ocean wide stagnation episode in the late cretaceous in this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid cretaceous here called the cenomanian turonian black shale horizon ctbsh the occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments the stratigraphic record above and below the ctbsh in environments as different as the deep north atlantic ocean and marginal and epicontinental seas over enormous areas in north america north africa and northwestern europe is characterized by a stratigraphic gap a disconformity or a continuous but strongly condensed stratigraphic section the anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2 no simple model has yet been found to explain the occurrence of the ctbsh in such a wide range of depth and palaeoenvironmental conditions

sapropelic deposits in a sediment from the guinea basin south atlantic until recently it has been generally thought that a stagnant water column is a prerequisite to the formation of organic rich deposits in deep water marine sediments a belief best exemplified by studies on the eastern mediterranean sapropels many workers have assumed that following the hydrological isolation of the deep waters stagnation of the eastern mediterranean basins and the concomitant development of anoxic conditions occurred before the deposition of the sapropelic layers1 10 opposing arguments suggesting a role for increased marine productivity have however been put forward both specifically with respect to the eastern mediterranean sapropels11 12 and more generally regarding deep water organic rich deposits13 15 we report here the discovery of sapropelic layers 0 5 organic carbon 16 in a recent sediment core from a deep water site in the guinea basin it is thought most unlikely that stagnant conditions could prevail in the water column at this site and preliminary analyses of the sediments suggest that the organic rich deposits have been a direct result of increased productivity in the overlying water column the most recent occurring about 18 000 yr ago and coinciding with the last glacial maximum

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

increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

organic facies of middle cretaceous black shales in deep north atlantic the middle cretaceous black shales of the deep north atlantic consist of alternating layers of sediment rich in total organic carbon toc that contains abundant amorphous types of organic matter and sediment poor in toc that contains mostly woody and coaly types of organic matter the amorphous materials are derived mostly from marine organisms in the eastern north atlantic off africa in the caribbean and on the demerara rise off surinam and from higher land plants in the western north atlantic and off europe marine amorphous material is important off africa because this was an area of upwelling and highly productive surface water amorphous marine organic matter was deposited across the entire north atlantic basin in the cenomanian in response to an ocean wide upwell ng event connected with the opening of the equatorial atlantic the difference between the toc rich and background toc layers reflects deposition of the former under reducing conditions which allowed the preservation of labile amorphous materials of marine and terrestrial orgin and of the latter under oxidizing conditions when nearly all that was preserved was refractory organic material

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

late quaternary paleoceanography as recorded by benthonic foraminifera in strait of sicily sediment sequences at specific times during the late quaternary a widespread low salinity surface water layer was produced over the eastern mediterranean which created stagnant conditions and associated deposition of sapropelic muds in the deep basins the strait of sicily has been positioned above the anoxic deeper water masses and is therefore devoid of sapropel deposits sediment sequences in the region contain a valuable record of upper bathyal 200 1000 m benthonic foraminiferal change during times of deep basin stagnation quantitative examiniation of benthonic foraminiferal assemblages in strait of sicily quaternary cores generally reveals changes coeval with sapropels s1 s2 s4 s5 and s6 the benthonic foraminiferal expression is seen as increases in frequency ofglobobulimina affinis globobulimina pseudospinescens chilostomella mediterranensis bolivina dilatata and otherbolivina species during intervals corresponding to the episodic abyssal stagnation events some cores also display a decrease incassidulina carinata and an increase inarticulina tubulosa similar assemblage changes have been previously documented to be closely associated with the sapropel layers in the deep basins of the eastern mediterranean the actual sapropel layers usually do not contain benthonic foraminifera however in the strait of sicily area the species exhibit less drastic changes than in the deep eastern basins because of the less severe anoxic conditions in the deep eastern basins benthonic foraminifera almost totally disappeared in sapropel layers at the same time there was a general reduction in foraminiferal numbers in the shallower strait area

organic carbon and sedimentation rate further evidence for anoxic deep water conditions in the cenomanian turonian atlantic ocean abstract the relationship between organic carbon content and sedimentation rate based on data derived from recent to miocene sediments deposited under oxic and anoxic sea water conditions is used to characterize the different depositional environments these data are compared with data of cenomanian turonian dsdp sediments from the atlantic ocean the results may support deposition in anoxic environments due to extremely reduced deep water circulation as the main cause for the formation of cenomanian turonian black shales in the north atlantic rather than increased supply of organic matter due to higher oceanic productivity

anoxic events in the mediterranean sea in relation to the evolution of late neogene climates stable isotopic and micropaleontological studies were made of selected sapropels organic rich sediments deposited in the mediterranean sea during the last 5 0 m y to determine the processes responsible for their formation distinct isotopic and faunal changes occur across sapropels of late pleistocene early pleistocene and latest pliocene age while smaller isotopic changes and more stable faunal assemblages are associated with the early and mid late pliocene sapropels the large 18o depletions and euryhaline fauna associated with latest pliocene pleistocene sapropels supports a density stratification model with a low salinity surface layer in contrast early pliocene and mid late pliocene sapropels appear to have been formed as the result of sluggish circulation and low oxygen contents in bottom waters of the eastern mediterranean due to the stable warm climatic conditions of that time period

dynamics of anoxia abstract a simple steady state one dimensional advective diffusive model of the ocean s coupled carbon oxygen and phosphorous system is developed the model is an extension of wyrtki s 1962 model of the oxygen distribution the occurrence of anoxia requires two conditions 1 sufficiently high productivity and 2 sufficiently low oxygen concentration in the bottom water it is shown that anoxic layers are most likely to occur fairly high in the water column anoxic events may be associated with timesof vigorous thermohaline circulation in contrast to stagnation arguments often invoked the model results are used to interpret both modern and ancient oceanic anoxic events

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

models for the deposition of mesozoic cenozoic fine grained organic carbon rich sediment in the deep sea the widespread occurrence of organic carbon rich strata black shales in certain portions of jurassic cretaceous and cenozoic sequences has been well documented from deep sea drilling project sites in the atlantic and pacific oceans and from sequences now exposed on land originally deposited in the tethyan ocean these ancient black shales usually have been explained by analogy with examples of modern deep sea sediments in which organic matter locally is preserved by 1 increasing the supply of organic matter 2 increasing the rate of sedimentation and or 3 decreasing the oxygen content of the bottom water however detailed examination of many black shales reveals characteristics that cannot be explained by simple local models including their approximate coincidence in time globally their occurrence in a variety of different environments including open oxygenated oceans restricted basins deep and shallow water their interbedding with organic carbonpoor strata which often dominate a so called black shale sequence their deposition by pelagic hemipelagic turbiditic and other processes and the variations in type and amount of organic matter that occur even within the same sequence a more complex model for the origin of black shales therefore appears most appropriate in which the cyclic preservation of organic matter depends on the interplay of the three main variables namely supply of organic matter sedimentation rate and deep water oxygenation each of which varies independently to some extent the variation and relative importance of these parameters in individual basins and widespread black shale deposition in general are linked globally and temporally by changes in global sea level climate and related changes in oceanic circulation an important and often overlooked factor for the supply of organic matter to deep basin sediments is the frequency and magnitude of redepositional processes the interplay of these variables is discussed in relation to the middle cretaceous and cenozoic organic carbon rich strata in particular which show marked differences in the relative importance of the different variables

repeat pass sar interferometry over forested terrain repeat pass synthetic aperture radar sar interferometry provides the possibility of producing topographic maps and geocoded as well as radiometrically calibrated radar images however the usefulness of such maps and images depends on our understanding of how different types of terrain affect the radar measurements it is essential that the scene coherence between passes is sdcient in this paper we derive a general system model including both radar system and scene scattering properties the model is used to interpret measurements over a forested area where the scene coherence varies between 0 2 and 0 5 the coherence is found to be sensitive to temperature changes around 0 c but surprisingly insensitive to wind speed the interferometric height discontinuity at the forest to openfield boundary shows good agreement with in situ tree height measurements for a dense boreal forest but is observed to decrease for a less dense forest this suggests the possibility of estimating bole volume from the interferometric tree height and a ground dem the decrease of scene coherence over a dense forest with increasing baseline is also used to estimate the effective scattering layer thickness

a methodology for ground motion area detection gma d using a dinsar time series in landslide investigations abstract in recent years the advanced differential interferometric synthetic aperture radar a dinsar technique has advanced rapidly for detecting and monitoring ground surface deformations due to landslides identification of the areas affected by ground motion through a dinsar data is generally based on visual inspection and hotspot or cluster analysis of average displacement rates however interpreting a dinsar time series of a particular area can provide a better indication of the real trend of displacement of a landslide while identifying the possible moment of acceleration of the deformation process as well in this work a novel methodology is proposed for identifying different typologies of ground motion areas mainly related to landslide phenomena at a regional scale by means of a dinsar data at high spatial and temporal resolutions this methodological approach was tested and validated in a wide area of the piedmont region northern italy by means of radarsat and cosmo skymed satellite data in both ascending and descending modes these sensors have a high spatial resolution allowing investigation of a higher number of landslides as compared to that of the older ers 1 2 and envisat data linear constant in time displacement and non linear acceleration or deceleration in the displacement rate trends were recognised allowing characterisation of the kinematic pattern of a landslide or a portion of it local and site specific scale analyses performed in an alpine valley and in two hillslopes representative of the main geological geomorphological contexts of the study area validated the results obtained at the regional scale this supported the interpretation of the driving mechanism for such known landslides or other geological processes which can cause ground motion along slopes the developed procedure can allow one to specify priority areas for prevention activities in order to optimise the costs and benefits of designing a plan to monitor instability phenomena at regional and site specific scales

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

reappraisal of anoxia and organic richness with emphasis on cretaceous of north atlantic accumulation of anoxic sediments in the north atlantic during barremian through turonian time early to middle cretaceous was controlled mainly by local conditions although global climatic and oceanographic factors played a supporting role evidence does not support the popular hypothesis developed over the past few years of global or oceanwide anoxia data which contradict this hypothesis are based on 1 a reevaluation of criteria for identifying sediments that accumulated in anoxic water 2 a critical reappraisal of reported worldwide occurrences of anoxic sediments of these ages and 3 an examination of the spatial and temporal distribution of anoxic sediments in the north atlantic and elsewhere a model is proposed in which the earliest anoxic sediments of cretaceous age in the north atlantic were deposited in deep restricted basins by middle cenomanian time about 97 m y ago sluggish circulation had led to a gradual expansion of the oxygen minimum layer permitting deposition of anoxic sediment in nonbasinal settings as well expansion of the oxygen minimum layer caused the calcite compensation depth to rise promoting oxidation of organic carbon and causing contraction of the oxygen minimum layer development of anoxia was thus self damping anoxia effectively disappeared by early senonian time 88 m y ago when improved circulation created oceans more like those of the present some evidence indicates that enhanced biologic productivity and upwelling may have been local factors in fostering anoxia but the early and middle cretaceous were generally not highly productive times

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

changes in paleoenvironments in the atlantic ocean during cretaceous times results from black shales studies large parts of the cretaceous atlantic ocean are characterized by the wide spread deposition of organic carbon rich sediments black shales with a maximum occurrence during aptian albian and cenomanian turonian times in order to explain the origin of these black shales changes in the amount and type of organic matter in relation to changes in paleogeography paleoceanic circulation and paleoclimate have been investigated in detail the study is mainly based on calculation of accumulation rates of marine and terrigenous organic carbon organic carbon sedimentation rate relationships and estimates of paleoproductivity