geochemistry of meteorite rich marine limestone strata and fossil meteorites from the lower ordovician at kinnekulle sweden abstract thirteen fossil meteorites 1 5 9 cm have been found in lower ordovician orthoceratite limestone at kinnekulle sweden the meteorites were recovered from a 3 5 m thick quarried interval in the middle of a 30 m thick section of orthoceratite limestone the section formed in an epicontinental sea at very slow sedimentation rates 0 2 cm ka the limestones of the lower two thirds of the section are reddish brown except in the quarried interval where a conspicuous 1 m thick grey limestone bed occurs ten of the meteorites were found in a thin bed below the grey limestone one was found in the grey limestone and two in the red limestone above the meteorites are almost completely pseudomorphosed primarily by calcite and barite they were identified by their content of chromite grains and chondrule pseudomorphs the central part of one of the meteorites shows iridium 800 ppb gold 550 ppb and chromium 4400 ppm concentrations in typical chondritic abundances centimeter resolution profiles for iridium and eight other elements have been established through the quarried interval at a site at 4 km distant from the meteorite producing quarry in the reddish brown parts ir concentrations carbonate free basis lie typically in the range 300 400 ppt compared with 50 ppt ir in average shale in the grey limestone the ir concentrations are lower around 100 150 ppt iridium correlates with iron and appears to be related to sedimentation rate and or iron redox state rather than to any variations in the composition of the siliciclastic fraction with estimated sedimentation rates as above the excess ir flux to the sediment was 30 ng cm 2 ma which is a factor 2 3 higher than the present total ir flux and one order of magnitude higher than the extraterrestrial ir flux to the pacific sea floor our data cannot discriminate to what extent the ordovician ir enrichments are related to extraterrestrial matter or to precipitation of ir from seawater in recent deep sea sediments seawater derived ir enrichments are associated with mn oxides but no similar association occurs in the orthoceratite limestone the ten meteorites in the bed below the grey limestone reflect minimum meteorite accumulation rates of one meteorite per 150 m 2 and 175 ka probably the ten meteorites are related to a local strewn field rather than to background influx minimum accumulation rates calculated on three meteorite finds 20 g in the entire quarried interval give one meteorite per 570 m 2 and 1 17 ma which is one order of magnitude higher than present day large area averaged meteorite influx rates the probability is low that the small area 2 of the sea floor studied would happen to be one where an unusually high number of meteorites struck our results may reflect that meteorite and possibly also extraterrestrial ir influx rates were substantially higher than at the present during a period in the early ordovician enhanced influx rates could be related to an asteroid collision in space

iron supply and demand in the upper ocean is extraterrestrial dust a significant source of bioavailable iron interplanetary dust particles accrete on the earth at a rate of 40 ktons yr 1 some 90 of this material evaporates in the atmosphere producing a bioavailable iron flux of 3 10 7 mol fe m 2 yr 1 this extraterrestrial fe flux is 30 300 of the eolian flux of bioavailable iron transported from terrestrial sources in remote marine regions and 20 of the upwelled fe flux in the southern ocean extraterrestrial fe may play an important role in regulating the marine carbon cycle in these regions

asteroid breakup linked to the great ordovician biodiversification event the great ordovician biodiversification event coincides 470 million years ago with the break up of a large asteroid and the resultant frequent bombardment of earth with asteroid fragments

a global rain of micrometeorites following breakup of the l chondrite parent body evidence from solar wind implanted ne in fossil extraterrestrial chromite grains from china previous studies of limestone beds of mid ordovician age from both sweden and china show that the earth saw an at least two orders of magnitude increase in the influx of extraterrestrial material approximately 470 ma following the disruption of an l chondrite parent body in the asteroid belt recovered extraterrestrial material consists of fossil meteorites and sediment dispersed extraterrestrial chromite sec grains both with l chondritic origin ne isotope analysis of sec grains from one of the swedish limestone sections revealed that the vast majority of the grains were delivered to earth as micrometeorites in this study we extend the previous work both in time and geographically by measuring concentrations and isotopic ratios of ne in individual sec grains 60120 mu m in diameter from three different beds from a contemporary middle ordovician limestone section in china all of the chinese sec grains 44 in total contain surface implanted ne of fractionated solar wind composition implying that these grains were as in the case of the swedish sec grains delivered to earth as micrometeorites this gives further compelling evidence that the two to three orders of magnitude increase in the influx of micrometeoritic material following the breakup of the l chondrite parent body was indeed a global event the rain of micrometeorites prevailed for at least 2 myr the estimated time of the deposition of the topmost chinese bed after the breakup event less

atmospheric forcing of fram strait sea ice export a closer look fram strait is the primary region of sea ice export from the arctic and therefore plays an important role in regulating the amount of sea ice and freshwater within the arctic we investigate the variability of fram strait sea ice motion and the role of atmospheric circulation forcing using daily data during the period 1979 2006 the most prominent atmospheric driver of anomalous sea ice motion across fram strait is an east west dipole pattern of sea level pressure slp anomalies with centers of action located over the barents sea and greenland this pattern also observed in synoptic studies is associated with anomalous meridional winds across fram strait and is thus physically consistent with forcing changes in sea ice motion the association between the slp dipole pattern and fram strait ice motion is maximized at 0 lag persists year round and is strongest on time scales of 10 60 days the slp dipole pattern is the second empirical orthogonal function eof of daily slp anomalies in both winter and summer when the analysis is repeated with monthly data only the barents center of the slp dipole remains significantly correlated with fram strait sea ice motion however after removing the leading eof of monthly slp variability e g the north atlantic oscillation the full east west dipole pattern is recovered no significant slp forcing of fram strait ice motion is found in summer using monthly data even when the leading eof is removed our results highlight the importance of high frequency atmospheric variability in forcing fram strait sea ice motion

stratigraphic record of the asteroidal veritas breakup in the tortonian monte dei corvi section ancona italy the discovery of elevated concentrations of the cosmogenic radionuclide 3he in deep sea sediments from ocean drilling program odp site 926 atlantic ocean and odp site 757 indian ocean points toward accretion of extraterrestrial matter probably as a result of the catastrophic disruption of a large asteroid that produced the veritas family of asteroids at ca 8 3 0 5 ma and which may have had important effects on the global climatic and ecologic systems here we investigated the signatures possibly related to the veritas event by performing a high resolution multiproxy stratigraphic analysis through the late tortonian early messinian monte dei corvi section near ancona italy closely spaced bulk rock samples through a 36 m thick section approximately spanning from ca 9 9 ma to ca 6 4 ma show an 5 fold 3he anomaly starting at ca 8 5 ma and returning to background values at ca 6 9 ma confirming the global nature of the event we then analyzed at 5 cm intervals bulk rock samples for sedimentary and environmental proxies such as magnetic susceptibility calcium carbonate content total organic carbon and bulk carbonate 18 o and 13 c through a 21 m thick section encompassing the 3he anomaly available high resolution sea surface temperature data via alkenone analyses for this site show a temperature decrease starting exactly at the inception of the 3he anomaly cyclostratigraphic fast fourier transform spectral analyses of the proxies indicate an age of 8 47 0 05 ma for the inception of the 3he anomaly a search for impact ejecta analogous to what is present in the late eocene where both a 3he anomaly and large scale impact events are recorded was not successful detailed cyclostratigraphic analyses of our data suggest that the changes in the stable isotope series and environmental proxy series through this late tortonian time interval had a common forcing agent and that perturbations of orbitally forced climate cycles are present exactly through the interval with the enhanced influx of extraterrestrial 3he thus the chemostratigraphic evidence for a collisional event that created the veritas family of asteroids coinciding with climate perturbations on earth suggests yet another form of interaction between earth and the solar system

beyond black shales the sedimentary and stable isotope records of oceanic anoxic events in a dominantly oxic basin silurian appalachian basin usa abstract episodes of instability in the global climato oceanic system have become the hallmark of the silurian period these events are marked by six large positive carbon isotope excursions associated with major extinctions the widespread environmental consequences of these perturbations of the global carbon cycle remain poorly documented a high resolution chronostratigraphic reconstruction of the appalachian foreland basin afb provides a framework to evaluate environmental signatures of two of these carbon isotope excursions valgu and ireviken events telychian sheinwoodian at a regional scale integration of published biostratigraphic range data mapping of sequence stratigraphic surfaces and facies and generation of high resolution carbon isotope profiles for several transects provides precise correlation of the basin stratigraphy yielding a high resolution temporal framework this chronostratigraphic reconstruction of the afb highlights the importance of time specific facies tsf during these intervals for instance packages of red green and gray marine rocks separately occupied discrete time intervals cutting across local facies belts indicative of shallow to deep marine environments similarly widespread iron mineralization occurred during discreet time slices as bathtub rings rimming the margins of the basin changes from one time specific facies to the next are coincident with changes in carbon isotope values indicating a genetic link between fractionation of the global carbon reservoir and redox changes from generally oxic to anoxic oceanic conditions in parts of the afb the basal part of the study interval was deposited during the valgu event this first event begins with an unconformity marking global lowstand this fall in sea level was coincident with rising carbon isotope values as recorded in adjacent basins a slight sea level rise and flooding of the subaerial unconformity occurred near the peak in carbon isotope values oxidized iron minerals were deposited in a zone that extended from the lower shoreface into the basin center pinching out into shallower parts of the basin thin pyrite phosphorite glauconite layers associated with black shales in the basin center were deposited over these ferruginous strata as the event ended and carbon isotope values shifted negatively to a more stable baseline temperatures warmed sea level reached a silurian high and oxic conditions associated with very low rates of organic carbon oc burial were established these conditions were relatively stable for nearly four million years this long period of stasis was punctuated by the ireviken event which displays a strikingly similar progression of tsf patterns yet more intense and longer lived than the preceding valgu event with the first positive shift in carbon isotopes at the onset of the ireviken event the basin redox system changed from largely oxidizing to reducing coincident with a rapid drop in sea level and an abrupt reappearance of iron mineralization on the basin margins the sea level fall associated with the shift to peak values of the carbon isotope excursion is marked by the progradation of a significant body of sand well out into the basin during this sea level drop conditions in the basin center became highly reducing and periodically sulfidic widespread ironstones and ankeritic carbonates were deposited isochronously rimming the shallow basin margins where they alternated with light gray pyritic shales indicating fluctuating redox conditions a large negative carbon isotope excursion of 3 is coincident with a shift from regression to transgression suggesting glacial melting via methane release continued deposition of ironstones through this time interval suggests a primary link to shallow marine redox processes rather than large scale transgression or regression of the shoreline the ironstones are overlain by gray to black pyritic shales deposited across all environments revealing a final stage of redox progression into sustained sulfidic conditions as peak values of the carbon isotope excursion returned to a high stable baseline near 4 the similar expression of tsfs within the afb of these two global events demonstrates that fractionation of the global atmospheric and oceanic carbon reservoirs had a predictable cascading impact on shallow sea floor environments the associated redox processes reveal the dynamic regional interactions of a shallow oxic epicontinental water mass with a broader anoxic oceanic water mass providing valuable insight into the origin of some of the largest extinctions in the silurian period

l chondrite asteroid breakup tied to ordovician meteorite shower by multiple isochron 40ar 39ar dating radiochronometry of l chondritic meteorites yields a rough age estimate for a major collision in the asteroid belt about 500 myr ago fossil meteorites from sweden indicate a highly increased influx of extraterrestrial matter in the middle ordovician 480 myr ago an association with the l chondrite parent body event was suggested but a definite link is precluded by the lack of more precise radiometric ages suggested ages range between 450 30 myr and 520 60 myr and can neither convincingly prove a single breakup event nor constrain the delivery times of meteorites from the asteroid belt to earth here we report the discovery of multiple 40ar 39ar isochrons in shocked l chondrites particularly the regolith breccia ghubara that allow the separation of radiogenic argon from multiple excess argon components this approach applied to several l chondrites yields an improved age value that indicates a single asteroid breakup event at 470 6 myr fully consistent with a refined age estimate of the middle ordovician meteorite shower at 467 3 1 6 myr according to a geologic time scale 2004 our results link these fossil meteorites directly to the l chondrite asteroid destruction rapidly transferred from the asteroid belt the increased terrestrial meteorite influx most likely involved larger projectiles that contributed to an increase in the terrestrial cratering rate which implies severe environmental stress

asteroidal source of l chondrite meteorites abstract establishing connections between meteorites and their parent asteroids is an important goal of planetary science several links have been proposed in the past including a spectroscopic match between basaltic meteorites and 4 vesta that are helping scientists understand the formation and evolution of the solar system bodies here we show that the shocked l chondrite meteorites which represent about two thirds of all l chondrite falls may be fragments of a disrupted asteroid with orbital semimajor axis a 2 8 au this breakup left behind thousands of identified 1 15 km asteroid fragments known as the gefion family fossil l chondrite meteorites and iridium enrichment found in an 467 ma old marine limestone quarry in southern sweden and perhaps also 5 large terrestrial craters with corresponding radiometric ages may be tracing the immediate aftermath of the family forming collision when numerous gefion fragments evolved into the earth crossing orbits by the 5 2 resonance with jupiter this work has major implications for our understanding of the source regions of ordinary chondrite meteorites because it implies that they can sample more distant asteroid material than was previously thought possible

plutonium 238 observations as a test of modeled transport and surface deposition of meteoric smoke particles 1 there are large uncertainties in the transport and surface deposition of upper atmospheric particles used to construct climate proxies here we use a 3 d chemistry climate model ccm to simulate the transport and deposition of plutonium 238 oxide nanoparticles formed after the ablation of a power unit in the upper stratosphere 11 s in 1964 the model reproduces both the observed hemispheric asymmetry and time scale of pu 238 deposition we then use the ccm to investigate the transport of meteoric smoke particles msps from the upper mesosphere the strongest msp deposition is predicted to occur at middle latitudes providing a significant source of fe fertilization to the southern ocean the model also predicts substantially more deposition in greenland than in antarctica by a factor of 15 in agreement with ice core measurements showing that climate proxy measurements from a limited number of sites must be interpreted with care

wintertime westward traveling planetary scale perturbations over the euro atlantic region the features of the wintertime westward traveling planetary scale perturbations over the euro atlantic region are examined through the use of space time spectral analysis applied to the 500 hpa geopotential height field the intention is to understand the nature of these phenomena and the performance of climate models data from both ecmwf re analyses and a simulation from the arpege general circulation model are used westward traveling planetary scale transients are found over the region as local perturbations resembling rossby normal modes with a maximum power over the eastern atlantic the westward traveling planetary scale transients north of 40 n have periods larger than 20 days south of this latitude wave periods are shifted to a band around 10 days so that they can be related to subtropical transient waves the atmospheric model used like other models which exhibit reasonable mean climatic properties tend to have less overall intraseasonal variability than observed nevertheless the model is able to capture most of the features of the westward traveling low frequency transients the differences in basic state partially produced by scale interactions would lead to the generation of westward traveling waves in the model distinct from the observed however it is suggested that the improvement of the present model version with regard to previous model versions is due to a better simulation of the time mean state the reasonable simulation of the synoptic scale variability south of 50 n and thus of its barotropic forcing on the basic state may also help to explain the realistic westward traveling transients in the model

a rain of ordinary chondritic meteorites in the early ordovician forty fossil meteorites with a total original mass of v7 7 kg have been recovered in the first systematic search for fossil meteorites pursued in an active quarry in lower ordovician 480 ma marine limestone in southern sweden the meteorites represent at least 12 different falls over a seafloor area of v6000 m 2 during 91 75 myr making the quarry one of the most meteorite dense areas known in the world geochemical analyses of relict chromite grains indicate that all or most of the meteorites are ordinary chondrites and probably l chondrites mechanisms for meteorite delivery from the asteroid belt to earth were the same 480 ma as today however the flux was one to two orders of magnitude higher most likely reflecting the disruption of the l chondrite parent body at about that time this is a major event in late solar system history which may also have led to an enhanced flux of asteroids to earth during v30 myr fl 2001 elsevier science b v all rights reserved

ooidal ironstones from ordovician gondwana a review abstract ooidal ironstones occur widely in the ordovician shelf sequences of sw europe the western european platform the avalonian terranes and north africa they form the most important group of deposits of the earlier of the two major periods of phanerozoic ooidal ironstone generation ordovician devonian and jurassic paleogene individual ooidal ironstone horizons are generally thin less than 2 m but may have a very wide lateral extent the ooidal ironstones represent sediments formed under extremely low sedimentation rates and were most commonly developed as the initial deposit above a disconformity ooidal ironstone producing events occurred almost synchronously over wide areas of the gondwanan shelf reflecting the uniform sedimentary conditions across large areas of the shallow low gradient shelf clastic sediments deposited during periods of normal sedimentation show similar remarkable uniformity over large areas this geometry together with the abundant fauna both micro and macro in the ironstone facies means that these thin ironstone beds form important marker horizons for correlation within the region the stratigraphic distribution of the ironstones shows strong correlation with periods of high relative sea level sedimentological study of examples in sw europe indicate that they separate transgressive systems tracts with parasequences bounded by phosphorites from the early part of the following highstand systems tracts without significant parasequences and are therefore interpreted to lie on maximum flooding surfaces such maximum flooding surfaces occur in the early llavirn the late llanvirn the early caradoc and the early ashgill of sw europe outside sw europe the ooidal ironstones may have a different relationship to the sequence stratigraphy possibly reflecting the influence of absolute water depth

phanerozoic oolitic ironstones geologic record and facies model oolitic ironstonesl composed predominantly of ooidsl of ferric oxide and chamosite accumulated throughout much of phanerozoic time figure 1 and some of them have been important ore deposits they are built of two very common products of weathering iron oxide and clay but they constitute a distinctive and subordinate sedimentary facies for which there is no simple modem analogue as a result considerable disagreement has attended more than 125 years of discussion about their origin early analyses of these rocks for example the minette are of france focused mainly on their chemical and mineral composition and on processes of diagenesis more recent work has described their sedimentary textures and structures as well as their general facies and depositional environments ad eleye 1973 brookfield 1973 corbin 1980 hallam 1975 karpov et a11967

an updated analysis of northern hemisphere submonthly retrograde waves abstractthis study performs an updated analysis of northern hemisphere retrograde disturbances that were first identified by classical observational studies as one of the dominating coherent struct

late miocene carbon isotope records and marine biological productivity was there a dusty link 1 we examine whether or not a relationship exists between the late miocene carbon isotope shift 7 6 6 6 ma and marine productivity at four sites from the indian and pacific oceans ocean drilling program sites 721 1146 1172 and 846 we use a multiproxy approach based on benthic foraminiferal accumulation rates elemental ratios and dissolution indices and we compare these data to benthic foraminiferal 13c values measured on the same samples although some of these sites have been targeted previously in studies of either the late miocene early pliocene biogenic bloom sites 721 and 846 or the late miocene carbon isotope shift site 1172 our records are the first to establish paired proxy records of carbon isotopes and paleoproductivity allowing a direct assessment of a potential link our results indicate that at all sites productivity increased sometime during the 13c shift at three sites 721 1146 and 846 productivity increased at the beginning of the shift the correlation coefficients derived from linear regression between micropaleontologically derived productivity and foraminiferal 13c values are relatively high during the time interval containing the late miocene 13c shift and statistically significant at three of the sites carbon flux and isotope mass balance considerations illustrate that transfer of organic matter between the terrestrial and marine reservoirs together with enhanced oceanic upwelling best approximates observed changes in carbon isotope records and paleoproductivity we note that long term trend in the site 846 paleoproductivity record can be correlated to the long term trend in the site 848 eolian flux reconstructions of hovan 1995 hinting at a link between strengthened wind regime and productivity during the late miocene

accretion rates of meteorites and cosmic dust in the early ordovician abundant fossil meteorites in marine condensed lower ordovician limestones from kinnekulle sweden indicate that accretion rates of meteorites were one to two orders of magnitude higher during an interval of the early ordovician than at present osmium isotope and iridium analyses of whole rock limestone indicate a coeval enhancement of one order of magnitude in the influx rate of cosmic dust enhanced accretion of cosmic matter may be related to the disruption of the l chondrite parent body around 500 million years ago

late miocene global cooling and the rise of modern ecosystems a period of continental aridification and ecosystem change occurred about seven million years ago a global sea surface temperature reconstruction identifies cooling temperatures and a strengthened meridional temperature gradient at this time

determination of lg wave attenuation using single station seismograms a case study for zimbabwe summary in this paper we show how the quality factor q may be calculated using a single seismograph station and a number of events recorded on analogue seismograms we followed nuttli s 1973 method and extended it to one seismograph station using the single station bulawayo bul we determined a mean q value of 650 for zimbabwe furthermore we considered different propagation paths over zimbabwe as the seismic waves travelled to bul and found a low q value of 350 for the deka fault zone the q value of 650 obtained in this study agrees well within error with that of 603 reported by chow et al 1980 using the multistation multi event method and lies within the range of q values 454 759 reported by xie mitchell 1990 using a back project method to image large scale lateral variations of lg coda q the results obtained are important as the q value constitutes part of the input data in seismic hazard calculations the method may be used to determine q in regions where there may be only one station with reliable analogue seismogram data

the late eocene 187os 188os excursion chemostratigraphy cosmic dust flux and the early oligocene glaciation abstract high resolution records ca 100 kyr of os isotope composition 187os 188os in bulk sediments from two tropical pacific sites odp sites 1218 and 1219 capture the complete late eocene 187os 188os excursion and confirm that the late eocene 187os 188os minimum earlier reported by ravizza and peucker ehrenbrink earth planet sci lett 210 2003 151 165 is a global feature using the astronomically tuned age models available for these sites it is suggested that the late eocene 187os 188os minimum can be placed at 34 5 0 1 ma in the marine records in addition two other distinct features of the 187os 188os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca 0 1 myr we propose a speculative hypothesis that higher cosmic dust flux in the late eocene may have contributed to global cooling and early oligocene glaciation oi 1 by supplying bio essential trace elements to the oceans and thereby resulting in higher ocean productivity enhanced burial of organic carbon and draw down of atmospheric co2 to determine if the hypothesis that enhanced cosmic dust flux in the late eocene was a cause for the 187os 188os excursion can be tested by using the paired bulk sediment and leachate os isotope composition 187os 188os were also measured in sediment leachates results of analyses of leachates are inconsistent between the south atlantic and the pacific sites and therefore do not yield a robust test of this hypothesis comparison of 187os 188os records with high resolution benthic foraminiferal 18o records across the eocene oligocene transition suggests that 187os flux to the oceans decreased during cooling and ice growth leading to the oi 1 glaciation whereas subsequent decay of ice sheets and deglacial weathering drove seawater 187os 188os to higher values although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine 187os 188os records are obscured by recovery from the late eocene 187os 188os excursion evidence of the global influence of glaciation on supply of os to the ocean is robust as it has now been documented in both pacific and atlantic records

a russian record of a middle ordovician meteorite shower extraterrestrial chromite at lynna river st petersburg region numerous fossil meteorites and high concentrations of sediment dispersed extraterrestrial chromite ec grains with ordinary chondritic composition have previously been documented from 467 1 6 ma middle ordovician darriwilian strata these finds probably reflect a temporarily enhanced influx of l chondritic matter following the disruption of the l chondrite parent body in the asteroid belt 470 6 ma in this study a volkhovian kundan limestone marl succession at lynna river northwestern russia has been searched for ec grains 63 mu m eight samples forming two separate sample sets were collected five samples from strata around the asaphus expansusa raniceps trilobite zone boundary in the lower middle kundan yielded a total of 496 ec grains in 65 5 kg of rock average 7 6 ec grains kg 1 but up to 10 2 grains kg 1 these are extremely high concentrations three orders of magnitude higher than background levels in similar condensed sediment from other periods ec grains are typically about 50 times more abundant than terrestrial chrome spinel in the samples and about as common as terrestrial ilmenite three stratigraphically lower lying samples close to the a lepidurusa expansus trilobite zone boundary at the volkhov kunda boundary yielded only two ec grains in 38 2 kg of rock 0 05 grains kg 1 the lack of commonly occurring ec grains in the lower interval probably reflects that these strata formed before the disruption of the l chondrite parent body the great similarity in ec chemical composition between this and other comparable studies indicates that all or most ec grains in these russian mid ordovician strata share a common sourcethe l chondrite parent body less

deposition and diagenesis of clinton ironstones silurian in the appalachian foreland basin of pennsylvania clinton ironstones mid silurian on the southeastern margin of the appalachian foreland basin in central pennsylvania consist largely of skeletal grainstone storm beds whose skeletal fragments are extensively impregnated and replaced by ferric oxide other forms of iron mineralization consist of ooids superficial ooids cavity fillings and cements composed of ferric oxide and or chamositic clay and two generations of iron rich carbonate spar true oolite is rare small proportions of ferruginized grains are present in coarse lags at tops of some small scale 1 to 5 m coarsening upward sequences which are the record of mid shelf shoals from which the skeletal grainstone storm beds were derived ooids and superficial ooids are likely to have formed in dysaerobic conditions where the pycnocline of a highly stratified sea intersected shoal flanks ferrous iron from anaerobic deeper waters precipitated on quartz and skeletal fragment nuclei in weakly reducing conditions with episodic gentle agitation several stages of early diagenetic ferruginization affected skeletal grainstone storm beds and sequence capping coarse lags chamositic clay precipitated in pores and cavities of skeletal fragments within quartz sand adjacent to crinoid ossicles and as bed parallel connectors of large skeletal fragments as diagenesis progressed with further burial many skeletal fragments were extensively replaced by ferric oxide most chamositic clay altered to ferric oxide other chamositic clay matured from berthierine to chamosite and clusters of bladed specularite replaced parts of primary grains and secondary carbonate cements paleomagnetic and fluid inclusion analysis indicates that many late diagenetic changes took place at elevated temperatures during deen burial in an early phase of the alleghanian orogeny