integrating the uranium series and elemental diffusion geochronometers in mixed magmas from volcan quizapu central chile magma mixing is a ubiquitous process in silicic magmatic systems we present pre and post mixing time scales for a single magma mixing event associated with the 1846 1847 eruption of volcan quizapu we compare and contrast 226 ra 230 th crystal residence ages between the mixed lavas of the 1846 1847 effusive eruption and the largely homogeneous plinian dacite eruption of 1932 both eruptions are dominated by the same dacite magma whereas the ear lier eruption contains evidence for a single episode of mafic recharge and mixing the use of uranium series mineral separate dating on a mixed magma requires deconvolution of different crystal populations we present a four component mixing model for the crystal separates to obtain dacite derived plagioclase model ages as well as andesite derived recharge plagioclase ages plagioclase model ages average 3 6 ka for dacite derived plagioclase from the mixed 1846 1847 eruption 1 4 kyr older than average plagioclase model ages of the 1932 eruption suggesting that magma mixing and reheating led to some resorption of young crystal rims in the 1846 1847 magmatic episode and or that some growth of plagioclase rims occurred during the repose time of 86 years the andesite derived plagioclase residence ages are younger than the corresponding dacite derived plagioclase residence ages but they are still of the order of thousands of years in addition we use mg diffu sion in plagioclase to constrain time scales of magma mixing we show that the 1846 1847 eruption was triggered by large volume mafic recharge magma that mixed and mingled with the resident dacite within probably days to weeks of the ensuing eruption

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

on facies belts and facies mosaics holocene isolated platforms south china sea although the general criteria for recognition and environmental interpretation of different carbonate facies are well established a predictive understanding of the areal extent and spatial patterning of facies bodies and why they might organize into facies belts or facies mosaics is poorly constrained to explore patterns and process dynamics of facies on isolated carbonate platforms quantitative analysis of thematic maps derived from remote sensing images of 27 holocene atolls of the paracel and spratly chains in the south china sea explores variability within and among platforms on these systems most annular shelf margin reefs are less than 500 m wide on both chains inboard of the reefs reef sand aprons range up to 500 m spratlys and 1000 m paracels wide around individual platforms spratly chain sand apron widths are wider to north west whereas apron widths in the paracel chain are more symmetrical collectively data indicate log normal width exceedance probability distributions platform interior patch reefs include area exceedance probability distributions and gap size distributions lacunarity consistent within chains but distinct between the chains to understand the processes underlying distinct distributions simulations explored distinct growth scenarios results suggest that differences may represent distinct process classes proportional growth processes with multiplicative random effects reef sand aprons belts versus non linear size proportional growth of randomly aged and distributed elements patch reefs mosaics the probabilistically distinct sizes and spatial patterns of geomorphic elements within these general process classes are interpreted to represent variations on themes related to different impacts of tropical storms winter cold fronts and circulation in each chain the results highlight fundamentally different growth patterns impacting the sizes and distribution of facies belts and mosaics on isolated carbonate platforms because these bodies ultimately construct stratigraphy the themes could be applied to understand and predict variability in the architecture of subsurface reservoir analogues this article is protected by copyright all rights reserved

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

what matters for flow and recovery in carbonate gas reservoirs insights from the mature central luconia province offshore sarawak malaysia miocene carbonate reservoirs in central luconia offshore sarawak malaysia have been delivering gas for over 30 yr in this paper learnings from that period of production are used to understand the key drivers affecting flow during production and recovery optimization in existing fields as well as development decisions for new discoveries the large data set generated over more than 40 yr was analyzed in a consistent manner through a holistic database constrained by a stratigraphic framework to allow reservoir units to be compared like for like integrated knowledge base ikb concept carbonate reservoir heterogeneities impacting flow are grouped into horizontal heterogeneities argillaceous flooding layers and exposure related karst and vertical heterogeneities large scale architectural elements found especially along platform margins both types of heterogeneities control water ingress during production and influence the recovery mechanism argillaceous flooding layers can act as baffles holding back water rise during production or can form pressure compartments long lived fault bounded reef margins carbonate shoals islands and karsts can be vertical conduits for aquifer inflow platform shape and architecture impact column height and hence recovery efficiency additional drivers impacting recovery were found to be gas column height aquifer size and permeability pressure connection to neighboring fields and field development concepts all drivers identified impact decisions throughout the field life e g well count and design intervention capabilities evaluation and mitigation of early water breakthrough reservoir management selecting enhanced recovery methods and abandonment pressure the ikb allowed to derive big rules on what matters for flow which were used to decide on development strategies for greenfields in central luconia the presented outcomes can be extrapolated to comparable carbonate systems whereas the ikb approach can be adapted and applied to other mature basins and reservoir types where equally vast and historic data sets are awaiting to be used in the current era of digitalization

numerical forward modeling of carbonate platform dynamics an evaluation of complexity and completeness in carbonate strata abstract it is clear that carbonate strata are complex and incomplete but the nature and origins of the complexity and the origin and distribution of hiatuses remain poorly understood a three dimensional numerical forward model of carbonate platform systems has been used to investigate how variations in complexity and completeness arise in carbonate strata the model includes depth dependent carbonate production occurring as a stochastic mosaic of producing elements across a topographic surface it also includes depth dependent sediment erosion transport and deposition governed by a regional transport direction that can vary stochastically through time and by wave refraction that causes local variations in transport direction combined mosaic production and variable sediment transport create a complex distribution of prograding islands generating self organizing shallowing upward parasequences of variable thickness and variable lateral extent hiatuses occur throughout the parasequences not just at the base and top generated by nondeposition due to mosaic production and by erosional scour this erosion is triggered by variations in water depth and fetch distance created by complex island morphologies preserved strata represent between 15 and 60 of total elapsed time measured at a 2 ky resolution and much of the preserved thickness represents punctuated deposition with depositional events spanning only a few thousand years stratigraphic completeness depends on subsidence rate and sediment transport rate so that completeness generally increases with increasing subsidence rate and decreasing transport rate but shows a nonlinear relationship with subsidence rate this suggests that reliable estimates of completeness of ancient carbonate strata require more than knowledge of subsidence rate and sea level change particularly because the real situation is likely to be considerably more complex than represented in this model the stochastic production mosaic and stochastic variations in regional transport direction create complex strata whereas the self organizing island progradation process creates simpler ordered strata a combination of the two processes creates an intermediate level of complexity producing strata consisting of laterally impersistent parasequences with numerous erosion surfaces and complex stacking patterns and complex thickness distributions this has important implications for parasequence correlation in outcrop and the subsurface

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

siliciclastic foundations of quaternary reefs in the southernmost belize lagoon british honduras analyses of a closely spaced lattice of seismic profiles from the southernmost belize lagoon combined with logs of nearby drill holes reveal that the quaternary late pleistocene plus holocene reefs and carbonate sediments are growing on siliciclastic sediments which have an alluvial and delta like morphology the residual relief of these coastal plain deposits localized initial coral growth or an accumulation of calcareous skeletal material favored sites for these were elevations such as levees and bars of remnant channels and deltaic lobes

nature and stability of atoll island shorelines gilbert island chain kiribati equatorial pacific islands rimming pacific atolls typically form narrow low lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea level rise as these low islands form the only habitable land for many island nations understanding the character of shorelines and the rates and controls that operate to bring about changes is an issue of central importance the purpose of this study is to unravel the characteristics of coastal change on atoll islands of the gilbert island chain of the equatorial pacific nation of kiribati especially as they relate to autogenic shoreline processes and el nino southern oscillation variability integration of field observations differential global positioning system data historical aerial photographs and ultra high resolution remote sensing images demonstrates the nature spatial patterns and rates of change from 17 islands on maiana and aranuka atolls the results illustrate that between 2005 and 2009 ca 50 of the shorelines on these islands displayed a discernable shift in position some shorelines were accretionary at net rates up to ca 8 m year 1 and others were erosional up to ca 18 m year 1 long term net rates of change on maiana between 1969 and 2009 were lower than short term net rates measured between 2005 and 2009 both short term and long term observations illustrate some of the greatest change occur near terminations of the largest north south oriented islands associated with longshore movement of coarse sand and gravel direct hits by tropical depressions and marked seasonality factors interpreted as being essential in island growth and shoreline dynamics elsewhere do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics similarly observations over four years suggested that shoreline variability probably is not influenced directly by marked sea level change although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long term increase in the rate of sea level rise within this framework of global change local anthropogenic effects autogenic shoreline processes and el nino southern oscillation influenced wind and wave variability control many aspects of these dynamic shorelines these results provide quantitative insights into the character and variability of rates of shoreline change information essential for evaluating and mitigating the vulnerability of island nations such as kiribati

progradational holocene carbonate tidal flats of crooked island south east bahamas an alternative to the humid channelled belt model the stratigraphic record of many cratonic carbonate sequences includes thick successions of stacked peritidal deposits representing accumulation at or near sea level these deposits have provided insights into past palaeoenvironments sea level and climate change to expand understanding of carbonate peritidal systems this study describes the geomorphology sedimentology and stratigraphy of the tidal flats on the crooked acklins platform south east bahamas the crooked island tidal flats extend continuously for ca 18 km on the platformward flank of crooked island reaching up to 2 km across tidal flats include four environmental zones with specific faunal and floral associations and depositional characteristics i supratidal continuous supratidal crust and pavement ii upper intertidal with the mangrove avicennia germinans and the cyanobacteria scytonema iii lower intertidal with the mangrove rhizophora mangal and iv non vegetated heavily burrowed subtidal submarine these zones have gradational boundaries but follow shore parallel belts coring reveals that the thickness of this mud dominated sediment package generally is 2 m with depth to pleistocene bedrock gradually shallowing landward the facies succession under much of the tidal flat includes a basal compacted organic rich skeletal lithoclast lag above the bedrock contact suggesting initial flooding this unit grades upward into rhizoturbated skeletal sandy mud subtidal overlain by coarsening upward peloid foraminifera gastropod muddy sand reflecting shallowing to intertidal elevations cores from landward positions include stacked thin indurated layers with autoclastic breccia root tubules and fenestrae interpreted as supratidal conditions collectively the data reveal an offlapping pattern on this prograding low energy shoreline and these holocene tidal flats may represent an actualistic analogue for ancient humid progradational tidal flats nonetheless their vertical facies succession is akin to that present beneath channelled belt examples suggesting that facies successions alone may not provide unambiguous criteria for prediction of the palaeogeomorphology lateral facies changes and heterogeneity in stratigraphic analogues

equatorial carbonates an earth systems approach the hypothesis here is that an earth systems processes to products approach can be used to better develop predictive models for the recognition and assessment of under evaluated equatorial carbonate systems warm temperatures together with common clastic fresh water and nutrient influx as well as basinal settings in the equatorial tropics all have a major impact on carbonate deposition and diagenesis specific features of equatorial carbonate systems resulting from the combination of processes acting in the region include common occurrence of photoautotrophs and heterotrophs aragonitic and or calcitic dominant mineralogies lack of coated grains or aggregates common associations with clastics lack of associations with evaporites and diversity of platform types including oligophotic ones additional diagenetic characteristics include common micritization and bioerosion paucity of marine cements extensive vadose dissolution and concomitant phreatic cementation there is also significant replacement of aragonite by calcite in regions of meteoric groundwater flow common burial compaction and leaching as well as localized massive dolomitization via sea water or continental derived groundwater flow although equatorial carbonates fall into the warm water photozoan association many of the features described above are at odds with models derived from their warm water arid zone counterparts instead a range of the equatorial carbonate features show some similarities with those formed in cool waters and there have been difficulties separating carbonates from these two very different climatic regimes recommendations for the recognition of phanerozoic regional equatorial carbonate development are i a diversity of calcitic and or aragonitic photoautotrophs plus ii common elements of the heterozoan association plus iii independent for example isotopic evidence for warm temperatures 22 c additional indicators towards a humid equatorial setting are iv situation in appropriate palaeolatitudes v lack of association with sedimentary evaporites coated grain or aggregates and vi geochemical evidence for reduced marine salinity and or nutrient upwelling the aim is that this work will lead to greater awareness and understanding of equatorial carbonate systems and contribute to the development of globally predictive models to better understand past and likely future environmental change

rock fabric controls on pore evolution and porosity permeability trends in oolitic grainstone reservoirs and reservoir analogs although the general influence of rock fabric on porosity and permeability k within carbonates is well documented if and how pore evolution and k scatter quantitatively relate to depositional fabric remains poorly constrained this project empirically explores this uncertainty within oolitic grainstones from a range of geologic ages and diagenetic histories to understand depositional sediment pore relationships and how they can evolve with lithification integrating data from point counting digital image analysis nuclear magnetic resonance and core analysis of holocene pleistocene pennsylvanian and mississippian oolitic grainstones reveals quantitative relations among rock fabric pores and petrophysical parameters oolitic grainstones of similar sedimentology taken from distinct diagenetic scenarios display a unique combination of pore size shape spatial distribution and k character within each scenario pore attributes and k are correlated more closely with grain size sorting and type than with cementation and compaction collectively these results are interpreted to suggest that sedimentology controls the trends or variability within an oolitic succession but that diagenesis defines the absolute values of pore attributes and petrophysical parameters these findings suggest that petrophysical variability within oolitic reservoirs may closely follow sedimentologic trends which may be predictable within a stratigraphic framework

depositional facies analysis and modeling of the judy creek reef complex of the upper devonian swan hills alberta canada judy creek located in west central alberta is one of the largest reservoirs in the swan hills oil field judy creek is an isolated reef complex of the upper devonian swan hills formation this mature field has about 350 wells drilled and nearly 6000 m 19 685 ft of cores and thus provides a good database for depositional facies analysis and testing methods for integrating descriptive and quantitative data in facies modeling general depositional facies and sequence stratigraphy of judy creek have been studied quite extensively however no three dimensional numeric facies model has been built to guide the field development one of the objectives in constructing such a model for this study was to establish a close linkage between the facies depositional analysis and modeling as a matter of fact there have been significant disconnects between descriptive analysis and numeric modeling in the exploration and production depositional facies analysis has focused on conceptual understanding for prospect generation and reservoir delineation whereas facies modeling has emphasized data mining for field development in this study a method that integrates the spatial propensity from the depositional conceptual models and facies data from the wells is used to bridge the gap between the depositional analysis and stochastic modeling such integration has proven to be critical in building realistic subsurface models in judy creek because it helped improve the estimation of subsurface resources

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

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

bucket structure in carbonate accumulations of the maldive chagos and laccadive archipelagos peritidal platforms rimmed by reefs and raised reefs rimming deep lagoons are characteristic morphologies of the tropical carbonate factory their geometry contrasts sharply with the seaward sloping shelves of siliciclastic margins the structure has been compared to a bucket stiff reef rims holding a pile of loose sediment remote sensing data from the maldive chagos and laccadive archipelagos of the indian ocean show that ring reefs with bucket structure are the dominant depositional pattern from patch reefs of tens of meters to archipelagos of hundreds of kilometers in diameter that is over more than 4 orders of magnitude in linear size over 2 5 orders of magnitude the bucket structures qualify as statistical fractals exhibiting self similar patterns and size distributions following power laws however most regional or genetic subsets of the data follow lognormal distributions and small subsets of lagoon reefs exhibit exponential distributions seismic data and boreholes in the maldives indicate that the bucket has been a dominant depositional motif since the oligocene ecological and hydrodynamic studies on modern reefs suggest that the bucket structure is a form of biotic self organization the edge position in a reef is favored over the center position because bottom shear is higher and the diffusive boundary layer between reef and water thinner thus the reef edge has easier access to nutrients and is less likely to be buried by sediment the bucket structure reflects these conditions karst processes have accentuated the surface relief of the buckets particularly in the late quaternary

challenges to carbonate evaporite peritidal facies models and cycles insights from lower cretaceous stromatolite bearing deposits oncala group n spain abstract peritidal carbonate evaporite successions since they are developed in the transition between continental and marine realms provide essential keys for palaeobathymetric and palaeoclimatic interpretations as a result several facies models have been proposed to assist on the interpretation of ancient tidal flat deposits and peritidal successions have been extensively used for cyclicity analyses in this study well exposed lower cretaceous peritidal deposits oncala group cameros basin n spain are analysed and compared with the most commonly used present day analogues from shark bay the arabian gulf and the bahamas and with ancient peritidal successions providing their palaeoenvironmental and palaeoclimatic interpretation assessing the usefulness and limitations of the facies models and evaluating the suitability of these deposits for analysis of decimetre to metre scale cycles the studied peritidal deposits consist of thinly bedded to laminated dolostones dolomitic stromatolites stromatolite breccias flat pebble and edgewise breccias and calcite and quartz pseudomorphs after anhydrite nodules abundant resemblances of the peritidal deposits of the oncala group with those of shark bay including that they are largely composed of microbialites and intraclasts makes the peritidal deposits of the oncala group one of the best fossil analogues of this present day setting however the presence of anhydrite nodules indicates pervasive evaporite precipitation in the supratidal zone which is a feature that does not occur in supratidal flats of shark bay but is characteristic of arid sabkhas of the arabian gulf nevertheless the fact that carbonate evaporite tidal flats of the oncala group were laterally related with siliciclastic tidal flats with large freshwater input and broadly inhabited by dinosaurs suggests that anhydrites precipitated under less arid climates than those of the arabian gulf nowadays pointing to semiarid climatic conditions during deposition moreover the fact that peritidal deposits with anhydrite nodules were exclusively formed in a low subsidence area of the cameros basin suggests that the rate of accommodation space creation also played an important role in their development regarding the comparison with other fossil peritidal sediments the studied deposits show more abundant similarities with proterozoic and cambrian successions composed mainly of stromatolites microbial laminites and intraclasts than with other mesozoic peritidal deposits in which bioclasts and burrowing are usually more abundant this highlights the difficulties for assigning specific features to certain geological ages finally peritidal facies of the oncala group may change laterally and vertically to any other facies showing a patchy lateral distribution of facies and an unsystematic vertical stacking pattern the sedimentary features of the stromatolite breccia and thinly bedded to laminated dolostone facies do not allow their assignment to a unique tidal zone moreover sedimentary features indicative of subaerial exposure such as anhydrite nodules formed in the capillary zone occur within any of the carbonate facies and show limited lateral extent this results in a succession that cannot be clearly subdivided into subsequent shallowing upward cycles not even by using erosive surfaces or the anhydrite nodule layers as marker horizons of the upper part of the cycles because their limited lateral extent prevents reliable correlations similar composite lateral and vertical facies relationships have been documented both in the present day analogues and in ancient successions which suggests that this kind of facies relationships may be common in peritidal successions and highlights the caution that must be taken when trying to perform cyclicity analysis on them

stratigraphic framework of sediment starved sand ridges on a mixed siliciclastic carbonate inner shelf west central florida abstract seismic reflection profiles and vibracores have revealed that an inner shelf sand ridge field has developed over the past few thousand years situated on an elevated broad bedrock terrace this terrace extends seaward of a major headland associated with the modern barrier island coastline of west central florida the overall geologic setting is a low energy sediment starved mixed siliciclastic carbonate inner continental shelf supporting a thin sedimentary veneer this veneer is arranged in a series of subparallel shore oblique and to a minor extent shore parallel sand ridges seven major facies are present beneath the ridges including a basal neogene limestone gravel facies and a blue green clay facies indicative of dominantly authigenic sedimentation a major sequence boundary separates these older units from holocene age organic rich mud facies marsh which grades upward into a muddy sand facies lagoon or shallow open shelf seagrass meadows cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies ravinement or sudden termination of seagrass meadows the shelly sand facies grades upward to a mixed siliciclastic carbonate facies which forms the sand ridges themselves this mixed siliciclastic carbonate facies differs from the sediment on the beach and shoreface suggesting insignificant sediment exchange between the offshore ridges and the modern coastline additionally the lack of early holocene pre ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively radiocarbon dating has indicated that these sand ridges can form relatively quickly 1 3 ka on relatively low energy inner shelves once open marine conditions are available and that frequent high energy storm dominated conditions are not necessarily required we suggest that the two inner shelf depositional models presented open shelf vs migrating barrier island may have co existed spatially and or temporally to explain the distribution of facies and vertical facies contacts

geomorphology and sediment transport on a submerged back reef sand apron one tree reef great barrier reef back reef sand aprons are conspicuous and dynamic sedimentary features in coral reef systems the development of these features influences the evolution and defines the maturity of coral reefs however the hydrodynamic processes that drive changes on sand aprons are poorly understood with only a few studies directly assessing sediment entrainment and transport current and wave conditions on a back reef sand apron were measured during this study and a digital elevation model was developed through topographic and bathymetric surveying of the sand apron reef flats and lagoon the current and wave processes that may entrain and transport sediment were assessed using second order small amplitude stokes wave theory and shields equations the morphodynamic interactions between current flow and geomorphology were also examined the results showed that sediment transport occurs under modal hydrodynamic conditions with waves the main force entraining sediment rather than average currents a morphodynamic relationship between current flow and geomorphology was also observed with current flow primarily towards the lagoon in shallow areas of the sand apron and deeper channel like areas directing current off the sand apron towards the lagoon or the reef crest these results show that the short term mutual interaction of hydrodynamics and geomorphology in coral reefs can result in morphodynamic equilibrium

morphometric patterns in modern carbonate platforms can be applied to the ancient rock record similarities between modern alacranes reef and upper palaeozoic platforms of the barents sea abstract in recent years considerable research has been undertaken in order to gain a better quantitative understanding of morphometric patterns within modern carbonate depositional systems the industrial application of the scaling juxtaposition relationships derived from the modern to subsurface cenozoic carbonate reservoirs appears relatively straightforward given that many key biota are common to both however the direct application of modern sedimentary insight further back into the geologic rock record is more controversial given the enormous changes in the biota climate sea level water chemistry and so on that have taken place to justify such an approach we contend that similar morphometric patterns should be observed in both the modern and ancient data in the norwegian barents sea numerous seismic surveys have imaged upper palaeozoic carbonate buildups arranged in polygonal networks or reticular patterns these patterns are observed in both warm water photozoan and cool water heterozoan carbonate stratigraphies and are developed atop platforms founded on stable shelves in tectonically active settings and platforms developed over basinal evaporites gis mapping of multiple seismic horizons allows the palaeozoic reticulated morphology to be numerically compared to that mapped in alacranes reef from quickbird satellite imagery quickbird s metre scale resolution allows identification of subtle cross platform trends such as windward leeward differences in the packing density of ridge and pond complexes which can be correlated with the kilometre scale patterning extracted in the barents subsurface despite different controls and architecture the patterning of reticular networks is statistically inseparable between the two systems once the metre scale modern dataset is down sampled to seismic resolution whilst other controls cannot unequivocally be ruled out these results suggest that biotic self organisation is a fundamental driver of sedimentary patterns on carbonate platforms to our knowledge this is the first quantitative comparison of morphometric patterns from the modern and palaeozoic that clearly reveals similar patterns of self organisation for the depositional environments considered the findings suggest that juxtaposition rules facies proportions and scaling relationships extracted from the modern can successfully be applied to the ancient

facies heterogeneity at interwell scale in a carbonate ramp upper jurassic ne spain abstract the well exposed upper kimmeridgian carbonate ramp near arroyo cerezo iberian basin eastern spain provides an excellent analog to stratigraphically equivalent subsurface reservoirs such as the carbonate ramps of the arab d of the middle east and the smackover of the gulf of mexico critical questions regarding interwell scale heterogeneity and correlation motifs for low angle ramp systems can be addressed using continuous exposures that encompass a full range of inner to outer ramp facies outcrops in this area provide a complete exposure of the ramp succession in depositional dip direction at arroyo cerezo a 40 m thick and 1 3 km long dip oriented continuous outcrop has been studied lithofacies and bounding surfaces have been mapped on a continuous photomosaic to build a detailed 2d cross section complemented by five stratigraphic sections 300 m apart and petrographic analysis the reconstructed section shows the facies transition from relative proximal to distal carbonate ramp settings carbonate facies associations are grouped according to the dominant carbonate types buildup dominated systems and coated grain dominated systems detailed mapping of facies and bounding surfaces documents distinct ramp depositional units with downdip facies changes occurring within the 1 3 km length of the outcrop the arroyo cerezo outcrop indicates that the ramp facies continuity when based on a 5 10 km distance well log correlation is mostly apparent use of detailed spatial and temporal analysis of high quality outcrop analogs promotes more realistic models for understanding the interwell meter scale heterogeneity and the scale of these depositional heterogeneities although being below resolution of subsurface tools governs in fact along with diagenetic modifications the fluid flows within a reservoir the scale of these stratigraphic heterogeneities needs to be considered in order to optimize and enhance hydrocarbon production and last recovery

the transient nature of the empty bucket model of reef sedimentation abstract the geometry of modern reefs has been likened to an empty bucket with the narrow reef rim comprising the container pail that encloses the water filled bucket while the analogy is valid the assumption that this constitutes a final geometry is not examples from the indian pacific and atlantic oceans individually and collectively demonstrate current filling of the lagoons by reef perimeter sand aprons since sea level only approximated its present position 3 to 6 ky ago it follows that the observed extent of modern highstand lagoon filling is minimal if the filling process was to continue unabated the result would be a flat topped bank but during the pleistocene low stands of sea level aborted the filling process extrapolating these relationships to the geologic record suggests that the empty bucket model of unfilled reef lagoon space is greatest during icehouse high frequency glacial fluctuations of sea level alternatively filled buckets in which cycle thickness approximates accommodation space are probably largely restricted to greenhouse time intervals the co occurrence of quaternary high amplitude frequency sea level changes with rapidly growing scleractinian corals probably enhanced the occurrence of empty bucket morphologies

seascape metrics of shelf margin reefs and reef sand aprons of holocene carbonate platforms shelf margin reefs and reef sand aprons are important geomorphic and facies elements associated with many isolated platforms today and in the stratigraphic record although it is generally appreciated that shelf margin reefs and reef sand aprons have formed at or near breaks in slope at the rims of platforms throughout geologic time possible environmental causes for variation in their sizes are not well understood to provide better constraints for assessing possible reasons for such variability in ancient systems this study relates local regional and global patterns of variation in the seascape attributes of holocene shelf margin reef and reef sand apron systems to a suite of potential environmental controls landsat data from more than 60 isolated carbonate platforms and atolls from the caribbean sea indian ocean south pacific ocean central pacific ocean south china sea and indonesian seas were investigated by digitization and spatial analysis of facies belts and compared with regional environmental parameters the results of this analysis suggest that 1 reefs cover from 1 to 55 of the spatial extent of lithotopes on platforms mean 20 whereas reef sand aprons represent between 0 and 65 mean 20 2 the spatial extent of reefs is inversely related to platform size but reef sand aprons show no comparable trend 3 widths of reefs and reef sand aprons are variable within and among platforms but widths from all platforms and from platforms within different regions are characterized by log normal size frequency distributions 4 widths of these facies belts vary as a function of environmental factors such as swell period swell height tidal amplitude latitude and margin orientation relative to direction of wind and wave approach these data indicate the presence of trends in widths of facies belts within different regions that correlate with regional oceanographic patterns nonetheless marked variability is evident on individual platforms among platforms within each region and globally these variations are not related to any of the parameterized environmental variables this observation are interpreted to reflect the influences of unknown and in some cases unknowable spatial and historical contingencies such as the depth to bedrock character of earlier holocene sea level change or changes in physical oceanographic state waves or tides the collective influence of these parameters each of which individually may have the potential to invoke a deterministic response may be reflected in reef and sand aprons with log normal width frequency distributions interpreted to reflect multiplicative random effects collectively however these results suggest that accurate a priori prediction of the details of the sizes of analogous facies bodies in the stratigraphic record may be impossible especially in the deep geologic past where biologic and physical controls are even less well constrained

facies sequences on a carbonate ramp the carboniferous limestone of south wales during early carboniferous times a major sea level rise led to the development of an extensive carbonate ramp over what is now south wales differential subsidence and sea level changes resulted in distinctive facies sequences in the ramp succession and a model is offered which recognizes three distinct geomorpho tectonic settings inner mid and outer ramp the inner ramp zone occurs in the more landward part of the province and was an area undergoing little or no subsidence the sequence is dominated by oolitic grainstones and peritidal limestones representing shoal and back shoal environments the peritidal units are transgressive deposits consisting of stacked asymmetrical shallowing up cycles the sequence contains many subaerial breaks and tectonic uplift resulted in base level changes and fluvial incision the mid ramp zone sequence is intermediate in thickness between the inner and outer ramp successions and consists mainly of bioclastic limestones deposited below fairweather wave base sedimentation periodically exceeded sea level rise and subsidence and regressive progradational oolitic sand bodies developed the thickest of which are stacked units with up to four individual sand bodies storm processes were of major importance in this setting the outer ramp zone is represented by a thick sequence of muddy bioclastic limestones deposited below storm wave base and major waulsortian reef mounds also developed none of the shallowing phases seen in the other ramp zones can be detected in this sequence subsidence and eustatic sea level rise seem to have been the major controls on deposition but the recognition of eustatic sea level falls is difficult the detailed facies model for ramp carbonates presented here may be applicable elsewhere in the geological record

physical oceanographic influences on sedimentology of reef sand aprons holocene of aranuka atoll kiribati equatorial pacific abstract depositional facies are the net product of a complex set of processes that impact sediment supply and transport in geomorphic systems although the general facies motifs of many isolated platforms throughout the geologic record are well documented the details of geomorphological and sedimentological patterns and the physical oceanographical processes that can impact sedimentological differentiation are less well constrained on these platforms accumulations of reef associated debris in platform top reef sand aprons can form expansive geomorphic elements hosting prolific hydrocarbon reserves in geologic analogs to better understand the nature and scale of reef sand apron accumulations this project integrates remote sensing field petrographical and granulometrical characterization of surficial holocene sediments with physical oceanographical observations and modeling of aranuka atoll republic of kiribati in the western equatorial pacific results illustrate trends in hydrodynamics geomorphology and sedimentology from the platform margin to the platform interior current meter data and modeling illustrate how the tides 2 5 m spring tide amplitude modulate wave energy open ocean annual average swell height of 2 m distal swell can be larger to produce dominant on platform flow speeds up to 90 cm s on the northern reef sand apron the strongest currents there appear to be impacted by southward propagating waves related to fronts that pass thousands of kilometers north of the atoll not local wind generated waves these hydrodynamical influences are interpreted to have led to the development of the expansive northern reef sand apron 2000 m wide the southeastern apron with currents that reverse with the tides includes a distinct narrower sand apron 1500 m wide concomitantly the hydrodynamical patterns and platformward decrease in energy across the reef sand apron coupled with changes in biota are interpreted to control variability in sedimentary structures bottom types and sediment attributes sediment near the margin on the reef sand apron contains coral and red algal rich coarse sand and gravel passing to foraminifera rich medium to coarse sand toward the lagoon the lagoon includes even finer sediment chiefly fine and very fine sand and patch reefs collectively the results of this study illustrate that selective winnowing differentiation of sediment size type and sorting and nature and size of geomorphic elements ultimately are linked to the hydrodynamical patterns across the platform the sedimentological depositional porosity and permeability and geomorphic facies bodies variability and the processes active on this reef sand apron provide a general conceptual model that may be applicable to predict trends in ancient reservoir analogs

assessing controls on isolated carbonate platform development in central luconia nw borneo from a regional 3d seismic facies and geomorphology investigation

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods

ra partitioning between phlogopite and silicate melt and 226ra ba 230th ba isochrons in this study we experimentally determine phlogopite melt partition coefficients of ra and other trace elements in a lamproitic system this work was achieved using an analytical technique la icp ms with low detection limits 0 01 fg permitting the measurement of the very low ra concentrations feasible in experiments 1 ppb d ra phlogopite melt was determined to 2 28 0 44 and 2 84 0 47 in two experiments the ratio d ra d ba is around 1 6 the compatibility of ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large xii coordinated interlayer site of phlogopite a re evaluation of d ra and d ra d ba for magmatic minerals containing appreciable ra yields d ra mineral melt ranging from 2 6 for phlogopite down to 2 3 10 5 for pyroxenes and d ra d ba mineral melt from 4 for leucite to 2 10 2 for orthopyroxene the influence of melt composition on d ra d ba is less than 10 all investigated minerals have different d ra d ba strongly fractionating ra from ba thus for magmatic systems 226 ra ba in the various minerals is not constant these minerals do not form a straight line in the 226 ra ba 230 th ba system at the time of crystallization and thus there is no 226 ra ba 230 th ba isochron at t 0 226ra 230th ba mineral dating is thus applicable only to model ages calculated from mineral glass pairs with known d ra