seismic detection of the lunar core despite recent insight regarding the history and current state of the moon from satellite sensing and analyses of limited apollo era seismic data deficiencies remain in our understanding of the deep lunar interior we reanalyzed apollo lunar seismograms using array processing methods to search for the presence of reflected and converted seismic energy from the core our results suggest the presence of a solid inner and fluid outer core overlain by a partially molten boundary layer the relative sizes of the inner and outer core suggest that the core is 60 liquid by volume based on phase diagrams of iron alloys and the presence of partial melt the core probably contains less than 6 weight of lighter alloying components which is consistent with a volatile depleted interior

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

a model for the thermal and chemical evolution of the moon s interior implications for the onset of mare volcanism crystallization of the lunar magma ocean creates a chemically stratified moon consisting of an anorthositic crust and magma ocean cumulates overlying the primitive lunar interior within the magma ocean cumulates the last liquids to crystallize form dense ilmenite rich cumulates that contain high concentrations of incompatible radioactive elements the underlying olivine orthopyroxene cumulates are also stratified with later crystallized denser more fe rich compositions at the top this paper explores the chemical and thermal consequences of an internal evolution model accounting for the possible role of these sources of chemical buoyancy rayleigh taylor instability causes the dense ilmenite rich cumulate layer and underlying fe rich cumulates to sink toward the center of the moon forming a dense lunar core after this overturn radioactive heating within the ilmenite rich cumulate core heats the overlying mantle causing it to melt in this model the source region for high tio2 mare basalts is a convectively mixed layer above the core mantle boundary which would contain small and variable amounts of admixed ilmenite and kreep this deep high pressure melting as required for the generation of mare basalts occurs after a reasonable time interval to explain the onset of mare basalt volcanism if the content of radioactive elements in the core and the chemical density gradients above the core are sufficiently high but within a range of values that might have been present in the moon regardless of details implied by particular model parameters gravitational overturn driven by the high density of magma ocean fe rich cumulates should concentrate high tio2 mare basalt sources and probably a significant fraction of radioactive heating toward the center of the moon this will have important implications for both the thermal evolution of the moon and for mare basalt genesis

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

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

magnetic study of large apollo samples possible evidence for an ancient centered dipolar field on the moon abstract we present new rock magnetic and paleomagnetic results obtained from seventeen apollo samples measurements of the magnetic properties of the samples confirm that the magnetic properties of lunar rocks are dominated by about 0 1 wt of multidomain feni grains the ferromagnetic mineral assemblage is to the first order the same in all lunar lithologies with higher concentration in basalts than in anorthosites some of which are diamagnetic impact processing leads to an increase of the ferromagnetic content out of the seventeen samples eleven show at least one stable component of natural remanent magnetization in some cases this magnetization may be a magnetic contamination however five basalt samples have a component of magnetization that may have recorded a lunar paleofield acquired on the moon for these samples plus two similar samples from a previous study using the rock magnetic fabric as a paleohorizontal proxy paleoinclinations can be estimated from the paleomagnetic data these paleoinclinations are best explained with a dipolar field and a magnetic paleopole located at 75 n therefore our results suggest the existence on the moon at least between 3 8 and 3 3 ga of a dipolar field whose axis is close to the present day rotation axis of the moon the estimated surface field intensities of several tens of t support previous result that the moon had a dynamo field in the past and the proposed paleofield geometry suggests that this dynamo was centered on the lunar present day rotation axis

re examination of the lunar magma ocean cumulate overturn hypothesis melting or mixing is required abstract there is a long standing hypothesis that the last fraction of the lunar magma ocean crystallized into a layer of dense ti rich cumulate minerals at shallow depths 100 km early in the moon s history many questions remain about the stability of these high ti cumulates it has been suggested that the cumulates subsequently sank deep into the moon because of gravitational instability but high ti material is required at shallower depths by 3 5 ga to create the high ti mare basalts and picritic glasses the high ti material may have re erupted from depth or some or all of it may have remained at shallow depths throughout lunar history data on phase stabilities bulk compositions densities and temperatures of melting and crystallizing in addition to results from numerical modeling suggest that the high ti cumulates would sink only under highly specific conditions five scenarios for sinking high ti cumulate materials are examined and only two are found plausible in particular it is found that simple sinking of solidified high ti cumulates is unlikely because the temperature at which the cumulates solidify is low and viscosity under these conditions is very high it is however possible that high ti cumulates mixed with a substantial fraction of olivine would have viscosity low enough to allow them to sink as solids further because clinopyroxene and ilmenite melt in a ratio of 2 1 remelted high ti cumulates would be negatively buoyant and sink as liquids percolating downward through the underlying mantle and beginning to recrystallize ilmenite at 200 km depth making a hybrid heterogeneous mantle

large scale carbonate platform development of cay sal bank bahamas and implications for associated reef geomorphology abstract the bahama archipelago consists of an arcuate chain of carbonate platforms average water depths on the platform tops such as the great bahama bank gbb are typically 10 m or less with coral reef rimmed margins thick sediment accumulations and the frequent occurrence of islands there are however exceptions for example cay sal bank csb a little studied detached bahamian carbonate platform with depths ranging from 30 to 7 m is only slightly deeper than the gbb but devoid of islands lacks platform margin coral reefs and holds little sediment on the platform top the platform is incipiently drowned csb is interesting as it is conspicuously larger 6000 sq km than other incipiently drowned platforms in the region such as serranilla bank 1100 sq km and the cat island platform 1500 sq km field and remote sensing data are assembled to provide insight into the sedimentology and geomorphology of the csb the influence of ocean climate regional hydrodynamics and holocene flooding history are investigated to understand why platform margin coral reef growth on csb has been unable to keep pace with holocene sea level rise a decade of regional sea surface temperature data for the bahamas report csb to be situated in the same ocean climate regime as gbb temperature cannot explain the platform s different morphologies the florida current has been evoked as a possible reason for the immature development of platform top processes on the csb but numeric modeling suggests its influence to be restricted to the deep flanks of the bank further sediment distribution on csb including infill patterns of karst depressions suggest trade winds easterlies to drive platform top hydrodynamics by assembling a satellite derived bathymetry map it can be shown that csb flooded earlier and at relatively higher rates of holocene sea level rise than its neighboring platforms flooding history is identified as the most feasible explanation for the atypical morphology of the csb by contrasting the present day morphology of the csb and the gbb the work emphasizes how subtle differences in relative sea level history can influence the growth of platform margin coral reefs features that in turn can conspire to set even closely neighboring carbonate platforms on divergent paths with regard to the development of marine landforms this insight is relevant to interpreting the morphological diversity of carbonate platforms in the modern ocean and in the rock record

asymmetric thermal evolution of the moon 1 the moon possesses a clear dichotomy in geological processes between the nearside and farside hemispheres the most pronounced expressions of this dichotomy are the strong concentration of radioactive heat sources on the nearside in a region known as the procellarum kreep terrane pkt and the mare basaltic lava flows that erupted in or adjacent to this terrane we model the thermochemical evolution of the moon using a 3 d spherical thermochemical convection code in order to assess the consequences of a layer enriched in heat sources below the pkt on the moon s global evolution we find that in addition to localizing most of the melt production on the nearside such an enriched concentration of heat sources in the pkt crust has an influence down to the core mantle boundary and leaves a present day temperature anomaly within the nearside mantle moderate gravitational and topographic anomalies that are predicted in the pkt but not observed may be masked either by crustal thinning or gravitational anomalies from dense material in the underlying mantle our models also predict crystallization of an inner core for sulfur concentrations less than 6 wt

facies geometry and growth phases of the valdorria carbonate platform pennsylvanian northern spain the 14 km wide valdorria outcrop pennsylvanian northern spain is one of the few examples of entirely exposed flat topped and high relief carbonate platforms reported in the fossil rock record laterally and vertically traceable stratal patterns expose three phases of growth phase i is a 430 m thick platform to slope succession that prograded over 6 km and is dated as early bashkirian akavasian askynbashian phase ii aggraded and prograded exhibiting 180 m thickness of cyclical platform top deposits dated as late bashkirian asatauian phase iii is a mound shape structure that developed over the platform top of phase ii as a new phase of platform nucleation it is 535 m thick and 2 km wide and dated as late bashkirian asatauian transition interval the observed changes of growth styles during platform evolution from a prograding to an aggrading prograding system and a rapid aggradational phase are inferred to be controlled by flexural subsidence in the active cantabrian foreland basin at the variscan orogenic front the metre scale shallowing upward cycles of the platform top are most probably due to glacioeustasy as evidenced by well recorded subaerial exposure surfaces superimposed on subtidal deposits and by a stratal pattern recurrent in a short interval of about 160 kyr observations of outcropping bashkirian cyclothems in an isolated carbonate system devoid of siliciclastic input are relevant for a better understanding of the impact of high frequency sea level fluctuations on the carbonate factory moreover progradation of the platform margin during phase i reaches a rate of 2500 m myr and 1810 m myr during phase ii rates that are high when compared to other pennsylvanian examples the aggradation rate of 447 m myr calculated for late bashkirian transition interval phases i and ii uncorrected for compaction missing beats and erosion is uncommonly high in comparison to coeval pennsylvanian examples the platform exhibits a self nourishing prograding microbial boundstone dominated slope thus the slope shedding model applies well to valdorria however phase ii recorded eustatic variations able to inhibit the slope microbial boundstone factory during low sea level stands this is marked by common slope red stained breccias synchronous to platform top subaerial exposure phases contrarily periods of relative high sea level and rapid subsidence in phase iii registered a greater development of cemented microbial boundstone these observed partly opposing relationships of sea level stands shedding modes and slope architecture provide an improvement of the currently used slope shedding model the overall architecture of the valdorria outcrop compares well with that of other contemporaneous platforms such as sierra del cuera and bolshoi karatau valdorria shares the high relief and flat topped steep slopes cyclothemic patterns and occurrence of karst features with the pricaspian basin platforms tengiz karachaganak and kashagan with minor variations in facies distribution of the internal platform furthermore the continuous seismic scale outcrop of valdorria together with its isolated setting and asymmetrical growth makes it an additional good candidate for potential subsurface analogues of hydrocarbon bearing systems

the extent and patterns of sediment filling of accommodation space on great bahama bank abstract great bahama bank gbb is the modern example of a flat topped isolated carbonate platform it is a major modern location of carbonate deposition that stands behind much of the understanding of modern processes of carbonate sedimentation serves as a training venue for academia and industry is the basis for numerous geological models and is commonly used as a reservoir analog gbb also provides valuable insight into the extent and patterns of sediment fill of accommodation space atop an isolated carbonate platform satellite imagery landsat tm and etm and an extensive set of water depth measurements n 5 723 were used to map bathymetry across gbb and derive a digital terrain model dtm analyzing the extent patterns and nature of sediment fill of accommodation space was facilitated by partitioning a depositional facies map on the basis of the dtm to show that 18 of accommodation on the gbb is overfilled and filled emergent to 1 5 m water depth 52 is underfilled 1 5 to 6 0 m and 30 is unfilled 1 5 m water depth and therefore the greater part of available accommodation 88 000 km2 remains incompletely filled with sediment areas of filled accommodation mostly extend platformward from the western coastlines of islands which in turn are preferentially distributed along the eastern windward margin of the gbb seventy percent of sediment in the areas of filled accommodation is rudstone high energy grainstone grainstone and mud poor packstone although dominated by grainstones 45 since it occupies so much space 55 000 km2 the underfilled sector also contains the most heterogeneous facies mosaic and by definition therefore the greatest and most complex lateral facies variations although islands are numerous n 1 430 they occupy only 8 or 8 700 km2 of the platform top despite their small proportional occupancy of the platform islands play a direct role in the accumulation of muddy fabrics and exert a sphere of influence over the character of sedimentation for many tens of kilometers from their coastlines further since islands represent the portion of the bank where accommodation has been overfilled their rarity emphasizes the challenges that such a large platform faces in filling accommodation space even given the diverse grain factories producing carbonate sediment mud precipitation through whitings ooids and reefs along the platform margins skeletal sediments and nonskeletal grains such as fecal pellets peloids and pelletoids two factors can be evoked to explain the inability of gbb to fill accommodation space first falling sea level during the pleistocene appears to have repeatedly aborted the filling process by analogy it will not be able to do so in the holocene either a situation exasperated by the second factor which is that most of the holocene gbb particularly areas away from islands presently lack any appreciable filling instead facies analysis suggest reduced sedimentation and enhanced cementation through regional mapping the work delivers a platform wide assessment of how accommodation is filled and the facies responsible for the filling amongst other trends by highlighting how the thickest accumulations of holocene sediment are skewed to the windward margin of the gbb and related to the presence of islands whereas the thinner accumulations which dominate the platform interior and are more grainy but also more heterogeneous than the thicker deposits these data might contain useful guidelines as to how depositional cycles might vary laterally in ancient systems

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

the magma ocean concept and lunar evolution the model of lunar evolution in which the anorthositic plagioclase rich oldest crust of the moon is formed over a period of 300 myr or less by crystallization as it floats on a global ocean of magma tens or hundreds of km thick is examined in a review of petrological and theoretical studies consideration is given to the classification of lunar rocks the evidence for primordial deep global differentiation constraints on the depth of the molten zone the effects of pressure on mineral stability relationships mainly liquid vs mainly magmifer ocean models and the evidence for multiple ancient differentiation episodes a synthesis of the model of primordial differentiation and its aftereffects is presented and the generalization of the model to the earth and to mars mercury venus and the asteroids is discussed

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

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

facies model on the modern isolated carbonate platform in the xisha archipelago south china sea abstract the xuande atoll with a discontinuous reef rim caused by platform drowning is a typical ellipse isolated platform on the northern slope of the south china sea based on the data of drilling holes the analysis of surface sediments and high resolution acoustic data six sedimentary facies are identified in the xuande atoll including reef outer slope reef front reef flat aeolianite sand island back reef slope and lagoon facies map shows that the elevated reef rimmed margins with islands are more noticeable on the windward of the platform with an elevated and discontinuous reef rimmed margin as well as coarse grained sediment in the interior platform xuande can serve as a case of a leaky bucket atoll which is characterized by initially drowning scenarios the facies architecture of the xuande atoll is evidently influenced by complex and interacting parameters including antecedent topography sea level wind driven currents water depth and tectonic subsidence different controlling factors exist in the drowning of the windward and leeward sides of the platform margin the study of modern depositional settings in the xuande atoll will provide insight on predictions for ancient carbonate provinces

formation and evolution of a lunar core from ilmenite rich magma ocean cumulates abstract in the absence of comprehensive seismic data coverage the size composition and physical state of the lunar core are still debated it has been suggested that a dense ilmenite rich layer which originally crystallised near the top of the lunar magma ocean may have sunk to the centre of the moon to form either an outer core surrounding a small metallic inner core or a complete core if the lunar metallic iron content is insignificant here we study the formation gravitational stability and thermal evolution of both an ilmenite rich outer core and a full ilmenite rich core using a two dimensional cylindrical thermo chemical convection model gravity acceleration in the lunar mantle decreases quickly with depth since the gravity acceleration directly influences the buoyancy of materials the low gravity acceleration near the centre was explicitly taken into account core formation and evolution were investigated by assessing the effects of varying two parameters the mg density and the internal heat production of the ilmenite rich layer varying these parameters changes the compositional and thermal buoyancy of the dense layer models show that a stable ilmenite rich outer core may indeed have formed in the lunar interior and that its density depends on the internal heating in and the mg of the ilmenite rich layer furthermore the sharpness of the core mantle boundary is shown to depend on the internal heat production in the ilmenite rich material surprisingly a higher internal heat production results in a sharper core mantle boundary and a higher ilmenite content in the core this is caused by lower viscosities as a result of higher temperatures although maximum core temperatures vary between different models by 700 1000 k around 2 gyr after the start of the models present day estimates vary by only about 350 500 k further narrowing of the range of internal heating values is essential for a better determination of both the present day lunar core temperature and its physical state

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

the paradox of tropical karst morphology in the coral reefs of the arid middle east despite differences in reef growth between the arabian gulf and the red sea a common distinctive pattern of polygonal sills surrounding ponded depressions consistently occurs in shallow water viewed from a satellite these seafloors are reticulated and maze like despite little current rainfall this patterning is best explained by karst dissolution of limestone during periods of lower sea level this is a paradox since such fine scale karstification is confined to areas with considerably more precipitation than currently observed in arabia we resolve this apparent contradiction by developing a pleistocene holocene chronology of sea level and climate for the red sea and arabian gulf and through the use of pattern analysis and computer simulation reveal the mechanism of formation for these structures we demonstrate that this patterning can be taken as a quaternary signature of paleohumidity in the now hyperarid red sea and arabian gulf

self organizing models of shallow water carbonate accumulation abstract the stratigraphic record of shallow water carbonate accumulation is remarkably complex the combination of a wide variety of facies elements the great abundances of individual elements that constitute even relatively short stratigraphic sections and the possibilities of both high and low frequency organization of those facies into hierarchical stratigraphic units has made shallow water carbonates one of the most closely studied and hotly debated of all sedimentary systems carbonate stratigraphy has until now been analyzed largely through a combination of field observations and simple one and two dimensional forward models of deposition herein we demonstrate the use of a cellular model of carbonate accumulation that displays emergent self organizational behavior the utility of such a model resides in its ability to generate stratigraphic patterns both vertically and spatially that are mathematically and geometrically similar to those encountered in natural systems importantly these cellular models reproduce significant components of natural stratigraphic complexity through the use of a single simple numerical algorithm it is the application of that linking algorithm across a cellular grid that produces emergent stratigraphic organization specifically simulations consisting of two modeled lithologies produce vertical records of facies composition that exhibit thickness frequency distributions similar to the negative exponential forms reported from numerous stratigraphic sections likewise area frequency distributions across simulated depositional surfaces are similar to those found to describe facies mosaics buildups patch reefs mud banks on modern carbonate platforms as such this stochastically driven cellular model produces successful simulations of shallow water carbonate stratigraphy and strongly indicates that the application of this and similar models potentially provides both a novel and an important avenue of investigation into the complex and dynamic carbonate depositional environment

neutral buoyancy of titanium rich melts in the deep lunar interior the absence of very deep moonquakes implies that the lower mantle of the moon is partially molten an analysis of the density range of lunar melts at high pressures suggests that only titanium rich melt is neutrally buoyant deep within the moon

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

bed thickness structure of multi sourced ramp turbidites devonian brallier formation central appalachian basin turbidite bed thickness frequency relationships within the upper devonian brallier formation of the central appalachian basin follow the form of a negative exponential distribution the presence of such distributions indicates that deposition occurred via poisson like stochastic processes wherein initiation of turbidite formation was largely independent of rates of sediment accumulation along shelf margins autocorrelation analysis of bed thicknesses from these sections likewise strongly supports an interpretation of temporally stochastic deposition autocorrelograms of turbidite sandstone and inter turbidite shale thicknesses fail to fall outside the expected range of a random arrangement of bed thickness consideration of the brallier formation relative to previously reported analyses of turbidites from other depositional systems indicates that the form of thickness frequency relations within any turbidite system is strongly dependent upon gross morphology of the depositional system as such multi sourced ramp turbidites are in this case found not to exhibit fractal scaling in their bed thickness relationships but rather an exponential form of scaling common to many sedimentary systems

an early lunar core dynamo driven by thermochemical mantle convection although the moon currently has no internally generated magnetic field palaeomagnetic data combined with radiometric ages of apollo samples provide evidence for such a magnetic field from 3 9 to 3 6 billion years gyr ago1 possibly owing to an ancient lunar dynamo1 2 but the presence of a lunar dynamo during this time period is difficult to explain1 2 3 4 because thermal evolution models for the moon5 yield insufficient core heat flux to power a dynamo after 4 2 gyr ago here we show that a transient increase in core heat flux after an overturn of an initially stratified lunar mantle might explain the existence and timing of an early lunar dynamo using a three dimensional spherical convection model6 we show that a dense layer enriched in radioactive elements a thermal blanket at the base of the lunar mantle can initially prevent core cooling thereby inhibiting core convection and magnetic field generation subsequent radioactive heating progressively increases the buoyancy of the thermal blanket ultimately causing it to rise back into the mantle the removal of the thermal blanket proposed to explain the eruption of thorium and titanium rich lunar mare basalts7 plausibly results in a core heat flux sufficient to power a short lived lunar dynamo

biological mediation of stochastic peritidal carbonate accumulation exponential thickness frequencies of peritidal carbonate units in the lower ordovician kindblade and west spring creek formations at ardmore oklahoma are readily interpreted in a context of probabilities of upsection transition from one lithology to another these largely reflect poisson random processes of deposition from suspended load traction load and microbialitic accumulation although grainy to muddy particulate and cyanobacterial elements exhibit nearly equal ranges of unit thickness carbonate generation and or entrapment via algally mediated processes was less likely to lapse and therefore led to lower probability of transition to some other sediment type the mean thickness of microbially bound units is roughly double those from the physical transport and deposition of particulate material greater persistence of algal accumulation probably related to intrinsically higher biologically induced rates of carbonate precipitation and or binding by cyanobacteria stratigraphic intervals between successive occurrences of suspended load traction load and microbial units are also closely approximated by exponential frequency distributions for which regression slopes define probabilities of upsection recurrence of a particular sediment type values for grainy and algal carbonates are similar and are nearly twice that of muddy suspended load units although biological processes resulted in significantly lower transition probabilities for thrombolitic bioherms and cryptalgal laminites spatial dominance of carbonate mud across the region led to higher rates of stratigraphic recurrence and a volumetric dominance of muddy lithologies in the ardmore sequence poissonian distributions of unit stratigraphic duration and recurrence suggest a significant component of haphazard variation in the type and amount of accumulated carbonate sediment if deposition was influenced by extrabasinal forcing such control must have been nearly random in both secular and spatial dimensions of water depth change stratigraphic durations and recurrences in this sequence more closely reflect the inherently stochastic nature of carbonate accumulation in epicratonic platformal settings than any influence of rhythmic eustatic forcing

controls on morphology and sedimentology of carbonate tidal deltas abacos bahamas abstract although the physical processes controlling siliciclastic shoal bodies are reasonably well understood the sedimentary processes that shape carbonate tidal shoal systems are poorly constrained the tidal deltas of the northwestern abaco islands bahamas provide a unique opportunity to explore the relationships between physical and sedimentary processes in a variety of sizes and shapes of tidal deltas the length of tidal deltas range in size from 350 m to 2 km from the inlet to the termination of the delta lobe and shoal crests consist primarily of well sorted ooid sands mean grain size between 400 and 500 m mcmanus sorting factor 0 70 coated grains are rare off the shoals and sorting decreases with distance from the shoal crests velocities in the rocky inlets can exceed 2 m s in the daily tidal cycles and the systematic distribution of grain types reflects tidal velocity variations areas with the highest velocities 0 80 m s correspond to hard rocky bottoms with some skeletal grains these regions of elevated velocities are focused within the inlets where jets of high velocity currents form during each tidal cycle these current jets extend outward from the inlet throat and velocities decrease outwards as the flow disperses velocities between 40 and 80 cm s occur in the regions with abundant ooids and peloids are most abundant in the lowest velocity regions the results of this study illustrate a clear relationship between quotidian physical processes and their geomorphic and sedimentologic products in a carbonate system in this context carbonates appear to share many geomorphic similarities with siliciclastic analogs the results represent an important step beyond qualitative facies interpretations and towards quantitative specified environmental and sedimentologic characterizations for carbonate systems

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

diversity in the geomorphology of shallow water carbonate depositional systems in the saudi arabian red sea article i nfo coral reefs and their associated accumulations of carbonate sediment adopt particularly complex planform geometries atop the coastal shelf of the saudi arabian red sea by assembling 95 000 km 2 of remote sensing data into a gis this study aims to relate the morphology of these shallow water depositional environments to processes that sculpt the coastal zone a typology that sorts carbonate systems into end members on the basis of their morphology and relationship to the coastline is developed the resulting gis was interrogated for spatial patterns in the distribution and abundance of the end members while several depositional morphologies are present throughout the length of the saudi arabian red sea the occurrence of others is restricted to narrow re gionsof latitude suchdifferencesindistributioncanbeexplainedinprocess termsbytherifttectonicsof thered sea basin spatial variability in the presence of sub seafloor evaporites and the input of siliciclastic detritus onto the coastal shelf via wadis this paper provides a foundation for understanding the morphological diversity of shallow water carbonate systems in both the modern ocean and rock records

lithofacies architecture and reservoir heterogeneity of tidal dominated platform marginal oolitic shoal an analogue of oolitic reservoirs of lower triassic feixianguan formation sichuan basin sw china abstract the yudongliang outcrop located in the northern part of the sichuan basin nicely exposes oolitic shoal complexes of the lower triassic feixianguan formation the outcrop is an analogue for the subsurface longgang and yuanba gas fields and other permo triassic reservoirs with dolomitized and nondolomitized oolite dominated grainstone bodies as the main producing zones based on five measured sedimentological sections and petrographic and petrophysical analysis of 200 plugs the architecture of the reservoir bodies has been reconstructed in detail and placed within a high frequency sequence stratigraphic framework the studied interval belongs to the highstand system tract hst of a single composite sequence and comprises three shallowing upward high frequency sequences which consist from base to top of oncoid peloid ooid grain dominated packstone cross bedded ooid grainstone dolograinstone fenestra laminated dolomite and crystalline dolomite the internal architecture of the oolitic shoal is the result of complex tidal dominated hydrodynamics facies and diagenetic partitioning with each high frequency sequence are the primary controls on pore types and reservoir properties original lithofacies texture and subsequent cementation resulted in interbedded thin effective reservoirs and permeability barriers that created a complex internal architecture of reservoir bodies the shapes of reservoir bodies generally follow those of the lithofacies but with the addition of intercalated thin flow barriers

further evidence for oceanic excitation of polar motion summary while the role of the atmosphere in driving variations in polar motion is well established the importance of the oceans has been recognized only recently further evidence for the role of the oceans in the excitation of polar motion is presented to estimate the equatorial excitation functions x 1 and x 2 for the ocean we use velocity and mass fields from a constant density ocean model driven by observed surface wind stresses and atmospheric pressure for the period 1993 1995 comparison with similar functions derived from a more complex density stratified ocean model indicates the evectiveness of the simple constant density modelling approach corresponding atmospheric excitation functions are computed from ncep ncar re analyses results indicate significant improvements in the agreement with the observed polar motion excitation when the simulated oceanic evects are added to atmospheric excitation correlations between the polar motion and the geophysical signals at periods of 15 150 days increase from 0 53 to 0 80 and from 0 75 to 0 88 for x 1 and x 2 respectively the oceanic signals are particularly important for seasonal variations in x 1 correlation increases from 0 28 to 0 85 when oceanic excitation is included a positive impact of the oceans on more rapid polar motion is also observed up to periods as short as 5 days the sensitivity of the results to diverent forcing fields and diverent amounts of friction in the oceans is also discussed

the lunar magma ocean reconciling the solidification process with lunar petrology and geochronology abstract the moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded ages of anorthositic crust range over at least 200 million years the model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine 1 the final thickness of flotation crust generated by a fractionally solidifying magma ocean 2 the timescale of crystallization before plagioclase is a stable phase 3 the timescale of solidification after the formation of the plagioclase flotation crust and 4 the post overturn lunar mantle composition and structure we find that magma oceans of as much as 1000 km depth are consistent with creating an anorthositic crust 40 to 50 km in thickness solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000 years and complete solidification would require additional ten to tens of millions of years reconciling these short model timescales with radiometric dates of crustal samples requires either a very late forming moon combined with finding older crustal ages to be incorrect or calling on tidal heating of the crust by the early earth to prolong solidification gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar mg suite of crustal rocks further we find that upon crystallization the moon likely began with an azimuthally heterogeneous gravitationally stable mantle after magma ocean cumulate overturn this result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials

a chemical model for generating the sources of mare basalts combined equilibrium and fractional crystallization of the lunar magmasphere abstract it is generally considered that mare basalts were generated by the melting of a cumulate mantle formed in an early moon wide magma ocean or magmasphere however the nature and chemistry of this cumulate mantle and the logistics of its origin have remained elusive extensive studies of terrestrial layered mafic intrusions over the past sixty years have emphasized the imperfection of fractional crystallization and attendant crystal crystal and crystal liquid separation in a convecting magma chamber crystal liquid and crystal crystal separations were similarly inefficient during evolution of the lunar magma ocean lmo allowing for the trapping of interstitial liquid and entrainment of a small proportion of less dense plagioclase into the denser mafic cumulate mush indeed petrography of lunar highlands samples demonstrates this for anorthosites with 1 10 olivine the residual liquid after 80 90 crystallization was very evolved in fact kreepy and even in small proportions 1 5 would have a noticeable effect on the trace element chemistry of melts generated from these cumulates this trapped residual liquid would elevate total ree abundances in the cumulate pile while synchronously deepening the already negative eu anomaly essentially this trapped liquid will make the cumulate more fertile for melting to generate both kreep basalt and mare basalt magmas plagioclase entrained in the mafic cumulate pile adds an essential al component to the high ti basalt source and will moderate the requisite negative eu anomaly in the cumulate early in the evolution of the lunar mantle when the lmo still was largely liquid it is likely that vigorous convection was an important factor in crystallization such convection would allow crystals to remain suspended and in equilibrium with the lmo liquid for relatively long periods of time this extended period of equilibrium crystallization would then have been followed by fractional crystallization once plagioclase became a liquidus phase and began to float to form the lunar highlands crust previous authors have proposed a three component model for the evolution of high ti mare basalt source regions this model includes kreep early olivine rich high mg cumulates and late ilmeniterich low mg cumulates in various proportions however we propose a model for high ti basalt parent magmas which is in accord with studies of terrestrial layered intrusions this model for the high ti source includes trapped instantaneous residual liquid tirl 1 3 and entrainment of a small 2 5 proportion of plagioclase into the late stage cumulate pile in order to account for both the observed al compositions and trace element characteristics of high ti mare basalts melting of this relatively shallow ilmenite and clinopyroxene bearing late stage cumulate can generate high ti mare basalt magmas furthermore we are in agreement with other workers that only through a process of nonmodal melting will the high ti values for the parent magmas be realized large scale convective overturn of the cumulate pile and mixing of kreep with early and late stage cumulates is not required however localized overturn of the upper tenth of the cumulate pile is likely and in fact required to achieve an appropriate major element balance for the high ti mare basalt source region

a 3 d numerical study of the thermal evolution of the moon after cumulate mantle overturn the importance of rheology and core solidification 1 models in which the mantle of the moon evolves from an initially stratified state following magma ocean solidification and overturn have been applied to address important features of long term thermal evolution of the moon including convective instability of overturned ilmenite bearing cumulates ibc at the lunar core mantle boundary generation of mare basalts core sulfur content and inner core radius paleomagnetism and the present day mantle structure whether a dense overturned ibc rich layer at the bottom of the mantle can become thermally unstable to generate a single upwelling is controlled largely by the temperature dependence of viscosity the activation energy convective instability of the ibc rich layer controls the heat flux out the core and the presence of an internally generated magnetic field a long period of 700 ma high positive core mantle boundary cmb heat flux after the instability of the ibc rich layer is expected from our models present day deep mantle temperatures inferred from seismic and gravitational inversion constrain the magnitude of mantle viscosity from 5 1019 to 1 1021 pa s the cmb temperature and solidified inner core radius inferred from seismic reflection constrain the core sulfur content our evolution models with 5 10 wt sulfur content can produce the observed 240 km radius inner core at the present day the asymmetrical distribution of the deep moonquakes only in the nearside mantle could be explained as the remnant structure of the single chemical upwelling generated from ibc rich layer our evolution model after the overturn results in an early 0 55 km expansion in radius for 1000 ma due to the radiogenic heating associated with ibc in the deep mantle and may provide a simple explanation for the early expansion inferred from the gravity recovery and interior laboratory mission

oceanic angular momentum and torques in a general circulation model abstract the ocean s angular momentum m and torques about the polar axis are analyzed using output from the global eddy resolving model of semtner and chervin seasonal variability in m is dominated by the annual cycle whose magnitude appears capable of helping explain the residual in the solid earth atmosphere annual momentum budget planetary m and relative mr ocean angular momentum components have comparable seasonal amplitudes most of the mean signal in mr results from flows in the antarctic circumpolar current region but flows as far north as approximately 30 s am needed to explain the seasonal cycle local1y the strongest variability in relative angular momentum is found in the tropics at all depths a manifestation of the zonal recirculating character of the tropical circulation the time rate of change of m is very small compared to the applied wind torque calculation of bottom pressure torques using the geostrophic relation reveals a dominant balance between them and the surface wi

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

michigan hockey meteoric precipitation and rhythmicity of accumulation on peritidal carbonate platforms on saturday afternoon march 30 1996 the university of michigan hockey team won the 1996 national collegiate athletic association division i national championship durations between wolverine goals between opponent goals and between all goals during the preceding 40 game regular season each describe an exponential distribution in which duration frequency depends only on number of shots on goal and probability of success compared to opponent scores university of michigan between goal duration frequencies describe a trend having a steeper slope university of michigan shot better and a higher intercept university of michigan took more shots over much of the past 100 yr meteoric precipitation on ann arbor occurred during 11 949 days time durations of the 6401 precipitation episodes that occurred over this interval as well as durations of contiguous days of precipitation and contiguous days of drought each define an exponential distribution in which duration frequency is largely defined by total interval length 35 101 days and probability of precipitation 34 roadcuts near wytheville virginia provide spectacular exposures of a 303 7 m thick section of peritidal carbonate in the middle to upper cambrian elbrook and conococheague formations stratigraphic durations thicknesses of the 527 lithologic units within this sequence of the 265 cyclic upward shallowing lithofacies associations that can be designated over this interval and of stratigraphic intervals between recurrences of like lithofacies also define exponential distributions wherein frequency of stratigraphic recurrence is only dependent on the total thickness and net abundance of designated stratal elements frequency of goal scoring and frequency and or magnitude of meteoric precipitation can be described in terms of random independent processes at short time scales similarly exponential distributions of lithologic and cyclic thickness frequencies at wytheville virginia as well as in most other epicratonic peritidal sequences indicate that meter scale variation in carbonate deposition was predominantly controlled by stochastic poisson processes that were largely unrelated to recurrent intrabasinal or extrabasinal forcing and or to periodic rhythmic sediment accumulation

linking process dimension texture and geochemistry in dolomite geobodies a case study from wadi mistal northern oman understanding the distribution and geometry of reservoir geobodies is crucial for net to gross estimates and to model subsurface flow this article focuses on the process of dolomitization and resulting geometry of diagenetic geobodies in an outcrop of jurassic host rocks from northern oman field and petrographic data show that a first phase of stratabound dolomite is crosscut by a second phase of fault related dolomite the stratabound dolomite geobodies are laterally continuous for at least several hundreds of meters 1000 ft and probably regionally and are one half meter 1 6 ft thick based on petrography and geochemistry a process of seepage reflux of mesosaline or hypersaline fluids during the early stages of burial diagenesis is proposed for the formation of the stratabound dolomite in contrast the fault related dolomite geobodies are trending along a fault that can be followed for at least 100 m 328 ft and vary in width from a few tens of centimeters to as much as 10 m 1 33 ft petrography geochemistry and high homogenization temperature of fluid inclusions all point to the formation of the dolomite along a normal fault under deep burial conditions during the middle to late cretaceous the high 87sr 86sr ratio in the dolomite and the high salinity measured in fluid inclusions indicate that the dolomitizing fluids are deep basinal brines that interacted with crystalline basement the dolomitization styles have an impact on the dimension texture and geochemistry of the different dolomite geobodies and a modified classification scheme compared to the one from jung and aigner 2012 is proposed to incorporate diagenetic geobodies in future reservoir modeling

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

a note on the representation of steric sea level in models that conserve volume rather than mass this note discusses the representation of steric sea level in ocean circulation models changes in steric sea level are caused when changes in the density of the water column imply an expansion or contraction of the column models usually make the boussinesq approximation and conserve volume rather than mass and so do not properly represent expansion or contraction this means that although expansion contraction is included in the equation of state it is not accounted for by the model dynamics in this note we examine the equation governing the time evolution of the sea level displacement it is shown that requiring conservation of mass rather than volume introduces a new term to this equation a simple example is used to show the relationship of the new term to the surface buoyancy flux the equilibrium response to the new term has two parts one part consists of the goldsbrough and stommel gyres for which in the ocean interior vortex stretching due to the local expansion contraction of the water column is balanced by changes in planetary vorticity the other part corresponds to the inverse barometer the effect is to adjust sea level by a globally uniform but timevarying factor determined by the net expansion contraction of the global ocean since this correction is globally uniform it has no dynamical significance both the goldsbrough stommel gyres and the inverse barometer solution are missing from models as currently formulated this does not represent a serious error however if comparison is made with observations of sea level model calculated sea level should be adjusted by a globally uniform time varying factor determined by the net expansion contraction of the global ocean this would be important for assessing the likely rise in sea level in response to global warming

current molded storm damaged sinuous columnar stromatolites mesoproterozoic of northern china abstract a thin 50 cm horizon of sinuous stromatolites occurs within a succession of elongate upright columns in the 1 4 ga tieling formation near jixian china the upright columns form aligned closely spaced ridges separated by narrow runnels with signs of current scour the sinuous and upright stromatolites and their intervening matrix were originally mainly composed of carbonate mud in end on view the sinuous columns incline back and forth each column consists of well defined laminae that successively rotate relative to column curvature maintaining their orientation approximately at right angles to the column axis in inclined parts of the columns laminae are typically asymmetric and the steeper side faces the direction of column inclination we interpret this column sinuosity to be a response to changes in current direction with accreting laminae facing into currents that supplied sediment we find no evidence for heliotropism mat growth towards the sun in these examples adjacent columns typically show similar shapes bending back and forth together but their angles of curvature and inclination can change laterally from column to column from near vertical to 45 over distances of 30 cm columns can show breakage and separation of adjacent laminae some of this is enhanced by compaction and stress but the occurrence of sinuous columns on their sides or upturned in spaces between undisturbed columns indicates that column curvature developed during growth and that toppling of columns was syndepositional we infer that sinuosity developed in response to changes in current direction that column inclination reflects current strength and that breakage and toppling was produced by strong currents curved and sinuous columns could reflect shoaling this would also have exposed them to storm damage and to the effects of currents that scoured sufficient matrix to locally break and topple columns markedly sinuous mesoproterozoic columns also occur in siberia and north america suggesting that similar conditions and processes of stromatolite formation may have been widespread at this time formation and preservation of the sinuous stromatolites described here required a combination of conditions that included abundant fine grained carbonate sediment microbial mats capable of trapping it reduced early lithification and absence of bioturbation

hydrological and oceanic effects on polar motion from grace and models 1 terrestrial water storage tws and ocean bottom pressure obp are major contributors to the observed polar motion excitations second only to atmospheric mass movement however quantitative assessment of the hydrological and oceanic effects on polar motion remains unclear because of the lack of global observations in this paper hydrological and oceanic mass excitations to polar motion are investigated using monthly tws and obp derived from the gravity recovery and climate experiment grace for january 2003 until december 2008 the results from this analysis are compared with hydrological model excitations from the european center for medium range weather forecasts ecmwf and oceanic model excitations obtained from the jet propulsion laboratory jpl using estimating the circulation and climate of the ocean ecco results show that the grace derived obp and tws better explain the geodetic residual polar motion excitations for the px component at the annual period while the grace obp and ecmwf hydrological angular momentum agree better with the geodetic residuals for the annual py excitation grace ocean and hydrology excitations better explain the geodetic residuals for the semiannual py excitation however the jpl ecco and ecmwf models better explain the intraseasonal geodetic residual of polar motion excitation in the px and py components the grace data demonstrate much higher intraseasonal variability than either the models or the geodetic observations

the oceanic contribution to the earth s seasonal angular momentum budget seasonal variations in the speed of the earth s rotation manifest themselves as fluctuations in the length of the day lod with an amplitude of about 1000 microseconds s we know from previous work that at least 95 of these variations can be accounted for in terms of angular momentum exchanged between the atmosphere and the solid earth here we examine the respective contributions of the antarctic circumpolar current acc and the global oceans to the earth s seasonal angular momentum budget using in situ data from the drake passage and results from both the oceanic regional model fine resolution antarctic model fram of webb et al 1991 and the global oceanic model of maier reimer et al 1993 as analyzed by brosche et al 1990 the estimated annual contribution of the acc 2 4 s is much smaller than the total variation in the oceanic models or the existing lod aam residual both 15 20 s the estimated semi annual acc contribution 3 8 s is offset by counter currents further north in both oceanic models which exhibit larger semi annual variations in planetary angular momentum further refinements in the earth s seasonal angular momentum budget therefore will require the full planetary plus relative contribution of the global oceans in addition to that of the acc

a dominant tectonic signal in high frequency peritidal carbonate cycles a regional analysis of liassic platforms from western tethys abstract meter scale peritidal carbonate cycles are a common feature of the geological record but debate continues about what processes lead to their formation three conceptual models or a combination thereof are commonly invoked to explain cycle formation eustasy tectonics or autocyclicity these three models are tested with a large new dataset from different early jurassic plate margins from western tethys study of seven logged sections from spain italy greece tunisia morocco and gibraltar enables an analysis of the possible roles of local versus regional patterns and controls on cyclicity within a sinemurian time slice cycle types are diverse and include shallowing upward cycles parasequences but also deepening upward and diagenetic cycles high frequency sequences and subtidal cycles numbers of cycles per section and cycle stacking patterns within this time slice vary from section to section statistical tests runs tests time series and bundling all indicate random stacking of cycles within sections and an absence of any bundling of thicknesses or of facies trends assessment of cycle types by their occurrence and stacking patterns indicates little support for either eustasy or autocyclicity being the dominant cycle forming mechanism however the variability in numbers of cycles per section thickness variations of the sections cycle type variability and randomness of stacking patterns all favor a pulsed tectonic control for the creation and filling of accommodation space this conclusion is further supported by evidence that has largely arisen during the course of this study of syndepositional extensional tectonics in the sinemurian on these rifted tethyan margins although tectonics appears to be the dominant control superimposed eustasy and or autocyclic processes cannot be discounted

thermal evolution of a thicker kreep liquid layer we consider the thermal evolution of the thickened potassium rare earth element and phosphorous kreep liquid layer that extends over a significant fraction of the lunar nearside with a prescribed thickness and heat production and beneath an insulating anorthosite crust this layer represents a subcrustal heat source beneath the procellarum imbrium terrane and may be responsible for the localized and anomalous enrichments of highly incompatible elements in this terrane in some models this thickened liquid layer is the thermal source for the remelting of mare basalts and also produces the parent magmas of the magnesian suite indeed a kreep liquid layer thickened from 5 to 10 km with more than 200 times chondritic heat producing elements does not continue to cool but undergoes a reheating and grows in thickness by dissolving several times its mass of anorthosite and ultramafic cumulates however such a liquid layer cannot give rise to the parent magmas to the magnesian suite because it cannot account for the extraordinarily high incompatible element content the primitive major element content or the positive end of the magnesian suite this growing layer will also form an impenetrable barrier to the eruption of mare basalts and is generally inconsistent with a number of geophysical constraints of the moon specifically the existence of mascons subsequent to the basin filling by mare basalts a thickened kreep liquid layer can however explain the asymmetry in the distribution of kreep rich rock on the lunar crust such a kreep layer must be efficiently cooled and be quickly solidified to avoid some of the difficulties described above a thinned anorthosite crust would allow efficient heat loss and induce crystallization of such a layer early in lunar history

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

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

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

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

dimensions texture distribution and geochemical heterogeneities of fracture related dolomite geobodies hosted in ediacaran limestones northern oman predicting spatial distribution dimension and geometry of diagenetic geobodies as well as heterogeneities within these bodies is challenging in subsurface applications and can impact the results of reservoir modeling in this outcrop based study we generated a data set of the dimensions of fracture related dolomite geobodies hosted in ediacaran khufai formation limestones of the oman mountains that are up to several hundreds of meters long and a few tens of meters wide the dolomite formed under burial conditions by fluids that interacted with siliciclastic layers as demonstrated by the enriched fe up to 4 4 and mn up to 0 8 contents and signatures dolomitization probably occurred during the hercynian orogeny or pre permian because dolomitization predates some folding and pre permian rocks have seen intense deformation related to the carboniferous hercynian orogeny moreover dolomitization occurred between the onset and termination of bedding parallel stylolitization and thus most likely before deep burial related to the alpine orogeny hence dolomitization most likely occurred before deep burial related to the alpine orogeny and during or following the intense deformation related to the carboniferous hercynian orogeny had affected pre permian rocks the clumped isotope signature yields a temperature of approximately 260 c 500 f interpreted as the apparent equilibrium temperature obtained during uplift after deepest burial during the late cretaceous lateral transects across the dolomite bodies show that zebra dolomite textures are common throughout the body and that vugs are more common at the rim than the center of the bodies moreover a weak geochemical trend exists with more depleted fe and mn concentrations in the core than at the rim of the dolomite bodies these results show that minor heterogeneities exist within the dolomite bodies investigated these data contrast with previous studies in which more significant variation is reported in width of the dolomitization halo and texture for larger dolomite bodies that formed in host rocks more permeable than the examples from the oman mountains

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

seasonal and interannual global surface mass variations from multisatellite geodetic data 1 monthly global surface mass distribution changes are estimated in the spherical harmonic domain with a complete spectrum up to degree and order 50 the estimates are derived by inverting gps displacement series measured at roughly 450 continuously tracking sites and ocean bottom pressure obp estimates of a data assimilated ocean circulation model from 1993 to 2004 the inversion uses a hybrid estimator after singular value decomposition of the normalized measurement equations with reduced reliance on a priori spectral information the results are then compared and combined with gravity recovery and climate experiment grace gravity data to provide enhanced spectral and geographic coverage high fidelity degree 1 surface mass variation coefficients are recovered corresponding to equivalent geocenter motion with better than 0 5 mm annual amplitude precisions in all three components a clear annual surface mass cycle occurs in both gps obp and grace derived results there is very good agreement among the low degree spherical harmonic coefficients and in global geographic pattern but with significant regional differences in amplitudes annual variations of average mass over the global oceans antarctica and greenland are then derived total surface mass over both antarctica and greenland peak in their respective summers due to increased atmospheric mass large interannual variations have also been found involving several continents in the 11 year gps obp solution the patterns of variation suggest that the recent satellite laser ranging slr observation of a reversal in trend of the earth s oblateness may be largely an interannual surface mass cycle with considerable contribution from the northern continents

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

the importance of melt tio2 in affecting major and trace element partitioning between fe ti oxides and lunar picritic glass melts abstract lunar mare basalts and picritic glasses have tio2 abundances ranging from less than 1 wt to over 16 any high ti mare basalt or picritic glass petrogenetic model must include fe ti oxides in the mantle source or invoke fe ti oxide assimilation during magma ascent to the lunar surface we conducted partitioning experiments to investigate high field strength element hfse rare earth element ree and transition metal distribution between fe ti oxides and lunar picritic glass melts over a range of melt compositions our results suggest that ilmenite melt and armalcolite melt hfse cr and v partition coefficients dhfse dcr dv are strongly dependent on melt tio2 content whereas ilmenite melt ree partition coefficients appear to be insensitive to melt composition as tio2 increases in picritic glass melts hfse cr and v activities in melt also increase and fe ti oxide melt dhfse dcr and dv decrease the effect of ti on partitioning behavior can be attributed to the formation of fe o ti melt species in high ti melts ilmenite dhfse range from compatible in oxides in equilibrium with low ti melts to incompatible in oxides in equilibrium with depolymerized high ti picritic glass melts dhfse are inversely correlated with tio2 abundance in the melt and become nearly constant for melts with more than 6 8 tio2 we present simple partitioning models that utilize the solubility of ilmenite and armalcolite in melt to effectively predict hfse partition coefficients across a wide range of picritic glass melt compositions the hfse budget of ilmenite cumulates that crystallize from the lunar magma ocean strongly depends on the composition of the magma ocean low ti and high ti lunar basalts can be produced by an ilmenite or armalcolite bearing hybridized mantle source or by assimilation of late stage magma ocean cumulates the dependence of dhfse and dcr on melt tio2 is consistent with the formation of lunar type 1 armalcolite from high tio2 picritic glass melt however lunar type 2 and 3 armalcolite have a more complicated yet undetermined history of formation

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

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

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

central magnetic anomalies of nectarian aged lunar impact basins probable evidence for an early core dynamo abstract a re examination of all available low altitude lp magnetometer data confirms that magnetic anomalies are present in at least four nectarian aged lunar basins moscoviense mendel rydberg humboldtianum and crisium in three of the four cases a single main anomaly is present near the basin center while in the case of crisium anomalies are distributed in a semi circular arc about the basin center these distributions together with a lack of other anomalies near the basins indicate that the sources of the anomalies are genetically associated with the respective basin forming events these central basin anomalies are difficult to attribute to shock remanent magnetization of a shocked central uplift and most probably imply thermoremanent magnetization of impact melt rocks in a steady magnetizing field iterative forward modeling of the single strongest and most isolated anomaly the northern crisium anomaly yields a paleomagnetic pole position at 81 19 n 143 31 e not far from the present rotational pole assuming no significant true polar wander since the crisium impact this position is consistent with that expected for a core dynamo magnetizing field further iterative forward modeling demonstrates that the remaining crisium anomalies can be approximately simulated assuming a multiple source model with a single magnetization direction equal to that inferred for the northernmost anomaly this result is most consistent with a steady large scale magnetizing field the inferred mean magnetization intensity within the strongest basin sources is 1 a m assuming a 1 km thickness for the source layer future low altitude orbital and surface magnetometer measurements will more strongly constrain the depth and or thicknesses of the sources

analyzing spatial patterns in modern carbonate sand bodies from great bahama bank abstract three carbonate sand bodies on great bahama bank which show a range of depositional facies patterns typifying modern deposits as well as their ancient counterparts are quantitatively interrogated to broaden our perspective of the types of information that can be derived from studies of modern environments rimming the southern end of tongue of the ocean toto is the broadest expanse of high energy sands found in the bahamas characterized by narrow sandbars separated by wide deep channels and a lack of islands a variation of the tidal bar motif with broader and more irregular sandbars relatively narrow channels and few small islands occurs at the northern end of exuma sound schooners sands associated with tidal channels and the numerous islands of the exumas chain along the western edge of exuma sound occur primarily as flood tidal deltas the geometry of sandbars that inhabit the three sand bodies is quantified using landsat remote sensing and assembled along with optically derived bathymetric surfaces into a gis this database is quantitatively examined using a suite of morphometric tools to compare and contrast geometric character of sandbars within and between the three sand bodies considered are properties such as the size shape complexity distribution orientation and topography of the individual sandbars profiles and spatial analysis tools enable sandbar and channel spacing position relative to the platform margin connectedness separation distances and density to be characterized as has been previously reported for reef dominated environments certain aspects of the geometry of the three systems are found to behave in a systematic and hence predictable manner though important mathematical differences are revealed between the scaling of reefal landscapes and the grainy geobodies considered by this study because the three sand bodies are disparate in their overall extent and depositional settings e g orientation prevalence of islands this predictable behavior has the potential to impart considerable insight to the characterization of grainstone systems

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

geostatistical facies modeling trends for oolitic tidal sand shoals to assess prospective modeling trends for oolitic tidal sand shoals and explore potential patterns of reservoir heterogeneity this study examines quantifies and models the cycle scale architecture of the holocene mobile oolitic tidal sand shoal complex at schooner cays bahamas process based stratigraphic trends are captured in quantitative geocellular models of the shoal from analyses of satellite imagery two dimensional high frequency seismic chirp data and sediment cores data show that longitudinal tidal sand ridges extend up to 8 km 5 mi along depositional dip gradually transforming bankward into channel bound compound barforms consisting of linear parabolic and shoulder bars these bars terminate into a laterally extensive 10 km 6 mi strike elongate sand sheet each bar type includes distinct internal architecture grain size and sorting related to feedbacks among hydrodynamics geomorphology and sedimentology building on these data and concepts from the holocene accumulations this study demonstrates a methodology for quantifying and validating probabilistic stratigraphic trends prior to their inclusion in stochastic based facies modeling algorithms inclusion of statistically robust facies probability volumes during truncated gaussian simulation generated ordered and geologically accurate facies distributions relative to bar crest centerlines water depth and geomorphic position petrophysical models that incorporate facies specific porosity permeability and water saturation functions display pronounced cycle scale heterogeneity that could provide insights into variable production rates and poor sweep efficiency commonly encountered during development of analogous oolitic reservoirs

the significant role of sediment bio retexturing within a contemporary carbonate platform system implications for carbonate microfacies development abstract assessments of carbonate platform reef lagoon sediments and benthic habitats around rodrigues island south west indian ocean have been undertaken in order to examine carbonate sediment textural properties and the controls on texturally defined sediment fabrics reef lagoon sediments sampled from across the expansive 8 km wide carbonate dominated windward platform principally comprise poorly sorted medium to coarse grained bioclastic sands composed of a low diversity of grain constituents predominantly non geniculate coralline algal bioclasts despite a marked homogeneity in sediment compositional and grain size properties eight distinct sediment textural groups can be identified that form a heterogeneous mosaic across the contemporary reef lagoon system only along the narrow outer platform margins reef crest sand apron and outermost lagoon environments do we observe consistent predictable transitions in sediment textural groups where physical processes are the primary drivers of selective sediment transport and sorting in contrast across the main expanse of the lagoon the sediment substrates are characterised by an irregular mosaic of texturally defined sediment groups formed primarily as a function of sediment bio retexturing the burrowing activities of alpheid and callianassid shrimps are particularly important in this respect and impart a distinctly unique textural fabric to the upper sediment horizons in the environments in which the respective organisms occur the consequence of this is that at the platform system scale individual texturally defined sediment groups are relatively poor indicators of prevailing hydrodynamic regimes or of local sediment production reflecting more the biological action of organisms inhabiting the substrate this has important implications for understanding the development of carbonate sediment fabrics in the context of palaeoenvironmental reconstructions and for interpreting a key diagnostic criteria of carbonate microfacies

does the moon possess a molten core probing the deep lunar interior using results from llr and lunar prospector 1 it is the main purpose of this study to examine the deeper structure of the moon in the light of four numbers these are lunar mass m mean moment of inertia i second degree tidal love number k2 and the quality factor q accounting for tidal dissipation within the solid body of the moon the former two have been measured by lunar prospector to high precision and more than 30 years of lunar laser ranging llr data have led to an estimate of the second degree tidal love number and quality factor the inverse problem dealt with here of obtaining information on the lunar density and s wave velocity profile from the four numbers follows our earlier investigations by employing an inverse monte carlo sampling method we present a novel way of analyzing the outcome using the bayes factor the advantage lies in the fact that rather than just looking at a subset of sampled models we investigate all the information sampled in different runs i e take into account all samples in order to estimate their relative plausibility the most likely outcome of our study based on the data their uncertainties and prior information is a central core with a most probable s wave velocity close to 0 km s density of 7 2 g cm3 and radius of about 350 km this is interpreted as implying the presence of a molten or partially molten fe core in line with evidence presented earlier using llr regarding the dissipation within the moon

depositional architecture and petrophysical variability of an oolitic tidal sand shoal pennsylvanian missourian kansas u s a

chronological evidence that the moon is either young or did not have a global magma ocean a new age determination for a moon rock collected close to the site of the apollo 16 lander has yielded a surprisingly young age of around 4 360 million years this age would require either that the moon solidified some 200 million years after the formation of the solar system significantly later than is assumed by most lunar formation models or that the long held theory that the moon once had a primordial global magma ocean is flawed in the latter case much of the lunar crust could have been produced by non magma ocean processes such as serial magmatism chemical evolution of planetary bodies ranging from asteroids to the large rocky planets is thought to begin with differentiation through solidification of magma oceans many hundreds of kilometres in depth1 2 3 the earth s moon is the archetypical example of this type of differentiation evidence for a lunar magma ocean is derived largely from the widespread distribution compositional and mineralogical characteristics and ancient ages inferred for the ferroan anorthosite fan suite of lunar crustal rocks the fans are considered to be primary lunar flotation cumulate crust that crystallized in the latter stages of magma ocean solidification according to this theory fans represent the oldest lunar crustal rock type2 3 4 attempts to date this rock suite have yielded ambiguous results however because individual isochron measurements are typically incompatible with the geochemical make up of the samples and have not been confirmed by additional isotopic systems5 6 7 8 9 by making improvements to the standard isotopic techniques we report here the age of crystallization of fan 60025 using the 207pb 206pb 147sm 143nd and 146sm 142nd isotopic systems to be 4 360 3 million years this extraordinarily young age requires that either the moon solidified significantly later than most previous estimates or the long held assumption that fans are flotation cumulates of a primordial magma ocean is incorrect if the latter is correct then much of the lunar crust may have been produced by non magma ocean processes such as serial magmatism10

fine grained agglutinated elongate columnar stromatolites tieling formation ca 1420 ma north china the mesoproterozoic tieling formation near jixian northern china contains thick beds of vertically branched laterally elongate columnar stromatolites carbonate mud is the primary component of both the stromatolites and their intervening matrix its abundance is attributed to water column whiting precipitation stimulated by cyanobacterial photosynthesis neomorphic microspar gives the stromatolites a streaky microfabric and small mud flakes are common in the matrix the columns consist of low relief mainly non enveloping laminae that show erosive truncation and well defined repetitive lamination in plan view the columns form disjunct elongate ridges 10 cm wide separated by narrow matrix filled runnels the stromatolite surfaces were initially cohesive rather than rigid and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud the pervasive ridge runnel system suggests scale dependent biophysical feedback between i carbonate mud supply ii current duration strength and direction and iii growth and trapping by prolific mat growth together these factors determined the size morphology and arrangement of the stromatolite columns and their laminae as well as their branching patterns alignment and ridge runnel spacing ridge runnel surfaces resemble ripple mark patterns but whether currents were parallel and or normal to stromatolite alignment remains unclear the formation and preservation of tieling columns required plentiful supply of carbonate mud mat building microbes well adapted to cope with this abundant sediment and absence of both significant early lithification and bioturbation these factors were time limited and tieling stromatolites closely resemble coeval examples in the belt purcell supergroup of laurentia the dynamic interactions between mat growth currents and sediment supply that determined the shape of tieling columns contributed to the morphotypical diversity that characterizes mid late proterozoic branched stromatolites this article is protected by copyright all rights reserved

quantitative interrogation of a fossilized carbonate sand body the pleistocene miami oolite of south florida exposures of the pleistocene miami oolite in south florida provide excellent examples of preserved primary sedimentary features and subsequent diagenetic changes of a fossilized ooid sand body that has been subaerially exposed in a tropical climate since its deposition during the last interglacial highstand marine isotope stage 5e using a robust airborne light detection and ranging digital terrain model and select outcrops a detailed analysis of the morphologies and dimensions of the different portions of the miami oolite was conducted the sand body extending 95 km north to south and approximately 15 km wide consists of shoals or bars separated by tidal channels and is partly bounded on the ocean facing side by a prograding barrier bar that collectively cover an area of approximately 1000 sq km results of the quantitative interrogation of the miami oolite are compared with those of previously published work from modern sand bodies on great bahama bank including the exumas schooners cays and tongue of the ocean digital terrain models developed for these modern sand bodies on the great bahama bank and the ancient miami oolite were used as the basis for the definition of shoals shoal crests peaks and channels which were examined with respect to their size shape and orientation the exumas sand body is the best morphometric match when analysing the bars and the channels and the joulter cays area is an analogue for the formation of the barrier bar and for burrow reworking of cross bedding within stabilized sand shoals the exumas is a particularly compelling analogue for the miami oolite with respect to length and overall visual comparison between the morphologies of the sand bodies shoal or bar shape number of tidal channels channel length and width and high areas parallel to the strike trend of the sand body islands in the exumas and possible islands as part of the miami oolite barrier bar despite ca 115 kyr of subaerial exposure and meteoric diagenesis including karst the morphology of the miami oolite is still relatively intact to the point where it can be easily analysed and meaningful comparisons to modern systems can be made the miami oolite serves as a key reference example for comparison to holocene sand units in the bahamas it validates the concept of comparative sedimentology and in particular emphasizes how results from the modern can improve the interpretation of a fossilized example

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

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

interactions between tidal flows and ooid shoals northern bahamas abstract oolitic strata are common through the geologic record ooids generally form in high energy environments but it remains unclear how ooids remain in such systems and form geomorphic features such as bars and shoals integrating remote sensing hydrodynamic bathymetric granulometric and field observations of modern tidal systems in the bahamas provides insight into this fundamental question oolitic tidal sands in the northern abacos display a geomorphic pattern in which bedrock islands restrict and focus tidal flow down a main channel within the channel a shallow shoal separates an ebb dominated subchannel from a flood dominated subchannel tidal velocities in these subchannels can exceed 1 m s enough to transport the oolitic sediments hydrodynamics and bathymetry in these subchannels produce a net circular hydrodynamic pattern around the shoal the spin cycle allowing the sands to remain in motion without being transported out of the ooid factory this general pattern is apparent in several other ooid shoal complexes this concept provides integrated insights into the physical influences impacting the formation suspension transport and deposition of ooids and the resulting geomorphic forms these results represent first steps toward developing more comprehensive and predictive analogs of spatial heterogeneity in ancient tidally dominated oolitic shoals

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

rapid ocean signals in polar motion and length of day 1 non tidal variability in ocean currents and bottom pressure is substantial at short periods but relating the associated signals in ocean angular momentum oam to observed polar motion and length of day fluctuations has been difficult our simulations using a barotropic ocean model reveal a clear connection between the estimated oam signals and both polar motion and length of day at periods of 3 10 days the dynamic response of the oceans to barometric pressure plays an important role in the excitation of rapid rotation signals the impact of oam variability is most clear when using gps based earth orientation measurements with little temporal smoothing using the gps series and accounting for oam in addition to atmospheric effects yields substantial improvements in the excitation budget for rapid polar motion and length of day the comparisons with earth rotation data provide a useful check on the rapid ocean variability simulated by the barotropic model

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

oceanic excitations on polar motion a cross comparison among models recent studies based on various ocean general circulation models ogcms demonstrate that the oceans are a major contributor to polar motion excitations in this paper we analyse and compare observed non atmospheric polar motion excitations with oceanic angular momentum oam variations determined from four ogcms which include the parallel ocean climate model pocm a barotropic ocean model bom the estimating the circulation and climate of the ocean ecco non data assimilating model ecco nda and the ecco data assimilating model ecco da the data to be analysed span a 5 yr overlapped period from 1993 to 1997 at annual timescale considerable discrepancies exist between pocm and the other three models which result mainly from differences in annual components of the forcing wind fields at semi annual timescale however pocm shows better phase agreement with observed non atmospheric polar motion excitation than the other three ocean models at intraseasonal timescales ecco da yields better agreement with observations and reduces the variance of non atmospheric excitations by similar to 60 per cent 10 20 per cent more than those explained by the other three models however at the very short periods of 4 20 days the bom estimates could explain about half of the observed variance twice as much as that by ecco nda and also shows considerably better correlation with observations due to different modelling schemes and methods significant discrepancies could arise with respect to the quality of modelling large scale oceanic mass redistribution and current variation a complete understanding of global oceanic contributions to polar motion excitation still remains a challenge

gravitational differentiation due to initial chemical stratification origin of lunar asymmetry by the creep of dense kreep abstract models for the evolution of the moon must explain a number of important characteristics of its magmatic history primary among them is the emplacement of mare basalts primarily on one side of the moon and in a region of the surface roughly correlating with that containing high subsurface concentrations of kreep it is thus important to explore mechanisms which will regionally concentrate a kreep layer early in lunar evolution and which 400 500 myr later give rise to mare basalt generation beneath the same region gravitational instability of a chemically dense ilmenite rich cumulate created during the fractionation of an anorthositic crust is one candidate model if so gravitational instability must occur at long wavelength to explain the hemispheric asymmetry we examine the rayleigh taylor instability of a dense layer near the surface of a sphere representing the lunar mantle in which the viscosity varies with depth our results show that spherical harmonic degree 1 is the fastest growing wavelength of instability if the viscosity of the dense layer is sufficiently low relative to that of the deeper mantle or if the viscosity of the mantle increases with depth however the viscosity increase cannot be distributed over a depth that is too large we explore whether a residual kreep like layer near the base of anorthositic crust might give rise to these needed conditions

oceanic signals in observed motions of the earth s pole of rotation motion of the earth s pole of rotation relative to its crust commonly referred to as polar motion can be excited by a variety of geophysical mechanisms1 in particular changes in atmospheric wind and mass fields have been linked to polar motion over a wide range of timescales but substantial discrepancies remain between the atmospheric and geodetic observations1 2 3 4 here we present results from a nearly global ocean model which indicate that oceanic circulation and mass field variability play important roles in the excitation of seasonal to fortnightly polar motion the joint oceanic and atmospheric excitation provides a better agreement with the observed polar motion than atmospheric excitation alone geodetic measurements may therefore be used to provide a global consistency check on the quality of simulated large scale oceanic fields

the participation of ilmenite bearing cumulates in lunar mantle overturn abstract the ilmenite bearing cumulates ibc formed from the solidification of the lunar magma ocean are thought to have significantly affected the long term evolution of the lunar interior and surface their high density is considered to trigger rayleigh taylor instabilities which allow them to sink into the solidified cumulates below and drive a large scale overturn in the lunar mantle knowledge of how the ibc participate in the overturn is important for studying the early lunar dynamo chemistry of surface volcanism and the existence of present day partial melt at the lunar core mantle boundary despite early efforts to study this process as rayleigh taylor instabilities no dynamical models have quantified the degree of ibc sinking systematically we have performed quantitative 2 d geodynamical simulations to measure the extent to which ibc participate in the overturn after their solidification and tested the effect of a range of physical and chemical parameters our results show that ibc overturn most likely happened when the magma ocean had not yet fully solidified with the residual melt decoupling the crust and ibc resulting in 50 70 ibc sinking participation of the last dregs of remaining magma ocean melt is unlikely leaving its high concentrations of radiogenic elements close to the surface our simulations further indicate that foundered ibc can stay relatively stable at the core mantle boundary until the present day at temperatures consistent with the presence of a partially molten zone in the deep mantle as inferred from geophysical data 30 50 of the primary ibc remain at shallow depths throughout lunar history enabling their assimilation by rising magma to form high ti basalts