carbonate platform evolution from a bioconstructed platform margin to a sand shoal system devonian guilin south china the depositional organization and architecture of the middle late devonian yangdi rimmed carbonate platform margin in the guilin area of south china were related to oblique extensional faulting in a strike slip setting the platform margin shows two main stages of construction in the late givetian to frasnian with a bioconstructed margin evolving into a sand shoal system in the late givetian the platform margin was rimmed with microbial buildups composed mainly of cyanobacterial colonies mostly renalcis and epiphyton these grew upwards and produced an aggradational locally slightly retrogradational architecture with steep foreslope clinoforms three depositional sequences s3 s5 are recognized in the upper givetian strata which are dominated by extensive microbialites metre scale depositional cyclicity occurs in most facies associations except in the platform margin buildups and upper foreslope facies in the latest givetian at the top of sequence s5 relative platform uplift subaerial exposure and associated rapid basin subsidence probably a block tilting effect caused large scale platform collapse and slope erosion to give local scalloped embayments along the platform margin and the synchronous demise of microbial buildups subsequently sand shoals and banks composed of ooids and peloids and a little later stromatoporoid buildups on the palaeohighs developed along the platform margin from which abundant loose sediment was transported downslope to form gravity flow deposits another strong tectonic episode caused further platform collapse in the early frasnian at the top of sequence s6 leading to large scale breccia release and the death of the stromatoporoid buildups siliceous facies banded cherts and siliceous shales were then deposited extensively in the basin centre as a result of the influx of hydrothermal fluids the platform margin sand shoal bank system possibly with gullies on the slope persisted into the latest frasnian until the restoration of microbial buildups four sequences s6 s9 characterized by abundant sand shoal deposits on the margin and gravity flow and hemipelagic deposits on the slope are distinguished in the frasnian strata smaller scale depositional cyclicity is evident in all facies associations across the platform slope basin transect the distinctive depositional architecture and evolution of this yangdi platform are interpreted as having been controlled mainly by regional tectonics with contributions from eustasy environmental factors oceanographic setting biotic and sedimentary fabrics

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

clinoforms and clinoform systems review and dynamic classification scheme for shorelines subaqueous deltas shelf edges and continental margins abstract clinoforms are inclined and normally basinward dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems the study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir seal and source rocks along shoreline to basin floor profiles here we review clinoform research and propose a more systematic description and classification of clinoforms this is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions together with the genesis drivers and dynamics of their constituent sedimentary units four basic clinoform types are here distinguished in delta shorelines lacustrine and marine environments on the basis of their overall spatial and temporal scale morphology outbuilding dynamic and geodynamic and depositional setting 1 2 delta scale clinoforms which in turns are sub divided into shoreline and delta scale subaqueous clinoforms 3 shelf edge clinoforms and 4 continental margin clinoforms delta scale clinoform sets are tens of metres high and typically represent 1 103 kyr with progradation rates ranging from 1 000 100 000 m kyr for shorelines and subaerial deltas to 100 20 000 m kyr for subaqueous deltas shelf edge clinoform sets are hundreds of metres high and are nucleated and accreted in 0 1 20 myr usual progradation rates of 1 100 m kyr by successive cross shelf transits of delta scale clinoforms continental margin clinoform sets are thousands of metres high hallmark key geodynamic crustal boundaries e g continent ocean transition and slowly prograde basinwards in ca 5 100 myr with typical rates of 0 1 10 m kyr as a consequence of the very different progradation rates and of the difficulty of large scale clinothems to backstep during transgressions shorelines are the most dynamic clinoforms with regards to position continental margins the least and shelf edges are intermediate shortly after a transgression therefore the four clinoform types may prograde synchronously along shoreline to abyssal plain transects forming compound clinoform systems during the subsequent regressive cycle however due to the dissimilarity in progradation rates different clinoform types will normally merge progressively with each other giving rise to hybrid clinoforms e g shelf edge deltas and fewer depositional breaks in slope are distinguished along a single shoreline to abyssal plain transect overall all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum regulated by the cyclical backstepping of the smaller scale system within natural progradational retrogradational cycles of larger scale clinothem outbuilding all clinothem types may show either an accretionary active or draping passive style depending on the proximity to the sediment source draping clinothems are nearly always composed of condensed fine grained sediments while actively accreting clinothems can be composed of predominantly coarse grained i e reservoir forming or predominantly fine grained i e non reservoir lithotypes a novel hierarchical classification scheme for both recent and ancient clinoforms is here proposed consisting of 12 classes the four basic clinoform types delta scale shoreline delta scale subaqueous shelf edge and continental margin are sub divided into eight accretionary active and draping passive sub types 8 division each accretionary sub type is then sub divided into a sandstone prone and mudstone prone variant 12 division which can be at least tentatively predicted on the basis of the clinoform morphology even in the absence of direct stratigraphic logs

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

ordovician paleotopography as evidenced from original dips and differential compaction of dolostone and shale unconformably overlying precambrian basement on manitoulin island canada abstract the middle to basal upper ordovician lindsay formation unconformably overlies the paleoproterozoic bar river and lorrain formations on manitoulin island ontario canada representing a depositional hiatus of at least 1 7 billion years the paleoproterozoic inliers currently exposed as basement highs in the sheguiandah region comprised a 14 km2 area of quartz arenite archipelago during the middle to late ordovician inland sea transgression of north america the quartz arenite outcrop collectively covers an area of approximately 1 8 km2 high energy transport and reworking during wave and tropical storm activity along a high relief rocky shoreline is indicated by dolostone containing 2 5 m size rounded to subrounded quartz arenite boulders with percussion marks up to 4 5 m size subangular quartz arenite blocks consistent with mechanical breakage along joints fractures or bedding planes lenticular conglomerate beds and cracks in quartz arenite basement containing mixtures of dolostone quartz granules and fossiliferous debris with continued transgression organic rich carbonate muds were deposited under low energy conditions either on carbonate strata or directly on quartz arenite basement in restricted regions protected from the open sea clast size distribution in the dolostone clast rounding and the location of the shale quartz arenite unconformity relative to basement highs are all consistent with a longshore current running from the present northeast to southwest with the leeward sides of rocky islands protected from high wave and storm energy processes subsequent deposition of upper ordovician and silurian strata resulted in burial and differential compaction of the lindsay formation units the compaction may have been associated with fractures through which mg rich fluids migrated locally altering the lowermost lindsay formation to dolostone evidence for differential compaction is provided by bed thickening down dip of basement highs and boulder flanks and higher regional dips in shale beds proximal to basement highs compared with dolostone strata the relatively high angle strata of the lindsay formation are a result of the combined effects of paleotopography a high relief rocky shoreline and differential compaction

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

acoustic properties of neogene carbonates and siliciclastics from the subsurface of the florida keys implications for seismic reflectivity abstract results of measurements of compressional wave velocity and shear wave velocity have been compared with other rock properties xrd and thin section analyses for over fifty minicores from two cores drilled through sedimentary rocks on stock island and long key florida keys the comparisons indicate that sonic velocity in siliciclastics and carbonates is mainly controlled by three factors 1 porosity and primary pore type 2 quartz content and 3 dolomite content in the case of two pliocene prograding formations the combination of depositional fabric and diagenetic alterations produced patterns and values of almost identical impedance for fine grained carbonates and siliciclastics consequently seismic sections can not be used to distinguish between the prograding quartz sands and the prograding fine grained carbonates compressional and shear wave velocities in the limestones are strongly controlled by total porosity and the primary pore type generally high porosity rocks have lower velocities than low porosity rocks but pore types can significantly influence velocities overall an increasing percentage of dolomite in carbonate rocks results in an increase in velocity some dolomitic fabrics deviate from this trend fabric preserving mimetic dolomites yield the highest velocities whereas samples that are of purely sucrosic dolomites produce lower velocities which however are still higher in average than non or only partly dolomitized samples quartz sandstones and quartz bearing limestones have generally low and uniform velocities the low velocities of the sandstones containing 80 quartz is a result of their primary interparticle porosity due to the low diagenetic potential of quartz grains a high quartz content inhibits major diagenetic alterations which would result in cementation and higher velocities synthetic seismograms and nearby seismic sections reveal two major seismic facies as a result of the observed velocity distribution 1 carbonates of the stock island formation and siliciclastics of the long key formation are both characterized by low seismic reflectivity or even seismic transparency this seismic facies is caused by a very similar uniform vertical distribution of low velocities with almost identical impedance values in the two formations thus the transition or an interfingering between the time equivalent siliciclastic long key formation and the carbonate stock island formation might not be detectable on a seismic section 2 the over and underlying shallow marine carbonates in contrast have higher velocities with a wider range of velocities resulting in a succession of high amplitude reflections

environmental control on granular clinoforms of ancient carbonate shelves the purpose of this paper is to document the influence of depositional environments on shallow water low relief clinoforms from the description of five ancient carbonate platforms the neoproterozoic namibia middle jurassic france lower cretaceous france upper cretaceous oman and miocene turkey these examples have been investigated on the basis of field observations the clinoforms are described with reference to geometric and compositional attributes declivity shape height sedimentary structures sediment fabric and components the results show great variability in stratal geometry declivity and facies distribution 1 depositional profiles vary from exponential to sigmoidal to oblique 2 maximal slope angles range from 3 to 25 most of them being grouped between 10 and 18 3 facies differentiation identified from lateral facies successions along beds and vertical facies successions through beds is pronounced to subtle this study documents linkages between depositional environments and clinoform attributes proximal shallow clinoforms display round edged exponential profiles sediment deposition has resulted from unidirectional currents in the upper convex section and storm generated oscillatory currents in the lower concave part the sediment fabric changes gradually along this type of clinoform there is little vertical facies differentiation through these clinobeds which have formed from a continuous amalgamation of deposits by contrast distal clinoforms shelf break distally steepened ramp settings yield a much broader spectrum of profiles and are generally shorter and steeper sedimentary structures in gravel sized deposits of the upper slope indicate pure traction by unidirectional currents conversely marks of oscillatory flows undular wavy top bounding surfaces of clinobeds are common in the lower slope intercalation of massive fine grained deposits suggests offshore transport of carbonate mud by suspension each distal clinobed represents a single flow event accordingly facies differentiation is weak laterally but may be pronounced through the clinobeds our study suggests that low relief forms of proximal shallow environments which contain coarse grained and photo independently produced debris record hydrodynamic equilibrium profiles whereas the higher relief forms of this setting rather reflect a high differential production rate of carbonate sediment with water depth the carbonate sediment of the distal clinobeds mainly derives from skeletal production by oligophotic and photo independent biota of the middle shelf ramp and upper portion of the clinoforms the contribution by in situ skeletal biota only becomes significant on the lower slope indicating that the distal submerged slopes of carbonate platforms are not organically but hydrodynamically generated our compilation shows that the slope angles of shallow marine low relief clinoforms do not simply correlate to the sediment grain size and fabric in contrast to what has been documented for the high linear slope profiles this difference stems from the depositional settings namely the involved transport mechanisms low relief clinoform accretion seems to be dominantly influenced by wave induced sediment transport in contrast to linear flanks of high relief clinoforms that build to the angle of repose and for which gravity is the primary transport process

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

chironomid inferred holocene temperature changes in the south carpathians romania we present a holocene summer air temperature reconstruction based on fossil chironomids from lake brazi 1740 m a s l a shallow mountain lake in the south carpathians summer air temperature rec

sedimentology and sequence stratigraphy of reefs and carbonate platforms wolfgang schlager aapg course notes no 34 price 14 members 20 non members

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

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

quaternary slope development of the western leeward margin of the great bahama bank abstract to date work on the great bahama bank s western leeward margin has centred chiefly on seismic scale expressions of carbonate sequences and systems tracts however periplatform slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres it is these small scale high frequency cycles within the larger scale facies successions of the quaternary which form the main topic of this paper previous studies have shown that the small scale cycles correlate to the orbitally forced high frequency sea level changes therefore these cycles should indicate how sea level has affected the slope development and thus platform margin evolution during this period through detailed high resolution sequence stratigraphy of the great bahama bank s leeward margin obtained via 18o isotope and mineralogical xrd analyses confined by u th dating and nannofossil bioevents a greater understanding of the bedding geometries within the pleistocene holocene seismic sequences and clues as to the nature of the slope development has been achieved the high resolution seismic profiles indicate that since the plio pleistocene change in geometry in which the great bahama bank developed into a rimmed platform continued steepening and subsequent progradation of the leeward margin has typified slope development during the quaternary which is described as an accretionary slope however on the basis of our observations we conclude that only the early to lower middle pleistocene section isotope stages 45 20 and the holocene isotope stage 1 of the leeward margin is accretionary this indicates that a degree of erosion and or by passing has occurred on the leeward margin since the lower middle pleistocene isotope stage 19 during the first part of this period isotope stages 19 12 erosion and or by passing occurred in the middle to lower slope regions and toe of slope by the end of the upper middle to late pleistocene phase isotope stages 11 2 erosion also occurred on the upper slope this erosion by currents at the toe of slope and oversteepening of the upper and middle slopes have led to back cutting upslope and resulted in the progressive retreat of the toe of slope towards the platform to the east however the rise in sea level since the last glacial maximum to its present day level has allowed high productivity on the platform top during the holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks this has led to the redevelopment of an accretionary slope and continued westward progradation of the great bahama bank s western leeward margin

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

3 d stratigraphic architecture sedimentary processes and controlling factors of cretaceous deep water resedimented carbonates gargano peninsula se italy abstract detailed geological mapping in 3 d supported by a lidar derived dom sedimentologic and biostratigraphic analyses and 3 d numerical modelling are used to characterise the stratigraphic architecture of deep water resedimented carbonate systems in the gargano peninsula se italy the base of slope succession spanning the upper aptian to danian p p was subdivided in five lithostratigraphic units that record the complex evolution and sedimentary dynamic along a segment of the apulian platform margin that was strongly influenced by syn sedimentary tectonic activity the characteristic location in a relay zone between the nw se trending platform margin and the e w oriented mattinata fault system favoured the existence of a transtentional zone from the upper aptian up to the end of the cretaceous the spatial distribution of the gravity flow deposits the stratal geometries the lateral facies changes and the biostratigraphic data demonstrate that the base of slope systems were sourced by distinct platform blocks characterised by different slope profiles abrupt to west and distally steepened to the north in this context the nature and origin of the resedimented carbonate material were controlled by the fracturation of the margin the response of the carbonate factory to relative sea level changes but were also strongly influenced by the slope profile this study demonstrates the relevance of combining traditional field work with numerical tools to improve the understanding of ancient sedimentary systems notably by mapping the stratal architecture and lithologies in continuity and at various scales on doms and by reconstructing the paleo topographies in 3 d

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

giant pockmarks in a carbonate platform maldives indian ocean abstract circular structures and depressions in carbonate platforms are known to represent karst chimneys or sinkholes which form as a response to rock solution this formation mechanism is plausible for shallow water carbonates which lie in the reach of meteoric diagenesis or fresh water lenses circular structures which occur in deeper waters however need an alternative interpretation such an example of sea floor depressions in more than 300 m deep waters occurs in the inner sea of the maldives carbonate platform in the indian ocean the structures were mapped with multibeam and parasound multi channel seismics were used to link the depressions with structures at depth the circular depressions have diameters of up to 3000 m and depths of up to 180 m the craters are interpreted as pockmarks formed through the venting of gas and fluids gas and fluid lenses below the pockmarks are reflected by bright spots in the seismic sections as well as a reduction of the instantaneous frequency these areas at depth are linked to chimneys connected to faults and drowned oligocene carbonate banks a model is presented that relates the different forms and sizes of the structures to distinct development stages of sea floor deformation to one process early stages of gas and fluid migration into the shallow part of the sedimentary succession induce formation of dome shaped bodies initial gas and fluid escape to the sea floor is reflected by the formation of sand volcanoes and aligned small pockmarks active pockmarks are the deepest and have the shape of truncated cones in cross section mature pockmarks are characterized by erosion of the flanks of the structure by bottom currents late stage pockmarks are bowl shaped in cross section and are to different degrees filled by drift sediments packages of strata revealing high reflection amplitudes and high interval velocities interpreted as microbially mediated carbonate precipitates underlie some of the pockmarks the pockmarks in the maldives show that circular structures other than solution related features can be abundant in carbonate platform deposits and that such structures may be more abundant in the geological record of carbonate platforms as previously thought pockmarks in the maldives indicate that the archipelago is an example of a hydrocarbon system which consists of an isolated oceanic carbonate platform overlying a volcanic basement and lacustrine source rocks

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

controls on facies architecture of a large triassic carbonate platform the great bank of guizhou nanpanjiang basin south china abstract the great bank of guizhou gbg is an exceptionally well exposed isolated triassic platform in the nanpanjiang basin of south china the platform is exhumed with its depositional profile preserved and is dissected by a faulted syncline that exposes a complete and uncomplicated cross section providing a unique opportunity to evaluate mechanisms involved in its birth evolution and demise the gbg formed near the southern margin of the yangtze platform during a deepening event that expanded the nanpanjiang basin and drowned the region surrounding the gbg in the latest permian initial accumulation of the gbg began in the latest permian with small reef mounds and open marine skeletal packstones following the end permian extinction cyanobacterial boundstones grew over the bank top during the early triassic the gbg developed a low relief bank profile with mobile oolite shoals at the margin shallow subtidal and peritidal deposits in the interior and gentle slopes dominated by pelagics debris flow deposits and turbidites at the basin margin in the middle triassic anisian the gbg developed a progressively steepening profile rimmed with massive tubiphytes reefs the platform was flat topped with tidal flat deposits across the interior basin margin deposition was dominated by turbidites and debris flow deposits but eventually shifted to avalanche and rock fall deposits as the slopes steepened to the angle of repose in the middle triassic ladinian an erosional escarpment up to 1700 m high developed at the margin platform margin strata are bedded packstones similar to interior strata whereas breccias at the basin margin contain coral boundstone clasts suggesting erosion of reefs from the escarpment a restricted subtidal lagoon formed in the interior producing an atoll like morphology later a flat topped profile was restored as tidal flats spread across the interior in the beginning of the late triassic deepening contributed to termination of the gbg before siliciclastic turbidites and shales were deposited over the platform in contrast with the well known platforms of the dolomites of northern italy the gbg contains abundant muddy carbonates and a progressively steepening bank to reef rimmed and escarpment architecture the italian platforms contain little mud and have angle of repose pinnacle geometries the gbg s larger size increased mud production and protected it from extensive winnowing of mud which in turn resulted in off bank shedding of muddy sediments that were stable on relatively gentle basin margin slopes which progressively steepened and ultimately led to avalanche deposits and a high relief erosional escarpment in contrast the lesser mud content of the dolomites platforms forced avalanche and talus deposition to dominate throughout deposition of basin margins which in turn produced their angle of repose geometries

influence of bathymetry and oceanic currents on the development of carbonate platforms northern carnarvon basin northwest shelf of australia abstract cenozoic continental shelf deposition in the northern carnarvon basin was dominated by heterozoan carbonates until siliciclastic sediments prograded across the shelf in the late middle miocene to pliocene these siliciclastic sediments were deposited as outer shelf and shelf edge deltas which created subtle bathymetric highs interpretation of extensive high quality multichannel seismic data shows broad flat topped carbonate platforms overlying the remaining bathymetric highs following the retreat of deltaic sedimentation platform geometries suggest that a combination of relative sea level changes and ocean currents controlled their internal architectures clinoforms on the northeastern flanks of the platforms are more steeply dipping than those on the southwestern flanks and this platform architecture may reflect strengthening or initiation of a proto leeuwin current the earliest platform developed in the northeast and successive platforms migrated southwest along strike a process that could have resulted either from differential compaction of the underlying clastic depocenters or variable rates of tectonic subsidence along depositional strike probably in combination with environmental factors

a pennsylvanian microbial boundstone dominated carbonate shelf in a distal foreland margin picos de europa province nw spain abstract a pennsylvanian bashkirian moscovian high rising microbial boundstone dominated carbonate platform 12 000 km2 developed in the external margin of a variscan foreland basin intensely studied in the northern domain cuera area the stratigraphy and sedimentology of the southern domain the picos de europa province is here revisited distribution of the bashkirian facies valdeteja formation defines a ramp low angle platform with an internal zone central and eastern sectors of the picos de europa province consisting of huge amounts of massive cement rich microbial boundstones surrounded by an external zone comprising lower slope boundstone derived breccias and basinal lime mudstones from the bashkirian moscovian transition to the early kasimovian picos de europa formation the carbonate platform moderately aggraded acquiring a high rising and flat topped geometry and then prograded rapidly into the external zone where platform derived carbonate sediment and clay sourced from the orogen were deposited seismic scale exposures of the western margin of the shelf show angular bedding relationship between basin toe of slope slope and platform top stratal domains with slope inclination up to 32 and a topographic relief of 550 m the platform evolution above described for the picos de europa province significantly differs with respect to the cuera area where platform mostly prograded during the bashkirian and subsequently aggraded during early moscovian the evolutionary differences between these two carbonate domains which are geographically close are interpreted as changes in tectonic subsidence distribution acting as the major factor controlling the large scale platform geometries in the active foreland basin context finally the tectonic overload due to the emplacement of the cuera thrust sheets during the moscovian kasimovian transition changed the platform growth style from progradational to aggradational and consequently the stacking pattern of the platform top cycles in the picos de europa province

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

facies architecture of an early jurassic carbonate platform slope jbel bou dahar high atlas morocco the plateau of jbel bou dahar high atlas morocco represents an outstanding example of a well preserved early mesozoic carbonate platform field observations of the large scale sedimentary structures and the arrangement of lithofacies associations within the mid and lower slope were combined with detailed microfacies analyses and gamma ray measurements the investigations were carried out in order to 1 resolve the sequence stratigraphic architecture of the slope and 2 reconstruct the sediment export patterns and depositional processes related to high frequency sea level variations the slope strata are arranged into two different types of lithofacies associations that are bounded by characteristic discontinuities and show a specific occurrence along the investigated slope section the steep 8 18 mid slope is dominated by thick to medium bedded limestone successions that were able to maintain a high angle of repose due to their detrital composition the sediment packages are bounded by basal low angle unconformities and wedge out within the lower slope or thin into the adjacent basin as single carbonate layers the sediments are characterized by coarse grained and poorly sorted floatstones to rudstones which show low gamma ray values and contain components derived mainly from the platform edge the facies associations were interpreted as debris flow deposits that were exported during sea level lowstands when the flattened platform top and extended parts of the margin were exposed and sediment production was restricted mainly to the outer margin and upper slope section in contrast the gently dipping lower slope 4 18 is characterized by rhythmic limestone marl alternations that show increasing thicknesses with increasing distance from the platform from the lower part of the mid slope down the successions onlap the debris flow deposits forming a characteristic interfingering pattern of different lithofacies associations the medium to thin bedded carbonates of the limestone marl alternations comprise two different microfacies types 1 mudstones to wackestones with high gamma ray values and a mixed shallow marine to deep marine microfacies overlain by 2 well sorted arenitic packstones to grainstones with low gamma ray values and a shallow marine component composition the latter points to the platform interior and margin as primary source areas the shallow marine material was exported during sea level highstands when the carbonate factory included the entire platform margin and the flooded lagoons of the platform top during these periods the exported fine grained sediments could maintain only low angles of repose thus they bypassed the steep upper and mid slope sections developed into turbidites during downslope transport and were finally redeposited on the gently dipping lower slope and in the adjacent basin the architecture of the investigated slope area shows a characteristic interfingering of different facies associations that can be interpreted as genetic highstand and lowstand stratigraphic sequences the arrangement of these sequences along the slope as well as their composition were controlled by high frequency sea level fluctuations affecting the primary sediment production source area export patterns and sedimentary processes resulting in a shift of the depositional centers during different sea level stands

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

clinoform composition and margin geometries of a lower cretaceous carbonate platform vercors se france the concept of sequence stratigraphy uses the stratal geometries at the margins of carbonate platforms to define depositional sequences and systems tracts the aim of this study was to research if prograding purely aggrading and retrograding phases of a cretaceous carbonate platform showed differences in the composition and facies type of the slope sediments the vercors plateau in se france provides excellent outcrops to study this relationship continuous exposure of the platform to basin transition allowed direct examination of the margin geometries five successions were measured and sampled in great detail samples were thin sectioned and point counted using point count groups characterizing palaeoenvironments along the platform to basin transect the composition logs as well as the numerical analysis of the point count data both show a clear relationship between grain composition and stratal geometry the prograding and purely aggrading intervals are similar in composition as they are both relatively coarse grained and enriched in platform biota and limeclasts retreating units are relatively fine grained and rich in basinal grains small benthic foraminifers sponge spicules non carbonate grains and embedding material these observations suggest that the retreating intervals represent incipient drownings of the platform however rather than distinctly separated groups the different phases of platform development form a continuous range of variation between high platform input and high basinal input compared to the prograding units the purely aggrading intervals are relatively rich in peloids which may be suggestive of relatively low energy conditions on the platform during aggradation the compositional analysis also revealed significant variation in the frequency of ooids but these variations showed no relationship with the progradation aggradation or retreat of the platform

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

the latemar a middle triassic polygonal fault block platform controlled by synsedimentary tectonics abstract detailed field mapping of a middle triassic carbonate buildup the latemar in the western dolomites northern italy has been carried out the latemar is an isolated carbonate buildup that nucleates on a fault bounded structural high horst cut into the underlying late anisian carbonate bank of the contrin fm this study demonstrates that extensional synsedimentary tectonics is the main factor controlling its geometry and provides an age for this tectonic phase in an early phase slopes were mostly composed of well bedded clinostratified grainstones and rudstones in a later stage the deposition of grainstones was accompanied by the emplacement of clinostratified megabreccias the upper portion of slopes is a microbial boundstone with abundant tubiphytes and patches or lenses of grainstone boundstones may occasionally expand into the platform interior and downward to the base of the slope the depositional profile was that of a mounded platform the buildup is dissected by a dense framework of high angle fractures and faults and by magmatic and sedimentary dikes exhibiting two principal directions trending nnw sse and ene wsw faults trending wnw ese were also observed magmatic dikes are related to the emplacement of the nearby predazzo intrusion and are thus upper ladinian kinematic indicators of strike slip activity were observed on fault planes trending nne ssw and nnw sse that can be attributed to cenozoic alpine tectonics faults magmatic dikes and sedimentary dikes show systematic cross cutting relationships with strike slip faults cutting magmatic dikes and magmatic dikes cutting sedimentary neptunian dikes ene wsw and wnw ese faults are cut by all other structures and record the oldest tectonic activity in the region structural analysis attributes this tectonic phase to an extensional stress field with a direction of maximum extension oriented ca n s several lines of evidence including sealed faults and growth wedge geometries allow us to recognize this old tectonic phase as syndepositional and to date it to the latest anisian avisianum and crassus ammonoid biochronozones the horse shoe shape of the platform and its margins rectilinear for long tracts are explained by the existence of a network of extensional faults whose activity lasted for part of the growth of the platform the latemar is thus a polygonal fault block platform controlled by synsedimentary tectonics the resulting sedimentary architecture is that of a growth wedge deposited probably on the uplifted side of a submerged half graben continuous reactivation of faults at platform margins locally determined anomalous facies transitions with well layered platform interior directly in contact with the clinostratified slopes

termination of carbonate slope progradation an example from the carnian of the dolomites northern italy abstract the demise of carbonate platforms during carnian time is a widespread phenomenon of the western tethys but the controlling factors are not well understood the dolomites of the southern alps northern italy are well known for their large scale ladinian and carnian prograding carbonate platforms platform growth stopped during the early carnian and both platforms and basinal areas were subsequently covered by mixed carbonate siliciclastic sediments raibl group we present a carbonate platform whose slope progradation came to a halt prior to draping by the siliciclastic sediments judging from the height of the clinoforms a platform to basin relief of at least 100 m existed during the final stage of progradation this paleo slope was colonized by coral patches draped by skeletal packstones to microbial bindstones forming typically lens shaped mounds on the steep slope the formation of mounds on the platform flank was only possible because the downslope transport of detritus from the platform and or upper slope was stopped the sedimentary evolution in the adjacent basin indicates a poorly oxygenated environment with abundant brackish water ostracods of low diversity based on the inherited platform to basin relief and the lithofacies of the basin fill a local sea level drop in the order of 60 80 m is postulated with rising sea level the accommodation space between former basin and platform became filled by shallow marine mixed carbonate siliciclastic sediments the abundance of epibenthic suspension feeders of the basin fill such as megalodonts suggests increased nutrient supply the termination of slope progradation was a multiphased process triggered by a stagnation of the regional subsidence a reduction of water circulation followed by a sea level drop the influx of freshwater and the input of siliciclastics fluctuating salinity caused intermittently a biotically stressed environment

gravity driven structures and deposits resulting from slope collapse in the margin of a carbonate platform pennsylvanian cantabrian zone nw iberia abstract lower slope to basin floor deposits associated to isolated microbial carbonate platforms of the valdeteja formation carboniferous foreland basin cantabrian zone nw spain containing large slid blocks and debrites exhibit a combination of contractional and extensional structures which include thrusts backthrusts folds extensional faults and joints and boudinaged beds several lines of evidence indicate that deformation took place in poorly lithified conditions such as thickened hinges hydroplastic fractures fold axes scatter or folding of microbial limestones once restored all structures indicate a transport direction towards the nne ene this azimuth coincides with the direction towards which the thrust nappes of the southern branch of the cantabrian zone were emplaced during the variscan orogeny however the interpretation of the deposits and structures as gravity related associated to the collapse of the carbonate platform slope is supported by features such as the rootless character of thrusts the parallelism between transport direction and paleocurrent orientation the concomitant development of contractional and extensional structures the development of normal listric faults affecting the valdeteja platform the sedimentary environment lower slope to basin floor and the geological context of the valdeteja carbonate platforms which predate the variscan deformation in the study area

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

growth and demise of late carboniferous carbonate platforms in the eastern cantabrian zone asturias northwestern spain abstract geometric relationships of seismic scale stratal patterns observed on aerial photographs of late carboniferous carbonate platforms in the cuera region in asturias northwestern spain allow the identification of two discrete stages of platform development with different styles of deposition the first phase represented by the bashkirian valdeteja formation is characterized by progradation of more than 10 km with steep clinoforms of up to 35 and slope heights up to 650 m during the second phase corresponding to the moscovian picos de europa formation the platform aggraded mainly vertically nearly 850 m both phases of platform growth were terminated by major relative sea level lowstands in conjunction with local filling of the adjacent basins by shales and mudstones that onlap the platform flanks calibration with outcrops suggests a subdivision into the following lithofacies directly related to the depositional profile 1 platform interior parallel well to thick bedded skeletal pack to grainstones 2 margin algal and sponge dominated bioherms with little internal structure 3 slope clinothems of medium to thick bedded margin derived breccia beds 4 toe of slope alternating grain and packstones with spiculites and 5 basin marly shales shales sandstones and calcareous mudstones relative sea level changes caused by regional tectonic movements are suggested to be responsible for the generation of the two platform phases sea level highstands triggered the nucleation and growth of the platforms whereas major sea level lowstands in combination with terrigenous infill of the basins terminated the platform growth in addition it is proposed that the termination of late carboniferous carbonate platforms is caused by the combined effect of a sea level fall subaerial exposure and erosion and finally a rapid transgression that drowned and polluted the platform with shales and mudstones local variations in the infilling of the basins controlled the variations in the style of progradation the subsidence rates for the vertically aggrading phase picos de europa formation were approximately twice that for the progradational phase valdeteja formation and may explain the aggradational versus progradational character

the importance of microbial binding in neogene quaternary steep slopes abstract the geometry and inclination of carbonate platform slopes are typically described as the result of the sediment texture components and grain size occurring in the slope three carbonate slopes from the holocene of the tongue of the ocean bahamas and three slopes from an upper miocene carbonate platform in se spain are investigated to identify the factors controlling dip angles although platforms differ in size and elevation with regard to the surrounding basin both locations present slopes with linear profiles and steep angles over 35 the slope facies in both locations are very similar with the matrix and some bioclasts presenting microfabrics that evidence microbial activity during deposition these include 1 clotted micrite patches locally connecting bioclasts or infilling primary pores 2 porostromate structures in the micrite 3 dense micritic masses 4 binding structures 5 micritic crusts and 6 peloidal textures the holocene and miocene depositional geometries and facies distribution are the response to various sedimentary processes including rockfalls gravity flows and in situ carbonate production extensive microbial binding is identified as the controlling factor for early stabilization of the slope which in combination with subsequent rapid cementation produces and maintains the steep slope angles consequently microbial induced stabilization of modern and neogene slopes is as significant as in paleozoic and triassic examples

geometric and depositional responses of carbonate build ups to miocene sea level and regional tectonics offshore northwest australia abstract the geometric and depositional responses of isolated carbonate build ups to miocene sea level change and regional tectonics are investigated using 3d seismic and borehole data from the browse basin north west australia combined with outcrop information from the cariatiz reef southeast spain the interpreted seismic volume documents five 5 miocene sequence boundaries and five 5 main seismic facies seismic attribute analyses proved to be a highly effective tool for interpreting carbonate facies but when compared with outcrop information from southeast spain attribute data are limited to features larger than 16 4 m vertically and 18 75 m horizontally estimations of reservoir potential are thus significantly underestimated when only based on the interpretation of seismic data as a corollary of the structural analysis in this work growth patterns suggest messinian structural partitioning across the browse basin with deformation associated with plate collision focused on preferentially oriented faults i e only influencing carbonate build up evolution at a local scale

petrography and geochemistry of the permian triassic boundary interval yangou section south china implications for early griesbachian seawater δ 13 c dic gradient with depth abstract the carbon isotopic composition 13 c carb recorded in shelf carbonates has been widely used as a proxy for the isotopic composition 13 c dic of surface ocean water to establish paleocean chemistry and circulation patterns however 13 c carb values do not necessarily preserve the 13 c dic due to post depositional diagenetic alteration in order to examine the early griesbachian surface to deep 13 c dic gradient with depth the diagenetic features of the permian triassic boundary interval beds 18 to 35 from yangou section located in the yangtze carbonate platform interior south china are delineated to compare with those of the slope gssp meishan section the petrographic and geochemical observations show that the early griesbachian carbonates in the yangou section underwent pervasive dolomitization in its early diagenetic history three types of early replacement dolomites and one type of dolomite cement are present the dolomite crystals display internal zonation with high ca calcian dolomite hcd core being encased successively by calcite and an outermost fe rich hcd cortex the initial dolomitization took place in anoxic seawater and underwent subsequent diagenetic system involved with meteoric water the two most negative 13 c values in claystones of beds 21 3 and 35 are probably related to meteoric diagenesis above and or below the meteorically influenced beds the dolomite and calcite have uniformly positive 13 c values the primary carbon isotopic compositions are probably preserved in the early griesbachian carbonate from the platform yangou section which could probably be related to the poor formation of the outermost fe rich hcd cortex compared to the slope carbonate from the meishan section the platform carbonate from the yangou section has lower primary 13 c carb values it is estimated that the 13 c dic gradient with depth between yangou and meishan is less than the previously suggested the results highlight the need for evaluation of local 13 c carb as record of 13 c dic in paleoseawater and carry important implications for understanding the permian triassic carbonate successions throughout the world

lithofacies and depositional processes on a high steep margined carboniferous bashkirian moscovian carbonate platform slope sierra del cuera nw spain the depositional slope of the sierra del cuera a carboniferous bashkirian moscovian high steep margined carbonate platform provides excellent cross sections of lithofacies zonations and associated stratal geometries the steep 30 40 and nearly planar upper slope is dominated by massive sheet like layers of microbial cement rich boundstone which alternate with intercalations of red stained bryozoan cementstone with crinoids and brachiopods the slightly gentler 20 26 and concave upward lower slope is characterized by clast supported resedimented deposits the upper slope extended from platform break to ca 300 m water depth whereas lower slope sediments were deposited in water depths up to 600 700 m at which level the slope beds flatten to a few degrees toe of slope and interfinger with spiculitic and argillaceous basinal sediments between 250 and 450 m water depth boundstones and breccias alternated in a transitional zone the lower slope sediments include clast supported breccias with radiaxial fibrous cement in interparticle space mud to clast supported breccias with red stained carbonate mud matrix and packstone to grainstone and rudstone beds most of the clasts comprise boundstone reworked from an upper slope setting and smaller grains are platform and slope derived a pervasive submarine cementation occurs along the upper two thirds of the flank and this stabilized the slope slope deposition is interpreted as follows during active boundstone accretion microbial boundstone layers slid off and formed breccia tongues extending from the lower upper slope down to the toe of slope rock falls and avalanches were generated whenever the shear strength of the substrate of loose or partly lithified sediment was exceeded upper slope boundstone accretion and shedding independent of the depth of light penetration controlled most of the depositional processes on the slope cement dominated intervals are considered to be related to early highstand and or flooding phases relative sea level fluctuations and or associated changes in the water conditions are believed to be responsible for intervals of low boundstone production or cement precipitation whether the in situ boundstone and breccia are preferentially related to lowstand or highstand periods is as yet unclear

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

rotation velocity of a thrust a paleomagnetic study in the external sierras southern pyrenees abstract an accurate calibration of chronologic and geologic data biostratigraphic and magnetostratigraphic with gpts has been performed for the middle and upper eocene syntectonic deposits in the surrounding areas of the pico del aguila anticline south pyrenean external sierras this calibration shows a variable sedimentation rate that changes from 4 8 cm ka at the bottom to 34 cm ka at the top with a maximum of 58 6 cm ka in the upper part of the studied stratigraphic section and gives a fine and continuous chronologic frame to understand the rotational kinematics of the infrajacent thrust system at the same time a detailed paleomagnetic study has been carried out 14 sites and a total of 157 thermally demagnetised samples to know the amount of rotation in the area taking advantage the tape recording effect of the syntectonic materials these samples display a chrm between 250 and 400 c both polarities that agree very well with the sequence of magnetostratigraphic zones and consistency with the magnetic reference due to the decreasing value of the magnetic declination from 46 to 3 of the primary components checked by fold and reversal test the calibration has been useful to assign an absolute age to every rotation value from 40 32 to 37 05 ma a time versus rotation curve does not show significant differences of rotation between the flanks of the pico del aguila anticline less than 8 thus the clockwise rotations detected in the study area result from the kinematics of the imbricate basal thrust system which is also responsible for the development of detachment folds e g pico del aguila anticline in a time against rotation graph the simplest fit for the overall rotation values is given by a linear segment rotation velocity of 10 ma however the best fit is given by a segment of a parabolic curve this pattern implies that there were changes of the rotation velocities between 21 ma and 5 3 ma that in this segment of the external sierras were caused by an acceleration of the rotational movement between 9 ma2 and 5 5 ma2 the thrust sheet shows maximum values of at least 40 of clockwise rotation

the changing climate framework and depositional dynamics of triassic carbonate platforms from the dolomites abstract the triassic of the dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms the reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological palaeobotanical pedological and geochemical proxies the triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts during the triassic the dolomites were placed at an intertropical northern latitude of about 16 18 and were generally dominated by dry climate and elevated temperature at least five pulses toward moister climate are however documented dated to early olenekian middle anisian late ladinian middle carnian and late norian times within this variable climatic scenario the carbonate systems record a global evolutionary trend from late permian early triassic regional shelves rich in loose micrites and bio calcarenites to anisian ladinian synsedimentary cemented steep sided 35 40 high relief platforms and back to carnian low angle ramps moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms probably because of the reduced space competition by syndepositional cementation structures the permo triassic boundary extinction dramatically impacted on the calcified organism communities but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary the early triassic and earliest anisian were commonly associated with hyperhaline sometimes evaporitic conditions intervals of moister climate and efficient river discharge are however documented by earliest induan and early olenekian sediments the latter terrigenous deposits matched a crisis in the carbonate production after a return to arid conditions during the anisian a fluctuation toward moister climate developed associated to a massive continental vegetation cover the anisian tectonic activation of the region fragmented the previous carbonate shelf triggering the development of three generations of fast prograding but globally backstepping isolated platforms recording an increasing role of the synsedimentary cementation a dry climate dominated the late anisian and early ladinian interval at the time a fast subsidence pulse was associated with platform drowning and basinal anoxia only a few aggrading pinnacles were able to survive providing the nuclei for larger prograding platforms during a dry climate interval massive syndepositional cementation generated a major source of carbonate carbonate production stayed active through the ladinian magmatic phase but the onset of volcanism was associated with a large modification in the platform carbonate facies which became dominated by automicrites moist climate phases are well documented again during the late ladinian followed by a return to dry conditions the late ladinian early carnian platforms prograded toward the eastern dolomites depocentre eventually infilling almost the whole of the accommodation space the middle portion of the carnian recorded renewed sharply moist phases associated with the demise of the rimmed platforms and with the return to loose sediment ramps at least four separated humid fluctuations can be identified in this carnian interval alone climate then returned to persistent aridity until the late norian moist phase

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

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

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

model for the sigmoidal curvature of submarine slopes sigmoidal slope profiles are common on the margins of continents and intracratonic basins we propose that these profiles consist of two genetically different segments the lower concave part reflects the exponential decrease of the sedimentation rate with increasing distance from the source at the shelf edge the upper convex part represents the gradational boundary between the shelf domain where sediment is moved by waves and wave induced currents and the slope domain where sediment is moved by gravity the boundary is narrow and the shelf edge is sharp if sedimentary base level remains stationary during progradation the boundary becomes gradational and the shelf edge becomes rounded if storms and sea level cycles induce significant fluctuations of base level this model is supported by observations on holocene sedimentary systems as well as numerical simulations with the program strata based on the diffusion equation for sediment dispersal

geomorphological evidence of carbonate build up demise on equatorial margins a case study from offshore northwest australia abstract the demise of miocene carbonate build ups in the browse basin northwest australia has been explained as relating to geological and oceanographic processes these include accelerated tectonic subsidence driven by subduction ocean cooling following the mid miocene climate optimum nutrient excess poisoning by sediment drifts and local erosion driven by current winnowing occurring discretely or simultaneously here we critically assess the evidence for these different mechanisms using a combination of high resolution 3 d seismic data regional 2 d seismic profiles and numerical stratigraphic forward modelling seismic interpretation and numerical modelling found that the proposed uniform subsidence rate of 125 m ma between 16 5 ma and 5 33 ma for the northern browse basin belde et al 2017 when combined with the published estimate of eustatic sea level in miller et al 2005 was insufficient to drown the miocene carbonate sequence and generate the geomorphological changes barrier reef to isolated carbonate build ups observed on seismic data instead a subsidence profile comprising pulses of rapid and slow subsidence is required significantly our results suggest that subsidence rates exceeded 400 m ma in the northern browse basin and that parts of the basin record the accumulation of sediment drifts these sediment drifts are interpreted to have buried some carbonate build ups while suspended sediment reduced light transmissivity inhibiting carbonate production thus we postulate that current activity and excess nutrient supply are key but often overlooked oceanographic processes that lead to the demise of carbonate build ups

micro topographic change on calcarenites grand cayman island west indies changes in micro topography as a result of varying erosion rates have been monitored on a calcarenite ridge on grand cayman island west indies using a traversing model of the micro erosion meter erosion takes place through the solution of a calcitic cement and solutional disintegration results in a rapid change of micro relief where a protective crust is present surface lowering is slower and also more uniform thus the original relative relief is maintained

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

depositional bias and environmental change important factors in sequence stratigraphy abstract differences among depositional systems here called depositional bias strongly influence sequence patterns siliciclastics and shallow water carbonates for instance shed most of their sediment during opposite phases of a sea level cycle lowstand shedding and highstand shedding respectively furthermore the two systems generate their own system specific relief on the sea floor disperse their sediment load along different avenues and differ in the way they are deactivated reefs and carbonate platforms can be drowned whereas siliciclastic deposition can be shut off and renewed at any depth as a consequence of these differences pronounced unconformities drowning unconformities develop where carbonate platforms are terminated and buried by siliciclastics the siliciclastic to carbonate transition tends to be more gradual drowned platforms and drowning unconformities appeared world wide in great abundance in the miocene cretaceous valanginian turonian jurassic toarcian and devonian frasnian famennian examples of drowning unconformities interpreted as sequence boundaries include those of the early cretaceous platforms off new jersey and off morocco the mid cretaceous unconformity in the gulf of mexico and miocene unconformities on top of reefs in the far east the eustatic cycles postulated from sequence stratigraphy are a very unlikely cause for the mass drownings of reefs and platforms either the rates of rise are an order of magnitude lower than the growth potential of platforms or cycle amplitudes are too small or the cycles are too short and subsidence too slow to remove platforms permanently from the photic zone the critical element in the mass drowning seems to be environmental stress that reduces the growth potential of carbonate systems thus drowning unconformities demonstrate the importance of environmental change as a control on sequence development other examples of dominantly environment controlled sequences include slope deposits shaped by shifting currents e g florida and blake plateau and basin fills that were controlled by changes in sediment input related to tectonic alteration of the drainage in the hinterland e g gulf of mexico environmental change must be considered as a third independent factor that competes with eustatic and tectonically driven regional changes of sea level for control of sequences the definition of sequences and sequence boundaries should be broad enough to include the possibility of non sea level controls

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

compositional changes in sigmoidal carbonate clinoforms late tithonian eastern sardinia italy insights from quantitative microfacies analyses quantitative analysis of sediment composition was performed on a kilometre wide section of upper tithonian low relief up to 70 m gently inclined 3 to 15 sigmoidal carbonate clinoforms eastern sardinia to identify changes in sediment composition along the slope and across the studied succession these changes may reflect modifications of the carbonate factory and of processes responsible for sediment transport point count analysis of carbonate microfacies q mode r mode cluster analysis and spearman s rank provided a composition based classification of microfacies and highlighted relationships among sediment components the studied clinoforms are mainly composed of non skeletal grains 70 such as peloids and lithoclasts together with micrite and cements and only a limited contribution from coated grains 2 among skeletal grains 28 the greatest contribution derives from a coral stromatoporoid encruster reef that provided 15 of the components crinoids brachiopods and other along slope thriving biota provided nearly 5 of the allochems whilst fragments of molluscs gastropods bivalves and diceratids from the backreef sourced another 2 the contribution of platform interior biota is negligible 1 the association of composition based facies varies along the slope the upper slope beds consist of coral stromatoporoid grainstone to rudstone the middle slope deposits are dominated by encruster lithoclast grainstone and packstone at the lower slope peloidal lithoclastic packstone as well as brachiopod crinoidal wackestone prevail also the association of skeletal grains changes along the slope the encruster frame builder association typifies the upper slope whilst encrusters characterize the middle slope sediments in the lower slope encrusters are equally represented as the brachiopod crinoid association along slope compositional changes evidence a scarce downslope transport of frame builders and a progressive enrichment in along slope thriving biota quantitative analysis of microfacies allowed the sigmoidal clinoforms to be grouped into six sets each set gathers sigmoids with a similar sediment composition coated grains are dominant in the first set whilst they are lacking in the overlying sets reflecting a change in the carbonate factory other major compositional changes among the sets concern the relative amounts of peloids micrite frame builders corals and stromatoporoids and encrusters the contribution of peloids varies inversely to that of cements and micrite as evidenced in the third and fifth sets which respectively record the highest occurrence of peloids or cement and micrite variations in the amount of frame builders and encrusters are instead non linear high percentages of both frame builders and encrusters as recorded in the second and fifth sets are related to low amounts of peloids and lithoclasts that probably reflect episodes of reduced background sedimentation this study demonstrates that quantitative analysis of carbonate microfacies represents a powerful tool that can improve the reconstruction of the stacking pattern in carbonate slope successions both in outcrop and in subsurface settings

genesis of limestone megabreccias and their significance in carbonate sequence stratigraphic models a review a re appraisal of the factors controlling the deposition of carbonate megabreccias and their sequence stratigraphic significance is presented based on an examination of the mechanisms for instigating carbonate seafloor slope instability and a review of the depositional settings of these distinctive rock deposits limestone megabreccias have classically been interpreted as formed by the catastrophic collapse of high angle metastable oversteepened carbonate platform margins however a review of megabreccia occurrence shows that these deposits formed on a broad range of carbonate slope angles and that metastable oversteepened slopes are not necessary for their genesis a re evaluation constructed from first principles of mechanisms promoting submarine gravitational instability indicates that pore water overpressure of confined aquifer horizons beneath the seafloor rather than slope oversteepening is the critical control on megabreccia deposition catastrophic release of overpressure may initiate gravitational instability of previously kinematically stable slopes the relative importance of endogenic processes intrinsically linked to the depositional system and exogenic processes operating independently in generating megabreccias is assessed two particularly important mechanisms in generating megabreccias are endogenic processes causing overpressure at discrete hydrologically confined horizons beneath the seafloor during relative sea level falls and increases in stress as pore fluid drains from the sediment when the platform top becomes subaerially exposed during relative lowstands of sea level the increased likelihood of megabreccia genesis during relative sea level falls is supported by an empirical trend identified from a review of the stratigraphic distribution of documented megabreccias exogenic causes of gravitational instability with inherently random periodicity especially seismicity may account for the small number of documented megabreccias that do not conform to this underlying trend the proposed endogenic pattern favouring megabreccia deposition during relative sea level falls is important in a sequence stratigraphic context megabreccia deposits may build volumetrically significant toe of slope wedges and aprons during relative lowstands of sea level partially compensating for the decrease loss in the supply of fresh granular sediment as the platform top carbonate factory contracts lowstand wedges and aprons in carbonate systems therefore generally differ in composition from equivalent highstand deposits in being composed not of calciturbidite deposits but of megabreccias cannibalized from the upper slope

high resolution magnetostratigraphic and lithostratigraphic correlations in middle triassic pelagic carbonates from the dolomites northern italy new magnetostratigraphic and lithostratigraphic data are reported from the pedraces and belvedere limestone sections from the dolomites region of northern italy these sections are comprised of the buchenstein beds of late anisian to ladinian middle triassic age the results from pedraces and belvedere are compared with data from the biostratigraphically and isotopically constrained frotschbach and seceda sections from the literature a satisfactory magnetostratigraphic correlation is obtained on laterally traceable limestone and volcaniclastic intervals these marker beds are then used to extend lithostratigraphic correlations to additional key sections from a palaeogeographically coherent area of around 500 km2 the aim of this study is to unravel the spatial and temporal evolution of the buchenstein basin and the surrounding carbonate platforms platforms in the northwestern dolomites show an early stage of aggradation followed by progradation whereas in the central dolomites the cernera platform after fast initial aggradation drowned and became a pelagic seamount in the intervening buchenstein basin the diverential subsidence between the northwestern and central dolomites is manifested by the lateral increase of thickness of lower pietra verde volcaniclastic sediments accumulation of volcaniclastic material reworked from adjacent carbonate platform slopes characterised the more subsiding and unstable central dolomites in the pelagic carbonate intervals the persistence over tens of kilometres of bedding patterns suggests that carbonate material presumably washed out from the surrounding still active carbonate platforms was volumetrically small and homogeneously distributed throughout the uniformly subsiding buchenstein basin a milankovitch precessional origin for the platform interior cycles at latemar as suggested elsewhere implies a net accumulation rate of 2 m ma or less for the correlative interval of pelagic buchenstein beds this value divers significantly from the average value of around 10 m ma as calculated using high resolution isotopic age data for the buchenstein beds 2000 elsevier science b v all rights reserved

bioclastic sediment lobes on a supply dominated upper cretaceous carbonate platform margin montagna della maiella italy a thick bioclastic sediment wedge was deposited on the slope of the maiella carbonate platform margin in the late campanian to late maastrichtian the wedge consists of lobate depositional units laterally and vertically convex structures the complex internal geometries of the lobes combine characteristics of unidirectional sandwaves and the alternating point sources of deltas excellent outcrop permits a detailed documentation and discussion of the depositional processes the sediment wedge constitutes a supersequence which prograded along the platform margin as a result of high sediment supply and forced regression within the supersequence a hierarchy of higher order stratigraphic units sequence sets and sequences are developed the individual bioclastic sediment lobes are interpreted as systems tracts and parasequences of the sequences within the sequence sets

distributed fracturing affecting isolated carbonate platforms the latemar platform natural laboratory dolomites north italy abstract isolated carbonate platforms are highly heterogeneous bodies and are typically composed of laterally juxtaposed first order domains with different sedimentological composition and organization i e a well stratified platform interior a massive margin and a slope with steeply dipping and poorly organized layers once subjected to overburden and tectonics forces directions and magnitudes of principal stresses inside such heterogeneous bodies are expected to deviate significantly from the regional trends potentially resulting in non obvious fracture patterns in addition characteristics such as fracture height and spacing distances are likely to change moving from one domain to the other as well as through time the middle triassic latemar platform dolomites n italy is affected by ubiquitous fractures typically joints orientation and height of more than 1500 fractures from 33 outcrops have been measured and their spatial characteristics were assessed with dedicated software fractures are organized in two directional sets nnw sse and ene wsw the orientation of each set is constant throughout the platform showing that the trajectories of causative stresses were not influenced by the platform architecture fracture spacings and heights of each set change moving from one domain to the other in the well bedded platform interior fractures are generally there are also significant differences in the characteristics of fractures of the two sets in all platform domains fractures of nnw sse set are less tall and more narrowly spaced than those of the ene wsw set in the platform interior fractures of the first set have a higher tendency to be confined to fracture units than those of the second set these differences are associated with diagenesis driven changes in bulk mechanical properties of the platform during its subsidence to maximum burial depth

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