a review of the orogenic events in the precambrian basement of nigeria west africa the basement complex of nigeria is polycyclic and retains memories of events dating back to about 3000 m y as in other parts of africa it suffered its most pronounced deformation and remobilisation during the pan african orogeny about 650 450 m y ago

non linear variation with salinity of sr ca and mg ca ratios in water and aragonitic bivalve shells and implications for paleosalinity studies abstract fresh water and sea water usually differ considerably in their sr ca and mg ca ratios this suggests that these ratios in fossil shells could be used to determine paleosalinities calculation of the sr ca and mg ca ratios in mixtures of sea water and average fresh water using a mixing equation shows that the ratios first increase rapidly with salinity to about 100 but subsequently remain nearly constant the source of most of the ca sr and mg in mixtures of fresh and sea water is the sea water thus except at low salinities the trace element to ca ratio of mixtures differs little from that in sea water analysis both of waters across a spectrum of salinities and of aragonitic mollusc shells growing in water of various salinities conforms to the predicted pattern however trace element to ca ratios offer potential for paleosalinity determination in waters of salinity below about 100

oxygen isotope compositions of phosphate from arvicoline teeth and quaternary climatic changes gigny french jura oxygen isotope compositions of biogenic phosphates from mammals are widely used as proxies of the isotopic compositions of meteoric waters that are roughly linearly related to the air temperature at high and mid latitudes an oxygen isotope fractionation equation was determined by using present day european arvicoline rodents tooth phosphate d 18 op 20 98 f0 59 0 572 f0 065 d 18 ow this fractionation equation was applied to the late pleistocene karstic sequence of gigny french jura comparison between the oxygen isotope compositions of arvicoline tooth phosphate and greenland ice core records suggests to reconsider the previously established hypothetical chronology of the sequence according to the d 18 o value of meteoric water mean air temperature relationships the d 18 o value of arvicoline teeth records variations in mean air temperatures that range from 0j to 15jc

ostracods as proxies for past seagrass a review abstract recently attention has been drawn to the recognition of past seagrass for which a number of proxies have been proposed several studies have quoted ostracods as having some value as proxies particularly loxoconcha xestoleberis and aurila although these may be found in a variety of marine environments they are often found with faunas containing seagrass or which can be interpreted as in proximity to seagrass in such situations they may be found with other possible seagrass proxies such as sirenians lucinid bivalves soritid and other benthic foraminiferans the presence of loxoconcha xestoleberis and aurila and other ostracods may be suggestive of past seagrass environments the interpretation of which is strengthened by the presence of other proxies in some collections

holocene environments from stable isotope stratigraphy of ostracods and authigenic carbonate in chilean altiplano lakes abstract sediment cores from three shallow 4000 m a s l paleoclimatic profiles show coherency within tropical subtropical circulation patterns climatic signals however are partially masked by local environmental systems results suggest similar arid mid holocene to less arid late holocene trends in the three lakes although each lake shows distinct response characteristics linked to differences in regional moisture balance isotopic signatures for each lake group in discrete 18o vs 13c populations high isotopic variability results from episodic flooding and brine evolution in the shallow lakes laguna seca 18 11 s 69 14 w 4500 m a s l is characterized by a diverse ostracod assemblage of at least 8 species indicating highest moisture levels among the three sites high 13c values are the result of continuous evasion of co2 derived from volcanically charged groundwaters and springs plus the formation of travertine and photosynthetic activity in the lake a 3 decrease in 18o about 4 7 m suggests an abrupt shift to wetter conditions at the transition from mid to late holocene lagunas miscanti 23 44 s 67 46 w 4140 m a s l and del negro francisco 27 28 s 69 14 w 4125 m a s l each contain only one ostracod species limnocythere sappaensis attesting to higher salinities although sediment facies and ostracod continuity and abundances imply a history of higher effective moisture at laguna del negro francisco sediment cores from each lake document more arid conditions in the lower sections with a sharp shift to wetter conditions in the upper sections highly variable isotope values at the transition from mid to late holocene suggest rapid short term climate shifts during this transition this overall trend can be correlated from laguna seca laguna miscanti and laguna del negro francisco to lago titicaca implying climatic coherency along the altiplano isotopic profiles show second order fluctuations and drought events that suggest short term variability along the transect in order to explain differences in the effective moisture among the three sites we postulate interactions of regional air masses in the north convective tropical precipitation dominates laguna seca as for lakes in the titicaca region effective moisture for lagunas del negro francisco and miscanti follows a south to north gradient generated by cold air masses from cut offs of pacific westerlies colliding with moist tropical air masses coherent shifts in the past therefore imply changes in available tropical air mass moisture

pan african displaced terranes in the tuareg shield central sahara concepts developed in the recently published model of the air region eastern tuareg shield niger africa as a college of three displaced terranes integrated in a single geodynamic model lead us to propose a terrane map of the tuareg shield 500000 km 2 the 23 terranes recognized have their own lithological metamorphic magmatic and tectonic characteristics and are separated by subvertical strike slip megashear zones that can be traced for hundreds of kilometres or by major thrust fronts some of these boundaries have ophiolitic assemblages or molassic deposits the tuareg shield was shaped and partly accreted during the pan african orogeny 750 550 ma but not as a homogeneous body

pan african granulite formation in the kabye massif of northern togo west africa pb pb zircon ages metamorphic zircons from seven granulite facies orthogneisses of tonalitic composition enderbites collected from four different nappes of the kabye massif in the dahomeyide belt of northern togo were dated by the pb pb evaporation method they yielded consistent neoproterozoic ages with a mean of 612 5 0 8 ma interpreted to reflect the peak of regional granulite facies metamorphism following pan african continental collision between the west african and benin nigerian plates these results support previous ages obtained by various chronometers on high grade rocks from the same suture zone and from surrounding units in togo benin and ghana they are also similar to zircon ages from granulites in the mozambique belt of souteastern africa these pan african metamorphic ages reflect continental amalgamation resulting in the formation of the gondwana supercontinent towards the end of the neoproterozoic

caracterisation du magmatisme proterozoique superieur en afrique de l ouest et implications geodynamiques des rifts intracratoniques au panafricain the main petrological mineralogical and geochemical features of the metavolcanites belonging to the late proterozoic tectono sedimentary units of southern mauritanides termesse and niokolo koba koulountou and western hoggar algeria timesselarsine permit a reconstruction of the geodynamic environment that controlled the evolution of the pan african ranges of western africa flows and pyroclastic beds metamorphosed under greenschist facies conditions are interbedded within detritic and carbonate platform sediments suggesting an unstable environment in the vicinity of a continental margin the association of oceanic tholeiites slightly enriched in lree and basalts more enriched in tio2 zr nb and lree displaying alkalic affinities suggests intracontinental rifting succeeded by expansion the lack of ultrabasic basic complexes oceanic paleosutures in southern mauritanides and their occurrence in the hoggar suggest that the opening was bigger in the north than in the south the later calc alkali

the potassic granites of the igbeti area further evidence of the polycyclic evolution of the pan african belt in southwestern nigeria abstract field geochemical and isotopic studies on granitic rocks in the igbeti area of southwestern nigeria indicate that this pan african belt was affected by two episodes of granite plutonism represented by an older augen gneiss and a younger relatively undeformed coarse grained porphyritic granite these rocks have similar major element characteristics but their trace element compositions are sufficiently different to warrant a suggestion that they are probably of different origin rb sr whole rock isotopic analysis give an eburnean age of 1904 18 ma for the augen gneisses and a pan african age of 617 37 ma for the coarse grained porphyritic granite a low initial 87 sr 86 sr ratio 0 7005 0 0025 for the augen gneiss suggests derivation from the mantle or a low rb sr source whereas a value of 0 7120 0 0016 for the coarse grained porphyritic granite indicates a significantly older crustal component in the magma alkaline magmatism may have been an important component of orogenic magmatism during the eburnean event

palaeogeographical reconstructions of the pan african brasiliano orogen closure of an oceanic domain or intracontinental convergence between major blocks abstract a reconstruction of the pan african brasiliano orogen has become possible thanks to new data from the southern pan african belt and by using published data geological mapping which included structural thermobarometric and geochemical studies in togo and neighbouring countries have enabled to define the existence of a preorogenic continental rift whose closure followed soon after its opening continental crust convergence induced an oblique collision that caused nappe stacking this involved external nappes thrust over the west african craton intermediate nappes including metabasic rocks with eclogitic assemblages and internal nappes composed of highgrade anatectic gneiss and intrusive granite and charnockite comparison with data from other regions hoggar adrar des iforas northeastern brazil nigeria central africa has led to the recognition of a pre orogenic continental rift that bordered the west africa sao francisco congo cratons in the southern part of the chain farther north in the hoggar and adrar des iforas this continental rift opened on a wider oceanic domain which involved a passive margin along the west african craton and an active margin to the east after these rifting and subduction stages continental collision followed that was dominated by strike slip movement oblique to the plate boundaries the general organization of the pan african brasiliano belt can be considered as the result of a confrontation between three major continental domains these were the west african and sao francisco congo cratons and a reworked shield composed in its inner part of polycyclic basement rocks and bounded by a fringe of monocyclic metasedimentary thrust belts that faced the cratons

a review of the in ouzzal granulitic terrane tuareg shield algeria its significance within the pan african trans saharan belt the in ouzzal terrane iot or in ouzzal granulite unit iogu is an elongated palaeoproterozoic block within the neoproterozoic pan african belt of north west africa the granulites derive from archaean protoliths that include a large volume of metasediments which were deposited on a 3 2 ga gneissic basement near peak granulite facies conditions between 2 17 and 2 ga were estimated at p 10 kbar and t rising from 800 to 1000 c premetamorphic orthogneisses were intruded at 2 5 ga and followed by the emplacement of syn to late kinematic charnockites syenites and carbonatites at around 2 ga cooling of the granulites occurred till 1800 ma shortly after its exhumation coeval with crustal extension and related alkaline magmatism in adjacent areas the iot was buried beneath late palaeoproterozoic and neoproterozoic cover sequences and then behaved as a rigid block both margins are lithospheric faults as evidenced by the occurrence of shear zone related mafic and felsic plutons pan african tectonothermal events were negligible in the north but granulites in the south were significantly reworked under lower greenschist facies conditions during the northern motion of the block with respect to both the western and the eastern pan african terranes the cambrian molasse associated with widespread alkaline volcanism and subvolcanic granites is horizontal in the north the iot which was part of a larger continental mass including its counterpart in northern mali is interpreted as an exotic terrane which may have docked during pan african plate convergence and lateral collision the unchanged pediplain since c 1 7 ga in the north suggests that the iot is underlain by thick palaeoproterozoic lithospheric mantle whereas its southern part is probably allochthonous and overlies pan african structural units

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

high resolution palynological analysis in late early middle miocene core from the pannonian basin hungary climatic changes astronomical forcing and eustatic fluctuations in the central paratethys high resolution palynological analysis in the karpatian sarmatian late early middle miocene interval of the borehole tengelic 2 hungary reveals the existence of a forest organized in altitudinal belts developed in a subtropical warm temperate humid climate reflecting the so called miocene climatic optimum pollen changes from the late early miocene to the middle miocene are related to climatic variations values of mean annual temperature ta between 18 and 20 8c and mean annual precipitation pa between 1200 and 1400 mm have been estimated bclimatic amplitude methodq for the badenian decreasing during late badenian and sarmatian ta and pa about 16 8c and 1100 mm have been interpreted as a climatic cooling correlated with the bmonterey cooling eventq and related to the development of the east antarctic ice sheet eais alternation in pollen taxa thermophilous vs altitudinal elements reflects the astronomical forcing on temperature and precipitation and then on vegetation where obliquity and eccentricity cycles dominated eustatic changes determine pinus and pinaceae and dinocyst variations

upper proterozoic schist belts in the nigerian sector of the pan african province of west africa abstract schist belts in nigeria occur in a 400 km wide zone which trends nne parallel to the boundary between the pan african province and the west african craton a polycyclic migmatite gneiss granite terrain ranging in age from archaean to lower palaeozoic flanks the schist belt zone to east and west and separates the individual belts within the zone the schist belts fall into two age groups the earlier group contains assemblages of mafic igneous rocks pelitic schists and phyllites banded iron formation and locally coarse grained clastics and carbonate rocks these belts show complex structural styles and are extensively invaded by granitic plutons belonging to the widely distributed pan african magmatic suite schists and gneisses within and adjacent to some of these belts have been dated at 1100 ma and this group is thought to belong to the kibaran orogeny similar kibaran rock associations can be recognised elsewhere in the pan african province in the hoggar and cameroun the kibaran orogeny in this region is interpreted as a largely ensialic event although with possible minor ocean basin formation that led into the more intense and widespread pan african orogeny the later group of schist belts is characterised by coarse to fine grained clastics insignificant mafic igneous rocks a simple straight structural style and an absence of internal granite plutons these schist belts are believed to belong to the pan african orogeny their sediments may have been deposited in a back arc basin related to an e dipping subduction zone at the western margin of the pan african province

late holocene fine grained sediments of the balearic abyssal plain western mediterranean sea abstract the late holocene fine grained sedimentation in the deep central balearic abyssal plain western mediterranean sea has been studied after the analysis of high quality sediment cores from three multicoring stations named a b and c the coring stations are 25 km apart from each other and form a triangle that is at the greatest distance from the nearest landmasses the sediments consist of foraminifer pteropod oozes layers u1 and u4 from bottom to top two pteropod oozes u2 and u5 and a turbidite layer u3 the same sequence has been identified in the three cores the turbidite layer u3 that lies on top of u2 14 c ams dated at 1814 cal yrs bp ranges from 5 to 11 cm thick and is clearly distinguished from the dominating hemipelagic sediments by colour variations higher water content and the absence of planktonic foraminifer shells rather uniform values of organic carbon and nitrogen are also characteristic of the u3 turbidite unit likely because of homogenisation during transport and emplacement in addition u3 unit shows higher contents of terrigenous elements such as k and fe otherwise the presence of zeolites in the turbidite layer supports the hypothesis of the sardinian continental margin where pyroclastic deposits are known as the most likely source area for u3 our results demonstrate the ability of turbidity currents originating on the margins surrounding the balearic abyssal plain to reach the very centre of the basin during high sea level still stands as the present one

an oligocene multi species foraminiferal oxygen and carbon isotope record from odp hole 758a indian ocean paleoceanographic and paleo ecologic implications abstract an oligocene basal miocene zones p19 p22 n4 oxygen and carbon isotope stratigraphy is presented based on mixed benthic foraminiferal faunas and different species of planktic foraminifers from eastern indian ocean odp hole 758a lack of covariance in planktic and benthic 18 o ratios indicates that many oligocene sea level fluctuations including the major fall at 30 ma are not of glacio eustatic origin 18 o values suggest that test morphology is a poor indicator of preferred depth habitat of oligocene planktic foraminifers also some groups show considerable shifts in preferred depth habitat reconstructed surface water temperature was nearly constant during the investigated period but even assuming a large antarctic icecap values are unrealistically low 18 20 c most likely water masses with markedly different oxygen isotopic composition existed this poses great problems for quantitative temperature reconstructions planktic foraminiferal species show similar 13 c ratios indicating well mixed surface waters this contrasts with the strong oxygen isotopic gradient which suggests well stratified surface waters during the oligocene the difference in 13 c ratio between the average ratio of planktic foraminiferal species and the benthic foraminifers 13 c p b shows an inverse relation with the known circulation intensity record and thus with productivity this 13 c pattern is interpreted as being caused by the presence of younger bottom waters at this site during periods with lower temperatures and or larger antarctic ice sheets

freshwater and atlantic water inflows to the deep northern barents and kara seas since ca 13 14 c ka foraminifera and stable isotopes foraminiferal stable isotopes and assemblages from franz victoria and st anna troughs provide a valuable record of freshwater and atlantic water flows to the northern barents and kara seas from deglaciation to present the d 18 o and d 13 c of planktonic neogloboquadrina pachyderma s and benthic elphidium excavatum were up to1 4 lower than present at ca 13 11 5 and 10 14 c ka global sea level corrected mostly reflecting substantial freshwater inputs coincident with glacial marine sediment deposition cassidulina teretis exceeded 40 of benthic foraminifera ca 13 and 10 14 c ka indicating subsurface penetrations of atlantic water the transition to postglacial marine conditions is marked by a 1 rise in foraminiferal d 18 o and a sharp fall in c teretis soon after 10 14 c ka these changes imply reduced inputs of freshwater and atlantic water subsequent isotopic and foraminiferal assemblage variations reflect changing atlantic water conditions upstream in the nordic seas and shifts between the warm fram strait and cold barents sea branches of atlantic water we hypothesize that glacial isostatically induced deepening by up to 150 m influenced atlantic water inflows to the northern barents sea during deglaciation and the holocene thus effects of isostatic recovery have to be factored into paleoceanographic reconstructions 2001 elsevier science ltd all rights reserved

paleogeographic evolution of the late miocene lake pannon in central europe abstract the paleogeographic evolution of lake pannon within the pannonian basin is reconstructed with eight maps ranging from the middle miocene to the early pliocene the maps are based on the distribution of selected biozones and specific fossils and on complementary sedimentological and seismic information our reconstruction shows that the history of lake pannon can be divided into three distinct intervals an initial stage with low water level which resulted in isolation from the sea at about 12 ma and might have led to temporary fragmentation of the lake an interval of gradual transgression lasting until ca 9 5 ma and a long late interval of shrinkage and infilling of sediments that persisted into the early pliocene the deep subbasins of the lake formed during the transgressive interval in more basinward locations than the deep basins of the preceding sarmatian age the southern shoreline running parallel with the sava and danube rivers along the northern foot of the dinarides changed very little during the lifetime of the lake while the northern shoreline underwent profound changes

high resolution paleosalinity reconstruction from laguna de la leche north coastal cuba using sr o and c isotopes abstract isotopes of sr o and c were studied from a 227 cm long sediment core in order to develop a high resolution paleosalinity record to investigate the paleohydrology of laguna de la leche north coastal cuba during the middle to late holocene palynological plant macrofossil foraminiferal ostracode gastropod and charophyte data from predominantly euryhaline taxa coupled with a radiocarbon based chronology indicate that the wetland evolved through four phases 1 an oligohaline 0 5 5 lake existed from 6200 to 4800 cal yr b p 2 water level in the lake increased and the system freshened from 4800 to 4200 cal yr b p 3 a mesohaline 5 18 lagoon replaced the lake 4200 cal yr b p and 4 mangroves enclosed the lagoon beginning 1700 cal yr b p forming a mesohaline lake isotopic ratios were measured on specimens of the euryhaline foraminifer ammonia beccarii although several measurements were also made on other calcareous microfossils in order to identify potential taphonomic and or vital effects the 87sr 86sr results show that the average salinity of laguna de la leche was 1 7 during the early lake phase and 8 during the lagoon phase a change driven by relative sea level rise the 18o results do not record the salinity increase seen in the 87sr 86sr data but instead indicate high evaporation from the lake surface this in turn suggests that the value of 1 7 may slightly underestimate the average salinity of the wetland at least for the period prior to 4800 cal yr b p variability in 13c was controlled by plant productivity episodic marine incursions and vegetation community change there is some evidence for seasonal effect and the lateral transport of microfossils prior to burial the isotopic data independently confirm the hydrological interpretations made using the euryhaline indicators and have permitted the reconstruction of a significantly higher resolution paleosalinity record than would be possible using the paleoecological data however our results show that sr isotopes while often cited as a powerful paleosalinity tool must be used in conjunction with other indicators when investigating paleosalinity trends relying solely on any single isotopic or ecological indicator can lead to inaccurate results especially in semi enclosed and closed hydrological systems

crust forming ages and proterozoic crustal evoluton in nigeria a reappraisal of current interpretations abstract radiometric ages in the nigerian basement cluster around 3 5 3 1 3 0 2 7 2 5 2 1 1 8 and 0 6 ga however not all these ages correspond to times of crust formation there are significant discrepancies between u pb and rb sr ages and nd and sr model ages with a definite trend for the orthogneisses and granitoids analysed results show good agreement between model ages tnd tsr and emplacement ages for early archaean and imply that these model ages date the time of crust mantle differentiation the archaean early proterozoic boundary was most probably a major crust forming period in sw nigeria as indicated by u pb zircon ages that are in agreement with nd model ages in that segment of the nigerian basement on the other hand late proterozoic and younger rocks which include migmatized gneisses pan african granitoids and jurassic younger granites have model ages in excess of their crystallization ages such model ages that lie between pan african or jurassic and well known older geologic ages do not correspond to any specific crust forming event rather they are mean crust residence ages reflecting contributions from juvenile material and remelted older archaean crustal components the overall scenario is consistent with widespread archaean crust and its involvement in the genesis of late proterozoic and younger crust in the nigerian basement this is in agreement with an intra cratonic setting far removed from the suture to the west

palaeoenvironmental reconstruction of the sarmatian middle miocene central paratethys based on palaeontological and geochemical analyses of foraminifera ostracods gastropods and rodents paleoenvironmental changes in the upper middle miocene central parathetys were reconstructed by using qualitative and quantitative palaeontological analyses of foraminifera and ostracods coupled with trace elemental mg ca and stable isotope delta 18 o and delta 13 c analyses of their carbonate skeletons and of gastropod sheets mean annual air temperatures were estimated using the oxygen isotope composition of contemporaneous rodent teeth the studied aquatic fossils come from two boreholes in the zsambek basin northern central hungary while the terrestrial ones are from localities in ne hungary and e romania in the studied sarmatian successions three zones could be distinguished based on palaeontological and geochemical results at the badenian sarmatian boundary faunal diversity decreased markedly in the lower zone a transgressive event culminated in a seawater incursion into the semi open basin system of the central paratheys stable bottom water temperature similar to 15 degrees c and variable salinites 20 22 are estimated for the early sarmatian sea the faunal changes notably a strong reduction in biodiversity occuring at the boundary between the lower and the middle zone can be explained by a sea leval highstand with dysoxic conditions a relative sea level fall is documented at the end of this middle zone after a short regressive event a marine connection between the paratethys and mediterranean was established at the beginning of the upper zone this is indicated by an increased microfaunal diversity and the re appearance of marine bademan ostracods and foraminifera which are completely absent from the older samatian series during the upper zone the temperatures and salmities are estimated to have fluctuated from 15 degrees c to 21 degrees c and from 15 parts per thousand to 43 parts per thousand respectively

tourmalinization related to late proterozoic early palaeozoic lode gold mineralization in the bin yauri area nigeria three types of tourmaline occurrence have been identified in the area of bin yauri nigeria mesothermal lode gold mineralization these are 1 stratabound tourmalinites in pelitic metasediments 2 tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks 3 tourmaline in auriferous quartz and quartz carbonate veins although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source two stages of tourmalinization are envisaged the earlier ca 1100 ma involved syngenetic diagenetic formation of tourmalinites while the later ca 500 ma involved epigenetic hydrothermal tourmaline gold mineralization possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline rich rocks or tourmalinites electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl dravite solid solution series plots involving feo mgo and or al2o3 from these analyses are used to constrain the sources and processes of tourmalinization two metallogenic implications are derived from this study one is that although the tourmalinites are barren of gold and base metal mineralization their occurrences nevertheless encourages exploration for syngenetic exhalative massive sulphide deposits in the region the other implication applies to the potential use of tourmaline in deciphering the physico chemical conditions of gold mineralizing fluids in the bin yauri area

oxygen and carbon isotopic composition of recent larger and smaller foraminifera from the madang lagoon papua new guinea abstract tests of recent benthic foraminifera from the madang lagoon papua new guinea were analyzed for their oxygen and carbon isotopic composition analyses were performed on scuba collected species from backreef and low oxygenated harbor environments covering a depth range of 0 to 45 m both rotaliid and miliolid symbiont bearing species were found to exhibit increasing 18o with depth while only the rotaliids reveal a comparable trend in their 13c composition the general trend of depletion in the heavier isotopes 13c and 18o appears to be depth and light dependant neither the symbiont type nor the nature of the microhabitat appear to affect the magnitude of 18 o 16 o fractionation in larger foraminifers from this environment the carbon isotope patterns of symbiont bearing species revealed distinct differences between rotaliids and miliolids consistently lower 13c values in rotaliid foraminifers may be related to a higher rate of photosynthetic activity the photosynthetic effect of carbon isotope fractionation may be overprinted by the presence absence of an internal carbon pool and or specific modes of biomineralization which may act as isotopic filters foraminifera collected from low oxygenated organic rich sediments in harbor inlets at madang were found to exhibit particularly low 13c values depletion 13c is suggested to be due to oxidative processes in the surrounding organic rich sediment coupled with preferential incorporation of isotopically lighter 12c

the algerian eddies abstract this paper synthetizes various previous analyses of the algerian eddies these mesoscale anticyclonic eddies are of primary importance to the circulation of all the water masses in the western mediterranean they are generated by instability processes disturbing the flow of modified atlantic water maw shortly after it reaches the african coast near 0 e namely the algerian current young eddies which have diameters of 50 100 km and the upwelling generally attached to their southwestern edges drift eastward along the coast at a few km per day sometimes during several months as they grow older and larger the most vigorous ones leave the coastal zone and drift seaward some of them may reach the sardinian continental slope where a well defined vein of levantine intermediate water liw flows we suspect them to be capable to pull fragments of liw seaward and in fact the least modified liw we encountered in the middle of the algerian basin had the form of rings or filaments trapped by one eddy eddies several months old may have diameters as large as 200km they also entrain the mediterranean deep water mdw and they probably extend down to the bottom in 1984 two such eddies occupied most of the algerian basin the maw was deflected seaward by the westernmost one from the algerian coast at 3 e as far as the balearic islands and was then dispatched by other eddies through the whole basin as though by a set of paddle wheels such interactions are perhaps not as exceptional as was previously expected these mesoscale phenomena have strong biological implications the western mediterranean sea thus appears to be a very suitable place for the observation and modelling of such mesoscale coherent structures

an integrated approach to the search for gold in a mature data rich brownfields environment a case study from sigma lamaque quebec abstract the greater than 1300 participants in the 2015 integra gold rush challenge the biggest gold exploration crowdsourcing competition to date were given access to six terabytes of historic data collected at the c 12 moz au sigma lamaque gold deposits val d or district quebec and asked to identify targets with the highest potential for the next big gold discovery at the property this paper describes our approach to exploration targeting at sigma lamaque with particular emphasis on i integrating and interrogating the available data ii identifying mappable expressions key ingredients of ore forming processes using spatial data modelling in particular inversion modelling and advanced filtering of the available geophysical data iii developing a conceptual model in the framework of a mineral systems approach and iv translating the conceptual model into an effective tool for targeting gold in the val d or district

a review of the mineral potential of liberia abstract the republic of liberia in west africa is underlain mostly by precambrian rocks of archaean liberian age in the west and of proterozoic eburnean age in the east by analogy with similar terranes elsewhere in the world and in west africa in particular the geology of liberia is favourable for the occurrence of deposits of a wide range of metals and industrial minerals including gold iron ore diamonds base metals bauxite manganese fluorspar kyanite and phosphate known gold deposits mostly orogenic in style occur widely and are commonly associated with north east trending regional shear zones gold mining commenced at the new liberty deposit in western liberia in 2015 while significant gold resources have also been identified at several other sites in both archaean and proterozoic terranes liberia has large resources of itabirite type iron ores most of which are located in the liberian terrane and was the largest producer in africa prior to the onset of civil war in 1989 production of iron ore is currently restricted to a single mine yekepa in the nimba range other important deposits some of them previously mined include bong the western cluster putu and goe fantro there is a long history of alluvial diamond production in western and central liberia together with more than 160 known occurrences of kimberlite most of the known kimberlites occur in three clusters of small pipes and abundant dykes located at kumgbor mano godua and weasua close to the border with sierra leone many of these are considered to be part of a single province that includes jurassic age diamondiferous kimberlites in sierra leone and guinea deposits and occurrences of a wide range of other metals and industrial minerals are also known several of these have been worked on a small scale in the past mainly by artisanal miners but most are poorly known in detail with sub surface information available at only a few localities by comparison with most other countries in west africa the geology of liberia is poorly known and there has been very little systematic exploration carried out for most commodities other than gold iron ore and diamonds since the 1960s and 1970s further detailed field and laboratory investigations using modern techniques are required to properly evaluate the potential for the occurrence of economic deposits of many minerals and metals in a variety of geological settings digital geological geochemical geophysical and mineral occurrence datasets including new national airborne geophysical survey data provide a sound basis for the identification of new exploration targets but in almost every part of the country there is a need for new and more detailed geological surveys to underpin mineral exploration

diversity dynamics and mass extinctions of the early middle jurassic foraminifers a record from the northwestern caucasus abstract the early middle jurassic foraminiferal assemblages of the northwestern caucasus including a total of 315 species and 68 genera were analysed to establish the principal diversity patterns at substage level of resolution an overall conclusion is that the number of species varied significantly in contrast to the number of genera the most diversified were late sinemurian pliensbachian late toarcian early aalenian and late bajocian assemblages significant diversity drops have been documented in the early toarcian and in the middle aalenian the first of them corresponds to the well known mass extinction which regionally was initiated in the pliensbachian and terminated when rapid late toarcian diversification began the second event could be considered as a regional evidence of a new mass extinction that appeared in the middle aalenian and was most likely associated with the aalenian bajocian regional anoxic event also recorded in the carpathian part of the western tethys the most intense foraminiferal turnovers took place in the toarcian and in the middle aalenian early bajocian the lazarus effect in spite of its high value has not much influenced the estimation of principal diversity trends

chronology of nappe assembly in the pan african dahomeyide orogen west africa evidence from 40ar39ar mineral ages abstract the pan african dahomeyide orogen represents the southwestern segments of the eastern tectonic zone along which the west african craton was incorporated into gondwana orogenic contraction produced nappe complexes comprised of passive margin sediments and accreted exotic magmatic rocks in ghana and togo external nappes include the atacora composed of lower amphibolite facies quartzite and mica schist which were structurally imbricated with mylonitic gneiss derived from c 2 0 ga foreland basement the suture zone is represented by high pressure granulite facies garnet homblende gneiss we have analyzed muscovite and homblende concentrates from external and suture zone nappes in incremental heating 40 ar 39 ar experiments muscovites which define the penetrative foliation in the atacora nappes and a shear foliation in the basement parautochthon record 40 ar 39 ar plateau ages of 579 4 0 8 ma and 578 1 0 5 ma respectively in contrast c 600 km to the north muscovite in quartz schist near the base of the atacora nappes displays a spectrum which gives a minimum age of 608 1 1 2 ma whereas muscovite in the overthrust kara nappes yields a plateau age of 633 8 0 5 ma the c 30 m y difference between the atacora nappes in the northern dahomeyides and the younger dates of the southern external nappes indicate out of sequence thrust imbrication however forward imbricating thrusting is also suggested by the older age of kara nappes relative to atacora nappes in the northern segment the youngest ages are inferred to date orogen parallel nappe transport at c 575 ma hornblende from the structurally lower sections of the suture zone nappes record a 36 ar 40 ar versus 39 ar 40 ar isotope correlation age of 587 4 3 ma hornblende from a tonalitic vein in the host garnet mafic gneiss yields an isotope correlation age of 581 9 2 4 ma these ages are interpreted to date the exhumation of the suture zone nappes and thus provide a minimum age of crustal thickening in the dahomeyide orogen the age data are consistent with coeval forward and hindward propagating thrusting and nappe imbrication and constrain the amalgamation in northwest gondwana to have occurred in the latest proterozoic rather than cambrian

badenian sarmatian chronostratigraphy in the polish carpathian foredeep abstract the miocene of the northern part of the polish carpathian foredeep contains a record of events particularly important in the evolution of the central paratethys basin there the paratethyan badenian salinity crisis resulted in the deposition of evaporite gypsum deposits of the krzyzanowice formation the ensuing post evaporite marine badenian deposition is recorded by the marly pecten beds the transition to the overlying clays of the syndesmya beds represents the initial deterioration of normal marine conditions within the basin and is associated with the disappearance of typical stenohaline faunal components during the badenian sarmatian extinction event and the subsequent appearance of endemic sarmatian taxa the history of these paratethyan events has hitherto been only poorly dated new 40ar 39ar dating of biotite and volcanic glass from a rhyolite tuff within the pecten beds babczyn 2 core constrains its depositional age to 13 06 0 11 ma this age suggests that the faunal extinction presumably took place after 13 06 0 11 ma and that the salinity crisis ended before then this result is consistent with other reliable radiometric age constraints that collectively suggest that the crisis began shortly after 13 81 0 08 ma de leeuw et al 2010 and that evaporite deposition took place ca 13 60 0 07 ma de leeuw et al 2010 both the badenian evaporites and the pecten beds in carpathian foredeep are thus serravallian in age and represent the lower part of neogene nannoplankton zone 6 nn 6

geology of the northern borborema province ne brazil and its correlation with nigeria nw africa the borborema and benin nigeria provinces of ne brazil and nw africa respectively are key areas in the amalgamation of west gondwana by continental collision during the brasiliano pan african orogenies both are underlain by complex basement nigeria has c 3 05 ga archaean crust but no known palaeoproterozoic rocks 2 0 ga in ne brazil 2 6 3 5 ga archaean rocks form small cores within palaeoproterozoic gneiss terrains affected by plutonism at c 2 17 ga both regions exhibit late palaeoproterozoic c 1 8 ga rift related magmatism and metasedimentary sequences overlying the basement the serido group of ne brazil 0 65 ga is similar to the igarra sequence in sw nigeria the ceara group which may date back to c 0 85 ga is a passive margin deposit on crust thinned during initiation of an oceanic domain in both provinces basement and sedimentary cover were involved in tangential tectonics that resulted in crust thickening by nappe stacking associated with closure of this ocean frontal collision between c 0 66 and 0 60 ga later evolved to an oblique collision generating north south continental strike slip shear zones at c 0 59 ga in ne brazil the main pan african suture is probably buried beneath the parnaiba basin the transbrasiliano lineament interpreted as the prolongation of the kandi 4 50 lineament in hoggar may represent a cryptic suture

transition from subduction to collision recorded in the pan african arc complexes mali to ghana abstract the 1000 km long suture zone of the dahomeyide belt exposed from southeast ghana to south mali corresponds to a narrow and lithologically diverse area with symptomatic coronitic hp granulitic massifs based on a review of published petrological geochemical and geochronological data along the dahomeyide belt we propose a global scenario for the closure of the pharusian ocean between the west african craton wac and the benino nigerian shield during the end of the neoproterozoic the onset of a long lived oceanic subduction by 800 780 ma is recorded by early magmatism in the amalaoulaou intra oceanic arc in mali contemporary to the gourma and adrar des iforas to the north and in brazil to the south the first occurrence of tonalitic plutons dated at 720 ma and the development of a forearc system around 650 ma mark the onset of active margin subduction beneath the benino nigerain shield and its northward prolongation in mali oceanic subduction beneath the active margin ended between 640 and 630 ma with the onset of subduction of the wac continental margin while subduction related magmatism continues till ca 600 ma on the upper plate during a short period between 620 and 610 ma the forearc system and the tip of the active continental margin were buried synchronously the positive bouguer anomaly observed to the east of the suture zone in benin and not beneath the suture zone itself supports the occurrence of a massive mafic body at the base of the crust that could correspond to the underplated buried forearc ultimately the exhumation and partial amphibolitization of the suture zone and a shift from a calc alkaline magmatism to anatectic magmatism along with the onset of strike slip faulting in the upper plate marks the transition from continental subduction to continental collision between 610 and 580 ma this work highlights the importance of the pharusian suture zone s l to our knowledge it represents a unique example in the world in where the forearc system is buried and partly exhumed at the transition from subduction to collision

accumulation rates and sediment deposition in the northwestern mediterranean abstract as part of the eros 2000 programme sediment mixing and accumulation rates in the northwestern mediterranean sea were determined applying the 210 pb dating method to a total of 49 cores and the results from 29 sediment cores are presented here on the basis of the results from the 49 sediment cores an attempt was made to present a general picture of sediment accumulation for the area of the northwestern mediterranean the total deposition of sediment in the area is estimated to be of the order of 34 15 10 6 ton year 1 which is half the value reported earlier by got and aloisi 1990 continental shelf research 10 841 855 for the same region the activity depth profiles of 210 pb show the presence of intensive mixing in the upper layer of near shore sediments but little or no mixing is observed in the deep water sediments based on a diffusion model sediment mixing rates calculated from excess 210 pb gradients vary from 0 002 to 7 cm 2 year 1 and the deposition rates from 0 01 to 0 60 cm year 1 a linear dependence of sedimentation rate on water depth derived from the sediment cores indicates an inverse correlation between these two the relatively high sedimentation rates and mixing rates found near the rho ne river suggest that the contribution from the river dominates the deposition system in the northwestern mediterranean in the deep water basin however atmospheric input and biological production are clearly more important

the myth of the brackish sarmatian sea the biota of the 1 5 ma period of the middle miocene sarmatian of the central paratethys lack stenohaline components this was the reason to interpret the sarmatian stage as transitional between the marine badenian and the lacustrine pannonian stages however our new data indicate that brackish water conditions could not have prevailed sarmatian foraminifera molluscs serpulids bryozoans dasycladacean and corallinacean algae as well as diatoms clearly indicate normal marine conditions for the entire sarmatian during the lower sarmatian however a sea level lowstand forced the development of many marginal marine environments during the late sarmatian a highly productive carbonate factory of oolite shoals mass occurrences of thick shelled molluscs and larger foraminifera as well as marine cements clearly point to normal marine to hypersaline conditions this trend is not restricted to the western margin of the pannonian basin system but can be observed in the entire central and even eastern paratethys

u pb dating of the end of the pan african orogeny in the tuareg shield the post collisional syn shear tioueine pluton western hoggar algeria abstract the tioueine pluton intrudes the neoproterozoic series of the iskel terrane located in the tuareg shield western hoggar the consistency of the internal structures as well as the nature and organization of the associated microstructures demonstrate that the tioueine pluton was emplaced syn kinematically while n s strike slip shear zones were active the syn tectonic emplacement of the tioueine massif implies that this pluton although belatedly crystallized entirely belongs to the concept of post collisional magmatism in order to date precisely the late pan african tectono metamorphic event in the studied area an u pb age of 523 1 ma was obtained from abraded zircons of a late quartz syenite from the tioueine pluton this early cambrian age is younger than the other plutons of the tuareg shield which were mainly emplaced between 630 ma and 580 ma this dating also shows that the tuareg shield was not a single coherent block at 525 ma but rather an amalgam of active terranes moving each other along major shear zones finally the tioueine massif represents probably the final welding of the tuareg shield assembly of terranes and consequently the end of the post collisional orogenic episode in the whole pan african belt

proterozoic history of the borborema province ne brazil correlations with neighboring cratons and pan african belts and implications for the evolution of western gondwana 1 geological and geochronological correlations between borborema province ne brazil and neighboring cratons and brasiliano pan african belts indicate that the amazonian west african and sao francisco congo cratons and the basement of the araguaia borborema nigerian and cameroon provinces were part of the atlantica supercontinent this continent was established at the end of the transamazonian eburnean cycle 2 0 ga and apart from ubiquitous taphrogenesis in the 1 8 1 7 ga interval remained largely unaffected for the following 1 ga around 1 ga an important magmatic event in borborema province correlates with rifting episodes and anorogenic magmatism in the sao francisco congo and amazonian cratons these events are interpreted as failed attempts to break up atlantica which at this time may have been part of the larger rodinia supercontinent renewed extensional conditions in borborema province during the middle and late neoproterozoic are attributed to far field stresses transmitted to the interior of atlantica by outwardly dipping subduction zones that encircled its northern present day coordinates portion the rarity of petrotectonic assemblages typical of subduction zone environments indicates that extension did not evolve enough to form large oceans basins and thus that the borborema province essentially includes reworked intracontinental domains regional deformation and metamorphism starting at 650 640 ma and shear zone development beginning at 590 595 ma were continuously developed through time and were synchronous throughout most of the borborema araguaia cameroon and nigerian provinces postorogenic conditions were reached 540 530 myr ago while active deformation was still occurring in other belts that accreted around atlantica to form western gondwana

metacraton nature genesis and behavior article i nfo in this paper we show with examples that cratons involved in intercontinental collisions in a lower plate position are often affected by orogenic events leading to the transformation of their margins in some cases craton interiors can also be shaped by intense collisional processes leading to the generation of intra cratonic orogenic belts we propose to call these events metacratonization and the resulting lithospheric tract metacraton metacratons can appear similar to typical orogenic belts i e active margin transformed by collisional processes but are actually sharply different their main distinctive characteristics not all are present in each metacraton are 1 absence of pre collisional events 2 absence of lithospheric thickening high pressure metamorphism being generated by subduction leading to high gradient in strain and meta morphic intensity 3 preservation of allochthonous pre collisional oceanic terranes 4 abundant post collisional magmatism associated with shear zones but not with lithospheric thickening 5 presence of high temperature low pressure metamorphism associated with post collisional magmatism 6 intraconti nental orogenic belts unrelated to subduction and oceanic basin closures reactivation of the rigid but fractured metacratonic lithosphere will cause doming asthenospheric volcanism emplacement and mineral izations due to repetitive mineral enrichments this paper provides several geological cases exemplifying these different metacratonic features in scandinavia sahara central africa and elsewhere a special focus is given to the saharan metacraton because it is where the term metacraton originated and it is a vastly ex panded tract of continental crust 5 000 000 km 2

marine carbonate systems in the sarmatian middle miocene of the central paratethys the zsambek basin of hungary the study of eight stratigraphic sections at the margin of the semi enclosed zsa mbe k basin hungary allows the sedimentary anatomy of oolitic bioclastic systems in the sarmatian of the central paratethys to be reconstructed the mollusc foraminiferal and ostracod associations indicate that the carbonate systems are latest badenian to late sarmatian in age the lower upper sarmatian deposits are organized in superimposed subaqueous dunes prograding towards the basin on a low angle ramp during the late sarmatian the ramp underwent subaerial erosion linked to a moderate relative fall in sea level lagoonal deposits were later formed and microbial nubeculariid bryozoan serpulid buildups were emplaced the abnormal marine conditions of the sarmatian conducive to the development of a poorly diversified flora and fauna and dominant non skeletal grains are linked to fluctuating salinities mesotrophic to eutrophic conditions and perhaps high alkalinity

applying spatial prospectivity mapping to exploration targeting fundamental practical issues and suggested solutions for the future abstract despite many decades of development spatial prospectivity modelling is not yet widely used or accepted throughout the global mineral exploration industry a common criticism of the method is that it is not practically useful because it has a bias to mature well known areas and generates excessively large areas of high prospectivity it is suggested that the reason for this is not primarily related to limitations in the prospectivity mapping algorithms but rather to issues relating to the use of input data sets specifically it is common that the input data such as geological interpretations do not uniformly and objectively represent the search space of interest omit critical targeting relevant geoscientific elements such as major deep seated ore controlling structures and have a large degree of unrecognised dependence it is considered that these problems are not in principle barriers to the eventual successful deployment of this technology however future approaches to spatial prospectivity modelling need to explicitly address these concerns it is suggested that the most effective method may be a hybrid of subjective human geological interpretation and objective machine based analysis that captures the best aspects of these alternative approaches i e an intelligence amplification ia rather than an artificial intelligence ai approach a roadmap is proposed for improving the effectiveness of spatial prospectivity modelling that has implications for the broader community interested in mineral exploration targeting

evolutionary mechanisms of the paratethys sea and its separation into the black sea and caspian sea abstract a possible mechanism leading to the transformation of the paratethys seas i e the sarmatian sea lake meotian sea pontian sea lake etc is here proposed the time period from the formation of the closed sarmatian sea lake to the present is also considered it will be shown that the main reason for the collapse of the sarmatian sea lake into the black and caspian seas was development of a canyon that cut through the mountains separating the black and mediterranean seas later this canyon was transformed into the bosporus and the dardanelles straits the canyon was formed mainly by erosive activity of a river that had periodically emerged from the paratethys abrasion of the canyon bottom and the related erosional lowering of its level led to gradual drainage of the paratethys basins the consequences of the messinian salinity crisis in the mediterranean sea contributed to the penetration of salt water into the paratethys and then to its temporary isolation and transformation into a closed sea lake later its level rose and the river was formed again that river flowed into the mediterranean sea in the process eroding its own bed during low levels of the world ocean the riverbed experienced increased erosion eventually dropping below high ocean level at which time the river was flooded by mediterranean water this process led to the formation of a corridor linking the seas together this corridor developed over the course of many glacioeustatic fluctuations in the world ocean

the origin and significance of non aqueous co2 fluid inclusions in the auriferous veins of bin yauri northwestern nigeria non aqueous co2 and co2 rich fluid inclusions are found in the vein quartz hosting mesothermal gold sulphide mineralization at bin yauri northwestern nigeria although mineralizing fluids responsible for gold mineralization are thought to be co2 rich the occurrence of predominantly pure to nearly pure co2 inclusions is nevertheless unusual for a hydrothermal fluid system many studies of similar co2 rich fluid inclusions mainly in metamorphic rocks proposed preferential loss leakage of h2o from h2o co2 inclusions after entrapment in this study however it is proposed that phase separation fluid immiscibility of low salinity co2 rich hydrothermal fluids during deposition of the gold mineralization led to the loss of the h2o phase and selective entrapment of the co2 the loss of h2o to the wallrocks resulted in increasing oxidizing effects there is evidence to suggest that the original co2 rich fluid was intrinsically oxidized or perhaps in equilibrium with oxidizing conditions in the source rocks the source of the implicated fluid is thought to be subducted metasediments subjected to dehydration and devolatilization reactions along a transcurrent anka fault shear system which has been described as a pan african 450 750 ma crustal suture

late proterozoic schist belts and plutonism in nw nigeria the deformed low grade metasedimentary volcanic schist belts of nw nigeria and the voluminous granitoid plutons which invaded them are expressions of late proterozoic early phanerozoic activity in the terrain separating the w african and congo cratons recent interpretations of nigerian geotectonic evolution have invoked two generations of schist belt one a product of kibaran c 1100 ma ensialic processes the other due to pan african 700 450 ma marginal basin development the detailed histories of the anka belt pan african maru belt kibaran and birnin gwari belt unknown age and the plutons emplaced in them are documented here on the basis of new field chemical and isotopic data each belt represents a dominantly quiet water sedimentary environment but volumetrically minor lithologies reveal important differences between the belts the volcanic rocks and early minor intrusions have strong affinities with those of destructive plate margins the schist belts were deformed congruently and simply before c 750 ma following the development of flat lying possibly thrust related structures in the maru and birnin gwari belts subsequent plutonism beginning c 750 ma ago has the calcalkaline i type characteristics of subduction zones but younger plutons have mildly peralkaline compositions due to thickening crust

low sea level stand emplacement of megaturbidites in the western and eastern mediterranean sea piston cores from the balearic and herodotus abyssal plains in the mediterranean sea show that the late pleistocene to holocene sedimentary sequence is dominated by turbidite muds on each plain one turbidite bed is conspicuous by its thickness and this bed can be correlated basinwide on the basis of geochemical compositional analysis and its apparent correspondence with a distinct acoustically transparent layer on high resolution seismic records these megabeds on the two plains represent megaturbidites of very large volume 300 600 km3 each and are shown by ams radiocarbon dating to have been emplaced during the last low stand of sea level at the height of the last glacial maximum the megabed on the balearic abyssal plain is derived from the southern european margin and is the main sedimentation event over the last 120 ka it emplaced as much material as was deposited by smaller flows during the previous 25 ka sedimentation rate curves for the balearic abyssal plain show that falling sea level correlates with increased terrigenous deposition and that gross sedimentation rates in the basin increased as sea level fell from 120 18 ka due to more frequent emplacement of distal turbidites the herodotus abyssal plain megabed is derived from the libyan egyptian continental shelf west of the nile delta and was the dominant sedimentation event in this basin during the past 60 kyr high resolution seismic profiles from the ionian and sirte abyssal plains in the central mediterranean also suggest possible low sea level emplacement of megabeds in these regions available evidence suggests widespread emplacement of megaturbidites throughout the mediterranean at the last glacial maximum although the triggering mechanisms for these events remain speculative catastrophic destabilisation of the margin after a long period of accumulation with an increased rate of sediment supply is suggested

gold potential of the pan african trans sahara belt and prospect for further exploration abstract the trans sahara belt is one of the mobile belts formed during the pan african orogeny that spans between 870 and 550 ma the trans sahara belt was formed as result of the collision between the converging west african craton congo craton and the sahara metacraton continental blocks the belt with major exposure in the tuareg and dahomeyan consists of pre neoproterozoic basement which were thoroughly reworked during the pan african orogeny neoproterozoic metasedimentary and metavolcanics and syn tectonic pan african granitoids which intrude archean and paleoproterozoic rocks the trans sahara belt though less endowed when compared to older archean orogenic greenstone belts in terms of gold mineralization displays reasonable gold mineralization in both the tuareg shield and dahomeyan shield with about 160 tons of gold reported so far across the belt mineralization is associated with varying lithologies across the belt and appears to have been regionally controlled by n s trending pan african shear zones in the tuareg shield mineralized quartz veins are associated with syntectonic granitoids mylonitic and meta volcanosedimentary rocks conversely gold mineralization is only associated with metasediments and migmatite gneisses in the dahomeyan shield with occurrences largely confined to metasedimentary sequence in benin and nigeria the prevailing tropical climate in the dahomeyan shield has also facilitated secondary concentration of gold in alluvial bed of river draining supracrustal rocks hosting primary gold mineralizations the occurrence of primary mineralization in variety of rocks across the tuareg and dahomeyan shield and widespread occurrence of placer gold deposits in the dahomeyan shield justifies the need for further exploration and evaluation of mineralization potential the emplacement of gold which occur between 535 and 500 ma is controlled by n s trending pan african mega shear zones however at the district scale it is evident that the pan african mega shear zones are not the only important structures lower order faults and shear zones are important structures to consider in exploration targeting exploration particularly at district scale might benefit from gis based prospectivity mapping considering the mineralizations are generally structural controlled gis based prospectivity mapping which integrates multifaceted digital data sets can provide a foundation for vectoring towards explorations targets in many mineralized districts within the trans sahara belt

palaeoenvironment and palaeoclimate of the middle miocene lake in the steinheim basin sw germany a reconstruction from c o and sr isotopes of fossil remains a differentiated reconstruction of palaeolimnologic environmental and climatic conditions is presented for the middle miocene long term freshwater lake 14 3 to 13 5 ma of the steinheim basin on the basis of a combined c o and sr isotope study of sympatric skeletal fossils of aquatic and terrestrial organisms from the lake sediments the oxygen isotope composition for lake water of the steinheim basin 18oh2o 2 0 0 4 vsmow n 6 was reconstructed from measurements of 18opo4 of aquatic turtle bones the drinking water calculated from the enamel of large mammals proboscideans rhinocerotids equids cervids suids has 18oh2o values 18oh2o 5 9 1 7 vsmow n 31 typical for middle miocene meteoric water of the area this 18oh2o value corresponds to a mean annual air temperature mat of 18 8 3 8 c calculated using a modern day 18oh2o mat relation hence large mammals did not use the lake water as principal drinking water in contrast small mammals especially the then abundant pika prolagus oeningensis drank from 18o enriched water sources 18oh2o 2 7 2 3 vsmow n 7 such as the lake water differences in sr and o isotopic compositions between large and small mammal teeth indicate different home ranges and drinking behaviour and support migration of some large mammals between the swabian alb plateau and the nearby molasse basin while small mammals ingested their food and water locally changes in the lake level water chemistry and temperature were inferred using isotopic compositions of ostracod and gastropod shells from a composite lake sediment profile calcitic ostracod valves ilyocypris binocularis 18o 1 7 1 2 vpdb 13c 0 5 0 9 vpdb n 68 and aragonitic gastropod shells gyraulus spp 18o 2 0 1 3 vpdb 13c 1 1 1 3 vpdb n 89 have 18o and 13c values similar to or even higher than those of marine carbonates 13c values of the biogenic carbonates parallel lake level fluctuations while 18o values scatter around 2 2 and reflect the short term variability of meteoric water inflow vs longer term evaporation 87sr 86sr ratios of aragonitic gyraulus spp gastropod shells parallel the lake level fluctuations reflecting variable inputs of groundwater and surface waters using a water 18oh2o value of 2 0 vsmow water temperatures calculated from skeletal tissue 18o values of ostracods are 16 7 5 0 c gastropods 20 6 5 6 c otoliths 21 8 1 4 c and fish teeth 17 0 2 7 c the calculated mat 19 c lake water temperatures 17 to 22 c and the 18o enriched water compositions are indicative of warm temperate climatic conditions possibly with a high humidity during this period vegetation in the area surrounding the basin was largely of the c3 type as indicated by carbon isotopic compositions of tooth enamel from large mammals 13c 11 1 1 1 vpdb n 40

tectonometamorphic evolution of ghana togo and benin in the light of the pan african brasiliano orogeny abstract the south pan african belt of west africa ghana togo and benin province can be divided into three domains 1 1 the external nappes thrust over the west african craton derived from passive margin sedimentary deposits middle to late proterozoic and displaying middle to high pressure metamorphism such as the kante and atacora nappes 2 2 the intermediate nappes including the suture zone rocks with eclogitic assemblages protoliths ca 800 ma and mainly monocyclic metasedimentary rock and orthogneiss that are found in central togo and northwest benin 3 3 the internal nappes composed of high grade commonly anatectic gneiss anatexis ca 600 ma including orthogneiss eburnian plutons elongated granulite belts reworked archean basement and an intrusive granite and charnockite association ca 600 ma which are exposed in benin and nigeria the p t t d paths calculated from rocks in these three domains show a prograde retrograde evolution 1 1 an initial clockwise evolution related to an early burial stage hp ht in the intermediate nappes followed by oblique thrusting in a sw direction that caused nappe stacking and subsequent uplift 2 2 a second anti clockwise evolution with late temperature and pressure increases only recorded in the more internal units this temperature increase was a consequence of the previous crustal thickening with subsequent doming extension and anatexis the pressure increase was related to movement along the kandi fault working as a dextral strike slip fault with a transpressional component under late e w shortening the retrograde trend corresponds to the final uplift the evolution of the belt can thus be divided into three successive stages 1 1 a first stage was characterized by an oblique collision inducing sw oblique thrusting with associated syn foliation reverse metamorphism 2 2 during a second stage anatectic doming took place followed by 3 3 a third stage at still high temperature with dextral wrench faulting and associated n s post foliation folding under late e w shortening comparison between the west african north brasiliano and central african late proterozoic belts shows very strong similarities between their lithology kinematics and metamorphism and indicates that the pan african brasiliano chain resulted from collision between three major continental domains the west african and sao francisco congo cratons and a late proterozoic mobile domain

geodynamic impact on the stable isotope signatures in a shallow epicontinental sea analyses were made of a mollusc based meta dataset of 859 d 13 c and d 18 o data of miocene nearshore settings in the european paratethys sea and its descendant lake pannon the observed trends document a strong tie to geodynamics which are largely decoupled from miocene open ocean isotope curves semi to fully enclosed initially marine water bodies such as the paratethys sea are prone to switching seawater isotope signatures because they respond rapidly to changes in the evaporation precipitation ratio two phases of positive deviations of oxygen isotope values of water relative to the modern ocean value smow occurred during the middle miocene both were initiated by tectonic constrictions of the seaways and became amplified by global warming and regionally decreasing precipitation with the final disintegration of the paratethys the marine isotope signatures vanish instead the observed isotope trends suggest a comparably simple system of an alkaline lake with steadily declining salinity the oceanderived paratethys sea may thus act as a key for understanding isotope trends in epicontinental seas

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

δ18o and ree contents of phosphatic brachiopods a comparison between modern and lower paleozoic populations 18o values of both carbonate 18 7 25 1 and phosphate 15 1 16 7 components of the francolite from the fossil brachiopod shells are interpreted as the result of a partial resetting of pristine isotopic compositions the similarity of hat shape ree patterns of some lower ordovician linguloids with those of extant littoral specimens suggests the preservation of a 500 myr old record of ree marine chemistry in agreement with the known paleogeography the phosphatic brachiopods have been deposited in a coastal environment under shallow and oxygenated marine waters however the contents and distribution of ree in some strongly altered brachiopod shells reveal an alteration of the original negative ce anomalies and both nd and sm enrichments that transformed the initial hat shape patterns of linguloids into strongly convex or bell shape patterns

a 200 year mid european air temperature record preserved in lake sediments an extension of the δ18op air temperature relation into the past abstract a detailed history of the water oxygen isotope ratios of lake ammersee southern germany was established for the last two centuries by analyzing oxygen isotope ratios of ostracod shells from a sediment core in a three to five year resolution empirical analysis and modelling of the isotope hydrology of the lake show that the oxygen isotopic composition of the lake water is mainly controlled by the isotopic composition of local precipitation for the last 200 years the lake isotope record is strongly correlated to the air temperature record from hohenpeisenberg situated within the lake s catchment area thus the mid european relation between 18 o in precipitation and air temperature documented for the last 20 years can be extended over a longer time and a larger temperature range the results provide further support for the validity of ostracod 18 o from ammersee sediments as a quantitative proxy for mean annual air temperature probably extending back to the last glaciation

middle to late miocene sequence stratigraphy of the transylvanian basin romania abstract the history of middle to late miocene evolution of the transylvanian basin was determined by the bordering carpathian orogen evolution the tectonic events being well recorded by the sedimentary history the basin evolved in a back arc setting under a regional compressional stress field the major tectonic events produced during the late sarmatian and post pannonian were related to the reactivation of the pre badenian fault systems the transylvanian basin got uplifted after the late pannonian during the pliocene and at least 500 m of sedimentary cover was eroded based on seismic and well log interpretation core and outcrop sedimentology and microfauna eight sequences were defined the early middle miocene sequences are roughly synchronous to five 3rd order global sea level cycles most of the recognized sequence boundaries are enhanced by regional tectonic events the sedimentary evolution was also strongly influenced by salt tectonics active starting with the late sarmatian two sequences were identified in the lower badenian deposits the third sequence late early badenian to early mid badenian preserves information about deeper shelf settings the lowstand of the following sequence was responsible for the deposition of the salt formation late mid badenian an important lithostratigraphic marker in the sedimentary record of the basin in general the upper badenian deposits parts of the 4th and 5th sequences belong to deep marine submarine fan systems the sarmatian partially 5th 6th and partially 7th sequences was characterized by diverse salinity conditions stretching from brackish to hypersaline and by high tectonic instability which induced several significant relative sea level falls during that time deltaic north and fandeltaic east systems fed submarine fans stacked between salt related submarine heights channeled deep marine depocenters most of the pannonian deposits partially 7th and 8th sequences belong to submarine fan systems but shallower facies were also found in the western and eastern part of the basin

the mafic layered complex of the kabye massif north togo and north benin evidence of a pan african granulitic continental arc root abstract between the predominantly neoarchean paleoproterozoic west african craton wac and the saharian metacraton smc the dahomeyides suture zone represents a valuable witness of continental amalgamation during pan african times in the kabye massif northern togo and northern benin mainly granulitic metagabbros associated with al rich kyanite and garnet bearing felsic dykes are exposed as tectonic lenses within the pre pan african gneisses of the smc new geochemical data suggest that the high grade rocks granulites in the kabye massif originated in a mature continental arc setting afc calculations constrain the amount of contamination of mantle wedge derived magmas by crustal metasediments to about 10 reconstruction of initial magmatic stratigraphy has been carried out using cipw norms for cumulitic sequences within the massif indicating a normal igneous polarity from west to east published geochemical signatures along the pan african suture zone of the dahomeyides in ghana togo and benin constrain the origin of mafic granulitic and eclogitic complexes a distinction is made between bodies with mainly morb signatures originated from the subducted wac plate passive margin and those with magmatic arc signatures originated from the over riding plate mantle wedge this suggests that the closure of the oceanic domain between the wac and the smc from 640 to 610 ma was mainly accommodated by oceanic subduction beneath the active continental margin before pan african collision

neogene flora and vegetation development of the pannonian domain in relation to palaeoclimate and palaeogeography abstract a survey of the neogene flora and vegetation pattern of the pannonian domain based on selected fossil plant assemblages is given the paper aims to reveal the complex interrelation of tectonic palaeogeographic evolution climate flora and vegetation development through the neogene of the pannonian domain flora and vegetation patterns are based on well documented and studied fossil plant assemblages macrofloras primarily leaves there are time intervals well represented in the fossil record e g the pannonian or the sarmatian and others with relatively few localities e g the badenian a general but slow cooling trend is definitely observable after the early miocene as reflected by both quantitative climate reconstructions and floristic change i e decrease of diversity slow disappearance of thermophilous and exotic elements as well as decrease in the variety of vegetation types a significant decline of coldest month temperatures as compared to warmest month temperatures must have played a defining role in forming flora and vegetation through the neogene as compared to climate estimates for the middle late miocene fossil floras warmer climate conditions are indicated by the ipolytarnoc flora and vegetation comprising an extremely high number of thermophilous taxa as well as complex vegetation structure the early and middle miocene fossil assemblages bear a significant relevance to the tectonic pattern of the pannonian domain a transitional character in both flora and vegetation is indicated by the karpatian magyaregregy locality knowledge of the badenian flora and vegetation is limited to the middle badenian nogradszakal assemblage indicating cooler climate conditions which contrasts with global climate change in contrast to the relatively poor azonal vegetation of nogradszakal and most pannonian localities the more diverse sarmatian and pliocene floras display a strong relation to each other attributable to palaeogeographic constraints

exploration information systems a proposal for the future use of gis in mineral exploration targeting abstract the advent of modern data collection and storage technologies has brought about a huge increase in data volumes with both traditional and machine learning tools struggling to effectively handle manage and analyse the very large data quantities that are now available the mineral exploration industry is by no means immune to this big data issue exploration decision making has become much more complex in the wake of big data in particular with respect to questions about how to best manage and use the data to obtain information generate knowledge and gain insight one of the ways in which the mineral exploration industry works with big data is by using a geographic information system gis for example gis platforms are often used for integration interrogation and interpretation of diverse geoscience and mineral exploration data with the goal of refining and prioritising known and identifying new targets here we i briefly discuss the importance of carefully translating conceptual ore deposit models into effective exploration targeting maps ii propose and describe what we term exploration information systems eis a new idea for an information system designed to better integrate the conceptual mineral deposit model i e the critical and constituent processes of the targeted mineral system with data available to support exploration targeting and iii discuss how best to categorise mineral systems in an eis as scale dependent subsystems to form mineral deposits our vision for the future use of eis in exploration targeting is one whereby the mappable ingredients of a targeted mineral system are translated and combined into a set of weighted evidence or proxy maps automatically resulting in an auto generated mineral prospectivity map and a series of ranked exploration targets we do not envisage the eis replacing human input and ingenuity rather we envisage the eis as an additional tool in the exploration toolbox and as an intelligence amplifying system in which humans are making use of machines to achieve the best possible results

stable isotope fractionation between mollusc shells and marine waters from martinique island abstract forty nine aragonitic and calcitic shells from 14 species of marine tropical molluscs bivalvia gastropoda polyplacophora and ambient waters from martinique have been analyzed for their carbon and oxygen isotope compositions mineralogy of shells was systematically determined by raman spectroscopy that reveals composite shell structures and early processes of diagenetic alteration in mangrove brackish waters result from the mixing between 89 1 of seawater and 11 1 of freshwater a hydrological budget quantified by both oxygen isotope and salinity mass balance calculations mollusc shells from the mangrove environment s 31 18 o 0 5 are characterized by mean 13 c values 1 2 lower than those 2 6 living in the open sea s 35 18 o 1 these low carbon isotope compositions result from the oxidation of organic matter into bicarbonate ions used in the building of mollusc shells the oxygen isotope compositions of the studied mollusc species are mainly controlled by the temperature and composition of seawater whereas the role of the so called vital effects is negligible contrasting with carbon isotopes variability in the 18 o values among and within species of mollusc shells is very low 1 0 15 for a given littoral environment using ambient temperatures of seawater 28 30 c oxygen isotope fractionations between all studied living species and environmental waters match those extrapolated from the fractionation equation established for molluscs by grossman and ku chem geol isot geosci sect 59 1986 59 in the range 3 20 c by analyzing calcite and aragonite layers from the same shell or by comparing shells from different species living in the same environment there is no evidence that oxygen isotope fractionation between aragonite and water differs from that between calcite and water on the basis of these results we conclude that the oxygen isotope compositions of shells from most fossil mollusc species are suitable to estimate past seawater temperatures at any paleolatitude

constraints on miocene oceanography and climate in the western and central paratethys o sr and nd isotope compositions of marine fish and mammal remains abstract the paratethys evolved as a marginal sea during the alpine himalayan orogeny in the oligo miocene sediments from the northern alpine molasse basin the vienna and the pannonian basins located in the western and central part of the paratethys thus provide unique information on regional changes in climate and oceanography during a period of active alpine uplift oxygen isotope compositions of well preserved phosphatic fossils recovered from the sediments support deposition under sub tropical to warm temperate climate with water temperatures of 14 to 28 c for the miocene 18o values of fossil shark teeth are similar to those reported for other miocene marine sections and using the best available estimates of their biostratigraphic age show a variation until the end of the badenian similar to that reported for composite global record the 87sr 86sr isotope ratios of the fossils follow the global miocene seawater trend albeit with a much larger scatter the deviations of 87sr 86sr in the samples from the well constrained seawater curve are interpreted as due to local input of terrestrially derived sr contribution of local sources is also reflected in the end values consistent with input from ancient crystalline rocks e g bohemian massif and or mesozoic sediments with end 7 excluding samples showing local influence on the water column an average end value of 7 9 0 5 may be inferred for the miocene paratethys this value is indistinguishable from the end value of the contemporaneous indian ocean supporting a dominant role of this ocean in the western and central paratethys

obliquely convergent tectonics and granite emplacement in the trans saharan belt of eastern nigeria a synthesis abstract the eastern nigeria terrane belongs to the 3000 km long trans saharan belt which was formed in the neoproterozoic between 750 and 500 ma by continental collision between the converging west african craton congo craton and east saharan block the study area consists mostly of gneisses and migmatites that underwent granulite facies metamorphism 800 c 800 mpa in contrast with western nigeria and cameroon no basement cover relationship has been identified which is in agreement with a monocyclic metamorphic history around 640 ma the area underwent a nappe tectonics with eastward displacement emplacement of bt ms granites and granulite facies peak later on around 615 ma nappes were towards the north numerous hbl bt granite plutons were emplaced around 585 ma during north south strike slip regional deformation the anisotropy of magnetic susceptibility fabric helps in defining strain localization along narrow north south to nne ssw vertical shear zones during the exhumation history exhumation of the terrane assessed using u pb ar ar and rb sr methods was presumably slow with uplift rates around 0 2 0 5 mm year preliminary estimates of contemporaneous horizontal movements suggest that they were one order of magnitude larger

early and late pan african orogenies in the air assembly of terranes tuareg shield niger our study of the 60 000 km 2 air massif which comprises the southeastern extension of the tuareg shield in the niger republic has identified three major displaced terranes aouzegueur barghot and assod6 these terranes were all affected differentially by the pan african orogeny during an early major phase 750 660 ma and a late follow up phase 650 580 ma the greenschist facies aouzegueur terrane comprises an ophiolite and is intruded by a late kinematic mediumk calc alkaline tonalite trondhjemite granodiorite ttg suite 730 ma the amphibolite facies barghot terrane made up of a basement and a supracrustal sequence is intruded by late to post kinematic high k calcalkaline granitoids 715 665 ma both terranes form a nne to e verging belt thrust 680 670 ma upon an unknown eastern rigid continent and are covered unconformably by an early pan african molasse in contrast the amphibolite facies assod6 terrane composed of a basement and several supracrustal sequences collided with the eastern rigid block without being thrust upon it tibetan type crustal thickening occurred and ht lp metamorphism proceeded to regional anatexis enhanced by widespread emplacement of anatectic granites of lower crustal origin 670 ma this thermal event is attributed to the delamination of the continental lithospheric mantle and consequent rise of the asthenosphere the late pan african phase affecting mainly the assod6 terrane is marked by the intrusion of high k calc alkaline n s elongated batholiths 645 580 ma and by right lateral displacement along the n s raghane mega shear zone located on the edge of the eastern rigid continent this movement along the northern extent of the rigid continent in eastern hoggar 8 30 e created the tiririne intracontinental linear fold belt made up of early panafrican molasse in the model proposed we estimate that the assod6 terrane driven by an oblique spreading ridge moved to the north over a distance of 1000 km during 60 ma along the lithospheric raghane shear zone the latter was the subsequent locus of the silurian devonian alkaline ring complexes the calc alkaline granitoids are regarded as subduction related mantle products contaminated by lower and medium level crust the model and mechanisms proposed can be applied to the entire tuareg shield

mg ca sr ca and stable isotopes in modern and holocene protothaca staminea shells from a northern california coastal upwelling region this study explores the potential of intertidal protothaca staminea shells as high resolution geochemical archives of environmental change in a coastal upwelling region mg ca and sr ca ratios were analyzed by excimer laser ablation inductively coupled plasma mass spectrometry la icp ms at sub weekly temporal resolution in shells growing 1 mm per month growth patterns of a modern p staminea shell from humboldt bay california collected in december 1999 made it possible to infer a lifespan from 1993 to 1998 growth hiatuses in the shell may have excluded records of extreme events mg ca ratios appeared to be partly controlled by water temperature the correlation coefficient between temperature and mg ca was r 0 71 in one of four growth increments significant year to year differences in the sensitivity of mg ca to temperature in p staminea could not be explained however sr ca ratios appeared to be more closely related to shell growth rate oxygen isotopes measured at 2 week temporal resolution in the same shell did not show a clear relation to local temperature in summer possibly because temperatures were higher and less variable at the king salmon mudflat where the shell was collected than in the main channel of humboldt bay where water properties were monitored negative shell 13c values 0 5 marked spring and summer coastal upwelling events the mg contents of p staminea midden shells dated to 3 ka and 9 ka were significantly lower than in the modern shell this may have resulted from degradation of a mg rich shell organic matrix and precluded quantitative interpretation of the older high resolution records elevated 13c values in the 3 ka shell suggested that the individual grew in highly productive or stratified environment such as a shallow coastal embayment or lagoon

palaeoenvironmental reconstructions by stable isotopes of middle miocene gastropods of the central paratethys abstract the stable isotopes of carbon and oxygen were used to provide information of mixing of marine and freshwater and subsequently used to determine palaeosalinities in the middle to late miocene st margarethen zollhaus section upper sarmatian mactra zone pannonian a succession of three gastropod assemblages indicates changing environmental conditions from a limnic fluviatile to littoral mudflat and a sublittoral marine environment several shells of the main representatives of the three assemblages potamides hartbergensis hilber granulolabium bicinctum brocchi potamides disjunctus sowerby and additionally shells of lymnaea sp a typical freshwater gastropod and pomatias conicus a terrestrial gastropod were taken for stable isotope analyses oxygen and carbon isotope data of the freshwater endmember are distinctively lower 18 o 4 5 13 c 9 than of the marine endmembers 18 o 2 2 13 c 2 3 in contrast to the expected intermediate isotopic composition between the freshwater and marine environment the shells of supposed brackish environments have higher 18 o values than the shells of the marine environment these higher 18 o values are explained by evaporation which affected the protected areas of riverine to lacustrine environments and small pools on mudflats formerly considered to be the habitats of the brackish assemblages thus the oxygen and carbon isotope data extend the already existing palaeoenvironmental information

investigating the history of east asian monsoon and climate during the last glacial interglacial period 0 140 000 years mineralogy and geochemistry of odp sites 1143 and 1144 south china sea abstract monsoon climate is an important component of the global climatic system a comprehensive understanding of its variability over glacial interglacial time scales as well as of its effects on the continent and in the ocean is required to decipher links between climate continental weathering and productivity a detailed multiproxy study including bulk and clay mineralogy grain size analysis phosphorus geochemistry sedex extraction organic matter characterization and nitrogen stable isotopes was carried out on samples from odp sites 1143 and 1144 leg 184 south china sea covering the past 140 000 years we tentatively reconstruct the complex sedimentation and climatic history of the region during the last glacial interglacial cycle when sea level variations linked to the growth and melting of ice caps interact with monsoon variability during interglacial periods of high sea level summer monsoon was strong and humid and warm climate characterized the adjacent continent and islands clay minerals bear signals of chemical weathering during these intervals high calcite and reactive phosphorus mass accumulation rates mars indicate high productivity especially in the southern region of the basin during glacial intervals strong winter monsoon provided enhanced detrital input from the continent as indicated by high detrital mar glacial low sea level resulted in erosion of sediments from the exposed sunda shelf to the south and clay mineral variations indicate that warm and humid conditions still prevailed in the southern tropical areas enhanced supply of nutrients from the continent both by river and eolian input maintained high primary productivity reduced circulation during these periods possibly induced active remobilization of nutrients such as phosphorus from the sediments intense and short cold periods recorded during glacial and interglacial stages correlate with loess records in china and marine climatic records in the north atlantic confirming a teleconnection between low and high latitude climate variability

geochronology of sedimentary and metasedimentary precambrian rocks of the west african craton abstract this contribution summarizes current knowledge of the geochronology of the upper proterozoic sedimentary rocks covering the west african craton this was done by using direct dating methods correlations between the northern edge of the tindouf basin and the northern and southern part of the taoudeni basin as well as the volta basin are proposed an important depositional lack over almost the entire craton is confirmed between 1 7 ga which represents the time of the latest eburnean activities or cooling effects and about 1 0 ga which is the start of the general upper proterozoic sedimentation this lack is remarkable as the other cratons from gondwana continent are covered by middle proterozoic sediments the upper proterozoic sedimentation on the west african craton may be divided into a basal mainly sandstone period ca 1000 900 ma a middle mainly limestone period ca 900 750 ma and an upper mainly siltstone period ca 750 650 ma tectonic volcanic and thermal activities in connection with the pan african orogeny are recorded only around the craton they induced either sedimentation lacks in morocco or sedimentation excesses in hoggar unsolved problems such as the precise stratigraphic position of the uppermost proterozoic tillitic episode and the correlation within the moroccan anti atlas are also raised

w au skarns in the neo proterozoic serido mobile belt borborema province in northeastern brazil an overview with emphasis on the bonfim deposit the serido mobile belt smb is located in the borborema province in northeastern brazil and consists of a gneiss basement archean to paleo proterozoic a metasedimentary sequence marble quartzites and schists and the brasiliano igneous suite both of neo proterozoic age in this region skarns occur within marble and at the marble schist contact in the metasedimentary sequence most of the skarn deposits have been discovered in the early 1940s and since then they have been exploited for tungsten and locally gold recently the discovery of gold in the bonfim tungsten skarn has resulted in a better understanding of the skarn mineralization in this region the main characteristics of the smb skarns are that they are dominantly oxidized tungsten skarns with the exception of the itajubatiba and bonfim gold bearing skarns which are reduced based on pyrrhotite as the dominant sulfide garnet with high almandine and spessartine component and elevated gold contents in the bonfim deposit pressure estimates indicate that the skarns formed at 10 to 15 km depth the mineralized skarns present the prograde stage with almandine diopside anorthite and actinolite magnesio hornblende and titanite apatite allanite zircon and monazite as accessory minerals the retrograde stage is characterized by alkali feldspar clinozoisite zoisite sericite calcite and quartz scheelite occurs in four ore shoots distributed within the marble and at the marble schist contact the main ore body is 5 120 cm wide and contains an average of 4 8 wt wo3 which occurs in the basal marble schist contact fold hinges appear to control the location of high grade scheelite the late stage gold mineralization contains bismite bi2o3 fluorine bearing bismite native bismuth bismuthinite bi2s3 and joseite bi4 te s 3 and also chlorite epidote prehnite chalcopyrite and sphalerite this gold bismuth tellurium mineralization exhibits a typical late character and occurs as a black fine grained mineral assemblage controlled by conjugate brittle ductile faults and extensional fractures that crosscut not only the banding in prograde skarn but also the retrograde alkali feldspar and clinozoisite zoisite sericite assemblage the au bi te bearing minerals are intergrown with retrograde epidote prehnite chlorite chalcopyrite and sphalerite indicating that gold mineralization at bonfim is linked to a late stage skarn event the polymetallic nature of the bonfim deposit can be used as an important guide for the exploration of this type of skarn deposit in the borborema province which potentially contains significant new undiscovered gold and polymetallic deposits

p t x conditions on the genesis of orogenic au as bi ag deposit in metasedimentary rocks of the buracao area arai group brasilia fold belt brazil the orogenic au as bi ag mineralization up to 31 g t of the buracao area is hosted in the metasedimentary paleo mesoproterozoic trairas formation arai group brasilia fold belt brazil in order to discuss the p t x conditions that generated this mineralization we present mineralogical geochemical and fluid inclusion data of veins gold and wall rocks coupled with previous structural data these additional data allow us to link metamorphism and deformation with fluid migration and ore genesis the integration of fluid inclusion microthermometry with mineral geothermobarometers and structures show that rocks of the study area evolved from i syn d1a metamorphic peak 400 560 c 6 kbar through to the ii development of syn d1b type i barren veins from low salinity h2o nacl fluids during syn to late metamorphic peak and to the iii development of syn d2a type ii veins with the pyritic ore precipitation from low to high salinity h2o co2 ch4 nacl hco3 fluids during post metamorphic peak 345 285 c 2 7 1 6 kbar the high fineness gold nuggets accompanied by as bi and ag within pyrite arsenopyrite bismuthinite association in the pyritic ore allows the buracao area to be classified as a gold only orogenic ore deposit fluid inclusion compounds and the enrichment of as bi pb cu te se and ag in pyrite from the pyritic ore point out to metamorphism of carbonaceous phyllites and carbonate rocks of the trairas formation as a source for ore forming fluids we suggest that sulfur and gold in these fluids were derived by metamorphism of sedimentary rocks and conversion of pyrite into pyrrhotite in a metamorphic hydrothermal system the au hs 2 bearing fluids percolated along intrabasinal d2a regional shear zones through the trairas formation towards the buracao area where they precipitated type ii ore bearing veins within local structures the ore precipitation was induced by contrasting fo2 fs2 related to the interaction between the sulfur bearing fluid and host magnetite graphite phyllites the lithological control is represented by a series of reactions such as 2feo in silicates magnetite 4au hs 2 aq 4h aq 2fes2 s 4au s 4h2s aq 2h2o l the deposits of the buracao area and other orogenic gold deposits hosted in metasedimentary rocks in the brasilia fold belt and worldwide confirm the potential of ore genesis in zones that do not show any relation with meta igneous rocks thus expanding the exploration possibilities in metasedimentary successions

thermal excursions in the ocean at the cretaceous tertiary boundary northern morocco δ18o record of phosphatic fish debris c lecuyer p grandjean j r o neil h cappetta and f martineau 1993 thermal excursions in the ocean at the cretaceous tertiary boundary northern morocco c lso record of phosphatic fish debris palaeogeogr palaeoclimatol palaeoecol 105 235 243 high precision oxygen isotope analyses were made of phosphate extracted from 17 samples of nektonic and benthic fish debris sampled across the stratigraphic cretaceous tertiary boundary in northern morocco a refinement of the silver phosphate method was used to isolate phosphate from biogenic materials measured 180 values of 18 6 20 5 o are interpreted as reflecting high resolution thermal variations that affected the ocean water column of the western tethys the warm 27 c water masses that characterized maastrichtian times underwent rapid cooling and stabilized at an average temperature of 19 c during the dano montian and thanetian this period of constant and cool temperature was followed by a relatively rapid but more gradual warming to about 25 c achieved in the middle ypresian significant small shifts in 6180 values between nektonic and benthic fauna recorded only during the stages of rapid warming or cooling may correspond to averaged thermal differences within the water column that developed in response to global climatic changes the indicated temperature distribution could have been caused by thermal changes in the atmosphere rather than some signal carried by deep ocean currents the oxygen isotope data coupled with previous measurements of ree and end ti on the same samples support the suggestion that paleo pacific westward currents progressed as far as the northwestern part of the african platform at the end of the cretaceous period

late kinematic timing of orogenic gold deposits and significance for computer based exploration techniques with emphasis on the yilgarn block western australia abstract orogenic gold deposits are a widespread coherent group of epigenetic ore deposits that are sited in accretionary or collisional orogens they formed over a large crustal depth range from deep seated low salinity h2o co2 ch4 n2 ore fluids and with au transported as thio complexes regional structures provide the main control on deposit distribution in many terranes first order faults or shear zones appear to have controlled regional fluid flow with greatest ore fluid fluxes in and adjacent to lower order faults shear zones and or large folds highly competent and or chemically reactive rocks are the most common hosts to the larger deposits focusing of supralithostatic ore fluids into dilatant zones appears to occur late during the evolutionary history of the host terranes normally within d3 or d4 in a d1 d4 deformation sequence reactivation of suitably oriented pre existing structures during a change in far field stress orientation is a factor common to many deposits and repeated reactivation may account for multiple mineralization episodes in some larger deposits absolute robust ages of mineralization support their late kinematic timing and in general suggest that deposits formed diachronously towards the end of the 100 to 200 m y long evolutionary history of hosting orogens for example in the yilgarn block a region specifically emphasised in this study orogenic gold deposits formed in the time interval between 40 and 90 m y with most about 60 to 70 m y after the youngest widespread basic ultrabasic volcanism and towards the end of felsic magmatism the late timing of orogenic gold deposits is pivotal to geologically based exploration methodologies this is because the present structural geometries of i the deposits ii the hosting goldfields and iii the enclosing terranes are all essentially similar to those during gold mineralization at least in their relative position to each other thus interpretation of geological maps and cross sections and three dimensional models can be used to accurately simulate the physical conditions that existed at the time of ore deposition it is particularly significant that the deposits are commonly related to repetitive and predictable geometries such as structural heterogeneities within or adjacent to first order structures around rigid granitoid bodies or in specific locked up fold thrust structures importantly the two giant greenstone hosted goldfields kalgoorlie and timmins show a remarkably similar geometry at the regional scale computer based stress mapping and gis based prospectivity mapping are two computer based quantitative methodologies that can utilize and take advantage of the late timing aspect of this deposit type to provide important geological aids in exploration both in broad regions and more localized goldfields both require an accurate and consistent solid geology map stress mapping requires knowledge of the far field stresses during mineralization and the empirical prospectivity mapping requires data from a significant number of known deposits in the terrane the kalgoorlie terrane in the yilgarn block meets these criteria and illustrates the potential of these methodologies in the exploration for orogenic gold deposits low minimum stress anomalies interpreted to represent dilational zones during gold related deformation coincide well with the positions of known goldfields rather than individual gold deposits in the terrane and there are additional as yet unexplained anomalies the prospectivity analysis confirms that predictable and repetitive factors controlling the siting of deposits are i proximity to and orientation and curvature of granitoid greenstone contacts ii proximity to segments of crustal faults which strike in a preferred direction iii proximity to specific lithological contacts which have similar preferred strike iv proximity to anticlinal structures and v the presence of preferred reactive host rocks e g dolerite the prospectivity map defines a series of anomalous areas which broadly conform to those of the stress map 78 correspondence the most prospective category on this map covers less than 0 3 of the greenstone belts and yet hosts 16 of the known deposits which have produced 80 of known gold thus it discriminates in favour of the larger economically more attractive deposits in the terrane the successful application of stress mapping and prospectivity mapping to geology based exploration for orogenic gold deposits indicates that more quantitative analysis of geological map data is a profitable line of research the computer based nature of these methodologies is ideal for the production of an ultimate integrated deposit target map which can be compared to other more conventional targeting parameters such as geophysical and geochemical anomalies such an integrated strategy appears the way forward in the increasingly difficult task of cost effective global exploration for orogenic gold deposits in poorly exposed terranes

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

sediment accumulation rates in the southern barcelona continental margin nw mediterranean sea derived from 210pb and 137cs chronology sediment cores were collected from the southern barcelona continental margin including the foix canyon in order to study sediment accumulation in this area for this purpose 210pb 137cs and to a lesser extent 239 240pu and heavy metals were determined in sediment sections using state of the art techniques 210pb concentration profiles and 137cs 239 240pu and heavy metals profile features were used to establish the sediment chronologies further information was also obtained from granulometric analyses the magnitudes studied and correlated in this work included surface activities mixing rates accumulation rates and inventories sediments on the continental shelf showed a varied degree of mixing except possibly cn 23 sedimentation rates were relatively small and the sedimentary material probably had a common origin cores from the slope showed less mixing and in cores cn 36 and eb 2 located in the foix canyon axis the 137cs signal vs depth was clear and well preserved accumulation rates and total 210pb inventories were maximum in core cn 36 at mid slope of the canyon which was considered to be an active depocenter core cn 38 collected on the open slope showed a much smaller accumulation rate therefore it was concluded that shelf material is being transported alongshore by the prevailing currents and becomes focused in the canyon which is acting as a natural trap within the canyon this material is preferentially deposited at a mid slope depocenter little extra material reaches the lower canyon area in this area core eb 2 appeared to show signs of the presence of resuspended material possibly derived from the canyon walls finally observed changes in sedimentation rates during the 1930s could not be explained on the basis of current knowledge and this is suggested to be an important subject for further research

metallogenesis of the late pan african gold bearing east ouzzal shear zone hoggar algeria in the w hoggar algeria the major transcurrent n s east ouzzal shear zone eosz hosts several world class gold deposits over a 100 km length the late pan african eosz separates two contrasting precambrian domains the archaean in ouzzal block to the west orthogneisses with subordinate metasediments reworked and granulitized in the c 2 ga eburnean event and a middle proterozoic block to the east again orthogneisses and metasediments involved in the c 600 ma pan african event the eosz is a mylonite belt 1 3 km wide with a 50 m wide ultramylonite belt hosting numerous quartz veins and lenses giant hydrothermal quartz system associated with a quartz sericite pyrite carbonate beresite alteration these hydrothermal events occurred under ductile evolving towards brittle conditions between 500 and 300 mpa at 500 300 c with aqueous carbonic fluids derived both from underlying devolatilized metamorphic rocks and a mantle source as recorded by stable c o isotope data no gold mineralization was associated with these typical mesothermal events following a pressure drop to 130 mpa related to the inception of extensional tectonics the eosz was later percolated by a new set of hydrothermal fluids evolved from basinal waters that deeply penetrated into the in ouzzal basement these fluids were ca bearing brines up to 25 wt eq nacl characterized by high d 9 to 18 range mobilized by the thermal energy released by the late pan african granite magmatism taourirt granites as demonstrated by pb isotope data the brines leached au from the in ouzzal granulites which contain 3 ppb au fluid inclusion studies indicate that gold was deposited from these brines in the eosz at a depth of c 5 km due to mixing and cooling with descending diluted fluids