paleomagnetic study of some cretaceous and tertiary sedimentary rocks of the klamath mountains province california paleomagnetic investigation of cretaceous outliers and tertiary sedimentary strata of the klamath mountains province and of onlapping cretaceous strata has shown the rocks to be largely remagnetized samples studied are from the upper jurassic to upper cretaceous great valley sequence upper cretaceous hornbrook formation eocene montgomery creek formation and oligocene weaverville formation cretaceous samples that survived the remagnetization have a mean remanence direction that is very close to the expected direction of the cretaceous magnetic field at the locality of the klamath mountains data from both primary and remagnetized samples suggest the possibility of 11 5 15 8 of post cretaceous clockwise rotation of the klamath mountains province none of the data from either the primary or remagnetized samples shows evidence of the large amounts 70 of clockwise rotation that other workers have measured for the lower tertiary of the oregon coast range our data indicate that the oregon coast range and klamath mountains province did not behave as a single rigid block during the early tertiary they also suggest that any post oligocene rotation of the klamath mountains province is less than the approximately 30 post oligocene rotation recently proposed for a combined oregon coast range klamath mountains cascade range block

winding down the chicxulub impact the transition between impact and normal marine sedimentation near ground zero abstract the chicxulub impact led to the formation of a 200 km wide by 1 km deep crater on mexico s yucatan peninsula over a period of hours after the impact the ocean re entered and covered the impact basin beneath several hundred meters of water a suite of impactites were deposited across the crater during crater formation and by the resurge tsunami and seiche events that followed international ocean discovery program international continental scientific drilling program expedition 364 drilled into the peak ring of the chicxulub crater and recovered 130 m of impact deposits and a 75 cm thick fine grained carbonate rich transitional unit above which normal marine sedimentation resumed here we describe the results of analyses of the uppermost impact breccia suevite and the transitional unit which suggests a gradual waning of energy recorded by this local k pg boundary sequence the dominant depositional motif in the upper suevite and the transitional unit is of rapid sedimentation characterized by graded bedding local cross bedding and evidence of oscillatory currents the lower transitional unit records the change from deposition of dominantly sand sized to mainly silt to clay sized material with impact debris that decreases in both grain size and abundance upward the middle part of the transitional unit is interrupted by a 20 cm thick soft sediment slump overlain by graded and oscillatory current cross laminated beds the uppermost transitional unit is also soft sediment deformed contains trace fossils and an increasing abundance of planktic foraminifer and calcareous nannoplankton survivors the transitional unit as with similar deposits in other marine target impact craters records the final phases of impact related sedimentation prior to resumption of normal marine conditions petrographic and stable isotopic analyses of carbon from organic matter provide insight into post impact processes 13corg values are between terrestrial and marine end members with fluctuations of 1 3 timing of deposition of the transitional unit is complicated to ascertain the repetitive normally graded laminae both below and above the soft sediment deformed interval record rapid deposition from currents driven by tsunami and seiches processes that likely operated for weeks to potentially years post impact due to subsequent continental margin collapse events highly siderophile element enrichment at the top of the unit is likely from fine grained ejecta that circulated in the atmosphere for several years prior to settling the transitional unit is thus an exquisite record of the final phases of impact related sedimentation related to one of the most consequential events in earth history

hybrid seismic modelling a technique to combine physical and computer methods for vertical wave incidence a hybrid seismic modelling technique has been developed to investigate complex geological phenomena those parts of a geological structure which are too complicated to be treated theoretically are studied by two dimensional physical models other sections of the structure which can be treated theoretically i e inhomogeneities in the vertical direction are modelled by computer methods a feedback process is used to combine the results of both physical and computer modelling horizontally layered coal seam models are presented to test the hybrid modelling technique for normal incidence a comparison of the hybrid seismograms with pure synthetic seismograms shows an acceptable conformity for normal incidence a hybrid zero offset section is shown to investigate a complex geological structure in the ruhr coalfield in germany

the cretaceous tertiary boundary cocktail chicxulub impact triggers margin collapse and extensive sediment gravity flows a distinctive mixture of reworked microfossils impact derived materials and lithic fragments occurs in sediments at the cretaceous tertiary boundary in the basinal gulf of mexico and caribbean we have named this mixture the cretaceous tertiary boundary cocktail lithologic and paleontologic evidence suggests that the cocktail was deposited by giant sediment gravity flows apparently triggered by the collapse of continental margins around the gulf of mexico as a result of the chicxulub impact as most microfossils in the gravity flow units are reworked biostratigraphy provides only maximum ages recognition of the cocktail is a reliable way to identify cretaceous tertiary boundary deposits in the basinal gulf of mexico and caribbean

mineralogy and phase relations in the blueschist facies of the black butte and ball rock areas northern california coast ranges microprobe study of minerals in rocks of the blueschist facies from the black butte and ball rock areas of the south fork mountain schist northern california coast ranges is the basis in this report for analysis of reactions and phase relations among lawsonite pumpellyite epidote and associated minerals observed assemblages are intermediate in a progression from those observed elsewhere in high p low t schists of the franciscan e 9 panoche pass where lawsonite is present in nearly all lithologies to the relatively low phigh t assemblages of the shuksan blueschist washington where epidote is ubiquitous two successive reactions in this sequence in order of increasing temperature are l lawsonite na amphibole epidote quartz albite chlorite hzo 2 na amphibole pumpellyite quartz epidote ca amphibole albite chlorite h2o the pressure of metamorphism for the black butte and ball rock areas is estimated from the jadeite content of pyroxene and from the stability of aragonite to have been approximately 7 kbar temperature estimates are not tightly constrained by mineral equilibria but are suggested to be in the range of 250 to 300 c

perspectives on proterozoic surface ocean redox from iodine contents in ancient and recent carbonate abstract the proterozoic eon hosted the emergence and initial recorded diversification of eukaryotes oxygen levels in the shallow marine settings critical to these events were lower than today s although how much lower is debated here we use concentrations of iodate the oxidized iodine species in shallow marine limestones and dolostones to generate the first comprehensive record of proterozoic near surface marine redox conditions the iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters to assess the validity of our approach neogene quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate iodine contents despite the potential for diagenetic loss maximum proterozoic carbonate iodine levels are elevated relative to those of the archean particularly during the lomagundi and shuram carbon isotope excursions of the paleo and neoproterozoic respectively for the shuram anomaly comparisons to neogene quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends the baseline low iodine levels in proterozoic carbonates relative to the phanerozoic are linked to a shallow oxic anoxic interface oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes however the diagnostically low iodine data from mid proterozoic shallow water carbonates relative to those of the bracketing time intervals are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans this redox instability may have challenged early eukaryotic diversification and expansion creating an evolutionary landscape unfavorable for the emergence of animals

provenance of franciscan graywackes in coastal california a systematic comparison of available detrital modes for graywacke sandstones of the franciscan subduction complex and for coeval sandstones of the great valley sequence in the california coast ranges indicates that both were apparently derived from the same general sources the inferred provenance terrane was the ancestral sierran klamath magmatic arc from which mixed volcanic and plutonic detritus readily entered the adjacent great valley forearc basin at intervals along the trend of the arc trench system arc derived detritus also bypassed the forearc region through submarine canyons that fed the franciscan trench longitudinal flow along both the great valley trough and the franciscan trench achieved wide dispersal of the turbidite sediment suites of both franciscan and great valley samples include an array of subquartzose compositions ranging from feldspatholithic to lithofeldspathic mean framework modes of 17 franciscan suites comprising 203 individual samples and of 23 great valley suites comprising 410 individual samples range from 14 to 44 quartz grains 15 to 54 feldspar grains and 7 to 71 total lithic fragments the ratio of quartz to feldspar remains relatively constant as the proportion of lithic fragments changes the compositional variations reflect differences mainly in the admixture of lithic fragments derived principally from volcanic cover with quartz and feldspar derived principally from erosion of underlying plutons despite major overlap in the compositions of the two sets of samples some franciscan sandstones are somewhat more feldspathic and less lithic than any known great valley counterparts and were probably derived from segments of the arc terrane where exposures of plutons were more extensive than within typical great valley sources higher proportions of non volcanic to volcanic lithic fragments in some franciscan sandstones probably reflect complex recycling processes on the trench slope diagenetic effects in many franciscan suites include apparent wholesale replacement of k feldspar by albite present age control is inadequate to test fully for time dependent trends in the compositions of franciscan sandstones analogous to the known stratigraphic variations in the composition of great valley sandstones this question ought to be investigated in future studies

accretionary tectonics of the north american cordillera continental geology stands on the threshold of a change that is likely to be as fundamental as plate tectonic theory was for marine geology ongoing seismic reflection investigations into the deep crustal structure of north america are verifying that orogenic zones are underlain by low angle faults of regional extent brown et al 1981 the growing body of regional field relations is likewise delineating numerous orogenic sutures that bound discrete crustal fragments paleomagnetic and paleobiogeographic studies are revealing major latitudinal shifts and rotations within and between suture bounded fragments particularly within the north american cordillera such interdisciplinary studies are leading to a consensus that the cordillera has been built by progressive tectonic addition of crustal fragments along the continent edge in mesozoic and early cenozoic time such crustal growth is referred to as accretionary tectonics in this paper we review some of the important concepts in accretionary tectonics discuss the nature of the materials accreted between central alaska and southern california in jurassic and cretaceous time and consider the general relations between cordilleran accretion and the movement of lithospheric plates the concept of continents growing by peripheral accretion through geologic time has long been a topic of great interest with the advent of plate tectonics a number of different mechanisms for crustal accretion have arisen along with mechanisms for crustal attrition accretion mechanisms include the growth of imbricated sedimentary prisms along inner trench walls slicing off of submarine topographic irregularities within subducting plates and collision of continents and volcanic arcs by ocean basin closure tectonic attrition mechanisms include rifting transform faulting and strike slip or underthrust removal of inner trench wall materials coincident with or in place of accretionary prism growth growth of intraorogenic ocean basins by seafloor spreading is an additional important mechanism for creating accretionary materials as well as displacing crustal fragments an important implication of plate kinematic theory is the likelihood for accretionary and attritionary mechanics to operate in series both in time and space along continental margins since attrition by nature leaves little material evidence of having operated one of the major problems confronting cordilleran geologists lies in the recognition of such attrition within the ancient record particularly when interspersed with accretionary events the spectrum of accretion and attrition mechanisms viewed at cm yr 1 plate transport rates over time scales of 100 m y leads one to suspect a highly mobile history for continental margin orogens the serial arrangement of subducting transform and rifting links along the modern cordillera plate juncture system and both serial and parallel arrangements in the western pacific systems show the complex interplay of such mechanisms through space similar arrangements overprinted through time are suggested by the rock assemblages and structural patterns within the cordillera which presently resemble a collage of crustal fragments davis et al 1978 recognition of the structural state of this collage geologic field mapping and geophysical investigations will bring about a new level of understanding in the growth of continental crust and the reading of stratigraphic records within the fragments and future palinspastic restorations will lead to a new level of understanding in paleogeography and earth history the first problem to be considered is the recognition of native north american crust from exotic fragments that have been accreted to its edge

phanerozoic continental accretion and the metamorphic evolution of northern and central california abstract the late paleozoic and younger tectonic fabric of california north of the transverse ranges consists of accreted exotic and parautochthonous lithic belts which extend north south and northwest southeast separated from one another by subvertical strike slip faults and gently to steeply east dipping thrust faults where recognizable folds in general verge to the west and stratigraphic tops face east a rough but systematic westward decrease in geologic age and metamorphic intensity may also be recognized exotic terranes of uncertain provenance include the central metamorphic belt of the klamath mountains and the salina sur obispo composite block of the central coast ranges pre permian sections of the eastern klamath terrane and portions of the sierran calaveras melones complex may also represent far traveled crustal entities allochthonous oceanic basement seamounts and pelagic sediments are additional transported materials widespread in most of the parautochthonous lithotectonic belts that make up much of the rest of northern and central california ophiolitic assemblages are especially abundant along the fault zones which mark boundaries between these units the parautochthonous lithotectonic belts appear to have been constructed in the vicinity of the continental margin and or an offshore arc judging from the nature and provenance of their constituent igneous and sedimentary rocks intimately associated tholeiitic calc alkaline complexes indicate that at least locally ophiolite generation occurred nearby the salinia sur obispo amalgamated terrane exhibits the effects of fragmentation and removal of crust now represented by the suture juxtaposing the two blocks other areas may have been subjected to similar truncations but relationships are not as clear far traveled terranes are characterized by ages of formation and recrystallization foreign to surrounding units the nature of the protoliths and grades of metamorphism developed within them contrast with those of juxtaposed lithotectonic belts on the other hand essentially in situ growth of many californian lithotectonic belts is suggested by a gradually decreasing age of formation and both monotonically decreasing times and grades of metamorphism proceeding towards the pacific basin some parautochthonous units as well as exotic terranes are locally bounded by discontinuous blueschist belts the latter attesting to at least episodic preservation of the effects of subduction metamorphism and offloading into the accreting continental margin phanerozoic evolution of northern and central california thus apparently consisted of a more or less in situ seaward encroachment of the continental margin relative to the craton involving occasional truncation and loss of section with a concomitant semi continuous or episodic incorporation of allochthonous seamounts oceanic crust and deep sea sediments and the less frequent arrival and juxtaposition of exotic microcontinental fragments of problematic but distant source

detection and resolution of thin layers a model seismic study1 the detection and resolution of a thin layer closely situated above a high impedance basement are predominantly determined by both the frequency content of the incident seismic wavelet and the existence of the nearby high impedance bedrock the separation of the thin layer and the basement arrivals is investigated depending on the low frequency content of the wavelet the high frequency content of the wavelet is kept constant the initial wavelet spectrum with low frequencies has a rectangular shape all wavelets used have zero phase characteristics numerical and analogue seismic modelling techniques are used the study is based on the geology of the pachangchi sandstone in west taiwan firstly the resolution of a thin layer between two half spaces is examined by applying the ricker and de voogd den rooijen criteria the lack of low frequency components of the incident seismic wavelet reduces the shortest true two way traveltime by about 20 in addition low frequency components of the wavelet diminish the deviation between true and apparent two way traveltime by about 65 for layer thicknesses in the transition from a thick to a thin layer the second step deals with the influence of a high impedance basement just below a thin layer on the detection and resolution of that thin layer reflected signal energies and apparent two way traveltimes are considered the reflected signal energy depends on the low frequency content of the incident wavelet the layer s thickness and the distance between the basement and the layer this applies only to layers with thicknesses less than or equal to one third of the mean wavelength in the layer and a distance to basement in the range of one to one half of the mean wavelength in the rock material between layer and basement the minimum thin layer thickness resolvable decreases with increasing distance to the basement i e for a layer thickness of one third of the mean wavelength in the layer the relative error of the two way traveltime increases from 5 to 30 if the distance is reduced from one to one half of the mean wavelength in the material between the basement and the thin layer finally a combination of vertical seismic profiling and downward continuation techniques is presented as a preprocessing procedure to prepare realistic data for the detection and resolution investigation

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

microscale trace element distribution across the cretaceous palaeogene ejecta layer at the agost section constraining the recovery of pre impact conditions abstract a high resolution sub mm scale analysis of the distribution of major and trace elements across the ejecta layer marking the cretaceous palaeogene boundary kpgb at the agost section se spain was performed using laser ablation inductivity coupled plasma mass spectrometry la icp ms a kpgb interval 17 mm thick has been selected for this study it includes gray calcareous marl from the uppermost maastrichtian cretaceous 2 02 mm thick red clay the ejecta layer and blackish gray clay boundary clay layer from the lowermost danian palaeogene the unconsolidated sediments were resin embedded under o2 free conditions and analyzed by la icp ms line continuous scan measurements at 20 m increments and a laser beam of 120 m these micron scale analyses show that the anomalous contents of trace and major elements in this boundary are restricted to the ejecta layer which displays a relatively uniform distribution over its 2 mm thickness trace and major elemental ratios such as ca al ti al cr al fe al ni al cu al zn al as al sb al and pb al have similar values below and above the ejecta layer consistent with similar palaeoenvironmental conditions prior to and after the impact event such element distribution points to anomalies exclusively restricted to the ejecta thus a nearly instantaneous re establishment of pre impact conditions right after the impact event is observed

seismic modelling with channel waves in seam structures influenced by mylonite zones1 channel waves generated in coal seams and their reflections from discontinuities are widely used to indicate the tectonic and stratigraphic features of coal deposits resulting in greater efficiency and safety in coal mining in the mining area of ibbenburen f r g seam structures sometimes contain so called mylonite zones which are crushed coal deposits capable of binding gas if mining hits a mylonite zone this would probably not only reduce output of the mine but could even cause gas explosions to investigate the influence of a mylonite zone on the propagation of channel waves rayleigh channel wave measurements for 2d analogue models were performed and synthetic seismograms of love channel waves were calculated analogue modelling of the mylonite zone using rayleigh seam waves within the seam was carried out using a perforation technique calculations were made to obtain an estimate of velocity reduction due to perforation the results agree well with velocity values measured up to a perforation of 25 in a 2d epoxy resin model reflected channel wave energy was found by applying dispersion analysis in the case where the impedance reduction between the mylonite seam structure and the undisturbed seam was approximately 5 the horizontal width of the mylonite structure was detectable from the time lag between reflected channel wave signals from both in seam borders of the mylonite zone resolution of two discrete borders was possible for a width of 1 5 s the influence of a vertical fault positioned within the mylonite zone could only poorly be resolved numerical model investigations of love seam waves were concerned mainly with the variation of the horizontal width of the mylonite zone mylonite zones with dimensions of the order of 0 4 s allow definite statements about their widths from dispersion and spectral analyses for zones with smaller widths down to 0 2 s it was found that reflectivity and transmissivity analyses give a qualitative criterion for distinguishing a mylonite structure surrounding a fault from a pure fault

extraterrestrial 3he in seafloor sediments evidence for correlated 100 kyr periodicity in the accretion rate of interplanetary dust orbital parameters and quaternary climate we have determined the helium abundance and isotopic composition of seafloor carbonate sediments from the flanks of the ontong java plateau western equatorial pacific ocean odp site 806 these results provide a two million year record of the burial flux of extraterrestrial 3he which we believe is a proxy for the terrestrial accretion rate of interplanetary dust particles the 3he burial flux prior to 700 ka was relatively low 0 5 pcc cm 2 kyr 1 but from 700 ka to the present the burial flux gradually increased to a value of 1 0 pcc cm 2 kyr 1 100 kyr periodicity in the 3he burial flux is apparent over the last 700 kyr and correlates with the oxygen isotope record of global climate with high 3he burial fluxes associated with interglacial periods this periodicity and phase are consistent with previous 3he measurements in north atlantic sediments although 100 kyr periodicity in 3he burial flux is in agreement with recent predictions of the accretion rate of interplanetary dust based on a model of the orbital evolution of asteroidal debris the measurements and predictions differ by one half cycle in phase nevertheless our observations suggest the terrestrial accretion rate of interplanetary dust is controlled by orbital eccentricity and or inclination relative to the solar system invariable plane such control is a necessary but not sufficient condition for the hypothesis of muller and macdonald 1995 that variations in extraterrestrial dust accretion modulates terrestrial climate with a 100 kyr period we also identify several brief 25 kyr intervals of strongly enhanced 3he burial possibly related to random and transient fluctuations in the accretion rate of asteroidal or cometary dust particles

asteroid impact not volcanism caused the end cretaceous dinosaur extinction the cretaceous paleogene mass extinction 66 ma included the demise of non avian dinosaurs intense debate has focused on the relative roles of deccan volcanism and the chicxulub asteroid impact as kill mechanisms for this event here we combine fossil occurrence data with paleoclimate and habitat suitability models to evaluate dinosaur habitability in the wake of various asteroid impact and deccan volcanism scenarios asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats conversely long term forcing from deccan volcanism carbon dioxide co2 induced warming leads to increased habitat suitability short term aerosol cooling volcanism still allows equatorial habitability these results support the asteroid impact as the main driver of the non avian dinosaur extinction by contrast induced warming from volcanism mitigated the most extreme effects of asteroid impact potentially reducing the extinction severity

mesozoic c cycle perturbations and climate evidence for increased resilience of the cretaceous biosphere to greenhouse pulses the mesozoic c isotope record traces the history of the global carbon cycle major perturbations of the carbon cycle triggered by extraordinary volcanic activity are recorded in negative spikes cou

post middle miocene accretion of franciscan rocks northwestern california deformed sedimentary rocks assigned to the franciscan assemblage in the king range south of cape mendocino northern california are dominantly deep water argillite and sandstone occurring as thick to thin bedded locally channelized marine turbidites of arkosic to andesitic volcani clastic composition these rocks structurally overlie late cretaceous coniacian to campanian basaltic pillow flows flow breccias diabase sills and arkosic sandstone turbidites that also are assignable to the franciscan assemblage and are well exposed along the coast at point delgada radiolarians and planktic and benthic foraminifers indicate that the oldest rocks in the king range may be early tertiary and that the youngest rocks are middle miocene or younger the youngest rocks yet reported from the franciscan assemblage partly coeval miocene relizian and luisian to quaternary rocks representing shallower sedimentary facies of the inner shelf to outer continental slope occupy the eel river basin and isolated fault bounded slivers adjacent to the king range on the north and east wide zones of penetrative shearing that may delineate a middle miocene or younger suture separate the deep water franciscan rocks of the king range from less severely deformed neogene rocks of the eel river basin the king range appears to be a displaced terrane of oceanic basement overlain by paleogene and neogene sedimentary and igneous rocks of continental and oceanic derivation this terrane may have been displaced north or eastward and obductively accreted to california 15 m y ago before or perhaps during northward passage of the pacific farallon north american plate junction

cretaceous paleogene boundary bathyal paleo environments in the central north pacific dsdp site 465 the northwestern atlantic odp site 1049 the gulf of mexico and the tethys the benthic foraminiferal record uppermost maastrichtian benthic foraminiferal assemblages n63 am are diverse indicating mesotrophic conditions in lower bathyal dsdp hole 465a hess rise central north pacific in 4 lower bathyal land sections in central east and northeastern mexico and in the upper to middle bathyal agost section tethys area southeastern spain they indicate more eutrophic conditions in lower bathyal odp hole 1049c blake nose northwestern atlantic benthic foraminifers did not suffer significant extinction at the k pg boundary but diversity and heterogeneity of the assemblages and the percentage of infaunal morphogroups decreased drastically in all sections with the exception of dsdp hole 465a where the percentage of infaunal taxa increased these faunal changes probably reflect the effect on the benthic faunas of a widespread decrease in the food supply to the sea floor as a result of the collapse of primary productivity at the k pg boundary the decrease in food supply apparently affected the benthic faunas least at more eutrophic nwatlantic odp site 1049 and at pacific dsdp site 465 which is distal from the impact site of the k pg bolide on the yucatan peninsula at these sites the faunas recovered within the parvulorugoglobigerina eugubina biozone 100 ky although diversity and heterogeneity remained low through the early danian possibly indicating environmental stress this stress might be related to a high or fluctuating food supply by primary producers that could not easily be used by the benthos such as various bloom species of dinoflagellates benthic assemblages recovered more slowly 300 ky in the mexican and spanish sections low oxygen conditions after the k pg boundary could be inferred from the benthic assemblages at agost southeastern spain only a short episode of hypoxia however may be obscured at pacific dsdp hole 465a by drilling disturbance and in the mexican sections and hole 1049c by incomplete sections due to downslope transport benthic foraminiferal assemblages thus appear to have been affected by the collapse of

the ophiolitic north fork terrane in the salmon river region central klamath mountains california the north fork terrane is an assemblage of ophiolitic and other oceanic volcanic and sedimentary rocks that has been internally imbricated and folded the ophiolitic rocks form a north trending belt through the central part of the region and consist of a disrupted sequence of homogeneous gabbro diabase massive to pillowed basalt and interleaved tectonitic harzburgite u pb zircon age data on a plagiogranite pod from the gabbroic unit indicate that at least this part of the igneous sequence is late paleozoic in age the ophiolitic belt is flanked on either side by mafic volcanic and volcaniclastic rocks limestone bedded chert and argillite most of the chert is triassic including much of late triassic age but chert with uncertain stratigraphic relations at one locality is permian the strata flanking the east side of the ophiolitic belt face eastward and depositional contacts between units are for the most part preserved the strata on the west side of the ophiolitic belt are more highly disrupted than those on the east side contain chert argillite melange and have unproven stratigraphic relation to either the ophiolitic rocks or the eastern strata rocks of the north fork terrane do not show widespread evidence of penetrative deformation at elevated temperatures except an early tectonitic fabric in the harzburgite slip fiber foliation in serpentinite phacoidal foliation in chert and mafic rocks scaly foliation in argillite and mesoscopic folds in bedded chert are consistent with an interpretation of large scale anti formal folding of the terrane about a north south hinge found along the ophiolitic belt but other structural interpretations are tenable the age of folding of north fork rocks is constrained by the involvement of triassic and younger cherts and crosscutting late jurassic plutons deformation in the north fork terrane must have spanned a short period of time because the terrane is bounded structurally above and below by middle or late jurassic thrust faults the north fork terrane appears to contain no arc volcanic rocks or arc derived detritus suggesting that it neither constituted the base for an arc nor was in a basinal setting adjacent to an arc sediment source details of the progressive accretion and evolutionary relationship of the north fork to other terranes of the klamath mountains are not yet clear

a short duration of the cretaceous tertiary boundary event evidence from extraterrestrial helium 3 analyses of marine carbonates through the interval 63 9 to 65 4 million years ago indicate a near constant flux of extraterrestrial helium 3 a tracer of the accretion rate of interplanetary dust to earth this observation indicates that the bolide associated with the cretaceous tertiary k t extinction event was not accompanied by enhanced solar system dustiness and so could not have been a member of a comet shower the use of helium 3 as a constant flux proxy of sedimentation rate implies deposition of the k t boundary clay in 10 2 10 3 years precluding the possibility of a long hiatus at the boundary and requiring extremely rapid faunal turnover

rapid recovery of life at ground zero of the end cretaceous mass extinction the cretaceous palaeogene mass extinction eradicated 76 of species on earth1 2 it was caused by the impact of an asteroid3 4 on the yucatan carbonate platform in the southern gulf of mexico 66 million years ago 5 forming the chicxulub impact crater6 7 after the mass extinction the recovery of the global marine ecosystem measured as primary productivity was geographically heterogeneous 8 export production in the gulf of mexico and north atlantic western tethys was slower than in most other regions8 11 taking 300 thousand years kyr to return to levels similar to those of the late cretaceous period delayed recovery of marine productivity closer to the crater implies an impact related environmental control such as toxic metal poisoning 12 on recovery times if no such geographic pattern exists the best explanation for the observed heterogeneity is a combination of ecological factors trophic interactions 13 species incumbency and competitive exclusion by opportunists 14 and chance 8 15 16 the question of whether the post impact recovery of marine productivity was delayed closer to the crater has a bearing on the predictability of future patterns of recovery in anthropogenically perturbed ecosystems if there is a relationship between the distance from the impact and the recovery of marine productivity we would expect recovery rates to be slowest in the crater itself here we present a record of foraminifera calcareous nannoplankton trace fossils and elemental abundance data from within the chicxulub crater dated to approximately the first 200 kyr of the palaeocene we show that life reappeared in the basin just years after the impact and a high productivity ecosystem was established within 30 kyr which indicates that proximity to the impact did not delay recovery and that there was therefore no impact related environmental control on recovery ecological processes probably controlled the recovery of productivity after the cretaceous palaeogene mass extinction and are therefore likely to be important for the response of the ocean ecosystem to other rapid extinction events

importance of pre impact crustal structure for the asymmetry of the chicxulub impact crater the final geometry of an impact crater can be significantly influenced by the geological and geomorphological structure of the impact site therefore it may not on its own provide accurate information regarding the direction and angle of impact

seismic modelling of seam waves excited by energy transmission into a seam1 the traditional method of exciting channel waves in coal deposits underground consists of firing explosive sources in a mid seam position generating seam waves of the rayleigh and love type we investigate various source positions and excitation mechanisms within the bedrock structure surrounding the seam to evaluate the effects of source positions adjacent to the seam the investigation is based on analogue and numerical modelling of half and full space cases for which the excitation and the nature of rayleigh channel waves are examined in the analogue modelling sources located from mid seam out into the bedrock along the edge of a 2d plate model excited channel waves through a conversion of the free surface rayleigh wave at the edge of the plate the excited channel wave belongs to the normal mode range frequency wavenumber analysis shows that the symmetric 2nd mode of the channel wave is excited with frequencies comparable to the forcing frequency of the source signal the polarization changes from retrograde to prograde as the wave develops from the front to the rear of the seam respectively the amplitude depth distribution resembles that of an ordinarily excited seam wave for the symmetric component however the antisymmetric component does not show the characteristic change of sign in amplitudes across the mid seam axis numerical modelling with sources located in the bedrock full space case shows that relocating the source away from the seam lowers the frequency content of the excited channel wave based on these investigations the influence of a lower frequency source signal on the excitation of the channel wave is examined in an analogue experiment sources are sited in the bedrock adjacent to the seam at three locations a lower frequency wavelet is calculated for each source location from the results obtained in the numerical analysis for comparison a higher frequency wavelet is also used which is known to be optimal for this model geometry when excited by a mid seam source location it is found that in two cases the use of the lower frequency wavelet improves the channel wave excitation while no amplification is achieved in one case

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

the formation of peak rings in large impact craters large impacts provide a mechanism for resurfacing planets through mixing near surface rocks with deeper material central peaks are formed from the dynamic uplift of rocks during crater formation as crater size increases central peaks transition to peak rings without samples debate surrounds the mechanics of peak ring formation and their depth of origin chicxulub is the only known impact structure on earth with an unequivocal peak ring but it is buried and only accessible through drilling expedition 364 sampled the chicxulub peak ring which we found was formed from uplifted fractured shocked felsic basement rocks the peak ring rocks are cross cut by dikes and shear zones and have an unusually low density and seismic velocity large impacts therefore generate vertical fluxes and increase porosity in planetary crust

review and revision of cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale planktonic foraminifera are widely utilized for the biostratigraphy of cretaceous and cenozoic marine sediments and are a fundamental component of cenozoic chronostratigraphy the recent enhancements in deep sea drilling recovery multiple coring and high resolution sampling both offshore and onshore has improved the planktonic foraminiferal calibrations to magnetostratigraphy and or modified species ranges this accumulated new information has allowed many of the planktonic foraminiferal bioevents of the cenozoic to be revised and the planktonic foraminiferal calibrations to be reassessed we incorporate these developments and amendments into the existing biostratigraphic zonal scheme in this paper we present an amended low latitude tropical and subtropical cenozoic planktonic foraminiferal zonation we compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the cenozoic and have incorporated these recalibrations into a revised cenozoic planktonic foraminiferal biochronology we review and synthesize these calibrations to both the geomagnetic polarity time scale gpts of the cenozoic and astronomical time scale ats of the neogene and late paleogene on the whole these recalibrations are consistent with the previous work however in some cases they have led to major adjustments to the duration of biochrons recalibrations of the early middle eocene first appearance datums of globigerinatheka kugleri hantkenina singanoae guembelitrioides nuttalli and turborotalia frontosa have resulted in large changes in the durations of biochrons e7 e8 and e9 we have introduced upper oligocene zone o7 utilizing the biostratigraphic utility of paragloborotalia pseudokugleri for the neogene period major revisions are applied to the fohsellid lineage of the middle miocene and we have modified the criteria for recognition of zones m7 m8 and m9 with additional adjustments regarding the globigerinatella lineage to zones m2 and m3 the revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress of the cenozoic time scale

an alternative age model for the paleocene eocene thermal maximum using extraterrestrial 3he a continuous age model for the brief climate excursion at the paleocene eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3he 3he et to the seafloor 3he et measurements from odp site 690 provide quantitative evidence for the rapid onset few kyr and short duration 120 kyr of global warming and of the associated disturbance to the earth s surficial carbon budget at this time these observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon possibly from seafloor methane hydrate as the proximal cause of the event however the 3he et technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre event values the 3he et based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle and so may indicate additional or accelerated mechanisms of carbon removal from the ocean atmosphere system during this period 3he et was also measured at odp site 1051 to test the validity of the site 690 chronology comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at site 1051 an observation consistent with sediment structures and previous age modeling efforts the site 1051 age model shows a 30 kyr period in which climate proxies return toward pre event values after which they remain invariant for 80 kyr if this rise represents the recovery interval identified at site 690 then the 3he et based age models of the two sites are in good agreement however alternative interpretations are possible and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion regardless of these details this work shows that the 3he et technique can provide useful independent evidence for the development and testing of astronomically calibrated age models

diverse patterns of ocean export productivity change across the cretaceous paleogene boundary new insights from biogenic barium 1 one of the best studied aspects of the k pg mass extinction is the decline and subsequent recovery of open ocean export productivity e g the flux of organic matter from the surface to deep ocean some export proxies including surface to deep water 13c gradients and carbonate sedimentation rates indicate a global decline in export productivity triggered by the extinction in contrast benthic foraminiferal and other geochemical productivity proxies suggest spatially and temporally heterogeneous k pg boundary effects here we address these conflicting export productivity patterns using new and compiled measurements of biogenic barium unlike a previous synthesis we find that the boundary effect on export productivity and the timing of recovery varied considerably between different oceanic sites the northeast and southwest atlantic southern ocean and indian ocean records saw export production plummet and remain depressed for 350 thousand to 2 million years biogenic barium and other proxies in the central pacific and some upwelling or neritic atlantic sites indicate the opposite with proxies recording either no change or increased export production in the early paleocene our results suggest that widespread declines in surface to deep ocean 13c do not record a global decrease in export productivity rather independent proxies including barium and other geochemical proxies and benthic community structure indicate that some regions were characterized by maintained or rapidly recovered organic flux from the surface ocean to the deep seafloor while other regions had profound reductions in export productivity that persisted long into the paleocene

iodine to calcium ratios in marine carbonate as a paleo redox proxy during oceanic anoxic events periods of globally distributed extreme oxygen depletion so called oceanic anoxic events oaes have been recognized in the mesozoic geological record and appear to be characteristic of episodes of extreme warmth here we explore the application of iodine calcium ratios i ca in marine carbonate as a new geochemical proxy to constrain seawater redox change and provide additional insights into the response of ocean chemistry to ancient climatic warming iodine has long been known as a redox sensitive and biophilic element mainly present as iodate and iodide in seawater iodate converting to iodide under anoxic conditions laboratory experiments growing calcite crystals from solutions spiked with iodate show that this is the ionic species incorporated into the carbonate structure likely substituting for the co 3 2 ion a fall in the i ca ratio measured in carbonates formed in shallow water by marine calcifiers during the early toarcian and cenomanian turonian oaes is interpreted both as a response to a decrease in the iodate iodide ratio in ocean waters and the drawdown of the global iodine inventory under conditions of accelerated organic matter burial the results suggest that i ca ratios in carbonates may be used to monitor seawater oxidation levels throughout earth history

age origin and significance of an unconformity that predates island arc volcanism in the northern sierra nevada the paleogeographic position of rocks of the northern sierra nevada relative to north america has long been the topic of debate a detailed study of the lakes basin region of the northern sierra nevada substantiates that the shoo fly complex of early paleozoic age was folded and unconformably overlain by an island arc sequence in late paleozoic time microfossils recovered during the study represent the first in situ fauna ever collected from the shoo fly complex and provide an ordovician silurian lower limit on the early deformation late jurassic nevadan deformation strongly affected all rocks in the region regional considerations suggest that mid paleozoic deformation may have been widespread in the sierra nevada and could indicate an early phase of an eastward prograding suture that ultimately resulted in emplacement of the roberts mountain allochthon of the great basin

permo triassic accretionary subduction complex southwestern klamath mountains northern california the western paleozoic and triassic subprovince of the southwestern klamath mountains has previously been subdivided into three relatively steeply dipping fault bounded litho tectonic terranes in descending structural order from east to west these terranes are 1 the north fork terrane 2 the hayfork terrane and 3 the rattlesnake creek terrane in a general fashion each of these terranes exhibits its own particular set of lithologic structural and temporal relationships that sets it apart from adjacent terranes this threefold subdivision of the southwestern klamath mountains needs modification only as far as the hayfork terrane is concerned the hayfork terrane is actually a composite terrane consisting of a structurally lower assemblage of predominantly basaltic metavolcaniclastic rocks and a structurally higher assemblage of chaotically disrupted metasedimentary rocks juxtaposed along a previously unrecognized major regional thrust these two lithologically and structurally distinct assemblages have been elevated to the status of a terrane in this report and are herein referred to as the western hayfork terrane structurally lower metavolcaniclastic assemblage and the eastern hayfork terrane structurally overlying metasedimentary assemblage and the fault which juxtaposes these two terranes is herein referred to as the wilson point thrust this paper will focus on the eastern hayfork and north fork terranes and their relationship to other roughly coeval tectonic elements of the klamath mountain province the eastern hayfork terrane is best described as a tectono stratigraphic unit consisting of a complex chert argillite and quartzose sandstone melange and broken formation that contains radiolarian cherts as young as late triassic in age scattered throughout this terrane are various types of blocks some of which are clearly exotic metachert is by far the most common type of metamorphic block and these blocks appear to have been derived via sedimentary processes from the paleozoic central metamorphic belt and or the mesozoic stuart fork formation shallow water permian limestone blocks are also plentiful and are interpreted as reefal accumulations which flanked seamounts that became incorporated into the melange and broken formation as proto pacific ocean floor was subducted beneath the western margin of north america during at least the permo triassic to early jurassic the north fork terrane has at its base basaltic rocks tentatively interpreted as an oceanic crustal remnant generated within an open ocean ridge setting that was removed from any appreciable source of continental or volcanic arc derived detritus overlying the basaltic rocks is a sequence of pelagic hemipelagic terrigenous and tuffaceous metasedimentary rocks that have yielded a late triassic and early or middle jurassic radiolarian fauna the metasedimentary rocks of the north fork terrane are lithologically very similar to those of the eastern hayfork terrane both terranes consist predominantly of chert and argillite contain blocks of metamorphic rock and permian limestone and are at least in part of overlapping age however the metasedimentary rocks of the north fork terrane are structurally coherent unlike the chaotic melange and broken formation of the eastern hayfork terrane taken together the north fork and eastern hayfork terranes bear remarkable similarities to both modern and ancient rock assemblages that occupy sites within zones of lithospheric plate convergence and are interpreted as tectonic elements of an underthrust plate margin developed oceanward of a volcanic arc represented by the permo triassic to middle jurassic volcanic strata of the eastern klamath belt

cretaceous sinistral strike slip along nacimiento fault in coastal california the san andreas and nacimiento faults of coastal california both separate granitic and metamorphic basement rocks of the salinian block from partly coeval but contrasting mesozoic terranes underlain by the franciscan subduction complex by analogy with neogene dextral strike slip along the san andreas fault cretaceous sinistral strike slip can be inferred along the nacimiento fault in preference to hypotheses for tectonic erosion during subduction or for dextral strike slip of unspecified amount following restoration of known san andreas and inferred proto san andreas dextral displacements reversal of about 560 km 350 mi of postulated sinistral slip on the nacimiento fault brings four major mesozoic lithotectonic belts of california and baja california into simple al gnment as subparallel terranes related to mesozoic subduction along the continental margin neogene deformation within the san andreas transform system involved a elongation of the salinian block by dextral slip along subsidiary faults that branch from the san andreas fault and b dextral rotation of crustal panels within the transverse ranges latest cretaceous and or earliest paleogene dextral slip along a proto san andreas fault followed the san andreas course in central california but diverged westward in southern california nacimiento sinistral displacements occurred in mid cretaceous to early or medial late cretaceous time after cretaceous emplacement of plutons now within the salinian block but prior to deposition of uppermost cretaceous sedimentary sequences in central california available data on mesozoic relative and absolute plate motions in the mesoameric n region support the likelihood of cretaceous sinistral strike slip subparallel to the california continental margin paleotectonic reconstruction of crustal blocks in california and baja california to their inferred mid cretaceous relative positions shows the salinian block inserted on a bias between the flanking mojave and peninsular ranges blocks salinian granitic rocks thus formed an interior part of the mesozoic batholith belt and their initial strontium isotopic ratios are compatible with the gradients displayed by values from the adjoining blocks the similar mesozoic terranes that now lie east and west of the salinian block were then adjacent to one another west of the sierra nevada block available paleomagnetic data neither support nor preclude the reconstruction but additional work together with future detailed lithotectonic comparisons potentially can confirm or refute the hypothesis i represents a correct interpretation of the nacimiento fault is important for understanding the overall tectonic framework of petroliferous basins both onshore and offshore in coastal california

a 35 myr record of helium in pelagic limestones from italy implications for interplanetary dust accretion from the early maastrichtian to the middle eocene we have determined the helium concentration and isotopic composition of a suite of early maastrichtian through middle eocene pelagic limestones in the italian apennines the results provide a 35 myr record of the implied flux of extraterrestrial 3he which is a proxy for the accretion rate of interplanetary dust particles idps our measurements show that the 3he flux was fairly constant in the maastrichtian except for possible minor increases factor of two or less from 70 5 ma to 68 ma and at 66 ma which probably reflect transient increases in the accretion rate of asteroidal and or cometary idps we find no evidence for an increase in idp accretion at or immediately before the k t boundary implying that the k t impact was not associated with enhanced solar system dustiness this observation precludes the possibility that the k t impactor was a member of a major comet shower and is more consistent with impact of a lone comet or asteroid our data suggest a 2 to 4 fold increase in idp accretion between 57 and 54 ma followed by a factor of three decrease over an 4 myr period in the early to middle eocene the duration and magnitude of this variability is inconsistent with previous observations attributed to a shower of long period comets and is more likely the result of collisions in the asteroid belt and or kuiper belt in the entire 35 myr record we find no evidence for major enhancements of the idp accretion rate of the type expected from comet showers our results in combination with earlier 3he measurements do not support models that predict recurrent comet showers with periods of 38 myrs if there is a periodicity in the cratering record that is caused by periodic modulation of the oort cloud it is not evident in the apennine sediment data along with the 3he measurements we also obtained 4he concentrations which record temporal changes in the flux or composition of terrigenous matter the most significant change in 4he occurs in the last 4 myrs of the cretaceous over which the concentration of 4he in the detrital component rises by 300 this rise tracks a strong increase in the seawater 87 sr 86 sr ratio suggesting a globally significant change in the composition of continental detritus delivered to the oceans possibly arising from increased continental weathering

significance of mid mesozoic peridotitic to dioritic intrusive complexes klamath mountains western sierra nevada california a mid mesozoic plutonic suite ranging from ultramafic gabbroic rocks to dioritic rocks and commonly intruded by younger granitoids is widespread in the klamath mountains western sierra nevada california the ultramafic gabbroic rocks are clinopyroxene rich and commonly vary from wehrlite to olivine hornblende clinopyroxenite and melagabbro associated dioritic rocks include biotite two pyroxene diorite monzodiorite and the granitic rocks typically range from tonalite to granodiorite these plutonic complexes are coextensive and broadly coeval with a suite of weakly metamorphosed volcanic rocks ranging in composition from basalt to basaltic andesite to andesite the volcanic rocks are chiefly volcaniclastic and are characterized by several distinct phenocryst assemblages clinopyroxene plagioclase olivine or hornblende the plutonic complexes and the associated volcanic rocks are restricted to terranes that lack continental sialic crust and that at least locally contain juvenile ophiolitic crust generated adjacent to the locus of magmatism thus their petrogenesis may be related to recurrent fracturing and magmatism within a rifted ensimatic arc

geographic controls on nannoplankton extinction across the cretaceous palaeogene boundary calcareous nannoplankton a large group of marine autotrophs that produce carbonate skeletons were decimated to less than 10 of species during the cretaceous palaeogene boundary mass extinction 65 million years ago although the mass extinction followed an impact event the exact cause of the nannoplankton mortality is not well understood here we assess the timing and spatial variability of nannoplankton extinction by analysing nannofossil counts in cretaceous palaeogene boundary sections from all of the main ocean basins we find that extinction rates were higher in the northern hemisphere oceans and diversity remained low for 310 000 years in contrast southern hemisphere oceans showed lower extinction rates and a nearly immediate recovery of normal nannoplankton populations we propose that the oblique northward impact concentrated ejected particulates into the northern hemisphere blocking sunlight and suppressing photosynthesis increased rates of extinction and a prolonged recovery would then be associated with the greatest concentration of particulates we speculate that metal poisoning from fallout of the particulates may have exacerbated and extended the nannoplankton crisis in the northern hemisphere and thereby slowed the recovery of the northern hemisphere marine food web over 90 of calcareous nannoplankton species disappeared during the cretaceous palaeogene mass extinction which occurred after an impact event palaeontological analyses show that the extinction was most pronounced in the northern hemisphere oceans possibly as a result of an increased concentration of particulates created by the impact in the north

experimental observations of marine iodide oxidation using a novel sparge interface mc icp ms technique abstract iodine speciation is used as a redox indicator and water mass tracer however the kinetics and mechanisms of oxidation of the reduced iodine species iodide i in seawater remain largely unresolved here we provide constraints on i oxidation rates from seawater incubation experiments using a sensitive radiotracer incubation approach with high precision mass spectrometry samples are inoculated with iodine 129 as i incubated under controlled conditions then oxidized and reduced iodine species are isolated using liquid chromatographic separation samples are subsequently aspirated using a novel sparging interface and the 129i 127i ratio of both iodine species is determined via multi collector inductively coupled plasma mass spectrometry this highly sensitive analytical approach is optimized for estimating the predicted slow rates of iodine redox transformations in small volume seawater samples at marine relevant total iodine concentrations application of this method to coastal samples from martha s vineyard sound usa evidences the heretofore elusive oxidation of i under marine analogue conditions our results demonstrate an increase in the 129i 127i of aqueous oxidized iodine species in unamended seawater most likely due to formation of hypoiodous acid and then dissolved organic iodine at rates of 118 189 nm yr these rates are comparable to those inferred from previous open ocean mass balance approaches but have the benefit of directly linking iodine speciation changes to in situ i oxidation though our treatment experiments do not definitively isolate the oxidation mechanism they provide preliminary insight into important roles for both abiotic and biotic factors as well as iodine transformations between dissolved particulate and gaseous forms ultimately the derived rates and novel experimental technique have potential to improve marine iodine cycling models and provide constraints on the importance of in situ processes in setting patterns of iodine speciation

time relations and structural stratigraphic patterns in ophiolite accretion west central klamath mountains california new geochronological data and published structural and stratigraphic data show that two distinctly different ophiolitic assemblages formed in general proximity to one another at nearly the same time and were subsequently imbricated along a regional thrust zone the josephine ophiolite constitutes a complete oceanic crust and upper mantle sequence which lies within the western jurassic belt of the klamath province within the study area the josephine ophiolite was formed by seafloor spreading at about 157 m y before present it was immediately covered by a thin pelagic and hemipelagic sequence which grades into a thick flysch sequence both of which comprise the galice formation the galice flysch was derived from volcanic arc and uplifted continental margin orogenic assemblages a major nonvolcanic source for the galice flysch appears to have been the western paleozoic and triassic belt of the klamath province exposed to the east proximal volcanic arc activity migrated to the site of the josephine galice section by 151 m y and is represented by numerous dikes and sills which intrude the ophiolite and galice formation the preston peak ophiolite is a polygenetic assemblage consisting of 1 a pre mid jurassic tectonitic peridotite amphibolite substrate which represents disrupted and unroofed basement of the western paleozoic and triassic belt and 2 an upper mafic complex which was intruded through and constructed above the tectonite substrate at about 160 m y the mafic complex consists primarily of diabase hypabyssal rocks that are overlain by diabase clast breccia and hemipelagic deposits a major arc plutonic complex was emplaced into the preston peak ophiolite in at least two pulses at 153 and 149 m y major phases of this complex consist of wehrlite gabbro pyroxene diorite and hornblende diorite the josephine ophiolite is interpreted as the remnants of interarc basin crust the preston peak ophiolite is interpreted as either a primitive remnant arc complex or a rift edge facies for the josephine interarc basin the galice formation represents a submarine fan complex that was built on juvenile crust of the josephine basin floor during the time interval of 153 to 149 m y the locus or arc magmatism migrated to an area which included the interarc basin floor and the remnant arc or basin edge the basin shortly thereafter closed by convergent tectonics during the nevadan orogeny resulting in the imbrication of the josephine and preston peak ophiolites and their superimposed arc assemblages the transition from seafloor spreading generation of josephine ophiolite to its tectonic accretion by convergence and basin closure occurred within 5 to 10 m y the process of rifting and ophiolite formation in series with convergence and ophiolite accretion is considered an important mechanism for generating and displacing allocthonous terranes in the klamath mountains sierra nevada region and perhaps throughout the western cordillera

imbricate low angle faulting in uppermost franciscan rocks south yolla bolly area northern california the south yolla bolly area of northern california contains the intersection of the franciscan complex the klamath mountains and the great valley sequence four distinct lithic units among them the south fork mountain schist as well as several subunits have been discerned in the franciscan rocks of this area these units are composed mostly of coherent or semi coherent layered sedimentary and mafic igneous rocks and their metamorphic equivalents rather than melange and are arranged in largely upright parallel imbricate fault slices four major low angle faults have been clearly recognized paleontologic data indicate that at least one fault places older material over younger lithic units exhibit various degrees of differences in metamorphic mineral assemblages textural grade and amount of internal deformation across the faults with more intensely deformed and metamorphosed material occupying successively higher structural positions these contrasts indicate that some of these faults served as surfaces by which deformed rocks were emplaced differentially upward during and or after metamorphism original bedding and compositional layering in all of the coherent units generally parallel the thrust faults two fault bounded units are each composed of a coherent sequence of basalt at the base overlain by bedded chert and further overlain by mudstone and graywacke or their metamorphic equivalents the faults which underlie these two sequences seem to have originated as decollements localized at or near a sedimentary rock mafic crust interface perhaps as discrete underthrust slices the distinct contrasts in original rock composition among these units plus the aforementioned characteristics seem to indicate that these faults had an early history in the accretionary prism apart from their later use as convenient surfaces for differential upward emplacement of metamorphosed material

oceanic plateaus the fragmentation of continents and mountain building many anomalous rises in today s oceans may be submerged continental fragments detached from previous continents ancient island arcs or basaltic piles formed by hot spots and spreading centers these rises are embedded in their respective moving oceanic plates and are fated to be consumed at active margins where such rises are being consumed at present e g the nazca ridge they cause cessation of volcanism disruption of the downgoing slab and possible shifts in plate boundary configuration many past rises including numerous continental fragments have been recognized within mountain belts as allochthonous terranes they constitute a large portion of the orogenic belts in the north pacific from mexico through western north america alaska east siberia japan and in new zealand the orogenic deformation in these belts is possibly the result of the accretion of the allochthonous terranes many terranes have been accreted with substantial deformation also in the alpine chain well before major continent continent collisions it is suggested therefore that the accretion of fragments may be the common process of the deformation phase of mountain building subduction of normal oceanic crust may be insufficient for deformation whereas full continent continent collision may not be necessary the general validity of this conclusion depends critically on whether allochthonous terranes caused orogenic deformation in the andes or not most of the accreted fragments with continental affinities in the mesozoic cenozoic orogenic belts of the world can be traced back to the breakup of gondwana beginning with a pacifica domain in the permian through a larger india domain in the early mesozoic and continuing through the separation of the somalia plate in the near future the reasons for this 250 million year breakup process are not known but some kind of thermal process possible of mantle wide scale is implied

the first day of the cenozoic highly expanded cretaceous paleogene k pg boundary section from the chicxulub peak ring recovered by international ocean discovery program iodp international continental scientific drilling program icdp expedition 364 provides an unprecedented window into the immediate aftermath of the impact site m0077 includes 130 m of impact melt rock and suevite deposited the first day of the cenozoic covered by

stratigraphic variation in ichnofabrics at the shackleton site iodp site u1385 on the iberian margin paleoenvironmental implications abstract ichnofabric analysis was conducted on cores from site u1385 iodp expedition 339 to interpret paleoenvironmental conditions at the southwest margin of the iberian peninsula during the pleistocene site u1385 provides an important record for the study of orbital and suborbital scale climate variability changes related to ocean atmosphere dynamics and affected environmental parameters a detailed study of the ichnofabric characterization is presented focusing on the types of ichnofabrics relative abundance amount of bioturbation grouping ichnofabric succession transitions and vertical distribution seven ichnofabrics were differentiated green mottled ichnofabric planolites ichnofabric taenidium planolites ichnofabric thalassinoides like palaeophycus ichnofabric planolites thalassinoides thalassinoides like ichnofabric zoophycos ichnofabric and chondrites ichnofabric they exhibit significant differences in terms of ichnofabric features as well as in their stratigraphic distribution the most abundant ichnofabrics are planolites thalassinoides thalassinoides like ichnofabric and green mottled ichnofabrics with a dominance of the middle tier ichnofabrics the degree of bioturbation is moderate with a mean bi around 3 but showing a clear bimodal distribution one group of intervals is characterized by high bioturbation bi 6 while another displays low moderate bi values bi 1 2 in general ichnofabric features confirm generally good environmental conditions oxic environment and high food availability for the macrobenthic tracemaker community especially favorable in the uppermost part of the sediment a complete ichnofabric succession from deep to shallow tier ichnofabrics is commonly registered i e zoophycos ichnofabric or chondrites ichnofabric to planolites thalassinoides thalassinoides like ichnofabric and then either to green mottled ichnofabric or to planolites ichnofabric and then green mottled ichnofabric however there are some intervals where an incomplete succession between deep and shallow ichnofabrics is observed i e chondrites ichnofabric to green mottled ichnofabric or zoophycos ichnofabric to green mottled ichnofabric indicating relevant modifications of environmental parameters such as oxygen or food supply types of ichnofabrics and the bioturbation index show significant short term changes through the studied core such variations are probably correlated to millennial scale climatic perturbations such as glacial terminations and related phenomena heinrich events ice rafting events etc or long term cyclic patterns related to orbital climate variability the patterns could be tied to a significant change in the climate system such as the one associated with the middle pleistocene transition

polygenetic ophiolite belt of the california sierra nevada geochronological and tectonostratigraphic development the assumption that ophiolite sequences are generated at essentially one point in geologic time by the process of sea floor spreading is critical for modern concepts in the tectonics of ophiolites and for topics dealing with their structure and petrology however this assumption has only been verified in a few locations by an integrated geochronological and structural stratigraphic approach many ophiolite sections are reconstructed from structurally disrupted sequences with the idealized ocean floor model in mind such reconstructions are prone to error without adequate age control on each of the reconstructed fragments this is a significant problem in structurally complex regions where more than one generation of ophiolite may be present in this paper new pb u zircon ages are presented for key locations along a 375 km segment of the western sierra nevada ophiolite belt these age data are combined with structural stratigraphic observations and published ages and significant tectonic implications for the ophiolite belt emerge three different ophiolitic assemblages are recognized with igneous ages of about 300 200 and 160 m y b p rocks of the 300 m y assemblage are in a completely disrupted array of metamorphic tectonite slabs and serpentinite matrix melange fragments of upper paleozoic seamounts occur in association with the ophiolitic melange and together these assemblages constitute the basement framework for the western sierra pb u and k ar isotopic systematics are complex within this framework and indicate a polymetamorphic history systematics in the 200 and 160 m y assemblages are less complex and give tighter igneous age constraints rocks of the 200 m y assemblage are in a semi intact state with only local tectonite and melange zones rocks of the 160 m y assemblage are intact but nevertheless deformed both the 200 and 160 m y assemblages have equivalent age basinal volcanic sedimentary sequences that lie unconformably above the ophiolitic melange basement in each case the basinal sequences locally extend conformably into the upper stratigraphic levels of the age equivalent ophiolite sections these relations along with vestiges of intrusive contacts between the edges of both younger ophiolites and the melange basement indicate that the younger ophiolites underwent igneous formation in proximity to the melange basement the sierran ophiolite belt is considered to have formed by a multistage process initiated by the early mesozoic tectonic accretion of upper paleozoic sea floor in general proximity to the ancient continental margin regional metamorphism and ophiolitic melange resulted this accretionary nucleus became the basement of jurassic age primitive volcanic arc terranes which underwent rifting episodes during the production of the 200 and 160 m y ophiolites the rifting episodes resulted in the formation of sedimentary basins which were the depositional sites of volcanic sedimentary sequences non volcanic sources for the basinal sedimentary rocks include the melange basement and continental margin terranes contact zones between pre existing basement and the juvenile ophiolitic sequences created during the rifting episodes consist of dynamothermal metamorphic aureoles protoclastic deformation zones and cross cutting dikes such edge zone assemblages are in most localities obscurred or destroyed by superimposed deformations resulting from convergent and perhaps transform motions along basin edges both the 200 and 160 m y basins were destroyed by compressional orogenic episodes shortly after their formational episodes destruction of young ophiolite floored basins may be a common course of events when small oceanic type plates are generated along continental margin environments such tectonic settings are ideal for the emplacement of young ophiolite sheets

hydrothermal alteration associated with the chicxulub impact crater upper peak ring breccias abstract the 66 ma 180 km chicxulub impact structure in the northern yucatan peninsula and southern gulf of mexico is the best preserved large impact crater on earth with a well developed peak ring the most recent drilling campaign took place offshore during the joint international ocean discovery program international continental scientific drilling program iodp icdp expedition 364 at site m0077a 21 45 n 89 95 w and recovered 830 m of continuous core initial examination revealed that the peak ring comprises four main lithological units from the base upwards crystalline basement granitoid rocks unit 4 a thin layer of impact melt rocks units 3a and b melt bearing breccias units 2a c and post impact sedimentary rocks unit 1 preliminary analysis of the drill core indicated that hydrothermal alteration has affected all lithologies and is especially pervasive in the melt bearing breccias of unit 2 721 6 to 617 33 meters below sea floor mbsf here we present the first detailed investigation of hydrothermal alteration within the melt bearing breccias alteration phases are predominantly fe mg clay minerals zeolites alkali feldspars calcite and minor sulfides sulfates opal and fe ti oxides alteration is especially intense proximal to lithologic contacts particularly at the base of subunit 2b where there is an abrupt increase in host rock porosity 30 m above the impact melt rocks the pervasiveness of clay minerals and zeolites is attributed to the high amounts of devitrified silicate glass throughout unit 2 the phases preserved here are consistent with the findings of previous hydrothermal studies in other areas of the chicxulub structure and suggest an evolving water rock system that was alkaline saline comparable to seawater volcanic glass alteration

character distribution and tectonic significance of accretionary terranes in the central alaska range the central part of the alaska range near mount mckinley is composed of nine separate tectonostratigraphic terranes that were accreted in southern alaska during late mesozoic time these terranes now form long linear fault bounded belts that are subparallel to the denali fault on the north but oblique to the fault on the south the postaccretion right lateral offset along the denali fault system is about 200 km from north to south the major terranes are 1 yukon tanana terrane metasedimentary and metavolcanic rocks mostly undated but including rocks of known late paleozoic age polymetamorphosed with terminal events in late mesozoic 2 pingston terrane isoclinally folded upper triassic deep water silty limestone quartzite and carbonaceous slate folded with upper paleozoic phyllite chert tuff and minor limestone 3 mckinley terrane upper paleozoic flysch chert and minor limestone intruded by large gabbro sills and dikes and overlain by thick piles of triassic porphyritic pillow lava the top of the section is thick sequence of upper mesozoic conglomerate flysch chert and phyllite 4 dillinger terrane very thick sequence of strongly folded lower paleozoic micaceous sandstone turbidites graptolitic shale and deep water limestone locally overlain unconformably by jurassic fossiliferous sandstone or triassic pillow basalt 5 windy terrane heterogeneous assemblage of serpentinite basalt tuff and chert ophiolite with paleozoic and mesozoic flysch and blocks of mid paleozoic fossiliferous limestone 6 mystic terrane predominantly upper paleozoic flysch and conglomerate but also includes lower paleozoic graptolitic shale pillow basalt and shallow water limestone and upper paleozoic fossiliferous limestone sandstone chert and undated pillow basalt 7 chulitna terrane upper devonian ophiolite overlain by upper paleozoic chert volcanic conglomerate limestone and flysch capped by lower triassic limestone and upper triassic red beds basalt and interbedded basalt and limestone later mesozoic rocks are sandstone chert and argillite 8 westfork terrane jurassic chert sandstone conglomerate and triassic and jurassic crystal tuff 9 broad pass terrane upper paleozoic chert tuff and argillite with blocks of devonian and older limestone locally associated with serpentinite these diverse terranes of mixed oceanic and continental affinities are now juxtaposed to form a complex sequence of folded and faulted rootless nappes major suture zones between them are occupied by intensely deformed upper mesozoic flysch all of the terranes differ markedly from wrangellia the southermost coherent accreted terrane in alaska paleomagnetic measurements from triassic rocks prove that wrangellia originated near the equator probably in the southern heimsphere paleolatitudes for terranes in the central alaska range are not yet determined but other lines of evidence biogeographic and lithologic suggest large scale northern transport for some terranes

benthic foraminifera at the cretaceous tertiary boundary around the gulf of mexico cretaceous tertiary k t boundary sections in northeastern mexico contain marly formations separated by a controversial clastic unit benthic foraminifera in seven sections indicate middle and lower bathyal depths of deposition for the marls with the exception of the upper bathyal northernmost section mixed neritic bathyal faunas were present in the clastic unit indicating redeposition in the deep basin by mass wasting processes resulting from the k t bolide impact in the gulf of mexico benthic foraminifera in the mexican sections and at other deep sea locations were not subject to major extinction at the time of impact but there were temporary changes in assemblage composition benthic faunas indicate welloxygenated bottom waters and mesotrophic conditions during the late maastrichtian and increased food supply during the latest maastrichtian the food supply decreased drastically just after the k t boundary possibly because of the collapse of surface productivity cretaceous and early paleogene benthic foraminifera however did not exhibit the benthic pelagic coupling of present day faunas as documented by the lack of significant extinction at the k t collapse of surface productivity much of the food supplied to the benthic faunas along this continental margin might have been refractory material transported from land or shallow coastal regions the decrease in food supply at the k t boundary might be associated with the processes of mass wasting which removed surface food rich sediment benthic faunas show a staggered pattern of faunal recovery in the lowermost paleogene consistent with a staged recovery of the vertical organic flux but also with a gradual buildup of organic matter in the sediment

opportunistic behaviour after the toarcian oceanic anoxic event the trace fossil halimedides abstract we present an analysis of the first well documented record of the trace fossil halimedides in lower jurassic toarcian sediments from the west iberian palaeomargin lusitanian basin portugal the abundant and well preserved specimens allow a detailed ichnological characterization supporting interpretation of the associated palaeoenvironmental conditions in terms of substrate consistency firmgrounds food availability and ethology of tracemaker agrichnial sequestrichnia behaviour the appearance of this enigmatic trace is just after the toarcian oceanic anoxic event t oae in agreement with previous records associated with oceanic anoxic events as the oae 1 and oae 2 however in the case study oxygenation at the seafloor can be discarded as the major factor inducing colonization by halimedides tracemakers the rapid appearance of this trace after the t oae is related to the opportunistic behaviour of the tracemaker agrichnial sequestrichnia behaviour capturing and storing food particles together with efficient microbial gardening favoured rapid colonization of the comparatively oligotrophic seafloor in a transgressive context the record of halimedides could be appraised as a tool to evidence significant palaeoenvironmental changes such as those associated with bio events

origin of a global carbonate layer deposited in the aftermath of the cretaceous paleogene boundary impact abstract microcrystalline calcite micrite dominates the sedimentary record of the aftermath of the cretaceous paleogene k pg impact at 31 sites globally with records ranging from the deep ocean to the chicxulub impact crater over intervals ranging from a few centimeters to more than seventeen meters this micrite rich layer provides important information about the chemistry and biology of the oceans after the impact detailed high resolution scanning electron microscopy demonstrates that the layer contains abundant calcite crystals in the micron size range with a variety of forms crystals are often constructed of delicate oriented agglomerates of sub micrometer mesocrystals indicative of rapid precipitation we compare the form of crystals with natural and experimental calcite to shed light on their origin close to the crater a significant part of the micrite may derive from the initial backreaction of cao vaporized during impact in more distal sites simple interlocking rhombohedral crystals resemble calcite precipitated from solution globally we found unique calcite crystals associated with fossilized extracellular materials that strikingly resemble calcite precipitated by various types of bacteria in natural and laboratory settings the micrite rich layer contains abundant bacterial and eukaryotic algal biomarkers and most likely represents global microbial blooms initiated within millennia of the k pg mass extinction cyanobacteria and non haptophyte microalgae likely proliferated as dominant primary producers in cold immediate post impact environments as surface water saturation state rose over the following millennia due to the loss of eukaryotic carbonate producers and continuing river input of alkalinity whitings induced by cyanobacteria replaced calcareous nannoplankton as major carbonate producers we postulate that the blooms grew in supersaturated surface waters as evidenced by crystals that resemble calcite precipitates from solution the microbial biomass may have served as a food source enabling survival of a portion of the marine biota ultimately including life on the deep seafloor although the dominance of cyanobacterial and algal photosynthesis would have weakened the biological pump it still would have removed sufficient nutrients from surface waters thus conditioning the ocean for the recovery of biota at higher trophic levels