genesis of palimpsest cool water carbonate sediment on the continental margin of southern australia abstract the continental margin of southern australia is a site of extensive quaternary cool water carbonate sedimentation seafloor sediments are a mixture of holocene biofragments and late pleistocene relict and stranded particles relict sediments produced during marine isotope stages 3 and 4 are generally preserved as iron stained intraclasts such grains in the great australian bight are photozoan in character they include symbiont bearing benthic foraminifers and coralline algal particles and indicate that the wide shelves were bathed in shallow relatively warm oligotrophic waters and floored by marine grasses similar to many modern shallow inboard embayments in the region today in contrast east of the great australian bight relict sediments are more heterozoan in character with coralline algal and molluscan facies on the inner shelf and bryozoan sediments on the outer shelf stranded sediments marooned during the sea level rise associated with marine isotope stage 2 are gray to buff in color and composed of both biofragments and intraclasts these particles are mainly heterozoan in character throughout the region with subtropical photozoan marine grassbank facies localized to portions of the inner great australian bight stranded sediments are interpreted to have accumulated in an areally restricted photic zone and upon an overall narrow shelf covered in cool nutrient rich waters swell driven seafloor sediment disturbance to depths of 100 m along the southern australian margin in conjunction with reduced rates of sedimentation that characterize the cool water carbonate realm have resulted in mixing of sediment currently being produced with exhumed relict and stranded sediments generated during previous sea level stands the composition of these deposits and the nature of their pre burial alteration are a function of sea level history late pleistocene relict sediments originally accumulated in low energy inboard environments but were modified in the surf zone during subsequent sea level fluctuations this resulted in the formation of intraclasts abraded infilled and cemented biofragments of local origin the widespread distribution of intraclasts and of composite grain assemblages derived from multiple sedimentary environments that display highly variable degrees of seafloor alteration may be signatures of modern cool water carbonate assemblages worldwide while such palimpsest sediments may complicate paleoenvironmental interpretation their differentiation in the rock record can be utilized to discern subtleties in paleoceanography and sea level history

shallow burial dolomitization and dedolomitization of cenozoic cool water limestones southern australia geochemistry and origin abstract the gambier limestone a bryozoan rich cool water carbonate of late eocene to early miocene age in the otway basin of southeastern australia is about one third variably dolomitized limestone and dolostone individual dolomite crystals range from 10 to 500 m and are of three types 1 silt size crystals 4 64 m diameters having a brightly luminescent core 10 20 m of nearly stoichiometric dolomite with 1 mol mnco3 and sio2 but no fe surrounded by a thin dull or alternating dark and bright cl cortex that is nonstoichiometric with 44 46 mol mgco3 but sharp to diffuse zoning in mn and fe 2 sand size crystals which also have a brightly luminescent and stoichiometric core and dark and bright non stoichiometric thin inner cortex but are mostly a thick outer cortex at ca 50 m diameter that is nonluminescent and nonstoichiometric with some fe but no mn and 3 identical sand size crystals with a variably leached core and inner cortex that is either a void or a void filled with late calcite cement these three crystal populations represent two distinct dolomites and their alteration product the smallest of the silt size crystals which are rarely preserved are also the cores of the larger crystals upon which grew an inner and outer cortex of somewhat different composition the 18o values of dolomite rhombs 1 6 to 2 9 correlate positively with 13c values 0 7 to 3 0 with the lowest values from silt size or small sand size crystals and the highest values from large sand size crystals with leached unfilled cores low and variable 18o and 13c values in conjunction with high and variable mn and fe contents in both the core and inner cortex of all crystals are consistent with formation from a mixture of brackish water and seawater higher values for the outer cortex in sand size crystals are typical of those expected for precipitation from normal or near normal seawater low sr mn and fe contents in the largest crystals in conjunction with fluid inclusions of seawater salinity in the outer cortex are also consistent with the bulk of the large crystals having precipitated from seawater using the sr isotope evolution curve for cenozoic seawater sr isotope ratios of the dolomites can be divided into four distinct groups which correspond to times of major transgressions this cenozoic example in which dolomite petrography and crystal chemistry can be explained in terms of simple transgression regression offers a simple sedimentological explanation for many similar dolomites where processes of formation cannot be so easily constrained

analysis of the spatial coverage of british rainfall fields abstract based on uk radar data the distribution of coverage of an area by rainfall fields is analysed including the influence of spatial and temporal resolution of the data size of the area and topographic and climatic variations the aim is to derive a method allowing the choice of a value of the coverage for example within an atmospheric general circulation model two cases are distinguished that of a coverage which is stationary with respect to the size of the area and that of a varying coverage for areas smaller than a critical size which is generally between 60 km 60 km and 70 km 70 km for the stationary coverage a proposed method consists of the selection based on topography of an average coverage for the given period and the choice of a value of the coverage e from a distribution of mean presenting some dependence on the season and the topography the self similarity of the coverage process for a wide range of area sizes leads to the determination of estimates of the fractal dimension and the examination of the temporal variation of this dimension for the non stationary coverage within the mesoscale and lower mesoscale ranges parabolic curves allow a good approximation to the decrease of coverage with area size

moments of catchment storm area the portion of a catchment covered by a stationary rainstorm is modeled by the common area of two overlapping circles given that rain occurs within the catchment and conditioned by fixed storm and catchment sizes the first two moments of the distribution of the common area are derived from purely geometrical considerations the variance of the wetted fraction is shown to peak when the catchment size is equal to the size of the predominant storm the conditioning on storm size is removed by assuming a probability distribution based upon the observed fractal behavior of cloud and rainstorm areas

influence of climate and dolomite composition on dedolomitization insights from a multi proxy study in the central oman mountains abstract dedolomitization is an important diagenetic process that can yield information on the history of paleo fluids in a given aquifer or outcrop and by extension it offers a window into past hydrologic conditions dedolomitization is also relevant economically as it can alter the porosity and permeability of carbonates thus affecting reservoir quality despite considerable research the process of dedolomitization is still not entirely understood here new findings from the central oman mountains highlight the importance of dolomite chemistry and fluctuating climate on dedolomitization petrographic mineralogical and geochemical data from both altered and pristine dolomite hosted in jurassic carbonate rocks from the sahtan group and outcropping at wadi mistal in the jebel akhdar tectonic window reveal two dolomite bodies with different characteristics stratabound and fault related dolostone the ferroan dolomite crystals are larger in the fault related dolostone whereas the non ferroan dolomite crystals are smaller in the stratabound dolostone petrography reveals a complex suite of alteration textures including pristine dolomite recrystallized dolomite and calcitized dolomite dedolomite iron oxides are present pervasively in the altered rocks and different alteration textures co occur in the same sample relative to unaltered dolomite in this outcrop the recrystallized dolomite is characterized by similar positive carbon isotope values but less negative oxygen isotope values and the calcitized dolomite is characterized by even less negative oxygen isotope values and more negative carbon isotope values based on field data and petrography two phases of alteration are evident an earlier dedolomitization event affecting the stratabound dolomite only and a more pervasive pleistocene holocene alteration phase associated with surface weathering that affected both the fault related dolomite and to a lesser extent the stratabound dolomite stable isotope results further suggest that the more recent subaerial weathering phase happened under two alternating climate regimes dedolomitization was triggered by meteoric fluids that interacted with soil related carbon during humid climatic period s whereas recrystallization of ferroan fault related dolomite happened during more arid climatic period s with less developed soils and lower fluid rock interaction these results suggest that weathering of ferroan fault related dolomite can lead to formation of goethite and recrystallized non stoichiometric dolomite with a reset stable oxygen isotope signature and sometimes to dedolomitization

multistage dolomitization in late jurassic early cretaceous platform carbonates berdiga formation basoba yayla trabzon ne turkey implications of the generation of magmatic arc on dolomitization abstract late jurassic early cretaceous berdiga formation which is widely distributed in an e w trending belt in the eastern pontides ne turkey is composed of platform carbonates the formation shows varying lithofacies changing from supratidal to platform margin reef both laterally and vertically the studied basoba yayla trabzon ne turkey area comprises one of the typical exposures of formation in the northern zone of eastern pontides in this area the lower parts of the formation are pervasively dolomitized by fabric destructive and fabric preserving replacive dolomites that are ca rich and nonstoichiometric ca56 60mg40 44 replacement dolomites rd are represented by 18o values of 15 3 to 4 2 vpdb 13c values of 3 7 1 5 vpdb and 87sr 86sr ratios of 0 70675 0 70731 petrographic and geochemical evidence implies that rd dolomites are formed before compaction at shallow moderate burial depths from late jurassic early cretaceous seawater and or partly modified seawater as a consequence of rock water interaction and they are recrystallized at elevated temperatures during subsequent burial during subsequent late cretaceous diagenetic process when the region became a magmatic arc rd1a and rd3 dolomite were recrystallized by hydrothermal fluids of marine origin the dolomite cements cd overlying the low amplitude stylolites have similar geochemical charasteristics than rd1a and rd3 dolomite and are characterized by high homogenization temperatures th this might indicate that cd dolomite was precipitated from hydrothermal fluids of marine origin that recrystallized the rd1a and rd3 dolomite the fact that cd dolomite comprising the latest phase of dolomitization is overlain by coarsely crystalline mosaic calcite and silica cements may indicate that diagenetic fluids were undersaturated with respect to dolomite and oversaturated with respect to calcite and silica

multiple episodes of dolomitization and dolomite recrystallization during shallow burial in upper jurassic shelf carbonates eastern swabian alb southern germany abstract the upper jurassic of the eastern swabian alb is composed of oolitic platform sands with associated microbe siliceous sponge mounds at the platform margins they are surrounded by argillaceous or calcareous mudstones and marl limestone alternations deposited in adjacent marl basins partial to complete dolomitization is predominantly confined to the mound facies six types of dolomite as well as one type of ankerite document a complex diagenetic history during shallow burial with multiple episodes of dolomite formation and recrystallization the earliest massive matrix dolomitization is ca rich has slightly depleted oxygen isotope values relative to late jurassic seawater and carbon isotopic values in equilibrium with late jurassic seawater this initial massive matrix dolomitization occurred during latest jurassic to earliest cretaceous and is related to pressure dissolution during very shallow burial at temperatures of at least 50 c hydrologic conditions and mass balance calculations indicate that burial compaction provided sufficient fluids for dolomitization mg is derived from negligibly modified seawater that was expelled from the adjacent off reef strata into the mound facies position of the mounds along the platform margins controlled the distribution of the shallow burial dolomite covariant trends between textural modification increasing stoichiometry partial changes in trace element content mn fe sr and depletion in stable isotopes as well as distinctive cl pattern illustrate two recrystallization phases of the precursor matrix dolomite during further burial at elevated temperatures strong sr enrichment of the second phase of recrystallized dolomite is ascribed to sr rich meteoric waters descending from overlying aragonite bearing reef limestones or evaporite bearing peritidal carbonates late stage coarsely crystalline dolomite cements occur as vug and fracture fillings and formed during burial ankerite associated with sulphide and sulphate minerals and saddle dolomite are assumed to have formed from hydrothermal waters that moved to higher stratigraphic levels along fracture conduit systems that developed during late cretaceous to tertiary alpine orogenesis

marine derived dolomite in the shallowly buried temperate port campbell limestone miocene otway basin australia the miocene port campbell limestone in the otway basin port campbell embayment south eastern australia is a shallowly buried 350 m temperate carbonate grainstone which consists primarily of benthonic foraminifera bryozoans brachiopods echinoids and planktonic foraminifera volumetrically insignificant calcite cements include scalenohedral blocky and syntaxial overgrowths dolomite is present in variable amounts 1 25 scattered throughout the unit as euhedral rhombs usually comprising 2 of the whole rock volume the dolomite post dates the calcite cements and is mainly an interparticle cement with crystal size varying between 10 and 150 m mean 50 m under cathodoluminescence the dolomite rhombs have a dull core and a nonluminescent outer rim the dolomite is nonstoichiometric ca rich ca54 62mg38 46 with high trace element concentrations the mn concentrations range from 0 to 310 p p m in the crystal cores mean 140 p p m and 80 240 p p m in the crystal rims mean 140 p p m the fe concentrations increase from the crystal cores range 640 5690 p p m mean 2030 p p m to the crystal rims range 2840 9440 p p m mean 6040 p p m whereas the sr concentrations decrease from the crystal cores range 690 1510 p p m mean 1280 p p m to the crystal rims 620 1240 p p m mean 930 p p m the 13cpdb values of the dolomite range between 2 5 and 2 6 whereas the 18opdb values range from 0 3 to 0 6 this dolomite occurrence supports the idea that marine or near marine dolomite can form not only syndepositionally but also in the shallow subsurface of temperate units soon after sediment deposition under reducing conditions the fine grained low permeability nature of the port campbell limestone contributed to the reducing conditions at shallow depth the high trace element concentrations of the dolomite especially in fe and the near marine composition of the dolomitizing fluids as large volumes of meteoric water were inhibited

area perimeter relation for rain and cloud areas following mandelbrot9s theory of fractals the area perimeter relation is used to investigate the geometry of satellite and radar determined cloud and rain areas between 1 and 1 2 x 106square kilometers the data are well fit by a formula in which the perimeter is given approximately by the square root of the area raised to the power d see equation in the pdf where d is interpreted as the fractal dimension of the perimeter it is concluded that rain and cloud perimeters are fractals they have no characteristic horizontal length scale between 1 and 1000 kilometers

dedolomitization reactions driven by anthropogenic activity on loessy sediments sw hungary abstract in the szigetvar area sw hungary shallow groundwaters draining upper pleistocene loess and holocene sediments are considerably contaminated by domestic effluents and leachates of farmland fertilizers the loess contains calcite and dolomite but gypsum was not recognized in these sediments the anthropogenic inputs contain significant amounts of ca and so 4 the ca from these anthropogenic inputs is promoting calcite growth with concomitant consumption of carbonate alkalinity undersaturation of the system with respect to dolomite and dolomite dissolution in brief is driving dedolomitization reactions geochemical arguments supporting the occurrence of dedolomitization reactions in the area are provided by the results of mass balance and thermodynamic analyses the mass balances predicted the weather sequence dolomite calcite plagioclase k feldspar at odds with widely accepted sequences of weatherability where calcite is the first mineral in the weathering sequence the exchange between calcite and dolomite can be a side effect of dedolomitization reactions because they cause precipitation of calcite the thermodynamic prerequisites for dedolomitization reactions are satisfied by most local groundwaters 70 since they are supersaturated or in equilibrium with respect to calcite undersaturated or in equilibrium with respect to dolomite and undersaturated with respect to gypsum the ca vs so 4 and mg vs so 4 trends are also compatible with homologous trends resulting from dedolomitization reactions

dedolomitization and calcite cementation in the middle devonian winnipegosis formation in central saskatchewan canada limestone consisting of finely to medium crystalline calcite mosaics is present in the upper part of the winnipegosis formation on the east central margin of the elk point basin where the overlying prairie evaporite deposits have been removed this type of crystalline limestone is interpreted as dedolomite based on petrographic observations the 18o and 13c values of the winnipegosis dedolomite vary from 12 8 to 11 9 vpdb vienna pee dee belemnite and from 0 5 to 1 7 vpdb respectively both values are significantly lower than those for the corresponding dolomite the 87sr 86sr ratios of the dedolomite are significantly higher between 0 7082 and 0 7087 the spatial distribution and geochemical data of the winnipegosis dedolomite suggest that dedolomitization was related to an influx of fresh groundwater and dissolution of the prairie evaporite anhydrite during the latest mississippian to the early cretaceous when the basin was subjected to uplift and erosion the winnipegosis dedolomite displays a series of replacement fabrics showing progressive calcitization of dolomite including the occurrence of dedolomite restricted along fractures and adjacent areas dolomite patches floating in the dedolomite masses and massive dedolomite with sparsely scattered dolomite relicts however the characteristic fabrics resulting from dedolomitization documented in the literature have not been observed in the winnipegosis dedolomite coarsely to very coarsely crystalline subhedral to euhedral calcite cement is restricted in the dedolomite the petrographic features isotopic compositions and homogenization temperatures coupled with the burial history of the winnipegosis formation constrain the precipitation of the calcite cement from a mixing of basinal brines and fresh groundwater during late cretaceous to neogene time the more negative c isotopic signatures of the calcite cement 5 3 to 2 3 vpdb probably reflect a hydrocarbon derived carbon

dedolomitization review and case study of uncommon mesogenetic formation conditions abstract dedolomitization converts a dolomite into a calcite and conventionally is interpreted to form in an eogenetic or telogenetic diagenetic environment where meteoric water dissolves evaporites to supply excess calcium hydrologic connectivity between a dolostone and the surface water may then lead to a dedolomitized interval often times being a diagnostic indicator for an erosional unconformity subaerial exposure and or karst in contrast to the classic models we present a case study for pervasive burial dedolomitization unrelated to meteoric fluids dedolomitization of the zechstein 2 carbonate ca2 gas reservoir in nw germany is strongly altering reservoir quality on a regional scale the ca2 shows a textbook correlation between reservoir quality and mineralogy petrographic analyses show that approximately 80 of all observed calcite reveal a dedolomite microtexture causing a reduction of average matrix porosity by 5 to 10 compared to the dolomite dedolomite follows initial layering and abundantly forms massive concretions which are surrounded by compaction related curvature of the depositional layering in the dolomite host rock such an early burial timing is supported by a slight burial related shift of 3 18o and 1 13c towards lighter values in the dedolomites compared to dolomite an exceptionally large amount of calcium rich fluids must have been mobilized to account for 50 of the ca2 rock volume to be dedolomitized however core fabrics related to meteoric diagenesis such as karst fabrics or typical fresh water stable isotope signatures have been observed neither in the ca2 nor in over and underlying anhydrite beds instead excess calcium likely comes from gypsum to anhydrite conversion and pressure solution within over and underlying anhydrites an influx of strontium rich waters from the anhydrite beds is indicated by up to 5 times higher strontium contents measured in dedolomite fabrics compared to their dolomite host rock homogenization temperatures between 51 and 56 c measured in some early fluid inclusions in dedolomite textures further exclude a pristine meteoric water input and suggest fluid entrapment in a burial depth range of 900 to 1400 m comparing these results with literature data furthermore indicates that mesogenetic dedolomite is either volumetrically underestimated in other carbonate evaporite settings or formed under unique diagenetic conditions across the southern permian basin during zechstein times

late neoproterozoic cap carbonates mackenzie mountains northwestern canada precipitation and global glacial meltdown the 3 27 m thick cap carbonate overlying marinoan ice brook formation glacigene sediments and keele formation carbonate and terrigenous clastic rocks consists of two distinctive stratigraphic units a lower splintery buff weathering microcrystalline dolostone of extensive lateral uniformity comprises mm laminated peloidal sediment with local low angle hummocky like cross stratification micro ridges and synsedimentary tepees all elongated per pendicular to depositional strike this dolostone is unconformably overlain by an upper limestone that exhibits pro nounced facies variation from inboard peloidal lime grainstone and mudstone to shelf edge cementstone to outboard lime wackestone and mudstone calcite cementstones range from isolated crystal fans in laminated limestone to huge decimetre scale crystal arrays to hemispherical and elongate crystal stromatolites wholly composed of acicular crystals that form decametre scale reeflike structures crystal stromatolites are precipitates and replaced microbiolites that con structed biostromes and bioherms like those on many flat topped reef rimmed platforms the calcite crystals have all the physical and chemical attributes of neomorphosed aragonite this aragonite extensively replaced sediment and microbiolite just below the sea floor and grew upward into the overlying water column such interpreted massive synsedimentary replacement is rare in geological history and attests to the highly saturated state of the immediate postglacial ocean all sediment is interpreted to have been caco3 originally low and constant 18 o values reflect diagenetic modification of these carbonates although chemical attributes such as sr and c isotopes in some lithologies are near pristine lower dolostones virtually identical to most other coeval marinoan caps worldwide were part of a global precipitation event of remarkable similarity upper limestones are a more local phenomenon deposited during sea level rise in an aragonitic sea returning to equilibrium after global glaciation low 87 sr 86 sr ratios and varying 13 c values with carbonate sedimentary facies indicate that both units must have formed relatively rapidly prior to significant flu vioglacial runoff or that the influence of this runoff on the chemistry of seawater along continental shelves was mini mal the cap carbonate is thus interpreted to have formed in two steps 1 during initial marine ice melting accompanied by oceanic overturn and upwelling preceding continental margin rebound and 2 during initial stages of sea level rise accompanying continental deglaciation while confirming brief but extensive carbonate precipitation from an ocean highly perturbed by global glaciation the rocks also suggest that this event did not permanently affect either late neoproterozoic ocean chemistry or the contained marine biosphere 1262

pleistocene aeolianites at cape spencer south australia record of a vanished inner neritic cool water carbonate factory aeolianites are integral components of many modern and ancient carbonate depositional systems southern australia contains some of the most impressive and extensive late cenozoic aeolianites in the modern world pleistocene aeolianites on yorke peninsula are sculpted into imposing seacliffs up to 60 m high and comprise two distinct imposing complexes of the late pleistocene bridgewater formation the lower aeolianite complex which forms the bulk of the cliffs is a series of stacked palaeodunes and intervening palaeosols the diagenetic low mg calcite sediment particles are mostly bivalves echinoids bryozoans and small benthic foraminifera this association is similar to sediments forming offshore today on the adjacent shelf in a warm temperate ocean by contrast the upper aeolianite complex is a series of mineralogically metastable biofragmental carbonates in a succession of stacked lenticular palaeodunes with impressive interbedded calcretes and palaeosols bivalves geniculate coralline algae and benthic foraminifera together with sparse peloids and ooids dominate sediment grains fragments of large benthic foraminifera including marginopora vertebralis a photosymbiont bearing protist are particularly conspicuous palaeocean temperatures are interpreted as having been sub tropical somewhat warmer than offshore carbonate factories in the region today the older aeolianite complex is tentatively correlated with marine isotope stage 11 whereas the upper complex is equivalent to marine isotope stage 5e marine isotope stage 5e deposits exposed elsewhere in southern australia glanville formation are distinctive with a subtropical biota including marginopora vertebralis thus in this example palaeodune sediment faithfully records the nature of the adjacent inner neritic carbonate factory by inference aeolianites are potential repositories of information about the nature of long vanished marine systems that have been removed due to erosion tectonic obliteration or are inaccessible in the subsurface such information includes not only the nature of marine environments themselves but also palaeoceanography

physical properties of sea ice discharged from fram strait it is estimated that 84 percent of the ice exiting the arctic basin through fram strait during june and july 1984 was multiyear ice and that a large percentage of this ice is ridged or otherwise deformed while freeboard and thickness data together with salinity measurements on cores usually sufficed to distinguish between first and multiyear floes preliminary identification could usually be made on the basis of snow cover measurements with snow cover being much thicker on multiyear ice cores from the top half meter of multiyear floes were generally very much harder and more transparent than cores from first year floes age estimates of multiyear floes based on petrographic and salinity characteristics of cores did not exceed 4 to 5 years for any of the floes that were observed exiting fram strait

shallow burial dolomite cement a major component of many ancient sucrosic dolomites dolomite cement is a significant and widespread component of phanerozoic sucrosic dolomites cements in dolomites that were never deeply buried are limpid have planar faces non saddle forms often distinct zonation in cathodoluminescence and form syntaxial overgrowths on crystals facing pores five samples of sucrosic dolomites interpreted as having had mostly limemudstone or wackestone precursors in four carbonate aquifers provide insights into the abundance of planar cements in sucrosic dolomites such cement comprises 11 to 45 32 mean of peritidal to sub tidal dolomites on an outcrop in the edwards aquifer early cretaceous of central texas 19 to 33 25 mean of ramp dolomites in the hawthorn group oligomiocene and 50 to 70 in shelf dolomites of the avon park formation eocene in the upper floridan aquifer of sub surface peninsular florida 18 to 45 32 mean of sub tidal shelf dolomites in quarry sections of the burlington keokuk formation early mississippian in south eastern iowa and 18 to 76 50 mean in shallow cores and outcrops of outer shelf dolomites from the gambier limestone oligo miocene of south australia backstripping the cement phases revealed by cathodoluminescence colour photomicrographs documents the effects of cements on textural coarsening pore space reduction induration and general maturation of these dolomites most pre holocene dolomites are multiphase crystalline rocks composed of i seed crystals or cores ii crystal cortices that concentrically enlarged the cores and iii free space syntaxial precipitates of limpid cement around the crystals remaining caco3 grains and micrite can be replaced by dolomite but typically they are dissolved between stages ii and iii creating systems of intercrystal and mouldic pores typical of sucrosic dolomites networks of cement overgrowths aided by water filled pore systems under hydrostatic to lithostatic pressure are judged to slow or prevent compaction in sucrosic dolomites it can be argued that cortex growth involves both replacement of caco3 particles and microcementation of their interparticle pores this interpretation and the abundance of cements in so many dolomites would obviate the controversy over the volumetrics of replacement dolomitization limpid planar and syntaxial dolomite cements of early diagenetic origin are interpreted to have precipitated from clear pore waters at low temperatures 30 to 35 c and shallow burial depths 100 m in water saturated networks of dolomite silt and sand cements in many dolomites in island and continental aquifer systems appear to result from event driven processes related to sea level highstands cementation events can follow replacement

sr isotopic composition of paleoproterozoic 13c rich carbonate rocks the tulomozero formation se fennoscandian shield abstract rb sr systematics has been studied in 13c rich carbonate rocks of the paleoproterozoic 2 09 0 07 ga tulomozero formation in the northern onega lake area the se fennoscandian shield the formation is divided into eight members a f consisting of greenschist facies grade variegated sandstones siltstones mudstones stromatolitic dolostones and subordinate crystalline limestones samples of carbonate rocks were obtained from two overlapping drillholes intersecting the entire thickness of the tulomozero formation prior to isotope analysis the rocks powders were treated with 1n ammonium acetate for partial removal of the late epigenetic carbonate phases major resetting of the rb sr systems in the tulomozero carbonate rocks appears to take place during the svecofennian regional metamorphic event and it was screened by using mn sr fe sr mg ca and 18o 16o ratios high sr content up to 2080 g g in limestones and 530 g g in dolostones coupled with low fe mn 0 40 in dolostones of the upper part of member b and of members g and h is indicative of seawater influxes sea transgression into the tulomozero basin the 87sr 86sr values in the least altered mn sr

partial area coverage distribution for flood frequency analysis in arid regions convective rainfalls of high intensity are largely responsible for most large floods occurring in arid regions convective storms are limited in size and rarely cover an entire basin therefore flood frequency is affected by the distribution of storm coverage c which is the fraction of basin area upon which rainfall occurs analytical probability density function pdf estimates of partial storm coverage are presented as a function of basin area sc and the probability distribution function for storm radius rs conditional pdfs for the covered area fraction c given the storm radius f c rs are obtained as a compound distribution with finite probability for maximum coverage and continuous density for smaller values the conditionality assumption is removed by assuming an exponential storm radius marginal distribution to obtain the catchment coverage pdf this pdf is compound with discrete probability for complete catchment coverage p c 1 and a continuous function for partial overlap the continuous function combines a weibull pdf and linear functions of c both p c 1 and f c depend on the average catchment to storm radius ratio the distribution explains the partial coverage data for the walnut gulch basin in arizona departures were observed however for slightly less than complete coverage namely for 0 9 c 1 a conceptual event classification and a method were designed to include partial coverage effects on flood frequency distribution

inside out dolomite abstract inside out dolomite crystals are unusual because their cores are younger than their encasing cortices in the cayman formation middle miocene of grand cayman they developed diagenetically from zoned dolomite crystals that have cores formed of high ca calcian dolomite hcd 55 mol caco3 and outer cortical zones formed of low ca calcian dolomite lcd 3 or oscillatory zoned lcd hcd the cores of these crystals labeled as type i have a euhedral rhombic outline with no embayments or angular reentrants and commonly contain calcite inclusions and or micropores hollow dolomite crystals evolved from these crystals as preferential dissolution removed all or part of the hcd core later calcite or dolomite cement was precipitated inside the hollow crystals the former produced dolomite crystals with a calcitic core i e dedolomite whereas the latter produced inside out dolomite crystals that have a dolomite core lcd or hcd encased by a dolomite cortex the cores of the inside out dolomite crystals labeled as type ii have an irregular outline characterized by angular reentrants and or embayments micropores that are usually larger than those in the type i cores but few calcite inclusions the cortical zones have a euhedral rhombic motif irrespective of the type of core development of insideout dolomite crystals may significantly alter the average ca of the dolostones as hcd is lost to dissolution and lcd or hcd cement is precipitated in its place the 18o may also change inasmuch as it is thought to covary with ca in some tertiary dolostones the genesis of inside out dolomite crystal may offer an alternative explanation for the textures e g clotted cathodoluminescence patterns in some ancient dolomite crystals that have been attributed to replacement and or recrystallization

dolomitization of the late cretaceous paleocene platform carbonates golkoy ordu eastern pontides ne turkey abstract late cretaceous paleocene agillar formation in the eastern pontide zone ne turkey is composed of shallow marine platform carbonates that were buried until uplift in late paleocene time the formation which is represented by 100 m thick reefal limestones around golkoy is completely dolomitized on the basis of petrographic and geochemical features four different replacive and cement dolomite phases are present the replacive dolomites which are cut by low amplitude stylolites include 1 fine crystalline planar s dolomite rd1 and 2 coarsely crystalline planar s e dolomite rd2 two types of dolomite cements were developed in minor amounts 1 a coarse dolomite cement cd1 that mostly fills molds vugs and fractures in rd1 dolomites and 2 rim dolomite cement cd2 that commonly develops on the space facing surfaces of rd2 dolomite the replacive dolomites are nearly stoichiometric ca 49 51 mg 48 50 and have 18 o values of 3 5 to 1 6 vpdb 13 c values of 1 1 to 0 8 vpdb and 87 sr 86 sr ratios of 0 707104 to 707458 sr na mn and fe concentrations of replacive dolomites are 102 171 ppm bdl 371 ppm 244 9941 ppm and 2643 8951 ppm respectively petrographic and geochemical data indicate that the replacive dolomites were formed prior to chemical compaction at shallow to intermediate burial depths from late cretaceous paleocene seawater and or seawater slightly modified by water rock interaction process and then recrystallized by meteoric waters at increasing burial depths and temperatures compared with replacement dolomites cd1 dolomites yield lower 18 o values 4 9 to 5 3 vpdb similar 13 c values 1 2 to 0 5 vpdb and higher 87 sr 86 sr ratios 0 707660 0 707609 the cd1 dolomites overlie the low amplitude stylolites and have homogenization temperatures between 94 and 112 c indicating that they were deposited from basinal brines although replacive dolomites and dolomite cements have similar na bdl 413 ppm mn 259 6990 ppm and fe 2184 6690 ppm concentrations the cements have lower sr contents 63 114 ppm like replacive dolomites cd1 dolomite is nearly stoichiometric ca 49 50 mg 47 49 but cd2 dolomite is slightly ca rich ca 51 52 mg 47 48 the cd2 dolomite is overlain by coarsely crystalline mosaic calcite cement indicates that diagenetic fluids eventually evolved to undersaturation with respect to dolomite and oversaturation with respect to calcite

shallow burial dolomitization and dedolomitization of mid cenozoic cool water calcitic deep shelf limestones southern australia abstract oligocene to mid miocene deep shelf bryozoan rich limestones across southern australia are variably altered to gray to orange ca rich medium crystalline sucrosic dolomite degree of replacement ranges from scattered rhombs to complete dolostone units several tens of meters thick and many kilometers in areal extent the locale and timing of dolomitization are tightly constrained to shallow burial and mid to late miocene dolostone varies from friable to dense and well lithified dolomitization is fabric specific muddy sediments are preferentially replaced calcite bryozoans and brachiopods form biomolds geochemistry suggests that dolomitization was predominantly by seawater limestone interaction but admixing of continental possibly meteoric groundwater is required by data on stable and radiogenic isotopes and trace elements sr isotopes confirm a mid miocene age for the dolomite if precipitated from seawater with no inherited limestone values dolomite crystals have undergone variable degrees of dissolution and meteoric calcite cement has locally filled the resultant rhombic voids dissolution began in the crystal cores implying some sort of metastability and expanded outward until in some ins ances the whole dolomite crystal was dissolved leaving dolomolds in otherwise unaffected limestone this dolomite occurrence well constrained by regional geology shows that widespread porous and permeable fabric destructive medium crystalline sucrosic dolostone can form in the shallow subsurface soon after sediment deposition such dolomite however may be metastable in the presence of variably mixed continental marine waters and newly formed crystals can undergo dedolomitization soon after precipitation