seismic stratigraphy and sedimentary facies analysis of the pre and syn messinain salinity crisis sequences onshore nile delta egypt implications for reservoir quality prediction abstract this study provides the first high resolution outlines of the messinian sequence in the nile delta based on an integrated sedimentological petrophysical and seismic stratigraphic approach the distribution pattern and architecture of the messinian facies deposited before during and after the messinian salinity crisis msc have been investigated in seismic the pre msc qawasim formation constitutes parallel oblique seismic facies interpreted as deltaic system prograding northward from prodelta distal sand bars into subaqueous distributary channels and mouthbars and subaerial delta plain distributary channels the msc abu madi formation consists of three seismic stratigraphic units infilling the eonile canyon a seismically chaotic lower unit paving the canyon floor is overlain by the continuous high amplitude reflectors of the middle unit which is capped by semi chaotic low amplitude facies of the upper unit the lower unit corresponds to the subaerial gravity flow deposits synchronously accumulated during the eonile incision whereas the middle unit comprises the aggradational progradational fluvial facies and the upper unit constitutes the retrogradational estuarine facies the superimposed diagenetic alterations on these various depositional facies produced complex reservoir heterogeneity fluid flow conduits are restricted to the coarse grained delta distributary channels and fluvial facies with limited marine influence and minimal depositional clay content and traces of diagenetic kaolinite and chlorite on the other hand flow baffles and barriers are common in the fine grained marine influenced facies with pervasive depositional clays diagenetic calcite and glauconite

late miocene to early pliocene climate variability off nw africa odp site 659 abstract a high resolution 18 o record obtained on benthic foraminifera cibicides wuellerstorfi combined with clay mineralogy major element concentrations and sr nd isotopes have been investigated for the odp site 659 located off north africa in order to reconstruct african monsoon intensity between 6 2 and 4 9 myr mineralogical and geochemical results indicate that sedimentation on the cape verde plateau results from a mixture of sediments deriving from the neighbouring saharan arid region and the wet african equatorial zone sahelian band characterised by a low and a high state of weathering respectively past variations in terrigenous inputs from these areas allow us to track past extension and displacement of the west african monsoon itcz system maximal summer insolation induced a northward migration of the inter tropical convergence zone itcz wetter conditions in the sahel and a diminishing of wind erosion over the south sahara and sahel in addition there was an increase in river input to the cape verde plateau of sediments derived from southern sedimentary sources which are characterised by high kaolinite contents and cia values and low k al and ti al ratios on the other hand minimal summer insolation induced a southward movement of the itcz drier climate in the sahel and stronger easterly winds resulting in an increase in dust transport from the sahara to the cape verde plateau dust particles are characterised by high illite and smectite content and by a low chemical state of weathering low cia values and high k al and ti al ratios finally our results provide new clues regarding the re flooding of the mediterranean sea at the end of the msc 5 33 myr this event was associated with enhanced aridity in the sahara implying a reorganisation of the atmospheric circulation and a southward migration of the itcz

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

climate modelling sensitivity experiments for the messinian salinity crisis abstract the repeated isolation of the atlantic ocean during the messinian led to at least the partial desiccation of the mediterranean sea and to the deposition of massive evaporites messinian salinity crisis overall proxy data do not indicate dramatic climatic changes in the mediterranean region for the time of the messinian salinity crisis but a constant climate seems to be unrealistic at first sight to analyse the climate response to environmental changes in the mediterranean region during the messinian salinity crisis we perform climate modelling sensitivity experiments as a reference base we use a tortonian simulation tort and simulate three messinian sensitivity scenarios 1 the mediterranean sea surface 1500 m lower than the normal sea level msc lowsea 2 the mediterranean basin completely desiccated the resulting land surface 1500 m lower and covered by grassland vegetation msc lowgrass and 3 the mediterranean sea simply replaced by grassland vegetation msc grass all sensitivity experiments represent extreme scenarios for analysis of general patterns of messinian climate change in msc lowsea mean annual temperatures in the mediterranean basin increase by 2 c and surrounding regions get cooler by up to 3 c as compared to tort the lowering of the mediterranean sea level increases the annual precipitation in the south western part of europe and in north western africa up to 1000 mm a in msc lowgrass as compared to tort the mediterranean basin strongly heats up by 7 c while temperatures in the surrounding areas do not change more than 2 c the precipitation in the mediterranean basin significantly decreases up to 600 mm a precipitation in the areas surrounding the mediterranean basin does not change substantially in msc lowgrass but rainfall in w africa increases up to 600 mm a in msc grass as compared to tort temperatures in the mediterranean region increase by 4 c this is twice as high as the temperature increase which resulted from lowering the mediterranean sea surface in msc lowsea annual rainfall over the mediterranean basin in msc grass is 400 mm a lower than the rainfall in tort proxy based climate reconstructions for the time of the messinian salinity crisis indicate no dramatic climatic changes around the mediterranean in contrast to this for eastern n africa and eastern europe climate changes are indicated the msc lowsea and msc lowgrass sensitivity experiments show that the strong environmental changes in the mediterranean realm during the msc did not necessarily cause strong climatic changes at the margins of the mediterranean basin therefore the present modelling studies are in agreement with climate proxy data from the mediterranean region additionally our results principally agree with the climate changes inferred from the fossil record of central and eastern europe for eastern n africa our modelling studies contradict proxy data based on our results weak climatic changes indicated by the fossil record at the mediterranean coastlines are realistic

late quaternary palaeoenvironments in the lake barombi mbo west cameroon deduced from pollen and carbon isotopes of organic matter abstract a sediment core 23 5 m long was recovered from a water depth of ca 110 m in lake barombi mbo a maar crater of the cameroon volcanic chain this paper presents a carbon isotopic curve of organic matter linked to the main results of the pollen analysis interpretation of this carbon isotopic curve is simplified 1 because of the weak role played by the phytoplankton in the balance of the organic particle flux and 2 because of the presumed absence of diagenetic alteration of the isotopic composition the carbon isotopic curve exhibits an almost linear correlation with that of total grass pollen which form the main part of the c4 biomass the major fluctuations of isotopic and pollen curves allow four main phases to be distinguished from ca 25 000 to 20 000 yr b p 13c values of 25 to 30 pdb are related to a forest environment associated with a montane floral element from 20 000 to 13 000 yr b p the 13c values are between 23 and 28 and are linked to openings of landscape with a mosaic of forest and savanna and a fall of lake level with colonization of the shores by cyperaceae and other aquatic plants from 13 000 to 10 000 yr b p the forest extended again reaching a maximum density during the period from 9500 until 3000 yr b p and with an average 13c value of 32 a new dry phase at around 2500 2000 yr b p with temporary openings in the forest marked by a 13c excursion above 30 but during the last 2 millennia the forest developed again with 13c values of 32

a laboratory study of particle ploughing and pore pressure feedback a velocity weakening mechanism for soft glacier beds if basal water discharge and pressure are sufficiently high a soft bedded glacier will slip over its bed by ploughing the process in which particles that span the ice bed interface are dragged across the bed surface results of laboratory experiments indicate that resistance to ploughing can decrease with increasing ploughing velocity velocity weakening during ploughing at various velocities 15 400 m a 1 till was compacted in front of idealized particles causing pore pressures there that were orders of magnitude higher than the ambient value this excess pore pressure locally weakened the till in shear thereby decreasing ploughing resistance by a factor of 3 0 6 6 with a six fold increase in ploughing velocity characteristic timescales of pore pressure diffusion and compaction down glacier from ploughing particles depend on till diffusivity ploughing velocity and sizes of ploughing particles these timescales accurately predict the ranges of these variables over which excess pore pressure and velocity weakening occurred existing ploughing models do not account for velocity weakening a new ploughing model with no adjustable parameters predicts ploughing resistance to no worse than 38 but requires that excess pore pressures be measured velocity weakening by this mechanism may affect fast glacier flow sediment transport by bed deformation and basal seismicity

tectonic and sedimentary evolution of the gulf of suez and the northwestern red sea abstract the structural pattern of the gulf of suez and red sea rift is inherited from the basement tectonics n140 faults clysmic direction parallel to the regional elongation of the rift are associated with submeridian aqaba direction and sub e w faults duwi direction that also play an important role in the rifting processes the pre rift sedimentary cover includes cretaceous and eocene platform deposits it was slightly deformed prior to rifting the syn rift sedimentary sequence comprises four major units groups a to d delimited by unconformities group a oligocene to early burdigalian continental to restricted subaquatic deposits group b burdigalian to middle miocene open marine sediments group c middle to upper miocene major evaporitic episode and group d plio pleistocene which returns to an open marine environment four majors stages of structuration are recorded an initial stage of compressive deformation direction of shortening close to nw se characterized by strike slip movements and associated drag folds early group a a tilted block stage late group a corresponding to the period of highest extensional rate a horst and graben stage group b resulting in the cutting out of the tilted blocks by numerous synthetic faults group b corresponds to the period of highest subsidence rate when a flexuration stage of the margin expressed by a centripetal evolution of the subsidence is associated with major periferal uplift

late miocene and pliocene large land mammals and climatic changes in eurasia the fossil teeth of land mammals offer a powerful tool to map the regional details of past climate change in the terrestrial realm we use meanplant eaterhypsodonty molarcrownheight oflateneogenemammallocalitiestomaplatemioceneandpliocenepalaeoprecipitation on the eurasian continent and with higher temporal resolution in europe the results show that the mid latitude drying in eurasia affected thecentral parts ofthecontinentfirst and thatthedrying of western europeafter about7 8maseemstohavecoincidedroughlyintimewith a return to more humid conditions in eastern asia with a return to a drier east and more humid west in the pliocene within europe the hypsodonty based palaeoprecipitation maps suggest that the sequence from mn 9 to mn 12 ca 11 1 6 8 ma was dominated by an east west continental marine humidity gradient which gradually intensified and with a shift of dryer conditions eastwards in mn 12 ca 7 5ma thiswaspartlyoverlainfrommn13onwardsbyanorth southorientedgradient whichpersistedatleasttotheendofthepliocene the maps for both the earliest late miocene mn 9 ca 11 1 9 7 ma and the earliest pliocene mn 14 ca 4 9 4 2 ma show very low regional differentiation possibly suggesting perturbed phases in the evolution of the mammal communities analysis of hypsodonty and dietary structure of the mammalian plant eater community in europe during the entire interval shows that the miocene pliocene boundary was marked by a strong decrease in mesodont species and mixed feeders and an increase in brachydont species and omnivores in this view the shift in the latest miocene from east west to partly north south polarised hypsodonty patterns corresponds mainly to an increase in hypsodont species and grazers it seems probable that the east west gradient was primarily driven by precipitation while the north south gradient would also have been strongly influenced by temperature related effects of humidity

magnetostratigraphic biostratigraphic and stable isotope stratigraphy of an upper miocene drill core from the sale briqueterie northwestern morocco a high resolution chronology for the messinian stage we report a high resolution stable isotope carbonate magnetostratigraphic and biostratigraphic record from a 175 m drill core from the sale briqueterie which is part of the bou regreg section in northwestern morocco the sale drill core spans the interval from paleomagnetic chron c4n partim to c3r earliest gilbert which represents the time leading up to and including the isolation and desiccation of the mediterranean i e the messinian salinity crisis during chrons c3an and c3ar 6 935 to 5 894 ma the isotope and carbonate signals display quasi periodic variations with estimated periods of 40 and 100 kyr respectively we interpret the 40 kyr 18o variations as reflecting changes in global ice volume caused by obliquity induced changes 41 kyr in solar insolation in polar regions the 100 kyr carbonate variations probably represent long term modulation of the amplitude of the precessional cycle 21 kyr which is not resolved by our sampling frequency the cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of shackleton et al 1994a from stage tg24 in chron c3r earliest gilbert to stage c3ar 18o 18 at the base of chron c3ar 6 935 ma a major change in paleoceanographic conditions is recorded across the tortonian messinian boundary which we correlate to chron c3bn at 7 04 ma benthic foraminiferal 18o values increased by an average of 0 4 in two steps at 7 17 ma and 6 8 ma and 13c values decreased by 0 7 0 8 between 7 1 and 6 8 ma representing the late miocene carbon shift the first step in 18o values coincides with an inferred reversal in deep water circulation through the rifian corridor and the second correlates with the base of the tripoli formation and onset of crisis conditions in the mediterranean we suggest that the increase in 18o values represents at least in part an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the mediterranean average 18o values remained high throughout most of chrons c3ar and c3an reaching maximum 18o values during isotope stages tg20 and 22 in chron c3r earliest gilbert the glacio eustatic falls associated with these events may have resulted in the complete isolation of the mediterranean from the world ocean shackleton et al 1994a following stage tg12 in the sale record there exists a trend toward progressively lower 18o values that may represent a series of marine transgressions that eventually reflooded the mediterranean and ended the salinity crisis

geomorphological processes and their palaeoenvironmental significance at the shum laka cave bamenda western cameroon abstract the climatic environmental history of the shum laka cave western cameroon and its surroundings has been established by means of geomorphological sedimentological and botanical data tied in a well dated stratigraphical sequence since 30 000 yr bp this mountainous area 1 650 2 000 m asl has never been a desert nor a tropical forest temperatures seldom significantly dropped below freezing mountain forest with galleries along the water courses and grassland in between prevailed most of the time a certain evolution can be observed from 31 000 to 20 000 yr bp annual precipitation was initially higher than today and subsequently somewhat lower from 13 000 yr bp onwards humidity and temperatures increased again around 9 000 yr bp they probably reached higher values than today from 9 000 yr bp human activity became very apparent this may have influenced the evolution of the natural landscape and obliterated climatological effects this evolution has been interrupted three times by dryer climatic conditions which each time lasted for only 1 or 2 millennia respectively at 33 000 at 11 000 and at 3 000 yr bp another important less humid episode occurred between 6 070 and 3 180 yr bp finally there is some evidence for a drier period between 8 480 and 7 150 yr bp the climatic evolution established for the shum laka cave confirms and refines former data from the area and is in good agreement with data from barombi mbo and chad

pollen corrected leaf wax d h reconstructions of northeast african hydrological changes during the late miocene abstract plant leaf wax hydrogen isotope dwax reconstructions are increasingly being used to reconstruct hydrological change this approach is based upon the assumption that variations in hydroclimatic variables and in particular the isotopic composition of precipitation dp dominate dwax however modern calibration studies suggest that offsets between plant types may bias the dwax hydrological proxy at times of vegetation change in this study i pair leaf wax analyses with published pollen data to quantify this effect and construct the first vegetation corrected hydrogen isotopic evidence for precipitation dcorrp in marine sediments from deep sea drilling program site 231 in the gulf of aden spanning 11 4 3 8 ma late miocene and earliest pliocene i find 77 swings in dwax that correspond to pollen evidence for substantial vegetation change similarities between dp and dcorrp imply that the hydrological tracer is qualitatively robust to vegetation change however computed vegetation corrections can be as large as 31 indicating substantial quantitative uncertainty in the raw hydrological proxy the resulting dcorrp values quantify hydrological change and allow us to identify times considerably wetter than modern at 11 09 7 26 5 71 and 3 89 ma more generally this novel interpretative framework builds the foundations of improved quantitative paleohydrological reconstructions with the dwax proxy in contexts where vegetation change may bias the plant based proxy the vegetation corrected paleoprecipitation reconstruction dcorrp represents the best available estimate as proof of concept for an approach that i hope will be refined and more broadly applied

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

palaeoenvironmental changes of the early pliocene zanclean in the eastern mediterranean pissouri basin cyprus evidenced from calcareous dinoflagellate cyst assemblages abstract the first 100 ka of the earliest pliocene zanclean sediments of the eastern mediterranean pissouri basin on cyprus have been investigated on calcareous dinoflagellate cyst assemblages these assemblages reflect the return in three phases to the open oceanic conditions following the messinian salinity crisis msc 5 33 ma ago the lowermost phase dominated by leonella granifera cysts indicates substantial land derived nutrient supply and low salinities this confirms earlier observations of enhanced continental water runoff during the earliest pliocene in the eastern mediterranean basin the second phase dominated by caracomia stella and calciodinellum albatrosianum cysts indicates a change to warmer meso to oligotrophic waters the third phase marks the first appearance and still continuing dominance of thoracosphaera heimii in the region in addition the endemic eastern mediterranean species lebessphaera urania peaks within this upper interval it probably survived the salinity crisis in the mediterranean the assemblage reflects the establishment of typical open marine well stratified and oligotrophic surface conditions similar but not yet identical to the situation in the mediterranean sea today this study points out a discrepancy between the fast refilling scenario 1 2 ka in the pissouri basin and a long time 100 ka environmental reorganisation in the surface waters as indicated by the calcareous dinoflagellate cysts the onset of the pliocene is also marked by the first appearance of calciodinellum elongatum and calciodinellum levantinum which must have migrated from the atlantic ocean

a methodology for targeting palaeo proxy data acquisition a case study for the terrestrial late miocene when planning the acquisition of new palaeo proxy data for reconstructing past climates many factors influence the decision of where the proxies are to be collected one such influence is the likelihood of recording a significant climate change relative to the modern another consideration which is less often considered is the desire to target regions in which there is significant uncertainty in numerical model predictions of past climate change new proxy data in these regions enables a more rigorous test of model simulations and results in better constraints on the various boundary conditions used to force the models in this paper we present a methodology for targeting new palaeo proxy data based on model simulations we use the terrestrial late miocene 11 6 to 5 3 ma as a case study the late miocene climate provides insights into future climate behavior as it is believed to have been considerably warmer than the modern we carry out a suite of late miocene atmosphere only general circulation model simulations which we initially evaluate relative to an example dataset of terrestrial temperature and precipitation in terms of targeting future data acquisition we locate those regions in the model which exhibit the largest change in temperature and or precipitation relative to the pre industrial we also locate those regions which display the largest variability between the model simulations because new data in these regions are most likely to provide a strict test of the reliability of the model results among other regions the amazon basin the chad basin central canada and northern india are identified as potentially useful areas to collect data

geology and palaeontology of the late miocene middle awash valley afar rift ethiopia the middle awash study area of ethiopia s afar rift has yielded abundant vertebrate fossils 10 000 including several hominid taxa1 2 3 4 the study area contains a long sedimentary record spanning late miocene 5 3 11 2 myr ago to holocene times exposed in a unique tectonic and volcanic transition zone between the main ethiopian rift mer and the afar rift sediments along the western afar rift margin in the middle awash provide a unique window on the late miocene of ethiopia these deposits have now yielded the earliest hominids described in an accompanying paper5 and dated here to between 5 54 and 5 77 myr these geological and palaeobiological data from the middle awash provide fresh perspectives on hominid origins and early evolution here we show that these earliest hominids derive from relatively wet and wooded environments that were modulated by tectonic volcanic climatic and geomorphic processes a similar wooded habitat also has been suggested for the 6 0 myr hominoid fossils recently recovered from lukeino kenya6 these findings require fundamental reassessment of models that invoke a significant role for global climatic change and or savannah habitat in the origin of hominids

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

dense shelf water cascading and messinian canyons a new scenario for the mediterranean salinity crisis the salt giant beneath the deep mediterranean seafloor is the impressive record of the messinian salinity crisis a dramatic event that occurred about 6 ma ago following the reduction of the connections with the atlantic ocean according to the shallow water deep basin model developed for these deposits hsu and others 1973a 1973b 1978a 1978b the messinian evaporites formed in a deep but desiccated mediterranean while shelves and slopes underwent subaerial erosion due to fluvial rejuvenation triggered by a 1500 m sea level drawdown deeply incised messinian canyons in the continental slopes surrounding the mediterranean are the main argument supporting this scenario using a state of the art model and idealized but realistic numerical simulations here we demonstrate that the activation of downslope flows of hypersaline dense waters in a process similar to present day dense shelf water cascading but much more energetic may account for both slope erosion and progressive salinity rise leading to the formation of deep seated supersaturated brines our findings support a deep water deep basin model schmalz 1969 1991 de benedetti 1976 1982 dietz and woodhouse 1988 thus implying that evaporite deposition may have occurred in a non desiccated basin with strongly reduced ocean connections

the major ion composition of cenozoic seawater the past 36 million years from fluid inclusions in marine halite fluid inclusions from ten cenozoic eocene miocene marine halites are used to quantify the major ion composition mg2 ca2 k na so42 and cl of seawater over the past 36 my criteria used to determine a seawater origin of the halites include 1 stratigraphic sedimentologic and paleontologic observations 2 br in halite 3 34s of sulfate minerals 4 87sr 86sr of carbonates and sulfates and 5 fluid inclusion brine compositions and evaporation paths which must overlap from geographically separated basins of the same age to confirm a global seawater chemical signal changes in the major ion chemistry of cenozoic seawater record the end of a systematic long term 150 my shift from the ca2 rich mg2 and so42 poor seawater of the mesozoic cacl2 seas to the mgso4 seas with higher mg2 and so42 ca2 of the cenozoic the major ion composition of cenozoic seawater is calculated for the eocene oligocene 36 34 ma serravallian tortonian 13 5 11 8 ma and the messinian 6 5 ma assuming chlorinity 565 mmolal salinity and the k concentration 11 mmolal are constant and the same as in modern seawater fluid inclusions from cenozoic marine halites show that the concentrations of mg2 and so42 have increased in seawater over the past 36 my and the concentration of ca2 has decreased mg2 concentrations increased from 36 mmolal in eocene oligocene seawater 36 34 ma to 55 mmolal in modern seawater the mg2 ca2 ratio of seawater has risen from 2 3 at the end of the eocene to 3 4 and 4 0 respectively at 13 5 to 11 8 ma and 6 to 5 ma and to 5 in modern seawater eocene oligocene seawater 36 34 ma has estimated ranges of so42 14 23 mmolal and ca2 11 20 mmolal if the ca2 so42 product is assumed to be the same as in modern seawater 300 mmolal2 eocene oligocene seawater had ca2 16 mmolal and so42 19 mmolal the same estimates of ca2 and so42 for serravallian tortonian seawater 13 5 11 8 ma are so42 19 27 mmolal and ca2 8 16 mmolal and so42 24 mmolal and ca2 13 mmolal if the ca2 so42 product is equal to that in modern seawater messinian seawater has an estimated range of so42 21 29 mmolal and ca2 7 15 mmolal with so42 26 mmolal and ca2 12 mmolal assuming the ca2 so42 product is equal to that in modern seawater regardless of the estimation procedure so42 shows progressively increasing concentrations from 36 ma to the present values which are the highest of the cenozoic

slope destabilization during the messinian salinity crisis abstract during the messinian salinity crisis 6 myr ago deep canyons were incised when a huge sea level drawdown of 1 5 km affected the mediterranean sea nearly contemporaneously more than 2 km of evaporites accumulated in the basin this event was the consequence of a complex interaction of tectonic movements and global sea level variation associated with climatic evolution this unusual event ended with the reflooding of the mediterranean area in this paper using seismic line interpretation we show that several landslides occurred in various parts of the mediterranean basin during this crisis three of these landslides are well preserved and their dynamics were analyzed modeling of the slope stability demonstrates that these landslides may have been due to i the relief created by the deep erosion and or ii the reflooding which triggered a pore pressure increase the relatively small run out distances of the three landslides suggest propagation in a submarine environment and triggering by sea level rise

the red sea gulf of aden re assessment of hydrocarbon potential abstract the results and conclusions of the undp world bank red sea gulf of aden regional hydrocarbons study project june 1989 january 1992 are summarized these derive from detailed examination of pooled public sector data provided to the project by the participating bordering states in the region these included samples and logs from about 56 wells drilled in the two basins out of a total of 71 and about 30 000 line km of reflection seismic data selected from 110 000 km available well logs were digitized and correlated and basinwide biostratigraphic lithostratigraphic and palaeoenvironmental studies source rock organic richness quality and maturity studies and sedimentological analyses studies were performed by contracted specialist staff in the uk and france these were integrated with basinwide seismic structural and isopach mapping for selected regional reflectors intervals by national task forces in cairo under project supervision academically acquired crustal seismic and other geophysical data and oil industry velocity and other borehole data were also integrated for the red sea modelling utilizing recently acquired geophysical data indicates crustal asymmetry for the red sea rift with oceanic crust of pull apart basin type flooring some portions of offshore egypt and sudan on the west and stretched continental crust underlying the eastern arabian flank these interpretations furthermore suggest that sinistral strike slip processes controlled the initial break up of the arabian plate shaping the african flank as a sharp plate boundary similar processes appear to have initially shaped the somalia flank of the gulf of aden rift only later did true seafloor spreading propagate in the eastern gulf of aden 10 12 ma about a regional lithostratigraphic nomenclature scheme for the miocene recent syn and post rift red sea successions keyed to detailed biostratigraphical distribution charts and microfaunal assemblage characteristics was erected tied to the well documented and understood petroliferous gulf of suez basin scheme this allows facies variations within the basin to be compared and allows consistent interpretation and correlations across the basin to which local informal nomenclature can be related pre rift pre oligocene marine sediments are present in most of the gulf of aden jurassic eocene but only incompletely on the basin margins in the red sea jurassic in the south upper cretaceous early palaeogene in the north significant pre rift oil gas prone upper jurassic cretaceous and palaeogene source rocks occur in gulf of aden sub basins initiated by late jurassic early cretaceous tensional tectonics with maturity levels ranging from early late to post mature whereas early synrift source rocks are generally immature in the red sea good quality pre rift source rocks outcrop in the north and south but are probably overmature for oil in the basin except in the extreme south if present good syn pre and post salt and post rift source levels occur throughout the basin but in the central southern sectors only the post salt remains within the oil window because of high geothermal gradients both basins are little explored attractive pre rift jurassic eocene exploration plays in rotated fault and horst blocks in predominantly carbonate but subordinate sandstone reservoirs are present in the gulf of aden confirmed by an important undeveloped eocene light oil discovery in offshore yemen with subordinate synrift potential where maturity is established relative continental shelf narrowness is economically limiting but wider sectors occur in the red sea the principal exploration plays are in miocene synrift pre and post salt successions rotated fault blocks occur in the pre salt but maturity for oil in the deeper levels is restricted to the northern sector these levels in the central and southern sectors are overmature except in the southernmost portion but excellent potential exists in the synrift post salt and early post rift sequences with a number of attractive play types reservoirs for synrift plays are mainly sandstones and potential is confirmed by several undeveloped gas and condensate discoveries and numerous oil seepages throughout the basin relatively wide continental shelves occur in the south and along much of the eastern flank

evolution of the late miocene mediterranean atlantic gateways and their impact on regional and global environmental change marine gateways play a critical role in the exchange of water heat salt and nutrients between oceans and seas as a result changes in gateway geometry can significantly alter both the pattern of global ocean circulation and associated heat transport and climate as well as having a profound impact on local environmental conditions mediterranean atlantic marine corridors that pre date the modern gibraltar strait closed during the late miocene and are now exposed on land in northern morocco and southern spain the restriction and closure of these miocene connections resulted in extreme salinity fluctuations in the mediterranean leading to the precipitation of thick evaporites this event is known as the messinian salinity crisis msc the evolution and closure of the mediterranean atlantic gateways are a critical control on the msc but at present the location geometry and age of these gateways are still highly controversial as is the impact of changing mediterranean outflow on northern hemisphere circulation here we present a comprehensive overview of the evolution of the late miocene gateways and the nature of mediterranean atlantic exchange as deduced from published studies focussed both on the sediments preserved within the fossil corridors and inferences that can be derived from data in the adjacent basins we also consider the possible impact of evolving exchange on both the mediterranean and global climate and highlight the main enduring challenges for reconstructing past mediterranean atlantic exchange

messinian subaerial erosion of the proto nile delta abstract the evaporitic drawdown and subsequent dessication of the mediterranean basins during the messinian salinity crisis has been confirmed by detailed seismic mapping of the ensuing erosion surface in the nile delta region the basal messinian unconformity determined by seismic analysis and borehole correlation extends from almost sea level in the southern delta area to depths of at least 5 km in the nile cone the onlap of the contemporaneously deposited fluvio deltaic clastics of the qawasim formation occurs at between 2 5 to 4 km below present gradual initial drawdown of the mediterranean sea with occasional sudden sporadic falls is implied by the presence of entrenched meanders and impaired rejuvenation terraces in the nile canyon formed as the proto nile river cut down into the pre existing tortonian delta complex the former tortonian delta slope became an extensive linear erosional front with over 3 km of vertical relief the uppermost levels of which were protected by tabular oligocene basalt flows preserved as mesas and buttes the lower slopes were the site of coalescing piedmont fans fed by upper slope wadi systems the piedmonts merged into the qawasim fluvio deltaic deposits of the proto nile fluvial flood plain the subcrop beneath the basal messinian unconformity reveals a remarkable diversity of rock type each with its own distinctive control on the geomorphology and geometry of the ensuing messinian erosional surface fracture patterns within the oligocene basalts produced a trellis drainage network which became later captured by a dendritic system developed on less resistant prodelta shales of the former tortonian delta slope close study of seismic profiles clearly demonstrates that the basal messinian erosional disconformity can be traced northwards to depths of at least 2 5 3 0 km before becoming affected by later pliocene faulting this validates a deep dessication model for the evolution of the messinian evaporites

petroleum geology and potential hydrocarbon plays in the gulf of suez rift basin egypt the gulf of suez in egypt has a north northwest south southeast orientation and is located at the junction of the african and arabian plates where it separates the northeast african continent from the sinai peninsula it has excellent hydrocarbon potential with the prospective sedimentary basin area measuring approximately 19 000 km 2 and it is considered as the most prolific oil province rift basin in africa and the middle east this basin contains more than 80 oil fields with reserves ranging from 1350 to less than 1 million bbl in reservoirs of precambrian to quaternary age the lithostratigraphic units in the gulf of suez can be subdivided into three megasequences a prerift succession pre miocene or paleozoic eocene a synrift succession oligocene miocene and a postrift succession post miocene or pliocene holocene these units vary in lithology thickness areal distribution depositional environment and hydrocarbon importance geological and geophysical data show that the northern and central gulf of suez consist of several narrow elongated depositional troughs whereas the southern part is dominated by a tilt block terrane containing numerous offset linear highs major prerift and synrift source rocks have potential to yield oil and or gas and are mature enough in the deep kitchens to generate hydrocarbons geochemical parameters sterane distribution and biomarker correlations are consistent with oils generated from marine source rocks oils in the gulf of suez were sourced from potential source rock intervals in the prerift succession that are typically oil prone type i and in places oil and gas prone type ii or are composites of more than one type multiple types i ii or iii for oil prone oil and gas prone or gas prone respectively the reservoirs can be classified into prerift reservoirs such as the precambrian granitic rocks paleozoic cretaceous nubian sandstones upper cretaceous nezzazat sandstones and the fractured eocene thebes limestone and synrift reservoirs such the miocene sandstones and carbonates of the nukhul rudeis kareem and belayim formations and the sandstones of south gharib zeit and

the mediterranean hydrologic budget from a late miocene global climate simulation during the late miocene the mediterranean experienced a period of extreme salinity fluctuations known as the messinian salinity crisis msc the causes of these high amplitude changes in salinity are not fully understood but are thought to be the result of restriction of flow between the mediterranean and atlantic eustatic sea level change and climate results from a new atmospheric general circulation model agcm simulation of late miocene climate for the mediterranean and adjacent regions are presented here the model hadam3 was forced by a late miocene global palaeogeography higher co2 concentrations and prescribed sea surface temperatures the results show that fluvial freshwater fluxes to the mediterranean in the late miocene were around 3 times greater than for the present day most of this water was derived from north african rivers which fed the eastern mediterranean this increase in runoff arises from a northward shift in the intertropical convergence zone caused by a reduced latitudinal gradient in global sea surface temperatures the northwards drainage of the late miocene chad basin also contributes numerical models designed to explore late miocene salt precipitation regimes in the mediterranean which typically make use of river discharge fluxes within a few tens of percent of present day values may therefore be grossly underestimating these fluxes although the agcm simulated late miocene river discharge is high the model predicts a smaller net hydrologic budget river discharge plus precipitation minus evaporation than for present day we discuss a possible mechanism by which this change in the hydrologic budget coupled with a reduced connection between the mediterranean and the global ocean could cause the salinity fluctuations of the msc

sedimentation and palaeoenvironment in crater lake barombi mbo cameroon during the last 25 000 years lake barombi mbo is situated in a maar crater of the cameroon volcanic chain sediment cores were recovered with a livingstone corer this paper presents data on core bm6 23 5 m long from a water depth of 110 m the sediments are mainly organic matter rich clays 5 to 10 total organic carbon showing alternating brown and yellowish horizontal laminae on a cm scale the lower part of a couplet basal sublamina is rich in siliciclastic quartz mica grains sponge spicules and documents the deposition of flood detritus the upper unit upper sublamina is composed of grey to bluish clay which becomes green toward the top with frequently yellow layered concretions of siderite it corresponds to quiet conditions with settling of fine clayey particles from suspension the overall recurrence rate of these laminae is about 15 years this frequency is similar to present day large flood events in this intertropical zone from 14 000 to 20 000 yrs bp the sediment accumulation rate was quite low 15 30 g cm 2 10 3 yrs with less abundant precipitation pedogenic clay formed from mica family minerals from 12 000 yrs bp throughout the holocene the rate of accumulation increased 40 g cm 2 10 3 yrs and increasing precipitation favoured the pedogenic formation of kaolinites turbidity currents became less important to the overall sedimentation plankton production remained low documented by organic matter which is more of the exinite than the alginite type siderite concretions occur as early diagenetic products possibly related to alkalinity in anoxic waters at the sediment water interface which limited the formation of fe3 thin ash layers occur between 11 5 and 18 m depth in core bm6 bearing witness to several volcanic events during the late quaternary sediments are disturbed below 21 m with folded laminations and inverse ages these probably result from a slump glide of lower slope sediment but could also signal a possible gas event

how dry was the mediterranean during the messinian salinity crisis the messinian salinity crisis msc 5 97 5 33 ma is an enigmatic episode of paleoceanographic change when kilometers thick evaporite units were deposited in the mediterranean basin it is generally accepted that during the msc interval there was a dry climate in the mediterranean region it is difficult to assess how dry the climate was during the msc because a modern analogue in size and duration is absent here we reconstruct hydrological changes in the mediterranean basin during the three main msc stages using excellently preserved biomarkers we used the hydrogen isotopic composition of the long chain n alkanes dn alkanes to reconstruct the hydrological changes on the land adjacent to the mediterranean sea additionally the d of long chain alkenones dalkenones is used to observe changes in the mediterranean sea water source the dn alkanes recorded during the deposition of primary lower gypsum stage 1 in monte tondo indicate a d of the precipitation comparable to the present day mediterranean implying a similar hydrologic regime indicated by experiments modelling the miocene pliocene transition elevated dalkenones values from halite unit stage 2 of the realmonte mine are associated with kainite and giant polygons consistent with presumably high evaporative conditions during halite deposition the dn alkanes recorded during the deposition of upper gypsum stage 3 in eraclea minoa indicate a dprecipitation typical for much drier settings similar to the red sea region the relative contribution of the different alkenones from eraclea minoa is similar to the one observed in present day marine settings suggesting that during stage 3 connections to the open ocean were likely maintained however the dalkenones records during deposition of the evaporites in eraclea minoa are similar to those synchronously registered in the black sea implying that a similar hydrologic regime characterized by extended drought covered large areas of southeastern europe based on the dalkenones similarity and the paratethys type of lago mare fauna in the mediterranean we speculate that the surface water during stage 3 was at times derived from the black sea

the late neogene sahabi rivers of the sahara and their climatic and environmental implications for the chad basin this paper is based on the concept that the drainage system of c 7 5 4 6 ma is still reflected in the geomorphology of northeastern chad and adjacent areas of libya during the messinian and early pliocene a large lake was present in the chad basin that is termed neogene lake chad it fluctuated in size in response to the precessional cycle and at times overflowed to the east ne or north giving rise to the sahabi rivers the eosahabi flowed during the drawdown of the mediterranean late messinian and eroded the erdi and part of the east tibesti valley the post rift miocene deposits of the chad basin some several hundred metres in thickness record a transgression over an irregular and faulted terrain with the deposition of coarse and fine clastic material fluviatile and lacustrine environments are represented at least part of the miocene succession belongs to a phase of late miocene lake development fluctuating climate during the messinian and early pliocene led to repeated changes in the environment of the chad and eosahabi basins with over 100 climatic cycles developed this would favour the development of animal species with high adaptability for example to littoral riparian woodland and savanna habitats

the late miocene climate of northeastern africa unravelling the signals in the sedimentary succession examination of the depositional profile of the miocene plio pleistocene succession at two locations in the gulf of suez and seven locations in the red sea leads to the conclusion that the messinian zeit formation and equivalent sedimentary rocks were deposited at a rate greater than other units of the miocene plio pleistocene in these areas the zeit formation contains a significantly higher clastic content than the underlying south gharib formation these two aspects of the stratigraphy are taken to indicate that the messinian was a time of high rainfall and high sediment yield rates this period named the zeit wet phase stands in marked contrast to the arid conditions of the preceding tortonian stage the latter stage is represented in the gulf of suez and red sea area by the halite bearing south gharib formation and its equivalents physical evidence for a humid messinian is provided by five lines of evidence involving four sites around the red sea and two sites offshore it is suggested that the zeit wet phase was marked by high monsoonal activity as demonstrated by drilling sites of the ocean drilling program it is probable that the wet phase peaked in the late messinian at the time of the low stand of the mediterranean during the messinian salinity crisis

miocene biofacies development and geological history of the gulf of suez egypt abstract miocene sediments of the gulf of suez were deposited in a rapidly subsiding rift which became active during late oligocene and early pliocene tectonic episodes complex lithological variations associated with the variable submarine structure commonly preclude detailed correlation of drilled subsurface successions thick middle to late miocene evaporites and their geometry obscure seismic interpretation of prospective sub evaporitic early and middle miocene sequences the thick miocene sediments are believed to have significantly furnished the source as well as the reservoirs and seals for the oil discovered in the gulf of suez over four billion barrels of oil have been established as recoverable reserves in miocene reservoirs a new gulf wide detailed correlation scheme is established based upon a series of newly defined microfaunal assemblage zones these zones are based on holistic analysis of microfauna utilizing planktonic and benthonic foraminifera diatoms otoliths and pteropods dating by planktonic foraminifera and calcareous nannofossils indicates the zones are isochronous vertical and lateral variations in assemblage characteristics have been identified mapped and are concluded to be the results of vertical and lateral differences in salinity water depth water clarity lithological variation and oxygen availability the correlative applicability of this scheme within the gulf of suez provides potential for it to serve as a reference for drilled sequences in the red sea where thicker evaporite sequences make sub evaporitic stratigraphic correlation even more difficult owing to the greater seismic attenuation isochronous palaeoenvironmental variations are detected utilizing the zonation scheme both within the gulf of suez and the red sea region which will assist in the correlation and mapping of stratigraphic sequences of hydrocabon potential detection confirmation and the degree of displacement of faults is also improved by the application of the scheme

aridity and humidity two aspects of the late miocene climate of north africa and the mediterranean abstract the physiography of north africa is not greatly changed from that of the messinian with the drawdown of the mediterranean in the late messinian the then existing river systems were incised into the landscape and emptied into lake cyrenaica which occupied the substantially drained eastern mediterranean basin the record of incision provides a record of the magnitude of the messinian river systems an analysis of these river systems demonstrates that messinian rainfall a consequence of the zeit wet phase was greatest in east and south central north africa in keeping with the derivation of the water mainly from the indian ocean in central north africa the eosahabi river flowed from messinian lake chad eroding the east tibesti valley and cutting a channel which is especially well preserved near the coast of the gulf of sirt the penetrated sediments of lake cyrenaica and the marginal basins of the messinian transgression are known as the upper evaporites and are generally fine clastics gypsarenites and gypsum anhydrite they were rapidly deposited underlying them is the halite of the lower evaporites this sequence of upper and lower evaporites is much like the lower halite of the tortonian south gharib formation and the overlying clastics and anhydrite of the messinian zeit formation in the gulf of suez red sea area this type of sequence is termed an evaporitic couplet and as has been demonstrated for the gulf of suez red sea is a consequence of a transition from a dry to a more humid climate in a restricted or semirestricted basin this transition occurred at about 7 5 ma in the gulf of suez red sea and at about 5 8 ma in the mediterranean the zeit wet phase manifest in the above events developed in association with the initiation and development of the asian monsoon and the drying of the mediterranean it can be understood in terms of the development of an evolving monsoon desert system the asian monsoon was initiated 8 7 ma in association with the uplift of tibet at this time the north african desert zone was displaced northwards to be over the mediterranean and central and eastern north africa became seasonally humid a concept is advanced in which the early stage of the development of the asian monsoon is seen as having two phases alternating at the precessional ca 21 ka cycle one phase transferred moisture from the indian ocean mainly to southern asia the other phase transferred moisture mainly to north africa with the drawdown of the mediterranean at about 5 8 ma the zeit wet phase intensified a further northward movement of the humid and desert zones occurred at the time of drawdown with the messinian and early pliocene transgressions the wet phase ameliorated but a substantial river system still crossed central north africa at about 4 6 ma north africa became drier probably in response to the developing dominance of the features of the monsoon that transferred moisture mainly to southern asia features of the monsoon that are well recognised today

the gulf of suez northern red sea neogene rift a quantitive basin analysis abstract subsidence analysis backstripping was carried out on a series of wells from the gulf of suez and northern red sea region of egypt in order to examine the interplay between tectonic events basin subsidence sedimentation and sea level changes in a young developing ocean basin and continental margin using constraints on chronostratigraphy and paleodepth from various sources combined with stratigraphic and structural information from industry wells and other geophysical sources it has been possible to compile the data necessary to perform geohistory analyses throughout the region major subsidence due to crustal thinning began 25 ma with sedimentation initially occurring in isolated sub basins these earliest sediments record the transition from continental to marine depositional environments subsequently during early and middle miocene times subsidence was rapid and uniform along and across the entire rift basin open marine sedimentation occurred across all structural regimes the mid clysmic tectonic event 16 5 ma resulted in structural rearrangement of the rift basin and uplift of the rift shoulders rapid subsidence continued as global sea level fell producing a series of prograding siliciclastic fan deltas at the rift margins at 15 5 ma opening of the suez rift was terminated tectonic subsidence decreased dramatically in the southern rift and ceased entirely in the northern rift tensional plate motion probably was transferred from the gulf of suez to sinistral strike slip movement on the dead sea transform at this time the quiescence in subsidence combined with a lowered global sea level resulted in the deposition of a thick up to 4 km series of evaporites within the central trough of the rift from the middle to latest miocene the accumulation of such a thick sequence of sediments during a phase of decreased tectonic subsidence is interpreted as a filling in of the rift topography which developed during the earlier period of rapid subsidence and rift shoulder uplift and continued compaction a rapid global sea level rise concomitant with a subsequent pulse of increased tectonic activity in the latest miocene earliest pliocene returned the rift to dominantly marine conditions

tracking provenance change during the late miocene in the eastern mediterranean using geochemical and environmental magnetic parameters 1 marls of the metochia section gavdos greece have been analyzed using geochemistry environmental magnetism and diffuse reflectance spectrometry to study late miocene paleoenvironmental changes in the eastern mediterranean region fuzzy c means cluster analysis fcm combined with nonlinear mapping nlm has been performed on a multiparameter data set to identify and characterize terrigenous source areas from north africa and the aegean margin the parameters included in the fcm were selected on the basis of their univariate characteristics and their ability to trace input changes from regional source areas the hard isothermal remanent magnetization hirm calculated on a carbonate free basis and the ti al ratio are used to distinguish aeolian dust and transport mechanisms of material originating from north africa mass accumulation rates of al and ni are employed to represent the input of terrigenous material originating from the aegean region caco3 calculated from ca abundance provides information concerning marine productivity and mn al is used to trace reductive diagenesis in the marls after performing the fcm and nlm analysis a four cluster solution has the greatest stability and describes paleoenvironmental changes in both the african and european source areas the cluster solution clearly reveals the change from input dominated by terrigenous material in the lower parts of the metochia section to marine input at the top of the section but also reveals changes in paleoenvironmental conditions in north africa from arid to more humid conditions at 8 2 ma

late miocene paleoenvironmental changes in north africa and the mediterranean recorded by geochemical proxies monte gibliscemi section sicily abstract the astronomically tuned marls of the monte gibliscemi section sicily constitute an archive to trace the late miocene palaeoenvironmental conditions 9 7 7 0 ma in north africa here we have utilised carbonate content and al normalised geochemical proxies to trace changes in terrigenous source area and bottom water ventilation the terrigenous input into the section is dominated by north african river systems draining into the eastern mediterranean the proxy parameters indicate that the palaeoenvironmental conditions in north africa were humid from 9 5 ma onward with high fluvial input to the mediterranean increases in the si al and mg al ratios occurred from 8 4 to 8 2 ma and from 8 05 to 7 75 ma with maximum values similar to those of messinian diatomites these peaks indicate conditions of enhanced biosiliceous productivity and the presence of authigenic clay formation sluggish water circulation in the mediterranean during those times is inferred from the mn al and v al behaviour late miocene changes of the betic southern spain and rifian morocco mediterranean atlantic gateways are interpreted as the driving force for the changes in water circulation and the transgression associated with the opening of the rifian corridor is interpreted to occur at 7 8 ma

the de ploey erosional susceptibility model for catchments es abstract this article is based on an unpublished manuscript by the late prof dr jan de ploey it focusses on the erosional susceptibility of catchments in terms of total energy input by the meteorological factors water and wind e s model the form and the universal character of the basic expression of the erosional susceptibility are explained applications of the model are illustrated for different processes such as landsliding and debris flows gullying creep and rill interrill combinations characteristic e s values exist for these processes also e s values vary in regions with differing pedo botanical characteristics and land use the difference between e s values for single storm events and longer periods are related to the magnitude frequency distribution of erosive activities and allow in many cases an assessment of the age of erosion phenomena and an estimation of the recurrence period of extreme single events

african climate change and faunal evolution during the pliocene pleistocene abstract environmental theories of african faunal evolution state that important evolutionary changes during the pliocene pleistocene interval the last ca 5 3 million years were mediated by changes in african climate or shifts in climate variability marine sediment sequences demonstrate that subtropical african climate periodically oscillated between markedly wetter and drier conditions paced by earth orbital variations with evidence for step like 0 2 ma increases in african climate variability and aridity near 2 8 ma 1 7 ma and 1 0 ma coincident with the onset and intensification of high latitude glacial cycles analysis of the best dated and most complete african mammal fossil databases indicates african faunal assemblage and perhaps speciation changes during the pliocene pleistocene suggesting more varied and open habitats at 2 9 2 4 ma and after 1 8 ma these intervals correspond to key junctures in early hominid evolution including the emergence of our genus homo pliocene pleistocene shifts in african climate vegetation and faunal assemblages thus appear to be roughly contemporary although detailed comparisons are hampered by sampling gaps dating uncertainties and preservational biases in the fossil record further study of possible relations between african faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries emerging molecular biomarker methods for reconstructing african paleovegetation changes tephra correlations between terrestrial and marine sequences as well as continuing collaborations between the paleoclimatic and paleoanthropological communities

neogene tectonic and stratigraphic events in the gulf of suez rift area egypt abstract the gulf of suez neogene syn rift section contains at least five datable intra basinal unconformities or stratigraphie hiatuses these events and associated changes in sedimentary sequences seen in the basin can be related to changes in suez rift subsidence miocene eustasy and the tectonic effects of adjacent red sea and dead sea rifting the first hiatus spans oligocene to earliest miocene time and separates syn rift from pre rift strata throughout the region this erosional event resulted from regional emergence during the oligocene and the initiation of suez rifting a second hiatus from 21 19 ma separates the poorly dated shallow marine nukhul formation of aquitanian to early burdigalian age from the overlying upper bathyal shales of the middle burdigalian to langhian nn3 5 rudeis formation this hiatus resulted from both a brief lowstand in early burdigalian sea level and increased suez rift related tectonism this event climaxed with the rapid tectonic subsidence that established deep marine conditions by 19 ma a third major event occurs within the rudeis at 17 ma nn4 n7 and marks the initiation of uplift of i he rift shoulders and margins and decelerated subsidence or even minor uplift in the axial trough hiatuses are seen over paleohighs e g tilted fault blocks whereas coarse elastics are deposited in more basinal areas in submarine fans and as turbidites a fourth unconformity at 14 ma separates the middle miocene kareem formation from overlying anhydrites and open marine shales of the belayim formation minor tectonic uplift throughout the suez region resulted from this event and a sill was established between the mediterranean and suez basins allowing cyclic anhydrite marl deposition from 14 to 11 ma this post kareem event may be the sedimentary response to initiation of movement along the dead sea aqaba transform a sharp drop in sea level at 11 ma restricted the suez basin even more and marked the initiation of massive halite precipitation in the central and southern suez well south of the sill area a final major neogene event occurs at the miocene pliocene boundary and is marked by a major unconformity caused by tectonic uplift this tectonic pulse is related to initiation of red sea sea floor spreading and acceleration of sinistral motion along the dead sea aqaba transform at 5 ma this event establishes the marine connection with the red sea and the sedimentary environments seen in the gulf of suez today

sedimentation of the neogene recent alasehir gediz continental graben system used to test alternative tectonic models for western aegean turkey abstract the alasehir gediz graben exemplifies clastic sedimentation in a long lived continental half graben in a semi arid setting developed within relatively incompetent metamorphic rocks early miocene to recent rift related sediments are exhumed on both flanks of the graben allowing detailed three dimensional study during the early miocene small fan delta lobes were shed northwards from the rugged menderes metamorphic massif into a bordering lacustrine basin during early to mid miocene time large alluvial fans prograded northwards into this basin through drainage to the aegean sea was established as the basin widened and filled discrete lobes of coarse alluvial fan sediments of latest miocene pliocene age also shedding northwards are likely to have been climatically influenced quaternary alluvium party infills the modern alasehir rift basin the sedimentary information can be used to test two alternative tectonic models for the alasehir graben in the first model an e w graben bounded by high angle faults was active during latest miocene recent time whereas earlier miocene sedimentation was controlled by n s faulting related to a n s compressional stress regime in the second hypothesis the alasehir graben was initiated much earlier in the early miocene and was then either continuously or episodically active until recent our results especially facies and palaeocurrent data from alluvial sediments indicate that clastic sedimentation was controlled by mainly e w faulting in a n s stress regime assuming the early miocene clastic sediments are correctly dated this supports the second long lived extension model however rather than steady state extension for ca 15 ma the sedimentary evidence and regional context are consistent with a pulsed extension model whereby initial early to mid miocene extension and related clastic sedimentation was followed by a second phase of extension in latest miocene pliocene time the driving force of initial early miocene extension was probably gravity spreading towards a south aegean subduction zone whereas the inferred second extension pulse is seen as being triggered by westward tectonic escape of anatolia towards the extending aegean back arc region