intermediate and abyssal depths while the late miocene deep ocean had a thermal structure generally similar to the modern ocean foraminiferal carbon isotope ratios at most of the sites varied quasi sympathetically throughout the miocene these variations must reflect comparable variations in the mean 13 c 12 c of marine hco 3 however the causes of such variations are not yet clear

discovery of distal ejecta from the 1850 ma sudbury impact event a 25 70 cm thick laterally correlative layer near the contact between the paleoproterozoic sedimentary gunflint iron formation and overlying rove formation and between the biwabik iron formation and overlying virginia formation western lake superior region contains shocked quartz and feldspar grains found within accretionary lapilli accreted grain clusters and spherule masses demonstrating that the layer contains hypervelocity impact ejecta zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca 1878 ma and 1836 ma the sudbury impact event which occurred 650 875 km to the east at 1850 1 ma is therefore the likely ejecta source making these the oldest ejecta linked to a specific impact shock features particularly planar deformation features are remarkably well preserved in localized zones within the ejecta whereas in other zones mineral replacement primarily carbonate has significantly altered or destroyed ejecta features

multiply deformed terrains problems of correlation abstract the best tools available for carrying out a structural analysis in a complex area are overprinting style and patterns of orientation unfortunately all have limitations which are reviewed briefly and discussed in areas of continuous unfaulted outcrop the deformational history can be established purely on the basis of overprinting but even in such areas there can be problems since not all overprinting relationships are unambiguous most fold interference patterns are reliable overprinting relationships based on foliations however are commonly unreliable and various examples are cited and discussed even in areas where the sequence of deformational events can be established their temporal significance is unclear since the methods applied only determine local relative timing and absolute relationships must vary in space and time across an orogen

evidence from en echelon cross grain ridges for tensional cracks in the pacific plate sea floor topography in the pacific is mainly aligned with original spreading directions1 but is overprinted by alignments created by mid plate processes spreading produces abyssal hills and fracture zones and mid plate volcanism generates seamounts isolated or in chains a different category of topography the cross grain discovered in geoid height data collected by the seasat radar altimeter2 comprises linear troughs and swells spaced 200 km apart oblique to fracture zones and abyssal hills but parallel to the hawaiian chain three models have been proposed for the cross grain small scale convection organized into longitudinal rolls by the shear of the pacific plate2 compressive buckling3 and lithospheric boudinage resulting from plate wide tensile stresses4 5 none of the previously available data ruled out any of these models here we report multi beam bathymetric data revealing long narrow en echelon ridges along the cross grain interpreted as evidence of tension cracks in the pacific plate

dynamic carbonate sedimentation on the northern line islands ridge palmyra basin abstract the line islands ridge lir located south of the hawaiian islands between 7 n and 1 s is one of the few large central pacific regions shallower than the regional carbonate compensation depth thick sequences of carbonate sediments have accumulated around the lir despite it being located in the sediment starved central tropical pacific the lir is an important source of carbonates to the surrounding region and deposition around the lir has expanded the equatorial pacific carbonate sediment tongue by about 5 of its total area furthermore sediments on the ridge are potentially important paleoceanographic archives a recent survey at the crest of the lir finds evidence for high current activity significant erosion but overall net sediment deposition currents are strong enough to form sediment waves and lee drifts in the palmyra basin at the northern terminus of the lir sediments along the lir are pelagic foraminiferal sands that are easily eroded and flow out into the surrounding abyssal plain in active submarine channel systems as channels migrate pelagic sediments fill in the abandoned channel arms despite significant sediment losses from the top of the ridge 1 3 km of sediment has accumulated in the upper palmyra basin over basement formed 68 to 85 million years ago ma late neogene erosion may be more extensive than earlier erosion cycles in response to reduced sediment production as the palmyra basin exited the high productivity equatorial latitudes sediments with good stratigraphic order needed for paleoceanographic study are limited in this dynamic sedimentary environment but can be found with proper survey

age stratigraphy and deposition of near k t siliciclastic deposits in mexico relation to bolide impact examination of 10 k t boundary sections in northeastern and east central mexico and new data presented from 7 sections permit the following conclusions 1 the globally recognized k t boundary and mass extinction in planktic foraminifera is stratigraphically above and separated by a thin marl layer of maastrichtian age from the siliciclastic deposit that is commonly interpreted as a short term hours to days k t impact generated tsunami deposit a similar relationship between the k t boundary and siliciclastic or breccia deposits is observed at brazos river in texas beloc in haiti and poty quarry in brazil 2 stratigraphic control indicates that deposition of the siliciclastic member occurred sometime during the last 150 k y of the maastrichtian and ended at least several thousand years prior to the k t boundary 3 at least four discrete horizons of bioturbation have been observed within the siliciclastic deposit that indicate episodic colonization by invertebrates over an extended time period 4 the glass and spherule rich unit which has been linked to the haiti spherule layer and the chicxulub structure is at the base of the siliciclastic deposit and thus significantly predates the k t boundary event the stratigraphic separation of the k t boundary and siliciclastic deposits and the evidence of long term deposition between them suggests the presence of two events 1 a globally recognized k t boundary impact event marked by ir anomaly and the mass extinction and 2 a caribbean event impact or volcanic and probably linked to the chicxulub structure that predates the k t boundary and is marked by glass and siliciclastic or breccia deposits

paleoecology of the cretaceous tertiary mass extinction in planktonic foraminifera abstract paleobiogeographic patterns of the cretaceous tertiary k t mass extinction in planktonic foraminifera in tunisia spanning environments from open marine upper bathyal to shelf and shallow marginal settings indicate a surprisingly selective and environmentally mediated mass extinction this selectivity is apparent in all of the environmental proxies used to evaluate the mass extinction including species richness ecological generalists ecological specialists surface and subsurface dwellers whether based on the number of species or the relative percent abundances of species the following conclusions can be reached for shallow to deep environments about three quarters of the species disappeared at or near the k t boundary and only ecological generalists able to tolerate wide variations in temperature nutrients salinity and oxygen survived among the ecological generalists heterohelicids guembelitrids hedbergellids and globigerinellids only surface dwellers survived ecological generalists which largely consisted of two morphogroups of opportunistic biserial and triserial species also suffered selectively biserials thrived during the latest maastrichtian in well stratified open marine settings and dramatically declined in relative abundances in the early danian triserials thrived only in shallow marginal marine environments or similarly stressed ecosystems during the latest maastrichtian but dominated both open marine and restricted marginal settings in the early danian this highly selective mass extinction pattern reflects dramatic changes in temperature salinity oxygen and nutrients across the k t boundary in the low latitude tethys ocean which appear to be the result of both long term environmental changes e g climate sea level volcanism and short term effects bolide impact

geochemistry of impact glasses from the k t boundary in haiti relation to smectites and a new type of glass we have individually analyzed twelve black and seven yellow glasses from the k t boundary section at beloc haiti plus three smectite mantles around black glasses the main chemical differences between black and yellow glasses are higher s ca mg zn as br sb and au but lower k na and si abundances in the yellow glasses we have found high cao yellow glasses with low s contents 0 08 0 17 wt which may be explained by fusion of carbonate rich sediments microprobe studies of individual glasses show that the black glasses are very homogeneous in their composition at the 10 100 m level while yellow glasses show much more variability and different intra sample elemental correlations one of the black glasses has higher sio2 and k2o abundances but lower concentrations of all other major elements this suggests the existence of a third glass type which we have named the high si k variety hsi k glass the glass shows areas consisting of pure sio2 maybe lechatelierite and some schlieren with lower sio2 content the chemical composition indicates that the hsi k glass may have originated from melting of a sedimentary source rock such as shale or argillite severe changes in major and trace element composition occur during alteration of the glass as documented by analyses of adhering smectites the ree patterns in the glass are similar to average upper crust but the smectites exhibit much lower abundances and flat patterns not unlike the patterns observed in claystones at numerous k t boundary sites the suggestion that the chicxulub structure in yucatan may be the source crater for the k t impact glasses is not fully supported by the currently available data impact glasses and tektites are produced from the surface layers of their targets at chicxulub the target stratigraphy comprised mainly carbonates and evaporites although we cannot exclude chicxulub as a source the present data do not provide any firm chemical evidence for a connection we conclude however that the haiti glasses have formed by impact and have later undergone alteration by low temperature hydrothermal processes to produce clays the boundary claystones at k t boundary sites may very well be alteration products of these impact glasses

near k t age of clastic deposits from texas to brazil impact volcanism and or sea level lowstand near k t boundary clastic deposits from texas mexico haiti guatemala and brazil often described as impact generated tsunami deposits are stratigraphically below well defined k t boundary horizons and appear not to be causally related to the k t boundary event stratigraphic evidence indicates that their deposition began during the last 170 200 kyr of the maastrichtian coincident with a major eustatic sea level lowstand that lowered sea level by as much as 70 100 m clastic deposition ended a few tens of thousands of years before the k t boundary during a rapidly rising sea level the presence of glass in clastic deposits in haiti northeastern mexico and yucatan suggests that the sea level lowstand coincided with a time of major volcanism or pre k t boundary bolide impact

downhole logging as a paeoceanographic tool on ocean drilling program leg 138 interface between high resolution stratigraphy and regional syntheses on ocean drilling program odp leg 138 standard shipboard procedures were modified to allow for the real time monitoring of several laboratory core scanning systems that provide centimeter scale measurements of saturated bulk density magnetic susceptibility and digital color reflectance these continuous high resolution data sets were used to ensure the proper offset of multiple holes and to splice together complete sedimentary sections typically the spliced continuous sediment sections were found to be about 10 longer than the section drilled as measured by the length of the drill string while the source of this elongation is not yet fully understood it must be compensated for in order to property determine sediment fluxes and mass accumulation rates downhole logging in conjunction with inverse correlation techniques provided a means to determine where the distortion occurred and to correct back to true in situ depths downhole logging also provides a means through the generation of synthetic seismograms of precisely relating the paleoceanographic events found in the core record to the high resolution seismic record once correlated to the seismic record the spatial and temporal extent of paleoceanographic events can be traced well beyond the borehole most seismic events in the equatorial pacific are related to rapid changes in carbonate content that in turn are related to both productivity events often expressed as monospecific laminated diatom oozes and times of enhanced dissolution while many of these events may have oceanwide extent others like the absence of carbonate in the late miocene to recent in the guatemala basin have been shown to be regional and confined to only the deeper portions of the guatemala basin as we identify and trace specific paleoceanographic events in the seismic record we can begin to explore the response of the ocean through gradients of latitude productivity and depth

seismic velocities for hydrate bearing sediments using weighted equation a weighted equation based on the three phase time average and wood equations is applied to derive a relationship between the compressional wave p wave velocity and the amount of hydrates filling the pore space the proposed theory predicts accurate p wave velocities of marine sediments in the porosity range of 40 80 and provides a practical means of estimating the amount of in situ hydrate using seismic velocity the shear s wave velocity is derived under the assumption that the p to s wave velocity ratio of the hydrated sediments is proportional to the weighted average of the p to s wave velocity ratios of the constituent components of the sediment in the case that all constituent components are known a weighted equation using multiphase time average and wood equations is possible however this study showed that a three phase equation with modified matrix velocity compensated for the clay content is sufficient to accurately predict the compressional wave velocities for the marine sediments this theory was applied to the laboratory measurements of the p and s wave velocities in permafrost samples to infer the amount of ice in the unconsolidated sediment the results are comparable to the results obtained by repeatedly applying the two phase wave scattering theory the theory predicts that the poisson s ratio of the hydrated sediments decreases as the hydrate concentration increases and the porosity decreases in consequence the amplitude versus offset avo data for the bottom simulating reflections may reveal positive negative or no avo anomalies depending on the concentration of hydrates in the sediments

tektite bearing deep water clastic unit at the cretaceous tertiary boundary in northeastern mexico the hypothesis of cretaceous tertiary k t boundary impact on yucatan mexico predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves an outcrop along the arroyo el mimbral in northeastern mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic marl sequence deposited at more than 400 m water depth the marls were found to be unsuitable for determining magnetostratigraphy but foraminiferal biostratigraphy places the clastic unit precisely at the k t boundary we interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact the elastic unit comprises three main subunits 1 the basal spherule bed contains glass in the form of tektites and microtektites glass spherules replaced by chlorite smectite and calcite and quartz grains showing probable shock features this bed is interpreted as a channelized deposit of proximal ejects 2 a set of lenticular massive graded laminated beds contains intraclasts and abundant plant debris and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water 3 at the top several thin ripple beds composed of fine sand are separated by clay drapes they are interpreted as deposits of oscillating currents perhaps a seiche an iridium anomaly 921 23 pg g is observed at the top of the ripple beds our observations at the mimbral locality support the hypothesis of a k t impact on nearby yucatan

a new seismic stratigraphy in the indian atlantic ocean gateway resembles major paleo oceanographic changes of the last 7 ma the exchange of water masses between the indian ocean and the atlantic constitutes an integral interocean link in the global thermohaline circulation long term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late miocene onward here we present results from international ocean discovery program site u1475 agulhas plateau located over a sediment drift proximal to the entrance of north atlantic deep water into the southern ocean and south indian ocean site u1475 comprises a complete carbonate rich stratigraphic section of the last 7 ma that provides an archive of climate induced variations in ocean circulation six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time the formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy prominent reflectors are related to late pleistocene glacial interglacial variability the middle and early pleistocene transitions and the onset of the northern hemisphere glaciation a peculiar early pliocene interval 5 3 4 0 ma bounded by two reflectors is characterized by fourfold elevated sedimentation rates 10 cm kyr and the occurrence of sediment waves we argue that this enhanced sediment transport to the agulhas plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of north atlantic deep water

development of framboidal pyrite during diagenesis low grade regional metamorphism and hydrothermal alteration distribution patterns microstructural relationships and compositional variations for framboidal pyrite in the paleozoic sedimentary host rocks to gold deposits on the northern carlin trend nevada and at fosterville in central victoria collectively demonstrate that it is not all of synsedimentary early diagenetic origin framboidal pyrite also nucleated in hydrothermal veins formed at several kilometers depth and along dissolution surfaces stylolites and crenulation cleavages formed during metamorphism at up to anchizonal grade i e prehnitepumpellyite facies there are no obvious differences in either the size range or internal morphology of framboids formed in these various settings suggesting that a single relatively simple crystallization path may operate over a wide depth range in the upper crust at fosterville anomalously metal rich including au framboidal pyrite is most abundant adjacent to laminated shear veins that developed by slip along bedding surfaces during folding of the sedimentary host rocks microstructural relationships and pb isotope compositions for the framboidal pyrite and other similarly distributed early formed sulfides support development in response to the localized episodic influx of metal enriched h 2s bearing hydrothermal fluids during regional deformation between 440 and 400 ma these findings may have implications for other similarly deformed metasedimentary successions where the discovery of au bearing framboidal pyrite has recently been cited as evidence for significant au enrichment during sedimentation 2009 society of economic geologists inc

isotopic comparison of k t boundary impact glass with melt rock from the chicxulub and manson impact structures the discussion of candidate source craters for the catastrophic impact that occurred at the boundary between the cretaceous and tertiary periods k t boundary has recently centred on two buried craters the chicxulub in mexico 200 km diameter and the manson in iowa 35 km diameter both of which have 40ar 39ar ages of 65 myr indistinguishable from that of impact glass spherules found in k t boundary sediments1 4 here we report the strontium neodymium and oxygen isotopic compositions of core samples of impact melt rock recovered from drill holes into both the chicxulub and manson craters and compare these with previously published isotopic data for impact glasses from the k t boundary of the beloc formation in haiti5 7 the chicxulub melt rocks are isotopically indistinguishable from the k t impact glass strongly supporting the proposition that chicxulub is a source crater for the k t catastrophe the manson melt rocks by contrast have a clearly different isotopic composition strongly suggesting that they are unrelated to the k t impact spherules

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