sea level reconstruction for turonian sediments from tanzania based on integration of sedimentology microfacies geochemistry and micropaleontology abstract despite many advances in sea level research the nature of cyclic eustatic sea level fluctuations during warm periods without or with much reduced polar ice remains enigmatic recently published 18 o records from extremely well preserved turonian microfossils from tanzania do not support the contentious idea of glacio eustatic control of global sea level changes during the warmest period of the cretaceous for the same locality site tdp 31 we reconstruct relative sea level changes based on sequence stratigraphy and integration of sedimentology microfacies geochemistry and micropaleontology four local sequence boundaries sbs tutz1 4 are recognized at the base middle and top of the helvetoglobotruncana helvetica zone and in the late turonian the lowstands are characterized by increased grain size enhanced organic carbon flux faunal assemblage changes and bulk 13 c org and foraminiferal 13 c f and 18 o f minima strong benthic and planktic foraminiferal turnovers above the top middle turonian sb tutz3 probably reflect shallowing from upper slope to outer shelf and or eutrophication the tdp 31 age model is refined through inter regional comparison of planktic foraminiferal ranges and 13 c records from three other south tethyan localities odp holes 762c and 763b exmouth plateau and the guru section tibet this age model enables correlation of the regressive events at a global scale and suggests that within stratigraphic uncertainty the tdp 31 depositional sequences are synchronous with the global turonian third order sequences and are likely driven by eustasy these correlations together with recent astrochronological and radiometric dating indicate a considerably younger age 91 17 0 52 ma for the top h helvetica zone than currently assumed resulting in zonal duration of 2 35 0 52 myr foraminiferal stable isotope data from tdp 31 indicate slight surface and bottom water warming during the regressions and possibly a minor surface water salinity decrease which is inconsistent with glacio eustatic forcing of turonian third order sea level cycles and is more in line with the model of aquifer eustasy

relative array analysis of upper mantle lateral velocity variations in southern california spatial averaging of short period teleseismic p wave arrivals across scarlet constrains upper mantle lateral velocity variations beneath southern california we compare dt d back azimuth and averaged arrival time estimates determined from the entire network for 154 events to the same parameters derived from small subsets of scarlet the resulting relative array diagrams and plots of net subarray delays computed for 171 overlapping subarrays exhibit large anomalies that vary smoothly as a function of subarray position implying substantial lateral heterogeneity under the network patterns of mislocation vectors for more than 100 subarrays permit identification of an east west striking high velocity antiform beneath the transverse ranges further constraints on both the lateral configuration and depth of the anomaly are obtained through thin lens analysis of the net delay data where all the time perturbations are assumed to originate at a single depth projection of 2798 net delays requires a lens deeper than 100 km a representative lens at 150 km depth features low velocities beneath the salton trough as well as a concentrated high velocity zone between 116 3 118 3 w and 33 7 34 8 n consistent with the relative array diagrams and the pkp delay contours of hadley and kanamori 1977 therefore the bulk of the high velocity material observed by hadley and kanamori may in fact lie at or deeper than 150 km rather than 40 100 km this possibility prompts renewed speculation regarding the relationship of this body to the plate tectonic history of the region

a comparison of precession and obliquity effects in a cretaceous paleocllmate simulation a set of 36 perpetual season simulations with an atmospheric gcm are used to investigate the effects of precession and obliquity variations on mid cretaceous climate climatic variables such as surface temperature pressure and moisture transport suggest that the mid cretaceous climate system is more sensitive to precession than to obliquity in most regions even at high latitudes obliquity variations affect our simulations primarily by modulating the western extent of the precession enhanced continental monsoons as a result sensitivity to obliquity can be important at low as well as high latitudes

clay mineral assemblages of mesozoic pelagic and flysch sediments of the lombardian basin southern alps implications for palaeotectonics palaeoclimate and diagenesis clay mineral assemblages determined by x ray diffraction in the jurassic to lower cretaceous hemipelagic pelagic sediments and in the upper cretaceous flysch sequences of the lombardian basin southern alps record tectonic and possibly climatic changes in the source areas and to a lesser extent alterations during burial diagenesis

a comparison of gcm simulated cretaceous greenhouse and icehouse climates implications for the sedimentary record abstract two general circulation model simulations of mid cretaceous climate are presented one representing a greenhouse and the other representing an icehouse world through a comparison of greenhouse and icehouse palaeoclimates differences in processes which are intrinsically linked with climate such as continental weathering and snow and ice accumulation may be observed a number of conspicuous and discrete climatic differences can be seen between the two simulations which may be translated into a number of identifiable signatures in the sedimentary record the climate at mid high latitudes in the icehouse simulation was more arid than the greenhouse simulation and could result in deposition of smectite dominated clay suites in contrast the climate of low latitudes of the icehouse simulation resulted in a moister climate than the greenhouse simulation which could affect the weathering regimes and result in deposition of kaolin dominated clay suites thus cool climate episodes do not necessarily result in a global increase in aridity the icehouse simulation predicts a small permanent icecap at high latitudes which could account for the origin of dropstones in marine sediments furthermore a sea level fall as a consequence of an accumulation of ice at high latitudes may also increase continentality and surface albedo which may also contribute to the causes of the drier climate at high latitudes hurricanes are likely to be more frequent in greenhouse than icehouse climates mid latitude depressions also important for generating storms are likely to be both intense and frequent during icehouse and greenhouse periods of the middle cretaceous

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

geological and mechanical study of argillaceous north sea chalk implications for the characterisation of fractured reservoirs abstract argillaceous chalk intervals from the north sea are characterised by matrix permeabilities lower than 0 2 md and therefore they are defined as tight chalks hence fracture networks within these chalks are of major importance to predict fluid flow and reservoir or seal behaviour this study aims to understand the geological parameters controlling the chalk petrophysical and mechanical properties using the outcrop analogue of the cenomanian chalk at cap blanc nez northern france sedimentological petrographic and petrophysical analyses were performed and show that the combination of the depositional environment and diagenetic imprint control the microtexture non carbonate content is ranging from 5 to 40 within the studied samples and is critical for the diagenetic imprint the fracture behaviour of the chalk was studied using a mechanical stratigraphy approach throughout the 70 m thick succession where a transition between lower cenomanian argillaceous chalk and middle upper cenomanian pure chalk is exposed twenty two mechanical units are distinguished and the amount of fractures crosscutting initiating and terminating on mechanical interfaces quantified manual scanlines show that fracture spacing ranges from 17 to 232 cm mechanical interfaces are associated with lithological heterogeneities with strong microtextural contrasts related to the non carbonate content and or degree of cementation the mechanical units are thus defined either by deposition or diagenesis the fracturing behaviour of about 10 m homogeneous pure chalk interval units defined as dfz densely fractured zones differs significantly from the rest of the succession large sigmoidal shaped fractures are confined to those intervals and a dense fracture network developed because of their plastic behaviour clay layers are able to accommodate part of the stress whereas homogeneous pure chalk show a more brittle behaviour

pn velocity anisotropy in southern california we analyze p n propagation as a function of azimuth across a 28 station 150 km aperture subarray of the scarlet network centered near the central transverse ranges california we selected signals from 81 earthquakes and explosions with epicentral distances ranging from 150 to 400 km covering all azimuths except a 40 gap from the southwest and a lesser gap from the northeast direction for each source the apparent velocity of p n was determined using a one norm measure of misfit the apparent p n velocity does not show any systematic variation with epicentral distance but exhibits a strong azimuthal dependence our preferred interpretation calls for a slightly dipping 2 to n40w planar moho with 3 to 4 per cent anisotropy of subcrustal material transverse isotropy with a nearly horizontal symmetry axis is sufficient to explain the data the direction of sagittal symmetry is n50w the isotropic velocity of p n is 7 8 km sec in contrast a higher 8 1 km sec p n velocity is found in the mojave block with no indication of anisotropy these observations are consistent with a subcrustal model of the pacific north america plate boundary where ductile flow is characterized by simple shear in a vertical plane with strike parallel to the direction of relative plate motion

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

extending the astronomical polarity time scale into the miocene an astronomical time scale is presented for the late miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the mediterranean to the 65 n summer insolation curve of la90 1 2 with present day values for the dynamical ellipticity of the earth and tidd dissipation by the moon this correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals and planktonic foraminiferal and dinoflagellate events the tortonian messinian t m boundary placed at the first regular occurrence of the globorofuliu conomiozea group in the mediterranean is dated at 7 24 ma the duration of the messinian is estimated at 1 91 myr because the miocene pliocene boundary has been dated previously at 5 33 ma 3 the new time scale is confirmed by oar 3gar ages of volcanic beds and by the number of sedimentary cycles in the younger part of the mediterranean messinian

tropical cyclones in the southwest pacific spatial patterns and relationships to southern oscillation and sea surface temperature abstract an analysis of a 20 yr dataset of tropical cyclones in the southwest pacific has been made to determine the spatial patterns of cyclone occurrence and how these depend on the southern oscillation so and sea surface temperature a local measure of cyclone incidence is defined as the number of cyclones that enter into a 2 lat long square during some period eg within one season and this quantity is mapped for four southern oscillation index soi categories the maps show that the geographical distribution of cyclone incidence shifts eastward and northward during negative soi phases and vice versa the mean annual incidence for the whole region is 28 higher than average for our strongly negative so category and 16 below average for our near zero category to explore the roles of the so and local sst correlation analysis was applied to mean values of cyclone incidence for four subregions of 20 longitude width between 10 and 22 s markedly different soi sst responses were found on either s

recognition of cyclic and non cyclic environmental changes in the mediterranean pliocene a palynological approach the interval between 2 8 and 2 3 ma b p from the south italian singa section has been investigated for its dinoflagellate cyst and sporomorph contents in order to facilitate palaeoenvironmental interpretation the following curves are derived from the data the ratios sporomorphs dinoflagellate cysts protoperidinioid gonyaulacoid dinoflagellate cysts warm cold water indicating dinoflagellate cysts inner neritic oceanic dinoflagellate cysts outer neritic oceanic dinoflagellate cysts and the reworked dinoflagellate cysts per gram of sediment furthermore the already available 18o curve has been used calibration of changes in the sporomorph dinoflagellate ratio against the computed astronomical insolation curve leads to an improved age assessment for the section frequency analysis on the curves shows the 23 41 and 100 ka frequency components to be most important phase and amplitude differences between the filtered 23 41 and 100 ka frequency components are used for environmental interpretation the 23 ka frequency band is best explained by changes in runoff induced transport the 41 ka frequency components are classified in a group with short response time to orbital forcing and a group with longer response time those signals having a short response time are attributed to local precipitation induced changes in runoff those signals having a longer response time are mainly attributed to changes in global temperature and to a lesser extent to changes in global ice volume finally longer term cyclic and non cyclic changes are mainly attributed to temperature and sea level variation

benthic faunal response to late maastrichtian chalk marl cyclicity at rordal denmark abstract chalk marl cyclicity is a common and characteristic feature of the upper cretaceous chalk group of nw europe the mainly small sized benthic fauna from an upper maastrichtian cyclic chalk marl succession at rordal denmark is analysed in order to interpret the composition and structure of the benthic fauna and to test if faunal density diversity composition and mode of life substrate were controlled by changes in lithology the material comprises 21 bulk samples weighing 5 kg each collected from all chalk and marl half cycles the samples were washed and sieved and yielded a total of 25 974 specimens these are referred to at least 75 species and 15 bryozoan morphotypes and form the basis for the establishment of 10 guilds the lithological cyclicity is not reflected by the distribution of individual species or by changes in average adult size but there is generally a higher species diversity and density in chalk compared to marl the chalk thus represents times of more favourable living conditions higher environmental stability and probably higher nutrient influx no changes in guilds between marl and chalk are found the variation in substrate character between the two lithologies was thus too small to have exerted any significant influence on the mode of life of the benthic fauna in spite of a difference in clay content averaging 10 two different fossil associations are recognized each covering one to two chalk marl cycles and characterized by a distinct fauna with similar ecological requirements if the chalk marl couplets represent precession cycles within the milankovitch band then the change from one association to the other and back again may represent the 100 000 years eccentricity cycle based on a calculated sedimentation rate of 6 cm ka 1

the paleoclimatic interpretation of clay minerals in sediments a review abstract the application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated levels relatively rich in chlorite illite palygorskite and quartz are interpreted as corresponding to relatively dry periods while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale such as kaolinite smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season using this and similar schemes the paleoclimates of areas adjoining the mediterranean basin north sea north atlantic southern arctic equatorial and north west pacific and north phillipine sea are reconstructed clay minerals in sediments particularly marine sediments can be useful indicators of paleoclimatic conditions while they do not produce direct indications of climatic parameters they provide integrated records of overall climatic impact occasionally they may be superior to the more conventional paleoclimatic methods such as pollen or oxygen isotope analysis the limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples the distinction between authigenic and detrital clay minerals is shown to be problematic particularly with regard to smectite the relationship between climatic parameters and clay mineral formation is complicated by the intervention of extra climatic factors such as topography geomorphology lithology and time post depositional diagenetic changes may not be recognized differentiation during transport due to size sorting or differential flocculation may overlap climate induced differentiation the association of clay mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency i e water ice or wind transport agencies are not constant with time by an interdisciplinary approach with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data many of these limitations can be overcome

reconstruction of mid cenomanian orbitally forced palaeoenvironmental changes based on calcareous dinoflagellate cysts abstract mid cenomanian precession controlled 21 ka chalk marl couplets of the cap blanc nez section anglo paris basin have been studied with focus on the effects which milankovitch cycles have had on the palaeoenvironment in this paper we present micropalaeontological and lithological proxies that enable the reconstruction of both the cycle architecture and the transformation of the orbitally forced signal into the sediment a palaeoecological reconstruction based on changes in calcareous dinoflagellate cysts c dinocysts assemblages was carried out in which two characteristic ecological assemblages of c dinocysts were identified gradual changes in absolute and relative abundance of the cyst species in these assemblages over several couplets depict a bundling pattern which is interpreted to reflect the modulation of the intensity of the precession cycle by the eccentricity cycle 100 ka the stacking pattern in the natural gamma ray signal and the carbonate and toc content has the same period and provides lithological support of the bundling a shelf basin circulation model is proposed to explain the relation between orbitally forced climate change its palaeoenvironmental consequences and the resulting sedimentary cyclicity variations in surface water circulation are reflected in the sediment by the chalk marl couplets the most distinctive couplets ocurring at the base and top of the bundles while the chalks reflect well mixed surface water conditions the marls particularly those at the bundle boundaries can be interpreted as the sedimentary expression of stratified water masses during deposition of these marls reduced oceanic mixing due to low seasonality during strong precession maxima at the eccentricity maxima caused periods of water column stratification that in turn led to nutrient depletion and decreased productivity in the surface water masses

the cenomanian turonian boundary event oae2 and palaeoenvironmental change in epicontinental seas new insights from the dinocyst and geochemical records abstract organic walled dinoflagellate cyst dinocyst and geochemical records across the cenomanian turonian boundary ctb are presented for the nw european reference section at eastbourne england dinocyst and nannofossil fertility indexes indicate that an upwelling driven productivity pulse accompanied a eustatic sea level fall that preceded by at least 40 kyr the global rise in 13 c values that marks the onset of oceanic anoxic event 2 oae2 and the deposition of black shales in the deep ocean a marine productivity collapse in the latest cenomanian is evidenced by the falling absolute and relative abundance of peridinioid dinocysts believed to be the product of heterotrophic dinoflagellates this biotic change accompanied transgression and sharply rising sea surface temperatures following an atlantic wide episode of short lived cooling geochemical tracers provide evidence of caribbean colombian plateau volcanism the increase in water depth caused by the latest cenomanian transgression resulted in less eutrophic waters in epicontinental seas where ctb biotic turnover was driven largely by water mass changes rather than oxygen depletion the species richness absolute abundance ratio of dinocysts is proposed as a water mass stability proxy

rhythmic bedding produced in cretaceous pelagic carbonate environments sensitive recorders of climatic cycles various types of rhythmic bedding are prominent features of cretaceous pelagic carbonates these bedding rhythms are the primary depositional result of variations in carbonate productivity terrigenous dilution redox conditions and or the energy of bottom currents each bedding cycle type is different in its expression in the stratigraphic record but ultimately was caused by rhythmic climatic variations related to variations in receipt of solar insolation as the result of the earth s orbital characteristics the so called milankovitch cycles stratigraphic sequences may contain a single bedding cycle type or a composite of several types although sediment type and sedimentary structures were influenced by variations in local climatic oceanographic tectonic and diagenetic parameters pelagic carbonate environments during the cretaceous were particularly sensitive recorders of orbitally induced changes in worldwide climate

digital processing of regional network data abstract much more than hypocenter location can be done with digital time histories obtained from regional seismic networks examples are given of how these data can be routinely processed to provide readily accessible intermediate results for subsequent studies among which are velocity inversion using teleseismic p residuals composite focal mechanism studies and spectral analysis the processing must be designed to be as routine and as complete as possible only with these two objectives achieved can the seismic networks be as productive as they should be

foraminiferal evidence for cenomanian sequence stratigraphy and palaeoceanography of the boulonnais paris basin northern france abstract a middle to upper cenomanian chalk succession in the northwestern european paris basin escalles section was investigated with respect to its sediment composition biofacies and foraminiferal content most planktic foraminifers exhibit a high frequency cyclicity in their distribution pattern and show little relationship to the sequence stratigraphic subdivision a few characteristic species of benthic foraminifers tritaxia pyramidata ataxophragmium compactum dorothia levis and gavelinella cenomana are related in their frequency distribution to certain systems tracts other benthic foraminiferal species are more evenly distributed through the systems tracts cluster analysis and factor analysis allow the separation of three benthic foraminiferal biofacies domains which exhibit a characteristic frequency distribution pattern with respect to sequence stratigraphy biofacies 1 is dominant in the highstand systems tract hst and biofacies 3 is characteristic for the transgressive systems tract tst biofacies 2 is most abundant around the maximum flooding downlap surface mfs and less abundant around the sequence boundary factor analysis shows that most of the variance in the data set is explained by variables related to plankton productivity variables related to changes in water depth and changes in sea level have minor influence on the variance of the whole data set but have some influence on the variance of the benthic foraminiferal data set the different reaction of benthic and planktic foraminifers to relative sea level changes is also recorded in the total number of foraminifers per gram sediment foraminiferal number and in the ratio between planktic and benthic foraminifers p b ratio the foraminiferal number is highest at the mfs and lowest at the sequence boundaries of the investigated depositional sequences the p b ratio has no correlation with the sequence stratigraphic subdivision but shows a high frequency cyclicity the abundance pattern of planktic foraminifers is controlled by changes in the productivity of calcareous plankton the regular variation in calcareous plankton productivity leads to marl low productivity chalk high productivity cycles that form conspicuous couplets in the section the productivity cycles are also recorded in gamma ray logs in the environmental setting of the escalles section in contrast the abundance patterns of benthic foraminifers are more influenced by relative sea level changes changes in water depth and variations in substrate composition the stacking of probably precession controlled development of couplets lead to a distinct 100 000 year cyclicity that does not match very well with published sequence stratigraphic subdivisions

milankovitch climatic origin of mid cretaceous black shale rhythms in central italy the earth s orbital variations reflected in pleistocene ice volume were also recorded in non glacial times carbonate production in pelagic mid cretaceous sediments quantified by calcium carbonate and optical densitometry time series reflects the orbital eccentricity and precessional cycles minimal eccentricity brought deep sea anoxia most of the sedimentary variability of this 100 myr old sequence lies within the milankovitch orbital frequency band

nannoplankton productivity fluctuations and rhythmically bedded pelagic carbonates of the greenhorn limestone upper cretaceous abstract comparison of calcareous nannofossil assemblages from rhythmically interbedded calcareous shales and adjacent bioturbated chalks of the greenhorn limestone cenomanian turonian of the western interior basin indicate significant changes in phytoplankton paleocommunity structure between lithotypes significantly higher shannon diversity and evenness values in the chalk assemblages indicate more stable surface water conditions with lower fertility three taxa indicative of high surface water fertility are significantly more abundant in marlstone assemblages which suggests that calcareous shale marlstone deposition corresponded with fluctuating surface water conditions with relatively high fertility the higher surface fertility and concomitant production of organic matter resulted in sediment anoxia during marlstone deposition leading to high rates of organic carbon storage reduced phytoplankton production during chalk deposition allowed oxygenation of the sea floor and establishment of diverse benthic invertebrate communities

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

diagenetically enhanced trilobite obrution deposits in concretionary limestones the paradox of rhythmic events beds abstract certain offshore facies with extraordinarily well preserved fossils particularly trilobites display distinctive motifs of rhythmically bedded decimeter scale concretionary limestone and dark gray shale examples are known from cambrian to neogene age but are especially common in the lower middle paleozoic the hollardops trilobite beds of the lower devonian emsian khebchia formation morocco provide the exemplar of this phenomenon comparative examples include trilobite beds from the upper ordovician katian of oklahoma new york state and ontario canada and the lower to middle devonian lochkovian givetian of tennessee oklahoma and new york state these lagerstatten are observed to crosscut facies belts occuring in both sparsely fossiliferous dysoxic facies and more abundantly fossiliferous sections articulated fossils occur in both limestones and interbedded shales indicating episodic deposition of fine grained sediments in both instances but those in the shales are highly compressed and difficult to extract conversely limestones yield particularly well preserved fossil material including in situ lingulid brachiopods and bivalves cephalopods and complete outstretched and enrolled trilobites articulated uncompressed fossils may occur in varied orientations relative to bedding this suggests that the organisms were locally entrained in mudflows although occurrence of exoskeletal molt ensembles in some beds suggests that in certain events organisms could be preserved in situ enclosing sediments are typically strongly bioturbated indicating prolonged periods of sediment starvation following mudflow events but prior to early diagenetic cementation however most burrows are small and evidently did not disrupt entombed organism remains pyritic and calcite spar fillings in internal spaces of fossils formed early and rarely preserve remnants of lightly sclerotized tissues carbonate cementation occurred during interludes of low sedimentation association with pyrite suggests formation within the zone of sulfate reduction these intervals are particularly well developed in relatively sediment starved transgressive intervals and constitute a type of time specific facies these rhythmic obrution beds are especially characteristic of the late ordovician and late early devonian emsian where they occur on at least four paleocontinents these beds formed selectively in warm in semi arid climates in which minor siliciclastics supplied from a relatively low relief hinterland were episodically re suspended in slurries and transported offshore they were favored in systems poised between deposition of siliciclastic and carbonate muds the commonly rhythmic bedding of these deposits records a regular recurring cyclic motif with overall durations of 10s of kyr of carbonate redistribution superimposed upon muds that include abundant obrution deposits

astronomically forced variations in gamma ray intensity late miocene hemipelagic successions in the eastern mediterranean basin as a test case amplitude variations of the gamma ray record of late miocene hemipelagic successions on crete correlate remarkably well with the amplitude variations of a published theoretical insolation curve chemical analyses of the sediments show a linear relation between radiation total counts above 400 kev and u enrichment due to authigenic formation of u containing minerals under anaerobic conditions the studied sections which are paleomagnetically and biostratigraphically and cyclostratigraphically well constrained and more than 100 km apart can be correlated on basis of gamma ray count rates

jurassic to cretaceous upper kimmeridgian lower berriasian calcispheres from high palaeolatitudes on the antarctic peninsula local stratigraphic significance and correlations across southern gondwana margin and the tethyan realm abstract we report upper jurassic lower cretaceous kimmeridgian berriasian calcispheres from the ameghino nordenskjold formation at high palaeolatitudes on the northern part of the antarctic peninsula the ameghino formation generally contains a relatively poorly preserved association of calcispheres which are often recrystallized or replaced by silica however early diagenetic calcite concretions are widespread in the mudstone tuff sequences and calcisphere in these contexts show very good preservation among the seventeen species recognized in this study thirteen are known from the upper jurassic lower cretaceous pelagic sediments of the tethyan and andean regions the remaining three include stomiosphaera and two new species that probably indicate an austral character for the calcisphere association the following calcisphere zones previously proposed for the tethyan realm and the andes are confirmed for the ameghino formation carpistomiosphaera borzai carpistomiosphaera tithonica parastomiosphaera malmica colomisphaera tenuis colomisphaera fortis and stomiosphaerina proxima zones indicate a late kimmeridgian to early berriasian age broadly consistent with previous age assignments based on ammonites and radiolarians however calcisphere ages allow partial stratigraphic re arrangement of the succession cropping out in sobral peninsula and support the intercalation of sandy conglomeratic beds deposited in submarine fan environment between the slope basinal facies typical of the ameghino formation facies changes suggest basin margins across the antarctic peninsula in a complex paleogeography with large emergent landmasses to the southwest of the study area possible dispersal routes along the southern gondwana margin occurred along the so called hispanic and mozambique corridors identified species show a global distribution being represented in the andean the tethyan and boreal realms the cosmopolitan character of mesozoic calcispheres proves their importance for interregional correlations

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

the cenomanian turonian eagle ford group of south texas insights on timing and paleoceanographic conditions from geochemistry and micropaleontologic analyses abstract the interbedded organic rich marls and limestones of the eagle ford group of south texas were deposited on the shelf of the central texas platform during the upper cenomanian through the turonian micropaleontological analyses of thin sections and residue samples from subsurface cores taken in atascosa and karnes counties yielded 13 biostratigraphic datums which were integrated with calcareous nannofossil datums stable carbon isotopic and bulk inorganic geochemical analysis to gain an understanding of the paleoceanographic conditions of the study area and their relationship to regional and global events the paired thin section residue sampling was necessitated by poor recovery of planktonic foraminifera in washed samples which were however abundant in most thin sections lower eagle ford marls were deposited under euxinic conditions produced by a stratified water column periodic enhanced water column mixing increased oxygen levels and surface water primary productivity which promoted calcite diagenesis and generation of limestones containing calcispheres and radiolaria an oxygenated bottom water mass entered the basin in the uppermost cenomanian prior to the onset of oceanic anoxic event oae 2 causing a spike in benthic foraminiferal diversity and decreasing preservation of organic matter although the lower portion of the upper eagle ford is age equivalent to oae2 as indicated by positive shift in 13corg it contains less organic matter and evidence of more oxygen than the lower eagle ford so deposition of the eagle ford black shales is not contemporaneous to oae2

chemical cyclicity and correlation of lower lias mudstones using gamma ray logs yorkshire uk natural gamma ray spectrometry on coastal sections from redcar and robin hood9s bay permits the radioactive characterization of five different mudstone units and the construction of an outcrop gamma ray log for the lower lias correlation of these five units with their equivalents in the gamma ray log of the felixkirk borehole located 40 km to the west has been established statistical comparison of tie points in the composite coastal section shows there to be a stratigraphic gap of 10 m between the two localities relative to the continuous section in the felixkirk borehole the distribution of th ppm k and u ppm are generally highly correlated with the total radioactivity however anomalies do occur a peak in the th k ratio can be related to an iron oolitic horizon marking a condensed sequence in the early mid sinemurian a sharp fall in the th k ratio followed by high u values coincides with the early pliensbachian transgression comparison with mineralogical clays and chemical si al and al k ratio v total organic carbon profiles of the same section allows for an evaluation of the significance of radioactive element distribution in terms of grainsize run off and oxygenation indicators a spline curve fitted through the total radioactivity data emphasizes low frequency cyclicity wavelengths of between 10 and 30 m in the outcrop section these cycles appear to be correlatable with cycles of comparable wavelengths in the low pass filtered gamma ray log of the felixkirk borehole sedimentological evidence confirmed high radioactivity peaks correspond to transgressive phases the gamma ray signal of the felixkirk borehole has also been analysed for high frequency cyclicity with an overall rate of accumulation of about 13m ma variation in the milankovitch band is marked by units 5 m or less in thickness evidence for eccentricity obliquity and precession cycles has been found both in borehole and in outcrop a typical shift from lower to higher frequencies occurs consistently in transgressive phases and is related to increased sedimentation rates

milankovitch scale palaeoclimate changes in pale dark bedding rhythms from the early cretaceous hauterivian and barremian of eastern england and northern germany abstract early cretaceous valanginian albian successions in northwestern europe occupy an ideal palaeoceanographic location in which to study the interplay between the arctic boreal and tethyan seaways or realms marine early cretaceous sediments of the north sea borderlands north germany eastern england are dominated by fine grained siliciclastic deposition with carbonates occasionally this succession is characterised by visually striking bedding rhythms comprising calcareous and less calcareous clays or pale dark alternations on a scale of 0 5 1 m such rhythmic sedimentation becomes most dominant in the early to late hauterivian parts of the early barremian and in the aptian this study concentrates on late hauterivian sections in england and germany which have remained relatively unaffected by deep burial tectonism or diagenesis changes in geochemistry are related to floral and faunal alternations and thus directly to palaeoenvironment the wide range of palaeontological and geochemical analyses show conclusively how bedding rhythms developed in the milankovitch band are the result of palaeoclimate change pale layers were tethyan influenced in their microflora and fauna indicating warm surface waters that were poor in nutrients and developed during warm seasonally arid hinterland climates dark layers were boreal influenced displaying features consistent with cooler waters rich in nutrients such dark layers reflect cooler more humid hinterland conditions the coincidence of tethyan taxa with bundles of pale layers displaying high gamma ray emission and elevated radioactive element contents suggests transgressive or condensed beds the bundling of pale dark rhythms coincides with the long term milankovitch eccentricity cycle this paper documents direct links between the reaction of hinterland weathering marine floras and floras to milankovitch scale changes in bed lithology and thickness

a milankovitch scale for cenomanian time a detailed cyclostratigraphy is present in the rhythmically bedded cenomanian hemipelagic chalks of the northern anglo paris basin which can be correlated over 100 000 km2 individual decimetre scale couplets probably represent the precession cycle modes at 18 or 23 kyr and can be readily grouped in sets averaging five indicative of the short cycle of eccentricity 100 kyr a composite cyclostratigraphy for the basin is presented here and is used as the basis for a cenomanian time scale 20 and 100 kyr units the total duration of the cenomanian thus obtained 4 4 myr compares well with recent radiometric dates of 4 0 4 5 myr the time scale is used to estimate the length of ammonite inoceramid and planktonic foraminiferal zones the rates of formation of authigenic minerals glauconite sedimentation rates and the duration of transgressions and anoxic events

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

palaeoecology of the biserial planktonic foraminifer heterohelix moremani cushman in the late albian to middle turonian circum north atlantic abstract the cretaceous heterohelix moremani cushman was the only biserial planktonic foraminiferal species from its first appearance in the late albian up to the cenomanian turonian boundary within that time it increased gradually in abundance relative to other planktonic foraminifera in five circum north atlantic sections it is generally rare in upper albian sediments common in most of the cenomanian and very abundant in sediments representing the latest cenomanian oceanic anoxic event short term variations on the overall abundance trend correlate with positive excursions in the bulk carbonate 13c record maximum rain rates of h moremani during oae2 show that this species was an opportunist that did well in extreme conditions but its overall distribution indicates that it is not necessarily a marker for very high palaeoproductivity environments stable oxygen and carbon isotope measurements on foraminiferal species indicate that h moremani was a surface water dweller at least in part of its geographic range but incorporated 13c out of equilibrium with ambient seawater it is depleted in 13c relative to other planktonic foraminifera which is attributed to vital effects related to its opportunistic character

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

limestone marl alternations as environmental archives and the role of early diagenesis a critical review limestone marl alternations and other micritic calcareous rhythmites have long appealed to sedimentologists as they appeared to directly reflect high frequency environmental change in particular when orbital forcing gained popularity amongst sedimentologists and paleoclimatologists in 1980s such rhythmites seemed to offer an ideal tool for high resolution chronostratigraphy and environmental reconstruction however in spite of the fact that orbital forcing has become a routine interpretation of calcareous rhythmites and that the processes of formation of calcareous rhythmites are considered well understood research in the past 10 years again has questioned their primary origin and their direct interpretability detailed petrographic paleontological and geochemical data from numerous successions through geological time provided the basis for testing whether or not the regular alternation of limestone beds and marl or shale interlayers represents bimodally fluctuating environmental conditions in a direct way in particular these data supplemented by box model simulations imply that post depositional alteration diagenesis has the potential to not only seriously distort primary environmental signals but also to mimic primary signals this questions the use of micritic calcareous rhythmites for high resolution chronostratigraphy and for environmental interpretations where independent data of diagenetically inert parameters are not available diagenetic changes appear to have a yet widely underestimated influence on the appearance of limestone marl alternations and other calcareous rhythmites the aim of the present review is to summarize new approaches and give an overview of our research results in this field of the past decade this review also aims at pointing to still enigmatic aspects that need to be addressed before the interpretation of micritic calcareous rhythmites can be considered a reliable tool for high resolution chronostratigraphy and paleoenvironmental interpretation

multi mode analysis of rayleigh type lg part 2 application to southern california and the northwestern sierra nevada the uc diagram technique described in the companion paper part 1 is applied to nine sets of lg phases recorded through the cedar system in southern california and two sets of lg phases recorded along the northwestern margin of the sierra nevada a clear image of the signal is obtained in time frequency wavenumber space and we discuss in particular observations at 2 5 sec period for events 200 to 300 km outside the profiles from the gross features of uc diagrams we conclude that a representation of lg as a single coherent multi mode wave train is oversimplified in the case of southern california but is more appropriate for the sierra block in southern california peaks observed at group velocities smaller than 3 2 km sec are not predicted by realistic crustal models of the area and are probably due to lateral heterogeneities effects such as mode conversion and multipathing on the other hand for group velocities between 3 2 and 3 6 km sec peaks observed in either area can generally be interpreted in terms of overtones excited at the source and propagating through spatially averaged structures although care must be taken to monitor the stability of the algorithm on actual short period records

foraminiferal response to mid cenomanian upper cretaceous palaeoceanographic events in the anglo paris basin northwest europe we have analysed the sedimentology macrofossil event horizons including pulse faunas and foraminiferal succession 80 samples from an 8 m succession in the upper lower and lower middle cenomanian upper cretaceous at folkestone southeast england comparative sedimentological analysis of successions in southern and northeastern england indicates the presence of three hierarchies of cycle 20 kyr productivity chalk marl couplets cycles attributed to the milankovitch precession cycle 100 kyr sea level cycles attributed to the milankovitch eccentricity cycle and l myr cycles attributed to longer term sea level cycles previously recognised macrofossil pulse faunas occur preferentially at the bases of the 100 kyr eccentricity cycles we analysed the foraminiferal fauna across the lower middle cenomanian boundary at abbott s cliff folkestone in great detail 80 samples in 8 m the foraminiferal succession is also intricately related to the 1 myr sea level and 100 kyr eccentricity cycles changes related to the long term cycles include variations in the abundance of the benthic foraminifera tritaxia gyroidinoides lingulogavelinella and dorothia and an increase in benthic diversity in the transgressive deposits changes related to the 100 kyr eccentricity cycles include the presence of rotalipora ex gr reicheli in the lower part and rarely upper part of cycles the abundance of planktics both absolute and relative in the middle to upper part of cycles an increase in the proportion of gavelinella berthelini and g reussi in the upper part of cycles we present a stratified water column model to explain the changes related to the 100 kyr scale cycle 1998 elsevier science b v

a warm equable cretaceous the nature of the problem abstract the nature of the problem of warm equable paleoclimates is defined by investigating the mid cretaceous period the problem consists of three components 1 defining precisely the climatic state during any specified interval of geologic time 2 specifying the external climatic forcing factors which may have been important and 3 understanding the climatic response to any specific modifying influence these components are characterized by limitations of critical importance in understanding paleoclimates the nature of the problem of a warm cretaceous is defined both qualitatively and quantitatively within these limits

simultaneous inversion for hypocenters and lateral velocity variations an iterative solution with a layered model an iterative inversion technique has been developed that uses the direct p and s wave arrival times from local earthquakes to compute simultaneously a three dimensional velocity structure and relocated hypocenters crustal structure is modeled by subdividing flat layers into rectangular blocks an interpolation function is used to smoothly vary velocities between blocks allowing ray trace calculations of travel times in a three dimensional medium tests using synthetic data from known models show that solutions are reasonably independent of block size and spatial distribution but are sensitive to the choice of layer thicknesses application of the technique to observed earthquake data from north central utah shows the following 1 lateral velocity variations in the crust as large as 7 occur over 30 km distances 2 earthquake epicenters computed with the three dimensional velocity structure were shifted an average of 3 0 km from locations determined assuming homogeneous flat layered models and 3 the laterally varying velocity structure correlates with anomalous variations in the local gravity and aeromagnetic fields suggesting that the new velocity information can be valuable in acquiring a better understanding of crustal structure

paleocene cyclic sedimentation in the western north atlantic odp site 1051 blake nose upper paleocene zone cp8b cyclic sediment from ocean drilling program odp site 1051 on blake nose western north atlantic alternates from white carbonate rich to green carbonate poor in response to precessional forcing compositional differences between the two bed types are minor mineral and nannofossil composition of the beds vary subtly but grain size of the terrigenous component and biogenic silica content remain constant iron content determined by sediment magnetic susceptibility and iron intensity determined by a core scanning xrf correlates negatively with carbonate content and are higher in green beds kaolinite content of green beds is slightly higher as well green beds exhibit lower evenness values than white beds for nannofossil assemblages and are more dominated by the species coccolithus dominance by coccolithus indicates more mesotrophic conditions over blake nose during deposition of the green beds which correlates with slightly higher iron and kaolinite contents the absence of change in terrigenous grain size and the absence of any indication of planktonic blooms indicate that there was a minor most likely eolian input of iron and kaolinite during deposition of the green beds the source area was most likely northwest africa which supplied iron and kaolinite when source areas deflated under drier conditions with this scenario kaolinite is an indi cator of drier climate and source area erosion rather than the warmer and or wetter conditions under which it forms in soils during precessional minima or perihelion summer the opposite of our current configuration there was an increased range of seasonal temperatures and an increase in the intensity of summer and winter monsoon circulation as a consequence there was more rainfall in northern africa and drier conditions in the continental interiors at mid latitudes green bed deposition occurred during precessional maxima when the north atlantic was cooler northwest africa drier and the eolian flux to the western north atlantic slightly increased

sedimentary and geochemical indicators of productivity and oxygen contents in modern and ancient basins the holocene black sea as the type anoxic basin data on the accumulation rates of organic carbon total phosphorus and reduced sulfur over the past 7000 yr from modern abyssal black sea sediments are examined as geochemical monitors of variations in biologic productivity and the development of deep water masses variations in organic carbon accumulation rates at both intermediate and deep water sites are believed to be controlled by the combined effects of enhanced preservation of organic matter under anoxic bottom conditions and the regulation of primary productivity in surface waters by nutrient availability estimates of variations in water column and pore water organic carbon consumption by sulfate reducing bacteria can be made using average carbon and sulfur accumulation rates for various depositional episodes and are examined in the light of changes in the thickness of the h2s zone in the water column the amount of available sulfate within this zone and the reactiveness of particulate organic matter sulfur and phosphorus accumulation rates are used to estimate the maximum amount of phosphorus regenerated from organic matter during bacterial sulfate reduction processes total phosphorus accumulation rates are found to markedly increase over the part 1000 yr and are not proportionally paralled by organic carbon accumulation rates these accelerated phosphorus accumulation rates appear to stem from organic matter degradation adsorption on surfaces of caco3 and perhaps diffusion into sediments from bottom waters and authigenic precipitation of phosphate minerals accumulation rates of organic carbon and phosphorus in black sea sediments are low in comparison to those typical of modern highly productive upwelling zones peru south west africa namibia accumulation rates of reduced sulfur and the ratios of reduced sulfur to organic carbon burial may be higher in anoxic basins than in oxic ones knowledge of accumulation rates therefore rather than concentrations alone may help to differentiate black shales which resulted from enhanced organic matter preservation under anoxic conditions from those resulting from high biologic productivity with or without accompanying oxygen deficiencies

benthic macrofauna variations and community structure in cenomanian cyclic chalk marl from southerham grey pit se england abstract cenomanian chalk marl couplets from england represent the 20 ka milankovitch precession cycle fossil communities from both chalk and marl are identified to test if the orbital fluctuations and the associated changes in substrate lithology and climate exerted any control on the benthic macrofauna the material comprises washing residues of 24 bulk samples collected from chalk and marl half cycles a total of 5055 invertebrate specimens were retrieved and referred to 68 species forming the basis for the recognition of six guilds in general the fauna is more diverse in marl than in chalk but it is remarkable and somewhat surprising that the guild assemblages of marl and chalk show no difference thus the substrate character of the two lithologies did not exert any influence on the modes of life of the benthic fauna in spite of a difference in clay content of about 20 the fauna was clearly well adapted to both facies and thus to the fine grain size of the substrate rather than to lithology the systematic difference in diversity between chalk and marl samples was possibly caused by long term climatic and oceanographic changes and thus could represent a biological response to milankovitch cyclicity