foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

the timing and environment of tepee formation in a marinoan cap carbonate thin carbonate units capping marinoan age glacial diamictites contain atypical tepee like structures that have been interpreted as evidence of seafloor dolomite cementation at parachilna gorge in the adelaide fold thrust belt a marinoan age cap dolomite contains paired tepee and growth fault structures that demonstrate the tepees grew 3 5 7 1 m below the sediment water interface in the early diagenetic zone although generally much larger such tepees and their associated sheet veins have an external morphology and internal structure identical to that of inter tidal tepee structures formed through expansive crystallisation on the other hand cap carbonate hosted tepees lack the size chaotic internal bedding carbonate crust and concretionary morphologies and expected carbon isotope geochemistry to be cold seep structures expansive crystallisation during early diagenesis seems the most likely means of forming tepees in cap carbonates the only cement common to all cap carbonate tepees is microcrystalline dolomite the crystallisation of this mineral phase drove both tepee growth and the fluid overpressure fracturing that formed the sheet veins the same microcrystalline dolomite is the component of cap carbonates routinely selected for isotopic analysis with the resulting 13c values assumed to be representative of coeval marine bicarbonate however the parachilna gorge tepees suggest that the microcrystalline dolomite contains both primary and early diagenetic components their separation is not achieved by current analytical methods

new discoveries of mud volcanoes on the eastern mediterranean ridge data from two mud volcanoes discovered on the eastern mediterranean ridge are presented showing that these features have erupted episodically within historical time both volcanoes mark the site of active gas and fluid venting from deep within the sedimentary pile large volumes of mud breccia have been extruded onto the volcano slopes for the first time clasts up to c 1 m in size have been recovered from sea floor mud volcanoes the submarine clasts show lithologies ranging from shallow water bioclastic sandstones to marls and limestones dated using microfauna as oligocene miocene and perhaps cretaceous in age deep towed video footage of one of the volcanoes shows clasts up to several metres across within the crater area deep towed high resolution side scan sonar data and core data are presented to compare the two examples the paper documents the discovery of the two volcanoes the dublin mud volcano and the stoke on trent mud volcano the clasts that have been recovered from them the intermittence of the eruptions as interpreted from gravity core data and how the volcanoes contrast with other mud volcanoes further to the west

crustal shortening at the sierra pie de palo sierras pampeanas argentina near surface basement folding and thrusting the sierras pampeanas consist of basement uplifts that are mainly controlled by w verging crustal thrusts one of these the sierra pie de palo is controlled by a blind thrust whose kinematics is debated we analysed the reverse faults located along the eastern side of the range and show that these are characterized by small displacements few hundreds of metres of the neogene and quaternary deposits controlled by the inherited basement metamorphic foliation and shear zones at the sierra scale the inherited foliation pattern appears already folded before the cenozoic shortening forming a series of antiforms and synforms with various wavelengths we propose that this structure is amplified during the plio quaternary shortening resulting in a large asymmetrical basement cored anticline where foliation parallel slip can act as folding mechanism the overall kinematics is consistent with an e verging fault propagation fold this proposed kinematics is an alternative to the frequently suggested w verging fault bend fold model finally we propose a new alternative and speculative crustal and lithospheric structure for this region consisting of two e verging basement thrusts coeval to w verging pampean thrusts both rooting below the precordillera above an eclogitized lower crust

episodic massive mud eruptions from submarine mud volcanoes examined through topographical signatures the role of mud volcanism on subsurface fluid migration and material cycling has long been debated here we compile the heights and radii of offshore mud volcanoes and estimate a mean volume of episodic massive mud eruptions based on previous studies into granular flows the volume is estimated as a function of the ratio of height to basal radius of the mud volcano s body under reasonable assumptions of the sizes of the mud conduit nearly all known offshore mud volcanoes are found to be polygenetic with the mean individual eruption volume of the pie type mud volcano being several orders of magnitude larger than that of the cone type the frequent occurrence of pie type mud volcanoes in accretionary margins characterized by high sediment influx is explained by their efficiency in the transport of large amounts of fluidized sediments from deep depths to the seafloor

the structure and geomorphology of the dashgil mud volcano azerbaijan the large scale and small scale 10 m structure and geomorphology of the active dashgil mud volcano in central azerbaijan have been studied through historical records it is known that this mud volcano has major eruptions every 6 32 years the activity observed during two field trips in 1995 consisted of low energy venting and debouching of mud water oil and gas from three mud pools salses and about 20 individual cones gryphons located on the summit plateau of the mud volcano besides the bubbling mud pools ranging from 30 to 75 m across and the cones ranging from 0 8 to 3 m height a 200 m long string of about 10 sinter mounds was found on the summit plateau the internal structure of the mud volcano and the processes responsible for the observed dashgil geomorphology are discussed assuming the dashgil mud volcano to be continuously active with an average methane production similar to that observed in 1995 between the rare major eruptions we have conservatively estimated the dashgil mud volcano to produce an annual amount of at least 800 sm3 standard cubic metres of gas mainly methane which is emitted directly into the atmosphere this estimate indicates that the natural contribution of atmospheric greenhouse radiatively active gases from the world s terrestrial and submarine mud volcanoes is highly significant

a viscoelastic coupling model for the cyclic deformation due to periodically repeated earthquakes at subduction zones vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic maxwell half space are obtained and compared with the observed deformation cycle coseismic strain release postseismic transients interseismic strain accumulation from japan the viscoelastic effects including the influence of buoyant restoring forces are obtained using the method developed by rundle and plate convergence and strain accumulation are incorporated following the procedure suggested by savage the resulting deformation cycle is compared with that of an analogous elastic half space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault cyclic deformation is similar but not identical for the two models and observations from southwest japan suggest the superiority of the viscoelastic coupling model in particular inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half space model and results in agreement with the observed interseismic movement pattern several aspects of the postseismic deformation its landward migration and its transition to the interseismic phase of the cycle are explained as well but the short duration of near trench transients relative to those observed farther inland is not matched the success of a buried slip model in explaining early postseismic near trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle elastic in the short term and ductile for longer term deformation and such a modification may reconcile remaining discordant observations however reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of japan and these regional differences remain unexplained

seismic architecture of a lower cretaceous platform to slope system santa agueda and poza rica fields mexico two three dimensional seismic data sets over the albian western golden lane margin and time equivalent basinal deposits of poza rica field allowed us to investigate the linked architecture of a steep sided carbonate platform el abra formation and a thick accumulation of redeposited carbonate sediment at the toe of the slope and in the basinal area tamabra formation regional seismic cross sections show that the most aggrading albian platform has an eroded platform top a scalloped margin and a channelized slope that are equivalent to a 20 km 12 4 mi wide westward thinning thick toe of slope apron made of chaotic contorted mounded moderate to high amplitude reflections detailed reflection geometries in the albian toe of slope and basinal deposits consist of chaotic to short discontinuous low amplitude reflection at the toe of the slope of the golden lane platform laterally changing to a discontinuous mounded shingling reflection which ultimately turns into high amplitude parallel reflections we interpret this lateral change to reflect the seismic signature of the change from the block and debris flow dominated toe of slope area to debris flow and concentrated density flow deposits in the basin that ultimately grade laterally into pelagic deposits on a flattened seismic slice mounded reflections correspond to lobate to fan shaped seismic events several kilometers wide that are interpreted as a carbonate basin floor fan comparison between core and seismic data shows a dominance of debris flows in the lower two albian sequences albian 1 and albian 2 that grade vertically into more lobate concentrated density flows and turbidites in the upper two albian sequences albian 3 and albian 4 seismic data used in this study combined with core observations do not support the interpretation of the albian tamabra formation being of shallow water origin seismic features identified as basin floor fan channel and debris flow deposits have a shape and size that are similar to those of other redeposited basinal carbonate deposits elsewhere the seismic architecture shows that the poza rica field is a typical example of thick accumulation of grainy porous carbonate deposits in a basinal setting this example shows the potential of a large hydrocarbon accumulation in a tectonically modified stratigraphic trap around shallow water carbonate platforms

emplacement of a passive margin evaporitic allochthon in the betic cordillera of spain the triassic section of the external domain of the betic cordillera is rootless and thus allochthonous the frontal accretionary wedge of the guadalquivir allochthon consists dominantly of triassic evaporites and red beds forming a melange with upper cretaceous paleogene deep water sedimentary rocks throughout the unit jurassic rocks are absent it is here proposed that the widespread triassic evaporites of the guadalquivir allochthon were originally emplaced as gravitational allochthonous masses in a passive margin setting much like the widespread allochthonous salt of the texas louisiana gulf of mexico thus on the betic passive margin allochthonous evaporites were first emplaced during the late cretaceous paleogene later during neogene time these evaporites were overthrusted as an accretionary wedge to form the guadalquivir allochthon a schematic reconstructed position of the guadalquivir allochthon places the original passive margin allochthon in its continental slope setting

surface deformation associated with the november 23 1977 caucete argentina earthquake sequence leveling data are combined with seismic observations from the november 23 1977 ms 7 4 caucete earthquake in western argentina in order to constrain models of crustal deformation in the sierras pampeanas tectonic province the spatial pattern and amount of uplift 1 m that accompanied this earthquake suggest 4 m of slip on a north south trending west dipping fault with a dip of 35 a downdip width of 24 km and a length of 80 km the top of the fault is 17 km below the surface these fault parameters are generally consistent with the seismic focal mechanism and moment of the main shock which occurred near the top of the fault the fault length is derived from the distribution of local and relocated teleseismic aftershocks and from analysis of the main shock a double event in which the two shocks occurred 21s apart and were separated by 65 km along the proposed fault plane strike the fault width is determined from the locations of the larger hypocenters along the preferred fault plane this fault is buried beneath the north south striking sierra pie de palo a laramide style crystalline basement uplift in the western part of the sierras pampeanas province the buried fault model is consistent with the lack of observed coseismic surface faulting and the broad east west symmetric character of the overlying sierra pie de palo by combining the 1977 earthquake observations with topographic relief and with estimates of the age of deformation for the sierras pampeanas basement uplifts we calculate a shortening rate of the order of 10 mm yr for the past 5 m y for this andean back arc province and estimate an average recurrence time of the order of 1000 years for earthquakes of this magnitude beneath the sierra pie de palo

ground deformation associated with the eruption of lumpur sidoarjo mud volcano east java indonesia abstract ground deformation associated with the eruption of lumpur sidoarjo mud volcano between 2006 and 2011 has been investigated from synthetic aperture radar images marked subsidence has been observed to the west of as well as around the vent line of sight changes in the both areas decayed since the middle of 2008 with a time constant of 1 5 2 5 years implying that the ongoing eruption won t last long this uniform decay time indicates that the western part is connected to the eruption center since the middle of 2008 to form a system with stationary geometry our observation that the decay started later to the west than around the vent suggests that the subsidence to the west has been triggered by the mud eruption a simple modeling suggests that 1 the conduit needs to be narrower at depth than at the surface 2 the effective rigidity of the mud needs to be lower than that estimated from the drilled sample or both to explain the observed decay constant of the deformation

mud volcanoes revealed and sampled on the western moroccan continental margin we surveyed and sampled two active and 3 inactive mud volcanoes on the atlantic continental margin of morocco the active mud volcanoes named yuma and ginsburg are each about 4 km in diameter rise between 150 250 meters above the seafloor and are the first active methane related mud volcanoes to be identified in this region the inactive volcanoes range in diameter from 1 3 km with relief between 50 and 80 meters gravity cores from the crest of the active mud volcanoes yielded methane hydrates and mud breccia deposits chemosynthetic communities of pogonophora worms and the bivalve solemya were found on the surface of the active mud volcanoes sediment cores from the inactive volcanoes contained hemipelagic sediments rich in foraminifera and ahermatypic coral debris overlying mud breccia

accurate source depths and focal mechanisms of shallow earthquakes in western south america and in the new hebrides island arc synthetic seismograms are matched to long period p waveforms in order to obtain accurate depths of shallow earthquakes with known focal mechanisms accurate depths are obtained for a large sample of moderate sized 6 ms 7 events which produced relatively simple p waveforms and do not require intensive analysis the estimated error in the determination of depth is about 5 km or less for most of the events considered the procedure is applied to two suites of events one in south america 83 events and one in the new hebrides 61 events in these two areas of contrasting styles of subduction the accurate depths provide new information on the bending of descending plates near trenches the seismicity and tectonics of the upper plate and the geometry and structure of the zone of contact between the upper and descending plates depths of suboceanic earthquakes which occurred near the trench and which have either tensional and compressional horizontal stress axes agree well with chapple and forsyth s 1979 preferred model of a bending elastic perfectly plastic plate however an unusually deep event occurred beneath the fiji plateau in an area of young ocean floor supposed to have been formed by sea floor spreading processes only since late miocene time the calculated depth of the event 48 km places it below the lithosphere asthenosphere boundary derived from thermal models vertical cross sections through the shallow parts of the subduction zones show that most of the earthquakes with thrust faulting focal mechanisms can be interpreted to be interplate events located in a thin 10 km thick curved zone of contact dipping arcward or landward from the trench axis however a few events with focal mechanisms similar to the interplate events do not fit on the inferred thin zone of contact these events would be accommodated by an interplate zone 15 km thick in both subduction zones interplate events occur at depths between about 15 and 50 km however the downdip width of the south american interplate zone is 2 to 3 times larger than that in the new hebrides most of the intraplate events near the interplate boundary are located in the descending plate in the upper plate seismicity is more pronounced in the back arc regions of the two subduction zones thus our results support the generality of a relatively aseismic zone in the upper plate located trenchward of the magmatic arc depths of shallow earthquakes in the eastern andes and sub andean regions of south america range between about 9 and 36 km indicating that both the upper and middle crust are seismically active about 75 of the events occurred in the upper 25 km furthermore the focal mechanisms indicate that from ecuador to argentina the crust of the eastern side of the andean cordilleran is in a state of east west compression oriented nearly parallel to the direction of convergence between the nazca and south american plates the depths the orientations of the earthquake nodal planes and the close relationships to quaternary tectonics imply basement involved crustal shortening in much of the eastern andes and sub andean zones of peru and argentina

trap and seal analysis in carbonate shelf margin stratigraphic trap exploration example from the lower miocene zhujiang formation pearl river mouth basin people s republic of china abstract carbonate shelf margin stratigraphic traps are a particularly risky play type because the same diagenetic factors responsible for secondary reservoir quality enhancement can be responsible for degrading seal quality and increasing trap risk the zhujiang fm prograded westward off the dongsha massif initially as a ramp which evolved into a prograding and aggrading shelf margin seismic interval velocity analysis modeled with data from a nearby oil bearing pinnacle reef indicates a thick porosity zone at the shelf margin wedging and pinching out eastward core data from the pinnacle reef indicated a short term exposure event was responsible for significant early secondary porosity enhancement this also may have influenced the adjacent shelf area enhancing porosity in the shelf margin but reducing seal capacity in the equivalent up dip shelf sequence the seal competency of the overlying hanjiang shales was demonstrated by hydrocarbons sealed in the adjacent pinnacle reef seal risk was evaluated by mercury injection capillary pressure analysis in a shelf carbonate well updip from the margin it was determined that the up dip shelf seal is sufficient to hold an economically favorable 300 500 ft 90 150 m hydrocarbon column seismic evidence revealed several large mega slumped portions of the shelf margin producing scalloped areas extending severalmore kilometers back into the shelf subsequent filling of these reentrants could produce lateral sealing by juxtaposing hanjiang shales against the sides of the remnant zhujiang carbonate salient the slump scar on the south side of the salient did not downcut to a significant stratigraphic depth to provide a critical closure to trap a minimum hydrocarbon column to meet economic thresholds less

alluvial fan and playa sedimentation in an andean arid closed basin the pacencia group antofagasta province chile the mid tertiary pacencia group comprises over 2 km of continental sediments it was deposited in a half graben basin thought to have been active since early tertiary times conglomerates along the western basin margin were deposited as longitudinal bars rare transverse bars and channel fills with subsidiary debris flows all in a distal fan pebbly braided stream environment no proximal fan sediments are exposed petrographic and palaeocurrent analysis indicates these sediments were derived from cretaceous and possibly jurassic source areas to the northwest to the east within the basin a succession of sands silts muds thick evaporites and rare carbonates were deposited in playa sub environments saliferous muds central salt pan are overlain by interbedded red mudstones and thin high energy ribbon and sheet sands marginal dry mudflat and sandflat certain sand bodies carry stratiform cui agi au mineralization lakes existed at various stages and were fed by permanent fluvial systems the playa sediments were derived from crystalline source areas to the east proximal fan facies and sediment sources are now buried under the volcanic andes

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

the structural evolution of the messinian evaporites in the levantine basin abstract the levantine basin in the south eastern mediterranean sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load because the messinian evaporites are comparatively young the sediment load varies along the basin margin they are hardly tectonically overprinted and the geometry of the basin and the overburden is well defined in this study we analyse depositional phases of the evaporites and their structural evolution by means of high resolution multi channel seismic data the basinal evaporites have a maximum thickness of about 2 km precipitated during the messinian salinity crisis 5 3 5 9 ma ago the evaporite body is characterized by 5 transparent layers sequenced by four internal reflections we suggest that each of the internal reflection bands indicate a change of evaporite facies possibly interbedded clastic sediments which were deposited during temporal sea level rises all of these internal reflections are differently folded and distorted proving that the deformation was syn depositional thrust angles up to 14 are observed backstripping of the pliocene quaternary reveals that salt tectonic is mainly driven by the sediment load of the nile cone the direction of lateral salt displacement is mainly ssw nne and parallel to the bathymetric trend apparent rollback anticlines off israel result rather from differential subsidence than from lateral salt displacement in the south eastern basin margin the deposition of the isreali slump complex isc is coeval with the onset of salt tectonic faulting suggesting a causal link between slumping processes and salt tectonics the superposition of thin skinned tectonics and thick skinned tectonics becomes apparent in several locations the fold belt off the israeli mediterranean slope mainly results from active strike slip tectonics which becomes evident in faults which reach from the seafloor well below the base of the evaporites owing to the wrenching of the crustal segments which are bounded by deep rooted fault lines like the damietta latakia pelusium and shelf edge hinge line the setting is transpressional south of 32 n where the fault lines bend further towards the west this adds a component of thick skinned transpression to the generally thin skinned compressional regime in the basin above 1 5 km of evaporites a mud volcano is observed with the mud source seemingly within the evaporite layer at the eastern cyprus arc the convergence zone of the african and the anatolian plates deep rooted compression heavily deformed the base of the evaporites whereas at the eratosthenes seamount mainly superficial compression affecting the post messinian sediments and the top of the evaporites is observed

the paragenetic history of a marinoan cap carbonate abstract carbonates that cap late neoproterozoic glacial diamictites contain large atypical tepee like structures that have been interpreted as evidence for seafloor dolomite cementation the nuccaleena formation in the adelaide fold thrust belt is the stratotype marinoan age cap dolostone at parachilna gorge the nuccaleena formation contains paired cogenetic tepees and growth faults that demonstrate these structures grew well below the sediment water interface these tepees and their associated sheet veins were the result of pore fluid overpressure driven by expansive early diagenetic dolomite cementation fluid overpressure resulted in two forces 1 macroscale lateral compression that overcame the lithostatic weight to buckle sediments upward forming the tepee structure and 2 macro to microscale extension that overcame the lithologic tensile strength to form sheet veins the physical processes of fluid overpressure within the parachilna gorge cap carbonate are in many ways analogous to the fluid overpressure dynamics in mud volcanoes and were sufficiently high to generate veins extending 17 m below the cap carbonate overpressure driven dewatering removed pore fluid clay and organic matter from the dolomicrospar matrix into dewatering structures and fabrics the latter are hierarchically arranged from small linear clay fabrics to clay lined dendritic arrays to clay choked curvilinear veins to large sheet veins packets of red clay laminae were deposited when pore fluids vented to the sea floor the early diagenetic chemical evolution of the parachilna gorge cap carbonate was equally dynamic in which an initial reducing trend was supplanted by an oxidation trend brought about by tepee sheet vein deformation once established the sheet vein network also reinvigorated diffusional processes that likely enhanced early diagenetic cementation of the cap dolostone the detailed paragenetic history also suggests that calcite not dolomite was the initial carbonate precipitated from the post glacial adelaidean sea the nuccaleena formation exhibits the dolomicrospar isotopic signatures and tepee like structures that distinguish marinoan age cap carbonates at parachilna gorge these typical features are a product of early diagenesis suggesting that other marinoan age cap carbonates may also be early diagenetic in origin

the structure and formation of mud volcano summit calderas circular depressions bounded by inward dipping faults found at the upper terminations of large mud volcano systems 500 m diameter are termed mud volcano summit calderas from new mapping and comparison with previously identified examples we describe a series of common structural and morphological features found at a number of calderas and propose a mechanism for caldera formation a typical example consists of concentric deformational and volcanic zones including an outermost topographic rim inward dipping circular fault system moat and raised central pedestal of freshly extruded mud volcanic sediment this distinctive moat and pedestal morphology can be explained in terms of the quantity and rheology of extruded mud and appears characteristic of calderas from the south caspian basin and elsewhere the association of fresh mud volcanic deposits with the calderas in combination with extensive literature on caldera modelling leads us to conclude that the most likely causal mechanism is subsidence as a result of evacuation of fluids and sediment from shallow structural levels during eruptions summit calderas mapped in this study characterize dormant periods of mud volcanism in subaerial and submarine settings and appear to be a common structural element in the extrusive domain of mud volcano systems

the role of mud volcanism and deep seated dewatering processes in the nankai trough accretionary prism and kumano basin japan circulation of water at moderate depths in subduction zones is dominantly driven by clay mineral dehydration over distinct pressure and temperature gradients the signature of these dehydration reactions is found in mud volcano pore waters however it is largely unknown how much of the deep seated fluids are emitted at mud volcanoes to unravel this relation for the region off the kii peninsula japan we calculated the water volume that is subducted in the nankai trough using input data from iodp holes c0011 and c0012 and the correspondent water volume released from the subducted plate under the kumano basin in an area where 13 mud volcanoes are located according to our model water released at depth in the mud volcano area is derived almost entirely from basaltic saponite and sedimentary smectite transformation up to 96 nonetheless the mud volcanoes themselves expel 1 of the total volume to test the contribution of the accreted strata and the kumano basin fill to the water budget we run a second model water loss due to compaction of sediments and smectite illite transition below the basin floor have been calculated the results were compared with salinity measurements on background cores scattered in the study area to extrapolate the volume of water loss at depth the comparison of the two methods yielded similar results and led us to conclude that the bulk part of the deep seated fluid re enters the hydrosphere via the basin floor a mechanism rarely taken into account in fluid budgets in the literature

paleogeography and andean structural geometry northwest argentina neogene tectonic segmentation of the andean cordillera in northwestern argentina is a function of both the dip of the subducted plate and of major paleogeographic structures and sedimentary basins vergence fault dip and lateral continuity of neogene structures can be related to the character and pre existing geometries and structures of the materials in which they form south of 27 s the thick skinned sierras pampeanas which occur mostly over a flat segment of the subducted nazca plate formed where little sedimentary cover overlay crystalline basement north of 24 s the thin skinned subandean belt overlying an inclined slab segment formed within a thick elongate eastward tapering trough of paleozoic and mesozoic sediments that may represent a complex of pre andean foreland basin deposits the transitional region between 24 27 s the santa barbara system and cordillera oriental is characterized paleogeographically by complex cross trending structures and irregular basin geometries and the neogene structures are equally complex and variable the paleogeographic features of nw argentina are a product of compressional tectonism during much of the paleozoic that resulted in an orogenic belt oriented obliquely to the modern andes this earlier orogen was disrupted by several zones of transverse structures and by cretaceous extensional or pull apart basins these features clearly influence the geometry of the superposed andean structures more intriguing however is the possibility that preexisting structures of the continental lithosphere may in some way help to modify the geometry of the subducted plate

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

late quaternary seismic facies of the gulf of cadiz spanish margin depositional processes influenced by sea level change and tectonic controls abstract seismic facies and quaternary depositional systems of the gulf of cadiz have been characterized by means of high resolution seismic profiles airguns geopulse and ore 3 5 khz a total of 11 pleistocene and two holocene sequences separated by type 1 or type 2 discontinuities were identified the age of the depositional sequences was determined based on foraminifera ages from boreholes and by correlation with seismic profiles of the slope areas with uniform deposition and without significant discontinuities these seismic units have been mapped throughout the margin allowing to establish the correlation with eustatic sea level curves and global climatic trends the distribution and geometry of the units reveals that most of the sedimentary record was developed during episodes of forced regression ten regressive periods corresponding to 5th order cycles arranged into 4th order were distinguished absolute water depths for the development of coastal deposits in each unit were calculated using depth from present day sea level corrected for tectonic subsidence in the area the model for the evolution of the depositional system of the gulf of cadiz continental margin highlights the strong influence of tectonism in the development of depositional bodies controlling the distribution of deposits generally produced during episodes of sea level fall

geometry and lithofacies of coarse grained injectites and extrudites in a late pliocene trench slope basin on the southern boso peninsula japan abstract this study investigates the geometry and internal structures of coarse to very coarse grained volcanic sandstones and volcanic breccias with many siltstone clasts interpreted to be sill like injectites and extrudites occurring in an upper pliocene trench slope basin succession on the southern boso peninsula japan the injectites occur in the uppermost shiramazu formation and pinch out laterally into siltstone dominated deposits of the mera formation their thicknesses vary from a few centimeters to 2 m the basal and upper contacts of the injectites with host muddy deposits are sharp and or erosional and are locally discordant with the bedding of the host deposits siltstone clasts which were ripped up or ripped down from the host muddy deposits are commonly incorporated into the injectites although some siltstone clasts have geological ages older than those of the host deposits seven lithofacies have been identified in the injectites based on the internal structures the combinations of internal structures are different from those of high density turbidity current deposits and debrites and suggest that injection was promoted by a combination of turbulent and laminar flow conditions the extrudites show an overall convex up geometry and possess lithological features similar to those of the injectites they have been identified in the rendaiji conglomerate member which is encased in the mera formation and which rests on the uppermost shiramazu formation the extrudites are characterized by gently undulating waveforms that show upstream migration and climbing stacking patterns similar to the cross sectional geometry of cyclic steps or upstream migrating antidunes the active eruption of solid liquid mixtures onto the seafloor and sedimentary piles may have subsequently collapsed to produce supercritical high density gravity currents down the flanks of a neptunian volcano the injectites and extrudites locally contain calyptogena shells and shell fragments as well as fragments of carbonate concretions that exhibit low carbon isotopic ratios suggesting that fluidization of the source sediments was triggered by a combination of seepage of cold methane bearing water into the source sediments and seismic shaking volcaniclastic deposits older than the host muddy deposits are present in the trench slope basin deposits and these are the likely source of the injectites and extrudites

structure and palaeogeography of the external betic cordillera southern spain abstract a structural interpretation of the external betic cordillera in the granada jaen area of southern spain is proposed based on the interpretation of seismic reflection profiles subsurface well control and a balanced cross section restoration of this balanced cross section results in a new palaeogeographical interpretation for the area and a total estimated shortening of approximately 200 km traditionally the betic fold thrust belt has been described as a series of north vergent imbricate thrust sheets each having relatively little displacement 10 15 km restoration of this structural model to an undeformed state results in a mesozoic palaeogeographical scenario of three carbonate platforms separated by two deep basins an alternative interpretation is presented in this paper that the structural style of the granada jaen area is characterized by large displacement thrust faults restoration of the proposed cross section leads to the palaeogeographical interpretation of a single mesozoic basin along the transect of the cross section this palaeo basin is bounded to the north and south by platformal margins the major implication of this study is that the palaeogeographical interpretation of a fold thrust belt can be highly dependent on the structural interpretation

why large earthquakes do not nucleate at shallow depths although by definition tectonic earthquakes may nucleate anywhere within the seismogenic layer in almost all cases those earthquakes that become large nucleate near the base of the seismogenic layer because frictional strength and stress drop should increase with depth and in situ stress measurements suggest that the ambient stress increases with depth we have examined spontaneous rupture models with gradients of both average stress drop and average strength relative to ambient stress to determine whether this explains the observed phenomena we report here that ruptures that are nucleated with in the low stress drop shallow regions of the model are inhibited from propagating but those that are nucleated within the high stress drop regions can propagate over the entire fault plane

nature and origin of sedimentary clasts associated with mud volcanoes in the nile deep sea fan relationships with fluid venting abstract during the last 10 years several marine geological geophysical surveys conducted on the nile deep sea fan have provided much new information about the large fluid seepage phenomenon which characterizes this passive margin segment among the data more than 60 sediment cores have been recovered in this area rock clasts were collected from eight of them as well as during deep sea dives notably in the area of isis osiris and amon mud volcanoes in few areas especially in the western and the north eastern provinces of the nile fan some clasts consist of crust fragments resulting from cementation of muddy sediment by precipitation of high mg calcite these clasts correspond to a simple cementation of the mud by precipitation of high mg calcite as a consequence no obvious textural or faunal difference with the ambient matrix mud can be observed these clasts are made of autochthonous crusts derived from microbial anaerobic oxidation of methane and release of bicarbonate and sulphide in the surrounding pore water these clasts also lack aragonite in most of the other cases menes caldera isis osiris and amon mud volcanoes allochthonous clasts characterized by low mg calcite cement siderite or dolomite mixed with expelled mud outcrop on the seafloor nannofossils have allowed us to date some of these clasts most of the ages range from pliocene to pleistocene one clast is lower cretaceous in age the lithological facies often indicate coastal or deltaic environments some clasts are closely linked to an evaporite rich environment halite gypsum and analcime they all provide useful information on the nature of buried sedimentary series covering the margin their presence on the seafloor is due to the expulsion of a pressurized mixture of sediment water and gas this process is believed to have used pre existing tectonic conduits

liquefaction during the 1977 san juan province argentina earthquake ms 7 4 liquefaction effects generated by the 1977 san juan province argentina earthquake ms 7 4 are described the larger and more abundant effects were concentrated in the 60 km long band of the lowlands in the valle del bermejo and in an equally long band along the rio san juan in the valle de tulum fissures in the valle del bermejo were up to several hundred meters long and up to several meters wide sand deposits from boils that erupted through the fissures covered areas up to tens of square meters fissures generally parallelled nearby stream channels because the valle del bermejo is undeveloped these large features caused no damage liquefaction in the valle del tulum caused important or unusual damage at several localities including the following five sites 1 at the barrio justo p castro a subdivision of caucete liquefaction of subsurface sediments decoupled overlying unliquefied stiff sediments producing a form of ground failure called ground oscillation the associated differential ground movements pulled apart houses and pavements in extension while shearing curbs and buckling canal linings in compression at the same locality 2 at the escuela normal in caucete the roof of a 30 m long single story classroom building shifted westward relative to the foundation that displacement fractured and tilted columns supporting the roof the foundation was fractured at several places leaving open cracks as wide as 15 mm the cumulative width of the open cracks was 48 mm an amount roughly equivalent to the 63 mm of offset between the roof and foundation at the east end of the building the ground and foundation beneath the building extended or spread laterally opening cracks and lengthening the foundation while the roof remained in place 3 the most spectacular damage to structures at the community of san martin was the tilting of a 6 m high water tower and the toppling of a nearby pump house into a 1 m deep crater similarly a small crater developed beneath a hand pump in an open area and a large 6 m diameter crater formed nearby the following sequence of events created the craters and toppled the pump structures during the earthquake ground shaking generated excess pore pressures which were dissipated by upward flow of groundwater free drainage was restricted by an impermeable plastic silt layer water apparently accumulated below the plastic silt layer and then burst to the surface through several holes and cracks including holes around well casings 4 at the san isidro winery nine storage tanks tilted 2 to 5 five reinforced concrete tanks were dismantled but four steel tanks were repaired by placing new footings and jacking the structures into an upright position 5 at escuela j j pasos differential settlement beneath building fractured several columns and walls the largest settlements were about 60 mm and the maximum settlement of footings supporting columns was about 40 mm in spite of the damage the buildings were in no danger of collapse

submersible study of mud volcanoes seaward of the barbados accretionary wedge sedimentology structure and rheology abstract in 1992 the nautile went to a mud volcano field located east of the barbados accretionary wedge near 13 50n using nannofossil analysis on cores we determined the sedimentation rate and provided a new estimation of the age of the mud volcanoes 750 000 years for the oldest one six structures have been explored with the submersible nautile and manifestations of fluid venting chimneys carbonate cementation and chemosynthetic communities were observed on all sedimentological analysis identifies two sources of diapiric mud most mud volcanoes expel mud containing late miocene to quaternary faunae that have the same composition as sediments drilled above the barbados wedge decollement one volcano also contains older oligocene taxa with a mud composition corresponding to the sedimentary sequence below the decollement we use diving observations to map the fine scale morphology the distribution of chemosynthetic fauna and define two end member types of structures mud pies flat topped mud volcanoes and conical mounds mud pies atalante and cyclops are characterised by the presence of a lake of highporosity mud 70 to 75 in their central parts chemosynthetic benthic communities calyptogena colonies and sponge bushes are concentrated in the outer parts contrasting morphologies of the two mud pies indicate different stages of activity cyclops is growing whereas atalante is collapsing expulsion of water and methane occurs mostly through the mud lake and may be stronger during the collapse phase on conical mounds there are no mud lakes fluid venting concentrates near the summit and occurs through carbonate cemented chimneys which form within the sediment viscosity measurements have been carried out on mud samples from the two mud pies and one conical mound all mud samples have a plastic fluid behaviour the plastic threshold decreases with porosity and thixotropy is observed for a porosity of more than 70 an analogue experiment shows that for this thixotropic mud shearing in the feeding conduit liquefies the mud which then spreads to form a mud pie conical mounds form when the mud remains plastic we show that the dissociation of methane hydrate is the cause of the high porosity in mud pies and confirm that these structures are a consequence of large scale dissociation of methane hydrate at the base of its stability field dissociation of hydrates before and during ascent is only slightly contributing to the pore fluid in conical mounds but solid hydrates still present in the mud may contribute to its buoyancy

the sirente crater italy impact versus mud volcano origins the sirente crater is a circular structure with a diameter of 80 m the rim deposit is an inverse graded matrix supported breccia sedimentological features of the rim deposit suggest that the crater is not related to an explosion or violent mechanical displacement the structure and texture of the deposit exhibit a primary sedimentary character the rim deposits do not contain artifacts and do not show evidence of reworking a multistage formation is reconstructed for the rim growth and associated deposits the geometry and sedimentology of the deposits indicate that they were produced by the extrusion and accumulation of mudflow deposits the dominant ejection mechanism was low mud fountains and the transport medium was water petrographic and geochemical evidence does not indicate any physical or cryptic trace of an extraterrestrial body the most realistic agent that explains the observed effects is a rapid local emission of mud and or water geological processes capable of producing these features include piping sinkholes or more probably caldera type mud volcanoes which may result from underground water table perturbation and or decompression of deep co2 hydrocarbon gas reservoirs due to tectonic deformation or faulting activity during a seismic event in both cases the name crater for this geological form may be maintained but there is no compelling evidence for an impact origin in this paper the scientific literature on the sirente crater is reconsidered in the light of new morphological sedimentological geochemical and archaeological data a new mechanism is proposed involving mud fountaining

modelling fluid flow in clastic eruptions application to the lusi mud eruption abstract clastic eruptions involve the rapid ascension of sedimentary clasts together with fluids gas and or liquid phases that may further deform and brecciate the host rocks these fluids transport the resulting mixture called mud breccia to the surface such eruptions are often associated with geological structures such as mud volcanoes hydrothermal vent complexes and more generally piercement structures they involve various processes acting over a wide range of scales which makes them a complex and challenging multi phase system to model although piercement structures have been widely studied and discussed only a few attempts have been made to model the dynamics of such clastic eruptions the ongoing lusi mud eruption in the east java back arc basin which began in may 2006 is a spectacular large scale clastic eruption the lusi eruptive behaviour has been extensively studied over the past decade and thus represents a unique opportunity to better understand ongoing clastic eruptions and thus fossil clastic systems we use both analytical formulations and numerical models to investigate simple relationships between the mud breccia properties density viscosity gas and clast content and the volumetric flow rate our results show that the conduit radius of such piercement systems cannot exceed a few metres at depth and that clasts if not densely packed will not affect the flow rate when they are smaller than a fifth of the conduit size using published data for the annual gas fluxes at lusi we infer a maximal depth at which exsolution starts this occurs between 1800 m and 3200 m depth for methane and between 750 m and 1000 m for carbon dioxide based on annual gas fluxes we estimate that the conduit radius should be no larger than 1 5 m to match the maximal mud discharge recorded at lusi

modeling cryogenic mud volcanism on pluto abstract subsurface ice cryofluids and ice interactions with ammonia for cryovolcanic materials give the potential ingredients for the formation of mud volcanoes on pluto in order to constrain the possible morphology from images acquired by the new horizons spacecraft we have modeled the formation of mud volcanoes isostatic layers of ice overlain by denser material from a series of possible solid liquid mud compositions methane and ammonia as well as accounting for the full range of eruption variables e g mud viscosity conduit diameter and eruption duration we categorize them into nine specific scenarios based on the composition of the top ice layer and mud composition from these scenarios the maximum height of the potential mud volcano can be calculated we find that ammonia mud sources produce smaller edifice heights and wider flow profiles compared to methane dominant mud cryovolcanoes assuming certain preliminary parameters we also propose the evolution and development of the edifice of wright mons in as little as 3 8 million years given a 10 wt ammonia subsurface mud composition if characterized on pluto s surface mud volcanoes would provide an interesting insight on the subsurface dynamics of solids and cryofluids on pluto

interaction between accretionary thrust faulting and slope sedimentation at the frontal makran accretionary prism and its implications for hydrocarbon fluid seepage 1 using high resolution seismic profiles and other geophysical data collected during r v meteor cruise m74 2 we investigate the distribution patterns of shallow sediments their structure and deformation processes and their role in the migration accumulation and seepage of hydrocarbon rich fluids here we show that rapid syn kinematic sedimentation at the frontal makran accretionary prism provides a mechanism by which emerging imbricated thrust packets override the footwall at the seafloor without significant mass wasting and destruction of fault related anticline in the hanging wall these anticlines may rise high above the seafloor to form plate boundary parallel ridges and distinguish from simple thrust blocks seen at convergent margins elsewhere with the fast burial of many thrust faults by the syn kinematic sediments anticlinal growth structures form in these syn kinematic sediments by continuous thrust activity the anticlinal structures preserved within the cores of the ridges or formed from these syn kinematic sediments act as structural traps for migrating hydrocarbon rich fluids above which fluid escape structures are generated leading to seafloor seeps most of the discovered hydrocarbon seeps around sixth ridge are sourced from these traps despite the compressional environment and the rapid syn kinematic sedimentation rates shallow subsurface of the frontal makran is a normally pressured regime in which the buoyancy of hydrocarbons may account for the fluid migration in this important respect the makran accretionary prism differs from many other convergent margins and accretionary prisms where fluid flow is largely driven by tectonically induced overpressure

compaction and porosity evolution of pliocene sandstones ventura basin california sandstones of the pico and repetto formations were studied to quantify the processes involved in compaction and to determine the porosity evolution of the beds during burial the sandstones are mineralogically immature and except for local carbonate cemented beds have insufficient cement to have prevented compaction stratigraphic studies and graphic porosity depth plots suggest that the samples maximum burial depths were approximately 10 000 ft 3 048 m deeper than the present day depths of 850 13 000 ft 259 3 962 m compaction produced closer grain packing as measured by the contact index ci average number of contacts per grain and tight packing index tpi average number of long sutured and embayed contacts per grain for samples with less than 10 cement the ci depth gradient is 0 21 1 000 ft 0 69 1 000 m and tpi depth gradient is 0 27 1 000 ft 0 89 1 000 m assuming sands had 40 initial porosity the sandstones that are at present most deeply buried lost a total absolute porosity of 26 by all compactional processes which includes 14 by grain rearrangement and 6 each by pressure solution and ductile grain deformation porosity loss by nondeformational grain rearrangement was complete by a present day depth of 5 000 ft 1 524 m but in uncemented sandstones pressure solution plus associated grain rearrangement and ductile grain deformation continued to the maximum depths sampled compaction is most abrupt in sands with abundant micas and ductile rock fragments the ci gradient is 0 14 1 000 ft 0 46 1 000 m for samples with ess than 10 ductile grains but 0 22 1 000 ft 0 72 1 000 m for samples with more than 10 ductile grains compaction was almost entirely the result of overburden pressure and was not noticeably retarded in overpressured zones suggesting that overpressures developed after maximum burial was achieved for samples with less than 10 cement the ci is a better depth predictor than the tpi r2 0 58 vs 0 45 but the tpi is a better predictor of pre cement porosity than the ci r2 0 54 vs 0 31 secondary porosity averages 20 40 of the total thin section porosity secondary porosity is present at all depths but makes up the greatest percentage of total porosity between present depths of 6 000 and 9 500 ft 1 829 and 2 896 m except for grain fracturing secondary porosity formed only by dissolution of framework grains fractured grain porosity contributes up to 29 of total porosity 5 absolute porosity in some samples fractures formed during pleistocene tectonic episodes

structure and emplacement of mud volcano systems in the south caspian basin the term mud volcano system is coined to describe the set of structures associated with a constructional edifice mud volcano and feeder complex that connects the volcano to its source stratigraphic unit three dimensional 3 d seismic data from the south caspian basin are used to investigate the structural elements and evolution of these systems mud volcano systems initiate via early kilometer scale biconic edifices termed pioneer cones these are fed by fluidization pipes tens of meters in width subsequent kilometer scale mud volcanoes grew via persistent extrusion fed by numerous additional fluidization pipes injected in the country rock this subvolcanic intrusion complex creates a densely intruded cylindrical zone similar in cross section to gryphon swarms observed at an outcrop onshore wall rock erosion and compaction of the intruded zone leads to the collapse of a downward tapering cone enveloping the cylindrical zone capped by ring faults that define a kilometer scale caldera that downthrows the overlying mud volcano mud volcanoes get buried during basin subsidence and can look like intrusive laccoliths at first glance on seismic data reactivation of mud flow through a conduit system generates a stack of superimposed mud volcanoes through time large volcanoes continue to dewater during burial and may locally remobilize this model of mud volcano evolution has similarities with igneous and salt tectonic systems to reduce drilling and geologic uncertainty mud volcano system extent and impacts on a reservoir can be assessed on 3 d seismic data simon stewart received his ph d from the imperial college london in 1992 in 1992 2000 he was seismic interpreter at amerada hess in support of exploration and appraisal drilling in the north sea in 2000 he moved to bp and has since worked on structural geology and well planning in the americas middle east and the former soviet union his special interest is in the integration of structural geology and seismic interpretation richard davies received his ph d from the university of edinburgh in 1995 in 1995 2003 he was with mobil and exxonmobil working on field development and exploration the north sea the west of shetlands and the west niger delta deep water slope in 2003 2005 he was a senior lecturer in earth sciences at cardiff university united kingdom currently he is professor and director of cerees center for research into earth energy systems durham university united kingdom his special interest is in seismic scale expression of fluid migration and diagenesis

carbonate ramp evolution during the late oligocene chattian salento peninsula southern italy abstract oligocene carbonate ramps and platforms are widespread and though they are important carbonate reservoirs detailed studies on the facies organization platform type and internal architecture are scarce within this context the chattian carbonate units cropping out in salento southern italy allow detailed study of the distribution of skeletal components and facies architecture the lower chattian castro limestone previously considered as a fringing reef is reinterpreted as a distally steepened ramp with a distal talus induced by a paleo escarpment in the substrate epiphytic biota and sediment dweller organisms thriving in seagrass meadows dominated production in the shallow water euphotic zone seawards large rotalid foraminifers dominated a detritic mesophotic zone near the edge of the escarpment also in the mesophotic zone luxurious growth of corals built discrete mounds with no evidences of wave resistant growth fabrics basinward 25 to 30 dipping clinobeds abut against the escarpment where coral rudstone floatstone textures resulted from downfall of corals and sediments the upper chattian porto badisco calcarenite represents a homoclinal ramp dominated by packstone textures in the euphotic inner ramp autochthonous biota suggests the occurrence of extensive seagrass meadows basinward large rotalid packstone and small coral mounds developed in mesophotic conditions and rhodolithic floatstone to rudstone and large lepidocyclinid packstone characterize the sediments of the deeper oligophotic zone comminuted skeletal debris depleted of light dependent organisms typifies deposition in the dysphotic aphotic zone in both examples the middle ramp meso oligophotic zones was the most prolific in terms of carbonate production whereas shallow water seagrass related production euphotic was much less important corals built mounds also in the mesophotic zone but never reached sea level hydrodynamic conditions in the meso oligophotic zone are better explained by breaking of internal waves and their induced up and down slope currents instead of the surface storm waves

composition and flux of explosive gas release at lusi mud volcano east java indonesia the lusi mud volcano has been erupting since may 2006 in the densely populated sidoarjo regency east java indonesia forcing the evacuation of 40 000 people and destroying industry farmland and over 10 000 homes mud extrusion rates of 180 000 m 3 d 1 were measured in the first few months of the eruption decreasing to a loosely documented 4000 m for methane and approximately 600 m for carbon dioxide however the mass fractions of these gases are insufficient to explain the observed dynamics rather the primary driver of the cyclic bubble bursting activity is decompressional boiling of water which initiates a few tens of meters below the surface setting up slug flow in the upper conduit our measured gas flux and conceptual model lead to a corresponding upper bound estimate for the mud water mass flux of 10 5 m 3 d 1

timing and nature of alluvial fan and strath terrace formation in the eastern precordillera of argentina abstract sixty eight 10 be terrestrial cosmogenic nuclide tcn surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper arid san juan region of the argentine precordillera this region is tectonically active and numerous fault scarps traverse quaternary landforms the three study sites marquesado strath complex loma negra alluvial fan and carpinteria strath complex reveal a history of alluvial fan and strath terrace development over the past 225 ka the marquesado complex q3 m surface dates to 17 3 ka whereas the loma negra q1 ln q2 ln q3 ln q4 ln and q5 ln surfaces date to 24 3 ka 48 2 ka 65 13 ka 105 21 ka and 181 29 ka respectively the carpinteria complex comprises eight surfaces that have been dated and include the q1 c 23 3 ka q2 c 5 5 ka q3a c 25 12 ka q3b c 29 15 ka q4 c 61 12 ka q5 c 98 18 ka q6 c 93 18 ka and q7 c 212 37 ka 10 be tcn depth profile data for the loma negra alluvial fan complex and carpinteria strath terrace complex as well as osl ages on some carpinteria deposits aid in refining surface ages for comparison with local and global climate proxies and additionally offer insights into inheritance and erosion rate values for tcns 10 10 4 10 be atoms g of sio 2 and 5 m ma 1 respectively comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the carpinteria and loma negra areas with only younger alluvial fan surfaces preserved both to the north and south these data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region

mud volcanism an updated review abstract mud volcanism or sedimentary volcanism represents one of the most intriguing phenomena of the earth s crust with important implications in energy resource exploration seismicity geo hazard and atmospheric budget of greenhouse gases since the first review papers were issued at the beginning of 2000s a large amount of new geological geophysical and geochemical data has been acquired which clarified ambiguous concepts and significantly improved our knowledge of mud volcanism here we offer an updated review of the knowledge and implications of mud volcanoes with emphasis on the terminology used to describe different processes and structures the physical chemical and morphological characteristics of the several fluid emission structures the chemical properties of the released fluids in particular the molecular and isotopic composition of the gas the mud volcano formation dynamics and the several implications for petroleum exploration geo hazards and global atmospheric methane budget this review integrates new fluids data collected in azerbaijan and is complemented with field observations from various mud volcano provinces worldwide although the total number of mud volcanoes on earth is still uncertain 600 main onshore structures with a large variety in shapes and sizes are documented in recent global data sets and several thousand are assumed to exist in the oceans it is clear that a mud volcanoes are broadly distributed throughout the globe in active margins compressional zones of accretionary complexes thrust and overthrust belts passive margins deep sedimentary basins related to active plate boundaries as well as delta regions b they are specifically located in hydrocarbon bearing basins along anticline axes strike slips and normal faults and fault related folds in petroleum systems c they represent a specific category of natural gas oil seepage manifestation often related to deep and pressurised reservoirs d the main engine driving mud volcanism is given by a combination of gravitative instability of shales and fluid overpressure build up followed by hydrofracturing e hydrocarbons are generally of thermogenic origin while microbial gas is released in only a few cases mud volcanism on other planets e g mars and titan and microbial activity associated with gas seepage represent emerging issues and opportunities for future research

formation and evolution of the chaotic terrains by subsidence and magmatism hydraotes chaos mars the origin of the martian chaotic terrains is still uncertain and a variety of geologic scenarios have been proposed we provide topographic profiles of different chaos landscapes notably aureum and hydraotes chaos showing that an initial shallow ground subsidence occurred at the first step of the chaos formation we infer that the subsidence was caused by intrusion of a volcanic sill which could have produced consequent melting as well as release of ground water from disrupted aquifer signs of a volcanic activity are observed on the floor of hydraotes chaos a complex and deep depression located at the junction of three channels the volcanic activity is represented by small 0 5 to 1 5 km diameter rounded cones with summit pits the cone s size and morphology as well as the presence of possible surrounding lava flows suggest that they are primary volcanic cones similar to terrestrial cinder cones the identification of volcanic activity on the deepest chaos where the lower crustal thickness and the faults fractures system contributed to the magma rising reveals that magmatic activity proved by the cones and possibly help by structural activity has been a major factor in the formation of chaotic terrains

seabed morphology and gas venting in the black sea mudvolcano area observations with the mak 1 deep tow sidescan sonar and bottom profiler abstract the central part of the black sea was investigated with the mak 1 deep tow acoustic system providing sidescan observations and acoustic profiling subsequently underwater tv recordings and bottom sampling was done in an area with extensive mudvolcanism the mud volcanoes can be divided into three types according to their dimensions and morphology the first type has a seabed diameter of more than 2 km reaches a height of 100 150 m has a complex top with a crater like structure and gentle slopes and reflects massive mudflows in the crater and at its flanks the second type has smaller dimensions is more conical in cross section almost without relief on its relatively steep slopes and is characterised by small radial mudflows the third type is made up by the only mud volcano with a partially collapsed rim and with massive and liquid mudflows the first type expectedly is in a mature relatively passive stage the latter two types seem to be younger and more active various types of low relief slides are found in the area and are related to the presence of shallow subbottom gas 40 100 m below the seafloor or mudvolcano activity evidence for the presence of gas in the mudvolcano area is shown by gas venting acoustic turbidity acoustic masking numerous pockmarks acoustic voids and acoustic windows gashydrates do occur associated with some of the mudvolcanoes

numerical modelling of mud volcanoes and their flows using constraints from the gulf of cadiz it is estimated that the total number of submarine mud volcanoes is between 1000 and 100 000 because many are associated with greenhouse gases such as methane it is argued that the global flux of these gases to the atmosphere from the world s terrestrial and submarine mud volcanoes is highly significant clues to the processes forming submarine mud volcanoes can be found in variations to their height shape surface morphology physical properties and internal structure a model of isostatic compensation between the mud column and the sediment overlying the mud source is used to predict a depth to the mud reservoir beneath mud volcanoes once erupted the general behaviour of an individual mud flow can be described and predicted using a viscous gravity current model the model shows that conical shaped mud volcanoes comprise multiple superimposed radial flows in which the thickness eruption rate and speed of individual mud flows strongly depends on the viscosity density and over pressure of the erupted mud using these parameters the model predicts the lowermost flows will be the oldest thickest and have the greatest length of run out while the uppermost flows will be the youngest thinnest and shortest this model is in contrast to more traditional models of stratiform mud volcano construction in which younger flows progressively bury older ones and travel furthest from the summit applying the model to the two mud volcanoes studied in the gulf of cadiz quantitative estimates are derived for the depths to mud sources exit and flow velocities eruption duration and volume fluxes flow thickness and conduit radii for example with an average kinematic viscosity of 1 5 m2 s 1 for the erupted mud a density of 1 8 103 kg m 3 and a thickness for the youngest flows of about 0 5 m the model predicts a lowermost flow thickness of 3 6 m an average eruption duration of 7 h and a conduit radius of about 9 m to construct a conical shaped mud volcano of 260 m height similar to those studied in the gulf of cadiz is estimated to require a mud source at 4 6 km depth and a total of at least 100 individually erupted flows

sedimentary and diagenetic controls on red bed ore genesis the middle tertiary san bartolo copper deposit antofagasta province chile the middle tertiary pacencia group of antofagasta province northern chile consists of over 2 km of continental sediments these include alluvial fan playa and lacustrine facies representing deposition in an arid closed basin copper mineralization is hosted by sheet and ribbon sandstone bodies which were deposited in a high energy playa marginal sandflat environment ore minerals occur dominantly as a matrix to these lithic arkoses replacing earlier carbonate and sulfate cements the main ore minerals are native copper cuprite and atacamite although there is an along strike passage into copper sulfide cements in a structurally complex zone copper iron and copper sulfides were deposited in crosscutting fractures commonly replacing evaporite veins primary chalcopyrite and bornite exhibit progressive oxidation to anilite digenite and djurleite chalcocite is not found much of this material has oxidized further to covellite of normal and blaubleibender varieties galena and native silver are present in uneconomic amounts atacamite has a complex paragenesis representing at least locally the earliest copper bearing phase provenance studies of the host sediments and lead isotope data for the sulfides indicate that both the sandstones and the metals were derived from a calc alkaline volcano plutonic complex to the east of the basin an area now obscured by the recent volcanic andes sulfur isotope results for copper sulfides show very light delta 34 s values 33ppm indicative of biogenic sulfate reduction under conditions of unrestricted sulfate supply

the origin of conical mounds at the mouth of chasma boreale 1 one hundred and six isolated conical mound landforms were identified proximal to the north polar cap of mars at the mouth of chasma boreale five unique morphologies were identified including moderately sloped 4 6 cratered mound forms including two mounds of abalos colles flat topped moderately sloped 4 6 polygonal mound forms steeper 6 13 conical mound forms subdued mound forms with low angle slopes 0 5 3 and small 2 km diameter clustered conical forms with low to moderate angle 1 5 flank slopes from first order relationships between flank slope and the volcano productivity index volume diameter ratio 16 mounds were found to be morphologically similar to terrestrial low angle basaltic shield volcanoes thirteen mounds exhibit summit craters that range in depth d to diameter d ratio from 1 9 to 1 320 the circularity and d d ratios of mound summit craters are consistent with highly modified northern plains impact craters image analysis of shield like mounds reveals morphologic characteristics inconsistent with pristine volcanic landforms for most features horizontal flank layering 10 100 m thick polygonal map view morphology topographic relationships and spatial association with retreating polar scarps suggest that mound forms at the mouth of chasma boreale represent remnants of a once thicker more continuous sequence of near polar layered material evidence for northward scarp retreat is visible along rupes tenuis a sinuous scarp located west of chasma boreale along this scarp a single 100 m thick resistant cap unit part of the early amazonian age rupes tenuis unit is being undermined by aeolian erosion solar ablation and mass wasting remnants of the cap unit rest along the scarp margin and in places form small conical mound clusters at the base of the scarp fracture controlled retreat of the scarp is visible along the eastern portion of rupes tenuis and along the escorial crater remnant mesa where small tongue like promontories have been sculpted into the cap unit isolation of these irregularities by scarp retreat has formed several volcanic like scarp and mesa proximal mounds mound forms located closest to the retreating rupes tenuis scarp above 78 n were found to be the steepest and tallest mound landforms in the region mounds located distal to rupes tenuis were found to be broad and subdued this observation is consistent with long term retreat of a once more extensive rupes tenuis scarp and long term modification of isolated conical remnants

structural evolution of the argentine precordillera the rio san juan section abstract the argentine precordillera ap represents a high level fold and thrust belt which was formed during the andean tertiary crustal shortening in a w e transect studied mostly e directed imbrications are combined with folding and involve a pile of cambrian to tertiary sediments the thrust belt is detached above a main decollement within the ordovician to lower devonian strata to the east it is bounded by a back thrust zone directed westwards restored sections allow an estimate of crustal shortening and also provide insight into the structural development during pre tertiary times carbonate platform sequences of cambrian to ordovician age grade into a volcani clastic succession with transitional melanges representing deposits along a western continental slope in the western and easternmost parts of the ap cambrian to silurian deposits are affected by a first folding which to the west is combined with a slight metamorphic overprint during carboniferous to permian times intensified mobility along the eastern rim and in the western parts of the ap leads to crustal extension which partly was triggered by the formation of synsedimentary normal faults in the central ap no angular unconformities at the base of carboniferous permian deposits were found there was no field evidence found to postulate a terrane boundary within the ap area and an onset of thrust tectonics during cretaceous to early tertiary times

a first order model for temperature rise for uniform and differential compression of sediments in basins we deduce algebraic expressions for temperature rise for ideal cases of uniform and spatially varying compression of sediments of single mineralogy according to the results of the present work the temperature rise is related to the coefficient of volume expansion isothermal compressibility dimension bulk density and specific heat of the sediment columns rise of temperature due to compression of sediment is effectively inversely proportional to the volume coefficient of expansion or contraction of sediments compression related temperature rise is expected to augment diagenesis a more realistic model of temperature rise dealing with the rate of compression of sediments that of the pore fluid s and the vacant pore space individually would be required

diagenesis of tertiary playa sandstones of northern chile implications for andean uplift and metallogeny the oligo miocene pacencia group of antofagasta province northern chile consists of over 2 km of molassic sediments deposited in a series of alluvial fan and playa sub environments sandstones of the artolla member exposed around san bartolo represent playa marginal sandflat deposits and locally host stratiform copper mineralization a detailed study of these sediments has revealed a complex sequence of diagenetic modifications to the arkosic detrital mineral assemblage early dissolution of unstable ferro magnesian minerals and calcic feldspar resulted in the release of ions into intra stratal solution and the subsequent formation of a suite of eogenetic authigenic minerals these include early hematite coatings on framework grains pore lining zeolite and pore filling calcite gypsum and celestite cements syntaxial overgrowths of albite quartz and less common k feldspar are well developed following early oxidative intrastratal conditions the influx of acidic fluids derived from mudrocks during mesogenesis resulted in an important secondary porosity generation and the establishment of an acidic reducing intrastratal environment this facilitated the subsequent introduction of low temperature mineralizing solutions and formation of the san bartolo copper deposit a return to oxidative diagenetic conditions is recorded by late stage overgrowths of k feldspar and quartz and the oxidation of native copper chalcopyrite cements to cuprite tenorite and chalcocite covellite assemblages this final telogenetic modification to the mineral assemblage is related to flushing by meteoric waters and provides independent evidence for an important phase of andean deformation and uplift in the middle to upper miocene

sea floor morphology of the ebro shelf in the region of the columbretes islands western mediterranean abstract widespread volcanism off eastern spain in the western mediterranean is associated with cenozoic crustal attenuation and sinistral motion along the trans moroccan western mediterranean european mega shear extending from northern morocco to the north sea via the alboran basin eastern iberia the valencian and lyons basins france and germany the quaternary columbretes islands volcanic field is the most prominent example of this volcanism associated with this mega shear the islands are located in the ebro continental shelf on top of a structural horst probably made of paleozoic metamorphic rocks surrounding the emerged islands are volcanic structures and associated flows partially mantled by a sediment drift whose morphology is controlled by the southwestward flowing catalan current this association is rather unique and appears to have never been described from a continental shelf in the mediterranean sea or outside the sea the morphology of both kinds of structures obtained by means of swath bathymetry data and very high resolution seismic profiles is presented in this study they provide striking images of this previously unstudied part of the western mediterranean seafloor these images suggest that the volcanic structures are intruded into the surficial holocene sediments indicating that volcanism in the columbretes has extended into holocene

tectonic and magmatic evolution of the andes of northern argentina and chile abstract two orogenic cycles both with different evolution are developed in the western margin of the south american continent in northern argentina and chile the paleozoic hercynic cycle and the meso cenozoic andean cycle the hercynic cycle a wide marine basin extending westward of the cordillera oriental which developed in cambrian ordovician times marks the beginning of this cycle in contrast to peru and bolivia where this basin developed between two precambrian blocks the western margin of this basin in northern argentina and chile is still unknown the ordovician sedimentation and accompanied volcanism ends with the ocloyic deformation phase and its synkinematic granitic plutonism two basins were developed in the silurian devonian separated by the puna arc uplifted during this ocloyic phase the shallow water marine terrigeneous sediments which were deposited in them were deformed by a new tectono magmatic associated phase chanic phase carboniferous to lower permian marine carbonates were deposited west of the puna arc and red beds east of it later on during the permian to triassic a magmatic belt was developed along the cordillera occidental the rhyolites ignimbrites and the granitic to granodioritic related intrusives are well represented in chile although the overall geologic history of this period is known many problems concerning its origin and relations to plate tectonics are still unsolved the andean cycle during this cycle a series of magmatic arc systems related to the subduction of the pacific crust was built up along the western margin of south america huge volumes of calc alkaline lavas and related plutons were emplaced since the jurassic along belts parallel to the present coastline showing a general eastward migration trend up to the lower cretaceous an ensialic back arc basin was formed east of this magmatic arc thousands of meters of marine and continental sediments were deposited in it this basin disappeared during the middle cretaceous probably as a result of the final opening of the atlantic and the active westward movement of the south american plate since middle cretaceous times the magmatic arc has been the fundamental paleogeographic element the arc progressively migrated stepwise eastward each step marked by a tectonic phase subduction related crustal erosion could explain the lack of fore arc petrotectonic assemblages the eastward magmatic polarity which characterizes this section of the andes could also be explained by such a mechanism

tectonic framework of the mud mounds associated bsrs and submarine landslides offshore nicaragua pacific margin the regional distribution of mounds associated bottom simulating reflectors bsrs and submarine landslides of the pacific margin of nicaragua suggests a genetic relationship between them in the landslide dominated parts of the margin mud mounds occur in groups upslope behind the scarps and aligned parallel to the headwall the morphotectonic features associated with the slides suggest that the slope failure could be triggered by slope oversteepening on the trailing flank of subducted seamounts geometric analysis of the faults triggering and controlling the mud mounds and associated bsrs also indicates that they were caused by collapses of the uplifted sea floor thus we propose a simple conceptual genetic model for the occurrences of the submarine landslides surrounding mud mounds and associated bsrs in the area seamount subduction created locally higher fluid overpressure in the decollement the uplift and fracturing of the margin wedge above the subducting seamount opened pathways for the overpressured fluid to escape leading to the formation of numerous mud mounds on the sea floor and the bsr in the subsurface the higher fluid supply locally reduced the shear strength of the sediments and facilitated failure of these sediments as landslides on the oversteepened slope caused by the subduction of the seamount

the effects of neogene thrusting on deposition in the bermejo basin argentina abstract in the bermejo basin of western argentina semi arid sandy low gradient sedimentation has accompanied deformation of the frontal cordillera and precordillera since the mid miocene utilizing the precise geochronology established for strata at sierra de huaco we document an immediate basinward migration of facies coincident with thrusting in the central precordillera 8 7 ma an earlier shift in environment 10 3 ma is related to a change in drainage patterns produced by more distant deformation in the western precordillera evidence from sierra de huaco suggests that depositional environments are largely independent of the net subsidence rate sedimentologic features observed at sierra de huaco bear directly on the nature and scale of the processes that operate in sandy ephemeral settings 1 lateral accretion was the dominant process within an ephemeral braidplain the jarillal formation 2 fining upward cycles in sandflat deposits were a consequence of the dynamics of unconfined flows coupled with lobe switching on alluvial fans the huachipampa and quebrada del cura formations and 3 unconfined flow deposition in the bermejo basin occurred and still occurs over distances on the order of 50 km from point sources at alluvial fan heads

building the crust at the mid atlantic ridge the morphology of the sea floor at mid ocean ridge spreading centres provides a key to understanding how ocean crust is constructed images of the axial zone of the slow spreading mid atlantic ridge obtained at a range of spatial scales show that crustal construction is complex and highly variable reflecting an underlying three dimensional variability in magmatic tectonic and hydrothermal processes

dip range for intracontinental reverse fault ruptures truth not stranger than friction abstract histograms of fault dips have been compiled for moderate to large m 5 5 reverse slip intracontinental earthquakes with the slip vector raking 90 30 in the fault plane the principal data set is restricted to earthquakes where the fault plane in the focal mechanism can be unambiguously distinguished from the auxilliary plane the reverse fault dips are bracketed within the range 12 1 the observed dip range is consistent with reactivation of faults possessing rock friction coefficients within byerlee9s 1978 range 0 85 s 0 6 undergoing frictional lockup at dips approaching 60 the broad 25 to 35 peak may arise from progressive domino steepening of imbricate reverse faults above the optimal dip for reactivation in regions undergoing bulk shortening paucity of very low angle thrusts implies that it is generally the steeper ramps within ramp flat assemblages that fail in moderate to large earthquakes the subsidiary peak at 45 to 55 likely results from compressional reactivation of former normal faults in areas undergoing tectonic inversion requiring some degree of fluid overpressuring the results are consistent with previous studies on the dip range for active normal faults that again demonstrate frictional lockup at reactivation angles approaching 60 together these analyses suggest that byerlee friction coefficients apply to faults with displacements of up to a few kilometers

10 years of lusi eruption lessons learned from multidisciplinary studies lusi lab abstract the spectacular lusi eruption started in northeast java indonesia on may 29th 2006 continuously erupting mud water gas oil and clasts ever since lusi provides an unprecedented opportunity to study the birth and the evolution of a large scale and hot mud eruption lusi is interpreted as a hybrid between a traditional hydrocarbon driven piercement structure mud volcano and a hydrothermal system fuelled by magmatic heat lusi is therefore an exciting natural laboratory for understanding analogue modern and palaeo piercement systems such as mud volcanoes sediment hosted hydrothermal systems and hydrothermal vent complexes this special issue collects recent multidisciplinary work completed in the framework of the erc funded lusi lab project these studies were conducted at and near lusi contributions span across disciplines such as engineering geochemistry geophysics geology and numerical modelling including fieldwork laboratory and theoretical approaches the acquired results contribute to characterise the dynamics of complex interactions between volcanism and an ongoing erupting clastic system lusi still saves many mysteries that will be unravelled by future scientific investigations

earthquake deformation cycle in the andean back arc western argentina repeated leveling surveys conducted in 1938 1967 1975 1976 1978 1979 1980 and 1981 provide information on preseismic coseismic and postseismic movements associated with the ms 7 4 1977 caucete argentina earthquake sequence the spatial pattern and amount of uplift 1 m that accompanied the earthquake suggest 4 m of slip on a north south trending west dipping fault buried 17 km below the surface with a dip of 35 a downdip width of 24 km and a length of 80 km these fault parameters are generally consistent with the seismic focal mechanism the moment of the double main shock and the distribution of aftershocks vertical movements during the first preseismic period 1938 1967 while an order of magnitude smaller have a spatial pattern similar to the observed coseismic movements the second period of preseismic deformation 1967 1976 is characterized by movements opposite those which accompanied the earthquake 2 1 cm of relative subsidence during the first postseismic interval 1978 1980 deformation continued in the same sense as the coseismic movements an additional 10 1 cm of relative uplift subsequent postseismic movements 1980 1981 were opposite in sense to the coseismic deformation 12 1 cm of relative subsidence we suggest that the preseismic movements for the 1938 1967 time period result from reverse slip 50 cm on a downdip section of the 1977 earthquake fault this slip may have been induced by a ms 7 5 earthquake that occurred near san juan in 1944 or may represent coseismic slip for a m 6 5 earthquake that occurred in 1941 deformation during the second preseismic period 1967 1976 is interpreted as being due to steady strain accumulation on the fault 9 mm yr 1 the initial postseismic movements 1978 1980 are roughly consistent with afterslip on the 1977 earthquake fault 40 cm in the same sense as the coseismic slip the second phase of postseismic deformation may represent the period of rapid postseismic recovery i e strain accumulation observed previously in interplate areas there is some evidence that strain accumulation following the earthquake began on the updip section of the fault this process of strain accumulation may be responsible for the fact that the 1977 main shock initiated at the updip end of the coseismic fault assuming that the time predictable model of earthquake occurrence is applicable to this area we estimate that the next earthquake on the 1977 earthquake fault will occur in 200 600 years

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

morpho acoustic characterization of a shallow water mud volcano offshore scoglio d affrica northern tyrrhenian sea responsible for a violent gas outburst in 2017 abstract a violent gas outburst occurred offshore the scoglio d affrica islet tuscan archipelago northern tyrrhenian sea on march 16th 2017 with local fishermen observing columns of dirty water rising up to 10 m above the sea surface the integration of video footage and dissolved ch4 measurements collected 5 days after the event with high resolution multibeam data collected 4 months later allowed us to characterize the source area of the outburst corresponding to a shallow water mud volcano the mud volcano covers an area of ca 170 000 m2 has a vertical relief of ca 30 m with respect to the surrounding seafloor and an estimated volume of ca 1 106 m3 based on bathymetric reconstruction the elongated nnw sse shape of the mud volcano is compatible with local structural trends indicating a tectonic control for its development the mud volcano is made up of two mounds whose tops are located at a depth of ca 10 m the southern mound was responsible for the 2017 outburst as testified by a 15 20 m wide circular crater on its summit where a large amount of mud breccia and diffuse seepage from small pockmarks were observed in video footage the flanks of the mud volcano are steep and characterized in the upper part by a hummocky morphology and multiple sediment flows on the western flank the characterization of the mud volcano and the deposits associated with the 2017 gas outburst provides insight into seafloor shaping processes linked to fluid seepage in shallow water sectors this is a particularly relevant issue considering both the paucity of studies on shallow water mud volcanoes as well as the hazard associated with violent gas outbursts in such settings as witnessed by the march 16th 2017 event

rheology of a two phase material with applications to partially molten rocks plastic deformation and saturated soils a global model is presented to account for the specific rheology of a two phase material examples of observations are taken from a crystallising magma applications are ported to a partially molten rock plastic deformation and soil liquefaction the general behaviour of the viscosity is drawn as a function of the strain rate and the amount of solid phase it constitutes a 3d diagram developing a cubic surface the cubic equation is justified by thermodynamic considerations it basically results from the mixing of a newtonian n 1 and a power law n 3 type of deformation the diagram shows two types of rheological response at high strain rate values the viscosity contrast between the two phases is the lowest a bulk en masse behaviour results as observed during tectonic activity it manifests by a homogeneous transport of magma during emplacement and fabric development an equivalent medium with averaged viscosity is a good proxy conversely at low strain rate values the viscosity contrast between the two phases is the highest the two end members behave according to their respective rheology in between a transitional state develops in which instability occurs depending on the strain rate and stress conditions it manifests in the 3d diagram by a cusp shape rheology presents continuous jumps between the liquid like and the solid like rheology they result in strain localisation or phase segregation the later preferentially develops during magma crystallisation deformation under a constant amount of each phase is also possible resulting in pressure dissolution like processes a major cause for instability results from a bifurcation in the solution plane of the equation of viscous motion it is comparable with strain softening a similar situation should develop when mixing newtonian and power law rheology as during diffusion and dislocation creep or water saturated sediment deformation owing to the continual jumps between the two types of rheology hysteresis or memory effect may develop rapid cyclic deformation may drive strain to extreme straining the effect of simple shear seems much more effective than pure shear compaction to segregate the weak phase out of its strong matrix the development of instabilities and continuous jumps from one rheology to the other lead to discontinuous motion of the weak phase in a molten region it corresponds to discontinuous burst of magma that are extracted

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

cementation and compaction history of synorogenic foreland basin sedimentary rocks from huaco argentina the sierra de huaco exposes the western flank of the bermejo foreland basin of central western argentina the exposed 5 400 m section is well dated 14 2 3 ma and consists of synorogenic continental strata petrographic data combined with decompaction techniques provide first order estimates of the absolute age of cementation of the sandstones this information can be used to interpret petroleum migration paths and reservoir potential three diagenetic zones have been recognized each characterized by a dominant cementing material within a distinct framework texture these textures reflect varying degrees of compaction and framework grain replacement prior to cementation the intergrain volume in the sandstones increases upward in a nonlinear nonexponential fashion and is interpreted to reflect the porosity at the time of cementation the lowest 550 m of strata exhibits abundant compaction features low intergrain volume 10 and is cemented by analcime the overlying 900 m exhibits little evidence of compaction relatively high intergrain volume up to 33 and is cemented by gypsum the remaining 4 000 m exhibits abundant evidence of framework grain replacement by calcite has very high intergrain volume up o 40 and is cemented by calcite the diagenetic histories of the three zones were genetically linked to thrusting in the adjacent precordillera changes in depositional environment and subsurface fluid flow the depth at which cementation occurred in each zone is constrained by comparison of observed intergrain volume to predicted volumes for uncemented sands at any given burial depth first order estimates of the absolute age of cementation in each zone were made possible by comparing these relationships with a curve of accumulation history of the decompacted strata the lowest zone compacted with little interstitial cement for as long as 11 m y after deposition the middle zone was cemented within 3 m y after deposition the upper zone experienced framework grain replacement by calcite at very shallow depths w thin 2 m y and experienced little compaction

modelling of possible mud volcanism on titan possible sedimentary basins on titan are potential sites for the formation of mud volcanoes in order to constrain the appearance of such features in remotely sensed imagery being acquired by the cassini spacecraft we have modelled the formation of mud volcanoes on titan for a series of plausible mud compositions climatic conditions and geological settings as well as addressing the full range of eruption variables mud viscosity conduit diameter and eruption duration we find that for an acetylene mud source containing 20 wt liquid methane in pore spaces overlain by a sheet of water ice 500 m thick a mud volcano can grow as high as 140 m assuming reasonable eruption parameters such an edifice may develop into a pancake like dome several kilometres in diameter if observed and properly characterised mud volcanoes would provide an important window on the subsurface distribution and dynamics of solids and liquids in sedimentary basins on titan

an organodiagenetic model for marinoan age cap carbonates abstract the nuccaleena formation cap carbonate is the global stratotype for the marinoan glaciation and ediacaran gssp a designation that emphasises the importance of cap carbonates to our current understanding of global neoproterozoic biogeochemistry sedimentology and stratigraphy however to date there is no agreed depositional model for cap carbonates and there remains minimal detailed paragenetic data for developing process based depositional models here an early diagenetic organodiagenetic dolomite cementation model for marinoan cap carbonate formation is hypothesised and explored it is demonstrated how this process based model can explain the three main atypical sedimentary structures that are the basis for correlation of marinoan age cap carbonates giant tepee like structures sheet veins and tubestones these features are interpreted to be products of fluid overpressure deformation induced by organodiagenetic expansive cementation giant tepee like structures the hallmark of marinoan cap carbonates conform to a simple structural analysis that is consistent with the predicted stress field induced by expansive cementation driven fluid overpressure the undeformed to highly deformed gradient of deformation features in cap carbonates is consistent with the range of rheologies in a shallowly buried cementing carbonate modification of matrix textures and bedding surfaces also conforms to the range of expected textures within this model overall it is hypothesised that the aggradational condensed section architecture of cap carbonates was the primary control over the generation of these atypical sedimentary features the available paragenetic analysis suggests that the geochemical data particularly the c isotopic data can be reinterpreted as supportive of the organodiagenetic model and that the neoproterozoic ocean was perhaps similar to that of today the proposed model indicates that the current criteria for the placement of the ediacaran gssp are non unique and potentially non isochronous perhaps the most important aspect of this model is that it is testable and is a call for focused research on the much overlooked paragenesis of cap carbonates

mio pliocene volcaniclastic deposits in the famatina ranges southern central andes a case of volcanic controls on sedimentation in broken foreland basins abstract a well constrained record of miocene pliocene explosive volcanism is preserved within the broken foreland of western argentina along the famatina ranges this paper focuses on the volcaniclastic record known as the rio blanco member of the el durazno formation three facies can be recognized in the study area 1 massive tuffs 2 volcaniclastic conglomerates and 3 pumiceous sandstones these facies are interpreted as primary pyroclastic flow deposits ignimbrites and reworked volcanogenic deposits within interacting volcanic fluvial depositional systems alternation between ignimbrites and volcanogenic sandstones and conglomerates suggest a recurrent pattern of sedimentation related to recurrent volcanic activity considering the facies mosaic and relative thicknesses of facies short periods of syn eruption sedimentation volcaniclastic deposits seem to have been separated by longer inter eruption periods where normal stream flow processes were dominant the volcaniclastic component decreases up section suggesting a gradual reduction in volcanic activity the mean sedimentation rate of the rio blanco member is higher 0 44 mm year than those obtained for the underlying and overlying units this increase cannot be fully explained by foreland basement deformation and tectonic loading hence we propose subsidence associated with volcanic activity as the causal mechanism volcanism would have triggered additional accommodation space through coeval pyroclastic deposition modification of the stream equilibrium profile flexural loading of volcanoes and thermal processes these mechanisms may have favored the preservation of volcaniclastic beds in the high gradient foreland system of famatina during the mio pliocene thus the rio blanco member records the response of fluvial systems to large volcanism induced sediment loads

probabilistic longevity estimate for the lusi mud volcano east java abstract a new method for estimating the duration of a mud volcano eruption is applied to the lusi mud volcano in east java the estimate is based upon carbonates at depths in the range 2500 3500 m being the water source with an estimated area of 100 600 km 2 thickness of 0 2 1 0 km porosity of 0 15 0 25 an initial pressure between 13 9 and 17 6 mpa and a separate shallower source of mud c 1200 1800 m depth the resulting 50 percentile for the time it takes for flow to decline to 1 is 26 years by analogy with natural mud volcanoes it can be expected to continue to flow at lower rates for thousands of years assuming subsidence rates of between 1 and 5 cm day 1 land surface subsidence of between c 95 and c 475 m can be expected to develop within the 26 year time period

drowning history of a miocene carbonate platform zhujiang formation south china sea abstract the identification and interpretation of drowning events in the geologic record can aid significantly to the reconstruction of the depositional tectonic and eustatic history of a study area and often improve reservoir and seal prediction in carbonate rocks the differentiation between drowned platforms showing a record of continuous deepening and those with a record of exposure followed by rapid deepening remains however problematic the zhujiang carbonate platform liuhua 11 1 field south china sea study shown here provides an example of an integrated approach combining high resolution geochemistry microfacies analyses and foraminiferal biostratigraphy in order to improve the reconstruction of environmental conditions prior during and after platform demise and drowning the zhujiang carbonate platform displays the following vertical succession of four facies types i skeletal grain facies with a miogypsinid lepidocyclinid dominated fauna deposited in a moderately deep heterostegina sp and spiroclypeids possibly capped by a subaerial exposure surface well rounded rhodoids representing a mesotrophic lagoon dominate the upper portions of the rhodoid facies iv pelagic marine shales of the hanjiang formation burying the carbonate platform after drowning this facies succession in combination with geochemical evidence suggests a deepening upward trend this trend might have been interrupted by transient subaerial exposure but no evidence for meteoric diagenesis was found at the drowning unconformity topping the carbonate platform instead microfacies analyses suggest that platform demise may be related to progressive changes in environmental conditions including increasing nutrient levels and or decreasing temperature up core towards the drowning unconformity these findings are of significance for those concerned with miocene carbonate factories and more specifically the demise of carbonate platforms in general