synchronous detachment folds and coeval sedimentation in the prepyrenean external sierras spain a case study for a tectonic origin of sequences and systems tracts this paper reports on the structural and sedimentary evolution of the middle to late eocene of the prepyrenean external sierras southern pyrenees spain the initiation duration and kinematics of a set of growth structures that developed in a shallow marine depositional setting is documented the detailed analysis of the syntectonic marine sediments not only confirms the already known east to west progression of deformation but also reveals the continued growth of the early formed structures as later ones propagate towards the foreland the sedimentary units coevally deposited with these growth structures are arranged in four depositional sequences their boundaries correspond to flooding surfaces which grade basinwards into correlative conformities they are also indicated by the presence of both angular unconformities and onlap geometries each depositional sequence generally consists of two systems tracts the lower one or transgressive systems tract is formed by up to 400 m of azoic marls deposited in outer ramp areas the upper one or highstand systems tract mainly consists of shallow siliciclastic and carbonate facies up to 200 m thick deposited in middle to inner ramp areas these depositional sequences are interpreted to be controlled by regional tectonic pulses an increase of tectonic activity resulted in the flooding of the basin and in the subsequent deposition of a thick succession of nearly azoic blue marls i e transgressive systems tract the overlying highstand systems tract developed following periods of diminished tectonism with the consequent growth and progradation of shallow carbonate platform facies

processes affecting paleogeography with examples from the tethys abstract as global change becomes a greater concern to society a more realistic procedure for interpretation of paleogeography is needed for a balanced view of earth history paleogeography is extrinsically affected by the changes in heat regime of the earth s interior manifested by a chain reaction of tectonic processes on the earth s surface tectonics largely controls oceanography climate and hence glacio eustasy which are the other major forcing factors of paleogeographic change since the heat budget of the earth has steadily declined for the last 4 5 ga rates of tectonic processes must have also changed and as a result paleogeography of the geological past cannot be a mirror image of the present thus actualism and uniformitarianism are not applicable to paleogeographic interpretation of geological record when time scale exceeds tens or hundreds of millions years major paleogeographic changes can be correlated to tectonic changes of the wilson cycle as documented for the late phanerozoic dispersion of pangea seaway opening in response to shifts in plate position has left variable signals in deposited sediments such as the termination of evaporite deposition and changes in ocean circulation bottom water chemistry sediment composition and faunal proviciality other processes related to plate tectonics like erratic latitudinal shift in the position of continental plates can lead to erroneous interpretations of climatic or oceanographic responses derived from sediments plate rotation under special conditions may result in crustal attenuation along one margin and compression along the other giving rise to synchronous sea level changes of opposite polarity first order eustatic sea level cycles operating on a scale of 45 90 ma in the atlantic have a long term controlling effect on paleogeography these cycles are probably the result of cyclic changes in rate of mantle upwelling and conductive heat transmission through the lithosphere because of this dependancy on the earth s heat budget the length of such cycles should have progressively increased through time if much more rapid paleogeographic changes resulting from third order exxon sea level cycles are caused by rapid stress induced vertical motions of the lithosphere then the influence of crustal and mantle inhomogeneities could explain different local and regional sea level responses to plate tectonic application of the generalized mesozoic cenozoic third order eustatic sea level cycles of vail and his colleagues on solutions of global geological problems can only be considered valid for divergent continental margins in areas under similar intraplate stress regime decreasing rates of fluctuation in intraplate stress on a cooling earth have direct consequences for paleogeographic trends in the gelogical past

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

a 56 million year rhythm in north american sedimentation during the phanerozoic abstract long term 10 myr fluctuations in climate sea level and sedimentation have been documented in the stratigraphic record but the lack of well constrained data series has made it difficult to rigorously evaluate cyclic periodic or quasi periodic changes at this scale here we utilize a new compilation of the coverage area of sedimentary rocks in north america to investigate the dominant modes orders of stratigraphic variability and to evaluate potential long period cyclic changes in sedimentation on the continent during the phanerozoic our analysis resolves two principal temporal modes of variability 1 a strongly sinusoidal mode with a periodicity of 56 myr 3 myr and 2 a longer term phanerozoic mode the m curve linked to the wilson cycle which is indistinguishable from a stochastic autoregressive process the newly identified 56 myr cycle in sedimentation delineates most of the cratonic sequences that have previously been identified qualitatively in north america but here we propose a quantitative redefinition that includes nine distinct units and two mega sequences the timing of the 56 myr beat in sedimentation is consistent with an orogenic oscillator source or an oscillatory dynamic in mantle convection and its tempo is statistically similar to a known rhythm in number of marine animal genera in the global fossil record thus the identification of a significant periodic signal in the sedimentary record of north america provides new evidence for an important tectonic and or mantle scale cyclic process that links both large scale biological evolution and physical environmental change

acoustic emission uncovers thermal damage evolution of rock abstract the thermal damage evolution of rock closely relates to many important scientific and engineering problems such as the mechanisms of earthquake and the effective extraction of deep geothermal energy however there is lack of rational thermal damage evolution model and the mechanisms of thermal damage are still unclear especially during cooling by use of a specially designed acoustic emission ae test system we explored the thermal damage evaluation in a rock and established a thermal damage evolution model which takes into account both heating and cooling processes the mechanisms of rock damage caused by heating and cooling were analyzed by using a lattice spring model and two different microstructural explanations were found i e heterogeneous microstructure and microdefect structure the damage evolution model can be used for more accurate modeling of these problems which involve rock thermal damage such as induced seismic activity during deep geothermal exploration

paleoatmospheric pco2 fluctuations across the cretaceous tertiary boundary recorded from paleosol carbonates in ne china abstract a dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the cretaceous k tertiary t transition following the chicxulub impact and deccan trap eruptions here pedogenic carbonates were collected from drill core of a borehole sk 1 n straddling the late cretaceous and early paleocene strata in the songliao basin northeast china to reconstruct atmospheric co 2 concentrations using a paleosol paleobarometer our estimates for atmospheric pco 2 from paleosol carbonates range between 277 115 ppmv and 837 164 ppmv between 67 8 ma and 63 1 ma one large 66 65 5 ma and several small co 2 spikes 64 7 64 2 ma during the latest maastrichtian to earliest danian are reported here and incorporated with previously published pco 2 estimates also estimated from paleosol carbonates these co 2 spikes are attributed to one million year long emplacement of the large deccan flood basalts along with the extraterrestrial impact at the k t boundary

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

detritus feeding as a buffer to extinction at the end of the cretaceous at the end of the cretaceous the principal animals that became extinct such as dinosaurs marine animals that lived in the water column and benthic filter feeders were in food chains tied directly to living plant matter animal groups less affected by extinction including marine benthic scavengers and deposit feeders small insectivorous mammals and members of stream communities were in food chains dependent on dead plant material the proposal that an asteroid or comet impact at the end of the cretaceous produced a dust cloud that cut off photosynthesis for several months is consistent with this pattern of extinction food chains dependent on living plant matter crashed while food chains based on detritus were buffered from extinction because there was a food supply adequate for the interval when photosynthesis was halted

eustasy as a test of a cretaceous superplume hypothesis the mantle plume model has been used to explain a variety of geological and geodynamic events for instance a large plume or superplume under the pacific basin has been proposed to account for a number of cretaceous events such as a global sealevel rise an increase in global average temperature and a pause in the reversals of the earth s magnetic field 1 2 the primary evidence for this hypothesis is a model for the rate of production of ocean ridge material and ocean plateaus with a high from about 120 80 ma mostly due to activity in the pacific basin which is claimed to have been driven by the upwelling of a large plume from the core mantle boundary the hypothesis requires that a large part of the primary evidence for this high productivity has disappeared by subduction here we test this hypothesis by comparing the cretaceous eustatic sealevel highstand which would result from the superplume model with generally accepted values our model includes estimates of eustatic sealevel change resulting from phenomena explicitly specified for the proposed plume such as the volume of ocean crust produced and the extent of lithospheric swelling associated with the plume head as well as other events known to affect eustatic sealevel such as glaciation and continental collision the estimated cretaceous highstand resulting from all the modeled effects is 220 470 m compared to the observed value of 120 200 m this discrepancy indicates a probable overestimate of the rate of seafloor and plateau creation and of the size of plume that could have existed the breakup of the pangean supercontinent is a more viable explanation of the cretaceous sealevel rise

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

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

effects of lithospheric in plane stress on sedimentary basin stratigraphy in plane lithospheric stress though known to exist has generally been ignored in the quantitative modeling of basin stratigraphy however low levels of intraplate lateral stress can induce observable plate deformations 10 100 m of vertical motion if the lithosphere contains a preexisting deformation such as a sedimentary basin the importance of in plane stress in modifying the stratigraphy of a sedimentary basin has been assessed using an elastic plate model for the lithosphere a compressive in plane stress generally induces basin subsidence with peripheral uplift shoreline regression while a tensile in plane stress induces basin uplift and peripheral subsidence shoreline transgression these simple results are complicated by variations in crustal thickness as now two interfaces are involved that is the sediment basement interface of the sedimentary basin and the moho topography the isostatic state of a sedimentary basin therefore ultimately controls the resultant deformation induced by in plane stress the implications of in plane stress modification of basin stratigraphy are profound regionally correlatable transgressions and regressions of basin interiors e g cyclothems and passive continental margins the third order variations of the vail et al 1977a coastal onlap curve may be tectonically produced by the interaction of stress induced base level changes and a basin tectonic driving subsidence in plane stress its generation magnitude and variation is considered a consequence of plate boundary reconfigurations during continental collisions rifting and subduction obduction

allogenic controls on the evolution of storm to tidal shelf sequences in the early proterozoic uncompahgre group southwest colorado usa dominantly coarse grained shallow marine metasedimentary rocks of the early proterozoic uncompahgre group ug record periods of shoaling and drowning on different temporal scales that are attributed to episodic long term oscillations in relative sea level with superimposed shorter duration excursions in relative sea level long term events are probably tectonic whereas short term events are eustatic the 2 5 km thick uncompahgre group consists of 250 600 m thick dominantly coarse grained quartzite units q1 q4 and 200 300 m thick mudstone pelite units p1 p5 five depositional systems comprise the uncompahgre group the outer shelf system oss is composed of bouma type beds and intercalated mudstones that are transitional vertically to parallel laminated to wave rippled sandstones and hummocky cross stratified sandstones of the inner shelf system iss trough cross stratified sandstones comprise the shoreface system shs the tidal inner shelf shoreface system tis shs consists of a complex interlayering of cross bedded sandstones thin bedded conglomerates mudstones and rippled sandstones trough cross bedded pebbly sandstones and thin to thick bedded conglomerates represent the alluvial system alls depositional systems in the ug are associated in transgressive and highstand systems tracts that make up four sequences 1 to 4 sequence boundaries do not correspond with lithostratigraphic boundaries but are defined by subtle unconformities the basal q1 p1 unit lower sequence 1 consists of alls to tis shs to iss comprising a transgressive systems tract a maximum marine incursion is reflected by deposition of oss facies in stratigraphic units p1 p2 shoaling in the transition from p2 to the uppermedial portion of q2 oss iss shs to a thick tis shs alls records the highstand systems tract of upper sequence 1 a subtle disconformity paraconformity delineates a type 2 sequence boundary at the top of the highstand systems tract the drowning to shoaling pattern is replicated in sequence 2 upper q2 to p3 to upper medial q3 sequence 3 upper q3 to p4 to upper medial q4 and an incomplete sequence 4 upper q4 through p5 thinner shoaling intervals of oss iss shs in p3 and in lower q2 q3 and q4 represent parasequences sequences of 107 years duration are attributed to periods of increasing and decreasing subsidence rates due to tectonism marginal to the sedimentary basin parasequences record shorter duration temporal controls of c 104 to 105 years related to eustatic oscillations as a consequence of shoaling and aggradation progradation in the highstand systems tract tis shs and alls overlie and are temporally separated from oss to iss to shs this transition records filling of the basin to sea level leading to a shelf geometry that was conducive to tidal amplification a composite relative sea level curve integrating long term pulsatory subsidence and short term eustasy best explains the stratigraphic evolution of the uncompahgre group

on the initiation of subduction zones analysis of the relation between intraplate stress fields and lithospheric rheology leads to greater insight into the role that initiation of subduction plays in the tectonic evolution of the lithosphere numerical model studies show that if after a short evolution of a passive margin time span a few tens of million years subduction has not yet started continued aging of the passive margin alone does not result in conditions more favorable for transformation into an active margin

inversion for parameters of tensile earthquakes the tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane the proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic iso compensated linear vector dipole clvd and double couple dc components in seismic moment tensors the most significant parameters inverted are the ratio at the fault denoted as the parameter and the inclination of the slip vector from the fault the parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes the inclination can be accurately determined from the dc component in the moment tensor because the dc component rapidly decreases with increasing for example the inclination of 20 causes dc being 50 60 only the inversion is applied to earthquakes which occurred in january 1997 in west bohemia czech republic it is shown that some of these earthquakes display tensile faulting the parameter is 0 1 the inclination of the slip from the fault attains values of up to 20 this inclination is a result of tensile traction and reduced shear traction along the fault and high fluid pressure in the region

shear failure of a granite pin traversing a sawcut fault abstract fault heterogeneities such as bumps bends and stepovers are commonly observed on natural faults but are challenging to recreate under controlled laboratory conditions we study deformation and microseismicity of a 76 mm diameter westerly granite cylinder with a sawcut fault with known frictional properties an idealized asperity is added by emplacing a precision ground 21 mm diameter solid granite dowel that crosses the center of the fault at right angles this intact granite pin provides a strength contrast that resists fault slip upon loading to 80 mpa in a triaxial machine we first observed a m 4 slip event that ruptured the sawcut fault slipped 40 m but was halted by the granite pin with continued loading the pin failed in a swarm of thousands of m 6 to m 8 events known as acoustic emissions aes once the pin was fractured to a critical point it permitted complete rupture events m 3 on the sawcut fault stick slip instabilities subsequent slip events were preceded by clusters of foreshock like aes all located on the fault plane and the spatial extent of the foreshock clusters is consistent with our estimate of a critical nucleation dimension h we also identified an aseismic zone on the fault plane surrounding the fractured rock pin a post mortem analysis of the sample showed a thick gouge layer where the pin intersected the fault suggesting that dilatancy of this gouge propped open the fault and prevented microseismic events in its vicinity recorded microseismicity separates into three categories slip on the sawcut fault fracture of the intact rock pin and off fault seismicity associated with pin related rock joints we found that pin fracture events were exclusively implosive anticrack even though the shear process zone was overall dilatant this shows how aseismic effects can lead to unexpected seismic manifestations of certain faulting processes

continental tectonics selected topics cause and effect relations between plate boundary processes and orogeny were investigated using new and refined plate models for the mesozoic and cenozoic terrane accretion and large components of horizontal shear were shown to be fundamental aspects of orogen evolution deep crustal thrust systems with large lateral transport and vertical stacking of slices of crystalline basement were documented in the cordillera and appalachians new geomechanical models of crystalline thrust sheets and foreland thrust belts emphasized the dominance of tectonic rather than gravitational stresses lithospheric thickening was shown to cause buoyancy forces that control the lateral spread of deformation outward from the interior of an orogen and may modify regional stresses in the vicinity of topographic fronts resulting in extension within the upper part of the lithosphere coeval with shortening at depth

lower mantle convection and geomagnetism the statistical properties of recent marine magnetic anomaly time scales covering the period from 165 ma to the present are analyzed via the methods presented in the companion paper mcfadden this issue the data no longer support the hypothesis that during the last 86 ma there were two periods separated by a discontinuity at about 45 ma when the properties were stationary instead there is strong evidence that the rate of reversals decreased in an approximately linear manner with time from 165 ma until it reached zero resulting in the cretaceous normal polarity interval at about 86 ma ago the process of reversals began again and the rate of reversals increased linearly with time there is a slight indication that the rate of reversals reached a maximum about 10 ma ago and is again decreasing analysis of the reversal sequences shows there is no good evidence for the concept of differences in the relative stabilities of the two polarity states nor need such a concept be invoked to explain long intervals without reversals such as the cretaceous normal polarity interval quite clearly there has been some form of thermal perturbation at the base of the mantle with a characteristic time of the order of 108 years our interpretations require convection deep within the mantle and suggest that the temperature at the base of the mantle attains a maximum during long magnetic quiet intervals

experimental investigation of acoustic emissions and their moment tensors in rock during failure abstract we study acoustic emissions aes associated with shear and tensile failures around a horizontal borehole in a sandstone sample subjected to triaxial stress the aim is to relate the ae event rate to macroscopic observations of sample deformation and the percentage of isotropic and deviatoric components of the seismic moment tensors to the expected failure mechanisms the horizontal hole interferes with the applied load and forms a strongly spatially dependent anisotropic stress field focusing the crack initiation into both shear and tensile failures the recorded aes follows reasonably well existing damage models but the elastic solution of hoop stress does not represent the onset of failure around the borehole the focal mechanisms correlate with the orientation of macroscopic fractures in the sample events close to the borehole show a higher fraction of isotropic percentage in moment tensors compared to events occurring in the macroscopic fracture featuring higher double couple percentages the inhomogeneous stress field due to the borehole and the stress induced damage is strongly affecting the axial and radial velocities which in turn affect the waveforms of the recorded aes and the resulting moment tensors the vp vs ratio obtained from the ratio of isotropic to compensated linear vector dipole components of the moment tensors is close to that obtained from ultrasonic velocity measurements

volcanism and vertical tectonics in the pacific basin related to global cretaceous transgressions abstract the dominance of volcanic processes and the importance of vertical tectonics in the geological evolution of the pacific basin has been recognised since the time of charles darwin data gathered on several legs of the deep sea drilling project dsdp and numerous marine expeditions in the past decade have confirmed menard s postulate that the pacific basin was the scene of volcanism on an enormous scale in mesozoic time widespread mid plate volcanism between 110 and 70 m y b p characterised the area bounded by the line islands the mid pacific mountains and the nauru basin marshall islands heating of the pacific lithospheric plate during this period of volcanism resulted in regional uplift and the bathymetric evolution of the area diverged significantly from a normal parsons sclater subsidence curve the farallon plate now almost entirely subducted was also the scene of mid plate volcanism that produced such features as the nicoya plateau now found as an allochthonous ophiolitic terrain landward of the middle america trench large benthonic reef associated foraminifera comprising a pseudorbitoid fauna hitherto considered to be largely restricted to central america have now been additionally recorded from dsdp sites 165 315 and 316 in the line islands site 462 in the nauru basin and in new guinea the distribution of this fauna of campanian maastrichtian age is interpreted as indicating stepping stone connections aseismic ridges plateaus and seamounts between the caribbean farallon and pacific plates 70 80 m y b p similarities between the geology of the nauru basin and the caribbean ocean crust reinforce the interpretation of the latter as a former part of the farallon plate estimates of the sea level and continental freeboard change caused by the thermally induced uplift of the pacific and farallon plates as well as substantial areas in the atlantic and indian ocean basins indicate that such shallowing of the sea floor could have been the major factor in causing global cretaceous transgressions

radiolarian palaeoecology and radiolarites is the present the key to the past abstract radiolarian productivity pulses and related radiolarite deposition are phenomena difficult to understand from an exclusively actualistic viewpoint evolutionary selection pressure among silica secreting marine plankton both radiolarians and diatoms has led toward more economic usage of rapidly shrinking nutrient resources including dissolved silica of the photic zone in the late cenozoic oceans and in particular a substantial modification of oceanic cycle by the diatom explosive radiation even if there is a proved link between biomineralization and dissolved silica loading among the phytoplankton only the relative independence of modern siliceous planktic biotas from the available silica pool reflects mainly their progressive physiological specialisation during evolutionary history oceanic chemistry and productivity as well as patterns of circulation upwelling have changed radically during the phanerozoic radiolarites apparently represent an anachronistic facies as exemplified by their long lived and ocean wide distribution in palaeo pacific and hitherto highlighted actualistic models of localized intra oceanic wind driven upwelling loci are of largely questionable applicability in addition to plate drift hypersiliceous domains and intervals are explainable mostly by a large scale volcano hydrothermal activity during major plate boundary reconfigurations which in many ways favoured siliceous biotas acme and their skeletal remains accumulation and preservation factors tied to rapid voluminous submarine eruptions such as thermal buoyant megaplumes and basin overturns offer a viable alternative for traditional climatic circulation scenarios in case of hypersiliceous high productivity events irrelevant to greenhouse to icehouse climatic change the evolving carbon and silica cycles were coupled through the greenhouse effect and enhanced chemical weathering volcano hydrothermal and tectonic uplift events related mostly to extensive rifting and or accelerated oceanic spreading were the endogenous driving force that created this perturbation of the exogenous system the present biogeochemical cycle is representative only for the overall silica depleted post eocene oceanic ecosystems which broadly correlates with a major expansion of diatoms groups extremely efficient in silica removal and closely linking the silica budget with phosphorus and nitrogen cycles thus an orthodox uniformitarian approach to biosiliceous sedimentation based on a silica starved vigorous ocean is of limited significance when applied to the pre neogene settings especially in the peculiar planktic habitats of epeiric seas as well as during biotic crises marked by strong geotectonic overprint the major turnovers in marine siliceous biota composition in particular after the end permian radiolarite gap may have been coupled with discernible changes in an increasing biological control on the long term oceanic silica cycling punctuated equilibrium the evolutionary turnovers have induced a stepdown decrease of dissolved silica levels through the phanerozoic contemporaneously with the general secular trend of upward scaling of nutrient related ecological processes and increased effectiveness of resource utilization

phase difference between sea level and magnetic reversal rate in this letter i report a negative correlation and a phase difference of 10 myr between recent data on long term eustatic sea level change1 and geomagnetic reversal rate for the past 150 myr the phase difference is detectable both by visual inspection and through a correlation analysis i also show that the same phase difference but with a positive correlation could theoretically have existed between this eustatic sea level data and sea floor creation rate in light of the ridge volume hypothesis of long term eustasy the analysis suggests the view that sea floor creation rate and or subduction rate and geomagnetic reversal rate are closely associated and perhaps synchronized in their changes

sea level variations global sedimentation rates and the hypsographic curve sea level changes during the neozoic have been estimated by two different methods the first involves measuring the amount of present day land area which was flooded during the past and using the present day hypsographic curve to estimate the amount of sea level rise necessary to produce this flooding the second involves the estimation of the changing volume of mid oceanic ridges through time and estimating sea level changes after having allowed for isostatic adjustment a difference in sea level of 170 m is obtained from the two methods for the cretaceous 80 100 m y b p this is equivalent to a difference in continental flooding of 24 mm 2 using the present day hypsographic curve we attempt to explain this difference firstly by allowing for the fact that the present day ocean basins have more sediment in them than did the cretaceous ocean basins this produces a sea level change in the opposite direction to that produced by the reduction in mid ocean ridge volume since the cretaceous secondly we suggest another large factor in producing the difference is that the present day hypsographic curve is not the correct one to use when studying sea level stands in the cretaceous present day average continental heights are closely related to continental areas accepting this principle if continents are joined together in the past their average height must be greater and so their hypsographic curve must be steeper a given sea level rise would produce less continental flooding during times of continental aggregation than it would today

acoustic emissions associated with the formation of fracture sets in sandstone under polyaxial stress conditions a polyaxial true triaxial stress loading system developed originally for determining all nine components of p and s wave velocities and attenuation and fluid permeability for 50 8 mm side cubic rock specimens tested to failure has been modified to permit the measurement of acoustic emission events associated with the failure process results are reported for crosland hill sandstone tested to failure under loading conditions leading to the formation of sets of aligned microcracks achieved by maintaining the minor principal stress at a low value while increasing the two other principal stresses until failure of the rock an ultrasonic survey associated with the test has been employed to map the transversely isotropic velocity structure created by through going parallel fractures resulting from the sets of aligned microcracks this velocity structure has then been employed to locate acoustic emission events recorded during the test by four acoustic emission sensors located in each of the six specimen loading platens a selection of acoustic emission events associated with one of the fractures has been processed for moment tensor analysis information in order to determine the source type and orientation of microcracking as the fracture grows the mechanisms indicate tensile behaviour during initial fracture propagation shear failure however appears to dominate as the fracture finally approaches the opposite face of the cubic specimen the work presented here has in part led to the development of new rock testing systems and geophysical monitoring and processing technologies that will enable laboratory study of rock behaviour under conditions better resembling those experienced in situ

pulsation tectonics as the control of long term stratigraphic cycles a new theory of pulsation tectonics involving the cyclic eruption of thermal plumes from the d layer in the lowermost mantle explains the long term cycles of marine stratigraphy heating of the mantle changes conditions at the core mantle boundary that result in the quiescence of the earth s magnetic field the rising plumes after a phase lag later induce faster plate spreading and widespread intraplate volcanism subsequently colder rock returning to the lower mantle reestablishes the d thermal boundary layer and sets up conditions for more turbulent core convection and frequent magnetic reversals meanwhile lower mantle plumes cease erupting and the plates spread more slowly the cycles of fast and slow plate spreading and quiet and reversing magnetic field have a duration of 60 100 m y global changes in spreading rate are one of the main causes of large scale 100 300 m eustatic sea level changes and variations in output of volcanic gases consequential changes in albedo global temperature humidity forestation atmospheric and oceanic co2 oceanic acidity and oxygenation lead to variations in the preservation of organic carbon in the oceans and epicontinental seas and in the level of the calcite compensation depth during rising sea levels there is an increase in organic carbon preservation and relatively little calcite is preserved with falling sea levels less organic carbon and more calcite are preserved in the deep sea the long term cycles in carbon and calcite bearing sediments correspond generally to the pulsations of grabau 1934 the long term rhythms which nearly equal the lengths of geologic time periods

ultrasonic velocities acoustic emission characteristics and crack damage of basalt and granite acoustic emissions ae compressional p shear s wave velocities and volumetric strain of etna basalt and aue granite were measured simultaneously during triaxial compression tests deformation induced ae activity and velocity changes were monitored using twelve p wave sensors and eight orthogonally polarized s wave piezoelectric sensors volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface p wave velocity in basalt is about 3 km s at atmospheric pressure but increases by 50 when the hydrostatic pressure is increased to 120 mpa in granite samples initial p wave velocity is 5 km s and increases with pressure by 20 the pressure induced changes of elastic wave speed indicate dominantly compliant low aspect ratio pores in both materials in addition etna basalt also contains high aspect ratio voids in triaxial loading stress induced anisotropy of p wave velocities was significantly higher for basalt than for granite with vertical velocity components being faster than horizontal velocities however with increasing axial load horizontal velocities show a small increase for basalt but a significant decrease for granite using first motion polarity we determined ae source types generated during triaxial loading of the samples with increasing differential stress ae activity in granite and basalt increased with a significant contribution of tensile events close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly a concomitant increase of double couple events indicating shear suggests shear cracks linking previously formed tensile cracks

stress induced changes in plate density vail sequences epeirogeny and short lived global sea level fluctuations the stratigraphic record contains clear evidence that broad regions have experienced rapid changes in sea level unrelated to changes in glacial ice volume e g third and higher order vail sea level variations continental foundering we propose that many of these changes can be caused by stress induced changes in plate density stress changes produce significant changes in the density of the crust and lithosphere a point missed in previous investigations and propagate across even the largest plates in less than 30 000 years lithospheric plates interacting at existing boundaries can produce stress related density changes sufficient to cause several meters change in plate elevation these may account for many of the regressions and transgressions seen in the stratigraphic record the creation of new rifts could increase plate compression enough to cause 50 m of plate subsidence plate elevation changes of up to 200 m could result from increased plate compression during continental collisions a particularly enigmatic kind of rapid nonglacial global ngg sea level change is a coupled 50 m sea level fall regression and roughly equal rise transgression occurring in less than 106 years these couplets associated with black shales and marine extinctions can be explained by the elastic snapback attending the rapid formation of a new rift isostatic disequilibria along the new rift depresses the seafloor sufficiently to cause a 50 m fall in sea level mantle flow restores isostatic equilibrium along the rift axis and erases the fall in 60 000 years unusually intense hydrothermal circulation along the new rift during the snapback promotes anoxic bottom water conditions and deposition of black shales a rapid drop in global sea levels reduces the area of ocean bottom within the photic zone causing overpopulation food exhaustion and extinctions the connections between changes in plate stress and density have many implications perhaps the most far reaching is that tectonic events on the 3 4 of the globe that is covered by oceans as well as the 1 4 that is subaerial are recorded in sedimentary strata

mercury as a proxy for volcanic activity during extreme environmental turnover the cretaceous paleogene transition abstract the usually low geological background concentrations of hg makes this trace element suitable for identifying accumulation pulses in sediments that can be tentatively related to weathering processes and thus to climatic changes intense volcanism has witnessed the cretaceous paleogene transition ktb and was perhaps responsible for dramatic climatic changes and decrease in biodiversity and mass extinction we have used hg concentrations as a proxy for volcanic activity and atmospheric hg and co2 buildup across the ktb at three localities in the salta basin argentina hg contents display several spikes across the ktb with a maximum value of 250 ng g 1 in three drill cores across the ktb in the paraiba basin northeastern brazil hg contents increase from the late maastrichtian to early danian and hg spikes predate the ktb perhaps as a record of volcanic activity before but very close to this transition at stevns klint denmark hg contents reached almost 250 ng g 1 within a 5 cm thick clay layer the fiskeler member fish clay that comprises the ktb some co variation between hg and al2o3 contents has been observed in all of the studied sections across the ktb suggesting that hg is probably adsorbed onto clays thermo desorption experiments in selected samples from the yacoraite formation showed hg 2 as the major species present which is in agreement with a volcanic origin combined hg and c isotope chemostratigraphy may become a powerful tool for the eventual assessment of the role of volcanic activity during extreme climatic and biotic events such as those during the ktb

faunal evidence for reduced productivity and uncoordinated recovery in southern hemisphere cretaceous paleogene boundary sections the mass extinction at the cretaceous paleogene boundary is generally explained by a severe crisis in primary productivity following a catastrophic bolide impact consistent with this scenario danian mollusk dominated benthic shelf ecosystems of southern middle paleolatitudes neuquen basin argentina are characterized by 1 a stratigraphically limited low in macrofossil abundances 2 an increase in starvation resistant nonplanktotrophic deposit feeders and chemosymbionts 3 a reduction in the average body size of individuals and 4 individuals with inactive lifestyles being more common than in the late maastrichtian return to pre extinction conditions of the various synecological attributes occurred over unequal time spans indicating that recovery was uncoordinated with respect to ecological traits global comparison of ecological patterns suggests that reduced food supply 1 was a controlling factor in both hemispheres 2 affected macrobenthic marine faunas at various distances from the chicxulub impact site and 3 was more effective in siliciclastic environments as compared to oligotrophic carbonate settings

the impact of lithification on the diversity size distribution and recovery dynamics of marine invertebrate assemblages lithified marine sediments are not equitably distributed through time raising the possibility that lithification masks biological signals when data from unlithified and lithified sediments are compared or combined using mollusk dominated assemblages from the early cenozoic of the gulf coastal plain we find that lithification conceals small taxa decreases taxonomic resolution and exacerbates the undersampling of rare taxa lithified assemblages appear less diverse and have less even abundance distributions than coeval unlithified samples these limitations cannot be overcome by standardization procedures nor are they likely to be circumvented by collecting larger samples the effects of this bias however can be mitigated by restricting analyses to a single lithification state or to specific size classes since lithification selectively obscures small taxa the magnitude of this bias will be most severe when organisms are particularly small such as in the aftermath of mass extinctions in the study area lithification artificially protracts the recovery period following the cretaceous paleogene mass extinction by 7 m y

the cenomanian turonian boundary event ctbe in northern lebanon as compared to regional data another set of evidences supporting a short lived tectonic pulse coincidental with the event abstract constrained by both foraminifera and isotope data the zeitoun and nahr ibrahim sections in northern lebanon record a steady flooding of the cenomanian carbonate platform during the uppermost cenomanian lower turonian interval the flooding began just before the inception of the ctbe 13c positive shift it is marked by the deposition of finely bedded to laminated fine grained limestone overlying platformal carbonates this scenario is entirely different to what has been published in northern israel where repeated emergences are instead recorded during the event a survey of published data from nearby middle east countries to north africa suggests that the ctbe is accompanied on a larger scale especially along the syrian arc by tectonic disturbances responsible for sequence stratigraphic heterogeneity and palaeogeographic changes detailed analysis of available data makes it possible to extract from the sedimentary record four sequence stratigraphic scenarios implying two phases of heterogeneity bounding the event and responsible for the outphasing of relative sea level changes in some sensitive areas these disturb a stepped early cenomanian to early turonian overall transgressive trend recorded in some large stable areas often used to support the concept of mesozoic eustasy the discussion focuses on the global processes that are possibly involved the hypothesized tectonic pulse does not explain the ctbe it is just another set of data to be taken into account in the search for causes

on the correlation between mantle plume flux and the frequency of reversals of the geomagnetic field the validity of concept that impulsive changes in the volume flux of material rising from the base of the mantle via plumes can cause rapid changes in the heat flux from the core and in the behavior of the geomagnetic field is investigated it is found that the natural time scale of variations in the heat flux from the core is about 109 years a time scale far longer than that associated with the long term changes in the frequency of reversals of the magnetic field following an impulsive change in plume flux the heat flux from the core changes on a time scale of several billion years i e on a time scale of the age of the earth a harmonic variation in the volume flux up plumes results in a similar harmonic variation in the heat flux from the core but with a phase lag of 4 and a greatly diminished amplitude the lack of correlation between mantle plume flux and core heat flux is due to the long natural time scale of the lower mantle and the large thermal inertia of the d layer compared with the heat flux from the core this calls into question the currently fashionable idea of a direct and immediate correlation between plume volume flux and heat flux from the core

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

origin of thick first cycle quartz arenite successions evidence from the 1 7 ga ortega group northern new mexico abstract the 1700 ma old ortega group in northern new mexico represents a 1000 m thick succession of metamorphosed quartz arenites and subordinate pelites published ages of detrital zircon grains from the ortega group indicate that the sediments were derived mainly from 1760 1700 ma old volcano plutonic basement rocks and not from the archean wyoming province to the north evidence for recycling within the ortega group also is lacking consequently the ortega group quartz arenites are considered to be first cycle sediments the compositional and textural maturity of these sandstones is attributed to intense chemical and mechanical weathering abnormally high al contents of pelites within the ortega group imply intense chemical weathering in the provenance similar to present day low relief tropical regions quartz arenites in the ortega group were deposited exclusively within a shallow marine shelf environment influenced by tide storm and wave processes prolonged sediment transport especially on the tide dominated inner shelf in conjunction with inferred gradual subsidence optimized mechanical destruction of labile grains and rounding of quartz grains although the maturity of sediments in the ortega group can be accounted for the mode of origin of 850 m of quartz arenites remains enigmatic thick quartz arenite sequences of global distribution in the phanerozoic coincide with first order eustatic sea level rises world wide occurrences of 1700 ma old thick quartz arenite shelf successions suggest that the ortega group may have accumulated in response to a similar major eustatic sea level rise

geomagnetic polarity in the early cretaceous and jurassic knowledge of the polarity history of the earth s magnetic field during the mesozoic stems primarily from oceanic m sequence magnetic anomalies certain of these anomalies have been biostratigraphically dated from sediments immediately overlying basaltic basement at deep sea drilling project d s d p sites within the m sequence the biostratigraphic control is such that these age estimates are generally imprecise and moreover the sediment ages represent only minimum ages for the basaltic basement itself magnetostratigraphy in sedimentary land sections provides improved age estimates for magnetozones which can then be correlated with m sequence anomalies magnetostratigraphy provides not only enhanced dating of the ocean floor and resolution of the behaviour of the geomagnetic field during the cretaceous and jurassic oceanic quiet zones but also a world wide correlation tool for sedimentary stratigraphy the middle cretaceous is characterized by a long period of normal polarity extending from the early aptian to the early campanian reversed magnetozones corresponding to oceanic anomalies m 0 m 1 and m 3 have been palaeontologically dated as early aptian middle barremian and early barremian respectively magnetozones corresponding to oceanic anomalies m 5 to m 15 are hauterivian to valanginian in age but have not been individually associated with stage boundaries mainly due to poor biostratigraphic control in italian pelagic limestone sections of this age however magnetozones corresponding to oceanic anomalies m 16 to m 22 have been individually correlated to lower berriasian and tithonian palaeontological zones and extrapolation of this correlation gives an age for anomaly m 25 close to the oxfordian kimmeridgian boundary the jurassic 9quiet zone in the oceans is recognized in land sections as an extended period of predominantly normal polarity and although poor biostratigraphic control in this interval limits our knowledge of its duration we consider that it extended through the oxfordian and callovian stages the bathonian and older jurassic stages are characterized by mixed polarity a precise correspondence of magnetozones to ammonite zonations and stage boundaries is only available for the aalenian to pliensbachian interval where the frequency of reversal was apparently very high

stable isotope records across the cretaceous paleogene transition stevns klint denmark new insights from the chromium isotope system abstract late cretaceous to early paleogene time represents a critical transitional period in earth history global events include short term instability in climate and ocean circulation large igneous province emplacement and catastrophic extinction of marine and terrestrial fauna due at least in part to a bolide impact event the response of the ocean system to cretaceous paleogene k pg global events has been the subject of much research yet fundamental questions remain regarding carbon cycling climate ocean mixing and redox conditions to help elucidate paleoceanographic changes across the k pg transition we revisit the classic maastrichtian to danian chalk limestone succession at stevns klint denmark with a suite of new geochemical data including insights from the redox sensitive chromium isotope system we use carbon and oxygen isotope trends to form a well constrained framework for the succession before presenting strontium isotope chromium isotope and rare earth element data for the units deposited both before and after the k pg event carbon isotopes show only minor perturbation across the k pg boundary and oxygen isotopes record a prominent positive excursion with both of these trends standing in contrast to many k pg boundary sections worldwide strontium isotopes record a spike towards more radiogenic values which is consistent with a globally observed short term weathering pulse the chromium isotope profile of maastrichtian chalk begins with strongly positive values followed by a sharp negative excursion associated with a facies shift and initiation of bottom currents in the chalk sea 53 cr values then recover before falling steadily across the k pg boundary and into the danian limestone chromium isotope trends do not correspond to changes in hydrothermal input or basin redox conditions instead we propose that mixing of water masses with distinct chromium isotope signatures controlled temporal chromium isotope variability the local mixing event inferred from our maastrichtian chromium isotope data could be related to a temporary inflow of tethyan bottom waters or the shift from end maastrichtian greenhouse warming associated with deccan volcanism to the worldwide cooling phase that immediately preceded the k pg boundary no immediate change in chromium isotopes is recorded across the k pg boundary indicating that the bolide impactor did not substantially perturb the marine chromium cycle at least at the scale resolvable by our data instead chromium isotope trends continued to be controlled by local oceanographic processes highlighting the potential of the chromium isotope system to record isotopic heterogeneity and mixing events in ancient oceans

continental drift runoff and weathering feedbacks implications from climate model experiments changes in atmospheric carbon dioxide have been proposed as a major regulator of climate during the last 570 million years continental weathering and its variation over time are hypothesized to be important for controlling atmospheric carbon dioxide continental weathering is altered by changes in total runoff as well as changes in the size and elevation of the land masses to be weathered when paleogeographic information for the phanerozoic 570 m y ago to present is used in a global climate model the model exhibits substantial variations in precipitation evaporation and runoff even with dramatically different land ocean distributions an increase in global surface temperature leads to an increase in global precipitation but not always an increase in global runoff during the early phanerozoic 514 342 ma when the continents are relatively small and widely distributed runoff depends on continental evaporation and temperature as the continents migrate into subtropical latitudes global runoff decreases as global land temperatures and evaporation increase as the continents shift to higher latitudes global runoff increases as global land temperatures and evaporation decrease during the middle to late phanerozoic 306 ma present when large continental land masses predominate runoff depends on continental precipitation experiments with increased atmospheric co 2 for the middle ordovician 458 ma when the paleocontinent of gondwana was centered at subtropical latitudes and the early silurian 425 ma when gondwana had shifted to middle and high latitudes also point to a correlation between land mass location and runoff global runoff increases 15 with increased co 2 at 425 ma but remains unchanged for 458 ma even though global mean temperature and precipitation increase comparable amounts for the two time periods these results imply that weathering feedback between temperature and runoff may be dependent on land ocean configuration

high resolution hg chemostratigraphy a contribution to the distinction of chemical fingerprints of the deccan volcanism and cretaceous paleogene boundary impact event abstract there is a renewed interest in volcanism as the major trigger for dramatic climatic changes at the cretaceous paleogene transition ktb which were accompanied by a decrease in biodiversity and mass extinction we have used hg contents as proxy for volcanic activity at the classical localities of gubbio italy and stevns klint denmark where the ktb layer is easily recognizable and at a near complete succession exposed at the bajada del jaguel locality in the neuquen basin argentina these three localities display similar 13ccarb trends with markedly negative excursion at the ktb layer bulk rock oxygen isotopes yielded similar pathways across the ktb layers in these localities and if considered near primary the negative 18o excursion at the ktb in gubbio and bajada del jaguel suggest warming temperatures during this transition whereas the negative excursion immediately followed by positive one at stevns klint points to a cycle of warm followed by colder climate at stevns klint hg contents reach 250 ng g 1 within the ktb layer fiskeler member and 45 ng g 1 at 1 5 m above that while within the scaglia rossa formation at gubbio three hg peaks across the ktb are observed one of them within the ktb layer 5 3 ng g 1 hg shows several peaks across the ktb in the neuquen basin with up to 400 ng g 1 in the jaguel formation the phenomena that caused dramatic changes at the ktb probably expelled huge amounts of hg into the atmosphere as recorded by these high hg levels a co variation between hg and al2o3 in the studied sections suggest that hg is adsorbed onto clays hg concentrations and also hg isotopes are perhaps a powerful tool in the assessment of the role of volcanic activity during extreme climatic and biotic events and in assessing the role of meteorite impact versus volcanism as the predominant cause of past global catastrophes and mass extinction

eustasy and epeirogeny of continents on time scales between about 1 and 100 m y eustatic changes are believed to be the cause of the extensive flooding of the continents by shallow marine seas during the cretaceous and much of the paleozoic the possible causes of eustatic change which can be easily quantified over the past 100 m y have been estimated in order to arrive at a value for the freeboard decrease of the continents these causes in order of decreasing importance are ridge crest volume thermal uplift associated with excessive volcanism in the pacific during the cretaceous formation of continental ice sheets the collision of india with asia and the cooling of the oceans several effects act in the opposite direction and they can be grouped together because they are all due to there being larger quantities of sediments in the ocean basins today than there were 100 m y ago another effect causing a freeboard increase is the thinning of continental masses during continental breakup and the formation of new ocean basins the total change in sea level after having allowed for isostatic response is 202 m during the last 80 m y flooding of the continents can also be used to determine sea level changes with help from modern hypsographic curves when this is done it is found that the freeboard decrease is considerably less than that calculated from volume estimates although the inaccuracy of the various data would allow these estimates to be not significantly different it is likely that the estimate of freeboard decrease using flooded areas and modern hypsographic data is an underestimate due to the probability that the hypsographic curve has become less steep with time individual estimates of flooding from continents require considerably different amounts of freeboard change the common signal is usually assumed to be the eustatic signal whereas when this common signal is removed from the freeboard estimate for an individual continent the remaining signal is the epeirogenic signal epeirogenic movements can be as large as 150 m and can occur on time scales of a few tens of millions of years other examples of epeirogenic variations are also discussed we have developed a rough power spectrum for epeirogenic movements of the continents this appears to have 1 f variation we suggest that the spectrum could be produced by temperature changes at the bottom of the lithosphere

cretaceous volcanism and jurassic magnetic anomalies in the nauru basin western pacific ocean the nauru basin contains a well documented pattern of late jurassic magnetic anomalies and a cretaceous volcanic complex that has not disturbed the older magnetic structure the following hypotheses are offered to explain this paradox the cretaceous basalts are normally and uniformly magnetized making them invisible to a surface towed magnetometer tension cracks and fractures associated with thermal uplift and or magma wedging provided pathways for the cretaceous magma through the jurassic basement without disrupting the jurassic magnetic structure the same tension cracks admitted sea water that convectively removed heat from the magnetic layer and thus maintained the jurassic basement below its magnetic blocking temperature for extended periods of time during intrusive thermal episodes finally the maximum uplift associated with cretaceous volcanism in the nauru basin could have been equal to but was probably something less than that associated with nearby seamount and atoll chains

acoustic emission induced by pore pressure changes in sandstone samples an understanding of microseismicity induced by pore pressure changes in stressed rocks is important for applications in geothermal and hydrocarbon reservoirs as well as for co 2 sequestrations we have studied the triggering mechanisms of microseismicity or acoustic emission in the laboratory as a function of triaxial stress conditions and pore pressure changes in investigating the spatiotemporal distribution of acoustic emission activity in water saturated triaxially stressed flechtingen sandstone samples subjected to changes in pore pressure we assumed that acoustic events were triggered by pore pressure increase to estimate pore pressure changes in the sample we used an analytical solution of the 1d diffusion equation a theoretical analysis of the spatiotemporal distribution suggested that for initially insignificantly stressed samples acoustic events were triggered by the migration of a critical pore pressure level through the sample the critical level was controlled by the applied pore press

phenomena of pulsation tectonics related to the breakup of the eastern north american continental margin abstract new data from the recent ipod drilling of dsdp site 534 in the blake bahama basin give a definite age for the spreading center shift involved in the breakup of the north american atlantic margin a basal callovian age 155 m y is determined for the blake spur magnetic anomaly marking this spreadingcenter shift that signals the birth of the modern north atlantic ocean this is some 20 m y younger than previously thought an implication of this younger age for the blake spur event is that very high spreading rates are now required for the jurassic outer magnetic quiet zone along the north american margin this association of a relatively high spreading rate with a magnetic quiet zone is similar to that for the mid cretaceous and implies a link between the processes controlling plate spreading which are in the upper mantle and the processes controlling the magnetic field which are in the outer core a theory of pulsation tectonics involving the cyclic eruption of plumes of hot mantle material from the lowermost mantle could explain the correlation plumes carry heat away from the core mantle boundary and later reach the asthenosphere and lithosphere to induce faster spreading the pulse of fast spreading in the jurassic apparently followed the breakup of continents bordering the north atlantic ocean other pulses of fast spreading appear to correlate with major ocean openings on various parts of the globe implying that this might be a prevalent process rifting of passive margins may be controlled by the more fundamental global processes described by the theory of pulsation tectonics

discriminating induced seismicity from natural earthquakes using moment tensors and source spectra earthquake source mechanisms and spectra can provide important clues to aid in discriminating between natural and induced events in this study we calculate moment tensors and stress drop values for eight recent induced earthquakes in the western canadian sedimentary basin with magnitudes between 3 2 and 4 4 as well as a nearby magnitude 5 3 event that is interpreted as a natural earthquake we calculate full moment tensor solutions by performing a waveform fitting procedure based on a 1 d transversely isotropic velocity model in addition to a dominant double couple dc signature that is common to nearly all events most induced events exhibit significant non double couple components a parameter sensitivity analysis indicates that spurious non dc components are negligible if the signal to noise ratio snr exceeds 10 and if the 1 d model differs from the true velocity structure by less than 5 estimated focal depths of induced events are significantly shallower than the typical range of focal depths for intraplate earthquakes in the canadian shield stress drops of the eight induced events were estimated using a generalized spectral fitting method and fall within the typical range of 2 to 90 mpa for tectonic earthquakes elastic moduli changes due to the brittle damage production at the source presence of multiple intersecting fractures dilatant jogs created at the overlapping areas of multiple fractures or non planar pre existing faults may explain the non dc components for induced events

dynamic response of pre stressed rock with a circular cavity subject to transient loading abstract scientists have attempted to investigate deep underground rock failure a key challenge to study underground rock failure is the difficulty to survey its process therefore a large number of important and insightful laboratory investigations of underground rock failure experiments are conducted in this paper an experimental method is proposed to explore dynamic failure process of pre stressed rock specimen with a circular hole the failure process of a rock specimen under different initial static stress coupled with dynamic loading is clearly illustrated by a high speed camera the experimental results indicated that high static pre stress coupled with dynamic loading induces rock debris to be ejected at the surrounding circular hole however lower static pre stress coupled dynamic loading cannot induce rock failure the dynamic stress concentration surrounding the circular hole by transient wave incidence was further demonstrated at the condition of half sine wave loading in this condition the results demonstrated that combined action of static and dynamic stress concentrations induces the primary fractures of rock specimen

palaeoecology of the late triassic extinction event in the sw uk a high resolution palaeoecological study of the shelly invertebrate macrofauna across two marine triassic jurassic boundary sections in the uk st audrie9s bay and lavernock point is presented loss of taxonomic richness occurs in the upper westbury formation to lower lilstock formation late rhaetian but if sample size is taken into account there is little convincing evidence of a catastrophic marine extinction there is however good evidence for significant palaeoecological change in the benthic marine ecosystem at this time the immediate post event recovery interval in the upper lilstock formation is characterized by assemblages of low abundance low diversity high dominance and low evenness body sizes of taxa that survived the event and originated afterwards were low until the later hettangian recovery to higher abundance higher diversity and higher evenness is recorded in the psiloceras planorbis zone recovery of the benthic ecosystem in the aftermath of the late triassic event was disrupted by marine anoxia and shows additional similarities to the much slower recovery that followed the late permian event the pattern of body size changes recorded in the shelly fossil record closely matches that of the trace fossil record shell thickness trends do not support a biocalcification crisis during the late triassic biotic event

thermal evolution of the north central gulf coast the subsidence history of the north louisiana salt basin determined from well data indicates that the region underwent extension during rifting and has since passively subsided due to conductive cooling of the lithosphere timing of the rifting event is consistent with opening of the gulf of mexico during late triassic to early jurassic time crustal extension by a factor of 1 5 to 2 was computed from tectonic subsidence curves however data from the early subsidence history are insufficient to distinguish between uniform and nonuniform extension of the lithosphere the magnitude of extension is in good agreement with total sediment and crustal thicknesses from seismic refraction data in the adjacent central mississippi salt basin the temperature distribution within the sediments is calculated using a simple heat conduction model temperature and subsidence effects of thermal insulation by overlying sediments are included the computed temperature distribution is in good agreement with bottom hole temperatures measured in deep wells temperature histories predicted for selected stratigraphic horizons within the north louisiana salt basin suggest that thermal conditions have been favorable for hydrocarbon generation in the older stata results from a two dimensional heat conduction model suggest that a probable cause for the early formation of the adjacent uplifts is lateral heat conduction from the basin rapid extension of the lithosphere underneath areas with horizontal dimensions of 50 100 km produces extremely rapid early subsidence due to lateral heat conduction the moderate subsidence rate observed in the north louisiana salt basin during the jurassic and early cretaceous suggests slow extension over a long period of time

thermal subsidence and eustasy in the lower palaeozoic miogeocline of western north america we have recently developed a procedure for calculating tectonic subsidence in fully lithified basin sequences and applied it to cambrian and ordovician strata of tbe cordilleran miogeocline exposed in the southern canadian rocky mountains1 the cumulative tectonic subsidence curves were found to be mainly thermal in form as predicted by the passive margin model for the miogeocline2 in this paper we extend the analysis to cambrian and ordovician strata in a much larger segment of the miogeocline extending from the yukon territory to central nevada the results indicate that thermal contraction was the dominant subsidence mechanism for more than 2 000 km along the eastern or inner part of the miogeocline in addition we find a slight but persistent deviation in the subsidence curves from a purely thermal form that is consistent with a global sea level change proposed by vail and others3 for cambrian to middle ordovician time

oceanic crust production and climate during the last 100 myr in order to evaluate the possible influence of oceanic crust production on climatic changes during the past 100myr variations in total oceanic crust for this period including production at mid ocean ridges oceanic plateaus and back arc basins were calculated using the most recent and accurate time scales the rates presented here differ from those of larson 1991a b on cenozoic fluctuations and show that 1 maximum production values occurred during the cenomanian palaeocene and late oligocene early miocene and 2 minimum values occurred in campanian maastrichtian late eocene and middle miocene significantly variations of oceanic crust production correspond with variations in the 18o of deep water benthic foraminifera maximum values of oceanic crust production correspond with minimum values of 18o and minimum production values with maximum values of 18o this latter synchronism suggests that changes in land sea relationships and atmospheric co2 related to major fluctuations in oceanic crust production were the main cause of mid cretaceous warming and late cretaceous cooling and of climatic quasi cycles having a periodicity of 33 38 million years over the last 100 myr this is the first report showing variations of ocean crust production synchronized with the cenozoic climate changes

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

fabric of the cretaceous tertiary marine macrofaunal transition at braggs alabama abstract the record of latest cretaceous and earliest tertiary macroinvertebrates in the k t boundary sequence at braggs alabama is documented by high resolution stratigraphic data latest maastrichtian and earliest danian strata lie within a reversed magnetic interval identified as chron c29r the faunal decline across this interval is abrupt and severe with 50 of the terminal cretaceous species dropping out of the record a pronounced lazarus effect is displayed across the boundary however persistently high cretaceous and low tertiary diversity coupled with good stratigraphic resolution and comparable quality of preservation of both cretaceous and tertiary faunas in similar lithologies all argue for a relatively abrupt decline the lazarus effect is most likely the result of local extinction and or migration rather than taphonomic or collection difficulties if only previously published species lists were used in this study either a gradual extinction pattern or a larger scale lazarus effect could have been invoked to explain the observed diversity changes extensive collecting however has revealed a persistently high diversity throughout the latest maastrichtian no stepwise extinctions were observed and most taxa represent widespread and long ranging clades the braggs faunal transition is consistent with proposed catastophic extinction hypotheses but a limit in temporal resolution of up to 0 8 ma for the faunal turnover at this site allows ample time for other longer term extinction processes and patterns to have developed this resolution is perhaps as good as can be expected with current methods and the shallow marine character of the sequence

acoustic emission and velocities associated with the formation of compaction bands in sandstone received 31 may 2005 revised 2 may 2006 accepted 22 june 2006 published 7 october 2006 1 a series of laboratory experiments has been conducted in which three dimensional 3 d locations of acoustic emissions ae were recorded and used to analyze the development of compaction bands in bleurswiller sandstone which has a porosity of 25 results were obtained for saturated samples deformed under triaxial compression at three different confining pressures 60 80 and 100 mpa a pore pressure of 10 mpa and room temperature we recorded acoustic emissions compressional and shear wave velocities and porosity reduction under hydrostatic condition and under triaxial loading conditions at a constant axial strain rate our results show that seismic velocities and their amplitude increased during hydrostatic pressure build up and during initial axial loading during shear enhanced compaction axial and radial velocities decreased progressively indicating an increase of stress induced damage in the rock in experiments performed at confining pressures of 80 and 100 mpa during triaxial loading acoustic emissions were localized in clusters during progressive loading ae clusters grow horizontally perpendicular to the maximum principal stress direction indicating formation of compaction bands throughout the specimens microstructural analysis of deformed specimens confirmed a spatial correspondence of ae clusters and compaction bands for the experiment performed at a confining pressure of 60 mpa ae locations and microstructural observations show symmetric compaction bands inclined to the cylinder axis of the specimen in agreement with predictions from recent theoretical models

effects of mantle heat source distribution on supercontinent stability a two dimensional cartesian geometry numerical model is used to study the influence of internal heating on the ability of mantle convection to rift and disperse an assembled supercontinent our wide aspect ratio models incorporate migrating plate boundaries and finite thickness rigid mobile oceanic and continental plates 12 000 km across we examine models characterized by both whole mantle and upper mantle convection parameters specifying different degrees of internal heating in the mantle we compare the patterns of convection that develop below stationary continental plates that form as a result of the aggregation of smaller mobile continents following continental collisions we find that a reorganization of mantle flow may result in the development of deviatoric stresses at the base of the continental lithosphere which are capable of initiating continental breakup our results suggest that continental basal stresses are largely controlled by the wavelength of the subcontinental convection pattern and that the inclusion of internal heating in the mantle generally increases this wavelength for models with 80 internal heating in which active upwellings are intrinsically absent basal stresses arise primarily from subduction at the continental margins and result in a geologically reasonable duration for our model supercontinent assemblages 200 myr for models with 40 or less internal heating continental breakup is controlled by mantle upwellings and our supercontinents remain intact much longer 600 700 myr

seismic moment tensors of acoustic emissions recorded during laboratory rock deformation experiments sensitivity to attenuation and anisotropy summary seismic moment tensors can provide information on the size and orientation of fractures producing acoustic emissions aes and on the stress conditions in the sample the moment tensor inversion of aes is however a demanding procedure requiring carefully calibrated sensors and accurate knowledge of the velocity model in field observations the velocity model is usually isotropic and time independent in laboratory experiments the velocity is often anisotropic and time dependent and attenuation might be significant due to opening or closure of microcracks in the sample during loading in this paper we study the sensitivity of the moment tensor inversion to anisotropy of p wave velocities and attenuation we show that retrieved moment tensors critically depend on anisotropy and attenuation and their neglect can lead to misinterpretations of the source mechanisms the accuracy of the inversion also depends on the fracturing mode of aes tensile events are more sensitive to p wave anisotropy and attenuation than shear events we show that geometry of faulting in anisotropic rocks should be studied using the source tensors since the p and t axes of the moment tensors are affected by velocity anisotropy and deviate from the true orientation of faulting the stronger the anisotropy is the larger the deviations are finally we prove that the moment tensor inversion applied to a large dataset of aes can be utilized to provide information on the attenuation parameters of the rock sample the method is capable of measuring anisotropic attenuation in the sample and allows for detection of dilatant cracking according to the stress regime

major episodes of geologic change correlations time structure and possible causes abstract published data sets of major geologic events of the past 250myr extinction events sea level lows continental flood basalt eruptions mountain building events abrupt changes in sea floor spreading ocean anoxic and blackshale events and the largest evaporite deposits have been synthesized with estimated errors these events show evidence for a statistically significant periodic component with an underlying periodicity formally equal to 26 6 myr and a recent maximum close to the present time the cycle may not be strictly periodic but a periodicity of 30myr is robust to probable errors in dating of the geologic events the intervals of geologic change seem to involve jumps in sea floor spreading associated with episodic continental rifting volcanism enhanced orogeny global sea level changes and fluctuations in climate the period may represent a purely internal earth pulsation but evidence of planetesimal impacts at several extinction boundaries and a possible underlying cycle of 28 36 myr in crater ages suggests that highly energetic impacts may be affecting global tectonics a cyclic increase in the flux of planetesimals might result from the passage of the solar system through the central plane of the milky way galaxy an event with a periodicity and mean phasing similar to that detected in the geologic changes

sedimentary evolution and drowning of a passive margin shelf giumal group zanskar tethys himalaya india palaeoenvironmental changes during final break up of gondwanaland

paralic parasequences associated with eocene sea level oscillations in an active margin setting trihueco formation of the arauco basin chile abstract the eocene trihueco formation is one of the best exposed successions of the arauco basin in chile it represents a period of marine regression and transgression of second order duration during which barrier island complexes developed on a muddy shelf the strata are arranged in classical shoaling upward parasequences of shoreface and beach facies capped by coal bearing back barrier lagoon deposits these fourth order cycles are superimposed upon third order cycles which caused landward and seaward shifts of the coastal facies belts the final punctuated rise in sea level is represented by shelf mudrocks with transgressive incised shoreface sandstones relative sea level oscillations as revealed in the stratigraphy of the trihueco formation show a reasonable correlation with published eocene eustatic curves

impact dust not the cause of the cretaceous tertiary mass extinction most of the 3 mm thick globally distributed chicxulub ejecta layer found at the cretaceous tertiary k t boundary was deposited as condensation droplets from the impact vapor plume a small fraction of this layer 14 g was submicrometer size dust the global mass and grain size distribution of the clastic debris indicate that stratospheric winds spread the debris from north america over the pacific ocean to europe and little debris reached high southern latitudes these findings indicate that the original k t impact extinction hypothesis the shutdown of photosynthesis by submicrometer size dust is not valid because it requires more than two orders of magnitude more fine dust than is estimated here furthermore estimates of future impact hazards which rely upon inaccurate impact dust loadings are greatly overstated

microfracturing damage and failure of brittle granites 1 the evolution of stress induced damage and the eventual brittle failure are experimentally analyzed for mount scott granite of oklahoma we quantify the damage intensity in two methods and directly compare model predictions and actual damage the 14 samples of the medium grain size granite were loaded triaxially at dry conditions room temperature and under 41 mpa confining pressure microfractures were mapped in five samples and the majority of them 80 belong to two groups tensile microfractures trending subparallel to the loading axis and shear microfractures trending 11 40 off the loading axis the tensile microfractures dominate the low stress stage and they remain intragranular with a stress increase the relative density of shear microfractures increases with increasing stresses and they formed elongated intergranular zones of coalescing microfractures we compared two independent values of damage intensity 1 the macroscopic experimentally measured reduction of the deformation modulus and 2 the expected reduction of this modulus calculated with several damage models for the density of the mapped microfractures our fracture density data best fit the model of noninteracting cracks of kachanov 1992

relative moment tensors of thermally induced microcracks in salt rock abstract p wave amplitudes were inverted to obtain relative moment tensors and the corresponding radiation patterns of thermally induced microcracks at 850 m depth in the salt mine asse near wolfenbuttel germany seismic waves of microcracks that occurred during a 3 week heating experiment and during the following 12 weeks of cooling were recorded with eight high frequency piezoelectric sensors 5 100 khz positioned a few metres from the sources about 42 000 microcracking events were automatically located during this observation period two microcrack clusters were studied that occurred immediately after switching off the heater power the clusters were located a few centimetres from the heater borehole the moment tensors of these clusters indicate dominant shear cracks with a strike slip radiation pattern the p and t axes directions appear to coincide with directions of measured maximum and minimum horizontal stresses

tectonic velocities dynamic topography and relative sea level 1 a simple dynamic model based on boundary layer theory shows that dynamic topography is unlikely to vary significantly in response to short term 20 myr variations in the mean tectonic velocity tectonic velocities essentially mirror variations in mantle viscosity but are not indicative of substantial modification of dynamic topography which primarily reflects mass anomalies in the mantle this implies that relative sea level is unlikely to be affected by tectonic pulses and also that observed tilting of cratonic margins cannot result from a pulse of increased tectonic velocities thus relative sea level is primarily controlled by the seafloor age distribution although long term 100 myrs changes in tectonic velocity will produce dynamic topography that reinforces sea level changes associated with changing ridge volume

lower danian bivalves stevns klint denmark continuity across the k t boundary abstract the paleoenvironmental change at the k t boundary at stevns klint is a change from an upper maastrichtian bryozoan bioherm environment with different faunas from the bioherms and from the interbiohermal basins to an early danian environment comparable to the biohermal basins except for a nearly complete lack of bryozoans in the lowermost danian the bivalves exhibit a drastic reduction in species number when the complete faunas are compared however a within habitat comparison between the maastrichtian interbiohermal basins and the danian shows an increase in the number of infaunal species across the boundary a decline in the number of epifaunal species is related to the lack of bryozoans acting as substrates for epibyssate bivalves comparison with other k t boundary sections rich in marine mesobenthos does not support the presence of general patterns in the faunal change at the boundary

the cenomanian turonian boundary mass extinction late cretaceous new insights from ammonoid biodiversity patterns of europe tunisia and the western interior north america major biological crises are attributed to a variety of factors whose respective contributions and interactions are often difficult to disentangle the cenomanian turonian boundary was a period of high organic matter burial coupled with a high positive excursion in the carbon isotope record this event has been widely recognized to reflect anoxic conditions the oceanic anoxic event 2 and is concomitant with one of the major mass extinctions of the phanerozoic it has been considered a typical example of global extinction caused by the spreading of anoxic waters however recent studies question this anoxia kill mechanism in europe both from palaeontological and sedimentological arguments hence this study analyzes the biodiversity patterns of ammonoids from three major areas europe tunisia and the western interior in order to better understand the relationships between ammonoid biodiversity patterns and abiotic factors during the cenomanian turonian interval the biodiversity patterns of ammonoids species richness origination extinction turnover poly cohort survivorship and taxonomic distinctness highlight that the mass extinction of the cenomanian turonian boundary is restricted to europe when considering only ammonoids only europe documents an actual decrease of species richness during the late cenomanian which results mainly from decreasing origination in tunisia where the onset of anoxic waters is synchronous with europe species richness increases during the late cenomanian and reaches its highest values in the lower turonian the western interior records relatively high species richness during the late cenomanian with only a single minor extinction event furthermore major changes in biodiversity patterns of ammonoids occurred around the middle upper cenomanian boundary i e ca 0 75 myr before the onset of the oae2 although there is extensive evidence for widespread anoxia during the cenomanian turonian boundary interval in deep sea environments the biodiversity patterns of ammonoids in europe tunisia and the western interior rule out global anoxia as a direct causal mechanism for changes in ammonoid diversity these biodiversity patterns also question the global scale character of the so called cenomanian turonian mass extinction observed biodiversity patterns of ammonoids strongly support the global warming of the late cenomanian as evidenced by the northward migration of the tethyan realm changes in ammonoid diversity are compatible with the exceptional high sea level occurring at that time and with concomitant regional climate changes

selective extinction and survival across the cretaceous tertiary boundary in the northern atlantic coastal plain the inner atlantic coastal plain in new jersey and the delmarva peninsula is underlain by an upper cretaceous lower tertiary sequence of marine and paralic sand clay and glauconitic beds campanian maastrichtian danian and thanetian deposits are especially fossiliferous and yield a succession of marine faunas that reveal a pattern of selective extinction and survival across the cretaceous tertiary k t boundary in this area cretaceous benthic invertebrate communities are dominated by oysters and other semi infaunal and infaunal molluscs with planktotrophic larval stages these are replaced in the danian by brachiopod dominated communities that are composed of epifaunal benthos with a variety of nonplanktotrophic reproductive strategies a similar pattern is observable in the nektonic cephalopod populations in this sequence the typical ammonites of the cretaceous became extinct at the k t boundary whereas the nautilids survived ammonites are thought to have had a planktotrophic larval stage whereas nautilids are known to lay large lecithotrophic eggs this pattern of differential survival is attributed to the planktonic population crash at the k t boundary which placed planktotrophically reproducing species at a disadvantage while favoring the varied groups that practiced alternative reproductive strategies

causes and consequences of the relation between area and age of the ocean floor the distribution of area of the ocean floor with age t is approximately described by da dt c0 1 t tm where c0 is the rate of crustal generation and tm the maximum age a linear differential area versus age relation can be explained by a balance between crustal generation and consumption where consumption is uniformly distributed with age the present distribution of consumption with age was estimated from the isochron map used to derive the area age relation and a recently published set of angular velocity vectors describing present plate motions the rate of consumption per unit age shows considerable scatter about a mean value equal to c0 tm 1 7 10 8 km2 yr2 but consumption is sufficiently close to being uniformly distributed with age to explain the observed degree of approximation to a linear differential area age relation the trenches appear to be distributed randomly with respect to age provinces in the oceans it was not possible to discern any trend of mean subduction velocities with age apart from the smaller velocities observed for the two youngest age provinces 0 9 ma changes in the rate of plate generation and the distribution of consumption with age result in shifts in the area age distribution in turn these shifts produce changes in the plate driving forces which act to restore the rate of plate generation and distribution of consumption to their initial states the ridge pushing force for example decreases as the rate of crustal generation increases this coupling between driving forces and the area age distribution provides a feedback mechanism limiting the extent of any changes a measure of the magnitude of shifts in the area age distribution is given by global changes in sea level if long term changes in sea level are less than 150 m as suggested by recent estimates then only small changes 12 in the rate of plate generation and distribution of consumption with age are required sea level changes as large as 300 m require about a 50 change in the rate of crustal generation the above area age relation can be combined with simple expressions for depth and heat flow versus age to obtain an empirical hypsometric distribution parameterized in terms of age and exact expressions for the heat loss from the ocean floor the latter is estimated to be 2 9 1013 w with 25 of this heat being lost by seafloor younger than 5 ma of the total heat loss from the mantle 26 is estimated to be transported by small scale convection

sea level cycles during the growth of atlantic type oceans abstract first order changes in global sea level are commonly thought to be the result of short term fluctuations in oceanic spreading rate however eustatic high stands have occurred only twice in phanerozoic time and in both cases have followed supercontinent break up by a lag period of 50 100 ma therefore if pulses in spreading rate were the primary control of eustasy then for some reason rate increases would have had to have occurred with predictable periodicity with respect to major rifting events alternatively we propose that the major control on first order sea level cycles is the formation of atlantic type oceans with its attendant changes in the area age distribution of the global ocean floor and the formation of extensional passive margins our calculations indicate that both the approximate magnitude and relative timing of sea level highstands relative to supercontinent break up are predicted by this mechanism thus the importance of short term spreading rate variations in eustatic cycles becomes secondary

modeling sea level changes as the atlantic replaces the pacific submergent versus emergent observers we evaluate the sea level changes caused by changing the age area relationship of the seafloor by altering the thermal structure and hence the elevation of the world seafloor we do this by having a passive margined and therefore continuously aging atlantic type ocean open at a uniform rate at the expense of an active margined and therefore constant age pacific type ocean this run of the model was specifically constructed to answer the question of how much sea level would change if the atlantic opened at a uniform rate therefore it specifically excludes the other major processes that change sea level these would include changes in ice volume other changes in plate generation consumption rates continental orogeny and epeirogeny lithospheric stretching lithospheric flexure and thermally induced subsidence at passive margins and amplification thereof caused by water and sediment loading the isostatic effects of continental flooding and oceanic unloading are accommodated by application of balanced global isostasy to an earth model consisting of 121 independent columns the lithospheric portions of the columns are linked to the hypsographic curve sea level changes are viewed from two different observational positions 1 geologically stable and continually emerged continental plateau and 2 geologically stable and continually submerged shelf break the modeled sea level that results from changing the age area relationship of the seafloor since 160 ma peaks at 85 ma and is 30 less for the emerged observer 34 m than for the submerged observer 48 m furthermore the peak is in phase with but only 1 4 48 m versus 200 m of that portrayed by either the eustatic curves inferred from seismic stratigraphy or the isostatically readjusted positions of marine strandlines of the stable platform of north america we therefore conclude that the other 3 4 of sea level rise that accompanies the opening of the atlantic must be partitioned among the other causes suggested above

terrestrial evidence for the lilliput effect across the cretaceous paleogene k pg boundary abstract recent research has demonstrated that the lilliput effect reduction of body size in biota associated with the aftermath of mass extinctions affected all trophic levels in the marine realm following the cretaceous paleogene k pg event however it is unclear if this size change was strictly a marine signal or a global phenomenon that also affected continental ecosystems herein we present the results of an ichnological proxy for body size of soil dwelling insects across the k pg boundary in big bend national park texas u s a quantitative efforts focused on naktodemasis bowni which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci these traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments as an approximation for the body size of the subterranean insects this dataset indicates that a smaller n bowni diameter dn is statistically correlated

patterns of bivalve biodiversity from early to middle triassic in the southern alps italy regional vs global events abstract the triassic records the severe effects of the end permian mass extinction and the beginning of the mesozoic modern adaptive radiation of marine invertebrates as far as bivalves are concerned a group which was relatively unaffected by the extinction diversification started in the middle triassic more particularly during the anisian thus the interval between the basal triassic induan and anisian is crucial in analysing the biodiversity changes and diversification patterns of these molluscs this analysis is discussed at genus level and based on the regional records of the southern alps biodiversity changes are examined in connection with palaeogeographic evolution the conquest of vacated ecologic niches and climatic changes the lowest point of generic richness as an immediate aftermath of the p t mass extinction is recorded in the induan units mazzin and siusi mbs of the werfen formation which include only five genera numerically dominated by claraia and unionites twelve genera are represented in the olenekian campil val badia and cencenighe members such an increasing richness is mostly connected with the recovery of pectinids and endobyssate bakevellids typical marine biota such as ammonoids tirolites and dinarites fauna and crinoids also appear in this time the richness and structure of the early anisian bithynian bivalve assemblages contained in the gracilis formation and equivalent units of southern alps do not significantly change 15 genera in comparison with those from olenekian the most relevant increase in bivalve genera 31 genera occurs in the late anisian mostly in the pelsonian calcare di recoaro and equivalent units when a strong tectonic phase considerably differentiated the marine habitats and ecological niches in the southern alps however bivalve pelsonian radiation is recorded in other tethyan and peri tethyan areas and coincides with the reappearance of marine stenotopic hard bottom dwellers and reef communities including scleractinian corals therefore it represents a global bioevent which indicates the fully recovery of the physical and chemical limiting factors of the sea water in the southern alps the diversification of bivalves after the end permian extinction occurred in two steps at the end of smithian early olenekian when their recovery began and in the pelsonian late anisian when their radiation parallels with the recovery of hard bottom communities and metazoan reefs both the events occurred at the end of humid phases

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

productivity across the cretaceous tertiary boundary in high latitudes in low and middle latitudes the cretaceous tertiary boundary is marked by a sudden and pronounced decrease in 13c values of near surface water carbonates and a reduction in the surface to bottom 13c gradient these isotopic data have been interpreted as evidence of a decline in surface water productivity that was responsible for the extinction of many planktic foraminiferal species and other marine organisms at or near the k t boundary we present planktic and benthic foraminiferal isotopic data from two almost biostratigraphically complete sections at ocean drilling program site 738 in the antarctic indian ocean and at nye klov in denmark these data suggest that planktic carbonate 13c values in high latitudes may not have decreased dramatically at the k t boundary thus surface water productivity may not have been reduced as much as in low and middle latitudes comparison of the records of site 738 with those of odp sites 690 and 750 indicates a pronounced decline in 13c values of planktic and benthic foraminifera and fine fraction bulk carbonate 200 000 yr after the k t boundary this reflects a regional shift in the carbon isotopic composition of oceanic total dissolved carbon tdc and correlates with a similar change in benthic foraminiferal 13c values at mid and low latitude deep sea drilling project sites 527 and 577 this oceanographic event was followed by the ecosystem s global recovery 500 000 yr after the k t boundary these data suggest that the environmental effects of the k t boundary may have been less severe in the high latitude oceans than in tropical and subtropical regions