late mississippian glacio eustasy recorded in the eastern paleo tethys ocean south china abstract long lived and extensive glaciation during the carboniferous and early permian has been the focus of many studies over the past decade revealing systematic changes in sea level and climatic conditions the nature of the inception of carboniferous glaciation however remains poorly resolved with uncertainty regarding the timing and dynamics of buildup of continental ice sheets here we present detailed sedimentary facies and depositional cycles from upper mississippian shallow water platform and contemporaneous carbonate slope successions from the eastern paleo tethys ocean region south china to reveal systematic variations that provide insight into the sedimentary response to the onset of carboniferous glaciation based on detailed sedimentological logging and facies analysis four upper visean cycles and four serpukhovian cycles were identified from the carbonate platform yashui section bounded by either subaerial surfaces or zones or transgressive surfaces the cycle tops roughly correspond to intervals rich in normally graded bioclastic wacke to packstones and with distinct rises 1 in conodont 18opo4 in the carbonate slope naqing section in particular the four serpukhovian cycles correlate well to depositional cycles defined in the lower yangtze platform succession of south china and in the cyclothemic successions in the donets basin ukraine suggesting a glacio eustatic control most likely caused by repeated advance and retreat of gondwana glaciation during the onset but prior to widespread glaciation across the mid carboniferous boundary

contrasting styles of post caldera volcanism along the main ethiopian rift implications for contemporary volcanic hazards abstract the main ethiopian rift mer 7 9 n is the type example of a magma assisted continental rift the rift axis is populated with regularly spaced silicic caldera complexes and central stratovolcanoes interspersed with large fields of small mafic scoria cones the recent latest pleistocene to holocene history of volcanism in the mer is poorly known and no eruptions have occurred in the living memory of the local population assessment of contemporary volcanic hazards and associated risk is primarily based on the study of the most recent eruptive products typically those emplaced within the last 10 20 ky we integrate new and published field observations and geochemical data on tephra deposits from the main late quaternary volcanic centres in the central mer to assess contemporary volcanic hazards most central volcanoes in the mer host large mid pleistocene calderas with typical diameters of 5 15 km and associated ignimbrites of trachyte and peralkaline rhyolite composition in contrast post caldera activity at most centres comprises eruptions of peralkaline rhyolitic magmas as obsidian flows domes and pumice cones the frequency and magnitude of events varies between individual volcanoes some volcanoes have predominantly erupted obsidian lava flows in their most recent post caldera stage fentale whereas other have had up to 3 moderate scale vei 3 4 explosive eruptions per millennium aluto at some volcanoes we find evidence for multiple large explosive eruptions corbetti bora baricha boset bericha which have deposited several centimetres to metres of pumice and ash in currently densely populated regions this new overview has important implications when assessing the present day volcanic hazard in this rapidly developing region

itrf2014 a new release of the international terrestrial reference frame modeling nonlinear station motions for the first time in the international terrestrial reference frame itrf history the itrf2014 is generated with an enhanced modeling of nonlinear station motions including seasonal annual and semiannual signals of station positions and postseismic deformation for sites that were subject to major earthquakes using the full observation history of the four space geodetic techniques very long baseline interferometry vlbi satellite laser ranging slr global navigation satellite systems gnss and doppler orbitography and radiopositioning integrated by satellite doris the corresponding international services provided reprocessed time series weekly from slr and doris daily from gnss and 24 h session wise from vlbi of station positions and daily earth orientation parameters itrf2014 is demonstrated to be superior to past itrf releases as it precisely models the actual station trajectories leading to a more robust secular frame and site velocities the itrf2014 long term origin coincides with the earth system center of mass as sensed by slr observations collected on the two lageos satellites over the time span between 1993 0 and 2015 0 the estimated accuracy of the itrf2014 origin as reflected by the level of agreement with the itrf2008 both origins are defined by slr is at the level of less than 3 mm at epoch 2010 0 and less than 0 2 mm yr in time evolution the itrf2014 scale is defined by the arithmetic average of the implicit scales of slr and vlbi solutions as obtained by the stacking of their respective time series the resulting scale and scale rate differences between the two solutions are 1 37 0 10 ppb at epoch 2010 0 and 0 02 0 02 ppb yr while the postseismic deformation models were estimated using gnss gps data the resulting parametric models at earthquake colocation sites were applied to the station position time series of the three other techniques showing a very high level of consistency which enforces more the link between techniques within the itrf2014 frame the users should be aware that the postseismic deformation models are part of the itrf2014 products unlike the annual and semiannual signals which were estimated internally with the only purpose of enhancing the velocity field estimation of the secular frame

lower triassic peritidal cyclic limestone an example of anachronistic carbonate facies from the great bank of guizhou nanpanjiang basin guizhou province south china abstract most shallow marine sections described from the lower triassic formed in mixed carbonate siliciclastic systems shallow marine limestones from an isolated carbonate platform the great bank of guizhou in the nanpanjiang basin south china provide a unique opportunity to examine a pure peritidal carbonate depositional system the platform had a low relief bank profile in the early triassic with oolite shoals at the margin shallow subtidal and peritidal deposits in the interior and pelagics debris flow deposits and turbidites on gentle basin margin slopes interior strata are 265 m thick beginning in the lowermost triassic with renalcis biostromes followed by lime mudstone oolite and cyclic peritidal limestone the cyclic limestone is olenekian in age 164 m thick and contains up to 83 cycles parasequences parasequences are 0 2 7 4 m thick and typically shallow upward from subtidal oolite grainstone and skeletal packstone facies followed by renalcis reef mounds or biostromes and capped by intertidal flaser bedded ribbon rock the skeletal packstone and reef mounds contain a low diversity biota of cyanobacteria echinoderms bivalves gastropods lingulid brachiopods spirorbids and ostracodes ribbon rock contains alternating lime mud and fine peloidal packstone and grainstone laminae scour surfaces ripple cross lamination lime mud drapes and minor prism cracks parasequence stacking patterns exhibit gradual increase and decrease of parasequence thickness defining a third order sequence boundary and several 4th order parasequence sets that correlate between interior sections parasequence stacking patterns similar to those of lower palaeozoic green house sequences and different from ice house sequences the lower triassic platform interior parasequences represent an anachronistic facies in that they are strikingly similar to the common renalcis mound ribbon rock parasequences of the lower palaeozoic and different from other permo triassic parasequences e g capitan shelf parasequences or loferites facies similarities such as renalcis mounds and flaser bedded intertidal ribbon rock reflect anomalous oceanic conditions resulting in low biodiversity and low intensity of bioturbation after the end permian extinction similarities in parasequence stacking patterns reflect low amplitude high frequency sea level fluctuations resulting from green house conditions common to the early palaeozoic and early triassic

local seismicity near the actively deforming corbetti volcano in the main ethiopian rift abstract corbetti is currently one of the fastest uplifting volcanoes globally with strong evidence from geodetic and gravity data for a subsurface inflating magma body a dense network of 18 stations has been deployed around corbetti and hawassa calderas between february 2016 and october 2017 to place seismic constraints on the magmatic hydrothermal and tectonic processes in the region we locate 122 events of magnitudes between 0 4 and 4 2 using a new local velocity model the seismicity is focused in two areas directly beneath corbetti caldera and beneath the city of hawassa the shallower 0 5 km depth below sea level b s l earthquakes beneath corbetti are mainly focused in ew to ns elongated clusters at urji and chabbi volcanic centres this distribution is interpreted to be mainly controlled by a northward propagation of hydrothermal fluids away from a cross rift pre existing fault source mechanisms are predominantly strike slip and different to the normal faulting away from the volcano suggesting a local rotation of the stress field these observations along with a low vp vs ratio are consistent with the inflation of a gas rich sill likely of silicic composition beneath corbetti in contrast the seismicity beneath hawassa extends to greater depth 16 km b s l these earthquakes are focused on 8 10 km long segmented faults which are active in seismic swarms one of these swarms in august 2016 is focused between 5 and 16 km depth b s l along a steep normal fault beneath the city of hawassa highlighting the earthquake hazard for the local population

a rapid mechanism to remobilize and homogenize highly crystalline magma bodies the largest products of magmatic activity on earth the great bodies of granite and their corresponding large eruptions have a dual nature homogeneity at the large scale and spatial and temporal heterogeneity at the small scale this duality calls for a mechanism that selectively removes the large scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal rich viscous conditions seemingly resistant to mixing here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization unzipping of highly viscous crystal rich mushes we demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning what distinguishes our model is the recognition that the process has two stages initially a stiff mushy magma is reheated from below producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer when the thickening mobile layer becomes sufficiently buoyant it penetrates the overlying viscous mushy magma this second stage rapidly exports homogenized material from the lower mobile layer to the top of the system and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption the agreement between calculated and observed unzipping rates for historical eruptions at pinatubo and at montserrat demonstrates the general applicability of the model this mechanism furthers our understanding of both the formation of periodically homogenized plutons crust building and of ignimbrites by large eruptions

the eruptive history and magmatic evolution of aluto volcano new insights into silicic peralkaline volcanism in the ethiopian rift the silicic peralkaline volcanoes of the east african rift are some of the least studied volcanoes on earth here we bring together new constraints from fieldwork remote sensing geochronology and geochemistry to present the first detailed account of the eruptive history of aluto a restless silicic volcano located in a densely populated section of the main ethiopian rift prior to the growth of the aluto volcanic complex before 500 ka the region was characterized by a significant period of fault development and mafic fissure eruptions the earliest volcanism at aluto built up a trachytic complex over 8 km in diameter aluto then underwent large volume ignimbrite eruptions at 316 19 ka and 306 12 ka developing a 42 km2 collapse structure after a hiatus of 250 ka a phase of post caldera volcanism initiated at 55 19 ka and the most recent eruption of aluto has a radiocarbon age of 0 40 0 05 cal ka bp during this post caldera phase highly evolved peralkaline rhyolite lavas ignimbrites and pumice fall deposits have erupted from vents across the complex geochemical modelling is consistent with rhyolite genesis from protracted fractionation 80 of basalt that is compositionally similar to rift related basalts found east of the complex based on the style and volume of recent eruptions we suggest that silicic eruptions occur at an average rate of 1 per 1000 years and that future eruptions of aluto will involve explosive emplacement of localised pumice cones and effusive obsidian coulees of volumes in the range 1 100 106 m3

preservation of forcing signals in shallow water carbonate sediments abstract no consensus has been reached on whether the metre scale cycles that commonly occur in peritidal carbonates are predominately a product of external relative sea level variations allocycles or an intrinsic property of carbonate production generated via the interaction of non linear processes autocycles for any forcing signal such as eustatic sea level change to be detectable in stratigraphy its effects must be preserved here a deterministic three dimensional geological process model is used to explore how such cycles are preserved in the geological record in the presence of autocyclic processes each simulation produced cycle thickness distributions that are statistically indistinguishable from a theoretical poisson process regardless of whether auto or allo cycles dominated spectral analysis of depositional time series constructed from idealised geological sections showed that all detectable signals occurred within the milankovitch forcing frequency bands even when no milankovitch forcing was present thus it is deduced that from any geological section alone external forcing signals are detectable but are not distinguishable from autocyclically produced signals interestingly there is no correlation between the percentage of sediment preserved and the accuracy with which signals are detectable in the preserved sediment in some model realisations even with preservation as low as 40 the correct forcing signal can be detected accurately while conversely sections with preservation as high as 90 can have poor signal preservation the reverse can also be true in other models it is therefore concluded that distinguishing allocyclic and autocyclic forcing in shallow marine or peritidal carbonate successions is likely to be extremely difficult except in cases of extraordinary sedimentary preservation and dating accuracy

sabkha facies and the preservation of a falling stage systems tract at the sauk ii iii supersequence boundary in the late cambrian eilean dubh formation nw scotland the durness group of northwest scotland represents a nearly one kilometer thick succession of mid cambrian to lower middle ordovician carbonates these rocks crop out in a narrow belt along the foreland of the caledonian orogen and in the moine thrust zone stretching some 170 km from loch eriboll southwestwards to the isle of skye the cambrian parts of the succession represent deposition on a paleo southeast facing low latitude passively subsiding continental margin situated at around 20 s carbonate deposition in scotland formed part of the extensive great american carbonate bank the sauk ii iii supersequence boundary occurs above an interval of thin meter scale shallowing upward peritidal cycles containing intraclast dolorudstones stromatolites tepees siliciclastic sand and surface karst evidence of former evaporites in the succession comprises pseudomorphs of nodular and bedded anhydrite crystal shaped calcite filled vugs representing growth of sulfate dissolution breccias and local halite casts these features represent sabkha facies arranged into cycles that constitute a preserved falling stage systems tract fsst the top of the fsst is marked by a pronounced karst surface of sandstone filled fissures the section preserves a rare snapshot of a seldom preserved environment on the cambrian laurentian margin its preservation during a time of falling relative sea level under slow tectonic subsidence is discussed

the origin of high frequency platform carbonate cycles and third order sequences lower ordovician el paso gp west texas constraints from outcrop data and stratigraphic modeling abstract the passive margin succession of the diablo platform lower ordovician west texas is represented by the second order sauk c supersequence set consisting of a basal transgressive clastic unit the bliss sandstone above the breakup unconformity marking the second order basal lowstand transgressive phase overlain by 750 m of drift related shallow marine platform carbonates the el paso group recording the second order highstand due to late paleozoic structuring of the gondwanan passive margin present exposures in texas are in an updip shelf position and lack internal stratal geometries across depositional strike so sequences and systems tracts are identified solely by the vertical stacking patterns of depositional subfacies and higher frequency fifth order cycles accommodation plots fischer plots of high frequency cycles gauge systematic shifts in third order accommodation of two complete third order sequences each about 2 m y long and 60 140 m thick within the el paso group this is expressed in the vertical succession of cycle types systematic changes in cycle thickness and variations in subfacies as revealed by histograms of subfacies types tied to fischer plots a complete el paso shelf sequence contains a thin lowstand systems tract of quartz arenite a thick transgressive systems tract dominated by upward thickening thrombolitic subtidal cycles and a highstand systems tract marked by dolomitic thinning upward peritidal cycles containing quartz sand the el paso third order depositional sequences have been correlated by biostrat graphy and cycle stacking pattern from the franklin mountains southeast to the diablo arch northeast into the ardmore basin and thence to the appalachian basin hence the third order sequences appear to be eustatic based on biostratigraphic correlation of accommodation plots around the periphery of gondwana time series analyses suggest that a strict allocyclic milankovitch driven glacio eustatic mechanism alone is insufficient to account for the higher frequency fifth order and lower frequency third order accommodation cycles we used a two dimensional forward computer simulation to compare allocyclic and autocyclic models for high frequency cycles the allocyclic simulation superimposes a deterministic milankovitch glacio eustatic driver on a lower frequency third order accommodation cycle and generates a two dimensional synthetic cross section composed of high frequency peritidal and subtidal cycles stacked into third order sequences the autocyclic simulation is generated by a ginsburg autocyclic mechanism for high frequency cyclicity triggered by third order accommodation changes the autocyclic simulation quantitatively replicates an autocyclic mechanism for fifth order cycle development linked to onshore sediment transport and seaward progradation of tidal flats the two dimensional internal facies architecture of a third order sequence and the high frequency cycle stacking patterns are simulated in both scenarios important differences in patterns of cycles and subfacies stacking in the simulations shed light on the interpretation of the diablo platform cycles and sequences as an alternative or a supplement to autocyclicity or milankovitch forced glacio eustasy we have studied stochastic models for driving high frequency changes in relative sea level these intriguing results maintain essentially all the features observed in the rock record our smoothed sto hastic simulations suggest that the cycle problem is much more complex than presently realized

geostatistical earth modeling of cyclic depositional facies and diagenesis in siliciclastic and carbonate reservoirs depositional facies are often described as being organized in cyclic successions that are overprinted by diagenesis most reservoir modelling workflows are not able to reproduce stochastically such patterns herein a novel geostatistical method is developed to model depositional facies architectures that are rhythmic and cyclic together with superimposed diagenetic facies the method uses truncated pluri gaussian random functions constrained by transiograms cyclicity is defined as an asymmetric ordering between facies and its direction is given by a three dimensional vector called shift this method is illustrated on two case studies outcrop data of the triassic latemar carbonate platform northern italy are used to model shallowing upward facies cycles in the vertical direction a satellite image of the modern bermuda platform interior is used to model facies cycles in the windward to leeward lateral direction as depositional facies architectures are modelled using two gaussian random functions a third gaussian random function is added to model diagenesis thereby depositional and diagenetic facies can exhibit spatial asymmetric relations the method is applied in two regions of the latemar carbonate platform that experience two different types of diagenetic transformation syn depositional dolomite formation and post depositional fracture related diagenesis the method can also incorporate proportion curves to model non stationary facies proportions this is illustrated in cretaceous shallow marine sandstones and mudstones book cliffs utah for which cyclic facies and diagenetic patterns are constrained by embedded transition probabilities

tides for a convective earth in this paper we give values of the tidal gravimetric factor as well as of the love numbers for the tidal surface displacement and for the tidal mass redistribution potential that are consistent with the presently adopted definitions we present analytical expressions for these quantities and compute numerical values for two rotating nonspherical earth models in the first model the earth is everywhere in hydrostatic equilibrium and the inner core and mantle are both elastic in the second model the earth is ellipsoidal with an inelastic mantle and with a nonhydrostatic initial state for which the effects of mantle convection and its associated boundary deformations are considered this latter model is constrained to reproduce the observed free core nutation period and global earth dynamical flattening

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

orbital cycles differential subsidence and internal factors controlling the high frequency sequence architecture in a sinemurian shallow carbonate platform mallorca island spain abstract the 125 m thick lower to lowermost upper sinemurian peritidal to shallow subtidal platform carbonates in the llevant mountains of mallorca spain have been analysed from four stratigraphic sections to provide new data on the hierarchical stacking pattern of high frequency depositional sequences due to the fact that in shallow water environments the stacking of carbonate facies can be controlled by external allocyclic and internal autocyclic processes deciphering the dominant controls on the high frequency sequence architecture of these platforms is a challenge the studied carbonates encompass a high variety of facies representative of open lagoon internal bars restricted lagoon and tidal flats with local beach sands based on a detailed analysis of vertical facies trends and bounding surfaces large medium and small scale sequences have been identified within the long term transgressive regressive facies cycle defined by the entire succession large scale sequences 10 30 m thick and medium scale sequences 1 10 m thick are generally shallowing upward sequences bounded by sharp facies changes to relatively deeper facies and have been related to sea level variations driven by long 400 kyr and short 100 kyr eccentricity cycles respectively the overprinting of differential subsidence probably related to extensional tectonic and carbonate production and accumulation processes varied throughout time controlling the lateral continuity and preservation potential of the 100 kyr medium scale sequences shallowing upward locally aggradational small scale sequences 0 3 to 5 m thick are very variable in number and thickness and cannot be correlated between sections pointing out that their most important controlling factor was the internal processes hiatuses and erosion related to subaerial exposure at the peritidal caps lateral migration of internal bars local wave and currents patterns depositional and erosional processes related to spring tides and storms in the frame of a complex mosaic of facies within the studied platform

recurrent explosive eruptions from a high risk main ethiopian rift volcano throughout the holocene martin jones was funded by a natural environment research council nerc algorithm ph d grant ne 10983 01 field work at lake chamo was funded by the german research foundation dfg within the scope of the crc 806 our way to europe smith acknowledges funding from the natural environment research council grant ne l013932 1 brown and frank acknowledge dfg spp 1488 grant ko2870 4 1

volcanic eruption prediction magma chamber physics from gravity and deformation measurements one of the greatest remaining problems in modern volcanology is the process by which volcanic eruptions are triggered it is generally accepted that eruptions are preceded by magma intrusion sigurdsson and sparks 1978 the degree of interaction between previously ponded magma in a chamber and newly intruded magma determines the nature and rate of eruption and also the chemistry of erupted lavas and shallow dykes here we investigate the physics of this interaction volcano monitoring at its most effective is a synergy between basic science and risk assessment while hazard mitigation depends on reliable interpretation of eruption precursors the simple and much used mogi model relates ground deformation h to changes in magma chamber volume gravity changes g combined with ground deformation provide information on magma chamber mass changes our new models predict how the g h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity thus by simultaneous measurement of deformation and gravity at a few key stations magma chamber processes can be identified prior to the onset of conventional eruption precursors

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

broad accommodation of rift related extension recorded by dyke intrusion in saudi arabia volcanic fields at the eastern margin of the red sea rift were regarded as seismically quiet until a swarm of 30 000 earthquakes struck in 2009 geological analyses reveal the intrusion of a volcanic dyke and indicate that rift related extension is spread over a broad region far from the rift axis

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

numerical evidence enabling reconciliation gravity and height changes in volcanic areas s u m m a r y gravity and height changes reflecting magma accumulation in subsurface chambers are evaluated using finite element models in order to resolve controversial relationships observed in some volcanic areas when significant gravity changes occur without any significant deformation or vice versa it is often difficult if not impossible to jointly explain the observations using the popular mogi model here we explore whether these discrepancies can be explained by magma compressibility and source geometry effects compression of resident magma and expansion of the chamber wall act concurrently to accommodate newly added magma gravityheight ratios are found to mainly depend on i geometry of the sources which control the volume expansion of the chamber ii magma compressibility which affects the contraction of the magma resident in the chamber and iii depth of the sources our numerical results show that when magma compressibility and non spherical sources are taken into account significant gravity variations can indeed be successfully reconciled with negligible height changes this may be the case at etna volcano where gravity changes about 40 gal without any significant deformation below 5 cm were observed during the 1994 1995 inflation period the numerical results point to the accumulation of a 1 4 1010 kg mass into an elongated source simulating a shallow storage region supplying the summit craters

stratigraphic architecture and gamma ray logs of deeper ramp carbonates upper jurassic sw germany abstract the objective of this paper is to contribute to the development of sequence stratigraphic models for extensive epicontinental carbonate systems deposited over cratonic areas epicontinental carbonates of the sw german upper jurassic were analysed in terms of microfacies sedimentology and sequence stratigraphy based on 2 5 km of core 70 borehole gamma ray logs and 24 quarries facies analysis revealed six major facies belts across the deeper parts of the carbonate ramp situated generally below fair weather wave base and mostly below average storm wave base but in the reach of occasional storm events observed stratigraphic patterns differ in some aspects from widely published sequence stratigraphic models 1 elementary sedimentary cycles are mostly more or less symmetrical and are thus referred to as genetic sequences or genetic units aaapg bull 55 1971 1137 frazier d e 1974 depositional episodes their relationship to the quaternary stratigraphic framework in the northwestern portion of the gulf basin university of texas austin bureau of economic geology geologicalo circular 71 1 aapg bull 73 1989 125 galloway w e hobday d k 1996 terrigenous clastic depositional systems 489 pp springer cross t a baker m r chapin m s clark m s gardner m h hanson m s lessenger m a little l d mcdonough k j sonnenfeld m d valasek d w williams m r witter d n 1993 applications of high resolution sequence stratigraphy to reservoir analysis edition technip 1993 11 33 bull cent rech explor prod elf aquitaine 16 1992 357 homewood p mauriaud p lafont f 2000 best practices in sequence stratigraphy elf ep mem 25 81 pp homewood p eberli g p 2000 genetic stratigraphy on the exploration and production scales elf ep mem 24 290 pp in contrast to the asymmetrical shallowing upward parasequences of the exxon approach 2 neither sequence boundaries nor maximum flooding surfaces could be clearly delineated cycle boundaries are generally not represented by sharp stratal surfaces but are always transitional and thus referred to as turnarounds nor pet soc spec publ 8 1998 171 several types of genetic sequences were delineated both major types of facies and sequences show characteristic gamma ray log signatures based on the cycle stacking and the gamma ray patterns a hierarchy of sequences was recognized probably driven in part by 100 000 and 400 000 year milankovitch signals the cyclicity allowed regional correlations across various depositional environments such as sponge microbial bioherms and coeval basins the basin wide correlation revealed evidence for a subtle clinoform type stratigraphic architecture along very gentle slopes rather than a so far assumed simple layer cake pattern

distributed nubia somalia relative motion and dike intrusion in the main ethiopian rift summary the main ethiopian rift mer in central ethiopia extended in the rift normal direction at a mean rate of 4 0 0 9 mm yr 1 1 during the period 1992 2003 nearly a factor of two slower than the opening rate estimated from global plate motion inversions rift opening near a geodetic array during this period was accommodated by a single dike injection event in 1993 spatially coincident with active magmatic segments probably triggered by observed seismicity following dike injection the crust in the rift relaxed as a layered medium with a 15 km thick elastic lid over a viscous half space of 10 18 pa s diking rather than normal faulting on rift bounding faults appears to be the predominant mechanism of extension in the mer explaining the very low regional rates of moment release the length scale and temporal behaviour of surface displacements require viscoelastic rheology in the rift

tectono depositional pattern and evolution of the middle yangtze platform south china during the late ediacaran abstract the depositional environments and evolution of the yangtze block during the ediacaran cambrian transition remain uncertain preventing a thorough understanding of the coeval ocean stratification redox heterogeneity and organism distribution in this study detailed facies and sequence stratigraphic analyses were carried out on the dengying formation and its correlatives to better constrain the tectono depositional pattern and evolution of the middle yangtze area in the late ediacaran twenty five lithofacies were identified in nineteen sections and grouped into six depositional facies intrashelf basin intrashelf shoal restricted platform interior platform margin upper middle slope and lower siliceous slope basin the spatiotemporal distributions of these depositional facies reveal an isolated rimmed middle yangtze carbonate platform embayed with a westward opening intrashelf basin this intrashelf basin gradually became wider and deeper westwards linking to a nne trending basinal seaway that separated the middle yangtze platform from its upper yangtze counterpart the enclosure of the marginal shoal reef complex with an intrashelf shoal chain formed a large scale restricted lagoon and associated tidal flat in the platform interior based on key sequence boundaries and cycle stacking patterns two and a half transgressive regressive sequences were distinguished in the dengying formation and its correlatives in the twelve representative sections furthermore these sequences can be correlated well with those identified in other upper ediacaran successions elsewhere in upper yangtze namibia india and oman indicating a eustatic origin for these sequences however the complex platform basin configuration with significant facies and thickness variations reflects a transtensional tectonic regime in the middle yangtze area during the late ediacaran the abrupt changes in lithofacies and thickness across the southern principal platform margin and those from sandy shoals banks to storm influenced shelf along the northern portion of the intrashelf basin in the three gorges western hubei suggest synthetic extensional faulting across the margins during deposition the two synthetic extensional fault zones might have been induced by nne trending transtensional faulting along the eastern margin of the upper yangtze platform this structural pattern fundamentally controlled the depositional differentiation of the middle yangtze platform during the late ediacaran and also laid the foundation for the subsequent facies distribution and depositional evolution during the early cambrian terreneuvian epoch

multiple inflation and deflation events at kenyan volcanoes east african rift the presence or absence of magma exerts a fundamental control on the distribution of strain in continental rift zones yet the time scales of magma intrusion remain unconstrained using more than a decade of measurements from interferometric synthetic aperture radar insar we detected geodetic activity at four of the eleven central rift volcanoes in the kenyan sector of the east african rift subsidence of 2 5 cm occurred at suswa and menengai over the period 1997 2000 9 cm of uplift was recorded at longonot in 2004 2006 and 21 cm of uplift occurred at paka during 2006 2007 the deformation is episodic and no deformation was observed at these volcanoes during other time periods preceding the infl ation at paka we observed transient uplift and subsidence of a second nearby source likely associated with fl ow through a complex plumbing system the best fi tting source models for each episode include infl ation or defl ation of a horizontal penny shaped crack at a depth of 2 5 km the episodic nature of the activity its lack of correlation with seasons and the preferred source geometry are all consistent with activity in the volatile rich cap to a crystal rich magma chamber beneath each of the four volcanoes the presence of active magmatic systems beneath more than 40 of the volcanoes and the 2007 2008 explosive eruptions at nearby oldoinyo lengai volcano have implications for models of continental rifting caldera volcanoes geothermal resources and volcanic and seismic hazard in rift zones

variations in architecture and cyclicity in fault bounded carbonate platforms early miocene red sea rift nw saudi arabia abstract the early miocene was a period of active rifting and carbonate platform development in the midyan peninsula nw saudi arabia however there is no published literature available dealing with the detailed characterization of the different carbonate platforms in this study area therefore this study aims to present new stratigraphic architectural models that illustrate the formation of different carbonate platforms in the region and the forcing mechanisms that likely drove their formation this study identified the following features formed during active rifting a a late aquitanian n4 fault block hangingwall dipslope carbonate ramp b a late burdigalian n7 n8 isolated normal fault controlled carbonate platform with associated slope deposits and c a late burdigalian n7 n8 attached fault bounded platform with reef buildups rimmed shelf developed on a footwall fault tip within a basin margin structural relay zone that formed coinciding with the second stage of rifting variations in cyclicity have been observed within the internal stratigraphic architecture of each platform and also between platforms high resolution sequence stratigraphic analysis shows to be parasequences the smallest depositional packages metre scale cycles within the platforms the hangingwall dipslope carbonate ramp and the attached platform demonstrate aggradational progradational parasequence stacking patterns these locations appear to have been more sensitive to eustatic cyclicities despite the active tectonic setting the isolated fault controlled carbonate platform reveals disorganized stratal geometries in both platform top and slope facies suggesting a more complex interplay of rates of tectonic uplift and subsidence variation in carbonate productivity and resedimentation of carbonates such that any sea level cyclicity is obscure this study explores the interplay between different forcing mechanisms in the evolution of carbonate platforms in active extensional tectonic regions characterization of detailed parasequence scale internal architecture allows the spatial variation in syn depositional relative base level changes to be inferred and is critical for understanding the development of rift basin carbonate platforms such concepts may be useful for the prediction of subsurface facies relationships beyond interwell areas in hydrocarbon exploration and reservoir modeling activities

sequential and climatic framework of the growth and demise of a carbonate platform implications for the peritidal cycles late jurassic north eastern france the middle oxfordian of the eastern paris basin constitutes a remarkable example of the growth and demise of a carbonate platform fischer plots sedimentary and diagenetic features allow the identification of four depositional cycles s5 to s8 in the transversarium zone they are inserted in a lower frequency cycle of increased decreased accommodation space soiii the long term period of accommodation creation occurred during the older s5 and s6 cycles the maximum accommodation zone being located in the lower part of the s6 cycle this high accommodation period was tectonically controlled and was coeval with local distensive activity of a hercynian fault a major minimum accommodation zone exists during the s8 cycle at that time the platform was isolated and presented both a windward and a leeward margin the growth of the platform was favoured by a warm and arid climate oligotrophic conditions and reduced siliciclastic input during a highstand in relative sea level these palaeoenvironmental features favoured the proliferation of phototrophic organisms producing carbonate material the death of the platform was generated by a reduction in the carbonate production surface during a lowstand in relative sea level and by the appearance of mesotrophic conditions induced by the increase in siliciclastic inputs at the beginning of a period with a cooler and more humid climate in the eastern paris basin during the middle oxfordian the parasequences are ordered and present greenhouse characteristics in contrast at the beginning of the s8 cycle the randomness in the thickness of contiguous parasequences increased decreased carbonate production during the lowstand caused by a transition from photozoan to heterozoan benthic communities certainly favoured this randomness and the appearance of catch down parasequences

sequence stratigraphy of lower cretaceous barremian albian carbonate platforms of northeastern mexico regional and global correlations abstract the lower cretaceous cupido and coahuila platforms of northeastern mexico form part of the extensive carbonate platform system that surrounded the ancestral gulf of mexico a sequence stratigraphic model for these barremian to albian platforms was constructed from regional correlations of vertical cycle stacking patterns constrained by newly acquired biostratigraphic data and c and sr isotope stratigraphy the cupido shelf lagoon barremian aptian is composed of up to 150 peritidal cycles which stack into high frequency sequences that are correlated across the shelf cupido high frequency sequences build into a lower partial composite sequence cu1 an overlying full composite sequence cu2 and the transgressive base of a third composite sequence cu co3 related to backstepping of the cupido platform the highstand part of cu co3 is recorded in evaporite and carbonate facies of the coahuila platform aptian albian more than 80 meter scale evaporite to carbonate cycles characterize the restricted interior of the coahuila platform and stack into two full composite sequences co4 co5 the coahuila platform was drowned in the latest albian or earliest cenomanian terminating shallow water carbonate sedimentation in the region regional correlations of the depositional sequences in northeast mexico with coeval platforms in texas and the northern gulf coast indicate that the lower two composite sequences of the cupido shelf correlate with the lower part of the sligo hosston platform in texas the transgressive systems tract of the third composite sequence of the cupido la pena is recorded in texas by the upper sligo and pearsall formations the highstand systems tract and the disconformable top of the third composite sequence coahuila platform is likely coeval with the upper glen rose platform in texas the fourth and fifth composite sequences are correlative with the fredericksburg platform and the washita devils river platforms of texas respectively we conservatively correlated our sequence stratigraphic framework with composite global sequences and eustatic curves derived from several other basins given the available time resolution results are variable but sequence boundaries at the top of cu co3 and co5 appear to have clear interbasinal equivalents

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

the invisible hand tectonic triggering and modulation of a rhyolitic supereruption identifying the processes that initiate and control large explosive eruptions on time scales of human interest is challenging we present evidence for syneruptive subsurface interactions between rhyolite magmas derived from distinctive sources that reflect tectonic processes starting then temporarily stopping the 27 ka oruanui supereruption 530 km 3 magma taupo new zealand subordinate 3 16 biotite bearing pumice lapilli occur in fall deposits from phases 1 and 2 of 10 among the biotite free normal pumices in the oruanui deposits the biotite bearing magma is sourced to an independent magmatic system 10 15 km northeast of taupo lateral migration of the biotite bearing magma was initiated during a rifting episode that also triggered the oruanui eruption limited physical mingling indicates that the biotite bearing and oruanui biotite free magmas interacted in the conduit simultaneously with eruption after phase 1 a time break of months elapsed before phase 2 explosive activity resumed from the same vent again with intermixed biotite bearing magma a rift related tectonic event with its accompanying stress change is inferred to have initiated diking from northeast to southwest transporting biotite bearing magma and triggering the oruanui eruption stress relaxation following the rifting event terminated phase 1 before a tectonic event caused renewed diking and activity in phase 2 tectonics may trigger large silicic eruptions through rupturing of shallow crustal magma chambers and lateral magma transport especially in extensional regimes without necessarily leaving any discernible geological imprint only the presence of a foreign magma in the oruanui deposits allows the tectonic control to be identified

the genesis of lofer cycles of the dachstein limestone northern calcareous alps austria peritidal carbonate platform lofer cycles have been regarded as a record of sea level oscillations driven by variations in the earth s orbit fresh analysis of a newly measured 700 m thick section from the steinernes meer is presented here estimation of stratigraphic completeness indicates that this sequence is only 0 75 9 5 complete strongly suggesting that milankovitch patterns are not preserved analysis of cycle thickness frequency distributions reveals an exponential pattern strongly suggestive of aperiodic random deposition rather than periodic deposition in response to orbital forcing evidence for the importance of autocyclic processes e g lateral migration of inter to supratidal mudbanks and subtidal areas and syn sedimentary tectonic downfaulting events within this already active late triassic extensional zone is presented

depositional sequences in shallow carbonate dominated sedimentary systems concepts for a high resolution analysis abstract oxfordian and berriasian sections representing shallow water carbonate dominated sedimentary systems have been studied in the swiss and french jura in spain and in normandy they all display a hierarchical stacking of depositional sequences facies evolution and stacking pattern allow to define elementary small scale medium scale and large scale sequences some depositional sequences display well marked sequence boundaries others are limited by transgressive or maximum flooding surfaces the hierarchical organisation of such sequence stratigraphic elements implies that sea level fluctuations were an important factor in their formation and that these fluctuations had different frequencies the superposition of high frequency sea level changes on a long term sea level trend leads to repetition of diagnostic surfaces defining sequence boundary and maximum flooding zones wherein the corresponding high frequency surfaces are well developed chronostratigraphic tie points permit us to estimate the duration of large scale sequences this time control and the observed hierarchical stacking suggest that the high frequency sea level changes were controlled by climatic cycles in the milankovitch frequency band the variability of stacking pattern and facies evolution between sections illustrates the complexity of the studied environments furthermore because of the minimal accommodation space available in these shallow water settings much of the geologic time is not recorded nevertheless detailed analysis of the depositional sequences allows the interpretation of the evolution of the sedimentary system with a high time resolution thus there is a potential to monitor sedimentological ecological and diagenetic processes on a time scale of 20 to 100 ka

viscosity of high crystal content melts dependence on solid fraction 1 the rheological properties of suspensions containing high solid fractions are investigated attention is focused on viscosity of silicate and magmatic melt systems a general empirical equation which describes the relative viscosity of suspensions as a function of suspended solid fraction is proposed in the limit of very dilute solid concentrations it reduces to the einstein equation the proposed relationship is satisfactorily applied to reproduce available experimental data relative to silicate melts moreover the extrapolation of the model to very high concentrations is compared with experimental observations on partially melted granite

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

evidence for cross rift structural controls on deformation and seismicity at a continental rift caldera abstract in continental rifts structural heterogeneities such as pre existing faults and foliations are thought to influence shallow crustal processes particularly the formation of rift faults magma reservoirs and surface volcanism we focus on the corbetti caldera in the southern central main ethiopian rift we measure the surface deformation between 22nd june 2007 and 25th march 2009 using alos and envisat sar interferograms and observe a semi circular pattern of deformation bounded by a sharp linear feature cross cutting the caldera coincident with the caldera long axis the signal reverses in sign but is not seasonal from june to december 2007 the region south of this structure moves upwards 3 cm relative to the north while from december 2007 until november 2008 it subsides by 2 cm comparison of data taken from two different satellite look directions show that the displacement is primarily vertical we discuss potential mechanisms and conclude that this deformation is associated with pressure changes within a shallow analysis of the distribution of post caldera vents and cones inside the caldera shows their locations are statistically consistent with this fault structure indicating that the fault has also controlled the migration of magma from a reservoir to the surface over tens of thousands of years spatial patterns of seismicity are consistent with a cross rift structure that extents outside the caldera and to a depth of 30 km and patterns of seismic anisotropy suggests stress partitioning occurs across the structure we discuss the possible nature of this structure and conclude that it is most likely associated with the goba bonga lineament which cross cuts and pre dates the current rift our observations show that pre rift structures play an important role in magma transport and shallow hydrothermal processes and therefore they should not be neglected when discussing these processes

ordovician metre scale cycles implications for climate and eustatic fluctuations in the central appalachians during a global greenhouse non glacial to glacial transition abstract metre scale shallowing upward cycles in ordovician carbonates of the central appalachian basin record climate and eustatic fluctuations during a transition from early ordovician global greenhouse to late ordovician icehouse conditions peritidal facies and shale abundance suggest a long term trend in this area from semi arid early ordovician to more humid middle to early late ordovician conditions with a return to semi arid conditions during the late ordovician the climatic fluctuations were most likely produced by tectonics uplift and erosion related to taconic orogenesis plate motion of north america and the areal extent of water covering the shelf peritidal cyclic facies indicate that high frequency relative sea level fluctuations were of small amplitude 20 m relative sea level fluctuations that decreased into the later ordovician if these sea level changes are eustatic then the increased amplitude may mark the early initiation of continental glaciation on gondwana in the late middle ordovician followed by waning of ice sheets prior to the latest ordovician glaciation

vertically extensive and unstable magmatic systems a unified view of igneous processes volcanoes are an expression of their underlying magmatic systems over the past three decades the classical focus on upper crustal magma chambers has expanded to consider magmatic processes throughout the crust a transcrustal perspective must balance slow plate tectonic rates of melt generation and segregation in the lower crust with new evidence for rapid melt accumulation in the upper crust before many volcanic eruptions reconciling these observations is engendering active debate about the physical state spatial distribution and longevity of melt in the crust here we review evidence for transcrustal magmatic systems and highlight physical processes that might affect the growth and stability of melt rich layers focusing particularly on conditions that cause them to destabilize ascend and accumulate in voluminous but ephemeral shallow magma chambers

how much magma is required to rift a continent article i nfo article history many continental rifts are associated with and preceded by the formation of large igneous provinces partial melting of a large region of anomalously hot upwelling mantle isrequired to explain these huge volumes of pre and syn rift basaltic magma the uplift associated with a shallow region of hot mantle is often invoked as a cause of the rift push force that may drive the observed extension the rift push force is likely to be an order of magnitude toosmall todrive tectonicstretching of normal continentallithosphere but may besufficient to drive opening of lithosphere cutting dikes intrusion of a sequence of such dikes along a narrow zone may provide enough heat to significantly weaken the lithosphere here we use a newly developed 2d numerical approach in which magma filled dikes open in continental lithosphere in response to an evolving model stress field and the advection and diffusion of heat is tracked to investigate the relation between the volume of magma and the amount of lithospheric weakening the available rifting force lithospheric structure and parameters controlling magma flux are varied in the numerical simulations for continental lithosphere 60 km thick hl h1200 c heat diffusion is unimportant and only a small amount of magma is required 10 20 m y similar to magmatic rifts like the red sea

high resolution sequence stratigraphy of the upper ordovician montoya group southern new mexico and western texas outcrop analog of an unconventional chert and carbonate reservoir the upper ordovician montoya group crops out in southern new mexico and westernmost texas and records predominantly subtidal deposition on a gently dipping carbonate ramp that was subsequently almost entirely dolomitized the montoya group is a third order composite sequence composed of six regionally correlative shallowing upward third order depositional sequences m0 m5 sequence m0 has sandstone at its base that is overlain by skeletal packstone grainstone sequence m0 occurs only locally and was likely deposited in a topographic low formed during regional development of the unconformity following el paso group deposition sequence m1 marking the initial widespread transgression over the ellenburger unconformity consists of sandstone updip that passes downramp into skeletal packstone the highstand systems tract hst of m1 consists of a prograding skeletal grainstone that was subaerially exposed upramp sequence m2 which contains the second order maximum flooding surface has abundant subtidal cherty carbonate at its base which shallows upward into a widespread prograding coral packstone grainstone in the hst sequence m3 also contains abundant downramp chert that passes upramp into an aggrading crinoidal shoal and farther upramp into peritidal mudstone sequence m4 records an extensive basinward shift in facies as peritidal burrowed and cryptalgalaminated mudstone prograded over subtidal carbonate sequence m5 is only locally developed downramp and consists of crinoidal grainstone with abundant evidence of subaerial exposure a regional unconformity separates the montoya group from the silurian fusselman dolostone or younger units parasequences meter scale cycles recording low to moderate amplitude relative sea level fluctuations are ubiquituous features at individual outcrops but are difficult to correlate regionally the abundance of syn or early depositional chert in the subtidal facies indicates that the montoya group was deposited within a region of strong regional upwelling along southern laurentia this early formed chert was the reservoir facies in a successful upper ordovician gas play in ward and reeves counties texas

modeling carbonate microfacies in the context of high frequency dynamic relative sea level and environmental changes sequence stratigraphic models are used to interpret stratal architecture and key stratal bounding surfaces in ancient carbonate platforms within the context of changing accommodation space during third order relative sea level cycles however individual systems tracts are still described using standard microfacies that give a snapshot of limestone composition but they do not take into account gradual changes in the marine environment resulting from variations in water depth during the cycle of relative sea level change water depth is the single most significant collective control on a wide range of environ mental gradients affecting carbonate sediment composition during dy namic relative sea level fluctuations stratigraphic changes in carbonate sediment composition are characterized by systematic shifts in the rel ative importance of different limestone component grain types forming temporal continuums or relays relays are detected using computer optimized jaccard s similarity coefficient matrices to analyze presence absence compositional data individual relays between grain types may link together samples that are generically unrelated to one another but are nevertheless genetically related to deposition during the same uni directional dynamic environmental gradient a stratigraphic relay identified within the basal beds of the mid cretaceous urgonian carbonate platform succession of se france re cords unidirectional environmental gradients linked to changing water depth characteristic of a transgressive systems tract periods of static water depth such as the keep up phase of a late highstand systems tract at the top of the urgonian carbonate platform succession are characterized by fixed compositional assemblages stratigraphic breaks between individual compositional relays and assemblages occur at in flections in changing water depth marking the boundaries between individual systems tracts and sequences currently identified using stra tal geometries and key stratal surfaces the use of relays to model microfacies and identify individual system tracts and sequence boundaries has several advantages over existing methods this approach can be used where key stratal surfaces are difficult to distinguish such as in planar and concordantly bedded inner platform settings and in arid depositional environments where physical evidence of subaerial platform exposure such as karstification is poorly developed the technique can also be used to determine the genetic significance of unconformities preserved in outcrop or core within a sequence stratigraphic context by differentiating unconfor mities formed at the extremes of relative sea level cycles from those formed by other abrupt acyclical environmental changes

the role of volatiles in magma chamber dynamics many andesitic volcanoes exhibit effusive eruption activity1 with magma volumes as large as 107 109 m3 erupted at rates of 1 10 m3 s 1 over periods of years or decades during such eruptions many complex cycles in eruption rates have been observed with periods ranging from hours to years2 3 4 5 6 7 longer term trends have also been observed and are thought to be associated with the continuing recharge of magma from deep in the crust and with waning of overpressure in the magma reservoir here we present a model which incorporates effects due to compressibility of gas in magma we show that the eruption duration and volume of erupted magma may increase by up to two orders of magnitude if the stored internal energy associated with dissolved volatiles can be released into the magma chamber this mechanism would be favoured in shallow chambers or volatile rich magmas and the cooling of magma by country rock may enhance this release of energy leading to substantial increases in eruption rate and duration

dynamics of cyclic carbonate deposition and biotic recovery on platforms during the famennian of late devonian in guangxi south china constraints from high resolution cycle and sequence stratigraphy to better understand the dynamics of platform carbonate deposition evolution and biotic recovery during the famennian high resolution cycle and sequence stratigraphic analyses were carried out upon three platform sections one in ramp and two in rimmed platforms along with a biostratigraphically well constrained basinal section in guangxi south china four main facies and fourteen lithofacies are identified in the three isolated platforms these are vertically arranged into decimetre to metre scale shallowing upward peritidal and subtidal cycles or parasequces in which the peritidal cycles predominate over the lower middle famennian six third order sequences s1 to s6 are identified based on the cycle stacking patterns as illustrated by fischer plots and vertical facies changes these sequences are temporally calibrated through correlation with basinal sequences constrained with conodont zonation and match well the six main famennian transgressive regressive cycles t1 to t6 in euramerica and elsewhere indicating a eustatic control however an opposite longer term trend in accommodation change s3 to s4 between platform interior and deeper open shelf to basin settings during the middle famennian suggests a differential subsidence across the platform basin section likely driven by block tilting thus both eustatic fluctuations and local tectonism had played an important role in platform development and evolution after the frasnian famennian biotic crisis main marine benthos preferentially recovered in the normal marine niches on the nearshore open shelves and radiated gradually into offshore restricted platforms brachiopods notably rhychonellides were the taxa recovering the earliest s1 in the normal or near normal marine conditions then echinoderms s3 stromatoporoids upper s3 and corals s5 stepped in episodically however these benthos generally appeared later in the restricted platform interiors only as if the ecological conditions were improved well enough for their colonization therefore the biotic recovery processes were diachronous both taxonomically and ecologically specified

the 2014 2015 eruption of fogo volcano geodetic modeling of sentinel 1 tops interferometry after 20 years of quiescence fogo volcano erupted in november 2014 the eruption produced fast moving lava flows that traveled for several kilometers and destroyed two villages this event represents the first episode of significant surface deformation imaged by the new european space agency s sentinel 1 satellite in its standard acquisition mode terrain observation by progressive scans tops which differs from that of previous synthetic aperture radar sar missions we perform a bayesian inversion of sentinel 1 tops sar interferograms spanning the eruption and accurately account for variations in the tops line of sight vector when modeling displacements our results show that magma ascended beneath the pico do fogo cone and then moved laterally toward its southwestern flank where the eruptive fissure opened this study provides important insights into the inner workings of fogo volcano and shows the potential of sentinel 1 tops interferometry for geophysical e g volcano monitoring applications

magma chamber properties from integrated seismic tomography and thermal modeling at montserrat it is widely believed that andesitic magmas erupted at arc volcanoes are stored in shallow reservoirs prior to eruption but high resolution images of focused regions of magma in the shallow crust are rare we integrate seismic tomography with numerical models of magma chamber growth to constrain the magma chamber beneath soufriere hills volcano montserrat our approach reveals the characteristics and dynamics of the magmatic system with a level of detail that no single method has yet achieved the integrated analysis suggests that a magma chamber of 13 km3 with over 30 melt fraction formed between 5 5 and at least 7 5 km depth a significantly higher melt fraction than inferred from the seismic data alone the magma chamber may have formed by incremental sill intrusion over a few thousand years and is likely to be a transient geologically short lived feature these volume and geometry estimates are critical parameters to model eruption dynamics which in turn are key to hazard assessment and eruption forecasting

post lgm faulting in central europe lidar detection of the 50 km long sub tatra fault western carpathians abstract the increasing availability of high resolution lidar data reveals surprisingly strong topographic evidence of late quaternary faulting in some intraplate regions characterized by weak recent tectonic activity for the first time we present evidence of a 50 km long post last glacial maximum lgm tectonic rupture along the southern margin of the tatra mountains slovakia in the highest part of the carpathian mountains using a high resolution 1 1 m lidar dem we recognize that the normal range bounding sub tatra fault stf and its eastward branch the ru bachy fault rbf offset late quaternary glacial moraines alluvial fans and colluvial slopes the fault zone morphology is dominated by a nearly continuous southward facing up to 18 m high main scarp locally accompanied by antithetic fault scarps and hanging wall grabens similar offsets of pre lgm and lgm deposits and the absence of fault scarps within holocene alluvium suggest that the stf and rbf were active for a relatively short time interval between 18 ka and the holocene using the vertical separation of dated lgm moraine crests we estimate that the minimum average postglacial slip rates along the stf and rbf varied from 0 1 0 3 mm year i e rates one order of magnitude higher than those reported for other faults in central europe additionally deep seated landslides and the presence of large rock avalanches along the fault suggest possible postglacial high magnitude earthquake s producing coseismic rupture of the stf and rbf we conclude that 1 southern range bounding faults of the tatra mountains are the longest 50 km and only documented post lgm ruptures revealing extensive offset of late quaternary deposits in the western carpathians and 2 relatively small along strike variations in postglacial offset mimic the long term exhumation trends and imply en block uplift of the southern margin of the tatra mountains with the highest displacement along the east stf

magma compressibility and the missing source for some dike intrusions 1 dike intrusions are often accompanied by localized deflation interpreted as depressurizing magma chambers feeding the dike in some cases the inferred volume decrease is a factor of 4 or 5 less than the volume increase of the dike here we explore whether this discrepancy can be explained by compressibility of the magma combined with the fact that cracks are much more compliant than equidimensional magma chambers if pressure changes are small the magma compressibility m is constant and the dike ends up in hydrostatic equilibrium with an ellipsoidal magma chamber at the same depth the ratio rv of the volume of the crack to the volume lost by the chamber is rv 1 4 m 3 1 where is the host rock rigidity for gas poor magmas m 0 6 2 10 10 pa 1 and 3 25 gpa we find 1 2 rv 7 7 large changes in magma compressibility due to gas exsolution increase rv

3 d analysis and interpretation of magnetotelluric data from the aluto langano geothermal field ethiopia the main ethiopian rift valley encompasses a number of volcanoes which are known to be actively deforming with reoccurring periods of uplift and setting one of the regions where temporal changes take place is the aluto volcanic complex it hosts a productive geothermal field and the only currently operating geothermal power plant of ethiopia we carried out magnetotelluric mt measurements in early 2012 in order to identify the source of unrest broad band mt data 0 001 1000 s have been acquired at 46 sites covering the expanse of the aluto volcanic complex with an average site spacing of 1 km based on this mt data it is possible to map the bulk electrical resistivity of the subsurface down to depths of several kilometres resistivity is a crucial geophysical parameter in geothermal exploration as hydrothermal and magmatic reservoirs are typically related to low resistive zones which can be easily sensed by mt thus by mapping the electrical conductivity one can identify and analyse geothermal systems with respect to their temperature extent and potential for production of energy 3 d inversions of the observed mt data from aluto reveal the typical electrical conductivity distribution of a high enthalpy geothermal system which is mainly governed by the hydrothermal alteration mineralogy the recovered 3 d conductivity models provide no evidence for an active deep magmatic system under aluto forward modelling of the tippers rather suggest that occurrence of melt is predominantly at lower crustal depths along an off axis fault zone a few tens of kilometres west of the central rift axis the absence of an active magmatic system implies that the deforming source is most likely situated within the shallow hydrothermal system of the aluto langano geothermal field

platform carbonates of the upper jurassic mozduran formation in the kopet dagh basin ne iran facies palaeoenvironments and sequences abstract the mozduran formation a thick carbonate succession over 1200 m of the upper jurassic callovian kimmeridgian in northeast iran has been studied to determine its palaeoenvironments and sequences detailed petrographic investigations have led to the recognition of several microfacies and microfacies groups which constitute four palaeoenvironmental associations tidal flat beach lagoonal platform margin and open marine most of the mozduran formation sediments were deposited on a rimmed carbonate platform adjacent to a deeper marine environment the mozduran carbonate succession consists of five thick shallowing upward sequences 3rd order cycles no major hiatus has been recognized between these cycles therefore the contacts are considered subtidal conformities drowning unconformities these 3rd order cycles can be correlated with those recognized in upper jurassic strata in other parts of the world thus they are considered largely eustatic mainly tectono eustatic in origin numerous small scale shallowing upward cycles parasequences are contained within the major shallowing upward cycles both subtidal and peritidal parasequences showing an abrupt deepening of microfacies have been recognized a combination of episodic subsidence and autocyclic processes could have been responsible for the formation of these small scale cycles rapid carbonate accumulation reflected in rare first generation marine cements including meteoric cements resulted in grain to grain pressure solution and sutured contacts during burial with late cements filling the remaining pores many of the platform margin grainstones packstones have been replaced by coarsely crystalline dolomite possibly through seawater pumping and kohout convection during the transgressive and highstand phases of sea level