sediment dynamics over sand ridges on a tideless mid outer continental shelf abstract a sand ridge field with crests oriented ne sw 52 located between 55 and 85 m water depth on the valencia continental shelf spain was mapped with multibeam swath bathymetry and characterized with seismic profiling and sediment sampling boundary layer hydrodynamic measurements conducted over a sand ridge at 66 m depth show evidence of wave and current sediment resuspension during a major storm event with a three year recurrence period from the measured intrawave sediment concentration profiles it is shown that the suspended sediment time evolution is related not only to mean currents but also to the wave field the near bottom shear stress generated during storm conditions reached around 1 n m2 and was able to resuspend and transport sandy and muddy sediments for more than 32 h the total suspended sediment transport in a layer of 1 m above the bottom was around 4000 kg per meter width and directed 160 it is argued that these sand ridges were developed in a shallow environment and there is no evidence of present day ridge migration or morphological degradation it is hypothesized that sediment dynamics affecting sand ridges during storms favors the maintenance of their morphology

superimposed tectono metamorphic episodes of jurassic and eocene age in the jadeite uplift myanmar as revealed by 40ar 39ar dating abstract the myanmar jadeite uplift forms an important link between the indo burma range and the tagaung myitkyina belt two contrasting ages of jurassic 152 4 1 5 ma of glaucophane from blueschist and eocene 44 8 1 1 and 45 0 1 3 ma of phengitic muscovites from quartz schists in the uplift were yielded using 40 ar 39 ar dating the jurassic age of the glaucophane even older than the forming age of the jadeitite from recent relevant literatures and for the reason of possible excess argon involved is interpreted as the lower limit of the subduction age previous studies correlated this subduction with the woyla intra oceanic arc or the incertus arc to the west the eocene ages of phengitic muscovites are interpreted as the time of an intra continental shearing deformation event against the timing of hp lt metamorphism as previously suggested combined with other studies it is suggested that the tagaung myitkyina belt and the indo burma range belonged to a single belt which has been separated by the sagaing fault leaving the jadeite uplift straddling along the fault between the belt and the range we propose a rapid exhumation model for the myanmar jadeitite at 45 ma coeval with onset of the sagaing fault

genesis and evolution of a mid shelf storm built sand ridge new jersey continental shelf u s a abstract sand ridges form discrete parts of a modern surficial veneer on many continental shelves worldwide yet are seldom cited as analogs for isolated marine sand bodies found in outcrop or the subsurface one reason may be that a comprehensive explanation for the evolution of modern mid shelf sand ridges has proven elusive new information most notably high resolution seismic data collected on modern sand ridges in adjacent areas by other workers has led to this reevaluation of a largely unpublished but extensive vibracore dataset from a mid shelf sand ridge off new jersey usa the presence of dipping reflections within other ridges is particularly notable on new high resolution seismic data but has yet to be confirmed in these other ridges by extensive coring reexamining the original well preserved vibracore peels from the mid shelf sand ridge sampled in the 1980s reveals that these internal reflections could be associated with burrowed low density mud beds new cross sections constructed with 20 vibracores suggest that the dipping internal reflections are accretionary surfaces associated with episodic ridge migration to the east and south radiocarbon dating indicates that the mid shelf sand ridge has migrated episodically over the last 5 ka and movement probably continues today during major storms this documented migration continues well after transgressive ravinement approximately 9 10 ka contradicting existing views that mid shelf ridges become moribund sometime after detachment from the shoreline the morphology migration history and internal sedimentary character suggest that the ridges are acting much like primary bedforms although these sand bodies are much larger in scale 5 to 8 m height or thickness than typical subaqueous dunes observed on modern storm dominated shelves

sediment deformation and hydrogeology of the nankai trough accretionary prism synthesis of shipboard results of odp leg 131 the main objective of leg 131 was to provide data on the deformational processes and associated hydrogeology of the nankai prism toe drilling succeeded for the first time in the history of ocean drilling in penetrating the complete sedimentary sequence to basaltic basement reaching 1327 mbsf metres below seafloor with good core recovery 55 excellent correlation of the lithology and structure including the frontal thrust and the decollement with seismic reflection images was also determined bedding dips faults and shear bands analyzed in the cores confirm the pattern of deformation to be mainly due to nw se shortening as expected from the plate tectonic convergence vector below the decollement no significant deformation features were observed indicating that the decollement is a sharp discontinuity in stress transmission physical properties data show major discontinuities at the decollement notably an increase in porosity below the later this may indicate excess pore pressure in the subducted section and decollement zone a less marked increase in porosity below the frontal thrust may reflect the youthfulness of this feature attempts to make downhole measurements were severely hampered by unstable hole conditions but useful constraints have been placed on the thermal regime and some calibration of laboratory physical properties toin situ conditions has been provided andin situ stress and pore pressure were measured in the uppermost sediments evidence of channelized fluid flows is inconclusive no sharp geochemical signatures or unequivocal geochemical anomalies indicative of channelized fluid flow were found thermal measurements are not significantly different from those predicted by a purely conductive heat flow model a signature of low chloride pore water near the decollement may partly be related to smectite diagenesis but may also be due to episodic fluid flow events we conclude that dewatering probably occurred dominantly through diffuse flow throughout the accreted sediments at this site

active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea shallow seismic profiles and borehole data revealed active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea the ridges consist of relatively clean well sorted sands with fairly uniform sequences the microfossil assemblage exhibits a high diversity including both euryhaline and stenohaline species the ridges are huge elongated sand bodies several kilometres wide 10 60 km long and up to 20 m thick and occur in groups with a spacing of several to 10 km normally they are parallel with each other extending in the direction of the tidal currents the field of tidal sand ridges on the east china sea shelf covers an area of 57 000 km2 tidal sand ridges in the east china sea and the southern yellow sea were formed in estuarine and shallow shelf environments where strong tidal currents reworked transported and redeposited large amounts of relict sands from older deltaic and fluvial sediments the development of tidal sand ridges in estuary mouth areas is accompanied by a net sand transport from the shelf into the estuary the evolution of tidal sand ridges is closely related to transgressions active tidal sand ridges are formed during sea level rises they show distinct morphology and active migrations in a lateral as well as in a landward direction they are generally in equilibrium with present day tidal processes and their distribution patterns are related to the flow field of the tidal currents as the sea level rises further these tidal sand ridges become moribund sand bodies with less distinct morphologies their upper surfaces are covered by a thin calcareous rich layer with very high contents of foraminifera tests reflecting a submarine hiatus condition on the shelf during the highstand period during the subsequent steady fall in sea level tidal sand ridges are often buried by fine grained shelf and prodelta sediments they have therefore a good chance of being preserved in stratigraphic records the sequential buildup during a sea level rise tr tract and a subsequent sea level fall hs and ls tract would consist of estuarine channel and tidal flat facies tidal sand ridge facies shelf mud facies delta facies and fluvial facies in an ascending order tidally dominated estuary conditions may also occur when a major distributary is abandoned such as at the northern branch of the modern changjiang river mouth where the accumulation of sand from an abandoned delta lobe and the development of tidal sand ridges have been observed the observed features have important implications for the subsurface recognition of fossil tidal sand ridges for the reconstruction of the regional palaeogeography and transgressional history and for the prediction of potential reservoir sandstones

lithology and biostratigraphy of franciscan like chert and associated rocks in west central baja california mexico we present the result of biostratigraphic and lithologic studies of ribbon chert and associated rocks in a mesozoic subduction complex in west central baja california mexico the subduction complex terrane is divided into three subterranes each of which consists of an originally coherent sequence of interbedded oceanic rocks including ocean floor basalt terrigenous siliciclastic turbidites radiolarian ribbon chert and limestone parts of the original stratigraphy are preserved in the least deformed least metamorphosed subterrane ocean floor pillow basalt on cedros island is overlain by about 40 m of radiolarian ribbon chert ranging in age from early jurassic or older to early cretaceous the chert is overlain by thin bedded turbidites on san benito west island radiolarian ribbon chert is interbedded with volcanogenic rocks including a megabreccia that contains blocks of metabasites folded late jurassic early cretaceous chert and marble in a mid cretaceous radiolarite matrix chert samples from tectonically thinned sequences elsewhere on cedros and san benito islands contain late triassic to early cretaceous radiolarian assemblages the 40 m thick chert section on cedros island probably accumulated atop oceanic crust in a large ocean basin for at least 65 m y and was later capped by terrigenous turbidites as it approached the subduction zone along the western margin of north america faulted chert sections on cedros and san benito central and west islands are subsets of the main section on cedros island the chert megabreccia section on san benito west island is interpreted to have accumulated at the foot of a volcanic edifice on the ocean floor for example seamount fracture zone or during extension and normal faulting of the downgoing oceanic plate in a subduction zone sedimentary structures and stratigraphic relations indicate that all ribbon chert in this subduction complex was deposited by sediment gravity flows that is they are turbidites

ancient shelf ridges a potentially significant component of the transgressive systems tract case study from offshore northwest java detailed stratigraphic evaluation of three dimensional 3 d seis mic volumes calibrated with well log and core data from the mio cene section of the offshore northwest java shelf reveals the exten sive presence of preserved shelf ridge deposits these features are long linear bodies ranging from 0 3 to 2 0 km wide more than 20 km long and up to 17 m high on close inspection these features appear to be asymmetric characteristically sharp edged and thicker on one side and gradually thinning with an irregular edge on the other side possible sand waves smaller in scale are observed super imposed on these ridges and oriented oblique to the long axes of the ridges the observed shelf ridge deposits tend to be sand prone and overlie ravinement surfaces the ridges appear to be oriented parallel with the axes of broad paleoembayments associated with the structural fabric of the basin in addition to shelf ridges shelf ribbons possibly less than 5 m thick and less than 100 m wide are also imaged sand ridges are common on modern shelves but significantly less commonly recognized in the subsurface or in outcrop the features observed here represent examples of preserved ancient shelf ridges these ridges are thought to have formed as a result of erosion and subsequent reworking of sand prone deltaic and or coastal plain deposits by shelf tidal currents which became active immediately after shoreline transgression these deposits appear to have migrated across the ancient sea floor and represent an important component of the transgressive systems tract these transgressive systems tract deposits have significant exploration potential because they are commonly sand prone and tend to be encased in shelf mudstone seal facies depending on the degree to which sand is present in interridge locations these linear sand bodies can comprise potential stratigraphic traps begin page 76

kinematic analysis of melange fabrics examples and applications from the mchugh complex kenai peninsula alaska permian to cretaceous melange of the mchugh complex on the kenai peninsula south central alaska includes blocks and belts of graywacke argillite limestone chert basalt gabbro and ultramafic rocks intruded by a variety of igneous rocks an oceanic plate stratigraphy is repeated hundreds of times across the map area but most structures at the outcrop scale extend lithological layering strong rheological units occur as blocks within a matrix that flowed around the competent blocks during deformation forming broken formation and melange deformation was noncoaxial and disruption of primary layering was a consequence of general strain driven by plate convergence in a relatively narrow zone between the overriding accretionary wedge and the downgoing generally thinly sedimented oceanic plate soft sediment deformation processes do not appear to have played a major role in the formation of the melange a model for deformation at the toe of the wedge is proposed in which layers oriented at low angles to s1 are contracted in both the brittle and ductile regimes layers at 30 458 to s1 are extended in the brittle regime and contracted in the ductile regime and layers at angles greater than 458 to s1 are extended in both the brittle and ductile regimes imbrication in thrust duplexes occurs at deeper levels within the wedge many structures within melange of the mchugh complex are asymmetric and record kinematic information consistent with the inferred structural setting in an accretionary wedge a displacement field for the mchugh complex on the lower kenai peninsula includes three belts an inboard belt of late triassic rocks records west to east directed slip of hanging walls a central belt of predominantly early jurassic rocks records north south directed displacements and early cretaceous rocks in an outboard belt preserve southwest northeast directed slip vectors although precise ages of accretion are unknown slip directions are compatible with inferred plate motions during the general time frame of accretion of the mchugh complex the slip vectors are interpreted to preserve the convergence directions between the overriding and underriding plates which became more oblique with time they are not considered indicative of strain partitioning into belts of orogen parallel and orogen perpendicular displacements because the kinematic data are derived from the earliest preserved structures whereas fabrics related to strain partitioning would be expected to be superimposed on earlier accretion related fabrics 1999 elsevier science ltd all rights reserved

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

internal dynamics of a paleoaccretionary wedge insights from combined isotope tectonochronology and sandbox modelling of the south central chilean forearc forearc accretionary wedges are cyclic systems in which material is frontally and or basally accreted material cycling involves underthrusting subduction underplating exhumation erosion transfer to the trench and underthrusting again in this study we present a novel tectonochronologic approach to constrain long term exhumation rates of basally accreted wedge complexes based on isotopic dating of structural features on petrological data and sandbox analogue simulations congruence between the structural inventory in nature and structures generated in scaled sandbox experiments allows detailed insights into wedge dynamics for the present day surface material of the paleoaccretionary wedge of south central chile valdivia area 40 s published u pb ages of detrital zircon place a maximum age of 278 ma for subduction prograde metamorphism at transitional greenschist to blueschist facies conditions 420 c 8 9 kbar was immediately followed by progressive penetrative deformation associated with basal accretion dated at 250 245 ma using rb sr internal mineral isochrons the accretion process involved duplex tectonics and antiformal stacking with formation of near horizontal mylonitic shear zones at around 241 ma continuous basal accretion at depth gave rise to an extensional tectonic regime at higher structural levels both semi ductile small scale extensional shear zones and post kinematic vein mineralizations yield rb sr ages of 235 ma tension gashes representing the latest isotopically dateable stage of structural evolution were formed at 210 ma at conditions of 230 c at 1 5 3 kbar as constrained by fluid inclusion data zircon fission track data indicate final cooling to below 200 c at 186 24 ma the results suggest continuous basal accretion for at least 50 ma with long term average exhumation rates of 0 6 0 2 mm a most probably outbalanced by similar long term average erosion rates changing plate boundary conditions at about 210 200 ma terminated the accretion process as evident from a dramatic decrease of exhumation rates at that time since then the paleoaccretionary wedge remained stably in place despite its delicate geotectonic position within the andean active margin the tectonochronologic approach complements thermochronologic and geomorphologic methods of exhumation research as it provides direct constraints on mass flux rates even for high temperature increments of p t trajectories

horizontal shortening versus vertical loading in accretionary prisms 1 the analysis of two phased deformation of subducted turbidites within the shimanto belt on kyushu japan shows strongly contrasted kinematics between an earlier noncoxial fold and thrust type stage and a later metamorphic coaxial vertical shortening stage the deep deformation is characterized by the development of a subhorizontal muscovite chlorite metamorphic foliation associated with pure shear deformation which overprinted the structures inherited from the earlier stage we associate the metamorphic deformation stage with the lower levels of accretionary prism landward segment inner wedge which was therefore deformed by vertical loading and horizontal extension much in contrast with prism trenchward segment outer wedge which often shows fold and thrust structures indicative of horizontal shortening a possible explanation based on wang and hu s 2006 model for these longitudinal variations in deformation kinematics of the prism may lie in the contrasted rheology of its basal surface strain weakening in the seismic portion below the inner wedge while strain strengthening in the aseismic portion below the outer wedge the vertical shortening active within the inner wedge revealed by this study possibly represents a large contribution to the exhumation of the deeper levels of accretionary prisms

conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone a conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone was developed based on the results of lithological studies and a series of ponded infiltration tests conducted at the box canyon site near the idaho national engineering and environmental laboratory the infiltration tests included one 2 week test in 1996 three 2 day tests in 1997 and one 4 day test in 1997 for the various tests initial infiltration rates ranged from 4 1 cm d 4 75 10 7 m s to 17 7 cm d 2 05 10 7 m s and then decreased with time presumably because of mechanical or microbiological clogging of fractures and esicular basalt in the near surface zone as well as the effect of entrapped air the subsurface moisture redistribution was monitored with tensiometers neutron logging time domain reflectrometry and ground penetrating radar a conservative tracer potassium bromide was added to the pond water at a concentration of 3 g l to monitor water flow with electrical resistivity probes and water sampling analysis of the data shows evidence of preferential flow rather than the propagation of a uniform wetting front we propose a conceptual model describing the saturation desaturation behavior of the basalt in which rapid preferential flow occurs through the largest vertical fractures followed by a gradual wetting of other fractures and the basalt matrix fractures that are saturated early in the tests may become desaturated thereafter which we attribute to the redistribution of water between fractures and matrix lateral movement of water takes place within horizontal fracture and rubble zones enabling development of perched water bodies

contemporary genesis of sand ridges in a tideless erosional shoreface abstract a sand ridge field located over a retreating deltaic lobe in the ebro delta nw mediterranean is characterized using three sets of co located multibeam bathymetric data acquired in 2004 2013 and 2015 measurements of near bottom currents high resolution seismic profiles and aerial photographs the aim of this study is to illustrate the processes and timing involved in the initial stages of sand ridge development the sand ridge field extends from the 5 to 15 m isobaths and the ridges have maximum heights and wavelengths of 2 5 and 400 m respectively they have straight crests that are arranged obliquely to the shoreline and are composed of fine sand in general the sand ridges are symmetric although asymmetries with the lee side of the ridge facing to the se and to the nw are also present the genesis of the sand ridge field is closely related to the contemporary evolution of the ebro river mouth the change of the main river channel in the 1940s led to progressive abandonment of the former river mouth and to severe coastal retreatment 37 m yr 1 making large amounts of sediment available for ridge formation the persistent mistral winds nw induce near bottom currents flowing towards the se which are able to rework and transport sandy sediments the sand ridges are currently active with mean se migration rates of 10 m yr 1 most likely in pulses when high speed currents occur wave storm events induce reverse flows e se which reshape the ridges to symmetric or opposite asymmetry geometries the bedform morphologies the oblique arrangement with respect to the shoreline the angle between the strongest current and the crestlines and the sediment grain size match well with those of shoreface connected attached sand ridges and particularly with the initial stages of sand ridge development on storm dominated continental shelves sediment availability shoreline retreat relatively strong near bottom currents induced by winds seafloor irregularities and relative sea level rise on the ebro delta combine to provide a suitable transgressive environment for sand ridge development time scales related to sand ridges are usually of hundreds thousands of years but here it is demonstrated that the genesis of sand ridges can take place within a few decades the studied bedforms are unlikely to persist in the absence of rapid sea level rise leading to sediment scarcity and wave and current reworking

recognition of ocean plate stratigraphy in accretionary orogens through earth history a record of 3 8billion years of sea floor spreading subduction and accretion abstract ocean plate stratigraphy ops is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust substratum from the time it forms at a spreading center to the time it is incorporated into an accretionary prism at a convergent margin in this study we review the major geological characteristics of relict cenozoic to early archean oceanic crust and ops persevered in alaska japan california franciscan complex central asia british isles canada slave province australia pilbara craton and greenland isua and ivisaartoq belts an assessment of ops in accretionary orogens spanning the duration of earth s rock record shows remarkable similarities between ops of all ages in terms of structural style major rock components sequence of accretion and trace element geochemical signatures volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts island arc picrites mid ocean ridge basalts back arc basalts oceanic plateau basalts ocean island basalts and boninites with extremely rare komatiites this demonstrates that sea floor spreading lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum and accretion at convergent margins have been major earth processes since at least 3 8 ga ago there have been some secular changes in the rock types in ops such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in phanerozoic times but absent in the precambrian but overall there have been few changes in the style of ops accretion with time komatiites and banded iron formations occur predominantly in archean orogenic belts reflecting higher mantle temperatures and less oxic seawater composition respectively before 2 5 ga this is clear documentation that plate tectonics including the lateral movement of oceanic lithosphere has been a major heat loss mechanism on earth since the early precambrian

liquid release tests in unsaturated fractured welded tuffs ii numerical modeling abstract we have carried out a numerical modeling study in conjunction with the in situ liquid release experiment described in salve et al j hydrol 257 2001 the experiment site is a highly fractured welded tuff accessed from the exploratory studies facility an underground laboratory in the unsaturated zone at yucca mountain nevada the experiment examines the effect of the rock matrix on liquid flow and transport that occurs primarily through the fracture network the purpose of the modeling is to aid in experimental design predict experimental results and study the physical processes accompanying liquid flow through unsaturated fractured welded tuff the model uses cubic elements arranged in a regular three dimensional grid to represent a 24 m3 block of fractured tuff high permeability fracture elements located deterministically preserve the connectivity of the fracture network which is crucial to its ability to conduct fluid because element thickness is much greater than fracture aperture fracture elements are assigned properties of a fracture continuum rather than of an individual fracture the fracture network is constructed using fracture geometry data taken from a fracture map of the walls and ceiling of the alcove adjacent to the field test site the network is then refined using the results of air permeability tests model results suggest that it may not be sufficient to conceptualize the fractured tuff as consisting of high permeability fractures embedded in a low permeability matrix the need to include a secondary fracture network with distinct characteristics from the network of larger mapped fractures is demonstrated by comparison to the liquid flow observed in the field

twenty five million years of subduction accretion exhumation during the late cretaceous tertiary in the northwestern caribbean the trinidad dome escambray complex central cuba the trinidad dome escambray complex central cuba forms part of an accretionary wedge built up during intra oceanic subduction in the caribbean from the late cretaceous 75 ma to tertiary fieldwork microscopic studies p t estimates and new 40ar 39ar isotopic data indicate a tectono metamorphic evolution involving five deformation phases three main stages d1 d2 and d3 were responsible for the subduction exhumation of the units during metamorphic development 40ar 39ar isotopic data allow for the first time an evaluation of the complete time interval from subduction collision to final exhumation d1 deformation took place at 60 5 0 6 ma during subduction and was characterized by a prograde path with hp peak metamorphic conditions in eclogite facies in the monforte nappe the highest structural nappe and greenschist metamorphism in the la sierrita yaguanabo and rio chiquito nappes at lower structural levels d2 deformation 56 32 0 40 ma included a short lived heating event in the lower nappes that caused incipient recrystallization at lower amphibolite facies but was generally linked to decompression and retrograde metamorphism to greenschist conditions during folding and nne thrusting of all nappes parallelism of the main s2 foliation and serpentinite lenses indicates d2 was the main phase of exhumation during d3 exhumation and nne thrusting continued as the units were progressively incorporated into the growing accretionary wedge until about 50 ma structures related to d4 are post metamorphic and reflect the domal structure d5 strike slip and normal faults cut the tectonic pile and low angle normal faults are more abundant towards the dome rim indicating exhumation of the escambray field observations structures and the inverted distribution of the p t conditions in the wedge suggest exhumation mechanisms by underthrusting underplating and erosion combined with extension at the surface subduction accretion exhumation in the trinidad dome thus occurred from 75 to 50 ma indicating a period of 25 million years of deformation history in the northern caribbean realm

ophiolite accretion in the lachlan orogen southeastern australia slivers of dismembered cambrian ophiolites are preserved in major fault zones of the turbidite dominated western and central lachlan orogen of southeastern australia geometrical chronological and metamorphic constraints indicate that these slivers did not undergo classic tethyan style obduction but were incorporated into evolving turbidite wedges as offscraped slices imbricated fault slivers or duplexes and as blocks in melange the processes involved include decoupling of the oceanic crustal stratigraphy predominantly above the moho formation and metamorphism of serpentinite talc matrix melange up to blueschist conditions and accretion via underplating or offscraping during underthrusting these processes have produced major large scale fault zones within the chevron folded turbidites that show marked along strike variation in structural complexity that relate to magnitude of displacement the fault zones may have formed preferentially where topographic highs occurred in the oceanic crust promoting fold and fault nucleation within irregularities in the layering these fault zones have predominantly brittle character due to their formation under a low geothermal gradient duplex like structures in the fault zones and the inferred development through buckling of then faulting of the oceanic lithosphere have analogues in modern oceanic environments e g indian ocean and young subduction systems e g sulu sea southeast asia they are interpreted to have formed due to convergence in a non collisional intra oceanic setting during closure of a cambrian backarc basin

formation of taconic melanges and broken formations in the hamburg klippe central appalachian orogenic belt eastern pennsylvania abstract the hamburg klippe of the central appalachian orogenic belt exposed in eastern pennsylvania displays a complex record of poly phase melange and broken formation development in a convergent margin setting it includes an imbricate stack of tectonic slices which consist of upper cambrian to upper ordovician deep water and continental slope sedimentary rocks emplaced by gravity sliding onto the laurentian passive margin during deposition of the upper ordovician martinsburg formation based on their internal structure and stratigraphy the block matrix ratios and relations and the inferred tectonic settings of origin we have differentiated the following melanges and broken formations whose evolutionary stages coincide with specific deformational phases in a complete orogenic cycle from subduction to collision i sedimentary broken formations without exotic blocks formed by in situ and local down slope remobilization during the early stages of closure of the octoraro sea basin in the early ordovician ii two types of sedimentary melanges with exotic blocks formed at the front of the advancing accretionary wedge during the middle ordovician subduction of the laurentian continental margin beneath a microcontinent magmatic arc tectonic assembly iii layer parallel extensional broken formation and a diapiric melange formed in the outer trench and at the toe of the accretionary wedge respectively during the early late ordovician iv precursory olistostromes formed during the late ordovician collisional episodes as the hamburg klippe was emplaced in the martinsburg formation on the downgoing laurentian continental margin and v contractional deformation related broken formations formed at the base of main thrust faults overprinting the previously formed melanges and broken formations this sequential development of different melange types in the central appalachians was strongly controlled by the degree of consolidation of the layered strata and their rheological differences the structural level of melange formation within the accretionary wedge and the kinematics of deformational processes

matrix deformation mechanisms in hp lt tectonic melanges microstructural record of jadeite blueschist from the franciscan complex california abstract exhumed high pressure low temperature metamorphic melanges of tectonic origin are believed to reflect high strain accumulated in large scale interplate shear zones during subduction rigid blocks of widely varying size are embedded in a weak matrix which takes up the deformation and controls the rheology of the composite the microfabrics of a highly deformed jadeite blueschist from the franciscan complex california are investigated to help understand deformation mechanisms at depth the specimen shows a transposed foliation with dismembered fold hinges and boudinage structures several generations of open fractures have been sealed to become veins at high pressure metamorphic conditions the shape of these veins frequently restricted to specific layers indicates distributed host rock deformation during and after sealing small cracks in jadeite and lawsonite are healed with tiny quartz inclusions aligned along the former fracture surface large jadeite porphyroblasts show strain caps and strain shadows open fractures are sealed by quartz and new jadeite epitactically grown on the broken host monophase glaucophane aggregates consist of undeformed needles with a diameter between 0 1 and 2 m grown after formation of isoclinal folds only quartz microfabrics indicate some stage of crystal plastic deformation followed by annealing and grain growth aragonite in the latest vein generation shows retrogression to calcite along its rims the entire deformation happened under hp lt metamorphic conditions in the stability field of jadeite and quartz at temperatures between 300 and 450 c and pressures exceeding 1 1 4 gpa the microfabrics indicate that dissolution precipitation creep was the predominant deformation mechanism accompanied by brittle failure and vein formation at quasi lithostatic pore fluid pressure this indicates low flow strength and combined with high strain rates expected for localized deformation between the plates a very low viscosity of material in the interplate shear zone at a depth 30 45 km

on fluid reserves and the production of superheated steam from fractured vapor dominated geothermal reservoirs vapor dominated geothermal reservoirs produce saturated or superheated steam and vertical pressure gradients are close to vapor static these observations have been generally accepted as providing conclusive evidence that the liquid saturation must be rather small 50 in order that liquid may be nearly immobile this conclusion ignores the crucial role of conductive heat transfer mechanisms in fractured reservoirs for vaporizing liquid flowing under two phase conditions we have developed a multiple interacting continuum method minc for numerically simulating two phase flow of a homogeneous fluid in a fractured porous medium application of this method to reservoir conditions representative of the geysers california and results from an analytical approximation show that for matrix permeability less than a critical value 2 5 to 5 microdarcies the mass flux of water from the matrix to the fractures will be continuously vaporized by heat transported due to conduction this gives rise to production of superheated steam even when the matrix has nearly full liquid saturation simple estimates also show that heat driven steam water counterflow can maintain a nearly vapor static vertical pressure profile in the presence of mobile liquid water in a reservoir with low vertical matrix permeability the implication of these findings is that the fluid reserves of vapor dominated geothermal reservoirs may be larger by a factor of about 2 than has generally been believed in the past

submerged shoreline preservation and ravinement during rapid postglacial sea level rise and subsequent slowstand submerged shorelines hold much potential for examining the interplay between the rate of sea level rise and geomorphic setting and informing the development of models of contemporary shoreline behavior this paper describes the sedimentary architecture of a submerged barrier shoreline complex off durban south africa the complex consists of several barriers that have survived the postglacial transgression and associated erosive ravinement processes the main shoreline sequence 60 m dates to 11 690 90 calibrated cal yr b p and rests on a pleistocene lagoonal deposit 35 395 592 cal yr b p the entire barrier shoreline complex is truncated by a strongly diachronous wave ravinement surface the ravinement surface seaward of the main 60 m shoreline is steep but the gradient declines across and landward of the subordinate landward shoreline complexes the steep ravinement surface is attributed to fast sea level rise possibly associated with meltwater pulse 1b while the gentle ravinement surface is associated with a subsequent slowing of the rate of sea level rise to 0 15 mm yr 1 preservation of the main barrier and back barrier deposits through overstepping is associated namely with rapid transgression and increased back barrier accommodation the smaller barriers landward of the main barrier were preserved through overstepping related to gentle antecedent gradients despite more intense ravinement during a very slow rise in sea level slowstand this process was assisted by a sediment deficit the resulting post transgressive drape is also influenced by antecedent topography created by the barriers themselves damming along the landward sides of overstepped barriers thickens the drape and creates a temporal disconnect between the migration of the shoreface and more landward elements of the littoral system in examining the rates of shoreline migration associated with the overstepped barrier system these are far greater than those calculated for the predicted rates of shoreline change on similarly steep coastal profiles future rates of shoreline migration appear to be insufficient to cause overstepping and rollover or erosional responses are more likely

modelling the formation of shoreface connected sand ridges on storm dominated inner shelves a morphodynamic model is developed and analysed to gain fundamental understanding of the basic physical mechanisms responsible for the characteristics of shorefaceconnected sand ridges observed in some coastal seas these alongshore rhythmic bed forms have a horizontal lengthscale of order 5 km and are related to the mean current along the coast the seaward ends of their crests are shifted upstream with respect to where they are attached to the shoreface the model is based on the two dimensional shallow water equations and assumes that the sediment transport only takes place during storms the flux consists of a suspended load part and a bed load part and accounts for the eects of spatially non uniform wave stirring as well as for the preferred downslope movement of sediment the basic state of this model represents a steady longshore current driven by wind and a pressure gradient the dynamics of small perturbations to this state are controlled by a physical mechanism which is related to the transverse bottom slope this causes a seaward deflection of the current over the ridges and the loss of sediment carrying capacity of the flow into deeper water the orientation spacing and shape of the modelled ridges agree well with eld observations suspended load transport and spatially non uniform wave stirring are necessary in order to obtain correct e folding timescales and migration speeds the ridge growth is only due to suspended load transport whereas the migration is controlled by bed load transport

dynamics diffusion and geomorphological significance of tidal residual eddies many shallow tidal areas show the occurrence of ebb and flood surplusses organized in cell like structures or tidal residual eddies they seem to arise from a nonlinear transfer of vorticity from the oscillating tidal field to the mean field the irregular structure of the bottom topography or the coastline acting as a catalyst to produce the necessary vorticity gradients the dynamical characteristics of the eddies assist our understanding of the geomorphology of the sea bed

preservation of a drowned gravel barrier complex a landscape evolution study from the north eastern english channel abstract landscape response to post glacial relative sea level during the quaternary is documented using an integrated dataset of multibeam bathymetry and 2d seismic reflection profiles from the hastings bank area in the north eastern english channel mapping of nine seismic stratigraphic units calibrated to lithological information from multiple vibrocores has enabled the interpretation of fluvial shoreface barrier washover fan back barrier and tidal environments of deposition the interpreted landscape evolution is as follows i fluvial incision of bedrock during sea level lowstand ii progradation of a shoreline and then development of a barrier complex as sea level rose iii recycling and breaching of the barrier iv rapid drowning of the barrier complex v landward migration of the shoreline through continued sea level rise and vi complete abandonment and submarine preservation of the barrier complex during sea level highstand the previously undocumented yet exceptionally well preserved drowned barrier complex at hastings bank records phases of barrier initiation breakdown and retreat and documents coastal response to high rates of relative sea level rise initial development of the barrier complex required a sufficient supply of sediment maintained by offshore sources to keep pace with rising sea level which permitted progradation of a shoreline and development of a barrier complex inherited topography in the north eastern english channel is an important factor in the development of the barrier complex phases of barrier breakdown occur when sediment supply is outpaced by a rapid increase in accommodation controlled by existing basement morphology and rising sea levels subsequently the barrier responds through internal reorganisation by breaching and reworking of existing sediment bodies barrier retreat is characterised by a phase of sediment surplus overstepping under rapid rates of sea level rise where increased water depths limit wave reworking followed by a phase of discontinuous retreat where the shoreline steps back through sediment deficit overstepping hastings bank presents a rare opportunity to examine the conditions and processes that control barrier response to sea level rise and to assess the preservation potential of barrier deposits as a function of the style of retreat

blueschist metamorphism during accretion in the lachlan orogen south eastern australia low t intermediate to high p assemblages indicative of the prehnite pumpellyite greenschist and blueschist facies are preserved in melange zones and slivers of oceanic crust within two major fault zones of the turbidite dominated lachlan orogen in one of these fault zones governor fault zone blueschists occur as franciscan like blocks in a serpentinite talc matrix that is interleaved with phyllites and slates and structurally overlain by a fault slice or duplex of predominantly pillow basalt chert and turbidite the blueschist metavolcanics are interpreted to have formed at 450 c and at a depth of approximately 21 27 km the presence of blue amphibole in the blocks rinds and matrix indicate that the metavolcanics were emplaced in the matrix prior to blueschist metamorphism blocks and matrix were partially exhumed interleaved with tectonic slices of phyllite and slate and subsequently folded at about 10 12 km depth inferred from bo values of the dominant mica fabric in the phyllites and slates metamorphic p t is highest in the structurally lowest slice melange zone and lowest in the overlying ophiolitic fault slice suggestive of an accretionary burial metamorphic pattern formed by underplating of the melange in the other fault zone heathcote fault zone blueschists transitional to greenschist facies are interpreted to have formed at 450 c and at a depth of approximately 15 21 km they occur as blocks in serpentinite talc matrix melange and are also associated with fault slices of oceanic crust textural and mineralogical evidence suggests that the protoliths for the blueschists in both fault zones were boninitic pillow lavas the metamorphic facies and patterns and the structural and lithological associations can be interpreted in terms of disruption of oceanic crust and overlying sediments during subduction and formation of serpentinite matrix melange overprinted by blueschist metamorphism either prior to or during underplating of the melange and duplex formation the presence of blueschist metavolcanics indicate that these processes occurred at considerable depth these interpretations have implications for the evolution of large scale fault zones in noncollisional convergent oceanic settings

origin evolution and distribution of shoreface sand ridges atlantic inner shelf u s a abstract a computer mapping system was employed to document the location of 259 shoreface attached and detached sand ridges in water although shoreface attached sand ridges appear to have several different modes of formation a two step process for the development of most shoreface attached and detached sand ridges along u s atlantic barrier island and cape coastlines is proposed 1 sand is deposited as ebb tidal deltas or river deltas along the lower shoreface and or inner continental shelf prior to or during transgression followed by 2 further transgression which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes the best developed shoreface sand ridge fields along the u s atlantic shelf lie adjacent to shorelines characterized by all of the following 1 transgression 2 mixed energy wave dominated barrier islands and 3 laterally migrating tidal inlet systems tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport ebb tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface attached sand ridges the oblique orientation and linear form of shoreface attached sand ridges appear to be a function of shoreline transgression lateral inlet migration and wave reworking of ebb tidal delta deposits concentrated along an ebb tidal delta retreat path shelf processes act as modifying agents in the evolution of sand ridges during and after ebb tidal delta deposition in general shoreface attached sand ridges are poorly developed or absent along eroding headlands spits and barrier island shorelines characterized by naturally stabilized tidal inlets these latter inlets and shoreline types are dominated or influenced by one or all of the following 1 antecedent topography 2 higher tidal ranges 3 larger tidal prisms 4 lower wave energies or 5 finer grain sizes the coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin evolution and distribution of shoreface sand ridges in the study area modern shoreface attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during or immediately before transgression commonly observed vertical and lateral interrelationships of holocene shoreface attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models in addition the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges

perspectives on the roles of melanges in subduction accretionary complexes a review abstract melanges play three principal overlapping roles in the architecture of subduction accretionary complexes sacs during and after sac formation first tectonic melanges serve as zones of concentrated deformation within and below the accreted rocks that are assembled during the subduction accretion process these melanges facilitate preservation of inter melange less deformed accretionary units aus beneath the trench side of the sac the initial deformation zone along the decollement at the top of the down going plate is marked by non melange tectonically dismembered formations or thinner units of scaly rock and breccia that separate accreted rocks above from the subducting rocks below olistostromal rocks may be incorporated into the decollement here in the mid arc to inner arc areas of the sac exotic block bearing melanges develop in zones of tectonic fragmentation and mixing of accreting ocean plate stratigraphy in mud diapirs and along out of sequence faults some of which facilitate uplift of high pressure rocks and serpentinite matrix melanges second after accretion the sedimentary tectonic diapiric and polygenetic melange units serve as single block or sheet architectural aus or subunits within larger accreted aus of the sac diapiric melanges and sedimentary olistostromal melanges formed in and above sac fault blocks respectively may become incorporated into the sac during ongoing deformation and become architectural units as well third melanges serve as post subduction stress guides that focus shear strain during continuing and post accretion deformation of sacs allowing ongoing modification of the sac during progressive deformation of the orogen examples of each type of role reveal the importance of all three processes in the current architecture of outer orogenic belts

geotectonic framework of the blueschist unit on anglesey lleyn uk and its role in the development of a neoproterozoic accretionary orogen abstract a 560 550 ma 5 km 25 km blueschist unit extends ne sw on the island of anglesey wales uk and continues to the southwest for more than 70 km along the northern coast of the lleyn peninsula it has the shape of a shallow dipping slab or sheet up to a few kilometres thick that was exhumed from the subduction zone and emplaced into the accretionary complex to the northwest today the top boundary of the slab is commonly a thrust that was originally a low angle normal fault at its top in the subduction zone above it is an accretionary complex and a unit of high grade gneisses the bottom boundary is today a thrust that was originally a thrust below which is a unit of low grade or unmetamorphosed rocks belonging to an olistostrome type accretionary complex this thrust was originally at the bottom of the slab when it was exhumed in the subduction zone the sandwiched assemblage was created by the tectonic insertion of the blueschist between the other units folding particularly during late doming of the tectonic sandwich rotated the top normal fault boundary into a thrust later high angle ne sw trending normal faults displaced the tectonic stratigraphy in horst and graben a 200 km long and 200 km wide 680 450 ma calc alkaline volcano plutonic belt extends southeastwards from the blueschist belt via northern wales to central england suggesting that the subduction of oceanic lithosphere was to the southeast and this is consistent with the extrusion of the thin high pressure slab into the accretionary complex to the northwest this took place on the western accretionary margin of avalonia finally we outline the key steps involved in unravelling the structure of a pacific type accretionary complex

a mechanism for the formation and maintenance of shore oblique sand ridges on storm dominated shelves a remarkable set of shore oblique sand ridges occupies the inner portion of the storm dominated middle atlantic and south atlantic bights off the east coast of the united states of america a mechanism for present day formation and growth of these distinctive geological features follows from a linearized analysis of the stability of alongshore periodic topographical perturbations based on a depth averaged fluid dynamical model with a simple representation of sediment transport the analysis indicates exponential growth of shore oblique features as a result of offshore deflection of storm driven alongshore flows at ridge crests which leads to a convergence of sediment flux because the effective carrying capacity decreases with increasing distance offshore the analysis indicates a set of conditions required for ridge growth model solutions for topography under conditions favorable for ridge growth are strikingly similar to the observed sand ridges

structure and tectonic evolution of the southwestern trinidad dome escambray complex central cuba insights into deformation in an accretionary wedge abstract the trinidad dome escambray complex cuba forms part of an accretionary wedge built during intra oceanic subduction in the caribbean from the late cretaceous to cenozoic the structure reflects syn subduction exhumation during thickening of the wedge followed by extension field mapping metamorphic and structural analysis constrain the tectonic evolution into five stages three ductile deformation events d1 d2 and d3 are related to metamorphism in a compressional setting and formation of several nappes d1 subduction fabrics are only preserved as relict s1 foliation and rootless isoclinal folds strongly overprinted by the main s2 foliation the s2 foliation is parallel to sheared serpentinised lenses that define tectonic contacts suggesting thrust stacks and underthrusting at mantle depths thrusting caused an inverted metamorphic structure with higher grade on top of lower grade nappes exhumation started during d2 when the units were incorporated into the growing accretionary wedge along nne directed thrust faults and was accompanied by substantial decompression and cooling folding and thrusting continued during d3 and marks the transition from ductile to brittle ductile conditions at shallower crustal levels the d4 5 events are related to extension and contributed to the final exhumation likely as a core complex d4 is associated with a regional spaced s4 cleavage late open folds and numerous extension veins whereas d5 is recorded by normal and strike slip faults affecting all nappes the p t path shows rapid exhumation during d2 and slower rates during d3 when the units were progressively incorporated into the accretionary prism the domal shape formed in response to tectonic denudation assisted by normal faulting and erosion at the surface during the final stages of structural development these results support tectonic models of sw subduction of the proto caribbean crust under the caribbean plate during the latest cretaceous and provide insights into the tectonic evolution of accretionary wedges in an intra arc setting

oblique strike slip faulting of the central cascadia submarine forearc at least nine wnw trending left lateral strike slip faults have been mapped on the oregon washington continental margin using sidescan sonar seismic reflection and bathymetric data augmented by submersible observations the faults range in length from 33 to 115 km and cross much of the continental slope five faults offset both the juan de fuca plate and north american plates and cross the plate boundary with little or no offset by the frontal thrust left lateral separation of channels folds and holocene sediments indicate active slip during the holocene and late pleistocene offset of surficial features ranges from 120 to 900 m and displaced subsurface piercing points at the seaward ends of the faults indicate a minimum of 2 2 to 5 5 km of total slip near their western tips fault ages range from 300 ka to 650 ka yielding late pleistocene holocene slip rates of 5 5 2 to 8 5 2 mm yr the geometry and slip direction of these faults implies clockwise rotation of fault bounded blocks about vertical axes within the cascadia forearc structural relationships indicate that some of the faults probably originate in the juan de fuca plate and propagate into the overlying forearc the basement involved faults may originate as shears antithetic to a dextral shear couple within the slab as plate coupling forces are probably insufficient to rupture the oceanic lithosphere the set of sinistral faults is consistent with a model of regional deformation of the submarine forearc defined to include the deforming slab by right simple shear driven by oblique subduction of the juan de fuca plate

modification of the quaternary stratigraphic framework of the inner continental shelf by holocene marine transgression an example offshore of fire island new york abstract the inner continental shelf off fire island new york was mapped in 2011 using interferometric sonar and high resolution chirp seismic reflection systems the area mapped is approximately 50 km long by 8 km wide extending from moriches inlet to fire island inlet in water depths ranging from 8 to 32 m the morphology of this inner continental shelf region and modern sediment distribution patterns are determined by erosion of pleistocene glaciofluvial sediments during the ongoing holocene marine transgression much of the shelf is thus an actively forming ravinement surface remnants of a pleistocene outwash lobe define a submerged headland offshore of central fire island east of the submerged headland relatively older pleistocene outwash is exposed over much of the inner continental shelf and covered by asymmetric sorted bedforms interpreted to indicate erosion and westward transport of reworked sediment erosion of the eastern flank of the submerged pleistocene headland over the last 8000 years yielded an abundance of modern sand that was transported westward and reworked into a field of shoreface attached ridges offshore of western fire island west of the submerged headland erosion of pleistocene outwash continues in troughs between the sand ridges resulting in modification of the lower shoreface comparison of the modern sand ridge morphology with the morphology of the underlying ravinement surface suggests that the sand ridges have moved a minimum of 1000 m westward since formation comparison of modern sediment thickness mapped in 1996 1997 and 2011 allows speculation that the nearshore shoreface sedimentary deposit has gained sediment at the expense of deflation of the sand ridges

storm graded layers on inner continental shelves examples from southern brazil and the atlantic coast of the central united states abstract size graded layers have been reported from the united states and brazilian atlantic continental shelves amid a bedform association that includes ripples megaripples sand waves and sand ridges graded layers are most apparent in the lag gravels and shell hashes that overlie an older substrate in the troughs between sand ridges but also occur as thinner isolated beds within the sand ridges at least four different models seem to be applicable to graded bed formation the stratigraphic graded model grading occurs within and immediately above the basal lag gravel of the holocene transgressive sand sheet it is a consequence of the generation of the sand sheet by erosional shoreface retreat such graded sequences are formed by landward facies displacement over thousands of years but the process is storm mediated and sequences may contain thinner storm graded layers the storm graded model calls for entrainment of sediment by storm flow and subsequent graded deposition under waning energy in the bedform migration model the migration of megaripples and sand waves may produce thin graded beds at any level within the holocene sand sheet and sand ridge migration can cause graded sequences in the basal part of the holocene sand sheet the bottom liquefaction model relies on storm wave pumping of the seafloor sands with their resultant liquefaction and settling of coarser clasts beds in which sorting is confined to coarse shell material may be of this origin these models are believed to be complementary rather than mutually exclusive

sharp based marine sandstone bodies in the mulichinco formation lower cretaceous neuquen basin argentina remnants of transgressive offshore sand ridges fil schwarz ernesto consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet la plata centro de investigaciones geologicas universidad nacional de la plata facultad de ciencias naturales y museo centro de investigaciones geologicas argentina

a 100 m y long window onto mass flow processes in the patagonian mesozoic subduction zone diego de almagro island chile diego de almagro island was formed by the subduction and accretion of several seafloor derived tectonic slices with very heterogeneous ages and pressure temperature time p t t paths the highest element of the pile the lazaro unit evidences subduction in the high p granulite field 1 3 gpa 750 c at ca 163 ma below it a thin tectonic sliver the garnet amphibolite unit preserves eclogite facies remnants 570 c and 1 7 gpa formed at ca 131 ma in situ u pb zircon rim ages peak assemblages were nearly fully amphibolitized during decompression down to 1 2 gpa and 600 c at 125 120 ma rb sr multimineral dating the underlying blueschist unit has 50 m y younger metamorphic ages and exhibits slightly cooler peak burial conditions 520 c 1 7 gpa ca 80 ma in situ white mica ar ar ages and multimineral rb sr dating and is devoid of amphibolitization the mylonites from the sinistral strike slip seno arcabuz shear zone bounding diego de almagro island to the east also exhibit amphibolite facies 620 c and 0 9 gpa deformation at ca 117 ma multimineral rb sr ages in situ white mica ar ar dating and multimineral rb sr dating of low t mylonites 450 c along the base of the lazaro unit reveal partial resetting of high t assemblages during tectonic displacement between 115 and 72 ma and exhumation of the slice stack detrital zircon u th pb ages indicate that the material accreted on diego de almagro island has been mostly recycled from a permian triassic accretionary wedge madre de dios accretionary complex exposed along the subduction buttress geological and geochronological constraints suggest that the rocks of the seno arcabuz shear zone and the lazaro unit were tectonically eroded from the buttress while the underlying garnet amphibolite and blueschist units instead derive from the subducted oceanic basin with increasingly younger maximum depositional ages the very long residence time of the rocks 90 m y for the lazaro unit along the hanging wall of the subduction interface recorded long term cooling along the patagonian subduction zone during the mesozoic diego de almagro island therefore represents a unique window onto long term tectonic processes such as subduction interface down stepping tectonic erosion and episodic underplating near the base of an accretionary wedge 40 50 km

on two phase relative permeability and capillary pressure of rough walled rock fractures this paper presents a conceptual and numerical model of multiphase flow in fractures the void space of real rough walled rock fractures is conceptualized as a two dimensional heterogeneous porous medium characterized by aperture as a function of position in the fracture plane portions of a fracture are occupied by wetting and nonwetting phase respectively according to local capillary pressure and accessibility criteria phase occupancy and permeability are derived by assuming a parallel plate approximation for suitably small subregions in the fracture plane for log normal aperture distributions a simple approximation to fracture capillary pressure is obtained in closed form it is found to resemble the typical shape of leverett s j function wetting and non wetting phase relative permeabilities are calculated by numerically simulating single phase flows separately in the wetted and non wetted pore spaces illustrative examples indicate that relative permeabilities depend sensitively on the nature and range of spatial correlation between apertures it is also observed that interference between fluid phases flowing in a fracture tends to be strong with the sum of wetting and nonwetting phase relative permeabilities being considerably less than 1 at intermediate saturations

deformation of mafic schists from subducted oceanic crust at high pressure and temperature conditions abstract we conducted triaxial deformation experiments using a griggs type solid pressure medium apparatus on two mafic schists that experienced different peak metamorphic conditions from the sambagawa metamorphic belt a greenschist and an epidote amphibole schist at a confining pressure of 1 gpa 400 c and strain rate of 10 5 1 s differential stresses for all mafic schists were higher than 1 gpa the greenschist samples were weaker than epidote amphibolite samples under all experimental conditions microstructures of recovered samples of greenschist indicate that deformation of mafic schist is accommodated by semi brittle deformation samples of the epidote amphibole schist deformed at 500 c show shear localization along a single fault oriented parallel to the foliation while mechanical data shows no rapid stress drop on the surface of the fault we observe the formation of slickensides with little gouge all sample types exhibit a high stress exponent n 15 and strain rate strengthening i e positive a b values frictional behavior that inhibits earthquake nucleation differential stress increased with increasing confining pressure while the friction coefficient decreased with increasing confining pressure and temperature greenschist and epidote amphibolite facies metamorphism typically occurs at hot subduction zones such as cascadia and southwest japan the lack of seismicity within the subducting oceanic crust at hot subduction zones could be explained by semi brittle deformation or frictional sliding with a positive a b during deformation of these types of metamorphic rocks weak and aseismic fault zones in subducting slabs might promote slab mantle decoupling at the corner of the mantle wedge and detachment and underplating of oceanic crust from the subducting slab to forearc crust

structural anatomy of the early paleozoic laohushan ophiolite and subduction complex implications for accretionary tectonics of the proto tethyan north qilian orogenic belt northeastern tibet

nonlinear dynamics in flow through unsaturated fractured porous media status and perspectives 1 the need has long been recognized to improve predictions of flow and transport in partially saturated heterogeneous soils and fractured rock of the vadose zone for many practical applications such as remediation of contaminated sites nuclear waste disposal in geological formations and climate predictions until recently flow and transport processes in heterogeneous subsurface media with oscillating irregularities were assumed to be random and were not analyzed using methods of nonlinear dynamics the goals of this paper are to review the theoretical concepts present the results and provide perspectives on investigations of flow and transport in unsaturated heterogeneous soils and fractured rock using the methods of nonlinear dynamics and deterministic chaos the results of laboratory and field investigations indicate that the nonlinear dynamics of flow and transport processes in unsaturated soils and fractured rocks arise from the dynamic feedback and competition between various nonlinear physical processes along with complex geometry of flow paths although direct measurements of variables characterizing the individual flow processes are not technically feasible their cumulative effect can be characterized by analyzing time series data using the models and methods of nonlinear dynamics and chaos identifying flow through soil or rock as a nonlinear dynamical system is important for developing appropriate short and long time predictive models evaluating prediction uncertainty assessing the spatial distribution of flow characteristics from time series data and improving chemical transport simulations inferring the nature of flow processes through the methods of nonlinear dynamics could become widely used in different areas of the earth sciences

late glacial to preboreal sea level rise recorded by the rhone deltaic system nw mediterranean abstract a unique late glacial preboreal record of changes in sea level and sediment fluxes originating from the alps is recorded in the rhone subaqueous delta in the western mediterranean sea the compilation of detailed bathymetric charts together with high resolution seismic profiles and long cores reveals the detailed architecture of several sediment lobes related to periods of decreased sea level rise and or increased sediment flux they are situated along the retreat path of the rhone distributaries from the shelf edge and canyon heads up to the modern coastline they form transgressive backstepping parasequences across the shelf the late holocene highstand deltas being confined to the inner shelf the most prominent feature is an elongated paleo shoreface deltaic system with an uppermost sandy fraction remolded into subaqueous dunes a long piston core into the bottomsets of this prograding unit allows precise dating of this ancient deltaic system in seismic data it displays aggradation starting at 15 cal kyr bp followed by progradation initiated during the first phase of the younger dryas a period of reduced sea level rise or stillstand the delta kept pace with resumed sea level rise during the preboreal which is estimated at about 1 cm yr as a result of increased sediment supply from the alps melting of glaciers and more humid climate flushing the sediment down to the sea abandonment of the delta occurred around 10 500 cal yr bp that is to say about 1000 yr after the end of the younger dryas probably because of decreased sediment flux

sand bodies at the shelf edge in the gulf of lions western mediterranean deglacial history and modern processes abstract the outer continental shelf of the gulf of lions is covered by thick mainly regressive sand deposits a combination of seismic sedimentological and geochronological methods allows us to demonstrate that a veneer of transgressive sand bodies few m to less than 1 m thick reworks these deposits they take the form of sand ridges and transverse dunes that formed at different periods in fact the low gradient outer shelf of the gulf of lions displays a complete record of deglacial history including not only transgressive deposits that formed during sea level rise but also bedforms that still evolve under episodic high energy events that occur under more highstand conditions core lithology 14 c dates and regional sea level curve suggest that the formation of the sand ridges was favoured during a period of deceleration of sea level rise such as during the younger dryas event the dunes are part of a mobile carpet here u160 the deposition of this marine sand veneer is possibly related to the interplay between different factors that trigger the turning on off for bottom currents sand deposition transport on the outer shelf in fact the sands appear to have been reworked intermittently due to high energy conditions in shallow water depth currents wave regime and wind driven circulation as well as they form current ridges superimposed to the transgressive deposits in the westernmost part of the studied area at the bourcart canyon s head

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

topographic and hydrodynamic controls on barrier retreat and preservation an example from dogger bank north sea abstract barrier retreat can occur due to in place drowning overstepping or rollover depending on the interplay of controls such as sea level rise sediment supply coastal hydrodynamic regime and topography offshore sedimentary archives of barriers active during rapid holocene sea level rise provide important records of marine transgression which are vital analogues to support appropriate mitigation strategies for future coastal realignment under projected relative sea level rise scenarios this study analyses the sedimentary archive at dogger bank which is a formerly glaciated area in the north sea dogger bank experienced marine transgression due to early holocene rapid relative sea level rise an integrated dataset of vibrocores and high resolution seismic reflection data permits a stratigraphic framework to be established which reveals the buried coastal geomorphology of the southern dogger bank for the first time a transgressive stratigraphy was identified comprising a topographically complicated basal glacial and terrestrial succession overlain by two phases of barrier and tidal mudflat deposition prior to shallow marine sedimentation barrier phase a was a recurved barrier drowned in place and discontinuously overstepped to barrier phase b which experienced continuous overstepping by linking barrier elevations to relative sea level curves the timing of each barrier phase was established both barrier phases retreated during periods of rapid sea level rise with abundant sediment supply coastal hydrodynamics increasing wave energy and antecedent topography with spatially variable accommodation are suggested to be the main reason for differing retreat mechanisms rather than the rate of sea level rise antecedent coastal geomorphology plays a critical role in erosional and depositional patterns during transgression and therefore on the timing rate and location of marine inundation which needs to be included in models that aim to forecast hazards in coastal areas

ophiolitic melanges in crustal scale fault zones implications for the late palaeozoic tectonic evolution in west junggar china the baijiantan and darbut ophiolites in west junggar are exposed in steep fault zones 70 containing serpentinite melange in contact on either side with regionally distributed upper devonian lower carboniferous ocean floor peperitic basalts and overlying sedimentary successions the ophiolitic melanges show classic structural features created by strike slip faulting and consistent shear sense indicators of left slip kinematics sandstone blocks within the melanges resemble the surrounding sediments in lithology and age indicating that the ophiolitic melanges consist of locally derived rocks the ophiolitic melanges therefore originated from left slip fault zones within a remnant basin and are not plate boundaries nor subduction suture zones sandstone is the youngest lithology involved in the melange and provides a maximum age for the melange of 322 ma whereas stitching plutons are younger than 302 ma multiple clusters in zircon ages from single gabbro blocks in the melange at 375 360 354 and 340 ma are inconsistent with accretionary incorporation of subducting ocean crust but rather suggest that episodic movement of the faults provided pathways for magma from the mantle into magma chambers late paleozoic tectonic evolution of west junggar involved late devonian to carboniferous relative motion between the junggar block and west junggar ocean basin which triggered the left slip fault zones within a remnant ocean basin along which the oceanic crust was disrupted to form linear ophiolitic melanges final filling of this remnant ocean basin and its dismemberment by strike slip faulting occurred in the late carboniferous followed by crustal thickening by juvenile granites at the carboniferous permian boundary

formation evolution and present day activity of offshore sand ridges on a narrow tideless continental shelf with limited sediment supply abstract an integrated approach combining swath bathymetry high resolution seismic reflection and seabed sediment sampling was performed to characterize a field of sand ridges on the murcia continental shelf in the western mediterranean sea the aim of this work was to improve knowledge about the formation evolution and present day dynamics of these bedforms on a narrow tideless continental shelf receiving little sediment input sand ridges are observed on the middle shelf at water depths ranging between 58 and 78 m the sand ridges are 1 5 to 3 m high and show a predominant e w orientation oblique to the present day shoreline smaller scale subaqueous dunes 0 3 1 3 m high appear superimposed on the sand ridges and beyond the ridge field the subaqueous dunes show a nw se orientation and asymmetric profiles with the lee side facing southwest the comparison of two bathymetric surveys 10 years apart revealed that the subaqueous dunes are migrating towards the southwest at very low rates 3 m yr 1 internally both sand ridges and dunes display southwestward dipping oblique reflections indicating long term migration in that direction the morphology architecture and distribution of the murcia sand ridges suggest that they were formed in a shallow water environment during the holocene transgression and were later detached from the coast due to the subsequent sea level rise the shallow architecture of the sand ridges reveals the presence of small mound like features within the sand ridges most probably associated with coastal deposits which could have served as a precursor for the development of the sand ridges the preservation of these deposits within the sand ridges evidences limited offshore ridge migration at present active subaqueous dunes superimposed on the sand ridges suggest that they may play a significant role in the ridge evolution at a regional scale the comparison of the murcia sand ridges with those described in the western mediterranean allows us to propose a gradation from partially evolved to fully evolved sand ridges with increasing water depth

well preserved underplating structure of the jadeitized franciscan complex pacheco pass california duplex structures several hundred metres thick bounded by marker beds exhibiting basalt chert association have been found in the franciscan complex near pacheco pass central diablo range california the terrane was regionally metamorphosed and deformed under blueschist facies conditions at 150 c and 7 8 kbar detailed mapping of the basalt chert sequence has clarified the change of environment from mid oceanic ridge to subduction zone eastward convergence of duplexing indicates eastward subduction of the oceanic plate during early cretaceous time the presence of duplexing and a reconstruction of oceanic plate stratigraphy recorded within the underthrust unit demonstrate the accretionary origin of protoliths of the franciscan coherent unit which has long been believed to have an in situ origin interpreted as either near trench volcanism or accreted terranes in which geosynclinal type volcanism occurred

submerged barrier shoreline sequences on a high energy steep and narrow shelf abstract late pleistocene holocene shoreline sequences and associated shelf stratigraphy are described from a high gradient high wave energy shelf although shoreline preservation by overstepping is considered unlikely in such an environment as a result of intense ravinement during shoreline translation the development and preservation of two distinct shorelines at 100 m and 60 m are evident and attributed to century to millennial scale periods of stillstand during these periods shoreline equilibrium forms developed characterised by early diagenesis of beachrock and aeolianite between these features the shelf is dominated by erosional surfaces reflecting ravinement during periods of slowly rising sea level where shorelines are not preserved areas of scarping in the ravinement surface at similar depths to the adjoining shorelines represent rocky headlands separating the sandy coastal compartments where the depositional shorelines formed shoreline preservation by overstepping was facilitated by rapid relative sea level rise associated with meltwater pulses 1a and 1b although the features preserved are likely to represent only the cemented cores of the coastal dunes and linear beachrock outcrops formed the steep antecedent shelf gradient fostered the erosion of significant portions of the shorelines by ravinement with loose sediment re organised into a thick post ravinement drape the removal of shorelines during ravinement was countered by the rapid rate of sea level rise and early sub tropical diagenesis it is clear that due to the combined effects of subtropical diagenesis long periods of stillstand and drowning by meltwater pulses the governing controls on shoreline preservation can be over ridden by combinations of local climatic and global eustatic factors

thickening of fault zones a mechanism of melange formation in accreting sediments sediments accreted at subduction zones undergo stratal disruption and form a type of melange the thickness of the disrupted zones grows with progressive deformation this suggests that initial fault surfaces are abandoned and deformation propagates into adjacent undeformed sediment factors causing the abandonment of fault surfaces during continuing deformation include 1 strengthening owing to porosity loss during consolidation 2 localized drops in fluid pressure on fault surfaces that act as dewaterinig conduits and 3 reorientation of fault surfaces the disruptive processes occurring in accretionary prisms result principally from the deformation of a consolidating sediment mass

a comparison of seasonal winds with currents on the continental slope of the catalan sea northwestern mediterranean the waters of the northwestern region of the mediterranean sea follow the continental shelf break in a flow that appears to be linked to a permanent shelf slope density front several studies are underway to evaluate the role of the possible forces that drive this circulation the continental margin located off the ebro river is an area of persistent and high intensity winds long term representative seasonal wind and current meter data are presented here in a comparative analysis of the temporal variability of both fields the data seem to indicate that the local wind field is not responsible for the characteristics of the marine circulation the wind is only able to develop significant inertial oscillations in spring and may contribute to the intensification of the currents only during the cold season in addition the variability of the current field shows no relationship to wind variability important mesoscale activity is probably associated with variations of the density structure and not with the wind in essence the wind provides no appreciable direct contribution to modifying the general circulation

kinematics and age constraints of deformation in a late carboniferous accretionary complex in western junggar nw china abstract the karamay area situated in the eastern part of western junggar southern altaids contains an ophiolitic melange with ultramafic rocks gabbro basalt chert and limestone which show typical block in matrix structures and coherent turbidites and tuffs these lithological associations are interpreted as incoherent and coherent series formed in an accretionary complex on the basis of detailed field mapping and analyses of the asymmetry of imbricate thrusts duplexes tilted structures shear band cleavages and the nw verging inclined to overturned folds we conclude that the overall movement in the accretionary complex was top to the nw the youngest tuff involved in the deformation contains detrital zircons that have a u pb age la mc icp ms of 308 7 ma 39ar 40ar resistance furnace step heating of amphibole separates from a diorite dike which cuts the folded and imbricated rocks in the accretionary prism yielded a plateau age of 307 2 ma consequently the age of the deformation in the prism is tightly constrained at 307 308 ma implying that the deformation occurred in an extremely short time span during se ward subduction combined contemporaneous occurrence of baogutu adakite high mg sr enriched and y poor dioritic dikes miaoergou charnockite and maliya mafic rocks we further suggest the accretionary complex was cut by near trench volcanic rocks and plutons possibly due to interaction with a spreading ridge

melanges through time life cycle of the world s largest archean melange compared with mesozoic and paleozoic subduction accretion collision melanges abstract melanges represent a significant component of collisional and accretionary orogenic belts we present a comparison of subduction accretion melanges of different ages to test how melange forming processes at convergent margins changed through time we describe the mesozoic mchugh melange in alaska and the paleozoic proto tethyan laohushan melange of the qilian orogenic belt of the alpine himalayan chain together with documentation of a neoarchean melange that marks the suture between the eastern block and central orogenic belt of the north china craton ncc the mchugh is a classic accretionary melange that has not yet experienced a collision and the laohushan is an accretionary collisional melange with structures related to both stages of its evolution we compare the characteristics of these melanges with the world s largest archean melange the newly documented circa 2 5 ga 1600 km long jianping zunhua zanhuang dengfeng jzzd melange of the north china craton the jzzd is a classical melange in terms of map patterns lithological relations structural characteristics including mixed rock types of different ages origins and metamorphic histories and preserves both paired metamorphic features and local blocks preserving ultra high pressure uhp assemblages it shows high stratal disruption with both block in matrix and highly mixed thrust bounded tectonic slices types of map patterns the melange is part of an arc accretionary complex that was emplaced over a 2 7 2 5 ga passive margin sequence on the western edge of the eastern block of the ncc at 2 5 ga the frontal zone of the accretionary complex marks the suture between the eastern block and an oceanic arc terrane in the central orogenic belt cob and exhibits significant along strike n s variations in the north the jianping pyroxenite melange contains blocks of 2 52 ga metapyroxenite metabasalt tonalite trondhjemite granodiorite diorite ttgd gneisses in a metasedimentary and serpentinite matrix intruded by 2 49 2 47 ga plutons metamorphosed to amphibolite granulite conditions at 2 47 ga the zunhua shangying ophiolitic melange contains relatively intact 2 5 ga ophiolitic sheets in a 2 5 ga metasedimentary melange intruded by 2 48 ga granitic dikes the zunhua ultra high pressure uhp podiform chromite melange has blocks of pillow basalt bif dikes gabbros pyroxenite harzburgite some with 2 55 ga podiform chromites in dunite envelopes enclosed in a 2 52 2 46 ga metasedimentary matrix metamorphosed and intruded by granitic dikes at 2 46 ga the chromites and dunite pods formed through reaction of a boninitic melt and harzburgite during subduction initiation bewtween 2 6 2 55 ga uhp conditions are documented by tio2 ii inclusions in chromites indicating subduction to at least 270 km depth the zanhuang melange includes blocks of metapsammites metagabbros metabasalts and ultramafic rocks in a metapelitic matrix intruded by 2 49 2 54 ga granites then imbricated with 2 65 ga marble metapelite quartzite of the passive margin of the eastern block the dengfeng melange includes upper plate blocks of metagabbro metabasalt bif and felsic rocks in a sandy to pelitic matrix thrust over a turbiditic broken formation melange unit in the east circa 2 5 ga metamorphic conditions record a relatively high t p anatexis 950 c gpa in the west whereas the central part of the belt records intermediate t p metamorphism

implication for the two stage layer parallel faults in the context of the izu forearc collision zone examples from the miura accretionary prism central japan abstract the southern tip of the miura peninsula central japan exposes nice outcrops of forearc sediment accreted to another forearc which occurred during a series of izu arc collision with the honshu arc neogene deep marine volcaniclastic sedimentary sequences the misaki formation show many types of faulting and folding associated with layer parallel faults besides many imbricate thrusts of the main deformation stage the layer parallel faults are divided into two stages one is related to northwestward gravity driven slump deposits the other is southeastward thrust faulting and the both are associated with many layer duplications with liquefaction of sediments the slumping is commonly developed in the upper part of the sequence in the surface of the down going slab before accretion whereas the thrusting is dominant in the lower part within the toe of the accretionary prism probably along the decollement zones in the prism thus the misaki formation represents a good example of deformation just before and after shallow forearc accretion in the arc collision zone

detailed investigation of continental shelf morphology using a high resolution swath sonar survey the eel margin northern california abstract the eel shelf northern california lies within an active compressional tectonic margin subject to abundant terrigenous sediment input from the eel river a recent high resolution swath sonar survey provides us with the opportunity to investigate seafloor morphology and acoustic backscatter patterns within this dynamic region our analysis of the statistical character of bathymetry demonstrates a clear separation into large and small scale morphologies at a 3 10 km scale with smaller scale morphology heavily damped relative to large scale morphology the eel shelf bathymetry is subtle but several structures can be readily discerned in a residual bathymetry formed by removal of the downslope gradient some shelf structures are evidently related to depositional processes as evidenced by correlation with 100 yr sediment accumulation rates whereas others appear related to tectonic processes as evidenced by correlation with subsurface synclines and anticlines the sidescan structure of the shelf is dominated by the low backscatter over the eel and mad river subaqueous deltas evidently associated with the sand to mud transition however contrary to usual correlations between backscatter and grain size in this situation higher backscatter is associated with the muddy sediments in addition we observe a series of shore perpendicular striations or ribbons spaced 0 2 1 0 km apart which extend northward from the eel river subaqueous delta and lie at or near the sand to mud transition some aspects of ribbon morphology suggest that they may be associated with down slope flows

hydrologic mechanisms governing fluid flow in a partially saturated fractured porous medium in contrast to the saturated zone within which fluid moves rapidly along fractures the fractures with apertures large relative to the size of matrix pores will desaturate first during the drainage process and the bulk of fluid flow would be through interconnected pores in the matrix within a partially drained fracture the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture the residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small normal to the fracture surfaces the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block a general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions results are obtained from an aperture distribution model for fracture saturation hydraulic conductivity and effective matrix fracture flow areas as functions of pressure the effects of distortion of flow paths by the air pockets are taken into account by a phase separation constriction factor in a generalized cubic law for fracture flow under a partially saturated condition the reduction of matrix fracture flow area is taken into account by summing the aperture distribution function to a saturation cutoff aperture which is inversely proportional to the suction head drainage from a column of fractured tuff is simulated using available parameters for the densely welded tuff of the topopah spring member at yucca mountain southern nevada the column is bounded by discrete vertical fractures and dissected by horizontal fractures with the fracture spacings determined by the frequencies and orientations of fractured cores the fraction of fracture surfaces with coatings is assumed to correspond to the fraction of in situ fracture contact area the characteristic curves for the matrix are based on laboratory measurements of tuff samples from the cases simulated for the fractured porous columns with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties however the quasi steady changes of the fluid flow of a partially saturated fractured porous system could be approximately simulated without taking the fractures into account

numerical model of water flow in a fractured basalt vadose zone box canyon site idaho a numerical model of a fractured basalt vadose zone has been developed on the basis of the conceptual model described by faybishenko et al his issue the model has been used to simulate a ponded infiltration test in order to investigate infiltration through partially saturated fractured basalt a key question addressed is how the fracture pattern geometry and fracture connectivity within a single basalt flow of the snake river plain basalt affect water infiltration the two dimensional numerical model extends from the ground surface to a perched water body 20 m below and uses an unconventional quasi deterministic approach with explicit but highly simplified representation of major fractures and other important hydrogeologic features the model adequately reproduces the majority of the field observation and provides insights into the infiltration process that cannot be obtained by data collection alone demonstrating its value as a component of field studies

metamorphism of franciscan tectonostratigraphic assemblage pacheco pass area east central diablo range california coast ranges the pacheco pass area well known for the relatively high pressure low temperature mineral assemblages developed in a well ordered section of chiefly metaclastic strata was restudied in order to elucidate the geologic paragenetic and textural relationships among the various lithologic units the mapped 7 minute quadrangle extends from 4 km west of the range crest eastward to the ortigalita fault tectonic contact of the franciscan assemblage with coeval great valley strata semicontinuous metachert beds underlain by scraps of na cpx and or na amphibole bearing metabasaltic rock mark the base of terrigenous tectonostratigraphic units evidently decoupled from the downgoing oceanic crust capped plate underplating along newly recognized bedding plane faults has juxtaposed members of an apparently conformable franciscan sedimentary sequence four depositional units each consisting of monotonous metagraywacke and interlayered metashale are stacked within the accretionary section from top down these are tectonostratigraphic members a b c and d unit d differs from overlying members in possessing a greater abundance of bluestone greenstone pods minor serpentinite bodies and rare metaconglomerate lenses varying degrees of stratal disruption indicate that it has been arrested in the transformation to broken formation the ortigalita fault is nearly vertical strikes north northwest and exhibits apparent dextral offset it truncates the east west striking gonzaga fault and other franciscan structures the topographic low occupied by san luis reservoir is a cenozoic tectonic depression sited at a releasing bend on the ortigalita fault newly acquired textural chemical mineralogic and areal relations of albitic and jadeitic pyroxene bearing franciscan metagraywacke near pacheco pass demonstrate that 1 na cpx and na amphibole are metamorphic minerals not clastic materials 2 pumpellyite is a minor neoblastic phase in albite bearing metagraywacke west of pacheco pass and in the north western corner of the quadrangle but it does not occur in jadeitic pyroxene bearing metaclastic rocks 3 higher textural grade metagraywacke specimens generally contain higher modal proportions of jd 4 abundance textural grade and chemistry of na cpx are not related to tectonostratigraphic units and 5 because of sluggish reaction rates albite persisted metastably into the higher pressure jadeitic pyroxene quartz p t field production of na cpx resulted from a reaction of the sort ab chl jd iws qtz gln h 2 o irregular oscillatory zoning within single jadeitic pyroxene prisms and variable jd ab modes for rocks of the same bulk composition reflect growth governed by diffusion rather than recrystallization within a p t transition zone high pressure overstepping of the phase boundary explains variable modal proportions of ab and jd as well as chemical heterogeneity of the jd elevated p attended metamorphism of na cpx bearing rocks exposed in the pacheco pass area as indicated by the wide spread coexistence of quartz and naalsi 2 o 6 rich pyroxene inferred physical conditions of prograde metamorphism were 150 50 c at 7 8 kbar or more franciscan rocks in the east central diablo range underwent subduction zone metamorphism accompanying paleo pacific lithospheric plate descent during mid cretaceous convergence underplating contraction and sequestering of the tectonostratigraphic assembly at depths of 25 30 km during underflow followed by gradual rise took place under conditions of refrigeration due to protracted descent of the oceanic slab paleogene diapiric uplift and extension followed indicating more complete decoupling of the buoyant trench complex from the downgoing plate finally passage of the east pacific rise triple junction in neogene time initiated the present dextral slip regime in the california coast ranges

underplating process from melange formation to duplexing example from the cretaceous shimanto belt kii peninsula southwest japan accretionary complexes are considered to form through off scraping and underplating which results in the lateral and vertical growth of an accretionary prism accretion of the upper part of the oceanic crust and the formation of melange are important components of the accretionary process although the origin of melange is considered controversial in order to better understand the origin of melange and its role in accretion in particular during underplating we have studied the relationship between the formation of melange and duplexing in the miyama assemblage here the melange is composed dominantly of shale basalt chert and sandstone this study stresses the following features 1 the structure of the miyama assemblage appears to be a composite suite of landward and seaward dipping duplexes 2 the melange fabric displays a systematic asymmetry which may have resulted through shearing along the decollement and 3 facing of horses within duplexes changes from north to south coinciding with a change in the sense of shear inferred from the melange fabric which suggests that it formed prior to duplexing

a study of thermally induced convection near a high level nuclear waste repository in partially saturated fractured tuff we present simple estimates for velocities of buoyancy driven flow of liquid and gas phases near a hypothetical high level nuclear waste repository in partially saturated fractured tuff these estimates indicate that gas phase convection could take place with appreciable velocity of the order of 20 m year while liquid convection is expected to be very slow of the order of 0 1 mm year detailed numerical simulations using an effective continuum approximation to represent fracture effects confirm these estimates and demonstrate a sensitivity of gas convection to the strength of binary diffusion

structural development of a high pressure collisional accretionary wedge the samana complex northern hispaniola abstract the samana metamorphic complex exposes a segment of a high pressure collisional accretionary wedge built during caribbean island arc north america continental margin convergence combined detailed mapping structural and metamorphic analysis and 40ar 39ar geochronology show that the deformation can be divided into five main events early subduction related d1 deformation and high p low t m1 metamorphism under lawsonite blueschist 325 425 c 12 18 kbar rincon marbles and santa barbara schists lower structural nappes and eclogite facies conditions 425 450 c 18 20 kbar punta balandra upper structural nappe was followed by m2 decompression and cooling in the blueschist facies conditions during d2 folding thrusting and nappe stacking 40ar 39ar plateau ages and t t p t estimations revealed late eocene to earliest miocene retrograde m2 metamorphism in the different nappes for a consistent d2 top to the ene tectonic transport which suggests a general northeastward progradation of deformation the d3 event substantially modified the nappe stack and produced open to tight folds with amplitudes up to kilometer scale and the d4 ductile to brittle normal shear zones and faults and related subhorizontal folding record a late extensional deformation which also affects the whole nappe pile non penetrative d3 and d4 fabrics indicate m3 cooling in and under the m3 greenschist facies conditions from the miocene to the present the nappe pile was cut and laterally displaced by a d5 sinistral strike slip and reverse fault system associated with the septentrional fault zone

near bottom suspended sediment variability caused by storms and near inertial internal waves on the ebro mid continental shelf nw mediterranean abstract near bottom currents and suspended sediment concentrations ssc recorded on the ebro continental shelf at 60 m depth during the transition between fair and stormy weather have revealed some of the major processes controlling the sediment re suspension and transport at mid shelf depths in this nw mediterranean area storm waves were the main contributor to the transport of sediment although they only resuspended surface sediments during extreme wave conditions h s 4 5 m and t s 11 s during the recording period the net suspended sediment flux along the shelf was one order of magnitude higher than the net suspended sediment flux across the shelf and the resultant transport was towards the sw and seaward fluctuations of the near bottom ssc during fair weather showed a periodicity around 17 h and were related to the occurrence of near inertial internal waves caused by wind pulses during storm events the energy propagation of these internal waves reached critical angles at the mid and outer shelf which could favor the development and maintenance of the bottom nepheloid layer on the ebro continental shelf as well as on other mediterranean continental shelves

formation and preservation of an overstepped segmented lagoon complex on a high energy continental shelf the duration of shoreline occupation at a given sea level coastal response to sea level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf using bathymetric and seismic observations this article documents the evolution and preservation of an incised valley and lithified barrier complex between 65 m and 50 m mean sea level on a wave dominated continental shelf the barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive back barrier sediments the ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons the incised valley trends shore parallel behind the barrier complex and records an early phase of valley filling followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley sea level stability at the outer barrier position ca 65 m enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sea level rise to 58 m when the lagoon formed these lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features an abrupt rise in sea level to 40 m correlated with melt water pulse 1b enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers this situation is unique to subtropical coastlines where early diagenesis is possible the overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement partly burying the ridges and protecting the underlying sediments the high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping

the franciscan complex california usa the model case for return flow in a subduction channel put to the test the model of return flow in a subduction channel rfsc is put to the test by opposing key assumptions of the model to an integrated review of field data petrology geochronology and structures of high p melanges of the franciscan subduction complex fsc to which rfsc has been first applied key assumptions are i the subduction channel sc is a low viscosity zone of finite width restrained by the rigid subducted and overriding plates ii forced return flow in the sc is associated with formation and km scale displacements of small tectonic blocks 1 km in a highly deformable matrix iii this results in apparently random distributions and close associations of blocks exhumed from different depths hence the block in matrix structures and exotic blocks in high p melanges would reflect the structural state at depth of the sc on the basis of the predictions ensuing from the key assumptions of the rfsc model on the rock record it is detailed why the actual record of the high p melanges of the fsc does not comply with this perception the record rather reflects recurring subduction underplating associated decollement erosion and mingling of high p rocks by sedimentary processes in the trench all occurring in an 80 m y lasting period distributed deformation of the melange matrix is unrelated to formation of apparently chaotic block in matrix structures since i creation subduction ascent and cooling of exotic blocks on counterclockwise p t paths predates deposition of the bulk of the metasediments constituting the matrix by 20 40 m y ii deformation of the matrix occurs during a second loop of high p metamorphism postdating creation and ascent of the exotic blocks by at least 20 40 m y iii the magnitudes of distributed deformation of the matrix are too low to cause juxtaposition of blocks different in p t paths against each other from km scale vertical distances instead narrow few tens of metres wide fault shear and decollement zones formed at locally high pore fluid pressures accumulate the major tectonic transport during high p metamorphism they bound several 100s of metres wide tabular tectonic bodies that are coherent sedimentary processes at the active continental margin formed the bulk of the melanges tectonically formed block in matrix structures within the shear and decollement zones are unrelated to juxtaposition of exotic blocks universal diagnostic criteria are developed to identify return rfsc as a mechanism that potentially amalgamates heterogeneous metamorphic terrains by using field data petrology and geochronology

recent and modern marine erosion on the new jersey outer shelf abstract recent chirp seismic reflection data combined with multibeam bathymetry backscatter and analysis of grab samples and short cores provide evidence of significant recent erosion on the outer new jersey shelf the timing of erosion is constrained by two factors 1 truncation at the seafloor of what is interpreted to be the transgressive ravinement surface at the base of the surficial sand sheet and 2 truncation of apparently moribund sand ridges along erosional swales oriented parallel to the primary direction of modern bottom flow and oblique to the strike of the sand ridges these observations place the erosion in a marine setting post dating the passage of the shoreface ravinement and the evolution of sand ridges that form initially in the near shore environment also truncated by marine erosion are shallowly buried fluvial channel systems formed during the last glacial maximum and filled during the transgression and a regional reflector r that is 40 kyr depths of erosion range from a few meters to 10 m the seafloor within eroded areas is often marked by ribbon morphology seen primarily in the backscatter data as areas of alternating high and low backscatter elongated in the direction of primary bottom flow ribbons are more occasionally observed in the bathymetry where observed crests exhibit low backscatter and troughs exhibit high backscatter sampling reveals that the high backscatter areas of the ribbons consist of a trimodal admixture of mud sand and shell hash with a bimodal distribution of abraded and unabraded sand grains and microfauna the shell hash is interpreted to be an erosional lag while the muds and unabraded grains are in this non depositional environment evidence of recent erosion at the seafloor of previously undisturbed strata the lower backscatter areas of the ribbon morphology were found to be a well sorted medium sand unit only a few 10 s of cm thick overlying the shelly muddy sandy material concentrations of well rounded gravels and cobbles were also found in eroded areas with very high backscatter and at least one of these appears to be derived from the base of an eroded fluvial channel seafloor reworking over the transgressive evolution of the shelf appears to have switched from sand ridge evolution which is documented to 40 m water depth to more strictly erosional modification at greater water depths we suggest that this change may be related to the reduction with water depth in the effectiveness of sediment resuspension by waves resuspension is a critical factor in the grain size sorting during transport by bottom currents over large bedforms like sand ridges otherwise we speculate displacement of sand by unidirectional currents will erode the seafloor

a deep strong reflector in the nankai accretionary wedge from multichannel seismic data implications for underplating and interseismic shear stress release 1 we present the results of structural and stratigraphic interpretations for the multichannel seismic profiles to reveal the structure of the nankai accretionary wedge off shikoku island on the basis of reflection characteristics we identify three major seismic units that correspond to a unit consisting of both oligocene miocene accretionary prism and the sedimentary cover unit a a unit of underthrust miocene pliocene hemipelagic sediments unit b and a unit of subducting pre miocene oceanic crustal rocks unit c according to relative strength of the topmost reflector of unit b the nankai accretionary wedge can be divided into three different structural zones along the cross strike direction apparent decollement reflector zone low amplitude reflector lar zone and deep strong reflector dsr zone despite the velocity uncertainty involved in the depth conversion and therefore thickness estimation error the decollement step down and the possible duplex structures in the lar and dsr zones support that the landward thickness variation of unit b is caused by the structural thickening such as the underplating process structural features and reverse polarity suggest that the dsr as an upper interface of the underplated layer unit b corresponds to a shear plane or a fault zone with high pore fluid pressures we found that most of the dsr was observed in a region which has not suffered from the 1946 coseismic dislocation even though it was locked during the interseismic period the dsr as a shear plane or a fault zone constrains a regional variety of the coseismic dislocation around the updip limit of the nankai seismogenic zone considering all of the dsr characteristics we propose a hypothesis for the dsr s development and role the dsr may play an important role as a possible releaser of the shear stress energy stored at the plate boundary around the updip limit of the nankai seismogenic zone a good correlation between the theoretical vertical displacement and seafloor topographic feature support the possible slip along the dsr as a shear plane

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 1 simulation studies with explicit consideration of fracture effects we have performed modeling studies on the simultaneous transport of heat liquid water vapor and air in partially saturated fractured porous rock formation parameters were chosen as representative of the potential nuclear waste repository site in the topopah spring unit of the yucca mountain tuffs the presence of fractures makes the transport problem very complex both in terms of flow geometry and physics the numerical simulator used for our flow calculations takes into account most of the physical effects believed to be important in multiphase fluid and heat flow it has provisions for handling the extreme nonlinearities that arise in phase transitions component disappearances and capillary discontinuities at fracture faces we model a region around an infinite linear string of nuclear waste canisters taking into account both the discrete fractures and the porous matrix thermohydrologic conditions in the vicinity of the waste packages are found to depend strongly on relative permeability and capillary pressure characteristics of the fractures which are unknown at the present time if liquid held on the rough walls of drained fractures is assumed to be mobile strong heat pipe effects are predicted under these conditions the host rock will remain in two phase conditions right up to the emplacement hole and formation temperatures will peak near 100 c if it is assumed that liquid cannot move along drained fractures the region surrounding the waste packages is predicted to dry up and formation temperatures will rise beyond 200 c a substantial fraction of waste heat can be removed if emplacement holes are left open and ventilated as opposed to backfilled and sealed emplacement conditions comparing our model predictions with observations from in situ heater experiments reported by zimmerman and coworkers some intriguing similarities are noted however for a quantitative evaluation additional carefully controlled laboratory and field experiments will be needed

laboratory measurement of capillary pressure saturation relationships in a rock fracture a laboratory technique has been developed to measure the hysteretic relationship between capillary pressure and fluid saturation for a rough walled rock fracture under different states of normal stress the technique incorporates a loading system and a uniquely designed capillary barrier to the nonwetting phase which allows for fracture closure and provides excellent hydraulic connection of the wetting phase in the fracture with external pressure control the method is applied to a single rough walled fracture in limestone using oil and water as the nonwetting and wetting phase respectively the measured capillary pressure curves were found to be well represented by a brooks corey porous media capillary pressure function a distinct entry pressure giving rise to initial nonwetting phase invasion was observed in each test it was found that the inferred aperture distributions became less skewed with increased normal load these aperture distributions were inferred using one of three conceptual models presented for nonwetting phase invasion of a rough walled fracture under conditions of main drainage

biostratigraphic constraints on formation and timing of accretion in a subduction complex an example from the franciscan complex of northern california the determination of the total age coverage of pelagic bedded chert is particularly important in studies of ancient accretionary complexes because the time span represents the minimum travel time of an oceanic plate before accretion at an island arc or continental margin the yolla bolly terrane of the franciscan complex consists of rare metabasalt overlain by bedded radiolarian chert which in turn is overlain by metagraywacke and subordinate slaty mudstone and conglomerate the bedded chert ranges in age from aaleian early middle jurassic to tithonian latest jurassic a lithologic gradation from pelagic bedded chert through hemipelagic siliceous mudstone occurred during the tithonian and thus marks the arrival of the oceanic sediments at the continental margin the tithonian age also agrees with previously reported tithonian to valanginian early cretaceous fossils in the overlying terrigenous metagraywacke both chert and metagraywacke are intruded by gabbroic sills suggesting off ridge volcanism

accreted kula plate fragment at 94ma in the yokonami melange shimanto belt shikoku japan abstract the cretaceous shimanto belt that is distributed along the pacific side of southwest japan contains one of the best records of accretionary processes and history of oceanic plate subduction in the circum pacific region yokonami melange shimanto belt shikoku sw japan is composed of pillowed basalt that erupted in the equatorial region about 200 m thick bedded radiolarian chert sequence that contains radiolarians with age determinations spanning ca 135 ma upper valanginian to 93 9 ma cenomanian younging southward with repetition and alternated sandstone and mudstone although the chronology of the bedded chert sequence is well studied using the radiolarian the chronology of the clastic units was not reported sufficiently we performed a detailed geologic mapping investigation of rock outcrops along the goshiki no hama coast the yokonami melange we have determined u pb ages of zircon grains extracted from tuffs and sandstones to determine the depositional age of the turbidite and hemipelagic units the youngest depositional age of these clastic sediments is interpreted to be the arrival time at the trench we reconstructed the ocean plate stratigraphy with our new chronological data which includes mid oceanic basalt bedded chert hemipelagic sediments and trench turbidite deposits we recognize that the turbidite sequence has been repeated by layer parallel thrust in the study area we have delineated the travel trajectory of the oceanic lithosphere based on 1 the relative plate motion model of the paleo pacific ocean 2 the arrival time of the subducted lithosphere at the trench 94 32 ma and 3 paleomagnetic measurement of the basalt and turbidite the trajectory suggests that the morb in the goshiki no hama coast yokonami melange erupted at the kula pacific ridge in the paleo pacific ocean traveled northward and eventually arrived at the continental margin of east asia at 94 32 ma

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 2 effective continuum approximation this paper presents an effective continuum approximation for modeling of fluid and heat flow in fractured porous media the approximation is based on the thermohydrologic behavior observed in detailed simulations with explicit consideration of fracture effects see the companion paper part 1 the crucial concept in the development of an effective continuum approximation is the notion of local thermodynamic equilibrium between rock matrix and fractures where applicable it provides a substantial simplification of the description of fluid and heat flow in fractured porous media we derive formulas for effective continuum characteristic curves relative permeabilities and capillary pressures in terms of the properties of fracture and matrix continua respectively numerical simulations demonstrate that under favorable conditions the effective continuum approximation closely matches predictions obtained from an explicit modeling of fracture effects it is also demonstrated that the approximation breaks down under unfavorable conditions very tight rock matrix a simple criterion for the applicability of an effective continuum approximation is derived from consideration of diffusive processes a quantitative evaluation shows the criterion to be consistent with results of our numerical simulations

a middle permian ophiolitic melange belt in the solonker suture zone western inner mongolia china implications for the evolution of the paleo asian ocean

early cementation and accommodation space dictate the evolution of an overstepping barrier system during the holocene abstract the morphology and stratigraphic features of a well preserved drowned barrier system located on the western coast of sardinia mediterranean sea are presented here the barriers were mapped using a multibeam echosounder the digital terrain model of the seabed revealed five sub parallel barriers in a depth range of 18 37 m with a distance of 300 m between each single barrier direct inspection by scuba diving revealed that the barriers consist of beachrocks topped by seagrass meadows growing on a biogenic hardground the inner most barrier is limited landward by a steep cliff 10 m high bordering the back barrier area about 200 km of seismic lines were collected along the barrier system using a 0 4 1 0 kj sparker source and a 3 5 khz chirp subbottom profiler the seismic data calibrated with vibrocores allowed us to recognize the subaerial topographic surface of the last glacial maximum as well as several seismic units interpreted as the pliocene marine sediments the pre holocene deposits and the holocene barrier lagoon complex composed of shoreface barrier lagoonal deltaic and beach deposits despite the relatively high seabed gradient 0 3 0 4 and the relatively low rate of sea level rise 10 15 mm y 1 the barriers were well preserved due to the early diagenetic processes which led to a rapid cementation with the formation of beachrocks and the subsequent overstepping with the rise of the sea level the development of the overstepping barrier system is strictly related to the antecedent subaerial topography which is in turn related to the tectonic setting of the area the pliocene seismic unit was lowered by a direct fault at the entrance of the gulf forming a depression filled by sediments the overstepping barrier system developed following the increase of the seabed gradient and was limited landward by the above mentioned depression which increased the accommodation space following the sea level rise and the barrier formation this depression was filled by lagoonal sediments washover fans and sediments coming from the rivers the age model of barrier evolution based on previous sea level rise curves during the holocene supported by radiocarbon data highlighted that the whole system evolved over a time period of 1 ka while the time elapsed from this formation to the drowning of single barriers was estimated to be in the order of magnitude of centuries scenarios of short term evolution of modern barrier lagoon systems of the adjacent coastal sector under conditions of accelerated sea level rise according to church et al 2013 2013 ipcc report and rahmstorf 2007 projections were elaborated the study of this ancient analogue suggests that the processes of adaptation of coastal systems to the rising sea level would require times evaluable from centuries to millennia

the role of glacio eustasy in sequence formation mid atlantic continental margin usa abstract previous studies of the mid atlantic continental margin had shown the lack of correlation between pleistocene glacio eustatic oscillations and sequence boundaries this study documents late pleistocene to holocene paleoenvironments within a seismic stratigraphic sequence in order to characterize sequence formation and the development of unconformities in response to glacio eustatic oscillations the data high resolution chirp subbottom profiling and 28 vibracores were collected in water depths of 38 m to 145 m as part of the r v endeavor cruise 370 survey to the mid atlantic continental margin sediment sources sedimentary and seismic facies associated with the last major glaciation and oxygen isotope stages ois 5 to ois 1 were examined and a chronology was constructed from mollusk assemblages of intertidal origin that allowed tracking the paleoshoreline from 19 to 6 ka bp the maximum extent of the last glacial maximum lgm paleoshoreline at 17 ka bp was documented near the 120 m modern isobath the shoreline was marked by sediment mounds up to 5 m high and troughs 15 m deep and 1 km wide interpreted as shoreface and tidal inlet or lagoons formed from 17 to 15 ka bp five kilometers seaward from the lgm shoreline and the head of the hudson canyon is a wedge shaped feature interpreted as a lowstand delta sediments older than the last glacial possibly ois 3 or ois 5 onlap a basal unconformity we correlate this unconformity to a previously identified sequence boundary approximately 20 m to 30 m of sediment accumulated on the outer shelf ne of the hudson canyon during the last glacial and little deposition has occurred since 11 ka bp the modern outershelf is covered by 1 m of mollusk rich glauconitic sand deposited from latest pleistocene to early holocene 15 to 11 ka bp these results showed a close correspondence between depositional environments and glacio eustasy but sequence development and sequence boundary formation appeared to be influenced by the incomplete filling of accommodation space due to poor preservation during ois 2 and low accumulation during the holocene

multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes sable island bank scotian shelf abstract storm formed sand ridges are important morphologic features occurring on many continental shelves of the world our understanding of the morphology migration and the controlling processes over this type of sand ridges under different environmental settings is still limited in the present study an integrated approach of combining multibeam bathymetry survey seabed sampling sidescan seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on sable island bank scotian shelf and to evaluate the relationship between sand ridge morphology migration and the storm processes on this storm dominated outer shelf bank multibeam data obtained at selected sites demonstrated the series of ne sw oriented sand ridges with an average height of 4 3 m and wavelength of 1 5 km sand ridges attain maximum spacing height and steepness in the intermediate depths sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition sediment grain size and depth sand ridge profiles show weak easterly asymmetry this morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long term sand ridge migration and net sediment transport in the study area sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east the likely cause is the nearly equal number of major storms passing to the south versus to the north of the island so that the westerly and easterly peak storm driven currents associated with these storm path scenarios affect equally the sand ridges on sable island bank a suite of smaller bedforms were found superimposed on the sand ridges sand waves widely superimposed on both flanks of sand ridges mixed 2d and 3d megaripples commonly occurring in the sand ridge troughs and on the lower western flanks and large wave ripples ubiquitously found in the troughs of all megaripples surficial sediment is coarsest coarse sand with shell fragments in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank while best sorting occurs near the sand ridge crest box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms

accreted oceanic materials in japan abstract the phanerozoic circum pacific orogenic belts contain numerous ocean derived materials accreted through plate converging processes japanese islands in particular display various kinds of oceanic materials of different origins including fragments of seamounts oceanic reef limestone morb like rocks and oceanic mantle and pelagic sediments the compilation of these rocks in many subduction complexes of late permian to the present led to following conclusions accretion processes work effectively only for materials primarily composing the upper portion of subducting oceanic crust i e layer 1 and layer 2 many fragments of seamount with alkali basalt 600 hot spot seamount 26 oceanic reef limestone 291 morb like basalt 200 and numerous cherts more than 1000 are recognized as ancient oceanic materials accreted to the japanese islands however gabbros and mantle materials of layer 3 and lower parts of the oceanic lithosphere scarcely occur in subduction accretion complexes except for a few examples of back arc basin or fore arc origin accretion occurs episodically in southwest japan oceanic materials were accreted intermittently in 1 a end permian 2 b middle late jurassic 3 c late cretaceous times 4 d at ca 50 ma and 5 e in miocene times while in northeast japan and hokkaido this occurred in b middle late jurassic c late cretaceous and f early cretaceous times in contrast to the general belief on accretion of younger oceanic plates the majority of japanese subduction accretion complexes were formed during the subduction of plates up to 160 ma old the accretionary events in end permian and middle late jurassic times coincide with northward collision of ancient island arcs oceanic rises or seamount chains of hot spot origin with the asian continent accretion relevant to subduction of older plates may be controlled by the collision subduction process of these topographic reliefs on an oceanic plate in addition the chronological coincidence with the continent collision amalgamation between the sino korean and siberian platforms and between the sino korean and yangtze blocks also implies collision induced voluminous supply of elastics from back arc regions and its contribution to the formation of huge accretionary complexes accreted fragments of ancient seamounts are much smaller than the average size of modern seamounts this implies that most parts of a colliding seamount are not accreted but subducted together with the underlying oceanic crust to much deeper levels with respect to the metamorphic grades for japanese subduction complexes oceanic materials have less than 1 vol in the zeolite facies 15 20 in the prehnite pumpellyite metagraywacke facies and ca 30 in the greenschist glaucophane schist facies and albite epidote amphibolite fades this relationship indicates that the major process for landward accretion of oceanic materials is not off scraping or sedimentary mixing at the trench but underplating subcretion at much deeper levels of a subduction zone

compound incised valley characterization by high resolution seismics in a wave dominated setting example of the aude and orb rivers languedoc inner shelf gulf of lion france a branch of a time calibrated late quaternary compound incised valley complex is investigated using high and very high resolution seismic data the incised valley system is confined on the inner shelf and entrenched parallel to the shore in unconsolidated pliocene deposits the infilling of the incised valley system comprises three sigmoidal bodies dipping progressively downstream representing depositional sequences the lowermost sequences are less well preserved at their downstream extremity and the whole system is both aggrading and prograding older pleistocene late quaternary sequences could be preserved under the coastal plain individual sequences are closely similar to the classic model of a microtidal incised valley fill nevertheless the central estuary bay basin muds are seen to interfinger locally with high energy deposits that represent potential reservoirs the properties prograding and aggrading architecture and occurrence of high energy deposits and preservation of these compound incised valley fill deposits are attributed to general glacio eustatic cycles and local atmospheric and oceanic regime and proximity of the hinge line conditions data acquisition strategy is a determining factor to interpret such systems

lateral growth of the continental crust through deep level subduction accretion a re evaluation of central greek rhodope abstract the rhodope massif of northern greece and southern bulgaria has been variably interpreted as a fragment of pre alpine possibly hercynian or precambrian age continental crust that was actively involved in european margin convergent tectonics during the mesozoic and tertiary alternatively we propose that for central greek rhodope the lithological associations and tectonothermal history are consistent with progressive south directed mesozoic crustal growth through deep level subduction accretion a process which involved the near continuous transferral of material of oceanic and continental margin affinity from footwall to hanging wall within a north directed palaeotethyan subduction system central greek rhodope comprises a sequence of schists gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing extensive occurrences of marble are associated with amphibolites variably retrogressed eclogites meta gabbros and ultramafic rocks quartzo feldspathic gneisses are abundant throughout the area and are associated with psammitic meta greywacke sequences pelites and quartzites the presence of intercalated marble slivers and thin manganiferous and iron rich siliceous bands is significant the various components exposed in the subduction accretion complex were first underthrust northwards to deep crustal levels subjected to high pressure eclogite facies metamorphism and underplated to the base of the overriding eurasian plate this latter accretion event was characterised by intense southwest directed ductile thrusting and pervasive amphibolite facies metamorphic overprinting it was accompanied by migmatisation and intracrustal melt generation and followed by subduction related magmatism deep level subduction accretion leads to southward growth of the continental margin which in turn leads to subduction retreat allowing the encroachment of the magmatic arc from the north subsequent extensional tectonic exhumation brought the complex up to its present position within the southern margin of eurasia this new interpretation may have implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre existing continental crust if so then the importance of deep level subduction accretion as a mechanism of continental crustal growth has hitherto been underestimated