mechanical properties of shale gas reservoir rocks part 2 ductile creep brittle strength and their relation to the elastic modulus we studied the elastic moduli ductile creep behavior and brittle strength of shale gas reservoir rocks from barnett haynesville eagle ford and fortst john shale in a series of triaxial laboratory experiments we found a strong correlation between the shale compositions in particular the volume of clay plus kerogen and intact rock strength frictional strength and viscoplastic creep viscoplastic creep strain was approximately linear with the applied differential stress the reduction in sample volume during creep suggested that the creep was accommodated by slight pore compaction in a manner similar to instantaneous strain there was more viscoplastic creep in samples deformed perpendicular to the bedding than parallel to the bedding the tendency to creep also correlated well with the static young s modulus we explained this apparent correlation between creep behavior and elastic modulus by appealing to the stress partitioning that occurs between the soft components of the shales clay and kerogen and the stiff components quartz feldspar pyrite and carbonates through a simple 1d analysis we found that a unique relation between the creep compliance and elastic modulus independent of composition and orientation can be established by considering the individual creep behavior of the soft and stiff components that arises from the stress partitioning within the rock this appears to provide a mechanical explanation for why long term ductile deformational properties can appear to correlate with short term elastic properties in shale gas reservoir rocks

facies distribution and textural variation in faro drift contourites velocity fluctuation and drift growth abstract detailed study of seismic profiles piston cores and bottom photographs from the faro drift on the southern margin of portugal has led to a better understanding of drift development and its relationship to bottom current circulation data on the contourite facies characteristics and the surface microphysiography have been published elsewhere here we concentrate on sediment distribution and geometry longitudinal trends in facies types mean grain size sedimentary structures and composition can be interpreted in terms of relative intensity of currents over different parts of the drift these are generally more intense in the marginal channels and at the upstream or eastern end of the drift three different scales of vertical variation of facies can be identified at the large scale 300 500 m of sediment has accumulated over 4 6 ma in a regular vertical succession due to the northward progradation of the drift at the medium scale the upper 20 30 m of sediment shows alternating phases of active lateral progradation and uniform vertical accumulation that may correlate with episodes of more and less current activity related to high and low sea level stands respectively over the past 0 3 ma at the small scale the topmost 2 3 m of sediment deposited in approximately 0 03 ma shows three zones of coarser grained sediments separated by finer grained contourites this sequence can also be interpreted in terms of long term fluctuation in bottom current activity although the signal is clearly complex this kind of analysis of sedimentary drifts can lead to more accurate reconstruction of paleocirculation patterns

bacterial fossil record in whale falls petrographic evidence of microbial sulfate reduction abstract whale fossils from a variety of geologic ages and depositional environments were thin sectioned and analyzed for evidence of microbial activity comprising a combination of microborings authigenic pyrite botryoidal cements and micropeloids borings are dense in some samples with an average diameter of 8 02 m framboidal pyrite crystals with an average diameter of 61 84 m in diameter occur within the pore spaces of the bone in borings and at the bone sediment interface the pyrite crystals are densely packed at the edges of the bone and scattered more randomly throughout the pore spaces aragonitic botryoidal cements line pore spaces in samples from deep bathyal settings potential bacterial peloids occur within pore spaces with an average size of 77 45 m or diffuse to comprise clotted micrite since bacterial body fossils are extremely rare in the fossil record recognition of past microbial ecosystems must be based on multiple lines of supporting evidence of the independent signatures studied the bacterial peloids and botryoids provide the most convincing evidence of a sulfophilic stage these fossil biosignatures suggest that a sulfophilic stage is preserved at least as far back as the eocene

ams carbon 14 dating of microbial carbonates in holocene coral reefs western luzon philippines abstract microbial carbonates microbialites occurred in the holocene coral reefs at paraoir the philippines these microbialites appeal grayish to buff in color with a stromatolitic to thrombolitic structures and encrust on corals directly or on a thin layer of calcareous red algae or encrusting foraminifera that covered the corals first the microbialites only occur in the lower earlier parts of the holocene reef sequence where heliopora coerulea dominated no microbial carbonates were observed in the upper younger part of the holocene reefs that is interpreted to grow in water depth shallower than 6 m on the basis of coral community samples of microbial carbonate and associated coral were dated by ams 14 c the results show that the microbialites formed about 10 to 7 5 kyr bp nearly coeval to or a few hundred years younger than the corals on which the microbialites encrusted ams 14 c ages of samples recovered at reef margins are consistent to 230 th ages of corals associated with the microbialites but those recovered in the back reef are much older that the previously published 230 th ages of corals and interpreted to be reworked into the backreef it is proposed that the microbialites at paraoir formed in early holocene on reef slope when the deglacial sea level was rising rapidly after 7 5 kyr bp when the sea level rise slowed down and coral reefs caught up with sea level the condition became favorable to corals prospered in shallow water and no longer suitable for microbialite formation

pressure and temperature dependence of p and s wave velocities seismic anisotropy and density of sheared rocks from the sierra alpujata massif ronda peridotites southern spain seismic wave velocities and densities and their pressure and temperature dependence of rock samples recovered from surface exposures at the sierra alpujata were determined in order to better understand the petrological controls on velocity and density the rock samples studied are representative of the major lithologies of the ronda ultramafic body and its metamorphic aureole the suite of ultramafic rocks includes dunite harzburgite and lherzolite exhibiting different degrees of deformation and serpentinization the rocks representing the metamorphic aureole comprise coarse grained migmatites to ultramylonitic migmatites gneisses and eclogites the experimental data include measurements of elastic wave velocities vp vs and densities at confining pressures up to 600 mpa and temperatures up 600 c at 600 mpa the determination of the pressure and temperature derivatives of velocities and densities and the determination of velocity anisotropy average p and s wave velocities at 600 mpa for rocks of the ultramafic body vary from 6 47 to 8 22 km s 1 and 3 27 to 4 75 km s 1 respectively mainly due to different degrees of serpentinization maximum vp and vs anisotropy is about 8 0 and 9 5 respectively and is primarily related to the preferred orientation of olivine in rocks of the metamorphic aureole average p velocities are in the range 5 61 7 23 km s 1 and s velocities vary from 3 48 to 4 04 km s 1 p and s velocity anisotropy is highest about 6 4 and 4 6 in sheared rocks mylonites and is mainly due to the preferred orientation of biotite and sillimanite the geophysical significance of the experimental data is briefly discussed

rare earth elements in manganese nodules from the south atlantic ocean as indicators of oceanic bottom water flow abstract the mineralogy and geochemistry of a suite of nine manganese nodules from the south atlantic have been determined the ce la ratios of the nodules were investigated to see if they could be used as redox indicators to trace the oxygen content of the ambient water mass and the flow path of the antarctic bottom water as has previously been successfully carried out in the pacific ocean the ce la ratios of the nodules decrease in the sequence lazarev sea weddell sea 10 4 and 9 7 east georgia basin 6 5 and 7 1 argentine basin 5 0 but then increase in the brazil basin 6 2 and angola basin 9 8 and 15 1 a further decrease was observed in the cape basin 7 6 an extremely high ce la ratio of 24 4 had already been determined for nodules sampled north of the nares abyssal plain in the western north atlantic these data reflect the more complicated pattern of bottom water flow in the south atlantic than in the south pacific the penetration of more oxygenated north atlantic deep water into the south atlantic accounts for the higher ce la ratios in the nodules from the angola and brazil basins based on this study the flow path of the antarctic bottom water could only be traced as far north as the argentine basin the unique geochemistry of nodules from the central angola basin high mn fe and ce la ratios high contents of ni cu zn and mo appears to be a function of the nature of the overlying water mass and of the multiple diagenetic sources of metals to the nodules

trilobite associations taphonomy lithofacies and environments of the silurian reefs of north greenland abstract llandovery silurian reefs in north greenland have yielded extensive collections of remarkably well preserved trilobites dominated by scutelluids these collections provide a unique opportunity to analyse the reefs and their trilobite faunas in a palaeoenvironmental context and the study highlights the importance of pre existing collections to which further scientific value can be added counts of trilobite sclerites from thirteen reef localities are analysed using cluster and correspondence analyses to identify trilobite associations and taphonomic signatures lithofacies analysis allows these to be understood in a detailed palaeoenvironmental context seven trilobite associations are identified scutelluid illaenimorph scutelluid scutelluid cheirurid scutelluid harpetid proetid encrinurid and illaenimorph the number of associations highlights the variable distribution of taxa within the reefs which is partly a reflection of intense hydrodynamic sorting in reef environments trilobites are predominantly associated with a cement rich microbial lithofacies it is apparent that microbial processes were the principal contributors to the production of carbonate mud and played a significant role in the development of the greenland reefs the observed associations comprise time averaged event beds in an otherwise low energy and slow sedimentation regime and possibly result from storm activity remobilising sclerites and depositing them within depressions and cavity fills within the reef surface correspondence analysis reveals two distinct taphonomic signatures within the reef and transport distance is the primary influence on these the proetid association is readily separated from the others by its taphonomic attributes representing the least amount of transport and suggesting the taxa involved took advantage of the more sheltered niches within the reef this is the first study of reef dwelling trilobites to take advantage of multivariate techniques to identify associations and describe their taphonomic attributes in particular the effectiveness of correspondence analysis in recognising taphonomic signatures is demonstrated

seismic bathymetric and photographic evidence of widespread erosion and a manganese nodule pavement along the continental rise of the southeast cape basin abstract the southeast cape basin is flanked by the extensive cape town slump at the foot of which is a widespread zone of erosion southward dipping reflectors that intersect this surface of erosion are truncated and the surface itself contains channels up to 35 m deep and 2 km wide an extensive moat up to 100 m deep and over 20 km wide runs along the northern edge of the subdued a pavement of well exposed large spheroidal botryoidal manganese nodules embedded in sandy mud was photographed and grab sampled in a depth of 4517 m south of the cape town slump and southwest of the argentina seamount the nodules are polynucleate and have increasing proportions of silicate detritus towards the outer edge it is suggested that the inner layer may be of early to middle pleistocene age because the nodules lie on a regional unconformity eroded into palaeogene neogene and in places early pleistocene sediments in contrast the outer layer is probably middle pleistocene to holocene and contains ice rafted detritus a camera grab station in 4749 m near the major erosional channels revealed evidence of southeastward flowing contour currents scouring a veneer of foraminiferal muddy sand draping a pavement of manganese nodules more powerful bottom currents in the agulhas ridge moat have formed westward moving current ripples of glauconitic muddy sand small friable spheroidal iron nodules in the troughs between the ripples have nuclei of glauconitic sandy mud and are probably goethite encrusted intraclasts derived from erosion of the underlying early pleistocene glauconitic pelagic clay

early diagenesis of carbonates on a cool water carbonate shelf southern australia abstract the southern australian continental margin is an immense cool water carbonate factory the high energy open shelf is blanketed by heterozoan carbonates of both holocene and late pleistocene age three distinct grain types have been identified and radiocarbon dated these include 1 relict grains highly abraded iron stained intraclasts formed during the intermediate sea level stands of marine isotope stages 3 and 4 2 stranded grains gray and buff colored abraded biofragments and intraclasts marooned during the sea level rise associated with marine isotope stage 2 and 3 holocene grains unaltered biofragments formed during marine isotope stage 1 optical mineralogical and chemical characterization of grains of each age has revealed pathways of early diagenesis in this realm both calcitic and aragonite biogenic grains undergo dissolution while dissolution of calcitic components is minor and incomplete relict sediments are predominantly mg calcite aragonitic skeletons undergo significant dissolution within 30 000 years in contrast to early dissolution of aragonite micritic calcite cement with 12 mol mgco3 is a significant diagenetic phase in these sediments infilling many stranded and most relict skeletons similar cement precipitates between grains forming small numbers of cemented grain aggregates in most samples microprobe and icp ms analysis demonstrates fe oxides mn oxides and associated clay minerals discolor stranded and relict grains by coating grain surfaces and infesting micropores such coatings begin to form on holocene grains during or soon after formation the oxides scavenge trace elements including v ti cr and ree altering the elemental compositions of biogenic carbonate

cryptic biostalactites in a submerged karst cave of the belize barrier reef revisited pendant bioconstructions cemented by microbial micrite abstract microbial carbonates are important components of postglacial tropical coral reef frameworks curious calcium carbonate protrusions in a submarine karst cave in the belize barrier reef platform were initially interpreted as being largely the product of physicochemical precipitation around a meshwork of serpulid tubes new petrographical mineralogical geochronological and inorganic and organic geochemical data suggest that sulfate reducing bacteria played a substantial role in carbonate formation just as in cryptic settings of other modern tropical coralgal reefs the bacterial involvement in carbonate authigenesis is indicated by the content and isotopic composition of carbonate associated sulfate the presence of non isoprenoidal sn 1 mono o alkyl glycerol monoethers mages and terminally branched fatty acids and the observation that the majority of molecular fossils assigned to sulfate reducing bacteria are tightly associated with the carbonate mineral lattice the carbonate protrusions that were formerly named pseudostalactites are termed biostalactites here to underline the significance of biological activity during carbonate formation the belize biostalactites are composed of four carbonate phases including serpulid tubes lithified sediment and microbial carbonate as well as unconsolidated sediment usually found in macroborings of bivalve molluscs lithified sediment and microbial carbonate are fine grained with clotted mottled and peloidal textures while serpulid tubes are aragonitic lithified sediment and microbial carbonates are mixtures of high magnesium calcite and aragonite magnesium calcite content increases with increasing consolidation lithified sediment and microbial carbonate are interpreted as fine biodetrital sediment that was subsequently cemented by authigenic micrite scalenohedral high magnesium calcite and acicular aragonite cements played a subordinate role in cementation carbon and oxygen stable isotope ratios of lithified sediment and microbial carbonate exhibit similar ranges as modern reefal microbialites our study exemplifies that heterotrophic bacteria can be a crucial agent that contributes to the formation of carbonate build ups by cementing skeletal frameworks in cryptic environments

microbialite development patterns in the last deglacial reefs from tahiti french polynesia iodp expedition 310 implications on reef framework architecture abstract the widespread occurrence of microbialites in the last deglacial reef frameworks 16 6 ka bp implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea level variations and environmental changes the present study is based on the sedimentological and chronological analysis 14c ams dating of drill cores obtained during the iodp expedition 310 tahiti sea level on the successive terraces which typify the modern reef slopes from tahiti it provides a comprehensive data base to investigate the microbialite growth patterns i e growth rates and habitats to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea level rise the last deglacial reefs from tahiti are composed of two distinctive biological communities 1 the coralgal communities including seven assemblages characterized by various growth forms branching robust branching massive tabular and encrusting that form the initial frameworks and 2 the microbial communities developed in the primary cavities of those frameworks a few meters 1 5 to 6 m below the living coral reef surface where they heavily encrusted the coralgal assemblages to form microbialite crusts the dating results demonstrate the occurrence of two distinctive generations of microbialites the reefal microbialites which developed a few hundred years after coralgal communities in shallow water environments whereas the slope microbialites grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities the development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies the most widespread microbialite development occurred in frameworks dominated by branching thin encrusting tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity 50 in contrast their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity 30 and could not host a significant microbialite expansion

sedimentary deposits on the southern south african continental margin slumping versus non deposition or erosion by oceanic currents seismic profiles extending from the southern south african shelf into the deep sea reveal a strong erosional activity which affects large parts of the continental margin quaternary to oligocene units and in places the complete sedimentary column appear to have been removed mass movements were previously considered as the origin of this erosion however structures indicating slumping can be identified in only a few places the erosional activity is confined to specific water depths which correlate well with the activity levels of water masses observed here we thus suggest that the agulhas current antarctic intermediate water north atlantic deep water and antarctic bottom water have intensively shaped the sedimentary units over a long period this indicates a stable circulation comparable to that at present day since the neogene

dolomitization in a mixing zone of near seawater composition late pleistocene northeastern yucatan peninsula abstract patches of dolomite occur in cores of reefal limestone from the shallow subsurface on the northeastern coast of the yucatan peninsula this limestone accumulated during an interglacial high stand of sea level about 200 000 years ago dolomitization was preceded by freshwater diagenesis including precipitation of sparry calcite cement stabilization of mg calcitic skeletal fragments and partial dissolution of aragonitic components this suggests a predolomitization lowering of sea level with the consequent freshening of pore water the subsequent precipitation of dolomite indicates a return to high sea level with the consequent increase in mg ca ratio of pore water dolomitization took place during a brief high stand of sea level either shortly after deposition about 200 000 yr bp r more likely about 125 000 yr bp dolomite occurs both as microcrystalline replacement dolomite and as cement the cement is part of the following diagenetic sequence 1 limpid euhedral subhedral calcian dolomite crystals 2 zoned dolomite crystals with zones formed by variations of the calcium magnesium ratio in dolomite 3 layers of alternating calcian dolomite and magnesian calcite or calcite and 4 calcite this sequence represents the progressive freshening of ground water during the initial stage of a fall in sea level average cation composition of the limpid dolomite cement is ca57mg43 electron microprobe analysis zoned cement crystals are composed of ca57 59mg43 41 layers and ca62mg38 layers most of the higher calcium dolomite layers are dissolved forming hollow zone crystals in cement with alternating dolomite and calcite zones the calcite is ca99 97mg1 3 low mg calcite and ca96 93mg4 7 mg calcite the dolomite and mg calcite zones are partially to totally leached 18o compositions of yucatecan dolomite and of modern ground water suggest dolomite precipitation from mixed water ranging from about 75 seawater 25 freshwater to nearly all seawater isotope analyses are for the most stable calcian dolomites more soluble calcium rich dolomite presumably is analyzed with calcite and thought to be isotopically lighter than the less soluble dolomite in the cement sequence the most stable dolomite is followed by more soluble dolomite as ground water becomes less saline isotope analyses together with position of dolomite in the cement sequence suggest the most stable calcian dolomite including limpid dolomite precipitated from mixed water with large proportions of seawater and the less stable more calcian dolomite precipitated from fresher mixed water

stress anisotropy and velocity anisotropy in low porosity shale abstract shales are known for often marked intrinsic anisotropy of many of their properties including strength permeability and velocity for example in addition it is well known that anisotropic stress fields can also have a significant impact on anisotropy of velocity even in an isotropic medium this paper sets out to investigate the ultrasonic velocity response of well characterised low porosity shales from the officer basin in western australia to both isotropic and anisotropic stress fields and to evaluate the velocity response to the changing stress field during consolidated undrained multi stage triaxial tests on core plugs cut normal to bedding vpv increases monotonically with increasing effective stress and vs1 behaves similarly although with some scatter vph and vsh remain constant initially but then decrease within each stage of the multi stage test although velocity from stage to stage at any given differential stress increases this has the impact of decreasing both p wave e and s wave anisotropy through application of differential stress within each loading stage however increasing the magnitude of an isotropic stress field has little effect on the velocity anisotropies the intrinsic anisotropy of the shale remains reasonably high at the highest confining pressures the results indicate the magnitude and orientation of the stress anisotropy with respect to the shale microfabric has a significant impact on the velocity response to changing stress fields

a giant underwater encrusted stalactite from the blue hole lighthouse reef belize revisited a complex history of biologically induced carbonate accretion under changing meteoric and marine conditions a late pleistocene to holocene submerged and encrusted speleothem exhibits a complex history including a meteoric phase and two marine phases a combined study using petrography mineralogy and inorganic and organic geochemistry as well as geochronology has shown that phototrophic and heterotrophic biological activity impacted carbonate precipitation during all phases of carbonate accretion the stalactite formed ca 30 m below modern sea level at a marginal overhang in the blue hole of lighthouse reef atoll unlike purely meteoric speleothems the belize example consists of a meteoric core a marine aragonite crust and a serpulid micrite rich outer crust as a result of postglacial flooding of the karst cave the core of the stalactite has a tufaceous texture containing algal or microbial remains and consists entirely of low magnesium calcite formed 19 55 10 68 kyr bp the texture suggests that the stalactite formed at the cave entrance and hence the former cave ceiling had apparently collapsed earlier during the pleistocene oxygen 18o and carbon 13c isotopes across the core suggest a trend towards drier conditions and reduced soil and plant cover after the last glacial maximum the marine aragonite crust consists of stacked botryoids in which individual crystals up to 700 lm have dark terminations enriched in high magnesium calcite this crust accreted from 10 82 to 9 95 kyr bp in warm shallow water during the early holocene thermal optimum carbonate accretion rates were considerable and averaged 125 m yr the crust has a dense laminated texture on one side and a porous shrubby texture on the other the presence of n c16 1 5 n c17 1 6 and 10me c16 fatty acids in the laminated crust suggests that sulfate reducing bacteria contributed to aragonite formation in an environment that was less open than the formation environment of the porous crust where these biomarkers are lacking n c16 1 5 n c17 1 6 or are less abundant 10me c16 enrichment of 34s and 18o in carbonate associated sulfate cas relative to seawater sulfate also suggests sulfate reduction during carbonate formation the greater contribution of heterotrophic processes to aragonite precipitation in the laminated crust is also reflected in 13c values as low as 1 3 whereas no such depletion is observed in the aragonite of the porous crust 13c values as low as 0 0 a pronounced isotopic variability and excursions to positive 13c values as high as 3 5 0 in the inner half of the laminated crust indicate an episodic local impact of photosynthesis on aragonite precipitation whereas the lack of such excursions in the porous crust 13c values as high as 1 5 0 is again best explained by a more open environment of formation after a ca 5 kyr hiatus from 4 39 kyr bp a biogenic crust of abundant serpulids and finely crystalline microbial and detrital carbonate consisting of high magnesium calcite and aragonite accreted on the outer surface of the stalactite outermost crust accretion was probably influenced by the inundation of the lighthouse reef lagoon that started to shed abundant fine grained carbonate sediment into the blue hole the stalactite broke off the cave ceiling either before or after the formation of the outermost crust likely due to seismic movements along the nearby plate boundary the study demonstrates that like speleothems from the terrestrial realm submerged stalactites may have had complex histories with great potential as paleoenvironmental archives

anaerobic diagenesis within recent pleistocene and eocene marine carbonate frameworks porewaters from a variety of recent pleistocene and eocene lithified marine carbonate frameworks displayed similar chemical characteristics highly depleted concentrations of dissolved oxygen 20 m elevated levels of dissolved methane 25 5000 nm and near seawater sulphate levels these porewaters also had low ph values 7 5 7 9 and contained elevated concentrations of sulphide 4 10 m dissolved inorganic carbon 2 05 2 46 mm and inorganic nutrients hydrocarbon composition data indicate that the methane is biogenic whereas the methane 13c values 47 4 2 7 0 suggest that it has been subject to oxidation the porewater dissolved inorganic carbon 13c values varied from 0 6 to 39 0 suggesting input of carbon dioxide from organic matter oxidation we conclude that anaerobic diagenesis involving bacterial degradation of organic matter is a common process in lithified marine carbonates and hypothesize that it may be an important factor controlling their carbonate geochemistry

energy components in rock blasting abstract ten production blasts and one single hole confined blast have been monitored in two quarries in order to assess the measurable forms of energy in which the energy delivered by the explosive is transformed in rock blasting the seismic field from seismographs readings the initial velocity of the blasted rock face obtained from high speed video camera records and the fragment size distributions from image analysis of the muckpile material are used to determine the seismic wave energy the kinetic energy and the fracture energy respectively transferred in the blasting process the blasting data and the methods of calculation of the energy terms from those are described in detail heat of explosion and useful work to 100 mpa have been used as descriptions of the energy of explosives the maximum total energy measured accounts for not more than 26 of the available explosive energy if this is rated as the heat of explosion though lower figures are usually obtained the values measured for each of the energy components range from 2 to 6 of the total energy available for the fragmentation energy 1 3 for the seismic energy and 3 21 for the kinetic energy for the confined shothole the seismic energy was 9 of the heat of explosion the uncertainty of the calculated energies is analyzed from the variability of the measured data particularly important influential parameters are the treatment of the fines tail of the fragment size distribution in the determination of the fragmentation energy and the use of p or s wave velocity values and whether these are determined from in situ or from laboratory measurements in the calculation of the seismic energy

late neogene erosion of the agulhas moat and the oligocene position of subantarctic surface water abstract the agulhas ridge moat is a scoured depression up to 100 m deep and over 20 km wide flanking the northern side of the agulhas ridge in the southeastern atlantic a core from the moat has been assigned a late oligocene age zone np 24 based on the nannoplankton present scouring was probably caused by westward flowing antarctic bottom water moving in excess of 15 20 cm s 1 possibly during the middle to late pleistocene oxygen isotope analyses indicate a late oligocene surface water temperature between 6 9 and 16 6 c over the core site these paleotemperatures suggest that the subantarctic surface water mass extended farther north during the oligocene modern sea surface temperatures over the site are about 21 c

geomechanical and ultrasonic characterization of a norwegian sea shale anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation including depth conversion and fluid identification in addition mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well preserved samples multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the norwegian sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation in addition standard rock physical properties were characterized as well as composition the shale microfabric is seen to be strongly laminated with alternating thick clay rich laminae and thin silt rich laminae occasional microfractures are also noted parallel to these laminations the shale has low friction coefficient and cohesive strength and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45 to the microfabric the orientation of the maximum principal stress parallel to the intrinsic fabric and microcracks was seen to significantly impact on velocity normal to the fabric as stress parallel to the fabric increased s wave anisotropy was significantly affected by the increasing stress anisotropy stress orientation with respect to fabric orientation was therefore found to be an important control on the degree of anisotropy of dynamic elastic properties in this shale

stromatolite reef crusts early cretaceous spain bacterial origin of in situ precipitated peloid microspar peloidal crusts are significant components of early cretaceous aptian reef carbonates in eastern spain the crusts form steep sided laminated deposits on coral and other skeletal surfaces their microfabric consists almost entirely of silt sized peloids in fenestral microspar matrix this microfabric contrasts with more poorly sorted and generally finer grained detrital wackestone packstone fabrics of the adjacent reef matrix scarcity of incorporated grains indicates that the crusts did not trap many particles it is proposed that the crusts are stromatolites and that peloids and inter peloid space were created concurrently by bacterial degradation of organic matter as they developed inter peloid voids were protected from infiltration of extraneous sediment by the organic rich exterior surface of the stromatolite even spacing of the peloids within microspar may reflect self organization of bacterial colonies in the decaying organic matrix compressed and partly amalgamated peloids marginal to burrows in the stromatolites suggest that the peloid fabrics were initially only partially lithified the grainstone like peloid fabric is therefore interpreted as having formed in situ by very early diagenetic processes driven by heterotrophic bacteria

bottom current erosion along a traverse in the south atlantic sector of the southern ocean abstract the magnetostratigraphy and biostratigraphy of twenty five piston cores on a profile from antarctica to the cape basin south of africa reveal disconformities in the sedimentary record which are attributed to bottom current erosion increased antarctic bottom water production removed all sediment in the weddell and cape basins younger than middle pliocene 2 5 m y with miocene sediment exposed at or near the seafloor at some locations increases in the velocity of the circumpolar deep water eroded lower pliocene to upper pliocene 4 0 2 0 m y sediment on the crest and south flank of the atlantic indian ridge and maintains an active scour zone today with middle pleistocene 1 0 m y sediment exposed at the seafloor

high energy coralgal stromatolite frameworks from holocene reefs tahiti french polynesia drill cores from holocene reefs on tahiti french polynesia reveal a framework composed of massive branching acroporids encrusted by coralline algae associated with sessile vermetid gastropods and arborescent foraminifers laminated micritic crusts form coatings over coral branches or more commonly over related encrusting organisms throughout the cored reef sections these crusts appear as a major structural and volumetric component of the reef framework the microbial nature of these micritic crusts is inferred from their typical organic growth forms and geometry the occurrence of microbial remains and stable isotope measurements the reef communities accumulated at depths less than 5 m below mean sea level in a high energy environment throughout vertical growth from 7140 170 yr bp to the present the nature of the involved benthic communities stable isotope data and high calcification rates of microbially encrusted corals strongly suggest that local environmental conditions have been optimal for reef development for the last 7000 years the causes of the predominance of microbial communities over actual encrusters red algae foraminifers remain problematic and could be related to short term fluctuations in ecological parameters microbial micritic crusts seemingly played a prominent role in protecting the coralgal colonies from bioeroders and grazers and possibly in strengthening the framework due to rapid lithification the record of similar microbial crusts in other quaternary reef tracts suggests that microbial communities may have played a more prominent role in quaternary reefs than presently recognized

microbialites in last glacial maximum and deglacial reefs of the great barrier reef iodp expedition 325 ne australia abstract microbialites are volumetrically abundant components in last glacial maximum and deglacial reefs in the australian great barrier reef sampled by iodp expedition 325 in 34 holes from 17 sites m0030 m0058 along four transects on the shelf edge detailed radiometric datings show that four distinct reef phases developed between 28and 10 ka displaying offlapping and then backstepping patterns the reef boundstone facies include coralgal coralgal microbialite and microbialite boundstone the microbialite consists of combinations of micrite microspar bioclasts siliciclastic grains up to 14 5 fenestrae and encrusting epibionts the micrite microspar is high magnesian calcite commonly irregularly clotted fenestral and peloidal mesoscale microbialite fabrics include laminated structureless digitate intraskeletal and boring filling and coatings on debris intraskeletal and boring filling is the first fabric to develop in skeletal voids and borings it is usually followed by structureless and laminated microbialite locally overlain by digitate fabric microbialite coated debris can occur at any stage in this succession including in bioclastic accumulations where the scarce in situ framework builders are mainly encrusting corals lipid biomarkers of intermediate to high specificity for sulfate reducing bacteria together with 13c values of these lipids indicate that microbialite formation was favored by sulfate reducing bacteria in anoxic microenvironments probably under high nutrient levels the microbialite in fore reef deposits accumulated in the photic zone in water depths of a few to several tens of meters within small spaces generated by large bioclasts and encrusting corals in the topmost centimeters of the sediment these crusts that formed on the illuminated surface constitute a previously unrecognized style of microbialite formation in quaternary reefs as with the cryptic crusts described from other reef locations its greatest development occurred during the last glacial maximum and early deglaciation microbial carbonate formation during this interval may reflect elevated seawater carbonate saturation corresponding with relatively low levels of atmospheric co2

hells bells unique speleothems from the yucatan peninsula mexico generated under highly specific subaquatic conditions abstract we here report on a type of meter sized pendant speleothem growing under water in the submerged el zapote sinkhole cenote west of puerto morelos on the mexican yucatan peninsula these conical mantle shaped downward expanding and diverging calcareous structures here termed as hells bells are yet unreported in the scientific literature they are characterized by bell or trumpet shaped longitudinal and circular elliptical or horse shoe like horizontal cross sections hells bells grow downward based on the downward divergence of the structures and the horizontally laminated internal texture of both blade shaped spar calcite and microspar laminae age dating confirms that hells bells are young

velocity anisotropy in shale determined from crosshole seismic and vertical seismic profile data crosshole and vertical seismic profile vst data made possible accurate characterization of the elastic properties including noticeable velocity anisotropy of a near surface late tertiary shale formation shear wave splitting was obvious in both crosshole and vsp data in crosshole data two orthologonally polarrized shear s waves arrived 19 ms in the uppermost 246 ft 75 m vertically traveling s waves of the vsp separated about 10 ms in the uppermost 300 ft 90 m but remained at nearly constant separation below that level a transversely isotropic model which incorporates a rapid increase in s wave velocities with depth but slow increase in p wave velocities closely fits the data over most of the measured interval elastic constants of the transvesely isotropic model show spherical p and s2 wave velocity surfaces but an ellipsoidal s1 wave surface with a ratio of major to minor axes of 1 15 the magnitude of this s wave anisotropy is consistent with and lends credence to s wave anisotropy magn

ultrasonic velocity and attenuation anisotropy of shales whitby united kingdom we have conducted ultrasonic experiments between 0 3 and 1 mhz to measure velocity and attenuation q 1 anisotropy of p and s waves in dry whitby mudstone samples as a function of stress we found the degree of anisotropy to be as large as 70 for velocity and attenuation the sensitivity of p wave anisotropy change with applied stress is more conspicuous than for s waves the closure of large aspect ratio pores and or micro cracks seems to be a dominant mechanism controlling the change of anisotropy generally the highest attenuation is perceived for samples that have their bed layering perpendicular 90 to the wave path the observed attenuation in the samples is partly due to the scattering on the different layers and it is partly due to the intrinsic attenuation changes in attenuation due to crack closure during the loading stage of the experiment are an indication of the intrinsic attenuation the remaining attenuation can then be attributed to the layer scattering finally the changes in attenuation anisotropy with applied stress are more dynamic with respect to changes in velocity anisotropy supporting the validity of a higher sensitivity of attenuation to rock property changes

lithified and unlithified mg calcite precipitates in tropical reef environments abstract push cores from the branching coral framework of lagoonal reefs in belize and panama indicate that the micritic mg calcite in the unlithified mud matrix is similar in composition to the well documented submarine lithified micritic crusts and infillings found in open reef framework the sediment matrix of the lagoonal framework contains significant concentrations of 12 to 13 mole mgco3 calcite that shows almost no signs of skeletal origins as indicated by a fairly consistent mineralogy and independent distribution patterns in sand silt and clay size fractions its sedimentological and mineralogical similarity to cemented micritic crusts and infillings suggests that the precipitation of micritic mg calcite is widespread in tropical reef waters and becomes lithified when precipitated in open frameworks but remains unlithified when trapped in impermeable lagoonal muddy sediments

hybrid carbonates in situ abiotic microbial and skeletal co precipitates abstract abiotic bioinduced and biocontrolled carbonates are process based sediment categories they successively reflect increasing levels of biotic control over carbonate precipitation from aqueous solutions are often closely linked to depositional environment and change with time hybrid carbonates are intimate in situ combinations of two or more of these categories hybrid carbonates are widespread and diverse in the marine geological record and reflect large scale changes in carbonate precipitation through time they also occur in fluvial and lacustrine carbonates marine and non marine reef systems and methane seep deposits plots of hybrid carbonate composition in time and space reveal complex backtracking and looping patterns that reflect changes in environmental conditions and biological processes of carbonate production recognition of hybridity emphasizes the importance of distinguishing abiotic and bioinduced precipitates until they were diversified by skeletal carbonates in the late proterozoic precambrian hybrid carbonates were abiotic bioinduced combinations during the phanerozoic hybrid carbonates were conspicuous during periods of overlap or transition between intervals of microbial and skeletal carbonate abundance microbial skeletal dual hybrids are common during the cambrian mid ordovician late devonian mississippian and late jurassic early cretaceous abiotic microbial skeletal triple hybrids were common from late pennsylvanian to mid triassic shallow marine hybrid carbonates declined in abundance after the mid cretaceous although late cenozoic reefs contain some striking examples of microbial skeletal hybrids recognition of hybrid carbonates draws attention to fundamental processes underlying carbonate sedimentation and their patterns and drivers of change in time and space

extensive submarine lithification in a cave in the belize barrier reef platform abstract extensive deposits of submarine cements discovered in a submerged pleistocene cave in the outer barrier reef platform off belize central america occur in an unusual setting on and within countless calcareous projections formed by serpulid worms on the ceiling of the cave the cements are predominantly dense submicrocrystalline and microcrystalline to porous chalky or submicrosucrosic magnesium calcite approximately 15 mole mgco3 and they contain minor amounts of acicular aragonite which generally forms a lining inside the aragonitic serpulid tubes radiocarbon dates three year artificial substrate experiments and evidence of the ceiling s original relief indicate a low rate of accumulation for the serpulid cement projections the characteristic 20 60 m peloidal texture associated with magnesium calcite submarine cements is well developed here and there within the projections these peloids are physiochemical precipitates having formed during the development of the submarine cement deposits which accumulated preferentially on substrates that have a slow rate of accumulation and that experience little or no disturbance of their sediment cover artificial substrates placed on the ceiling of the cave for three years revealed that the initial stage of precipitation of magnesium calcite from seawater is in the form of a submicrocrystalline magnesium calcite dust

pendant bioconstructions cemented by microbial carbonate in submerged marine caves holocene se sicily abstract unusual pendant bioconstructions occur within two submerged caves in the plemmirio marine protected area south of syracuse se sicily these cm to dm sized bioconstructions project downward from the cave roofs the main framework builders are serpulids belonging to the genera protula semivermilia and josephella encrusting bryozoans corals hydrozoans and sponges are subordinately present whereas bivalves and brachiopods are overall rare these faunal associations are characteristic of the studied caves but only in some places they form small bioconstructions that are cemented by microbial carbonates made up by autochthonous peloidal to clotted peloidal and aphanitic micrite the autochthonous micrite stabilizes the pendant bioconstructions herein referred to as biostalactites the microbial carbonate reveals high contents of bacterial lipid biomarkers among the most abundant compounds are mono o alkyl glycerol ethers mages and branched fatty acids 10 me c16 0 iso and anteiso c15 0 and c17 0 interpreted as biomarkers of sulfate reducing bacteria other compounds preserved in the autochthonous carbonates include lipids derived from marine zoo and phytoplankton brassicasterol dinosterol and monounsaturated short chain fatty acids unspecified marine bacteria saturated and monounsaturated short chain fatty acids and land plants long chain fatty acids long chain alcohols stigmasterol sitosterol and campesterol the observed lipid biomarker signatures are remarkably similar to those of post glacial reefal microbialites where microbialite formation in cavities of the coral framework was also mediated by sulfate reducing bacteria in the submerged caves of plemmirio marine protected area serpulid colonies apparently occur preferentially where freshwater is seeping through crevices in the limestone the consequent nutrification is believed to favor serpulid aggregation and the growth of other skeletal i e bryozoans and corals and soft bodied organisms i e sponges and ascidiae the resultant accumulation of biomass and its taphonomy provide niches for sulfate reducing bacteria which induce carbonate precipitation cementing and stabilizing the biostalactites the finding of pendant cemented bioconstructions in the mazzere and granchi caves of the plemmirio marine protected area reveals that sulfate reducing bacteria are involved in microbialite formation in various cryptic environments the formation of such peloidal to clotted peloidal microcrystalline carbonates in cryptic ecosystems is a significant factor for the stabilization of different kinds of bioconstructions spanning from small biostalactites to large reefs

x ray ct and hydraulic evidence for a relationship between fracture conductivity and adjacent matrix porosity abstract multi phase flow in fractured rocks plays an important role in any hydrocarbon recovery process be it for environmental remediation or natural oil and gas extraction fractures may form the primary production conduits and the mass transport at the fracture interfaces with the matrix determines the effectiveness of extraction processes this paper presents specific evidence for a relationship between fracture apertures and the porosity of the adjoining perpendicular layers in berea sandstone samples measurements of fracture apertures were done with high resolution micro computed tomography mct with a voxel resolution of about 0 05 mm in three dimensions multi phase fluid flow experiments were done using a medical ct scanner with a voxel resolution of about 1 00 0 25 0 25 mm mct evidence shows a correlation between aperture and the porosity of the intersected layers the comparison was made by generating two dimensional maps of matrix porosity and ct values adjacent to the fracture and of the corresponding fracture apertures high porosity layers are lined up with large fracture apertures multi phase fluid experiments provided hydraulic evidence that the high porosity layers have high permeability oil injection into a water saturated sample was tracked by a sequence of transverse scans near the downstream tip of a fracture the hydraulic evidence from the two phase flow experiments also confirms high permeability in fracture strips adjacent to high porosity and high permeability layers the reasons for the relationship between fracture aperture and the properties of the adjacent layers are not fully understood some explanation for the physical and hydraulic observations rests in the method of fracturing fracture propagation and the lithological characteristics of the rock

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

the microbial nature of laminated limestones lessons from the upper aptian araripe basin brazil abstract the araripe basin located in northeastern brazil originated during the gondwana continental break up responsible for the opening of the south atlantic during the early cretaceous in the araripe basin the post rift aptian sequence corresponds to the santana group which is composed in upward succession of mostly clastic continental and rare carbonate layers of the barbalha crato ipubi and romualdo formations the laminated limestones of the crato formation were deposited in a lacustrine environment preceding the deposition of the ipubi formation evaporites they are age equivalent to the limestones of the pre salt interval of the east coast of brazil which contains large petroleum reserves the excellent preservation of its macrofossils has made the crato formation known worldwide as a fossil lagerstatte the limestones are macroscopically homogeneous and their deposition has been previously attributed to chemical precipitation although the carbonate laminites are macroscopically undifferentiated mineralogical variations microscopic texture and distinctive biotic aspects supported the characterization of four microfacies planar laminated crustiform nodular and rhythmic the microfacies analysis indicated a strong and pervasive biological activity in the crato limestone morphogenesis organominerals precipitated by the metabolic action of cyanobacteria and or sulfate reducing bacteria and methanogenic oxidizing archea are represented by calcite and pyrite calcified coccoid and filaments are common furthermore the presence of calcified biofilms composed of exopolymeric substances eps is ubiquitous the presence of amorphous organic matter aom and gypsum particularly in the rhythmic microfacies indicates anoxic dysoxic conditions and stressful environments during periods of drought and low lake levels which favored the development and preservation of microbial biofilms phytoclasts and miospores when present in the succession indicate an extrabasinal contribution during wetter periods although the environment remained of very low energy the evidence of microbial influence in the formation of the laminated limestones of the crato formation is of great importance for understanding the excellent preservation of the unit s fossils and for modeling the evolution of the aptian carbonate sequences in brazil

north atlantic deep water export to the southern ocean over the past 14 myr evidence from nd and pb isotopes in ferromanganese crusts the intensity of north atlantic deep water nadw production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate here we present a new approach to reconstruct the overall strength of nadw export from the north atlantic to the southern ocean over the past 14 myr applying the deep water nd and pb isotope composition as recorded by ferromanganese crusts and nodules we present the first long term nd and pb isotope time series for deep southern ocean water masses which are compared with previously published time series for nadw from the nw atlantic ocean these data suggest a continuous and strong export of nadw or a precursor of it into the southern ocean between 14 and 3 ma an increasing difference in nd and pb isotope compositions between the nw atlantic and the southern ocean over the past 3 myr gives evidence for a progressive overall reduction of nadw export since the onset of northern hemisphere glaciation nhg the nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37 depending on location

internal precipitation of microcrystalline carbonate a fundamental problem for sedimentologists abstract recent studies of submarine lithification have shown that microcrystalline carbonate or carbonate mud traditionally thought to represent ooze deposited in quiet water commonly forms as an internal precipitate below the sediment water interface this internally precipitated micrite alters the mud grain ratio of pre existing sedimentary deposits and invalidates classifications that relate the amount of micrite matrix in limestones to the degree of water energy associated with the environment of deposition

peloidal fabrics in upper jurassic reefal limestones weald basin southern england abstract coraliferous limestones from the corallian group upper jurassic of subsurface of the weald basin southern england record the localized development of superimposed patch reefs and banks the reefal limestones exhibit a variety of peloidal fabrics in particular well sorted peloids 10 60 m in diameter with a well developed euhedral rim of fibrous sparry calcite around a micritic anhedral nucleus they occur in confined intraskeletal pores corals molluscs and borings growth cavities between framebuilders and as stromatolitic crusts the peloids in interskeletal cavities and as crusts resemble microbial precipitates and merge into spongiostromate fabrics the distribution of these peloidal fabrics seems to be facies related and is best developed in zones which had relatively low framework growth rates low sedimentation rates and moderate energy levels the peloids are identical in form and occurrence to those in some ancient and quaternary reefs the association of the peloids with stromatolitic coatings and spongiostromate fabrics leads us to interpret the peloids as microbial precipitates either by direct precipitation or by induction the abundance of microbial carbonate in these reefal limestones places them in an intermediate category between frame built reefs and microbial mud mounds

a preliminary report on long term bottom current measurements and sediment transport erosion in the agulhas passage southwest indian ocean abstract continuous measurements of bottom current velocity direction and temperature are reported from two sites in the agulhas passage sw indian ocean these are the first long term records from the indian ocean site 1 4850 m 262 days and site 2 4690 m 356 days they show fluctuating bottom current movements with periods between 4 and 40 days and marked contrasts in average velocities and direction site 1 20 cm s 1 with a nnw progressive vector site 2 5 5 cm s 1 with a nne progressive vector preliminary examination of the data suggest that the periodic fluctuations in direction and strength may be related to eddies in the overlying agulhas current but also points to a nne movement of antarctic bottom water in the agulhas passage along its northern side both sites appear in seismic records as areas of erosion or non deposition and whilst the current meter data support this conclusion at site 1 on the southern side of the passage data from site 2 suggest that along the foot of the se african continental margin no sediment erosion or transportation is likely except during short periods 8 hrs when the currents are temporarily capable of transporting material up to 200 m and eroding unconsolidated silt and fine sand

nature and environmental significance of microbialites in quaternary reefs the tahiti paradox drill cores from the bamer reef edge of tahiti exhibit 85 93 m thick coralgal sequences recording at least 13 500 years of continuous reef growth in optimal environmental conditions the cored reef sequences form an overall shallowingupward succession with assemblages of branching or massive colonies of porires at the base overlain by a robust branching community acropom gr dmmi robirstn heavily encrusted by coralline algae sessile vermetid gastropods and arborescent foraminifers which grew at depths less than 6 m microbialites generally form the last stage of encrustation of coral colonies or more commonly of related encrusting organisms thus appearing as a major structural component of the reef sequence where they may locally form 809 of the rock by volume they developed in an open cavity system of the reef framework with freely circulating normal marine water microbialites include laminated crusts and clotted micritic masses commonly associated in compound crusts probably feflecting differences in the composition of the involved biological communities and in biomineralization processes that controlled the accretion of the crusts the isotopic composition of the microbialites 2 05 to 3 92 i they underwent also indivitlual processes of biominrlali2ation besicles the overall decrease in lizht and enqy conditions rttlecting progressive burial by conil growth the widespread development of microbialites within the reef framework may be related to increased alkalinity and niitrient availability in interstitial waters due to temstrial groundwwr seepage and puiodic runoffs the tlevelopment of micrubialites in the cryptic niches of the reef framework ceased about 6000 years

anisotropy of elastic wave velocities in deformed shales part 1 experimental results elastic wave velocity measurements in the laboratory are used to assess the evolution of the microstructure of shales under triaxial stresses which are representative of in situ conditions microstructural parameters such as crack aperture are of primary importance when permeability is a concern the purpose of these experiments is to understand the micromechanical behavior of the callovo oxfordian shale in response to external perturbations the available experimental setup allows for the continuous simultaneous measurement of five independent elastic wave velocities and two directions of strain axial and circumferential performed on the same cylindrical rock sample during deformation in an axisymmetric triaxial cell the main results are 1 identification of the complete tensor of elastic moduli of the transversely isotropic shales using elastic wave velocity measurements 2 assessment of the evolution of these moduli under triaxial loading and 3 assessment of the evolution of the elastic ani

regional variation of manganese nodule facies on the wake tahiti transect morphological chemical and mineralogical study abstract during the gh80 1 cruise of rv hakurei maru january to march 1980 conducted by the geological survey of japan a significant regional variation of manganese nodule facies was found on the 4000 km long transect from wake to tahiti more than 190 bottom samplings and 120 sea bed photography using box corer free fall grab and piston corer revealed three characteristic nodule facies each extending over hundreds of kilometers in the northern central pacific basin and the mid pacific mountains area zeolitic pelagic clay surface sediment discoidal to irregular shaped smooth surface nodules are dominant they consist of inner fragmented older nodules composed of mno2 and surrounding 2 5 mm thick layers of mno2 and 10 a manganate mn fe and cu ni are low averages 1 4 and 0 85 wt consistent with mineralogy in the central to southern central pacific basin siliceous clay or ooze surface sediment spherical and rough surface nodules with concentric structure predominate each concentric layer consists of 10 a manganate yielding high mn fe and cu ni averages 4 1 and 2 41 wt in the penrhyn basin zeolitic clay surface sediment spherical to discoidal shaped smooth surface nodules of simple internal structure are distributed they consist mostly of mno2 and consequently mn fe and cu ni are low averages 1 3 and 0 85 wt the manihiki plateau covered with thick calcareous sediments is a barren area these regional variation in surface and internal structures and chemical characteristics are principally due to preferential growths of the two ferromanganese minerals the mode of regional variation of the minerals and its close relationship to surface sediments variability are consistent with the two supply route model of these minerals the 10 a manganate forming rough surface dominantly developed within surface sediments as a result of diagenesis of siliceous sediments in the central and southern central pacific basin whereas mno2 develops through direct supply of metal elements from the overlying bottom waters forming smooth surface nodules in the northern central pacific basin and penrhyn basin

preservation of siliceous sponges in the jurassic of southern england and northern france reef forming lithistid sponges in the middle jurassic bathonian of normandy france were lithified on the sea floor by a peloidal cement probably of an original low mg calcite composition precipitated under bacterial influence this early lithification permitted early dissolution of the siliceous skeleton without the collapse or distortion of the resulting moulds these moulds were encrusted and bored this pathway for the fossilization of sponges is shown by other examples of jurassic lithistids and is likely to be widely applicable throughout the fossil record particularly at times during which calcite was the primary marine precipitate

high resolution non destructive measurement and characterization of fracture apertures abstract we measure at high resolution the fracture aperture of several consolidated materials and statistically characterize the aperture distribution for future studies on single and multiphase flow and transport through fractured porous media the images of the real fractures in granite and sandstone rocks are obtained with a computer aided tomography cat x ray scanner the minimum pixel size is 0 27 0 27 mm but fractures as small as 35 m can be accurately measured using a calibration standard for the variation in ct number due to the missing rock mass in a given pixel the distribution of fracture apertures is best described by a lognormal function this was also corroborated by comparing the theoretical to actual ratio of geometric mean to arithmetic mean apertures the mechanical roughness of the fractures ranged from 0 17 to 1 5 the variability in fracture aperture displayed only short range structure with correlation lengths of 0 8 to 7 mm at maximum which is at most one tenth of the minimum dimension width of the fracture plane fracture aperture distribution is rather heterogeneous potential flow channels can be deduced from the fracture aperture distribution

contribution of microbialites to the development of coral reefs during the last deglacial period case study from vanuatu south west pacific coral reefs have grown continuously during the last 24 ka on the island of espiritu santo vanuatu south west pacific in a setting characterized by frequent tectonic uplifts related to subduction of the australia plate beneath the vanuatu island arc sedimentological and geochemical studies of two neighbouring areas having much different mean uplift rates and environmental settings provides an opportunity to analyze the environmental factors that promoted the widespread development of microbialite crusts from about 24 to 6 ka b p nutrient supplies and probably the rapidity of the sea level rise are critical to an explanation of the distinctive distribution of microbialites in reef cores nutrient flux has been related to terrigenous fluxes in the tasmaloum reef system that fringed the south west uplifting coast of espiritu santo and possibly to upwelling in the urelapa sequence that was isolated from the main island during its growth a peak in microbialite abundance occurred between 16 and 10 ka b p a time window characterized by increasing erosional processes and or more intense upwelling during a very rapid rise in sea level