southern san andreas fault seismicity is consistent with the gutenberg richter magnitude frequency distribution the magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the gutenberg richter gr distribution on some major faults however paleoseismic rates are higher than a gr extrapolation from the modern rate of small earthquakes would predict this along with other observations led to the formulation of the characteristic earthquake hypothesis which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large earthquake rate wesnousky et al 1983 schwartz and coppersmith 1984 we examine the rate difference between recent small to moderate earthquakes on the southern san andreas fault ssaf and the paleoseismic record hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from gr statistics we find that with reasonable assumptions the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic type aftershock sequence modeling where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes the necessary rate changes are also comparable to rate changes observed for other faults worldwide these results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the ssaf and the absence of m 7 earthquakes on the ssaf since 1857

oceanic plateau formation a cause of mass extinction and black shale deposition around the cenomanian turonian boundary the cenomanian turonian boundary 90 4 ma represents a major period of worldwide environmental disturbance the physical manifestations of this are elevated atmospheric and oceanic temperatures a significant sea level transgression and a period of widespread anoxia leading to the formation of oceanic black shales and the extinction of 26 of all genera elevated 13 c values and enrichment of trace elements in cenomanian turonian boundary sediments combined with a reduction in 87 sr 86 sr also imply a severe environmental perturbation at this time oceanic crustal production rates reached their highest level of the last 100 million years this was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere and the development of vast areas up to 1 10 6 km 2 of thickened oceanic crust in the pacific and indian oceans the anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c 90 ma these eruptions would also have resulted in the emission of large quantities of co 2 into the atmosphere leading to global warming additionally the emission of so 2 h 2 s co 2 and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate and further release of co 2 this run away greenhouse effect was probably put into reverse by the decline of the anomalous volcanic activity and by increased co 2 driven productivity in oceanic surface waters leading to increased organic carbon burial black shale deposition anoxia and mass extinction in the ocean basins

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

the cretaceous tertiary boundary transition in the antarctic ocean and its global implications abstract three antarctic ocean k t boundary sequences from odp site 738c on the kerguelen plateau odp site 752b on broken ridge and odp site 690c on maud rise weddell sea have been analyzed for stratigraphic completeness and faunal turnover based on quantitative planktic foraminiferal studies results show that site 738c which has a laminated clay layer spanning the k t boundary is biostratigraphically complete with the earliest tertiary zones p0 and p1a present but with short intrazonal hiatuses site 752b may be biostratigraphically complete and site 690c has a hiatus at the k t boundary with zones p0 and p1a missing latest cretaceous to earliest tertiary planktic foraminiferal faunas from the antarctic ocean are cosmopolitan and similar to coeval faunas dominating in low middle and northern high latitudes although a few endemic species are present this allows application of the current low and middle latitude zonation to antarctic k t boundary sequences the most abundant endemic species is chiloguembelina waiparaensis which was believed to have evolved in the early tertiary but which apparently evolved as early as chron 30n at site 738c since this species is only rare in sediments of site 690c in the weddell sea this suggests that a watermass oceanographic barrier may have existed between the indian and atlantic antarctic oceans the cosmopolitan nature of the dominant fauna began during the last 200 000 to 300 000 years of the cretaceous and continued at least 300 000 years into the tertiary this indicates a long term environmental crisis that led to gradual elimination of specialized forms and takeover by generalists tolerant of wide ranging temperature oxygen salinity and nutrient conditions a few thousand years before the k t boundary these generalists gradually declined in abundance and species became generally dwarfed due to increased environmental stress there is no evidence of a sudden mass killing of the cretaceous fauna associated with a bolide impact at the k t boundary instead the already declining cretaceous taxa gradually disappear in the early danian and the opportunistic survivor taxa ch waiparaensis and guembelitria cretacea increase in relative abundance coincident with the evolution of the first new tertiary species

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

boltysh another end cretaceous impact the chixculub impact occurred at the cretaceous tertiary k t boundary and although several other late cretaceous and paleogene impact craters have at times been linked with the k t boundary isotope geochronology has demonstrated that all have significantly different ages the currently accepted age of the 24 km diameter boltysh crater a k ar whole rock age places it in the coniacian at 88 3 ma however comprehensive ar ar dating of a range of melt samples yields a mean age of 65 17 0 64 ma within errors of the k t boundary several of the fresh samples exhibit signs of excess argon but this seems to be concentrated in rapidly crystallized glass rich samples the ar ar age confirms an earlier fission track measurement and thus two dating techniques have yielded an age within errors of the k t boundary for this crater crucially although the ages of boltysh and chixculub are within errors they may not have formed synchronously craters of 24 km diameter occur much more commonly than impacts of chixculub dimensions but their proximity does raise the important question of how many impacts there might have been close to the k t boundary

40ar 39ar dating of mineral separates and whole rocks from the western ghats lava pile further constraints on duration and age of the deccan traps abstract there has been an ongoing debate for almost two decades on the age and duration of deccan trap volcanism some of the best available ages have been determined using the 40 ar 39 ar method but differences in sample location laboratory procedure type of analyzed material and ages of monitors may have been responsible for much of the apparent spread in the data we have collected and analyzed samples from close to the bottom and top of the main lava pile in the western ghats near bombay we confirm previous findings that alteration and ar recoil strongly affect these rocks particularly measurements made on whole rocks when mineral separates mostly plagioclase are analyzed the spread is much reduced we find a mean age of 65 4 0 7 ma for five flows near the base of the section jahwar and igatpuri formations and 65 2 0 4 ma for a dyke cross cutting the poladpur formation below the topmost mahabaleshwar formation this implies that at least 1800 m out of the 2500 m composite trap section were erupted in a short interval less than 1 ma long and close to 65 5 ma i e close to the cretaceous tertiary boundary we find that older ages near 67 ma found by several authors are essentially based on whole rock samples which display disturbed spectra when this can be checked i e when the spectra are published

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

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

age and paleoenvironment of the maastrichtian to paleocene of the mahajanga basin madagascar a multidisciplinary approach abstract lithology geochemistry stable isotopes and integrated high resolution biostratigraphy of the berivotra and amboanio sections provide new insights into the age faunal turnovers climate sea level and environmental changes of the maastrichtian to early paleocene of the mahajanga basin of madagascar in the berivotra type area the dinosaur rich fluvial lowland sediments of the anembalemba member prevailed into the earliest maastrichtian these are overlain by marginal marine and near shore clastics that deepen upwards to hemipelagic middle neritic marls by 69 6 ma accompanied by arid to seasonally cool temperate climates through the early and late maastrichtian an unconformity between the berivotra formation and betsiboka limestone marks the k t boundary and juxtaposes early danian zone plc or pld and latest maastrichtian zones cf2 cf1 micula prinsii sediments seasonally humid warm climates began near the end of the maastrichtian and prevailed into the early danian accompanied by increased volcanic activity during the late danian zones p1d p2 a change to seasonally arid climates was accompanied by deepening from middle to outer neritic depths

cosmic ray exposure histories of the lunar meteorites aau 012 and shisr 166 we measured the concentrations and isotopic compositions of the stable isotopes of he ne ar kr and xe in the two lunar impact melt breccias abar al uj aau 012 and shisr 166 to obtain information on their cosmic ray exposure histories and possible launch pairing the latter was suggested because of their similar chemical composition aau 012 has higher gas concentrations than shisr 166 and clearly contains implanted solar wind gases indicating a shallow to moderate shielding for this meteorite in the lunar regolith the maximum shielding depth of aau 012 was most likely 310 g cm 2 and its lunar regolith residence time was 420 70 ma our results indicate that in shisr 166 the trapped component is a mixture of air and solar wind the low concentration of cosmogenic and solar wind gases indicate substantial diffusive gas loss and a shielding depth of 700 g cm 2 on the moon for shisr 166 all differences seen in the concentrations and isotopic compositions of the noble gases suggest that aau 012 and shisr 166 are most likely not launch pairs although a different exposure history on the moon does not exclude the possibility that the two meteorites were ejected by a single large impact event

paleocology of late maastrichtian heterohelicidae planktic foraminifera from the atlantic region abstract late maastrichtian planktic foraminiferal heterohelicidae from deep sea drilling project sites in the northwestern atlantic 111 and 605 the south atlantic 356 and 357 and from mediterranean land sections near e1 kef tunisia and caravaca spain show two bioprovinces site 111 has transitional heterohelicid faunas in which a few heterohelix species dominate while the other localities have diverse tethyan faunas a quantitative analysis allows for a more detailed subdivision within the tethyan faunas heterohelicid species occur in different relative frequencies at the south atlantic the north atlantic and the mediterranean localities the south atlantic dsdp sites contain heterohelix rajagopalani govindan in addition to all other tethyan species the faunas from the two mediterranean sections are comparable however the overall diversity at el kef is the lowest of all tethyan sections and the area is interpreted as representing paleo upwelling the otherwise diverse faunas from the north atlantic site 605 contain some transitional elements which suggests mixing with cooler surface waters possibly derived from a proto labrador current

impact production of co2 by the cretaceous tertiary extinction bolide and the resultant heating of the earth evidence at the cretaceous tertiary boundary suggests that the proposed extinction bolide struck a continental or shallow marine terrane this evidence includes shocked quartz and feldspar grains found in the boundary layer inherited from a range of rock types a high 87 sr 86 sr ratio in some planktonic fossils which could reflect continental derived sr ref 5 and evidence that the platinum group element rich clay layer is underlain at some localities by a deposit of possible tsunamic origin these observations and data demonstrate that sea level at the end of the cretaceous was 150 200 m higher than at present suggesting the possibility that the extinction bolide struck a shallow marine carbonate rich sedimentary section here we show that the impact of such a bolide 5km in radius onto a carbonate rich terrane would increase the co 2 content of the atmosphere by a factor of two to ten additional dissolution of co 2 from the ocean s photic zone could release much larger quantities of co 2 the impact induced release of co 2 by itself would enhance atmospheric greenhouse heating and give rise to a worldwide increase in temperature from 2 k to 10 k for periods of 10 4 to 10 5 years

guembelitria dominated late maastrichtian planktic foraminiferal assemblages mimic early danian in central egypt abstract during the late maastrichtian 66 8 65 5 ma the asyut basin in central egypt experienced a breakdown of the surface to bottom gradient of the 13c 12c ratio with planktic 13c values 0 2 0 8 lighter than benthic values planktic foraminiferal species diversity was reduced by more than 50 with assemblages dominated 60 90 by the opportunistic blooms of the disaster species guembelitria cretacea which mimic the early danian the prolonged breakdown in productivity occurred during a time of tectonic activity and increased terrestrial runoff that may have resulted in highly eutrophic waters coupled with a sea level regression 65 5 ma that led to restricted circulation increased productivity during the short climate warming between 65 4 and 65 2 ma is associated with increased species diversity abundant rugoglobigerinids and common heterohelicids at the end of the maastrichtian decreased productivity coincided with the k t impact and mass extinction followed by characteristically early danian low diversity assemblages the similarity of the late maastrichtian and post k t impact guembelitria dominated assemblages reveals that the planktic foraminiferal response to the k t catastrophe was not unique but followed a predictable pattern of response to severe environmental perturbations

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

calcareous nannofossil biostratigraphy and paleoecology of the cretaceous tertiary transition in the central eastern desert of egypt abstract the gebel qreiya and nearby wadi hamama sections of the central eastern desert are among the most complete k t boundary sequences known from egypt the two sections were analyzed spanning an interval from l 83 myr below to about 3 myr above the k t boundary a 1 cm thick red clay layer at the k t boundary at gebel qreiya contains an ir anomaly of 5 4 ppb the high resolution study and well preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the k t transition in egypt four zones micula murus micula prinsii np1 and np2 were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern tethys region latest maastrichtian assemblages are abundant and diverse though cretaceous species richness progressively decreased across the k t boundary dominant species include arkhangelskiella cymbiformis micula decussata and watznaueria barnesae with high abundance of dissolution resistant m decussata reflecting periods of high environmental stress thoracosphaera blooms mark the k t boundary and are followed by an acme of the opportunistic survivor braarudosphaera bigelowii the first appearance of the new tertiary species cruciplacolithus primus and an acme of coccolithus cavus pelagicus these successive abundance peaks provide the basis for subdivision of the early danian zones np1 and np2 into five subzones correlation of selected nannofossil taxa from the egyptian sections with those from various onshore marine and deep sea sections provides insights into their paleoenvironmental and paleoecological affinities

decline of the maastrichtian pelagic ecosystem based on planktic foraminifera assemblage change implication for the terminal cretaceous faunal crisis an outer shelf upper slope tropical tethyan pelagic environment existed over southern israel during maastrichtian time planktic foraminifera in the 63 and 149 m size fractions from four sections in this area were studied quantitatively for a high resolution ecostratigraphic analysis of the pre cretaceous tertiary k t paleoenvironment during the maastrichtian 41 of the planktic foraminifera species became extinct mostly keeled globotruncanidae which also became quantitatively reduced near the end of the maastrichtian from as much as 35 to only 5 of the planktic foraminifera population evolutionary replacement of extinct species by new forms nearly ceased in that interval two major opportunistic blooms of guembelitria took place associated with reduced abundances of keeled forms and the dominant species heterohelix globulosa the first bloom occurred within the upper gansserina gansseri to lower abathomphalus mayaroensis zones and the second within the plummerita hantkeninoides zone the extinctions concomitant changes in faunal dominance and opportunist blooms indicate that the pelagic ecosystem in the negev area experienced multiple stresses during the maastrichtian the planktic foraminiferal assemblages were taxonomically impoverished and in decline prior to the k t boundary crisis

the impact of the cretaceous tertiary bolide on evaporite terrane and generation of major sulfuric acid aerosol abstract impact glasses from the k t boundary in haiti include high ca glasses with up to 1 wt so3 formed by the fusion of anhydrite or gypsum rich evaporite sediments in the presence of high silica melts derived from melting of continental crust experimental studies have duplicated these two melts by fusion of gypsum and andesite and suggest a formation temperature of 1300 c geochemical evidence from the glasses is consistent with their derivation from the 180 km diameter chicxulub impact crater on the yucatan peninsula mexico situated in a thick late cretaceous evaporite succession this large diameter crater is most likely the result of a cometary impact on the basis of bolide scaling from the ir anomaly in k t boundary sediments the sulfur degassing associated with formation of the high ca glass alone could have formed a2 1016 g h2so4 stratospheric aerosol however the total sulfur degassing from the evaporite rich sediments in the chicxulub impact site may have led to formation of3 8 1018 to1 3 1019 g sulfate aerosol and global atmospheric mass loading from the sulfate aerosol alone is estimated to beof the order of 1 2 6 g cm 2 combined with the great optical depth estimates of pollack et al 1 and covey et al 2 resulting from an impact dust cloud the sulfate aerosol may have contributed not only to a rapid decline in global surface temperatures to near freezing in about one week but also prolonged the cooling for several years because of the time dependent conversion of so2 to h2so4 aerosol in the atmosphere the contribution of sulfur to acid rain following the k t boundary event may have equalled the proposed rainout of nitric acid

terminal cretaceous warming event in the mid latitude south atlantic ocean evidence from poleward migration of contusotruncana contusa planktonic foraminifera morphotypes abstract spatial and temporal patterns in test size and shape test conicity and spiral roundness and absolute abundance accumulation rate of the planktonic foraminifer contusotruncana contusa were studied in the south atlantic ocean dsdp sites 356 516 525 and 527 during an interval corresponding to the last 800 kyr of the cretaceous the variation in absolute abundance of c contusa was characterised by alternating periods of high and low abundance some of these periods were traceable across the entire mid latitude south atlantic ocean while the mean spiral roundness did not show any interpretable patterns a sudden increase of the mean test size and mean test conicity occurred between 65 3 and 65 2 ma based on linear interpolation within the cretaceous part of subchron c29r at all sites studied indicating a poleward migration followed by rapid withdrawal of the low latitude c contusa morphotypes from the mid latitude south atlantic ocean we suggest that this event was caused by a short period of surface water warming in the southern mid latitudes corresponding to the brief high latitude warming event and associated faunal migrations in the boreal and austral realms

biotic effects of late maastrichtian mantle plume volcanism implications for impacts and mass extinctions abstract during the late maastrichtian dsdp site 216 on ninetyeast ridge indian ocean passed over a mantle plume leading to volcanic eruptions islands built to sea level and catastrophic environmental conditions for planktic and benthic foraminifera the biotic effects were severe including dwarfing of all benthic and planktic species a 90 reduction in species diversity exclusion of all ecological specialists near absence of ecological generalists and dominance of the disaster opportunist guembelitria alternating with low o2 tolerant species these faunal characteristics are identical to those of the k t boundary mass extinction except that the fauna recovered after site 216 passed beyond the influence of mantle plume volcanism about 500 kyr before the k t boundary similar biotic effects have been observed in madagascar israel and egypt the direct correlation between mantle plume volcanism and biotic effects on ninetyeast ridge and the similarity to the k t mass extinction which is generally attributed to a large impact reveal that impacts and volcanism can cause similar environmental catastrophes this raises the inevitable question are mass extinctions caused by impacts or mantle plume volcanism the unequivocal correlation between intense volcanism and high stress assemblages necessitates a review of current impact and mass extinction theories

a 20 km diameter multi ringed impact structure in the north sea most craters found on earth are highly eroded poorly preserved and only exposed on land here we describe a multi ringed impact structure discovered in the north sea from the analysis of three dimensional seismic reflection data the structure is 20 km in diameter and has at least ten distinctive concentric rings located between 2 and 10 km from the crater centre the structure affects cretaceous chalk and jurassic shales and is well preserved below several hundred metres of post impact tertiary strata which constrains its age to be 60 65 myr old the formation of concentric ringed impact structures at this relatively small scale had not previously been thought possible especially on the terrestrial planets we have mapped the ring structures at a resolution of tens of metres both laterally and in depth and show that the rings are fault bounded graben structures similar to fault arrays formed in low strain rate detachment tectonic settings strata deeper than 500 m palaeodepth appear unfaulted and we infer that the concentric ring structures may have accommodated post impact extension towards the excavated crater through detachment on weak layers within the chalk

gradual mass extinction species survivorship and long term environmental changes across the cretaceous tertiary boundary in high latitudes stable isotope and planktic foraminiferal analyses across the cretaceous tertiary k t boundary transition at nye klov indicate longterm oceanic instability associated with global sea level fluctuations a gradual mass extinction and decreased magnitude of the 13 c shift in high latitudes oceanic instability which began at least 100 kyr before the k t boundary and continued for about 300 kyr into the tertiary was accompanied by a gradual faunal turnover the maximum sea level lowstand during latest maastrichtian is recorded about 75 cm below the k t boundary a sea level rise first in evidence at 20 cm to 40 cm below the boundary continued into zone p0 boundary clay this sea level rise was accompanied by 2 c of cooling in surface and bottom waters prior to the k t boundary 13 c values remained relatively stable up to 10 cm below the k t boundary a negative shift of 0 5 to 1 0 per mil occurred in the boundary clay in both planktic and benthic foraminifera the surface to deep 13 c gradient remained nearly unchanged in contrast to low latitudes where this gradient is virtually eliminated no sudden mass extinction occurred in this cosmopolitan high latitude fauna and nearly all cretaceous taxa thrived well into the tertiary when they gradually disappeared shallow seas dominated by cretaceous survivor taxa and a well developed oxygen minimum zone prevailed during the earliest tertiary short term sea level lowstands are marked by hiatuses at the top of zones p0 and p1a about 50 kyr and 230 kyr after the k t boundary respectively rising sea level reestablished normal marine conditions about 300 kyr to 350 kyr after the k t boundary coincident with the first post k t boundary recovery of the tertiary fauna and extinction of cretaceous survivors during this time high latitude regions temporarily acted as centers of origin and dispersal for planktic foraminifera long term oceanic instability gradual faunal turnover absence of a sudden mass extinction and greatly diminished 13 c shift in high latitudes suggest that a k t boundary bolide impact was not the primary cause for the k t boundary faunal transition moreover these data strongly imply that the destructive effects of the bolide impact would have been greatest in low latitudes and negligible in high latitudes

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

high stress late maastrichtian paleoenvironment inference from planktonic foraminifera in tunisia high resolution v5 10 kyr planktonic foraminiferal analysis at elles tunisia reveals major changes in the structure of the tethyan marine ecosystem during the upper maastrichtian during the first 1 5 myr of the late maastrichtian 68 3 66 8 ma relatively stable environmental conditions and cool temperatures are indicated by diverse planktonic foraminiferal populations with abundant intermediate and surface dwellers a progressive cooling trend between v66 8 65 45 ma resulted in the decline of globotruncanid species intermediate dwellers this group experienced a further decline at the climax of a rapid warm event about 300 kyr before the k t boundary at the same time relative abundances of long ranging dominant species fluctuated considerably reflecting the high stress environmental conditions times of critical high stress environments during the late maastrichtian and particularly at the k t boundary are indicated by low species diversity and blooms of the opportunistic genus guembelitria at warm cool transition intervals during the last 100 kyr of the maastrichtian rapid cooling is associated with accelerated species extinctions followed by the extinction of all tropical and subtropical species at the k t boundary fl 2002 elsevier science b v all rights reserved

biotic effects of impacts and volcanism the biotic effects of late maastrichtian mantle plume volcanism on ninetyeast ridge and deccan volcanism mirror those of the cretaceous tertiary kt mass extinction and impact event planktonic foraminifera responded to high stress conditions with the same impoverished and small sized species assemblages dominated by the disaster opportunists guembelitria cretacea which characterize the kt mass extinction worldwide similar high stress late maastrichtian assemblages have recently been documented from madagascar israel and egypt biotic effects of volcanism cannot be differentiated from those of impacts though every period of intense volcanism is associated with high stress assemblages this is not the case with every impact the most catastrophic biotic effects occurred at the kt boundary 65 0 ma when intense deccan volcanism coincided with a major impact and caused the mass extinction of all tropical and subtropical species the chicxulub impact which now appears to have predated the kt boundary by about 300 kyr coincided with intense deccan volcanism that resulted in high biotic stress and greenhouse warming but no major extinctions the unequivocal connection between intense volcanism and high stress assemblages during the late maastrichtian to early danian and the evidence of multiple impacts necessitates revision of current impact and mass extinction theories

the k t boundary in oman identified using magnetic susceptibility field measurements with geochemical confirmation abstract recognizing distal ejecta marker horizons and correlating these among widely separated sections is typically difficult in the absence of visually distinctive marker beds here we propose a magnetic susceptibility ms field method to locate such horizons and explore the k t boundary interval at abat oman as a test of the method a distinctive pattern of high ms values was used to approximately locate the k t boundary interval in a sequence of platform carbonates which were then sampled in detail whole rock geochemical enrichments in ir v as ni co zn and zr and a large negative carbon isotope anomaly confirmed the inferred boundary location common microspherules whose chemistry reflects the whole rock geochemistry are associated with the boundary interval the association suggests that the microspherules formed during or as a result of the impact the geochemical record at the abat locality shows two levels where ir is high 1 ppb suggesting input from two impacts separated in the section by 1 35 m the upper level is chosen as the boundary interval based on the high ir 1 19 ppb 13c negative excursion 7 and distinctive ms pattern