concentrations en uranium et desequilibres radioactifs iou en mediterranee orientale discussion sur l origine des sapropeles abstract sedimentation rates of the oxidized sediments from the eastern basin of the mediterranean sea are about a few centimetres per 1000 years not very different from the sedimentation rates of the western basin the sapropels levels show strong u enrichment from 10 to 30 times and ionium 230 th daughter of 238 u is in radioactive equilibrium with u at these levels these facts together with the high surficial productivity and or conservation factor implied by the strong organic material concentration of the sediments are hardly explained if sapropels are formed in the sea it seems that they are largely made up by continental material debris accumulated during propitious epochs of vegetation growth they would be expelled massively from the continent lagoons or closed seas when the sea level goes down causing the ablation of continental or coastal formations by the running waters then deposited onto the sea floor sapropel s 5 for instance could be made up by material from the last interglacial rich in organic matter but dispatched to the sea at the beginning of the glacial era

sources of sediment to the ionian sea and western levantine basin of the eastern mediterranean during s 1 sapropel times abstract the provenance of sediments to the ionian sea and western levantine basin during s 1 sapropel times was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on sediment profiles from 5 box cores in the eastern mediterranean on saharan dust and on a core from the nile delta which included sediment deposited during s 1 sapropel times in the sediment profiles there was a decrease in 87 sr 86 sr ratio 1 sr ti al mg al and si al ratio starting at the upper mn peak and finishing at the base of the organic rich layer this showed that there was a major change in the nature of the detrital input during s 1 sapropel times the timing of the change in detrital input was similar to the change in surface salinity as measured by 18 o there was linear relationship between 87 sr 86 sr and 1 sr and for 87 sr 86 sr and ti al for all the sediment samples the favoured interpretation of this pattern was that the detrital input was a mixture of saharan dust similar to that being deposited today on corsica and a local riverine sediment source the data were incompatible with the riverine source to the ionian sea and western levantine basin being from the river nile the minor variations in sr isotopes and metal al ratios in the nile delta core was interpreted as due to changes in the proportion of blue nile to white nile inputs brought about by climatic variations it was calculated that the change in detrital input during s 1 time was caused by a simultaneous increase in riverine input and decrease in saharan dust input

fabric transitions from shell accumulations to reefs an introduction with palaeozoic examples one unresolved conceptual problem in some palaeozoic sedimentary strata is the boundary between the concepts of shell concentration and reef in fact numerous bioclastic strata are transitional coquina reef deposits because either distinct frame building skeletons are not commonly preserved in growth position or skeletal remains are episodically encrusted by stabilizer reef like organisms such as calcareous and problematic algae encrusting microbes bryozoans foraminifers and sponges the term parabiostrome coined by kershaw can be used to describe some stratiform bioclastic deposits formed through the growth and destruction by fair weather wave and storm wave action of meadows and carpets bearing frame building archaeocyaths bryozoans corals stromatoporoids etc and or epibenthic non frame building e g pelmatozoan echinoderms spiculate sponges and many brachiopods organisms this paper documents six palaeozoic examples of stabilized coquinas leading to pseudo reef frameworks some of them formed by storm processes generating reef soles aborted reefs or being part of mounds on ramps and shelves and were consolidated by either encrusting organisms or early diagenesic processes whereas others bioclastic dominated shoals in barrier shelves were episodically stabilized by encrusting organisms indicating distinct episodes in which shoals ceased their lateral migration a paramount quantity of information characterizes the formation and distribution of shell concentrations and reefs in modern and cenozoic strata but the knowledge of phanerozoic shell concentrations and reefs is decreasing when increasing in age the palaeozoic is a key time span in the history of life owing to the wide occurrence of skeletonized metazoans the so called cambrian explosion zhuravlev riding 2000 and the successive biodiversifications related to i major extinctions such as the end ordovician cooper 2004 the frasnian famenian boundary buggisch 1991 copper 2002 racki house 2002 and the endpermian extinction wignall hallam 1992 and ii major community replacements such as the lower middle cambrian transition 2 j j alvaro et al remains webb 1996 following wood s 1998 definition reefs develop due to the aggregation of sessile epibenthic marine organisms with the resultant higher rate of in situ carbonate production than in surrounding sites although the relative capacity of some gregarious epibenthic organisms bearing mineralized skeletons to be preserved in living position is a common characteristic of reef organisms this character is also shared with other non reef metazoans adapted to soft substrates and forming bundles like clusters one group of these organisms named secondary soft bottom dwellers by seilacher 1984 differs from mud stickers e g non encrusting pelmatozoans and sponges in the heavy weight of their shells these metazoans mainly brachiopods and molluscs develop common cup boulderand fan shaped convergent morphologies favouring recliner strategies seilacher 1984 savazzi 1999 skeletal concentrations can be subdivided according to their biostratinomic features into biogenic sedimentary diagenetic and mixed concentrations kidwell et al 1986 biogenic concentrations can be intrinsic or extrinsic in character the former generated by the organisms that produce the hard parts resulting from intrinsic gregarious behaviours of autochthonous and parautochthonous skeletal organisms e g preferential colonization by larvae and single colonization events of opportunistic species and the latter produced by other organisms that interact with skeletonized organisms on their discarded hard parts leading to the formation of parautochthonous and allochthonous concentrations e g hard part rich fecal masses and shell filled pits sedimentary concentrations result from physical usually hydraulic processes of concentration in which hard parts behave as sediment particles and non bioclastic matrix is either reworked or fails to accumulate e g shelly storm lags aeolian beach pavements channel lags in fluvial intertidal and subtidal environments or shell paved turbidities diagenetic concentrations form or are significantly enhanced by processes acting after burial such as compaction or selective dissolution of matrix and finally mixed concentrations form by the interplay of two or more kinds of the aforementioned processes and can display both autochthonous parautochthonous and allochthonous shell

uranium and radium diffusion in organic rich sediments sapropels among the late quaternary mediterranean sapropels the s5 125 ka is one of the best preserved due to its high organic carbon content that has limited postdepositional oxidation the high uranium content in this sapropel 40 dpm g 1 makes this layer interesting for studying uranium series disequilibrium in organic rich sediments for this reason the present work provides isotopic measurements of the u decay series in a s5 sapropel by applying more precise mass spectrometric methods tims mc icpms and gamma spectrometry assuming that u in the sapropel mostly originated from seawater the 234u 238u 230th 238u 226ra 230th and 231pa 235u activity ratios show systematic deviations from the theoretical values for a closed system evolution of the u series over the 125 ka since sapropel formation the radiogenic 234urad and 226ra show clear evidence of migration in the sapropel with modeled diffusion coefficients of 7 1 1 1 10 12 cm2 s 1 and 1 6 0 2 10 10 cm2 s 1 respectively the diffusion of 234urad cannot explain the high 230th 238u and 231pa 235u activity ratios observed in the sapropel two possible mechanisms or a combination of both are proposed for explaining the irregular 230th 238u and 231pa 235u activity profiles in sapropel s5 the first one is an enhanced export flux of 230thxs and 231paxs excesses exceeding the production rate in seawater during the time of sapropel formation and the second one is diffusion of authigenic uauth in the sapropel however the ambiguous determination of 230thxs and 231paxs in the sapropel and the poorly understood processes that might lead to uauth migration in anoxic sediments still limit a final explanation for the deviation of 230th 238u and 231pa 235u activity ratios from their expected theoretical values

adriatic deep water formation during the holocene implication for the reoxygenation of the deep eastern mediterranean sea under modern conditions the reoxygenation of eastern mediterranean deep water is the result of the formation of dense bottom water in the southern adriatic sea oxygen isotopic records of planktonic foraminfera used as a paleosalinity tracer show that po river and or the alpine glaciers meltwater are not directly responsible of the inhibition of the deep water formation in the adriatic during sapropel s1 formation at 9 000 years b p sedimentological evidence indicates that fully oxygenated conditions in the deep adriatic occurred only by 1 650 100 years b p a long time after the total reoxygenation of the deep eastern mediterranean organic carbon content and isotopic ratio indicate that persistence of a reduced sediment phase until 1 650 years b p does not result from increased primary productivity or large input of terrestrial organic matter

duration of s1 the most recent sapropel in the eastern mediterranean sea as indicated by accelerator mass spectrometry radiocarbon and geochemical evidence slowly accumulated 5 cm kyr 1 and rapidly accumulated 5 20 cm kyr 1 sediments have been compared to define the initiation and termnation times of the most recent sapropel s1 in the eastern mediterranean sea the ba a1 ratio has been employed as a more persistent index of productivity than cg accelerator mass spectrometry radiocarbon dating of pelagic foraminifera indicates a maximum duration for increased ba a1 levels in s 1 from 9500 6000 uncorrected radiocarbon convention years b p in the rapidly accumulated sediments and 9500 5300 years b p in the slowly accumulated sediments this difference is ascribed to bioturbation affecting the slower accumulated s1 sediments in the two most rapidly accumulated s1 units from the adriatic and aegean seas there is a saddle of lower values centered on 7500 years b p in the corg and ba ai profiles so that the visual s 1 unit appears as a doublet geochemical evidence indicates that this intervening period is best interpreted as an episode of increased ventilation and bottom water oxygenation during the period of sapropel accumulation

geochemical and paleomagnetic evidence for the occurrence of missing sapropels in eastern mediterranean sediments the cyclic occurrence of sapropels appears to be associated with maxima in the 65 n summer insolation target curve studies of the most recent sapropel have revealed extensive oxidation of organic matter or even the complete removal of this unit geochemical and magnetic signals allow for the detection of such a missing sapropel in older sediments these signals are altered by ongoing diagenetic processes an important parameter to reveal missing sapropels is ba elevated concentrations of ba are always found in visible sapropels and even after oxidation of part of the sapropel the initial ba profile remains visible we use this tool to trace down missing sapropels in kc01b a 37 m kullenberg core from the calabrian ridge eastern mediterranean at least 8 of 11 sampled intervals around insolation maxima contain evidence of a completely oxidized sapropel ba trace metal distributions and magnetic parameters are similar to those observed around visible sapropels

middle and late quaternary depositional sequences and cycles in the eastern mediterranean although most of the quaternary sediments of the eastern mediterranean appear reworked extensive areas of hemipelagic sediments occur mainly in the central part of the basin mediterranean ridge the most obvious character of these muddy sediments is the numerous changes in colour they result from the organic carbon content as well as from concentration and chemical form of metallic elements mn fe cu zn the succession of coloured layers is arranged into sequences developed between two sharp contacts a complete sequence involves five lithofacies from an oxidized layer at the base to a reduced sapropel at the top and displays progressive internal changes of colour from ochre beige greyish beige grey and black layers several sequence variants top truncated base truncated recurrent are identified these sequences are a consequence of changes in oceanographic conditions i e from oxidizing to reduced environments resulting in different organic and mineral contents based on detailed studies of quaternary sediments collected by coring a synthesized standard succession representative of the ordered sequences in the eastern mediterranean is proposed from about 650 000 yr as deduced from the calculated rate of sedimentation of 1 7 mm 1000yr 1 this succession appears modulated by cyclic events large scale periods 200 000 yr of reduced and oxidized sequences correlate with major alternate phases of flooding and reduced flow of the nile river during the quaternary subsequent sequences of shorter time scale 20 000 50 000 yr results from two factors heaviest monsoons leading to an increase of the influx of the nile river and global climatic changes eurasian ice sheet meltwater these two factors act synchronously or independently along the studied time span these interplaying factors result in periodic stages of increasingly restricted conditions in the basin and explain the complexity of the eastern mediterranean succession at least since 650 000 yr ago

complex calc alkaline volcanism recorded in mesoarchaean supracrustal belts north of frederikshab isblink southern west greenland implications for subduction zone processes in the early earth we present new geochemical data for three mesoarchaean supracrustal belts ravns storo bjornesund and perserajoorsuaq situated north of frederikshab isblink in southern west greenland for which we propose the collective name the ikkattup nunaa supracrustal association they comprise mainly amphibolites of tholeiitic basalt composition and leucoamphibolites of calc alkaline andesite composition both lithological units are cut by aplite sheets of tonalite trondhjemite granodiorite ttg composition with u pb zircon ages of c 2900 ma lu hf and sm nd isochrons based on whole rock amphibolite and leucoamphibolite samples yield ages of 2990 41 ma and 3020 78 ma respectively which are within error of the age of the fiskenaesset complex situated 5 25 km to the north leucoamphibolites from the three supracrustal belts show apparent geochemical mixing trends between tholeiitic amphibolites and ttg gneisses as the end members by assimilation fractional crystallisation afc modelling we can show that one group of leucoamphibolites can indeed be explained by contamination of the parental melts by a ttg like end member and another group of high p2o5 la and nb leucoamphibolites can be explained by contamination involving a hypothetical low silica adakite end member however the leucoamphibolites are juvenile with epsilon nd 2970 ma from 2 1 to 3 5 and epsilon hf 2970 ma of 3 5 to 4 3 thus the mafic source of the felsic contaminant melts must have been derived from a depleted mantle source more or less at the same time 60 ma as the volcanism took place our preferred interpretation of the geochemical and isotope data is that the protoliths of the supracrustal rocks formed in an island arc setting where early tholeiitic volcanism gave way to calc alkaline volcanism in a maturing arc the apparent afc trends are thus explained by in situ partial melting of basaltic arc crust to form juvenile ttg and adakite melts that mixed with mafic magmas or contaminated their mantle source to produce the calc alkaline leucoamphibolite protolith this model has important implications for the general interpretation of other archaean supracrustal belts because afc and geochemical mixing trends towards a ttg end member are not uniquely diagnostic of crustal contamination but may rather reflect processes operating at lower crustal or source levels in arcs such as melting assimilation storage homogenisation mash or slab melt low silica adakite metasomatism of the mantle source respectively c 2012 elsevier b v all rights reserved less

depositional models for fine grained sediment in the western hellenic trench eastern mediterranean sediment in tectonically active topographically restricted settings of the western hellenic arc eastern mediterranean consists primarily of clayey silt and silty clay failure of metastable sediment temporarily stored on relatively steep slopes is triggered by earthquake tremors and eustatic oscillations redeposition of these materials by gravitative transport has resulted in markedly different lithofacies from site to site most piston cores include three late quaternary stratigraphic units that can be correlated with sections in other parts of the eastern mediterranean numerous radiocarbon age determinations enhance the correlation seven fine grained sediment types are identified in cores from eight distinct depositional environments some muds are closely related to specific environments slump and debris flow deposits on slope and high relief environments or to time well laminated mud during the latest pleistocene mid holocene or to both uniform and faintly laminated muds restricted to trench basins turbiditic and hemipelagic muds are common throughout the study area mud distribution patterns correlate closely with calculated sedimentation rates we propose two depositional models for these sediments the first emphasizes downslope transformations resulting in progressively reduced flow concentration during transport from slump and debris flow turbidity current low density turbidity current or turbid layer mechanisms the distal end member deposits settling from low concentration flows are thick rapidly emplaced fine grained uniform muds closely associated with faintly laminated muds these were ponded in flat trench basin plains planktonic and terrigenous fractions in the turbiditic finely laminated and uniform muds record mixing of materials of gravitative and suspension origin during redeposition this sequence prevails under conditions of minimal stratification of water masses as characterized by the present mediterranean in the second model developed for conditions of well developed water mass stratification well laminated rather than uniform mud prevails as the end product of low concentration flows these very finely laminated and graded muds record particle by particle settling from detached turbid layers concentrated along density interfaces they include material from turbid layers complemented by the normal rain of pelagic material stratification barriers resulted in region wide distribution of such deposits in both slope and trench environments

mediterranean climate and oceanography and the periodic development of anoxic events sapropels mediterranean sapropels are layers with elevated organic carbon concentrations that contrast with surrounding sediments which are organic poor sapropels occur quasi periodically in sedimentary sequences of the last 13 5 million years and exist both in the eastern and western mediterranean sub basins they have been the subject of extensive study based on records from both short conventional and long ocean drilling program sediment cores and from a wide variety of uplifted marine sediment sequences on the basin margins and islands previous syntheses in the 1990s and 2000s have discussed how the formation of sapropels is commonly ascribed to deep sea anoxia enhanced export productivity or a combination of these effects however a wealth of new evidence and insights has emerged during the past 1 2 decades based on traditional and novel proxy data as well as modelling which has revealed intriguing new aspects and nuances to the reconstructed conditions hence it is timely to present a new synthesis of current understanding of the processes behind the formation of sapropels which have over the past decade also become a matter of commercial interest in sub salt hydrocarbon exploration in this review we present a context of modern mediterranean climate and oceanography followed by an integrated assessment of the growing understanding of climatological and ocean circulation changes that were associated with sapropel deposition we find that sapropels predominantly formed during astronomically timed episodes when climatic and oceanographic conditions and ecological responses broadly preconditioned the basin for sapropel deposition there is strong correspondence with times of monsoon intensification fuelling runoff from north africa into the mediterranean sea while preconditioning due to sea level rise and regional precipitation and runoff may have contributed as well within these broad episodes of surface buoyancy gain and resultant decline in deep water ventilation specific deposition under dysoxic anoxic or even euxinic conditions occurred within a clearly dynamic system that was characterised by complex spatial and depth dependent patterns gradients with distinct temporal variability on at least decadal to centennial millennial timescales in the final section we evaluate the implications of different modes of deep water removal from silled basins to investigate why sapropels are more frequently and often more intensely developed in the eastern mediterranean than in the western mediterranean

on the late pleistocene holocene sapropel record of climatic and oceanographic variability in the eastern mediterranean sapropels and intercalated marls in a piston core from the eastern mediterranean are chemically and mineralogical distinct kaolinite smectite and total s contents fe a1 ba a1 co a1 mo a1 and v a1 are higher whereas quartz mg calcite illite contents si a1 ti a1 k a1 rb a1 and zr a1 are lower in the sapropels missing and ghost sapropels are identified by mineralogical and chemical properties that are not prone to diagenesis primary production was higher ba a1 and bottom water and or interstitial oxygenation was lower co a1 mo a1 ni a1 and v a1 during sapropel formation wind speeds quartz clay si a1 and zr a1 and bottom water salinities mg calcite calcite were higher during periods of marl formation sapropels represent a fundamentally different sedimentary facies whose formation is linked to changes in the hydrological balance in the basin driven by precessionally modulated changes in monsoon strength and subtropical precipitation changes which altered circulation production and sediment source areas

geochemistry of an exotic sediment layer above sapropel s 1 mud expulsion from the urania basin eastern mediterranean in a gravity core from the eastern mediterranean sea a chemically and mineralogically distinct 5 5 cm thick layer is present above sapropel s 1 and overlain by hemipelagic marls calcite is completely absent in this exotic layer dolomite is present only in small amounts and the cr concentrations are significantly enhanced the layer was deposited primarily under reducing conditions but the distributions of redox sensitive elements show that a large part of the exotic layer is now oxidised by a downward progressing oxidation front sediments from within the nearby anoxic hypersaline urania basin are similar to those from the exotic layer in particular in s c and o isotope distributions of pyrite and dolomite as well as increased cr concentrations mud expulsion due to expansion of gas rich mud is proposed to explain the presence of the exotic layer outside the urania basin the deposition of an anoxic layer above s 1 shielded the sapropel from oxidation which resulted in the rare occurrence of a complete preservation of s 1 and provides the first minimum age for the start of anoxic mud accumulation in the urania basin

palaeoproductivity and post depositional aerobic organic matter decay reflected by dinoflagellate cyst assemblages of the eastern mediterranean s1 sapropel abstract in the reconstruction of bioproductivity in surface waters the extent to which a proxy has been diagenetically altered is often a matter of debate here we investigate how organic and calcareous walled dinoflagellate cysts can be used for separately estimating bioproductivity and oxygen related diagenesis this is achieved by studying the cyst content of the most recent eastern mediterranean sapropel s1 that is thought to have been deposited under conditions of increased primary production in surface waters and possible anoxia in the bottom waters based on chemical evidence it has been shown that the visible sapropelic layer represents only the residual lower part of what was initially a much thicker sapropel as a result of post depositional decay of organic matter related to oxygen penetration into the sediments the effect of aerobic organic matter decay on the cyst associations is studied through the comparison of the unaffected lower part of the initial sapropel and the oxidised upper part comparing the unaffected sapropelic sediments with pre and post sapropelic material gives insight into the relationship between fossil cysts assemblages and palaeoproductivity impagidinium aculeatum impagidinium patulum operculodinium israelianum polysphaeridium zoharyi and probably impagidinium spp impagidinium paradoxum and nematosphaeropsis labyrinthus are very resistant against aerobic decay and their accumulation rates appear to be primarily related to productivity in surface waters protoperidinium and echinidinium species on the other hand are shown to be very sensitive and can be used to recognise oxygen related decay the calcareous walled dinoflagellate cysts seem to be unaffected by oxic organic matter decay in mediterranean sediments

review of recent advances in the interpretation of eastern mediterranean sapropel s1 from geochemical evidence abstract the sediments of the eastern mediterranean basin contain c org enriched layers sapropels interbedded with the c org poor sediments which form by far the greater part of the record while it is generally appreciated that different surface ocean productivity and bottom water conditions are necessary for the formation and preservation of these two sediment types less attention has been paid to diagenetic effects which are an expected consequence of transitions between dramatically different bottom water oxygenation levels a geochemical interpretation has emerged of post depositional oxidation of the most recent sapropel s1 initially based on the relationship of the mn fe c org and s concentration depth profiles observed around s1 and the characteristic shapes of these elemental profiles known from other situations this indicates that post depositional oxidation has removed approximately half of the visual evidence of the sapropel 6 cm from a total of 12 cm in the deep basin the oxidation interpretation from redox sensitive element redistribution profiles has subsequently been consolidated with evidence from pore water o 2 no 3 mn 2 and fe 2 studies from characteristic solid phase ba profiles which yield palaeoproductivity records and from oxidation sensitive indicator trace elements i and se so far these geochemical observations have been concentrated in the deeper central parts of the basin where sediment accumulation rates are lower than on the basin margins and radiocarbon dating indicates that s1 formation occurred between 5 3 and 9 0 ky uncorrected conventional radiocarbon time it remains to be demonstrated whether or not these times are applicable to the entire e mediterranean basin the implications of these findings to guide sampling in future work on the s1 productivity episode and on older sapropels for palaeoenvironmental investigations are discussed

active post depositional oxidation of the most recent sapropel s1 in sediments of the eastern mediterranean sea abstract over a wide area of the eastern mediterranean basin two mn rich layers have been observed above the most recent sapropel s1 one immediately above the sapropel top and one a few centimetres closer to the sediment surface different mechanisms have been proposed to explain the occurrence of these two mn peaks either both peaks have a diagenetic origin in which case the upper mn peak is actively forming or the lower peak is actively forming and the upper peak has a different formation mechanism high resolution porewater including a gel sampler used for the first time in marine sediments and solid phase data are now used to demonstrate that the oxidation front is located at the level of the lower mn peak which therefore is presently being formed a barium organic carbon relationship is used to calculate the initial organic carbon profile of the s1 sapropel the palaeoproductivity profiles generated by this method demonstrate that the original sapropel unit was bounded by the upper mn peak this implies that the interval between the two mn peaks where a low organic carbon content is now observed was originally part of the sapropel the initially deposited organic carbon has been oxidised by a progressive downwards moving oxidation front the penetration depth of this oxidation front i e the distance between the two mn peaks is mainly determined by the organic carbon content the sediment accumulation rate and the bioturbation depth the upper mn peak appears to have formed as a result of either mn precipitation upon oxygenation of previously anoxic eastern mediterranean deep water or preservation of a surficial mn peak at the end of the high productivity episode in either case the upper mn peak marks the end of sapropel formation as indicated by the ba profiles this means that formation of the s1 sapropel ceased more recently than is indicated by radiocarbon dating of the visible top of s1

reef geometries erosion surfaces and high frequency sea level changes upper miocene reef complex mallorca spain the upper miocene reef complex of mallorca is a 20 km prograding unit which crops out in sea cliffs along the southern side of the island these vertical and exceptionally clean outcrops permit i identification of different facies lagoon reef front reef slope and open platform and their geometries and boundaries at different scales ranging from metre to kilometre and ii construction of a 6 km long high resolution cross section in the direction of reef progradation this cross section shows vertical shifts of the reefal facies and erosion surfaces linked to a general progradational pattern that defines the accretional units four hierarchical orders of magnitude 1 m to 4 m of accretional units are identified by consideration of the vertical facies shifts and by which erosion surfaces are truncated by other erosion surfaces all these orders show similar patterns horizontal beds of lagoonal facies in the upper part landward reefal and slope facies with sigmoidal bedding in the central part and open platform facies with subhorizontal bedding in the lower part basinwards the boundaries are erosion surfaces horizontal over the lagoon facies dipping basinwards over the reef front facies and connecting basinwards with their correlative conformities over the reef slope and open platform facies the four orders of accretional units are interpreted in terms of four 1 m to 4 m hierarchies of sea level cycles because i there is a close relation between the coral growth and the sea surface ii there are vertical shifts in the reefal facies and their relation to the erosion surfaces and iii there was very little tectonic subsidence in the study area during the late miocene additionally all these units can be described in terms of their position relative to the sea level cycle i the reefs prograde on the open platform sediments during low stands of sea level ii aggradation of the lagoon reef and open platform facies dominates during sea level rises and the lagoonal beds onlap landwards upon the previous erosion surface iii reefal progradation occurs during high stands of sea level and iv the 2 m sea level fall produces an off lapping reef and there is progradation with downward shifts of the reefal facies and erosion landward on the emerged older reefal units a erosion surfaces the 3 m and 4 m sea level falls produce only erosion b and c erosion surfaces although precise age data do not exist at present some speculations upon the frequency of these miocene relative sea level cycles can be made by comparisons with pleistocene cyclicity there is a good correlation between the miocene 2 m cycles and the 100 ka pleistocene cycles consequently the 1 m cycles can be assigned to a fourth order in relation to previously proposed global cycles and the 2 m to fifth order cycles all these accretional units could be defined as sequences according to the definition as commonly used in sequence stratigraphy however they represent higher than third order sea level cycles but are not parasequences the term subsequence therefore is suggested to define a part of a sequence bounded by erosion surfaces mostly subaerial and their correlative conformities basinwards a hierarchy of subsequences can be established

unraveling north african riverine and eolian contributions to central mediterranean sediments during holocene sapropel s1 formation hydroclimate variability has exerted a fundamental control on the alternating deposition of organic lean marl and organic rich sapropel sediments in the eastern mediterranean sea ems however the exact mechanisms regarding the freshwater sources and related changes are still debated here sr and nd isotopes and high resolution elemental data are used to constrain different riverine and eolian supplies to the central mediterranean over the past 9 8 ka the detrital sediments in core cp10bc taken at the margin of the libyan shelf in the southwestern ionian sea can be described by a three endmember mixing system based on sr and nd isotopic compositions the same systematics can also be deduced from ti and k compositional variability the endmembers comprise saharan dust aegean nile and libyan soil representing the eolian supply from north africa the riverine inputs from the aegean nile areas as well as the riverine and shelf derived fluxes from the libyan tunisian margin respectively for the sapropel s1 period in particular we find important detrital supplies from fossil river wadi systems along the libyan tunisian margin activated by intensified african monsoon precipitation combining the temporal profiles with the consistent variability observed in the 87sr 86sr 1000 sr diagram such libyan contribution has been most prominent during the uppermost period of sapropel s1 in core cp10bc this observation is in agreement with hydroclimate reconstructions of northwestern libya comparison of the sr nd isotope data between core cp10bc and four cores taken along a west east transect throughout the ems shows that this detrital supply originated mainly from western libya tunisia and was transported as far eastward as 25 e while being diluted by an increasing nile contribution

mediterranean quaternary sapropels an immediate response of the african monsoon to variation of insolation abstract in the subsurface of the east mediterranean sea eleven discrete basin wide organic rich black sapropels were deposited during the last 465 000 years they are dated by oxygen isotopic chronostratigraphy the most recent sapropel has been shown to be the consequence of heavy nile river summer floods due to increased monsoonal summer precipitation over ethiopia and not of scandinavian ice sheet meltwater influx into the east mediterranean sea as was previously believed while most sapropels were deposited during interglacials two thick sapropels formed during glacial periods as shown by their position in the oxygen isotopic stratigraphy and by their pollen record in core rc9 181 the new evidence presented here is that the sapropel sequence in this core including the two glacial sapropels correlates on a one to one basis with the highest values of an index of insolation on top of the atmosphere the concept of this index derives from an analysis of the african monsoon process the index variation is computed for the last 465 000 years from the caloric northern summer insolation in the tropical latitudes controlled by variations of the earth s orbital parameters it is conjectured that this index might be linked through the climate system to the monsoonal precipitation which in africa produces the nile river summer flood

on the origin of upper miocene sapropelites a case study from the faneromeni section crete greece for the first time results of an integrated geochemical and micropalaeontological study of upper miocene sapropelites in a land based section in the mediterranean are presented three sapropelites and adjacent homogeneous intervals in the cretan faneromeni section have been investigated in detail the chemical and foraminiferal characteristics were found to be markedly similar to those of plio pleistocene sapropelites as the physiography and climate of the late miocene mediterranean were not fundamentally different from those of today our preferred model for late miocene sapropelite formation is similar to the one recently developed for plio pleistocene sapropelites increased seasonality and freshwater input during northern hemisphere summer insolation maxima triggered high export production and oxygen consumption rates which in combination with a concomitant decrease in deep water formation rate resulted in the observed high organic matter content of the sapropelites

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

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

sedimentation on the ionian active margin hellenic arc provenance of sediments and mechanisms of deposition abstract lithological sedimentological mineralogical and faunal analyses of twenty cores from the western peloponnesus margin and adjacent matapan trench permit the origin of the sediments and the processes of sedimentation to be defined in some detail except for the ash layers derived from the ischian province the major part of the sediment is local in origin peloponnesus analyses of heavy light and clay minerals enable three main provinces to be distinguished each of these provinces includes one or more slope basins and a portion of trench without lateral connection between them and mixing of inputs the diversity and complexity of sedimentary structures the granulometric characters the mixed fauna molluscs and ostracods and the variability of rates of sedimentation all testify to the prevalence of reworking phenomena and gravitative processes these data confirm and elaborate on the model of sedimentation deduced from seismic studies in which sediments are successively trapped released by the slope basins and transferred via channels and canyons towards the underlying trench basins this cascade feeding appears characteristics of this subductive sedimentary environment

african monsoons an immediate climate response to orbital insolation the croll milankovitch astronomical theory of climate1 3 has received strong support from the evidence of a linear climatic forcing by obliquity and precession although nonlinearity had to be assumed for eccentricity4 5 moreover interglacials have appeared to be controlled by the orbital insolation6 although a phase shift of 6 000 5 000 yr is seen between an astronomical climate index and terrestrial climate indicators dominated by the northern ice sheet dynamics climate proxy data of low latitudes are less directly dependent on the ice sheets here it is shown that during the past 464 000 yr african monsoons signalled by the east mediterranean sapropels were heaviest always and only when a northern summer monsoon index computed from the orbital variation of insolation reached maximum values this occurred during all the interglacials but also twice during glacial periods thus tropical aridity is not the single climatic pattern of glacial periods an immediate terrestrial climate response to orbital variations of insolation is established

organic geochemical evidence of late glacial holocene climate instability in the north aegean sea sedimentary molecular biomarker compositions organic carbon and caco3 concentrations and bulk organic 13c and total 15n values document a series of paleoclimatic changes that have affected organic matter production and sedimentation in the north aegean sea from the termination of the latest glacial maximum through the middle holocene continental environmental conditions have been inferred from land plant biomarkers paleoproductivity patterns of diatoms prymnesiophytes dinoflagellates and nannoplankton were discerned from marine derived biomarkers although organic matter is predominantly marine variations in the proportion of marine and land contributions and in its general preservation are evident rapid changes in the eastern mediterranean thermohaline circulation evidently occurred in parallel to sea surface temperature oscillations enhanced deep water ventilation accompanied cold intervals in the late last glacial the younger dryas and during an interruption of deposition of the s1 sapropel probably in response to strengthening of north winds over the region in contrast decreased thermohaline circulation occurred during the warm interval associated with the s1 sapropel during this period increased freshwater inputs diminished ventilation of deep water masses and enhanced organic matter production and preservation intriguing fluctuations in sea surface temperatures and the concentrations of marine and terrestrial biomarkers within the sapropelic layer most prominently in the interruption from 8 2 to 7 8 calibrated radiocarbon conventional kyr bp support the hypothesis that several distinct events of deep water reoxygenation occurred in the north aegean sea during deposition of the s1 sapropel these events reflect centennial excursions to the more common low productivity and well ventilated conditions of the mediterranean that may possibly be related to north atlantic oscillation cycles

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

redistribution and geochemical behaviour of redox sensitive elements around s1 the most recent eastern mediterranean sapropel the youngest eastern mediterranean sapropel s1 is generally believed to have formed 7 9 14c ky b p the distribution of redox sensitive elements above in and below the sharply defined organic rich unit reveal that s 1 has already suffered heavy diagenetic alteration its present thickness based on its dark colour is only a fraction of its original thickness in one core visual evidence of s1 with an inferred initial thickness of 6 cm has been destroyed and a similar thickness appears to have been lost from the tops of another two examples this is caused by oxidation of the upper reaches of s 1 by a progressive oxidation front which commenced 5 2 5 4 14c ky ago and still appears to be active in the three cores studied diagenetic relocation of many redox sensitive elements has occurred most elements expected to be enriched in sapropels or sulphide rich sediments already have maximum concentrations above or below rather than in the present s 1 layers similarities are observed in the geochemical behaviour of as fe and p of co cu mn ni and zn and of cd mo sb ti u and v the behaviour of ba is distinctive and its immobility as barite makes it an indicator for palaeoproductivity and the original high s1 corg content the elements se and i exhibit particularly large sharp concentration peaks and together are proposed as useful indicators of the present boundary between oxic and post oxic conditions

anoxic development of sapropel s1 in the nile fan inferred from redox sensitive proxies fe speciation fe and mo isotopes abstract redox conditions and the mechanisms of redox development are a critical aspect of eastern mediterranean sapropels whose formation in oxygen depleted waters is closely related to water column stratification at times of global sea level rise and insolation maxima sapropels in the nile fan formed at relatively shallow water depths under the influence of the monsoon driven freshwater output from the river nile this work evaluates the redox evolution of holocene sapropel s1 in valpamed cruise core md9509 recovered at 880 mbsl in the ne nile fan using a combination of geochemical element proxies fe speciation fe and mo isotopes studies the productivity and redox proxies ba al mo al u al v al sb al show well defined enrichments in the sapropel but with a marked minimum at ca 8 2 ka indicative of reventilation corresponding to a well known global cooling event peak productivity and reducing signals occur close to the initiation of sapropel formation the proxy signals in sapropel 9509 are stronger and of longer duration than those of a second sapropel s1 recovered at the same depth but 380 km to the north md9501 supporting the notion suggested in previous studies of more reduced conditions in the nile fan the moef vs uef enrichment factor variations in core 9509 infer a transition from open marine suboxic conditions in the enclosing non sapropel sediments to anoxic non sulphidic water column conditions in the sapropel correspondingly the highly reactive fe pool fehr measured in fe speciation studies is dominated by fe oxyhydr oxide minerals in the background sediments whereas pyrite fepy becomes the dominant component of the fehr pool in the sapropel maximum fepy values in the sapropel coincide with peak productivity and reducing conditions implying a clear link between trace element uptake diagenetic bacterial sulphate reduction in anoxic porewater and fe mobilization in the sapropel iron isotope compositions 56fe in the sapropel do not show any departure from primary marine and detrital source sediment values and the absence of an fe al vs 56fe trend strongly argues against an fe shuttle molybdenum isotopes however show marked non conservative fractionation patterns background sediment 98 95mo values 0 2 to 0 7 are compatible with fractionation upon absorptive uptake by fe oxyhydr oxides and pyrite in contrast minimum 98 95mo values exhibited at peak sapropel reducing and pyrite producing conditions are most closely modeled by mo isotope fractionation during kinetically controlled conversion of aqueous molybdate to thiomolybdate species the conservative fe isotope behavior mo isotope fractionation minima in the sapropel may be a characteristic of organic rich sediment diagenesis below an anoxic non sulphidic water body without the operation of a benthic fe shuttle

the diagenetic formation of metal rich layers in sapropel containing sediments in the eastern mediterranean two cores recovered from different locations in the eastern mediterranean contain intercalations of organic rich sapropels in organic poor hemipelagic sediments in both cores enrichments of mn and fe were found in the oxidised section of the sediment above the sapropel s1 the sediments followed a diagenetic cycle which began after the sapropel formation finished about 7000 years ago first during a non steady state diagenetic phase metal rich layers were formed at a downward moving oxidation front the front decelerated at the top of the sapropel as a consequence of increasing amounts of corg and sulphides that had to be oxidised during the second part of this non steady state phase the oxidation front starts moving upwards with respect to the sapropel manganese is remobilised in preference to iron due to thermodynamics reinforced by kinetics when the upward movement of the oxidation front becomes equal to the sedimentation rate steady state is established with respect to the new organic poor sedimentary circumstances at location 31g1 the system is at or close to steady state at location 9g1 however this steady state phase has never been reached between 1900 and 1350 years bp the organic carbon accumulation rate probably increased suddenly inducing a retreat of the oxidation front and the non steady state formation of double peaks

extraction of pore water from marine sediments a review of possible artifacts with pertinent examples from the north atlantic abstract great care must be taken in extracting pore water if results are to be reliable errors can arise by inadequate storage conditions prior to pore water extraction by a difference between extraction temperature and the in situ temperature by oxygen contamination and possibly by high squeezing pressures three different extraction methods have been applied to samples from 30 m long piston cores collected in two abyssal plains in the north atlantic ocean the results demonstrate that all of the above mentioned errors have occurred these errors are discussed ad examples are shown

evidence from molybdenum and iron isotopes and molybdenum uranium covariation for sulphidic bottom waters during eastern mediterranean sapropel s1 formation redox exerts a critical control on organic carbon rich sedimentation this is particularly true for eastern mediterranean sapropels where seawater stratification is regarded as a major driving force for oxygen depletion but in which sulphidic euxinic bottom waters occur only sporadically here we apply a powerful array of geochemical proxies fe and mo stable isotopes together with mo u ratios and redox sensitive trace elements rste to the determination of water redox evolution during the deposition of holocene s1 sapropel and its underlying and overlying sediments odp core 967d 2550 m depth rste are asymmetrically distributed within the sapropel with peak enrichments occurring in its lower early part negative correlations are found between fe57 and both fe al and s wt in the lower sapropel and are consistent with the benthic fe shuttle model fe enrichment in euxinic basins moef uef enrichment factor variations show well defined trends identical to those proposed for open marine settings in which sub oxic conditions in the background sediments give way to sulphidic waters at the rste peak in the lower sapropel the most notable features of the mo isotope profile are atypically light values mo98 95 0 7 in the lower sapropel such light mo isotope values relative to sea water mo98 95 2 3 have been related to oxic remobilisation however negative correlations between mo98 95 and fe al ba al mo al and s imply that the lowest mo isotopic compositions are associated with peak reducing conditions taken in conjunction with the evidence from the other proxies for a sulphidic water column the light mo isotope values in the lower sapropel are best explained by a large isotopic fractionation between sea water molybdate and thiomolybdate species in mildly euxinic bottom waters h2s aq 10 m the data from this study thus show that hitherto unrecognised euxinic conditions occur during the early stages of deposition of the holocene sapropel s1 molybdenum isotopes and ba al ratios identify a short lived sapropel re ventilation event timed to coincide with the 8 2 ka cold climatic event

paleomagnetic and geochemical record from cores from the sea of marmara turkey age constraints and implications of sapropelic deposition on early diagenesis abstract we present results of a multi proxy analysis of two sediment cores from the marmara sea the cores were analyzed using paleomagnetic and geochemical measurements two sapropels are documented in the last 11 kyr and are recorded in several locations across the marmara sea these two sapropels have contrasting magnetic properties the magnetic record is affected by intense early diagenesis the most recent upper sapropelic layer has low remanence and susceptibility values a record of paleomagnetic inclinations could still be isolated above the diagenesis front and is compared with secular variation models the lower sapropel is identified in the deep part of the oldest studied core klg07 and has distinct magnetic properties characterized by high remanence and susceptibility values using the magnetic properties it is possible to constrain bottom water ventilation and reconnection episodes between the marmara sea and the black sea following the sea level rise during the last glacial to inter glacial transition

quaternary isotope stratigraphy and paleoclimate of coral reef terraces gulf of aqaba south sinai egypt five quaternary coral reef terraces have been recognized along sharm elsheikh ras mohammed coast of which terraces v to ii form a well developed staircase at um seed while recognized separately at ras mohammed terrace i was only observed as a reef pathches at sharm elsheikh ras mohammed road terraces v to i exist at elevations of 1 b s 1 to 0 m 3 6 m 10 12 m 15 20 m and 25 35 m a s 1 respectively uranium series dates of samples representing terraces v iv iii ii and i show ages grouped as ka 118 125ka 200ka 280 300ka and older 300ka which are related to isotope stages 1 5e 7 9 and 11 respectively the variation of 18o for samples from these terraces show evidence of at least four major warm wet climatic periods in relationship to high sea level and contemporaneous with the formation of the reef terraces faulting affects only the older terraces i and ii and along with the occurrence of terrace iv of last interglacial age at elevation of 3 6 m suggest that the coastal area has not been subjected to major tectonic activities at least with the last 125 ka

emplacement of the recent sedimentary cover and processes of deposition on the matapan trench margin hellenic arc abstract high resolution seismic surveys across the southern peloponnesus margin help to define the configuration and geometry of the unconsolidated sedimentary cover on the basis of acoustic character structural framework and results of dsdp cores two sedimentary units are distinguished a well stratified quaternary unit and an acoustically transparent pliocene series overlying a deep acoustic unit of different nature and age the plio quaternary series appears highly discontinuous along most of the margin the slope displays a series of basins where locally sediment thicknesses exceed 1000 m these basins separated by structural ridges generally devoid of sediment are often connected to the trenches by canyons the mechanism of sedimentation termed cascade feeding consists in a succession of depositions and of removals of sediment from basin to basin until the trench basins are reached the major physiographic features involved in this mechanism slope basins canyons ridges depressions trenches are directly controlled by structural trends oriented n140 and n70 related with the neotectonic evolution of the hellenic arc

a geochemical model of the peru basin deep sea floor and the response of the system to technical impacts a geochemical model of the peru basin deep sea floor based on an extensive set of field data as well as on numerical simulations is presented the model takes into account the vertical oscillations of the redox zonation that occur in response to both long term glacial interglacial and short term el nino southern oscillation enso time scale variations in the depositional flux of organic matter field evidence of reaction between the pore water no3 and an oxidizable fraction of the structural fe ii in the clay mineral content of the deep sea sediments is provided the conditions of formation and destruction of reactive clay fe ii layers in the sea floor are defined whereby a new paleo redox proxy is established transitional no3 profile shapes are explained by periodic contractions and expansions of the oxic zone ocean bottom respiration on the enso time scale the near surface oscillations of the oxic suboxic boundary constitute a redox pump mechanism of major importance with respect to diagenetic trace metal enrichments and manganese nodule formation which may account for the particularly high nodule growth rates in this ocean basin these conditions are due to the similar depth ranges of both the o2 penetration in the sea floor and the bioturbated high reactivity surface layer hrsl all against the background of enso related large variations in depositional corg flux removal of the hrsl in the course of deep sea mining would result in a massive expansion of the oxic surface layer and thus the shut down of the near surface redox pump for centuries which is demonstrated by numerical modeling

abnormal carbonate diagenesis in holocene late pleistocene sapropel associated sediments from the eastern mediterranean evidence from emiliania huxleyi coccolith morphology in studying the holocene late pleistocene record of the eastern mediterranean considerable emiliania huxleyi size shape variation not clearly assignable to primary or secondary calcification was observed accordingly different morphotypes were distinguished by light microscope lm a subsequent scanning electron microscope sem analysis of selected samples has indicated that emiliania huxleyi coccoliths are variably affected by carbonate diagenesis in these sediments a series of diagenetic stages were qualitatively defined comprising well preserved specimens three overgrowth og1 to og3 and one etching e1 stage comparing sem and lm observations a tentative correlation between the e huxleyi calcified lm morphotypes and e huxleyi sem overgrowth stages is proposed here our study not only indicates that emiliania huxleyi coccoliths are strongly influenced by carbonate diagenesis but also that they show effects of carbonate precipitation and dissolution much more clearly than other coccoliths the relative abundances of the different lm morphotypes were used to define an e huxleyi overgrowth index exo that qualitatively estimates carbonate precipitation dissolution on coccoliths in this sediment this resulted in definition of five diagenetic intervals d1 to d5 deposition of sapropel s1 was a time of good preservation with variable dissolution and no overgrowth of e huxleyi coccoliths whereas calcite overgrowth was high during the last glacial maximum lgm and interglacial period and to a lesser extent during the younger dryas and through the last 5 ka d 2004 elsevier b v all rights reserved

selective aerobic and anaerobic degradation of lipids and palynomorphs in the eastern mediterranean since the onset of sapropel s1 deposition abstract selective degradation of organic matter in sediments is important for reconstructing past environments and understanding the carbon cycle here we report on compositional changes between and within lipid classes and kerogen types represented by palynomorph groups in relation to the organic matter flux to the sea floor and oxidation state of the sediments since the early holocene for central eastern mediterranean site abc26 this includes the initially oxic but nowadays anoxic presapropelic interval the still unoxidised lower part of the organic rich s1 sapropel its postdepositionally oxidised and nowadays organic poor upper part as well as the overlying postsapropelic sediments which have always been oxic a general 2 3 times increase in terrestrial and marine input during sapropel formation is estimated on the basis of the total organic carbon toc pollen spore dinoflagellate cyst n alkane n alkanol and n alkanoic acid concentration changes in the unoxidised part of the sapropel the long chain alkenones 1 15 diols and keto ols loliolides and sterols indicate that some plankton groups notably dinoflagellates may have increased much more apart from the terrestrial and surface water contributions to the sedimentary organic matter anomalous distributions and preservation of some c 23 c 27 alkanes alkanols and alkanoic acids have been observed which are interpreted as a contribution by organisms living in situ comparison of the unoxidised s1 sapropel with the overlying oxidised sapropel and the organic matter concentration profiles in the oxidised postsapropelic sediments demonstrates strong and highly selective aerobic degradation of lipids and palynomorphs there seems to be a fundamental difference in degradation kinetics between lipids and pollen which may be possibly related with the absence of sorptive preservation as a protective mechanism for palynomorph degradation the n alkanes impagidinium and nematosphaeropsis are clearly more resistant than toc the n alkanols and n carboxylic acids are about equally resistant whereas the pollen all other dinoflagellate cysts and other lipids appear to degrade considerably faster which questions the practice of normalising to toc without taking diagenesis into account selective degradation also modifies the relative distributions within lipid classes whereby the longer chain alkanes alcohols and fatty acids disappear faster than their shorter chain equivalents accordingly interpretation of lipid and palynomorph assemblages in terms of pre or syndepositional environmental change should be done carefully when proper knowledge of the postdepositional preservation history is absent two lipid based preservation proxies are tested the diol keto ol oxidation index based on the 1 15c 30 diol and keto ols doxi and the alcohol preservation index api whereby the former seems to be the most promising

quaternary crusts on slopes of the mediterranean sea a tentative explanation for their genesis abstract quaternary deep sea crusts i e lithified omission surfaces are widespread on slopes and subsea relief features in the western and especially the eastern mediterranean sea the lithification is induced by the early precipitation of a magnesian calcite cement in the uppermost few centimetres of a calcareous ooze based on their thickness and degree of hardening the collected samples have been divided into three main types each of them corresponding to a different degree of lithification except in rare probably old crusts collected at water depths below 2000 2500 m and in infills of some sponge skeletons or in the case of inferred internal tension recrystallization and generally mineral alterations are very limited the precipitation mechanisms appear to be essentially physicochemically controlled and ions involved in cementation come from the seawater reservoir by means of an inward diffusion of solutions diffusion is enhanced by bottom currents these currents maintaining a low or zero rate of sedimentation moreover lithification also depends on the chemical characteristics of the seawater i e supersaturation with respect to low magnesian calcite and low contents of phosphates and dissolved organic matter which would inhibit crystal growth local factors and primary composition of the original sediment also appear to influence the speed of early lithification when conditions of lithification are favourable a few hundreds of years to a few thousand years at the most seem sufficient for the first two stages of lithification to be reached the submarine lithification was active during the last glacial episode and as exhibited by numerous samples especially towards the end of this period the previous cold stages were probably also episodes of efficient lithification this correlation with quaternary climatic cycles certainly reflects an intensification of thermohaline and bottom current circulations during periods of severe climatic conditions there is also some evidence of holocene and even present day crusts

the formation of eastern mediterranean sapropels abstract sapropel formation in the eastern mediterranean is explained by an oceanographic approach it is suggested that sapropels are not only a consequence of eustatic sea level changes as earlier proposed by olausson a model which is widely accepted but rather a result of a very sensitive reaction of the eastern mediterranean to any small climatic amelioration present day aeration of the deep eastern mediterranean basin results from circulation of oxygen rich deep water originating mainly in the adriatic assuming present day conditions a climatic amelioration towards more humid and warmer conditions leading to an increase of the water temperature in the adriatic basin by 0 7 c or to a decrease of its salinity by only 0 2 will cause stratification of water masses and enhance sapropel formation