glass from the cretaceous tertiary boundary in haiti tektite like glasses preserved at the cretaceous tertiary boundary at beloc in haiti provide clear evidence of an impact event the glass composition suggests that the impact occurred on a continental shelf region generating a silica rich glass with chemical composition that reflects the melting of continental crustal rocks and a calcium rich glass produced by the fusion of marl sediments these findings indicate that catastrophic release to the atmosphere of 1015 moles of c02 from vaporized marl occurred during the impact

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

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

regional tilt of the mount stuart batholith washington determined using aluminum in hornblende barometry implications for northward translation of baja british columbia we have developed a new quantitative method to estimate paleohorizontal in granitic plutons using the aluminum in hornblende ah barometer the method is used to correct previously published paleomagnetic data from the 93 96 ma mount stuart batholith of the cascades mountains washington state for the effects of postemplacement tilting ah barometry was done on 46 samples from the batholith using the compositions of hornblende rims coexisting with the full mineral assemblage required for pressureestimation high contrastback scatteredelectronimagingwas usedtoensurethattheanalyzedhornblendeswerenotsignificantly affected by subsolidus alteration the success of the ah barometry is indicated by two observations first increases in the al content of the hornblendes are governed almost entirely by a pressure sensitive tschermak type substitution second amphibole plagioclase thermometry indicates that assemblage equilibration occurred at or very near magmatic conditions 650 c and that temperature has a negligible effect on our pressure estimates ah barometry results indicate that the depth of crystallization across the batholith decreases systematically from 0 3 gpa in the northwest to 0 15 gpa in the southeast consistentwithindependentbarometryforthecontactaureole ofthebatholithandregionalstructuralandstratigraphicrelations using a best fit planar tilt model and bootstrap analysis of uncertainties we estimate that the paleohorizontal plane has a strike of 43 630 4 and dip of 7 62 0 southeast 695 confidence our estimated paleohorizontal allows us to restore the paleomagnetic data of beck et al 1981 and to estimate the original paleolatitude of the mount stuart batholith beck et al found that the southern part of the batholith yielded a number of sites with a well defined high coercivity remanence the carrier of this remanence was not resolved but the following four lines of evidence stronglysuggestthatthepublisheddirectionswereacquiredshortly after emplacement of the batholith 1 the stable sites all came from the shallowest and most rapidly cooled portions of the batholith as indicated by our ah results and concordant k ar ages for hornblende biotite pairs 2 the high coercivity component was always normal in polarity which is consistent with emplacement of the mount stuart batholith at the end of the cretaceous long normal 3 sites from the batholith and the contact aureole gave similar directions 4 the directions show no indication of tilt related smearing after restoration the paleomagnetic data indicate 42 6 11 clockwise rotation and 3100 6 600 km of northward offset

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

magnetostratigraphy of the cretaceous tertiary boundary at agost spain a detailed magnetostratigraphic investigation of the agost section spain containing the cretaceous tertiary k t boundary is reported thermal demagnetization contrary to alternating field demagnetization succeeds in revealing the polarity of the characteristic remanent magnetization although an overlap in blocking temperature spectrum exists with a normal polarity secondary magnetization component the k t boundary occurs at two thirds from the base of a reversed polarity zone and by comparison with earlier results 1 this polarity zone is correlated to chron c29r linear regression of sedimentation rates in other sections with an established magnetostratigraphy and containing the k t boundary yields an age of 66 45 ma for this boundary on the basis of this age and the magnetic reversal ages of the berggren et al 13 polarity time scale new first appearance fad ages around the k t boundary are suggested for the planktonic speciesmorozovella trinidadensis bolli 66 04 ma morozovella pseudobulloides plummer 66 34 ma eoglobigerina taurica bang 66 41 ma and globigerina eugubina luterbacher premoli silva 66 43 ma

conventional and ion microprobe u pb dating of detrital zircons of the tentudia group serie negra sw spain implications for zircon systematics stratigraphy tectonics and the precambrian cambrian boundary conventional multi grain and ion microprobe dating of detrital zircons from a very low grade metagraywacke of the tentudia group upper part of the serie negra ossa morena zone sw spain reveals an uppermost vendian age for the deposition of the metagraywacke the youngest detrital zircon grain provides a maximum depositional age of about 565 ma thus these data contradict earlier middle to upper riphean ca 1350 850 ma estimates on the age of the tentudia group and favour a precambrian cambrian boundary falling into the range of 540 to 530 ma the presence of about 20 of pan african detrital zircons ranging from about 700 to 550 ma indicates the derivation from gondwana from the upper intercept ages of the fan shaped data field defined by conventionally determined zircon fractions it can be deduced that 2 1 ga old zircons as well as archean zircons existed in the provenance s of the serie negra sediments this mixing of crustal components of different ages is in line with the nd crustal residence age of 1 9 ga the latter value as well as other model ages of the iberian massif indicates unusually high amounts of ancient crust to be present in the strata this is different to other meta sediments of the european hercynides and suggests that the iberian strata of uppermost precambrian age may contain the detritus of more internal older parts of gondwana than other european strata of comparable ages geochemical data on the analysed sample and further metagraywackes of the tentudia group argue for a deposition in an arc environment such a scenario would conform with the syn to post orogenic shallow marine deposition of the studied sediments furthermore an upper time limit for the pre lower cambrian deformational history including two phases of regional deformation is given by the maximum age of deposition implying a very short time interval for deposition and deformation of the tentudia group concerning the u pb systematics of detrital zircon fractions it is probable that numerous previously published conventional multi grain zircon data on meta sedimentary rocks of the european hercynides readily can be explained by the presence of up to 20 of pan african detrital zircons and later phanerozoic lead loss during metamorphic transformation of the sedimentary protoliths moreover this implies that such metasediments originated from post pan african sedimentary precursors

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

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

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

structure of the castillo granite southwest spain variscan deformation of a late cadomian pluton a geometrical reconstruction of the 500 ma old castillo granite pluton sw iberia is completed on the basis of structural and geophysical rock magnetism techniques the pluton is intrusive into latest proterozoic earliest cambrian metasediments and conforms a tabular intrusion 6 km in diameter and 1 7 km thick that was emplaced at a depth of 10 km its magnetic fabric reveals that the strike of moderately to steeply dipping magmatic flow planes forms a high angle to the regional tectonic trends magnetic foliations and associated moderately to gently plunging magnetic lineations represent magmatic flow planes and directions the internal anisotropy of the granite together with the structure shown by the country rocks attest the lateral propagation of the pluton and its latter inflation the pluton s root zone would correspond to a likely thin subvertical feeder structure initiated near the orientation of regional 1 at the time of emplacement during the variscan orogeny the pluton was tilted and underwent localized brittle ductile strain in relation to shear zone deformation in the footwall of a major ductile thrust tilting permits the observation and study of a vertical profile of the intrusion localized deformation caused superposition of tectonic zonations on the magmatic ones a reactivation of the basal contact of the pluton and dismemberment from its root this and other granitoid plutons of similar age emplaced at a similar depth constrained the creation of crustal mechanical heterogeneity and anisotropy this controlled the site of pluton emplacement the nucleation of a major ductile thrust and localization of deformation and tectonic displacements along the pluton margins during later orogenic reactivation

magnetic fabric implications for the relationships between deformation mode and grain growth in slates from the borrowdale volcanic group in the english lake district abstract in the less chlorite rich slates from the borrowdale volcanic group chlorite magnetic fabric almost corresponds to fabric resulting from deformation following the march fernandez model but chlorite grain rotation could be related to the first stages of the tectonic deformation in the other slates the chlorite grains probably impinging after these stages upon one another and a simple grain rotation mechanism being therefore no longer possible

magnetic fabric and microstructural evidence for a tectono thermal overprint of the early proterozoic murray pluton central ontario canada abstract the 2 38 ga old murray granite pluton intruded the southern footwall of the sudbury igneous complex and was subjected to repeated ductile deformation its nw and se domains display differences in strain state ams signature and the nature and distribution of fe oxide minerals the magnetic foliation is parallel to the visible foliation in the nw domain but discordant to it in the se domain microstructural data show that the magnetic fabric in the nw domain coincides with a foliation formed at high temperature probably in response to thermal softening during the emplacement of the adjacent sudbury igneous complex this tectono thermal overprint affected pre existing shape fabrics and was facilitated by incipient melting of the granite near the intrusive contact with the sudbury igneous complex rocks of the se domain are only partially overprinted and two mineral subfabrics are preserved prolate susceptibility ellipsoids and clusters of maximum susceptibility directions at the intersections of the two planar fabrics suggest oblique superposition of strain increments increases in bulk magnetic susceptibility and magnetic anisotropy degree towards the intrusive contact with the sudbury igneous complex can be explained by respective increases in the proportion of magnetite over ilmenite and strain intensity in the murray pluton

control of granite emplacement by regional deformation abstract a combination of structural measurements and gravity data is used to investigate the mode of granite emplacement in various tectonic settings the deepest zones revealed by gravity data provided those zones also show vertical lineations in outcrop are interpreted as magma feeder channels these structures or root zones reflect the flow pattern of the upwelling magma while being emplaced they can be interpreted within the regional stress field active during that time granites intruded during transcurrent shearing have only a few feeder channels these roots are not connected to the main shear zone all of them lie within locally extensional areas of the regional stress field this situation is also observed in granites emplaced during a compressional phase of deformation when emplaced during a regionally extensional phase the granitic plutons are very thin with many small deeper zones in which variously evolved granite types may be intrusive these regions vertically differentiated are also interpreted as feeder channels the different morphology at depth as well as the difference in the number of root zones suggest that deformation controls the emplacement of granitic plutons the root zones are oriented at a high angle to the direction of maximum compression when magma is emplaced in a plastic crust if the pluton is emplaced higher in a brittle crust then the roots are aligned with the maximum compression according to the andersonian theory of fracture the orientation of the root zone along the direction of extension in a plastic crust may be explained by shearing which acts as a valve mechanism for segregating magma in all the examples the geometry of the root zone relative to the major fault plane implies that the shear zone does not induce magma generation and that it does not serve as a guide for magma emplacement

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

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

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

the association between enso and winter atmospheric circulation and temperature in the north atlantic region the association among enso the northern hemisphere sea level pressure slp and temperatures in europe has been analyzed during the period 1873 1995 in the first part the sst of the nino 3 region has been used to select extreme cold and warm enso events and periods that can be regarded as normal the study was carried out for winter with the constraints that the enso events were well developed during the winter of study and that they are extreme events composites of winter slp and temperatures have been made for the selected cold and warm events as well as for normal cases and compared with each other in the north atlantic area no statistically significant slp anomaly patterns were found associated with warm events while during cold events a statistically significant anomaly pattern resembling the positive phase of the north atlantic oscillation nao was found the temperature analysis shows statistically significant negative anomalies during cold events over the iberian peninsula and positive anomalies over the british isles and southern scandinavia consistent with the slp anomalies the slp and temperatures have also been analyzed for spring the patterns resemble those found for winter but the anomalies have lower amplitudes for the completion of the composite analysis the consistency among events of the relationship between enso and slp as well as between enso and temperatures was examined the results show that the significant patterns found in the composite analysis in the north atlantic area are not the result of a few major events but rather because both the slp and temperature anomalies in this area during cold enso events are stable and qualitatively similar to those found during the positive phase of the nao the possible physical basis for this association between nao and enso is discussed

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

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

aureole deformation by flattening around a diapir during in situ ballooning the cannibal creek granite the cannibal creek granite a foliated pluton within a strongly deformed aureole shows several diagnostic features of a diapir the intensity of the aureole deformation diminished away from the contact the aureole foliation is continuous with that of the granite and forms closed elliptical trend lines and the contact metamorphic minerals are synkinematic with regard to the aureole foliation the pluton deformed its aureole in three stages involving initially brittle then ductile and finally brittle deformation styles initial intrusion of a low strength magma stoped kinked and flexed aside its overburden crystallization of the magma prevented further rise and it ballooned and deformed its aureole evidently entirely by ductile bulk shortening perpendicular to the contact this the major stage of aureole deformation records no evidence of vertical movement of the pluton or of progressive simple shear along its margin during this stage the magma may have been theologically a high strength bing

chicxulub impact event is cretaceous paleogene boundary in age new micropaleontological evidence abstract high resolution and quantitative planktic foraminiferal biostratigraphy from two se mexico stratigraphic sections bochil guayal shows that the chicxulub related complex clastic unit ccu is synchronous with the ejecta rich airfall layer and the cretaceous paleogene k pg catastrophic mass extinction horizon in the el kef tunisia and caravaca spain sections the lowermost danian h holmdelensis subzone biozone p0 was identified in both sections in a thin dark clay bed just above the ccu proving that such bed is chronostratigraphically equivalent to the k pg boundary clay of the el kef stratotype these new micropaleontogical data confirm that the k pg impact event and the chicxulub impact event are the same one this contradicts the suggestion by others that the chicxulub impact predated the k pg boundary by about 300 ka

late maastrichtian to early danian calcareous nannofossils at elles northwest tunisia a tale of one million years across the k t boundary a detailed study of calcareous nannofossils of the elles section tunisia was extended over an interval of about 1 myr including the k t boundary the late maastrichtian assemblages are rich and well preserved pulses of surface water cooling probably related to episodic upwelling are revealed by the increase in abundance of cool water taxa mainly kamptnerius magnificus nephrolithus frequens gartnerago spp in certain late maastrichtian samples paralleled by a decrease of the warm water species watznaueria barnesae a sensible decrease in abundance of arkhangelskiella cymbiformis and its return to smaller specimens was also recorded at elles probably as the result of surface water productivity changes in the latest maastrichtian some maastrichtian samples at elles contain neobiscutum romeinii and chiasmolithus sp these taxa formerly thought to be tertiary coccoliths are here considered as truly maastrichtian occurrences as at el kef the danian of elles is characterised by successive blooms of surviving and newly evolved species though the abundance of calcareous nannofossils rapidly reached the same level as in the maastrichtian the lower diversity still points to a mesotrophic poorly stratified marine environment the reworking versus survivorship of cretaceous species found in danian samples remains an unresolved question but a hypothesis of survivorship is also strengthened by the presence of several coccospheres of w barnesae and bidiscus rotatorius well above the boundary the effect of the marine environmental change across an expanded k t boundary section as elles appears complex if seen through calcareous nannofossils from a geological point of view the k t boundary floral turnover at elles seems dramatically synchronous with the signatures of an extraterrestrial impact superimposed on long term background environmental and climatic changes however a precise succession of events based on appearance disappearance of nannofossil species across the cretaceous paleocene transition is far from being unanambiguous

magnetic susceptibility of the mont louis andorra ilmenite type granite pyrenees a new tool for the petrographic characterization and regional mapping of zoned granite plutons we have observed remarkably consistent patterns of concentric zonation in the values of low field magnetic susceptibility measurements over the variscan age mont louis andorra granite pluton of the eastern pyrenees of andorra spain and france this zonation is a function of the rock petrology since a close correlation is shown between the petrographic nature as defined by chemical analysis and the magnetic susceptibility magnitude of the rocks it reflects the dominantly paramagnetic nature of the granite carried by fe bearing silicates and this is demonstrated by the fact that low field susceptibilities of representative specimens are almost equal to 1 their high field susceptibilities and 2 their calculated susceptibilities using fe contents assuming a null ferromagnetic contribution we conclude that this technique accurately reflects the modal abundances of ferromagnesian phases in rocks of the ilmenite series and that it represents a powerful and efficient tool for the reconnaissance surveying of petrological variations in granitoid plutons

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

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

evidence for a meteoritic component in impact melt rock from the chicxulub structure abstract the chicxulub structure in yucatan mexico has recently been recognized as a 200 km diameter multi ring impact crater of k t boundary age crystalline impact melt rocks and breccias from within the crater which have compositions similar to those of normal continental crustal rocks and which show shock metamorphic effects have been studied for trace element and re os isotope compositions re os isotope systematics allow the sensitive and selective determination of an extraterrestrial component in impact derived rocks a melt rock sample shows elevated indium concentrations an osmium concentration of 25 ppb and a low 187 os 188 os ratio of 0 113 which are incompatible with derivation from the continental crust even though the 187 os 188 os ratio is slightly lower than the range so far measured in meteorites a mantle origin seems unlikely for mass balance reasons and because the cratering event is unlikely to have excavated mantle material the data support the hypothesis of a heterogeneously distributed meteoritic component in the chicxulub melt rock a sample of impact glass from the haitian k t boundary at beloc yielded about 0 1 ppb osmium and an 187 os 188 os ratio of 0 251 indicating the presence of a small meteoritic component in the impact ejecta as well

gravity and magnetic signatures of the ackley granite suite southeastern newfoundland implications for magma emplacement a detailed gravity survey 255 stations over an area of 3000 km2 over the posttectonic devonian ackley granite suite in southeastern newfoundland suggests that a set of northwest trending geophysical lineations interpreted as faults controlled the bottom morphology of the magma chamber during emplacement the main negative bouguer gravity anomaly over the ackley granite suite trends in a north south direction across the trace of the dover hermitage bay fault the boundary between the gander and avalon terranes inversion of the gravity and density data indicates that the thickness of the granite suite varies between 2 and 8 km magnetic interpretation and modelling suggest that the southeast portion of the suite is underlain by mafic volcanic rocks typical of the avalon terrane the magnetically determined depth to the top of these is consistent with that calculated from the gravity data the combined geophysical models are indicative of a process of megablock stoping in which large crustal blocks wer

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

on the changing nature of the regional connection between the north atlantic oscillation and sea surface temperature 1 evidence is presented that the correlation between the north atlantic oscillation nao in terms of the nao index and the north atlantic sea surface temperature sst is not stationary this is inferred from both reanalysis data from the u s national centers for environmental prediction national center for atmospheric research ncep ncar and the kaplan sea surface temperature data set two phases of winterly north atlantic atmosphere ocean covariability are identified by means of linear regression and correlation analysis during the recent decades since the late 1960s early 1970s and during the first 3 decades of the twentieth century the north atlantic sst is strongly correlated to the regional atmospheric circulation in the north atlantic sector i e the north atlantic oscillation during these periods the nao index defined as the difference of normalized sea level pressures on the azores and iceland is characterized by pronounced decadal variability and by mainly positive values in contrast the nao index is only weakly correlated to the north atlantic sst from the 1930s to the early 1960s when the nao index is characterized by weak decadal variability remote influences in particular from the tropical pacific region become important especially for the sst in the western tropical north atlantic

global environmental changes preceding the cretaceous tertiary boundary early late maastrichtian transition stable carbon oxygen and strontium isotope data from maastrichtian planktic and benthic foraminifera from southern high latitude ocean drilling program sites 690 750 and 761 reveal major changes in climate and ocean chemistry during the early to late maastrichtian transition some 4 to 6 m y prior to the cretaceous tertiary k t boundary the 18o results suggest accelerated cooling resulting in the lowest marine temperatures of the late cretaceous the late maastrichtian rise in the seawater 87sr 86sr ratio begins at the time of this change and suggests increased rates of continental weathering and or runoff the 13c values show a negative shift of 0 5 followed by a positive shift of 1 these 13c fluctuations may reflect change in deep water chemistry with cooling variation in reduced carbon storage in coastal areas caused by eustatic sea level fluctuation and increased surface water productivity these findings contradict the common representation of stable and climatically equable environmental conditions in the latest cretaceous before the k t boundary event

the nonlinear association between enso and the euro atlantic winter sea level pressure a nonlinear projection of the tropical pacific sea surface temperature anomalies ssta onto the northern hemisphere winter sea level pressure slp anomalies by neural networks nn was performed to investigate the nonlinear association between el nino southern oscillation enso and the euro atlantic winter climate while the linear impact of enso on the euro atlantic winter slp is weak the nn projection reveals statistically significant slp anomalies over the euro atlantic sector during both extreme cold and warm enso episodes suggesting that the euro atlantic climate mainly responds to enso nonlinearly the nonlinear response mainly a quadratic response to the ssta reveals that regardless of the sign of the ssta positive slp anomalies are found over the north atlantic stretching from eastern canada to europe with anomaly center located just northwestward of portugal and negative anomalies centered over scandinavia and norwegian sea consistent with the excitation of the positive north atlantic oscillation pattern

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

stable seafloor conditions sea level and food supply during the latest maastrichtian at brazos river texas abstract the cretaceous paleogene k pg boundary extinction event is inextricably linked to the chicxulub impact environmental changes like sea level changes and changes in food supply prior to or after the impact could however have contributed to the biotic turnover in this study benthic foraminifera from two cores from the brazos river area in texas are quantitatively analyzed in order to reconstruct environmental changes across the k pg boundary cluster analysis as well as non metric multidimensional scaling reveals three distinct benthic foraminiferal assemblages an upper maastrichtian assemblage a post impact assemblage and a lower danian assemblage the rather uniform upper maastrichtian assemblage at brazos river composed of e g clavulinoides midwayensis gavelinella dumblei cibicidoides harperi gyroidinoides aequilateralis and bulimina kickapooensis indicates a stable paleodepth of about 75 100 m up to the k pg boundary food supply indicators such as percentage buliminaceae and foraminiferal numbers suggest a relatively low and stable food supply during this interval environmental disruption caused by the chicxulub impact led to the settlement of a typical pioneer assemblage characterized by endobenthic morphotypes such as ammobaculites spp and pseudouvigerina naheolensis during the early danian the typical midway type benthic foraminiferal shelf fauna e g alabamina midwayensis anomalinoides acutus gyroidinoides subangulatus praebulimina carseyae and cibicidoides alleni developed indicating a paleodepth of 75 100 m no clear water depth changes can be derived from the benthic foraminiferal record during this interval although the sedimentary record suggests a shallowing followed by a transgressive pulse in zone p1a food supply indicators suggest a lower food supply in the early danian than during the upper maastrichtian because of the stability of the late maastrichtian environment we conclude that environmental disruption caused by the impact was most likely the principal cause of the benthic foraminiferal turnover across the k pg boundary observed at brazos river

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

mineralogy and petrology of the haiti cretaceous tertiary section abstract the cretaceous tertiary sections in haiti consist of a sequence of graded beds of turbidity current or gravity flow origin each section may consist variously of five major constituents 1 black glass 2 brown globules veinlets and blobs 3 argillaceous limestone clasts 4 white clasts and shards and 5 a fine grained matrix rich in smectite zeolites and calcite in addition there are trace amounts of a high calcium yellow glass the black glass particles are vesicular apparently unaltered with an andesitic to dacitic composition and in sharp contact with the secondary matrix and veinlet alteration products the brown globules veinlets and blobs consist of a palagonite smectite mix of a distinctly different composition than the black glasses white clasts and shards of a still different more hydrated composition are also present all of these materials are sometimes associated with accretionary lapilli the hydration or alteration products brown globules white clasts and shards and matrix amount to something in excess of 95 of the total deposits the sedimentology mineralogy and petrology of the haiti sections has provided a record of a sequence of probable volcanic events

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

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

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

tectonic setting of cadomian low pressure metamorphism in the central ossa morena zone iberian massif sw spain abstract the upper proterozoic serie negra a monotonous pre and syntectonic slate greywacke series including volcanic episodes crops out widely in the central area of the ossa morena zone sw iberian massif iberian peninsula this unit was affected by complex late precambrian tectonothermal events the cadomian orogeny during which two phases of deformation d1 and d2 are recognized in the 610 585 ma time span the second deformational episode d2 was the most prominent and was related to progressive low pressure high temperature metamorphism lp ht reaching the highest grade in the lower structural levels where thermal evolution led to extensive migmatization and gave rise to the generation of different kinds of anatectic granitoids in this work we present field petrographic and analytical data dealing with the metamorphic evolution of a cadomian lp ht terrane from the central ossa morena zone iberian massif sw spain whose tectonic setting is unclear so far the tectonic setting proposed herein for cadomian d2 lp ht events is discussed in terms of its relationship to plate convergence or to extensional tectonic regimes modelling of the p t t trajectories undergone by a crust moderately overthickened by the thrusting of thinned sialic crust slices reproduces well the observed p t t aths if moderate or low uplift rate and high geothermal gradients are assumed for the uplift history numerical simulations combined with structural and metamorphic evidence support a compressional tectonic setting as responsible for the observed facies series distribution and deformation metamorphism relationships furthermore the regional geodynamic context coeval high pressure metamorphism in neighboring areas of the ossa morena zone and extensive calc alkaline magmatism is consistent with such a tectonic setting a correlation is tentatively proposed here between compressional cadomian deformations in the ossa morena zone upper proterozoic docking of avalonian terranes in ne america and cadomian orogenesis in the northern armorican massif

variations in near global sea level pressure abstract analysis of a near global sea level pressure slp data set for the period 1951 80 was carried out in terms of complex empirical orthogonal function a large scale propagating slp signal was discovered that seems to include variability previously associated with the southern oscillation monsoons and tropical midlatitude teleconnection patterns in this sense the new feature offers an empirical framework for many of the well known features of the global climate system extensive comparisons show the feature to be observable in the raw data field and thus not a figment of the analysis technique the large slp signal may have its origins in a slp snow feedback loop that acts over the region from siberia to india it is suggested that the maintenance of the slp signal involves slp precipation feedbacks and more importantly the excitation of a major natural mode of climate variation the slp signal is only excited at time scales larger than about 18 mouths i e time scales characteristic of ocea

strain patterns of crescentic granitoid plutons in the archean greenstone terrain of ontario abstract granitoid plutons of crescentic outcrop pattern in the archean terrain of northwestern ontario are dominated by constrictive strains that are interpreted to be due to intrusion rather than regional deformation the strain patterns of antiformal plutons are characterized by subvertical lineations in contrast the strain patterns of synformat plutons are characterized by subhorizontal lineations presumably only the last flow increments were recorded by the deformed mineral aggregates employed as strain gauges and occurred when the granitoid magma was largely crystalline simple kinematic models are capable of explaining many but not all elements of the natural strain patterns

a possible causal relationship between extinction of dinosaurs and k t iridium enrichment in the nanxiong basin south china evidence from dinosaur eggshells multiple distinct iridium anomalies have been observed in dinosaur eggshells in the k t boundary sections of the nanxiong basin guangdong province south china the eggshells collected at and near the fossil pollen defined k t boundary interval show iridium increases of about 19 and 28 times respectively above the background level the enrichment of other trace elements in the eggshells occurs mostly at and near the interval the distribution of ir bearing levels proves the existence of at least six ir delivering events from the latest cretaceous into the earliest paleocene the enrichment of ir and other trace elements in eggshells may have been caused by the assimilation of these elements into the dinosaur body through food and then into the eggs laid by them two types of pathological development i e variation in eggshell thickness and eggshell microstructure have been observed from the basin it seems that they occur frequently during the k t transition the physiological mechanisms producing pathologic dinosaur eggshells are evaluated in the light of homologous phenomena occurring in living birds on this basis it is concluded that the formation of pathologic dinosaur eggshells was caused by anomalous trace element concentrations the extinction of the dinosaurs in the nanxiong basin did not occur instantaneously but spread out within 250 ka with major extinction beginning at the boundary interval the cause may have been environmental poisoning and adverse changes in climatic conditions as indicated by the geochemical analyses of the dinosaur eggshells a repeating short and long term geochemically induced environmental stress adversely affected the reproductive process and contributed to the extinction of the dinosaurs c 2002 elsevier science b v all rights reserved

two stage deformation of the mont louis andorra granite pluton variscan pyrenees inferred from magnetic susceptibility anisotropy the mont louis andorra granodiorite pluton eastern pyrenees france andorra and spain was the subject of a thorough study of its internal structures principally the measurement of the anisotropy of its magnetic susceptibility and the classification of its microstructures regularly spaced sampling 281 sites allowed the precise mapping of the susceptibility magnitudes consistent with mapped rock types the magnetic structures fall into two distinct families which occur in separate parts of the pluton and have different microstructures family i is observed almost everywhere and has close to horizontal lineations remarkably constant in ne sw azimuth magmatic to submagmatic microstructures characterize these rocks in contrast family ii is confined within nw se trending corridors where moderate to steep nw plunges of the lineations are recorded and subsolidus microstructures are observed magnetic structures of family i are argued to equate with the kinematic framework of the deforming magma during its emplacement family ii structures represent a late to post consolidation reworking and therefore record a second stage of deformation in the pluton it is concluded that magma emplacement was related to a ne sw trending strike slip and or thrust fault system coeval with the sw verging thrust episode documented in the pyrenees the second stage corresponds to dextral shear movements with a thrust component on nw se striking planes corridors containing family ii structures are shear zones responsible for dissection of the massif into three blocks the eastern block representing the former base and the western block the top of the pluton restoration of the pluton9s shape along these corridors demonstrates the importance of the early variscan ne sw kinematic direction because the family ii structures that form shear zones affecting the pluton have similar orientation and kinematics as the compressive steep main phase of deformation ubiquitous in the pyrenees the pluton of mont louis andorra was probably emplaced before this main phase of deformation

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

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

north atlantic oscillation sensitivity to the el nino southern oscillation polarity in a large ensemble simulation a large ensemble modeling experiment with the melbourne university general circulation model is presented thirty 17 year long independent simulations were performed all integrations were forced by the same observed sea surface temperatures obtained from the atmospheric model intercomparison project ii the simulations were analyzed to assess the sensitivity of the north atlantic oscillation nao to the el nino southern oscillation enso polarity the results show signals of the enso phases both in the mean strength of the nao as well as in its internal variability during the cold enso phase the probability density function of the nao index presents a small but positive mean value whereas it is negative during the warm enso phase also the nao variability associated with each enso phase shows a different behavior during the warm phase the probability density function of the nao index presents a larger variance and suggests a bimodality whereas no bimodality is suggested in the cold phase

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

the cretaceous tertiary boundary event in ecuador reduced biotic effects due to eastern boundary current setting a multidisciplinary study of a new cretaceous tertiary k t boundary section near guayaquil ecuador reveals an unusually cool water low diversity planktic foraminiferal fauna and a high diversity radiolarian fauna similar to those found in southern high latitude k t sequences despite the fact that this section was deposited near the cretaceous equator the k t boundary is located by planktic foraminifera within a narrow interval bounded by last appearances of tropical cretaceous species and first appearances of tertiary species including parvularugoglobigerina eugubina as in southern high latitudes there is no major mass extinction of either planktic foraminifera or radiolarians at this level a major radiolarian faunal discontinuity occurs some 6 m higher in the section within foraminiferal zone plc some 300 500 kyr after the k t event 13c values from bulk carbonates show both high and low latitude characteristics similarly to low latitudes there is a 3 negative 13c excursion at the k t boundary which is generally interpreted as a major decrease in primary productivity but unlike the low latitudes recovery occurs within a few thousand years as compared with 300 500 kyr and suggests rapid nutrient influx from the antarctic region via a current similar to the humboldt current today similarly to high latitude k t sequences a negative 13c shift occurs in the early danian zone plb about 300 kyr after the k t boundary sedimentologic and mineralogic data indicate a late maastrichtian with relatively low biogenic quartz and high carbonate followed by increasing biogenic quartz 50 and decreasing carbonate 5 during the early danian this suggests intensified atmospheric and oceanic circulation and upwelling off ecuador during the early danian the k t transition is marked by increased volcanic activity continental erosion and terrigenous influx but this also occurs in the early danian zone at the p1ap1b zonal transition and is thus not unique to the k t boundary we suggest that the catastrophic biotic effects normally observed at the k t boundary in low latitudes are greatly reduced or absent in the eastern equatorial pacific because this region was dominated then as now by upwelling and current transport of nutrient rich waters from the antarctic ocean as a result the biotic patterns are characteristic of southern high latitudes whereas the 13c pattern combines ameliorated low latitude effects with predominantly high latitude trends

nonlinear modes of north american winter climate variability derived from a general circulation model simulation abstract nonlinear principal component analysis nlpca via a neural network nn approach was applied to an ensemble of six 47 yr simulations conducted by the canadian centre for climate modelling and analysis cccma second generation atmospheric general circulation model agcm2 each simulation was forced with the observed sea surface temperature from the global sea ice and sea surface temperature dataset gisst from january 1948 to november 1994 the nlpca modes reveal nonlinear structures in both the winter 500 mb geopotential height z500 anomalies and surface air temperature sat anomalies over north america with asymmetric spatial anomaly patterns during the opposite phases of an nlpca mode only during its negative phase is the first nlpca mode related to the el nino southern oscillation enso the positive phase is related to a weakened jet stream spatial patterns of the nlpca mode for the z500 anomalies generally agree with those for the sat anomalies nonlinear canonical correlation

analysis of three dimensional strain modified uniform distributions andalusite fabrics from a granite aureole a method of analysing finite strain from an initial random distribution of lines or planes is presented the shape of the strain ellipsoid is mapped to the eigenvalue ratios of an orientation matrix the method is used to interpret the andalusite fabrics from the aureole of the ardara granite county donegal ireland the high flattening strains determined in the aureole are accompanied by oblate strains in the granite margins and support the concept of deformation produced by expansion of the pluton

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

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

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

high and low latitude types of the downstream influences of the north atlantic oscillation using reanalysis data we find that the downstream propagating quasi stationary rossby wave train associated with the north atlantic oscillation nao generally propagates along a high low latitude pathway during warm cold el nino southern oscillation enso boreal winters consistent with the different propagation directions of the nao related downstream wave train during the warm cold enso winters the nao is associated with significant 300 hpa geopotential height anomalies over eastern siberia the arabian sea the east coast of asia at around 40 n and the north pacific and the near surface air temperature perturbations associated with the nao over the high latitudes of asia are relatively strong weak based on these differences we argue that the nao has two distinct types of downstream influence a high latitude type and a low latitude type furthermore we argue that the two types of nao s downstream influence are modulated by the intensity of the subtropical potential vorticity pv meridional gradient over africa when this gradient is weak strong as in the warm cold enso winters the nao s downstream influence tends to be of the high low latitude type these results are further supported by analysis of intraseasonal nao events we separate nao events into two categories in terms of the intensity of the subtropical pv gradient over africa composites of the nao events accompanied by a weak strong subtropical pv gradient show that the nao related downstream wave train tends to propagate along a high low latitude pathway

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

three dimensional structure of low frequency pressure variations in the tropical atmosphere abstract results of a recent study show eastward propagation of information in the low frequency variations of the tropical sea level pressure slp field the current work extends that analysis to investigate the vertical structure of this signal it is found that the propagating signal exists to a height of at least 850 mb at 500 mb the signal is not so clear while at 200 mb there is little evidence of propagation of information instead the low frequency variations in 200 rnb height appear coherent for the tropical belt around the entire globe the analysis suggests that the anomalies discussed here appear first at the surface and later at higher levels in the atmosphere

the cretaceous tertiary boundary sedimentology and micropalaeontology at el mulato section ne mexico in the el mulato section ne mexico the upper cretaceous marly mendez and the lower palaeogene marly velasco formations are separated by a clastic unit benthic foraminifera from both marly formations indicate lower bathyal depths the clastic unit in contrast contains platform sands muddy pebbles and neritic shallow faunas mixed with microspherules indicating that it was allochthonously deposited into the deep basin the diversity and the variability in origin of the components in the clastic unit and its sedimentological features support a model of deposition by turbidity currents related to mass wasting processes triggered by the creta ceous tertiary k t boundary impact planktic foraminifera were affected by a catastrophic extinction at the k t boundary whereas benthic foraminifera show reorganization of the community structure rather than significant extinction the benthic faunal turnover may have resulted from the drop in primary productivity after the asteroid impact at the end of the cretaceous

oceanic influence on the north atlantic oscillation and associated northern hemisphere climate variations 1959 1993 the north atlantic oscillation nao ex hibits variations at interannual to multidecadal time scales and is associated with climate variations over eastern north america the north atlantic europe and north africa therefore it is very important to understand causes of these nao variations and assess their predictability it has been hypothesized based on observations that sea surface temperature sst and sea ice variations in the north atlantic ocean influ ence the nao we describe results of an ensemble of sixteen experiments with an atmospheric general cir culation model in which we used observed sst and sea ice boundary conditions globally during 1949 1993 we show that multiyear nao and associated climate variations can be simulated reasonably accurately if re sults from a large number of experiments are averaged we also show that the ambiguous results of previous nao modeling studies were strongly influenced by the ensemble size which was much smaller than that in the present study the implications of these results for understanding and predictability of the nao are dis cussed