early marine diagenesis of biogenic aragonite and mg calcite new constraints from high resolution stem and aem analyses of modern platform carbonates prior studies of porewater compositions from modern shallow marine carbonates have established that dissolution and recrystallization of metastable aragonite and mg calcites occur during the earliest stages of sedimentation yet significant microstructural and mineralogical changes in sediment allochems have not been observed in part this is due to the high resolution required to identify diagenetic changes in these finely crystalline materials herein we present ultrastructural and microgeochemical evidence for early marine diagenesis using scanning electron microscopy sem and high resolution scanning transmission analytical electron microscopy stem aem methods to characterize original biogenic materials and sediment boxcores from modern deposits on the floridan bahamas platform we selected the two most common sediment producers a mg calcite foraminifer peneropolid and an aragonitic green algae halimeda for study both are composed of submicron sized crystallites whose excess free energy could provide a thermodynamic driving force for recrystallization stem observations of grain mounts containing dispersed mg calcite and aragonite crystallites from gently disaggregated individual peneropolids and halimeda segments indicate that living specimens contain euhedral prismatic crystals with blunt terminations and smooth faces specimens from the sediment column show abundant evidence for alteration the most dramatic changes involve crystallite dissolution and precipitation of thin overgrowths causing the overall aspect ratio of crystallites to shorten and widen direct measurements of several hundred individual crystallites confirm that crystallite length and width distributions differ significantly between original and altered materials these changes are consistent with crystal growth processes that tend to minimize surface free energy by increasing overall crystal size and by producing more equant shape the precipitated material has a composition and structure which is grossly similar to the host crystallite as determined by aem and electron diffraction analyses aem analyses of hundreds of mg calcite crystallites from living specimens of peneropolid foraminifera indicate a composition of 13 14 mol mgco3 whereas crystallites from altered tests are 1 3 mole lower taken together these data suggest that early diagenesis in shallow marine carbonates is indeed manifested in the solids as well as the sediment pore waters producing significant changes in biogenic mg calcite and aragonite crystallite size and shape this alteration would not produce changes in the mineral assemblage because dissolution is accompanied by precipitation of compositionally similar overgrowths under major element conditions not drastically dissimilar from overlying seawater however crystallite recrystallization likely has implications for incorporation of minor elements which undergo cycling via organic matter decomposition or redox changes e g uranium cadmium manganese rare earth elements

sediment distribution pattern of the south caspian sea possible hydroclimatic implications the south caspian subbasin extends from the foot of the alborz mountains to the deepest part of caspian sea the lithological background and tectonic setting of the study area primarily control the

the belize margin revisited 1 holocene marine facies belize is best known for its 260 km long barrier reef and associated lagoon reef shoals but also exhibits a complete transition from near shore siliciclastics to pure carbonate deposits across a narrow shelf lagoon and in addition has three of the very few occurrences of caribbean atolls published holocene facies relationships on the belize shelf have been semi quantitative in that they are based on quantitative point count thin section data in the northern shelf lagoon and on qualitative estimates of thin section composition in the southern shelf lagoon this contrast has been rectified by point counting southern shelf lagoon thin sections and incorporating the result with published point count data from the northern shelf supplemented by additional information to produce a modified factor analysis facies distribution for the entire shelf the resulting nine facies are extended seaward to include previously published analysis of sediment on the three belize off shelf atolls resulting in a total of 11 facies in addition the carbonate mud distribution has been mapped over both the shelf and atolls with the not unexpected result that in places the distribution pattern clearly indicates a barrier platform source of lagoon deposited carbonate mud dunham s limestone classification terminology has been used as a basis for description to make these relationships more useful to those reconstructing ancient limestone depositional environments

late quaternary halimeda bioherms and aragonitic faecal pellet dominated sediments on the carbonate platform of the western continental shelf of india abstract the fifty fathom flat is a drowned carbonate platform located on the outer continental shelf of western india it is unique because the carbonate depositional environment prevailed until early holocene in spite of its proximity to a major siliciclastic tidal embayment study of the bathymetry seismic and sonograph data together with the petrology mineralogy and geochemistry of the carbonate sediments and limestones recovered from the platform resulted in a the discovery of late quaternary halimeda bioherms and b aragonitic faecal pellet dominated sediments echograms reveal buried pinnacles between 62 and 38 m and exposed 2 to 14 m high pinnacles between 65 and 85 m on the platform these pinnacles occur as narrow to broad mounds bioherms in seismic profiles and as linear ridges and massive structures in sonographs seismic profiles also show a prominent reflector about 25 m below the sea bed identified by boreholes as a late pleistocene erosion surface the platform consists of relict carbonate sands and limestones rounded and ovoid to ellipsoidal aragonite grains are predominant in the sediments sem studies indicate elongated parallel canals and crescent to hook shaped canals corresponding to faecal pellets occur in some grains algal grains and pellets enclosing algal fragments are also present the grains in the limestones are similar to those in the sediments halimeda and crustacean faecal pellets are abundant components with minor echinoid mollusc and benthic foraminifera the limestones are characterised by abundant pores dissolution cavities relic aragonite needles meniscus cements and drusy calcite fill the pores produced by dissolution of aragonite needles these features indicate vadose diagenesis the stable isotopes of the carbonate sands and limestones are almost identical and similar to isotope values of beachrocks of the red sea the limestones ages 8400 9200 yr b p lie within the same age limits 10 400 8300 yr b p as the surficial sediments it appears that fluvial sediments largely accumulate in the inner shelf and did not hinder carbonate growth on the platform lying on the outer shelf we presume that arid climate and nutrients brought by river runoff and shelf edge currents favoured the growth of algal bioherms dominated by halimeda between 13 700 and 8300 yr b p the absence of late holocene and modern carbonates on the platform may be due to the combined influence of climatic change upwelling and neo tectonic activity at about 9000 yr b p the bioherms dominated by halimeda produced abundant aragonite muds deposit feeding crustaceans and other invertebrates subsequently excreted these muds as faecal pellets the platform thus contains faecal pellet dominated sediments

the major ion composition of silurian seawater one hundred fluid inclusions in silurian marine halite were analyzed in order to determine the major ion composition of silurian seawater the samples analyzed were from three formations in the late silurian michigan basin the a 1 a 2 and b evaporites of the salina group and one formation in the early silurian canning basin australia the mallowa salt of the carribuddy group the results indicate that the major ion composition of silurian seawater was not the same as present day seawater the silurian ocean had lower concentrations of mg2 na and so42 and much higher concentrations of ca2 relative to the ocean s present day composition furthermore silurian seawater had ca2 in excess of so42 evaporation of silurian seawater of the composition determined in this study produces kcl type potash minerals that lack the mgso4 type late stage salts formed during the evaporation of present day seawater the relatively low na concentrations in silurian seawater support the hypothesis that oscillations in the major ion composition of the oceans are primarily controlled by changes in the flux of mid ocean ridge brine and riverine inputs and not global or basin scale seawater driven dolomitization the mg2 ca2 ratio of silurian seawater was 1 4 and the k ca2 ratio was 0 3 both of which differ from the present day counterparts of 5 and 1 respectively seawaters with mg2 ca2 2 e g modern seawater facilitate the precipitation of aragonite and high magnesian calcite therefore the early paleozoic calcite seas were likely due to the low mg2 ca2 ratio of seawater not the pco2 of the silurian atmosphere

structural styles and regional tectonic setting of the gela nappe and frontal part of the maghrebian thrust belt in sicily the gela nappe of south central sicily provides an example of a curved segment of an orogenic front that can be examined both onshore and offshore for deformational style and amount of shortening synorogenic sediments allow the deformation to be dated two distinct structural styles are observed in the gela nappe the central salient part of the nappe caltanissetta basin consists of a single thrust sheet containing a train of continuously tightening folds and the reentrant margins of the nappe sciacca and monte judica consist of a stack of several thrust sheets these different structural styles correspond to the pretectonic mesozoic stratigraphy of the foreland plate carbonate platforms exist on the adventure bank and hyblean plateau ahead of sciacca and monte judica respectively while the caltanissetta basin region appears to have accumulated basinal clay facies where the resistant carbonate stratigraphy provides a buttress to the propagation of the thrust front deformation is taken up by imbrication on steep ramps through the carbonates generating a relatively thick orogenic wedge in the basinal setting where no strong rheology exists the low angle of friction on the clay detachment levels requires the growing thrust wedge to be much thinner with a very low foreland dip hence the thrust front propagates much farther forward into the basin than it does in the adjacent platformal areas producing a nonlinear thrust front in the basinal region accretion of foreland material to the nappe by imbrication was only prominent during the messinian when subaerial exposure prevented low friction transport of the nappe across the highest levels of the stratigraphy a steady thickening of the nappe by internal folding suggests an increase in friction along the basal detachment possibly due to progressive compaction of the clays

geochemical and petrographical characterization of fine grained carbonate particles along proximal to distal transects the origin of carbonate ooze particles is often poorly understood this is due to their polygenic origin and potential post depositional alteration here the outcome of a physical separation study with regard to different component classes of micritic carbonates is shown the focus is on grain size and morphology mineralogy and isotope signatures two contrasting proximal to distal transects were investigated 1 the miocene leeward margin of great bahama bank odp leg 166 and 2 the transition between the maiella platform and the umbria marche basin in central italy near the cenomanian turonian boundary in both case settings carbonate particles of biogenic origin include at least three groups of organisms i planktonic foraminifera ii calcareous nannofossils and iii fragments of unspecified neritic skeletal material two further particle types lack diagnostic structures and based on particle size and mineralogy are here referred to as iv macroparticles 5 20 m mainly xenomorphic and v microparticles 12 m mainly automorphic to sub automorphic macro and microparticles represent 50 to 80 of the carbonate phase in slope and toe of slope domains and share characteristic carbon and oxygen isotope signatures macro and microparticles are considered shallow water precipitation products subsequently exported into the slope and toe of slope domains macroparticles are probably related to the fragmentation of neritic skeletal components while microparticles point to inorganic and or bioinduced precipitation in the water column in some cases macro and microparticles may have an early diagenetic origin the identification of the origin of fine grained particles allows for a quantitative assessment of exported in situ and diagenetic carbonate materials in periplatform environments the data shown here represent an important step towards a more complete characterization of carbonate ooze and micrite

sea level change along the italian coast during the holocene and projections for the future published and new sea level data are used to provide projections of sea level change in italy for the year 2100 by adding new isostatic and tectonic component to the ipcc and rahmstorf projections comparison of the observations from more than 130 sites with different geomorphological and archaeological sea level markers with the predicted sea level curves provides estimates of the vertical tectonic contribution to the relative sea level change the results are based on the most recent anu model for the ice sheets of both hemispheres including an alpine deglaciation model on the basis of the eustatic tectonic and isostatic components to the sea level change projections are provided for marine inundation scenarios for the italian coastal plains for the year 2100 that today are at elevations close to current sea level

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

massive recrystallization of low mg calcite at high temperatures in hydrocarbon source rocks implications for organic acids as factors in diagenesis we document massive recrystallization of low mg calcite lime mudstone source rocks at moderately high temperatures in the smackover formation of mississippi this process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons secondary porosity generation in reservoirs and global environmental change this interpretation is based on contrasting the following petrographic and bulk rock geochemical characteristics of organic poor vs organic rich lime mudstones

a review of the nature and origin of limestone microporosity abstract limestone microporosity is ubiquitous and extensively developed in most phanerozoic limestones from an economic perspective microporosity is important because it contributes substantially to the carbonate pore system which can host significant volumes of water and hydrocarbons therefore determining the presence and distribution of limestone micropores is necessary for accurate hydrocarbon estimations reservoir characterization and fluid flow simulations from an academic standpoint microporosity is important because its genesis is intimately linked with the mineralogical stabilization of metastable sediments a fundamental process in carbonate diagenesis many types of micropores contribute to what has been referred to as microporosity but the vast majority is hosted among low magnesium calcite lmc microcrystals that are present in limestone matrix and allochems geochemical textural and mineralogical data from natural settings and laboratory experiments indicate that lmc microcrystals are diagenetic in origin more specifically these data support a diagenetic model of mineralogical stabilization that involves dissolution of precursor sediments dominated by aragonite and high magnesium calcite hmc minerals and precipitation of lmc microcrystal cements the stabilization process is inferred to take place in the meteoric marine and burial diagenetic realms although it has not been directly observed carbon and oxygen isotopes as well as trace element data suggest that lmc microcrystals form during burial diagenesis in marine like fluids evidence suggests that porosity is not generated during this dissolution precipitation process but rather inherited from the precursor sediments the final arrangement of the micropores in a limestone however depends on the precise diagenetic pathway lmc microcrystals exhibit a range of microcrystalline textures that are classified on the basis of crystal morphology and size the three main textural classes granular framework fitted mosaic and clustered have been recognized across a wide range of ages depositional settings burial depths and precursor types and are characterized by distinct petrophysical properties such as porosity permeability and pore throat size observations from modern sediments also support the hypothesis that lmc microcrystals develop from aragonite and hmc dominated lime mud the origin of lime mud has been extensively studied but still highly debated of particular interest to the discussion of microporosity are proposed secular variations in the dominant mineralogy of carbonate sediments through the phanerozoic microporous limestones comprised of lmc microcrystals are equally abundant during times of aragonite seas and calcite seas which suggests that no special mineral precursor is required microporous textures are also observed in deep marine chalks where micropores are hosted between chalk constituents unlike shallow marine limestones deep marine sediments start out as mostly lmc therefore mineralogical stabilization is not a significant process in chalk diagenesis

imprint of foreland structure on the deformation of a thrust sheet the plio pleistocene gela nappe southern sicily italy 1 in sicily the progressive imbrication of the apenninic thrust belt above the pelagian african foreland is traced by the southward migration of marine basins that were progressively shortened during the late miocene pleistocene the outermost and youngest thrust sheet gela nappe displays a peculiar shortening with messinian to early pliocene e w folds refolded in the late pliocene early pleistocene by approximately n s folds subparallel to the transport direction of the thrust sheets this structural interference is documented in south sicily within localized belts of refolding spaced 5 8 km apart the significance of this fold interference pattern is highlighted by our analysis of the offshore seismic reflection line m23a crop mare project that intersects the gela nappe along a trace suborthogonal to the thrust transport direction migration and depth conversion of the line reveal multiple imbrications and draping of the allochthonous units above structural highs of the foreland delimited by inherited n s faults the largest faults bound mid late miocene extensional basins but were reactivated in compression during the late pliocene early pleistocene causing 1 superposed folding along discordant n s structural trends 2 compressional extrusion of the whole wedge of the gela nappe and 3 offset of its sole thrust the reactivation of faults subparallel to the transport direction accommodates differential flexure of the rigid foreland beneath the apenninic wedge and these late stage deformations in the foreland are responsible for the superposition of e w finite shortening onto n s shortening

variations in pyrite texture sulfur isotope composition and iron systematics in the black sea evidence for late pleistocene to holocene excursions of the o2 h2s redox transition time dependent variations in the physicochemical properties of pyrite were investigated in four sediment cores from the black sea in the laminated deep basin sediments of unit i and unit ii 86 of pyrite particles are present as fine grained framboidal aggregates in these sediments the dominance of pyrite framboids with a narrow size distribution and maximum size 18 m is evidence of syngenetic water column pyrite formation subjacent to the o2 h2s boundary sediments from the basin margin collected below the impingement of the o2 h2s boundary contain an increased proportion of fine grained euhedral grains of pyrite relative to framboidal aggregates suggesting increased additions of diagenetic pyrite below the sediment water interface the more efficient reduction and sulfidation of iron in the water column of the central region of the basin implies a more reactive source of iron there compared to the basin margins and is tied to increasing pyrite as framboids and greater degrees of pyritization dop in the basin center relative to the basin margins an evaluation of fe s c relations indicates that pyrite formation was limited by sulfate availability during deposition of the oldest lacustrine sediments of unit iii c limited for upper unit iii due to the input of sulfate rich mediterranean seawater and fe limited in the laminated organic carbon rich sediments of units i and ii these changes in pyrite limiting factors occurred within 4 m of compacted burial representing 15 ka sediment fabric and framboid size distributions at a shallow basin margin site suggest that during two extended periods of unit ii deposition the o2 h2s transition retreated to depths below 200 m however during these same intervals the 34s of pyrite remains uniform compared to overlying and underlying laminated sediments implying that this chemical signature may not be uniquely tied to the position of the o2 h2s boundary relative to the sediment water interface but rather is likely related to biogeochemical processes

sortable silt and fine sediment size composition slicing parameters for palaeocurrent speed and palaeoceanography fine sediment size 63 ixm is best measured by a sedimentation technique which records the whole size distribution repeated size measurement with intermediate steps of removal of components by dissolution allows inference of the size distribution of the removed component as well as the residue in this way the size of the biogenic and lithogenic noncarbonate fractions can be determined observations of many size distributions suggest a minimum in grain size frequency curves at 8 to 10 ixm the dynamics of sediment erosion deposition and aggregate breakup suggest that fine sediment behavior is dominantly cohesive below 10 1xm grain size and noncohesive above that size thus silt coarser than 10 ixm displays size sorting in response to hydrodynamlc processes and its properties may be used to infer current speed silt that is f mer than 10 ixm behaves in the same way as clay 2 xm useful parameters of the distribution are the 10 63 ixm mean size and the percentage 10 63 ixm in the fine fraction we cannot use size distributions to distinguish the nature of the currents therefore to infer water mass advection speeds i e the mean kinetic energy of the flow ku regions of high eddy kinetic energy ke must be avoided at the present such abyssal regions lie under the high surface k e of major current systems gulf stream kuroshio agulhas antarctic circmpolar current and brazil falldand currents in the argenthe basin this is probably a satisfactory guide for the pleistocene with regard to the carbonate subfraction of the size spectrum size modes due to both cocco iths and foramlnlferal fragments can be recognized and analyzed with the boundary between them again at about 10 lm the flux of less than 10 lm carbonate at pelagic sites above the lysocline is another candidate for a productivity indicator

active thrust tectonics in western sicily southern italy the 1968 belice earthquake sequence the 1968 belice earthquake sequence characterized by six main shocks with 5 m 5 4 represents the strongest seismic event recorded in western sicily in historical times the epicentral area is located in the belice valley a region lacking any topographic lineament likely to result from a fault with significant offsets of any kind instrumental data show that hypocentres of the major shocks are distributed along a roughly n dipping plane extending from about 36 km to 1 km depth fault plane solutions show pure thrusting mechanisms on n dipping ene trending planes or oblique slip with a right lateral component of motion along steep wsw dipping planes both as a result of approximate n s shortening the observed destruction indicates that isoseismal areas are elongated in an ene direction similarly the epiccntral distribution of events with m 4 outlines a roughly elliptical ene elongated area located 20 km nw of the sciacca rocca ficuzza thrust front this ene striking structure representing the regional morphotectonic feature closest to the epicentral area consists of two main imbricate fan systems in the southernmost system quaternary deposits tentatively dated as 1 0 0 7 myr old are involved in a large ramp anticline uplifting them to a maximum altitude of 346 m the occurrence of holocene lacustrine piggy back basins on the rear of this structure also indicates late quaternary activity of the underlying thrust seismological structural and morphotectonic observations suggest that multiple ruptures might have occurred during the 1968 sequence on a blind crustal thrust ramp located beneath the epicentral area slip propagated southwards along the shallow ramp flat system characterizing the thin skinned foreland fold and thrust belt of southwestern sicily being dispersed in flexural folding processes and diffuse strain along this path

a regional scale discontinuity in western sicily revealed by a multidisciplinary approach a new piece for understanding the geodynamic puzzle of the southern mediterranean the results of an integrated stratigraphic structural geophysical and geochemical study reveal the presence of a crustal discontinuity in western sicily that at present runs roughly n s along a band from san vito lo capo to sciacca svcs the boundary between the two zones of this discontinuity is nearly orthogonal to the main thrust propagation of the sicilian thrust and fold belt the different permian to tertiary sedimentary evolution recorded by the two zones appears related to this discontinuity with thick carbonate platforms in the western sector facing deep water successions in the eastern one the presence of upper triassic reefs huge megabreccias bodies and widespread submarine volcanisms along the transition zone suggest the presence of a long lasting weakness zone this zone has been reactivated episodically as transpressional and or transtensional faults in relation to the different geodynamic stress acting in central mediterranean area in different epochs we speculate that this transition zone has represented a segment of the passive margin of the ionian tethys during the maghrebian convergence a different style of deformation has affected the two sectors floored by different sedimentary multilayers the orthogonal to oblique differential convergence between the two sectors has resulted in right lateral transpressional motions leading to oblique thrusting of deep water derived thrusts onto platform derived thrusts associated with clockwise rotations the oblique convergence is still ongoing as demonstrated by the seismicity of the area by the geothermal field with high mantle derived helium fluxes and by the gps measurements collected by different authors

origin and role of major strike slip transfers during plate collision in the central mediterranean variations in the crustal structure along the northern african plate margin have caused different modes of collision with eurasia lateral density variations along the central mediterranean collision zone are expressed in a change of the angle of the downbending african plate and lead to the formation of strike slip transfers in these transition zones that are roughly perpendicular to the trend of the collisional zone in some cases these transfer zones are developed into hinge faults while in others they can be developed into transform faults this process governs the segmentation of the collision zone in the central mediterranean region south of the maghrebian thrust belt in tunisia and sicily through the calabrian arc to the northeastern hellenic arc extending further to the cyprian arc and to the taurus zagros chain

the major ion composition of permian seawater abstract the major ion mg2 ca2 na k so42 and cl composition of permian seawater was determined from chemical analyses of fluid inclusions in marine halites new data from the upper permian san andres formation of texas 274 272 ma and salado formation of new mexico 251 ma analyzed by the environmental scanning electron microscopy esem x ray energy dispersive spectrometry eds method along with published chemical compositions of fluid inclusions in permian marine halites from north america two formations of different ages and the central and eastern european basins eight formations of four different ages show that permian seawater shares chemical characteristics with modern seawater including so42 ca2 at the point of gypsum precipitation evolution into mg2 na k so42 cl brines and mg2 k ratios 5 permian seawater however is slightly depleted in so42 and enriched in ca2 although modeling results do not rule out ca2 concentrations close to those in present day seawater na and mg2 in permian seawater are close to slightly below their concentrations in modern seawater permian and modern seawater are both classified as aragonite seas with mg2 ca2 ratios 2 conditions favorable for precipitation of aragonite and magnesian calcite as ooids and cements the chemistry of permian seawater was modeled using the chemical composition of brine inclusions for three periods lower permian asselian sakmarian 296 283 ma lower permian artinskian kungurian 283 274 ma and upper permian tatarian 258 251 ma parallel changes in the chemistry of brine inclusions from equivalent age evaporites in north america central europe and eastern europe show that seawater underwent secular variations in chemistry over the 50 million years of the permian modeled so42 concentrations are 20 mmol per kg h2o mmolal and 19 mmolal in the asselian sakmarian and artinskian kungurian with higher concentrations in the upper permian tatarian 23 mmolal modeled ca2 is at or above its concentration in modern seawater throughout the permian mg2 is close to slightly below its concentration in modern seawater 55 mmolal in the asselian sakmarian 52 mmolal and tatarian 52 mmolal but slightly higher than modern seawater in the artinskian kungurian 60 mmolal mg2 ca2 ratios are 3 5 total range 2 7 to 5 5 in the lower permian and rose slightly to 3 7 total range 3 1 to 5 8 in the upper permian primarily due to decreases in ca2 these results are consistent with models that predict oscillations in the major ion composition of phanerozoic seawater on the basis of changes in the midocean ridge river water flux ratio driven by changes in the rate of midocean ridge crust production the permian was characterized by low sea levels icehouse conditions and southern hemisphere glaciation such conditions analogous to the present ice age and the similarities between permian seawater and modern seawater all suggest that general phanerozoic supercycles driven by mantle convection and global volcanicity also control the major ion chemistry of seawater

composition and genesis of temperate shallow marine carbonate muds spencer gulf south australia abstract the origin of carbonate muds grain sizes 63 m in shallow nontropical marine environments is poorly documented coarse grained carbonates often characterize coastal temperate seafloors but many such deposits also have abundant carbonate muds spencer gulf a large shallow embayment along the southern australian margin 60 m water depth contains mixtures of carbonate gravels sands and muds with muds constituting up to 84 volumetrically benthic environments include dense seagrass meadows sand barrens and rhodolith pavements where bivalves benthic foraminifera coralline algae and bryozoans dominate heterozoan carbonate assemblages mud grain morphologies were investigated using scanning electron microscopy leading to the conclusion that muds are predominantly composed of skeletal fragments bivalves benthic foraminifera ascidians echinoderms and coralline algae interpreted to have formed due to breakdown of rigid material via maceration x ray diffraction analysis confirms that these muds contain combinations of intermediate mg calcite low mg calcite and aragonite with concentrations varying among locations according to skeletal grain types spencer gulf muds differ in mineralogy and composition from those of classic models of tropical and deep water carbonate mud deposition unlike shallow water tropical carbonate muds these temperate muds are not dominated by aragonite and there is no evidence of carbonate precipitation from seawater pelagic organisms contribute only trivial amounts to these deposits in contrast to deep water muds

submarine hydrothermal weathering global eustasy and carbonate polymorphism in phanerozoic marine oolites abstract the age and fabric of 347 phanerozoic marine oolites have been compiled in order to evaluate secular variations in the original mineralogy of these physicochemically precipitated sedimentary carbonates variation in the abundance of oolite correlates with positions of global sea level ooids were common during transgressions and regressions but were rare during lowstands and highstands the rarity of oolite during continental emergence early cambrian permo triassic late tertiary quaternary probably relates to a diminished areal extent of shallow carbonate environments causes for a similar paucity during continental submergence silurian devonian late cretaceous are more problematic higher atmospheric co2 and lower hydrospheric co3 concentration during highstands may have inhibited a biotic carbonate precipitation ooids coeval with highstands display a preponderance of fabrics evincing a primary calcite mineralogy ooids formed during lowstands are more diverse but record dominance of aragonite variations in cortical mineralogy relate more closely to flooded continental areas than to sea level elevations supporting the suggestion of mackenzie and pigott 1981 that variations in hydrospheric carbonate concentrations were more important in determining phanerozoic ooid mineralogy than were magnesium calcium concentrations these data on oolite abundance and mineralogy demonstrate that abiotic phanerozoic marine carbonates have been responsive to secular changes in atmospheric hydrospheric chemistry and global eustasy and suggest that these changes are directly related to past rates of submarine weathering and sea floor hydrothermal activity

calcification of cyanobacterial filaments girvanella and the origin of lower paleozoic lime mud the origin of lime mud in ancient shallow marine carbonate platforms is one of the most vexing mysteries in sedimentary geology possible sources previously suggested include the physical and biological disintegration of animal and algal bioclasts mineralizing pelagic organisms and spontaneous whitings from either abiotic precipitation or calcification of suspended picoplankton and organic matter the styles of occurrence of micrite walled tubes referred to girvanella in lower paleozoic limestones argue that occasional permineralization of mucilaginous sheaths of the benthic filamentous cyanobacteria precursor could have produced lime mud when the tubes fell apart estimated volumes are comparable to those calculated for the modern bahama platform the copious growth of cyanobacteria typical in shallow marine settings indicates that this mechanism could account for a considerable amount of lime mud especially in the early paleozoic

deriving thrust fault slip rates from geological modeling examples from the marche coastal and offshore contraction belt northern apennines italy abstract we present a reconstruction of the central marche thrust system in the central northern adriatic domain aimed at constraining the geometry of the active faults deemed to be potential sources of moderate to large earthquakes in this region and at evaluating their long term slip rates this system of contractional structures is associated with fault propagation folds outcropping along the coast or buried in the offshore that have been active at least since about 3 myr the ongoing deformation of the coastal and offshore marche thrust system is associated with moderate historical and instrumental seismicity and recorded in sedimentary and geomorphic features in this study we use subsurface data coming from both published and original sources these comprise cross sections seismic lines subsurface maps and borehole data to constrain geometrically coherent local 3d geological models with particular focus on the pliocene and pleistocene units two sections crossing five main faults and correlative anticlines are extracted to calculate slip rates on the driving thrust faults our slip rate calculation procedure includes a the assessment of the onset time which is based on the sedimentary and structural architecture b the decompaction of clastic units where necessary and c the restoration of the slip on the fault planes the assessment of the differential compaction history of clastic rocks eliminates the effects of compaction induced subsidence which determine unwanted overestimation of slip rates to restore the displacement along the analyzed structures we use two different methods on the basis of the deformation style the fault parallel flow algorithm for faulted horizons and the trishear algorithm for fault propagation folds the time of fault onset ranges between 5 3 and 2 2 myr overall the average slip rates of the various thrusts are in the range of 0 26 1 35 mm yr

phase difference between sea level and magnetic reversal rate in this letter i report a negative correlation and a phase difference of 10 myr between recent data on long term eustatic sea level change1 and geomagnetic reversal rate for the past 150 myr the phase difference is detectable both by visual inspection and through a correlation analysis i also show that the same phase difference but with a positive correlation could theoretically have existed between this eustatic sea level data and sea floor creation rate in light of the ridge volume hypothesis of long term eustasy the analysis suggests the view that sea floor creation rate and or subduction rate and geomagnetic reversal rate are closely associated and perhaps synchronized in their changes

a series of volcanic edifices discovered a few kilometers off the coast of sw sicily abstract the graham and terrible banks located about 35 km from the south western coast of sicily host a large number of volcanic constructs the most famous being the ephemeral ferdinandea island these volcanoes occur along two n s trending strike slip lineaments that constitute the lithospheric scale capo granitola sciacca fault zone here we present recently acquired swath bathymetric data and magnetic measurements in conjunction with high resolution seismic profiles which reveal the presence of another six volcanic edifices located very close to the sicilian coasts one of which is only 7 km away three of these volcanic constructs have been previously identified only on the basis of available seismic profiles but their morphology and their volcanic nature had so far not been documented two edifices to the north show a possible tuff cone ring like morphology modified by crater breaching while the three southernmost volcanoes have a truncated conical shape the northwestern most volcano here called actea shows a more complex morphology probably representing the remnants of a previous crater rim seismic data analysis suggests that the six volcanic edifices were generated during a pre last glacial maximum lgm ca 20 ka b p magmatic phase associated with a tectonic event only the actea volcano shows indications of magmatic reactivation possibly between the lgm and the initial post lgm transgressive phase this reactivation is evident by the emplacement of a prominent young lava flow the discovery of submerged volcanoes so close to the populated coast of sicily demonstrates that there are large submerged areas near the littoral that are still little known and studied and underlines how crucial it is to analyze the issue of volcanic risk for densely inhabited coastal areas like sicily

sedimentary facies of bora bora darwin s type barrier reef society islands south pacific the unexpected occurrence of non skeletal grains abstract barrier reefs when encircling small islands have been comparatively little noticed by voyagers but they well deserve attention in their structure they are little less marvelous than atolls and they give a singular and most picturesque character to the scenery of the islands they surround darwin 1842 p 2 sediment sampling revealed six modern sedimentary facies in the barrier reef system around the volcanic island of bora bora including mixed skeletal packstone peloidal packstone halimeda rich packstone to grainstone coralgal grainstone wackestone and mudstone whereas sediments rich in corals and coralline algae are abundant on reefs and carbonate shoals mud rich sediments with mollusks and foraminifera occur in deep lagoons 15 40 m carbonate mud is composed largely of aragonite needles probably derived from codiaceans like halimeda and coccoliths in moderate abundances despite the proximity to a volcanic island the content of siliciclastics in the sediments is low 10 on average which is a consequence of the absence of permanent water courses in addition to skeletal grains non skeletal grains cemented fecal pellets aggregates occur in high abundance 30 50 in shallow lagoons 5 m on the eastern side of bora bora this observation opposes the widely held concept that non skeletal carbonate grains are abundant on platforms from the atlantic ocean but virtually missing in recent indo pacific reefs and carbonate platforms in bora bora non skeletal grains and aggregates apparently form in warm shallow 5 m moderately agitated areas with relatively low sedimentation rates in addition early cementation is probably favored by elevated alkalinity and ph in surface waters in this part of the south pacific in the same area some 900 km to the southwest of the study area ooids and peloids have recently been discovered in the shallow lagoon of aitutaki cook islands more occurrences of abundant non skeletal grains probably exist in the indo pacific region however too few locations have been systematically studied a comparison of the new bora bora data with other modern reefs and platforms shows that sediment occurrence and distribution exhibits basic patterns in that marginal areas are dominated by coarse grained coralgal sediment whereas lagoons and platform interiors are characterized by mollusk foram halimeda and non skeletal grains and fines still grain abundances may vary significantly among locations and again suggest the need for more studies in order to fully understand the factors controlling occurrence and distribution of modern sediments

controls on grain size patterns in periplatform carbonates marginal setting versus glacio eustacy the importance of grain size as a fundamental property controlling other physically derived properties is well known recent grain size studies on periplatform sediments of the caribbean and western north atlantic have shown that grain size variability is coupled with changes in carbonate platform productivity and export in response to pleistocene holocene glacio eustacy these findings showed that periplatform sediments are dominated by fine grained material during sea level highstands and coarser material during sea level lowstands this paper addresses the question of grain size patterns in periplatform settings and their relationship to glacio eustacy furthermore it considers whether these patterns are applicable to different types of margin settings accretionary erosional here existing data pleistocene holocene from the accretionary western leeward margin of great bahama bank odp leg 166 and new data from the erosional eastern windward margin odp leg 101 are used the results show that the grain size patterns of both margins are controlled by late neogene sea level fluctuations the accretionary leeward margin sediments indicate the same grain size pattern as previously described in the literature however the erosional windward margin shows a reverse pattern with coarser sediments in interglacials and finer deposits in glacials this proposes that the leeward margin grain size pattern is controlled by the productivity export mode of the platform this is indicated by the platform top derived fine muds transported off bank to form a thick sediment wedge on the low angled slope during interglacials in contrast on the windward margin the sediment flux pattern is controlled by the impact of mass transport processes this is indicated by the increased occurrence of turbidites during interglacials that might be more frequent at this time because the steep angled erosional slope is less apt for the deposition of excess fine material this material is eroded and or bypasses the slopes and is redeposited in the periplatform basin setting

primary aragonite and high mg calcite in the late cambrian furongian potential evidence from marine carbonates in oman acknowledgements fieldwork and sampling was funded by petroleum development oman during s al marjibis s ph d their help is gratefully acknowledged we also thank colleagues at the university of aberdeen julie dougans suerc for assisting with stable isotope analysis and dr richard hinton eimf for assistance with ion microprobe analysis profs kiessling tucker bosence coleman dr dickson and an anonymous reviewer are thanked for their helpful and encouraging comments

multiproxy approach for determination of nature and origin of carbonate micro particles so called micarb in pelagic sediments abstract carbonate fractions of pelagic and hemipelagic sediments may contain significant proportions of microcrystalline 6 m calcitic particles with no specific structure so called micarb depending on the authors this term is related to different descriptions and yet there is no clear consensus on their origin although micarb can dominate the sediment compositions in the pelagic realm their isolation from the other carbonate particles is not easy due to their small size the use of a granulometric separation method of the main carbonate particles allows the characterization and quantification of the compositions of the carbonate phases of the sediments and gives access to the geochemical signatures oxygen and carbon stable isotopes and mineralogical characteristics of each type of carbonate particles in the sediments this approach was applied to three sections the mid pliocene punta piccola section south sicily the upper campanian bidart section sw france and the aptian sediments from la marcouline quarry se france the quantifications showed quite important proportions up to 70 of the carbonated phases of micarb in the sections studied excepted in the mid pliocene punta piccola samples however depending on the sedimentary context it appears that those fine calcitic particles may result from fine biogenic fragmentation aptian la marcouline quarry authigenic precipitation in the water column mid pliocene punta piccola section or they may have an allochthonous origin upper campanian bidart section based on these interpretations it is then possible to estimate precisely the composition of the carbonate fractions in each studied section this work shows that except for the bidart sediments which are dominated by fine exported carbonate mud the other sections mainly consist in biogenic carbonates

whiting related sediment export along the middle miocene carbonate ramp of great bahama bank modern aragonite needles are present all along the modern leeward margin of great bahama bank odp leg 166 while middle miocene sediments contain needles only in more distal areas sites 1006 and 1007 in contrast to the rimmed flat topped platform topography during the plio pleistocene the miocene great bahama bank morphology is a carbonate ramp profile this might imply a different location and precipitation type for miocene aragonite needles in this study aragonite needles in miocene sediments were isolated using a granulometric separation method furthermore the isolation of the various carbonate components enables the identification of primary versus diagenetic components the miocene aragonite needles are concentrated in the finest granulometric sediment fractions 12 m the fraction specific geochemical analyses 13c 18o and sr elemental abundance represent useful tools to assess the possible sources of the aragonite mud the geochemical variation of the fractions rich in pristine aragonite needles and the characteristics of the needle morphology point to whiting phenomena as the main sediment source and algal fragmentation as a minor component both components indicate shallow water environments as the main sediment source area ramp top related fine grained particles now present at distal sites were likely exported as suspended material similar to present day transport mechanisms the scarcity of needles at proximal sites is probably linked to hydrodynamic processes but dissolution and recrystallization processes cannot be excluded the granulometric separation approach applied here enables a better characterization of the finest carbonate particles representing an important step towards the discrimination between primary and diagenetic fine grained components

multi temporal tectonic evolution of capo granitola and sciacca foreland transcurrent faults sicily channel abstract joint analysis of high penetration multi channel and high resolution single channel seismic reflection profiles calibrated by deep well boreholes allowed a detailed reconstruction of the late miocene to recent tectonic history of the capo granitola and sciacca fault systems offshore southwestern sicily these two fault arrays are part of a regional system of transcurrent faults that dissect the foreland block in front of the neogene sicilian fold and thrust belt the capo granitola and sciacca faults are thought to reactivate inherited mesozoic to miocene normal faults developed on the northern continental margin of africa during latest miocene pliocene the two nne ssw striking faults were active in left transpression which inverted late miocene extensional half grabens and created push up ridges along both systems tectonic activity decreased during the pleistocene but transpressional folds deform middle late pleistocene sediments as well suggesting that the two fault systems are active the 40 km long longitudinal amplitude profile of 1st order folds capo granitola and sciacca anticlines shows 15 20 km bell shaped undulations that represents 2nd order folds the length of these undulations together with the map pattern of faults allowed to divide the cgfs and sfs into two segments northern and southern respectively total uplift of the sciacca anticline is twice than the uplift of the capo granitola anticline incremental fold growth rates decreased during time from 0 22 mm yr capo granitola anticline and 0 44 mm yr sciacca anticline in the pliocene to 0 07 and 0 22 mm yr respectively during the last 1 8 ma

rates of carbonate dissolution in permeable sediments estimated from pore water profiles the role of sea grasses in this study we estimate sediment carbonate dissolution rates for sandy sea grass sediments on the bahamas bank using an inverse pore water advection diffusion reaction model constrained by field observations this model accounts for sea grass o2 input to these sediments and also parameterizes pore water advection through these permeable sediments as a nonlocal exchange process the resulting rates of carbonate dissolution are positively correlated with sea grass density and are comparable with previous rate estimates for florida bay sediments in contrast the advective uptake of o2 by these sediments decreased with increasing sea grass density this suggests that the competing interplay between bottom water flow near seabed pressure gradients and the presence of a sea grass canopy is important in controlling this type of sediment oxygen uptake when the carbonate dissolution rates estimated here are examined in the context of carbonate budgets for shallow water carbonate platforms systems they suggest that carbonate dissolution may be a significant loss term in these budgets sea grass mediated carbonate dissolution may also exert a negative feedback on rising atmospheric co2 although the magnitude of this effect remains to be quantified

the source of ions for biomineralization in foraminifera and their implications for paleoceanographic proxies the global carbon cycle is strongly perturbed by fossil fuel burning leading to atmospheric co2 increase climatic warming followed by polar ice melting and global sea level rise are predicted due to the greenhouse effect of increasing co2 in the atmosphere houghton et al 1995 the ocean plays a major role in neutralizing the excess co2 because the amount of inorganic carbon available for exchange with the atmosphere in the ocean is approximately 50 60 times larger than in the atmosphere e g siegenthaler and sarmiento 1993 the bulk of the atmospheric co2 excess will eventually be neutralized by caco3 dissolution in the deep marine environment this is however is a relatively slow process that operates on the time scale of ocean circulation 1000 yrs and is therefore causing an accumulation of co2 in the atmosphere this phenomenon will result in potentially severe consequences to the well being of global ecological systems obviously the scientific attention of many biogeochemists is focused on processes controlling the response of the marine system to changes in atmospheric co2 concentrations e g archer and maier reimer 1994 broecker 1997 sigman and boyle 2000 berger 2002 foraminifera corals and coccolithophores in the global carbon cycle there are four dominant processes involved in neutralizing the excess atmospheric co2 in the ocean these are 1 gas exchange at the air sea interface and reaction with the carbonate ion to form bicarbonate 2 net primary productivity 3 caco3 production and dissolution and 4 ocean circulation most of these processes are biologically mediated and may have special importance in shallow tropical environments where the exchange with the atmosphere is more direct in this review we address the mechanism of biomineralization in one of the major groups that precipitates caco3 in the ocean the foraminifera as we will show this group

holocene atlantic climate variations deduced from carbonate periplatform sediments leeward margin great bahama bank a marine sediment core from the leeward margin of great bahama bank gbb was subjected to a multiproxy study the aragonite dominated core md992201 comprises the past 7230 years in a decadal time resolution and shows sedimentation rates of up to 13 8 m kyr aragonite mass accumulation rates age differences between planktonic foraminifera and aragonite sediments and temperature distribution are used to deduce changes in aragonite production rates and paleocurrent strengths aragonite precipitation rates on gbb are controlled by exchange of carbonate ions and co2 loss due to temperature salinity conditions and biological activity and these are dependent on the current strength paleocurrent strengths on gbb show high current velocities during the periods 6000 5100 years bp 3500 2700 years bp and 1600 700 years bp lower current speeds existed during the time intervals 5100 3500 years bp 2700 1600 years bp and 700 100 years bp bahamian surface currents are directly linked to the north atlantic atmospheric circulation and thus periods with high low current speeds are proposed to be phases of strong weak atmospheric circulation

an active oblique contractional belt at the transition between the southern apennines and calabrian arc the amendolara ridge ionian sea italy high resolution single channel seismic and multibeam bathymetry data collected at the amendolara ridge a key submarine area marking the junction between the apennine collision belt and the calabrian subduction forearc reveal active deformation in a supposedly stable crustal sector new data integrated with existing multichannel seismic profiles calibrated with oil exploratory wells show that middle to late pleistocene sediments are deformed in growth folds above blind oblique reverse faults that bound a regional pop up data analysis indicates that 10 to 20 km long banks that top the 80 km long nw se trending ridge are structural culminations above en echelon fault segments numeric modeling of bathymetry and stratigraphic markers suggests that three 45 dipping upper crustal 2 10 km fault segments underlie the ridge with slip rates up to 0 5 mm yr segments may be capable with m 6 1 6 3 earthquakes although an unknown fraction of aseismic slip undoubtedly contributes to deformation the fault array that bounds the southern flank of the ridge amendolara fault system parallels a belt of mw 4 7 strike slip and thrust earthquakes which suggest current left oblique reverse motion on the array the eastern segment of the array shows apparent morphologic evidence of deformation and might be responsible for mw 5 2 historic events late pliocene quaternary growth of the oblique contractional belt is related to the combined effects of stalling of adriatic slab retreat underneath the apennines and subduction retreat of the ionian slab underneath calabria deformation localization was controlled by an inherited mechanical interface between the thick apulian adriatic platform crust and the attenuated ionian basin crust

seasonal hydrochemical changes and spatial sedimentological variations in lake iznik nw turkey abstract the marmara region is a key area to investigate the interconnection and environmental changes between the black sea and the eastern mediterranean related to climate patterns lake iznik is an oligohaline lake located in the southeast of the marmara sea to decipher the long term signals recorded in the sediment column requires better understanding of the processes in the modern lake environs seasonal limnological investigations were paired with geochemical and sedimentological analyses lake iznik is an alkaline warm monomictic lake during warm seasons a thermocline is established between 15 m and 20 m water depth anaerobic bottom water is mixed during spring surface water currents became visible during a whiting event in the summer corresponding with spatial accumulation patterns found in geochemical proxies of the surface sediment

skeletal mineralogy and biodiversity of marine invertebrates size matters more than seawater chemistry it is now well established that seawater chemistry as well as influencing non skeletal marine precipitation calcite and aragonite seas has affected skeletal mineral secretion in some algal and marine invertebrate groups skeletal mineralogy has had a yet more profound consequence on fossil preservation the realization that the fossil record of marine organisms with an aragonite shell is widely depleted in some shelf settings through early effectively syn depositional dissolution missing molluscs effect has led to a re evaluation of the composition diversity ecological and trophic structure of marine benthic communities comparisons of molluscan lagerstatten from calcite and aragonite seas show a similar pattern of skeletal mineralogical loss that is no differences are discernibly linked to changed seawater geochemistry it is notable that the rare mollusc rich skeletal lagerstatten faunas in the fossil record include many small individuals micromolluscs are quantitatively important among modern shell assemblages yet small size is a major source of taphonomic and biodiversity loss in the fossil record in skeletal lagerstatten faunas micromolluscs contribute variably to mollusc biodiversity but appear particularly significant through at least to triassic times they highlight a further missing molluscs effect of taphonomic loss through early dissolution

calcite dissolution in two deep eutrophic lakes the calcium cycle in particular carbonate dissolution was analyzed in two deep eutrophic lakes lago di lugano 288 m maximum depth and sempachersee 87 m located in switzerland a box model approach was used to calculate calcite dissolution in the water column and at the sediment water interface based on various lake monitoring data such as sediment traps sediment cores water and pore water analysis a model for stationary conditions allowing the calculation of calcite dissolution in the water column for a given particle size distribution was developed the relative values of the simulated aux were consistent with sediment trap observations the best fit of the dissolution rate constant of sinking calcite in lago di lugano was on the same order of magnitude 3 10 10 kg 1 3 s 1 as published laboratory values for this surface controlled process both lakes show a similar specific calcite precipitation rate of 170 g ca m 2 a 1 the diffusive flux across the sediment water interface amounts to about 15 and 10 of total calcite precipitation in sempachersee and lago di lugano respectively however 61 of the precipitated calcite is dissolved in the water column of lago di lugano compared to only 13 in sempachersee these results point towards the importance of grain size distributions and settling times in stratified deep waters as the two most important factors determining calcite retention in sediments of hard water lakes copyright c 1999 elsevier science ltd

the use of paleoceanographic proxies in carbonate periplatform settings opportunities and pitfalls in a sediment core from the leeward side of the great bahama bank ocean drilling program odp leg 166 1006a 24h early pliocene several paleoceanographic proxies were compared with carbonate mineralogy the proxies measured on the planktonic foraminifera species globigerinoides sacculifer are mg ca and sr ca elemental ratios and 18o values these proxies are widely used in pelagic sediments to derive parameters of water masses such as paleo temperature and salinity to produce quantitative estimates it is necessary to verify that the primary shell mineralogy of the foraminifera was not altered diagenetically diagenetic alteration can be rapid in periplatform settings relative to pelagic deep sea sediments since the meta stable carbonate phases provide an additional driving force for recrystallisation we show that the sr ca ratio of foraminiferal calcite can be used to assess the degree of diagenetic alteration of their shell chemistry using this method we demonstrate that the primary signal in the oxygen isotope ratios is preserved in the studied core in the mg ca record the relative change of foraminiferal mg ca ratios seems to be preserved but absolute values are influenced by diagenesis the second set of proxies comprises 13c and c n ratios of organic carbon these are used in pelagic sediments in order to assess the origin of organic carbon terrestrial or marine phytoplankton it is demonstrated here that a simple two end mixing model cannot explain the observed co occurrence of relatively high 13corg and c n values as the 13corg values co vary with the aragonite content we attribute this signature to varying contribution of organic carbon from benthic algae which are also the major aragonite producers on the platform top

structural analysis and miocene to present tectonic evolution of a lithospheric scale transcurrent lineament the sciacca fault sicilian channel central mediterranean sea abstract seismo stratigraphic and structural analysis of a large number of multichannel seismic reflection profiles acquired in the northern part of the sicilian channel allowed a 3 d reconstruction of a regional ns trending transfer zone which displays a transcurrent tectonic regime and that is of broad relevance for its seismotectonic and geodynamic implications it is constituted of two major transcurrent faults delimiting a 30 km wide mostly undeformed basin the western fault capo granitola does not show clear evidence of present day tectonic activity and toward the south it is connected with the volcanic area of the graham bank the eastern fault sciacca is structurally more complex showing active deformation at the sea floor particularly evident along the nerita bank the sciacca fault is constituted of a master and splay faults compatible with a right lateral kinematics sciacca fault is superimposed on an inherited weakness zone a mesozoic carbonate ramp which borders to the east a 2 5 km thick plio quaternary basin and that was reactivated during the pliocene a set of scaled claybox analogue models was carried out in order to better understand the tectonic processes that led to the structural setting displayed by seismic data tectonic structures and uplift subsidence patterns generated by the models are compatible with the 3 d model obtained from seismic reflection profiles the best fit between the tectonic setting deriving from the interpretation of seismic profiles and the analogue models was obtained considering a right lateral movement for the sciacca fault nevertheless the stress field in the study area derived from gps measurements does not support the present day modelled right lateral kinematics along the sciacca fault moreover seismic events along this fault show focal mechanisms with a left lateral component we ascribe the slip change along the sciacca fault from a right lateral transcurrent regime to the present day left lateral kinematics to a change of principal horizontal stress direction starting from late pliocene

genesis and dispersal of carbonate mud relative to late quaternary sea level change along a distally steepened carbonate ramp northwestern shelf western australia abstract accumulation of carbonate mud is minor on the northwest shelf western australia a broad 200 300 km wide distally steepened tropical carbonate ramp it is negligible along most of the inner ramp 0 to 50 m water depth owing to siliciclastic riverine input it is also negligible along the mid from 50 to 120 m ramp and where the entire ramp narrows to 100 km owing to constant reworking by storm waves and ocean swell in these areas carbonate mud is derived mostly from mechanical degradation of skeletal fragments but this does not include calcified remains of calcareous green algae e g halimeda although these plants grow locally only along the outer 120 to 200 m water depth ramp and slope is there any relatively abundant accumulation of carbonate mud here the sediment consists of modern pelagic foraminifer pteropod and nannoplantkon ooze and aragonitic needle rich 2 m micrite the latter having an age based on ams 14c of 19 ka distribution of aragonite micrite defines an extensive 5 0 104 km2 yet relatively narrow 40 km tract running 600 km along the platform margin crystal morphology mineralogy and isotope c o composition identify the micrite to be a seawater precipitate its production and seaward export having occurred during the last glacial maximum when lowered sea level transformed the otherwise broad platform into a narrow epicontinental shelf margin now the modern distal slope today this sediment body lies stranded in deep water about 200 300 km seaward of the shallow inner ramp the volume of micrite produced appears equal to the present day production potential of the great bahama bank rapid postglacial rise in sea level and change in platform geometry climate and oceanography were very influential factors in addition to water depth and area of submergence in the production and distribution of aragonite micrite along the northwest shelf in general 1 epicontinental carbonate platforms can lack substantial micrite accumulation when oceanic current and wave energies sweep unimpeded across a platform and coastal clastics and absence of shoal barriers prevent development of protective lagoons and carbonate tidal flats 2 not all highstand carbonate systems are associated with significant amounts of micrite in shallow water environments nor do they necessarily export large volumes of micrite to the periplatform realm and 3 some lowstand systems can produce and export volumes of carbonate mud that rival highstand systems

late miocene halimeda alga microbial segment reefs in the marginal mediterranean sorbas basin spain a 6 ma messinian late miocene bioherm unit on the southern slope of the sorbas basin se spain contains numerous biotically diverse lensoid patch reefs that formed on a shelf to basin slope during a cycle of relative sea level change halimeda reefs are the largest and most complex of the patch reefs and are divisible into core cap and flank facies on the upper and midslope they are up to 40 m thick and 400 m long they become smaller downslope the core consists of jumbled halimeda segments released by spontaneous disaggregation of the alga the segments were stabilized close to their sites of growth and rapidly lithified by micritic and peloidal microbial crusts residual cavities were further veneered by isopachous marine cements flank facies consisting of bedded packstones to rudstones form wedge shaped units lateral to the mounds cap facies consist of bioclastic calcarenites calcirudites and microbial carbonates synsedimentary lithification assisted rapid accretion and inhibited off mound export of sediment allochthonous reef derived blocks on the mid slope reflect penecontemporaneous rigidity of the halimeda bioherms proximal porites coral frame patch reefs associated with calcarenites were located near the shelf margin during the initial lowstand stage halimeda segment reefs associated with calcarenites and silty marls developed on the midslope and bivalve bryozoan serpulid reefs formed on the lower slope in silty marls with occasional turbidites during the transgressive stage coral patch reefs near the shelfbreak were overgrown by halimeda during highstand progradation cap facies spread basinward as a sheet connecting many of the midslope patch reefs these ancient analogues differ from most modern halimeda reefs in being discrete laterally restricted patch reefs surrounded by marly sediment and located on a slope they are however broadly comparable in biota thickness and depositional depth intense early lithification by microbial crusts and marine cements is an important feature of these messinian segment reefs it has not been reported from modern examples

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

evidences of a lithospheric fault zone in the sicily channel continental rift southern italy from instrumental seismicity data sicily channel is a portion of mediterranean sea between sicily southern italy and tunisia representing a part of the foreland apennine maghrebian thrust belt the seismicity of the region is commonly associated with the normal faulting related to the rifting process and volcanic activity of the region however certain seismic patterns suggest the existence of some mechanism coexisting with the rifting process in this work we present the results of a statistical analysis of the instrumental seismicity and a reliable relocalization of the events recorded in the last 30 yr in the sicily channel and western sicily using the double difference method and 3 d vp and vs tomographic models our procedure allows us to discern the seismic regime of the sicily sea from the tyrrhenian one and to describe the main features of an active fault zone in the study area that could not be related to the rifting process we report that most of the events are highly clustered in the region between 12 5 13 5 e and 35 5 37 n with hypocentral depth of 5 40 km and reaching 70 km depth in the southernmost sector the alignment of the seismic clusters the distribution of volcanic and geothermal regions and the location of some large events occurred in the last century suggest the existence of a subvertical shear zone extending for least 250 km and oriented approximately nne ssw the spatial distribution of the seismic moment suggests that this transfer fault zone is seismically discontinuous showing large seismic gaps in proximity of the ferdinandea island and graham and nameless bank

heterozoan carbonates from the equatorial rocky reefs of the galapagos archipelago strongly influenced by seasonal and interannual i e el nino southern oscillation upwelling the equatorial setting of the galapagos archipelago is divided into well defined temperature nutrient and calcium carbonate saturation aragonite regions to understand the relationship between oceanographic properties and sediment grain associations grain size carbonate content and components from sea floor surface samples were analysed representing the main geographical regions of the galapagos archipelago the shallow water rocky reefs of the galapagos archipelago are characterized by mixed carbonate siliciclastic slightly gravelly sands despite minor differences in carbonate content major differences exist in the distribution and composition of key carbonate producing biota halimeda is absent and benthic foraminifera occur in extremely low abundance the western side of the galapagos archipelago is strongly influenced by nutrient rich low aragonite subtropical water which generates a heterozoan carbonate biofacies in a tropical realm resembling cold water counterparts i e serpulid echinoderm gastropod barnacle and bryozoan rich facies the central east region is composed of a transitional heterozoan biofacies biofacies observed in the northern region have an increased occurrence of tropical corals albeit with a minor overall contribution to the carbonate components although the temperature gradient would allow for a broader distribution of photozoan biofacies the increased nutrient concentration and related reduced light penetration from the upwelled waters favour heterozoan carbonate factories mimicking cool water deeper or higher latitude environments the recent sedimentary record of the galapagos archipelago presents a range of tropical heterozoan carbonate communities responding to more than simply latitude or temperature but a much more complex mixture of physical evolutionary and geological processes

production of lime mud by breakdown of foraminiferal tests abstract many sources of lime mud have been discussed in the literature however foraminifers despite their abundance and importance in recent as well as in ancient sediments have been generally disregarded this study is based on stereo microscope observations and on a detailed sem study of modern carbonate sediments from new caledonia and french polynesia and of foraminiferal tests many particles of the mud fraction have a morphology and composition similar to particles observed in benthic foraminiferal tests the particles are calcitic or mg calcitic needles or are columns composed of crystallites less than 0 5 m in size in tropical environments foraminifers can produce as much as 1 kg m 2 of carbonate annually and their tests may form more than 80 of the sediment these observations show the genetic link from mud back to foraminiferal tests and show that at least a noticeable part of the carbonate mud can result from the breakdown of foraminiferal tests the role of foraminifers for the production of calcitic mud may be as important as the role of halimeda for the production of biogenic aragonite

accretionary mechanisms and temporal sequence of formation of the boda limestone mud mounds upper ordovician siljan district sweden abstract late ordovician mud mounds in the boda limestone siljan area central sweden consist mainly of massive spiculitic stromatactis limestone similar to other well known paleozoic mud mounds the mound cores are predominantly formed by spiculite and ostracod rich mudstone and or wackestone and networks of spar filled syndepositional cavities the mounds of the boda limestone are specific in two ways 1 large parts of the lower mound cores are formed by a palaeoporella framestone and or bafflestone with signs of early recrystallization and cementation and 2 the stromatactis facies is accompanied by masses of limestone with non stromatactis cryptocrystalline patches cryptocrystalline patches are filled with massive fibrous low mg calcite have cloudy transitional margins contain randomly spaced skeletal grains and dolomitic micro inclusions and are interpreted as recrystallized patches of the original host lime mud models of formation of paleozoic mud mounds generally hypothesize accretionary processes that are based on sponge biomass degradation and associated diagenetic processes in the boda limestone palaeoporella skeleton disintegration early recrystallization and additionally cementation were essential for the mound formation the boda mounds exemplify that formation of paleozoic mud mounds reflects a spectrum of different essentially diagenetic accretionary mechanisms this diversity should be taken into account in future discussions about paleozoic mud mound formation the new name osmundsberget formation is given for a hirnantian succession of brachiopod rich limestone above the boda limestone the osmundsberget formation occurs only in direct geographical vicinity to the mud mounds

authigenic calcium carbonate flux in groundwater controlled lakes implications for lacustrine paleoclimate records groundwater dominated lakes are an important feature of many landscapes their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce where groundwater and lake composition are favorable carbonate mineral precipitation evaporative concentration of lake water and microbial processes can combine to strongly deplete dissolved ca relative to influent groundwaters the authigenic carbonate flux acf can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge here we analyze sedimentary records from two marl producing groundwater controlled lakes and demonstrate a link between one dimensional acf and the palmer drought severity index pdsi a measure of land surface wetness in a restricted outflow lake with high carbonate alkalinity acf is enhanced during historically wet climatic periods in response to increased aquifer recharge rates acf in this lake declines during droughts a neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between acf and pdsi history ionic chemistry carbonate mineral equilibria and 13 c patterns of dissolved inorganic carbon show that the sensitivity of the acf signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover copyright 2005 elsevier ltd

calcium magnesium and strontium cycling in stratified hardwater lakes lake kinneret sea of galilee israel abstract in stratified hardwater lakes calcite crystallization in the epilimnion and partial dissolution in the hypolimnion play important roles in the cycling of ca2 in the water column mg2 and sr2 coprecipitate with this mineral to be released together with ca2 upon its dissolution here we focus on lake kinneret sea of galilee israel a stratified warm hardwater lake searching for an interpretable high resolution picture of the processes that drive ca2 mg2 and sr2 cycling in this and similar lakes elsewhere in total 1428 water samples were collected from the lake and another 81 samples were collected from the jordan river and two small streams discharging into it covering a full monomictic cycle from december 2001 through march 2003 particulate material was retrieved from sediment traps in the hypolimnion the water samples were analyzed for na k mg2 ca2 sr2 cl so42 hco3 and br and the trapped particulates were examined under sem and analyzed for their ca mg and sr content individual calcite crystals within the particulate material underwent la icp ms analysis for ca mg and sr downward transport of ca2 involves crystallization of calcite in the epilimnion followed by its settling through the water column followed by its partial dissolution in the hypolimnion magnesium and sr2 follow ca2 by coprecipitation in calcite and are released upon its dissolution in the hypolimnion upward cycling of the three solutes occurs through an admixture of the hypolimnetic water into the epilimnion during thermocline deepening terminated by overturn of the lake removal rates of mg2 and sr2 from the lake relative to that of ca2 and the water calcite distribution coefficients dmg and dsr were calculated from the analyses using 1 epilimnion water and bulk particulates 2 epilimnion water only and 3 epilimnion water and calcite crystals in the particulates the dsr values obtained were internally consistent 0 194 5 9 0 22 0 28 and 0 204 0 232 respectively however the dmg value for the bulk particulates 0 0477 was 6 times higher than that corresponding to calcite crystals included therein 0 00841 this difference is attributed to phytoplankton debris in the bulk particulates and should be of concern to geochemists using mg ca ratios in limestone to reconstruct ancient aquatic environments the cycling of ca2 mg2 and sr2 in the stratified lake is monitored by mg ca vs sr ca regression diagrams where each line represents the water column composition on a specific date the distance of the data points from the initial mixed lake coordinates reflects the fractionation of ca2 mg2 and sr2 after the onset of stratification the regression lines rotate in an orderly anticlockwise direction in response to the high calcite flux from the epilimnion in spring and the higher rate of mg2 replenishment than that of sr2 compensating for their loss in calcite the release of mg2 and sr2 from dissolving calcite in the hypolimnion at an mg sr ratio 7 5 eq eq much lower than that in the surrounding water 160 eq eq lends additional support to the anticlockwise rotation reversal of rotation occurs in summer when calcite crystallization and the freshwater supply slow down and brackish and saline water sources take control over the mg sr ratio in the lake subsequent turnover and mixing of the lake in winter reset the mg ca and sr ca ratios to their original values before the next stratification

model of seawater composition for the phanerozoic we present an inverse model of phanerozoic seawater com position calibrated against updated paleoseawater compositions from fluid inclusions in marine halites the model considers step wise alteration of seawater composition via 1 variable input of river water 2 variable rates of alteration of seawater through reactions at mid ocean ridges and 3 variable rates of alteration of seawater through reactions on ridge flanks and across the ocean floor in general the model achieves agreement with paleoseawater fluid inclusion data for na 1 c a 2 1 s o 4 2 2 and k 1 particularly when variable runoff is considered variable rates of basalt seawater interactions at both ridges and ridge flanks are required to understand the evolution of seawater particularly the observed near constant concentration of k 1 through time

mg fractionation in crustose coralline algae geochemical biological and sedimentological implications of secular variation in the mg ca ratio of seawater the mg ca ratio of seawater has varied significantly throughout the phanerozoic eon primarily as a function of the rate of ocean crust production specimens of the crustose coralline alga neogoniolithon sp were grown in artificial seawaters encompassing the range of mg ca ratios shown to have existed throughout the phanerozoic significantly the coralline algae s skeletal mg ca ratio varied in lockstep with the mg ca ratio of the artificial seawater specimens grown in seawater treatments formulated with identical mg ca ratios but differing absolute concentrations of mg and ca exhibited no significant differences in skeletal mg ca ratios thereby emphasizing the importance of the ambient mg ca ratio and not the absolute concentration of mg in determining the mg ca ratio of coralline algal calcite specimens grown in seawater of the lowest molar mg ca ratio mmg ca 1 0 actually changed their skeletal mineralogy from high mg skeletal mmg ca 0 04 to low mg calcite skeletal mmg ca 0 04 suggesting that ancient calcitic red algae which exhibit morphologies and modes of calcification comparable to neogoniolithon sp would have produced low mg calcite from the middle cambrian to middle mississippian and during the middle to late cretaceous when oceanic mmg ca approached unity by influencing the original mg content of carbonate facies in which these algae have been ubiquitous this condition has significant implications for the geochemistry and diagenesis of algal limestones throughout most of the phanerozoic the crustose coralline algae s precipitation of high mg calcite from seawater that favors the abiotic precipitation of aragonite indicates that these algae dictate the precipitation of the calcitic polymorph of caco3 however the algae s nearly abiotic pattern of mg fractionation in their skeletal calcite suggests that their biomineralogical control is limited to polymorph specification and is generally ineffectual in the regulation of skeletal mg incorporation therefore the mg ca ratio of well preserved fossils of crustose coralline algae when corrected for the effect of seawater temperature may be an archive of oceanic mg ca throughout the phanerozoic magnesium fractionation algorithms that model algal skeletal mg ca as a function of seawater mg ca and temperature are presented herein the results of this study support the empirical fossil evidence that secular variation of oceanic mg ca has caused the mineralogy and skeletal chemistry of many calcifying marine organisms to change significantly over geologic time

florisphaera profunda and the origin and diagenesis of carbonate phases in eastern mediterranean sapropel units high relative concentrations of the lower photic zone nannofossil florisphaera profunda have been reported in all recent eastern mediterranean sapropels in the most recent sapropel s1 high bulk sediment sr ca ratios occur along with high f profunda contents toward the base of the unit exemplified here in four cores from 1 5 3 5 km water depth co occurring biogenic carbonates contain insufficient sr to account for these high sr concentrations and x ray diffraction and selective leaching show that the high sr ca ratios are due to aragonite the caco3 polymorph that is rarely preserved in deep marine sediments with 1 wt sr the possible sources of this aragonite include 1 precipitation with surface ocean production 2 detrital input from shallow water sediments by high continental runoff or 3 postdepositional diagenetic formation driven by increased pore water alkalinity resulting from sulphate reduction the third formation mechanism for the aragonite is favored in which case the similarity in the positions of the aragonite and f profunda abundance maxima in sapropels is probably related to corg accumulation and resulting sulphide diagenesis that produces high pore water alkalinity there is clear micropaleontological evidence that dissolution of the less soluble biogenic low mg caco3 is occurring or has occurred during early diagenesis in these sediments despite the coexistence of the more soluble high mg calcite and aragonite polymorphs similar sr ca maxima are also found associated with older sapropels always located close both to local minima in surface ocean 18o that signal maximum monsoon driven runoff and to maxima in diagenetic sediment sulphide contents high freshwater flows from monsoons are believed to drive eastern mediterranean sapropel formation through water column stabilization that favors f profunda production and later through development of deep water column dysoxia anoxia because of reduced ventilation the relative abundances of f profunda are high between 5 and 11 14c kyr b p with a maximum at 9 14c kyr b p the surface ocean production changes marked by f profunda therefore begin earlier and finish later than the formation of the s1 sapropel which only develops between 6 and 10 14c kyr b p

an overview of biomineralization processes and the problem of the vital effect biomineralization links soft organic tissues which are compositionally akin to the atmosphere and oceans with the hard materials of the solid earth it provides organisms with skeletons and shells while they are alive and when they die these are deposited as sediment in environments from river plains to the deep ocean floor it is also these hard resistant products of life which are mainly responsible for the earth s fossil record consequently biomineralization involves biologists chemists and geologists in interdisciplinary studies at one of the interfaces between earth and life leadbeater and riding 1986 biomineralization refers to the processes by which organisms form minerals the control exerted by many organisms over mineral formation distinguishes these processes from abiotic mineralization the latter was the primary focus of earth scientists over the last century but the emergence of biogeochemistry and the urgency of understanding the past and future evolution of the earth are moving biological mineralization to the forefront of various fields of science including the earth sciences the growth in biogeochemistry has led to a number of new exciting research areas where the distinctions between the biological chemical and earth sciences disciplines melt away of the wonderful topics that are receiving renewed attention the study of biomineral formation is perhaps the most fascinating truly at the interface of earth and life biomineralization is a discipline that is certain to see major advancements as a new generation of scientists brings cross disciplinary training and new experimental and computational methods to the most daunting problems it is however by no means a new field the first book on biomineralization was published in 1924 in german by w j schmidt schmidt 1924 and the subject has continued to intrigue a dedicated community of scientists for many years until the early 1980s the field was known as

spatial variation of present day stress field and tectonic regime in tunisia and surroundings from formal inversion of focal mechanisms geodynamic implications for central mediterranean we compiled 123 focal mechanisms from various sources for tunisia and adjacent regions up to sicily to image the current stress field in the maghrebides chain from tunisia to sicily and its foreland stress inversion of all the available data provides a first order stress field with a n150 e horizontal compression shmax and a transpressional tectonic regime but the obtained stress tensor poorly fit to the data set we separated them into regional subsets boxes in function of their geographical proximity kinematic regime homogeneity of kinematic orientations and tectonic setting their respective inversion evidences second and third order spatial variations in tectonic regime and horizontal stress directions the stress field gradually changes from compression in the maghrebides thrust belt to transpression and strike slip in the atlassic and pelagian foreland respectively where preexisting nw se to e w deep faults system are reactivated this spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data the major slab transfer edge propagator faults i e north south axis hammamet relay and malte escarpment which laterally delimit the subducting slabs play an active role in second and third order lateral variations of the tectonic regime and stress field orientations over the tunisian sicilian domain the past and current tectonic deformations and kinematics of the central mediterranean are subordinately guided by the plate convergence i e africa eurasia controlled or influenced by lateral slab migration segmentation and by deep dynamics such as lithosphere mantle interaction

re examination of the recent history of meromictic waldsea lake saskatchewan canada abstract waldsea lake a small 5 km 2 meromictic lake in central saskatchewan is one of the most intensely studied saline lacustrine environments in western canada the high salinity and meromixis of this topographically and hydrologically closed basin result in exceptional preservation of fine lamination coupled with a diverse endogenic and authigenic mineral suite this study applies new high resolution paleolimnological techniques to decipher the chemical and hydrologic fluctuations that have occurred in waldsea over the past several thousand years and shows that significant geolimnological fluctuations have occurred within the past two millennia

low magnesium calcite produced by coralline algae in seawater of late cretaceous composition abstract shifts in the mg ca ratio of seawater driven by changes in midocean ridge spreading rates have produced oscillations in the mineralogy of nonskeletal carbonate precipitates from seawater on time scales of 108 years since cambrian time skeletal mineralogies of anatomically simple organisms functioning as major reef builders or producers of shallow marine limestones have generally corresponded in mineral composition to nonskeletal precipitates here we report on experiments showing that the ambient mg ca ratio actually governs the skeletal mineralogy of some simple organisms in modern seas coralline algae produce skeletons of high mg calcite 4 mol mgco3 we grew three species of these algae in artificial seawaters having three different mg ca ratios all of the species incorporated amounts of mg into their skeletons in proportion to the ambient mg ca ratio mimicking the pattern for nonskeletal precipitation thus the algae calcified as if they were simply inducing precipitation from seawater through their consumption of co2 for photosynthesis presumably organic templates specify the calcite crystal structure of their skeletons in artificial seawater with the low mg ca ratio of late cretaceous seas the algae in our experiments produced low mg calcite 4 mol mgco3 the carbonate mineral formed by nonskeletal precipitation in those ancient seas our results suggest that many taxa that produce high mg calcite today produced low mg calcite in late cretaceous seas

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

effects of secular variation in seawater mg ca ratio calcite aragonite seas on caco3 sediment production by the calcareous algae halimeda penicillus and udotea evidence from recent experiments and the geological record independent lines of geological evidence suggest that fluctuations in the mg ca ratio of seawater between 1 0 and 5 2 have caused the oceans to alternate between favouring the precipitation of the aragonite and high mg calcite polymorphs of calcium carbonate mmg ca 2 aragonite seas and the low mg calcite polymorph mmg ca 2 calcite seas throughout phanerozoic time the rise of aragonite secreting bryopsidalean algae as major producers of carbonate sediments in middle palaeogene time a role that they maintained through to the present has been attributed to a transition from calcite to aragonite seas in early cenozoic time recent experiments on the modern carbonate sediment producing bryopsidales halimeda penicillus and udotea reveal that their rates of calcification linear extension and primary production decline when reared in experimental calcite seawaters mmg ca 2 these normally aragonitesecreting algae also began producing at least one quarter of their caco3 as calcite under calcite sea conditions indicating that their biomineralogical control can be partially overridden by ambient seawater chemistry the observation that primary production and linear extension declined along with calcification in the mineralogically unfavourable seawater suggests that photosynthesis within these algae is enhanced by calcification via liberation of co2 and or h thus the reduced fitness of these algae associated with their low rates of calcification in calcite seas may have been exacerbated by concomitant reductions in tissue mass and algal height

fine scale recognition and use of mesoscale fronts by foraging cape gannets in the benguela upwelling region oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes these fronts generally attract fish and may therefore be targeted by marine top predators in the southern benguela upwelling system such fronts might be used as environmental cues by foraging seabirds in this study we analyzed high frequency foraging tracks gps 1 s sampling of cape gannets morus capensis from two colonies located on the west and east coast of south africa in relation to mesoscale fronts detected on daily high resolution chlorophyll a maps modis 1 km we tested the association of i searching behavior and ii diving activity of foraging birds with mesoscale fronts we found that cape gannets shift from transiting to area restricted search mode ars at a distance from fronts ranging between 2 and 11 km median is 6 7 km this suggests that cape gannets may be able to sense fronts smell or vision or other predators and that such detection triggers an intensified investigation of their surroundings i e ars also we found that diving probability increases near fronts in 11 out of 20 tracks investigated 55 suggesting that cape gannets substantially use fronts for feeding in the remaining cases 45 birds may have used other cues for feeding including fishing vessels particularly for gannets breeding on the west coast we demonstrated in this study that oceanographic structures such as mesoscale fronts are important environmental cues used by a foraging seabird within the rich waters of an upwelling system there is now need for further investigations on how cape gannets actually detect these fronts

the effects of secular calcium and magnesium concentration changes on the thermodynamics of seawater acid base chemistry implications for eocene and cretaceous ocean carbon chemistry and buffering reconstructed changes in seawater calcium and magnesium concentration ca2 mg2 predictably affect the ocean s acid base and carbon chemistry yet inaccurate formulations of chemical equilibrium constants are currently in use to account for these changes here we develop an efficient implementation of the miami ionic interactionmodel to predict all chemical equilibrium constants required for carbon chemistry calculations under variable ca2 and mg2 we investigate the impact of ca2 and mg2 on the relationships among the ocean s ph co2 dissolved inorganic carbon dic saturation state of caco3 and buffer capacity increasing ca2 and or mg2 enhances ion pairing which increases seawater buffering by increasing the concentration ratio of total to free uncomplexed carbonate ion an increase in ca2 however also causes a decline in carbonate ion to maintain a given thereby overwhelming the ion pairing effect and decreasing seawater buffering given the reconstructions of eocene ca2 and mg2 ca2 20mm mg2 30mm eocene seawater would have required essentially the same dic as today to simultaneously explain a similar to modern and the estimated eocene atmospheric co2 of 1000 ppm during the cretaceous at 4 times modern ca2 ocean buffering would have been at a minimum overall during times of high seawater ca2 caco3 saturation ph and atmospheric co2 were more susceptible to perturbations of the global carbon cycle for example given both eocene and cretaceous seawater ca2 and mg2 a doubling of atmospheric co2 would require less carbon addition to the ocean atmosphere system than under modern seawater composition moreover increasing seawater buffering since the cretaceous may have been a driver of evolution by raising energetic demands of biologically controlled calcification and co2 concentration mechanisms that aid photosynthesis

aragonite and calcite preservation in sediments from lake iznik related to bottom lake oxygenation and water column depth this study examines the forcing mechanisms driving long term carbonate accumulation and preservation in lacustrine sediments in lake iznik north western turkey since the last glacial currently carbonates precipitate during summer from the alkaline water column and the sediments preserve aragonite and calcite based on x ray diffraction data carbonate accumulation has changed significantly and striking reversals in the abundance of the two carbonate polymorphs have occurred on a decadal time scale during the last 31 ka cal bp different lines of evidence such as grain size organic matter and redox sensitive elements indicate that reversals in carbonate polymorph abundance arise due to physical changes in the lacustrine setting for example water column depth and lake mixing the aragonite concentrations are remarkably sensitive to climate and exhibit millennial scale oscillations extending observations from modern lakes the iznik record shows that the aerobic decomposition of organic matter and sulphate reduction are also substantial factors in carbonate preservation over long time periods lower lake levels favour aragonite precipitation from supersaturated waters prolonged periods of stratification and consequently enhanced sulphate reduction favour aragonite preservation in contrast prolonged or repeated exposure of the sediment water interface to oxygen results in in situ aerobic organic matter decomposition eventually leading to carbonate dissolution notably the iznik sediment profile raises the hypothesis that different states of lacustrine mixing lead to selective preservation of different carbonate polymorphs thus a change in the entire lake water chemistry is not strictly necessary to favour the preservation of one polymorph over another therefore this investigation is a novel contribution to the carbon cycle in lacustrine systems

sicily s fold thrust belt and slab roll back the si ri pro seismic crustal transect sicily is a thick orogenic wedge formed by 1 the foreland african and its sicilian orogen and 2 the thick skinned calabrian peloritani wedge the crust under central sicily from the tyrrhenian margin to the coastline of the sicily channel has been investigated by the multidisciplinary si ri pro research project the project dealt with the nature and thickness of the crust and depth and geometry of the moho which is essential in formulating subduction models and improving the knowledge of african and tyrrhenian european lithospheres the results resolve features such as 1 the main orogenic wedge 2 the very steep nw se trending regional monocline suggesting inflection of the foreland crust 3 the deep caltanissetta synform imaged for the first time to about 25 km and 4 the top of the crystalline basement and the inferred crust mantle boundary the si ri pro transect confirmed that the nnw dipping autochthonous iblean platform of se sicily and its basement extends all the way into central sicily further nw towards the nnw end of the transect a large uplift involves the iblean platform and its underlying basement the associated gravity anomaly is interpreted as the southern wedge edge of the tyrrhenian mantle that splits the subducting iblean pelagian african continental slab from an overlying synformal stack of allochthonous thrust sheets supplementary materials additional data are available at www geolsoc org uk sup18594

carbonate and organic matter sedimentation and isotopic signatures in lake chungara chilean altiplano during the last 12 3 kyr abstract sediments in lakes in the andean volcanic setting are often made up of diatomaceous ooze together with volcaniclastics and small amounts of carbonates despite their scarcity carbonates along with organic matter provide significant paleoenvironmental information about lake systems this study focuses on the carbonates in lake chungara their morphologies distribution and origin deduced from the isotopic markers these markers reflected changes in the water and the biomass between the onset of the holocene and around 9 6 cal kyr bp these changes are marked by general increases in toc tn and tn 15nair and by fluctuating values of toc 13cvpdb in its sediments and are probably related to major shifts in the lake surface volume associated with rises in lake level an increase in salinity around 10 cal kyr bp is thought to be linked to a short dry period giving rise to the onset of carbonate production the mid holocene arid period between 7 3 and 3 5 cal ka bp with a maximum of aridity around 6 0 cal kyr bp was deduced from 18ovpdb values in the endogenic carbonates these results match the reconstructions in lake titicaca based on benthic diatoms and paleoshore levels offshore sediments mainly consist of a diatomaceous ooze laminated in the lower half unit 1 and banded massive with tephra layers in the upper half of the sequence unit 2 toc 13cvpdb and the c n ratio confirm that phytoplankton was the main source of organic matter in these sediments shallower sediments units 3 to 5 developed in platform and littoral settings providing evidence of subaqueous macrophytes and to a lesser extent land plants carbonate content ranges between 0 1 and 6 wt in offshore settings 30 to 40 m water depth and reaches the maximum values in the lower part of unit 2 carbonate minerals low magnesium calcite and minor amounts of high magnesium calcite and aragonite are scarce and are arranged in mm thick layers commonly forming cm thick levels or bioclasts carbonate layers are made up of euhedral to subhedral spindle shaped calcite crystals and to a lesser extent aragonite needles all in the m range aragonite spheroids coexist in littoral sediments with other carbonate shapes and charophyte remains where carbonate reaches locally up to 20 wt co2 photosynthetic depletions related to seasonal phytoplankton blooms were responsible for the high frequency deposition of mm thick carbonate layers the average values for 13cvpdb in lake water plankton and sediments of lake chungara as organic matter or as carbonate are around 15 higher than commonly reported values in other lakes this 13c enrichment is attributed to carbon assimilation from a dic affected by methanogenesis in which hco3 is the dominant species the 13cvpdb and 18ovpdb variations and their covariation in endogenic carbonates suggest that lake water volume and lake level increased along the holocene

size fraction analysis of fish derived carbonates in shallow sub tropical marine environments and a potentially unrecognised origin for peloidal carbonates abstract marine bony fish are now known as primary producers of calcium carbonate furthermore within the shallow sub tropical platform settings of the bahamas this production process has been shown to occur at rates relevant to carbonate sediment production budgets fish excrete these carbonates as loosely aggregated pellets which post excretion exhibit a range of distinctive crystal morphologies and have mineralogies ranging from low 0 4 mol mgco 3 to high 4 40 mol mgco 3 mg calcites aragonite and amorphous carbonate phases here we provide the first quantitative assessment of the size fractions of the carbonates produced by a range of tropical fish species and document the extent of post excretion carbonate pellet break down under a range of physical agitation conditions specifically we document the morphologies and size fractions of i intact pellets at the point of excretion ii intact pellets after agitation in seawater and iii the particles released from pellets post disaggregation results indicate that fish derived pellets initially fall within the very fine to very coarse sand fractions exposure to conditions of moderate seawater agitation for 30 days results in significant pellet diminution 66 of initial pellet mass being released as individual particles whilst 34 is retained as partially intact pellets that are smaller fine sand grade and more rounded than initial pellets in contrast pellets exposed to very gently agitated conditions for up to 200 days show little change where pellet disaggregation does occur particles are commonly released as individual clay and silt grade crystals however some morphotypes e g polycrystalline spheres can be intergrown and are released as strongly cohesive particle clusters falling within the coarse silt to fine sand fractions only very vigorous agitation may disaggregate such particles resulting in the release of their component clay grade crystals we conclude that fish derived carbonates may thus contribute not only to the mud fraction of marine carbonates but also to the fine sand fraction as intergrown particles and to the fine to coarse sand fractions as intact and partially intact pellets these experimental data indicate that hydrodynamic regimes local to sites of excretion will influence the generation of carbonates with different size fraction ranges rapid pellet disaggregation is more likely in high energy settings hypothesised to result in redistribution of liberated mud grade particles to lower energy platform top settings and or off platform in contrast pellets excreted in lower energy settings are more likely to be preserved intact and are thus proposed as a previously unrecognised source of pelletal and peloidal carbonate sediments

capo granitola sciacca fault zone sicilian channel central mediterranean structure vs magmatism abstract the tectonic framework of the northern sector of the capo granitola sciacca fault zone cgsfz a nne oriented lithospheric strike slip fault zone located in the sicilian channel southern italy has been reconstructed with the aim to clarify the relationships between geometry and kinematics of the structures and the occurrence and distribution of the magmatic manifestations observed in the area this has been achieved by the interpretation of a large dataset composed of 2 d multichannel seismic profiles chirp profiles magnetic data and borehole information in addition to the volcanic edifices known in the graham and terribile banks this study has allowed to recognize several other magmatic manifestations the magmatic occurrences consist of small volcanic cones buried magma ascents and potential igneous sills the cgsfz is bounded by two strike slip fault systems the capo granitola fault system cgfs to the west and the sciacca fault system sfs to the east dominated by positive flower structures generated by tectonic inversion of nne oriented late miocene extensional faults only the southern part of the cgfs shows the presence of a sub vertical n s oriented strike slip master fault the sector between the two fault systems does not show a significant pliocene quaternary tectonic deformation except for its southern part hosting the terribile bank which is dissected by wnw to nw trending normal faults developed during late miocene and later reactivated this set of faults is currently active at the terribile bank whereas is buried by pliocene quaternary deposits in the central and northern sectors of the cgsfz the observed magmatism is driven by a mechanism of non plume origin magmas have used as open paths the faults of the cgfs and sfs which cut the whole lithosphere reaching the asthenosphere and producing partial melting by simple pressure release most of the magmatism develops along the strike slip master fault associated with the cgfs and the normal faults affecting the terribile bank the magmatic feeding of the terribile bank would be related to lateral magma migration coming from the structures of the sfs which would use the open pathways represented by active normal faults in the central northern part of the cgsfz magmas migrate upward along lithospheric faults then move laterally and rise toward the surface through nne and nw trending buried normal faults these late miocene faults do not reach the surface and this may have favoured the emplacement of igneous sills which in turn may explain the observed volcanic centres

interference between shallow and deep seated structures in the sicilian fold and thrust belt italy abstract the fold and thrust belt in western sicily is characterized by the presence and interference of shallow and deep seated compressional structures which were generated and developed at different structural levels the shallow structures consist of imbricated thrusts and asymmetric folds with a typical wavelength of 2 km involving relatively thin deep water units these units are superimposed on thick platform carbonate units along a wide and originally almost flat floor thrust the axial trend of the folds is variable as multi phase folding often occurred producing a characteristic interference pattern reflecting continuous variations of the apparent transport direction during the emplacement i e rotation of the allochthonous thrust sheets the deep seated structures consist of large double verging pop up structures with a typical wavelength of 5 10 km involving thicker platform carbonate successions the deep seated structures are characterized by large folds with vertical to overturned limbs caused by high angle transpressive ramps that reactivated previous i e mesozoic synsedimentary normal or transtensional faults the floor thrust of the shallow structures was passively deformed by the subsequent growth of the underlying younger deep seated structures large clockwise rotations of the tectonic units occurred during the compressional deformation and the amount of rotation is apparently related to the timing and amount of the tectonic transport

scleractinian corals produce calcite and grow more slowly in artificial cretaceous seawater the mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the calcite hexagonal and aragonite orthorhombic polymorphs of caco3 throughout the phanerozoic eon these intervals of calcite and aragonite production or calcite seas and aragonite seas are thought to be caused primarily by secular variation in the molar magnesium calcium ratio of seawater mmg ca 2 5 aragonite 1 high mg calcite mmg ca 2 5 low mg calcite a ratio that has oscillated between 1 0 and 5 2 throughout the phanerozoic in laboratory experiments we show that three species of scleractinian corals which produce aragonite in modern seawater and which have flourished as important reef builders primarily during aragonite seas of the past began producing calcite in artificial seawater with an ambient mmg ca ratio below that of modern seawater 5 2 the corals produced progressively higher percentages of calcite and calcified at lower rates with further reduction of the ambient mmg ca ratio in artificial seawater of imputed late cretaceous composition mmg ca 5 1 0 which favors the precipitation of the calcite polymorph scleractinian corals produced skeletons containing 30 low mg calcite skeletal mmg ca 0 04 these results indicate that the skeletal mineral used by scleractinian corals is partially determined by seawater chemistry furthermore slow calcification rates resulting from the production of largely aragonitic skeletons in chemically unfavorable seawater mmg ca 2 probably contributed to the scleractinians diminished reef building role in the calcite seas of late cretaceous and early cenozoic time

evaluating the ca isotope proxy the use of ca isotopes as a proxy for mass flux imbalances in the ca cycle is evaluated critically a compiled ca isotope record for the last 45 ma derived from bulk nannofossil ooze and with a temporal resolution of 0 5 ma and an interpretation of the record are presented in the context of the global ca cycle this analysis which assumes that nannofossil ooze records isotopic variations in seawater indicates a dynamic ca cycle in the cenozoic such dynamic behavior has serious implications for the c cycle and suggests feedbacks between the ca and c cycles to stabilize or buffer the oceanic carbon reservoir alternative applications of the ca isotope proxy are investigated using numerical models to determine the extent to which ca isotopes are sensitive to other aspects of the ca cycle the results of the simulations are applied to specific cases in the cenozoic the simulations illustrate how variations in the global fractionation factor between calcium carbonate and seawater can produce trends similar to those observed when comparing previously published ca isotopic compositions of marine barite to the nannofossil ooze record the large drop in the 44 ca value of bulk nannofossil ooze near the eocene oligocene boundary can be reconciled in two ways either as a substantial increase in weathering relative to sedimentation or as an indicator of changing depositional mode within the ocean though the preferred interpretation is not clear at present it is evident that ca isotopes stand to be a unique proxy for ca cycling once the isotope systematics are elucidated

increased production of calcite and slower growth for the major sediment producing alga halimeda as the mg ca ratio of seawater is lowered to a calcite sea level abstract laboratory experiments were conducted to subject the calcareous alga halimeda a prolific producer of aragonite in the modern ocean to a variety of ambient mg ca ratios these experiments were based on three predictions 1 that halimeda would calcify at a lower rate when the ambient mg ca ratio was reduced from its high level in modern seawater 5 2 2 that this alga would grow more slowly under these conditions because its calcification yields as a byproduct co2 which is available for photosynthesis and 3 that the calcite content of halimeda s skeleton would increase as a percentage of total caco3 as predicted reduction of the mg ca ratio of ambient artificial seawater from its modern level to estimated early oligocene and early eocene levels 2 5 and 1 5 respectively resulted in progressively lower rates of calcification production of organic matter and linear growth for halimeda incrassata colonies the ambient mg ca ratio exerted a stronger influence over the rate of calcification than ca2 which in the geologic past has risen in seawater whenever the ambient mg ca ratio has declined thus although elevation of ca2 at such times would have promoted the calcification and growth of halimeda the concomitant decline of the mg ca ratio would have had a stronger negative effect in addition the percentage of skeletal material consisting of calcite rose from 8 in modern day seawater to 16 in artificial early oligocene seawater and 46 in artificial early eocene seawater magnesium was incorporated into this calcite as a function of the ambient mg ca ratio with a fractionation pattern differing only slightly from that of nonskeletal calcite halimeda exerts less biological control over its biomineralization than the related genera penicillus and udotea which in previous experiments produced only 22 25 of skeletal caco3 as calcite in seawater having a very low mg ca ratio 1 0 nonetheless it is likely that many taxa of green algae that produce little or no calcite today would have produced a substantial proportion of skeletal low mg caco3 as calcite in ancient seas such as those of the cretaceous whose mg ca ratios were close to unity

aragonitic algae in calcite seas effect of seawater mg ca ratio on algal sediment production abstract secular variation in seawater mg ca would have subjected the aragonite producing codiacean algae to two intervals of low mg calcite seas mmg ca mmg ca 2 seas since their origin in the ordovician it is asserted that the aragonite high mg calcite affinity of modern and recent tropical seas mmg ca 2 has enabled the aragonitic codiaceae to act as major carbonate sediment producers in these seas to test this assertion specimens of the sediment producing codiacean alga udotea flabellum were grown in artificial seawaters formulated at mmg ca ratios 1 0 2 5 5 2 that have occurred in the oceans throughout the geologic history of the codiaceae while the u flabellum algae produced exclusively aragonite in both the artificial boundary seawater mmg ca 2 5 and the artificial aragonite high mg calcite seawater modern seawater mmg ca 5 2 the algae produced a portion 25 3 of their caco3 as low mg calcite 4 mol mgco3 in the artificial calcite seawater mmg ca 1 0 suggesting that their caco3 polymorph control can be partially overridden by ambient seawater chemistry primary productivity calcification and linear growth of the algae decreased with reductions in ambient mg ca despite increases in absolute ca concentration of the seawater reduced calcification in the lower mg ca seawaters is probably due to kinetic difficulties of producing aragonite from seawater that favors the nucleation of calcite the decreased linear growth and primary production are likely associated with reductions in the ambient co2 available for photosynthesis resulting from the reduced calcification these findings support the assertion that the dominant ecological and sedimentological roles of codiacean algae in recent tropical seas is facilitated by a seawater mg ca ratio that favors the nucleation of aragonite over calcite furthermore producing aragonite in seawater that favors the nucleation of low mg calcite mmg ca

finite amplitude evolution of instabilities associated with the coastal upwelling front abstract a primitive equation model is used to study the finite amplitude evolution of instabilities associated with the coastal upwelling front simulations of increasing complexity are examined that represent idealizations of summer conditions off the oregon coast including cases with steady and with time variable wind in a domain with alongshore uniform bathymetry and with time variable wind in a domain with realistic oregon coast bathymetry the numerical results indicate that the fastest growing mode in this system has approximately an 8 10 km alongshore wavelength but that once the disturbances grow to finite amplitude the predominant alongfront scale increases rapidly because of nonlinear effects separation of the total kinetic energy into contributions from the alongshore average flow and perturbation about that average shows that the initial growth of the perturbation kinetic energy is due to potential energy conversion but transfer of energy from the kinetic energy of the alongshore average

sediment characteristics in reef areas influenced by eutrophication related alterations of benthic communities and bioerosion processes abstract this study investigated sediment deposits and suspended particulate matter in three reef areas of reunion island characterized by varying benthic communities and bioerosion processes as a result of different eutrophication levels the sediments were sampled using two different methods hand collecting directly on the reef bottom and sampling by traps this approach allowed a comparison between the composition of reefal bottom sediments and suspended particles in locations where algal communities prevailed over corals as a result of nutrification a shift from coral to coralline algae dominated sediments could be observed in addition a decrease in sediment production and a prevalence of very fine sand to mud sized grains over medium to fine sands existed in the nutrient enriched areas this grain size difference probably is caused by a decrease in grazing activity in the enriched areas high proportions of coralline algal debris and sponge spicules were specifically found in the sediments within areas receiving high nutrient input these two diagnostic components were abundant in both the suspended particulate matter and in the fine fractions

top marine predators track lagrangian coherent structures meso and submesoscales fronts eddies filaments in surface ocean flow have a crucial influence on marine ecosystems their dynamics partly control the foraging behavior and the displacement of marine top predators tuna birds turtles and cetaceans in this work we focus on the role of submesoscale structures in the mozambique channel in the distribution of a marine predator the great frigatebird using a newly developed dynamic concept the finite size lyapunov exponent fsle we identified lagrangian coherent structures lcss present in the surface flow in the channel over a 2 month observation period august and september 2003 by comparing seabird satellite positions with lcs locations we demonstrate that frigatebirds track precisely these structures in the mozambique channel providing the first evidence that a top predator is able to track these fsle ridges to locate food patches after comparing bird positions during long and short trips and different parts of these trips we propose several hypotheses to understand how frigatebirds can follow these lcss the birds might use visual and or olfactory cues and or atmospheric current changes over the structures to move along these biologic corridors the birds being often associated with tuna schools around foraging areas a thorough comprehension of their foraging behavior and movement during the breeding season is crucial not only to seabird ecology but also to an appropriate ecosystemic approach to fisheries in the channel

architecture and neogene to recent evolution of the western calabrian continental margin an upper plate perspective to the ionian subduction system central mediterranean the western calabria continental margin forms the transition between the pliocene to recent marsili spreading center and continental calabria all parts of the upper plate of the ionian subduction zone integrating high resolution and crustal seismic images constrained by gravity modeling we provide a detailed reconstruction of the architecture of the margin and develop a new scheme for its miocene to present evolution this time span encompasses the continent continent collision between africa and eurasia subsequent orogenic collapse and rifting apart between the two continental masses and the pliocene to recent emplacement of oceanic crust in the vavilov and marsili basins the crust of the margin thins from the calabria coast 25 km to the marsili continent ocean transition 12 km on the whole upper and lower crusts thin proportionally with pure shear geometry the continental margin is covered by an oligocene to present sedimentary succession reaching a maximum thickness of 6 0 km in the paola basin during the miocene the continental margin experienced regional shortening accommodated by a large number of mainly west vergent thrusts possibly associated with the late stages of the kabilo calabrian chain shortening continued through pliocene to recent but was accommodated by a limited number of west vergent thrust faults located in the western part of the margin and by a few tens of kilometers wide syncline located in the eastern part of the profile the accommodation space created in the syncline core hosted a 4 5 km thick plio quaternary sedimentary succession the paola basin no significant extensional fault is observed along the profile miocene to recent subsidence was controlled by 1 a short wavelength component related to shortening and responsible for the formation of the paola basin syncline and possibly contributing to the uplift of onshore calabria and 2 a long wavelength component responsible for the regional subsidence and oceanward tilting of the calabria margin short wavelength subsidence ended in the late pliocene but long wavelength downward movements persisted and even accelerated during late pliocene to quaternary times when the present day bathymetry was achieved both horizontal deformations and vertical movements are difficult to explain in the context of a normal back arc basin without taking into consideration patterns of secondary mantle flow generated by the retreat of the subducting slab