dolomites and dolomites in mesozoic platform carbonates of the southern apennines geometric distribution petrography and geochemistry abstract a multidisciplinary study of the dolomitized bodies present among the late triassic to late cretaceous carbonate deposits of the monti lattari belt southern apennines of italy compares the different dolomitization styles present within this succession of these mesozoic platform carbonates and furnishes an overview of their formative genetic models the revealing traces of the diverse modes of diagenesis in this region include both surface and subsurface mechanisms utilizing a geometric reconstruction of the dolomitized bodies an integrated facies and petrographic analysis of the components and a geochemical characterization of the sediments including detailed mineralogy and associated stable isotope values the data presented demonstrate that some intervals are characterized by surface related dolomitization processes middle late triassic and cretaceous while others latest triassic to lower middle jurassic and are mainly dominated by later large scale subsurface dolomitization processes all of the middle late triassic norian successions are pervasively dolomitized exhibit fabric preserving textures and have a distinctly heavy stable isotope signature their origin has been related to diagenesis due to particular climatic and palaeoceanographic conditions leading to the formation of extended blankets of shallow warm saline seawater this setting was terminated by climatic and palaeoceanographic changes during the latest triassic which dramatically reduced the significance of surface related dolomitization on a regional scale the overlying latest triassic rhaetian outcrops consist of a widespread coarse fabric destructive massive dolomite with a lighter isotopic signature these dolomites seem genetically related to the ones of the lower middle jurassic which share the same geometrical petrographic and geochemical characteristics caused by large scale fluid circulation this diagenetic pattern apparently started in the early jurassic during burial driven by thermal convection due to the different temperatures between the oceanic waters and the warmer carbonate platform the middle upper jurassic units feature local episodes of early dolomitization that partially replaced the muddy carbonate facies due to tidal pumping and reflux mechanisms dolomitization is not a pervasive feature during this phase of deposition in the cretaceous portion of the succession dolomites have a totally different and distinct character and are generally related to bedding and show variability in textures and mg ca ratios local association with evaporites geometry of dolomitized bodies and stable isotope geochemistry suggest processes comprising evaporative pumping and reflux all related to the surface environment this evidence points to a renewal of a climatic context more favorable for early dolomitization thus this study permits recognition of the presence of three quite different dolomitization styles within the carbonate platform succession of the southern apennines fold thrust belt one ascribed to the norian one to the rhaetian lower jurassic and one to the cretaceous

internal tide scattering at seamounts ridges and islands 1 the scattering of mode 1 internal tides from idealized gaussian topography in a nonrotating ocean with constant and realistic stratifications is examined with a primitive equation numerical model incident mode 1 energy fluxes of 20 and 2000 w m 1 are used to examine the linear regime and a more realistic situation simulations using two dimensional or infinite ridges compare well with ray tracing methods and illustrate how the size and shape of the topography influence wave scattering the height affects energy transmission and reflection while the slope and width determine the conversion of low mode internal tides into beams or higher modes three dimensional topographic scattering is considered for seamounts finite width ridges and islands scattering from finite ridges focuses wave energy directly downstream while scattering from seamounts produces azimuthal energy dispersion scattering to higher wave modes occurs in the lee of near critical and supercritical seamounts and ridges nonlinear interactions transfer energy into the mode 1 m4 internal tide the mellor yamada level 2 5 submodel parameterizes turbulent mixing for the near critical and supercritical ridges with realistic stratification elevated mixing is found over the leading edge of the topography and along a tidal beam up to the first surface bounce a transition from a beam structure near the topography to a low mode structure farther away occurs due to an increased contribution from the mode 1 internal tide as it refracts around the topography and not due to turbulent dissipation internal tide scattering at topography leads to a loss of energy to mixing and to a redistribution of energy flux in space frequency and mode number

stratigraphic architecture palaeogeography and sea level changes of a third order depositional sequence the late turonian early coniacian in the northern iberian ranges and central system spain abstract this paper reports a high resolution stratal palaeogeographical and quantitative analysis of a late turonian early coniacian carbonate ramp the northern iberian ranges and its siliciclastic coastal margin the central system the analyzed succession comprises a complete 3rd order depositional sequence with a shelf margin wedge a transgressive systems tract and a highstand systems tract based on the existence of a subaerial exposure evidences and early diagenetic overprints b stratal relationships onlap offlap toplap regarding underlying and overlying sequences and c changes in the vertical facies evolution the depositional sequence was bounded by two major sequence boundaries these indicate that a major fall in relative sea level occurred in these boundaries the comparative study of the internal stratal surfaces and the vertical facies succession allowed the identification of superimposed higher order depositional parasequences sets and parasequences 4th to 5th order which record short term changes in the relative sea level thus when vertical facies trends in the parasequences are arranged in the framework of a parasequence set a clearer palaeogeographic picture is obtained and palaeogeographic maps can more clearly show the evolutionary trend of the basin each parasequence set was composed of a basal lowstand transgressive systems tract in turn composed of fringing siliciclastic shoreface deposits and offshore muds older sequences were partially exposed further landwards the sedimentation of these sands resulted in the progradation of the coastal systems during times of low relative sea level during which the basal parasequence set boundary was also generated subsequent transgression remobilised underlying lowstand sands the early highstand was composed of carbonate sediments in platform areas and mixed siliciclastic carbonate sediments landwards separated by a narrow fringe of muddy marl offshore sediments the late highstand showed a progressive shallowing trend with carbonate littoral and tidal sediments covering broad areas of the basin and lagoon facies were restricted to the northern outcrops during late highstand underlying transgressive systems tract and older highstand deposits were exposed landwards sea level and accommodation curves have been obtained from paleogeographical sedimentological and sequence stratigraphical data the mean sea level curve for the entire 3rd order sequence shows a rise of the sea level and then an overall stillstand but accommodation curve shows a positive trend along the sequence the 3rd order sea level cycle has a mean amplitude of 52 m and high frequency cycles have amplitudes of 20 40 m 4th order and about 1 5 4 m 5th order the mean final rise in the sea level 46 6 m is quite similar to the total accommodation deduced from fischer plot 45 75 m the sea level cycles are considered to be eustatic in origin and driven by orbital forcing in the milankovitch band based on the estimated 4th order 400 kyr and 5th order cycle lengths 80 kyr

cenozoic dolomites of carbonate islands their attributes and origin abstract dolomites found on and below carbonate islands atolls and oceanic platforms provide useful insights into the origin of dolomite insights that may not be attainable from the study of more ancient cratonic dolomites for this reason they have been the subject of study for decades a critical mass of case studies now exist and some significant conclusions can be drawn from the cumulative data in most cases the association with an island is causal and not genetic nevertheless these dolomite occurrences are referred to herein as island dolomites one type of dolomite on carbonate islands is penecontemporaneous dolomite a phase that forms while the host sediment is in its original depositional setting island examples are holocene in age occur in holocene sediments and originate as a direct precipitate from either normal or evaporated seawater these are microcrystalline poorly ordered ca rich 18o enriched and geochemically unstable phases that are susceptible to recrystallization in the setting in which they formed post depositional dolomite is the other type of dolomite associated with carbonate islands this type of dolomite replaces older precursors and forms as cement distinctive characteristics include a dominance of fabric preserving texture pore lining cement rims that may exhibit micron scale banding with low mg calcite and formation in association with precursor dissolution sr isotopic dating indicates that all examples are neogene or quaternary in age those formed during the middle miocene through pliocene are massive laterally continuous and often multigenerational in contrast younger examples tend to be localized partial replacements of a single generation sr isotope ages also suggest global synchroneity in many dolomitization events which suggests a connection between dolomitization global eustacy and or global climatic factors geochemical attributes of post depositional island dolomites are ca enrichment positive 18o and 13c low sr contents 150 300 ppm and low fe global similarity in petrography and geochemistry of replacive island dolomites argues for a similar origin inferred origins however depend primarily on how 18o and sr data are interpreted values for 18o and dsr must be assumed due to uncertainties in oxygen isotope fractionation and sr partitioning there is no consensus or uniformity in those assumptions thus interpretations can vary and be biased to a desired result covariant trends in 13c and 18o some negative 13c values and high sr all favor a mixing zone origin but examples with these attributes are few lack of covariance in the isotopes mean 18o of 2 0 to 3 5 and low sr future studies should standardize the type of data collected and the analytical techniques employed multiple geochemical attributes should be measured on microsampled components and quantitative modeling should be employed in order to constraint interpretations as much as possible also needed are a better understanding of the kinetic processes that form these dolomites more careful assessment of their recrystallization status and an improved understanding of dsr and 18o at low temperature

internal anatomy of a mixed siliciclastic carbonate platform the late cenomanian mid turonian at the southern margin of the spanish central system the late cenomanian mid turonian succession in central spain is composed of siliciclastic and carbonate rocks deposited in a variety of coastal and marine shelf environments alluvial plain estuarine lagoon shoreface offshore hemipelagic and carbonate ramp three depositional sequences third order are recognized the atienza patones and el molar sequences the patones sequence contains five fourth order parasequence sets while a single parasequence set is recognized in the atienza and el molar sequences systems tracts can be recognized both in the sequences and parasequence sets the lowstand systems tracts only recognized for atienza and patones sequences are related to erosion and sequence boundary formation transgressive systems tracts are related to marine transgression and shoreface retreat the highstand systems tracts are related to shoreface extension and progradation and to carbonate production and ramp progradation sequences are bounded by erosion or emergence surfaces whose locations are supported by mineralogical analyses and suggest source area reactivation probably due to a fall in relative sea level transgressive surfaces are subordinate erosion and or omission surfaces with a landward facies shift interpreted as parasequence set boundaries the co existence of siliciclastic and carbonate sediments and environments occurred as facies mixing or as distinct facies belts along the basin mixed facies of coastal areas are composed of detrital quartz and clays derived from the hinterland and dolomite probably derived from bioclastic material siliciclastic flux to coastal areas is highly variable the maximum flux postdates relative sea level falls carbonate production in these areas may be constant but the final content is a function of changing inputs in terrigenous sediments and carbonate content diminishes through a dilution effect carbonate ramps were detached from the coastal system and separated by a fringe of offshore fine grained muds and silts as distinct facies belts the growth of carbonate ramp deposits was related to the highstand systems tracts of the fourth order parasequence sets during the growth of these ramps some sediment starvation occurred basinwards progradation and retrogradation of the different belts occur simultaneously suggesting a sea level control on sedimentation in the study area the co existence of carbonate and siliciclastic facies belts depended on the superimposition of different orders of relative sea level cycles and occurred mainly when the second order third order and fourth order cycles showed highstand conditions

dolomitization by penesaline sea water in early jurassic peritidal platform carbonates gibraltar western mediterranean peritidal carbonates of the lower jurassic liassic gibraltar limestone formation which form the main mass of the rock of gibraltar are replaced by fine and medium crystalline dolomites replacement occurs as massive bedded or laminated dolomites in the lower 100 m of an 460 m thick platform succession the fine crystalline dolomite has d 18 o values either similar to or slightly higher than those expected from early jurassic marine dolomite and d 13 c values together with 87 sr 86 sr ratios that overlap with sea water values for that time indicating that the dolomitizing fluid was early jurassic sea water absence of massive evaporitic minerals and or evaporite solution collapse breccias in these carbonate rocks indicates that the salinity of sea water during dolomitization was below that of gypsum precipitation the occurrence of peritidal facies a restricted microbiota and rare gypsum pseudomorphs are also consistent with penesaline conditions salinity 72 199 the medium crystalline dolomite has some d 18 o and d 13 c values and 87 sr 86 sr ratios similar to those of early jurassic marine dolomites which indicates that ambient sea water was again a likely dolomitizing fluid however the spread of d 18 o d 13 ca nd 87 sr 86 sr values indicates that dolomitization occurred at slightly increased temperatures as a result of shallow 500 m burial or that dolomitization was multistage these data support the hypothesis that penesaline sea water can produce massive dolomitization in thick peritidal carbonates in the absence of evaporite precipitation taking earlier models into consideration it appears that replacement dolomites can be produced by sea water or modified sea water with a wide range of salinities normal penesaline to hypersaline provided that there is a driving mechanism for fluid migration the gibraltar dolomites confirm other reports of significant early jurassic dolomitization in the western tethys carbonate platforms

fluid rock interaction history during stabilization of early dolomites upper knox group lower ordovician u s appalachians abstract the lower ordovician upper knox group is characterized by shallowing upward peritidal cycles that are extensively dolomitized to form massive dolomite most 85 replacive dolomite is stratigraphically controlled composed of very fine to medium crystalline planar to nonplanar early dolomite composed of zones 1 2 and 3 dolomites remaining dolomite occurs as medium to coarsely crystalline nonplanar late replacive dolomite zones 2 and 3 late dolomites that selectively replaces limestone associated with stylolites and fractures or forms massive dolomite fronts complexly zoned zone 2 to 6 saddle dolomite cements make up less than 5 of all dolomite and primarily fill solution voids and fractures early dolomites are near stoichiometric and relative to early ordovician marin carbonates are similar to or significantly depleted in 18o and sr slightly to significantly enriched in mn and fe and have similar 87sr 86sr values relative to early dolomites late zones 2 and 3 dolomites are depleted in 18o and st enriched in mn and fe and have similar 87sr 86sr values early dolomites are interpreted to have formed from modified seawater during seaward progradation of tidal flats within each high frequency fifth and fourth order cycle duration late dolomites based on their texture and geochemistry formed as a result of recrystallization of early dolomites as direct replacement of limestone at elevated temperatures and as cement in fractures and secondary solution voids covariant trends between textures and geochemical compositions for early dolomite indicate that presentday compositions of knox early dolomite record a history of progressive diagenetic modification stabilization or recrystallization involving varying degrees of changes of textural and geochemical compositions during multiple episodes of dolomitization early dolomites wit the most extensively altered textures are more stoichiometric more depleted in 18o and sr and more enriched in mn and fe relative to texturally less altered early dolomite initial stabilization may have occurred syndepositionally in modified seawater continued stabilization of early dolomite likely occurred in fresh or mixed waters of a middle ordovician meteoric aquifer associated with knox unconformity development final stabilization occurred by deep burial brines at elevated temperatures as indicated by 1 extensive replacement and overgrowth of early dolomite by late dolomites 2 a progressive increase in crystal size and abundance of nonplanar crystal boundaries with increase in replacement by late dolomites and 3 the similarity of the geochemical compositions of texturally most extensively altered early dolomites and late dolomites

plate reconstruction of the bay of biscay a plate reconstruction of the bay of biscay to a predrift stage is proposed on the basis of 1 an aptian albian tectonic pattern of the basque cantabrian region in northern spain which suggests major left lateral strike slip movements and 2 a continental margin that matches predrift stages plate reconstruction results from the juxtaposition of the two continental margins of the bay of biscay so that the eastern north spanish margin lies laterally adjacent to the southwest french margin landes plateau and the western north spanish margin borders the eastern part of the meriadzek terrace in the armorican margin the restoration obtained is supported by both the implied amount of clockwise rotation of iberia 37 very close to the 35 suggested by paleomagnetism and the positive matching of north south oriented transform structures from the south biscay margin with northeast southwest oriented transform structures from the north biscay margin

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

compilation and time series analysis of a marine carbonate δ18o δ13c 87sr 86sr and δ34s database through earth history abstract the sr s o and c isotope database of marine carbonates contains over 55 000 published isotope values of low mg calcite from diagenetically little altered phanerozoic fossil shells as well as samples of whole rocks and calcite cements of ordovician to archean age carbon and oxygen isotope data for the shell material are divided into habitat subsets high mid low latitude and deep sea and whole rock data are separated by mineralogy into calcite dolomite subsets trend correlation wavelet and spectral analyses on gaussian filtered isotope records were applied to detect and quantify similarities and patterns in temporal records with the following results 1 oxygen isotope trends from the high latitude and deep sea habitats are almost indistinguishable through the last 115 ma consistent with the existence of the oceanic conveyor belt throughout this interval 2 all oxygen isotope habitat records show a strong coherent 30 45 ma 38 ma cyclicity throughout the cretaceous and the cenozoic 3 up to 70 of the multi million year variability in the 18o record of the last 115 ma can be simulated by the following equation 18 o 0 64 sin 2 t 120 ma 0 9 x sin 2 t 38 3 ma 1 1 with x ranging from 0 4 0 6 for the low high latitude and deep sea habitats to 0 8 for the mid latitude realm 1 a 120 20 ma cycle occurs in the paleozoic and neoproterozoic 18o record consistent with paleoclimate variability as interpreted from sedimentological and faunal records 2 the offset of 13c values between deep water and high latitude vs surficial habitats at lower latitudes is consistent with the operation of a biological pump in the oceans since at least the cretaceous 3 sr and s isotope records exhibit a 60 70 ma cyclicity throughout the phanerozoic

reactive transport modeling of brine reflux dolomitization anhydrite precipitation and porosity evolution abstract both geothermal convection and brine reflux drive circulation of sea water derived fluids through carbonate platforms during early burial but dynamic interactions between heat and solute transport and resulting diagenesis are at present poorly understood this paper describes high resolution reactive transport model rtm simulations that suggest that reflux of 85 ppt brines rapidly restricts geothermal convection to the platform margin with flow focused in the more permeable shallow carbonates in a baseline simulation involving an elongate 25 km wide grain dominated packstone platform brine reflux resulted in complete dolomitization beneath the 5 km wide brine pool in 335 ky the dolomite body then extends downward at c 22 m 100 ky into an underlying broad area of partial dolomitization this process enhances porosity at shallow depth but beneath the dolomite body precipitation of anhydrite occludes porosity and limits the depth of reflux in contrast geothermal convection at the platform margin forms a smaller partially dolomitized body over a longer time 60 dolomite after 1 my with very minor associated anhydrite cementation reflux diagenesis is sensitive to platform geometry with higher rates of fluid flow increasing the depth of alteration beneath the brine pool for a circular platform compared to the linear baseline fluid flow across thermal gradients enhances reaction rates and ignoring heat transport by 85 ppt brine reflux underestimates the extent of reflux dolomite by 25 and associated anhydrite by 90 the depth and rate of anhydritization is sensitive to the geothermal heat flux whereas platform top temperatures affect dolomitization rate reflux diagenesis is also sensitive to brine density which affects both fluid flow and reaction rates sediment permeability and reactive surface area rsa are key intrinsic controls on diagenesis where the permeability structure permits sufficient fluid flow diagenesis preferentially affects more reactive fine grained sediments however as flow rates decline reactions become focused in the more permeable but less reactive sediments simulations thus shed light on why in some settings reflux preferentially dolomitizes muddy sediments but elsewhere favors grainstones once active reflux ceases brines continue to flow in the subsurface but this latent reflux causes only minor dolomitization due to prior mg2 consumption at shallow depth

windblown desert sands in coeval shallow marine deposits a key for the recognition of coastal ergs in the mid cretaceous iberian basin spain introductionthe action of the wind in ancientsedimentary records is commonlybased on the direct observations ofdune and interdune deposits within ahierarchy of aeolian bounding surfa ces a direct observation of ancientaeolian systems is not always possibleas they are prone to erosion and to theremoval of sand into other uvial andmarine systems although the aeoliandeposits may no longer be present their former existence can be inferredon the basis of grain size characteris tics and aeolian features on grainsurfaces aeolian sediments indeedconstitute an important source formarine deposits kukal and saadal lah 1973 fryberger et al 1983 widespread ne grained very well sorted quartz sandstones characterizeshallow marine facies in the mid cre taceous of the eastern spain iberianbasin the good sorting and round ness of the grains hint at the presenceof a nearby erg system suggestive ofan arid climatic zone along the west ern tethyan margin during the mid cretaceous geological settingthe mesozoic iberian basin along thewestern tethyan margin has one ofthe more complete lower middle cre taceous sedimentary records in eur ope the iberian range is a nw sestriking intraplate fold belt generatedby the tectonic inversion of theiberian basin during the palaeogene fig 1a b salas and casas 1993 capote et al 2002 this basin wasformed by crustal thinning duringthe late permian triassic and latejurassic early cretaceous rift stages salas and casas 1993 arche andlo pez go mez 1996 during thesecond rift stage extensional sub basins were formed as part of thelarger maestrazgo basin i e the east ern sector of the iberian basin fig 1b soria 1997 sands of boththe last synrift unit of these sub basins the escucha formation and of the rst post rift unit of the iberian basin the utrillas formation were depos ited across the estuarine deltaic and uvial environments fig 1c quer ol et al 1992 the sands are domi nantly ne grained show excellentsorting and as they consist almostpurely of quartz they are mineralog ically very mature the escucha and the utrillasformationsthe upper aptian middle albian es cucha formation aguilar et al 1971 sole de porta et al 1994 fig 1c was formed during the last phases ofthe second rift stage that a ected theiberian basin salas and casas 1993 it is a tidally in uenced heterolithicunit dominated by very well sorted ne sand and clay with coal bearingdepositsinitslowerpart andlocallyinthe basal part coarse grained siliciclas tic levels it lies upon the limestonesand marls of the urgonian platform aptian and is covered by sandstonesof the utrillas formation fig 1c pardo 1979 querol 1990 the es cucha formation was interpreted as adeltaic estuarine succession querolet al 1992 with a barrier island sys tem in the northern part of the olietesub basin rodri guez lo pez et al 2005 it was deposited in extensionalsub basins bounded by palaeogeo graphic thresholds produced by listricand block rotation faults the utrillasformation overlies the escucha for mation and is late albian early cen omanian in age and represents uvialdeposits pardo 1979 however theabstract

paleomagnetic evidence for rotation of the iberian peninsula and the external betic cordillera southern spain abstract paleomagnetic investigations of jurassic cretaceous and tertiary sites in the external betic cordillera indicate that while the observed remanence vectors have inclinations which are conformable with the expected inclinations for stable iberia declinations deviate significantly these results indicate that 1 the mesozoic limestones of the penibetic have been rotated clockwise with respect to stable iberia and 2 there is a differential rotation between the cretaceous sites dec 61 11 and the jurassic sites dec 38 8 the differential rotation of 23 between the late jurassic and late cretaceous is consistent with the cretaceous anticlockwise rotation of the iberian peninsula with respect to eurasia it follows that during this time period this part of the betic mobile belt waspart of the continental margin of the iberian peninsula a study which was confined to a single unbroken stratigraphic section west of ronda indicates that most of the anticlockwise rotation 20 probably occurred between the cenomanian and the campanian the anticlockwise rotation of these rocks must have been followed by a clockwise rotation of at least 60 to account for the observed clockwise declination anomalies

the interaction of tectonics climate and eustasy in controlling dolomitization a case study of cenomanian turonian shallow marine carbonates of the iberian basin

sequences cycles and hiatuses in the upper albian cenomanian of the iberian ranges spain a cyclostratigraphic approach abstract the upper albian cenomanian deposits in the iberian ranges are composed of a complex alternation of continental sandstones coastal lime sandstones and marls and marine carbonates facies facies are arranged mainly in transgressive and deepening upward sequences and parasequences but deepening shallowing upwards sequences and parasequences also exist depositional sequences and parasequences are bounded by subaerial erosive surfaces or ferruginous crusts and by their correlative conformities it is evident from the facies alternation that deposition reflects a cyclic process in which is superimposed several orders of cycles of relative sea level rise and fall the cycles are preserved as 3rd order depositional sequences and 4th and 5th order discontinuity bounded parasequences the latter being the basic blocks of the field record a cyclostratigraphic model for sedimentation shows that each of the 3rd order cycles is composed of five 4th order cycles a 4th order cycle is also composed of five 5th order cycles this 1 5 5 ratio reflects the maximum number of parasequences observed in the most complete and marine sections the ratio remains unchanged throughout the basin except by onlap caused by relative sea level rises or truncations caused by relative sea level falls a detailed correlation of sections separated by more than 200 km shows that thickness differences are caused mainly by parasequence disappearance not parasequence thinning cycles are mainly eustatic in origin controlled by accommodation space increased accommodation generates thick parasequences of wider regional extension they contain the more marine facies in any section only some sequences with a restricted regional distrubution are recorded if the accommodation is low the average duration of 3rd order cycles was 1 95 ma ranging from 1 33 to ma an average 4th order cycle was 390 ka 266 533 ka and a 5th order cycle was 78 ka 53 106 ka

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

sequence stratigraphy of mixed carbonate siliciclastic platforms developed in a tectonically active setting upper cretaceous betic continental margin spain abstract the late cretaceous platforms in the betic continental margin record a prolonged interval 30 m y in which eustasy and tectonics operated simultaneously but with well differentiated frequencies this resulted in development of two types of unconformity bounded units sequence sets which are tectonically controlled and depositional sequences which are the result of variations in relative sea level unconformities bounding sequence sets are the result of tectonic episodes that induced great changes in basin geometry and basin subsidence they operated without apparent rhythmicity at intervals ranging from i to 12 m y regional tectonics was related to variations in the intraplate stress regime associated with 1 the mid atlantic spreading 2 the tectonic regime in the africa iberia boundary still poorly documented 3 the opening of the bay of biscay between the aptian and the early campanian and 4 the oblique convergence between iberia and europe in the pyrenees which started in the early campanian during periods of relative tectonic quiescence eustasy and subsidence controlled development of depositional sequences these resulted from relative sea level oscillations most of them interpreted as third order eustatic cycles however the correlation between our depositional sequences and the global cycles of the exxon chart is not always easy mainly because subsidence can mask or enhance the eustatic signal

eustatic control on early dolomitization of cyclic peritidal carbonates evidence from the early ordovician upper knox group appalachians the early ordovician upper knox group is characterized by stacked meter scale peritidal cycles that repeat at high frequencies 10 4 to 10 5 yr stacking patterns stratigraphic trends in lithofacies and cycle thickness of meter scale cycles define five depositional sequences that in conjunction with fischer plots delineate five long term relative sea level fluctuations during upper knox deposition intrabasinal and interbasinal correlation of upper knox fischer plots suggests that the third order sea level events were eustatic meter scale peritidal cycles likely formed in response to high frequency fourth and fifth order eustatic sea level fluctuations superimposed on these third order sea level events upper knox cyclic carbonates are extensively dolomitized as much as 85 of all dolomite is stratiform and consists of early dolomite exhibiting minor to extensive modification by burial dolomite synsedimentary dolomitization likely occurred in modified sea water during tidal flat progradation governed by high frequency sea level events this is suggested by the common association of dolomite with mud cracked laminites and silicified evaporite nodules the systematic decrease in dolomite abundance below laminite cycle caps and the presence of dolomite clasts in regoliths veneering high frequency cycle tops or in transgressive limestones of the overlying cycle dolomite distribution within depositional sequences shows a strong relationship to third and fourth order eustatic sea level events indicating that long term eustasy also strongly controlled early dolomitization of upper knox carbonates mass balance calculations show that the proposed sabkha model of dolomitization in concert with composite eustasy could generate stratiform dolomite of considerable vertical and lateral extent in peritidal cyclic carbonates this reflects the duration of progradation and supratidal exposure 10 4 to 10 5 yr available for dolomitization to proceed and the broad zone of active dolomitization that would develop during continued progradation throughout each cycle period

observed and predicted bed forms and their effect on suspended sand concentrations abstract in this paper we study the effect of bed forms on suspended sand concentrations and we compare three existing bed form predictors to field and laboratory measurements over a wide range of conditions and propose a new predictor that better collapses the measured bed form dimensions we apply the different bed form predictors to estimate the suspended sediment concentration distributions based on the 1d advection diffusion equation and the bed form enhanced shear stress which includes the flow contraction effect according to nielsen coast eng 10 1986 23 predictions of suspended sand concentration improve when including a bed form predictor interestingly it does not make much difference which bed form predictor is implemented but more whether a bed form predictor is implemented however the choice of a particular bed form predictor is more important when the bed form effect in the sand transport model is based a roughness length scale k s and thus on 2 instead of where k s is nikuradse s equivalent roughness length scale is the bed form height and is the bed form length this is the case in the van rijn van rijn l c 2000 general view on sand transport by currents and waves data analysis and engineering modelling for uniform and graded sand transpor 2000 and crosmor 2000 models z2899 20 z2099 30 z 2824 30 wl delft hydraulics delft the netherlands sand transport model for example we discuss the effect of so called long wave ripples on the suspended sand concentrations

sedimentology and geochemistry of lowstand peritidal lithofacies at the cenomanian turonian boundary in the cretaceous carbonate platform of israel abstract the upper cenomanian shallow marine platform dolostone in northern israel is topped by a calcrete crust it is unconformably overlain by a chaotic unit 8 m thick consisting of various peritidal lithofacies including tidalite desiccated and brecciated tepee dolostone and algal stromatolites enveloped within a calcite matrix the latter originally mainly a carbonate mud was exposed and dolomitized but later underwent large scale dedolomitization leaving a massive nonbedded limestone host open marine sedimentation resumed when sea level again rose depositing turonian biomicritic limestone this chaotic unit is a manifestation of lowstand deposition at the cenomanian turonian boundary in israel and may equate to a sea level drop of similar age from the same period reported in britain and france field petrographic trace element and stable isotope data suggest that the platform dolostone formed by seawater dominated fluid dolomitization of foraminiferal carbonate mud the tepee dolomite in the chaotic unit formed under the influence of mixed sea water fresh water fluids associated with an intertidal setting certain geochemical variations suggest a subtle difference in the composition of the mud precursors rather than involvement of meteoric waters dedolomitization involved meteoric solutions depleted in 18o and 13c that reacted with decayed organic matter in soils sr fe and na were removed in solution together with the mg in a relatively open system an increase in p and k in the dedolomite suggests a better exchange mechanism between k and p with ca as compared to mg

midlatitude shelf seas in the cenomanian turonian greenhouse world temperature evolution and north atlantic circulation 1 an 8 million year record of subtropical and midlatitude shelf sea temperatures derived from oxygen isotopes of well preserved brachiopods from a variety of european sections demonstrates a long term cenomanian temperature rise 16 20 c midlatitudes that reached its maximum early in the late turonian 23 c midlatitudes superimposed on the long term trend shelf sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations in the mid cenomanian and the late turonian two minor shelf sea cooling events 2 3 c coincide with carbon cycle perturbations and times of high amplitude sea level falls although this evidence supports the hypothesis of potential glacioeustatic effects on cretaceous sea level the occurrence of minimum shelf sea temperatures within transgressive beds argues for regional changes in shelf sea circulation as the most plausible mechanism the major carbon cycle event in the latest cenomanian oceanic anoxic event 2 is accompanied by a substantial increase in shelf sea temperatures 4 5 c that occurred 150 kyr after the commencement of the 13c excursion and is related to the spread of oceanic conditions in western european shelf sea basins our oxygen isotope record and published 18o data of pristinely preserved foraminifera allow the consideration of north atlantic surface water properties in the cenomanian along a transect from the tropics to the midlatitudes on the basis of fossil derived 18o estimated w ranges and modeled salinities temperature salinity density ranges were estimated for tropical subtropical and midlatitude surface waters accordingly the cenomanian temperate shelf seas waters have potentially the highest surface water density and could have contributed to north atlantic intermediate to deep waters in the preopening stage of the equatorial atlantic gateway

mid cenomanian separation of atlantic and tethyan domains in iberia by a land bridge the origin of larger foraminifera provinces abstract the middle and late cretaceous shallow water carbonate platforms widely exposed across the eastern half of the iberian peninsula including the betic cordillera the iberian ranges and the pyrenees provides an excellent material for analyzing the origin of two iberian late cretaceous larger foraminifera provinces the betic and the pyrenean the former corresponds to the tethyan domain the latter to the atlantic domain the spatiotemporal distribution in the three studied areas of the larger foraminifera k strategists the alveolinaceans from the latest albian cenomanian time interval suggests that separation of the two faunal provinces started during early cenomanian mid cretaceous global community maturation cycle and the shelves of the iberian seaway formed the boundaries of the corresponding bioprovinces this occurred before the betic pyrenean communication near the middle late cenomanian transition was interrupted by a land bridge therefore the separation of the two bioprovinces cannot be due to the physical barrier created by the opening or closure of the shallow seaway across the iberia here it is attributed to the differences in the ecological gradients at the end of the cenomanian the cenomanian turonian eutrophication event eliminated all the k strategist larger foraminifera to such a degree that all their essential k strategy information was lost the newly arising k strategist foraminifera needed a considerable time 8 10 m y to recover their lost genetic complexity this occurred during the coniacian in the following gcm cycle

alteration of early formed dolomite during shallow to deep burial mississippian mission canyon formation central to southwestern montana dolomite in the mississippian mission canyon formation osagean to middle meramecian of central and southwestern montana precipitated during multiple episodes of dolomitization and or recrystallization the earliest generation of dolomite most likely precipitated from evaporated sea water in near surface diagenetic environments when the mission canyon platform intermittently aggraded to sea level this dolomite has relatively positive delta sup 18 o values minus 1 5 to 7 5 and typically is nonstoichiometric and trace element enriched a second generation of dolomite has very negative delta sup 18 o values minus 11 2 to minus 1 5 and always is stoichiometric and trace element depleted dolomite with delta sup 18 o values minus 6 8 is in the upper 100 180 m of the mission canyon formation beneath a regional post mission canyon unconformity and karst surface that extends across the entire study area dolomite depleted in sup 18 o may have 1 precipitated initially in a regional mixing zone during post mission canyon subaerial exposure and karstification 2 precipitated at elevated temperatures during later diagenesis or 3 recrystallized from an earlier generation of dolomite during later shallow to deep burial diagenesis very negative delta sup 18 o values and low trace element contents for the second generation of dolomite suggest that diagenetic solutions were dominated by meteoric water whereas delta sup 13 c values indicate that diageneticmore fluids were buffered by osagean carbonate rocks 54 refs 10 figs less

extremely high sea surface temperatures at low latitudes during the middle cretaceous as revealed by archaeal membrane lipids the middle cretaceous 125 88 ma greenhouse world was characterized by high atmospheric co 2 levels the general absence of polar ice caps and much higher global temperatures than at present both 1 8 o based and model based temperature reconstructions indicate extremely high sea surface temperatures ssts at high latitudes however there are a number of uncertainties with sst reconstructions based on 1 8 o isotope data of foraminifera due to diagenetic overprinting effects and tenuous assumptions with respect to the 1 8 o value of cretaceous seawater the paleoecology of middle cretaceous marine organisms and seawater ph here we applied a novel sst proxy i e text tetraether index of 86 carbon atoms based on the membrane lipids of marine crenarchaeota derived from middle cretaceous sedimentary rocks deposited at low latitudes the text proxy indicates that tropical ssts in the proto north atlantic were at 32 36 c during the early albian and late cenomanian early turonian this finding agrees with sst estimates based on 1 8 o paleothermometry of well preserved foraminifera as well as global circulation model calculations the text proxy indicates cooler ssts 27 32 c for the equatorial pacific during the early aptian which is in agreement with sst estimates based on 1 8 o paleothermometry

reactive transport modeling of early burial dolomitization of carbonate platforms by geothermal convection reactive transport models rtms permit quantitative investigation of diagenesis and its effects on reservoir quality the rtm toughreact is used to investigate diagenesis in an isolated platform driven by geothermal kohout convection of seawater which has been invoked to explain dolomitization during early burial previous short 0 1 m y rtm simulations suggested that convection can drive dolomitization mostly at greater than 50c and anhydritization but complete dolomitization requires greater than 30 60 m y our more extended rtm simulations 30 m y indicate significant nonlinearities in the system consistent with high temperature experiments with parts of the platform completely dolomitized within 10 15 m y as dolomitization proceeds the process becomes predominantly flux controlled with development of a wedge shaped dolomite body which thins from the margin to the interior at considerably shallower depth and cooler temperatures 20 30c than suggested by short simulations dolomitization is relatively insensitive to boundary conditions such as relative sea level and platform geometry but is significantly slower in circular than elongate platforms sediment permeability and reactive surface area commonly inversely related are key controls dolomitization is limited to the margin of low permeability muddy platforms despite a high reactive surface area dolomitization of more permeable grainy platforms is limited by a lower reactive surface area occurring only in the platform core due to widespread cooling sedimentary layering produces a complex diagenetic stratigraphy dolomitization favoring more reactive beds at shallow depth where permeability is not limiting but switching to more permeable beds at depth bank marginal fracturing limits dolomitization of the platform interior whether the fractures are baffles or conduits for flow

evolution and demise of a mid cretaceous carbonate shelf the altamira limestones cenomanian of northern cantabria spain abstract in northern cantabria the cenomanian transgression is pulsatory in character and progressively onlaps onto deltaic siliciclastics of latest albian to earliest cenomanian age this pronounced 2nd order sea level rise can be subdivided into an earlier constructive phase and a later destructive phase separated by a significant low sea level stand at the early mid cenomanian boundary in the first phase the flooding of the north iberian continental margin in the early early cenomanian caused the sources of terrigenous sediments located on the iberian meseta to retreat thus promoting the development of a carbonate ramp this ramp evolved into a shelf attached platform altamira platform during the course of the early cenomanian pronounced sea level fall in the early mid cenomanian boundary interval exposed the platform increased fluvial input and terminated the constructive phase the destructive phase started in the early mid cenomanian and lasted until the late cenomanian carbon and oxygen stable isotopes microfacies analysis palaeontological criteria and sequence stratigraphy are used to elucidate the complex interplay of climatic changes sea level history nutrient supply and platform drowning three 3rd order sea level rises early and late mid cenomanian early late cenomanian resulted in a westward backstepping and final drowning of the altamira platform the drowning succession is accompanied by a negative shift of 18 o and a positive 13 c excursion interpreted to reflect progressive climatic warming and elevated nutrient levels the resulting eutrophication is represented by the biotic community of the drowning succession and negatively influenced the carbonate budget of the depositional system as a result the stressed platform was readily drowned during the mid and earliest late cenomanian 3rd order sea level rises