the nature of shallow water carbonate lithofacies thickness distributions carbonate lithofacies thickness distributions are of fundamental importance to understanding shallow water carbonate deposystems because they record evidence of the lateral distribution and migration of lithofacies elements as well as evidence for the various other intrinsic and extrinsic controls on stratal geometries and accumulation rates previous analyses of lithofacies thickness data led to the suggestion that exponential distributions are ubiquitous in the ancient record this has been interpreted to indicate deposition by stochastic poisson process lithofacies mosaics to further investigate these ideas statistical analysis of 56 outcrop and core examples was performed the kolmogorov smirnov test was used to identify the degree to which measured lithofacies thicknesses are well represented by a theoretical exponential distribution results from this analysis show that 16 of the 56 examples can be confidently shown to be exponential while 28 are very probably not exponential this indicates that stochastic poisson processes are a plausible explanation for many carbonate successions but they do not explain all of those tested here suggesting that other non poisson processes either stochastic or deterministic in nature or both must also be important thus lithofacies planform geometries and the processes controlling vertical stacking in ancient carbonate platform top deposystems were likely more diverse than has been suggested requiring significant further quantitative analysis and numerical forward modeling to properly understand

sedimentary facies of the eastern pacific s northernmost reef like setting cabo pulmo mexico abstract cabo pulmo mexico is often cited as the eastern pacific s northernmost coral reef we investigated sedimentary dynamics to verify whether the system functions sedimentologically as a reef which would mean that it retained internal sediment in a framework and exported peri reefal sediment creating clearly identifiable facies dominated by reefal fauna we mapped distribution of sediments using grab samples the acoustic ground discrimination systems qtc view and echo plus at 50 khz signal frequency and an ikonos satellite image morphologically the bay of cabo pulmo can be divided into intrusive dikes and rocky hardgrounds in less than 10 m depth and a sandy interior with rocky outcrops sloping to over 40 m reefal fauna without lasting framework building but with production of typically reef associated carbonate sediments as well as a patch reef facies were found on the dikes and hardgrounds sediments in the bay were a mixture of carbonates and siliciclastics and were influenced by a seasonal river near the bay s center that imported siliciclastic material to the north and south sediments had a higher carbonate content although overall the bay was characterized by 50 siliciclastics the shallower subtidal sands were dominated by mollusk fragments whereas in depths 30 m planktonic foraminiferal sand was found acoustically and optically remote sensed maps were used to differentiate between the rocky and sandy areas and to identify the presumed off shelf transport pathway of reef derived carbonates overall the sedimentary system is characterized by carbonate production but the coarser reef derived carbonates coral and reef dwelling mollusks are transported off shelf along a steep depth gradient and little typical peri reef sediment remains this transport is likely aided by storms since no sediment retaining frameworks are formed the dikes cannot retain internal sediment and the reefal fauna was not dominant in sediments throughout the bay we conclude that cabo pulmo sedimentologically functions only in a limited way like a coral reef

facies mosaics across the persian gulf and around antigua stochastic and deterministic products of shallow water sediment accumulation abstract among broadly different types of sedimentary successions those that accumulate in nearshore settings are perhaps unique in that a very wide range of rock types recurs with high frequency over relatively short stratigraphic intervals this vertical lithofacies heterogeneity suggests that deposition of any sedimentary unit at any site was short lived that many different sediment types existed within a complex mosaic over the depositional surface and that this facies montage repeatedly moved across surfaces of accumulation in response to eustatic sedimentologic and or tectonic forcing data on numbers and thicknesses of lithofacies units from several dozen such sequences define the size frequency distribution expected if horizons of lithologic change occur randomly within sedimentary successions walther s law suggests that the amount of vertical lithologic heterogeneity manifest in a sedimentary sequence should reflect the degree of lateral heterogeneity in sediment composition that existed across depositional surfaces if so this repetition should also be manifest in sizes and areal distributions of sediment patches constituting the depositional mosaic in order to examine size frequency relations of sediment bodies across surfaces of sediment accumulation we tabulated numbers and areal extents of lithotopes across two rather dissimilar settings across the persian gulf and around the caribbean island of antigua although compositions and lateral extents of different sediment types exhibit broad lateral variation across interior to margin transects in either area lithotope abundances and areal extents define frequency distributions that are in excellent agreement with those anticipated for a facies mosaic of elements whose mean linear widths constitute an exponential frequency distribution these are the size frequency distributions one would expect if mosaic element boundaries occur randomly across regions of sediment accumulation and suggest that distributions of lithotope areas from holocene surfaces are directly analogous to lithofacies thickness frequencies from ancient successions in addition to the fact that both of the size frequency distributions attest to the importance of stochastic processes during sediment deposition they also afford numerical descriptors of abundances and areal extents of holocene lithosomes that can then be used as controlling parameters in computational models of sediment accumulation importantly results derived from such simulations are based not on inference of water depth varying in response to change in subsidence sea level and rate of sediment accumulation but on statistical attributes intrinsic to modern and ancient marginal marine successions

mapping facies distributions on modern carbonate platforms through integration of multispectral landsat data statistics based unsupervised classifications and surface sediment data benthic sediment facies maps were constructed for a series of large isolated carbonate platforms including 1 great and little bahamas banks 2 caicos platform british west indies 3 chinchorro bank mexico 4 glovers reef belize 5 south cocos keeling atoll indian ocean and 6 bu tini shoal persian gulf facies maps were generated by applying statistics based image analysis algorithms called unsupervised classifications to landsat 7 multispectral satellite data classification results were subsequently validated with sediment data to create geologic facies maps landsat derived facies maps demonstrate 82 85 agreement when compared to sediment data at the platform scale landsat derived facies maps accurately capture the principal depositional facies observed on each platform and are in general agreement with published maps generated through conventional mapping techniques examination at more detailed scales reveals that landsat derived maps differ from conventional maps with respect to the spatial dimensions and shapes of facies bodies landsat derived maps show a level of complexity and heterogeneity that is more realistic than shown in previously published maps which are characterized by broad homogeneous facies belts these results suggest that application of statistical algorithms to landsat data coupled with sediment data provides a cost and time efficient method for quantitatively mapping spatial variability of depositional facies in modern carbonate environments landsat derived facies maps like the ones presented here provide depositional analogs for subsurface carbonate reservoirs as well as a global data set for extracting predictive relationships between the occurrence and distribution of carbonate sediments that can aid in global hydrocarbon exploration and production

the statistics of natural shapes in modern coral reef landscapes abstract spatial heterogeneity is a fundamental characteristic of modern and ancient depositional settings and the scaling of many carbonate environments has been shown to follow power function distributions the difficulty in obtaining information on the horizontal persistence of sedimentary lithotopes at the basin scale has however hampered evaluation of this fact over larger geographic areas in recent years large scale maps of reef facies derived from remotely sensed data have become widely available allowing for an analysis of reef scale map products from 26 sites spread through four reef provinces covering 7000 km2 of shallow water habitat in the u s territorial pacific for each site facies maps were decomposed to polygons describing the perimeter of patches of differing sedimentologic benthic character a suite of geospatial metrics quantifying unit shape fractal dimension and frequency area relations was applied to investigate the intra and intersite variability the spatial architect

anomalous diffusion of electromagnetic eddy currents in geological formations controlled source electromagnetic em induction in some geological formations isshown here to be compactly described by an anomalous subdiffusion process such aprocess which is not universal is governed by a fractional diffusion equation oralternatively the convolutional form of ohm s law a subdiffusing eddy current vortex or electromagnetic smoke ring propagates in such a way that its position of medianintensity overruns its position of peak intensity this behavior is not allowed in classicaldiffusion but is a simple consequence of diffusion within a stationary fractal medium a similar analysis has been applied to understand heavy tailed traveltime distributions thatappear in certain hydrological time series the tell tale signature of anomalouselectromagnetic diffusion is a slope b of the magnetic zero crossing moveout curve that isconstant with transmitter receiver rx offset and significantly different from unity neither lateral heterogeneity nor unixial anisotropy can generate such a constant slopemoveout curve with an economy of model parameters controlled source em data fromtwo sites in texas and one in new mexico are used in this study to test the eddy currentsubdiffusion hypothesis

patterns of sedimentation in the contemporary red sea as an analog for ancient carbonates in rift settings abstract patterns of sedimentation in the red sea offer a contemporary analog for carbonate deposition in marine rift settings covering 20 of latitude the sea is sufficiently long to display pronounced climate differences and the clear tropical waters support vigorous coral reef growth and associated production of carbonate sediment six focus areas within the red sea each covering exactly 1 600 sq km illustrate the variability of spatial patterns in reefal and other carbonates in this rift setting five of the focus areas are located on a north south transect along the western margin of the sea 1 gubal straits egypt 2 shalatayn egypt 3 trinkitat sudan 4 dahlak eritrea and 5 halib eritrea and one is from the eastern margin 6 farasan banks saudi arabia using landsat imagery water depth and two marine facies classes reefal frameworks and sediments were mapped lumping these two classes define carbonate bodies that were analyzed for trends in orientation relation to local fault networks and size frequency distribution fault lineaments digitized from the literature are closely related to the orientation of carbonate bodies with areas exceeding 5 sq km smaller bodies do not preferentially align with fault trends water depth and the occurrence of reefal frameworks and sediments for the six focus areas are not systematically related used as an analog these data from the contemporary red sea may provide insight into the orientation and scale of accumulation of carbonates in subsurface marine rift settings

lateral continuity of facies and parasequences in middle cambrian platform carbonates carrara formation southeastern california u s a abstract lateral and vertical changes within a 40 m thick interval of peritidal carbonates middle cambrian jangle limestone member carrara formation se california produce a mosaic pattern of laterally continuous and discontinuous facies shallowing upward cycles 2 20 m thick parasequences and surfaces bounding parasequences this mosaic pattern was traced bed by bed across 1 8 km of continuously exposed outcrop and then correlated to sections in nearby ranges within parasequences contacts between successive subtidal facies tend to be sharp but may pass laterally into gradational contacts most subtidal facies extend laterally for less than 300 m passing gradationally over tens of centimeters to meters into other laterally adjacent subtidal facies lateral facies contacts between subtidal nodular ribbon rock and intertidal fenestral limestone are gradual over a few meters whereas contacts between vertically juxtaposed facies generally are sharp parasequence boundaries generally are sharp and locally show several tens of centimeters of erosional relief over lateral distances of several meters most parasequences and their bounding surfaces extend for the 1 8 km of outcrop studied and correlate to nearby ranges with varying degrees of confidence several parasequences however do not extend laterally for more than a few hundred meters and are not distinguishable in a vertical profile from those that extend laterally for tens of kilometers the stratigraphic relationships at eagle mountain southeastern california support a model in which the lateral continuity of parasequence surfaces is principally determined by accommodation variations and the lateral continuity of facies is most strongly influenced by the intrinsic dynamics of spatially and temporally heterogeneous sediment production the presence of parasequence boundaries of highly variable lateral extent suggests that the magnitude of accommodation variations was comparatively small consistent with the independent evidence for passive margin subsidence and transitional greenhouse conditions for the middle cambrian

spatial patterns of sediment accumulation on a holocene carbonate tidal flat northwest andros island bahamas abstract to characterize spatial patterns of sedimentation and analyze the morphology of part of the modern tidal flats of northwest andros island in the bahamas this study integrated remote sensing geographic information systems gis and carbonate sedimentology the fundamental data are a landsat tm image that has been classified to create a thematic map of eight subfacies interpreted to represent a distinct tidal flat subenvironment such as adjacent marine exposed levee beach ridge pond and algal marsh spatial statistics of the thematic map characterize the patterns of sediment accumulation quantitative analysis highlights several interesting results concerning subfacies character and distribution 1 of the eight mapped subfacies low algal marsh is most widespread representing 27 5 of the total area whereas exposed levee beach ridge is the least widespread accounting for 10 of the area 2 the patches of different subfacies have different shape complexities with low algal marsh high algal marsh and mangrove ponds being the least complex and exposed levee beach ridge being the most complex 3 markov chain analysis suggests that lateral transitions between different subfacies are highly ordered and 4 frequency distribution of subfacies patch area and lacunarity gap size distribution data exhibit power law relationships over several orders of magnitude consistent with fractal characteristics the fractal nature of patch size and gaps between facies illustrate that on this tidal flat neither the size nor the spatial distribution of subfacies has a characteristic scale this statistical behavior is consistent with the presence of self organization or emergence of pattern in the absence of a template or external forcing the statistical self organization on the tidal flat is the cumulative expression of local processes but it becomes apparent only through analysis of the whole system these results are inconsistent with models suggesting that tidal flats include a migrating complex of randomly distributed randomly sized subenvironments ancient successions that include random patterns may reflect the more pronounced influence of forces external to the sedimentary system instead of an absence of those forces

remote sensing of geomorphology and facies patterns on a modern carbonate ramp arabian gulf dubai u a e abstract the occurrence of power law relationships in the spatial distribution of sedimentary lithotopes has been identified in both modern and ancient carbonate depositional bodies in this study facies patterns and their spatial relationships are investigated quantitatively in an arabian gulf shallow subtidal carbonate ramp setting using a synergy of ikonos satellite imagery and vessel based acoustic bathymetry survey three dimensional reconstruction of the facies distribution on the seabed enabled quantification of relationships between eight dominant facies classes and the association of particular lithotopes to water depth fractal behavior was investigated using a combination of boundary and patch based metrics and the spatial distribution of early diagenetically cemented hardgrounds and unconsolidated carbonate sand were shown to display strong fractal properties in contrast we show that landscape scale processes can be treated as essentially deterministic and facies neighborhood patterns are strongly probabilistic identifying that the heterogeneity of shallow subtidal carbonate facies scales with a power law within certain thresholds has the potential to serve as a tool in environmental reconstruction in the ancient where information on the lateral persistence of facies units is difficult to obtain the findings are relevant to the interpretation of stratigraphic sequences and paleo depth analysis

fractals in geology and geophysics the definition of a fractal distribution is that the number of objectsn with a characteristic size greater thanr scales with the relationn r d the frequency size distributions for islands earthquakes fragments ore deposits and oil fields often satisfy this relation fractals were originally introduced by mandelbrot to relate the length of a coastline to the length of the measuring stick this application illustrates a fundamental aspect of fractal distributions scale invariance the requirement of an object to define a scale in photographs of many geological features is one indication of the wide applicability of scale invariance to geological problems scale invariance can lead to fractal clustering geophysical spectra can also be related to fractals these are self affine fractals rather than self similar fractals examples include the earth s topography and geoid

poisson processes of carbonate accumulation on paleozoic and holocene platforms abstract cambro ordovician carbonate lithofacies units in the elbrook and conococheague formations exposed at wytheville virginia as well as those in many other phanerozoic peritidal sequences exhibit exponential thickness frequency distributions that is occurrence frequency decreases exponentially with linear increase in unit thickness such distributions are characteristic of waiting times between independent poisson events this relative frequency of spaces of different size between horizons of lithologic change is what one would expect if the horizons were distributed randomly throughout carbonate successions abundances of different lithologies both as net stratigraphic thickness and as number of occurrences also decreases exponentially among successively rare sediment types with each lithology being about 60 as plentiful as the next more abundant rock type relations between net thickness and number of occurrences for each facies define a linear trend coincident with a mean thickness for all wytheville units of 0 48 m a relation indicating that thickness distribution is independent of facies type similar relations are apparent for the horizontal extent of carbonate sediment bodies from the holocene florida bahama platform areal extents of individual facies units lithotopes are described by a frequency distribution in agreement with that anticipated for a population of equidimensional facies elements whose diameter distribution follows an exponential frequency distribution although regional gradients in sediment texture and composition are also apparent along most transects from platform margin to interior such frequency distributions indicate that lateral extents of individual sediment reflect a largely stochastic distribution of facies boundaries across this holocene surface lithotope abundances also yield trends of exponentially decreasing dominance among successively subordinate facies with each being about 70 as extensive the next more abundant sediment type relations between areas and abundances for all lithotopes define a covariant trend corresponding to a mean area of 2 2 103 km2 for all florida bahamas lithotopes we consider several numerical models of stochastic carbonate accumulation although not demonstrably unique scenarios incorporating the sequential superposition of randomly placed coniform lithotopes result in thickness and area frequency distributions that are the same as those observed in ancient and modern platform deposits such simulations of poisson processes of sediment accumulation are in general agreement with stochastic models of lithologic heterogeneity that have been more widely applied to petroleum reservoirs and groundwater aquifers to the as yet unknown degree that peritidal lithofacies area and thickness are correlated data from paleozoic and holocene platforms suggest that carbonate units should exhibit length height ratios of approximately 105 given the decimeter scale over which facies are designated in most paleozoic peritidal successions these relations predict mean lateral extents on the order of several tens of kilometers a value in general agreement with the few data that exist on spatial continuities of peritidal lithotopes in paleozoic carbonate sequences

enhanced detection of the coral acropora cervicornis from satellite imagery using a textural operator the strength of a texture based classification lies in the fact that it detects spatial patterning as a function of spectral variation within a particular facies class as opposed to spectral consistency which drives standard probability driven image classifiers following this premise the moran s i spatial autocorrelation metric was proven to return values which differed significantly for areas characterised by dense interlocking thickets of the coral acropora cervicornis versus areas populated by a sparse mixed coral assemblage dominated by montastrea annularis the different behaviour of the metric was sufficient to facilitate spatial discrimination of the two assemblages using a supervised classifier with accuracies that surpass the level of prediction offered by standard spectral based methods discrimination was optimum when autocorrelation was evaluated within a moving window with side lengths ranging between circa 30 70 m the discrimination ability is postulated to be linked to intrinsic differences in the spatial patterning of the two assemblages at scales of tens of metres the observed patterning can be further related to the growth form and architecture of the differing coral assemblages the study demonstrates the potential of using kernel based autocorrelation metrics in unison with satellite data and offers a pertinent tool for monitoring ecologically important coral assemblages that are statistically indistinct using traditional spectral methods d 2005 elsevier b v all rights reserved

a reef up approach to classifying coral habitats from ikonos imagery monitoring coral reef benthos with satellites has typically followed a sensor down approach with the classification algorithm driven by statistics derived from the imagery i adopt a reef up method drawing on statistics derived from hyperspectral optical field measurements of substrate reflectance to train image classification in order to calibrate the satellite data with direct physical measurements of reflectivity it is necessary to process both the imagery and in situ data to common units of albedo building upon a proof of concept study conducted by the author in the red sea the link is made by correcting the remote sensing data for the effect of varying bathymetry using in situ measurement of water column optical properties and a digital elevation model constructed from a vessel based acoustic survey thereby yielding units of substrate reflectance extensive ground verification of the predictive benthic habitat map resulting from image classification showed that eight substrate classes were resolved with an overall accuracy of 69 down to a depth of 6 m including live and dead coral framework as compared to conventional from image classification techniques the reef up method offers the potential for higher thematic accuracy while maintaining a greater degree of flexibility for repeat survey using platforms of higher spectral and spatial resolution expected to come online in the near future the fact that image acquisition and optical ground truthing did not occur concurrently is of particular relevance in confirming that in situ measurements can be made independent of image acquisition and retrospectively linked to appropriate substrate classes considering the wealth of hyperspectral data already acquired for shallow reef facies the work highlights the potential of the reef up approach for quantifying substrate distribution in coral environments using both air and spaceborne platforms

relations between geomorphic form and sedimentologic stratigraphic variability holocene ooid sand shoal lily bank bahamas although the linkages among surface sediments geomorphic forms and hydrodynamics in holocene ooid tidal sand shoals have been evaluated recently how these factors are reflected in the geomorphic evolution and stratigraphic record of shoals is less constrained yet such understanding is essential to developing meaningful predictive conceptual models of three dimensional architecture of ancient reservoir analogs integrating remote sensing imagery high frequency seismic data and core characterization from lily bank a modern tidally dominated bahamian ooid shoal in which sedimentologic processes are well documented reveals the stratigraphic record of geomorphic change an irregular gently dipping rocky surface interpreted as the top pleistocene with no pronounced topographic high underlies the holocene oolitic succession a 6 m 20 ft thick poorly sorted gravelly muddy sand with few ooids overlies this basal surface this lower interval is overlain by sand with an upward increase in proportion of ooids sorting and grain size the uppermost unit present only under active bar forms is well sorted oolitic medium sand with accretionary foresets sediments vary stratigraphically and geomorphically the lower unit is finer and less well sorted than the upper units and in the oolitic upper unit sediment size and sorting on bar crests are distinct from bar flanks collectively these results suggest that a marked antecedent bump is not necessary for occurrence of ooid shoals and that the stratigraphic record of analogous ooid shoal systems may preserve clues of geomorphic position as well as geobody size and orientation

electrical and fluid flow properties of carbonate microporosity types from multiscale digital image analysis and mercury injection electrical and fluid flow properties of porous media are directly related to the morphology of pores and the connectivity of the pore network both are closely linked to the amount and type of intrinsic microporosity in carbonate rocks which is not resolved by conventional techniques broad ion beam bib milling produces high quality true two dimensional cross sections for scanning electron microscopy sem and enables accurate quantification of carbonate microporosity for the first time the combination of bib sem mosaics with optical micrographs yields a multiscale digital image analysis msdia spanning six orders of magnitude in this paper the pore structures of 12 different carbonate rock samples from various rock types are quantified using msdia mercury injection capillary pressure measurements are used to assess pore throat properties the quantified pore structure parameters are correlated with plug measurements of electrical resistivity and permeability results indicate that petrophysical properties are closely linked to the type of microporosity which is distinctive for a certain rock type rock types with crystalline microporosity such as mudstone and dolomite generally show good connectivity in which the size of the pore network determines if the rock favors either hydraulic or electric flow rock types with intercement or micromoldic microporosity such as bindstone and travertine show variations in connectivity due to layering and moldic micropores of biological origin furthermore pore size distributions psd follow a power law in all samples despite their depositional and diagenetic differences the slope of the psd correlates with the electric properties in which samples with a steeper slope show lower cementation factors the linearity of the power law distribution enables predictions of pore populations outside the investigated length scales

gas venting and late quaternary sedimentation in the persian arabian gulf abstract high resolution 3 5 khz echo sounding profiles and piston cores were used to reconstruct the microtopography and late quaternary depositional history of the persian gulf perversive throughout the seafloor of the gulf is an extensive network of pockmarks formed by seepages of thermogenic gas these gas seeps and bottom water exiting the gulf via the strait of hormuz are the most significant processes controlling present day sedimentation in the region erosion by these seeps has been so intense in the baiban shelf in the strait of hormuz as to create a hoodoo like terrain on the outer shelf the surfical geology of the gulf documents a short lived transgression 29 400 to 22 800 years ago during the wisconsin regression which began 125 000 years ago the wisconsin regressive maxima when sea level dropped to 120 130 m about 21 000 20 000 years ago and the climate was dry and eolian and paralic sedimentation characterized the gulf the holocene transgression 18 000 to 12 000 years ago when the climate was more humid than during the climax of the wisconsin regression a dry phase 12 000 to 9000 years ago when the persian gulf was a site of eolian and carbonate deposition and the present sediment cycle during the last 9000 years under a more humid regime it was during the present cycle that southeast trending marl lobes were deposited off iran arabia acquired its hyper arid climate about 3000 years ago and the gulf attained its present configuration about 1000 years ago as a result of the construction of the tigris euphrates delta at its head and tectonism and aggradation along its arabian and iranian flanks

a 3d seismic study of the morphology and spatial distribution of buried coral banks in the porcupine basin sw of ireland an industrial 3d seismic data volume supplemented by high resolution 2d seismics was used to study part of a province of buried mound structures in the porcupine basin southwest of ireland these magellan mounds and their associated moat structures interpreted as scour marks were mapped semi automatically from time structure and isopach maps image analysis techniques such as a tophat transformation mathematical morphology were applied for feature extraction size measures of both mounds and moats were derived from the resulting maps and summarised by means of some descriptive statistics spatial variability in mound occurrence and characteristics was investigated comparison with other mound structures in the area allowed the magellan mounds to be identified as coral banks associated with the growth of cold water deep sea coral species such as lophelia pertusa l and madrepora oculata l mound growth clearly started in a single event confined in time and space bottom currents and oceanographic characteristics of the surrounding water masses influenced this sudden process and the further mound development however the analysis of the 3d seismic data set did not allow us to identify unambiguously the actual cause for the sudden mound start up the mounds appear to have formed a dense cluster of structures of moderate size which are significantly elongated in a n s direction they are associated with even more elongated moats implying a periodically reversing n s directed current influence a spatial density of one mound per km2 was measured which remains more or less constant over the area investigated mound width and cross sectional area and moat shape gradually change across the mound province due to spatially changing environmental conditions at the initial growth stages of the mounds and during their further development interplay between current regime and sedimentation

the signal and the noise forward modeling of allocyclic and autocyclic processes influencing peritidal carbonate stacking patterns recent carbonate sequence stratigraphic models suggest that the degree of order present in successions of carbonate parasequences is determined by temporal variations in eustatic amplitude and by varying levels of autocyclicity ordered parasequence stacking is suggested to occur during greenhouse periods dominated by low amplitude eustatic oscillations conversely disordered vertical successions are said to occur when amplitudes of eustatic oscillations are high or when autocyclic processes dominate and thus drown the periodic external signal these assertions of causal mechanism are tested here by application of a three dimensional stratigraphic forward model the three dimensional model generates parasequences via a ginsburg type mechanism of sediment transport and shoreline progradation parasequence stacking is controlled by a superimposed longer term eustatic oscillation and parasequences generated are analyzed using runs analysis and durbin watson autocorrelation results from the modeling suggest that autocyclic parasequences generated by shoreline progradation form ordered vertical successions when accommodation changes driven by a low amplitude relative sea level oscillation suggesting that partly autocyclic strata may not be inherently any less ordered than entirely allocyclic strata addition of stochastic processes such as mosaic carbonate production and fluctuations in regional sediment transport direction tend to decrease the level of measurable order present in the autocyclic strata increasing the frequency and amplitude of relative sea level oscillations also tends to decrease the measurable order in stacked autocyclic peritidal parasequence thicknesses these results suggest that controls on parasequence stacking patterns are likely to be more complex and varied than suggested by recent sequence stratigraphic models more outcrop and modeling investigation is required with appropriately circumspect interpretations applied

a model for the development of a carbonate mound population in the rockall trough based on deep towed sidescan sonar data a large carbonate mound population is identified on deep towed tobi towed ocean bottom instrument sidescan data along the eastern margin of the rockall trough west of ireland individual mounds are circular to elliptical in plan view varying from 50 to 850 m in width and up to about 200 m in height strong ne flowing contour currents at 800 m water depth are inferred from large scale sedimentary bedforms smaller mound arrays are spatially associated with slope parallel escarpments produced by mass wastage while around the largest mounds the sharp escarpments may have been smoothed by the vigorous contour currents current streamlining effects control the shape of the mounds which become more elliptical as their size increases thereby minimising the hydraulic drag force the frequency distribution of mound size follows a general power law which is determined by the growth rate of the framework building coral species and the rate at which they colonised the substrate initially bottom currents support mound growth until the mounds become so large that hydraulic drag forces retard their growth a model for the evolution of the population predicts that increased hydraulic drag forces on the larger mounds cause a sharp decrease in their number in agreement with the observations the model also allows an age structure for the population to be determined and correlations between the growth of the mound population and palaeoclimatic variations in the ne atlantic to be attempted

fractal nature of stratigraphic sequences orders of stratigraphic sequences are being used loosely and with widely varying definitions the orders seem to be subdivisions of convenience rather than an indication of natural structure it is proposed that at least at time scales of 103 106 yr sequences and systems tracts are scale invariant fractal features in which units bounded by exposure surfaces and units bounded by flooding surfaces are about equally likely support for this conceptual model derives from the well known facts that 1 sediment architecture is largely scale invariant over a wide range of scales in time and space 2 first order trends of sea level movements and sedimentation rates are fractal on all geologically relevant time scales and 3 detailed studies in carbonates indicate approximately equal abundance of flooding surfaces and demonstrable exposure surfaces among unit boundaries finally traces of prograding shelf edges that step up and step down in response to sea level changes are demonstrated in this study to have a fractal nature

area perimeter relation for rain and cloud areas following mandelbrot9s theory of fractals the area perimeter relation is used to investigate the geometry of satellite and radar determined cloud and rain areas between 1 and 1 2 x 106square kilometers the data are well fit by a formula in which the perimeter is given approximately by the square root of the area raised to the power d see equation in the pdf where d is interpreted as the fractal dimension of the perimeter it is concluded that rain and cloud perimeters are fractals they have no characteristic horizontal length scale between 1 and 1000 kilometers

diatom records in the quaternary marine sequences around the japanese islands abstract understanding the quaternary is a key to estimating what the earth s climate will be like in the future such studies demand high resolution analyses based on paleoclimatic proxy records of changing earth s orbital forcing and solar insolation that affect the climate system quaternary diatom biostratigraphy and paleoceanography have been well established based on the quaternary marine sequences obtained by piston coring and deep sea drilling around the japanese islands this paper firstly reviews the quaternary diatom datum levels that are directly tied to magnetic polarity and then the late pleistocene and holocene rhythmic fluctuations in td derived ssts c which correlate with the earth s orbital parameters and finally reveals the large and abrupt climatic changes that have occurred around the japanese islands on centennial to millennial time scales the main aim is to provide the results of td ssts c based on the late pliocene to pleistocene sequences from three holes obtained by deep sea drilling dsdp odp the main difference between td and twt is that twt gives 0 5 values to xt warm transitional taxa thalassiosira oestrupii is grouped with xt in twt but with warm water species in td differences between the twt and td ssts c curves at hole 436 are unremarkable the remarkable variations of paleo temperatures based on td ssts c show four conspicuous episodes which correspond to the double precession cycle of mis 11 in the japan sea the twt ratio remarkably decreases at 2 6 ma due to a large increase in cold water taxa and indicates the beginning of the glacial age defined as the pliocene pleistocene boundary both twt and td ssts c increase at 2 60 2 0 ma and coincide with the lithologic change from diatom bearing clay with few dark colored layers to fine grained sediments with distinct dark light colored cycles wavelet analysis of td ssts c at site 798 indicates a reversed saw tooth pattern of 48 to 24 ky periods during 1 2 0 7 ma and 24 to 12 ky periods during 0 7 0 ma resulting in a change from longer to shorter cycles these fluctuations correlate with the earth s orbital parameters and climatic changes on a millennial time scale

detection of shallow subtidal corals from ikonos satellite and qtc view 50 200 khz single beam sonar data arabian gulf dubai uae we compared the results of seafloor classifications with special emphasis on detecting coral versus non coral areas that were obtained from a 4 4 m pixel resolution multispectral ikonos satellite image and two acoustic surveys using a qtc view series 5 system on 50 and 200 khz signal frequency a detailed radiative transfer model was obtained by in situ measurement of optical parameters that then allowed calibration of the ikonos image against in situ optical measurements and a series of ground truthing points eight benthic classes were distinguished optically with an overall accuracy of 69 and a tau index t of 65 the classification of the ikonos image allowed discrimination of three different coral assemblages dense live dense dead sparse which were confirmed by ground truthing data evaluation of the acoustic surveys involved culling of datapoints with 90 accuracy and 30 probability were used and 60 accurate t 53 when less processed data selcted classes only all data were used accuracy against ground truthing points of the most highly processed dataset was 56 t 46 these results indicate that results from optical and acoustic surveys have some degree of commonality therefore there is a potential to produce maps outlining coral areas from optical remote sensing in shallow areas and acoustic methods in adjacent deeper areas beyond optical resolution with the limitation that acoustic maps will resolve fewer habitat classes and have lower accuracy

ground penetrating radar characterization and porosity evolution of an upper pleistocene oolite capped depositional cycle red bays northwest andros island great bahama bank abstract linkages among surface sediments depositional processes geomorphic forms stratigraphic architecture and pore distribution in bahamian sand bodies and oolite capped depositional successions have been characterized in recent studies an understanding of how these parameters especially porosity are preserved or modified in the eogenetic environment is essential in bridging the gap between modern and ancient analogs two complementary 3d 200 mhz and 400 mhz ground penetrating radar surveys and three shallow cores reveal that the uppermost part of the upper pleistocene marine isotope stage 5e lucayan formation at red bays andros island great bahama bank comprises a single 6 m thick upward shallowing parasequence six radar packages p1 p6 bounded by radar surfaces s1 s6 have been identified in the two 3d radar volumes the stratigraphic succession indicates development of a burrowed backshoal lagoon during early flooding of the bank top followed by deposition of flood tide driven low angle sheet sands and sigmoidal subaqueous dune deposits as the shelf margin sand shoal moved bankward as a function of continued sea level rise constructional accommodation on the front of the prograding subaqueous dune in the northwest part of the survey area and erosional accommodation created by downcutting of a shallow tidal channel into the upper part of the subaqueous dune depositional unit in the northeast part of the study area were filled with peloid and ooid dominated carbonate sands as sea level stabilized the uppermost radar package is a thin 0 15 to 0 55 m partially calichified carbonate sand sheet that mantles the entire survey site and that reflects late highstand and fall of sea level exposure of the studied interval to meteoric vadose diagenesis over the past 100 000 years has resulted in partial stabilization of the largely aragonitic precursor sediment through selective partial dissolution of aragonitic grains mainly ooid cortical layers peloids and mollusk shells accompanied by precipitation of patchily distributed low magnesium calcite cement core data demonstrate a relationship between stratigraphically controlled sedimentological attributes diagenesis and pore distribution three distinctive zones of porosity were present upon deposition a lower zone of relatively high interparticle porosity 21 3 to 33 2 in the medial part of p1 a low porosity zone

quantifying the relationship between water depth and carbonate facies abstract carbonate facies often are used to define meter scale parasequence or cyclic structure in ancient sedimentary basins these parasequences constitute the fundamental stratigraphic unit in many studies of ancient climate and life on earth of interest is the uncertainty associated with the assumptions that underpin the parasequence definition and interpretation this work presents a method that uses modern maps of bathymetry and the geographic distribution of facies atop the great bahama bank to extract a signal of water depth change from facies transitions in vertically stacked carbonate strata this probabilistic approach incorporates the observed complexity in the water depth distribution of immediately adjacent modern carbonate environments and results in an impartial and explicit interpretation of stratigraphic data with quantified uncertainties specifically this analytical tool can distinguish sequences of facies that are likely to record information about changing water depths from sequences of facies that do not additionally the quantitative signal extracted from sequences of discrete or qualitative data can be used for the correlation of stratigraphic sequences by quantifying geologic observations through a lens of modern data the reproducibility and accuracy of sedimentary interpretations can be improved to build a more authentic picture of earth history

sediments of the dry tortugas south florida usa facies distribution on a ramp like isolated carbonate platform abstract four sedimentary facies may be delineated based on quantitative analysis of texture and composition of modern surface sediments on the dry tortugas carbonate platform these include 1 mollusk halimeda wackestone 2 mollusk packstone to grainstone 3 coralgal halimeda grainstone and 4 coralgal grainstone even though the tortugas platform is characterized by an open circulation due to deep broad marginal channels and a lack of a continuous surface breaking marginal reef facies are not distributed at random and show bathymetrical zonation also facies appear to cover wide belts rather than forming a mosaic mollusk halimeda wackestone occurs in protected platform interior areas ca 10 18 m deep mollusk packstone to grainstone occurs in more open platform interior settings adjacent to channels and in deeper outer reef areas of 14 25 m water depth coralgal halimeda grainstone is found on shallow marginal shoals 1 11 m deep and coralgal grainstone on the somewhat deeper 3 16 m seaward edges of these shoals however there is bathymetrical overlap of facies in intermediate depths of ca 5 17 m this limitation has implications for the interpretation of the fossil record because changes in water depth are commonly thought to be reflected in facies changes e g in sequence stratigraphy comparison with previous sediment studies of the 1930s 1960s and 1970s in the area exhibit a decrease in coral fragments and increases in coralline algal and mollusk shell fragments these observations might be a result of environmental changes such as coral decline and die outs during temperature events disease and the increase in macroalgae due to the ecological extinction of the echinoid diadema the results suggest that more long term studies are needed that further explore the influence of environmental change on reef sediment composition dry tortugas surface sediments consist of lower portions of halimeda plates and mollusk shell fragments and higher percentages of coralline algal fragments as compared to sediments of the adjacent florida reef tract possibly as a consequence of differences in platform morphology and exposure to waves and currents

modern fringing reef carbonates from equatorial se asia an integrated environmental sediment and satellite characterisation study abstract fringing reefs of se asia may conservatively comprise 30 of the world s coral reef area but remain almost unstudied white 1987 tomascik et al 1997 this study provides insights into the primary sedimentological and early alteration characteristics of an isolated fringing reef system kaledupa hoga from the tukang besi archipelago se asia a combined multispectral satellite imagery field and petrographic study allowed for the generation of an environmental facies map which acts as a model for the distribution of primary sedimentological characteristics in relation to the primary environmental facies the islands of the tukang besi archipelago are mesotidal 71 accuracy when compared with field and sedimentary data with the exception of the reef crest and reef slope that commonly have widths on a sub imaging resolution although field and satellite imagery observations reveal ten environmental facies sedimentological characterisation results in a lower number of distinctive categories due to the similarity of many deposits foreshore backshore and bare intertidal deposits are distinctive and are composed of reef derived material that has been reworked shorewards seagrass associated facies all show some fine silt clay sized material

vertical to lateral transitions among cretaceous carbonate facies a means to 3 d framework construction via markov analysis the search for and extraction of hydrocarbons in carbonate rocks demands a thorough understanding of their depositional anatomy the complexity of carbonate systems however hinders detailed direct characterization of their volumetric heterogeneity information with which to construct a reservoir model must therefore be based on information gathered from wells or outcrops transecting the sequence of interest most particularly exploration wells are vertical presenting a problem for geostatistical modeling while understanding vertical stratal stacking is straightforward it is difficult to obtain lateral facies information though in some situations outcrop surfaces seismic data and horizontal wells may somewhat mitigate this bias the likelihood remains that the lateral dimension of a buried system will be vastly undersampled with respect to the vertical however through the principle of walther s law walther 1894 or due to the geometry of basinward inclined beds comparable facies frequencies and transition probabilities may link vertical and lateral stratal arrangements the implication being that a reservoir model competent at least in terms of transition statistics could be built against information harvested down core taking an interpreted outcrop panel from lewis canyon albian pecos river texas we use markov chains to first ascertain that vertical and lateral stratal ordering is nonrandom second we show lithofacies transition probabilities in the outcrop as being interchangeable between the vertical and lateral directions the work concludes by demonstrating the utility of an existing 3 d markov random field simulation to volumetrically model the lewis canyon outcrop on the basis of vertical facies transition tendencies statistical interrogation of the 3 d model output reveals the simulation to contain realistic facies associations compared to the outcrop this suggests that the reconstruction process based on markov chains produces a useful representation of 3 d heterogeneity in this lower cretaceous carbonate succession markov random field simulation might provide an important tool for prediction and simulation of subsurface carbonate reservoirs

the rio tinto basin spain mineralogy sedimentary geobiology and implications for interpretation of outcrop rocks at meridiani planum mars abstract exploration by the nasa rover opportunity has revealed sulfate and hematite rich sedimentary rocks exposed in craters and other surface features of meridiani planum mars modern holocene and plio pleistocene deposits of the rio tinto southwestern spain provide at least a partial environmental analog to meridiani planum rocks facilitating our understanding of meridiani mineral precipitation and diagenesis while informing considerations of martian astrobiology oxidation thought to be biologically mediated of pyritic ore bodies by groundwaters in the source area of the rio tinto generates headwaters enriched in sulfuric acid and ferric iron seasonal evaporation of river water drives precipitation of hydronium jarosite and schwertmannite while mg al fe3 copiapite coquimbite gypsum and other sulfate minerals precipitate nearby as efflorescences where locally variable source waters are brought to the surface by capillary action during the wet season hydrolysis of sulfate salts results in the precipitation of nanophase goethite holocene and plio pleistocene terraces show increasing goethite crystallinity and then replacement of goethite with hematite through time hematite in meridiani spherules also formed during diagenesis although whether these replaced precursor goethite or precipitated directly from groundwaters is not known the retention of jarosite and other soluble sulfate salts suggests that water limited the diagenesis of meridiani rocks diverse prokaryotic and eukaryotic microorganisms inhabit acidic and seasonally dry rio tinto environments organic matter does not persist in rio tinto sediments but biosignatures imparted to sedimentary rocks as macroscopic textures of coated microbial streamers surface blisters formed by biogenic gas and microfossils preserved as casts and molds in iron oxides help to shape strategies for astrobiological investigation of meridiani outcrops

unravelling the influence of water depth and wave energy on the facies diversity of shelf carbonates carbonate sequence stratigraphy is founded on the principle that changes in relative sea level are recorded in the rock record by the accumulation of sediment with relative water depth dependent attributes while at the scale of a shelf to basin transect facies clearly arrange by water depth the relation blurs for depths 40 m the most vigorous zone of carbonate production the reason for this change in behaviour is two fold firstly in shallow water the intrinsic processes of storm and wave reworking influence the seabed through submarine erosion and sediment redistribution secondly facies diversity tends to be greater in shallow water than deep water because of a greater diversity in grain producers remote sensing imagery field observations and hydrodynamic models for two reef rimmed shore attached carbonate platforms in the red sea show neither water depth nor energy regime to be reliable indicators of facies type when considered in isolation considered together however the predictive power of the two variables rises significantly the results demonstrate it to be an oversimplification to assume a direct link between palaeo water depth and depositional diversity of subtidal lithofacies while highlighting the importance of hydrodynamics in directing the accumulation of carbonate sediments in the shallow photic zone while the size distributions of facies extents in the two focus areas follow power laws no direct relation between the lateral continuity of the facies belts and water depth or wave height is reported the work is relevant for the interpretation of metre scale subtidal carbonate cycles throughout the geological record by demonstrating how caution must be applied when inferring palaeowater depths from depositional facies

on the interpretation of shallow shelf carbonate facies and habitats how much does water depth matter abstract many stratigraphic studies of ancient shallow water carbonate platforms focus interpretation on the primacy of changes in accommodation inferred by assuming a direct and deterministic link between depositional facies and water depth the purpose of this study is to test this assumption explicitly and quantitatively by exploring relations between substrate type classified on the basis of both habitats and facies and the water depth at which they occur on a modern well studied shallow rimmed shelf margin gis analysis of digital benthic habitat and bathymetry maps of the shallow 8 m south florida shelf illustrate that most substrate types occur across a range of water depths similarly at greater water depths habitats and facies are more constrained more dominance of one class more deterministic with generally decreasing dominance more diversity at shallower water depths at a scale of shelf to basin transects facies and habitats clearly are related to water depth yet on this narrower 10 km shallow shelf margin at the scale of this study water depth and habitats and facies are not uniquely related or linked this general lack of correspondence between bottom type and water depth may be a manifestation of landscape disequilibrium a state in which habitats and facies do not fully reflect ambient environmental conditions perhaps recording the influence of rapid change in sea level alternatively it may reflect the impact of variables other than water depth although more general consequences of these results for other depositional settings remains to be evaluated they do emphasize the fact that variables other than bathymetry may significantly influence the ecological and sedimentologic attributes of depositional surfaces they do allow for the quantification of some of the potential uncertainties inherent in the interpretation of analogous ancient platforms and can serve to focus future observations on the causes and consequences of vertical and lateral heterogeneity in ancient stratigraphic sequences

implications for controls on upper cambrian microbial build ups across multiple scales mason county central texas usa abstract the morphological architecture and distribution of modern and ancient carbonate systems has been shown to follow spatial self organization however limited studies describe the morphometrics of microbial carbonates upper cambrian microbial build ups outcropping in central texas are exposed laterally plan view enabling a study of their morphological architecture and spatial distribution drone imagery was acquired to capture the outcrop features and develop a digital terrain model cm scale resolution for a bedding plane outcrop 600 200 m in size four scales of microbial growth s1 few dm s2 few m s3 few tens of m and s4 few hundreds of m were identified and mapped a series of morphometric analysis including ripley s k univariate multivariate and grouping were conducted and results demonstrate that the scales s1 s2 and s3 display clustering and the spatial organization of microbial buildups is naturally organized and not random further as the size of the build ups increases from s1 s4 the anisotropy length width increases their shape becomes oblong and they become aligned s2 s4 with the inferred regional winds and tide associated currents ne sw according to the present geography the s1 scale does not align itself with the regional currents instead the build ups behaved as a baffle during growth and modified the currents locally leading to preferential alignment at the edges within s2 as the scales increases in sizes s2 s3 s4 there is competition for space and due to regional currents the larger scales preferentially align parallel to high energy currents the trends and spatial relationships identified in this study are particularly relevant and provide a scenario for sub seismic scale heterogeneities for subsurface microbial hydrocarbon reservoirs

inhibition of reef framework by frequent disturbance examples from the arabian gulf south africa and the cayman islands abstract the environmental processes that prevent reef framework development in areas with a diverse and dense cover of coral were investigated in the southern arabian gulf dubai uae the southwestern indian ocean south africa and the central caribbean cayman islands bwi in dubai temperature anomalies predicted to recur every 10 15 yr cause repeated mass mortalities of acropora spp the dominant potential framebuilding species subsequent bioerosion of the dead coral skeletons renders them brittle and susceptible to fragmentation during winter storms as a consequence regrowth of the next generation of framebuilders which takes about 10 yr has to initiate on the original bedrock surface this cycle of mass mortality framework break down and regrowth inhibits in situ framework accumulation in south africa the formation of coral frameworks is prevented by annually recurring high wave energy events which stunt coral to such small sizes that no framework is built the situation is further aggravated by the fact that branching coral fragments which could serve as asexual propagules are washed off the reefs and lost in the cayman islands no coral framestones of in situ skeletons are formed in areas shallower than about 5 m in these areas coral frameworks formed by acropora palmata are removed by hurricanes broken up and deposited in the form of a rubble accumulation further inland on the island shelf thus although a coral deposit remains it is not an in situ grown framework however since the build ups in the upper 5 m are mostly made up by coral fragments such structures would likely be identified as reefs if encountered in a fossil outcrop situation these three models can help to explain the paleoecology of allochthonous peri reefal or non reefal coral deposits i e coral rudstones floatstones bindstones they also demonstrate that at least in recent coral systems species richness and high coral coverage alone need not necessarily translate into high in situ framebuilding potential

quantified rates of geomorphic change on a modern carbonate tidal flat bahamas comparison of aerial photographs and ultrahigh resolution remote sensing data reveals changes in the geomorphology of a modern carbonate tidal flat in the 58 yr between acquisition of the two data sets several tidal channels have extended headward more than 100 m channel bars have stabilized the shoreline has eroded as much as 50 m the inland algal marsh locally has prograded as much as 90 m and many mangrove ponds have increased in size these changes over the known time interval allow quantification of the rates of these geomorphic processes and suggest rates of migration of landforms to several meters per year some observed rates appear to be different than rates averaged over the past several thousand years however possibly because of changes in storm activity or circulation patterns these data illustrate the dynamic nature of the entire coastal tidal flat system not just the shoreline and reflect the system9s response to factors including relative rises in sea level

delineating and quantifying depositional facies patterns in carbonate reservoirs insight from modern analogs modern carbonate settings have long been used as analogs for interpreting various environments of deposition in subsurface data sets based on well log and core data and have provided examples of how these environments can be interrelated within a larger context this study focuses on carbonate sands in the exuma islands part of the great bahama bank to show how modern settings can be better used for reservoir analogs by emphasizing visualization and quantification techniques that conceptually delineate aspects of potential grainstone reservoir distribution and heterogeneity along the windward margin of the exumas the association of tidal deltas channels and islands forms an exploration scale linear belt of mostly ooid sand approximately 5 10 km 3 1 6 mi wide and 170 km 106 mi long paralleling the platform margin but set back from the platform edge the distribution of carbonate sands in the exumas was assessed with a digital elevation model and satellite imagery by selecting different water depth intervals parts of the sand belt were highlighted for visual analysis and extracted for measurements of size and shape for example 37 of the sand belt comprises shallowest sands in which the largest areas greater than 100 000 m2 1 07 million ft2 are highly sinuous and maintain connectivity the sand belt was also subdivided into various depositional settings flood tidal delta lobes comprise 85 of the sand belt tidal channels and islands add further heterogeneity to the sand belt channels average about 3 km 1 8 mi in length and have regular but locally variable spacing a representative island shows how the syndepositional topography of holocene ridges develops complexly around antecedent pleistocene topography

shoreline reconstructions for the persian gulf since the last glacial maximum abstract sea level change in the persian gulf since the time of the last maximum glaciation at about 18 000 yr bp is predicted to exhibit considerable spatial variability because of the response of the earth to glacial unloading of the distant ice sheets and to the meltwater loading of the gulf itself and the adjacent ocean models for these glacio hydro isostatic effects have been compared with observations of sea level change and palaeoshoreline reconstructions of the gulf have been made from the peak of the glaciation until about 14 000 yr bp the gulf is free of marine influence out to the edge of the biaban shelf by 14 000 yr bp the strait of hormuz had opened up as a narrow waterway and by about 12 500 years ago the marine incursion into the central basin had started the western basin flooded about 1000 years later momentary stillstands may have occurred during the gulf flooding phase at about 11 300 and 10 500 yr bp the present shorelines was reached shortly before 6000 yr ago and exceeded as relative sea level rose 1 2 m above its present level inundating the low lying areas of lower mesopotamia these reconstructions have implications for models of the evolution of the euphrates tigris karun delta as well as for the movements of people and the timing of the earliest settlements in lower mesopotamia for example the early gulf floor would have provided a natural route for people moving westwards from regions to the east of iran from the late palaeolithic to early neolithic

the intrinsic effect of shape on the retrogradation motif and timing of drowning of carbonate patch reef systems lower frasnian bugle gap canning basin western australia the evolution and architecture of a set of retreating lower frasnian patch reef outcrops in the canning basin of western australia were evaluated and their depositional and stratigraphic contacts spatially recorded using digital surveying tools the geological data together with high resolution digital elevation models were assembled in three dimensional visualization and modelling software and subsequently used for building two dimensional surface models and three dimensional volumetric models numerical data on geometry and shape were extracted from these models and used to quantitatively assess the retrogradation motif of patch reef development the development of the patch reefs comprises three stages during stages 1 and 2 the patch reefs exhibited an overall retrogradational escarpment type configuration displayed by on average 60 steep reef margin walls that lacked the support of coeval slope deposits the subdivision between stages 1 and 2 is based on minor backstepping reducing less than 10 of the platform top area the onset of stage 3 is recognized by stromatolite development fringing reef margin walls during stage 3 an aggrading accretionary reef margin developed comprising allochthonous and autochthonous slope deposits both types of slope deposit onlap the previous stages and are distributed unevenly with allochthonous slope deposits being noticeably absent around the smaller and more elongate patch reefs the variation in distribution of slope sediment type can be explained by the amount linked to platform size of platform top shedding small patch reefs were unable to fill the available accommodation adjacent to escarpments with allochthonous slope sediments and were thus encroached by autochthonous slope sediments the variation which cannot be explained by the size difference in the platform top factory has been related to the difference in perimeter length for patch reefs with similar platform top production areas a more elongate patch reef inherits a longer perimeter and a proportionally smaller volume of allochthonous slope sediment per margin length will be transported to the flanks thus the more elongate patch reef intrinsically contained more sites within which autochthonous slope sediments developed digital outcrop modelling and numerical evaluation of the evolution of the patch reefs revealed the major differences in retrogradation motif the quantified variations in progressive decline of platform top area with height were confirmed by hypothetical decline curves for ellipse shaped carbonate systems for which aspect ratio ratio between length and width varied this mathematical model demonstrates that the progressive decline of the production area is highly sensitive to shape and can be used to numerically assess and predict the relative timing of drowning i e when the platform top production area becomes nil of retrogradational isolated carbonate platforms that are controlled by high accommodation wider implications can be surmised for highstand systems tracts and prograding carbonate systems for example for equally sized platforms with hypothetically similar carbonate factories and identical external forces the potential to prograde by platform top shedding is higher with a smaller aspect ratio because the shorter perimeter implies less accommodation space needing to be filled up to commence slope progradation clearly there are intrinsic effects of shape on the development of carbonate platform systems

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

submarine fan environment inferred from turbidite thickness distributions recent studies of turbidite bed thickness distributions have demonstrated power law as well as log normal statistical distributions the different distributions may reflect different fan processes and environments and therefore could be used as a quantitative method to help identify those environments including those devoid of sequential patterns the cumulative distributions of well known turbidite deposits spanning a range of interpreted fan subenvironments are used to illustrate the potential correlation between cumulative distribution and environments assuming that power law distributions may for some systems be the primary input signal one dimensional modelling allows semi quantitative characterization of the effects of different fan processes such as erosion and bed amalgamation environments indicative of different fan processes may be characterized based on the degree to which processes have acted as a filter to modify the assumed power law distribution systematically this model of the effect of fan processes on the power law distribution is used to help to account for bed thickness distributions observed in several field sites

visualizing lateral anisotropy in modern carbonates statistical stationarity is a key assumption for the many modeling techniques based on variograms and transiograms used for geostatistical reconstruction of the subsurface stationarity expresses the property that the rules of geometry and neighborhood in the model are translation invariant that is no directional change in either mean or variance is observed these criteria are met when the lateral arrangement of lithologic elements into a facies mosaic is isotropic the balance between isotropy and anisotropy is a defining statistic in the configuration of both real and modeled carbonate landscapes even a cursory look at a satellite image of a modern carbonate platform shows that gradients in environment and hydrodynamics cause radical departures from isotropy although reef forming organisms have changed through time we do not expect that ancient reef systems behaved any differently than today hence significant anisotropy should also be anticipated in the vertical and lateral arrangements of lithologies in the subsurface to maintain sufficient geologic realism it is paramount that process imitating and pattern replicating models alike be capable of honoring an expected degree of nonstationarity despite this need few studies exist that provide quantitative information to the reach and location of zones of geometric isotropy and anisotropy in carbonate systems let alone methods with which this property can be assessed in an effort to close this disjoint we develop a method for evaluating a modern pacific depositional system the saipan lagoon for which we have created a geographic information system stack consisting of mapped facies distributions and a seabed topographic model both at meter scale resolution by developing a lagged spatial metric based on the markov property of facies transitions we demonstrate that the degree of anisotropy is influenced by water depth the shallowest areas 5 m 16 ft of the platform interior tend to be anisotropic whereas areas at greater depth are isotropic this behavior suggests a possible extension to a genetic rule set that could be imparted to subsurface models based on the environment of deposition this marks an advance in the understanding and ultimately handling of geometric nonstationarity in models of carbonate depositional systems