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

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

coherence between solar activity and the east asian winter monsoon variability in the past 8000 years from yangtze river derived mud in the east china sea ams 14 c dating and grain size analysis for core pc 6 located in the middle of a mud area on the inner shelf of the east china sea ecs were used to rebuild the holocene history of the east asian winter monsoon eawm the 7 5 m core recorded the history of environmental changes during the postglacial transgression the core s mud section the upper 450 cm has been formed mainly by suspended sediment delivered from the yangtze river mouth by the ecs winter coastal current ecswcc since 7 6 kyr bp using a mathematical method called grain size vs standard deviatiow we can divide the core pc 6 s grain size distribution into two populations at about 28 mu m the fine population 28 mu m is considered to be transported by the ecswcc as suspended loads content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation thus variation of mean grain size from the fine population would reflect the strength of ecswcc which is mainly controlled by the east asian winter monsoon abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ecswcc which was caused by the strengthened eawm thus the high resolution mean grain size variation might serve as a proxy for reconstruction of the eawm a good correlation between sunspot change and the mean grain size of suspended fine population suggests that one of the primary controls on centennial to decadal scale changes of the eawm in the past 8 ka is the variations of sun irradiance i e the eawm will increase in intensity when the number of sunspots decreases spectral analyses of the mean grain size time series of core pc 6 show statistically significant periodicities centering on 2463 1368 128 106 100 88 91 7678 and 70 72 years the eawm and the east asian summer monsoon easm agree with each other well on these cycles and the east asian monsoon eam and the indian monsoon also share in concurrent cycles in holocene which are in accord with the changes of the sun irradiance c 2005 elsevier b v all rights reserved

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

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

sea surface temperature variation during the last deglaciation in the southern okinawa trough modulation of high latitude teleconnections and the kuroshio current abstract three paleotemperature records foraminiferal mg ca tex86 and uk 37 were generated for the past 17 3 ka in the southern okinawa trough ot using a sediment core okt 3 taken at a water depth of 1792 m temperature estimates based on the inorganic and organic indices for the okt 3 core top sample approximated modern sea surface temperature sst and extended to the mixed layer

pollen quantitative distribution in marine and fluvial surface sediments from the northern south china sea new insights into pollen transportation and deposition mechanisms in order to improve the understanding of pollen transportation and deposition mechanisms in northern south china sea scs 45 seafloor surface sediment samples from the scs and nine surface sediment samples from the pearl river mouth were analyzed palynologically the spatial distributions of pollen and spore taxa suggest that various transport mechanisms and the production at the source the dominant pollen pinus poaceae cyperaceae and fern spores are most abundant in the river mouth and decrease with increasing distance from the land suggesting they are mainly derived from the pearl river drainage basin and strongly dispersed by river plume and ocean currents which reflects a dominant pollen transportation pattern in the northern scs podoconpus and temperate broad leaved components pollen such as evergreen quercus and castanopsis pollen is common in marine samples and is scattered in the pearl river samples reflecting their extensive source areas and dispersal in more than one route however some pollen types of conifers are mostly deposited close to the shore such as dacrydium picea and abies which are restricted near hainan island and taiwan island excluding evergreen quercus and castanopsis pollen the total tropical and subtropical components poorly reflect their parent plants and fewer such pollen are transported over long distances however the source areas of some other pollen taxa e g phyllociadus artemisia and chenopodiaceae are unclear spatially varying ratios of spores to pollen indicate that spores are relatively easily transported by water over longer distances than are pollen grains this study provides a sound basis for interpreting quaternary pollen deposits from the northern scs and for further evaluation of pollen dispersal and deposition in marine and fluvial deposits c 2013 elsevier ltd and inqua all rights reserved

late quaternary paleoenvironmental changes in the southeastern yellow sea korea abstract a 34 meter long ams 14 c dated sediment core was examined in order to reconstruct the paleoenvironmental changes that have taken place in the southeastern yellow sea during the last 16 600 years to achieve this we analyzed the geochemical compositions of organic matter the benthic foraminiferal assemblages and the stable isotopes of benthic foraminiferal tests the organic geochemical results show that terrigenous organic matter was dominant in the southeastern yellow sea between 16 600 and 4300 cal yr bp probably due to the influence of river runoff marine organic matters originating from surface primary productivity began increasing drastically after 4300 cal yr bp benthic foraminiferal assemblages reveal that brackish species were dominant before 3500 cal yr bp but the saline species dominated after this time the 18 o values of the benthic foraminifer cibicides lobatulus showed that a change from high amplitude to low amplitude fluctuations took place at 3500 cal yr bp these multi results indicate that the southeastern yellow sea changed from an estuarine to a modern marine shelf environment probably due to the inflow of the yellow sea warm current between 4300 and 3500 cal yr bp the time discrepancy of 800 years indicates that a modern marine shelf environment was not fully developed in the southeastern yellow sea until 3500 cal yr bp even though the sea began to be influenced by the oceanic current at 4300 cal yr bp

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

sedimentary evolution of the yangtze river mouth east china sea over the past 19 000 years with emphasis on the holocene variations in coastal currents abstract water mass variations in the early yangtze estuary during the postglacial transgression have not been thoroughly studied this research gap has hampered the understanding of riverine sediment source to sink processes in this region this study presents the results of integrated analyses of grain size pollen spore dinocyst assemblages benthic foraminifera and ostracods from a borehole h5 located at the northern yangtze mouth to investigate the complete sedimentary history and associated variations in coastal currents since 19 ka at the core site a fluvial floodplain developed from ca 19 11 3 ka whereas an estuary to shelf to subaqueous delta prevailed during most of the holocene based on changes in the dominant microfauna species which mainly consist of chinese coastal water species two main current patterns were distinguished one dominated by the yellow sea coastal current yscc before ca 7 9 ka and one dominated by the yangtze dilute water ydw marked increases in open sea saline species including bolivina robusta and stratified water dinocyst species spiniferites ramous and spiniferites spp were interpreted as the encroachment of the taiwan warm current twwc and the intensification of the ydw respectively the ydw and twwc penetrated the area dominated by the yscc before 7 9 ka which was likely related to intensity variations in the kuroshio current kc and asian summer monsoon asm under maximal asm and kc conditions upwelling resulted from the intensified intrusion of the twwc as indicated by the blooming of bolivina robusta from 7 9 6 3 ka after ca 6 ka the ydw clearly weakened due to the decline of the asm yet the yangtze plume prevailed due to the rapid seaward migration of the yangtze mouth considering the dominance of the yscc in the early holocene yellow river derived sediment likely represented a large proportion of the material delivered to the early yangtze estuary

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

environmental change in yellow sea during the last deglaciation to the early holocene 15 000 8 000 bp abstract this study is the first reconstruction of the paleoenvironment and paleovegetation during the holocene interglacial and last deglaciation periods of the yellow sea carbon isotope and biomarker n alkane and alkenone compositions of organic carbon matter om from core 11 ys pcl14 collected from the central yellow sea recorded past changes in east asian monsoon eam climates the result shows the variability of the eam affected the sedimentary profile of total organic carbon toc the stable isotopes of bulk organic carbon 13 c org the atomic ratio of carbon and nitrogen c n ratio and biomarker content the oscillations of toc along the sediment core might be associated with the paleoceanographic conditions changes in the sea level related to the contribution of the autochthonous and allochthonous om input two climatic conditions were distinguished warm humid and cold dry based on the n alkane proxy and the observed changes in 13 c of individual n alkane 13 c alk between the holocene and last deglaciation were attributed to changes in plant distribution type a shift in vegetation type between climatic periods occurred as a result of different photosynthetic response to co 2 and temperature among c 3 and c 4 plants the most interesting new finding of this work is the fact that alkenone derived temperature changed independently with global climate change which might be related to the influence of the kuroshio current in the yellow sea the variations in the intensity of the eam could be the main mechanism accounting for the paleoenvironmental and paleoceanographic variation observed in the central yellow sea

stratigraphy and paleoenvironmental changes in the yangtze delta during the late quaternary the yangtze delta area may be subdivided into paleo valley and paleointerfluves of the last glaciation the postglacial transgressive sedimentary cycle ptsc on the front zones of the paleointerfluves is composed of marsh nearshore and barrier lagoon shallow marine and nearshore tidal flat units with a basement in stiff clay the ptsc in back zones of the paleointerfluves consists of lacustrine marsh deposits the ptsc in the incised valley contains river channel floodplain estuary estuarine shallow marine and deltaic units with an erosional surface at its bottom the stiff clay and the erosional surface constitute the ptsc lower boundary the stiff clay consisting of a paleosol experienced deposition alternating with pedogenesis during the falling of sea level during 18o stage 3 ongoing pedogenesis in the sea level lowstand of 18o stage 2 and early diagenesis after paleointerfluve inundation by the sea level rise of 18o stage 1 the climate during the paleosol formation was temperate with more than 500 mm a 1 rainfall and frequently fluctuating groundwater the yangtze river incised its course during falling sea level of stage 3 and a huge incised valley was formed during the sea level lowstand stage 2 the filling of the incised valley took place during the postglacial sea level rise and delta formation occurred at a late stage of ptsc development

reconciliation of hydroclimate sequences from the chinese loess plateau and low latitude east asian summer monsoon regions over the past 14 500years we discuss replicated stalagmite 18o records with interannual to multidecadal resolution from lianhua cave on the chinese loess plateau to illustrate the precipitation history of the east asian summer monsoon easm region over the last 14 5 thousand years ka bp before 1950 ce hereafter and to re evaluate the inconsistency in the proxy inferred palaeoclimate time series in northern china agreement between the stalagmite 18o from lianhua and other caves from central southern china indicates that regional climate changes after the last glacial were concurrent across mainland china indicating that insolation was the primary factor controlling the evolution of the asian summer monsoon asm the stalagmite 18o enrichment of 2 5 in the younger dryas and 1 7 during the 8 2 ka bp event in lianhua were larger than those in caves from central and southern china the evidence suggests that different meridional responses of weak precipitation conditions in the asm realm occurred during these two abrupt events driven by high latitude forcing in the northern hemisphere the heterogeneous hydroclimate sequences in northern china inferred from different natural archives are most likely attributable to the complexity of the formations and or some chronological uncertainty

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

heinrich event imprints in the okinawa trough evidence from oxygen isotope and planktonic foraminifera planktonic foraminiferal faunas oxygen isotope and modern analog technique sea surface temperature records were obtained in piston core dgks9603 28degrees08 869 n 127degrees16 238 e water depth 1100 in collected from the middle okinawa trough during the last glaciation four cold events were identified and correlate heinrich events he h2 5 of the last 45 ka during the last deglaciation core dgks9603 has begun to be influenced by the kuroshio since about 16 cal ka bp three weakenings of this warm current occurred at about 2 8 5 3 11 4 and 15 5 cal ka bp respectively among the three fluctuations the oldest one is synchronous with he1 and could be a response to the strong cooling observed in the north atlantic ocean the fluctuation occurring at about 11 4 cal ka ago corresponds to the younger dryas within the age error bars our observations provide new evidence that the hes documented from greenland and the northern north atlantic had a global climatic impact changes in the intensity of the east asian monsoon could be the main mechanism responsible for the paleoccanographic variations observed in the okinawa trough c 2001 elsevier science b v all rights reserved

nw african climate variations during the last 47 000years evidence from organic walled dinoflagellate cysts nw african climate shows orbital and millennial scale variations which are tightly connected to changes in marine productivity we present an organic walled dinoflagellate cyst dinocyst record from a sediment core off cape yubi at about 27 n in the canary basin covering the time period from 47 to 3 ka before present bp the dinocyst record reflects differences in upwelling intensity and seasonality as well as the influence of fluvial input sea level changes play an important role for the upwelling pattern and productivity signals at the core site within the studied time interval four main phases were distinguished 1 from 45 to 24 ka bp when sea level was mostly about 75 m lower than today high relative abundances of cysts of heterotrophic taxa point to enhanced upwelling activity especially during heinrich events while relatively low dinocyst accumulation rates indicate that filament activity at the core location was strongly reduced 2 at sea level lowstand during the lgm to h1 dinocyst accumulation rates suggest that local filament formation was even more inhibited 3 from the early holocene to about 8 ka bp extraordinary high accumulation rates of most dinocyst species especially of lingulodinium machaerophorum suggest that nutrient supply via fluvial input increased and rising sea level promoted filament formation at the same time the upwelling season prolongated 4 a relative increase in cysts of photoautotrophic taxa from about 8 ka bp onwards indicates more stratified conditions while fluvial input decreased our study shows that productivity records can be very sensitive to regional features from the dinocyst data we infer that marine surface productivity off cape yubi during glacial times was within the scale of modern times but extremely enhanced during deglaciation

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

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

palynological record of climate change during the last deglaciation from the song hong red river delta vietnam abstract the palynological sequence from core nd 1 on the song hong delta in the northern vietnam reveals the climate change during the last deglaciation the identified pollen in the core is dominated by castanopsis lithocarpus elaeocarpus ficus piperaceae and quercus high percentages of temperate taxa including the conifers dacrydium podocarpus pinus cupressaceae txodiaceae and cryptomeria and broad leaved taxa of carpinus alnus juglans carya ulmus fagus ilex castanea quercus which have a mainly upland distribution is possibly associated with a lowering of the montane vegetation boundary on the other hand intensified river influence can also result in an increase in the temperate allochthonous taxa after analyzing the magnitude of river influence on pollen assemblages during the sedimentary environment evolution we extracted the climate information and used this to reconstruct climate change during the last deglaciation a cooler climate during 14 5 10 9 cal kyr bp than at present is indicated by higher percentage of temperate types than at present under a similar river influence on the floodplain the younger dryas cooling event is recognized by widely developed grasslands between 12 9 and 11 6 cal kyr bp adding to the evidences for this period from both terrestrial and marine records in regions influenced by the east asian monsoon two other cooling periods 9 4 9 0 cal kyr bp and 6 5 5 2 cal kyr bp are indicated by increases of temperate pollen taxa such as cryptomeria alnus quercus and castanea

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

an early holocene sea level jump and delta initiation 1 early holocene sea level change controlled the evolution of clastic coastal depositional systems radiocarbon dated borehole cores obtained from three incised valley fill systems in asia changjiang song hong and kiso river record very similar depositional histories especially between about 9000 and 8500 cal bp sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period in addition large decreases in sediment accumulation rates occurred a sea level jump causes an estuarine system and its depocenter to move rapidly landward it is possible that the final collapse of the laurentide ice sheet accompanied by catastrophic drainage of glacial lakes at approximately 8500 cal bp caused such a jump the jump was followed immediately by a period of decelerated sea level rise that promoted delta initiation

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

initiation of the changjiang yangtze delta and its response to the mid holocene sea level change abstract the changjiang yangtze delta in eastern china is one of the largest tide dominated deltas in the world to obtain a more detailed information on its initiation we drilled three sediment cores pk01 hg01 and xj03 from the uppermost region of the delta plain on the basis of sedimentary facies and ams 14c dating we identified three depositional systems 1 a fluvial system 2 an estuarine system and 3 a deltaic system including an initial delta estuary delta transition and a typical delta the maximum flooding surface separates the estuarine and deltaic systems and occurred at ca 8 0 cal kyr bp when brackish water intruded landward and reached the nanjing area the changjiang delta was initiated at the area between nanjing and yizheng when the sea level rise decelerated after the rapid rise in sea level during 9 0 8 2 cal kyr bp the subsequent evolution of the changjiang delta has been shown as a seaward development model of river mouth bars with shoreline migration the oldest river mouth bar called hongqiao sand body which is located most landward was dated at 6 0 5 5 cal kyr bp in this study nearly one thousand years younger than the previous estimates a tide dominated funnel shaped estuary was formed at 8 0 cal kyr bp and lasted until the hongqiao sand bar became exposed this stage is regarded as an aggradation dominated initial stage of the changjiang delta followed by a progradation dominated stage that is characterized by the formation of a series of seaward migrating river mouth bars a relative sea level highstand in the mid holocene may be associated with glacio hydro isostatic tilting

lithological and palynological evidence of late quaternary depositional environments in the subaqueous yangtze delta china abstract ams 14c ages of post glacial core sediments from the subaqueous yangtze delta along with sedimentary structures and distributions of grain size pollen spores and dinoflagellate cysts show an estuarine depositional system from 13 to 8 4 cal ka bp and a deltaic system from 5 9 cal ka bp to the present the estuarine system consists of intertidal to subtidal flat estuarine and estuarine front facies characterized by sand mud couplets and a high sedimentation rate the deltaic system includes nearshore shelf and prodelta mud featured by lower sedimentation rate markedly fewer coastal wetland herbaceous pollens and more dinoflagellate cysts we explain the extremely high sedimentation rate during 9 2 8 4 cal ka bp at the study site as a result of rapid sea level rise high sediment load due to the unstable monsoonal climate and subaqueous decrease of elevation from inner to outer estuary a depositional hiatus occurred during 8 2 5 9 cal ka bp the transition from estuarine to deltaic system caused possibly by a shortage of sediment supply resulting from delta initiation in paleo incised yangtze valley and strong tidal or storm related reworking in offshore areas the subsequent development of deltaic system at the study site indicates accelerated progradation of yangtze delta post 5 9 cal ka bp

surface water evolution of the eastern east china sea during the last 36 000 years abstract planktic foraminifera have been studied in two high resolution cores raised from the continental slope of the eastern east china sea ecs to reconstruct the surface water history ams 14c dating on fifteen horizons revealed that the two cores kh82 4 14 and rn80 pc3 contain continuous records of the last 36 and 17 thousand cal years respectively thirty one planktic foraminiferal species which are commonly found in the present western north pacific and the ecs are recognized in down core samples three faunal phases iii ii and i distinguished by characteristic planktic foraminiferal assemblages suggest three major paleoenvironmental stages of the surface water of the eastern ecs since 36 000 yr b p 1 a stage influenced by coastal water from 36 000 to 19 500 yr b p 2 a stage also influenced by coastal water and extremely low salinity from 19 500 to 10 500 yr b p and 3 a stage controlled by the modern open sea water related to the kuroshio with both higher temperature and higher salinity since 10 5 8 5 thousand years b p oxygen isotope records of the planktic foraminiferal species g bulloides show that the three planktic foraminiferal faunal phases correspond to the last glacial deglacial and postglacial stages respectively the planktic foraminiferal assemblage during the deglacial stage which is represented by high percentages of g quinqueloba is quite different from those during the glacial and postglacial stages linked to a large amount of river discharge from the chinese continent a negative oxygen isotope excursion in g bulloides during the same period is highly correlated to the g quinqueloba anomaly also indicating a decrease in surface water salinity furthermore the sedimentation rate of core kh82 4 14 during 19 15 thousand years b p is much higher than the rates during the glacial and postglacial stages suggesting a great increase in the supply of terrigenous material related to an increased river and sediment discharge during the early deglaciation the coastal water influenced stage of the eastern ecs terminated gradually at 10 5 8 5 thousand years b p since the warm kuroshio current and its branches flowed in the eastern ecs as today the formation of the postglacial surface water circulation pattern in the eastern ecs was closely related to the flow patterns of the kuroshio current

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

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

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

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

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

deglacial meltwater pulse 1b and younger dryas sea levels revisited with boreholes at tahiti reconstructing sea level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets the resolution of the few sea level records covering the critical time interval between 14 000 and 9 000 calendar years before the present is still insufficient to draw conclusions about sea level changes associated with the younger dryas cold event and the meltwater pulse 1b mwp 1b we used the uranium thorium method to date shallow living corals from three new cores drilled onshore in the tahiti barrier reef no significant discontinuity can be detected in the sea level rise during the mwp 1b period the new tahiti sea level record shows that the sea level rise slowed down during the younger dryas before accelerating again during the holocene

modeling the effects of a time dependent wetted perimeter on infiltration from ephemeral channels the effects of a time dependent wetted perimeter on infiltration from ephemeral stream channel cross sections are explored using a conceptually simple mathematical model the model is based on the assumptions of vertical soil moisture flow and the validity of the green ampt model for vertical infiltration by using a simple channel geometry an analytic solution is found for the case in which the gravitational component of soil moisture flow may be neglected an efficient accurate numerical technique provides approximate solutions in the general case application of the model demonstrates that cross sectional infiltration that is infiltration per unit length of channel is a complex function of soil properties channel geometry and hydrograph shape for the channel geometry considered the direct effects of variable water pressure at the ground surface are overshadowed by the effects of variation in the wetted perimeter with the result that the temporal variation in infiltration rate is quite unlike that which would be predicted assuming ponded infiltration alone

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

paleoenvironmental change in the middle okinawa trough since the last deglaciation evidence from the sedimentation rate and planktonic foraminiferal record well dated high resolution records of planktonic foraminifera and oxygen isotopes from two sediment cores a7 and e017 in the middle okinawa trough reveal strong and rapid millennial scale climate changes since similar to 18 to 17 thousand years before present kyr b p sedimentation rate shows a sudden drop at similar to 11 2 cal kyr b p due to a rapid rise of sea level after the younger dryas yd and consequently submergence of the large continental shelf on the east china sea ecs and the retreat of the estuary providing sediment to the basin during the last deglaciation the relative abundance of warm and cold species of planktonic foraminifera fluctuates strongly consistent with the timing of sea surface temperature sst variations determined from mg ca measurements of planktonic foraminifera from one of the two cores these fluctuations are coeval with climate variation recorded in the greenland ice cores and north atlantic sediments namely heinrich event 1 h1 bolling allerod b a and yd events at about 9 4 kyr b p a sudden change in the relative abundance of shallow to deep planktonic species probably indicates a sudden strengthening of the kuroshio current in the okinawa trough which was synchronous with a rapid sea level rise at 9 5 9 2 kyr b p in the ecs yellow sea ys and south china sea scs the abundance of planktonic foraminiferal species together with mg ca based sst exhibits millennial scale oscillations during the holocene with 7 cold events at about 1 7 2 3 4 6 6 2 7 3 8 2 9 6 10 6 cal kyr bp superimposed on a holocene warming trend this holocene trend together with centennial scale sst variations superimposed on the last deglacial trend suggests that both high and low latitude influences affected the climatology of the okinawa trough c 2006 elsevier b v all rights reserved

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

a high resolution absolute dated holocene and deglacial asian monsoon record from dongge cave china abstract we present a continuous record of the asian monsoon over the last 16 ka from 18o measurements of stalagmite calcite over 900 oxygen isotopic measurements providing information on shifts in monsoon precipitation are combined with a chronology from 45 precise 230th dates 18o and therefore asian monsoon intensity generally follows changes in insolation although changes in 18o are generally accommodated in abrupt shifts in contrast to smoothly varying insolation indicating that threshold effects may be important 18o decreased dramatically 3 at the start of the holocene 11 5 ka and remained low for 6 ka four positive 18o events centered at 11225 97 yr bp 1 05 10880 117 yr bp 1 15 9165 75 yr bp 1 4 and a double event centered at 8260 64 yr bp 1 1 and 8080 74 yr bp 1 0 punctuated this period of high monsoon intensity all four events correlate within error with climate changes in greenland ice cores thus the relationship between the asian monsoon and the north atlantic observed during the glacial period appears to continue into the early holocene in addition three of the four events correlate within error with outburst events from lake agassiz the decline of monsoon intensity in the mid late holocene is characterized by an abrupt positive shift in 18o which occurs at 3550 59 yr bp 1 1 in 100 yr in addition the holocene is punctuated by numerous centennial and multi decadal scale events amplitudes 0 5 to 1 up to half the amplitude of the glacial interstadial events seen in the last glacial period thus holocene centennial and multi decadal scale monsoon variability is significant although not as large as glacial millennial scale variability the monsoon shows a strong connection with northern south american hydrological changes related by changes in itcz position spectral analysis of the 18o record shows significant peaks at solar periodicities of 208 yr and 86 yr suggesting variation is influenced by solar forcing however there are numerous other significant peaks including peaks at el nino frequencies observed for high resolution portions of the record between 8110 and 8250 yr which suggest that changes in oceanic and atmospheric circulation patterns in addition to those forced by solar changes are important in controlling holocene monsoon climate in addition for this high resolution portion we observe a distinctive biennial oscillation of the asian monsoon which has been associated with the tropospheric biennial oscillation tbo

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

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

a unique middle pleistocene beech fagus rich deciduous broad leaved forest in the yangtze delta plain east china its climatic and stratigraphic implication abstract pollen analysis of middle pleistocene sediments from the yangtze delta plain provides a paleoecological reconstruction and has implications for stratigraphic correlation in east china the pollen assemblage is characterized by high values of fagus 16 8 on average which is unusual because fagus is generally present only sporadically in other lowland quaternary pollen records from the region in addition to fagus the assemblage has a rich diversity of broad leaved deciduous trees including quercus ulmus carpinus ostrya juglans betula and liquidambar as well as conifers including pinus picea abies larix and tsuga thus the pollen flora suggests a broad leaved deciduous forest mixed with abundant conifers which developed under cooler and more humid conditions than present the stable pollen sequence throughout the studied section suggests a stable environment beech forests also characterize the middle pleistocene of taiwan and japan and thus may be a stratigraphic indicator of the middle pleistocene in east asia the yangtze delta plain may have been an important refugium for the last survival of fagus in the lowlands