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

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 stratotype section at el kef tunisia how catastrophic was the mass extinction abstract the cretaceous tertiary k t boundary stratotype section at el kef tunisia represents the most complete and expanded sedimentary record across this important mass extinction horizon presently known high resolution analysis of planktic foraminifera in two outcrops el kef i stratotype and el kef ii along with comparisons between planktic and benthic foraminifera calcareous nannofossils ostracods pollen and spores and dinoflagellates indicate that major changes across the k t boundary are registered only in benthic and planktic foraminifera and calcareous nannofossils biotic changes in benthic foraminifera are unique to el kef and similarly shallow continental shelf sections and appear to be the result of a sea level regression in the latest maastrichtian followed by a sea level rise across the k t boundary that was accompanied by expansion of the local oxygen minimum zone omz biotic changes in planktic foraminifera appear partly related to these conditions also but in general reflect more global oceanographic changes for instance species extinctions are gradual and selective as observed in k t sections worldwide rather than random and abrupt although there is a 69 decline in species richness between 25 cm below and 10 cm above the k t boundary only rare species disappeared their combined relative abundance constitute less than 20 of the total population about 52 of these extinct taxa 8 of the population are large ornate morphologically complex tropical subtropical forms that lived at or below the thermocline no planktic foraminifera from this depth range survived the k t boundary event all survivor taxa were surface dwellers living within the photic zone their relative abundance 80 dominates both cretaceous and early tertiary populations these data indicate that the k t biotic record in the shallow continental shelf section at el kef was significantly influenced by local conditions which combined with the latest maastrichtian sea level regression and subsequent sea level rise resulted in shallowing of the local omz relative to the sea surface shallowing of the local omz lead to the selective disappearance of benthic faunas and may have adversely affected the surviving photic zone dwellers the selective nature of species extinctions however appear to be related partly to long term global oceanographic changes which were accelerated at the k t boundary possibly by a bolide impact

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

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

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

chicxulub multiring impact basin size and other characteristics derived from gravity analysis the buried chicxulub impact structure in mexico which is linked to the cretaceous tertiary k t boundary layer may be significantly larger than previously suspected reprocessed gravity data over northern yucatan reveal three major rings and parts of a fourth ring spaced similarly to those observed at multiring impact basins on other planets the outer ring probably corresponding to the basin s topographic rim is almost 300 kilometers in diameter indicating that chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago

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

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

high stress paleoenvironment during the late maastrichtian to early paleocene in central egypt biostratigraphic mineralogical geochemical and isotopic analyses of the gebel qreiya section in the asyut basin of central egypt indicate a depositional environment interrupted by periods of erosion due to local tectonic activity exacerbated by eustatic sea level fluctuations and by high stress environmental conditions akin to those normally experienced during the cretaceous tertiary boundary transition during the late maastrichtian 66 8 65 4 ma this region experienced a breakdown of the biologically mediated 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 faunal assemblages dominated 75 90 by the opportunistic disaster species guembelitria cretacea which alternate with abundance of small low oxygen tolerant heterohelicids heterohelix navarroensis h dentata h globulosa this prolonged breakdown in ocean primary productivity occurred during a time of global climate cooling and sea level regressions at 66 8 and 65 5 ma though clay mineralogy suggests that locally low seasonality warm wet tropical and subtropical conditions prevailed the high detrital influx suggests that the biologically high stress environment was primarily linked to the existing shallow shelf conditions in southern egypt and possibly to local tectonic activity and restricted circulation a normal carbon isotope gradient was briefly re established during the short climate warming and rising sea level between 65 4 and 65 2 ma a time of increased species diversity peak abundance of rugoglobigerinids and common heterohelicids during the last 200 000 years of the maastrichtian increased precipitation and terrestrial runoff increased phyllosilicates and kaolinite and increasing total organic carbon values are associated with heterohelix dominated planktic foraminiferal assemblages the k t boundary is marked by a red clay layer and ir anomaly of 5 4 ppb during the early danian planktic foraminiferal populations and stable isotope data indicate that similarly fluctuating high stress conditions prevailed in central egypt as elsewhere in the marginal eastern tethys

petrology of impact melt rocks at the chicxulub multiring basin yucatan mexico compositions and textures of melt rocks from the upper part of the chicxulub structure are typical of melt rocks at other large terrestrial impact structures apart from variably elevated iridium concentrations less than 1 5 to 13 5 0 9 ppb indicating nonuniform dissemination of a meteoritic component bulk rock and phenocryst compositions imply that these melt rocks were derived exclusively from continental crust and platform sediment target lithologies modest differences in bulk chemistry among samples from wells located approximately 40 km apart suggest minor variations in relative contributions of these target lithologies to the melts subtle variations in the compositions of early formed pyroxene and plagioclase also support minor primary differences in chemistry between the melts evidence for pervasive hydrothermal alteration of the porous mesostasis includes albite k feldspar quartz epidote chlorite and other phyllosilicates as well as siderophile element enriched sulfides suggesting the possibility that chicxulub like sudbury may host important ore deposits

ichnosedimentologic evidence for a noncatastrophic origin of cretaceous tertiary boundary sands in alabama the clayton sands thin discontinuous sand bodies found at or near the cretaceous tertiary k t boundary at various sites in alabama previously have been attributed to 1 catastrophic tsunami deposition associated with a k t boundary impact or alternatively 2 noncatastrophic transgressive infilling of incised valleys cut during a preceding sea level low stand new observations on the geometry and ichnosedimentologic character of a clayton sand body enveloping strata and associated bounding surfaces exposed along mussel creek central alabama refute the tsunami origin and support the latter mechanism studies of other boundary deposits in the gulf region which may similarly benefit from ichnofossil investigations should consider more rigorously the evidence for sea level change near the k t transition

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

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

paleooceanography of the mesogean sea based on ostracods of the northern tunisian continental shelf between the late cretaceous and early paleogene a new method analysis used in the study of the el kef section north western tunisia led to the paleooceanographic reconstruction of the mesogean between late cretaceous and early paleogene several changes observed are in fact worthy of particular mention paleobathymetrically the area changed from an upper bathyal environment of about 400 m deep to an outer shelf domain of 100 50 m furthermore the oxygen minimum zone o m z became highly intense at a the cretaceous tertiary transition catastrophic event b the p1 p2 boundary intense thermic stratification and c between p4 and p6 very active paleoproductivity in this last episode the continental shelf environment was subjected to intense upwelling responsible for the formation of a prephosphatic environment at water sediment interface the paleooceanographic history of phosphates in the gafsa metlaoui basin is in fact in perfect stratigraphic and paleoenvironmental agreement with the paleobathymetric evolution of the kef region finally paleooceanographic communication between the mesogean and the north atlantic was at this period highly free because of lack of hydrologic relations between the north atlantic and the norwegian sea

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

new links between the chicxulub impact structure and the cretaceous tertiary boundary the 200 km diameter chicxulub structure1 3 in northern yucatan mexico has emerged as the prime candidate for the cretaceous tertiary k t boundary impact crater3 6 concentric geophysical anomalies associated with enigmatic occurrences of upper cretaceous breccias and andesitic rocks led penfield and camargo1 to suspect that this structure was a buried impact basin more recently the discovery of shocked quartz grains in a chicxulub breccia3 and chemical similarities between chicxulub rocks and k t tektite like glasses3 6 have been advanced as evidence that the chicxulub structure is a k t impact site here we present evidence from core samples that chicxulub is indeed a k t source crater and can apparently account for all the evidence of impact distributed globally at the k t boundary without the need for simultaneous multiple impacts or comet showers shocked breccia clasts found in the cores are similar to shocked lithic fragments found worldwide in the k t boundary ejecta layer7 8 the chicxulub melt rocks that we studied contain anomalously high levels of iridium up to 13 5 parts per 109 also consistent with the iridium enriched k t boundary layer9 our best estimate of the crystallization age of these melt rocks as determined by 40ar 39ar analyses is 65 2 0 4 1 myr in good agreement with the mean plateau age of 64 98 0 05 myr recently reported10 furthermore these melt rocks acquired a remanent magnetization indicating that they cooled during an episode of reversed geomagnetic polarity the only such episode consistent with40ar 39ar constraints is chron 29r which includes the k t boundary

u th age evidence from carbonate veins for episodic crustal deformation of central anatolian volcanic province abstract central anatolia represents one of the most outstanding examples of intraplate deformation related to both continental collision and back arc extension generating non uniformly distributed stress fields in this study we provide direct field evidence of various stress directions and investigate carbonate filled fracture systems in the central anatolian volcanic province using u th geochronology and isotope geochemistry for evaluating the episodes of latest volcanic activity under regional stress field data reveal two independent fracture systems in the region successive fracture development has been controlled by two different volcanic eruption centers hasandag composite volcano and acigol caldera trace element and stable c and o and radiogenic sr isotope compositions of carbonate veins indicate different fluid migration pathways for two different fracture systems the u th age data for carbonate veins of two independent fracture systems indicate that the crustal deformation intensified during 7 episodic periods in the last 150 ka the nne trending first fracture system was formed as a result of strain cycles in a period from 149 2 5 through 91 1 5 to 83 2 5 ka bp subsequent deformation events represented by the ene trending second fracture zone have been triggered during the period of 53 3 5 44 0 6 and 34 1 ka bp before the first fracture zone resumed the activity at about 4 7 0 15 ka bp although further studies are needed to evaluate statistical significance of age correlations the periods of carbonate precipitation inferred from u th age distributions in this study are comparable with the previous dating results of surrounding volcanic eruption events

the k t boundary at beloc haiti compared stratigraphic distributions of the boundary markers at beloc haiti the cretaceous tertiary boundary ktb is characterized by a spherule bed containing glass particles these particles are considered by some authors as remains of tektites resulting from a nearby impact however because of the stratigraphic complexity of the beloc sections the genetic link between the ktb cosmic event and the spherule bed is not obvious in this paper we report new data on shocked quartz and ni rich spinels at haitian ktb sites the detailed stratigraphy of these minerals shows that there is no empty gap in the sedimentary sequence the first and largest shocked quartz is found in the upper part of the spherule layer they are abundant and size graded over the 25 30 cm of carbonate rich sediments overlying this layer the first ni rich spinels which are also rich in cr appear in the carbonate sediments the size grading of the spherules and shocked quartz and the stratigraphical overlapping of their distributions suggests that these two components were derived from the same event although different from typical impact glasses tektites beloc glass particles must be considered as impact derived products the enormous fluence of shocked quartz 104 grains cm2 is consistent with a proximal event the upper part of the sequence is more complex a second distribution of shocked quartz associated with ni rich spinels of different compositions appears in the layer containing the maximum ir concentration we propose that these features which are not easily explained by a sedimentary artifact result from a second collisional event

mexican site for k t impact crater research throughout the caribbean suggests that the geophysical anomalies in the yucatan first noted by penfield and camargo 1981 and called the chicxulub crater could be the site of the impact purported to have caused the k t extinctions a semicircular ring of sink holes known locally as cenotes which correlates with the geophysical anomalies has been identified and it is argued that the origin of the cenote ring is related to postimpact subsidence of the chicxulub crater rim if there is indeed a crater the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km if confirmed as a site of impact the chicxulub crater would be the largest terrestrial impact crater known which is consistent with the uniqueness of the k t global catastrophe

chicxulub crater a possible cretaceous tertiary boundary impact crater on the yucatan peninsula mexico we suggest that a buried 180 km diameter circular structure on the yucatan peninsula mexico is an impact crater its size and shape are revealed by magnetic and gravity field anomalies as well as by oil wells drilled inside and near the structure the stratigraphy of the crater includes a sequence of andesitic igneous rocks and glass interbedded with and overlain by breccias that contain evidence of shock metamorphism the andesitic rocks have chemical and isotopic compositions similar to those of tektites found in cretaceous tertiary k t ejecta a 90 m thick k t boundary breccia also containing evidence of shock metamorphism is present 50 km outside the crater s edge this breccia probably represents the crater s ejecta blanket the age of the crater is not precisely known but a k t boundary age is indicated because the crater is in a thick carbonate sequence shock produced co2 from the impact may have caused a severe greenhouse warming

size and structure of the chicxulub crater revealed by horizontal gravity gradients and cenotes it is now widely believed that a large impact occurred on the earth at the end of the cretaceous period and that the buried chicxulub structure in yucatan mexico is the resulting crater24 knowledge of the size and internal structure of the chicxulub crater is necessary for quantifying the effects of the impact on the cretaceous environment although much information bearing on the crater s structure is available diameter estimates range from 170 to 300 km refs 1a 7 corresponding to an order of magnitude variation in impact energy here we show the diameter of the crater to be 180 km by examining the horizontal gradient of the bouguer gravity anomaly over the structure this size is confirmed by the distribution of karst features in the yucatan region mainly water filled sinkholes known as cenotes the coincidence of cenotes and peripheral gravity gradient maxima suggests that cenote formation is closely related to the presence of slump faults near the crater rim

estimation of sediment trapping behind check dams using high density electrical resistivity tomography abstract check dams are very important structures for torrent control areas throughout the world measuring the sediment deposition behind check dams is thought to be an effective method of estimating the sediment yield of small catchments in this study we employed a high density electrical resistivity system to detect sediment at six check dams distributed in the hilly and gully area of the loess plateau a total of 11 lines were arranged with 60 electrodes along each line the resultant resistivity data were inverted into subsurface structures using least squares inversion techniques the results indicate that the sediment bottom can been identified using an electrical resistivity contour method using trenches boreholes and drillings to calibrate the calculated values the accuracy of the high density electrical resistivity tomography method was found to be quite high 95 7 the bulk density increases with the sediment deposit depth and can reach a maximum of 1 6 g cm 3 geometric methods considering three shapes v shaped u shaped and trapezoidal were used to estimate the profile area of the check dams the v shaped geometric method showed high accuracy this study provides a four step approach based on high density electrical resistivity tomography and a geometric method to estimate sediment yield for check dam controlled catchments this methodology enables the measurement of the total sediment yield including both the suspended and bedload sediment transport from an ungauged catchment

chicxulub crater yucatan tektites impact glasses and the geochemistry of target rocks and breccias a comparison of breccias and basement rocks from four drill holes near the chicxulub impact structure yucatan a possible cretaceous tertiary k t boundary crater with black and yellow impact glasses from the haitian k t boundary layer shows that mixtures of andesite like rocks with carbonates and evaporites from chicxulub are compositionally different from the yellow glasses at the time of impact the chicxulub area was covered by evaporitic and carbonate deposits several kilometres thick because impact glasses are generally produced by shock melting of surface rocks a link between the haitian glasses and chicxulub is difficult to understand the 34 s isotopic signature of chicxulub breccias and evaporites is incompatible with that of a continental k t boundary we suggest that the pre impact target stratigraphy at chicxulub as well as the interpretation of the carbonate evaporite rocks as breccias should be revised

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

yucatan subsurface stratigraphy implications and constraints for the chicxulub impact much of the discussion about the effects of an end of cretaceous impact by a large extraterrestrial body in northwestern yucatan has been done in the context of limited and partly erroneous published data on the mesozoic stratigraphy of that area reexamination of cores and geophysical logs taken in several pemex wells has produced improved lithologic and biostratigraphic correlation of the jurassic to maastrichtian section across the northern yucatan peninsula these data suggest that major disturbance of strata by an impact would have been confined to within about 100 km of the proposed impact center near chicxulub the only unusual lithologic unit is polymict breccia which apparently was penetrated at or near the top of the cretaceous section in all the deep wells of northern yucatan this breccia in pemex wells yucatan 1 2 4 5a and 6 is composed predominantly of detrital dolomite limestone and anhydrite clasts set in dolomitized carbonate mud matrix which contains upper maastrichtian foraminifers these constituents mixed with fragments of altered glass or melt rock shocked quartz and feldspar and basement rock suggest an impact as the most likely origin for the breccia the timing of brecciation is poorly constrained by biostratigraphic data there is some evidence however that the breccia unit is overlain by about 18 m of uppermost maastrichtian marls suggesting an impact before the cretaceous tertiary boundary in addition there may have been more than one episode of breccia deposition

the cretaceous tertiary transition in guatemala limestone breccia deposits from the south peten basin limestone breccia deposits in southern mexico guatemala and belize have recently been interpreted as proximal to distal ballistic fallout deposits generated by a bolide impact that struck yucatan at k t boundary time we review the age lithology and the depositional environment of five k t boundary sections in the south peten area of guatemala caribe aserradero chisec actela chemal in order to evaluate the nature and origin of k t limestone breccia deposition the sections are located 500 km south of the proposed impact site at chicxulub and trend in an east west direction from the guatemala mexico border to southern belize in four of the five sections examined a breccia unit up to 50 m thick overlies reef bearing shallow water limestones of late cretaceous campanian maastrichtian age rhythmically bedded limestones marls and siltstones of early danian age overlie the breccia and were deposited under middle to outer neritic conditions the breccia consists of differently coloured layers of shallow water limestones clast size generally decreases upsection to thin layers of predominantly rounded clasts and these fine grained rudstones grade into grainstones at the top in at least one section ei caribe diagenetically altered glass spherules are present in the uppermost layers of the grainstone these glass spherules are of stratigraphic position and chemical composition similar to black and yellow glass from beloc haiti and mimbral mexico which some workers have chemically linked to melt glass within the breccia of the chicxulub cores we suggest that breccia deposition in guatemala may have been multi event over an extended time period and related to the collision of the yucatan and chortis plates as well as related to a major impact or volcanic event at the end of the cretaceous

theropod avian pterosaur and arthropod tracks from the uppermost cretaceous las encinas formation coahuila northeastern mexico and their significance for the end cretaceous mass extinction two unique localities that combine an unusual diversity of avian pterosaurian and dinosaur tracks as well as trails of arthropods were recently discovered by us in uppermost maastrichtian siliciclastic sediments of the las encinas formation in the mexican state of coahuila 40 km north of saltillo the trackway assemblages at amargos and rancho san francisco were produced by at least six different types of birds while trackways of azhdarchoid pterosaurs are rare only a single footprint was produced by a nonavian theropod a diverse ichnofauna of arthropod traces is also present in a different facies the tetrapod trackway assemblage was deposited during the very latest maastrichtian as indicated by an up to 2 5 m thick unit with abundant smectite spherules attributed to the chicxulub impact less than 8 5 m stratigraphically up section at amargos sphenodiscus pleurisepta is the last ammonite at amargos and may have crossed the cretaceous paleogene boundary

bedrock detection beneath river terrace deposits using three dimensional electrical resistivity tomography abstract we describe the use of a fully volumetric geophysical imaging approach three dimensional electrical resistivity 3d ert for bedrock detection below mixed sand and gravel deposits typical of fluvial valley fill terraces we illustrate the method through an analysis of terrace deposits of the great ouse river uk where up to 4 m of sand and gravel have filled the valley bottom during the latest pleistocene we use an edge detector to identify the steepest gradient in first derivative resistivity profiles which yields an estimate of bedrock depth verified by drilling to a precision better than 0 2 m average and 0 4 m standard deviation comparison of a range of drilling techniques at the site has revealed that borehole derived interface depths suffered from levels of uncertainty similar to those associated with the 3d ert indicating that the reliability of bedrock interface depths determined using these two approaches is comparable in this case the 3d ert method provides a high spatial resolution that enabled a previously unknown erosional bedrock structure associated with the change from deeper first terrace to second terrace deposits to be identified in the great ouse valley the method provides a relatively quick method to quantify terrace fill volume over large sites to a greater degree of precision than currently available

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

the cretaceous tertiary boundary in southern low latitude regions preliminary study in pernambuco northeastern brazil a preliminary integrated study of a cretaceous tertiary k t boundary section in pernambuco northeastern brazil provides evidence for an extraterrestrial bolide impact in the earliest danian a non graded nodular carbonate mudstone wackestone bed is interpreted as a slump or a mud flow deposit induced by a tsunami event or by a gravity mass movement during a sea level lowstand the former possibly generated by the k t boundary yucatan impact this bed overlies marlstones deposited in an upper bathyal environment and marks the top of the cretaceous nearly all known latest maastrichtian planktonic foraminifera are recovered from the cretaceous strata iridium shows a marked peak in a thin hemipelagic claystone layer about 75 cm above the k t boundary deposited in a middle to deep neritic environment the claystone overlies alternating beds of finegrained limestones and marlstones and a 50 cm thick graded bioclastic packstone which rests upon a marly limestone breccia of the lowermost danian abundant reworked cretaceous and rare lowermost danian microfossils e g e edita e eobulloides e fringa g irregularis p eugubina p cf pseudobulloides w claytonensis and w hornerstownensis have been recovered from these strata these lowermost danian beds record the sudden appearance of abundant shock metamorphosed quartz grains with several sets of intersecting deformation lamellae and microtektite like microspherules this suggests that these deposits were formed by an additional tsunami caused by a second impact event in the earliest danian near or at the boundary between the palaeocene p and p 1a foraminiferal zones impact derived material has not been found in the uppermost cretaceous beds

the cretaceous tertiary boundary at beloc haiti no evidence for an impact in the caribbean area abstract the k t boundary at beloc in haiti is characterized by a bed containing more or less spheroidal globules composed of either smectite or calcite a small fraction of these objects still contains well preserved glass particles which have been interpreted as the remains of tektites resulting from a bolide impact in the caribbean area however beloc glasses are markedly different from tektites and microtektites their structure and composition suggest that they are not impact generated products but are likely of volcanic origin on the other hand in sections which have probably preserved their original stratigraphy the globule bed showing well developed grading appears first in the sedimentary column followed by the ubiquitous cretaceous tertiary boundary ktb clay layer containing ir and ni rich spinels granulometric considerations indicate that the globule bed and the ir and spinel rich clay layer correspond to two distinct events we conclude that the globules at the ktb depositional sequence of beloc represent a local volcanic event slightly preceding the great ktb cosmic catastrophe our observations do not provide any unequivocal evidence that a cratering event occurred nearby

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

using dc resistivity tomography to detect and characterize mountain permafrost direct current dc resistivity tomography has been applied to different mountain permafrost regions despite problems with the very high resistivities of the frozen material plausible results were obtained inversions with synthetic data revealed that an appropriate choice of regularization constraints was important and that a joint analysis of several tomograms computed with different constraints was required to judge the reliability of individual features the theoretical results were verified with three field experiments conducted in the swiss and the italian alps at the first site near zermatt switzerland the location and the approximate lateral and vertical extent of an ice core within a moraine could be delineated on the murtel rock glacier eastern swiss alps a steeply dipping boundary at its frontal part was observed and extremely high resistivities of several m indicated a high ice content the base of the rock glacier remained unresolved by the dc resistivity measurements but it could be constrained with transient em soundings on another rock glacier near the stelvio pass eastern italian alps dc resistivity tomography allowed delineation of the rock glacier base and the only moderately high resistivities within the rock glacier body indicated that the ice content must be lower compared with the murtel rock glacier

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

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

deposition and age of chicxulub impact spherules on gorgonilla island colombia the end cretaceous mass extinction 66 ma has long been associated with the chicxulub impact on the yucatan peninsula however consensus on the age of this impact has remained controversial because of differing interpretations on the stratigraphic position of chicxulub impact spherules relative to the mass extinction horizon one side argues that the impact occurred precisely at the cretaceous paleogene boundary thus coinciding with the mass extinction the other side argues that the impact predated the cretaceous paleogene boundary based on the discovery of primary impact spherules deposits in ne mexico and texas near the base of planktic foraminiferal zone cf1 dated at 170 k y before the cretaceous paleogene boundary a recent study of the most pristine chicxulub impact spherules discovered on gorgonilla island colombia suggested that they represent a primary impact deposit with an absolute age indistinguishable from the cretaceous paleogene boundary here we report on the gorgonilla section with the main objective of evaluating the nature of deposition and age of the spherule rich layer relative to the cretaceous paleogene boundary the gorgonilla section consists of light gray yellow calcareous siliceous mudstones pelagic deposits alternating with dark olive brown litharenites turbidites a 3 cm thick dark olive green spherule rich layer overlies an erosional surface separating maastrichtian and danian sediments this layer consists of a clast supported normally graded litharenite with abundant chicxulub impact glass spherules lithics mostly volcanic and maastrichtian as well as danian microfossils which transitions to a calcareous mudstone as particle size decreases mineralogical analysis shows that this layer is dominated by phyllosilicates similar to the litharenites turbidites that characterize the section based on these results the spherule rich layer is interpreted as a reworked early danian deposit associated with turbiditic currents a major hiatus 250 k y spanning the cretaceous paleogene boundary and the earliest danian is recorded at the base of the spherule rich layer based on planktic foraminiferal and radiolarian biostratigraphy and carbon stable isotopes erosion across the cretaceous paleogene boundary has been recorded worldwide and is generally attributed to rapid climate changes enhanced bottom water circulation during global cooling sea level fluctuations and or intensified tectonic activity chicxulub impact spherules are commonly reworked and redeposited into younger sediments overlying a cretaceous paleogene boundary hiatus of variable extent in the caribbean central america and north atlantic while primary deposits are rare and only known from ne mexico and texas because of their reworked nature gorgonilla spherules provide no stratigraphic evidence from which the timing of the impact can be inferred

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

yucatan subsurface stratigraphy implications and constraints for the chicxulub impact comment and reply 92 geology january 1997david j and syme e c 1994 u pb geochronology of the late neoarcheantonalites in the flin flon belt trans hudson orogen surprise at the surface canadian journal of earth sciences v 31 p 1785 1790 david j bailes a h and mac hado n 1996 evolution of the sno w lake portionof the paleoproterozoic flin flon and kisseynew belts trans hudson orogen manitoba canada precambrian research in press gale d lucas s b and dixon j m 1996 structural geology of the flin flonarea manitoba and saskatchewan geological survey of canada current re search 1996 c p 93 103 gordon t m and lemk ow d r 1987 geoc hemistr y of the missi gr oup v olcanicrocks wekusk o lake manitoba geological survey of canada open filereport1442 gordon t m hunt p a bailes a h and syme e c 1990 u pb ages from theflin flon and kisse ynew belts manitoba chronology of crust formation at anearly proter ozoic accr etionar y mar gin in lewry j f and stauf fer m r eds the ear ly proter ozoic trans hudson or ogen of nor th amer ica geolo gical as socia tion of canada special p aper 37 p 177 199 machado n and zwanzig h v 1995 u pb geochronology of the kisseynew do main in manitoba provenance ages for metasediments and timing of magma tism in trans hudson orogen transect lithoprobe report 48 p 133 138 zwanzig h v 1995 alternative structural restorations of the flin flon beltkisseynew belt boundary zone in trans hudson orogen transect lithoprobereport 48 p 135 142

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

characteristics and origin of the glass spherules from the paleocene flood basalt province of western greenland abstract glass spherules have been found in several paleocene sandstone beds in central nuussuaq western greenland these beds are a mixture of glass smectite and calcite with rare occurrence of graphite and metal the glass varies from a basaltic to a basic andesitic composition and displays on a micrometer scale mg al ca fe ni and cu enrichments relative to the bulk composition these enrichments are associated with resorbed silicate crystals plagioclase pyroxene and olivine and partly oxidized metal sulphide inclusions the spherules have high co ni cu and ir concentrations positively correlated with fe the high cu content of the glass and the nonmeteoritic ir cu and ir ni or ir co ratios of the spherules exclude a meteoritic origin for these elements these compositional characteristics indicate a purely terrestrial origin and likely result from the contamination of a basaltic andesitic melt by sulphide liquid formed through reduction of a magma by c rich sediments this mechanism has already been proposed to account for the occurrence of fe bearing basalts and andesites in the nuussuaq and disko area this origin is further supported by the high cr content of the glasses consistent with a highly magnesian tholeiitic picrite basalt for the parent magma and the presence of metal sulphide and graphite in the spherule layers the occurrence in the glass of rounded magnetite resulting from the oxidation of sulphide and of dendritic spinel crystals characteristic of a rapid growth from a high temperature melt show that the spherules were quenched in an oxidizing environment we conclude that nuussuaq glass spherules result from rapid and incomplete oxidation of liquid droplets generated by one or several episods of lava fountains

cretaceous tertiary chicxulub impact angle and its consequences the chicxulub impact structure exhibits asymmetries in its geophysical signatures that closely resemble asymmetries produced by oblique impacts in laboratory experiments and recognized on planetary surfaces these asymmetric signatures suggest a trajectory for the chicxulub bolide from the southeast to the northwest at a 20 30 angle from the horizontal as a result biotic extinctions may have been most severe and catastrophic in the northern hemisphere geographic variation in the magnitude of the cretaceous tertiary k t fern spike and palynofloral extinctions are consistent with the proposed trajectory

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

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

the dimensions of the chicxulub impact crater and impact melt sheet the chicxulub impact crater which is the principal source of impact debris in cretaceous tertiary boundary sediments is currently buried by a 1 km thick sequence of carbonate sediments because the crater is not exposed for direct scrutiny its size has remained uncertain and in particular estimates ranging from 100 to 300 km have been made on the basis of gravity and magnetic field data in this study the physical properties of the k t boundary impact ejecta and chicxulub impact melt sheet have been used to test the geophysical estimates of the impact crater s size on the basis of the measured thickness of impact ejecta in haiti and north america the calculated volume of the impact melt sheet and the chemical and isotopic composition of the melt sheet the chicxulub impact crater is inferred to be 180 km in diameter and to contain a 3 to 7 km thick melt sheet and breccia sequence within a centrally located 100 km diameter region that corresponds to the limits of the transient cavity

gravity and magnetic field modeling and structure of the chicxulub crater mexico the chicxulub crater is an 180 km diameter peak ring crater based on drill hole logs and samples potential fields seismic reflection profiles and surface fracture patterns a structural cross section produced based on these constraints has the features expected for a large complex impact crater the bouguer gravity anomaly consists of a broad 90 km radius 30 mgal low with a central 20 km radius 20 mgal high and two 5 mgal concentric lows at 35 and 60 km radius the gravity anomaly is disrupted by large scale basement anomalies and possibly by large scale slumping and backwash erosion effects the magnetic field anomaly over the crater consists of three zones an outer zone from 45 to 90 km radius of low amplitude short wavelength anomalies with an irregular perimeter a middle zone from 20 to 45 km radius of high amplitude short wavelength anomalies slightly elongated nnw sse and an inner 20 km radius single large amplitude anomaly magnetic field modeling indicates that the melt pool averages 90 km in diameter and the melt volume in the crater is estimated at 20 000 km3 the melt pool size constrains the collapsed transient cavity diameter to 90 km gravity and magnetic field modeling indicate that the structural uplift is irregular in shape but 40 km in diameter and underlies or protrudes into the melt pool the preliminary structural cross section indicates that the inferred peak ring is decoupled from the structural uplift the geometry and bouguer gravity signature of the crater indicate that no significant uplift of the moho or relaxation of the crater has occurred

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

disaster opportunists guembelitrinidae index for environmental catastrophes blooms of the disaster opportunist guembelitria species are proxies for environmental catastrophes whether impact or volcanism leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions during the late maastrichtian and early danian zones p0 and pla guembelitria blooms show global distributions but with the largest blooms 40 80 guembelitria in low and middle latitudes and only minor blooms 10 20 in high latitudes late maastrichtian guembelitria blooms are so far known from the indian ocean and eastern tethys the most intense guembelitria blooms 60 guembelitria occurred in shallow continental shelf areas slope shelf margins and volcanic provinces of the indian ocean what these environments have in common is high nutrient influx eutrophication either from continental runoff upwelling along continental margins or volcanic input at times of biotic crises guembelitria blooms may have spread rapidly to the exclusion of most or all other species much like today s red tides but with near global distributions a simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species within such highly stressed environments guembelitria is the only genus to thrive and without competition rapidly reproduce and exponentially increase their populations when nutrients are depleted populations rapidly decrease leading to ecologic niches for other generalists and ecosystem recovery small low o2 tolerant heterohelicid populations mark this second stage followed by small trochospiral and planispiral species with further environmental recovery increasing competition niche development and restoration of a well stratified water mass oligotrophic conditions are restored opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages this ecological succession is observed in association with mantle plume volcanism in the indian ocean and eastern tethys during the late maastrichtian and in association with the k t impact and volcanism during the early tertiary d 2004 elsevier b v all rights reserved

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

rates and spatial variations of soil erosion in europe a study based on erosion plot data an extensive database of short to medium term erosion rates as measured on erosion plots in europe under natural rainfall was compiled from the literature statistical analysis confirmed the dominant influence of land use and cover on soil erosion rates sheet and rill erosion rates are highest on bare soil vineyards show the second highest soil losses followed by other arable lands spring crops orchards and winter crops a land with a permanent vegetation cover shrubs grassland and forest is characterised by soil losses which are generally more than an order of magnitude lower than those on arable land disturbance of permanent vegetation by fire leads to momentarily higher erosion rates but rates are still lower than those measured on arable land we also noticed important regional differences in erosion rates erosion rates are generally much lower in the mediterranean as compared to other areas in europe this is mainly attributed to the high soil stoniness in the mediterranean measured erosion rates on arable and bare land were related to topography slope steepness and length and soil texture while this was not the case for plots with a permanent land cover we attribute this to a fundamental difference in runoff generation and sediment transfer according to land cover types on the basis of these results we calculated mean sheet and rill erosion rates for the european area covered by the corine database estimated rill and interrill erosion rates are ca 1 2 t ha 1 year for the whole corine area and ca 3 6 t ha 1 year 1 for arable land these estimates are much lower than some earlier estimates which were based on the erroneous extrapolation of small datasets high erosion rates occur in areas dominated by vineyards the hilly loess areas in west and central europe and the agricultural areas located in the piedmont areas of the major european mountain ranges c 2010 elsevier b v all rights reserved