fishes and palaeogeography of the african drainage basins relationships between chad and neighbouring basins throughout the mio pliocene article i nfo keywords miocene pliocene palaeobiogeography africa the neogene african fossil record of two fishes i e semlikiichthys perciformes indet and calarius siluriformes ariidae is reviewed including new material from chadian outcrops their distribution confirms the existence of a nilo sudan ichthyological province during an early part of the miocene an east west waterway is demonstrated to have crossed africa allopatric speciation in the chadian and east african areas suggests that a split occurred in this system prior to 7 ma moreover our data support the existence of hydrographical connections between the chadian basin and the syrte basin after 7 ma at about the mio pliocene boundary finally our study also demonstrates that connections between the niger and chad basins

modelling facies belt distribution in fan deltas coupling sequence stratigraphy and geostatistics the eocene sant llorenc del munt example ebro foreland basin ne spain abstract the eocene sant llorenc del munt fan delta complex developed in the ebro foreland basin the stratigraphy of this succession about 1000 m thick has been described as made up of several transgressive regressive composite sequences each composed of a stack of fundamental sequences in turn made up of a transgressive systems tract and an overlying regressive systems tract systems tracts are composed of several facies belts proximal alluvial fan distal alluvial fan fan delta front carbonate platform and fan delta slope and prodelta a 3d facies model of a 130 m thick stratigraphic succession was built using outcrop data from one of the composite sequences the modelling followed a hierarchical approach a deterministic method was used to reconstruct the surfaces bounding fundamental sequences and their constituent systems tracts data input was outcrop traces digitized on photorealistic terrain models the stacking trend and interfingering of adjacent facies belts within each systems tract was added by means of a geostatistical algorithm and was conditioned to measured stratigraphic logs the analysis of the resultant 3d facies distributions allows revising the architectural interpretation of the studied interval leading to the conclusion that the observed arrangements are accommodation not supply driven furthermore the 3d models were flow simulated in two injector producer scenarios up depositional and down depositional dip waterflooding flow simulation results show that the depositional architecture of the studied succession controls potential recovery efficiencies in that a considerable proportion of moveable oil is trapped at the dead ends in depositional pinch outs of the main potential reservoir fan delta front deposits also that up dip waterflooding predicts better recovery efficiencies than down dip the dataset methods and results herein make the sant llorenc del munt complex a ready for application analogue for marine transitional reservoirs

the architectural variability of small scale cycles in shelf and ramp clastic systems the controlling factors many sedimentary successions are composed of metre to decametre scale cycles exhibiting various stratal architectures that depend on the complex interplay among several syndepositional controlling factors these controlling factors may produce extremely different stratal and facies architectures along relatively brief distances in the same basin but in contrast they also may form similar architectures in basins that experience a radically different tectonic setting the recognition of factors that controlled the architecture of small scale cycles therefore is very important to reconstruct the depositional history of sedimentary successions these factors include 1 the interplay between the rate of accommodation development and the rate of sediment supply a s 2 the amplitude and shape of the relative sea level curve 3 the position in the shoreface shelf system 4 the basin physiography 5 the shoreline trajectory 6 the climate driven environmental energy 7 the siliciclastic input vs carbonate production shoreface to shelf small scale cycles can be grouped into three main categories r cycles showing a dominant regressive interval t r cycles with transgressive and regressive intervals of similar thickness t cycles showing a dominant transgressive interval although some depositional settings may favour the deposition of a particular type of cycle these cycle motifs appear to be mainly controlled by the interaction of local and wider scale controlling factors for example t cycles may be present in both subsiding and uplifting settings depending on the interplay between the a s and the other factors cited above as a result r t r and t cycles may be recognized within the same depositional system these evidences suggest that care must be taken to apply general models that predict the stratal architecture of cycles mainly in function of the long term a s the correct prediction of the cycle architecture is important also for hydrocarbon researches as the thickness of potential reservoir deposits is the result of the interplay among factors discussed here

temporal changes of a delta example from the holocene yahagi delta central japan abstract the depositional history of a delta was investigated by using radiocarbon dated borehole cores from the yahagi delta nishimikawa plain central japan in particular historical changes in the gradient thickness and grain size distribution of the delta front and sediment discharge of the yahagi river are discussed the latest pleistocene to holocene sequence in the yahagi delta is interpreted as an incised valley fill system formed after the last glacial and subdivided into five sedimentary facies facies a fluvial facies b estuary facies c prodelta facies d delta front and facies e gravelly tidal flat in the main axis of the incised valley facies a facies b facies c facies d and facies a are deposited in ascending order in the western area of the valley facies e adjoins facies d the delta front was formed by river floods without reworking by wave or tide the succession was interpreted as a transgressive systems tract and highstand systems tract formed under sea level rise until ca 7 cal kyr bp and the subsequent highstand after the formation of the delta in ca 7 cal kyr bp characteristic features of the delta front changed twice as the delta prograded first during 4 5 cal kyr bp the delta front became thicker and steeper this change was induced by differences in water depth between the middle incised valley and the outer incised valley which resulted from a buried clinoform second in ca 3 cal kyr bp the grain size distribution of the delta front became coarser and the sorting became poorer the sediment discharge of the yahagi river also increased abruptly this change was induced by the increase of erosional capacity in the hinterland increasing human activities such as deforestation and poor soil conservation might have induced this change

geologic structure and neotectonics of the north african continental margin south of sicily abstract marine geological and geophysical data together with drilling information indicate that the north african passive continental margin has been subjected to extension and wrenching after it collided with the northern part of sicily the area of the tripolitania basin jarrafa trough melita and medina bank and the ragusa malta plateau has formed part of a sinking passive margin since the dispersal of gondwanaland at about 180 my ago as observed from geohistory diagrams a record of rifting in a nw se direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data the rifting started during the neocomian and lasted until the eocene when activity became minor a pre middle miocene period of northward subduction of oceanic crust is inferred from the geology in ne sicily uplift of the northern part of the african margin after collision in the middle miocene is seen in wells in southern sicily after the messinian a rift and dextral shear zone established itself across the african margin from the strait of sicily to the medina ridge in the lonian basin the zone is marked by up to 1 7 km deep grabens narrow active wrench faulted channels volcanic fissures and local uplifted keilhorsts such as malta this zone which varies in width from 100 to 35 km forms the southern boundary of a microplate which includes sicily we speculate that the present motion of this microplate is partly due to the eastward movement of the calabrian arc with the sicilian block over the last remaining oceanic lithosphere in the eastern mediterranean

architecture and trace fossil characteristics of a 10 000 20 000 year fluvial to marine sequence se ebro basin spain abstract the eocene sant llorenc del munt fan delta complex lies on the southeastern edge of the ebro basin in ne spain alluvial fans and fan deltas prograded northwestwards from the catalan coastal range to form a series of clastic wedges that were interrupted by marine transgressions of period varying from 60 000 to a few hundred years resulting in a highly cyclic succession the cyclicity of the succession was controlled by a combination of syndepositional basin margin tectonics high sediment supply and eustatic sea level changes analysis of one of the component 25 40 m thick transgressive to regressive sequences 10 000 20 000 year duration shows that within its transgressive part the alluvial and coastal plain deposits are extensive and thickly developed whereas shoreline lithosomes are narrow and thin in the overlying regressive part the opposite relationship is documented the transgressive and regressive tracts thus have an overall landward expanding and seaward expanding geometry respectively six ichnofabrics have been documented in the succession ranging from nonmarine to offshore transition in origin these ichnofabrics are used to help define sequence boundaries flooding surfaces and maximum flooding surfaces as well as to increase the resolution of the stratigraphic analysis within the transgressive tract of the main sequence nonmarine deposits are separated from marine deposits by a steep landward inclined complex of wave ravinement surfaces successive ravinement surfaces have a vertical spacing of about a meter are offset landwards from each other by less than 100 m and diverge slightly from each other as they climb through the section these same erosion surfaces merge with each other basinwards causing the transgressive tract to thin significantly five high frequency sequences are recognized within the main sequence the middle one is nearly symmetrical the lower two are asymmetric and dominated by their transgressive tract and the upper two are asymmetric but dominated by their regressive tract

a finfoot from the late miocene of toros menalla chad africa palaeobiogeographical and palaeoecological implications a fossil humerus from the hominid fossiliferous area of toros menalla ca 7 ma chad africa belongs to the heliornithidae aves gruiformes it is the second documented fossil record for the family and the first in the old world it is compared with all the living species the sungrebe heliornis fulica the masked finfoot heliopais personata and the african finfoot podica senegalensis it belongs to the genus heliopais and is very similar to the only species h personata the masked finfoot appears to have evolved little morphologically since the miocene this poorly known and threatened genus and species is today confined to tropical south east asia its presence in the late miocene of chad is a further asian element in the late neogene african avifaunas today the distribution of heliopais is highly relictual and some heliornithidae will certainly be encountered in the paleogene and the miocene deposits of the palearctic region the african finfoot is today the heliornithidae geographically the closest to the site area and occurs in forested regions south of the sahelian area apparently this genus was already absent further north where the asian genus was present in the late neogene palaeoecologically the presence of this heliornithidae is indicative for toros menalla of a freshwater body with thick overhanging vegetation and partly forested edges this kind of precise indication about a component of the palaeoenvironment is critical for the study of hominid sites and early hominid evolution a growing number of fossil birds from african hominid localities is yielding important clues regarding biogeography and environment

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

iles clastic wedge development and sediment partitioning within a 300 km fluvial to marine campanian transect 3 m y western interior seaway southwestern wyoming and northern colorado a 300 km 186 mi transect was reconstructed across the 500 m 1640 ft thick 3 m y duration iles clastic wedge in southern wyoming and northern colorado using well logs and stratigraphic columns this wedge developed into the middlelate campanian aged western interior seaway by progradation from the active sevier fold and thrust belt and adjacent uplifted areas the wedge thickens basinward because late stage widespread uplift of the fold belt caused multiple unconformities across the proximal former foredeep reaches of the foreland basin transect analysis allows the wedge and its component sequences to be better understood and permits a two dimensional characterization of the sand and mud distribution the iles wedge exhibits 11 low gradient regressive transgressive high frequency sequences that were correlated across several hundred kilometers sediment partitioning analysis along the transect shows the following 1 within the regressive limb of the iles wedge the component higher order regressive compartments tend to thicken into the medial reaches of the wedge whereas transgressive compartments thicken landward this geometry is driven by preferential erosion in proximal areas during regression bypassing much sediment to the marine shorelines and transgressive backfilling into proximal areas previously eroded more deeply 2 the greatest concentration of sands tends to be located in the proximal fluvial and estuarine facies of the transgressive compartments and within the medial shoreline deltaic facies of the regressive compartments 3 as the high frequency sequences develop the effectiveness of basinward sand partitioning reaches a maximum value near the peak regression level of the wedge apparently reflecting stronger erosion and sediment bypass during these times

discrimination between wave ravinement surfaces and bedset boundaries in pliocene shallow marine deposits crotone basin southern italy an integrated sedimentological micropalaeontological and mineralogical approach the lower pliocene belvedere formation cropping out in the crotone basin southern italy exhibits a metre scale to decametre scale shallow marine cyclicity that shares features of both high frequency sequences linked to shoreline shifts and controlled by minor relative sea level and or sediment supply changes and sedimentological cycles unrelated to shoreline shifts in order to better understand the high frequency sequence stratigraphic framework of this succession an integration of sedimentological micropalaeontological micro foraminifera assemblages and mineralogical heavy minerals abundance data is used from a sedimentological stratigraphic point of view wave ravinement surfaces bounding high frequency sequences and associated substrate controlled ichnofacies are prominent in outcrop and document environmental and water depth changes whereas bedset boundaries separating sedimentological cycles have a more subtle field appearance and are only associated with changes of environmental energy moreover condensed deposits are present only above wave ravinement surfaces and the high frequency sequences bounded by these surfaces have a thickness that is an order of magnitude greater than that of the bedsets micro foraminifera assemblages may change and the content of heavy minerals usually increases across wave ravinement surfaces whereas both parameters do not change significantly across bedset boundaries the abundance of heavy minerals is systematically higher with respect to the underlying and overlying deposits in the condensed shell beds that overlie wave ravinement surfaces an integrated sedimentological micropalaeontological and mineralogical approach represents a powerful tool to discriminate between wave ravinement surfaces bounding high frequency sequences and bedset boundaries and in general to investigate at the intra high frequency sequence scale this integrated approach is expected to be very useful in the study of potentially all shallow marine successions composed of small scale cycles in order to delineate a detailed sequence stratigraphic framework and understand the factors that controlled the cyclicity this article is protected by copyright all rights reserved

low accommodation detrital apron alongside a basement uplift pennsylvanian of midcontinent north america abstract the northern end of the 650 km long nemaha uplift nebraska and kansas usa is an important example of basin margin sedimentation in the north american midcontinent an apron of coarse basal pennsylvanian arkosic clastic sediments bpc was deposited on the flanks of the uplift while marine cyclothems were encroaching from the east small scale fining upward intervals many with demonstrably erosional bases dominate the bpc and are interpreted as overridingly fluvial in origin weak paleosols desiccation cracks and reddened intervals in the bpc record episodic subaerial exposure multiple burrowed horizons and heterolithic strata of probable tidal origin and rare marine fossils also indicate episodic marine influence the bpc appear to have been deposited as a thin apron of coalesced alluvial fans and fan deltas deposition of the bpc occurred during the waning of uplift and subsequent quiescence the comparative thinness and large scale packaging of the bpc are compatible with the controlling effects of relict relief regional subsidence and eustasy rather than ongoing major vertical displacements along active faults a strong autocyclic influence on sedimentation is evidenced by stacked fining upward intervals of poorly sorted conglomerates sandstones and sandy mudstones correlations demonstrate that the accumulation of the bpc took place over more than seven major sea level cycles beginning in cherokee group times middle moscovian middle pennsylvanian and ending only when the eroded uplift was inundated and buried by marine cyclothems on the basis of local correlations with marine cyclothems and using black phosphatic shales so called core shales of heckel p h 1986 sea level surve for pennsylvanian eustatic marine transgressive regressive depositional cycles along midcontinent outcrop belt north america geology 14 330 334 heckel p h 1994 evaluation of evidence for glacio eustatic control over marine pennsylvanian cyclothems in north america and correlation of possible tectonic effects in dennison j m ettensohn f r eds tectonic and eustatic controls on sedimentary cycles sepm concepts in sedimentology and paleontology no 4 pp 5 87 as marker beds we speculate that the bpc exist in backstepping sequences and or parasequences alongside the flanks of the nemaha uplift the bpc are lithologically comparable to contemporaneous deposits alongside the ancestral rockies amarillo wichita uplift and other buried basement highs in north america nonetheless the bpc are an order of magnitude thinner are dominantly retrogradational rather than progradational and their occurrence was not associated with major displacements along basin bounding faults in this manner the bpc are a useful example of low accommodation eustasy dominated coarse grained terrigenous clastic deposition around an uplifted basement block

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

anatomy of regressive tracts in a regressive sequence set vilomara unit sant llorenc del munt ebro basin ne spain abstract the sant llorenc del munt fan delta succession forms a clastic wedge ca 3 my duration that built out into the ne ebro basin in response to transpression and uplift along the paleogene catalan coastal range this fan delta succession is arranged in a series of transgressive regressive sequences of different scales a large scale composite megasequence the milany megasequence includes the whole fan delta succession this megasequence is subdivided in seven composite sequences that in turn can be subdivided into fundamental sequences the vilomara composite sequence the vilomara unit is located in the regressive part of the milany megasequence the regressive part of the vilomara composite sequence consisting of a seaward stepping set of fundamental sequences the vilomara unit has been studied to understand the facies relations geometries and the characteristics of key surfaces in progradational settings the vilomara regressive sequence set is formed by stacked alluvial fan fan delta plain proximal and distal fan delta front fan delta slope within the regressive part of fundamental sequences and carbonate platform usually within the transgressive part of fundamental sequences deposits the vilomara regressive unit shows a sigmoidal geometry in contrast to the underlying el marcet transgressive unit which thickens landwards this sigmoidal geometry for the regressive unit and landward thickening for the transgressive unit is common for all scales of sequence composite megasequences composite sequences and fundamental sequences there are evident facies arrangement differences between transgressive and regressive deposits within a fundamental sequence key surfaces have been recognised from vertical trend changes from transgressive to regressive and vice versa the facies successions immediately above and below the surfaces bounding fundamental sequences may indicate at different stratigraphic levels a basinward or a landward shift of facies belts

the late neogene sahabi rivers of the sahara and the hamadas of the eastern libya chad border area abstract this paper contributes to the concept that during the late tortonian messinian and early pliocene c 7 5 4 6 ma in addition to the nile the sahabi rivers also crossed the sahara having originated from tropical neogene lake chad examination of two hamadas lying just to the north of the libya chad border using landsat images and srtm topographic data enables one of them hamada ibn battutah west to be recognised as an uplifted palaeosurface which preserves late miocene early pliocene fluvial activity this surface is referred to as the yangara palaeosurface of particular interest on the hamada are two long c 50 km wide c 4 km channels a 50 km 2 relic landscape and a short well defined 5 km channel about 1 km wide the location of hamada ibn battutah west is significant because the hamada provides evidence of extensive fluvial activity part way between the place of origin of the sahabi rivers and their preserved record at the gulf of sirt the yangara palaeosurface is considered to extend southwards to the adjacent hamada in northeastern chad the total palaeosurface extends 165 km in an approximate north south direction and averages 45 km in width it lies in the central part of an area of complex post miocene uplift involving four hamadas at the libya chad border

new termite trace fossils galleries nests and fungus combs from the chad basin of africa upper miocene lower pliocene abstract four new trace fossils of termites are described from the upper miocene and lower pliocene continental sandstones of the northern chad basin coatonichnus globosus ichnogenus and ichnospecies nov is a large ellipsoidal termite calie 20 40 cm in diameter more or less flattened at both poles it is morphologically very similar to the nest of extant termite hodotermes mossambicus from south africa it exhibits an internal shelved pattern of modern hodotermitidae such as the superposition of flat chambers separated vertically by ramps columns walls and pillars it is interpreted as the nest of an ancestral species of hodotermes hodotermitidae the new ichnospecies vondrichnus planoglobus is composed of dense swarms of tens of chambers connected by a net of straight galleries developed in a single plane the chambers 5 12 cm in diameter have a spherical shape with a planar base generally short galleries connect each chamber to the straight main tunnel of meter to decameter scale length vondrichnus planoglobus is interpreted as polychambered diffuse nests of fungus growing termites macrotermitinae termitidae microfavichnus alveolatus ichnogenus and ichnospecies nov is a small scale alveolar mass 3 8 cm by 2 4 cm the base of the construction is flat to concave it is entirely composed of a sub horizontally layered alveolar like structure composed of a regular juxtaposition of millimetre scale round pellets or balls mylospheres microfavichnus alveolatus is interpreted as fossilized fungus combs of fungus growing termites macrotermitinae termitidae termitichnus schneideri ichnospecies nov is a large scale extremely flattened construction 15 60 cm in diameter and 6 18 cm in height the internal shelved pattern is composed of flat chambers separated by columns walls and pillars each level is connected by ramps an external wall surrounds the framework constructed one to several peripheral funnel shaped tunnels occur sub perpendicular to the construction this new termitichnus ichnospecies is interpreted as being a possible central hive of the vondrichnus planoglobus net

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

the holocene giant lake chad revealed by digital elevation models abstract the chad basin is a closed basin in the central part of north africa a southern sub basin which is supplied by the humid tropics includes the present day lake chad the northern sub basin is presently dry as it only receives drainage from sahara rivers in these areas the existence of a giant lake known as the lake mega chad has been debated for a long time its level would be controlled by the mayo kebbi threshold in the southern part of the lake which joined the lake mega chad and the niger river via the benoue trough digital elevation models the topo6 and globe data sets are used to characterise a well defined shelf like morphology locally up to 50 km wide followed at a constant elevation over hundreds of kilometers this strictly horizontal geomorphic feature is interpreted as a wave cut lacustrine shoreline terrace it is associated with a sandridge that represents a barrier island system built by wave generated currents this study demonstrates that a holocene lake mega chad was present from 11 n to 18 n across the southern and northern sub basins the influence of such a water vapour source must be considered in palaeoclimatological reconstructions

unusual features of sediment supply dominated transgressive regressive sequences paleogene clastic wedges se pyrenean foreland basin spain abstract the paleogene marine to nonmarine succession in the southeastern pyrenean foreland basin consists of a series of 3rd order 3 5 m y transgressive to regressive sequences that can be related directly to the stacking and southward displacement of successive basement cover thrust sheets the regressive limbs of the 3rd order clastic wedges are coeval with thrust movement with maximum subsidence developing towards peak regression this relationship between sedimentation and tectonics is sediment supply driven one of these 3rd order wedges which was produced by the montserrat and sant llorenc del munt fan delta systems demonstrates how such steep sloped coarse grained high sediment supply systems generate a hierarchy of transgressive regressive architectures striking features of this rapidly subsiding supply dominated basin margin in addition to the tectonics wedge architecture relationship include the nonperiodic character of the contained high frequency sequences the unusual thickness and landward thickening geometry of transgressive systems tracts a tendency for misfit between alluvial fan and shorezone sectors of sequences a lack of marked incision associated with the tops of coarse grained regressive phases of sequences most of the features are symptomatic of high subsidence rates and very high sediment supply the last feature suggestive of few major relative falls of sea level is also consistent with continuous rapid subsidence however it should be remembered that lack of incision may be a poor indicator for lack of base level fall in a setting where the steepness of alluvial slopes exceeds the slope of the coeval shelf

nearshore and alluvial facies in the sant llorenc del munt depositional system recognition and development abstract the eocene sant llorenc del munt fan delta complex forms a part of the coarse grained foreland basin fill of the southeastern margin of the ebro basin it was sourced from the rising catalan coastal range in the se and shows an overall northwesterly progradation during a time period of approximately six million years coarse clastic deposits coarse sands and gravels dominated this fan delta whereas finer grained sands silts and muds were deposited laterally off active sedimentation sites or in the more marine area depositional processes were clearly influenced by the high sediment input giving a dominance of sediment gravity flow deposits the sediments studied have been grouped into four distinct facies belts including coastal plain proximal fan delta front distal fan delta front and fan delta slope sediments respectively the facies belts combine to form the nearshore and coastal alluvial reaches of the fan delta system developed during a transgressive phase lasting some 50 000 years

freshwater fish δ18o indicates a messinian change of the precipitation regime in central africa tracking terrestrial environmental change throughout the neogene is a challenge notably in areas such as central africa where the few available data consist of a few vertebrate fossil assemblages here we aim to quantify the evolution of the 18 o of the main water body between four neogene wet episodes in the chad basin ranging from the late miocene to the early pliocene the 18 o of the open water body was inferred from oxygen isotope measurements of phosphate in the apatite of open water fish tooth enamel the more open the fish habitat the lower the 18 o as revealed by the teeth of the large tiger fish hydrocynus sampled in the four available chadian vertebrate fossiliferous areas i e toros menalla anthracotherid unit kossom bougoudi kolle and koro toro all located in the djurab desert chad and dated at 7 04 0 18 ma 5 26 0 23 ma 3 96 0 48 ma and 3 58 0 27 ma respectively the 18 o values increased by 2 between the two sites having ages that bracket the messinian time period and there was a slight increase of 0 6 difference between the three pliocene sites these results reflect unambiguously change in the water cycle in central africa during the late neogene interpreted as a constant drying trend between the four successive wet episodes registered in the djurab and a shift during the messinian

a review of wave dominated clastic shoreline deposits abstract barrier islands beaches wave dominated deltas and chenier plains probably form more than one fifth of present coasts and constitute an even larger proportion of the subsiding lowland coasts likely to be preserved in the stratigraphic record the geometry vertical sequences and composition of their deposits are the result of 1 shoreline behaviour whether transgressive regressive or stable 2 physical processes particularly the relative intensities of waves and tides 3 climate 4 global tectonic setting and 5 topography of underlying deposits published interpretations indicate that equivalent deposits are abundant in the geological record sandstones are mostly quartzose cemented by carbonates and quartz and have sheet or linear geometries ancient deposits can provide evidence of palaeogeography and some are economically significant particularly as hydrocarbon reservoir rocks four end member sedimentation models are proposed for the interpretation of ancient deposits 1 transgressive sheet sands associated with deltas 2 non deltaic transgressive sheet sands 3 regressive sheet sands and 4 linear sand bodies probable depositional settings geometries characteristics of deposits and palaeocurrent patterns are discussed

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

the last big marine transgression of the western interior seaway almond formation development from barrier spits across south wyoming abstract the stratigraphic response to marine shoreline transgressions have been debated for the last six decades a particularly interesting aspect is that transgressive ravinement often removes evidence of the shoreline itself until there is turnaround to regression to elucidate this topic we present a high resolution chronostratigraphic study of an overall transgressive coastline documented with evidence from over 1450 wells covering an area of 6200 km2 to define the fundamental sandbodies and relevant stratigraphic surfaces the mapping of 15 elongate sandstone units stacked into 6 reservoirs shows that there was a spectacular westward rising of back stepping barrier spits sourced by long shore currents mobilizing sand from a delta to the north each fundamental barrier spit unit bsu is a 6 12 metres thick regressive southward elongate and narrowing sandbody generated by longshore drift of sandy sediment each barrier sand body and its related overlying transgression is estimated to represent some 20 ky strong transgressive ravinement events periodically flooded the barrier spits and shifted the deposition westward in four to 35 km steps westward transgressive stepping across and into a structurally generated embayment progressively dampened wave energy with each backstep morphologically there were two endmember sandbody types 1 narrow drum stick like sandbodies built mostly by longshore accretion i e true barrier bars and 2 broader and more extensive regressive belts of sandstone that resemble strandplains the former display typically longer backsteps across lagoonal areas whereas the latter show a more aggradational stacking arrangement which evidences a quasi balance between accommodation and sediment supply there is no evidence of a smooth and continuous transgression controlling sandstone deposition and preservation a hybrid punctuated transgression model that considers the alternation of long term coastal retrogradation and short lived barrier spit development by longshore accretion and seaward progradation is the most appropriate model for creating and preserving upper almond sandbodies

depositional processes and basin analysis of messinian evaporites in cyprus messinian evaporites in cyprus resulted from the interplay of mediterranean wide and eustatic sea level changes and local tectonics in an inferred above subduction zone setting distinctive tortonian early messinian pre evaporitic facies include diatomaceous marls and microbial carbonates overlain by a variety of gypsum facies and then by lagoonal lacustrine deposits and local palaeosols facies analysis and comparisons allow construction of a simple model in which evaporites formed in semi isolated small basins not far below global eustatic sea level coarsely crystalline gypsum formedin situ along the margins of small basins and within shallow water lagoons 10 m deep this comprised common banded stacked i e layered selenite swallowtail selenite botryoidal selenite and sugary bedded selenite fine grained gypsum precipitated widely and was reworked into basinal areas 70 m deep by weak traction currents and low density turbidity currents shallow water derived selenite was also reworked basinwards by high density turbidity currents and debris flows slumps indicate tectonic instability more detailed basin analysis can be achieved by study of individual sub basins in the polemi sub basin in the west a lower unit up to 60 m thick comprises basinal gypsum interbedded with gypsum turbidites and mass flow deposits with slumps this is overlain by an extensive mega rudite up to 20 m thick including up to metre sized clasts of marginal gypsum facies above the upper unit up to 70 m thick includes shallow water gypsum e g swallowtails marl and minor microbial carbonates the pissouri sub basin in the south west exposes marginal facies of the upper unit including deltaic elastics and palaeosols the maroni sub basin in the south exhibits a basinal lower gypsum unit with laterally equivalent marginal facies up to 50 m thick overlain by an extensive mega rudite up to 20 m thick finally the mesaoria subbasin in the north exposes relatively marginal gypsum facies in an unstable tectonic setting formation of the polemi pissouri and mesaoria gypsum sub basins relates to coeval extensional faulting and graben development evaporites in south cyprus maroni sub basin formed in elongate basins between former compressional lineaments created by localized early miocene thrusting in the sub basins of west south west and south cyprus large scale slumping of marginal gypsum facies took place towards depocentres to form megarudite debris flows triggered by one or several phases of extensional faulting

overview of the late tertiary recent tectonic and palaeo environmental development of the mediterranean region the late tertiary history of the mediterranean region exemplifies processes of ocean basin closure and continental collision as determined from integrated land and marine evidence during the mesozoic early tertiary tectonic settings were dominated by evolution of neotethys this ocean generally widened eastwards with a number of oceanic strands in the eastern mediterranean area great diversity of tectonic settings and palaeo environments developed during the tertiary closure history of these oceanic basins in the eastern mediterranean region more northerly neotethyan strands were closed by the mid tertiary while oceanic crust remained in the south in the present eastern mediterranean sea area northwards subduction of the remaining southerly neotethyan strand was probably active by the early miocene different areas exhibit different stages of convergence and ocean basin closure in the east the amalgamated eurasian plate had collided with the arabian margin africa by the late miocene while oceanic crust still persisted further west steady state subduction during the late tertiary gave rise to the mediterranean ridge as a substantial mud dominated accretionary wedge in the aegean area sufficient northward subduction took place to activate arc volcanism and pervasive back arc extension short of marginal basin opening in the easternmost mediterranean only limited subduction took place associated with supra subduction zone extension e g in cyprus today steady state subduction continues only locally where vestiges of neotethys remain e g herodotus abyssal plain in the western mediterranean area suturing of the african and eurasian plates initially took place in the betic region early mid tertiary where the neotethys had existed only as a narrow connection with the central north atlantic in the central mediterranean region where the western neotethys was wider northward subduction was active apparently as early as the late cretaceous in a widely accepted interpretation an andean type magmatic arc developed along the southern margin of europe and was then rifted off in the late oligocene early miocene to form the corsica sardinia block opening the north balearic marginal basin in its wake the migrating subduction zone and microcontinent then collided diachronously with north africa related continental units north africa and apulia from late oligocene early miocene giving rise to collisional thrust belts in the northern and southern apennines and along the north african continental margin i e the maghrebian chain to the betic rif area from the early miocene onwards a separate subduction system became active related to removal of neotethyan oceanic crust to the southeast ionian sea fueling suprasubduction zone extension and opening of the tyrrhenian sea orogenic collapse is an alternative mechanism of such extension and is widely believed to have caused divergent thrusting in the betic and rif regions of the westernmost mediterranean at the same time as crustal extension and subsidence of the alboran sea

reconstruction of bedform dynamics controlled by supercritical flow in the channel lobe transition zone of a deep water delta sant llorenc del munt north east spain eocene

hydrodynamics in holocene lake mega chad holocene lake mega chad lmc was the largest late quaternary water body in africa the development of this giant paleo lake is related to a northward shift of the isohyetes interpreted as evidence for an enhanced monsoon african humid period numerous preserved coastal features have been described all around the lmc shore such features reveal the main paleo hydrodynamical tendencies in the context of a closed water body like lmc hydrodynamics are forced mainly by winds we use a three dimensional numerical model symphonie to simulate the mean hydrodynamics in lmc under both harmattan like northeasterly trade winds and monsoon like southwesterly winds forcings the northern part of lmc displays coastal features such as sand spits that are consistent with the simulations forced by harmattan like winds geomorphic features related to monsoon driven hydrodynamics are not clearly expressed they could have developed during the early stage of lmc but subsequently reworked at the time of sand spit building harmattan like driven hydrodynamics prevailed and related coastal features were preferentially preserved in the sedimentary record

anatomy of a compound delta from the post glacial transgressive record in the adriatic sea abstract on the mediterranean continental shelves the post glacial transgressive succession is a complex picture composed of seaward progradations related to sea level stillstands and or increased sediment supply to the coasts and minor flooding surfaces associated with phases of enhanced rates of sea level rise among late pleistocene examples major mid shelf progradations have been related to the short term climatic reversal of the younger dryas event a period during which the combination of increased sediment supply from rivers and reduced rates of sea level rise promoted the formation of progradations up to tens meter thick while the documentation of coastal and subaqueous progradations recording the younger dryas interval is widely reported in literature the model of compound progradation within transgressive deposits has not yet been proposed here we present the documentation of a deltaic system where both delta front sands and related fine grained subaqueous progradations prodeltaic to shallow marine have been preserved the paleo gargano compound delta pgcd formed offshore the modern gargano promontory southern adriatic sea and is composed of a coastal coarse grained delta of reduced thickness and a muddy subaqueous clinoform up to 30 m thick the pgcd probably the first worldwide documentation of a compound delta within the transgressive record provides the opportunity to investigate the processes controlling the formation of a compound delta system during an overall sea level rise and the factors that allowed its preservation the finding of the pgcd provides the opportunity for a comparison with modern worldwide compound systems

bored pebbles and ravinement surface clusters in a transgressive systems tract sant llorenc del munt fan delta complex se ebro basin spain abstract a 25 m thick transgressive systems tract in the sant llorenc del munt wave influenced fan delta system eocene se ebro basin has an internal framework consisting of a cluster of transgressive erosion surfaces each of which has minor relief and which are collectively stacked vertically no more than two metres apart each erosion surface bounds a cycle containing a conglomeratic lag up to 0 5 m thick followed by a coarsening upward sandstone to conglomeratic unit the uppermost levels of which can be nonmarine individual cycles become entirely nonmarine landwards of the termination of the basal bounding erosion surface whereas they thin and eventually become entirely marine basinwards the individual erosion surfaces within the transgressive tract some 16 of them within a 20 m thick lithosome are interpreted as wave ravinement surfaces that repeatedly eroded into the conglomeratic shoreface during transgression this interpretation rather than one invoking nonmarine flooding or other marine erosion surface types is consistent with the arrangement of bivalve and sponge borings on the top surfaces of clasts and with the associated lag pavements multiphase boring around the entire surface of clasts as well as erosion of the clasts at some horizons particularly in reaches of the tract where the ravinement trajectory is sub horizontal suggest repeated reworking of previously generated lag pavements in zones of minimal aggradation during transgression where the transgressive shoreline trajectory rises more steeply and there has been more rapid aggradation during transgression the lag pavements show only single phase borings with the borings on the upper surface of the pebble pavement only the close spacing of erosion surfaces within the transgressive systems tract together with estimates of time span in the tract suggest that transgressive erosion occurred with a frequency of less than 500 years

study of the messinian carbonate evaporite lithofacies offshore western libya this study represents a preliminary investigation of the late messinian subsurface marsa zouaghah formation in the western libyan offshore central mediterranean sea the formation was deposited in three major environmental settings a marginal sabkha b open lagoon and c hypersaline lagoon the marginal sabkha and open lagoonal settings are locally interrupted by intertidal oolitic shoal deposits the marginal sabkha facies is replaced in central parts of the libyan offshore by a narrow zone of aeolian fluvial facies the distribution and thickness of which is entirely controlled by a local uplift the tripoli nose the marginal sabkha facies broadly defines the late messinian palaeoshoreline lying parallel to and north of the e w jifarah fault system which dominated the southern part of the libyan offshore this fades is thus interpreted as being structurally controlled by fault systems the hypersaline lagoonal facies is developed in areas of relatively higher rates of subsidence than that of adjacent facies belts it is therefore related to restriction formed by continuous subsidence and evaporation the marsa zouaghah formation constitutes saltern evaporates deposited over a wide platform in sabkha and lagoonal settings forming part of the basin wide evaporites of the mediterranean basin deposited during the messinian salinity crisis the evaporites formed during a major relative sea level fall within a subsiding basin situated on the northern continental margin of the african plate local vertical and lateral variations in lithofacies and thickness within the messinian deposits of the north west libyan offshore were controlled by contemporaneous strike slip movements in addition to sea level change

an experimental study of subaquaeous slipface deposition abstract a flume study indicates that grainflow on slipfaces accounts for most cross strata formed in unidirectional shallow water flows the slipfaces studied were on small megaripples and delta like steps 0 06 0 28 m high during intermittent avalanching at relatively low flow velocities periods between avalanches were marked by grainfall onto the slipface the intensity of which was greatest near the brink of the slipface and increased with current velocity nearly all grainfall deposits however were incorporated into subsequent grainflows grain flow cross strata were made up of relatively distinct layers at least near the base of the slipface continuous avalanching at high flow velocity was marked by a steady stream of grains forming more poorly defined cross strata although the fundamental cause of grain flow is the gradual buildup of sediment on the upper slipface to the angle of initial yield four other processes were recognized as promoting avalanching 1 migration of superimposed bedforms to the brink 2 generation of turbulent pulses upstream of the brink 3 lee eddy impingement on the lower slipface and 4 extension of the lee eddy above the brink the lee eddy proved very significant in slipface processes by redistributing grainfall sediments and both promoting and impeding grainflow regression analyses showed that the slipface advance per avalanche sa is strongly correlated with the slipface height h expressed approximately by sa 0 060h in addition sa is a direct function of the rate of slipface advance vb the relationship among sa h and vb can be expressed as sa h 0 0385 1 0 134 min cm vb 1 cross strata dip angles between 28 and 34 show no systematic relation to h and vb but dip angles greater than 34 occurred only when both h and vb were small and dip angles less than 28 occurred only when both h and vb were large

implications of diagenesis for the isotopic analysis of upper miocene large mammalian herbivore tooth enamel from chad high resolution chemical and textural investigation of upper miocene mammalian tooth enamel from chad using electron microprobe and scanning electron microscope techniques provide direct evidence of extensive diagenetic alteration when compared with some modern and contemporaneous fossil specimens chemical and textural changes in chadian fossil enamel during fossilization include large amounts of secondary fe si mn and al bearing oxides both as coarse precipitation in cracks and permeating the apatite high fluorine contamination i e apatite alteration ca p cl na and mg depletion and sulphur contamination such diagenetic contamination significantly affects the oxygen and carbon isotope analysis of carbonate in apatite altering the delta o 18 and delta c 13 biogenic signals towards more positive values isotopic alteration is however greater for oxygen than for carbon indeed isotopic analysis of the heavily oxide and s contaminated chadian fossil tooth enamel samples on a classical dual inlet multiprep system versus three continuous flow irms mass spectrometers show great differences in both the delta o 18 and delta c 13 values while the multiprep dual inlet approach provides carbon and oxygen isotopic results that are indubitably altered and generally inconsistent with any biological values isotopic analysis on continuous flow systems which automatically filter out contaminating gases allow to attain or at least greatly approach primary isotopic signals some of the chadian fossil enamel samples analysed in this work come from the very important upper miocene tm266 fossil locality that yielded sahelanthropus tchadensis a k a toumai the oldest member of the hominid clade known so far at this site as in others a few or no other environmental proxies than isotopic analysis of biomaterials are available for palaeoenvironmental and palaeoecological reconstructions therefore to obtain reliable environmental information from the time of this ancient hominid recovering uncontaminated biogenic isotopic signals is crucial and from these results it is now technically possible c 2008 elsevier b v all rights reserved

anatomy of high sediment supply transgressive tracts in the vilomara composite sequence sant llorenc del munt ebro basin ne spain abstract the sant llorenc del munt fan delta succession forms a clastic wedge ca 3 m y duration that built out into the ne ebro basin in response to transpression and uplift along the catalan coastal range the wedge contains a series of composite transgressive regressive sequences the transgressive part of one of these sequences the vilomara composite sequence has been examined to highlight the character of transgressive successions in a highly aggradational setting the analysis focuses on the nature of the component high frequency fundamental sequences there is a marked difference in how alluvial and marine sediment volumes are partitioned within the transgressive and regressive tracts of the three fundamental sequences within this overall landward stepping succession in transgressive tracts the marine shoreline clastics are well developed but only in narrow 250 m wide strike parallel zones which are closely associated with ravinement clusters the time equivalent alluvial strata are thick and extensive in regressive tracts the marine clastics are extensively developed along both dip and strike as prograding shoreline sheets whereas the interfingering alluvial deposits are only thinly developed or eroded out completely by their overlying sequence boundary in regressive intervals there was significant sediment bypass in the alluvial reaches with feeding to the shorezone and shelf in transgressive intervals in contrast great volumes of sediment were stored in the coastal plains this partitioning of sediment volumes commonly led to wedge shaped seaward thickening regressive geometries and wedge shaped landward thickening transgressive geometries the unusual thickness of transgressive strata the aggradationally stacked nature of successive ravinement surfaces and the thick development of nonmarine strata during times of transgression are symptomatic of an unusually high supply of sediment to the system during high rates of accommodation creation and a near continuous rise of relative sea level an unusual type of parasequence in the transgressive tracts showing well developed transgressive and regressive components is probably also symptomatic of the high sediment supply setting

interplay between shoreline migration paths architecture and pinchout distance for siliciclastic shoreline tongues evidence from the rock record facies geometry and key internal stratigraphic surfaces from eight cretaceous and eocene clastic shoreline tongues have been documented the regressive parts of all the studied tongues represent storm wave influenced strandplains deltas or fan deltas and the regressive shoreline trajectories varied from descending to ascending the transgressive parts of the tongues are dominated by either estuarine or coastal plain deposits the distance from the coeval up dip non marine deposits to the basinward pinchout of amalgamated shoreface sandstones measured along depositional dip is here termed the sand pinchout distance the study shows that the angle of regressive to transgressive turnaround defined by the angle between the regressive and subsequent transgressive shoreline trajectories and the process regime during turnaround largely control the sand pinchout distance the amount of transgressive erosion can also partly control the pinchout distance but this parameter was comparable for the different examples presented here if the type of depositional system at turnaround and the depth of transgressive erosion are constant small angles of turnaround are associated with large pinchout distances whereas larger angles of turnaround result in smaller pinchout distances the model developed allows sand pinchout distance to be predicted using data for the landward parts of shoreline tongues the dataset also shows that steeply rising aggrading shoreline trajectories tend to produce more heterolithic sandstone tongues than those formed by lower angle trajectories

geology and palaeontology of the upper miocene toros menalla hominid locality chad all six known specimens of the early hominid sahelanthropus tchadensis come from toros menalla site 266 tm 266 a single locality in the djurab desert northern chad central africa here we present a preliminary analysis of the palaeontological and palaeoecological context of these finds the rich fauna from tm 266 includes a significant aquatic component such as fish crocodiles and amphibious mammals alongside animals associated with gallery forest and savannah such as primates rodents elephants equids and bovids the fauna suggests a biochronological age between 6 and 7 million years taken together with the sedimentological evidence the fauna suggests that s tchadensis lived close to a lake but not far from a sandy desert perhaps the oldest record of desert conditions in the neogene of northern central africa

dental mesowear analysis of the late miocene bovidae from toros menalla chad and early hominid habitats in central africa this study aimed to reconstruct the environmental conditions that prevailed in the chadian palaeo lake basin ca 7 ma ago based on the feeding preferences of late miocene bovidae from toros menalla chad this is a key issue for understanding the circumstances regional landscapes under which the earliest known hominid sahelanthropus tchadensis evolved a dental mesowear analysis was applied to 117 specimens of bovids representing the four tribes present in the anthracotheriid unit localities hippotragini reduncini antilopini and bovini all these bovids fed on grasses at least partially previous analyses and the present results indicate the presence of a mosaic like environment containing various habitats from grasslands to woodlands in the surroundings of the chadian lake basin indeed our data support the availability of grass or grass like plants and therefore open patches in the vicinity of the chadian palaeo lake shores