atlantic paleogene biserial heterohelicid foraminifera and oxygen minima through most of the paleogene the planktonic foraminifera called biserial heterohelicids record the most depleted carbon isotope ratios among planktonic foraminiferal species they are interpreted to occupy an oxygen minimum habitat stronger interplanktonic carbon isotope contrasts and more enriched near surface carbon isotope values correspond to higher abundances of biserial heterohelicids this group appears to have preferred latitudes and times when the oxygen minimum was well developed biserial heterohelicid generic and specific diversity are directly related to the interplanktonic carbon isotope contrast minimal specific diversity characterizes the oligocene when interplanktonic and surface to bottom carbon isotope contrasts were consistently low diversity and abundance decreases were coeval with increased oceanic ventilation

climatic control on the late permian main dolomite ca2 deposition in northern margin of the southern permian basin and implications to its internal cyclicity

geochemistry of central tethyan upper permian and lower triassic strata abadeh region iran nearly 2 km of upper permian to lower triassic limestones are exposed in the hambast mountain abadeh region iran lime mud matrix and most bioclasts of permian age are recrystallized into large calcite crystals and contain 600 4000 ppm sr suggesting a probable aragonite precursor low bulk rock 18 o values 7 to 10 pdb and recrystallized textures are also indicative of diagenetic alteration within the murghabian and abadehian two gradual upward increases in carbonate and organic matter 13 c compositions each roughly 3 pdb in magnitude are documented both are attributed to increased organic productivity and sequestration of organic matter in sediments within the julfian and across the permian triassic p t boundary two sharp upward decreases in carbonate and organic matter 13 c values each 4 pdb in magnitude are observed both are best explained by mixing of a deep water mass having low 13 c values and a shallow water mass having high 13 c compositions early triassic 13 c values initially low 1 pdb increase to 3 pdb within 100 m above the p t boundary variations in 13 c compositions of carbonate and organic matter and changes in 13 c 13 ccar 13 corg indicate that early triassic 13 c values were controlled by productivity cycles

vulnerability of coral reefs to bioerosion from land based sources of pollution ocean acidification oa the gradual decline in ocean ph and co32 caused by rising levels of atmospheric co2 poses a significant threat to coral reef ecosystems depressing rates of calcium carbonate caco3 production and enhancing rates of bioerosion and dissolution as ocean ph and co32 decline globally there is increasing emphasis on managing local stressors that can exacerbate the vulnerability of coral reefs to the effects of oa we show that sustained nutrient rich lower ph submarine groundwater discharging onto nearshore coral reefs off west maui lowers the ph of seawater and exposes corals to nitrate concentrations 50 times higher than ambient rates of coral calcification are substantially decreased and rates of bioerosion are orders of magnitude higher than those observed in coral cores collected in the pacific under equivalent low ph conditions but living in oligotrophic waters heavier coral nitrogen isotope 15n values pinpoint not only site specific eutrophication but also a sewage nitrogen source enriched in 15n our results show that eutrophication of reef seawater by land based sources of pollution can magnify the effects of oa through nutrient driven bioerosion these conditions could contribute to the collapse of coastal coral reef ecosystems sooner than current projections predict based only on ocean acidification

the stratigraphic distribution of ni rich spinels in cretaceous tertiary boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122 abstract ni rich spinels have been found throughhout the world at the cretaceous tertiary boundary these minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris suggesting that the cretaceous tertiary boundary spinels result from an extraterrestrial event their stratigraphic distribution which has been observed at the cretaceous tertiary boundary sites of el kef tunisia caravaca spain and hole 761c odp leg 122 indian ocean are markedly different from site to site and are all much less extended than the ir anomalies regional differences in ni rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions the wider stratigraphic dispersion of ir is attributed to postdepositional chemical processes at el kef the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate the 1 2 mm thick ni rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years this upper limit is consistent only with the collision of an asteroid or a comet at the close of the cretaceous

dinoflagellate cysts sea level changes and planktonic foraminifers across the cretaceous tertiary boundary at el haria northwest tunisia abstract dinoflagellate cysts and planktonic foraminifers have been studied from the cretaceous tertiary k t boundary interval at el haria northwest tunisia a high resolution integrated biostratigraphy is presented the k t boundary is drawn at the level of extinction of cretaceous planktonic foraminifers and is coincident with the first occurrence of the dinoflagellate cyst species danea californica the final extinction of planktonic foraminifers is foreshadowed by a reduction in their total abundance some 5 kyr earlier at the base of the boundary clay this reduction is coeval with reported anomalies in siderophyle elements and 13 c values in the same area dinoflagellate cysts do not show accelerated rates of extinction at k t time associations of dinoflagellate cysts however change drastically and parallel changes in relative numbers of sporomorphs spores and pollen and in the quantity of land derived organic matter jointly these changes reflect a rapidly falling sea level during the final 17 kyr of the mesozoic which culminates at the level of the k t boundary this steep sea level fall at k t time represents a peak regressive pulse at the end of the well documented latest cretaceous regressive trend this short term sea level fall might show to be a wide spread phenomenon which could have caused an excess shrinking of the already reduced areal extent of marginal seas since deep waters in cretaceous oceans were primarily produced in shallow marginal seas the rate of formation of deep water might have been minimized at k t time minimum rates of formation of deep water might have curtailed the slow upward mixing of relatively cool and nutrient rich deeper water through which the thermocline weakened and surficial waters became depleted in nutrients consequently phytoplankton productivity rapidly diminished which in combination with a weakened thermal gradient pushed the highly depth stratified cretaceous planktonic foraminiferal fauna to extinction over a period of time of some 5 kyr guembelitria cretacea was the sole planktonic foraminifer which could accommodate to the low productivity conditions the oscillating rise in sea level at the beginning of the cenozoic reinforced the upward mixing of relatively cool and nutrient rich deeper water steepened the thermocline and replenished the photic layer with nutrients concomitant niche differentiation in the photic layer progressively stimulated morphological innovation amongst early cenozoic planktonic foraminifers the final return of normally sized planktonic foraminifers and of stable and well balanced dinoflagellate cyst associations at about 125 kyr after the k t boundary seems to indicate that primary productivity and niche differentiation in the photic layer begin to revert to optimum levels the earliest cenozoic planktonic foraminiferal species globoconusa minutula and parvularugoglobigerina fringa are thought to have developed from a benthic foraminiferal species rather than having a planktonic ancestry

mass mortality and its environmental and evolutionary consequences the latest mesozoic and earliest tertiary sediments at deep sea drilling project site 524 provide an amplified record of environmental and biostratographic changes at the end of cretaceous closely spaced samples representing time intervals as short as 102 or 103 years were analyzed for their bulk carbonate and trace metal compositions and for oxygen and carbon isotopic compositions the data indicate that at the end of cretaceous when a high proportion of the ocean9s planktic organisms were eliminated an associated reduction in productivity led to a partial transfer of dissolved carbon dioxide from the oceans to the atmosphere this resulted in a large increase of the atmospheric carbon dioxide during the next 50 000 years which is believed to have caused a temperature rise revealed by the oxygen isotope data the lowermost tertiary sediments at site 524 include fossils with cretaceous affinities which may include both reworked individuals and some forms that survived for a while after the catastrophe our data indicate that many of the cretaceous pelagic organisms became extinct over a period of a few tens of thousands of years and do not contradict the scenario of cometary impact as a cause of mass mortality in the oceans as suggested by an iridium anomaly at the cretaceous tertiary boundary

nearshore euxinia in the photic zone of an ancient sea part ii the bigger picture and implications for understanding ocean anoxia abstract biomarker palaeontological and isotopic evidence suggests that the late permian carbonate seas i e the northern npb and southern spb permian basins of northern pangea were characterized by significant spatial and temporal variations in the palaeowater column redox state this is particularly the case with regard to the deposition of the lopingian zechstein cycle 2 carbonate rocks a shelf to basin reconstruction of environmental conditions was achieved by analysing nearly 400 core samples from 49 wells this allowed an evaluation of the spatial variations in facies and broad oceanographic conditions at the basin scale specifically in the lower slope and shallow basin facies of the northern margin of the spb present day northern poland and eastern germany highly variable concentrations of the green sulphur bacterial biomarkers chlorobactane and isorenieratane and their likely degradation products c 15 to c 31 2 3 6 aryl isoprenoids indicative of photic zone euxinia and homohopane indices indicative of anoxia combined with the presence of a benthic fauna and bioturbation indicate a variable but occasionally anoxic euxinic water column locally in lagoonal facies in the northern and southern margin of the spb euxinic conditions also developed but these were likely associated with localised conditions or benthic production in association with microbialites the presence of gammacerane in the eastern spb south eastern germany and eastern poland suggests elevated salinities there compatible with the restricted configuration of the basin however a lack of these signatures in basinal settings of the eastern spb indicates that strongly reducing conditions were restricted to the lower slope and shallow basin locations and restricted lagoons and were not developed in the basin centre moreover this anoxia euxinia in marginal settings is restricted to the north eastern part of the spb the south eastern part of the spb se poland in contrast is devoid of evidence for pze the southern margin of the spb is also characterized by generally oxic suboxic conditions with local anoxia limited to more restricted embayments and elevated salinities limited to restricted oxic anoxic lagoons in the western spb ne england and adjacent offshore and the npb outer moray firth offshore scotland the water columns were oxic suboxic overall it appears that high but episodic primary bioproductivity of organic matter was concentrated on or even limited to the lower slopes of the spb s north eastern margin and the restricted lagoons and shallow basin of its southern margin leading to the formation of source rocks for petroleum in these areas in addition the temporal and geographical restriction of anoxia appears to have prevented the accumulation of large and more widespread quantities of organic matter in fact toc contents exhibit a poor correlation with ecological and anoxia indicators crucially this work confirms that the strong evidence for pze observed in shelf and lower slope shallow basin facies of the north eastern spb need not be associated with widespread basin scale anoxia this conclusion has implications for organic matter burial carbon cycling and biotic crises during other times in earth history

growth rate and stable isotopic character of modern stromatolites from san salvador bahamas abstract 14 c 18 o and 13 c stratigraphies were measured on the successive carbonate crusts within large mushroom shaped stromatolitic heads from hypersaline storrs lake san salvador bahamas and also on the finely laminated soft sediment that enclose them 14 c dates show that the carbonate layers in these stromatolites range in age from 2310 70 years b p at the base to modern at the surface this suggests that the heads develop at an overall rate of 16 cm 1000 yr because there are 1 5 macroscopic laminae per cm less than one crustose layer is preserved in the heads per decade thin section examination of the crusts reveals numerous discontinuous micro unconformities which suggest multiple intervals of accretion and erosion these factor complicate any history of slow growth that may occur values of 18 o in the carbonates suggest that the heads were formed in waters with isotopic and temperature conditions similar to those that presently exist in the lake however carbonate 13 c values from the heads and sediments vary over 7 5 1 2 0 pdb and are significantly out of equilibrium with atmospheric co 2 the fluctuations in the 13 c values within the heads could not be correlated between adjacent heads nor with adjacent sediment on the basis of 14 c ages thus the sampled macroscopic layers mm cm in these calcified stromatolites do not appear to be recording simultaneous basin wide events but rather local diagenetic effects and micro environmental conditions in or under the microbial mats these data do not encourage basin wide interpretations of isotopic stratigraphies observed within ancient stromatolites where independent chronologies like 14 c are not available

high resolution holocene environmental changes in the thar desert northwestern india sediments from lunkaransar dry lake in northwestern india reveal regional water table and lake level fluctuations over decades to centuries during the holocene that are attributed to changes in the southwestern indian monsoon rains the lake levels were very shallow and fluctuated often in the early holocene and then rose abruptly around 6300 carbon 14 years before the present 14c yr b p the lake completely desiccated around 4800 14c yr b p the end of this 1500 year wet period coincided with a period of intense dune destabilization the major harrapan indus civilization began and flourished in this region 1000 years after desiccation of the lake during arid climate and was not synchronous with the lacustral phase

solutions in chronostratigraphy the paleocene eocene boundary debate and aubry vs hedberg on chronostratigraphic principles abstract in several recent papers m p aubry et al have argued that hedbergian principles of chronostratigraphy are being violated by the international commission on stratigraphy ics when selecting global stratotype sections and points gssps for the formal divisions of the geological time scale the current debate over the definition of the paleocene eocene p e boundary has been a major focus of their arguments unfortunately aubry et al have obscured matters by misusing the term unit stratotype and by equivocally using the term stage for the very different concepts of synthem and global chronostratigraphic stage the p e boundary option most repugnant to aubry et al carbon isotope excursion cie p e thanetian ypresian boundary is perfectly compatible with h d hedberg s views in contrast another option preferred by aubry et al recognition of new 1 m y duration age stage between thanetian and ypresian is inconsistent with hedberg s views additional problems with the p e boundary arguments of aubry et al include the fact that a ypresian unit stratotype does not exist the fact that the base of the ypresian synthem is not immutable and the fact that the nannofossil tribrachiatus digitalis is of dubious relevance to the boundary debate as for chronostratigraphy in general aubry et al have misrepresented hedberg s views by 1 falsely claiming that the content of a stage is what determines its boundaries 2 misunderstanding the general concept of the boundary stratotype 3 distorting the base defines boundary principle 4 falsely claiming that traditional pre gssp chronostratigraphic boundaries cannot be changed 5 falsely implying that traditional stage unit stratotype boundaries can be adjusted by no more than 300 000 years when defining formal age stage boundaries with gssps 6 falsely claiming that the definition of a geochronologic chronostratigraphic boundary should precede its correlation 7 claiming that traditional unconformable stage boundaries may be suitable horizons for gssps 8 distorting the meaning of arbitrariness in regard to the definition of geochronologic chronostratigraphic boundaries and 9 claiming that gssps are inherently unstable in that they are subject to redefinition whenever a more powerful element of correlation is discovered if taken seriously the unit stratotype sanctifying chronostratigraphic philosophy of aubry et al would require the creation of perhaps dozens of new phanerozoic ages stages of relatively very short duration wherever there was a significant gap between two successive historical stage unit stratotypes for all of these reasons the arguments of aubry et al have no merit

coral macrobioerosion is accelerated by ocean acidification and nutrients author posting the author s 2014 this is the author s version of the work it is posted here by permission of geological society of america for personal use not for redistribution the definitive version was published in geology 43 2015 7 10 doi 10 1130 g36147 1

differential dissolution modification of late pleistocene oxygen isotope records in the western equatorial pacific deep sea records of the pacific ocean show dramatic variations in the dissolution intensity of calcium carbonate through the late pleistocene extremes are characterized by much depressed dissolution intensity during deglaciation preservation spikes and much enhanced dissolution intensity during ice growth dissolution spikes increased dissolution intensity at dissolution spikes distorts 18o records by preferential removal of 16o rich shells resulting in heavier 18o values at these sections the 18o values tend to remain unaltered at deglacial preservation spikes thus the fluctuations of carbonate dissolution intensity modify the late pleistocene oxygen isotope records in such a fashion that apparent climate optima as defined by the lightest 18o values tend to shift toward preservation spikes while apparent glacial maxima characterized by the heaviest 18o values shift toward dissolution spikes

some comparative marine chemistries of rhenium gold silver and molybdenum abstract four metals re au ag and mo whose dissolved forms in seawater can potentially be reduced to insoluble states have been measured in a variety of solids depositing under anoxic conditions hydrothermal sulfides coastal sediments and phosphorites for comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions rhenium appears to be a unique sentinel for identifying reducing depositional environments where enrichments of greater than three orders of magnitude above crustal concentrations are found molybdenum follows re in these sediments but mo is enriched also in those that accumulate under oxidizing conditions the reported mo crustal concentrations appear low in comparison to our measured sedimentary values gold and ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements coastal sediments adjacent to a domestic outfall of los angeles california contain extraordinary high accumulations of anthropogenic au ag and pt the study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle further anthropogenic contributions to their sedimentary concentrations are identified

extended cretaceous tertiary boundary extinctions and delayed population change in planktonic foraminifera from brazos river texas high resolution planktonic foraminiferal analysis of three brazos river sections indicates a nearly continuous cretaceous tertiary k t boundary sedimentary record second only to the world s most complete record at el kef tunisia species extinctions occur over an extended period of time and with two major extinction episodes the first extinction episode with 46 of the species extinct occurs at and just below 10 15 cm a short hiatus at the base of a sandy shell hash and clay sand unit which was interpreted by bourgeois et al 1988 to represent a tsunami bed generated by the k t boundary bolide impact the top of this tsunami bed is about 17 20 cm below the k t boundary as defined by the first appearance of tertiary planktonic foraminifera the second extinction phase with 45 of the species extinct occurs 25 cm above the k t boundary zone p0 p1a boundary of the remaining seven surviving cretaceous species six gradually disappear during planktonic foraminiferal subzones p1a and basal p1b no species extinctions or major faunal assemblage changes are directly associated with the k t boundary iridium distribution is ambiguous with one peak in the upper part of the tsunami bed and a second peak at the micropaleontologically defined k t boundary relative abundances of dominant species are stable through the late maastrichtian and only minor abundance changes coincide with the first extinction episode or the k t boundary the first major faunal change in the dominant species group coincides with the second extinction episode and leads to decline and eventual extinction of this group in subzone p1a species disappearing at the two extinction episodes 46 and 45 constitute only a small percentage 8 and 5 of the individuals of the total planktonic foraminiferal population this suggests that weakened species with low numbers of individuals and sensitive to relatively minor environmental changes were primarily affected by these extinction episodes magnetostratigraphy indicates that the first extinction phase began about 310 000 years before the k t boundary and the second extinction phase occurred 50 000 years after the k t boundary this stepped pattern of species extinctions suggests a progressively stressed ecosystem in continental shelf settings which may be related to an observed sea level regression and global cooling the hypothesis of a global catastrophic mass extinction at the k t boundary caused by a large extraterrestrial impact is not supported by the brazos river planktonic foraminiferal data

holocene paleoclimates of india we present a comprehensive summary of the available palaeoclimate records from india and compare the results from different proxies the results indicate i fluctuating lake levels during the early holocene the period of relatively higher lake levels from increased precipitation efficiency was reached only 7 2 6 0 cal kyr bp possibly due to increased contribution from winter rainfall ii the onset of aridity in nw india could have begun as early as 5 3 cal kyr bp subsequently there were multiple wet events but of shorter duration and smaller magnitude than during the mid holocene iii there is evidence of several short term climate events in the proxy record however in the absence of a rigorous chronological framework a detailed regional correlation is not possible at this stage finally a comparison between marine and terrestrial records indicates that episodes of strongest and weakest monsoon winds were not always associated with wettest and driest episodes respectively in the nw indian lakes

drivers of pco2 variability in two contrasting coral reef lagoons the influence of submarine groundwater discharge the impact of groundwater on pco2 variability was assessed in two coral reef lagoons with distinct drivers of submarine groundwater discharge sgd diel variability of pco2 in the two ecosystems was explained by a combination of biological drivers and sgd inputs in rarotonga a south pacific volcanic island 222rn derived sgd was driven primarily by a steep terrestrial hydraulic gradient and the water column was influenced by the high pco2 5501 atm of the fresh groundwater in heron island a great barrier reef coral cay sgd was dominated by seawater recirculation through the sediments i e tidal pumping and pco2 was mainly impacted through the stimulation of biological processes the rarotonga water column had a higher average pco2 549 atm than heron island 471 atm however pco2 exhibited a greater diel range in heron island 778 atm than in rarotonga 507 atm the rarotonga water column received 29 0 8 2 mmol free co2 m 2 d 1 from sgd while the heron island water column received 12 1 4 2 mmol free co2 m 2 d 1 over the course of this study both systems were sources of co2 to the atmosphere with sgd derived free co2 most likely contributing a large portion to the air sea co2 flux studies measuring the carbon chemistry of coral reefs e g metabolism and calcification rates may need to consider the effects of groundwater inputs on water column carbonate chemistry local drivers of coral reef carbonate chemistry such as sgd may offer more approachable management solutions to mitigating the effects of ocean acidification on coral reefs

paleoceanography of the cretaceous tertiary boundary event inferences from stable isotopic and other data we report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction whole rock and benthic foraminifers caco3 and coarse fraction percentage determinations and trace element sr analyses on carbonate constituents across the cretaceous tertiary k t boundary in deep sea drilling project dsdp sites 47 2 356 384 and 577 and compare them with published results from k t boundary sections in other dsdp sites we used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study the 18o data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late maestrichtian followed by somewhat fluctuating temperatures in the early paleocene however there is no indication of either a significant warming or cooling at or following the k t boundary several sites do exhibit somewhat heavier 18o values by about 0 5 across the boundary which might suggest a 2 3 c cooling at most however we interpret these somewhat heavier 18o values as reflecting slightly better preservation of 18o of carbonate constitutents in relatively clay rich intervals e g lower diagentic potential characteristic of the k t boundary the 13c values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary the surface water and deepwater 13c values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest paleocene are consistent with a major decrease in productivity across the k t boundary the decrease in caco3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters the low productivity episode lasted at least 1 m y beyond the k t boundary crisis suggesting that hypothesized catastrophic events alone such as impact of an apollo object are not the only explanation for the observed long term decrease in productivity there is also an indication in the 13c curves from several sites that the surface water 13c decrease began in the latest maestrichtian suggesting that the decrease in productivity may have been independent of a hypothesized impact event

ecology and paleoecology of triserial planktic foraminifera guembelitrinidae are a group of small sized planktic foraminifera that ranges from the middle cretaceous to the present in this paper we discuss the morphology and stratigraphic distribution of triserial planktic foraminifera and establish the ecology of the living ones to draw parallels with fossil counterparts in surface water plankton pump samples 0 5 m from the north indian ocean the modern representativegallitellia vivans cushman has its highest relative frequencies south of india where upwelling waters cause highly variable conditions on the outer shelf oxygen isotope analysis on specimens from a core taken in the banda sea indonesia indicates thatg vivans belongs to the planktic community and that in open marine circumstances it lives inbetween the surface dwellersglobigerinoides trilobus reuss andglobigerina bulloides d orbigny and the deep dwellinggloborotalia menardii d orbigny similar habitats can be deduced for fossil guembelitrinidae the triserials can live in environments with variable or extreme conditions as exemplified byguembelitria cretacea cushman which is one of the few cretaceous planktic foraminiferal species that survived the cretaceous tertiary boundary event for the most part open ocean sediments contain few specimens but triserials may be common to abundant in assemblages from sediments that represent unstable marine conditions e g el kef tunisia presumed gaps in the stratigraphic range of triserial planktics appear to be a sampling artifact caused by their patchy geographic distribution and their small size only very rare specimens are present in the 63 m fraction we foundguembelitria cretacea to be present in the 45 63 m fraction of coniacian santonian and campanian sediments of a section near el kef tunisia an extensive search of the small sized fractions 63 125 m of samples from various localities and ages showed that the range ofgallitellia vivans can be extended into the late pliocene as a part of this stratigraphic study a new species guembelitria turrita kroon and nederbragt is described from upper campanian lower maastrichtian sediments

new insights on the dissolved platinum behavior in the atlantic ocean abstract the water column profiles of dissolved pt were determined in samples taken during the geotraces ga02 section at three stations located in the north central and south west atlantic ocean average concentrations obtained in this study for dissolved pt 0 22 0 04 pm n 59 are in agreement with the only previous dataset for the atlantic ocean reported in the early nineties however results presented here do not show invariant concentrations with depth as previously indicated for the atlantic and recently reported for the pacific ocean instead these new data suggests that i atmospheric inputs can account for the observed pt enrichment in surface waters of the north west atlantic ii conservative mixing control the pt distribution in deep 1000 m waters and iii oxygen may play a major role on the pt distribution in the oceans since similar trends of pt with dissolved oxygen were observed with pt depletion at water depths of maximum oxygen utilization there is still however important open questions on the bio geochemistry of pt in natural waters including the redox behavior of the pt ii pt iv couple and its impact on particle inorganic and or biogenic reactivity which impedes a better characterization of the observed distribution in this study also potential analytical artifacts that could be behind the differences in the pt distributions observed for the different ocean basins must be further explored this article is part of a special issue entitled cycles of trace elements and isotopes in the ocean geotraces and beyond edited by tim m conway tristan horner yves plancherel and aridane g gonzalez

cretaceous tertiary boundary extinction pattern and faunal turnover at agost and caravaca s e spain abstract planktonic foraminiferal extinctions at caravaca and agost occurred over an extended time period similar to el kef and brazos river some species disappeared well below the boundary about 39 45 of the species but less than 15 of the individuals in the population became extinct at or near the k t boundary a second phase of extinction occurred at the top of the boundary clay po pla and the remaining cretaceous species except g cretacea disappeared in subzone pla species extinctions were selective eliminating geographically restricted large complex and deeper dwelling forms first and favoring survival of cosmopolitan small simple surface dwellers only surface dwellers survived the k t boundary event whereas all deeper dwelling species as well as some surface dwellers disappeared at the boundary we interprete the selective abundance decline during the latest cretaceous as a result of the seal level regression that reached a maximum just prior to the k t boundary the highly selective nature of the two phased species extinctions at and above the boundary we believe to be related to the major reduction in surface productivity and the breakdown in the water mass stratification that was associated with the rapid sea level transgression across the k t boundary a bolide impact however may have hastened the demise of an already declining cretaceous fauna

aerial infrared imaging reveals large nutrient rich groundwater inputs to the ocean 1 regional high resolution 0 1 c 0 5 m low altitude thermal infrared imagery tir reveals the exact input locations and fine scale mixing structure of massive cool groundwaters that discharge into the coastal zone as both diffuse flows and as 30 large point sourced nutrient rich plumes along the dry western half of the large volcanic island of hawaii these inputs are the sole source of new nutrient delivery to coastal waters in this oligotrophic setting water column profiling and nutrient sampling show that the plumes are cold buoyant nutrient rich brackish mixtures of groundwater and seawater by way of example we illustrate in detail one of the larger plumes which discharges ca 12 000 m3 d 1 ca 8 600 m3 d 1 freshwater rates comparable in volume to high flux groundwater outputs in better known tropical karst terrains we further show how nutrient mixing trends may be integrated into tir sea surface temperatures to produce surface water nutrient maps of regional extent

post depositional mobility of platinum iridium and rhenium in marine sediments the discovery of high concentrations of iridium in cretaceous tertiary boundary sediments engendered the hypothesis1 that a meteorite collided with the earth 65 million years ago coincident with the mass extinction that occurred at that time iridium spikes of various magnitudes have subsequently been reported at more than 10 other extinction horizons2 11 it has been suggested on the other hand that geochemical processes might create or modify many of these spikes5 11 4 but a critical evaluation of these suggestions has been hindered by incomplete understanding of low temperature iridium geochemistry other platinum group elements ru rh pd re os pt au are often found to be associated with ir spikes and inter element ratios have been used to assess the cosmic or terrestrial nature of the enrichments5 7 9 28 29 but the geochemical influences on these relative abundances are also poorly constrained here we describe analyses of recent abyssal marine sediments which allow us to characterize the behaviour of pt re and ir during early diagenesis these elements are redistributed by changes in sedimentary redox conditions such changes can probably account for many of the small platinum group element spikes found in the geological record and may render ambiguous attempts to interpret inter element ratios

stable isotope toc and caco3 record across the cretaceous tertiary boundary at el kef tunisia we report the results of stable oxygen and carbon isotope analysis of carbonate fine fraction and benthic and planktic foraminifers caco3 and toc determinations of sediments across the cretaceous tertiary k t boundary at el kef tunisia we used grain size analysis of the fine fraction carbonate to determine possible compositional effects and smearslide and scanning electron microscope examinations to evaluate possible diagenetic alteration and microfossil preservation the data suggests the following sequence of events upper maastrichtian oxygen and carbon isotope signals indicate relatively warm temperatures a decreasing thermal gradient possibly related to a shallowing sea and relatively high surface water productivity a sharp cooling appears to begin just below the k t boundary the k t boundary is characterized by a sudden 2 negative shift in fine fraction 13c a slight 0 6 enrichment in benthic 13c and a reduction of about 40 in caco3 sedimentation these data imply strongly reduced surface water productivity as also observed in numerous deep sea sequences worldwide the lower danian planktic foraminiferal zones p0 p1a is marked by generally low productivity and unstable environmental conditions as indicated by generally low but fluctuating fine fraction 13c values and low 5 15 carbonate deposition at the base of subzone p1b caco3 benthic and fine fraction 13c values increase gradually and reach near pre k t boundary levels in subzone p1c indicating initial recovery after the k t boundary event about 300 000 400 000 years after the k t boundary the prolonged low productivity episode after the k t crisis and the pre k t boundary cooling associated with a major reduction in planktic foraminiferal diversity are difficult to explain by a single k t boundary bolide impact

geochemistry of campanian maastrichtian brachiopods from the rordal 1 core denmark differential responses to environmental change and diagenesis abstract past marine environmental conditions can be reconstructed from geochemical signatures of both benthic and planktic organisms and particularly brachiopods have been extensively used for this purpose however it is seldom possible to investigate the links between environmental conditions and shell geochemistry in monospecific records over extended periods of time here we present geochemical data from the 100 m thick brachiopod rich upper campanian upper maastrichtian chalk 73 8 68 6 ma of the rordal 1 drill core northern denmark two species that lived attached to small substrate argyrotheca bronnii roemer and gisilina jasmundi steinich and one secondarily free living species magas chitoniformis schlotheim have been studied for element concentrations as well as c and o isotope signatures each species has a unique chemical signature with m chitoniformis showing lowest mg and mn concentrations a bronnii the highest mn concentrations and g jasmundi the highest sr concentrations all three species display decreasing mg ca ratios throughout the studied interval and distinct mn enrichments in the campanian maastrichtian boundary cmb interval in the campanian part of the succession the three species are slightly enriched in 13 c median 13 c values of 0 0 to 0 5 and 18 o median 18 o values of 0 3 to 0 6 with respect to coeval chalk in the course of the maastrichtian the two attached species acquire progressively lighter isotopic compositions with a bronnii reaching 13 c and 18 o values 1 0 lower than coeval chalk the secondarily free living species m chitoniformis on the other hand becomes isotopically heavier and reaches 13 c and 18 o enrichments of 1 0 at the top of the core the observed differences between the species illustrate species specific signatures of biomineralisation diagenesis and response to environmental change this geochemical complexity illustrates that a comprehensive geochemistry based picture of the late cretaceous chalk sea can only be painted using detailed multi species and multi proxy datasets

platinum and the platinum anomaly in the marine environment abstract platinum is markedly enriched over palladium in ferromanganese minerals compared to seawater concentrations of these two elements this anomalous behavior similar to that of cerium in the rare earth series is attributed to the oxidation of platinum from the dissolved divalent state in seawater to the tetravalent state during mineral formation the platinum to palladium weight ratio in seawaters is around 4 5 in marine sediments around 1 and in ferromanganese nodules between 50 and 1000 platinum similar to palladium shows a nutrient type profile in seawater

dissolved platinum in major rivers of east asia implications for the oceanic budget 1 dissolved platinum concentrations of eleven large pristine river systems in east asia 200 samples were determined to better constrain the oceanic platinum budget most samples had concentrations less than 1 4 pm relatively high concentrations up to 5 8 pm were measured in only approximately 6 of the samples the median pt concentrations of the individual river systems had only a small range from 0 18 pm duman to 0 63 pm huang he and the difference in pt yield mainly resulted from the difference in runoff the rivers draining the eastern tibetan plateau the salween mekong chang jiang yangtze hong red and huang he yellow had higher pt yield than the rivers of the russian far east the amur lena yana indigirka and kolyma if the discharge weighted mean pt concentration of our samples 0 36 pm is extrapolated globally the estimated riverine flux of dissolved pt to the ocean is 13 103 mol y 1 based on this riverine flux the estimated oceanic residence time of pt is 24 10 kyrs a 50 release and 50 uptake of pt in estuaries would modify this to 16 kyrs and 45 kyrs respectively

south pacific evidence for the long term climate impact of the cretaceous paleogene boundary event abstract the cretaceous paleogene k pg boundary is well represented across a range of depositional settings in new zealand trends in fossil assemblages and marine lithofacies indicate that the k pg event was followed by a pronounced and long term 1 myr perturbation in climate and ocean conditions these findings are supported by a tex86 derived sea surface temperature sst reconstruction across the k pg boundary at mid waipara river north canterbury the bayspar calibration indicates that sst was very stable in the uppermost cretaceous 20 c but abruptly warmed by 4 c in a 25 cm thick lowermost paleocene interval this interval is overlain by a 2 m thick interval in which sst abruptly cooled by 10 c and then progressively returned to 20 c the basal paleocene warm interval is associated with an acme in the dinoflagellate species trithyrodinium evittii and the succeeding cool interval is associated with an acme in palaeoperidinium pyrophorum biostratigraphic correlation of the shelfal mid waipara section to the pelagic k pg sections in marlborough reveals that a significant unconformity separates these two acme events with the t acme event occurring in the earliest paleocene and the p pyrophorum acme occurring 1 myr later and lasting 200 kyr a succession of dinoflagellate acme events within the intervening interval in the marlborough sections implies unstable climatic and environmental conditions in the lead up to the p pyrophorum acme and cooling event at 65 ma this event also coincides with a peak in biogenic silica accumulation in the marlborough sections we suggest that disruption to biogeochemical pathways at the k pg boundary caused long term climatic cooling in the southern pacific region

the distribution and geochemistry of platinum group elements as event markers in the phanerozoic abstract the discovery of the platinum group element pge enrichment in the cretaceous tertiary k t boundary impact layer popularized the use of pges as geochemical event markers and prompted an explosion of interest in these elements whose geochemical behavior is poorly understood instead of concentrating on the more easily analyzed pges e g iridium many studies now include the entire group analytical methods have been improved to the point where small samples 5 g can be analyzed confidently at the sub ppb level allowing the determination of the distribution of pges in the oceans atmosphere and biosphere the presence or absence of a pge anomaly is often used as a criterion for determining whether an event horizon is impact related however to date only the k t boundary yields a distinct pge anomaly with positive interelement correlations and solar interelement ratios terrestrial sources such as volcanic emissions are also being investigated as potential contributors to pge anomalies at other phanerozoic event horizons primary signatures e g interelement ratios characteristic of the pge source may be altered during various high and or low temperature processes for example fractionation during impact melting vaporization condensation remobilization redistribution and diagenesis can obscure original signatures and make determination of the pge source difficult future research might be directed towards establishing the behavior of the pges during such processes

stable isotopic fractionation among particles in quaternary coccolith sized deep sea sediments oxygen and carbon isotopic ratios of individual grain size splits of the 38 m fraction of deep sea carbonate particles vary systematically with size over a range of 1 25 4 0 most splits are dominated by just a few coccolith taxa and other types of particles the 18o and 13c values of individual splits are linearly related to each other with a slope of 1 5 13c 18o in all holocene and glacial samples analyzed although the observed variability is less than predicted from culture experiments of individual components compositional variations can significantly influence the stable isotopic stratigraphies measured on the nannofossil fraction

end cretaceous cooling and mass extinction driven by a dark cloud encounter abstract we have identified iridium in an 5 m thick section of pelagic sediment cored in the deep sea floor at site 886c in addition to a distinct spike in iridium at the k pg boundary related to the chicxulub asteroid impact we distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a co ir diagram calling it the extraterrestrial index f ex this new index reveals a broad iridium anomaly around the chicxulub spike any mixtures of materials on the surface of the earth cannot explain the broad iridium component on the other hand we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component especially if the molecular cloud has a size of 100 pc and the central density of over 2000 protons cm 3 kataoka et al 2013 2014 pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction solid particles from the hypothesized dark cloud would combine with the global environment of earth remaining in the stratosphere for at least several months or years with a sunshield effect estimated to be as large as 9 3 w m 2 the dark cloud would have caused global climate cooling in the last 8 myr of the cretaceous period consistent with the variations of stable isotope ratios in oxygen barrera and huber 1990 li and keller 1998 barrera and savin 1999 li and keller 1999 and strontium barrera and huber 1990 ingram 1995 sugarman et al 1995 the resulting growth of the continental ice sheet also resulted in a regression of the sea level the global cooling which appears to be associated with a decrease in the diversity of fossils eventually led to the mass extinction at the k pg boundary

the source of ions for biomineralization in foraminifera and their implications for paleoceanographic proxies the global carbon cycle is strongly perturbed by fossil fuel burning leading to atmospheric co2 increase climatic warming followed by polar ice melting and global sea level rise are predicted due to the greenhouse effect of increasing co2 in the atmosphere houghton et al 1995 the ocean plays a major role in neutralizing the excess co2 because the amount of inorganic carbon available for exchange with the atmosphere in the ocean is approximately 50 60 times larger than in the atmosphere e g siegenthaler and sarmiento 1993 the bulk of the atmospheric co2 excess will eventually be neutralized by caco3 dissolution in the deep marine environment this is however is a relatively slow process that operates on the time scale of ocean circulation 1000 yrs and is therefore causing an accumulation of co2 in the atmosphere this phenomenon will result in potentially severe consequences to the well being of global ecological systems obviously the scientific attention of many biogeochemists is focused on processes controlling the response of the marine system to changes in atmospheric co2 concentrations e g archer and maier reimer 1994 broecker 1997 sigman and boyle 2000 berger 2002 foraminifera corals and coccolithophores in the global carbon cycle there are four dominant processes involved in neutralizing the excess atmospheric co2 in the ocean these are 1 gas exchange at the air sea interface and reaction with the carbonate ion to form bicarbonate 2 net primary productivity 3 caco3 production and dissolution and 4 ocean circulation most of these processes are biologically mediated and may have special importance in shallow tropical environments where the exchange with the atmosphere is more direct in this review we address the mechanism of biomineralization in one of the major groups that precipitates caco3 in the ocean the foraminifera as we will show this group

ferromanganese nodules from manop sites h s and r control of mineralogical and chemical composition by multiple accretionary processes abstract the chemical composition of ferromanganese nodules from the three nodule bearing manop sites in the pacific can be accounted for in a qualitative way by variable contributions of distinct accretionary processes these accretionary modes are 1 1 hydrogenous i e direct precipitation or accumulation of colloidal metal oxides in seawater 2 2 oxic diagenesis which refers to a variety of ferromanganese accretion processes occurring in oxic sediments and 3 3 suboxic diagenesis which results from reduction of mn 4 by oxidation of organic matter in the sediments geochemical evidence suggests processes 1 and 2 occur at all three manop nodule bearing sites and process 3 occurs only at the hemipelagic site h which underlies the relatively productive waters of the eastern tropical pacific a normative model quantitatively accounts for the variability observed in nearly all elements zn and na however are not well explained by the three end member model and we suggest that an additional accretionary process results in greater variability in the abundances of these elements variable contributions from the three accretionary processes result in distinct top bottom compositional differences at the three sites nodule tops from h are enriched in ni cu and zn instead of the more typical enrichments of these elements in nodule bottoms in addition elemental correlations typical of most pelagic nodules are reversed at site h the three accretionary processes result in distinct mineralogies hydrogenous precipitation produces mno2 oxic diagenesis however produces cu ni rich todorokite and suboxic diagenesis results in an unstable todorokite which transforms to a 7 a phase birnessite upon dehydration the presence of cu and ni as charge balancing cations influence the stability of the todorokite structure in the bottoms of h nodules which accrete dominantly by suboxic diagenesis na and possibly mn 2 provide much of the charge balance for the todorokite structure limited growth rate data for h nodules suggest suboxic accretion is the fastest of the three processes with rates at least 200 mm 106 yr oxic accretion is probably 10 times slower and hydrogenous 100 times slower since these rates predict more suboxic component in bulk nodules than is calculated by the normative analysis we propose that suboxic accretion is a non steady state process variations in surface water productivity cause pulses of particulate flux to the sea floor which result in transient mn reduction in the surface sediments and reprecipitation on nodule surfaces

accretion of extraterrestrial matter during the last 80 million years and its effect on the marine osmium isotope record the flux of particulate extraterrestrial et matter to the deep sea has been calculated using a four component mixing model based on osmium concentrations and isotope ratios in slowly accumulating pelagic sediments from the pacific ocean nineteen published bulk leach osmium isotope data pairs that cover the last 80 million years have been used for the calculation the calculated annual particulate flux averaged over several 100 ka by slow accumulation and bioturbation ranges from 18 000 to 67 000 tons with a mean value of 37 000 13 000 tons the data indicate no significant variability in the flux with time except at the k t boundary and are thus compatible with results based on ir accumulation in deep sea sediments the inferred constancy of the et matter flux is in contrast to recent results based on the et 3he flux that integrates only a small size fraction of the entire et matter flux 3he data indicate variability by a factor of 6 over the past 70 ma and a fivefold increase in the et flux between 3 ma and 1 ma that is not seen in the bulk et matter flux based on osmium isotope data the apparent constancy of the cosmic matter flux over the past 80 ma stands in marked contrast to the dynamic nature of the marine osmium isotope record and indicates that dissolution of cosmic matter does not drive changes in this record except at the k t boundary a comparison between osmium isotope and ir data from two pelagic sediment cores from the pacific dsdp site 596 and ll44 gpc3 indicates that the seawater soluble fraction of et os cannot exceed 36 kg a and most likely is significantly smaller the maximum value of 36 kg a can account for approximately one half of the seawater soluble et matter flux necessary to balance the radiogenic continental runoff of os without any additional unradiogenic source simple mass balance calculations indicate that an additional unradiogenic source of os to the oceans most likely alteration of oceanic crust is required to balance the present day seawater osmium isotopic composition this source is probably more important in balancing radiogenic continental runoff than is dissolution of cosmic matter in seawater

late cretaceous to early paleocene climate and sea level fluctuations the tunisian record abstract climate and sea level fluctuations across the cretaceous tertiary k t transition in tunisia were examined based on bulk rock and clay mineralogies biostratigraphy and lithology in five sections el melah el kef elles ain settara and seldja spanning from open marine to shallow inner neritic environments late campanian to early danian trends examined at el kef and elles indicate an increasingly more humid climate associated with sea level fluctuations and increased detrital influx that culminates at the k t transition this long term trend in increasing humidity and runoff in the tethys region is associated with middle and high latitude cooling results of short term changes across the k t transition indicate a sea level lowstand in the latest maastrichtian about 25 100 ka below the k t boundary with the regression marked by increased detrital influx at el kef and elles and a short hiatus at ain settara a rising sea level at the end of the maastrichtian is expressed at elles and el kef by deposition of a foraminiferal packstone a flooding surface and condensed sedimentation mark the k t boundary clay which is rich in terrestrial organic matter the p0 p1a transition is marked by a sea level lowstand corresponding to a short hiatus at ain settara where most of p0 is missing and a period of non deposition and erosion in the lower part of p1a 64 95 ma at seldja p0 and possibly the topmost part of cf1 are missing these sea level fluctuations are associated with maximum humidity these data suggest that in tunisia long term environmental stresses during the last 500 ka before the k t boundary and continuing into the early danian are primarily related to climate and sea level fluctuations within this long term climatic trend the pronounced warm and humid event within the latest maastrichtian zone cf1 may be linked to greenhouse conditions induced by deccan volcanism the absence of any significant clay mineral variations at or near the k t boundary and ir anomaly suggests that the bolide impact had a relatively incidental short term effect on climate in the tethys region

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

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

mechanisms to explain the platinum concentration in ferromanganese seamount crusts abstract ferromanganese seamount crusts cover large areas of hard substrates of sea floor edifices in the central pacific they can be distinctly enriched in pt and show pt pd ratios which are several orders of magnitude greater than those orders of magnitude greater than those of seawater thirty four selected samples of the younger and the older crust generation were analyzed for mn fe ni co and pt the bulk pt concentration varies between 0 14 and 1 02 ppm and averages to 0 51 0 24 ppm the older generation is generally somewhat richer in pt 0 63 0 25 ppm than the younger one 0 39 0 15 ppm compared to the earth s upper continental crust the ferromanganese material contains about 100 times more pt in the studied depth range between 1100 and 3800 m the pt concentration is controlled by the water depth in addition to the bulk data the distribution of pt and pd is recorded through a complete ferromanganese crust profile the average pd value amounts to 16 2 8 ppb for the younger and 16 4 8 ppb for the older generation two immediate sources may be responsible for the pt concentration in the ferromanganese crusts seawater and cosmic spherules the presented thermodynamic approaches are based on the presumption that the pt tetrachlorocomplex is the prevailing species under seawater conditions precipitation of pt in seawater may take place if this complex is decomposed by reduction of pt 2 to the elemental state on the other hand the mno 2 precipitation is caused by oxidation of dissolved mn 2 ions which are supplied from the oxygen minimum zone a model reaction by combining the two half reactions is formulated assuming a coprecipitation of pt with mno 2 an alternative mechanism to explain pt enrichment in ferromanganese crusts might be surface adsorption of anionic pt tetrachloro complexes onto positively charged amorphous iron hydroxide particles cosmic spherules were discovered in samples of the older ferromanaganese crust generation the spherules are mostly concentrated in the upper part of this crust layer iron meteorites often have pt concentrations up to 20 ppm the relative quantity recovered in the grain size class 0 1 0 4 mm only amounts to 2 10 4 which is significantly too low to explain the pt content of the crust samples however smaller cosmic particles may exist and also contribute to the pt enrichment suggesting that rough crust surfaces are excellent collectors of denser detrital material the maximum pt values observed in the youngest part of the older crust generation may be explained by physical incorporation of cosmic particles

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

stable isotope and foraminiferal changes across the cretaceous tertiary boundary at stevns klint denmark arguments for long term oceanic instability before and after bolide impact event abstract stable isotope and planktic and benthic foraminiferal analyses of the k t boundary transition at stevens klint denmark indicate a 100 500 kyr long period of instability in oceanic bottom water temperature and sea level during the latest maastrichtian from 2 7 m below and up to the k t boundary bottom water temperatures gradually cooled about 1 5 c as surface water temperatures remained constant at the k t boundary bottom water temperatures decreased additionally 3 c and then returned to pre boundary values just above the boundary interval coincident with the onset of the first temperature decrease there was a prominent sea level fall estimated between 50 100 m as observed in benthic and planktic foraminiferal assemblages as well as in a decreasing surface to bottom 13 c gradient about 40 cm below the iridium rich k t boundary clay sea level began to rise poor preservation of foraminifera above the k t boundary allows only tentative interpretation of danian events at stevns klint however sea level generally continued to rise interrupted by short sea level falls associated with the observed sea level changes are three important hiatuses at the contact between the white chalk and overlying grey white bryozoan chalk about 2 7 m below the k t boundary at or near the top of the fish clay zone pla parvularugoglobigerina eugubina missing and at the contact of the cerithium limestone and overlying bryozoan limestone about 60 cm above the k t boundary part of zone plc missing these unconformities are coeval with hiatuses observed in many continental shelf sections and indicate a global eustatic rather than regional isostatic response notable is that at stevns klint the episode of oceanic instability is registered over approximately the same stratigraphic interval in which supposed extraterrestrial amino acids occur a circumstance that may indicate a connection a gradual positive shift in 13 c is registered in both benthic and planktic foraminiferal assemblages in the upper maastrichtian at stevns klint the positive shift is followed by a prominent negative 13 c shift 1 3 at the k t boundary an upper maastrichtian positive 13 c excursion followed by a negative 13 c anomaly at or near the k t boundary has previously been observed in deep sea cores from the pacific ocean and the weddell sea antarctica implying a global event previous suggestions of a relation between the uppermost maastrichtian positive 13 c excursion and sea level variation are not supported by the data for stevns klint

rhenium molybdenum and uranium in groundwater from the southern great basin usa evidence for conservative behavior abstract dissolved re mo and u concentrations and the concentrations of the major cations and anions were measured in groundwaters from twenty three springs in the southern great basin usa from june 1992 through march 1994 rhenium concentrations ranged from 5 1 pmol kg to 190 20 pmol kg the highest re values were observed in the saline groundwater of saratoga spring in death valley and cold spring in ash meadows whereas the lowest re concentrations were found in nevares spring in death valley the mean re concentration for all of the spring waters sampled is 44 33 pmol kg the concentrations of re differs dramatically for groundwaters that discharge from the regional paleozoic carbonate aquifer and for local groundwaters from felsic volcanic rocks the mean re concentration for groundwaters issuing from the carbonate aquifer is 37 14 pmol kg which is similar to the average re value reported for seawater i e 39 8 0 2 pmol kg whereas for the spring waters that discharge from the felsic volcanic aquifers the mean re concentration is 18 3 5 pmol kg the overall mean concentrations of u and mo in these groundwaters are 18 12 nmol kg and 120 60 nmol kg respectively differences in the u and mo concentrations for groundwaters from the carbonate aquifer and those from the volcanic aquifer are also observed such that the mean u and mo concentrations in the carbonate groundwaters are 13 5 nmol kg and 106 40 nmol kg respectively and the mean u and mo concentrations in the volcanic spring waters are 31 5 4 nmol kg and 94 12 nmol kg respectively by comparison u and mo concentrations reported for seawater are 13 9 nmol kg and 107 nmol kg respectively in the oxygenated groundwaters of the great basin re mo and u appear to be acting conservatively as in seawater as evidenced by the covariance observed between re mo and u with chloride sodium and sulfate groundwaters discharging from the regional carbonate aquifer in ash meadows typically exhibit a u re ratio of about 300 while groundwaters that discharge in death valley from local felsic volcanic sources have ratios of about 1700 waters in the remainder of the death valley springs are intermediate and may result from the mixing of the carbonate and volcanic derived waters the re mo and u concentrations in addition to the major solute chemistry indicates that dissolution of carbonate rocks is of primary importance in the groundwaters from ash meadows whereas the weathering of felsic volcanic rocks contributes substantially to the chemical signatures of the death valley groundwaters the differences between u re ratios and different aquifer materials suggest that there is a relationship between the dissolved u re ratios and the aquifer materials similar re mo u ratios for the groundwaters from the carbonate aquifer and seawater are strongly suggestive of quantitative uptake of these trace elements from seawater by carbonate mineral precipitation and subsequent quantitative release of these trace elements during dissolution of the carbonate rocks by groundwater the substantially larger salinity normalized re mo and u concentrations in the groundwaters compared to seawater rule out the possibility that these groundwaters represent simple mixing of dilute terrestrial waters and seawaters or reconstitution of evaporite deposits by groundwater dissolution

steep rock lake sedimentology and geochemistry of an archean carbonate platform abstract the 2800 ma mosher carbonate formation at steep rock lake in south central canada is one of earth s oldest limestone deposits it is both thick up to 500 m and relatively well preserved and was one of the first precambrian successions to be noted for evidence of early life it continues to provide information on the antiquity of such processes as photosynthesis the carbonate contains a variety of fabrics and facies from apparently fine grained bedded limestones with domal and columnar stromatolites atikokania radial fans and sheet cracks to closely packed metric scale hybrid domes of originally aragonite seafloor crust interlayered with fenestral fabric here we review previous work provide new observations concerning these sediments and their geochemistry and discuss the inception overall development and ultimate demise of the steep rock platform we divide the mosher carbonate into the lower hogarth member and upper elbow point member these units constitute a shallow water carbonate platform succession the hogarth member overlies eroded 3000 ma tonalite and is at least 120 m thick thin horizons of domal pseudocolumnar columnar and fenestral stratiform stromatolites and occasional layers of atikokania radial crystal fans occur within relatively fine grained thin bedded limestone with iron carbonate horizons in the upper part meter scale domes occur locally with sheet cracks and stromatactis the irregular laminae that build the small domal and columnar stromatolites are interpreted to be lithified mats and biofilms presumably cyanobacteria dominated fine grained well bedded facies of the lower hogarth member and its varied association of small stromatolites is interpreted to have accumulated in a relatively protected inner platform environment numerous very thin horizons of iron carbonate in the lower and upper parts of the hogarth member suggest temporally limited influence of iron rich offshore waters vertical trends in fe mn ba sr ce and 13 c probably reflect progressive restriction of circulation with at least one abrupt but short lived change back to more open seawater conditions the upper hogarth member with large banded domes and fenestral crusts and stromatolites is interpreted as back margin facies the overlying elbow point member is at least 70 m thick and appears to be entirely composed of innumerable juxtaposed elongate smooth and thickly layered domes lacking intervening sediment each dome is typically several meters across and composed of centimetric alternations of cuspate fenestral fabric possibly microbial and crystal fan fabric that is probably abiotic seafloor aragonite precipitate adjacent cuspate fenestral and crystal fan fabric show significant differences in concentration of 13 c sr ba fe and mn this giant dome facies is interpreted as a platform margin deposit in which alternating calcite aragonite mineralogies within each dome reflect a laterally fluctuating offshore redox boundary negative ce anomalies positive gd anomalies and reduced positive eu anomalies relative to laterally correlative deep water iron formation occur in the majority of crystal fan samples and in some cuspate fenestral fabric samples ca carbonate precipitation at the margin of an anoxic iron rich sea would have been promoted by oxygenic removal of iron from seawater otherwise fe carbonate would have been favored over ca carbonate precipitation the mosher carbonate formation is interpreted as an early marine oxygen oasis a shallow platform that favored cyanobacterial productivity was sufficiently isolated from open marine circulation for the seawater to become relatively oxygenated and where carbonate sediment aggradation was a positive feedback that sustained these shallow water conditions limestone accumulation terminated as transgressive suboxic and anoxic seawater deposited first manganese oxide rich and then manganese oxide poor iron formation sediments

sedimentology and ichnology of the cretaceous tertiary boundary in denmark implications for the causes of the terminal cretaceous extinction abstract trace fossils and other sedimentologic evidence of bioturbation in latest cretaceous and earliest tertiary marine deposits in denmark provide important clues to understanding the ecology of the sea bottom immediately before during and after the terminal cretaceous boundary event trace fossil associations at all the onshore danish boundary sites indicate a general upward shoaling of the late maastrichtian chalk sea which was accompanied by an abrupt shift from a carbonate ooze sea floor to a marly clay rich unstable substrate at the boundary although the substrate condition may have become more stable in the early danian water depths never did return to their former deep level there is evidence of localized anoxia during the deposition of some boundary sediments in the fish clay in shallow parts of the danish maastrichtian sea but no clear evidence of anaerobic conditions occurring at the era boundary was observed in boundary strata deposited in deeper water near the center of the basin in fact earliest danian marl there is totally bioturbated a pulse of calcite dissolution in shallow water coincided precisely with the era boundary and this event played a major role in the formation of the fish clay in eastern denmark which is a condensed series of smectitic clay rich layers from which much calcite has dissolved the effects of this dissolution episode however were not so extreme in the marl that was deposited at the same time in slightly deeper water in northwestern denmark evidence from cretaceous tertiary boundary sequences in denmark and elsewhere suggests that no single catastrophe can account for the major biotic extinctions that occurred at the end of the cretaceous period the primary causal factors of the terminal cretaceous extinction event appear to be drastic global sea level regression occurring simultaneously with extensive volcanism on land and a strong pulse of calcite dissolution in ocean surface waters

planktonic foraminifera differential dissolution and the quaternary stable isotope record in the west equatorial pacific differential dissolution affects the isotopic composition of different species of planktonic foraminifera in different ways in the two species studied here in cores from ontong java plateau the less resistant species globigerinoides sacculifer is more readily affected at a shallower depth than the more resistant species pulleniatina obliquiloculata 2 9 versus 3 4 km but shows a smaller and less predictable response to partial dissolution 0 2 to 0 3 per mil versus 0 6 to 0 7 per mil comparison of isotopic values from the last glacial period with those from the late holocene indicates that the apparent dissolution effect is considerably reduced during the last glacial presumably due to reduced dissolution intensity during glacial time a change in the level of the lysocline of about 400 m is suggested in the published isotope records from pacific cores v28 238 and v28 239 the dissolution generated difference in 18o noted previously by shackleton and opdyke 1976 is seen to describe a mid brunhes dissolution maximum between 300 and 500 thousand years ago this mid brunhes dissolution excursion is well known from the pacific and the indian ocean

the end of the cretaceous sharp boundary or gradual transition evidence indicates that the cretaceous tertiary boundary is very sharp and within the limits of resolution it is apparently synchronous at the various boundary localities arguments to the contrary particularly those of officer and darke are shown to invalid

how complete are cretaceous tertiary boundary sections a chronostratigraphic estimate based on graphic correlation cogent interpretations of data bearing on the cretaceous tertiary k t extinction controversy depend on the existence of accurate chronostratigraphic models for the various k t boundary sections we have employed the graphic correlation technique to summarize biostratigraphic and lithostratigraphic data from 15 intensively sampled k t boundary sections within a common chronostratigraphic model our results indicate that almost all of these sections along with 13 additional boundary sections not used to construct the model contain prolonged and in many cases multiple hiatuses of these 28 boundary sections only six were found to contain a continuous record of sediment accumulation across the k t boundary itself these six k t complete sections are el kef tunisia agost spain caravaca spain and three sections along the brazos river texas a comparative analysis of hiatus distributions among these 28 k t boundary sections also reveals the presence of systematic differences between continental shelf and deep sea depositional environments the lower danian interval immediately following the k t boundary and extending into biochronozones p0 and p1a is typically missing from the deep sea whereas boundary sections deposited in shallower middle neritic to upper slope environments are in most cases complete across the k t boundary these shallow neritic boundary sections however are in many instances disrupted by hiatuses at the p0 p1a boundary and again in the upper part of zone p1a these differential patterns of hiatus distribution between deep sea and continental shelf depositional settings appear to be linked to sea level fluctuations our data suggest that the apparently sudden mass extinction of planktonic foraminifera and anomalies in the occurrence of geochemical tracers that are characteristic of the k t boundary in deep sea sections may be artifacts of a temporally incomplete deep sea stratigraphic record

origin of microlayering in worldwide distributed ir rich marine cretaceous tertiary boundary clays the three most ir rich marine cretaceous tertiary boundary clays are found in denmark spain and new zealand the clays have many features in common the most interesting being a thin basal red layer that together with an overlying organic rich zone contains enhanced concentrations of elements such as ir ni co cr zn cu as and sb at first glance the global correlation of element enrichments may seem to be strong evidence for a dust cloud origin of the basal red layers however detailed layer by layer major element analyses e g si al mg ca k and na together with studies of trace element phase partitioning reveal that the elastic allogenic fraction of the red layers at each site is predominantly locally derived water transported material and that concentrated metals exist in authigenic phases the red layers most likely represent precipitation horizons and not fallout layers metal precipitation was induced by various redox controlled processes in connection with decomposition of the abundant algal matter that settled on the end maastrichtian sea floor the concentrated trace elements derive from sea water however the ultimate origin of some of the elements may have been an earth impacting asteroid

utilizing multichannel electrical resistivity methods to examine the dynamics of the fresh water seawater interface in two hawaiian groundwater systems 1 multichannel electrical resistivity er measurements were conducted at two contrasting coastal sites in hawaii to obtain new information on the spatial scales and dynamics of the fresh water seawater interface and rates of coastal groundwater exchange at kiholo bay located on the dry kona side of the big island and at a site in maunalua bay oahu there is an evidence for abundant submarine groundwater discharge sgd however the hydrologic and geologic controls on coastal groundwater discharge are likely to be different at these two sites while at kiholo bay sgd is predominantly through lava tubes at the maunalua bay site exchange occurs mostly through nearshore submarine springs in order to calculate sgd fluxes it is important to understand the spatial and temporal scales of coastal groundwater exchange from er time series data subsurface salinity distributions were calculated using site specific formation factors a salinity mass balance box model was then used to calculate rates of point source i e spatially discreet and total fresh water discharge from these data mean sgd rates were calculated for kiholo bay 9 200 m3 d and for the maunalua bay site 5 900 m3 d while such results are on the same order of magnitude to geochemical tracer derived sgd rates the er sgd rates provide enhanced details of coastal groundwater exchange that can enable a more cohesive whole watershed perspective

extended period of extinctions across the cretaceous tertiary boundary in planktonic foraminifera of continental shelf sections implications for impact and volcanism theories discussion and reply

multiple factors in the origin of the cretaceous tertiary boundary the role of environmental stress and deccan trap volcanism a review of the scenarios for the cretaceous tertiary k t boundary event is presented and a coherent hypothesis for the origin of the event is formulated many scientists now accept that the event was caused by a meteorite impact at chicxulub in the yucatan peninsula mexico our investigations show that the oceans were already stressed by the end of the late cretaceous as a result of the long term drop in atmospheric co2 the long term drop in sea level and the frequent development of oceanic anoxia extinction of some marine species was already occurring several million years prior to the k t boundary the biota were therefore susceptible to change the eruption of the deccan traps which began at 66 2 ma coincides with the k t boundary events it erupted huge quantities of h2so4 hcl co2 dust and soot into the atmosphere and led to a significant drop in sea level and marked changes in ocean temperature the result was a major reduction in oceanic productivity and the creation of an almost dead ocean the volcanism lasted almost 0 7 m y extinction of biological species was graded and appeared to correlate with the main eruptive events elements such as ir were incorporated into the volcanic ash possibly on soot particles this horizon accumulated under anoxic conditions in local depressions and became the marker horizon for the k t boundary an oxidation front penetrated this horizon leading to the redistribution of elements the eruption of the deccan traps is the largest volcanic event since the permian triassic event at 245 ma it followed a period of 36 m y in which the earth s magnetic field failed to reverse instabilities in the mantle are thought to be responsible for this eruption and therefore for the k t event we therefore believe that the k t event can be explained in terms of the effects of the deccan volcanism on an already stressed biosphere the meteorite impact at chicxulub took place after the onset of deccan volcanism it probably played a regional rather than a global role in the k t extinctions

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

a cretaceous and jurassic geochronology an integrated geomagnetic polarity and geologic time scale for the jurassic and cretaceous periods is presented based on various methods according to the availability of definitive isotopic ages an age calibrated sea floor spreading model is used to interpolate the ages of the kimmeridgian to barremian and the campanian to maestrichtian stages numerical age estimates for the aptian to santonian stage boundaries follow published isotopic age determinations the hypothesis of equal duration of ammonite zones is employed as a vernier to apportion time for the hettangian to oxfordian stages the new scale results in ages of 208 ma for the base of the jurassic 144 ma for the jurassic cretaceous boundary and 66 5 ma for the top of the cretaceous the integrated biostratigraphic magnetostratigraphic and geochronometric record serves as a working hypothesis for geologic correlation of jurassic and cretaceous strata

stable isotope evidence for gradual environmental changes and species survivorship across the cretaceous tertiary boundary high resolution 13c and 18o records have been generated from analyses of the planktonic foraminiferal species heterohelix globulosa and the benthonic foraminiferal taxon lenticulina spp from 3 m of a cored section spanning the cretaceous tertiary k t boundary at brazos river texas these are the first stable isotope records across the k t boundary based on monospecific and monogeneric foraminiferal samples they show a gradual decrease in 13c values of about 2 5 permil beginning at the k t boundary as defined by the first appearance of tertiary planktonic foraminifera and continuing 17 20 cm above the boundary approximately 40 000 years later gradual 13c depletion contrasts with the sudden 13c drop at the k t boundary observed in many deep sea sections the surface to bottom 13c gradient decreased to less than zero approximately 25 000 30 000 years after the k t boundary and remained negative for at least the next 140 000 years concomitant with change in 13c values is a gradual decrease of about 2 5 permil in 18c values which has not been observed at other localities this 18o depletion suggests changes in temperature and or salinity in the earliest paleocene gulf of mexico no extinction of foraminiferal species is associated with the k t boundary or the onset of 18o and 13c depletions instead two phases of cretaceous species extinctions occur one extinction phase is below the k t boundary and below the tsunami bed of bourgeois et al 1988 and may be linked to sea level regression and environmental perturbations the second extinction phase coincides with the minimum in 13c and 18o values in the early danian zone p0 pla and appears directly related to environmental changes reflected in the isotopic record h globulosa which is commonly present in maastrichtian and danian sediments exhibits significantly lower 18o 16o and 13c 12c ratios in tertiary sediments relative to specimens from maastrichtian sediments demonstrating the survival of this important cretaceous taxon after the k t boundary event

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

hiatus distributions and mass extinctions at the cretaceous tertiary boundary much disagreement over the interpretation of data bearing on various cretaceous tertiary k t extinction scenarios results from a failure to view these data within their appropriate stratigraphic context combined biostratigraphic and chronostratigraphic analyses of k t boundary sequences have revealed systematic differences in patterns of sediment accumulation within continental shelf and deep sea depositional settings although virtually all deep sea boundary sequences are marked by intervals of nondeposition or hiatus formation during the latest cretaceous and earliest tertiary many continental shelf slope sequences appear to be temporally complete over this same interval this differential pattern of sediment accumulation can be related to the latest maastrichtian earliest danian sea level rise during which deep sea sediment accumulation rates would be expected to drop as the locus of sediment deposition migrated across the continental shelf our data suggest that the abrupt shifts in carbon isotope abundances single peak ir anomalies and apparently instantaneous mass extinctions of marine plankton which are routinely reported from deep sea k t boundary sequences and used to support a causal relation between late cretaceous bolide impacts and k t mass extinctions may be artifacts of a temporally incomplete or extremely condensed deep sea stratigraphic record

end cretaceous mass extinction event argument for terrestrial causation the end cretaceous mass extinctions were not a geologically instantaneous event and were selective in character these features are incompatible with the original alvarez hypothesis of their being caused by a single asteroid impact that produced a world embracing dust cloud with devastating environmental consequences by analysis of physical and chemical evidence from the stratigraphic record it is shown that a modified extraterrestrial model in which stepwise extinctions resulted from encounter with a comet shower is less plausible than one intrinsic to the earth involving significant disturbance in the mantle

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

extinction survivorship and evolution of planktic foraminifera across the cretaceous tertiary boundary at el kef tunisia an expanded sediment record at el kef shows that the k t boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary ir anomaly to 7 cm above species extinctions appear sequential with complex large ornate forms disappearing first and smaller less ornate forms surviving longer the 14 species extinctions below the boundary appear unrelated to an impact event cretaceous species survivorship is greater than previously assumed about 10 species survive 22 into subzone p1a globigerina eugubina all cretaceous survivors are small primitive forms which are generally smaller than their ancestors in cretaceous sediments species evolution after the k t event occurs in two pulses the first new paleocene species evolve in the basal black clay zone po immediately after the major cretaceous extinctions evolving species are small and primitive similar to cretaceous survivors the second pulse in species evolution occurs in the lower part of subzone p1b with the appearance of larger more diverse species the first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300 000 years after the k t event the species extinctions prior to the generally assumed impact event implied by the ir anomaly and the long recovery period of the ecosystem thereafter cannot be explained by a single impact but suggest that multiple causes may be responsible such as climatic changes volcanism a sea level drop production of warm saline bottom water and the chemical consequences associated with increased salinity

the origin of the clay minerals at the cretaceous tertiary boundary in denmark the distinctive mg smectite that is the predominant clay mineral in the cretaceous tertiary k t boundary marl at stevns klint denmark that is the fish clay which has been previously believed to have formed from impact derived glass is also present in the upper of two marls of probable early danian age at limhamn quarry sweden approximately 8 m above the k t boundary this danian marl is devoid of anomalous iridium we contend that this mg smectite is the result of alteration of a volcanic ash precursor perhaps reworked and that impact debris is a relatively minor component of the k t boundary marls studied herein k ar dates demonstrate that caledonian detrital potassic phases that is illite are present in the coarse clay fraction of the fish clay the fish clay is thus composed predominantly of volcanic detrital phases and lesser amounts of impact phases in addition we have discovered subhedral labradorite in the organic rich black clay of layer iii of the fish clay therefore we suggest that pyroclastic basaltic volcanism was the predominant progenitor of the boundary clay unit and is responsible for its high mg content our results indicate that the main carrier of ir in the k t boundary marls is of submicron size and that ir is mobile during diagenesis and or weathering in addition our results show that pt and au are present in the upper limhamn marl and for comparison in the permian kupferschiefer shale at amounts comparable to those of the k t boundary it is thus possible that some or much of the pt and au at the k t boundary is derived from nonimpact sources similar to those that apparently contributed to the parts per billion concentrations of pt and au in the permian kupferschiefer shale we cannot reject the impact hypothesis summarily because shocked quartz with multiple planar sets is distinct to the k t boundary and this distinctive shocked quartz has not yet been identified in distal volcanic tephras or flows if shocked quartz is of impact origin then the collision of either a smaller asteroid or a comet is more consistent with the relatively small amount of impact derived material in the fish clay alternatively if shocked quartz is proven to be formed by explosive volcanism then our evidence would permit explaining the k t boundary events as entirely due to volcanism rather than impact

mass wasting and hiatuses during the cretaceous tertiary transition in the north atlantic relationship to the chicxulub impact deep sea sections in the north atlantic are claimed to contain the most complete sedimentary records and ultimate proof that the chicxulub impact is cretaceous tertiary boundary ktb in age and caused the mass extinction a multi disciplinary study of north atlantic dsdp sites 384 386 and 398 based on high resolution planktonic foraminiferal biostratigraphy carbon and oxygen stable isotopes clay and whole rock mineralogy and granulometry reveals the age stratigraphic completeness and nature of sedimentary disturbances results show a major hiatus across the ktb at site 384 with zones cf1 p0 and p1a missing spanning at least 540 ky similar to other north atlantic and caribbean localities associated with tectonic activity and gulf stream erosion at sites 386 and 398 discrete intervals of disturbed sediments with mm to cm thick spherule layers have previously been interpreted as the result of impact generated earthquakes at the ktb destabilizing continental margins prior to settling of impact spherules however improved age control based on planktonic foraminifera indicates spherule deposition in the early danian zone p1a 2 upper parvularugoglobigerina eugubina zone more than 100 ky after the ktb at site 386 two intervals of white chalk contain very small 63 m early danian zone p1a 2 assemblages 65 and common reworked cretaceous 35 species in contrast the in situ red brown and green abyssal clays of this core are devoid of carbonate in addition high calcite mica and kaolinite and upward fining are observed in the chalks indicating downslope transport from shallow waters and sediment winnowing via distal turbidites at site 398 convoluted red to tan sediments with early danian and reworked cretaceous species represent slumping of shallow water sediments as suggested by dominance of mica and low smectite compared to in situ deposition we conclude that mass wasting was likely the result of earthquakes associated with increased tectonic activity in the caribbean and the iberian peninsula during the early danian well after the chicxulub impact

chemostratigraphy of paleoproterozoic carbonate successions of the wyoming craton tectonic forcing of biogeochemical change the archean wyoming craton is flanked on the south and east by belts of paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop however carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy the 10 km thick paleoproterozoic snowy pass supergroup in the medicine bow mountains was deposited on the present day southern flank of the wyoming craton it contains three discrete levels of glacial diamictite correlative with those in the huronian supergroup on the southern margin of the superior craton the nash fork formation of the upper snowy pass supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the paleoproterozoic glacial epoch carbonates at the base of the nash fork formation record remarkable 13 cenrichment up to 28 v pdb whereas those from overlying members of the lower nash fork formation have d 13 c values between 6 and 8 carbonates from the upper nash fork formation above the carbonaceous shale have carbon isotope values ranging between 0 and 2 5 the transition from high carbon isotope values to those near 0 in the nash fork formation is similar to that at the end of the ca 2 2 2 1 ga carbon isotope excursion in fennoscandia this chemostratigraphic trend and deposition of bifs mn rich lithologies carbonaceous shales and phosphorites at the end of the global ca 2 2 2 1 ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the kenorland supercontinent correlative carbonates from the slaughterhouse formation in the sierra madre wy and from the whalen group in the rawhide creek area in the hartville uplift wy have highly positive carbon isotope values in contrast carbonates from other exposures of the whalen group in the hartville uplift and all carbonate units in the black hills sd have carbon isotope values close to 0 combined with existing geochronologic and stratigraphic constraints these data suggest that the slaughterhouse formation and the succession exposed in the rawhide creek area of the hartville uplift are correlative with the lower and middle nash fork formation and were deposited during the ca 2 2 2 1 ga carbon isotope excursion the estes and roberts draw formations in the black hills and carbonates from other exposures in the hartville uplift postdate the ca 2 2 2 1 ga

the extraterrestrial component in marine sediments description and interpretation the influx of extraterrestrial matter to the earth is dominated by two size fractions sub millimeter interplanetary dust and impacting asteroids and comets over geologic time the major contribution of extraterrestrial matter is from the largest impactors interplanetary dust is largely vaporized by atmospheric entry but some surviving material is found in sediments as cosmic spherules impacting asteroids and comets can produce fallout layers either regionally or globally which may contain a significant fraction of meteoritic material as well as shock metamorphosed and shock melted terrestrial material iridium is a sensitive tracer of extraterrestrial matter although high concentrations of ir in marine sediments probably have an extraterrestrial origin they do not necessarily indicate the presence of a major impact event of the thousands of impact horizons which must be resolvable in the sedimentary record to date only seven probable impact horizons have been identified in the entire phanerozoic the marine geochemistry and occurrence of ir is still poorly understood but the thousands of ir analyses performed in the last several years have demonstrated that the global occurrence high ir 10 ng g concentrations in cretaceous tertiary boundary sediments is a truly anomalous phenomenon

evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates new osmium os isotope and platinum group element pge concentration data are used in conjunction with published 3 he and th isotope data to determine the relative proportions of lithogenic extraterrestrial and hydrogenous iridium ir in a pacific pelagic carbonate sequence from the ocean drilling program odp site 806 on the ontong java plateau ojp these calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary ir budget are minor while hydrogenous ir accounts for roughly 85 of the total ir application of analogous partitioning calculations to previously reported data from a north pacific red clay sequence ll44gpc3 yields very similar results total ir burial fluxes at site 806 and ll44 gpc3 are also similar 45 and 30 pg cm 2 kyr 1 respectively average ir 3 he and ir xs 230 thinitial ratios calculated from the entire site 806 data set are similar to those reported earlier for pacific sites in general down core profiles of ir 3 he and xs 230 thinitial are not well correlated with one another however all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two while these results indicate that ir concentration has potential as a point paleoflux tracer in pelagic carbonates ir based paleoflux estimates are likely subject to uncertainties that are similar to those associated with co based paleoflux estimates consequently local calibration of ir flux in space and time will be required to fully assess the potential of ir as a point paleoflux tracer measured 187 os 188 os of the ojp sediments are systematically lower than the inferred 187 os 188 os of contemporaneous seawater and a clear glacial interglacial 187 os 188 os variation is lacking mixing calculations suggest os contributions from lithogenic sources are insufficient to explain the observed 187 os 188 os variations the difference between the 187 os 188 os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic os carried by particulate extraterrestrial material down core variations of 187 os 188 os with pt ir and os ir also point to contributions from extraterrestrial particles mixing calculations for each set of several triplicate analyses suggest that the unradiogenic os end member cannot be characterized by primary extraterrestrial particles of chondritic composition it is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions 187 os 188 os of pelagic carbonates has greater potential compared to abundances of pge an attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial os in the ojp samples and previously reported extraterrestrial os flux throughout most of the ojp record os isotope based paleoflux estimates are within a factor of two of those derived using other constant flux tracers meaningful flux estimates cannot be made during glacial maxima because the ojp sediments do not record the low 187 os 188 os reported previously we speculate that this discrepancy may be related to focusing of extraterrestrial particles at the ojp as has been suggested to explain down core 3 he variations

iridium and other platinum group elements as geochemical markers in sedimentary environments iridium anomalies are commonly used as indicators of extraterrestrial processes which caused global extinctions however platinum group element pge anomalies may result from several different processes both syn and postdepositional acting separately or jointly the sources and processes of enrichment involved are extraterrestrial asteroid comet cosmic dust impact ejecta volcanogenic pge rich condensates precipitation from seawater low sedimentation rate anoxic conditions microbial concentration dissolution reprecipitation exhalative hydrothermal leaching transport and precipitation at a redox boundary geochemical characteristics of pge and accompanying elements in sediments can be used to identify the contributions of some specific sources and processes 1 extraterrestrial chondritic ru ir and os ir ratios low 187os 186os ratio high ir compared to pt pd and au 2 volcanogenic high iridium and se as sb and in contents 3 exhalative hydrothermal high au pd and pt relatively low ir contents 4 precipitation from seawater high pt and low pd contents also high cd and ag contents under anoxic conditions and 5 reduction from intermediate and low temperature solutions high pge and cu or mo u ni contents

some comparative marine chemistries of platinum and iridium abstract iridium has seawater concentrations about one hundred times less than those of platinum as a consequence of its weaker complexing abilities with halides and of a stronger tendency to hydrolyze iridium like platinum is enriched in some ferromanganese minerals compared to palladium platinum and iridium are probably oxidized during mineral formation from the divalent and trivalent states respectively to the tetravalent ones the pelagic sediment contents of irridium as well as those of platinum are related to the manganese contents for higher platinum contents of the authigenic ferromanganese minerals the pt ir ratios approach the seawater ratio suggesting little dilution by platinum and iridium in detrital minerals the marked enrichments of platinum and iridium in the ferromanganese concretions enhance their value as potential ores for heavy metals

eogenetic siderites in lacustrine oil shales from queensland australia a stable isotope study abstract tertiary lacustrine oil shales from the lowmead and duaringa basins in queensland australia contain siderite as a ubiquitous minor phase and in ironstone bands within the sequence there are two distinctive types of siderite in the ironstone bands sphaerosiderites and finely crystalline siderites petrological evidence indicates that the sphaerosiderites in the ironstone bands formed eogenetically by growing displacively within the soft sediment the geological setting of the basin and the sedimentological evidence indicate a lacustrine environment the deposition of siderite is therefore considered to be controlled by processes in the lacustrine water body and sediments the maximal burial depth is estimated to be 1400 m and consequently the oil shales have not undergone any advanced thermal alteration stable oxygen and carbon isotope analysis of the siderites show a wide compositional range 18o 12 8 to 2 4 vs pdbg and 13c 5 5 to 12 9 vs pdb for the lowmead basin 18o 9 6 to 1 2 vs pdb and 13c 18 6 to 16 4 vs pdb for the duaringa basin the oxygen isotope compositions indicate that the siderite formed in a to 16 4 vs pdb for the duaringa basin the oxygen isotope compositions indicate that the siderite formed in a freshwater environment but generally show a range more negative than the expected equilibrium composition with coeval meteoric waters the carbon isotope composition may reflect deposition within the bacterial oxidation and fermentation zones the shallow lake setting with high productivity results in siderite precipitation under high ph either at the water sediment interface or within the sediment the 13c of the dissolved carbonate will be elevated by intense photosynthesis under these conditions of co2 depletion high ph isotopic disequilibrium during siderite formation will result in 13c and 18c lower than the equilibrium composition in agreement with the recorded isotopic data

new constraints on early tertiary palaeoproductivity from carbon isotopes in foraminifera one of the most pronounced features of marine sections at the cretaceous tertiary k t boundary is the negative excursion in biogenic carbonate 13c in the early tertiary carbon isotope record1 9 the coincidence of this excursion with the elimination of many marine plankton species supports predictions that large scale reduction of primary productivity in the oceans would disrupt the biological carbon pump resulting in a diminished surf ace to deep 13c gradient10 13c carbonate accumulation rates and other geochemical indices support the idea that the oceans were less productive in the early palaeocene9 here we present carbon isotope analyses of individual species of benthic and planktonic foraminifera spanning the k t boundary in oop hole 690c weddell sea antarctica which demonstrate that primary productivity following the k t extinctions may not have diminished to the extent or for the duration indicated by previous isotope studies the magnitude of the 13c gradient change is dependent on the species analysed reflecting differing depths of calcification seasonal contrasts and or disequilibrium effects the lack of any change in benthic 13c at the k t boundary indicates that the antarctic may not have been a significant source of deep water during the early palaeocene contrary to previous suggestion11 13

fractionation between inorganic and organic carbon during the lomagundi 2 22 2 1 ga carbon isotope excursion article i nfo the lomagundi 2 22 2 1 ga positive carbon isotope excursion in shallow marine sedimentary carbonates has been associated with the rise in atmospheric oxygen but subsequent studies have demonstrated that the carbon isotope excursion was preceded by the rise in atmospheric oxygen the amount of oxygen released to the exosphere during the lomagundi excursion is constrained by the average global fractionation between inorganic and organic carbon which is poorly characterized because dissolved inorganic and organic carbon reservoirs were arguably larger in the paleoproterozoic ocean at a time of lower solar luminosity and lower ocean redox state decoupling between these two variables might be expected we determined carbon isotope values of carbonate and organic matter in carbonates and shales of the silverton formation south africa and in the correlative sengoma argillite formation near the border in botswana these units were deposited between 2 22 and 2 06 ga along the margin of the kaapvaal craton in an open marine deltaic setting and experienced lower greenschist facies metamorphism the prodelta to offshore marine shales are overlain by a subtidal carbonate sequence carbonates exhibit elevated 13 c values ranging from 8 3 to 11 2 vs vpdb consistent with deposition during the lomagundi positive excursion the total organic carbon toc contents range from 0 01 to 0 6 and 13 c values range from 24 8 to 13 9 thus the isotopic fractionation between organic and carbonate carbon was on average 30 3 2 8 n 32 in the shallow marine environment the underlying sengoma shales have highly variable toc contents 0 14 to 21 94 and 13 c values 33 7 to 20 8 with an average of 27 0 3 0 n 50 considering that the shales were also deposited during the lomagundi excursion and taking 13 c values of the overlying carbonates as representative of the 13 c value of dissolved inorganic carbon during shale deposition a carbon isotope fractionation as large as 37 appears to characterize the production of bulk organic matter in the deeper part of the pretoria basin at that time this enhanced fractionation relative to that observed in shallow water environments likely reflects heterotrophic secondary and chemotrophic productivity at and below a pronounced redoxcline consistent with the euxinic conditions inferred from independent evidence for the deeper part of the pretoria basin greater variability in organic carbon vs carbonate carbon isotopic values on the shallow marine carbonate platform suggests that the carbon cycling was dominated by a large dissolved inorganic carbon reservoir during the lomagundi excursion our study suggests that in contrast to the late neoproterozoic and phanerozoic when carbon isotope fractionation between carbonate and organic carbon in the open ocean was mostly controlled by primary producers in the paleoproterozoic redox stratified ocean heterotrophic and chemotrophic productivity overprinted a signal of primary productivity below the redoxcline this strong imprint of heterotrophic and chemotrophic productivity on organic carbon isotope records complicates the reconstruction of spatial patterns and secular trends in the 13 c values of dissolved inorganic carbon in the paleoproterozoic seawater

clay mineralogy of the cretaceous tertiary boundary clay analyses of the clay mineralogy of samples from the cretaceous tertiary boundary layer at four localities show that the boundary clay is neither mineralogically exotic nor distinct from locally derived clays above and below the boundary the significant ejecta component in the clay that is predicted by the asteroid impact scenario was not detected

some patterns of planktic foraminiferal assemblage turnover at the cretaceous tertiary boundary abstract three uppermost cretaceous through basal paleocene stratigraphic sequences are examined for planktic foraminiferal assemblage stability and temporal succession patterns these sequences are at mid latitude south atlantic dsdp site 528 then equatorial pacific dsdp site 577 and the tethyan shelf ben gurion section of the negev israel in order to better estimate biogeographic patterns and habitat preferences the results of these analyses are compared to previous cretaceous biogeographic studies and to previous analyses of cretaceous tertiary k t boundary shelf and epicontinental sections results indicate that immediately following the k t boundary the examined epicontinental and open ocean sites were exploited primarily by previously epicontinental planktic foraminiferal assemblages this pattern of k t boundary assemblage dominance suggests the geologically instantaneous break down of late cretaceous epicontinental and open ocean biogeographic provincialization this shift in open ocean foraminiferal assemblages is not consistent with models of non selective k t boundary extinctions but is consistent with models of extinction resistence and offshore expansion of near shore taxa the re establishment of stable biogeographic differences between open ocean and epicontinental planktic foraminiferal assemblages occurs by the basal parvularugoglobigerina eugubina zone at open ocean sites 528 and 577 and the outer shelf ben gurion section po and p eugubina zone faunal records are marked by a pronounced alternation between paleocene biserial and non biserial dominated assemblages this alternation appears strongly damped at shelf and epicontinental sections previously examined the first appearance and peak magnitude of abundant earliest paleocene trochospiral forms parvularugoglobigerina eoglobigerina morozovella globoconusa also vary from site to site and may depend closely on levels of primary carbonate productivity

biotic geochemical and paleomagnetic changes across the cretaceous tertiary boundary at braggs alabama exposed near braggs alabama is one of the few well studied nearly continuous shallow marine cretaceous tertiary boundary sections it allows a glimpse of the biotic and environmental changes that occurred in the latest cretaceous to earliest paleocene paleomagnetic strontium isotopic and biostratigraphic data closely constrain the age of a series of lithologic geochemical and biotic variations and suggest that no more than 100 200 ka could be missing at the boundary a major reduction in macrofaunal diversity associated with lithofacies changes occurs prior to but within 300 ka of the nannofossil defined boundary approximately 40 of the apparent faunal reduction is attributed to the lazarus effect faunal and floral assemblages trends in carbon isotopic composition of benthic invertebrates and lithologic characteristics indicate that a latest maestrichtian regression culminated near the boundary chron c29r micula murus zone significantly later than recent estimates water depths at this site remained shallow during the subsequent early paleocene zone np1 transgression and did not reach depths equivalent to those of the late maestrichtian until zone np2 relatively minor climatic changes across the boundary are suggested by a 4 c cooling trend seen in the oxygen isotope paleotemperatures a high resolution 87 sr 86 sr record from well preserved macrofossil calcite shows a pattern of smooth variation and elevated values near the boundary however the early paleocene spike of other workers was not found

geochemical behavior of pt and pd in coastal marine sediments southeastern margin of the japan sea abstract eighty one argillaceous marine sediments collected from the southeastern coastal margin of the japan sea were analyzed for pt and pd by atomic absorption spectrometry using a graphite furnace atomizer after solvent extraction separation the average pt 1 2 0 5 ppb and pd 1 6 0 9 ppb contents are generally similar to those of the published crustal abundances the pt or pd is generally enriched in the fine sediment fraction and positively correlated with cu pb and water depth the inverse correlation between the pt or pd content and redox potential of the sediment suggests that significant amounts of pt and pd are supplied in their dissolved forms and reduced to their metallic states it is concluded that the pt and pd distributions in the coastal marine sediments are controlled by the geological characteristics of the studied area grain size and redox potential of sediments water depths and dissolved o 2 concentration of sea water

biotic turnover in benthic foraminifera across the cretaceous tertiary boundary at el kef tunisia abstract the cretaceous tertiary boundary section exposed near el kef tunisia is the most complete boundary sequence known to date it contains nearly 1 m of black and gray boundary clay containing planktic foraminiferal zone poa b 2 m of clayey shales of p1a globigerina eugubina zone and 4 m of shales and marls of p1b g taurica zone quantitative analysis of the benthic foraminiferal fauna suggests that deposition during the latest cretaceous occurred in an upper slope to outer shelf environment which shallowed at the k t boundary to an outer to middle shelf depth and shallowed further by p1b time to mid shelf depth a major reduction in benthic diversity occurred near the k t boundary with about 50 of the fauna disappearing diversity remained an average of 37 lower during deposition of the first 3 m of sediment above the boundary poa b p1a and productivity was very low surviving and thriving foraminifers during this interval were primarily low oxygen tolerant epifaunal and infaunal species a sharp decrease in the low oxygen tolerant fauna and appearance of a shallow mid shelf fauna at about 4 m above the boundary p1b zone signals a second regression return to higher oxygen levels and higher productivity although the environmental effects of the k t boundary event can be inferred from benthic faunas the ultimate cause remains elusive faunal changes prior to and the long recovery period after the k t boundary are difficult to explain by a single impact hypothesis

extreme 13c depletions in seawater derived brines and their implications for the past geochemical carbon cycle extreme depletions in the 13c content of the total dissolved inorganic carbon ct were found in brines overlying microbial mat communities total alkalinity at and ct in the brines suggest that intense photosynthetic activity of the microbial mat communities depletes the ct from the brine we suggest that this depletion drives a large kinetic negative fractionation of carbon isotopes similar to that observed in highly alkaline solutions in brines of extreme salinity where microbial mat communities no longer exist the 13c content of the ct increases probably because photosynthesis no longer dominates the gas exchange processes this mechanism explains light carbon isotope compositions of carbonate rocks from evaporitic sections and bears on the interpretation of 13c values in bedded stromatolitic limestones that are ca 3 5 b y old

geochemistry of precambrian carbonates v late paleoproterozoic seawater in an effort to obtain better constrained data for the first and second order variations in the isotopic composition of late paleoproterozoic 1 8 0 2 ga seawater we report a study of mineralogy chemistry and isotopic composition of the coronation supergroup 1 9 ga nwt canada and the mcarthur group 1 65 ga nt australia petrologically both carbonate sequences are mostly dolostones the mcarthur population however contains more abundant textural features that attest to the former presence of sulfates and halite and the facies investigated herein probably represent ancient equivalents of modern evaporitic sabkhas and lacustrine playa lakes this is reflected in 18 o enrichment up to 2 9 pdb and high mn fe and sr concentrations nonetheless the available 18 o data indicate that the best estimate for the archean to late paleoproterozoic limestones is about 7 pdb with dolostones some 3 2 heavier the observed 18 o doiomitc calcite is thus within the range of the proposed fractionation factor for a cogenetic mineral pair this together with the consistency of isotopic patterns for sedimentological facies over almost 2 billion years from the late paleoproterozoic to the present suggest that dolomitization was an early diagenetic event and that the 18 o depletion of the archean to late paleoproterozoic carbonates is not an artefact ofpost depositional alteration the 13 c although within the range of other precambrian and phanerozoic carbonates indicates a possible secular evolution from 0 2 pdb at 1 9 ga ago to 1 1 5 at 1 65 ga ago the secular evolution for reflects the 87 sr increase from 0 7031 0 0008 at 3 5 0 1 ga ago through 0 7025 0 0015 at 2 8 0 2 ga 0 7033 at 2 5 ga 0 7050 at 2 25 0 25 ga 0 7047 at 1 91 to 0 706 at 1 65 ga ago

stable isotope composition of benthic foraminifera from the equatorial pacific when ranked according to deviation from isotopic equilibrium deep sea benthic foraminifera exhibit no correlation between the rankings for oxygen and for carbon both rank sequences are stable from east to west in the equatorial pacific fertility independent and from glacial to post glacial time independent records for the past 15 000 yr suggest marked changes in deep sea circulation during this time interval