3d stratigraphic forward modelling for analysis and prediction of carbonate platform stratigraphies in exploration and production abstract stratigraphic forward modelling sfm has been used to answer important questions in stratigraphic analysis this has been demonstrated through generic modelling of synthetic data and numerous two dimensional 2d real data case studies but the method has rarely been used to further our understanding of specific real three dimensional 3d carbonate data sets by quantitative comparison this paper applies carbonate 3d a sfm program to a hydrocarbon reservoir and outcropping carbonate platforms at both exploration and production scales we show the value of sfm in the exploration and production of hydrocarbons through predicting facies distributions and stratigraphic geometries between wells and by analysing and answering fundamental questions about the formation of specific carbonate strata first the model is tested using the 3d outcrops of a miocene attached carbonate platform at nijar se spain where 78 of mapped facies are matched in the simulations second sfm of an 80 000 km 2 jurassic ramp in ne spain exploration scale predicts new facies in areas without data leads to an improved understanding of ramp evolution modification of the interpreted sea level curve and re interpretation of the main sediment transport direction application to the isolated platform reservoir judy creek devonian canada exemplifies the advantages of applying sfm at reservoir scale the simulations yield information on platform geometries and facies distributions an improved understanding of the factors that control platform evolution and propose a revised sea level history wider applications of sfm in exploration include assessment of the possibilities and probabilities of facies distributions and evaluation and ranking of different interpretations of platform evolution at the reservoir scale facies probability distributions and layer geometries derived from sfm can serve as input into static reservoir models to guide geostatistical simulations

kimmeridgian palaeogeography and basin evolution of northeastern iberia abstract two sedimentary basins were developed during the kimmeridgian in the northeastern part of iberia the basque cantabrian basin to the northwest and the iberian basin to the east these basins were mainly filled by carbonates deposited in a shallow epicontinental sea that was connected to the open marine realms of both the north atlantic and the western tethys respectively during the late jurassic they were temporarily linked by means of the soria seaway the uppermost oxfordian to lowermost tithonian of northeastern iberia consists of two depositional sequences sequence j3 5 spans latest oxfordian to early late kimmeridgian times sequence j3 6 spans the late kimmeridgian and early tithonian during sequence j3 5 coralgal reefs were developed in the sedimentary domains of the basque cantabrian basin and the soria seaway whereas the marginal areas of the iberian basin were dominated by oolitic shoals with variable siliciclastic influence outer ramp areas located in the central and eastern part of the iberian basin were dominated by carbonate muds and marls during the late kimmeridgian earliest tithonian shallow reefal and oolitic facies prograded over the micritic outer ramp facies the sedimentation areas were reduced and sequence j3 6 was only deposited in the iberian basin most of the western margin of the iberian basin and the southern areas of the soria seaway were covered by reefal facies during this sequence major transgressive events in the iberian basin took place in the latest oxfordian early kimmeridgian and in the middle late kimmeridgian whereas eustatic falls in sea level are recognised at the onset of the late kimmeridgian and at the kimmeridgian tithonian transition these events have also been described in other west european basins synsedimentary extensional tectonics is also evident and has been related to the onset of the late jurassic early cretaceous rifting stage synsedimentary normal faulting resulted in the presence of several troughs and highs within the basin the tectonic uplift of the western basin margin explains the progressive basinwards shift of the shorelines as observed in the iberian basin towards the end of the jurassic

testing 3d computer simulation of carbonate platform growth with repro the miocene llucmajor carbonate platform mallorca abstract repro a 3d computer based simulation program for reef and carbonate platform growth was tested using published data from the late miocene llucmajor carbonate platform in mallorca the device central to the program is a depth dependent logistic growth function for carbonate growth combined with linear diffusion so accounting for the lateral spreading of reefs evolution of the carbonate platform was simulated using a composite sea level curve consisting of superposed sine functions with different frequencies and amplitudes overall carbonate platform shape and internal geometries as produced by the program match fairly well with the outcrop data thus we demonstrate that repro has the potential to model lateral facies changes and lateral variations in the depositional geometries of carbonate platforms in three dimensions

development patterns and controlling factors of tertiary carbonate buildups insights from high resolution 3d seismic and well data in the malampaya gas field offshore palawan philippines abstract the comprehensive subsurface database of the malampaya buildup late eocene to early miocene offshore nw palawan provides a rare insight into the development of south east asian cenozoic carbonate systems and their controlling factors the newly acquired high resolution three dimensional seismic survey combined with facies and well log analysis allowed a better understanding of the internal architecture of a carbonate platform whose development was largely controlled by tectonic deformation the malampaya carbonate system was initiated in the late eocene as an attached shelf influenced by significant clastic input the late eocene early oligocene shelf was subject to syn depositional extensional tectonics eastward tilting and block faulting that favoured the development of small size buildups on structural highs after a stage of eastward reef progradation an aggrading carbonate shelf frequently affected by subaerial exposure developed from the earliest late oligocene to the early miocene during this period recurrent reactivation of highs along the western and northeastern buildup margins determined the asymmetric morphology and internal architecture of the carbonate system the final demise of the carbonate buildup occurred in the late early miocene it resulted from an increase in subsidence rate and or a sharp increase in nutrient input additional parameters like eustacy oceanographic conditions and the type of carbonate producers played a subordinate role in the buildup development and ultimate demise

new u pb zircon ages and the duration and division of devonian time newly determined u pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the devonian time scale they are 1 417 6 1 0 ma for an ash within the conodont zone of icriodus woschmidti i w hesperius early lochkovian 2 408 3 1 9 ma for an ash of early emsian age correlated with the conodont zones of po dehiscens lower po inversus 3 391 4 1 8 ma for an ash within the po c costatus zone and probably within the upper half of the zone eifelian and 4 381 1 1 3 ma for an ash within the range of the frasnian conodont palmatolepis punctata pa punctata zone to upper pa hassi zone u pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites lepidophyta spore zone are dated at 363 8 2 2 ma and 363 4 1 8 ma respectively suggesting an age of363 ma for a level within the late famennian pa g expansa zone these data together with other published zircon ages suggest that the base and top of the devonian lie close to 418 ma and 362 ma respectively thus lengthening the period by20 over current estimates we suggest that the duration of the middle devonian eifelian and givetian is rather brief perhaps no longer than 11 5 myr 394 ma 382 5 ma and that the emsian and famennian are the longest stages in the period with estimated durations of15 5 myr and 14 5 myr respectively 1998 elsevier science b v all rights reserved

radio interferometric observations of cloud to ground lightning phenomena in florida radio frequency observations of cloud to ground lightning in florida have been analyzed to document a number of features of the lightning the observations have been made using an interferometer system which determined the direction to the lightning radiation as a function of time during close lightning discharges observations are presented for about 50 radiating events during five multiple stroke normal polarity flashes to ground the results confirm and extend results of a similar study of new mexico lightning by rhodes et al 1994 dart leaders in cloud k events and attempted leaders are found to be the same phenomena namely a negative polarity streamer that propagates horizontally and or vertically to ground at estimated speeds of about 10 7 ms 1 down to 10 6 ms 1 the step or impulsive fast electric field change produced by some k events is found to be caused by positive breakdown back at the starting point of the negative streamer after the streamer has progressed over some or all of its distance this breakdown appears to initiate a forward stroke along the streamer channel which can renew the breakdown at the front end of the channel k breakdown which happens to occur during a continuing current discharge to ground produces an m event channel brightening when it connects with the conducting channel to ground the step fast field change of the m events is found to be produced at the time of connection inside the cloud no fast field change is detected when this breakdown reaches ground that would be associated with a return stroke m events can also be initiated by fast 10 7 ms 1 positive streamers which often propagate away from the leader source region within a few milliseconds of the arrival of a return stroke back in the source region these streamers often generate an even faster negative recoil event back along their extent which propagates down the channel to ground as the m event in all cases the current increase or channel brightening produced by k and m events is predicted to occur in a forward direction that is toward or down the channel to ground in the same direction as the initiating negative streamer positive breakdown is detected only immediately following return strokes or during some k streamers in both cases the electric stresses are expected to be very large suggesting that positive breakdown which produces a conducting channel is difficult to initiate results for one flash suggest that negative charge was left at low altitude by the initial stroke to ground this forced the subsequent leaders to develop a new path to ground first as series of attempted leaders and then as a dart stepped leader

astrochronology for the messinian sorbas basin se spain and orbital precessional forcing for evaporite cyclicity the sorbas basin of se spain contains one of the most complete sedimentary successions of the mediterranean reflecting the increasing salinity during the messinian salinity crisis a detailed cyclostratigraphic study of these successions allows a correlation of the sedimentary cycle patterns to astronomical target curves here we present an astrochronological framework for the messinian of the central part of the sorbas basin this framework will form a solid basis for high resolution correlations to the marginal carbonate facies and to the central mediterranean area the early messinian abad member contains 55 precession induced sedimentary cycles marked by homogeneous marl opalrich bed alternations in the lower abad and by homogeneous marl sapropel alternations in the upper abad astronomical tuning results in an age of 5 96 ma for the transition to the yesares evaporites and thus for the onset of the messinian salinity crisis the marl sapropel cycles of the upper abad are replaced by gypsum sapropel cycles 14 in the yesares member indicating that the evaporite cyclicity is related to precession controlled oscillations in circum mediterranean climate as well as a consequence gypsum beds correspond to precession maxima insolation minima and relatively dry climate sapropelitic marls to precession minima insolation maxima and relatively wet climate an alternative glacio eustatic obliquity control for evaporite cyclicity can be excluded because the number of sedimentary cycles with a reversed polarity is too high sedimentation during the abad yesares and the overlying coastal sequences of the sorbas member took place in a continuously marine environment indicating that marine conditions in the sorbas basin prevailed at least until 5 60 5 54 ma according to our scenario deposition of the yesares and sorbas member took place synchronously with deposition of the lower evaporites in the central mediterranean finally the continental zorreras member consists of 8 sedimentary cycles of alternating reddish silts dry climate and yellowish sands wet climate which correlates very well with the upper evaporites and lago mare facies of the mediterranean q 2001 elsevier science b v all rights reserved

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

computer modeling the internal architecture of carbonate platforms a numerical computer model is described that calculates the internal architecture of carbonate platforms in response to varying values of carbonate production subaerial and submarine erosion sediment redeposition and sea level changes the computer generated sections closely resemble large scale outcrops and interpreted seismic profiles through carbonate platforms stillstand and transgressive sequences have prograding and downlapping platform geometries with lagoons developing in transgressive systems regressive sequences have downlapping clinoforms and erosional upper surfaces glacioeustatic scale cycles have a major control on platform geometry with erosional sequence boundaries developing during low stands and platform drowning occurring during transgressive periods lowstand downlapping wedges are minor features when compared with clastic systems and major progradation and downlap of slope deposits develop with transgressions and flooding of platform tops carbonate erosion rates are varied and have an important effect on the morphology of foodback surfaces which have a major control on platform top production the computer program contributes to the analysis of carbonate systems in two ways it gives a visual picture of the quantitative effects of the many parameters controlling carbonate geometries and it aids quantitative analysis of the architectures and time scales of ancient outcrop or seismic sequences

proximal distal facies relationships and sedimentary processes in a storm dominated carbonate ramp kimmeridgian northwest of the iberian ranges spain abstract facies analysis of the upper kimmeridgian rocks in the outcrops located near ricla zaragoza province northeast spain and the integration of the resultant data in a broader context the northern part of the iberian basin has produced two general models showing the facies distribution and the processes that controlled the sedimentation in the kimmeridgian carbonate ramp using these two models the transition from shallow to relatively deep environments of the carbonate ramp is examined in detail model 1 corresponds to the development of a mixed carbonate siliciclastic ramp during a slow rise and stillstand of sea level sequence 1 hst whereas model 2 represents the growth of a pure carbonate ramp during a rapid rise of sea level sequence 2 tst carbonate production was higher in the shallow ramp domains coral reefs and oolitic shoals in model 1 and reefs in model 2 than in deeper domains where there is no indication of significant pelagic or benthic production the activity of unidirectional return flows induced by winter storms and hurricanes played an important role in the redistribution of the sediment across the ramp generating different coarse grained deposits in the inner and mid ramp settings dunes lower scale bedforms and tempestites occur in model 1 and storm lobes bars and tempestites in model 2 moreover a significant bulk of the carbonate mud produced in shallow areas would eventually be resedimented in the outer ramp as suspended load in the density currents stillstand of sea level in model 1 involved a rapid progradation of the inner and proximal mid ramp carbonate and siliciclastic facies the rapid relative sea level rise of model 2 is determined by the dominance of the carbonate facies and by the presence of aggradational geometries in the transitional area between shallow and deep ramp domains the presence of relatively thick sections in the outer ramp settings instead of condensed sections as observed in model 1 during times of sea level rise model 2 can mainly be explained by the increase of the shallow production in the reef dominated areas

dolomitization anhydrite cementation and porosity evolution in a reflux system insights from reactive transport models significant volumes of world hydrocarbon reserves occur in dolostones and the majority of these reservoirs are interpreted to be of reflux origin we used a two dimensional numerical reactive transport model to investigate systematically the temporal and spatial distribution of replacement dolomitization dolomite cementation anhydrite cementation and porosity evolution in a reflux system we tested the sensitivity of reflux dolomitization to brine concentration mesohaline to near halite saturated brines near surface temperature flow rate porosity permeability feedback relationships reactive surface area and the effect of initial porosity permeability heterogeneity simulations support the contention that hypersaline reflux is capable of extensive pervasive dolomitization and that mesohaline reflux dolomitization is viable reflux generated a tabular dolomite body that is thickest close to the brine source and thins basinward incorporation of initial porosity and permeability heterogeneity resulted in a dolomite body with pronounced lateral fingers replacement dolomitization increased porosity up to 8 but postreplacement reflux resulted in the precipitation of minor dolomite cements overdolomitization anhydrite cements that were spatially and temporally associated with replacement dolomitization caused a significant porosity reduction of up to 25 simulated rates of replacement dolomitization by reflux are fast up to three orders of magnitude faster than seawater dolomitization the rate of dolomitization and anhydrite mineralization proved to be critically sensitive to the flow rate and the brine chemistry temperature and reactive surface area were important controls on the rate of dolomitization whereas the feedback relationship between porosity and permeability was a relatively moderate control our reactive transport models predict the general spatial and temporal trends in dolomite porosity and anhydrite observed in some major dolomite reservoirs

computer simulation of reef growth light is one of the major controls on reef growth and carbonate production the growth of present reef builders depends largely upon the amount of light available for photosynthesis as light decreases with water depth so does reef growth the computer model presented extends this principle by combining two functions one for photosynthesis and the other for the extinction of light in water the model is used to simulate the growth of alacran reef mexico two reefs of the great barrier reef and the reefs of the windward platform of st croix us virgin islands the model also gives an accurate simulation of the growth of fore reef walls in belize in agreement with the accretion hypothesis developed for this feature

the coral reef of nijar messinian uppermost miocene almeria province s e spain abstract the nijar reef is a thoroughly exposed and representative example of the messinian coral reefs outcropping along the periphery of the western mediterranean facies patterns in the nijar reef complex are presented in this paper as a generalized guide or model for the study of other messinian reefs messinian paleogeography of this area was characterized by an archipelago whose islands are present day sierras at the beginning of the messinian and before development of the reefs marine terrigenous sediments marginal terrigenous complex were deposited on an irregular erosion surface on the metamorphic basement the reef complex developed as a belt fringing the positive areas islands when terrigenous deposition decreased the reef complex consists of 1 reef core constructed by a framework of vertical branching colonies of porites coated by laminated micrite probably submarine cements which form pinnacles as well as thickets and 2 fore reef made of sloping beds of broken skeletons and debris the fore reef is subdivided into i reef talus slope ii proximal slope and iii distal slope the reef talus forms massive strata with dips of 20 30 and abundant pebble to boulder size slumped blocks of reef core and coral breccia the proximal slope shows dips of 10 20 of well bedded thick strata with internal parallel layering of granule to sand size skeletal calcarenites the distal slope is made of predominant bioturbated skeletal calcisiltites and fine grained calcarenites with ngles lower than 10 the distal slope grades into the basinal pelagic marls of the nijar plains the original reef morphology is well preserved in present day topography with relicts of pinnacles reef valleys and slopes messinian volcanic highlands located to seaward complicated the local paleogeography with atoll like features reef growth was concomitant with a gradual fall of sea level and occurred before the messinian gypsum was deposited on top of the basinal marls in what is now the plains area the reef complex is partially truncated by a major erosion surface and it is overlain by oolitic shoals and stromatolites of the so called terminal carbonate complex the terminal complex is interpreted as an upslope equivalent in age to the messinian upper evaporite and it implies a new cycle of sea level rise

genesis of metasomatic gold mineralization in the pahardiha rungikocha gold deposit eastern india constraints from trace element signatures in chromite cored magnetite and bulk rock geochemistry abstract the pahardiha rungikocha gold deposit is located south of the dalma volcano sedimentary belt within the north singhbhum mobile belt nsmb in the eastern part of india the rocks of this area have undergone three phases of deformation viz d1 d2 d3 while the d1 and d2 events signify progressive regional metamorphism the d3 stage was a consequence of continued n s compression resulting in e w trending displacement fractures this d3 deformation event was responsible for the mobilization of auriferous fluids within the host quartz chlorite schist and subsequent gold precipitation here gold occurs as native grains either within the cracks or along grain boundaries of euhedral pyrite detailed mineral paragenesis reveals that euhedral pyrite associated with gold is coeval with abundant chromite cored magnetite the chromite cored magnetite shows a complex paragenetic history i e an initial chromite alteration event followed by epitaxial growth of magnetite rims on the chromite cores as revealed by la icp ms trace element data and epma x ray compositional maps the paragenetic stages of the chromite cored magnetite is synchronous with the successive deformation events of the host rock the final phase of deformation is responsible for the formation of the chromite cored magnetite rims which is coeval with the gold mineralizing event these magnetite rims formed as a result of metasomatism brought about by the interaction of hydrothermal fluids with the wall rock the chromite cored magnetite trace element signatures resemble the high temperature ca fe alteration and high temperature k fe alteration facies reported from various iocg and ioa type deposits there is a distinct enrichment of mafic elements such as ni cr v mg v cu within magnetite rims a similar pattern of enrichment in mafic elements is also seen in the bulk rock geochemical data major element discrimination diagrams reveal that the chlorite schists evolved from a mixed provenance of felsic and mafic ultramafic rocks consequently the d3 induced metasomatism most likely resulted in preferential stripping of the mafic elements which is well reflected in the analyzed magnetite rims thus we propound that the bulk rock chemical composition of the host chlorite schist had a first order control on the chemistry of the chromite cored magnetite coeval with the gold mineralizing event given the fact that there are no causative igneous intrusions underlying the host chlorite schists we infer that the gold mineralizing fluids were intrabasinal in nature and were mobilized due to reactivation of pre existing faults and fractures during the d3 deformation event

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

quantitative controls on location and architecture of carbonate depositional sequences upper miocene cabo de gata region se spain abstract sequence stratigraphy pinning point relative sea level curves and magnetostratigraphy provide the quantitative data necessary to understand how rates of sea level change and different substrate paleoslopes are dominant controls on accumulation rate carbonate depositional sequence location and internal architecture five third order 1 10 my and fourth order 0 1 1 0 my upper miocene carbonate depositional sequences ds1a ds1b ds2 ds3 tcc formed with superimposed higher frequency sea level cycles in an archipelago setting in se spain overall our study indicates when areas of high substrate slope 15 are in shallow water independent of climate the location and internal architecture of carbonate deposits are not directly linked to sea level position but instead are controlled by location of gently sloping substrates and processes of bypass in contrast if carbonate sediments are generated where substrates of low slope 15 6 cm ky to 2 cm ky and overall relative sea level rose at rates of 17 21 4 cm ky higher frequency sea level rates were about 111 to more than 260 cm ky producing onlapping fining deepening upward cycles decreasing accumulation rates resulted from decreasing surface area for shallow water sediment production drowning of shallow water substrates and complex sediment dispersal related to the archipelago setting typical systems tract and parasequence development should not be expected in bypass ramp settings facies of onlapping strata do not track base level and are likely to be significantly different compared to onlapping strata associated with coastal onlap basal and upper ds2 reef megabreccias indicating the transition from cool to warmer climatic conditions were eroded from steep upslope positions and redeposited downslope onto areas of gentle substrate during rapid sea level falls 22 7 cm ky of short duration such rapid sea level falls and presence of steep slopes are not conducive to formation of forced regressive systems tracts composed of downstepping reef clinoforms the ds3 reefal platform formed where shallow water coincided with gently sloping substrates created by earlier deposition slow progradation 0 39 1 45 km my is best explained by the lack of an extensive bank top progressively falling sea level and low productivity resulting from siliciclastic debris and excess nutrients shed from nearby volcanic islands although ds3 strata were deposited during a third order relative sea level cycle a typical transgressive systems tract is not recognizable indicating that the initial relative rise in sea level was too rapid 19 cm ky downstepping reefs forming a forced regressive systems tract were deposited during the relative sea level fall at the end of ds3 indicating that relatively slow rates of fall 10 cm ky or less over favorable paleoslope conditions are conducive to generation of forced regressive systems tracts consisting of downstepping reef clinoforms the tcc sequence consists of four shallow water sedimentary cycles that were deposited during a 400 ky to 100 ky time span such shallow water cycles typical of many platforms form only where shallow water intersects gently sloping substrates the relative thicknesses of cycles 2 m to 15 m thick magnitudes of relative sea level fluctuations associated with each cycle 25 30 m high rates of relative sea level fluctuations minimum of 25 120 cm ky and the widespread distribution of similar tcc cycles in the mediterranean and elsewhere are supportive of a glacio eustatic influence with rates of sea level change so high typical systems tracts do not form

carbonate platform facies models various types of carbonate platforms are characterized by distinctive profiles facies and evolutionary sequences ramps may be homoclinal or distally steepened and may have fringing or barrier shoal water complexes of ooid pellet sands or skeletal banks homoclinal ramps pass seaward into deeper water without major break in slope and lack deep water breccias distally steepened ramps may be low energy and characterized by widespread shallow subwave base mud blankets or high energy with coastal beach dune complexes and widespread skeletal sand blankets slope facies may contain abundant breccias of slope derived clasts rimmed shelves have relatively flat tops and marked break in slopes at the high energy shallow shelf edge where they pass into deep water such shelves may be aggraded with peritidal facies extending over much of the shelf or incipiently drowned depending on magnitude of sea level fluctuations they may be accretionary or bypass types that include gullied slope escarpment and high relief erosional forms intrashelf basins occur on some shelves controlling distribution of reservoir and source beds isolated platforms are surrounded by deeper water and may be located on rifted continental margins or on submarine volcanoes most have high relief rimmed margins platforms that have been subjected to rapid sea level rise may be incipiently drowned and characterized by raised rims elevated patch or pinnacle reefs and widespread subwave base carbonate or fine clastic blankets completely drowned shelves develop where the shelf is submerged to subphotic depths terminating shallow water deposition and commonly resulting in blanketing of the shelf by deeper water facies some margins show extensive down to basin faulting that is contemporaneous with carbonate deposition or associated with thick prograding clastic sequences the various types of platforms change in response to variations in sedimentation subsidence or sea level rise and may form distinctive evolutionary sequences the relatively few models presented appear to accommodate most geological examples some of which contain major reservoir facies

a u pb and 40ar 39ar time scale for the jurassic published time scales provide discrepant age estimates for jurassic stage boundaries and carry large uncer tainties the u pb or 40 ar 39 ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration a radiometric age database consisting of fifty u pb and 40 ar 39 ar ages was com piled to construct a revised jurassic time scale accepted ages have a precision of 5 ma 2 or better and are con fined to no more than two adjacent stages the majority of these calibration points result from integrated bio and geochronologic dating in the western north american cordillera and have not been previously used in time scales di rect dates are available only for the triassic jurassic boundary and the initial boundary of the crassicosta chron and the callovian stage the chronogram method was used to estimate all early and early middle jurassic zone boundaries attempted here for the first time late middle jurassic substage boundaries and late jurassic stage boundaries signif icant improvement is achieved for the pliensbachian and toarcian where six consecutive zone boundaries are deter mined the derived zonal durations are disparate varying between 0 4 and 1 6 ma the latest jurassic isotopic database remains too sparse therefore chronogram estimates are improved using interpolation based on magnetochronology the initial boundaries of jurassic stages are proposed as follows berriasian jurassic cretaceous 1418 18

a genetic classification of carbonate platforms based on their basinal and tectonic settings in the cenozoic abstract this paper reassesses the usefulness of the morphological classification of carbonate platforms into rimmed shelves and ramps whilst the existing classifications have value in describing platform margin morphology at any one time the terms rimmed shelf and ramp are less successful at categorising the entire morphology and stratigraphy of carbonate platforms research on cenozoic carbonate platforms from a range of different tectono stratigraphic settings indicates that the basinal and tectonic setting of a platform can be used to erect a first order genetic classification of carbonate platforms the basinal and tectonic setting of carbonate platforms is shown to control their occurrence the overall 3 d platform morphology the large scale stratigraphic features and depositional sequences climate ocean chemistry and biological evolution control grain types facies and some elements of platform margins but not the larger scale features considered in this new classification from a review of well exposed outcropping and seismically imaged cenozoic platforms it is proposed that eight types of carbonate platform can currently be recognised and characterised based on their basinal and tectonic setting fault block salt diapir subsiding margin offshore bank volcanic pedestal thrust top delta top and foreland margin carbonate platforms these eight types are described using information from cenozoic platforms worldwide and the controls on their development are discussed many platform types e g subsiding margin offshore bank salt diapir thrust top and foreland margin are typical of particular classes of sedimentary basins others e g fault block volcanic pedestal and delta top are more widespread in their occurrence and occur in a range of basin types the value of this classification is that it is genetic rather than morphological the classification reflects the entire morphology and large scale stratigraphy of the platform and the controls on its development in addition the platform models can be used to understand the details of less well exposed or seismically imaged platforms so that they can be characterised and understood in terms of tectono sedimentary processes conversely the classification also provides valuable information on basin evolution as carbonate platforms house information on palaeoenvironments sea level change and are sensitive recorders of the tectonic environment

late miocene mediterranean desiccation topography and significance of the salinity crisis erosion surface on land in southeast spain reply abstract the result of sea level fall at the margins of the mediterranean during the late miocene salinity crisis was the creation of an extensive erosion surface however the shape of this salinity crisis unconformity reflects local factors and in turn significantly determined local conditions during subsequent reflooding at sorbas in southeast spain erosional overdeepening of a pre existing basin during drawdown created a depression over 200 m deep with an incised floor patterned by 30 m deep gullies during reflooding this semi enclosed palaeovalley temporarily became a barred basin in which gypsum was deposited these sorbas evaporites thus resulted from local basin sculpture diverse local effects elsewhere during drawdown and reflooding account for marked stratigraphic variations that continue to complicate recognition and correlation of the salinity crisis in marginal successions the drawdown erosion surface is itself the key indicator of this important event in marginal mediterranean basins

the simulation of the sedimentary fill of basins an interactive computer simulation which erects models of sedimentary geometries by filling in a two dimensional basin from both sides with a combination of clastic sediment and or in situ and transported carbonate sediments is described the simulation program is implemented in c using graphical plotting functions data entry including the initial basin configuration the local tectonic behavior the sea level curves the amount and source direction of clastic sediment and the growth rates of carbonates as a function of water depth is performed interactively geometries of clastic and carbonate sediments evolve through time and respond to tectonic movement eustasy and sedimentation clastic modeling includes sedimentary bypass and erosion and sedimentation in alluvial and coastal plains marine shelf basin slope and basin floor settings carbonate modeling includes progradation the development of hard grounds downslope aprons keep up catch up back step and drowned reef settings as well as lagoonal and epeiric settings also included in the model are extensional vertical faulting of the basin sediment compaction and isostatic response to sediment loading sediment geometries are plotted on a graphics terminal as they are computed so the user can immediately view the results based on these observations parameters can be changed and the program rerun until the user is satisfied with the resultant geometry this paper includes output showing the simulation s sensitivity to eustatic sea level variations and variations in sedimentation and subsidence rates also shown are outputs demonstrating the modeling of some examples from the geologic section in the permian basin of west texas and the upper permian of the sichuan basin

testing a seismic interpretation of great bahama bank with a computer simulation sixty million years of carbonate deposition were simulated to test an interpretation of platform development based on seismic data and limited well control from northwestern great bahama bank seismic profiles of the northwestern great bahama bank document the lateral growth potential of isolated platforms that were welded together by progradation to form the modern bank the mechanism we proposed responsible for an evolution from aggradation to progradation was sediment overproduction on the platform the excess of which was transported offbank and which caused a decrease in accommodation space on the marginal slope progradation occurred in pulses that were interpreted to be the result of third order sea level fluctuations to evaluate the proposed mechanism 15 input p rameters were used to model the platform evolution the simulation program which uses empirical relationships to model basin fill successfully reproduced the geometries seen on the seismic lines indicating that the proposed interplay of mechanisms could have built the observed platform architecture the simulation demonstrated in particular that in a setting like the bahamas a basin must be substantially filled before progradation can take place and that sea level changes can drive the pulses of progradation this implies that laterally stacked sequences often contain the record of sea level changes and therefore have potential use in sequence stratigraphy the simulation can also be used to estimate the quantitative importance of individual factors controlling aggradation and progradation in the bahamas we show how close the balance between aggradation and progradation is and how small changes in the rate of subsidence or accumulation can cause immediate switches from aggradation to progradation in particular we show that the rate of subsidence exerts the major control on the timing of progradation more so than basin width carbonate production rates similar to modern rates were required to produce the necessary sediment input for progradation which suggests that carbonate production has been consistently high since the early tertiary repeated exposure and erosion however have decreased the overall accumulation rate the simula ion also suggests that the asymmetric progradation in the bahamas was only possible where there were extreme differences between windward and leeward conditions with a maximum sediment input of 10 from the windward side

digital outcrop models applications of terrestrial scanning lidar technology in stratigraphic modeling abstract laser ranging is extremely accurate and efficient terrestrial scanning lidar light detection and ranging applied to outcrop stratigraphic mapping enables researchers to capture laser range data at a rate of thousands of individual x y z and laser intensity points per second these data in conjunction with complementary remotely and directly sampled data are used to conduct high precision facies characterization and to construct 3d geological computer models outcrop data are presented here to explain our workflow and to discuss the construction of rock based 3d digital outcrop models doms reproducibility and quantification are the drivers of this methodology high resolution terrestrial lidar acquisition processing interpretation and visualization are discussed and applied to mapping of geological surfaces in three dimensions laser generated models offer scientists an unprecedented visualization medium in a quantitative 3d arena applications of this technology include constructing and visualizing complex 3d earth models from outcrops for improved reservoir modeling flow simulation in hydrocarbon and aquifer systems and property modeling to constrain forward seismic modeling

identification of systems tracts in low angle carbonate ramps examples from the upper jurassic of the iberian chain spain abstract the upper jurassic of the iberian chain in northeast spain was selected for the study and identification of sequence boundaries and systems tracts in low relief carbonate ramp systems the study area provides a special opportunity for sequence stratigraphic analysis because the outcropping upper jurassic carbonate ramps are relatively undeformed well exposed from proximal to distal areas and have an established ammonite zonation two sequences are recognized sequence a uppermost callovian to uppermost oxfordian in age up to 60 m thick in the proximal areas and between 15 and 5 m thick in the middle and distal areas and sequence b kimmeridgian to lowermost tithonian from 80 to 160 m in thickness across the basin the evolution of the first sequence is related to regional relative sea level changes i e tectono eustatic changes superimposed on the sedimentary basin on the other hand the larger accommodation created during the second sequence is regarded as controlled mainly by steady subsidence sequence boundaries indicative of subaerial exposure show as unconformities with stratigraphic hiatuses in the proximal areas of the basin the lowstand systems tract in sequence a is represented by a decimetre thick reworked level consisting of several ammonite biozones in sequence b this systems tract consists of a thick wedge shaped marly unit in both sequences the transgressive surface overlaying these lowstand deposits is generally planar and marks a sharp boundary between the restricted and open marine fossils however in sequence b in the middle part of the basin the transgressive surface can be absent instead a transitional change to open marine facies exists the transgressive systems tracts show sedimentary condensation at least in the distal areas of the basin with mostly ammonites and benthic fossil wackestones the transgressive unit is generally overlain by a hard ground surface that corresponds to a maximum flooding surface finally in the upper part of both sequences highstand systems tracts are represented by progradational siliciclastic and shallow carbonate complexes in the proximal areas of the basin in sequence a sedimentation is condensed in the distal areas with glauconite marl levels present the descriptions of sedimentary features of the systems tracts of these two sequences developed in a low angle carbonate ramp are suggested to be used as tools for the recognition of systems tracts patterns within sequences in comparable depositional settings

sedimentology and budget of a recent carbonate mound florida keys the sedimentology of a recent carbonate mound is investigated to further our understanding of mound building communities surface and subsurface mound sediments and the overall sediment budget of mounds nine sedimentary facies of the surface of tavernier mound florida keys are described these sediments are composed of neogoniolithon halimeda porites mollusc and foraminiferal grains and lime mud muds rich in aragonite and high magnesian calcite show little mineralogical variation over the mound surface geochemical evidence suggests that the mud is mainly formed from breakdown of codiacean algae and thalassia blade epibionts production rates of the facies are established from in situ growth rate experiments and standing crop surveys annual calcium carbonate production is c 500gm 2 intermediate between reef and other bay and lagoonal environment production rates in the caribbean the internal structure of the mound studied from piston cores and sediment probes indicates that seven facies can be identified five of these can be related to the present day facies and occur in the upper part of the mound gravel mound stage the remaining two facies characterized by molluscs and aragonite rich muds occur in the lower part of the mound mud mound stage and are most similar to facies from typical florida bay mud mounds mangrove peats within the mound indicate former intertidal areas and c14 dates from these peats provide a time framework for mound sedimentation the mound appears to have formed because of an initial valley in the pleistocene surface which accumulated mud in a shallow embayment during the holocene transgression a sediment budget for the mound is presented which compares production rates from present day facies with subsurface sediment masses during the mud mound stage production rates were similar to accumulation rates and the mound was similar to the present day mounds of florida bay during the gravel mound stage 3400 yr bp present day conditions were more normal marine and the establishment of porites and neogoniolithon on the mound increased production rates 10 over accumulation rates this excess sediment is thought to be transported off the mound to the surrounding seabed models are proposed which divide carbonate mounds on the basis of internal versus external sediment supply comparisons are made with other recent and ancient mounds similarities exist between the roles of the biotic components of late palaeozoic mounds but major differences are found when structures and early diagenesis are compared

magmatic evolution of the alboran region the role of subduction in forming the western mediterranean and causing the messinian salinity crisis the magmatic evolution of the alboran region westernmost mediterranean contains important clues for improving our understanding of the origin of mediterranean style back arc basins and the desiccation of the mediterranean sea in the messinian we use new laser 40ar 39ar age and geochemical major and trace element and o sr nd pb isotope data from igneous rocks from southern spain the alboran sea and northern morocco to reconstruct the magmatic evolution of the westernmost mediterranean since the eocene lower oligocene dikes near malaga 33 6 0 6 ma and middle to upper miocene volcanic rocks from the alboran sea area 6 57 0 04 to 11 8 0 4 ma can be subdivided into two groups 1 lree depleted relative to n morb primarily tholeiitic series and 2 lree enriched primarily calc alkaline series volcanic rocks both groups are generally enriched in fluid mobile elements e g rb th u k and pb relative to fluid immobile elements e g nb ta lree the lree depleted group has 143nd 144nd 0 5128 0 5130 isotope ratios similar to atlantic morb but higher 87sr 86sr 0 7046 0 7100 in contrast the lree enriched group has less radiogenic nd 0 5121 0 5126 and tend to more radiogenic sr 0 7066 0 7205 isotopic composition pb isotope ratios are surprisingly uniform and have compositions similar to marine sediments analyses of mineral separates show that mafic melts with relatively low 18o 5 6 7 2 had high 87sr 86sr 0 7048 0 7088 7 4 10 6 14 1 and 8 4 40 0 49 3 modeling of the trace elements and sr nd pb o isotopic compositions provides compelling evidence for the contamination of the mantle source with hydrous fluids melts which can be explained through subduction of oceanic lithosphere beneath the alboran basin but not through detachment delamination of lithospheric mantle we present a geodynamic model that reconstructs the late eocene to quaternary evolution of the western mediterranean through westward roll back of subducted tethys oceanic lithosphere slab roll back resulted in a large scale reorganization of the western mediterranean paleogeography causing the closure of marine gateways linking the atlantic ocean to the mediterranean sea isolation of the mediterranean sea led to its desiccation causing the messinian salinity crisis

3d and 4d controls on carbonate depositional systems sedimentological and sequence stratigraphic analysis of an attached carbonate platform and atoll miocene nijar basin se spain this study investigates the controls on three dimensional stratigraphic geometries and facies of shallow water carbonate depositional sequences a 15 km2 area of well exposed mid to late miocene carbonates on the margin of the nijar basin of se spain was mapped in detail an attached carbonate platform and atoll developed from a steeply sloping basin margin over a basal topographic unconformity and an offshore dacite dome late miocene the older strata comprise prograding bioclastic mollusc and coralline algae dominated sediments and later messinian porites reefs form prograding and downstepping geometries falling stage systems tract seven depositional sequences their systems tracts and facies have been mapped and dated using sr isotopes to define their morphology stratigraphic geometries and palaeo environments a relative sea level curve and isochore maps were constructed for the three messinian depositional sequences that precede the late messinian evaporative drawdown of the mediterranean the main 3d controls on these depositional sequences are interpreted as being i local tectonically driven relative sea level changes ii the morphology of the underlying sequence boundary iii the type of carbonate producers bioclastic coralline algal and mollusc dominated sequences accumulated in lows and on slopes of 14 whereas the porites reef dominated sequence accumulated on steep slopes up to 25 and shallow water highs further controls were iv the inherited palaeo valleys and point sourced clastics v the amount of clastic sediments and vi erosion during the following sequence boundary development the stratigraphy is compared with that of adjacent miocene basins in the western mediterranean to differentiate local tectonics clastic supply erosion history carbonate producing communities versus regional climatic tectonic palaeogeographic sea level controls

models for generation of carbonate cycles computer modeling provides a quantitative approach to a better understanding of actual carbonate cyclic sequences to model carbonate cycles the authors can use water depth dependent sedimentation rate for each facies an initial lag time linear subsidence tidal range and period and amplitude of sea level oscillation about a horizontal datum tidal flat capped cycles up to a few meters thick result from low amplitude sea level oscillation of a few meters and short lag times nonerosive caps reflect sea level lowering being balanced by subsidence and basinward migration of the shoreline not exceeding tidal flat progradation rate when higher amplitude sea level oscillations occur the tidal flats are abandoned on the inner shelf during sea level fall because seaward movement of the strandline outpaces progradation rate of flats increased amplitude also results in sea level falling faster than flats can subside so that disconformities with thick vadose profiles develop high amplitude 100 m or more oscillations result in incipient drowning of platforms and juxtaposition of deep water facies against shallow water facies within cycles sea level falls before the platform can build to the sea level highstand and the shoreline migrates much more rapidly than tidal flats can prograde thus cycles are disconformity bounded and lack tidal flat caps 10 references

digital characterization of thrombolite stromatolite reef distribution in a carbonate ramp system terminal proterozoic nama group namibia the stratigraphic architecture of a terminal proterozoic carbonate ramp system ca 550 ma nama group namibia was mapped quantitatively with digital surveying technologies the carbonate ramp consists of a shoaling upward ramp sequence in which thrombolite stromatolite reefs developed at several stratigraphic levels the reefs are associated with grainstone and heterolithic facies and exhibit diverse geometries and dimensions related to the position in the sequence stratigraphic framework laterally extensive reefs with a tabular geometry developed when accommodation was relatively low whereas discontinuous oblate dome shaped reefs developed during times when accommodation space was relatively high collecting sedimentological and stratigraphic data digitally in an extensive canyon system allowed a comprehensive documentation of the three dimensional 3 d architecture and dimensions of the reefal buildups both deterministic and stochastic methods were used to extend outcrop observations to construct 3 d models that honor the observed stratigraphy in particular the accuracy with which dimensions of reefal buildups can be measured is critically important in the statistical modeling of the dome shaped buildups calculations and corrections can be applied directly to the digital data set and serve as input during model building the final 3 d model faithfully reproduces the outcrop distribution of facies and geological objects and has a high spatial resolution compared with petroleum industry reservoir models the organization of the reefal buildups in the stratigraphic framework has direct implications for reservoir continuity and connectivity in analogous settings the digital characterization and 3 d outcrop models presented in this article can be subsequently used to condition dynamic reservoir simulation modeling of geologically similar areas