aragonite relic preservation in jurassic calcite replaced bivalves shells of the aragonite bivalve neomiodon great estuarine group jurassic scotland replaced by coarse neomorphic calcite contain oriented relics of the original aragonite ultrastructure the presence of these relics in such old altered shells as well as the high sr content of the replacement calcite indicate that the process of calcite replacement of aragonite is not a cumulative slow process involving repeated alteration events but rather a rapid one step process aragonite relics once encased in neomorphic spar will survive as unequivocal evidence of original aragonite mineralogy barring total remobilization of the enclosing stable calcite a generally unlikely event the retention of this residual aragonite and high sr calcite supports recent isotopic studies which suggest that the multiple phases of alteration recrystallization invoked in earlier literature are unlikely events in the diagenesis of most undolomitized limestones retention of aragonite relics appears to be independent of whether alteration occurs in shallow meteoric or as in the case of our neomiodon material deeper burial environments pseudopleochroism of the replaced neomiodon shells appears to be due to organic largely graphitic relics not to the aragonite relics

semidiurnal internal tides off the east coast of korea inferred from synthetic aperture radar images 1 semidiurnal internal tides propagating toward and along the east coast of korea are elucidated from the surface manifestation of non linear internal wave nliw packets in synthetic aperture radar sar images taken on september 2 1996 the sar images reveal two pairs of nliw packets one on the northern side of the southwestern east japan sea and the other on the western side the nliw packets appear to be generated by the semidiurnal internal tide and influenced by a temperature front and bottom topography during their propagation a geometric optics model simulates westward refraction of semidiurnal internal tides under the influence of a mesoscale circulation pattern during august 1996 and bottom shoaling this westward refraction contrasts with the eastward refraction of two year mean vertical displacements and is consistent with the distribution of nliws seen in the sar images

m2 baroclinic tide variability modulated by the ocean circulation south of japan we analyze a concurrent simulation result of the ocean circulation and tidal currents using a data assimilative ocean general circulation model covering the western north pacific with horizontal resolution of 1 36 to investigate possible interactions between them four sites of active m2 internal tide variability in open ocean hot spots such as tokara strait izu ridge luzon strait and ogasawara ridge are detected from both the satellite observation and the simulation energy cycle analysis of the simulated m2 baroclinic tide indicates two types of the hot spots dissipation tokara strait and izu ridge and radiation luzon strait and ogasawara ridge dominant sites energy conversion from barotropic to baroclinic m2 tides at the hot spots is modulated considerably by the lower frequency changes in the density field modulation at the two spots tokara strait and izu ridge is affected by the kuroshio path variation together with the seasonal variation of the shallow thermocline at the other two sites influence from changes in the relatively deep stratification through the kuroshio intrusion into south china sea luzon strat and mesoscale eddy activity ogasawara ridge is dominant in the modulation

meteoric like fabrics forming in marine waters implications for the use of petrography to identify diagenetic environments petrographic fabrics have long been used to identify meteoric diagenesis of carbonate sediments however on the basis of oxygen isotopic data we document similar fabrics forming in marine pore fluids in the shallow subsurface of great bahama bank therefore petrographic fabrics alone are not reliable indicators of diagenetic environments even for shallow water sediments in our study skeletal grainstones show two distinct diagenetic assemblages either dissolution of aragonitic grains and minimal cementation high permeability intervals or abundant blocky spar cement and neomorphism of aragonitic skeletal grains low permeability intervals these marine burial fabrics are present as shallow as 110 m below sea level well above the aragonite compensation depth a feature that must be considered for models of diagenesis in ancient carbonate sediments marine burial diagenesis may be important in ancient carbonate sediments deposited in moderate water depths or in shallow water during rising sea level where meteoric diagenesis is suppressed

atlas of japan east sea hydrographic properties in summer 1999 abstract hydrographic properties from ctd and discrete bottle sample profiles covering the japan east sea in summer 1999 are presented in vertical sections maps at standard depths maps on isopycnal surfaces and as property property distributions this data set covers most of the sea with the exception of the western boundary region and northern tatar strait and includes nutrients ph alkalinity and chlorofluorocarbons as well as the usual temperature salinity and oxygen observations

controls on carbonate mineral accumulation in bahamian basins and adjacent atlantic ocean sediments abstract carbonate mineralogical studies of surface bahamian periplatform ooze containing pelagic calcite as well as bank derived aragonite and magnesian calcite were coupled with studies of the carbonate chemistry of the waters overlying these sediments the presence of metastable aragonite and magnesian calcite in the periplatform ooze presents a unique opportunity to assess the relation between the extent of carbonate saturation in the water column and the disappearance of metastable carbonate minerals in an area of the north atlantic ocean where intermediate and deep waters are saturated with respect to calcite aragonite is present in the fine fraction of the surface sediment to a water depth of 4 800 m but decreases sharply below 4 000 m this is also the depth limit of the occurrence of pteropod tests and fragments in the coarse fraction of the sediment the aragonite compensation depth should be by extrapolation between 5 000 and 5 200 m the saturation depth with respect to aragonite was estimated to be located between 3 800 and 4 500 m this corresponds fairly well with the depth of a sharp decrease of the fine aragonite as well as the depth of pteropod disappearance magnesian calcite in the fine fraction of the sediment decreases irregularly with depth and disappears between 3 700 and 4 000 m the calculated saturation depth with respect to magnesian calcite 13 mole mgco3 is between 900 and 1 500 m at this depth a significant drop in the concentration of magnesian calcite occurs this decrease of magnesian calcite from 25 to 15 percent could be caused by both dissolution and the increasing distance of deeper waters from the banks however the higher values of specific alkalinity of the waters ranging between 750 and 2 000 m when compared with the alkalinity values of the sargasso sea at the same latitude are interpreted to be indicative that some dissolution of magnesian calcite occurs in the bahamian basins at these water dept s our results show depressed levels by 500 m or more of the aragonite saturation depth in the water column as well as of the depth of aragonite disappearance in the surface sediment when compared with open ocean studies in the northwest atlantic in addition our results indicate that fine magnesian calcite 12 to 13 mole mgco3 disappears 1 200 to 1 500 m above the extrapolated disappearance depth of aragonite this observation is consistent with results for experimental studies showing that aragonite is more stable in seawater than a magnesian calcite of 12 to 13 mole mgco3

redistribution of energy available for ocean mixing by long range propagation of internal waves ocean mixing which affects pollutant dispersal marine productivity and global climate1 largely results from the breaking of internal gravity waves disturbances propagating along the ocean s internal stratification a global map of internal wave dissipation would be useful in improving climate models but would require knowledge of the sources of internal gravity waves and their propagation towards this goal i present here computations of horizontal internal wave propagation from 60 historical moorings and relate them to the source terms of internal waves as computed previously2 3 analysis of the two most energetic frequency ranges near inertial frequencies and semidiurnal tidal frequencies reveals that the fluxes in both frequency bands are of the order of 1 kw m 1 that is 15 50 of the energy input and are directed away from their respective source regions however the energy flux due to near inertial waves is stronger in winter whereas the tidal fluxes are uniform throughout the year both varieties of internal waves can thus significantly affect the space time distribution of energy available for global mixing

post rift uplift and focused fluid flow in the passive margin of northern south china sea an important post rifting tectonic event with extensive uplift and fluid flow took place at the northern margin of the south china sea scs during the late miocene based on an analysis of two and three dimensional seismic data plus drilling well data the tectonic event mainly affected the dongsha rise and the adjacent depressions tectonic deformation likely occurred in the dongsha rise the eastern part of the panyu swell and several depressions of the zhu i sag the post rifting deformation in the study area was characterized by faulting erosion igneous activity and hydrothermal fluid flow the tectonic movement caused abundant secondary nw and wnw tensional and transtensional faults with lengths of 1 to 10 km it also created a clear angular unconformity which marks the time of the tectonic movement late neogene igneous rocks are found in the strata in the dongsha rise only close to the continent ocean transition zone geothermal activity occurred in the liuhua carbonate platform and adjacent depressions deformation is more intense in the eastern area than in the western area according to sequence stratigraphy we infer that the tectonic event mainly occurred in the late period of late miocene and ended at the mio pliocene boundary 5 5 ma the dynamic mechanism for tectonic movement could be associated with subduction of the south china sea slab beneath the philippine sea plate at the manila trench when subduction of lower density crust within the continental ocean transition zone was initiated large resistance stresses may have led to lithosphere bending and crustal uplift in the dongsha area c 2014 elsevier b v all rights reserved

segmentation and coalescence of cenozoic carbonate platforms northwestern great bahama bank seismic profiles over the northwestern great bahama bank reveal that it is formed by the coalescence of three smaller platforms and significant lateral progradation this conclusion is contrary to previous models which assumed that the bank is the result of continuous accumulation on one huge buildup in late cretaceous to early tertiary time a north south trending depression the straits of andros separated an eastern platform andros bank from a western platform bimini bank initially the straits of andros had dimensions similar to the modem tongue of the ocean but was progressively filled from east to west in early to middle tertiary time a second depression the bimini embayment formed within bimini bank by folding it had a maximum depth of about 470 m this depression was also filled from east to west in addition prograding systems built the western margin of bimini bank more than 25 km westward into the straits of florida

aragonite to calcite transformation during fresh water diagenesis of carbonates insights from pore water chemistry dissolved strontium and calcium concentrations in fresh water lenses fwl and associated mixing zones mz on two small holocene ooid sand islands in the schooner cays bahamas were monitored during a 1 yr period to quantitatively analyze the transformation of aragonite to calcite the observed characteristics of this mass transfer are functions of climate and hydrology aragonite to calcite transformation in all hydrologic zones is primarily associated with meteoric recharge the transformation occurs throughout the fwl and in the mz to relative salinities of 19 and 36 sea water on the two islands rates of transformation are rapid in all zones and are greatest in the fwl a limestone composed of 100 calcite should form from an aragonite precursor within 4 700 to 15 600 yr in the fwl and within 8 700 to 60 000 yr in the upper mz efficiencies of transformation can vary between hydrologic zones due to pco2 effects yet the efficiency of the entire system fwl mz is high 87 this indicates that most caco3 derived from aragonite dissolution is reprecipitated as calcite somewhere in the fresh water system or upper mixing zone co2 effects fresh water sea water mixing and the differing solubilities between aragonite and calcite all drive the mass transfer the latter is the most significant accounting for up to nine times more mass transfer than co2 effects and at least ten times more mass transfer than fresh water sea water mixing differing solubilities should also cause mass transfer to occur throughout the hydrologic cycle but it apparently becomes ineffective after the rainy season possibly due to the inhibition of calcite precipitation

limitations on lowstand meteoric diagenesis in the pliocene pleistocene of florida and great bahama bank implications for eustatic sea level models data from three bahamian and south floridan cores with deeper water facies show that contrary to current models there is no phreatic meteoric diagenesis that can be attributed to large scale sea level lowstands models of meteoric diagenesis in carbonate sediments commonly assume major phreatic alteration during glacio eustatic sea level lowstands however the diagenesis previously attributed to large scale 80 m lowstands is found in shallow water facies that have been repetitively exposed in order to document diagenesis from large scale lowstands an interval is needed that was deposited in deeper water and not immediately exposed to meteoric fluids three cores with such deeper water facies indicate that the majority of phreatic meteoric diagenesis in florida and the bahamas happened during glacio eustatic highstands not during lowstands the data also suggest that diagenetically active meteoric lenses in florida and the bahamas are restricted to within 60 m and perhaps less of the land surface the most likely reasons deeper lenses are chemically inactive are 1 the greater percolation distance allows the water to reach saturation prior to entering the lens and 2 the large distance exceeds the reach of soil derived organic matter known to drive diagenesis in meteoric lenses models that currently assume a constant rate for alteration in meteoric fluids need to accommodate this variation with thickness of the vadose zone this study also questions the use of paleophreatic lenses as records of eustatic sea level as the large scale falls may not leave any record

geohydrology of the laura fresh water lens majuro atoll a hydrogeochemical approach in small limestone islands the depositional history and subsequent chemical interactions between ground water and the aquifer host rock play critical roles in the occurrence movement and chemical quality of ground water the hydrogeochemistry of the laura fresh water lens majuro atoll marshall islands is an example of these relations laura is underlain by two principal hydrologic units the upper unit is a back reef marginal lagoonal deposit which formed during the holocene interglacial stage it is composed of moderately permeable carbonate sediments the lower hydrologic unit consists of highly permeable limestone that was subaerially exposed most likely during a pleistocene glacial lowstand similar stratification is found at bikini and enewetak atolls the upper hydrologic unit contains a calcium bicarbonate rich fresh water lens in which a potable fresh water nucleus as much as 14 m thick occurs on the lagoon side of the island storage in the fresh water nucleus ranged from 1 70 x 10 6 to 2 08 x 10 6 m 3 during 1984 1985 ground water occurrence and flow are governed by an asymmetric distribution of lithofacies about the longitudinal axis of the island and an abrupt increase in permeability at the contact between the upper and lower hydrologic units the highly permeable lower hydrologic unit contains sea water and truncates the fresh water sea water mixing zone the fresh water lens and associated fresh water sea water mixing zone are the site of continuously occurring diagenetic reactions that significantly affect the porosity and permeability of the aquifer non equilibrium dissolution precipitation reactions coupled with variations in co 2 input control the chemical evolution of laura ground water at the present rate of chemical weathering 465 m 3 of sediment are being dissolved and transported to the sea by ground water each year this dissolution results in an annual increase in porosity of 0 01 the primary factors controlling the occurrence and flow of ground water in the leeward reef islet of laura are 1 the depositional history of the upper hydrologic unit which has resulted in a greater accumulation of low permeability fine grained sediments beneath the lagoon side of the island and a high to low permeability coarse to fine grained sediment gradation between the ocean and lagoon and 2 the diagenetic history of the lower hydrologic unit which has resulted in a highly permeable basement

transformation of aragonite dominated lime muds to microcrystalline limestones scanning electron microscopy of textures in several well lithified pleistocene micrites mixed micrite and microspar from south florida and the bahamas shows significant diagenetic alteration of the lime mud precursors the dominance of aragonite in those precursor muds is supported by the surprising presence of abundant aragonite relics in the neomorphic calcite crystals confirmed by feigl stain x ray and electron diffraction polished very lightly etched surfaces of neomorphic calcite crystals even in the microspar show aragonite relics and pits both absent in coexisting void fill cements similarities between micrite and microspar crystals indicate their common origin through a one step neomorphic process of calcitization that is the mud did not first calcitize to micrite and then alter to microspar by aggrading neomorphism this conclusion has more general implications for the interpretation of the origins of other older microsparitic carbonates both early calcitization and concurrent early meteoric cementation were significant in producing the florida bahamas micrites studied which have low porosities similar to those found in most ancient fine grained limestones these low porosities despite the absence of significant overburden indicate that major porosity reduction without compaction can occur in calcitized aragonite dominated muds

tectonic and diagenetically induced seal failure within the south western great bahamas bank abstract a deep 6 km well the doubloon saxon 1 well drilled in early 1986 on the great bahamas bank shows evidence of massive seal failure through tectonic and post tectonic diagenetic alteration seal failure occurred through a hydrodynamically induced chemical alteration of a carbonate limestone dolomite evaporite anhydrite halite sequence into a carbonate dolomite and dedolomite sequence evidence for this alteration includes a thick 3 5 km fractured dolomite sequence interbedded with dedolomites fracture origins include solution collapse of original evaporites as shown by anhydrite cement on fracture surfaces and cavernous porosity and by tectonic fracturing a major reverse fault penetrated with 1 km repeat additional evidence includes a temperature regression and geochemical anomalies above and below the proposed altered sequence it is concluded that massive seal failure is a contributing factor in limiting the petroleum potential of portions of the south western bahamas platform

second mode internal tides in the east china sea deduced from historical hydrocasts and a model during the two year deployment period to obtain temperature t and specific volume anomaly d profiles from t and sea surface temperature sst observed respectively by pies and satellite we constructed multi index gravest empirical mode mi gem fields park et al 2005 using historical hydrocasts however comparison between the mi gem fields and the historical hydrocasts reveals that the mi gem fields fail to capture 44 and 52 of the t and d variance respectively in the p 100 200 dbar layer this may be caused by 2nd or higher mode variations of vertical structure since t is insensitive to all but the lowest baroclinic mode watts and rossby 1977 4 in this study we demonstrate that 2nd mode its in the ecs are responsible for failure of the mi gem fields to captureadequatelytand dvariationsinthep 100 200 dbar layer as seen in historical hydrographic measurements we verify our observations with a numerical simulation of its

questioning carbonate diagenetic paradigms evidence from the neogene of the bahamas carbonate diagenetic models have been heavily influenced by numerous studies of exposed quaternary limestones as a result meteoric diagenesis is often assumed to be the principle means of altering aragonite rich sediments into calcitic limestones however these models are limited by the scarcity of examples of aragonite rich sediments buried in seawater that have never been influenced by meteoric fluids the bahamas transect cores recovered originally aragonite rich sediments deposited in deep water beyond the easy reach of meteoric waters and provide an opportunity to test current diagenetic paradigms the bahamas transect consists of seven cores drilled in the prograding western margin of great bahama bank the two proximal cores clino and unda were drilled on the platform top and recovered shallow water platform to reef facies overlying deeper margin and proximal slope facies the five distal cores were drilled by odp leg 166 in up to 660 m of water and recovered carbonate slope facies all studied sections are neogene to pleistocene in age diagenetic environments were identified based on petrographic and scanning electron microscopy sem observations xrd mineralogy carbon and oxygen stable isotopic data and trace elements the upper 100 150 m of the two proximal cores were altered in meteoric to mixing zone diagenetic environments but all other intervals were altered exclusively in marine pore fluids during seafloor marineburial and deep burial diagenesis several of the findings of this study question current carbonate diagenetic paradigms these include 1 large scale sea level lowstands may not have chemically active meteoric lenses as we found no meteoric alteration at the 3120 m elevation of the latest pleistocene lowstand rather phreatic meteoric diagenesis appears restricted to within w10 m of the land surface 2 mixing zone diagenesis includes aragonite dissolution and minor lmc cementation but does not show the cavernous porosity or dolomitization predicted by mixing zone diagenetic models current models are based on coastal mixing zones which do not appear to be applicable to these more inland and perhaps more typical locations 3 marine burial diagenesis produces a mature limestone with fabrics formerly considered diagnostic for meteoric diagenesis such as moldic porosity aragonite neomorphism blocky calcite spar and calcite microspar however oxygen stable isotopic data average n 18 o 1x indicate alteration in marine pore fluids only the character of marine burial diagenesis is partially controlled by the nature of the sediment being altered we have identified two end member styles an open system style characterized by dissolution of aragonite without significant cementation and a more closed system style with aragonite dissolution

mechanical compaction versus early cementation in fine grained limestones differentiation by the preservation of organic microfossils abstract in many fine grained limestones the differentiation of mechanical compaction and early cementation is difficult because of the frequent lack or ambiguity of compaction indicators here a new complementary criterion is proposed for the assessment of compaction in fine grained carbonates the deformation of thin walled organic microfossils within the sediment it is shown that they are reliable indicators of compaction two general styles of preservation can be distinguished early cemented limestones contain spherical to slightly deformed microfossils whereas mechanically compacted carbonates always show flattened specimens

petrologic and geochemical constraints on the origin of subsurface dolomite enewetak atoll an example of dolomitization by normal seawater dolomite is present 1 250 1 400 m below sea level in eocene strata of enewetak atoll petrographically the deep enewetak dolomite postdates brittle compaction of rigid grains in the host eocene strata the 87 sr 86 sr ratio of these dolomites 0 70865 0 70901 indicates that they formed at one or more times between the middle miocene and the present since the top of the lower miocene is more than 900 m above the deep dolomitic interval the dolomite must have formed at a minimum burial depth of 900 m stable oxygen isotope determinations suggest dolomite precipitation from cold marine water lower miocene and eocene carbonate strata on the atoll are apparently in open communication with cold modern ocean water suggesting that those same strata were in open communication with ocean water during dolomitization at a depth of about 1 000 m modern pacific ocean water becomes undersaturated with respect to calcite but is still supersaturated with respect to dolomite therefore it is proposed that the deep enewetak dolomite precipitated from cold deep ocean water undersaturated with respect to calcite at a burial depth of more than 900 m

carbonate crusts around volcanic islands composition origin and their significance in slope stability abstract extensive carbonate crusts discovered forming on the slopes of seamounts in many parts of the world s oceans are providing extra stability to the volcanic edifices these crusts are hardgrounds composed of mixtures of volcaniclastic debris and bioclastic material in most cases cemented by calcite in the form of isopachous coatings around grains and pore filling spar such crusts which have been collected by a remotely operated vehicle rov are described here from moderate depth to deeper water slopes 180 820 m around the volcanic island of montserrat in the caribbean and from the nearby kick em jenny submarine volcano off grenada radiogenic 87sr 86sr isotope ratios from the carbonates give an indication of age up to 0 4 ma years old but they also demonstrate that some samples have been altered by hydrothermal volcanic processes to give ages much older than expected 14 to 18 ma based on the foraminifera present such alteration is also supported by carbon and oxygen isotope 13c and 18o ratios although most samples retain typical marine values in many cases 18o is usually a little more positive than expected from modern caribbean shallow water carbonates likely reflecting cooler water at their moderate depths of lithification just one sample from kick em jenny has very negative 13c 42 indicating methanogenesis crusts are also reported here from the mediterranean sea with an example described from kolumbo submarine volcano northeast of the santorini volcanic complex in the hellenic subduction zone that are similar in many respects to those from the caribbean typically the biota of the crusts consists of calcareous red algae commonly encrusting volcanic clasts foraminifera benthic some also encrusting and planktic subordinate serpulids bivalves pteropods and heteropods and rare deeper water corals some bioclasts are derived from shallower water others from the moderate depths of the slope itself and planktic fallout in addition there is evidence for the former presence of microbes from the occurrence of calcified filaments and peloids in intragranular cavities several generations of sponge borings are usually present as well as calcite cement dissolution and calcite replacement of aragonitic bioclasts and cement and sponge spicules originally opaline silica have taken place the carbonate crusts are attributed to seawater circulating within the surficial sediment in some cases mixing with hydrothermal fluid driven by geothermal and volcanic processes submarine volcanic slopes clearly provide a location for moderate depth carbonate production and cementation but a further significance of these hardgrounds is in stabilising seamounts enabling their slopes to avoid frequent collapse dissection and readjustment however when failure does occur larger scale submarine landslides involving coherent slabs are more likely

the effects of geothermal heating on the east japan sea circulation 1 the magnitude of geothermal heating in the east japan sea is about 100 mw m2 twice that of a typical abyssal plain in addition bottom stratification in the east japan sea is much weaker than that typical of the open ocean thus geothermal heating could have more prominent effects in the east japan sea than in the open ocean and we tested this hypothesis via numerical modeling with less than 100 mw m2 bottom heat flux we were able to reproduce bottom mixed layers that are thicker than 1000 m as observed previously no numerical model has been successful in reproducing such bottom mixed layers geothermal heating intensifies the bottom flows but the simulated flows are not as strong as the observed ones over the northern part of the east japan sea reduction in deep stratification strengthens deep water mass formation intensifying cyclonic circulations located over this area so the effects of the heating extend to the surface as the cyclonic circulation becomes stronger the water at the center of the gyre is trapped and more exposed to cold air so it becomes cooler and colder deep water is produced when the geothermal heating is strong enough the surface cooling effect dominates the bottom heating and the deep layer becomes cooler showing that the nonlinear effects of geothermal heating are far reaching thus to account for the observed dynamics the full three dimensional circulation at the basin scale is needed

dupuit ghyben herzberg analysis of strip island lenses dupuit ghyben herzberg analysis follows from combination of the continuity equation and darcy s law with the ghyben herzberg principle and the dupuit assumptions of horizontal flow the analysis is used to derive the position of the water table and salt water interface in island lenses in terms of island geometry distribution of hydraulic conductivity k and distribution of recharge r for small islands and cases for which the salt water head is zero application of dupuit ghyben herzberg analysis gives good results because the low r k ratios of natural lenses assure that height width ratios of natural lenses are extremely low 1 30 to 1 100 in earlier publications the dupuit ghyben herzberg differential equation has been integrated with the boundary condition that the water table and interface meet at sea level at the shoreline that is no outflow face the dimensions of an outflow face however are known from results of potential theory analysis integration of the dupuit ghyben herzberg equation with a boundary condition consistent with the potential theory outflow face a places the interface indistinguishably close to its position given by potential theory and b allows calculation of ghyben herzberg ratios interface depth to water table elevation which in this case depart from their usual value of 40 because equipotentials are curved close to the outflow face for natural sized lenses however such analysis is necessary only within a narrow strip within 1 to 5 of the island width of the shoreline outside this strip the regular analysis that ignores the presence of the outflow face positions the interface indistinguishably close to that of the potential theory solution analytical solutions are developed for a number of infinite strip islands it is shown by analysis of the homogeneous rectangular island case that an island can be considered an infinite strip to 0 1 accuracy if its length width ratio is larger than 4 4 asymmetric lenses occur if the island is composed of strips of different k or different r with the greater asymmetry occurring with differences in k a high k basement compresses the root of the lens and thereby decreases the water table in the island a lens perched on impermeable basement has a higher water table than would otherwise occur in the island but the volume of the lens is less

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

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

internal tides and ocean mixing recent satellite and in situ observations have shown that at ocean ridges and other seafloor topographic features a substantial amount of energy is transferred from the main ocean tides into internal tides in his perspective garrett explains how these internal waves with tidal periods propagate through the density stratified deep ocean and eventually break down into turbulence the resulting mixing affects ocean stratification and ocean circulation it thus influences climate as well as biological production the energy for the internal tides is derived from the rotational energy of the earth moon system changes of the length of the day and the distance to the moon

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

three dimensional numerical simulation of m2 internal tides in the east china sea the east china sea and adjacent seas are one of the most significant generation regions of the m 2 internal tide in the world s oceans in the present study we investigate the distribution and energetics of the m 2 internal tide around the continental shelf edge in the east china sea using a three dimensional numerical model the numerical experiment shows that m 2 internal tides are effectively generated over prominent topographic features such as the subsurface ridges in the bashi luzon and tokara straits the ridges along the ryukyu island chain and the continental shelf slope in the east china sea the former particularly so all of these topographic features are characterized by steep slopes at the depth of the thermocline onto which the m 2 barotropic tide is almost normally incident the m 2 internal tides propagating away from these multiple source regions interfere with each other to create a complicated wave pattern it is found that the calculated pattern of the m 2 internal tide agrees well with topex poseidon altimeter observations the conversion rate from m 2 barotropic to baroclinic energy over the whole analyzed model domain is estimated to be 35 gw roughly 10 of the energy in the m 2 surface tide incident on the prominent topographic features is converted to the m 2 internal tide although about half of the m 2 internal tidal energy is subject to local dissipation in close proximity to the generation sites

acoustic properties of young carbonate rocks odp leg 166 and boreholes clino and unda western great bahama bank acoustic properties determined from logs and discrete measurements along a borehole transect across the slope of the western great bahama bank margin odp leg 166 show a distinct relationship with primary sediment composition and noncarbonate content dominant sediment types are alternating cemented and uncompacted calciturbidites with shallow water derived grains and poorly to uncemented and compacted periplatform ooze of globigerinid dominated wackestone to packstone comparison of the velocity porosity variation from logs and discrete measurements reveals that both tend to follow the trend of generally accepted velocity transforms primary control on the acoustic velocity is exerted by total porosity whereas the remaining variation in velocity is explained by differential diagenesis the less cemented to uncemented and compacted background sediments have velocities that at a given porosity fall below the time average equation for calcite the cemented turbidites however have velocities that are higher than those predicted by the time average equation although it is unclear whether the original volume of aragonite or presence of organic matter controlled this difference it is suggested that the acoustic properties reflect an input signal the presence of noncarbonate material some of which is clay increases basinward and further reduces the acoustic velocities in the background sediment in contrast earlier work on the more proximal slope and nearly pure carbonate intervals in clino and unda cores documents diagenetic differentiation in compositionally similar sediment resulting in alternating acoustically fast and slow layers marginal and nearly pure limestones have a more complex acoustic behavior and hence are difficult to predict though both velocity logs and discrete velocity measurements show comparable general trends logging data show a considerably larger variation at a given porosity value up to 3 5 km s than discrete data which ranges between 1 0 and 2 5 km s to improve the quality of velocity logs it is suggested to groundtruth these data with other logging data general velocity transforms and ideally discrete measurements on core plugs

bahama carbonate platforms the deep and the past abstract carbonate deposition prevailed for 150 ma in the bahama florida segment of the west atlantic margin and provides an interesting test for actualism present day facies patterns on the banks are controlled by the backward decrease of waves and tides and the concomitant increase of temperature and salinity variation in the troughs influx of sand and rubble from gravity flows varies with topography and distance from shallow water sources and allows one to define facies belts a rhythmic sequence of ooze and graded beds on the basin floors subdivided into a basin margin belt of coarse thick turbidites and basin interior with fine turbidites slope facies change with increase in height and declivity from accretionary to by pass to erosional regimes stratigraphic history of the bahamas is not simply a projection of the holo scene back in time both long term natural evolution decrease in subsidence upbuilding of the banks submarine erosion and outside factors climate eustacy have caused significant changes since the jurassic the bahamas seem to have evolved from a clastics evaporite province to a single carbonate evaporite platform and finally to an array of platforms and troughs during the platform trough stage the rate of upbuilding of the platforms decreased submarine canyon erosion increased platform flanks steepened as they grew higher and changed from accretionary to by pass to erosional slopes a change imposed by extraneous factors occurred in the pliocene when the great bahama bank changed from a giant reef rimmed atoll to a flat platform covered by oolites and peloid sands the bahamas share both long term trends as well as random changes by extraneous factors with other platforms in the geologic record compared to ancient platforms however they are unusually long lived and at a more advanced stage of growth they are deeply dissected by erosion their flanks are unusually high and steep and the troughs very narrow the neogene platform sequence is strongly controlled by eustatic sea level fluctuations

phyllosilicates and zeolite assemblages in the carbonate periplatform of the great bahama bank origin and relation to diagenetic processes odp leg 166 sites 1006 and 1007 abstract the western flank of the great bahama bank drilled during odp leg 166 at seven sites represents a prograding carbonate sequence from late oligocene to holocene eberli et al proc odp init reports 166 1997 the signatures of the detrital input and of diagenetic alteration are evident in clay enriched intervals from the most distal sites 1006 and 1007 in the straits of florida mineralogical and chemical investigations xrd tem sem icp ms run on bulk rocks and on the clay fractions enable the origin and evolution of silicate parageneses to be characterized plio pleistocene silt and clay interbeds contain detrital clay assemblages comprising chlorite illite interstratified illite smectite smectite kaolinite and palygorskite the greater smectite input within late pliocene units than in pleistocene oozes may relate either varying source areas or change in paleoclimatic conditions and weathering intensity the clay intervals from miocene upper oligocene wackestone sections are fairly different with prevalent smectite in the fine fraction whose high crystallinity and mg contents that point towards an authigenic origin the lower miocene section below 1104 mbsf at depths where compaction features are well developed is particularly characterized by abundant authigenic na k clinoptilolite filling foraminifer tests the authigenic smectite and clinoptilolite paragenesis is recorded by the chemical trends both of the sediment and the interstitial fluid this diagenetic evolution implies si and mg rich fluids circulating in deeper and older sequences for lack of any local volcaniclastic input the genesis of zeolite and the terms of water rock interaction are discussed the location of the diagenetic front correlates with that of the seismic sequence boundary p2 dated as 23 2 ma this correspondence may allow the chronostratigraphic significance of some specific seismic reflections to be reassessed

global m 2 internal tide and its seasonal variability from high resolution ocean circulation and tide modeling 1 the present study describes a model simulation where ocean tide dynamics are simulated simultaneously with the ocean circulation the model is forced by a lunisolar tidal forcing described by ephemerides and by daily climatological wind stress heat and fresh water fluxes the horizontal resolution is about 0 1 and thus the model implicitly resolves meso scale eddies and internal waves in this model simulation the global m2 barotropic to baroclinic tidal energy conversion amounts to 1 2 tw we show global maps of the surface signature of the m2 baroclinic tide and compare it with an estimate obtained from 19 years of satellite altimeter data further the simulated seasonality in the low mode internal tide field is presented and as an example the physical mechanisms causing the non stationarity of the internal tide generated in luzon strait are discussed in general this study reveals the impact of inter annual changes of the solar radiative forcing and wind forced ocean circulation on the generation and propagation of the low mode internal tides the model is able to simulate non stationary signals in the internal tide field on global scales which have important implications for future satellite altimeter missions citation muller m j y cherniawsky m g g foreman and j s von storch 2012 global m2 internal tide and its seasonal variability from highresolution ocean circulation and tide modeling geophys res lett 39 l19607 doi 10 1029 2012gl053320

pore networks in holocene carbonate sediments abstract permeabilities of holocene carbonate sediments from florida and the bahamas determined for 74 samples by water flow rates in a variable head permeameter range from 0 6 to 57 000 millidarcies porosities range from 40 to 78 percent these parameters are related to depositional texture as follows table the muddiest sediments i e the finest grained have the highest porosities but lowest permeabilities this negative correlation between porosity and permeability is the reverse of the situation found in carbonate rocks even as young as pleistocene high porosity and low permeability in sediments show a strong correlation with percentage of fines 62 m from capillary pressure curves it is inferred that many of the pore throats of muddy carbonate sediments are less than 1 m in diameter at least after drying measured permeabilities are used to calculate cementation rates for simple models of upper phreatic zone cementation the calculated rates would require excessive time to produce the degree of cementation seen in late pleistocene rocks of florida and the bahamas the amounts of rainfall and evaporation are the most important factors in the degree of cementation

sedimentary patterns and geometries of the bahamian outer carbonate ramp miocene lower pliocene great bahama bank core logging and high resolution seismic data from odp leg 166 were used to analyse deposits of the neogene miocene lower pliocene bahamian outer carbonate ramp ramp sediments are cyclic alternations of light and dark grey wackestones packstones with interbedded calciturbidite packages and minor slumps cyclicity was driven by high frequency sea level changes light grey layers containing shallow water bioclasts were formed when the ramp exported material whereas the dark grey layers are dominantly pelagic calciturbidites are arranged into mounded lobes with feeder channels internal bedding of the lobes shows a north directed shingling as a result of the asymmetrical growth of these bodies calciturbidite packages occur below and above sequence boundaries indicating that turbidite shedding occurred during third order sea level highstands and lowstands highstand turbidites contain shallow water components such as green algal debris and epiphytic foraminifera whereas lowstand turbidites are dominated by abraded bioclastic detritus gravity flow depocentres shifted from an outer ramp position during the early miocene to a basin floor setting during the late miocene to early pliocene this change was triggered by an intensification of the strength of bottom currents during the tortonian which was also responsible for shaping the convex morphology of the outer ramp the miocene and lower pliocene of the leeward flank of great bahama bank provides an example of the poorly known depositional setting of the outer part of distally steepened carbonate ramps the contrast between its sedimentary patterns and the well known upper pliocene quaternary slope facies associations of the flat topped great bahama bank shows the strong control that the morphology of a carbonate platform exerts on the depositional architecture of the adjacent slope and base of slope successions

shallow burial diagenesis of deep water carbonates northern bahamas results from deep ocean drilling transects rates of burial diagenesis and subsurface distribution of chalk and limestone in modern deep water carbonate slopes were little known prior to 1985 when the ocean drilling program established two drill transects in the northern bahamas north of little bahama bank and in southwestern exuma sound from these transects different shallow burial along the accretionary north margin of little bahama bank the amount of lithified strata decreases seaward because of a decreasing volume of bank derived aragonite the rate of bulk carbonate calcitization increases seaward as the rate of diagenesis begins to match then exceed the rate of burial mineral controlled diagenesis is of little consequence below about 20 m subsurface only 30 km seaward of the bank margin along the bypass margin in exuma sound the extent of lithification increases downslope toward preferential accumulation of bank derived aragonite much higher accumulation rates and high percentages of aragonite along this margin sustain a still present mineral controlled diagenetic potential in limestone at 300 m from analogy of modern bahama slopes considerable diagenetic heterogeneity within the shallow burial realm may be expected along some ancient carbonate margins our results serve to illustrate carbonate mineral stabilization and early limestone formation with secondary porosity in a sea water mediated environment and they further highlight the high diagenetic potential of periplatform carbonates

long range propagation of the semidiurnal internal tide from the hawaiian ridge abstract the northeastward progression of the semidiurnal internal tide from french frigate shoals ffs hawaii is studied with an array of six simultaneous profiling moorings spanning 25 5 37 1 n 1400 km and 13 yr long ocean topography experiment topex poseidon t p altimeter data processed by a new technique the moorings have excellent temporal and vertical resolutions while the altimeter offers broad spatial coverage of the surface manifestation of the internal tide s coherent portion together these two approaches provide a unique view of the internal tide s long range propagation in a complex ocean environment the moored observations reveal a rich time variable and multimodal internal tide field with higher mode motions contributing significantly to velocity displacement and energy in spite of these contributions the coherent mode 1 internal tide dominates the northeastward energy flux and is detectable in both moored and altimetric data over the entire array phase and group prop

tidal effects on intermediate waters a case study in the east japan sea although tides are believed to be the most important source for diapycnal mixing in the ocean few studies have directly simulated open ocean circulation including tides because the east japan sea ejs has been considered to be a miniature ocean tidal effects on the intermediate water of the ejs are investigated by using an eddy resolving ocean general circulation model that can take account of m2 and k1 tides as well as oceanic flows the simulated temperature and salinity in the intermediate layer are significantly improved by including tides the improvement results from the combined effect of two internal tides the m2 internal tide propagating into the interior of the ejs enhances vertical mixing and brings watermass characteristics closer to those observed the k1 internal tide trapped along the coast induces southwestward flow along the russian coast in the upper layer and thereby enhances the so called liman current which transports fresh waters with density conducive to the ventilation of intermediate waters in the ejs

the hydrogeochemistry of early meteoric diagenesis in a holocene deposit of biogenic carbonates abstract this study presents the results of a quantitative hydrogeochemical investigation of early meteoric diagenesis in a deposit of biogenic mixed mineralic holocene carbonate sediments at ocean bight in the southeastern bahamas ground water samples were collected from a network of 27 wells arranged into 4 transects across the 1 5 km2 strand plain deposit four wells provided multi depth samples at 0 5 m intervals thus allowing for the construction of vertical chemical profiles analyses of the water consisted of temperature ph alkalinity ci ca2 mg2 sr2 so42 and 13c data derived from these analyses were used in a series of equilibri m and mass balance equations to calculate mineral saturation levels and magnitudes and rates of mineral transformation reactions interpretation of measured and calculated parameters provided a detailed picture of patterns and processes of meteoric diagenesis at ocean bight four features of meteoric diagenetic processes operating at ocean bight are distinct from processes documented at previously studied non biogenic and aragonite dominated holocene systems 1 lighter cementation with respect to magnitudes of calcite precipitation 2 diminished magnitudes of aragonite dissolution 3 elevated rates of mineral stabilization and 4 lower efficiencies of transformation reactions another distinction of this study which is not thought to be attributed solely to the presence of mixed biogenic carbonates is the isolation of transformation reactions to the vadose and upper phreatic zone this result contradicts the popularly held belief that metastable carbonate deposits undergo rapid equilibration throughout the freshwater phreatic zone this distribution of diagenetic reactions along with the analytical results characterizes a chemical environment dominated by carbonate mineral transformation reactions linked mainly to the oxidation of organic matter and not only to the relative solubility of the different carbonate minerals this finding may prove important in attempts to explain the preservation of metastable minerals in ancient geologic sequences despite repeated exposure to freshwater phreatic zones this finding also questions the assumption that the extent of paleo phreatic lenses is equal to the observed extent of freshwater phreatic alteration

microspar development during early marine burial diagenesis a comparison of pliocene carbonates from the bahamas with silurian limestones from gotland sweden comparison of ultrastructures in pliocene periplatform carbonates from the bahamas with silurian limestones from gotland sweden reveals that despite the differences in primary sediment composition and age they reflect a similar mechanism of lithification in both sequences calcite microspar was formed as a primary cement at an early stage of marine burial diagenesis neither significant compression nor meteoric influence are necessary for the formation of calcite microspar a model is proposed for the process of microsparitic cementation of fine grained aragonite needle muds comprising four stages 1 unconsolidated aragonite dominated carbonate mud 2 precipitation of microspar that engulfs aragonite needles 3 dissolution of aragonite resulting in pitted surfaces of the microspar crystals and 4 slight recrystallization our results contradict the widespread opinion that microspar necessarily is a product of secondary recrystallization of a previously lithified micrite

evolution of pore space in the poza rica trend mid cretaceous mexico the poza rica trend of the tampico embayment mexico will ultimately produce more than 2 3 109 barrels of oil from mid cretaceous albian cenomanian basin margin deposits bioclastic grainstone packstone and wackestone are interbedded with polymictic lime breccia and dolomitized debris all were deposited by sediment gravity flow indigenous sediment was pelagic lime mud typical reservoir porosities are about 10 permeabilities average 2 md and rarely exceed 100 md porosity is largely the result of selective dissolution of rudist fragments which were originally aragonite detailed petrographic study with emphasis on the diagenetic products allows quantitative assessment of porosity at various diagenetic stages from original sediment to reservoir rock a relatively simple diagenetic history is reflected by about 90 of the samples studied primary porosity was reduced through lithification of matrix mud and initial cementation by clear equant to bladed non ferroan calcite later dissolution produced extensive skelmoldic and minor vuggy porosity subsequently non ferroan calcite cement reduced porosity before the emplacement of hydrocarbons reconstructed sediment porosities are comparable to but lower than modern counterparts the initial phase of cementation and presumed lithification of mud greatly reduced porosity in all lithologies but appreciably more porosity persisted in grainstone and packstone than in wackestone or mudstone dissolution produced a porosity resurrection which exceeded that of the initial sediment in some grainstones calcite cementation and local multiphase quartz cementation and dolomitization reduced porosity to present average values of 8 12 in grain supported rocks and 3 in mud supported rocks the greater persistence of primary porosity and therefore permeability in grain supported rocks probably accounts for their greater secondary porosity development and ultimate reservoir quality geometrically averaged permeabilities range from only 0 17 md in wackestone to 3 85 md in dolomite but differ significantly with rock type and grain size permeability increases with porosity in all lithologies the rate of increase is greater at higher porosities and with coarser grain sizes the agent for both early cementation and development of secondary porosity appears to have been meteoric water subaerial exposure appears to be ruled out however by a basin margin depositional environment and continued burial beneath upper cretaceous pelagic sediments early exposure to meteoric water can be explained by a hydrologic head developed during penecontemporaenous exposure that produced cavernous porosity in the adjacent golden lane trend descending meteoric water likely emerged as submarine springs along the tamabra trend deposition of pelagic limestone during the turonian blanketed part of the golden lane escarpment to enhance development of a large freshwater lens gaps in the blanket localized springs and influenced flow patterns within the poza rica field analogous freshwater circulation exists today in northern florida

authigenic dolomite in bahamian peri platform slope sediment authigenic calcium rich dolomite has been discovered in poorly consolidated lower pliocene upper miocene carbonate slope sediments north of little bahama bank the dolomite was recovered from a 5 6 m long piston core that penetrated a slide scar in 600 m of water below an unconformity at 105 cm which extends from the late pleistocene to about the miocene pliocene boundary x ray diffraction data indicate only calcite 85 99 and dolomite as much as 15 and scanning electron microscopy observations indicate in situ precipitation of dolomite stable carbon isotope data indicate a normal open marine source of carbon and oxygen isotope values are consistent with precipitation of both calcite and dolomite from deep cold open marine waters trace element data reveal that dolomitic sediments are depleted in sr 2 and mg 2 relative to nondolomitic upper pleistocene oozes dolomitization occurred in a deep open marine diagenetic environment via whole scale dissolution of aragonite and magnesian calcite and reprecipitation of calcite and dolomite

the origin of dolomites in tertiary sediments from the margin of great bahama bank abstract based on an integrated geochemical and petrographic investigation of dolomites from two cores drilled on great bahama bank we have determined three different environments of formation for the dolomites that are common throughout the pliocene and miocene parts of these cores the first environment of dolomitization occurs in association with development of nondepositional surfaces dolomite typically forms below each of these surfaces the concentration and extent of which is governed by the length of the period of nondeposition these dolomites are recognized by their association with the nondepositional surfaces characteristic positive 18o values indicative of formation from cold bottom waters and 18o and sr profiles with depth that suggest formation in the presence of diffusive temperature and sr gradients the second environment of dolomitization occurs in pore fluids where the cation and anion profiles are governed by diffusive processes the dolomite forming here is termed background dolomite this is a microsucrosic dolomite and forms both by recrystallization of the existing sediment and precipitation directly into void space dolomitization by this mechanism uses a local source of mg2 and consequently the dolomite never constitutes more than between 5 and 10 of the sediment this type of dolomite is characterized by extremely high sr concentrations which reflect concentrations of sr2 in the pore fluids from which it formed the high concentrations of sr2 in the pore fluids arise through the continued recrystallization of metastable aragonite and high mg calcite to dolomite and low magnesium calcite driven by oxidation of organic material by sulfate not only does sulfate reduction provide an additional thermodynamic drive for recrystallization but because the absolute concentration of sr2 in the pore fluids is governed by the solubility of celestite srso4 removal of sulfate allows the sr2 ca2 ratio of the interstitial fluid to become much higher than normally encountered the final type of environment of dolomitization is associated with coarse grained reefal sediments the pervasive nature of the dolomitization and the relatively normal sr concentrations suggest the circulation of normal marine water in a relatively open system

carbonate shedding and sedimentary cyclicities of a distally steepened carbonate ramp miocene great bahama bank depositional geometries as imaged in seis mic lines logging data and quantitative petrographic data were used to analyse the slope and toe of slope deposits of the miocene distally steepened carbonate ramp of great bahama bank the shedding pattern along the slope of this ramp is more complex than it is along the slope of the pliocene pleistocene flat topped carbonate platform compositional changes and compositional trends of periplatform sediments correlate with the positions of geophysically defined sequence boundaries two types of depositional sequences occur the first sequence is characterised by laterally traceable sequence internal reflections whereas the second type contains major intrasequen tial incisions erosional incisions and sedimentary infills of these canyons by turbidites formed during sea level lowstands as is indicated by the composition of the turbidites having a mixture of shallow water and pelagic particles highstand turbidites are charac terised by more extensive laterally traceable geome tries and by the occurrence of abundant shallow water particles in contrast to highstand turbidites shed from the pliocene pleistocene flat topped platform shal low water components in highstand turbidites of the miocene ramp are of skeletal origin the stacking pat tern of the periplatform deposits is controlled by sea level fluctuations four orders of sea level changes are distinguished third order cycles are delimited by sequence boundaries and fourth 100 000 a order cycles govern the bundling of turbidites into packages fifth 40 000 a and sixth 23 000 a order cycles are recorded in the background sediments and resolvable with spectral analysis

simulations of temperature and turbulence structure of the oceanic boundary layer with the improved near surface process an improved model for the oceanic boundary layer is presented in view of the recent observation of the microstructure of the upper ocean including the high dissipation rate near the sea surface in the new model the surface boundary conditions for both the turbulent kinetic energy flux and the roughness length scale are modified the parameterization of stratification effects on turbulence is improved and the convective process is reformulated on the basis of the observation of uniform temperature and velocity profiles within the convective mixed layer evolutions of the profiles of both the dissipation rate and temperature of the observation data patches experiment as well as the time series of the sea surface temperature over the observation days are successfully simulated during a diurnal cycle for the first time it is also shown that the model reproduces various important features of the oceanic boundary layer for example the formation of a diurnal thermocline the profiles of buoyancy flux and the magnitudes of the buoyancy gradients both within the mixed layer and at the diurnal thermocline performance of the model is compared with that of the widely used mellor yamada model

biochemostratigraphy of an upper albian turonian succession from the southeastern neo tethys margin sw iran abstract a neo tethyan upper albian turonian hemi pelagic carbonate succession sarvak formation accessible in outcrop in the zagros sw iran was investigated using sedimentology microfacies analysis planktonic foraminifera biostratigraphy and carbon isotope stratigraphy the succession contains six biozones including thalmanninella th appenninica th globotruncanoides rotalipora cushmani whiteinella archaeocretacea helvetoglobotruncana helvetica and marginotruncana schneegansi some of these biozones show variable stratigraphic positions throughout the tethyan and boreal realms that hinder correlation of the studied iranian section with european reference sections therefore the correlation of the existing biostratigraphic framework was complemented by carbonate carbon isotope stratigraphy based on bulk carbonate material despite the low resolution of the presented carbon isotope record pronounced global events including the late turonian events cenomanian turonian boundary ctb event oae 2 and albian cenomanian boundary acb event can be distinguished the 13c excursions provide global synchronous time lines for correlation the distinguished biozones were compared among the sections regarding their stratigraphic positions relative to these time lines the correlation tentatively suggests that the biostratigraphic datum marking the acb is diachronous with an se nw trend first appearance datum fad of th appenninica varies from the upper albian to the lower cenomanian the fad of th globotruncanoides is also variable from the upper albian to the lower cenomanian however the middle cenomanian turonian biozones including rotalipora cushmani and whiteinella archaeocretacea zones are synchronous elevated pco2 contributed to the gradual increase of the sst sea surface temperature during the cenomanian and the dramatic climax at the earliest turonian this trend closely correlates with the change from the diachronous acb biozones to synchronous ctb biozones possibly increasing ssts provided temperature tolerance range for the species throughout different latitudes and assisted their rapid distribution moreover the warming raised the sea level from the latest albian to turonian that inundated landbridges resulting in an enhanced marine circulation and faster distribution of planktonic species throughout the neo tethys ocean

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

differential diagenesis of rhythmic limestone alternations supported by palynological evidence alternating cemented and uncemented fine grained layers from pliocene periplatform carbonates of the great bahama bank have fundamentally different diagenetic features the cemented layers consist predominantly of microspar interpreted as an early marine shallow burial cement the intercalated uncemented softer layers are devoid of microspar cement and exhibit signs of mechanical compac tion precursor sediments of both cemented and uncemented layers apparently consisted largely of aragonite needles the needles in the compacted layers show signs of dissolution suggesting that the calcium carbonate required for cementation of the uncompacted layers was provided by aragonite dissolution within the compacted layers the lack of compaction in the cemented layers shows that cementation and hence aragonite dissolution in the adjacent compacted layers took place in the shallow burial realm the dissolved carbonate was trans ported by diffusion to adjacent layers and reprecipitated as calcite cement thereby preventing significant compaction of these layers these processes are not yet complete in the material examined and some aragonite remains in the compacted layers the sedimentary composition of the two rock types compacted and uncompacted is similar indicating a similar precursor sediment for both between 1 5 and 7 times the concentration of palynomorphs oc curs in the compacted layers apparently the result of passive diage netic enrichment although the trigger for diagenetic differentiation has not been determined the pure limestone succession studied here appears to serve as a clay free analog to limestone marl alternations

isotopic signature of burial diagenesis and primary lithological contrasts in periplatform carbonates miocene great bahama bank the stable isotope geochemistry of miocene sediments from the leeward margin of the great bahama bank was examined to investigate burial diagenetic processes in periplatform carbonates data indicate that in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined the present study focuses on ocean drilling program sites 1006 and 1007 the most distal of five sites drilled from marginal to deep basin environments during leg 166 these miocene sections are characterized by their cyclic appearance manifest as decimeter to meter scale alternations between light colored ooze chalk limestone and dark colored marl marlstone the section at site 1006 contains a high proportion of pelagic carbonate and is unlithified to a subbottom depth of 675 m fluctuations in 18 o and 13 c values at this site are independent of lithological variation and reflect primary conditions at site 1007 located at the toe of slope and composed of a mixture of bank derived and pelagic carbonate limestones are densely cemented show little evidence of compaction and have 18 o values up to 2 higher than coeval sediments at site 1006 marlstones at site 1007 are poorly cemented exhibit an increase in compaction related features with depth and have lower and more variable 18 o values that are similar to those of coeval sediments at site 1006 isotopic and petrographic characteristics of limestone interbeds result from cement precipitation from cold sea water during the first 100 m of burial higher proportions of insoluble materials and pelagic carbonate seem to have inhibited diagenetic alteration in adjacent marlstones in spite of significant compaction and pressure solution during burial original isoto pic compositions appear to be best preserved in these intervals at site 1007 the documented contrasts in petrographic and isotopic patterns illustrate the role of primary sediment composition in controlling lithification processes in periplatform carbonates and stress the importance of consid ering such factors when interpreting geochemical data from ancient shelf and slope limestones

effects of kuroshio intrusions on nonlinear internal waves in the south china sea during winter 1 during winter the kuroshio tends to cross luzon strait penetrating the northeastern south china sea where it forms energetic mesoscale structures luzon strait is also a site where westward propagating large amplitude internal waves are generated we describe observations of these waves acquired in the deep basin of the south china sea during the winter of 2010 2011 with the goal of assessing the influence of mesoscale variability on their properties combining tidal current simulations with an internal wave generation and evolution model we obtain time series of deviations between our observations and the model simulations these deviations are analyzed in terms of mesoscale variability based on the data assimilated hybrid coordinate ocean model hycom simulations we find that simplified models of nonlinear internal wave response to changes in horizontal stratification gradients and vertical shear provide at best weak simulations of amplitude modulation in contrast to these results deviations of internal wave arrival time occurring up to 2 h early during kuroshio inflows are quite well simulated when derived from integration of the first internal mode phase speed along two dimensional ray traced paths using hycom simulations of velocity and density fields together with bathymetry refraction of the internal waves by kuroshio intrusions can lead to substantial distortion of the paths sufficient to provide a potential explanation for the apparent suppression of waves during previous winter measurements our results suggest that the internal wave field can be a sensitive indicator of mesoscale variability in luzon strait and the northeastern south china sea

magnetostratigraphic dating of shallow water carbonates from san salvador bahamas magnetostratigraphic results are reported here from a sequence of late neogene quaternary shallow water carbonate sediments from a continuous core drilled on the island of san salvador bahamas on the basis of the remanent magnetism of 136 samples from a 91 m measured section of core the polarity sequence can be correlated with the magnetic polarity time scale from the gilbert chron early pliocene through the late brunhes chron late pleistocene holocene magnetic polarities were determined on the basis of relative up down direction in the unoriented core extraction studies of the magnetic particles reveal the presence of single domain crystals of magnetite resembling those produced by the magnetotactic bacteria and algae the sequence of reversals provides a minimum of six new major chronostratigraphic markers for the pliocene pleistocene of the bahamas it confirms and refines the local timing of both the lithologic change from skeletal to nonskeletal sediments and the disappearance of coral and molluscan species from the bahamas as upper late pliocene between 2 6 and 2 7 ma that the primary magnetic remanence is preserved in shallow water carbonates including replacement dolomites suggests that this technique could be used to date similar tertiary and possibly even older carbonate sequences the establishment of a reliable magnetostratigraphy provides refined dating of shallow water carbonates and regional faunal appearances or disappearances sediment accumulation rates subsidence and depositional events

carbonate dissolution in a modern mixing zone the potential for dissolution of calcite and aragonite and precipitation of dolomite by the mixing of fresh and saline ground waters has been demonstrated theoretically1 3 although geologists have used these processes in the explanation of the diagenesis of recent4 7 and ancient8 12 carbonates there has been only limited investigation of the geochemical processes of modern mixing zones13 14 here we report the results of chemical and rock profiling through a modern mixing zone on andros island in the bahamas our results demonstrate undersaturation of the waters in the mixing zone with respect to aragonite and calcite and corresponding pervasive dissolution of the carbonate rocks at this level undersaturation is significantly enhanced by bacterial processes which are also responsible for precipitation of an iron rich crust despite chemical supersaturation precipitation of dolomite was not observed thereby casting some doubt on the mixing zone model of dolomitization

late holocene temperature fluctuations on the tibetan plateau abstract proxy data of palaeoclimate like ice cores tree rings and lake sediments document aspects of climate changes on the tibetan plateau during the last 2000 years the results show that the tibetan plateau experienced climatic episodes such as the warm intervals during ad 800 1100 and 1150 1400 the little ice age between ad 1400 and 1900 and an earlier cold period between the 4th and 6th centuries in addition temperatures varied from region to region across the plateau a warm period from ad 800 to 1100 in the northeastern tibetan plateau was contemporaneous with cooling in the southern tibetan plateau which experienced warming between ad 1150 and 1400 large scale trends in the temperature history from the northeastern tibetan plateau resemble those in eastern china more than the trends from the southern plateau the most notable similarities between the temperature variations of the tibetan plateau and eastern china are cold phases during ad 1100 1150 1500 1550 1650 1700 and 1800 1850

internal tides in the southwestern japan east sea abstract this paper investigates the internal tidal energy distribution in the southwestern japan east sea using vertical round trip travel time data from 23 pressure sensor equipped inverted echo sounders pies the records are analyzed by bandpass filtering to separate time dependent variability of the semidiurnal and diurnal bands the semidiurnal internal tides exhibit a horizontal beam pattern of high energy propagating into the open basin they originate from a restricted portion of the shelf break where the korea strait enters the ulleung basin the generation appears to occur at 200 m water depth near 35 5 35 7 n and 130 131 e where the slope of bottom topography matches that of the wave characteristics coinciding with the location where the semidiurnal barotropic cross slope tidal currents are strongest maximum vertical displacement of the thermocline interpreted as a long wave first baroclinic mode from the measured is about 25 m near the generation region annual and monthly var

the tsushima warm current through tsushima straits estimated from ferryboat adcp data abstract current structures across the tsushima straits are studied using results from long term acoustic doppler current profiler adcp observations by a ferryboat between hakata and pusan conducted since february 1997 two maxima of the northeastward current are observed in the central parts of the eastern and western channels and the maximum velocity in the western channel is stronger than that of the eastern channel downstream of the tsushima islands a southwestward countercurrent is observed associated with a pair of cyclonic and anticyclonic eddies in the western channel the deep countercurrent is observed pronouncedly on the bottom slope of the korean side from summer to winter the volume transport of the tsushima warm current through the straits has strong seasonal variation with a minimum in january and two maxima from spring to autumn double peaks the spring peak of the volume transport through the eastern channel is more pronounced than the autumn peak and the autumn peak of the west

seasonal variation of semidiurnal internal tides in the east japan sea the seasonal variation of semidiurnal internal tides in the east japan sea was investigated using 25 month long output from a real time ocean forecasting system the z coordinate eddy resolving high resolution numerical model called the riam ocean model incorporates data assimilation that nudges temperature and salinity fields together with volume transport through the korea strait to produce realistic oceanic currents and stratification in addition to atmospheric forcing it includes tidal forcing of 16 major components along open boundaries the model generates energetic semidiurnal internal tides around the northern entrance of the korea strait energy conversion from barotropic to baroclinic internal tides varies seasonally with maxima in september ranging 0 48 0 52 gw and minima in march ranging 0 11 0 16 gw this seasonal variation is induced by the seasonality in stratification near the southwestern east japan sea the propagation distance of the internal tides is associated with generation intensity and wavelength from late summer to early winter the semidiurnal internal tides travel relatively far from the generation region due to stratification changes its energy dissipates less as a result of longer wavelengths our results suggest that spatiotemporal variation of internal tide induced mixing due to the seasonality in the generation propagation and dissipation of internal tides should be considered for a more realistic simulation of water masses and circulation in models of the east japan sea

coastal mixing zone dolomite forward modeling and massive dolomitization of platform margin carbonates abstract dolomite of mixed water origin occurs in three late pleistocene raised reef terraces in southeastern barbados west indies dolomite concentrations range from trace quantities to locally complete with a general increase in dolomite percentage with increasing terrace age most of the dolomite is replacive both mimetic and fabric selective with limpid pore lining dolomite cements common in the oldest terrace stratigraphic relationships suggest that mixing zone dolomitization occurred locally during three temporally separate sea level events the rapidity of quaternary glacio eustasy constrains dolomitization to have occurred within about 5 000 yr in each terrace rapid recurring dolomitization resulted from development of similar hydrologic and hydrochemical conditions during each ea level event barbados data are used as conceptual input for a computer based forward model which simulates the development of thick platform margin sections of mixing zone dolomite through the interaction of sea level fluctuations sedimentation rapid recurring dolomitization and subsidence sensitivity tests of the model indicate that the most important parameters for producing thick sections of platform margin dolomite are 1 dolomitization rate 2 sea level still stand duration and 3 rate of sea level change dolomite thus formed may provide nuclei for later burial dolomitization or may provide an intrabasinal magnesium source for stepwise stabilization of platform interior dolomites

dating and characterization of polymorphic transformation of aragonite to calcite in pleistocene bivalves from rhodes greece by combined shell microstructure stable isotope and electron spin resonance study absolute dating of diagenesis is a challenging yet significant problem reconstructing the depositional and diagenetic history of a late pleistocene coralligene type red algal reef and overlying maerl red algal sand from the plimiri coastal cliff se island of rhodes greece is enabled using a combination of microstructure stable isotope analyses and electron spin resonance of large bivalve shells partially altered by diagenesis these shells consisting of both original shell aragonite and polymorphic transformed rims now consisting of neomorphic spar provide the opportunity to date the primary age when the shells were precipitated as well as the age of their polymorphic transformation the contamination of samples presented a significant problem for interpreting ages based on data from electron spin resonance esr alone however sample contamination was evaluated with quantitative xrd providing the opportunity to apply corrections which increased reliability of the ages the carbon and oxygen stable isotope values and the neomorphic spar microtexture suggested that the polymorphic transformation at plimiri took place in a meteoric environment with a high and increasing fluid rock ratio the electron spin resonance dates combined with the vertical sedimentary evolution allowed to assign the formation of the red algal reef to the marine isotope stages 6 to 5e transgressive event ca 135 to 120 ka and to identify meteoric diagenetic phases during possibly the marine isotope stage 5d and the upper marine isotope stage 5c to lower 3 the use of electron spin resonance dating of neomorphic spar and age correction for sample contamination is presented herein for the first time and the results suggest that it might provide a useful tool to date late pleistocene diagenesis

rapid burial diagenesis of deep water carbonates exuma sound bahamas well lithified deep water periplatform limestones of late miocene age occur at subsurface depths from 113 m to total depth of 283 m at ocean drilling program odp site 632 in exuma sound bahamas this occurrence marked by a dramatic increase in compressional wave velocities up to 5 0 km s represents the most rapid transformation of ooze to limestone yet discovered in either periplatform or open ocean settings the burial diagenetic pathway is similar to those for meteoric and deep burial diagenetic environments aragonite dissolves magnesian calcites exsolve or dissolve low mg calcite precipitates as cement and secondary moldic vuggy porosity develops stable isotope ratios suggest precipitation of low mg calcite from cold marine derived pore waters accelerated diagenesis is a response to the influx of large quantities up to 80 of bank derived metastable carbonates and rapid burial via high accumulation rates up to 210 m m y our findings 1 document carbonate mineral stabilization and lithification in a seawater mediated shallow burial diagenetic environment 2 highlight the very high diagenetic potential of periplatform carbonates and 3 call into question the use of seismic velocities as support for the bahama megabank hypothesis

from the great bahama bank into the straits of florida a margin architecture controlled by sea level fluctuations and ocean currents high resolution multichannel seismic data collected across the great bahama bank margin and the adjacent straits of florida indicate that the deposition of neogene quaternary strata in this transect are controlled by two sedimentation mechanisms 1 west dipping layers of the platform margin which are a product of sea level controlled platform derived downslope sedimentation and 2 east or north dipping drift deposits in the basinal areas which are deposited by ocean currents these two sediment systems are active simultaneously and interfinger at the toe of slope the prograding system consists of sigmoidal clinoforms that advanced the margin some 25 km into the straits of florida the foresets of the clinoforms are approximately 600 m high with variable slope angles that steepen significantly in the pleistocene section the seismic facies of the prograding clinoforms on the slope is characterized by dominant partly chaotic cut and fill geometries caused by submarine canyons that are oriented downslope in the basin axis seismic geometries and facies document deposition from and by currents most impressive is an 800 m thick drift deposit at the confluence of the santaren channel and the straits of florida this santaren drift is slightly asymmetric thinning to the north the drift displays a highly coherent seismic facies characterized by a continuous succession of reflections indicating very regular sedimentation leg 166 of the ocean drilling program odp drilled a transect of five deep holes between 2 and 30 km from the modern platform margin and retrieved the sediments from both the slope and basin systems the neogene slope sediments consist of peri platform oozes intercalated with turbidites whereas the basinal drift deposits consist of more homogeneous fine grained carbonates that were deposited without major hiatuses by the florida current starting at approximately 12 4 ma sea level fluctuations which controlled the carbonate production on great bahama bank by repeated exposure of the platform top controlled lithologic alternations and hiatuses in sedimentation across the transect both sedimentary systems are contained in 17 seismic sequences that were identified in the neogene quaternary section seismic sequence boundaries were identified based on geometric unconformities beneath the great bahama bank all the sequence boundaries could be traced across the entire transect into the straits of florida biostratigraphic age determinations of seismic reflections indicate that the seismic reflections of sequence boundaries have chronostratigraphic significance across both depositional environments

internal solitary waves induced by flow over a ridge with applications to the northern south china sea 1 the generation of internal solitary waves by barotropic tides over a ridge is studied in a nonhydrostatic numerical model under idealized oceanographic settings the experiments examine the effects of ridge width barotropic tidal strength and stratification on wave generation the barotropic tidal flow produces internal wave beams emitting from the ridge top if the slope of the ridge exceeds a critical value equal to the slope of the wave beam reflection and refraction of a wave beam in an upper ocean waveguide associated with a strong shallow thermocline produce horizontally propagating internal tides when the local froude number over a ridge is not small lee waves generated on the ridge convert enough energy from the barotropic tides to the internal tides to form tidal bores and solitary waves increasing stratification at ridge depths enhances the generation of internal waves particularly at the diurnal periods in the luzon strait the slope of the wave beam decreases in spring and summer as stratification at the ridge depths increases favoring the generation of internal tides without the presence of a strong shallow thermocline internal solitary waves are not observed east of the luzon strait in the northern south china sea internal solitary waves are likely observed from april to july when a strong shallow thermocline is present a deep mixed layer in winter suppresses the production of internal solitary waves