residual circulation in shallow estuaries 1 highly stratified narrow estuaries long wave theory and simple turbulence closures have been used to show that three distinct types of circulation highly stratified weakly stratified and partially mixed arise in narrow shallow estuaries from the finite amplitude of the tide and the interaction of stratification with vertical mixing each type has a different dominant process causing the vertical exchange of salt and fresh water on the flood and each gives rise to a characteristic residual circulation the tidal circulation in highly stratified shallow estuaries described herein is the result of a finite amplitude internal motion driven by the barotropic tide shear instabilities at the interface are the major vertical exchange mechanism the residual circulation is caused primarily by ebb flood asymmetry in interface position and thickness a model based on our theoretical analysis shows that the interface thickness on flood is much less than the depth of flow up to a critical tidal amplitude at which the two layer flow is destroyed and correctly predicts the tidal amplitude of the neap spring transition in the columbia river estuary tidal frequency internal wave motion is not found in weakly stratified and partially mixed estuaries because of the reduced tidal shear shear instabilities are weak or absent and the residual circulation assumes a very different character as described in part 2

regional geology and petroleum systems of the illizi berkine area of the algerian saharan platform an overview abstract the berkine and illizi basins are palaeozoic mesozoic intraplate depressions that preserve an over 7000 m thick sedimentary rock record and contain world class petroleum systems with over 39 bboe eur hydrocarbon reserves regional seismic transects and a wealth of well data are used to review the tectonostratigraphic evolution of the area the gondwana palaeozoic and tethys mesozoic supercycles make up the bulk of the phanerozoic succession these 1st order cycles record extensional basin formation followed by a protracted period of overall net subsidence and conclude with basin inversion and regional uplift during the hercynian and alpine orogenies respectively structural styles were dictated by transpressional or transtensional reactivation of mostly nne oriented basement structural grain of late proterozoic ea cambrian pan african age and vertical movement of long wavelength regional highs and lows local tectonism is considered to be the far field effect of plate tectonic processes that affected the north african plate boundaries such as the caledonian and hercynian orogenies the opening of the tethys and atlantic oceans and the alpine orogeny these were accompanied by localised thermal mantle processes regional unconformities subdivide the gondwana and tethys supercycles into eight and seven megasequences respectively these regional units often record 2nd order transgressive regressive cycles that constrain the mapping of reservoir seal pairs and of main source rock intervals the lower palaeozoic megasequences are characterised by sand rich laterally extensive coarse grained fluvial and shallow marine reservoirs interbedded with thin and widespread marine shales they were mostly deposited in shorelines of shallow epeiric seas and continental braided river systems or during the late ordovician in a short lived continental glacial system third order sequences display ramp style geometries with largely parallel to low angle sigmoidal stratal patterns early mesozoic sedimentation followed the late palaeozoic uplift and peneplanation in the form of hinterland sequences containing fluvial and alluvial sandstones and playa lake mudstones and evaporites interbedded with thin lacustrine or shallow marine shales and dolomites the prolific petroleum systems that evolved within these series are associated with the early silurian and late devonian world class source rocks and numerous paleozoic and triassic reservoirs this regional review provides a renewed comprehensive insight into the geological evolution of the area that can help guide local exploration efforts but also serves as a model for exploration in other intracratonic basins of the world

deltaic sedimentation in the devonian of western libya abstract middle and upper devonian deposits from the aouinet ouenine formation in the southern ghadames basin of western libya provide a well exposed example of a deltaic complex containing both progradational and transgressive facies progradational facies comprise both laterally accreting and incised distributary channels overlying prodelta deposits also present is a progradational beach environment showing build up from an offshore shelf through nearshore shelf to shoreface and foreshore sub environments over lying these progradational facies are transgressive tidal flat washover fan foreshore and nearshore deposits the characteristics and interrelationships of the different facies are explained by two sedimentation models progradational facies existed contemporaneously during phases of active sediment supply whereas the transgressive facies existed contemporaneously during periods of diminished or absent detrital influx

cyclostratigraphic calibration of the frasnian late devonian time scale western alberta canada until now the duration of the frasnian stage has remained very poorly constrained hampering a detailed understanding of sedimentation processes and environmental and evolutionary change in this study timeseries analyses of high resolution 10 20 k y magnetic susceptibility data identify sixteen 405 k y eccentricity cycles in the magnetic susceptibility stratigraphy of the frasnian late devonian derived from carbonate platform and surrounding slope and basin deposits in western alberta canada previous studies demonstrated the generally consistent pattern of magnetic susceptibility change across the alberta basin and thus demonstrated the utility of magnetic susceptibility stratigraphy as a refi ned regional correlation tool compared to biostratigraphy in the present study we show that the magnetic susceptibility stratigraphy of the frasnian interval in western alberta has been signifi cantly infl uenced by astro nomical forcing using the sixteen 405 k y eccentricity cycles as a geochronometer we constructed a frasnian astronomical time scale this time scale indicates a duration of 6 5 0 4 m y for the frasnian calibrating this duration to the best available devonian chronology the absolute age of the givetian frasnian boundary is recalculated to 383 6 3 0 ma and the age of the frasnian famennian boundary is recalculated to 376 7 3 0 ma these new absolute ages take into account the astronomically derived duration of the frasnian but they also yield a narrowing of the error margins of the absolute ages by several hundreds of thousands of years

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

frasnian conodonts at high palaeolatitude amazonas basin north brazil abstract a conodont fauna is studied from the subsurface of upper devonian black shales belonging to the abacaxis member of the barreirinha formation amazonas basin two samples of other members of this formation are barren the fauna consists of cryptotaxis sp a mehlina gradata ozarkodina aff sannemanni polygnathus sp and probably prioniodina sp this association suggests a late frasnian age agreeing with the age previously assigned to the latest frasnian to middle famennian palynomorphs the conodont fauna is added to another two late frasnian middle famennian conodont occurrences in bolivia and brazil the coincidence in age and facies black shales seems to indicate a unique time environment favourable to the immigration and development of conodonts in the devonian of northern south america the low diversity association suggests cold water dwelling taxa spreading to a high palaeolatitude during an episode of gentler latitudinal temperature gradient

suspended sediment response to semidiurnal and fortnightly tidal variations in a mesotidal estuary columbia river u s a abstract a turbidity maximum is the dominant feature of the suspended sediment concentration field in the columbia river estuary u s a in this estuary the turbidity maximum is an unsteady feature which changes on semidiurnal fortnightly and seasonal time scales in response to the semidiurnal tides the turbidity maximum is advected landward and seaward and may have an excursion of approximately 20 km in response to the fortnightly tidal variations the turbidity maximum degenerates or decreases in concentration during neap tides and regenerates or increases in concentration during spring tides finally in response to seasonal freshwater discharge variations suspended sediment concentrations in the turbidity maximum increase and its general location is pushed seaward during high discharge conditions and conversely concentrations decrease and its general location is farther landward during low discharge conditions the magnitude of suspended sediment concentration variations for these three time scales is similar therefore any consideration of estuarine dynamics and the suspended sediment concentration field in the columbia river estuary should include the semidiurnal and fortnightly time scales as well as the seasonal ones because the columbia is a mesotidal estuary and fortnightly tidal variations are not extremely large it is expected that these time scales and associated processes may be important in many other estuarine systems

modelling salinity and circulation for the columbia river estuary abstract simulations of the time and depth dependent salinity and current fields of the columbia river estuary have been performed using a multi channel laterally averaged estuary model the study simulated two periods the first in october 1980 with low riverflow of about 4 000m 3 s 1 which showed marked changes in the salinity intrusion processes between neap and spring tides and second in spring 1981 with high riverflow varying between 7 000 and 15 000m 3 s 1 which showed the rapid response of the salinity intrusion to changes in riverflow and that vertical mixing did not change character with increasing tidal energy because of the maintenance of stratification by freshwater flow an extreme low flow simulation riverflow of 2 000m 3 s 1 showed a more partially mixed character of the estuary channels with tidal dispersion of salt across the taylor sands from the north channel to the upper reaches of the navigation channel asymmetries in the non linear tidal mean flows in the flood and ebb circulations and salinity intrusion characteristics between the two major channels were observed at all riverflows the model confirms jay and smith s 1990 analysis of the circulation processes in that tidal advection of salt by the vertically sheared tidal currents is the dominant mechanism by which the salinity intrusion is maintained against large freshwater flows an accurate finite difference method which minimized numerical dispersion was used for the advection terms and was an important component in reasonably simulating the october neap spring differences in the salinity intrusion the simulations compare favorably with elevation current and salinity time series observations taken during october 1980 and spring 1981

temporal spatial reconstruction of the early frasnian late devonian anoxia in nw africa new field data from the ahnet basin algeria anoxic conditions were widespread in nw africa during the early frasnian late devonian that resulted in deposition of organic rich shales and limestones with total organic carbon toc values of up to 14 organic richness and thickness of these sediments vary laterally and organic rich vs organic poor facies boundaries are likely to have been diachronous a precise temporal spatial reconstruction of this anoxic phase in nw africa is complicated because the organic matter in outcrops is largely oxidised and biostratigraphic resolution in boreholes is generally low due to the lack of recoverable conodonts this contribution is based on eight outcrop sections at the margin of the central algerian ahnet basin where detailed spectral gammaray measurements were carried out using a handheld instrument the pre weathering organic richness in frasnian outcrop sections is approximated using the characteristic uranium enrichment in the anoxic facies that based on well studies is positively correlated with the total organic carbon content conodont biostratigraphic results from these sections suggest that the uraniumenriched interval the anoxic interval at the basin margin is most common in the basal frasnian conodont biozones 1 2 confirming previous results from the anti atlas in morocco in three of the eight localities studied the basal frasnian has not been deposited and the frasnian here commences with distinctly younger uranium enriched intervals including zones 4 11 well data from the eastern algerian berkine basin is interpreted to indicate a significantly longer anoxic phase there million yearscale diachroneities of the frasnian anoxia therefore clearly exist across the north africa shelf it is assumed that the palaeorelief might have been a major factor in controlling the onset duration and intensity of anoxia in the region d 2003 elsevier b v all rights reserved

historical changes in the columbia river estuary historical changes in the hydrology sedimentology and physical oceanography of the columbia river estuary have been evaluated with a combination of statistical cartographic and numerical modelling techniques comparison of data digitized from us coast and geodetic survey bathymetric surveys conducted in the periods 1867 1875 1926 1937 and 1949 1958 reveals that large changes in the morphology of the estuary have been caused by navigational improvements jetties dredged channels and pile dikes and by the diking and filling of much of the wetland area lesser changes are attributable to natural shoaling and erosion there has been roughly a 15 decrease in tidal prism and a net accumulation of about 68 106m3 of sediment in the estuary large volumes of sediment have been eroded from the entrance region and deposited on the continental shelf and in the balance of the estuary contributing to formation of new land the bathymetric data indicate that ignoring erosion at the entrance 370 to 485 106m3 of sediment has been deposited in the estuary since 1868 at an average rate of about 0 5 cm y 1 roughly 5 times the rate at which sea level has fallen locally since the turn of the century riverflow data indicate that the seasonal flow cycle of the columbia river has been significantly altered by regulation and diversion of water for irrigation the greatest changes have occurred in the last thirty years flow variability over periods greater than a month has been significantly damped and the net discharge has been slightly reduced these changes in riverflow are too recent to be reflected in the available in the available bathymetric data results from a laterally averaged multiple channel two dimensional numerical flow model described in hamilton 1990 suggest that the changes in morphology and riverflow have reduced mixing increased stratification altered the response to fortnightly neap spring changes in tidal forcing and decreased the salinity intrusion length and the transport of salt into the estuary the overall effects of human intervention in the physical processes of the columbia river estuary i e decrease in freshwater inflow tidal prism and mixing increase in flushing time and fine sediment deposition and net accumulation of sediment are qualitatively similar to those observed in less energetic and more obviously altered estuarine systems a concurrent reduction in wetland habitats has resulted in an estimated 82 reduction in emergent plant production and a 15 reduction in benthic macroalgae production a combined production loss of 51 675 metric tons of organic carbon per year this has been at least partially compensated by a large increase in the supply of riverine detritus derived from freshwater phytoplankton primary production comparison of modern and estimated preregulation organic carbon budgets for the estuary indicates a shift from a food web based on comparatively refractory macrodetritus derived from emergent vegetation to one involving more labile microdetritus derived from allochthonous phytoplankton the shift has been driven by human induced changes to the physical environment of the estuary while this is a relatively comprehensive study of historical physical changes it is incomplete in that the sediment budget is still uncertain more precise quantification of the modern estuarine sediment budget will require both a better understanding of the fluvial input and dredging export terms and a sediment tranport model designed to explain historical changes in the sediment budget oceanographic studies to better determine the mechanisms leading to the formation of the turbidity maximum are also needed the combination of cartography and modelling used in this study should be applicable in other systems where large changes in morphology have occurred in historical time

sedimentary geology of the columbia river estuary abstract a multiyear study of the sedimentary geology of the columbia river estuary has provided valuable data regarding sediment distribution bedform distribution and suspended sediment distribution on spatial and temporal scales that permit delineation of sedimentary environments and insight into the sedimentary processes that have shaped the estuary in comparison to other more intensively studied estuaries in north america the columbia river estuary has relatively larger tidal range maximum semidiurnal range of 3 6m and large riverflow 6 700m3s 1 variations in riverflow sediment supply and tidal flow occur over a range of time scales making the study of modern processes as they relate to long term effects particularly challenging analyses of more than 2000 bottom sediment grab samples indicate that the bed material of the estuary varies in a relatively narrow range between 0 and 8 phi 1 0 and 0 0039mm with an overall mean size of 2 5 phi 0 177mm sediment size decreases generally in the downstream direction sediments from the upriver channels are coarse 1 5 2 0phi 0 25 0 35mm and moderately sorted sediments in the central estuary show wider range and variation in grain size and sorting 1 75 6 0phi 0 016 0 3mm sediment from the entrance region has a mean size of 2 75phi 0 149mm and is well sorted seasonal changes in sediment size distributions occur and are best delineated by those samples containing more than 10 mud silt plus clay sediments containing a significant fine fraction generally occur only in the peripheral bays and in channels isolated from strong currents thin deposits of fine sediments are occasionally found in main channels and the ephemeral nature of these sediments suggest that they may erode and produce the silty rip up clasts that appear intermittently in the same regions the distribution of bedforms of various size and shape has been mapped with side scan sonar during three seasons and at various tidal stages the presence of bedforms with wavelengths of 6 8m and alternating slip faces about 40cm high indicates that the deeper portion of the entrance region is dominated by tidally reversing lower flow regime sediment transport bedforms in the upper reaches of the estuary are much larger with heights of up to 3m and wavelengths of up to 100m these bedforms and the smaller superimposed bedforms imply downstream transport under fluvial conditions in the central estuary bedforms in the deep portion of the main channels are oriented upriver while those on the shallow flanks of the channels are oriented seaward the landward limit of upriver bedform transport varies seasonally in response to riverflow fluctuations a complex array of sedimentary environments exists in the columbia river estuary each environment is influenced by the relative importance of waves fluvial currents and tidal currents as modified by the presence or absence of estuarine circulation vegetation or human activity the importance of these enviroments to the ecosystem of the estuary is discussed in subsequent papers in this volume

modelling tidal energetics of the columbia river estuary abstract the columbia river estuary is shallow and has a mixed diurnal and semidiurnal tide strong riverflow broad tidal flats and variable channel cross section it is weakly non linear with respect to tidal forcing as measured by a ratio of tidal amplitude to depth these features common to many shallow estuaries were incorporated into a one dimensional harmonic transport model the harmonic method utilizes the fact that nearly all of the energy in the system is in a few fundamental tidal frequencies the first overtides thereof and the mean flow this allows the representation of the flow as a series of harmonic components whose spatial variability is determined by the model the model provides a qualitative explantation for and accurate quantitative predictions of along channel variations in tidal properties in terms of the momentum balance near the mouth of the estuary the boundary shear stress the pressure gradient and the acceleration terms are all important in the force balance and the tide behaves like a damped oscillator far upriver the pressure gradient is primarily balanced by friction at the bed and tidal wave propagation can be described as a diffusion process changes in the channel width in mid estuary cause partial reflection of the tidal wave and a maximum in tidal range this partial reflection decreases the tidal energy flux in the upstream direction the distribution of the time averaged energy fluxes was also determined from the model the analysis shows that there are two regions of high energy dissipation energy is supplied near the mouth of the estuary by the divergence of the landward flux of tidal potential energy and far upriver by the divergence of the seaward flux of fluvial potential energy these two regions of high dissipation are separated by a region of low dissipation the energy flux divergence minimum this spatial division of the estuary is mirrored in the system biology and geology it is likely that the energy flux divergence minimum is a common feature of shallow estuaries with strong riverflow

holocene sedimentary activity in a non terrestrially coupled submarine canyon cook strait canyon system new zealand abstract the cook strait canyon system located between the north and south islands of new zealand is a large 1800 km 2 multi branching shelf indenting canyon on an active subduction margin the canyon comes within 1 km of the coast but does not intercept fluvial or littoral sediment systems and is therefore defined as a non terrestrially coupled system sediment transport associated with a strong tidal stream and seafloor disturbance related to numerous high activity faults is known from previous studies little is known however about the rates of sedimentary activity in the canyon and the processes driving it a substantial dataset of em300 multibeam bathymetry gravity cores 3 5 khz seismic reflection profiles camera and video transects and current meter data have been collected across the region between 2002 and 2011 the canyon system therefore provides an excellent study area for understanding sediment transport in a non coupled submarine canyon system analysis of the data reveals a two staged sediment transport system where 1 oceanographic tidal processes mobilise sediment from the continental shelf and transport it to depocentres in the upper central canyons and 2 tectonic earthquake processes remobilise sediment that is transported through the lower canyon to the deep ocean tidal boundary layer currents within the canyon reach velocities up to 0 53 m s and are capable of mobilising fine sand in the central reach of the upper canyons the velocity is higher at the canyon rim and capable of mobilising coarse sand sediment depocentres resulting from this tidally forced sediment transport have a well formed geomorphology within the mid upper canyon arms of cook strait and nicholson canyons pseudo static stability modelling supported by sediment core analysis indicates that sediment accumulated in the upper canyons fails during seismic events approximately every 100 years the 100 year return period ground shaking level peak ground acceleration ignoring the effect of the water column above the seabed at this site is estimated to be 0 23 g fresh rock outcrops and bed scour in the lower canyon floor indicate that remobilised material is transported to the deep ocean the processes identified here are likely to be analogous to those occurring in many non coupled shelf indenting canyons on active margins globally and provide a framework within which the biological response to geomorphic processes in submarine canyons can be assessed

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

reconstruction of sediment supply from mass accumulation rates in the northern adriatic basin italy over the past 19 000 years reconstruction of sediment supply is hampered by the incompleteness of the stratigraphic record this problem may be partly circumvented by studying mass accumulation rates in closed systems i e basins in which no sediment has bypassed the site of deposition over the time interval of interest we present time averaged basin wide mass accumulation rates and their associated uncertainties from a well documented closed basin the northern adriatic basin italy spanning the time interval from 19 ka b p to the present the sediment masses of five basin wide lithosomes and their associated uncertainties are derived by means of stochastic simulation using highresolution seismic data porosity profiles and radiocarbon datings this study demonstrates that inferring rates of sediment supply from conformity bounded stratigraphic units is feasible as indicated by the excellent agreement of our results of mass accumulation over the past 400 years with two independently derived estimates formation of the stratigraphic record is not an instantaneous process by comparing spatial patterns of mass accumulation rates on three different timescales decadal centennial and millennial we demonstrate a low preservation potential of sediments presently accumulating near the coast and a continuous cross shore and alongshore sediment transport regime the change from transient to persistent accumulation patterns in the highstand systems tract of the northern adriatic basin occurs at the centennial to millennial timescale intrabasinal erosion and recycling of sediments obscure the relation between rates of sediment supply and net basin wide mass accumulation which limits the amount of information that can be extracted from the stratigraphic record hence a mismatch between rates of sediment supply and accumulation rates is expected for unconformity bounded sequence stratigraphic units given the uncertainties associated with our estimates we are unable to reject the hypothesis that net basin wide mass accumulation rates have been constant over the time interval of 19 000 years at a 10 significance level

compactional behavior of fine grained sediments examples from deep sea drilling project cores laboratory experiments statistical analysis of field data and theoretical models are combined in the attempt to derive standard compaction curves for various deep sea sediments which are in compaction equilibrium with the overburden a revised and generalized version of athy s law together with laboratory experiments allows the classification of sediments in terms of the amount of porewater structurally bound to the particles surfaces especially suction pressure experiments are useful in quantifying the forces that bind water on the particle surfaces the sediments analyzed almost range from systems of suspended grains to nearly perfect colloidal systems the methods and equations required to derive the relevant parameters are given for both downhole porosity density measurements and laboratory experiments

ichnofabrics and chemostratigraphy argue against persistent anoxia during the upper kellwasser event in new york state abstract organic rich strata coeval with bioevents of varying magnitudes characterize global devonian sedimentary successions the upper kellwasser ukw black shale depositional event is coincident with the largest pulse of diversity loss within the marine late devonian mass extinction and has been shown to be an ecologically critical turnover for shallow water species marine anoxia euxinia is widely thought to be an important and ubiquitous driver of this biotic crisis though the duration intensity and global extent of these environmental conditions during the ukw event are not well constrained we characterized redox conditions during deposition of the ukw in the northern appalachian basin to constrain local variability and relative magnitude of dissolved oxygen fluctuations we used a combination of proxies relating to the bottom waters water column and photic zone to compile an integrated picture of basinal oxygen dynamics our multi faceted approach combines trace fossil evidence for faunal activity at the sediment water interface with inorganic and organic geochemical proxies for redox conditions within the water column minor biological disruptions to laminated sedimentary fabric indicate at least intermittent oxygenation of the bottom waters during deposition of the ukw albeit in a low dissolved oxygen seafloor setting trace metal proxies mo mn u and v and fe mineral speciation provide compelling evidence for a water column experiencing intermittent rather than persistent anoxic euxinic conditions lipid biomarkers reinforce the interpretation of variable dissolved oxygen conditions with very low concentrations of chlorobi carotenoid biomarkers pointing to seasonal rare episodes of photic zone euxinia this integrated dataset provides evidence for local redox variability in ukw deposition and supports the likelihood that marine anoxia and euxinia were not globally persistent at the frasnian famennian boundary

deciphering the upper famennian hangenberg black shale depositional environments based on multi proxy record abstract presented for the first time in this paper are the results of a detailed multi proxy investigation conducted on the hangenberg black shale hbs from the polish part of the laurussian shelf which provide details about the environmental conditions in existence during deposition of the shale and the role played by anoxic conditions in the mass extinction events that occurred at the end of the devonian times inorganic and organic redox indicators indicate that bottom water redox conditions changed periodically from being mainly anoxic euxinic to oxic or being partially depleted in oxygen u th values above 1 25 ni co values above 7 and v v ni values above 0 8 recorded from the lower part of the hbs all point to anoxic euxinic conditions being present as do high total organic carbon contents toc above 10 and degree of pyritisation dop values around 0 75 however the presence of benthic fauna over the lower part of the hbs attests to opportunistic colonisation of the seafloor during oxic episodes evidence for similar episodes has also been recognised over the middle part of the hbs e g u th values below 1 25 ni co values below 4 v v ni values below 0 8 toc values of 3 to 5 5 and dop values of 0 4 to 0 75 plus the common occurrence of benthic fauna anoxic conditions returned during the deposition of the upper part of the hsb though they were not as well developed as when the lower part of the shale was laid down of interest is the presence of small pyrite framboids and isorenieratene biomarkers in all the analysed samples which suggest that euxinic conditions persisted in the photic zone of the water column a twenty centimetre thick layer of volcanogenic deposits tuffites is present in the middle part of the hbs the geochemical characteristics of which are typical of ocean floor basalts the occurrence of volcanogenic material below and within the hbs together with an absence of calcium carbonate over its upper part the presence of abundant tetrads just above the black shale and a drastic decrease in faunal frequency in the upper part of the hbs imply that volcanism may have caused oceanic acidification or hypercapnia that in turn potentially may have influenced the hangenberg mass extinction event

energetics and sedimentary processes in the columbia river estuary abstract the columbia river estuary is an energetic sand bedded system mixed tides with a spring tidal range of about 3 6m and a large freshwater discharge produce bottom shear stresses capable of transporting nearly all the sizes of sediment present in the estuary as a result the morphology of the estuary is closely related to the fluxes of tidal and fluvial energy to investigate the relationship between energetics and sedimentary processes an energy budget based on a one dimensional harmonic tidal model was developed for the estuary tidal river system and has been compared with the results of geological studies of the bedforms large scale morphology sediment distribution and suspended sediment field the pattern of energy fluxes predicted by the model suggests the division of the system into three regimes a tidally dominated lower estuary a mid estuary energy flux divergence efd minimum region and a fluvially controlled tidal fluvial reach model results also show that non linear interactions between the tidal and fluvial flows are responsible for the suppression of the tides in the tidal fluvial reach during periods of high flow finally changes in tidal amplitude at the mouth result in a less than proportionate response in tidal elevations at points inside the estuary because the cubic dependence of dissipation on tidal amplitude damps system responses to such changes many features of the observed sediment transport patterns and sedimentary environments can be related to the energy budget most of the medium to coarse sands entering the system from the river are permanently retained within the efd minimum much of this deposition takes place upstream of the limits of salinity intrusion and is not therefore related to baroclinic circulatory effects most of the fine sands and the silts and clays entering the system are not permanently retained some of the silts and clays are however temporarily retained in a turbidity maximum whose mean position is near the lower end of the efd minimum this position is dictated by the inability of salinity intrusion to extend up the fluvial potential energy gradient although some aspects of sedimentary processes cannot readily be related to the energy budget our model provides a valuable conceptual approach to the dominant long term sedimentary processes of sand transport and deposition in the columbia river estuary that structure the observed sedimentary environments biological processes are in turn strongly influenced by these geological patterns

determination of organic matter content of appalachian devonian shales from gamma ray logs the organic matter content of the devonian shale of the appalachian basin is important for assessing the natural gas resources of these rocks and patterns of organic matter distribution convey information on sedimentary processes and depositional environment in most of the western part of the appalachian basin the organic matter content of the devonian shale can be estimated from gamma ray wire line logs using the equation phgro ggrb ggr 1 378a where phgro is the organic matter content of the shale fractional volume ggr the gamma ray intensity api units ggrb the gamma ray intensity if no organic matter is present api units and a the slope of the crossplot of gamma ray intensity and formation density api units g cm3 the quantities a and ggrb vary regionally and are mapped using data from gamma ray and formation density wire line logs organic matter contents estimated using this equation are compared with organic matter contents determined from direct laboratory analyses of organic carbon for 74 intervals of varying thickness from 12 widely separated wells the organic matter content of these intervals ranges from near zero to about 20 by volume excluding the cleveland member of the ohio shale and the lower part of the olentangy shale the distribution of the differences between volume percent organic matter content determined from core samples and estimated from gamma ray logs has a mean of 0 44 and a standard deviation of 1 98 which indicates that the accuracy of the gamma ray method is adequate for most geologic applications the gamma ray intensity of the cleveland member of the ohio shale and the lower pa t of the olentangy shale is anomalously low compared to other devonian shales of similar richness so that organic matter content computed for each of these units from gamma ray logs is likely to be too low wire line methods for estimating organic matter content have the advantages of economy readily available sources of data and continuous sampling of the vertically heterogenous shale section the gamma ray log in particular is commonly run in the devonian shale its response characteristics are well known and the cumulative pool of gamma ray logs forms a large and geographically broad data base the quantitative computation of organic matter content from gamma ray logs should be of practical value in studies of the appalachian devonian shale the general approach described here may also be applicable to other formations with physical and geochemical characteristics similar to the appalachian devonian shale

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

extent and persistence of photic zone euxinia in middle late devonian seas insights from the canning basin and implications for petroleum source rock formation abstract late devonian mass extinctions attributed to extensive anoxia and or euxinia of the oceans are associated with widespread deposition of organic rich shales also in the epeiric waters of the canning basin western australia photic zone euxinia pze prevailed during the givetian frasnian with geochemical evidence for pze on the northern lennard shelf and southern barbwire terrace margins of the fitzroy trough on the lennard shelf shales record episodic pulses of pze associated with high algal activity due to enhanced nutrient supply whereas a restricted marine setting on the barbwire terrace is thought to be the main driver for the development of persistent pze and associated bacterial predominance structural evidence indicates that the fitzroy trough was a confined basin during the late devonian with the possibility of limited ocean circulation widespread pze is expected to have developed in the poorly mixed water column if the basin received sufficient nutrient supply for enhanced primary production notwithstanding the presence of anoxia during deposition of potential source rocks only two small devonian sourced oil fields and numerous oil shows have been found in the canning basin biomarker assemblages show that the oils produced from the lennard shelf fields i e blina 1 blina 4 and janpam north 1 have substantially different molecular compositions to the minor oil recovered from mirbelia 1 on the barbwire terrace a correlation was established between the lennard shelf oils and rock extracts from the gogo formation at blina 1 and mcwhae ridge 1 based on their hopane sterane and carotenoids abundances a definitive source correlation was not obtained for the mirbelia 1 oil but it did show some genetic affinity to the givetian frasnian extracts from the barbwire terrace suggesting that local source rocks are developed in the region

large scale coastal change in the columbia river littoral cell an overview abstract this overview introduces large scale coastal change in the columbia river littoral cell crlc covering 165 km of the southwest washington and northwest oregon coasts the littoral cell is made up of wide low sloping dissipative beaches broad coastal dunes and barrier plains three large estuaries and is bounded by rocky headlands the beaches and inner shelf are composed of fine grained sand from the columbia river and are exposed to a high energy winter wave climate throughout the holocene the crlc has undergone large fluctuations in shoreline change trends responding to a variety of coastal change drivers including changing rates of sea level rise infrequent yet catastrophic co seismic subsidence events a large regional sediment supply inter annual climatic fluctuations el nino cycles seasonally varying wave climate and numerous anthropogenic influences human influences on the crlc include construction of over 200 dams in the columbia river drainage basin dredging of navigation channels removing sand to upland sites and offshore deep water sites and construction of large inlet jetties at the entrances to the columbia river and grays harbor the construction of these massive entrance jetties at the end of the 19th century has been the dominant driver of coastal change through most of the littoral cell over the last hundred years presently some beaches in the littoral cell are eroding in response to nearshore sediment deficits resulting from a ebb jets of the confined entrances pushing the previously large shallow ebb tidal deltas offshore into deeper water and b waves dispersing the nearshore delta flanks initially onshore and then alongshore away from the jetties this overview describes 1 the motivation for developing a system wide understanding of sediment dynamics in the littoral cell at multiple time and space scales 2 the formation and approach of the southwest washington coastal erosion study and 3 an introduction to the papers in this special issue

shale compaction and statistical physics summary after a short historical outline of the development of the ideas on the compaction of clays and shales it is shown that the exponential porosity depth dependence of compacted shales expressed by athy s law can be derived using standard methods of statistical physics the main result of the paper states that the exponential compaction law expresses the maximum entropy equilibrium state of the pores in the rock that is compaction is an irreversible process where clay particles tend towards a statistically defined final equilibrium connections with the classical theory of consolidation are pointed out

dissolved iron speciation in two distinct river plumes and an estuary implications for riverine iron supply dissolved iron fe speciation in the columbia river plume the san francisco bay plume and the columbia river estuary was investigated using competitive ligand exchange adsorptive cathodic stripping voltammetry cle acsv with the added ligand salicylaldoxime a stronger l1 type fe binding ligand class was measured in all surface samples and in the columbia river estuary a weaker l2 type ligand class was present in the far field columbia river plume and the san francisco bay plume but was not observed in the low salinity s 1 4 22 5 waters of the near field columbia river plume or estuary concentrations of total dissolved fe were correlated with the concentrations of the stronger l1 type ligand in nonestuarine s 13 surface samples leachable particulate 0 4 m fe concentrations in the columbia river plume were measured to supplement existing data from the san francisco bay plume there is a large concentration of readily leachable particulate fe in the two plumes yet it is the concentration of ambient l1 type ligands that appears to dictate the concentration of dissolved fe in these waters and consequently the supply of dissolved fe to neighboring coastal waters the correlation between dissolved fe and l1 ligand concentrations in both plume waters as well as in california current and upwelled surface waters suggests that this relationship will persist in other coastal environments and should be considered when evaluating and modeling coastal fe cycling and supply

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

validation of a coupled wave flow model in a high energy setting the mouth of the columbia river 1 a monthlong time series of wave current salinity and suspended sediment measurements was made at five sites on a transect across the mouth of columbia river mcr these data were used to calibrate and evaluate the performance of a coupled hydrodynamic and wave model for the mcr based on the delft3d modeling system the mcr is a dynamic estuary inlet in which tidal currents river discharge and wave driven currents are all important model tuning consisted primarily of spatial adjustments to bottom drag coefficients in combination with near default parameter settings the mcr model application is able to simulate the dominant features in the tidal flow salinity and wavefields observed in field measurements the wave orbital averaged method for representing the current velocity profile in the wave model is considered the most realistic for the mcr the hydrodynamic model is particularly effective in reproducing the observed vertical residual and temporal variations in current structure density gradients introduce the observed and modeled reversal of the mean flow at the bed and augment mean and peak flow in the upper half of the water column this implies that sediment transport during calmer summer conditions is controlled by density stratification and is likely net landward due to the reversal of flow near the bed the correspondence between observed and modeled hydrodynamics makes this application a tool to investigate hydrodynamics and associated sediment transport

influence of early diagenesis on geotechnical properties of clay sediments romania black sea abstract the geotechnical properties of clay sediments were investigated using laboratory and in situ measurements as part of the geohazard assessment in the romanian sector of the black sea affected by landslides and seafloor deformation features the sediments were characterized as predominantly high plastic silty clay of high compressibility low undrained shear strength low cohesion and moderate sensitivity a shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction e g cryptic sulfur cycle and anaerobic oxidation of methane comparison of the compression behaviour of natural and reconstituted samples indicated that precipitation of these materials at particle contacts produced cementation the analysis of deeper sediments sharing similar geochemical properties illustrated that the early precipitation of even low quantity of sulfur and carbonate cements allowed clays to develop sufficient strength to preserve an abnormal high water content even under tens of meters burial depth because this cementation process was observed to be associated with an enhanced sensitivity and a strain softening response to undrained shearing it was concluded that such early diagenesis should be considered as a key environmental factor leading to weak layer formation that may influence the susceptibility of seafloor to failure

tide transformation in the guadalquivir estuary sw spain and process based zonation an edited version of this paper was published by agu copyright 2012 american geophysical union

effective petroleum source rocks of the world stratigraphic distribution and controlling depositional factors six stratigraphic intervals representing one third of phanerozoic time contain petroleum source rocks that have provided more than 90 of the world s discovered original reserves of oil and gas in barrels of oil equivalent the six intervals are 1 silurian generated 9 of the world s reserves 2 upper devonian tournaisian 8 of reserves 3 pennsylvanian lower permian 8 of reserves 4 upper jurassic 25 of reserves 5 middle cretaceous 29 of reserves and 6 oligocene miocene 12 5 of reserves this uneven distribution of source rocks in time displays no obvious cyclicity and the factors that controlled the formation of source rocks vary from interval to interval maps that show facies structural forms and petroleum source rocks were prepared for this study analysis of the maps indicates that several primary factors controlled the areal distribution of source rocks their geochemical type and their effectiveness i e the amounts of discovered original conventionally recoverable reserves of oil and gas generated by these rocks these factors are geologic age paleolatitude of the depositional areas structural forms in which the deposition of source rocks occurred and the evolution of biota the maturation time of these source rocks demonstrates that the majority of discovered oil and gas is very young almost 70 of the world s original reserves of oil and gas has been generated since the coniacian and nearly 50 of the world s petrole m has been generated and trapped since the oligocene the term petroleum as used in this study includes oil gas condensate and gas but does not include bitumen and other solid and semisolid oil derivatives

silica diagenesis porosity evolution and mechanical behavior in siliceous mudstones mowry shale cretaceous rocky mountains u s a quartz in mudstones of the mowry shale cretaceous rocky mountain region takes several forms extrabasinal detrital silt some with transported overgrowths replacement of skeletal debris minor overgrowth on detrital quartz and replaced radiolaria pore filling in the intragranular pores of allochems and authigenic microquartz that is dispersed through the clay size matrix the matrix dispersed microquartz has cl character similar to the overgrowths with which it is intergrown supporting the interpretation that it is authigenic and pore filling radiolaria are widely observed in these mudrocks but are poorly preserved by partial mineral replacement quartz dolomite calcite pyrite we interpret dissolved radiolaria and possibly now cryptic diatoms as the likely source of silica for the overgrowths and microquartz through a reaction pathway that entailed the formation of opal ct lepispheres that subsequently recrystallized to microquartz a newly devised variation of the igv intergranular volume concept a parameter igvm is applied for partitioning the causes of porosity decline in mudstones all of the samples examined contain authigenic microquartz which averages around 40 of the rock volume the large volume of microquartz together with the volumes of surviving intergranular pores and pore filling solid hydrocarbon constrain the porosity to around 50 at the time of initial lepisphere formation despite the exceptional abundance of cement overall porosity decline is compaction dominated the presence of significant volumes of cement has implications for mechanical rock properties in the mowry shale which is expected to manifest brittle behavior where cements are most prominently developed

minor and trace element and re os chemistry of the upper devonian woodford shale permian basin west texas insights into metal abundance and basin processes the trace and minor element and re os geochemistry of the upper devonian woodford shale are analyzed in order to characterize elemental abundances to identify associations among trace elements and to constrain paleoceanographic conditions and depositional processes this organic carbon rich mudstone in the permian basin west texas is a major source of hydrocarbons in the basin and is coeval with many other upper devonian shales in north america the woodford lacks enrichment in many trace metals only mo u s and se are significantly enriched other redox sensitive elements are depleted or similar to average shale composition including pb bi cr ti cu zn co and v elements associated with granitic sources such as rare earths th ce and tio2 are also depleted relative to average shale this appears to be related to be a source control a strong basin reservoir effect is noted among several redox sensitive elements including mo cu and ni which largely accounts for the depletion dilution by biogenic silica had an additional effect on metal concentrations multivariate factors analysis identified associations between elements including groupings of rare earth elements elements enriched in granitic crust silica varying antithetically with elements in carbonate minerals organic carbon mo and u v phosphate fe and s noteworthy among the results are the different behavior of redox sensitive elements suggesting different precipitation mechanisms or varying dependence on reservoir effects a strong redox effect is noted in the toc ptot ratio at approximately the frasnian famennian boundary indicating an abrupt transition to an anoxic column boundary that coincides with a short term significant fall in sea level this suggests that anoxia was induced by isolation of the basin from the global ocean however with the exception of the uppermost famennian initial 187os 188os values determined from re os geochronology for the permian basin are similar to correlative sections of the appalachian and peace river basins of north american and the rhenohercynian basin of europe this indicates that although the permian basin became restricted during the upper devonian and early mississippian ocean connectivity remained between regional and global basins

petroleum assessment of berkine ghadames basin southern tunisia hydrocarbon exploration in the berkine ghadames basin in southern tunisia has generally followed global economic trends in recent years improvements in seismic data acquisition combined with experience gained in log interpretation in low resistivity reservoirs have resulted in oil and gas discoveries in the upper silurian acacus formation enriching the hydrocarbon potential of the berkine ghadames basin in southern tunisia presently the tunisian daily oil production is approximately 43 000 bbl about half of which comes from the fields located in southern tunisia and is produced from the acacus formation the berkine ghadames basin is an intracratonic basin formed during the pan african orogeny it covers an area of approximately 350 000 km2 135 135 mi2 and extends into algeria libya and tunisia the sedimentary section within the basin ranges from cambrian to present and is approximately 7000 m 23 000 ft thick in the depocenter the basin has experienced several tectonic events which have modified its architecture and affected the petroleum systems and hydrocarbon pathways in this study the main elements of the petroleum geology systems are described with the geochemical modeling results the petroleum potential hydrocarbon generation expulsion time and quantity of hydrocarbon are assessed the main petroleum systems are also defined they are represented by the silurian tannezuft hot shale source rock with ordovician djeffara and silurian acacus reservoirs by silurian tannezuft hot shale with kirchaou reservoirs and by the devonian aouinette ouinine formation member iii source rock with kirchaou reservoirs the hydrocarbon traps in the area are mainly structural types the study describes and emphasizes the hydrocarbon migration pathway mechanism from source rocks to traps to predict and derisk future drilling locations fairway maps are generated for the three plays ordovician silurian and triassic although the paper focuses on southern tunisia an attempt is made to introduce libyan and algerian knowledge to evaluate the basin in a regional context

friction experiments on saturated sediments and their implications for the stress state of the nankai and barbados subduction thrusts the nankai and barbados forearcs have low stress subduction thrusts the sediments entering the subduction zone and namely the material in the decollement zones have been well characterized by numerous deep sea drilling legs and studies of the recovered cores nankai has high heat flow and significant amounts of illite while barbados is a smectite dominated system based on results from ring shear 2 mpa normal stress and direct shear 30 mpa tests on marine sediments and mineral standards this translates into a residual frictional resistance of r 0 25 and r 0 11 in clay horizons respectively such values agree with theoretical estimates from critical wedge theory nankai b 0 16 0 26 and barbados b 0 06 0 09 and fault spacing geometries from seismic profiles nankai b 0 12 0 23 and barbados b 0 11 0 19 maximum pore pressure ratios of 0 85 and 0 73 for nankai and barbados respectively allow us to estimate effective shear stresses as a function of friction coefficient and density of the sediment gouge to reach only 10 mpa or less in the frontal 50 km of the decollement zone respectively our data support the contention that fluid pressure transients and sediment composition contribute equally to the weakness along plate boundary faults down to the seismogenic zone with the first probably dominating the shallow decollement shear velocity stepping tests show that the clay dominated gouges strengthen velocity irrespective of the clay mineralogy and hence suggest that clay transformation does not affect the onset of seismogenesis

the global frasnian famennian kellwasser event during the uppermostp gigas conodont zone p linguiformis zone the stepwise frasnian extinction culminates in the global transgressive regressive frasnian famennian kellwasser event most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction during the early upper devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the shelf sediments contemporaneous positive excursions of the 13c recorded from pelagic limestones of europe and australia prove a worldwide change in the co2 content of the oceans surface water which is in balance with the atmosphere if the climate is controlled by the co2 content of the atmosphere a cyclic operation process might have developed with the succession transgression high organic production deposition of organic carbon lowering of co2 in the atmosphere icehouse effect polar glaciation regression erosion of organic carbon and re supply of co2 to the ocean and atmosphere greenhouse effect deglaciation transgression during the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

the hydrocarbon systems of north africa abstract north africa s hydrocarbon reserves are spread over a wide range of reservoirs and play types but derive from only a few key source rock intervals particularly those in the silurian late cretacous and eocene source rock maturity together with the timing of the generation relative to trap forming and destructive events seem to be the key controlling factors on success or failure at a basin level in most cases generation clearly post dates trap formation although a more complex relationship is evident in various parts of algeria where some traps did not form until gas was being generated source rock deposition and maturation can be tied to two main extensional tectonic cycles which ended in the compressional and destructive events of the hercynian and alpine orogenies remaining exploration potential in mature provinces may be tied largely to subtle and stratigraphic traps in addition significant frontier potential can be identified in two main fairways corresponding to regions where silurian devonian and cretaceous eocene sources respectively are likely to have generated petroleum critical factors in these areas are timing of generation and preservation the gas discoveries in the ahnet basin provide analogues for palaeozoic generation preservation models in the interior silurian devonian source fairway similarly the key to success for the mesozoic basins of the atlas region lies in demonstrating a favourable relationship between trap formation destruction and generation from late cretaceous and eocene source rocks

organic matter deposition in the ghadames basin libya during the late devonian a multidisciplinary approach the organic rich deposits of late devonian age are the second most important petroleum source rocks in the ghadames basin libya from available stratigraphy the peak of organic matter deposition corresponding to a level of radioactive shales easily recognized in gamma ray logs occurred at the frasnian famennian transition the present study was focused on samples from borehole d1 26 located in the central part of the ghadames basin belonging to the aouinet ouenine iii and iv formations frasnian to famennian the mineral and organic content of the rocks were analyzed in order to determine the origin of organic matter accumulation and estimate if the organic matter enrichment could be related to the well known upper kellwasser event the results indicate that during the frasnian the planktonic primary productivity was moderate but anoxic conditions reaching the euphotic zone were frequent and allowed efficient preservation of the organic matter at the frasnian famennian transition the deposition of the radioactive shales level can be related to a eustatic rise which allowed incursion of nutrient rich water in the basin leading to increase in primary productivity and photic zone anoxia during the famennian the conditions changed associated with a relative sea level fall and or a progradation of detrital sediments originating from the south photic zone anoxia was only episodic and plankton derived organic matter was poorly preserved nevertheless the important influx of organic matter of terrestrial origin allowed significant enrichment of the sediment in organic matter several indications suggest the radioactive shales interval could be coeval with the upper kellwasser level nevertheless further stratigraphic work is needed to confirm this hypothesis

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

interaction of fluctuating river flow with a barotropic tide a demonstration of wavelet tidal analysis methods wavelet transforms provide a valuable new tool for analysis of tidal processes that deviate markedly from an assumption of exact periodicity inherent in traditional harmonic analysis a wavelet basis adapted to nonstationary tidal problems is constructed and employed to analyze the modulation of the external tide in a river by variations in streamflow interaction of a surface tide with river flow is the best available demonstration of the continuous wavelet transform cwt methods developed it is the simplest and perhaps the only nonstationary tidal process for which both sufficient data and dynamical understanding exist to allow detailed comparisons between cwt analyses and analytical predictions of the response of tides to nontidal forcing variations at upriver locations of low frequency elevation river stage zr and three tidal species are deduced from cross sectionally integrated equations for landward propagation in a channel of constant cross section with quadratic friction the log of the amplitude of the diurnal d1 semidiurnal d2 and quarterdiurnal d4 elevations should vary at far upriver locations with the square root of the river flow qr and river stage zr should depend on the square of river flow convergent geometry and species species frictional interactions modify these predictions somewhat cwt analyses show that the predicted amplitude behavior for the tidal species is approximately correct best results are obtained for the dominant dynamically simplest processes zr and d2 in the past further progress in understanding river tides has been limited by a lack of data analysis tools data analysis tools are now clearly better than the available analytical solutions

tidal energy loss in coastal embayments the tidal energy balance for an embayment over the spring neap cycle is used to obtain a relationship between the phase of the m 2 and s 2 tidal flow at the entrance using solely tidal elevation harmonic constants as inputs for possible values of the phase of the flow the calculated frictional drag coefficient k or comparison with observation of the variation of the phase of the flow through the spring neap cycle may be used to allow the frictional energy dissipation to be estimated application to the bristol channel for values of k which are consistent with the generally accepted range of values used in two dimensional numerical models give estimates of the phase of the flow within the range of those observed and of the tidal energy dissipation consistent with previous estimates the method should allow estimates of the energy dissipation per unit mass to be made in embayments where tidal elevation harmonic constants alone are available and thus provide an insight into the potential mixing

impacts of columbia river discharge on salmonid habitat 1 a nonstationary fluvial tide model 1 this is the first part of a two part investigation that applies nonstationary time series analysis methods and the st venant equations to the problem of understanding juvenile salmonid access to favorable shallow water habitat in a tidal river habitat access is a function of river stage tidal range and the distribution of bed elevation part 1 models nonstationary tidal properties species amplitudes and phases and tidal range part 2 models low frequency river stage in the lower columbia river and reconstructs historical water levels using the tidal model from part 1 to incorporate the nonstationary frictional effects of variable river discharge into the tidal model we decompose the tidal wave into tidal species and calculate daily tidal range our one dimensional tidal model is based on analytic wave solutions to the linearized st venant equation and uses six coefficients per tidal species to represent the upstream evolution of the frictionally damped tidal wave the form of the coefficients is derived from the st venant equations but their values are determined objectively from the data about 50 station years of surface elevation data collected 1981 2000 below bonneville dam 235 km from the ocean were processed with a wavelet filter bank to retrieve time series of tidal species properties a min max filter was used to estimate daily tidal range tidal range diurnal and semidiurnal amplitudes were predicted with mean root mean square errors 30 mm which is significantly more accurate than predictions obtained from harmonic analysis thus despite the compact form of our solution we model nonstationary fluvial tidal properties with a high level of accuracy

tide tsunami interaction in columbia river as implied by historical data and numerical simulations the east japan tsunami of 11 march 2011 propagated more than 100 km upstream in the columbia river visual analysis of its records along the river suggests that the tsunami propagation was strongly affected by tidal conditions a numerical model of the lower columbia river populated with tides and a downstream current was developed simulations of the east japan tsunami propagating up the tidal river reproduced the observed features of tsunami waveform transformation which did not emerge in simulations of the same wave propagating in a quiescent state river this allows us to clearly attribute those features to nonlinear interaction with the tidal river environment the simulation also points to possible amplification of a tsunami wave crest propagating right after the high tide previously deduced from the recordings of the 1964 alaska tsunami in the river

factors affecting the diagenesis of quaternary sediments at odp leg 172 sites in western north atlantic evidence from pore water and sediment geochemistry abstract pore waters and quaternary sediments at odp leg 172 sites on the carolina slope cs site 1054 blake outer ridge bor sites 1057 and 1060 bahama outer ridge baor 1062 and bermuda rise br site 1063 were studied the sediments are mainly clayey and silty mud with intercalations of nannofossil rich and lutite rich beds towards the top sedimentation rate ranges from 4 2 cm ky at site 1054 to 23 cm ky at site 1060 average total organic carbon toc contents of the upper sediment units range from 0 40 to 0 58 at sites 1057 1060 1062 and 1063 and from 0 86 to 1 25 at site 1054 the organic matter at all the sites is mostly degraded except at site 1054 sediments at sites 1062 and 1063 have lower total sulfur ts 0 00 0 62 average 0 06 than those at the other sites site 1054 has the highest ts 0 8 1 4 and the lowest reactive iron 0 003 0 074 contents among all the sites the deep water sites 1062 and 1063 have concave down pore water sulfate concentration depth profiles relatively deep sulfate methane interfaces smis 65 and 38 meters below sea floor mbsf respectively and steep methane gradients at the base of the smi whereas the shallow water sites 1054 1057 and 1060 have near linear sulfate and relatively shallow methane gradients the near linear sulfate depth profiles and shallow smis 17 and 14 mbsf respectively at sites 1057 and 1060 are primarily due to high sulfate consumption by anaerobic methane oxidation amo at the smi concave down profiles and deep smis at sites 1062 and 1063 are the result of low rates of sulfate consumption through organic matter degradation due to a limitation of metabolizable organic matter site 1054 is unusual in having an 8 m thick oxic suboxic zone a 48 m deep smi and a linear sulfate depth profile despite the high organic matter content of sediments at this site the thick oxic suboxic zone is mainly due to intense bioturbation while the linear sulfate depth profile and the deep smi are likely caused by low sedimentation rate and by reactive iron limitation pore water magnesium calcium and strontium profiles indicate that carbonate precipitation has occurred near the smi this is confirmed by the presence of authigenic dolomite rhombs and nodules especially at and below smi at all sites

the relationship of undrained shear strength and porosity with depth in shallow 50 m marine sediments abstract in this paper we review the relationship between undrained shear strength and porosity with depth of marine sediments in the upper 50 m below the seafloor based on a compilation of data from 46 ocean drilling program odp legs we find that only about half of the drill sites show the anticipated increase in strength 59 and associated decrease in porosity 49 down hole moreover a significant correlation coefficient for both strength and porosity with depth is found at only 31 of the sites four categories of sediments are distinguished based on the significance of correlation coefficients we observe an influence of sediment composition and texture on the relationship between strength and porosity with depth fine grained siliciclastic sediments clayey and silty sediments and nannofossil oozes with less than 50 carbonate frequently show significant correlation coefficients for strength and porosity with depth while fine grained carbonates with high carbonate concentrations calcareous muds and nannofossil oozes with an average carbonate content of 87 as well as reef facies carbonates lack significant trends down hole moreover correlation patterns vary considerably with geological or tectonic setting for instance delta deposits of the amazon fan and sediments from the atlantic passive continental margins frequently show significant correlation coefficients for both properties extensional arcs often show significant correlation only for one property shear strength or porosity correlation patterns are discussed in the light of sediment composition geological and tectonic setting the methods used for shear strength measurement and previous work published on compaction behaviour

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