microtektites and mass extinctions evidence for a late devonian asteroid impact glass spherules similar to microtektites have been found near the frasnian famennian boundary f f upper devonian at senzeilles belgium contemporaneous with one of the largest marine mass extinctions of the phanerozoic these spherules exhibit a wide range of compositions and display teardrop dumbbell and compound morphologies analogous to microtektites in addition they lack crystallites have few or no vesicles and have a low content of volatile material these characteristics are supportive of an impact origin the siljan ring sweden and charlevoix structure quebec canada are candidate craters of this age the presence of microtektites near the f f boundary supports the hypothesis that an impact caused the upper devonian worldwide benthic mass extinctions

frasnian famennian biotic crisis undervalued tectonic control the prime cause of the late devonian kellwasser crisis culminating in a mass extinction event near the frasnian famennian f f boundary remains conjectural nevertheless rapid sea level fluctuations of uncertain origin during tectono eustatic highstand paired with repeated oceanic anoxia and climatic changes are usually thought at present to be one of the main immediate triggers the cathles hallam model of stress induced changes in plate density accompanying rapid rift formation furnishes an alternative for understanding the enigmatic sudden eustatic variations in the non glacial time late devonian tectonic extension causing rifting and volcanicity appears to be strongly marked in several regions of eurasia particularly in kazakhstan and eastern laurussia all larger devonian continents were more or less tectonically affected a subtle record of this tectonic rearrangement is implied even for distant and apparently quiet carbonate platforms in local extensional block faulting and tilting hydrothermal mineralisation geochemical anomalies and localized blooms of siliceous biota interpreting the late frasnian regressive transgressive pattern in terms of the cathles hallam tectono eustatic model two major rifting events are hypothesized one at about the beginning of the rhenana zone and a second principal pulse in the late linguiformis zone that encompassed the f f transition developing the veimarn milanovsky scenario of the global extensional pulse it is assumed that the key endogenous factors were related to episodic super plume activity the tectonically triggered changes climaxed in thermal and nutrient pulses and induced the stepdown ecosystem destabilization observed in the f f bio crisis minor cometary strike s might have eventually participated in this prolonged multicausal environmental stress mainly due to additional thermal shocks but perhaps effective on a regional scale only

microtektite like impact glass associated with the frasnian famennian boundary mass extinction abstract glass spherules of probable impact origin occur in the late devonian hony section in belgium they are found at the stratigraphic level of the frasnian famennian boundary which is marked by one of the largest mass extinctions in the phanerozoic the hony glass spherules are chemically identical to those previously described from the stratigraphically equivalent senzeille section located 90 km to the west southwest in contrast to the senzeille layer the age of the hony spherule layer is well constrained by conodont biostratigraphy the spherules have morphological and chemical characteristics similar to tektites and microtektites they have a broad range of chemical composition with generally high k2o na2o and al2o3 na2o k2o their water content is in the range measured for tektites and impact glasses small inclusions of lechatelierite may be present in the spherules these glass spherules are likely to be the product of an impact event that occurred at or very near the frasnian famennian boundary the target rock was probably a clay rich pelitic sediment intermixed with carbonates the 368 1 ma siljan ring crater sweden is the most likely impact site candidate the hony and senzeille glass spherules represent the first substantial evidence that an impact event may be linked to the frasnian famennian mass extinction

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

eutrophication by decoupling of the marine biogeochemical cycles of c n and p a mechanism for the late devonian mass extinction the late devonian mass extinction was unusually protracted and ecologically selective with preferential diversity losses among reefbuilding organisms and tropical shallow water faunas in general we have investigated the link between the extinction s unique characteristics and changes in biogeochemical cycling through analyses of the 13 c and c n p atomic ratios of organic matter buried across the kellwasser horizons in western new york state each horizon is characterized by 1 a long term 4 5 excursion in 13 c 3 of which occurs within the horizon and 2 a dramatic increase in the burial ratios of c n p from values of 100 15 1 to an average of 5000 170 1 on the basis of these results we propose that 1 increased efficiency of biolimiting nutrient recycling resulting from cyclic water column stratification and mixing promoted eutrophication during kellwasser deposition in new york and 2 the isotope excursions represent the composite effect of long term global organic c burial and local changes in photosynthetic c isotope fractionation related to nutrient availability this eutrophication model forges a mechanistic link between proposed late devonian climatic cooling and the selective demise of taxa likely to have been narrowly adapted to oligotrophic conditions

globorotalia truncatulinoides in central western mediterranean sea during the little ice age abstract globorotalia truncatulinoides oscillations have been recorded from different marine sediment cores collected in the central and western mediterranean sea the abundances of this species over the last 500 yrs demonstrates its potential value as bio indicator of particular oceanographic condition during the maunder minimum mm event of the little ice age lia the comparison between the g truncatulinoides abundance patterns of the balearic basin central and south tyrrhenian sea and central and eastern sicily channel allows to highlight a similar response of this species during the mm event in the central western mediterranean sea the ecological meanings of this species and its peculiar high abundance percentages in the total assemblages suggest the development of enhanced vertical mixing conditions during mm winter season with a strong advection of nutrients from the nutrient rich deeper layers and enhances the productivity levels in the mixed layer the intensified vertical mixing could be linked to persistence of an atmospheric blocking event recorded by several authors during the mm

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

nutrient enriched waters and the early skeletal fossil record this paper examines the role of stratified oxygen depleted and nutrient enriched water masses new in transforming the fossil record over the precambrian cambrian boundary interval the following may serve as markers for the encroachment of new over low latitude cratons trace element enriched black shales stone coals and hydrocarbon source rocks phosphorites phosphatized shells and organic matter sponge spicule cherts early appearance of silica and phosphatic skeletons appearance of anabarites and coleoloides biofacies peak diversity of phosphatic species occurrence of black shale lagerstatten and light 13 c values of carbonates nutrient depleted waters ndw are inferred over inner cratonic areas and nutrient starved waters nsw may well have developed over deeper waters at times through the later cambrian related to the effects of sea level rise and salinity stratification carbon isotopic fluctuations are suggested to record the history of these water masses with major changes in carbon burial and palaeoproductivity the latter may well imply episodes of greenhouse climate with globally raised levels of carbon dioxide and relatively high ocean temperatures

coesite and shocked quartz discovered in the australasian and north american microtektite layers samples from the north american australasian and ivory coast microtektite layers were examined for unmelted impact ejecta 125 m size coesite and shocked quartz identified by x ray diffraction were found at all the sites where a well defined north american microtektite layer had previously been documented coesite and shocked quartz were also foundin seven out of 33 cores from the australasian strewn field however no coesite or shocked quartz was found associated with the ivory coast microtektite layer stishovite was also found at three of the australasian sites all of the australasian cores containing coesite and shocked quartz were taken from within 2000 km of indochina which is believed by most to be the source area for the australasian tektites and microtektites six of the seven cores have the highest concentrations of microtektites ever determined for australasian microtektite bearing cores the seventh core did not contain any microtektites which may be consistent with the hypothesis that the microtektites were deposited in a raylike pattern the discovery of coesite and impact ejecta associated with both the north american and australasian microtektite layers provides further support for the hypothesis of terrestrial impact origin of tektites

palaeoenvironmental changes at the frasnian famennian boundary in key european sections chemostratigraphic constraints abstract the study aims to put constraints on global environmental changes which took place during the frasnian famennian f f transition by using a geochemical multiproxy approach for this several key european f f boundary sections deposited in different palaeogeographic settings were selected including in addition to the stratotype and parastratotype sections of coumiac montagne noire france and steinbruch schmidt branau germany respectively also some other sections thoroughly characterized by other authors the drilling budesheimer bach prumer mulde germany kowala section holy cross mountains poland la serre france changes in the detrital flux along the sections were evaluated on the basis of both variations in mineral composition and in some diagnostic element ratios like ti al the biogenic flux was assessed as a function of the corg content the input of nutrients or the palaeoproductivity was determined by the p2o5 and ba in excess the degree of anoxia during deposition was constrained by determining the concentration of redox sensitive metals e g fe mn in the bulk sediment of specific element ratios e g v cr as well as the size of pyrite grains together with the degree of pyritization dop in the budesheimer bach core the hydrothermal and volcanic influence in the sedimentary record was detected using e g the al al fe mn and zr al2o3 ratios the kellwasser horizons are characterized by a general decrease in the detrital input together with the increase of al normalized concentration of some of the transition metals these changes are interpreted as reflecting a relative sea level rise and a higher hydrothermal influence in contrast to these the establishment of dysoxic anoxic conditions in the depositional environment as well as the increase of organic matter burial are not always restricted to the kellwasser horizons kwh moreover the hydrothermal influence can lead to misinterpretation with respect to redox conditions and productivity due to the additional input of some specific elements our results indicate the coincidence of sea level rise with hydrothermalism and volcanism during the deposition of the kwh in the area of south laurussia and north gondwana the resulting enrichment in metals and nutrients is coupled in several f f boundary sections with a higher microbial activity as already observed by some authors these effects coupled with a general lowering of the degree of oxygenation of the water bodies could have played a significant role in the demise of the biota

the frasnian famennian boundary interval in the south polish moravian shelf basins integrated event stratigraphical approach abstract the late devonian mass extinction event near the frasnian famennian f f boundary has been analysed using conodont biostratigraphy and biofacies sedimentology magnetic susceptibility and geochemistry in reference sections of the south polish moravian shelf holy cross mountains cracow and brno areas high resolution biostratigraphic study revealed difficulties in the precise recognition of this natural stage boundary but confirmed the occurrence of a major third order sequence boundary in the f f transition in an active synsedimentary tectonic setting marked by erosional discontinuities hardgrounds and brecciation or omission surfaces conclusive evidence of an extraterrestrial impact has not been found among earth bound factors the main devastating role in the shelf habitats is ascribed to fluctuating anoxia and or nutrient dynamics in a disturbed greenhouse climatic setting the long term facies changes were determined by a conspicuous break in carbonate production accompanied by replacement of mature stromatoporoid coral reefs by pioneer shelly crinoid banks microbial mounds and localised oolitic bars the key f f passage interval was marked by intermittent but generally accelerated periplatform ooze debris input and severe storm events as well as by probably highly fluctuating oxygenation and biological overproduction best manifested in radiolarian silicisponge and cephalopod acmes eutrophication phenomena at least partly stimulated by various hydrothermal and volcanic processes were one of the major biogeochemical processes during this climax of the late devonian biotic crisis however significant oceanographic perturbations were also linked with the onset of the transgressive hypoxic upper kellwasser event still within the latest frasnian linguiformis zone i e well before the f f conodont collapse implied variations in the redox state of seawater through the kellwasser timespan probably in regionally highly variable temporal scales are in agreement with recent palaeoecological and biogeochemical inferences in particular suggesting recovering oxygenation just prior to the f f boundary in the other laurussian intrashelf basins all the data support a long time multicausal earth bound crisis instead a worldwide cosmic catastrophe

frasnian famennian mass extinction and cold water oceans suturing of laurussia and africa elimination of easterly tropical currents and consequent equatorial diversion of cold and possibly dysaerobic waters are suggested as prime causes of the frasnian famennian late devonian extinction these are explained by using a new paleogeographic model evidence for stepdown extinctions that took place from givetian through frasnian time is taken particularly from atrypoid brachiopods one of the most abundant representatives of the global tropical shelly marine benthos during the middle and late devonian only 5 of 17 frasnian genera or subgenera of atrypoids are known to be present in late frasnian sediments and possibly only a single genus spinatrypa was present at the frasnian famennian boundary evidence for stepdown extinction from other invertebrate and vertebrate groups in general corroborates that provided by brachiopods

anoxia pre dates frasnian famennian boundary mass extinction horizon in the great basin usa abstract major and trace metal results from three great basin stratigraphic sections with strong conodont biostratigraphy identify a distinct anoxic interval that precedes but ends approximately 100 kyr before the frasnian famennian f f mid late devonian boundary mass extinction horizon this horizon corresponds to the final and most severe step of a more protracted extinction period these results are inconsistent with data reported by others from the upper kellwasser horizon in europe which show anoxia persisting up to the f f boundary in most sections conditions returned to fully oxygenated prior to the f f boundary in the study area these data indicate that the worst part of the f f extinction was not related directly to oceanic anoxia in this region and potentially globally

boudinage structure some new interpretations based on elastic plastic finite element simulations abstract an elastic plastic finite element method based on the prandtl reuss equations of plastic flow and involving equivalent stresses and strains is used to study boudinage structure our choice of data for the simulations was guided by published stress strain curves for marble matrix and quartzite boudin the essential parameters being yield stress and rock hardness defined by the slope of the stress strain curve all models assume an initial fracture and slight separation and therefore only simulate post fracture behaviour the simulations suggest that boudin shape is determined by boudin hardness maximum stresses are concentrated in the corners which therefore shows the most shape modification matrix hardness determines the amount of boudin separation direct comparison with natural examples is restricted to boudins suffering no significant pre fracture plastic deformation i e rectangular and barrel shaped boudins although other types are likely to have the characteristics of barrel and pinch and swell styles the simulations do not consider the nature and timing of boudin defining fractures but these are important in determining the style of boudinage which ultimately develops some mechanical problems associated with the infilling of inter boudin gaps by ductile rock matrix are discussed and two models proposed the first based on yielding fracture mechanics is used to explain boudins with wedge shaped or otherwise nonmatching ends the second a hydraulic model is proposed to account for gaps between rectangular boudins that are filled by ductile rock matrix

ocean stagnation and end permian anoxia ocean stagnation has been invoked to explain the widespread occurrence of organic carbon rich laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end permian mass extinction however to a first approximation stagnation would severely reduce the upwelling supply of nutrients to the photic zone reducing productivity moreover it is not obvious that ocean stagnation can be achieved numerical experiments performed with a three dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the late permian ocean we find that polar warming and tropical cooling of sea surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization buildup of quantities of h2s and co2 in the late permian ocean sufficient to directly cause a mass extinction however would have required large increases in the oceanic nutrient inventory

a stress transfer model for the development of extension fracture boudinage abstract the term boudinage is used to describe a wide variety of extensional structures in deformed rocks this paper is mainly concerned with boudinage resulting from through layer extension fractures followed by separation of the layer segments thus forming boudins with more or less rectangular cross sections in principle this process is similar to the break up of fibres in fibre reinforced composite materials extended parallel to the fibre direction both processes are controlled by the transfer of stress from the matrix to the fibre or layer and a mathematical model for fibre matrix stress transfer the fibre loading model is well established we have used this as a basis for developing a stress transfer model for boudinage the only difference in the basic mathematical formulation results from geometric differences between the two systems the geometric expressions in the fibre loading model have therefore been rederived for the layer matrix case stress transfer theory predicts that the tensile stress in a layer segment rises from a minimum at the end of a segment to a maximum at the centre this behaviour which is clearly shown by finite element models of boudinage structure suggests that extension fracture boudinage develops by successive mid point fracturing according to stress transfer theory the process will continue until a layer is reduced to segments boudins all of which are shorter than some critical length for which the tensile fracture strength of the layer is equal to the tensile stress at the mid point in practice successive fracturing will be influenced by two other factors 1 in nature the controlling material properties tensile fracture strength elastic moduli will not be single valued but will have a distribution reflecting local variations in lithology and microstructure and 2 major pre deformation flaws may be present in a layer which will control the starting length of layer segments these factors are incorporated with the stress transfer theory into a statistical monte carlo model for extension fracture boudinage which results in a prediction of boudin aspect ratios the predicted distribution compares very closely with the observed distribution of 91 quartzite boudins within lower carboniferous slates at tintagel cornwall the stress transfer model implies that boudin defining fractures occur sequentially so that inter boudin gap lengths will be unequal strain estimates based on boudinage structure will vary according to which part and how much of a layer is sampled a much improved strain estimate is possible based on sequentially closing the inter boudin gaps the stress transfer theory also leads to the possibility of estimating palaeostress from boudinage structure and is the only model available which predicts an aspect ratio distribution of boudins formed by extension fracture other than our own we know of no published data on boudin aspect ratio distributions hence further elaboration of the model is not possible until more field data is available we hope that our work will encourage the systematic measurement of boudinage as well as the development of alternative models

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

geochemical analysis and paleoecological implications of phosphatic microspherules otoliths from frasnian famennian boundary strata in the great basin usa phosphatic microspherules 1 mm diameter recovered from the upper devonian uppermost frasnian guilmette limestone in eastern nevada are interpreted here to be fish otoliths and thus provide insight into ocean water chemistry just prior to the frasnian famennian mass extinction boundary analysis by scanning electron microscope sem and electron microprobe indicates that they are apatite francolite and consist of radially aligned concentrically banded crystals around a central nucleus this type of microspherule previously interpreted to be conodont pearls has compositions more similar to fish teeth derived from the same unit than to conodonts microspherules and fish teeth have consistently lower concentrations in wt of p2o5 31 88 36 32 f 3 05 5 12 sro 0 15 0 34 and analysis totals indicating higher concentrations of oh and or co3 90 66 96 09 and higher cao 51 67 55 15 so2 0 50 0 90 mgo 0 09 0 15 and fe2o3 0 11 0 21 than the associated conodonts p2o5 37 32 40 01 f 4 99 6 89 sro 0 32 1 79 totals 96 07 100 55 cao 52 32 53 06 so2 0 05 0 21 mgo 0 01 0 05 fe2o3 0 02 0 11 these differences in composition are consistent from core to rim in all microfossils analyzed and reflect primary biogenic compositions rather than diagenetic or metamorphic signatures we interpret the apatite microspherules to be genetically related to the fish teeth rather than to the conodonts based on the geochemical analysis the microspherules are morphologically similar to modern teleost fish otoliths the fish teeth found associated with the microspherules are from acanthodian or actinopterygian fish which possessed otoliths in the devonian and are the distant ancestors to modern teleost fish modern fish otoliths normally have a calcium carbonate composition but their trace element composition is highly sensitive to ambient water temperature and chemistry we speculate that the stratigraphically restricted range and phosphatic composition of the devonian otoliths reflects secretion by fish under conditions of excess dissolved reactive phosphorus in the water column that was most likely associated with upwelling and cooler water conditions on the shelf during maximum transgression

mountain building enhanced continental weathering and organic carbon burial as major causes for climatic cooling at the frasnian famennian boundary c 376 ma the late devonian was a period of drastic environmental changes as exemplified by a major biotic crisis at the frasnian famennian boundary ffb and the onset in famennian times of glaciations across southern gondwana worldwide evidence for the coeval development of the major acadian eovariscan belt led us to propose a model relating the late frasnian famennian environmental perturbations to extensive continental uplift through two atmospheric co2 depleting mechanisms 1 the intensification of silicate weathering on the continental areas as attested by a major rise in the 87 sr 86 sr composition of sea water at the ffb and 2 the massive burial of organic carbon kellwasser events in partially confined basins due to the collisional induced reduction of equatorial oceanic communications between the palaeotethysian and panthalassic oceans this process is also suggested to have been controlled by an important primary productivity connected to an increased nutrient availability triggered by the enhanced continental run off

microspherules in devonian sediments origins geological significance and contamination problems we have studied various microspherules 0 5 mm across that were found in devonian sediments from canada and china during our micropaleontological studies e g conodont picking these spherules are similar in appearance but they are quite different in origin a combined scanning electron microscope energy dispersive x ray x ray microdiffraction and electron microprobe analysis enables us to determine their probable origins phosphatic conodont pearls of biological origin silicate glass microtektites of terrestrial meteorite impact origin and black magnetic iron spherules of probable extraterrestrial origin we also observed some contaminant spherules glue spatters and steel slag of artificial origins studies of natural spherules in sediments can provide important geological information that may be otherwise undetectable

phosphorus phosphorites and skeletal evolution at the precambrian cambrian boundary clustering of sedimentary phosphate deposits around the precambrian cambrian boundary is related to a global phosphogenic event this event probably resulted from a complex interplay of factors and had a profound effect on the biota with high concentrations of phosphorus in the photic zone producing an increase in the total shallow marine biomass faunal diversification the precipitation of skeletal structures and explosive evolution

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

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

textural and rb sr isotopic evidence for late paleozoic mylonitization within the honey hill fault zone southeastern connecticut a petrographic and rb sr isotopic study of rocks within and near the honey hill fault zone places important constraints on its history of movement rb sr apparent ages for micas and plagioclase from these rocks have been reset and range from permian to triassic considerably younger than the minimum stratigraphic age ordovician of the rocks studied or of acadian devonian regional metamorphism permian rb sr ages of dynamically recrystallized muscovite date the development of mylonite fabric an older age is precluded by the excellent preservation of unrecovered quartz which indicates that these rocks did not experience temperatures high enough to anneal quartz or thermally reset rb sr isotopic systems in muscovite since the time of mylonitization metamorphic mineral assemblages and mineral apparent ages in rocks north of the fault zone indicate recrystallization under similar upper greenschist lower amphibolite grade conditions during permian to triassic time collectively these results indicate that the honey hill fault zone was active during the late paleozoic and that ductile deformation and metamorphism associated with the alleghanian orogeny extend well into southern connecticut an alleghanian age for mylonitization within the honey hill fault zone suggests it should be considered as a possible site for the major late paleozoic strike slip displacementsmore inferred from paleomagnetic studies for parts of coastal new england and maritime canada less

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

asymmetrical pull aparts and foliation fish as kinematic indicators abstract from field observations asymmetrical boudins pinch and swell structures and ellipsoidal volumes of oblique foliation segments in anisotropic rocks lacking competent layers are potentially useful kinematic indicators in shear zones they are derived by the modification of initially symmetrical pull aparts and or layering by superposed layer parallel shearing the response of boudins to such shear is a synthetic flow of those corner volumes lying within the extensional quadrants of the kinematic framework of the deformation into the inter boudin gaps type 1 asymmetrical pull aparts the response of pinch and swell structure is a back rotation of the swells to form type 2 asymmetrical pull aparts discrete extensional shears in the pinches may be either absent type 2a or present type 2b analogues of types 2a and 2b asymmetrical pull aparts occur in anisotropic materials with no compositionally distinct competent members where ellipsoidal volumes contain back rotated foliation segments foliation fish the field based kinematic interpretation was successfully tested by laboratory experiment wherein initially symmetrical trains of pre formed competent internally anisotropic boudins and pinch and swell structures were deformed in bulk simple shear a mechanical model is presented in terms of two material properties of the inclusions competence viscosity and internal rheological anisotropy in an attempt to account for the observed flow in the experiments and the deduced flow and kinematic significance of the natural examples in the presence of angular corners and associated geometrical stress concentrations competence viscosity controls the response to shear in the boudins in the absence of angular corners internal anisotropy controls the response to shear in the pinch and swell structures and in the foliation fish

lamina scale analysis of sedimentary components in cretaceous black shales by chemical compositional mapping implications for paleoenvironmental changes during the oceanic anoxic events abstract relative abundances and distribution patterns of mineral components in finely laminated livello bonarelli lb black shale from the cenomanian turonian boundary cretaceous were investigated by 10 m resolution compositional mapping using an electron probe microanalyzer sedimentary components such as biogenic silica si bio calcium phosphate calcium carbonate and pyrite were reconstructed by image processing of the compositional maps total organic carbon c org content was also determined at a sampling interval of 1 5 mm the depth profiles of these sedimentary components covering 60 of the total 104 cm lb sequence indicate the highly variable nature of their deposition especially the c org contents vary widely ranging from org are clearly discernible in the lb and correspond to dark colored intervals repeated occurrences of c org rich and si bio rich intervals are one of the most prominent features in the lb these features could be explained partly by dilution of c org by si bio but largely by the presence of two distinct paleoenvironmental settings one involves predominant deposition of organic matter and the other is dominated by si bio deposition the thickness of individual intervals varies widely mostly ranging from 1 5 to 35 mm representing oceanic changes on the order of 10 3 10 4 years furthermore we found 100 m scale laminations of fine grained pyrite aluminosilicate and calcium carbonate which when superimposed on the alternation of c org rich and si bio rich intervals suggests 10 2 year scale fluctuations in oceanic environments

factors affecting the kinematic interpretation of asymmetric boudinage in shear zones abstract based on work along a major mylonite zone in the northern appalachians and scale model studies a new mechanism for the origin of asymmetric boudins in shear zones is proposed along the honey hill fault in southern connecticut granitic sills intruded into calc silicate gneisses and schists were oblique to the boundaries of the mylonite zone and experienced the following sequence in the production of sigmoidal boudins 1 as the calc silicate schists experienced mylonitization and flow the more competent coarse grained granitic sills deformed by extensional fracturing and quartz veining 2 continued extension of granitic sills was accommodated by normal shear on early formed quartz veins 3 continuing extension of sills and ductile modification of the corners of boudins resulted in granitic fish with tails which stream from the top of the boudin in the down dip direction and from the bottom in the up dip direction based on a variety of kinematic indicators the sense of asymmetry of the tails is identical to that expected for recrystallization tails on sheared augen structure models composed of silicone putty and plasticine were created to investigate the effect of pre shearing geometry on boudin evolution and were deformed in a simple shear device the models reproduce the kinematics deduced from field relations and suggest that one of the primary factors in controlling the amount of extension is the angle which early veins make with the shear zone boundary varying the angular relationships in the models suggests that other pre shearing geometric factors may affect the geometry of boudins formed in this way boudins formed through this mechanism appear very similar to hanmer s type ii asymmetric boudins because the pre shearing geometry can exert a control on boudin asymmetry caution should be used when attempting to deduce shear sense or shear strain values from asymmetric boudinage

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity