the interplay of dynamic topography and eustasy on continental flooding in the late paleozoic abstract global sea level change can be inferred from sequence stratigraphic and continental flooding data these methods reconstruct sea level from peri cratonic and cratonic basins that are assumed to be tectonically stable and sometimes called reference districts and from spatio temporal correlations across basins however it has been understood that long wavelength typically hundreds of km and low amplitude

chemical stability of the atmosphere and ocean abstract the earth system processes most of the chemical components of its atmosphere and oceans in geologically short periods of time it does this in a regulated way one that maintains a remarkably constant surface environment this we know primarily from the fossil record of uninterrupted complex life on earth that extends over the last billion years we are only beginning to understand the feedbacks that control the chemistry of the oceans and atmosphere numerical models of biogeochemical cycles are most stable when there is feedback between the amount of a chemical component in the ocean or atmosphere and its transfer to or from that reservoir coupling of subsystem especially of those operating on different time scales enhances stability an example of the role of feedback in stabilizing earth s chemical environment is the mechanism of control of atmospheric oxygen there appears to be no strong relationship between oxygen level and oxygen consumption however oxygen production may be a function of oxygen level the burial rate of organic carbon oxygen production in marine sediments may be sensitive to bottom water oxygenation levels also combustion may be an effective mechanism of transferring nutrients namely phosphorus from efficient terrestrial ecosystems to less efficient marine ecosystems when o2 rises fires become more frequent and p is transferred to the ocean stimulating marine organic carbon burial but depressing global burial rates global o2 production rates decline as does the o2 level a negative feedback models of ocean chemical composition are presently incapable of reproducingthe temporal constancy indiated by geological observations these models do not incorporate ion exchange equilibria as important processes in marine geochemical cycles when included these equilibria significantly damp the fluctuations in ion ratios calculated by the extant models

stratigraphic overview of palaeogene tuffs in the faroe shetland basin ne atlantic margin tuffs form key stratigraphic markers that assist with determining the timing of volcanic margin development a number of laterally extensive tuffs are preserved along the north atlantic margin in the offshore faroe shetland basin fsb a product of early palaeogene volcanism associated with the break up and seafloor spreading between greenland and nw europe these tuffs which are dominantly basaltic in composition are widely preserved in the contiguous north sea basin however less attention has been paid to them in the fsb this study integrates multiple regional datasets including 3d seismic data and released commercial well logs to detail the character and distribution of early palaeogene tuffs in the fsb the earliest tuffs are more locally identified by their presence in core whereas later tuffs are more regionally recognizable highlighting more widespread volcanism with time the distribution of tuffs also reveals the timing of formation of the previously enigmatic volcanic centres importantly owing to constraints of vertical resolution in well data we argue that the number of tuffs in the north atlantic margin is probably underestimated and biased towards basaltic tuffs which are easier to identify on well logs

interpretation of the minch linear magnetic anomaly and of a similar feature on the shelf north of lewis by non linear optimization the linear negative magnetic anomaly which stretches continuously for 110 km across the north minch extending slightly west of north from loch ewe is interpreted in terms of an unusually wide dyke which does not reach the surface fourteen profiles taken from the aeromagnetic map have been interpreted using non linear optimization giving an excellent fit to a dyke having an average and fairly constant width of c 1 1km the depth to the upper surface of the interpreted dyke varies between 0 3 km and over 2 km it is reversely magnetized in a direction consistent with a tertiary or possibly earlier origin the average magnetization is estimated to be 0 51 am 1 a similar magnetic feature on the shelf to the north west of the butt of lewis is also interpreted in terms of a reversely magnetized dyke having a poorly resolved width of about 0 8 km a depth of about 0 7 km and a magnetization of 1 6am 1 on seismic evidence the minch dyke appears to be post jurassic in age and an early tertiary age seems most likely for both dykes it is suggested that they may be related either to the postulated large igneous pile of early tertiary age which forms the wyville thomson ridge or to the skye centre they appear to represent early tertiary extension of the crust which is taken up by more numerous narrow dykes further south

mean age of oceanic lithosphere drives eustatic sea level change since pangea breakup abstract the atlantic and indian oceans and the oceanic part of the antarctic plate have formed at the expense of panthalassa as a result of pangea breakup over the last 180 myr this major plate reorganization has changed the age vs surface distribution of oceanic lithosphere and has been a likely driver of sea level change assuming that the age surface structure of panthalassa has remained similar to the present day global distribution from 180 ma to present and using the isochron patterns preserved in the newly formed oceans we model resulting relative sea level change we find a first slower phase of sea level rise by 90 to 110 m culminating between 120 and 50 ma followed by a faster phase of sea level drop we show that this result is not strongly sensitive to our hypothesis of constant mean age of panthalassa for which much of the information is now erased due to subduction when the effects of oceanic plateau formation and ice cap development are added the predicted sea level curve fits remarkably well the first order variations of observed sea level change we conclude that the changes in mean age of the oceanic lithosphere varying between 56 and 62 0 2 myr which are simply the expression of the wilson cycle following pangea breakup are the main control accounting for 70 of first order changes in sea level

kick starting ancient warming rapid global warming marked the boundary between the palaeocene and eocene periods 55 6 million years ago but how the temperature rise was initiated remains elusive a catastrophic release of greenhouse gases from the kilda basin could have served as a trigger

interpretation of aeromagnetic anomalies over part of southeastern nigeria using three dimensional hilbert transformation we present the results of the application of three dimensional hilbert transformation to the analysis of airborne total field magnetic anomalies over part of southeastern nigeria this study not only substantiates the usefulness of 3 d hilbert transforms in the interpretation of magnetic anomaly maps but also more clearly delineates the structural pattern of the area of study results from the previous study are discussed in relation to the results of previous geological and geophysical studies of the area

stratigraphical and δ13c records of permo carboniferous platform carbonates south china responses to late paleozoic icehouse climate and icehouse greenhouse transition abstract little attention has been focused on the stratigraphical imprints of the late paleozoic ice age on the equatorial eastern paleo tethys an integrated study of biostratigraphy microfacies and stable carbon isotope stratigraphy was carried out on pennsylvanian middle guadalupian carbonates of the gongchuan section in the bama platform south china it records seven cooling and two warming pulses in the pre kungurian interval comparing with ice proximal stratigraphical records and far field indirect proxies in lower latitudes a kungurian negative 13 c excursion from 4 4 at the base of the kungurian to 1 6 recorded only in the subequatorial belt is documented here it is followed by a global positive 13 c trend reaching 5 3 near the cisuralian guadalupian boundary seven third order shallowing upward cycles are reported for the first time from the kungurian succession the duration of each cycle is estimated to ca 1 myr these cycles are interpreted as being of glacioeustatic origin and mainly driven by long period modulations of obliquity 1 2 myr under major p co 2 decreasing condition this interpretation is supported by recent climate ice sheet modeling and cenozoic glaciation studies which argue that astronomical forcing will be amplified by large magnitude perturbations in the carbon cycle when only localized ice centers persist our results emphasize the need for integration of sedimentological and paleoclimatological proxies in elucidating the dynamics of the deglacial phases of the late paleozoic ice age

leaching of uranium and thorium from monazite i initial leaching interaction of three natural monazite specimens with a bicarbonate carbonate solution was investigated for times up to 6 8 years dissolution was observed to be incongruent with respect to 238u and 232th as well as their radiogenic daughters 234u 230th and 228th leaching was divided into a very rapid initial stage lasting a few hours and a slower process active for the remaining time the initial stage was modeled as the sum of a contribution from a mechanico chemically damaged portion of the specimen which did not exhibit isotopic selectivity in leach properties and a contribution from the selective removal of recoil daughter products from their recoil tracks in the surface of the otherwise undamaged bulk mineral the latter effect is greater for short lived 228th compared to long lived 234u a correlation between the magnitude of the effect and the half life of the radiogenic nuclide suggests an upper limit of 106 years for the timescale of natural track annealing after the initial dissolution stage insoluble precipitates of the intermediate product in the th chain 228ra provide a supplementary source of 228th by radioactive decay contributions to these precipitates come from dissolution released and recoil released 228ra this source is manifest as large apparent release rates of 228th which begin after several weeks of leaching preannealing of a specimen at 800 c depresses the elemental th leach rate but enhances the amount of 228th232th fractionation this enhancement is associated with rejection of ra from the mineral during annealing of recoil damage

eocene stratigraphy of the north sea basin abstract the eocene of the north sea basin has been divided into five stratigraphic sequences named the dornoch balder frigg alba and grid the palaeocene eocene boundary lies at the base of the dornoch sequence whereas the grid extends into the lower oligocene the sequences display consistent and predictable patterns on electric log data and are bounded by high gamma log peaks which mark thin condensed claystone sections the sequences have been calibrated using a detailed dinocyst zonation that recognizes a succession of 30 biovents it can be shown that individual sequence boundaries consistently fall within the same dinocyst subzone giving a high degree of confidence that these boundaries represent time lines the sequences can be mapped over the whole of the north sea basin retaining their internal character from quadrant 3 in the north to quadrants 21 and 22 in the south a distance of 400 km the high gamma peaks marking the sequence boundaries are interpreted as surfaces of maximum condensation that record the effect of greatly reduced sediment input into the basin these surfaces are believed to have a variety of origins including eustatic sea level rise changes in sediment supply to the basin and changes in rates of tectonic subsidence or uplift

seismic geomorphology and sequence stratigraphy as tools for the prediction of reservoir facies distribution an example from the paleocene and earliest eocene of the south buchan graben outer moray firth basin ukcs

the occurrence of the dinoflagellate cyst apectodinium costa downie 1976 lentin williams 1977 in the moray and montrose groups danian to thanetian of the uk central north sea

the paleocene of antarctica dinoflagellate cyst biostratigraphy chronostratigraphy and implications for the palaeo pacific margin of gondwana abstract the paleocene 66 56 ma was a critical time interval for understanding recovery from mass extinction in high palaeolatitudes when global climate was warmer than today a unique sedimentary succession from seymour island antarctic peninsula provides key reference material from this important phase of the early cenozoic dinoflagellate cyst data from a 376 m thick stratigraphical section including the cretaceous paleogene boundary is correlated with biozones from new zealand the east tasman plateau and southeastern australia a detailed age model is suggested for the lopez de bertodano ldbf and sobral sf formations based on dinoflagellate cyst biostratigraphy and u pb dating of zircons supported by correlated magnetostratigraphy and strontium isotope values from macrofossils the top of the ldbf is confirmed as latest maastrichtian to earliest danian 66 2 65 65 ma in age the overlying sf is mostly danian in age with an inferred hiatus near the top overlain by sediments dated as late thanetian rare apectodinium homomorphum first appear in the uppermost sf the earliest in situ record from antarctica the distribution of marine and terrestrial fossils from uppermost cretaceous to eocene sediments in patagonia antarctica new zealand and australia required both sea and land connections between these fragments of gondwana fossil evidence and reconstructions of antarctic palaeogeography and palaeotopography reveal evidence for persistent embayments in the proto weddell and ross sea regions at this time we conclude that a coastal dispersal route along the palaeo pacific margin of gondwana could explain the fossil distribution without requiring a transantarctic strait or closely spaced archipelago a region in the west to east antarctic boundary zone elevated until the early paleogene perhaps acted as a site for high elevation ice caps this supports fossil geochemical and sedimentological evidence for cold climate intervals and significant sea level falls during the maastrichtian and paleocene

a plume model of transient diachronous uplift at the earth s surface convection in the earth s mantle appears to be strongly time dependent on geological time scales however we lack direct observations which would help constrain the temporal variation of convection on timescales of 1 10 ma recently it has been demonstrated that transient uplift events punctuated the otherwise uniform thermal subsidence of sedimentary basins which fringe the icelandic plume in the faroeshetland basin three dimensional seismic reflection surveys calibrated by well logs have been used to reconstruct a 55 million year old transient event the minimum amount of uplift is 490 m which grew and decayed within 2 ma this event has also been mapped 400 km further east in the north sea basin where peak uplift with an amplitude of 300 m occurred 0 3 1 6 ma later neither observation can be explained by glacio eustatic sea level changes or by crustal shortening we describe a simple fluid dynamical model which accounts for these transient and diachronous observations in this model we assume that the icelandic plume was already in existence and that it had an axisymmetric geometry in which hot e g 1400 c asthenospheric material flows away from a central conduit within a horizontal layer a transient temperature anomaly introduced at the plume center flows outward as an expanding annulus its geometry is calculated using radial flow between two parallel plates with a poiseuille cross stream velocity profile the expanding annulus of hot asthenosphere generates transient isostatic uplift at the earth s surface stratigraphic observations from both basins can be accounted for using a plume flux of 1 3 10 8 km 3 ma 1 for a layer thickness of 100 km plume flux is broadly consistent with that required to account for neogene 0 20 ma v shaped ridges south of iceland although our transient temperature anomalies are larger we suspect that the stratigraphic expression of transient convective behaviour is common and that a careful examination of appropriate records could yield important insights

long term sea level fluctuations driven by ocean basin dynamics earth9s long term sea level history is characterized by widespread continental flooding in the cretaceous period 145 to 65 million years ago followed by gradual regression of inland seas however published estimates of the late cretaceous sea level high differ by half an order of magnitude from 40 to 250 meters above the present level the low estimate is based on the stratigraphy of the new jersey margin by assimilating marine geophysical data into reconstructions of ancient ocean basins we model a late cretaceous sea level that is 170 85 to 270 meters higher than it is today we use a mantle convection model to suggest that new jersey subsided by 105 to 180 meters in the past 70 million years because of north america9s westward passage over the subducted farallon plate this mechanism reconciles new jersey margin based sea level estimates with ocean basin reconstructions

transient convective uplift of an ancient buried landscape sedimentary basins in the north atlantic ocean preserve a record of intermittent uplift during cenozoic times1 these variations in elevation are thought to result from temperature changes within the underlying icelandic mantle plume2 when parts of the european continental shelf were episodically lifted above sea level new landscapes were carved by erosion but these landscapes then subsided and were buried beneath marine sediments3 here we use three dimensional seismic data to reconstruct one of these ancient landscapes that formed off the northwest coast of europe during the palaeocene eocene thermal maximum we identify a drainage network within the landscape and by modelling the profiles of individual rivers within this network we reconstruct the history of surface uplift we show that the landscape was lifted above sea level in a series of three discrete steps of 200 400 m each after about 1 million years of subaerial exposure this landscape was reburied we use the magnitude and duration of uplift to constrain the temperature and velocity of a mantle plume anomaly that drove landscape formation we conclude that pulses of hot chemically depleted mantle material spread out radially beneath the lithospheric plate at velocities of 35 cm yr 1

control of regional sea level by surface uplift and subsidence caused by magmatic underplating of earth s crust magmatic underplating of the crust is a common feature of major basalt provinces the emplacement of magma within the lithosphere leads to surface uplift with a magnitude of the order of 10 of the thickness of the underplated material the composition of associated igneous rock samples suggests that much of the underplated material is made of gabbro this gabbro is denser than the magma from which it crystallizes so uplift of earth s surface caused by the emplacement of magma at the crust mantle boundary must be followed by subsidence as the magma solidifies this subsidence is equal to approximately half the original uplift and takes place within 0 1 m y of injection of the magma the association of magmatic underplating with surface uplift followed by subsidence provides a mechanism for changes of sea level including previously unexplained episodic highstands of sea level

high resolution biostratigraphic zonation for the uk central north sea paleocene abstract this paper presents the high resolution biostratigraphic zonation scheme for the paleocene of the central north sea area uk and the application to formation characterization well correlation reservoir modelling and wellsite activities the scheme is developed from detailed and consistently recorded palynological events supported by microfossil data which have been applied successfully to the majority of proprietary biostratigraphic studies from the basin nine zones and 29 subzones have been defined based on first downhole occurrence fdo or abundance events with chronostratigraphic significance and can be consistently correlated across the studied area the nine biozones are described based on a dominant palynological marker from base upward senoniasphaera inornata and spiniferites magnificus danian isabelidinium viborgense and palaeoperidinium pyrophorum selandian cordosphaeridium gracile spiniferites fentonii spiniferites rhomboideus areoligera gippingensis and base apectodinium spp thanetian the defined bioevents have been consistently linked with the published lithostratigraphy stratigraphic sequences and interpreted depositional environments

stratigraphic and spatial distribution of palynomorphs in deep water turbidites a meta data study from the uk central north sea paleogene abstract the paleogene sele formation spans across the basinal areas of the uk central north sea and comprises a very laterally extensive deep marine fan system namely the forties sandstone member a very important oil and gas reservoir horizon the development of this turbidite system across the basin floor resulted from the response to sea level changes and fluctuating sediment yield from the continental landmass influenced by hinterland uplift and climate in order to understand the distribution of terrestrially sourced and marine palynomorphs in this depositional system comprising stacked turbidite flows statistical analyses of palynology data from 41 wells have been conducted these statistical studies support the division of the microplankton into nine groups clustering taxa depending on their ecology and taphonomy it is observed that the palynological assemblages are influenced by sediment provenance across the turbidite fans the landmass vegetation ecology and the marine microplankton populations varying across the basin the dominant derived cluster groups b peridinioids dominated by apectodinium species and e probably autotrophic gonyaulacoids comprise about 70 of the taxa recorded these dinoflagellates bloomed as a result of low salinity surface waters and an increase in water mass eutrophication resulting from the greenhouse climate optimal conditions of the petm the pollen and spore data although challenging to interpret due to the varied quality of the data set supports the interplay of a coastal wetland vegetation on extensive marginal delta systems with associated wetland and swamp environments

a model for late quaternary methane ice core signals wetlands versus a shallow marine source 1 a three reservoir model with first order kinetics for methane records in the vostok antarctica and gisp2 greenland ice cores reproduces the sawtooth pattern and the maximum and minimum concentrations the model also returns an atmospheric methane relaxation time of 10 years for both cores which is the same as current estimates the characteristics of the source reservoirs are long relaxation times 33 3 and 100 ky and high initial methane concentrations 2500 and 7000 ppm for gisp2 and vostok respectively these characteristics are consistent with gas hydrate sources in shallow marine sediments but not with wetland sources which have insufficient storage capacity and low source strength

palaeocene biostratigraphy and sequence stratigraphy of the uk central north sea abstract the palaeocene of the central north sea can be divided into four stratigraphic sequences named the ekofisk maureen lista and forties these sequences display consistent and predictable patterns on electric log data and are bounded by high gamma log peaks which represent thin condensed mudstones five additional subsequences are recognized within the lista sequence biostratigraphic analysis has enabled the palaeocene to be divided into six dinocyst zones and 11 subzones based on last occurrence or last abundance events that are considered to have chronostratigraphic significance across the north sea basin the dinocyst zonation has been integrated with bioevents based on other microfossil groups and correlated with onshore nw european sections permitting calibration with the standard worldwide nannoplankton and planktonic foraminiferal zones these bioevents display a consistent relationship with the stratigraphic sequences allowing the construction of a confident stratigraphic framework for the palaeocene

phanerozoic transgressions and regressions on the continents a quantitative approach based on areas flooded by the sea and areas of marine and continental deposition

palaeoenvironmental changes at col des tribes montagne noire france a reference section for the famennian of north gondwana related areas we present detailed biostratigraphy based on conodonts and palaeoenvironmental trends deduced from microfacies and conodont abundance through the famennian late devonian at col des tribes montagne noire france the succession is characterized by micritic limestones deposited in settings oscillating between mid to outer ramp facies contain poor fauna widely dominated by nektonic organisms this section is complete and one of the most conodont rich for the famennian of the north gondwana related area the upper kellwasser event frasnian famennian boundary and the hangenberg devonian carboniferous boundary have been lithologically identified they are characterized by decimetre thick black dysoxic to anoxic argillaceous sediments the condroz and annulata events although not materialized by lithological changes have been positioned due to the precise stratigraphy the first event occurred during the deposition of condensed ferruginous facies griotte limestones and the second event during the deposition of micrites barren of benthic fauna the combination of information from both facies and conodont biofacies changes allows a general sea level curve through the entire famennian for north gondwana to be proposed for the first time at col des tribes the general trend is a slight deepening upwards from triangularis to trachytera zones then a pronounced shallowing upwards trend from upper trachytera to praesulcata zones this curve correlates with the well known reference curve from euramerica concerning the late famennian trachytera to praesulcata zones there are some discrepancies in minor cycles which can be explained by tectonical phenomena at the onset of the edification of the variscan belt in europe

palaeocene uplift and subsidence events in the scotland shetland and north sea region and their relationship to the iceland plume this paper documents stratigraphic evidence for palaeocene uplift and subsidence events in the scotland shetland and north sea region and considers whether these were generated by the initiating iceland plume the palaeocene succession in the north sea contains two types of stratigraphic surface the high gamma mudstone represents a maximum flooding event associated with marine transgression the unconformity surface is overlain by sandstone reworked chalk or tuff and represents submarine or subaerial erosion and missing section biostratigraphic dating allows these surfaces to be correlated throughout the basin where they occur within a suite of shelf slope and basinal sedimentary rocks at least 14 short duration 0 1 0 3 ma unconformity maximum flooding couplets are recognized within the danian to lowest ypresian interval which lasted from 65 to 54 ma these uplift subsidence cycles may have been caused by episodic plume related magmatic injection near the moho and associated fluctuations in dynamic support alternatively the short term cycles may reflect a eustatic control regional mapping of the 14 events is required to confirm the relative importance of plume related and eustatic events

stable isotope paleoclimatology of brine inclusions in halite modeling and application to searles lake california abstract the isotopic composition of brine inclusions in halite can be used as paleohydrologic and paleoclimatic indicators in arid environments for this purpose steady state isotopic models of the brine inclusions in halite were developed for three hydrologic regimes the evaporation pan terminal lake and through flow lake or strait exchange sea the model calculations predict that the steady state isotopic compositions are sensitive to the hydrologic regime to the normalized relative humidity and to the isotopic compositions of atmospheric water vapor and inflow water short term fluctuations of the isotopic parameters in the steady state equations are not important and in general only the long term mean values are recorded in the brine inclusions in halite modern and old up to 1 95 ma samples of nonmarine halite from searles lake california were analyzed for the chemical and isotopic compositions of the brine inclusions from the modern surface halite the isotopic composition of the atmospheric water probably of the winter time and the probable seasons when the halite samples were deposited were obtained from brine inclusions of the 1 3 ma halite the annual mean isotopic compositions of atmospheric water vapor and inflow water were calculated using the steady state terminal lake model the calculated isotopic composition of the 1 3 ma inflow water shows a d enrichment of about 60 compared to the modern counterpart the amount of this d enrichment is similar to that found from the calcite veins at the spring mountain in nevada wionograd et al 1985 which was attributed to the effect of the orogeny of the sierra nevada the chemical composition of the brine inclusions indicates that the owens river was more enriched in hco 3 co 3 2 10 000 and 28 000 a ago than at present probably due to larger contribution of long valley caldera hot spring waters

depth estimation from the scaling power spectrum of potential fields summary depth estimation from potential field power spectra requires a realistic assumption of the statistical properties of the source distributions density and susceptibility distributions in the earth s crust exhibit a long range dependence which is adequately described by scaling random fields with a spectral density proportional to some power of the wavenumber the theoretical power spectrum for a half space model of scaling sources explains the shape of observed power spectra of real potential field data very well minimizing the misfit between the model and the observed power spectrum yields an estimate for the depth to the top of the sources after demonstrating this approach on synthetic magnetic data we reinterpret power spectra of gravity and aeromagnetic data from utah hawaii and saskatchewan finding depth values that differ significantly from earlier interpretations all three power spectra are best explained by source distributions starting at surface level even the power spectrum from an aeromagnetic survey of a sedimentary basin with virtually non magnetic basin fill in the latter case a priori information on the intensity and the scaling exponent of the field caused by the basement had to be included to obtain an approximate estimate of the basin depth in general potential field power spectra are dominated by scaling properties of their source distributions and contain only limited depth information

a critical analysis of the structure and tectonic significance of rift oblique lineaments transfer zones in the mesozoic cenozoic succession of the faroe shetland basin ne atlantic margin abstract nw se trending rift oblique lineaments transfer zones9 occur along the length of the ne atlantic margin previous workers have suggested that these lineaments played an important role in providing conduits and or barriers to sedimentation during the cretaceous and palaeocene it has also been suggested that they were active as discrete basin wide strike slip faults this study uses a well calibrated 3d seismic survey of regional extent to critically assess the structural and stratigraphic evidence for three rift oblique lineaments in the uk sector of the faroe shetland basin victory clair and judd lineaments structures previously attributed to basin wide strike slip deformation can be more simply explained as igneous intrusions hydrothermal vent complexes gas chimneys and or faults that transfer extensional strain between en echelon rift segments there is little evidence to suggest that activity along discrete basin wide lineaments controlled palaeocene sedimentation within the faroe shetland basin rather sediment transport and deposition at this time are likely to have been controlled by along and across strike variations in the magnitude of thermal subsidence which in turn reflect the 3d nature of the underlying mesozoic rift architecture

geochemical mass balances and weathering rates in forested watersheds of the southern blue ridge ii effects of botanical uptake terms abstract geochemical mass balance methods are commonly used in small watershed studies to estimate rates of primary mineral weathering and soil formation and the contribution of these processes to cation budgets nutrient cycling and landscape susceptibility to acid deposition many researchers employ the balance sheet approach a system of simultaneous linear equations with constant coefficients which represent the steady state behavior of the modelled system most workers also assume that the steady state assumption for the entire system means that botanical factors can be ignored in other words that there is no net elemental transfer between biomass and inorganic compartments of the system however the widely invoked assumption that biomass is at steady state is mathematically a second explicit assumption not a built in mathematical consequence of the assumption of overall steady state the common assumption that the biomass is necessarily at steady state in a steady state system ignores the possibility of uptake of elements into the forest biomass to quantify the implications of the separate mathematical assumptions weathering rates for seven forested watersheds in the southern blue ridge mountains are calculated twice once allowing for net element exchange with biomass and once assuming no net exchange with biomass our calculations show that misunderstanding the mathematical constraints which are built into the most widely used geochemical mass balance equations commonly causes errors underestimates of up to a factor of 4 in the calculated rates of mineral weathering and soil formation this problem is most pronounced for minerals which contain major nutrient elements and for rates calculated from mass balances of those nutrient elements

palaeoenvironmental changes across the danian selandian boundary in the north sea basin abstract the danian selandian boundary 60 ma marks the cessation of 40 million years of carbonate deposition in the north sea basin and a shift to siliciclastic deposition on the basis of variations in lithology benthic and planktonic foraminifera and calcareous nannofossils in three cores from storebaelt in the eastern part of the north sea basin we have reconstructed the palaeoenvironmental changes across the boundary the benthic foraminiferal faunas belong to the midway type fauna they are extremely rich and more than 260 taxa have been recognized q mode cluster analysis groups the benthic assemblages into four biofacies which correspond fairly closely to lithological units correlation of the storebaelt records with marine palaeorecords from the danish basin and the north sea basin indicate that the transformation of the north sea from a carbonate to a siliciclastic basin occurred in four steps separated by relatively long stable periods the most important external factors involved in the change are firstly a drop in the relative sea level during the late danian leading to the disappearance of bryozoans from the north sea basin and to non deposition and erosion in many areas secondly coinciding with the danian selandian boundary an uplift of the scotland shetland area resulting in a massive input of siliciclastic deposits to the north sea basin thirdly during the early selandian inversion of the sorgenfrei tornquist zone and mesozoic basins in the southern and eastern part of the north sea basin resulted in a huge influx of reworked cretaceous chalk and an almost complete stop of carbonate production finally later in the early selandian in connection to a general sea level rise and a reduction in the gateway between the north sea basin and the tethys sea the sea bottom conditions became colder and more acidic this resulted in partial dissolution of the carbonates and the deposition shifted from marl to clay comparison with records from the western pyrenees the nile basin and the eastern north america suggests that sea level changes across the danian selandian boundary are primarily of eustatic nature

discrimination of local and global effects on upper mississippian stratigraphy illinois basin u s a abstract interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics eustasy tides and climate on upper mississippian middle chesterian stratigraphy in the tectonically active tide dominated illinois basin the cross sections show that five mixed carbonate siliciclastic high frequency sequences in the bethel through glen dean formations can be correlated around the outcrop belt through areas with very different subsidence histories the sequence boundaries are marked by paleosols and incised valleys and can be correlated basin wide within a framework of distinctive marker beds because of its updip position lowstand systems tracts are not preserved in the illinois basin the transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open marine skeletal limestone shallow marine shale and heterolithic siliciclastic tidal flat deposits the maximum flooding surface mfs for the sequences is picked at the base of the deepest water limestone facies highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal flat facies the basin wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea level changes rather than local tectonics or autogenic processes the sequences were likely produced by moderate to high amplitude 30 100 m fourth order 400 ky glacio eustatic sea level changes driven by the transition from the greenhouse conditions of the early mississippian to the icehouse conditions of the late paleozoic the lateral extent and frequency of component parasequences suggests that they were likely produced by fifth order sea level changes 10 100 ky the sequences may be bundled into third order composite sequences but the third order signal is obscured by the magnitude of the fourth order sea level changes a feature typical of ice house stratigraphies the sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the cincinnati arch and the more rapidly subsiding basin interior episodes of high and low differential subsidence occurred every two to three sequences these subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences the occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the appalachian orogenic belt to the east even in this tectonically active setting however it is the eustatic signal that generates basin wide mappable stratigraphic sequences

oscillatory silicon and aluminum aqueous concentrations during experimental aluminosilicate weathering abstract granodiorite amphibolite and feldspar samples were dissolved in acidic neutral and basic solutions under ambient conditions as laboratory batch experiments oscillations of silicon and aluminium concentrations in leaching solutions during long term weathering of aluminosilicates have been observed a simple kinetic nonlinear model based on polymerization of soluble aluminosilicate is proposed to explain the oscillatory behavior

microfossil biostratigraphy of the palaeogene succession in the davis strait offshore west greenland abstract a new microfossil based biostratigraphy of the paleocene and lower eocene sediments of the hellefisk 1 ikermiut 1 kang miut 1 nukik 1 and nukik 2 boreholes offshore west greenland has been established in general the five boreholes contain fairly well preserved diverse microfossil faunas and floras consisting mainly of foraminifera radiolaria ostracods and diatoms the studied interval was subdivided into three foraminiferid biostratigraphic intervals in ascending stratigraphic order the stensioeina beccariiformis praeglobobulimina ovata and pseudohastigerina wilcoxensis intervals and five biostratigraphic intervals based on additional microfossil groups the thalassiosiropsis wittiana fenestrella antiqua coscinodiscus morsianus ostracod aulacodiscus hirtus and cenodiscus cenosphaera intervals the intervals are more easily recognised in the two basinal boreholes ikermiut 1 and kang miut 1 than in the three more nearshore boreholes nukik 1 nukik 2 and hellefisk 1 due to a higher microfossil diversity and abundance

us gulf coast vegetation dynamics during the latest palaeocene abstract pollen and spore floras from the bear creek section in western alabama us gulf coast record vegetation events from the lower to middle tuscahoma formation late palaeocene mid np9 sporomorphs are abundant and well preserved in these sediments and are used as a proxy to record vegetation change over time we present results from both palynofloral and clay mineral analyses in the interval approximately 0 4 0 1 my before the paleocene eocene thermal maximum petm a period of transient and intense global warming that had a profound effect on animal and plant groups in high latitudes an important factor that has a significant bearing on our understanding of turnover across the petm is that of climate environmental stability prior to the petm in terrestrial ecosystems palynological analysis with a between sample resolution of 4 10 5 yr clay mineral suites show the dominance of smectite and illite throughout the studied section with minor fluctuations in the abundance of kaolinite ranging from 2 to 10 that indicates a high seasonality of precipitation throughout our studied section the exact stratigraphic position of the petm is unknown on the us gulf coast but data from existing publications suggests there is little change in the vegetation type across the palaeocene eocene boundary with no major immigration or turnover events dinocysts are restricted in both diversity and occurrence but apectodinium homomorphum is present with 30 abundance throughout the studied section and provides some evidence that the apectodinium acme is not correlative with the petm at middle latitudes

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

aqueous geochemistry on early mars abstract a geochemical cycle model is presented for the interaction between the atmosphere hydrosphere and regolith of mars it was developed to study how this interaction might have produced the present martian environment from a primitive martian environment much like that of the primitive earth the model is a simple system consisting of an unweathered starting material calcium bearing and magnesium bearing silicates a co 2 atmosphere an ocean of water in contact with both the atmosphere and the unweathering starting material and both calcite and dolomite precipitates several interesting points arise from this model a 1 bar co 2 atmosphere can be removed by carbonate precipitation alone in about half a billion years this is roughly fifty times longer than earlier estimates which were not based on time varying models fanale et al 1982 carr 1986 pollack et al 1987 one of the chief problems in martian geology has been how to explain the large number and wide variety of surface features that were apparently formed by aqueous erosion this longer atmospheric lifetime may be enough to explain the large number of channels seen on older martian terrain if the atmosphere started out with more than 1 bar of co 2 it would take correspondingly longer to remove it if there should be no other means to remove co 2 from the atmosphere this long time constant would indicate that the atmosphere could never have contained more than a few bars of co 2 or else there would still be remnants present today the increase in alkalinity of the ocean as the atmosphere disappears even without the effects of reduction in the amount of water available indicates that evaporite deposits may have formed on mars if these deposits are still present they may even yet contain some liquid water

potential field power spectrum inversion for scaling geology we propose a method for inverting the power spectrum of gravity and magnetic data the method is demonstrated on aeromagnetic and bore well data from the german continental deep drilling project ktb density and susceptibility distributions in the earth s crust exhibit scaling behavior with power spectra proportional to f where f is the wavenumber and is the scaling exponent of the source distribution we model the sources of the potential field by a random function with scaling properties defined on a half space with its top at a specified depth beneath the observation plane comparing the theoretical power spectrum for this model with the power spectrum of the measured data we obtain the best values for the depth to source and the scaling exponent as a global minimum of the misfit function despite the simplicity of the model it offers a new understanding of the factors influencing the shape of the potential field power spectrum in particular the low wavenumber part of the power spectrum can be dominated by the scaling properties of the source distribution and not by the depth to some kind of basement the scaling exponent of the field varies with the type of surface geology the question of whether the scaling exponent can actually be used to identify different types of geology gives an interesting new aspect to power spectrum inversion

a high resolution north sea eocene dinocyst zonation abundant dinoflagellate cysts dinocysts from eocene strata of the north sea exhibit a consistent succession of events based on the analysis of 120 wells from quadrant 3 in the north to quadrants 21 and 22 in the south these events have a constant relationship with stratigraphic sequences and subsequences throughout the area eight eocene dinocyst zones and 23 subzones and the uppermost palaeocene apectodinium augustum biozone are defined by last occurrence or abundance events the north sea dinocyst succession is similar to that in denmark northwest germany belgium the netherlands and southern england permitting correlation with calcareous nannoplankton zones for sections in these areas and hence allowing correlation of north sea stratigraphy with northwest european and worldwide events

west of shetland revisited the search for stratigraphic traps the west of shetland area has scope for the stratigraphic entrapment of hydrocarbons at various jurassic to palaeogene stratigraphic levels mapping and identification of such traps requires a fundamental understanding of the regional geology the study of analogues and source kitchens and a thorough approach to trap validation since 1982 47 exploration wells have been positioned on paleocene prospects with a significant stratigraphic component but few have found hydrocarbons many failing as a result of poor trap definition and overconfidence in the predictive use of amplitude anomalies hydrocarbon sourcing of many of the failed prospects was also poorly constrained few amplitude related stratigraphic features could be tied with confidence to a viable source kitchen the presence of a regional seal is a prerequisite ingredient for a successful paleocene play many remaining undrilled subtle prospects rely on a stratigraphic trapping component and high quality 3d seismic data are seen as an essential search tool examples of undrilled prospects are presented from the paleocene of the northern faroe shetland basin and the mesozoic of the east solan basin and corona ridge

regional uplift gas hydrate dissociation and the origins of the paleocene eocene thermal maximum much of the north atlantic region experienced hundreds of metres of transient uplift during the latest paleocene regional uplift should cause dissociation of gas hydrates stored in marine sedimentary strata and the subsequent release of carbon to the atmosphere should enhance warming through the greenhouse effect we have developed models of the spatial distribution of uplift to match observational constraints from sedimentary basins fringing the north atlantic in order to provide quantitative estimates of the carbon released upon uplift these models are coupled to a simple parameterisation of carbon storage in sub seafloor gas hydrates results of modelling indicate that large quantities of carbon can be released by uplift with some models generating over 2000 gt of carbon release the possibility that latest paleocene regional uplift occurred over the same time interval as onset of the paleocene eocene thermal maximum petm around 30 kyr cannot be ruled out using current stratigraphical observations or mantle convection models in this case the uplift mechanism alone can account for the magnitude and timing of the carbon isotope excursion associated with the petm alternatively if the duration of latest paleocene uplift was closer to the upper bound of around 1 myr or if other paleocene uplift events were equally significant then gas hydrate dissociation upon uplift could have contributed to longer term changes in ocean temperature and carbon isotope composition through the late paleocene these temperature changes in combination with development of the north atlantic land bridge during the latest paleocene culmination of uplift may be able to force rapid changes in ocean circulation and cause phenomena such as the petm

architecture and evolution of calciclastic marginal slope fans of the ordovician carbonate platform in the yijianfang outcrop of the bachu area west tarim basin the ordovician carbonate platform at the yijianfang outcrop of the bachu uplift region in the western tarim basin contains four types of genetic facies associations developed in the calciclastic slope fan depositional system an olistostrome zone fan channels lobes and a marginal slope the olistostrome zone is characterized by olistoliths and slump fans whereas the fan channels and lobes are further divided into proximal and distal facies the marginal slope deposits constitute the background sedimentation in which the calciclastic slope fans are intercalated from proximal to distal parts of the fan channels and lobes their scale gradually becomes smaller and the size and sorting of grains become finer and better respectively analysis of the stratigraphic framework indicates that the fans formed in the lower strata of the upper ordovician lianglitage formation in four high frequency sequences i e pss1 pss4 field paleocurrent measurements indicate northeast southwest depositional strike for the early platform margin of the lianglitage formation sediments in the calciclastic slope fans were derived from the platform margin and evolution of the calciclastic slope fans was generally progradational from pss1 to pss2 and then continuously retrogradational from pss2 to pss4 the calciclastic slope fans in the outcrop area are not reservoir prone rocks but interpretation on these fans can provide useful information about potential hydrocarbon reservoirs along the platform margin the p wave velocity s wave velocity and density variations in each genetic facies may be used to identify the subsurface calciclastic slope fan depositional system

dinoflagellate based sea surface temperature reconstructions across the cretaceous tertiary boundary abstract quantitative analysis of organic walled dinoflagellate cyst dinocyst assemblages from closely spaced samples across the cretaceous tertiary boundary ktb at el kef nw tunisia caravaca se spain and stevns klint e denmark allows for reconstructions of sea surface temperature sst trends the combined dinocyst based sst curves indicate relatively stable warm conditions during the latest maastrichtian in contrast to strongly fluctuating and on average cooler conditions during the earliest danian in detail the results indicate cooling across the ktb immediately followed by an interval of pronounced warming the latter recorded in all studied sections two more cooling pulses may be recognized in the overlying interval followed by a gradual return to stable relatively warm conditions our data furthermore show that these ktb related climatic changes invoked distinct migration among organic walled cyst producing dinoflagellates a group not pushed to extinction at the ktb recordable in both hemispheres recent models predict periods varying between several months to 8 13 yr of global cooling impact winter and reduced solar transmission as a direct result of the chicxulub ktb impact followed by relatively long term excess co 2 related global warming our results are in line with such models but suggest that the impact related cooling phase may have lasted longer and that marked climatic instability continued to some 100 000 yrs following the ktb event s

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

geochemistry of high ph waters from serpentinites of the gruppo di voltri genova italy and reaction path modeling of co2 sequestration in serpentinite aquifers abstract the large number of geochemical data gathered on the gruppo di voltri springs confirm that progressive interaction of meteoric waters with ultramafic rocks variably affected by serpentinization leads initially to the formation of mg hco3 waters when the system is open to co2 and na hco3 and ca oh type water upon further interaction with the rock under highly reducing closed system conditions with respect to co2 as indicated by 3h data these high ph waters have had long residence times underground in deep aquifers hosted by serpentinitic rocks these waters are the only available evidence of the presence of such deep aquifers high pressure injection of co2 into these deep aquifers was simulated by reaction path modeling results indicate that this is a feasible methodology to reduce the inputs of anthropogenic co2 into the atmosphere serpentinitic rocks have a high capacity for co2 sequestration mainly through formation of carbonate minerals dissolution of serpentinitic rocks and precipitation of magnesite and silica minerals occurs naturally in areas of high terrestrial co2 fluxes such as in southern tuscany corroborating the feasibility of this methodology of co2 sequestration however this process causes a progressive decrease in the porosity of the aquifer at least under closed system conditions these side effects must be carefully evaluated by means of further laboratory tests and field activities

quantifying transient mantle convective uplift an example from the faroe shetland basin the icelandic mantle plume generated maximum uplift in early paleogene times the faroe shetland basin which fringes the north atlantic margin of europe was close to the center of early paleogene icelandic plume activity three dimensional seismic reflection data from the faroe shetland basin reveal sedimentary geometries that allow a phase of transient uplift to be accurately reconstructed and quantified close to the paleocene eocene boundary circa 56 ma rapid uplift resulted in fluvial incision into marine sediments this unconformity was buried by nonmarine sediments recording the decay of transient uplift relief on the unconformity was 550 m constraining the minimum amount of surface uplift some 60 m of this uplift can be attributed to the isostatic response to erosional unloading tectonic uplift of over 490 m peaked and decayed within 3 ma rates of water loaded tectonic subsidence following peak uplift are several times greater than maximum expected postrift subsidence rates the amplitude and duration of this transient effect is best explained by a mantle convective phenomenon we suggest that a region of hot plume material flowed laterally beneath the lithosphere producing transient uplift which decayed when plume material was advected farther away our analysis suggests that under certain circumstances stratigraphic records can yield valuable quantitative information about aspects of mantle convective circulation

lower palaeozoic unconformities in an intracratonic platform setting glacial erosion versus tectonics in the eastern murzuq basin southern libya the stratigraphic record of the eastern murzuq basin has been importantly influenced by deformation resulting in angular and or deeply erosional unconformities though the overall context is intracratonic major transgressive events and the ordovician glaciation are nevertheless documented allowing the delineation of tectonic eustasy or climate driven unconformities lower palaeozoic key events and related unconformities that characterize the north gondwana platform have therefore a signature in the eastern murzuq basin the basement cover unconformity also known as the infra tassilian surface truncates all the deformed and metamorphosed lower cambrian and older rocks above is a middle cambrian to lower ordovician megasequence murizidie and hasawnah fms which is in turn truncated by an intra ordovician angular unconformity this megasequence is unconformably overlain by a middle ordovician hawaz fm to silurian tanzzuft and akakus fms megasequence which includes the upper ordovician glaciogenic unit mamuniyat fm bounded at the base by a polygenic glacial erosion surface showing corrugated glacial lineations tillites and glaciotectonic structures the middle ordovician to silurian megasequence is finally truncated by a base devonian angular unconformity overlain by fluvial sandstones regarding the possibility that those fluvial deposits may be as younger as late devonian in the eastern murzuq basin based on palaeoflora the so called caledonian unconformity might be here a much younger mid eifelian surface and the occurrence of the lower devonian tadrart fm is questioned the upper ordovician glacial erosion surface which is sometimes referred to as the taconic unconformity usually truncates middle ordovician strata in the murzuq basin but reaches significantly deeper stratigraphic levels in places that have been previously involved in the intra ordovician deformation event in the murizidie southeastern murzuq basin the infra tassilian surface the intra ordovician unconformity and the upper ordovician glacial erosion surface amalgamate together here an estimate of the glacial erosion depth cannot be derived from the stratigraphic hiatus beneath the glacial incision the main part of which relate to the intra ordovician tectonic event the upper ordovician climate related glacial erosion surface is not a valid unconformity for a sequence hierarchy framework of the lower palaeozoic although it presents most of the physical attributes of tectonic driven unconformities

high frequency eustatic sea level changes during the middle to early late ordovician of southern jordan indirect evidence for a darriwilian ice age in gondwana abstract the middle to early late ordovician hiswah and dubaydib formations in southern jordan provide a well constrained sedimentary record of 4th and 3rd order relative sea level change along the northern tectonically quiescent subpolar gondwana continental margin cyclic deposition occurred on a wave and storm dominated microtidal shelf dominated by shoreface and offshore transition zone facies cycles are commonly bounded by amalgamated bounding surfaces sb ts or sb mfs and are characterised by stacked transgressive systems tracts tsts the small facies dislocation across key sequence bounding surfaces indicates a 15 50 m change in relative sea level fourth order sequences are hypothesized to be paced by the long eccentricity 405 kyr cycle and consequently 3rd order sequences are calculated to be 1 2 m y and 2 4 m y long these correlate with the global eustatic sea level curve in comparison with mesozoic and cenozoic sequence stratigraphical data we conclude that the 1 2 m y cycles correspond with long obliquity cycles predominant in icehouse conditions and the 2 4 m y cycles with the long eccentricity cycle predominant during greenhouse conditions we propose a darriwilian ice age during which orbitally induced cold snaps caused the expansion and amalgamation of small medium scale ice sheets the reduced size of the correlative positive carbon isotope excursion compared to that in the hirnantian may indicate that the darriwilian ice sheets only reached the sea in a few places the absence of glacio terrestrial deposits of middle ordovician age is most likely due to subsequent glacial erosion during repeated ice advances up to and including those in the hirnantian the existence of darriwilian ice sheets is consistent with zooplankton province distributions that indicate a polar front at 40 s during the ice age it is likely that polar ice existed throughout the ordovician

multiple sulfur isotope records at the end guadalupian permian at chaotian china implications for a role of bioturbation in the phanerozoic sulfur cycle abstract a recent study on quadruple sulfur isotopes 32s 33s 34s and 36s of sedimentary pyrite suggested that the end guadalupian extinction was caused by shoaling of the sulfidic deep water this scenario is based on the assumption that sulfur isotopic compositions of pyrite from hosting sediments were controlled by benthos activities thus by the redox conditions of the sedimentary environments nonetheless the relationship between the sulfur isotope records and redox conditions reconstructed from litho and bio facies are poorly known in order to examine the effect of bioturbation in sediments quadruple sulfur isotopic compositions of sedimentary pyrite from the end guadalupian succession in chaotian south china were analyzed black mudstones of deep water facies immediately below the extinction horizon have consistently high 33s values of ca 0 079 clearly suggesting a sulfate reduction in the anoxic water column our new data are consistent with the emergence of a sulfidic deep water mass prior to the end guadalupian extinction the upwelling of the toxic deep water may have contributed to the extinction in contrast shallow marine bioclastic limestones with burrows deposited under oxic conditions have negative 33s values this anomalous isotopic signal indicates the mixing of two distinct types of pyrite one generated during the sulfate reduction in an open system and the other in a closed system we interpret that bioturbation supplied sulfate in the sediments and promoted sulfate reduction and in situ sulfide precipitation within the sediments the negative 33s values of oxic sediments in chaotian are inconsistent with the previous model and demonstrate that the sedimentary sulfur cycle associated with bioturbation was more complicated than previously thought our study also implies that more generally the role of bioturbation in increasing seawater sulfate concentration in the phanerozoic may have been overestimated in the previous studies because bioturbation may have enhanced sulfide burial or sulfur output from the oceans

biostratigraphic evidence for evolving palaeoenvironments in the lower paleogene of the faeroe shetland basin the results of biostratigraphic analysis of the palaeocene to lower eocene section in four faeroe shetland basin wells are presented the succession of bioevents is shown to be the same as that documented for wells in the north sea evolution of microfossil assemblages within the basin reflects the change from an open marine setting in the danian to more restricted marine and non marine conditions in the late thanetian and early ypresian this change is accompanied by a number of microfossil extinctions that form useful regional biomarkers for the faeroe shetland and north sea basins these events include the extinction of planktonic foraminifera close to the danian selandian boundary and the extinction of dinocyst taxa palaeoperidinium pyrophorum and areoligera cf coronata at the selandian thanetian boundary within the thanetian section the extinction of areoligera coincides with an abrupt reduction in numbers and diversity of agglutinated foraminifera the thanetian ypresian boundary is marked by the extinction of apectodinium augustum well 208 19 1 lies in the marine northeastern part of the basin which was connected to the north sea by a narrow seaway however upper thanetian to lower ypresian biofacies become increasingly restricted when traced southwestwards along the basin axis with this interval being non marine in 204 24 1a

lower palaeogene stratigraphy of the northern north sea abstract the lower palaeogene stratigraphy of the northern north sea is described using wireline log and biostratigraphic data at group and formation level a close similarity can be shown with the stratigraphy defined in the outer moray firth area of the central north sea a two fold subdivision into the montrose and moray groups is recognized the montrose group consists of the maureen and lista formations while the succeeding moray group contains the sele balder dornoch and beauly formations the maureen and lista formations are dominantly argillaceous units that contain poorly defined sandstones the most laterally extensive of these is the heimdal member developed within the lista formation the dornoch and beauly formations are shelfal sandstone units that pass eastwards and northwards into the age equivalent dominantly argillaceous sele and balder formations the sele formation contains the hermod member while the balder formation contains the odin member these are massively developed sandstone units of very limited extent the lower palaeogene succession contains a number of high gamma log markers that are often associated with influxes of microfossils and microflora these are interpreted as condensed claystone horizons representing pauses in marine sedimentation during episodes of maximum transgression they can be correlated with similar marker horizons described from the outer moray firth area giving further confidence that the stratigraphy forms a regional framework that can be applied over the whole north sea area

three dimensional model of the koyna area of maharashtra state india based on the spectral analysis of aeromagnetic data the estimation of thickness of trap rocks in the earthquake affected koyna area is an important parameter for revealing the topography that existed before the deccan volcanism in the present work a case history is presented delineating a three dimensional block model for the koyna area by the spectral analysis of aeromagnetic data the thickness in the area was found to vary from 700 to 2200 m which correlates well with the results of other geophysical investigations

constraining paleo latitude of a biogeographic boundary in mid panthalassa fusuline province shift on the late guadalupian permian migrating seamount abstract the guadalupian paleo atoll limestone iwato formation in sw japan was primarily formed in low latitude mid panthalassa and was later tectonically accreted to south china japan margin during the jurassic the present biostratigraphic study clarified that the iwato formation consists of 5 biostratigraphical intervals i e four fusuline assemblage zones assemblage zones 1 to 4 and a barren interval on the top assemblage zones 1 to 4 correspond to the neoschwagerina craticulifera zone n margaritae zone yabeina globosa zone and lepidolina multiseptata zone of the conventional tethyan fusuline stratigraphy respectively the present study newly clarified the following significant aspects of paleobiogeography of the permian fusulines as to the extinction of large tested taxa in the latest guadalupian 1 the long unknown stratigraphic relationship was documented for the first time between the yabeina dominant interval and the overlying lepidolina dominant one within a single limestone unit 2 the occurrence of lepidolina cf kumaensis kanmera the unique last runner of large tested fusuine was detected for the first time in mid oceanic paleo atoll limestones 3 with respect to the northbound migration history of the paleo seamount capped by the iwato formation the development of the two coeval fusuline biogeographic territories in the low latitude panthalassa i e the yabeina territory on the south and the lepidolina territory on the north was confirmed 4 the paleo latitude of the biogeographic boundary between the yabeina and lepidolina territories is constrained around 12 in the southern hemisphere on the basis of the latest geomagnetic data from the same limestone this new approach utilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo latitude data is applicable to other cases in different time space co ordinates and of other fossil groups for constraining position of ancient biogeographic boundaries within lost oceanic domains of deep past

frasnian upper devonian integrated facies analysis magnetic susceptibility and sea level fluctuations in the nw algerian sahara changes in the palaeoenvironment are investigated in two representative frasnian sections of the nw algerian sahara integrating sedimentology and magnetic susceptibility ms the ben zireg section is characterized by condensed and ferruginous calcareous deposits in the south marhouma section the sedimentation rate is high dominated by muddy nodular limestones with several hypoxic shale intervals in both sections sediments were mostly emplaced on pelagic outer ramps below the limit of storm wave base evolving through time from proximal to distal setting investigations of the temporal evolution of facies and ms data permit a first estimate of the local sea level trends in nw algeria these trends match the overall long term rise of sea level recognized worldwide from frasnian zone 5 upwards noteable positive excursions of the sea level curve related to the semichatovae transgression as well as to the late frasnian transgression prior to the late kellwasser event can be established in this area although the sharp regression of sea level at the upper kellwasser level can be confirmed from our data no particular trend is depicted at the transition of conodont zones frasnian zones 12 13 where the presence of the lower kellwasser level has not yet been clearly recognized

amplitudes of late pennsylvanian glacioeustasy the late paleozoic is well documented as a time of significant continental glaciation but the extents of the glaciation and attendant glacioeustasy are not well constrained because precise amplitudes of eustasy are difficult to extract from the stratigraphic record in this paper we use preserved relief on ancient subaerial exposure surfaces of large algal bioherms to demonstrate directly that late pennsylvanian glacioeustasy reached minimum amplitudes of 80 m and probably exceeded 100 m upper paleozoic algal bioherms accreted predominantly during sea level falls but also during sea level rises and highstands and were capable of remarkably rapid growth rates eustatic amplitudes in excess of 100 m approach amounts documented for the pleistocene and place constraints on models for gondwanan ice volume climate dynamics and potential character and magnitude of glacioclimatic fluctuations

dynamic treatment of geochemical cycles global kinetics some of the key concepts needed to understand global kinetics of geochemical cycles are discussed residence times are related in a simple way to the kinetics of a cycle with one reservoir because geochemical cycles may sometimes require non linear global kinetics and because non linear systems can behave quite differentialy from their linear counterparts two particularly important aspects of non linear global kinetics are discussed first non linearity may lead to the existence of multiple steady state and under some circumstances systems may incur sudden changes from one steady state to another the second aspect of non linearity deals with the effects of coupling feedback between the cycles of different elements coupling between elements occurs within a local environment or in a true global sense and the kinetics analyzed show that coupling can have dramatic effects of the stability of the cycles hence the relative constancy of the amounts of some elements in various global reservoirs can be understood from the point of view of coupling of the global kinetics jmt

biomineralization and global biogeochemical cycles biological activity is a dominant force shaping the chemical structure and evolution of the earth surface environment the presence of an oxygenated atmosphere hydrosphere surrounding an otherwise highly reducing solid earth is the most striking consequence of the rise of life on earth biological evolution and the functioning of ecosystems in turn are to a large degree conditioned by geophysical and geological processes understanding the interactions between organisms and their abiotic environment and the resulting coupled evolution of the biosphere and geosphere is a central theme of research in biogeology biogeochemists contribute to this understanding by studying the transformations and transport of chemical substrates and products of biological activity in the environment biogeochemical cycles provide a general framework in which geochemists organize their knowledge and interpret their data the cycle of a given element or substance maps out the rates of transformation in and transport fluxes between adjoining environmental reservoirs the temporal and spatial scales of interest dictate the selection of reservoirs and processes included in the cycle typically the need for a detailed representation of biological process rates and ecosystem structure decreases as the spatial and temporal time scales considered increase much progress has been made in the development of global scale models of biogeochemical cycles although these models are based on fairly simple representations of the biosphere and hydrosphere they account for the large scale changes in the composition redox state and biological productivity of the earth surface environment that have occurred over geological time since the cambrian explosion mineralized body parts have been secreted in large quantities by biota because calcium carbonate silica and calcium phosphate are the main mineral phases constituting these hard parts biomineralization plays an important role in the global biogeochemical cycles of carbon calcium silicon and phosphorus the chapter starts with introducing the basic concepts of

progress problems and prospects an overview of the guadalupian series of south china and north america abstract the guadalupian epoch is marked by the formation of the pangean supercontinent global sea level change rifting and drifting of the cimmerian continents formation of large igneous provinces and dramatic biotic changes a high resolution biostratigraphic chemostratigraphic and high precision geochronologic framework of this critical transition is fundamental to understanding these events extensive studies of the latest cisuralian and guadalupian series in both south china and north america reveal the same conodont lineages but the conodont interval zones based on jinogondolella within the guadalupian series are slightly diachronous high precision u pb geochronological studies ca id tims method calibrate the base of the guadalupian series base roadian at 273 01 0 14 ma a previously reported age from an ash bed overlying the emeishan flood basalts 259 51 0 21 ma is adopted for the guadalupian lopingian boundary glb based on recently published geochronology and bayesian age modeling from the guadalupian series the base of the capitanian is constrained at 264 28 0 16 ma and the base of the wordian is interpolated to be 266 9 0 4 ma the illawarra reversal is of early middle wordian age both north america and south china possess a distinct negative 13ccarb excursion of 3 5 at the latest kungurian and early roadian lk er cie which coincides with the early stages of a significant 3rd order sea level rise the large end guadalupian 13ccarb negative excursion may have been affected by post depositional diagenesis or a warming event associated with the emeishan volcanism the 87sr 86sr ratios in both regions declined from the latest kungurian to the late capitanian but have different ratios and reveal several fluctuations in the middle guadalupian measured 18oapatite values suggest that the delaware basin was 3 4 c cooler than the eastern yangtze block analysis of a new high resolution database of marine taxa indicates only a minor pre lopingian diversity drop from 261 04 ma to 259 98 ma which coincides with the peak emeishan volcanism the widely perceived end guadalupian mass extinction in north america is evidently masked by and possibly an artefact of a stratigraphic truncation effect due to rapid lithofacies changes from limestone to laminated evaporites with the closure of the west texas basins

the magnitude of late paleozoic glacioeustatic fluctuations a synthesis a comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the carboniferous and permian and that at least eight distinct phases can be recognized facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20 25 m and occasionally as much as 60 m took place throughout the early mississippian tournaisian a widely recognized glacial period middle mississippian mid chadian through holkerian shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10 25 m a decrease that matches well with the paucity of coeval glacial deposits late visean asbian through mid brigantian glacioeustatic fluctuations of 10 50 m record the initial phases of ice accumulation in advance of the widespread mid carboniferous glacial event the latest mississippian earliest pennsylvanian mid brigantian through langsettian was a time of widespread glaciation and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40 100 m although middle pennsylvanian duckmantian through asturian glacial deposits are present in eastern australia paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m glacioeustatic fluctuations of as much as 100 120 m have been widely reported from late pennsylvanian earliest permian stephanian through mid sakmarian successions in north america an increase that corresponds to the growth of large ice sheets across much of gondwana and the accumulation of ice in the northern hemisphere incision and facies juxtaposition in early middle permian mid sakmarian through kungurian successions in eastern australia indicate that glacioeustatic fluctuations of 30 70 m occurred during the waning stages of major glaciation erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in australia suggests that eustatic fluctuations of 10 60 m occurred during the final stages of glaciation in the middle to late permian roadian through capitanian but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature this review demonstrates that far field cyclic successions record changing glacial conditions in gondwana that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice that carboniferous permian glacioeustasy was more variable than previously recognized and that generalizations from short temporal intervals are probably not representative of the late paleozoic ice age as a whole although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study

marine and terrestrial environmental changes in nw europe preceding carbon release at the paleocene eocene transition environmental changes associated with the paleocene eocene thermal maximum petm 56 ma have not yet been documented in detail from the north sea basin located within proximity to the north atlantic igneous province naip the kilda basin and the northern rain belt paleolatitude 54 1n during the petm this is a critical region for testing proposed triggers of atmospheric carbon release that may have caused the global negative carbon isotope excursion cie in marine and terrestrial environments the cie onset is identified from organic matter d 13 c in exceptional detail within a

revised lower palaeogene lithostratigraphy for the outer moray firth north sea abstract the lower palaeogene lithostratigraphy of the outer moray firth has been revised using wireline log and biostratigraphic data a two fold subdivision into the montrose and moray groups is recognized the montrose group consists of the maureen and lista formations whereas the younger moray group contains the sele balder dornoch and beauly formations the lista formation contains the arenaceous andrew and balmoral members separated by the tuffaceous glamis member the dornoch and beauly formations are prograding shelfal sandstone units that pass basinwards into the age equivalent dominantly argillaceous sele and balder formations the sele formation contains the forties and cromarty members which are locally developed sand rich units stratigraphic analysis has led to the identification of a number of consistently developed high gamma log markers that are interpreted as condensed mudstone horizons these markers are believed to record clastic sediment starvation during periods of maximum marine transgression they often have a strong biostratigraphic fingerprint coinciding with influxes of rich concentrations of microfossils and microflora they are interpreted as the product of synchronous regional transgressive events and have been an important aid to the development of a confident lithostratigraphic framework for the lower palaeogene of the outer moray firth

evidence for weathering and volcanism during the petm from arctic ocean and peri tethys osmium isotope records sudden global warming during the paleocene eocene thermal maximum petm 55 9 ma occurred because of the rapid release of several thousand gigatonnes of isotopically light carbon into the oceans and atmosphere however the cause of this release is not well understood some studies have linked carbon injection to volcanic activity associated with the north atlantic igneous province naip while others have emphasised carbon cycle feedbacks associated with orbital forcing this study presents the osmium isotope compositions of mudrocks that were deposited during the petm at four locations one from the arctic ocean and three from the peri tethys the os isotope records all exhibit a shift of similar magnitude towards relatively radiogenic values across the petm this observation confirms that there was a transient global increase in the flux of radiogenic os from the weathering of continental rocks in response to elevated temperatures at that time the tectonic effects of naip volcanic emplacement near the onset of the petm is recorded by anomalously radiogenic os isotope compositions of petm age arctic ocean samples which indicate an interval of hydrographic restriction that can be linked tectonic uplift due to hotspot volcanism in the north atlantic seaway the peri tethys data also document a transient higher flux of unradiogenic osmium into the ocean near the beginning of the petm most likely from the weathering of young mafic rocks associated with the naip these observations support the hypothesis that volcanism played a major role in triggering the cascade of environmental changes during the petm and highlight the influence of paleogeography on the os isotope characteristics of marine water masses

analysis of magnetic data over part of the younger granite province of nigeria the results of a magnetic study of part of the younger granite province of nigeria are presented here spectral analysis of the magnetic anomalies over the area has been carried out in an effort to estimate the depth to magnetic sources average magnetic source depth of 286 m has been obtained for the area and this is thought to be related to the depth to the top of the main anomalous structures in the area observed magnetic anomaly profiels taken across the area have been interpreted in terms of arbitrarily shaped bodies whose existence was confirmed by 3 d hilbert transformation using nonlinear optimization techniques the modelled bodies occur at depths of 200 760 m and have magnetizations of 0 29 0 47 a m the results from the analysis of the magnetic field are discussed in relation to the results from previous gravity studies over the area and the mode of emplacement of the younger granites