controls on the 87sr 86sr composition of seawater from the middle eocene to oligocene hole 689b maud rise antarctica a 87sr 86sr isotope curve of the middle eocene to oligocene was produced from analysis of foraminifera in ocean drilling program hole 689b maud rise near the coast of antarctica sediments from the hole are well preserved with no evidence of diagenetic alteration the sequence is nearly complete from 46 3 to 24 8 ma with an average sampling interval of 166 kyr excellent magnetostratigraphy in hole 689b allows calibration to the geomagnetic polarity time scale of cande and kent 1992 marine strontium isotopic ratios were nearly stable from 46 3 to 35 5 ma averaging near 0 70773 after which they began to increase a slow increase began after 40 4 ma rising at a rate of only about 8 10 6 m y from base values of 0 707707 from 35 5 ma to 24 8 ma the average slope increased to 40 10 6 m y the slope remained constant at least until 24 8 ma when the record becomes discontinuous owing to unconformities we evaluate several possible controls on the marine strontium isotope curve that could have led to the observed growth in 87sr 86sr ratios near the eocene oligocene boundary three mechanisms are considered including the onset of antarctic glaciation increased mountain building in the himalayan tibetan region and decreased hydrothermal activity none of the mechanisms alone seems to adequately explain the increased 87sr 86sr ratios during the oligocene glaciation as a weathering agent was too episodic and probably began too late to explain the upturn in marine 87sr 86sr ratios there is evidence that uplift in the himalayan tibetan region began in the miocene much too late to control oligocene strontium isotope ratios lastly hydrothermal flux changes since the eocene were apparently not great enough alone to account for the rise in marine 87sr 86sr ratios we suggest that a combination of causes such as decreased hydrothermal activity perhaps followed by increased glaciation and mountain building might best explain the growth of the marine 87sr 86sr curve during the oligocene

volcano dome dynamics at mount st helens deformation and intermittent subsidence monitored by seismicity and camera imagery pixel offsets the surface deformation field measured at volcanic domes provides insights into the effects of magmatic processes gravity and gas driven processes and the development and distribution of internal dome structures here we study short term dome deformation associated with earthquakes at mount st helens recorded by a permanent optical camera and seismic monitoring network we use digital image correlation dic to compute the displacement field between successive images and compare the results to the occurrence and characteristics of seismic events during a 6 week period of dome growth in 2006 the results reveal that dome growth at mount st helens was repeatedly interrupted by short term meter scale downward displacements at the dome surface which were associated in time with low frequency large magnitude seismic events followed by a tremor like signal the tremor was only recorded by the seismic stations closest to the dome we find a correlation between the magnitudes of the camera derived displacements and the spectral amplitudes of the associated tremor we use the dic results from two cameras and a high resolution topographic model to derive full 3 d displacement maps which reveals internal dome structures and the effect of the seismic activity on daily surface velocities we postulate that the tremor is recording the gravity driven response of the upper dome due to mechanical collapse or depressurization and fault controlled slumping our results highlight the different scales and structural expressions during growth and disintegration of lava domes and the relationships between seismic and deformation signals

the petrogenesis of the lac guyer komatiites and basalts and the nature of the komatiite komatiitic basalt compositional gap a sequence of ultramafic rocks in the lac guyer archean greenstone belt exhibit brecciated flow tops pillow structures and spinifex textures testifying to their volcanic origin massive spinifex textured and differentiated flows in the sequence have the chemical characteristics of peridotitic komatiite with mgo ranging from 19 25 wt associated pillowed flows have compositions that straddle the conventional boundary between komatiite and komatiitic basalt with mgo contents ranging from 16 to 19 wt mgo and are best termed pyroxenitic komatiites unlike other komatiitic occurrences the peridotitic and pyroxenitic komatiites at lac guyer constitute a continuous chemical spectrum with no evidence of population minimum near 18 wt mgo the contrasting behaviour of highly compatible elements such as ni and cr versus incompatible elements such as zr indicate that this compositional spectrum was produced by a variation in the extent of partial melting 10 40 of a garnet lherzolite source in the archean mantle the pyroxenitic komatiites represent liquids produced during lower 10 20 degrees of melting during which garnet remained in the mantle residue however a change in slope in the distribution of zr vs y between the pyroxenitic and the peridotitic komatiites indicates that garnet was completely consumed at the more extensive degrees of melting which produced the peridotitic komatiites the lac guyer volcanic rocks display a population minimum at 15 wt mgo separating komatiitic magmas whose compositions are controlled by partial melting from basalts whose composition is controlled by crystal fractionation the population minimum near 18 wt mgo which is taken as the boundary between komatiite and komatiitic basalt may have a similar origin

velocity field of the la clapiere landslide measured by the correlation of aerial and quickbird satellite images 1 two displacement maps of the la clapiere landslide france have been derived over two periods of 4 years 1995 1999 and 1999 2003 by correlation of aerial photographs and a quickbird satellite image the movement of the landslide ranges from 2 5 m to 20 m per year those values have been validated over 13 points monitored by conventional tacheometric measurements three areas with significant differences in velocity field have been mapped limits of those areas are in good agreement with in situ observations velocity maps show the low long term temporal variability of the landslide movement and its spatial variability the optical correlation method using images derived from various sensors airborne and spatial is a promising technique for improving the spatial resolution of velocity field observation of landslides over several years

video monitoring reveals pulsating vents and propagation path of fissure eruption during the march 2011 pu u ō ō eruption kilauea volcano abstract lava fountains are a common eruptive feature of basaltic volcanoes many lava fountains result from fissure eruptions and are associated with the alignment of active vents and rising gas bubbles in the conduit visual reports suggest that lava fountain pulses may occur in chorus at adjacent vents the mechanisms behind such a chorus of lava fountains and the underlying processes are however not fully understood the march 2011 eruption at pu u kilauea volcano was an exceptional fissure eruption that was well monitored and could be closely approached by field geologists the fissure eruption occurred along groups of individual vents aligned above the feeding dyke we investigate video data acquired during the early stages of the eruption to measure the height width and velocity of the ejecta leaving eight vents using a sobel edge detection algorithm the activity level of the lava fountains at the vents was determined revealing a similarity in the eruption height and frequency based on this lava fountain time series we estimate the direction and degree of correlation between the different vents we find that the height and velocity of the eruptions display a small but systematic shift in time along the vents indicating a lateral migration of lava fountaining at a rate of 11 m s from w to e this finding is in agreement with a propagation model of a pressure wave originating at the kilauea volcano and propagating through the dyke at 10 m s from w to e based on this approach from videos only 30 s long we are able to obtain indirect constraints on the physical dyke parameters with important implications for lateral magma flow processes at depth this work shows that the recording and analysis of video data provide important constraints on the mechanisms of lava fountain pulses even though the video sequence is short it allows for the confirmation of the magma propagation direction and a first order estimation of the dyke dimensions

relations between relative changes in sea level and climate shifts pennsylvanian permian mixed carbonate siliciclastic strata western united states study of pennsylvanian virgilian permian wolfcampian strata of the western united states parts of idaho utah new mexico and kansas reveals complex relations between relative changes in sea level and shifts in climate relative falls in sea level are indicated by subaerial exposure of subtidal sediments and fluvial incision through subtidal sediments changes in the character of pedogenesis and sediment transport deposition and supply and the variable distribution of climatically sensitive lithofacies within cyclothems are interpreted to reflect shifts in climate during deposition of each cyclothem the majority of stratal relationships documented herein from a number of long term climatic sedimentologic and shelf settings are consistent with a hypothesis that relative highs in sea level are accompanied by more seasonal conditions whereas relative lows are characteristically more arid uncommon deviations are present however and may be due to 1 shoaling caused by sedimentation or tectonic uplift independent of a eustatic climatic signal 2 complex sedimentologic or geomorphic responses to climate change 3 leads lags or thresholds in either glacial advance and retreat or the climatic response to such changes this study shows that coupled climatic shifts and changes in sea level exert a pronounced but varied influence on stratigraphic architecture in depositional settings across late paleozoic ramps the proposed climatically enhanced cyclic and reciprocal sedimentation model predicts that during a single eustatic fall updip areas have features indicating a more seasonal or humid climate that are overlain or overprinted by characteristics suggesting more arid climate in downdip areas that were not subaerially exposed until the late stages of a eustatic fall only more arid climatic features are represented in the terrestrial or subaerial exposure features

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

long period earthquakes and co eruptive dome inflation seen with particle image velocimetry dome growth and explosive degassing are fundamental processes in the cycle of continental arc volcanism johnson et al present novel optical geodetic observations to constrain the sources responsible for long period volcanic earthquakes which are coincident with frequent explosive eruptions at santiaguito volcano guatemala they find that acceleration in deformation of the volcanic dome extracted from high resolution optical image processing is coincident with recorded long period seismic sources based on these observations abrupt mass shift of solidified domes conduit magma or magma pads seem to be part of the mechanism responsible for generating long period earthquakes at silicic volcanic systems this study presents optical geodetic observations to constrain the sources responsible for long period volcanic earthquakes which are coincident with frequent explosive eruptions at santiaguito volcano guatemala it is found that acceleration in deformation of the volcanic dome extracted from the high resolution optical image processing is coincident with recorded long period seismic sources on the basis of these observations abrupt mass shift of solidified domes conduit magma or magma pads seem to be part of the mechanism responsible for generating long period earthquakes at silicic volcanic systems dome growth and explosive degassing are fundamental processes in the cycle of continental arc volcanism1 2 because both processes generate seismic energy geophysical field studies of volcanic processes are often grounded in the interpretation of volcanic earthquakes3 although previous seismic studies have provided important constraints on volcano dynamics4 5 6 such inversion results do not uniquely constrain magma source dimension and material properties here we report combined optical geodetic and seismic observations that robustly constrain the sources of long period volcanic earthquakes coincident with frequent explosive eruptions at the volcano santiaguito in guatemala the acceleration of dome deformation extracted from high resolution optical image processing is shown to be associated with recorded long period seismic sources and the frequency content of seismic signals measured across a broadband network these earthquake sources are observed as abrupt subvertical surface displacements of the dome in which 20 50 cm uplift originates at the central vent and propagates at 50 m s 1 towards the 200 m diameter periphery episodic shifts of the 20 80 m thick dome induce peak forces greater than 109 n and reflect surface manifestations of the volcanic long period earthquakes a broad class of volcano seismic activity that is poorly understood and observed at many volcanic centres worldwide7 on the basis of these observations the abrupt mass shift of solidified domes conduit magma or magma pads may play a part in generating long period earthquakes at silicic volcanic systems

application of image cross correlation to the measurement of glacier velocity using satellite image data abstract image to image cross correlation software is applied to pairs of digital satellite images to map the velocity field of moving ice this technique uses small scale glacial surface features such as crevasse scars and snow dunes as markers on the surface of the moving ice displacements of the surface features are mapped by selecting small image areas centered on distinct features or by dividing a large area of densely featured glacial surface into a grid of areas and searching a subsequent image for matching areas using a cross correlation algorithm interpolation of the peak correlation values allows the displacements to be measured to subpixel accuracy resulting in very precise velocity measurements cross correlation is also applied to provide image coregistration in areas devoid of bedrock exposures in such areas subtle large scale topographic undulations in the ice surface related to underlying bedrock structure may be correlated by using large image areas and low pass filtered images both types of applications are demonstrated using ice stream d and ice stream e in west antarctica as test areas a high resolution map of the velocity field of the central portion of ice stream e generated by the displacement measuring technique is presented the use of cross correlation software is a significant improvement over previous manually based photogrammetric methods for velocity measurement and is far more cost effective than in situ methods in remote polar areas

sequence stratigraphy and relative sea level history of the middle and upper ordovician of the nashville dome tennessee abstract eleven depositional sequences are present in the middle and upper ordovician of the nashville dome all but one lack lowstand systems tracts and many display evidence of subaerial exposure such as paleokarst or regional erosional truncation at their sequence boundaries which are combined with transgressive surfaces features formed during the transgression such as hardgrounds are more prominent at most sequence boundaries than are those features related to subaerial exposure all sequences have maximum flooding zones with aggradational stacking rather than discrete maximum flooding surfaces condensation features are much more common at transgressive surfaces than within the maximum flooding zone the expression of these parasequences and sequences changes with the onset of the taconic orogeny although parasequences from equivalent depositional environments can be recognized before and after the onset of the orogeny their facies composition changes completely sequences following the orogeny display fewer paleokarst features more pyritized and iron stained hardgrounds at flooding surfaces and transgressive surfaces and more phosphatic lags and mineralization at transgressive surfaces than those preceding the orogeny a relative sea level curve for the nashville dome has a long term 5 m y component presumably dominated by subsidence and a short term 1 3 m y component consisting of 10 50 m fluctuations that is primarily the result of eustasy

an upper pennsylvanian desert paleosol in the d zone of the lansing kansas city groups hitchcock county nebraska abstract this study suggests that the upper shale regressive shale in the upper pennsylvanian missourian lansing kansas city groups d zone from hitchcock county nebraska is a paleosol pedogenesis of this unit occurred during prolonged subaerial exposure on a semiarid to arid alluvial flood plain pedogenesis occurred during maximum retreat of the late pennsylvanian sea during the d zone sedimentary cycle initially clays in this unit were deposited in marine environments but as eustatic sea level continued to drop deposition became dominated by continental alluvial processes characteristics which distinguish the upper shale as a paleosol are the presence of 1 a basal subsoil caliche c soil horizon characterized by weathered limestone regolith clasts soil nodules thin laminated calcrete beds with pseudo fenestral fabric pelleted and clotty calcareous and dolomitic caliche weathered clays circumgranular cracks and root casts and 2 an upper unit b soil horizon characterized by authigenic hematite intensely weathered clays soil nodules slickensides and gypsum root casts

insights into lava dome and spine extrusion using analogue sandbox experiments abstract lava dome formation is a common process at stratovolcanoes involving the shallow intrusion or extrusion of viscous lava and may lead to the rise of spines spines are protrusions observed to extrude episodically during lava dome growth yet the structural and mechanical factors controlling their formation are only partially understood here we provide new detailed insight into lava dome growth and the production of spines using a novel set of analogue experiments extruding sand plaster mixtures from a fixed diameter conduit under isothermal conditions we trace displacement and strain with photogrammetric methods for precise and detailed monitoring of the extrusion process results show initial dome growth forming a steep sided and flat topped shape through extrusion of new material leading to slumping of oversteepening slopes forming a talus spines are found to protrude at a later stage through the dome surface along discrete circular faults that originate from the conduit walls starting a cycle of spine growth and collapse as our spines only appear after prolonged extrusion we relate their appearance to the compaction and strengthening of material within the conduit we find that spine diameter height and volume are positively correlated with increasing cohesion and therefore material strength the spine diameter was also observed to be smaller or equal to the diameter of the underlying conduit as shear extrusion occurs along vertical to outward dipping fault planes for natural domes our findings imply that spine growth may be the consequence of compaction and densification via porosity loss shearing and or outgassing of conduit magma during ascent more efficient compaction will yield wider and taller spines as a result of increasing rock strength our study further highlights the relevance of analogue experiments in the study of lava domes and spines which remain one of the most hazardous and unpredictable features at dome forming volcanoes worldwide

monitoring lava dome growth during the 2004 2008 mount st helens washington eruption using oblique terrestrial photography abstract we present an analysis of lava dome growth during the 2004 2008 eruption of mount st helens using oblique terrestrial images from a network of remotely placed cameras this underutilized monitoring tool augmented more traditional monitoring techniques and was used to provide a robust assessment of the nature pace and state of the eruption and to quantify the kinematics of dome growth eruption monitoring using terrestrial photography began with a single camera deployed at the mouth of the volcano s crater during the first year of activity analysis of those images indicates that the average lineal extrusion rate decayed approximately logarithmically from about 8 m d to about 2 m d 2 m d from november 2004 through december 2005 and suggests that the extrusion rate fluctuated on time scales of days to weeks from may 2006 through september 2007 imagery from multiple cameras deployed around the volcano allowed determination of 3 dimensional motion across the dome complex analysis of the multi camera imagery shows spatially differential but remarkably steady to gradually slowing motion from about 1 2 m d from may through october 2006 to about 0 2 1 0 m d from may through september 2007 in contrast to the fluctuations in lineal extrusion rate documented during the first year of eruption dome motion from may 2006 through september 2007 was monotonic 0 10 m d to gradually slowing on time scales of weeks to months the ability to measure spatial and temporal rates of motion of the effusing lava dome from oblique terrestrial photographs provided a significant and sometimes the sole means of identifying and quantifying dome growth during the eruption and it demonstrates the utility of using frequent long term terrestrial photography to monitor and study volcanic eruptions

localized and distributed erosion triggered by the 2015 hurricane patricia investigated by repeated drone surveys and time lapse cameras at volcan de colima mexico abstract in october 2015 patricia a major category 5 hurricane made landfall in western mexico resulting in 500 mm cumulated rainfall and lahar generation along the southerly directed montegrande valley of volcan de colima we monitored lahar deposition and erosion using time lapse trail cameras and conducted repeated camera drone overflights two days before and after the hurricane using photogrammetric processing we derive a unique dataset of high resolution digital terrain models and study the geomorphologic impacts of a single lahar event results reveal different types of erosion at 8 km distance from the volcano with overland flow and rill networks developing into major erosion gullies exceeding a depth of 4 m as well as bank collapse oversteepening and marginal erosion we find alternating deposition and erosion zones that depend on general slope and valley width and find that the overland flow related erosion is an important contributor to the bulking process of lahars moreover this study shows that camera monitoring is very useful for studying the relationship between volcano landscape evolution and hydrometeorological extremes and for rapid assessment associated with single lahar events

the role and impact of freshwater seawater mixing zones in the maturation of regional dolomite bodies within the proto floridan aquifer usa palaeogene dolostones from the sub surface of florida are ideal for the study of dolomite maturation because they record the early stages of a secondary dolomite overprint without destruction by later diagenetic overprints two distinct dolomite textures occur in the dolostones of the upper eocene ocala and lower oligocene suwannee limestones in west central florida a porous and permeable sucrosic dolomite and a less porous and relatively impermeable indurated non sucrosic dolomite in both textures the initial matrix dolomite is dully luminescent whereas the secondary overprint is dominantly luminescent cement in the suwannee and only neomorphic luminescent dolomite in the ocala the abundance of luminescent dolomite ranges from 2 to 38 which translates to 1 6 km3 of material in the suwannee and 13 5 km3 in the ocala extrapolated trace element contents sr and na and 18o values for the matrix and luminescent end members indicate a marine origin for the matrix dolomite in both units and a freshwater seawater mixing zone origin for the secondary luminescent dolomites the 18o values indicate that a saline middle mixing zone environment overprinted the suwannee but a more dilute mixing zone affected the ocala fluid fluid mixing models constrained by modern floridan aquifer hydrochemistry and extrapolated 87sr 86sr values of the luminescent phases indicate that the mixing zones operated during the late miocene to pliocene in the ocala and affected the suwannee in the pliocene the luminescent suwannee mixing zone cement reduced porosity up to threefold and permeability up to 100 fold which converted many sucrosic dolomites to indurated dolomites by contrast the neomorphic luminescent ocala dolomite did not have an appreciable impact on the maturations although freshwater seawater mixing zones were not the sites of the initial dolomitization the mixing zone environment did dramatically overprint and mature the regionally widespread dolomites of the ocala and suwannee limestones this maturation occurred shortly after formation of the proto floridan aquifer the timing suggests the matrix dolomites were ripe for alteration and that the only prerequisite for mixing zone dolomite is pre existing dolomite substrates to reduce kinetic barriers in contrast to recent claims the results of this study demonstrate that mixing zones can be effective in forming regionally significant amounts of secondary dolomite and influencing the petrophysical maturation of dolomite bodies

geochemistry of meteoric diagenesis in carbonate islands of the northern bahamas 2 geochemical modelling and budgeting of diagenesis geochemical characterization and numerical modelling of surface water and ground water combined with hydrological observations provide quantitative estimates of meteoric diagenesis in pleistocene carbonates of the northern bahamas meteoric waters equilibrate with aragonite but water rather than mineral controlled reactions dominate dissolutional lowering of the undifferentiated bedrock surface is an order of magnitude slower than that within soil filled topographic hollows generating small scale relief at a rate of 65 140 mm ka 1 and a distinctive pocketed topography oxidation of organic matter within the subsoil and vadose zones generates an average pco2 of 4 0 10 3 atm which drives dissolution during vadose percolation and or at the water table however these dissolution processes together account for 60 of the average rock derived calcium in groundwaters pumped from the freshwater lens the additional calcium may derive from oxidation of organic carbon within the lens accounting for the high pco2 of the lens waters mixing between meteoric waters of differing chemistry is diagenetically insignificant but evapotranspiration from the shallow water table is an important drive for subsurface cementation porosity generation in the shallow vadose zone averages 1 6 3 2 ka 1 phreatic meteoric diagenesis is focused near the water table where dissolution generates porosity at 1 4 2 8 ka 1 maximum dissolution rates however are similar to those of evaporation driven precipitation which occludes porosity of 4 0 s 0 6 ka 1 this drives porosity inversion from primary interparticle to secondary mouldic vug and channel porosity in the deeper freshwater lens oxidation of residual organic carbon and reoxidation of reduced sulphur species from deeper anaerobic oxidation of organic carbon may generate porosity up to 0 06 ka 1 meteoric diagenesis relies critically on hydrological routing and vadose thickness controlled by sea level as well as the geochemical processes active a thin vadose zone permits direct evaporation from the water table and drives precipitation of meteoric phreatic cements even where mineral stabilization is complete copyright 2007 john wiley sons ltd

metallogeny of the marco zone corvet est disseminated gold deposit james bay quebec canada the corvet est gold deposit is hosted by archean rocks of the superior province in the james bay region northern quebec canada the marco zone is hosted by amphibolite grade strongly foliated volcanic rocks and consists of disseminated gold with an apparent thickness ranging from 1 8 to 39 5 m and gold grades up to 23 g t 1 over 1 m that is continuous along strike for 1 3 km the lithotectonic sequence comprises footwall basaltic andesite amphibolite overlain by a lenticular unit of metadacite and then by hanging wall basaltic andesite amphibolite all intruded by quartz feldspar porphyry dikes dacite basaltic andesite amphibolite and quartz feldspar porphyry show a calc alkaline to transitional affinity and plot in the plate margin arc basalt field with typical volcanic arc trace element patterns mineralization consists of pyrite arsenopyrite pyrrhotite chalcopyrite and gold disseminated in deformed dacite in andesite amphibolite and in quartz feldspar porphyry dikes dacite and andesite display weak alteration characterized by silicification native gold forms inclusions in metamorphic quartz garnet feldspar arsenopyrite and pyrite or free grains interstitial to quartz feldspar pyrite chalcopyrite and arsenopyrite free gold in late quartz veins cut the serici tized metamorphic fabric inclusion and interstitial native gold within minerals annealed during metamorphism shows that gold mineralization is pre to syn metamorphic with some gold remobilized in later veins rhenium osmium dating of arsenopyrite yields an isochron age of 2663 13 ma for mineralization and a weighted average model age of 2632 7 ma for arsenopyrite formed during peak metamorphism the 2663 ma arsenopyrite has a low initial 187 os 188 os of 0 19 0 10 suggesting a juvenile crust or a mantle os source the sulfur isotope composition of marco zone pyrite and arsenopyrite shows that sulfur could have been leached from its volcanic host rocks or from reduction of archean seawater the corvet est deposit is interpreted to be an oro genic gold deposit 2663 ma deformed and recrystallized during amphibolite grade metamorphism 2632 ma

unconformities and porosity development in carbonate strata ideas from a hedberg conference the purpose of this paper is to highlight ideas from a hedberg conference concerning detection of unconformities and associated porosity in carbonate strata many types of information including cores and outcrops seismic data eustatic sea level curves wireline logs biostratigraphic data stable isotope trends cycle stacking patterns and tectonic and basin evolution models can be used to predict and or detect subaerial unconformities all methods of detecting subaerial exposure with these types of information have limits and pitfalls detailed analysis of the stratigraphy sedimentology and diagenetic history of a rock sequence from outcrop or core data is considered the most reliable means of detecting subaerial exposure though an integrated approach using all a ailable information is recommended the relationship between subaerial exposure and subsurface porosity in carbonates is not simple or easily predicted subsurface porosity is the product of many factors operating during deposition subaerial exposure and burial several concepts should be recognized when evaluating porosity associated with subaerial unconformities 1 carbonate diagenesis during subaerial exposure rearranges pore networks but usually does not increase the total porosity near surface dissolution can simply lower a topographic surface without increasing porosity within the host limestone in many cases total porosity in carbonates under unconformities is actually reduced during subaerial exposure 2 permeability is likely to change more than porosity during subaerial exposure increasing in some c ses but decreasing in others 3 pore systems evolve with time during subaerial exposure short periods of subaerial exposure 10 000 400 000 yr are often associated with greater porosity than long intervals of subaerial exposure 1 20 million yr prolonged subaerial exposure may change permeability less than porosity because high permeability karst related conduits can form quickly and persist for millions of years 4 many carbonates subjected to subaerial exposure have little or no porosity in the deep subsurface because compaction cementation and stratal collapse reduce porosity during burial 5 unconformity related diagenesis may enhance reservoir potential by creating pore systems that are resistant to compaction during deeper burial 6 vugs caverns and breccias can fo m in the deep subsurface because of dissolution by basinal fluids independent of subaerial exposure 7 lithologic changes at unconformities like shales overlying carbonates can influence the flow of subsurface fluids during end page 857 deeper burial resulting in deep burial dissolution localized along unconformities if subaerial exposure and exposure surfaces are integrated into a sequence stratigraphic paleogeographic and climatic framework systematic and hopefully predictable patterns will emerge however we do not fully understand the complex interplay between the factors critical to creating and preserving porosity in carbonates additional research is needed to quantify critical processes and products so we can reliably predict porosity associated with subaerial exposure during exploration in frontier basins and on a smaller scale during reservoir analysis

surface motion of mountain glaciers derived from satellite optical imagery a complete and detailed map of the ice velocity field on mountain glaciers is obtained by cross correlating spot5 optical images this approach offers an alternative to sar interferometry because no present or planned radar satellite mission provides data with a temporal separation short enough to derive the displacements of glaciers the methodology presented in this study does not require ground control points gcps the key step is a precise relative orientation of the two images obtained by adjusting the stereo model of one slave image assuming that the other master image is well georeferenced it is performed with numerous precisely located homologous points extracted automatically the strong ablation occurring during summer time on the glaciers requires a correction to obtain unbiased displacements the accuracy of our measurement is assessed based on a comparison with nearly simultaneous differential gps surveys performed on two glaciers of the mont blanc area alps if the images have similar incidence angles and correlate well the accuracy is on the order of 0 5 m or 1 5 of the pixel size similar results are also obtained without gcps an acceleration event observed in early august for the mer de glace glacier is interpreted in term of an increase in basal sliding our methodology applied to spot5 images can potentially be used to derive the displacements of the earth s surface caused by landslides earthquakes and volcanoes

permeability loss with depth in the cenozoic carbonate platform of west central florida relationships between matrix permeability and depth in shallow buried 500 m cenozoic limestones of florida were investigated using more than 12 000 minipermeameter measurements on 1210 m of slim hole core these data are considered representative of the matrix permeability reduction that accompanies early burial of shallow water subtidal to peritidal nonreefal carbonates of sta ble cratonic margins platforms shelves and ramps measured matrix permeabilities range from less than 4 0 to 6450 md for both limestones and dolostones although the median permeability of limestones 88 md exceeds that for dolostones 15 md sucrosic dolostones which have high intercrystalline po rosities have median matrix permeabilities of 1000 md non sucrosic dolostones which are much less porous have median matrix permeabilities of only 13 md neither population of dolostones exhibits a permeability with depth trend low permeability limestones consist of mudstones wackestones tidal laminites pedogenetically altered limestone lime mud rich breccia and well cemented grain supported rocks these low permeability limestones all exhibit median matrix permeabilities less than 35 md and none exhibit permeability with depth trends in contrast high mud packstones low mud packstones very low mud packstones and grainstones exhibit larger median matrix permeabilities 69 129 181 and 418 md respectively and a systematic reduction with depth in their mean and maximum permeabilities least squares exponential regressions indicate that burial depth explains 22 31 of the permeability variance in these grain supported rocks the balance of the variability within each textural class is attributed to variation in facies grain types grain sizes sorting etc and the amount of early preburial cementation in the absence of permeability enhancement by deep subsurface diagenesis or fracturing extrapolation of the permeability with depth trends suggests that the limestones that have the best reservoir potential in the deeper subsurface are grain supported limestones that have higher than begin page 1254 average matrix permeabilities in the near surface realm petrographic analyses and consideration of diagenetic histories suggest that matrix permeability of the dolostones and low permeability limestones was determined by early near surface dolomitization and cementation respectively and has yet to be affected by burial processes petrographic observations also suggest that the depth signal in grain supported limestones results from mechanical compaction and the onset of grain to grain pressure solution extrapolation of the matrix permeability data indicates that permeability loss with burial occurs faster than the documented burial related porosity loss for the same group of rocks this indicates that limestone permeability is more sensitive to burial compaction than limestone porosity thus preservation of reservoir quality rock during burial is more dependent on permeability preservation than on porosity preservation

reinterpretation of the peninsular florida oligocene an integrated stratigraphic approach abstract a very thick 300 m nearly continuous oligocene section exists in southern peninsular florida as revealed by lithostratigraphic biostratigraphic mollusks and dinocysts chronostratigraphic sr isotopes and petrographic analyses of twelve cores and two quarries the oligocene deposits in the subsurface of southern florida are the thickest documented in the southeastern u s and they also may represent the most complete record of oligocene deposition in this region no major unconformities within the oligocene section are detected in the southern portion of the peninsula hiatuses at the eocene oligocene boundary the early oligocene late oligocene boundary and the late oligocene miocene boundary are of limited duration if they exist at all no significant disconformity is recognized between the suwannee limestone and the arcadia formation in southern florida however on the coast of florida a hiatus of more than 12 m y spanning from at least the middle of the early oligocene to early miocene is present the suwannee limestone was deposited during the early oligocene the top of the suwannee limestone appears to be diachronous across the platform the suwannee limestone previously identified incorrectly as a late oligocene unit is herein documented to be early oligocene and is encompassed in the lower oligocene suwannee limestone an unnamed limestone found on the east coast of the peninsula is at least in part correlative with the suwannee limestone the arcadia formation basal hawthorn group accounts for a large portion of the oligocene deposition in southern florida spanning the interval from the middle of the early oligocene to at least the early miocene comparisons of the depositional patterns and the distribution of dolomite and phosphate within the suwannee limestone and the arcadia formation suggest fluctuating sea levels and that the paleo gulf stream played a role in determining the nature and extent of oligocene deposition in peninsular florida

time partitioning in cratonic carbonate rocks dissimilarity in relations between thickness duration and accumulation rate in holocene sections metre scale phanerozoic cycles and epoch interval phanerozoic sequences reflects variation in the distribution of depositional and hiatal time at different scales of observation modern accumulation rates are strongly dependent on duration of deposition lower rates correspond to longer durations phanerozoic cycle thicknesses are similar to those of holocene sections suggesting that both formed while filling similar amounts of accommodation space however accumulation rates of phanerozoic cycles and sequences are about two orders of magnitude less than in modern settings and they show neither strong dependence on duration of accumulation nor significant variation over phanerozoic time hence net accumulation is primarily controlled by regional subsidence rate these relations also allow for determination of that fraction of cycle period recorded as rock and that corresponding to hiatal time at intercycle boundaries depending on subsidence rate and amount of compaction most cratonic carbonate units accumulated over 3 to 30 of the time represented by sequences in which they occur

low cost volcano deformation monitoring optical strain measurement and application to mount st helens data summary this paper describes an innovative method of volcano deformation measurements applied to camera images taken from the 2004 2008 eruption period at mount st helens dome growth was thought to be characterized by sustained near linear rates of a solid dacite plug through spatial digital image correlation dic analysis of the camera images new evidences arise that the deformation and strain rate of the spine was more complex dic yielded cumulative and incremental displacements strain and shear planes at decimetre resolution it was found that dome extrusion rates are highly non linear decelerating prior to partial collapse followed by a pronounced dome extrusion increase and direction change associated processes have been identified through dic such as shallow landslides and reworking of talus apron material the work highlights the strengths of camera strain monitoring and illustrates that dome growth and collapse is a very dynamic process complexly interplaying with the surrounding

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

first u pb zircon ages of granitoid plutons from the la grande greenstone belt james bay area new quebec zircon ages from three granitoid plutons are the first to be reported from the la grande greenstone belt two of the dated samples are from highly tectonized early tectonic plutons that at the present level of erosion are just outside the greenstone belt proper their zircon ages of ca 2740 ma are emplacement ages or alternatively represent the age of maximum deformation of the greenstone belt the third sample is from a mildly deformed late tectonic pluton within the greenstone belt its zircon age of ca 2670 ma probably represents the emplacement age the above dates and the relationships of the dated plutons to the greenstone belt as a whole suggest that the bulk of the volcanism in the la grande belt is older than 2 7 ga this limiting age indicates that the age of the la grande supracrustals is similar to those of the other greenstone belts in the superior province

an extensive erosion surface of a strongly deformed limestone bed in the gushan and chaomidian formations late middle cambrian to furongian shandong province china sequence stratigraphic implications abstract in order to understand sequence development and sea level fluctuations during the late middle cambrian to early furongian on the north china epeiric platform the present study focuses on a unique subtle erosion surface of an extensive approx 100 km strongly deformed limestone bed in the uppermost part of the gushan formation shandong province china the gushan formation and the overlying chaomidian formation consist mainly of shales and a variety of carbonates that were deposited in subtidal environments e g deep subtidal shallow subtidal shoreface shoal subtidal microbial flat and restricted platform interior three third order depositional sequences s1 3 are identified each of which comprises a thin transgressive systems tract tst and a relatively thick highstand systems tract hst each sequence is bounded by a drowning unconformity sb1 a subaerial unconformity sb2 or a surface of submarine erosion sb3 the upper sequence boundary sb2 of sequence 1 s1 is represented by a subtle erosion surface of an extensive deformed limestone bed with a wide variety of soft sediment deformation structures e g lime mudstone breccias chaotic wacke packstone laminae and fragments homogenized oolites and clastic dykes and is overlain by small sporadic microbial buildups and an extensive bioclastic grainstone bed the deformed limestone was formed during early diagenesis by differential deformation processes brecciation liquefaction fluidization and injection which were most likely induced by pore water overpressure during the period of rapid sea level fall despite the lack of subaerial exposure features e g paleokarst paleosol etc the characteristics of the erosion surface cutting well lithified sediment below the missing of a significant geological record the prochuangia biozone and the worldwide correlatable positive carbon isotope excursion collectively indicate that the erosion surface developed under conditions of subaerial exposure after contemporaneous marine cementation of the deformed sediment the missing of the prochuangia biozone is most likely due to non deposition at a subaerial hiatal surface the erosion surface was submerged as a result of subsequent rise in sea level where sporadic microbial buildups formed under suitable conditions freshly deposited winnowed shell dominated transgressive lag deposits containing chuangia trilobite fragments brachiopod shells and abundant glauconite grains formed with continued rise in sea level which became in turn overlain by shale dominated facies the unique combination of the subtle erosion surface sensu stricto a subaerial unconformity and the underlying deformed limestone bed provides an important criterion for recognizing the subtle changes in relative sea level on shallow epeiric platforms

deciphering the impact of sea level changes and tectonic movement on erosional sequence boundaries in carbonate successions a case study from tertiary strata on grand cayman and cayman brac british west indies abstract the stratigraphic architecture of carbonate successions that develop on geographically isolated islands reflects the balance between sea level highstands lowstands and tectonic activity this is readily apparent in the tertiary carbonate sequences on the cayman islands that are formed of the bluff group which includes the brac formation lower oligocene cayman formation middle miocene and pedro castle formation middle pliocene these strata are overlain by the pleistocene ironshore formation the unconformities that define the boundaries between these formations are variable because some developed during one cycle of past erosion others developed through two or more past erosional cycles and some are still developing today some unconformities like the one at the top of the cayman formation are geographically variable because they underwent different developmental histories in different areas the challenge with architectural complex successions like those on the cayman islands is that of deciphering the impact of sea level changes as opposed to tectonic influences during sea level lowstands the older carbonate successions were exposed on land and modified by surface and subsurface karst development at the same time marine erosional processes affected the coastal areas surface karst modification which commonly produced rugged topographies with erosional relief at least 62 m was controlled largely by rainfall runoff and stratal dip weathering on grand cayman at the end of the miocene for example produced a dish shaped topography with elevated peripheral rims in contrast uplift of the east end of cayman brac between the late pliocene 3 6 ma and 400 ka elevated the basal part of the cayman formation 33 m above sea level subsequent karst development which is still ongoing today removed most of the cayman formation on the eastern part of the island and produced peripheral rims that are higher than those on grand cayman during some lowstands like that between the late pliocene and 400 ka coeval coastal erosion led to the development of coastal benches that cut into the older carbonate strata the combination of karst development in the islands interiors and coastal erosion produced complex rugged topographies that strongly influenced patterns of deposition during the following highstand the complex stratigraphic architecture of the carbonate successions on the cayman islands reflects the variable impact of tectonics karst development and coastal erosion that was associated with each lowstand highstand cycle

accommodation and sedimentary architecture of isolated icehouse carbonate platforms insights from forward modeling with carb3d abstract a fundamental control on the evolution of carbonate platforms is accommodation the space available for sediment deposition here we adopt a sensitivity analysis approach using the process based forward model carb3d to quantitatively investigate the sedimentary response of isolated carbonate platforms to individual accommodation drivers of eustasy subsidence and surface dissolution sediment production the mechanism invoked to fill accommodation is also investigated fourth order milankovich driven sea level cycles dominate icehouse carbonate sedimentology with 400 ky cycles modulating the effect of 100 ky cycles of comparable magnitude when both cycles are present both overwhelm higher frequency lower amplitude fifth order cycles which are rarely preserved on the platform top subsidence is a fundamental control on sedimentary stacking patterns sequence boundary frequency sbf and platform geometry with rapid subsidence increasing the preservation of platform top sequences most icehouse platforms are subject to extended periods of platform top exposure missed beats when the platform top remains emergent at a sea level maximum are common and create non milankovich sbfs furthermore during platform emergence surface lowering via surface dissolution also creates accommodation for the subsequent platform flooding event with surface dissolution rates in humid climates comparable to moderate rates of subsidence however accommodation generation by surface dissolution is self limiting in as much as accommodation generated by dissolution is rapidly refilled on flooding sediment production is a key control on unfilled accommodation which our simulations suggest is considerable on icehouse platforms increased shallow water 3 m depth sediment production enhances intra platform bathymetric relief between the margin and interior this is driven in large part by a higher sedimentation rate at the margin than in the interior platforms can be flooded to depths up to 45 m during marine transgressions and accommodation often remains unfilled there are two distinct phases of platform top sedimentation during the transgression and early highstand platform margins accumulate at a greater rate than interior sediments generating differential intra platform bathymetry subsequently accommodation in the interior fills by forced regression and progradation from the margins into the platform interior numerical forward models can augment our understanding of icehouse carbonate platform evolution by identifying the nature of the sedimentary response to individual controls they can thus contribute to improving characterization of carbonate reservoirs in icehouse platforms such as the large hydrocarbon fields in the north caspian and s e asia

u pb zircon ages for rocks from the island lake greenstone belt manitoba the archean hayes river group of the island lake greenstone belt superior province sachigo subprovince comprises mafic to felsic metavolcanics subvolcanics and associated metasedimentary rocks the hayes river group is intruded by granitoid rocks belonging to the early intrusive complex one such pluton the bella lake tonalite is intrusive into the metabasalt of the hayes river group and has a u pb zircon age of 2886 15 ma similar intrusives of this complex either internal or marginal to the greenstone belt yield zircon ages of 2801 8 ma pipe point tonalit and 2768 22 ma linklater island prophyry this suggests that the early intrusive complex was emplaced over an 120 ma long interval by at least three separate intrusive episodes subsequent to the emplacement of the early intrusive complex the isoclinally folded hayes river group and the early intrusive complex were uplifted eroded and followed by the unconformable deposition of the island lake group comprising fluvial to marine

two hundred million years of karst history dachstein limestone hungary platform carbonates of the upper triassic dachstein limestone in naszaly hill have been karstified extensively over the past 200 million years they provide an excellent example of polyphase karstic diagenesis that is probably typical of many subaerially exposed carbonate sequences seven karstic phases are recognized in the area each of which include polyphase karstic events the first karst phase was associated with the lofer cycles meteoric waters caused dissolution enlarged fractures and cavities were filled by marine and or vadose silts and cement the second karst phase was caused by local tectonic movements bedding plane controlled phreatic caves were formed and filled by silts the third karst phase lasted from the end of the triassic to the eocene this was a regional multiphase karstic event related to younger composite unconformities bauxitic fill is the most characteristic product of this phase the karst terrain reached its mature or senile stage with very little porosity narrow veins and floating rafts of white calcite marks karst phase 4 which resulted from hydrothermal activity associated with palaeogene magmatism the early rupelian phase of alpine uplift caused large scale rejuvenation of the former karst terrain karst phase 5 subsequently naszaly hill was buried as an area of juvenile karst with significant porosity a second period of hydrothermal activity in the area karst phase 6 was induced by miocene volcanism which resulted in wide pale green calcite veins finally karst phase 7 was of tectonic origin following the most recent miocene uplift of the naszaly hill the carbonates have again become the site of vadose karst development

late dinantian palaeokarst of england and wales implications for exposure surface development palaeokarst is an important feature of late dinantian exposure surfaces soil filled depressions are widely developed these are comparable to modern day solution dolines and were probably interspersed by areas of relatively bare limestone pavement the palaeokarst primarily exhibits a smooth mamillated to potholed surface form consistent with its formation beneath a soil cover areas between the depressions have been extensively stylolitised and would likely have originally been characterized by small scale fretted and sculpted karren forms typical of subaerial karstification palaeokarst pits making up the depressions are thought to have been initiated through stem flow drainage from trees rain water intercepted by the crown of the tree was concentrated at specific sites on the emergent surface and dissolution beneath the trunk produced cylindrical pits that propagated vertically downwards trees responsible for concentrating drainage may also have enhanced the acidic nature of the rain water through leaching of organic acids from foliar and woody tissues downward propagation of the pits was limited to the uppermost 1 2 m and enlargement primarily occurred through lateral amalgamation of adjacent pits once initiated continued development of the depressions would have been self perpetuating the preferential accumulation of volcanic ash and organic matter enhancing water retention and encouraging further vegetation growth in contrast intervening areas would have been characterized by slow vertical denudation only karstification likely took of the order of a few hundred years in the case of potholed palaeokarstic surfaces formed solely by stem flow drainage to a few tens of thousands of years where the palaeokarst is more mature

imaging the 2013 explosive crater excavation and new dome formation at volcan de colima with terrasar x time lapse cameras and modelling abstract the summit region of steep volcanoes hosting lava domes often displays rapid geomorphologic and structural changes which are important for monitoring the source region of hazards explosive crater excavation is often followed by new lava dome growth which is one of the most dynamic morphometric changes that may occur at volcanoes however details of these crater formations and the ensuing new dome growth remain poorly studied a common problem is the lack of observational data due to hazardous field access and the limited resolution of satellite remote sensing techniques this paper describes the destructive constructive crater activity at volcan de colima mexico which occurred between january and march 2013 the crater geometry and early dome formation were observed through a combination of high resolution terrasar x spotmode satellite radar images and permanently installed monitoring cameras this combined time lapse imagery was used to identify ring shaped gas emissions prior to the explosion and to distinguish between the sequential explosion and crater excavation stages which were followed by dome growth by means of particle image velocimetry the digital flow field is computed from consecutive camera images showing that vertical dome growth is dominant at the beginning the upward growth is found to grade into spreading and a lateral growth domain after approximately two months of gradually filling the excavated craters with new magma the dome overflows the western margin of the crater and develops into a flow that produces block and ash flow hazards we discuss and compare the observations to discrete element models allowing us to mimic the vertical and lateral growth history of the dome and to estimate the maximum strength of the bulk rock mass moreover our results allow a discussion on the controls of a critical dome height that may be reached prior to its gravitational spreading

glacial eustasy during the cenozoic sequence stratigraphic implications a newly constructed composite oxygen isotope record is a proxy for eustasy that extends back to the cretaceous tertiary boundary and provides an independent test of sequence stratigraphic based eustatic curves the isotope record shows several eustatic episodes that are consistent with the geological record of ice sheet evolution the first evidence for the existence of an ice sheet in east antarctica occurs near the lower middle eocene boundary base of the lutetian stage there is no evidence for a large ice sheet on antarctica prior to this time however strata of this age are lacking over most of the continent the isotope curve also indicates that the ice sheet experienced phases of growth during the late eocene and middle oligocene followed by a decrease in volume in the early miocene the ross sea stratigraphic record indicates initial evolution of the west antarctica ice sheet during the early miocene by the middle miocene the ice sheet spread across the ross sea weddell sea and antarctic peninsula continental shelves the pliocene pleistocene record of glaciation in antarctica includes numerous glacial erosion surfaces on the continental shelf indicating repeated advance and retreat of both east and west antarctica ice sheets these volume changes in the antarctica ice sheet were in response to the rise and fall of sea level caused by expanding and contracting northern hemisphere ice sheets there is a reasonable correlation between eustatic curves derived from sequence stratigraphic studies and the composite oxygen isotope record since the middle eocene this correlation indicates that glacial eustasy has been the principal factor regulating stratal stacking patterns on a global scale since the middle eocene

the recognition and interpretation of paleokarsts two examples from the lower carboniferous of south wales abstract criteria for the identification and interpretation of paleokarstic surfaces in ancient carbonate sequences are discussed and two examples of such surfaces are described from the lower carboniferous of south wales one type is compared to kavornossen karren a type of tropical karst well developed today on puerto rico the second example a mammillated paleokarstic surface of a type common in the lower carboniferous is interpreted as a deckenkarren formed beneath a vegetation cover and similar to the makondo karsts of south africa paleokarsts can provide information on the paleoclimates paleohydrology and vegetation cover existing at the time of their formation

magmatic interaction between mantle and crust during the evolution of the archean lac guyer greenstone belt new quebec the lac guyer greenstone belt was one of a series of volcanic troughs active during the archean in the james bay territory of the superior province of quebec the belt consists of a succession of i

large volumes of anatectic melt retained in granulite facies migmatites an injection complex in northern quebec abstract the opinaca subprovince in the superior province of northern quebec is a metasedimentary belt characterized by metagreywacke rocks that record a late archean granulite facies metamorphism and contains abundant thin veins of leucogranite regional scale study of this subprovince provides insight to the net budget of anatectic melt loss versus accumulation in the lower middle continental crust during anatexis a petrological study indicates that the metagreywackes partially melted at 820 c and 7 kbar and generated 1 from the metamorphic peak at 2666 ma to the granite solidus at 2636 ma the large discrepancy about 50 between the volume of anatectic melt produced locally in situ and the observed volume of leucogranite in the terrain indicates that anatectic melt accumulated in the opinaca subprovince it is an injection complex this finding that granulite facies terranes can be enriched in melt contrasts with the general view that granulite terranes are melt depleted the presence of an injection complex in the deep crust has several broad implications for the continental crust 1 h 2 o released as the injected melt crystallized rehydrated the adjacent granulite facies rocks which is evident from orthopyroxene replaced by amphibole and biotite consequently these deep rocks would be more fertile in a subsequent anatectic event than non rehydrated residuum 2 the retention of voluminous leucogranite in the injection complex has thermal consequences for the crust first the bulk composition of the crust containing the injection complex is necessarily more felsic thus the budget of heat producing elements th u and k is locally enhanced and radiogenic heat production is higher secondly latent heat of crystallization is released at a deeper level where the leucogranite solidifies the combined effect of both maintains the lower crust several tens of degrees warmer for longer period of time

investigating lava flow rheology using video analysis and numerical flow models abstract lava rheology is a major control on lava flow behavior and a critical parameter in flow simulations but is very difficult to measure at field conditions or correctly extrapolate from the lab scale we present a new methodology for investigating lava rheology through a combination of controlled experiments image analysis and numerical forward modeling our experimental setup part of the syracuse university lava project http lavaproject syr edu includes a large furnace capable of melting up to 450 kg of basalt at temperatures well above the basalt liquidus the lava is poured onto either a tilted bed of sand or a steel channel to produce meter long flows this experimental setup is probably the only facility that allows such large scale controlled lava flows made of natural basaltic material we document the motion of the lava using a high resolution video camera placed directly above the flows and the temperature using infrared probes and cameras after collecting the footage we analyze the images for lava deformation and compare with numerical forward models to constrain the rheological parameters and laws which best describe the flowing lava for the video analysis we employ the technique of differential optical flow which uses the time variations of the spatial gradients of the image intensity to estimate velocity between consecutive frames an important benefit for using optical flow compared with other velocimetry methods is that it outputs a spatially coherent flow field rather than point measurements we demonstrate that the optical flow results agree with other measures of the flow velocity and estimate the error due to noise and time variability to be under 30 of the measured velocity our forward models are calculated by solving the stokes flow equations on an unstructured finite element mesh defined using the geometry of the observed flow itself we explore a range of rheological parameters including the lava s apparent viscosity the power law exponent m and the thermal activation energy our measurements of apparent viscosity agree well with predictions of the composition based shaw 1972 and grd model giordano russell and dingwell 2008 we find that for the high temperature portion of the flow a weakly shear thinning or newtonian rheology m 0 7 with an effective activation energy of b 5500 j gives the best fit to the data our methodology is the first time that high resolution optical flow analysis of flowing lava is combined with numerical flow models to constrain rheology the methodology we present here can be used in field conditions to obtain in situ information on lava rheology without physical interaction with the flow and without being limited to point wise low strain rate local measurements currently available through the use of rotational viscometers in the field

volcano tectonic control of merapi s lava dome splitting the november 2013 fracture observed from high resolution terrasar x data abstract volcanism at active andesite dacite volcanoes is often associated with the formation and collapse of circular shaped protrusions of extruded highly viscous lava the so called domes which are emplaced in the near summit region growing domes may experience stable and instable structural phases with a gradual transition in between dome collapse and the break off of instable blocks of viscous lava may lead to pyroclastic flows one of the most lethal hazards at stratovolcanoes at merapi volcano indonesia a new dome started growing in the summit region in the amphitheater formed in the course of the climactic 2010 eruption three years later the dome reached a height of approximately 100 m and diameters of 220 and 190 m with a plateau like surface area of 40 000 m2 approximately on 18 11 2013 an explosion occurred without identified precursors leaving a major fracture cutting the complete dome structure based on high resolution terrasar x satellite radar imagery we could identify the linear fracture traceable over 200 m in the long axis up to 40 m wide after geocoding of the radar amplitude imagery the fractures azimuthal trend could be compared to other structural lineaments indicative of a significant nnw sse structural direction that has formed on merapi volcano in the past the merapi dome fractured in a nw se direction and is consistent with the alignment of regional tectonic structures and of anticipated directions of pyroclastic flows the fracture may be part of a larger volcano tectonic system and may affect the dynamics and the stability of the merapi dome

penetrative calcretes and their stratigraphic implications multiple calcrete horizons previously considered representative of true subaerial exposures may in fact be false penetrative calcretes related to only one subaerial exposure event individual subaerial exposure periods can produce a true surficial calcrete plus a series of penetrative calcretes although penetrative calcrete horizons are not laterally traceable over long distances they are very similar to surficial calcretes are commonly found at sequence and or lithologic boundaries permeability anomalies and can be easily misinterpreted in core borings as representing individual exposure events recent penetrative calcretes are common on elevated limestone ridges of the caicos islands where roots penetrate downward seeking ground water moisture in glacial times penetrative calcretes may have been present throughout carbonate platforms as ground water levels were much lower penetrative and surficial calcretes can be differentiated by the lower concentrations of insoluble al and fe in penetrative calcretes

karst controlled reservoir heterogeneity in ellenburger group carbonates of west texas petroleum production from restricted shelf carbonates of the lower ordovician ellenburger group is commonly considered to have been a result of a pervasive relatively homogeneous tectonic fracture system within the reservoir rock however regional facies and diagenetic paleokarst studies of ellenburger strata based on cores and wireline logs have demonstrated that significant reservoir compartmentalization was caused by karst modification in the upper part of the unit ellenburger group carbonates which attain a thickness of over 1 700 ft 520 m record sedimentation on a shallow water restricted shelf occupying most of west texas logging of over 10 000 ft 3 050 m of core from 63 wells has allowed recognition of six facies assemblages 1 lithic arenite 2 mixed siliciclastic carbonate packstone grainstone 3 ooid peloid grainstone 4 mottled mudstone 5 laminated mudstone and 6 gastropod intraclast packstone grainstone these facies assemblages record initial transgression and subsequent progradation and aggradation paleoslope was generally south and east from the texas arch toward the ouachita and marathon orogenic belts all facies assemblages with the local exception of the ooid peloid grainstone assemblage are characterized y very low intergranular and intercrystalline porosity porosity development in ellenburger group carbonates is directly related to a prolonged period of subaerial exposure that coincided with a middle ordovician eustatic lowstand prior to transgression of simpson group siliciclastics during this episode a widespread system of caves sinkholes joint controlled solution features and collapse breccias developed of particular importance to reservoir development was the formation of a regionally extensive cave system between 100 and 300 ft 30 and 90 m beneath the exposed ellenburger surface infill of this cave system by simpson group sand and clay segmented the upper ellenburger into three karst facies which are in descending order 1 cave roof dolomites fracture and mosaic breccias 2 laterally persistent cave fill facies siliciclastic matrix supported and carbonate matrix supported breccias and 3 lower collapse facies chaotic clast supported breccias of the cave floor pronounced vertical segregation of permeable zones defined by the three karst facies is evident in the emma andector martin block 13 and several other major ellenburger reservoirs lateral reservoir heterogeneities formed by localized laterally extensive collapse structures such as in the shafter lake reservoir also contribute to compartmentalization of producing zones within the upper ellenburger group secondary and tertiary recovery programs in these ellenburger reservoirs can be optimized by integrating concepts of lateral and vertical heterogeneity predicted by the karst model

palaeosols in microtidal carbonate sequences sierra de utiel formation upper cretaceous se spain abstract the sierra de utiel formation upper coniacian to lowermost campanian of the prebetic and iberian ranges consists of a thick 70 120 m carbonate series of stacked thin shallowing up cycles 0 4 0 6 m average that were developed in an extensive shallow epeiric sea control was mainly by a humid climate and by the virtual absence of tides each of these cycles basically consists of a shallow subtidal unit capped by a supratidal unit characterized by calcrete development by considering the maturity of the soils as a guide to its formation time palaeosol analysis emerges as a useful tool for the analysis of these monotonous peritidal series a statistical study of the variations of degree of calcrete maturation and of other variables such as cycle thickness and subtidal facies up through the sierra de utiel formation allows the recognition of three transgressive regressive sequences that correspond to three successive 3rd order cycles further each small cycle could be the result of 5th order sea level changes in tune with milankovitch orbital rhythms the available data however do not allow the rejection of a sedimentary autocyclical origin for the smaller cycles

evolution and distribution of porosity associated with subaerial exposure in upper paleozoic platform limestones west texas middle pennsylvanian lower permian limestones in the subsurface of west texas were studied to determine how subaerial exposure and freshwater diagenesis karstification affected porosity distribution in meter scale cycles approximately 87 depositional cycles are present in the gross reservoir interval depths of 2600 3000 m and each cycle is interpreted to represent a glacio eustatic sea level fluctuation using recent radiometric age dating average cycle duration is estimated at 160 000 yr per cycle reservoir grade porosity 4 occurs in 5 25 of the gross reservoir section porosity is stratified occurring in 1 6 m thick intervals in the upper part of cycles that were subaerially exposed however many cycles that were subaerially exposed now lack porosity diagenesis and porosity development have distinct patterns related to duration of subaerial exposure four stages of porosity development are identified 1 very brief or no subaerial exposure estimated at less than 5000 yr caused little or no diagenetic change 2 brief to moderate subaerial exposure estimated at 5000 50 000 yr resulted in most primary pores being filled with calcite cement and dissolution creating fine matrix pores molds and intercrystalline pores 3 moderately long subaerial exposure estimated at 50 000 130 000 yr resulted in cements filling primary pores and some fine secondary pores and dissolution creating small conduit pores vugs fractures fissures 4 prolonged subaerial exposure estimated at greater than 130 000 yr resulted in most primary and secondary matrix pores being filled with calcite cement but dissolution enlarged conduit pores vugs fractures fissures present subsurface porosity in this field preferentially occurs in thick grainstones phylloid algal boundstones and a few wackestone packstones in cycles subjected to brief subaerial exposure stages 2 and 3 matrix porosity molds intercrystalline pores is dominant because most conduit pores formed during prolonged subaerial exposure were filled with either shale during subsequent transgressions or burial cements derived from pressure solution associated with the shales the distribution of porosity in the southwest andrews area indicates that duration of subaerial exposure and supply of clastics are major factors determining ultimate porosity in limestones subjected to subaerial exposure and karstification

paleosols of late pennsylvanian cyclic strata new mexico cyclically deposited siliciclastic and carbonate rocks of the late pennsylvanian virgilian holder formation of south central new mexico were deposited on a narrow shelf between the pedernal uplift and the orogrande basin in the dry canyon area sacramento mountains shelf to basin palaeotopography is indicated by onlapping beds and primary dips calcareous alteration zones are developed on the tops of major carbonate units these detailed studies confirm earlier interpretations that alteration zones represent subaerial exposure events and provide new evidence for and further documentation of a paleosol environment the paleosols contain 1 rhizoliths 2 tangential needle fibres of calcite 3 five types of alveolar texture 4 upward oriented ribbon spar 5 brownish and clear isopachous spar 6 blackened grains 7 random needle fibres of calcite 8 coated grains 9 micritized grains 10 glaebules 11 desiccation cracks 12 possible microcodium and 13 well developed laminated crusts isopachous cements upward oriented cements which mark the former tops of capillary fringes dark colour and shallow depth of penetration of rhizoliths less than 1 m indicate significant paleosol formation in waterlogged hydromorphic and drier conditions pennsylvanian palaeohydrogeology of the system is reflected in the type of paleosol alteration paleosols developed on subtidal strata and paleosols which drape tens of metres of palaeotopography indicate cyclic sedimentation was not controlled by delta lobe switching local tectonic up and down movement would be an unlikely mechanism to explain the repeated tens of metres of relative sea level fluctuation eustatic sea level fluctuations induced by late pennsylvanian gondwana glaciation probably were of the correct magnitude and frequency to have caused the holder cycles

the geochemical signature of a felsic injection complex in the continental crust opinaca subprovince quebec abstract the archean opinaca subprovince of the superior province in northern quebec is an injection complex consisting of lower granulite facies metasedimentary terrane that was pervasively injected with a large volume of leucogranitic melt which forms innumerable thin dykes and veins the typical microstructure of most leucogranites can be divided into two groups 1 one has an open framework constructed of k feldspar crystals in which the interstices are filled with albite rich plagioclase and quartz and 2 a microstructure defined by a framework of albite rich plagioclase crystals in which the interstices are filled by quartz and in some cases small pink garnets however pegmatitic and aplitic textures also occur the leucogranites that form the injection complex are all sio 2 rich above 70 wt and have low feo t mgo tio 2 contents compared to granitic melts obtained from partial melting experiments the mafic minerals were fractionated from the magma before its emplacement into the injection complex as leucogranite the leucogranites form a coherent trend on major element diagrams that is best explained by the removal of a cumulate dominated by k feldspar from a granitic initial melt composition the cumulate rocks are enriched in k 2 o whereas the residual melts are richer in sio 2 and na 2 o based on these results leucogranites with a k feldspar framework are interpreted as cumulate rocks this indicates that the early crystallising calcic plagioclase had already been fractionated from the magma before its injection into the complex the leucogranites have rare earth element ree patterns typical of feldspar accumulation the residual melts extracted after the k feldspar framework developed are those that have the framework of albite rich plagioclase these have ree patterns typical of highly evolved melts from which accessory minerals have also been fractionated the highly evolved nature of the leucogranites that were injected into granulite facies host rocks in the opinaca subprovince has several important implications for crustal evolution 1 the large volume of evolved melts emplaced at depth released a significant amount of h 2 o into the adjacent crust thus injection complexes should be considered as a potentially important source of h 2 o in the middle crust that is capable of rehydrating the granulite terranes into which they are injected 2 a corollary of the evolved nature of the leucogranite in the injection complex is that there should be evidence of accumulation of the early fractionated material still deeper in the crust 3 these findings are natural examples that corroborate predictions from numerical modelling which suggest that the whole process from melting to crystallisation of leucogranite can be confined to deep levels of the crust below or close to the solidus this has important impact on our general view of the transfer of leucogranites in the continental crust which is the main mechanism of crustal differentiation

paleoweathering of mississippian monteagle limestone preceding development of a lower chesterian transgressive systems tract and sequence boundary middle tennessee and northern alabama the contact between the hartselle sandstone mississippian lower hombergian and the underlying monteagle limestone mississippian upper gasperian in central tennessee and northeastern alabama is a regional disconformity a paleoweathering surface developed in the uppermost monteagle is truncated by this disconformity and only remnant pedogenic features are preserved these paleosol remnants and associated meteoric diagenetic features are evidence for the subaerial exposure and weathering of the monteagle limestone prior to intense erosional scour accompanying deposition of the hartselle sandstone petrographic evidence for subaerial exposure and meteoric diagenesis includes extensive micritization reddening dissolution and calcitization of allochem grains stable carbon and oxygen isotope compositions of whole rock samples exhibit depth patterns consistent with subaerial exposure pedogenesis and meteoric diagenesis stable isotope compositions of nonferroan calcite spar occluding moldic pores are considerably depleted relative to mississippian marine carbonate compositions further evidence for subaerial exposure and meteoric diagenesis the paleoweathering surface was modified after burial when reducing conditions developed resulting in pyritization stabilization of high mg calcite grains and cements after burial provided a source of magnesium for localized replacement by ferroan dolomite this disconformity is interpreted to be a third order vail exxon sequence boundary that marks a dramatic basinward shift in facies belts in the overlying hartselle sand stone the result of a sea level fall

carbonate platform stratal geometries and the question of subaerial exposure abstract integrated petrographic geochemical and fluid inclusion analyses indicate that the most prominent exposure unconformity at the southern margin of the vercors carbonate platform in southeastern france does not coincide with the major break in depositional geometry therefore changes in sediment supply and dispersal strongly influenced the resulting stratal geometries and prevent direct reconstructions of sea level from the stratal patterns platform to basin transects exposed in the cirque d archiane contain two prograding grainstone tongues separated by a wedge of finer grained slope sediments that thin toward the platform diagenetic analyses have been done at several strategic platform top bedding planes to determine the extent to which these sedimentologic breaks represent subaerial exposure while many bedding planes contain some evidence of meteoric alteration one of these bedding surfaces is unique in that it exhibits several generations of overprinted meteoric calcite cements bladed to blocky morphology precipitation in biomolds extinct to zoned cathodoluminescence low mg and 18 o variable 13 c freshwater fluid inclusions that are cross cut by marine borings eroded dolomitized clasts derived from this exposure surface occur in the uppermost portion of the finer grained wedge this combined evidence indicates that a significant episode of subaerial exposure took place at this horizon prior to deposition of the overlying platform top sediments the most significant change in depositional style and therefore the most likely position for a sequence boundary defined by stratal geometry is the top of the lower grainstone tongue however the intensely altered exposure surface and its basinward equivalent in the wedge lie 50 m above the top of the lower grainstone tongue therefore the surface containing the most extensive record of meteoric diagenesis does not stratigraphically coincide with the surface representing the most significant lateral shift in depositional facies

void filling deposits in karst terrains of isolated oceanic islands a case study from tertiary carbonates of the cayman islands caves fossil mouldic cavities sinkholes and solution widened joints are common in the cayman and pedro castle members of the bluff formation oligocene miocene on grand cayman and cayman brac because they have been subjected to repeated periods of karst development over the last 30 million years many voids contain a diverse array of sediments and or precipitates derived from marine or terrestrial environs mineral aerosols and groundwater exogenic sediment was transported to the cavities by oceanic storm waves transgressive seas runoff following tropical rain storms and or in groundwater at least three periods of deposition were responsible for the occlusion of voids in the cayman and pedro castle members voids in the cayman member were initially filled or partly filled during the late oligocene and early miocene this was terminated with the deposition of the pedro castle member in the middle miocene subsequent exposure led to further karst development and void filling sedimentation in both the cayman and pedro castle members speleothems are notably absent the void filling deposits formed during these two periods which were predominantly marine in origin were pervasively dolomitized along with the host rock 2 5 million years ago the third period of void filling deposition after dolomitization of the bluff formation produced limestone various types of breccia terra rossa speleothemic calcite and terrestrial oncoids most of these deposits formed since the sangamon highstand 125 000 years ago voids in the present day karst are commonly filled or partly filled with unconsolidated sediments study of the bluff formation of grand cayman and cayman brac shows that karst terrains on isolated oceanic islands are characterized by complex successions of void filling deposits that include speleothems and a variety of sediment types the heterogenetic nature of these void filling deposits is related to changes in sea level and climatic conditions through time

paleosols in shallow marine carbonate sequences abstract shallow water carbonate sequences in the geological record commonly exhibit numerous exposure surfaces reflecting emersion of sediment due to progradation processes and sealevel oscillations some ancient platform sequences contain hundreds of such surfaces associated with paleosols fossil soils typically calcretes a wide range of macro and microstructures are associated with these calcretes which are reviewed profile types and stages in profile development can be defined the nature of the exposure surface and associated paleosols can be used to identify the nature of the prevailing climate although hydromorphic effects related to marine flooding of the platforms can modify the paleosols a potentially important use of paleosols is to define the nature of sequence boundaries several studies have identified sets of paleosols with varying maturities reflecting changes in rates of accommodation space creation during sealevel rises and falls

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

quantification of macroscopic subaerial exposure features in carbonate rocks abstract the macroscopic features that characterize subaerial exposure surfaces in carbonates are well known but their significance has not been quantitatively evaluated this study presents such an analysis in the lower oligocene suwannee limestone of west central florida eleven cores were point counted on a foot by foot basis for the abundance of caliche rhizoliths karst breccia open vugs infiltrated sediment fractures and pedogenic alteration these features occur at and below intraformational exposure surfaces which represent hiatuses estimated at 104 to 105 years and an uppermost sequence bounding unconformity representing 0 5 myr as revealed by sr isotope data statistical analyses of the point count data reveal only a few significant relationships 1 the hierarchy of exposure surfaces and by inference duration of exposure is differentiated only at a marginally significant level by sediment filled vugs preferentially associated with the sequence boundary duration of exposure did not have a significant impact on the relative abundance of all other features 2 proximity 5 ft to both types of surfaces fractures open vugs and infiltrated sediment show no proximal or distal preference for either type of surface 3 depositional texture has no statistically significant affect on the presence or abundance of the exposure features with the exception that rhizoliths and open vugs are preferentially more abundant in packstones relative to grainstones this is interpreted to be the result of a soil moisture effect factor analysis defines four factors that explain 46 to 52 of the total variance in the abundance data relative to the sequence boundary and the intraformational surfaces respectively the loading of each exposure feature on each factor is the same with respect to both types of surfaces which is further evidence that the abundance of exposure features is independent of duration of exposure factor 1 is interpreted to be the amplitude of base level changes and controls the abundance of karst breccia factor 2 is interpreted to be abundance of vegetation and relates to the abundance of rhizoliths and fractures factor 3 is interpreted to be a combination of soil zone pco2 and the availability of water and affects the abundance of pedogenic overprinting caliche and open vugs factor 4 is stratigraphic proximity to the sequence boundary which controls the presence of sediment filled voids the amount of uncorrelated unique variance associated with infiltrated sediments pedogenic overprinting caliche and open vugs is large 60 meaning that feature abundance is also influenced by other unidentified site specific factors these results demonstrate that quantifying the abundance of macroscopic subaerial exposure features in limestones has the potential to yield more insight into the significance of those features than a mere qualitative assessment this is particularly true when assessing the potential role of the many variables that can affect the development of these features

cycle stratigraphy and porosity in pennsylvanian and lower permian shelf limestones eastern central basin platform texas pennsylvanian and lower permian shelfal limestones were studied in core and wireline logs on the eastern side of the central basin platform in west texas sixty three 63 cycles were delineated in the study interval which includes 200250 m of canyon missourian cisco virgilian and wolfcamp strata four general lithofacies are present fossiliferous wackestones and packstones grainstones phylloid algal boundstones and shales these lithologies typically occur in 118 m thick cycles bounded by subaerial exposure surfaces grainstones in the upper part of some cycles indicate a shallowing of environments prior to subaerial exposure many cycles have subaerial exposure surfaces developed on subtidal fossiliferous wackestones or packstones suggesting rapid falls in se level long term transgressive intervals transgressive systems tracts or tst are dominated by thick 4 m cycles whereas long term regressive intervals highstand systems tracts or hst are dominated by thinner cycles stable carbon isotope data suggest that thick cycles in tsts were subjected to short periods of subaerial exposure whereas thin cycles in the hsts were subjected to much longer subaerial exposure porosity is quite variable beneath subaerial exposure surfaces at any given well reservoir grade porosity 4 is present below only 1045 of the identified subaerial exposure surfaces where pres ent reservoir grade porosity occurs in the upper part of cycles 0 35 m below subaerial exposure surfaces porosity in thick cycles of the tst is relatively widespread and not facies selective porosity is less abundant and facies selective in the hst with porosity occurring only in relatively thick 1 54 m grainstones which are concentrated near the shelf margin thin

hierarchy of high frequency orbital cycles in cretaceous carbonate platform strata abstract lower cretaceous valanginian hauterivian carbonate platform strata which are well exposed in the matese mountains of the southern apennines italy have been analyzed on a microstratigraphic cm scale to exemplify the high frequency cyclic nature of the mesozoic shallow water sedimentation in southern italy based on the vertical organization of lithofacies and their early diagenetic signature 46 metre scale cycles are recognized these elementary cycles are hierarchically organized into groups bundles and superbundles the elementary cycles are prevalently formed by subtidal deposits and show emersion related features at the top suggesting repeated sea level fluctuations the number of elementary cycles compared to time as constrained by biostratigraphy and their grouping into sets implying higher order complexity in the environmental oscillation suggest an orbital control on sedimentation spectral analysis of recurrent thickness in stratal features defines and quantifies the cyclicity which is characterized by lithofacies thickness periodicities of 1271 391 159 124 and 69 cm linear correlation of the relative ratio set rrs of these periodicities with the corresponding rrs of the orbital perturbation periodicities shows that 1271 and 391 cm fit the 404 220 and 94 890 year cycles of early cretaceous orbital eccentricity 159 and 124 cm fit the 49 010 and 38 030 year cycles of the earth s axial obliquity whereas 69 cm corresponds to the precession periodicity thus the san lorenzello section required not less than 1 6 ma to form at an average rate of 26 mm ka each 400 ka cycle can be viewed as a depositional sequence in which sequence boundaries maximum flooding surfaces and system tract equivalents have been recognized the microstratigraphic approach is very promising for understanding the fine structure of climate related environmental fluctuation recorded by the 3000 m thick carbonate platform successions of the southern apennines over a time span of about 150 ma upper triassic upper cretaceous and for deriving a more precise chronostratigraphy for global correlation

controls on early diagenetic overprinting in icehouse carbonates insights from modeling hydrological zone residence times using carb3d abstract icehouse carbonate diagenesis is complex with carbonate sequences being exposed to multiple meteoric hydrozones vadose zone freshwater lens mixing zone on multiple occasions a forward modeling approach using carb3d has enabled quantitative exploration of the nature of this diagenetic overprinting by explicit simulation of meteoric hydrozone residence times during evolution of an isolated carbonate platform a sensitivity analysis was performed encompassing the fundamental controls on hydrozone residence time frequency and magnitude of sea level variation subsidence rate and climate the latter via its effect on freshwater lens thickness and rate of dissolutional lowering of the land surface residence time within all meteoric hydrozones is characterized by a high degree of lateral continuity vertical continuity is much more limited with significant variations on a fourth order sequence scale across the platform below sequence boundaries prolonged exposure to the vadose zone results from multiple missed beats when the platform remains exposed at relative sea level maxima overprinting gives total meteoric residence times significantly in excess of the duration of exposure of the overlying sequence boundary there is a hierarchy of eustatically driven overprint cycles with higher frequency cyclicity modifying the primary signal generated by lower frequency cycles fifth order cycles thus have only a minor impact on hydrozone residence times whilst third order seismic scale cycles are a critical control and could be used as a first order approximation of the amount of diagenetic overprinting subsidence has a strong control on residence time with greater overprinting at lower subsidence rates but in high subsidence regimes sediment packages move below the zone of meteoric water influence sufficiently rapidly that residence time can be minimal high land surface dissolution rates which result from a wetter climate remove a large proportion of the subaerially exposed sediment and reduce vadose zone residence time higher effective recharge can increase the thickness of freshwater lens and mixing zones which increases residence times significantly residence times in the vadose zone can be directly linked to a sequence stratigraphic framework but for the freshwater lens and the mixing zone this is possible only with a well constrained relative sea level history

a review of polyphase karstification in extensional tectonic regimes jurassic and cretaceous examples betic cordillera southern spain abstract five karstification phases are recognized and analysed in the mesozoic carbonate sequences of the external and internal subbetic betic cordilleras southern spain these phases are related to important stratigraphic discontinuities in the following ages 1 intra carixian 2 early middle jurassic boundary 3 late bathonian early callovian 4 intra kimmeridgian and 6 late albian the importance of each karstification phase is variable according to the region moreover not all the karstic phases occur in every area although in some places several phases may be superimposed appearing as discrete palaeokarst features or overprinting earlier ones in the case of polyphase karstification each successive karstic process modified earlier features and was also conditioned by them this interdependence complicates any attempt to isolate the individual karst events the interpretation of the genetic history of the palaeokarst as a whole therefore requires the integration of data from different outcrops where they need to be particularly well exposed this is the only way to arrive at an accurate hypothesis the five described palaeokarst phases are closely related to the rifting evolution of the southern iberian palaeomargin they coincide with episodes of sudden sea level fall in the external and internal subbetic caused by local tectonic events commonly involving block tilting related to the movement of listric faults differing in magnitude in each palaeogeographic palaeotectonic range and eustatic sea level changes

image based measurement of flux variation in distal regions of active lava flows 1 understanding the processes involved with the advance of lava flows is critical for improving hazard assessments at many volcanoes here we describe the application of computer vision and oblique photogrammetric techniques to visible and thermal images of active a flows in order to investigate distal flow processes at mount etna sicily photogrammetric surveys were carried out to produce repeated topographic data sets for calculation of volumetric lava flux at the flow fronts velocity profiles from a distal channel were obtained by rectification of a thermal image sequence and are used to investigate the rheological properties of the lava significant variations of the magma flux were observed and pulses of increased flux arrived within the flow front region on timescales of several hours the pulses are believed to be the distal result of more frequent flux changes observed in the vent region hence they reflect the importance of flow processes which are believed to cause the coalescence of flux pulses along the channel system as well as short period variations in effusion rate in considering advance processes for the individual flow fronts it must be assumed that they were fed by a highly unsteady flux which was volumetrically at least an order of magnitude lower than that observed near the vent

magnetite chemistry as a provenance indicator in archean metamorphosed sedimentary rocks abstract conventional provenance studies of high grade e g amphibolite facies metamorphic sandstone are limited due to intense recrystallization destruction of original minerals and growth of new minerals magnetite is a heavy mineral common in a wide range of sedimentary rocks it can originate from a wide range of rock sources from high temperature to low temperature magmatic metamorphic or hydrothermal environments laser ablation la icp ms and electron microprobe analytical techniques allowed determination of a wide range of trace elements at sub ppm levels in magnetite to identify the provenance of two archean sedimentary formations in eeyou istchee baie james quebec canada results were plotted on multi element diagrams the most compatible elements in magnetite were identified as the most discriminant elements to differentiate four potential different rock sources for the magin formation overlap between the spectra of the magin and keyano formations substantiate the existence of a common source interbedded conglomerate magnetite bearing clasts were examined to determine potential source rocks mafic clasts apparently do not contain magnetite detrital magnetites analyzed have low ti values that would support either felsic to intermediate plutonic or a hydrothermal source the trace element spectra of detrital magnetite from the sandstone beds were compared to magnetite spectra from conglomerate clasts of banded iron formation and felsic to intermediate plutonic rocks only magnetites from felsic plutonic rocks have a signature similar to those from the sandstone to further substantiate a felsic plutonic source a detailed study of magnetite chemistry from ten felsic and intermediate regional plutons from a regional databank allowed us to recognize that each of these plutons has a particular signature on the basis of wide variations in ni and cr from this data base four individual plutons were identified as potential sources for the magin formation recently published magnetite discrimination diagrams proposed for mineral deposits can be applied to sedimentary magnetite provenance however our database shows the importance of identifying low ti magnetite from felsic rocks since these could be misidentified as low ti magnetite from hydrothermal mineral deposits thus we propose improvement to these diagrams by differentiating magnetite from felsic magmatic low ni cr and hydrothermal high ni cr sources before applying the mineral deposit discrimination diagrams