a self consistent model of melting magma migration and buoyancy driven circulation beneath mid ocean ridges numerical modeling and analysis are used to investigate the processes leading to the eruption of mantle derived magma at mid ocean ridges our model includes the following effects melting due to decompression magma migration by percolation and circulation of the mantle driven by both the oceanic plates and the distribution of buoyancy beneath the ridge the distribution of buoyancy is due to both the low density of the liquid and the difference in the density of the residual solids relative to unmelted mantle material the calculation of densities is based on a simple petrological model in which garnet spinel lherzolite melts to form a basaltic liquid and a harzburgite residue we find that the system spontaneously evolves to a state in which a rapid upwelling beneath the ridge axis faster than the plate velocity is confined laterally by stably stratified residual material beneath the newly formed plates this effect is exaggerated if a modest decrease in the shear viscosity of the solid upon melting is included our results provide a simple explanation for the narrowness of the zone of crustal formation at mid ocean ridges the model also predicts a transition from steady state to episodic crustal formation as the spreading velocity is reduced perhaps giving rise to along axis variations in the character of seafloor spreading the narrow rapid upwelling gives rise to substantial porosities at depths that are a large fraction of the depth to the solidus this may allow the liquid at depth to segregate into macroscopic channels which would account for the consensus from experimental petrology that the liquids parental to morb are derived from well below the base of the crust

the role of fungi in the diagenetic alteration of spar calcite fungi may play a far more important role in carbonate diagenesis than has been previously suspected this can be demonstrated by placing known species of fungi on crystals of iceland spar calcite such experiments show that fungi can 1 cause sparmicritization through dissolution 2 produce spiky calcite through dissolution 3 trap and bind loose particles of calcite and 4 promote the growth of new calcite crystals although not observed in this series of experiments fungi can bore into substrates and cause sparmicritization the activity of fungi involves a complex interplay of substrate destruction and construction without the intervention of vast quantities of fluid

petrography and genesis of spicular and columnar geyserite from the whakarewarewa and orakeikorako geothermal areas north island new zealand domal masses of geyserite which surround many geyser vents in the whakarewarewa geothermal area are formed largely of spicules spicule columns and shrub columns the non branching spicules and the branches of branching spicules individually up to 3 cm high and 1 mm diameter have a laminated core encased by siliceous cortex silicified microbes are rare in the core but common in the cortex silicified microbial mats and pseudodendrites are found in the crevices between neighbouring spicules shrub columns up to 5 cm high and 1 5 cm in diameter are formed of opal a that was precipitated around a three dimensional branching shrub like microbial structure the shrub branches which are hollow with scalloped walls do not contain any evidence of the original microbes or minerals that formed them silicified microbial mats are present between the columns microbial boring and etching by acidic steam led to local diagenetic degradation of these columns in the geyserite mounds at whakarewarewa spicules and spicule columns are common whereas shrub columns are rare interbedding and intercalation of spicular geyserite with shrub columnar geyserite indicate however that these different morphologic entities probably formed under similar environmental conditions on the mounds around the geyser vents petrographic evidence shows that the spicules spicule columns and shrub columns grew through a combination of biotic and abiotic processes

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

sedimentary evolution of the torrecilla reef complex in response to tectonically forced regression early kimmeridgian northern spain the early kimmeridgian torrecilla reef complex in the northern iberian basin of spain consists of a fringing reef composed of eight accretionary units the first four were deposited along a steep margin they display down lapping and off lapping geometries and are characterised by poor reef framework development large volumes of reworked corals and transported sediment and limited growth of micro encrusters in contrast deposition of the fifth and younger accretionary units occurred on a shallow platform without a pronounced slope where coral reefs grew in a shallow protected environment the main features of these reefs are an absence of reef slope facies a high proportion of preserved framework elements relatively low volumes of intrareef sediment high proportions of terrigenous material and abundant micro encrusters and microbialites these reefs were protected from storm waves by long shore sand bars which also protected a very shallow lagoon during the last stage of sedimentation the early kimmeridgian was a period of rising global sea level a trend apparent across other portions of the iberian basin however geometry and sedimentary evolution of the torrecilla reef complex is consistent with those of off lapping reefs that develop during sea level fall thus we conclude that down stepping geometries and evolution to progressively shallower environments within the torrecilla reef complex occurred as a result of a tectonically forced regression d 2005 elsevier b v all rights reserved

the ellipsactinia limestones of the marsica area central apennines a reference zonation model for upper jurassic intra tethys reef complexes abstract this study presents a new and innovative distribution model of the main reef builders that thrived on bioconstructed margins of upper jurassic intra tethys platforms the proposed model is based on the zonation of an upper jurassic reef complex presently exposed in the central apennines excellent exposures allow the reconstruction of the reef profile across the platform margin biota are mainly represented by corals and calcified demosponges distributed with different amounts and aggregating structures along the reef complex microencrusters represent a secondary but important component that actively contributes to the reef construction process reef builders are distributed in variable quantities and with variable aggregating structures along the reef complex revealing a strong reef zonation like the biota the sedimentary features grain size sorting and reworking degree bioerosion cement crusts and cavities show a distinctive distribution along the reef complex three main zones have been recognized along the studied reef complex an internal more protected and deeper zone corresponding to a relatively deep back reef lagoon is dominated by corals and chaetetids a central zone reef flat where well preserved coral bioconstructions give rise to a true but discontinuous framework and a more external zone corresponding to the reef crest characterized by the shallowest depths recorded across the reef complex and dominated by stromatopores the latter forms mound shaped structures playing a role essential for the zoned character of the reef complex these structures actively contribute to the construction of a moderately high topographic relief in the reef crest

outcrop analogs for reservoir characterization and modeling of smackover microbial reefs in the northeastern gulf of mexico area abstract upper jurassic oxfordian smackover microbial reef buildups in the northeastern gulf of mexico consist primarily of shallow water thrombolites that develop on hardgrounds or rockgrounds associated with paleozoic basement paleohighs these microbolites are typically associated with late transgressive to early highstand systems tract deposits and range from 10 ft 3 m to 150 ft 45 m in thickness because the smackover strata are not exposed at the surface in this region determination of the geometries and extent of these thrombolitic buildups which are critical to devising hydrocarbon development strategies for these reservoirs is difficult upper jurassic oxfordian and kimmeridgian microbial buildups are exposed in western europe where they are also associated with late transgressive to highstand systems tract deposits in france these microbial reefs have been observed in outcrop to consist of layered to dendroidal thrombolitic buildups that generally do not exceed 10 ft 3 m in thickness in portugal microbial reefs consist primarily of thrombolitic buildups that attain thicknesses of 100 ft 30 m these buildups are associated with sediment starvation surfaces and hardgrounds and occur in early highstand systems tract deposits the use of upper jurassic microbial reef outcrops in europe to characterize and model the smackover thrombolitic reefs in the subsurface of the northeastern gulf of mexico greatly facilitates the design of hydrocarbon development strategies for delineating smackover microbial reefs through 3 d geologic and seismic modeling

late jurassic epiphyton like cyanobacteria indicators of long term episodic variation in marine bioinduced microbial calcification abstract epiphytaceans occur in late jurassic shallow marine reef limestones at several localities in the carpathian mountains of romania these calcified dendritic microfossils are well preserved in sparry calcite as sub millimetric radial clusters of narrow well defined filaments 10 30 m in diameter that show dichotomous branching and consist of dense dark micrite locally with tubiform structure epiphytaceans are widely interpreted as photosynthetic algae or bacteria but their precise affinities remain elusive and the group may be heterogeneous these late jurassic examples most closely resemble cambrian tubomorphophyton and late devonian paraepiphyton we interpret them to be calcified cyanobacterial sheaths post devonian records of epiphytaceans are extremely scarce the kimmeridgian tithonian specimens reported here represent one of the youngest known occurrences of epiphytaceans their highly sporadic geological distribution resembles that of marine calcified cyanobacteria which show phanerozoic abundance peaks in the early paleozoic late devonian mississippian and late jurassic early cretaceous we propose that kimmeridgian tithonian epiphytacean cyanobacteria reflect environmental conditions that favored bioinduced calcification in particular elevated seawater carbonate saturation state

mid ocean ridges fine scale tectonic volcanic and hydrothermal processes within the plate boundary zone a first order model of spreading centers as idealized linear boundaries of crustal and lithospheric generation provides only a gross understanding of global scale plate kinematics as we attempt to understand the complexity of crustal and lithospheric structure of two thirds of the earth s surface it is becoming increasingly necessary to study the tectonic volcanic and hydro thermal processes within the spreading center plate boundary zone all ocean ic crust bears the imprint of these processes this review focuses on a few selected topics concernining the fine scale tectonics and geophysics of the active axial zone of mid ocean ridges with reference to associated volcanic and hydrothermal processes it draws heavily on recent studies that use deeply towed instrument packages multi beam bathymetric mapping ocean bottom instruments and alvin e g the famous amar rise and galapagos expeditions we begin with a review of the large scale structure of spreading centers we then take a close look at the axial neovolcanic zone and progress away from the axis through the active tectonic zones next we consider the characteristics of the axial magma chamber and associated hydrothermal actvity as well as the generation of magnetic anomaly stripes and their implications for crustal generation one of our findings is that the initial two dimensional model of volcanic and tectonic zones must be expanded upon to allow for variations

marine carbonate cements biofilms biomineralization and skeletogeneis some bivalves do it all recent years have seen a growing interest in the direct and indirect roles of organisms and more explicitly of organic matter in the crystallization of minerals in sediments two bivalve genera form extensive biofilms that are apparently responsible for the growth of a variety of isolated crystals together with a marine cement granicorium indutum and samarangia quadrangularis are infaunal species that cover their shells with a cemented coating of sand sculpted to mimic the surface ornament typical of many bivalves granicorium has an exceptionally mobile mantle margin that produces large volumes of mucus harboring a diverse microbial community the sand grains surrounding both species are initially bound by a biofilm that provides structural integrity but also acts like others as a template for the crystallization of a variety of carbonate polymorphs these include varied prismatic crystals rice grain and wheatsheaf forms and more importantly large volumes of acicular crystals indistinguishable from typical marine cements the distribution of these crystals is related to positions accessible to the mantle of the animal and in samarangia appears to result from the active emplacement of grains and mucus several times a year summing the evidence it seems that these species are responsible not only for the biomineralization involved in the formation of their shells but also for crystallization mediated through biofilms and for the generation of cements that are morphologically indistinguishable from typical marine cements the boundaries between these three strategies may be closer than we think

internal waves as controlling factor in the development of stromatoporoid rich facies of the apulia platform margin upper jurassic lower cretaceous gargano promontory italy abstract during the late jurassic stromatoporoid rich buildups were developed in south and intra tethys realms these stromatoporoid buildups are mainly characterized by the high percentage of intraclastic bioclastic debris as main components of buildup bodies however the source of hydrodynamic energy resulted in debris production is still a matter of debate this study examines the upper jurassic lower cretaceous stromatoporoid rich buildups of monte sacro limestones msl apulia carbonate platform acp in order to describe the main carbonate facies along the study area as well as the possible source of turbulence three main lithofacies have been distinguished lf1 stromatoporoid rich facies with two subfacies lf1 s1 floatstone with wackestone to fine grained packstone lf1 s2 rudstone floatstone with intraclastic bioclastic packstone grainstone lf2 stromatoporoid coral facies distributed in wackestone to packstone matrix lf2 s1 and tabular stromatoporoid corals surrounded by wackestone matrix lf2 s2 and lf3 stromatoporoid microbial facies these facies were deposited along the mid part of a distally steepened ramp the in situ form of stromatoporoids was developed in a mud dominated matrix lf1 s1 under low energy conditions while the intraclastic bioclastic rich facies lf1 s2 were deposited under a high energy condition the distribution of lf2 and lf3 in muddy matrix suggests occurrence of these lithofacies in quiet environments the biotas were influenced by several factors including nutrient and light availability as well as by hydrodynamism the stromatoporoid rich buildups in acp can be categorized as phototrophic heterotrophic reefs generated in a pure carbonate environment the light penetration was confined resulted in the high development of light independent micro encrusters tubiphytes morronensis in a mesophotic condition where the environment was not ideal for light dependent microencrusters lithocodium bacinella to grow we suggest that debris dominated stromatoporoid rich lithofacies lf1 thrived in meso oligophotic setting along the nutricline and were affected by more than episodic high energy events in a context where the surface waves were not effective in such environments internal waves can be an effective candidate to explain the episodic turbulences to produce the debris rich facies of lf1 s2 moreover internal waves can pump the nutrient rich waters to the buildups and create an ideal setting where these metazoan communities thrived

coloured mineral coatings on monument surfaces as a result of biomineralization the case of the tarragona cathedral catalonia successive coloured coatings on the taragona cathedral catalonia were analyzed using chemical microbiological and mineralogical techniques the coatings consist of mainly biogenic minerals calcite several oxalates phosphates and their fabric and composition is independent of the underlying rock the origin of the crusts or patinas is attributed to bygone sub fossil microflores which formed biofilms and microbial mats on and within the surface of the limestones and marbles of the cathedral the staining of the patina layers is not related to the mineral colours nor to anthropogenic dust or fly ashes the colours are most probably organic pigments embedded between the crystals and fe and mn organic compounds remaining from bioactivity a sequential hypothesis of the origin s of the patina layers is given

bacteria fungi and biokarst in lechuguilla cave carlsbad caverns national park new mexico lechuguilla cave is a deep extensive gypsumand sulfur bearing hypogenic cave in carlsbad caverns national park new mexico most of which 90 lies more than 300 m beneath the entrance located in the arid guadalupe mountains lechuguilla s remarkable state of preservation is partially due to the locally continuous yates formation siltstone that has effectively diverted most vadose water away from the cave allocthonous organic input to the cave is therefore very limited but bacterial and fungal colonization is relatively extensive 1 aspergillus sp fungi and unidentified bacteria are associated with iron manganese and sulfur rich encrustations on calcitic folia near the suspected water table 466 m below the entrance 2 92 species of fungi in 19 genera have been identified throughout the cave in oligotrophic nutrient poor soils and pools 3 cave air condensate contains unidentified microbes 4 indigenous chemoheterotrophicseliberius andcaulobacter bacteria are known from remote pool sites and 5 at least four genera of heterotrophic bacteria with population densities near 5 105 colony forming units cfu per gram are present in ceiling bound deposits of supposedly abiogenic condensation corrosion residues various lines of evidence suggest that autotrophic bacteria are present in the ceiling bound residues and could act as primary producers in a unique subterranean microbial food chain the suspected autotrophic bacteria are probably chemolithoautotrophic cla utilizing trace iron manganese or sulfur in the limestone and dolomitic bedrock to mechanically and possibly biochemically erode the substrate to produce residual floor deposits because other major sources of organic matter have not been detected we suggest that these cla bacteria are providing requisite organic matter to the known heterotrophic bacteria and fungi in the residues the cavewide bacterial and fungal distribution the large volumes of corrosion residues and the presence of ancient bacterial filaments in unusual calcite speleothems biothems attest to the apparent longevity of microbial occupation in this cave

the multiphase grain control percolation its implication for a partially molten rock a model of percolation process named the multiphase grain control percolation mgcp is proposed in order to estimate the connectivity of the melt phase in a partially molten rock in which spatial melt distribution is determined by the combination of surrounding grain species according to the stability of the melt phase at the grain boundaries three types of percolation model are introduced the corner percolation the edge percolation and the corner edge ce percolation the ce percolation can be reduced to the corner or edge percolation the connectivity of the melt phase is determined as a function of modal composition in a multiphase grain system for various combinations of grain species surrounding the corner or edge occupied by the melt phase we obtain the critical grain fraction at which the connectivity changes abruptly from 0 to 1 the critical grain fraction estimated from the mgcp does not coincide with that from the ordinary percolation model in which random distribution of the melt phase is assumed as a geophysical application of the mgcp we construct the connectivity diagrams modal composition diagram of the connectivity of the melt phase for two partially molten peridotites by using the experimental results of dihedral angle measurements from these diagrams we predict that the melt phase is connected extensively if fraction of olivine exceeds 63 vol for a natural peridotite composed of olivine orthopyroxene and clinopyroxene and 38 vol for a synthetic peridotite composed of olivine and orthopyroxene for the former peridotite we further estimate critical melt fraction it is shown that the melt phase can be connected extensively when the melt fraction exceeds 0 8 vol in the peridotite composed of more than 63 vol olivine

holocene climate variability in europe evidence from δ18o textural and extension rate variations in three speleothems time series o isotope profiles for three u th dated stalagmites have revealed that for much of the holocene a site on the atlantic seaboard sw ireland exhibits first order 18o trends that are almost exactly out of phase with coupled 18o curves from two southern european sites se france and nw italy in the irish stalagmite cc3 from crag cave sw ireland low 18o at 10 000 cal yr bp reflects cool conditions by the early to mid holocene 9000 6000 cal yr bp 18o had increased reflecting the onset of warmer conditions on the atlantic seaboard this shift to higher 18o was accompanied by a marked increase in the stalagmite extension rate reinforcing our interpretation that this was a period of relative warmth except for an episode of increased extension rate about 5500 yr ago 18o in the crag stalagmite exhibits a gradual decrease accompanied by declining extension rates between 7800 and 3500 cal yr bp interpreted as a cooling trend there is evidence for increases in both 18o and stalagmite extension rate in the period from 3500 cal yr bp to the present day suggesting a return to warmer conditions on the atlantic seaboard in the stalagmite from nw italy er76 grotta di ernesto trentino province the early holocene c 9200 7800 cal yr bp is characterised by high 18o probably indicative of warm and or dry conditions exceptionally low 18o from 7800 to 6900 cal yr bp at this site reflects a well defined wet phase cerin wet phase in the last three millennia this stalagmite exhibits a shift to lower 18o interpreted as some combination of cooler and or wetter conditions unlike the irish stalagmite the italian sample does not show a correlation between 18o and extension rate instead its extension rate correlates roughly with 13c presumably reflecting a climate driven vegetation change in the early holocene 18o in the french stalagmite cl26 grotte de clamouse herault province se france was low relative to its holocene average for much of the period since c 3500 cal yr bp this stalagmite exhibits higher 18o than in the early holocene suggesting warmer conditions like the irish stalagmite the french sample exhibits a well defined correlation between 18o and extension rate had drip water availability been the dominant control on 18o at this semi arid site then higher 18o would have been accompanied by lower not higher extension rates this suggests strongly that temperature rather than rainfall amount was the dominant control at this site while conclusions regarding the patterns of climate variability on a continent scale must remain tentative because of the limited number of stalagmites studied we argue that early holocene warm conditions on the atlantic seaboard irish site coincided with relatively cool conditions at the clamouse site by c 3500 yr ago the pattern appears to have been reversed

speleothems from mawsmai and krem phyllut caves meghalaya india some evidences on biogenic activities the mawsmai cave and krem phyllut caves east khasi hills meghalaya india has so far not yet attracted the attention of geomicrobiologists observations and hypotheses on the possible influence of identified microorganisms for speleothem formations in meghalaya are reported for the first time xrd studies identified calcite in speleothems and gypsum in cave wall deposits as the dominant minerals sem edax showed interesting microfabric features showing strong resemblance with fossilised bacteria calcified filaments needle calcite and numerous nano scale calcite crystals highly weathered and disintegrated crystals of calcite that point towards a significant microbial influence in its genesis thin section petrography showed laminated stromatolitic features the microorganisms identified by conventional isolation and further evaluation of isolates by molecular techniques include bacillus cereus bacillus mycoides bacillus licheniformis micrococcus luteus and actinomycetes microscopic observations also showed unidentifiable cocci and four unidentifiable strains of caso4 gypsum precipitating bacteria experimental studies confirmed that these bacteria are able to precipitate calcium minerals calcite gypsum minor amounts of dolomite in the laboratory these results allow us to postulate that species like these may contribute to active biogenic influence in the cave formations at meghalaya

oxfordian upper jurassic coral reefs in western europe reef types and conceptual depositional model comparative sedimentology and palaeoecology of oxfordian upper jurassic coral dominated reefs of england france italy and switzerland has been used to 1 identify and characterize different types of late jurassic coral reefs with regard to their litho and biofacies and 2 develop a depositional model for these reefs relating different reef types to each other within a palaeoenvironmental framework eight generic reef types and one associated reef facies are recognized these are i biostromal units dominated by platy microsolenids developed within clean limestone facies ii biostromal units dominated by platy microsolenids developed within marly facies iii reefal thickets dominated by tall dense phaceloid colonies developed within pure carbonate muds iv microbial coral reefs dominated by massive branching ramose and phaceloid colonies v large high diversity reefal units associated with large volumes of bioclastic material vi small species poor reefs developed within mixed carbonate siliciclastic facies vii microbial coral reefs dominated by massive colonies viii reefal thickets dominated by branching ramose colonies with widely spaced branches developed amongst sand shoals and coral debris channels and ix conglomerates rich in rounded coral fragments the reef associated facies the development of these different constructional and compositional reef types is interpreted as being primarily a function of light intensity hydrodynamic energy levels and sediment balance a conceptual depositional model based on these parameters can be used to predict the spatial and temporal distribution of different reefal carbonates and highlight sedimentological and palaeoecological trends in reef development

origins of carbonate spherulites implications for brazilian aptian pre salt reservoir abstract spherulites spherical to elliptical allochems composed of crystals radiating from a common core investigated from a variety of depositional settings e g hot springs ambient water temperature geyser tufa and caliche are all composed of a fine grained nucleus made up of carbonate encrusted bacterial bodies biofilms and or eps and surrounded by a cortex of radiating crystals of either aragonite or calcite the microbes and their by products in the nucleus induced the precipitation of carbonate overcoming the inhibition to initiate crystal formation the enveloping radiating crystals comprising aragonitic cortices tended to grow abiotically producing well formed euhedral crystals with a paucity of included bacterial fossils whereas those cortical crystals made up of calcite commonly contained bacterial fossils indicating that the bacterial colonies contributed to the calcitic cortical crystal precipitation similar spherulites form a thick widespread accumulation in the aptian pre salt lacustrine deposits in the campos basin offshore brazil as with the travertine tufa and caliche spherulites the pre salt spherulites most likely initiated carbonate precipitation around bacterial colonies and or their bioproducts probably while afloat in a lacustrine water column before settling to the water sediment interface absence of inter spherulite sediment and the spherulite to spherulite compaction indicate that cortical crystal growth continued while the spherulites were at the sediment water interface rather than displacively within a sediment

experimental formation of spiky calcite through organically mediated dissolution abstract cultures of known species of fungi placed on crystals of iceland spar calcite resulted in extensive dissolution of the calcite this organically mediated dissolution produced large patches of spiky calcite within a period of 253 days the dissolution of the calcite occurred via surface reaction controlled kinetic processes that were mediated by the fungi this occurred despite the lack of vast quantities of fluids undersaturated with respect to calcite locally at least 10 m of calcite was removed from the original crystal surface

depositional environments and iron ooid formation in condensed sections callovian oxfordian south eastern paris basin france carbonate platforms across western europe were superseded at the middle upper jurassic callovian oxfordian boundary either by alternating marl limestone and widespread marl deposits or by condensed sections containing iron ooids the characteristics of marine condensed sections in the south eastern part of the paris basin france and their distribution pattern are examined here and a model of iron ooid formation is developed iron ooids are found from the shoreface to the offshore zone they are most abundant in the median to distal offshore transition zone where they originally formed they also occur commonly albeit often as reworked grains in the proximal offshore zone to which they were transported the contemporaneous thick predominantly marl sections that occur laterally are devoid of iron ooids and were deposited in deeper settings distal offshore zone the iron ooids are composed of goethite typically they have a nucleus made up of a clump of goethite crystals and a laminated cortex three distinctive nanostructures are identified in the cortex laminae i a nanograined crystalline structure typical of primary goethite ii a secondary nanoflaked structure thought to have formed mechanically by reorientation of the goethite crystals and iii a coalesced structure acquired by subsequent diagenetic recrystallization the iron ooids formed successively i by lamina growth when goethite precipitated in the surface layer of the sediment nanograined structure and ii by interruption of growth when the ooids were remobilized by hydrodynamic agents as reflected by the flaked nanostructure iii these two nanostructures were sometimes transformed into a coalesced structure by recrystallization when ooids were buried

the descriptive nomenclature and classification of growth fabrics in fossil scleractinian reefs abstract framework sensu stricto is a concept originally relating to modern reefs and is defined by structural ecological and sedimentological criteria however in the geological literature the term framework has come to be applied to almost any organically influenced in situ accumulation including non calcareous non rigid facies associated with sea grasses this drastic departure from the original meaning is misleading and scientifically unhelpful the concept of wave resistance is integral to that of framework but in the geological record it is not easy to evaluate and the term may be of little comparative use between reef environments it is suggested that the term growth fabric be generally applied as a descriptive term for the presence of aggregated in situ corals or other organisms in growth position within a facies the term growth fabric should be used as an alternative to framework as a purely descriptive term the term framework should be restricted to its original definition and used only where the criteria for framework can be clearly demonstrated two end member types of scleractinian growth fabric genesis are recognised termed superstratal and constratal terms adapted from gili e masse j p skelton p w 1995 rudists as gregarious sediment dwellers not reef builders on cretaceous carbonate platforms palaeogeogr palaeoclimatol palaeoecol 118 245 267 in a superstratal growth fabric the constituent organisms collectively projected decimetres to metres above the substratum creating positive topographic relief in contrast constratal growth is where vertical organic accretion occurred at a similar rate to sediment accumulation hence the majority of the skeletal material remained continuously embedded in the sediments and only a small proportion of the skeleton projected centimetres above the sediment surface the architectural palaeoecological sedimentological and diagenetic implications of different types of growth fabric genesis is discussed a review of the classification of reef fabrics suggests that there is currently no adequate system to describe fossil scleractinian growth fabrics the most commonly used classification of reefal fabrics is that of embry and klovan 1971 embry a f klovan j e 1971 a late devonian reef tract on northeastern banks island northwest territories bull can pet geol 33 730 781 there are a number of shortcomings in this scheme which may be grouped into three categories 1 the interpretative nature of the classification 2 problems in interpreting biological effect from form and 3 insufficient categories to adequately describe mesozoic and cenozoic growth fabrics moreover there appears to be a lack of a standardised nomenclature for growth fabrics which has hindered meaningful comparisons of scleractinian growth fabrics through time and space a descriptive system based on a modification and expansion of the embry and klovan system 1971 is proposed and a revised nomenclature for growth fabrics presented the system is designed to be flexible in its application it can be used simply to describe a growth fabric or through the use of genetic and non genetic modifiers to imply types of reef building processes and growth fabric heterogeneity although the concepts and terminology discussed in this paper relate to scleractinian growth fabric they are equally applicable to fabrics comprising other organisms

phosphatic precipitates associated with actinomycetes in speleothems from grand cayman british west indies abstract calcitic speleothems from a cave located on the north central coast of grand cayman commonly include corrosion surfaces that developed when calcite precipitation ceased and corrosion mediated by condensates became the operative process dissolution features associated with these surfaces including etched crystal surfaces microcavities and solution widened boundaries between crystals are commonly occupied by microbes and microbial mats that have been replaced by calcium phosphate and or coated with calcium phosphate no mineralized microbes were found in the calcite crystals that form the speleothems the morphology of the mineralized hyphae eight morphotypes and spores nine morphotypes are indicative of actinomycetes a group of microbes that are ideally adapted to life in oligotrophic cave environs superb preservation of the delicate hyphae aerial hyphae and delicate ornamentation on the hyphae and spores indicate that the microbes underwent rapid mineralized while close to their original life positions although these actinomycetes were extremely susceptible to replacement by calcium phosphate there is no evidence that they directly or indirectly controlled precipitation nevertheless the association between the p rich precipitates and microbes shows that the use of phosphorus as a proxy for seasonal climate changes in paleoclimate analyses must be treated with caution

dolomite carbonate replacement textures in veins cutting carboniferous rocks in east fife abstract carbonate veins cutting carboniferous sediments in fife scotland contain three apparently paragenetically equivalent types of ferroan dolomite all of which show somewhat unusual fabrics the most spectacular of these are fence textured crystals comprising an open rhombic network of inclusion rich dolomite which is partially filled by later syntaxial inclusion free ankerite the more common paragenetic equivalents to the fence textured dolomite are dolomite filled rhombic moulds and two dolomite intergrowth fabrics all three fabrics appear to indicate dolomite replacement of a rhombohedral carbonate precursor and seem to reflect different degrees of development in a common sequence of events 1 precipitation of a metastable phase 2 precipitation of dolomite 3 precipitation of dolomite coupled with dissolution of the metastable phase neomorphism 4 dissolution of the metastable phase this progression is compatible with gradual cooling within a series of hydrothermal systems centred on adjacent namurian volcanics and the range of fabrics developed by the dolomite may reflect differential cooling in different parts of these hydrothermal systems the ankerite which partially fills the fence texture and the rhombic moulds also occurs in veins cutting stephanian rocks indicating a much later origin

231pa and230th chronology of mid ocean ridge basalts mass spectrometric measurements of235u231pa and238u230th disequilibria are used to further constrain processes producing u series disequilibria in young mid ocean ridge basalts morb and to determine eruption ages for samples from 9 10 n east pacific rise and juan de fuca gorda ridges 231pa 235u activity ratios for axial basalts are large and relatively uniform within ridge segments the systematically large231pa 235u 230th 238u and226ra 230th activity ratios in morb are inconsistent with simple equilibrium melting models and crustal contamination or seawater alteration processes more complicated melting processes involving disequilibrium or heterogeneous melting of mantle sources and disequilibrium transport of melts to the crust could produce the large u series disequilibria in morb 231pa and230th model ages were determined by estimating initial231pa 235u and230th 232th ratios from axial samples and by assuming constancy of these ratios over time all231pa and230th ages agree to 0 7 ka for samples with ages of 0 130 ka these concordant ages validate the model assumptions of the two dating methods and suggest that mantle sources and melt generation processes have been uniform for these areas during the past 130 ka consequently 231pa and230th age dates can be used to quantify the temporal and spatial dependence of volcanism at oceanic spreading centers during the past 375 ka

oxfordian reef architecture of the la manga formation neuquen basin mendoza province argentina abstract the neuquen back arc basin is located on the west margin of the south american platform between latitudes 36 and 40 s the basin is famous for its continuous sedimentary record from the late triassic to cenozoic comprising continental and marine clastic carbonate and evaporitic deposits up to 2 600 m in thickness the stratigraphical and paleontological studies of the outcrops of the la manga formation argentina located near the bardas blancas region mendoza province 35 s and 69 o allow the reconstruction of the sedimentary environments of an oxfordian carbonate ramp where outer ramp middle ramp inner ramp oolitic shoal inner ramp margin patch reef lagoon and paleokarst were differentiated the reefs consist of back reef facies and in situ framework of coral boundstones that was formed at the top of shallowing upward succession coral reefs were analyzed by defining coral colonies shapes paleontological content coral diversity and taphonomy studies in some studied sections abundant fragments of gryphaeids encrusting bryozoans and isolated sponges provided a suitable substrate for coral colonization however other sections show an increase in the proportions of ooids peloidal and coral intraclasts the core reef facies is composed of white grey unstratified and low diversity scleractinian coral limestone dominated by robust and thinly branching corals with cerioid phocoid growths and massive coral colonies with meandroid thamnasteroid growth forms the assemblage is characterized by actinastraea sp australoseris sp thamnasteria sp and garateastrea sp internal facies organization and different types of coral colonies allow to recognize the development of varying framework as well as intercolony areas a superstratal growth fabric characterizes the coral assemblage on the basis of coral growth fabric branche and domal types the reef of la manga formation is considered a typical mixstones the intercolony areas consist of biomicrites and biomicrorudites containing abundant coral fragments parautochthonous gryphaeids and another bivalves ctenostreon sp gastropods harpagodes sp natica sp echinoderms test and spines plegiocidaris sp miliolids cayeuxia sp acicularia sp salpingoporella sp intraclasts ooids peloids and coated grains the domal growth forms are probably more protected against biological and physical destruction meanwhile delicate branching growth forms with very open and fragile framework were more affected and fragmented due to wave action and bioerosion the reef fabric shows different intervals of truncation as consequence of erosion resulting from coral destruction by storm waves or currents the maximum flooding surface separates oolitic shoal facies below from the aggradational and progradational coralline limestones facies above subsequent sea level fall and karstification 148 ma affected reef and oolitic facies

u series disequilibria in morb from the garrett transform and implications for mantle melting abstract here we report 238u 230th 231pa 226ra disequilibria and 87sr 86sr measurements in 11 mid ocean ridge basalt morb glasses from the garrett transform 13 30 s latitude on the east pacific rise epr whose compositions range from primitive depleted high mgo basalts to evolved basalts u and th concentrations of samples range between 3 and 75 ppb and between 6 and 220 ppb respectively with a corresponding large variation in th u 1 5 2 9 230th 232th varies from 1 2 to 1 6 such that 230th 238u range from 15 excess 230th in a high th u evolved sample to 25 excess 238u in a high mgo sample with low th u out of 11 samples 7 have 238u excess an unusual feature for morb all samples have 226ra excesses with 226ra 230th varying between 1 3 and 3 8 constraining ages since eruption to comparing the garrett transform to the siqueiros transform shows a remarkable correspondence between sample setting composition and disequilibria systematics both settings produce linear trends of 230th 238u as a function of th u consistent with mixing between two melts derived from different depths in the melting column the mixing relationships are identical in both locations the most incompatible rich samples with the highest th u and 230th excess come from the ridge transform intersection rti whereas the most incompatible element poor basalts with the lowest 230th 238u and th u are erupted along leaky transform faults samples with intermediate th u and 230th 238u all come from within intra transform spreading centers consistent with the spreading centers acting to homogenize these diverse magmas the cause of variation in th u could reflect either melting processes or different long lived sources no clear indication exists within these data

dynamical consequences of compositional and thermal density stratification beneath spreading centers extraction of partial melt to form oceanic crust reduces the density of upwelling mantle beneath spreading centers this compositional buoyancy can significantly affect both the rate of upwelling and the pattern of mantle flow the relative importance of buoyant upwelling and upwelling due to plate spreading depends on the mantle viscosity for a low enough mantle viscosity buoyant upwelling can significantly enhance the thickness of the crust relative to that which would be produced by plate spreading alone for a mantle viscosity of 1022 pa s upwelling due to plate spreading is dominant and crustal thickness is predicted to be a strong function of spreading rate however for a mantle viscosity of 1019 pa s buoyancy dominates mantle upwelling and the calculated crustal thickness like the oceanic crust is nearly independent of spreading rate thermal and compositional density variations result in opposing buoyancy forces that can cause time dependent upwelling for a mantle viscosity of 1020 pa s and a low 1 cm yr spreading rate this behavior takes the form of undamped crustal thickness oscillations with a single well defined period for even slightly lower mantle viscosity the frequency increases and crustal thickness oscillations become more complex with two or more frequencies present while numerical experiments have thus far been carried out only for viscosities significantly greater than that likely to characterize the mantle beneath spreading centers we speculate that these crustal thickness oscillations may explain important aspects of seafloor structure

platy corals from the middle triassic of upper silesia poland implications for photosymbiosis in the first scleractinians abstract coral patch reefs from middle triassic upper pelsonian lower illyrian strata in the upper silesia region of southern poland germanic domain of the peri tethys are rare examples of the first scleractinian buildups the shallowing upward succession in the tarnow opolski quarry records a transition from sponge to coral patch reefs interbedded with bioclastic limestones coral pillarstones built by thin branching volzeia szulci are succeeded by platy pamiroseris silesiaca constructing two platestone layers each up to 50 cm thick serial sections through platestones revealed flat to undulose growth form of p silesiaca the maximum observable dimension of the coral plates is 24 cm wide typically up to 12 cm while thickness of most plates is 1 1 5 cm coral plates are interlayered with crinoidal wacke to packstone and microbialites which are locally important component of the platestone platy corals grew in a shallow turbid water environment with changing but dominantly moderate hydrodynamics net sedimentation was low as indicated by the epibionts encrusted to the undersides of the coral plates and locally common microbial fabrics growth interruptions of p silesiaca record events of storm induced sediment input and resuspension of carbonate mud based on the euphotic floor model the flattened morphology of p silesiaca is interpreted as an optimal growth form in a turbid low light environment platy scleractinian assemblages from silesia are the oldest occurrences of this ecological coral group mostly representing deeper mesophotic habitats and support the hypothesis that some of the earliest scleractinians had photosymbionts like modern zooxanthellae

the role of mantle depletion and melt retention buoyancy in spreading center segmentation abstract numerical experiments are used to examine the structure of mantle flow beneath the axis of a spreading center buoyancy results from the depletion of residual mantle in iron relative to magnesium as melt is extracted mantle depletion buoyancy and from the presence of low density melt melt retention buoyancy 3 d buoyant mantle flow arises spontaneously from an initially 2 d solution for low mantle viscosity and low spreading rate at high viscosity and high spreading rate initially 2 d solutions remain 2 d this may explain the fundamentally different structure of fast and slow spreading centers in a uniform viscosity halfspace the along axis wavelength of 3 d buoyant upwelling scales with the maximum depth of melting the only length scale in this system for reasonable maximum depths of melting 60 90 km along axis wavelengths of 200 300 km are preferred longer than the 50 100 km segmentation length of slow spreading centers in a viscosity layered halfspace the thickness of the asthenosphere introduces another length scale a wavelength of segmentation comparable to the asthenosphere thickness also develops in our numerical experiments this suggests the possibility that a wavelength corresponding to the spacing between gravity lows may be controlled by the asthenosphere thickness while the spacing of major fracture zones corresponds to the longer wavelength 3 times the maximum depth of melting intrinsic to the melting region the along axis structure of 3 d flow varies from narrow focused upwellings at low spreading rates and mantle viscosities to broad regions of upwelling at high spreading rates and mantle viscosity to allow an along axis crustal thickness variation no larger than that which is observed 3 4 km the highly focused upwelling and crustal production predicted at slow spreading rates requires appreciable along axis transport of melt

petrological variability of recent magmatism at axial seamount summit juan de fuca ridge 1 a combined study of mapping observational age constraint and geochemical data at the summit of axial seamount juan de fuca ridge has revealed its recent petrological history multiple basalt types erupted at the summit in a time sequence at least three different magma batches have been present beneath the axial summit caldera during the last millennium each with a range in differentiation the first prior to 1100 ce was compositionally diverse dominantly aphyric t morb the second from 1220 to 1300 ce was dominantly plagioclase phyric more mafic n morb erupted mostly in the central portion of the caldera since 1400 ce lavas have been more differentiated and nearly aphyric t morb mostly erupted in the caldera s rift zones parental magmas vary subtly due to small coupled differences in the degree of melting and sources but all share a uniform differentiation trend indicating pooling at similar depths thus melts percolate through melt rich lenses that remain partially isolated in space and or time centennial magmatic timescales at axial seamount are similar to those for fast spreading ridge segments the fluctuation between aphyric and plagioclase phyric lava likely reflects different pathways or velocities of melt migration

238u 230th disequilibria and mantle melting processes a discussion abstract this paper discusses the implications of 238 u 230 th disequilibria in morb and oib on mantle melting it is shown that melting rates can only be calculated if the melting process is not batch melting at present however the uncertainties in u and th partition coefficients are such that in most cases batch melting cannot be discarded moreover a simple argument based on the th sr isotope correlation suggests that batch melting might best approximate the actual melting process in the mantle at least in the case of oib the existence of mantle heterogeneities e g the marble cake model of allegre and turcotte allegre c j turcotte d 1986 implications of a two component marble cake mantle nature 323 123 127 when taken into account suggests that complex melting models might not be necessary to interpret 238 u 230 th data in particular preferential melting of garnet pyroxenites could explain the origin of oib whereas morb could derive from larger degrees of melting of garnet lherzolites however the large 231 pa and 226 ra excesses found in morb are better explained by dynamic melting models if they are actually produced through crystal melt partitioning during mantle melting in any case it is worth emphasizing that derivation of melting rates is strongly model dependent and should be taken with caution

microbial nucleation of calcium carbonate in the precambrian microbial sulfate reduction is thought to stimulate carbonate precipitation in modern stromatolites yet whether this metabolism was important in shaping precambrian stromatolites is unknown here we use geochemical modeling to suggest that the influence of sulfate reduction on the saturation index of calcite si is negligible when seawater is in equilibrium with high pco 2 as is thought for the precambrian our laboratory experiments with heterotrophic bacteria in a medium mimicking precambrian seawater chemistry show that even if sulfate reduction does not significantly change the si the presence of bacteria stimulates calcite precipitation over sterile controls by effectively increasing the si over a ph range from 7 3 to 7 8 under our experimental conditions dead cells stimulate in situ carbonate precipitation equally if not more than active sulfate reducing bacteria heterogeneous nucleation of calcite by microbial cell material appears to be the driving mechanism that explains this phenomenon

uranium series age constraints on lavas from the axial valley of the mid atlantic ridge mark area abstract mass spectrometric measurements of 230 th 226 ra 235 u 231 pa and 238 u 230 th disequilibria are used to determine eruption ages for four mid ocean ridge basalts from the median valley of the mid atlantic ridge south of the kane fracture zone mark area three samples were collected across axis on the axial volcanic ridge i e the neovolcanic ridge near the snake pit hydrothermal mound and one sample was collected near the crest of serocki volcano 50 km south of snake pit 226 ra 230 th and 230 th 238 u activity ratios are low and uniform for all four samples while 231 pa 235 u activity ratios are elevated and somewhat more variable age constraints suggest that these lavas from the most robust volcanic edifices in the mark area are 10 000 20 000 yr old the age data are used to evaluate the efficacy of commonly used age estimate scales based on qualitative indicators e g sediment cover glass quality and to begin to quantify the temporal and spatial dependence of volcanic tectonic and hydrothermal processes at slow spreading oceanic ridges

investigating solid mantle upwelling beneath mid ocean ridges using u series disequilibria ii a local study at 33 s mid atlantic ridge abstract uranium series disequilibria have been used to study the physical melting regime along a section of the southern mid atlantic ridge where the largest mantle bouguer anomaly yet observed on ridges exists zero age excesses for 230th 238u and 231pa 235u are age constrained by the presence of measured 226ra 230th disequilibria by this criterion 7 out of 15 samples are younger than 8000 years zero age 230th 238u range between 1 06 and 1 25 while zero age 231pa 235u range between 1 77 and 3 57 concentrations of th range from 100 to 866 ppb and strongly correlate with k ti the u series data differentiate the segment with the large gravity anomaly from the surrounding segments specifically this segment shows combined 231pa and 230th systematics unlike any observed in morb thus far having exceptionally low zero age 231pa excesses the u series data can be modeled using upwelling rates similar to the half spreading rate of this area of ridge the disequilibria systematics for the anomalous segment 4 possibly suggest a solid upwelling rate that is a factor of two higher than the adjacent segments the similarity between melting at segment 4 and at ocean islands is noted

cyclic development of large complex calcite dendrite crystals in the clinton travertine interior british columbia canada abstract bands of large up to 4 cm long three dimensional crystallographic dendrites form the terrace fronts in an old travertine mound exposed near clinton british columbia the dendrites with their long axes perpendicular to the terrace front are characterized by numerous levels of branching each branch is formed of multitudes of skeletal rhombs four and six sided bipyramidal crystals or prismatic hexagonal crystals that are precisely aligned along crystallographic precepts although individual branches are formed of one type of subcrystal neighbouring branches may be formed of different subcrystal types highly supersaturated waters that were generated by rapid co 2 degassing of the spring water during its turbulent flow over the steep terrace fronts probably drove dendrite precipitation the presence of growth lines indicates that growth was episodic type i growth lines probably formed annually in response to seasonal climate changes whereas type ii growth lines which formed less frequently may reflect changes in the flow velocity and or flow patterns of the spring waters early diagenetic modification of the dendrites involved crystal face enlargement cements formed of trigonal prisms or needle fiber crystals microbial infestation that mediated substrate dissolution and or deposition of detrital calcite crystals that formed in the water column much of the diagenetic modification may have taken place during the periods when the dendrites had temporarily stopped growing the dendrites in the clinton travertine are an excellent example of complex episodic calcite crystal growth that was extensively modified by early diagenetic processes in a surface environment the same spring waters from which the dendrites were precipitated mediated much of the early diagenesis

sequential and climatic framework of the growth and demise of a carbonate platform implications for the peritidal cycles late jurassic north eastern france the middle oxfordian of the eastern paris basin constitutes a remarkable example of the growth and demise of a carbonate platform fischer plots sedimentary and diagenetic features allow the identification of four depositional cycles s5 to s8 in the transversarium zone they are inserted in a lower frequency cycle of increased decreased accommodation space soiii the long term period of accommodation creation occurred during the older s5 and s6 cycles the maximum accommodation zone being located in the lower part of the s6 cycle this high accommodation period was tectonically controlled and was coeval with local distensive activity of a hercynian fault a major minimum accommodation zone exists during the s8 cycle at that time the platform was isolated and presented both a windward and a leeward margin the growth of the platform was favoured by a warm and arid climate oligotrophic conditions and reduced siliciclastic input during a highstand in relative sea level these palaeoenvironmental features favoured the proliferation of phototrophic organisms producing carbonate material the death of the platform was generated by a reduction in the carbonate production surface during a lowstand in relative sea level and by the appearance of mesotrophic conditions induced by the increase in siliciclastic inputs at the beginning of a period with a cooler and more humid climate in the eastern paris basin during the middle oxfordian the parasequences are ordered and present greenhouse characteristics in contrast at the beginning of the s8 cycle the randomness in the thickness of contiguous parasequences increased decreased carbonate production during the lowstand caused by a transition from photozoan to heterozoan benthic communities certainly favoured this randomness and the appearance of catch down parasequences

correlation of reefal oxfordian episodes and climatic implications in the eastern paris basin france oxfordian reefal episodes of lorraine and burgundy have a long time been considered as contemporaneous biostratigraphic data and sequential evolutions peculiar to each region indicate their structural autonomy during oxfordian times a north south oriented well logging transect shows that during the middle oxfordian a shallow reefal platform developed in lorraine while thin deeper deposits occurred in burgundy in spite of their different ages reefal episodes of middle oxfordian in lorraine and upper oxfordian in burgundy exhibit a broadly similar vertical evolution of coral communities during the late oxfordian the contemporaneous occurrence of a diversified assemblage in the burgundy region a colder coral assemblage characterized by eurytopic genera and the decrease in seawater isotopic temperatures in lorraine can be explained by a shift in trophic conditions a climatic change related to structural rearrangements in this strategic place and a modification of oceanic circulations between the arctic and the tethyan regions

comparison of high resolution sub annual records of trace elements in a modern 1911 1992 speleothem with instrumental climate data from southwest australia high spatial resolution measurements of mg p u sr ba and na using 193 nm excimer laser ablation inductively coupled plasma mass spectrometry has revealed clearly resolvable annual cycles in a modern speleothem from southwestern australia the age of this stalagmite is established by the dates of emplacement and removal of the boardwalk where it grew 1911 1992 this chronological constraint allows for the first confident comparison between the instrumental climate record and speleothem trace element content eleven laser ablation transects across a 0 5 mm wide section of the speleothem growth axis were measured cycles that could be matched between adjacent transects were stacked into a master record to minimise variability between tracks and permit greater confidence in comparing the trace elements to the instrumental climate record p and u positively and mg inversely mimic the sudden 20 decrease in annual rainfall experienced by this region since 1965 we argue that p from seasonal vegetation decay is transported to the speleothem before it is mineralised in the soil owing to the low p retention capacity of southwest australian soils both vegetation activity and the transport of vegetation derived hpo42 are sensitive to rainfall groundwater p concentration may also influence the transport of u through the strong affinity between phosphate and uranyl ions mg appears to be sensitive to groundwater residence time as this affects drip water mg ca composition by preferential loss of ca during drier episodes when calcite precipitates before reaching the stalagmite the effects of groundwater residence time may also be important for sr on inter annual scales however the behaviour of sr on the annual cycle is opposite to mg but compatible with ba and na which are shown to depend on speleothem growth rate

u series isotope data on lau basin glasses the role of subduction related fluids during melt generation in back arc basins new thermal ionization mass spectrometry u series disequilibrium data are presented for 24 basaltic to dacitic glasses from active spreading centres in the back arc lau basin sw pacific together with additional inductively coupled plasma mass spectrometry trace element analyses and sr nd pb isotope data valu fa ridge samples adjacent to the arc front have high u th and 230th 238u 1 implying a recent 350 ka addition of a u rich slab derived fluid the valu fa data can be combined with existing 230th 238u data for the central tonga arc to infer a fluid addition event at 50 ka the similar sources and time scales for fluid transfer beneath the valu fa ridge and beneath the arc itself suggest that the valu fa ridge is propagating into the arc front region central lau basin samples further behind the arc have lower u th and 230th 238u 1 similar to typical mid ocean ridge basalts morb within the central lau basin a water rich subduction component is seen only in samples closest to the arc and this fluid does not have the high u th composition of the fluid at valu fa melt generation in the central lau basin appears to be dominated by normal ridge type processes but the relatively low 230th 238u for these shallow ridges compared with global morb could be a consequence of increased melt productivity as a result of the elevated water contents the transition from 238u to 230th excesses within the back arc basin is not a smooth function of decreasing addition of a u rich fluid moving away from the arc front but also reflects the complex dynamics between two major mantle domains within the mantle wedge pacific beneath valu fa ridge indian beneath the central lau basin

weathering processes on the rock surface in natural outcrops the case of an ancient marble quarry belevi turkey weathering and mineralogical processes observed in a marble quarry in turkey are compared with similar processes occurring on monument surfaces patina formations microstromatolitic microlaminated monolayered as well as destructive processes mainly biopitting and bioerosion are associated with microbial colonisation of the rock surfaces and one influenced by microclimatic conditions patina stratification is independent of substrate rock but is affected by the position and orientation of rock surfaces the different layers formed by mineralisation processes may reflect the seasonality of climatic events and the consequent colonisation bio deteriorative processes take place mainly when the climatic conditions cause the organisms to live below the surface

paleoclimatic control of biogeographic and sedimentary events in tethyan and peri tethyan areas during the oxfordian late jurassic abstract the paleobiogeographical distribution of oxfordian ammonites and coral reefs in northern and central europe the mediterranean area north and east africa and the middle east and central asia is compared with the distribution in time and space of the most important lithofacies interest in the oxfordian is focused on changes in facies and in biogeographical patterns that can be interpreted as the results of climatic events paleotemperature trends inferred from oxygen isotopes and paleoclimatic simulations are tested against fossil and facies data a late callovian early oxfordian crisis in carbonate production is indicated by the widespread absence of lower oxfordian reefal formations there is a gap hiatus in deposition on epicontinental platforms with middle oxfordian deposits resting paraconformably on upper callovian while shales accumulated in adjacent intracratonic basins simultaneously in mediterranean tethys radiolarites accumulated in deep troughs while rosso ammonitico facies formed on pelagic swells however deposition on swells was also discontinuous with numerous gaps hiatuses and sequences that are much reduced in thickness middle callovian deposits are generally overlain by middle oxfordian limestones the dearth of carbonates is consistent with a cooling event lasting about 1 my by the middle oxfordian a warming leading to greenhouse type conditions is suggested on the basis of both biogeographical mostly coral reef distribution and geochemical data carbonates spread onto an extensive european platform while radiolarites reached a maximum development in the mediterranean tethys two distinct latitudinal belts with seemingly different accumulation regimes are therefore inferred similar latitudinal belts were also present in the late oxfordian when carbonates were widespread the distribution of reefal facies in the late oxfordian early kimmeridgian fits relatively well with gcms simulations that imply low rainfall in the tethyan mediterranean area and slightly higher precipitation in central and northern europe local salinity variations reflecting more arid or humid conditions may bias the paleotemperature signal inferred from 18o values biogeographical and facies distributions combined with 18o values unravel the ambiguity and support a late callovian early oxfordian cooling followed by warming in the later oxfordian

the use of laboratory velocity data for estimating temperature and partial melt fraction in the low velocity zone comparison with heat flow and electrical conductivity studies peridotite is widely considered to be the dominant component of the upper most mantle seismic velocities of a dry peridotite determined in the laboratory at high pressure and hypersolidus temperature show a rapid decrease with increasing temperature the strong temperature dependence of velocities can be used to estimate temperature and melt fraction in the low velocity zone of the earth the laboratory results show that the pressure dependence of both velocity and melt fraction appears to be well accounted for by the pressure dependence of the solidus temperature of the peridotite i e homologous temperature dependence this observation allows us to extrapolate laboratory results to higher pressures greater depths with some confidence requiring only a knowledge of the solidus as a function of pressure using the ratios of lithospheric to asthenospheric velocities temperature and melt fraction in the asthenosphere the low velocity zone can be determined from laboratory velocity data examples of thermal structures of the upper mantle beneath oceanic plates are presented we choose three locations of geophysical interest iceland plateau pacific ocean and philippine sea where reliable seismic velocities have been determined in the upper mantle from surface wave studies a large amount of partial melt 5 vol and a higher temperature than the dry peridotite solidus are inferred in 0 5 m y asthenosphere under the iceland plateau and the active marginal basin of the east philippine sea the partial melt zone appears to extend deeper 100 km and to greater ages 20 m y in the pacific ocean region than under the slowly spreading iceland plateau partial melting is not expected in the asthenosphere older than 5 m y under the iceland plateau even though the volume fraction of partial melt is not so large 3 vol beneath the pacific plate the melting zone may extend to a distance of above 2000 km from the ridge many seamounts observed in the pacific ocean may result from this vast region of melting under the plate we suggest a linear relation between the width of melting zone and the plate velocity the laboratory results are also applied to other low velocity zones it is suggested that a velocity drop up to about 6 in the asthenosphere does not necessarily require the existence of partial melt but can be explained by high subsolidus temperature this implies that partial melt may not exist generally but only in limited areas in the low velocity zone comparison of seismic results with theoretical models may overestimate the temperature and melt fraction if the velocity drop at subsolidus temperature is neglected temperature and melt fraction obtained in this study are discussed together with results from heat flow and electrical studies almost the same temperatures as inferred from seismic velocity and a dry peridotite solidus are calculated from heat flow data indicating that the upper mantle under mid ocean ridges may be fairly dry even a water or co2 undersaturated solidus 0 1 wt does not give a temperature consistent with the lithospheric geotherm and laboratory velocity results it is noted that electrical conductivity studies generally yield lower temperatures and larger melt fractions than this study unknown pressure frequency and impurity effects on laboratory conductivities of partially molten mantle rocks are suggested as possible reasons for this discrepancy

stalactite growth mediated by biofilms example from nani cave cayman brac british west indies growth lines evident in cross sections through stalactites from nani cave provide a temporal record of their growth many of these dark organic rich laminae developed as biofilms that are recognized by the presence of 1 a diverse microbial biota that is dominated by actinomycetes 2 calcified filaments 3 films formed of extracellular polymeric substances eps 4 grain coating sheets of calcite crystals that grew in eps 5 biterminal calcite crystals and 6 etching this biosignatures suite encompasses a variety of constructive and destructive processes where fully developed the features generated by the biofilms form a distinctive microstratigraphic succession collectively 50 m thick which can be traced laterally across the stalactite s surface the use of speleothems in paleoclimate studies is commonly framed against a chronology that relies at least in part on annual growth couplets the dark organic rich lamina that forms one part of the growth couplet is typically ascribed to abiotic precipitation that incorporated exogenic organic matter that was flushed into the cave following the first major rainfall of the wet season this assumption ignores the possibility that dark organic rich growth laminae can be the record of biofilms that developed on the surface of the stalactites and hence may not be a record of annual events

the paradox of the axial profile isostatic compensation along the axis of the mid atlantic ridge mantle bouguer gravity anomalies mba and bathymetry on three profiles covering more than 1000 km along the axis of the mid atlantic ridge mar are highly correlated suggesting that along axis topographic relief is locally compensated by variations in crustal thickness and or mantle density structure the quantitative relationship between topography and gravity on these profiles could be explained by the flexure of a thin narrow elastic strip representing the response to isostatic loads of an inner rift valley isolated from the rest of the plate by weak bounding normal faults the paradox is that across axis profiles show that the median valley is an uncompensated feature apparently created by a dynamic mechanism new extensive off axis coverage of the mar from 31 to 36 s shows that the high correlation does not persist outside the axial zone we suggest that the on axis correlation exists because the mechanism creating the median valley is controlled by the mantle thermal structure and along axis variations in crustal thickness both of which contribute to the mba if the mechanism is extension of a brittle ductile lithosphere the critical parameter controlling topographic relief is the thickness of the relatively stiff mantle layer immediately beneath the crust at the ridge axis a three dimensional 3 d thermal model incorporating passive mantle flow hydrothermal circulation the plate boundary geometry and variable magmatic heating associated with observed variations in crustal thickness predicts variations in the thickness of the stiff mantle layer that correlate with the observed axial topography we model the expected topography using cross axis sections of the 3 d thermal model and a 2 d finite element model of an extending lithosphere that incorporates temperature and strain dependent rheology as well as the flexural response of a thickening plate the predicted topographic signal produced by the combined dynamic and isostatic effects matches the amplitude of the observed axial bathymetry at the 18 mm yr 1 spreading half rate in our south atlantic survey the 2 d models also reproduce the observed rapid transition along the axis between rift valley no rift valley morphology we conclude that extensional forces acting on segmented oceanic lithosphere with varying rates of crustal production produce the highly variable morphology of the southern mar and the along axis correlation between mba and bathymetry

evidence of very rapid reef accretion and reef growth under high turbidity and terrigenous sedimentation global scale deteriorations in coral reef health are projected to lead to a progressive decline in reef building potential and ultimately to states of net reef erosion these transitions may be driven by various human disturbances and by climate change however increased terrestrial sediment and nutrient yields from anthropogenically modified coastal catchments are widely recognized as a major threat as water quality deteriorates reduced coral cover and species diversity are commonly inferred and lower reef accretion rates and impaired reef development are assumed consequences here we present a detailed chronostratigraphic growth history constrained by 40 accelerator mass spectrometry radiocarbon dates for middle reef an inshore turbid zone reef on australia s great barrier reef that challenges the assumption that high terrestrial sediment inputs inherently restrict reef accretion rates and inhibit reef development we establish that middle reef has vertically accreted very rapidly for more than 700 yr at an average rate of 8 3 mm yr accretion rates varied across the reef at different times but it is significant that the periods of most rapid accretion averaging 13 0 mm yr coincide with phases of reef development dominated by fine grained terrigenoclastic sediment accumulation we suggest that this is in large part a function of a high rate of terrigenous sediment accumulation aiding the postmortem preservation of coral skeletal material both maximum and site averaged accretion rates match or exceed those documented for most clear water mid and outer shelf reefs in the region over the past 9000 yr and those determined for many reefs throughout the indian and pacific oceans over the same period while examples of inshore coral reefs that have been degraded in the short term by excessive terrestrial sedimentation clearly exist others clearly tolerate high sedimentation and turbidity and our data confirm that sustained and long term rapid reef growth is possible in these environments

evidence for initial excess 231pa in mid ocean ridge zircons abstract a limiting factor in the accuracy and precision of u pb zircon dates is accurate correction for initial disequilibrium in the 238u and 235u decay chains the longest lived and therefore most abundant intermediate daughter product in the 235u isotopic decay chain is 231pa t1 2 32 71 ka and the partitioning behavior of pa in zircon is not well constrained here we report high precision thermal ionization mass spectrometry tims u pb zircon data from two samples from ocean drilling program odp hole 735b which show evidence for incorporation of excess 231pa during zircon crystallization the most precise analyses from the two samples have consistent th corrected 206pb 238u dates with weighted means of 11 9325 0 0039 ma n 9 and 11 920 0 011 ma n 4 but distinctly older 207pb 235u dates that vary from 12 330 0 048 ma to 12 140 0 044 ma and 12 03 0 24 to 12 40 0 27 ma respectively if the excess 207pb is due to variable initial excess 231pa calculated initial 231pa 235u activity ratios for the two samples range from 5 6 1 0 to 9 6 1 1 and 3 5 5 2 to 11 4 5 8 the data from the more precisely dated sample yields estimated dpazircon duzircon from 2 2 3 8 and 5 6 9 6 assuming 231pa 235u of the melt equal to the global average of recently erupted mid ocean ridge basaltic glasses or secular equilibrium respectively high precision id tims analyses from nine additional samples from hole 735b and nearby hole 1105a suggest similar partitioning the lower range of dpazircon duzircon is consistent with ion microprobe measurements of 231pa in zircons from holocene and pleistocene rhyolitic eruptions schmitt 2007 schmitt 2011 the data suggest that 231pa is preferentially incorporated during zircon crystallization over a range of magmatic compositions and excess initial 231pa may be more common in zircons than acknowledged the degree of initial disequilibrium in the 235u decay chain suggested by the data from this study and other recent high precision datasets leads to resolvable discordance in high precision dates of cenozoic to mesozoic zircons minor discordance in zircons of this age may therefore reflect initial excess 231pa and does not require either inheritance or pb loss

ground penetrating radar application in a shallow marine oxfordian limestone sequence located on the eastern flank of the paris basin ne france abstract a ground penetrating radar gpr survey has been carried out in upper jurassic limestones located on the eastern flank of the paris basin ne france the potential of the investigation method is assessed for delineating geologically meaningful stratifications in the shallow subsurface the fundamentals of the gpr technique are described penetration depth and vertical resolution depends on the soil conditions the characteristics of input signal and the configuration of the transmitter receiver assembly in the studied carbonates the penetration level is rather good and the electromagnetic signal reaches up to 1000 nanoseconds maximum i e approximately 55 m several depositional units are outlined on the gpr profiles six different lithological units are recognised with distinct gpr reflection characteristics the profiles illustrate the internal 3d organisation of the carbonate platform and its geometry they provide detailed insight into the nature of an oxfordian reefal build up the high resolution subsurface model is directly calibrated with geological field observations and it results in a predictive 3d depositional working model the gpr method is a non destructive remote sensing technique that is cost effective the method is considered complementary to other conventional high resolution reservoir characterisation studies it represents a powerful investigation tool in earth science studies concerning the imaging of the structure of the shallow subsurface

high resolution temporal record of holocene ground water chemistry tracing links between climate and hydrology strontium isotope analysis of precisely dated calcite growth layers in holocene speleothems from barbados west indies reveals high resolution temporal variations in ground water composition and may provide a new approach to documenting the links between climate variability andfluctuations in the hydrologic cycle such as recharge rates andflow paths the speleothems grew in a cave that developed in a fresh water aquifer in upliftedpleistocenereeflimestones threeperiodsofground watersrisotopeevolutionare observed 87 sr 86 srvaluesdecreasedfrom6to4ka increasedfrom4to1ka anddecreased again after 1 ka the sr isotope oscillations appear to record periodic variations in the relative sr fluxes to ground water from exchangeable soil sites vs carbonate mineral reactions asreflectedin 87 sr 86 srvaluesofmodernbarbadosgroundwaters ahydrologic model that explains changes in ground waterflow routes in karst aquifers as a function of amountofrainfallrechargecanaccountforthespeleothemsrisotoperecord independent holoceneclimaterecordsthatindicateamajorperiodofaridityataround1 3 1 1kainthe american tropics correspond with periodic variations in rainfall on barbados that are predicted by this hydrologic model

facies and stratigraphic architecture of the korallenoolith formation in north germany lauensteiner pass ith mountains abstract during the oxfordian bahamian type shallow water carbonates formed in the lower saxony basin of north germany the outcrop of the korallenoolith formation in a quarry in the ith mountains lauensteiner pass contains a series of well exposed coral and coral microbial reefs intercalated with oolites six different facies are distinguished which can be assigned to the inner part of a carbonate ramp based on textural variations and facies stacking patterns accommodation space to sediment supply and or sediment production cycles of different hierarchies were defined in this succession a multispectral outcrop gamma ray log was measured as additional tool to separate facies and to identify the cyclicity a good correlation between fluctuations in the gamma ray log and the lithological changes exists generally coral and coral microbial reefs reflect times of higher available accommodation space oolites indicate sedimentation in shallower waters we thus show how based on sequence stratigraphy the succession of the korallenoolith fm can be subdivided into genetic packages this approach may contribute in providing a tool for a firm high resolution correlation of the different outcrops of this formation which is presently only poorly constrained the good correlation between gamma ray log and the cyclicity may also be helpful for subsurface correlations in the lower saxony basin

238u 230th 226ra fractionation in historical lavas from the azores long lived source heterogeneity vs metasomatism fingerprints abstract this study reports 238u 230th 226ra nuclides measured by mass spectrometry trace elements and 87sr 86sr isotopes on historical alkali basalts from the azores region the 230th 232th activity in the alkali basalts spans a range from 0 897 in sao miguel to 1 382 in terceira island that is almost as large as the global variation of mid ocean ridge basalts morb and oceanic island basalts oib the 230th 238u activity 10 40 th u 2 92 3 74 and the 87sr 86sr 0 70354 0 70467 also display large variations the 226ra 230th activity varies from 0 84 in sao miguel to 1 60 in pico island samples from pico faial and terceira islands are found to plot on the negative 230th 238u vs 226ra 230th correlation defined by the 1730 1736 eruption of lanzarote canary islands sigmarsson et al earth planet sci lett 162 1998 137 except for the sample from sao miguel island we propose that the negative correlation reflects a mixing between two end member melts one displaying a low 230th 238u and a high 226ra 230th and the other end member displaying a high 230th 238u and a low 226ra 230th numerical model suggests that the high 226ra low 230th excesses end member represented by samples from pico island can be explained by partial melting of a garnet lherzolite the other end member represented by the terceira lava is shown to result from the interaction of low degree melts with the metasomatized mantle containing phlogopite phlogopite crystals in contact with a melt enriched in 226ra and ba have a 226ra 230th 1 and high ba th because of crystal affinities for ra and ba relative to th and u after 8000 years however the unsupported 226ra excess will have decreased down to 0 as phlogopite displays little amount of u and th so during the process of interaction with phlogopite crystals low degree melts formed in the garnet stability field that are characterized by high 230th 238u 226ra 230th and ba th will loose the 226ra excess scavenged by phlogopite while the 230th 238u and ba th will remain unaffected one finds that this process may be valid over 250 years maximum so that only the first interacting melts may preserve a high 230th 238u low 226ra 230th activity on sao miguel island it is shown that the low 230th 238u while the source is clearly enriched in th cannot be explained by a lack of garnet in the mantle neither by a higher degree of melting the 226ra deficit 15 and low ba th and sr th are explained by partial melting of an enriched mantle in the presence of phlogopite

mis 7 interglacial sea surface temperature and salinity reconstructions from a southwestern subtropical pacific coral abstract we generated a 5 5 yr snapshot of biweekly to monthly resolved time series of carbon and oxygen isotope composition 13 c and 18 o and sr ca and mg ca from annually banded aragonite skeleton of a 197 ka pristine porites coral collected at niue island 19 00 s 169 50 w in the southwestern subtropical pacific ocean this report is the first of a high resolution coral based paleoclimate archive during the marine isotope stage mis 7 interglacial statistical results suggest that annual averages of sea surface temperature sst and salinity sss at 197 ka were not significantly different from and 1 2 higher than at present respectively monthly mean variations showed increased sss at 197 ka that was higher 1 4 1 9 relative to today in the austral summer than in the austral winter monthly sst and sss anomalies at 197 ka indicated smaller amplitudes by 0 3 c 11 and 0 3 24 relative to the present possibly suggesting less influence of interannual climate variability around niue our results taken together with other climate proxy records imply seasonal and interannual modulation of thermal and hydrological conditions different from today in the southwestern subtropical pacific ocean associated with the western pacific warm pool and the south pacific convergence zone variability during the mis 7 interglacial

the shifting biogeography of reef corals during the oxfordian late jurassic a climatic control until recently the jurassic was thought to have been a period characterised by a predominantly warm and equable climate during the oxfordian a time span of six million years in the late jurassic the distribution of tropical coral reefs was limited to about 35 n and near to 25 s however in middle oxfordian time coral reefs were abundant only at higher latitudes and almost entirely missing near the equator during that time the area of maximum reef development had shifted poleward to a belt lying between 20 n and 35 n leaving hardly any coral formations at the lower inner tropical latitudes after demise towards the end of middle oxfordian time the low latitude reefs recovered during the late oxfordian accompanied by a southward migration of reef corals in the northern hemisphere as suggested by stable isotope and palynological data the faunal migration can be correlated with a significant rise in seawater temperature during the middle oxfordian

interaction of rock and atmosphere patinas on mediterranean monuments this paper analyzes chemically mineralogically and petrolographically the patinas developed on several mediterranean monuments made with different stones siliceous and carbonatic in order to establish their origin and their evolution under the present environmental conditions and to evaluate the environmental parameters controling their development most of the patinas show a common sequence of layers which from the outer to the inner zone are 1 present bioactivity and or biological remains 2 gypsum rich patina and 3 calcitic brown to orange patina each one may exhibit different fabrics from micritic to stromatolitic and may be more or less continuous and homogeneous the main mineral components are calcite and gypsum but ca oxalates and ca phosphates have also been found associated to biological structures as well as quartz and clays the different fabrics and textures have been interpreted as consequence of changes in the environmental conditions which seem to be related to the biological activity facilitating the growth of different organisms and leading to the development of a deposit with distinct characteristics fabric texture porosity etc the gypsum rich patina has been interpreted as a sulphation of the underlying calcitic layer by the action of atmospheric pollutants or as dry or wet deposition from the atmospheric dust the mineralogy and texture of the patina is independent of the nature of the underlying rock and only in few cases a micritization process has been observed as interaction between patina and rock recently the penetration of endolithic microflora produced drillings and the development of a fissuration system parallel to the surface and thus the detachment of the crust from the rock and even flackening of the rock itself has been observed consequently under the present climatic conditions in the mediterranean basin erosion is a more active process than deposition and the crusts and patinas show a tendency to disappear from the surface of the monuments

off axis volcanism at the east pacific rise detected by uranium series dating of basalts recent detailed surveys of the east pacific rise have revealed the complexity of the volcanic and magmatic processes occurring along and across fast spreading ocean ridge crests1 7 in parallel with geological and geochemical investigations it is now possible to investigate the temporal and spatial pattern of volcanism at ocean ridges by dating young basalts using mass spectrometric uranium series disequilibria methods8 11 here we use 238u 230th and235u 231pa ages for basalts to quantify the spatial extent of young volcanism and crustal accretion at 9 31 n on the east pacific rise most of the ages are younger than would be expected based on off axis distance and spreading rate we infer from these anomalously young ages that most of the dated basalts on the crestal plateau were erupted 0 5 2 km outside the axial summit caldera with some volcanism occurring as far as 4 km off axis melts erupted outside the axial summit caldera can have crustal residence times and magmatic supply systems that differ from those of axial lavas

microbes in caves agents of calcite corrosion and precipitation abstract diverse biogenic and abiogenic processes produce calcite speleothems from a biogenic perspective cave microbes mediate a wide range of destructive and constructive processes that collectively influence the growth of calcite speleothems and their internal fabrics destructive processes include substrate breakdown by dissolution boring and residue micrite production whereas constructive processes include microbe calcification trapping and binding of detrital particles to substrates and microbial induced calcite precipitation biogenesis can be established from 1 the presence of mineralized microbes 2 fabrics such as stromatolite like structures that can be attributed to microbial activity and or 3 geochemical proxies carbon and oxygen isotopes lipid biomarkers considered indicative of microbe activity such criteria have for example been used to demonstrate microbial involvement in the formation of pool fingers stalactites stalagmites cave pisoliths and moonmilk nevertheless absolute proof of microbial biogenesis in calcitic speleothems is commonly difficult because taphonomic processes and or diagenetic processes commonly mask evidence of microbial activity the assumption that calcitic speleothems are abiogenic which has been tacitly assumed in many studies is dangerous as there is clear evidence that microbes thrive in most caves and can directly and indirectly influence calcite precipitation in many different ways

evaluating the development of upper jurassic reefs in the smackover formation eastern gulf coast u s a through fuzzy logic computer modeling abstract a three dimensional 3d numerical stratigraphic model has been built to simulate the development of microbial reefs on a jurassic carbonate platform using fuzzy logic modeling methods the flexibility of the model allows for the examination of a large number of variables the relative importance of local environmental conditions and global changes on the frequency of reef development are examined relative to the temporal and spatial constraints from upper jurassic oxfordian smackover reef datasets from two alabama oil fields the fuzzy model simulates the deposition of reefs and carbonate facies by integrating local and global variables local scale factors include basement relief sea level change climate latitude water energy water depth background sedimentation rate and substrate conditions regional and global scale changes include relative sea level change climate and latitude the model confirms preexisting theories that background sedimentation rate water energy substrate relative sea level change and climate influenced the development of jurassic reefs additionally the model determines the degree of control each variable has on if where and when reefs develop the variables that control if reefs develop are the global parameters of climate and amplitude of sea level change the model specifies that the variables that influence the lateral distribution of reefs or where reefs occur are substrate water energy and background sedimentation rate the model also indicates a strong correlation between when reefs develop and the rate of sea level rise in all simulations reefs initially develop in conjunction with the greatest rate of sea level rise i e the inflection point on the sea level curve and reach peak development before the time of deepest water

stratigraphic architecture of upper jurassic oxfordian reefs in the northeastern gulf coast u s and the eastern paris basin france abstract the late jurassic was a major period of reef expansion many jurassic reefs are potential hydrocarbon reservoirs but their stratigraphic distribution has been difficult to predict examination of the stratigraphic architecture of oxfordian reefs in the northeast u s gulf coast and the eastern paris basin france affords a comparison of mixed coral algal sponge reefs versus microbial dominated reefs the smackover formation in the northeastern gulf coast contains microbial dominated reefs the smackover represents deposition during a major transgression and reefs occur within late transgressive system tract tst deposits reefs of mixed coral algae and sponges characterize the oxfordian of the eastern paris basin in the ardennes lorraine reefs appear after the maximum flooding event of a stratigraphic sequence and are maintained through the highstand systems tract hst deposition and into the overlying stratigraphic sequence in burgundy reefs occur in association with the maximum flooding event of the upper stratigraphic sequence dominated by platy microsolenids reef growth begins in the tst this interval is traditionally called the lower reef complex more diverse reef growth the upper reef complex continues above the maximum flooding event through the early hst reef growth ceases by deposition of the late hst with the introduction of grainstones and other high energy lithologies all reefs in this examination regardless of biota are associated with maximum flooding events the sequence stratigraphy of the oxfordian reefs in france and the gulf coast provides a framework for studying jurassic reefs of both mixed and microbial dominated assemblages

uzth isotopic systematics at 13 n east pacific ridge segment fresh basaltic glasses have been analyzed for uzth disequilibrium systematics as part of an extensive study on the east pacific rise epr at 12 45 n these samples are well described in terms of major and trace elements as well as in nd pb and sr isotopes our results show significant heterogeneities in the mantle source at a small scale and show heterogeneities at larger scales also when compared to other epr data u and th concentration and isotopic data rule out fractional crystallization as a main process and support a mixing model in agreement with the marble cake model developed by alle gre and turcotte and constrained by trace elements and nd sr and pb isotopes on the same samples by prinzhofer et al based on the high 230th 232th isotopic ratios on recent tholeiites especially the th u values inferred for their sources clearly show that the upper mantle th u has decreased with time

mid ocean ridge basalt generation along the slow spreading south mid atlantic ridge 5 11 s inferences from 238u 230th 226ra disequilibria u series disequilibria have provided important constraints on the physical processes of partial melting that produce basaltic magma beneath mid ocean ridges here we present the first 238u 230th 226ra isotope data for a suite of 83 basalts sampled between 5 s and 11 s along the south mid atlantic ridge this section of the ridge can be divided into 5 segments a0 a4 and the depths to the ridge axis span much of the global range varying from 1429 to 4514 m previous work has also demonstrated that strong trace element and radiogenic isotope heterogeneity existed in the source regions of these basalts accordingly this area provides an ideal location in which to investigate the effects of both inferred melt column length and recycled materials 226ra 230th disequilibria indicate that the majority of the basalts are less than a few millennia old such that their 230th values do not require any age correction the u th isotope data span a significant range from secular equilibrium up to 32 230th excess also similar to the global range and vary from segment to segment however the 230th 238u ratios are not negatively correlated with axial depth and the samples with the largest 230th excesses come from the deepest ridge segment a1 two sub parallel and positively sloped arrays for segments a0 2 and a3 and a4 between 230th 238u and th u ratios can be modelled in various ways as mixing between melts from peridotite and recycled mafic lithologies despite abundant evidence for source heterogeneity there is no simple correlation between 230th 238u and radiogenic isotope ratios suggesting that at least some of the trace element and radiogenic isotope variability may have been imparted to the source regions 350 kyr prior to partial melting to produce the basalts in our preferred model the two 230th 238u versus th u arrays can be explained by mixing of melts from one or more recycled mafic lithologies with melts derived from chemically heterogeneous peridotite source regions

melting dynamics beneath the tonga kermadec island arc inferred from 231pa 235u systematics measurement of 231pa 235u disequilibrium in tonga kermadec island arc lavas north of new zealand permits discrimination of the time scales and mechanisms of fluid addition and partial melting for tonga lavas the 231pa 235u ratios are less than 1 and can be explained by fluid addition from the subducting plate around 60 000 years ago in contrast the effects of partial melting overprinted those of fluid addition in the kermadec lavas resulting in 231pa 235u ratios greater than 1

microbialite morphology structure and growth a model of the upper jurassic reefs of the chay peninsula western france abstract during the early kimmeridgian the northern margin of the aquitaine basin western france is characterised by a significant development of coral reefs the reef formation of the chay peninsula comprises two main reefal units in which the microbial structures can contribute up to 70 of framework the microbial crusts which played an important role in the stabilisation and growth of the reef body show the characteristic clotted aspect of thrombolitic microbialites corals are the main skeletal components of the build ups the bioconstructions of the chay area are thus classified as coral thrombolite reefs four main morpho structural types of microbial crusts are distinguished 1 pseudostalactitic microbialites on the roof of intra reef palaeocaves 2 mamillated microbialites found either on the undersides or on the flanks of the bioherms 3 reticular microbialites in marginal parts of the reefs and between adjacent bioconstructed units and 4 interstitial microbialites in voids of bioclastic deposits thrombolitic crusts developed on various substrates such as corals bivalves or bioclasts the thrombolites formed a dense clotted and or micropeloidal microbial framework in which macro and micro encrusters also occur variations in accumulation rate strongly influenced the reef morphology in particular its relief above the sediment surface the coalescence of the coral microbialite patches created numerous intra reef cavities of metre scale dimensions the direction of microbial growth which defined the macroscopic microbialite forms strongly depended on the position within the reef framework but was also controlled by water energy accumulation rate and light availability

the great barrier reef a 700 000 year diagenetic history a deep borehole through ribbon reef 5 in the great barrier reef off north eastern australia has identified a variety of cements including epitaxial radial prismatic and spherular aragonite together with blocky prismatic and fibrous calcite these cements are discontinuously arranged within the sequence that consists predominantly of grainstones but locally includes clotted muddy and filamentous textures that may be of microbial origin calcite cements vary in morphology with groups of crystals that include acute scalenohedral rhombohedral and flattened concordant terminations these show varying densities of inclusions that locally define growth zones and in some terminations divide in the manner of split crystals to form fibrous fringes morphological changes in calcite are inferred to reflect changes in water chemistry and crystal growth rates at the time of growth allied to their relationship to the palaeo water table and linked in turn to changes in sea level neomorphism and dissolution are widespread and variations in the severity of both imply response to the degree of undersaturation of pore waters that at times were probably balanced within very narrow limits a total of 10 depositional units are identified those units at the base of the borehole reflect deposition and diagenesis within a marine environment the influence of meteoric waters indicated by stable isotopes is first apparent at the top of unit 1 and in unit 2 184 to 155 m below sea floor petrographic evidence of vadose conditions appears at the tops of unit 3 131 to 99 m below sea floor units 4 to 8 all deposited under marine conditions provide isotopic evidence of meteoric or mixing zone waters and petrographic indicators of vadose conditions typically at the top of the units evidence indicates that in unit 5 the water table was mobile and units 6a 6b 7 and 8 all characterized by ultraviolet fluorescent cements are capped by sub aerial erosion surfaces unit 9 the holocene reflects the recent re establishment of marine conditions the extent of alteration of the entire sequence reflects the substantial and pervasive influence of meteoric waters this effect is interpreted as a result of a greater rainfall and river flow from the mainland during early and late stages of interstadial periods the study reflects progress in the ability to recognize the diagenetic signal generated by sea level change however whereas the isotopic results reflect the changing relationships between vadose and phreatic zones in groundwater systems beneath successive emergent surfaces their correspondence with petrographic features is expressed only weakly and commonly lacks the systematic sequential overprinting implied by the distribution of cathodoluminescent zones of cements in many ancient limestones

facies partitioning and stratal pattern in salt controlled marine to continental mini basins examples from the late oligocene to early miocene of the sivas basin turkey the sivas basin turkey records a complex interaction between sedimentation salt tectonics and regional shortening leading to the formation of numerous mini basins the segmentation into mini basins was initiated during the oligocene by the deposition of the fluvio lacustrine karayun fm this continental succession is overlain abruptly by an oligo miocene shallow marine succession karacaoren fm which comprises two main sub environments i mixed deltaic and carbonate ramp ii coastal plain and lagoon the karacaoren fm forms a marine succession more than 1500 m thick that passes vertically upwards into a continental succession the fluvial dominated benlikaya fm these two formations are the focus of the present study during the period of marine sedimentation the competing accumulation of carbonates and clastics is related not only to the topography inherited from salt tectonics but also to relative sea level variations expressed by two large scale transgressive regressive cycles we analyse these complex facies and stratal relationships to illustrate the modifications induced by salt tectonics this study is based on extensive fieldwork and mapping making use of numerous measured stratigraphic sections and aerial photos over a large area comprising more than fifteen adjacent outcropping mini basins the aim of this study is to provide a detailed description of the stratigraphic relationships correlations and sedimentary systems distribution in mini basins during deposition of the oligo miocene shallow marine and continental successions we first clarify the vertical stratigraphic succession of the oligo miocene marine and continental deposits and establish correlations between the studied mini basins these correlations then allow us to characterize and assess the local effects of salt withdrawal in relation to the regional forcings associated with flexural subsidence tectonic shortening and relative sea level changes an improved understanding of the complex interactions of these variables provides a framework to distinguish the mechanisms that control facies distribution and stratal geometry in salt basins

annual to sub annual resolution of multiple trace element trends in speleothems this study aims to establish evidence for the widespread existence of preserved high resolution trace element variations in speleothems that may have climatic significance ion microprobe analysis of speleothems reveals that annual to sub annual variations in element chemistry exist at five shallow western european cave sites crag cave county kerry and ballynamintra county waterford ireland uamh an tartair sutherland scotland grotte pere noel belgium grotta di ernesto ne italy with widely varying climatic geomorphic and geological settings the variations are not restricted to species mg sr and ba known to substitute directly for ca in the calcite lattice but include h f na and p phosphorus as phosphate displays the greatest variability and may have the most significance as a proxy for the seasonal temperature cycle because of its role as a nutrient element the technique allows estimation of growth rate of speleothems at any interval of interest which is one of several possible uses in palaeoclimatology

the depth of pelagic deposits in the tethyan jurassic and the use of corals an example from the apennines abstract assessing the palaeobathymery of pelagic deposits is rather speculative as proof through lithology or fossils significant for depth estimates is sparse this is unfortunate as the bathymetric history of pelagic successions allows to conceive the evolution of continental margins and oceanic basins discoveries in coral biology bring an unexpected impact on basin analysis evidence strongly suggests that pennular corals fossil and modern constitute a zooxanthellate group with an outstanding specialization in colonizing deeper parts of the marine photic zone this adaptation includes light amplification by autofluorescent pigmented cells and particular feeding witnessed by peculiar gastric ducts and skeletal features such corals occur in the umbria marche and sabina apennines on top of late jurassic submarine highs and at basin margins values of palaeodepth relative to pelagic deposits are provided by corals and other environmental data because depth reconstruction involves classical tethyan facies such as ammonitico rosso aptychus limestone and radiolarian cherts we must note that these results do not meet with actualistic models relying on carbonate dissolution for estimating depth deposits viewed as bathyal to abyssal could also have accumulated within or just below the photic zone thus a new insight opens on mesozoic bathymetries regarding vast areas middle east to caribbean and on subjects ranging from platform drowning to regional extension styles

geomicrobiology of carbonate silicate microbialites from hawaiian basaltic sea caves abstract modern microbial mats and microbialites are described from basaltic sea caves on the island of kauai hi the mats grow on the ceilings and walls in the photic zone of several open caves where fresh water seeps out of the rock scanning sem and transmission electron microscopy tem showed that the active mats are dominated by filamentous and nonfilamentous cyanobacteria in the surface layers and heterotrophic bacteria in deeper layers energy dispersive x ray analysis revealed that copious amounts of extracellular polymeric substances eps are rich in mg si o and ca likely concentrated from solution petrographic microscopy and electron microprobe analysis of the mineralized microbialites showed textures reminiscent of stromatolitic laminations consisting mainly of alternating calcium carbonate calcite and aragonite and magnesium rich silicate kerolite thin coatings rich in magnesite hydromagnesite and monohydrocalcite surround the microbialites on the rock surfaces and are likely inorganic in origin within the mats minerals tend to form and concentrate within or around dense matrices of eps microenvironments with geochemical conditions favorable for mineral crystallization likely develop in the mats as a result of the mucilaginous extracellular material and the development of bacterial microcolonies in addition copious amounts of extracellular polymers bind ions from solution and provide nucleation sites for mineral crystallization and growth this combination of biological and inorganic processes can explain the occurrence of the secondary minerals in these caves as well as the stromatolitic textures of the microbialites

sedimentary evolution of a coral microbialites and debris rich upper jurassic reef upper tithonian eastern sardinia italy abstract this work investigates a portion of a poorly documented upper tithonian reef lower mt bardia reef lbr developed along the northern platform margin of the eastern sardinia platform esp the lbr was probably one of the most southerly reefs of the northern tethys margin and this study provides the first comprehensive description of facies and internal structure giving insights for the depositional setting detailed compositional and facies analyses of lbr have been carried out in three quarries located in the orosei gulf eastern sardinia the main reef components are represented by carbonate bioclastic debris microbialites and microencrusters and reef building organisms mainly corals and stromatoporoids these components combine in various proportions forming several facies and facies associations ten reef facies rf grouped into three main facies associations have been identified within the studied reef portion the distribution and arrangement of facies reveal a sedimentary evolution evolving from a microframework dominated reef to a carbonate debris dominated one with the internal reef architecture evolving from massive to patchy to coarsely stratified and roughly bedded the reef components and facies indicate that the investigated portion of the lbr corresponds to a shallow back reef zone characterized by well lit and generally low energy hydrodynamic conditions possibly developed in back position with respect to a higher energy zone that was closer to the edge of the platform in this depositional context the arrival of large amounts of debris and the evolving internal architecture are interpreted as the result of the infilling process of the back reef zone due to the progradation of a sand apron during a long term regional regressive phase

a new method for u th pa ra separation and accurate measurement of 234u 230th 231pa 226ra disequilibria in volcanic rocks by mc icpms abstract a new method for the chemical separation and mc icpms measurements of u th pa ra disequilibria in volcanic samples from a single sample aliquot is presented the accuracy and precision of our techniques is assessed by replicate analyses of the synthetic u and th isotope standards irmm 184 and irmm 35 and the secular equilibrium rock standards bcr 2 w 2a and tml a measure of true sample reproducibility including the errors related to sample processing and the chemical separation is obtained from analysis of multiple digestions of the rock standards 234u 238u 230th 238u 231pa 235u and 226ra 230th activity ratios on ten separate dissolutions of usgs rock standard bcr 2 for example reproduce to 0 4 1 4 1 1 and 2 4 2 sd respectively all elements u th pa ra are separated from a single spiked sample aliquot and the elemental concentrations are measured on the same solutions as the isotopic compositions analytical artefacts from determination of elemental and isotopic concentrations on different sample aliquots due to sample heterogeneity are therefore avoided in addition our new chemical separation protocol is time efficient and allows for rapid processing of volcanic samples with less than 25 fg of pa and ra

crustal thickness on the mid atlantic ridge bull s eye gravity anomalies and focused accretion spreading segments of the mid atlantic ridge show negative bull9s eye anomalies in the mantle bouguer gravity field seismic refraction results from 33 s indicate that these anomalies can be accounted for by variations in crustal thickness along a segment the crust is thicker in the center and thinner at the end of the spreading segment and these changes are attributable to variations in the thickness of layer 3 the results show that accretion is focused at a slow spreading ridge that axial valley depth reflects the thickness of the underlying crust and that along axis density variations should be considered in the interpretation of gravity data