waulsortian type buildups and resedimented carbonate turbidite facies early mississippian burlington shelf central missouri abstract the crinoidal carbonates of the lower mississippian osagean burlington limestone in central missouri consist of individual and multiple interconnected waulsortian type buildups and associated resedimented debris carbonate turbidite facies this association of waulsortian type buildups and turbidity current sedimentation developed on the foreslope toe of slope and basinal near toe of slope areas of the prograding burlington shelf the waulsortian type buildups contain a core facies of dolomitized bryozoan crinoid lime mudstone and a flank facies of symmetrically disposed thin bedded crinoidal packstone and grainstone the core developed where bryozoan crinoid thickets trapped carbonate fines of upslope turbidity current origin lime mud hardgrounds in the cores developed during prolonged breaks in the influx of lime mud the flank beds developed by in situ disarticulation of indigenous crinoids and minor gravity slide processes the resedimented debris facies are laterally continuous and normally graded grainstone and packstone the beds show 1 a subdivision of bouma intervals a and b 2 coarse tail grading 3 scours flutes and load casts 4 a generally random fabric except for crinoid ossicle alignment in bouma interval b and 5 no articulation of crinoid stems or calyxes these features combined with the absence of infiltration textures escape burrows shell imbrication and hummocky cross stratification are useful in distinguishing these resedimented beds from lag suspension deposits of storm origin the lower part of the burlington 5 15 m thick consists exclusively of waulsortian type buildup core and flank facies these buildups rest on a thin laminated dolomitic shale bed starved basin sediment and represent basinal near toe of slope deposition the upper and middle parts of the burlington limestone corresponding to foreslope and toe of slope depositional settings consist of waulsortian type buildups and resedimented debris facies considering approximate modern analogues the resedimented debris probably came from various linear near shelf margin sources the resedimented debris contains algal bored grains from the shelf margin and foreslope biogenic grains and clasts

precipitation regime of dronning maud land antarctica derived from antarctic mesoscale prediction system amps archive data 1 the precipitation regime of dronning maud land dml antarctica was studied using antarctic mesoscale prediction system amps archive data precipitation is the most important component of the mass balance of the antarctic ice sheet precipitation studies of dml are particularly important because two deep ice core drilling sites kohnen station and dome fuji are located in this region for the correct interpretation of the ice core properties a thorough understanding of the precipitation regime is necessary we used the high resolution amps archive data for the years 2001 2006 to investigate the temporal and spatial distribution of precipitation the results were compared to a recently published mass balance map derived from glaciological data of western dml the mass balance map and the amps mean annual precipitation field show fairly similar patterns which are mostly related to topography and prevailing wind systems precipitation is found to generally decrease from the coast to the inland plateau along the escarpment between the low altitude coastal areas and the interior plateau local minima and maxima in precipitation correspond to the leeward and windward sides of topographical ridges interannual variability of monthly sums of precipitation is fairly high owing to the influence of cyclone activity on precipitation which affects not only the coastal regions but also the interior of the continent more than previously thought

the heat burst of 29 may 1976 abstract an unusual phenomenon occurred in central oklahoma in the late evening and early morning hours of 29 30 may 1976 surface temperatures suddenly rose as much as 6 c the sudden large temperature rise and humidity fall which sometimes accompanies nocturnal thunderstorms defines the heat burst the origin of a heat burst may be adiabatic subsidence near dissipating or rear edges or storms in addition to increasing temperature and falling relative humidity the hear burst is characterized by the erosion of clouds and radar echoes and gusty winds this paper documents the mesoscale events associated with this phenomenon

geostatistical three dimensional modeling of oolite shoals st louis limestone southwest kansas in the hugoton embayment of southwestern kansas reservoirs composed of relatively thin 4 m 13 1 ft oolitic deposits within the st louis limestone have produced more than 300 million bbl of oil the geometry and distribution of oolitic deposits control the heterogeneity of the reservoirs resulting in exploration challenges and relatively low recovery geostatistical three dimensional 3 d models were constructed to quantify the geometry and spatial distribution of oolitic reservoirs and the continuity of flow units within big bow and sand arroyo creek fields lithofacies in uncored wells were predicted from digital logs using a neural network the tilting effect from the laramide orogeny was removed to construct restored structural surfaces at the time of deposition well data and structural maps were integrated to build 3 d models of oolitic reservoirs using stochastic simulations with geometry data three dimensional models provide insights into the distribution the external and internal geometry of oolitic deposits and the sedimentologic processes that generated reservoir intervals the structural highs and general structural trend had a significant impact on the distribution and orientation of the oolitic complexes the depositional pattern and connectivity analysis suggest an overall aggradation of shallow marine deposits during pulses of relative sea level rise followed by deepening near the top of the st louis limestone cemented oolitic deposits were modeled as barriers and baffles and tend to concentrate at the edge of oolitic complexes spatial distribution of porous oolitic deposits controls the internal geometry of rock properties integrated geostatistical modeling methods can be applicable to other complex carbonate or siliciclastic reservoirs in shallow marine settings

snow density along the route traversed by the japanese swedish antarctic expedition 2007 08 during the japanese swedish antarctic traverse expedition of 2007 08 we measured the surface snow density at 46 locations along the 2800 km long route from syowa station to wasa station in east antarctica the mean snow density for the upper 1 or 0 5 m layer varied from 333 to 439 kg m 3 over a region spanning an elevation range of 365 3800 m a s l the density variations were associated with the elevation of the sampling sites the density decreased as the elevation increased moving from the coastal region inland however the density was relatively insensitive to the change in elevation along the ridge on the antarctic plateau between dome f and kohnen stations because surface wind is weak in this region irrespective of elevation the wind speed was suggested to play a key role in the near surface densification the results of multiple regression performed on the density using meteorological variables were significantly improved by the inclusion of wind speed as a predictor the regression analysis yielded a linear dependence between the density and the wind speed with a coefficient of 13 5 kg m 3 m s 1 1 this relationship is nearly three times stronger than a value previously computed from a dataset available in antarctica our data indicate that the wind speed is more important to estimates of the surface snow density in antarctica than has been previously assumed

temporal and spatial variability of surface mass balance at dome fuji east antarctica by the stake method from 1995 to 2006 the surface mass balance smb at dome fuji east antarctica was estimated using 36 bamboo stakes grid of 6 6 placed at 20 m intervals from 1995 to 2006 the heights of the stake tops from the snow surface were measured at 0 5 cm resolution twice monthly in 1995 1996 1997 and 2003 and once a year for the rest of the study period to account for snow settling the average snow density at the stake base during the measurements was used for converting the stake height data to smb the annual smb from 1995 to 2006 at dome fuji was 27 3 1 5 kg m 2 a 1 this result agrees well with the annual smb from ad 1260 to 1993 26 4 kg m 2 a 1 estimated from volcanic signals in the dome fuji ice core over the period 1995 2006 there were 37 8 6 of the measurements negative or zero annual smb results variation in the multi year averages of annual smb decreased with the square root of the number of observation years and 10 years of observations of a single stake allowed the estimation of annual smb at 10 accuracy the frequency distributions of annual and monthly smb were examined the findings clarify the complex behavior of the annual and monthly smb at dome fuji which will be common phenomena in areas of low snow accumulation of the interior of the antarctic ice sheet

the carbonate signal and calcareous nannofossil distribution in an upper jurassic section balingen tieringen late oxfordian southern germany total abundance assemblage composition and the stratigraphic distribution of the six most abundant species of calcareous nannofossil were analysed in the upper oxfordian succession of balingen tieringen western swabian alb south germany this locality represents a deep shelf less than 200 m environment that is strongly influenced by its proximity to the jura shallow platform nannofossil abundance negatively correlates with carbonate content as well as with accumulation rate calcareous nannofossils thus did not produce the bulk of carbonates and their abundance was essentially controlled by the import of allochthonous carbonate mud gradual increase in carbonate content in the balingen tieringen succession can be related to an intensified carbonate mud export from the jura shallow platform to the swabian alb deep shelf during the late oxfordian changes in the nannofossil assemblage composition along the profile are interpreted as primary although a partial control by diagenesis on the assemblage can not be completely excluded the coccoliths lotharingius hauffii watznaueria britannica cyclagelosphaera margereli watznaueria barnesae watznaueria manivitae and the incertae sedis schizosphaerella spp display their highest relative abundance one after the other in a stratigraphic order this nannofossil succession parallels the gradual increase in allochthonous carbonate mud accumulation on the deep shelf as well as the gradual decrease in the intensity of siliciclastic input recorded on the jura shallow platform this suggests a climatic control by humidity on shallow platform carbonate production and export basinwards and on nutrient availability in deep shelf surface waters that itself controlled the nannofossil assemblage composition therefore the succession of highest relative abundance of l hauffii w britannica c margereli w barnesae w manivitae and schizosphaerella spp can represent a trophic preference continuum from more eutrophic to oligotrophic conditions

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

spatial variability of surface mass balance along a traverse route from zhongshan station to dome a antarctica stakes at 2 km intervals were installed in january 1997 and remeasured in february 1998 january 1999 january 2005 and during the 2007 08 austral summer along a 1248 km traverse route from zhongshan station to dome a east antarctica based on topographical parameters meteoro logical features and the records of 650 stakes and six stake arrays the route is divided into five zones we find that the snow accumulation rate decreases with increasing altitude as one progresses inland except in the zone 800 1128 km from the coast where the average annual accumulation rate is higher than in the zone 524 800 km from the coast the dome a zone 1128 1248 km has the lowest accumulation rate 35 kg m 2 a 1 2005 08 due to having the highest elevation and being furthest from the coast the surface mass balance in the region 202 1128 km from the coast exhibits no temporal change from 1999 2005 to 2005 08 but there is a change in the accumulation distribution the zone from 202 to 524 km shows a decrease in surface mass balance from 84 kg m 2 a 1 in 1999 2005 to 67 kg m 2 a 1 in 2005 08 while the zone between 800 and 1128 km shows an increase from 67 kg m 2 a 1 in 1999 2005 to 75 kg m 2 a 1 in 2005 08

spatial and temporal variability of surface mass balance near talos dome east antarctica 1 predictions concerning antarctica s contribution to sea level change have been hampered by poor knowledge of surface mass balance snow accumulation is the most direct climate indicator and has important implications for paleoclimatic reconstruction from ice cores snow accumulation measurements stake core snow radar taken along a 500 km transect crossing talos dome east antarctica have been used to assess accumulation signals and the representativeness of ice core records stake readings show that accumulation hiatuses can occur at sites with accumulation rates below 120 kg m 2 yr 1 differences between cores and stakes can lead to statistical misidentification of annual layers determined from seasonal signals at sites with accumulation rates below 200 kg m 2 yr 1 because of nondetection of higher and lower values achieving 10 accuracy in the reconstruction of snow accumulation from single cores requires high accumulation 750 kg m 2 yr 1 low accumulation sites are representative if cumulative rates computed over several years are used to reach the 750 kg m 2 yr 1 threshold temporal variability of accumulation over the last two centuries shows no significant increase in accumulation wind driven processes are a fundamental component of surface mass balance spatial variations in accumulation are well correlated with surface slope changes along the wind direction and may exceed 200 kg m 2 yr 1 within 1 km wind driven sublimation rates are less than 50 kg m 2 yr 1 in plateau areas and up to 260 kg m 2 yr 1 in slope areas and account for 20 75 of precipitation whereas depositional features are negligible in surface mass balance

glaciation aridification and carbon sequestration in the permo carboniferous the isotopic record from low latitudes to evaluate the isotopic record of climate change and carbon sequestration in the late paleozoic we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from carboniferous through middle permian 359 260 ma strata we focus on the isotopic records from the u s midcontinent and the russian platform because these two regions provide well preserved marine fossils spanning a broad time interval both regions show a 18o increase at the mid carboniferous boundary ca 318 ma that roughly correlates with geologic evidence for an expansion of gondwanan glaciers only the russian platform record shows a 18o maximum during the glacial maximum in the asselian in contrast to a previous study korte c jasper t kozur h w and veizer j 2005 18o and 13c of permian brachiopods a record of seawater evolution and continental glaciation palaeogeogr palaeoclimatol palaeoecol 224 333 351 our data show no oxygen isotope evidence for glacial retreat in the early permian but instead show increasing 18o values related to aridification dissimilarity in the 18o trends for the epicontinental seas of north american and the russian platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater 18o values these results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western north america intermediate values in the midcontinent and high values in the sverdrup basin russian platform and northern spain nevertheless both u s midcontinent and russian platform records show a late serpukhovian minimum a sharp increase across the mid carboniferous boundary and a minimum centered on the kasimovian the correlative increase in brachiopod 13c and 18o values at the mid carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the permo carboniferous

patterns of precipitation and mesolow evolution in midlatitude mesoscale convective vortices abstract surface pressure manifestations of mesoscale convective vortices mcvs that traversed oklahoma during the periods may august 2002 05 are studied using the weather surveillance radar 1988 doppler wsr 88d the oklahoma mesonet and the noaa profiler network data forty five mcvs that developed from mesoscale convective systems mcss have been investigated 28 62 of which exhibit mesolows detectable at the surface within this group three distinct patterns of precipitation organization and associated mesolow evolution have been identified the remaining 17 38 of the cases do not contain a surface mesolow two repeating patterns of precipitation organization are identified for the latter group the three categories of mcvs possessing a surface mesolow are as follows nineteen are classified as rear inflow jet mcvs and tend to form within large and intense asymmetric mcss rear inflow into the mcs enhanced by the development of an mcv on the left hand side relative to system motion pro

na2so4 and mgso4 salts during the holocene period derived by high resolution depth analysis of a dome fuji ice core we analyzed the profiles of ionic chemical species in three 500 mm sections of an ice core from dome fuji antarctica dated 3 0 8 9 and 13 3 kyr bp before present and compared the profiles to those in the surface snow the 3 0 and 8 9 kyr sections are from the holocene and the 13 3 kyr section slightly predates the holocene the analyses were done on 2 mm thick slices within each section at each depth the primary ionic species were na h cl and so 4 2 a the so 4 2 na and mg 2 levels varied with depth in each section over distances ranging from several millimeters to several centimeters also the correlation coefficients between na and so 4 and between mg 2 and so 4 2 for each depth were 0 90 or greater in contrast to the value of 0 59 or less in the surface snow defined here as 0 3 4 m from the surface these results suggest that almost all na and mg 2 in the holocene ice exists as na 2 so 4 and mgso 4 salts and the formation of these salts occurs not only in the atmosphere during transport but also in the firn layer

densification of layered firn in the ice sheet at dome fuji antarctica in order to better understand the densification of polar firn firn cores from the three sites within 10 km of dome fuji antarctica were investigated using surrogates of density dielectric permittivities e v and e h at microwave frequencies with electrical fields in the vertical and horizontal planes respectively dielectric anisotropy e e v e h was then examined as a surrogate of the anisotropic geometry of firn we find that layered densification is explained as a result of complex effects of two phenomena that commonly occur at the three sites basically layers with initially smaller density and smaller geometrical anisotropy deform preferentially throughout the densification process due to textural effects second layers having a higher concentration of cl ions deform preferentially during a limited period from the near surface depths until smoothing out of layered cl ions by diffusion we hypothesize that cl ions dissociated from sea salts soften firn due to modulation of dislocation movement moreover firn differs markedly across the three sites in terms of strength of geometrical anisotropy mean rate of densification and density fluctuation we hypothesize that these differences are caused by textural effects resulting from differences in depositional conditions within various spatial scales

isotopic records of brachiopod shells from the russian platform evidence for the onset of mid carboniferous glaciation we performed isotopic analyses of carboniferous brachiopod shells from the russian platform to examine global and regional environmental change along the western and eastern margins of laurussia during the formation of pangea and specifically to examine the isotopic evidence for the onset of mid carboniferous glaciation shell preservation was evaluated from shell microstructure cathodoluminescence trace element content and isotopic comparison with matrix material most interior nonluminescent nl prismatic shell appears to be chemically well preserved as indicated by low to undetectable si al fe and mn contents with minor exception nl shell 13c and 18o values are higher than those of corresponding cements and matrix the 13c record for the russian platform clearly shows a 3 increase from 2 4 0 7 to 5 5 0 6 in the serpukhovian or early bashkirian this shift was first reported by popp et al popp b n anderson t f sandberg p a 1986 brachiopods as indicators of original isotopic compositions in some paleozoic limestones geol soc am bull 97 1262 1269 but had not been documented for a single region widespread occurrence of high 13c values in the late carboniferous support the interpretation of popp et al with regard to this shift as a record of increased burial of organic carbon north american sections show a mid carboniferous 13c shift of only 1 5 we hypothesize that the reduced 13c shift reflects enhanced upwelling on the epicontinental seas of north america after the closing of the seaway between laurussia and gondwana the 18o record for the russian platform shows a 1 8 increase in the mid carboniferous correlative with increased occurrence of glacial sediments and a drop in sea level as a first approximation ice volume calculations suggest that 0 7 of the mid carboniferous 18o shift is due to changes in seawater 18o and 1 1 is due to 5 c cooling concurrent positive 13c and 18o shifts provide evidence for a relationship between mid carboniferous glaciation and burial of organic carbon presumably through changes in atmospheric co2 levels

multi carbonate component reconstruction of mid carboniferous chesterian seawater δ13c abstract this study presents the first stratigraphically continuous 13ccarb record for the chesterian interval developed from antler foreland basin platform successions the bulk carbonate derived 13c curve was constructed using 700 biostratigraphically constrained samples providing a 105 yr resolution a multi component study of 13c and 18o variability in petrographically and geochemically screened abiotic and biogenic calcite components delineates the degree of preservation and 13c heterogeneity in these ancient epicontinental carbonates furthermore it constrains the influence of kinetic and vital effects and local to regional scale c cycling on their 13ccarb values the 13c and 18o values of micrites and bulk carbonates overlap regardless of lithofacies and show minimal intrasample variability overall biogenic calcite 13c and 18o values are higher than the average isotope compositions of bulk carbonates and micrites although 13c values in contemporaneous samples are only minimally 0 3 2 std err of 0 3 different relative to much larger differences in 18o values although brachiopod 13c and 18o values are higher than average bulk carbonate and micrite values their 13c values exhibit considerable isotopic variability by taxa and ultrastructure notably the 13c values of brachiopod secondary shell layers overlap with bulk carbonate micrite and marine cement 13c values conversely 13c values of brachiopod tertiary prismatic layers including composita are on average 2 to 5 higher than the 13c values of contemporaneous bulk carbonates micrites and brachiopod secondary shell layers an observed average 2 decrease in the 13c values of secondary cross bladed laminar layers in productids relative to contemporaneous bulk carbonate micrite and marine cement values suggests a previously unrecognized kinetic and or vital effect on carboniferous productid 13c values given that they have the highest 18o values of all analyzed components the observed higher 13c values in these tertiary prismatic layers are comparable to greater than the 13c enrichment 1 previously documented in pennsylvanian composita the overlap in 13c values of bulk carbonates with diagenetically screened microdrilled matrix marine cements and brachiopod secondary shell layers indicates that the chesterian bulk carbonate derived 13c values may reliably record to within 1 the evolution of ambient seawater 13c in the outer carbonate ramp of the antler basin comparison of the chesterian 13c record to the bulk carbonate c isotope curve derived from the arrow canyon nv carbonate succession further suggests that these bulk carbonate derived 13c records are reliable proxies of the composition and trends in seawater 13c regionally along the equatorial eastern panthalassan margin the newly resolved chesterian stratigraphy documents multiple 13c excursions including previously unrecognized significant c isotope shifts a shift to higher frequency and amplitude shorter term 13c fluctuations in the upper third of the chesterian stage occurred simultaneously with a change in stratigraphic cyclicity from dominantly 3rd order to 4th order carbonate cycles suggesting a mechanistic linkage between ambient seawater 13c and sea level fluctuations in the antler basin this change in the character of the shorter term 13c fluctuations coupled with a subsequent significant 4 positive c isotope excursion across the mid carboniferous boundary previously recognized in all carboniferous curves is interpreted to record the onset of late paleozoic glaciation and glacio eustasy

on the frequency distribution of net annual snow accumulation at the south pole the frequency distribution of stratigraphic layer thickness in cores and a snowmine at south pole is not compatible with a significant number 1 of missing layers associated with zero accumulation years inferred from pole height measurements a reconciliation of these data sets is needed if observed stratigraphic records are to be used as reliable paleoclimate indicators three explanations for the discrepancy are offered namely i during a significant number of years a visible stratigraphic horizon does not form or is not identified ii the true distribution is characterized by two maxima with a secondary maximum centered around zero layer thickness or iii the pole height measurements are misinterpreted and there are very few zero accumulation years at south pole with the currently available data it is not possible to discriminate among these three possibilities

climate dependent contrast in surface mass balance in east antarctica over the past 216 ka documenting past changes in the east antarctic surface mass balance is important to improve ice core chronologies and to constrain the ice sheet contribution to global mean sea level change here we reconstruct past changes in the ratio of surface mass balance smb ratio between the epica dome c edc and dome fuji df east antarctica ice core sites based on a precise volcanic synchronization of the two ice cores and on corrections for the vertical thinning of layers during the past 216 000 a this smb ratio denoted smb edc smb df varied between 0 7 and 1 1 being small during cold periods and large during warm periods our results therefore reveal larger amplitudes of changes in smb at edc compared with df consistent with previous results showing larger amplitudes of changes in water stable isotopes and estimated surface temperature at edc compared with df within the last glacial inception marine isotope stages mis 5c and mis 5d the smb ratio deviates by up to 0 2 from what is expected based on differences in water stable isotope records moreover the smb ratio is constant throughout the late parts of the current and last interglacial periods despite contrasting isotopic trends

a 4100 year record of explosive volcanism from an east antarctica ice core extensive archives of volcanic history are available from ice cores recovered from the antarctic and greenland ice sheets that receive and preserve sulfuric acid fallout from explosive volcanic eruptions the continuous detailed average 1 2 samples per year sulfate measurements of a 200 m ice core from a remote east antarctica site plateau remote provide a record of southern hemisphere volcanism over the last 4100 years this extends the volcanic record beyond the last 1000 years covered by previous antarctic ice cores an average of 1 3 eruptions per century is recorded in east antarctic snow during the last 4100 years the record shows that on average eruptions have been more frequent and more explosive during the most recent 2000 years than in the previous 2100 years intervals up to 500 years are observed in which few explosive volcanic signals are detected these periods include 2000 1500 b c no eruptions 500 1 b c two eruptions and 700 1200 a d two eruptions this new plateau remote volcanic record is compared with those from previous antarctic ice cores covering the last 1000 years in terms of dates for volcanic events the new record is in excellent agreement with the earlier records however significant discrepancies are found between these records in relative signal magnitude volcanic flux of several well known events the discrepancies among the records may be explained by the differences in the glaciology at the ice core sites analytical techniques used for sulfate and sulfuric acid measurement and the selection of detection thresholds for volcanic signals comparison with greenland ice core volcanic records indicates that during the last millennium nine large low latitude eruptions contributed significant amounts of volcanic aerosols to the atmosphere of both hemispheres potentially affecting global climate in contrast only one or possibly two such eruptions are found in the first millennium a d

snow density for measuring surface mass balance using the stake method a measure of snow density is required to estimate water equivalent ice sheet surface mass balance smb from stake measurements previous studies have utilized the snow density at different depths within the snow by considering the snow densification process in the time interval between stake height measurements we find that use of the snow density at the base of the stake is more appropriate we assume the stakes are firmly anchored at the bottom and that sorge s law holds i e the density depth profile does not change with time applying this method to the data for 36 snow stakes on dome fuji the smb in 2003 was 36 5 kg m 2 a 1 27 larger than the previous estimate which used surface snow density correct selection of the snow density for smb estimations is important especially for antarctic inland areas where accumulation is low e g dome fuji vostok dome c and south pole and where the snow density near the surface varies markedly

metamorphism of stratified firn at dome fuji antarctica a mechanism for local insolation modulation of gas transport conditions during bubble close off 1 the evolution of the structure of a 112 59 m long firn core recovered at dome fuji east antarctica was investigated in order to improve understanding of firn densification and bubble formation processes which are important for interpreting local insolation proxies used for astronomical dating of deep ice cores using selected samples we measured physical properties including 1 the relative dielectric permittivities in both the vertical and horizontal planes 2 the bulk density at a resolution of millimeters 3 the three dimensional geometric structure of pore space and 4 crystal orientation fabrics we found that the firn at dome fuji contains horizontal strata with thicknesses of several centimeters near the surface of the ice sheet these strata are characterized by contrasting bulk density earlier field studies suggest that summer insolation causes densification of surface firn down to 30 m density maxima exhibited a clear positive correlation with the strength of structural anisotropy and c axis clustering around the vertical in contrast the correlation is negative in deeper firn confirming previous findings that initially less dense firn became denser than initially dense firn in addition numerous examples of textures indicating that deformation preferentially occurred in weaker layers were found moreover the initially dense firn layers were more permeable for air near the bottom of firn we propose a model linking firn properties with conditions for the gas transport processes near the bottom of firn the model explains how stronger insolation can lead to bulk ice with a lower o2 n2 ratio and smaller total gas content

eocene spiculites and spongolites in southwestern australia not deep not polar but shallow and warm siliceous spongolite and spiculite are generally interpreted as deep and or cold water deposits largely because modern analogs are found mostly in cold and or deep water environments however extensive shallow water biosiliceous accumulations are present in late eocene age deposits of southern western australia the attributes and paleoenvironmental setting of these accumulations frame the specific climatic and or oceanographic constraints that allow such shallow neritic sediments to form the generally fine grained siliciclastic biosiliceous sediments accumulated in a nearshore shallow water setting around numerous islands and offshore from a warm temperate rainforest covered upland sponges compose a lithistid hexactinellid assemblage of mesozoic tethyan affinity confined to deep water in the modern ocean that migrated into neritic paleoenvironments during late eocene time lithistids dominated shoreface environments and were reworked into sponge conglomerate beaches while hexactinellids flourished offshore in muddy subshoreface environments these deposits also contain common soft demosponge spicules and a rare but otherwise normal marine calcareous biota the biosiliceous sediments grade offshore into bryozoan rich marls and limestones sponges outcompeted the calcareous benthos in these inner shelf environments because of elevated amounts of land derived nutrients that included high dissolved silica and a calm hydrodynamic setting these deposits suggest that neither temperature nor water depth are critical factors for prolific sponge colonization the rarity of such deposits in the rock record likely reflects the necessity for the coincidence of all of these factors or they are misinterpreted

glacioeustasy meteoric diagenesis and the carbon cycle during the middle carboniferous middle carboniferous carbonates in the western u s have undergone pleistocene bahamas style meteoric diagenesis that may be associated with expanding late paleozoic ice sheets fourteen stratigraphic sections from carbonate platforms illustrate the regional distribution and variable intensity of physical and chemical diagenesis just below the middle carboniferous unconformity these sections contain top negative carbon isotope excursions that terminate in regional exposure surfaces that are associated with some combination of karst towers desiccation cracks fabric destructive recrystallization or extensive root systems the timing of the diagenesis is synchronous with similarly scaled top negative carbon isotope excursions observed by others in england kazakhstan and china the mass flux of negative carbon required to generate similar isotopic profiles across the areal extent of middle carboniferous platform carbonates is a significant component of the global carbon cycle we present a simple carbon box model to illustrate that the 13c of dissolved inorganic carbon in the ocean could be elevated by 1 4 as isotopically light carbon from the weathering of terrestrial organic matter reacts with exposed platforms before reaching the ocean and atmosphere these results represent an improvement on global biogeochemical models that have struggled to provide a congruent solution to the high 13c of the late paleozoic icehouse

carbon isotopes and the rise of atmospheric oxygen new data for the isotopic composition of carbon in carbonate sediments deposited between 2 6 and 1 6 ga indicate that the value of 13c in these sediments underwent a very large positive excursion between 2 22 and 2 06 ga a reassessment of the earlier 13c data for carbonate sediments shows that this excursion was probably worldwide and that it was preceded and followed by several hundred million years during which the 13c of carbonate sediments differed little from that of modern carbonates the large 13c excursion between 2 22 and 2 06 ga was probably related to an abnormally high rate of organic carbon deposition which generated an abnormally high rate of o2 production we estimate that the total excess o2 produced during the excursion was between 12 and 22 times the present atmospheric o2 inventory the 13c data therefore suggest that the o2 content of the atmosphere increased very significantly between 2 22 and 2 06 ga this inference is supported strongly by several other lines of evidence

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

the rates of sea salt sulfatization in the atmosphere and surface snow of inland antarctica 1 most of the aerosol particles present in the surface snow and ice of inland antarctica come from primary sea salt sodium chloride and marine biological activity methansulfonic and sulfuric acids melted water from surface snow firn and holocene ice contains mainly sodium chloride and sulfate ions although it is well known that sea salt aerosols react rapidly with sulfuric acid a process known as sulfatization it is not known when this process takes place in this research we undertake to measure the proportion of sea salt aerosols that undergo sulfatization in the atmosphere and surface snow as opposed to deeper ice in order to understand the suitability of sea salt aerosols as a proxy for past climates in deep ice cores we directly measure the sulfatization rates in recently fallen snow 0 4 m in depth collected at the dome fuji station using x ray dispersion spectroscopy to determine the constituent elements of soluble particles and computing the molar ratios of sodium chloride and sodium sulfate we estimate that about 90 of the initial sea salt aerosols sulfatize as they are taken up by precipitation over dome fuji or in the snowpack within one year after being deposited on the ice sheet

recent increase in south pole snow accumulation this paper summarizes the 37 year history of net accumulation measurements at the geographic south pole obtained by numerous investigators using a variety of techniques these data lead to the conclusion that annual net snow accumulation has increased in the vicinity of south pole station sps since 1955 the records were examined for evidence of a station effect and it is concluded that not all of the observed increase can be attributed to snow drift associated with the presence of the station furthermore the accumulation increase at the south pole appears consistent with increases observed at other locations on the east antarctic plateau and in the peninsula region as well these data suggest that the recent accumulation increase at sps may be regionally extensive over the east antarctic plateau

petroleum reservoirs within a spiculite dominated depositional sequence cowley formation mississippian lower carboniferous south central kansas oil and gas reservoirs in the cowley formation upper osagean to lower meramecian are within a thick up to 400 ft 122 m section of spiculite dominated rocks derived from demosponges deposited in a low latitude setting these rocks are present in the subsurface for 325 mi 523 km along paleostrike in southern kansas and some adjoining states they represent a stratigraphically significant lithosome that markedly contrasts thin and areally restricted spiculitic rocks present in some mississippian reservoirs elsewhere in the mid continent cowley lithologies represent a low gradient ramp whereon 1 bedded spiculites were deposited in moderate energy shallow water inner ramp settings 2 lenticular nodular or flaser l n f bedded spiculite and shale were moderate to low energy progressively deeper water medial ramp deposits and 3 dark shales are deepest water outer ramp facies the internal stratigraphic architecture of the unconformity bounded cowley identifies it as a depositional sequence with component deepening upward basal strata transgressive systems tract overlain by shallowing upward progradational clinoforms highstand systems tract sequence deposition was punctuated by several unconformities attending short periods of subaerial exposure suppression of otherwise warm shallow water carbonate production and instead spiculite deposition in this low latitude setting was likely a consequence of elevated concentrations of dissolved silica and nutrients in the ambient marine environment three successive generations of silicification are recognized in the rocks early partial silicification is presumed to have begun in the marine environment and ensuing silicification and attendant porosity formation were likely coincident with falling sea level as pore fluids evolved from being of mixed marine meteoric to meteoric composition petroleum reservoirs mainly with vuggy porosity are present in relatively high porosity bedded spiculites and less porous l n f bedded rocks traps commonly are developed in structurally modified subunconformity buried hills and truncated gently dipping strata reservoirs in the l n f bedded rocks locally extend considerable distances downdip within individual clinoformal parasequences in the section thereby locally creating thick gas saturated reservoir columns because of its great subsurface extent the cowley section commonly bypassed during drilling offers considerable potential for as yet discovered fields in the mid continent

the effectiveness of the paleoproterozoic biological pump a δ13c gradient from platform carbonates of the pethei group great slave lake supergroup nwt samples of carbonate cements collected along a depth transect of the pethei platform a 1 9 ga stromatolitic reef reveal a small 0 5 carbon isotope gradient between shallow and basinal facies the magnitude of this gradient would conventionally be interpreted as indicating low export of organic matter from ocean surface waters but steady state simulations using a two box model of the paleoproterozoic ocean suggest that the small carbon isotope gradient could instead be due to high partial pressures of carbon dioxide in the paleoproterozoic atmosphere which would increase the ocean9s dissolved inorganic carbon content and damp the effects of biological pumping if the paleoproterozoic atmosphere were indeed enriched in atmospheric co 2 in compensation for a less luminous sun these results indicate that the planktonic biota was a significant component of the precambrian global carbon and nutrient cycles affecting if not regulating as today the composition of both surface and deep ocean waters

stable isotope chemostratigraphy as a tool to correlate complex mississippian marine carbonate facies of the anadarko shelf oklahoma and kansas the mississippian section of the united states mid continent anadarko basin oklahoma and kansas has been a prolific hydrocarbon reservoir since the 1920s yet large scale regional correlations between individual stratigraphic units remain difficult because of the complex and heterogeneous nature of the carbonate facies new sedimentologic and carbon isotopic data from a nearly continuous mississippian core pan american 1 albert severin from the anadarko basin oklahoma garfield county united states provides insight into the potential of carbon isotope chemostratigraphy as a correlation tool in complex stratigraphic successions for which biostratigraphic data are not available the carbon isotopic composition of whole rock samples was analyzed to determine if stratigraphic trends reflect global changes in the carbon cycle a large positive shift 5 6 in the lower tournaisian kinderhookian consistent values averaging 2 3 in the upper tournaisian through middle visean upper kinderhookian meramecian and a negative shift 2 3 in the uppermost visean lower chesterian correspond to trends in the carbon isotopic compositions values from other regional data sets including the global type section at arrow canyon nevada further analysis of the data reveals that isotopic compositions are not facies dependent suggesting that marine chemistry and depositional changes in the anadarko basin reflect global environmental changes during the mississippian these inferences demonstrate the potential of the pan american 1 albert severin core to be a mississippian type section for the anadarko basin and that stable isotope chemostratigraphy can be used as a correlation tool to better understand the subsurface in complex successions such as the mississippian limestone of the united states mid continent

recent surface mass balance from syowa station to dome f east antarctica comparison of field observations atmospheric reanalyses and a regional atmospheric climate model stake measurements at 2 km intervals are used to determine the spatial and temporal surface mass balance smb in recent decades along the japanese antarctic research expedition traverse route from syowa station to dome f to determine smb variability at regional scales this traverse route is divided into four regions i e coastal lower katabatic upper katabatic and inland plateau we also perform a regional evaluation of large scale smb simulated by the regional atmospheric climate model versions 2 1 and 2 3 racmo2 1 and racmo2 3 and the four more recent global reanalyses large scale spatial variability in the multi year averaged smb reveals robust relationships with continentality and surface elevation in the katabatic regions smb variability is also highly associated with surface slope which in turn is affected by bedrock topography stake observation records show large inter annual variability in smb but did not indicate any significant trends over both the last 40 years for the coastal and lower katabatic regions and the last 20 years record for the upper katabatic and inland plateau regions the four reanalyses and the regional climate model reproduce the macro scale spatial pattern well for the multi year averaged smb but fail to capture the mesoscale smb increase at the distance interval 300 to 400 km from syowa station thanks to the updated scheme in the cloud microphysics racmo2 3 shows the best spatial agreement with stake measurements over the inland plateau region era interim jra 55 and merra exhibit high agreement with the inter annual variability of observed smb in the coastal upper katabatic and inland plateau regions and moderate agreement in the lower katabatic region while ncep2 and racmo2 1 inter annual variability shows no significant correlation with the observations for the inland plateau region

a critical evaluation of carbon isotope stratigraphy and biostratigraphic implications for late cretaceous global correlation abstract climate variability is driven by a complex interplay of global scale processes and our understanding of them depends on sufficient temporal resolution of the geologic records and their precise inter regional correlation which in most cases cannot be obtained with biostratigraphic methods alone chemostratigraphic correlation based on bulk sediment carbon isotopes is increasingly used to facilitate high resolution correlation over large distances but complications arise from a multitude of possible influences from local differences in biological diagenetic and physico chemical factors on individual 13c records that can mask the global signal to better assess the global versus local contribution in a 13c record it is necessary to compare numerous isotopic records on a global scale as a contribution to this objective this paper reviews bulk sediment 13ccarb records from the late cretaceous in order to identify differences and similarities in secular 13c trends that help establish a global reference 13c record for this period the study presents a global scale comparison of twenty 13c records from sections representing various palaeo latitudes in both hemispheres and different oceanic settings from the boreal tethys western interior indian ocean and pacific ocean and with various diagenetic overprinting the isotopic patterns are correlated based on independent dating with biostratigraphic and paleomagnetic data and reveal good agreement of the major isotope events despite offsets in absolute 13c values and variation in amplitude between the sites these differences reflect the varying local influences e g from depositional settings bottom water age and diagenetic history whereas the concordant patterns in 13c shifts might represent 13c fluctuations in the global seawater dissolved inorganic carbon the latter is modulated by variations in organic matter burial relative to re mineralization in the global scale formation of authigenic carbonate and in partitioning of carbon between organic carbon and carbonate sinks these variations are mainly controlled by changes in climate and eustasy additionally some globally synchronous shifts in the bulk 13ccarb records could result from parallel variation in the contribution of authigenic carbonate to the sediment formation of these cements through biologically mediated early diagenetic processes is related to availability of oxygen and organic material and thus can be globally synchronized by fluctuations in eustasy atmospheric and oceanic oxygen levels or in large scale oceanic circulation because the influence of early diagenetic cements on the bulk 13ccarb signal can but need not be synchronized chemostratigraphy should not be used as a stand alone method for trans continental correlation and especially minor isotopic shifts have to be interpreted with utmost care nevertheless the observed consistency of the 13c correlations confirms global scale applicability of bulk sediment 13c chemostratigraphy for the late cretaceous including sediments that underwent lithification and burial diagenesis such as the sediments from the himalayan and alpine sections limitations arise from increased uncertainties 1 in sediments with very low carbonate content 2 from larger 13c variability in sediments from very shallow marine environments 3 from unrecognized hiatuses or strong changes in sedimentation rates and 4 in sections with short stratigraphic coverage or with few biostratigraphic marker horizons the combination of chemostratigraphy with biostratigraphy and magnetostratigraphy substantially increases the precision and temporal resolution of inter regional correlations and helps overcome problems that arise from differences in biostratigraphic schemes facies or provincialism of key fossils by using an iterative approach to stepwise increase precision of the correlations isochroneity of first and last occurrences of marker species versus chemostratigraphy is tested which helps to improve biostratigraphic zonations to assess zonal boundary ages and to identify useful criteria for defining late cretaceous stage boundaries many of which are still not formally defined the presented correlations indicate a consistent position for most planktic foraminifer zonal boundaries relative to corresponding isotope shifts during the mid cretaceous sea level high whereas diachroneity appears to be more pronounced during the late campanian and maastrichtian global sea level fall a similar pattern is observed for trans continental consistency in the 13c shifts graphic correlation of isotopic shifts magnetostratigraphic and biostratigraphic events among the compared sections is used to detect hiatuses or relative changes sediment accumulation rates and visualizes consistency or offsets of individual biostratigraphic markers relative to chemo and magnetostratigraphy finally an attempt of a global average 13c stack is presented for the turonian through maastrichtian

supply of allochthonous sediment and its effects on development of carbonate mud mounds mississippian lake valley formation sacramento mountains south central new mexico u s a abstract carbonate mud mounds in the mississippian lake valley formation new mexico can be classified according to their external morphology internal growth phases and paleogeographic location along the lake valley ramp most of the lake valley mounds grew during a complete third order accommodation cycle alamogordo nunn tierra blanca interval 3 6 myr duration which directly influenced mound biota facies types and the physical interactions between the mounds and sediment gravity flows that transported skeletal sediment around and over the mounds during the regressive phase of the cycle lenticular mounds are found in updip parts of the preserved lake valley ramp which largely consists of outer ramp facies most lenticular mounds grew exclusively during deposition of the transgressive alamogordo member when outer parts of the ramp were somewhat sediment starved coarse grained carbonate gravity flow deposits nunn and tierra blanca members typically onlap lenticular mounds and only locally interfinger with mound core facies these relationships indicate lenticular mounds were buried by carbonate gravity flow deposits which accumulated much faster than mound cores could aggrade the sediment gravity flows constructed shingled lobes sand sheets and oblique clinoforms and were erosive at times which also probably helped to shape lenticular mounds transitional mounds are typically located downdip from the lenticular mounds and had an initial lenticular growth phase which was followed by aggradational growth of mound cores aggradational mound cores were locally modified by submarine erosion or failure which created sharp stratal truncation surfaces that were later onlapped by gravity flow deposits after the aggradational phase and stratal onlap mounds with remnant seafloor relief served as substrates for continued growth during deposition of the tierra blanca member this final growth phase in transitional mounds records minor aggradation and significant typically asymmetric lateral accretion which suggests that 1 the mounds had grown to some accommodation limit possibly storm wave base and 2 the complex dispersal and accumulation patterns for the gravity flows also influenced how mound cores accreted laterally for example the upcurrent sides of some transitional mounds were buried preferentially by onlapping tierra blanca gravity flow deposits whereas their downcurrent sides locally accreted for significantly greater distances and with very different stratal geometries hemispherical mounds are located farthest downdip on the lake valley ramp they are the largest mounds and contain all three lenticular aggradational and accretionary growth phases later growth phases of hemispherical mounds have steeply dipping mound core to flank relationships with abrupt facies transitions because of their distal position along the lake valley ramp and greater distance from the progradational sand bodies the hemispherical mounds were the dominant sources for coarse grained carbonate sediment to adjacent non mound environments during nunn and tierra blanca time thus the distance of lateral accretion and overall morphology of hemispherical mounds were not affected greatly by allochthonous sediment from updip parts of the ramp

revisiting sites of the south pole queen maud land traverses in east antarctica accumulation data from shallow firn cores 1 ground based accumulation measurements are scarce on the high east antarctic plateau but highly necessary for model validation and the interpretation of satellite data for the determination of antarctic mass balance here we present accumulation results obtained from four shallow firn cores drilled in the antarctic summer season 2007 2008 the cores were drilled along the first leg of the norwegian us ipy traverse through east antarctica visiting sites like plateau station and pole of relative inaccessibility that have been covered by the south pole queen maud land traverses spqmlt in the 1960s accumulation has been determined from volcanic chronology established from the conductivity records measured by dielectric profiling dep the tambora 1815 unknown 1809 double peak is clearly visible in the conductivity data and serves as a reliable time marker accumulation rates averaged over the period 1815 2007 are in the range of 16 to 32 kg m 2 a 1 somewhat lower than expected from the spqmlt data the spatial pattern is mainly influenced by elevation and continentality three of the firn cores show a decrease of more than 20 in accumulation for the time period 1815 2007 in relation to accumulation rates during the period 1641 1815 the spatial representativity of the firn cores is assessed by ground penetrating radar showing a rather smoothly layered pattern around the drill sites validation of the dep results is utilized by comparison with chemistry data proving the validity of the dep method for dating firn cores the results help understanding the status of the east antarctic ice sheet and will be important for e g future model derived estimates of the mass balance of antarctica

homogeneous climate variability across east antarctica over the past three glacial cycles recent ice core studies have raised the disturbing possibility that glacial interglacial climate changes may be non uniform across antarctica1 2 these findings have been confined to records from the ross sea sector of the continent but significant deviations in other areas would call into question the widely assumed validity of the climate record obtained from vostok east antarctica on large spatial scales3 here we present an isotopic profile from a core drilled at dome fuji4 5 situated 1 500 km from vostok in a different sector of east antarctica the two records show remarkable similarities over the past three glacial cycles the extent of the dome fuji record in both large amplitude changes such as terminations interglacials and interstadials and more subtle glacial events even when the origin of precipitation is accounted for our results indicate that antarctic climate is essentially homogeneous at the scale of the east antarctic plateau possibly as a consequence of the symmetry of the plateau and the adjacent ocean

the stable carbon isotopic composition of organic material in platform derived sediments implications for reconstructing the global carbon cycle in pelagic carbonate sediments the degree to which the 13c values of inorganic and organic fractions co vary has been used to interpret rates of production burial and decomposition of organic carbon this relationship is relatively consistent through time permitting estimates of organic carbon production and preservation however as the majority of pelagic sediments older than 200 myr have been subducted carbonate sediments deposited in epeiric seas and platforms are often substituted for pelagic carbonates in analyses of ancient global carbon cycling there are well known pitfalls to using shallow marine carbonate materials including diagenesis semi isolation of depositional environments and input of different types of sediments with varying inorganic 13c 13cinorganic values which can obscure any global signatures one method used to assess whether global changes in 13c are accurately represented by 13cinorganic records is to examine variations in the 13c of co occurring organic material 13corganic if a 13corganic record co varies with a co occurring 13cinorganic record it is argued that the signals must be related to variations in the global carbon cycle this assumption has been investigated by analysing the isotopic composition of the organic carbon preserved in the uppermost 150 m of periplatform sediments recovered during odp leg 166 from the western margin of great bahama bank the 13corganic values measured in this study were compared to previously published 13cinorganic records measured on identical samples thus allowing a study of the correlation between the two records through time these analyses showed that the correlation coefficient between 13cinorganic and 13corganic increased from the proximal location site 1005 r2 0 1 to the distal site site 1006 r2 0 63 the importance of platform derived carbonate and organic material at the proximal location site 1005 is reflected in the absence of a co variation between inorganic and organic 13c records which exhibit no correlation on the platform itself in contrast the co variance in 13c values at the basinal location site 1006 is explained by a two point mixing model which demonstrates the importance of both pelagic and platform derived carbonate and organic carbon in generating the positive correlation between the organic and inorganic 13c values this results in a correlation between 13cinorganic and 13corganic records at site 1006 that is unrelated to global carbon cycling such data question the applicability of using 13corganic values to support the ability of 13cinorganic values to record global carbon cycling in carbonates recovered from environments where multiple sources of carbonate and organic carbon contribute to the bulk 13c signal

early cementation during marine meteoric fluid mixing mississippian lake valley formation new mexico abstract pre pennsylvanian low magnesium calcite cements from the mississippian lake valley formation of south central new mexico comprise three major cathodoluminescent zones previous work by meyers and lohmann 1985 suggested that interzonal isotopic and minor element variation resulted from spatial and temporal exchange between meteoric water and marine carbonate within a single meteoric system that the carbonate for cementation was derived from dissolution of metastable carbonate grains and that any contribution from marine water was insignificant isotopic analysis of the first two cathodoluminescent zones using detailed micron scale sampling methods revealed a record of simultaneous variation in 18o and 13c values at the intrazonal scale that is incompatible with compositional change anticipated from the evolution of meteoric fluids in response to progressive water rock interaction rather isotopic data in conjunction with stratigraphic and petrographic constraints suggest that regionally extensive mixing between marine and meteoric water along the basal margin of the phreatic lens is the process responsible for the cementation of much of this platform succession although trends of progressive 18o and 13c depletion in cement composition are compatible with precipitation from a fluid that evolved from a marine to a meteoric dominated composition low mg and sr concentrations are problematic in the context of experimentally derived partition coefficients for calcite because of compelling evidence indicating a mixing zone origin for these cements however we attribute low mg and sr contents to temperature and or pco2 effects or to differences in conditions under which calcite is precipitated

frontal analysis in the light of abrupt temperature changes in a shallow valley abstract the authors examine selected cases of abrupt temperature changes in a shallow valley in rural oklahoma and examine their wider associations all changes in the valley whether rise or fall are accompanied by a northerly wind shift at or shortly before the time of the abrupt change cases of cooling show a drop of as much as 20 f 11 c in less than 1 h the pattern of surface potential temperature over the central united states indicates that these cases represent ideal cold front passages although little or no weather accompanies them cases of abrupt warming which are entirely nocturnal on the other hand are associated with weak regional temperature gradients and with strong nocturnal cooling prior to the event under nearly clear skies and with light winds the imputed surface inversion does not occur at a nearby urban location and the breakdown is an important factor in the temperature rise at the rural site the important distinction between these cases and the cold front passages that

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

effect of accumulation rate on water stable isotopes of near surface snow in inland antarctica 1 postdepositional changes in water stable isotopes in polar firn were investigated at three sites characterized by different accumulation rates along the east antarctic ice divide near dome fuji water stable isotopes major ion concentrations and tritium contents of three 2 4 m deep pits were measured at high resolution 2 cm temporally the snow pits cover the past 50 years with snow accumulation rates in the range of 29 41 kg m 2 a 1 around dome fuji oxygen isotopic profiles in the three pits do not show annual fluctuations but instead exhibit multiyear cycles these multiyear cycles are lower in frequency at dome fuji as compared with the other two sites peaks of water stable isotopes in the multiyear cycles correspond to some ion concentration minima in the pits although such relationships are not observed in coastal regions we propose that the extremely low accumulation environment keeps the snow layer at the near surface which result in postdepositional modifications of isotopic signals by processes such as ventilation and vapor condensation sublimation we estimate that oxygen isotopic ratios could be modified by 10 and that the original seasonal cycle could be completely overprinted under the accumulation conditions at dome fuji moreover stake measurements at dome fuji suggest that the large variability in snow accumulation rate is the cause of the multiyear cycles

paired carbonate organic carbon and nitrogen isotope variations in lower mississippian strata of the southern great basin western united states abstract the early mississippian k o kinderhookian osagean carbon isotope 13c excursion or tice mid tournaisian carbon isotope excursion is one of the most prominent positive 13c excursions of the phanerozoic recent studies raise uncertainties about the representative shape single vs double spikes and magnitude of this 13c excursion 3 to 6 in south china 5 5 in europe and 7 in north america and the 3 unidirectional increase in nitrogen isotopes across the 13c excursion which is unanticipated considering the amount of organic carbon burial required to form the 13c excursion and the resultant oxygen increase and global cooling to test if stratigraphic completeness and spatial isotope variations caused such uncertainties we have conducted paired carbonate carbon 13ccarb organic carbon 13corg and nitrogen 15n isotope analyses across the k o interval in two well exposed sections of the southern great basin western united states the two sections represent proximal shallow water and distal deep water depositional settings of a west dipping carbonate ramp in the distal ramp section where no exposure surface is present both 13ccarb and 13corg show double spikes with peak 13ccarb values up to 7 and a negative shift down to 4 between the peaks in the proximal shallower water section where two karstic disconformities are observed 13corg shows similar double spikes but 13ccarb displays only a single peak with the highest value of 5 5 the missing 13ccarb spike is likely caused by diagenetic alteration below a karstic disconformity that lowered 13ccarb but not 13corg values resulting in smaller magnitude of the 13ccarb excursion these features suggest that the 7 magnitude and double spikes are more representative of the k o 13c excursion in the southern great basin the smaller magnitude of the k o 13ccarb excursion in some sections of the great basin and the tice in other sections globally may have overprinted with local environmental diagenetic signal or resulted from stratigraphic hiatus truncation which needs to be clarified in future research the 15n across the k o 13c excursion in the distal ramp section is decoupled from 13c with the majority of 15n values around 4 1 that do not show any obvious temporal trend in contrast 15n values in the shallow water section is coupled with the k o 13c excursion with a 3 positive shift from 4 to 7 at the rising limb of the 13c excursion and a negative shift from 7 to 1 2 at the falling limb of the 13c excursion the 15n trend from the distal ramp section is in some extent comparable with that documented from a section in south china while the coupled 13c 15n pattern in the proximal section seems better explain the potential redox change across a prominent 13c excursion considering the sensitivity of 15n to redox conditions of depositional environments a more comprehensive 15n study in a broader paleogeographic context is required to better understand the interactions between carbon and nitrogen cycles across the k o interval a critical transition from the mid paleozoic greenhouse clime to late paleozoic ice age lpia

deposition and diagenesis of mississippian chat reservoirs north central oklahoma the mississippian chat present at the unconformity between the pennsylvanian and mississippian in north central oklahoma and south central kansas is a weathered and or detrital interval of highly porous or hard tight chert at or near the top of the osagean hydrocarbon exploration and development of these rocks has been going on for more than 50 years study of well logs and completion records of more than 6600 wells in north central oklahoma shows that the chat is widespread but not continuous and that chat res ervoirs are very heterogeneous the depositional environment and diagenetic alteration of the chat suggest it formed through a combination of uplift and either erosional detritus or weathering in place of osagean mississippian cherty limestone fossiliferous clasts found in chat cores were likely eroded in a high energy environment such as that found above wave base in mississippian shallow seas the limestone clasts were trans ported by small scale debris flows into a lower energy environment and deposited in a lime mud matrix the chat producing trend be ginning in t25n r3e in osage county oklahoma and extending eastward beyond the study area for about 20 mi suggests a rela tionship between probable shelf edge erosion and the development of a chat reservoir other chat deposits formed from the weathering in place of mississippian limestone on structural highs thin sections reveal that diagenesis resulted in partial replacement of calcite shells and cement with silica following the debris flow preserved original fossil structures suggest molecule by molecule silica replacement of calcite dissolution of remaining calcitic material possibly by meteoric water created secondary porosity and a potential hydrocarbon reservoir the chat appears on well logs as a low resistivity zone having low density and high porosity that by normal interpretation methods would calculate wet and nonproductive oil and gas produced from such zones are generally accompanied by salt water examination of drill cuttings can indicate whether the zone is highly porous or dense chert with the former needed for a quality reservoir begin page 116 commercially productive zones generally have a minimum porosity of 25 30 and water saturations less than 80 micrologs provide indications of permeability that in core analysis is low 0 1 to 50 md average 20 md completion techniques should be designed for a siliceous reservoir containing detrital clays and no carbonate fracture treatment can generate additional permeability ultimate recovery from unitized fields having tens of wells ranges from 1 to 4 million bbl of oil and 1 to 3 bcf gas individual wells in good quality reservoirs have produced more than 150 000 bbl of oil and varying amounts of gas from depths of 3000 to 5000 ft 914 1524 m

petrology and palaeoenvironmental significance of glaucony in the eocene succession at whitecliff bay hampshire basin uk following the investigations of odin and others into the distribution of green granules glaucony has been widely assumed to be a reliable indicator of a fully marine open shelf environment with a low sedimentation rate we have investigated the value of glaucony as a palaeoenvironmental indicator through an investigation of the pellets and their distribution and reworking in the predominantly brackish to shallow marine tertiary sediments of the hampshire basin together with a re evaluation of the sedimentology glaucony has apparently formed in situ in all lithofacies from shallow marine to estuarine of the three highest glaucony concentrations all dominated by in situ glaucony two occur within highstand system tracts the third is at a sequence boundary several important surfaces do not have more than a few percent glaucony with very variable proportions of mature and in situ pellets the correlation between glaucony concentration and sequence stratigraphy is most obvious in the london clay and wittering formations where least reworking of pellets has occurred in the barton group there are no major concentrations of glaucony at any of the important stratal surfaces we believe this more random glaucony distribution is due to limited glaucony formation and reworking of older glaucony in these sediments ideal conditions for glaucony formation are interpreted to have been fully marine 10 30 m water depth a warm temperature plus low sedimentation rate with periodic winnowing to concentrate the pellets although most of these conditions for glaucony formation occurred in the selsey formation and barton group a factor or factors mitigated against glauconitization we suggest that this was lowering of the water temperature the london clay and wittering formations were deposited relatively rapidly 50 60 m ma 1 and include intervals of estuarine sedimentation both factors that we believe inhibited glaucony formation glaucony maturity reflects the minimum length of time spent in surface sediments close to the oxic sub oxic interface point count data and chemical data for glaucony indicate widespread reworking and an overall increase in reworking with time possibly due to uplift on the isle of wight monocline the apparently wide range of conditions in which glaucony will form and the frequency with which it is reworked suggest that it is a less useful indicator palaeo environmental indicator than is commonly supposed

spatial and temporal distribution of calcareous nannofossils along a proximal distal transect in the lower jurassic of the umbria marche basin central italy abstract three upper pliensbachian lower toarcian successions of the umbria marche basin were analysed for sedimentology and calcareous nannofossil content across a 120 km long transect from proximal to distal areas with respect to the shallow latium abruzzi platform the uppermost part of the corniola unit uppermost pliensbachian and the marne di monte serrone formation p p lower toarcian polymorphum to levisoni ammonite zones that contains organic matter rich levels were studied in the three localities the analysis of the sedimentary structures in the studied successions indicates that the basin was a shallow water system above storm wave base during the late pliensbachian early toarcian the stratigraphic evolution of the sedimentary structures recorded in the studied localities shows that the upper pliensbachian corresponded to a regressive sedimentary interval whereas a complete transgressive regressive relative sea level cycle occurred during the lower toarcian polymorphum zone a further transgression occurred in the lowermost levisoni zone lower toarcian changes from carbonate dominated to marl dominated sediments form decimetre to metre scale lithological units that can be correlated from succession to succession and may have resulted from short term sea level and or palaeoenvironmental variations the mean duration of these lithological units suggests that they formed in tune with the first orbital eccentricity cycle 100 ka the analysis of calcareous nannofossil quantities abundance per mm2 of the smear slide percentage mean abundance shows both spatial and temporal changes in the community structure schizosphaerella spp and crepidolithus crassus were more abundant in proximity to the shallow latium abruzzi platform these two taxa were likely affiliated to oligotrophic conditions in marine surface waters explaining why they were generally more abundant in carbonate rich intervals than in marls mitrolithus jansae is interpreted as being a deep dwelling species which was more abundant during rising sea level in the earliest toarcian species of the genera lotharingius biscutum and calyculus were more abundant when higher trophic conditions occurred and were thus more common during periods of marl deposition the stratigraphic distribution of calcareous nannoplankton and its interpretation in terms of palaeoecological affinities allow three main phases in the environmental evolution during the early toarcian anoxic event to be recognised the first phase corresponds to a long term transgression and high nannoplankton abundance in distal areas mainly lotharingius biscutum and calyculus species suggests high productivity that may have resulted from upwelling the beginning of accumulation and preservation of organic matter in the sediments occurred during this phase the scarcity of nannoplankton during the second phase may indicate oligotrophic conditions in surface waters possibly due to water stratification during the highest sea level stand a high abundance of schizosphaerella spp and c crassus is recorded in proximal areas probably resulting from sporadic nutrient input from continental or shallow platform areas the maximum of organic matter preservation is recorded during this phase during the third phase relative sea level fall and efficient water mixing by frequent storm events led to enhanced nannoplankton productivity in proximal and distal areas and to a decrease in organic matter accumulation in the umbria marche basin

occurrence frequency of thickness of annual snow accumulation layers at south pole this paper describes the frequency analysis of 2000 annual snow accumulation layers at the south pole it proposes application of this analysis to objective extraction of meteorological parameters from the south pole snow accumulation record we have compared the 200 year snow mine accumulation record of giovinetto and schwerdtfeger and a 2000 layer pit and core record obtained in 1982 frequency analysis of the number of occurrences of layers with respect to thickness or mass of the layer showed the logarithms of thickness or mass to be normally distributed this lognormality is quite robust arbitrary partitioning of the data by depth or systematic partition of the data by densification or firn ice transition does not destroy the lognormality of the accumulation series the geometric standard deviation of the mass of annual layers was the same as the geometric standard deviation of the thickness of these same layers as the layers densified from firn to ice this agrees with kapteyn s theory of transformability of lognormal distributions we have also compared the snow accumulation and marine aerosol sodium accumulation in recent annual layers with the station meteorological record and the surface aerosol record the amounts of snow and sodium accumulated are proportional to the number of warmings salt storms in most years of this short record the accumulation record may be transformable to provide an index of this meridional transport we propose that the magnitude of snow accumulation with respect to frequency of that accumulation provides an objective criterion for comparing individual years of meteorological history and that the geometric standard deviation of accumulation provides an objective index for estimation of climatic fluctuation during the period of accumulation

a 10 century comparison of prominent bipolar volcanic events in ice cores measurements of key chemical and physical parameters made along continuous and selected long sections of polar ice cores provide reliable past snow accumulation rates and other environmental records the prime accumulation indicators include variations found in the stable isotopes ionic constituents and acidity concentration levels and physical changes in the strata and structure cross correlations of the time series curves resulting from multiparameter analyses of ice cores from antarctica nby89 sp78 bs68 and greenland cr74 d3 81 d3 18c have been made the results permit construction of a bipolar chemical stratigraphy chronology of volcanic events that is coherent with the 18 o and electrical conductivity method data sets and consistent back in time with historically recorded volcanic activity a bihemispheric comparison of high non sea salt so 4 2 peaks shows strong correlation at 1885 1836 1816 1810 1459 1346 1287 1278 1259 1228 and 1168 a d at time of snow deposit the prominent 1259 a d volcanic signal appears to be a significant bipolar ice core index horizon

a relationship between ion balance and the chemical compounds of salt inclusions found in the greenland ice core project and dome fuji ice cores 1 we have proposed a method of deducing the chemical compounds found in deep polar ice cores by analyzing the balance between six major ions cl no3 so42 na mg2 and ca2 the method is demonstrated for the holocene and last glacial maximum regions of the dome fuji and grip ice cores the dominant compounds depend only on the ion balance and the sequence of chemical reactions in priority order the principle salts are calcium sulfate other sulfates nitrate chloride and carbonate the chemical abundances deduced by this method agree well with the results of raman spectroscopy on individual salt inclusions the abundances in the ice cores are shown to reflect differences in climatic periods the acidic environment of the holocene versus the reductive environment of the last glacial maximum and regional conditions the marine environment of antarctica versus the continental environment of greenland

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

parallel trends in organic and inorganic carbon isotopes across the permian triassic boundary stable carbon isotope ratios in both inorganic and organic reservoirs have been widely applied to model environmental and sedimentological changes on a global scale most studies dealing with major extinction events have used the record of inorganic carbon in this paper the authors report the relation between shifts in carbon 13 content of organic matter and coexisting carbonate fractions at a major extinction event the permian triassic boundary they found that both delta sup 13 c sub carb and delta sup 13 c sub org of the surface ocean varied dramatically across the boundary but the fractionation delta sup 13 c between organic matter and carbonate remained constant this result appreciably restricts the interpretation of changes in the carbon cycle during this critical interval the new data are best explained by a combination of two mechanisms for variation in delta sup 13 c sub carb 1 burial and erosion of organic carbon with a long time constant and 2 sequestration of organic carbon into shallow and deep oceanic reservoirs with a shorter time constant for application to their case the first mechanism is limited by possible buildup of marine pco sub 2 which would increase the isotopic fractionation factor the second mechanism is limited in application to short term transient variations in delta sup 13 c modelingmore of the carbon cycle and its variations of delta sup 13 c must take both mechanisms into account less

mississippian chat reservoirs south kansas low resistivity pay in a complex chert reservoir mississippian chert of variable character and diagenetic history defines a unique and prolific series of reservoirs in south central kansas and northern oklahoma known collectively as the chat these reservoirs occur beneath and are partly associated with a major regional unconformity separating mississippian and pennsylvanian deposits chat fields occur in an arcuate fairway extending approximately 160 km along the flanks of the southward plunging pratt anticline a southern extension of the central kansas uplift initial discoveries were made in the 1920s and 1930s with major expansion of the trend in the 1940s and 1950s chat wells have been among the most productive in the southern midcontinent yielding oil and gas at rates up to 1500 bbl or 40 mmcf per day from depths of 909 1515 m the better reservoirs have exceptional porosities 30 50 but moderate permeabilities 20 100 md fracturing is assumed to play an important role in reservoir performance few detailed characterizations of chat reservoirs exist to date recent study has identified three reservoir types 1 in situ spiculitic chert 2 in situ brecciated and partly weathered spiculitic chert and 3 highly weathered transported chert conglomerate these types can be broadly categorized according to paleostructural position current depositional models interpret the chert as mainly primary in origin related to subtidal sponge spicule bioherms along a subtle shelf break entrapment is predominantly stratigraphic in nature bioherms grade laterally into impermeable carbonate and are truncated updip beneath the sub pennsylvanian unconformity total production from the chat trend is on the order of 381 million bbl oil and 2 3 tcf gas new infill drilling field expansion and enhanced recovery projects in the 1990s have helped revitalize interest in the chat future exploratory and development efforts should add significant new data to the characterization of these complex and highly profitable reservoirs

direct surface thermodynamic observations within the rear flank downdrafts of nontornadic and tornadic supercells abstract despite the long surmised importance of the hook echo and rear flank downdraft rfd in tornadogenesis only a paucity of direct observations have been obtained at the surface within hook echoes and rfds in this paper in situ surface observations within hook echoes and rfds are analyzed these mobile mesonet data have unprecedented horizontal spatial resolution and were obtained from the verifications of the origins of rotation in tornadoes experiment vortex and additional field experiments conducted since the conclusion of vortex the surface thermodynamic characteristics of hook echoes and rfds associated with tornadic and nontornadic supercells are investigated to address whether certain types of hook echoes and rfds are favorable or unfavorable for tornadogenesis tornadogenesis is more likely and tornado intensity and longevity increase as the surface buoyancy potential buoyancy as measured by the convective available potential energy and equivalent potential temperature in the r

tornado maintenance investigated with high resolution dual doppler and enkf analysis abstractdual doppler wind synthesis and ensemble kalman filter analyses produced by assimilating doppler on wheels velocity data collected in four tornadic supercells are examined in order to further understand the maintenance of tornadoes although tornado scale features are not resolved in these analyses larger scale processes involved with tornado maintenance are well represented the longest lived tornado is maintained underneath the midlevel updraft within a zone of low level horizontal convergence along a rear flank gust front for a considerable time and dissipates when horizontally displaced from the midlevel updraft the shortest lived tornado resides in a similar zone of low level convergence briefly but dissipates underneath the location of the midlevel updraft when the updraft becomes tilted and low level convergence is displaced several kilometers from the tornado this suggests that a location beneath the midlevel updraft is not always a sufficient condition for tornado maintenance particu

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

mesoscale surface pressure and temperature features associated with bow echoes abstract this study examines observed mesoscale surface pressure temperature and wind features of bow echoes bow echo events in the area of the oklahoma mesonet are selected for study to take advantage of high resolution surface data thirty six cases are identified using 2 km resolution radar reflectivity data over a 4 yr period 2002 05 their surface features are interrogated using the mesonet data distinct surface features usually associated with squall lines the mesohigh and cold pool are found to also accompany bow echoes a common surface pattern preceding bowing is identified prior to new bowing development the mesohigh surges ahead of the convective line while the cold pool remains centered behind it surface winds shift to a ground relative outflow pattern upon arrival of the mesohigh surge approximately 30 min later a new bowing segment forms with its apex slightly to the left with respect to the direction of system motion of the mesohigh surge the cold pool follows the convective

snow accumulation and its moisture origin over dome argus antarctica the spatial and temporal variability of snow accumulation near dome argus antarctica is assessed using new snow pit and stake measurement data together with existing snow pit ice core and automatic weather station records snow accumulation rate shows large inter annual variations but stable multi decadal levels over the last seven centuries spatial variations in snow accumulation within the space of 50 km of dome argus are relatively small probably thanks to the smooth topography a comparison of theses accumulation observations with ecmwf reanalyses era 40 and era interim suggests ecmwf reanalysis captures the seasonal variations but underestimates the overall snow accumulation at dome argus by 50 the moisture sources for precipitation over dome argus are examined by means of a lagrangian moisture source diagnostic based on the tracing of specific humidity changes along air parcel trajectories for the period 2000 2004 using operational ecmwf analysis data dome argus mainly receives moisture from the mid latitude 46 4 s south indian ocean with a seasonal latitudinal shift of about 6 compared to other central east antarctic deep ice core sites such as dome f dome c vostok and epica dronning maud land dome argus has a more southerly moisture origin probably due to topographic influences on the moisture transport paths these results have important implications for the interpretation of future ice cores at dome argus

antarctic sea ice extent during the holocene reconstructed from inland ice core evidence 1 interannual fluctuations in the antarctic sea ice extent sie affect the global albedo and heat balance and they may affect global co2 levels we found that the annual trend of sodium ion fluxes in the snowpack in the dome fuji region of east antarctica can serve as a proxy for the present day sie in the southern indian ocean and weddell sea sectors we then used sodium ion profiles obtained from the dome fuji ice core to reconstruct the sie during the holocene we observed that 1 the beginnings of both the climatic optimum 12 0 ka bp and neoglaciation 5 4 ka bp in the southern ocean indicated by siliceous microfossil records are consistent with decreases 11 8 ka bp and increases 5 4 ka bp in the sodium ion fluxes in the dome fuji ice core and 2 the interannual fluctuation in the sie during some periods of the neoglaciation was greater than the interannual fluctuation during the climatic optimum

chemostratigraphy versus biostratigraphy data from around the cenomanian turonian boundary a detailed isotopic profile is presented for a stratigraphically expanded cenomanian turonian boundary section in chalk facies exposed at eastbourne sussex and compared with data from pueblo colorado in both sections macro and micropalaeontological markers first appearances and disappearances are well constrained and their relative positions and relationship to the structure of the carbon isotope curve are identical this consistent relationship between two independent phenomena one geochemical the other biostratigraphical is taken as evidence for the likely synchroneity of both the biostratigraphical markers and the carbon isotope excursion in these two areas this interpretation contrasts with suggestions made recently by other authors whose data have been taken to imply a lack of correlation between the carbon isotope excursion in europe and north america

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

paleogeographic and paleo oceanographic influences on carbon isotope signatures implications for global and regional correlation middle upper jurassic of saudi arabia abstract carbon isotope data 13c can provide an essential means for refining paleogeographic and paleo oceanographic reconstructions and interpreting stratigraphic architecture within complex carbonate strata although the primary controls on global 13c signatures of marine carbonates are well understood understanding their latitudinal and regional variability is poor to better constrain the nature and applications of 13c stratigraphy this study 1 presents a new high resolution 13c stratigraphic curve from middle to upper jurassic carbonates in the upper tuwaiq mountain hanifa and lower jubaila formations in central saudi arabia 2 explores their latitudinal and regional variability and 3 discusses their implications for stratigraphic correlations analysis of 13c data identified six mappable units with distinct 13c signatures units 1 6 between up dip and down dip sections and one unit unit 7 that occurs only in the down dip section of the study succession 13c data from the upper tuwaiq mountain formation and the lower hanifa formation units 1 2 which represent upper callovian to middle oxfordian strata and record two broad positive 13c excursions in the upper part of the hanifa formation units 3 6 early oxfordian late kimmeridgian 13c values decreased upward to unit 7 which showed a broad positive 13c excursion isotopic data suggest similar 13c trends between the southern margin of the tethys ocean arabian plate low latitude represented by the study succession and northern tethys oceans high latitude despite variations in paleoclimatic paleogeographic and paleoceanographic conditions variations in the 13c signal in this succession can be attributed to the burial of organic matter and marine circulation at the time of deposition our study uses 13c signatures to provide independent data for chronostratigraphic constraints which help in stratigraphic correlations within heterogeneous carbonate successions

mississippian carbonate ramp to basin transitions in south central new mexico sequence stratigraphic response to progressively steepening outer ramp profiles abstract the sequence stratigraphic architecture of mississippian strata from the sacramento and san andres mountains south central new mexico illustrates the combined effects of relative sea level change and progressively increasing depositional gradients on sedimentary processes and resultant stratal geometries along the outer parts of a carbonate ramp to basin transition mississippian strata can be subdivided into three progradational sequences sequences 1 3 and a fourth basin restricted onlapping sequence sequence 4 sequences 1 3 contain wackestone to mudstone dominated transgressive systems tracts that are overlain by packstone to grainstone dominated progradational systems tracts progradational systems tracts created distinct ramp to basin transitions outer ramp margin that are characterized by basinward stratal thinning and a concomitant change to muddy lithofacies sequence 4 consists of onlapping fining upward stratal packages of peloidal skeletal grainstone that grade upward to laminated spiculitic lime mudstone the outer ramp margin facies of sequences 1 through 3 gradually steepened the outer ramp profile until the cumulative effects of the steepening caused the depositional gradient to surpass an equilibrium grade i e the gradient at which deposition and erosion bypass are about equal once the depositional gradient exceeded the equilibrium grade for the caliber of sediment supplied to the outer ramp margin widespread submarine erosion and sediment bypass on the outer ramp was initiated resulting in deposition of basin restricted strata of sequence 4 similar relationships and inferred processes have been recognized in progradational siliciclastic shelf deposits and are collectively described by previous workers as slope readjustment the mississippian ramp to basin transition in south central new mexico illustrates how sediment deposition dispersal and erosion responded to evolving depositional gradients and in turn controlled resultant large scale stratal geometries

thermodynamic and vertical velocity structure of two gust fronts observed with a wind profiler rass during mctex high time resolution wind profiler rass observations are used to describe the vertical velocity temperature and reflectivity fields of two gust fronts in detail the first was a freely propagating gust front and the second interacted with a rain cell near the profiler site the first of these shows a large updraft confined to the warm air ahead of the front this updraft coincided with the nonhydrostatic pressure jump the vertical motions within the gust front were an order of magnitude smaller the updraft impinging on the top of the boundary layer excited a clear gravity wave signature in the free troposphere the interaction of the vertical circulation and the weakly precipitating cloud in the second case coincided with explosive growth of the cell with reflectivities increasing from 30 dbz to 50 dbz in 6 min a descending reflectivity core was observed at this time precipitation loading played a significant role in a downdraft behind the gust front head leading to adiabatic warming as no evidence of evaporative cooling in the downdraft was seen a distinct clear air peak was visible in the profiler doppler spectra even during the heavy rain

cometary dust in antarctic ice and snow past and present chondritic porous micrometeorites preserved on the earth s surface abstract chondritic porous interplanetary dust particles cp idps collected in the stratosphere are regarded as possibly being cometary dust and are therefore the most primitive solar system material that is currently available for analysis in laboratories in this paper we report the discovery of more than 40 chondritic porous micrometeorites cp mms in the surface snow and blue ice of antarctica which are indistinguishable from cp idps the cp mms are botryoidal aggregates composed mainly of sub micrometer sized constituents they contain two components that characterize them as cp idps enstatite whiskers and gems glass with embedded metal and sulfides enstatite whiskers appear as 2 o 6 rich high ca pyroxene roedderite k na 2 mg 5 si 12 o 30 and carbonaceous nanoglobules these components have previously been discovered in primitive solar system materials such as the cp idps matrices of primitive chondrites phyllosilicate rich mms ultracarbonaceous mms and cometary particles recovered from the 81p wild 2 comet the most outstanding feature of these cp mms is the presence of kosmochlor rich high ca pyroxene and roedderite which suggest that they have building blocks in common with cp idps and cometary dust particles and therefore suggest a possible cometary origin of both cp mms and cp idps it is therefore considered that cp mms are cp idps that have fallen to earth and have survived the terrestrial environment

characterization of the mississippian chat in south central kansas to understand production from low resistivity high porosity mississippian chat reservoirs in south central kansas it is necessary to understand the nature of deposition and diagenesis how tectonics is a factor the lithofacies controls on petrophysical properties and log response to these properties the initial mudstones to sponge spicule wacke packstones were deposited in transgressive regressive t r cycles on a shelf to shelf margin setting resulting in a series of shallowing upward cycles sponge spicule content appears to increase upward with increasing cycle thickness after early silicification inter and post mississippian subaerial exposure resulted in further diagenesis including sponge spicule dissolution vuggy porosity development in moldic rich rocks and autobrecciation meteoric water infiltration is limited in depth below the exposure surface and in distance downdip into unaltered cherty cowley formation facies areas of thicker preserved chat and increased diagenesis can be correlated with structural lineaments and in some areas with recurrent basement block movement combination of folding or block fault movement prior to or during development of the basal pennsylvanian unconformity sponge spicule concentration and possibly thickness of overlying bioclastic wacke grainstones resulted in variable reservoir properties and the creation of pods of production separated by nonproductive cherty dolomite mudstones these events also resulted in alteration of the depositional cycles to produce a series of lithofacies that exhibit unique petrophysical properties from bottom to top in a complete cycle seven lithofacies are present 1 argillaceous dolomite mudstone 2 argillaceous dolomite mudstone that has chert nodules 3 clean dolomite mudstone that has nodular chert 4 nodular to bedded chert 5 autoclastic chert 6 autoclastic chert that has clay infill and 7 bioclastic wacke grainstone the uppermost cycle was terminated by another lithofacies a chert conglomerate of mississippian and or pennsylvanian age the chert facies exhibit porosities ranging from 25 to 50 and permeabilities greater than 5 md the begin page 86 cherty dolomite mudstones argillaceous dolomite mudstones and bioclastic wacke grainstones exhibit nonreservoir properties reservoir production numerical simulation and whole core data indicate fracturing can be present in chat reservoirs and can enhance permeability by as much as an order of magnitude capillary pressure data indicate the presence of microporosity and can explain high water saturations and low resistivity observed in wire line logs relative permeabilities to oil decrease rapidly for saturations greater than 60 and may be influenced by dual pore systems archie cementation exponents increase from 1 8 for mudstones to more than 2 5 in the cherts that have increasing sponge spicule mold and vug content detailed modified pickett plot analysis of logs reveals critical aspects of chat character and can provide reliable indices of reservoir properties and pay delineation models developed provide additional insight into the chat of south central kansas and understanding of the nature of controls on shallow shelf chert reservoir properties

facies cycles and controls on the evolution of a keep up carbonate platform kimmeridgian swiss jura during the late jurassic accelerated ocean floor spreading and associated sealevel rise were responsible for a worldwide transgression which reached its maximum in the late kimmeridgian in many western european basins this major sea level rise led to the formation of marly and condensed sections in the swiss jura however a shallow carbonate platform kept growing and only subtle changes in the stratigraphic record suggest an increasingly open marine influence field observations and thin section analyses reveal that the central swiss jura was at that time occupied by tidal flats and by more or less open marine lagoons where shoals and bioherms developed the evolution through time of sedimentary facies and bed thicknesses permits the definition of small medium and large scale depositional sequences the diagnostic features of these sequences are independent of scale and seem largely controlled by the kimmeridgian second order transgression a high resolution sequencestratigraphic correlation with biostratigraphically well dated hemipelagic and pelagic sections in the vocontian basin in france reveals that i the most important increase in accommodation recorded in the kimmeridgian of the central swiss jura occurs in the eudoxus ammonite zone late kimmeridgian and corresponds to the second order maximum flooding recognized in many sedimentary basins ii the small and medium scale sequences have time durations corresponding to the first and second orbital eccentricity cycle i e 100 and 400 ka respectively suggesting that sedimentation on the platform and in the basin was at least partly controlled by cyclic environmental changes induced by insolation variations in the milankovitch frequency band the comparison of the high resolution temporal framework defined in the swiss jura and vocontian basin with the sequencestratigraphic interpretation realized in other western european basins shows that the large scale sequence boundaries defined in the kimmeridgian of the swiss jura appear in comparable biostratigraphic positions in most western european basins discrepancies that occur are probably because of local or regional tectonics

origin and composition of carbonate buildups and associated facies in the fort payne formation lower mississippian south central kentucky an integrated sedimentologic and paleoecologic analysis an integrated sedimentologic paleoecologic and taphonomic analysis is used to test competing hypotheses for the origin of the fort payne formation of south central kentucky characteristics of eight distinct facies both carbonate and siliciclastic support the hypothesis that the lower mississippian fort payne formation is a progradational shallowing upward basin filling sequence five facies are considered in detail including the autochthonous fossitiferous green shale facies two autochthonous carbonate facies wackestone buildups and crinoidal packstone buildups and two transported carbonate facies channelform packstone facies and sheetlike packstone facies the two types of carbonate buildups are independent features but both developed on mounds of green fossiliferous shale the fort payne wackestone buildups are interpreted to be waulsortian buildups the fort payne waulsortian and associated facies were deposited in the lower portion of the photic zone which is phase d the shallowest phase of the lees and others 1985 waulsortian model the source of carbonate mud in the buildups must have been autochthonous all autochthonous facies had distinct faunas dominated by crinoids and bryozoans the channelform and sheetlike packstone facies are interpreted to be proximal and distal portions respectively of carbonate apron deposits both are composed principally of crinoid packstones and represent deeper water portions of the fort payne basin filling sequence the siltstone facies records background sedimentation