late cenomanian to middle turonian high resolution carbon isotope stratigraphy new data from the munsterland cretaceous basin germany abstract new high resolution carbon isotope stratigraphies from two basinal pelagic carbonate successions in northern germany halle and oerlinghausen munsterland cretaceous basin resolve late cenomanian to early mid turonian carbon cycle variations at timescales of less than 100 kyr beside the major carbon isotope excursion of the late cenomanian oceanic anoxic event oae 2 11 small scale distinct features are precisely resolved in the 13c carbonate curve and related to boreal macrofossil zonations the small scale carbon isotope events correspond to secular 13c carbonate variations identified previously in the english chalk the boreal high resolution 13c carbonate curve shows a detailed coincidence with two tethyan 13c curves from italy what demonstrates the interregional significance of the 13c dates and allows their correlation within error limits of 40 kyr furthermore the new 13c curve enables the calibration of boreal and tethyan macro and microfossil zonations accordingly the tethyan calcareous nannoplankton boundary nc13 nc14 corresponds to the boreal fo of c woollgari the index taxon for the lower middle turonian boundary the cyclic appearance and the temporal spacing of the small scale carbon isotope events suggest that orbital forcing exerted control on surface water productivity and organic matter preservation at the sea floor

the effect of hot spots on the oceanic age depth relation hot spots located both midplate and on midocean ridges can bias the empirical age depth relation ocean floor bathymetry for seafloor greater than 80 m y b p in age has been previously used to determine if the oceanic lithosphere behaves as a cooling half space or as a cooling plate however large areas of the ocean basins do not fit a simple age depth relation anomalously shallow swells approximately 1000 km wide and 1 km high surround hot spots such as iceland the azores and the cape verde islands by sorting seafloor depth data by distance to the nearest hot spot track we show that the along isochron variation in depth in the north atlantic correlates with distance from a hot spot track due to the absence in the north atlantic of seafloor both old and far from hot spots we compare depth versus age at constant distance and do not observe flattening of the age depth relation in any distance range the age depth relation depth meters 2700 295 t m y 1 2 derived for seafloor 1200 to 1800 km from a hot spot track represents our best estimate of the age depth relation appropriate to seafloor unaffected by a hot spot track in the north atlantic the previously inferred flattening of the age depth relation appears to be caused by the inclusion of hot spot swells this implies that hot spots may be the primary means of heat transfer from the deeper mantle to the base of the lithosphere

the effects of chemical density differences on convective mixing in the earth s mantle subducted lithosphere and crust are chemically distinct from ambient mantle and some have hypothesized that the resulting anomalous buoyancy may affect mixing and in particular may cause chemical heterogeneity to persist to explore this effect two dimensional convective mixing calculations have been carried out boundary conditions mimicking features of plate kinematics have been imposed and negatively buoyant tracers placed beneath converging plate margins to simulate subduction the principal parameter of interest is the density anomaly ratio o t the ratio of the chemical to the thermal buoyancy for a density anomaly ratio appropriate to complete separation of the oceanic crust from the rest of the lithosphere it is marginally possible for the tracers to segregate into the warm region near the bottom and neutralize the thermal buoyancy there for internally heated flows and to segregate to the base of the uprising limbs of convection for bottom heated flows however for the more likely scenario of oceanic crust and lithosphere maintaining their layering after subduction there is neither segregation nor neutralization of thermal buoyancy the average residence time is the average time tracers remain in the box from subduction to sampling beneath ridges and could be increased by 4 from the passive case at the very most if the crust and lithosphere remain layered even in the more extreme case of separation of crust from lithosphere the residence times are only increased by 15 from the passive case

extraction of a lithospheric cooling signal from oceanwide geoid data abstract the geoid an equipotential surface of earth s gravity field reflects the distribution of mass within the planet and hence a variety of geodynamic processes because these data are dominated by sublithospheric processes notably mantle convection they have not played a major role in the ongoing debate concerning models of the thermal evolution of oceanic lithosphere application of spatial filtering to the age derivative of the geoid however extracts an age dependent signal which reflects lithospheric thermal evolution the data are much better fit by a thin about 100 km thick thermal plate than by a cooling halfspace and so provide a valuable constraint complementary to and consistent with the variations in oceanic depth and heat flow with age

cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode oceanic anoxic events oaes were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen deficient bottom waters oae2 occurring at the cenomanian turonian boundary about 93 5 myr ago is the most widespread and best defined oae of the mid cretaceous although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios the actual trigger mechanism corresponding closely to the onset of these episodes of increased carbon sequestration has not been clearly identified it has been postulated that large scale magmatic activity initially triggered oae2 refs 4 5 but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of oae2 has not yet been found here we report seawater osmium isotope ratios in organic rich sediments from two distant sites we find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of oae2 using a simple two component mixing equation we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin a approximately 30 50 fold increase relative to pre oae conditions furthermore the magmatic osmium isotope signal appears slightly before the oae2 as indicated by carbon isotope ratios suggesting a time lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial which may reflect the reaction time of the global ocean system our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of oae2 which may have triggered the subsequent deposition of large amounts of organic matter

chemical weathering in two adirondack watersheds past and present day rates rates of chemical weathering in two forested adirondack watersheds were determined from mineral and elemental depletion trends in soil profiles and from input output budgets based on precipitation and surface water chemistry long term rates of weathering have averaged about 500 to 600 eq ha yr for both watersheds since the glaciers retreated from the region about 14 000 yr ago present day denudation rates average 1679 eq ha yr in the panther lake watershed and only 198 eq ha yr in the woods lake watershed mineral weathering reactions in both watersheds involve primarily the dissolution of plagioclase potassium feldspar and hornblende mass balance calculations however indicate that hornblende weathers in disproportionately large amounts in the panther lake watershed relative to its abundance in soils and till cation exchange in the glacial till mantling the panther lake watershed may also play an important role in controlling surface water chemistry in the basin in the panther lake watershed the current rate of weathering which is about a factor of 3 greater than the long term average may reflect a recent adjustment for higher hydrogen ion fluxes brought about by acid deposition the capacity of the thick till deposits in the panther lake watershed to neutralize acidity is ultimately reflected by the circum neutrality of panther lake in the woods lake watershed the soils and thin till deposits cannot effectively neutralize current acid loadings and therefore woods lake is acidic with a ph below 5

the rhine linth glacier in the upper wurm a model of the last alpine glaciation abstract the wurmian glaciation of the alpine foreland has been reconstructed in different phases as a result of investigations in the rhine bodan region as well as in the linth area the whole high glacial is divided in four main phases ice advance into the piedmont basins building up of the foreland glaciation high stages and retreat into the inner alps this epoch took up perhaps less than 12 000 years during the period of building an average increase of ice thickness of about 12 cm per year was sufficient to form an extensive foreland glacier within 5000 7000 years the snow lines of the stades of the piedmont glaciation as well as of the local glaciers are calculated snow lines at about 1500 m a s l led to an inner alpine ice build up and an advance of glaciers towards the piedmont basins to produce the foreland ice sheet low snow lines of 900 1000 m a s l were necessary an interstadial phase before the maximum glaciation is evidenced by sediment sequences and a 14c date of 22 100 bp the chronology of ice retreat after 18 ka bp is still uncertain

iron oxides and clay minerals within profiles as indicators of soil age in northern italy abstract nine profiles representing the alfisol inceptisol and entisol orders were sampled on three terraces forming a chronosequence total iron dithionite extractable iron and oxalate extractable iron were determined for all horizons of all profiles and the clay mineralogy for horizons of three profiles the percentage of total fe fet extracted by dithionite fed increased with age of terraces as did the difference between fed and feo oxalate extractable analysis of variance anova of the horizon data showed that the ratios fed fet and fed feo fet were closely related to the ages of the terraces clay minerals were also related to terrace ages with 2 1 minerals dominant in the profiles on the youngest and mixed layer minerals and kaolinite more abundant in profiles on the older terraces

the pedological heritage of the dolomites northern italy features distribution and evolution of the soils with some implications for land management abstract since 1997 the department of environmental sciences of ca foscari university of venice has undertaken numerous research projects aimed at deepening understanding of pedogenic processes in the dolomites and at highlighting the fundamental contribution that soil science can give to the conservation of natural resources and achieve sustainable management of mountain ecosystems a total of several hundred profiles have been described analyzed and mapped this paper reports the results from the analysis of pedo environmental characters of profiles developed from different parent materials at altitudes between 1300 m and 2900 m and in different conditions of slope exposure and vegetation cover soil forming factors landforms and land surfaces have been interpreted to understand the soil landscape in the mapped areas and to develop a qualitative model of soil geography into the dolomites scenery the application of land evaluation methods in some of the investigated territories that are subjected to intensive tourist fluxes revealed some criticisms collected results also highlighted the high environmental heterogeneity of soils of the dolomites

the effect of a shallow low viscosity zone on the mantle flow the geoid anomalies and the geoid and depth age relationships at fracture zones summary using a 2 d finite element method we studied the flow that is driven by the horizontal temperature gradient at a fracture zone and calculated the resulting geoid and topography anomalies assuming a three layered viscosity structure for the upper mantle consisting of a conducting lid overlying a low viscosity channel which in turn overlies a unit viscosity layer extending to the base of the upper mantle we studied the effect of varying 1 the viscosity contrast between the fluid layers 2 the rayleigh number based on the viscosity of the bottom layer and 3 the thickness of the low viscosity channel the flow at first downwells immediately adjacent to the fracture zone on the older side its time scale and characteristic wavelength depend on the viscosity and depth of the top layer which is nearest the largest temperature gradient in the fluid after the initiation of the driven flow additional flows are generated away from the fracture zone through shear and thermal coupling and boundarylayer instabilities eventually however the flow extends throughout the fluid so that the time scales and the characteristic wavelengths of the flow depend on the thickness and viscosity of both layers when the rayleigh number that is based on the viscosity of the top layer and the depth of both fluid layers is less than lo6 the geoid anomalies are dominated by the convective signal when this rayleigh number exceeds lo6 the geoid anomalies retain a step across the fracture zone out to large ages we compared our results with geoid anomalies over the udintsev fracture zone and found that the predicted geoid anomalies are in good agreement with the observed anomalies when the viscosity of at least the top layer is greater than one order of magnitude less than post glacial rebound values 102 pas however we also compared the calculated topographic steps with those predicted by the average depth age relationships observed in the oceans and found that a viscosity contrast of at least one order of magnitude at a depth in the uppermost mantle is required to produce realistic topographic steps

convection beneath young oceanic lithosphere implications for thermal structure and gravity small scale convection under the oceanic lithosphere which begins in the first 5 m y of cooling can produce a gravity signal with the amplitude and wavelength observed for large areas of the central pacific and southern indian oceans using seasat altimeter data the trend of the observed anomalies is parallel to the direction of plate motion as might be expected if they were produced by small scale convection models predict that the wavelengths of gravity anomalies increase more rapidly with age than is observed the persistence of short relatively uniform wavelength anomalies 200 km to crustal ages of 50 ma may indicate that they were produced when the lithosphere was very young and thin and were frozen in as cooling thickened the elastic lithosphere small scale convection which begins under very young lithosphere does not violate other geophysical data such as the rate of seafloor subsidence and variations of geoid height with age after convection has begun the subsidence due to thermal contraction within the lithosphere varies linearly with age in the absence of mantle heat sources although the rate of change of these quantities is affected by convection much of the variation of the geoid height across fracture zones can be fit by a model which includes small scale convection

brine mixing in the middle devonian of western canada and its possible significance to regional dolomitization abstract the desiccation that most large evaporite basins experienced in their history created large elevation heads these heads must have induced flows of ground or formation waters into the evaporite basins the consequences of such groundwater flows are believed to be 1 provision of the necessary hydrodynamic drive to allow dolomitization of carbonates beneath and adjacent to the evaporite basin and 2 the formation of anomalously distributed evaporites in the basin adjacent to sites of groundwater inflow sites where the groundwaters mixed with marine derived brines such brine mixing may also have been responsible for depleting the marine derived brines of their contained sulfate so explaining later development of sulfate impoverished potash deposits anomalous developments of anhydrite surrounding older carbonate buildups in the distal parts of the middle devonian elk point basin of western canada may represent such products of brine mixing and provide evidence of dolomitization of underlying lower palaeozoic and devonian carbonates coevally with the filling of the evaporite basin regional dolomitization in the williston basin is stratigraphically confined beneath the middle prairie evaporite suggesting a genetic link between the dolomitization and evaporite deposition dolomitization by refluxing brines generated in the evaporite basin appears unlikely because of the presence of an aquitard at the base of the evaporite succession developments of laminar and pisolitic carbonates adjacent to the carbonate buildups are believed to indicate the former presence of subaerial springs that carried calcium rich groundwaters into the evaporite basin anhydrite envelopes around the buildups are interpreted to be reaction products that formed when calcium bearing spring waters mixed with sulfate rich but calcium depleted marine brines the calcium in the spring waters is believed to have entered the groundwaters as a by product of the dolomitization of carbonates underlying the evaporite basin precipitation of gypsum now anhydrite as a consequence of brine mixing must have depleted the sulfate content of the marine derived brines it is possible that the sulfate depleted potash deposits in the prairie evaporite originate by this mechanism on the other hand the stratigraphic position of these deposits lends little support for this hypothesis

thermal cooling of the oceanic lithosphere new constraints from geoid height data abstract up to now tests of thermal models of the oceanic lithosphere as it cools and moves away from the ridge crest have been based mainly on topography and heat flow data however large areas of the ocean floor deviate from the normal subsidence due to thermal contraction and heat flow data are not very sensitive to the form of the model cooling of the lithosphere causes a short wavelength step in the geoid across fracture zones that can also be used to constrain thermal models we have analyzed geoid data at fracture zones from the seasat altimeter measurements in the entire pacific ocean and redetermined parameters of the cooling models we find that the data reveal two distinct regimes of cooling one for seafloor ages in the range 0 30 ma the other beyond 30 ma this does not appear to be correlated with particular fracture zones but rather it is representative of the whole area studied i e the entire south pacific and northeast pacific ocean these two trends may be interpreted in terms of two different asymptotic thermal thicknesses of the plate model the smaller thermal thickness 65 km found for ages from the results obtained in this study we conclude that the half space cooling model is unable to explain the data that beyond 30 ma a simple plate model gives a satisfactory fit to the data but in the younger plate portion ages

speculations on the thermal and tectonic history of the earth summary the connection between the earth s thermal history and convection in the mantle is exploited to elucidate the early evolution of the earth it appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the earth s history only in boundary layers at the surface and at a depth of 650 700 km is conduction likely to be important the resulting evolution appears to be consistent with geological observations on early precambrian rocks various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km the large scale flow is related to the motion of major plates and must be ordered over distances of more than 5000 km its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the earth s surface and to reconcile the geophysical observations with the results of numerical experiments though the existence of the small scale flow is at present speculative various tests of its presence are proposed

effect of north and south exposure on weathering rates and clay mineral formation in alpine soils abstract a comparison was made between two soil climosequences on north and south facing slopes in northern italy to determine the influence of slope aspect on soil processes the climosequences span an elevational gradient ranging from moderate 1200 m a s l to high alpine 2420 m a s l climate zones on surfaces having an age of about 15 000 years the soils were investigated with respect to organic c oxalate and dithionite extractable fe al and si elemental losses ca mg k na fe al si mn and clay minerals the stocks of soil org c as well as of oxalate extractable fe and al was greatest in the subalpine zone near the timberline there are no clear differences in organic c content between the soils on north and south facing sites fe oxalate and to a lesser extent alo stocks were however greater on north facing sites indicating that weathering is greater there eluviation and illuviation of al and fe within the soil profile typical for podzolisation was more distinctly expressed on the n slopes the probability of itm imogolite type material formation in the soil seemed to be greater on south facing sites on the north facing sites element leaching was most intense in the subalpine zone close to the timberline while on the south facing sites this was only the case for the base cations the n slopes exhibited higher leaching of elements which generally indicates a higher weathering intensity on south facing sites typical podzolisation processes were measurable only above 2000 m a s l the development of smectites is also a reflection of the weathering intensity smectite was discernible in the surface horizon at all sites on n slopes but the highest amount was detected in the sub alpine climate zone for the south facing sites only in the alpine climate zone could smectite be detected higher temperatures and an increased number of freeze thaw cycles on south facing slopes should theoretically enhance rates of chemical weathering this could however not be confirmed with our measurements the degree of chemical weathering increases from the south to the north facing sites that are characterised by lower temperatures lower evapotranspiration and consequently by a higher humidity although precipitation in alpine regions is abundant the availability and flux of water through the soil is the prime factor in weathering intensity

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes

cenomanian turonian carbon isotope events recorded in terrestrial organic matter from northern japan carbon isotopic fluctuations recorded in terrestrial organic matter from the upper cretaceous cenomanian turonian succession of hokkaido japan show a remarkably similar pattern to isotopic fluctuation in carbonate carbon reported from southern england and the italian apennines chronological correlation for the cenomanian turonian section of japan is based on planktonic foraminiferal biostratigraphy with some additional data from macrofossils allowing a detailed comparison of isotope stratigraphies for japan and europe three distinct features of the isotope profile namely a positive spike near the cenomanian turonian boundary a shoulder in the lower middle turonian and a level segment in the middle upper turonian are observed in japan these features are biostratigraphically comparable and correlative with isotope profiles reported from europe the single factor influencing isotopic composition of both terrestrial organic carbon and marine carbonate carbon is isotopic change in the global co2 reservoir of the ocean atmosphere system if these three carbon isotope features are synchronous they may be inferred as having been caused by global phenomena and as providing global high resolution chemo stratigraphic markers carbon isotope stratigraphy could be an important bridge between terrestrial inland sequences and marine sequences

a model for the plate tectonic evolution of the east central pacific based on seasat investigations abstract a complete seasat dataset is used to investigate the small scale bathymetry of a 15 by 15 area of the east central pacific northeast of pitcairn island which was involved in the miocene ridge jump and reorientation two fracture zones fz1 and fz2 are mapped along 450 km at an azimuth of n95 e while the signature of the austral fracture zone disappears east of 135 w several seamounts are discovered or confirmed along the oeno henderson ducie lineament and the degree of isostatic compensation of a number of islands at the eastern end of the tuamotu group is studied islands of the northern branch have practically no signatures in the geoid while the southern ones must have formed on lithosphere at least 10 ma old on the basis of these constraints we present a model of the evolution of spreading since 40 ma b p in which the deactivation of the austral fracture zone and the transfer of its offset to fz1 in the late oligocene is interpreted as due to rift propagation triggered by a northern tuamotu hotspot we propose that the oeno ducie chain is the surface expression of a southern tuamotu hotspot deviated 15 in azimuth by the presence of a young and fresh fracture zone thus our model predicts that hotspots and ridge systems can have a moderate influence on each other s kinematics and surface expressions which does not however extend to permanent trapping

localization of geoid anomalies and the evolution of oceanic lithosphere a case study from the mendocino fracture zone 1 the thermal evolution of oceanic lithosphere is investigated by focusing on geoid offsets occurring across the mendocino fracture zone where plates with different ages are juxtaposed various processing techniques have been devoted to separate the geoid signal of the age contrast from regional and shorter wavelength components unrelated to the thermal structure of lithosphere nevertheless due to processing differences estimates of geoid offsets vary and no agreement on the thermal evolution of oceanic lithosphere has been found so far in this study we propose to use a continuous wavelet analysis to accurately characterize the components of the geoid at different spatial scales and to estimate a new geoid slope age relationship from localized signals we also apply the same wavelet transform on a set of synthetic geoid calculated with different assumptions on plate cooling the comparison of the observed geoid offsets with those predicted from cooling models indicates that our approach can successfully remove unwanted regional contributions and isolate the geoid signature due to lithospheric cooling our results suggest that contrary to previous studies geoid slopes measured at the mendocino fracture zone are compatible with both the half space cooling model and the plate model

constitutive mass balance relations between chemical composition volume density porosity and strain in metasomatic hydrochemical systems results on weathering and pedogenesis relations characterizing the chemical physical and mechanical changes resulting from metasomatic hydrochemical processes are developed using mass balance models which formally link chemical composition to bulk density mineral density volumetric properties porosity and amount of deformation strain rigorous analysis of aqueous solute transport effects is then made possible in a variety of porous media flow environments including chemical weathering pedogenesis soil formation diagenesis ore deposition and enrichment and metamorphism application of these linear constitutive relations to chemical weathering profiles shows that immobile and locally mobile chemical elements with masses conserved on the scale of soil profiles can be accurately identified from analysis of appropriate data arrays and then used as natural geochemical tracers to infer the nature and extent of hydrochemical weathering processes and volume changes during pedogenesis assumptions commonly made in the past about the supposed immobility of certain elements e g ti and zr become unnecessary quantitative differentiation between the effects of residual and supergene fractionation is then easily made these methods are applied to ni rich laterites developed by weathering of ultramafic rocks showing that during ordinary residual enrichment ni is concentrated by as much as 4 protolith peridotite concentrations this occurs simply by silicate mineral dissolution and removal of chemical elements other than ni e g mg with a corresponding reduction in saprolite density and increase in bulk porosity without significant deformation in contrast laterites with mineable concentrations of ni which are similarly undeformed such as the nickel mountain mine in riddle oregon have experienced in addition to residual enrichment strong supergene enrichment by fractionation of ore elements between a leached zone from which ni is extracted and a complementary enriched zone positioned farther along the direction of ground water flow soil forming processes in podzol chronosequences developed on sandy beach terraces of the mendocino coast of california involved soil column collapse of 60 percent by dissolution of silicate minerals in the albic horizon of al and fe leaching and 70 percent dilation expansion in the overlying organic rich layer by root growth the amount of erosion based upon paleosurface reconstructions using the excess mass of fe al pb ga and cu in the zone of supergene enrichment spodic horizon below the ground water table indicates that subsurface erosion by dissolutional collapse is three times that of surficial erosion finally using published chemical data for ti zr and cr on major bauxite deposits in australia where erosion rates are thought to be low we infer that there may have been major amounts of dissolutional collapse to explain the upwards increase of detrital zircon and rutile in weathering profiles

geochemical and climatic effects of increased marine organic carbon burial at the cenomanian turonian boundary perhaps the most significant event in the cretaceous record of the carbon isotope composition of carbonate1 2 other than the 1 2 5 negative shift in the carbon isotope composition of calcareous plankton at the cretaceous tertiary boundary3 is the rapid global positive excursion of 2 13c enrichment which took place between 91 5 myr and 90 3 myr late cenomanian to earliest turonian c t boundary event 1 4 5 this excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon tdc reservoir resulting from an increase in rate of burial of 13c depleted organic carbon which coincided with a major global rise in sea level5 during the so called c t oceanic anoxic event oae 6 here we present new data from nine localities which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the c t boundary7 8 is nearly synchronous with that for carbonate and is widespread throughout the tethys and atlantic basins fig 1 as well as in more high latitude epicontinental seas the postulated increase in the rate of burial of organic carbon may have had a significant effect on co2 and o2 concentrations in the oceans and atmosphere and consequent effects on global climate and sedimentary facies

link between cyclic eustatic sea level change and continental weathering evidence for aquifer eustasy in the cretaceous abstract cyclic fluctuations in global sea level during epochs of warm greenhouse climate have remained enigmatic because absence or subordinate presence of polar ice during these periods precludes an explanation by glacio eustatic forcing an alternative concept suggests that the water bearing potential of groundwater aquifers is equal to that of ice caps and that changes in the dynamic balance of aquifer charge versus discharge as a function of the temperature related intensity of the hydrological cycle may have driven eustasy during warm climates however this idea has long been neglected for two reasons 1 the large storage potential of subsurface aquifers was confused with the much smaller capacity of rivers and lakes and 2 empirical data were missing that document past variations in the hydrological cycle in relation to eustasy in the present study we present the first empirical evidence for changes in precipitation continental weathering intensity and evaporation that correlate with astronomically long obliquity forced sea level cycles during the warmest period of the cretaceous cenomanian turonian we compare sequence stratigraphic data with changes in the terrigenous mineral assemblage in a low latitude marine sedimentary sequence from the equatorial humid belt at the south tethyan margin levant carbonate platform jordan thereby avoiding uncertainties from land ocean correlations our data indicate covariance between cycles in weathering and sea level predominantly chemical weathering under wet climate conditions is reflected by dominance of weathering products clays in deposits that represent sea level fall aquifer charge discharge conversely preservation of weathering sensitive minerals feldspars epidote and pyroxenes in transgressive sediments reflects decreased continental weathering due to dryer climate aquifer discharge charge based on our results we suggest that aquifer eustasy represents a viable alternative to glacio eustasy as a driver of cyclic 3rd order sea level fluctuations during the middle cretaceous greenhouse climate and it may have been a pervasive process throughout earth history

albeluvisol development with time in loamy marine sediments of southern norway abstract this paper reports a study on soil development in loamy marine sediments on both sides of the oslofjord vestfold ostfold this region has been subject to steady glacio isostatic uplift during the whole holocene hence land surface age continuously increases from the coast inland several sea level curves based on radiocarbon datings enable estimation of land surface age for all locations clay illuviation starts in less than 1650 years e horizons become lighter with age but their lower boundary stays around 40 cm for more than 10 000 years albeluvic tongues develop between 4600 and 6200 years initially they form along intersections of cracks as preferential flow and leaching along the cracks continues the tongues increase in length and width progressively consuming the prisms between the cracks in the upper bt horizon the fe d fe t ratios weighted means of the upper meter show a clear linear increase with soil age and may be used for pedo dating i e for estimating the ages of non dated land surfaces covered with similar sediments in contrast the logarithmic decrease of base saturation and ph with rapid changes in the first time but only very slight changes between 2000 and 10 000 years makes these parameters unsuitable for pedo dating

quantitative aspects of carbonate leaching of soils with differing ages and climates abstract carbonate leaching rates in several soils in switzerland and in the lake constance region were calculated and related to landscape development the leached depth of the soil the carbonate content and the soil density profile are sensitive to soil age a first database of carbonate leaching and its relationship to soil age is presented a simple relationship between the amount of precipitation and carbonate losses was found water draining from calcareous soils from subarctic to temperate areas was usually close to equilibrium with calcite and dolomite thus the annual amount of rainfall and consequently the percolation are the most important factors in carbonate leaching the influence of temperature is comparatively low carbonate dissolution rates amounted to approximately 1 7 3 0 mol m 2 year 1 if they are referred normalised to 1000 mm soil water fluxes soils on coarse parent material may have slightly lower carbonate dissolution rates in the order of approximately 1 7 2 2 mol m 2 year 1 normalised to a 1000 mm output while other sites with smaller grain sizes had slightly higher dissolution rates 2 2 3 0 mol m 2 year 1

topography of the ocean floor thermal evolution of the lithosphere and interaction of deep mantle heterogeneities with the lithosphere topography associated with large wave length geoid is derived by two methods first the bathymetry corrected for sediment loading is decomposed using a least squares method as a function of age plus terms proportional to the geoid the topography at old ages is flatter predicted by the law at degrees 2 and 3 very little topography is associated with the geoid the transfer function is not even certain in sign but is never smaller than 0 6 more topography seems associated with higher degree harmonics 6 and 7 second the function of age alone best fitting the topography is determined the correlation coefficients of the residual topography with the geoid are then computed a slight correlation appears for degree 6 but not for degrees 2 and 3 these results suggest a mechanical decoupling between the lower mantle mass heterogeneities and the lithosphere

weathering mineralogical evolution and soil organic matter along a holocene soil toposequence developed on carbonate rich materials a toposequence of holocene soils located between 1100 2400 m asl in the italian alps served as the basis for the following analyses the weathering of limestone and dolomite the calculation of mass balances understanding the formation of pedogenic fe and al the determination of soil mineral and clay mineral reactions and transformation and the measurement of accumulation and stabilisation mechanisms of soil organic matter leaching of carbonates is most intense at the lower elevations although calcite and dolomite have a higher solubility at low temperatures the pco2 in the soil is higher at lower elevations and weathering is driven mainly by carbonic acids at higher elevations organic acids appear to determine the mineral transformations and weathering reactions to a greater extent this suggests that two very different weathering regimes carbonic and organic acid weathering exist along the toposequence the transformation of mica into vermiculite is the main process in both the clay and fine earth fraction weathering of silicate minerals started even before the carbonates had been completely removed from the soils the transformation mechanisms of silicate minerals in the a and o horizon at higher elevations was at least as intensive as that at the climatically warmer sites the neoformation of pedogenetic clays at climatically cooler sites was slightly greater than that at the warmer sites however the formation rate of secondary fe and al phases was more pronounced at lower elevation which means that this process seemed to be driven dominantly by carbonic acid weathering of primary minerals soil organic matter som abundance in the mineral soil is nearly 15 kg m2 at all sites and surprisingly no climate driven effect could be detected in general the preservation and stabilisation of som was due to poorly crystalline al and fe phases and vermiculite regardless of some variations in the composition of the parent material varying calcite dolomite ratio

ocean bathymetry and mantle convection 2 small scale flow numerical models demonstrate that a boundary layer instability of the lower lithosphere does not stop the lithosphere from subsiding and so it cannot explain the so called flattening of old seafloor the slower subsidence of the old seafloor is in any case better seen as a perturbation probably due to plumes furthermore if a boundary layer instability or any mode of upper mantle convection transported most of the heat emerging from old seafloor there would be pervasive large amplitude local bathymetrie gravity and geoid anomalies such anomalies have never been convincingly differentiated from the effects of the cooling lithosphere and hotspot tracks except for some low amplitude linear geoid anomalies near spreading centers the only modes of mantle convection with horizontal scales less than those of plates for which there is reasonably clear evidence are hotspot plumes and some possible near ridge boundary layer instabilities hotspots transport less than about 10 of the earth s heat flux and other small scale modes are probably less important

carbon and oxygen isotope stratigraphy of the english chalk and italian scaglia and its palaeoclimatic significance a detailed carbon and oxygen isotope stratigraphy has been generated from upper cretaceous coastal chalk sections in southern england east kent culver cliff isle of wight eastbourne and seaford head sussex norfolk coast and the british geological survey bgs trunch borehole norfolk data are also presented from a section through the scaglia facies exposed near gubbio italian apennines wherever possible the sampling interval has been one metre or less both the chalk and scaglia carbon isotopic curves show minor positive excursions in the mid cenomanian mid and high turonian basal coniacian and highest santonian lowest campanian there is a negative excursion high in the campanian in chalk sections that span that interval the well documented cenomanian turonian boundary spike is also well displayed as is a broad positive excursion centred on the upper coniacian a number of these positive excursions correlate with records of organic carbon rich deposition in the atlantic ocean and elsewhere the remarkable similarity in the carbon isotope curves from england and italy enables cross referencing of macrofossil and microfossil zones and pinpoints considerable discrepancy in the relative positions of the turonian coniacian and santonian stages the oxygen isotope values of the various chalk sections although showing different absolute values that are presumably diagenesis dependent show nonetheless a consistent trend the east kent section which is very poorly lithified indicates a warming up to the cenomanian turonian boundary interval then cooling thereafter regional organic carbon burial documented for this period is credited with causing drawdown of co 2 and initiating climatic deterioration inverse greenhouse effect data from other parts of the world are consistent with the hypothesis that the cenomanian turonian temperature optimum was a global phenomenon and that this interval represents a major turning point in the climatic history of the earth

geoid anomalies across ascension fracture zone and the cooling of the lithosphere twenty three seasat altimeter profiles crossing the ascension fracture zone are used together with seafloor ages inferred from a kinematic model to estimate a geoid slope age relation between ages of 5 and 50 ma the data do not definitely contradict a half space cooling model slope 9 5 3 cm ma if biases are accepted resulting in large scatter however the data would seem to support a puzzling explanation in terms of a plate cooling model involving two distinct thermal thicknesses one of 70 km for ages 35 ma although preliminary this result is similar to that found in the pacific with a much larger data set

carbon isotope stratigraphy recorded by the cenomanian turonian oceanic anoxic event correlation and implications based on three key localities we present new detailed carbon isotope records for bulk carbonate total organic carbon toc and phytane from three key sections spanning the cenomanian turonian boundary interval eastbourne england gubbio italy tarfaya morocco with the purpose of establishing a common chemostratigraphic framework for oceanic anoxic event oae 2 isotope curves from all localities are characterized by a positive carbon isotope excursion of c 4 for toc and phytane and c 2 5 for carbonate although diagenetic overprinting appears to have obliterated the primary carbonate carbon isotope signal in at least part of the tarfaya section stratigraphically peak 13 c values for all components are followed by intervals of high near constant 13 c in the form of an isotopic plateau recognition of an unambiguous return to background 13 c values above the plateau is however contentious in all sections hence no firm chemostratigraphic marker for the end point of the positive isotopic excursion can be established the stratigraphically consistent first appearance of the calcareous nannofossil quadrum gartneri at or near the cenomanian turonian boundary as established by ammonite stratigraphy in conjunction with the end of the 13 c maximum characteristic of the isotopic plateau provides a potentially powerful tool for delimiting the stratigraphic extent and duration of oae 2 this oceanic anoxic event is demonstrated to be largely if not wholly confined to the latest part of the cenomanian stage

an analysis of geoid anomalies across the mendocino fracture zone implications for thermal models of the lithosphere geoid height increases in a steplike fashion across oceanic fracture zones owing to the juxtaposition of lithosphere with different ages and density structures at a ridge transform intersection the initial geoid offset depends on the age difference across the fault and is approximately equal to 0 15 m m y of age offset the amplitude and shape of this anomaly will change along the length of a fracture zone depending on how the lithosphere cools if the lithosphere thickens indefinitely boundary layer model then the geoid offset will remain constant although the width of the transition zone from one side of the fracture zone to the other will increase owing to both heat transfer across the fault and an increase in the average depth of compensation if however the lithosphere eventually approaches a constant thickness plate model the total geoid offset will decrease with time an analysis of 18 seasat altimetry profiles across the mendocino fracture zone offset 25 30 m y indicates geoid anomaly amplitudes systematically decrease from more than 4 m across the eastern younger part of the fracture zone to about 1 m across the western older part of the fault although the geoid offsets across the older portion of the mendocino fracture zone may have been underestimated by as much as 20 25 this large decrease in geoid offset strongly suggests that the lithosphere approaches a constant thickness along the older part of the fracture zone a plate thickness of 100 km fits the observed change in geoid offset along the mendocino but with uncertainties in the offset determination the age difference across the older part of the fault and the presence of areas of anomalous depths on both sides of the fracture zone this probably represents a minimum estimate of the total plate thickness

secular variation in late cretaceous carbon isotopes a new δ13c carbonate reference curve for the cenomanian campanian 99 6 70 6 ma carbon stable isotope variation through the cenomanian santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven chalk successions in england the sections show consistent stratigraphic trends and 13c values that provide a basis for highresolution correlation positive and negative 13cexcursions and inflection points on the isotope profiles are used to define 72 isotope events key markers are provided by positive 13c excursions of up to 2 the albian cenomanianboundary event mid cenomanian event i thecenomanian turonian boundary event the bridgewick hitch wood and navigation events of late turonian age and the santonian campanian boundary event isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons an age calibrated composite 13c reference curve and an isotope event stratigraphy are constructed using data from the english chalk the isotope stratigraphy is applied to successions in germany france spain and italy correlation with pelagic sections at gubbio central italy demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the cenomanian turonian stages confirming established relationships between tethyan planktonic foraminiferal and boreal macrofossil biozonations correlation of the coniacian santonian stages is less clear cut magnetostratigraphic evidence for placing the base of chron 33r near the base of the upper santonian is in good agreement with the carbon isotope correlation but generates significant anomalies regarding the placement of the santonian and campanian stage boundaries with respect to tethyan planktonic foraminiferal and nannofossil zones isotope stratigraphy offers a more reliable criterion for detailed correlation of cenomanian santonian strata than biostratigraphy with the addition of campanian 13c data from one of the english sections a composite cenomanian campanian age calibrated reference curve is presented that can be utilized in future chemostratigraphic studies the cenomanian campanian carbon isotope curve is remarkably similar in shape to supposedly eustatic sea level curves increasing 13c values accompanying sea level rise associated with transgression and falling 13c values characterizing sea level fall and regression the correlation between carbon isotopes and sea level is explained by variations in epicontinental sea area affecting organic matter burial fluxes increasing shallow sea floor area and increased accommodation space accompanying sea level rise allowedmore efficient burial ofmarine organic matter with the preferential removal of 12c from the marine carbon reservoir during sea level fall reduced seafloor area marine erosion of previously deposited sediments and exposure of basin margins led to reduced organiccarbon burial fluxes and oxidation of previously deposited organic matter causing falling 13c values additionally drowning of carbonate platforms during periods of rapid sea level rise may have reduced the global inorganic relative to the organic carbon flux further enhancing 13c values while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition variations in nutrient supply changing rates of oceanic turnover and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon isotope ratios

sequence architecture and carbonate platform configuration late cenomanian santonian sinai egypt relative sea level changes on the mixed carbonate siliciclastic platform of sinai are manifested in shifts of distinct facies belts deep water facies highenergy subtidal shallow subtidal lagoon shallow shoreface siliciclastics supratidal and are interpreted in terms of sequence stratigraphy eight sedimentary sequences are recognized for the upper cenomanian to santonian their correlation along a north south transect reveals distinct changes in lithofacies and progradation retrogradation patterns within the individual systems tracts the number and stratigraphy of the sequence boundaries of sinai correlate well with those from adjacent areas patterns of increased subsidence are documented for the central sinai basin since the late cenomanian by increased thickness of the stratal packages post cesin 7 hst post tusin 1 lst and hst post tusin 2 lst and are balanced by varying accumulation rates based on new sedimentological and biostratigraphic data large scale palaeogeographic maps and cross sections show the 1 temporal and spatial evolution of the central sinai basin e g its latest cenomanian initial formation lower turonian deep water facies middle turonian to coniacian synsedimentary subsidence 2 drowning of the cenomanian platform coinciding with the latest cenomanian to early turonian relative sea level rise 3 re establishment of the platform in middle late turonian times and 4 a coniacian basin and swell morphology

relative sea level changes during the cretaceous in israel detailed lithologic microfaunal and biometric investigations using relative abundances diversity indexes and duration charts of ostracods and foraminifera allowed the recognition of sea level changes during the cretaceous of israel three major transgressive regressive sedimentation cycles occur on the northwest margins of the arabian craton these cycles are the neocomian aptian which is mostly terrigenous sediments the albian turonian which is basin marls and platform carbonates and the senonian which is uniform marly chalks the cycles are separated by two major regional unconformities the aptian albian and turonian coniacian boundaries the sedimentary cycles are related to regional tectonic and volcanic events and eustatic changes the paleodepth curve il ustrates the gradual sea level rise reaching its maximum during the late cretaceous with conspicuous advances during the late aptian late albian cenomanian early turonian early santonian and early campanian major lowstands occur at the aptian albian cenomanian turonian turonian coniacian and campanian maastrichtian boundaries this model for israel agrees well with other regional and global sea level fluctuations four anoxic events black shales accompanying transgressions correspond to the cretaceous oceanic record we hypothesize the presence of mature oil shales in the present day eastern mediterranean basin close to allochthonous reef blocks detached from the cretaceous platform

global correlation of cenomanian upper cretaceous sequences evidence for milankovitch control on sea level we have investigated the sequence stratigraphy of two widely separated marine cenomanian successions in southeast india and northwest europe and used high resolution ammonite biostratigraphy to demonstrate that sea level changes are globally synchronous and therefore must be eustatically controlled sequence scale sea level changes in the cenomanian were driven by the long eccentricity cycle 400 k y in the milankovitch band we hypothesize that during pre quaternary time the third order sequences of vail and haq are essentially a sediment response to sea level changes driven by the 400 k y cycle construction of a relative sea level curve for the marginal marine succession in india demonstrates that the short term sea level changes are rapid 10 100 m m y and have a magnitude of 2 20 m glacioeustasy is a possible but unproven driving mechanism

landslides and climate change in the italian dolomites since the late glacial abstract the paper deals with the relationship between the temporal occurrence of landslides and climatic changes in the italian dolomites since the late glacial after an introduction on the state of the art with particular reference to the alpine region the results of recent investigations in the two study sites are illustrated at cortina d ampezzo several landslides were dated mainly by the radiocarbon method the most ancient landslide event there involved large rock slides which affected the dolomitic slopes following the withdrawal of glaciers after the last glacial maximum lgm and also slides and flows mainly occurring in pelitic materials of the valley floors from 13 000 to 10 000 cal bp a later series of flows occurred between 5500 and 2500 cal bp in the upper badia valley alta badia the most ancient events go back to 10 000 and 9000 cal bp and correspond with earth flows that followed vast rotational slides affecting the bedrock up to a depth of about 50 m more recent earth flows involving more modest amounts of material took place between 6500 and 2300 cal bp by analysing the dates from the two study areas it was possible to correlate the recorded increase of landslide activity with the climatic changes occurring at the boundary between the late glacial and the holocene and between the atlantic and the subboreal and to compare the results with those derived from other european regions the types and causes of landslides taking place in these two periods were substantially different reflecting the different morphoclimatic conditions that existed in the two areas when these mass movements were triggered finally notwithstanding the importance of non climatic causes such as geological structural factors and possible human influences it is concluded that many of the dated landslides can be considered as indicators of climatic change

thermal isotasy in the south atlantic a new approach we present a new way to estimate the thermal diffusivity and the thickness of the oceanic lithosphere based on admittances computed from geoid and bathymetry profiles which roughly parallel the ridge this method appears to operate in die medium wave band 500 1500 km and may be of help in remote oceanic areas where only poor bathymetry is available we apply the method to 32 profiles on each flank of the south atlantic spreading ridge between the equator and 35 s and obtain the solution domain for both the plate thickness and the thermal diffusivity anomalously high admittance values obtained for the west flank at wavelengths around 700 km may be due to deeper asthenospheric density heterogeneities

orbital time scale intra platform basin correlation carbon isotope stratigraphy and sea level history of the cenomanian turonian eastern levant platform jordan two cenomanian turonian boundary ctbe sections kb3 and gm3 of the karak silla intra platform basin of the eastern levant carbonate platform jordan are correlated based on high resolution calcimetry kb3 contains black shales with over 7 wt total organic carbon toc gm3 was deposited at shallower water depth and reveals four conspicuous gypsum beds used for sea level reconstruction spectral analysis of carbonate content and toc reveals forcing mainly by the 100 ka cycle of earth s orbit eccentricity whole rock stable carbon isotope data show a conspicuous positive d13c excursion representing the oceanic anoxic event 2 oae2 the carbon isotope records of kb3 and gm3 correspond well with the cycles in the dc record of the global stratotype gssp at pueblo usa the gssp orbital timescale thus can be applied to the jordan record furthermore all stable isotope events defined in the english chalk reference record are recognized in jordan our orbital model for the jordan sequence stratigraphical framework reveals approximately 1 2 0 2 ma duration of a third order sequence proposed to represent one cycle of the long obliquity 1 2 ma this longterm period is superimposed on three fourth order fluctuations of 400 ka length long eccentricity fourth order sea level fluctuations each of which comprises four carbonate cycles 100 ka eccentricity fifth order sea level fluctuations demise of the levant platform occurred during the phase of decreasing dc values after oae2 in the interval between the cenomanian turonian c t boundary and the end of the early turonian the levant carbonate platform deposits of central jordan represent a textbook like shallow marine platform setting subdivided into intra platform basins during cenomanian turonian c t times kuss et al 2003 the morphological structuring by these basins induced lithologically highly variable successions especially during black shale deposition that preferably occurred in deeper subbasins a correlation of these different successions is possible by means of high resolution calcimetry and stable carbon isotope stratigraphy in this paper we present such a correlation that enables the study of three research aspects a linking different palaeoenvironments over the c t boundary interval b refining the sequence stratigraphic model by constructing an orbital time scale c correlating the successions to the global record exemplified for the well dated c t boundary interval in order to eliminate ambiguities in the local stratigraphy furthermore our data support the global picture and estimates of duration of the c t boundary interval that includes the global oceanic anoxic event 2 oae2 the duration of oae2 has been the matter of many studies in recent years resulting in a range of values from 320 to 960 ka obradovitch 1993 sageman et al 2006 partly caused by considering different intervals an orbital timescale for the pueblo stratotype section was given by sageman et al 2006 providing a precise time measure for the period investigated in our study in addition a comprehensive study of stable carbon isotope records in europe was given by jarvis et al 2006 providing a detailed set of isotope events suitable for global correlation recently an orbital model was also presented for the wunstorf germany section voigt et al 2008 this record correlates well with the present results and can be used to support the new hypothesis put forward in the present paper regarding the orbital trigger of third order sequences

geoid anomalies across pacific fracture zones summary cooling of the oceanic lithosphere and related subsidence of the ocean floor are usually understood in terms of simple conductive thermal models half space and plate cooling models which predict the same behaviour for heat flow sea floor depth and geoid on very young sea floor but large deviations at greater ages since geoid data are much more sensitive to the thermal structure of the lithosphere at depth than other kinds of data satellite derived geoid anomalies in particular geoid steps observed across fracture zones are currently analysed to discriminate between the two thermal models in this study we present results for the geoid step h estimated along altimeter profiles of the seasat satellite across five fracture zones fzs of the ne pacific clipperton clarion molokai murray and mendocino and across the udintsev fz in the s pacific for each fz the quantity geoid offset h divided by the age offset t is plotted as a function of plate age except for mendocino and clipperton fzs along which the variation of h t with age is consistent with the prediction of the thermal plate model with a plate thickness of 90 100 km the dependence on age of h t along the other fzs is different from that predicted by conductive cooling models large fluctuations of the h t age relationship are observed along murray clarion and udintsev fzs suggesting that the thermal structure of the oceanic lithosphere under a fz is more complex than is to be expected from conductive cooling alone according to recent convection models small scale convective instabilities developed underneath the fz in a shallow low viscosity layer could explain the observed h t age behaviour

thermal parameters of the oceanic lithosphere estimated from geoid height data geoid height anomalies derived from seasat altimeter data have been analyzed across fracture zones and over ocean ridges in two limited regions of the south pacific eltanin fracture zone system east pacific rise and southeast indian ocean observed geoid height age and geoid height derivative with respect to age age relationships have been established comparison with theoretical relationships computed for the plate model of lithospheric cooling permits an estimation of the thermal parameters entering into the model two quantities can be derived the product tm thermal diffusivity volume coefficient of thermal expansion tm bottom boundary temperature and the thickness h of the plate the best fitting values for the south pacific and the southeast indian ocean are tm 0 52 10 3 cm2 s 1 and h in the range 50 70 km for ages less than 30 m y whereas for larger ages 30 m y geoid observations are better explained by a larger h value in the range 70 90 km the depth age relationship observed in the south pacific region is consistent with these parameters on the other hand data for the northeast pacific argue rather for a lithospheric thickness larger than 100 km this suggests that local and regional variations exist in the thermal properties of the oceanic lithosphere

upper cretaceous sequence stratigraphy of the galala plateaux western side of the gulf of suez egypt abstract based on the study of lithology biostratigraphy and analysis of facies this study deduces the occurrence of nine third order upper cretaceous cenomanian maastrichtian depositional sequences which are bounded by eleven sequence boundaries of geographic extent in the galala plateaux situated along the western side of the gulf of suez egypt some of the recorded sequence boundaries e g cenomanian turonian turonian coniacian intra santonian and campanian maastrichtian sequence boundaries are not yet confirmed to eustatic sea level changes fourteen main mixed carbonate siliciclastic facies associations were recognized on a lateral transition between inner to outer ramp settings with apparent subsidence towards the south the tectonic position of the galala plateaux played an important role in the profound complexity of facies changes and the configuration of depositional sequences representing variable time gaps

geoid data and thermal structure of the oceanic lithosphere a long standing question is whether old oceanic lithosphere continues cooling as the boundary layer of a halfspace or approaches thermal equilibrium as modeled by a finite thickness plate although the latter is the most direct inference from seafloor depths and heat flow other explanations have been proposed we investigate this issue using published results for the derivative of the oceanic geoid with age estimated from geoid offsets across fracture zones such data have not been used extensively in analyses of the thermal evolution of the lithosphere primarily because they are inconsistent with two commonly used thermal models a halfspace or a 125 km thick plate recent studies however find that depth and heat flow data are better fit by a thinner 95 km plate model we thus compile published geoid slope results and find that these data though scattered can discriminate between the models geoid slope changes with age rather than being constant as predicted for a cooling halfspace this variation is greater than predicted for a thick plate and is better fit by a thin plate geoid data should thus be useful for improving thermal models of the lithosphere

uppermantle anisotropy and the oceanic lithosphere rayleigh wave and love wave dispersion data for oceanic paths cannot be satisfied by an isotropic uppermantle and it is incorrect to invert these two datasets independently for separate isotropic structures available phase and group velocity data are inverted for oceanic structure as a function of age taking into account anelastic dispersion sphericity and anisotropy the resulting models are quite different from previous results which ignore the above effects and the extra parameters involved in proper anisotropic inversion the models have a high velocity nearly isotropic layer at the top of the mantle that thickens with age and an anisotropic low velocity zone with an age dependent anisotropy the lid or seismic lithosphere reaches a maximum thickness of 50 km which is about one half the thickness obtained in previous isotropic or pseudo isotropic inversions the seismic lithosphere therefore may be comparable in thickness to the elastic or flexural lithosphere raising the possibility that both are controlled by effects other than temperature stress and time such as mineralogy crystal orientation or partial melting the velocities in the low velocity zone are higher than inferred by previous surface wave studies

interplay of variable thermal conductivity and expansivity on the thermal structure of oceanic lithosphere we have extended our previous analysis of the effects of constant vs variable i e pressure and temperature dependent thermal conductivity k and constant thermal expansivity on the thermal structure of the oceanic lithosphere we apply our analysis to the actual data set including information on the geoid slope the heat flow and ocean floor depth data constrain the thermal expansivity 3 10 5 1 c including geoid slope data may loosely constrain both the thermal expansivity and the thermal conductivity the probable value of thermal conductivity is 3 w m c for the constant k case and 4 w m c at ambient conditions for the variable k case these a and k are generally consistent with laboratory data of appropriate lithospheric materials our analysis supports the plate model with thin lithosphere and high bottom temperature such as gdh1 95 km 1450 c variable k case requires slightly thinner and higher temperature lithosphere 85 km and 1500 c and gives a slightly better fit to the geoid slope data

clay mineral formation in soils of two different chronosequences in the swiss alps two chronosequences of soils developed from postglacial tills at two different sites in the swiss alps were studied with respect to their soil mineralogy and chemistry the age of these soils ranged between 0 and 11 500 years the parent material for both chronosequences was similar but differences were found in the clay fraction within the considered time span podzols developed at both sites however at one site already after about 3000 years and at the other a few years later especially trioctahedral minerals were strongly weathered within the time span of about 11 000 years smectite and regularly interstratified dioctahedral mica smectite could be found in the most weathered horizons at one site the origin of smectite could be traced back to both chlorite and trioctahedral mica which supports the fact that smectite is the end product of chlorite alteration and regularly interstratified mica smectite or even smectite the end product of mica weathering in strongly leached and acidified horizons at the other site smectite was already present in the parent material most presumably due to hydrothermal formation during the first 500 years of soil formation a kind of retrograde podzolisation was observed leading to the elimination of this smectite within the same time increased amounts of dioctahedral minerals were formed and after 11 000 years a small proportion of pedogenic smectite was discernible again main clay mineral transformations occurred at both sites within the first 3000 years of soil development weathering and transformation reactions were most advanced in the e horizon being almost complete after 3000 years at one site the presence of significant amounts of chlorite and or a minimal content of mica of ca 5 seems however to be compulsory in order to detect low charge expandable minerals already after a 3000 year duration of soil formation in the alps otherwise smectite formation is retarded

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

on the thermo mechanical evolution of continental lithosphere elastic thickness of continental lithosphere is modified by both mechanical thickening and thinning events and thermal evolution a simple thermo mechanical model can account for the processes of tectonic alteration and subsequent thermal reequilibration of lithospheric thermal structure mechanical thinning or thickening of the lithosphere directly affects its thickness and flexural rigidity after a tectonic event thermal reequilibration proceeds at a rate dependent upon the amount of thinning or thickening and total lithospheric thickness previous tectonic history and the heat flux at the base of the lithosphere heat flux at the base of the lithosphere is controlled by the efficiency of convective mantle heat delivery rapid heat delivery to the base of the lithosphere retards lithospheric thickening whereas slow conductive heat delivery allows lithospheric thickening at the maximum rate the relative importance of thermal effects to mechanical alterations of lithospheric elastic thickness depends on the time scale of concern very thin lithosphere undergoes rapid thermal evolution such that cooling between tectonic events significantly thickens the lithosphere for thick lithosphere conductive heat transport is so slow that only minor changes in thermal structure and no significant changes in elastic thickness take place between tectonic events model results with infinite stretching agree with observations of oceanic lithospheric thickness evolution showing a divergence from a cooling half space at about 70 m y model results also agree with independent estimates of continental thermal evolution in the absence of tectonic events on the longest time scales approaching the age of the earth thermal reequilibration is attained and any tectonic effects are overprinted the time scale at which the transition between mechanically and thermally dominated elastic thickness evolution occurs depends on the heat transport efficiency of the convecting mantle for high nusselt numbers thermal effects take longer to become important even for lower nusselt numbers mechanical effects still dominate on time scales of 108 years crustal radiogenic heat production reduces the equilibrium lithospheric thermal and elastic thickness it also introduces a dependence of equilibrium thickness on tectonic crustal thinning or thickening model results indicate that on time scales of thrust sheet and sedimentary loading in foreland basins mechanical effects dominate the evolution of elastic thickness except for very thin lithosphere the model can be applied to the lithosphere beneath foreland basins so that observed basin geometry can be used to constrain tectonic history prior to loading by thrust sheets and basin sediments

orbital scale record of the late cenomanian turonian oceanic anoxic event oae 2 in the tarfaya basin morocco high sedimentation rates up to 12 cm kyear of laminated organic carbon rich biogenic limestones in the tarfaya basin provide an unusually high millennial resolution record of the late cenomanian oceanic anoxic event oae 2 the global positive carbon isotope excursion across the cenomanian turonian corresponds to 11 light dark sedimentary cycles we interpret these cycles as a response to orbital obliquity variation and estimate the duration of the complete excursion as 440 kyear or one long eccentricity cycle on this time scale the main increase in delta 13 c values occurred over a short time interval of less than 20 kyear in the late cenomanian and reached a first maximum approximately 15 kyear prior to the bulk mainly coccoliths delta 18 o derived sea surface maximum temperature that occurs coeval to the extinction of rotalipora cushmani organic carbon accumulation rates follow obliquity cycles reaching a maximum approximately 10 kyear after the last occurrence of r cushmani then slowly decreasing during the early turonian thus the maximum temperature and the maximum organic carbon accumulation in the tarfaya basin lagged by at least 15 kyear behind the global carbon isotope shift and a proposed reduction of atmospheric co 2 content the climate change across the cenomanian turonian boundary probably occurred independent of co 2 levels and may have been controlled by different greenhouse gases water vapour and methane and changes in ocean circulation i e opening of the equatorial atlantic gateway

weathering rates as a function of climate results from a climosequence of the val genova trentino italian alps a soil sequence in northern italy along an elevational gradient ranging from moderate 950 m a s l to high alpine 2440 m a s l climate zones was investigated with respect to element losses ca mg k na fe al si mn and the development of clay minerals element losses were derived from mass balance calculations that are based on enrichment depletion factors using immobile element contents ti mass balance calculations indicated that extensive mineral weathering resulted in significant leaching losses of major base cations with losses up to 80 of the initial content in the parent material al particularly from upper horizons and si element denudation was greatest in subalpine forests near the timberline weathering rates decreased with both higher and lower altitudes the pattern of smectite distribution along the climosequence has strong similarities to the al si na and k losses while an inverse trend could be detected for clay minerals with a high amount of interlayered al highest smectite contents with up to 30 of the clay fraction and also highest weathering rates were found at sites in subalpine forest near the timberline higher precipitation rates and the production of chelating compounds in the soil are believed to promote the appearance of smectites weathering rates of na and k were additionally modelled as a function of precipitation and temperature the relationship between climate and element weathering is strongly nonlinear and is thought to be overshadowed by the pronounced podzolisation effect near the timberline

cenomanian turonian transition in a shallow water sequence of the sinai egypt environmental and depositional changes across the late cenomanian oceanic anoxic event oae2 in the sinai egypt are examined based on biostratigraphy mineralogy 13c values and phosphorus analyses comparison with the pueblo colorado stratotype section reveals the whadi el ghaib section as stratigraphically complete across the late cenomanian early turonian foraminifera are dominated by high stress planktic and benthic assemblages characterized by low diversity low oxygen and low salinity tolerant species which mark shallow water oceanic dysoxic conditions during oae2 oyster biostromes suggest deposition occurred in less than 50 m depths in low oxygen brackish and nutrient rich waters their demise prior to the peak 13c excursion is likely due to a rising sea level characteristic oae2 anoxic conditions reached this coastal region only at the end of the 13c plateau in deeper waters near the end of the cenomanian increased phosphorus accumulations before and after the 13c excursion suggest higher oxic conditions and increased detrital input bulk rock and clay mineralogy indicate humid climate conditions increased continental runoff and a rising sea up to the first 13c peak above this interval a dryer and seasonally well contrasted climate with intermittently dry conditions prevailed these results reveal the globally synchronous 13c shift but delayed effects of oae2 dependent on water depth

geoid anomalies over two south atlantic fracture zones abstract seasat altimetry profiles across the falkland agulhas fracture zone fz and the ascension fz in the south atlantic were examined for evidence of step like geoid offsets predicted from thermal modeling of the lithosphere the geoid profiles exhibit much short wavelength power and the step like offsets are often small making reliable estimation of the heights of the observed geoid offsets difficult the offsets were estimated by the least squares fitting of quadratic curves incorporating a step function to the altimetry profiles a preferred offset value was determined for each profile by taking the average of step heights computed with various distances around the fracture zone excluded from the fit the age of the crust surrounding the fracture zones necessary for computing a theoretical geoid offset was determined from surface ship magnetic anomaly data and from existing ocean floor age maps observed variations in geoid step height with age of the lithosphere are not consistent with those predicted from standard thermal plate models for ages less than 30 ma the step offsets across both fracture zones decrease in a manner appropriate for an unusually thin plate with a thickness of 50 75 km at greater ages the offsets show complex behavior that may be due to bathymetric features adjacent to the fracture zones similar geoid patterns on opposite branches of the falkland agulhas fz are indicative of processes that act symmetrically on both sides of the mid atlantic ridge this behavior of the geoid is consistent both with small scale convection occurring beneath the lithosphere and with bathymetric features originally produced along the ridge crest and now located symmetrically on opposite sides of the ridge the west flank of the ascension fz displays a regrowth in step height at about 40 ma consistent with small scale convection and in agreement with other studies of pacific and south atlantic fracture zones

a new analysis of gravity and topography data over the mid atlantic ridge non compensation of the axial valley abstract topographic and associated gravity signals often result from the interference of several phenomena in the present paper an admittance function for the superposition of several physical mechanisms acting in the same waveband is derived if the processes are not phase related the resulting admittance function is the average of the individual admittance functions weighted by the squared amplitude of the topography for each process we use this concept of superposition of different processes to understand the compensation of the atlantic ridge valley classical transfer function studies applied to slow spreading ridges have concluded that the topography was emplaced on an elastic plate about 10 km thick these analyses of gravity and topography seem to contradict the physical models explaining the median rift valley which is thought to be due to dynamical effects and thus to be uncompensated we obtain an average axial valley gravity and topography profile by stacking several profiles perpendicular to the mid atlantic ridge and subtracting a long wavelength thermal effect we find that the gravity over topography spectral ratio of the average axial valley signal is consistent with an uncompensated process our study thus confirms that the mode of formation of the axial valley of a slow spreading ridge involves an uncompensated mechanism the presence of an additional process characterized by low admittance values uncorrelated from one profile to the other is also suggested in order to explain the observed admittance function the study of the long wavelength 300 km gravity and topography signal leads us to invoke the cooling of the upper portion of the crust by water circulation and to exclude the presence of a large amount of partial melt at depth more than 5 over a 20 km thick layer at a mean depth of 60 km

geoid height age relation from seasat altimeter profiles across the mendocino fracture zone twenty eight seasat altimeter profiles crossing the mendocino fracture zone are used together with seafloor ages determined from magnetic lineations to estimate the change in oceanic geoid height with age between ages of 15 and 135 m y an unbiased estimate of the overall geoid offset along each profile is determined from a least squares fit of the along track derivative of the geoid to the geoid slope predicted from a simple two layer gravitational edge effect model uncertainties based upon the statistical properties of each profile are also determined a geoid slope age relation is constructed by normalizing the geoid offsets and uncertainties by the age offsets the results are in agreement with geoid slope age relations determined from symmetrically spreading ridges sandwell and schubert 1980 however the fracture zone estimates have smaller uncertainties and show less scatter a comparison of these results with the geoid slope age prediction of the boundary layer cooling model shows that the thermal structure begins to deviate from this model at an early age 20 40 m y a plate cooling model with a thickness of 125 km is most compatible with the geoid slope age estimates although significant deviations occur these may indicate that the lithospheric thermal structure is not entirely age dependent

c isotope stratigraphy and paleoenvironmental changes across oae2 mid cretaceous from shallow water platform carbonates of southern mexico the stratigraphic and geochemical record of the mid cretaceous cenomanian turonian oceanic anoxic event 2 oae2 has been studied in numerous tethyan and proto atlantic hemi pelagic pelagic successions but little data comes from nearshore carbonate successions from the proto pacific region here we present the results of a combined stratigraphic and 13c study of c t platform carbonates from southern mexico which were deposited within the proto pacific two scales of sedimentary cyclicity are recognized high frequency peritidal and subtidal cycles 0 4 8 m display little evidence of cycle capping subaerial exposure and are not correlative between sections these relationships suggest that the amplitudes of high frequency sea level changes were minimal during the peak mid cretaceous greenhouse longer term transgressive regressive sequences 18 40 m are correlated between sections and using 13c trends can be correlated with sequences developed in northern europe and india the mexican successions were sampled at a high resolution 10 ky for stable isotopes inorganic organic carbon and oxygen total organic carbon insoluble residues and trace metals the 13ccarb curve matches global trends including 6 distinct isotopic stages permitting identification of oae2 despite the lack of characteristic anoxic facies using the 13ccarb trends we tie the previously identified ammonite planktonic foram and nannofossil biostratigraphy from england and the western interior seaway of colorado into the mexican sections the initiation of oae2 defined by an abrupt positive 3 4 13c shift coincides with a long term sea level rise though the sedimentary expression of the deepening is no greater than that observed for any of the other sea level events across the studied interval oae2 termination transition from gradually decreasing to background 13c values is not associated with a particular sea level trend stratigraphic changes in insoluble residues proxy for continental sediment discharge across oae2 are not correlative between sections and do not show consistent systematic relationships with 13c or sea level variations therefore do not support the hypothesis that oae2 was associated with increased continental derived nutrient influx two peaks in trace metal concentrations coincide with the abrupt increase in 13c ratios onset of oae2 and during the transition from elevated to decreasing 13c values near the c t stage boundary these trends are similar to those recorded in coeval deposits of the western interior seaway and are consistent with the hypothesis that oae2 development was related to the release of reduced metals during the short lived 1 my caribbean oceanic plateau basalt eruption in this scenario oxidation of the metals depleted the existing low dissolved o2 concentrations and thermally buoyant plumes of seawater enriched in biolimiting elements mixed with surface waters stimulated primary productivity and further reduced o2 concentrations leading to widespread anoxia and a large positive 13c shift

frequency modulation reveals the phasing of orbital eccentricity during cretaceous oceanic anoxic event ii and the eocene hyperthermals abstract major advances in our understanding of paleoclimate change derive from a precise reconstruction of the periods amplitudes and phases of the milankovitch cycles of precession obliquity and eccentricity while numerous quantitative approaches exist for the identification of these astronomical cycles in stratigraphic data limitations in radioisotopic dating and instability of the theoretical astronomical solutions beyond 50 myr ago can challenge identification of the phase relationships needed to constrain climate response and anchor floating astrochronologies here we demonstrate that interference patterns accompanying frequency modulation fm of short eccentricity provide a robust basis for identifying the phase of long eccentricity forcing in stratigraphic data one and two dimensional models of sedimentary distortion of the astronomical signal are used to evaluate the veracity of the fm method and indicate that pristine eccentricity fm can be readily distinguished in paleo records apart from paleoclimatic implications the fm approach provides a quantitative technique for testing and calibrating theoretical astronomical solutions and for refining chronologies for the deep past we present two case studies that use the fm approach to evaluate major carbon cycle perturbations of the eocene and late cretaceous interference patterns in the short eccentricity band reveal that eocene hyperthermals etm2 elmo h2 i1 and etm3 x 52 54 myr ago were associated with maxima in the 405 kyr cycle of orbital eccentricity the same eccentricity configuration favored regional anoxic episodes in the mediterranean during the middle and late cenomanian 94 5 97 myr ago the initial phase of the global oceanic anoxic event ii oae ii 93 9 94 5 myr ago coincides with maximum and falling 405 kyr eccentricity and the recovery phase occurs during minimum and rising 405 kyr eccentricity on a myr scale the event overlaps with a node in eccentricity amplitudes both studies underscore the importance of seasonality in pacing major climatic perturbations during greenhouse times

mid latitude terrestrial climate of east asia linked to global climate in the late cretaceous reply the late cretaceous late campanian to maastrichtian was characterized by a variable greenhouse climate with evidence for cooling and or glaciation and warming events most of these climatic signals are derived from marine records and knowledge of the terrestrial climate especially in the mid latitudes is limited due to fragmentary geological records on continents here we report mid latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous late cretaceous age sk 1 core drilled in the songliao basin northeastern china our data indicate a punctuated mid latitude terrestrial climate in the late cretaceous we interpret the negative excursion of pedogenic carbonate 18o in the early maastrichtian to be the result of decreasing temperature and or strengthened westerlies during global cooling and possible glaciation providing valuable mid latitude terrestrial evidence for this event the negative 13c isotopic excursion ca 66 ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest cretaceous our continuous stable isotopic records in the songliao basin are in accordance with previously published global late cretaceous records of climate variability from marine and terrestrial regions and demonstrate the sensitivity of mid latitude terrestrial climate in a greenhouse world

middle and late cenomanian oceanic anoxic events in shallow and deeper shelf environments of western morocco the response of shallow water sequences to oceanic anoxic event 2 and mid cenomanian events 1a and 1b was investigated along the west african margin of morocco north of agadir azazoul and correlated with the deep water sequence of the tarfaya basin mohammed beach based on biostratigraphy mineralogy phosphorus and stable isotopes in the deeper mohammed beach section results show double peaks in 13corg for mid cenomanian events 1a and 1b rotalipora reicheli biozone lower cc10a biozone the characteristic oceanic anoxic event 2 13c excursion rotalipora cushmani extinction top of cc10a biozone and laminated anoxic black shale in the shallow environment north of agadir a fluctuating sea level associated with dysoxic brackish and mesotrophic conditions prevailed during the middle to late cenomanian as indicated by oyster biostromes nannofossils planktonic and benthonic foraminiferal assemblages anoxic conditions characteristic of oceanic anoxic event 2 for example laminated black shales did not reach into shallow water environments until the maximum transgression of the early turonian climate conditions decoupled along the western margin of morocco between mid cenomanian event 1b and the cenomanian turonian boundary as also observed in eastern tethys north of agadir alternating humid and dry seasonal conditions prevailed whereas in the tarfaya basin the climate was dry and seasonal this climatic decoupling can be attributed to variations in the intertropical convergence zone and in the intensity of the north east trade winds in tropical areas

cenomanian turonian carbonate platform deposits in west central jordan we studied upper albian to turonian shallow marine shelf deposits ajlun group of west central jordan along a nne ssw running transect the carbonate dominated succession includes few siliciclastic intercalations claystones and shales and can be subdivided into five formations the naur fuheis and hummar formations of upper albian to upper cenomanian age represent shallow subtidal to supratidal platform environments the uppermost cenomanian to middle turonian shueib formation includes deeper water deposits of the inner mid shelf and locally toc rich black shales shallow marine platform environments once again dominate the wadi as sir formation middle upper turonian a new multibiostratigraphic framework is based on ammonites mainly of the middle cenomanian rhotomagense zone to the middle turonian woollgari zone and calcareous nannofossils biozones cc 9 cc 11 supplemented by benthic and planktonic foraminifers and ostracods it forms the base of a sequence stratigraphic subdivision containing eight sedimentary sequences s1 s8 which are separated by four cenomanian sequence boundaries cejo1 cejo4 and three turonian sequence boundaries tujo1 tujo3 this scheme allows the correlation of the platform succession from distal to proximal shelf areas in contrast to previous correlations using lithologic units furthermore comparisons between the platform successions and sequence patterns of west central jordan and those from neighbouring areas allow to differentiate local regional and global controlling factors of platform development within the study area

pedogenic processes and soil landscape relationships in north cascades national park washington thunder creek watershed tcw in the northern cascade range washington state provides a complex environment for studying soil formation approximately 15 000 cal yrs b p the cordilleran ice sheet cis overrode the watershed during the last glacial maximum and deposited glacial drift that provides the substratum for soil formation today since then the watershed has been blanketed by tephra from mount mazama glacier peak and mount st helens soils with the gross morphology of spodosols podzols and andisols andosols occur in a complex landscape mosaic in tcw and along the entire washington cascade range the pedologic conundrum addressed in this paper is whether true spodosols are forming in these areas or are they mimics of spodosols based on field morphology and lab analysis soils in tcw are andic subgroups of spodosols and andisols in approximately equal abundance with lesser areas of inceptisols cambisols and some entisols gleysols field morphology and electron microprobe analysis of glass shards shows that the major volume of tephra about 8 cm compacted thickness is predominantly from the eruption of mount mazama 7600 cal yrs bp tephra from this eruption has been mixed into the upper 50 cm of glacial drift and colluvium fallout from other eruptions in tcw had individual compacted thicknesses less than 2 cm we conclude that true spodosols are widespread in tcw they have albic and spodic horizons no pseudo albic horizons of white unweathered tephra layers were found in tcw the cold wet and dominantly conifer covered landscape supports podzolization in tephra rich materials on parts of landforms that have been stable for several thousand years andisols are forming in drier microclimates on gravitationally active landscapes and under herbaceous vegetation inceptisols dominate landforms controlled by water erosion and deposition where tephra has not been preserved in the soil and on active avalanche chutes entisols were found only on active or recent floodplains the distribution of each soil order in tcw corresponds to the preservation of tephra vegetation type and stability of the landform

pedogenic carbonates and carbon pools in gypsiferous soils of a semiarid mediterranean environment in south italy abstract soil carbonates are key features in soils of arid and semiarid environment playing an important role from pedogenetic landscape history paleoclimatic and environmental points of view the objectives of this work were i to study pathways of pedogenic carbonate pc formation ii to distinguish between lithogenic and pedogenic inorganic c by using the natural c isotope abundance and iii to estimate the soil c pools in a gypsiferous semiarid mediterranean environment sicily italy five soil pedons developed on calcareous and non calcareous parent materials from holocene 10 000 years bp to upper tortonian 7 2 5 3 ma bp in age were surveyed during field soil description the highest stage of carbonate morphology was found in soils developed on non calcareous holocene colluvial deposits youngest deposits in age which also showed the highest amount of pc the great amount of pc in soils developed on youngest deposits was ascribed to a soil landscape relationships being located in a doline overhung by gypsum outcrops precipitation of ca 2 from gypsum dissolved by rainfall and biogenic co 2 is reliable the significant positive relationship between soil organic c and pedogenic carbonates 13 c values confirms that pc was formed from biogenic co 2 organic c pool in the first cubic meter of soil ranged from 17 to 42 kg whilst pedogenic inorganic c pool from 2 8 to 30 7 kg the estimated rate of inorganic c accumulation in soils developed on youngest deposits was 2 5 g m 3 y 1 whereas the rate was negligible on older parent material the hypothesized pathways of pc formation were ex novo precipitation of gypsum ca 2 and biogenic co 2 and dissolution of lithogenic caco 3 and re precipitation of ca 2 with biogenic co 2 from an environmental prospective investigated soils may act as a sink of c when ca 2 from gypsum is available for the formation of pedogenic carbonates

geoid anomalies over the north east pacific fracture zones from satellite altimeter data summary seasat altimeter profiles have been used to recover geoid height anomalies over the north east pacific fracture zones geoid anomalies observed over fracture zones show a step like signal of 1 4m amplitude downward from the younger shallower side to the older deeper side of the fracture zone assuming that fracture zones are in isostatic equilibrium at the base of the lithosphere the geoid offset occurs because the portions of lithosphere on each side of the fracture have different thickness and density structures as predicted by thermal models of lithospheric cooling along the mendocino fracture zone whose age offset is of the order of 20 30myr the observed geoid anomalies present a clear change from east to west both in shape and in amplitude in the youngest part of mendocino around 130 w longitude there is a marked step in the geoid 3 4m amplitude while west of 140 w the older part of mendocino the geoid offset does not exceed 1 5 m the signal becoming more and more distorted the geoid offset age offset relation estimated at different locations along mendocino presents a progressive decrease from east to west e g from the young part to the old part of the fracture zone for the pioneer fracture zone the geoid offset is barely visible never exceeding 40 cm using the known bathymetry and crustal structure inferred from seismic refraction data at 128 30 w longitude as well as ages inferred from magnetic lineation data we have computed the theoretical geoid height anomaly at this location assuming local isostatic compensation at the base of the lithosphere we have deduced the subcrustal density structure from lithospheric cooling models taking account of the age thickness relationship comparison between computed and observed geoid anomaly at 128 30 w longitude is very satisfactory although a very slight overcompensation at depth needs to be assumed in order to give a better agreement over the western older part of mendocino observed geoid anomalies approach isostatic anomalies since subcrustal lateral density contrasts are smaller than in the young part of the fracture zone their isostatic shape and smaller amplitude imply smaller crustal discontinuities this suggests that the crustal thickness discontinuity across a fracture zone may decrease with age

cooling of the oceanic lithosphere evidence from geoid anomalies across the udintsev and eltanin fracture zones abstract the often step like variation in the marine geoid across fracture zones is believed to reflect the change in age of the ocean floor and hence in temperature structure of the plate across the fracture zone the rate of change of the geoid with age has been estimated as a function of age from geoid offsets across fracture zones and used to constrain thermal models of lithospheric cooling results from three studies of the geoid offsets across the mendocino fracture zone are consistent with a thermal plate cooling model having a plate thickness between 100 and 125 km this is in contrast to results obtained from the combined measurements from fracture zones in the south pacific which are not consistent with either the plate model or boundary layer model of cooling to examine this inconsistency we have measured geoid offsets on seasat profiles across the udintsev and eltanin fracture zones in the south pacific and tested the robustness of the measurement technique we used a second order polynomial that included a step function centered on the fracture zone to estimate the regional geoid and the geoid offset the polynomials were fit to the geoid profiles using least squares minimization criteria data within a certain distance of the fracture zone were excluded from the fitting procedure in order to minimize the effects of horizontal cooling and lithospheric deformation near the fracture zone we find that the estimate of the geoid offset is very sensitive to the length of data excluded and that generally an exclusion width of 100 200 km is needed to avoid anomalies unrelated to the regional geoid offset near the fracture zone exclusion widths of less than 100 km generally lead to unpredictable errors in the geoid offset estimates using exclusion widths of between 150 and 200 km on most profiles we constructed geoid slope geoid offset divided by the age offset versus average age plots for each of the limbs of the two fracture zones similar trends were found on both the east and west limbs of the eltanin and the east limb of the udintsev the trends were inconsistent with a single thermal plate thickness and instead showed an initial decrease in slope between 0 and 35 m y followed by an abrupt increase followed again by a decrease in slope in contrast the west branch of the udintsev shows an increase in geoid slope values between 20 and 35 m y followed by a decrease the difference in observed trends across the western limb of the udintsev may be due to the effects of the louisville ridge north of the fracture zone on the regional geoid the similarity in trends on the remaining three limbs argues against the effects of isolated thermal or bathymetric anomalies and appears instead to reflect a general feature of the geoid slope versus average age relationship across fracture zones although the thermal plate cooling model is successful in predicting both seafloor depths and heat flow values out to ages of at least 80 m y b p it cannot explain the observed geoid slope values for these two fracture zones it is not clear at this point whether this is due to inadequacies in the cooling model or to peculiarities in fracture zone evolution possibly caused by small scale convection driven by the horizontal temperature gradients beneath fracture zones

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

variation of the apparent compensation depth of hotspot swells with age of plate abstract most oceanic hotspot swells are associated with anomalously shallow seafloor and broad geoid anomalies these depth and geoid anomalies are generally positively correlated and linearly related the linear relationship can be used to infer an apparent depth of isostatic compensation of the swell we have analysed geoid and depth anomalies over 23 oceanic hotspot swells almost the majority of oceanic hotspots and deduced the apparent depth of compensations of these features the data indicate a linear increase of the compensation depth with the square root of seafloor age t on the order of 7 km m y 1 2 this trend is comparable to that predicted by conductive cooling models for the deepening of the isotherms inside the oceanic lithosphere

thermal evolution of the lithosphere beneath fracture zones inferred from geoid anomalies a global survey of seasat derived geoid anomalies across fracture zones fz has been conducted to characterize the behaviour of the geoid slope with age of plate in response to lithospheric cooling we present new results for the geoid slope versus age along six fz of the atlantic ocean gibbs pico doldrums romanche ascension and agulhas falkland fz including results of a previous study on pacific fz mendocino murray clarion and unditsev fz we confirm that the geoid slope does not vary with age as conductive cooling models predict and show that its complex behaviour is a worldwide phenomenum two trends are clearly shown up by the data 1 a sharp initial decrease of the geoid slope at very young ages 2 a subsequent increase which typically starts at ages around 30 40 ma and culminates at 60 ma in a few cases the rise of the geoid slope occurs later beyond 80 ma according to the recent models developed by robinson parsons and driscoll these trends may result from small scale convection induced by the horizontal thermal gradients underneath the fz instabilities developing in a sublithospheric low viscosity layer whose properties vary with age

late cretaceous orbitally paced carbon isotope stratigraphy from the bottaccione gorge italy abstract a refined astronomical tuning of the upper albian lower campanian is proposed from the bottaccione reference section gubbio central italy long term eccentricity cycles filtered from a high resolution 13c record were tuned to the highly stable 405 kyr cycles of the new la2010 astronomical solution for the earth s orbital elements the achieved orbital tuning provides a new precise and accurate age model for dating biostratigraphic magnetostratigraphic and carbon isotope events through a 23 myr long record cycles of 8 0 4 7 3 4 and 2 4 myr modulate the entire 13c record thus extending their detection from the cenozoic to 100 ma and represent primary and stable long term oscillation modes of earth s climate ocean system although an ultimate driver of these long term periodicities is lacking we speculate that specifically the periodicity at 4 7 myr represents a homologue of the present eccentricity grand cycles evolved by the chaotic behaviour of solar system planets during the mesozoic the long term periodicities potentially reflect an unexplored expression of the low frequency response of the carbon cycle to global biogeochemical dynamics of major nutrients particularly phosphorus associated with modulation of inputs to the ocean in turn triggered by high order marine transgressions and formation of highly productive shelf seas this very long term eccentricity control modulated by periodic low energy cycles is suggested to play a crucial role in carbon cycling controlling a chain of climate sensitive global biogeochemical processes on the earth finally these grand cycles provide a potential tool for geological correlation and provide a robust constraint for accurate calculation of the orbital evolution of the solar system

palaeoenvironmental turnover across the cenomanian turonian transition in oued bahloul tunisia foraminifera and geochemical proxies abstract the integrated analysis of foraminiferal assemblages geochemical proxies and stable isotopes in the oued bahloul section tunisia allowed us to reconstruct the environmental turnover across the cenomanian turonian boundary an increase in palaeoproductivity proxies p ti u al sr al and in 13 c values and a decrease in foraminiferal diversity and 18 o values mark the beginning of the oceanic anoxic event 2 oae2 at the rotalipora cushmani and whiteinella archaeocretacea biozones boundary eutrophic conditions at the seafloor and in the water column are evidenced by high proportions of buliminids and the replacement of planktic oligotrophic specialist rotalipora by eutrophic opportunist hedbergella the enrichment in organic matter and redox sensitive elements together with the abundance of low oxygen tolerant benthic foraminifera indicate dysoxic conditions in the deep water column and at the seafloor higher u aut than mo aut among planktic foraminifera deep and intermediate dwellers disappear rotalipora and globigerinelloides and surface dwellers proliferate hedbergella the persistency of the poorly oxygenated conditions during the w archaeocretacea biozone locally produced euxinic conditions where mo ef and mo aut reach high values diversity presents minimum values and benthic foraminifera temporarily disappear the maximum percentage of heterohelicids indicates a stratified water column with a well developed oxygen minimum zone improved oxygen conditions returned in the upper part of the w archaeocretacea biozone and helvetoglobotruncana helvetica biozone with a slow recovery of foraminiferal assemblages decrease in eutrophic genera heterohelix and increase in mesotrophic genera whiteinella a gradual increase in 18 o values suggests decreased temperatures in surface waters the oae2 has been attributed to global temperature changes and palaeoceanographic reorganization the poor mixing of surface and deep waters and enhanced primary productivity related to global warming associated with increasing continental weathering and nutrient runoff may have favored the eutrophication of the ocean and the expansion of the oxygen minimum zone

parent material and chemical weathering in alpine soils on mt mansfield vermont usa we compared the elemental composition of soil and bedrock samples to determine the extent of chemical weathering and the nature of the soil parent material in alpine soils on vermont s highest summit previously it was unclear whether these soils formed through weathering of bedrock glacial till or eolian sediment or solely through the accumulation of organic matter in eighteen profiles no evidence was found to indicate that soils have developed in glacial till despite evidence that the mountain was completely inundated by the laurentide ice sheet in contrast results strongly support the theory that pedogenesis in this environment involves in situ bedrock weathering under a thickening blanket of acidic organic litter weathering indices reveal an increase in weathering intensity upwards from the bedrock and trends of normalized rare earth elements demonstrate a strong similarity between bedrock and soil samples leaching has concentrated less mobile elements such as al cr la p pb and ti in soil horizons and removed mobile elements such as co fe k mg mn si and zn x ray diffraction reveals that chlorite which is present in all bedrock samples and some saprolites has weathered completely from upper soil horizons and that hydrobiotite vermiculite kaolinite gibbsite and goethite have formed in the soil ratios of immobile elements ce cr nb ta ti y and zr in soil and bedrock samples are however notably different furthermore the moderately mobile trace elements cu mo and sr are actually more abundant in soil than in bedrock and soil concentrations of zr are up to an order of magnitude greater than in bedrock samples together these data argue for at least a modest eolian influx which may have arrived during the regression of lake vermont during the latest pleistocene or from an outwash source in the immediate post glacial period similarly increased ca and na concentrations in soil samples may signify modern deposition of dust bearing ca from agricultural fields and na from roads

thermal diffusivity of the lithosphere derived from altimetry and bathymetry profiles across the southwest indian ridge in standard models for computing oceanic lithosphere thickness the lithosphere s thermal diffusivity is one of the basic parameters required and present estimates have a substantial uncertainty extending the work of crough 1979 lister 1982 and gibert and courtillot 1990 we propose a new method for the determination of thermal diffusivity of oceanic lithosphere in the near ridge crest domain the method requires geoid height and depth data both of which reflect wavelengths associated with the lithospheric cooling process and expressed as a function of seafloor age over the southwest indian ridge the thermal diffusivity so found 0 55 0 17 10 2cm2s 1 is consistent with data from the south atlantic differences in diffusivity calculated on either side of the ridge and caused by asymmetrical subsidence are possibly linked to a differential thermal regime beneath the ridge and or to the general motion of the ridge our findings are interpreted in terms of a lithospheric boundary layer less than 14age kmmyr thick and initial temperature between 1050 and 1390 c

global relationship between oceanic geoid and topography in order to compare model predictions of upper mantle convection with surface observations we have computed global residual depth and geoid anomalies on a 5 5 grid over all oceans after removal of lithospheric cooling effects and long wavelength geoid components 4000 km related to lower mantle sources we have derived the transfer function admittance of geoid over topography as a function of wavelength in the range 1000 4000 km the observed admittance is positive at all and presents a maximum of 2 5 3 5 m km at 2750 km comparing this result with the theoretical admittance computed for the lithospheric cooling plate model we ascribe most of the admittance peak at 2750 km to errors in the depth age and geoid age correction this suggests that a standard age correction applied to all seafloor is not valid at shorter wavelengths the admittance remains roughly constant on the order of 1 5 m km and can be explained in terms of sediment loading and crustal thickening effects comparing spatially the residual geoid and depth anomaly maps we note a positive correlation over a few areas coinciding with hot spot swells volcanic plateaus or seafloor deeps the geoid versus depth ratio amounts then to 6 8 m km in agreement with the values predicted above upwellings and downwellings by models of constant viscosity convection however the global admittance analysis leads to much lower values at all wavelengths suggesting that these areas are too limited in number and in extent to produce any significant signal

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

the role of lithospheric phase transitions on seafloor flattening at old ages abstract uplift of old ocean seafloor relative to the familiar t 1 2 curve is generally presumed to be a consequence of an additional heat source at the base of the oceanic lithosphere several geodynamical mechanisms have been invoked to explain this behavior we have taken a petrological rather than geodynamical approach and considered whether the causes of the flattening can be found within the conductive portion of the lithosphere where viscous creep is insignificant accordingly self consistent calculations of the phase assemblages of several candidate mantle compositions have been performed subject to the constraint of experimentally determined calorimetric measurements we have found that in general for temperatures below around 800 c and pressures greater than 10 kbar the phase change from spinel peridotite to garnet peridotite has a significantly negative clapeyron slope which could cause some amount of uplift of old seafloor the transition for representative thermal profiles should be depressed from about 35 km at 40 ma to 45 km at 160 ma since spinel peridotite is of lower density the net effect is to raise the seafloor topography the extent of the uplift which depends primarily on the al 2 o 3 content of the peridotite and on the effective thermal diffusivity of the lithosphere should be on the order of 140 220 m

depositional environments and paleogeography of the cretaceous gypsum horizon in west central jordan abstract in the upper cretaceous upper cenomanian gypsum horizon of west central jordan the lithofacies of gypsum limestone and dolomite as well as their sedimentary structures and petrography indicate a coastal intertidal supratidal sabkha environment very much like the persian gulf model 1500 km 2 in area and elongated n s parallel to the dead sea rift fact that this is the second time in the cenomanian of the mujib area that total emergence has happened is taken as an example of synsedimentary tectonics in an unstable area along the not yet existing dead sea rift

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

from a black to a gray box a mass balance interpretation of pedogenesis we utilize chemical elements as tracers in a mass balance analysis that provides functional relationships among soil chemical composition bulk density and volume change in relation to parent material these analytical functions are based on the principle of conservation of mass and include a term quantifying mass flux into out of the soil and between horizons we apply the technique to the oldest member of a chronosequence developed on marine terraces in northern california it is an alfisol that evolved from beach sand to its present state nearly one third of its weight is composed of secondary clay minerals in about 240 ky aside from large increases in organic carbon desilication is the dominant factor in soil evolution 29 50 83 g cm 2 si was leached from the beach sand during pedogenesis the rate of desilication is roughly 2 1 t km 2 yr 1 0 21 g cm 2 ky 1 an order of magnitude slower than that implied by the si denudation rate calculated for the mattole river watershed weathering of primary minerals and synthesis of secondary minerals is relatively well advanced suggesting that the rate of desilication may be declining the local beach is composed of quartz and sodic plagioclase with smaller amounts of chlorite mica and kaolinite the soil has substantially different mineralogy sand is dominated by quartz and clay is dominated by kaolinite halloysite chloritic intergrades and gibbsite bases are also leached though the total mass was much less 57 2 55 g cm 2 of na in the beach sand was lost as plagioclase weathered by focusing on elemental and mineralogical gains and losses we emphasize the essential connection between the pedologic environment and the external hydrochemical environment

the cenomanian turonian oceanic anoxic event i stratigraphy and distribution of organic carbon rich beds and the marine δ13c excursion marine strata deposited during late cenomanian and early turonian time display lithological faunal and geochemical characteristics which indicate that significant parts of the world ocean were periodically oxygen deficient at or very close to the cenomanian turonian boundary between 90 5 and 91 5ma ago oxygen deficiencies were particularly marked over a period of 1ma this short lived episode of oceanic oxygen deficiency has been termed the cenomanian turonian oceanic anoxic event oae the widespread distribution of anoxic sediments deposited synchronously during such a short lived event indicates that such sediments are not simply the product of coincidental local climatic or basinal water mass characteristics but are the result of a global expansion and intensification of the cenomanian turonian oxygen minimum zone related to feedback between sea level rise and regional palaeoceanography the palaeoceanography of the cenomanian turonian oae is discussed in detail in a companion paper by arthur et al 1987 from authors

cenomanian turonian stable isotope signatures and depositional sequences in northeast egypt and central jordan abstract lithostratigraphic biostratigraphic and microfacies studies of two cenomanian turonian shallow marine siliciclastic carbonate successions at gebel ekma plateau southwestern sinai egypt and wadi karak section central jordan are calibrated with 13c profiles to reveal relative sea level changes within a sequence stratigraphic framework the study provides significantly enhanced stratigraphic resolution and key sections for regional correlation lithofacies are dominated by well developed peritidal to subtidal facies associations indicating deposition in a rimmed carbonate shelf setting biostratigraphic analysis indicates the presence of 6 ammonite zones 3 calcareous nannofossil zones and 3 planktonic foraminiferal zones within the cenomanian to turonian succession six third order depositional sequences bounded by correlatable sequence boundaries can be traced across the african arabian platform comparison with 13c records in deeper water pelagic sequences help to improve the resolution of the boundaries of each depositional sequence recognition of time gaps at the sequence boundaries on the platform recorded in different parts of african arabian platform is attributed to local tectonic activity associated with the change from passive to active margins which are overprinted by the global eustatic signature