the mid cretaceous earth paleogeography ocean circulation and temperature atmospheric circulation a reconstruction of the global paleogeography of the mid cretaceous 100 m y ago including adjustment of continental outlines to account for microplate movements cmstal shortening and accretion in mid cretaceous and later orogenic regions is described and a map presented on the modified continents coastlines and significant mountain ranges are added this paleogeography is used as a framework for a reconstruction of ocean surface circulation and temperature distribution then the main features of the atmospheric circulation are deduced using the paleogeography and ocean temperatures as boundary conditions relative to the present these features are a much weaker westerly wind belt and greater seasonality of wind patterns leading to more extreme surface climates over the continents slightly equatorward positions of the subtropical anticyclones and monsoonal regimes over the continental margins bordering tethys and the central atlantic a comparison of the results with climatic evidence from t

highly evolved juvenile granites with tetrad ree patterns the woduhe and baerzhe granites from the great xing an mountains in ne china abstract in ne china voluminous granitoids were emplaced in late paleozoic and mesozoic times we report here sr nd o isotopic and elemental abundance data for two highly evolved granitic plutons woduhe and baerzhe from the great xing an mountains they show a rather juvenile sr nd isotopic signature and a spectacular tetrad effect in their ree distribution patterns as well as non charac charge and radius controlled trace element behavior the emplacement ages are constrained at 130 4 ma for the woduhe and 122 5 ma for the baerzhe granites by rb sr and sm nd isotope analyses both granites are also characterized by low but imprecise initial 87sr 86sr ratios of about 0 703 the nd sr isotope data argue for their generation by melting of dominantly juvenile mantle component with subordinate recycled ancient crust this is largely compatible with the general scenario for much of the phanerozoic granitoids emplaced in the central asian orogenic belt the parental magmas for both the woduhe and baerzhe granites have undergone extensive magmatic differentiation during which intense interaction of the residual melts with aqueous hydrothermal fluids probably rich in f and cl resulted in the non charac trace element behavior and the tetrad effect of ree distribution both the woduhe and baerzhe granites show the characteristic trace element patterns of rare metal granites but their absolute abundances differ by as much as two orders of magnitude the oxygen isotope compositions of the two granites have been severely disturbed significant 18o depletion in feldspar but not so much in quartz suggests that the hydrothermal alteration took place in a temperature condition of 300 500 c this subsolidus hydrothermal alteration is decoupled from the late stage magma fluid interaction at higher temperatures despite the two distinct and intense events of water rock interaction the rb sr and sm nd geochronological systems seem to have maintained closed hence suggesting that the two events occurred shortly after the plutonic emplacements

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

a model for granite evolution based on non equilibrium magma separation evidence from the gharib and qattar fluorite bearing granites eastern desert egypt we present 77 new granite whole rock analyses from the qattar and gharib areas eastern desert egypt both areas include a normal granite and either a hypersolvus gharib or an almost plagioclase free granite qattar enriched in fluorite according to earlier results f influences element distribution in granitic melts forming complexes with specific elements as nb ta ga hf th zn sn whereas f excludes ba and sr we use principal component analyses to split the granite into chemical groups allowing an unbiased study of the inter group element distribution this adds the heavy rees and y to the earlier lists of elements with an affinity for f the light rees show a decreasing affinity with decreasing atomic mass fluorine separates sm from nd whereas zr follows la opposite to some but in accordance with other earlier results the ratio nb ta is higher in the fluorite enriched than in the other granite weak tetrad effects are present zircon in the hypersolvus granite is high in common lead we suggest f to be instrumental for separating pb 2 from pb 4 two hypotheses may explain the occurrence of the two contrasting granites they have either different sources or they are co magmatic but the magma was split into two discrete types we apply the second hypothesis as our working hypothesis the liquidus has a gentler slope with pressure than the diapir requiring crystallisation to be most important in the lower part of the magma chamber our hypothesis suggests that globules of magma enriched in volatile components form during crystallisation due to slow diffusion rates in the crystallizing magma elements accompanying f are distributed into this magma batch which has a lowered density and viscosity than the rest of the magma due to its increased contents of volatile components a mushroom formed diapir rises forming the hypersolvus or almost plagioclase free granite due to an edge effect it is concentrated close to the wall of the magma chamber the size and form of the outcropping granite depend on the intersection of the diapir with the erosion surface fluorine only makes it possible to follow the process the model may be generalised to explain the diversification of non f enriched granite since the buoyancy of a magma batch several thousand m 3 in size has a much larger impact on the system than the small negative buoyancy of crystals or small crystal aggregates a type granite classified merely from its trace element content may form from separated f enriched magma batches this may be the reason for their high frequency in the eastern desert

palaeoenvironmental analysis of late cretaceous dinoflagellate cyst assemblages using high resolution sample correlation from the western interior basin usa abstract the cretaceous geological record of the western interior seaway of north america is one of the most thoroughly studied in the world extensive work on the lithostratigraphy biostratigraphy and geochemistry has resulted in a high resolution chronostratigraphic framework allowing precise bed by bed correlation between sections hundreds of kilometres apart late cenomanian to early turonian marine strata from five sites along a transect from arizona to kansas have been analysed for their palynological assemblages at the time of deposition the sites are thought to have been palaeoenvironmentally very different in terms of shoreline proximity bathymetry and salinity precise correlation of samples between the sites using the high resolution stratigraphy has provided a valuable testing ground for a comparison of the dinoflagellate cyst assemblages a number of species are determined to have palaeoenvironmental preferences in terms of salinity and shoreline proximity and this is supported by integration with the lithostratigraphy macropalaeontology micropalaeontology and geochemistry previous palaeoenvironmental interpretations suggest that one kansas site had comparatively much higher levels of primary productivity and this is reflected in the high ratio at this site of peridinioid to gonyaulacoid cysts the high resolution correlation also shows that a number of the biostratigraphically useful dinoflagellate cyst taxa had synchronous or near synchronous range tops and bases across the basin this integrated high resolution study with tight chronostratigraphic control supports the use of dinoflagellate cysts not only as biostratigraphic tools but also for palaeoenvironmental and palaeoecological interpretation

sediment resuspension mechanisms in old tampa bay florida the mechanisms that resuspend bottom sediments in old tampa bay a shallow microtidal subtropical estuary in west central florida were determined by analysing data collected during several periods from 1988 to 1990 hydrodynamic and suspended solids concentration data were collected at a relatively deep 4 m site where a permanent platform was built and at a relatively shallow 1 5 m site where a submersible instrument package was deployed bottom sediments were non cohesive silts and fine sands the primary sediment resuspension mechanism at both sites was wind waves which were generated by strong and sustained winds associated with winter storms and tropical storms at the platform waves were depth transitional and estimated bottom shear stresses were most sensitive to wave period and water depth concentrations of suspended solids at this site corresponded well with wave motion and non linear wave current interaction was small at the shallow water site concentrations of suspended solids were elevated during periods of strong north easterly winds and large bottom orbital velocities at both sites wind direction was an important factor in determining the occurrence and magnitude of sediment resuspension resuspended sediments settled within several hours as storm intensity diminished winds and waves generated by thunderstorms were more transient than those generated by winter storms and tropical storms based on the data collected during this study thunderstorms are less likely to resuspend bottom sediment than winter storms and tropical storms maximum tidal currents at the study sites are usually less than 15 cm s 1and did not increase observed concentrations of suspended solids

origin of shore normal channels from the shoreface of sable island canada a suite of modern shore normal channels was discovered on the southern shoreface of sable island canada repetitive multibeam and sidescan surveys of these features as well as box coring and sampling showed that the depressions were perennial features of the shoreface they occurred in fine and medium sand and were most abundant in depths less than 20 m they were up to 1 m deep and 50 m wide increased in size seawards and generally followed the seabed slope the channels dominated the inner shoreface becoming wider and deeper seawards to depths in excess of 40 m there is a continuum of scales in width and depth of these channels the smallest of which are equated with gutters preserved in the geological record the internal structure of the shoreface sediments where the gutters are found is characterised by normally graded tempestites composed of cut and fill structures overlying an erosion surface thus the environmental setting internal structure and scale are similar to ancient counterparts gutters have been interpreted to result from downwelling over palaeo shorefaces during ancient storms myrow 1992b the composition of gutter infill as well as the stability evolution associated bedforms and hydrodynamic conditions under which they formed were examined to verify genetic interpretations of the ancient counterparts the multi sensor benthic lander ralph was deployed within a field of shore normal channels for 17 days during late winter 1998 ralph burst sampled flow at hourly intervals whilst imaging the seabed resulting sequential imagery revealed the genesis of a group of five gutters during storm spin down that was coincident with the formation of large scale wave ripples this was followed by infilling of the gutters and wave ripple destruction within 20 hours by longshore sand transport the gutters were located within and parallel to a larger channel 50 m wide and 0 50 m deep they were formed by coastal set up and subsequent downwelling that was triggered by the rotation of storm winds from seawards onshore wind to landwards offshore wind the gutters formed within 2 to 3 hours during spin down of a winter storm under live bed conditions of sand transport wave height and mean tidal flows were well below those of the storm peak and so they were not directly responsible for creating the gutters the mechanism we propose for the evolution of gutters supports the geological interpretations that is a storm driven downwelling event as described by swift and niedoroda 1985 however the downwelling event appeared to take place suddenly rapid acceleration in flow briefly few hours duration and within narrow corridors guided by wider and deeper channels of the shoreface high turbidity during the time of gutter formation leads us to believe that the phenomenon of inner shelf turbidity currents as suggested by walker 1985 exists and may be instrumental in channel formation

sediment transport over an accretional intertidal flat with influences of reclamation jiangsu coast china this paper focuses on the hydrodynamic and suspended sediment transport processes in response to sequential reclamations over the intertidal flat jiangsu coast which used to be one of the widest intertidal flats in china investigations into the sediment transport patterns reveal that net suspended sediment fluxes increased from 102 kg m 1 on the upper intertidal flat to 103 4 kg m 1 on the lower intertidal flat per tidal cycle this variation was caused mainly by the phases of the current velocity suspended sediment concentration ssc local bed geomorphology inundation patterns and extreme weather conditions the longshore component of tidal currents intensifies seaward over the intertidal flat extreme weather conditions e g storms and strong winds were important factors affecting the current velocity structures the intensity of residual currents and the sscs the sscs were characterized by several peaks throughout the tidal cycle these peaks were associated with strong currents combined wave current interactions and intense turbulences due to the initial flood surge furthermore the suspended sediment was finer and contained more clay materials during the flood phase of the tidal cycle than during the ebb fine particles were transported within the upper water column by landward residual currents but coarse particles were transported within the lower water column by seaward residual currents overall residual currents were apt to transport fine grained sediment landward and coarse grained sediment seaward this pattern indicates that the suspended sediment fluxes are highly variable in the water column even for very shallow tidal environments the cross shore component accounted only for a small percentage of the total sediment flux however this part of sediment supply dominated accretion over the intertidal flat the intertidal flat has become narrower and steeper following sequential reclamations a negative feedback process existed to maintain the convex profile shape although the human activities i e reclamation could have modified the natural process the surficial sediment tended to become finer on the mid upper intertidal flat but coarser on the lower intertidal flat following reclamations in response to a reduction in the tidal currents over the intertidal zone and enhancement of wave action over the lower intertidal flat accretion with high rates was maintained by landward transport of sediment in such an accretional system with influences of reclamation the width or slope of the intertidal flat is adjusted continuously before the cease of reclamation the intertidal flat is unable to achieve an equilibrium shape

control of estuarine sediment dynamics by interactions between currents and waves at several scales abstract the effect of interactions between continuous tidal currents and intermittent waves processes on sediment dynamics and transport is addressed by presenting detailed field measurements of waves boundary layer currents and suspended sediment from an estuarine channel and an adjacent intertidal sandflat in manukau harbour new zealand the aim is to determine in what ways it is necessary to couple waves and currents in numerical models and thereby put limits on the fundamental structure of process based estuarine sediment transport models waves were important on the intertidal flat turbidity switched on and off with the appearance and disappearance of waves wave groups dominated entrainment of bed sediment a wave current boundary layer model explained measured bed shear stress and hydraulic roughness and the measured near bed time averaged suspended sediment concentration was mostly well predicted by a pure wave model both the waves themselves and wave related processes varied markedly over the tidal cycle the variation in the former principally changes in wave height was related to changes in fetch caused by the harbour wide emergence and submergence of intertidal regions the variation in the latter was related to changes in water depth relative to the wavelength of the waves which controlled the penetration to the bed of wave orbital currents in addition to the variation over the tidal cycle in the intensity of wave processes there was also a change in kind which occurred with the arrival at the measurement site of the turbid fringe which is the narrow highly turbid edge of the estuarine water body the relationship between suspended sediment concentration and wave orbital velocity in the turbid fringe was radically different to the relationship in the estuarine water body proper which suggests a change in dynamics perhaps related to breaking waves a hybrid modelling approach is required i e one that treats discrete events but resolves tidal cycle scale variation within the event there is a need to resolve the variation in the wave train over the tidal cycle and the penetration to the bed of wave orbital motions both of which could only be done adequately within an estuary tidal model in contrast to the situation on the intertidal flat where waves intermittently entrained sediment sediment transport in the channel was continuous driven by tidal currents to predict sediment flux in the channel we need to know the upstream sediment transporting capacity of the flow including that contributed by waves the character of the bed sediment and the sediment settling time scale these factors confounded even the simplest notion of flood and ebb dominance which frequently has been applied to understand estuarine morphodynamics

seabed stresses in combined wave and steady flow conditions on the nova scotia continental shelf field measurements and predictions abstract a tripod holding electromagnetic flowmeters at two heights within 1 m above the seabed has been deployed at two shallow sites 25 and 45 m depths on the continental shelf off nova scotia canada wave flows are comparable with the small mean flows at both sites friction velocities have been estimated from the observed spectra of vertical turbulent velocities using a modification of the dissipation method appropriate to low reynolds number conditions the results from each site show no significant change of friction velocity with height as expected for measurements from within the constant stress layer however in each case the observed friction velocities are considerably larger than would be predicted on the basis of the observed bottom roughness and the mean flows alone indicating that the wave flows were important in enhancing the friction velocity the theory of grant and madsen 1979 has been used to predict the friction velocities based on the observed mean and wave velocities and o

exsolution of magmatic volatile phases from cl enriched mineralizing granitic magmas and implications for ore metal transport abstract to understand cl dissolution in aluminosilicate liquids and the exsolution of cl rich magmatic volatile phases experiments were conducted to determine the solubility of nacl kcl and h2o in felsic liquids at 0 5 and 2 kbar the cl content of h2o poor nacl saturated and kcl saturated silicate liquids is low i e 1 3 wt to very low i e 0 2 wt and varies with changes in pressure and composition the cl concentration increases with the f concentration and the molar al na ca mg si ratio of the liquid and decreases with increasing activity of h2o in the system exsolution of a volatile phase depends on the partial pressures of all dissolved volatiles and low cl solubilities in nacl saturated and kcl saturated silicate liquids imply that exsolution of a cl bearing volatile phase will occur early in cl bearing granitic magmas i e prior to extensive melt crystallization and or at comparatively low water fugacities the solubility behavior of h2o and cl is very similar to that of co2 and h2o in felsic liquids small quantities of co2 are known to facilitate volatile phase exsolution holloway 1976 and in a similar manner volatile phases may exsolve early in cl enriched granite magmas whereas 5 to 6 wt dissolved h2o is necessary for volatile phase exsolution from a co2 free and cl free haplogranite liquid at 2 kbar and 800 c a cl rich brine will exsolve if the liquid contains only 1 wt h2o and 0 26 wt cl at the same conditions these new solubility data are interpreted in light of h2o f and cl concentrations in felsic liquids determined from silicate melt inclusions to constrain the exsolution of cl bearing magmatic volatile phases from mineralizing granitic magmas felsic magmas genetically associated with cu porphyry and mo porphyry mineralization contain sufficient h2o and cl to become saturated with respect to a hypersaline brine without strong pressure reduction boiling of the volatile phase i e exsolution of immiscible vapor and brine or strong volatile enrichment resulting from extensive crystal fractionation experiments were also conducted to investigate the solubility of mo in highly saline volatile phases coexisting with granitic liquids at 2 and 0 5 kbar the apparent partition coefficient for mo in the volatile phase s relative to silicate liquid d mo is defined as the computed concentration of mo in a volatile phase or phases the measured concentration of mo in granite glass d mo ranges from 8 to 80 as the nacl and kcl content of the volatile phase s increases from 15 to 90 wt because mo does not complex with cl in aqueous fluids it appears that mo solubility may be a strong function of the activity of na and k in alkali chloride rich volatile phases

influence of paleoenvironmental factors on preservation of organic matter in middle cretaceous greenhorn formation pueblo colorado sedimentological and geochemical studies of the upper cretaceous hartland shale and overlying bridge creek limestone members of the greenhorn formation reveal close associations between abundance of current induced sedimentary structures extent of bioturbation and type of preserved organic matter abundant hydrogen rich organic matter 4 5 wt and low sulfur to organic carbon ratios are characteristic of the laminated facies which lack current induced sedimentary structures sparse hydrogen poor organic matter 0 1 0 5 wt and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies which contain numerous sedimentary structures indicative of currents the concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively by currents rather than by the rate of oxygen consumption by decomposition thus paleoclimatic and paleo oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units it is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen depleted bottom water and high preservation of organic matter thus accounting for the intermittent widespread deposition of organic rich strata during maximum transgression and depth of the greenhorn sea the lateral association of voluminous deltaic deposits with dee water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the hartland shale and bridge creek limestone members

anoxic events productivity rhythms and the orbital signature in a mid cretaceous deep sea sequence from central italy albian pelagic sediments from the umbrian apennines exhibit rhythmic bedding in outcrop high temporal resolution 4 kyr spacing sampling of carbonate si and al along a 1 6 m y interval of core demonstrates that changes in accumulation rate of calcareous and siliceous microorganisms were controlled by insolation cycles optical densitometry logging correlates variations of geochemical parameters to episodes of deep sea anoxia indicated by numerous black laminated zones black shales harmonic analysis of data shows oscillations at three frequencies which correspond closely in estimated duration and ratio to the modern eccentricity and precessional orbital cycles as in pleistocene marine sequences the eccentricity approximately 100 kyr term dominates the sedimentary variance in the umbrian cycles anoxic episodes occur in phase with a limestone marl repetition and reflect minima of the precessional 21 kyr cycle the covariance of carbonate and silica with estimates of foraminiferal abundances suggest that carbonate cycles are the result of changes in surface productivity of calcareous organisms rather than an effect of dissolution or diagenesis recognition of orbital cyclicity provides a tool for making quantitative estimates of these changes productivity during anoxic events was uniformly low 0 4 0 5 g cm2 kyr carbonate 0 05 g cm2 kyr silica but it rose to high levels during oxygenated periods 1 2 5 g cm2 kyr carbonate 0 1 0 3 g cm2 kyr silica vertical overturning and organic carbon flux decreased during anoxic episodes but decreased oxygenation of the deep water led to enhanced preservation of the organic matter delivered the degree of paleoceanographic variability indicated by this study requires that accepted notions of climate stability and oceanic quiescence during nonglacial times be reassessed

organic rich sedimentation at the cenomanian turonian boundary in oceanic and coastal basins in the north atlantic and tethys one of the most striking results of the deep sea drilling project is the proof that organic rich sediments have a widespread geographical distribution during the period from upper cenomanian to middle turonian such sediments were drilled at north atlantic dsdp sites 105 135 137 138 367 398 551 603 they are also present from outcrops or oil wells on the shelf of the african continental margin senegal tarfaya and agadir basins in the tethys former alboran block southern spain algeria tunisia and umbrian apennines italy and in the north sea although these sediments have different lithologies and depositional environments from shelf areas to the deep sea their study mainly based on organic geochemistry with additional data on sedimentology biostratigraphy and palaeo bathymetry suggests that a unique pulse of organogenic accumulation characterizes the cenomanian turonian boundary event ctbe the content and type of organic matter are related to the depositional environment and organic preservation the organogenic accumulation is distributed according to various trends off the african continental margin the organic content increases from onshore areas to the shelf casamance area and moreover increases also in deep sea areas with a gradual transition from terrestrial type iii to marine type ii the best preservation of the organic matter being in the deepest areas i e site 367 off the american continental margin site 603 shows the same toc and type of organic matter as at site 105 the ctbe is also well recorded in the northern part of the atlantic celtic margin north sea by a drastic lithological change black shales within chalks but the type of organic matter is mainly terrestrial in the tethyan area the organic matter is of marine origin and well preserved results are compared with those of pratt 1984 from the western interior basin of the usa different hypotheses to explain this synchronous widespread accumulation of organic matter are discussed 1986 the geological society

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

hunting for paleoclimatic periodicities in a geologic time series with an uncertain time scale an 8 m section of a mid cretaceous albian deep sea sediment core from piobbico italy contains 2 cycles m compositional oscillations as postdepositional chemical migration in the core is weak the relative amount of carbonate is a primary indicator of cretaceous paleoclimate variability we report results of spectral analysis of two series caco3 wt measurements taken at roughly 2 cm intervals and a more densely sampled photodensitometer record of light dark variation the uncertainty in the age depth relation i e unknown fluctuations in sedimentation rate hampers a detailed assessment of the suggested eccentricity correlation we fit for long term time scale greater than 75 kyr fluctuations in sedimentation rate by tracking the local frequency modulation of the dominant harmonic in the data series assuming the true input signal to be monochromatic we estimate uncertainty in the observed local frequency by means of a statistical jackknife we fit a smoothed cubic spline to the set of discrete frequency modulation estimates specifying a 2 n misfit criterion where n is the number of frequency estimates from this analysis we infer fluctuations of a factor of two in the sedimentation rate which occur predominately on a time scale of 400 kyr we generate tuned series using several candidate age depth relations from the carbonate and densitometer series the tuned carbonate series returns greater correlation with the modern milankovitch periodicities the 2 cycles m energy resolves principally into two harmonic components whose frequency ratio corresponds to an observational accuracy of 1 2 to that of the 97 0 and 127 6 kyr eccentricity oscillations at frequencies lower than 2 cycles m we find harmonic oscillations whose phase correlates with the beating envelope of the 2 cycles m energy in a manner consistent with the modern milankovitch insolation we also observe a sinusoidal oscillation of lower amplitude with period scaled by those of the presumed eccentricity oscillations of 39 2 1 1 kyr which agrees with the period of the modern obliquity cycle after correction for the effects of tidal friction oscillations corresponding to milankovitch precessional frequencies are not established owing possibly to low signal level and unknown short term deposition fluctuations the tuned densitometer series recovers few new periodic features although its inferred age depth relation correlates well with that of the carbonate series we calibrate the depth variable downcore to the orbital cycles to estimate r 5 0 0 15 m m y as the effective sedimentation rate

the coastal depositional system of a small mountainous river a perspective from grain size distributions abstract tseng wen river is a small mountainous river on a wave dominated coast of taiwan the spatial distribution patterns of 17 individual grain sizes offshore near the river mouth show strong morpho textural relationships with the bathymetry which also vary considerably according to the grain size the influence of seven hypothetical factors that could affect the observed grain size patterns were examined individually by using a methodology that combines filtering concept and a multivariate analysis technique eof these factors include the sediments discharged by the river offshore palimpsest sediments sediments eroded from a submarine sand ridge and the remnant river delta the effect of wave sorting and the northward and southward littoral drift the study results indicate that the tseng wen river is the most important source for modern sediments in the study area the reworking of offshore palimpsest sediments is also an important sediment source the agitation by waves is an important sorting mechanism in the study area and the net sediment transport in the study area is northward the findings based on grain sizes are also corroborated by short term observations of the near bed sediment dynamics and transport during the flood season of the tseng wen river

measuring suspended sediment concentrations using acoustic backscatter devices abstract in recent years the requirement to develop a technique for measuring suspended sediment concentration profiles with similar temporal and spatial resolution to that of electromagnetic current meter measurements of the flow has led to the development of an acoustic approach acoustic backscatter devices have been constructed and deployed in marine environments and measurements of backscattered signal profiles obtained however the translation from acoustic returns to suspended load has been an empirical procedure resulting in some uncertainty regarding the accuracy and reliability of the conversion process to address this problem a series of laboratory measurements of acoustic backscattering from marine suspensions were conducted using two acoustic backscatter instruments operating at 3 0 and 5 65 mhz a simple semi empirical backscattering theory has been developed to predict the form of the scattered signal and comparisons have been made of the concentrations predicted from the theory against concentration measurements made in laboratory tanks the results show that the main features of the backscattering signal can be explained and accurate concentration estimates can be made from the acoustic returns it is concluded that acoustic backscatter techniques are potentially powerful tools for examining at high resolution the structure of suspended sediment concentration profiles near the seabed

the importance of combined tidal and meteorological forces for the flow and sediment transport on intertidal shoals estuarine intertidal areas are shaped by combined astronomical and meteorological forces this paper reveals the relative importance of tide surge wind and waves for the flow and sediment transport on large intertidal shoals results of an intensive field campaign have been used to validate a numerical model of the roggenplaat intertidal shoal in the eastern scheldt estuary the netherlands in order to identify and quantify the importance of each of the processes over time and space we show that its main tidal creeks are not the cause for the dominant direction of the net flow on the shoal the tidal flow over the shoal is steered by the water level differences between the surrounding channels also during wind events the tidal flow enhanced by surge is dominant in the creeks in contrast wind speeds of order 40 times the typical tidal flow velocity are sufficient to completely alter the flow direction and magnitude on an intertidal shoal this has significant consequences for the sediment transport patterns apart from this wind driven flow dominance during these events the wind also increases the bed shear stress by waves for the largest intertidal part of the roggenplaat only 1 10 of the yearly transport results from the 50 least windy tides even if the shoal is artificially lowered half the tidal range this dominance of energetic meteorological conditions in the transports matches with field observations in which the migration of the creeks and high parts of the shoal are in line with the predominant wind direction

the late cretaceous western interior seaway as a model for oxygenation change in epicontinental restricted basins abstract deoxygenation is a critical problem facing the ocean as the world warms and has the potential to effect coastal upwelling zones shelf areas influenced by high runoff and nutrification and restricted and semi restricted basins the mechanisms that drive deoxygenation in these diverse environments are still not fully understood in part because the modern record of redox change is short and anoxia is still relatively rare in the modern ocean here we address this problem of scale by studying deoxygenation in the geologic past we summarize decades of individual studies of benthic foraminifera to generate a record of bottom water oxygen change in the cretaceous western interior sea wis of north america over 13 myr cenomanian campanian spanning two major sea level cycles the wis was prone to major changes in dissolved oxygen content throughout its long history sometimes directly antiphase to trends in the global ocean presented as maps our data show that bottom water oxygen within the wis was controlled by a combination of water mass source and mixing moderated by sea level and basin restriction areas flooded by cool boreal northern sourced waters in the northern and western parts of the seaway were better oxygenated than the eastern and southern portions of the seaway which were flooded by warmer tethyan southern sourced waters beyond east west differences explained by water mass the entire seaway was better oxygenated during periods of transgression and more poorly oxygenated to anoxic during periods of peak transgression highstand and regression we suggest that this pattern was due to the formation and downwelling of western interior intermediate water by the mixing of tethyan and boreal waters during transgressions an increasing volume of these watermasses entered the seaway mixed and downwelled well oxygenated surface water to the seafloor during late transgression highstand partial stratification and the encroachment of low oxygen waters from the open ocean caused dissolved oxygen levels to drop at the seafloor but continued downwelling prevented anoxia during the subsequent regression a decline in the volume of outside watermasses entering the seaway caused a reduction in mixing and weakened downwelling which led to stratification and seafloor anoxia as a model for other semi restricted basins the trends observed in the wis show that local changes in relative sea level mixing and circulation are critical in controlling oceanic deoxygenation in these environments in clear contrast to continental margins impinged by oxygen minimum zones like the contemporaneous demerara rise in the southern caribbean although the wis is larger than most semi restricted basins it is characterized by quasi estuarine circulation driving the interaction of normal marine and brackish watermasses and thus serves a model for similar shallow epicontinental basins of any size understanding how these processes vary in different environments is key to predicting susceptibility of regional water bodies to deoxygenation in the future with a warming world

strong localised country rock contamination and partial homogenisation of a mafic magma an example from west central sweden a dolerite sill cutting slightly older basalt in west central sweden shows a strong chemical variation 54 sio2 73 within a restricted area 100x100 m 2 the linear correlation among almost all elements is extremely high in addition epsilon ndt is strongly correlated with the sio2 content least square hyperbolic ratio and three element ratio modelling common denominator suggests that most of the chemical variation is explained by mixing and or micro mingling in all we test 407 hyperbolas of which 402 are fitted the five ratio pairs which could not be fitted to a hyperbola using a least square fitting procedure have the ratio th eu in common testing the goodness of fit is problematic for hyperbolic distributions for comparing purposes we 4 sum the distances to chords approximating the hyperbola mobile and immobile elements behave similarly suggesting that no a elements are lost or added from outside the system the data suggests that already the most mafic of the analysed rocks is a mixture of the normal dolerite and a siliceous crustal rock a mafic magma intruded into the base of the crust where it fractionated resulting in a decreased mg number the magma was then contaminated with country rocks in an intermediate magma chamber due to country rock melting during mixing mingling almost no fractionation took place the contaminated rock suggests the presence of a fluid phase this was probably a prerequisite for country rock melting enrichment in some incompatible elements suggests that besides major mixing mingling a thermochemical separation process has affected the most felsic rock enriching it in light rare earths and zr less

nearly contemporaneous evolution of the a and s type fractionated granites in the krusne hory erzgebirge mts central europe abstract the krusne hory erzgebirge mountains is one of the best known provinces of granite magmatism and associated metallogenesis in europe variscan magmatic activity in the krusne hory erzgebirge area spanned the period from 330 to 295 ma for much of this time two types of magma were generated and emplaced in close proximity in this province strongly peraluminous p rich s type melts were formed alongside slightly peraluminous p poor melts a type two suites of strongly peraluminous p f li rb cs u sn rich and zr th y hree poor magmas were intruded in rapid succession over a period of about 10 ma about 330 320 ma over the entire region of the krusne hory several peraluminous rhyolitic dykes near gottesberg mark an isolated event at about 295 ma slightly peraluminous f li rb cs sn zr y hree rich and p poor magmas were intruded in several events separated in space and time 325 295 ma both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions accompanied by explosive brecciation and followed by sn w mineralization of greisen type successive volcanic eruption of rhyolites and dacites of s type and rhyolites of a type form the fill of the altenberg teplice caldera atc thus demonstrating the close temporal and spatial relationship between these two types of magma when these two geochemically distinct types of rock are in direct contact then the rocks of a type are always younger the absolute time difference between the two types can range from less than 1 ma the first eruption of the teplice rhyolite versus the schonfeld dacite in the atc to about 15 ma eruption of rhyolites at gottesberg versus emplacement of the eibenstock granite the assumed protolith of all late variscan granites in the area of krusne hory erzgebirge is a mixture of fertile quartzo feldspathic rocks with micaceous metapelites enriched in lile and sn w the differences in chemical composition of s and a type melts originated from local changes in the proportion of quartzo feldspathic and pelitic lithologies different pt conditions of melting the degree of melting and the degree of metamorphic dehydratation of the protolith prior to the melting

morphological responses of an estuarine intertidal mudflat to constructions since 1978 to 2005 the seine estuary france abstract since 1834 the seine estuary france has been the site of numerous construction projects with the aim to accommodate and secure boat traffic since 1978 the increasing of the activities of le havre port located at the mouth of the estuary has accelerated the construction work rate several dykes a bridge and new port facilities have been constructed in rapid succession modifying considerably the hydrodynamic conditions which sustain a partially vegetated sandy muddy tidal flat located in the north bank of the estuary between the new port of le havre and the normandy bridge achieved in 1995 the present study deals with the morphological evolution of this zone from 1978 to 2005 the use of a low altitude remote sensing technique combined with traditional methods of ground survey and probes allow to demonstrate the impact of human activities on sedimentary and vegetation dynamics the northern mudflat of the estuary is the most affected by these human activities which surface have reduced of 62 during the last 27 years with an intensified local erosion during the last 27 months corresponding to a loss 1 250 000 m 3 of fine grained sediment at the same time the general sanding up in the channel of the zone has caused a loss of more than 31 of the tidal prism more than three quarters of which occurred during the last three years results also establish that the response times of the sedimentary or topographic readjustment to an installation depend on the extent and the nature of the construction in fact the sedimentary readjustments to an installation can be delayed by up to 10 years in the case of the seine estuary this delay is explained by a rapid succession of construction works which may occult the effect of a single installation except in the case of a dyke built perpendicular to ebb and flood currents the impacts of these installations reach a hydro sedimentary equilibrium on the level between 1 and 7 years after their completion

geometry of upper cretaceous bentonite beds implications about volcanic source areas and paleowind patterns western interior united states four bentonite beds near the cenomanian turonian stage boundary ca 90 ma can be traced through much of the western interior of the united states isopach maps constructed for these bentonite beds indicate that volcanic source areas were positioned both northwest and southwest of the central u s western interior basin and also indicate both easterly and southeasterly paleowind directions volcanism of this age has not been reported previously in the southern source area

early diagenesis and its relationship to depositional environment and relative sea level fluctuations upper cretaceous marshybank formation alberta and british columbia early diagenesis of the upper cretaceous late coniacian to early santonian marshybank formation was controlled by depositional environment composition of depositional water fe and organic content of the sediment sedimentation rate proximity to the shoreline and influx of meteoric water related to relative sea level fall five depositional environments each characterized by a distinct early diagenetic mineral assemblage have been recognized offshore shelf sediments that were deposited in a dysaerobic environment are characterized by abundant framboidal pyrite and rare septarian concretions composed of early calcite and siderite intense sulphate reduction promoted by the dysaerobic depositional water was the primary influence on early diagenesis offshore shelf sediments deposited under aerobic conditions are characterized by abundant concretions composed of two generations of siderite s1 and s2 in this environment methanogenesis rather than sulphate reduction was more important early diagenesis of the inner shelf sands was generally limited however in sands deposited proximal to the shoreline mixing of marine and meteoric waters promoted crystallization of fe rich chlorite and siderite the shoreface was characterized by dissolution of detrital minerals in the upper portion and precipitation of kaolinite or illite smectite in the lower portion in the coastal plain environment brackish water and early reducing conditions resulted in formation of abundant euhedral pyrite ankerite rather than siderite is the typical early diagenetic carbonate the 18o values of the earliest cements i e early calcite siderite s1 inner shelf siderite indicate crystallization from a low 18o marine derived porewater assuming crystallization at 25 c a 18o value of about 7 smow can be estimated for the seaway during marshybank formation time similar calculations for the overlying dowling member puskwaskau formation suggest that the 18o value of the seaway increased to about 4 smow consistent with its transgressive nature very low 18o values are exhibited by siderite s2 these results indicate crystallization during intermediate diagenesis 60 c from meteoric water 15 smow that entered the marshybank formation during sea level lowstand

tetrad effect in rare earth element distribution patterns a method of quantification with application to rock and mineral samples from granite related rare metal deposits abstract in some geological environments the tetrad effect can be observed as a split of rare earth element ree patterns into four rounded segments a new method is proposed to quantify the sizes of the individual segments and for the first time the significance of observed tetrad effects is evaluated by taking analytical errors into account the outlined method was applied to lanthanide patterns of whole rock and fluorite samples collected from granite related rare metal deposits the ree patterns of the granite and greisen samples investigated exhibit significant tetrad effects that may not be accounted for by analytical uncertainties it is shown that the study of whole rock samples is insufficient to determine whether this effect is developed during fractional crystallization or is due to other processes such as fluid rock interaction a concave tetrad effect mirroring the pattern of the whole rock samples was not observed in the ree patterns of related vein fluorite samples therefore it is unlikely that the convex tetrad effect in the samples from the magmatic environment can be explained by removal of a respective complementary ree pattern by a coexisting hydrothermal fluid as previously suggested it is proposed that the tetrad effect formed within the magma fluid system before emplacement in the subvolcanic environment where phase separation caused a split of this system into fluid and magma subsystems alternatively the tetrad effect may also be inherited from an external fluid influencing the system during or after the emplacement of the magma on the basis of the fluorite data it is shown that the behavior of eu in the fluids is not related to the tetrad effect consequently different physico chemical factors control the occurrence of both phenomena y was found to be strongly enriched in samples precipitating from hydrothermal fluids that experienced prolonged interaction with the wall rocks whereas the tetrad effect in the fluids vanished with time and increasing distance from the ore bearing granite thus these different geochemical parameters can be used to reconstruct different aspects of the fluid evolution within this type of deposit

an initial study of the sensitivity of modeled cretaceous climate to cyclical insolation forcing some cretaceous rhythmic sedimentation such as the colorado greenhorn formation deposited in the western interior seaway u s may have been produced by cyclic precipitation intensity change responding to orbitally produced insolation forcing to test this hypothesis a general circulation model was forced with the seasonal maximum and minimum insolation calculated from assumed cretaceous orbital parameters geographic comparisons for july and january of surface temperature surface pressure and precipitation were prepared for january maximum land sea contrast produced an increase of more than 6 mm day precipitation over the interior seaway however the july maximum simulation did not produce precipitation increase despite an anticipated monsoonlike circulation over the region north america appears to be very arid during cretaceous northern hemisphere summer

the significance of palynofacies fluctuations in the greenhorn formation cenomanian turonian of the western interior basin usa abstract in the greenhorn limestone formation of the pueblo section colorado the palynofacies in the hartland shale member is remarkably homogeneous this is in marked contrast to that of the overlying bridge creek limestone member in which the alternating limestones and marlstones are characterized by rhythmic variations in the terrestrial phytoclasts such variations appear to be related to milankovitch cycles as well as to both the dilution and productivity models the marine palynofacies includes three dinocyst associations and scytinascia foraminiferal linings changes in the marine palynofacies do not appear to be related to the cyclical limestone marlstone deposits however the alternating dinocyst associations suggest mesotrophic oligotrophic rhythms in the surface waters the discrepancy between the dinocyst cycles and the lithological couplets could reflect the modulation of the sea level rises in the milankovitch frequency band by a barrier during deposition of the hartland shale member within the second order t6 transgression of kauffman the discrepancies between the foraminifer nannofossil and dinocyst fluctuations are interpreted as reflecting specific responses by each planktic group to global oceanographic changes and diagenesis

aluminous granite as a source magma of hydrothermal ore deposits an experimental study partition ratios of zinc and lead between synthetic granitic melts and aqueous phase were determined at 800 degrees c and under p sub h 2 o 3 5 or 0 25 kb two starting glasses in the system sio 2 al 2 o 3 cao na 2 o were prepared their bulk chemical compositions are similar i e sio 2 content of 75 65 percent in glass 1 and of 74 68 percent in glass 2 glass 1 is prepared to be slightly alkaline with 1 89 percent normative wollastonite and glass 2 is slightly aluminous with 2 42 percent normative corundum the partition ratio of sodium between aqueous fluid and melt k p na can be expressed by the following equation over the whole range of chloride concentrations in the aqueous solution m v cl mole kg regardless of the normative composition of the melt k p na 0 468 x m v cl however the partition ratio of zinc k p zn for the aluminous melt is more than two orders of magnitude larger than that for the alkaline melt k p zn varies with the square of the chloride concentration in the aqueous phase and is satisfied by the following two equations k p zn 9 40 x m v cl 2 aluminous melt 2 and k p zn 0 0833 x m v cl 2 alkaline melt 1 a similar contrast was also observed in the partition ratios of lead between aqueous phase and melts k p pb 2 26 x m v cl 2 aluminous melt 2 and k p pb 0 0474 x m v cl 2 alkaline melt 1 the log of the partition ratio shows an excellent inversely proportional relation with the ph at 25 degrees c of the aqueous solution which was equilibrated with granitic melts and quenched a slope of 2 is obtained for alkaline melt and is reasonably explained by the equation pbo melt 2h super vapor 2cl super vapor pbcl sub 2 vapor h 2 o the slope for the aluminous melt 1 2 may be explained only by complex reactions involving silicate ligands in the melt the results indicate that only aluminous granite is capable of producing hydrothermal fluids which would contain a significant amount of ore metals in other words aluminous granite can be ore bearing by postmagmatic processes this is likely to happen when a granitie magma which originally was slightly alkaline changed its composition to slightly aluminous during diapiric uplift by assimilation of pelitic sediments if this compositional evolution happened then granitic magma would tend to store up base metals during the early stages of its evolution and release them very efficiently in the later stages to form a hydrothermal ore solution

geochemical anomalies at the cenomanian turonian boundary northwest new mexico a high resolution section of 64 carbonates and calcareous shales from northwest new mexico spanning the cenomanian turonian c t boundary is examined for selected elemental concentrations as well as carbon isotopic and molecular distributions spatial and temporal sampling resolutions for the entire sample set are 1 spl 19 cm and 1 spl 33 ka respectively in proximity to the c t boundary respective spatial and temporal resolutions increase to 1 spl 10 cm and 1 spl 17 ka results show the occurrence of several geochemical anomalies all with coincident maxima at about 0 5 m below the c t boundary stable carbon isotope ratios of the kerogen and the aliphatic and aromatic hydrocarbon fractions increase by approximately 4 within 20 m of the boundary this entire c t boundary event isotope anomaly occured over approximately 2 5 ma a 5 fold increase in the concentrations of u and th occurs synchronous with the isotope excursion although this u th spike occurs over a period of only 0 2 0 3 ma elevated u and th concentrations at this spike co occur with a the highest 20s 20s 20r sterane epimer ratios b c27 c27 30 sterane homolog ratios and c the lowest n alkane yields in kerogen pyrolyzates these observations suggest an effect of radiogenic heat production on the organic matter in the section the origin of the carbon isotope excursion is attributed as in previous studies to atmospheric co2 drawdown in latest cenomanian time caused by rapid burial of organic matter due to a global marine transgression the u and th spike is probably secondary perhaps resulting from adsorption of these elements onto clays concentrated at the c t boundary although the occurrence of coeval maxima for these isotopic and elemental anomalies suggests a common cause extrapolation of the co2 drawdown model to explain the u th anomaly is unwarranted at this time ongoing mineralogical analysis of clays and carbonates close to the c t boundary in the red wash section may ultimately explain the occurrence of this u and th spike

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

suspended sediment transport processes in cumberland basin bay of fundy cumberland basin located at the head of chignecto bay bay of fundy exhibits a seaward exponential decreasing time dependent surface sediment concentration there is a strong correlation between suspended sediment concentration and longitudinal concentration gradient a similar correlation was found in shepody bay chignecto bay and minas basin suggesting that an equilibrium condition exists between the two variables total suspended mass in cumberland basin was constant over 2 years of observation 1011 g despite changes in sediment concentration and concentration gradient temporal controls on suspended sediment concentration are river influx ice melting dispersion settling on the intertidal mud flats and water mass exchange at the mouth of the basin this exchange is due to cross channel velocity variations exchanges due to tidal current asymmetry and settling lag are small a simple box model was developed to study the temporal variation of total suspended sediment in the basin the results show that the water mass exchange at the basin mouth varies with time and is the dominant factor controlling suspended mass due to efficient dampening of temporal fluctuations in suspended mass

cretaceous black shales of venezuelan andes preliminary results on stratigraphy and paleoenvironmental interpretations abstract this paper deals mainly with the late cretaceous la luna formation on the venezuelan andean platform the studied area the so called transversale de barquisimeto is located at the contact zone between the andes of merida and allochthonous slabs thrusted from the caribbean domain and is crosscut by a major active transform fault the bocono fault which is part of the contact zone between the caribbean and south american plates the la luna formation is made of dark organic rich laminated limestones and shales and though always appearing with black shale facies is different in the areas located in the north or in the south of the bocono fault we provide here some new information about the biostratigraphic frame of the la luna formation and of the overlying colon formation in the studied area the depositional environment of the la luna formation was certainly rather shallow near storm wave base and stratified during deposition of la luna formation dysaerobic to anoxic conditions prevailed which may be linked with a regional anoxic event perhaps related to seasonal upwelling along the northern coast of south america during late cretaceous time

vertical distribution of suspended sediment concentrations seawards of the breaking zone abstract on the basis of the current concepts on the wave flow structure and solid particle motion in turbulent flow an equation was derived which enables the suspended sediment concentration profile to be computed from known wave parameters the equation was verified by laboratory and full scale experiments which proved that it can be implemented for practical computations of the concentration profile seawards of the breaking zone the formula yields the best results when operating on wave characteristics corresponding to maximum spectral density

the measurement of constituent concentrations in nonhomogeneous sediment suspensions using optical backscatter sensors abstract a method is proposed for estimating the concentrations of the constituents of nonhomogeneous sediment suspensions using optical backscatter sensors the method is predicated on the assumption that constituent interaction e g grain shielding and multiple scattering does not significantly affect sensor response this fundamentally linear approach was verified by laboratory tests of a backscatter sensor in a range of silt sand mixtures implementation of the method will require further development of the optical backscatter sensor or possibly the pairing of an acoustic backscatter sensor with an optical sensor the method has the potential for resolving small scale spatial and temporal changes in the suspended sediment population and therefore could be employed in studies of winnowing and bed armouring for example

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

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

petrogenesis of u and mo bearing a2 type granite of the gattar batholith in the arabian nubian shield northeastern desert egypt evidence for the favorability of host rocks for the origin of associated ore deposits abstract hydrothermal ore deposits associated with granitic rocks are the result of combinations and series of successive processes events and conditions in a magma system and at post magmatic stage the metal content of a granitic magma as well as fractional crystallization metal ligand complexation emplacement mechanisms and tectonic processes influence the metal precipitation and content of a hydrothermal ore deposit the present study of the gattar batholith evaluates how these processes contribute to the generation of an ore deposit gattar batholith in the north eastern desert of egypt as part of the northern region of the arabian nubian shield ans is geographically mineralogically and geochemically divided into two distinctive areas the southern part mainly consists of syenogranite while the northern part is dominated by highly evolved alkali feldspar granite uranium and mo mineralization occurring here is mostly limited to the margin of the highly evolved alkali feldspar granites new u pb zircon geochronology within this study indicates an age of 620 600 ma although high common pb and discordant age data of many zircon grains reflect alteration by f rich fluids some zircons with distinct older u pb ages were considered to be inherited from the wall rocks representing juvenile crust of the ans the two different granitic rocks are comagmatic in origin and have a type characteristics generated by partial melting of lower juvenile crust of the ans geochemical data are in good agreement with a magmatic origin of the alkali feldspar granites suggesting fractional crystallization of a syenogranitic source as the most favorable process of their formation petrography geochemistry and geochronology studies of the gattar granites along with field observations provide evidence for multiple intrusions as a result of successive magma pulses with different chemical composition this led to the formation of reverse zoning within the intrusive complex this kind of magma emplacement promotes the escape of exsolved metal bearing volatile rich fluids into the boundary of the hammamat sedimentary rocks hsr and gattar granite at the northern part of the batholith build up of volatiles is a common phenomenon in granitic rocks and typically results in enhanced contents of f alkalis and ore metals released at subsolidus stage

origin of limestone marlstone cycles astronomic forcing of organic rich sedimentary rocks from the cenomanian to early coniacian of the cretaceous western interior seaway usa abstract we present an integrated multidisciplinary study of limestone marlstone couplets from a continuously cored section including parts of the upper buda limestone the entire eagle ford group boquillas formation and lower austin chalk from the shell iona 1 research borehole texas usa which provides a 8 million year myr distal clastic sediment starved intrashelf basin record of the early cenomanian to the earliest coniacian stages results show that despite variable yet minimal diagenetic overprints several unambiguous primary environmental signals are preserved and support greater water mass ventilation and current activity promoting increased silica carbonate productivity during the deposition of limestone beds compared to deposition of marlstone beds which reflect greater organic matter productivity and preservation furthermore our astronomical analyses demonstrate that the limestone marlstone couplets in the iona 1 core reflect climatic forcing driven by solar insolation resulting from integrated milankovitch periodicities in particular we propose that obliquity and precession forcing on the latitudinal distribution of solar insolation may have been responsible for the observed lithological and environmental variations through the cenomanian turonian and coniacian in this mid latitude epicontinental sea setting our data also suggests that rhythmic lithological alternations deposited in greenhouse periods in general may simply reflect climate driven cycles related to earth sun dynamics without the need to invoke significant sea level variations

seabed drag coefficient under tidal currents in the eastern irish sea over a 2 month period the seabed drag coefficient c100 at a site in the eastern irish sea 26 m water depth had a mean value of 0 0025 which is the value typically assumed but was highly variable the objective of the analysis was to unravel the causes of the variability in c100 an error analysis revealed that a considerable part of the variability could be due simply to random errors in the estimates of friction velocity from which c100 was deduced but the error bounds did not enclose all of the data wave current interaction was ruled out as the principal cause of the variability because waves were small and there was no noticeable correlation between c100 and ratio of wave orbital speed to tidal current speed classifying the boundary layer flow into smooth turbulent transitional and rough turbulent regimes implied that flow regime transitions could explain much of the variability however inspection of the data revealed a contradiction that made that explanation unlikely the classification implied that the boundary layer flow was rough turbulent during neap tides but was smooth turbulent under peak spring tide currents the classification scheme was based on the assumption of neutral stability which according to the stability parameter z l was violated for a considerable portion of the time boundary layer stratification by suspended sediment was found to provide a coherent explanation for drag coefficient variability when z l 0 03 the buoyancy flux due to the suspended sediment caused c100 to vary widely the analysis of the stratified flow dynamics includes the development of an equation correct to second order in z l where z l is small for estimating bed shear stress from the velocity spectrum which extends the applicability of the well known inertial dissipation method into the region z l 0 03

molecular fossil constraints on the water column structure of the cenomanian turonian western interior seaway usa abstract bulk geochemical and biomarker molecular fossil data were collected for four cenomanian turonian sections in the western interior basin usa the four sections represent a 900 km wide transect across the basin from kansas to new mexico rock eval and biomarker analyses indicate an east west thermal maturity trend due to progressive deeper burial associated with the tectonic flexure of the foreland basin since the cenonamian turonian at each site the source of extractable organic matter is dominantly marine with minor terrestrial contribution the presence of isorenieratene derivatives in samples from bunker hill ks pueblo co and red wash nm indicates the presence of the green sulfur bacterium chlorobium in the water column and shows that the southern part of the western interior seaway wis experienced events of photic zone anoxia at maximum transgression sedimentary features indicative of water column oxygenation occur within single beds with geochemical evidence of photic zone anoxia this is consistent with a scenario in which bottom waters experienced alternating oxic dysoxic and anoxic conditions these so called intermittent anoxic events underline the high variability in redox conditions in the wis the distribution of isorenieratene derivatives shows a dynamic water column structure of the wis and indicates that anoxia was a permanent feature of the transgressive and regressive intervals of the greenhorn cyclothem rather than at maximum transgression hence the oceanographic circulation is dominated by near field effects inherent to the seaway rather than by direct proto atlantic elements such as the oceanic anoxic event oae

the lanthanide tetrad effect and its correlation with k rb eu eu sr eu y ho and zr hf of evolving peraluminous granite suites lanthanide tetrad effects are often observed in ree patterns of more highly evolved variscan peraluminous granites of mid eastern germany central erzgebirge western erzgebirge fichtelgebirge and northern oberpfalz the degree of the tetrad effect te1 3 is estimated and plotted vs k rb sr eu eu eu y ho and zr hf the diagrams reveal that the tetrad effect develops parallel to granite evolution and significant tetrad effects are strictly confined to highly differentiated samples mineral fractionation as a cause for the tetrad effect is not supported by a calculated rayleigh fractionation which also could not explain the fractionation trends of sr eu and eu eu the strong decrease of eu concentrations in highly evolved rocks suggests that eu fractionates between the residual melt and a coexisting aqueous high temperature fluid mineral fractionation as a reason for the tetrad effect is even more unlikely as ree patterns of accessory minerals display similar tetrad effects as the respective host rocks the accessory minerals inherit the ree signature of the melt and do not contribute to the bulk rock tetrad effect via mineral fractionation these results point in summary to significant changes of element fractionation behavior in highly evolved granitic melts ionic radius and charge which commonly control the element distribution between mineral and melt are no longer the exclusive control the tetrad effect and the highly fractionated trace element ratios of y ho and zr hf indicate a trace element behavior that is similar to that in aqueous systems in which chemical complexation is of significant influence this distinct trace element behavior and the common features of magmatic hydrothermal alteration suggest the increasing importance of an aqueous like fluid system during the final stages of granite crystallization the positive correlation of te1 3 with bulk rock fluorine contents hints at the importance of ree fluorine complexation in generating the tetrad effect as the evolution of a ree pattern with tetrad effect m type implies the removal of a respective mirroring ree pattern w type the tetrad effect identifies open system conditions during granite crystallization

river flow control on intertidal mudflat sedimentation in the mouth of a macrotidal estuary abstract the objective of this study is to analyze the impact of hydrological variability influenced by climatic phenomena upon the sedimentary exchange between the turbidity maximum tm and a river mouth intertidal mudflat this study carried out over a period of 10 years 1997 2006 in the seine estuary france is specifically focused on two extreme periods a wet one from 2001 to 2002 and a drier one from 2005 to 2006 this study is based on an original approach combining data gathered via low altitude remote sensing with altimeter readings and ground level measurements during this 10 year period we observed a link between climate change and the sedimentary processes on the mudflat surface the modifications of sedimentary processes are mainly connected to the multiannual variability of hydrological flow rates that control the positioning of the turbidity maximum the source of the sedimentary material deposited in this intertidal zone the tm at the mouth of the seine estuary is well developed its maximum mass is estimated to be between 300 000 tons and 500 000 tons avoine et al 1981 with maximum concentrations in the surface waters ranging from 1 to 2 g l 1 le hir et al 2001 most of the fine particles stored within the tm have been found to originate from within the catchment area dupont et al 1994 in the seine estuary the dynamics of the estuarine tm in response to hydrodynamic forcings have been previously described avoine et al 1981 and modeled e g brenon and le hir 1999 le hir et al 2001 the tm is upstream of the northern mudflat when the river flow is low

sediment transport in the mouth of the eden estuary abstract observations of water movement and sediment transport were made from a fixed platform at an intertidal location in the mouth of the eden estuary the effects of wave activity on water movement and suspended sediment fluxes were evaluated and an empirical relationship between suspended sediment concentrations and near bed water movement is described the circulation of water in st andrews bay indicates a residual movement onshore near to the bed onshore movement of sediment in the mouth of the estuary is indicated by suspended sediment fluxes and bedload transport determined from bedform migration the relative roles of suspended sediment and bedload transport are discussed morphological changes in the estuary mouth over the three year survey period are relatively small and indicate a stable environment

stepwise mass extinctions the case for the late cenomanian event the various extinctions of marine taxa in the late cenomanian can be shown as conforming to the step wise extinction model the order of such extinctions is however compatible with the presence of an expanded oxygen minimum zone in the world ocean the occurrence of iridium anomalies at this level in the succession may however indicate a volcanogenic control on the global environment detailed time analysis of the late cenomanian event has been used to produce a correlation of some key successions

interregional model for deposition of upper cretaceous pelagic rhythmites u s western interior the bridge creek member of the greenhorn limestone and fort hays member of the niobrara chalk comprise rhythmic sequences of bioturbated pelagic limestone or chalk beds that alternate with generally shaly interbeds within each member individual couplets are time parallel and can be traced with great precision for hundreds of kilometers certain of the bridge creek beds can be traced from northeastern kansas to the four corners area a distance exceeding 1000 km regional stratigraphic analysis of these remarkable bedding sequences permits integration of concepts generated by several students of pelagic sedimentary sequences into a comprehensive model in the basin center bridge creek rhythms resulted from dilution cycles wherein a background of pelagic sedimentation was punctuated by episodes of increased siliciclastic influx and water column stratification consequent development of oxygen depleted bottom waters created high potential for preservation of laminae and organic matter in shaly interbeds within a given couplet predominating influence of western siliciclastic source areas is evident in westward decrease of carbonate content in both bioturbated limestones and shaly interbeds disappearance of one and then another of the limestone beds and increase in abundance of the coarse detrital fraction toward the east both bioturbated limestones and shaly interbeds grade progressively into chalky lithotypes at some point where effects of detrital dilution episodes were minimal and the water was probably shallower stratification of the water column was not possible and interbeds are not only thinner but also bioturbated because of erosion this facies is not preserved in the bridge creek interval of kansas but it is exemplified there by the fort hays member still farther eastward where detrital influx was negligible most of the bridge creek equivalent comprises a massive bioturbated chalk sequence that lacks interbeds this facies is preserved in northwestern iowa in condensed sections the bridge creek member contains considerable skeletal grainstone that bespeaks improved benthic circulation even during deposition of shaly interbeds the condensed sections developed on seafloor highs that apparently presaged the laramide orogeny the foregoing interpretation of regional variations in the bridge creek member is generally applicable to the less widespread fort hays rhythmic sequence in which simple dilution cycles seem to have predominated

oceanographic processes and sediment mixing on a sand flat in an enclosed sea manukau harbour new zealand abstract studies of oceanographic and sedimentary processes on intertidal sand flats in an enclosed sea were undertaken to gain a better understanding of the factors controlling the mixing and dispersal of sediment bound contaminants field investigations included a 90 day process experiment during which wind waves tidal currents tides depth of disturbance and sand flat morphology were measured and 27 months of sand flat profile monitoring sediment entrainment by strong spring tidal currents is restricted to the middle and lower regions of the sand flat which are inundated during the peak tidal flows the upper 2 3 cm of sediment is re worked across the middle and upper sand flat by mild storm wave events h s 70 cm which occurred four times during the 90 day experiment numerous ridges and runnels in the upper sand flats are wave formed features and are maintained by the lack of currents of sufficient magnitude to re work the features the ridge and runnel morphology is testimony to large infrequent storm events which re work the sediment to depths of 20 cm such storms are an important mechanism for the release of contaminants and were recorded on 3 occasions in the 27 month profile record

suspended sediment concentrations under waves abstract a predictive formula is derived for calculation of the magnitude of time averaged suspended sediment concentrations under waves by taking into account the effect of flow contraction near ripple crests the formula applies equally well for rippled beds and sheet flow conditions the formula is in qualitative agreement with the bed load flux formula of madsen and grant 1976

cretaceous rhythmic bedding sequences a plausible link between orbital variations and climate abstract simple oscillation cycles have been recognized in cretaceous pelagic sequences as a marked periodicity in carbonate and or organic carbon content the estimated periodicities of these cycles resemble milankovitch type variations in orbital elements however during warm geologic periods the nature of the link between orbital variations and the sedimentary record has been problematic climate model studies show that the intensity of continental margin precipitation in specific low latitude regions is a function of land sea thermal contrast which is sensitive to orbital variations cretaceous climate model simulations are characterized by regions of intense precipitation the locations of which are controlled by geographic configuration in particular in the model simulation the northern margin of the tethys ocean has all the climatic characteristics necessary to exhibit a sensitivity to orbital variations detailed studies of the biota sedimentology and geochemistry of the bedding rhythms in greenhorn cyclothem in the western interior seaway of north america are best interpreted in terms of variations in precipitation runoff and stable stratification of the seaway combined the geologic and model studies support a link between orbital periodicities variations of intense precipitation associated with specific paleogeographic situations and cretaceous bedding patterns this hypothesis has important implications for the sensitivity of the atmosphere hydrosphere lithosphere system to external forcing

authigenic kaolinite and associated pyrite in chalk of the cretaceous niobrara formation eastern colorado abstract cores from the smoky hill chalk member of the cretaceous niobrara formation have several zones containing authigenic kaolinite as spherical moldic polycrystalline aggregates that occur within single or multichambered foraminiferal tests and are commonly associated with framboidal pyrite such kaolinite is inferred to result from volcanic ash deposited during chalk sedimentation shortly after burial a colloidal aluminous gel or solution formed from the unstable ash and moved into organic rich foraminiferal tests where sulfate reducing bacteria created a favorable microenvironment for the simultaneous crystallization of kaolinite and pyrite

testing the astronomical time scale for oceanic anoxic event 2 and its extension into cenomanian strata of the western interior basin usa the development of integrated astronomical and radioisotopic time scales from rhythmic strata of the western interior basin wib has played a fundamental role in the refi nement of late cretaceous chronostratigraphy in this study x ray fl uorescence xrf core scanning is utilized to develop a new elemental data set for cyclostratigraphic investigation of cenomanianturonian strata in the wib using material from the aristocrat angus 12 8 core northcentral colorado the xrf data set yields the fi rst continuous 5 mm resolution analysis of lithogenic biogenic and syngeneticauthigenic proxies through the uppermost lincoln limestone member the hartland shale member and the bridge creek limestone member including oceanic anoxic event 2 oae 2 the 40 ar 39 ar ages from ashes in three biozones including a new age from the dunveganoceras pondi biozone uppermost lincoln limestone member provide geochronologic constraints for the cyclostratigraphic analysis astrochronologic testing of the 5 mm resolution xrf weight percent caco3 data via average spectral misfi t analysis yields strong evidence for astronomical infl uence on climate and sedimentation results from the bridge creek limestone member are consistent with the previously published astrochronology from the u s geological survey 1 portland core central colorado and identifi cation of an astronomical signal in the underlying hartland shale member now permits extension of the wib astrochronology into the earlier cenomanian prior to oae 2 high rates of sedimentation in the angus core during the interval of oae 2 initiation as compared to the portland core allow recognition of a strong precessional control on bedding development as a consequence the new results provide a rare high resolution chronometer for the onset of oae 2 and the timing of proposed hydrothermal trace metal enrichment as observed in the 5 mm xrf data

turbidity and sediment transport in a muddy sub estuary abstract sub estuaries i e tidal creeks and also larger estuaries that branch off the stem of their main estuary are commonplace in many estuarine systems their physical behaviour is affected not only by tributary inflows winds and tides but also by the properties and behaviour of their main estuary measurements extending over more than an annual cycle are presented for the tavy estuary a sub estuary of the tamar estuary uk generally waves are small in the tavy because of the short wind fetch a several hour period of up estuary winds blowing at speeds of between 7 and 10 m s 1 generates waves with significant wave heights of 0 25 m and a wave periodicity of 1 7 s that are capable of eroding the bed over the shallow ca 1 5 m deep mudflats waves also influence sedimentation within and near salt marsh areas an estuarine turbidity maximum etm occurs in the tavy s main channel close to the limit of salt intrusion at hw suspended particulate matter spm concentrations typically are less than 40 mg l 1 at hw although concentrations can exceed 80 mg l 1 when tides and winds are strong flood tide spm inputs to the tavy from the tamar are greater during high runoff events in the river tamar and also at spring tides when the tamar has a high concentration etm higher spm concentrations are experienced on the mudflats following initial inundation without wave resuspension this is followed by a rapid decrease in spm for most of the tide indicating that the mudflats are depositional at those times spm concentrations on the mudflats again increase sharply prior to uncovering peak ebb tidal speeds at 0 15 m above the mudflat bed can exceed 0 26 m s 1 at spring tides and 0 4 m s 1 following high runoff events which are sufficient to cause resuspension time series measurements of sediment bed levels show strong seasonal variability higher and lower freshwater flows are associated with estimated monthly mean sediment transport that is directed out of or into the upper sub estuary respectively seasonal sediment transfers between the estuary and its sub estuary are discussed

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

origin of the cretaceous bridge creek cycles in the western interior united states abstract alternating beds of burrowed limestone and laminated organic carbon rich marlstone in the bridge creek member of the greenhorn formation were deposited during maximum transgression of the cenomanian turonian sea in the western interior of the united states one view of the origin of the bridge creek limestone marlstone rhythms holds that they represent dilution cycles produced by alternating climates within the western interior the marlstones recording wet episodes when high runoff produced a sediment laden brackish lid on the seaway and the limestones recording dry episodes when runoff was low and the water column well mixed a second view holds that the rhythms represent productivity cycles the limestones representing times of high productivity of calcareous planktonic skeletons and the marlstones representing times of low productivity in this view the rhythms were produced by alternations in vertical circulation that characterized much of the world ocean at the time the productivity origin of the rhythms is supported by the presence of abundant calcispheres in the limestone beds the concentration of clay size quartz in many of the limestone beds the comparatively high 18 o and low 13 c in limestone beds the similarity in proportion of clay minerals in marlstone and limestone beds the pelagic depositional rate of the bridge creek member and by the discovery that bridge creek deposition began with a marlstone and not a limestone bed the dilution model is not consistent with these features and it has not been supported by modeling of paleoclimates and lithofacies that were predicted from it nor by macrofaunal distributions within the seaway the dilution model is not consistent with the occurrence of diverse and abundant planktonic foraminifera in both marlstone and limestone beds which indicate that near normal marine salinities prevailed during deposition of both bed by bed analysis of the bridge creek member may provide an analog for events in the tethys that are poorly recorded in deposits from the deep sea itself

mid cretaceous of the gibraltar arch area mid cretaceous depositional environments of the gibraltar arch and adjacent areas exhibit at the cenomanian turonian boundary a special type of organic carbon rich siliceous sedimentation which is intercalated in all the different environments from the shelf down to the deep of this area this will be called the cenomanian turonian boundary event ctbe summarizing the most important features of the ctbe it can be pointed out 1 the initiation of the ctbe is nearly coeval 2 very high tocs especially at the base of turonian 3 kerogen is exclusively of type i ii in the undiluted strata 4 independent of given palaeogeographic setting e g e and w margin of the atlantic ocean 5 bituminous sedimentation is also very pronounced in environments with high detrital input and strong dilution e g deep sea fans here too most strata comprise kerogen of type ii 6 as far as we know there is a striking co occurrence of these sediments with strong enrichment in biogenic silica from diagenetically altered radiolaria but there is no link between good preservation of radiolaria and bituminous sediments e g scaglia facies 7 rich radiolarian faunas are common in the carbon rich and carbon free sediments of shallow marine and deep sea environments 8 the important change in the evolution of planktonic organisms foraminifera radiolaria which marks the cenomanian turonian boundary coincides with the peak of anoxic conditions and biogenic silica rich sedimentation all these features of the ctbe observed in the gibraltar arch area are comparable with coeval dsdp facies in the north atlantic and allow on shore off shore tracing of the ctbe 1986 the geological society

integrated quantitative stratigraphy of the cenomanian turonian bridge creek limestone member using evolutive harmonic analysis and stratigraphic modeling abstract secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata in this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation the method exploits a moving window fourier technique that we designate evolutive harmonic analysis eha we calibrate this methodology to a specific set of geologic conditions i e changes in bulk sedimentation using a series of stratigraphic models and then apply the technique to the cenomanian turonian greenhorn formation of the western interior basin application of eha to strata that preserve a record of orbital forcing allows the reconstruction of a high resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified using the data on bulk sedimentation rate rates of accumulation for geochemical proxies representing detrital biogenic and authigenic contributions to the sediment can be calculated by integrating these quantitative assessments of siliciclastic dilution primary production and depositional redox conditions within a high resolution chronostratigraphic framework we are able to deconvolve secular trends in hemipelagic sedimentation during the late cenomanian early turonian in the western interior basin this integrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the western interior basin during the interval representing oceanic anoxic event ii

bed level changes on intertidal wetland in response to waves and tides a case study from the yangtze river delta short term bed level variability in tidal wetlands has important implication both for ecology and engineering in this study we combined in situ measurements with model simulations to quantify short term bed level changes on a meso macrotidal wetland in the yangtze river delta on the middle flat we observed erosion during neap to mean tides under onshore moderate to strong winds and bed recovery during subsequent spring tides when winds were both offshore and weaker suggesting that winds can overturn the neap spring cyclicity of bed level changes even on meso macrotidal mudflats the magnitude of bed level changes was smaller on both sides of the middle flat while the smallest changes occurred on the salt marsh observed bed level changes were reconstructed using a single point bed level change model which incorporates in situ measured parameters of hydrodynamics waves and currents suspended sediment concentrations and bed sediment properties we conclude that the relative importance of waves and tides in intertidal wetland erosion and accretion can vary temporally due to changes in balance between wave and tidal energies and spatially because of changes in elevation and vegetation in the cross shore profile our study also reflects the advantage of combination of in situ measurement with simulation in detecting short term variability of tidal flats

elemental abundance anomalies in the late cenomanian extinction interval a search for the source s elemental abundances have been measured by neutron activation methods across the cenomanian turonian late cretaceous extinction interval in samples collected from sixteen sites in the western interior basin of north america and from twelve widely separated locations around the globe including six odp dsdp sites in most western interior basin sites in colombia and in western europe weaker two closely spaced elemental abundance peaks occur in the upper cenomanian 92 m y spanning the ammonite zones ofsciponoceras gracile throughneocardioceras juddii elements with anomalously high concentrations include sc ti v cr mn co ni ir pt and au the lower peak coincides with the disappearance extinction of the foraminiferrotalipora cushmani in north american sectionsr greenhornensis also disappears at or just below this horizon but in europe it disappears considerably earlier thanr cushmani a series of molluscan extinction and speciation or migration events also begins near the stratigraphic level of the lower elemental abundance peak the well documented positive 13c excursion begins just before the extinctions and the elemental anomalies and continues into the lower turonian well above the upper anomaly this carbon isotope excursion has been observed in east european sections where we find little or no evidence of the elemental anomalies suggesting that the two phenomena may not be tightly coupled elemental abundance ratios in the anomalies closely resemble those of mid atlantic ridge basalt or hawaiian lava tholeiitic but not those of c1 chondrite black shale average crustal rocks or lamproite and kimberlite of roughly similar age in southeastern kansas the excess ir and other siderophiles hint at possible large body impact s for the source however we have not located microspherules other than biogenic calcispheres or shocked mineral grains in any of our samples furthermore sc ti v and mn are not enriched in differentiated solar system bodies although the weak geochemical signal from comet impact s could be masked by the strong terrestrial like overprint these anomalies more likely resulted either from intense seafloor spreading activity or merely from increased circulation of deep metal rich water associated with the large late cenomanian through early turonian eustatic rise and deep water opening of the south atlantic the flooding of continental seaways and margins also could have contributed to the anomalies by preventing much continental detritus from diluting the normal background marine geochemical component

paleoenvironmental and paleoceanographic changes across the cenomanian turonian boundary event oceanic anoxic event 2 as indicated by foraminiferal assemblages from the eastern margin of the cretaceous western interior sea abstract two sites near the eastern margin of the cretaceous western interior sea wis were investigated the section at cuba kansas ck is 630 km east of the gssp for the cenomanian turonian boundary at rock canyon colorado rc and the section near sioux city iowa sci is 315 km northeast of the cuba site surprisingly planktic foraminifera dominate all the studied samples despite the relative proximity of the sites to the paleo shoreline and presumed neritic water depths such dominance suggests inhospitable benthic environments and benthic foraminiferal assemblages indicate that seafloor oxygen in the wis decreased eastward therefore the hypothesis of an influx of freshwater into the wis from the western margin forming a fresh water cap that diminished eastward is not supported benthic foraminifera are scarce in most studied samples and species diversity is low in the ck section diversity and abundance increase abruptly in the uppermost cenomanian benthonic zone at the initiation of the 13corg positive excursion marking the onset of oceanic anoxic event oae 2 in the sci section however the benthonic zone is recognized only by presence of nodosaria bighornensis that has a stratigraphic range restricted to this interval other benthic taxa are very rare or absent the favorable conditions of the benthonic zone were short lived while relatively diverse planktic foraminiferal assemblages including keeled species characterize the initial 13c excursion at the ck site dwarfed specimens of heterohelix and hedbergella dominate the assemblages at the more proximal sioux city site furthermore most of the biostratigraphic events recognized in the basin center rc section can be traced into the ck section but not into the sci section including the rotalipora spp and globigerinelloides bentonensis extinctions the heterohelix shift event and the brief benthic recovery event correlation between eastern wis sites shows that the sci section is thicker suggesting a major sediment source to the east this may explain the inhospitable benthic conditions and development of a dead zone seasonal hypoxia analogous to the modern shelf of the northern gulf of mexico proximal to active discharge of the mississippi river development of estuarine circulation in the wis provided the eastern part of the basin with input of calcareous plankton from the south including planktic foraminifera foraminiferal assemblages total organic carbon toc and 13c data of the studied sections suggest a two fold history of greenhorn transgression and oae 2 development the initial phase is a global signal characterized by a positive 13c excursion low toc values and high foraminiferal species diversity the second phase is characterized by overprinting by local conditions in the wis including high fluvial input relatively high toc values and low foraminiferal species diversity these findings suggest that the eastern margin records unique depositional and biotic environments further revealing the dynamic and complex nature of the wis and its sedimentary cycles

coastal lagoons geologic evolution in two phases abstract estuaries formed globally when river valleys and bays were inundated by the rising sea towards the end of the holocene post glacial marine transgression and have been supplied with sediment ever since coastal lagoons estuaries that are partially or wholly cut off from marine influence are said to evolve through sedimentation from an immature unfilled state to a mature filled state at a rate dependent on sediment supply the existence of numerous examples of lagoons that remain unfilled worldwide however despite thousands of years of sedimentation suggests that a discontinuity in the geologic evolution of lagoons occurs before maturity is reached presented here is a hypothesis that geologic evolution takes place in two phases which are defined by changes in physical processes the early phase aligns with the traditional view but ends when a depth threshold is reached in the late phase sedimentation is inhibited by the local energy regime and can only proceed if the lagoon surface area is reduced validation of the existence of these two distinct process based phases of geologic evolution will improve the reliability of predictive models for lagoon shoreline changes and rates of basin fill as well as reduce the risk of misinterpreting past conditions from the geological record

silt and sand transport in a deep tidal channel of a large estuary manukau harbour new zealand abstract time series of suspended silt concentration measured by an optical backscatter sensor and suspended sand concentration measured by an acoustic backscatter sensor in a deep channel 14 m msl of a large new zealand estuary manukau harbour are analysed suspended sand concentration varied in phase with the current speed and bed shear stress on a 6 2 h cycle but suspended silt concentration varied on a semidiurnal 12 4 h cycle such that the channel was clear of silt at high tide and maximum silt concentration occurred at low tide threshold for initiation of sand motion was found to be related to local skin friction sand concentration profiles were consistent with settling flux balanced by gradient diffusion with a two layer sediment diffusivity dependent on local friction velocity suspended sand reference concentration was explainable in terms of local skin friction and changes in the channel bed sediment were correlated with the suspended sand load therefore sand suspension in the channel is a local process and the channel bed is the source of the suspended sand load suspended sand flux was found to be a highly nonlinear function of the tidal current speed in the channel in that case tidal current velocity asymmetry is the principal determinant of direction of net sand transport and the ebb flood dominance concept is valid the relative phase of the m 2 and m 4 constituents of the tidal current velocity which quantifies tidal current asymmetry was calculated from a tide model of the estuary and results were mapped the harbour was found to be broadly ebb dominant and therefore self flushing of sand silt suspension in the channel was not related to the local boundary layer dynamics but was explainable in terms of the movement up and down the channel of a horizontal gradient in silt concentration which implies the existence of a turbid water mass that is perched on the surrounding intertidal flats at high tide and that drains into the channel during ebb tide silt concentration in the channel increased during a short storm which corresponded to the passage through the measurement site of a turbid fringe that was formed on the surrounding intertidal flats during the previous high tide under the action of breaking waves wave activity on the surrounding intertidal flats is therefore the principal determinant of suspended silt load in the channel and an approach that treats waves and sediment pathways between intertidal flats and channels is needed for modelling silt transport

the cenomanian turonian boundary event in central poland abstract stable isotopes 13c 18o caco3 content carbon content insoluble in hcl corg and in the carbonates ccarb and foraminifers have been investigated in the cenomanian turonian boundary interval rotalipora cushmani zone and lower whiteinella archaeocretacea zone in southeast central poland a higher content of corg in the uppermost rotalipora cushmani zone and lowermost whiteinella archaeocretacea zone a 13c and 18o stable isotope anomaly in the uppermost cenomanian and substantial changes in the foraminiferal assemblages have been recorded a major carbon stable isotope excursion with a shift of up to 1 6 pdb recorded in the lower part of the whiteinella archaeocretacea zone within the marly limestone in the uppermost cenomanian a late cenomanian expanding oxygen minimum zone is thought to be responsible for changes in foraminiferal assemblages

enhanced bioturbation on the down drift flank of a turonian asymmetrical delta implications for seaway circulation river nutrients and facies models extant models predict delta front environments down drift of river mouths as unfavourable for organisms because of the physico chemical stresses caused by sediment and fresh water influx this study however finds evidence for near optimal living conditions down drift of contemporaneous mouth bars and distributary channels as well as at the tops of abandoned lobes in part of the asymmetrical notom delta complex of the ferron sandstone turonian south eastern utah usa presented herein is a sedimentological and ichnological model using thirty two detailed measured sections along a 16 km transect through two continuously exposed ca 10 m thick allomembers containing delta front mouth bar and distributary channel facies azimuths from sedimentary structures show south eastward deflection of near shore palaeocurrents relative to the inferred north south shoreline as well as minor reversal of flow two end member trace fossil suites are recognized in delta front sandstones i a stressed suite of low abundance low diversity diminutive traces reflecting mobile deposit feeding resting and locomotion behaviours and ii a comparatively unstressed high abundance moderate diversity suite with a regular heterogeneous distribution of deep vertical or u shaped suspension feeding burrows which in places thoroughly homogenize the sandstones the down drift side of the delta was colonized by suspension feeders during seasonal reversal of the seaway gyre when mud plumes were swept northward or when river derived nutrients were sufficiently concentrated relative to fresh water and sediment input during normal seaway circulation very high sedimentation rates and mud laden wave dampened waters down drift of the river mouths heightened the preservation potential of the pervasively bioturbated facies up drift of the river mouths these bioturbated facies were either not preserved or not developed until the lobe was abandoned this alternative model for delta planform asymmetry contributes to the refinement of facies models for deltaic systems and provides a framework for predicting the distribution of bioturbation enhanced porosity and permeability in lobe deflected deltas

the mount gharib a type granite nubian shield petrogenesis and role of metasomatism at the source the mount gharib peralkaline a type complex 476 2 ma located in the nubian shield of egypt contains sodic calcic to sodic amphiboles accessory astrophyllite zircon fluorite apatite allanite aenigmatite elpidite and ilmenite this within plate hypersolvus suite is enriched in large ion lithophile lil and high field strength hfs elements and characterized by a fractionated ree pattern ce yb 49 and a significant negative eu anomaly a fine grained acicular amphibole bearing roof facies shows further enrichment in the lil and hfs elements the suite was emplaced in a pan african granodiorite adamellite host which it locally metasomatized the affected rocks contain hydrothermal albite end member arfvedsonite astrophyllite and levels of the lil and hfs elements intermediate between those in the peralkaline granite and the roof facies trace element and isotopic modeling of this a type granite with its high initial 87sr 86sr value 0 7110 documents an active role of the lithosphere in magma generation lithospheric extension expressed by regional dyke swarms was caused by cooling fracturing and relaxation of the thin newly formed pan african crust localized partial melting took place in an open system possibly as a result of an influx of alkali rich fluid derived from a sublithospheric source metasomatic reactions similar to those observed in the metasomatized wallrocks are considered to have played an important role just prior to the onset of anatexis and generation of the a type melt

in situ estimation of erosion and deposition thresholds by acoustic doppler velocimeter adv abstract field based estimations of bed shear stress have been made using sontek ysi 10 mhz advs a coustic d oppler v elocimeter at the kongsmark mudflat danish wadden sea in order to test if it was possible to estimate erosion and deposition thresholds in situ by use of unidirectional tidal and orbital wave currents the results were promising and erosion thresholds were in the same range as those observed in eromes erosion experiments carried out at the same site similarly the short term erosion rates which could be calculated matched closely those obtained with eromes and were in the same range as those published for a large annular flume sea carousel from another fine grained site this indicates that the erosion rates obtained with those two erosion instruments are reasonable estimates of the actual erosion taking place under natural tidal current and waves one advantage of the use of advs to characterize sediment erodibility is that measurements can be carried out for long periods which makes it possible to examine the temporal variation of erosion threshold erosion rate and sedimentation the maximum bed shear stresses which was observed during a strong storm in january 2005 was only 0 7 n m 2 which is three to four times lower than the highest thresholds measured by eromes experiments on sediment with biofilms during previous studies this shows that such strong biofilms at this site will not get eroded unless degraded or physically disrupted by some other mechanism a prerequisite for the determination of any of the erodibility and sedimentation parameters is that the actual bed level changes at the measuring site are known in detail this information is obtained automatically by the advs used in the present study accurate estimates of the bed shear stress under waves in very shallow water are difficult to obtain and in the present study a simple method based on instantaneous velocities and assumption of a logarithmic velocity profile was used further field studies are required of the boundary layer under these extreme conditions in order to refine this simple method of calculating bed shear stresses

high resolution organic record of bridge creek deposition northwest new mexico abstract organic and inorganic geochemical data are presented and interpreted for a high resolution sample set from the uppermost portion of a transgressive systems tract condensed interval spanning the cenomanian turonian boundary at red wash northwest new mexico source potential toc rock eval yields thermal maturity vr elemental ca th and u in whole rock and molecular n alkanes steranes terpanes data are presented for a 64 sample 12 4 m composite section of limestones marlstones and shales of the bridge creek member of the greenhorn formation vertical sampling resolutions of 1 spl 19 cm spatial and 1 spl 33 ka temporal are used to monitor the progress of the transgression from the uppermost cenomanian up to the beginning of the highstand systems tract the section is thermally immature and maturity fluctuations are absent indicating that organic parameters are a function of organic matter production and preservation including diagenesis the rhythmic lithologic fluctuation within the bridge creek is not reflected in the source potential elemental or molecular data which show either no obvious pattern e g carbonate content toc or a unidirectional trend toward development of anoxia upsection e g hydrogen index sterane distributions homohopane index the distribution of the triaromatic steroid hydrocarbons c 20 21 26 28 according to side chain length also varies significantly despite the absence of maturity differences all of the unidirectional trends in the data are interpreted as related to either productivity differences e g sterane hopane ratios and changes in the relative concentration of r c 28 and r c 30 desmethylsteranes or the development of anoxia in the lower water column e g decreases in the diasterane regular sterane ratio increases in the homohopane index westward movement of the paleoshoreline during bridge creek time is also monitored by upsection decreasing th u ratios at red wash

bedding rhythms and cyclic sequences as documented in organic carbon carbonate patterns upper cretaceous western interior u s abstract a three component sedimentation model is introduced for estimating the relative effects of major changes in sediment flux coupled organic carbon carbonate changes reflecting different dilution concentration styles are utilized to detect the changing flux between the carbonate siliciclastic and organic matter components the three component model is then applied to upper cretaceous rhythmically bedded units of the greenhorn and niobrara cycles of the western interior seaway the cycles are related to third order sea level changes the western interior seaway was sensitive to small scale climatic cycles only during periods of maximum flooding due to combined variations in carbonate productivity redox conditions and siliciclastic supply from continental sources rhythmic deposition is different for different parts within the periods of maximum flooding for each of the two investigated third order sea level cycles section intervals reflecting peak flooding show variations in carbonate productivity and variations in redox conditions slightly more regressive intervals show variations in calcareous productivity and siliciclastic dilution with stagnant dysaerobic bottom waters for most of the investigated bedding rhythms persistent dysaerobic bottom waters are largely uninfluenced by variations in pelagic carbonate productivity except for section intervals representing peak flooding this suggests the existence of a circulation pattern in which a mixed surface water zone was underlain by more stratified oxygen depleted water masses with slow circulation

late cretaceous cenomanian to campanian paleoenvironmental history of the eastern canadian margin of the western interior seaway bonebeds and anoxic events abstract upper cretaceous strata in the pasquia hills of the northern manitoba escarpment eastern saskatchewan canada provide a detailed paleoenvironmental and sea level record of the eastern margin of the western interior seaway sediments deposited during the cenomanian turonian greenhorn marine cycle are dominantly black mudstones deposited in a stratified water column with bottom water anoxia recurrently reaching into the photic zone a middle cenomanian sea level lowstand event followed by transgression left a series of bonebeds within the belle fourche member of the ashville formation indicating a sedimentary environment starved of coarse siliciclastics maximum sea level resulted in the formation of limestone beds within the favel formation further favoured by reduced terrigenous sediment input compared to the western margin limestone sedimentation was followed by a phase of increased freshwater input under lower sea level conditions and reducing zoo and phytoplankton diversities during final greenhorn regression eastern saskatchewan probably turned into a restricted basin severely limiting marine circulation poor or absent benthic foraminiferal assemblages and biomarker analysis suggest prevailing watermass stratification throughout the cenomanian turonian transgressive regressive cycle this was caused either by a freshwater lid stratification of boreal and tethyan derived watermasses or both to various intensities affected by changing sea level basin oxygenation during niobrara time varies between localities along the eastern margin as documented by presence absence of benthic and planktic foraminifera

the influence of waves and seagrass communities on suspended particulates in an estuarine embayment resuspension of bottom sediments by waves corresponding changes in suspended particulate material spm concentrations in the overlying water column and transport pathways of spm were investigated in a shallow estuarine embayment colonized by seagrass communities in chesapeake bay in shallow 2 m unvegetated regions significant resuspension of bottom sediments was evident when northerly winds exceeded 25 km h 1 increasing spm concentrations up to 10 fold high concentrations of spm generated by resuspension dissipated rapidly within 24 h after winds became calm patterns of spm along the embayment s depth gradient suggest that part of this resuspended material was transported offshore into deeper reaches of the estuary in areas of the embayment colonized by seagrasses wave energy was attenuated by the vegetation suppressing resuspension and enhancing deposition as a result spm concentrations were significantly lower inside seagrass beds than in adjacent unvegetated areas during periods of high winds when wave induced resuspension occurred in unvegetated areas spm concentrations remained unchanged inside the bed at normal water levels however when water levels were elevated by spring tides or storm surges plants were less effective at attenuating wave energy and spm concentrations increased inside the seagrass bed due to resuspension and advective processes calculations based on the results of this study indicate that sedimentation rates are substantially higher in seagrass communities than in unvegetated areas

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

field measurements of the suspended sand concentration profiles and fluxes and of the resuspension coefficient γ0 over a rippled bed measurements of the acoustic backscatter from suspended sand over a rippled bed and of currents were made near the crest of a ridge and runnel beach on the macrotidal north norfolk coast of the united kingdom two 12 min records were taken close to high water in a depth of 1 7 0 2 m visual inspection of the data shows that sand was intermittently suspended to heights of 20 30 cm but that these events were not always correlated with strong wave induced currents the structure of some of the suspension events suggest that they are due to vortex shedding from a rippled bed the observed time averaged concentration profiles were compared with predictions generated using glenn and grant s 1987 combined flow model the nondimensionalised concentrations showed good correspondence in the first 8 to 10 cm above the wave boundary layer supporting the use of a value of 0 74 drawn from atmospheric data for the constant of proportionality between sediment and momentum diffusivity above this height observed values of the proportionality constant tended to approach 1 0 which may have been due to a decrease in sediment settling velocity with height which is consistent with finer sand being suspended higher in the flow or alternatively to nonuniform turbulence in the vicinity of the wave ripples absolute concentrations measured 2 cm above the bed were consistent with values of o 10 4 for the empirical constant 0 in smith and mclean s 1977 pickup function concentrations within the wave boundary layer were observed to decrease much more rapidly than predicted by the model sand transport fluxes were computed for both the cross shore and alongshore components of the flow using a current profile based on the combined flow model of glenn and grant 1987 for the two records vertically integrated fluxes of 1 5 mg s cm width and 0 89 mg s cm width directed towards the shore were calculated for the wave oscillatory component of the transport the mean flow produced shoreward vertically integrated fluxes of 5 1 and 10 5 mg s cm width the uncertainty associated with these estimates is considerable 50 the vertical profile of the total flux wave oscillatory and mean for both records showed a strong shoreward transport close to the bed an offshore transport between 5 and 15 cm above the bed and a further weak onshore flux above this demonstrating the necessity for measurements of the whole concentration profile rather than a few point samples for the calculation of sand transport over a rippled bed in a wave dominated environment