sea level change and superstorms geologic evidence from the last interglacial mis 5e in the bahamas and bermuda offers ominous prospects for a warming earth abstract geological observations from last interglacial lig mis 5e eemian carbonate landscapes in the bahamas and bermuda reveal a turbulent climate transition at the close of the peak interglacial the interval is associated with rapid multi meter shifts in sea level as major ice sheets melted and or collapsed sedimentary evidence from the eastern bahamas includes wave transported megaboulders lowland chevron storm ridges and hillside runup deposits this trilogy collectively provides direct geological evidence of frequent intense storms generating sustained long period waves from the northeast atlantic ocean penecontemporaneous with wave deposits is the subtidal production and flux of a massive volume of ooid sediments associated with amplified winds and storminess during the latter half of mis 5e that resulted in exponential island growth steeper temperature and pressure gradients were evident in the north atlantic ocean while the southern ocean appears to have had a major role in affecting atmospheric co2 as warming of the southern ocean drives ventilation of the deep ocean co2 in turn acts as a tight control knob on global climate the dramatic oceanographic and island building events of late mis 5e are unique among other interglacial periods of the past half million years the lig record reveals that strong climate forcing is not required to yield major impacts on the ocean and ice caps antarctic ice cores document that lig atmospheric co2 was 275 ppm while global temperature was in terms of lyellian uniformitarian principles the trilogy of coeval deposits of mis 5e described herein do not translate to our modern climate parameters and further cannot be explained by coincidental megatsunami in our industrial world rapidly increasing atmospheric co2 rates 2 ppm yr have surpassed 408 ppm levels not achieved since the pliocene 3 ma ago while global temperature increased 1 c since the 1870s with greatly increased co2 forcing at unmatched rates except perhaps during global extinction events dramatic change is certain in the interest of our future world we must seek to understand the complex set of linked natural events and field observations that are revealed in the geology of past warmer climates

sedimentary architecture of a prograding oolitic siliciclastic wedge response to changes in wave base oscillation kimmeridgian iberian basin abstract a detailed facies and sequential architectural analysis has been carried out along the wedge shaped shallow marine cross bedded oolitic siliciclastic ricla member kimmeridgian northern iberian basin the obtained results are based on fieldwork along the 4 1 km continuous outcrops with the use of high resolution photomosaics and drone made videos which have led to a precise and extensive facies reconstruction three main facies that are laterally related a to b to c in down dip direction have been differentiated which correspond to the topset foreset and bottomset parts of a sloping depositional surface sedimentation was controlled by sweeping drift and downwelling storm induced currents causing avalanching processes with the deep action of oscillatory currents the sedimentary architecture consists in 5 successive units composed by several sub units arranged according to different stacking patterns which reflect the sedimentary response to wave base oscillations superimposed to the regressive part of a third order transgressive regressive cycle the sedimentological features indicate that this unit which has been previously interpreted as a dune complex fit with an infralittoral prograding wedge model as it is observed in geographically close and stratigraphically similar units the ricla member is therefore regarded as an example of a well exposed grain supported unit with broad potential application to other prograding grain dominated lithosomes that do not conform to the traditional sand shoal model

production and off bank transport of carbonate sediment black rock southwest little bahama bank abstract surficial sediments between the intertidal zone and 600 m were studied with the objectives of characterizing their source dispersal pathways and sites of accumulation bioerosion is a major source of sediment in the intertidal and shallow subtidal environments in situ enclosure experiments showed that the urchin echinometra lucunter produced 667 mg sediment cm 2 yr 1 and an associated diverse rock infauna produced an additional 183 mg cm 2 yr 1 microborers caused erosion of 25 mg cm 2 yr 1 and feeding activity by the chiton acanthopleura granulata caused additional erosion of 10 mg cm 2 yr 1 sequential weighing of tethered limestone plates showed an abrasion rate of 5 5 mg cm 2 yr 1 due chiefly to impacts on the plate edges surficial sediments between the intertidal zone and the top of the bank margin wall at 30 m are gravel sand mixtures containing 0 2 mud molluscs and halimeda plates are the main constituents of gravel fractions sand fractions are composed of bioerosion produced carbonate rock fragments 1 70 skeletal material from halimeda 3 63 forams 1 33 molluscs 6 15 and coral 0 6 gravel and sand are transported as bedload in chutes across the narrow rocky shelf chutes end at 45 m and sediment traps indicate an average flux of 5 4 kg chute 1 yr 1 equivalent to 945 kg km 1 yr 1 moving to deep water a dense population of halimeda living on the wall between 30 70 m contributes gravel and sand to sediment on wall ledges at the base of the steep wall 65 a ramp slopes into the northwest providence channel between 120 300 m the ramp 30 slope is a zone by passed by coarse and fine sediment at 300 m the slope decreases to an average of 13 and an apron shaped body of mud is accumulating the apron extends parallel to the bank margin and wall and reaches depths 600 m traps showed that sediment flux to the ramp is 0 12 kg m 2 yr 1 which is 2 of the particle flux overtopping the bank margin surficial sediment of the ramp is mostly mud 70 which is primarily of shallow water origin some form of bottom current transporting gravel and sand mostly halimeda and abraded coral heads has cut gullies into the ramp this bottom flow is probably episodic and turbulent enough to suspend and supply halimeda sand to sediment traps on the ramp at 463 m

controls and predictability of carbonate facies architecture in a lower jurassic three dimensional barrier shoal complex djebel bou dahar high atlas morocco spatial information on lithofacies from outcrops is paramount for understanding the internal dynamics external controls and degree of predictability of the facies architecture of shallow water carbonate platform tops to quantify the spatial distribution and vertical stacking of lithofacies within an outer platform shoal barrier complex integrated facies analysis and digital field technologies have been applied to a high relief carbonate platform exposed in the djebel bou dahar lower jurassic high atlas morocco the outer platform is characterized by subtidal cross bedded coarse grainstone to rudstone grading into supratidal pisoidal packstone rudstone with tepees that together formed a 350 to 420 m wide shoal barrier belt parallel to the margin this belt acted as a topographic high separating a restricted lagoon from the subtidal open marine region low energy tidal flats developed on the protected flank of the barrier facing the lagoon lithofacies patterns were captured quantitatively from outcrop and integrated into a digital outcrop model the outcrop model enabled rapid visualization of field data and efficient extraction of quantitative data such as widths of facies belts in addition the spatial heterogeneity was captured in multiple time slices i e during different phases of cyclic base level fluctuations in general the lateral continuity of lithofacies is highest when relative water depth increased during flooding of the platform top establishing low energy subtidal conditions across the whole platform and when the accommodation space was filled with tidal flat facies heterogeneity increased during deposition of the relief building bar facies that promoted spatial diversification of depositional environments during the initial phases of accommodation space creation cycles commonly are composed of a thin transgressive tidal flat unit followed by coated grain rudstone bar facies lateral to the bar facies pisoidal grainstone beach deposits accumulated these bar and beach deposits were overlain by subtidal lagoonal facies or would grow through the maximum flooding and highstand there the bars either graded into supratidal pisoidal facies with tepees when accommodation space was filled or were capped by subaerial exposure due to a sea level fall modified embedded markov analysis was used to test the presence of common ordering in vertical lithofacies stacking in a stationary interval constant depositional mode analysis of individual sections did not reveal any ordering which may be related to the limited thickness of these sections composite sections however rejected the null hypothesis of randomness the addition of stratigraphically significant information to the markov analysis such as exposure surfaces and lateral dimensions of facies bodies strengthens the verdict of unambiguous preferential ordering through careful quantitative reconstruction of stratal geometry and facies relationships in fully integrated digital outcrop models accurate depositional models could be established that enhanced the predictability of carbonate sediment accumulation 2009 the authors journal compilation 2009 international association of sedimentologists

holocene oolitic marine sand complexes of the bahamas abstract although the general factors influencing the occurrence and distribution of oolitic systems are well known details of their landscape scale patterns and formative processes are less systematically explored by reviewing published studies and presenting new data and insights this review systematically examines a suite of holocene systems from the bahamas in which patterns and processes are characterized and explicitly linked with the goal of providing more realistic and accurate models for variability heterogeneity and predictability in these systems and their ancient analogs sedimentological geomorphic and hydrodynamical data document that each ooid shoal is unique in detail yet shoals share common elements within bar forms systematic trends in grain size type and sorting are related to spatial and temporal variability in wave tide and current energy these trends are driven by connections among sedimentology hydrodynamics and geomorphic forms as they shape and concomitantly are shaped by each other similarly due to feedbacks a limited number of bar forms occur among shoals including tidal sand ridges parabolic bars transverse shoulder bars tidal deltas and sand flats the dominant bar form broadly corresponds with flow velocities within and among shoals among bahamian tidal shoals the mean grain size of ooids maximum bar heights and the width of the oolitic facies belts are all positively correlated collectively these results illustrate the mode and magnitude of variability in shapes orientations and sedimentology of holocene oolitic bodies interpreted to be driven by self organization and autogenic processes these perspectives provide testable qualitative and quantitative insights that can be used to understand and predict the character of ancient analogs

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

using 230th in marine sediments to reconstruct the late quaternary history of sea level we propose a method to determine past sea levels based on the record of 230th accumulating in seafloor sediments the decay of uranium in seawater produces this nuclide which then adsorbs rapidly onto particles settling to the seafloor since the concentration of uranium is similar at all depths in the water column the flux of 230th to the seafloor at any location is proportional to water column height consequently changes in sea level must cause changes in these fluxes at shallow depths 1000 m fluctuations of sea level cause changes in the expected 230th flux that are large enough to produce measurable changes in the 230th content of the sediment we have developed two approaches to determine past sea levels from the content of 230th in sediments 1 in a single core the ratio of the past and present fluxes of 230th to a site on the seafloor is a measure of the ratio of the past and present depths of the site below sea level and 2 in two or more cores from a region where the vertical input of sediment is similar at all depths in the water column the concentrations of 230th in synchronous sediment samples are linearly related to depth and indicate past sea level as the depth where the concentrations extrapolate to zero the latter approach requires fewer assumptions and allows sea level to be estimated at discrete points in time the methodology assumptions advantages and disadvantages of the first approach is illustrated using preliminary data from a core recovered from the margin of little bahama bank

sea water circulation on an oolite dominated carbonate system in an epeiric sea middle jurassic switzerland the middle jurassic burgundy carbonate platform occupied a central part of the central european epeiric sea during the middle jurassic the facies architecture of the oolitic calcarenite bodies was affected by tidal currents on the platform and relative sea level changes the 13c values of inorganic carbonates sampled in biostratigraphic defined intervals do not match very well between closely spaced sections and hence are of restricted use for stratigraphic purposes it appears that the platform interior might have been decoupled from the global carbon pool although deposited in a rapidly accumulating setting the recorded isotope signatures might be affected by some local stratigraphic gaps nonetheless the carbon isotope data imply lateral changes of the platform waters these appear to be related to the position on the platform and to the sediment dispersal pattern as evidenced by clay minerals adjacent to the eastern margin of the platform detrital chlorite and illite occur in considerable proportions both ascribed to a boreal source to the east and the north east in contrast smectite rich mixed layer clay mineral content increases significantly towards the platform interior pointing to a delivery from the north west all these data are suggestive of an overall clockwise current pattern in the central european epeiric sea during the middle jurassic

sedimentation and diagenesis along open and island protected windward carbonate platform margins of the cretaceous el abra formation mexico abstract the windward margin of the mid cretaceous valles san luis potosi carbonate platform in northeastern mexico included open and island protected segments depositional environments and diagenesis vary markedly with margin type sand shoals near the windward open margin are composed of oncoid bioclastic and cross laminated carbonates increasingly restricted and finer lagoonal and tidal flat environments occurred bankwards recording gradually decreasing wave and current energy lithofacies include peloid miliolid cryptalgal laminite lime mudstone and molluscan carbonates islands along the windward margin are composed of rudistid skeletal debris from adjacent reefs lagoonal to tidal flat sediments were deposited bankwards similar lithofacies occur as in these environments along the open margin but they are muddier and contain less diverse fauna the different energy regimes along the margin influenced the distribution and packaging of banktop sediments the bankward transition to low energy restricted environments was gradual across the open margin in contrast muddy sediments with restricted fauna accumulated in close proximity to the island protected margin non cyclic vertical lithofacies successions characterized the open platform margin whereas asymmetric shoaling upward sequences characterized the island protected margin early diagenesis along the open margin was minor burial diagenesis was of major importance thin rinds of marine cement are widespread but meteoric diagenesis was minor burial promoted extensive compaction mg rich connate brines expressed from guaxcama gypsum resulted in dolomitization and lithification thereby precluding further compaction pore fluids resulting from dehydration of guaxcama gypsum to anhydrite yielded pore filling and replacement anhydrite in the el abra formation burial and laramide deformation maastrichtian paleocene resulted in stylolitization and extensive fracturing uplift produced widespread meteoric diagenesis for the first time resulting in dissolution of anhydrite calcitization of dolomite and equant calcite cementation early diagenesis along the windward protected margin was extensive prolonged subaerial exposure resulted in calcrete cementation and secondary porosity subsequent marine cementation and internal sedimentation reduced porosity equant calcite cement precipitated during local upper cretaceous exposure burial diagenesis was limited to traces of dolomite anhydrite and late stage equant calcite cement suggesting similar pore fluids as in the open margin depositional environment determined the type and degree of early diagenesis which strongly influenced subsequent diagenetic events subtidal sediments of the open margin underwent minimal early diagenesis and entered the burial realm much as they were deposited they were subjected to intensive compaction and alteration by brines in contrast sediments exposed to meteoric diagenesis and marine cementation on near backreef islands and tidal flats entered the mesogenetic realm as stabilized lithified rocks much as they are at present

sedimentary dynamics and high frequency sequence stratigraphy of the southwestern slope of great bahama bank abstract new geophysical data from the leeward slope of great bahama bank show how contour currents shape the slope and induce re sedimentation processes along slope segments with high current control drift migration and current winnowing at the toe of slope form a deep moat here the slope progradation is inhibited by large channel incisions and the accumulation of large mass transport complexes triggered by current winnowing in areas where the slope is bathed by weaker currents the accumulation of mass transport complexes and channel incision is rather controlled by the position of the sea level large slope failures were triggered during the mid pleistocene transition and mid brunhes event both periods characterized by changes in the cyclicity or the amplitude of sea level fluctuations within the seismic stratigraphic framework of third order sequences four sequences of higher order were identified in the succession of the upper pleistocene these higher order sequences also show clear differences in function of the slope exposure to contour currents two stochastic models emphasize the role of the contour currents and slope morphology in the facies distribution in the upper pleistocene sequences in areas of high current influence the interplay of erosional and depositional processes form a complex facies pattern with downslope and along strike facies alterations in zones with lower current influence major facies alternations occur predominately in downslope direction and a layer cake pattern characterizes the along strike direction therefore this study highlights that contour currents are an underestimated driver for the sediment distribution and architecture of carbonate slopes

mapping bathymetry and depositional facies on great bahama bank satellite imagery and an extensive set of water depth measurements have been used to map and critically evaluate the magnitude and patterns of bathymetry across great bahama bank descriptions of previously collected sediment samples were combined with satellite imagery to map and refine the interpreted distribution of surficial carbonate sediments depositional facies data reveal that 60 of great bahama bank lies in 5 m or less of water the deep portion occurs mainly in a generally east west trending area in the southern portion of the platform the re evaluation of the facies reveals that great bahama bank is essentially a very grainy platform with muddier accumulations primarily in the lee of andros island this area of great bahama bank also experiences currents related to an excursion of the florida current onto the platform top possibly enhancing sediment mud production through the generation of whitings sediment equivalents to mudstones wackestones and mud rich packstones cover 8 5 and 14 respectively of the platform top whereas sediment equivalents to mud poor packstones grainstones and rudstones account for 20 45 and 3 of the surface area boundstones reefs were not specifically mapped in this study due to the resolution of the mapping there is a poor relationship between the occurrence of the depositional texture and water depth in that the grainier sediment types are abundant across the full range of water depths the most abrupt lateral facies changes portrayed on the facies maps are observed leeward of islands areas which also hold the highest diversity in facies type the majority of the islands on the platform align with the north west south east strike of the platform margin and these islands in turn exert control on the shape and orientation of facies belts that develop in proximity to them for this reason regions of the platform that contain principal islands host facies belts that align with the principal axis of the platform whereas for regions lacking islands the facies belts adopt an east west trend consistent with prevailing winds and currents there is a clear trend that the wide southern portion of the platform hosts the most continuous expanses of grain rich sediments

genetic sequence stratigraphy of cool water slope carbonates pleistocene eucla shelf southern australia the south australian eucla shelf belongs to the world s largest cool water carbonate sedimentary system during the pleistocene it exported large amounts of sediment to the shelf edge and upper slope resulting in an expanded sedimentary wedge wedge internal clinoforming seismic reflectors suggest a stacking of the deposits into genetic sequences high resolution stable oxygen and carbon isotope point counting grain size and carbonate mineralogical xrd analyses were carried out to characterize these genetic sequences along a dip parallel transect of three odp leg 182 drill holes located between the shelf edge and upper slope oxygen and carbon isotope fluctuations show that the genetic sequences formed as a response to sea level fluctuations within the genetic sequences facies differentiation and sediment volume partitioning occur along the transect lowstand deposits are fine grained and contain more sponge spicules and micrite highstand deposits are coarse grained with tunicate spicules brown bioclasts as well as bryozoan and corallinacean debris boundaries separating highstand and lowstand deposits are triggered by sea level fall and are expressed as abrupt grain size changes or as turning points in grain size trends analyzed components vary in abundance along the transect genetic sequences show dip parallel variations in thickness combined with changing relative proportions of lowstand versus highstand deposits

holocene millennial to centennial carbonate cyclicity recorded in slope sediments of the great bahama bank and its climatic implications a 38 m long sediment core md992201 retrieved from a water depth of 290 m from the leeward margin of the great bahama bank gbb 25 53 49 n 79 16 34 w has been investigated for changes in aragonite content the core covers the mid to late holocene the past 7230 yr sediment lightness l values was used as a proxy for aragonite content based on a high linear correlation r 0 93 between the x ray diffraction derived aragonite content and l values the resulting time resolution of the l values derived aragonite content ranges from 1 yr at the base of the core to 4 yr at the top detailed time series analysis using monte carlo singular spectrum analysis and spectral analysis lomb scargle fourier transform identifies the presence of seven signals with varying amplitudes and wavelengths that could be traced throughout the past 5500 yr during the first 1600 yr of sedimentation the aragonite record is dominated by the initial flooding of the flat topped gbb superimposed on a multimillennial signal related to holocene sea level changes a millennial scale fluctuation and five quasi periodic oscillations were detected 1 3 2 kyr 500 600 yr 380 yr 260 yr 200 yr and 100 yr period comparisons with other proxies e g tree ring 14c 10be and 18o in ice cores provides information on the origin and dynamics of the individual signals the analysis shows that the 200 yr and 100 yr signals can be attributed to solar forcing the 260 yr 380 yr and the 500 600 yr quasi periodic signals are found to be of climatic origin whereas the millennial scale fluctuations remain enigmatic although solar forcing mechanisms seem likely the data show that variability of solar output as well as past oceanographic and atmospheric changes have modulated the mid to late holocene climate which in turn controlled sediment input variations found in the holocene wedge leeward of the gbb although these periplatform sediments have a rather uniform appearance they still contain a large variety of subtle sedimentary variations

sequence stratigraphy and tectonosedimentary history of the upper jurassic of the eastern paris basin lower and middle oxfordian northeastern france in the present study the difficulty which lies in the identification of sea level fall discontinuities in deep depositional environments led the authors to use the transgressive surfaces i e the most noticeable surfaces in the present case to determine depositional cycles four 3rd order lower and middle oxfordian cycles were identified s1 s2 s3 and s4 in the eastern paris basin these four cycles can be organised into two lower frequency cycles so i and so ii which comprise the s1 s2 and the s3 s4 cycles respectively during the time intervals of the s1 s2 and s3 cycles sedimentation occurred along a southward dipping carbonate siliciclastic ramp prograding from the northern ardennes area the s4 cycle shows the development of a reefal distally steepened ramp which subsequently evolved into a flat topped platform as a result of the compensation infill of the available accommodation space by the carbonate production during a climatic warming in this case reef growth isopach and facies maps suggest synsedimentary activities of hercynian faults coevals with the floodings of the so i and so ii cycles one of these events generated a diachronism of the maximum flooding plicatilis zone during the so ii cycle between the northwestern and southeastern parts of the studied area the depositional patterns found in the eastern paris basin and the swiss jura show great similarities for the early middle oxfordian both regions were probably connected and recorded the same tectonosedimentary evolution in contrast a tectonic control certainly generated differences between the sequence stratigraphic framework of the eastern paris basin and the eustatic chart

structural configuration of the early cretaceous cordilleran foreland basin system and sevier thrust belt utah and colorado abstract stratigraphic and provenance data from lower cretaceous rocks in utah and colorado and structural evidence from the sevier belt in west central utah allow recognition of the ties between early thrust belt evolution and foreland basin system development regional isopach patterns of lower cretaceous strata define foreland basin system depozones lower cretaceous strata in west central utah that thicken westward from 100 m to 1 2 km were deposited within the flexurally subsiding foredeep depozone correlative units in eastern utah and western colorado 100 m thick were deposited in the back bulge depozone these thickness trends indicate the lower cretaceous foreland basin system consisted of a foredeep 100 180 km wide and forebulge 260 460 km wide a computer generated flexural model of the foreland basin system produces a reasonable match of the observed basin geometry using a 400 km wide l

form function and feedbacks in a tidally dominated ooid shoal bahamas although the general aspects of oolitic depositional systems are well documented seascape scale 10 3 10 6 m 2 patterns of oolitic shoals and the details of processes acting on them are not well understood or quantified to begin to fill this basic gap in understanding this paper describes the morphology and hydrodynamics of lily bank a modern tidally dominated bahamian ooid shoal in this study integrating remote sensing imagery with quantitative geo located bathymetrical hydrological and granulometric data in a geographic information system documents geomorphic and sedimentological patterns and facilitates interpreting these patterns in the context of the processes operating in this system the results of these analyses reveal that parabolic bars up to several kilometres in wavelength and several metres in height form a common morphologic motif although there is considerable variation on that general theme the seascape scale configuration of bars and superimposed sedimentary structures is closely linked to spatial patterns of tidal movements and includes the presence of mutually evasive flood and ebb channels sedimentologically bars are neither homogenous nor random bodies instead granulometric parameters such as sorting and percentage mud vary systematically as shaped by hydro geomorphic controls the best sorted coarsest ooids are on bar crests whereas the finest grains are found in the lower energy deeper interior and flanking regions in short results clearly document hydrodynamic bathymetrical influences on these ooid shoals and their granulometry linkages akin to siliciclastic analogues sedimentological hydrodynamic and geomorphic observations are consistent with a conceptual model for the formation of parabolic bars in which initial irregularities in nonparabolic bars are enhanced through their effect of focusing flow constricted flow leads to higher flow velocities tidal flow velocity asymmetries differential net sediment transport and growth of bathymetrical highs this bathymetrical divergence creates separate paths for flood and ebb tides facilitating emergence of better developed parabolic forms the resultant parabolic geometries and component bedforms appear to be either in dynamic equilibrium with both ebb and flood tide flows or evolving toward that state in exploring patterns and processes within carbonate shoals this study illustrates some of the first documented insights on quantitative details of morphology and dynamics and in the links between geomorphic framework and grain size and sorting in an oolitic carbonate system assuming a

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

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

morphometric analysis of plunge pools and sediment wave fields along western great bahama bank abstract a systematic assessment of morphometric parameters of over 200 plunge pools along the steep escarpment base of western great bahama bank and 2000km2 of sediment wave fields of upslope migrating cyclic steps documents the importance of cascading density currents for sedimentation on the slope the abrupt downslope termination of the holocene mud wedge with the cyclic steps shows that strike parallel bottom currents interacting with the off bank currents are responsible for slope sediment distribution the plunge pools and sediment waves were generated by density cascading and both are related to a hydraulic jump caused by two gradient changes along the slope profile the bedforms highlight both the erosional and depositional nature of this current regime which is controlled by slope gradient and the directional confinement by either grooves on the steep escarpment or gullies on the middle to lower slope the 20 m deep plunge pools are ellipsoidal with an average width of 211 m and length of 283 m but variations between 80 360 m and 100 650 m for width and length occur they are caused by an average gradient break of 16 on the cemented upper slope gradient breaks of as low as 2 are reported to be sufficient to scour a plunge pool like the ones in the study area but higher gradient breaks between 10 and 20 are quite common for consistent plunge pool development a second gradient break further down slope changes flow conditions for the generation of cyclic steps with asymmetric waveforms of 4 m high average in large wave fields in the entire the study area orientation is mainly orthogonal to the main slope direction but wave lengths and sinuosity vary depending on the morphologic location of the wave field the comparison with sediment wave fields with similar geometries or in similar environments shows that flow reconstruction based on the wave height and wave length alone along with a characterization of sediment grain size however yields non unique results and is site specific

holocene atlantic climate variations deduced from carbonate periplatform sediments leeward margin great bahama bank a marine sediment core from the leeward margin of great bahama bank gbb was subjected to a multiproxy study the aragonite dominated core md992201 comprises the past 7230 years in a decadal time resolution and shows sedimentation rates of up to 13 8 m kyr aragonite mass accumulation rates age differences between planktonic foraminifera and aragonite sediments and temperature distribution are used to deduce changes in aragonite production rates and paleocurrent strengths aragonite precipitation rates on gbb are controlled by exchange of carbonate ions and co2 loss due to temperature salinity conditions and biological activity and these are dependent on the current strength paleocurrent strengths on gbb show high current velocities during the periods 6000 5100 years bp 3500 2700 years bp and 1600 700 years bp lower current speeds existed during the time intervals 5100 3500 years bp 2700 1600 years bp and 700 100 years bp bahamian surface currents are directly linked to the north atlantic atmospheric circulation and thus periods with high low current speeds are proposed to be phases of strong weak atmospheric circulation

decoding the mechanism of formation in marine ooids a review abstract ooid shoals sedimentary structures consisting of carbonate grains are often used as proxies to explore changes in seawater chemistry over earth history despite their importance as contributors to the global carbonate budget and as paleo environmental indicators for water depth ph temperature and water energy the mechanism of formation of these concentric sub spherical concretions of tangentially or radially arranged aragonite or calcite crystals is still the subject of intense debate unlike oncoids whose microbial origins are well acknowledged ooids are traditionally viewed as abiotic grains mainly produced in suspension by agitated warm waters that are supersaturated with respect to caco3 yet there is considerable evidence including geochemical bio signatures and detection of viable microbes capable of mineralization and biofilm production and degradation to suggest otherwise the emergence of new and sophisticated technologies reveals that the level of microbial diversity of these sedimentary grains exceeds that of some microbialite systems these findings have refined our understanding of ooid genesis and ooid accretion processes and argue toward microbial mediation both as a direct result of metabolic activities inducing changes in the environment conducive to precipitation and by a passive mechanism in which mucilaginous extracellular polymeric substances eps act as a template for mineral nucleation furthermore new developments in the field indicate that carbonate mineralization in marine ooids occurs through sequential precipitations that involve an amorphous calcium carbonate phase acc which some argue are of biotic origins herein we discuss the most relevant theories of ooid formation including some of the early pioneering studies that laid the groundwork for new theories attempting to decode the origins of these controversial grains

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

sequential and climatic framework of the growth and demise of a carbonate platform implications for the peritidal cycles late jurassic north eastern france the middle oxfordian of the eastern paris basin constitutes a remarkable example of the growth and demise of a carbonate platform fischer plots sedimentary and diagenetic features allow the identification of four depositional cycles s5 to s8 in the transversarium zone they are inserted in a lower frequency cycle of increased decreased accommodation space soiii the long term period of accommodation creation occurred during the older s5 and s6 cycles the maximum accommodation zone being located in the lower part of the s6 cycle this high accommodation period was tectonically controlled and was coeval with local distensive activity of a hercynian fault a major minimum accommodation zone exists during the s8 cycle at that time the platform was isolated and presented both a windward and a leeward margin the growth of the platform was favoured by a warm and arid climate oligotrophic conditions and reduced siliciclastic input during a highstand in relative sea level these palaeoenvironmental features favoured the proliferation of phototrophic organisms producing carbonate material the death of the platform was generated by a reduction in the carbonate production surface during a lowstand in relative sea level and by the appearance of mesotrophic conditions induced by the increase in siliciclastic inputs at the beginning of a period with a cooler and more humid climate in the eastern paris basin during the middle oxfordian the parasequences are ordered and present greenhouse characteristics in contrast at the beginning of the s8 cycle the randomness in the thickness of contiguous parasequences increased decreased carbonate production during the lowstand caused by a transition from photozoan to heterozoan benthic communities certainly favoured this randomness and the appearance of catch down parasequences

upper permian zechstein supergroup carbonate evaporite platform palaeomorphology in the uk southern north sea abstract seismic interpretation geological mapping and depth conversion of the zechstein supergroup z2 cycle using high quality well calibrated three dimensional 3 d seismic has revealed the complex palaeomorphology of a deeply buried ancient carbonate shelf margin on the southwestern margin of the southern permian basin the new mapping shows that the margin comprises a series of corrugated embayments and promontories which extend up to 5 km 3 mi into the basin and locally have a palaeobathymetric relief of 200 m 650 ft well calibration across the margin demonstrates a strongly bipartite lateral thickness distribution between a high velocity anhydrite dominated shelf and a lower velocity halite dominated basin strong lateral and vertical velocity variations in the upper permian zechstein supergroup are known to have major impacts upon seismic imaging and depth conversion in the spb the resulting uncertainty remains one of the major challenges when interpreting and assessing the prospectivity of the underlying upper permian rotliegend group leman sandstone formation reservoirs in the uk southern north sea an understanding of the zechstein shelf edge s 3 d physiography and its velocity variation has implications for the delineation of traps containing the prospective reservoirs that lie below recognition of the complexity and effects of this shelf margin contributed to the recent juliet discovery whose position outside of the presently defined rotliegend group play fairway suggests that prospectivity is more extensive along the basin margin than previously thought as such the work provides a means by which to identify and delineate new structures and extend the life of this mature yet prolific gas province

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

carbonate sand bodies along contrasting shallow bank margins facing open seaways in northern bahamas high resolution seismic profiling bottom sampling and aerial and space imagery show that widely contrasting carbonate sand bodies are present along the shallow windward leeward and tide dominated margins of little and great bahama banks which face open seaways the northwest providence channel and the northern straits of florida this high diversity in sand bodies and their associated bank margins is due to variations in the level duration and magnitude of the physical energy flux across the edges of the platforms in the bahamas the dominant winds waves and currents are from the east hence easterly facing margins are windward westerly facing margins are leeward where strong tidal currents are present because of adjacent basin shape the windward and leeward effects are diminished thus bank margin orientation relative to the climatic energy patterns appears to assert the major controls upon sedimentation antecedent topography in the form of islands or subtidal rock ridges creates energy barriers which can control the direction and volume of sediment flux on or off the banks along windward margins energy barriers such as large islands not only block the bankward transport of sands but appear to augment offbank transport by setting up seaward flows in contrast along leeward margins energy barriers prevent the vigorous offbank sand transport that normally occurs when these margins are open and water flow is unrestricted in addition sand body geometry and grain type are controlled by bank margin orientation along windward open margins skeletal sands accumulate in the lee of low relief mostly relict reefs these margins are generally sediment barren having only a sporadic thin veneer of sand along leeward open margins a broad 10 10 km thick 12 m bankward thinning blanket of sand rich in nonskeletal components peloids composite grains lies on top of rock ridges and reefs large asymmetric sand waves superimposed on this sand body indicate net offbank sand transport along the tide dominated margin large broad oolitic sand lobes have migrated onto adjacent lagoonal muddy sands and indicate net bankward transport we suggest the following classification of modern shallow carbonate bank margins 1 windward open 2 windward protected 3 leeward open 4 leeward protected 5 tide dominated this classification seems to fit many ancient analogs and may be useful in paleoenvironmental reconstructions

carbonate petrography as an indicator of climate and sea level changes new data from bahamian quaternary units coeval stratigraphic units of similar petrology occur throughout the northern bahamas islands the petrographic composition of these limestones provides clues about regional sea level and climate changes during the late quaternary at least eight fossil shoreline units which are linked to transgressive episodes between the middle pleistocene and the late holocene are recognized in the bahamas the petrographic composition of these units is either dominated by ooids and peloids or by bioclasts sedimentological observations demonstrate that oolitic peloidal units were formed when sea level was higher than today whereas skeletal units were deposited at or below modern ordnance datum skeletal units may reflect times of partial or modest platform flooding when the bulk of sediments brought to islands originates from bank margin reefs in contrast oolitic peloidal units correspond to major flooding events and active water circulation on the bank top cement fabrics further show that the early diagenesis of oolitic units took place during warm and humid climatic conditions whereas skeletal rock bodies underwent subaerial diagenesis during drier climatic conditions characterized by marked seasonal changes this example from the bahamas suggests that compositional analysis of limestone from fossil carbonate platforms could be used for resolving ancient climate and sea level changes

offbank transport of carbonate sands along open leeward bank margins northern bahamas abstract vigorous offbank transport of carbonate sands occurs along the west facing leeward open margins of little and great bahama bank large offbank oriented sand waves thick sand bodies covering reefs and shallow water sands mostly non skeletal obtained from adjacent deep flanks all demonstrate the existence of this shallow to deep pathway of sediment transport a variety of data suggests that transport occurs during storms and not during normal tidal current fluctuations an abundance of composite grains as well as vertical sequences of submarine cemented horizons seen via seismic profiling within the marginal sand bodies indicate cyclic periods of relative quiescence followed by moments of intense sediment movement current meter data obtained during six weeks of low wind activity show that critical threshold velocities for sand transport are only barely exceeded during portions of the tidal cycle these flows coupled with higher frequency bottom currents generated by surface gravity waves winnow the sands but do not provide significant net offbank transport offbank sand transport provides material to the shallow and deep bank margins enabling them to expand during sea level highstands each sea level fluctuation is likely to produce within the shallow margins a vertical sequence of basal reefs covered by a thick non skeletal calcarenite capped by a subaerially exposed diagenetically altered surface shallow water sands carried off the marginal escarpment help to construct deep flanks and large sediment drifts

integration of static and dynamic data and high resolution sequence stratigraphy to define reservoir architecture and flow units within a super giant gas condensate and oil field kazakhstan abstract the upper serpukhovian mississippian interval of the karachaganak reservoir comprises stratified platform interior carbonates which are characterised by relatively high porosity and matrix permeability maximum 23 8 and 2198 md respectively and comprise high frequency fourth order glacio eustatic cycles based on static geological and dynamic well test and production data this cyclicity exerts a strong control on gas migration pathways and reservoir quality is predictable within a third and fourth order sequence stratigraphic framework that defines two discrete flow units the contribution to flow made by fourth order cycles within flow units is dependent on their position within third order transgressive or highstand systems tracts an upper flow unit comprises thick up to 40 m fourth order cycles within a third order transgressive systems tract these fourth order cycles contain large scale clinoformal bedforms can be correlated for up to 6 km and are the main pathways of injected gas through the upper serpukhovian reservoir a lower flow unit comprises fourth order cycles within a third order highstand systems tract that are thinner and less laterally continuous than those in the upper flow unit and contribute far less to horizontal gas flow pressure data indicate that vertical permeability baffles are developed at the third order sequence boundary that separates the two flow units linked to diagenetic alteration during prolonged subaerial exposure and also within the low porosity mud rich transgressive bases of thick fourth order cycles of the upper flow unit that formed during periods of increased accommodation space across the platform top during third order transgression the scale at which this data set is observed is critical to understanding the dynamic behaviour of the reservoir relatively small differences in the composition of microfacies of cycles within both flow units do not explain the variations in dynamic data this variation is better explained within the broader context of the sequence stratigraphic framework as defined from analysis of cycle stacking patterns thicker high frequency cycles deposited in increased accommodation space on the platform top during third order transgressive intervals are key to developing thick intervals of net pay

cause of tectonic reactivation and subtle uplifts in the rocky mountain region and its effect on the stratigraphic record stratigraphic studies show that widespread albeit subtle topographic uplifts have occurred throughout the u s rocky mountain region during middle and late mesozoic time individual paleotopographic highs generally have wavelengths on the order of tens of kilometres and amplitudes on the scale of metres in places these features correspond to sites of previous or later deformation and so suggest the possibility of tectonic reactivation along pre existing zones of structural weakness in the crust observations of modern features and modeling studies indicate that uplifts of small magnitude are both a common and expected result of changes in intraplate stress levels finite element modeling suggests that broad wavelength low amplitude topography can develop in a heterogeneous elastic plate under high stress magnitudes along preexisting faults and under low stress magnitudes where zones of high and low strength are juxtaposed although these features are small they have sufficient topography to bring about large changes in paleocurrent patterns for low gradient streams and significantly affect isopach patterns although subtle uplifts from this cause are difficult to predict they are likely a common occurrence and may be the most dramatic features in an area that is otherwise tectonically quiescent thus subtle uplift may be a background noise rather than a harbinger of regional orogenesis

sea level controls on the post glacial development of the great barrier reef queensland abstract the central great barrier reef is situated on a 125 km wide continental shelf with a shallow shelf break at ca 70 m in consequence the earlier post glacial reef tract was confined to a narrow fringing belt along the present upper slope and outer shelf the reef province only started to assume its modern dimensions after ca 10 ky b p when sea level stabilised at depths around 28 m reef growth since 18 ky b p has been controlled by the episodic nature of the post glacial transgression being related to shorelines s8 to s1 developed at estimated eustatic depths and ages of 114 m 18 ky b p 88 m 17 ky b p 75 m 15 ky b p 56 m 12 ky b p 45 m 11 ky b p 39 m 10 ky b p 28 m 9 5 ky b p 23 m 9 ky b p 9 m 7 5 ky b p and 0 m 6 5 ky b p rates of sea level rise as high as 12 m ky 1 occurred between stillstands outpacing coral growth response and resulting in many mid outer shelf reefs being drowned in situ

windward leeward effects on triassic carbonate bank margin facies of the dolomites northern italy abstract triassic carbonate bank margins of the dolomites show compared to modern carbonate margins relatively low energy narrow facies belts distinctive facies depend on the geographical margin orientation and suggest windward leeward effects low energy deposits such as algal stabilized sand flats and tepee pisolite facies occur along margins facing deeper water in the north and east higher energy deposits such as algal reefs and cross bedded sand bars characterize margins facing southwest and west locally clinoforms show asymmetric distribution being thick at the eastern bank margin and thin or absent at the western bank margin while the overall low energy conditions could have been caused by the small size and in the late anisian the shallowness of the basins facies differentiations suggest a net energy flux of surface waters caused by storms and possibly consistent winds from the southwest to west in the triassic of the dolomites

genesis and growth of a carbonate holocene wedge on the northern little bahama bank abstract the study focuses on the sedimentary dynamics at the transition between the modern bahamas carbonate platform and related adjacent slopes and deeper environments a holocene carbonate sedimentary wedge is developed at the edge of the carbonate platform extending along the northern little bahamas bank lbb bahamas the transition area between the platform and the wedge shows superposed terraces the holocene wedge thickness varies from 0 to 35 m its surface is dominated by homogeneous fine grained soft sediments it lies on a pleistocene substratum and fills depressions corresponding to lowstand erosional surfaces on the uppermost slope this wedge represents the main depocenter of fine grained bank derived sediments since the last bank flooding twelve gravity cores were sampled from this wedge and allow the identification of both the processes that can supply this wedge and the wedge evolution based on content analyses and 19 radiocarbon ages at present particle export from the lbb margins mostly occurs during episodes of winter cold fronts but also occurs during hurricanes evidence of hurricane impact in the sedimentary record is suggested by the recovery of two laminated sequences showing both decreasing sedimentation rates and varying velocities during platform export the local morphology of the platform edge allows the better sorting and export of sediments according to the presence of tidal outlets and sediment sorting on the wedge however because no ooids from tidal deltas located on the platform edge were found in cores tidal currents are probably not energetic enough to both mobilize and export sediment even if tide induced currents may help the export of fine grained carbonate particles remobilized by either cold fronts or hurricanes on the platform and upper slope the formation of the wedge started at 13 6 3 5 kyr cal bp following the meltwater pulse 1 a it was supplied by shallow environment derived particles produced on four narrow terraces between 60 and 20 mbsl after meltwater pulses since the lgm last glacial maximum terrace formation seems to correspond to periods of sea level stillstands and wedge formation whilst escarpments correspond to periods of high rates of rising sea level due to meltwater pulses the main period of wedge growth started around 6 5 0 9 kyr cal bp when sea level finally reached the platform margins the maximum flooding period around 4 kyr cal bp is characterized by the highest contents of aragonite needles exported from the platform

cay sal bank bahamas a partially drowned carbonate platform abstract recent high resolution seismic reflection profiling sediment sampling scuba observations and landsat imagery show that cay sal bank csb has very limited reef development no active sand shoals few islands a thin to non existent sedimentary cover and a relatively deep margin 20 30 m and shelf lagoon system 10 20 m windward and leeward margins can be discerned but their general development is poor when compared to the shallower more active margins of little bahama bank lbb and great bahama bank gbb windward margins facing north and east along csb are generally deep rocky sediment barren terraces supporting limited low relief relict reefs leeward margins have small sand bodies maximum thickness 10 m covering reef structures at the bank edge indicating that offbank transport of sands has occurred however these marginal sand bodies are limited in areal extent suggesting that this transport system was not ubiquitous along the south and west facing margins seismic and grab sample data from the deep 200 500 m slopes seaward of the leeward margins show a thin discontinuous unit of periplatform sand containing halimeda molluscs and non skeletal components derived from shallow water the limited basinward extent no deeper than 300 m of this unit recognized by its reflection free seismic facies also indicates that sand production and transport off the bank were never prolific this is in stark contrast to new seismic data from the leeward margins of gbb which clearly show thick 20 m sand bodies covering high reefs 12 15 m along the outer margin and multiple reflection free units extending to great depths 600 m all along the adjacent slope the apparent immature development of normal bank top processes and facies and the absence of key modern depositional environments on csb may be related to the rate at which this platform was submerged due to its comparatively low elevation the initial holocene flooding occurred at approximately 8 10 ka when sea level rise was rapid 6 m ka 1 by comparison the higher lbb gbb were flooded later at a much slower rate 1 5 m ka 1 the relatively rapid flooding of csb provided little time for the shallow depositional environments to start up the continued rapid rate of sea level rise after drowning and offbank transport of sediment and the export of chilled waters formed during winter months prevented the resulting facies from catching up consequently csb appears to be partially drowned particularly when compared to the other healthier rimmed bahamian platforms drowned carbonate banks are very common in the ancient record and potentially provide excellent stratigraphic traps for hydrocarbons csb provides a modern example of a bank that may be in the very early stages of termination final drowning of carbonate platforms may occur as a result of frequent higher order sea level fluctuations superimposed on initial stage of a lower order sea level cycle

carbonate mounds in the santaren channel bahamas a current dominated periplatform depositional regime abstract new hydroacoustic data high resolution multichannel seismic reflection data ctd casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the santaren channel off great bahama bank and cay sal bank based on these data sets three types of carbonate mounds have been identified in water depths between 285 and 685 m their distribution is strongly related to the present current regime bank driven sediments are caught up by the currents and redeposited mainly in the channel center resulting in the accumulation of giant confined drifts flanked by moats the moats at the banks toe of slope are formed by a southward and northward flowing water mass respectively mainly antarctic intermediate water and subtropical underwater the observed carbonate mounds are concentrated in these moats mound type 1 has an elongated shape parallel to the prevailing bottom current direction a gently inclined flank facing the water flow and a steep flank in its current shadow its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour type 1 occurs at both bank margins but mainly off great bahama bank consisting of cold water coral rubble floating in a sediment matrix and is thus interpreted as cold water coral mound by contrast type 2 mounds are restricted to the cay sal margin and have a predominately conical outline bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos except corals the mounds are situated in pockmark like depressions that are underlain by fluid escape structures like pipes and chimneys these fluid pathways are generated by a network of fractures mound type 2 is probably formed by abiotic carbonate precipitation however a chemoherm nature cannot be ruled out mound type 3 has a conical to polygonal shape and occurs off cay sal bank and great bahama bank it is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction a sediment bulge formed at its front this type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity controlled mass movements at the steep bank slopes principally two habitats can be distinguished the great bahama bank periplatform deep water province dominated by mound type 1 and the cay sal bank slope to basin province occupied by mound type 2 that is associated with pockmark like structures mound type 3 occurs in both habitats physical water mass properties for the existence of cold water corals are limited to a depth range of ca 430 to 685 m with seawater densities of 26 93 to 27 29 kg m and temperatures below 13 c their dominance off great bahama bank might be addressed to a more effective food supply induced by local downwelling

mineralogy and grain size variations along two carbonate margin to basin transects pedro bank northern nicaragua rise abstract the analysis of nine periplatform cores in the surrounding of the pedro bank carbonate platform showed the presence of characteristic depositional environments during the last 300 ky this subdivision is based on mineralogical and grain size variations in space and time along the leeward downcurrent transect the fine sediment fraction 40 km aragonite is still the most abundant mineral but the percentage decreases while the pelagic carbonate mineral content lmc increases within the subordinate coarse fraction classes 63 m the very fine sand fraction dominates at proximal sites 20 km show a more bimodal distribution pattern in the coarse grain sizes with maximum percentages within the very fine and medium sand fraction indicating a mixed neritic pelagic signal during glacial lowstands in sea level a twofold division in the spatial distribution of the periplatform sediments is evident a proximal environment 28 km showing a strong dominance of the fine fraction 90 the increased coarse fraction percentage during glacials at proximal sites results from various interacting processes 1 lower input of fine neritic sediments 2 increased current winnowing and 3 redepositional processes at the upper slope during lowered sea level and the export of this material to proximal basinal sites at upcurrent sites the mineralogy displays a similar spatial evolution as seen along the downcurrent margin but with overall reduced percentages this is the result of the lower export potential of the platform against the main direction of the caribbean current the most important factor for neritic sediment dispersal in the study area the coarse fraction content is slightly higher during interglacials compared to the downcurrent margin during glacials a similar reduction in the percentage of the coarse fraction is evident in a spatial context this also substantiates the reduced sediment export and redeposition potential at the upcurrent margin

a facies distribution model controlled by a tectonically inherited sea bottom topography in the carbonate rimmed shelf of the upper tithonian valanginian southern tethyan continental margin nw sicily italy the upper tithonian valanginian shallow water carbonates outcropping in the palermo mts nw sicily consist of several facies associations reflecting different depositional environments of a carbonate rimmed shelf pertaining to the southern tethyan continental margin the reconstructed depositional model based on the sedimentological features cyclic facies arrangement and biota distribution shows that a wide protected lagoon dominated by algae molluscs and scattered patch reefs was bordered landward by a tidal flat where stromatolitic algal mats were cyclically subaerial exposed and seaward by a marine sand belt and reef complex oolitic packstone grainstone lithofacies cyclically subjected to subaerial exposure suggests the occurrence of a barrier island located nearly to the lagoonal carbonate shoreline allowing the development of narrow embayments with restricted circulation in the outer platform the oolitic lithofacies of the marine sand belt pass landward into the protected lagoon where washover oolite sands occur and seaward into a high energy zone back reef apron gradually merging in the reef complex in the latter coral framestone occupied the inner sector reef flat while the facies association dominated by boundstone with ellipsactinia sp developed in the outer sectors reef wall adjacent to the fore reef and upper slope environments stratigraphic evidence associated with the recognized facies associations helped to reconstruct the geo tectonic setting of the carbonate platform where the distribution of the depositional facies along the shelf and their extension were influenced by the tectonically inherited sea bottom topography in a regime of extensional tectonics localized and thin succession of high energy prograding oolite sand belt depositional facies occupied structural highs footwall uplift while the largely diffused and thick low energy aggrading peritidal to lagoonal depositional facies developed in subsiding hanging wall the reef complex and the fore reef depositional facies exhibiting lateral migration and prograding geometries with clinoforms and downlap stratal terminations developed on a subsident stepped margin adjacent to a faulted shelf break this morphostructural setting can be comprised in a model where the tilted and faulted blocks inner platform and stepped margin outer platform paleo topography inherited from the rifting tectonics was the most important factor controlling the geometry and depositional architecture of a carbonate platform growing on the southern tethyan passive margin

controls on modern carbonate preservation in the southern florida straits abstract the water masses in the florida straits and bahamas region are important sources for the northern atlantic surface ocean circulation in this study we analyse carbonate preservation in surface sediments located above the chemical lysocline in the florida straits and bahamas region and discuss possible reasons for supralysoclinal dissolution calcite dissolution proxies such as the variation of the foraminiferal assemblage fragmentation index benthic foraminifera index and resistance index displayed a good preservation in both areas the pteropod species limacina inflata showed very good preservation in sediments of inter platform channels from the great bahama bank providence channel exuma sound above the aragonite lysocline supralysoclinal aragonite dissolution however was observed at two water depth levels 800 1000 m and below 1500 m in the florida straits our observations suggest that the supralysoclinal dissolution in the florida straits is due to the degradation of organic material the presence of antarctic intermediate water aaiw may be a contributing factor for the significant aragonite dissolution in 800 1000 m the comparison of modern preservation patterns of the surface sediments with hydrographical measurements shows that the l inflata dissolution index ldx might be an adequate proxy to reconstruct paleo water mass conditions in an area which is highly saturated with respect to calcium carbonate

thrust timing growth of structural culminations and synorogenic sedimentation in the type sevier orogenic belt western united states most of the regional shortening in the type area of the sevier orogenic belt in central utah was accommodated by displacement on the canyon range neocomian aptian pavant aptian albian paxton cenomanian campanian and gunnison late campanian paleocene thrust systems inception of each thrust system generated synorogenic sediment associated with frontal thrust tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland the sevier culmination a large antiformal duplex cored by crystalline basement rocks developed during paxton and gunnison thrusting west of and structurally beneath the canyon range and pavant thrusts growth of the sevier culmination was coeval with reactivation of the canyon range and pavant thrust systems and produced a second culmination in proterozoic lower cambrian rocks in the canyon range these structural highs provided much of the sediment to the adjacent foreland basin from late cenomanian to late paleocene time and may have helped to maintain critical taper in the thrust belt