open system coral ages reveal persistent suborbital sea level cycles sea level is a sensitive index of global climate that has been linked to earth s orbital variations with a minimum periodicity of about 21 000 years although there is ample evidence for climate oscillations that are too frequent to be explained by orbital forcing suborbital frequency sea level change has been difficult to resolve primarily because of problems with uranium thorium coral dating here we use a new approach that corrects coral ages for the frequently observed open system behavior of uranium series nuclides substantially improving the resolution of sea level reconstruction this curve reveals persistent sea level oscillations that are too frequent to be explained exclusively by orbital forcing

sedimentology and clast orientations of the 18 may 1980 southwest flank lahars mount st helens washington abstract three lahars that resulted from the flow transformation of an milled pyroclastic surge caused by ejected lithic debris and hydrothermal water during the cataclysmic mount st helena eruption of 18 may 1980 deposited about 1 106 m3 of massive poorly sorted poorly graded volcaniclastic sediment on the southwest flank swf mean peak flow velocities over a 5 km radius ranged from more than 30 m s in the proximal area mean slope angle of 13 to about 5 m s in the distal area mean slope angle of 4 9 the lahars rapidly decelerated as deposition occurred on forested slopes average yield strength of the swf lahars ranged from 9 000 to 12 000 dn cm2 bingham viscosity ranged from 2 8 103 to 50 103 poises average flow density of the swf lahars was about 2 0 g cm3 to determine the grain size distribution of the swf lahars spot sampling of deposit matrix from vertical exposures was supplemented with point count sampling of larger particles results from these analyses indicate that downflow changes in mean gram size and sorting occur only in the coarse fraction of the deposits larger than a critical diameter of about 4 mm and occur only in the basal portion of the deposits both mean grain size and sorting coefficient increase slightly with distance the deposits show weak inverse grading with respect to mean grain size and exhibit a weak trend of upwardly poorer sorting fabric analyses of clast long axes indicate strong planar orientations parallel to flow surfaces an eigenvalue analysis demonstrates the occurrence of both flow parallel long axis orientations with upstream dips and flow transverse orientations similar clast fabric results were obtained for deposits of the north fork toutle river lahar however the mean clast long axis dip in the swf lahars is significantly shallower than the mean clast long axis dip in the north fork toutle lahar and is more like clast long axis dips reported for tills and other sediment flows the data from the swf lahars indicate that lahar clast fabric may be more complex and variable than previously suggested

hydrostratigraphic analysis of the made site with full resolution gpr and direct push hydraulic profiling 1 f ull resolution 3d ground penetrating radar gpr data were combined with high resolution hydraulic conductivity k data from vertical direct push dp profiles to characterize a portion of the highly heterogeneous macro dispersion experiment made site this is an important first step to better understand the influence of aquifer heterogeneities on observed anomalous transport statistical evaluation of dp data indicates non normal distributions that have much higher similarity within each gpr facies than between facies the analysis of gpr and dp data provides high resolution estimates of the 3d geometry of hydrostratigraphic zones which can then be populated with stochastic k fields the lack of such estimates has been a significant limitation for testing and parameterizing a range of novel transport theories at sites where the traditional advection dispersion model has proven inadequate citation dogan m r l van dam g c bohling j j butler jr and d w hyndman 2011 hydrostratigraphic analysis of the made site with full resolution gpr and direct push hydraulic profiling geophys res lett 38 l06405 doi 10 1029 2010gl046439

mapping porosity variation in a welded pyroclastic deposit with signal and velocity patterns from ground penetrating radar surveys ground penetrating radar gpr is used to both image and quantify porosity variations in a variably welded pyroclastic flow deposit characteristic radar signals for nonwelded constant high porosity and welded porosity lower and variable zones are identified by comparison of radar signals to exposed stratigraphy a moderate rate of change in porosity with depth generates abundant unresolvable reflections a relatively constant porosity results in a flat zero amplitude response lastly a discrete jump or extremely high rate of change in porosity abrupt at scale of radar wavelength can produce a strong distinct reflection common midpoint cmp survey data are analyzed to determine relative radar velocity patterns in the pyroclastic flow changes in radar velocity are linked to changes in relative porosities that are attributed to differential welding our analysis shows that welding causes substantial reductions in radar velocity moisture in subsurface stratigraphy also strongly affects velocity therefore we advocate the interpretation of radar data in terms of relative changes in porosity our results also suggest that in areas of rapid facies changes multiple cmp surveys are required for accurate conversions of travel time to depth

dynamics of the 1984 rock avalanche and associated distal debris flow on mount cayley british columbia canada implications for landslide hazard assessment on dissected volcanoes abstract in 1984 a mass of quaternary pyroclastic rock est vol 0 74 106m3 slid from the western flank of mount cayley volcano in southwest british columbia the disintegrating rock mass entrained a further 0 20 106 m3 and formed a rock avalanche that travelled a horizontal distance of 3 46 km from its source over a vertical elevation difference of 1 18 km equivalent to a fahrboschung of 19 from the superelevation of the debris trimline in the mid path it is estimated that velocities reached at least 42 m s in the upper part of its path velocities may have approached 70 m s the rock avalanche was partially transformed into a distal debris flow that travelled a further 2 6 km down turbid creek in a narrow channelised path to the squamish river temporarily blocking it the motion of the rock avalanche including the production of a distal debris flow was successfully simulated using a dynamic analytical model both the results of this analysis and field evidence indicate that the rock avalanche did not come to a halt in the upper part of its path as suggested by cruden and lu 1992 but travelled to its distal limit in one uninterrupted movement this finding has important implications for landslide hazard assessment at mount cayley and similar sites the landslide is typical of those which occur on the steep slopes of dissected volcanoes and is one of seven high velocity rock avalanches that have occurred in the garibaldi volcanic belt of southwest british columbia since 1855

geology of new providence island bahamas contrary to the popular notion that the bahama islands are built of eolianite deposits at least new providence island consists principally of elevated marine sand flat and protected lagoon deposits narrow eolianite ridges separate such deposits from reef tract deposits capped by prograding beach deposits on the northern bank margin side of the island all exposed depositional phases are quaternary the most extensively exposed deposits we correlate with the 125 000 yr high sea level recognized world wide elevations of keystone vugs in beach deposits of that depositional phase indicate paleo mean sea levels of as high as 10 m deposits of an earlier depositional phase suggest that there was then no island but only a barrier sand shoal and reef tract holocene additions to the island9s area have been minor and in the form of prograding beach deposits classical superpositional stratigraphy has limited value in the elucidation of new providence geology due to the nature of the deposits which are partially overlapping thin facies sheets and lenses therefore we have also used a morphostratigraphic approach and as paleontological markers species of cerion a very rapidly evolving genus of land snail limited radiometric dating is reported islands on bahama type banks of earlier geologic periods were probably built almost entirely of beach deposits rather than the eolianites and elevated marine deposits of which new providence is built

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

two dimensional kinematic and rheological modeling of the 1912 pyroclastic flow katmai alaska pyroclastic flow emplacement is strongly influenced by eruption column height a surface along which kinetic energy is zero theoretically connects the loci of eruption column collapse with all coeval ignimbrite termini this surface is reconstructed as a two dimensional energy line for the 1912 katmai pyroclastic flow in the valley of ten thousand smokes from mapped flow termini and the runup of the ignimbrite onto obstructions and through passes extrapolation of the energy line to the vicinity of the source vent at novarupta suggests the eruption column which generated the ignimbrite eruption was approximately 425 m high the 1912 pyroclastic flow travelled about 25 km downvalley empirical velocity data calculated from runup elevations and surveyed centrifugal superelevations indicate initial velocities near novarupta were greater than 79 88 m s 1 the flow progressively decelerated and was travelling only 2 8 m s 1 when it crossed a moraine 16 km downvalley the constant slope of the energy line away from novarupta suggests the flow was systematically slowed by internal and basal friction using a simple physical model to calculate flow velocities and a constant kinetic friction coefficient heim coefficient of 0 04 derived from the reconstructed energy line the flow is estimated to have decelerated at an average rate of 0 16 m s 2 and to have taken approximately 9 5 minutes to travel 25 km down the valley of ten thousand smokes the shear strength of the flowing ignimbrite at the moraine was approximately 0 5 kpa and its bingham viscosity when it crossed the moraine was 3 5 103p if the flow was newtonian its viscosity was 4 2 103p reynolds and froude numbers at the moraine were only 41 62 and 0 84 1 04 respectively indicating laminar subcritical flow

lessons from ontake san a comparative analysis of debris avalanche dynamics abstract dynamic aspects of the long runout ontake san debris avalanche are evaluated by a comparison of several models an unsteady numerical model assumes two dimensional flow of an incompressible biviscous or newtonian fluid represented as a continuum with a free surface internal deformation of the flowing mass is considered as well as boundary resistances thus flow thinning and deposit shape as well as flow kinematics may be modeled parameters are adjusted to match observed runout with additional constraints on velocity and emplacement time with abundant constraints for ontake san from careful field investigations by japanese research teams our analysis indicates that a substantial decrease in flow resistance occurred as a function of displacement constant property models that match runout tend to overestimate the peak velocities and to underestimate the emplacement times a staged increase in mobility in both constant volume and variable volume models leads to results consistent with field data runout in a channel overflow area was also modeled qualitatively similar results have been obtained by other researchers using simple sliding block models with empirical parameters a slide block model with rational parameter selection a modified flood simulation and a multi element frictional slide model the relative merits of these models are compared the field mechanisms associated with this mobility increase with displacement are poorly understood but the question is now identified as a target for future research at debris avalanche sites and some plausible mechanisms are considered the main reason probably involves the entrainment of river water and saturated sediment leading to enhanced efficiency of fluid pressure mechanisms with undrained shear in addition progressive shearing reduced the mean particle size and angularity and the cohesion and friction and apparent viscosity of avalanche debris near the wetted perimeter hydroplaning the shearing of water films and slurries may have occurred locally

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

ice sheet collapse following a prolonged period of stable sea level during the last interglacial sea level during the last interglacial period reached a peak of between 5 and 9 m above the present day level a detailed reconstruction of sea level and isostatic rebound from western australia indicates a prolonged period of sea level stability at 3 4 m above present followed by an abrupt sea level rise of 5 6 m

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

numerical modelling of entrainment deposition in rock and debris avalanches abstract rock and debris avalanches as well as debris flows are characterized by peculiar behaviour influenced by geometry of the initial failure surface topography involved materials involved and water content during their motion rock avalanches can entrain large volumes of sediments both in a dry and in a saturated state entrained dry material has generally the consequence to reduce the total landslide runout whereas entrainment of almost saturated material can have more complex consequences we use a finite element code to simulate the motion of a moving landslide mass on materials with different properties and along very sharp topographies erosion and deposition can be modelled as well as interaction with obstacles of different characteristics we present two examples of the modelling problems and capabilities we simulated the runout of a rock avalanche on a ground formed by alluvial material under dry and saturated conditions this material can be entrained and plowed by the impacting and running rock avalanche material sensitivity of the erosion and transport mechanisms has been analysed by performing different analyses the simulated case study is the 6 10 5 m 3 arvel rock avalanche 1922 switzerland for which a reliable set of pre and post failure observations is available final geometry mass redistribution velocities and runup are used to validate the model capabilities and study the effects of different material properties

depositional features and transportation mechanism of valley filling iwasegawa and kaida debris avalanches japan the depositional features of two valley filling debris avalanche deposits were studied to reveal their transportation and depositional mechanisms the valley filling iwasegawa debris avalanche deposit ca 0 1 km3 is distributed along the valleys at the southeastern foot of tashirodake volcano northern honshu japan debris avalanche blocks range in size from 0 3 km3 is distributed along the valleys at the eastern southeastern foot of ontake volcano central japan debris avalanche blocks range in size from 25 m proximally to 7 m in the medial zone debris avalanche matrix percentages increase from 50 70 in the proximal zone to 80 in the distal zone the debris avalanche matrix is more abundant 80 90 at the bottom part of the deposit deformation structures observed in the debris avalanche blocks include elongation folding conjugate reverse faults and numerous minor faults in unconsolidated materials lithic components within the debris avalanche matrix tend to have a higher percentage of plucked clasts from the adjacent underlying formations a bingham plug flow model is consistent with the transportation and depositional mechanisms of the valley filling debris avalanches in the plug of the debris avalanche fragile blocks were transported without major rupturing due to relatively small shear stresses in regions of small strain rate the debris avalanche matrix was mainly produced by shearing at the bottom and margins of the avalanche valley filling debris avalanches tend to have smaller debris avalanche blocks and larger amounts of debris avalanche matrix than do unconfined debris avalanches these differences may be due to disaggregation of debris avalanche blocks by shearing against valley walls and interaction between debris avalanche blocks and valley walls oriented wood logs and branches reverse grading of clasts at the base and a higher proportion of incorporated clasts at the base are interpreted to result from shearing along the bottom and valley walls

rheological properties of mudflows associated with the spring 1980 eruptions of mount st helens volcano washington rheological properties of three recent mudflows at mount st helens were estimated using techniques developed for determining the properties of debris flows based on the geometry of their deposits calculated yield strengths of 1100 1000 and 400 pa maximum flow velocities of 10 to 31 m s volumetric flow rates of 300 to 3400 m s and plastic viscosities of 20 to 320 pa s all compare favorably with measured and estimated values cited in the literature a method for determining likely sites of future mudflow initiation based on these data is outlined

classification of large scale subaqueous bedforms a new look at an old problem sepm bedforms and bedding structures abstract a symposium entitled classification of large scale flow transverse bedforms was convened at the 1987 mid year meeting of sepm in austin texas with the purpose of examining the problems involved in classifying large subaqueous flow transverse bedforms developed in fluvial intertidal and marine environments and recommending changes in nomenclature the consensus of the participants is that despite the wide spectrum of morphologies of large scale flow transverse bedforms excluding antidunes they all occupy a similar position in the lower flow regime sequence between ripples and upper plane bed the wide variety of forms is a reflection of secondary effects such as channelization fluctuating water levels and unsteady and reversing flows the bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1 000 m the symposium panel proposes therefore that they should have only one name dune dune is preferred as it has historical precedence over other terms in use such as megaripple and sand wave the term dune should be modified by rimary descriptors of shape i e 2 d or 3 d and size based on spacing small 0 6 5 m medium 5 10 m large 10 100 m or very large 100 m and the adjective subaqueous when it is important to distinguish them from eolian dunes the panel recommends a morphologically based classification that is descriptive with an underlying genetic rationale second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature

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

the pandemonium creek rock avalanche british columbia in 1959 a rock spur became detached from the headwall of a cirque near pandemonium creek in the southern coast mountains of british columbia approximately 5 000 000 cu m of blocky gneissic quartz diorite debris travelled 9 0 km along a highly irregular path descending a vertical distance of 2 km to the valley of south atnarko river the high mobility of the rock avalanche is manifested by superelevation in valley bends two run ups and two right angle changes in flow direction this mobility is due in part to 1 peculiarities in the path of the landslide lateral moraines for example funnelled and accelerated the debris and 2 travel over a glacier below the detachment zone although most of the debris came to rest on the upper part of a fan at the mouth of pandemonium creek one lobe traversed the fan and entered knot lakes where it generated displacement waves that destroyed trees along the shore run up and superelevation data indicate that the debris was moving between 81 and 100 m s as it entered the run up zone at pandemonium creek and 21 38 m s in pandemonium valley to the east these velocities were analysed by applying the dynamic model of h j korner rock mechanics 1976 8 225 256 to the path of the landslide the analysis suggests that the rock avalanche had two phases a very rapid initial phase from detachment to the beginning of the run up and following sudden energy losses at the run up a second phase involving much lower velocities the pandemonium creek landslide is similar in many respects to much larger highly mobile rock avalanches in other parts of the world for example huascaran peru and little tahoma peak washington u s a although much less common than rockfalls and debris flows rock avalanches are capable of far greater damage this is a consequence of their size and the fact that they travel great distances at high velocities the potential exists for other highly mobile landslides of the pandeminium creek type in the mountains of western canada highlighting the need for caution in the future development of this region

microbes and ooids abstract the bahamian archipelago is one of the few locations in the world where ooid formation is actively occurring ooid cortices from six locations in the region were incrementally dissolved and analyzed for 14c 18o 13c mg ca and sr ca ratios ooids were examined under sem after each step in the incremental analyses to characterize the nature of dissolution radiocarbon dating indicates that ooids presently at the sediment water interface began forming across the archipelago between 1000 and 2800 yr bp and continue to form today the ooids have the same pattern of microboring alteration across the region the surface and outer cortex of the ooids are punctuated with unfilled microborings whereas the inner cortex contains two morphologies of aragonite cement filling the microborings the two morphologies of cement form in association with two different species of cyanobacteria one is solentia sp the other is interpreted to be hyella sp the chemistry of ooids from across the region is remarkably similar 18o and 13c values for all samples vary directly having a slope of approximately 1 the outer cortex has low 18o and 13c values of 3 4 and 0 2 respectively whereas the 18o and 13c values of the inner cortex are high with values of 1 9 and 6 8 respectively the presence of aragonite cement in microborings in the inner cortex increases the overall isotopic composition of both oxygen and carbon in the ooid causing it to appear close to equilibrium with seawater the isotopic variation in 18o and 13c within the cortex can be characterized as a mixing line between the low values in the unaltered ooid laminae and the aragonite cement in the microborings the most exterior portion of the ooid has very high mg ca values and is interpreted as an amorphous calcium carbonate acc coating there are two other phases in the cortex both being aragonite the outer cortex has a higher mg ca ratio and lower sr ca ratio than the inner cortex this difference in chemistry is a result of the presence of aragonite cement in the inner cortex stable isotopic and trace element results coupled with sem investigations indicate that microbes do not play a role in ooid formation but instead alter the texture and chemistry of ooids after they have formed a new model of ooid formation is proposed whereby a veneer of acc precipitates on an ooid while it is at the sediment water interface the active phase this veneer of acc later recrystallizes to aragonite needles and a new cortex layer is formed the stationary phase observations from this study lead to a deeper understanding of the chemical processes involved in ooid genesis which allow a better understanding of paleoenvironments hosting ooid formation

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

the evolution of volcanic systems following sector collapse abstract sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass comparable in scale to the largest magmatic eruptions the eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage which imply that collapse driven unloading may lead to changes in eruption rate and erupted magma compositions large sector collapses are infrequent events globally with all historical examples being relatively small in comparison to many of the events documented in the geological record as a result exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses but this is often hindered by poorly resolved stratigraphic relationships and dating uncertainties nevertheless observations from a number of volcanoes indicate sharp changes in activity following sector collapse here a global synthesis of studies from individual volcanoes in both arc and intraplate settings is used to demonstrate a number of common processes in post collapse volcanism multiple examples from large 5 km3 sector collapses in arc settings show that collapse may be followed by compositionally anomalous large volume and often effusive eruptions interpreted to originate via disruption of a previously stable upper crustal reservoir these anomalous eruptions highlight that magma compositions erupted during periods of typical i e unperturbed by sector collapse volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir if eruptible magma is not present upper crustal reservoirs may rapidly solidify following collapse without further eruption allowing more mafic compositions to ascend to the surface with only limited upper crustal modification resulting in edifice regrowth at temporarily elevated eruption rates subsequent re establishment of an upper crustal reservoir further supports a relationship between surface loading and crustal storage but long term chemical and mineralogical differences between pre and post collapse evolved magmas imply that a newly developed reservoir can overprint the influence of a preceding reservoir forming a spatially and compositionally distinct plumbing system these broad patterns are replicated in intraplate settings despite differences in scale and melting processes current evidence suggests that post collapse evolution of intraplate volcanoes can be explained by unloading induced destabilisation of the magma plumbing system rather than increased melt production what emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent storage and pressurisation eruption rates erupted compositions and the style of volcanism at any particular system may thus be modulated from the surface and long term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems observations of sharp post collapse changes in erupted compositions including the ascent of primitive mafic magmas also require a crystal dominated mid to upper crustal reservoir consistent with recent models of crustal magmatic systems

comparing landslides to fluidized crater ejecta on mars 1 we use the mars global surveyor and viking data sets to compare and contrast the geomorphology of four large martian landslides located in valles marineris to fluidized ejecta of seven fresh martian craters located in lunae planum both mass movements have flowed over the martian surface and possess characteristics seen in terrestrial mass movements we combine these comparisons with simple flow models to determine how the planar geometry of landslides and the cylindrical geometry of ejecta can generate different topographic expressions for the same input constraints our purpose is to better understand the emplacement processes of both types of mass movements our geomorphic analyses are consistent with previous views that the large martian landslides resemble large terrestrial long run out flows the planar flow model supports this inference martian landslides probably flowed as a basal glide where motion is limited to a narrow interface at the base of the mass movement geomorphic investigations of fresh multilayered ejecta indicate that their inner portions with their subtle rampart probably flowed like their landslide counterparts as a basal glide distal pronounced contiguous ramparts however resemble features akin to terrestrial debris flows the cylindrical flow model shows that differences in geometry can mask the dynamics of flow emplacement this model suggests as expected a basal glide origin for the inner portions of the ejecta surprisingly basal glide also best explains the topography of the distal ejecta ramparts

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

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

improving resolution and understanding controls on gpr response in carbonate strata implications for attribute analysis for more than a decade environmental engineering groundwater and shallow stratigraphic studies have demonstrated and advanced the usefulness of ground penetrating radar gpr in lithified and unconsolidated sedimentary deposits e g see neal 2004 and references therein despite the advances important questions still remain on factors that control the actual appearance and characteristics of gpr reflections and diffractions in any given setting

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

imaging rainfall drainage within the miami oolitic limestone using high resolution time lapse ground penetrating radar 1 the vadose zone of the miami limestone is capable of draining several centimeters of rainfall within a fraction of an hour once the water enters the ground little is known about the flow paths in the oolitic rock a new rotary laser positioned ground penetrating radar gpr system enables centimeter precise and rapid acquisition of time lapse surveys in the field two dimensional 2 d gpr time lapse surveying at a 3 min interval before during and after rainfall shows how buried sand filled dissolution sinks efficiently drain the bulk of the rainwater hourly repeated 3 d imaging of a dissolution sink in response to surface infiltration shows how the wetting front propagates at a rate of 0 6 1 2 m h traversing the 5 m thick vadose zone within hours at the same time some of the water migrates laterally into the host rock guided by stratigraphic unit boundaries average lateral propagation measured over a 28 hour period was of the order of 0 1 m h on a seasonal time frame redistribution involves the entire rock volume comparing 3 d surveys acquired after wet summer and dry winter conditions shows good gpr event correspondence but also time shifts up to 20 ns caused by the change of overall water content within the vadose zone high precision time lapse gpr imaging can therefore be used to noninvasively characterize natural drainage inside the vadose zone ranging from transient loading to seasonal variation

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

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

3d gpr reveals complex internal structure of pleistocene oolitic sandbar active oolitic sandbars like those in the bahamas figure 1 exhibit complex internal architecture with a multitude of stacked sedimentary structures ooids are round carbonate coated grains that form in tropical climates the internal anatomy of carbonate sandbars is often too complex to be captured in one and two dimensional data outcrops cores and 2d geophysical profiles provide a limited vertical view of the geologic record depositional processes are confined to the momentary subhorizontal boundary surface between sediment and water or air vertical 2d views limit the visibility of features developed on subhorizontal surfaces making interpretation of 3d internal anatomy and reconstruction of related depositional parameters difficult closely spaced 3d data are needed to accurately map sedimentary structures and improve fluid flow modeling used in water and hydrocarbon resource management 3d reflection seismic imaging has successfully been used to delineate oolitic bars in sub surface oil field

geological and geomorphological precursors of the chiu fen erh shan landslide triggered by the chi chi earthquake in central taiwan abstract special features were correlated to the geological causes of the chiu fen erh shan landslide a gigantic rockslide on a dip slope induced by the chi chi earthquake ml 7 3 in central taiwan in 1999 an aerial photo interpretation and the succeeding geological mapping of the failure were employed in this study a linear depression a steep step and a low drainage density in the landslide area were detected from the aerial photos taken in 1998 the gravitational creep was believed to result in the features of the linear depression and the low drainage density the steep step represented a buckling feature found in the field the landslide area is composed of stratified sandstone and shale with dip angles ranging 20 36 the slip surface developed along a pre existing bedding fault that resulted from flexural slip folding before the chi chi earthquake the rock on the upslope side buckled and was retained by a thick bedded sandstone downslope the earthquake shock seriously damaged the sandstone support and led to the catastrophic landslide this type of landslide is likely to occur on the moderately dipping slope of stratified rocks that were previously deformed by flexural slip folding

integration of sedimentology and ground penetrating radar for high resolution imaging of a carbonate platform ground penetrating radar has not been applied widely to the recognition of ancient carbonate platform geometries this article reports the results of an integrated study performed on an upper jurassic outcrop from the south east paris basin where coral bioherms laterally change into prograding depositional sequences ground penetrating radar profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop a ground penetrating radar profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled the excellent penetration depths of the ground penetrating radar 20 m with a monostatic 200 mhz antenna images the carbonate platform geometries ranging between outcrop workscale a few metres and seismic scale several hundreds of metres this study supports recent evidence of icehouse conditions and induced sea level fluctuations controlling the upper jurassic carbonate production

continuum simulation of flow failures dynamic aspects of several catastrophic slope failures have been evaluated by unsteady flow modelling assuming two dimensional or quasi three dimensional transient flow of an incompressible bivi

full resolution 3d radar stratigraphy of complex oolitic sedimentary architecture miami limestone florida u s a abstract at the field scale m s to 100 s m it is often difficult to define the true three dimensional form of depositional units or facies within sediments or sedimentary rocks due to inherent spatial bias in traditional data sources such as outcrops and cores full resolution 3d ground penetrating radar gpr surveying has the potential to overcome this problem southwest of miami paleotopography on the upper pleistocene miami limestone formation indicates the former presence of a large oolitic barrier bar backed by extensive ooid shoals data from three closely spaced cores and two large outcrops on the barrier bar allow initial subdivision of the miami limestone in to a lower mottled oolitic facies and an upper bedded oolitic facies however detailed correlation between the cores and outcrops is problematic due to spatial aliasing a 250 mhz full resolution 3d gpr data set was collected over an area of 45 m 24 m that encompassed the location of the three cores depth of radar wave penetration was around 6 m and both horizontal and vertical resolution was approximately 0 1 m for the 6500 m3 rock volume such that the upper bedded oolitic facies was imaged without spatial aliasing radar surfaces and intervening radar facies define two main radar package types low angle sheet and sigmoidal the low angle sheet radar packages are interpreted as oolitic shoal deposits consisting of tidal bars covered by ebb orientated straight crested sand waves the overlying sigmoidal radar packages record barrier bar formation through alongshore progradation comparable sedimentary successions from both pleistocene and modern deposits in the bahamas suggest that the three evolutionary stages recorded for the miami limestone are typical of many transgressive ooid shoal complexes

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

volcanic dry avalanche deposits identification and comparison with nonvolcanic debris stream deposits abstract a volcanic dry avalanche deposit is defined as a volcaniclastic deposit formed as a result of a large scale sector collapse of a volcanic cone associated with some form of volcanic activity avalanche transport occurred in response to the gravitational field in a manner similar to the transport of nonvolcanic debris streams e g hsu 1975 such deposits are characterized by megablock structure deformed and fractured large blocks up to several hundreds meters in diameter a megablock preserves original layering intrusive contacts or weathered surfaces of the source volcanic edifice surface topography of the deposit is characterised with hummocky relief ratios of fell height to travel distance for volcanic dry avalanche deposits are between 0 18 and 0 06 this range is similar but smaller than the value of 0 58 to 0 08 for nonvolcanic debris stream deposit this similarity suggests similar transportation mechanisms excessive travel distances as defined by hsu 1975 calculated for volcanic dry avalanche deposits give values larger than for debris stream deposits of the same volume the difference is explained by lower rigidity of the collapsing mass due to the existence of soft pyroclastic layers alteration around the vent development of fractures owing to new cryptodome intrusion and boiling of supercritical fluid contained within the collapsed mass

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

evolution of a coquina barrier in shark bay australia by gpr imaging architecture of a holocene reservoir analog abstract the holocene hypersaline carbonate system in shark bay australia is represented by microbial deposits stromatolites and thrombolites and a supratidal coquina beach ridge system which overlies the pleistocene bibra formation and is prograding seaward since 4500 years ago over supratidal intertidal microbial deposits as a consequence of late holocene sea level fall and the high volume of bivalve shells available the extent internal architecture and ridge constructional types of coquina deposits in this world heritage area have not been previously investigated in detail by cores tied with geophysical images here we document external and internal architecture of the holocene coquina system in southeast hamelin pool showing three depositional units which comprise the ridge system construction 1 tabular layers complex 2 convex up ridges and 3 washover deposits bivalve skeletons represent almost the total amount of bioclasts with symmetrical semi circular formats and valve sizes 5 9 mm based on ground penetrating radar gpr images the number of prograding layers present in each transect line varies from 252 to 433 which when compared with the measured 14 c ages shows lateral growth of the system at average rates from 10 years per layer on proximal older sequences to 30 years per layer in the younger and thicker packages which display more gentle inclination and sub horizontal arrangement divergent orientation of tabular layers relates to changes in energy of currents and waves and involves time gaps and erosion after earliest crest construction the system experienced a decrease in sea level 3600 3000 14 c years bp that left behind a sequence of parallel tabular layers with dip angles 10 to

cortical fabrics of upper jurassic ooids arab formation saudi arabia implications for original carbonate mineralogy abstract this study reports the occurrence of partly leached ooids interpreted to have been originally aragonitic that still preserve intra cortical fabric details in the upper jurassic of saudi arabia a thin dark layer of insoluble material probably organic matter separates adjacent carbonate lamellae selective leaching of carbonate occurs in each lamella yielding intra cortical moldic porosity it is the presence of the thin dark layers that allows fabric details to be preserved during and after leaching of the ooids locally the intra cortical moldic pores may be infilled by finely crystalline equant calcite cement that is interpreted to be of meteoric origin in all cases this equant calcite cement has nucleated on top of the underlying dark layer of insoluble material and has grown upward and outward until reaching the next layer if allowed to go to completion crystal growth in this fashion will produce a radial fabric similar to or even mimicking that seen in many ancient ooids this is an important observation because well preserved radial fabrics seen in ancient ooids have previously been interpreted to represent original calcite mineralogy results from this study suggest that a well preserved radial calcite fabric may be indicative of either originally aragonite or calcite mineralogy

multiconfiguration gpr measurements for geometric fracture characterization in limestone cliffs alps rock mass fracturing is a key parameter in rock fall hazard assessment however traditional geologic observations can provide information only about discontinuities at the surface in this case study detailed ground penetrating radar gpr measurements with antennas of 50 mhz 100 mhz 200 mhz and 400 mhz were conducted on a test site using different acquisition configurations deployed on vertical cliff faces conventional 2d profile data common midpoint cmp survey data and transmission data were acquired to evaluate the potential use of radar waves to characterize the geometry and properties of the major discontinuities fractures within a mesozoic limestone massif results showed that the continuity and geometry orientation and dip of the major observed fractures which are crucial parameters for assessing rock stability can be obtained by combining vertical and horizontal profiles measured along the cliff we used 100 mhz antennae and reached a maximum penetration of 20 m which limi

sediment transport and bedforms in a carbonate tidal inlet lee stocking island exumas bahamas an active oolitic sand wave was monitored for a period of 37 days in order to address the relationship between the direction and strength of tidal currents and the resultant geometry and amount and direction of migration of bedforms in carbonate sands the study area is situated in a tidal channel near lee stocking island exumas bahamas containing an estimated 5 5 to 6 105 m3 of mobile oolitic sand tidal ranges within the inlet are microtidal and the maximum current velocity at the studied site is 0 6 m s 1 at least 300 400 m3 of mostly oolitic sand are formed within or brought into the channel area every year the tidal inlet is subdivided into an ocean orientated segment in which sand waves are shaped by both flood and ebb tides and a platform orientated segment where sand waves are mainly shaped by flood tides the studied sand wave lies on the platformward flood tide dominated segment in a water depth of 3 5 4 5 m during the 37 days of observation the oolitic and bioclastic sand wave migrated 4 m in the direction of the dominant flood current the increments of migration were directly related to the strength of the tide during each tidal cycle bedforms formed depending on the strength of the tidal current tidal range and their location on the sand wave during flood tides a steep lee and a gentle stoss side formed and current ripples and small dunes developed on the crest of the sand wave while the trough developed only ripples the average lee slope of the sand wave is 24 2 and therefore steeper than typical siliciclastic sand waves during ebb tides portions of the crest are eroded creating a convex upward ebb stoss side covered with climbing cuspate and linguoid ripples and composite dunes the area between the ebb lee side and the trough is covered with fan systems sinuous ripples and dunes the migration of all bedforms deviated to a variable degree from the main current direction reflecting complex flow patterns in the tidal inlet small bedforms displayed the largest deviation migrating at an angle of up to 90 and more to the dominant current direction during spring tides

ground penetrating radar application in a shallow marine oxfordian limestone sequence located on the eastern flank of the paris basin ne france abstract a ground penetrating radar gpr survey has been carried out in upper jurassic limestones located on the eastern flank of the paris basin ne france the potential of the investigation method is assessed for delineating geologically meaningful stratifications in the shallow subsurface the fundamentals of the gpr technique are described penetration depth and vertical resolution depends on the soil conditions the characteristics of input signal and the configuration of the transmitter receiver assembly in the studied carbonates the penetration level is rather good and the electromagnetic signal reaches up to 1000 nanoseconds maximum i e approximately 55 m several depositional units are outlined on the gpr profiles six different lithological units are recognised with distinct gpr reflection characteristics the profiles illustrate the internal 3d organisation of the carbonate platform and its geometry they provide detailed insight into the nature of an oxfordian reefal build up the high resolution subsurface model is directly calibrated with geological field observations and it results in a predictive 3d depositional working model the gpr method is a non destructive remote sensing technique that is cost effective the method is considered complementary to other conventional high resolution reservoir characterisation studies it represents a powerful investigation tool in earth science studies concerning the imaging of the structure of the shallow subsurface

ice volume and sea level during the last interglacial during the last interglacial period 125 000 years ago sea level was at least several meters higher than at present with substantial variability observed for peak sea level at geographically diverse sites speculation that the west antarctic ice sheet collapsed during the last interglacial period has drawn particular interest to understanding climate and ice sheet dynamics during this time interval we provide an internally consistent database of coral u th ages to assess last interglacial sea level observations in the context of isostatic modeling and stratigraphic evidence these data indicate that global eustatic sea level peaked 5 5 to 9 meters above present sea level requiring smaller ice sheets in both greenland and antarctica relative to today and indicating strong sea level sensitivity to small changes in radiative forcing

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

diffraction imaging of sub vertical fractures and karst with full resolution 3d ground penetrating radar abstract vertical fractures with openings of less than one centimetre and irregular karst cause abundant diffractions in ground penetrating radar gpr records gpr data acquired with half wavelength trace spacing are uninterpretable as they are dominated by spatially undersampled scattered energy to evaluate the potential of high density 3d gpr diffraction imaging a 200 mhz survey with less than a quarter wavelength grid spacing 0 05 m 0 1 m was acquired at a fractured and karstified limestone quarry near the village of cassis in southern france after 3d migration processing diffraction apices line up in sub vertical fracture planes and cluster in locations of karstic dissolution features the majority of karst is developed at intersections of two or more fractures and is limited in depth by a stratigraphic boundary such high resolution 3d gpr imaging offers an unprecedented internal view of a complex fractured carbonate reservoir model analogue as seismic and gpr wave kinematics are similar improvements in the imaging of steep fractures and irregular voids at the resolution limit can also be expected from high density seismic diffraction imaging

large scale landslides in toyama prefecture central japan and their probable relationship with earthquakes large scale landslides along the kubusu and besso rivers in toyama prefecture are developed in the miocene iwaine formation which is composed of andesitic lava tuff and tuff breccia in the middle member of this formation the tuff is easily altered to montmorillonite bearing rock and subsequently plays an important role in the development of landslides events which tend to be large scale events as the massive lava of the upper member forms a cap rock over the tuff the kiritani and koinami basins which are flat intermontane basins located along the kubusu and besso rivers respectively are interpreted as landslide dammed lakes later filled with sediment accelerator mass spectrometry 14c ages show that the landslides forming each dam occurred simultaneously at approximately 2500 bp these ages were measured from wood fragments embedded in the landslide material of kiritani and from an in situ stump drowned during the impoundment of koinami if the trigger of these landslides was an earthquake it is most likely to have been the penultimate event along the atotsugawa fault zone

controls on platform scale patterns of surface sediments shallow holocene platforms bahamas isolated carbonate platforms occur throughout geological history and commonly exhibit considerable spatial variability to evaluate the controls on the nature of sediment accumulation across the expansive shallow platform tops this study systematically compares and contrasts patterns in surface sediments from several shallow 10 m holocene bahamian examples remote sensing data field observations petrographic characterization and quantitative grain size analyses reveal the spatial patterns of sediment accumulation on crooked acklins platform and the berry islands bank integration of these data with synoptic observations of waves tides and currents along with regional geochemical data provides a means to explore the factors that influence platform scale sedimentary patterns these data illustrate that the platform interiors of both crooked acklins platform and berry islands bank are blanketed with medium to coarse sand size sediment peloids are most common in the interior of crooked acklins platform whereas the berry islands bank includes more abundant composite grains in both areas very little mud is present with surface sediments averaging 2 mud comparison of these results with published data from little bahama bank great bahama bank and caicos platform suggest that contrary to previous interpretations the presence of open margins and or brisk winds are not necessary for the occurrence of a platform top with little mud although the muddy sediment fraction of the interior can be suspended by elevated wave energy wind generated current speeds in protected platform interiors are relatively low instead in parts of the platform interiors transport and winnowing of fines is enhanced greatly by tidal currents which carry suspended sediments off the shallow platforms even if shielded by islands beyond physical influences however regional geochemical compilations suggest that the bahamian tides supply highly supersaturated waters rich in dissolved oxygen to these platform interiors this exchange is interpreted to facilitate favourable conditions for calcium carbonate precipitation in the form of ooids marine cements and hardened peloids across vast expanses of the platform interiors such fundamental controls on holocene platform scale sediment dynamics are likely to have influenced carbonate systems through the geological record

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

three dimensional architecture and development of danian bryozoan mounds at limhamn south west sweden using ground penetrating radar bryozoan mounds from the middle danian lower palaeocene of the danish basin represent a possibly new class of non cemented skeletal mounds the sedimentology and palaeoecology of the mounds have recently been studied in detail three dimensional images of middle danian bryozoan mound structures in the limhamn limestone quarry south west sweden obtained from combined reflected ground penetrating radar signals and outcrop analysis provide new information about the architecture and growth development of such mounds the mounds are composed of bryozoan limestone and dark grey to black flint bands which outline mound geometries ground penetrating radar data sections are collected over a 120 m by 60 m grid of data lines with trace spacing of 0 25 m providing a depth penetration of 7 to 12 m and a vertical resolution of ca 0 30 m the ground penetrating radar images outline the geometry of the internal layering of the mounds which typically have widths and lengths of 30 to 60 m and heights of 5 to 10 m mound architecture and growth show great variability in the ground penetrating radar images small scale mound structures with a palaeorelief of only a few metres may constitute the basis for growth of larger mounds the outermost beds of the individual mounds are commonly characterized by sub parallel to parallel reflections which have a circular to slightly oval appearance in map view the mounds are mainly aggrading and do not show clear signs of pronounced lateral migration during growth although some mound structures indicate a preferential growth direction towards the south growth patterns interpreted from the ground penetrating radar images suggest that the palaeocurrents in the study area may have shown great variability even on a small scale this observation is in contrast to results from studies of extensive slightly older early danian mound complexes exposed in coastal cliffs at stevns klint and karlby klint located 50 and 200 km away from the study area respectively at these locations the mounds show a remarkably uniform development and typically are asymmetrical clearly showing migration directions towards the south these differences in mound geometry may be the result of differences in the current systems and water depths that existed during formation of the early and middle danian mounds respectively the mounds at limhamn were located closer to the basin margin in shallower water than those at stevns klint and karlby klint in addition the difference in mound architecture may be due to the occurrence of non layered irregular coral mounds intercalated with the bryozoan mounds at limhamn

three dimensional ground penetrating radar imaging of sedimentary structures fractures and archaeological features at submeter resolution contemporary geoscientific shallow subsurface assessment chiefly relies on outcrops drilling excavations and sometimes geophysics often the information gathered is insufficient to accurately characterize the archaeological and or geologic record and ongoing shallow subsurface processes that affect a variety of economic and environmental aspects of our society the extra effort of acquiring very dense ground penetrating radar gpr survey grids and three dimensional 3d data processing transforms uncorrelatable and uninterpretable gpr signals into clear images of complex shallow subsurface anatomy with an unprecedented resolution here we present two examples of noninvasive 3d shallow subsurface imaging example 1 images decimeter to meter scale sedimentary structures in a pleistocene oolite shoal barrier bar setting example 2 images the fracture network in a triassic limestone quarry denser than quarter wavelength grid acquisition in combination with 3d migration processing focuses scattered energy and removes out of plane reflections in addition to conventional vertical cross sections horizontal depth slices and data volume animations reveal previously unseen diagnostic patterns of past human activities laterally changing depositional processes and fracture networks including near vertical joints with millimeter apertures

initiation and flow behavior of the 1980 pine creek and muddy river lahars mount st helens washington two large high velocity lahars volcanic debris flows were triggered by a pyroclastic surge during the first few minutes of the may 18 1980 eruption of mount st helens the initial surge cloud evolved progressively by gravity segregation from a gas mobilized highly inflated density flow to a dense water mobilized basal debris flow lahar and accompanying ash cloud as it flowed down the east flank of the volcano the main source of the water for the lahars was probably from eroded snow and ice incorporated into the flow by turbulent mixing but ground water expelled together with the rock debris by the initiating volcanic explosions also may have contributed peak lahar discharge from the pine muddy fan upper smith creek and ape canyon probably exceeded 250 000 m 3 s initially but decreased exponentially in the downstream direction total volume of the lahars was in excess of 1 4 10 7 m 3 initial peak flow velocities in excess of 30 m s also decreased markedly downstream where flow was not impeded velocity was strongly related to the depth slope term r 2 3 s 1 2 from the manning uniform flow equation as a power law function during much of the route traveled lahar flow appears to have been supercritical deposits left in channels were generally thin relative to flow depth 0 to 2 5 m particles up to small boulder size were randomly distributed in the poorly sorted nonstratified matrix indicating complete suspension in a fully developed debris flow slurry however much larger clasts were transported as bed load computed sediment concentrations of matrix slurry samples ranged from 84 to 91 solids by weight and were similar for the two lahars two indirect methods for computing peak flow velocity previously only tentatively applied to debris flows were tested for accuracy by comparing computed lahar arrival times with recorded arrival times at swift reservoir the computed velocities appear to be 15 slower than the recorded velocities which is consistent with the restriction that the velocity formulas produce only minimum values

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

isotope signatures associated with early meteoric diagenesis the environments in which carbonate diagenesis proceeds have been documented in previous studies of holocene and late pleistocene sediments and limestones on barbados west indies variations in the carbon and oxygen isotopic composition of limestones produced during early freshwater diagenesis have been observed in this study to occur in specific patterns six potentially useful patterns emerge when one views stable isotope data within a stratigraphic framework 1 the subaerial exposure surface is characterized by strongly 12c enriched limestones 13c compositions of underlying limestones grow progressively heavier with increasing depth 2 the subaerial exposure surface may also be marked by slight 18o enrichment 3 an abrupt shift in 18o values may differentiate sediments above the exposure surface from those below 4 sediments altered in the marine meteoric mixing zone may be characterized by positive covariance between their 18o and 13c compositions 5 the vadose phreatic boundary may be marked by a sharp increase in 13c values in the seaward portions of a fresh groundwater system and 6 samples contemporaneously altered in a single fresh groundwater system within an areally restricted region should display a narrow range of 18o and a wide range of 13c compositions analysis of samples from five palaeozoic and mesozoic formations which contained petrographic evidence of early freshwater diagenesis showed that isotope patterns similar to those observed in barbados limestones have been preserved in rocks as old as mississippian these isotope patterns could prove to be useful for identifying diagenetically induced porosity trends in carbonate rocks they might be used to identify limestones diagenetically altered in meteoric environments to identify mixing zone cements and dolomites and to trace the regional and vertical distributions of early meteoric groundwater systems in ancient carbonate formations

microboring versus recrystallization further insight into the micritization process sem observations of lightly etched thin sections of bahamian sediments reveal an unusual process of micritization that involves carbonate precipitation in microborings concurrent with endolithic activity a coccoid cyanobacterium tentatively identified as solentia sp bores tunnels which initially penetrate just beneath grain surfaces and eventually extend throughout the entire grain these tunnels are filled by radial fibrous aragonite which is precipitated as the microorganism advances extensive multicyclic repetitions of this process result in obliteration of original grain textures with almost complete preservation of grain margins and rare empty bore holes the rapidly filled tunnels cannot be detected by resin cast embedding techniques that are commonly used to study microboring this type of multicyclic boring and concurrent filling of bore holes forms micritized grains that can be difficult or impossible to distinguish from micritized grains formed by recrystallization

rheologic properties and kinematics of emplacement of the chaos jumbles rockfall avalanche lassen volcanic national park california the chaos jumbles is a rockfall avalanche deposit that was emplaced by three separate events 300 years ago deposits from each event are distinguishable on the basis of morphology size variation of large dacitic surface clasts and by the color of both the matrix and entrained dacitic blocks steep lateral and distal deposit margins and surface features such as folds and apparent strike slip faults indicate that each rockfall avalanche had a finite yield strength and was being actively deformed and sheared throughout the body of the moving deposit rather than strictly along a basal surface kinematic analysis of the three deposits indicates that each had a very low apparent coefficient of friction and was emplaced at velocities of up to 100 m s these data suggest that each rockfall avalanche can be modeled as a pseudoplastic material undergoing flow parallel compression above a frictionless base this model allows calculation of deposit volumes ranging from 1 2 to 1 7 108 m3 and also suggests that a future rockfall avalanche from the same location would have a more restricted runout than the previous events

correction to regional moment magnitude relations for earthquakes and explosions in the paper regional moment magnitude relations for earthquakes and explosions by h j patton and w r walter geophysical research letters 20 277 280 1993 figure la is incorrect because of an error in our database the mb pn values due to the formula from evernden 1967 were plotted instead of the intended values of mb pn due to the formula of denny et al 1987 this error only affected the earthquakes in figure l a and the corrected figure l a is given below this error does not change any of the conclusions in the original paper the corrected figure la still shows good separation between earthquakes and explosions independent of magnitude best fit regression lines were calculated separately for the earthquake and explosion populations and are shown in fig l a the two populations now have the same slope and show a separation of 1 13 log moment units lmu one event treated as an earthquake falls quite close to the explosion population in figure la this event is the may 14 1981 event which taylor 1994 determined to be a large mine collapse at gentry mountain utah it was not treated separately from the earthquakes in the original paper but here it was excluded from the earthquake regression line fit this event has some similarities to the explosions since it occurred at a very shallow depth of approximately 200 m and is expected to radiate relatively more of its seismic energy as p waves than an earthquake

gpr imaging of dual porosity rocks insights to fluid flow dual porosity rocks such as those that are fractured and or karstic are highly heterogeneous and present a great challenge to predicting fluid flow properties

full resolution 3d gpr imaging noninvasive 3d ground penetrating radar gpr imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface full resolution imaging requires unaliased recording of reflections and diffractions coupled with 3d migration processing the gpr practitioner can easily determine necessary acquisition trace spacing on a frequency wavenumber f k plot of a representative 2d gpr test profile quarter wavelength spatial sampling is a minimum requirement for full resolution gpr recording an intensely fractured limestone quarry serves as a test site for a 100 mhz 3d gpr survey with 0 1 m 0 2 m trace spacing this example clearly defines the geometry of fractures in four different orientations including vertical dips to a depth of 20 m decimation to commonly used half wavelength spatial sampling or only 2d migration processing makes most fractures invisible the extra data acquisition effort results in image volumes with submeter resolution both

a sliding consolidation model for flow slides a model is proposed for the behaviour of flow slides in loose cohesionless materials in which the debris spreads out as a uniform sheet excess pore fluid pressures are assumed to be generated for example by undrained loading arising from the collapse of metastable structure in the source area of the flow slide under the influence of these the leading element of the debris moves downslope by basal sliding consolidating as it does so by single upward drainage as a result the pore pressure at the base of the element eventually decays to a value that brings the element to rest hence defining the run out of the flow slide the model is applicable in principle to subaqueous and subaerial flow slides and to pore fluids consisting of water gas or both of these the predictions of the model are tested against the observed behaviour and measured properties of the 1966 flow slide at aberfan south wales the results show that a sliding consolidation model provides a possible mechanism for that event

global sea level fluctuations during the last interglaciation mis 5e the geomorphology and morphostratigraphy of numerous worldwide sites reveal the relative movements of sea level during the peak of the last interglaciation marine isotope stage mis 5e assumed average duration between 13072 and 11972 ka because sea level was higher than present deposits are emergent exposed and widespread on many stable coastlines correlation with mis 5e is facilitated by similar morphostratigraphic relationships a low degree of diagenesis uranium thorium u th ages and a global set of amino acid racemization aar data this study integrates information from a large number of sites from tectonically stable areas including bermuda bahamas and western australia and some that have experienced minor uplift 2 5 m 100 ka including selected sites from the mediterranean and hawaii significant fluctuations during the highstand are evident at many mis 5e sites revealed from morphological stratigraphic and sedimentological evidence rounded and flat topped curves derived only from reef tracts are incomplete and not representative of the entire interglacial story despite predictions of much different sea level histories in bermuda the bahamas and western australia due to glacio and hydro isostatic effects the rocks from these sites reveal a nearly identical record during the last interglaciation the last interglacial highstand is characterized by several defined sea level intervals slis that include sli 1 post glacial mis 6 5e termination ii rise to above present before 130 ka sli 2 stability at 2 to 3 m for the initial several thousand years 130 to 125 ka during which fringing reefs were established and terrace morphology was imprinted along the coastlines sli 3 a brief fall to near or below present around 125 ka sli 4 a secondary rise to and through 3 4 m 124 to 122 ka followed by sli 5 a brief period of instability 120 ka characterized by a rapid rise to between 6 to 9 m during which multiple notches and benches were developed and sli 6 an apparently rapid descent of sea level into mis 5d after 119 ka u th ages are used to confirm the last interglacial age of the deposits but unfortunately in only two cases was it possible to corroborate the highstand subdivisions using radiometric ages sea levels above or at present were relatively stable during much of early mis 5e and the last 6 7 ka of mis 1 encouraging a comparison between them the geological evidence suggests that significant oceanographic and climatic changes occurred thereafter midway through and continuing through the end of mis 5e fluctuating sea levels and a catastrophic termination of mis 5e are linked to the instability of grounded and marine based ice sheets with the greenland gis and west antarctic wais ice sheets being the most likely contributors late mis 5e ice volume changes were accompanied by oceanographic reorganization and global ecological shifts and provide one ominous scenario for a greenhouse world r 2007 elsevier ltd all rights reserved