geology and tectonics of the betic zone se spain abstract the southern margin of the iberian continent comprises a complex geological history which can be traced back into the proterozoic when a gneissic basement was formed a cover of nevado filabride rocks was deposited onto this proterozoic basement during the palaeozoic the permian intrusion of the bedar granite suggests that the palaeozoic sedimentary rocks now exposed in the betic cordilleras have been affected by the hercynian orogeny similar to that of palaeozoic rocks in the adjoining ossa morena zone the hercynian basement was probably covered by alpujarride carbonates in the mesozoic when rifting opened tethys and intruded 140 ma old basic dyke swarms the palaeozoic basement of the betic cordilleras comprises a suture of late cretaceous subduction 80 85 ma b p this can be inferred from hp lt metamorphic facies obducted in coeval thrust slices of nevado filabride rocks the nevado filabride nappes include mesozoic carbonates transformed into marbles macael the suture was probably annnealed after the closure of tethys the mesozoic boundary between africa and europe and the rifting in tethys ceased during the palaeogene when the atlas mountains were formed 36 ma b p subsequently relative movements between africa and europe in the neogene were accommodated by strike slip faults these define the iberian microplate moving eastward by atlantic spreading and possibly subducting under italy neogene deformation of iberia is most intensive in southeastern spain due to emplacement of a mantle diapir under the alboran area this occurred early in the neogene aquitanian and caused nappe spreading involving alpujarride and malaguide rocks the subsequent neogene history has now been studied in great detail and is reviewed here it involves clear examples of calc alkaline volcanism most probably not related to subduction seismic motion along strike slip faults within the iberian microplate and syntectonic deposition in intermontane neogene basins

paleolatitude distribution of phanerozoic marine ooids and cements opdyke b n and wilkinson b h 1990 paleolatitude distribution of phanerozoic marine ooids and cements palaeogeogr palaeoclimatol palaeoecol 78 135 148 data on 493 phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric co2 and or oceanic temperature gradient holocene ooid and cement precipitation occurs over similar latitudes with means centered around 24 and 28 respectively aragonite and calcite also display roughly comparable distributions with average occurrences between 25 and 28 surface seawater saturation values requisite for ooid cement carbonate precipitation are at least 3 8 rs for aragonite and 3 4 a s for calcite ancient ooid cement occurrences vary in space and time with depositional zones generally closer to the equator during continental emergence greatest extent correlates with periods of maximum transgression aragonite formation is favored in more equatorial localities than calcite when cement ooid distributions are narrow and continents are emergent similarity of latitude distribution of marine ooids cement and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in phanerozoic seas than biological processes related to net productivity of various carbonate platform communities continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time

middle miocene serravallian temperate carbonates in a seaway connecting the atlantic ocean and the mediterranean sea north betic strait s spain abstract miocene deposits in the contact area between the prebetic and subbetic domains betic cordillera s spain record the last stages of marine deposition on the southern iberian margin and the final closure of the north betic strait in the early tortonian late miocene serravallian middle miocene shallow water carbonates and mixed carbonate siliciclastics formed on a platform at the southern margin of the north betic strait these shallow water deposits informally termed the la escalera formation onlap an erosion surface carved into underlying miocene and older rocks carbonate components are mainly bryozoans coralline red algae molluscs and benthic and planktonic foraminifers typical of heterozoan lithofacies several facies types can be distinguished based on different grain sizes and sedimentary structures large scale geometries and stratigraphic facies relationships indicate that the la escalera formation was deposited on a homoclinal ramp attached to a deeply eroded emergent relief to the south a beach system developed at the southern margin with backshore lagoons and local incursions of coarse terrigenous sediments seawards of the beach system was a submarine dune belt that extended over several square kilometres at the northeastern end of the la escalera formation longshore currents shifted submarine dunes to the northeast maximum production of carbonate skeletons took place seawards of the dune field from this factory area skeletal debris was moved landwards and incorporated into the dunes and beaches whereas other skeletal particles were transported downslope by storms and fed a facies belt with hummocky and swaley cross stratified sediments the finest grained particles accumulated below a storm wave base along with significant planktic debris carbonate deposits change laterally westwards to terrigenous sediments formed in similar facies belts terrigenous influx limited carbonate production on the western part of the ramp by disturbing the growth of coralline algae and bryozoans vertical variations of facies within the formation depict a major transgressive regressive cycle modulated by up to 10 higher frequency cycles despite its location in an atlantic linked basin the sedimentary model of the la escalera formation shows similarities to the models proposed for neogene mediterranean temperate carbonates which imply a relatively low energy regime on the ramp in comparison with the open ocean platforms this relatively low energy regime can be explained by the position of the north betic strait at the eastern end of the guadalquivir basin however hummocky and swaley cross stratified deposits are significantly more developed in la escalera deposits than in known examples of neogene mediterranean carbonates

structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

origin of late pleistocene bryozoan reef mounds great australian bight bryozoan rich biogenic mounds grew periodically on the prograding carbonate slope of the central great australian bight throughout pliocene pleistocene time cores from three odp leg 182 drill sites provide a record of mound growth during the last 300 000 years over a stratigraphic thickness of similar to 150 m these mounds the first such structures described from the modern ocean grew between paleodepths of 100 and 240 m we infer that the upper limit of growth was established by swell wave base and the lower boundary was fixed by an oligotrophic water mass detailed chronostratigraphy based on radiometric and u series dating benthic foraminifer stable isotope stratigraphy and planktonic foraminifer abundance ratios confirms that buildups flourished during glacial lowstands even numbered marine isotope stages but were largely moribund during interglacial highstands and are not extant today mound floatstones are compositionally a mixture of in situ bryozoans comprising 96 genera and characterized by fenestrate flat robust branching encrusting nodular arborescent and delicate branching growth forms the packstone matrix comprises autochthonous and allochthonous sand size bryozoans benthic and planktonic foraminifers serpulids coralline algae sponge spicules peloids and variable glauconite and quartz grains together with mud size ostracods tunicate spicules bioeroded sponge chips and coccoliths intermound allochthonous packstone and local grainstone contain similar particles but they are conspicuously worn abraded blackened and bioeroded an integrated model of mound accretion during sea level lowstands begins with delicate branching bryozoan floatstone that increases in bryozoan abundance and diversity upward over a thickness of 5 10 m culminating in thin intervals of grainstone characterized by reduced diversity and locally abraded fossils mound accumulation was relatively rapid 30 67 cm ky and locally punctuated by rudstones and firmgrounds intermound highstand deposition was comparatively slow 17 25 cm ky and typified by meter scale fining upward packages of packstone and grainstone or burrowed packstone with local firmgrounds overlain by characteristically abraded particles mound growth during glacial periods is interpreted to have resulted from increased nutrient supply and enhanced primary productivity such elevated trophic resources were both regional and local and thought to be focused in this area by cessation of leeuwin current flow together with northward movement of the subtropical convergence and related dynamic mixing

sedimentological and palaeoecological integrated analysis of a miocene channelized carbonate margin matese mountains southern apennines italy abstract lower middle miocene temperate marine carbonates occur in the matese mountains southern apennines italy these carbonates formed in an open shelf depositional system with an uneven margin 10 km long and up to 6 km wide shelf margin morphology shows multiple submarine channelized carbonate deposits which are dominated by coralline red algae and subordinate bryozoans two main channel networks pietraroia and regia piana channels with their sedimentary bodies were analysed the studied submarine channels grew by sediment accumulation as prograding bodies on a tectonic modelled substrate shallow water rhodalgal skeletal debris from moderately re mobilized up to significantly re worked built up the complex channel system fills in which sedimentary lenses overlapped and partially amalgamated one another when they were still unlithified the early channelized succession is characterized by parautochthonous bryozoan floatstone and rhodolith bryozoan floatstone representing soft muddy substrates in a low water turbulence and high turbidity setting the rhodoliths dominated by melobesioid coralline algae are sub discoidal and sub spheroidal in shape with a characteristic loosely packed inner arrangement these sediments whose latter portion underwent submarine diagenetic processes incipient to evoluted hard grounds were eroded and successively covered by shallower water gravitative deposits constituted by rhodolith floatstone rudstone their rhodoliths constituted by melobesioids mastophoroids and subordinate lithophylloids and sporolithaceans are mainly spheroidal sub spheroidal in shape with subordinate sub discoidal specimens with massive and laminar inner arrangements the lack in early lithification can be drawn back to the physiography of the channelized shelf margin to the active tectonic as well as to the temperate type carbonate dominant biogenic components the depositional surface profile and local hydrodynamic conditions were the major factors controlling sedimentary facies which differ in their relative proportions of dominant components their internal structures and sedimentary body geometries

holocene carbonate sedimentation on the west eucla shelf great australian bight a shaved shelf the southern continental margin of australia is a cool water carbonate sedimentary province located in a high energy swell dominated oceanographic setting a vibrocore transect of 14c dated sediments across the centre of the eucla shelf is the first record of holocene shelf deposition in the great australian bight much of the seafloor shallower than 70 m water depth the base of wave abrasion is bare cenozoic limestone in some places encrusted by late pleistocene coral rich limestone that is cemented by high magnesium calcite 12 mole mgco3 the areally extensive 100 km wide hard bored substrate supports an epibiota of coralline algae minor bryozoans and soft algae or is covered by patches of holocene sediment up to 1 5 m thick generally a basal bivalve lag 3 ka overlain by quartzose bioclastic palimpsest sand this pattern of active carbonate production but little accretion on the wave swept mid to inner shelf is similar to that on other parts of the southern australian continental margin the term shaved shelf is proposed for this style of carbonate platform formed by alternating periods of sediment accretion cementation and erosion the palimpsest sand is typically rich in bivalves coralline algae and locally detrital dolomite outer shelf holocene sediment below the base of wave abrasion but inboard of the shelf edge is a metre thick unit of fine microbioclastic muddy sand with minor delicate bryozoans overlying a 9 13 ka rhodolith gravel some of this outer shelf sediment appears to have been resedimented the shelf edge is a sandy and rocky seafloor with active bryozoan growth and sediment production the holocene sediments are enriched in coralline algal particles and conspicuous large foraminifers cf marginopora and depleted in bryozoans as compared to coeval deposits on the lacepede and otway shelves off southeastern australia these differences are interpreted to reflect warmer waters of the leeuwin current and prevalent downwelling in this area as opposed to the general upwelling and colder waters in the east

circulation in the algerian basin during june 1986 hydrographic measurements made in the algerian basin during june 1986 as part of the western mediterranean circulation experiment together with satellite infrared images are used to describe the flow of major water types in the region modified atlantic water flows eastward along the algerian coast as the algerian current to 4 e where it breaks into a series of eddies and spreads far offshore it then flows partly northward into the ligurian provencal basin and partly eastward through the strait of sardinia the subsurface levantine intermediate water turns sharply northward after flowing westward through the strait of sardinia and forms a narrow vein along the sardinian coast winter intermediate water flows southward around the balearic islands its eastern branch recirculates back to the north whereas part of the western branch contributes to the algerian current by flowing eastward beneath the modified atlantic water two large long lived eddies are confirmed in the area the easternmost of these and other features with unresolved horizontal structure between sardinia and menorca extend from the surface through the pycnocline

complexity of characterizing mafic ultramafic remnants of archean layered complexes in high grade terranes the scenario from motloutse complex southwestern zimbabwe craton abstract mafic to ultramafic rocks of archean layered complexes in high grade terranes typically occur as inclusions closely associated with supracrustal rocks in granitoid gneiss the reconstruction of the original stratigraphy and sequence of events related to archean layered complexes is complicated by the fragmental occurrence and effect of overprint event s the case study presented here highlight these issues from the motloutse complex terrane southwestern zimbabwe craton peridotite pyroxenite and gabbro leucogabbro anorthosite form separate bodies closely associated with amphibolite in the lechana area they occur as inclusions within 2 65 ga tonalite gneiss amphibolite is massive has a stratiform occurrence and is folded with gabbro leucogabbro anorthosite intruding along the fold limbs rare amphibolite xenoliths occur in gabbro leucogabbro anorthosite and peridotite pyroxenite modal and cyclic layering is well preserved in the mafic and ultramafic intrusive bodies anatectic and alkali metasomatic overprints the later related to shear deformation locally affected the lechana rocks the late stage events are contemporaneous and is dated by the 2 0 ga 2013 18 ma u pb zircon overgrowth age amphibolite exhibit prominent granoblastic polygonal fabric defined by amphibole plagioclase gabbro leucogabbro anorthosite are locally gneissic the different mafic rocks are variably affected by overprint events and contain garnet related to anatectic overprint and epidote related to metasomatic overprint peridotite pyroxenite exhibits no metamorphic re equilibration textures but are serpentinized and host widespread magnetite rich layers amphibolite and associated gabbro have conspicuous sulphide concentration up to 5 modal and include pyrrhotite chalcopyrite replaced by covellite pyrite and pentlandite no magnetite or sulphide concentration occur with leucogabbro anorthosite whole rock geochemical characteristics of the amphibolites are similar to tholeiitic basalts but that of the peridotite pyroxenite and gabbro leucogabbro anorthosite indicate different lineage the suggested model considers amphibolite as a stratiform meta basalt which was folded during an earlier deformation event based on the presence of meta basalt amphibolite roof pendants on top of both mafic and ultramafic intrusions it is argued that the peridotite pyroxenite and gabbro leucogabbro anorthosite were emplaced into archean oceanic crust the mafic ultramafic intrusions could either be part of a single mesoarchean layered complex or represent two different suites in view of the restricted occurrence lack of interlayering different pyroxene affinities clinopyroxene in gabbro and orthopyroxene in peridotite pyroxenite and wide compositional gap between mafic and ultramafic intrusions we favour the later scenario peridotite pyroxenite interpreted as part of a mesoarchean layered ultramafic complex intruded the mafic volcanics layered gabbro leucogabbro anorthosite also intruded into the basaltic rock separate from the ultramafic complex the intrusion of protolith of the tonalite gneiss then dismembered the mafic and ultramafic sequences the results of the present study highlight the need for detailed evaluation of spatially associated mafic ultramafic rock remnants in high grade terranes they need not be genetically related but could be part of different magmatic episodes such exercise has implications in properly understanding the geodynamic setting of formation of these archean upper mantle derived rocks the current arguments polarised between two end member settings plate margin versus intraplate setting

the messinian post evaporitic deposits of the gafares area almeria nijar basin se spain a new view of the lago mare facies abstract the exceptional exposures of the evaporitic and post evaporitic messinian deposits in the gafares area ne almeria nijar basin se spain make it possible to elucidate those processes affecting this region during the critical period of the messinian salinity crisis the contact between the pre evaporitic and the evaporitic units is an erosional unconformity the transition from the evaporitic to the post evaporitic units is gradual since the gypsum beds of the evaporitic unit thin upward and the siliciclastic interbeds concomitantly thicken thus passing gradually to the overlaying post evaporitic unit the presence of globorotalia miotumida group in the last pelitic intercalation of the evaporitic unit as well as throughout the post evaporitic one indicates a messinian age the post evaporitic unit consists of a variety of sediments formed in continental and marine settings continental facies are characterised by fluvial channel filled conglomerates and alluvial plain sands and silts marine sediments are represented by silty marls with foraminifers a river dominated delta developed in the transitional zone at the nw edge of the gafares area localised fan delta deposits coming from the ese also occur in the southeastern part of the study area microbial carbonates locally colonised the fan delta conglomerates during the deposition of the lower half of the post evaporitic unit sedimentation took place in a sheltered embayment with restricted water circulation and relatively isolated from the mediterranean sea by an e w trending sill located at the south of the study area in this palaeogeographic context freshwater influx from the delta exerted a certain influence on the distribution of microorganisms thus brackish settings developed close to the river outflows that were occupied by caspibrackish ostracod assemblages the presence of gastropods of the family cerithiidae as well as fishes attributable to the genus aphanius organisms that preferentially inhabit sheltered lagoons is consistent with these settings beyond the freshwater influx foraminifers dominated the microfossil assemblages in the upper half of the post evaporitic unit microfossil assemblages dominated by planktonic forms are consistently found thus revealing a better connection of the semi enclosed gafares area with the marine domain this is related to the deepening of the sill due to a progressive rise of the sea level the continental and brackish deposits zorreras like facies have been equated with the lago mare facies which were supposed to spread throughout the whole mediterranean at the end of the messinian nevertheless in the gafares area these deposits change laterally to and interbed with marine deposits this stratigraphic architecture and facies relationship has two important implications on the one hand marine waters at the latest messinian occupied at least the western mediterranean predating the long claimed early pliocene deluge on the other hand the continental brackish lago mare facies were spatially restricted as a consequence neither the presence of the caspibrackish ostracods nor the continental brackish facies can be plausibly taken to support the hypothesis that widespread lago mare facies occupied the whole mediterranean synchronously at the end of the messinian therefore this type of facies is expected to be found albeit with varying degrees of development in marginal basins at different times but not throughout the mediterranean

holocene late pleistocene non tropical carbonate sediments and tectonic history of the western rift basin margin of the southern gulf of california abstract using high resolution seismic reflection profiling and dating of 1 shallow marine vibracores and 2 sediments collected from uplifted marine terraces we reconstruct the tectonic history and sediment accumulation patterns of holocene to late pleistocene warm temperate to subtropical carbonates in the southern gulf of california mexico the study was conducted in the vicinity of la paz where carbonates form along the fault bounded narrow western shelf of the tectonically active gulf of california rift basin the non tropical nature of the setting is responsible for 1 poor cementation of the bioclastic carbonates and 2 a composition which is dominated by rhodoliths coralline red algae corals and mollusks unrimmed carbonate flats forming in small pocket bays and a rhodolith bioherm which has a surface area of more than 20 km2 and is up to 16 m thick constitute the major carbonate factories holocene carbonate accumulation rates were deduced from seismic and core data and are highest on the rhodolith bioherm 260 cm ka and in subtidal zones of pocket bays 210 cm ka and lowest on the inner and middle shelf 100 cm ka taken together rates of carbonate accumulation are intermediate in magnitude between higher rates recorded in fully tropical carbonate settings and lower rates typical of cool water carbonates seismic reflection profiles demonstrate that isla espiritu santo in the center of the study area is a west dipping fault block which is tectonically influenced by two distinct faults the la paz and espiritu santo faults the latter fault accommodates at least 700 m of east side down normal offset and forms a steep eastern escarpment leading into the la paz slope basin some of the sediments produced in the shallow carbonate factories of the narrow la paz shelf are transported across this escarpment and are redeposited in the slope basin at a water depth of 750 m uranium series dates of marine terraces exposed on isla espiritu santo indicate that late pleistocene uplift along the eastern side of the island could be as high as 310 mm ka whereas downdropping along the western side of the island occurred at a rate of up to 15 mm ka isla espiritu santo therefore constitutes part of the uplifted shoulder of the western margin of the gulf of california rift basin patterns of vertical tectonic movements of isla espiritu santo together with fault offsets on the surrounding seafloor and slump features on steep submarine slopes point to continuous activity of the la paz and espiritu santo faults results of this study will assist in recognizing and interpreting similar settings along ancient non tropical rift basin margins worldwide and especially in the neogene of the gulf of california

diagenetic evolution of tortonian temperate carbonates close to evaporites in the granada basin se spain abstract the granada basin se spain is a small basin located in the central part of the betic cordillera structured as such in the late tortonian and initially connected to the atlantic ocean and to the mediterranean sea during the late tortonian normal marine conditions prevailed leading to the deposition of skeletal carbonate sediments on platforms around structural highs the marine connections were later interrupted first to the atlantic ocean and then to the mediterranean sea and a thick evaporite sequence marking the transition from marine to continental conditions was deposited during the latest tortonian in this work the diagenetic evolution of the tortonian temperate carbonates ttc underlying and close to the evaporite bodies is revealed and discussed the diagenetic study includes petrographic analyses conventional petrography cathodoluminescence and fluorescence geochemical analyses major minor and trace elements and 13c and 18o stable isotopes and microthermometry of fluid inclusions in the ttc marine diagenetic processes such as micritization and fibrous calcite cement precipitation and mechanical compaction took place during or just after deposition eogenesis an initial burial event mesogenesis 1 is characterized by 1 stabilization of the temperate water carbonates by freshwater and 2 porosity occlusion via precipitation of low mg bladed and syntaxial mosaic calcite cements the ttc were then subaerially exposed or got close to the surface during evaporite deposition and underwent pedogenesis mg smectite infiltration and pyrite formation telogenesis 1 subsequent brine related diagenetic alterations such as dolomitization and silica halite and sylvite replacements of carbonate grains occurred during a second burial episode mesogenesis 2 concomitant with the messinian lacustrine deposition this being followed by chemical compaction stylolite formation finally the area was uplifted and the ttc exhumed microstalactitic dripstone and fibre whisker calcite cement precipitation and extensive dissolution relate to this pliocene quaternary late event telogenesis 2 in the study case diagenetic history is closely linked to basin evolution as diagenetic pathways of carbonate rocks were related to major geodynamic events including basin restriction leading to evaporite deposition and several episodes of subsidence and uplift up to now only very few diagenetic studies have attempted to demonstrate this correlation between diagenetic history and basin evolution

atlantic water in the strait of sicily historical and recently acquired hydrographic and current meter data are used to study the behavior and the annual cycle of the surface layer of atlantic water aw within the sicilian channel section of the strait of sicily from january to march the surface layer isotherms and isohalines are much more steeply sloped toward the african coast the transition from winter to summer stratification occurs during the april to may period and by july both temperature and salinity isolines are quite horizontal the seasonal variations in temperature and salinity can be characterized by corresponding values of mean velocity mean kinetic energy and eddy kinetic energy during winter these values increased 2 3 times their summer values hydrographic and satellite data show that the stream of warmer and less saline aw enters the strait of sicily close to the tunisian coast south of cap bon the aw appears to decelerate forming meanders and detached parcels or small rings these structures are seen in satellite images more often during winter than summer when the aw current in the strait of sicily is more energetic

facies analysis and palaeoenvironmental interpretation of the late oligocene attard member lower coralline limestone formation malta the oligocene represents a key interval during which coralline algae became dominant on carbonate ramps and luxuriant coral reefs emerged on a global scale so far few studies have considered the impact that these early reefs had on ramp development consequently this study aimed at presenting a high resolution analysis of the attard member of the lower coralline limestone formation late oligocene malta in order to decipher the internal and external factors controlling the architecture of a typical late oligocene platform excellent exposures of the lower coralline limestone formation occurring along continuous outcrops adjacent to the victoria lines fault reveal in detail the three dimensional distribution of the reef associated facies a total of four sedimentary facies have been recognized and are grouped into two depositional environments that correspond to the inner and middle carbonate ramp the inner ramp was characterized by a very high energy shallow water setting influenced by tide and wave processes this setting passed downslope into an inner ramp depositional environment which was colonized by seagrass and interfingered with adjacent areas containing scattered corals the middle ramp lithofacies were deposited in the oligophotic zone the sediments being generated from combined in situ production and sediments swept from the shallower inner ramp by currents compositional characteristics and facies distributions of the attard ramp are more similar to the miocene ramps than to those of the eocene an important factor controlling this similarity may be the expansion of the seagrass colonization within the euphotic zone this expansion may have commenced in the late oligocene and was associated with a concomitant reduction in the aerial extent of the larger benthonic foraminifera facies stacking pattern analysis shows that the depositional units parasequences at the study section are arranged into transgressive regressive facies cycles this cyclicity is superimposed on the overall regressive phase recorded by the attard succession furthermore a minor highstand correlated with the ru4 ch1 sequence and subsequent minor lowstand ch2 sequence have been recognized the biota assemblages of the attard member suggest that carbonate sedimentation took place in subtropical waters and oligotrophic to slightly mesotrophic conditions the apparent low capacity of corals to form wave resistant reef structures is considered to have been a significant factor affecting substrate stability at this time the resulting lack of resistant mid ramp reef frameworks left this zone exposed to wave and storm activity thereby encouraging the widespread development of coralline algal associations dominated by rhodoliths

mesoarchean ttg magmatism from the northeastern margin of the kaapvaal craton southern africa arguments for an exotic terrane remnant of pilbara craton abstract high grade terranes along archean cratonic margins either represent remobilized equivalents of the adjacent low grade domain or an exotic entity which accreted to the developing craton this study addresses this debate for the southern marginal zone high grade terrane along the northeastern margin of the kaapvaal craton the hout river shear zone separates the high grade terrane from the adjacent low grade pietersburg block of the kaapvaal craton tonalite trondhjemites of the baviaanskloof gneiss unit constitute the dominant rock in the southern marginal zone both pyroxene bearing and pyroxene absent variants occur locally the granitoids are affected by anatectic and metasomatic overprints magmatic textures are better preserved in the massive granitoids u pb zircon analyses of two orthopyroxene bearing granitoids gave mesoarchean crystallization ages 3088 11 ma massive 3121 9 ma banded however overprint ages differ with 2706 50 34 ma from the massive variety and 1925 19 ma 1976 11 ma from the banded variety the syn tectonic 2 71 ga is interpreted as metamorphic overprint age while the post tectonic 2 ga represent age of local overprint available geochemical data on the baviaanskloof granitoids are similar to archean ttgs a possible spatial temporal transition from 3 13 ga low pressure through 3 12 2 98 ga medium pressure to 2 92 ga high pressure ttg is delineated from the northwest towards the southeastern southern marginal zone this trend is compatible with the southward directed polarity of accretion events recognised in the adjacent low grade pietersburg block we argue that the northeastern margin of the kaapvaal craton north of the hout river shear zone is an exotic terrane because 1 the baviaanskloof granitoid event 3 1 2 9 ga with peak at 3 1 ga is older than the accretion episodes 2 97 2 92 ga with peak at 2 95 ga and 2 87 2 84 ga with peak at 2 86 ga in the adjacent pietersburg block 2 the younger 2 86 ga event occurs closer to the hout river shear zone while the older 2 95 ga event was away from it and 3 contemporaneous 3 1 3 0 ga detrital zircons are absent in greenstone belts of the pietersburg block that are proximal to the hout river shear zone possible connection to rocks of similar age from the pilbara craton as part of the vaalbara supercraton is explored

nearshore temperate carbonate depositional systems lower tortonian agua amarga basin southern spain implications for carbonate sequence stratigraphy abstract the bryozoan rich lower tortonian carbonates of the agua amarga basin in southern spain province of almeria provide an example of sediments formed in a nearshore non tropical depositional setting based on data derived from logging of sections and from field mapping these lower tortonian carbonates form a depositional sequence which is subdivided into several depositional systems a lowstand systems tract which consists of volcaniclastic fan deltas and washover deposits formed on the leeward side of a basement shoal which delimited the basin towards the south a transgressive systems tract which is characterised by a landward encroachment of deposits is represented by submarine bars and dune deposits a highstand systems tract consists of progradational beach deposits owing to strong reworking and re distribution of the particles by currents and waves microfacies differentiation of the deposits in poor these tortonian non tropical carbonates display a style of deposition similar to siliciclastics suggesting that sequence stratigraphic concepts derived from tropical carbonates do not apply to non tropical carbonates

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

the pikwitonei granulite domain manitoba a giant neoarchean high grade terrane in the northwest superior provincethis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh n machado t e krogh and w weber are deceased the pikwitonei granulite domain located at the northwestern margin of the superior province is one of the largest neoarchean high grade terranes in the world with well preserved granulite metamorphic assemblages preserved in a variety of lithologies including enderbite opdalite charnockite and mafic granulite u pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities natawahunan lake sipiwesk lake and cauchon lake the u pb age results indicate that some of the layered enderbite gneisses are mesoarchean 3 4 3 0 ga and the more massive enderbites are neoarchean the high grade metamorphic history of the pikwitonei granulite domain is complex and multistage with at least four episodes of metamorphic zircon growth identified 1 2716 1 3 8 ma 2 2694 6 0 6 ma 3 2679 6 0 9 ma and 4 2642 5 0 9 ma metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent corresponding

components analysis of sediment composition in early miocene temperate carbonates from the austrian paratethys abstract causal factors controlling the sediment composition in the early miocene zogelsdorf formation of lower austria have been derived using r mode principal components analysis on the point counts of sediment components in thin sections four factors are found to be primarily responsible for the distribution of sedimentary components which comprise coralline algae bryozoans bivalves barnacles echinoderms foraminifers brachiopods serpulids as well as terrigenous components and muddy matrix the interpretation of factors is based on the relationships of these components within the factors the ecology of the calcareous organisms the distribution of components within the formation and the comparison to similar recent and fossil sedimentary environments 1 the supply of terriginous sediments controls the distribution of bryozoans and serpulids 2 increased hydrodynamic energy is advantages for bivalves and barnacles 3 the occurrence of seagrass might explain an increased presence of foraminifers and echinoderms 4 the distribution of coralline algae is controlled by light intensity which is dependent on water depth and suspension load biological interactions with shell incrustations by epibionts intensify the relationships of components within the above mentioned associations

altimetric signal and three dimensional structure of the sea in the channel of sicily the 1996 altimeter synoptic mesoscale plancton experiment alt symplex was specifically designed to perform in situ measurements simultaneous with the passage of topex poseidon t p and ers 2 over selected tracks in the central and eastern sicily channel this experiment made it possible to have for the first time a validation of altimetry with in situ data over the mediterranean where weak dynamics results in a modest sea elevation rarely exceeding 10 cm historical infrared and altimetric satellite data were first analyzed in order to study the variability of the circulation in the area the comparative and integrative analysis of simultaneous satellite data and in situ measurements permitted investigation of the relation between the altimeter derived surface topography and the three dimensional structure of the sea the pearson correlation coefficients between altimeter data and dynamic heights along track resulted to be 0 72 0 89 t p and 0 88 ers 2 when using conventional repeat track analysis for t p a correlation value of 0 87 was found for time differences computed basing on a collinear analysis technique this analysis also led to the identification of a strong barotropic component of the velocity field located near the sicilian continental shelf where it is responsible for approximately 60 of the signal

an epeiric ramp low energy cool water carbonate facies in a tertiary inland sea murray basin south australia the murray supergroup records temperate water carbonate deposition within a shallow mesotrophic oligo miocene inland sea protected from high energy waves and swells of the open ocean by a granitic archipelago at its southern margin rocks are very well preserved and exposed in nearly continuous outcrop along the river murray in south australia most facies are rich in carbonate silt contain a background assemblage of gastropods especially turritellids and infaunal bivalves and are packaged on a decimetre scale defined by firmground and hardground omission surfaces bioturbation is pervasive and overprinted resulting in rare preservation of physical sedimentary structures facies are grouped into four associations large foraminiferan bryozoan echinoid bryozoan mollusc and clay facies interpreted to represent shallow water 50 m deposition under progressively higher trophic resource levels from low mesotrophy to eutrophy and restricted marine conditions from relatively offshore to nearshore regions a large scale shift from high to low mesotrophic conditions within lower miocene strata reflects a change in climate from wet to seasonally dry conditions and highlights the influence terrestrially derived nutrients had upon this shallow land locked sea overall low trophic resource levels during periods of seasonally dry climate resulted in a deepening of the euphotic zone a widespread proliferation of foraminiferan photozoan fauna and a relatively high carbonate productivity inshore heterozoan facies became progressively muddier and restricted towards the shoreline in contrast periods of wet climate led to rising trophic resource levels resulting in a shallowing of the euphotic zone a decrease in epifaunal and seagrass cover and widespread development of a mostly heterozoan biota dominated by infaunal echinoids rates of carbonate production and accumulation were relatively low the murray basin is best described as an epeiric ramp wide facies belts developed in a shallow sea on a low angled slope reaching many hundreds of kilometres in length grainy shoal and back barrier facies were absent internally generated waves impinged the sea floor in offshore regions and because of friction along a wide and shallow sea floor created a low energy expanse of waters across the proximal ramp storms were the dominating depositional process capable of disrupting the entire sea floor

climatic signatures in shallow water carbonates high resolution stratigraphic markers in structurally controlled carbonate buildups late miocene southern spain abstract neogene intramontane basins of the betic cordillera se spain have a complex tectonic and sedimentary history in the eastern almeria province movements along the carboneras strike slip fault system n50 e and its conjugated faults n140 e controlled the distributions of depocenters and stratigraphic architectures of late miocene sediments we have chosen the agua amarga area 1 to exemplify the potential of climatic signatures of biogenic associations in shallow water carbonates for high resolution chronostratigraphic correlations and 2 to describe stratigraphic architectures and facies distributions in a setting subject to synsedimentary tectonics the southwestern margin la higuera is formed by a gentle ramp dipping in a n50 e direction late tortonian and messinian deep and shallow water carbonates divide into eight depositional units neptunian autoclastic breccias neptunian dikes and submarine biogenic pavements unit h 1 document rapid flooding of the basin during a phase of intense tectonic dilatation late tortonian units h 2 7 late tortonian early messinian form wedges which dip and thicken in a basinward direction little lateral facies change and internal stratifications parallel with the basal surfaces imply deposition on a subhorizontal substratum the upper bounding surfaces are erosional and formed by truncation of tilted strata from wedge to wedge the angle of dip decreases upsection and is near zero in between the last units which have parallel bounding surfaces and rest subhorizontally unit h 7 8 this pattern results from cumulative rotational uplift which decreased upward but does not necessarily exclude vertical displacements of the youngest units the southeastern margin of the basin is mostly eroded but may have trended n50 e as indicated by the distribution of slumped reef blocks a relict of the margin is preserved at mesa de roldan and exhibits steep clinoforms dipping towards the nw n300 e and w n250 e synsedimentary tectonics are documented by nine shallow marine depositional units unit r 1 conglomerates associated with neptunian dikes units r 2 9 skeletal carbonates and reefs bounded by deep erosion surfaces and or truncation of individual units along a miocene fault at both flanks the shallow water biofacies record an identical trend of climatic warming and therefore bracket a similar amount of time temperate conditions prevailed during the latest tortonian and earliest messinian whereas tropical temperatures existed during the early and late messinian and perhaps during the tortonian messinian transition the number of depositional units reflecting these climatic periods of time and the stratal geometries however differ at both sites and within the basin which implies spatial variations in the generation of accomodation space on independent fault blocks these data also suggest that there cannot be any universal sequence stratigraphic model for late miocene shallow water carbonates of se spain and that the downstepping geometries observed in many other early messinian reefs of the betic cordillera reflect tectonic uplift

role of climate in partial drowning of the queensland plateau carbonate platform northeastern australia abstract ocean drilling program leg 133 core data samples and geophysical data logs and seismics were analyzed to document late miocene early pliocene partial drowning of the queensland plateau carbonate platform off northeast australia the modern plateau consists of a mosaic of pinnacle reefs and larger 10 50 km reefs representing relicts of early to middle miocene buildups late miocene early pliocene floatstones packstones and mudstones rich in the larger benthic foraminifers lepidocyclina and cycloclypeus drilled in a transect of sites across the drowned margin of a middle miocene buildup show that the late pliocene partial drowning of the platform was preceded by 4 myr of neritic carbonate deposition without any reefs the carbonate factory was unable to aggrade to sea level during this period as indicated by the lack of any shallowing trend in the succession monitoring of the miocene to recent neritic shedding pattern on the windward and leeward side of a pinnacle reef on the queensland plateau supports this interpretation shedding on the leeward side of the reef which records periods of active reef growth played a minor role during the late miocene increased during the pliocene and reached very high values during the late pliocene and pleistocene shedding on the windward side of the reef which was active during lowstands of relative sea level occurred during the late middle early late miocene and during the pliocene quaternary the data presented here when combined with paleoceanographic data points to low surface water temperatures 17 19 c as a major factor which suppressed reef growth during the late miocene early pliocene period

high resolution chemostratigraphy of a miocene wedge top carbonate shelf san marino fm northern apennines italy the major role of the monterey global fertility event abstract the evolution of the san marino carbonate succession developed on a wedge top basin of the northern apennines during the middle miocene torriana outcrop marecchia valley was studied through a high resolution stable isotope analysis on different carbonate components a marked positive carbon isotopic excursion is identified at ca 16 ma the excellent correlation of the san marino 13c carbonates with the global 13c reference curve from zachos et al 2008 allows to link the marked positive 13c present in the san marino section with the global carbon isotope maximum of the monterey event subordinate long eccentricity driven 13c cycles 405 kyr as recorded by holbourn et al 2007 were also identified the correlation with carbon signatures of coeval successions of the mediterranean region shows that this main carbon isotopic excursion at the burdigalian langhian boundary is widely recorded and predates the crisis of these heterozoan shelves the demise of the san marino shelf resulted from a combination of global and regional factors that controlled the nutrient budget the detrital input and the subsidence of the basin the high resolution chemostratigraphy of san marino succession shows that even though the shelf evolved in the complex setting of a wedge top basin which should be largely influenced by local factors i e tectonic subsidence and detrital input it records the monterey event and its eccentricity paced rhythms with high precision this highlights the strong connection of the monterey event with the development and subsequent demise of shallow water carbonate depositional systems in the mediterranean irrespective of variable and changing local conditions

temperate skeletal carbonate sediments on scott shelf northwestren vancouver island canada abstract scott shelf 2000 km 2 centred at scott islands northwestern vancouver island is mainly shallower than 150 m topographically diversified and floored by bedrock outcrops and terrigenous lithic gravels and sands left stranded following the post glacial rise in sea level 13 000 yrs b p it lies in a zone of vigorous wind wave currents and strong tidal flows but is largely starved of modern terrigenous sediment as a consequence it is slowly accumulating a thin discontinuous blanket of clean skeletal carbonate sands and gravels admixed to varying degrees with the underlying terrigenous deposits principal skeletal contributors are infaunal bivalves on coarse sandy and gravelly substrates barnacles on low amplitude gravelly ridges bryozoans on bedrock outcrops and boulders and benthic foraminifera on fine sands in deep 100 m waters south of the scott islands living carbonate benthos are scattered and generally sparse occupying specific ecologic niches and the shelf wide rate of carbonate production is low skeletons are fragmented transported and mixed during storms and are concentrated within bedrock hollows and crevices and shallow depressions between gravel ridges where infaunal bivalves are abundant the carbonates are dominated by aragonite but otherwise the skeletal hashes are predominantly calcitic many grains and especially aragonitic ones are corroded and weakened by epilithic and endolithic bioerosion and probably also by marine and dissolution the most corroded shells have ages of only about 1000 yrs so that their preservation potential is low the character of scott shelf skeletal carbonate deposits reflects their temperate latitude cold water heritage

carbonate dissolution in nearshore terrigenous muds the role of physical and biological reworking because shallow marine sediments generally underlie waters which are saturated with respect to arago nite and calcite physical chemical dissolution of carbonate in these environments is sometimes discounted the present investigation as well as others before it show such an assumption to be unwarranted in this case study of terrigenous mud deposits from long island sound u s a demonstrates extensive dissolution of molluscan shell debris near the sediment water interface net buildup of carbonate varies significantly between different regions of the sound despite fairly uniform production of shell debris and similar total sedimentation rates aside from this apparent discrepancy between rate of supply and net carbonate sedimentation evidence for carbonate dissolution comes from the pitting of shells elevated ca levels in pore water and calculated undersaturation of pore waters with respect to carbonate minerals models of pore water distributions and carbonate supply imply dissolution ra

vast amount of accommodation space controlled evolution of a continuous pliocene pleistocene mixed cool water carbonate siliciclastic prograding wedge in the bay of oran western mediterranean abstract the bay of oran is part of the northern algerian continental margin located in the western mediterranean sea between europe and northern africa a regional terrace in ca 320 m water depth described in earlier studies and a second deeper located one 1200 m water depth provide an unusually vast amount of accommodation space for an observed prograding wedge seismo stratigraphic interpretation of high resolution reflection seismic data show different phases of mixed cool water carbonate siliciclastic deposition ia initial aggradation with low dipping foreset deposition during early pliocene relative sea level highstand ib deposition transitions to progradation when aggradation reaches the base level iia once progradation reaches the shelf break terrace deposition is reduced to coarse fraction foreset deposits until it ceases entirely iib finer sediments are bypassed and start to aggrade on the lower slope terrace until deposits reach the shelf terrace depth iii due to accommodation space prolongation progradation recommences phase iia and phase iii deposits are separated by a hiatus a drop in mean sea level during the mid pleistocene will have caused the base level to fall below the upper strata hence causing some reworking and redeposition however sea level variations are not considered to be a main controlling factor of the depositional sequences the evolution of this continuous pliocene pleistocene mixed cool water carbonate siliciclastic prograding wedge is instead attributed to the controlling factor of this unusually vast amount of accommodation space in closest proximity to the sea floor sparse recent sedimentation in form of 5 10 m thick sediment lobes can be observed in subbottom profiler data only from a tectonic point of view a prolongation of the yusuf fault into the survey area though expected by other authors could not be supported with the available dataset

salt deposition and brine evolution in the granada basin late tortonian se spain abstract a group of sedimentary basins in the betic chain were formed during the middle late miocene as a result of the closure of the tethys during the alpine orogeny in the late miocene tortonian messinian the connections between the atlantic ocean and mediterranean sea were interrupted and those basins hosted major evaporites the granada basin an inner basin located far from the mediterranean contains a thick rock salt deposited during the latest tortonian in the transition from marine to non marine conditions in the centre of the basin three halite bearing units overlie a basal anhydrite bed the lower halite unit the intermediate sandstone unit and the upper halite unit fluid inclusion compositions and bromine concentrations in halite together with stable isotopes 34 s sulfate 18 o sulfate and 87 sr 86 sr indicate a mixture of different inflow waters in the granada basin beginning with a marine lagoon that evolved into a salt pan strongly isolated from the sea saline waters evolved from sulfate rich marine derived to sulfate depleted non marine brines influenced by the addition of cacl 2 rich inputs these cacl 2 rich waters were probably linked to thermal fluids associated with a major crustal fracture system crevillente or cadiz alicante fault system that cuts through the granada basin

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

complex empirical orthogonal functions analysis of ers 1 and topex poseidon combined altimetric data in the region of the algerian current maps of sea level anomalies sla relative to the 1993 annual mean sea level combine the data from the two altimetric missions ers 1 and topex poseidon during the overlap period october 1992 to december 1993 these regular maps in space and time of residual sea level every 10 days on a 0 2 regular grid are used in the region of the algerian current where the mesoscale eddies are of primary importance to the circulation of all the mediterranean water masses they are first compared with ers 1 along track scanning radiometer sea surface temperature images to get information on two anticyclonic eddies produced by instabilities of the algerian current and visible in both infrared and altimetric data sets then an analysis of complex empirical orthogonal functions ceofs is performed on the sla data set to see the correlation of the different dynamic features of the observed variability the ceof analysis is applied to the complex time series formed from the original sla time series and their hubert transforms to separate the variability into spatially coherent modes the spatially correlated signal in the study area 0 15 e and 35 40 n was found to be dominated by the first two ceofs these first two modes explain nearly 85 of the variability with 80 of the total variance for the first one and 5 of the total variance for the second one the temporal phase of the first mode indicates that a constant frequency of one cycle per year is clearly dominant corresponding to the seasonal signal the strongest amplitude is obtained in the southern part of the channel of sardinia and south of the strait of sicily the temporal amplitude and the temporal phase of the second mode show a periodicity of about 6 months which appears to be associated with the variability of the algerian current as the phase isolines are parallel to the mean current path along the algerian coast the strongest amplitude of the second mode is located near the african coast at 4 e and 8 e these two points of high variability could correspond to eddy detachments from the main current

the behaviour of nd and pb isotopes during 2 0 ga migmatization in paragneisses of the central zone of the limpopo belt south africa and botswana we have carried out major and trace element analyses and nd pb isotope measurements on different components of two migmatite outcrops in the limpopo belt lose quarry botswana and palala south africa in order to assess the effect of migmatization during a high grade metamorphic event on sm nd systematics and nd model ages the outcrops studied are located in the mahalapye tshipise straightening zone at the south western part of the limpopo central zone close to its contact with the kaapvaal craton leucosomes of peraluminous granitic composition were formed by incongruent biotite melting in an fe rich metagreywacke lose quarry and in a metapelite palala respectively monazite u pb and garnet sm nd ages yield close to 2 0 ga for the high grade event confirming other recent work in the central zone the chemical compositions of the main mineral phases feldspar biotite and garnet indicate minimum melt formation at t 750 c and low pressure isocon plots and pb isotope data indicate that the partial melts are locally derived however lil trace element distribution between the leucosomes and paleosomes indicate the incomplete equilibration of the nascent melts with the residual feldspars and biotite in the paleosomes sm nd results on leucosomes and paleosomes of the metagreywacke migmatite show considerable scatter when calculated back to 2 0 ga the paleosomes fall in a narrow range of nd 4 and give tdm model ages between 2 45 and 2 66 ga the nd values of leucosomes are on average four units lower causing them to have apparent tdm ages of 2 7 2 92 ga on average 250 ma older than those of the paleosomes the ree th p2o5 and zr budgets of paleosomes and leucosomes indicate dominance of the lree by monazite and the hree by apatite incorporation of proportionally more monazite than apatite into the melt is inferred as the cause for the nd isotope discrepancy and hence the uncertainty of the average protolith mantle derivation age in contrast pb pb results define an apparent age of 2025 29 ma reflecting nearly full pb isotope exchange in the case of the palala metapelitic migmatite the nd values at 2 0 ga of all but two migmatitic constituents cluster between 7 and 9 5 pointing out extensive nd isotope equilibration during migmatization whereas the pb isotopes yield an errorchron date of 2311 65 ma indicating incomplete pb isotope exchange here garnet dominates the hree distribution whereas the lree are controlled by feldspar and monazite considering that nd isotope equilibration was nearly reached during migmatization nd model ages on the whole rocks represent a good approximation of those of the original protolith 3 0 3 2 ga in the regional context the pb isotope data from the lose quarry locality combined with the nd model age uncertain but within the range of 2 5 2 9 are reminiscent of the northern marginal zone of the limpopo belt and the southern zimbabwe craton whereas the nd and pb isotope data from the palala locality are typical for the limpopo southern marginal zone and the northern kaapvaal craton

observations on the circulation in the alboran sea using ers1 altimetry and sea surface temperature data abstract data from the altimeter onboard the european remote sensing satellite ersi was used to study the circulation of the alboran sea between 35 and 38 n 0 and 6 w this region is dominated by two anticyclonic gyres that are quasi stationary in space but at times collapse over periods as short as 9 days maps of sea level residual between february 1992 and december 1993 were created from the ersi data with high correlation between sea surface temperature and residual sea level in the eastern part of the alboran sea the spatially coherent signal was then extracted using the technique of complex empirical orthogonal analysis with the first three modes statistically significant the variability of the first complex empirical orthogonal function mode appears to be associated with the incoming jet through the straits of gibraltar with three time periods of high amplitude during the 1992 93 time frame the second and third modes appear to be associated with the variability of both the western and eas

non tropical carbonates related to rocky submarine cliffs miocene almeria southern spain abstract upper miocene deposits in the cabo de gata region se spain provide a unique opportunity to study cliff related temperate carbonates a poorly known type of fossil non tropical carbonates the studied submarine cliffs lie on the western flank of the monte ricardillo volcanic dome two main biocenoses colonised the cliff walls vertical and subvertical walls were either overgrown by vermetid gastropods forming a vermetid framestone or colonised by robust branching bryozoans which were reworked post mortem and accumulated as aprons at the foot of the submarine cliffs coralline algae in the vermetid build up indicate palaeodepths below 15 20 m depressions in front of the cliffs were occupied by nodular bryozoans and bivalves within these depressions barnacles settled on secondary hard substrates with progressive flooding of the depositional area substrate relief was filled in and a carbonate ramp with facies belts following the palaeobathymetric gradient evolved a delicate branching bryozoan facies occurs in the proximal part of the ramp and a nodular bryozoan bivalve facies in its middle part distally these deposits give way to a coralline algal facies these results provide a first insight into temperate water carbonates related to rocky submarine cliffs this work also reveals a major control of substrate relief on temperate carbonate facies and biofacies

a 2 051 ga anatectic event and peraluminous leucogranite from the mahalapye complex northern edge of the kaapvaal craton record of an effect of bushveld mafic magmatism abstract anatectic events and related leucogranites are rarely reported from precambrian large igneous provinces lips however their appearance is possible in relation to the intrusion of later pulses of mafic magmas into the earlier rocks silicic intrusive rocks associated with the 2 06 2 05 ga bushveld lip within the kaapvaal craton include granites syenites or granophyres this study reports syn bushveld partial melting of 2 061 ga diorite gneiss producing leucogranite from the mahalapye complex high grade terrane at the northern edge of the kaapvaal craton both the migmatitic diorite gneiss and associated leucogranite are crosscut by the 2 039 ga granodiorite the different stages of melting of the biotite bearing diorite gneiss from onset of melting to melt segregation are well preserved petrographic continuity between the leucosomes and concordant and discordant leucogranite bodies point to a melt flow accumulation network garnet formed after biotite during partial melting phase equilibria modelling and conventional thermobarometry indicate conditions of 730 c and 7 2 7 5 kbar for the anatectic event the predicted melt composition is peraluminous magnesian and alkali calcic that is comparable to the chemistry of leucogranites the low content of anatectic melt for the estimated p t condition corresponds to the occurrence of leucogranites as thin veins to dykes la mc icpms u pb zircon age of 2051 3 6 8 ma is interpreted to date the anatectic event the leucogranite exhibits co mingling structures with dyke like and sill like syn bushveld norite intrusions associated with diorite gneiss preferential accumulation of the leucocratic material along the contact of diorite gneiss and norite and the liquid liquid interface with the norite indicate the close age of leucogranite and norite this is supported by the la q icpms u pb zircon age of 2054 7 9 ma from the norite thus the partial melting of the diorite gneiss and formation of the leucogranites is argued as a response to bushveld mafic magmatism the present study shows that one of the causative agents of overprint event s in high grade terranes along archean cratonic margins can be mafic magmatism of similar age within the craton however in the case of lip related magmatism the footprints are restricted to terranes immediately adjacent to the cratonic margins

precise age of the platiniferous merensky reef bushveld complex south africa by the u pb zircon chemical abrasion id tims technique the bushveld complex south africa is the world s largest layered intrusion and host to the majority of the known resources of platinum group elements chromium and vanadium despite intensive study determining the precise crystallization age of the bushveld complex has proven to be difficult in this study zircon and rutile were identified in thin section and separated from a sample of pegmatitic feldspathic orthopyroxenite from the pge rich merensky reef west mine townlands shaft rustenburg section low u 21 105 ppm zircon occurs with interstitial biotite and is locally in direct contact with sulfide rutile occurs mainly as inclusions within or overgrowths on chromite especially in the chromitite stringers that bound the reef and also as acicular grains with biotite a u pb crystallization age of 2054 4 1 3 ma was determined from single crystal chemical abrasion id tims u pb dating of zircon and multigrain fractions of rutile yielded a u pb cooling age of 2055 0 3 9 ma integration of the merensky reef crystallization age with existing u pb age determinations for intrusions that pre and postdate emplacement and crystallization of the layered rocks of the bushveld complex indicate that magmatism occurred at ca 2054 ma and is contemporaneous with related magmatic activity across the northern kaapvaal craton of south africa and botswana

some features of the algerian current an analysis of infrared images leads to a new conception of the dynamics of the atlantic water in the algerian basin in situ current measurements are not yet available but coherent hypotheses are presented with the aim to initiate further experimental and theoretical works the algerian current flows steadily along the coast near 0 and becomes unstable near 1 2 e eddies of both signs are generated that are advected by the mean current but only the anticyclonic eddies increase in size diameter about 100 km as they extract more energy from the mean current they are advected more slowly and they may detach from the coast and drift for several weeks in the algerian basin they grow as deep as 1000m at least and they are able to pull lenses of intermediate water seaward from the sardinian continental slope coastal upwelling cells are generated near 1 2 e between the cyclonic and the anticyclonic eddies they are also advected by the mean current and are definitively not wind induced these turbulent structures create intense mixing between the atlantic and mediterranean waters which account for the large eastward gradient of salinity encountered in the surface layer therefore the algerian basin is characterized by a large mesoscale variability mainly due to the instability of the algerian current it appears to be a reservoir in which the water of atlantic origin is amassed and it forms a buffer zone which disconnects the flow of atlantic water coming in at gibraltar from the flow of hygly modified atlantic water exiting the basin through the strait of sardinia and into the ligurian sea

an isotopic and geochemical study of the northern kaapvaal craton and the southern marginal zone of the limpopo belt are they juxtaposed terranes abstract to test existing lateral accretion models for the archean kaapvaal craton in south africa metapelites and leucocratic granitoids from two different provinces the granulite facies southern marginal zone of the limpopo belt and the northern part of the adjacent greenschist to amphibolite facies kaapvaal craton have been studied both provinces resemble each other in terms of isotope and trace element characteristics they show a general depletion of incompatible elements independent from the grade of metamorphism this observation conflicts with theories involving mobilisation during granulite facies metamorphism a further common fingerprint is the unusually high cr and ni concentrations in the metapelites in addition they define a very narrow range of nd model ages 2 9 3 05 ga constraining the average crustal age of their cratonic source region the granitoid gneisses show somewhat larger variations of nd model ages indicating some age heterogenity within the crust however the data from both provinces completely overlap the southern marginal zone and the kaapvaal craton also show uniform low 207 pb 204 pb relative to their 206 pb 204 pb ratios that differ clearly from other southern african provinces these results support the view that the southern marginal zone represents a part of the kaapvaal craton exposed at a deeper crustal level it rules out a hypothesis that both provinces are separate amalgamated terranes furthermore there is very little difference between granitoids and metapelites which indicates that the latter largely derived from the former the exposure of the granulite facies metapelites of the southern marginal zone at the same level as the lower grade metamorphic rocks of the kaapvaal craton indicates uplift along a sharp tectonic boundary

carbonate deposition in restricted basins a pliocene case study from the central mediterranean northwestern apennines italy abstract carbonate depositional models are often informed by the study of platforms of good lateral continuity and sizable thickness because of their significance in petroleum geology however spatially restricted and more ephemeral carbonate accumulations can be an important but frequently overlooked component of otherwise siliciclastic dominated or mixed carbonate siliciclastic systems pliocene successions of tuscany and the tyrrhenian shelf northern apennines italy record a regional pulse of nontropical carbonate deposition across several restricted basins that has not yet been precisely constrained in its genesis and correlation this study investigates the stratigraphic expression of these carbonates to extract general aspects applicable to carbonate sedimentation across tectonically structured and physiographically complex shelves analyses of the extension composition facies and sequence stratigraphic architecture of the studied piacenzian carbonate units are complemented by new biostratigraphic and magnetostratigraphic data which document the slightly diachronous development of the carbonates within mediterranean planktonic foraminifera subzones mpl4b and mpl5a and magnetic polarity chron c2an the carbonate units are part of a regionally defined tectonically controlled sequence and represent the first transgressive unit overlying the basal sequence boundary but are also found in the regressive portion of the sequence collectively the units document the establishment of a shallow marine carbonate factory dominated by calcareous red algae the larger benthic foraminifer amphistegina and heterozoan skeletal components along the margins of a complex archipelago like coastal domain a review of the studied successions and other examples from the literature indicates that carbonate accumulations in settings with varied coastal physiography and active partitioning of depocenters are generally characterized by a spatial discontinuity b an overall skeletal association consistent across separate basins but with local variability in dominant skeletal components c preferential accumulation along basin margins or over isolated structural highs not in direct proximity to a hinterland with major drainage systems d predominance of low to moderate energy facies e preferential onset of deposition during transgression with possible development of mixed carbonate siliciclastic facies and f differing internal stratigraphic architecture tied to the specific subsidence and uplift history of coeval individual basins these observations built upon the study of mid piacenzian carbonate units from the central mediterranean contribute to the refinement of carbonate facies models and their application in the fields of sequence stratigraphy and basin analysis

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

the messinian guadalhorce corridor the last northern atlantic mediterranean gateway miocene tectonics with the last survi ving gateway occurring during the early messinian north west of malaga in the region of the guadalhorce river valley the guadalhorce gateway pro vided a significant control on messin ian pre evaporitic oceanic circulation in the mediterranean sea it acted as a major outflow channel of mediterra nean water into the atlantic and its closure induced water mass restriction and stratification in the western medi terranean immediately prior to the messinian salinity crisis abstract messinian marine deposits of the guadalhorce river valley in southern spain record evidence of the last northern gateway that existed between the mediterranean and the atlantic they comprise sandstones and conglomerates with unidirectional cross bed sets up to nearly 1 km long in their down sedimen tary dip direction these cross bed sets relate to extremely fast 1 0 1 5 m s 1 bottom currents flowing from the mediterra nean into the atlantic the guadalhorce gateway which had a maximum width of 5 km and a maximum water depth of 120 m was an important element controlling the messinian pre evaporitic oceanic circulation in the mediterranean sea as it acted as a major outflow channel its closure limited the exchange of water between the atlantic and the mediterranean to the rifian corridors of morocco inducing water mass restriction and stratification in the western mediterranean immediately prior to the messinian salinity crisis

submarine lobes and feeder channels of redeposited temperate carbonate and mixed siliciclastic carbonate platform deposits vera basin almeria southern spain temperate carbonates and mixed siliciclastics carbonates of upper tortonian age were deposited on a narrow platform along the southeastern margin of the sierra de los filabres on the western side of the vera basin the temperate carbonates were unlithified or were only weakly lithified on the seafloor and so were easily prone to synsedimentary removal part of the shelf sediments were eroded reworked and redeposited in submarine lobes up to 40 m thick and 1 km wide the lobes consist of turbiditic carbonates calcarenites and calcirudites and mixed siliciclastics carbonates which contain up to 30 siliciclasts derived from the sierra de los filabres to the northwest and abundant bioclasts of coralline algae bivalves and bryozoans in the inner platform the feeder channels of the lobes cross cut beach and shoal deposits and are filled by strings of debris flow conglomerates up to 3 m thick and a few metres wide these channels presumably developed as the continuation of river courses entering the sea further towards the outer platform they pass into large channels up to several hundred metres wide and 20 m deep steeply cutting into the horizontally bedded strata of the platform significant quantities of platform sediment were removed by erosion during their excavation once abandoned they were filled by new platform sediments further towards the basin the channels associated with the lobes exhibit lateral accretion and internal cut and fill structures and are intercalated between hemipelagic deposits the channel filling sediments are in this latter case coarse grained carbonates and mixed siliciclastics carbonates lobe development concentrated first at cortijo grande on the western side of the

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

archaean to proterozoic crustal evolution in the central zone of the limpopo belt south africa botswana constraints from combined u pb and lu hf isotope analyses of zircon a combined set of u pb and lu hf in situ laser ablation icp mc ms zircon analyses were obtained from orthogneisses and granitoids in the central zone of the limpopo belt which comprises the beit bridge and mahalapye complexes the results indicate that by combining the two isotope systems primary magmatic zircon domains can be distinguished from those formed during later metamorphic events even if the distinct zircon domains underwent multiple pb loss and the texture age relationships as obtained by cathodoluminescence images and u pb analyses are ambiguous furthermore the applied technique allows distinction of zircon grains formed in juvenile magmas from those generated by melting of older continental crust or affected by substantial crustal contamination the combined u pb and lu hf data reveal that the sand river gneiss suite of the beit bridge complex was emplaced at 3283 8ma and formed from melting of an older archaean crust which was derived from a depleted mantle source at around 3 65 ga the hafnium model age tdm is significantly older than those obtained from zircons from numerous neoarchaean granitoids of the beit bridge complex comprising the singelele gneiss 2647 12ma the bulai granite 2612 7ma the regina gneiss 2649 9ma and two samples of the zanzibar gneiss 2613 6ma these granitoids show initial ehf t values between 0 5 and 7 1 which correspond to initialtdm between 3 46 and 3 01ga these variable tdminitial and ehf t initial values are interpreted to be the result of different mixtures of reworked 3 65 ga palaeoarchaean crust with juvenile magmas extracted from the depleted mantle during the neoarchaean at 2 65 ga this conclusion is supported by results obtained from the mahalapye complex which was affected by migmatization and granite intrusions during the palaeoproterozoic at 2 02 2 06 ga the mokgware granite 2019 9ma contains zircon xenocrysts with pb pb ages of 2 52 2 65 ga and 2 93 ga and hafnium model ages of 3 0 3 4 ga indicating that this granite is derived from remelting of archaean crust in contrast uniformtdm hf initial ages of 2 61 2 67 ga obtained from a diorite gneiss 2061 6ma of the mahalapye complex indicate that its protolith may have been formed from remelting of a neoarchaean juvenile crust variable ehf t initial values from 3 7 to 6 3 of zircon cores 2711 11ma in an adjacent leucosome also support a model of mixing of juvenile mantle derived matter with older crust in the neoarchaean

recent advances in observing the physical oceanography of the western mediterranean sea the mediterranean sea has been investigated intensively since the early nineties using modern techniques and collaborative approaches this overview summarizes some of the resulting advances that were made concerning the physical oceanography of the western mediterranean the water mass formation processes are now much better understood and have been quantified to a large extent the boundary conditions of the system in terms of surface fluxes and strait transports can be determined with improved accuracy thus enabling future investigation of interannual variability the dynamics of the surface and intermediate layers have revealed a variety of eddy and mesoscale processes that are important for the circulation and spreading of water masses the deep circulation is being investigated with lagrangian techniques tracers and floats first results show a large component of the deep water originating from the tyrrhenian sea and intense cyclonic and anticyclonic eddy flows

ultrahigh temperature granulites and magnesian charnockites evidence for neoarchean accretion along the northern margin of the kaapvaal craton abstract shrimp u pb analysis of zircon grains from an ultrahigh temperature mg al granulite from the northern margin of the kaapvaal craton southern marginal zone shows ages of 2 72 ga for the peak metamorphism geochemical characteristics of syn tectonic charnockites in the area are similar to magnesian charnockites typically formed in subduction settings in contrast to the prevailing models on peak metamorphism in the context of neoarchean continent collision between archean zimbabwe and kaapvaal cratons resulting in the formation of the limpopo complex we relate the neoarchean events to the accretion of this marginal block to the rest of the kaapvaal craton in this model the subduction event is marked by the formation of magnesian charnockites and the ultrahigh temperature metamorphism dates the collision event

observations on the long period variability of the gulf stream downstream of cape hatteras to examine the long period variability of the gulf stream sea level residuals relative to a 2 year mean sea level in the gulf stream downstream of cape hatteras between 75 w and 60 w longitude are used residuals as derived from geosat altimetry between november 1986 and december 1988 were gridded in space and time at a temporal resolution of 10 days and spatial resolution of 1 4 complex empirical orthogonal function ceof analysis was applied to the data set to extract the spatially correlated signal with the original data sub sampled to 1 2 in addition to determining the space time scales and propagation characteristics of the different modes wavenumber frequency spectral techniques were used to separate the variability into propagating and stationary components the ceof technique applied to the data set indicated that the first four ceof modes accounted for 60 of the variability and were found to be above the noise level 99 of the time ceof 1 was associated with westward propagation at 5 km d at a wavelength of 2000 km and eastward propagation at 1 2 km d centered at a 500 km wavelength this first ceof is in good agreement with thin jet equivalent barotropic models which predict westward propagation for wavelengths greater than 1130 km a deflection of the wavelike pattern at 65 w also indicates a possible topographic effect a simple scaling of the effect of topography indicates that for length scales longer than the internal rossby radius of deformation the topographic term is at least of the same order of magnitude as the beta effect the second ceof was more broadbanded in wavenumber space with eastward propagation occurring in a wavenumber frequency band between 300 and 1400 km and 0 5 and 2 0 cycles yr the third ceof is similar in structure to the first but with less energy ceof 4 was clearly identifiable with higher frequencies than the first three with westward propagation at 4 km d the spatial location of this mode along with the westward propagation indicates possible influences from eddy stream interactions thus topography rossby wave dynamics and eddy stream interactions all appear to have a significant role in determining the space time scales and propagation properties of the long period response of sea level in the gulf stream

spatial structure of anticyclonic eddies in the algerian basin mediterranean sea analyzed using the okubo weiss parameter abstract three algerian eddies open sea big anticyclonic eddies in the algerian basin western mediterranean sea are studied in detail using altimetric and in situ data to characterize their spatial structure we make use of the okubo weiss parameter which allows to separate the flow into vorticity dominated and deformation dominated regions the application of this parameter to geostrophic velocity fields obtained from sea level anomaly maps show that the observed eddies have a spatial structure in close resemblance to that found in coherent vortices of two dimensional turbulence these eddies appear to have a rather coherent vorticity dominated core region surrounded by an outer region dominated by deformation with a very complicated and variable in time structure this analysis is also applied to ctd data collected across three eddies sampled between 1997 and 1998 from these data eddy cores are equivalently defined as the interior region enclosed by the maximum of azimuthal velocity and are consistent with the horizontal structures seen in sla maps the distinction between the core and the outer region circulation cell is particularly important to understand the role of transport and stirring of properties associated to eddies as illustrated by the observed salinity structure some selected sst images and drifter trajectories the core is characterized by very small isopycnal salinity gradients while the surrounding cell is characterized by a strong slope of isohalines with respect to isopycnals persistent stagnation points are observed around the eddy and correspond to regions of high values of deformation with respect to vorticity these regions allow analyzing characteristic patterns seen in the corresponding sst images in addition drifters trajectories exhibit very different behavior when crossing such regions

origin of a cool water oligo miocene deep shelf limestone eucla platform southern australia the abrakurrie limestone is an areally extensive bryozoan rich unit within the eucla platform a tertiary carbonate shelf which caps the central part of the southern australian continental margin the onshore portion the topic of this study has been exposed since middle miocene time and lies beneath the nullarbor plain the rocks are fine sand to granule sized calcarenites composed of bryozoans bivalves benthic foraminifera and echinoids with lesser numbers of brachiopods solitary corals and serpulids they conspicuously lack significant numbers of planktonic foraminifera and coralline algae most bryozoan remains are from delicate branching cyclostomes although delicate branching robust branching foliose fenestrate multilaminar encrusting and free living cheilostomes are variably abundant in specific units the poorly lithified sequence is punctuated by well cemented layers with erosional tops which are interpreted as hardgrounds the limestone is interpreted as a cool water deep shelf deposit which accumulated in water depths generally greater than 50 m on the inner part of the eucla platform a model which involves deposition and cementation on a carbonate shelf swept by open ocean swells is proposed to explain the style of sedimentation the shelf is envisaged as partitioned by the depth of the zone of wave abrasion sediments were produced throughout but accumulated only below this depth when the seafloor was above this depth it was an environment of cementation and erosion the vertical sequence correlates in a general way with the global sea level model for the mid cenozoic while accumulation rates for southern australian carbonates are similar to rates of cool water carbonate deposition elsewhere c 2 5 cm kyr 1 the rate of abrakurrie accumulation is much less suggesting that significant time periods are represented by the hardgrounds

the chronology of magma influxes to the eastern compartment of the bushveld complex as exemplified by its marginal border groups the floor contact of the eastern compartment of the bushveld complex has been mapped in detail for 130 km field relations petrographical and geochemical data have enabled 3 important marginal border groups and a possible parent to the lower zone to be demarcated these represent the 4 main magma influxes which formed the malic phase of the bushveld complex and are in chronological order 1 a contaminated magnesian basalt b1 which gave rise to a saucer shaped laminated marginal zone at the base of the complex with diverse related sills 2 a harrisitic peridotite representing quenched lower zone magma 3 a border group to the more evolved probably basaltic critical zone magma which was intruded in two phases an early quenched norite facies n being followed by a chilled bulk critical zone facies b2 which forms a skin to the whole critical zone finally 4 a border group to the main and upper zone b3 which represents an early magnesian pulse of this last immense volume of tholeiitic liquid there is also evidence for minor influxes of magma within the critical zone and main zone

environmental factors influencing skeletal grain sediment associations a critical review of miocene examples from the western mediterranean the presence of foramol rhodalgal and bryomol skeletal grain associations in ancient shallow marine limestones is commonly interpreted as evidence for non tropical palaeoclimate despite temperature being only one of several factors influencing skeletal grain associations such interpretations neglect the multitude of factors other than temperature that influence carbonate producing biota these include nutrients water energy water transparency depth of the sea floor salinity oxygen ca2 and co2 concentrations mg ca ratio alkalinity substrate requirements competitive displacement as well as biological and evolutionary trends this uniformitarian approach also disregards the probability that conditions of present day biological systems may not be representative of past conditions of analogous systems here the importance of considering these other factors is illustrated through two examples of carbonate platforms in the western mediterranean these platforms are dominated by foramol rhodalgal and bryomol associations of miocene age in spite of having formed in tropical conditions the platforms discussed are 1 the lower tortonian ramp on menorca balearic islands and 2 the lower middle miocene ramps of the central apennines italy evidence for tropical conditions in the mediterranean during the period of growth of these platforms is provided by species of red algae and larger foraminifera by data from coeval continental basins and by global oxygen isotope data

spit platform temperate carbonates the origin of landward downlapping beds along a basin margin lower pliocene carboneras basin se spain lower pliocene temperate carbonates exhibit landward downlapping beds at the southern margin of the carboneras basin in south eastern spain this rarely documented stratal geometry resulted from the accumulation of bedded bioclastic carbonate sand and gravel by longshore currents along a spit platform located a few hundred metres from the palaeoshoreline the top of the spit platform was covered by shoals that extended over a gently dipping ramp inclined to the north on the landward slope of the spit sediments washed over from the shoal area were deposited in parallel laminated beds with a southward dip of 8 11 these beds aggraded and retrograded after an increase in accommodation space probably related to an early pliocene eustatic sea level rise as a result the beds downlap onto the underlying unconformity surface in a shoreward direction eventually the depression between the shoreline and the spit platform was filled and a gentle ramp became established these pliocene exposures in the carboneras basin and a similar upper miocene example in southern spain suggest that landward downlapping stratal geometries can be expected in nearshore temperate carbonates along basin margins and demonstrate a similarity in sedimentary dynamics to siliciclastic sands and gravels

lithofacies modelling and sequence stratigraphy in microtidal cool water carbonates a case study from the pleistocene of sicily italy quaternary carbonates in se sicily were deposited in seamount and short ramp settings during glacio eustatically driven highstand conditions they provide an excellent opportunity to investigate the depositional and erosional aspects of cool water carbonate sedimentation in a microtidal marine water body the derived ramp facies model differs significantly from modern day open ocean ramp scenarios in projected facies depth ranges and in the preservation of inshore facies a sequence stratigraphic study of the carbonates has confirmed many established aspects of carbonate sedimentation e g production usually only occurred during highstands it has also revealed several new features peculiar to water bodies with little tidal influence including catch up surfaces taking the place of transgressive facies second order sequence boundary events being most important as triggers for initiating resedimentation and a virtual absence of sediment shedding to the basin during the terminal lowstand production in the carbonate factory lasted for about 0 5 myr despite this carbonate production was considerable and included both bioconstructional and bioclastic dominated facies and the production of abundant lime muds a model for eustatically controlled cool water carbonate production and resedimentation in microtidal marine water bodies is presented this is considered to be more applicable to neogene and quaternary strata in the mediterranean region than are current open ocean models

additional evidence of liw entrainment across the algerian subbasin by mesoscale eddies and not by a permanent westward flow abstract the circulation of the levantine intermediate water liw in the algerian subbasin western basin of the mediterranean sea has been much debated for more than fifteen years now together with the old circulation diagrams several numerical models claim that a branch of liw is permanently flowing westwards across the algerian subbasin i e directly from the channel of sardinia towards the strait of gibraltar only a few models support the fact that the unique continuous flow of liw is structured as an alongslope counterclockwise vein which is thus directed northwards off sardinia in the algerian subbasin and hence support the diagram published by millot in 1987 millot c 1987a circulation in the western mediterranean oceanologica acta 10 2 143 149 according to this diagram any little mixed liw found in the central subbasin corresponds to fragments which have been pulled away from the vein and entrained there by mesoscale eddies originated from the algerian current the elisa experiment 1997 1998 as a follow up of other ones conducted since about 15 years was designed partly to validate the diagram in addition to about 40 current meters set in place for one year four main campaigns were conducted with a sampling strategy guided in real time by infrared satellite information the data set we present clearly provides additional evidence that the little mixed liw found in the central algerian subbasin has been entrained there by the mesoscale eddies and not by a permanent westward flow

taxonomic diversity and stratigraphic distribution of mediterranean pliocene bivalves abstract the mollusc disappearance extinction events throughout the mediterranean pliocene suggest the definition of four faunistic units mediterranean pliocene molluscan units mpmus the bivalve taxonomic diversity the paleobiogeographic significance and the chronological classification of each unit are analyzed in detail the boundaries of the mpmus approximate the major climatic changes of the northern hemisphere respectively at 3 0 2 5 and 2 1 ma on the whole the molluscan fauna changes 356 species of shallow water bivalves have been considered record the transition from a tropical unit mpmu1 to a biogeographic unit mpmu4 comparable with that of the recent mediterranean

mean sea level and surface circulation variability of the mediterranean sea from 2 years of topex poseidon altimetry we describe the circulation and mean sea level variations of the mediterranean sea from 2 years of topex poseidon altimetric data it is first shown that the response of the mediterranean sea to atmospheric pressure forcing is close to an inverse barometer except at high frequencies which means that the adjustment is accompanied by a flow through the straits of sicily and gibraltar we then use topex poseidon to study the mean sea level variations representing steric effects and integrated large scale changes of the mass of the mediterranean sea we observe an annual cycle with a fast drop during winter steric effects account for about half of the observed variations the remaining signal is believed to be driven by evaporation minus precipitation e p forcing and internal hydraulic control in the straits of gibraltar using suboptimal space time objective analysis the classic components of the mediterranean surface circulation are recovered despite low signal to noise ratio the rms of sea level variability is less than 10 cm the variable mediterranean circulation is seen as a complex combination of mesoscale and large scale variations the surface circulation is more complex in the eastern basin than in the western basin in the east it is composed of subbasin scale gyres such as the so called mersa matruh and shikmona gyres which do not have an obvious recurrence period we also observe an intensification of the large scale cyclonic winter circulation in the western and in the ionian basins several mesoscale structures such as the alboran gyres and the ierepetra gyre show a clear seasonal cycle with a maximum in summer the good qualitative and quantitative agreement of the results with previous data from the mediterranean illustrates the improved accurary of topex poseidon over its predecessors

vortices of the mediterranean sea an altimetric perspective the presence of coherent vortices makes observed mesoscale fields of the ocean resemble twodimensional turbulence using this analogy a common definition of a coherent structure has been used to study the statistical properties of mediterranean sea vortices observed by satellite altimeters over a 7 yr period a vortex has been defined as the simply connected region with values of the okubo weiss parameter w 0 2w where w is the spatial standard deviation of w and the same sign of vorticity this definition is shown to be appropriate to detect and characterize statistically properties such as size mean kinetic energy and amplitude of vortices in the mediterranean basin from sea level anomaly maps corresponding to the period from october 1992 to october 1999 the distribution of such properties for the mediterranean vortices suggests a heuristic criterion to extract and select very coherent and long lived vortices from the whole set of structures identified in altimetric maps such coherent vortices appear to be selected for amplitudes greater than 2w where the amplitude has been defined in terms of the okubo weiss parameter rather than vorticity and strongly correspond to those reported from observations with independent data systematic locating and tracking of such vortices provide for the first time a general picture of their preferential paths in the mediterranean basin which are characterized by complex but rather well defined patterns

the facies distribution of carbonate sediments on porcupine bank northeast atlantic porcupine bank 51 54 n 12 15 w approximately 10 000 km2 in area and 150 500 m deep is effectively removed from present day terrigenous sedimentation by the broad irish shelf to the east and deep water to the north west and south water temperatures range from 10 to 14 5 c carbonate sediments presently accumulate on the bank mixing with relict quartz sands and lithic pebbles cobbles and boulders of glacial origin traction current structures are absent but biogenic hollows pits mounds and trails are prevalent the lithofacies have a crudely concentric zonation with pelagic foraminiferal oozes in the deepest waters 500 m passing to foraminiferal pelagic and benthic glauconitic quartz sands over the bulk of the bank 500 200 m where scattered patches of lophelia pertusa coral branches are found which in turn pass into a narrow zone associated with the lithic boulder field at the bank crest 500 m pelagic foraminiferans 500 200 m benthic foraminiferans plus lophelia coral patches 200 100 m bivalve echinoderm 100 50 m bryozoan bivalve gastropod serpulid 50 m calcareous red algae bivalve gastropod barnacle

norite from the mahalapye granitoid complex northern edge of kaapvaal craton implications for the extent of the paleoproterozoic bushveld lip abstract the paleoproterozoic centred at 2 054 ga bushveld lip is one of the largest intracratonic lips in the world its components are primarily distributed within the archean kaapvaal craton this study reports dyke like and sill like norite intrusions from lose quarry within the mahalapye complex a paleoproterozoic granitoid migmatitic gneiss terrane along the northern edge of kaapvaal craton field relations indicate the norite postdate the 2 061 ga diorite gneiss and predate the 2 039 ga granodiorite significantly it exhibit structures indicative of comingling with 2 053 ga leucosome leucogranite a product of partial melting of diorite gneiss the cross cutting relations provide unequivocal evidence that the norite and the leucogranite were liquid at the same time and should be of similar age fe rich orthopyroxene xmg 0 43 0 46 constitutes the dominant mafic mineral in the norite geochemical characteristics of the mahalapye complex norites are similar to those of marginal facies norites from the bushveld complex b1 sills and molopo farms complex layered intrusions two of the prominent constituents of the bushveld lip this is the first solid evidence that the original extent of the bushveld lip covered an area larger than the current known limits of the archean kaapvaal craton into the youngest and westernmost terrane of the high grade limpopo complex the potential of high grade terranes along archean cratonic margins as locales to look for lip fragments is explored

the late archean record a puzzle in ca 35 pieces abstract the global archean record preserves ca 35 large cratonic fragments and a less well defined number of smaller slivers most archean cratons display rifted margins of proterozoic age and therefore are mere fragments of supercratons which are defined herein as large ancestral landmasses of archean age with a stabilized core that on break up spawned several independently drifting cratons the tectonic evolution of individual archean cratons such as the slave craton of north america or the kaapvaal craton of southern africa should therefore always be considered in the context of their ancestral supercratons this is particularly true for many of the smaller cratons which are too limited in size to preserve the complete tectonic systems that led to their formation these limitations not only apply to the crustal geology of archean cratons but also to their underlying lithospheric mantle keels if these keels are archean in age as their broad correlation with ancient surface rocks suggests they also are rifted and drifted remains of larger keels that initially formed below ancestral supercratons the study of archean cratons and their lithospheric keels should thus be global in scope in the search for late archean supercratons a craton like the slave with three to four rifted margins has a ca 10 maximum probability of correlating with any of the ca 35 remaining cratons around the globe assuming wholesale recycling of archean cratons has been limited since ca 2 0 ga alternatively if the original number of independently drifting cratons was significantly larger the probability of successful correlations is much less due to repeated cycles of break up and plate tectonic dispersal since ca 2 0 ga the probability of correlation is probably independent of present day proximity unless there is independent evidence that two neighbouring cratons were only separated by a narrow ocean nevertheless most previously proposed craton correlations rely erroneously on present day proximity implicitly extrapolating relatively recent paleogeography back to the archean considering the fundamental differences between some of the better known cratons such as the slave superior and kaapvaal it seems likely that these cratons originated from independent supercratons sclavia superia vaalbara with distinct amalgamation and break up histories this is contrary to widely held opinion based largely on an idealized view of the supercontinent cycle that all cratons shared a common history in a single late archean supercontinent in contrast to the superior and kaapvaal cratons which are radically different from the slave craton and each other the dharwar craton of peninsular india the zimbabwe craton of southern africa and the wyoming craton of north america all show significant similarities to the slave craton it thus seems likely that at least some of these were nearest neighbours to the slave craton in the ca 2 6 2 2 ga sclavia supercraton

the bushveld complex south africa formation of platinum palladium chrome and vanadium rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large relatively slowly cooling subsiding magma chamber platinum group element pge deposits in the bushveld complex and other layered intrusions form when large incompletely solidified magma chambers undergo central subsidence in response to crustal loading resulting in slumping of semi consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides oxides olivine and pyroxene and less dense layers enriched in plagioclase the most economic pge cr and v reefs form in large multiple replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification the depth of emplacement has to be relatively shallow as otherwise ductile crust would not be able to flex and collapse in smaller intrusions cooling rates are faster subsidence is less pronounced and where it occurs the cumulate may be largely solidified resulting in insignificant mush mobility and mineral sorting layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower but the reefs can be relatively thicker an additional factor controlling the pge cr and v prospectivity of intrusions is their location within cratons intra cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large layered igneous bodies furthermore intrusions sited within cratons are more readily preserved because cratons are underlain by thick buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust

geochronology of a late archaean flood basalt province in the pilbara craton australia constraints on basin evolution volcanic and sedimentary accumulation and continental drift rates abstract eleven high precision 2 5 million years shrimp zircon u pb ages have been obtained from felsic rocks within a single stratigraphic section of late archaean volcanic and sedimentary rocks in the east pilbara of western australia the stratigraphic succession nullagine and mount jope supersequences in sequence stratigraphic terminology fortescue group in lithostratigraphic terminology is interpreted to be the rock record of three major geotectonic cycles that formed in an extensional rift related environment between about 2772 and 2715 ma the geochronology is constrained by a detailed stratigraphic framework based on unconformities and supported by a preliminary magnetostratigraphy field mapping geochemical and petrographic studies have shown that previously unrecognised thin felsic tuff bands are interbedded in subaerial flood basalt piles and mafic tuffs while flood basalts and proximal felsic volcanic rocks comprise by volume most of the volcanogenic components of the succession felsic volcanism is now known to have been active periodically through each geotectonic cycle the succession covers a time period of about 57 million years the lower 1400 m of a thick 1700 m clastic sedimentary succession from the oldest geotectonic cycle was deposited at a rate of about 100 m per million years over a mean time period of 14 million years in contrast a younger 150 m thick cogenetic tuff basalt unit accumulated in less than 3 million years and others probably accumulated at similar rates comparable to those of phanerozoic flood basalts unconformities in the succession are shown to be of variable duration and one unconformity marking the boundary between the first and second geotectonic cycles may represent a time gap of more than 10 million years the unconformity based stratigraphic framework the new geochronology and palaeomagnetic studies j geophys res 108 2003 b12 2551 emp 2 1 to 2 21 have been combined to determine a possible late archaean continental drift rate for one part of the succession implying a period of motion as fast as or up to five times faster than any known from the phanerozoic

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

sedimentary model and high frequency cyclicity in a mediterranean shallow shelf temperate carbonate environment uppermost miocene agua amarga basin southern spain uppermost tortonian to lower messinian temperate carbonates crop out in the agua amarga basin se spain they consist of four units the lower three units can be tentatively assigned to the lowstand systems tract of a fourth order sequence constituting in turn the lowstand megatrough unit transgressive breccia unit and highstand bedded unit stages of a higher order cycle all these materials were deposited in a small pull apart basin related to the sinistral carboneras strike slip fault system the best represented is the bedded unit up to 25 m thick which consists of bioclastic bryozoan bivalve dominated calcarenites calcirudites with abundant fragments of echinoids barnacles benthic foraminifers coralline algae brachiopods and solitary corals facies trends within this unit are roughly arranged in an e w direction with the coastline to the north of the basin the depositional model is that of a gentle ramp with prograding beaches and shoals in its higher parts seaward of the shoals was the factory area where most organisms lived and maximum carbonate production took place from this area some of the skeletons were washed landwards by waves and or currents during storms and incorporated into the shoals and beaches and others moved downslope along the ramp as mass flows accumulating to form the fan bedded zone the factory area and fan bedded sediments intercalate five well defined thick beds of calcarenites fine grained calcirudites they show bar morphologies single or amalgamated or make up sand waves with very consistent tabular cross bedding pointing landwards these beds formed in a very shallow wave current influenced coastal environment the bars and sand waves in the fan bedded zone developed during lowstands while those located higher up in the ramp interbedded with the factory facies are related to transgressive stages prograding beaches shoals factory facies and fan bedded layers developed during the highstands net skeletal production occurred mainly during the highstands sediment accretion values of these sediments are similar to those of present and ancient shallow marine temperate carbonates considering that the whole bedded unit was deposited in a 100 000 year interval equivalent to the short eccentricity cycle the five cycles inside the bedded unit would therefore correspond to the c 20 000 year precession cycles of the milankovitch band

pliocene pleistocene sedimentary tectonic development of the mesaoria mesarya basin in an incipient diachronous collisional setting facies evidence from the north of cyprus

mediterranean messinian salinity crisis constraints from a coeval marginal basin sorbas southeastern spain abstract the extent timing and effects of late miocene desiccation and evaporite deposition in the mediterranean sea remain controversial marginal basins containing messinian 5 3 7 1 ma sequences now exposed onland supplement information from the deep mediterranean but have evaporites of a variety of ages some of these messinian evaporites pre date and others post date deep desiccation none appears to be exactly coeval with those of the deep mediterranean in the betic cordillera of southern spain basins e g granada basin far from the present day mediterranean lost connection with the mediterranean due to uplift 1 ma before the salinity crisis and have marine evaporites of early not late messinian age in contrast basins such as the sorbas basin in southeastern spain adjacent to the present day mediterranean record events directly reflecting the course of the salinity crisis the sorbas basin retained marine connection with the western mediterranean up until evaporative drawdown in the mid messinian and was rapidly reflooded immediately afterwards the sorbas messinian sequence is up to 320 m thick it is complete and normal marine except for an incised basinwide erosion surface overlain by a 130 m thick gypsum deposit we propose that this surface marks the interval of deep desiccation of the adjacent mediterranean basin erosion occurred shortly after 5 9 ma and the irregular unconformity has relief of at least 240 m confirming mediterranean drawdown significantly below the atlantic level sorbas gypsum deposits overlie the unconformity and are intercalated with marls estimated at 5 5 ma containing normal marine messinian biotas these gypsum deposits therefore post date deep desiccation and formed in a silled basin immediately following marine reflooding they mark the end of the salinity crisis and are overlain by 70 m of normal marine sediments containing unreworked foraminifers of latest messinian age this succession demonstrates that the salinity crisis occurred faster and was completed sooner than previously believed it took place within 0 4 ma time scale of berggren et al 1995b is 0 2 ma on the time scale of baksi 1993 and was completed before the end of the messinian this corrects previous views that the salinity crisis continued until the early pliocene there is no evidence in the sorbas basin for brackish lago mare conditions and the normal marine biotas that directly precede and follow drawdown rebut earlier suggestions of prolonged salinity effects

vaalbara earth s oldest assembled continent a combined structural geochronological and palaeomagnetic test the only remaining areas of pristine 3 6 2 7 ga crust on earth are parts of the kaapvaal and pilbara cratons general similarities of their rock records especially of the overlying late archean sequences suggest that they were once part of a larger vaalbara supercontinent here we show that the present geochronological structural and palaeomagnetic data support such a vaalbara model at least as far back as 3 1 ga and possibly further back to 3 6 ga vaalbara fragmented prior to 2 1 ga and possibly as early as 2 7 ga suggesting supercontinent stability of at least 400 myr consistent with neoproterozoic and phanerozoic analogues

headland associated banner banks generated during the last deglaciation near the strait of gibraltar gulf of cadiz sw spain the inception and evolution of large scale bedforms on the barbate platform gulf of cadiz sw iberian peninsula are investigated based on a detailed study of multibeam bathymetric data high resolution seismic profiles and tidal current simulations elongated rocky outcrops and several large scale bedforms classified as sand banks were identified on the platform barbate zahara el palmar el varadero and canos de meca banks the barbate and zahara banks exhibit the most complex internal stratigraphic architecture which comprises five seismic units the basal unit u1 is interpreted as incised valley infill and is overlain by nearshore bars u2 two high energy growth phases u3 and u4 that combine progradation and accretion form the present day external bank shape superimposed bedforms covered these banks under the modern hydrodynamic regime u5 the multiphase accretion and progradation of u3 and u4 in the zahara and barbate banks were closely linked to the presence of a palaeo headland termed here as palaeo cape trafalgar and strong tidal current eddies that resulted from the progressive flooding of the barbate platform during the last deglaciation this configuration was relatively stable while the rocky outcrops were exposed to sub aerial conditions forming a palaeo coast with coastal bluffs we suggest that during this period of coastal stabilization u3 and u4 grew as banner banks on either side of the palaeo cape trafalgar the present study proposes that the configuration of palaeo headland associated with palaeo banner banks zahara and barbate banks along each side of the palaeo cape trafalgar represents a transgressive analogue model of headland associated tidal bank systems developed in funnel shaped coastal systems terminating in narrow straits

the oxygen and carbon isotope distribution in the mediterranean water masses abstract the oxygen and carbon stable isotope compositions of the present day mediterranean waters have been measured in order to evaluate their variability which is related to the specific climatic and hydrological conditions within the basin the experimental equation between the 18 o value and the salinity of water based on 300 measurements on surface intermediate and deep waters sampled during the vicomed 2 and 3 cruises in the western central and eastern mediterranean has a slope of 0 27 a value which is significantly lower than the slope of 0 45 as defined in the northeast atlantic ocean this difference in the 18 o salinity relationship which occurs immediately in the alboran basin is basically a characteristic of the climatic regime of the mediterranean i e of an excess evaporation over fresh water input the largest variations of these two parameters 18 o of water and 13 c of co 2 are observed in the surface waters mostly in the western mediterranean this evolution mirrors the progressive eastward restriction which separates the less evaporated and more productive western basins from the more evaporated and less productive eastern basins the intermediate waters constitute a homogeneous layer however their 18 o values decrease eastward by 0 35 at maximum due to progressive dilution by mixing with overlying and underlying water masses their 13 c values decrease also eastward by 0 35 at maximum due to an increasing input of nutrients issued from the regeneration of sinking organic particles the deep waters have similar 18 o values but slightly higher 13 c values often by less than 0 1 than the overlying intermediate waters indicating generally well ventilated conditions due to active winter convection

quaternary bryozoan reef mounds in cool water upper slope environments great australian bight bryozoan reef mounds are common features in the geological record occurring within mid ramp slope paleoenvironments especially in paleozoic carbonate successions but until now have not been recorded from the modern ocean recent scientific drilling in the great australian bight ocean drilling program leg 182 has confirmed the existence of shallow subsurface bryozoan reef mounds in modern water depths of 200 350 m these structures have as much as 65 m of synoptic relief and occur both as single mounds and as mound complexes they are unlithified have a floatstone texture and are rich in delicate branching encrusting and or nodular arborescent flat robust branching fenestrate and articulated zooidal bryozoan growth forms the muddy matrix is composed of foraminifers serpulids fecal pellets irregular bioclasts sponge spicules and calcareous nannofossils the 14c accelerator mass spectrometry dates of 26 6 35 1 ka indicate that the most recent mounds the tops of which are 7 10 m below the modern seafloor flourished during the last glacial lowstand but perished during transgressive sea level rise this history reflects changing oceanographic current patterns strong upwelling during lowstands and reduced upwelling and lowered trophic resources during highstands large specimens of benthic foraminifers restricted to the mounds confirm overall mesotrophic growth conditions the mounds are similar in geometry scale general composition and paleoenvironments to older structures but lack obvious microbial influence and extensive synsedimentary cementation such differences reflect either short term local conditions or long term temporal changes in ocean chemistry and biology