patterns of family extinction depend on definition and geological timescale the recent claim1 of an approximate 26 myr periodicity in the pattern of mass species extinction over the past 250 myr has already stimulated much astrophysical speculation and debate on causal mechanisms2 13 however as shown here the evidence for that claim is strongly contingent on arbitrary decisions concerning the absolute dating of stratigraphical boundaries14 the culling of the database and the definition of what is mass extinction as opposed to background extinction this evidence becomes insufficient under other plausible geological timescales and other acceptable definitions of mass extinction analysis of the nonculled database shows that the reliability of identification of mass extinctions and their timing is at present extremely limited it also suggests that the apparent periodicity of mass extinctions results from stochastic processes

bolides and biostratigraphy address as retiring president of the geological society of america october 1982 the stratigraphic record is punctuated by episodes of mass extinction these must be accounted for by major changes in the evolution of the earth three groups of forces have acted on the earth through time and may be adduced as the ultimate causes of many geological phenomena including extinctions these are internal earth changes solar system changes and astronomical accidents immediate causes are many and may stem from more than one ultimate cause among astronomical accidents asteroid or cometary impacts by bodies ranging up to 10 km in diameter or more occur at a known rate and must be accepted as an ongoing phenomenon evidence for large body impacts exists locally in the presence of craters and ejecta but regional or worldwide evidence is harder to assess it is probable that geochemical sedimentological and biological effects will prove the most reliable indicators although each involves difficulties in preservation and interpretation mass extinctions and animal or plant diversity are commonly demonstrated by plotting numbers of taxa that disappeared against an interval of time for example genera or families per stage or series a better measure of the real effect on life of an extinction event is to estimate changes in the biomass a measure of the number or volume of organisms and their extent the difference in biomass between two taxa of equal rank can be and frequently is many orders of magnitude changes in the physical environment are seen as the driving force of evolution and may be slow acting or sudden only accurate biochronological and sedimentological studies can determine how sudden an event has been evidence for some extinctions is found by changes at a bedding plane in each section examined if the possibility of gaps in sedimentation in such sections can be eliminated and the horizon accurately correlated then this constitutes strong evidence for a sudden event and an astronomical accident must be considered the phanerozoic record contains at least five major extinctions late ordovician late frasnian mid late devonian late permian late trias and late cretaceous detailed evidence on the time of disappearance of the taxa affected is hard to come by and much more work is required before any hypotheses of extinction can be substantiated although the cretaceous tertiary extinction is marked by noble metal anomalies at many sections the reason for such anomalies remains controversial there appears to be a substantial extinction of biomass at the same horizon in considering the five mass extinctions the likelihood that a large body impact has contributed to each extinction event is assessed as follows probability high enough to take seriously late frasnian late cretaceous possibility late ordovician late trias least likely late permian

global volcanism biological mass extinctions and the galactic vertical motion of the solar system summary the recent findings of nearly matching long term cyclicity in biological mass extinctions geomagnetic reversals impact cratering and other terrestrial processes have evoked a major controversy we report here a compilation and analysis of major global magmatic episodes showing a significant enhancement of volcanic activity with a periodicity of 33 million years for the last 250 million years these magmatic episodes match extremely well the best available astronomical estimates of the periodic 31 5 myr galactic disc crossing events during vertical motions of the solar system these events also have a close linkage with the marine biological mass extinctions and other geological rhythms it is argued that the prolonged volcanic activity instead of impact cratering may have been the more immediate primary cause for profound climatic and other environmental deterioration sufficient to create biological crises on a global scale the volcanic periodicity scheme is well supported by the evidence of recent increases in volcanic activity however the alternative hypothesis of the death star nemesis can be rejected since it does not explain the recent increase in volcanism and impact cratering during the last 4 3 myr in view of its quieter apehelion position lying beyond the oort cloud of comets

an oceanic model for lithological and faunal changes tested on the silurian record a model for oceanic cycles is presented the cycles are expressed as changes between more humid low latitude and cooler high latitude climates p episodes and dryer low latitude and warmer high latitude climates s episodes the cyclicity may be self regulating through changes in the co 2 storage capacity of the deep ocean due to temperature changes and through changes in the oceanic input and output of dissolved carbonate the model permits over 30 predictions regarding observable changes in both deep water and shelf lithologies and variations in the abundance diversity and extinction rate of planktic and benthic faunas sedimentary changes involve fluctuations in the rate of clay deposition and carbonate production the advance and retreat of carbonate deposition on the shelf edge the timing of oolite reef and black shale formation and changes between oxic and anoxic deep water faunal effects include both iterative evolution and intermittently widespread taxa lazarus taxa these predictions agree well with changes observed in well known sequence of wenlock and ludlow age as well as changes seen in selected older and younger sequences

randomness in the pattern of mass extinctions and waves of origination mass extinctions and waves of origination are defined as peaks in the average probability of family extinction and origination per geologic stage respectively a simple neutral model is proposed assuming only that the average probabilities of family extinction and origination have varied independently and had equal chances of going up and down from one stage to another as a null hypothesis this model is not rejected by the available palaeontologic data on marine animal and nonmarine invertebrate families in the phanerozoic the only discrepancy between the model and the empirical pattern is due to a systematic bias introduced by fossil lagerstatten the alleged periodicity of late phanerozoic mass extinctions follows inevitably from the model

a predictive model for reservoir distribution in the permian leonardian clear fork and glorieta formations robertson field area west texas through the collaborative efforts of a multidisciplinary team various subsurface data types have been integrated to produce a conceptual geologic model for reservoir prediction within the upper clear fork and glorieta formations of the robertson field area west texas detailed description of 1434 m of core 109 thin sections and 241 line kilometers of 2 d two dimensional seismic indicates the stratigraphic interval accumulated as a progradational succession of platform interior subtidal and intertidal facies reservoir intervals preferentially occur within subtidal facies having intercrystalline porosity associated with replacement by coarsely crystalline dolomite intertidal facies were replaced by a finely crystalline phase of fabric preserving dolomite and are dominated by an ineffective fenestral pore system facies and reservoir distribution is largely controlled by antecedent topography structural highs generated during the terminal phase of ouachita marathon compression were the preferred site of intertidal facies deposition adjacent structural lows have a higher proportion of reservoir prone subtidal facies analysis of compensated neutron log porosity indicates that subtidal prone intervals may be broadly characterized as having less than 11 porosity whereas intertidal prone intervals generally exceed 11 porosity from this observation a simple computer algorithm allows facies interpretation within wells lacking core intertidal subtidal facies ratio maps generated from this algorithm closely match the distribution of pre wolfcampian structural elements and present day structure intertidal facies are more common across the crest of structural highs future drilling in the north jenkins area should pursue structural flank positions where subtidal facies are volumetrically more abundant care should be taken however to avoid completions below the composite oil water contact subtidal facies are compartmentalized within individual sequences of a progradational sequence set progradational stacking and compactional drape over deeper structures produces discrete flow units with potentially independent oil water contacts

search for impact remains at the frasnian famennian boundary in the stratotype area southern france abstract in order to detect whether the end frasnian worldwide biotic crisis is related to an extraterrestrial impact the global stratotype section of the frasnian famennian boundary and auxiliary sections within the stratotype area have been examined for impact indicators iridium ni rich spinel bearing spherules and glassy microtektites this area is particularly well suited to the search for discrete events because it exhibits biostratigraphically continuous sections of sedimentologically homogenous off shore deposits different environmental settings on oxygenated deep water seamounts such as the stratotype section at coumiac and in oxygen depleted depressions la serre section are available the latter is investigated in more detail because it is the least condensed across the boundary which is determined by the first occurrence of the typical morphotype of palmatolepis triangularis the indicator of the first famennian conodont biozone samples from the biostratigraphically defined boundary and adjacent levels failed to provide significantly high ir values and no ni rich spinel or microtektite has been recovered this is in contradiction with the results of earlier investigations carried out by h geldsetzer on the same section in contrast the values of ir concentrations that we measured are always very low or not detectable the small overabundances observed in some samples which are about two orders of magnitude lower than what is currently observed at the cretaceous tertiary boundary are probably due to the accumulation of the normal flux of cosmic dust during periods of relatively low depositional rates or to a terrestrial origin at present we have no evidence that an extraterrestrial impact occurred at the f f transition

an iridium anomaly in the middle lower jurassic of the venetian region northern italy a significant iridium enrichment has been found in a jurassic marine sequence about 180 million years old outcropping in the alps of the venetian region the maximum iridium concentration of 3 2 0 2 ng g 1 occurs in a brown crust 2 3 mm thick containing essentially iron hydroxide this crust characterized by a nearly total absence of detritic components lies on top of upper lias limestones and is overlaid with bajocian bathonian limestones the origin of the ir anomaly is not clearly understood yet but could be explained by either a drop in the sedimentation rate resulting in the concentration within a thin sediment layer of the normally infalling cosmic dust and or by an increase of cosmic material infall following an asteroid or comet impact s

a significant correlation between fluctuations in seafloor spreading rates and evolutionary pulsations this report presents the results of a detailed correlation analysis which reveals a remarkable correspondence between variations in seafloor spreading rates and marine taxonomic diversity the implications of this analysis are that the evolution of some biota was influenced by tectonic processes operative in the ocean basins such a conclusion suggests the need to seek a terrestrial explanation for extinction crises an indirect link via tectonism rise axis hydrothermal activity and the carbon dioxide cycle may provide a partial explanation

evidence from crater ages for periodic impacts on the earth recent evidence has indicated that the impact of a comet or asteroid may have been responsible for mass extinction at the ends of both the cretaceous1 and the eocene2 4 quantitative analysis by raup and sepkoski5 showed that mass extinctions occur with a 26 myr period similar to the period seen in qualitative pelagic records by fischer and arthur6 to account for the possibility of periodic comet showers davis et al 7 proposed that such showers could be triggered by an unseen solar companion star as it passes through perihelion on a moderately eccentric orbit to test a prediction implicit in this model we examined records of large impact craters on the earth we report here that most of the craters occur in a 28 4 myr cycle within measurement errors this period and its phase are the same as those found in the fossil mass extinctions the probability that such agreement is accidental is 1 in 103

role of temperature and nutrients in extinction of turritelline gastropods cenozoic of the northwestern atlantic and northeastern pacific abstract turritelline gastropods mesogastropoda turritelline are common to abundant components in many fossil cretaceous cenozoic and recent marine benthic communities but the environmental factors affecting their evolution and extinction are poorly understood this is in large part because today they occur most abundantly in cooler waters associated with upwelling or other high nutrient conditions but thermal tolerances and preferences are unclear for extinct turritelline species turritellines were diverse and abundant throughout the new world for much of the cenozoic beginning in the early neogene through both extinction and range contraction however they started to disappear from higher latitudes on both atlantic and pacific coasts of north and central america the highest rate of extinction took place in the western atlantic in the plio pleistocene when almost all turritelline species in this area became extinct preliminary comparison of the available stratigraphic record suggests that this paleobiogeographic pattern is not an artefact of the record this biogeographic shift coincides with a postulated regional mass extinction among all marine mollusks in the western atlantic at around the same time causes for turritelline extinction however appear to be more complex than the decline in temperature that is cited most often as the probable cause of the western atlantic molluskan extinction event neogene turritellines in the western atlantic appear to have been adversely affected by collapse and or major reorganization of oceanic productivity associated with the formation of the isthmus of panama nutrients thus may have been more important than temperature change in controlling extinction probability in this group

what determines the thickness of layers in a thermohaline staircase the article of record as published may be found at http dx doi org 10 1017 s0022112004002290

extraterrestrial impact events the record in the rocks and the stratigraphic column abstract the known terrestrial impact record is a biased sample of a much larger population of impact events the biases are due to the modifying effects of terrestrial geologic processes coupled with incomplete searches for impact structures and impact related materials terrestrial impact structures have the same basic forms as impact craters on the other planets of the inner solar system but because of post impact modification by terrestrial geologic process are recognised by the occurrence of shock metamorphic effects in some cases siderophile anomalies have been identified in impact lithologies and have been used to estimate the composition of the impacting body similar shock metamorphic effects and a siderophile anomaly in k t boundary materials are indicative of a major impact event which has been correlated with the formation of the chicxulub structure mexico evidence of a small number of other impacts occur in the stratigraphic record most commonly as tektite or microtektite horizons in some cases they are known to be accompanied by geochemical anomalies in other cases a number of ir anomalies have been reported in the stratigraphic record but there is no confirmatory evidence that they are due to impact the majority of known impact events in the stratigraphic record are from relatively recent geologic time logic dictates however that many more impacts must be recorded in terrestrial sediments and model calculations indicate that relatively small impacts d 20 km have the potential to cause atmospheric blow out and thus global dispersion of some of the impact products geochemical detection however of such events may not be easy in some cases because of relatively small absolute signals against the background of the daily infall of cosmic material in addition non chondritic bodies may result in no appreciable geochemical anomaly in view of this any claim to a geochemical signature of impact in the stratigraphic record should be accompanied by a physical search for impact materials although in the case of impacts into oceanic crust this too will be difficult given the k t experience however and the fact that large scale impact on earth is a natural consequence of the character of the solar system the potential of impacts to provide local and global marker horizons can not be ignored similarly the fact that impacts may have the potential to result in short term biologic or climatic excursions can not be dismissed arbitrarily when considering the causes of such phenomena as stable isotope anomalies in the stratigraphic record

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

temperature and biotic crises in the marine realm climatic change has been a prominent cause of marine mass extinction but areal restriction of seafloor during global regression has not late eocene and pliocene pleistocene cooling for example caused major extinctions but profound global oligocene and pleistocene regressions had little or no direct effect on benthic diversity recurrent themes of pre cenozoic marine crises suggest that global temperature change also served as a major and perhaps dominant agent of extinction in these events 1 mass extinctions have frequently been concentrated in the tropics which seem to have become a refrigerated trap from which there has been no escape biotas previously occupying high latitudes have shifted equatorward to replace disappearing tropical biotas 2 some crises were not instantaneous but followed protracted and pulsatile temporal patterns as would be predicted for complex global climatic crises 3 several mass extinctions coincided with recognized intervals of climatic cooling

mechanics of merging events for a series of layers in a stratified turbulent fluid this study attempts to explain the evolutionary pattern of a series of well mixed layers separated by thin high gradient interfaces frequently observed in stratified fluids such layered structures form as a result of the instability of the equilibrium with uniform stratification and their subsequent evolution is characterized by a sequence of merging events which systematically increase the average layer thickness the coarsening of layers can take one of two forms depending on the realized vertical buoyancy flux law layers merge either when the high gradient interfaces drift and collide or when some interfaces gradually erode without moving vertically the selection of a preferred pattern of coarsening is rationalized by the analytical theory the merging theorem which is based on linear stability analysis for a series of identical layers and strongly stratified interfaces the merging theorem suggests that the merger by erosion of weak interfaces occurs when the vertical buoyancy flux decreases with the buoyancy variation across the step if the buoyancy flux increases with step height then coarsening of a staircase may result from drift and collision of the adjacent interfaces our model also quantifies the time scale of merging events and makes it possible to predict whether the layer merging continues indefinitely or whether the coarsening is ultimately arrested the merging theorem is applied to extant one dimensional models of turbulent mixing and successfully tested against the corresponding fully nonlinear numerical simulations it is hypothesized that the upscale cascade of buoyancy variance associated with merging events may be one of the significant sources of the fine scale 10 m variability in the ocean

the great latest ordovician extinction on the south china plate chemostratigraphic studies of the ordovician silurian boundary interval on the yangtze platform continuous samples from four ordovician silurian boundary sections of graptolitic shales and mudstones in the yangtze basin yangtze platform on the south china plate spanning the latest ordovician mass extinction of many unrelated groups of organisms were chemically analyzed for the abundances of about 40 common and trace elements and iridium it is observed that the abundances of ir and other siderophile and chalcophile elements e g co cr as mo sb and v show elevated values in the extinction horizon at the base of the graptolite persculptus zone which corresponds to the stratigraphic level for the local systematic boundary in china between the ordovician and silurian iridium abundances show maxima at this extinction level in three of the four sections analyzed with varying strength 230 ppt at yichang 92 ppt at jinxian and 88 ppt at youyang but 50 ppt at xiushan these geochemical patterns appear to be of global significance since similar geochemical anomalies including weak ir anomaly were also recorded at about the same stratigraphic level in many other sections previously studied in quebec yukon arctic and northwest territories canada and scotland although impact by a comet with low platinum group element abundances could have been responsible for the geochemical anomalies we find it is most plausible to attribute the geochemical signal to the effects of a lower sedimentation rate and reducing water conditions at this horizon the beginning of a rapid transgression induced by rapid melting of the ice caps on gondwana carbon isotope excursions in organic material at yichang together with other carbon isotope data from central sweden northwestern canada latvia quebec and wisconsin suggest that after a period of decreasing atmospheric and marine pco2 in the latest ordovician the hirnantian a sudden large pco2 increase in the ocean and atmosphere may have occurred at the extinction horizon at the base of the persculptus zone a greenhouse effect might have existed for a short time what triggered such a sudden pco2 increase is uncertain but a rapid co2 degassing caused by volcanism tectonics and or extraterrestrial impact could have been responsible

a review of oceanic salt fingering theory salt fingering is a potentially important mechanism for mixing different water masses in those parts of the ocean where warm salty waters overlie cooler fresher this review surveys advances in salt fingering theory as they pertain to ocean mixing basic equations are presented along with steady maximum buoyancy flux and fastest growing finger solutions attempts to quantify theoretically finger induced fluxes of heat salt and buoyancy and to understand staircase formation and maintenance are described also considered are the confounding influences of internal wave shear and strain and intermittent internal wave shear driven turbulence which are present in the ocean but in few theories finally outstanding theoretical questions about the role of salt fingers in the ocean are raised

estimation of ice shelf melt rate in the presence of a thermohaline staircase abstractdiffusive convection favorable thermohaline staircases are observed directly beneath george vi ice shelf antarctica a thermohaline staircase is one of the most pronounced manifestations of double diffusive convection cooling and freshening of the ocean by melting ice produces cool freshwater above the warmer saltier water the water mass distribution favorable to a type of double diffusive convection known as diffusive convection while the vertical distribution of water masses can be susceptible to diffusive convection none of the observations beneath ice shelves so far have shown signals of this process and its effect on melting ice shelves is uncertain the melt rate of ice shelves is commonly estimated using a parameterization based on a three equation model which assumes a fully developed unstratified turbulent flow over hydraulically smooth surfaces these prerequisites are clearly not met in the presence of a thermohaline staircase the basal melt rate is estimated by applying an ex

recovery of marine primary producers after the cretaceous tertiary mass extinction paleocene calcareous red algae from the iberian peninsula abstract calcareous red algae corallines solenoporaceans and peyssonneliaceans are major contributors to paleocene platform deposits in the pyrenean basin n spain and prebetic zone betic cordillera se spain the earliest danian middle thanetian time interval in the pyrenean basin is represented by four depositional sequences the ma da earliest danian da 1 early danian da 2 late danian and th 1 selandian mid thanetian sequences from bottom to top this precise chronostratigraphic framework allows an accurate assessment of the recovery of these calcareous algal groups after the cretaceous tertiary k t mass extinction calcareous algae are recorded shortly after the k t boundary 0 2 0 3 ma after the k t although the richness of identifiable species remains low during the danian 9 species in the earliest danian 9 species in the early danian and 11 species in the late danian in addition no change in taxonomic composition is observed in this interval since approximately the same algal species occur in all three danian sequences the same low species richness 11 species and species composition is observed in the danian algal assemblages of the betic cordillera however this low level of diversification changes radically in the selandian mid thanetian interval when 29 species are recorded together with the increase in species richness the taxonomic composition also changes since 19 species of corallines are recorded for the first time in the th 1 sequence therefore it can be deduced that species diversity recovery due to a significant radiation of corallines was delayed 6 ma after the end cretaceous event the recovery of corallines during the paleocene shows a characteristic depth dependent pattern throughout the danian middle thanetian interval representatives of the family hapalidiaceae subfamily melobesioideae and plants of the family sporolithaceae largely dominate the algal assemblages in the deep water outer platform settings as they do in present day seas members of these two groups are also the most abundant coralline algae in the paleocene reef and back reef paleoenvironments indicating that the shallowest and best illuminated areas were occupied by algal groups that in modern tropical seas mainly occur in relatively deep habitats this suggests that all platform habitats were re occupied after the end cretaceous event by the groups that selectively survived the extinction only after a time interval of about 6 ma did the habitat distribution of coralline groups change to its modern patterns the subfamilies most abundant in present day shallow tropical waters that is mastophoroideae and lithophylloideae for the first time account for more than 1 of the algal assemblages in the thanetian and even then they remain very minor components these shallow water coralline groups were affected more intensively by the k t extinction event accounting for the delay in their recovery in their preferred shallow water habitats shallow water lithophylloids and geniculate corallines have not been found in danian sequences

origin of thermohaline staircases hypotheses concerning the origin of thermohaline staircases in salt fingering regions are reviewed and assessed one such hypothesis that staircases arise from thermohaline intrusions is developed into a quantitative theory it is shown that growing intrusions evolve toward staircases when the background density ratio lies below a threshold value and nonlinear computations confirm that staircases are viable intrusion equilibria staircase properties such as step heights lateral density ratios and layer slopes lie closest to observed values when salt fingers are assumed not to contribute to shear stress and when turbulent mixing rates are smaller than usual thermocline values

iridium anomaly in the upper devonian of the canning basin western australia a moderate iridium anomaly about 20 times the local background has been found in upper devonian rocks in the canning basin it occurs at or near the frasnian famennian boundary which is known to be associated with a major massextinction event of global extent the anomaly occurs in an extremely condensed limestone sequence laid down under quiet deepwater conditions its occurrence suggests a causal link with some form of meteoroid impact moreover carbon isotope data indicate that a large reduction in biomass could have occurred at this level however the anomaly coincides with a stromatolite bed containing the fossil cyanobacterium frutexites iridium platinum iron manganese cobalt arsenic antimony and cerium are preferentially concentrated in filaments of this organism with concentrations ranging from two to five times that of the matrix it is possible that frutexites extracted these elements directly from seawater without the need for their derivation from an extraterrestrial source

event stratigraphic markers within the kellwasser crisis near the frasnian famennian boundary upper devonian in germany abstract short time intervals of anomalous conditions often referred to as global events yield excellent tools for detailed stratigraphic correlations in addition to pronounced effects minor features may be applied for fine scale comparisons of rock sequences these include alternations within a given portion of rock or distinct layers at exactly the same position such marker horizons are often traceable over long distances recognition of these specific markers allows for a more detailed search for possible causes of anomalous events

ichnofabrics and chemostratigraphy argue against persistent anoxia during the upper kellwasser event in new york state abstract organic rich strata coeval with bioevents of varying magnitudes characterize global devonian sedimentary successions the upper kellwasser ukw black shale depositional event is coincident with the largest pulse of diversity loss within the marine late devonian mass extinction and has been shown to be an ecologically critical turnover for shallow water species marine anoxia euxinia is widely thought to be an important and ubiquitous driver of this biotic crisis though the duration intensity and global extent of these environmental conditions during the ukw event are not well constrained we characterized redox conditions during deposition of the ukw in the northern appalachian basin to constrain local variability and relative magnitude of dissolved oxygen fluctuations we used a combination of proxies relating to the bottom waters water column and photic zone to compile an integrated picture of basinal oxygen dynamics our multi faceted approach combines trace fossil evidence for faunal activity at the sediment water interface with inorganic and organic geochemical proxies for redox conditions within the water column minor biological disruptions to laminated sedimentary fabric indicate at least intermittent oxygenation of the bottom waters during deposition of the ukw albeit in a low dissolved oxygen seafloor setting trace metal proxies mo mn u and v and fe mineral speciation provide compelling evidence for a water column experiencing intermittent rather than persistent anoxic euxinic conditions lipid biomarkers reinforce the interpretation of variable dissolved oxygen conditions with very low concentrations of chlorobi carotenoid biomarkers pointing to seasonal rare episodes of photic zone euxinia this integrated dataset provides evidence for local redox variability in ukw deposition and supports the likelihood that marine anoxia and euxinia were not globally persistent at the frasnian famennian boundary

phanerozoic shallow water diversity driven by changes in sea level shallow water 50 m marine diversity curves for the phanerozoic based on area changes due to sea level variation and continental movements are presented it is shown that a change in the degree of endemism can alter diversity more than the effect of sea level change or change in the number of faunal provinces the pattern produced for a constant degree of endemism shows some rapid but not periodic falls in diversity these occur in the middle cambrian at the end of the ordovician devonian permian cretaceous and eocene and in the messinian there is no recurring single cause for these falls

osmium isotopic evidence against an impact at the frasnian famennian boundary two sections across the frasnian famennian boundary were analyzed for re and os concentrations and 187os 188os ratios to evaluate evidence for a meteoritic input coincident with this boundary and its associated mass extinction these sections are from a siltstone and shale sequence at irish gulf in new york us and a calcareous shale and ferromanganese oxide sequence at la serre in france the irish gulf section with an initial 187os 188os of about 0 49 does not show the characteristic meteoritic os imprint with an 187os 188os of about 0 13 the integrity of the section with regard to re and os retention is indicated by the construction of an isochron with an age of 388 41 ma consistent with independently determined ages for the frasnian famennian boundary although the la serre section with os concentrations as high as 33 ppb and re concentrations ranging from 1 4 to 7 4 ppb might be expected to show excellent evidence for a meteoritic contribution the highly radiogenic isotopic composition 187os 188os 2 42 3 61 instead suggests recent massive re loss or addition of radiogenic os these possibilities prevent the reconstruction of an initial 187os 188os value for the boundary for this site assuming reasonable re concentrations prior to loss the os isotopic composition is inconsistent with a large meteoritic component this inconsistency emphasizes that platinum group element pge concentrations are not reliable indicators of extraterrestrial addition

high resolution carbon isotopic records from the ordovician of south china links to climatic cooling and the great ordovician biodiversification event gobe abstract the great ordovician biodiversification event gobe represented the largest increase in diversity in the marine biosphere during the phanerozoic eon yet its causes and consequences remain poorly understood patterns of isotopic variation in high resolution 13ccarb and 13corg records from a well exposed section at honghuayuan in south china may provide important insights regarding the gobe the honghuayuan isotopic profiles which can be correlated with c isotopic records from contemporaneous sections globally reveal large perturbations to the global carbon cycle during the ordovician a 8 increase in 13corg values in the floian implies a large albeit transient increase in the burial rate of organic matter during the mid early ordovician that may have contributed to climatic cooling and played an important role in triggering the gobe a 4 increase in 13ccarb and high frequency variation in 13corg in the darriwilian to sandbian suggest a second episode of elevated organic carbon burial rates accompanied by substantial instability in the global carbon cycle during the late middle and early late ordovician this pattern may mark the onset of climate changes culminating in the end ordovician hirnantian glaciation and mass extinction event that terminated the gobe

the relationship between double diffusive intrusions and staircases in the arctic ocean abstractthe origin of double diffusive staircases in the arctic ocean is investigated for the particular background setting in which both temperature and salinity increase with depth motivated by observations that show the coexistence of thermohaline intrusions and double diffusive staircases a linear stability analysis is performed on the governing equations to determine the conditions under which staircases form it is shown that a double diffusive staircase can result from interleaving motions if the observed bulk vertical density ratio is below a critical vertical density ratio estimated for particular lateral and vertical background temperature and salinity gradients vertical background temperature and salinity gradients dominate over horizontal gradients in determining whether staircases form with the linear theory indicating that perturbations to stronger vertical temperature gradients are more likely to give rise to a staircase examination of arctic ocean temperature and salinity measurements

periodicity in extinction and the problem of catastrophism in the history of life the hypothesis that extinction events have recurred periodically over the last quarter billion years is greatly strengthened by new data on the stratigraphic ranges of marine animal genera in the interval from the permian to recent these data encompass some 13 000 generic extinctions providing a more sensitive indicator of species level extinctions than previously used familial data extinction time series computed from the generic data display nine strong peaks that are nearly uniformly spaced at 26 ma intervals over the last 270 ma most of these peaks correspond to extinction events recognized in more detailed if limited biostratigraphic studies these new data weaken or negate most arguments against periodicity which have involved criticisms of the taxonomic data base sampling intervals chronometric time scales and statistical methods used in previous analyses the criticisms are reviewed in some detail and various new calculations and simulations including one assessing the effects of paraphyletic taxa are presented although the new data strengthen the case for periodicity they offer little new insight into the driving mechanism behind the pattern however they do suggest that many of the periodic events may not have been catastrophic occurring instead over several stratigraphic stages or substages

the influence of the late devonian kellwasser events on deep water ecosystems evidence from palaeontological and geochemical records from south china abstract the late devonian frasnian famennian f f event consisting of the lower and upper kellwasser events had a severe impact on shallow water ecosystems while the effect on deep water ecosystems is ambiguous in order to recognize the kellwasser events and to evaluate their influences on the deep water ecosystems a newly refined conodont biostratigraphic framework spanning the lower palmatolepis rhenana zone to the pa delicatula platys zone has been established in the nandong section basinal facies guangxi south china the upper devonian lower and upper kellwasser horizons lkh and ukh have been recognized in the deep water facies on the basis of lithological variations biological turnovers and positive carbon isotope 13ccarb excursions the lkh is characterized by the enrichment of marine nektonic communities e g conodonts homoctenids and entomozoacean ostracods whereas the top of the ukh is barren of fossil organisms suggesting that the upper kellwasser event had a more severe effect on nekton than the lower kellwasser event the upper kellwasser uk 13ccarb positive excursion lags behind the enrichment of cu ni mo and v indicating that the uk 13ccarb positive excursion was probably related to elevated primary productivity which induced oxygen depletion in the water column the uk 13ccarb positive excursion peak prior to the f f boundary indicates a more limited effect of riverine influx on the deep water setting which suggests that the regional palaeogeographic configuration played an important role in the carbon cycle

carbon and sulfur isotope anomalies across the frasnian famennian extinction boundary alberta canada stable isotopes of carbonate and organic carbon from two upper devonian sections in alberta canada indicate a heavy carbon event across the frasnian famennian f f boundary and a negative 13 c shift at the boundary at cinquefoil mountain 13 c values in carbonate are anomalously high 3 5 to 4 5 pdb peedee belemnite within an interval 10 m below to 23 m above the f f boundary representing about 1 m y two standard conodont zones compared to background values of 1 above and below this interval superimposed on this positive excursion is a marked 13 c decrease of about 1 at precisely the f f boundary at medicine lake a similar 13 c excursion in organic carbon from a background of 29 to a high of 26 5 is recorded across the f f boundary the 34 s data for iron sulfide in these sections show unusually high values as much as 15 to 20 cdt canon diablo troilite in the f f boundary interval these data together with those from other areas indicate a period of major global changes e g greenhouse and marine anoxia that took place well before and after the sudden biomass killing event at the f f boundary existing evidence suggests that the f f mass extinction was probably caused by a large extraterrestrial impact on earth at a time when the global ecosystem was already severely stressed

ice tethered profiler observations of the double diffusive staircase in the canada basin thermocline vertical heat fluxes through the staircase are in the range 0 05 0 3 w m 2 only about one tenth of the estimated mean surface mixed layer heat flux to the sea ice it is thus concluded that the vertical transport of heat from the atlantic water in the central basin is unlikely to have a significant impact to the canada basin ocean surface heat budget icebreaker conductivity temperature depth data from the beaufort gyre freshwater experiment show that the staircase is absent at the basin periphery turbulent mixing that presumably disrupts the staircase might drive greater flux from the atlantic water at the basin boundaries and possibly dominate the regionally averaged heat flux

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

dynamics of fingering convection part 1 small scale fluxes and large scale instabilities received and in revised form double diffusive instabilities are often invoked to explain enhanced transport in stablystratified fluids the most studied natural manifestation of this process fingering convection commonly occurs in the ocean s thermocline and typically increases diapycnal mixing by two orders of magnitude over molecular diffusion fingering convection is also often associated with structures on much larger scales such as thermohaline intrusions gravity waves and thermohaline staircases in this paper we present an exhaustive study of the phenomenon from small to large scales we perform the first three dimensional simulations of the process at realistic values of the heat and salt diffusivities and provide accurate estimates of the induced turbulent transport our results are consistent with oceanic field measurements of diapycnal mixing in fingering regions we then develop a generalized mean field theory to study the stability of fingering systems to large scale perturbations using our calculated turbulent fluxes to parameterize small scale transport the theory recovers the intrusive instability the collective instability and the instability as limiting cases we find that the fastest growing large scale mode depends sensitively on the ratio of the background gradients of temperature and salinity the density ratio while only intrusive modes exist at high density ratios the collective and instabilities dominate the system at the low density ratios where staircases are typically observed we conclude by discussing our findings in the context of staircase formation theory

warm water benthic foraminifera document the pennsylvanian permian warming and cooling events the record from the western pangea tropical shelves abstract shallow warm water benthic foraminifera swwbf including all larger fusulinids symbiont bearing benthic foraminifera are among the best indicators of paleoclimate and paleogeography in the carboniferous and permian the distribution of benthic foraminifera in space and time constrain important tectonic paleogeographic and climatic events at a global scale the north american shelves during pennsylvanian and permian time though geographically within the tropical belt are characterized by temperate environments with significantly lower foraminifera diversification and rare occurrences of warm water tethyan forms that are in general appear in the region as a migration entities such environments allow documentation of warming episodes associated with sudden immigration of warm water and exotic forms of swwbf that evolved elsewhere into the area first occurrence datum fod of the forms exotic to north america during warming episodes are always delayed in respect of their first appearance datum fad elsewhere the time of delay and taxonomic diversity of fusulinids in north america shelves depended on the scale and intensity of the warming episodes cooling events on the other hand are associated with decreased taxonomic diversity and appearances of endemic forms characteristic only of temperate water provinces the occurrence of these forms in boreal and north american provinces appears to be isochronous as their environments are uniform and induce their uniform and isochronous distribution several warming and cooling episodes during pennsylvanian permian time are recognized the differences between taxonomic variations in each event could potentially be used for provisional estimation of the degree of climatic change a strong link between biotic and climatic events in north american province and the similarity of biotic changes in the north american and other provinces suggests that paleoclimatic events in north american province were controlled by global factors

geological and biological consequences of giant impacts it seems inescapable that large impacts have been an ongoing phenomenon throughout geological time in the phanerozoic the estimated frequency of impact by bodies of 5 km diameter or more is on the order of 1 0 every 1 00 myr the 5 km lower limit is chosen arbitrarily but it is shown in this review that such a body is certainly large enough to cause very large terrestrial effects a small decrease in this size limit would lead to a large increase in the frequency of occurrence it may be claimed that bodies of a size likely to have drastic and sudden effects on niany physical and biological features of the earth have arrived with a frequency comparable to the average duration of a biostratigraphic stage nothing is said of the interval between arrivals which may be random i e stochastic currently there is not enough geological evidence to allow recognition of other than random spacing between a few positively identified events during the phanerozoic since impacts by extraterrestrial bodies have been clearly established it is reasonable to postulate that they must leave a record in the stratigraphic column why then do we currently have so few horizons that have been claimed to contain evidence of a global impact event since the effects we are considering are unquestionably global in this paper we bring together evidence from several disciplines that

no geochemical evidence for an asteroidal impact at late devonian mass extinction horizon one way to test the proposed causal relationship between mass biotic extinction and asteroidal impact is to search for the geochemical signature of such an event at additional mass extinction horizons other than the cretaceous tertiary k t boundary we report here the results of an extensive search for an indium ir anomaly across the late devonian frasnian famennian f f extinction horizon 367 myr bp over a decade ago mclaren1 proposed that this extinction was caused by an astrophysical catastrophe we have examined three sedimentary sequences in new york state the standard reference section for eastern north america and one in belgium the type locality which cross the f f boundary no ir anomaly was found in any of the analysed stratigraphie sections the highest values of ir detected ranged from only 0 2 to 2 of those reported for the marine and terrestrial ir analyses at the k t boundary further devonian pyrite rich sediments similar to those at the k t boundary do not contain high ir concentrations

a forest fire and soil erosion event during the late devonian mass extinction abstract the late devonian mass extinction occurred in a stepwise manner and culminated close to the frasnian famennian f f boundary 372 million years ago organic molecular indices from marine sedimentary rocks at the sinsin section belgium indicate that the sequence of combustion of land vegetation soil erosion and anoxia euxinia occurred close to this boundary the increased concentrations of biomarkers indicating forest fire and soil erosion measured in the sinsin section suggest that fire became widespread at this time leading to various damaging consequences increased runoff and oceanic anoxia that caused marine extinctions magnetic susceptibility data in the sinsin section indicate a relatively dry climate spanning the f f boundary which would have encouraged forest fires the study of organic biomarkers presents several lines of evidence to link forest fire and soil erosion to the late devonian mass extinction

reassessment of extinction patterns of pliocene molluscs from california and environmental forcing of extinction in the san joaquin basin abstract thirty latest miocene through late pleistocene molluscan faunas from coastal california and the san joaquin basin sjb central california were reviewed to better understand the pattern of pliocene mollusc extinction in california and particularly in the etchegoin group informal sjb nomenclature species lists were compiled for each fauna taxonomy reviewed to eliminate synonyms and uncertain identifications and the extinct versus living status of each species determined only 34 of molluscan species 40 of bivalves and 21 of gastropods in the etchegoin group are extant as compared to 61 of molluscs 64 of bivalve and 56 of gastropod species in pacific coastal faunas the etchegoin group was deposited in a marginal basin connected to the pacific ocean through a long and narrow silled strait subject to its connection being cut by eustatic regression and regional tectonism seven major regional extinctions affected the etchegoin group molluscan faunas where 40 species became extinct two in the early pliocene upper etchegoin formation at 4 4 and 4 0 ma and five in the early late pliocene san joaquin formation at 4 0 2 9 2 6 and 2 4 ma and that coincident with the final ocean connection closure at 2 3 ma peak diversities corresponded with periods of highest sea level at 4 5 4 2 3 1 2 7 2 5 and 2 4 ma when immigrant faunas became established during periods of warm climate and normal marine conditions upon sea level fall the basin became cooler brackish and faunas adapted to warmer and normal marine conditions became extinct with slow recovery of diversity afterwards low diversity faunas characterize periods of low and rising sea level when circulation through the connecting strait was insufficient to maintain normal marine conditions thus hindering establishment of most immigrants from coastal faunas restricted circulation with the pacific substantially reduced the nutrient supply to the basin leading to a long term productivity collapse that exacerbated the effects of a deteriorating environment thus leading to the major extinction event observed at the etchegoin san joaquin formations contact at 4 0 ma increasing restriction from the pacific ocean during the pliocene limited immigration of coastal species into the san joaquin basin to those opportunistic species best able to adapt to the environment inside the basin while species unable to adapt to conditions inside the sjb were filtered out in the strait stenotopy of endemic species precluded range expansion through the connecting strait into the pacific ocean thus abrupt regression driven hydrologic change productivity collapse from coincident geochemical and sedimentary change and climatic change led to the major extinction events in the pliocene sjb speciation events following extinctions suggest diversification of surviving faunas into habitats created by changed environmental conditions despite the number and wide geographic distribution of faunas reviewed in this paper only 50 90 of extant mollusc species found in pliocene etchegoin group faunas are also found in coastal california pliocene faunas demonstrating the incompleteness of the california fossil record

glassy microspherules microtektites from an upper devonian limestone the properties of microspherules recovered from an upper devonian marine limestone immediately overlain by a geochemical anomaly of siderophile and chalcophile elements are similar to those of impact derived microtektites these microspherules are glass have splash form shapes contain spherical vesicles and lechatelierite inclusions and show oxide compositional variations similar to those in known microtektites these characteristics suggest that these upper devonian microspherules have an impact origin a bolide impact may have occurred about 365 million years ago on the south china plate and caused a faunal extinction on eastern gondwana

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

distribution stereochemistry and stable isotope composition of amino acids in k t boundary sediments abstract the cretaceous tertiary k t boundary with an age of 65 million years before present is associated with the mass extinctions of dinosaurs and other terrestrial and marine organisms evidence for the k t boundary is reported in both marine and non marine stratigraphic units the presence of two exotic amino acids aminoisobutyric acid and isovaline has been reported from stevns klint denmark sediments two hypotheses have been proposed for the occurrence of aiba and i val in the stevns klint sediments 1 they are of extraterrestrial origin and 2 they are the by products of the thermal alteration of coal to test these hypotheses samples were obtained from three k t boundary sites two starkville south and raton pass located in the non marine raton basin of colorado and new mexico and one from the marine sequence at stevns klint denmark the samples were analyzed for amino acid distributions and stereochemistry bulk stable c and n isotope compositions and stable c isotope compositions of individual amino acids at the starkville south site protein and non protein amino acid components are present in the k t boundary sediments at nmol g levels and are primarily of the l configuration the non protein amino acids aiba and i val were detected in several of the sediment samples based on retention times and verified through coinjections of authentic standards protein and non protein amino acid components of the murchison meteorite are enriched in 13 c relative to terrestrial materials the 13 c values of individual amino acids in the starkville south samples are however depleted in 13 c in all samples with values ranging from 13 for glycine to 31 for l isoleucine in contrast the 13 c value for glycine in murchison is 22 also bulk organic 13 c and 15 n values for the k t boundary sediments are substantially depleted in 13 c and 15 n relative to bulk values for the murchison meteorite it is therefore suggested that the amino acids in these k t boundary sediments are primarily of terrestrial biogenic origin

thermohaline staircases in a caribbean eddy and mechanisms for staircase formation the structure of a cyclonic eddy in the eastern caribbean was observed by caribbean vorticity experiment cruise cavortex i in august 2003 prominent thermohaline staircases are evident in profiles of temperature and salinity at locations that appear to correlate with the presence of lateral property gradients and shear within the eddy although such a connection is less than definitive due to the coarseness of horizontal sampling these observations are examined in light of predictions from two theories for staircase formation aspects of the data are found to be consistent with each raising the possibility that both mechanisms are operating

double diffusive recipes part ii layer merging events this study explores the dynamics of thermohaline staircases well defined stepped structures in temperature andsalinityprofiles commonlyobservedin regionsofactive doublediffusion theevolutionofstaircases in time is frequently characterized by spontaneous layer merging events these phenomena the authors argue are essentialin regulating theequilibriumlayerthicknessin fullydevelopedstaircases thepatternand mechanics of merging events are explained using a combination of analytical considerations direct numerical simulations and data analysis the theoretical merger model is based on the stability analysis for a series of identical steps and pertains to both forms of double diffusion diffusive convection and salt fingering the conceptual significance of the proposed model lies in its ability to describe merging events without assuming fromtheoutsetspecificpowerlawsfortheverticaltransportofheatandsalt theapproachadoptedbyearlier merging models the analysis of direct numerical simulations indicates that merging models based on the four thirds flux laws offer adequate qualitative description of the evolutionary patterns but are less accurate than models that do not rely on such laws specific examples considered in this paper include the evolution of layers in the diffusive staircase in the beaufort gyre of the arctic ocean

the diffusive regime of double diffusive convection the diffusive regime of double diffusive convection is discussed with a particular focus on unresolved issues that are holding up the development of large scale parameterizations some of these issues such as interfacial transports and layer interface interactions may be studied in isolation laboratory work should help with these however we must also face more difficult matters that relate to oceanic phenomena that are not represented easily in the laboratory these lie beneath some fundamental questions about how double diffusive structures are formed in the ocean and how they evolve in the competitive ocean environment

sequence stratigraphy of the frasnian famennian transitional strata a comparison between south china and southern belgium the sedimentological evolution of the frasnian famennian transitional strata in south china and southern belgium has been investigated a similar trend in the deepening and shallowing of the sedimentation environment occurs in the two palaeogeographically distinct areas the stratigraphic succession has been subdivided into depositional sequences a general deepening occurs in the palmatolepis rhenana conodont zone during the most rapid rise in sea level a transgressive systems tract formed this transgressive systems tract is followed by a highstand systems tract in the late p rhenana zone a major sequence boundary within the latter zone is indicated by an unconformity in intraplatform and platform areas and by a conformity in the basinal area the uppermost sediments within the late rhenana zone correspond to a lowstand systems tract a rapid flooding took place near the base of the palmatolepis linguiformis zone and dark shales and limestones formed a second sequence boundary coincides with or is very close to the frasnian famennian boundary base p triangularis zone the global extinction event at the frasnian famennian boundary coincides with an important eustatic fall in sea level the proposed stratigraphic subdivision should allow worldwide correlations of shallow and deep water deposits

terrestrial impact structures impact structures are the dominant landform on planets that have retained portions of their earliest crust the present surface of the earth however has comparatively few recognized impact structures this is due to its relative youthfulness and the dynamic nature of the terrestrial geosphere both of which serve to obscure and remove the impact record although not generally viewed as an important terrestrial as opposed to planetary geologic process the role of impact in earth evolution is now receiving mounting consideration for example large scale impact events may have been responsible for such phenomena as the formation of the earth s moon and certain mass extinctions in the biologic record the importance of the terrestrial impact record is greater than the relatively small number of known structures would indicate impact is a highly transient high energy event it is inherently difficult to study through experimentation because of the problem of scale in addition sophisticated finite element code calculations of impact cratering are gen erally limited to relatively early time phenomena as a result of high com putational costs terrestrial impact structures provide the only ground truth against which computational and experimental results can be com pared these structures provide information on aspects of the third dimen sion the preand postimpact distribution of target lithologies and the nature of the lithologic and mineralogic changes produced by the passage of a shock wave they also provide data for cratering rate estimates and in some cases on the nature of the impacting body in this review emphasis is placed on the nature of terrestrial impact structures the criteria for their identification and their contribution to

mass extinctions the view of a sceptic the concept of periodic mass extinctions by extraterrestrial impacts has contributed very strongly to the current revival of interest in the problem of mass extinctions in this context several radical claims have been made asserting that the newly emerging picture of mass extinctions as a separate class of biological phenomena caused by a separate class of processes demands a far reaching revision of the the neodarwinian paradigm of evolution and implies a vindication of the cuvierian perspective on earth9s history the validity of these claims however is questionable at all levels from the interpretation of particular events to the concept of mass extinctions as a special class of phenomena to their proposed causation by impacts and to their alleged historical pedigree and implications for current evolutionary theory mass extinctions may actually be clusters of more or less accidentally aggregated in time but causally distinct extinction episodes

migration origination and extinction of southern hemisphere brachiopods during the middle carboniferous abstract the migration patterns and latitudinal diversity gradients of early and middle carboniferous articulate brachiopod genera from the paleoequatorial zone and southern hemisphere are consistent with the paleoclimatic history of these intervals interpreted from the study of paleoequatorial and northern hemisphere forms both poles apparently became warmer between the middle and late visean south polar cooling associated with glaciation probably began in the late visean at this time 44 of 92 southern hemisphere nonequatorial genera migrated toward the equator the north pole remained warm into the namurian a and cooled during the namurian a to b both northern and southern hemisphere non equatorial genera reacted to high latitude warming with significant increases in percent origination genera from all latitudinal zones responded to high latitude cooling with significant increases in percent extinction during the namurian a to b when both poles were cool a small but statistically significant number of equatorial genera 8 out of 70 migrated out of the equatorial zone into the non equatorial northern hemisphere no similar migration into the southern hemisphere occurred at this time perhaps due to the steep latitudinal temperature gradient several lines of evidence suggest that the latitudinal temperature gradient was steeper in the southern hemisphere than in the northern hemisphere whereas percent origination in northern non equatorial latitudes rose significantly following north polar cooling origination rates in southern non equatorial latitudes did not rise significantly following south polar cooling southern hemisphere non equatorial brachiopods suffered a greater loss of diversity during the interval of polar cooling than either equatorial or northern hemisphere non equatorial brachiopods and there may be namurian tillites within 20 s of the paleoequator veevers and powell 1987

the global frasnian famennian kellwasser event during the uppermostp gigas conodont zone p linguiformis zone the stepwise frasnian extinction culminates in the global transgressive regressive frasnian famennian kellwasser event most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction during the early upper devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the shelf sediments contemporaneous positive excursions of the 13c recorded from pelagic limestones of europe and australia prove a worldwide change in the co2 content of the oceans surface water which is in balance with the atmosphere if the climate is controlled by the co2 content of the atmosphere a cyclic operation process might have developed with the succession transgression high organic production deposition of organic carbon lowering of co2 in the atmosphere icehouse effect polar glaciation regression erosion of organic carbon and re supply of co2 to the ocean and atmosphere greenhouse effect deglaciation transgression during the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms

a unique geochemical record at the permian triassic boundary a 330 metre core drilled through the marine permian triassic boundary in the carnic alps of austria allows closely correlated studies of geochemistry petrography and palaeontology across the boundary the isotope shifts and metal concentrations are extended multiple and complex and do not resemble those seen at the cretaceous tertiary boundary both the carbon isotope shifts and the chemical events including an indium anomaly may have causes related to a major regression of the sea

incremental oil recovery using a horizontal drainhole in the san andres formation olson field west texas oolitic carbonates and associated rocks in the san andres formation produce hydrocarbons at olson field west texas mudstones dolomitized fusulinid peloid packstones and wackestones ooid peloid grainstones and packstones and minor siliciclastic sediments occur in the field the reservoir is stratigraphically compartmentalized by lenticular oolite deposits that are overlain by algal laminated mudstones and siltstones pore filling anhydrite cement common in all lithologies adds to porosity heterogeneity interwell communication is poor as indicated by variable bottomhole pressures and erratic waterflood response a medium radius lateral hole was drilled to a total depth approximately 50 ft 15 m from an offset vertical well at this depth the horizontal well intersected a previously existing artificial fracture that occurred in the nearby vertical well the intersection of this fracture by the lateral borehole had a significant economic impact the production rate in the vertical well jumped from a few barrels per day to an average of 70 bopd and less than 20 bwpd the ensuing years maintained relatively high flow rates projected incremental oil recovery is 153 000 bbl roughly equivalent to production from an average well drilled during the early life of the field other unsuccessful horizontal wells have been drilled at olson field but they have not targeted preexisting hydrofractures in offset vertical wells therefore the concepts presented in this paper have not been retested this approach intentionally drilling a drainhole to intersect a preexisting hydrofracture could add new life to many older compartmentalized reservoirs

the cretaceous tertiary extinction a lethal mechanism involving anhydrite target rocks the chicxulub crater yucatan mexico is a leading contender as the site for the impact event that caused the cretaceous tertiary k t extinctions a considerable thickness of anhydrite caso4 forms part of the target rock high temperatures resulting from impact would drive so2 off from the anhydrite hundreds of billions of tonnes of sulfuric acid aerosol would thus enter the stratosphere and cause considerable cooling of the earth s surface decrease photosynthesis by orders of magnitude deplete the ozone layer and permit increased uv radiation to reach the earth s surface finally the aerosol would fall back to earth as acid rain and devastate land and some lacustrine biota and near surface marine creatures the presence of anhydrite in the chicxulub target rock may thus help explain the many extinctions observed at the k t boundary

mid devonian to mid permian floral and faunal regions and provinces summary the middle to late palaeozoic biota in seas adjacent to the caledonide appalachian orogen included an abundant generally cosmopolitan benthos in both carbonate and clastic environments where low clastic sediment input permitted organic reefs and build ups were characteristic of this tropical area early devonian biogeographic provinces did not persist into later times the pelagic fauna dominated by ammonoidea bivalvia conodonts and vertebrates was rich rapidly evolving and again cosmopolitan vertebrates and conodonts in particular were wide ranging among the land plants heterospory and arborescence evolved during the middle and late devonian in a number of classes particularly the lycopsida and progymnospermopsida genera were largely cosmopolitan during this time and only one floristic region can be recognized worldwide although there is some evidence for slight provincial floral variation outside laurussia during the early carboniferous arborescent lycopsida were abundant three floristic regions can be identified worldwide of which one is the circum tethyan region including laurussia kazakhstania and china two floral provinces are recognized within the laurussian part of this region in late carboniferous and early permian times when gymnosperms replaced the pteridophytes as the dominant forms there is a more clear cut separation of floral regions and by early permian two floral regions are recognized within laurussia which are clearly different from those away from this land mass non marine bivalvia and vertebrates were highly cosmopolitan from mid devonian time onwards with amphibia appearing in greenland in the late devonian and reptiles appearing in eastern canada and western europe in westphalian a time

the frasnian famennian extinction event in a stable cratonic shelf setting trout river northwest territories canada abstract the frasnian famennian f f extinction event occurs in platformal carbonates along the trout river n w t paleogeographically the site was about 150 km east of the western cratonic margin faunal evidence based primarily on corals and sedimentation rates of passive cratonic margins suggest that the late frasnian redknife and kakisa formations include both the upper rhenana and the linguiformis conodont zones the high biodiversity of the benthic fauna during the late frasnian decreases sharply at the f f boundary and recovers only gradually during the early famennian this trend is also expressed by the profile of 13c values microfacies analysis has identified two minor hiatuses at the f f boundary the lower break is represented by an unconformity at the upper contact of the latest frasnian kakisa formation and is associated with surficial karstification and brecciation of the underlying biostromal carbonates anomalous trace element concentrations at the unconformity are interpreted as possible fallout material related to a bolide impact this hiatus probably corresponds to the lower triangularis zone because no diagnostic conodonts of that time interval are present the lower and upper hiatuses are separated by the deposition of a wackestone sandstone facies with an impoverished fauna of sponges calcareous algae and some foraminifera preserved only in neptunian dykes in the upper kakisa and as fragments in the overlying famennian trout river formation the depauperate fauna suggests hostile conditions and or a habitat ravaged by a catastrophic event common characteristics after a global extinction event conodont evidence suggests that this brief depositional interval corresponds to the middle triangularis zone the upper hiatus probably straddles the contact of the middle and upper triangularis zones evidence for this break are angular fragments of the wackestone sandstone facies in the basal trout river formation conodonts from the basal siliciclastics of the trout river formation assign the lower part of this unit to the upper triangularis zone in alberta 900 km to the south similar platformal carbonates show a longer hiatus the entire triangularis zone at the f f contact whereas slope sediments indicate continuous sedimentation with a sharp drop in biodiversity and a temporary proliferation of primitive organisms at the f f boundary

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

climate change and the selective signature of the late ordovician mass extinction selectivity patterns provide insights into the causes of ancient extinction events the late ordovician mass extinction was related to gondwanan glaciation however it is still unclear whether elevated extinction rates were attributable to record failure habitat loss or climatic cooling we examined middle ordovician early silurian north american fossil occurrences within a spatiotemporally explicit stratigraphic framework that allowed us to quantify rock record effects on a per taxon basis and assay the interplay of macrostratigraphic and macroecological variables in determining extinction risk genera that had large proportions of their observed geographic ranges affected by stratigraphic truncation or environmental shifts at the end of the katian stage were particularly hard hit the duration of the subsequent sampling gaps had little effect on extinction risk suggesting that this extinction pulse cannot be entirely attributed to rock record failure rather it was caused in part by habitat loss extinction risk at this time was also strongly influenced by the maximum paleolatitude at which a genus had previously been sampled a macroecological trait linked to thermal tolerance a model trained on the relationship between 16 explanatory variables and extinction patterns during the early katian interval substantially underestimates the extinction of exclusively tropical taxa during the late katian interval these results indicate that glacioeustatic sea level fall and tropical ocean cooling played important roles in the first pulse of the late ordovician mass extinction in laurentia

a perspective on the evidence for periodic cometary impacts on earth abstract recent suggestions of periodic cometary showers coincident with mass extinctions have prompted a review of the terrestrial cratering record from the point of view of completeness of search and crater retention the record used to argue for statistical periodicities is incomplete and may not be representative estimates of crater ages are of variable accuracy and precision and in some cases different dating methods yield discordant results it is possible to define through time series analysis a number of periodicities of different magnitude 29 m y 21 m y 18 5 m y 13 5 m y and phase depending on which craters are considered the most representative sample of the record arguing against periodic cometary showers is the observation that estimates of the average cratering rate in recent time and observations on apollo bodies are equivalent in addition siderophile element data from impact melt rocks suggest a variely of projectile types were responsible for relatively large terrestrial craters given these observations it is concluded that statements regarding periodic cometary showers are not categorical and require evidence beyond arguments based on time series analyses of an incomplete cratering record

iridium and other platinum group elements as geochemical markers in sedimentary environments iridium anomalies are commonly used as indicators of extraterrestrial processes which caused global extinctions however platinum group element pge anomalies may result from several different processes both syn and postdepositional acting separately or jointly the sources and processes of enrichment involved are extraterrestrial asteroid comet cosmic dust impact ejecta volcanogenic pge rich condensates precipitation from seawater low sedimentation rate anoxic conditions microbial concentration dissolution reprecipitation exhalative hydrothermal leaching transport and precipitation at a redox boundary geochemical characteristics of pge and accompanying elements in sediments can be used to identify the contributions of some specific sources and processes 1 extraterrestrial chondritic ru ir and os ir ratios low 187os 186os ratio high ir compared to pt pd and au 2 volcanogenic high iridium and se as sb and in contents 3 exhalative hydrothermal high au pd and pt relatively low ir contents 4 precipitation from seawater high pt and low pd contents also high cd and ag contents under anoxic conditions and 5 reduction from intermediate and low temperature solutions high pge and cu or mo u ni contents

accretion rate of extraterrestrial matter iridium deposited 33 to 67 million years ago iridium measured in 149 samples of a continuous 9 meter section of pacific abyssal clay covering the time span 33 to 67 million years ago shows a well defined peak only at the cretaceous tertiary boundary in the rest of the section iridium ranges from a minimum concentration near 0 35 nanograms per gram in the paleocene to a maximum near 1 7 in the eocene between 63 and 33 million years ago the mean iridium accumulation rate is approximately 13 nanograms per square centimeter per million years correction for terrestrial iridium leads to an extraterrestrial flux of9 3 nanograms of iridium per square centimeter per million years and an estimated annual global influx of 78 billion grams of chondritic matter consistent with recent estimates of the influx of dust meteorites and crater producing bodies with masses ranging from 10 13 to 1018 grams combining the recent flux of objects ranging in mass from 106 to 107 grams with the flux of 1014 to 1015 gram objects indicates that the number of objects is equal to 0 54 divided by the radius in kilometers to the 2 1 power periodic comet showers should increase the cometary iridium flux by a factor of 200 to 600 on a time scale of 1 to 3 million years the predicted iridium maxima more than 30 times background are not present in the intervals associated with the cretaceous tertiary boundary or the tektiteproducing late eocene events

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

a latest carboniferous warming spike recorded by a fusulinid rich bioherm in timor leste implications for east gondwana deglaciation abstract during the late paleozoic and early mesozoic timor lay in the northern part of the north south east gondwana rift system along which the western margin of australia later developed discovery of a latest gzhelian bioherm in the central highlands of timor leste has implications for latest carboniferous earliest permian climate history and deglaciation in basins further south in the rift system limestone outcrop of the maubisse formation near the village of kulau is recognized as a bioherm with a massive lower unit including reef framework at the base and a bedded grainstone upper unit the bioherm developed on a basalt substrate in warm shallow water as indicated by photozoan assemblages in the massive lower unit foraminifera belonging to 17 genera are recorded from the bioherm these include representatives of the families biseriamminidae biwaellidae bradyinidae cornuspiridae lasiodiscidae palaeotextulariidae pseudotaxidae ozawainellidae schubertellidae schwagerinidae staffellidae and textrataxidae twenty one species have been referred to known types and 12 species are left in open nomenclature the assemblage probably belongs within the uppermost gzhelian schwagerina robusta ultradaixina bosbytauensis zone although a possible lowest asselian correlation cannot be excluded the bioherm is the oldest carbonate unit so far recorded from the maubisse formation and the oldest sedimentary unit biostratigraphically dated in timor the dominantly heterozoan composition of the skeletal component of the limestone except for the basal photozoan assemblage and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a paleolatitude of about 40 s the late pennsylvanian was a time of glaciation that in australia is represented by a significant stratigraphic hiatus in basins to the south of timor in the east gondwana rift system the development of the kulau bioherm during the latest gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment alternating diamictite and mudstone in the southern basins

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

pre quaternary sea level changes while the paramount importance of global sea level changes has been widely accepted by quaternary geologists throughout this century it is only within the last decade that such changes in the rest of the phanerozoic have received much attention there are two principal reasons for this arousal of interest first increased exploration of the stratigraphic record across the earth both on land and under the sea and significant improvement in biostratigraphic correlation have drawn attention to what appear to have been globally synchronous events second oceanographic research has demonstrated the importance of tectonically controlled changes in the cubic capacity of the ocean basins notably variations in ridge volume which provide a ready mechanism for sea level changes even at nonglacial times the adjective eustatic was first proposed for global changes of sea level by suess 1906 in his great treatise the face of the earth the corresponding noun is eustasy not eustacy as it is commonly misspelt the unconvinced reader need only think of ecstasy eustatic sea level changes can be inferred as suess recognized by a plotting the temporal spread of marine sediments over the continents and b estimating the depositional depth variations in marine stratal sequences which can be correlated across and between continents to these methods can be added seismic stratigraphy in which biostratigraphically age determined seismic sequences on the con tinental margins are analyzed in terms of cycles of coastal onlap and offiap when the results of these methods are broadly in accord confidence in a eustatic interpretation is increased but the range of confidence can vary considerably it is widely accepted that there was an exceptionally high sea

double diffusive recipes part i large scale dynamics of thermohaline staircases abstractthree dimensional dynamics of thermohaline staircases are investigated using a series of basin scale staircase resolving numerical simulations the computational domain and forcing fields are chosen to reflect the size and structure of the north atlantic subtropical thermocline salt finger transport is parameterized using the flux gradient formulation based on a suite of recent direct numerical simulations analysis of the spontaneous generation of thermohaline staircases suggests that thermohaline layering is a product of the gamma instability associated with the variation of the flux ratio with the density ratio after their formation numerical staircases undergo a series of merging events which systematically increase the size of layers ultimately the system evolves into a steady equilibrium state with pronounced layers 20 50 m thick the size of the region occupied by thermohaline staircases is controlled by the competition between turbulent mixing and double diffusion assuming in acc

neritic southern extratropical foraminifera and the terminal eocene event abstract if the terminal eocene event tee records a major bolide impact or other extraterrestrial happening then there ought to be disruption of benthonic foraminiferal communities especially in rather shallow neritic environments we record the arrivals and departures of 180 species in a composite succession through the later middle eocene late eocene and earliest oligocene in southern australia the rate of new arrivals increases at each of several transgressions each of which also marks a climatic amelioration the sharpest increase in rate of departure is found at a regional regression within the latest eocene there is no evidence of major disruption of the fauna at the end of the eocene the tee on this data was not extraterrestrial in origin and was hardly cataclysmic the study suggests instead that the origins of late eocene biotic change should be sought through earthly configurations of climate and sea level

catastrophic extinctions and the inevitability of the improbable the earth as we know it today has been shaped by natural processes of the past uniformitarianism emphasizes the cumulative effects of processes operating at uniform rates catastrophists single out the importance of rare and unusual events this article proposes a scale to measure the magnitude of rare events and cites the inverse magnitude frequency relation of naturally occurring events to formulate the philosophical basis for actualistic catastrophism mass extinction at the end of the cretaceous is held up as an example that a catastrophe such a bolide impact could influence the course of biologic evolution improbability of such an event is no argument against such a hypothesis because the improbable even those with odds of once every billion years must have taken place a few times in the geological history the immensity of geological time is not only important because of the immensity of the cumulative effects but also because the long duration provides a chance for the improbable to take place

using borehole images for target zone evaluation in horizontal wells horizontal wells are rarely horizontal instead operators commonly try to drill such wells into particular rock layers or target zones which may or may not be truly horizontal thicknesses of target zones commonly range from a few feet to a few tens of feet 1 10 m target zone evaluation concerns whether a horizontal well was successfully located and drilled in a given rock layer borehole imaging logs provide a powerful tool for stratigraphic interpretation and target zone evaluation in the austin chalk niobrara formation san andres formation and other units this study uses borehole images generated by schlumberger s formation microscanner fms a microconductivity logging device open fractures and clay rich interbeds appear as dark high conductivity traces on the fms log these traces can be fit with sinusoidal curves and oriented on a computer workstation the shape of the sinusoidal curve that fits a particular bedding plane tells the interpreter whether the borehole was moving upward or downward through the strata stratlog trademark of sierra geophysics inc a halliburton company software has been used to display borehole profiles by combining fms data on fracture intensities and bedding plane intersections with gamma ray logs mud logs and borehole deviation surveys to aid in planning future wells multiple penetrations of he same horizon can be detected and used to calculate highly accurate bedding plane dips fault interpretation including the detection of rollover beds is also possible finally stratigraphic interpretation can be combined with observed fractures to determine which rock layers are most highly fractured and therefore should be target zones

double diffusion in saline powell lake british columbia powell lake contains a deep layer of relic seawater separated from the ocean since the last ice age permanently stratified and geothermally heated from below this deep layer is an isolated geophysical domain suitable for studying double diffusive convection high resolution ctd and microstructure measurements showseveraldouble diffusivestaircases rr 51 6to6 inthedeepwater separatedverticallybysmoothhighgradientregionswithmuchlargerdensityratios theloweststaircasecontainsstepsthatarelaterallycoherent on the basin scale and have a well defined vertical structure on average temperature steps in this staircase are 4mk salinity steps are 2mgkg 21 and mixed layer heights are 70cm the ctd is capable of measuring bulk characteristics of the staircase in both temperature and salinity microstructure measurements are limited to temperature alone but resolve the maximum temperature gradients in the center of selected laminar interfaces two different algorithms for characterizing the staircase are compared consistent estimates of the steady state heat flux 27mwm 22 are obtained from measurements above and below the staircase as well as from microstructure measurements in the center of smooth interfaces estimates obtained from bulk interface gradients underestimate the steady state flux by nearly a factor of 2 the mean flux calculated using a standard 4 3 flux law parameterization agrees well with the independent estimates but inconsistencies between the parameterization and the observations remain these inconsistencies are examined by comparing the underlying scaling relationship to the measurements