synchronous detachment folds and coeval sedimentation in the prepyrenean external sierras spain a case study for a tectonic origin of sequences and systems tracts this paper reports on the structural and sedimentary evolution of the middle to late eocene of the prepyrenean external sierras southern pyrenees spain the initiation duration and kinematics of a set of growth structures that developed in a shallow marine depositional setting is documented the detailed analysis of the syntectonic marine sediments not only confirms the already known east to west progression of deformation but also reveals the continued growth of the early formed structures as later ones propagate towards the foreland the sedimentary units coevally deposited with these growth structures are arranged in four depositional sequences their boundaries correspond to flooding surfaces which grade basinwards into correlative conformities they are also indicated by the presence of both angular unconformities and onlap geometries each depositional sequence generally consists of two systems tracts the lower one or transgressive systems tract is formed by up to 400 m of azoic marls deposited in outer ramp areas the upper one or highstand systems tract mainly consists of shallow siliciclastic and carbonate facies up to 200 m thick deposited in middle to inner ramp areas these depositional sequences are interpreted to be controlled by regional tectonic pulses an increase of tectonic activity resulted in the flooding of the basin and in the subsequent deposition of a thick succession of nearly azoic blue marls i e transgressive systems tract the overlying highstand systems tract developed following periods of diminished tectonism with the consequent growth and progradation of shallow carbonate platform facies

the future of applied sedimentary geology the turn of the millenium is for many of us an occasion to pause and consult the crystal ball sedimentary geologists have added incentive to do so because the calendar event coincides with a profound change in what one may call our professional hinterland the part of society that requires our expertise and offers jobs sedimentary geology and its sister paleontology originated as historical sciences dedicated to the study of the sediment record as a history book of the evolution of life and the changing environments at the earth s surface to this day deciphering earth history remains a principal task of sedimentary geology and a source of major scientific contributions however increased quantitative understanding of geologic systems and societal demand have established prediction besides description as an increasingly important part of the natural sciences earth scientists are expected to deliver predictions of two sorts prediction in the space domain notably the inaccessible subsurface and prediction in the time domain the future behavior of the solid earth and its fluid envelopes sedimentary geologists are involved in both types of prediction exploring for resources such as petroleum metallic ores or drinking water as well as determining the spread of underground pollution requires mainly prediction in space predicting oceanic and atmospheric climate constitutes the principal task in the time domain prediction in time also includes catastrophic changes related to energy bursts of the solid earth such as earthquakes volcanic eruptions or landslides as is typical for the natural sciences work in sedimentary geology spans the full range from pure curiosity driven research to applied research driven by the demand of economies both pure and applied research may be relevant for society and may make fundamental contributions to knowledge i will first discuss major challenges in pure research and then make a tour of the horizon

sedimentology of a marine intermontane pleistocene gilbert type fan delta complex in the crati basin calabria southern italy the crati basin is a pliocene holocene extensional basin filled by the progradation of different types of marine fan delta systems coarse grained gilbert type fan deltas developed during the pleistocene they represent the sedimentary response to a strong differential uplift involving the basin margins and the basin itself the differential uplift was responsible for the fragmentation of the basin into several sub basins into which these fan deltas prograded the protection and lateral confinement by structural highs steep coastlines and the absence of strong tidal action in the adjacent ionian sea allowed the regular progradation of these fan deltas in the restricted gulfs and narrow embayments of the crati basin for the classical gilbert type fan deltas in lacustrine settings homopycnal inflow favours a rapid mixing of water masses and deposition of sediment close to the river mouth in the case of the example described here the density contrast between the sea water and the inflowing river water caused the separation of the muddy fraction from the coarse sandy and conglomeratic part of the sediment this allowed the development of steep mud poor coarse grained delta foresets slope instability features slump scars conglomeratic flow slides are fairly scarce in the proximal parts of the san lorenzo del vallo system towards the north where protection from the ionian sea was less they increase in importance

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

seismic architecture and seismic geomorphology of heterozoan carbonates eocene oligocene browse basin northwest shelf australia abstract seismic characterization of eocene oligocene heterozoan carbonate strata from the browse basin northwest shelf of australia defines marked progradation of nearly 10 km stratal terminations and stacking subdivide the succession into mappable seismic units stratal architecture and seismic geomorphology varies systematically through the succession individual surfaces discerned by toplap onlap and truncation outline sigmoidal to tangential oblique clinoforms with heights of ranging from 350 to 650 m and maximum gradients between 8 and 18 sigmoidal clinoforms can include aggradation in excess of 200 m prograde more than 500 m and have slopes characterized by inclined wavy to discontinuous reflectors that represent ubiquitous gullies and channels in contrast the overlying tangential oblique clinoforms include downstepped shelf margins limited on shelf aggradation the associations of shelf aggradation shelf margin progradation and slope channeling within sigmoidal seismic units and the less marked progradation and channeling within tangential oblique seismic units contrast with the classic sequence model in which sediment delivery to the slope and pronounced progradation is favored by limited shelf accommodation this distinct divergence is interpreted to reflect the prolific heterozoan production across the shelf during periods of rising and high base level when the shelf is flooded perhaps enhanced by downwelling comparison with purely photozoan systems reveals similarities and contrasts in seismic stratigraphic heterogeneity and architecture interpreted to be driven by distinct characteristics of heterozoan sedimentary systems

shelf geometry response to changes in relative sea level on a mixed carbonate siliciclastic shelf in the guyana basin abstract differences in the shelf margin geometry for various depositional regimes show how siliciclastic and carbonate margins respond differently to changes in accommodation space during the cenozoic sequences of carbonate and siliciclastic sediment were deposited in the guyana basin on the passive continental margin of ne south america study of the sequence geometries reveal significantly different geometric responses to changes in relative sea level of intervals dominated by carbonates to intervals dominated by siliciclastics using the geometrical shelf break as a reference point aggradation and progradation rates for the carbonate and siliciclastic depositional systems were measured in siliciclastics the lateral position of the margin remains roughly stationary with relative sea level rises in the order of 30 m my at higher rates the margin retreats at lower rates it progrades carbonate margins remain stationary or slightly progradational even with relative sea level rises of up to 100 m my the fastest rates observed in this study this illustrates the strong tendency of carbonate platforms to stack their margins and keep up with relative rises in sea level rather than gradually retreat landward as do siliciclastics this observation may explain why carbonate platforms preferentially try to defend a margin prior to ultimate backstepping the high aggradation potential of carbonate margins also gives onlap and downlap termination patterns on seismic profiles where carbonate platforms develop on sloping siliciclastic shelves the resulting unconformities are a result of differences in sediment dispersal between the two systems and not necessarily from changes of relative sea level

growth mode of middle triassic carbonate platforms in the western dolomites southern alps italy abstract the correlation of carbonate platform and slope sediments with biostratigraphically and radiometrically dated basinal successions in the western dolomites allows the reconstruction of the growth of a middle triassic carbonate platform schlern rosengarten over a time interval of approximately five ammonoid zones reitzi secedensis curionii gredleri archelaus zones the whole platform evolution had a total duration of

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

modelling of time dependent behavior of the basal sliding surface of the aknes rockslide area in western norway abstract numerical modelling based on the finite difference code flac3d and the burger creep viscoplastic material model has been used for analysing time dependent behavior of the unstable rock slope at aknes in western norway the rockslide has an estimated volume of 43 million m3 with a basal sliding surface located 105 115 m below the surface displacement measurements by gps and reflector points which since 2004 have revealed average annual displacements in the order of 26 mm year in the central part of the sliding area have been used to calibrate the model the modelling shows that a set of parameters believed to represent the conditions of the slope at present time 3 intact rock in the sliding plane and surface conditions representing good surface conditions in the gsi system results in displacements which stabilise within a 100 year period however as the shear strength parameters are reduced according to 1 intact rock in the sliding layer and surface conditions representing fair surface conditions in the gsi system increased displacement and indications of failure at the toe of the slope are evident within the same time span

shallow subsurface diagenesis of pleistocene periplatform ooze northern bahamas previous studies on early submarine diagenesis of periplatform carbonates have implied that these originally polymineralic aragonite magnesian calcite calcite sediments are susceptible to early diagenesis only in current swept open seaways or where surficially exposed by erosion on the seafloor it has also been proposed that while in the shallow subsurface periplatform oozes retain their original mineralogy for at least 200 000 400 000 yr and remain unlithified for tens of millions of years evidence is reported here for extensive calcitization and selective lithification of periplatform oozes of late pleistocene age in two piston cores collected from water depths of 1 000 m north of little bahama bank it is shown that shallow 30 m subsurface diagenesis can significantly alter the original mineralogy of periplatform oozes to predominantly calcite in less than 440 000 yr and that cementation by calcite can produce chalk ooze sequences within the same time frame periplatform oozes that originally contain a high percentage of bank derived magnesian calcite appear to have a higher diagenetic potential than those originally low in magnesian calcite shallow subsurface calcitization and fithification greatly reduce the diagenetic potential of periplatform carbonates and chalk ooze sequences apparently can persist for tens of millions of years and to burial depths of at least 300 m shallow subsurface diagenesis at water depths 1 000 m proceeds via dissolution of magnesian calcite and aragonite and reprecipitation of calcite as allochem fillings exterior overgrowths and cement it is speculated that density driven kohout convection where seawaters under saturated with respect to magnesian calcite and aragonite and saturated supersaturated with respect to calcite flow through the margins of carbonate platforms is the primary driving mechanism for shallow subsurface diagenesis removal of mg during early stages of deep seafloor and shallow subsurface diagenesis should increase the mg content of interstitial waters which is likely to increase the dolomitizing potential of kohout convection fluid flow

synthetic stratigraphy of carbonate platform and basin systems a forward numerical model of the carbonate platform and basin depositional system aids in understanding the roles played by different variables in controlling the growth patterns of carbonate platforms and thus their internal facies architecture the numerical model simulates the two dimensional development of a carbonate platform and adjacent basin by successively calculating and depositing discrete sediment budgets generated over short time periods 10 sup 4 yr and displaying the results in synthetic cross sections through the carbonate buildup a series of model experiments shows that the effect of changing the eustatic sea level is largely dependent on the rate of subsidence in general sea level fluctuations tend to restrict progradation of the platform by producing periods of exposure of the platform top that decrease the overall sediment budget available for deposition on the marginal slope either increasing the amplitude or decreasing the period of the sea level cycle also restricts progradation which suggests that the higher order short period sea level cycles that are evident in the rock record may play an important role in controlling the cross sectional geometry of carbonate platforms forward models such as the one presented here may provide a basis for creating an inverse model that could be used tomore closely constrain the variables such as sediment production rate subsidence and sea level history that led to the cross sectional geometry observed in the field or in a seismic section less

a comparison of shear strength in calcareous and siliciclastic marine sediments abstract more than 2000 measurements of shear strength versus depth in fine grained marine sediments were collected from the literature and our own experiments in order to study the relationship between carbonate content and strength behavior of marine sediments depositional environments include slope rise and abyssal plain with most data originating from the slopes the depth range is restricted to 6 m subbottom depth in order to minimize diagenetic effects contour plots of shear strength versus depth for calcareous and siliciclastic sediments clearly reveal different trends whereas shear strength in siliciclastic sediments shows low variability and increases only gradually with depth the shear strength in the calcareous population is highly variable and increases rapidly with depth the difference in strength behavior of the two sediment groups has implications for the stability of submarine slopes previous research has shown that carbonate sediments build up steeper and more variable slopes than siliciclastic sediments this difference in slope angle can be explained at least in part by the higher internal strength of the carbonate sediments

factors controlling carbonate platform asymmetry preliminary results from the great bank of guizhou an isolated permian triassic platform in the nanpanjiang basin south china abstract a well exposed isolated carbonate platform the great bank of guizhou in the nanpanjiang basin of south china developed from the latest permian to the earliest late triassic platform strata are dissected by a faulted syncline exposing a complete cross section through the interior margins and flanks enabling a detailed assessment of depositional controls previous studies portrayed the platform as having a relatively symmetrical architecture even though much of the former work was focused on the platform interior and northern margin basin transition our research reveals five aspects of the southern margin facies and stratigraphy that are significantly different from those of the northern margin 1 subaerial exposure and unconformity developed on top of the upper permian sponge boundstone and in the overlying lower triassic strata 2 permian and triassic clasts chaotically admixed within early triassic breccias 3 lower triassic strata remarkably thinner on the southern margin 4 a much narrower tubiphytes reef facies preserved along the southern margin in the middle triassic and 5 large scallop shaped reentrants at the southern margin evident in satellite images three end member models may explain the asymmetry 1 antecedent topography of the underlying upper permian reef rimmed margin coupled with eustatic sea level fluctuation 2 differential tectonic uplift and 3 large scale submarine collapse of the platform margin subaerial exposure and admixing of permian and triassic clasts observed at yungan section is best explained by the tectonic uplift model however the submarine collapse model also explains several of the observations if it is associated with uplift s or sea level fall s submarine collapse is supported by large concave erosional reentrants scallops visible in satellite images taken together our observations suggest that a combination of tectonic uplift and margin collapse contributed to platform asymmetry further work promises to further constrain the details and timing of processes that contributed to the asymmetry

sedimentation rates and growth potential of tropical cool water and mud mound carbonate systems carbonate fixation in the ocean proceeds in three basic modes abiotically biotically induced with organic trigger and biotically controlled where organisms determine timing location and composition of the product the three modes combine in a variety of ways to produce carbonate sediment when viewed on the scale of formations and global facies belts three benthic carbonate production systems or factories emerge 1 the tropical shallow water system dominated by biotically controlled mainly photoautotrophic and abiotic precipitates 2 the cool water system dominated by biotically controlled mainly heterotrophic precipitates and 3 the mud mound system dominated by abiotic and biotically induced mainly microbial precipitates the sedimentation rates of all three factories decrease as the time span of observation increases this scaling trend is not just an artifact of ratio correlation it is almost certainly related to the episodic pulsating nature of sedimentation the growth potential of the three systems can be estimated by drawing the envelope of the maximum observed rates of aggradation the tropical system shows the highest rates 10

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

bahama carbonate platforms the deep and the past abstract carbonate deposition prevailed for 150 ma in the bahama florida segment of the west atlantic margin and provides an interesting test for actualism present day facies patterns on the banks are controlled by the backward decrease of waves and tides and the concomitant increase of temperature and salinity variation in the troughs influx of sand and rubble from gravity flows varies with topography and distance from shallow water sources and allows one to define facies belts a rhythmic sequence of ooze and graded beds on the basin floors subdivided into a basin margin belt of coarse thick turbidites and basin interior with fine turbidites slope facies change with increase in height and declivity from accretionary to by pass to erosional regimes stratigraphic history of the bahamas is not simply a projection of the holo scene back in time both long term natural evolution decrease in subsidence upbuilding of the banks submarine erosion and outside factors climate eustacy have caused significant changes since the jurassic the bahamas seem to have evolved from a clastics evaporite province to a single carbonate evaporite platform and finally to an array of platforms and troughs during the platform trough stage the rate of upbuilding of the platforms decreased submarine canyon erosion increased platform flanks steepened as they grew higher and changed from accretionary to by pass to erosional slopes a change imposed by extraneous factors occurred in the pliocene when the great bahama bank changed from a giant reef rimmed atoll to a flat platform covered by oolites and peloid sands the bahamas share both long term trends as well as random changes by extraneous factors with other platforms in the geologic record compared to ancient platforms however they are unusually long lived and at a more advanced stage of growth they are deeply dissected by erosion their flanks are unusually high and steep and the troughs very narrow the neogene platform sequence is strongly controlled by eustatic sea level fluctuations

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

granitoid associated gold mineralization in egypt a case study from the atalla mine gold bearing sulfide quartz veins cutting mainly through the atalla monzogranite intrusion in the eastern desert of egypt are controlled by subparallel ne trending brittle shear zones these veins are associated with pervasive sericite altered silicified and ferruginated rocks the hosting shear zones are presumed as high order structures of the najd style faults in the central eastern desert 615 585 ma ore minerals include an early pyrite arsenopyrite pyrrhotite mineralization partly replaced by a late pyrite galena sphalerite chalcopyrite gold electrum tetrahedrite hessite assemblage gold occurs as small inclusions in pyrite and arsenopyrite or more commonly as intergrowths with galena and sphalerite tetrahedrite in microfractures arsenopyrite geothermometry suggests formation of the early fe as sulfide mineralization at 380 340 c while conditions of deposition of the late base metal gold assemblage are assumed to be below 300 c rare hessite electrum and bi galena are associated with sphalerite and gold in the late assemblage the early and late sulfide minerals show consistently a narrow range of 34s 3 4 6 5 that overlaps with sulfur isotopic values in ophiolitic rocks

the early cretaceous platform off northwest florida controls on morphologic development of carbonate margins abstract an analysis of approximately 3500 km of multifold and 1000 km of singlefold seismic reflection data correlated with two exploration wells and other available geologic information records the morphologic development of the early cretaceous carbonate platform margin off northwest florida early cretaceous depositional patterns apparently controlled the concurrent formation of gently dipping declivities 10 carbonate platform margin slopes in the vicinity of desoto canyon northeastern gulf of mexico we suggest that the pronounced along strike change in morphology reflects variations in platform width input of terrestrial clastics and overall sediment availability to the platform s seaward margin slope southeast of the canyon the early cretaceous slope bordered a relatively broad platform removed from terrigenous sediment input environmental conditions favored the uninterrupted development of skeletal and nonskeletal buildups along the paleo shelf edge which effectively prevented large quantities of shelf derived clastic sediments from moving seaward consequently as the carbonate platform grew and its height increased the declivity of its seaward slope also increased as predicted by models of long term carbonate platform development in contrast northwest of the canyon the slope bordered a narrower platform adjacent to a source of terrigenous clastics more vigorous cross platform transport of clastics and resultant adverse environmental conditions at the paleo shelf edge inhibited consistent development of carbonate buildups thereby creating only an intermittent sediment barrier to the adjacent slope resultant higher sedimentation rates on the slope caused it to aggrade and prograde along with the carbonate platform allowing the margin slope to maintain its gentle morphology throughout the early cretaceous

high resolution stratigraphic forward modeling of a quaternary carbonate margin controls and dynamic of the progradation abstract the relationships between the margin sedimentary regime and the platform progradation are studied using forward stratigraphic numerical simulations on the leeward western prograding margin of the great bahama bank gbb during the quaternary 1 7 0 ma the corresponding sedimentary regime in the slope and the platform is well known from the odp leg 166 and bahamas drilling project wells located along the western line seismic transect however the sedimentary regime on the margin is not well established the coral reefal margin observed before between 1 7 and 0 8 ma in the well clino is not active anymore at present day and the holocene sedimentary regime is geometrically unable to account alone for the progradation this study is based on three 2d high resolution forward stratigraphic numerical modeling experiments with the software dionisosflow that include the platform margin and slope domains on the western line section in the same sedimentary models the results are compared to the six sedimentary cores and to the present day bathymetry in order to identify the more realistic scenario the three experiments test different models of carbonate sediment production and transport experiment 1 shows that the highstand shedding of the fine grained uncemented platform production is unable to reproduce the progradation and the present day profile experiments 2 and 3 incorporate cemented facies in the margin with the best results obtained with the cemented marginal wedges produced in experiment 2 during platform emersion from these results a high resolution interpretation of the margin seismic section is proposed this study shows that the platform progradation can be decoupled from the highstand shedding of the fine grained platform production it is dependent on the accumulation in front of the steep margin of coarse or cemented material before 0 8 ma this corresponds to the coral reef identified in clino the transition after 0 45 ma to 100 kyr large eustatic cycles with total platform flooding created two distinct marginal regimes 1 during platform flooding aggrading accumulation of non skeletal sands and 2 during platform emersion prograding cemented marginal wedges produced in situ

halokinetic sequences in carbonate systems an example from the middle albian bakio breccias formation basque country spain in diapir flanks unconformity bounded sedimentary packages associated with gravity driven deposits controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences the bakio breccias formation basque country spain corresponds to redeposited carbonate deposit that developed in response to the bakio diapir growth during the middle albian these deposits provide on of the rare documented example of carbonate dominated halokinetic sequences the bakio breccias formation consists of an alternation of clast and matrix supported breccias calcirudite calcarenite and marl deposited along the flanks of the diapir the description and the analysis of the bakio breccias formation lead to a new model for carbonate dominated halokinetic sequences these sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs while sediments are preferentially deposited in the mini basins adjacent of the diapirs in siliciclastic settings during transgressive system tract carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs forming thick and resistant roof which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities wedge halokinetic sequences during late highstand system tract deposition and lowstand system tract if present platform progradation results in high sediment accumulation in the adjacent depocenters loading the autochthonous salt layer and promote diapir growth and creation of topographic relief in addition if the diapir roof reaches emersion karstification of the carbonate platform top may also favour roof destruction and diapir growth depending on the thickness of the roof developed previously and the amplitude of the sea level fall the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities hook halokinetic sequences furthermore gravity driven deposits are assumed to be more common in carbonate dominated halokinetic sequences compared to their siliciclastic counterparts since carbonate platform aggradation creates steep slopes on the diapir margins leading to the partial collapse of the margin even when limited diapir growth occurs the carbonate dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed

accommodation and sedimentary architecture of isolated icehouse carbonate platforms insights from forward modeling with carb3d abstract a fundamental control on the evolution of carbonate platforms is accommodation the space available for sediment deposition here we adopt a sensitivity analysis approach using the process based forward model carb3d to quantitatively investigate the sedimentary response of isolated carbonate platforms to individual accommodation drivers of eustasy subsidence and surface dissolution sediment production the mechanism invoked to fill accommodation is also investigated fourth order milankovich driven sea level cycles dominate icehouse carbonate sedimentology with 400 ky cycles modulating the effect of 100 ky cycles of comparable magnitude when both cycles are present both overwhelm higher frequency lower amplitude fifth order cycles which are rarely preserved on the platform top subsidence is a fundamental control on sedimentary stacking patterns sequence boundary frequency sbf and platform geometry with rapid subsidence increasing the preservation of platform top sequences most icehouse platforms are subject to extended periods of platform top exposure missed beats when the platform top remains emergent at a sea level maximum are common and create non milankovich sbfs furthermore during platform emergence surface lowering via surface dissolution also creates accommodation for the subsequent platform flooding event with surface dissolution rates in humid climates comparable to moderate rates of subsidence however accommodation generation by surface dissolution is self limiting in as much as accommodation generated by dissolution is rapidly refilled on flooding sediment production is a key control on unfilled accommodation which our simulations suggest is considerable on icehouse platforms increased shallow water 3 m depth sediment production enhances intra platform bathymetric relief between the margin and interior this is driven in large part by a higher sedimentation rate at the margin than in the interior platforms can be flooded to depths up to 45 m during marine transgressions and accommodation often remains unfilled there are two distinct phases of platform top sedimentation during the transgression and early highstand platform margins accumulate at a greater rate than interior sediments generating differential intra platform bathymetry subsequently accommodation in the interior fills by forced regression and progradation from the margins into the platform interior numerical forward models can augment our understanding of icehouse carbonate platform evolution by identifying the nature of the sedimentary response to individual controls they can thus contribute to improving characterization of carbonate reservoirs in icehouse platforms such as the large hydrocarbon fields in the north caspian and s e asia

carbonate buildup flank deposits an example from the permian barents sea northern norway challenges classical facies models mounds seen on seismic in the barents sea offshore northern norway occur in the upper palaeozoic of the finnmark platform a 160 m long cored section from such a mound dated as unspecified asselian artinskian lower permian documents a carbonate buildup of microbial origin and rich in stromatactis fabric the cored section of a buildup where depositional dip angles vary from a few degrees to about 45 approximately 2 3 of the flank consists of in situ microbial boundstone with abundant stromatactis and in the upper part bryozoan cement framestone the remainder is gravity flow sediment deposited on the flank and at the toe of the buildup consisting of argillaceous sediment alternating with crinoid grainstones modal thin section analysis indicates that biogenic particles make up 38 of the buildup flank diagenetic products such as early fibrous cement microcrystalline cement and late blocky calcite 46 and lime mud including that interpreted as microbially induced 16 the studied core interval shows that steeply inclined buildup flanks can be largely in situ deposits rather than allochthonous as predicted in classical facies models

synthetic passive margin stratigraphy synthetic stratigraphic cross sections are derived mathematically for a variety of simple conditions the variables considered in the mathematical model include variations in sea level rate of tectonic subsidence rate of sedimentation and rate of erosion derived stratigraphic relationships include unconformities correlative conformities and disconformities coastal onlap coastal toplap erosional truncation pinch out and sigmoidal progradational clinoforms an important conclusion is that the rate of erosion is a dominant variable in determining the type of stratigraphic section observed the proposed approach may provide the basis for either a forward or inverse modeling of seismic stratigraphic sections

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

depositional architecture of a rimmed carbonate platform albian gorbea western pyrenees a lower cretaceous carbonate platform depositional system with a rimmed margin and an adjacent oversteepened slope was analysed in order to determine its depositional architecture and major depositional controls the platform is made up of coral rudist orbitolinid and algal limestones and in a 12 km dip transect there is a gradation from lagoon to platform margin slope and basin environments each characterized by distinctive sedimentological features and facies associations the rimmed platform is an aggradational system developed during approximately 4 2 million years of fluctuating relative sea level rise and it is bounded by unconformities at its base and top internal cyclicity in the construction of the system is evident mainly in platform interior and slope settings the seven recognized sequences average 0 6 million years in duration and are related to minor relative sea level changes carbonate deposition occurred in shallow and deep water settings during periods of high relative sea level reduced rates of sea level rise led to the development of shallowing upward sequences and eventually to the exposure of the shallowest parts of the platform during relative sea level falls during low relative sea level erosion surfaces developed on the slope and gravitational resedimentation occurred at the toe of slope basinwards resedimented units pinch out over distances of a few hundred metres active faults controlled sedimentation at the platform margin promoting the development of steep slopes up to 35 and preventing progradation of the shallow water platform despite high sediment production rates the development of sequences is interpreted to be related to tectonic activity

facies and geologic history of an exposed miocene rift margin carbonate platform gulf of suez egypt abu shaar is a small exhumed carbonate platform of lower to middle miocene age on a horst of precambrian crystalline rock along the western side of the gulf of suez the reef rimmed complex is entirely dolomite but with exquisitely preserved primary and diagenetic microfabrics similar platforms some of which contain hydrocarbons are buried beneath evaporites in the gulf the platform developed in three stages defined as local members of the rudeis formation the first stage records deposition during progressive marine onlap as aprons of mixed terrigenous carbonate sediments evolved into a wide reef rimmed platform synsedimentary platform margin collapse subsequently removed the most seaward portions of the reefs along the eastern gulf facing margin these truncation surfaces were then covered by a second phase of reef growth and deposition of fore reef carbonates the third and final stage deposited following a sea level drop and subaerial exposure is a series of well bedded peritidal carbonates that become progressively more evaporitic upward fore reef facies are again truncated by synsedimentary slope failure former evaporites are now recorded as collapse breccias contorted bedding black chert nodules and evaporite molds porosity is mainly secondary as vugs and molds and is highest in platform interior facies these more porous sediments contained more aragonitic components originally and were less affected by submarine cementation in contrast the higher degree of synsedimentary lithification of platform margin reef and fore reef sediments is comparable with what is commonly observed in modern reef dominated platform margins

seismic sedimentologic interpretation of a carbonate slope north margin of little bahama bank abstract analyses of seismic profiles and descriptions of sediments from odp leg 101 cores were combined to investigate the evolution of the northern margin of little bahama bank which has been prograding northward since the early mio cene modern depositional systems on the midslope and lower slope are found to be uncharacteristic of interpreted an cient sedimentary environments large slump masses covered much of the lower slope during the middle miocene pos sibly triggered by a regional tectonic event throughout the late miocene and most of the pliocene a channel and levee system meandered across the sediment apron of the lower slope the modern lower slope contains no meandering chan nels although gullies incised in the midslope funnel sediments to the base of slope apron actively promoting sediment bypass on an accretionary margin these changes in sedimentation pattern on the lower slope indicate increasing strength of ocean bottom contour following currents from the pliocene pliocene to holocene gravitational creep has produced large scale rotational movement of unlithified sediments and a major detachment surface along the base of the middle miocene slump masses these creep lobes extend far into the lower slope where sediments are contorted by propagation of and movement along multiple minor detachment surfaces

shelf architectures of an isolated late cretaceous carbonate platform margin galala mountains eastern desert egypt abstract an asymmetrical carbonate platform margin to basin transect has been investigated in the upper campanian maastrichtian succession of the galala mountains northern egypt identification of systems tracts and their lateral correlation was possible in slope sections only whereas the monotonous chalk marl alternations of the basinal sections could not be subdivided with respect to sequence stratigraphic terminology the platform asymmetry is expressed by varying large scale depositional architectures exhibiting a rimmed platform with a sigmoidal slope curvature in south easterly dip sections and a ramp with a linear slope curvature in south westerly dip sections the rimmed platform is subdivided into a gentle upper slope and a steep lower slope the platform formed as a result of the initial topography that was controlled by the tectonic uplift of the northern galala wadi araba syrian arc structure the calculated angles of the steep lower slope of the rimmed part range from 5 to 8 whereas the ramp part has an angle of less than 0 1

anatomy of a modern open ocean carbonate slope northern little bahama bank the open ocean carbonate slope north of little bahama bank consists of a relatively steep 4 upper slope between water depths of 200 and 900 m and a more gentle 1 2 lower slope between depths of 900 and 1300 m the upper slope is dissected by numerous small submarine canyons 50 150 m in relief that act as a line source for the downslope transport of coarse grained carbonate debris the lower slope is devoid of any well defined canyons but does contain numerous small 1 5 m hummocks of uncertain origin and numerous larger 5 40 m patchily distributed ahermatypic coral mounds sediments along the upper slope have prograded seaward during the cenozoic as a slope front fill seismic facies of fine grained peri platform ooze surface sediments show lateral gradation of both grain size and carbonate mineralogy with the fine fraction derived largely from the adjacent shallow water platform near surface sedimentary facies along the upper slope display a gradual downslope decrease in the degree of submarine cementation from well lithified hardgrounds to patchily cemented nodular ooze to unlithified peri platform ooze controlled by lateral variations in diagenetic potential and or winnowing by bottom currents submarine cementation stabilizes the upper part of the slope allowing upbuilding of the platform margin and controls the distribution of submarine slides as well as the headward extent of submarine canyons where unlithified sediments are heavily bioturbated and are locally undergoing dolomitization upper slope sediments are also conditioned eustatically resulting in vertical cyclic sequences of diagenetically unstable aragonite and magnesian calcite rich and stable calcite rich carbonates that may explain the well bedded nature of ancient peri platform ooze sequences lower slope sediments have prograded seaward during the cenozoic as a chaotic fill seismic facies of coarse grained carbonate turbidites and debris flow deposits with subordinate amounts of peri platform ooze coarse clasts are internally derived from fine grained upper slope sediments via incipient cementation submarine sliding and the generation of sediment gravity flows gravity flows bypass the upper slope via a multitude of canyons and are deposited along the lower slope as a wedge shaped apron of debris parallel to the adjacent shelf edge consisting of a complex spatial arrangement of localized turbidites and debris flow deposits a proximal apron facies of thick mud supported debris flow deposits plus thick coarse grained ta turbidites grades seaward into a distal apron facies of thinner grain supported debris flow deposits and thinner finer grained ta b turbidites with increasing proportions of peri platform ooze both the geomorphology and sedimentary facies relationships of the carbonate apron north of little bahama bank differ significantly from the classic submarine fan model as such a carbonate apron model offers an alternative to the fan model for palaeoenvironmental analysis of ancient open ocean carbonate slope sequences

carbonates and relative changes in sea level abstract in the geologic record some of the most accurate gauges of changes in sea level are the sediment type geometry and diagenesis of carbonate shelves and platforms this is because carbonates frequently occur at or very near sea level and are usually less compacted than siliciclastics world wide changes in relative sea level the sum of eustatic sea level changes sedimentation and crustal movements have occurred repeatedly and cyclicly through geologic time producing characteristic responses in carbonates 1 1 relative rises in sea level usually caused by the cumulative effect of tectonic subsidence and eustatic rise may result in the following 1 1 a drowned carbonate reefs or platforms here carbonate growth potential is exceeded by relative sea level rise and is characterized by shallow water sediments overlain by hardgrounds and or deep water sediments some of which may be condensed sequences 1 2 b platforms where only the fast growing rim and patches of the interior are able to match sea level rise while the remainder of the platform is drowned temporarily 1 3 c platforms which keep up and maintain a flat top at sea level and contain shallow water sediments whose thickness at the least matches the height of the sea level rise if terrigenous supply is limited prograding sheets of shelf carbonate occur frequently capped by supratidal evaporites with prograding shelf margin carbonate clinoforms and turbidites if terrigenous supply is high the shelf carbonates encroach on deltaics 2 2 relative drops in sea level caused by crustal uplift or by subsidence being outpaced by a eustatic drop in sea level cause karst and soil development over shelves and platforms deposition of deep water evaporites in adjacent semi enclosed basins and in open marine basins the deposition of deltaic and aeolian clastics that bypassed the shelf falls are accompanied by platform wide fresh water diagenesis during relative sea level rises marine diagenesis is common in the subtidal portions of the shoaling upward carbonates and fresh water diagenesis and dolomitization and sulphate deposition is common in their intertidal and supratidal portions the stratigraphic significance of these reponses to relative sea level change is that many are tied to eustatic events and so are predictable within a basin of deposition

role of autochthonous versus detrital micrite in depositional geometries of middle triassic carbonate platform systems middle triassic platforms formazione di contrin upper anisian in the italian dolomites southern alps record large changes in carbonate production and depositional geometry the changes include variation in the abundance of detrital micrite i e allochthonous calcareous mud relative to the autochthonous micrite which formed in situ and was syndepositionally lithified carbonate factory dynamics controlled the geometry of the clinostratified slope units and were probably associated with changes in oxygenation early anisian low relief platforms were followed by late anisian high relief buildups associated with basinal dysoxic anoxic environments the geometric evolution of the platform slopes records a progressive increase in the dip angle of clinostratifications matched by a deepening evolution of the basinal environments at the same time the slope sediments record a gradual change from loose detrital micrite characterizing the lower portion to autochthonous micrite dominating the upper part and recording massive syndepositional lithification the development of the autochthonous micrite was associated with the preservation of significant amounts of organic matter this sharp increase in automicrite formation was probably induced by a rapid change from oxic to suboxic conditions in the carbonate slope and margin environments while anoxic conditions developed in the adjacent organic rich basin moena formation the low oxygen level promoted the preservation of organic matter and the activity of sulfate reducing bacteria which in turn induced in situ deposition of autochthonous micrite through biomediated processes this pervasive early cementation and lithification induced the development of steep platform slopes the conceptual model distilled from this middle triassic case can support the interpretation of analogous buildups where the skeletal framework is subordinate to the micrite component

carbonate slide deposits in the middle jurassic of portugal abstract a bajocian to callovian carbonate sequence at mareta beach sagres portugal contains slide deposits laid down on the southern continental slope of the iberian meseta translational slide deposits form nine discrete zones up to 6 m thick intercalated hard and soft beds in lobate slide masses were deformed into megascopic recumbent folds isolated fold noses and imbricate slabs in a partially coherent to incoherent manner a prominent lineation on planar and folded surfaces is due to microfold and microfault sets which formed while the beds were semi consolidated bioturbated omission surfaces overlie some slide deposits suggesting that slides incorporated near surface sediments and formed topographically high sea floor features early partial cementation of the hard beds may have contributed to sliding by increasing pore pressure a rotational slide scar closely associated with the deformed zones and low angle truncation surfaces beneath some zones suggest that rotational failure may have initiated the translational slides a southerly paleoslope toward the tethys ocean is indicated by orientations of folds bedding plane lineations and slide scars