modeling study of turbulent mixing over the continental shelf comparison of turbulent closure schemes limitation is imposed during upwelling favorable winds the majority of turbulent mixing occurs in the top and the bottom boundary layers and in the vicinity of the vertically and horizontally sheared coastal jet turbulent mixing in the coastal jet is primarily driven by shear production the near surface flow on the inner shelf becomes convectively unstable as wind stress forces the upwelled water to flow offshore in the surface layer during downwelling favorable winds the strongest mixing occurs in the vicinity of the downwelling front the largest turbulent kinetic energy and dissipation are found near the bottom of the front turbulence in the bottom boundary layer offshore of the front is concentrated between recirculation cells which are generated as a result of symmetric instabilities in the boundary layer flow index terms 4219 oceanography general continental shelf processes 4568 oceanography physical turbulence diffusion and mixing processes 4255 oceanography general numerical modeling 4279 oceanography general upwelling and convergences

pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

modeling semidiurnal internal tide variability in the southern california bight abstractthe regional oceanic modeling system roms is applied in a nested configuration with realistic forcing to the southern california bight scb to analyze the variability in semidiurnal internal wave generation and propagation the scb has a complex topography with supercritical slopes that generate linear internal waves at the forcing frequency the model predicts the observed barotropic and baroclinic tides reasonably well although the observed baroclinic tides feature slightly larger amplitudes the strongest semidiurnal barotropic to baroclinic energy conversion occurs on a steep sill slope of the 1900 m deep santa cruz basin this causes a forced near resonant semidiurnal poincare wave that rotates clockwise in the basin and is of the first mode along the radial azimuthal and vertical directions the associated tidal mean depth integrated energy fluxes and isotherm oscillation amplitudes in the basin reach maximum values of about 5 kw m 1 and 100 m and are strongly modulated by the sprin

planetary surface dating from crater size frequency distribution measurements partial resurfacing events and statistical age uncertainty abstract we describe the procedure to fit a cumulative production function polynomial to a partial crater size frequency distribution the technique is of particular use in deriving ages for surfaces which have undergone partial resurfacing events namely erosional or depositional events which have affected a limited diameter range of the crater population we demonstrate its use in obtaining times for both the surface formation and the resurfacing event we give a practical outline of the method for making age measurements from crater counts and how to identify resurfacing effects in the results we discuss the conversion of production function polynomials between common presentations and the statistical uncertainty of the determined ages with respect to the non linear chronology function and a minor refinement of data binning

numerical simulation of m2 internal tides in the south brazil bight and their interaction with the brazil current 1 a fully three dimensional nonlinear primitive equation ocean model is applied to study the semidiurnal internal tide in the south brazil bight under summer conditions along the shelf break and upper slope of this region the upper layer 0 600 m is occupied by the southward flowing brazil current several numerical experiments were conducted to investigate the generation and propagation of the m2 internal tide using horizontally homogeneous and vertically stratified density fields internal tides were generated over the whole bight with a clear signal on the continental shelf when a more realistic summer stratification was considered a baroclinic jet representative of the brazil current developed and comparisons between current observations and modeled results were improved this jet acts as a barrier to the coastward propagation of the internal tide generated over the slope reflecting it back towards the open ocean on the negative relative vorticity side of the brazil current located over the shelf internal tides are trapped enhancing vertical current variability and hence tidally induced mixing the results highlight the importance of considering background flows when investigating internal tides in regions of strong along slope baroclinic flows such as western boundary currents

electron optical investigation of sedimentary dolomites transmission electron microscope studies demonstrate a structural distinction between stoichiometric and ancient calcian dolomites of sedimentary origin a modulated or tweed structure similar in appearance to spinodal microstructures characterizes ancient calcian dolomites whereas stoichiometric dolomites are homogeneous recent calcium rich dolomites lack a modulated structure but have a heterogeneous microstructure with high densities of growth defects electron and optical diffraction and lattice imaging suggest a fluctuation in interplanar spacing in a coherent lattice in addition lattice imaging also reveals discontinuous faults throughout the modulated structure ordering and possibly incipient exsolution are suggested c reflections in sad patterns of calcian dolomites document a new superstructure in at least part of the lamellar structure and raise questions of different ordering states throughout the structure

time dependent wind driven flow over a shallow midshelf submarine bank 1 during summer 2001 high resolution hydrographic velocity and bio optical surveys were conducted over heceta bank off central oregon north of the bank upwelling over simple bottom topography exhibited a classic response with a midshelf baroclinic coastal jet and upwelled isopycnals the coastal upwelling jet follows the bank topography as it widens offshore before reaching the southern end of the bank where the shelf break turns almost 90 back toward the coast the ensuing adjustment involves the offshelf transport of coastal water and the material it contains the jet meanders anticyclonically in the lee of the bank before resuming its equatorward path seaward of the shelf break a pool of high chlorophyll 15 mg m 3 near surface water is found in the low velocity lee region created by the bank a low temperature high salinity bottom water pool supplied primarily from the south lies over the inshore region of the bank this bottom pool is up to 40 m thick and contains elevated levels of suspended material by creating an east west perturbation in the coastal upwelling front the flow topography interaction introduces an alongshore pressure gradient when southward upwelling favorable winds relax this alongshore pressure gradient can drive flow back to the north this leads to northward flow on the inshore side of the bank ultimately setting up the potential for recirculation around the entire bank complex on a timescale of about 10 days strong northward winds during summer lead to downwelling within 15 km of the coast accompanied by significant 0 2 m s 1 wind driven northward currents

modeling study of variable upwelling circulation in the east china sea response to a coastal promontory abstracta three dimensional high resolution numerical model is used to investigate processes and dynamics of an intensified upwelling that is induced by a coastal promontory over the east china sea ecs shelf the center of the intensified upwelling around the promontory has been constantly observed but so far it has been dynamically unexplained forced by an idealized southeasterly wind stress the model results well capture the observed upwelling at the lee of the coastal promontory the intensified upwelling is formed by a strengthened shoreward transport downstream of the promontory as the upwelling jet veers shoreward the jet is mainly controlled by a cross shore geostrophic balance and is largely modulated by both centrifugal acceleration associated with nonlinear advection and by bottom stress the strengthened shoreward transport is mainly attributed to the cross shore geostrophic current that is induced by a countercurrent negative pressure gradient force pgf and partly attributed to th

how old are young lunar craters 1 the accurate definition of the lunar cratering chronology is important for deriving absolute model ages across the lunar surface and throughout the solar system images from the lunar reconnaissance orbiter narrow angle cameras and wide angle camera and the selene kaguya terrain camera provide new opportunities to investigate crater size frequency distributions csfds on individual geological units at lunar impact craters we report new csfd measurements for the copernican aged craters north ray tycho and copernicus which are crucial anchor points for the lunar cratering chronology we also discuss possible reasons for an age discrepancy observed between the impact melt and ejecta units our csfds for north ray and tycho crater ejecta deposits are consistent with earlier measurements however for copernicus crater and one of its rays we find significantly lower cumulative crater frequencies than previous studies our new results for copernicus crater fit the existing lunar absolute chronologies significantly better than the previous counts our derived model ages of the ejecta blankets of north ray tycho and copernicus agree well with radiometric and exposure ages of the apollo 16 17 and 12 landing sites respectively and are generally consistent with a constant impact rate over the last 3 ga however small variations of the impact rate cannot be resolved in our data and require further investigations

the sequence and mechanism of low temperature dolomite formation calcian dolomites in a pennsylvanian echinoderm abstract middle pennsylvanian fossils from the buckhorn asphalt quarry of southern oklahoma are unusual in that early sealing by tar has preserved many of their original textural and mineralogic features and those of the earliest stages of diagenesis echinoderm fragments collected from this locality axe well preserved with original stereom morphology clearly visible optically one to five micrometer anhedral calcian dolomite grains occupy as much as 30 percent of the original stererom of the fragments as displayed by differential etching and mgk x my maps the composition of skeletal fragments is 75 percent ca 98mg 02co3 25 percent ca 54mg 46co3 single crystal x ray di fraction xrd empa tem and stem microanalysis were used to characterize the calcian dolomite phase tem micrographs revealed an approximate 100 a tweed structure identical to that reported by reeder and wenk 1979 our data imply that magnesium in the calcian dolomites was derived largely from the original magnesian calcite of the echinoderm stereom original biogenic high magnesium calcite is altered via local microdissolution reprecipitation to anhedral disordered calcian dolomite grains within low magnesium calcite the product phases low magnesium calcite and calcian dolomite retain the original crystallographic orientation of the stereom these products of early diagenesis are apparent precursors to well defined ordered euhedral microdolomites the relationships between the low magnesium calcite and calcian dolomite and the chemistry and complex ultrastructure of the calcian dolomites support the kind of low temperature mechanism of dolomite formation postulated by gains 1977 goldsm th and graf 1958 and others on the basis of hydrothermal experiments

preservation of organic carbon in dolomitized cambrian stromatolites and implications for microbial biosignatures in diagenetically replaced carbonate rock abstract stromatolites have been a major focus in the search for ancient microbial life however the organic carbon biosignatures of dolomitized stromatolites have not yet been fully characterized or correlated with their dolomitizing conditions although dolomitization rarely preserves microbial morphology the presence of organic carbon can provide valuable information for characterization of fossils biogenicity syngenicity and indigeneity to their host rock the cambrian allentown formation in new jersey usa is an excellent example of dolomitized stromatolites and thrombolites containing diagenetically modified microbial biosignatures based on xrd and epma data the dolomite composition is typically stoichiometric with varying degrees of cationic ordering the outcrop underwent early dolomitization in a marginal marine setting and later burial diagenesis resulting in multi generational dolomite formation 1 microspar dolomite formed by early diagenetic replacement at or near the surface 2 zoned dolomite formed penecontemporaneously with the microspar phase as rhombohedral crystals by infilling primary pore spaces within the microspar matrix the rhombic crystals continued to grow outward in alternating stages of fe enriched and depleted fluids which were preserved in zoned rims and revealed by cathodoluminescence and 3 saddle dolomite formed during late stage deep burial with fe and mn rich fluids and occurs as a void filling high temperature phase organic carbon characterized using confocal raman microscopy has an exclusive distribution within the microspar dolomite and the d and g bands characteristics reveal similar thermal alteration to the host rock indicating that the mapped organic carbon is indigenous and syngenetic with the cambrian carbonates the findings presented in this study reveal organic matter found within microspar of various dolomitized facies deriving from different source pools of organic carbon this study sheds light on biosignatures in secondary dolostones and may aid biosignature detection in older carbonate rocks on earth and mars

modulation of the semidiurnal cycle of turbulent dissipation by wind driven upwelling in a coastal embayment with two 25 hour series of turbulent microstructure and currents observations carried out in august 2013 during spring chaos 1 and neap tides chaos 2 we investigated the semidiurnal cycle of turbulent dissipation in an embayment affected by coastal upwelling ria de vigo nw iberia at the time of sampling the bay hosted a net wind driven bi directional positive exchange flow and thermal stratification turbulent kinetic energy tke dissipation e at the interface between upwelled and surface waters was enhanced by two orders of magnitude during the ebbs 10 6 w kg 1 with respect to the floods 10 8 w kg 1 this pattern was caused by the constructive interference of the shear associated with the upwelling and tidal currents the vertical structure of the tidal currents was consistent with a deformation of tidal ellipses by stratification which was tightly coupled to the intensity of upwelling this two pronged interaction resulted in a modulation of the semidiurnal cycle of turbulent dissipation by coastal upwelling thus as a result of the upwelling relaxation conditions experienced during chaos 1 depth integrated interior tke dissipation rates were higher by a factor of 2 compared to chaos 2 by using a simple model we determined that observed variations in turbulent mixing had a limited influence on the tidal variations of stratification which were dominated by straining and advection the mixing mechanism described here is potentially relevant for the ecology of upwelling bays as it can stimulate the transport of nutrients from deep upwelled waters to the sun lit surface layers where primary production takes place

evidence for basaltic volcanism on the moon within the past 100 million years the majority of basaltic volcanism on the moon occurred more than 3 billion years ago small mounded formations on the lunar nearside may be products of basaltic eruptions less than 100 million years ago suggesting a long decline of magmatic activity

three dimensional double ridge internal tide resonance in luzon strait abstractthe three dimensional 3d double ridge internal tide interference in the luzon strait in the south china sea is examined by comparing 3d and two dimensional 2d realistic simulations both the 3d simulations and observations indicate the presence of 3d first mode semi diurnal standing waves in the 3 6 km deep trench in the strait as in an earlier 2d study barotropic to baroclinic energy conversion flux divergence and dissipation are greatly enhanced when semidiurnal tides dominate relative to periods dominated by diurnal tides the resonance in the 3d simulation is several times stronger than in the 2d simulations for the central strait idealized experiments indicate that in addition to ridge height the resonance is only a function of separation distance and not of the along ridge length that is the enhanced resonance in 3d is not caused by 3d standing waves or basin modes instead the difference in resonance between the 2d and 3d simulations is attributed to the topographic blocking

a nested grid model of the oregon coastal transition zone simulations and comparisons with observations during the 2001 upwelling season 1 the oregon coastal transition zone octz extends several hundred kilometers offshore where shelf flows interact with the northern california current a primitive equation numerical ocean model is used to study the upwelling circulation in this region from 1 may to 1 november 2001 this octz model obtains initial and boundary conditions from a larger scale model of the california current system and forcing from a regional atmospheric model product the model results are compared with extensive in situ and remotely sensed data and the model is found to provide a realistic representation of flows both over the shelf and in the broader octz simulation of coastal sea level and shelf currents over the complex topography of the central oregon coast is improved quantitatively relative to previous regional models a particularly significant qualitative improvement is realistic representation of coastal jet separation and eddy formation offshore of cape blanco three dimensional lagrangian analysis of water parcel displacement shows that the surface waters inshore of the separated jet are upwelled from near the bottom along the shelf as far north as 45 5 n a large eddy which incorporates some of this upwelled water and carries it farther westward forms offshore in the late summer ensemble simulations show a distinction between the strongly deterministic response to wind forcing over the shelf and the more unstable less predictable jet separation and offshore eddy formation processes in the region near cape blanco

a regional model of the semidiurnal internal tide on the australian north west shelf a fully three dimensional nonlinear primitive equation model is applied to a study of the semidiurnal internal tide on the australian north west shelf a region of strong barotropic and baroclinic tide the model shows a significant internal tide over most of the continental slope region predominantly between 100 and 1000 m depths energy flux is highly variable with regions of onshore flux and regions of offshore flux corresponding to regions of subcritical and supercritical seabed slopes a comparison between the model and detailed observations from one region shows reasonable agreement in vertical displacement currents and depth integrated energy flux the comparison also highlights the difficulty in obtaining appropriate observations to provide a rigorous verification of internal tide models the m2 and s2 internal tides show similar patterns of flow with energy in the s2 internal tide about 25 of that in the m2 constituent estimates of the total baroclinic m2 energy are about 2 2 gw for the north west shelf nearly an order of magnitude larger than suggested by earlier studies this represents about 5 of the dissipation of the m2 barotropic tide in the model domain the seasonal variability in the baroclinic energy flux is about 20 from the mean the baroclinic energy extracted from the tide is expected to make a significant contribution to mixing in the region

gld100 the near global lunar 100 m raster dtm from lroc wac stereo image data 1 we derived near global lunar topography from stereo image data acquired by the wide angle camera wac of the lunar reconnaissance orbiter camera lroc system from polar orbit tracks the lroc wac provides image data with a mean ground resolution at nadir of 75 m pixel with substantial cross track stereo overlap wac stereo images from the one year nominal mission and the first months of the science mission phase are combined to produce a near global digital terrain model dtm with a pixel spacing of 100 m the global lunar dtm 100 m or gld100 it covers 79 s to 79 n latitudes 98 2 of the entire lunar surface we compare the gld100 with results from previous stereo and altimetry based products particularly with the lunar orbiter laser altimeter lola altimetry which is the current topographic reference for the moon we describe typical characteristics of the gld100 and based upon the comparison to the lola data set assess its vertical and lateral resolution and accuracy we conclude that the introduced first version of the stereo based gld100 is a valuable topographic representation of the lunar surface complementary to the lola altimetry data set further improvements can be expected from continuative investigations

energetics of barotropic and baroclinic tides in the monterey bay area abstracta detailed energy analysis of the barotropic and baroclinic m2 tides in the monterey bay area is performed the authors first derive a theoretical framework for analyzing internal tide energetics based on the complete form of the barotropic and baroclinic energy equations which include the full nonlinear and nonhydrostatic energy flux contributions as well as an improved evaluation of the available potential energy this approach is implemented in the stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans results from three dimensional high resolution suntans simulations are analyzed to estimate the tidal energy partitioning among generation radiation and dissipation a 200 km 230 km domain including all typical topographic features in this region is used to represent the monterey bay area of the 152 mw energy lost from the barotropic tide approximately 133 mw 88 is converted into baroclinic energy through internal tide generation and 42 56

combined effects of wind driven upwelling and internal tide on the continental shelf abstract internal tides on the continental shelf can be intermittent as a result of changing hydrographic conditions associated with wind driven upwelling in turn the internal tide can affect transports associated with upwelling to study these processes simulations in an idealized alongshore uniform setup are performed utilizing the hydrostatic regional ocean modeling system roms with conditions corresponding as closely as possible to the central oregon shelf wind only wo tide only to and tide and wind tw solutions are compared utilizing cases with constant upwelling favorable wind stress as well as with time variable observed stress the tide is forced by applying cross shore barotropic flow at the offshore boundary with intensity sufficient to generate an internal tide with horizontal velocity amplitudes near 0 15 m s 1 corresponding to observed levels the internal tide affects the subinertial circulation mostly through the changes in the bottom boundary layer variability re

modeling bottom mixed layer variability on the mid oregon shelf during summer upwelling abstract results from a model of wind driven circulation are analyzed to study spatial and temporal variability in the bottom mixed layer bml on the mid oregon shelf in summer 2001 the model assimilates acoustic doppler profiler velocities from two cross shore lines of moorings 90 km apart to provide improved accuracy of near bottom velocities and turbulence variables in the area between the mooring lines model results suggest that the response of the bml thickness to upwelling and downwelling favorable winds differs qualitatively between an area of simple bathymetric slope at 45 n and a wider shelf area east of stonewall bank 44 5 n at 45 n the bml grows in response to downwelling favorable conditions in agreement with known theories east of stonewall bank the bml thickness is increased following upwelling events in this area the southward upwelling jet detaches from the coast and flows over a wider part of the oregon shelf creating conditions for ekman pumping near the bottom based on

crater degradation on the lunar maria topographic diffusion and the rate of erosion on the moon landscape evolution on the moon is dominated by impact cratering in the post maria period in this study we mapped 800 m to 5 km diameter craters on 30 of the lunar maria and extracted their topographic profiles from digital terrain models created using the kaguya terrain camera we then characterized the degradation of these craters using a topographic diffusion model because craters have a well understood initial morphometry these data provide insight into erosion on the moon and the topographic diffusivity of the lunar surface as a function of time the average diffusivity we calculate over the past 3 ga is 5 5 m2 myr with this diffusivity after 3 ga a 1 km diameter crater is reduced to approximately 52 of its initial depth and a 300 m diameter crater is reduced to only 7 of its initial depth and craters smaller than 200 300 m are degraded beyond recognition our results also allow estimation of the age of individual craters on the basis of their degradation state provide a constraint on the age of mare units and enable modeling of how lunar terrain evolves as a function of its topography

internal tides and mixing in a submarine canyon with time varying stratification abstractthe time variability of the energetics and turbulent dissipation of internal tides in the upper monterey submarine canyon msc is examined with three moored profilers and five adcp moorings spanning february april 2009 highly resolved time series of velocity energy and energy flux are all dominated by the semidiurnal internal tide and show pronounced spring neap cycles however the onset of springtime upwelling winds significantly alters the stratification during the record causing the thermocline depth to shoal from about 100 to 40 m the time variable stratification must be accounted for because it significantly affects the energy energy flux the vertical modal structures and the energy distribution among the modes the internal tide changes from a partly horizontally standing wave to a more freely propagating wave when the thermocline shoals suggesting more reflection from up canyon early in the observational record turbulence computed from thorpe scales is greatest in the bottom 5

development of magnesian carbonates in quaternary soils on the island of hawaii abstract pedogenic carbonate minerals have progressively developed on basalt in a quaternary weathering chronosequence 5 350 ka on the island of hawaii the sites were isolated from direct contact with seawater or the water table and were minimally influenced by eolian input throughout their history the carbonates consist chiefly of high magnesium calcite hmc and well ordered stoichiometric dolomite pedogenic development of such minerals is rare and the conditions of their formation bear on interpretations of paleosols and the development of sedimentary magnesian carbonates 87sr 86sr ratios of chronosequence carbonates range from 0 7038 to 0 7048 the data indicate that 75 of the strontium was derived from the weathering of volcanic parent material even in the oldest soils where few primary minerals are available to provide ca and mg this is in contrast to continental calcretes which are commonly dominated by atmospheric inputs and are generally composed of low mg calcite lmc stable isotope data are consistent with carbonate precipitation from soil waters in an arid environment the magnesium content of the carbonate increases with substrate age and textural and mineralogical changes suggest direct precipitation of dolomite as well as dolomitization of early formed lmc and hmc opal was detected in young 5 10 ka samples and gibbsite is present in older samples indicating a shift from silica dominated to aluminum dominated soil solution high concentrations of dissolved silica and aluminum during early weathering likely precluded formation of mg rich secondary clay minerals such as smectite or palygorskite weathering of basalt with a molar mg ca ratio of 0 8 1 5 and the absence of secondary magnesian silicates can account for elevated soil water mg ca ratios 0 7 1 0 in soils 70 ka that led to magnesian carbonate formation over time the formation of a clay rich soil profile prevented rapid evaporation of soil water possibly facilitating crystallization of stoichiometric dolomite

global observations of open ocean mode 1 m2internal tides abstracta global map of open ocean mode 1 m2 internal tides is constructed using sea surface height ssh measurements from multiple satellite altimeters during 1992 2012 representing a 20 yr coherent internal tide field a two dimensional plane wave fit method is employed to 1 suppress mesoscale contamination by extracting internal tides with both spatial and temporal coherence and 2 separately resolve multiple internal tidal waves global maps of amplitude phase energy and flux of mode 1 m2 internal tides are presented the m2 internal tides are mainly generated over topographic features including continental slopes midocean ridges and seamounts internal tidal beams of 100 300 km width are observed to propagate hundreds to thousands of kilometers multiwave interference of some degree is widespread because of the m2 internal tide s numerous generation sites and long range propagation the m2 internal tide propagates across the critical latitudes for parametric subharmonic instability 28 8 s n

on the evolution of dolomite stoichiometry and cation order during high temperature synthesis experiments an alternative model for the geochemical evolution of natural dolomites abstract data collected from a series of high temperature dolomitization experiments in which dolomite replaces calcite in mg ca cl solutions indicate that dolomite composition mol mgco 3 and cation order evolve independently as a function of reaction progress despite a wide range of initial solution mg ca 0 43 1 50 the first product to form in all experiments is disordered dolomite both the rate of replacement and the composition of these dolomite products are strongly dependent on the initial mg ca in solution experimental solutions with lower mg ca yield less stoichiometric more ca rich dolomite and have reactions that progress at a slower rate conversely solutions with higher mg ca yield more stoichiometric dolomite and are characterized by faster overall reaction rates in all experiments dolomite composition remains constant during most of the reaction despite a solution chemistry that continually evolves to lower mg ca as magnesium is captured from solution by growing dolomite and calcium is liberated from calcite into solution despite a dolomite composition that remains relatively constant the degree of cation order increases with the percentage of dolomite shortly before complete consumption of calcite reactants when 95 of the calcite reactants have been replaced by dolomite products dolomite composition rapidly becomes more stoichiometric after all calcite reactants have been consumed dolomite is completely stoichiometric regardless of the mg ca in solution at the onset of experimental conditions however the degree of cation order in the stoichiometric dolomite products continues to increase with time in dolomitizing solutions the observation that dolomite composition remains constant throughout most of the dolomitization reaction is different than data from some previous studies this suggests that the mechanism by which dolomite replaces caco 3 is not clear and is more complex than previously recognized the data presented here suggest that the initial dolomite phase provides a compositional template for future dolomite growth thus new material being added to the crystal surface is forced to follow the established composition the data presented here support an alternative model for the commonly observed field relationship between the percent dolomite in a carbonate rock and the stoichiometry of that dolomite we propose that dolomite does not evolve toward more stoichiometric compositions simply because the percent dolomite in the rock increases i e indicating further reaction progress rather carbonate rocks with a higher dolomite to limestone ratio where the dolomite is more stoichiometric can be better explained as having been dolomitized in solutions with higher mg ca which cause both faster rates of dolomitization and more stoichiometric compositions this model explains field observations from evaporative reflux settings that show spatial variations in dolomite composition and crystal texture as the result of chemical evolution of interstitial pore fluids along a flow path the new model may also provide a new framework for investigating the chemical evolution of dolomite in reactive transport models which numerically track chemical reactions and constituents

global mapping and analysis of lunar wrinkle ridges lunar wrinkle ridges were globally mapped and the morphological parameters including length width elevation offset and orientation were also calculated the results include the identification of 2839 segments with a total length of 25 560 69km and the mean width height elevation offset and orientation of all the wrinkle ridges are 3 70km 0 31km 46 37m and 1 99 degrees respectively after weighted by the length based on their morphologies and distribution lunar wrinkle ridges were classified into three categories concentric parallel and isolated ridges and most of the wrinkle ridges are distributed over basalts although a few extend to nearby highlands the relations between the morphological parameters were further quantitatively analyzed and a similar linear correlation between the width and height was found in each class of lunar ridges implying that small and large ridges were formed as a continuum and that the three classes of ridges were probably formed by some common processes finally the relations between the lunar wrinkle ridges and other geomorphic phenomena were analyzed indicating that purely volcanic origin or buried premare structures are difficult to reconcile with the investigation in addition the consistency between the occurrence of the lunar wrinkle ridges and the some thickness of lunar maria indicates that the formation of lunar wrinkle ridges is closely related to the lunar maria however the statistical nw or ne orientation of each class of lunar wrinkle ridges also suggests a suitable global stress field involved in their formation process

mineralogy nucleation and growth of dolomite in the laboratory and sedimentary environment a review dolomite camg co3 2 forms in numerous geological settings usually as a diagenetic replacement of limestone and is an important component of petroleum reservoir rocks rocks hosting base metal deposits and fresh water aquifers dolomite is a rhombohedral carbonate with a structure consisting of an ordered arrangement of alternating layers of ca2 and mg2 cations interspersed with co32 anion layers normal to the c axis dolomite has r3 symmetry lower than the caco3 r3 c symmetry of calcite primarily due to ca mg ordering high magnesium calcite also has r3 c symmetry and differs from dolomite in that ca2 and mg2 ions are not ordered high magnesium calcite with near dolomite stoichiometry 50 mol mgco3 has been observed both in nature and in laboratory products and is referred to in the literature as protodolomite or very high magnesium calcite many dolomites display some degree of cation disorder ca2 on mg2 sites and vice versa which is detectable using transmission electron microscopy and x ray diffractometry laboratory syntheses at high temperature and pressure as well as studies of natural dolomites show that factors affecting dolomite ordering stoichiometry nucleation and growth include temperature alkalinity ph concentration of mg and ca mg to ca ratio fluid to rock ratio mineralogy of the carbonate being replaced and surface area available for nucleation in spite of numerous attempts dolomite has not been synthesized in the laboratory under near surface conditions examination of published x ray diffraction data demonstrates that assertions of dolomite synthesis in the laboratory under near ambient conditions by microbial mediation are unsubstantiated these laboratory products show no evidence of cation ordering and appear to be very high magnesium calcite elevated temperature and elevated pressure experiments demonstrate that dolomite nucleation and growth always are preceded by very high magnesium calcite formation it remains to be demonstrated whether microbial mediated growth of very high magnesium calcite in nature provides a precursor to dolomite nucleation and growth analogous to reaction paths in high temperature experiments

wind relaxation and a coastal buoyant plume north of pt conception ca observations simulations and scalings in upwelling regions wind relaxations lead to poleward propagating warm water plumes that are important to coastal ecosystems the coastal ocean response to wind relaxation around pt conception ca is simulated with a regional ocean model roms forced by realistic surface and lateral boundary conditions including tidal processes the model reproduces well the statistics of observed subtidal water column temperature and velocity at both outer and inner shelf mooring locations throughout the study a poleward propagating plume of southern california bight water that increases shelf water temperatures by 5 c is also reproduced modeled plume propagation speed spatial scales and flow structure are consistent with a theoretical scaling for coastal buoyant plumes with both surface trapped and slope controlled dynamics plume momentum balances are distinct between the offshore 30 m depth region where the plume is surface trapped and onshore of the 30 m isobath within 5 km from shore where the plume water mass extends to the bottom and is slope controlled in the onshore region bottom stress is important in the alongshore momentum equation and generates vertical vorticity that is an order of magnitude larger than the vorticity in the plume core numerical experiments without tidal forcing show that modeled surface temperatures are biased 0 5 c high potentially affecting plume propagation distance and persistence

tidal currents on the central oregon shelf models data and assimilation 1 measurements of tidal currents on the central oregon shelf are available from several sources including recent high frequency hf coastal radar and acoustic doppler profiler adp deployments and historical current moorings in this paper we use a generalized inverse gi approach to compare these data to and then assimilate them into numerical models for the barotropic tides harmonic analysis of the data in short time windows using a modified admittance approach reveals that tidal currents on the oregon shelf are highly variable in time and can contain significant baroclinic components data from the winter months when waters on the shelf are only weakly stratified are found to be most nearly barotropic and thus most reasonable for assimilation into the shallow water equations model the various data sources are used in several different combinations for assimilation and validation forcing the prior forward model with normal flow open boundary conditions obtained from a regional barotropic inverse model results in semidiurnal barotropic currents that are consistent within estimated error limits with all available data in contrast diurnal currents on the shelf are very sensitive to details of the model configuration and are significantly improved by data assimilation very similar solutions result from assimilation of either the hf radar or adp data sets the high sensitivity of the diurnal band currents can be understood dynamically in terms of trapped shelf waves a short 85 km long section of shelf off the central oregon coast is wide enough to allow first mode barotropic shelf waves at the subinertial diurnal frequencies this results in locally resonant large amplitude diurnal tidal currents that are very sensitive to details in the local forcing and hence quite variable in time

a relationship between d104 value and composition in the calcite disordered dolomite solid solution series x ray diffraction has been widely used in analyzing ca mg carbonates compositions of biogenic and inorganic ca mg co3 crystals are often calculated by comparing their d 104 values with published empirical curves however previous studies suggested that these curves do not apply to very high mg calcite and disordered dolomite based on synthesized high mg calcite and disordered dolomite a new empirical curve between values of magnesian calcite d 104 and mgco3 content in the calcite disordered dolomite solid solution series is constructed this new curve is consistent with the significant cell parameter changes accompanying the mg ca cation disorder in dolomite and it can help the characterization of the mgco3 content of both natural and synthetic magnesian calcite and disordered dolomite especially for the mineral mixtures that are not suitable for other analysis methods

powder x ray diffraction analysis of homogeneous and heterogeneous sedimentary dolostones abstract the ca molar ca ca mg 100 in sedimentary dolomite which ranges from 48 ca to 62 5 ca can be determined by atomic absorption spectrometry electron microprobe analysis or powder x ray diffraction analysis the latter procedure which relies on the fact that the position of the d104 reflection depends linearly on the ca content offers an easy and relatively inexpensive method of determining ca in dolomite to date such analyses have assumed that the dolostone is homogeneous with respect to the ca content of its constituent dolomite crystals herein the xrd technique is extended to compositionally heterogeneous dolostones a considerable amount of important information can be derived from x ray diffractograms of dolostones if they are analyzed with peak fitting techniques pf xrd specifically this technique allows 1 determination of the ca with an accuracy of 0 5 ca 2 identification of heterogeneous dolostone samples formed of more than one population of dolomite crystals as defined by their ca content and 3 derivation of the proportion of each population of dolomite crystals with an accuracy of 10 the pf xrd technique is a powerful analytical tool that provides valuable information on the major element composition of low fe dolomite compared to other techniques the pf xrd technique is accurate rapid relatively inexpensive and easy to use

beginning and end of lunar mare volcanism mare volcanism on the moon is commonly attributed to an important but relatively short lived epoch of internal heating after 3 900 myr bp but before about 2 500 myr bp refs 1 2 although some studies suggested that mare volcanism had started earlier3 5 than times indicated by dated lunar samples only recently have photogeological spectral and geochemical data6 8 documented the importance of a pre 4 000 myr bp epoch similarly early earth based geological mapping revealed a bright rayed crater lichtenberg superposed by mare units9 thereby indicating that mare volcanism must have extended to times significantly more recent than 3 100 myr bp lunar orbital photography confirmed this inferred strati graphical relationship10 but crater statistics indicated that the youngest units were at least twice the age of copernicus or between 1 700 and 2 000 myr bp refs 11 13 we present here the inferred distribution and style of the early phases of mare volcanism based on current evidence and conclude that certain regions of the moon underwent two distinct pulses of igneous activity we then examine crater statistics for the post lichtenberg mare unit and other selected units and conclude that mare volcanism extended to a time comparable with that of the copernicus impact or 1 myr bp these reassessments of the oldest and youngest maria provide new constraints on geophysical models of the internal thermal history of the moon

the role of bacterial sulfate reduction during dolomite precipitation implications from upper jurassic platform carbonates the early diagenetic formation of dolomite in modern aquatic environments is limited mostly to evaporitic and marine anoxic organic rich sediments dominated by bacterial sulfate reduction bsr in such environments bacterial activity lowers the energy barriers for the nucleation and growth of dolomite and thus promotes the formation of non stoichiometric highly disordered and metastable proto dolomite although the boundary conditions for the formation of modern proto dolomites are considered to be generally understood the role of bsr during limestone dolomitization in ancient marine environments remains questionable herein we present a study about the physicochemical conditions and processes which led to the formation of partly dolomitized limestone and dolostone in the presence of bsr on a stable carbonate platform during the upper jurassic at oker northern german basin the dolomite textures the spatial trace elemental patterns of the dolomite and of the surrounding limestone and the results of 18o and 13c isotope analyses reveal that the oker dolomite has been formed by the early diagenetic replacement of magnesian calcite precursors at temperatures between 26 c and 37 c we interpret the mineralizing fluids responsible for dolomitization as pristine marine to slightly evaporitic and reducing seawater being modified during shallow seepage reflux and or evaporitic tidal pumping the elevated 34scas values 17 9 to 19 7 v cdt of the oker dolomite compared to ambient upper jurassic seawater indicate that bsr facilitated dolomite formation for the first time we show that a linear anti correlation exists between decreasing carbonate associated sulfate cas contents in dolomite and increasing ordering ratio of the dolomite lattice structure with the degree of cation order in dolomite to be given by degree of cation order dol 0 018 cas dol 68 3 r2 0 98 this correlation implies that the cas content of sedimentary dolomite can be used as a measure for dolomite maturity the relationships between the ambient paleo environmental controls the resultant dolomitization pathways and subsequently the structure and the composition of the precipitating dolomite are presented and discussed in relation to the stability of modern and ancient proto dolomites throughout burial diagenesis

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

circulation in the eastern bering sea inferences from a 2 km resolution model abstract a 2 km resolution model of the eastern bering sea is developed to capture dynamical processes on the scale of the rossby radius of deformation on tidal to seasonal time scales the model spans the region from 178 e to the alaskan coast and from roughly 50 to 66 n including the aleutian islands in the south and the bering strait in the north the high resolution throughout ensures that the mesoscale dynamics of significant subregions of the domain such as the aleutian island passes bering sea slope and the shelf canyons are captured simultaneously without the concern for loss of interconnectivity between regions simulations are performed for the ice free season june october of 2009 with tidal and atmospheric forcing the model compares favorably with observations from avhrr and envisat satellites argo drifters and bering sea shelf moorings the mesoscale dynamics of the mixing and exchange flow through the eastern aleutian island passes which exhibit strong diurnal and two week variability are well represented the two week oscillation in volume flux through the largest of these passes amukta pass is found to be out of phase with the transport through the neighboring passes e g seguam and samalga passes mesoscale structure is also found to be ubiquitous along the mixing front of the cold pool structures at the scale of o 20 km persist and play a role in determining the pattern of erosion of the water mass as the shelf warms and mixes on the bering sea shelf tidal motions are dominant and variability on the horizontal scale of the first mode internal tide develops o 30 km from the shelf break to the onshore edge of the bering shelf cold pool

deep burial diagenesis its implications for vertical movements of the crust uplift of the lithosphere and isostatic unroofing a review abstract various techniques of study of strata exposed at the surface in undeformed areas of the appalachian basin and ozark done imply that these strata have been heated to temperatures that suggest a former great depth of burial the data reveal that the strata have been much more deeply buried than previously thought if such former deep burial has taken place then subsequent uplift and erosion must also have taken place to bring these formerly deeply buried strata to the present land surface unexpectedly large amounts of uplift and erosion ranging from 4 3 to 7 km have re exposed these formerly deeply buried rocks this leads to the surprising conclusion that isostatic unroofing has stripped off thick sections of strata whose presence was previously unsuspected therefore the lithosphere in its isostatic unroofing of thick sequences of sedimentary strata has undergone much larger vertical motions than many geologists had previously estimated case histories in this review include strata of the silurian of the northern appalachian basin and of the ordovician of the ozark dome which reached interpreted maximum burial depths of 5 and 4 3 km respectively devonian strata in the catskill mountains of new york imply a former depth of burial of 6 5 km lower ordovician carbonate sequences of the northern appalachian basin imply a depth of burial in excess of 7 km middle ordovician strata from the same basin signify a depth of burial of approximately 5 km and devonian strata a paleodepth of 4 5 5 km such former great depths of burial of undeformed strata which are now exposed at the surface reflect large scale vertical movements of the crust and uplift of the lithosphere these drastic changes represent isostatic unroofing with widespread implications for paleogeography of a kind unrecognized at present

microarchitecture of dolomite crystals as revealed by subtle variations in solubility implications for dolomitization abstract despite their small size most dolomite crystals in the dolostones of the miocene cayman formation on grand cayman are zoned with a core formed of high calcium calcian dolomite hcd encased by a cortex formed of low calcium calcian dolomite lcd these two different types of dolomite are separated by a sharp well defined cortical boundary acid etching shows that the hcd cores are characterized by numerous growth defects including twinning modulations and dissolution slots whereas the lcd that forms the cortex contains far fewer and less well developed growth defects the fact that the hcd is far more soluble than the lcd is attributed to its higher caco 3 content and greater density of growth defects the cortical boundary that separates the hcd core from the lcd cortex is a discontinuity that may have developed as a response to a change in diagenetic regimes or a change in the composition of the dolomitizing fluids deciding between these two possibilities however is difficult because the small size of the crystals precludes collection of data needed to resolve the issue irrespective of the underlying cause the development of the zoning is critical from a diagenetic perspective because the hcd with its high caco 3 content and high density of growth defects is far more prone to dissolution than the lcd cortex thus zoned crystals of this type are highly susceptible to diagenetic modifications that will lead to the development of hollow crystals dedolomite or inside out dolomite

textural and isotopic evidence for ca mg carbonate pedogenesis abstract models for evaluating the terrestrial carbon cycle must take into account not only soil organic carbon represented by a mixture of plant and animal remains but also soil inorganic carbon contained in minerals mainly in calcite and dolomite thick soil caliches derived from weathering of mafic and ultramafic rocks must be considered as sinks for carbon storage in soils the formation of calcite and dolomite from pedogenic alteration of volcanic tephras under an aridic moisture regime is studied in an unusually thick 3 m soil profile on gran canaria island canary islands spain the biological activity of the pedogenic environment soil respiration releases co2 incorporated as dissolved inorganic carbon dic in waters it drives the formation of low magnesian calcite and calcian dolomite over basaltic substrates with a 13c negative signature 8 to 6 vs v pdb precipitation of authigenic carbonates in the soil is accompanied by the formation of mg rich clay minerals and quartz after the weathering of basalts mineralogical textural compositional and isotopic variations throughout the soil profile studied indicate that dolomite formed at greater depths and earlier than the calcite the isotopic signatures of the surficial calcite and deeper dolomite crusts are primary and resulted from the dissolution precipitation cycles that led to the formation of both types of caliches under different physicochemical conditions dolomite formed within a clay rich matrix through diffusive transport of reactants it is precipitated from water with more negative 18o values 1 5 to 3 5 vs v smow in the subsoil compared to those of water in equilibrium with surficial calcite thus calcite precipitated after dolomite and directly from percolating solutions in equilibrium with vadose water enriched in 18o 0 5 to 1 5 due to the evaporation processes the accumulation of inorganic carbon reaches 586 1 kg m 2 in the soil studied which means that the carbon sequestration capacity of mafic rocks must be taken into account for certain terrestrial settings dolomite together with calcite should be assessed when quantifying carbon stored in arid semiarid soils as a result of the natural weathering processes

isotopic evidence for dolomite formation in soils abstract dolomite formation in soils constitute a particular challenge because of 1 scant magnesium content in continental environments as opposed to the marine medium 2 the kinetic problem related to the incorporation of magnesium into the carbonate and 3 the unknown role of soil dolomites in the global carbon cycle pedogenic dolomite formed at deeper soil levels subsoil before the development of petrocalcic horizon barriers was investigated in a semiarid region of se spain guadix baza basin mineralogical characterization textural relationships and isotopic data concerning soil dolomite together with the results of a precipitation experiment provided fuller knowledge of the processes and conditions governing neoformation of dolomite in these soils in the study case dolomite enrichment occurs beyond the limit of major biological activity which coincides with the rooting depth of native perennial plants in the semiarid soils studied textural studies reveal the corrosion of inherited dolomite crystals in the upper soil horizons and the formation of dolomite in depth in relation to a clayey material composed mainly of smectites stable isotope distribution in dolomites throughout the profiles indicates a fractionation with depth this is explained by the formation of dolomites after the dissolution of the pedogenic calcite the calcite detected in the subsoil is interpreted here as a precursor of the neoformed dolomites that transport the isotopic signal associated with biological activity of soils to deeper layers dolomite formation appears to be favoured by the presence of clay minerals in the precipitation media clays retain water during evapotranspiration stages which drastically change the transport properties of the media and promote the incorporation of mg into the structure of the neoformed ca mg carbonate as confirmed by laboratory experiments diffusion controlled crystal growth processes lead to the formation a precursory protodolomite with disordered ca mg distribution from a fluid locally supersaturated in dolomite

study of an ordovician carbonate with alternating dolomite calcite laminations and its implication for catalytic effects of microbes on the formation of sedimentary dolomite

recent extensional tectonics on the moon revealed by the lunar reconnaissance orbiter camera on the moon extensional tectonic features have only been observed close to the influence of the mare basalt filled basins and floor fractured craters analysis of lunar reconnaissance orbiter camera images reveals several potentially very young extensional tectonic features in the farside highlands implying that extensional stresses may locally exceed compressional ones

sar observing large scale nonlinear internal waves in the white sea abstract the compiled archive of synthetic aperture radar sar images acquired by the advanced sar asar onboard the envisat satellite over the white sea during the extended summer periods may september between 2007 and 2011 provides the first detailed analysis of 2 d patterns of internal waves iws in the white sea unambiguously the primary region of iw activity is the southwestern sw gorlo strait gs iw packets emerging from this area are regularly observed to reach crest lengths up to 200 km and also to propagate a few hundred kilometers from their origin model results confirm that large scale iws can be generated every tidal cycle and are able to cross the entire sea as suggested the source of these packets is governed by the intense dynamics of the frontal zone in the tidal cycle over local complex bottom as further revealed these large scale iws cascade into intense large amplitude short iw packets on the shoaling white sea shelf significantly impacting vertical turbulent exchange and the overall hydrology

the influence of disordered non equilibrium dolomites on the mg solubility in calcite in the system caco 3 mgco 3 the influence of different degrees of disorder of dolomites on the solubility of mgco3 in calcite has been studied under isothermal and isobaric conditions at 900 c 4kb and 1000 c 5 and 7kb x mgco 3 calcite varied smoothly as function of the particular structural and cationic disorder of coexisting dolomite higher degrees of disorder of dolomite estimated by the d 00 6 d 11 0 values and the peak height ratio i 01 5 i00 6 lead to greater solubility of mgco3 in calcite the run time for all experiments was 96 h much longer than in previous work the influence of disorder of dolomite on x mgco 3 calcite appears to be larger than that of temperature as shown by the large range of x mgco 3 calcite 0 12 0 30 in calcite at 900 c 4 kb found in this study the state of order of dolomite seems to control the solubility limits in this system and may explain discrepancies found in previous experimental work

enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet to vertical aspect ratios of 10 2 to 10 3 median value 300 these patches are clearly defined by regions of low richardson number and occur where and when the linear superposition of the three dominant shear constituents near inertial m2 and thermal wind interferes constructively this is most pronounced at the base of the coastal jet where the thermal wind shear is largest while the effect of the turbulence stress divergence on the jet is small compared to geostrophy 1 it is significant in the second order force balance governing secondary circulation the timescale associated with the decay of the thermal wind shear via turbulence stress is o 10 days we confirm that the vertical salt flux due to mixing is comparable to the net ekman transport of salt onto the shelf within the bottom boundary layer because numerical models of coastal circulation lack turbulence in midwater column any vertical transport of scalars including salt and heat must be achieved inshore of the 40 m isobath this is inconsistent with the observations presented in this study in which significant vertical turbulent salt transport is found to exist across the entire shelf

recrystallization of dolomite evidence from the monterey formation miocene california dolomites from the upper calcareous siliceous member of the miocene monterey formation exposed west of santa barbara california were analysed for geochemical isotopic and crystallographic variation the data clearly document the progressive recrystallization of dolomite during burial diagenesis in marine pore fluids recrystallization is recognized by the following compositional and crystallographic variations dolomites have decreasing 18o and 13c compositions decreasing sr contents and increasing mg contents with increasing burial depths and temperatures from east to west in the study area 18o values vary from 5 3 in the east to 5 5 pdb in the west and are interpreted to reflect the greater extent and higher temperature of dolomite recrystallization in the west 13c values correlate with 18o and decrease from 13 6 in the east to 8 7 pdb in the west sr concentrations correlate positively with 18o values and decrease from a mean of 750 ppm in the east to a mean of 250 ppm in the west mol mgco3 values inversely correlate with 18o values and increase from a minimum of 41 0 in the east to a maximum of 51 4 in the west rietveld refinements of powder x ray diffraction data indicate that the more recrystallized dolomites have more contracted unit cells and increased cation ordering the fraction of the ca sites in the dolomites that are occupied by ca atoms increases slightly with the approach to stoichiometry the fraction of the mg sites occupied by mg atoms strongly correlates with mol mgco3 even in early diagenetic non stoichiometric dolomites there is little substitution of mg in ca sites during recrystallization the amount of mg substituting for ca in ca sites decreases even further most of the disorder in the least recrystallized non stoichiometric dolomites is related to substitution of excess ca on mg sites

a model study of internal tides in coastal frontal zone abstract internal tides near a midlatitude shelf slope front are studied using an idealized numerical model with emphasis on their structure energetics and mixing effects it is found that the properties of internal tides are highly dependent on frontal configuration and tidal frequency at a winter front energetic internal tides are generated and arrested in the frontal zone the cross shelf flow tends to be surface bottom intensified by a large internal circulation cell at the diurnal semidiurnal frequency at a summer front the diurnal internal tide is still trapped but a semidiurnal internal tide propagates out of the frontal zone in the offshore direction while arrested at the inshore boundary the presence of the shelf slope front enhances the generation of internal tides and it also causes an amplification of the semidiurnal internal tide by trapping its energy in the frontal zone this amplification is most prominent at the offshore boundary of the winter front and the inshore boundary

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

semidiurnal baroclinic tides on the central oregon inner shelf abstractsemidiurnal velocity and density oscillations are examined over the mid and inner continental shelf near heceta bank on the oregon coast measurements from two long term observation networks with sites on and off the submarine bank reveal that both baroclinic velocities and displacements are dominated by the first mode with larger velocities on the midshelf and northern parts of the bank midshelf sites have current ellipses that are near the theoretical value for single progressive internal tidal waves compared to more linearly polarized currents over the inner shelf baroclinic current variability is not correlated to the spring neap cycle and is uncorrelated between mooring locations an idealized model of two internal waves propagating from different directions reproduces some of the observed variability in semidiurnal ellipse parameters at times the phasing between moorings along a cross shelf transect are consistent with onshelf wave propagation a characteristic also present in the out

energetics of calcium rich dolomite abstract the enthalpy of formation of sedimentary ca rich dolomite has been determined by oxide melt calorimetry the results show that ca rich dolomite is energetically different from well ordered stoichiometric dolomite the enthalpy of formation from calcite and magnesite becomes strongly more endothermic with increasing excess ca content this supports the idea that the substitution of ca in the mg layer of dolomite is energetically unfavorable ca rich dolomite is unstable relative to well ordered stoichiometric dolomite and calcite the enthalpy behavior for excess ca substitution in dolomite is different from that of mg substitution in calcite the enthalpy change is much larger in magnitude in dolomite and is more strongly dependent on composition differences in cation order as well as the presence of a modulated structure and low symmetry domains in ca rich dolomite cannot be discerned from the enthalpy data the findings confirm that the growth and occurrence of ca rich dolomite in sedimentary environments must be attributed to kinetic factors rather than to equilibrium

the aftermath of the carnian carbonate platform demise a basinal perspective dolomites southern alps in the dolomites of northernmost italy the carbonate platform growth came to a standstill late in the early carnian late triassic the response to this shutdown of shallow water carbonate production in the interplatform basins is largely unknown because erosion has removed most of the soft basinal sediments giving rise to today s scenic landscape of the dolomites mapping in the central part of the dolomites and newly available core material has recently revealed a wellpreserved succession of basinal rocks within the heiligkreuz hospiz basin ital ospizio di santa croce basin in this paper the regional depositional nature of arrested carbonate platform production is reconstructed by tracing its sedimentological record across the slope and into the basin the uppermost st cassian formation the time equivalent basinal rocks to the prograding carbonate platforms is overlain by the heiligkreuz formation whose basal succession was deposited in a restricted and oxygen depleted environment immediately post dating the platform demise the succession consists mainly of mudrocks marlstones and peloidal packstones with abundant low diversity ostracod and pelecypod fauna and early diagenetic dolomite c and o isotope values of the basal heiligkreuz formation post dating platform demise average 2 ae4 and 2ae4 respectively and largely overlap the isotopic composition of st cassian carbonates a shift toward slightly lower d 13 c values in the heiligkreuz formation may reflect incorporation of isotopically depleted c released during bacterial sulphate reduction in the heiligkreuz sediments sedimentological palaeobiological and geochemical indices suggest that nearnormal marine conditions persisted long after the shutdown of shallow water carbonate platform growth although there are clear indications of severely reduced oxygen levels in the restricted heiligkreuz hospiz interplatform basin the early carnian platform demise induced a distinct switch in the locus of carbonate production from the shallow water platform and slope to the basin floor and a decrease in the availability of dissolved oxygen in the basinal waters it is inferred that anoxia extended at least temporarily to the top of the carbonate slope as indicated by the onlap of normal marine mounds by dark marlstones of the basal heiligkreuz formation

spatial and temporal variability of the m2 internal tide generation and propagation on the oregon shelf abstracta 1 km horizontal resolution model based on the regional ocean modeling system is implemented along the oregon coast to study average characteristics and intermittency of the m2 internal tide during summer upwelling wind driven and tidally driven flows are simulated in combination using realistic bathymetry atmospheric forcing and boundary conditions the study period is april through august 2002 when mooring velocities are available for comparison modeled subtidal and tidal variability on the shelf are in good quantitative agreement with moored velocity time series observations depth integrated baroclinic tidal energy flux ef its divergence and topographic energy conversion tec from the barotropic to baroclinic tide are computed from high pass filtered harmonically analyzed model results in a series of 16 day time windows model results reveal several hot spots of intensive tec on the slope at these locations tec is well balanced by ef divergence changes in background stratific

groundwater dolocretes from the upper triassic of the paris basin france a case study of an arid continental diagenetic facies thick dolomite cemented horizons dolocretes occur within a fluvial sandstone mudstone sequence of late triassic age in the western part of the paris basin france two types of dolomites can be distinguished a nodular dolomitic beds less than a few metres thick which formed within mottled overbank siltstones and mudstones and b massive dolomite up to 16 m thick which occurs in coarse grained channel sandstones and conglomerates the majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and less commonly dolomicrite glaebules irregular spar filled cracks spheroidal dolomite silicification and vuggy porosity are locally abundant in the massive dolomite in contrast biologically induced micromorphological features such as rhizocretions and alveolar septal fabrics were observed in the thin nodular dolomite beds the dolomite is near stoichiometric well ordered and non ferroan 18o values range from 7 7 to 0 4 o pdb and 18o values range from 5 1 to 1 8 0 pdb and no obvious difference in the stable isotopic composition between both types of dolomites was observed sr isotope ratios range from 0 7101 to 0 7126 and are invariably higher than the contemporary triassic sea water a vadose pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures several features however argue against a pedogenic origin for the massive carbonates most notably the absence of biologically induced structures the occurrence in coarse grained channel and not overbank deposits and the great thickness these units are thus interpreted as groundwater in origin phreatic calcretes of quaternary age widespread in inland australia are regarded as a modern analogue for the triassic paris basin dolocretes petrographic observations argue in favour of primary proto dolomite precipitation although early diagenetic replacement of calcite by proto dolomite cannot be ruled out strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non marine continental origin for the groundwaters the poorly ordered and non stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near stoichiometric well ordered dolomite that clearly lacks evidence for pervasive recrystallization

a modeling study of the three dimensional continental shelf circulation off oregon part ii dynamical analysis abstract sixty day simulations of the subinertial continental shelf circulation off oregon are performed for a hindcast study of summer 1999 in part i the model results are shown to compare favorably with in situ currents and hydrographic measurements obtained from an array of moored instruments and field surveys and high frequency radar derived surface currents in this paper the modeled three dimensional time varying circulation and dynamical balances are analyzed providing a detailed synoptic description of the continental shelf circulation off oregon for summer 1999 the circulation is clearly wind driven and strongly influenced by alongshore variations in shelf topography in the region of the coast where the alongshore topographic variations are small the upwelling circulation is consistent with standard conceptual models for two dimensional across shore circulation in the regions where the alongshore topographic variations are greater the upwelling circulation is highly three dimensional ov