msec data sets record glacially driven cyclicity examples from the arrow canyon mississippian pennsylvanian gssp and associated sections abstract here we report magnetic susceptibility ms analyses from three mainly marine sections the mississippian pennsylvanian mid carboniferous global boundary stratotype section and point gssp in arrow canyon se nevada and two secondary sections nearby one in arrow canyon 200 m distant and the second in battleship wash 2 km south of the gssp all three sections are easily correlated using the magnetosusceptibility event and cyclostratigraphy method msec cyclicity is clearly apparent in all three sections and time series analysis independently verifies the ms zonation developed from the smoothed data set the periods determined in the three sections support the argument that deposition of these mid carboniferous rocks resulted from climate controlled glacio eustatic fluctuations that were driven by gondwana glaciation given the published average thicknesses of t r cycles 50 m and the estimates for timing of glacial interglacial cyclicity during the mid carboniferous we assign the strong ft peak observed for the three ms data sets a value of 400 000 years corresponding to the milankovitch e1 eccentricity band we then calculate a floating point time scale fpts for the sampled sequence the fpts results indicate that 1 sediment accumulation rates bracketing the mid carboniferous boundary averaged 0 7 cm 1000 years and 2 were relatively constant for these reference sections

defining the timing and duration of the kacak interval within the eifelian givetian boundary gssp mech irdane morocco using geochemical and magnetic susceptibility patterns abstract here we present new geochemical and magnetic susceptibility ms data from the global boundary stratotype section and point gssp for the middle devonian eifelian givetian e g boundary at mech irdane in the anti atlas mountains of eastern morocco these data come from 395 samples collected over a stratigraphic interval of 20 m beginning 4 5 m below the boundary and extending to the upper pumilio marker bed 14 5 m above the boundary ms data show long term transgressive regressive t r eustatic cyclicity upon which is superimposed shorter term climate cyclicity fourier analysis of these data yield high power at four frequencies that are consistent with milankovitch band orbital forcing eccentricity e1 and e2 at 400 and 100 kyr obliquity o1 at 32 kyr and precession p2 at 20 kyr the latter two corrected for secular changes in earth s orbit since the middle devonian a floating point time scale fpts for the boundary interval has been developed using a p2 cyclicity that allows temporal resolution to 10 kyr within the section based on the stratigraphic ranges of geochemical and ms anomalies as well as previously reported biostratigraphic extinctions from the boundary interval we estimate the kacak interval to extend from 1 0 m below the e g boundary to 1 0 m above it with a duration of 200 10 kyr geochemical proxies demonstrate that the kacak interval was characterized by more reducing conditions greater organic carbon burial and an increase in the flux of detrital materials especially clays reflecting an increase in subaerial weathering rates the pumilio beds located 12 15 m above the e g boundary were deposited during successive maximum highstands under conditions of elevated primary productivity and reduced detrital influx

isotopic and chemical compositions of bentonites as paleoenvironmental indicators of the cretaceous western interior seaway oxygen and hydrogen isotopic compositions of volcanic ashes extensively deposited in the cenomanian turonian greenhorn and campanian claggett seas of the cretaceous western interior basin are commonly at variance with the isotopic compositions of the seas themselves as inferred from well preserved fossils the 18o values of montmorillonite from bentonite beds in manitoba montana south dakota wyoming colorado kansas oklahoma and new mexico range from 13 to 28 and translate into values for the greenhorn and claggett seas of 14 to 4 at 10 25 c these values are significantly more variable than the 18o values of fossils which translate into values of 8 to 2 for the same seas the discrepancies are attributed to post formational alteration of the bentonites the d values of turonian and campanian bentonites are unusually low at 120 to 110 relative to those to be expected from the respective late greenhorn and claggett seas whereas some samples of the cenomanian x bentonite seem to be in oxygen and hydrogen isotopic equilibrium with the earlier greenhorn sea mg and ca contents of montmorillonite from the bentonites vary regularly with 18o values but not with d values and sem analyses show the presence of neoformed fibrous smectite in bentonites with the highest 18o and mg and ca contents the chemical and isotopic data indicate that the variations in mineralogy and alteration of the bentonites result from widely disparate depositional environments and alteration of smectites by interaction with basinal brines

impact ejecta layer from the mid devonian possible connection to global mass extinctions we have found evidence for a bolide impacting earth in the mid devonian 380 million years ago including high concentrations of shocked quartz ni cr as v and co anomalies a large negative carbon isotope shift 9 per mil and microspherules and microcrysts at jebel mech irdane in the anti atlas desert near rissani morocco this impact is important because it is coincident with a major global extinction event kacak otomari event suggesting a possible cause and effect relation between the impact and the extinction the result may represent the extinction of as many as 40 of all living marine animal genera

the temperature dependence of hydrogen isotope fractionation between clay minerals and water evidence from a geopressured system abstract d values of water samples from two gulf coast geopressured fields vary linearly with temperature while the d values from the coexisting clays remain constant and are independent of temperature fluid how rates on the order of millimeters per year characteristic of gulf coast geopressured systems provide adequate residence time for hydrogen isotope equilibrium to be achieved between the extant porewaters and clay minerals since equilibrium is achieved these d values are used to calculate the temperature dependence of the hydrogen isotope fractionation factor between illite smectite and water clay waterh between 0 and 150 c 1000 in clay water h 45 3 10 3 t 94 7 this equation predicts values for clay waterh at 96 c which are equal to those predicted by a similar equation derived by yeh 1980 above and below 96 c this new equation predicts values which diverge from those predicted by the equation of yeh 1980 with a difference of 9 at 150 c and 25 at 0 c the possibility is raised that the very slow upward component of flow characteristic of gulf coast geopressured sediments combined with the slow downward subsidence of the clay rich sediments can result in a system which is rock dominated with respect to hydrogen

stable isotopic investigation of clay minerals and pedogenesis in an interfluve paleosol from the cenomanian dunvegan formation n e british columbia canada abstract mineralogical and stable hydrogen and oxygen isotopic compositions have been obtained for clay minerals comprising an interfluve paleosol clayhurst ch 2 from the early to middle cenomanian dunvegan formation british columbia canada this paleosol provides a special opportunity to determine the stable isotopic composition of early late cretaceous paleoprecipitation on the western coast of the western interior seaway at a very northerly paleolatitude 65 detrital kaolinite and illite and complex dioctahedral mixed layer clay minerals of pedogenic origin are abundant throughout the paleosol in the d values of 93 to 81 and 18 o values of 12 9 to 11 6 were generally obtained for the ancient soil water and hence paleoprecipitation for one thin interval near the top of the paleosol higher values are indicated for the ancient soil water these results may indicate processes arising from a westward transgression of the western interior seaway

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

influence of sedimentary setting on the use of magnetic susceptibility examples from the devonian of belgium bulk magnetic susceptibility measurements on sedimentological samples from all geological periods have been used widely in the last two decades for correlations and as a proxy for sea level variations this paper explores the link between magnetic susceptibility depositional setting and environmental parameters these environmental parameters include distal proximal transects microfacies successions and fourth order trends on different carbonate platform types platform ramp carbonate mound or atoll during different devonian stages eifelian givetian and frasnian average magnetic susceptibility values over a distal proximal trending facies succession vary markedly with depositional setting on carbonate platforms average magnetic susceptibility generally increases towards the top of shallowing upward sequences on a distal proximal transect average magnetic susceptibility is intermediate for the deepest facies decreases for the reef belts and increases to a maximum in the back reef zone in ramps and atolls magnetic susceptibility trends clearly differ average magnetic susceptibility generally decreases towards the top of shallowing upward sequences and is highest in the deepest facies the strong relationship between magnetic susceptibility facies and sequences implies a strong environmental influence however the different responses in the different platform types suggest that sea level changes leading to variation in detrital input is not the only parameter controlling average magnetic susceptibility values other primary or secondary processes also probably influenced magnetic mineral distribution primary processes such as carbonate production and water agitation during deposition are probably key factors when carbonate production is high the proportion of magnetic minerals is diluted and the magnetic susceptibility signal decreases high water agitation during deposition will also selectively remove magnetic minerals and will lead to low average magnetic susceptibility values these parameters explain the lowest values observed on the reef platform inner ramp and atoll crown which are all in areas characterized by higher carbonate production and greater water agitation during deposition the lowest values observed in the lagoon inside the atoll crown can be related to detrital isolation by the atoll crown however other parameters such as biogenic magnetite production or diagenesis can also influence the magnetic signal diagenesis can change magnetism by creating or destroying magnetic minerals however the influence of diagenesis probably is linked strongly to the primary facies permeability amount of clay or organic matter and probably enhanced the primary signal the complexity of the signal gives rise to correlation problems between different depositional settings thus while magnetic susceptibility has the potential to be an important correlation tool the results of this investigation indicate that it cannot be used without consideration of sedimentary processes and depositional environments and without strong biostratigraphical control

magnetic susceptibility evolution and sedimentary environments on carbonate platform sediments and atolls comparison of the frasnian from belgium and alberta canada article i nfo magnetic susceptibility ms measurements on carbonate rocks are considered as a proxy for impurities delivered to the carbonate environments in the absence of strong climatic or tectonic variations bulk ms values have been linked to sea level variations because sea level fall increases clastic supply and therefore increases in magnetic mineral deposition in this paper we explore the relationship between the average magnitude of bulk ms with shallowing up sequences and facies evolution in different devonian carbonate complexes similarities and differences between these parameters have been scrutinized in carbonate attached platform and detached platforms mounds and or atolls from belgium and canada in the carbonate attached platforms from belgium and canada the ms patterns are directly related to depositional environment mean ms values increase from the most distal towards the most proximal facies and towards the top of the majority of fourth order shallowing up sequences these trends are in agreement with theoretical background ms increases with regression

recognising the taghanic crisis in the devonian terrestrial environment and its implications for understanding land sea interactions the late mid devonian eday marl formation from the orcadian basin scotland is a terrestrial equivalent of the marine devonian taghanic crisis the eday marl from orkney contains a high resolution archive of climatic change controlled by the relative strength of the seasonal insolation this includes several distinct and discrete episodes of basin flooding as demonstrated by the deposition of lacustrine laminites bedded evaporites marginal sheet flood sands and marine influenced bioturbated sheet sands these flooding events are intercalated with intense and sustained episodes of aridity indicating that insolation was relatively weak and the monsoon climate was ineffective at drawing in seasonal rainfall recognition of these basin flooding events has enabled the definition of three new units the wha taing roeberry and berstane members the eday marl formation can be correlated offshore and also recognised within marginal facies as an aeolian intercalation an environmental hydrological and climatic interpretation is given for the different events recognised in the eday marl this sequence of events when combined with the palynological age dates enables a detailed correlation to be made with the marine tully formation of new york state this suggests that regressions forced by climatic aridity are significant for understanding the deposition of the shallow water carbonates of the tully formation in what is otherwise a clastic depositional system comparison with the pelagic marine record shows that the latter as yet gives only limited resolution of the taghanic crisis recognising the taghanic as a rapid alternation of cool arid and relatively hotter pluvial events provides a unifying explanation for the associated collapse in the terrestrial vegetation and the parallel faunal changes in the marine realm

stable isotope composition of bentonites from the swiss and bavarian freshwater molasse as a proxy for paleoprecipitation abstract the hydrogen and oxygen isotope compositions of bentonites and smectite rich tuffs from the north alpine foreland basin were measured for samples dated between 9 and 21 ma assuming clay mineral formation shortly after the deposition of the volcanic ash layers and at surface temperatures estimated from paleoclimatic studies the h and o isotope composition of water in equilibrium with the clay minerals can be calculated a comparison with values derived from other proxies of paleoprecipitation in the molasse basin such as pedogenic carbonates and mammal remains and 18 o values of carbonate in the bentonite beds suggests that the 18 o values of water estimated by this method are typical for foreland precipitation at this time and for this region therefore the 18 o value of smectite in bentonites and altered tuff layers can be a useful tool for studies of paleoclimate and topography there are however indications that the clay minerals did not retain their initial hydrogen isotopic composition but that a postformational exchange of h isotopes has occurred

magnetosusceptibility event and cyclostratigraphy method applied to marine rocks detrital input versus carbonate productivity magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion we show here that the magnetic susceptibility signature found in two forms resides mainly in paramagnetic and other detrital constituents in most marine rocks the first form is a short term low magnitude high frequency cyclic climate signature that is often useful for regional correlation the second form is a longer term higher magnitude low frequency signature resulting from transgressive and regressive events that can be used for global correlation fluctuations in detrital input due to eustatic based erosion are the primary cause of events these fluctuations are driven by large scale processes such as global orogenic cycles however variations in carbonate productivity cannot be ruled out when explaining the low magnitude climate driven cyclicity also observed in magnetic susceptibility data sets

cenomanian turonian and δ13c and δ18o sea level and salinity variations at pueblo colorado stable isotopes of the surface dwelling planktic foraminifera hedbergella planispira its abundance variations and mineralogical analysis of the cenomanian turonian at pueblo co reveal cyclic variations in surface salinity due to changes in precipitation freshwater influx marine incursions and long term sea level fluctuations hedbergella planispira is a proxy for salinity variations as indicated by 2 4 more negative 18o values in intervals of peak abundances as compared to intervals with reduced populations negative 18o values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods accompanied by increased clastic transport more positive 18o values reflect more normal marine salinities as a result of arid periods and or marine incursions and correlate with intervals of increased biogenic carbonate deposition the magnitude of salinity variations during the low sea level of the hartland shale is twice that during the sea level transgression of the bridge creek limestone the rapid positive 13c shift that marks the onset of oceanic anoxic event 2 oae 2 at pueblo occurred over a period of about 100 ky 93 90 94 00 ma and coincided with the major sea level transgression that culminated in the deposition of the basal bridge creek limestone a positive 13c shift also occurred in the rotalipora cushmani zone prior to oae 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter the likely cause for oae 2 is depletion of 12c in the water column as a result of high primary productivity whereas an earlier r cushmani zone event was primarily caused by increased input of terrigenous organic matter both 13c events are associated with enhanced organic matter preservation and anoxic or dysoxic bottom waters

late cretaceous climate changes recorded in eastern asian lacustrine deposits and north american epieric sea strata abstract cretaceous climate data of the long lived cretaceous songliao basin sb in eastern asia is correlated and compared with the western interior seaway wis on the northern american plate in order to understand better the dynamics of the earth s past greenhouse climates nearly continuous late cretaceous terrestrial deposition in the songliao basin is represented by two cores totaling 2431 m in length the turonian maastrichtian age of the section is based on integrated stratigraphy and is comparable in age with upper cretaceous strata in the wis being consistent with global trends the dynamic late cretaceous climates of both the sb and wis gradually cooled from the warmest albian cenomanian time to the end of the maastrichtian with several intervening warm periods as did the global climate however regional differences existed the songliao basin climate was humid to semi humid warm temperate subtropical and the western interior seaway was in the humid warm temperate zone and experienced only moderate climatic changes the shifts of oxygen isotope data in the songliao basin were frequent and abrupt whereas wis records more gradual change affected mainly by fresh water runoff mixing with southern tethyan and northern arctic waters sedimentary cycles of eccentricity obliquity and precession bands are recorded in both the sb and wis basins the sedimentary cycles in the wis and sb are interpreted to be related to variations of the wet dry runoff cycles which indicate that orbital forcing played an important role in global climate change in late cretaceous the most favorable condition for organic carbon burial in both the sb and wis basin was bottom water anoxia regardless of the cause of the anoxia but the organic carbon burial rate was usually much higher in the songliao lake than in the wi epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric co 2 in both basins organic rich deposits formed during a rise in water level and incursion of saline waters the integration of paleoclimate data from cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the cretaceous greenhouse climate change and may provide insights for a future greenhouse world

interpreting carbon isotope excursions strangelove oceans large negative excursions in marine carbonate delta sup 13 c are commonly associated with period boundaries and mass extinctions explanations for these events must be consistent with limitations imposed by carbon isotope mass balance at steady state i e for excursions lasting more than 10 sup 5 yr the surface ocean delta sup 13 c is set by the organic fraction of the total carbon burial rate and the magnitude of the photosynthetic isotope effect the delta sup 13 c of the deep ocean and the surface to deep isotope gradient are set by both the organic fraction of the ocean s remineralized particulate flux and the magnitude of the isotope effect thus it is the carbon isotope composition of the deep ocean that is most reflective of internal oceanic processes the surface ocean records changes in the longer term throughput of carbon in the system the cessation of organic export from the surface ocean such as is presumed to have caused the strangelove ocean condition of the cretaceous tertiary k t boundary leads to an isotopically homogeneous ocean in decades to centuries if this condition persists the ocean s isotopic composition approaches that of the riverine weathering input in 10 sup 5 yr failure to approach this value during the k t event suggests continued production andmore burial of organic carbon dominantly in either terrestrial or shallow marine environments less

stable isotopic evidence for a pre middle miocene rain shadow in the western basin and range implications for the paleotopography of the sierra nevada 1 a recently proposed method for approximating the paleorelief of mountain belts makes use of the predictable relationship between the isotopic depletion of precipitation and the net elevation of an orographic barrier over which an air mass rises this rain shadow effect often creates desert regions on the lee side of mountain belts in which precipitation is isotopically light changes in the isotopic composition of precipitation can be estimated from the isotopic composition of authigenic or pedogenic minerals which can then be used to infer both the development of relief during orogenesis as well as the stability of a rain shadow formed by developing mountains the 18o of smectites formed from the weathering of middle miocene to late pliocene volcanic ashes currently exposed in the rain shadow of the modern sierra nevada of california show no indication of large scale late cenozoic surface uplift of the sierra and corresponding regional rain shadow development rather smectite isotope data tentatively suggest that elevations may have decreased over this time by as much as 2000 m toward the southern end of the range and 700 m in regions farther north this suggests that the modern rain shadow cast over the western basin and range has been in existence since pre middle miocene and that the sierra nevada have been a prominent orographic barrier since before this time these interpretations are in accord with several recent studies also suggesting a possible cenozoic elevation loss of an already developed sierra nevada mountain range

stratification and paleocirculation of the late cretaceous western interior seaway of north america paleotemperature and salinity profiles for the western interior seaway are reconstructed by use of oxygen and carbon isotopic signatures of shell material data have been gathered on different groups of molluscs distributed in three distinct habitat types infaunal benthonic epifaunal benthonic and nektonic isotopic variations and inferred environmental tolerances of the organisms were used to determine upper and lower temperature boundaries for each habitat group and therefore water depth zones water density for each temperature salinity combination within a habitat range was calculated and used to develop a physically stable stratification model the results clearly show that the water column consisted of denser more saline warm bottom layers that were overlain by and decoupled from cooler less saline intermediate layers it is proposed that this profile originated due to a surface current transporting runoff water from the western highlands toward the eastern shallow border of the seaway where evaporation and heating of surface water in a warm humid atmosphere caused increased density and sinking followed by westward return flow of the warm saline bottom water this model is compatible with known climatic and oceanographic information for the cretaceous

trace element geochemistry of a thick till and clay rich aquitard sequence saskatchewan canada abstract samples collected from a 170 m borehole penetrating till bentonitic clay and sand at the birsay site saskatchewan canada has been studied as a first step for understanding the controls on dissolution and transport of trace elements including rees in porewaters of a clay rich aquitard the ree budgets of the till clay and sand are dominated by apatite and monazite with sporadic zircon and y phosphate apatites contain 0 3 to 1 7 wt ree and monazites 12 to 55 wt all three units are characterized by unusual bulk sample ree patterns with maxima at eu gd convex down patterns from la sm with minima at ce and variably fractionated hree apatites feature maxima at eu gd consequently the complex patterns arise from variable modal proportions of apatite monazite and plagioclase feldspar relative to post archean average shale paas the till is sio2 and cao rich with about half the contents of al2o3 tio2 and fe2o3 these compositional relationship stem from relatively high proportions of quartz and carbonate but low modal abundances of ferromagnesian and ti oxide minerals similarly the till has cs co ni sc v cu pb and zn contents at about half paas the bentonite clay has slightly higher sio2 and cao contents than paas with lower abundances of most other trace elements including ree which plot at 0 7 to 0 9 paas the major and trace element composition is similar to continental arc andesites and the clay is interpreted to have a mixed provenance of arc andesite and eroded underlying sands the composition of the till appears to reflect mixed provenance erosion of the underlying cretaceous clay and sand paleozoic carbonate rocks and the precambrian shield the silicious ardkenneth sand has lower concentrations of ree and most trace elements compared to the clay but the most fractionated ree patterns the clay and till have inherited more subdued ree patterns in part from the underlying sand unit compositional variations between the units are marked by an upturn of nb th u and ree concentrations at the till clay interface 80 2 m and decrease of these elements at the clay sand boundary 156 2 m ce and eu anomalies vary erratically with depth the anomalies appear to reflect the degree of sedimentary sorting which in turn controls the modal abundances of detrital monazite apatite zircon and plagioclase feldspar zr zr hf hf and zr hf ratios are higher in the till than the clay and sand indicating an additional zr hf bearing phase with a distinctively high zr hf ratio the observed small compositional variations in the till and clay are not reflected in variations of geotechnical properties given that the ree budget of the till and clay are dominated by highly insoluble trace minerals it is unlikely that the ree patterns of porewaters will be controlled by bulk sample ree concentrations weathering of the upper 3 m of the till has oxidized fe2 bearing silicates oxides and sulphides and dissolved carbonates relative to the underlying unoxidized till weathering has not disturbed major ree or other trace element compositions

spherule layers records of ancient impacts abstract a large extraterrestrial object striking earth at cosmic velocity melts and vaporizes silicate materials which can condense into highly spheroidal sand size particles that get deposited hundreds to thousands of kilometers from the point of impact these particles known as impact spherules have been detected in great abundance in a relatively small number of thin discrete layers ranging in age from less than a million years to 3 47 billion years unaltered impact spherules consist entirely of glass microtektites or a combination of glass and crystals grown in flight microkrystites impact spherule layers form very rapidly and can be very extensive even global in extent e g the cretaceous tertiary k t boundary layer so they form excellent time stratigraphic markers because they are always found in a stratigraphic context spherule layers are probably superior to terrestrial craters and related structures for assessing the environmental and biotic effects of large impacts a reco

strangelove ocean before the cambrian explosion the palaeozoic and mesozoic eras were terminated by faunal changes involving mass extinction of the old and explosive evolution of the new fauna but the fossil record shows only a cambrian explosion at the end of the precambrian stanley speculated that the explosion was only possible after the ubiquitous algae community had been largely eliminated1 ecological niches were thus liberated for explosive evolution if the cambrian explosion were preceded by a mass mortality or by a mass extinction such an event should leave a record in the form of geochemical anomalies we have undertaken a search for geochemical anomalies at the precambrian cambrian contact we report here the discovery of a sharp negative carbon isotope shift in the carbonate of a clay immediately above a marker in the precambrian cambrian boundary the china c marker and interpret this signal as evidence of sudden decrease in fertility before the cambrian explosion of invertebrate evolution the discovery suggests that the precambrian cambrian boundary might be defined by an event marker at a palaeontologically correlative horizon

diagenesis of clay minerals and k bentonites in late permian early triassic sediments of the sichuan basin chaotian section central china abstract detailed clay mineralogical analyses were carried out on late permian early triassic carbonate sediments exposed on the chaotian section sichuan basin central china the clay assemblages are dominantly composed of illite in platform carbonates and clay seams and illite smectite mixed layers i s in tuff layers k bentonites intercalated in the carbonate succession detrital and authigenic volcanogenic clay minerals have been partially replaced through illitisation processes during burial raising questions about diagenetic effects the precise determination of i s occurring in k bentonites shows that the sediments reached a temperature of about 180 c which is consistent with 1 previous estimates based on fluid inclusion homogenisation temperature analysis 2 the burial depth of the sedimentary series deduced from the post palaeozoic geological history of the sichuan basin and 3 the new data t max obtained on organic matter indicating the transition between oil and gas windows the wangpo bed located close to the guadalupian lopingian boundary is interpreted either as a volcanic acidic tuff or as a clastic horizon this controversial origin probably results from mixed volcanogenic and detrital influences the wangpo bed is therefore interpreted as a reworked bentonite as revealed by the occurrence of i s similar to those found in tuff layers together with preserved detrital kaolinite

geochemical relationships in cretaceous bentonites as inferred from linear discriminant analysis abstract bentonites serve as an important stratigraphic tool for facies correlation due to their instantaneous deposition and preservation across multiple depositional environments correlating one bed to another can be a complex issue limited by the 3 dimensional availability of outcrops and core this process is reliant on the assumption that the geochemical signatures of ash beds do not vary enough to statistically alter the correlation coefficients that tie one ash fall to another this assumption may be faulty however and the problem compounds as bentonite bed thickness increases because the chemical composition varies through an eruption due to stratification of the magma chamber and through physical transport linear discriminant analysis lda can significantly aid with this issue allowing for the utilization of a multivariate dataset to statistically separate chemically similar groups here we present a statistical approach to assessing the primary discriminatory variables on a suite of 87 cretaceous bentonites deposited in the bighorn basin wyoming usa that span five geologic stages and seven formations from the cloverly formation 110 ma to the meeteetse formation 70 ma and includes nine named ash beds using lda bentonites were sorted into groups based on geologic stage formation and unique beds using key elemental concentrations and radiogenic isotopes e g 87sr 86sr tio2 sc na and th additionally distinct similarities in the discrimination pattern between formations reveal two periods of magmatism the development of the idaho batholith and the migration and development of the boulder batholith and surrounding related plutons with well preserved temporally constrained ash lda can correlate ancient tephra deposits while also shedding light on the cyclical nature of geochemical trends in a migrating subduction zone

hydrogen isotope systematics of submarine basalts the d h ratios and water contents in fresh submarine basalts from the mid atlantic ridge the east pacific rise and hawaii indicate that the primary d h ratios of many submarine lavas have been altered by processes including 1 outgassing 2 addition of seawater at magmatic temperature and 3 low temperature hydration of glass decreases in d and h2o from exteriors to interiors of pillows are explained by outgassing of water whereas inverse relations between d and h2o in basalts from the galapagos rise and the famous area are attributed to outgassing of ch4 and h2 a good correlation between d values and h2o is observed in a suite of submarine tholeiites dredged from the kilauea east rift zone where seawater added directly to the magma affected only the isotopic compositions of hydrogen and argon analyses of some glassy rims indicate that the outer millimeter of the glass can undergo lowtemperature hydration by hydroxyl groups having d values as low as 100 d values vary with h2o contents of subaerial transitional basalts from molokai hawaii and subaerial alkali basalts from the society islands indicating that the primary d values were similar to those of submarine lavas extrapolations to possible unaltered d values and h2o contents indicate that the primary d values of most thoteiite and alkali basalts are near 80 5 the weight percentages of water are variable 0 15 0 35 for mor tholeiites about 0 25 for hawaiian tholeiites and up to 1 1 for alkali basalts the primary d values of 80 for most basalts are comparable to those measured for deep seated phlogopites these results indicate that hydrogen in marked contrast to other elements such as sr nd pb and o has a uniform isotopic composition in the mantle this uniformity is best explained by the presence of a homogeneous reservoir of hydrogen that has existed in the mantle since the very early history of the earth

the interplay between massive volcanism and the local environment geochemistry of the late permian mass extinction across the sydney basin australia abstract the isotopic geochemical and physical characteristics of the late permian mass extinction have been identified and assessed from terrestrial sections across the sydney basin eastern australia these new data are used to both correlate the extinction event across the basin and elucidate its cause two stratigraphically well constrained cores were examined one each from the northern and southern regions of the sydney basin both sections show uninterrupted transitions from the last permian coal to a carbonaceous shale overlain by siltstones mudstones sandstones and shales whose mineralogical and physical characteristics are consistent with non marine origins these non marine origins are also broadly supported by elemental data carbon isotopic data were the primary means for identifying the stratigraphic position of the late permian mass extinction across the basin the data show that the mass extinction occurred as an interval with the form of a closely spaced double negative 13corg excursion within 1 m of the top of the last permian coal a feature previously unrecognised in the basin this result is supported by coincident excursions in 15n and 34spyrite the first measurements of their kind for the late permian mass extinction in the sydney basin the interrelationships between the c n and s isotopic data concentrations and elemental ratios together with major trace and rare earth element concentrations ratios and statistical analyses show severe environmental disruption occurred at the time of the extinction event with die off of terrestrial vegetation and the injection of sulphate into the water column consistent with massive volcanism geochemical evidence also shows however that local conditions have the potential to disrupt the late permian mass extinction signature and hence the data need to be interpreted carefully

laser argon dating of melt breccias from the siljan impact structure sweden implications for a possible relationship to late devonian extinction events in earlier studies the 6575 km diameter siljan impact structure in sweden has been linked to the late devonian mass extinction event the siljan impact event has previously been dated by kar and ar ar chronology at 342368 ma with the commonly quoted age being 362 7 2 2 ma 2 recalculated using currently accepted decay constants until recently the accepted age for the frasnian famennian boundary and associated extinction event was 364 ma which is within error limits of this earlier siljan age here we report new ar ar ages extracted by laser spot and laser step heating techniques for several melt breccia samples from siljan interpreted to be impact melt breccia the analytical results show some scatter which is greater in samples with more extensive alteration these samples generally yield younger ages the two samples with the least alteration yield the most reproducible weighted mean ages one yielded a laser spot age of 377 2 2 5 ma 95 confidence limits and the other yielded both a laser spot age of 376 1 2 8 ma 95 confidence limits and a laser stepped heating plateau age over 70 6 39ar release of 377 5 2 4 ma 2 our conservative estimate for the age of siljan is 377 2 ma 95 confidence limits which is significantly different from both the previously accepted age for the frasnian famennian f f boundary and the previously quoted age of siljan however the age of the f f boundary has recently been revised to 374 5 2 6 ma by the international commission for stratigraphy which is within error the same as our new age however the currently available age data are not proof that there was a connection between the siljan impact event and the f f boundary extinction this new result highlights the dual problems of dating meteorite impacts where fine grained melt rocks are often all that can be isotopically dated and constraining the absolute age of biostratigraphic boundaries which can only be constrained by age extrapolation further work is required to develop and improve the terrestrial impact age record and test whether or not the terrestrial impact flux increased significantly at certain times perhaps resulting in major extinction events in earths biostratigraphic record

geochemical consequences of the permian triassic mass extinction in a non marine succession sydney basin australia abstract the identification of the permian triassic boundary ptb and permian triassic mass extinction event ptme in eastern australia is based primarily on palynological and plant fossil evidence with limited 13 c org data from the northern part of the sydney basin consequently the ptb in the sydney basin has been placed at the top of the last permian coal measures here we report carbon and nitrogen isotopic data together with major element trace element and mineralogical data for a continuous non marine permian triassic p tr section from the southern sydney basin the ptme is identified by a negative shift in 13 c org of 3 8 occurring approximately 1 m above the bulli coal seam lack of correlation between 13 c org and toc indicates that the isotopic signature has not been affected by contamination or diagenetic processes the interrelationships between c n and s data indicate severe environmental disruption and increased weathering at the time of the extinction event with die off of terrestrial vegetation and the injection of sulphuric acid into the water column positive excursions in ni cr and co are coincident with the negative 13 c org shift and are most consistent with a reduction in oxygen availability due to a major volcanic eruption

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

the boron isotope geochemistry of smectites from sodium magnesium and calcium bentonite deposits abstract the mineralogical chemical and isotopic analyses of smectites with variable interlayer cation occupancies from bentonite deposits in various depositional environments reveal new insights into the boron sources and the fluids involved in bentonitization in marine and non marine environments smectites from bentonites have non exchangeable structural boron concentrations of 0 2 to 196 g g b smectites from sodium bentonites have higher boron concentrations 30 g g than those from magnesium or calcium bentonites most smectites have a small interstratified illitic component that has a major influence on boron concentrations requiring the use of modified fluid mineral boron partitioning coefficients which indicate that bentonites formed from fluids of highly variable boron concentrations of 100 mg l b and a chlorine content of 76 4 mg l to 59 076 mg l the sodium bentonites formed from boron rich saline fluids or brines whereas the fluids involved in calcium and magnesium bentonite formation have a more variable boron composition and salinity the 11b values of the structural boron in tetrahedral sites of smectites range from 30 1 to 12 2 the smectites from terrestrial depositional settings have 11b values of 30 1 to about 0 whereas smectites from marine depositional settings have negative as well as positive 11b values the boron isotope values indicate that all examined bentonites from terrestrial depositional settings as well as many bentonites from marine depositional settings formed from basinal fluids or brines the boron isotope geochemistry of smectites is demonstrated to be a tool for elucidating the fluids involved in the formation of clay mineral deposits it also has great potential for tracing fluids in other settings involving authigenic clay minerals such as sedimentary basins and surficial crystalline rocks as well as man made applications such as in disposal sites for highly active nuclear waste

lithic geochemistry of the claggett marine cyclothem in south central saskatchewan sediments of the lea park formation in south central saskatchewan were deposited in the claggett sea during the late cretaceous campanian claggett marine cycle rocks of the lea park formation have remained virtually unaffected by diagenetic alteration hence variations in mineralogical and chemical compositions result primarily from changes in the source of detritus quartz feldspar discrete illite kaolinite and chlorite were derived from weathering of the western highlands whereas illite smectite i s the dominant clay phase originated from volcanic ash changes in the proportions of these minerals suggest a large scale volcanic episode during deposition of the lea park sediments an episode that affected not only the detritus delivered to the seaway but also the chemical and isotopic compositions of the sea water itself 13c values of organic matter increase with little change in the quantity of organic carbon preserved through both the transgressive and regressive phases of the claggett cy

visual identification and quantification of milankovitch climate cycles in outcrop an example from the upper ordovician kope formation northern kentucky

stable isotope record of the eifelian givetian boundary kacak otomari event middle devonian from hungry hollow ontario canada the kacak event in the middle devonian eifelian givetian e g boundary is a period of apparent global anoxia coincident with widespread deposition of black shale in hemipelagic pelagic and som

extra basinal fluid infiltration mass transfer and volume strain during folding insights from the idaho montana thrust belt finite strain and geochemical variations along strain gradients were used to study cleavage development in carbonates in the lost river range idaho deformation accommodating layer parallel shear was partitioned into thin deforma tion zones during folding of willow creek anticline cleavage intensity is strong to very strong in deformation zones and weak in surrounding rocks strain magnitudes range from e s0 32 1 15 0 93 0 73 x y z principal axes of strain outside to e s0 64 1 29 0 80 0 52 inside deformation zones we found a positive linear correlation between strain cleavage development and negative dilation volume loss at a cubic centimeter scale ranges from 12 percent to 49 percent cleavage selvages are depleted in ca and 18 o and enriched in other elements relative to microlithons and less deformed protolith carbonates mass balance considerations indicate that cleavage was formed by incongruent pressure solution leading to a passive concentration of less soluble components during ca loss and metasomatic additions of si al and k to produce authigenic clay minerals in selvages data for the willow creek locality and elsewhere in the lost river range davidson and others 1998 pioneer mountains and the tendoy range bebout and others 2001 show that across the sevier orogen fluid infiltration was heterogeneous at centimeter kilometer scales and resulted from positive feedback between deforma tion and far traveled surficial fluids metasomatic strain softening enhanced deforma tion zone development which generated increased permeability as the thrust belt evolved from a porosity based closed system to a discontinuity based open system increased fluid infiltration and isotopic exchange was associated with volume loss increasingly prolate strains and crystallization of clays to produce the cleavage selvages mass transfer was accommodated by diffusion early and advection later in the deformation history mesoscopic structures deformation zones faults veins focused fluid flow and were kinematically related to larger scale structures faults fault related folds the inferred addition of surficial fluids to depths of 7 kilometers in the thrust belt implies a fluid regime involving significant topographically driven recharge deformed whole rocks and microsamples are lower in 18 o than unde formed samples which have o and c isotope compositions similar to those of marine carbonates veins are even lower in 18 ov smow with minimum values of 5 permil reflecting penetration of the crust by ocean derived precipitation with 18 o near to somewhat lower than 0 permil range of 7 5 to 2 5 calculated for h2 oi n equilibrium with these veins the inferred penetration into the thrust belt of nearshore meteoric waters is consistent with proximity to the reconstructed western interior seaway later fluid infiltration locally lowered the 18 o of carbonates even further based on the o isotope compositions of veins related to younger compres sional deformation and to the onset of crustal scale extension in the eocene this progression toward lowered 18 o of the surficial waters is compatible with the retreat of the seaway during emergence of the thrust wedge and paleogene extension uplift and subaerial volcanism

bentonite chemical features as proxy of late cretaceous provenance changes a case study from the western interior basin of canada abstract bentonite beds are fairly common in both marine and terrestrial upper cretaceous campanian maastrichtian deposits of the western interior basin of western canada and northwestern united states a detailed stratigraphic sedimentologic geochemical x ray fluorescence and mineralogical x ray diffraction study of twenty one bentonites from the puskwaskau and wapiti formations in the grande prairie area west central alberta canada is here presented major and trace element concentrations from altered volcanic ashes document the presence in the study area of predominantly trachyandesitic and rhyolitic volcanogenic products resulted from intense volcanic arc to within plate pyroclastic activity concentration values of high field strength elements hfse and selected large ion lithophile elements lile e g nb zr th and y obtained by x ray fluorescence spectroscopy strongly support the presence of multiple volcanic sources integrated paleoenvironmental and geochemical criteria for provenance determination indicate a bimodal occurrence of basic and acid volcanic products interpreted as reflection of source areas characterized by different tectonic setting and magmatic composition a comparative analysis of geochemical compositions between grande prairie bentonites and 30 known volcanic beds from central and southern alberta manitoba and montana 1 documents a trend toward more acidic and alkali depleted volcanic products during the late campanian early maastrichtian interval and 2 suggests a well constrained stratigraphic and geographic subdivision of the non marine successions of the foreland basin on the basis of geochemical characteristic of volcanic ash beds furthermore geochemical fingerprints of several decimeter to meter thick bentonite beds have been coupled with volcanic ash subsurface signature in order to investigate their role as marker beds this multiple approach provides a reliable tool for basin scale identification and correlation of non marine sedimentary successions

comment on impact ejecta layer from the mid devonian possible connection to global mass extinctions the interesting report by ellwood et al 1 1 demonstrated the applicability of magnetic susceptibility field methods to the identification of distal impact deposits however the evidence that they have presented for a bolide impact during the middle devonian immediately preceding the

stratigraphic correlations in mid to late proterozoic carbonates of the democratic republic of congo using magnetic susceptibility abstract in this paper we have tested the application of magnetic susceptibility measurements in cu ag zn pb fe mineralized carbonates of the bie subgroup democratic republic of congo as an efficient tool for regional and global high resolution stratigraphic correlations in the neoproterozoic marine carbonates to achieve this goal we integrate the low field magnetic susceptibility xlf data with facies analyses geochemistry and isotope stratigraphy the microfacies analyses of two cores tshinyama s70 and kafuku 15 drilled in the early neoproterozoic carbonates of the mbuji mayi supergroup reveal a deep carbonate ramp setting associated with a microbial stromatolitic mid ramp environment high resolution stratigraphic correlations using magnetic susceptibility and c isotope curves established for both cores 190 km apart suggest a sedimentary hiatus at the base of the tshinyama s70 succession c o and sr isotopes and sr ca and fe abundances show that a diagenetic meteoric overprint affected the series of the tshinyama s70 core and a thermal effect related to mineralizing fluids affected the kafuku 15 core carbonates

a climate driven model and development of a floating point time scale for the entire middle devonian givetian stage a test using magnetostratigraphy susceptibility as a climate proxy abstract here we propose an approach to establish a preliminary age chronology for complete stages within the phanerozoic by applying cyclostratigraphic methods that employ high resolution data sets this requires use of geochemical or geophysical data known to serve as a cyclic climate proxy to demonstrate the method we use the magnetostratigraphic susceptibility technique as the basis for fitting a climate model to the givetian stage of the middle devonian system we show a milankovitch eccentricity climate zonation for the givetian that is pinned to time series analyses from outcrop samples from its upper givetian frasnian france and lower eifelian givetian morocco stage boundaries using these data sets we construct a uniform cyclicity model designed to conform to a 405 kyr cyclicity with a duration corresponding to the published duration for the givetian of 4 4 myr kaufmann 2006 to this model we fit two well established conodont zonation schemes thus allowing time estimates for conodont ranges for the givetian indicating a range from 1 8 myr to 100 kyr before extinction of an individual conodont species we then test and adjust the model using independent data sets from the eastern united states adjustments to the initial model yield a duration of 28 climate half cycles zones for the givetian stage and an increased age to 5 6 myr these zones allow high correlation among sections to better resolve timing of major bio events and provide a floating point time scale to which absolute ages can be applied

magnetostratigraphy susceptibility of the upper ordovician kope formation northern kentucky abstract as a test of the utility of magnetic susceptibility ms measurements for correlation among lithified marine sequences samples were collected from well studied shale and limestone outcrops of the upper ordovician kope formation northern kentucky the bulk initial low field ms of these samples is compared among two litho and biostratigraphically correlated sections containing the same beds the results of this comparison demonstrated an excellent correlation among equivalent beds thermomagnetic susceptibility analysis supports previous xrd work indicating that illite is primary and is the main paramagnetic mineral responsible for the ms variations observed in this study a composite of ms results for a sequence of 31 named shale limestone couplets is used to build a composite section of kope sequences for the area these ms variations permit division of the various sections into a set of 28 ms cycles within the kope formation covering 50 m of section these cycles suggest a systematic control by climate on the influx of detrital material that formed these sedimentary sequences and support other work indicating kope climate cyclicity

assessing the preservation and provenance of sr and nd isotopic signatures in cretaceous volcanic ash beds abstract bentonite a claystone formed from the devitrification of volcanic ash demonstrates varying amounts of alteration in elemental concentrations through the transition from glass to clay many studies have sought to characterize and correlate bentonites using various elemental signatures but the information garnered from this can be misleading since 1 volcanoes produce highly variable compositions during single events making tephra classifications reliant on the position within the bed and the distance from the source and 2 the elemental concentrations may vary significantly due to devitrification strontium and neodymium isotopic signatures offer a powerful dataset to supplement these efforts but the extent to which the isotopic ratio is preserved during devitrification and post depositional diagenesis is not well documented here we perform a detailed isotopic geochemical and mineralogical examination of sixteen bentonites preserved in cenomanian and campanian strata late cretaceous from south dakota in order to characterize the diagenetic factors that may influence the ash geochemistry while checking for the fidelity of the isotopic signatures to the magmatic source a mixing model between the isotopic composition of bentonite and seawater can be generated to determine the original endmember composition of each deposit since sr was likely derived from both sources during devitrification initial 87sr 86sr ratios from cenomanian samples ranged higher than the campanian demonstrating a negative correlation with end values that point towards magmatic signatures with the influence of crustal assimilation x ray diffraction was utilized to determine the speciation of the clay mineral and sedimentary input displaying a complete lack of smectite illitization that would indicate the presence of a hydrothermal influence bentonite isotopic chemistry therefore is reliably traced to the magmatic source under the appropriate diagenetic conditions with careful consideration for diagenesis the isotopic composition of the cretaceous bentonites can be used for provenance identification and points towards magmatic emplacement within an evolved crustal source on the laurentian craton this isolates the most likely provenance of cenomanian bentonites as being the idaho batholith while campanian bentonites were likely derived from the elkhorn volcanic complex

book review hydrous phyllosilicates exclusive of micas reviews in mineralogy 19 s w bailey editor mineralogical society of america washington d c 1988 xiii 725 pp u s 18 00 paperback

the petrogenesis of brines in devonian potash deposits of western canada abstract recent mine level floods in some potash mines in the elk point basin of saskatchewan canada have demonstrated the need to identify accurately the source of water leaks so as to assist in remedial or preventative action most chemical constituents of the waters are inadequate tracers of the origin of these leaks because the concentrations of most elements change substantially during migration of the fluids to the mining level in marked contrast to most of the chemical constituents dissolved in the water oxygen and hydrogen isotopes are conservative elements of the water within the elk point basin d and 18 o values of basinal waters normally increase with depth because of mixing between trapped formation waters and local surface waters such that the water in each aquifer within the basin generally has a unique isotopic composition floodwaters in the potash mines of saskatchewan have chemical and stable isotopic compositions that indicate three different origins for mine level fluids 1 halite and sylvite saturated basinal brines from devonian formations directly above the deposits which are predominantly connate waters 2 undersaturated waters of predominantly meteoric origin from stratigraphically higher aquifers such as the cretaceous mannville group and 3 ca rich brines that may represent devonian fluids associated with recrystallization of the evaporites the salt undersaturated formation waters most likely are directed to lower stratigraphic units through collapse structures or related features which may be reactivated through mining

the origin of infrasonic ionosphere oscillations over tropospheric thunderstorms thunderstorms have been observed to introduce infrasonic oscillations in the ionosphere but it is not clear what processes or which parts of the thunderstorm generate the oscillations in this paper we present a new technique that uses an array of ground based gps total electron content tec measurements to locate the source of the infrasonic oscillations and compare the source locations with thunderstorm features to understand the possible source mechanisms the location technique utilizes instantaneous phase differences between pairs of gps tec measurements and an algorithm to best fit the measured and the expected phase differences for assumed source positions and other related parameters in this preliminary study the infrasound waves are assumed to propagate along simple geometric raypaths from the source to the measurement locations to avoid extensive computations the located sources are compared in time and space with thunderstorm development and lightning activity sources are often found near the main storm cells but they are more likely related to the downdraft process than to the updraft process as a result the sources are also commonly found in the convectively quiet stratiform regions behind active cells and are in good coincidence with extensive lightning discharges and inferred high altitude sprites discharges

response to comment on impact ejecta layer from the mid devonian possible connection to global mass extinctions new international efforts to define global boundary stratotypes gssps and resolve biostratigraphic uncertainties should make it possible to test key questions in geology and biostratigraphy our study 1 1 contributed toward an answer to one such question whether and how often bolide

the magneto susceptibility event and cyclostratigraphy msec method used in geological correlation of devonian rocks from anti atlas morocco magneto susceptibility event and cyclostratigraphy msec is used here as a means of establishing sensitive chronostratigraphic markers and chronohorizons useful for high resolution correlation msec is a composite of the magnetic susceptibility ms record of marine strata and the coeval biostratigraphic record and similar to chronozones zones based on msec data have boundaries that are isochronous ms a measure of the concentration of magnetic grains in sediments proxies for the ratio of lithogenic to biogenic components controls on the detrital input of lithogenic material include eustasy and climate however induced and sea floor basin subsidence the development of an initial msec composite reference curve for the middle upper devonian of the anti atlas region of southern morocco is presented and discussed in the context of global sea level transgressive and regressive cycles msec trends composed of increasing ms magnitudes correlate well with episodes of regression whereas trends of decreasing ms magnitudes correlate with episodes of transgression

correlation of physical surfaces bentonites and biozones in the cretaceous colorado group from the alberta foothills to southwest saskatchewan and a revision of the belle fourche second white specks formational boundary new allostratigraphic correlations in west central alberta show that flooding surfaces in the sunkay and basal vimy members of the blackstone formation can be traced eastward from burnt timber creek for 500 km to western saskatchewan and for 350 km northward into the dunvegan and kaskapau formations at burnt timber creek a miliammina manitobensis microfauna in the lowest 1 m of the sunkay member indicates equivalence to the westgate formation and an overlying 70 cm conglomerate is correlative with the fish scales formation overlying mudstones contain foraminifera of the verneuilinoides perplexus zone indicative of the middle cenomanian belle fourche formation the base of the second white specks formation as currently defined in core in eastern alberta equates in outcrop with the lower part of the sunkay rather than the base of the vimy member as previously thought the base of the second white specks formation should be placed about 35 m higher in the stratotype core a bentonite located 9 3 m

concentric waves and short period oscillations observed in the ionosphere after the 2013 moore ef5 tornado 1 we detected clear concentric waves and short period oscillations in the ionosphere after an enhanced fujita scale ef 5 tornado hit moore oklahoma u s on 20 may 2013 using dense wide coverage ionospheric total electron content tec observations in north america these concentric waves were nondispersive with a horizontal wavelength of 120 km and a period of 13 min they were observed for more than 7 h throughout north america tec oscillations with a period of 4 min were also observed to the south of moore for more than 8 h a comparison between the tec observations and infrared cloud image from the goes satellite indicates that the concentric waves and short period oscillations are caused by supercell induced atmospheric gravity waves and acoustic resonances respectively this observational result provides the first clear evidence of a severe meteorological event causing atmospheric waves propagating upward in the upper atmosphere and reaching the ionosphere

the world s most spectacular carbonate mud mounds middle devonian algerian sahara abstract in the southern ahnet basin of algeria a unique middle devonian underwater scenery is revealed which consists of 191 mud mounds 15 mud ridges and 2 mud atolls distributed over nine discrete areas of a shallow pelagic carbonate shelf all the buildups are totally exhumed thus perfectly exhibiting their original morphologies slope angles elevations and the pattern of the onlapping strata as well as their relationship to the surrounding off buildup sequences types of buildups include 1 small mud mounds 1 5 m high 10 20 m diameter 2 large mud mounds up to 40 m high up to 200 m diameter 3 lens shaped mounds 1 30 m thick 10 15 slopes 4 mud ridges up to 100 m high 150 8500 m long and 5 semicircular mud atolls 2500 2800 m long 20 30 m high the buil ups were constructed during a short time span in the early givetian part of the lower varcus zone probably not exceeding a few hundred thousand years sedimentation rates in coeval off buildup areas were at least 3 10 times lower the lithology of the buildups is a massive boundstone with a high proportion of irregular spar filled cavities stromatactis but only very scattered potential frame builders the carbonate mud is considered to be an in situ cyanobacterial precipitate although evidence of such is poor organic components of the buildups are not significantly different from those of the off buildup lithologies and include numerous crinoid ossicles some tabulate and solitary rugose corals brachiopods mollusc debris trilobites and very rare sponge spicule and bryozoans the total absence of stromatoporoids large tabulate and colonial rugose corals green algae and micritic envelopes around grains suggests growth of the buildups in the lower part of the photic zone 100 200 m they are onlapped by a discontinuous sequence a few meters thick of skeletal packstones and grainstones and locally orthoceratid floatstones that were deposited later in the givetian a widespread rise of sea level in the early frasnian buried both buildups and adjacent areas under shales and siltstones postdepositional alteration of the mud buildups includes 1 formation of stromatactis cavities probably by dewatering and internal erosion 2 cementation of stromatactis cavities and interparticle pore spaces by early high mg calcite and late blocky low mg calcite 3 neomorphic transformation of mg calcitic mud and aragonitic skeletal debris 4 occasional formation of neptunian dikes 5 slight erosion of buildup surfaces 6 compaction and slumping of onlapping capping beds and 7 local dolomitization the formation and growth of the mud build ups is envisaged as a sequence of stages starting with patchy coral thickets evolving into small mud mounds that coalesced into larger mounds by continuous vertical and lateral growth closely spaced mounds amalgamated into mud ridges and mud atolls regular nw se and n s patterns of some mound rows and ridges show a relationship of buildup formation to rejuvenated late precambrian tectonic lineaments which reappear in the hercynian orogeny the isotopic signature of matrix and early ements of mound rocks however does not support the idea of fluid migration and hydrothermal co2 supply during buildup growth

paleoenvironment of the western interior seaway inferred from δ18o and δ13c values of molluscs from the cretaceous bearpaw marine cyclothem abstract 18 o and 13 c values of ammonites and inoceramids provide information on the paleoenvironmental conditions in the western interior seaway wis during the campanian maastrichtian bearpaw marine cycle the last major transgression regression t r cycle to affect the seaway during the cretaceous period ammonites and inoceramids exhibit distinct stable isotope values inoceramids have higher 13 c values 0 6 to 5 0 and lower 18 o values 4 0 to 2 8 whereas coeval baculitid ammonites have lower 13 c values 4 8 to 0 3 and higher 18 o values 2 3 to 0 0 with other ammonites having stable isotope values ranging between the baculitids and inoceramids the isotopic composition of the inoceramids and ammonites are unlikely due to kinetic or vital effects because species from open ocean environments have values expected from marine water and there is no correlation between the 13 c and 18 o values of the inceramids as has been reported for modern foraminifers and calcareous algae suspected of exerting vital effects the heterogeneity in stable isotope values of coeval molluscs implies that the bearpaw sea was isotopically stratified isotopic exchange between the water and sediments and the formation of 18 o depleted deepwater mass by mixing of tethyan and boreal waters in the wis may have caused such isotopic stratification a clear relationship exists between the 18 o values of bearpaw zonal baculitids and their biostratigraphic sequence baculitids from zones during peak transgression have the lowest average 18 o values 2 3 to 0 7 whereas those from the underlying and overlying zones have higher 18 o values 0 8 to 0 2 this pattern of 18 o values can be explained by fluctuations in temperature rather than variations in freshwater influx this influx probably having been reduced by lower precipitation and run off under drier warmer climatic conditions the bearpaw sea was not brackish and other paleoenvironmental factors likely account for the character of the bearpaw fauna that is dominated by ammonites and inoceramids and lacks many of the taxa prevalent in the contemporaneous open oceans and seas

modeling the carbon and sulfur isotope compositions of marine sediments climate evolution during the devonian abstract a model of global biogeochemical cycles coupled to an energy balance climatic model modified after the combine model godderis y joachimski m m 2004 global change in the late devonian modeling the frasnian famennian short term carbon isotope excursions palaeogeogr palaeoclimatol palaeoecol 202 309 329 is used to calculate the short term evolution of atmospheric p co 2 during the devonian the geochemical cycles for carbon alkalinity phosphorus sulfur and oxygen are included in this model with also 13 c and 34 s cycles high resolution records of 13 c of marine carbonates and 34 s of marine sulfates are used as forcing parameters of the geochemical cycles in an inverse modeling atmospheric p co 2 and p o 2 at the end of the silurian are calculated to have been 3000 ppmv and 0 165 bar 0 75 pal respectively a long term decrease in p co 2 is modeled for almost the entire devonian short term lowering of p co 2 to concentrations around 2000 ppmv is calculated for the silurian devonian transition and the pragian contents around 900 ppmv are modeled for the eifelian givetian givetian frasnian and frasnian famennian boundaries as a consequence of enhanced organic carbon burial during deposition of lochkovian eifelian and frasnian grey and black shales organic carbon burial is enhanced by the increase of phosphorus delivery to the ocean triggered by short term sea level falls the corresponding short term global climatic cooling at the silurian devonian boundary at the end of the pragian and the givetian frasnian as well as frasnian famennian boundaries reached 2 c at the equator the rapid colonization of continental surface by land plants during the middle and late devonian increasing chemical alteration of the continents and co 2 consumption by silicate weathering is assumed to have caused cooling of surface seawater as suggested by the 18 o values of biogenic apatites

diagenesis of middle devonian carbonate mounds of the mader basin eastern anti atlas morocco abstract in the mader basin of the eastern anti atlas middle devonian carbonate mounds were established on a gently sloping ramp at moderate water depths primary stromatactis cavities in these mounds exhibit early marine shallow burial and deeper burial cementation the mound matrix was affected by neomorphic alteration stylolitization and dolomitization earliest cementation occurred in the marine environment nonluminescent to blotchy luminescent cloudy radiaxial calcites of originally high mg calcite composition coat the walls of stromatactis cavities and take up more than 50 of the primary pore space the isotopic signature d18o 2 6 0 2 pdb d13c 2 7 0 5 pdb is close to that of nonluminescent fabric retentive brachiopod shells in the same mounds and taken as the nearly pristine stable isotopic signature of mader basin seawater the high d18o values compared with middle devonian data of north america are interpreted to result from the mid latitudinal ca 35 s temperate water settings of the mader basin carbonate mounds the transition to the shallow burial realm is indicated by a typical non bright dull luminescence sequence nonluminescent scalenohedral cements pass into bright luminescent and banded luminescent scalenohedral cements which are overgrown in turn by dull to moderate luminescent blocky spar meteoric influence on that cement sequence can be excluded deeper burial diagenesis is represented by stylolitization ferroan calcite cementation and neomorphic alteration of the fine grained mound carbonates pressure solution and or outgassing of co2 are possible ion sources for ferroan calcite precipitation in the remaining pore space 18o depletion d18o 6 8 to 8 9 pdb of these cements can be calculated to elevated precipitation temperatures of 21 33 5 c and burial depths of 420 670 m microspar making up the bulk of the mounds was formed by a one step transformation of a precursor calcitic micrite low d18o values 6 9 p 2 1 pdb mottled luminescence and high fe concentrations indicate that this transformation also took place in the deeper burial realm

paleoenvironmental geochemistry of the claggett marine cyclothem in south central saskatchewan the upper cretaceous campanian lea park formation of south central saskatchewan a product of continuous deposition in the claggett sea of the western interior basin contains unusually well preserved fossil shells ideally suited for analysis of their chemical and isotopic compositions although both ammonites and bivalves secreted shells in isotopic equilibrium with the waters in which they lived ammonites usually have higher 18o and lower 13c values than coexisting bivalves these values point to the ammonites and bivalves having inhabited isotopically distinct waters within the claggett sea the benthonic bivalve inoceramus is inferred to have lived in a thin bottom layer the isotopic composition of which was modified by that of pore waters expelled at the sediment water interface following compaction of sediments the nekto benthonic ammonites scaphites and baculites are inferred to have lived mostly at successively higher levels in the water column the isotopic composition of which was modified

changes of palaeoenvironmental conditions recorded in late devonian reef systems from the canning basin western australia a biomarker and stable isotope approach abstract although the late devonian extinctions were amongst the largest mass extinction events in the phanerozoic the causes nature and timing of these events remain poorly restrained in addition to the most pronounced biodiversity loss at the frasnian famennian f f boundary and the end famennian there were also less extensively studied extinction pulses in the middle to late givetian and the frasnian here we used a combination of palynological elemental molecular and stable isotope analyses to investigate a sedimentary record of reef systems from this time period in the canning basin western australia the acquired data generally showed distinct variations between sediments from i the time around the givetian frasnian g f boundary and ii later in the frasnian and indicated a distinct interval of biotic stress particularly for reef builders in the older sediments alterations of pristane phytane ratios gammacerane indices chlorobi biomarkers dkerogen and chroman ratios describe the change from a restricted marine palaeoenvironment with an anoxic euxinic hypolimnion towards a presumably open marine setting with a vertically mixed oxic to suboxic water column simultaneous excursions in 13c profiles of carbonates organic matter om and hydrocarbons in the older sediments reflect the stratification induced enhancement of om recycling by sulfate reducing bacteria alterations in sterane distributions and elevated abundances of methyltrimethyltridecylchromans mttcs and perylene indicate an increased terrigenous nutrient input via riverine influx which would have promoted stratification phytoplankton blooms and the development of lower water column anoxia the detected palaeoenvironmental conditions around the g f boundary may reflect a local or global extinction event our data furthermore suggest a contribution of the higher plant expansion and photic zone euxinia to the late devonian extinctions consistent with previous hypotheses furthermore this work might contribute to the understanding of variations in devonian reef margin and platform top architecture relevant for petroleum exploration and development in the global devonian hydrocarbon resources

low latitude ordovician to triassic brachiopod habitat temperatures bhts determined from δ18o brachiopod calcite a cold hard look at ice house tropical oceans abstract some researchers have suggested that phanerozoic land based ice sheets extended occasionally into the tropical realm if true the tropical ocean at those times must have been distinctly colder than at the last glacial maximum lgm when northern hemisphere ice sheets did not extend below 38 latitude low latitude ocean temperatures derived from oxygen isotopes of brachiopod shells test this hypothesis by comparing the temperature regime for paleozoic and early mesozoic low latitude settings to the tropical temperature regime of the modern interstadial ocean and to mean temperatures estimated for the tropical ocean at lgm a running mean of ph adjusted brachiopod habitat temperatures bhts shows that paleozoic low latitude oceans were on average cool to cold relative to the modern interstadial tropical ocean at times during pennsylvanian serpukhovian tournaisian and ordovician silurian glaciations these tropical seas were indeed significantly colder on average than at the lgm ice sheets within tropical latitudes can be reasonably predicted at those times abundant and diverse paleozoic brachiopod communities reflect these cool tropical oceans consistent with modern brachiopod ecological preference for colder waters amplified paleozoic temperature oscillations suggest recurring global warming events which episodically drove these cold tropical oceans to temperatures significantly higher than the warmest modern tropical ocean

late devonian carbonate margins and foreslopes of the lennard shelf canning basin western australia part b development during progradation and across the frasnian famennian biotic crisis abstract many studies document the occurrence of carbonate progradational successions that are driven by overall accommodation limited conditions and represent periods when substantial volumes of sediment are stored in slope settings however few have reported on the detailed internal anatomy and components of prograding clinothems and furthermore little is known about how environmental parameters affect the development of carbonate margins and slopes when superimposed on the long term low accommodation signal upper devonian frasnian and famennian carbonate outcrop exposures along the lennard shelf northeast canning basin western australia offer the examination of reefal margin and foreslope development in a variety of settings one of which is long term 10 ma progradation during the late frasnian and famennian in the early phases of progradation a global biotic crisis and faunal overturn occurred around the frasnian famennian f f boundary and indications of global climatic cooling are interpreted at points throughout the late devonian these extrinsic and intrinsic controls provide ecologic context and a stratigraphic framework to assess carbonate margin and foreslope architectures and facies distributions in order to better characterize and predict their complex heterogeneity the outcrop dataset collected includes measured sections tied to interpreted photomosaics and detailed mapping using aerial photographs from the south lawford range windjana gorge and dingo gap areas the outcrop observations highlight distinctive changes in margin style foreslope composition stratigraphic packaging and strike variability within the contexts of the f f biotic crisis long term highstand hst progradation and late devonian climatic changes intervals before and after the f f boundary exhibit notable increases in downslope calcimicrobial boundstone encrustation and evidence for waning foreslope contributions from other previously flourishing carbonate factories reflecting stressed ecological conditions and consequent calcimicrobial opportunism during gradual buildup and recovery periods that bracket the extinction the famennian slope post effects related to the f f crisis can be subdivided into a calcimicrobial boundstone dominated upper slope with a highly complex downdip transition into a mixed debris and grain dominated middle slope and a silt dominated lower slope to toe of slope and exhibits a highly complex lateral heterogeneity associated with multiple contributing sediment factories and temporal partitioning of resedimentation a repeated stacking pattern is observable in the famennian middle slope setting consisting of upward successions of debris followed by a gradation from silt dominated deposits into grain dominated deposits we here interpret these as the expression of high frequency sequences superimposed upon the longer term progradation and a function of transitional greenhouse to icehouse climates these findings offer predictive relationships that link the internal depositional heterogeneity of prograding slope systems to the interplay of long term accommodation drivers ecological conditions affecting carbonate sediment factories and climatic conditions that control the development of high frequency sequences

oxygen and hydrogen isotope geochemistry of cretaceous bentonites and shales from the disturbed belt montana the mineralogy o18 and d of the 0 1 m fraction of 22 cretaceous bentonites and the mineralogy and o18 of the 0 1 m fraction of 14 adjacent shales collected from outcrops in the sweetgrass arch and disturbed belt montana have been determined mixed layer illite smectite i s is the dominant mineral in the bulk bentonite and usually the only mineral in the 0 1 m fraction i s is also the major clay mineral in the shales the diagenetic grade in bentonite is qualitatively given by the percentage of illite layers in i s which varies from 2 to 25 sweetgrass arch to as high as 95 disturbed belt o18 of 0 1 m bentonite generally decreases from about 20 to about 13 with increasing diagenetic grade on a plot of d versus o18 data for the 0 1 m bentonite define a field that generally parallels but falls on the meteoric water line side of the smectite water line savin and epstein 1970 o18 of bulk bentonite is 1 to 3 more negative than the o18 of the 0 1 m fraction due to the presence of volcanic quartz and feldspar o18 of several size fractions of clay sized quartz separated from the bentonite varies from 11 to 24 and in a given bentonite generally increases with decreasing grain size among the different bentonites the o18 range of the different grain sizes decreases as the percentage of illite layers in the coexisting i s increases the o18 of 0 1 0 5 m shale quartz is generally 1 to 4 more positive than clay sized quartz from an adjacent bentonite and the o18 of 0 1 m i s concentrate of shales is generally 1 to 4 more negative than the 0 1 m i s from an adjacent bentonite isotopic temperatures interpreted to be maximum burial temperatures range between about 160 c shale to about 250 c bentonite the isotopic data can be interpreted using the stages 1 1 deposition of volcanic glassy ash containing some quartz and feldspar 2 2 devitrification into mostly 100 expandable smectite with a o18 of about 20 and d of 60 to 80 3 3 tectonic burial beneath thrust sheets in the disturbed belt region which induced elevated temperatures that allowed oxygen and hydrogen isotope reequilibration as the percentage of illite layers in i s increased and diagenetic quartz formed and 4 4 exhumation of the strata with preservation of o18o16 and d h attained during burial

clay mineralogy of shale limestone rhythmites in the scaglia rossa turonian eocene italian apennines abstract the scaglia rossa turonian eocene part of the miogeoclinal series exposed in the italian apennines consists of pelagic limestones and marly limestones rhythmically punctuated by thin shale partings the variations in lithology in part reflect variations in carbonate productivity and or preservation during deposition samples of the shale partings and the intercalated limestones were collected from the botaccione gorge near gubbio semiquantitative methods of analysis described herein were used to characterize the clay mineralogy of the two lithologies the mineralogical compositions of the shales differ qualitatively and quantitatively from those of the limestones suggesting that the clay fractions of the two lithologists were derived either from different sources or from diff rent proportions of the same multiple sources because variations in provenance occur concurrently with variations in carbonate productivity preservation a climatic mechanism is most likely responsible for the shale limestone alternations the rhythmic nature of these alternations is interpreted as evidence for cyclic climatic variability in the late mesozoic mediterranean tethys stratigraphic variation in clay mineralogy independent of lithology is limited to a brief but significant influx of kaolinite at the cretaceous tertiary boundary this influx is not related to a single geologically instantaneous event but may correspond to continental margin progradation and retreat shifting depositional patterns climatic change and or exploitation of new source terrains the clay mineralogy of the shale parting lying at the cretaceous tertiary boundary the so called boundary layer clay does not differ qualitatively or quantitatively from that of shales above and below the boundary it is accordingly deemed unlikely that the layer is composed entirely of transported impact derived material exotic to the gubbio section although the possibility that a small proportion of the layer is made up of such material cannot be excluded

the k t boundary in oman identified using magnetic susceptibility field measurements with geochemical confirmation abstract recognizing distal ejecta marker horizons and correlating these among widely separated sections is typically difficult in the absence of visually distinctive marker beds here we propose a magnetic susceptibility ms field method to locate such horizons and explore the k t boundary interval at abat oman as a test of the method a distinctive pattern of high ms values was used to approximately locate the k t boundary interval in a sequence of platform carbonates which were then sampled in detail whole rock geochemical enrichments in ir v as ni co zn and zr and a large negative carbon isotope anomaly confirmed the inferred boundary location common microspherules whose chemistry reflects the whole rock geochemistry are associated with the boundary interval the association suggests that the microspherules formed during or as a result of the impact the geochemical record at the abat locality shows two levels where ir is high 1 ppb suggesting input from two impacts separated in the section by 1 35 m the upper level is chosen as the boundary interval based on the high ir 1 19 ppb 13c negative excursion 7 and distinctive ms pattern

platinum group elements and os 187 os 188 in a purported impact ejecta layer near the eifelian givetian stage boundary middle devonian a global faunal crisis close to the eifelian givetian stage boundary in the mid devonian has been purported to be related to the impact of one or two major extraterrestrial bodies this was based on unusual mineralogical and chemical features within a distinct composite marl bed at a level c 40 cm below the global stratotype section and point gssp for the eifelian givetian boundary at jebel mech irdane in morocco the impact relation has been challenged based partly on the absence of platinum group element data we present here detailed ir os pd and pt as well as os isotopic data across the bed at mech irdane and from a correlated 10 cm bed at a nearby site rich haroun iridium concentrations of 0 13 0 28 ng g in the beds represent a small enrichment compared to average shale but ir al ratios are only a factor 1 5 2 higher than background at respective site such small enrichments can readily be explained by terrestrial diagenetic processes and do not require the presence of an extraterrestrial component on an al normalized basis pd and pt show weak enrichments typically a factor 2 4 higher than background high os 187 os o 188 ratios 1 1 3 8 reflect ingrowth of radiogenic os from re which is also evident from os concentrations of up to 3 ng g the platinum group inter element ratios are clearly non chondritic the overall platinum group and trace element e g co ni as v patterns indicate that diagenetic processes at redox fronts have played a crucial role in shaping most element enrichments if an excess siderophile rich extraterrestrial component exists in these beds it represents less than 0 2 by weight c 2006 elsevier b v all rights reserved less

magnetic susceptibility and selected geochemical mineralogical data as proxies for early to middle frasnian late devonian carbonate depositional settings in the holy cross mountains southern poland abstract the magnetic susceptibility ms and other petromagnetic features of early to middle frasnian carbonates from the holy cross mountains southern poland were studied they were correlated with the eovariscan tectonic activity and palaeoenvironmental changes the ms logs were compared with the available geochemical and mineralogical data a substantial paramagnetic contribution to the ms of the frasnian carbonates is evidenced by a poor correlation of this parameter with the isothermal remanent magnetization values and by a decrease of ms values at low temperatures an estimation of paramagnetic input indicates the dominance of this contribution to the magnetic susceptibility in 60 of studied samples the ms low widely documented in samples through the palmatolepis punctata zone is particularly due to limited input of paramagnetic mineral particles into the basin where also amounts of larger detrital grains of quartz hematite and goethite were significantly reduced this depression corresponds well to anomalously high carbon isotope 13c values for carbonates nevertheless a transient ms rise across the e mf boundary linked with an increase in detrital quartz content suggests together that both the initiation and termination phases of the punctata event indeed coincided with increased terrigenous eolian input from uplifted lands the ms high identified in the lower part of the palmatolepis hassi zone coincides with higher content of detrital quartz hematite and goethite being accompanied by low 13c values in spite of similar ms stratigraphic signatures in other basins the increased detrital input of proximal provenance is likely connected with the first variscan tectonic events that spread over the region and subsequently led to gradual closing of the saxothuringian ocean segments with basement uplift in the area of the mid german crystalline high