rock composition dolomite stoichiometry and rock water reactions in dolomitic carbonate rocks dolomitic carbonate rock units from a variety of phanerozoic localities and depositional environments throughout north america were evaluated with respect to their dolomite content and dolomite composition by x ray diffraction analysis dolomite compositions range from 48 to 57 mole caco 3 with well defined modes at 51 nearly stoichiometric dolomite and 55 distinctly calcian dolomite caco 3 values of percentage of dolomite also exhibit a pronounced albeit less well defined bimodal distribution with modes at 97 dolostones and 20 dolomitic limestones dolomite similar distributions characterize most other published data on phanerozoic dolomitic carbonates these data suggest that two separate processes may lead to two distinct populations of sedimentary dolomite 1 dolomitic limestones originate in diagenetically closed systems during magnesian calcite dissolution calcite and dolomite precipitation reactions and 2 dolostones originate in diagenetically open systems during th

dolostones from grand cayman british west indies abstract pervasively dolomitized tertiary strata on grand cayman are dominated by heterogeneous dolostones that are composed of both low ca calcium dolomite lcd 55 mol caco3 homogeneous dolostones formed of either lcd or hcd are rare some dolostones contain dolomite crystals that are characterized by oscillatory zones 1 10 m thick of lcd and hcd whereas others have rims of lcd surrounding cores of hcd in some dolostones bioclasts formed of lcd are embedded in a matrix of hcd an 1 18o difference between the lcd and hcd can be attributed to the natural covariance that exists between the 18o and mol caco3 in dolomite there are no significant differences in the 87sr 86sr ratios of the lcd and hcd there is no consistent vertical or lateral pattern to the distribution of lcd and hcd in the cayman dolostones even in closely spaced sampling sites such variability is more consistent with growth of individual dolomite crystals being controlled by processes that operated around the surfaces of individual crystals rather than by large scale changes in the dolomitizing fluids this interpretation is consistent with the development of oscillatory zoning which is attributed to precipitation of different phases or minerals from the same parent fluid because of competition between interface controlled and diffusion controlled growth kinetics dolomitization of the tertiary strata on grand cayman was probably mediated by seawater or modified seawater nevertheless small scale intrinsic factors controlled the incorporation of ca in the dolomite lattice and accordingly the geochemical parameters that are intimately linked to the mol caco3 these small scale intrinsic controls must be factored into any model to explain the formation of tertiary island dolostones

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

carnian norian biomagnetostratigraphy at silicka brezova slovakia correlation to other tethyan sections and to the newark basin correlations of upper triassic magnetic stratigraphies from tethyan sections have been hampered by difficulties with conodont biostratigraphy and taxonomy and discontinuous sedimentation particularly in the hallstatt limestones of turkey and austria the magnetic stratigraphy and conodont biostratigraphy from the upper carnian to upper norian limestones exposed at silickabrezova slovakia can be correlated to other tethyan sections and to the continental succession in the newark basin the resulting correlations help to resolve some of the apparent discrepancies in existing conodont zonations and result in a revised correlation to north american terrestrial vertebrate and palynological zones the correlations imply that the norian rhaetian boundary lies within newark polarity zone e17r at v207 ma the carnian norian boundary lies close to the base of newark polarity zone e7r at v226 ma this implies durations for the norian and rhaetian stages of 19 myr and 7 myr respectively 2002 elsevier science b v all rights reserved

formation of dolomite mottling in middle triassic ramp carbonates southern hungary abstract the middle triassic carbonates of the villany mountains were deposited on a homoclinal carbonate ramp many of the carbonates from the 700 m thick sequence show partial or complete dolomitization the present paper describes dolomites that occur in a limestone unit as irregular mottles and as pore and fracture filling cements replacement type scattered dolomite rhombs in the mottles having inclusion rich very dull luminescent cores and limpid non luminescent outer zones represent the initial phase of dolomitization the isotopic composition of these dolomites 13 c 2 30 vpdb 18 o 3 60 vpdb is similar to that of the calcitic micrite 13 c 2 6 vpdb 18 o 4 00 vpdb indicating that no external fluids were introduced during dolomite formation the elevated sr content of the micrites implies that sediment was originally aragonite or high mg calcite dolomitization took place in the burial realm from a marine pore fluid in a partly closed system later fracture related saddle dolomite reflects elevated formation temperatures and increasing burial five calcites were identified multiple generations of calcite filled fractures were formed during burial diagenesis generally having dull or no luminescence 13 c 1 80 vpdb 18 o 6 40 vpdb the latest phase calcites are related to karst formation having a very negative isotopic composition 13 c 5 0 to 7 2 vpdb and 18o 7 4 vpdb the karst related processes include dissolution calcite precipitation and partial replacement of dolomites by complex zoned bright yellow calcite the timing of dolomitization is uncertain but the first phase took place in a partly closed system prior to stylolite formation late stage saddle dolomites were precipitated during maximum burial in the cretaceous the dissolution of dolomites and karst related calcite replacement was not earlier than late cretaceous

diagenetic stabilization of the upper permian dalan formation persian gulf basin abstract the upper permian dalan formation is a supergiant gas reservoir in the persian gulf basin reservoir quality is controlled by the original facies type dolomitization and anhydrite cementation this study focuses on the texture petrographic analysis bulk stable isotope values and trace element composition in order to identify the original mineralogy of carbonate grains and cements and to assess the synsedimentary and diagenetic processes including the timing and setting of dolomitization the limestone data suggest that the initial precipitation of isopachous acicular to fibrous aragonite cements in the marine phreatic environment was followed by dissolution of aragonite grains and cements in the meteoric phreatic zone and neomorphism and low mg calcite cementation blocky and drusy crystals syntaxial overgrowths in the active freshwater phreatic zone the relatively pristine 18o and 13c values low mn and relatively high sr and na contents indicate that this meteoric diagenesis was relatively limited the remaining porous space was cemented by blocky calcite later during burial four types of dolomites are identified within a complex mixture of texturally and isotopically different dolomites dolomicrite dolomicrosparite dolosparite and saddle dolomite dolomicrite formed syndepositionally from the evaporated permian seawater or by reflux of dense evaporated brines during shallow burial the second major episode of dolomitization dolomicrosparite and dolosparite was driven by reflux of warmer and more saline fluids at greater depth which affected both previously non dolomitized and dolomitized sediments the final diagenetic stabilization during deep burial is associated with extensive pressure solution fracturing vein filling of calcite and dolomite cements and crystallization of saddle dolomite

paleomagnetic and magnetic fabric data from lower triassic redbeds of the central western carpathians new constraints on the paleogeographic and tectonic evolution of the carpathian region in the central western carpathians cwc most published paleomagnetic results from permo mesozoic rocks document extensive remagnetizations and come from thin skinned thrust units that have undergone multistage deformation we present results from lower triassic redbeds from the autochthonous cover overlying the basement that carry a primary magnetization petromagnetic results indicate that the dominant ferromagnetic carrier is hematite while magnetic susceptibility and its anisotropy are controlled by both ferromagnetic and paramagnetic minerals magnetic fabrics document weak deformation related to late cretaceous shortening the directions of the high unblocking temperature remanence components pass both reversal and fold tests attesting to their primary nature paleomagnetic inclinations are flatter than expected from reference datasets suggesting small latitudinal separation between the cwc and stable europe paleomagnetic declinations are mostly clustered within individual mountain massifs implying their tectonic coherence they show only minor differences between the massifs indicating a lack of significant vertical axis tectonic rotations within the studied central parts of the cwc the paleomagnetic declinations are therefore representative of the whole of the cwc in terms of regional paleogeographic interpretations and imply moderate counterclockwise rotations c 26 of the region with respect to stable europe since the early triassic

cementation in oligo miocene non tropical shelf limestones otway basin australia abstract the oligocene to miocene heytesbury group of the otway basin southeastern australia is a non tropical carbonate shelf succession this subsurface stratigraphic succession consists of bioclastic grainstones to mudstones containing bryozoa benthonic and planktonic foraminifera echinoderms brachiopods and molluscs the basal bryozoa dominated clifton formation was deposited in relatively shallow waters the overlying gellibrand marl rich in planktonic foraminifera and bryozoa formed under deep waters the uppermost unit benthonic foraminifera dominated port campbell limestone was deposited in a moderately deep middle shelf environment cementation is limited and includes 1 scalenohedral calcite non luminescent to bright mn and fe poor in inter and intraparticle porosity 2 blocky equant calcite dull mn and fe rich in interparticle porosity 3 syntaxial calcite overgrowths on echinoderm particles non bright dull zoned 4 euhedral dolomite in the interparticle pore space of the port campbell limestone 5 bladed prismatic calcite ferroan in planktonic foraminifera 6 fibrous calcite non luminescent in intraparticle porosity and 7 glauconite and iron oxides only in intraparticle porosity all caco3 cements are low mg calcites the cements observed in the heytesbury group appear to have formed in three successive diagenetic environments 1 early shallow burial early fe and mn poor non luminescent syntaxial overgrowths and non luminescent scalenohedral calcite under oxidising conditions 2 late shallow burial bright more mn rich syntaxial overgrowth zone i e more than the initial non luminescent one and bright scalenohedral calcite under moderately reducing pore water conditions and 3 moderate burial ferroan dull blocky calcite and dull syntaxial overgrowth zone under reducing conditions pressure solution was the main cement producing mechanism although seawater and aragonite dissolution could account for the precipitation of the early non luminescent cements scarcity of early interparticle cements may have been caused by the calcite rich character of the original sediments the ferroan dully luminescent blocky equant calcite and syntaxial overgrowths typically interpreted to represent products of deep burial in ancient carbonate successions are observed in the shallow buried port campbell limestone

hydrothermal dolomites in sw sardinia italy evidence for a widespread late variscan fluid flow event abstract epigenetic replacive and saddle dolomite frequently forming zebra structures geodic dolomite affected cambrian limestones and early diagenetic dolomites across large areas of the iglesiente sulcis mining district sw sardinia italy the dolomite crops out in an area of more than 500 km 2 and reaches a thickness of up to 600 m or even more this rock represents one of the most extensive dolomites of epigenetic origin yet documented prior to dolomitization the cambrian carbonates underwent ductile deformation and greenschist facies metamorphism the same is true for the overlying tectonic nappes fluid inclusion analysis combined with o and sr isotope data indicate that the dolomitizing fluid can be categorized as a basinal brine the spread in homogenization temperatures shows a gradient with values decreasing from east to west the higher temperatures mean of around 100 c have been measured in eastern parts of the iglesiente area whereas the lowermost temperatures mean of about 85 c have been found along the western coast of iglesiente this fluid certainly can neither have come directly from the low grade metamorphic lithotypes undergoing dolomitization nor from the low temperature metamorphic rocks within the overlying nappes it is assumed that a late variscan hydrothermal event which coincided with extensional tectonics set brine circulation into motion dolomitization may have occurred within circulation cells which were driven by high heat flow fluids originated in the underlying rocks and circulated upward to affect the overlying cambrian carbonates an alternative model is that the dolomitization was caused by hydrothermal brines that originated within basinal areas of the variscan orogenic pile circulating deep within the crust and ascended in the external zone iglesiente sulcis whatever the origin these reducing saline fluids which carried radiogenic sr dolomitized a large volume of early paleozoic rocks the many subhorizontal open cavities within the geodic dolomite only partly filled with cement might indicate fluid overpressure at the time of dolomitization

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

statistical evaluation of elemental concentrations in shallow marine deposits cretaceous lusitanian basin abstract the elemental geochemistry of ancient shallow marine carbonates represents an often underexplored archive of paleoenvironmental change and diagenetic pathways complex multi parameter datasets from a lithologically heterogeneous sedimentary succession in the southern part of the lusitanian basin ericeira portugal are presented and interpreted the section comprises marly carbonate and sandstone rich coastal marine deposits of early albian to early cenomanian age principal component analysis of bulk elemental abundance ca mg sr fe and mn lead to define four geochemical clusters based on common elemental attributes siliciclastics and dolomitized limestones facies yield evidence for significant diagenetic alteration but still preserve information on paleoshoreline position mixed carbonate siliciclastics and limestone facies bear evidence for relative sea level position and relevant paleoclimatic information in their elemental record accordingly mid albian mixed carbonate siliciclastic deposits present variable degrees of continental influx specifically a sharp increase of fe and mn concentrations in relation to continental input is in agreement with periods of enhanced hydrological cycling and increased weathering on adjacent emerged lands the progressive transition towards more marine conditions is accompanied by higher ca and sr content and represented by limestone facies corresponding to a higher sea level position during late albian to early cenomanian times moreover this facies records a trend towards warmer and more arid conditions early diagenetic stabilization and or dissolution of aragonite into low mg calcite can account for major elemental variations including higher sr content strongly coupled with ca content along with lower mg fe and mn concentrations data shown here provide solid evidence that the statistical analysis of the elemental record of ancient marine deposits when combined with conventional sedimentology and thin section petrography allow for elaborate conclusions on their depositional environment and diagenetic pathways cored wells and facies specific reservoir properties can be addressed by these methodologies able to detect and quantify changes in patterns both industry and academy can therefore benefit from approaching such a complex interplay

correlating paleomagnetic geochemical and petrographic evidence to date diagenetic and fluid flow events in the mississippian turner valley formation moose field alberta canada abstract petrographic geochemical and paleomagnetic analyses of the mississippian turner valley formation provide constraints on diagenesis and fluid flow events in the western canada sedimentary basin paleomagnetic plugs and companion geochemical samples were taken from two drillcores with fullbore microimage log orientations dolomite from both wells yielded two magnetization directions the low temperature low coercivity direction is a drilling induced remanence rather than a viscous remanent magnetization the high temperature high coercivity remanence direction is cretaceous and there is no sign of a primary mississippian direction geochemical analyses of matrix dolomite yield 18o values ranging from 0 65 to 3 34 vpdb standard and 13c values ranging from 1 77 to 3 05 vpdb the least depleted samples have stable isotope values consistent with or only slightly depleted from postulated mississippian dolomite values the remaining sample values exhibit a negative covariant trend consistent with either mixing with another diagenetic fluid or recrystallization during burial petrographic analysis reveals the presence of a recrystallization event that caused zoning and a gradual increase size of the dolomite crystals this event is thought to have caused both the cretaceous paleomagnetic remanence and the altered geochemical values the minor enrichment in sr radiogenic isotopes relative to coeval seawater values suggests that both an extrabasinal source for any fluid and large scale fluid flow are unlikely the results also indicate that magnetic remanences are very sensitive to visually minor changes in carbonate recrystallization from heat or pressure so that great care must be taken in correlating paleomagnetic and geochemical data

marine cements in mid tertiary cool water shelf limestones of new zealand and southern australia large areas of southern australia and new zealand are covered by mid tertiary limestones formed in cool water shelf environments the generally destructive character of sea floor diagenesis in such settings precludes ubiquitous inorganic precipitation of carbonates yet these limestones include occasional units with marine cements 1 within rare in situ biomounds 2 within some stacked cross bedded sand bodies 3 at the top of metre scale subtidal carbonate cycles and 4 most commonly associated with certain unconformities the marine cements are dominated by isopachous rinds of fibrous to bladed spar interstitial homogeneous micrite and interstitial micropeloidal micrite often precipitated sequentially in that order internal sedimentation of microbioclastic micrite may occur at any stage the paradox of marine cemented limestone units in an overall destructive cool water diagenetic regime may be explained by the precipitation of cement as intermediate mg calcite from marine waters undersaturated with respect to aragonite in some of the marine cemented limestones aragonite biomoulds may include marine cement sediment internally suggesting that dissolution of aragonite can at times be wholly marine and not always involve meteoric influences we suggest that marine cementation occurred preferentially but not exclusively during periods of relatively lowered sea level probably glacio eustatically driven in the mid tertiary at times of reduced sea level there was a relative increase in both the temperature and the carbonate saturation state of the shelf waters and the locus of carbonate sedimentation shifted towards formerly deeper shelf sites which now experienced increased swell wave and or tidal energy levels fostering sediment abrasion and reworking reduced sedimentation rates and freer exchange of sediment pore waters energy levels were probably also enhanced by increased upwelling of cold deep waters onto the southern ocean margins of the australasian carbonate platforms where water mass mixing warming and loss of co2 locally maintained critical levels of carbonate saturation for sea floor cement precipitation and promoted the phosphate glauconite mineralization associated with some of the marine cemented limestone units

convection over tropical africa and the atlantic ocean during northern summer part ii modulation by easterly waves abstract using meteosat data and european centre for medium range weather forecast ecmwf analyses we examine easterly waves and their relation with the cloudiness over west africa and the tropical atlantic ocean for three summers june july august and september 1983 85 spectral analysis of the low level meridional wind in the 2 8 5 1 day band reveals maximum wave amplitude near the west african coast at 20 n during august and september the wave amplitude is larger than during june and july and a secondary maximum appears around 7 5 n composites of the mean structure of the wave and the associated cloud modulation reveal consistent relationship between observed cloudiness and ecmwf analyses the phase of the wave modulation of the cloudiness is strongly dependent on the geographical location in response to changes in the mean climatological conditions this phase varies however grossly in four large land and ocean regions centered at 7 5 and 17 5 n respectively for which we derive vertical cro

african easterly wave variability and its relationship to atlantic tropical cyclone activity abstract automatic tracking of vorticity centers in european centre for medium range weather forecasts analyses has been used to develop a 20 yr climatology of african easterly wave activity the tracking statistics at 600 and 850 mb confirm the complicated easterly wave structures present over the african continent the rainy zone equatorward of 15 n is dominated by 600 mb activity and the much drier saharan region poleward of 15 n is more dominated by 850 mb activity over the atlantic ocean there is just one storm track with the 600 and 850 mb wave activity collocated based on growth decay and genesis statistics it appears that the 850 mb waves poleward of 15 n over land generally do not get involved with the equatorward storm track over the ocean instead there appears to be significant development of 850 mb activity at the west african coast in the rainy zone around 10 n 10 w which it is proposed is associated with latent heat release based on the tracking statistics it has been shown th

diagenetic comparisons between non tropical cenozoic limestones of new zealand and tropical mississippian limestones from indiana usa is the non tropical model better than the tropical model abstract mississippian limestones exposed in indiana u s a were deposited in a shallow tropical ocean however many properties of these limestones are more like those of modern and cenozoic non tropical limestones such as those found in new zealand the dominant skeletal grains in the indiana limestones are calcitic echinoderms bryozoans and brachiopods the dominant skeletal grains in most cenozoic limestones of new zealand are calcitic bryozoans echinoderms bivalve molluscs and foraminifera in contrast modern and cenozoic tropical limestones contain an abundance of aragonitic green algae corals and molluscs early in diagenesis the metastable aragonite dissolves and reprecipitates as calcite causing early cementation of the sediments originally aragonitic fossils that have dissolved can be identified as molds that are commonly filled with secondary calcite because they contained little aragonite most of the indiana and new zealand limestones did not have an abundant source of early cement except for local cases in which grains were cemented in contact with carbonate supersaturated seawater grainstones were relatively deeply buried with little cement between the grains this resulted in mechanical and chemical compaction of skeletal grains producing a fitted fabric with greatly reduced pore space either open or filled with cement between the grains cement in these aragonite poor grainstones comes largely from pressure dissolution between grains and along stylolitic seams in the rock features that are common only after burial beyond a few hundred meters the final product of deeply buried up to 2000 m cenozoic new zealand grainstones is similar to the mississippian grainstones of indiana in the indiana limestones we have only the final product of this extensive burial diagenesis however the new zealand sediments and rocks reveal all steps of formation of the final deeply buried limestone the reason for the scarcity of originally aragonitic fossil grains in paleozoic rocks worldwide is unknown organisms with aragonitic skeletons such as some molluscan groups and calcareous green algae were present but seldom in much abundance the aragonitic scleractinian corals had not yet evolved previous researchers have noted that non skeletal precipitates such as ooids and cements have at times during the paleozoic been predominantly aragonite and at other times calcite they have attributed this difference to secular variation in seawater chemistry icehouse vs greenhouse seas abundance of aragonitic and calcitic skeletal grains does not follow this pattern

burial dominated cementation in non tropical carbonates of the oligocene te kuiti group new zealand abstract cementation of bryozoan echinoid benthic foraminiferal temperate shelf carbonates of the oligocene te kuiti group north island new zealand occurred mainly during subsurface burial the calcite cements in the limestones are dominated by equant and syntaxial rim spar which typically becomes ferroan given an iron supply and compared to the skeletal material with normal marine 18o values from 2 to 1 more depleted in 18o with depth of burial the 18o composition of bulk cement samples ranging from 1 to 7 these trends reflect the establishment in pore waters during sediment burial of reducing conditions and gradually increasing temperatures 20 50 c respectively the 13c values 0 to 3 of the cements remain the same as the host marine shells suggesting the source of carbon in the cements was simply redistributed marine carbonate derived from shell dissolution two gradational burial diagenetic environments influenced by marine derived porewaters are arbitrarily distinguished shallow burial phase and moderate burial phase during the shallow burial phase down to 500 600 m sub bottom depth the carbonates lost at least 25 of their original porosity by mechanical compaction and were selectively cemented by non ferroan or usually ferroan variably luminescent slightly 18o depleted sparry calcite cement 18o 2 to 4 mainly as syntaxial rims about echinoid grains these shallow burial cements form less than about 10 of total cement in the majority of the limestones and their source was probably mainly mild intergranular dissolution of calcitic skeletal fragments accompanying the onset of chemical compaction during the moderate burial phase between about 600 and 1100 m sub bottom depth porosity loss continued typically to about 70 of its original value as a result of pressure solution of calcitic bioclasts associated with more advanced stages of chemical compaction this involved development of a wide variety of non sutured and microstylolitic solution seams including both single and composite wispy or continuous bedding parallel types and non parallel reticulate forms the released carbonate was precipitated as ferroan or non ferroan where iron supply was negligible dull luminescent strongly 18o depleted 18o 4 to 7 mainly equant calcite spar cement occluding available pore space in the limestones

low level african easterly wave activity and its relation to atlantic tropical cyclogenesis in 2001 abstract this paper provides new information on the low level 850 hpa structure and behavior of african easterly waves aews and relates this information to previous studies individual aews that occurred during june september of 2001 are studied by a synoptic approach that employs hovmoller diagrams wave track maps and case studies the focus is on two aew regimes in the lower troposphere over north africa a dry regime to the north of the african easterly jet aej coincident with the surface position of the monsoon trough near 20 n and a wet regime to the south of the jet coincident with the near equatorial rainbelt near 10 n the following issues are addressed the origin of the waves seen in the two wave regimes relation of the wave activity to the mean positions of the surface monsoon trough and the 600 700 hpa aej collocation of the tracks of the two wave regimes off the african coast and diversity in low level wave behavior that includes merging splitting and dissipation of the cyclonic

burial dolomitisation in a non tropical carbonate petroleum reservoir the oligocene tikorangi formation taranaki basin new zealand abstract the oligocene tikorangi formation is a subsurface non tropical limestone rich fracture producing oil reservoir in taranaki basin new zealand the formation is distinct from uplifted and exposed age equivalent new zealand limestones due to partial dolomitisation by modest quantities of silt sized scattered inclusion rich euhedral dolomite rhombs occasionally displaying idiotopic fabrics rhombs commonly have dull luminescent fe rich cores and oscillatory bright and dull concentric outers the dolomites are non stoichiometric high calcian and highly ferroan varieties dolomite 18 o and 13 c values are moderately depleted while associated precursor calcite phases are less depleted petrographic geochemical and geohistory evidence suggest that the dolomite formed during and following the later stages of pressure dissolution cementation in a relatively closed moderately deep burial environment ca 0 85 1 9 km burial depth ca 33 65 c in the early miocene ca 24 18 ma from warm saline enriched pore fluids by mainly mimic fabric selective replacement of interparticle and rarely intraparticle micrite matrix dolomitisation did not affect skeletal grains or calcite cements or develop any secondary porosity mg supply was restricted and was likely sourced internally from micritic inter and intraparticle precursor material and from the pressure dissolution of calcitic skeletons importantly dolomitisation occurred prior to compression related brittle fracturing of the carbonates responsible for creating extensive hydrocarbon bearing fracture networks because of the greater susceptibility of the dolomitised limestones to brittle fracturing their location and distribution may have important implications for hydrocarbon prospectivity and production within the tikorangi formation

petrographic and geochemical characteristics of dolomite types and the origin of ferroan dolomite in the trenton formation ordovician michigan basin u s a three major types of dolomite occur in the trenton formation mid ordovician of the michigan basin these are 1 regional dolomite which is confined to the extreme western edge of the basin 2 cap dolomite which occurs in the upper portion of the trenton and is confined to the basin s southern margin and 3 fracture related dolomite which occurs in association with both large and small scale faults and fractures these three dolomite types can be distinguished from one another by their major element chemistry oxygen isotope ratios and rock texture the regional dolomite is fine grained has 0 34 mol feco3 and mean 18o of 6 8 opbd the cap dolomite is texturally similar to regional dolomite but contains 3 13 0 mol feco3 and has a mean 18o of 7 7 fracture related dolomites are coarse grained low in iron and have the most depleted 18o ratios x 9 0 pdb petrographic relationships imply that the regional dolomite formed prior to the cap dolomite probably during early diagenesis the cap dolomite formed at relatively shallow depths as a result of the interaction of the overlying utica shale and the trenton limestone fracture related dolomites post date the cap dolomite and formed during deeper burial a temperature of precipitation of approximately 80 c was calculated for fracture related dolomites using oxygen isotope data the distribution of the cap dolomite was controlled by the availability of fe2 which was in turn controlled by the availability of s2 in the centre of the basin trenton utica deposition was continuous the upper trenton contained relatively high concentrations of organic matter which was used by sulphate reducing bacteria to produce h2s from seawater sulphate the precipitation of iron sulphides pyrite iron monosulphide followed and used up most of the available fe2 as a result only small amounts of ferroan dolomite formed on the periphery of the basin subaerial exposure resulted in the oxidation of most of the available organic matter sulphate reducing bacteria were therefore limited and produced limited amounts of h2s as a result only a minor amount of iron sulphide iron monosulphide formed the remaining fe2 was then available for the formation of the ferroan cap dolomite this model is supported by the following 1 in the southern margin of the basin the contact between trenton cap dolomite and the overlying utica shale is sharp and probably unconformable in the centre of the basin the contact is gradational 2 in the centre of the basin the total organic carbon content in the upper trenton is an order of magnitude higher than in the cap dolomite 3 the whole rock concentration of iron is high in both the cap dolomite and in slightly dolomitized equivalent beds in the basin centre 4 iron sulphides are abundant in the centre of the basin and mostly in the form of pyrite in the cap dolomite iron sulphide is minor and primarily in the form of iron monosulphide

genesis of tropical storm debby 2006 within an african easterly wave roles of the bottom up and midlevel pouch processes abstractthe bottom up generation of low level vortices lvs and midlevel vortices mvs during the genesis of tropical storm debby 2006 and the roles of a midlevel marsupial pouch associated with an african easterly wave aew are examined using an 84 h simulation with the finest grid size of 1 33 km results show that several mvs are generated in leading convective bands and then advected rearward into stratiform regions by front to rear ascending flows because of different lagrangian storm scale circulations mvs and lvs are displaced along different paths during the early genesis stages mvs propagate cyclonically inward within the aew pouch while experiencing slow intensification and merging under the influence of converging flows the mvs merging into a mesovortex is accelerated as they come closer to each other in the core region in contrast the low level lagrangian circulation is opened as a wave trough prior to tropical depression td stage so the lvs tend to escape from the pouch r

merger of african easterly waves and formation of cape verde storms there are two easterly wave tracks over west africa one to the south and the other to the north of the african easterly jet aej a northern wave sometimes merges with a southern wave near the coast of west africa the dynamic and thermodynamic evolution of the waves during the merger and the impacts of the merger on subsequent storm development are examined in this study three groups of storms are identified non merger developers merger developers and merger non developers relative to non merger developers merger developers have a weaker circulation near the surface prior to the merger but the merger leads to a stronger and deeper wave pouch which is more conducive to tropical cyclogenesis the dryness of the northern disturbances does not seem to hinder the storm development composite analysis shows that merger developers are associated with a warmer and broader heat low over west africa and a more extensive aej which helps to maintain the northern waves over the east atlantic merger developers and non developers resemble each other prior to the merger but dry air intrusion west of the wave trough in the middle and upper troposphere contributes to the non development of some mergers the dry air in non developers is related to a strong and broad upper tropospheric trough and the associated subsidence west of the low level wave pouch the trough advects dry air from the extratropical atlantic in the middle and upper troposphere and also induces a strong westerly vertical shear composites of aerosol optical depth suggest that the saharan air layer has a limited contribution to the dryness in the vicinity of the non developers

regional differences in the kinematic and thermodynamic structure of african easterly waves this study examines regional differences in the structure of african easterly waves aews at four locations between east africa and the east atlantic in a 12 yr 1998 2009 climatology we focus on the cold core convectively active portions of the aews which are typically found between 5 and 15 n african easterly wave composites are produced from three reanalyses using the tracks of synoptic scale middle tropospheric vorticity maxima the vertical structure of temperature and vorticity in the composite aews are related to regional differences in the climatological and vortex centred diabatic heating and diabatic potential vorticity pv generation profiles from the reanalyses in addition differences in aew structure and activity between the three reanalyses are related to differences in rainfall and diabatic heating between the reanalyses the climatological diabatic heating over east africa which is associated mostly with latent heating peaks at 450 hpa with diabatic cooling below 750 hpa in contrast the convectively active west african coast and the east atlantic have increased diabatic heating in the lower troposphere due to these regional differences in diabatic heating diabatic pv generation peaks near 700 hpa over the continent and below 800 hpa over the east atlantic moving westwards from east africa to the east atlantic aew composites have weaker lower tropospheric cold cores and significantly increased lower tropospheric vorticity within the convectively active troughs the shape of the diabatic heating and pv generation profiles within the trough of the regional aew composites are similar to the climatological profiles in each respective region this suggests that regional differences in moist convection particularly the land ocean contrast provide a strong constraint on the diabatic process within the aew trough and therefore the vertical structure of the aews

structural applications and discussion of a paleomagnetic post paleozoic data base for the central mediterranean abstract a post paleozoic paleomagnetic data base has been compiled for the central mediterranean with the intention of listing directions at the highest possible level of data combination the value of the entries depends on the number and quality of data available the most reliable data are those based on regionally distributed localities and sites where the age is known to a stage and where tectonic correction has been made these represent a whole tectonic unit in a given period of time the lowest quality directions are those based on few samples and isolated in space and time in the tectonic interpretation of the listed data this variation in quality of data has been taken into consideration indications for cenozoic movements having a fundamental influence on the now observable distribution of the clockwise and counter clockwise rotated paleomagnetic directions were treated first and those for older movements afterwards microplate block and nappe movements were considered as possible mechanisms for the rotation of these the last two mechanisms explained satisfactorily the occasional local deviations from a general pattern other differences however such as those which exist between the northern calcareous alps or the tisza unit and the counter clockwise rotated superunit of the central mediterranean which are large and persisted through a longer period of time are best explained by independent movement of the whole unit

characteristics of an african easterly wave observed during namma abstract the evolution of an african easterly wave is described using ground based radar and ancillary datasets from three locations in west africa niamey niger continental dakar senegal coastal and praia republic of cape verde oceanic the data were collected during the combined african monsoon multidisciplinary analyses amma and nasa amma namma campaigns in august september 2006 two precipitation events originated within the wave circulation and propagated with the wave across west africa mesoscale convective systems mcss associated with these events were identified at all three sites ahead of within and behind the 700 mb wave trough an additional propagating event was indentified that originated east of the wave and moved through the wave circulation the mcs activity associated with this event did not show any appreciable change resulting from its interaction with the wave the mcs characteristics at each site were different likely due to a combination of life cycle effects and

stratigraphic sedimentology of tertiary cool water limestones se australia abstract mid tertiary limestones exposed as sea cliffs along the coast of victoria southeastern australia accumulated on the inner part of a cool water distally steepened ramp or open shelf all sediments are bioclastic dominated by particles of bryozoans echinoderms benthic foraminifers brachiopods and molluscs shallow grainy facies also contain coralline algae quartz and glauconite while deep muddy facies include ahermatypic corals ostracodes sponge spicules planktic foraminifers and terrigenous clays the fundamental depositional unit is a meter scale subtidal cycle or rhythm shallow shelf cycles are shallowing upward cross bedded or burrowed grainstone capped by a marine cemented hardground or quartz granule lag while mid shelf cycles are upward coarsening and thickening proximal to distal tempestites such cycles are interpreted to form by eustatically driven climatically controlled oscillations in abrasion wave base and swell wave base deep shelf rhythms are interbedded bryozoan marl and calcareous clay thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution lowstand systems tracts are depositional or erosional sequence boundaries are complex multigeneration mostly submarine surfaces condensed cycle boundaries that can be traced offshore into multiple omission surfaces and conformable contacts basinward facies shifts result in deposition of condensed lowstand wedges of stacked shallowing upward grainstone cycles transgressive systems tracts are thick bryozoan marl calcareous clay rhythms associated with facies backstepping and abrupt deepening such rhythmites typically grade stratigraphically upward into tempestite cycles highstand systems tracts are highly progradational wedge shaped rock bodies of shallowing upward grainy cycles these limestones provide the critical link of stratigraphy between modern cool water carbonate shelf deposits and the older mesozoic and paleozoic record of similar sediments

palaeomagnetism and palaeogeography of the western carpathians from the permian to the neogene geodynamic models for the western carpathians require evaluation of palaeomagnetic data from the outer carpathian flysch belt from limestones of the klippen belt and from volcanic and sedimentary rocks of the inner carpathians palaeomagnetic data for the permian to the neogene are evaluated the data indicate marked mostly anticlockwise tectonic rotations of larger rock complexes and nappes the distribution of palaeomagnetic poles is characteristic of a collision zone and crosses the apparent polar wandering path for the african plate tectonic rotations are observed in both the inner carpathians and the klippen belt as well as in the outer carpathian flysch belt most drift occurred during the permian to triassic interval with northward movement from initial southern equatorial latitudes drift decelerated from the jurassic to the neogene fig 1 simplified geological map of the western carpathians showing the localities mentioned in the text the carpathian mountains represent a complex alpine fold and thrust belt which is over 1500 km long and has a pronounced arcuate shape figure 1 shows that part of the western carpathians within the territories of slovakia and moravia the system can be subdivided into three main tectonostratigraphic zones namely the outer zone or outer carpathian flysch belt the klippen belt and the inner zone or inner carpathians this paper summarizes palaeomagnetic data obtained in the western carpathians from units of permian to neogene age by various authors these data come from flysch deposits of the outer carpathians limestones of the klippen belt and volcanic and sedimentary rocks of the inner carpathians and mainly come from morris a tarling d h eds 1996 palaeomagnetism and tectonics of the mediterranean region geological society special publication no 105 pp 175 184 175

geochemical study of calcite veins in the silurian and devonian of the barrandian basin czech republic evidence for widespread post variscan fluid flow in the central part of the bohemian massif abstract carbonate fracture cements in limestones have been investigated by fluid inclusion and stable isotope analysis to provide insight into fluid evolution and deformation conditions of the barrandian basin silurian devonian of the czech republic the fractures strike generally north south and appear to postdate major variscan deformation the most common fracture cement is calcite that is locally accompanied by quartz natural bitumen dolomite mn oxides and fluorite three successive generations of fracture filling calcite cements are distinguished based on their petrographical and geochemical characteristics the oldest calcite cements stage 1 are moderate to dull brown cathodoluminescent fe rich and exhibit intense cleavage subgrain development and other features characteristic of tectonic deformation less tectonically deformed variable luminescent fe poor calcite corresponds to a paragenetically younger stage 2 cement first melting temperatures t e of two phase aqueous inclusions in stages 1 and 2 calcites are often around 20 c suggesting that precipitation of the cements occurred from h 2 o nacl fluids the melting temperature t m has values between 0 and 5 8 c corresponding to a low salinity between 0 and 8 9 eq wt nacl homogenization temperatures t h from calcite cements are interpreted to indicate precipitation at about 70 c or less no distinction could be made between the calcite of stages 1 and 2 based on their fluid inclusion characteristics in some stage 2 cements inclusions of highly saline up to 23 eq wt nacl brines appear to coexist with low salinity inclusions the low salinity fluid possibly contains na k mg and ca chlorides the high salinity fluid has a h 2 o nacl cacl 2 composition blue to yellow green fluorescing hydrocarbon inclusions composed of medium to higher api gravity oils are also identified in some stages 1 and 2 calcite cements stage 1 and 2 calcites have 18 o values between 13 2 and 7 2 pdb the lower range of the calculated 18 o values of the ambient fluids 3 5 to 2 7 smow indicate precipitation of these cements from deeply circulating meteoric waters the presence of petroleum hydrocarbon inclusions in some samples is interpreted to reflect partial mixing with deeper basinal fluids the paragenetically youngest stage 3 calcite cement has only been encountered in a few veins these calcites are characterised by an intensely zoned luminescence pattern with bright yellow and non luminescent zones inclusions of mn oxides and siliceous sinters are commonly associated with stage 3 calcite which is interpreted to have precipitated from shallower meteoric waters regional structural analysis revealed that the calcite veins of the barrandian basin belong to a large scale system of north south trending lineaments that run through the territory of the czech republic the veins probably reflect episodes of fluid migration that occurred along these lineaments during late stages of the variscan orogeny

palaeomagnetic results from the fold and thrust belt of the western carpathians an overview the western carpathians are separated into an outer and inner carpathians both comprising several nappe systems by the extremely narrow and highly deformed pieniny klippen belt the main phase of deformation and thrusting took place during the late cretaceous in the inner carpathians at the end of cretaceous paleocene in the pieniny klippen belt and in the miocene in the outer carpathians in this paper a large amount of palaeomagnetic results of different quality available from several nappe stacks and from overstep sequences were reviewed and interpreted in terms of tectonics the data suggest that all three main units participated in two phases of anticlockwise rotation starting at 18 5 ma that is the outer carpathian nappes in front of the already consolidated alpine carpathian pannonian block became accreted to the block late cretaceous nappe transport neogene uplift of core mountains and possibly oroclinal bending of pre oligocene age can account for important differences in pre cenozoic palaeomagnetic declinations most of them exhibit less or no anticlockwise rotation suggested by the overstep sequences implying pre cenozoic clockwise rotations of variable angles

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

understanding and simulating the link between african easterly waves and atlantic tropical cyclones using a regional climate model the role of domain size and lateral boundary conditions using a suite of lateral boundary conditions we investigate the impact of domain size and boundary conditions on the atlantic tropical cyclone and african easterly wave activity simulated by a regional climate model irrespective of boundary conditions simulations closest to observed climatology are obtained using a domain covering both the entire tropical atlantic and northern african region there is a clear degradation when the high resolution model domain is diminished to cover only part of the african continent or only the tropical atlantic this is found to be the result of biases in the boundary data which for the smaller domains have a large impact on tc activity in this series of simulations the large scale atlantic atmospheric environment appears to be the primary control on simulated tc activity weaker wave activity is usually accompanied by a shift in cyclogenesis location from the mdr to the subtropics all era40 driven integrations manage to capture the observed interannual variability and to reproduce most of the upward trend in tropical cyclone activity observed during that period when driven by low resolution global climate model gcm integrations the regional climate model captures interannual variability albeit with lower correlation coefficients only if tropical cyclones form in sufficient numbers in the main development region however all gcm driven integrations fail to capture the upward trend in atlantic tropical cyclone activity in most integrations variations in atlantic tropical cyclone activity appear uncorrelated with variations in african easterly wave activity

a refined apparent polar wander curve for the transdanubian central mountains and its bearing on the mediterranean tectonic history abstract recently obtained palaeomagnetic data have given a fairly detailed apparent polar wander a p w curve for the mesozoic of the transdanubian central mountains which has been compared with other a p w curves from the mediterranean area the similarity of the a p w curves enabled a unified a p w curve to be constructed for the central mediterranean region it has been shown that the new mediterranean a p w curve is in full agreement even in details with the updated a p w curve for africa this confirms the existence during the entire mesozoic of a single central mediterranean megatectonic unit rigidly attached to africa its positions with respect to the pole can now be traced back in more detail than before

holocene sediment dynamics on a cool water carbonate shelf otway southeastern australia the otway shelf is covered by cool ocean waters and veneered by bryozoan dominated carbonate sediments radiocarbon dating and stratigraphy of shelf vibracores and slope gravity cores document late pleistocene holocene deposition shelf sediments of the late pleistocene highstand 60 26 ky are rare either never having been deposited or having been removed during the following sea level fall 26 17 ky during the subsequent lowstand the shelf was exposed facies shifted basinward and beach dune complexes were constructed near the shelf edge the deep shelf was characterized by nondeposition and hardground formation and the shelf margin became locally erosional upper slope bryozoan sponge assemblages continued to grow actively and lower slope foraminifera and nannofossil ooze was increasingly enriched in hemipelagic terrigenous mud swept off the wide shelf coarse shelf debris and lowstand dune sands were erosively reworked and transported onto the upper slope and redistributed to deep slope aprons during early transgression 17 10 ky this event locally terminated shelf edge bryozoan and sponge growth continued erosive shoreface retreat formed a bored and cemented ravinement surface mantled by bivalves and lithoclasts across the open shelf base level rise reduced the amount of terrigenous material reaching the continental slope slower transgressive flooding from 10 to 6 5 ky allowed infilling of shallow embayments on the shelf and outer shelf sediment accumulation began by 7 ky sea level stabilized near its present level by 6 5 ky and the area is now partitioned into three zones by an energetic wave and swell regimen 1 inboard protected embayments and or beach dune complexes with high sediment accumulation rates about 100 cm ky 2 an open shelf where although sediment production is active accumulation is patchy 3 5 cm ky to nonexistent within the zone of wave abrasion and minimal about 23 cm ky between maximum abrasion depth and swell wave base and 3 a deep shelf edge and upper slope where sediment is accumulating at rates of 2 50 cm ky interpreted deep water 100 m bryozoan sponge mounds are growing at rates of 105 cm ky accumulation decreases progressively down slope with deep slope pelagic carbonate sedimentation at rates of 5 cm ky the late quaternary shelf record resembles that of flat topped warm water platforms with holocene sediment overlying pleistocene tertiary limestone but for different reasons much of this high energy shelf is still within lag depth more than 10 ky after flooding the steady state deep water shelf margin bryozoan factory has been largely unaffected by 50 100 m eustatic changes in sea level and has contributed to slow but continuous platform progradation the slow growth potential uniform profile of sediment production and distribution and inability of constituent organisms to construct rigid frameworks favor maintenance of a shallow ramp profile and makes the cool water carbonate system an excellent modern analog for interpretation of many ancient ramp successions

palaeomagnetic evidence of tectonic rotations in the southern margin of the inner west carpathians abstract palaeomagnetic samples were collected at 33 triassic localities from three nappes and a pseudo autochthonous unit in the aggtelek rudabanya mountains in order to establish the rotation pattern of the area as a whole with respect to the enclosing principal continents and to check whether relative movements in the past between the various units that make up the region are resolvable by the palaeomagnetic data after detailed thermal demagnetization and careful data selection it has emerged that the entire study area was rotated anticlockwise with respect to both europe and africa i e in a similar manner and to a similar degree as other units in the central mediterranean region e g the transdanubian central mountains on the other hand small scale relative movements such as those between the aggtelek and rudabanya areas are not apparent in the present data

alteration of cenozoic cool water carbonates to low mg calcite in marine waters gambier embayment south australia abstract the oligo miocene gambier limestone is a poorly lithified fine grained bryozoan rich grainstone wackestone and marl allochems in these rocks which are typical of many modern and ancient cool water carbonates were originally calcite lmc mg calcite imc and hmc and minor aragonite but most are now neomorphosed to lmc with the exception of calcretes most limestones have 5 cement 13c and 18o values from 0 to 1 5o oo and preserved 87sr 86sr ratios that indicate that neomorphism occurred in seawater rather than meteoric or evolved pore waters marine diagenesis of the limestones was facilitated by their slow accumulation rates which were ca 15 mm ky based on sr isotope stratigraphy relatively fine grain size and high porosities which locally reach 50 the sr and mg contents of grainstones are significantly lower than in the original sediments whereas a less porous marl has higher sr and mg contents the grainstones have about 300 ppm sr and 6000 ppm mg consistent with slow abiotic precipitation of calcite under near equilibrium conditions with seawater which is the thermodynamic drive for this diagenesis the higher sr and mg content of the marl results from variable preservation of original allochems of biotic calcite the results from this study and others on modern cool water carbonates indicate that the extent of diagenesis varies with lithology but much neomorphism occurred in seawater with minimal effects from meteoric waters as such the chemical characteristics of seawater may be effectively preserved in some ancient cool water carbonates

mesozoic palaeomagnetism of the transdanubian central mountains and its tectonic implications abstract the mesozoic apparent polar wandering apw of the transdanubian central mountains determined from thermally isolated natural remanences at 13 localities shows a remarkable similarity to the mesozoic apw of africa in that they both exhibit the same loop like movement moreover the difference between the two apw s can practically be eliminated by a 35 clockwise rotation of the palaeodeclinations it is concluded therefore that the region of the transdanubian central mountains was part of the african adriatic plate up to some time in the cenozoic when it moved to its present position resulting in a 35 anticlockwise rotation relative to africa

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

diagenetic potential for lithification of cool water carbonate shelf mud abstract recent studies of cool water shelf carbonates have emphasized that lithification of fine grained carbonates is generally delayed post mechanical compaction due to near surface aragonite dissolution and greatly reduced effective permeability of mud size sediment a more complex response may exist texture mineral and stable oxygen carbon isotope attributes of sediment offshore of northernmost new zealand are used as input parameters to understand diagenetic pathways preserved in outer shelf te kuiti group and equivalent inner shelf torehina formation carbonate mudstones of oligo miocene age on north island new zealand modern seafloor mud is unlithified and consists of low magnesium calcite 13 c 8 to 15 by shallow burial concretions and oyster shell calcite the comparison of modern and oligocene sediment suggests that diagenetic potential for lithification of cool water shelf carbonate mud is driven by diagenesis of in situ and allochthonous mud size aragonite lithification rates may approach those associated with tropical deep water periplatform shelf derived sediment the oligocene carbonate mud lithified faster than regionally intercalated coarser grained skeletal calcarenites and likely contributes to deeper burial intrabasinal diagenetic heterogeneity

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

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

the low level structure of african easterly waves in 1995 abstract the existence of african easterly waves aews north of the african easterly jet aej core with maximum amplitude at low levels has been confirmed and clarified using radiosonde data and the u k meteorological office global model analysis from the hurricane season of 1995 at bamako 12 5 n 8 0 w the aews were characterized mainly by maximum amplitudes at the level of the aej around 700 mb whereas at dakar 14 7 n 17 5 w the waves were characterized by maxima between 850 and 950 mb the low level waves to the north of the aej arise in association with baroclinic interactions between the negative meridional potential vorticity pv gradients in the jet core and the positive low level gradient of potential temperature enhanced by the presence of low static stability air north of the aej these waves follow the positive meridional gradients over northern africa in contrast to the jet level aews that follow the meridional pv gradients at the level of the aej cross correlation analysis

modification of fracture porosity by multiphase vein mineralization in an oligocene nontropical carbonate reservoir taranaki basin new zealand the nontropical oligocene carbonate rich tikorangi formation is an important oil producer in the taranaki basin new zealand hydrocarbons are hosted and produced from mineralized natural fracture systems petrographic trace element stable isotope 18o and 13c and fluid inclusion data have enabled a complex sequence of eight paragenetic events to be determined the tikorangi formation host rock was cemented by low mg calcite event 1 during burial diagenesis from temperatures of 27c corresponding to 0 5 km burial and continued until 37c 1 km burial depth producing tight pressure dissolved fabrics with essentially no porosity and permeability the host rock was partially dolomitized 5 50 event 2 by ca and fe rich dolomite rhombohedra at burial depths and temperatures of 1 0 1 5 km and 35 50c without secondary porosity development subsequent brittle fracturing formed by neogene compression event 3 is constrained to a period following lithification and dolomitization but before precipitation of first generation vein calcite event 4 this initial ferroan low mg vein calcite formed after a period of burial from fe rich meteorically modified fluids at temperatures of about 50 60c and 1 4 1 9 km burial depth baroque dolomite formed event 5 following a period of mg enriched basinal fluid input precursory to hydrocarbon emplacement per se the dolomite formed mainly as a primary cement but also as a calcite replacement at temperatures following further burial to 2 2 5 km and temperatures of 65 80c formation of celestite and quartzine phases event 6 coincided with or marginally postdated dolomite at similar depths and temperatures to event 6 and formed as both replacements and cements second generation ferroan vein calcite formed event 7 at cooler temperatures 53 65c perhaps resulting from the introduction of cooler meteoric fluids from upsection the presence of petroleum fluid inclusions in the second generation calcite suggests precursory hydrocarbon bearing fluids have migrated along with aqueous fluids from about 10 ma with hydrocarbon emplacement event 8 occurring in the last 6 m y following a period of rapid late miocene burial an improved understanding of the paragenesis of the tikorangi formation may assist in hydrocarbon production from its reservoirs

new berriasian palaeopole from the central west carpathians tatra mountains southern poland does it look apulian summary a palaeomagnetic study was carried out in the northern part of the central west carpathians in the tatra mts 20 e 49 n berriasian pelagic carbonates from the krizna nappe fatricum were investigated at three localities 166 samples embracing a 100 m vertical section a mixed polarity pre folding magnetite related component was calculated for 87 samples representing the lower and middle berriasian the palaeopole 152 e 63 n is located close to the coeval eurasian palaeopole implying a net post berriasian 15 20 clockwise tectonic rotation of the krizna nappe in the investigated area relative to stable europe berriasian palaeolatitudes from the tatra mts are similar to those from the pieniny klippen belt and northern calcareous alps but systematically higher than in the transdanubian and italian apulian sections taking into account the fact that palaeomagnetic data from the overlying ter tiary rocks indicate 60 counter clockwise rotation of the central west carpathians after the oligocene the krizna nappe must have rotated clockwise before the eocene probably during the late cretaceous thrusting available palaeomagnetic data point to a palaeotectonic affinity of the central west carpathi ans and northern calcareous alps in the mesozoic the central west carpathians and northern calcareous alps reveal a rotation pattern that is predominantly clockwise whereas areas be longing to the apulian plate e g transdanubian mts southern alps and appenines show mostly counter clockwise rotations

a skeletal assemblage classification system for non tropical carbonate deposits based on new zealand cenozoic limestones abstract cenozoic limestones in new zealand are mainly skeletal grainstones and packstones formed under non tropical climatic conditions in open marine shelf or ramp environments following petrographic analysis of the nature and abundance of the skeletal components in nearly 500 samples of these limestones a complete linkage cluster analysis identified seven major skeletal assemblages that may be regarded as subdivisions of the single foramol skeletal association defined by lees and buller 1972 for temperate region carbonate deposits the seven assemblages are given contracted names as follows a barnamol barnacle bivalve dominated b bimol bivalve dominated c bryomol bryozoan bivalve dominated d echinofor echinoderm benthic foraminiferal dominated e nannofor nannofossil planktonic foraminiferal dominated f rhodalgal calcareous red algal dominated and g rhodechfor calcareous red algal echinoderm benthic foraminiferal dominated a composite triangular classification diagram has been devised for naming the skeletal assemblage of an unknown sample on the basis of its three main skeletal components the diagram successfully characterises more than 85 of the new zealand cenozoic limestone samples and also appears to be applicable for the skeletal assemblage designation of many overseas examples of non tropical carbonate deposits limitations relate mainly to locally common skeletal types e g serpulids brachiopods that are presently not incorporated into the new zealand based scheme the general ecological preferences of the main skeletal contributors in each of the seven skeletal assemblages form a basis for relating the assemblages to broad shelf habitats consequently as well as the benefits of providing a more consistent skeletal assemblage terminology for comparative studies between different workers the scheme can assist with the paleoenvironmental interpretation of non tropical skeletal carbonate facies

observations of seven african easterly waves in the east atlantic during 2006 abstract the african monsoon multidisciplinary analyses amma experiment and its downstream nasa extension namma provide an unprecedented detailed look at the vertical structure of consecutive african easterly waves during august and september 2006 seven easterly waves passed through the namma domain two waves developed into tropical cyclones debby and helene two waves did not develop and three waves were questionable in their role in the development of ernesto florence and gordon ncep global data assimilation system gdas analyses are used to describe the track of both the vorticity maxima and midlevel wave trough associated with each of the seven easterly waves dropsonde data from namma research flights are used to describe the observed wind structure and as a tool to evaluate the accuracy of the gdas to resolve the structure of the wave finally satellite data are used to identify the relationship between convection and the organization of the wind structure results support a necessary d

a characterization of african easterly waves on 2 5 6 day and 6 9 day time scales abstractthis study shows that the african easterly wave aew activity over the african monsoon region and the northern tropical atlantic can be divided in two distinct temporal bands with time scales of 2 5 6 and 6 9 days the results are based on a two dimensional ensemble empirical mode decomposition 2d eemd of the modern era retrospective analysis for research and applications merra the novel result of this investigation is that the 6 9 day waves appear to be located predominantly to the north of the african easterly jet aej originate at the jet level and are different in scale and structure from the well known low level 2 5 6 day waves that develop baroclinically on the poleward flank of the aej moreover they appear to interact with midlatitude eastward propagating disturbances with the strongest interaction taking place at the latitudes where the core of the atlantic high pressure system is located composite analyses applied to the mode decomposition indicate that the interaction of the

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

geometry and kinematics of vertical axis rotations in fold and thrust belts abstract vertical axis rotations indicated by palaeomagnetic study are a common and important component of deformation in fold and thrust belts the kinematics of rotating thrust sheets may be best described as a combination of a far field rotation or translation in a planar geometry and a near field or local rotation so that the instantaneous rotation axis lies outside the body of the sheet this simplifies the thrust sheet kinematics significantly as it means that all the points on the sheet have a component of forward motion and the bounding fault is a thrust over all its area the consequences of a simple thrust sheet rotation for the interpretation of fault lineation data are investigated the lineations recorded in the footwall and the hangingwall are likely to be different the hangingwall lineations being skewed towards the direction of rotation the principal mechanism for local thrust sheet rotation is differential shortening either on folds or thrusts or by a combination of these structures the forward propagation of thrusting towards the foreland can accumulate large 120 rotations on the uppermost sheets these rotational thrust sheets cannot extend indefinitely along strike instead they terminate against lateral ramps or transfer faults sidewall duplexes may form as a consequence of rotation over a lateral ramp examples of rotational geometries from the subbetic zone of southern spain are described on a larger scale obliquely convergent orogenic wedges can evolve by rotation of faults with an initial thrust geometry into progressively greater components of strike slip motion reliable palaeomagnetic data are not always available for fold and thrust belts so independent evidence for rotational deformation is of great importance fold and thrust geometries particularly along strike variability in fold geometries highly variable axial traces of folds evidence for near synchronous refolding and the deviation of regional trends may all be a consequence of thrust sheet rotation detailed mapping and particularly the identification of the position of footwall and hangingwall cut offs can also provide strong evidence for rotation

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less

reconciliation of late quaternary sea levels derived from coral terraces at huon peninsula with deep sea oxygen isotope records a major discrepancy between the late quaternary sea level changes derived from raised coral reef terraces at the huon peninsula in papua new guinea and from oxygen isotopes in deep sea cores is resolved the two methods agree closely from 120 ka to 80 ka and from 20 ka to 0 ka ka 1000 yr before present but between 70 and 30 ka the isotopic sea levels are 20 40 m lower than the huon peninsula sea levels derived in earlier studies new high precision u series age measurements and revised stratigraphic data for huon peninsula terraces aged between 30 and 70 ka now give similar sea levels to those based on deep sea oxygen isotope data planktonic and benthic 18o data using the sea level and deep sea isotopic data oxygen isotope ratios are calculated for the northern continental ice sheets through the last glacial cycle and are consistent with results from greenland ice cores the record of ice volume changes through the last glacial cycle now appears to be reasonably complete