40ar 39ar dating and magnetostratigraphic correlation of the terrestrial cretaceous paleogene boundary and puercan mammal age hell creek tullock formations eastern montana the recovery and subsequent prolific radiation of mammals in the northern western interior of north america following the cretaceous paleogene k p boundary is well documented in rocks attributed to the puercan land mammal age the most complete puercan record is that of the tullock formation which crops out widely in garfield and mccone counties eastern montana the tullock formation overlies the dinosaur bearing hell creek formation and consists of a stratigraphic series of channel and overbank deposits from which well preserved puercan faunas have been collected these channel deposits are typically bracketed by widespread coal beds the irz and z coals mark the base of the puercan at the k p boundary as defined by the highest appearing local occurrences of in situ dinosaur fossils the highest stratigraphic occurrence of cretaceous pollen and an anomalously high concentration of the element iridium ir the irz coal is overlain sequentially by the z hfz y w and u coals fossil vertebrates

geometry mechanisms and significance of extensional folds from examples in the rocky mountain basin and range province u s a abstract geologic mapping and structural analysis in paleogene half graben of idaho and montana have revealed over 70 extensional folds that form orthogonal sets with mostly ne and se trending axes on a regional scale they parallel or lie perpendicular to the strikes of the largest normal faults transverse folds at a high angle to the fault and folds oblique to the fault comprise more than half of the folds and reflect the highly three dimensional nature of the bulk strain detailed geometric analysis of 15 folds in the salmon horse prairie and medicine lodge basins shows that they typically have an upright to steeply inclined bisecting surface an interlimb angle of 141 and a plunge of 19 based on our synthesis of the eight common mechanisms of extensional folding and their distinguishing characteristics we were able to determine how some of the investigated folds formed fault bend folding above both fault parallel and fault perpendicular bends in the underlying normal fault produced most of the folds in the study area but displacement gradients along normal faults fault drag isostatic adjustments and transtension were also factors in the deformation most of the compound folds which result from more than one mechanism of folding are oblique to all adjacent normal faults recognition of such extensional folds is critical because they might be misinterpreted as contractional structures they influence sediment thickness patterns and dispersal in rift basins and may control the migration and trapping of petroleum and groundwater resources

upheavals during the late maastrichtian volcanism climate and faunal events preceding the end cretaceous mass extinction abstract the late maastrichtian was a time of major climate evolution and extinction extremes rapid climate warming of 2 3 c in intermediate waters between 69 5 and 68 ma top c31r to base c30n accompanied maximum evolutionary diversification 43 increase zone cf5 to low cf4 in planktic foraminiferal history followed immediately by a cluster of extinctions during the last 250 ky of the maastrichtian c29r zones cf2 cf1 rapid warming of 4 c in intermediate waters and 8 c on land resulted in high stress environments ending in the mass extinction the end cretaceous mass extinction is recorded in sediments between massive deccan lava flows in india and attributed to so 2 and co 2 outgassing leading to ocean acidification the early late maastrichtian climate and faunal upheavals are not well known here we document the faunal similarities of both events from the indian ocean through the tethys and gulf of mexico results show that both extreme warm events are marked by high stress environments characterized by decreased abundance and diversity of large specialized species and dwarfing high abundance of low oxygen tolerant species and disaster opportunist surface dweller guembelitria blooms the similarity in faunal response with the deccan warming of c29r cf2 cf1 suggests that volcanism was also responsible for the warming and faunal upheaval of the early late maastrichtian major volcanic activity at this time included the onset of deccan eruptions and ninetyeast ridge volcanism the role of the chicxulub impact appears to have been a contributing rather than causal factor in the mass extinction

implications of pre eruptive magmatic histories of zircons for u pb geochronology of silicic extrusions zircons in silicic magmas begin to crystallize 10 s to 100 s of thousands of years ka prior to their eruption u pb and u th dating for zircons from 32 young extrusions indicate a range of mean pre eruption ages from 33 to 247 ka with a median of 92 ka explosive large volume widespread eruptions show a narrower range and a younger median of 70 ka these results indicate that the difference between initial zircon growth and eruption age measured by other e g 40ar 39ar techniques is in excess of the achievable analytical uncertainty for eruptions 30 million years ma and likely for eruptions of up to 300 ma protracted pre eruption zircon growth is well established by an increasing number of studies on magma process time scales but this source of eruption age bias has been largely ignored in chronostratigraphic applications of high precision u pb data until intrinsic properties of zircons or their host deposits enable a priori estimates of pre eruption age bias it is prudent to expand the uncertainties attending all u pb zircon ages interpreted as deposition ages in e g chronostratigraphic studies by 0 200 ka

determination of rapid deccan eruptions across the cretaceous tertiary boundary using paleomagnetic secular variation 2 constraints from analysis of eight new sections and synthesis for a 3500 m thick composite section 1 the present paper completes a restudy of the main lava pile in the deccan flood basalt province trap of india chenet et al 2008 reported results from the upper third and this paper reports the lower two thirds of the 3500 m thick composite section the methods employed are the same i e combined use of petrology volcanology chemostratigraphy morphology k ar absolute dating study of sedimentary alteration horizons and as the main correlation tool analysis of detailed paleomagnetic remanence directions the thickness and volume of the flood basalt province studied in this way are therefore tripled a total of 169 sites from eight new sections are reported in this paper together with the results of chenet et al 2008 these data represent in total 70 of the 3500 m combined section of the main deccan traps province this lava pile was erupted in some 30 major eruptive periods or single eruptive events see each with volumes ranging from 1000 to 20 000 km3 and 41 individual lava units with a typical volume of 1300 km3 paleomagnetic analysis shows that some sees with thicknesses attaining 200 m were emplaced over distances in excess of 100 km both likely underestimates due to outcrop conditions and up to 800 km the total time of emission of all combined sees could have been much less than 10 ka with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence so called big red boles the number of boles thickness of the pulses and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end on the basis of geochronologic results published by chenet et al 2007 and paleontological results from keller et al 2008 we propose that volcanism occurred in three rather short discrete phases or megapulses an early one at 67 5 1 ma near the c30r c30n transition and the two largest around 65 1 ma one entirely within c29r just before the k t boundary the other shortly afterward spanning the c29r c29n reversal we next estimate sulfur dioxide likely a major agent of environmental stress amounts and fluxes released by sees they would have ranged from 5 to 100 gt and 0 1 to 1 gt a respectively over durations possibly as short as 100 years for each see the chemical input of the chicxulub impact would have been on the same order as that of a very large single pulse the impact therefore appears as important but incremental neither the sole nor main cause of the cretaceous tertiary mass extinctions

upper cretaceous paleocene biostratigraphy and magnetostratigraphy hell creek and tullock formations northeastern montana fossils from the hell creek and tullock formations in northeastern montana provide detailed documentation of terrestrial faunal and floral evolution during latest cretaceous lancian and early paleocene puercan time here the replacement of lancian faunas by those of puercan age most obviously signaled by the extinction of dinosaurs and the changes in pollen floras sometimes used to mark the cretaceous tertiary boundary occurred during a period of reversed magnetic polarity paleontological correlations suggest that dinosaur extinction and the change in pollen floras took place in the red deer valley area alberta during the same period of reversed polarity furthermore also on the basis of paleontological correlations the extinction of dinosaurs in the san juan basin new mexico appears to have occurred either during the same period of reversed polarity or possibly during the preceding period of normal polarity

characterization of hematite α fe2o3 goethite α feooh greigite fe3s4 and pyrrhotite fe7s8 using first order reversal curve diagrams 1 first order reversal curve forc diagrams have become a standard tool in rock magnetism yet magnetite is the only magnetic mineral that is well characterized using forc diagrams we present forc diagrams for predominantly single domain sd synthetic aluminous hematite a fe2 xalxo3 and goethite a feal ooh and natural greigite fe3s4 and pyrrhotite fe7s8 to constrain interpretation of forc diagrams from natural samples hematite and goethite have low spontaneous magnetizations and negligible magnetic interactions while greigite and pyrrhotite have higher spontaneous magnetizations and can have strong magnetic interactions the coercivity of hematite systematically increases with al content only for samples produced using the same synthesis method but it is variable for samples produced with different methods even for similar al content this precludes use of magnetic coercivity alone to quantify the al content of natural hematites goethite has much higher coercivity than hematite for all measured samples sd and superparamagnetic sp behavior is common in natural greigite samples with peak coercivities ranging from

magnetostratigraphy of the ludlow member of the fort union formation lower paleocene in the williston basin north dakota to determine the geomagnetic polarity stratigraphy and the duration and age of the ludlow member of the fort union formation lower paleocene we constructed a 325 m composite lithostratigraphic section of the upper cretaceous hell creek formation and the lower paleocene ludlow and tongue river members of the fort union formation in the little missouri river valley of north dakota usa we analyzed paleomagnetic samples from nine of the logged sections the principal magnetic carrier in the ludlow member sediments is likely titanomaghemite as indicated by predominantly irreversible thermomagnetic curves measured from sandstone siltstone and carbonaceous shale samples the analyzed paleomagnetic samples document a series of polarity zones that can be correlated from c29n to c27r on the geomagnetic polarity time scale gpts we infer that the magnetization of the samples is primary because the characteristic directions are consistent with those of the paleocene of north america and the reversal stratigraphy from this section corresponds to the gpts with reasonable sediment accumulation rates by extrapolating the measured sediment accumulation rate from the cretaceous tertiary k t boundary to the top of c28n and then to the top of the ludlow member we estimate the duration of the member to range from 2 31 to 2 61 m y this is the fi rst estimate for the duration and age of the ludlow member and it can be used as an important tool for interpreting rates of biotic recovery after the k t extinction

astronomical calibration of the maastrichtian late cretaceous abstract recent improvements to astronomical modeling of the solar system have contributed to important refinements of the cenozoic time scale through astronomical calibration of sedimentary series we extend this astronomical calibration into the cretaceous on the base of the 405 ka orbital eccentricity variation thanks to the recovery of well preserved maastrichtian sedimentary series from odp ocean drilling program holes 1258a leg 207 equatorial atlantic 1267b leg 208 south atlantic 762c leg 122 indian ocean and dsdp deep sea drilling program hole 525a leg 74 south atlantic cyclostratigraphic analysis is performed on high resolution measurements of magnetic susceptibility on sediments cored during legs 207 and 208 and gray level variations of sediment color obtained from core photographs from legs 122 and 74 astronomical control on sedimentation is evident at every site with the presence of cycles corresponding to forcing by precession obliquity and orbital eccentricity variations identification of these cycles leads to the definition of a detailed cyclostratigraphic frame covering nearly 8 ma from the upper campanian to the cretaceous paleogene k pg boundary durations of each magnetochron from c32r 2r to c29n are inferred by cycle counting astronomical calibrations of maastrichtian sedimentary series are proposed based on the 405 ka eccentricity variation according to the most recent astronomical solution la2010a two different ages are suggested for the k pg boundary considering the uncertainty of the long term variation of the 405 ka eccentricity cycle the first proposal provides a cretaceous paleogene boundary age of 65 59 0 07 ma and the second an age of 66 0 07 ma which is coherent with the most recent radio isotopic datings magnetochron boundaries and the campanian maastrichtian boundary are dated relative to these numerical ages of the k pg boundary

the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary the cretaceous paleogene boundary similar to 65 5 million years ago marks one of the three largest mass extinctions in the past 500 million years the extinction event coincided with a large asteroid impact at chicxulub mexico and occurred within the time of deccan flood basalt volcanism in india here we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction notably a single ejecta rich deposit compositionally linked to the chicxulub impact is globally distributed at the cretaceous paleogene boundary the temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations for example darkness and cooling lead us to conclude that the chicxulub impact triggered the mass extinction

untangling the palaeocene climatic rhythm an astronomically calibrated early palaeocene magnetostratigraphy and biostratigraphy at zumaia basque basin northern spain abstract the magnetostratigraphy of a 54 m long section above the cretaceous tertiary boundary at the sea cliff section of zumaia in the basque basin northern spain has been established the section encompasses the entire danian and the lower part of the selandian stages as indicated by calcareous plankton biostratigraphy the studied interval consists of hemi pelagic limestone marl alternations in the form of couplets and bundles which range from centimetre decimetre to metre scale respectively and a few thin bedded calcareous turbidites the magnetostratigraphy based on samples from about 200 stratigraphic levels allows the identification of six reversal boundaries from chron c29r to c26r at a bed level the spatial or temporal evolution of periodicities from a lithologically coded series is studied with the continuous wavelet transform technique a preliminary age model based on the standard ck95 gpts indicates that the basic lithologic carbonate marl couplet corresponds to the 19 23 kyr precession cycle 21 31 cm cycle in the depth domain and that a bundle cycle usually groups of four to six basic couplets with global periodicity centred at 1 22 m corresponds to the 110 kyr eccentricity cycle we have tuned the bundle cycles to the va03 r7 eccentricity orbital solution astrophys j 592 2003 620 630 following an initial match of a node of the 2 4 ma eccentricity modulatory cycle in the target time series to particularly carbonate rich bundles from the upper part of the zumaia section that displays significant power of a 4 4 m period cycle corresponding to the 404 kyr eccentricity cycle consistency between lithologic patterns and characteristics in the eccentricity target is reasonably met although the 404 kyr eccentricity cycle is not persistent throughout the tuning however appears robust as it brings the age of the k t boundary at 65 8 ma it is argued that a sea level signal tectonically driven is superimposed on the climatic forcing at the milankovitch band masking the full expression of the low frequency astronomical periods we provide a cycle tuned duration for all intervening early palaeocene polarity chrons and estimate relative ages for bioevents the cycle tuned chronology indicates that the ck95 gpts overestimates the duration of chrons c28 and c27 by 20 and 26 respectively our data may prove useful to better constrain early palaeocene biostratigraphy of calcareous plankton and in the redefinition of the boundary between the danian and selandian stages

high precision zircon u pb geochronology of astronomically dated volcanic ash beds from the mediterranean miocene several orbitally tuned miocene sedimentary sequences around the mediterranean contain abundant intercalated volcanic ash beds these sequences provide the rare opportunity to directly compare radioisotopic dating methods with independent and accurate deposition ages derived from astrochronology we present a large data set n 16n 16 n 166n 166 of zircon u pb dates obtained by chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims techniques for ash beds from an almost continuous orbitally tuned messinian to langhian 6 2 15 4 ma sedimentary sequence exposed along the adriatic coast south of ancona italy we use this unique data set to evaluate 1 the accuracy of zircon u pb dates 2 the significance of initial intermediate daughter product disequilibria for zircon u pb geochronology of young rocks 3 the effect of prolonged pre eruption zircon crystallization and zircon recycling on u pb derived ash bed deposition ages and 4 discuss the implications for the intercalibration of radioisotope geochronometers and the calibration of the geologic time scale

closing the mid palaeocene gap toward a complete astronomically tuned palaeocene epoch and selandian and thanetian gssps at zumaia basque basin w pyrenees abstract an integrated magneto bio and cyclostratigraphic framework is presented for the mid palaeocene interval from the hemi pelagic sea cliff section of zumaia in the basque basin the new 55 m long studied section expands about 3 5 myr and closes the gap between previously published integrated studies in the section the occurrence of magnetochron c26n is now documented and its duration complemented also by data from the ibaeta section and that for chrons c26r and c25r is estimated by counting precession related lithologic couplets assigned to have 21 kyr duration c25r 1449 kyr c26n 231 kyr c26r 2877 kyr consequently the zumaia section now provides the first complete palaeocene astronomically derived chronology rendering this section a master reference section due to limitations in the orbital calculations and uncertainties in the radiometric dating method no robust tuning and absolute ages can be given for the moment however the fos first occurrences of key calcareous plankton species and the mid palaeocene biotic event mpbe are placed within the magnetostratigraphic and cyclostratigraphic template along the studied mid palaeocene interval in addition the dataset provides the key elements for a proper settling of the thanetian and selandian global stratotype section and point gssps which is one of the primary objectives of the ics international commission of stratigraphy we consider the base of chron c26n and the criteria associated to the lithostratigraphic change between the danian limestone fm and the itzurun marl fm at zumaia as the respective delimiting points for the thanetian and selandian bases as recently agreed by the paleocene working group of the international subcommission of the paleogene stratigraphy of the ics consequently the duration of the thanetian selandian and danian component stages can be estimated at zumaia to be about 3129 kyr 2163 kyr and 4324 kyr respectively see text for error considerations however the mpbe located 8 precession cycles below the base of c26n in correspondence to a short eccentricity maxima at zumaia could also serve as a guiding criteria to approximate or redefine the thanetian base if this level demonstrated synchronous

response to comment on a high precision 40ar 39ar age for the nordlinger ries impact crater germany and implications for the accurate dating of terrestrial impact events by schmieder et al geochimica et cosmochimica acta 220 2018 146 157 abstract rocholl et al 2018 claim that the 40ar 39ar age of 14 808 0 038 ma 2 full external error for the ries impact recently obtained from step heating analysis of tektites schmieder et al 2018 geochim cosmochim acta 220 146 157 is geologically impossible and violates paleomagnetic constraints we demonstrate that the moldavite age of schmieder et al 2018 is in good agreement with recalculated isotopic ages for ash layers and magnetic sub chrons that define the langhian stage in the astronomically tuned neogene time scale using updated k decay constants and monitor ages in 40ar 39ar geochronology moreover we stress that the normally magnetized basal pelitic sediments of the ries crater lake which are separated from the reversely magnetized suevite by a thick unit of post impact conglomerates and sandstones may not have been deposited immediately after the impact the paleomagnetic constraints proposed by pohl 1977 1978 and rocholl et al 2018 are therefore questionable

extinction patterns δ18 o trends and magnetostratigraphy from a southern high latitude cretaceous paleogene section links with deccan volcanism although abundant evidence now exists for a massive bolide impact coincident with the cretaceous paleogene k pg mass extinction event 65 5 ma the relative importance of this impact as an extinction mechanism is still the subject of debate on seymour island antarctic peninsula the lopez de bertodano formation yields one of the most expanded k pg boundary sections known using a new chronology from magnetostratigraphy and isotopic data from carbonate secreting macrofauna we present a high resolution high latitude paleotemperature record spanning this time interval we find two prominent warming events synchronous with the three main phases of deccan traps flood volcanism and the onset of the second is contemporaneous with a local extinction that pre dates the bolide impact what has been termed the k pg extinction is potentially the sum of multiple independent events at least at high latitudes

cf wortmania from the early paleocene of montana and an evaluation of the fossil record of the initial diversification of the taeniodonta mammalia the garbani channel deposits part of the tullock formation exposed in northeastern montana have yielded a large sample of vertebrates that probably lived during the puercan 3 north american land mammal age nalma four fossils in this sample three isolated teeth and a medial phalanx document the presence of a stylinodontid taeniodont cf wortmania discovery of cf wortmania in the tullock formation extends the documented range of taeniodonts during puercan 3 approximately 500 miles 800 km northward from the san juan basin new mexico evaluation of the oldest records of taeniodonts from the lancian puercan and torrejonian nalmas highlights biases warranting future research recent phylogenetic analyses that resulted in numerous ghost lineages indicate that the available fossil record is far from complete they open the possibility that the origin and initial radiation of taeniodonts occurred in areas yet to be sampled and their first occurrences might reflect immigration of invasive species

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

cretaceous extinctions multiple causes figure 1 deccan plateau basalts lava from deccan volcanism formed distinct layering credit gsfc nasa in the review the chicxulub asteroid impact and mass extinction at the cretaceous paleogene boundary p schulte et al 5 march p 1214 2 the terminal cretaceous

abrupt deep sea warming at the end of the cretaceous climatic and oceanographic variations during the last 2 m y of the maastrichtian inferred from high resolution 10 k y stable isotope analysis of the mid latitude south atlantic deep sea drilling project site 525 reveal a major warm pulse followed by rapid cooling prior to the cretaceous tertiary boundary between 66 85 and 65 52 ma cool but fluctuating temperatures average 9 9 and 15 4 c in intermediate and surface waters respectively this interval is followed by an abrupt short term warming between 65 45 and 65 11 ma which increased temperatures by 2 3 c in intermediate waters and decreased the vertical thermal gradient to an average of 2 7 c this warm pulse may be linked to increased atmospheric pco 2 increased poleward heat transport and the switch of an intermediate water source from high to lowmiddle latitudes during the last 100 k y of the maastrichtian intermediate and surface temperatures decreased by an average of 2 1 and 1 4 c respectively compared to the maximum temperature between 65 32 and 65 24 ma

environmental change across a terrestrial cretaceous paleogene boundary section in eastern montana usa constrained by carbonate clumped isotope paleothermometry the cretaceous paleogene k pg mass extinction has been attributed to the impact of a large bolide at the end of the cretaceous period although other potential causes have also been proposed most notably climate change caused by deccan traps india flood volcanism reconstructing paleoclimate particularly in terrestrial settings has been hindered by a lack of reliable proxies the recent development of carbonate clumped isotope paleothermometry has contributed to temperature reconstructions using geochemical proxies in terrestrial settings we employ this method along with new stratigraphic constraints in the hell creek cretaceous and overlying fort union paleogene formations montana usa to examine changes in temperature leading to and across the k pg boundary we demonstrate that well preserved ca 66 ma aragonitic bivalves serve as suitable paleoclimate archives although there are limitations in the stratigraphic availability of fossil bivalves for clumped isotope analysis we record an apparent 8 c decrease in summer temperatures over the last 300 k y of the cretaceous that corresponds broadly with patterns observed in other paleotemperature proxies this observed decrease plausibly could be explained by an absolute temperature decrease or by other environmental stresses on the organisms but in either case suggests changing living conditions over the interval previously documented declines in vertebrate and invertebrate biodiversity occur over the same stratigraphic interval at this study location these results are consistent with published models of the end cretaceous mass extinction in which destabilized ecosystems become more susceptible to an abrupt event like a bolide impact

main deccan volcanism phase ends near the k t boundary evidence from the krishna godavari basin se india abstract recent studies indicate that the bulk 80 of the deccan trap eruptions occurred over less than 0 8 m y in magnetic polarity c29r spanning the cretaceous tertiary k t boundary determining where within this major eruptive phase the k t mass extinction occurred has remained problematic for this reason models estimating the biotic and environmental consequences have generally underestimated the rate and quantity of deccan gas emissions by orders of magnitude leading to conclusions that volcanism could not have been one of the major causes for the k t mass extinction in this study we report that the most massive deccan trap eruption occurred near the k t mass extinction these results are based on sedimentologic microfacies and biostratigraphic data of 4 9 m thick intertrappean sediments in four quarry outcrops in the rajahmundry area of the krishna godavari basin of southeastern india in this area two deccan basalt flows known as the rajahmundry traps mark the longest lava flows extending 1500 km across the indian continent and into the bay of bengal the sediments directly overlying the lower rajahmundry trap contain early danian planktic foraminiferal assemblages of zone p1a which mark the evolution in the aftermath of the k t mass extinction the upper rajahmundry trap was deposited in magnetic polarity c29n preceding full biotic recovery these results suggest that volcanism may have played critical roles in both the k t mass extinction and the delayed biotic recovery

importance of titanohematite in detrital remanent magnetizations of strata spanning the cretaceous paleogene boundary hell creek region montana intermediate composition titanohematite fe2 ytiyo3 with 0 5 y 0 7 is seldom the focus of paleomagnetic study and is commonly believed to be rare in nature while largely overlooked in magnetostratigraphic studies intermediate titanohematite has been identified as the dominant ferrimagnetic mineral in an array of late mesozoic and early cenozoic laramide clastic deposits throughout the central united states intermediate titanohematite is ferrimagnetic and has similar magnetic properties to titanomagnetite except its unique self reversing property due to these similarities and with detrital remanent magnetizations masking its self reversing nature intermediate titanohematite is often misidentified in sedimentary deposits past studies relied upon nonmagnetic techniques including x ray diffraction and electron microprobe analysis while these techniques can identify the presence of intermediate titanohematite they fail to test whether the mineral is the primary recorder to facilitate the identification of intermediate titanohematite in sedimentary deposits we characterize this mineral using low temperature magnetometry and high temperature susceptibility experiments and present a new identification technique based on titanohematite s self reversing property for sediments that span the cretaceous paleogene boundary hell creek region montana results from the self reversal test indicate that the majority of remanence is held by minerals that become magnetized parallel to an applied field but that intermediate self reversing titanohematite y 0 53 0 63 is an important ancillary carrier of remanence while earlier literature suggests that intermediate titanohematite is rare in nature reanalysis using specialized rock magnetic techniques may reveal that it is more abundant in the rock record particularly within depositional basins adjacent to calc alkaline volcanics than previously thought

evaluation of the astronomical time scale for the paleocene and earliest eocene abstract the astronomical tuned time scale is rapidly extended into the paleogene but due to the existence of an eocene gap different tuning options had to be presented for the paleocene these options differ both in number and tuning of 405 kyr eccentricity related cycles and are only partially consistent with recalculated 40 ar 39 ar constraints for the cretaceous paleogene k pg and paleocene eocene p e boundaries in this paper we evaluate the cyclostratigraphic interpretation of records from odp leg 198 and 208 sites and the zumaia section to solve the problem of the different tuning options we found that the interval between the k pg boundary and the early late paleocene biotic event elpe comprises 17 instead of 16 405 kyr eccentricity related cycles as previously proposed while the entire paleocene contains 25 405 kyr cycles starting from 40 ar 39 ar age constraints for the k pg boundary a new tuning to 405 kyr eccentricity is presented for the paleocene and earliest eocene which results in ages of 66 0 and 56 0 ma for the k pg and p e boundaries respectively this tuning introduces considerable differences in age for a number of nannofossil events at odp sites 1209 and 1262 in the interval between 61 and 63 ma but eliminates large and abrupt changes in the seafloor spreading rate the tuning seems further consistent with recalculated 40 ar 39 ar ages for ash layer 17 of early eocene age however despite this apparent consistency with existing radio isotopic constraints an alternative 405 kyr younger or less likely older tuning cannot be excluded at this stage

climatic fluctuations and sea surface water circulation patterns at the end of the cretaceous era calcareous nannofossil evidence abstract new paleoecological data are presented for late maastrichtian calcareous nannofossil assemblages of the indian ocean and the boreal epicontinental chalk sea these data are compiled with recent results in the tropical atlantic pacific and tethys oceans in order to characterize environmental changes by the end of the cretaceous era the paleobiogeographic distribution of the warm water species micula murus is updated and indicates the existence of major sea surface currents in the late maastrichtian atlantic ocean similar to the present day the end maastrichtian greenhouse warming is characterized at tropical and subtropical latitudes by an increase in abundance of m murus and the temporary disappearance of the high fertility marker biscutum constans in the boreal realm the greenhouse episode is marked by a contemporaneous acme of watznaueria barnesiae coincident with very rare occurrences of m murus and other tropical nannofossil species which have never been reported before at boreal latitudes a review of cyclostratigraphic and calcareous nannofossil data in the atlantic pacific indian and tethys oceans points to the following evolution of sea surface paleotemperatures for the last ca 350 380 kyr of the cretaceous the end maastrichtian greenhouse warming lasted on average a little more than 200 kyr and was followed by a ca 100 120 kyr cooling in the tethys a 30 40 kyr additional pulse of warming is highlighted immediately below the cretaceous paleogene boundary these findings indicate an important instability of the climate system at the end of the maastrichtian most likely caused by deccan volcanism the calcareous nannofossil species richness dropped during the end maastrichtian greenhouse warming which may indicate environmental stress and or ocean acidification however nannoplankton diversity returned rapidly to higher values after this climatic episode and remained high up to the cretaceous paleogene boundary no significant extinction is recorded in this biotic group prior to the boundary clay

40k 40ar dating of the main deccan large igneous province further evidence of ktb age and short duration most mass extinctions coincide in time with outpourings of continental flood basalts cfb some 20 years ago it was shown courtillot v besse j vandamme d montigny r jaeger j j cappetta h 1986 deccan flood basalts at the cretaceous tertiary boundary earth planet sci lett 80 361 374 courtillot v feraud g maluski h vandamme d moreau m g besse j 1988 deccan flood basalts and the cretaceous tertiary boundary nature 333 843 846 duncan r a pyle d g 1988 rapid eruption of the deccan flood basalts at the cretaceous tertiary boundary nature 333 841 843 that the age of the deccan traps was close to the cretaceous tertiary kt boundary and its duration under 1 myr we have undertaken a new geochronological study using the unconventional 40k 40ar cassignol gillot technique which is particularly well suited to the potassium poor deccan lavas the mean of 4 determinations from the topmost ambenali and mahabaleshwar formations is 64 5 0 6 ma they straddle the c29r c29n reversal boundary for which they provide a new constraint the mean age of 3 determinations from the oldest jawhar formation is 64 8 0 6 ma the difference in age between top and bottom of a 3500 m composite section probably comprising 80 of the total deccan volume is statistically insignificant with the overall mean age being 64 7 0 6 ma n 7 our results are consistent with the most recent 40ar 39ar determinations knight k b renne p r halkett a white n 2003 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps earth planet sci lett 208 85 99 knight k b renne p r baker j waight t white n 2005 reply to 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps discussion by a k baksi earth planet sci lett 239 374 382 confirming that there should be no systematic difference between the two methods when they are used in an optimal way an earlier smaller but significant pulse of volcanism between 68 and 67 ma extending over at least 500 km in latitude in the northern part of the deccan cfb has also been identified after 2 to 3 ma of quiescence the second major phase of volcanism occurred near 65 ma expanding over most of the area covered by the first pulse and another 500 km to the south consistent with drift of india by 300 to 450 km at not vert similar 150 mm yr during the quiescence period new paleontological data from the remote rajahmundry section keller g adatte t gardin s bartolini a bajpai s humler e in prep the cretaceous tertiary boundary in deccan traps of the krishna godavari basin of southeastern india epsl to be submitted suggest that this second pulse can itself be divided into two major pulses one starting in c29r and ending at the kt boundary the second starting in the upper part of c29r and ending within c29n

the chicxulub shiva extraterrestrial one two killer punches to earth 65 million years ago abstract two large asteroids struck earth at almost the same time 65 million years ago causing the major extinctions recognized as ending the mesozoic era although occurring close together in time the earth s magnetic pole had moved from the south pole to the north pole in between allowing a time difference between the impacts to be calculated the first strike produced a 180 km diameter crater named chicxulub on the yucatan shelf of southern mexico the second hit the shelf of the northward drifting indian continent in the southern indian ocean producing a crater 450 600 km named shiva hitherto the main obstacle to verifying this scenario has been the paucity of geological sections containing evidence of both impacts here we present such evidence and conclude that the two impacts were separated by about 40 000 years

direct high precision u pb geochronology of the end cretaceous extinction and calibration of paleocene astronomical timescales abstract the cretaceous paleogene k pg boundary is the best known and most widely recognized global time horizon in earth history and coincides with one of the two largest known mass extinctions we present a series of new high precision uranium lead u pb age determinations by the chemical abrasion isotope dilution thermal ionization mass spectrometry ca id tims method from volcanic ash deposits within a tightly constrained magnetobiostratigraphic framework across the k pg boundary in the denver basin colorado usa this new timeline provides a precise interpolated absolute age for the k pg boundary of 66 021 0 024 0 039 0 081 ma constrains the ages of magnetic polarity chrons c28 to c30 and offers a direct and independent test of early paleogene astronomical and 40ar 39ar based timescales temporal calibration of paleontological and palynological data from the same deposits shows that the interval between the extinction of the dinosaurs and the appearance of earliest cenozoic mammals in the denver basin lasted 185 ky and no more than 570 ky and the fern spike lasted 1 ky and no more than 71 ky after the k pg boundary layer was deposited indicating rapid rates of biotic extinction and initial recovery in the denver basin during this event

on impact and volcanism across the cretaceous paleogene boundary the cause of the end cretaceous mass extinction is vigorously debated owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary disentangling their relative importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing impact and extinction we used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing we found support for major outgassing beginning and ending distinctly before the impact with only the impact coinciding with mass extinction and biologically amplified carbon cycle change our models show that these extinction related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide thus limiting the global warming otherwise expected from postextinction volcanism

mineralogy and titanite geochronology of the caojiaba w deposit xiangzhong metallogenic province southern china implications for a distal reduced skarn w formation the caojiaba tungsten deposit 19 03 mt 0 37 wt wo3 is hosted by skarn along the contact between clastic and carbonate rocks in the xiangzhong metallogenic province of southern china the deposit is characterized by an early prograde skarn containing low andraditic garnet ad0 7 21 9 and hedenbergitic pyroxene hd52 9 77 3 overprinted by a retrograde biotite chlorite assemblage and then by quartz scheelite veins similar to well studied reduced tungsten skarns worldwide scheelite has low moo3 0 01 0 16 wt and ore commonly contains up to 1 5 ppm au and up to 0 33 wt sb sensitive high resolution ion microprobe shrimp u pb analyses of hydrothermal titanite coexisting with scheelite in three skarn ore samples provide ages between 206 5 ma and 196 3 ma 2 our new ages demonstrate that the tungsten mineralization took place at caojiaba between 206 and 196 ma overlapping the 228 201 ma emplacement age of granitic rocks in the xiangzhong metallogenic province mineralogical and geochronological evidence collectively indicates that caojiaba is a distal reduced w skarn deposit the 226 196 ma granite related w mineralization recognized throughout the province has a possible link with the widespread sb au mineralization in the region

does large igneous province volcanism always perturb the mercury cycle comparing the records of oceanic anoxic event 2 and the end cretaceous to other mesozoic events mercury hg is increasingly being used as a sedimentary tracer of large igneous province lip volcanism and supports hypotheses of a coincidence between the formation of several lips and episodes of mass extinction and major environmental perturbation however numerous important questions remain to be answered before hg can be claimed as an unequivocal fingerprint of lip volcanism as well as an understanding of why some sedimentary records document clear hg enrichment signals whilst others do not of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle as well as the role played by depositional processes in recording global hg cycle perturbations here new mercury records of cretaceous oceanic anoxic event 2 oae 2 94 ma and the latest cretaceous 67 66 0 ma are presented oae 2 is associated with the emplacement of multiple predominantly submarine lips the latest cretaceous with subaerial volcanism of the deccan traps both of these connections are strongly supported by previously published trends towards unradiogenic osmium os isotope values in globally distributed sedimentary records hg data from both events show considerable variation between different locations attributed to the effectiveness of different sediment types in registering the hg signal with lithologically homogeneous records documenting more clear hg enrichments than sections with major changes in lithology such as limestones to claystones or organic rich shales crucially there is no geographically consistent signal of sedimentary hg enrichment in stratigraphic records of either oae 2 or the latest cretaceous that matches os isotope evidence for lip emplacement indicating that volcanism did not cause a global hg perturbation throughout the entire eruptive history of the lips formed at those times it is suggested that the discrepancy between os isotope and hg trends in records of oae 2 is caused by the limited dispersal range of hg emitted from submarine volcanoes compared to the global scale distribution of os a similar lack of correlation between these two proxies in uppermost cretaceous strata indicates that although subaerial volcanism can perturb the global hg cycle not all subaerial eruptions will do so these results highlight the variable impact of different volcanogenic processes on the efficiency of hg dispersal across the globe factors that could influence the impact of lip eruptions on the global mercury cycle include submarine versus subaerial volcanism volcanic intensity or explosivity and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic rich sediments

constraints on the volume and rate of deccan traps flood basalt eruptions using a combination of high resolution terrestrial mercury records and geochemical box models abstract deccan traps continental flood basalt eruptions spanned the cretaceous paleogene mass extinction erupting over a million cubic kilometers of basalt over a total duration of approximately a million years the environmental consequences of flood basalt eruptions depend on the timing and amount of volatile release eruption rates are thus needed to evaluate their potential to cause climate change radioisotopic dates are not currently sufficient to resolve sub ten thousand year eruptive tempos necessary for constraining the effects of short lifetime volatiles including sulfur dioxide recent studies have demonstrated that increases in mercury concentration in sedimentary records correlate with flood basalt eruptions under some circumstances however mercury concentrations have primarily been used to show the presence or absence of flood basalt eruptions we show that this proxy can be used to quantitatively estimate eruptive rates using a mercury geochemical cycle framework we illustrate this using new mercury chemostratigraphic records from terrestrial cretaceous paleogene boundary sections in eastern montana usa with multiple high resolution chronologic constraints we estimate that deccan eruptions lasted on the order of centuries and released 500 3000 megagrams mg of mercury per year corresponding to 50 250 km3 a of lava the box model framework highlights the importance of carefully accounting for differences in sedimentation rate and sampling resolution when comparing mercury records from different locations and depositional environments while there are uncertainties in the box model estimates due to possible variation in flood basalt mercury emissions and sedimentation rates they provide a useful framework to quantitatively evaluate the global mercury budget change indicated by changing concentration in sedimentary records eruptions of the estimated size would have released enough so2 if it reached the stratosphere to cause significant cooling for the duration of the eruption however given our constraints on the duration of individual eruptions these colder periods are likely too brief to be clearly visible in most existing paleoclimate records

high resolution chronostratigraphy of the terrestrial cretaceous paleogene transition and recovery interval in the hell creek region montana detailed understanding of ecosystem decline and recovery attending the cretaceous paleogene boundary kpb mass extinctions is hindered by limited constraints on the pace and tempo of environmental events near the boundary to mitigate this shortcoming high resolution 40ar 39ar geochronology was performed on tephras intercalated between fossiliferous terrestrial sediments of the upper hell creek and lower fort union formations in the western williston basin of northeastern montana usa tephra samples were collected from 10 stratigraphic sections spanning an area of 5000 km2 several distinctive tephras can be correlated between sections separated spatially by as much as 60 km the tephras are thin distal deposits generally preserved only in lignite beds which are interbedded with clastic deposits yielding vertebrate faunas of lancian late maastrichtian to torrejonian early danian north american land mammal ages sanidine from 15 tephra samples was analyzed in 1649 total fusion experiments 1597 on single crystals and 12 incremental heating analyses of multigrain aliquots ages were determined for 13 distinct tephras ranging from 66 289 0 051 to 64 866 0 023 ma including only analytical uncertainties this level of precision is sufficient to resolve the ages of all of the coal beds that have served as a basis for a regional stratigraphic framework the data confirm that the hell creek fort union formational contact is diachronous and further support the age of the kpb impact layer at 66 043 0 010 ma or 0 043 ma considering systematic uncertainties application of the new results to previous magnetostratigraphic data indicates an appreciably compressed time interval between the base of chron c29r and the top of chron c28r with a maximum duration estimate of 1 421 0 066 ma most notable is the implied brevity of chron c29r with a maximum estimate of 457 54 ka and possibly as brief as 345 38 ka compared to the 710 ka estimate from the geologic time scale 2012 gts2012 further application of new results to terrestrial biostratigraphy adds higher precision to the timing and tempo of biotic change before and after the kpb our results indicate that the timing of pre kpb ecological decline is constrained to the last 200 ka of the cretaceous adding further support to the press pulse extinction hypothesis additionally the duration of the depauperate basal paleogene puercan 1 disaster fauna is confined to a 70 ka interval faunal recovery in this region indicated by the appearance of primitive members of the placental mammal radiation and the restoration of taxonomic richness and evenness occurred within 900 ka after the kpb these results show that biotic recovery after the mass extinction in the terrestrial realm was more rapid than in the marine

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

coeval 40ar 39ar ages of 65 0 million years ago from chicxulub crater melt rock and cretaceous tertiary boundary tektites 40 ar 39 ar dating of drill core samples of a glassy melt rock recovered from beneath a massive impact breccia contained within the 180 kilometer subsurface chicxulub crater in yucatan mexico has yielded well behaved incremental heating spectra with a mean plateau age of 64 98 0 05 million years ago ma the glassy melt rock of andesitic composition was obtained from core 9 1390 to 1393 meters in the chicxulub 1 well the age of the melt rock is virtually indistinguishable from 40 ar 39 ar ages obtained on tektite glass from beloc haiti and arroyo el mimbral northeastern mexico of 65 01 0 08 ma mean plateau age for beloc and 65 07 0 10 ma mean total fusion age for both sites the 40 ar 39 ar ages in conjunction with geochemical and petrological similarities strengthen the recent suggestion that the chicxulub structure is the source for the haitian and mexican tektites and is a viable candidate for the cretaceous tertiary boundary impact site

conceptual models for short eccentricity scale climate control on peat formation in a lower palaeocene fluvial system north eastern montana usa fluvial systems in which peat formation occurs are typified by autogenic processes such as river meandering crevasse splaying and channel avulsion nevertheless autogenic processes cannot satisfactorily explain the repetitive nature and lateral continuity of many coal seams compacted peats the fluvial lower palaeocene tullock member of the fort union formation western interior williston basin montana usa contains lignite rank coal seams that are traceable over distances of several kilometres this sequence is used to test the hypothesis that peat formation in the fluvial system was controlled by orbitally forced climate change interacting with autogenic processes major successions are documented with an average thickness of 6 8 m consisting of ca 6 m thick intervals of channel and overbank deposits overlain by ca 1 m thick coal seam units these major coal seams locally split and merge time stratigraphic correlation using a cretaceous palaeogene boundary event horizon several distinctive volcanic ash fall layers and the c29r c29n magnetic polarity reversal shows consistent lateral recurrence of seven successive major successions along a 10 km wide fence panel perpendicular to east south east palaeo flow the stratigraphic pattern complemented by stratigraphic age control and cyclostratigraphic tests suggests that the major peat forming phases resulting in major coal seams were driven by 100 kyr eccentricity related climate cycles two distinct conceptual models were developed both based on the hypothesis that the major peat forming phases ended when enhanced seasonal contrast at times of minimum precession during increasing eccentricity intensified mire degradation and flooding in model 1 orbitally forced climate change controls the timing of peat compaction leading to enhancement of autogenic channel avulsions in model 2 orbitally forced climate change controls upstream sediment supply and clastic influx determining the persistence of peat forming conditions at the scale of the major successions model 2 is supported because interfingering channel sandstones do not interrupt lateral continuity of major coal seams

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

chemical and pb isotope composition of phenocrysts from bentonites constrains the chronostratigraphy around the cretaceous paleogene boundary in the hell creek region montana an excellent record of environmental and paleobiological change around the cretaceous paleogene boundary is preserved in the hell creek and fort union formations in the western williston basin of northeastern montana these records are present in fluvial deposits whose lateral discontinuity hampers long distance correlation geochronology has been focused on bentonite beds that are often present in lignites to better identify unique bentonites for correlation across the region the chemical and pb isotopic composition of feldspar and titanite has been measured on 46 samples many of these samples have been dated by 40ar 39ar the combination of chemical and isotopic compositions of phenocrysts has enabled the identification of several unique bentonite beds in particular three horizons located at and above the cretaceous paleogene boundary can now be traced based on their unique compositions across the region clarifying previously ambiguous stratigraphic relationships other bentonites show unusual features such as pb isotope variations consistent with magma mixing or assimilation that will make them easy to recognize in future studies this technique is limited in some cases by more than one bentonite having compositions that cannot be distinguished or bentonites with abundant xenocrysts the pb isotopes are consistent with a derivation from the bitterroot batholith whose age range overlaps that of the tephra these data provide an improved stratigraphic framework for the hell creek region and provide a basis for more focused tephrostratigraphic work and more generally demonstrate that the combination of mineral chemistry and pb isotope compositions is an effective technique for tephra correlation

time scale controversy accurate orbital calibration of the early paleogene 1 timing is crucial to understanding the causes and consequences of events in earth history the calibration of geological time relies heavily on the accuracy of radioisotopic and astronomical dating uncertainties in the computations of earth s orbital parameters and in radioisotopic dating have hampered the construction of a reliable astronomically calibrated time scale beyond 40 ma attempts to construct a robust astronomically tuned time scale for the early paleogene by integrating radioisotopic and astronomical dating are only partially consistent here using the new la2010 and la2011 orbital solutions we present the first accurate astronomically calibrated time scale for the early paleogene 47 65 ma uniquely based on astronomical tuning and thus independent of the radioisotopic determination of the fish canyon standard comparison with geological data confirms the stability of the new la2011 solution back to 54 ma subsequent anchoring of floating chronologies to the la2011 solution using the very long eccentricity nodes provides an absolute age of 55 530 0 05 ma for the onset of the paleocene eocene thermal maximum petm 54 850 0 05 ma for the early eocene ash 17 and 65 250 0 06 ma for the k pg boundary the new astrochronology presented here indicates that the intercalibration and synchronization of u pb and 40ar 39ar radioisotopic geochronology is much more challenging than previously thought

subannual stable isotope records reveal climate warming and seasonal anoxia associated with two extinction intervals across the cretaceous paleogene boundary on seymour island antarctica

mineralogy of magnetic minerals and revised magnetic polarity stratigraphy of continental sediments san juan basin new mexico detailed paleomagnetic and rock magnetic analyses have been performed on samples from multiple sections through the cretaceous tertiary k t boundary and throughout a 750 m thick sequence of late cretaceous through middle paleocene continental deposits in the san juan basin new mexico curie temperatures have been determined for magnetic separates from 52 levels and with only two exceptions they range from 180 to 300 c along with microprobe and x ray analyses these data indicate that the detrital ferrimagnetic mineral is titanohematite with composition 0 45 x 0 60 this magnetic mineralogy indicates derivation of the continental san juan basin sediments from a volcanic probably dacitic or andesitic source these mineralogical data along with other geological data and the pattern of magnetic polarity zonation in multiple sections across the basin argue strongly for deposition of the late cretaceous and paleocene continental deposits in the san juan basin as a clastic wedge derived from a sourc

north atlantic warming during global cooling at the end of the cretaceous differences in regional responses to climate fluctuations are well documented on short time scales e g el nino southern oscillation but with the exception of latitudinal temperature gradients regional patterns are seldom considered in discussions of ancient greenhouse climates contrary to the expectation of global warming or global cooling implicit in most treatments of climate evolution over millions of years this paper shows that the north atlantic warmed by as much as 6 c 1 5 decrease in 18o values of planktic foraminifera during the maastrichtian global cooling interval we suggest that warming was the result of the importation of heat from the south atlantic decreasing north atlantic 18o values are also associated with increasing gradients in planktic 13c values suggesting increasing surface water stratification and a correlated strengthening of the north atlantic polar front if correct this conclusion predicts arctic cooling during the late maastrichtian beyond implications for the maastrichtian these data demonstrate that climate does not behave as if there is a simple global thermostat even on geologic time scales

astronomical calibration of upper campanian maastrichtian carbon isotope events and calcareous plankton biostratigraphy in the indian ocean odp hole 762c implication for the age of the campanian maastrichtian boundary abstract an integrated framework of magnetostratigraphy calcareous microfossil bio events cyclostratigraphy and 13c stratigraphy is established for the upper campanian maastrichtian of odp hole 762c exmouth plateau northwestern australian margin bulk carbonate 13c events and nannofossil bio events have been recorded and plotted against magnetostratigraphy and provided absolute ages using the results of the cyclostratigraphic study and the recent astronomical calibration of the maastrichtian thirteen carbon isotope events and 40 nannofossil bio events are recognized and calibrated with cyclostratigraphy as well as 14 previously published foraminifer events thus constituting a solid basis for large scale correlations results show that this site is characterized by a nearly continuous sedimentation from the upper campanian to the k pg boundary except for a 500 kyr gap in magnetochron c31n correlation of the age calibrated 13c profile of odp hole 762c to the 13c profile of the tercis les bains section global stratotype section and point of the campanian maastrichtian boundary cmb allowed a precise recognition and dating of this stage boundary at 72 15 0 05 ma this accounts for a total duration of 6 15 0 05 ma for the maastrichtian stage correlation of the boundary level with northwest germany shows that the cmb as defined at the gssp is 800 kyr younger than the cmb as defined by belemnite zonation in the boreal realm odp hole 762c is the first section to bear at the same time an excellent recovery of sediments throughout the upper campanian maastrichtian a precise and well defined magnetostratigraphy a high resolution record of carbon isotope events and calcareous plankton biostratigraphy and a cyclostratigraphic study tied to the la2010a astronomical solution this section is thus proposed as an excellent reference for the upper campanian maastrichtian in the indian ocean

glacioeustatic sea level fall marking the base of supercycle ta 1 at 66 5 ma recorded by the kaolinization of the whitemud formation and the colgate member of the fox hills formation abstract the maastrichtian continental whitemud formation in the cypress hills of southwestern saskatchewan canada has been kaolinized by in situ leaching to a depth of at least 20 m produced by a lowered water table the first stage of leaching took place during accumulation of the coal zone in the middle of the 20 m thick whitemud a second stage took place after deposition of the lower few meters of the overlying organic rich battle formation the u pb age on bentonite zircon in the lower battle is 66 5 0 2 ma indicating the last stage of sea fall using an average compacted sediment accumulation rate of 72 m m y based upon the thicknesses of magnetozones 29r and 30r the time spanning the two stages of lowered sea level is 200 000 years or less the colgate member of the fox hills formation in montana is an exact correlative of the whitemud and kaolinization of the colgate is due to the same sea level fall from the international boundary to central north dakota the age correlates to the sea level cycle marking the base of supercycle ta 1 and the short duration indicates that this sea level cycle was glacioeustatic

sedimentology stratigraphy and extinctions during the cretaceous paleogene transition at bug creek montana bug creek valley the source of an unusual and controversial cretaceous paleogene coincidence of mammals dinosaurs pollen and indium exemplifies the importance of depositional process in the reconstruction of evolutionary events five sedimentary facies are recognized at bug creek a cross stratified sandstone a green and purple siltstone a lateral accretionary sandstone a coal and a variegated siltstone repeated fluvial channeling restricts the accuracy of lateral correlations and the relationship of the fossil assemblage to the presumed cretaceous paleogene boundary cannot be established sedimentologically the cretaceous paleogene transition is represented here by cretaceous meandering channels that gave way initially to paleogene swamp deposition

climate control on quaternary coal fires and landscape evolution powder river basin wyoming and montana late cenozoic stream incision and basin excavation have strongly influenced the modern rocky mountain landscape but constraints on the timing and rates of erosion are limited the geology of the powder river basin provides an unusually good opportunity to address spatial and temporal patterns of stream incision numerous coal seams in the paleocene fort union and eocene wasatch formations within the basin have burned during late cenozoic incision as coal was exposed to dry and oxygen rich near surface conditions the topography of this region is dominated by hills capped with clinker sedimentary rocks metamorphosed by burning of underlying coal beds we use u th he ages of clinker to determine times of relatively rapid erosion with the assumption that coal must be near earth s surface to burn ages of 55 in situ samples range from 0 007 to 1 1 ma clinker preferentially formed during times in which eccentricity of the earth s orbit was high times that typically but not always correlate with interglacial periods our data therefore suggest that rates of landscape evolution in this region are affected by climate fluctuations because the clinker ages correlate better with eccentricity time series than with an oxygen isotope record of global ice volume we hypothesize thatmore variations in solar insolation modulated by eccentricity have a larger impact on rates of landscape evolution in this region than do glacial interglacial cycles less